VARIABLE VALVE ACTUATION APPARATUS FOR INTERNAL COMBUSTION ENGINE

Abstract

A variable valve actuation apparatus for an internal combustion engine includes a first link arm which has a projected portion that is engageable with and disengageable from a guide rail, and which is displaceable in the axis direction of a camshaft, and a link shaft linked to the first link arm in such a manner as to allow rotation but constrain movement in the axis direction. When an electro-magnetic solenoid is electrified, the first link arm rotates about the link shaft so that the projected portion engages with the guide rail. In association with the displacement of the link arms that occurs during the engagement, the state of motion of second rocker arms changes, so that the opening characteristic of valves provided for each cylinder is switched.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a variable valve actuation apparatus for an internal combustion engine.

2. Description of the Related Art

Japanese Patent Application Publication No. 6-33714 (JP-A-6-33714), for example, discloses a variable valve actuation apparatus for an internal combustion engine. This related-art variable valve actuation apparatus includes an intake or exhaust valve, a low-speed cam, a high-speed cam, a main rocker arm that is drivable by the low-speed cam and that drives the intake valve or the exhaust valve, and a sub-rocker arm that is driven by the high-speed cam. Furthermore, the variable valve actuation apparatus includes a hydraulic piston mechanism as mode switch means for switching between a non-coordination mode in which the sub-rocker arm is not coordinated with the main rocker arm and a coordination mode in which the sub-rocker arm is coordinated with the main rocker arm.

By the way, in the variable valve actuation apparatus of an internal combustion engine, when the opening characteristic of valves is switched in association with an motion performed by an actuator, the actuator's drive force needed in order to drive a member that is driven by the actuator becomes inconveniently large if the inertia of the member is large, or if the friction force that occurs on the member when the actuator drives the member is large. Therefore, in order to switch the opening characteristic of valves while minimizing the required power, it is desirable that the inertia of the foregoing member be small and that the friction force that occurs on the member be small.

SUMMARY OF THE INVENTION

The invention provides a variable valve actuation apparatus for an internal combustion engine which reduces the inertia of a member that is driven by an actuator and reduces the friction that occurs on the member, and which favorably switches the opening characteristic of valves that are provided for at least two cylinders of the engine in association with motion performed by the actuator.

A variable valve actuation apparatus for an internal combustion engine in accordance with a first aspect of the invention includes: transfer members that are disposed between cams and valves and that transfer operating force of the cams to the valves; a camshaft on which the cams are provided; a guide rail provided on an outer peripheral surface of a cylindrical portion that is provided on the camshaft; a main displacement member which has an engagement portion that is engageable with and disengageable from the guide rail and which is displaceable in an axis direction of the camshaft; a member-linked shaft which is linked to the main displacement member in such a manner that, relative to the member linked shaft, the main displacement member is allowed to rotate and is constrained from moving in the axis direction; and an actuator that produces drive force for engaging the engagement portion of the main displacement member with the guide rail, wherein when the actuator operates, the main displacement member rotates about the member-linked shaft so that the engagement portion engages with the guide rail, and in association with displacement of the main displacement member and the member-linked shaft that occurs when the engagement portion and the guide rail are engaged, state of motion of the transfer member changes so that opening characteristic of the valves that are provided for at least two cylinders is switched.

According to the first aspect of the invention, since the main displacement member and the member-linked shaft is linked together in such a manner that relative rotation therebetween is possible, the main displacement member rotates alone without involving rotation of the member-linked shaft, when the actuator operates so as to engage the engagement portion of the main displacement member with the guide rail. Therefore, according to the first aspect, it becomes possible to reduce the inertia of the member that is driven by the actuator and reduce the friction force that occurs on the member, and to favorably switch the opening characteristic of valves that are provided for at least two cylinders in association with motion performed by the actuator.

Besides, in the foregoing construction, the main displacement member, the guide rail and the actuator may be provided corresponding to at least one but not all of the cylinders of the internal combustion engine, and the variable valve actuation apparatus may further include a subsidiary displacement member which is provided for at least one other cylinder that is not provided with the main displacement member, and which is displaced in operative connection with the main displacement member via the member-linked shaft, and the state of motion of the transfer member provided for the cylinder that is provided with the main displacement member may change in association with the displacement of the main displacement member that occurs when the engagement portion and the guide rail are engaged, and the state of motion of the transfer member provided for the at least one other cylinder that is provided with the subsidiary displacement member may change in association with the displacement of the subsidiary displacement member which is in operative connection with the displacement of the main displacement member.

Therefore, due to the construction provided in the first aspect, the inertia of the member that is driven by the actuator can be reduced, and the friction force that occurs on the member can be reduced. Besides, the state of motion of the transfer member of each cylinder can be changed through the utilization of the displacement of the main displacement member and the displacement of the subsidiary displacement member that is in operative connection with the displacement of the main displacement member.

In the foregoing construction, the transfer member, for each of the at least two cylinders, may include a first rocker arm that is oscillatable synchronously with the cams, and a second rocker arm that is able to push the valves, and the variable valve actuation apparatus may further include a switch pin that is disposed movably in a pin hole formed in the first rocker arm and in a pin hole formed in the second rocker arm, and the switch pin for the cylinder provided with the main displacement member may be displaced in operative connection with the displacement of the main displacement member, and the switch pin for the at least one cylinder that is provided with the subsidiary displacement member may be displaced in operative connection with the displacement of the subsidiary displacement member, and for the cylinder provided with the main displacement member, the first rocker arm and the second rocker arm may be switched via the switch pin between a linked state in which the first rocker arm and the second rocker arm are linked together and an unlinked state in which linkage between the first rocker arm and the second rocker arm is removed, in operative connection with the displacement of the main displacement member, and for the at least one cylinder provided with the subsidiary displacement member, the first rocker arm and the second rocker arm may be switched via the switch pin between the linked state in which the first rocker arm and the second rocker arm are linked together and the unlinked state in which the linkage between the first rocker arm and the second rocker arm is removed, in operative connection with the displacement of the subsidiary displacement member.

According to the foregoing construction, in a variable valve actuation apparatus of a type that switches between the state in which the first rocker arm and the second rocker arm are linked together and the unlinked state in which the linkage therebetween is removed, by utilizing the displacement of the switch pin, it becomes possible to reduce the inertia of the member that is driven by the actuator and reduce the friction force that occurs on the member and to switch between the foregoing linked state and the unlinked state.

In the foregoing construction, the member-linked shaft may be disposed within a rocker shaft that supports the first rocker arms and the second rocker arms.

According to this construction, by effectively utilizing the space present over the cylinder head of the internal combustion engine, it is possible to improve the mountability of the variable valve actuation apparatus on the internal combustion engine, in comparison with a construction in which the member-linked shaft is supported by a member that is separate from the rocker shaft.

Besides, in the foregoing construction, the second rocker arm may be used for a plurality of the valves that are provided for a cylinder.

According to this construction, a mounting space for the main displacement member and the subsidiary displacement member can be secured by utilizing the unoccupied space obtained as a result of the use, of the second rocker arm for two or more valves provided for a cylinder, in comparison with a construction in which one valve is driven by one second rocker arm.

Besides, in the foregoing construction, an outer peripheral surface of the member-linked shaft may be provided with a groove that has an annular or arcuate shape, and the member-linked shaft may penetrate an interior of the main displacement member, and the variable valve actuation apparatus may further include a pin that penetrates the main displacement member and that engages with the groove.

According to the foregoing construction, due to the engagement between the groove formed in the member-linked shaft and the pin that penetrates the main displacement member, it is possible to favorably realize the linkage between the main displacement member and the member-linked shaft in a manner that allows relative rotation between the main displacement member and the member-linked shaft but constrains relative movement therebetween in the axis direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, advantages, and technical and industrial significance of this invention will be described in the following detailed description of example embodiments of the invention with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a perspective view showing a variable valve actuation apparatus for an internal combustion engine according to an embodiment of the invention;

FIG. 2A and FIG. 2B are sectional views of portions of the variable valve actuation apparatus shown in FIG. 1, except a camshaft, which are taken on a plane that includes the axis of a rocker shaft shown in FIG. 1 and the axis of a switch pin also shown in FIG. 1;

FIG. 3 is an exploded perspective view of characteristic component elements of the variable valve actuation apparatus shown in FIG. 1; and

FIG. 4 is a view of the variable valve actuation apparatus of FIG. 1 which is taken in an axis direction of the camshaft (and the rocker shaft) (more specifically, the direction indicated by an arrow 4A in FIG. 2A).

DETAILED DESCRIPTION OF EMBODIMENTS

EMBODIMENT 1. Hereinafter, Embodiment 1 of the invention will be described with reference to FIG. 1 to FIG. 4. [CONSTRUCTION OF VARIABLE VALVE ACTUATION APPARATUS] (BASIC

CONSTRUCTION OF VARIABLE VALVE ACTUATION APPARATUS) FIG. 1 is a perspective view showing a variable valve actuation apparatus 10 for an internal combustion engine 1 according to Embodiment 1 of the invention. Incidentally, in FIG. 1, the illustration of a later-described camshaft 18 is omitted. Besides, although FIG. 1 shows only two cylinders (cylinders No. 1 and No. 2) while omitting the illustration of other cylinders and the like, the internal combustion engine 1 of Embodiment 1 is, for example, an in-line four-cylinder engine that has four cylinders (No. 1 to No. 4). Besides, each cylinder of the internal combustion engine 1 is provided with two intake valves and two exhaust valves. The variable valve actuation apparatus 10 functions as an apparatus that drives two intake valves or two exhaust valves that are disposed on each cylinder.

As shown in FIG. 1, each cylinder of the internal combustion engine 1 is provided with a first rocker arm 12 and a second rocker arm 14 that are adjacent to each other. The rocker arms 12 and 14 of each cylinder are rotatably (oscillatably) supported by one rocker shaft 16.

FIG. 2A and FIG. 2B are sectional views of portions of the variable valve actuation apparatus 10 excluding a camshaft 18, which are taken on a plane that includes the axis of the rocker shaft 16 shown in FIG. 1 and the axis of a switch pin 38 described below. FIG. 2A shows the variable valve actuation apparatus 10 in a linked state described below, and FIG. 2B shows the variable valve actuation apparatus 10 in an unlinked state described below. The camshaft 18 is linked to a crankshaft (not shown) by a timing chain or a timing belt so as to rotate at half the speed of the crankshaft. As shown in FIG. 2A and FIG. 2B, the camshaft 18 is provided with a main cam 20 and a subsidiary cam 22 for each cylinder. Besides, the rocker shaft 16 is disposed parallel to the camshaft 18.

The main cams 20 are each constructed as a cam that has an arcuate base circle portion that is coaxial with the camshaft 18 (i.e., a lift cam), and a nose portion formed so that a portion of the base circle portion is expanded radially outward. Besides, in Embodiment 1, the subsidiary cams 22 are each constructed as a cam that has only a base circle portion (i.e., a zero-lift cam).

As shown in FIG. 1, FIG. 2A and FIG. 2B, with regard to each cylinder, the first rocker arm 12 has a first roller 24 that is rotatably attached at such a position on the first rocker arm 12 that the first roller 24 can contact the main cam 20. The first rocker arm 12 is urged so that the first roller 24 is always in contact with the main cam 20, by a coil spring (not shown) that is attached to the rocker shaft 16. The first rocker arm 12 constructed as described above oscillates about the rocker shaft 16 that serves as a fulcrum, through cooperation of the operating force of the main cam 20 and the force of the aforementioned coil spring.

Besides, with regard to each cylinder, the second rocker arm 14 has a second roller 26 that is rotatably attached at such a position on the second rocker arm 14 that the second roller 26 can contact the subsidiary cam 22. Besides, at a rocker shaft 16-side end portion of the second rocker arm 14, the rocker shaft 16 is supported by a cam carrier 27 (or a cylinder head or the like) that is a stationary member of the internal combustion engine 1, via a lash adjuster (not shown). The second roller 26 provided on the second rocker arm 14 is urged toward the subsidiary cam 22 as the second roller 26 receives upward force from the lash adjuster.

Besides, an opposite end portion of the second rocker arm 14 from the rocker shaft side thereof is provided with a contact portion 14a that contacts two valves 28. Specifically, the second rocker arm 14 is used for both valves 28. More specifically, the second rocker arm 14 is disposed so as to be at an intermediate position between the two valves 28 that are provided for each cylinder. Besides, each valve 28 is urged in the closing direction by a valve spring 30 as shown in FIG. 1.

(CONSTRUCTION OF SWITCHING MECHANISM) The variable valve actuation apparatus 10 includes a switching mechanism 32 that switches between the linked state in which the first rocker arm 12 and the second rocker arm 14 are linked together (see FIG. 2A) and the unlinked state in which the linkage between the first rocker arm 12 and the second rocker arm 14 is removed. Due to the provision of the switching mechanism 32, the opening characteristic of the valves 28 is switched by switching between the state in which the operating force of the main cam 20 is transferred to the second rocker arm 14 via the first rocker arm 12 (the foregoing linked state) and the state in which the operating force of the main cam 20 is not transferred to the second rocker arm 14 (the foregoing unlinked state).

Hereinafter, the construction of the switching mechanism 32 will be described in detail with reference to FIG. 3 and FIG. 4 as well as FIG. 1 and FIGS. 2A and 2B. As shown in FIG. 2A and FIG. 2B, a first pin hole 34a concentric with the first roller 24 is formed within a spindle 34 of the first roller 24. Likewise, a second pin hole 36a concentric with the second roller 26 is formed within a spindle 36 of the second roller 26.

The centers of the pin holes 34a and 36a are disposed on an arc whose center is the rocker shaft 16, which is the rotation center of the rocker arms 12 and 14. Then, when the first roller 24 is in contact with the base circle portion of the main cam 20 and the second roller 26 is in contact with the base circle portion of the subsidiary cam 22, the position of the first pin hole 34a coincides with the position of the second pin hole 36a in a view in the axis direction.

Furthermore, a cylindrical switch pin 38 is slidably disposed in the pin holes 34a and 36a. Besides, an opposite end portion of the first pin hole 34a from the second rocker arm 14 is closed, and a second rocker arm 14-side end portion of the first pin hole 34a is open. The first pin hole 34a contains therein a return spring 40 that urges the switch pin 38 in the direction to the second rocker arm 14 (hereinafter, referred to as “advancement direction of the switch pin”). More specifically, the return spring 40 is constructed so as to always urge the switch pin 38 to the second rocker arm 14 side when it is actually mounted.

Besides, the second pin hole 36a is a penetration hole in which a cylindrical piston 42 is slidably inserted. Furthermore, for the cylinder No. 1, a first link arm 44 that has an arm portion 44a that contacts the piston 42 is disposed at a side surface of the second rocker arm 14 opposite the first rocker arm 12-side surface thereof. The first link arm 44 is attached to the rocker shaft 16.

On another hand, for the cylinder No. 2, a second link arm 46 that has an arm portion 46a that contacts the piston 42 is disposed at a side surface of the second rocker arm 14 opposite the first rocker arm 12-side surface thereof. The second link arm 46 is attached to the rocker shaft 16.

The first link arm 44 is different from the second link arm 46 in the following respects. That is, a distal end of the arm portion 44a of the first link arm 44 is provided with a projected portion 44b that is projected toward a peripheral surface of the camshaft 18. Besides, an opposite end portion of the first link arm 44 from the arm portion 44a is provided with a pressurization surface 44c that is pressurized by an electromagnetic solenoid 54 (described below). Incidentally, the link arms provided for the cylinders No. 3 and No. 4 are the same as the second link arm 46 of the cylinder No. 2.

FIG. 3 is an exploded perspective view of characteristic component elements of the variable valve actuation apparatus 10 shown in FIG. 1. Incidentally, FIG. 3 omits the first roller 24, the second roller 26, the switch pin 38 disposed in the first and second rollers, etc. Besides, FIG. 4 shows a view of the variable valve actuation apparatus 10 of FIG. 1 which is taken from the axis direction of the camshaft 18 (and of the rocker shaft 16) (more specifically, from the direction indicated by the arrow 4A in FIG. 2A).

As shown in FIGS. 3 and 4, the rocker shaft 16 has a hollow shape. Inside the rocker shaft 16, a link shaft 48 is inserted slidably relative to the rocker shaft 16. The link shaft 48 is provided for enabling the first link arm 44 disposed for the cylinder No. 1 and the second link arms 46 disposed for the cylinders No. 2 to No. 4 to be simultaneously displaced in the axis direction of the rocker shaft 16.

The link shaft 48 is provided with four annular grooves 48a that correspond to the placement sites of the link arms 44 and 46 of the four cylinders, as shown mainly in FIG. 3. Besides, a peripheral surface of the rocker shaft 16 is provided with four penetration holes 16a that correspond to the annular grooves 48a of the link shaft 48.

Besides, as shown in FIG. 4, the link shaft 48 and the rocker shaft 16 in which the link shaft 48 is inserted penetrate an interior of each link arm 44, 46. The link arms 44 and 46 have press-fit pin holes 44d and 46b, respectively, each of which receives a press-fit pin 50 that is press-fitted thereinto, as shown in FIG. 3. The press-fit pins 50, each penetrating a wall of a corresponding one of the link arms 44 and 46 through its pressure-fit hole 44d, 46b, are engaged with the corresponding annular grooves 48a, as shown in FIG. 4.

The width of the annular grooves 48a is set so as to be substantially equal to the diameter of the press-fit pins 50. Besides, each penetration hole 16a of the rocker shaft 16 has such a generous size as to avoid causing interference between the press-fit pin 50 and the electromagnetic solenoid 54 and therefore avoid impeding the rotation of the first link arm 44 (or the second link arm 46) when the first link arm 44 (or the second link arm 46) rotates in association with motion of the electromagnetic solenoid 54. Furthermore, each penetration hole 16a has such an elongated hole shape as to avoid causing interference between the penetration hole 16a and the press-fit pin 50 and therefore avoid impeding the movement of the link shaft 48 when the link shaft 48 moves in the axis direction thereof in association with motion of the electromagnetic solenoid 54.

Since the foregoing construction is adopted, the first link arm 44 is linked to the link shaft 48 in such a manner that the first link arm 44 is allowed to freely rotate but is constrained from moving in the axis direction of the link shaft 48. Likewise, the second link arms 46 are also linked to the link shaft 48 in such a manner that the second link arms 46 are allowed to freely rotate but are constrained from moving in the axis direction.

Besides, as shown in FIG. 2A, FIG. 2B and FIG. 4, a cylindrical portion 18a that has a cylindrical shape is provided on an outer peripheral surface of the camshaft 18 which faces a projected portion 44b that is provided on the arm portion 44a of the first link arm 44. An outer peripheral surface of the cylindrical portion 18a is provided with a helical guide rail 52 that extends in a circumferential direction. In this construction, the guide rail 52 is formed as a helical groove.

Besides, the switching mechanism 32 includes an electromagnetic solenoid 54 as an actuator that produces drive force for causing the projected portion 44b to be engaged with (inserted into) the guide rail 52. The electromagnetic solenoid 54 is duty-controlled on the basis of commands from an electronic control unit (ECU) 56. The ECU 56 is an electronic control unit that controls the state of operation of the internal combustion engine 1.

Besides, the electromagnetic solenoid 54 is fixed to a stationary member, such as the cam carrier 27 or the like, at such a position that a drive shaft 54a of the solenoid 54 is able to pressurize the pressurization surface 44c of the first link arm 44 toward the guide rail 52.

Besides, the orientation of the helix of the guide rail 52 is set such that when the camshaft 18 rotates in a predetermined rotation direction shown in FIG. 4 while the projected portion 44b is inserted in the helical groove, the first link arm 44, the link shaft 48 that moves in operative connection with the first link arm 44, and the second link arms 46 that are driven by the link shaft 48 are displaced in the leftward direction in FIG. 2. More concretely, the leftward direction in FIG. 2 is the direction in which each of the first link arm 44 and the second link arms 46 approaches its adjacent rocker arms 12 and 14 while pushing the switch pin 38 in the withdrawal direction thereof (that is opposite the foregoing advancement direction of the switch pin) against the force of the return spring 40.

The position of the first link arm 44 in FIG. 2A, that is, the position of the first link arm 44 at which the switch pin 38 is inserted in both the first pin hole 34a and the second pin hole 36a due to force of the return spring 40, is referred to as “displacement end Pmax1”. When the first link arm 44 is positioned at the displacement end Pmax1, the first rocker arm 12 and the second rocker arm 14 assume the foregoing linked state. The position of the first link arm 44 in FIG. 2B, that is, the position of the first link arm 44 at which the switch pin 38 and the piston 42 are inserted only in the first pin hole 34a and the second pin hole 36a, respectively, as the switch pin 38 receives from the link arm 44 the force that is caused by torque of the camshaft 18, is referred to as “displacement end Pmax2”. That is, when the first link arm 44 is positioned at the displacement end Pmax2, the first rocker arm 12 and the second rocker arm 14 assume the foregoing unlinked state.

In Embodiment 1, the position of a beginning end 52a of the guide rail 52 in the axis direction of the camshaft 18 is set so as to coincide with the position that the projected portion 44b assumes when the first link arm 44 is positioned at the displacement end Pmax1. The position of a terminating end 52b of the guide rail 52 in the axis direction of the camshaft 18 is set so as to coincide with the position that the projected portion 44b assumes when the first link arm 44 is positioned at the displacement end Pmax2. That is, Embodiment 1 is constructed so that the first link arm 44 is displaced between the displacement end Pmax1 and the displacement end Pmax2, in a range determined by the guide rail 52 guiding the projected portion 44b.

Furthermore, as shown in FIG. 4, the guide rail 52 is provided with a shallow bottom portion 52c in which the guide rail 52 gradually becomes shallower with rotation of the camshaft 18, as a predetermined section of the guide rail 52 on a terminating end 52b side which is used after the first link arm 44 reaches the displacement-end Pmax2. Incidentally, the depth of the guide rail 52 except the shallow bottom portion 52c is constant.

Besides, the first link arm 44 is provided with a cut-out portion 44e that is formed in a recess shape by cutting out a portion of the pressurization surface 44c. The pressurization surface 44c is provided so that contact thereof with the drive shaft 54a is maintained while the first link arm 44 is displaced from the displacement end Pmax1 to the displacement end Pmax2. Then, the cut-out portion 44e is provided at such a site on the first link arm 44 as to be engageable with the drive shaft 54a when the projected portion 44b is taken out from the guide rail 52 to the surface of the cylindrical portion 18a due to operation of the shallow bottom portion 52c during a state in which the first link arm 44 is positioned at the displacement end Pmax2.

The cut-out portion 44e is formed so as to engage with the drive shaft 54a in a manner such that the engagement of the cut-out portion 44e with the drive shaft 54a can restrict the first link arm 44 from rotating in such a direction that the projected portion 44b is inserted into the guide rail 52, and such that the engagement can restrict the first link arm 44 from moving in the advancement direction of the switch pin 38.

As described above, the switching mechanism 32 is constructed of the switch pin 38, the return spring 40, the piston 42, the first link arm 44, the second link arm 46, the link shaft 48, the press-fit pin 50, the guide rail 52, and the electromagnetic solenoid 54 whose electrification is controlled by the ECU 56.

[MOTIONS OF VARIABLE VALVE ACTUATION APPARATUS] (DURING VALVE ACTING STATE) During a valve acting state, the driving of the electromagnetic solenoid 54 is off. Therefore, the first link arm 44 is apart from the camshaft 18, and is positioned at the displacement end Pmax1 due to the force that the first link arm 44 receives from the return spring 40. In this state, the first rocker arm 12 and the second rocker arm 14 are linked together via the switch pin 38 (the foregoing linked state), with regard to each cylinder, as shown in FIG. 2A. As a result, the operating force of the main cam 20 is transferred from the first rocker arm 12 to the two valves 28 via the second rocker arm 14. Therefore, in accordance with the profile of the main cams 20, normal lift motion of the valves 28 is performed.

(DURING VALVE STOP CONTROL) A valve stop motion is performed when the ECU 56 detects a demand for executing a predetermined valve stop motion, for example, a demand for the fuel-cut of the internal combustion engine 1, and the like. Firstly, the electrification of the electromagnetic solenoid 54 is started at a predetermined timing. As a result, the first link arm 44 rotates about the rocker shaft 16 (the link shaft 48) clockwise in FIG. 4. As stated above, the first link arm 44 is linked to the link shaft 48 in such a manner as to be rotatable. Therefore, the link shaft 48 does not rotate while the first link arm 44 rotates.

If the first link arm 44 rotates as described above, the projected portion 44b engages with the guide rail 52. As a result, since the projected portion 44b is guided by the guide rail 52, torque of the camshaft 18 is utilized to produce a force to move the first link arm 44 toward the displacement end Pmax2. Then, the drive force of the first link arm 44 engaged with the guide rail 52 is transferred to the second link arms 46 via the press-fit pins 50 thereof and the link shaft 48. Therefore, the link shaft 48 linked to the first link arm 44, and the second link arms 46 linked to the link shaft 48 are displaced in operative connection with the first link arm 44.

When the first link arm 44 reaches the displacement end Pmax2, the switch pin 38 is returned into the first pin hole 34a, so that the first rocker arm 12 and the second rocker arm 14 assume the unlinked state. As a result, the operating force of the main cam 20 discontinues being transferred from the first rocker arm 12 to the second rocker arm 14. Besides, the subsidiary cams 22 that is in contact with the second rollers 26 of the second rocker arms 14 are zero-lift cams. Therefore, after the transfer thereto of the operating force of the main cam 20 discontinues, the second rocker arms 14 are no longer given force for driving the valves 28. As a result, irrespective of the rotation of the main cam 20, the second rocker arm 14 is in a stationary state, and the lift motion of the valves 28 is stopped at the closed valve position.

(MOTION FOR MAINTAINING THE VALVE STOPPED STATE) Besides, after the first link arm 44 reaches the displacement end Pmax2, the first link arm 44 is rotated in such a direction as to separate from the camshaft 18 (the guide rail 52) due to operation of the shallow bottom portion 52c of the guide rail 52. Then, when the first link arm 44 is further rotated so that the cut-out portion 44e of the first link arm 44 coincides with the drive shaft 54a that continues being driven by the electromagnetic solenoid 54, the contact site of the first link arm 44 with the drive shaft 54a switches from the pressurization surface 44c to the cut-out portion 44e. As a result, since the drive shaft 54a engages with the cut-out portion 44e, the first link arm 44 is held in a state in which the projected portion 44b is apart from the camshaft 18 and in which the drive shaft 54a bears the force of the return spring 40. Therefore, the state in which the first rocker arm 12 and the second rocker arm 14 are unlinked from each other, that is, the valve stopped state, is maintained. Besides, according to the motion of the drive shaft 54a holding the first link arm 44 through the utilization of the cut-out portion 44e, it is possible to maintain the valve stopped state while avoiding occurrence of friction and abrasion of the drive shaft 54a associated with the sliding between the drive shaft 54a and the camshaft 18 when the camshaft 18 rotates.

(DURING VALVE RETURNING MOTION) A valve returning motion for returning the valve state from the valve stopped state to the valve acting state is performed when the ECU 56 detects a demand for executing a predetermined valve returning motion, for example, a demand for return from the fuel-cut (a demand for discontinuation of the fuel-cut), or the like. This valve returning motion is started by turning off the electrification of the electromagnetic solenoid 54 at a predetermined timing. When the electrification of the electromagnetic solenoid 54 is turned off, the engagement between the cut-out portion 44e of the first link arm 44 and the drive shaft 54a of the electromagnetic solenoid 54 is removed. As a result, the force for retaining the switch pin 38 within the first pin hole 34a against the force of the return spring 40 disappears. Due to this, the force of the return spring 40 moves the switch pin 38 in the advancement direction, bringing back the state in which the first rocker arm 12 and the second rocker arm 14 are linked together via the switch pin 38, that is, the state in which the lift motion of the valves 28 can be carried out by the operating force of the main cams 20. Besides, as the switch pin 38 moves in the advancement direction due to the force of the return spring 40, the first link arm 44 (as well as the link shaft 48 and the second link arm 46 that is operatively connected to the first link arm 44) is returned from the displacement end Pmax2 to the displacement end Pmax1 by the piston 42.

According to the variable valve actuation apparatus 10 of Embodiment 1 constructed as described above, the position of the first link arm 44 in the axis direction is moved between the displacement end Pmax1 and the displacement end Pmax2 by utilizing the turning on and off of the electrification of the electromagnetic solenoid 54, the torque of the camshaft 18, and the force of the return spring 40. Therefore, as for the cylinder No. 1 equipped with the first link arm 44, it becomes possible to switch the motion state of the valves 28 between the valve acting state and the valve stopped state. Furthermore, as for the other cylinders (No. 2 to No. 4), too, it becomes possible to switch the motion state of the valves 28 between the valve acting state and the valve stopped state, via the link shaft 48 and the second link arms 46 that are operatively connected to the first link arm 44. Thus, according to the variable valve actuation apparatus 10, the motion state of the valves 28 disposed for the four cylinders of the internal combustion engine 1 can be switched by using one electromagnetic solenoid 54. Besides, according to the variable valve actuation apparatus 10 having the foregoing construction, the valve stopped state can be brought about with high response during one rotation of the camshaft 18, by utilizing the torque of the camshaft 18.

Besides, in the foregoing variable valve actuation apparatus 10, the first link arm 44 is linked to the link shaft 48 in such a manner that, relative to the link shaft 48, the first link arm 44 is allowed to freely rotate but is constrained from moving in the axis direction. According to this linking method, the first link arm 44 will rotate alone without involving rotation of the link shaft 48, when the electromagnetic solenoid 54 presses the first link arm 44. Unlike this construction, in a construction in which the first link arm is fixed to the link shaft, when the first link arm is rotated due to electrification of the electromagnetic solenoid, the link shaft will rotate together therewith. As a result, when the projected portion is engaged with the guide rail, the inertia of the member that is driven by the electromagnetic solenoid increases by an amount that corresponds to the link shaft, and the friction that occurs on the members at the time of driving of the electromagnetic solenoid increases by an amount that corresponds to the sliding between the link shaft and the rocker shaft that occurs during rotation of the link shaft. Therefore, the required thrust force of the electromagnetic solenoid increases, and a large-side electromagnetic solenoid becomes necessary.

In Embodiment 1, however, the first link arm 44 and the link shaft 48 are constructed so as to be rotatable relative to each other. Therefore, the inertia of the member that is driven by the electromagnetic solenoid 54 in order to engage the projected portion 44b with the guide rail 52 can be made small, and the friction force that occurs on the member can be made small. Therefore, the required thrust of the electromagnetic solenoid 54 can be favorably reduced, and the size of the electromagnetic solenoid 54 can be reduced.

Besides, in the variable valve actuation apparatus 10, the first link arm 44 and the second link arms 46 are mounted on the rocker shaft 16 that functions as a support shaft for the first rocker arms 12 and the second rocker arms 14. Besides, the two valves 28 of each cylinder are simultaneously driven by the second rocker arm 14 that has the contact portion 14a that contacts the two valves 28. This construction, in comparison with a construction in which one valve is driven by one second rocker arm, makes it possible to utilize the unoccupied space obtained as a result of the use of a second rocker arm 14 for two valves in order to mount the first link arm 44 and the second link arms 46 for switching the motion state of the valves 28. Due to this, by effectively utilizing the space present over the cylinder head of the internal combustion engine 1, it is possible to improve the mountability of the variable valve actuation apparatus 10 on the internal combustion engine 1.

Besides, in the foregoing variable valve actuation apparatus 10, the link shaft 48 that transfers the drive force of the first link arm 44 engaged with the guide rail 52 to the second link arms 46 of the other cylinders is disposed within the rocker shaft 16. This construction, in comparison with a construction in which the link shaft is supported by a member apart from the rocker shaft, makes it possible to effectively utilize the space present over the cylinder head of the internal combustion engine 1 in order to improve the mountability of the variable valve actuation apparatus 10 on the internal combustion engine 1. Besides, the construction eliminates the need for component parts for supporting the link shaft. Besides, in a construction in which a rocker arm is directly supported by a link shaft, unlike the construction of Embodiment 1, friction force occurs between the link shaft and the rocker arm that receives the operating force of the cams when the link shaft is displaced in the axis direction thereof. On the other hand, according to the construction of Embodiment 1, since the link shaft 48 is disposed within the rocker shaft 16, the operating force of the main cams 20 does not directly act on the link shaft 48 via the first rocker arms 12 and the second rocker arms 14, and therefore the friction force that occurs when the link shaft 48 is displaced in the axis direction can be reduced.

By the way, in Embodiment 1 described above, in association with displacement of the first link arm 44 and the link shaft 48 (as well as the displacement of the second link arms 46 that occurs during the engagement between the projected portion 44b of the first link arm 44 and the guide rail 52, the switch pin 38 of each cylinder is displaced. Then, as the first rocker arm 12 and the second rocker arm 14 of each cylinder are switched between the linked state and the unlinked state by displacement of the switch pin 38, the opening characteristic of the valves 28 of each cylinder is switched between the valve acting state and the valve stopped state. However, the variable valve actuation apparatus of the invention is not limited to the foregoing constructions as long as the opening characteristic of valves that are provided for at least two cylinders is switched as the motion state of a transfer member is switched in association with displacement of a main displacement member and a member-linked shaft which occurs when the engagement portion and the guide rail are engaged.

Concretely, the member that is displaced so as to switch the state of motion of the transfer member in association with displacement of the main displacement member and the member-linked shaft which occurs when the engagement portion and the guide rail are engaged is not limited to the switch pin 38. That is, for example, in a construction in which a rocker arm corresponding to the transfer member is rotatably supported by a rocker shaft, the foregoing member may also be a member that causes an operation in which in association with the movement of the main displacement portion and the member-linked shaft, the rocker arm is displaced on the rocker shaft in the axis direction of the rocker shaft, so that the cam that contacts the rocker arm is switched to another cam and therefore the state of motion of the rocker arm is switched. Alternatively, for example, in a construction that includes a rocker arm that has a roller that contacts cams, the foregoing member may also be a member that causes an operation in which in association with the displacement of the main displacement member and the member-linked shaft, the roller is displaced on the rocker arm in the axis direction of the spindle of the roller, so that the cam that contacts the roller is switched to another cam and therefore the state of motion of the rocker arm (transfer member) is switched. Also alternatively, for example, in a construction in which a rocker arm corresponding to the transfer member is rotatably supported by a rocker shaft, the foregoing member may also be a member that causes an operation in which in association with displacement of the main displacement member and the member-linked shaft, the rocker shaft itself is displaced in its own axis direction, so that the cam that contacts the rocker shaft is switched to another cam and therefore the state of motion of the rocker arm is switched. Furthermore, for example, in a construction in which a member equipped with two kinds of cams is mounted on a camshaft so as to be movable in the axis direction of the camshaft, the foregoing member may also be a member that causes an operation in which in association with displacement of the main displacement member and the member-linked shaft, the member equipped with two kinds of cams is displaced in the axis direction of the camshaft, so that the cam that contacts the transfer member is switched to another cam and therefore the state of motion of the transfer member is switched.

Besides, Embodiment 1 is described above with reference to an example that is the variable valve actuation apparatus 10 that drives the two valves that are disposed on each one of the four cylinders of the internal combustion engine 1. However, the variable valve actuation apparatus of the invention is not limited to the foregoing constructions but may have any construction as long as the opening characteristics of the valves provided for at least two cylinders are switched. That is, the variable valve actuation apparatus of the invention may be, for example, an apparatus constructed so as to drive the valves of all the cylinders of the internal combustion engine that has two or more cylinders, or may also be an apparatus constructed so as to drive the valves of at least two cylinders of an internal combustion engine that has three or more cylinders.

Besides, in Embodiment 1 described above, only the cylinder No. 1 of the four cylinders is equipped with the cylindrical portion 18a that has the guide rail 52, and with the electromagnetic solenoid 54 and the first link arm 44. However, in the invention, the cylinder equipped with elements that correspond to the foregoing components is not limited so, but may be any one or more of the cylinders of the engine as long as the foregoing cylinder does not correspond to each one of the cylinders. Alternatively, it is also permissible to adopt a construction in which the foregoing elements are provided separately from an arbitrary one of the cylinders and each cylinder is equipped with a subsidiary displacement member such as the second link arm 46 that does not have the projected portion 44b.

Besides, in Embodiment 1 described above, the first link arm 44 and the second link arms 46 are rotatably supported by utilizing the rocker shaft 16 that is provided for supporting the first rocker arm 12 and the second rocker arms 14. However, the member that supports the main displacement member or the subsidiary displacement member in the invention is not limited to the rocker shaft. That is, the member that supports the main displacement member and the subsidiary displacement member in the invention may be, for example, a shaft that is provided separately from the rocker shaft. Alternatively, the main displacement member and the subsidiary displacement member in the invention may be supported only by a member that functions as a member-linked shaft in the invention (for example, by the ring shaft 48).

Besides, in Embodiment 1 described above, the link shaft 48 is disposed within the rocker shaft 16. However, the technique of disposing the member-linked shaft in the invention is not limited to this disposal, but it is also permissible to adopt, for example, a construction in which a shaft that functions as the member-linked shaft is provided at an outer peripheral side of the rocker shaft.

Besides, in Embodiment 1 described above, the link shaft 48 is provided with the annular grooves 48a that engage with the press-fit pins 50, in order to link the first link arm 44 (and the second link arms 46 as well) to the link shaft 48 in such a manner that the first link arm 44 is allowed to rotate relative to the link shaft 48, and is constrained from moving in the axis direction of the link shaft 48. However, in the invention, the element provided for realizing the function of linking the main displacement member in such a manner that the main displacement member is allowed to freely rotate and is constrained from moving in the axis direction does not need to be the annular grooves 48a. That is, for example, in the case where there is provided a construction in which the press-fit pins are press-fit into the first link arms as in the construction of Embodiment 1 and where the link shaft has grooves that engage with the press-fit pins, it is not altogether necessary that the grooves be annular if the grooves are provided so that the press-fit pins will move without rotating the link shaft when the first link arm is rotated by the electromagnetic solenoid. For example, the grooves may be arcuate grooves.

Besides, although in Embodiment 1 described above, the subsidiary cams 22 are zero-lift cams, the subsidiary cam in the invention is not limited to a zero-lift cam. That is, in a construction as in the foregoing variable valve actuation apparatus 10, the subsidiary cams may have a nose portion that achieves a smaller lift than the nose portion of the main cams 20.

Besides, Embodiment 1 described above includes the electromagnetic solenoid 54 as an actuator that produces drive force for engaging the projected portion 44b with the guide rail 52. Therefore, the opening characteristic of the valves 28 can be switched by utilizing the actuator that is excellent in responsiveness. However, in the invention, the actuator is not limited so, but may also be, for example, a hydraulically driven actuator.

Incidentally, in Embodiment 1 described above, the main cams 20 function as a “cam” in the first aspect of the invention, and the first rocker arms 12 and the second rocker arms 14 each function as a “transfer member” in the first aspect, and the projected portion 44b functions as an “engagement portion” in the first aspect, and the first link arm 44 functions as a “main displacement member” in the first aspect, and the link shaft 48 functions as a “member-linked shaft” in the first aspect, and the electromagnetic solenoid 54 functions as an “actuator” in the first aspect. Besides, in Embodiment 1 described above, the second link arms 46 each function as a “subsidiary displacement member” in the first aspect. Besides, in Embodiment 1 described above, the annular grooves 48a function as a “groove” in the first aspect, and the press-fit pins 50 function as a “pin” in the first aspect.

Claims

1. A variable valve actuation apparatus for an internal combustion engine comprising:

transfer members that are disposed between cams and valves and that transfer operating force of the cams to the valves;

a camshaft on which the cams are provided;

a guide rail provided on an outer peripheral surface of a cylindrical portion that is provided on the camshaft;

a main displacement member which has an engagement portion that is engageable with and disengageable from the guide rail and which is displaceable in an axis direction of the camshaft;

a member-linked shaft which is linked to the main displacement member in such a manner that, relative to the member-linked shaft, the main displacement member is allowed to rotate and is constrained from moving in the axis direction; and

an actuator that produces drive force for engaging the engagement portion of the main displacement member with the guide rail, wherein when the actuator operates, the main displacement member rotates about the member-linked shaft so that the engagement portion engages with the guide rail, and in association with displacement of the main displacement member and the member-linked shaft that occurs when the engagement portion and the guide rail are engaged, state of motion of the transfer member changes so that opening characteristic of the valves that are provided for at least two cylinders is switched.

2. The variable valve actuation apparatus according to claim 1, wherein the main displacement member, the guide rail and the actuator are provided corresponding to at least one but not all of the cylinders of the internal combustion engine, and the variable valve actuation apparatus further comprising:

a subsidiary displacement member which is provided for at least one other cylinder that is not provided with the main displacement member, and which is displaced in operative connection with the main displacement member via the member-linked shaft, wherein the state of motion of the transfer member provided for the cylinder that is provided with the main displacement member changes in association with the displacement of the main displacement member that occurs when the engagement portion and the guide rail are engaged, and the state of motion of the transfer member provided for the at least one other cylinder that is provided with the subsidiary displacement member changes in association with the displacement of the subsidiary displacement member which is in operative connection with the displacement of the main displacement member.

3. The variable valve actuation apparatus according to claim 2, wherein the transfer member, for each of the at least two cylinders, includes a first rocker arm that is oscillatable synchronously with the cams, and a second rocker arm that is able to push the valves, the variable valve actuation apparatus further comprising:

a switch pin that is disposed movably in a pin hole formed in the first rocker arm and in a pin hole formed in the second rocker arm, wherein the switch pin for the cylinder provided with the main displacement member is displaced in operative connection with the displacement of the main displacement member, and the switch pin for the at least one other cylinder that is provided with the subsidiary displacement member is displaced in operative connection with the displacement of the subsidiary displacement member, and wherein for the cylinder provided with the main displacement member, the first rocker arm and the second rocker arm are switched via the switch pin between a linked state in which the first rocker arm and the second rocker arm are linked together and an unlinked state in which linkage between the first rocker arm and the second rocker arm is removed, in operative connection with the displacement of the main displacement member, and for the at least one other cylinder provided with the subsidiary displacement member, the first rocker arm and the second rocker arm are switched via the switch pin between the linked state in which the first rocker arm and the second rocker arm are linked together and the unlinked state in which the linkage between the first rocker arm and the second rocker arm is removed, in operative connection with the displacement of the subsidiary displacement member.

4. The variable valve actuation apparatus according to claim 3, wherein the member-linked shaft is disposed within a rocker shaft that supports the first rocker arms and the second rocker arms.

5. The variable valve actuation apparatus according to claim 3, wherein the second rocker arm is used for a plurality of the valves that are provided for a cylinder.

6. The variable valve actuation apparatus according to claim 1, wherein an outer peripheral surface of the member-linked shaft is provided with a groove that has an annular or arcuate shape, and the member-linked shaft penetrates an interior of the main displacement member, and the variable valve actuation apparatus further comprising:

a pin that penetrates the main displacement member and that engages with the groove.