Variable Valve Apparatus
A motor 30 or the like is used to drive a camshaft 22 or the like having a cam 18 or the like to push a valve 12 biased in the closing direction of the valve by a valve spring 17. Between the cam 18 or the like and the valve 12 is present a valve lifter 16 that abuts the cam 18 or the like. The valve lifter 16 includes a top face 16a formed so that when viewed from the axial direction of the camshaft 22 or the like, a tangential direction to the nose tip 18c of the cam 18 or the like inclines with respect to the direction perpendicular to the axial line of a valve stem 14.
Latest Toyota Patents:
- WIRELESS COMMUNICATION CONTROL METHOD, RECEIVING STATION, AND NON-TRANSITORY STORAGE MEDIUM
- COMMUNICATION DEVICE AND VIDEO TRANSMISSION SYSTEM
- ELECTRICALLY HEATING SUPPORT
- NEO 360: NEURAL FIELDS FOR SPARSE VIEW SYNTHESIS OF OUTDOOR SCENES
- MAGNET ARRANGEMENT METHOD, METHOD FOR MANUFACTURING ROTOR, MAGNET ARRANGEMENT JIG, AND MAGNET INDUCTION APPARATUS
The present invention relates to a variable valve apparatus that drives a valve of an internal combustion engine.
BACKGROUND ARTReferring to conventional techniques, Patent Document 1, for example, discloses an internal combustion engine that includes a valve-driving system using a motor to drive the opening and closing of a valve. If an error in the synchronous control of camshaft and crankshaft speeds occurs in this conventional valve-driving system, evacuation driving becomes possible by stopping the opening/closing of the valve by use of a lost-motion mechanism or by switching to a low-lift cam for driving the valve at a smaller amount of lift.
Including the above-mentioned document, the applicant is aware of the following documents as a related art of the present invention.
- [Patent Document 1] Japanese Laid-open Patent Application Publication No. 2005-54732
- [Patent Document 2] Japanese Laid-open Utility Model Application Publication No. Hei 6-87605
- [Patent Document 3] Japanese Laid-open Patent Application Publication No. 2004-225562
- [Patent Document 4] Japanese Laid-open Patent Application Publication No. 2004-225610
- [Patent Document 5] Japanese Patent No. 3359524
The type of variable valve apparatus that uses a cam to drive a valve via a valve lifter is known as one form of apparatus that conducts motor driving of a camshaft, as with the conventional valve-driving system discussed above. In such a type of variable valve apparatus, if the variable valve apparatus becomes abnormal and motor driving is stopped with the cam having its nose tip abutted upon the valve lifter, this stoppage could leave the valve open with the amount of valve lift maximized. If this situation happens, interference is likely to occur between the valve remaining stopped in the maximum lift state, and the piston continuing a reciprocating motion.
In the type of variable valve apparatus that uses a motor to rotationally drive a camshaft, if the evacuation control mechanism as used in the above conventional valve-driving system, that is, the mechanism for stopping the opening/closing of the valve or for switching to the low-lift cam, is equipped only to avoid the above interference, this will complicate the system configuration uselessly. In addition, in the type that employs the above evacuation control mechanism, after the error in the synchronous control of the camshaft and crankshaft speeds, the valve-piston interference could occur during the period of switching to the evacuation control.
The present invention was made for solving the foregoing problems, and an object of the invention is to provide a variable valve apparatus that uses a motor to rotationally drive a camshaft including a cam to push a valve biased to close by a valve spring, the apparatus being adapted for valve-piston interference in case of an abnormality to be reliably resolved using a simple configuration.
Means For Solving the ProblemA first aspect of the present invention for achieving the above first object is a variable valve apparatus that uses a motor to drive a camshaft including a cam for pushing a valve biased in the closing direction thereof by a valve spring, the variable valve apparatus, further comprising:
a valve lifter which abuts the cam between the cam and the valve;
wherein the valve lifter includes a top face formed such that when viewed from an axial direction of the camshaft, the direction of a tangential line to a nose tip of the cam inclines with respect to the direction perpendicular to the axial line of a valve stem.
A second aspect of the present invention is the variable valve apparatus according to the first aspect of the present invention,
wherein the inclining direction of the tangential line is a direction in which the distance between the tangential line and a bottom face of the valve lifter decreases as the inclination goes in the traveling direction of a contact point between the cam during forward rotation thereof and the valve lifter.
A third aspect of the present invention is the variable valve apparatus according to the first or second aspect of the present invention,
wherein the top face, when viewed from the axial direction of the camshaft, is formed into a convexedly curved shape to be convex toward the cam.
A fourth aspect of the present invention is the variable valve apparatus according to the third aspect of the present invention,
wherein on the top face formed into the convexedly curved shape to be convex toward the cam, an apical point whose height above the bottom face of the valve lifter is maximized, and the contact point between the nose tip and the valve lifter are spaced from each other when viewed from the axial direction of the camshaft.
A fifth aspect of the present invention is the variable valve apparatus according to the third or fourth aspect of the present invention,
wherein the top face having the convexedly curved shape to be convex toward the cam is formed to have a maximum achievable height above the bottom face of the valve lifter, on a central axis of the valve lifter; and
the camshaft is disposed such that a central axis thereof and the central axis of the valve lifter do not intersect with each other when viewed from the axial direction of the camshaft.
A sixth aspect of the present invention is the variable valve apparatus according to the third or fourth aspect of the present invention,
wherein the camshaft is disposed such that a central axis thereof intersects with the central axis of the valve lifter when viewed from the axial direction of the camshaft; and
the top face having the convexedly curved shape to be convex toward the cam is formed such that when viewed from the axial direction of the camshaft, an apical point whose height above the bottom face of the valve lifter is maximized takes up an offset position relative to the axial line of the valve stem.
A seventh aspect of the present invention is the variable valve apparatus according to the first or second aspect of the present invention,
wherein the top face, when viewed from the axial direction of the camshaft, is an inclined surface having a constant gradient.
An eighth aspect of the present invention is the variable valve apparatus according to any one of the first to seventh aspect of the present invention, further comprising:
electric power supply control means for stopping supply of electric power to the motor when a command value assigned to the motor to drive the camshaft reaches a predetermined value.
A ninth aspect of the present invention is the variable valve apparatus according to any one of the first to eighth aspect of the present invention, further comprising:
a torque reduction mechanism that generates a reduced torque for reduction in a driving torque of the camshaft;
wherein the torque reduction mechanism is constructed such that the reduced torque is small in comparison with a camshaft torque based upon a biasing force of the valve spring.
Advantages of the InventionAccording to the first aspect of the present invention, even if the driving of the camshaft by the motor is stopped with the cam nose tip abutting upon the top face of the valve lifter, the biasing force of the valve spring acts to rotate the cam as well as to push the cam upward. The invention, therefore, allows the valve to be properly prevented from remaining open in case of the abnormality, thus valve-piston interference to be avoided reliably.
According to the second aspect of the present invention, even if the driving of the camshaft by the motor is stopped with the cam nose tip abutting upon the top face of the valve lifter, the cam is returned in its forward rotational direction. After the occurrence of the abnormality, therefore, the invention allows easy cam-piston synchronization during a restart, and hence, reduction of likelihood of valve-piston interference. A reduction in the amount of electric power required immediately after the restart is additionally anticipated.
According to the third to seventh aspects of the present invention, even if the driving of the camshaft by the motor is stopped with the cam nose tip abutting upon the top face of the valve lifter, the biasing force of the valve spring acts to rotate the cam as well as to push the cam upward. The invention, therefore, allows the valve to be properly prevented from remaining open in case of the abnormality, thus valve-piston interference to be avoided reliably.
According to the eighth aspect of the present invention, even if an abnormality that leaves a driving force of the camshaft with respect to the motor occurs in the variable valve apparatus, the biasing force of the valve spring is permitted to be converted into a torque that rotates the cam. Accordingly, valve-piston interference can be avoided reliably.
According to the ninth aspect of the present invention, a sufficient biasing force of the valve spring in the variable valve apparatus with the torque reduction mechanism for reducing the driving torque of the camshaft can be obtained as a torque that rotates the cam, and thus, valve-piston interference can be avoided reliably.
Hereinafter, a basic configuration of a variable valve system 10 according to a first embodiment of the present invention will be described referring to
The configuration shown in
Each valve lifter 16 has a corresponding cam 18 or 20 at its upper section. As shown in
A first driven gear 26 is coaxially fixed to the camshaft 22. The first driven gear 26 has a first output gear 28 meshed therewith. The first output gear 28 is fixed to an output shaft of a first motor 30. The first motor 30 is a servomotor controllable in rotational speed and in the amount of rotation. For example, a brushless motor or the like is preferably used as the first motor 30. The first motor 30 contains a rotational angle detection sensor such as a resolver or rotary encoder to detect the rotational position (rotational angle) of the motor. This configuration allows a torque of the first motor 30 to be transmitted to the camshaft 22 via the gears 26 and 28.
A second driven gear 32 is coaxially fixed to the camshaft 24. The second driven gear 32 has a second output gear 36 meshed therewith via an intermediate gear 34. The second output gear 36 is fixed to an output shaft of a second motor 38. A detailed configuration of the second motor 38 is substantially the same as that of the first motor 30. This configuration allows a torque of the second motor 38 to be transmitted to the camshaft 24 via the gears 32, 34, and 36.
The system shown in
As shown in
When a rotary motion of the first motor 30 is transmitted to the camshaft 22 via the gears 26, 28, the cam 18 rotates integrally with the camshaft 22 and while the nose 18b gets over the valve lifter 16, the valve lifter 16 is pushed downward to lift (open) the valve 12 in defiance of the biasing force of the valve spring 17.
In the forward driving mode, the rotational speed of the cam 18 is controlled, whereby the operating angle of the valve is controlled. In the swinging mode, the operating angle and maximum lift amount of the valve 12 can be controlled by controlling the rotational speed of the cam 18 and the swinging angle range thereof.
Feature Sections of the Present EmbodimentNext, feature sections of the present embodiment are described below referring to
Some abnormality associated with the variable valve apparatus A, such as a loss of rotational synchronization between its camshaft and crankshaft, may result in a stoppage of a motor. Under the stopped motor state, despite such factors resisting the rotation of the camshaft as friction between the cam and the valve lifter, friction between the motor and the camshaft, and inertia of the motor, the camshaft itself is basically in a rotatable state. If the variable valve apparatus A becomes abnormal, therefore, when a nose portion other than a tip of the nose is in contact with the valve lifter (e.g., when the state shown in
However, in the case that the top face of the valve lifter is of such a planar shape as described above, the valve is likely to remain open with the maximum amount of lift if, as shown in
The above situation occurs because, in the configuration shown in
The occurrence of the above situation could cause interference between the valve that will remain open and a piston that will continue reciprocating. In the present embodiment, therefore, the configuration shown in
Additionally, in order that the inclining direction of the tangent line matches a direction in which the distance between the tangent line and a bottom face 16b of the valve lifter 16 decreases as the tangent line extends in the traveling direction of the contact point between the forward rotating cam 18 and the valve lifter 16 (i.e., a leftward direction in
In the present embodiment, the top face 16a of the valve lifter 16, when viewed from the axial direction of the camshaft 22 as shown in
Furthermore, in the configuration of
Furthermore, the present embodiment has a swirl-stopping mechanism to prevent the valve lifter 16 from rotating with respect to the cam 18 so that during actual operation of the variable valve apparatus, the above tangential direction is always maintained in the foregoing direction. Such a swirl-stopping mechanism, although details are omitted in
As described above, in the configuration of
This means that according to the above configuration, not only a component of the axial-line direction of the valve stem 14 but also a decomposition component (marked with an arrow in
By virtue of this, according to the configuration of the present embodiment, interference between the valve 12 and the piston during the occurrence of an abnormality can be avoided reliably in a mechanical manner using a simple configuration, without relying upon such evacuation control mechanism as provided in the conventional technology. If an error in the synchronous control of the camshaft and crankshaft speeds is detected, interference between the valve and the piston can also be avoided during the period of switching to such evacuation control.
Furthermore, in the foregoing configuration that
According to such a configuration, if the motor is stopped with the nose tip 18c of the cam 18 abutting upon the top face 16a of the valve lifter 16, the cam 18 is made to escape in the forward rotational direction. As a result, the final stopping position of the cam 18 after the escape operation thereof has been conducted becomes the position that the normal valve 12 occupies immediately after the lifting operation thereof has ended. If this consideration is given to the escape direction of the cam 18, the excellent effects described below can be yielded.
That is to say, in the configuration with the two motors, 30 and 38, that share the driving of all cylinders' air intake valves, as in the present embodiment, when the cam 18 is rotated during the restart following the occurrence of an abnormality, a cam angle margin of about 60° will be created until the lifting of the valve is started next time. If a phase of the cam angle is discriminated in the section of about 60°, synchronization with a piston phase can be implemented and the likelihood of valve-piston interference can be reduced. In addition, since kinetic energy can be given to the cam 18 by raising the rotational speed thereof to a sufficiently high level in the section of about 60°, a reduction in the amount of electric power required immediately after the restart is anticipated.
Meanwhile, in the above-described first embodiment, the top face 16a of the valve lifter 16, when viewed from the axial direction of the camshaft 22, is formed into a convexedly curved shape to be convex with respect to the cam 18, and more specifically, into a cylindrical shape. Additionally, the top face 16a formed into the convexedly curved shape is formed for the valve lifter 16 to have the maximum achievable height on its central axis, and the camshaft 22 is disposed for the central axis thereof to be distant from that of the valve lifter 16 when viewed from the axial direction of the camshaft 22. However, if the top-face shape of the valve lifter in the present invention and the arrangement relationship between the valve lifter and the camshaft incorporate the consideration needed to ensure that when viewed from the axial direction of the camshaft, the tangential direction connecting the nose tip of the cam and the top face of the valve lifter inclines with respect to the direction perpendicular to the axial line of the valve stem, application of the invention is not limited to the above configuration shown in
However, unlike the above-described configuration shown in
Furthermore, in the configuration of
The valve lifter 42 can have substantially the same swirl-stopping mechanism as used in the configuration of the first embodiment.
The valve lifter 44 can have substantially the same stopping-stopping mechanism as used in the configuration of the first embodiment.
Second EmbodimentNext, a second embodiment of the present invention is described below referring to
An apparatus according to the present embodiment can be implemented by using the hardware configurations shown in
If an abnormality that has been caused to the variable valve apparatus 10 is of a mode that completely powers off the motor, adoption of the above-described configuration shown in
Consequently, interference between the valve 12 and the piston is likely. In the present embodiment, therefore, in order to ensure reliable avoidance of valve-piston interference even in the event of the abnormality of the above mode, supply of electric power to the motor is stopped when the driving repulsion force for motor driving of the cam 18 reaches or exceeds a predetermined level, and more specifically, when a current command value (torque command value) assigned from the ECU 40 to the motor reaches a predetermined value.
Next, whether the current command value that was acquired in above step 102 is in excess of the predetermined value is discriminated (step 104). If the camshaft 22 is in a stopped state and the electric power is supplied to the motor, the position of the cam 18 is maintained with the valve 12 remaining lifted by the cam 18. If the amount of lift at this time increases above a certain level, interference is likely to occur between the valve 12 and the piston that is continuing the reciprocating motion. The driving repulsion force due to the valve-spring repulsion force existing when the cam 18 presses the valve 12 increases with increases in the amount of lift of the valve 12, since the valve spring repulsion force increases. The current command value that has been assigned to the cam 18, therefore, increases with the increases in the amount of lift of the valve 12. The predetermined value in step 104 is set to be a value allows discrimination of whether the amount of lift of the valve 12 has increased to such a level that causes valve-piston interference.
If, in step 104, the current command value is judged to be in excess of the predetermined value, supply of the electric power to the motor is stopped (step 106).
According to the above-described routine shown in
In the second embodiment, which has been described above, the “electric power supply control means” in the earlier description of the eighth aspect of the present invention herein will be realized when the routine process shown in
Next, a third embodiment of the present embodiment is described below with reference to
The variable valve apparatus 50 of the present embodiment is constructed similarly to the variable valve apparatus 10 of the first embodiment, except that the apparatus 50 includes the torque reduction mechanism 52 shown in
As represented using a waveform denoted by a broken line in
As a result, when the torque reduction mechanism is used at such general settings as described above, even if contact with the valve lifter is occurring at whatever position of the cam nose, that is, even except when the nose tip of the cam comes into contact with the valve lifter, the torque that rotates the cam in the closing direction of the valve is not exerted upon the camshaft. Therefore, the cam is likely to stop with the valve in a lifted state. This is liable to cause valve-piston interference.
Additionally, the reduced torque that the torque reduction mechanism 52 assigns is determined so that the resulting differential torque is slightly greater than a sum of cam-valve lifter friction, meshing friction of gears arranged between the motor and the camshaft, motor inertia, and other factors resisting the rotation of the camshaft.
Even when the settings shown in
According to the above-described configuration of the present embodiment, even in the variable valve apparatus 50 having the torque reduction mechanism 52 intended to reduce the driving torque of the camshaft 22 or the like, interference between the valve 12 and the piston can be reliably avoided using a simple configuration, irrespective of the stopping position of the cam 18 or the like in case of an abnormality.
Claims
1.-8. (canceled)
9. A variable valve apparatus that uses a motor to drive a camshaft including a cam for pushing a valve biased in the closing direction thereof by a valve spring, the variable valve apparatus, further comprising:
- a valve lifter which abuts the cam between the cam and the valve;
- wherein the valve lifter includes a top face formed such that when viewed from an axial direction of the camshaft, the direction of a tangential line to a nose tip of the cam inclines with respect to the direction perpendicular to the axial line of a valve stem; and
- wherein the inclining direction of the tangential line is a direction in which the distance between the tangential line and a bottom face of the valve lifter decreases as the inclination goes in the traveling direction of a contact point between the cam during forward rotation thereof and the valve lifter.
10. A variable valve apparatus that uses a motor to drive a camshaft including a cam for pushing a valve biased in the closing direction thereof by a valve spring, the variable valve apparatus, further comprising:
- a valve lifter which abuts the cam between the cam and the valve;
- wherein the valve lifter includes a top face formed such that when viewed from an axial direction of the camshaft, the direction of a tangential line to a nose tip of the cam inclines with respect to the direction perpendicular to the axial line of a valve stem; and
- wherein the top face, when viewed from the axial direction of the camshaft, is formed into a convexedly curved shape to be convex toward the cam.
11. The variable valve apparatus according to claim 10,
- wherein on the top face formed into the convexedly curved shape to be convex toward the cam, an apical point whose height above the bottom face of the valve lifter is maximized, and the contact point between the nose tip and the valve lifter are spaced from each other when viewed from the axial direction of the camshaft.
12. The variable valve apparatus according to claim 10,
- wherein the top face having the convexedly curved shape to be convex toward the cam is formed to have a maximum achievable height above the bottom face of the valve lifter, on a central axis of the valve lifter; and
- the camshaft is disposed such that a central axis thereof and the central axis of the valve lifter do not intersect with each other when viewed from the axial direction of the camshaft.
13. The variable valve apparatus according to claim 10,
- wherein the camshaft is disposed such that a central axis thereof intersects with the central axis of the valve lifter when viewed from the axial direction of the camshaft; and
- the top face having the convexedly curved shape to be convex toward the cam is formed such that when viewed from the axial direction of the camshaft, an apical point whose height above the bottom face of the valve lifter is maximized takes up an offset position relative to the axial line of the valve stem.
14. The variable valve apparatus according to claim 9,
- wherein the top face, when viewed from the axial direction of the camshaft, is an inclined surface having a constant gradient.
15. The variable valve apparatus according to claim 9, further comprising:
- electric power supply control means for stopping supply of electric power to the motor when a command value assigned to the motor to drive the camshaft reaches a predetermined value.
16. The variable valve apparatus according to claim 9, further comprising:
- a torque reduction mechanism that generates a reduced torque for reduction in a driving torque of the camshaft;
- wherein the torque reduction mechanism is constructed such that the reduced torque is small in comparison with a camshaft torque based upon a biasing force of the valve spring.
17. The variable valve apparatus according to claim 10, further comprising:
- electric power supply control means for stopping supply of electric power to the motor when a command value assigned to the motor to drive the camshaft reaches a predetermined value.
18. The variable valve apparatus according to claim 10, further comprising:
- a torque reduction mechanism that generates a reduced torque for reduction in a driving torque of the camshaft;
- wherein the torque reduction mechanism is constructed such that the reduced torque is small in comparison with a camshaft torque based upon a biasing force of the valve spring.
Type: Application
Filed: Nov 13, 2007
Publication Date: Apr 15, 2010
Applicant: Toyota Jidosha Kabushiki Kaisha (Toyota-shi)
Inventors: Akio Kidooka (Ashigarakami-gun), Shuichi Ezaki (Susono-shi)
Application Number: 12/310,974
International Classification: F01L 1/34 (20060101);