VALVE TIMING REGULATOR

Abstract

A valve timing adjusting apparatus includes: recesses provided opposite to the wall surfaces in a circumferential direction of a shoe and a vane in an advance hydraulic chamber; a holding member insertion-disposed into the recesses from an axial direction; and an assist spring disposed between the holding member on the shoe side and the holding member on the vane side to urge a rotor in an advance direction, and further a clearance formed by a length in the axial direction of the holding member provided on the vane side and a length in the axial direction of the case is set to not less than a sum of an increment of the length in the axial direction in consideration of a tilt of the holding member produced by a gap between the holding member and recess, and an increment due to the thermal expansion.

Description

TECHNICAL FIELD

The present invention relates to a valve timing adjusting apparatus that changes automatically opening and closing timings of an exhaust valve in response to an operating condition of an internal combustion engine.

BACKGROUND ART

This type of valve timing adjusting apparatus includes: a camshaft for driving an exhaust valve of an internal combustion engine to open and close; a case that is rotatably provided on the camshaft and rotationally driven by an output of the internal combustion engine; a rotor that is relatively rotatably housed inside the case and coupled to the camshaft; and a locking means that constrains a relative rotation between the case and the rotor when operated by a mechanical urging force, and releases the constraint when operated by a fluid control pressure applied from an internal hydraulic chamber in a direction opposing the mechanical urging force.

With the aim of applying the thus constructed valve timing adjusting apparatus to an exhaust side thereof, it has been proposed that an assist spring is disposed as a urging means for urging the rotor in an advance direction within the internal hydraulic chamber. Patent Document 1, for example, discloses a constitution for holding the assist spring in which a resin holding member is inserted into recesses provided in the rotor and the case.

Prior Art Documents

Patent Documents

Patent Document 1: Japanese Patent Publication No. 3,964,207

SUMMARY OF THE INVENTION

As described above, Patent Document 1 discloses that one pair of holding members are set to hold the two ends of the assist spring, but provides no detailed descriptions of an axial direction length of the holding members or an inlet shape of an assist spring insertion hole. Therefore, in a practical use, the holding member may tilt within the range of a gap between the holding member and the recess or is fallen in a stretched state between a cover and a housing at the two ends thereof due to the thermal expansion or the like; thus, there is a problem such that inconveniences such as a reduction in a rotor operating speed due to the friction and an increase in leakage due to the wear on the sliding surface between the cover and the housing are concerned.

The present invention has been made to solve the aforementioned problem that is caused by a holding member for holding an assist spring disposed in an hydraulic chamber, and an object thereof is to provide a valve timing adjusting apparatus in which decrease in the operating speed, reduction in the durability and so on are solved.

A valve timing adjusting apparatus according to the present invention includes: a plurality of shoes formed on an inner peripheral surface of a case; a plurality of vanes provided on an outer peripheral surface of a rotor relatively rotatably housed in the case, each forming a retard hydraulic chamber and an advance hydraulic chamber between the vane and the two side-wall surfaces in a circumferential direction of the corresponding shoe; recesses provided opposite to the wall surfaces in the circumferential direction of the shoe and the vane in the advance hydraulic chamber; a holding member insertion-disposed into the recess from an axial direction; and an assist spring disposed between the holding member on the shoe side and the holding member on the vane side to urge the rotor in an advance direction, wherein a clearance formed by a length in the axial direction of the holding member provided on the vane side and a length in the axial direction of the case is set to be equal to or greater than a sum of an increment of the length in the axial direction in consideration of a tilt of the holding member produced by a gap between the holding member and the recess, and an increment due to the thermal expansion.

According to the invention, in order to enhance the ease of attachment of the assist spring, it is configured that the clearance formed by the length in the axial direction of the holding member provided on the vane side and the length in the axial direction of the case is set to be equal to or greater than the sum of the increment of the length in the axial direction in consideration of the tilt of the holding member produced by the gap between the holding member and the recess, and the increment due to the thermal expansion; thus, even when the holding member tilts within the range of the gap provided between the member and the recess in the vane or shoe, or even when there occurs the tilt due to the thermal expansion upon an increase of oil temperature (the rotor and case are formed out of iron-based materials and have a smaller linear expansion coefficient than the holding member made of resin), the tilt of the holding member during the assembly of the member and the assist spring, or the tilt due to rotor operations or vibrations; the following inconveniences can be prevented reliably: the occurrence of a stretched state between a cover and a housing at the two ends, the reduction in the rotor operating speed due to the friction, the increase in leakage due to the wear on the sliding surface of the cover, and so on.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a radial direction sectional view of a valve timing adjusting apparatus of a first embodiment of the present invention, taken along a line 2-2 in FIG. 2.

FIG. 2 is an axial direction sectional view of the valve timing adjusting apparatus of the first embodiment of the present invention, taken along a line 1-1 in FIG. 1.

FIG. 3 is a front view showing a condition in which an assist spring is attached to an assist spring insertion hole provided in a holding member inserted into a recess of a vane.

FIG. 4 is a longitudinal sectional side view taken along a line 3-3 in FIG. 3.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, to describe the present invention in further detail, an embodiment of the invention will be described with reference to the attached drawings.

First Embodiment

FIG. 1 is a radial direction sectional view of a valve timing adjusting apparatus of a first embodiment in the present invention, taken along a line 2-2 in FIG. 2, and FIG. 2 is an axial direction sectional view of the valve timing adjusting apparatus of the first embodiment in the invention, taken along a line 1-1 in FIG. 1.

In the drawings, a sprocket portion 2 for transmitting a driving force from a crank (not shown) is formed on the outer periphery of a case 1, and shoes 3a to 3d forming hydraulic chambers are provided in the inner peripheral portion of the case 1. Vanes 7a to 7d that divide the four hydraulic chambers formed by the shoes 3a to 3d of the case 1 into advance-side hydraulic chambers 5a to 5d and retard-side hydraulic chambers 6a to 6d, and that are also hydraulic pressure reception portions are disposed on the outer side of a rotor 4 at intervals of substantially 90 degrees. In the rotor 4, a boss portion 9 is in sliding contact with an inner sliding portion 8 of the case 1 having a predetermined clearance, and has oil seal and bearing functions.

Further, a recess is formed on the tip portion of the vanes 7a to 7d, and a seal member 10 for restricting a flow of oil between the hydraulic chambers is disposed thereon. Further, the rotor 4 is inserted into a camshaft (not shown) inside the boss portion 9 and fastened fixedly by a bolt (not shown). As shown in FIG. 2, the end surfaces of the case 1 and the rotor 4 are sealed by a cover 11 and a housing 12, and these are fastened by four bolts 13.

Hereinafter, oil passages formed in the rotor 4 will be described. It is configured that advance-side passages 17a to 17d and retard-side passages 18a to 18d are provided in the boss portion 9 of the rotor 4, each formed to penetrate the boss portion 9 in a radial direction to communicate with an oil passage (not shown) formed in the camshaft, and are communicated respectively with the advance-side hydraulic chamber 5a to 5d and the retard-side hydraulic chambers 6a to 6d, so that working oil can be supplied to the hydraulic chambers.

A hole 21 penetrated in the radial direction is formed in the shoe 3b of the case 1; when fitted into a fitting hole 22 formed in the boss portion 9 of the rotor 4, a lock pin 23 restricts the rotor 4 at the most advanced position that is a startup reference position, and is accommodated therein to be movable in an axial direction. The lock pin 23 is urged in a fitting direction by a spring 24, and the spring 24 is held by a stopper 25. Further, a retard-side hydraulic pressure is exerted on the lock pin 23 through a retard-side oil passage 26 opened at the bottom portion of the fitting hole 22, and when the hydraulic pressure is received at the tip portion thereof, the lock pin 23 retreats in a radial outward direction against the spring 24, thereby releasing the restriction on the rotor 4.

Next, an assist spring 27 for urging the rotor 4 in the advance direction will be described. Recesses 28, 29 penetrated in the axial direction are formed respectively in the vane 7a (to 7d) of the rotor 4 and the shoe 3a (to 3d) of the case 1, and holding members 30, 31 made of resin are inserted respectively into the recesses 28, 29. The assist spring 27 is inserted into assist spring insertion holes 32, 33 formed on the sides of the holding members 30, 31.

In such a way, the assist spring 27 is disposed in the advance-side hydraulic chamber. In the illustrated example, two assist springs 27 are disposed in each hydraulic chamber for a total of eight assist springs 27. In the most advanced position where a set length of the assist spring 27 is lengthened at a maximum, the assist spring 27 is disposed in a straight line, in view of ease of assembly thereof so that an assembly of the pair of holding members and the assist spring 27 can be inserted easily using a machine, and also with the aim of preventing an inconvenience in which the assist spring 27 is displaced in the radial direction to be deformed due to shortage of a support length provided by the holding members relative to the set length. In other words, in FIG. 1, a bottom surface: P of the holding member 30 and a bottom surface: Q of the holding member 31 are disposed to be parallel to each other.

In the most retarded position where the set length of the assist spring 27 is shortened at a minimum, the assist spring 27 is disposed to be in an arc shape that warps toward the inside of the apparatus. Further, a taper 35 for narrowing an opening is formed as a falling-out prevention portion in an opening edge portion of the recess 28 provided in the vane 7a (to 7d) on the side of the rotation-operating rotor, and a taper 34 that comes in contact with the taper 35, as shown in FIG. 4, is formed on the two sides of the holding member 30. In this manner, the holding member 30 can be prevented from falling out of the recess 28 mistakenly during a rotor operation.

The aim of disposing the holding members 30, 31 is to facilitate the ease of assembly when the plurality of assist springs 27 are disposed in the irregularly shaped space of the hydraulic chambers. Therefore, a predetermined gap is set between the holding members 30, 31 and the recesses 28, 29, respectively, so that the holding members can be inserted easily therein. As a result of this gap, it is configured that the holding members 30, 31 have backlash within the recesses 28, 29, respectively, whereby the holding members 30, 31 can produce tilts in longitudinal and latitudinal directions by the gap.

Hereupon, the holding members 30, 31 are formed out of resin, and a linear expansion coefficient thereof is larger than that of the case 1 (made of an iron-based sintered metal in the first embodiment) forming the space into which the holding members are inserted; thus, the dimension of the holding members 30, 31 in the axial direction of the apparatus is set to be smaller than that of the case 1 by an amount: AT corresponding to the difference in the linear expansion coefficient such that the holding members 30, 31 are not stretched within the case 1 at the time of the thermal expansion.

However, when the tilts of the holding member 30 discussed above are produced, as shown in FIG. 3, the dimension of the holding members 30, 31 in the axial direction of the apparatus is apparently larger than that of the vertical case, and as a result of such an expansion of the dimension, the holding members 30, 31 may be stretched within the case 1. Such a condition occurs on the rotor side, which may cause the reduction in the operating speed, the wear of the cover 11 and housing 12, and so on due to an increase in the frictional force.

In other words, when glass or the like, for example, is used in the holding member 30 as an add-in material to suppress the wear on the bearing surface of the assist spring 27, the wear on the other material is developed remarkably. In the first embodiment, a clearance between the holding members 30, 31 and the cover 11 and housing 12 is set at (ΔT+ΔC) or more in consideration of an increment: ΔC in the dimension in the axial direction of the apparatus due to the tilt of the holding member 30. Note that the thermal expansion ΔT of the holding member 30 is 40 μm at the maximum, and the tilt ΔC is 90 μm at the maximum. With such a configuration, the holding members 30, 31 are not stretched within the case 1 notwithstanding the backlash, so that the stable operability and durability of the apparatus can be obtained.

Further, as shown in FIG. 4, a tapered portion 36 of which the width: Lh is greater than a wire-to-wire distance: Ls of the assist spring 27 in the most advanced position (Lh>Ls) is formed in the inlets of the assist spring insertion holes 32, 33 in the holding members 30, 31. With such a setting, the assist spring 27 is gradually compressed with being deformed into an arc shape as the rotor 4 operates in the retard direction from the most advanced position (i.e. the wire-to-wire distance of the assist spring is reduced). However, an assist spring wire is not caught on the edge of the inlet portion of the holding member 30, and the assist spring 27 can be held with stability.

Next, an operation of the apparatus will be described. First, when the valve timing adjusting apparatus is controlled to the most advanced position that is a reference position during engine startup, idling or the like, an oil control valve (not shown) is not energized; hydraulic pressure is not supplied to the advance-side hydraulic chambers 5 through an in-engine advance-side passage (not shown), and the rotor 4 is fixed in the most advanced position. At this time, the bottom surfaces P, Q of the holding members 30, 31 are parallel to each other and the assist spring 27 is disposed in a straight line, as shown in FIG. 1. Further, the lock pin 23 is fitted into the fitting hole 22.

Subsequently, when a retard operation command is issued to the valve timing adjusting apparatus in response to an increase in the RPM (revolutions per minute) or the like, a predetermined current is applied to the oil control valve; as a result, a retard-side output port is opened, so that oil is initially supplied to the retard-side oil passage 26 of the valve timing adjusting apparatus through an in-engine retard-side passage (not shown); the pressure is received at the tip portion of the lock pin 23, so that the lock pin 23 is displaced in the radially outward direction against the urging force of the spring 24 to be drawn from the fitting hole 22, to thus release the restriction on the rotor 4.

Hereupon, in the fitting position of the lock pin 23, the retard-side passages 18a to 18d are closed by the shoe portions of the case 1, and therefore hydraulic pressure is not supplied to the retard-side hydraulic chambers 6. When the lock pin 23 is released, the rotor 4 is swung by cam alternating torque; thus, the closed retard-side passages are opened, so that the oil is supplied to the retard-side hydraulic chambers.

When the oil is supplied to the retard-side hydraulic chambers, rotary torque is generated in the rotor 4 in the retard direction; thus, the rotor 4 begins to operate against the torque of the assist spring in the advance direction, in combination with the cam torque in the retard direction. At this time, even when the tilts of the holding members 30, 31 are produced within the range of the gap between the members and the recesses 28, 29 by the vibrations of the engine and the like, and further engine oil that is a working fluid of the valve timing adjusting apparatus is heated to approximately 100° as the engine revolves, so that the holding members 30, 31 undergo thermal expansion, no holding members 30, 31 are stretched within the case 1, and the rotor 4 can operate normally.

As described above, according to the first embodiment, since the aim of disposing the holding members is to enhance the ease of attachment of the assist springs, it is configured that a predetermined gap is arranged between the holding members and the recesses in the vane and the shoe, so that the holding members can tilt within the range of the gap. In doing so, however, due to the tilts of the holding members caused by the thermal expansion upon an increase of oil temperature (the rotor and case are formed out of iron-based materials and thus have a smaller linear expansion coefficient than the holding members made of resin) or the tilts on the attachment of the holding members and the assist springs, the tilts due to rotor operations or vibrations, and so on, the holding members are fallen in a stretched state between the cover and the housing at the two ends, which leads to inconveniences such as the reduction in the rotor operating speed due to the friction and an increase in leakage due to the wear on the sliding surface of the cover; however, the clearance formed by the length in the axial direction of the holding member provided on the vane side and also the length in the axial direction of the case is set to be equal to or greater than the sum of an increment of the length in the axial direction in consideration of the tilt of the holding member produced by the gap between the holding member and the recess, and an increment due to the thermal expansion, and therefore the above conveniences can be prevented.

Further, since it is configured that the falling-out prevention means of the holding member is provided on the rotor side to thus prevent the holding member from tilting, the following inconvenience, for example, can be prevented: the holding member cannot keep up with the rotor which carries out a rapid advance operation under a high hydraulic pressure, resulting in falling out.

Furthermore, since the width of the taper provided in the inlet of the assist spring insertion hole of the holding member is set to be larger than the assist spring wire-to-wire distance in the most advanced position, even when the assist spring wire traverses the inlet portion of the holding member due to the tilt of the holding member and/or the compression of the assist spring accompanied by a rotor operation, no assist spring wire is caught on the edge of the inlet portion of the holding member; thus, a correct load of the assist spring can be generated, and the inclination of the holding member can also be suppressed. Moreover, the wear in the event that the outer side of the assist spring wire rubs against the inlet can be suppressed.

Further, it is configured that in the most advanced position where the set length of the assist spring is at a maximum, the assist spring is disposed to be in a straight line; therefore, the assist spring and holding member can be set with stability such that the backlash (tilt) of the holding member during the assembly can be suppressed to a minimum. Furthermore, since the assist spring is disposed to be in a straight line in the most unstable and easily deformed state such that the set length of the assist spring is at a maximum, the assist spring can be prevented from deforming into a U-shape.

INDUSTRIAL APPLICABILITY

The valve timing adjusting apparatus of the present invention is effective when applied to be attached to the camshaft on the exhaust side of the internal combustion engine to control opening and closing timings of the exhaust valve.

Claims

1. A valve timing adjusting apparatus having: a camshaft that drive a valve of an internal combustion engine to open and close; a case that has a plurality of shoes on an inner peripheral surface thereof, is rotatably provided on the camshaft, and is rotationally driven by an output of the internal combustion engine, and; a rotor that has a plurality of vanes provided on an outer peripheral surface thereof, each forming a retard hydraulic chamber and an advance hydraulic chamber between the vane and two side-wall surfaces in a circumferential direction of the corresponding shoe, is relatively rotatably housed in the case, and is coupled to the camshaft, comprising:

recesses provided opposite to the wall surfaces in the circumferential direction of the shoe and the vane in the advance hydraulic chamber;

a holding member insertion-disposed into each of the recesses from an axial direction of the rotor; and

an assist spring disposed between the holding member on the shoe side and the holding member on the vane side to urge the rotor in an advance direction,

wherein a clearance formed by a length in the axial direction of the rotor of the holding member provided on the vane side and a length in the axial direction of the rotor of the case is set to be equal to or greater than a sum of an increment of the length in the axial direction of the rotor in consideration of a tilt of the holding member produced by a gap between the holding member and the recess, and an increment due to thermal expansion thereof.

2. The valve timing adjusting apparatus according to claim 1, wherein a falling-out prevention portion for narrowing an opening is provided on the recess provided on the wall surface in the circumferential direction of the vane, and a first tapered portion that comes into contact with the falling-out prevention portion is formed on the holding member.

3. The valve timing adjusting apparatus according to claim 1, wherein a width in the axial direction of the assist spring of a second tapered portion provided on the holding member is set to be greater than a wire-to-wire distance of the assist spring when the assist spring is set in the most advanced position.

4. The valve timing adjusting apparatus according to claim 1, wherein the bottom surfaces of the holding members on the shoe side and on the vane side are parallel to each other in the most advanced position where a set length of the assist spring is at a maximum.