Valve Timing Control Apparatus for Internal Combustion Engine, and Method of Producing Same

Abstract

A valve timing control apparatus for an internal combustion engine, includes a housing body, a sealing plate, a vane rotor, and a sealing ring. The housing body includes an opening at an axial end which is closed by the sealing plate. The sealing ring is disposed between the housing body and the sealing plate. The housing body is formed of an aluminum-based metal material and anodized, wherein the housing body includes a base layer and an anodic oxide coating film layer. The sealing ring abuts on the base layer of the housing body at the axial end.

Description

BACKGROUND OF THE INVENTION

The present invention relates to valve timing control apparatuses for internal combustion engines, and methods of producing same.

Japanese Patent Application Publication No. 5-113112 discloses a valve timing control apparatus for an internal combustion engine, which includes a housing connected to a crankshaft, and a phase change mechanism mounted in the housing, and connected to a camshaft. The housing is formed with a pulley at its outside periphery to which torque is transmitted from the crankshaft through a timing belt that is wound around the pulley, so that the housing rotates in synchronization with the crankshaft. The phase change mechanism operates in response to supply and drainage of working fluid, for changing valve timing, i.e. rotational phase of the camshaft with respect to the crankshaft.

SUMMARY OF THE INVENTION

The valve timing control apparatus described above is subject to a problem that the timing belt may be degraded by adhesion of working fluid exiting out of the housing. Accordingly, it is desirable to provide a valve timing control apparatus for an internal combustion engine in which such a problem is solved by suitable sealing.

According to one aspect of the present invention, a valve timing control apparatus for an internal combustion engine, comprises: a housing body having a hollow cylindrical shape including an opening at an axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and formed integrally with a shoe at an inside periphery of the housing body, wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine, and wherein the shoe projects inwardly in a radial direction of the housing body; a sealing plate fixed to the axial end of the housing body, the sealing plate closing the opening of the housing body; a vane rotor adapted to be fixed to a camshaft of the internal combustion engine, and rotatably mounted in the housing body, wherein the vane rotor includes a vane, wherein the vane defines a working fluid chamber between the vane and the shoe, and wherein the working fluid chamber is adapted to supply and drainage of working fluid; and a sealing ring disposed between the housing body and the sealing plate, the sealing ring sealing the working fluid chamber, wherein: the housing body is formed of an aluminum-based metal material and anodized, wherein the housing body includes a base layer and an anodic oxide coating film layer; the anodic oxide coating film layer is present at the outside periphery; and the sealing ring abuts on the base layer at the axial end.

According to another aspect of the present invention, a valve timing control apparatus for an internal combustion engine, comprises: a housing body having a tubular shape including an opening at an axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine; a sealing plate facing an axial end surface of the housing body, and closing the opening of the housing body; a phase change mechanism mounted in the housing body, and adapted to change a rotational phase of a camshaft of the internal combustion engine with respect to the housing body in response to supply and drainage of working fluid; and a sealing ring disposed between the housing body and the sealing plate, wherein: the housing body is formed of an aluminum-based metal material and anodized, wherein the housing body includes a base layer and an anodic oxide coating film layer; and the anodic oxide coating film layer is present at the outside periphery and an inside periphery of the housing body, and absent at the axial end surface of the housing body facing the sealing plate.

According to a further aspect of the present invention, a valve timing control apparatus for an internal combustion engine, comprises: a housing body having a tubular shape including an opening at an axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine; a sealing plate fixed to the axial end of the housing body, the sealing plate closing the opening of the housing body; a phase change mechanism mounted in the housing body, and adapted to change a rotational phase of a camshaft of the internal combustion engine with respect to the housing body in response to supply and drainage of working fluid; and a sealing ring disposed between the housing body and the sealing plate, wherein: the housing body is formed of an aluminum-based metal material and anodized, wherein the housing body includes a base layer and an anodic oxide coating film layer; and the anodic oxide coating film layer is present at the outside periphery of the housing body, and absent at a surface of the housing body on which the sealing ring abuts.

According to a still further aspect of the present invention, a method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a housing body having a hollow cylindrical shape including an opening at each axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and formed integrally with a shoe at an inside periphery of the housing body, wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine, and wherein the shoe projects inwardly in a radial direction of the housing body; at least one sealing plate fixed to an axial end surface of the housing body, the sealing plate closing a corresponding one of the openings of the housing body; a vane rotor adapted to be fixed to a camshaft of the internal combustion engine, and rotatably mounted in the housing body, wherein the vane rotor includes a vane, wherein the vane and the shoe define an advance chamber and a retard chamber between the vane rotor and housing body, and wherein the advance chamber and the retard chamber are adapted to supply and drainage of fluid; and at least one sealing ring disposed between the sealing plate and the axial end surface of the housing body, the method comprises a process of producing the housing body, the process comprising: an extruding operation of forming a first workpiece by extruding an aluminum-based metal material, wherein the first workpiece extends in a direction of extrusion; a coating operation of forming a second workpiece by anodizing an entire surface of the first workpiece; and a cutting-off operation of forming a third workpiece by cutting out of the second workpiece to a predetermined length so as to form the third workpiece with a cut surface forming the axial end surface of the housing body on which the sealing ring abuts.

According to another aspect of the present invention, a method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a housing body having a hollow cylindrical shape including an opening at each axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and formed integrally with a shoe at an inside periphery of the housing body, wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine, and wherein the shoe projects inwardly in a radial direction of the housing body; at least one sealing plate fixed to one of the axial ends of the housing body, the sealing plate closing a corresponding one of the openings of the housing body; a vane rotor adapted to be fixed to a camshaft of the internal combustion engine, and rotatably mounted in the housing body, wherein the vane rotor includes a vane, wherein the vane and the shoe define an advance chamber and a retard chamber between the vane rotor and housing body, and wherein the advance chamber and the retard chamber are adapted to supply and drainage of fluid; and at least one sealing ring disposed between the sealing plate and the housing body, the method comprises a process of producing the housing body, the process comprising: an extruding operation of forming a first workpiece by extruding an aluminum-based metal material, wherein the first workpiece extends in a direction of extrusion; a coating operation of forming a second workpiece by anodizing an entire surface of the first workpiece; a cutting-off operation of forming a third workpiece by cutting out of the second workpiece to a predetermined length; and a carving operation of carving a longitudinal end surface of the third workpiece so as to form the third workpiece with a cut surface forming a surface of the housing body on which the sealing ring abuts.

According to another aspect of the present invention, a method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a housing body having a tubular shape including an opening at each axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine; at least one sealing plate fixed to one of the axial ends of the housing body, the sealing plate closing a corresponding one of the openings of the housing body; a phase change mechanism mounted in the housing body, and adapted to change a rotational phase of a camshaft of the internal combustion engine with respect to the housing body in response to supply and drainage of working fluid; and at least one sealing ring disposed between the sealing plate and the housing body, the method comprises a process of producing the housing body, the process comprising: an extruding operation of forming a first workpiece by extruding an aluminum-based metal material, wherein the first workpiece extends in a direction of extrusion; a coating operation of forming a second workpiece by anodizing an entire surface of the first workpiece; and a cutting-off operation of forming a third workpiece by cutting out of the second workpiece to a predetermined length so as to form the third workpiece with a cut surface forming a surface of the housing body on which the sealing ring abuts.

According to another aspect of the present invention, a method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a housing body having a tubular shape including an opening at each axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine; at least one sealing plate fixed to one of the axial ends of the housing body, the sealing plate closing a corresponding one of the openings of the housing body; a phase change mechanism mounted in the housing body, and adapted to change a rotational phase of a camshaft of the internal combustion engine with respect to the housing body in response to supply and drainage of working fluid; and at least one sealing ring disposed between the sealing plate and the housing body, the method comprises a process of producing the housing body, the process comprising: an extruding operation of forming a first workpiece by extruding an aluminum-based metal material, wherein the first workpiece extends in a direction of extrusion; a coating operation of forming a second workpiece by anodizing an entire surface of the first workpiece; a cutting-off operation of forming a third workpiece by cutting out of the second workpiece to a predetermined length; and a carving operation of carving a longitudinal end surface of the third workpiece so as to form the third workpiece with a cut surface forming a surface of the housing body on which the sealing ring abuts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a valve timing control apparatus according to an embodiment of the present invention in which a pair of intake valve timing control apparatuses and a pair of exhaust valve timing control apparatuses are mounted to an internal combustion engine, as viewed in an axial direction of the internal combustion engine.

FIG. 2 is an exploded perspective view of the intake valve timing control apparatus.

FIG. 3 is a partial side sectional view of the intake valve timing control apparatus, taken along a plane passing through an axis of rotation of the intake valve timing control apparatus.

FIG. 4 is a front view of the intake valve timing control apparatus in a most retarded state, as viewed along the axis of rotation.

FIG. 5 is a front view of the intake valve timing control apparatus in a most advanced state, as viewed along the axis of rotation.

FIGS. 6A, 6B and 6C are views of a housing body of the intake valve timing control apparatus, where FIG. 6A is a front view along the axis of rotation, FIG. 6B is a side sectional view taken along a plane indicated by F6B-F6B in FIG. 6A, and FIG. 6C is a rear view along the axis of rotation.

FIG. 7 is a perspective view of a first workpiece for the housing body of the intake valve timing control apparatus or a housing body of the exhaust valve timing control apparatus.

FIG. 8 is a perspective view of a third workpiece for the housing body of the intake valve timing control apparatus or exhaust valve timing control apparatus.

FIGS. 9A and 9B are views of a vane rotor of the intake valve timing control apparatus, where FIG. 9A is a front view along the axis of rotation, and FIG. 9B is a side sectional view taken along a plane indicated by F9B-F9B in FIG. 9A.

FIG. 10 is a perspective view of a first workpiece for the vane rotor of the intake valve timing control apparatus or a vane rotor of the exhaust valve timing control apparatus.

FIG. 11 is a perspective view of a second workpiece for the vane rotor of the intake valve timing control apparatus or exhaust valve timing control apparatus.

FIG. 12 is a perspective view of a front plate of the intake valve timing control apparatus.

FIG. 13 is a partial side sectional view taken along a plane passing through a central longitudinal axis of a positioning pin according to the embodiment that is fixed to an axial end surface of an intake camshaft.

FIG. 14 is a partial side sectional view taken along a plane passing through a central longitudinal axis of a lock mechanism according to the embodiment.

FIG. 15 is a partial side sectional view of the exhaust valve timing control apparatus, taken along a plane passing through an axis of rotation of the exhaust valve timing control apparatus.

FIG. 16 is a front view of the exhaust valve timing control apparatus in a most advanced state, as viewed along the axis of rotation.

FIG. 17 is a front view of the exhaust valve timing control apparatus in a most retarded state, as viewed along the axis of rotation.

FIGS. 18A, 18B and 18C are views of the housing body of the exhaust valve timing control apparatus, where FIG. 18A is a front view along the axis of rotation, FIG. 18B is a side sectional view taken along a plane indicated by F18B-F18B in FIG. 18A, and FIG. 18C is a rear view along the axis of rotation.

FIGS. 19A and 19B are views of the vane rotor of the exhaust valve timing control apparatus, where FIG. 19A is a front view along the axis of rotation, and FIG. 19B is a side sectional view taken along a plane indicated by F19B-F19B in FIG. 19A.

DETAILED DESCRIPTION OF THE INVENTION

<<Construction of Valve Timing Control Apparatus>> FIG. 1 is a front view of a valve timing control apparatus according to an embodiment of the present invention in which a pair of intake valve timing control apparatuses 1a and a pair of exhaust valve timing control apparatuses 1b are mounted to an internal combustion engine, as viewed in an axial direction of the internal combustion engine. The axial direction is an axial direction of a crankshaft of the internal combustion engine, which is identical to an axial direction of intake camshafts or exhaust camshafts. The intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b are individually or collectively referred to as valve timing control apparatus or system 1. The internal combustion engine is arranged in a vehicle engine room so that the axial directions of the crankshafts and camshafts are perpendicular to a vehicle longitudinal direction. In other words, FIG. 1 is a view of valve timing control apparatus 1 in a vehicle lateral direction. In a typical motor vehicle, an engine room has a unique three-dimensional curved side wall because of provision of frames (structural members or skeletal members), so that the side wall has a portion projecting inwardly in the engine room. FIGS. 1 and 15 show an example in which a projection W1 projects from an engine room side wall W close to one exhaust valve timing control apparatus 1b, as schematically shown by a long-dashed short-dashed line. FIG. 1 shows a section of engine room side wall W (projection W1) taken along the plane indicated by F1-F1 in FIG. 15, which is a view in the vehicle lateral direction. FIG. 15 shows a section of projection W1 of engine room side wall W taken along the plane indicated by F15-F15 in FIG. 1 and parallel to the axial direction of the internal combustion engine (X-axis), which is a view in the vehicle lateral direction. The internal combustion engine is a V-type DOHC engine in which a pair of cylinder banks are arranged in a V-shape spreading from the crankshaft as viewed in the axial direction, and each cylinder bank is provided with a camshaft for actuating intake valves, or intake camshaft 3a, and a camshaft for actuating exhaust valves, or exhaust camshaft 3b. Intake camshafts 3a and 3a are arranged inside of exhaust camshafts 3b and 3b in a lateral direction of a cylinder block of the internal combustion engine, as shown in FIG. 1.

Valve timing control apparatus 1 is mounted to one axial end of the internal combustion engine. Specifically, each intake valve timing control apparatus 1a is fixedly mounted to an axial end of respective intake camshaft 3a, whereas each exhaust valve timing control apparatus 1b is fixedly mounted to an axial end of respective exhaust camshaft 3b. Valve timing control apparatus 1 may be provided with only one of intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b. However, provision of both of intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b makes it possible to control the valve timing in a more flexible manner. Each intake valve timing control apparatus 1a is provided with a pulley 100. Similarly, each exhaust valve timing control apparatus 1b is provided with a pulley 100. A timing belt 1010 is put over pulleys 100, as indicated by long dashed double-short dashed lines in FIG. 1, so that intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b are connected to one another. Timing belt 1010 is a toothed belt (or cogged belt) made of rubber, but may be alternatively made of a material preferable for weight reduction and cost reduction, such as a synthetic resin. Timing belt 1010 transmits torque from the crankshaft to pulleys 100. Each of intake valve timing control apparatuses 1a and exhaust valve timing control apparatuses 1b is rotated by the torque transmitted through the pulley 100. While rotating, each of intake valve timing control apparatuses 1a and exhaust valve timing control apparatuses 1b optimally controls variable opening and closing timings of respective intake valves or exhaust valves according to a state of operation of the internal combustion engine. The combination of pulley 100 and timing belt 1010 may be replaced with a combination of a sprocket and a chain as a means for transmitting torque from the crankshaft to a housing “HSG” of intake valve timing control apparatus 1a or exhaust valve timing control apparatus 1b. Alternatively, the torque from the crankshaft may be transmitted indirectly, for example, in such a manner that the torque from the crankshaft is transmitted directly to one of intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b, and transmitted through the one to the other.

In the following, an X-axis is assumed to extend in the axial direction of the internal combustion engine, or in the axial direction of camshaft 3a or 3b. Along the X-axis, a positive direction is defined as a direction from an axial end of camshaft 3a or 3b where no intake valve timing control apparatus 1a or no exhaust valve timing control apparatus 1b is provided to an axial end of camshaft 3a or 3b where intake valve timing control apparatuses 1a and exhaust valve timing control apparatuses 1b are mounted.

<Construction of Intake Valve Timing Control Apparatus> The following describes construction of intake valve timing control apparatus 1a with reference to FIGS. 2 to 14. FIG. 2 is an exploded perspective view of intake valve timing control apparatus 1a, where parts are arranged in the axial direction. FIG. 3 is a partial side sectional view of intake valve timing control apparatus 1a, taken along a plane passing through an axis of rotation “O” (shown in FIG. 4) of intake valve timing control apparatus 1a, i.e. taken along a plane indicated by a long dashed short dashed line F3-F3 in FIG. 4. FIGS. 4 and 5 are front views of intake valve timing control apparatus 1a under a condition that a front plate 8, etc. are removed, as viewed from the X-axis positive side. In FIGS. 3 and 4, fluid passages and grooves which are formed in intake camshaft 3a, etc. are indicated by broken lines.

Intake camshaft 3a is made of an iron-based material, and rotatably supported on bearings in a laterally-inside portion of an upper end portion of the cylinder head of the internal combustion engine. Intake camshaft 3a is formed with drive cams (intake cams) at the outside peripheral surface, which are located to face or conform to positions of the intake valves. When intake camshaft 3a is rotated, the intake cams open and close the intake valves via valve lifters, rocker arms, etc. Intake valve timing control apparatus 1a is fixedly attached to an X-axis positive side axial end portion 30 of intake camshaft 3a by three camshaft bolts 33, 34 and 35. Each camshaft bolt 33, 34 or 35 is a hexagonal-head bolt having a head 331, 341 or 351 in the form of a regular hexagonal prism, and a shank formed with a male thread at its outside periphery. Each head 331, 341 or 351 is formed integrally with a plane washer 332, 342 or 352, for protection of a bearing surface, etc. The hexagonal-head bolt may be replaced with another fixing means. Each washer 332, 342 or 352 is optional. The axial end portion 30 of intake camshaft 3a is formed with: three bolt holes 32 through which camshaft bolts 33, 34 and 35 are inserted; a portion constituting a retard passage 20; and a portion constituting an advance passage 21. Each bolt hole 32 is formed with a female thread at its inside periphery, and substantially evenly spaced with one another in the circumferential direction around the axis of rotation O, extending from an X-axis positive side axial end surface 300 of axial end portion 30 to a predetermined depth in the X-axis direction. The axial end portion 30 of intake camshaft 3a is formed with grooves 200, 204, 210 and 214, first fluid passages 202 and 212, and second fluid passages 201, 203, 211 and 213. Each groove 200, 204, 210 or 214 is an annular circumferential groove formed at the outside periphery of the axial end portion 30 to a predetermined depth, extending all around the outside periphery in the circumferential direction. Grooves 200 and 204 constitute retard passage 20, whereas grooves 210 and 214 constitute advance passage 21. Grooves 210 and 200 are arranged in this order as followed from the X-axis negative side to the X-axis positive side, and located in the cylinder head and outside of intake valve timing control apparatus 1a. Grooves 214 and 204 are arranged in this order as followed from the X-axis negative side to the X-axis positive side, and located at an X-axis positive side portion of the axial end portion 30 to which a vane rotor 4 is attached. Each first fluid passage 202 or 212 is an axial fluid passage formed in the axial end portion 30, extending in the X-axis direction. First fluid passage 202 constitutes retard passage 20, whereas first fluid passage 212 constitutes advance passage 21. Each second fluid passage 201, 203, 211 or 213 is a radial fluid passage formed in the axial end portion 30, extending in a radial direction perpendicular to the X-axis. Second fluid passages 201 and 203 constitute retard passage 20, whereas second fluid passages 211 and 213 constitute advance passage 21. Each first fluid passage 202 or 212 has a smaller diameter than bolt hole 32, extending from the axial end surface 300 in the negative x-axis direction. In other words, each first fluid passage 202 or 212 extends in the axial end portion 30, and has an opening at the axial end surface 300. First fluid passage 202 is arranged between bolt hole 32 for camshaft bolt 34 and bolt hole 32 for camshaft bolt 35 in the circumferential direction around the axis of rotation O. Specifically, the distance from the axis of rotation O to the central axis of first fluid passage 202 is substantially equal to the distance from the axis of rotation O to the central axis of each bolt hole 32, and the central axis of first fluid passage 202 is located on a circular line passing through the central axis of each bolt hole 32, and in a substantially central position between camshaft bolts 34 and 35. The size of first fluid passage 202 in the X-axis direction is set so that first fluid passage 202 overlaps with groove 200 in the X-axis direction, and further extends to a position slightly on the X-axis negative side of groove 200. On the other hand, first fluid passage 212 is arranged between bolt hole 32 for camshaft bolt 33 and bolt hole 32 for camshaft bolt 35 in the circumferential direction, similar to first fluid passage 202. The size of first fluid passage 212 in the X-axis direction is set so that first fluid passage 212 overlaps with groove 210 in the X-axis direction, and further extends to a position slightly on the X-axis negative side of groove 210. Second fluid passage 201 extends through between groove 200 and first fluid passage 202, for fluid communication therebetween. Second fluid passage 203 extends through between groove 204 and first fluid passage 202, for fluid communication therebetween. Second fluid passage 213 extends through between groove 214 and first fluid passage 212, for fluid communication therebetween.

Intake valve timing control apparatus 1a controls variable valve timing of the intake valves by continuously changing a rotational phase of intake camshaft 3a with respect to the crankshaft by supplied working fluid. Intake valve timing control apparatus 1a includes housing HSG formed with pulley 100, and a vane rotor 4 as a driven member mounted in housing HSG. Pulley 100 transmits torque from the crankshaft to housing HSG. Vane rotor 4 is mounted inside of housing HSG for relative rotation with respect to housing HSG. The torque is transmitted from housing HSG to vane rotor 4 through working fluid. Vane rotor 4 transmits the torque to intake camshaft 3a. Vane rotor 4 constitutes a phase change mechanism for changing the rotational phase of intake camshaft 3a with respect to housing HSG or the crankshaft by supply and drainage of working fluid. The phase change mechanism may be of another type, such as a trochoid type. In other words, the driven member of intake valve timing control apparatus 1a is not limited to a vane rotor. For example, the relative rotational phase between the housing and the camshaft may be changed according to movement of a member in the axial direction of the valve timing control apparatus, wherein the member has a helical gear (spline). Intake valve timing control apparatus 1a is a hydraulic actuator or hydraulically driven type phase actuation mechanism which is operated by receipt of supply of working fluid from a hydraulic fluid supply and drainage mechanism 2 or drainage of working fluid to hydraulic fluid supply and drainage mechanism 2. Supply and drainage of working fluid by hydraulic fluid supply and drainage mechanism 2 is controlled by a controller “CU” as a control means.

Housing HSG includes a housing body 10, a front plate 8 as a sealing plate, and a rear plate 9 as a sealing plate. Housing body 10 has a hollow cylindrical shape with open longitudinal ends. This is because housing body 10 is formed by extrusion as described in detail below. Front plate 8 has a disc shape, which is fixed to a front longitudinal end (X-axis positive side end) of housing body 10, for sealing and closing the opening of housing body 10. Rear plate 9 has a disc shape, which is fixed to a rear longitudinal end (X-axis negative side end) of housing body 10, for sealing and closing the opening of housing body 10. Housing body 10 may be alternatively formed with an opening only at one longitudinal end. Namely, housing body 10 may have a hollow cylindrical shape with a closed bottom, or a cup-shape. In other words, one of the sealing plates may be formed integrally with housing body 10. Housing body 10 is not limited to a cylindrical shape. Housing body 10 is formed integrally with pulley 100 extending over the entire length of the outside periphery of housing body 10 in the X-axis direction. Pulley 100 includes a plurality of projections (teeth) and recesses extending in the X-axis direction, which are arranged in the circumferential direction, and substantially evenly spaced, thus forming a gear or cogged belt wheel over which timing belt 1010 is wound. Pulley 100 is not limited to the integral forming with housing body 10, but may be formed separately from and coupled to housing body 10. The torque transmission based on tooth meshing may be replaced with a construction in which torque is transmitted frictionally through surface-to-surface contact between a belt and a pulley. For example, a housing body is formed with a pulley that has a groove at a central position in its width direction, and a belt that has no tooth and has a cross section fitted to the pulley having the groove. The combination of pulley 100 and toothed timing belt 1010 according to the embodiment is advantageous in enhancement in the efficiency of power transmission. When pulley 100 is rotated by the crankshaft, pulley 100 and housing body 10 rotate as a solid unit in a clockwise direction as viewed in FIG. 4 or in a direction of an arrow shown in FIG. 1.

FIGS. 6A, 6B and 6C are views of housing body 10, where FIG. 6A is a front view along the axis of rotation from the X-axis positive side, FIG. 6B is a side sectional view taken along a plane indicated by F6B-F6B in FIG. 6A, and FIG. 6C is a rear view along the axis of rotation from the X-axis negative side. FIGS. 7 and 8 are perspective views of workpieces during a process of manufacturing the housing body 10. Housing body 10 is manufactured by a process including an extrusion operation, a coating operation, a cutting-off operation, and a carving operation, which are carried out in this order. First, in the extrusion operation, an aluminum-based metal material, such as aluminum, or aluminum alloy such as A6000 or A7000, is heated and extruded from a mold, to form an aluminum extrusion or first workpiece P1 shown in FIG. 7, which extends in the direction of extrusion, and in which continuous shapes of first, second and third shoes 11, 12 and 13 are formed at an inside periphery, and a continuous shape of pulley 100 is formed at an outside periphery. Second, in the coating operation, the entire surface, i.e. the inside and outside peripheral surfaces of first workpiece P1 are applied with anodic oxidation treatment or alumilite treatment, to form a second workpiece P2 which has anodic oxide coating films at the inside and outside peripheries. Third, in the cutting-off operation, second workpiece P2 is cut laterally at intervals of a predetermined distance along the axial direction, to form a plurality of identically-shaped third workpieces P3, as shown in FIG. 8. Finally, in the carving operation, each third workpiece P3 is applied with carving or cutting, to form a fitting recess 101, bolt holes 110, 120 and 130, and a positioning recess 114, as described in detail below, and thereby form a final shape of housing body 10 shown in FIGS. 6A, 6B and 6C. In this way, each housing body 10 in the final shape is formed with an anodic oxide coating film layer at the inside and outside peripheral surfaces, but the cut surfaces obtained by the cutting-off operation (the axial end surfaces in the X-axis direction) are formed with no anodic oxide coating film layer. Instead, a base layer of the aluminum-based metal material is exposed at the cut surfaces. As shown in FIGS. 6B and 6C, the open X-axis negative side end of housing body 10 is formed with fitting recess 101 which is a cylindrical recess having a center at the axis of rotation O, and extending to a predetermined depth in the X-axis direction. Specifically, fitting recess 101 is formed by cutting away a part of third workpiece P3, into a cylindrical shape having a predetermined radius R about the axis of rotation O, and having a predetermined depth in the X-axis positive direction. Fitting recess 101 includes a bottom surface 102 having a circular shape, and an inside peripheral surface 103 surrounding the bottom surface 102. Inside peripheral surface 103 has the radius R with respect to the axis of rotation O. Where Ri represents a radius of the inside peripheral surface of housing body 10 about the axis of rotation O, and Ro represents a maximum radius of housing body 10 which is a distance between a tooth tip of pulley 100 and the axis of rotation O, it holds that Ro:Ri≈10:8. It also holds that (Ro+Ri)/2≈R. In other words, fitting recess 101 extends in the radial direction of housing body 10 substantially to a midpoint between the inside and outside peripheral surfaces of housing body 10. On the other hand, where L represents an axial length L of housing body 10, and L2 represents a distance between the bottom surface 102 of fitting recess 101 and the X-axis negative end surface 104 of housing body 10, it holds that L:L2≈10:2. In other words, fitting recess 101 is formed to extend in the X-axis direction over a range of about 20% or more of the axial length of housing body 10. The axial length of the inside periphery of housing body 10, L1, is shorter than that of the outside periphery, or that of pulley 100, L (L1<L). In other words, the axial length of pulley 100 in the X-axis direction, L, is set longer than that of the inside periphery of housing body 10, L1. The inside periphery of housing body 10 is formed integrally with first, second and third shoes 11, 12 and 13 which extend inwardly in the radial direction. Specifically, first, second and third shoes 11, 12 and 13 are arranged in a circumferential direction or direction of rotation about the axis of rotation O, at substantially even intervals, extending from the inside periphery of housing body 10 inwardly toward the axis of rotation O. First, second and third shoes 11, 12 and 13 are arranged in this order in the clockwise direction in FIG. 4. Each of first, second and third shoes 11, 12 and 13 extends in the X-axis direction, and has a cross section having a substantially trapezoidal shape. The width of each of first, second and third shoes 11, 12 and 13 in the circumferential direction is set substantially equal to each other. The space between second shoe 12 and third shoe 13, and the space between third shoe 13 and first shoe 11, are set substantially equal to each other. The space between first shoe 11 and second shoe 12 is set slightly larger than the other spaces, for accommodating a first vane 41 having a wider width, which is described in detail below. First shoe 11 is formed with a bolt hole 110 substantially at the center of the trapezoidal cross section, where bolt hole 110 extends through the first shoe 11. Similarly, second shoe 12 and third shoe 13 are formed with a through bolt hole 120 and a through bolt hole 130 respectively. The X-axis positive side end surface of each of first, second and third shoes 11, 12 and 13 is fixedly attached to front plate 8. The X-axis negative side end surface of each of first, second and third shoes 11, 12 and 13, which is a part of the bottom surface 102 of fitting recess 101, is fixedly attached to rear plate 9. As viewed from the X-axis positive side, or as shown in FIG. 6A, second shoe 12 and third shoe 13 are formed with a flat portion 121 and a flat portion 131 in their clockwise sides, respectively. Each of flat portion 121 and flat portion 131 is in a straight line passing through the axis of rotation O of housing body 10, as viewed in the X-axis direction. On the other hand, the clockwise side of first shoe 11 is formed with a rounded portion 112 at a root portion in an outward position in the radial direction of housing body 10, and formed with a recess 113 at a tip portion in an inward position in the radial direction of housing body 10, as viewed in FIG. 6B. First shoe 11 is formed with a flat portion 111 between rounded portion 112 and recess 113, similar to second shoe 12 and third shoe 13. Rounded portion 112 has an inwardly curved and substantially arced edge, as viewed in the X-axis direction. The edge of rounded portion 112 gradually rises from the inside peripheral surface of housing body 10 to merge into the clockwise side edge of first shoe 11. As shown in FIG. 6C, on the X-axis negative side of first shoe 11, rounded portion 112 in bottom surface 102 of fitting recess 101 is formed with a positioning recess 114 adjacent to bolt hole 110. Positioning recess 114 has a smaller diameter than bolt hole 110. Rounded portion 112 serves to allow arrangement of positioning recess 114 in first shoe 11, and enhance rigidity of the root portion of first shoe 11 in the circumferential direction, so as to bear a stress resulting from contact between first vane 41 and first shoe 11. As viewed from the X-axis positive side, or as viewed in FIG. 6A, the counterclockwise sides of first, second and third shoes 11, 12 and 13 are formed with recesses 115, 125 and 135, respectively. Recesses 115, 125 and 135 are relatively wide grooves extending over the entire axial length of housing body 10 in the X-axis direction. As shown in FIG. 6A, as viewed in the X-axis direction, the tips 116, 126 and 136 of first, second and third shoes 11, 12 and 13 have radially inside surfaces facing the axis of rotation O, which are inwardly curved like an arc fitted with an outside peripheral surface of a rotor 40 of vane rotor 4, which is described in detail below. The tip 116 of first shoe 11 is formed with a sealing groove 117 which extends in the X-axis direction. A sealing member 118 and a sealing spring such as a leaf spring 119 not shown are fitted and retained in sealing groove 117. Sealing member 118 is in liquid-tight sliding contact with the outside peripheral surface of rotor 40. Leaf spring 119 presses the sealing member 118 onto the outside peripheral surface of rotor 40. Sealing member 118 is formed of a grass fiber plastic, having a substantially U-shape. Similarly, the tips 126 and 136 of second shoe 12 and third shoe 13 are formed with sealing grooves 127 and 137, sealing members 128 and 138, and leaf springs 129 and 139, respectively, as shown in FIGS. 3 and 4.

Front plate 8 is formed by forging an iron-based metal material, such as an iron alloy, into a thinner disc shape than rear plate 9, wherein the iron-based metal material is harder than aluminum-based metal materials. Front plate 8 closes and seals the front axial end of housing body 10, namely closes and seals the X-axis positive side ends of first, second and third advance chambers A1, A2 and A3, and first, second and third retard chambers R1, R2 and R3 defined in housing body 10. In the present description, “hardness” of an object means a degree of difficulty of changing the outline of the object, and can be measured by a commonly known hardness test. “Wear” of an object means that a surface of the object is worn, and can be categorized in terms of dynamics into sliding wear, collision wear, etc. “Wear resistance” of an object can be measured by a suitable test selected according to the category, or may be determined indirectly based on the hardness test. As shown in FIG. 3, the diameter of front plate 8 is set slightly larger than the diameter (specifically, the diameter of tooth top circle) of pulley 100, so that over the entire circumference of pulley 100, an outside periphery 80 of front plate 8 projects from pulley 100 outwardly in the radial direction as viewed in the X-axis direction. As shown in FIG. 2, front plate 8 is formed with a female thread portion 82 located substantially at the center of the X-axis positive side surface of front plate 8. Female thread portion 82 projects in the X-axis positive direction. Female thread portion 82 is formed with a large-diameter hole 81 at its center, which extends through front plate 8 in the X-axis direction, and through which camshaft bolts 33, 34 and 35 (see FIG. 4) are inserted to pass, when intake valve timing control apparatus 1a is assembled. Large-diameter hole 81 of female thread portion 82 is formed with a female thread 820 to which a male thread 700 of a cap 7 is screwed. The annular X-axis positive side surface of female thread portion 82 is formed with an annular sealing ring groove 821. Front plate 8 is formed with bolt holes 83, 84 and 85 located between female thread portion 82 and outside periphery 80. Bolt holes 83, 84 and 85 are arranged and evenly spaced in the circumferential direction as viewed in the X-axis direction, through which bolts b1, b2 and b3 inserted to pass. In the X-axis direction, bolt holes 83, 84 and 85 are located to face or conform to bolt holes 110, 120 and 130, which are formed in first, second and third shoes 11, 12 and 13 of housing body 10, respectively. Front plate 8 is formed with thicker portions 86, 87 and 88 around bolt holes 83, 84 and 85 respectively. Thicker portions 86, 87 and 88 are slightly thicker than the other portion in the X-axis direction, in order to bear the axial force applied by bolts b1, b2 and b3. Each of thicker portions 86, 87 and 88 has a shape that is spreading inwardly in the radial direction, and continuous with female thread portion 82. In other words, front plate 8 is formed as thin as possible, except thicker portions 86, 87 and 88 for providing a strength enough to bear the axial force applied by bolts b1, b2 and b3. FIG. 12 is a perspective view of front plate 8 as viewed from the X-axis negative side. The X-axis negative side surface of front plate 8 is formed with an annular sealing ring groove 89. Annular sealing ring groove 89 has a shape including three inwardly curved sections like a three-leaved clover, so that annular sealing ring groove 89 extends circumferentially along the outside periphery 80 with a slight radial clearance r, and passes inside of bolt holes 83, 84 and 85, i.e. passes between the axis of rotation O and each of bolt holes 83, 84 and 85.

Cap 7 is formed by forging an iron-based metal material into a hollow cylindrical shape with a bottom, and detachably attached to front plate 8, thus constituting a front plate (in a broad sense) together with front plate 8. Cap 7 includes a male thread portion 70, a division wall portion 71, and a flange 72. Male thread portion 70 has a hollow cylindrical shape, extending in the X-axis direction. Division wall portion 71 closes the opening of male thread portion 70. Flange 72 spreads outwardly in the radial direction from the X-axis positive side end of male thread portion 70. Male thread portion 70 is formed with a male thread 700 at the outside periphery. Division wall portion 71 is formed integrally with a bolt head portion 710 substantially at the center of the X-axis positive side surface, which has the form of a regular hexagonal prism. Bolt head portion 710 is turned so that cap 7 is screwed into front plate 8, i.e. male thread 700 of cap 7 is screwed into female thread 820 of front plate 8, and that large-diameter hole 81 of front plate 8 is closed and sealed. Under this condition, the X-axis negative side surface of flange 72 faces the X-axis positive side axial end surface of female thread portion 82, and the X-axis negative side axial end surface of male thread portion 70 is located slightly on the X-axis positive side of the X-axis negative side surface of front plate 8, as shown in FIG. 3. Cap 7 is formed with a recess 73 at the X-axis negative side, wherein recess 73 is defined by the X-axis negative side surface of division wall portion 71 as a bottom surface, and the inside periphery of the X-axis negative side portion of male thread portion 70 as a side wall. The depth or size in the X-axis direction, of recess 73, is half or more of the height or size in the X-axis direction, of head 331, 341 or 351 of each camshaft bolt 33, 34 or 35.

Rear plate 9 is fixedly inserted in fitting recess 101 of housing body 10, so as to close and seal the rear axial open end of housing body 10 closer to intake camshaft 3a, i.e. the X-axis negative side open end of first, second and third advance chambers A1, A2 and A3, and first, second and third retard chambers R1, R2 and R3 which are defined in housing body 10. Rear plate 9 is formed by forging an iron-based metal material such as S45C or S48 that is harder than the aluminum-based metal material of vane rotor 4. Rear plate 9 includes a plate body 90 and a cylindrical portion 91. Cylindrical portion 91 has a cylindrical shape extending in the X-axis negative direction from the X-axis negative side of plate body 90. As viewed in the X-axis direction, cylindrical portion 91 is located substantially at the center of plate body 90, coaxially with the axis of rotation O. Cylindrical portion 91 is formed with a through hole 92 inside, through which intake camshaft 3a is inserted to pass. Through hole 92 is formed to extend in the X-axis direction, and pass through rear plate 9, substantially coaxially with the axis of rotation O. The diameter of through hole 92 is set slightly smaller than that of large-diameter hole 81 of front plate 8. The length of plate body 90 in the X-axis direction is set at most slightly larger than the depth of fitting recess 101 (the length in the X-axis direction, L2). The length of an outside peripheral surface 93 of plate body 90 in the X-axis direction is set substantially equal to the depth of fitting recess 101 (L2). The diameter of plate body 90 is set substantially equal to the diameter of fitting recess 101 (R×2). Plate body 90 is formed with female thread portions 901, 902 and 903 around cylindrical portion 91, which are arranged and evenly spaced in the circumferential direction. Female thread portions 901, 902 and 903 are formed with bolt holes extending through plate body 90 in the X-axis direction. The bolt holes are formed with female threads in the inside peripheral surfaces, respectively. Male threads of an X-axis negative side end portions of bolts b1, b2 and b3 are screwed into the female threads respectively. As viewed in the X-axis direction, female thread portions 901, 902 and 903 (bolt holes) are located to face or conform to the bolt holes 110, 120 and 130 of first, second and third shoes 11, 12 and 13, and bolt holes 83, 84 and 85 of front plate 8. As shown in FIG. 2, plate body 90 is formed with a recess 900 which is located adjacent to and in the clockwise direction from one female thread portion 901 which faces bolt hole 110 of first shoe 11, as viewed from the X-axis positive side. Recess 900 is formed to extend in the X-axis negative direction to a predetermined depth in plate body 90. The outside peripheral surface 93 of plate body 90 is formed with a sealing ring groove 906 which extends in the circumferential direction. The X-axis positive side surface of plate body 90 is formed with annular sealing ring grooves 907, 908 and 909 which extend circumferentially around female thread portions 901, 902 and 903 respectively. Plate body 90 is formed with a pin hole 904 having a bottom, which is located at the outside periphery of the X-axis positive side surface of plate body 90, and adjacent to and in the counterclockwise direction from recess 900. Pin hole 904 is located between recess 900 and female thread portion 901, and in a position in the radial direction of plate body 90 which faces positioning recess 114 of housing body 10 shown in FIG. 6C. A positioning pin 905 is press-fitted and fixed in pin hole 904. Positioning pin 905 is a dowel pin whose longitudinal end projects to a predetermined height in the X-axis positive direction from the X-axis positive side surface of plate body 90. The diameter of the longitudinal end of positioning pin 905 is set slightly smaller than positioning recess 114, and adapted to be inserted and fitted from the X-axis negative side into positioning recess 114. The diameter of the longitudinal end of positioning pin 905 and the diameter of positioning recess 114 are set so as to prevent play between housing body 10 and rear plate 9 in the circumferential direction under a condition that positioning pin 905 is inserted and fitted in positioning recess 114. Pin hole 904 is located in rear plate 9 so that under the condition that positioning pin 905 is inserted and fitted in positioning recess 114, bolt hole 110 of first shoe 11 of housing body 10 is in substantially the same position as female thread portion 901 of rear plate 9 as viewed in the X-axis direction, and that when flat portion 415 of first vane 41 of vane rotor 4 is in contact with flat portion 111 of first shoe 11 as shown in FIG. 4, a slide hole 501 of first vane 41 is in substantially the same position as recess 900 of rear plate 9, as viewed in the X-axis direction. Pin hole 904 is located closer to first retard chamber R1 than sealing ring grooves 906 and 907, and positioning pin 905 is located adjacent to recess 900.

Front plate 8, housing body 10, and rear plate 9 are fixed together in the X-axis direction by bolts b1, b2 and b3. Bolts b1, b2 and b3 are inserted from the X-axis positive side to pass through bolt holes 83, 84 and 85 of front plate 8, and bolt holes 110, 120 and 130 of housing body 10, and screwed into female thread portions 901, 902 and 903 of rear plate 9, so as to fix front plate 8 and rear plate 9 to housing body 10. Sealing rings S1, S2 and S3 are inserted between housing body 10 and rear plate 9, and between front plate 8 and housing body 10. A sealing ring S4 is inserted between cap 7 and front plate 8. Sealing rings S1, S2, S3 and S4 are annular sealing members to be mounted, each of which is an O-ring having a circular cross section in this example. Sealing rings S1, S2, S3 and S4 are formed of a rubber such as an acrylic rubber or fluorine rubber, which is superior in durability against working fluid. The rubber may be a nitrile rubber, etc. Each sealing rings S1, S2, S3 or S4 is not limited to O-rings, but may have a different cross section. Sealing rings S1 and S2 are disposed between rear plate 9 and housing body 10. Sealing ring S1 is arranged between the inside peripheral surface 103 of fitting recess 101 of housing body 10 and outside peripheral surface 93 of plate body 90 of rear plate 9. Each sealing ring S2 is arranged between a portion surrounding a respective one of female thread portions 901, 902 and 903 in the X-axis positive side end surface of rear plate 9 and the X-axis negative side end surface (bottom surface 102 of fitting recess 101) of a respective one of first, second and third shoes 11, 12 and 13 of housing body 10. Sealing ring S3 is arranged between portions of front plate 8 and housing body 10 which face each other, i.e. between the X-axis negative side end surface of front plate 8 and the X-axis positive side end surface 105 of housing body 10 (first, second and third shoes 11, 12 and 13). Sealing ring S3 has the form of a three-leaved clover which is substantially identical to the form of annular sealing ring groove 89 of front plate 8. Sealing ring S4 is arranged between the X-axis positive side end surface of female thread portion 82 of front plate 8 and the X-axis negative side end surface of flange 72 of cap 7.

As shown in FIG. 3, cylindrical portion 91 of rear plate 9 is provided with an oil seal “OS” at the outside peripheral surface of its X-axis negative side portion, and is rotatably supported through the oil seal OS by the cylinder block of the internal combustion engine.

FIGS. 9A and 9B are views of vane rotor 4, where FIG. 9A is a front view along the axis of rotation from the X-axis positive side, and FIG. 9B is a side sectional view taken along a plane indicated by F9B-F9B in FIG. 9A. In FIG. 9A, fluid passages 408 and 409 formed inside the vane rotor 4, and a recess 44 formed the X-axis negative side of vane rotor 4 are indicated by broken lines. In FIG. 9B, the opening of one of retard fluid passages 408 and the opening of one of advance fluid passages 409 are shown. FIGS. 10 and 11 are perspective views of workpieces during a process of manufacturing the vane rotor 4. Vane rotor 4 is manufactured by a process including an extrusion operation, a cutting-off operation, a carving operation, and a coating operation, which are carried out in this order. First, in the extrusion operation, an aluminum-based metal material as used for housing body 10 is extruded from a mold, to form a first workpiece Q1 shown in FIG. 10, which extends in the direction of extrusion, in which continuous shapes of rotor 40 and first, second and third vanes 41, 42 and 43 are formed. Second, in the cutting-off operation, first workpiece Q1 is cut laterally at intervals of a predetermined distance along the axial direction, to form a plurality of identically-shaped second workpieces Q2 including a rotor and vanes, as shown in FIG. 11. Third, in the carving operation, second workpiece Q2 is applied with carving or cutting, to form a boss portion 401, a camshaft insertion hole 402, a slide hole 501, etc., and thereby form a final shape of vane rotor 4 shown in FIGS. 9A and 9B. Finally, in the coating operation, the entire surface of second workpiece Q2 is applied with anodic oxidation treatment, to form a third workpiece Q3 which has an anodic oxide coating film layer. When vane rotor 4 is finalized, the anodic oxide coating film layer is formed in the axial end surfaces of vane rotor 4, and also in the surface of boss portion 401, camshaft insertion hole 402, slide hole 501, etc. Vane rotor 4 is a driven member or driven rotator which can rotate relative to pulley 100 or housing HSG, and serves as a vane member which rotates in the clockwise direction in FIG. 4 as a solid unit with intake camshaft 3a. Vane rotor 4 includes: rotor 40 fixed to intake camshaft 3a with three camshaft bolts 33, 34 and 35, substantially coaxially with intake camshaft 3a; and first, second and third vanes 41, 42 and 43 projecting outwardly in radial directions from rotor 40, wherein first, second and third vanes 41, 42 and 43 are adapted to receive hydraulic pressure.

Rotor 40 includes a rotor body 400 and a boss portion 401 which are arranged coaxially. Rotor body 400 is a body of rotor 40, having a cylindrical shape. In the X-axis direction, the length of rotor body 400 is substantially equal to the length of housing body 10 excluding the length of the fitting recess 101, L1. The outside diameter (i.e. the diameter of the outside periphery) of rotor body 400 is slightly larger than the diameter of large-diameter hole 81 of front plate 8. Boss portion 401 is cylindrically formed to project from rotor body 400 in the axial direction, or in the X-axis negative direction. The length of boss portion 401 in the X-axis direction, L3, is slightly shorter than the length of fitting recess 101 of housing body 10 in the X-axis direction, L2. Boss portion 401 has a slightly smaller outer diameter than rotor body 400, which is slightly smaller than the diameter of through hole 92 of rear plate 9. The surface of boss portion 401, including the inside and outside peripheral surfaces of boss portion 401, is formed with the anodic oxide coating film layer, as described above. Rotor 40 is formed with a camshaft insertion hole 402 having a bottom, which is positioned coaxially with rotor 40, and extends inside of boss portion 401 and rotor body 400, where camshaft insertion hole 402 has a diameter that is substantially equal to and slightly larger than the diameter of intake camshaft 3a. Camshaft insertion hole 402 extends over the entire axial length of boss portion 401 and a range of two thirds or less of the axial length of rotor body 400, as shown in FIG. 9B. Camshaft insertion hole 402 is adapted to intake camshaft 3a so that an inserted portion 301 of intake camshaft 3a (an X-axis positive side portion of axial end portion 30 of intake camshaft 3a) is inserted and mounted in camshaft insertion hole 402. Rotor body 400 is formed with bolt holes 403, 404 and 405 at the bottom of camshaft insertion hole 402, wherein each bolt hole 403, 404 or 405 extends through rotor body 400. Bolt holes 403, 404 and 405 are arranged in the circumferential direction around the axis of rotation O, in this order in the clockwise direction, and substantially evenly spaced from one another. The positions of bolt holes 403, 404 and 405 are set to face and conform to bolt holes 32 of axial end portion 30 of intake camshaft 3a in the X-axis direction, so that the central axes of bolt holes 403, 404 and 405 are substantially identical to the central axes of bolt holes 32 as viewed in the X-axis direction. Namely, the distance between each bolt hole 403, 404 or 405 and the axis of rotation O is substantially equal to the distance between the corresponding bolt hole 32 and the axis of rotation O, and the angle defined by the line connecting the axis of rotation O and one of bolt holes 403, 404 and 405 and the line connecting the axis of rotation O and another one of bolt holes 403, 404 and 405 is substantially equal to the angle defined by the line connecting the axis of rotation O and one of bolt holes 32 and the line connecting the axis of rotation O and another one of bolt holes 32. Rotor body 400 is formed also with a pin hole having a bottom (recess 44 for positioning) at the bottom of camshaft insertion hole 402, wherein recess 44 extends to a predetermined depth. As viewed in the X-axis direction, recess 44 has an elliptic shape whose outline includes two straight line sections extending in a radial direction of rotor 40 and facing one another in the circumferential direction, and two curved sections having the form of semicircles and facing one another in the radial direction of rotor 40. Recess 44 is positioned between bolt hole 404 and bolt hole 405. Specifically, the distance between the axis of rotation O and the central axis of recess 44 is substantially equal to the distance between the axis of rotation O and each bolt hole 403, 404 or 405, and recess 44 has a central axis at a substantially central position between bolt holes 404 and 405, on the circle passing through the central axes of bolt holes 403, 404 and 405. On the other hand, in intake camshaft 3a, first fluid passage 212 opens at axial end surface 300, constituting a pin hole or recess. FIG. 13 is a partial side sectional view taken along a plane passing through a central longitudinal axis of a positioning pin 45. As shown in FIG. 13, positioning pin 45 is press-fitted and fixed to the open end of first fluid passage 212. Positioning pin 45 is a dowel pin whose longitudinal end portion projects to a predetermined height in the X-axis positive direction from axial end surface 300 of intake camshaft 3a. Positioning pin 45 may be of a type other than a dowel pin. The longitudinal end portion of positioning pin 45 has a slightly smaller diameter than the size of recess 44 in the circumferential direction, namely, than the distance between the two straight line sections of recess 44, and adapted to be inserted and fitted from the X-axis negative side into recess 44. The diameter of the longitudinal end portion of positioning pin 45 and the size of recess 44 are set so that when positioning pin 45 is inserted and fitted in recess 44, no backlash occurs between vane rotor 4 and intake camshaft 3a in the circumferential direction. Recess 44 is located in vane rotor 4 so that when positioning pin 45 is inserted and fitted in recess 44, bolt holes 403, 404 and 405 of rotor 40 are located coaxially with bolt holes 32 of intake camshaft 3a. Camshaft bolts 33, 34 and 35 are inserted from the X-axis positive side into corresponding ones of bolt holes 403, 404 and 405, under condition that inserted portion 301 is inserted and fitted in camshaft insertion hole 402, and positioning pin 45 is inserted and fitted in recess 44, thereby positioning the vane rotor 4 and intake camshaft 3a with respect to one another in the circumferential direction. The head 331, 341 or 351 of each camshaft bolt 33, 34 or 35 is located at the X-axis positive side of rotor 40, whereas a portion of the shank of each camshaft bolt 33, 34 or 35 projecting from the X-axis negative side of rotor 40 is inserted into the corresponding bolt hole 32, and the male thread of each camshaft bolt 33, 34 or 35 is screwed with the female thread of bolt hole 32. In this way, rotor 40 is fixed to the axial end surface 300 of intake camshaft 3a so that the axial end portion 30 of intake camshaft 3a is fixedly mounted to vane rotor 4. Bolt holes 403, 404 and 405 thus constitute a plurality of fixing portions for fixing the rotor 40 to the axial end surface 300 of intake camshaft 3a.

As shown in FIG. 3, boss portion 401 of rotor 40 is inserted from the X-axis positive side into the through hole 92 of cylindrical portion 91 of rear plate 9. Boss portion 401 is mounted with a slight clearance with through hole 92. The insertion of boss portion 401 in through hole 92 serves to make the axes of rotation of rear plate 9 and vane rotor 4 substantially identical to one another, position the axis of rotation of vane rotor 4 at the axis of rotation O, and make the boss portion 401 to bear the rear plate 9. Namely, vane rotor 4 is positioned with respect to housing HSG through the boss portion 401 and cylindrical portion 91, while housing HSG is rotatably supported with respect to vane rotor 4 or intake camshaft 3a. Boss portion 401 serves as a bearing (slide bearing) for bearing a load from housing HSG through the cylindrical portion 91, and supporting the housing HSG for free rotation thereof. The outside peripheral surface of boss portion 401 is in sliding contact with the inside peripheral surface of through hole 92. The sliding outside peripheral surface of boss portion 401 is provided with an anodic oxide coating film, as described above.

Rotor body 400 is formed with first, second and third vanes 41, 42 and 43 at the outside periphery, which are arranged and substantially evenly spaced in the circumferential direction, extending outwardly in the radial direction from the axis of rotation O. First, second and third vanes 41, 42 and 43 are arranged in this order in the clockwise direction in FIG. 4. Specifically, first vane 41 is disposed between bolt holes 403 and 404, second vane 42 is disposed between bolt holes 404 and 405, and third vane 43 is disposed between bolt holes 405 and 403. First, second and third vanes 41, 42 and 43 are formed integrally with rotor 40 (rotor body 400), and have a cross section having a substantially trapezoidal shape spreading outwardly in the radial direction, as viewed in the X-axis direction. The length of first, second and third vanes 41, 42 and 43 in the X-axis direction is set equal to the length of rotor body 400 in the X-axis direction, L1. When vane rotor 4 is mounted in housing HSG, the X-axis positive side surfaces (formed with an anodic oxide coating film) of first, second and third vanes 41, 42 and 43 face with a quite slight clearance the X-axis negative side surface of front plate 8. On the other hand, the X-axis negative side surfaces (formed with an anodic oxide coating film) of first, second and third vanes 41, 42 and 43 face with a quite slight clearance the X-axis positive side surface of rear plate 9. The lengths of second vane 42 and third vane 43 in the circumferential direction of vane rotor 4 are substantially equal to each other. The circumferential length of first vane 41 is set larger that those of second vane 42 and third vane 43, so as to provide a space where a lock mechanism 5 is mounted. The centers of gravity of first, second and third vanes 41, 42 and 43 are arranged and substantially evenly spaced in the circumferential direction. However, first vane 41 is slightly heavier than the other vanes, because first vane 41 is large and provided with lock mechanism 5. Accordingly, the space between first vane 41 and second vane 42, and the space between third vane 43 and first vane 41, are set slightly larger than the space between second vane 42 and third vane 43, so that the center of gravity of the entire vane rotor 4 is conformed to the axis of rotation O. When vane rotor 4 is mounted in housing HSG, first vane 41 is mounted between first shoe 11 and second shoe 12, second vane 42 is mounted between second shoe 12 and third shoe 13, and third vane 43 is mounted between third shoe 13 and first shoe 11. Outside peripheral surfaces 411, 421 and 431 of first, second and third vanes 41, 42 and 43 are curved to have arced shapes which are fitted with the inside peripheral surface of housing body 10, as viewed in the X-axis direction, as shown in FIG. 4. Outside peripheral surface 411 of first vane 41 is formed with a groove 412 which extends in the X-axis direction. A sealing member 413 and a sealing spring such as a leaf spring 414 not shown are fitted and retained in groove 412. Sealing member 413 is in liquid-tight sliding contact with the inside peripheral surface of housing body 10. Leaf spring 414 presses the sealing member 413 onto the inside peripheral surface of housing body 10. Similarly, outside peripheral surfaces 421 and 431 of second vane 42 and third vane 43 are formed with grooves 422 and 432, sealing members 423 and 433, and leaf springs 424 and 434, respectively. The counterclockwise side of first vane 41 is formed with a flat portion 415 as viewed from the X-axis positive side, as shown in FIG. 9A. Flat portion 415 is substantially in a straight line passing through the axis of rotation O of rotor 40 as viewed in the X-axis direction. First vane 41 is formed with a recess 416 between flat portion 415 and the root of first vane 41. Recess 416 has an inwardly curved and substantially arced edge, as viewed in the X-axis direction. Similarly, second vane 42 and third vane 43 are formed with flat portions 425 and 435, and recesses 426 and 436, respectively. As viewed from the X-axis positive side, the counterclockwise side of first vane 41 is formed with a rounded portion 417 at a tip portion outside of flat portion 415. Rounded portion 417 has an outwardly curved and substantially arced edge having a predetermined curvature that is slightly smaller than the curvature of rounded portion 112 of first shoe 11. Rounded portion 417 serves to allow the flat portion 415 of first vane 41 to be in surface-to-surface contact with the flat portion 111 of first shoe 11 as shown in FIG. 4, and serves to reduce the weight of first vane 41. On the other hand, as viewed from the X-axis positive side, the clockwise sides of first, second and third vanes 41, 42 and 43 are formed with recesses 418, 428 and 438 respectively, where recesses 418, 428 and 438 are relatively wide recesses extending over the entire axial length of vane rotor 4. As viewed from the X-axis positive side, the clockwise side of first vane 41 is formed integrally with a projection 419 that is located at the root and extends over a predetermined distance, along the outside periphery of rotor 40 (rotor body 400) in the clockwise direction. The projection 419 is formed continuous with the root of first vane 41, and projects from the outside periphery of rotor 40 (rotor body 400) outwardly in the radial direction. Similarly, the clockwise side of the root of second vane 42 is formed integrally with a radial projection 429.

Vane rotor 4 defines, in the space between vane rotor 4 and housing HSG, a plurality of working fluid chambers, namely, first, second and third advance chambers A1, A2 and A3, and first, second and third retard chambers R1, R2 and R3, which working fluid is supplied to or drained from. Namely, as viewed in the X-axis direction, three chambers are formed by two adjacent shoes and the outside peripheral surface of rotor 40 (rotor body 400), and each of the three chambers is divided by vane 41, 42 or 43 into one advance chamber and one retard chamber. First, second and third advance chambers A1, A2 and A3, and first, second and third retard chambers R1, R2 and R3 are separated liquid-tightly from each other by sealing member 413, etc. Working fluid is supplied from an oil pump 1020 to first, second and third advance chambers A1, A2 and A3, and first, second and third retard chambers R1, R2 and R3, and serves to transmit torque between vane rotor 4 and housing HSG. More specifically, first, second and third advance chambers A1, A2 and A3, and first, second and third retard chambers R1, R2 and R3 are defined by the X-axis negative side surface of front plate 8, the X-axis positive side surface of rear plate 9, the circumferentially-facing surfaces of first, second and third vanes 41, 42 and 43, and the circumferentially-facing surfaces of first, second and third shoes 11, 12 and 13. For example, first advance chamber A1 is defined between the clockwise surface of first shoe 11, the counterclockwise surface of first vane 41, whereas first retard chamber R1 is defined between the clockwise surface of first vane 41 and the counterclockwise surface of second shoe 12, as shown in FIG. 4. Similarly, second advance chamber A2 is defined between second shoe 12 and second vane 42, second retard chamber R2 is defined between second vane 42 and third shoe 13, third advance chamber A3 is defined between third shoe 13 and third vane 43, and third retard chamber R3 is defined between third vane 43 and first shoe 11. Alternatively, one of the set of first, second and third advance chambers A1, A2 and A3 and the set of first, second and third retard chambers R1, R2 and R3 may be omitted. For example, valve timing control apparatus 1 may include a single advance chamber or a single retard chamber. The number of advance chambers and the number of retard chambers are not limited to three, but may be more or less than three. The shoes of the housing body may be omitted, so that the working fluid chambers are defined between the inside peripheral surface of the housing body and the vanes without the shoes. The cylindrical rotor may be omitted so that the vane member is constituted only by the vanes.

The range of relative rotation of vane rotor 4 with respect to housing HSG is defined by first and second stopper mechanisms as follows. When vane rotor 4 rotates with respect to housing HSG in the counterclockwise direction by a predetermined angle as viewed from the X-axis positive side, the flat portion 111 of first shoe 11, which is formed in the clockwise surface of first shoe 11, is brought into surface-to-surface contact with flat portion 415 of first vane 41, which is formed in the counterclockwise surface of first vane 41, as shown in FIG. 4. Under this condition, the flat portion 121 of second shoe 12 and the flat portion 425 of second vane 42 face each other with a slight clearance, namely the circumferentially-facing surfaces of second shoe 12 and second vane 42 are kept out of contact with each other. Similarly, flat portion 131 of third shoe 13 and flat portion 435 of third vane 43 face each other with a slight clearance, and are kept out of contact with each other. In this way, rotation of vane rotor 4 with respect to housing HSG in the counterclockwise direction is restricted by contact between flat portion 111 of first shoe 11 and flat portion 415 of first vane 41. Flat portion 111 of the circumferentially-facing surface of first shoe 11 and flat portion 415 of the circumferentially-facing surface of 41 serve as first stopper portions constituting a first stopper mechanism for restricting relative rotation of vane rotor 4 in the counterclockwise direction (in the retard direction). In FIG. 4 where relative rotation between vane rotor 4 and housing HSG is restricted, an angle α, which is defined about the axis of rotation O by the clockwise side end surface of radial projection 419 and the counterclockwise side end surface of tip 126 of second shoe 12, is slightly smaller than an angle β, which is defined about the axis of rotation O by the clockwise side end surface of radial projection 429 and the counterclockwise side end surface of tip 136 of third shoe 13. According to the above relationship, when vane rotor 4 rotates with respect to housing HSG from the position shown in FIG. 4 by the angle α in the clockwise direction, the tip 126 of second shoe 12 and the radial projection 419 of first vane 41 are brought into surface-to-surface contact with each other as shown in FIG. 5. Under this condition, the tip 136 of third shoe 13 and the radial projection 429 of second vane 42 face each other with a predetermined slight clearance in the circumferential direction, so that third shoe 13 and second vane 42 are kept out of contact with each other. Similarly, first shoe 11 and third vane 43 face each other with a predetermined slight clearance, and thus kept out of contact with each other. In this way, rotation of vane rotor 4 with respect to housing HSG in the clockwise direction is restricted by contact between tip 126 of second shoe 12 and radial projection 419 of first shoe 11. The clockwise surface of radial projection 419 and the counterclockwise surface of tip 126 of second shoe 12 serve as second stopper portions constituting a second stopper mechanism for restricting relative rotation of vane rotor 4 in the clockwise direction (in the advance direction). The contact area between tip 126 of second shoe 12 and radial projection 419 of first shoe 11, i.e. the contact area of the second stopper mechanism, SS2, is set smaller than the contact area between flat portion 111 of first shoe 11 and the flat portion 415 of first vane 41, i.e. the contact area of the first stopper mechanism, SS1 (SS1>SS2). Incidentally, all over a possible range of the rotational angle of vane rotor 4 with respect to housing HSG, the volumetric capacities of first, second and third advance chambers A1, A2 and A3, and first, second and third retard chambers R1, R2 and R3 are prevented from becoming zero. Also, the openings of retard fluid passages 408 and advance fluid passages 409 in first, second and third advance chambers A1, A2 and A3, and first, second and third retard chambers R1, R2 and R3 are constantly prevented from being closed. For example, in FIG. 4, the volumetric capacity of first advance chamber A1 and the opening of advance fluid passage 409 are provided by the space defined between recess 113 of first shoe 11 and recess 416 of first vane 41. Similarly, the volumetric capacity of second advance chamber A2 and the opening of advance fluid passage 409 are provided by the space, i.e. the clearance described above, which is defined by flat portion 121 of second shoe 12, and recess 426 and flat portion 425 of second vane 42. Similarly, the volumetric capacity of third advance chamber A3 and the opening of advance fluid passage 409 are provided by the space, i.e. the clearance described above, which is defined by flat portion 131 of third shoe 13, and recess 436 and flat portion 435 of third vane 43.

Hydraulic fluid supply and drainage mechanism 2 supplies working fluid to or drains working fluid from first, second and third advance chambers A1, A2 and A3, and first, second and third retard chambers R1, R2 and R3, so that vane rotor 4 rotates with respect to housing HSG by a predetermined angle in the advance direction or retard direction. Specifically, supply and drainage of working fluid causes changes in the volumetric capacities of first, second and third advance chambers A1, A2 and A3, and first, second and third retard chambers R1, R2 and R3, to generate a torque to rotate vane rotor 4 with respect to housing HSG, so that the torque is transmitted therebetween, and the phase of rotation of intake camshaft 3a with respect to rotation of the crankshaft is changed. Hydraulic fluid supply and drainage mechanism 2 includes an oil pump 1020 as a hydraulic pressure source, and a directional control valve 24 as a hydraulic control actuator. The hydraulic circuit includes a retard passage 20 through which working fluid is supplied to or drained from first, second and third retard chambers R1, R2 and R3, and an advance passage 21 through which working fluid is supplied to or drained from first, second and third advance chambers A1, A2 and A3. Retard passage 20 and advance passage 21 are connected through the directional control valve 24 to a supply passage 22 and a drain passage 23. Oil pump 1020 is provided in supply passage 22 for pressurizing and supplying working fluid from oil pan 25 to directional control valve 24. Oil pump 1020 is mounted to the crankshaft, and may be implemented by a unidirectional variable displacement vane pump. The downstream end of drain passage 23 is hydraulically connected to oil pan 25. Intake camshaft 3a and vane rotor 4 (rotor 40) include portions constituting the retard passage 20 and advance passage 21. Rotor body 400 is formed with three retard fluid passages 408 and three advance fluid passages 409. Each fluid passage 408 or 409 extends through the rotor body 400 in a radial direction of rotor body 400, and hydraulically connects the inside periphery of camshaft insertion hole 402 and the outside periphery of rotor 40 to one another, so that when vane rotor 4 is fixed to intake camshaft 3a, the fluid passage 408 or 409 hydraulically connects the corresponding one of first, second and third advance chambers A1, A2 and A3 and first, second and third retard chambers R1, R2 and R3 to corresponding ones of first fluid passages 202 and 212 and second fluid passages 201, 203, 211 and 213. As viewed from the X-axis positive side, each retard fluid passage 408 is located at the root of the clockwise side of vane 41, 42 or 43, and each advance fluid passage 409 is located at the root of the counterclockwise side of vane 41, 42 or 43, as shown in FIGS. 4 and 9A. In the X-axis direction, each retard fluid passage 408 is located at an X-axis positive side portion of camshaft insertion hole 402 or at a substantially central position of rotor body 400 in the axial direction, and each advance fluid passage 409 is located at an X-axis negative side portion of camshaft insertion hole 402 or at an X-axis negative side portion of rotor body 400, as shown in FIGS. 3 and 9B. Under condition that the axial end portion 30 of intake camshaft 3a is fixedly inserted in camshaft insertion hole 402, the position of each retard fluid passage 408 is substantially identical to the position of groove 204 in the X-axis direction, so that the retard fluid passage 408 hydraulically communicates at the inside periphery of rotor 40 with groove 204, and hydraulically communicates at the outside periphery of rotor 40 with retard chamber R1, R2 or R3. Similarly, the position of each advance fluid passage 409 is substantially identical to the position of groove 214 in the X-axis direction, so that the advance fluid passage 409 hydraulically communicates at the inside periphery of rotor 40 with groove 214, and hydraulically communicates at the outside periphery of rotor 40 with advance chamber A1, A2 or A3. Extending from directional control valve 24, retard passage 20 includes groove 200 which is located at the X-axis negative side portion of axial end portion 30 of intake camshaft 3a, wherein intake camshaft 3a is a rotating member. Groove 200 is hydraulically connected to first fluid passage 202 through the second fluid passage 201, and first fluid passage 202 is hydraulically connected to groove 204 through the second fluid passage 203, and groove 204 hydraulically communicates with first, second and third retard chambers R1, R2 and R3 through retard fluid passages 408. Incidentally, the opening of first fluid passage 202 at the axial end surface 300 of intake camshaft 3a is closed by the bottom surface of camshaft insertion hole 402 when intake camshaft 3a is fixed to vane rotor 4 by camshaft bolts 33, 34 and 35. Similar to retard passage 20, extending from directional control valve 24, advance passage 21 includes groove 210 which is located at the X-axis negative side portion of axial end portion 30 of intake camshaft 3a. Groove 210 is hydraulically connected to first fluid passage 212 through the second fluid passage 211, and first fluid passage 212 is hydraulically connected to groove 214 through the second fluid passage 213, and groove 214 hydraulically communicates with first, second and third advance chambers A1, A2 and A3 through advance fluid passage 409. Incidentally, the opening of first fluid passage 212 at the axial end surface 300 of intake camshaft 3a is closed by positioning pin 45. The annular shape of each groove 204 or 214 extending in the circumferential direction serves to enhance the flexibility of layout of retard fluid passages 408 and advance fluid passages 409 in vane rotor 4. Each groove 204 or 214 may be replaced with an annular groove that is formed in the inside periphery of camshaft insertion hole 402 of vane rotor 4 to extend in the circumferential direction. However, the arrangement of each groove 204 or 214 in intake camshaft 3a is advantageous in easiness of forming or machining same. Directional control valve 24 is a direct-acting type solenoid valve with four ports and three positions, for controlling the hydraulic pressures of working fluid which is supplied to or drained from first, second and third advance chambers A1, A2 and A3, and first, second and third retard chambers R1, R2 and R3. Directional control valve 24 includes a valve body fixed to the cylinder head, a solenoid “SOL” fixed to the valve body, and a spool valve element slidably mounted inside the valve body. The valve body is formed with a supply port 240 hydraulically connected to supply passage 22, a first port 241 hydraulically connected to retard passage 20, a second port 242 hydraulically connected to advance passage 21, and a drain port 243 hydraulically connected to drain passage 23. When an electromagnetic coil of solenoid SOL is energized, then solenoid SOL presses the spool valve element to move. The electromagnetic coil is electrically connected to controller CU through a harness. Each of first port 241 and second port 242 opens or closes according to movement of the spool valve element. When solenoid SOL is de-energized, the spool valve element is biased by return spring RS to a position such that the supply port 240 (supply passage 22) and second port 242 (advance passage 21) are hydraulically connected to each other, and first port 241 (retard passage 20) and drain port 243 (drain passage 23) are hydraulically connected to each other. On the other hand, when solenoid SOL is energized, the spool valve element is controlled according to a control current from controller CU, to move against the elastic force of return spring RS to a predetermined intermediate position such that the supply port 240 (supply passage 22) and first port 241 (retard passage 20) are hydraulically connected to each other, and second port 242 (advance passage 21) and drain port 243 (drain passage 23) are hydraulically connected to each other. Controller CU is an electrical control unit which is configured to measure a current operating state of the internal combustion engine on the basis of signals from sensors such as a crank angle sensor for measuring engine rotational speed, an air flow meter for measuring a quantity of intake air, a throttle valve opening sensor, and a coolant temperature sensor for measuring a coolant temperature of the internal combustion engine. Moreover, controller CU performs a flow direction control of selectively supplying working fluid to or draining working fluid from first, second and third advance chambers A1, A2 and A3, and first, second and third retard chambers R1, R2 and R3, by energizing or de-energizing the solenoid SOL of directional control valve 24 with a pulse control signal, according to the measured operating state of the internal combustion engine.

Intake valve timing control apparatus 1a is provided with an arrangement that a lock piston 51 locks relative rotation between vane rotor 4 and housing HSG when vane rotor 4 is in a most retarded position which is defined by the first stopper mechanism. Lock piston 51 is an engagement member which is provided in vane rotor 4, and arranged to move forward or rearward in the X-axis direction according to a state of operation of the internal combustion engine. Lock mechanism 5 is arranged between first vane 41 and rear plate 9, for locking or releasing relative rotation of vane rotor 4 with respect to rear plate 9 (or housing HSG). Lock mechanism 5 includes slide hole 501, lock piston 51, a sleeve 52, and a coil spring 53. FIG. 14 is a partial side sectional view taken along a plane passing through a central longitudinal axis of lock mechanism 5, showing a state of operation of lock piston 51 when the internal combustion engine is at rest, or the internal combustion engine is being started.

First vane 41 is formed with slide hole 501 which extends through first vane 41 in the X-axis direction. Slide hole 501 is a hollow cylindrical portion or cylinder formed to extend in the axial direction of vane rotor 4. The surface (inside peripheral surface) of slide hole 501 is anodized as described above. A sealing member 502, which has an annular shape or a hollow cylindrical shape, is formed separately from vane rotor 4, and pressed-fitted in an X-axis negative side portion of slide hole 501. Sealing member 502 is a hollow cylindrical member (or ring-shaped member) having a smaller longitudinal size than slide hole 501, specifically half or less of the longitudinal size of slide hole 501, wherein sealing member 502 is inserted from the X-axis negative side end of slide hole 501 and press-fitted into the inside of slide hole 501. Slide hole 501 may be set and fixed in an alternative manner other than press-fitting. Sealing member 502 is formed of a material having a higher wear resistance than anodic oxide coating. Specifically, sealing member 502 is formed of an iron alloy such as a carbon steel such as S45C, into a ring shape, and carburized.

Lock piston 51 as a lock member is formed of iron into a pin, having a hollow cylindrical shape with a bottom portion 510 at the X-axis negative side. Lock piston 51 is mounted in slide hole 501 for sliding in the X-axis direction, and projecting from the X-axis negative side of slide hole 501 closer to intake camshaft 3a or retreating into the X-axis negative side of slide hole 501. Lock piston 51 includes a smaller-diameter portion and a larger-diameter portion. The smaller-diameter portion is a distal-side portion of lock piston 51 that is disposed in slide hole 501, and arranged to move out of and into slide hole 501. The smaller-diameter portion includes a sliding portion 512, and an engaging portion 511. Sliding portion 512 has a hollow cylindrical shape having a closed bottom. Engaging portion 511 is adjacent to and in the X-axis negative direction from bottom portion 510, where a step is formed between bottom portion 510 and engaging portion 511. Engaging portion 511 has the form of a substantially truncated cone having a substantially trapezoidal longitudinal section. In this way, engaging portion 511 has an inclined surface or tapered surface with respect to the longitudinal direction, wherein the diameter of the tapered surface decreases as followed toward the tip at the X-axis negative side. The larger-diameter portion is a proximal-side portion of lock piston 51 that is disposed in slide hole 501. The larger-diameter portion includes an annular flange 513 at the X-axis positive side end, which is adjacent to and on the X-axis positive side of sliding portion 512. The larger-diameter portion (or flange 513) has a larger diameter than the smaller-diameter portion (or sliding portion 512 and engaging portion 511). The outside periphery of sliding portion 512 has a slightly smaller diameter than the inside periphery of sealing member 502. Sliding portion 512 includes an X-axis negative side portion that is accommodated in sealing member 502 so that the outside periphery of sliding portion 512 is in sliding contact with the inside periphery of sealing member 502. The outside periphery of flange 513 has a slightly smaller diameter than the inside periphery of slide hole 501. Flange 513 is accommodated in slide hole 501 so that the outside periphery of flange 513 is in sliding contact with the inside periphery of slide hole 501. The radial clearance between the outside periphery of sliding portion 512 and the inside periphery of sealing member 502 is set smaller than that between the outside periphery of flange 513 and the inside periphery of slide hole 501. In this way, lock piston 51 has a portion (sliding portion 512) in sliding contact with the inside periphery of sealing member 502, another portion (flange 513) in sliding contact with the inside periphery of slide hole 501, and a tip (engaging portion 511) arranged to move forward and rearward in the axial direction (in the X-axis direction) with respect to vane rotor 4 according to the state of operation of the internal combustion engine.

On the other hand, rear plate 9 is formed with recess 900 in the X-axis positive side surface. Recess 900 is located in the chamber between first shoe 11 and second shoe 12, and more adjacent to first shoe 11 on the clockwise side of first shoe 11. Recess 900 has a bottom in rear plate 9, without passing through rear plate 9. Recess 900 is located to face or conform to the tip (engaging portion 511) of lock piston 51 as viewed in the X-axis direction, when intake valve timing control apparatus 1a is in the most retarded state shown in FIG. 4. Sleeve 52, which is formed in a hollow cylindrical shape separately from rear plate 9, and referred to as lock recess constituent member, is press-fitted in recess 900 of rear plate 9. Sleeve 52 may be fixed in an alternative manner other than press-fitting. Sleeve 52 is formed of an iron-based metal material. The inside peripheral surface of sleeve 52 defines engaging recess 521. Engaging recess 521 is a lock recess in which the smaller-diameter portion (engaging portion 511) of lock piston 51 can be inserted. The longitudinal size of engaging recess 521 (sleeve 52) is substantially equal to the longitudinal size of engaging portion 511. Engaging recess 521 has a slightly larger diameter than engaging portion 511. Engaging recess 521 has a substantially trapezoidal section taken along a plane passing through the central longitudinal axis of sleeve 52, and gradually spreads toward the X-axis positive side opening. Namely, engaging recess 521 has an inclined surface or tapered surface with respect to the longitudinal direction, wherein the diameter of the tapered surface gradually decreases as followed toward the X-axis negative side bottom. The angle of inclination of the inside peripheral surface (inclined surface) of engaging recess 521 with respect to the X-axis is substantially equal to that of engaging portion 511. Engaging recess 521 is provided in housing HSG, and on the X-axis positive side surface of rear plate 9, or on the axial end of housing HSG closer to intake camshaft 3a, similar to recess 900. When vane rotor 4 is relatively rotated toward the most retarded position and the rotation of vane rotor 4 is restricted by the first stopper mechanism, namely, when the volumetric capacity of first advance chamber A1 is minimized, the position of lock piston 51 (engaging portion 511) overlaps or is identical with the position of engaging recess 521 as viewed in the X-axis direction, since recess 900 is located as described above. In other words, the rotational position of vane rotor 4 with respect to housing HSG is set to the most retarded position which is optimal at start of the internal combustion engine, under the condition that lock piston 51 is engaged with engaging recess 521 of sleeve 52. Under this condition, the central axis of engaging recess 521 is located with a slight offset from the central axis of engaging portion 511 in the counterclockwise direction shown in FIG. 4 (toward first shoe 11) of vane rotor 4.

The inside of slide hole 501 is formed with a back pressure chamber 50 for lock piston 51. Back pressure chamber 50 is a low pressure chamber that is defined in slide hole 501 by lock piston 51, and is located opposite to sleeve 52 (or rear plate 9 or intake camshaft 3a) with respect to lock piston 51. Specifically, back pressure chamber 50 is defined by the X-axis negative side surface of front plate 8, and the inside periphery of lock piston 51 (sliding portion 512, flange 513).

Coil spring 53 is a biasing member that constantly biases lock piston 51 in the X-axis negative direction, i.e. toward rear plate 9, specifically toward engaging recess 521 of sleeve 52. Coil spring 53 is mounted in a compressed state in back pressure chamber 50, wherein the X-axis positive side end of coil spring 53 is in contact with the X-axis negative side surface of front plate 8, and the X-axis negative side end of coil spring 53 is in contact with the bottom portion 510 of lock piston 51. Namely, in slide hole 501, coil spring 53 is provided on one side (larger-diameter side or X-axis positive side) of lock piston 51, and arranged to bias the lock piston 51 toward the other side (smaller-diameter side or X-axis negative side) of lock piston 51. A spring retainer 54 is mounted in the X-axis positive side of back pressure chamber 50. Spring retainer 54 has an annular shape, and retains coil spring 53. The outer diameter of spring retainer 54 is substantially equal to the diameter of the inside peripheral surface of slide hole 501. The X-axis positive side surface of spring retainer 54 faces the X-axis negative side surface of front plate 8, whereas the X-axis negative side surface of spring retainer 54 faces the X-axis positive side surface of flange 513 of lock piston 51. The X-axis positive side end portion of coil spring 53 is fitted with the inside periphery of spring retainer 54, so as to prevent coil spring 53 from deviating with respect to slide hole 501 in the lateral direction of lock piston 51.

Slide hole 501 is formed with first and second pressure-receiving chambers 55 and 59 for applying hydraulic pressure to lock piston 51. In slide hole 501, first pressure-receiving chamber 55 is defined by the X-axis positive side end surface of sealing member 502, the X-axis negative side surface of flange 513, the outside peripheral surface of sliding portion 512, and the inside peripheral surface of slide hole 501. Second pressure-receiving chamber 59 is defined by the surface (the X-axis negative side tip surface, and inclined surface) of engaging portion 511, the X-axis positive side surface of rear plate 9 (or the inside peripheral surface of sleeve 52 and the bottom of recess 900, in the lock state in which engaging portion 511 engages with engaging recess 521). First vane 41 is formed with fluid passages for guiding hydraulic pressure from the working fluid chambers to first and second pressure-receiving chambers 55 and 59. A communication hole 56 is formed to extend in first vane 41 in the circumferential direction of first vane 41. First retard chamber R1 is constantly hydraulically connected to first pressure-receiving chamber 55 through the communication hole 56, so that the hydraulic pressure in first retard chamber R1 is constantly supplied to first pressure-receiving chamber 55. The X-axis negative side surface of first vane 41 is formed with a communication groove 57 that extends in the circumferential direction of first vane 41. First advance chamber A1 is constantly hydraulically connected to the X-axis negative side end of slide hole 501 through the communication groove 57, so that the hydraulic pressure in first advance chamber A1 is constantly supplied to second pressure-receiving chamber 59 (engaging recess 521 in the lock state).

Communication hole 56 and communication groove 57 constitute a mechanism for engaging and disengaging the lock piston 51, together with coil spring 53 as an elastic member for engagement. When vane rotor 4 relatively rotates to the most retard side, and rotation of vane rotor 4 is restricted by the first stopper mechanism, then the position of lock piston 51 is identical to the position of engaging recess 521 as viewed in the X-axis direction, so as to allow lock piston 51 to move in the X-axis negative direction. Under this condition, the biasing force of coil spring 53 serves to assist the lock piston 51 in moving in the X-axis negative direction so that the engaging portion 511 moves out of slide hole 501 of first vane 41, and engages with engaging recess 521. The engagement of lock piston 51 with engaging recess 521 restricts or locks relative rotation between rear plate 9 and vane rotor 4, or relative rotation between housing HSG and intake camshaft 3a. On the other hand, lock piston 51 is subject to a hydraulic force at the flange 513 in the X-axis positive direction, wherein the hydraulic force is based on the hydraulic pressure supplied from first retard chamber R1 to first pressure-receiving chamber 55 through the communication hole 56. Lock piston 51 is also subject to a hydraulic force at the engaging portion 511 in the X-axis positive direction, wherein the hydraulic force is based on the hydraulic pressure supplied from first advance chamber A1 to second pressure-receiving chamber 59 through the communication groove 57. Both of the hydraulic forces serve to assist the lock piston 51 in moving in the X-axis positive direction against the biasing force of coil spring 53, so that the engaging portion 511 moves out of engaging recess 521, and into slide hole 501 of rear plate 9. The engagement of lock piston 51 with engaging recess 521 is thus released. In this way, coil spring 53 serves to maintain the lock state, while communication hole 56 and communication groove 57 serve as a hydraulic circuit for releasing the lock state.

Intake valve timing control apparatus 1a is provided with a back pressure relief section for relieving pressure in back pressure chamber 50 and keeping same low. The back pressure relief section includes a first back pressure passage 31, a back pressure hole 407, and a second back pressure passage. First back pressure passage 31 is formed in intake camshaft 3a, whereas back pressure hole 407 and the second back pressure passage are formed in vane rotor 4. These constituents serve as a passage for relieving the pressure in back pressure chamber 50 to a space in the internal combustion engine. The space in the internal combustion engine is a low pressure space that is defined by a housing (cylinder head, cylinder block, etc.) of the internal combustion engine, and separated liquid-tightly from timing belt 1010. First back pressure passage 31 is a breathing hole formed in intake camshaft 3a to extend in the X-axis direction, from the X-axis positive side axial end surface 300 to a predetermined depth in the X-axis direction. First back pressure passage 31 has an opening at the axial end surface 300, and hydraulically communicates the axial end surface 300 with an oil-lubricated space in the internal combustion engine. First back pressure passage 31 is located at the axis of rotation of intake camshaft 3a, namely, the axis of rotation O, having the same diameter as first fluid passages 202 and 212. First back pressure passage 31 may be formed to communicate with a low pressure section of hydraulic fluid supply and drainage mechanism 2, instead of or in addition to the oil-lubricated space in the internal combustion engine. In other words, the space in the internal combustion engine which is related to first back pressure passage 31 includes a hydraulic circuit of hydraulic fluid supply and drainage mechanism 2. For example, back pressure chamber 50 may be hydraulically connected to directional control valve 24, so that the working fluid in back pressure chamber 50 is drained to oil pan 25 through the drain passage 23. If intake valve timing control apparatus 1a is constructed so that only first, second and third advance chambers A1, A2 and A3 are supplied with working fluid, and first, second and third retard chambers R1, R2 and R3 are supplied with no working fluid, the working fluid in back pressure chamber 50 may be released to a passage that is hydraulically connected to first, second and third retard chambers R1, R2 and R3. Back pressure hole 407 is a breathing hole extending through the rotor 40 along the axis of rotation of rotor 40 (axis of rotation O) in the X-axis direction, having a smaller diameter than first back pressure passage 31, as shown in FIG. 4. Back pressure hole 407 faces first back pressure passage 31 in the X-axis direction, wherein the central axis of back pressure hole 407 is identical to the central axis of first back pressure passage 31 as viewed in the X-axis direction. The opening of back pressure hole 407 at the X-axis negative side surface of rotor 40 (at the bottom surface of camshaft insertion hole 402) is located to face the opening of first back pressure passage 31 at the axial end surface 300 of intake camshaft 3a. As shown in FIG. 9A, the second back pressure passage is a recess for breathing that is formed in the X-axis positive side end surface of vane rotor 4, including a circular recess 406 and a radial groove 58. Circular recess 406 is a shallow cylindrical recess having a central axis that is substantially identical to the central axis of rotor 40, wherein circular recess 406 extends from the X-axis positive side in the X-axis negative direction to a depth of about 13% of the axial size of rotor body 400. The bottom of circular recess 406 is formed with bolt holes 403, 404 and 405, and back pressure hole 407. The depth (size in the X-axis direction) of circular recess 406 is about half or more of the height (size in the X-axis direction) of each head 331, 341 or 351. The diameter of circular recess 406 is slightly smaller than the outside diameter of rotor body 400, slightly smaller than the diameter of large-diameter hole 81 of front plate 8, and substantially equal to the diameter of recess 73 of cap 7. Circular recess 406 is located to face the recess 73 in the X-axis direction. Radial groove 58 is a rectangular groove for hydraulically communicating the circular recess 406 and back pressure chamber 50 with one another, extending from circular recess 406 through the root of first vane 41 outwardly in a radial direction of rotor 40, and including an end connected to the X-axis positive side end of slide hole 501. The depth (size in the X-axis direction) of radial groove 58 is substantially equal to that of circular recess 406. Back pressure chamber 50 is hydraulically connected to back pressure hole 407 and first back pressure passage 31 through the second back pressure passage, and thereby hydraulically connected to the inside of the internal combustion engine. Namely, back pressure chamber 50 is hydraulically connected to circular recess 406 and back pressure hole 407 through the radial groove 58, and further connected to the low pressure space in the internal combustion engine through the first back pressure passage 31, as shown in FIG. 3.

<Construction of Exhaust Valve Timing Control Apparatus> The following describes construction of exhaust valve timing control apparatus 1b which is provided for the exhaust valves of the internal combustion engine, with reference to FIGS. 15 to 19. In the following, constituent parts of exhaust valve timing control apparatus 1b, which are identical or similar to those of intake valve timing control apparatus 1a, are provided with identical reference characters, and with no duplicate description, and only different constituent parts are described. FIG. 15 is a partial side sectional view of exhaust valve timing control apparatus 1b, taken along a plane passing through an axis of rotation “O” (shown in FIG. 16) of exhaust valve timing control apparatus 1b, i.e. taken along a plane indicated by a long dashed short dashed line F15-F15 in FIG. 16. FIGS. 16 and 17 are front views of exhaust valve timing control apparatus 1b under the condition that the front plate 8, etc. are removed, as viewed from the X-axis positive side. Exhaust valve timing control apparatus 1b controls variable valve timing of the exhaust valves by continuously changing a rotational phase of exhaust camshaft 3b with respect to the crankshaft by supplied working fluid. Pulley 100, as well as housing body 10, is rotated by the crankshaft of the internal combustion engine, in the clockwise direction in FIG. 16, according to movement of timing belt 1010 shown by the arrow in FIG. 1. As shown in FIG. 15, front plate 8 of exhaust valve timing control apparatus 1b is provided with no outside periphery 80 which is provided in intake valve timing control apparatus 1a, so that the diameter of front plate 8 of exhaust valve timing control apparatus 1b is smaller than the diameter (specifically, the diameter of tooth bottom circle) of pulley 100. The outside periphery of front plate 8 is more adjacent to annular sealing ring groove 89 with a shorter distance than distance r shown in FIG. 12. Accordingly, as shown in FIG. 1, as viewed in the X-axis direction, the outside periphery (i.e. teeth) of pulley 100 of exhaust valve timing control apparatus 1b projects radially outwardly from the outside periphery of front plate 8. In other words, the diameter of exhaust valve timing control apparatus 1b is set smaller than that of intake valve timing control apparatus 1a where outside periphery 80 of front plate 8 projects radially outwardly from the outside periphery of pulley 100. Housing body 10 of exhaust valve timing control apparatus 1b is a mirror image of the housing body of intake valve timing control apparatus 1a with respect to a plane perpendicular to the X-axis. FIGS. 18A, 18B and 18C are views of housing body 10 of exhaust valve timing control apparatus 1b, where FIG. 18A is a front view as viewed from the X-axis positive side, FIG. 18B is a side sectional view taken along a plane indicated by F18B-F18B in FIG. 18A, and FIG. 18C is a rear view as viewed from the X-axis negative side. FIGS. 7 and 8 are perspective views of workpieces during a process of manufacturing the housing body 10 also for exhaust valve timing control apparatus 1b. Housing body 10 of exhaust valve timing control apparatus 1b is formed from an aluminum extrusion shown in FIG. 7, similar to intake valve timing control apparatus 1a. Third workpiece P3 shown in FIG. 8 is obtained through the second workpiece P2 from first workpiece P1. Finally, third workpiece P3 is applied with carving or cutting, to form a fitting recess 101, bolt hole 110, etc., and thereby form a final shape of housing body 10 shown in FIGS. 18A, 18B and 18C. In contrast to intake valve timing control apparatus 1a where fitting recess 101 and positioning recess 114 are formed in the side “A” (shown in FIG. 8) of third workpiece P3 as shown in FIGS. 6A, 6B and 6C, fitting recess 101 and positioning recess 114 are formed in the side “B” (shown in FIG. 8) of third workpiece P3 for exhaust valve timing control apparatus 1b, as shown in FIGS. 18A, 18B and 18C. Also, vane rotor 4 of exhaust valve timing control apparatus 1b is a mirror image of the vane rotor of intake valve timing control apparatus 1a with respect to a plane perpendicular to the X-axis. FIGS. 19A and 19B are views of vane rotor 4 of exhaust valve timing control apparatus 1b, where FIG. 19A is a front view as viewed from the X-axis positive side, and FIG. 19B is a side sectional view taken along a plane indicated by F19B-F19B in FIG. 19A. FIGS. 10 and 11 are perspective views of workpieces during a process of manufacturing the vane rotor 4 also for exhaust valve timing control apparatus 1b. Vane rotor 4 of exhaust valve timing control apparatus 1b is formed from an aluminum extrusion (first workpiece Q1) shown in FIG. 10, similar to intake valve timing control apparatus 1a. Then, second workpiece Q2, which is obtained from first workpiece Q1, is applied with carving or cutting, to form a boss portion 401, a camshaft insertion hole 402, etc., and thereby form a final shape of vane rotor 4 shown in FIGS. 19A and 19B. In contrast to intake valve timing control apparatus 1a where boss portion 401 and camshaft insertion hole 402 are formed on the side “A” of second workpiece Q2, boss portion 401 and camshaft insertion hole 402 are formed on the side “B” of second workpiece Q2 for exhaust valve timing control apparatus 1b, as shown in FIGS. 19A and 19B. Finally, the entire outside surfaces of second workpiece Q2 are applied with anodic oxidation treatment, to form a third workpiece Q3 which has hardened surfaces. In this way, housing bodies 10 and vane rotors 4 of intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b are mirror images which are formed from the identical or common workpieces P3 and Q2 which are formed before the application of carving. As shown in FIGS. 16 and 4, the shapes and relative positions of housing body 10 and vane rotor 4 of exhaust valve timing control apparatus 1b are mirror images of those of intake valve timing control apparatus 1a as viewed from the X-axis positive side. First, second and third shoes 11, 12 and 13 are arranged in this order in the counterclockwise direction in FIG. 16. As viewed from the X-axis positive side, the clockwise surfaces of first, second and third shoes 11, 12 and 13 are formed with recesses 115, 125 and 135 respectively. The counterclockwise surfaces of first, second and third shoes 11, 12 and 13 are formed with flat portions 111, 121 and 131 respectively. First, second and third vanes 41, 42 and 43 are arranged in this order in the counterclockwise direction in FIG. 16. As viewed from the X-axis positive side, the clockwise surfaces of first, second and third vanes 41, 42 and 43 are formed with flat portions 415, 425 and 435 respectively. The counterclockwise surfaces of first, second and third vanes 41, 42 and 43 are formed with recesses 418, 428 and 438 respectively. The counterclockwise surfaces of the roots of first and second vanes 41 and 42 are formed with radial projections 419 and 429 respectively. Under the condition that the vane rotor 4 is mounted in housing HSG, first vane 41 is mounted in the space between first shoe 11 and second shoe 12, second vane 42 is mounted in the space between second shoe 12 and third shoe 13, and third vane 43 is mounted in the space between third shoe 13 and first shoe 11. Rotor body 400 is formed with three retard fluid passages 408 and three advance fluid passages 409 which are connected between camshaft insertion hole 402 and the outside peripheral surface of rotor 40 (rotor body 400). In the case of first vane 41, retard fluid passage 408 is formed substantially in a midpoint in the X-axis direction as shown in FIG. 19B, and in the clockwise side of the root of first vane 41 as viewed from the X-axis positive side, as shown in FIG. 16, where retard fluid passage 408 is formed to extend through in the radial direction, as shown in FIG. 16. On the other hand, advance fluid passage 409 is formed in the X-axis negative side in first vane 41, and in the counterclockwise side of the root of first vane 41 as viewed from the X-axis positive side, as shown in FIG. 16, where advance fluid passage 409 is formed to extend through in the radial direction, as shown in FIG. 16. Similarly, retard fluid passages 408 and advance fluid passages 409 are formed in the roots of second vane 42 and third vane 43, extending through in the radial direction. First, second and third advance chambers A1, A2 and A3, and first, second and third retard chambers R1, R2 and R3 are defined by the X-axis negative side surface of front plate 8, the X-axis positive side surface of rear plate 9, the circumferentially-facing surfaces of first, second and third vanes 41, 42 and 43, and the circumferentially-facing surfaces of first, second and third shoes 11, 12 and 13. For example, first advance chamber A1 is defined between the clockwise surface of second shoe 12, the counterclockwise surface of first vane 41, whereas first retard chamber R1 is defined between the clockwise surface of first vane 41 and the counterclockwise surface of first shoe 11, as shown in FIG. 16. Similarly, second advance chamber A2 is defined between first shoe 11 and third vane 43, second retard chamber R2 is defined between third vane 43 and third shoe 13, third advance chamber A3 is defined between third shoe 13 and second vane 42, and third retard chamber R3 is defined between second vane 42 and second shoe 12. Rotation of vane rotor 4 with respect to housing HSG in the clockwise direction is restricted by contact between flat portion 111 of first shoe 11 and flat portion 415 of first vane 41, where rotation of vane rotor 4 is locked by lock piston 51, similar to intake valve timing control apparatus 1a, as shown in FIG. 16. Flat portion 111 of the circumferentially-facing surface of first shoe 11 and flat portion 415 of the circumferentially-facing surface of 41 serve as first stopper portions constituting a first stopper mechanism for restricting relative rotation of vane rotor 4 in the clockwise direction (in the advance direction). On the other hand, rotation of vane rotor 4 with respect to housing HSG in the counterclockwise direction is restricted by contact between tip 126 of second shoe 12 and radial projection 419 of first shoe 11, where vane rotor 4 is in the end position in the direction away from the position where rotation of vane rotor 4 is locked by lock piston 51, similar to intake valve timing control apparatus 1a, as shown in FIG. 17. The counterclockwise surface of radial projection 419 and the clockwise surface of tip 126 of second shoe 12 serve as second stopper portions constituting a second stopper mechanism for restricting relative rotation of vane rotor 4 in the counterclockwise direction (in the retard direction). The first and second stopper mechanisms define a range of relative rotation of vane rotor 4 with respect to housing HSG. As in intake valve timing control apparatus 1a, the contact area between tip 126 of second shoe 12 and radial projection 419 of first shoe 11, i.e. the contact area of the second stopper mechanism, SS2, is set smaller than the contact area between flat portion 111 of first shoe 11 and the flat portion 415 of first vane 41, i.e. the contact area of the first stopper mechanism, SS1 (SS1>SS2).

Exhaust camshaft 3b is made of iron, and rotatably supported on bearings in a laterally-outside portion of the upper end portion of the cylinder head of the internal combustion engine. Exhaust camshaft 3b is formed with drive cams (exhaust cams) at the outside peripheral surface, which are located to face or conform to positions of the exhaust valves. When exhaust camshaft 3b is rotated, the exhaust cams open and close the exhaust valves via valve lifters, rocker arms, etc. Exhaust valve timing control apparatus 1b, which is fixed to exhaust camshaft 3b, is constructed to be locked by lock piston 51 as an engagement member, under the condition that rotation of vane rotor 4 is restricted by the first stopper mechanism at the most advanced position.

In contrast to intake valve timing control apparatus 1a, exhaust valve timing control apparatus 1b is provided with a biasing member for biasing the vane rotor 4 with respect to housing HSG in the advance direction. The biasing member, which is collectively referred to as biasing member 6, includes three spring units, i.e. first, second and third spring units 61, 62 and 63. First, second and third spring units 61, 62 and 63 are mounted in first, second and third advance chambers A1, A2 and A3 respectively, for biasing the first, second and third vanes 41, 42 and 43 of vane rotor 4 with respect to first, second and third shoes 11, 12 and 13 of housing body 10 in the clockwise direction. Biasing member 6 may be provided in part of first, second and third advance chambers A1, A2 and A3. Biasing member 6 may be provided in first, second and third retard chambers R1, R2 and R3. This construction may be used in cases where vane rotor 4 needs to be biased with respect to housing HSG in the retard direction, which cases are possible according to the form of transmitting torque from the crankshaft to the camshaft. Specifically, first spring unit 61 is mounted in first advance chamber A1 between second shoe 12 and first vane 41, second spring unit 62 is mounted in second advance chamber A2 between first shoe 11 and third vane 43, and third spring unit 63 is mounted in third advance chamber A3 between third shoe 13 and second vane 42. The longitudinal ends of first, second and third spring units 61, 62 and 63 are mounted in recesses 418, 428 and 438, and recesses 115, 125 and 135, where recesses 418, 428 and 438 are formed in the counterclockwise surfaces of first, second and third vanes 41, 42 and 43, respectively, and recesses 115, 125 and 135 are formed in the opposite clockwise surfaces of first, second and third shoes 11, 12 and 13, respectively. First spring unit 61 includes a coil spring 610, and retaining portions 611 and 612 which are spring retainers provided at the longitudinal ends of coil spring 610. Retaining portion 611 includes a plate portion in which a through hole is formed, and a hollow cylindrical portion which projects from one side surface of the plate portion, and surrounds the through hole. One longitudinal end of coil spring 610 is fitted with the outside periphery of the hollow cylindrical portion of retaining portion 611. The plate portion of retaining portion 611 has a rectangular shape adapted to be fitted in recess 125 of second shoe 12 without play, and is fitted in recess 125. Recess 125 restricts movement of retaining portion 611 with respect to second shoe 12 of housing HSG in the radial direction of housing HSG. Front plate 8 and rear plate 9, which are in contact with the X-axis ends of the plate portion of retaining portion 611, restrict movement of retaining portion 611 in recess 125 in the X-axis direction within a predetermined range. First advance chamber A1 is hydraulically connected to first pressure-receiving chamber 55 of lock mechanism 5 shown in FIG. 14 through the through hole of retaining portion 611 and communication hole 56 of first vane 41. First retard chamber R1 is hydraulically connected to engaging recess 521 of lock mechanism 5 through the communication groove 57 of first vane 41. Retaining portion 612 of first spring unit 61 is constructed similar to retaining portion 611. Specifically, the hollow cylindrical portion of retaining portion 612 retains the other longitudinal end of coil spring 610, and the plate portion of retaining portion 612 is supported in recess 418 of first vane 41 so that the recess 418 restricts movement of retaining portion 612 of first spring unit 61 with respect to first vane 41 of vane rotor 4 in the radial direction and in the axial direction of housing HSG. In this way, the positions of the longitudinal ends of coil spring 610 in the radial direction and the axial direction of housing HSG are restricted. During assembling operation, first spring unit 61 is inserted in the X-axis direction into first advance chamber A1, so that the retaining portion 611 is fitted in recess 125, and retaining portion 612 is fitted in recess 418. Coil spring 610 is mounted in first advance chamber A1 in a compressed state, so as to constantly bias first vane 41 with respect to second shoe 12 of housing body 10 in the clockwise direction. Second spring unit 62, and third spring unit 63 are constructed and mounted similar to first spring unit 61. Second spring unit 62 includes a coil spring 620, and retaining portions 621 and 622, and third spring unit 63 includes a coil spring 630, and retaining portions 631 and 632. The biasing forces of coil springs 610, 620 and 630 are set substantially equal to each other. The diameters of coil springs 610, 620 and 630 are equal to about 70% of the maximum widths of first, second and third advance chambers A1, A2 and A3 in the radial direction, respectively. As compared to cases where another biasing member such as a leaf spring is used, the use of coil springs is effective for easily adjusting the biasing force, and enhancing the mountability to first, second and third advance chambers A1, A2 and A3. The construction that a single coil spring is mounted in each of first, second and third advance chambers A1, A2 and A3, is effective for making the exhaust valve timing control apparatus 1b compact in the axial direction, as compared to cases where two coil springs are arranged in double layers in the X-axis direction in each of first, second and third advance chambers A1, A2 and A3. In cases where double coil springs are mounted in each of first, second and third advance chambers A1, A2 and A3, it may be difficult to assemble the coil springs to first, second and third advance chambers A1, A2 and A3, unless the double coil springs are mounted to retaining portions to form a single spring unit. On the other hand, according to the present embodiment where a single coil spring is mounted in each of first, second and third advance chambers A1, A2 and A3, it is easy to mount the coil spring to from a spring unit. Moreover, it is also possible as an alternative to directly mount the coil spring in first, second and third advance chambers A1, A2 and A3 (recesses 418, 125, etc.), without mounting each of coil springs 610, 620 and 630 to retaining portions to form a spring unit. Since recesses 418, 428 and 438, and recesses 115, 125 and 135 restrict deviations of first, second and third spring units 61, 62 and 63 during operation of exhaust valve timing control apparatus 1b, this achieves normal operations of biasing member 6 and exhaust valve timing control apparatus 1b, with no special support member. For example, retaining portions 611 and 612 may be omitted. However, the provision of retaining portions 611 and 612 according to the present embodiment is effective for more securely preventing deviations of first, second and third spring units 61, 62 and 63. When vane rotor 4 rotates with respect to housing HSG in the counterclockwise direction, coil springs 610, 620 and 630 are compressed. The clockwise side portion of coil spring 610 is located outside of radial projection 419 of first vane 41 in the radial direction of housing HSG. The height of radial projection 419 in the radial direction of vane rotor 4 is set so that the outside periphery of radial projection 419 is close to the outside periphery of coil spring 610 with a slight clearance. Accordingly, when coil spring 610 is compressed and deformed, the periphery of coil spring 610 facing the radial projection 419 is brought into contact with the outside peripheral surface of radial projection 419, so that coil spring 610 is prevented from deforming over a predetermined distance inwardly in the radial direction of vane rotor 4. Namely, radial projection 419 serves to guide the coil spring 610. Radial projection 429 of second vane 42 is constructed similar to radial projection 419, so as to guide coil spring 630 when vane rotor 4 relatively rotates so as to compress coil spring 630. As shown in FIG. 17, when rotation of vane rotor 4 in the counterclockwise direction is restricted by contact between tip 126 of second shoe 12 and radial projection 419 of first shoe 11, the opposite shoe-side and vane-side retaining portions 611 and 612 or 621 and 622 or 631 and 632 of each of first, second and third spring units 61, 62 and 63 are out of contact with each other, and wounded wires of each of coil springs 610, 620 and 630 are out of contact with each other. In other words, when the counterclockwise rotation is restricted by the second stopper mechanism, the circumferential length of each of first, second and third advance chambers A1, A2 and A3 is set larger than the length of the respective one of coil springs 610, 620 and 630 under the condition the wounded wires are completely in contact with each other.

Hydraulic fluid supply and drainage mechanism 2 of exhaust valve timing control apparatus 1b is constructed similar to intake valve timing control apparatus 1a. Exhaust valve timing control apparatus 1b includes directional control valve 24 other than directional control valve 24 of intake valve timing control apparatus 1a, but shares oil pump 1020 and oil pan 25 with intake valve timing control apparatus 1a.

<<Operations and Produced Effects by Valve Timing Control Apparatus>> The following describes operations of intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b.

<Operations and Produced Effects Related to Phase Change> The following describes control operations and produced effects related to phase change by intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b. However, the control operations may be adjusted or modified as appropriate. First, the following describes how intake valve timing control apparatus 1a performs a phase change control. FIG. 4 shows the most retarded state when the internal combustion engine is at rest or at start. FIG. 5 shows the most advanced state when the internal combustion engine is operating. At start of the internal combustion engine, lock mechanism 5 keeps vane rotor 4 locked in the most retarded position as an initial position which is optimal for cranking the internal combustion engine, as shown in FIG. 4. When an ignition switch is turned on, intake valve timing control apparatus 1a achieves smooth cranking operation, improving the startability of the internal combustion engine. In a predetermined low speed and low load region after start of the internal combustion engine, the controller CU maintains a condition that no control current is outputted to directional control valve 24. Accordingly, in directional control valve 24, the spool valve element is maintained by the elastic force of return spring RS at the position such that the supply port 240 is hydraulically connected to second port 242, and first port 241 is hydraulically connected to drain port 243. Accordingly, working fluid, which is discharged by oil pump 1020, flows in supply passage 22, enters the valve body through supply port 240, flows through the second port 242 into advance passage 21, flows in the first and second fluid passages of intake camshaft 3a and the advance fluid passages 409 of vane rotor 4, and finally flows into first, second and third advance chambers A1, A2 and A3. The internal pressures of first, second and third advance chambers A1, A2 and A3 increase with an increase in the discharge pressure of oil pump 1020. On the other hand, working fluid is drained from first, second and third retard chambers R1, R2 and R3 to oil pan 25 through retard passage 20 and drain passage 23, so that the internal pressures of first, second and third retard chambers R1, R2 and R3 are held low (at atmospheric pressure). As the internal pressure of first advance chamber A1 rises, this hydraulic pressure is supplied through the communication groove 57 shown in FIG. 14 to second pressure-receiving chamber 59, so that the engaging portion 511 of lock piston 51 is subject to a hydraulic force in the X-axis positive direction. When the hydraulic force is above the elastic force of coil spring 53, lock piston 51 moves in the X-axis positive direction. When engaging portion 511 has moved completely out of engaging recess 521, the lock state is canceled. This allows vane rotor 4 to rotate freely, so that the valve timing can be changed arbitrarily. Under the hydraulic pressures supplied to first, second and third advance chambers A1, A2 and A3, vane rotor 4 rotates with respect to housing HSG from the position shown in FIG. 4, so as to change the rotational phase (relative rotational change angle) of intake camshaft 3a with respect to the crankshaft in the advance direction. This advances the opening and closing timing of the intake valves, and thereby increases a valve overlap which is a period when both of the intake valves and exhaust valves are opened. As a result, in the low speed and low load region, the combustion efficiency is improved because of use of inertial charge, thereby stabilizing the rotation of the internal combustion engine, and improving the fuel efficiency. As shown in FIG. 5, when vane rotor 4 rotates with respect to housing HSG and reaches the most advanced position such that the volumetric capacities of first, second and third advance chambers A1, A2 and A3 are maximized, and the volumetric capacities of first, second and third retard chambers R1, R2 and R3 are minimized, then the valve overlap is maximized. On the other hand, when the internal combustion engine shifts to an operating state in a predetermined high speed and high load region, the controller CU outputs a control current to directional control valve 24. In directional control valve 24, the spool valve element moves against the elastic force of return spring RS to the position such that the supply port 240 is hydraulically connected to first port 241, and second port 242 is hydraulically connected to drain port 243. Accordingly, working fluid, which is discharged by oil pump 1020, flows through the first port 241 of directional control valve 24 into retard passage 20, and flows through the first and second fluid passages of intake camshaft 3a and the retard fluid passages 408 of vane rotor 4 to first, second and third retard chambers R1, R2 and R3, so that the internal pressures of first, second and third retard chambers R1, R2 and R3 rise. On the other hand, working fluid is drained from first, second and third advance chambers A1, A2 and A3 to oil pan 25 through the advance passage 21 and drain passage 23, so that the internal pressures of first, second and third advance chambers A1, A2 and A3 fall. Under the condition described above, the hydraulic pressure in second pressure-receiving chamber 59 falls in lock mechanism 5. On the other hand, as the internal pressure of first retard chamber R1 increases, this hydraulic pressure is supplied through the communication hole 56 shown in FIG. 14 to first pressure-receiving chamber 55, so as to apply a hydraulic force to a pressure-receiving surface of flange 513 of lock piston 51. Accordingly, lock mechanism 5 is maintained in a released state in which lock piston 51 is brought out of engaging recess 521 against the elastic force of coil spring 53. When the internal pressures of first, second and third retard chambers R1, R2 and R3 are above the internal pressures of first, second and third advance chambers A1, A2 and A3, then the vane rotor 4 rotates with respect to housing HSG in the counterclockwise direction which is opposite to the direction of rotation of housing HSG indicated by the arrow in FIG. 4, so as to change the rotational phase (relative rotational change angle) of intake camshaft 3a with respect to the crankshaft in the retard direction. This retards the opening and closing timing of the intake valves, and thereby reduces the valve overlap so as to enhance the output of the internal combustion engine in the high speed and high load region. As shown in FIG. 4, when vane rotor 4 rotates with respect to housing HSG and reaches the most retarded position such that the volumetric capacities of first, second and third advance chambers A1, A2 and A3 are minimized, and the volumetric capacities of first, second and third retard chambers R1, R2 and R3 are maximized, the valve overlap is minimized. Moreover, for example, when the internal combustion engine shifts into a predetermined middle speed and middle load region, the controller CU controls directional control valve 24 so as to hold the spool valve element in the intermediate operation position such that the supply passage 22 and drain passage 23 are hydraulically disconnected from each other. Accordingly, the internal pressures of first, second and third retard chambers R1, R2 and R3, and first, second and third advance chambers A1, A2 and A3 are held constant, and vane rotor 4 is set in an intermediate rotational position. This serves to achieve a suitable valve timing control in the middle speed and middle load region, and a suitable balance between the fuel efficiency and the output of the internal combustion engine.

When the internal combustion engine is operating, and intake camshaft 3a is rotating, an alternating torque (or reverse torque) acts on intake camshaft 3a due to a reaction torque that is transmitted to the intake cams of intake camshaft 3a from the valve springs which bias the intake valves in a closing direction. Namely, depending on the shape of the intake cams, intake camshaft 3a is subject to alternately a negative torque which is a counterclockwise torque against clockwise rotation of intake camshaft 3a, and a positive torque which is a clockwise torque against counterclockwise rotation of intake camshaft 3a. The alternating toque is offset to the negative side as a whole. Namely, if the positive torques and negative torques, which are generated in each period of rotation of intake camshaft 3a, are integrated with time, the integral is negative. Accordingly, intake camshaft 3a is subject to a negative torque as a whole. When the internal combustion engine is stopped, then operation of oil pump 1020 is stopped, and energization of directional control valve 24 by controller CU is turned off. Accordingly, supply of working fluid to first, second and third advance chambers A1, A2 and A3, and first, second and third retard chambers R1, R2 and R3 is stopped. In summary, immediately after the internal combustion engine is stopped, the friction or alternating torque offset to the negative side, which is applied to intake camshaft 3a, serves to rotate vane rotor 4 with respect to housing HSG in the direction opposite to the direction of rotation of housing HSG indicated by the arrow in FIG. 4, i.e. serves to rotate vane rotor 4 with respect to housing HSG in the retard direction. As a result, after the internal combustion engine is stopped, vane rotor 4 mechanically moves to the predetermined initial position suitable for start or restart of the internal combustion engine, i.e. vane rotor 4 mechanically moves to the most retarded position shown in FIG. 4, under the friction or alternating torque applied to intake camshaft 3a. In other words, after the internal combustion engine is stopped, the valve timing is mechanically brought to a phase suitable for start or restart of the internal combustion engine. When vane rotor 4 rotates with respect to housing HSG, and reaches the most retarded position, then lock piston 51 overlaps with engaging recess 521 in lock mechanism 5 as viewed in the X-axis direction. When the internal combustion engine is stopped, the engaging portion 511 of lock piston 51 fits and engages with engaging recess 521 by the elastic force of coil spring 53, so that the lock piston 51 prevents free rotation of vane rotor 4. As discussed above, in intake valve timing control apparatus 1a, vane rotor 4 is mechanically rotated to the most retarded position with respect to housing HSG as an initial position, when the internal combustion engine is stopped. This is effective for setting the intake valve timing control apparatus 1a in the initial position when the internal combustion engine is restarted, and achieving a stable start and operation of intake valve timing control apparatus 1a.

The following describes how exhaust valve timing control apparatus 1b performs a phase change control. Exhaust valve timing control apparatus 1b operates similar to intake valve timing control apparatus 1a, except that the advance side and the retard side are reversed. FIG. 16 shows the most advanced state when the internal combustion engine is at rest or at start. FIG. 17 shows the most retarded state when the internal combustion engine is operating. At start of the internal combustion engine, lock mechanism 5 holds vane rotor 4 in the most advanced position as an initial position which is optimal for cranking the internal combustion engine, as shown in FIG. 16. When the ignition switch is turned on, exhaust valve timing control apparatus 1b achieves smooth cranking operation, improving the startability of the internal combustion engine. In the predetermined low speed and low load region after start of the internal combustion engine, first, second and third retard chambers R1, R2 and R3 are supplied with hydraulic pressures. When the hydraulic force based on the hydraulic pressures exceeds the biasing force of first, second and third spring units 61, 62 and 63, then vane rotor 4 rotates in the retard direction with respect to housing HSG. This retards the rotational phase of exhaust camshaft 3b, so as to increase the valve overlap. As shown in FIG. 17, when vane rotor 4 rotates with respect to housing HSG and reaches the most retarded position such that the volumetric capacities of first, second and third advance chambers A1, A2 and A3 are minimized, and the volumetric capacities of first, second and third retard chambers R1, R2 and R3 are maximized, the valve overlap is maximized. On the other hand, when the internal combustion engine shifts to an operating state in the high speed and high load region, working fluid is supplied to first, second and third advance chambers A1, A2 and A3. When the sum of a torque resulting from the hydraulic pressures of first, second and third advance chambers A1, A2 and A3, and a torque resulting from the biasing forces of first, second and third spring units 61, 62 and 63 is above a torque resulting from the hydraulic pressures of first, second and third retard chambers R1, R2 and R3, then the vane rotor 4 relatively rotates in the advance direction. Accordingly, the rotational phase (relative rotational angle) of exhaust camshaft 3b is advanced so as to reduce the valve overlap. In other words, first, second and third spring units 61, 62 and 63 also serve to assist the phase change in the advance direction. As shown in FIG. 16, when vane rotor 4 rotates with respect to housing HSG and reaches the most advanced position such that the volumetric capacities of first, second and third advance chambers A1, A2 and A3 are maximized, and the volumetric capacities of first, second and third retard chambers R1, R2 and R3 are minimized, the valve overlap is minimized. When the internal combustion engine is operating, exhaust camshaft 3b is subject to an alternating torque which is a negative torque or counterclockwise torque as a whole against clockwise rotation of exhaust camshaft 3b. When the internal combustion engine is stopped so as to turn off energization of directional control valve 24, then the alternating torque acts on the vane rotor 4 in the counterclockwise direction or in the retard direction with respect to housing HSG. On the other hand, biasing member 6 (first, second and third spring units 61, 62 and 63) constantly biases vane rotor 4 with respect to housing HSG in the clockwise direction or advance direction. Accordingly, after the internal combustion engine is stopped, vane rotor 4 is moved by the biasing force of biasing member 6 under little influence of the alternating torque, to the initial position suitable for start or restart of the internal combustion engine, i.e. to the most advanced position. In other words, the valve timing is mechanically brought to the phase suitable for start or restart of the internal combustion engine. When vane rotor 4 rotates with respect to housing HSG, and reaches the most advanced position, then lock piston 51 overlaps with engaging recess 521 in lock mechanism 5 as viewed in the X-axis direction. When the internal combustion engine is stopped, engaging portion 511 of lock piston 51 fits and engages with engaging recess 521 by the elastic force of coil spring 53, so that lock piston 51 prevents free rotation of vane rotor 4. As discussed above, in exhaust valve timing control apparatus 1b, vane rotor 4 is rotated by the biasing force of biasing member 6 to the most advanced position as an initial position with respect to housing HSG, when the internal combustion engine is stopped. This is effective for setting the exhaust valve timing control apparatus 1b in the initial position when the internal combustion engine is restarted, and achieving a stable start and operation of exhaust valve timing control apparatus 1b.

<Operation and Produced Effects by Lock Mechanism> As discussed above, each lock mechanism 5 operates to allow a corresponding one of intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b to start from its initial position shown in FIG. 4 or 16, independently of presence or absence of hydraulic pressures. This serves to suppress vibration of vane rotor 4 which may result from the alternating torque applied to camshaft 3a or 3b, and thereby suppress abnormal noise due to collision between first, second and third shoes 11, 12 and 13 of housing HSG and first, second and third vanes 41, 42 and 43 of vane rotor 4, when the internal combustion engine is started. Moreover, it is possible to prevent knocking, etc., and thereby achieve stable operations of the internal combustion engine, intake valve timing control apparatus 1a, and exhaust valve timing control apparatus 1b. These effects are produced, not only when the internal combustion engine is at start, but also when the internal combustion engine is at idle when no high hydraulic pressure is generated and supplied. The lock position is located at the most retarded position or the most advanced position in the present embodiment, but may be modified to a position between the most retarded position and the most advanced position which is suitable for start, etc., of the internal combustion engine, and used as an initial position of intake valve timing control apparatus 1a or exhaust valve timing control apparatus 1b.

As described above, lock mechanism 5 includes: slide hole 501 formed in vane rotor 4; lock piston 51; engaging recess 521 formed in the inside surface of housing HSG; and coil spring 53. Lock piston 51 moves out of and into vane rotor 4 according to the operating state of the internal combustion engine, and thereby allows or prevents relative rotation between housing HSG and vane rotor 4. For example, when vane rotor 4 is rotated to the predetermined initial position by the biasing force of biasing member 6 and/or the alternating torque, then lock piston 51 is mechanically engaged with engaging recess 521 by the biasing force of coil spring 53. This eliminates the necessity of provision of an actuator for actuating the locking operation. This is also effective for simplifying the mechanism, and reducing the manufacturing cost, and enhancing the reliability of the locking operation, as compared to cases where the locking means is implemented by a clutch mechanism or lever mechanism. Instead of or in addition to coil spring 53, another elastic member, such as a leaf spring, may be used as a biasing member for biasing the lock piston 51. Although the lock state is released by application of hydraulic pressure to lock piston 51 in the present embodiment, another releasing mechanism may be provided to release the lock piston 51 from engaging recess 521. Although the lock mechanism (i.e. lock piston 51) is provided in first vane 41 of vane rotor 4 in the present embodiment, the lock mechanism may be provided in rotor 40 of vane rotor 4. However, the provision in first vane 41 is advantageous in reducing the diameter of rotor 40. Alternatively, the lock mechanism (i.e. lock piston 51) may be provided in housing HSG, for locking the vane rotor 4 with respect to housing HSG. However, the provision in vane rotor 4 is advantageous in reducing the size of housing HSG.

<Locking Operation Smoothed by Suitable Direction of Movement of Lock Piston> Lock piston 51 may be arranged to move forward and rearward in a direction other than the direction of the axis of rotation O, for example, in a radial direction of housing HSG. In other words, the cylinder accommodating the lock piston 51 may be formed to extend in a direction other than the direction of the axis of rotation O, for example, in a radial direction of housing HSG. However, in the present embodiment, slide hole 501 is formed to extend in the direction of the axis of rotation O (or in the X-axis direction), wherein the tip (engaging portion 511) of lock piston 51 moves into or out of slide hole 501 in the direction of the axis of rotation O. This construction is advantageous in reducing the diameter of intake valve timing control apparatus 1a or exhaust valve timing control apparatus 1b. Moreover, the construction is effective for preventing the operation of lock mechanism 5 from being influenced by the centrifugal force resulting form rotation of vane rotor 4. For example, if lock piston 51 is arranged to move in a radial direction of housing HSG, lock piston 51 is applied with the centrifugal force resulting form rotation of vane rotor 4 which acts in the direction of movement of lock piston 51. In such cases, when engine speed changes so as to change the magnitude of the centrifugal force, then the force required to actuate the lock piston 51 also changes. The construction according to the present embodiment is however subject to no such problem, and thereby serves to stabilize the locking operation of intake valve timing control apparatus 1a or exhaust valve timing control apparatus 1b.

<Locking Operation Smoothed by Back Pressure Relief Section> The back pressure relief section serves to smooth the movement of lock piston 51 by eliminating the effect of pressure in back pressure chamber 50, when intake valve timing control apparatus 1a or exhaust valve timing control apparatus 1b is in operation. Specifically, when engaging portion 511 moves out of engaging recess 521 so that lock piston 51 moves in the X-axis positive direction, and the volumetric capacity of back pressure chamber 50 decreases, then air in back pressure chamber 50 escapes through the back pressure relief section to the low pressure space in the internal combustion engine. This serves to keep the internal pressure of back pressure chamber 50 low. On the other hand, working fluid leaks through the clearance around the back pressure chamber 50, and flows into back pressure chamber 50. This working fluid is also drained through the back pressure relief section to the oil-lubricated space in the internal combustion engine. Accordingly, when back pressure chamber 50 is contracting, the movement of lock piston 51 is prevented from being disturbed by such air and oil, and the back pressure of lock piston 51 is relieved. In this way, the back pressure relief section serves to achieve smooth operation of lock piston 51, i.e. smooth sliding motion of lock piston 51 in slide hole 501, and allow the lock state to be smoothly released.

<Locking Operation Smoothed by Wedging Effect> Since the tip (or engaging portion 511) of lock piston 51 has the form of a truncated cone, and has a diameter that gradually decreases as followed in the X-axis negative direction toward engaging recess 521 as described above, lock piston 51 can easily engage with engaging recess 521. This effect is enhanced by the shape of engaging recess 521 whose diameter gradually increases as followed in the X-axis positive direction toward the opening of engaging recess 521. The locking operation is thus smoothed. Moreover, each of engaging portion 511 and engaging recess 521 has an inclined surface or tapered surface. Specifically, the outside periphery of engaging portion 511 is formed with the inclined surface whose diameter gradually decreases as followed in the X-axis negative direction toward the tip of engaging portion 511, whereas the inside periphery of engaging recess 521 is formed with the inclined surface whose diameter gradually decreases as followed in the X-axis negative direction toward the bottom of engaging recess 521. Under the condition shown in FIG. 4 that the relative rotation between housing HSG and vane rotor 4 is restricted by the first stopper mechanism, the central axis of engaging recess 521 is located with a slight offset with respect to the central axis of engaging portion 511 in the counterclockwise direction toward first shoe 11, as shown in FIG. 14. Accordingly, when lock piston 51 is inserted in engaging recess 521 to establish the lock state, the inclined surfaces of engaging portion 511 and engaging recess 521 are brought into contact with one another on the clockwise side, thereby causing a component of force for pressing the first vane 41 in the counterclockwise direction toward the first shoe 11. This is a wedging effect. Namely, when engaging portion 511 is moved in the X-axis negative direction, and engaged with engaging recess 521 under the biasing force of coil spring 53, the clockwise side inclined surface of engaging portion 511 is brought into sliding and pressing contact with the clockwise side inclined surface of engaging recess 521, while engaging portion 511 of lock piston 51 is subject to a reaction force in the counterclockwise direction. Accordingly, first vane 41 accommodating the lock piston 51 is also subject to the reaction force in the counterclockwise direction toward the first shoe 11. As a result, the engagement of lock piston 51 with engaging recess 521 is effective for pressing the first vane 41 onto first shoe 11, and thereby ensuring that the vane rotor 4 is retained at the bound defined by the first stopper mechanism (i.e. the most retarded position as the initial position). The contact between the inclined surfaces of engaging portion 511 and engaging recess 521 described above is thus achieved by the provision of the offset between the central axes of engaging portion 511 and engaging recess 521, but may be achieved by suitably modifying the shapes of engaging portion 511 and engaging recess 521. However, the provision of the offset between the central axes of engaging portion 511 and engaging recess 521 is advantageous in simplifying the structure. Although both of engaging portion 511 and engaging recess 521 are formed with the inclined surfaces in the present embodiment, this construction may be modified so that only one of engaging portion 511 and engaging recess 521 is provided with the inclined surface. This alternative construction can produce a wedging effect as in the present embodiment. However, the construction according to the present embodiment is effective for reducing friction between engaging portion 511 and engaging recess 521, while effectively producing a wedging effect.

<Locking Operation Smoothed by Positioning Means> The positioning between lock piston 51 and engaging recess 521 is accurately implemented by a positioning means including the positioning pin 905, etc., so as to achieve smooth engaging operation of lock piston 51. The following describes operation of the positioning means including the positioning pin 905, etc. First, the following briefly describes a process of assembling the intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b. First, rear plate 9 is inserted and mounted in fitting recess 101 of housing body 10. This is implemented by: mounting the sleeve 52 in recess 900 of rear plate 9; setting the rear plate 9 so that the X-axis positive side surface of rear plate 9 is directed upwardly in the vertical direction; mounting and holding the sealing ring S1 in sealing ring groove 906, and sealing rings S2 in annular sealing ring grooves 907, 908 and 909 in rear plate 9; and assembling the housing body 10 from the X-axis positive side (from above in the vertical direction) to rear plate 9 so that the rear plate 9 is fitted in fitting recess 101. In assembling the housing body 10 to rear plate 9, the rotational position of housing body 10 with respect to rear plate 9 is adjusted so that the positioning recess 114 of housing body 10 faces or conforms to positioning pin 905 of rear plate 9. Then, positioning pin 905 is fixedly fitted in positioning recess 114. In this way, the position of housing body 10 with respect to rear plate 9 in the circumferential direction is set suitably. Under this condition, the bolt holes of female thread portions 901, 902 and 903 of rear plate 9 face or conform to bolt holes 110, 120 and 130 of housing body 10, respectively, as viewed in the X-axis direction. Next, vane rotor 4 is inserted and mounted in housing body 10. Simultaneously, sealing members 118, 128 and 138, and sealing members 413, 423 and 433 for sealing between the working fluid chambers A1, A2, A3, R1, R2 and R3 are also mounted. For exhaust valve timing control apparatus 1b, biasing member 6 is also mounted. Moreover, lock mechanism 5 is mounted by: inserting the lock piston 51 in sealing member 502 press-fitted in slide hole 501 of vane rotor 4; inserting the coil spring 53 into the inside of lock piston 51; and inserting the spring retainer 54 into slide hole 501. According to the positioning by positioning pin 905, the sleeve 52, which is fixed in engaging recess 521 in rear plate 9, faces and conforms to lock piston 51 in slide hole 501 with a slight offset, under the condition that first vane 41 of vane rotor 4 is in contact with first shoe 11 of housing body 10. Then, front plate 8 is brought from the X-axis positive side (from above in the vertical direction), and attached to housing body 10, and bolts b1, b2 and b3 are used to fix the front plate 8, housing body 10, and rear plate 9 together. Front plate 8 is mounted to housing body 10 under the condition that the sealing ring S3 is mounted in annular sealing ring groove 89 of front plate 8. The provision of sealing ring grooves 906, 907, 908, 909 and 89 is effective for easily retaining the sealing rings S1, S2 and S3, and thereby easily assembling the intake valve timing control apparatus 1a or exhaust valve timing control apparatus 1b. As described above, positioning pin 905 in pin hole 904 and positioning recess 114 serve as a positioning means for adjusting and defining the rotational position of rear plate 9 with respect to housing body 10 by adjusting relative circumferential position between lock piston 51 and engaging recess 521 during assembling operation of intake valve timing control apparatus 1a or exhaust valve timing control apparatus 1b. The radial positions of lock piston 51 and engaging recess 521 are set substantially identical, when rear plate 9 is fitted in fitting recess 101 of housing body 10. In this way, lock piston 51 and sleeve 52 are correctly positioned, so that the lock piston 51 can smoothly engage with sleeve 52. The construction that the positioning pin 905 is located adjacent to recess 900 (engaging recess 521) is effective for correctly positioning the lock piston 51 and engaging recess 521. The construction that the pin hole 904 is located on the side of sealing ring grooves 906 and 907 where first retard chamber R1 is located, is effective for preventing the sealing performance of the sealing rings S1 and S2 from being adversely affected. Vane rotor 4 is supported in through hole 92 which is formed in the center of rear plate 9 and through which intake camshaft 3a passes, and fixed to the axial end portion 30 of intake camshaft 3a. Accordingly, under the influence of a force applied from timing belt 1010 which is wound around pulley 100 of housing HSG, housing HSG may be inclined within a slight angle range with respect to the axis of rotation of vane rotor 4 (i.e. the X-axis), and swing about cylindrical portion 91 of rear plate 9 in which through hole 92 is formed. As a result, engaging recess 521 provided in housing HSG may be deviated with respect to lock piston 51 provided in vane rotor 4. However, according to the present embodiment where rear plate 9 is formed with engaging recess 521, the distance (moment arm) between engaging recess 521 and cylindrical portion 91 as a fulcrum, is shorter than in the case where the engaging recess is formed in front plate 8 alternatively. Accordingly, displacement of engaging recess 521 due to swinging motion of housing HSG in a direction perpendicular to the X-axis, is smaller, so that deviation of lock piston 51 from engaging recess 521 is smaller or suppressed. Moreover, the construction that the boss portion 401 of vane rotor 4 is inserted in through hole 92, is effective for suppressing the inclination and displacement of vane rotor 4 with respect to housing HSG within a predetermined range.

<Produced Effects by Timing Belt and Pulley> In the present embodiment, the torque from the crankshaft is transmitted to intake valve timing control apparatus 1a or exhaust valve timing control apparatus 1b by the combination of timing belt 1010 and pulley 100 driven by timing belt 1010. As compared to an alternative combination of a timing chain and a sprocket driven by the timing chain, the construction according to the present embodiment is advantageous in the quietness, manufacturing cost, and lightness of intake valve timing control apparatus 1a or exhaust valve timing control apparatus 1b.

<Produced Effects by Weight Reduction> Housing HSG and vane rotor 4 may be formed of a material other than aluminum-based metal materials, for example, an iron-based metal material. However, in a typical valve timing control apparatus using a timing belt and a pulley, the width of the timing belt needs to be wide enough to transmit adequate torque. Accordingly, the width of the pulley needs to be wide enough to engage with the timing belt. This results in an increase in the size of the valve timing control apparatus in the axial direction (the width direction of the pulley), and thereby results in an increase in the weight of the valve timing control apparatus. In contrast, intake valve timing control apparatus 1a or exhaust valve timing control apparatus 1b according to the present embodiment is formed light in weight, because both of housing body 10 and vane rotor 4 are formed of a light metal material, specifically, an aluminum-based metal material. Conversely, the combination of the timing belt and the pulley can be adapted in intake valve timing control apparatus 1a or exhaust valve timing control apparatus 1b, because the moment of inertia of housing body 10 and vane rotor 4 is small so that the load applied to the torque transmitting section is low.

<Durability of Apparatus Enhanced by Features of Form of Fixing Vane Rotor> A typical valve timing control apparatus of so-called a vane type may be subject to a problem that when a vane rotor mounted in a housing is fixed to a camshaft by a single fixing portion, the strength of fixation between the vane rotor and the camshaft is insufficient. For example, in cases where a vane rotor is fixed to a camshaft by a single camshaft bolt that is provided at the axis of rotation, an alternating torque is transmitted from valve springs and applied to the camshaft around the central axis of the camshaft (or camshaft bolt), so that the camshaft bolt tends to be easily loosed. On the other hand, if the camshaft is fixed to the vane rotor by tightly screwing the single camshaft bolt for preventing the looseness, the axial force of the camshaft bolt may cause a large contact pressure to act on the vane rotor. This may result in deforming the vane rotor, when the vane rotor is made of a soft material, such as an aluminum material. In contrast, according to the present embodiment, the fixation is implemented by forming the rotor 40 of vane rotor 4 with a plurality of fixing portions (bolt holes 403, 404 and 405) for fixing the vane rotor 4 to camshaft 3a or 3b. In this construction, the applied torque around the central axis of camshaft 3a or 3b is distributed to the fixing portions (bolt holes 403, 404 and 405) arranged in the circumferential direction around the central axis of camshaft 3a or 3b, so that the load to each fixing portion is reduced, and the direction of the force applied to each fixing portion is changed, as compared to cases where the fixation between vane rotor 4 and camshaft 3a or 3b is implemented by a single fixing portion. Therefore, the strength of fixation between vane rotor 4 and camshaft 3a or 3b can be enhanced in the present embodiment. The number of the fixing portions is three in the present embodiment, but may be changed to another number greater than or equal to two. However, the fixation based on the three fixing portions is advantageous in enhancing the strength of fixation, while reducing the number of parts, and enhancing the ease of processing and assembling. Each fixing portion is not limited to the form of bolt hole 403, 404 or 405, but may be implemented by swaging, welding, etc. However, the construction according to the present embodiment is advantageous in simplifying the attachment of the valve timing control apparatus to the camshaft, and simplifying the management of fixing force. Specifically, the construction that vane rotor 4 is fixed by three camshaft bolts 33, 34 and 35, is effective for preventing the alternating torque around the axis of rotation O from applying each camshaft bolt 33, 34 or 35 with a torque applied around the central axis of camshaft bolt 33, 34 or 35. This prevents camshaft bolt 33, 34 or 35 from being loosed. This also serves to provide a sufficient fixing force as a whole, while reducing the axial force of each camshaft bolt 33, 34 or 35. This results in reducing the contact pressure applied to vane rotor 4, and thereby reducing the deformation of vane rotor 4. These advantageous effects may be produced by an alternative construction that the fixing portions are spaced from one another, but arranged in the radial direction as different from the present embodiment. However, the construction according to the present embodiment that the fixing portions are arranged in the circumferential direction is advantageous in reliably and evenly distributing the load in the circumferential direction around the axis of rotation O to the plurality of fixing portions, as compared to the alternative construction. In this way, the construction according to the present embodiment is effective for efficiently enhancing the entire strength of fixing, while reducing the load to each fixing portion. The plurality of fixing portions may be unevenly spaced from one another as different from the present embodiment. However, the construction according to the present embodiment that the fixing portions (bolt holes 403, 404 and 405) are substantially evenly spaced from one another is advantageous in easily keeping the vane rotor 4 in balance around its axis of rotation. This is also advantageous in easily keeping the camshaft 3a or 3b in balance around its axis of rotation, because the fixing portions (bolt holes 32) of camshaft 3a or 3b are also substantially evenly spaced in conformance with the positions of bolt holes 403, 404 and 405. In addition, according to the present embodiment, each portion between adjacent two of the fixing portions can be formed to have an even and relatively large thickness. This serves to ensure the strength of rotor 40, even when the fixing portions are formed by removing parts from the base product of rotor 40, like the bolt hole 403, 404 or 405 in the present embodiment, which tends to adversely affect the strength of rotor 40. The even spacing is also advantageous in effectively preventing the interference among the heads 331, 341 and 351 of camshaft bolts 33, 34 and 35 that are inserted in bolt holes 403, 404 and 405.

<Durability of Apparatus Enhanced by Features of Anodic Oxide Coating Film> Each of housing body 10 and vane rotor 4 is formed of an aluminum-based metal material, and thereby relatively soft. Accordingly, each of housing body 10 and vane rotor 4 is applied with surface treatment, for enhancing the wear resistance and durability. The surface treatment is implemented by anodic oxidation treatment, which is advantageous in rust resistance, wear resistance, evenness of coating thickness, operating facility, etc. Each aluminum-based metal material may be selected from materials that are advantageous in enhancing the wear resistance of the oxide coating film. An anodic oxide coating film is a kind of oxide coating film, which has a relatively high surface roughness, and which is formed with a lot of pores (or projections and recesses). The pores may be sealed or filled by pore-sealing treatment after the anodic oxidation treatment, so that the anodic oxide coating film loses adsorptive activity. In such cases, half pore-sealing treatment is more desirable than full pore-sealing treatment, in order to avoid complicated management, and avoid the occurrence of cracks. In cases of half pore-sealing treatment, each pore still has an opening, and is capable to hold oil therein, thus maintaining a lubricated state, as in cases where no pore-sealing treatment is performed. In order to further enhance the wear resistance, the surface treatment may be implemented by hard alumilite treatment. In such cases, it is desirable that no pore-sealing treatment is performed, because pore-sealing treatment may adversely affect the enhanced wear resistance. The enhancement of wear resistance may be implemented by surface treatment other than anodic oxidation treatment, such as hard chrome plating, or nickel electroless plating. With regard to housing body 10, the pulley 100 is formed of an aluminum-based metal material, as part of housing body 10. It is highly desirable to enhance the wear resistance of pulley 100, because pulley 100 is subject to a driving torque transmitted through the timing belt 1010. On the other hand, the aluminum-based metal material of housing body 10 is implemented by a relatively soft material, so that it becomes easy to accurately form the teeth of pulley 100. In the present embodiment, the outside periphery of housing body 10, i.e. the surface of pulley 100, is anodized, so that an anodic oxide coating film layer is present at the outside periphery of housing body 10. This feature is effective for enhancing the hardness and wear resistance of the surface of pulley 100 in meshing contact with timing belt 1010. On the other hand, the inside periphery of housing body 10 is formed with an anodic oxide coating film layer. This feature serves to enhance the hardness and wear resistance of the inside periphery of housing body 10 that is in sliding contact with first, second and third vanes 41, 42 and 43, and rotor 40, and in contact with biasing member 6. Incidentally, at both axial ends of housing body 10, all of longitudinal end surface 105, bottom surface 102, inside peripheral surface 103, and longitudinal end surface 104 are applied with no anodic oxidation treatment. There is however no problem, because the longitudinal end surface 105, bottom surface 102, and inside peripheral surface 103 are in fixed contact with the sealing plates (front plate 8, and rear plate 9), and the longitudinal end surface 104 is in contact with no other member, so that all of longitudinal end surface 105, bottom surface 102, inside peripheral surface 103, and longitudinal end surface 104 are not in sliding contact. With regard to vane rotor 4, the outside peripheral surface of first, second and third vanes 41, 42 and 43, and rotor 40 (the outside peripheral surface 411, etc.) is applied with anodic oxidation treatment. This is effective for enhancing the wear resistance of the surface of vane rotor 4 in sliding contact with the inside periphery of housing body 10. The axial end surfaces of vane rotor 4 are also applied with anodic oxidation treatment. This enhances the wear resistance of the surface of vane rotor 4 in sliding contact with the sealing plates (front plate 8, and rear plate 9) at the axial ends of housing body 10. Vane rotor 4 may be formed of a slightly harder material than housing body 10, because the requirement about hardness is lower for vane rotor 4 than for housing body 10 for which it is desirable to use a soft material for accurately forming the teeth of pulley 100. More specifically, the first stopper mechanism, which is constituted by flat portion 111 of housing body 10 and flat portion 415 of vane rotor 4, and the second stopper mechanism, which is constituted by tip 126 of housing body 10 and radial projection 419 of vane rotor 4, are applied with anodic oxidation treatment. This feature is effective for ensuring the hardness of the contact surfaces of each stopper mechanism, and thereby preventing the deformation thereof, enhancing the wear resistance, and enhancing the operation of the stopper mechanisms as described in detail below. Moreover, in valve timing control apparatus 1, boss portion 401 of vane rotor 4 is subject to a relatively high load in the radial directions, when housing HSG is rotating under condition that torque is transmitted through the timing belt 1010 so that the tension of timing belt 1010 is applied to pulley 100, because boss portion 401 pivotally supports the housing HSG. This may cause wear in boss portion 401, if vane rotor 4 including the boss portion 401 is formed of a relatively soft material, such as an aluminum-based metal material. Specifically, it tends to cause adhesion between the inside periphery of through hole 92 of housing HSG and the outside periphery of boss portion 401 in sliding contact with one another, and thereby cause adhesion wear in boss portion 401. In contrast, in the present embodiment, vane rotor 4 is formed of an aluminum-based material, and the outside periphery of boss portion 401 is formed with an anodic oxide coating film. This serves to suppress such adhesion at the surface of boss portion 401 in sliding contact with housing HSG, and thereby suppress wear of boss portion 401. The pores of anodic oxide coating film can hold lubricating oil for a long period of time. For example, even in situations where the internal combustion engine is at rest for a period from some days to some months so that the valve timing control apparatus 1 is also at rest, the lubricating oil is held at the sliding contact surface of boss portion 401, and the held lubricating oil functions well at restart of the internal combustion engine, and serves to suppress wear of boss portion 401. Namely, the effect of reducing wear of boss portion 401 is further enhanced by the characteristic shape of the anodic oxide coating film. In this way, valve timing control apparatus 1 is maintained in a preferable condition where wear is suppressed by a synergy of the effect of reducing adhesion and the effect of holding lubricating oil.

<Durability of Apparatus Enhanced by Features of Materials> Each sealing plate (front plate 8, rear plate 9) are formed of a harder material (iron-based metal material) than housing body 10 (aluminum-based metal material). This feature serves to enhance the strength of front plate 8 that serves as a seat receiving the bolts b1, b2 and b3, and enhance the strength of each female thread portion 901, 902 or 903 of rear plate 9 in which bolt b1, b2 or b3 is screwed, thus enhancing the durability of valve timing control apparatus 1. This feature also serves to suppress wear that may be caused by sliding contact between coil spring 53 of lock mechanism 5 and the X-axis negative side surface of front plate 8. Moreover, each sealing plate 8, 9 is formed of a material (iron-based metal material) having a higher wear resistance than vane rotor 4 (aluminum-based metal material). This feature serves to enhance the durability of the portions of the sealing plates in sliding contact with vane rotor 4 (axial end surfaces, and boss portion 401). In other words, the durability of valve timing control apparatus 1 is enhanced, because the sliding surface of vane rotor 4 (axial end surfaces, and boss portion 401) is hardened by anodic oxidation treatment, and also the corresponding sliding surface of housing HSG is hardened. Specifically, each sealing plate 8, 9 is formed of an iron-based metal material, such as stainless steel, and thereby has a high hardness, high wear resistance, and high durability. This feature is advantageous also in the processing facility, manufacturing cost, etc. More specifically, each sealing plate 8, 9 is formed by forging, which is advantageous in strengthening. However, each sealing plate 8, 9 may be formed by another processing, such as stamping, casting, etc. Each sealing plate 8, 9 may be formed of a material having a higher hardness or higher wear resistance than aluminum-based metal materials, for example, a metal material such as magnesium, or a non-metal material such as ceramics. Sealing plates 8, 9 may be formed of an aluminum-based metal material, and anodized at the contact axial end surfaces and the inside periphery of through hole 92 so as to enhance the wear resistance of the portion in sliding contact with vane rotor 4 (axial end surfaces, and boss portion 401).

<Durability of Apparatus Enhanced by Features of Lock Mechanism> The construction that the vane rotor 4 is formed of an aluminum-based metal material may cause a concern about wear of the cylinder (slide hole 501) that is formed in vane rotor 4 and accommodates the lock piston 51. This is because lock piston 51 moves forward and backward in the cylinder during operation of lock mechanism 5, and because first, second and third vanes 41, 42 and 43 may vibrate due to the alternating torque from camshaft 3a or 3b, so as to cause fluctuations in hydraulic pressures in the working fluid chambers A1, R1, and thereby cause fluctuations in hydraulic pressures in first pressure-receiving chamber 55 and second pressure-receiving chamber 59, even when lock mechanism 5 is not operated. In order to solve this problem, in the present embodiment, sealing member 502 is fixed in slide hole 501, and lock piston 51 is slidably mounted in sealing member 502. Sealing member 502 is formed of a material having a higher wear resistance than aluminum-based metal materials, specifically, formed of an iron-based metal material. Namely, sealing member 502 having a higher wear resistance than slide hole 501 is in sliding contact with lock piston 51. This feature serves to suppress wear of the cylinder (slide hole 501) which may be caused by forward and backward movement of lock piston 51 without sealing member 502. Sealing member 502 is provided separately from vane rotor 4. This feature is advantageous in enhancing the forming accuracy of the sliding surface of the cylinder, because it is possible to select a material that is highly desirable for sealing member 502 constituting the sliding surface. Sealing member 502 may be formed small, if sealing member 502 remains in contact with lock piston 51. If lock piston 51 moves in the entire range of slide hole 501, the size of sealing member 502 in the longitudinal direction may be set equal to that of slide hole 501. The cross-sectional shape (inside periphery, outside periphery) of sealing member 502 may be other than a circular shape, for example, an elliptic shape or a rectangular shape. In such cases, the cross-sectional shape of slide hole 501 is conformed to the shape of sealing member 502.

On the other hand, the feature that the sealing member 502 is formed of a material having a higher wear resistance and hardness than vane rotor 4 (slide hole 501) may cause a concern that during assembling operation, sealing member 502 is fixed in slide hole 501 under condition that the sealing member 502 is inclined with respect to the longitudinal axis of slide hole 501 (which is called galling). In such cases, lock piston 51, which is slidably mounted in sealing member 502, is also inclined with respect to the longitudinal axis of slide hole 501, so that lock piston 51 may be in unbalanced contact with housing HSG (engaging recess 521). The unbalanced contact may cause friction, or cause a trouble that lock piston 51 tends to be undesirably easily moved out of engaging recess 521, thus adversely affecting the operation of lock mechanism 5. This tends to be more significant in the present embodiment where each of engaging portion 511 and engaging recess 521 is formed with an inclined surface to produce a wedging effect. This may cause a trouble that lock piston 51 tends to be undesirably more easily moved out of engaging recess 521. In order to solve this problem, in the present embodiment, the surface of slide hole 501 is anodized so as to enhance the hardness. This feature serves to prevent the inclination of sealing member 502 when sealing member 502 is fixed in slide hole 501, thereby suppressing the occurrence of unbalanced contact, keeping the operation of lock mechanism 5 normal, and keeping the controllability of valve timing control apparatus 1 normal. This advantageous effect is further significant, because each of engaging portion 511 and engaging recess 521 is formed with an inclined surface to produce a wedging effect. Incidentally, the anodic oxidation treatment may be applied only to a portion of the surface of slide hole 501 with which sealing member 502 is in fixed contact. The form of fixing the sealing member 502 to slide hole 501 may be easily implemented by press-fitting. However, the fixation based on press-fitting may cause a relatively high possibility that the sealing member 502 is set with inclination (galling of sealing member 502 is caused against vane rotor 4). In contrast, in the present embodiment, sealing member 502 is press-fitted in slide hole 501 that is anodized, namely, sealing member 502 is press-fitted in slide hole 501 whose surface is hardened by anodic oxidation treatment. This feature serves to suppress the inclination of sealing member 502, while making it easy to mount and fix the sealing member 502 to slide hole 501. In addition, in the present embodiment, sealing member 502 is formed of a material having a higher hardness or wear resistance than anodic oxidation coating, specifically, formed of an iron-based metal material. This feature serves to enhance the effect of suppressing wear of the cylinder (slide hole 501) as compared to cases where the anodized slide hole 501 is directly in sliding contact with lock piston 51. The feature further serves to suppress the deformation of sealing member 502, when sealing member 502 is press-fitted in the anodized slide hole 501.

Moreover, the durability of lock mechanism 5 is further enhanced by suppressing the frequency of operation of lock piston 51. Specifically, lock mechanism 5 is configured so that lock piston 51 operates against the biasing force of coil spring 53 in response to hydraulic pressures in first and second pressure-receiving chambers 55 and 59 which are supplied according to the operating state of the internal combustion engine. Specifically, first pressure-receiving chamber 55 is supplied with the hydraulic pressure in first retard chamber R1, whereas second pressure-receiving chamber 59 is supplied with the hydraulic pressure in first advance chamber A1. Accordingly, during operation of valve timing control apparatus 1, lock piston 51 is maintained in its released state, constantly when at least one of the hydraulic pressures in first advance chamber A1 and first retard chamber R1 is supplied to lock mechanism 5. This feature serves to eliminate the necessity of provision of an additional actuator for canceling the lock state, simplify the construction, maintain the reliability of the locking operation, lower the manufacturing cost, and prevent that the locking operation and the releasing operation are frequently repeated in response to movement of vane rotor 4 in the advance direction and the retard direction. This serves to reduce the frequency of operation of lock piston 51, and thereby enhance the durability of valve timing control apparatus 1. The construction may be modified so that first pressure-receiving chamber 55 is supplied with the hydraulic pressure from first advance chamber A1, and second pressure-receiving chamber 59 is supplied with the hydraulic pressure from first retard chamber R1. More specifically, slide hole 501 and sealing member 502 constitute a stepped cylinder having a larger-diameter portion and a smaller-diameter portion, wherein sealing member 502 is inserted and mounted in slide hole 501, and wherein the size of sealing member 502 in the X-axis direction is smaller than slide hole 501. In conformance with this shape, lock piston 51 has the form of a stepped pin having a larger-diameter portion (flange 513) and a smaller-diameter portion (sliding portion 512, engaging portion 511). The smaller-diameter portion (sliding portion 512) of lock piston 51 is disposed in sliding contact with the inside periphery of sealing member 502, whereas the larger-diameter portion (flange 513) of lock piston 51 is disposed in sliding contact with the inside periphery of slide hole 501. This construction defines the first pressure-receiving chamber 55 in slide hole 501 between sealing member 502 and the larger-diameter portion (flange 513) of lock piston 51. In this way, the provision of sealing member 502 makes it possible to easily define the first pressure-receiving chamber 55 and second pressure-receiving chamber 59 liquid-tightly separated from one another, and apply the lock piston 51 with hydraulic forces which are produced by first advance chamber A1 and first retard chamber R1 independently of one another. Alternatively, the shapes of the cylinder (slide hole 501) and lock piston 51, and the arrangement of communication hole 56 and communication groove 57 may be modified so as to modify the shapes and positions of the first and second pressure-receiving chambers 55 and 59 as desired. For example, sealing member 502 may be inserted and mounted from either one of the longitudinal ends of slide hole 501. The larger-diameter portion (part of flange 513) of lock piston 51 may be constructed to move out of vane rotor 4, and move into engaging recess 521, whereas the smaller-diameter portion of lock piston 51 constantly remains in slide hole 501. In such cases, the larger-diameter portion of lock piston 51 serves as the distal end portion of lock piston 51, whereas the smaller-diameter portion of lock piston 51 serves as the proximal end portion of lock piston 51. In such cases, the biasing member (coil spring 53) may be arranged to bias the lock piston 51 in a direction from the smaller-diameter portion (proximal end) to the larger-diameter portion (distal end).

The feature that the slide hole 501 is formed with an anodic oxidation coating film serves to suppress wear of slide hole 501 that may be caused by sliding motion of flange 513 of lock piston 51. Moreover, the many pores of the anodic oxidation coating film hold lubricating oil for a long period of time. The lubricating oil held at slide hole 501 serves to suppress wear of slide hole 501, even when the internal combustion engine is restarted so that valve timing control apparatus 1 operates and the rear end corner of flange 513 of lock piston 51 slides on the inside peripheral surface of slide hole 501 after the condition that the internal combustion engine is at rest for a period from some days to some months so that the valve timing control apparatus 1 is also at rest. Namely, the effect of reducing wear of slide hole 501 is further enhanced by the function of holding lubricating oil which is based on the characteristic shape of the anodic oxide coating film. In this way, the anodic oxidation treatment serves to suppress the inclination of sealing member 502 (and the inclination of lock piston 51), and enhance the wear resistance and lubrication of the portion of slide hole 501 in sliding contact with flange 513 of lock piston 51. Moreover, sealing member 502 is formed of a material having a higher wear resistance than anodic oxidation coating, and the clearance between the smaller-diameter portion (sliding portion 512) of lock piston 51 and the inside periphery of sealing member 502 is set smaller than the clearance between the larger-diameter portion (flange 513) of lock piston 51 and the inside periphery of slide hole 501. Namely, the frequency or degree of contact between the smaller-diameter portion (sliding portion 512) of lock piston 51 and the inside periphery of sealing member 502 is relatively increased, in consideration that the wear resistance of the inside periphery of sealing member 502 is higher than the inside periphery of slide hole 501. This feature is effective for suppressing wear of the portion of the inside periphery of the cylinder in sliding contact with lock piston 51. Although sealing member 502 is provided separately from vane rotor 4 in the present embodiment, sealing member 502 may be formed integrally with vane rotor 4 into a stepped shape, and the entire inside peripheral surface of slide hole 501 may be applied with anodic oxidation treatment. This alternative construction also serves to enhance the wear resistance, while defining the first and second pressure-receiving chambers 55 and 59. However, the construction according to the present embodiment that sealing member 502 is formed separately and mounted in slide hole 501 is advantageous in enhancing the wear resistance of the cylinder against the sliding motion of lock piston 51, and simply defining the first and second pressure-receiving chambers 55 and 59.

Lock piston 51 is formed of a material having a higher wear resistance than anodic oxidation coating, specifically, formed of an iron-based metal material. This feature serves to enhance the hardness of lock piston 51, and suppress wear of lock piston 51 effectively. The construction that the slide hole 501 is formed with an anodic oxidation coating film, and sealing member 502 is formed of a material having a higher wear resistance than anodic oxidation coating, is also effective for suppressing wear of lock piston 51 that is in sliding contact with slide hole 501 and sealing member 502. Sleeve 52 is formed of a material having a high wear resistance, such as an iron-based metal material. This feature is effective for enhancing the hardness of engaging recess 521 that is the inclined surface in sliding contact with engaging portion 511, and suppressing wear of engaging recess 521. Although sleeve 52 may be formed integrally with rear plate 9, the feature according to the present embodiment that the sleeve 52 is provided separately from rear plate 9 makes it possible to adjust the shape, material, etc., of engaging recess 521 so as to allow the lock piston 51 to smoothly engage or disengage with engaging recess 521, and serves to suppress wear and deformation of rear plate 9 resulting from engagement and disengagement of lock piston 51. Namely, the feature according to the present embodiment is advantageous in making it possible to use a material particularly suited for high wear resistance, and enhancing the forming accuracy of the inclined surface of engaging recess 521.

<Durability of Apparatus Enhanced by Features of Stopper Mechanism> Contact between the first stopper portions of the first stopper mechanism is frequently repeated, when vane rotor 4 is in the initial position where vane rotor 4. Moreover, this contact is generally hard, because hydraulic control is at rest when the internal combustion engine is being stopped. Accordingly, the first stopper mechanism may deform due to frequency and hardness of contact in the first stopper mechanism, so that the limit of rotation of vane rotor 4, i.e. the initial position of vane rotor 4 may change or deviate. In intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b, the contact area of the first stopper mechanism SS1 is set larger than the contact area of the second stopper mechanism SS2 (SS1>SS2). This prevents the first stopper mechanism from deforming or deviating the position within which rotation of vane rotor 4 is restricted. The first stopper mechanism is constituted by the circumferentially-facing surface of first vane 41. Accordingly, the root of first vane 41 has a longer circumferential length, which is advantageous because first vane 41 has a high rigidity, and has a strength enough to restrict and receive relative rotation of vane rotor 4. On the other hand, radial projection 419 of the second stopper mechanism is formed at the root of first vane 41, extending outwardly in the radial direction from rotor 40. As compared to cases where the second stopper mechanism is constituted by the tip of first vane 41, the bending moment or moment arm about the root of first vane 41 in the circumferential direction when the second stopper mechanism functions to restrict rotation of vane rotor 4, is smaller so that the root of first vane 41 is generally subject to no excessive force. This is advantageous for enhancing the durability of first vane 41. In this way, these features according to the present embodiment serve to enhance the rigidity of the first and second stopper mechanisms, suitably restrict the relative rotation, and thereby enhance the durability of valve timing control apparatus 1. Incidentally, one or more combinations of contact portions of second and third vanes 42 and 43, and first, second and third shoes 11, 12 and 13 may be modified to form first and second stopper mechanisms. In exhaust valve timing control apparatus 1b, the second stopper mechanism also serves to limit the amount of displacement (amount of compression) of biasing member 6 (coil springs 610, 620 and 630) to a predetermined amount. This prevents plastic deformation of biasing member 6 (coil springs 610, 620 and 630), and prevents the biasing force of biasing member 6 from changing in an irreversible form. Radial projection 429 of second vane 42 and the tip of third shoe 13 serve as a backup stopper mechanism instead of the second stopper mechanism, even when errors occur during manufacturing and assembling operations, or when the stopper portions of the second stopper mechanism are worn. This improves the reliability and accuracy of intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b. Especially in exhaust valve timing control apparatus 1b, this is effective for securely preventing the biasing member 6 from plastically deforming. Coil springs 610 and 630 are arranged outside of radial projections 419 and 429 of first and second vanes 41 and 42, respectively, so that radial projections 419 and 429, which constitute the second stopper mechanism and backup stopper mechanism respectively, guide the coil springs 610 and 630 of biasing member 6. This ensures normal operations of biasing member 6 and exhaust valve timing control apparatus 1b.

<Sealing Performance Enhanced by Features of Forming> In general, a device including a housing formed with a pulley to which torque is transmitted through a timing belt that is formed of rubber or synthetic resin and is wound around the pulley, is subject to a problem that the timing belt may be degraded by adhesion of working fluid exiting out of the housing. The housing has to be suitably sealed to solve the problem. This is true for valve timing control apparatus 1. The feature according to the present embodiment that the housing body 10 is formed by extruding an aluminum-based metal material, serves to prevent working fluid from seeping and leaking through the inside of housing body 10 and arriving at the outside periphery (pulley 100) of housing body 10, as compared to cases where housing body 10 is formed by another processing, for example, by sintering an aluminum-based metal material. The feature that the sealing plates (cap 7, front plate 8, and rear plate 9) are formed by forging an iron-based metal material, serves to prevent working fluid from seeping and leaking through the inside of the sealing plates (cap 7, front plate 8, and rear plate 9), as compared to cases where the sealing plates (cap 7, front plate 8, and rear plate 9) are formed by another processing, for example, by sintering an iron-based metal material.

<Sealing Performance Enhanced by Features of Sealing Members> The feature that the sealing rings S1, S2, S3 and S4 are provided in housing HSG serves to prevent working fluid from leaking through clearances, and thus ensure liquid-tightness of housing HSG. Each sealing ring may be replaced with a sealing compound. For example, sealing rings S2 may be replaced with an adhesive that serves also as a sealing compound, which serves to strengthen the fixing force of each bolt b1, b2 or b3. However, the construction according to the present embodiment is advantageous in simply implementing the sealing function. In the present embodiment, with regard to sealing ring S1 between housing body 10 and rear plate 9, under the condition that the sealing ring S1 is mounted in sealing ring groove 906 of rear plate 9, the inside peripheral surface 103 of fitting recess 101 of housing body 10 is pressed onto sealing ring S1, so that sealing ring S1 is compressed. This construction provides a function of sealing, so as to prevent working fluid from leaking through the boundary between rear plate 9 and housing body 10, and thus seal the working fluid chambers. With regard to sealing rings S2, under the condition that sealing rings S2 are mounted in annular sealing ring grooves 907, 908 and 909 around female thread portions 901, 902 and 903, the X-axis negative side end surface 102 of housing body 10 (first, second and third shoes 11, 12 and 13) is pressed onto sealing rings S2, so that sealing rings S2 are compressed. This configuration provides a function of sealing, so as to prevent working fluid from leaking through the boundary between rear plate 9 and housing body 10, and the bolt holes of female thread portions 901, 902 and 903, and thus seal the working fluid chambers. With regard to sealing ring S3 between housing body 10 and front plate 8, under the condition that sealing ring S3 is mounted in annular sealing ring groove 89 of front plate 8, the X-axis positive side end surface 105 of housing body 10 is pressed onto sealing ring S3, so that sealing ring S3 is compressed. This construction provides a function of sealing, so as to prevent working fluid from leaking through the boundary between front plate 8 and housing body 10, and thus seal the working fluid chambers. The feature that the sealing ring S3 and annular sealing ring groove 89 have the form of a three-leaved clover, passing inside of bolt holes 83, 84 and 85, so that the bolt holes 83, 84 and 85 are hydraulically separated from the inside of housing HSG, is effective for reducing the number of parts, and improving the facility of assembling, because no individual sealing members are required for bolt holes 83, 84 and 85. Incidentally, sealing ring S3 may be replaced with a plurality of sealing rings, i.e. a sealing ring that seals the inside portion of front plate 8 and passes outside of bolt holes 83, 84 and 85, and sealing rings each of which surrounds the bolt hole 83, 84 or 85 for sealing. With regard to sealing ring S4, under the condition that sealing ring S4 is mounted in annular sealing ring groove 821 of female thread portion 82 of front plate 8, the X-axis negative side end surface of flange 72 of cap 7 is pressed onto sealing ring S4, so that sealing ring S4 is compressed. This construction provides a function of sealing, so as to prevent working fluid from leaking through the boundary between cap 7 and front plate 8, and thus sealing the back pressure relief section. Incidentally, sealing ring grooves are optional, and the sealing rings may be mounted for sealing with no annular sealing ring groove formed. Housing body 10, front plate 8, and rear plate 9 are fixed together with the plurality of bolts b1, b2 and b3 which extend in the axial direction of housing HSG. Each bolt b1, b2 or b3 formed with the male thread is screwed in the female thread formed in the inside periphery of female thread portion 901, 902 or 903 of rear plate 9. The axial force of each bolt b1, b2 or b3 presses the X-axis negative side end surface (bottom surface 102) of housing body 10 (first, second and third shoes 11, 12 and 13) on sealing rings S2 around female thread portion 901, 902 or 903, thereby compresses sealing rings S2 in the X-axis direction. Similarly, the axial force of each bolt b1, b2 or b3 presses the X-axis positive side end surface 105 of housing body 10 (first, second and third shoes 11, 12 and 13) on sealing ring S3 around bolt holes 83, 84 and 85, thereby compresses sealing ring S3 in the X-axis direction. These features further enhance the sealing of housing HSG. The reaction force of sealing rings S2 and S3 serves to strengthen the fixation of bolt b1, b2 and b3, and prevent bolts b1, b2 and b3 from being released. Each female thread portion 901, 902 or 903 may be in the form of a recess. Although rear plate 9 is formed with female threads in the present embodiment, this construction may be modified so that each bolt b1, b2 or b3 extends through and projects from the rear plate 9, and the projected portion of bolt b1, b2 or b3 is engaged with a nut. The female threads may be formed in front plate 8 not in rear plate 9, wherein each bolt b1, b2 or b3 is inserted from the X-axis negative side to fix the front plate 8, rear plate 9, and housing body 10 together. The feature that each sealing ring S1, S2, S3 or S4 is an O-ring having a circular cross-section, makes it easy to mount each sealing ring S1, S2, S3 or S4 in sealing ring groove 906, etc. When compressed between two contact surfaces, each sealing ring S1, S2, S3 or S4 is brought into intimate contact with the contact surfaces, thereby enhancing the sealing performance. For sealing, it is sufficient that the surfaces of housing body 10 and sealing plate 8 or 9 facing one another abut on the sealing rings, and it is optional that the surfaces of housing body 10 and sealing plate 8 or 9 are in direct contact with one another. Specifically, it is sufficient that the X-axis negative side surface of front plate 8 (i.e. the bottom of sealing ring groove 89) abuts on sealing ring S3, and the X-axis positive side surface 105 of housing body 10 abuts on sealing ring S3, and it is optional that the X-axis negative side surface of front plate 8 and the X-axis positive side surface 105 of housing body 10 abut on one another. Similarly, it is sufficient that the X-axis positive side surface of rear plate 9 (i.e. the bottom of each annular sealing ring groove 907, 908 or 909) abuts on sealing ring S2, and the X-axis negative side surface 102 of housing body 10 abuts on sealing rings S2, and it is optional that the X-axis positive side surface of rear plate 9 and the X-axis negative side surface 102 of housing body 10 abut on one another. Further, it is sufficient that the bottom of sealing ring groove 906 abuts on sealing ring S1, and the inside peripheral surface 103 of fitting recess 101 of housing body 10 abuts on sealing ring S1, and it is optional that the bottom of sealing ring groove 906 and the inside peripheral surface 103 of fitting recess 101 of housing body 10 abut on one another.

<Sealing Performance Enhanced by Portion Applied with No Anodic Oxidation Coating> If the surfaces 102, 103 and 105 of housing body 10 on which sealing rings S1, S2 and S3 abut are formed with an anodic oxidation coating film, the valve timing control apparatus 1 may be subject to a problem that the sealing rings S1, S2 and S3 are not completely in intimate contact with the surfaces 102, 103 and 105, which adversely affects the sealing performance of housing body 10 at the surfaces 102, 103 and 105. This is because an anodic oxidation coating film is an oxidation coating film, having a relatively high surface roughness. Namely, that is because an anodic oxidation coating film is a porous coating film provided with a lot of pores at the surface, unless full pore-sealing treatment is applied after anodic oxidation treatment. In contrast, in the present embodiment, the axial end surfaces of housing body 10 to which the sealing plates 8 and 9 are fixed, namely, the surfaces 102, 103 and 105 of housing body 10 to which the sealing rings S1, S2 and S3 are mounted, are formed with no anodic oxidation coating film. This serves to allow intimate contact between sealing rings S1, S2 and S3 and surfaces 102, 103 and 105 with no clearance therebetween, and thereby enhance the sealing performance of sealing rings S1, S2 and S3. The surfaces 102, 103 and 105 of housing body 10 are sealed by the sealing plates 8 and 9, and in sliding contact with no other member. Accordingly, it is unnecessary to enhance the wear resistance of surfaces 102, 103 and 105. The feature that the surface 102, 103 or 105 is provided with no anodic oxidation coating film and with the base layer of aluminum-based metal material exposed, is effective for eliminating the necessity of further treatment or processing for surfaces 102, 103 and 105, and thereby reducing the manufacturing cost, while maintaining the sealing performance of housing body 10. Specifically, the surface of housing body 10 abutting on sealing ring S3 is a cut surface (X-axis positive side axial end surface 105) that is obtained by the cutting-off operation, and the surfaces of housing body 10 abutting on sealing rings S1 and S2 are surfaces (bottom surface 102 and inside peripheral surface 103 of fitting recess 101 at the X-axis negative side of housing body 10) that are obtained by the carving operation of carving the axial end surface of housing body 10. Since the cutting-off operation and the carving operation are performed after the coating operation, the surfaces 102, 103 and 105 of housing body 10 are formed with no anodic oxidation coating film, so that the base layer is exposed on the surfaces 102, 103 and 105. The surfaces 102, 103 and 105 of housing body 10 are thus adapted to be in intimate contact with sealing rings S1, S2 and S3. The surfaces 102, 103 and 105 of housing body 10, on which the base layer is exposed, may be formed with a coating film other than anodic oxidation coating films, which coating film does not adversely affect the sealing performance, although such construction increases the manufacturing cost due to additional treatment. Even in cases where the surfaces 102, 103 and 105 of housing body 10 to which sealing rings S1, S2 and S3 are mounted are formed with an anodic oxidation coating film, the sealing may be maintained by applying pore-sealing treatment so as to seal the openings of the pores, and thereby reduce the surface roughness. Such construction is disadvantageous in that the additional treatment causes an increase in the manufacturing cost. Moreover, if the pore-sealing treatment is undesirably applied to other portions, the required characteristics of the other portions may be adversely affected. In contrast, the feature according to the present embodiment that at least the open axial ends of housing body 10 are applied with no pore-sealing treatment, is advantageous in reducing the manufacturing cost, while maintaining the sealing performance.

It is sufficient that the open axial ends of housing body 10 abut on the sealing rings, and it is optional that the open axial ends of housing body 10 directly abut on the sealing plates 8 and 9, as discussed above. However, the optional feature is advantageous as follows. Each surface 102 or 105 of housing body 10 is formed with no anodic oxidation coating film, and thereby not hardened, whereas each sealing plate 8 or 9 is formed of a harder material (iron-based metal material) than housing body 10 (aluminum-based metal material). When the sealing plate 8 or 9 are fixed to housing body 10, the intimateness of contact between housing body 10 and sealing plate 8 or 9 can be enhanced by screwing the bolts b1, b2 and b3 tightly so as to bring the housing body 10 and sealing plate 8 or 9 into direct contact with one another. Specifically, the axial end surfaces of the sealing plates (the X-axis negative side surface of front plate 8, and the X-axis positive side surface of rear plate 9) may be formed with slight roughness (with fine projections and depressions) by the manufacturing process, but the projections and depressions at the relatively hard surface are pressed on the relatively soft surface 102 or 105 of housing body 10, so that the relatively soft surface 102 or 105 deforms slightly in conformance with the shape of the projections and recesses. This enhances the intimateness of contact between housing body 10 and sealing plate 8 or 9, and thereby further enhances the sealing performance.

<Sealing Performance Enhanced by Sealing at Journal Portion of Housing> The oil seal OS provided at the outside periphery of cylindrical portion 91 of rear plate 9 of housing HSG serves to seal the clearance between the cylinder head and the outside periphery of the cylindrical portion 91. This serves to prevent that working fluid leaking out to the cylinder head side through the clearance CL shown in FIG. 3 between the inside periphery of cylindrical portion 91 and the outside periphery of camshaft 3a or 3b, or working fluid in the internal combustion engine, leaks through the clearance at the outside periphery of cylindrical portion 91 into contact with timing belt 1010 or other equipment. The feature that the cylindrical portion 91 of rear plate 9 is formed of an iron-based metal material and thereby has a higher wear resistance, is effective for suppressing wear of the outside peripheral surface of cylindrical portion 91 resulting from sliding contact with oil seal OS, and thereby reliably sealing the outside periphery of cylindrical portion 91.

<Sealing Performance Enhanced by Arrangement of Back Pressure Relief Section> In general, in a valve timing control apparatus in which an engaging member in a housing functions to lock the valve timing at engine start, the engaging member can be smoothly released from its engaged state by suitably lowering the back pressure of the engaging member. If the back pressure is lowered by relieving the back pressure directly to the outside of the housing, then working fluid may get in touch with a timing belt that drives the valve timing control apparatus. In order to solve this problem, the back pressure relief section is provided, which relieves the pressure in back pressure chamber 50 into the internal space of the internal combustion engine, and keeps the pressure in back pressure chamber 50 low, while maintaining the sealing performance of housing HSG. The fluid passage for reliving the back pressure of back pressure chamber 50 communicates with the inside of the internal combustion engine, but has no intermediate point that communicates directly with the outside of housing HSG. The back pressure relief section serves to discharge working fluid of back pressure chamber 50 to the internal space of the internal combustion engine, so as to prevent the timing belt 1010 from being degraded by oil, and thereby enhance the durability of timing belt 1010.

<Apparatus Made Compact in Radial Direction by Features of Pulley> The outside periphery of housing body 10 is formed integrally with pulley 100. This feature makes it possible to reduce the diameter of valve timing control apparatus 1, as compared to cases in which a pulley is provided separately from a housing body. The construction that the pulley 100 is formed over the entire axial length of the outside periphery of housing body 10, makes it possible to provide the teeth of pulley 100 with a width enough to engage with timing belt 1010, even if the width of timing belt 1010 is required to be above a predetermined lower limit. Namely, even when the axial length of housing HSG is set as small as the width of timing belt 1010 where rear plate 9 is fixedly inserted in fitting recess 101 of housing body 10, it is possible to provide the teeth of pulley 100 with a width enough to engage with timing belt 1010 and transmit a torque to timing belt 1010

<Apparatus Made Compact in Axial Direction by Formation of Fitting Recess in Housing Body> In valve timing control apparatus 1, the axial ends of housing body 10 are closed and sealed by front plate 8 and rear plate 9 respectively. The construction that the rear plate 9 is fixedly inserted in fitting recess 101 of housing body 10 which is formed at one axial end of housing body 10, makes it possible to reduce the axial size of valve timing control apparatus 1, as compared to cases where front plate 8 and rear plate 9 are simply fixed to the axial end surfaces 104 and 105 of housing body 10 respectively. The construction that the entire axial length of the outside periphery of rear plate 9 in the X-axis direction, i.e. the entire axial length of plate body 90 in the X-axis direction, is fixedly inserted in fitting recess 101, is further advantageous in minimizing the axial size of valve timing control apparatus 1. Rear plate 9 is formed with engaging recess 521 (or recess 900 for fixing the sleeve 52) which extends in the X-axis direction, where engaging recess 521 engages with lock piston 51 which is mounted to move in and out from vane rotor 4 in the X-axis direction. Accordingly, the axial length of rear plate 9 is set larger than that of front plate 8. If the thicker rear plate 9 is simply fixed to the axial end surface of housing body 10, the axial length of the entire valve timing control apparatus 1. According to the present embodiment, the construction that the fitting recess 101 is formed in one axial end of housing body 10, and rear plate 9 (not front plate 8) is fixedly inserted in fitting recess 101, makes it possible to efficiently reduce the axial size of valve timing control apparatus 1. This enhances the flexibility of layout of an engine room to which valve timing control apparatus 1 is mounted. Front plate 8, rear plate 9 and housing body 10 are fixed by the plurality of bolts b1, b2 and b3. The female thread hole into which the male thread of each of bolts b1, b2 and b3 is screwed is required to have a some length. The construction according to the present embodiment that all of engaging recess 521 and the female thread holes are formed in rear plate 9, is further advantageous in minimizing the axial size of valve timing control apparatus 1. Front plate 8 may be formed thinner than rear plate 9, because front plate 8 is formed with no female thread hole, etc. Accordingly, even when front plate 8 is simply fixed to the axial end surface 105 of housing body 10, the axial length of valve timing control apparatus 1 is little increased. On the other hand, the construction that the female thread holes are formed in rear plate 9 which is formed thicker because rear plate 9 is formed with engaging recess 521, and the thicker rear plate 9 is fixedly inserted in fitting recess 101, is advantageous in minimizing the axial size of valve timing control apparatus 1. Engaging recess 521 may be formed in front plate 8, not in rear plate 9. Moreover, housing body 10 may be formed with another fitting recess to which front plate 8 is fixedly inserted. However, in the present embodiment, front plate 8 is simply fixed to the axial side surface 105 of housing body 10, in order to provide lock piston 51 with a required range of movement in the axial direction or provide slide hole 501 of vane rotor 4 with a required length in the X-axis direction.

<Apparatus Made Compact in Radial Direction by Features of Sealing Structure> It is generally difficult to provide a space for a sealing member, in cases where the boundary between the axial end surfaces of housing body 10 and rear plate 9 is sealed, i.e. the boundary between the bottom surface 102 of fitting recess 101 and the X-axis negative side surface of rear plate 9 is sealed. Specifically, as shown in FIG. 6C, the radial length of bottom surface 102 of fitting recess 101 except the portions where first, second and third shoes 11, 12 and 13 are formed, (R−Ri), is short to form a sealing groove where a sealing member is mounted. Accordingly, when the boundary (bottom surface 102 of fitting recess 101) where the axial end surfaces are in contact with each other is provided with an adequate space where a sealing member is mounted or a sealing groove is formed, the diameter of housing body 10 in the radial direction is increased. On the other hand, the length of fitting recess 101 in the X-axis direction and the length of rear plate 9 in the X-axis direction are relatively large so that a sealing member can be mounted or a sealing groove can be formed. Accordingly, the problem described above can be solved by providing a sealing member between the inside periphery of fitting recess 101 and the outside periphery of rear plate 9. However, the radial length (Ro−R) of housing body 10 is small to form a sealing groove in the inside peripheral surface of housing body 10 (inside peripheral surface 103 of fitting recess 101). Accordingly, if the sealing groove is formed in the inside peripheral surface of housing body 10 (inside peripheral surface 103 of fitting recess 101), the radial size of housing body 10 must be increased so as to increase the radial length (Ro−R). In order to solve this problem, the outside periphery of rear plate 9 is formed with sealing ring groove 906 to which sealing ring S1 is mounted, so as to seal the boundary between fitting recess 101 and rear plate 9. This sealing structure makes it possible to reduce the radial length (Ro−R), i.e. the radial thickness of housing body 10, and thereby minimize increase in the radial size of valve timing control apparatus 1, while minimizing the axial size of valve timing control apparatus 1 by the provision of fitting recess 101. On the other hand, the X-axis negative side surfaces of first, second and third shoes 11, 12 and 13 have adequate spaces where sealing members are mounted around bolt holes 110, 120 and 130. Accordingly, rear plate 9 is formed with annular sealing ring grooves 907, 908 and 909 around female thread portions 901, 902 and 903, where annular sealing ring grooves 907, 908 and 909 faces bolt holes 110, 120 and 130, and sealing rings S2 are mounted in annular sealing ring grooves 907, 908 and 909. It is possible as an alternative to prevent working fluid from leaking through the bolt holes of female thread portions 901, 902 and 903 by a construction that the bolt holes of female thread portions 901, 902 and 903 are formed with bottoms, without passing through the rear plate 9. In this case, however, the provision of the bottoms may cause an increase in the axial length of rear plate 9, because the lengths of female thread portions 901, 902 and 903 are increased to maintain the axial lengths of the female threads for bolts b1, b2 and b3. In contrast, according to the present embodiment, the construction that the bolt holes of female thread portions 901, 902 and 903 are formed to extend through the rear plate 9 with no bottoms, is effective for reducing the axial length of rear plate 9. Incidentally, the construction that the recess 900 of rear plate 9 and pin hole 904 have bottoms, causes no increase in the axial length of rear plate 9, because the length of recess 900 in the X-axis direction is only required to allow engagement of lock piston 51, and the length of pin hole 904 in the X-axis direction is only required to allow fixation of the positioning pin 905. This feature is effective for preventing working fluid from leaking from housing HSG to outside without sealing for recess 900 and pin hole 904. On the other hand, the boundary between front plate 8 and housing body 10 includes a space having an adequate radial size where a sealing member can be mounted, because the X-axis positive side surface of housing body 10 is formed with no fitting recess. Specifically, as shown in FIG. 6A, the radial length Ro−Ri of housing body 10 is large enough to mount a sealing member or form a sealing groove. Accordingly, sealing ring S3 is arranged between the contact axial end surfaces of housing body 10 and front plate 8, i.e. between the X-axis negative side surface 105 of housing body 10 and the X-axis positive side surface of front plate 8. For mounting the sealing ring S3, front plate 8 is formed with annular sealing ring groove 89. The sealing groove may be formed in housing body 10, not in front plate 8. However, housing body 10 has an inside space for accommodating the phase change mechanism, and thereby has only a small space (area or thickness) at the axial end which can be formed with a sealing groove, without adversely affecting the strength of housing body 10. On the other hand, sealing plate 8 or 9 is subject to no such requirement, so that it is easy to form the sealing plate 8 or 9 with a sealing groove. The feature according to the present embodiment that the annular sealing ring grooves 907, 908, 909 and 89 are formed in sealing plates 8 and 9, serves to reduce the manufacturing cost of valve timing control apparatus 1. If sealing plates 8 and 9 are formed integrally with sealing grooves by casting, the manufacturing cost is further lowered.

<Apparatus Made Compact by Arrangement of Back Pressure Relief Section> Back pressure chamber 50 is formed at the X-axis positive side of slide hole 501 of vane rotor 4, wherein the tip (or engaging portion 511) of lock piston 51 is arranged to move and project in the X-axis negative direction from vane rotor 4. On the other hand, the internal combustion engine is located on the X-axis negative side of vane rotor 4 and rear plate 9. Accordingly, in order to relieve the internal pressure (oil or air) of back pressure chamber 50 while ensuring the sealing performance of housing HSG, the back pressure relief section needs to include a fluid passage (back pressure hole 407) that passes through the vane rotor 4 in housing HSG from the X-axis positive side axial end to the X-axis negative side axial end. In valve timing control apparatus 1, the fixing portions (bolt holes 403, 404 and 405) are formed in rotor 40 and arranged and spaced from one another in the circumferential direction, which fixing portions serve to fix the vane rotor 4 to camshaft 3a or 3b. Accordingly, the fluid passage (back pressure hole 407) of the back pressure relief section needs to be arranged with no interference with the fixing portions (bolt holes 403, 404 and 405). Moreover, camshaft bolts 33, 34 and 35, which are inserted in bolt holes 403, 404 and 405, respectively, have heads 331, 341 and 351 (including the washers 332, 342 and 352) located at the X-axis positive side surface of vane rotor 4. Accordingly, in cases where the fluid passage (back pressure hole 407) is formed to have an opening at the X-axis positive side surface of vane rotor 4, the fluid passage of the back pressure relief section needs to be arranged with no interference with the heads 331, 341 and 351. In order to satisfy these requirements, it may be conceived that the back pressure hole 407 is located in an annular outside space surrounding the fixing portions (i.e. in a space farther from the axis of rotation O than the farthest point of the inside periphery of each bolt hole 403, 404 or 405, or in a space outside a circle containing and circumscribing the bolt holes 403, 404 and 405 as viewed in the X-axis direction), specifically, in an annular outside space surrounding the heads 331, 341 and 351 of camshaft bolts 33, 34 and 35 (i.e. in a space outside a circle circumscribing the heads 331, 341 and 351). This construction tends to result in an increase in the radial size of rotor 40. In contrast, in the present embodiment, back pressure hole 407 is located radially inside of or closer to the axis of rotation O than the fixing portions (bolt holes 403, 404 and 405), or in the space inside the circle circumscribing the bolt holes 403, 404 and 405, and specifically at the axis of rotation of rotor 40 (at the axis of rotation O). Specifically, since the fixing portions are implemented by bolt holes 403, 404 and 405, camshaft bolts 33, 34 and 35 have heads 331, 341 and 351, and back pressure hole 407 has an opening at the X-axis positive side of rotor 40 in the present embodiment, back pressure hole 407 needs to be located with no interference with heads 331, 341 and 351. The construction according to the present embodiment makes it possible to make the valve timing control apparatus 1 compact, because no space for back pressure hole 407 is needed at the outside space of rotor 40. In other words, the construction according to the present embodiment that the plurality of bolt holes 403, 404 and 405 are formed for insertion of camshaft bolts 33, 34 and 35, provides rotor 40 and camshaft 3a or 3b with a space for back pressure hole 407 at the inside space (including the axis of rotation O) surrounded by the bolt holes 403, 404 and 405, in contrast to cases where a single bolt hole is formed at the axis of rotation. Although back pressure hole 407 is formed in rotor 40 so as to extend through the rotor 40 in the X-axis direction, and located to face the first back pressure passage 31 of camshaft 3a or 3b in the X-axis direction in the present embodiment, this construction may be modified so that the back pressure hole 407 is inclined with respect to the X-axis, and the opening of back pressure hole 407 at the X-axis negative side of rotor 40 faces the first back pressure passage 31 of camshaft 3a or 3b in the X-axis direction. Although the second back pressure passage communicating the back pressure chamber 50 and back pressure hole 407 with one another is composed of radial groove 58 and circular recess 406 in the present embodiment, this construction may be modified so that the second back pressure passage is constituted by a hole extending in vane rotor 4 with inclination. In the modification, back pressure hole 407 may be constructed to have no opening facing the circular recess 406 at the X-axis positive side of rotor 40. The construction according to the present embodiment may be modified so that the X-axis negative side opening of back pressure hole 407 is located distant from the first back pressure passage 31, and one of the X-axis negative side end surface of rotor 40 and the X-axis positive side end surface of camshaft 3a or 3b is formed with a portion such as a groove or recess for communicating the X-axis negative side opening of back pressure hole 407 and the first back pressure passage 31 with one another. This modification makes it possible to locate the back pressure hole 407 independently of the position of first back pressure passage 31, and thereby enhances the flexibility of design. The construction according to the present embodiment that the back pressure hole 407 is formed to extend in the X-axis direction, is advantageous because it is unnecessary to intricately form an inclined hole constituting the back pressure hole 407. The construction that the X-axis negative side opening of back pressure hole 407 is located to face the first back pressure passage 31, is advantageous in the facility of forming and the manufacturing cost, because it is unnecessary to form a groove or recess connecting the back pressure hole 407 and first back pressure passage 31 to one another. However, the construction that the X-axis negative side opening of back pressure hole 407 is located to face the first back pressure passage 31, is subject to a requirement that back pressure hole 407 must be located in consideration of a positional relationship with the fluid passages formed in camshaft 3a or 3b other than first back pressure passage 31. Namely, the first back pressure passage 31, which is formed in camshaft 3a or 3b to extend in the X-axis direction, is required not to overlap with first fluid passages 202 and 212, and second fluid passages 201, 203, 211 and 213 (see FIG. 3) as viewed in the X-axis direction. Accordingly, the X-axis negative side opening of back pressure hole 407 facing the first back pressure passage 31 in the X-axis direction is also required to be located to satisfy the same requirement. For example, if the arrangement that the X-axis negative side opening of back pressure hole 407 is located in the inside space surrounded by bolt holes 403, 404 and 405, is implemented by a construction that that the X-axis negative side opening of back pressure hole 407 is located between bolt holes 404 and 405, or between bolt holes 405 and 403, then it is possible that the first back pressure passage 31 facing the X-axis negative side opening of back pressure hole 407 interferes with first fluid passages 202 and 212, and second fluid passages 201, 203, 211 and 213 in camshaft 3a or 3b. In this viewpoint, the construction that the back pressure hole 407 is located between bolt holes 403 and 404 where first fluid passages 202 and 212, and second fluid passages 201, 203, 211 and 213 are not located, is advantageous. In the present embodiment, first fluid passages 202 and 212 are the closest to the axis of rotation O among all the fluid passages formed in camshaft 3a or 3b, wherein the central axes of first fluid passages 202 and 212, and the central axes of bolt holes 403, 404 and 405 are arranged substantially on the same circle having a center at the axis of rotation O. Accordingly, the construction that the back pressure hole 407 is located in the space that is inside the above circle, and excludes the space of first fluid passages 202 and 212, and bolt holes 403, 404 and 405, makes it possible to avoid interference between back pressure hole 407 and the fluid passages of camshaft 3a or 3b. Specifically, if the X-axis negative side opening of back pressure hole 407 is located radially inside of or closer to the axis of rotation O than first fluid passages 202 and 212, or in the space inside the circle containing and circumscribing the first fluid passages 202 and 212 about the axis of rotation O as viewed in the X-axis direction, then it is unnecessary to adjust the arrangement of fluid passages 202, etc. of camshaft 3a or 3b, wherein the strength of fixation is ensured by the plurality of fixing portions, while expansion of the radial size of rotor 40 is suppressed. In other words, in cases where three or more fixing portions (bolt holes) are arranged and spaced from one another in the circumferential direction so that three or more intermediate spaces are defined between the fixing portions as in the present embodiment, a pair of advance-side and retard-side fluid passages formed in camshaft 3a or 3b are located in two of the intermediate spaces so that one intermediate space remains in which no fluid passage is formed. The remaining intermediate space is available for provision of back pressure hole 407 (and first back pressure passage 31). For example, back pressure hole 407 (and first back pressure passage 31) may be located between bolt holes 403 and 404 in the circumferential direction, which is advantageous in reducing the distance between back pressure hole 407 and back pressure chamber 50. For example, circular recess 406 may be omitted, wherein radial groove 58 is extended inwardly in the radial direction and connected to both of back pressure hole 407 and back pressure chamber 50. More specifically, in the present embodiment, back pressure hole 407 is located at the axis of rotation of rotor 40. This feature serves to enhance the balance of vane rotor 4 around the axis of rotation O. This feature further makes it possible to ensure the radial thickness of rotor 40, and thereby enhance the strength of rotor 40 formed with bolt holes 403, 404 and 405, because the distance between back pressure hole 407 and the outside periphery of rotor 40 is constant as followed along the outside periphery of rotor 40. The feature still further makes it possible to easily arrange the bolt holes 403, 404 and 405 evenly spaced in the circumferential direction around the axis of rotation, and thereby further enhance the balance of vane rotor 4 around the axis of rotation.

It is advantageous that the diameter of back pressure hole 407 is set as small as possible, because the small diameter of back pressure hole 407 makes it possible to enhance the flexibility of layout of back pressure hole 407, and make rotor 40 compact. However, if the size of back pressure hole 407 in the X-axis direction in rotor 40 is large, the facility of forming is lowed because it is generally difficult to form a narrow long hole. In the present embodiment, rotor 40 is formed with circular recess 406 and camshaft insertion hole 402 having a bottom, wherein back pressure hole 407 extends through the rotor 40, and has an opening at the bottom of each of circular recess 406 and camshaft insertion hole 402. Namely, the length of back pressure hole 407 in the X-axis direction is reduced by the depth of camshaft insertion hole 402 and the depth of circular recess 406, which makes it easy to form the rotor 40 with back pressure hole 407. In this way, the construction according to the present embodiment is advantageous in enhancing the facility of forming of back pressure hole 407, and makes rotor 40 compact by forming the back pressure hole 407 with a relatively small diameter (smaller than the diameter of first back pressure passage 31 of camshaft 3a or 3b).

The feature that the first back pressure passage 31 communicating with the oil-lubricated space of the internal combustion engine is formed in camshaft 3a or 3b, makes it possible to make valve timing control apparatus 1 compact, as compared to cases where a back pressure passage is provided separately and arranged outside (for example, at the outside periphery) of camshaft 3a or 3b. This feature serves to eliminate the necessity of increasing the diameter of the portion of valve timing control apparatus 1 that is connected to the internal combustion engine, i.e. the diameter of the cylindrical portion 91 provided with oil seal OS that is disposed between cylindrical portion 91 and the cylinder head. Moreover, it is possible to avoid interference between first back pressure passage 31 and groove 204 or 214. Specifically, first back pressure passage 31 is formed at the axis of rotation (axis of rotation O) of camshaft 3a or 3b so to face the X-axis negative side opening of back pressure hole 407. This feature serves to maintain the balance of camshaft 3a or 3b about the axis of rotation, and makes it possible to easily connect the first back pressure passage 31 and the fluid passages that are formed in camshaft 3a or 3b for lubrication, because the fluid passages are located at the axis of rotation O in many cases. Moreover, the location of first back pressure passage 31 according to the present embodiment is advantageous in the strength of camshaft 3a or 3b, and makes it easy to form the first back pressure passage 31, even if the length of first back pressure passage 31 is relatively large. This feature enhances the flexibility of layout of first fluid passages 202, etc. in camshaft 3a or 3b. Namely, since there are remaining a lot of even spaces around first back pressure passage 31 in camshaft 3a or 3b, the first fluid passage 202, etc. can be located in any space of the remaining spaces. Incidentally, in contrast to rotor 40 that is subject to demand for compactness, camshaft 3a or 3b is subject to no such demand, so that the diameter of first back pressure passage 31 may be larger than that of back pressure hole 407, which is advantageous in that first back pressure passage 31 can be more easily formed than back pressure hole 407.

With regard to the back pressure relief section, the second back pressure relief passage is formed in vane rotor 4, so that valve timing control apparatus 1 can be made compact. Specifically, radial groove 58 and circular recess 406 constituting the second back pressure relief passage are formed at the X-axis positive side axial end surface of vane rotor 4. On the other hand, front plate 8 is formed with no recess nor groove constituting the second back pressure relief passage. Accordingly, the axial size of valve timing control apparatus 1 can be reduced, because it is unnecessary to increase the thickness of housing HSG for formation of such a recess or groove. On the other hand, the size of vane 41, 42 or 43 in the X-axis direction is unchanged through formation of the second back pressure relief passage. This serves to maintain the pressure-receiving area of vane rotor 4 against working fluid, and thereby maintain the ability of operation of vane rotor 4. Circular recess 406 is formed with bolt holes 403, 404 and 405 in addition to back pressure hole 407. In other words, circular recess 406 serves to provide a space accommodating the heads 331, 341 and 351, and constitute the back pressure relief section. The construction that the heads 331, 341 and 351 are accommodated in circular recess 406 is advantageous because the heads 331, 341 and 351 do not project excessively from the axial end surface of vane rotor 4 in the X-axis positive direction toward the front plate 8. Cap 7 is formed with recess 73 at the surface facing the circular recess 406, wherein the recess 73 accommodates the heads 331, 341 and 351 that project from the axial end surface of vane rotor 4. Namely, as shown in FIG. 3, part of each head 331, 341 or 351 extends into recess 73. This feature makes it possible to reduce the axial size of valve timing control apparatus 1. Circular recess 406 may be replaced by forming the rotor 40 with a plurality of recesses each of which accommodates a corresponding one of heads 331, 341 and 351. In other words, circular recess 406 may be modified to have a non-circular shape. However, circular recess 406 is advantageous in the facility of forming, and in reducing the inertial mass of vane rotor 4, because a relatively large portion is removed to form the circular recess 406. Circular recess 406 may be omitted, wherein the back pressure relief section is implemented, for example, by a construction that the radial groove 58 is extended toward the axis of rotation O, and connected to back pressure hole 407.

<Guiding for Timing Belt> A pulley that includes projections and depressions extending in the axial direction can be subject to a problem that a timing belt tends to move in the axial direction with respect to the pulley. In intake valve timing control apparatus 1a, the front plate 8, which is provided at the X-axis positive side of housing HSG, serves as a belt guide to restrict movement of timing belt 1010 in the X-axis direction. Specifically, the construction that the outside periphery 80 of front plate 8 projects outwardly in radial directions with respect to the bottom of each depression of pulley 100, and has an outside edge that is located outside of the roots of teeth of pulley 100, serves to prevent the timing belt 1010 from moving in the X-axis positive direction, wherein the movement of timing belt 1010 is obstructed by the outside periphery 80 of front plate 8. The outside edge of the outside periphery 80 of front plate 8 is located radially outside of the outside edge of timing belt 1010 putted on pulley 100, so that front plate 8 serves more effectively as a belt guide to restrict the movement or deviation of timing belt 1010. This feature is optional, because it is sufficient that the construction that the outside periphery 80 of front plate 8 projects outwardly in radial directions with respect to the bottom of each depression of pulley 100. It is sufficient that the outside periphery 80 of front plate 8 includes at least a portion projecting outwardly in radial directions with respect to the bottom of a depression of pulley 100, where the portion is within a range where timing belt 1010 and pulley 100 are in contact with one another (in an angular range of about 90 degrees in intake valve timing control apparatus 1a in FIG. 1). It is optional that the entire outside periphery 80 of front plate 8 projects outwardly in radial directions with respect to the bottom of each depression of pulley 100. The restriction of movement of timing belt 1010 in the X-axis positive direction results also in restricting the movement of timing belt 1010 in the X-axis negative direction, and preventing the timing belt 1010 from dropping from pulley 100. Namely, it is sufficient that the belt guide is provided at at least one axial end of pulley 100, and it is optional that the belt guide is provided at another axial end of pulley 100. Although exhaust valve timing control apparatus 1b is provided with no belt guide, the movement of timing belt 1010 can be restricted by the belt guide of intake valve timing control apparatus 1a, wherein timing belt 1010 is putted on both of intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b.

<Mountability Enhanced> In recent years, motor vehicles are subject to increasing demand for compactness in size, while internal combustion engines are provided with an increasing number of auxiliary devices. For compactness, an engine and auxiliary devices are arranged efficiently in an engine room, wherein the remaining space is minimized. Accordingly, it is desirable to make a valve timing control apparatus compact by designing dimensions in millimeter so that the valve timing control apparatus can be mounted efficiently in an engine room. For example, if a valve timing control apparatus is arranged close to a side wall of an engine, and is provided with a belt guide that can interfere with the side wall, it is desirable to enhance the mountability of the valve timing control apparatus. In order to solve this problem, in the present embodiment, the belt guide is provided in intake valve timing control apparatus 1a which is farther from the engine room side wall W than exhaust valve timing control apparatus 1b, and is attached to intake camshaft 3a which is farther from the engine room side wall W than exhaust camshaft 3b. In other words, no belt guide is provided in exhaust valve timing control apparatus 1b which is closer to the engine room side wall W than intake valve timing control apparatus 1a, and is attached to exhaust camshaft 3b which is closer to the engine room side wall W than intake camshaft 3a. This feature serves to avoid interference with the engine room side wall W, and thereby enhance the mountability of valve timing control apparatus 1. In the present embodiment, where the engine room side wall W includes the projection W1, the exhaust valve timing control apparatus 1b, which is disposed outside in the width direction of the cylinder block, tends to be close to the projection W1 in the X-axis direction as shown in FIG. 15, or in the direction perpendicular to the X-axis direction as shown in FIG. 1. Particularly, the ends of exhaust valve timing control apparatus 1b in the X-axis direction tend to interfere with the projection W1. This problem is solved by the construction according to the present embodiment that each depression of pulley 100 of exhaust valve timing control apparatus 1b is opened at both ends in the X-axis direction. This construction serves to reduce the possibility of interference between the outside portion (specifically, the ends in the X-axis direction) of exhaust valve timing control apparatus 1b and the projection W1 of engine room side wall W, however the projection W1 is shaped. In contrast to the case of intake valve timing control apparatus 1a, the construction that the front plate 8 of exhaust valve timing control apparatus 1b has no portion or no belt guide that projects outwardly in a radial direction with respect to the bottom of a depression of pulley 100, and each depression of pulley 100 is fully opened at the X-axis positive side end, serves to avoid interference with the projection W1. Each depression of pulley 100 of exhaust valve timing control apparatus 1b is fully opened also at the X-axis negative side end, which serves to avoid interference with the projection W1. These features serve to enhance the flexibility of layout of the engine room in which valve timing control apparatus 1 is mounted. According to the present embodiment, the mountability of exhaust valve timing control apparatus 1b is enhanced, especially for vehicles in which severe dimensional requirements are present about the X-axis positive side of exhaust valve timing control apparatus 1b (the side farther from the cylinder block, or the camshaft tip side). This is because the movement of timing belt 1010 in the X-axis positive direction is restricted more effectively than in the X-axis negative direction, where intake valve timing control apparatus 1a is provided with the belt guide closer to front plate 8 at the X-axis positive side. If intake valve timing control apparatus 1a is provided with the belt guide closer to rear plate 9 at the X-axis negative side, then the mountability of exhaust valve timing control apparatus 1b is enhanced especially for vehicles in which severe dimensional requirements are present about the X-axis negative side of exhaust valve timing control apparatus 1b (the side closer to the cylinder block, or the camshaft root side). Incidentally, even if each depression of pulley 100 is not fully but partly opened at the X-axis positive side end, the advantageous effect described above can be achieved to some extent, although it is smaller. Specifically, even in cases where the diameter of front plate 8 of exhaust valve timing control apparatus 1b is larger than in the present embodiment, so as to form a belt guide, the interference between the projection W1 and the belt guide can be avoided to some extent, if the maximum diameter of the belt guide is smaller than the diameter of tooth top circle of pulley 100. Moreover, even in cases where the diameter of front plate 8 of exhaust valve timing control apparatus 1b is larger than in the present embodiment, so as to form a belt guide for completely closing the X-axis positive side of each depression of pulley 100, the interference between the projection W1 and the belt guide can be avoided to some extent, if the belt guide does not project outwardly with respect to the outside surface of timing belt 1010 putted on pulley 100, although the effect is smaller. This is because the diameter of this exhaust valve timing control apparatus 1b is still smaller than that of intake valve timing control apparatus 1a, so as to make it possible to reduce the width of the unit of the internal combustion engine, intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b are mounted, and thereby enhance the flexibility of layout in the engine room, as compared to cases where exhaust valve timing control apparatus 1b is provided with a belt guide that is identical to that of intake valve timing control apparatus 1a, i.e. a belt guide projecting outwardly with respect to timing belt 1010.

The construction according to the present embodiment that the intake valve timing control apparatus 1a farther from the engine room side wall is provided with the belt guide is adapted to a V-type DOHC engine in which a pair of cylinder banks are arranged in a V-shape spreading from the crankshaft, and each cylinder bank is provided with an intake camshaft and an exhaust camshaft, wherein intake valve timing control apparatus 1a is attached to the intake camshaft, and exhaust valve timing control apparatus 1b is attached to the exhaust camshaft. However, this construction may be adapted to another type engine, such as a straight-type engine, thus producing similar advantageous effects. As in the present embodiment, a general V-type engine is subject to more severe requirements than other type engines, because auxiliary devices mounted to the sides of the V-type engine project toward an engine room side wall, and the size of the V-type engine itself tends to increase in recent years. The present embodiment is adapted to such a V-type engine, in which intake valve timing control apparatus 1a farther from the engine room side wall W is provided with a belt guide. This feature is effective for enhancing the mountability of the valve timing control apparatus, especially for V-type engines that are subject to more severe requirements. Specifically, in each cylinder bank, only intake valve timing control apparatus 1a, which is attached to one of intake camshaft 3a and exhaust camshaft 3b closer to the other cylinder bank, i.e. attached to intake camshaft 3a, is provided with a belt guide, wherein intake camshaft 3a closer to the other cylinder bank is inside of exhaust camshaft 3b in the width direction of the cylinder block, and farther from the engine room side wall W. In other words, exhaust valve timing control apparatus 1b, which is attached to exhaust camshaft 3b that is outside of intake camshaft 3a in the width direction of the cylinder block, is provided with no belt guide, so that each depression of pulley 100 is opened at both longitudinal ends. This construction is applied to each cylinder bank in the present embodiment, but may be applied only one cylinder bank. Although the single timing belt 1010 is wound around intake valve timing control apparatuses 1a and exhaust valve timing control apparatuses 1b at both cylinder banks so that the timing belt 1010 drives both of intake camshaft 3a and exhaust camshaft 3b in the present embodiment, this construction may be modified so that two timing belts are provided each of which is driven by the crankshaft and wound around intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b of a corresponding one of the cylinder banks, and each of which drives intake camshaft 3a and exhaust camshaft 3b of the corresponding cylinder bank. In cases where a V-type engine is mounted in an engine room so that camshafts extend in a direction that crosses a vehicle longitudinal direction, for example, the camshafts extend in a direction perpendicular to the vehicle longitudinal direction as in the present embodiment, exhaust valve timing control apparatus 1b, which is provided outside in the width direction of the cylinder block, projects toward a front or rear side wall of the engine room. This construction is subject to severe requirements for dimensional management. In the present embodiment, of intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b attached to the V-type engine, only intake valve timing control apparatus 1a is provided with a belt guide, which serves to solve the disadvantage in the mountability. Incidentally, the construction according to the present embodiment may be adapted to an engine of an arbitrary type in which a camshaft extends in a vehicle longitudinal direction, or extends in a diagonal direction with respect to the vehicle longitudinal direction.

<Manufacturing Cost Reduced by Mirror Image Arrangement> Intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b are constituted by the common third workpiece P3 for housing body 10, and the common second workpiece Q2 for vane rotor 4. Housing body 10 and vane rotor 4 of intake valve timing control apparatus 1a, and housing body 10 and vane rotor 4 of exhaust valve timing control apparatus 1b, are formed as mirror images of each other, by application of carving to respective ones of the opposite surfaces (side A, or side B) of the common extrusions (P3, Q2). This feature serves to simplify the process of manufacturing, and thereby reduce the manufacturing cost. Moreover, vane rotor 4 and housing body 10 of exhaust valve timing control apparatus 1b are transformed into mirror images, and the stoppers are arranged in mirror positions, to constitute the intake valve timing control apparatus 1a. This feature allows the first stopper mechanism of each of intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b functions at the initial position, where the first stopper mechanism has a larger contact area, as shown in FIGS. 4 and 16, and thereby prevents the stopper mechanisms from deforming and changing the rotation limit position.

<Manufacturing Cost Reduced by Extrusion Forming> The components (housing HSG, vane rotor 4) of valve timing control apparatus 1 may be formed by an operation other than extrusion, such as die-casting. The formation by extrusion according to the present embodiment makes mass production easy. In the case of housing body 10, a plurality of base workpieces (third workpieces P3) are formed simultaneously by obtaining a long continuous member (first workpiece P1, second workpiece P2), and dividing it. In this way, many base workpieces (third workpieces P3) are obtained by a few steps, and commonly used to construct the intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b. This is effective for further simplifying the process of manufacturing, and thereby reducing the manufacturing cost. The feature according to the present embodiment that the pulley 100 of housing body 10 is constituted by a plurality of projections which are arranged in the circumferential direction, and extend in the axial direction, makes it possible to form the pulleys 100 of a plurality of housing bodies 10 simultaneously by the extrusion operation in the form of first workpiece P1, where it is unnecessary to form the pulley 100 of each housing body 10 one by one. This feature makes it possible to reduce the workload, and make the forming easy, and reduce the cost of forming. For example, if die-casting such as high-pressure die-casting is used for forming the housing body 10, it is impossible to eliminate a tapered shape which is provided so that a formed material can be drawn from a mold. If the outside periphery of housing body 10 has a tapered shape, when housing body 10 is formed integrally with pulley 100, it is difficult to form the projections or teeth of pulley 100 with high accuracy. On the other hand, according to the present embodiment, housing body 10 is formed by extrusion, and formed with no tapered shape, so that it is possible to form the pulley 100, etc. with high accuracy. In the case of vane rotor 4, a plurality of base workpieces (second workpieces Q2) are formed simultaneously by obtaining a long continuous member (first workpiece Q1), and dividing it. In this way, many base workpieces (second workpieces Q2) are obtained by a few steps, and commonly used to construct the intake valve timing control apparatus 1a and exhaust valve timing control apparatus 1b. This is effective for further simplifying the process of manufacturing, and thereby reducing the manufacturing cost.

<Manufacturing Cost Reduced by Features of Manufacturing Process> The manufacturing process for manufacturing the components of valve timing control apparatus 1 according to the present embodiment is characterized at least in the order of operations constituting the manufacturing process, and serves to reduce the manufacturing cost as follows. According to the present embodiment, housing body 10 is manufactured by the process including the extrusion operation, the coating operation, and the cutting-off operation (and the carving operation) which are performed in this order. Accordingly, first workpiece P1 is applied with surface treatment, before first workpiece P1 is cut and divided into a plurality of second workpieces P2. If the extrusion operation, the cutting-off operation (and the carving operation), and the coating operation are performed in this order, it is necessary to apply each second workpiece P2 with anodic oxidation treatment one by one, which increases the workload and time, and thereby increases the manufacturing cost. This supposed process is subject to a further problem that for maintaining the sealing performance by ensuring the intimate contact between housing body 10 and sealing rings S1, S2 and S3, the open end surfaces 105, 102 and 103 of housing body 10 need to be applied with full pore-sealing treatment at the anodic oxidation coating film or treatment of removing the anodic oxidation coating film. Namely, it is necessary to apply surface treatment to the surfaces of each second workpiece P2 one by one, which surfaces face the sealing plates 8 and 9, and abut on the sealing rings S1, S2 and S3. This increases the cost of forming (workload, and time). In contrast, the forming process according to the present embodiment that the entire first workpiece P1 which is obtained by extrusion is applied with anodic oxidation treatment at one time, is advantageous in reducing the cost of forming. Moreover, the feature according to the present embodiment that the cut surfaces obtained by the cutting-off operation are used without further treatment, to constitute surfaces abutting on the sealing rings S1, S2 and S3. Specifically, housing body 10 is formed in a shape having openings at axial ends by the extrusion operation and the cutting-off operation. For sealing the openings of housing body 10, sealing rings S1, S2 and S3 are provided between housing body 10 and respective ones of sealing plates 8 and 9. One axial end surface (the X-axis positive side cut surface 105) of housing body 10 obtained by the cutting-off operation is used as a surface abutting on the sealing ring S3. The feature that the cut surface 105 is formed with no anodic oxidation coating film, serves to ensure the intimate contact with sealing ring S3, and thereby maintain the sealing performance. This feature serves to eliminate the necessity of full pore-sealing treatment or the like for the anodic oxidation coating film at the X-axis positive side end of housing body 10, and further reduce the cost of forming. The feature that the cut surface 105 where the base layer of aluminum-based metal material is exposed is applied with no further surface treatment, and used to abut on the sealing ring S3, is advantageous in eliminating the necessity of treatment for forming a coating film for maintaining the sealing performance, and thereby further reducing the cost of forming. The forming process according to the present embodiment includes the carving operation of carving the other axial end surface (the X-axis negative side open end surface) of housing body 10. Similar to the cut surfaces obtained by the cutting-off operation, the cut surfaces obtained by the carving operation are formed with no anodic oxidation coating film, so that the sealing rings can be arranged to abut on any place in the cut surfaces. This serves to reduce the cost of forming, while maintaining the sealing performance. In other words, this feature serves to maintain the sealing performance however the axial end surface of housing body 10 is shaped, and thereby enhance the flexibility of design. In the present embodiment, the X-axis negative side longitudinal end surface 104 of housing body 10 is applied with carving to form the fitting recess 101 in which rear plate 9 is fixedly inserted. This is advantageous in making the valve timing control apparatus 1 compact in the axial direction. Since the fitting recess 101 obtained by carving is formed with no anodic oxidation coating film, the intimate contact with sealing ring S1 is well maintained. Of second workpieces P2 of housing bodies 10 obtained through the cutting-off operation, the second workpiece P2 of housing body 10 that is obtained from one longitudinal end of first workpiece P1 is formed with an anodic oxidation coating film at one axial end through the coating operation. For this housing body 10, at least part of this anodic oxidation coating film is removed during the carving operation at the axial end surface, and adapted to abut on the sealing rings S1 and S2, thus maintaining the sealing performance. Incidentally, both of the axial end surfaces of housing body 10 may be applied with carving for forming a recess in which a sealing plate is inserted. The carving operation may be omitted, where the cut surfaces obtained by the cutting-off operation can be used as surfaces abutting on the sealing rings. On the other hand, vane rotor 4 is manufactured by the process including the extrusion operation, the cutting-off operation, the carving operation, and the coating operation, which are performed in this order. This feature is advantageous in that the sliding portions of the surface of vane rotor 4 can be formed with an anodic oxidation coating film simultaneously, and the vane rotor 4 can be thus easily formed to have enhanced hardness and wear resistance. Specifically, during the forming process, first, second and third vanes 41, 42 and 43, and boss portion 401 of rotor 40 are formed, and thereafter the entire surface of vane rotor 4 is applied with anodic oxidation treatment. Accordingly, the single coating operation is sufficient for applying anodic oxidation treatment to the surface of each vane 41, 42 or 43 in sliding contact with housing HSG, the surface of each axial end surface of vane rotor 4 in sliding contact with sealing plate 8 or 9, and the surface of boss portion 401 in sliding contact with housing HSG. This makes it possible to easily manufacture the valve timing control apparatus 1 in which the sealing member 502 is prevented from being mounted in slide hole 501 with inclination, or wear of vane rotor 4 resulting from sliding motion of flange 513 of lock piston 51 is suppressed. Incidentally, it is conceivable that the sealing performance at the boundary between advance chamber A1, A2 or A3 and retard chamber R1, R2 or R3 may be lowered due to the feature that the outside periphery of vane rotor 4 and the inside periphery of housing body 10, including the portions in sliding contact with sealing member 118 and sealing member 413, are formed with anodic oxidation coating. However, this feature is relatively insignificant, because this sealing place is not subject to severe requirements as the boundary between the inside and outside of housing HSG (at the axial ends of housing body 10).

<Manufacturing Cost Reduced by Facility of Attachment> The initial phase of camshaft 3a or 3b with respect to the crankshaft is set by the positioning means (positioning pin 45, etc.) during attachment of valve timing control apparatus 1. First, the following describes a process of attaching the valve timing control apparatus 1 to the internal combustion engine, before describing advantageous effects. The attaching process is implemented by attaching an assembly unit without cap 7 to camshaft 3a or 3b, and then fixing the cap 7 to the assembly unit. The attaching process is started by an operation of inserting the axial end portion 30 of camshaft 3a or 3b from the X-axis negative side into the through hole 92 of housing HSG, and inserting and setting same into camshaft insertion hole 402 of vane rotor 4 mounted in housing HSG of the assembly unit. The attaching process proceeds to an operation of inserting and setting the camshaft bolts 33, 34 and 35 from the X-axis positive side through the large-diameter hole 81 of housing HSG into bolt holes 403, 404 and 405 of vane rotor 4, and into bolt holes 32 of camshaft 3a or 3b. Then, the attaching process proceeds to an operation of setting the sealing ring S4 in annular sealing ring groove 821, and fixing the cap 7 to the female thread portion 82 of housing HSG so as to close the large-diameter hole 81. The provision of annular sealing ring groove 821 serves to easily retain the sealing ring S4 in position, and enhance the facility of assembling. The bottom of camshaft insertion hole 402 is formed with recess 44. The axial end surface 300 includes the opening of first fluid passage 212 in which positioning pin 45 is fixedly inserted, thus forming a projection. When the axial end portion 30 of camshaft 3a or 3b is set in camshaft insertion hole 402, the projection (positioning pin 45) is fitted in recess 44, and the axial end portion 30 is inserted toward the bottom of camshaft insertion hole 402, so as to make the axial end surface 300 abut on the bottom of camshaft insertion hole 402. The fitting between positioning pin 45 and recess 44 serves to restrict the relative rotation between vane rotor 4 and camshaft 3a or 3b, and thus position the vane rotor 4 and camshaft 3a or 3b with one another in the rotational direction, and thereby set the rotational phase of camshaft 3a or 3b (vane rotor 4) with respect to the crankshaft (housing HSG). In this way, positioning pin 45 serves as a blind plug closing the first fluid passage 212, and also serves as a positioning means in combination with recess 44. Positioning pin 45 (in first fluid passage 212) and recess 44 constitute a positioning means for the rotational position of vane rotor 4 with respect to camshaft 3a or 3b, i.e. the rotational phase of camshaft 3a or 3b with respect to the crankshaft, when valve timing control apparatus 1 is attached to camshaft 3a or 3b. Incidentally, the cross-section of recess 44 is not limited to an elliptic shape, but may have a different shape, such as a circular shape, if recess 44 is adapted to be fitted to positioning pin 45 for restricting the relative rotation. However, the construction according to the present embodiment that recess 44 has an elliptic cross-section, makes it easy to fit the positioning pin 45 with recess 44, because recess 44 is provided with a margin in the radial direction of rotor 40 so that errors in manufacturing and the like can be absorbed. First fluid passage 212 serves as a passage of working fluid, and also serves as a hole for fixing the positioning pin 45. This feature is advantageous in eliminating the necessity of an additional operation of forming the axial end portion 30 with a projection for positioning, and thereby reducing the manufacturing cost. Since the opening of first fluid passage 202 of camshaft 3a or 3b at the axial end surface 300 is in intimate contact with and closed by the bottom of camshaft insertion hole 402, it is unnecessary to provide a blind plug for closing the opening. This serves to reduce the number of parts, and the manufacturing cost. Incidentally, the positioning means may be implemented by a construction that the bottom of camshaft insertion hole 402 is formed with a projection which is adapted to be fitted in a recess of the axial end surface 300 (for example, the opening of first fluid passage 212). However, the construction according to the present embodiment that the axial end surface 300 is formed with the projection for positioning is advantageous in ease of assembling operation, as compared to the case of the construction that the bottom of camshaft insertion hole 402 is formed with a projection. The projection for positioning is implemented by a combination of a pin hole and a pin in the present embodiment, but may be implemented by machining or the like. However, the form according to the present embodiment is advantageous in making it possible to arbitrarily select a pin that is suitable for positioning, as compared to the case of direct formation based on machining or the like. The recess for positioning is constituted by the opening of the fluid passage in the present embodiment, but may be implemented by a recess that is formed by machining or the like.

The provision of boss portion 401 makes it easy to attach the valve timing control apparatus 1 to an existing engine. In cases where a housing is directly rotatably supported by a camshaft, attachment of a valve timing control apparatus to an engine needs to be implemented by attaching a vane rotor to the camshaft while checking a clearance between the housing and the camshaft, which may be disadvantageous in ease of assembling operation. Moreover, it is further necessary to change the design in conformance with the attachment, for example, by extending the end portion of the camshaft, so that the housing is suitably rotatably supported by the end portion of the camshaft, and thereby it is difficult to attach the valve timing control apparatus 1 to an existing engine. In contrast, the feature according to the present embodiment that the attachment of the valve timing control apparatus 1 to the engine is implemented by inserting the boss portion 401 into the through hole 92, and then inserting the axial end portion 30 of camshaft 3a or 3b, is advantageous in ease of inserting operation, because the axis of rotation of vane rotor 4 is suitably positioned to be identical to the axis of rotation of housing HSG. Namely, it is unnecessary to care about whether camshaft 3a or 3b is accurately positioned with a predetermined clearance with housing HSG, because the insertion of axial end portion 30 into camshaft insertion hole 402 serves to mechanically position the axis of rotation of vane rotor 4 to be identical to the axis of rotation of housing HSG, and thereby it is easy to attach the vane rotor 4 to camshaft 3a or 3b. Moreover, the feature that the housing HSG is rotatably supported by boss portion 401 in a predetermined angular range beforehand, makes it unnecessary to change the design in conformance with the attachment, for example, by extending the end portion of the camshaft, so that the housing is suitably rotatably supported by the end portion of the camshaft. In this way, valve timing control apparatus 1 can be easily attached to an existing engine.

The feature that the front plate 8 is provided with the detachable cap 7, makes it easy to turn and engage the camshaft bolts 33, 34 and 35. Specifically, while valve timing control apparatus 1 is being attached, the assembly unit without cap 7 is attached to camshaft 3a or 3b so that housing HSG has an opening (large-diameter hole 81) at one axial end, through which the camshaft bolts 33, 34 and 35 can be inserted, and turned to fix the assembly unit (vane rotor 4) to camshaft 3a or 3b. Thereafter, the opening of housing HSG is closed by cap 7. Incidentally, when attached to housing HSG, the cap 7 faces the circular recess 406 of vane rotor 4, and faces the heads 331, 341 and 351 of camshaft bolts 33, 34 and 35, and thereby serves to prevent working fluid from leaking from the back pressure relief section, and serves with the recess 73 to accommodate the heads 331, 341 and 351 of camshaft bolts 33, 34 and 35.

The following describes a first group of technical features, and advantageous effects produced by the features. Japanese Patent Application Publication No. 5-113112 discloses a valve timing control apparatus for an internal combustion engine, which includes a housing connected to a crankshaft, and a phase change mechanism mounted in the housing, and connected to a camshaft. The housing is formed with a pulley at its outside periphery to which torque is transmitted from the crankshaft through a timing belt that is wound around the pulley, so that the housing rotates in synchronization with the crankshaft. The phase change mechanism operates in response to supply and drainage of working fluid, for changing valve timing, i.e. rotational phase of the camshaft with respect to the crankshaft. The valve timing control apparatus described above is subject to a problem that the timing belt may be degraded by adhesion of working fluid exiting out of the housing. Accordingly, it is desirable to provide a valve timing control apparatus for an internal combustion engine in which such a problem is solved by suitable sealing. The problem is solved by a valve timing control apparatus comprising: a housing body having a tubular shape including an opening at an axial end; a sealing plate closing the opening of the housing body; and a sealing ring disposed between the housing body and the sealing plate; wherein an anodic oxide coating film layer is absent at a surface of the housing body in contact with the sealing ring. This feature serves to suitably maintain the sealing performance. The following describes each technical feature, and advantageous effects produced by the feature in detail.

<1-1> A valve timing control apparatus for an internal combustion engine, comprises: a housing body (10) having a tubular shape including an opening at an axial end (105), wherein the housing body (10) is formed integrally with a pulley (100) at an outside periphery of the housing body (10), and wherein the pulley (100) is adapted to receive torque from a crankshaft of the internal combustion engine; a sealing plate (8, 9) fixed to the axial end (104, 105) of the housing body (10), the sealing plate (8, 9) closing the opening of the housing body (10); a phase change mechanism (vane rotor 4) mounted in the housing body (10), and adapted to change a rotational phase of a camshaft (3a, 3b) of the internal combustion engine with respect to the housing body (10) in response to supply and drainage of working fluid; and a sealing ring (S1, S2, S3) disposed between the housing body (10) and the sealing plate (8, 9), wherein: the housing body (10) is formed of an aluminum-based metal material and anodized, wherein the housing body (10) includes a base layer and an anodic oxide coating film layer; and the anodic oxide coating film layer is present at the outside periphery of the housing body (10), and absent at a surface (axial end surface 105, bottom surface 102, inside peripheral surface 103) of the housing body (10) on which the sealing ring (S1, S2, S3) abuts. The feature that the housing body (10) is formed integrally with the pulley (100), serves to reduce the radial size of the valve timing control apparatus (1). The feature that the housing body (10) is formed of the aluminum-based metal material, serves to reduce the weight of the valve timing control apparatus (1). The feature that the housing body (10) is anodized and the anodic oxide coating film layer is present at the outside periphery of the housing body (10), serves to enhance the wear resistance of the pulley (100). The feature that the anodic oxide coating film layer is absent at the surface (axial end surface 105, bottom surface 102, inside peripheral surface 103) of the housing body (10) on which the sealing ring (S1, S2, S3) abuts, serves to maintain the sealing performance, and suppress degradation of a timing belt (1010) put over the pulley (100).

<1-2> In addition to the feature <1-1>: the housing body (10) has a hollow cylindrical shape, wherein the housing body (10) is formed integrally with a shoe (11, 12, 13) at an inside periphery of the housing body (10), and wherein the shoe (11, 12, 13) projects inwardly in a radial direction of the housing body (10); the phase change mechanism (4) includes a vane rotor (4) adapted to be fixed to a camshaft (3a, 3b) of the internal combustion engine, and rotatably mounted in the housing body (10), wherein the vane rotor (4) includes a vane (41, 42, 43), wherein the vane (41, 42, 43) defines a working fluid chamber (advance chamber A1, A2 or A3, retard chamber R1, R2 or R3) between the vane (41, 42, 43) and the shoe (11, 12, 13), and wherein the working fluid chamber (A1, A2, A3, R1, R2, R3) is adapted to supply and drainage of working fluid; and the sealing ring (S1, S2) seals the working fluid chamber (A1, A2, A3, R1, R2, R3) at the axial end (104, 105) of the housing body (10). The feature <1-1> can be thus adapted to the valve timing control apparatus provided with the vane-type phase change mechanism (4).

<1-3> In addition to the feature <1-1>, the sealing ring (S1, S2, S3) abuts on the base layer at the axial end (104, 105). This feature serves to reduce the workload of manufacturing the housing body (10), and thereby reduce the manufacturing cost.

<1-4> In addition to the feature <1-1>, the anodic oxide coating film layer is present also at an inside periphery of the housing body (10). This feature serves to enhance the wear resistance of the inside periphery of the housing body (10) in sliding contact with the phase change mechanism (vane rotor 4).

<1-5> In addition to the feature <1-1>, the valve timing control apparatus further comprises a plurality of bolts (b1, b2, b3) extending in an axial direction of the housing body (10), and fixing the sealing plate (8, 9) to the housing body (10). This feature serves to compress the sealing ring (S1, S2, S3) by the axial force of the bolts (b1, b2, b3), and thereby further enhance the sealing performance.

<1-6> In addition to the feature <1-5>, the sealing plate (8, 9) is formed of a harder material than the housing body (10, aluminum-based metal material). This feature serves to enhance the durability of the sealing plate (8, 9), and enhance the intimateness of contact between the housing body (10) and the sealing plate (8, 9), thereby further enhancing the sealing performance. Specifically, the feature that the sealing plate (8, 9) is formed of an iron-based metal material, serves to further enhance this advantageous effect.

<1-7> In addition to the feature <1-1>: the housing body (10) includes an opening at another axial end (104, 105); and the valve timing control apparatus further comprises another sealing plate (8, 9) fixed to the other axial end (104, 105). This feature serves to maintain the sealing performance of the housing body (10) at its both axial ends.

<1-8> In addition to the feature <1-1>, the sealing plate (8, 9) includes a sealing ring groove (906, 907, 908, 909, 89) that retains the sealing ring (S1, S2, S3). This feature serves to easily retain the sealing ring (S1, S2, S3), and thereby enhance the facility of assembling the valve timing control apparatus. The feature that the sealing plate (8, 9) includes the sealing ring groove (906, 907, 908, 909, 89), serves to make the valve timing control apparatus compact, and reduce the manufacturing cost.

<1-9> A method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a housing body (10) having a tubular shape including an opening at each axial end (104, 105), wherein the housing body (10) is formed integrally with a pulley (100) at an outside periphery of the housing body (10), and wherein the pulley (100) is adapted to receive torque from a crankshaft of the internal combustion engine; at least one sealing plate (8) fixed to one of the axial ends (105) of the housing body (10), the sealing plate (8) closing a corresponding one of the openings of the housing body (10); a phase change mechanism (vane rotor 4) mounted in the housing body (10), and adapted to change a rotational phase of a camshaft (3a, 3b) of the internal combustion engine with respect to the housing body (10) in response to supply and drainage of working fluid; and at least one sealing ring (S3) disposed between the sealing plate (8) and the housing body (10), the method comprises a process of producing the housing body (10), the process comprising: an extruding operation of forming a first workpiece (P1) by extruding an aluminum-based metal material, wherein the first workpiece (P1) extends in a direction of extrusion; a coating operation of forming a second workpiece (P2) by anodizing an entire surface of the first workpiece (P1); and a cutting-off operation of forming a third workpiece (P3) by cutting out of the second workpiece (P2) to a predetermined length so as to form the third workpiece (P3) with a cut surface (axial end surface 105) forming a surface (105) of the housing body (10) on which the sealing ring (S3) abuts. This feature allows to form a plurality of the third workpieces (P3) of the housing body (10) by dividing the first workpiece (P1) that is obtained by extrusion, and thereby serves to enhance the production efficiency. The feature that the process comprises the coating operation of forming the second workpiece (P2) by anodizing the entire surface of the first workpiece (P1), serves to reduce the cost of anodic oxidation treatment. The feature that the process comprises the cutting-off operation of forming the third workpiece (P3) with the cut surface (105) forming the surface (105) of the housing body (10) on which the sealing ring (S3) abuts, serves to further reduce the cost of anodic oxidation treatment.

<1-10> In addition to the feature <1-9>: the housing body (10) has a hollow cylindrical shape, wherein the housing body (10) is formed integrally with a shoe (11, 12, 13) at an inside periphery of the housing body (10), and wherein the shoe (11, 12, 13) projects inwardly in a radial direction of the housing body (10); the phase change mechanism (4) includes a vane rotor (4) adapted to be fixed to a camshaft (3a, 3b) of the internal combustion engine, and rotatably mounted in the housing body (10), wherein the vane rotor (4) includes a vane (41, 42, 43), wherein the vane (41, 42, 43) defines a working fluid chamber (advance chamber A1, A2 or A3, retard chamber R1, R2 or R3) between the vane (41, 42, 43) and the shoe (11, 12, 13), and wherein the working fluid chamber (A1, A2, A3, R1, R2, R3) is adapted to supply and drainage of working fluid; and the sealing ring (S1, S2) seals the working fluid chamber (A1, A2, A3, R1, R2, R3) at the corresponding axial end (104, 105) of the housing body (10). The feature <1-9> can be thus adapted to the valve timing control apparatus provided with the vane-type phase change mechanism (4).

<1-11> In addition to the feature <1-9>, the pulley (100) includes a plurality of projections arranged in a circumferential direction of the housing body (10), and wherein each projection extends in an axial direction of the housing body (10). This feature makes it possible to form a plurality of the housing bodies (10) with the pulleys (100) simultaneously with high accuracy, and thereby reduce the manufacturing cost.

<1-12> A method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a housing body (10) having a tubular shape including an opening at each axial end (104, 105), wherein the housing body (10) is formed integrally with a pulley (100) at an outside periphery of the housing body (10), and wherein the pulley (100) is adapted to receive torque from a crankshaft of the internal combustion engine; at least one sealing plate (9) fixed to one of the axial ends (104) of the housing body (10), the sealing plate (9) closing a corresponding one of the openings of the housing body (10); a phase change mechanism (vane rotor 4) mounted in the housing body (10), and adapted to change a rotational phase of a camshaft (3a, 3b) of the internal combustion engine with respect to the housing body (10) in response to supply and drainage of working fluid; and at least one sealing ring (S1, S2) disposed between the sealing plate (9) and the housing body (10), the method comprises a process of producing the housing body (10), the process comprising: an extruding operation of forming a first workpiece (P1) by extruding an aluminum-based metal material, wherein the first workpiece (P1) extends in a direction of extrusion; a coating operation of forming a second workpiece (P2) by anodizing an entire surface of the first workpiece (P1); a cutting-off operation of forming a third workpiece (P3) by cutting out of the second workpiece (P2) to a predetermined length; and a carving operation of carving a longitudinal end surface of the third workpiece (P3) so as to form the third workpiece (P3) with a cut surface (inside peripheral surface 103, bottom surface 102) forming a surface of the housing body (10) on which the sealing ring (S1, S2) abuts. This feature serves to maintain the sealing performance while allowing the open axial end of the housing body (10) to be carved into an arbitrary shape, and thereby serves to enhance the flexibility of design of the valve timing control apparatus while reducing the cost of anodic oxidation treatment.

<1-13> In addition to the feature <1-12>, the carving operation is implemented by carving the longitudinal end surface of the third workpiece (P3) so as to form the third workpiece (P3) with a fitting recess (101), wherein the fitting recess (101) includes the cut surface (103, 102), and wherein the sealing plate (9) is fixed in the fitting recess (101). The feature that the sealing ring (S1, S2) is mounted in the fitting recess (101) including the cut surface (103, 102), serves to maintain the sealing performance, while reducing the axial size of the valve timing control apparatus, and thereby enhancing the mountability of the valve timing control apparatus.

<1-14> In addition to the feature <1-13>, the method further comprises providing the sealing ring (S1) between an inside periphery of the fitting recess (101) and an outside periphery of the sealing plate (9). This feature serves to reduce the radial size of the valve timing control apparatus in addition to the axial size.

<Second Group of Technical Features> The following describes a second group of technical features, and advantageous effects produced by the features. Japanese Patent Application Publication No. 2001-115807 discloses a valve timing control apparatus for an internal combustion engine, which includes a housing connected to a crankshaft, and includes a vane rotor including a boss portion, wherein the boss portion serves as a bearing for the housing. In this valve timing control apparatus, the housing is rotating, while being subject to a torque transmitted from the crankshaft, so that the boss portion is subject to a high load from the housing. If the vane rotor including the boss portion is formed of a relatively soft material, such as an aluminum-based metal material, the boss portion may be worn heavily. In view of the foregoing, it is desirable to provide a valve timing control apparatus for an internal combustion engine, in which wear of a boss portion can be reduced. The problem is solved by a valve timing control apparatus in which a portion of a boss portion in sliding contact with a housing is applied with anodic oxidation treatment. This feature serves to reduce the wear of the boss portion. The following describes each technical feature, and advantageous effects produced by the feature in detail.

<2-1> A valve timing control apparatus for an internal combustion engine, comprises: a housing (HSG) adapted to receive torque from a crankshaft of the internal combustion engine, and formed with a through hole (92) extending along an axis of rotation (O); and a vane rotor (4) rotatably mounted in the housing (HSG), wherein the vane rotor (4) includes a boss portion (401) adapted to be fixed to a camshaft (3a, 3b) of the internal combustion engine, and wherein the boss portion (401) extends along the axis of rotation (O), and includes a portion in sliding contact with the through hole (92), wherein the vane rotor (4) is formed of an aluminum-based metal material, and the portion of the boss portion (401) is anodized. The feature that the boss portion (401) bears the housing (HSG) through the through hole 92, serves to enhance the facility of attaching the valve timing control apparatus to the camshaft (3a, 3b) of an existing internal combustion engine. The feature that the vane rotor (4) is formed of the aluminum-based metal material, serves to reduce the weight of the valve timing control apparatus. The feature that the boss portion (401) includes a portion in sliding contact with the through hole (92), wherein the portion of the boss portion (401) is anodized, serves to suppress wear of the boss portion (401).

<2-2> In addition to the feature <2-1>: the housing (HSG) includes: a housing body (10) having a hollow cylindrical shape including an opening at an axial end (104), wherein the housing body (10) is adapted to receive torque from the crankshaft, and formed integrally with a shoe (11, 12, 13) at an inside periphery of the housing body (10), and wherein the shoe (11, 12, 13) projects inwardly in a radial direction of the housing body (10); and a sealing plate (rear plate 9) fixed to the axial end (104) of the housing body (10), the sealing plate (9) closing the opening of the housing body (10), wherein the sealing plate (9) is formed with the through hole (92) at a central portion (91); and the vane rotor (4) includes: a rotor (40) from which the boss portion (401) projects along the axis of rotation (O); and a vane (41, 42, 43) projecting outwardly in the radial direction of the housing body (10) with respect to the rotor (40), and defining a working fluid chamber (advance chamber A1, A2 or A3, or retard chamber R1, R2 or R3) between the vane (41, 42, 43) and the shoe (11, 12, 13), wherein the working fluid chamber (A1, A2, A3, R1, R2, R3) is adapted to supply and drainage of working fluid.

<2-3> In addition to the feature <2-1>, the vane rotor (4) has an anodized axial end surface in sliding contact with the housing (HSG). This feature serves to enhance the wear resistance of the portion of the vane rotor (4) in sliding contact with the housing (HSG: sealing plate 8, 9).

<2-4> In addition to the feature <2-2>, the sealing plate (9) is formed of a harder material than the vane rotor (4). This serves to enhance the durability of the valve timing control apparatus. Specifically, the sealing plate (9) is formed of an iron-based metal material. This feature is advantageous in the facility of processing, the manufacturing cost, etc.

<2-5> In addition to the feature <2-1>, an entire surface of the vane rotor (4) is anodized. This feature serves to enhance the facility of manufacturing the valve timing control apparatus which produces the advantageous effects according to the features <2-1> and <2-3>, because it is sufficient to apply surface treatment once to the entire surface of the vane rotor (4) that includes portions in sliding contact with the housing (HSG).

<2-6> A method of producing the valve timing control apparatus according to the feature <2-1>, the method comprises a process of producing the vane rotor (4), the process comprising anodizing an entire surface of the vane rotor (4). This feature serves similar to the feature <2-5>. Specifically, the method is a method of producing the valve timing control apparatus according to the feature <2-2> that is provided with the housing (HSG) and the vane rotor (4), the method comprising a process of producing the vane rotor (4), the process comprising: forming the vane (41, 42, 43) and the rotor (40); and then anodizing an entire surface of the vane rotor (4).

<2-7> In addition to the feature <2-6>, the process comprises: an extruding operation of forming a first workpiece (Q1) by extruding an aluminum-based metal material, wherein the first workpiece (Q1) extends in a direction of extrusion; a cutting-off operation of forming a second workpiece (Q2) by cutting out of the first workpiece (Q1) to a predetermined length; and a carving operation of forming the second workpiece (Q2) with the boss portion (401) by carving. This feature makes it possible to produce many vane rotors (4) at one time, and thereby serves to reduce the manufacturing cost.

<Third Group of Technical Features> The following describes a third group of technical features, and advantageous effects produced by the features. Japanese Patent Application Publication No. 2005-520084 discloses a valve timing control apparatus for an internal combustion engine, which is adapted to be fixed to a camshaft, and to which torque is transmitted through a belt, and which includes a belt guide for restricting movement of the belt in an axial direction of the camshaft. This valve timing control apparatus is subject to a problem that in an engine room of a motor vehicle to which the internal combustion engine is mounted, the belt guide is close to a side wall of the engine room so that the mountability of the valve timing control apparatus is low. In view of the foregoing, it is desirable to provide a valve timing control apparatus for an internal combustion engine, whose mountability is maintained in spite of provision of a belt guide. This problem is solved by a valve timing control system which includes an intake valve timing control apparatus fixed to an intake camshaft and an exhaust valve timing control apparatus fixed to an exhaust camshaft, and includes a belt wound over the intake camshaft and the exhaust camshaft for transmitting torque therebetween, wherein one of the intake valve timing control apparatus and the exhaust valve timing control apparatus farther from an engine room side wall is provided with a belt guide. This feature serves to maintain the mountability of the valve timing control apparatus. The following describes each technical feature, and advantageous effects produced by the feature in detail.

<3-1> A valve timing control system for an internal combustion engine, wherein the internal combustion engine includes an intake camshaft (3a) adapted to drive an intake valve, an exhaust camshaft (3b) adapted to drive an exhaust valve, and a belt (1010) wound over the intake camshaft (3a) and the exhaust camshaft (3b) for transmitting torque therebetween, the valve timing control system comprising: a first valve timing control apparatus (1a) adapted to be fixed to one of the intake camshaft (3a) and the exhaust camshaft (3b); and a second valve timing control apparatus (1b) adapted to be fixed to another one of the intake camshaft (3a) and the exhaust camshaft (3b), and adapted to be located closer to a side wall (W) of an engine room in which the internal combustion engine is mounted than the first valve timing control apparatus (1a), wherein: the first valve timing control apparatus (1a) includes a belt guide (80) adapted to restrict movement of the belt (1010) in at least one axial direction (in the X-axis positive direction); and the movement of the belt (1010) is free with respect to the second valve timing control apparatus (1b). Namely, only the first valve timing control apparatus (1a) farther from the side wall (W) is provided with a belt guide (80). This feature serves to maintain the mountability of the valve timing control system.

<3-2> In addition to the feature <3-1>: each of the first and second valve timing control apparatuses (1a, 1b) includes a pulley (100) including a projection and a recess, wherein the projection and recess extend in the axial direction; and the belt (1010) is wound around each pulley (100) for transmitting torque. This feature serves to effectively restrict the movement of the belt (1010) by the belt guide (80), although the belt guide (80) tends to move in the axial direction with respect to the pulley (100) because the projection and recess of pulley (100) extend in the axial direction.

<3-3> In addition to the feature <3-2>: the belt guide (80) is disposed at an axial end of the pulley (100) of the first valve timing control apparatus (1a), wherein the belt guide (80) projects outwardly with respect to a bottom of the recess in a radial direction of the pulley (100); and the recess of the pulley (100) of the second valve timing control apparatus (1b) is open at both axial ends. This feature serves to prevent each axial end of the second valve timing control apparatus (1b) from interfering with the side wall (W: projection W1), and thereby maintain the mountability of the valve timing control apparatus further effectively.

<3-4> In addition to the feature <3-3>, the belt guide (80) extends outside of the belt (1010) in the radial direction of the pulley (100) in the first valve timing control apparatus (1a). This feature serves to enhance the function of the belt guide (80).

<3-5> In addition to the feature <3-3>: each of the first and second valve timing control apparatuses (1a, 1b) includes: a housing body (10) adapted to be attached to an axial end of the corresponding one of the intake camshaft (3a) and the exhaust camshaft (3b), and formed integrally with the pulley (100) at an outside periphery of the housing body (10); a front plate (8) sealing a first axial end (X-axis positive side axial end) of the housing body (10); and a rear plate (9) sealing a second axial end (X-axis negative side axial end) of the housing body (10) closer to the corresponding one of the intake camshaft (3a) and the exhaust camshaft (3b); and the front plate (8) of the first valve timing control apparatus (1a) forms the belt guide (80). The feature that the housing body (10) is formed integrally with the pulley (100), serves to reduce the radial size of each of the first and second valve timing control apparatuses (1a, 1b), and thereby enhance the mountability of the valve timing control system. The feature that the front plate (8) of the first valve timing control apparatus (1a) forms the belt guide (80), serves to maintain the mountability of the valve timing control system, especially for a motor vehicle where the axial end (the X-axis positive side axial end) of the camshaft farther from the camshaft is subject to severe dimensional requirements in an engine room.

<3-6> In addition to the feature <3-1>, axial directions of the intake camshaft (3a) and the exhaust camshaft (3b) cross a vehicle longitudinal direction. Specifically, the axial directions of the intake camshaft (3a) and the exhaust camshaft (3b) are substantially perpendicular to the vehicle longitudinal direction.

<3-7> In addition to any one of the features <3-1> to <3-6>: the internal combustion engine is a V-type engine; and the first and second valve timing control apparatuses (1a, 1b) are adapted to the intake camshaft (3a) and the exhaust camshaft (3b) that are provided at least one bank of the internal combustion engine. The produced effects <3-1> to <3-6> are more significant for V-type engines which are subject to severe dimensional requirements. Especially, the features <3-1> to <3-5> serve to maintain the mountability of the valve timing control system more significantly for V-type engines applied with the feature <3-6> where the axial directions of the intake camshaft (3a) and the exhaust camshaft (3b) cross (specifically, substantially perpendicular to) the vehicle longitudinal direction. Specifically, of the first and second valve timing control apparatuses (1a, 1b) of one cylinder bank, only the first valve timing control apparatus (1a) is provided with the belt guide (80) according to the feature <3-1>, wherein the first valve timing control apparatus (1a) is attached to one of the intake camshaft (3a) and the exhaust camshaft (3b) closer to the other cylinder bank. More specifically, each of the first and second valve timing control apparatuses (1a, 1b) includes a pulley (100) including a projection and a recess, wherein the projection and recess extend in the axial direction; and the belt (1010) is wound around each pulley (100) for transmitting torque. The belt guide (80) is disposed at an axial end of the pulley (100) of the first valve timing control apparatus (1a), wherein the first valve timing control apparatus (1a) is attached to the intake camshaft (3a) closer to the other cylinder bank, wherein the belt guide (80) projects outwardly from a bottom of the recess in a radial direction of the pulley (100); and the recess of the pulley (100) of the second valve timing control apparatus (1b) is open at both axial ends, wherein the second valve timing control apparatus (1b) is attached to one of the intake camshaft (3a) and the exhaust camshaft (3b) that is located outside of the cylinder bank (farther from the other cylinder bank).

<Fourth Group of Technical Features> The following describes a fourth group of technical features, and advantageous effects produced by the features. Japanese Patent Application Publication No. 11-218008 discloses a valve timing control apparatus of a vane type for an internal combustion engine, which includes a housing to which torque is transmitted form outside, and a vane rotor rotatably mounted in the housing, wherein the vane rotor is fixed to a camshaft by a single bolt at the axis of rotation of the vane rotor. This valve timing control apparatus is subject to a problem that the bolt tends to be released, for example, by an alternating torque from valve springs. In view of the foregoing, it is desirable to provide a valve timing control apparatus in which fixation of a vane rotor to a camshaft is strengthened. This problem is solved by a valve timing control apparatus in which a rotor of a vane rotor includes a plurality of fixing portions which are arranged and spaced from one another in a circumferential direction. This feature serves to strengthen the fixation of the vane rotor. The following describes each technical feature, and advantageous effects produced by the feature in detail.

<4-1> A valve timing control apparatus for an internal combustion engine, comprises: a hollow housing (HSG) adapted to receive torque; and a vane rotor (4) rotatably mounted in the housing (HSG), including a rotor (40) adapted to be fixed to a camshaft (3a, 3b) of the internal combustion engine, wherein the rotor (40) includes a plurality of fixing portions (bolt holes 403, 404 and 405) adapted to be fixed to the camshaft (3a, 3b), and wherein the fixing portions (403, 404, 405) are arranged in a circumferential direction of the rotor (40), and separated from one another. The feature that the rotor (40) includes the plurality of fixing portions (403, 404, 405), serves to strengthen the fixation of the vane rotor (4) to the camshaft (3a, 3b). The feature that the fixing portions (403, 404, 405) are arranged in the circumferential direction of the rotor (40), and separated from one another, serves to strengthen the fixation of the vane rotor (4) effectively.

<4-2> In addition to the feature <4-1>: the torque is transmitted to the housing (HSG) through a belt (1010); the vane rotor (4) includes: a plurality of vanes (41, 42, 43) projecting outwardly in radial directions of the rotor (40) with respect to the rotor (40), and defining at least one working fluid chamber (first, second and third advance chambers A1, A2 and A3, and first, second and third retard chambers R1, R2 and R3) in the housing (HSG), wherein the working fluid chamber (A1, A2, A3, R1, R2, R3) is adapted to supply and drainage of working fluid; and a cylinder (slide hole 501) formed in the vane rotor (4), extending in a direction of an axis of rotation (O) of the vane rotor (4); and the valve timing control apparatus further comprises: an engaging member (lock piston 51) slidably mounted in the cylinder (501), and arranged to move forward and rearward in the cylinder (501) according to an operating state of the internal combustion engine; an engaging recess (521) provided in an axial end portion of the housing (HSG) closer to the camshaft (3a, 3b); a biasing member (coil spring 53) mounted in a back pressure chamber (50) formed in the cylinder (501), and arranged to bias the engaging member (51) toward the engaging recess (521); and a back pressure relief section (back pressure hole 407) formed in a central portion of the rotor (40) surrounded by and closer to the axis of rotation (O) than the fixing portions (bolt holes 403, 404 and 405), for relieving pressure from the back pressure chamber (50) to a space within the internal combustion engine. The feature that the torque is transmitted through the belt (1010), serves to reduce the manufacturing cost, and reduce the weight of the valve timing control apparatus. The feature that the cylinder (501), engaging member (51), engaging recess (521), and biasing member (coil spring 53) constitute a lock mechanism, serves to suppress, by the simply-constructed lock mechanism, noise that may be caused by the valve timing control apparatus at start of the internal combustion engine. The feature that the cylinder (slide hole 501) extends in the direction of the axis of rotation (O) of the vane rotor (4), serves to stabilize the locking operation. The feature that the back pressure relief section (407) is formed for relieving pressure from the back pressure chamber (50), serves to smooth the lock release operation of the lock mechanism, namely, smooth the disengaging motion of the engaging member (51) from the engaging recess (521). The feature that the back pressure relief section (407) is formed for relieving pressure from the back pressure chamber (50) to the space within the internal combustion engine, where the back pressure chamber (50) is formed in the cylinder (501) and located at a side (the X-axis positive side) farther from the camshaft (3a, 3b) or the internal combustion engine, serves to enhance the durability of the belt (1010). The feature that the back pressure relief section (407) is formed in the central portion of the rotor (40) surrounded by and closer to the axis of rotation (O) than the fixing portions (403, 404, 405), serves to reduce the radial size of the rotor (40) or the vane rotor (4), and thereby make the valve timing control apparatus compact in size. The plurality of vanes (41, 42, 43) define at least one advance chamber (A1, A2 or A3) and at least one retard chamber (R1, R2 or R3) between the vanes (41, 42, 43) and shoes (11, 12 and 13), wherein the advance chamber and the retard chamber (A1, A2, A3, R1, R2, R3) are adapted to supply and drainage of working fluid.

<4-3> In addition to the feature <4-2>: the rotor (40) is formed with a communication hole (retard fluid passage 408, advance fluid passage 409) hydraulically connected between the working fluid chamber (A1, A2, A3, R1, R2, R3) and a fluid passage (first fluid passages 202 and 212; second fluid passages 201, 203, 211 and 213) formed in the camshaft (3a, 3b), wherein the fluid passage (202, 212; 201, 203, 211, 213) is located between adjacent two of the fixing portions (403, 404, 405) in a circumferential direction of the rotor (40); and the back pressure relief section (back pressure hole 407) is located closer to the axis of rotation (O) than the fluid passage (202, 212; 201, 203, 211, 213). This feature serves to make the valve timing control apparatus compact in size, wherein it is unnecessary to rearrange the passages (first fluid passage 202, etc.) for supply and drainage of working fluid.

<4-4> In addition to the feature <4-1>, each of the fixing portions (bolt holes 403, 404 and 405) is a bolt insertion hole extending through the rotor (40), wherein a camshaft bolt (33, 34, 35) extends through the bolt insertion hole, and fixes the rotor (40) to an axial end surface (300) of the camshaft (3a, 3b). This feature makes it possible to easily assemble the valve timing control apparatus, and easily manage the strength of fixation, as compared to another manner such as swaging or welding.

<4-5> In addition to the feature <4-2>: the camshaft (3a, 3b) is formed with a first back pressure passage (31) inside, wherein the first back pressure passage (31) is hydraulically connected between the axial end surface (300) of the camshaft (3a, 3b) and the space within the internal combustion engine; and the back pressure relief section (407) is a back pressure hole that is hydraulically connected to the back pressure chamber (50), and arranged in such a position at a surface closer to the camshaft (3a, 3b) as to face the first back pressure passage (31). The feature that the camshaft (3a, 3b) is formed with a first back pressure passage (31) inside, serves to make the valve timing control apparatus compact in size. The feature that the opening of the back pressure relief section (407) faces the first back pressure passage (31), is advantageous in the facility of processing, and the manufacturing cost.

<4-6> In addition to the feature <4-5>, the back pressure hole (407) is located at the axis of rotation (O) of the rotor (40). This feature serves to enhance the balance of the vane rotor (4) around the axis of rotation, and serves to ensure the radial thickness of the rotor (40), and thereby ensure the strength of the vane rotor (4).

<4-7> In addition to the feature <4-5>: the first back pressure passage (31) is located at an axis of rotation (O) of the camshaft (3a, 3b); and the back pressure hole (407) extends through the rotor (40), and faces the first back pressure passage (31). This feature serves to enhance the balance of the camshaft (3a, 3b) around the axis of rotation, and also produces the same effect according to the feature <4-6>.

<4-8> In addition to the feature <4-1>, the fixing portions (bolt holes 403, 404 and 405) are substantially evenly spaced in the circumferential direction. This feature makes it easy to maintain the balance of each of the vane rotor (4) and the camshaft (3a, 3b) around the axis of rotation. The further feature that each fixing portion is a bolt insertion hole (bolt hole 403, 404 or 405), serves to maintain the strength of the rotor (40).

<4-9> In addition to the feature <4-2>: the rotor (40) is formed with a communication hole (retard fluid passage 408, advance fluid passage 409) hydraulically connected between the working fluid chamber (A1, A2, A3, R1, R2, R3) and a fluid passage (202, 212; 201, 203, 211, 213) formed in the camshaft (3a, 3b), wherein the fluid passage (202, 212; 201, 203, 211, 213) is located between adjacent two of the fixing portions (403, 404, 405) in a circumferential direction of the rotor (40); the rotor (40) is formed with a camshaft insertion hole (402) having a bottom, wherein the camshaft (3a, 3b) is inserted in the camshaft insertion hole (402); and the communication hole (retard fluid passage 408, advance fluid passage 409) extends through the rotor (40) in a radial direction of the rotor (40). This feature serves to enhance the facility of processing and the flexibility of layout of the back pressure relief section (back pressure hole 407), and makes it easy to make the rotor (40) compact in size.

<4-10> In addition to the feature <4-9>: the fluid passage (202, 212; 201, 203, 211, 213) includes: a first fluid passage (202, 212) extending in an axial direction of the camshaft (3a, 3b); and a second fluid passage (201, 203, 211, 213) extending from the first fluid passage (202, 212) in a radial direction of the camshaft (3a, 3b) and communicating with the communication hole (retard fluid passage 408, advance fluid passage 409); and the first fluid passage (202) has an opening at an axial end surface (300) of the camshaft (3a, 3b), wherein the opening of the first fluid passage (202) is closed by the bottom of the camshaft insertion hole (402). This feature serves to eliminate the necessity of providing the first fluid passage (202) with a blind plug, and thereby reduce the number of parts and the manufacturing cost.

<4-11> In addition to the feature <4-10>, the valve timing control apparatus further comprises a positioning pin (45) fixedly inserted in the opening of the first fluid passage (202), and inserted in a recess (44) formed in the bottom of the camshaft insertion hole (402), so as to position the rotor (40) and the camshaft (3a, 3b) with respect to one another in a rotational direction. The feature that the opening of the first fluid passage (202) is used to fix the positioning pin (45), and thereby constitutes a positioning means, serves to reduce the manufacturing cost.

<4-12> In addition to the feature <4-2>: the vane rotor (4) is formed with a second back pressure passage (58, 406) that includes a recess formed in an axial end surface (X-axis positive side axial end surface) of the vane rotor (4) farther from the camshaft (3a, 3b); and the back pressure relief section (407) is a back pressure hole that is hydraulically connected to the back pressure chamber (50) through the second back pressure passage (radial groove 58, circular recess 406). This feature serves to reduce the axial size of the housing (HSG), while maintaining the working ability of the vane rotor (4).

<4-13> In addition to the feature <4-12>: each of the fixing portions (bolt holes 403, 404 and 405) is a bolt insertion hole extending through the rotor (40), wherein a camshaft bolt (33, 34, 35) extends through the bolt insertion hole, and fixes the rotor (40) to an axial end surface (300) of the camshaft (3a, 3b); the second back pressure passage (58, 406) includes: a circular recess (406) formed in the axial end surface of the vane rotor (4); and a radial groove (58) extending from the circular recess (406) outwardly in a radial direction of the rotor (40), and hydraulically communicating with the back pressure chamber (50); and the circular recess (406) is formed with the bolt insertion holes (403, 404, 405) and the back pressure hole (407). This feature serves to suppress projection of the head (331, 341 or 351) of the camshaft bolt (33, 34 or 35), and thereby reduce the axial size of the valve timing control apparatus. This feature also serves to enhance the facility of processing and the flexibility of layout of the back pressure hole (407), and thereby makes it easy to make the rotor (40) compact in size.

<4-14> In addition to the feature <4-13>, the housing (HSG) includes: a housing body (10) having a hollow cylindrical shape; a front plate (8) sealing a first axial end of the housing body (10), and including a detachable cap (7) in a position to face the circular recess (406) of the vane rotor (4); and a rear plate (9) sealing a second axial end of the housing body (10) closer to the camshaft (3a, 3b), wherein the camshaft (3a, 3b) is inserted in the rear plate (9). This feature serves to suppress degradation of the belt (1010), while enhancing the mountability of the valve timing control apparatus.

<4-15> In addition to the feature <4-14>, the cap (7) is formed with a recess (73) at a surface facing the circular recess (406), wherein the recess (73) accommodates at least a part of a head (331, 341, 351) of the camshaft bolt (33, 34, 35). This feature serves to absorb the projection of the head (331, 341, 351) of the camshaft bolt (33, 34, 35), and thereby serves to make the valve timing control apparatus compact in size.

<Fifth Group of Technical Features> The following describes a fifth group of technical features, and advantageous effects produced by the features. Japanese Patent Application Publication No. 2000-002104 discloses a valve timing control apparatus of a vane type for an internal combustion engine, which includes an engaging member for restricting relative rotation between a vane rotor and a housing, wherein: the vane rotor is formed with a cylinder in which a hollow cylindrical member is fixed; and the engaging member is mounted in the cylinder, in sliding contact with an inside periphery of the hollow cylindrical member. This valve timing control apparatus is subject to a problem that the hollow cylindrical member may be fixed with inclination with respect to the cylinder, and thereby the engaging member may be mounted with inclination with respect to the cylinder. In view of the foregoing, it is desirable to provide a valve timing control apparatus for an internal combustion engine, in which inclination of an engaging member is suppressed. This problem is solved by a valve timing control apparatus in which a cylinder to which a cylindrical member is fixed is applied with anodic oxidation treatment. This feature serves to suppress inclination of the engaging member. The following describes each technical feature, and advantageous effects produced by the feature in detail.

<5-1> A valve timing control apparatus for an internal combustion engine, comprises: a hollow housing (HSG) adapted to receive torque; a vane rotor (4) formed of an aluminum-based metal material, and rotatably mounted in the housing (HSG), the vane rotor (4) including: a plurality of vanes (41, 42, 43) defining at least one working fluid chamber (first, second and third advance chambers A1, A2 and A3, first, second and third retard chambers R1, R2 and R3) in the housing (HSG), wherein the working fluid chamber (A1, A2, A3, R1, R2, R3) is adapted to supply and drainage of working fluid; and a cylinder (slide hole 501) formed in the vane rotor (4), and anodized; a hollow cylindrical member (sealing member 502) fixed in the cylinder (501); a lock member (lock piston 51) slidably mounted in the hollow cylindrical member (502), the lock member (51) including a tip arranged to move forward and rearward with respect to the vane rotor (4) according to an operating state of the internal combustion engine; a lock recess (engaging recess 521) provided in an axial end portion of the housing (HSG) facing the tip of the lock member (51), wherein the tip of the lock member (51) is adapted to be inserted in the lock recess (521); and a biasing member (coil spring 53) mounted in the cylinder (501), and arranged to bias the lock member (51) toward the lock recess (521). The feature that the cylinder (501), lock member (51), lock recess (521), and biasing member (coil spring 53) constitute a lock mechanism, serves to suppress, by the simply-constructed lock mechanism, noise that may be caused by the valve timing control apparatus at start of the internal combustion engine. The feature that the vane rotor (4) is formed of the aluminum-based metal material, serves to reduce the weight of the valve timing control apparatus (1). The feature that the hollow cylindrical member is fixed in the cylinder whose surface is hardened by anodic oxidation treatment, serves to suppress inclination of the hollow cylindrical member, and thereby maintain the working ability of the lock member, and maintain the controllability of the valve timing control apparatus. The feature <5-1> is implemented so that: the torque is transmitted from a crankshaft to the housing (HSG); the housing (HSG) is formed integrally with a shoe (11, 12, 13) at an inside periphery of the housing (HSG), and wherein the shoe (11, 12, 13) projects inwardly in a radial direction of the housing (HSG); the plurality of vanes (41, 42, 43) define an advance chamber (A1, A2 or A3) and a retard chamber (R1, R2 or R3) in cooperation with the shoe (11, 12, 13); a rotor (40) is disposed in a position surrounded by and closer to an axis of rotation than the vanes (41, 42, 43); the lock member is a lock pin (51); and the hollow cylindrical member (sealing member 502) is a ring-shaped member.

<5-2> In addition to the feature <5-1>, the cylinder (slide hole 501) extends in an axial direction of the vane rotor (4) so that the tip of the lock member (lock piston 51) moves forward and rearward in the cylinder (501) in the axial direction of the vane rotor (4). This feature serves to stabilize the locking operation.

<5-3> In addition to the feature <5-1>, the hollow cylindrical member (sealing member 502) is formed of a material having a higher wear resistance than anodic oxide coating. This feature serves to suppress wear of the cylinder (slide hole 501) effectively.

<5-4> In addition to the feature <5-1>, the hollow cylindrical member (sealing member 502) is press-fitted in the cylinder (slide hole 501). This feature makes it easy to set and fix the hollow cylindrical member, and prevent the hollow cylindrical member from being fixed with inclination.

<5-5> In addition to the feature <5-1>, a surface of the vane rotor (4) including an inside peripheral surface of the cylinder (slide hole 501) is anodized. This feature makes it possible to easily manufacture the valve timing control apparatus according to the feature <5-1>, while enhancing the wear resistance of a portion of the vane rotor (4) in sliding contact with the housing (HSG).

<5-6> In addition to the feature <5-1>: the hollow cylindrical member (sealing member 502) has a shorter longitudinal size than the cylinder (slide hole 501), and extends from a longitudinal end of the cylinder (501); the lock member (lock piston 51) includes a small-diameter portion (sliding portion 512, engaging portion 511) and a large-diameter portion (flange 513); the small-diameter portion (512, 511) is slidably fitted to an inside periphery of the hollow cylindrical member (502); and the large-diameter portion (513) is slidably fitted to an inside periphery of the cylinder (501). This feature serves to simply define a plurality of chambers for applying individual forces to the lock member. The feature <5-6> is implemented so that: the small-diameter portion (engaging portion 511) of the lock member (lock piston 51) is adapted to move forward and backward with respect to the vane rotor (4), and move into the lock recess (engaging recess 521). The small-diameter portion (512, 511) is a distal end portion of the lock member, whereas the large-diameter portion (513) is a proximal end portion of the lock member, wherein the biasing member is arranged to bias the lock member from the large-diameter portion (proximal end portion) to the small-diameter portion (distal end portion).

<5-7> In addition to the feature <5-6>: the vanes (41, 42, 43) define at least two of the working fluid chambers as an advance chamber (first advance chamber A1) and a retard chamber (first retard chamber R1) in the housing (HSG); one of the advance chamber and the retard chamber (A1) is hydraulically connected for hydraulic pressure supply to a space (second pressure-receiving chamber 59) between the tip of the lock member (lock piston 51) and the axial end portion (the X-axis positive side surface of rear plate 9) of the housing (HSG) facing the tip of the lock member (51); and another one of the advance chamber and the retard chamber (R1) is hydraulically connected for hydraulic pressure supply to a space (first pressure-receiving chamber 55) between the large-diameter portion (flange 513) of the lock member (51) and the hollow cylindrical member (sealing member 502). This feature serves to reduce the frequency of operation of the lock member, and thereby enhance the durability of the valve timing control apparatus.

<5-8> In addition to the feature <5-6>: the hollow cylindrical member (sealing member 502) is formed of a material having a higher wear resistance than anodic oxide coating; and a smaller clearance is provided between the small-diameter portion (sliding portion 512) of the lock member (lock piston 51) and the inside periphery of the hollow cylindrical member (502) than between the large-diameter portion (flange 513) of the lock member (51) and the inside periphery of the cylinder (slide hole 501). This feature serves to further suppress wear of the sliding portion in sliding contact with the lock member.

<5-9> In addition to the feature <5-1>: the housing (HSG) is formed with a shoe (11) at an inside periphery of the housing (HSG); and one of the tip (engaging portion 511) of the lock member (lock piston 51) and the lock recess (engaging recess 521) has an inclined surface through which the biasing member (coil spring 53) applies a biasing force so as to press one of the vanes (41) to the shoe (11). This feature serves to produce a wedging effect by which the vane rotor (4) can be reliably fixed in a lock position, while maintaining the working ability of the lock member according to the feature <5-1>. The feature <5-9> is implemented so that the tip (engaging portion 511) of the lock member is formed with a tapered surface whose diameter gradually decreases as followed toward the tip end, whereas the lock recess (engaging recess 521) is formed with a tapered surface whose diameter gradually decreases as followed toward the bottom end. This feature serves to reduce wear of the surfaces of the lock member and the lock recess, while enhancing the wedging effect, because both of the lock member and the lock recess are formed with inclined surfaces.

<5-10> A method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a hollow housing (HSG) adapted to receive torque, and is formed with a shoe (11, 12, 13) at an inside periphery of the housing (HSG), wherein the shoe (11, 12, 13) projects inwardly in a radial direction of the housing (HSG); a vane rotor (4) formed of an aluminum-based metal material, and rotatably mounted in the housing (HSG), the vane rotor (4) including: a rotor (40); a plurality of vanes (41, 42, 43) projecting outwardly with respect to the rotor (40), and defining at least one working fluid chamber (advance chamber A1, A2 or A3, or retard chamber R1, R2 or R3) together with the shoe (11, 12, 13), wherein the working fluid chamber (A1, A2, A3, R1, R2, R3) is adapted to supply and drainage of working fluid; and a cylinder (slide hole 501) extending in an axial direction of the vane rotor (4); a ring-shaped member (sealing member 502) formed of a material having a higher wear resistance than anodic oxide coating, and fixed in the cylinder (501); a lock pin (lock piston 51) including a tip (sliding portion 512) slidably mounted in the ring-shaped member (502), wherein the tip (engaging portion 511) is arranged to move forward and rearward in the axial direction with respect to the vane rotor (4) according to an operating state of the internal combustion engine; a lock recess (engaging recess 521) provided in an axial end portion of the housing (HSG) facing the tip of the lock pin (51), wherein the tip of the lock pin (51) is adapted to be inserted in the lock recess (521); and a biasing member (coil spring 53) mounted in the cylinder (501), and arranged to bias the lock pin (51) toward the lock recess (521), the method comprises: a first operation of forming the cylinder (501) in the vane rotor (4); a second operation of anodizing an entire surface of the vane rotor (4) after the first operation; and a third operation of press-fitting the ring-shaped member (502) into the cylinder (501) so as to fix the ring-shaped member (502) to the cylinder (501), after the second operation. This feature makes it possible to easily manufacture the valve timing control apparatus according to the features <5-1> to <5-5>.

The entire contents of Japanese Patent Application No. 2009-214723 filed Sep. 16, 2009 are incorporated herein by reference.

Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims.

Claims

1. A valve timing control apparatus for an internal combustion engine, comprising:

a housing body having a hollow cylindrical shape including an opening at an axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and formed integrally with a shoe at an inside periphery of the housing body, wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine, and wherein the shoe projects inwardly in a radial direction of the housing body;

a sealing plate fixed to the axial end of the housing body, the sealing plate closing the opening of the housing body;

a vane rotor adapted to be fixed to a camshaft of the internal combustion engine, and rotatably mounted in the housing body, wherein the vane rotor includes a vane, wherein the vane defines a working fluid chamber between the vane and the shoe, and wherein the working fluid chamber is adapted to supply and drainage of working fluid; and

a sealing ring disposed between the housing body and the sealing plate, the sealing ring sealing the working fluid chamber, wherein:

the housing body is formed of an aluminum-based metal material and anodized, wherein the housing body includes a base layer and an anodic oxide coating film layer;

the anodic oxide coating film layer is present at the outside periphery; and

the sealing ring abuts on the base layer at the axial end.

2. A valve timing control apparatus for an internal combustion engine, comprising:

a housing body having a tubular shape including an opening at an axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine;

a sealing plate facing an axial end surface of the housing body, and closing the opening of the housing body;

a phase change mechanism mounted in the housing body, and adapted to change a rotational phase of a camshaft of the internal combustion engine with respect to the housing body in response to supply and drainage of working fluid; and

a sealing ring disposed between the housing body and the sealing plate,

wherein:

the housing body is formed of an aluminum-based metal material and anodized, wherein the housing body includes a base layer and an anodic oxide coating film layer; and

the anodic oxide coating film layer is present at the outside periphery and an inside periphery of the housing body, and absent at the axial end surface of the housing body facing the sealing plate.

3. A valve timing control apparatus for an internal combustion engine, comprising:

a housing body having a tubular shape including an opening at an axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine;

a sealing plate fixed to the axial end of the housing body, the sealing plate closing the opening of the housing body;

a phase change mechanism mounted in the housing body, and adapted to change a rotational phase of a camshaft of the internal combustion engine with respect to the housing body in response to supply and drainage of working fluid; and

a sealing ring disposed between the housing body and the sealing plate,

wherein:

the housing body is formed of an aluminum-based metal material and anodized, wherein the housing body includes a base layer and an anodic oxide coating film layer; and

the anodic oxide coating film layer is present at the outside periphery of the housing body, and absent at a surface of the housing body on which the sealing ring abuts.

4. The valve timing control apparatus as claimed in claim 3, wherein:

the housing body has a hollow cylindrical shape, wherein the housing body is formed integrally with a shoe at an inside periphery of the housing body, and wherein the shoe projects inwardly in a radial direction of the housing body;

the phase change mechanism includes a vane rotor adapted to be fixed to a camshaft of the internal combustion engine, and rotatably mounted in the housing body, wherein the vane rotor includes a vane, wherein the vane defines a working fluid chamber between the vane and the shoe, and wherein the working fluid chamber is adapted to supply and drainage of working fluid; and

the sealing ring seals the working fluid chamber at the axial end of the housing body.

5. The valve timing control apparatus as claimed in claim 3, wherein the sealing ring abuts on the base layer at the axial end.

6. The valve timing control apparatus as claimed in claim 3, wherein the anodic oxide coating film layer is present also at an inside periphery of the housing body.

7. The valve timing control apparatus as claimed in claim 3, further comprising a plurality of bolts extending in an axial direction of the housing body, and fixing the sealing plate to the housing body.

8. The valve timing control apparatus as claimed in claim 7, wherein the sealing plate is formed of a harder material than the housing body.

9. The valve timing control apparatus as claimed in claim 3, wherein:

the housing body includes an opening at another axial end; and

the valve timing control apparatus further comprises another sealing plate fixed to the other axial end.

10. The valve timing control apparatus as claimed in claim 3, wherein the sealing plate includes a sealing ring groove that retains the sealing ring.

11. A method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a housing body having a hollow cylindrical shape including an opening at each axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and formed integrally with a shoe at an inside periphery of the housing body, wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine, and wherein the shoe projects inwardly in a radial direction of the housing body; at least one sealing plate fixed to an axial end surface of the housing body, the sealing plate closing a corresponding one of the openings of the housing body;

a vane rotor adapted to be fixed to a camshaft of the internal combustion engine, and rotatably mounted in the housing body, wherein the vane rotor includes a vane, wherein the vane and the shoe define an advance chamber and a retard chamber between the vane rotor and housing body, and wherein the advance chamber and the retard chamber are adapted to supply and drainage of fluid; and at least one sealing ring disposed between the sealing plate and the axial end surface of the housing body, the method comprising a process of producing the housing body, the process comprising:

an extruding operation of forming a first workpiece by extruding an aluminum-based metal material, wherein the first workpiece extends in a direction of extrusion;

a coating operation of forming a second workpiece by anodizing an entire surface of the first workpiece; and

a cutting-off operation of forming a third workpiece by cutting out of the second workpiece to a predetermined length so as to form the third workpiece with a cut surface forming the axial end surface of the housing body on which the sealing ring abuts.

12. A method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a housing body having a hollow cylindrical shape including an opening at each axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and formed integrally with a shoe at an inside periphery of the housing body, wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine, and wherein the shoe projects inwardly in a radial direction of the housing body; at least one sealing plate fixed to one of the axial ends of the housing body, the sealing plate closing a corresponding one of the openings of the housing body; a vane rotor adapted to be fixed to a camshaft of the internal combustion engine, and rotatably mounted in the housing body, wherein the vane rotor includes a vane, wherein the vane and the shoe define an advance chamber and a retard chamber between the vane rotor and housing body, and wherein the advance chamber and the retard chamber are adapted to supply and drainage of fluid; and at least one sealing ring disposed between the sealing plate and the housing body, the method comprising a process of producing the housing body, the process comprising:

an extruding operation of forming a first workpiece by extruding an aluminum-based metal material, wherein the first workpiece extends in a direction of extrusion;

a coating operation of forming a second workpiece by anodizing an entire surface of the first workpiece;

a cutting-off operation of forming a third workpiece by cutting out of the second workpiece to a predetermined length; and

a carving operation of carving a longitudinal end surface of the third workpiece so as to form the third workpiece with a cut surface forming a surface of the housing body on which the sealing ring abuts.

13. A method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a housing body having a tubular shape including an opening at each axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine; at least one sealing plate fixed to one of the axial ends of the housing body, the sealing plate closing a corresponding one of the openings of the housing body; a phase change mechanism mounted in the housing body, and adapted to change a rotational phase of a camshaft of the internal combustion engine with respect to the housing body in response to supply and drainage of working fluid;

and at least one sealing ring disposed between the sealing plate and the housing body, the method comprising a process of producing the housing body, the process comprising:

an extruding operation of forming a first workpiece by extruding an aluminum-based metal material, wherein the first workpiece extends in a direction of extrusion;

a coating operation of forming a second workpiece by anodizing an entire surface of the first workpiece; and

a cutting-off operation of forming a third workpiece by cutting out of the second workpiece to a predetermined length so as to form the third workpiece with a cut surface forming a surface of the housing body on which the sealing ring abuts.

14. The method as claimed in claim 13, wherein:

the housing body has a hollow cylindrical shape, wherein the housing body is formed integrally with a shoe at an inside periphery of the housing body, and wherein the shoe projects inwardly in a radial direction of the housing body;

the phase change mechanism includes a vane rotor adapted to be fixed to a camshaft of the internal combustion engine, and rotatably mounted in the housing body, wherein the vane rotor includes a vane, wherein the vane defines a working fluid chamber between the vane and the shoe, and wherein the working fluid chamber is adapted to supply and drainage of working fluid; and

the sealing ring seals the working fluid chamber at the corresponding axial end of the housing body.

15. The method as claimed in claim 13, wherein the pulley includes a plurality of projections arranged in a circumferential direction of the housing body, and wherein each projection extends in an axial direction of the housing body.

16. A method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a housing body having a tubular shape including an opening at each axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine; at least one sealing plate fixed to one of the axial ends of the housing body, the sealing plate closing a corresponding one of the openings of the housing body; a phase change mechanism mounted in the housing body, and adapted to change a rotational phase of a camshaft of the internal combustion engine with respect to the housing body in response to supply and drainage of working fluid; and at least one sealing ring disposed between the sealing plate and the housing body, the method comprising a process of producing the housing body, the process comprising:

an extruding operation of forming a first workpiece by extruding an aluminum-based metal material, wherein the first workpiece extends in a direction of extrusion;

a coating operation of forming a second workpiece by anodizing an entire surface of the first workpiece;

a cutting-off operation of forming a third workpiece by cutting out of the second workpiece to a predetermined length; and

a carving operation of carving a longitudinal end surface of the third workpiece so as to form the third workpiece with a cut surface forming a surface of the housing body on which the sealing ring abuts.

17. The method as claimed in claim 16, wherein the carving operation is implemented by carving the longitudinal end surface of the third workpiece so as to form the third workpiece with a fitting recess, wherein the fitting recess includes the cut surface, and wherein the sealing plate is fixed in the fitting recess.

18. The method as claimed in claim 17, further comprising providing the sealing ring between an inside periphery of the fitting recess and an outside periphery of the sealing plate.