Variable valve operating apparatus for internal combustion engine

Abstract

A variable valve operating apparatus including a drive cam, a rocker cam swingably moveable about the swing axis so as to move an engine valve to open and closing positions, a motion transmission mechanism operative to convert a rotational motion of the drive cam to a swing motion of the rocker cam, and a control shaft operative to control an attitude of the motion transmission mechanism to vary a valve lift of the engine valve. A roller or a follower portion are disposed on one end portion of the motion transmission mechanism on a side of the drive cam and contacted with the drive cam. A biasing member is arranged to bias the roller onto the drive cam through a roller shaft or biases the follower portion onto the drive cam through a support for the biasing member.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a variable valve operating apparatus for an internal combustion engine which variably controls a lift amount of engine valves, i.e., intake and/or exhaust valves.

Japanese Translation No. 2004-521234T of International Patent Application First Publication No. WO02092972 discloses a variable valve operating apparatus for an internal combustion engine. The variable valve operating apparatus of the conventional art includes a swing lever which is pivotally moved by a drive cam on a camshaft. The swing lever is operative to open and close an engine valve through a swing arm which is connected with the engine valve. The swing lever is contacted with a disk disposed on a control shaft to rotate the disk. A swing fulcrum of the swing lever is thus moved to thereby variably control a lift amount of the engine valve. A biasing spring applies a load to a tip end side of the swing lever.

SUMMARY OF THE INVENTION

The load applied by the biasing spring produces a counterclockwise moment in the swing lever about a contact point between the drive cam and a central roller mounted on a central portion of the swing lever. This moment is converted into a load which is applied to the disk through a roller mounted on an upper end portion of the swing lever. Therefore, the biasing force of the biasing spring acts on a bearing portion which supports the control shaft, and generates a load which is applied to the bearing portion. The load which is caused by the biasing force of the biasing spring is applied to the bearing portion even when the contact point between the drive cam and the central roller is placed in a base circle area of the drive cam, that is, even when the lift amount of the intake valve is 0.

When the variable valve operating apparatus is in a state before the control shaft is rotationally driven, an oil film is not fully formed between an inner circumferential surface of the bearing portion and an outer circumferential surface of the control shaft. In this condition, it is likely that metal-to-metal contact is caused between the inner circumferential surface of the bearing portion and the outer circumferential surface of the control shaft. The bearing portion undergoes load F of the biasing spring and friction of large friction coefficient p0 approximating to coefficient of static friction.

At this time, if the control shaft is rotated by a driving source such as an electric motor so as to vary valve lift characteristic, a large friction moment will be exerted on the bearing portion. The friction moment is given by the following expression: F×r×μ0

wherein r represents a radius of the bearing portion.

The friction moment suppresses a smooth rotational motion of the control shaft, causing delay in response to changeover of variable control of the valve lift. In particular, since a sliding speed is low until rotation of the control shaft is increased, the friction coefficient becomes large to thereby cause significant influence on the response to changeover of variable control of the valve lift.

It is an object of the present invention to solve the above-described problems of the conventional art and to provide a variable valve operating apparatus for an internal combustion engine, which is capable of enhancing response to changeover of variable control of the valve lift of engine valves.

The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.

In one aspect of the present invention, there is provided a variable valve operating apparatus for variably operating an engine valve of an internal combustion engine, the variable valve operating apparatus comprising:

a drive cam which is rotationally driven by a crankshaft of the engine;

a rocker cam having a swing axis and swingably moveable about the swing axis so as to move the engine valve to an open position and a closing position;

a motion transmission mechanism operative to convert a rotational motion of the drive cam to a swing motion of the rocker cam, the motion transmission mechanism including a roller shaft which is disposed on one end portion of the motion transmission mechanism on a side of the drive cam, and a roller which is rotatably supported on the roller shaft and contacted with the drive cam;

a control shaft rotatable depending on an operating condition of the engine, the control shaft being operative to control an attitude of the motion transmission mechanism to vary a valve lift of the engine valve; and

a biasing member which biases the roller onto the drive cam through the roller shaft.

In a further aspect of the invention, there is provided a variable valve operating apparatus for variably operating an engine valve of an internal combustion engine, the variable valve operating apparatus comprising:

a drive cam which is rotationally driven by a crankshaft of the engine;

a rocker cam having a swing axis and swingably moveable about the swing axis so as to move the engine valve to an open position and a closing position;

a motion transmission mechanism operative to convert a rotational motion of the drive cam to a swing motion of the rocker cam, the motion transmission mechanism including a follower portion which is disposed on one end portion of the motion transmission mechanism on a side of the drive cam, the follower portion being contacted with the drive cam and having a generally arcuate cross-section;

a control shaft rotatable depending on an operating condition of the engine, the control shaft being operative to control an attitude of the motion transmission mechanism to vary a valve lift of the engine valve;

a biasing member support disposed on the one end portion of the motion transmission mechanism on the side of the drive cam; and

a biasing member which biases the follower portion onto the drive cam through the biasing member support,

wherein the biasing member support is disposed on or near a line that extends across an axis of the drive cam and a center of curvature of the follower portion.

In a still further aspect of the invention, there is provided a variable valve operating apparatus for variably operating an engine valve of an internal combustion engine, the variable valve operating apparatus comprising:

a drive cam which is rotationally driven by a crankshaft of the engine;

a rocker cam having a swing axis and swingably moveable about the swing axis so as to move the engine valve to an open position and a closing position;

a motion transmission mechanism operative to convert a rotational motion of the drive cam to a swing motion of the rocker cam, the motion transmission mechanism including one end portion which is contacted with the drive cam;

a control shaft rotatable depending on an operating condition of the engine, the control shaft being operative to control an attitude of the motion transmission mechanism to vary a valve lift of the engine valve;

biasing means for biasing the one end portion of the motion transmission mechanism onto the drive cam; and

support means for supporting the biasing member thereon;

wherein the biasing means and the support means are arranged such that a biasing force of the biasing means is applied to the one end portion of the motion transmission mechanism through the support means substantially along a line that extends across the support means and an axis of the drive cam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a first embodiment of a variable valve operating apparatus according to the present invention.

FIG. 2 is a perspective view of the variable valve operating apparatus of the first embodiment.

FIG. 3 is a perspective view of the variable valve operating apparatus of the first embodiment when viewed from a direction different from that in FIG. 2.

FIG. 4 is an explanatory diagram showing a non-lift operation of the variable valve operating apparatus of the first embodiment under minimum valve lift control of an engine valve.

FIG. 5 is an explanatory diagram showing a lift operation of the variable valve operating apparatus of the first embodiment under the minimum valve lift control of an engine valve.

FIG. 6 is an explanatory diagram showing a non-lift operation of the variable valve operating apparatus of the first embodiment under maximum valve lift control of an engine valve.

FIG. 7 is an explanatory diagram showing a lift operation of the variable valve operating apparatus of the first embodiment under the maximum valve lift control of an engine valve.

FIG. 8 is an explanatory diagram showing a biasing action of a spring in the variable valve operating apparatus of the first embodiment upon the non-lift operation under the minimum valve lift control of an engine valve.

FIG. 9 is an explanatory diagram showing a biasing action of the spring in the variable valve operating apparatus of the first embodiment upon the non-lift operation under the maximum valve lift control of an engine valve.

FIG. 10 is a cross-section of an essential part of a second embodiment of the variable valve operating apparatus according to the present invention.

FIG. 11 is a cross-section of an essential part of a third embodiment of the variable valve operating apparatus according to the present invention.

FIG. 12 is a side view of an essential part of a fourth embodiment of the variable valve operating apparatus according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1-9, a first embodiment of a variable valve operating apparatus for an internal combustion engine according to the present invention, is explained. For ease of understanding, various directional terms, such as right, left, upper, lower, rightward and the like are used in the description. However, such terms are to be understood with respect to only a drawing or drawings on which a corresponding part or portion is shown. The variable valve operating apparatus of the first embodiment is used on an intake side of the engine with two intake valves per cylinder.

As illustrated in FIGS. 1-3, variable valve operating apparatus 100 of the first embodiment includes two intake valves 2, 2 provided on cylinder head 1, drive shaft 3 which is rotatably supported on cylinder head 1 through bearing member 8, two swing arms 4, 4 each having one end portion contacted with a stem end of each of intake valves 2, 2, two hydraulic lash adjusters 5, 5 which are contacted with the other end portion of each of swing arms 4, 4, a pair of rocker cams 6, 6 which operate intake valves 2, 2 through swing arms 4, 4, motion transmission mechanism 7 which acts to convert torque of drive shaft 3 to a swing motion of respective rocker cams 6, 6, and a control mechanism which controls an attitude of motion transmission mechanism 7 depending on an operating condition of the engine.

Intake valves 2, 2 as engine valves are operative to open and close a pair of intake ports, not shown, which are formed in cylinder head 1. Each of intake valves 2, 2 has an open position in which intake valve 2 opens the intake port and a closing position in which intake valve 2 closes the intake port. Intake valves 2, 2 is slidably held in cylinder head 1 through a valve guide, not shown. Intake valve 2 is biased toward the closing position by valve spring 9. Valve spring 9 is arranged between a spring retainer fixed to the vicinity of the stem end of intake valve 2, namely, the vicinity of an upper end of intake valve 2 as shown in FIG. 1, and a bottom of a recess, not shown, formed in cylinder head 1.

Drive shaft 3 extends in a fore-and-aft direction of the engine. Drive shaft 3 has axis X and is driven by a crankshaft of the engine so as to rotate about axis X. Drive shaft 3 receives input torque from the crankshaft through a driven sprocket, not shown, that is mounted to one end portion of drive shaft 3, and a timing chain, not shown, that is wound on the driven sprocket. Drive shaft 3 has drive cam 10 which is fixedly disposed on an outer circumferential surface of drive shaft 3.

Single drive cam 10 is provided for each cylinder of the engine. Drive cam 10 is integrally formed with drive shaft 3 and rotatable about axis X of drive shaft 3 in synchronization with the crankshaft of the engine. Drive cam 10 has a generally cocoon shape in a side view as shown in FIG. 1. Drive cam 10 includes base-circle portion 10a and lift portion 10b which projects from base-circle portion 10a and has a generally arcuate shape as shown in FIG. 1.

As shown in FIG. 1, drive shaft 3 is rotatively supported by bearing member 8. Specifically, bearing member 8 includes frame 8a fixedly disposed on an upper end of an outer periphery of cylinder head 1, bracket 8b for cylinder head 1, and cap 8c on bracket 8b. Frame 8a and bracket 8b cooperate with each other to support drive shaft 3 so as to be rotatable about axis X. Frame 8a has a bearing groove on an upper surface opposed to a lower surface of bracket 8b. Bracket 8b has a bearing groove on the lower surface thereof. The bearing groove of frame 8a and the bearing groove of bracket 8b have a semi-circular section. Drive shaft 3 is rotatively supported in the bearing grooves of frame 8a and bracket 8b. Bearing member 8 further supports control shaft 20 which is disposed above drive shaft 3. Specifically, bracket 8b and cap 8c cooperate with each other to support control shaft 20. Bracket 8b has a bearing groove on an upper surface opposed to a lower surface of cap 8c, and cap 8c has a bearing groove on the lower surface thereof. The bearing groove of bracket 8b and the bearing groove of cap 8c have a semi-circular section. Control shaft 20 is rotatably supported in the bearing grooves of bracket 8b and cap 8c.

As shown in FIGS. 1 and 2, each of swing arms 4, 4 has an elongated rectangular shape in plan view. The one end portion of swing arm 4 is contacted at a lower surface thereof with the stem end of each of intake valves 2, 2. The other end portion of swing arm 4 is formed with a semi-spherical recess on a lower surface thereof and contacted at the recess with a semi-spherical head of plunger 5b of each of hydraulic lash adjusters 5, 5. The other end portion of swing arm 4 thus is pivotally supported by hydraulic lash adjuster 5. Swing arm 4 includes a roller retaining hole between the opposed end portions of swing arm 4. Roller 4a is rotatably supported by roller shaft 4b within the roller retaining hole.

Each of hydraulic lash adjusters 5, 5 is of a known type. Hydraulic lash adjuster 5 includes a closed-ended cylindrical body 5a fixedly fitted to cylindrical mount hole la that is formed in cylinder head 1, and plunger 5b that is disposed in body 5a so as to be slidable in an axial direction of body 5a. Plunger 5b has a hydraulic chamber therein and a communication hole on a lower end portion of plunger 5b. The hydraulic chamber is communicated with a higher pressure chamber within body 5a through the communication hole. A check valve is disposed within the higher pressure chamber and biased to close the communication hole. When, under operation of the engine, plunger 5b is downwardly moved by the other end portion of swing arm 4, the hydraulic pressure in the hydraulic chamber is increased to open the check valve and supply the higher pressure chamber with a hydraulic pressure. At this time, plunger 5b is forced to move upwardly so that a clearance between the one end portion of swing arm 4 and the stem end of the corresponding intake valve 2 is adjusted to zero.

As seen from FIGS. 1-3, rocker cams 6, 6 are supported on drive shaft 3 so as to be swingable about axis X as a swing axis and be slidable on drive shaft 3. Drive cam 10 is disposed between rocker cams 6, 6. Each of rocker cams 6, 6 has a generally C-shape in side view as shown in FIG. 1 and is formed with cylindrical central groove 6a in which drive shaft 3 is engaged. As shown in FIG. 1, rocker cam 6 includes cam surface 6b on an outer peripheral surface of a lower portion of rocker cam 6, and boss portion 6c disposed circumferentially adjacent to cam surface 6b. Boss portion 6c radially extends from the outer peripheral surface of rocker cam 6 and has a pin mount hole for receiving pin 19 as explained later.

Central groove 6a is formed into a generally U-shape in side view as shown in FIG. 1. Rocker cam 6 includes opposed contact surfaces which extends in parallel to each other and define an opening of U-shaped central groove 6a therebetween. The contact surfaces are engaged with two planar contact surfaces 3a which are formed in a predetermined position of an outer circumferential surface of drive shaft 3 as shown in FIG. 2. Rocker cam 6 is fitted onto the outer circumferential surface of drive shaft 3 by moving in an axial direction of drive shaft 3 after engaging the contact surfaces of rocker cam 6 and drive shaft 3 with each other. Rocker cam 6 is thus rotatably and slidably supported on the outer circumferential surface of drive shaft 3. Cam surface 6b includes base-circle surface 6d located on a side of the opening of U-shaped central groove 6a, and lift surface 6e located on a side of boss portion 6c.

Motion transmission mechanism 7 includes rocker arm 11 which is swingably supported on control cam 21 as explained later, roller 14 which is contacted with drive cam 10, roller shaft 17 which supports roller 14, and a pair of links 15, 15 which connect rocker arm 11 and rocker cams 6, 6.

Specifically, rocker arm 11 is bent to form a generally arcuate shape in side view as shown in FIG. 1. Rocker arm 11 includes cylindrical base portion 16 formed with support bore 16a through which base portion 16 is swingably fitted onto control cam 21. Rocker arm 11 further includes one end portion 12 which is downwardly curved into a generally arcuate shape and projects from base portion 16 toward drive cam 10, and the other end portion 13 which is downwardly curved into a generally arcuate shape and projects from base portion 16 toward link rods 15, 15.

One end portion 12 of rocker arm 11 has at least a pair of support walls for supporting roller shaft 17. In this embodiment, a pair of support walls 12a, 12a are provided as shown in FIG. 3. Support walls 12a, 12a are spaced from each other along an axial direction of control cam 21 and integrally formed with rocker arm 11. Support walls 12a, 12a are relatively thinned and parallel to each other and formed with shaft insertion holes into which roller shaft 17 is inserted as explained later. As shown in FIGS. 2 and 3, the other end portion 13 is bifurcated into two end portions. Bifurcated end portions 13, 13 are substantially symmetrically arranged with respect to a center line of base portion 16 which extends perpendicular to a swing axis of base portion 16, in order to attain balance between bifurcated end portions 13, 13. In this embodiment, bifurcated end portions 13, 13 form a generally V-shape as shown in FIG. 2. Each of bifurcated end portions 13, 13 has a pin insertion hole on a tip end portion thereof into which pins 18, 18 are inserted as explained later.

As seen from FIGS. 1 and 3, roller 14 is disposed between support walls 12a, 12a of one end portion 12 of rocker arm 11. Roller 14 is rotatably supported on an outer circumferential surface of roller shaft 17 extending between support walls 12a, 12a, through a suitable bearing, for instance, a needle bearing or a plain bearing. Roller shaft 17 is press-fitted into the shaft insertion holes of support walls 12a, 12a and has opposite end portions 17a and 17b which outwardly extend from the shaft insertion holes over a predetermined length.

Each of link rods 15, 15 is pressed into a generally C-shape in cross-section in view of weight reduction and facilitation in forming operation. Link rod 15 has one end portion 15a which is connected with each of bifurcated end portions 13 of rocker arm 11 through pin 18 and pivotally supported at end portion 13. One end portion 15a is bifurcated as shown in FIG. 2. The other end portion 15b of link rod 15 is connected with boss portion 6c of each of rocker cams 6, 6 through pin 19 and pivotally supported at boss portion 6c. Pin 19 acts as a fulcrum of the swing motion of rocker arm 11 relative to each of rocker cams 6, 6.

In thus-constructed motion transmission mechanism 7, roller shaft 17, rocker arm 11, link rods 15, 15 and rocker cams 6, 6 are in positive motion connection with each other. That is, rocker cams 6, 6 are forced to swing in both of a clockwise direction and a counterclockwise direction by motion transmission mechanism 7.

The control mechanism includes control shaft 20 arranged parallel to drive shaft 3, control cam 21 disposed on control shaft 20, an actuator, not shown, which operates control shaft 20 in positive and reverse rotational directions depending on an engine operating condition, and an electronic controller, not shown, which controls the actuator.

Control shaft 20 extends in the fore-and-aft direction of the engine. As seen from FIGS. 1 and 2, control shaft 20 is rotatably supported by bearing member 8 through journals 20a, 20a. Control shaft 20 is rotatable about axis P depending on an operating condition of the engine. Control shaft 20 is operative to control an attitude of motion transmission mechanism 7 to vary a valve lift of intake valves 2, 2. Control shaft 20 has one end portion which is connected with a drive shaft of the actuator.

Control cam 21 is disposed in a predetermined position on an outer circumferential surface of control shaft 20 and integrally formed with control shaft 20. There is provided one control cam 21 per cylinder. As shown in FIG. 1, control cam 21 is arranged within support bore 16a of base portion 16 of rocker arm 11 such that axis P1 of control cam 21 is offset from axis P of control shaft 20 by predetermined distance α.

The actuator may be electrically operated and may include an electric motor and a speed reducer. The actuator is so constructed as to operate control shaft 20 in the positive and reverse rotational directions and hold control shaft 20 in a predetermined rotational position thereof depending on the engine operating condition. The electric motor as the actuator may be controlled by the electronic controller.

The electronic controller is so constructed as to detect the current operating condition of the engine by calculating input signals from various sensors such as a crank angle sensor, a throttle position sensor, a water temperature sensor and an airflow meter, and control an electric current that is outputted to the electric motor on the basis of the detected engine operating condition.

As shown in FIGS. 1-3, variable valve operating apparatus 100 further includes biasing member 22 that biases roller 14 onto drive cam 10 through roller shaft 17. Biasing member 22 is arranged to apply the biasing force through roller shaft 17 substantially along a line that extends across an axis of roller shaft 17 and the axis of drive cam 10, namely, axis X of drive shaft 3.

Biasing member 22 is in the form of a return spring which has a generally U-shape in plan view. As seen from FIGS. 1-3, biasing member 22 includes U-shaped base portion 22a, turned portions 22b, 22b downwardly extending from opposite sides of base portion 22a, and tip end portions 22c, 22c which extend from turned portions 22b, 22b. As seen from FIGS. 1 and 3, tip end portions 22c, 22c are contacted with an upper portion of an outer circumferential surface of end portions 17a and 17b of roller shaft 17 and applies the biasing force to end portions 17a and 17b of roller shaft 17. Base portion 22a is fixed to rocker cover 23 through bracket 24 by means of bolts 25, 25. Turned portions 22b, 22b are spaced from and opposed to each other in a direction substantially parallel to axis X of drive shaft 3. Tip end portions 22c, 22c are elastically contacted with an upper side of an outer circumferential surface of end portions 17a and 17b of roller shaft 17 and bias end portions 17a and 17b in a downward direction as shown in FIG. 1. Biasing force FS of biasing member 22 is exerted on end portions 17a and 17b in a direction that extends across the axis of roller shaft 17, namely, an axis of roller 14, and the contact portion between each of tip end portions 22c, 22c and the corresponding end portion 17a and 17b substantially toward axis X of drive shaft 3. In FIG. 1, biasing force FS of biasing member 22 extends from the contact point between tip end portion 22c and the corresponding end portion 17a of roller shaft 17 across the axis of roller shaft 17 as indicated by an arrow of solid line. Biasing force FS thus acts on roller 14 so as to press roller 14 against drive cam 10.

An operation of the variable valve operating apparatus of the embodiment will be explained hereinafter. A rotational force that is transmitted from the crankshaft of the engine to drive shaft 3 is transmitted to drive cam 10 to thereby rotate drive cam 10. The rotation of drive cam 10 is transmitted to roller 14 so that rocker arm 11 swings around control cam 21. Thus, the rotational motion of drive cam 10 is converted to the swing motion of rocker arm 11. The swing motion of rocker arm 11 is transmitted to rocker cams 6, 6 via respective link rods 15, 15 so that rocker cams 6, 6 swing about pins 19, 19 at boss portions 6c, 6c. Owing to the swing motion of rocker cams 6, 6, roller 4a of each of swing arms 4, 4 rolls on cam surface 6b of each of rocker cams 6, 6, namely, base-circle surface 6d and lift surface 6e. Swing arm 4 is swung about plunger 5b of hydraulic lash adjuster 5 as a fulcrum of the swing motion and operate intake valve 2 against the spring force of valve spring 9.

Next, an operation of variable lift control of the variable valve operating apparatus of the embodiment is explained with reference to FIGS. 4-7. When the engine is operated in a low-rotation and low-load range such as idle running and the electronic controller has detected this operating condition of the engine, the electronic controller performs small-lift control. FIG. 4 shows non-lift state under the small-lift control, and FIG. 5 shows a peak lift state under the small-lift control. In the small-lift control, the electronic controller operates the actuator so as to rotationally move control shaft 20 to predetermined rotational positions shown in FIGS. 4 and 5. At this time, control cam 21 integrally formed with control shaft 20 is moved to the rotational positions in which axis P1 is rightward offset from axis P of control shaft 20 as shown in FIGS. 4 and 5. In the positions shown in FIGS. 4 and 5, a thickened portion of control cam 21 is located on a right side.

The rotational movement of control cam 21 causes rocker arm 11 to be slightly rotated in a clockwise direction as shown in FIGS. 4 and 5. Owing to the rotational movement of rocker arm 11, each of rocker cams 6, 6 which is coupled to rocker arm 11 via each of link rods 15, 15 is slightly rotated about pin 19 in the clockwise direction as shown in FIGS. 4 and 5. The contact point between roller 4a of swing arm 4 and cam surface 6b of rocker cam 6 is displaced from a substantially central portion of cam surface 6b to a portion of cam surface 6b close to base-circle surface 6d.

Under the small lift control, each of intake valves 2, 2 which is moved to the open position and the closed position by each of rocker cams 6, 6 has a minute peak-lift amount as indicated at L1 in FIG. 5. As a result, a flow rate of an air-fuel mixture can be increased, thereby facilitating producing a turbulent flow of the air-fuel mixture. This serves for enhancing combustion of the air-fuel mixture and therefore increasing fuel economy and stability of the engine rotation.

On the other hand, when the operating condition of the engine is shifted to a high-rotation and high-load range and the electronic controller has detected that the operating condition of the engine is in this range, the electronic controller performs large-lift control. FIG. 6 shows non-lift state under the large-lift control, and FIG. 7 shows a peak lift state under the large-lift control. In the large-lift control, the electronic controller operates the actuator so as to rotationally move control shaft 20 to rotational positions shown in FIGS. 6 and 7. At this time, control cam 21 is moved to the rotational positions in which axis P1 is downwardly offset from axis P of control shaft 20 as shown in FIGS. 6 and 7. In the positions shown in FIGS. 6 and 7, a thickened portion of control cam 21 is located on a right-lower side.

The rotational movement of control cam 21 causes rocker arm 11 to be slightly rotated in a counterclockwise direction as shown in FIGS. 6 and 7. Owing to the rotational movement of rocker arm 11, each of rocker cams 6, 6 is slightly rotated about pin 19 in the counterclockwise direction as shown in FIGS. 6 and 7 and is placed in a position where each of boss portions 6c, 6c is held closer to swing arms 4, 4. The contact point between roller 4a of swing arm 4 and cam surface 6b of rocker cam 6 is displaced from a substantially central portion of cam surface 6b to a portion of cam surface 6b close to lift surface 6e.

Under the large-lift control, each of intake valves 2, 2 has a large peak-lift amount as indicated at L2 in FIG. 7. As a result, a power output of the engine can be enhanced.

Referring to FIGS. 8 and 9, a relationship between the biasing force of biasing member 22 and a load that acts on control shaft 20 due to the biasing force of biasing member 22, is explained.

FIG. 8 shows the relationship between the biasing force of biasing member 22 and the load that acts on control shaft 20 in the non-lift state under the small-lift control as shown in FIG. 4. In the non-lift state under the small-lift control, the contact point between roller 4a of swing arm 4 and cam surface 6b of rocker cam 6 is placed in base-circle surface 6d, whereby rocker cam 6 is substantially free from a rotation moment that is caused by the spring force of valve spring 9. Therefore, rocker arm 11 is substantially prevented from undergoing a load that is applied to rocker arm 11 through link rod 15 and rocker cam 6.

In this condition, as illustrated in FIG. 8, load FS is exerted on end portions 17a, 17b of roller shaft 17 through tip end portions 22c, 22c of biasing member 22 due to the biasing force of biasing member 22. Load FS is indicated as a vector that extends from the axis of roller shaft 17 substantially toward axis X of drive shaft 3 as shown in FIG. 8.

In reaction to load FS, load FC is exerted on roller 14 contacted with drive cam 10, through the contact point between an outer circumferential surface of roller 14 and an outer circumferential surface of drive cam 10. Load FC is indicated as a vector that extends from the axis of roller shaft 17 in a direction substantially opposed to the direction of load FS which extends across axis X of drive shaft 3.

A resultant of loads FS and FC is considerably small in magnitude as compared to load FS. This is because load FS and load FC act in substantially diametrically opposite directions relative to roller shaft 17 and have a same magnitude. The resultant of loads FS and FC is indicated as a vector FT in FIG. 8. In this state, load FT′ acts on control cam 21 and journals 20a, 20a of control shaft 20. Load FT′ is equal to resultant FT of loads FS and FC owing to the balance between the resultant and load FT′. Accordingly, load FT′ is considerably small. Load FT′ is shared by two journals 20a, 20a, and therefore, the shared load is FT′/2. Load FT′ as a bearing load is applied to a circumferential surface, namely, a bearing surface, of support bore 16a of rocker arm 11 through control cam 21. The shared load FT′/2 as a bearing load is applied to a bearing surface of bearing member 8 through journals 20a, 20a. Thus, the load that acts on journals 20a, 20a of control shaft 20 and the bearing surface of bearing member 8 is remarkably small.

FIG. 9 shows the relationship between the biasing force of biasing member 22 and the load that acts on control shaft 20 in the non-lift state under the large-lift control as shown in FIG. 6. In the non-lift state under the large-lift control, load FT′ that acts on control cam 21 and the bearing surface of support bore 16a of rocker arm 11 is considerably small, and the load that acts on journals 20a, 20a of control shaft 20 and the bearing surface of bearing member 8 is considerably small, similar to in the non-lift state under the small-lift control.

Thus, the load that acts on control cam 21 and journals 20a, 20a of control shaft 20 is considerably small in the respective non-lift state under the small-lift control and the large-lift control, irrespective of the valve lift amount.

On the other hand, in the respective peak-lift state under the small-lift control and the large-lift control, rocker cam 6 undergoes the rotation moment that is caused by the spring force of valve spring 9. Owing to the rotation moment, a load is exerted on control cam 21 and journals 20a, 20a of control shaft 20 via rocker arm 11 and link rods 15, 15. Further, a load acts on control cam 21 and journals 20a, 20a of control shaft 20 due to the biasing force of biasing member 22, but the load is considerably small similar to the respective non-lift state under the small-lift control and the large-lift control.

As explained above, in variable valve operating apparatus 100 of this embodiment, the load that acts on control cam 21 and journals 20a, 20a of control shaft 20 due to the biasing force of biasing member 22 is considerably small in both of the non-lift state and the peak-lift state under the small-lift control and the large-lift control. This allows quick start of rotation of control shaft 20 in response to changeover of the valve lift control of engine valves 2, 2. As a result, a response to changeover of the valve lift control in this embodiment can be improved as compared to the conventional art.

Specifically, the response at the moment at which control shaft 20 starts to rotate is more likely to undergo influence in the non-lift state in which the load exerted on the bearing surface of bearing member 8 through journals 20a, 20a of control shaft 20 is small. That is, control shaft 20 can quickly start to rotate in the non-lift state in which the bearing load exerted on the bearing surface of bearing member 8 is small.

In this embodiment, the bearing load that is exerted on the bearing surface of bearing member 8 through journals 20a, 20a of control shaft 20 is remarkably reduced in the non-lift state. In contrast, a large bearing load is kept exerted on the bearing member over one cycle of the drive shaft of the conventional art as described above. In this embodiment, owing to the remarkable reduction of the bearing load, an oil film can be readily formed between the outer circumferential surface of each of journals 20a, 20a of control shaft 20 and the corresponding bearing surface of bearing member 8 and between the outer circumferential surface of control cam 21 and the corresponding inner circumferential surface of support bore 16a of rocker arm 11 under the influence of an oil pressure to be supplied.

In particular, a friction coefficient at the journal of the control shaft and the corresponding bearing portion tends to have a value close to coefficient of static friction μ0 due to a small sliding movement between the journal and the corresponding bearing portion. However, in this embodiment, a friction coefficient at journal 20a of control shaft 20 and the bearing portion of bearing member 8 has a value close to coefficient of dynamic friction μD owing to the sufficiently small bearing load and the influence of the oil pressure to be supplied.

In a case where control shaft 20 is rotated by a driving source such as an electric motor to thereby vary the valve lift characteristic, friction moment MF is expressed by the following formula: MF=(FJ′/2)×r×μD

wherein FJ′/2 represents a bearing load for control shaft 20, and r represents a radius of the bearing portion.

In this embodiment, since the value FJ′/2 is sufficiently small and the value μD is a small value close to the coefficient of dynamic friction, control shaft 20 can smoothly start to rotate. Thus, a friction moment that acts on the bearing surface of bearing member 8 which supports journals 20a, 20a of control shaft 20 is reduced to thereby allow a smooth rotational movement of control shaft 20. This serves for enhancing a response to changeover of valve lift characteristics of intake valves 2, 2.

As understood from the above explanation, since the biasing force of biasing member 22 acts on roller 14 through roller shaft 17 in such a direction as to press roller 14 against drive cam 10, the biasing force of biasing member 22 is not largely exerted on the bearing surface of support bore 16a of rocker arm 11 and the bearing surface of bearing member 8. Therefore, a friction moment that acts on the bearing surface of bearing member 8 upon rotating control shaft 20 is reduced. Accordingly, smooth and quick start of rotation of control shaft 20 can be achieved upon changing valve lift characteristics of intake valves 2, 2, thereby serving for enhancing a response to changeover of valve lift characteristics of intake valves 2, 2.

Further, in this embodiment, biasing member 22 can restrict the swing motion of rocker cams 6, 6 in a predetermined region without directly acting on rocker cams 6, 6 and can allow a stable behavior of motion transmission mechanism 7. Biasing member 22 can restrict the swing motion of rocker cams 6, 6 in the predetermined region via the positive motion connection between roller shaft 17, rocker arm 11, rocker cams 6, 6 and link rods 15, 15. With this construction, the respective parts to be positively connected with each other can be prevented from being separated from each other, and therefore, the behavior of motion transmission mechanism 7 can be stabilized.

Specifically, in this embodiment, biasing member 22 biases roller shaft 17 onto drive cam 10 to thereby restrict the motion of roller shaft 17 within a predetermined region in which roller shaft 17, rocker arm 11, link rod 15 and rocker cam 6 are in positive motion connection therebetween in both of opposite swing directions of rocker cam 6 without being separated from each other. Accordingly, the swing motion of rocker cam 6 can be restricted within the predetermined region in which rocker cam 6 is free from separation from the other parts in the positive motion connection.

Here, the positive motion connection means that roller shaft 17 is fixed to one end portion 12 of rocker arm 11, and link rod 15 is pivotally connected with the other end portion 13 of rocker arm 11 through pin 18 so as to move in both of lift-up and lift-down directions of link rod 15 and is connected with rocker cam 6 through pin 19 so as to pivot about pin 19 in the opposite swing directions of rocker cam 6. Therefore, rocker cam 6 can be positively operated in the non-lift state of variable valve operating apparatus 100 without directly undergoing the biasing force of biasing member 22. As a result, occurrence of separation of the parts to be in the positive motion connection therebetween can be suppressed and an operation of variable valve operating apparatus 100 can be always stabilized.

Further, in this embodiment, roller shaft 17 is supported between opposite support walls 12a, 12a of one end portion 12 of rocker arm 11, and opposite end portions 17a, 17b of roller shaft 17 are supported by support walls 12a, 12a. Thus, end portions 17a, 17b of roller shaft 17 can be readily and surely supported, and roller 14 can be easily assembled to rocker arm 11 through roller shaft 17.

Further, tip end portions 22c, 22c of biasing member 22 are contacted with end portions 17a, 17b of roller shaft 17 which project from support walls 12a, 12a of rocker arm 11, so that the biasing force of biasing member 22 acts on end portions 17a, 17b of roller shaft 17. Therefore, a point of action of the biasing force of biasing member 22 is located on a side of each of end portions 17a, 17b of roller shaft 17. With this construction, degree of freedom of installation of biasing member 22 can be increased.

Furthermore, in this embodiment, an attitude of rocker arm 11 can be changed by varying a rotational phase of control shaft 20, namely, a rotational position of control cam 21. This serves for readily varying valve lift characteristic of the engine valve.

Referring to FIG. 10, there is shown a second embodiment of the variable valve operating apparatus, which differs from the first embodiment in provision of an annular sleeve and a roller bearing on roller shaft 17. Like reference numerals denote like parts, and therefore, detailed explanations therefor are omitted. As illustrated in FIG. 10, variable valve operating apparatus 200 of the second embodiment includes annular sleeves 30, 30 rotatably mounted onto opposite end portions 17a, 17b of roller shaft 17 which outward project from support walls 12a, 12a of rocker arm 11. End portions 17a, 17b have a diameter smaller than a diameter of an intermediate portion between end portions 17a, 17b. Each of annular sleeves 30, 30 is formed on an outer peripheral surface thereof with engaging groove 30a which has a U-shape in cross-section as shown in FIG. 10. Each of tip end portions 22c, 22c of biasing member 22 is engaged in engaging groove 30a and retained therein. Roller bearing 31 is disposed between an outer circumferential surface of the intermediate portion of roller shaft 17 and the inner circumferential surface of roller 14.

The second embodiment can have the same effects as those of the first embodiment and can further attain the following effects. With the provision of annular sleeves 30, 30 with engaging grooves 30, 30, tip end portions 22c, 22c of biasing member 22 can be stably supported in engaging grooves 30, 30 of annular sleeves 30, 30. Further, owing to rotation of annular sleeves 30, 30, resistance to slide friction between annular sleeves 30, 30 and tip end portions 22c, 22c of biasing member 22 can be reduced. As a result, the bearing load that acts on the bearing portions for control shaft 20 can be further reduced and the swing motion of rocker arm 11 can be facilitated.

Referring to FIG. 11, there is shown a third embodiment of the variable valve operating apparatus, which differs from the second embodiment in arrangement of annular sleeve 30. Like reference numerals denote like parts, and therefore, detailed explanations therefor are omitted. As illustrated in FIG. 11, in variable valve operating apparatus 300 of the third embodiment, support walls 12a, 12a of rocker arm 11 are spaced from each other with a relatively large space therebetween and opposite end portions 17a, 17b of roller shaft 17 are fixedly disposed on an inside of support walls 12a, 12a without projecting from support walls 12a, 12a. Roller 14 is rotatably supported on a substantially middle portion of roller shaft 17 in the axial direction of roller shaft 17 through roller bearing 31. Biasing member 22 applies the biasing force to the portion of roller shaft 17. Each of annular sleeves 30, 30 is rotatably disposed between each of opposite side faces of roller 14 in the axial direction of roller 14 and the corresponding side face of each of support walls 12a, 12a which is opposed to the side face of roller 14. Each of tip end portions 22c, 22c of biasing member 22 is contacted with a portion of roller shaft 17 which is disposed between the side face of roller 14 and the corresponding side face of support wall 12a through annular sleeve 30. Biasing member 22 thus applies the biasing force to roller shaft 17.

In the third embodiment, it is not necessary that the opposite end portions of roller shaft 17 outward project from support walls 12a, 12a of rocker arm 11, thereby serving for downsizing variable valve operating apparatus 300. Further, each of support walls 12a, 12a and the corresponding side face of roller 14 cooperate with each other to restrain each of annular sleeves 30, 30 from being displaced in a direction of thrust.

Referring to FIG. 12, there is shown a fourth embodiment of the variable valve operating apparatus, which differs from the first embodiment in that a follower portion is provided on one end portion 12 of rocker arm 11 instead of support walls 12a, 12a and roller 14 of the first embodiment and a biasing member support is provided on one end portion 12 of rocker arm 11. As illustrated in FIG. 12, variable valve operating apparatus 400 of the fourth embodiment includes follower portion 32 which is integrally formed with a tip end of one end portion 12 of rocker arm 11. Follower 32 is contacted with the outer circumferential surface of drive cam 10 and has a generally arcuate cross-section. Follower 32 has a width that is equal to a width of drive cam 10 in an axial direction of drive cam 10, namely, in the direction of axis X of drive shaft 3. Follower 32 has tip end surface 32a which has an arcuate section and is in line contact with the outer circumferential surface of drive cam 10.

Variable valve operating apparatus 400 further includes biasing member support 33 which is disposed on a boss formed on one end portion 12 of rocker arm 11. Biasing member support 33 is constructed to support biasing member 22 thereon, through which biasing member 22 biases and presses follower portion 32 against drive cam 10. In this embodiment, biasing member support 33 is in the form of a support pin press-fitted into a pin mount hole which is formed in the boss on one end portion 12. Biasing member support 33 has opposite end portions which outward project from opposite side surfaces of the boss of one end portion 12, respectively. Tip end portions 22c, 22c of biasing member 22 are directly elastically contacted with an upper portion of the outer circumferential surface of the opposite end portions of biasing member support 33 as shown in FIG. 12. Biasing member support 33 is disposed on or near line Q which extends across axis X of drive shaft 3, i.e., the axis of drive cam 10, and center of curvature Z of follower portion 32. Line Q extends in a direction of load FC which acts on follower portion 32 from the side of drive cam 10 through the contact portion between follower portion 32 and the base-circle portion of drive cam 10.

Biasing member 22 is arranged to apply the biasing force through biasing member support 33 substantially along a line that extends across an axis of biasing member support 33 and the axis of drive cam 10, namely, axis X of drive shaft 3. Load FS that is caused by the biasing force of biasing member 22 acts on follower portion 32 through biasing member support 33 so as to press follower portion 32 against drive cam 10. Load FT′ acting on control cam 21 is considerably small, and therefore, the load that acts on control shaft 20 and bearing member 8 through journals 20a, 20a of control shaft 20 is considerably small. Accordingly, the fourth embodiment can attain the same effects as those of the first embodiment. That is, in the fourth embodiment, a friction moment acting on bearing member 8 through journals 20a, 20a can be reduced to thereby allow a smooth rotational movement of control shaft 20. As a result, a response to changeover of valve lift characteristics of intake valves 2, 2 can be enhanced.

Especially, since biasing member support 33 is disposed on or near line Q as described above, a direction of load FS that is caused by the biasing force of biasing member 22 and a direction of load FC that is caused due to reaction against load FS are substantially opposed to each other to thereby mutually cancel loads FS and FC. Therefore, the load that is exerted on control shaft 22 due to the biasing force of biasing member 22 can be considerably reduced.

Further, in the fourth embodiment, the construction of variable valve operating apparatus 400 is simplified by omitting the roller that is supported on rocker arm 11 and contacted with drive cam 10. This serves for facilitating a production process and an assembling work and suppressing increase in costs.

The present invention is not limited to the above embodiments. A coil spring can be used as the biasing member instead of the return spring. Further, the control shaft can be formed into a crank shape with the control cam which has a reduced diameter. Further, the biasing member can be constructed so as to be contacted with an end portion of the roller shaft which projects from at least one of the opposite side walls, and can bias the end portion of the roller shaft. Further, the drive cam can be formed into an eccentric-circular shape. Further, the drive cam can be rotatably supported by a rolling bearing. Furthermore, a hydraulically operated actuator can be used instead of the electrically operated actuator.

This application is based on a prior Japanese Patent Application No. 2006-153005 filed on Jun. 1, 2006. The entire contents of the Japanese Patent Application No. 2006-153005 is hereby incorporated 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 variable valve operating apparatus for variably operating an engine valve of an internal combustion engine, the variable valve operating apparatus comprising:

a drive cam which is rotationally driven by a crankshaft of the engine;

a rocker cam having a swing axis and swingably moveable about the swing axis so as to move the engine valve to an open position and a closing position;

a motion transmission mechanism operative to convert a rotational motion of the drive cam to a swing motion of the rocker cam, the motion transmission mechanism including a roller shaft which is disposed on one end portion of the motion transmission mechanism on a side of the drive cam, and a roller which is rotatably supported on the roller shaft and contacted with the drive cam;

a control shaft rotatable depending on an operating condition of the engine, the control shaft being operative to control an attitude of the motion transmission mechanism to vary a valve lift of the engine valve; and

a biasing member which biases the roller onto the drive cam through the roller shaft.

2. The variable valve operating apparatus as claimed in claim 1, wherein the roller shaft, the motion transmission mechanism and the rocker cam are in a positive motion connection without separation therebetween during the swing motion of the rocker cam.

3. The variable valve operating apparatus as claimed in claim 1, wherein the control shaft has a control cam on an outer circumferential surface thereof, the motion transmission mechanism comprises a rocker arm swingably supported on an outer circumferential surface of the control cam, and the roller shaft and the roller are disposed on one end portion of the rocker arm on a side of the drive cam.

4. The variable valve operating apparatus as claimed in claim 3, wherein the rocker arm comprises at least a pair of support walls which are disposed on the one end portion of the rocker arm, and the roller shaft is supported between the support walls of the rocker arm.

5. The variable valve operating apparatus as claimed in claim 4, wherein the biasing member is contacted with an end portion of the roller shaft which outward projects from the at least one of the support walls of the rocker arm, and the biasing member applies a biasing force to the end portion of the roller shaft.

6. The variable valve operating apparatus as claimed in claim 4, wherein the biasing member is contacted with a portion of the roller shaft which is disposed between the at least a pair of support walls and a side face of the roller, and the biasing member applies a biasing force to said portion of the roller shaft.

7. The variable valve operating apparatus as claimed in claim 1, further comprising an annular sleeve which is mounted to the roller shaft, the biasing member applying a biasing force to the roller shaft through the annular sleeve.

8. The variable valve operating apparatus as claimed in claim 7, wherein the annular sleeve is formed on an outer peripheral surface thereof with an engaging groove in which the biasing member is engaged.

9. The variable valve operating apparatus as claimed in claim 1, wherein the biasing member comprises a spring.

10. The variable valve operating apparatus as claimed in claim 1, wherein the drive cam is rotatably supported by a rolling bearing.

11. A variable valve operating apparatus for variably operating an engine valve of an internal combustion engine, the variable valve operating apparatus comprising:

a drive cam which is rotationally driven by a crankshaft of the engine;

a rocker cam having a swing axis and swingably moveable about the swing axis so as to move the engine valve to an open position and a closing position;

a motion transmission mechanism operative to convert a rotational motion of the drive cam to a swing motion of the rocker cam, the motion transmission mechanism including a follower portion which is disposed on one end portion of the motion transmission mechanism on a side of the drive cam, the follower portion being contacted with the drive cam and having a generally arcuate cross-section;

a control shaft rotatable depending on an operating condition of the engine, the control shaft being operative to control an attitude of the motion transmission mechanism to vary a valve lift of the engine valve;

a biasing member support disposed on the one end portion of the motion transmission mechanism on the side of the drive cam; and

a biasing member which biases the follower portion onto the drive cam through the biasing member support,

wherein the biasing member support is disposed on or near a line that extends across an axis of the drive cam and a center of curvature of the follower portion.

12. The variable valve operating apparatus as claimed in claim 11, wherein the control shaft has a control cam on an outer circumferential surface thereof, the motion transmission mechanism comprises a rocker arm swingably supported on an outer circumferential surface of the control cam, and the biasing member support comprises a support pin press-fitted into a pin mount hole which is formed in a boss on the one end portion of the rocker arm.

13. The variable valve operating apparatus as claimed in claim 11, wherein the biasing member comprises a spring.

14. The variable valve operating apparatus as claimed in claim 11, wherein the drive cam is rotatably supported by a rolling bearing.

15. A variable valve operating apparatus for variably operating an engine valve of an internal combustion engine, the variable valve operating apparatus comprising:

a drive cam which is rotationally driven by a crankshaft of the engine;

a rocker cam having a swing axis and swingably moveable about the swing axis so as to move the engine valve to an open position and a closing position;

a motion transmission mechanism operative to convert a rotational motion of the drive cam to a swing motion of the rocker cam, the motion transmission mechanism including one end portion which is contacted with the drive cam;

a control shaft rotatable depending on an operating condition of the engine, the control shaft being operative to control an attitude of the motion transmission mechanism to vary a valve lift of the engine valve;

biasing means for biasing the one end portion of the motion transmission mechanism onto the drive cam; and

support means for supporting the biasing member thereon;

wherein the biasing means and the support means are arranged such that a biasing force of the biasing means is applied to the one end portion of the motion transmission mechanism through the support means substantially along a line that extends across the support means and an axis of the drive cam.