WO2006043683A1

WO2006043683A1 - Variable valve timing apparatus for internal combustion engine

Info

Publication number: WO2006043683A1
Application number: PCT/JP2005/019444
Authority: WO
Inventors: Takahiro Harada; Shinobu Shimasaki
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2004-10-18
Filing date: 2005-10-17
Publication date: 2006-04-27
Also published as: JP2006112405A

Abstract

A variable valve timing apparatus includes a driving mechanism that includes an actuator, a plunger, and a moving direction converting mechanism. The actuator is located in a position away from a driven member with respect to an axial direction of a camshaft. The plunger is driven by the actuator so as to move along the axial direction of the camshaft. The moving direction converting mechanism changes linear movement of the plunger along the axial direction of the camshaft into rotation and transmits the rotation to a limit releasing member.

Description

DESCRIPTION

VARIABLE VALVE TIMING APPARATUS FOR INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present invention relates to a variable valve timing apparatus for an internal combustion engine that varies valve timings of engine valves such as intake valves and exhaust valves according to the operating state of the engine.

BACKGROUND ART

In a typical internal combustion engine, rotation of a crankshaft is transmitted to camshafts. Accordingly, cams on the camshafts press down intake and exhaust valves (engine valves) periodically so that the valves reciprocate to selectively open and close intake and exhaust passages. In such an internal combustion engine, the rotational phase of each camshaft is always constant relative to the crankshaft.

In recent years, to increase the power and improve emission of engines, a number of internal combustion engines are provided with variable valve timing apparatuses. Such an apparatus changes the rotational phase of a camshaft relative to a crankshaft, thereby varying the actuation timing (valve timing) of engine valves.

Japanese Laid-Open Patent Publication No. 6-10964 discloses an example of such a variable valve timing apparatus. The apparatus uses torque fluctuation accompanying rotation of a camshaft to vary the valve timing of the engine valves. This variable valve timing apparatus includes a driven member (support member) that is located on and rotates integrally with a camshaft. A driving member (sprocket member) is located outward of the driven member. The driving member is rotated by the crankshaft and rotates relative to the driven member.

To transmit rotation of the driving member to the driven member, a part of the outer circumferential surface of the driven member is cut out to form a flat surface. The space between the cutout portion and the inner circumferential surface of the driving member is widest at the middle with respect to the rotation direction of the driven member. The farther from the middle toward the leading end or trailing end with respect to the rotation direction, the narrower the space becomes. An advance limiting roller, a compression spring and a retard limiting roller are provided in the space defined by the cutout portion and the driving member. The advance limiting roller, which is located on the trailing side with respect to the rotation direction of the driven member compared to the compression spring, is engaged with a wedge- shaped advance limiting groove between the driving member and the driven member, thereby limiting relative rotation of the driven member in a direction advancing the rotational phase relative to the driving member. Likewise, the retard limiting roller, which is located on the leading side with respect to the rotation direction compared to the compression spring, is engaged with a wedge-shaped retard limiting groove between the driving member and the driven member, thereby limiting relative rotation of the driven member in a direction retarding the rotational phase relative to the driving member. The engagement of the rollers limits relative rotation of the driven member in the phase advancing direction and the phase retarding direction, and causes the driven member to rotate integrally with the driving member.

To rotate the driven member relative to the driving member either in the phase advancing direction or the phase retarding direction, a spider (limit releasing member) is located between the driving member and the driven member. The spider rotates relative to the driven and driving members. When the spider is relatively rotated in one direction, the advance limiting roller is disengaged from the advance limiting groove. In this state, relative rotation of the driven member is permitted in the phase advancing direction. Torgue fluctuation that accompanies closing of the engine valves, or negative torque, causes relative rotation of the driven member in the phase advancing direction. When the spider is relatively rotated in the direction opposite to the one direction, the retard limiting roller is disengaged from the retard limiting groove. In this state, relative rotation of the driven member is permitted in the phase retarding direction. Torque fluctuation that accompanies opening of the engine valves, or positive torque, causes relative rotation of the driven member in the phase retarding direction.

To cause relative rotation of the spider, a plunger that reciprocates in the axial direction of the camshaft, and a moving direction converting mechanism that changes linear movement of the plunger into rotation and transmits the rotation to the spider.

Further, Japanese Laid-Open Patent Publication No. 6- 10964 discloses several mechanisms for moving a plunger along the axial direction of the camshaft, among which is an embodiment where electromagnetic force is used. In this embodiment, an electromagnetic coil is attached to a housing member (rotating body) that rotates with a camshaft. The plunger and the housing member are both formed of magnetic material. The plunger is urged by a spring in a direction away from the electromagnetic coil. Therefore, when the electromagnetic coil is supplied with electricity and magnetic attraction force is generated, the plunger is moved toward the electromagnetic coil against the spring. When the supply of electricity is stopped and the magnetic attraction force disappears, the plunger is moved away from the electromagnetic coil due to the spring. In this manner, by controlling supply of electricity to the electromagnetic coil, the plunger is moved along the axial direction.

In the variable valve timing apparatus disclosed in Japanese Laid-Open Patent Publication No. 6-10964, the electromagnetic coil, which constantly rotates, must be supplied with electricity from the outside. Therefore, leads provided in the cylinder head are electrically connected to the housing member (electromagnetic coil) via a slip ring attached to the cylinder head or the housing member.

In a case where the slip ring is fixed to the cylinder head, the housing member slides on the slip ring. In a case where the slip ring is fixed to the housing member, the slip ring slides on the cylinder head. The sliding unavoidably wears the slip ring and the leads, which hinders stable supply of electricity for an extended period.

Since the electromagnetic coil is attached to the housing member, which rotates with the camshaft, the weight of the rotating portion is increased. This requires an increased force to rotate the camshaft. Accordingly, the fuel economy of the internal combustion engine is lowered.

DISCLOSURE OF THE INVENTION

Accordingly, it is an objective of the present invention to provide a variable valve timing apparatus that uses torque fluctuation of a camshaft for varying valve timing, and is capable of permitting relative rotation of a limit releasing member without supplying electricity to a portion that rotates with the camshaft, thereby eliminating drawbacks caused by such supply of electricity.

To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a variable valve timing apparatus for an internal combustion engine including a driving member, a driven member, an advance limiting mechanism, a retard limiting mechanism, a limit releasing member, and a driving mechanism is provided. The driving member is provided on a camshaft that rotates to drive an engine valve. The driving member rotates relative to the camshaft and being coupled to a crankshaft. The driven member is provided on the camshaft so as to rotate integrally with the camshaft. The advance limiting mechanism limits rotation of the driven member in a phase advancing direction relative to the driving member. The retard limiting mechanism limits rotation of the driven member in a phase retarding direction relative to the driving member. The limit releasing member rotates to release the limitation by the advance limiting mechanism or the limitation by the retard limiting mechanism. The driving mechanism rotates the limit releasing member. In a state in which the limitation by the advance limiting mechanism or the retard limiting mechanism on the driven member has been released by the limit releasing member, the driven member is rotated relative to the driving member to a position where the limitation by the advance limiting mechanism or the retard limiting mechanism is imposed by using torque fluctuation accompanying rotation of the camshaft, so that actuation timing of the engine valve in relation to rotation of the crankshaft is changed. The driving mechanism includes an actuator, a plunger, and a moving direction converting mechanism. The actuator is located in a position away from the driven member with respect to an axial direction of the camshaft. The plunger is driven by the actuator so as to move along the axial direction of the camshaft. The moving direction converting mechanism changes linear movement of the plunger along the axial direction of the camshaft into rotation and transmits the rotation to the limit releasing member.

Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

Fig. 1 is a partial-cross sectional view illustrating an engine provided with a variable valve timing apparatus according to a first embodiment of the present invention; Fig. 2 is a diagram showing changes of valve timing caused by the variable valve timing apparatus with respect to the relationship between the crank angle and the valve lift;

Fig. 3 is a diagram showing torque fluctuation that accompanies rotation of a camshaft of the engine;

Fig. 4 is a partially cross-sectional view illustrating the variable valve timing apparatus;

Fig. 5 is a cross-sectional view taken along line 5-5 of Fig. 4;

Fig. 6 is a partially cross-sectional view illustrating the variable valve timing apparatus, in which a rotation lever has been rotated in the phase advancing direction from the state of Fig. 5;

Fig. 7 is a partially cross-sectional view illustrating the variable valve timing apparatus, in which the rotation lever has been rotated in the phase retarding direction from the state of Fig. 5; Fig. 8 is a partially cross-sectional view illustrating a variable valve timing apparatus according to a second embodiment of the present invention, which view corresponds to Fig. 4; and Fig. 9 is a cross sectional view taken along line 9-9 of Fig. 8.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of the present invention will now be described with reference to Figs. 1 to 7.

Fig. 1 shows a multi-cylinder engine (hereinafter, simply referred to as an engine) 11, which functions as an internal combustion engine, of a vehicle. The engine 11 includes a cylinder block 13 having a plurality of cylinders 12, and a cylinder head 14 provided on the cylinder block 13. A piston 15 is accommodated in each of the cylinders 12. Each piston 15 reciprocates in the associated cylinder 12. Each piston 15 is coupled to a crankshaft 16, which is an output shaft, with a connecting rod 20. When each piston 15 reciprocates, the reciprocation is converted into rotation by the associated connecting rod 20 and transmitted to the crankshaft 16. Accordingly, the crankshaft 16 is rotated in a direction depicted by an arrow in Fig. 1.

A space in each cylinder 12 that is above the piston 15 is a combustion chamber 17. Intake ports 18 are defined in the cylinder head 14. The intake ports 18 form a part of an intake passage. The downstream end of each intake port 18 is connected to one of the combustion chambers 17. Air outside of the engine 11 is drawn into the combustion chamber 17 through the intake port 18. Exhaust ports 19 are defined in the cylinder head 14. The exhaust ports 19 form a part of an exhaust passage. The upstream end of each exhaust port 19 is connected to one of the combustion chambers 17. Combustion gas generated in each combustion chamber 17 is exhausted to the outside of the engine 11 through the exhaust port 19.

The cylinder head 14 has intake valves 21 for opening and closing the intake ports 18 and exhaust valves 22 for opening and closing the exhaust ports 19. Each intake valve 21 and each exhaust valve 22 correspond to one of the cylinders 12. All the intake and exhaust valves 21, 22 are each urged by a valve spring 23 in a direction closing the intake and exhaust ports 18, 19 (valve closing direction, or substantially upward direction as viewed in Fig. 1) .

A valve actuation mechanism is provided for lifting (pressing down) the intake and exhaust valves 21, 22 in a direction for opening the intake and exhaust ports 18, 19 (valve opening direction) against the valve springs 23. The valve actuation mechanism will now be described. An intake camshaft 25 having intake cams 24 is rotatably supported substantially directly above the intake valves 21 in the cylinder head 14. The intake camshaft 25 drives the intake valves 21. An exhaust camshaft 27 having exhaust cams 26 is rotatably supported substantially directly above the exhaust valves 22 in the cylinder head 14. The exhaust camshaft 27 drives the exhaust valves 22. The intake and exhaust camshafts 25, 27 are coupled to the crankshaft 16 with a timing chain 34, a sprocket 33 and other components (see Fig. 5) .

A rocker arm 29 having a roller 28 is pivotally provided between each of the exhaust and intake cams 24, 26 and the upper portion of the corresponding one of the intake and exhaust valves 21, 22. Further, a hydraulic lash adjuster 31 is located in the cylinder head 14 in the vicinity of the upper end of each of the intake and exhaust valves 21, 22. Each rocker arm 29 receives compression reaction force of the corresponding valve spring 23 and upward force of the corresponding lash adjuster 31. Accordingly, each roller 28 contacts the corresponding one of the intake and exhaust cams 24, 26.

In response to rotation of the intake and exhaust cams 24, 26, the rocker arms 29 pivots upward and downwards with the lash adjusters 31 functioning as fulcrums, which presses down the intake and exhaust valves 21, 22 against the valve springs 23. Accordingly, the intake and exhaust ports 18, 19 are open (open state) .

The engine 11 is provided with a variable valve timing apparatus 32. The variable valve timing apparatus 32 is a mechanism that changes the rotational phase of the intake camshaft 25 relative to the crankshaft 16, thereby varying actuation timing (valve timing) of the intake valves 21 with respect to the crank angle (rotation angle of the crankshaft 16) . The valve timing of each intake valve 21 is represented by, for example, opening point IVO and closing point IVC of the intake valve 21 as shown in Fig. 2. The valve timing is advanced or retarded while the opening period of each intake valve 21 (a period from the opening point IVO to the closing point IVC) is maintained constant. In Fig. 2, EVO and EVC represent the opening point and closing point of each exhaust valve 22, respectively.

Fig. 4 is a cross-sectional view of the variable valve timing apparatus 32, and Fig. 5 is a cross-sectional view taken along line 5-5 of Fig. 4.

The sprocket 33, which functions as a driving member, is rotatably provided on an end of the intake camshaft 25 corresponding to a timing chain cover 48 of the engine 11 (left end as viewed in Fig. 4) . As described above, the sprocket 33 is coupled to the crankshaft 16 with the timing chain 34 and other components, so that rotation of the crankshaft 16 is transmitted to the sprocket 33 with the timing chain 34 and other components. Accordingly, the sprocket 33 is rotated in a direction depicted by an arrow in Fig. 5 (clockwise) . A rotor accommodation portion 33A is provided on the sprocket 33. The rotor accommodation portion 33A has a cylindrical shape with a rotation axis aligned with the axis L of the intake camshaft 25.

A rotor 35, which functions as a driven member, is fastened to an end of the intake camshaft 25 with a fastener such as a bolt 36. The rotor 35 is accommodated in the rotor accommodation portion 33A. The rotor 35 is coupled to the intake camshaft 25, for example, with a knock pin (not shown) , so that the rotor 35 rotates integrally with the intake camshaft 25. A cover 40 is placed over an open end of the rotor accommodation portion 33A (left end as viewed in Fig. 4), which accommodates the rotor 35.

To transmit rotation of the sprocket 33 to the rotor 35, an adjacent pair of recesses are formed in the outer circumference of the rotor 35. One of the pair of recesses, which is located on the leading side with respect to the rotation direction of the intake camshaft 25 (on the right side in Fig. 5), functions as an advance limiting recess 37 that limits relative rotation of the rotor 35 in a direction advancing the rotational phase with respect to the sprocket 33. An inclined section 37X is formed in a trailing portion of the advance limiting recess 37 with respect to the rotation direction. The inclined section 37X approaches the inner circumferential surface of the rotor accommodation portion 33A toward the trailing end (rear end) with respect to the rotation direction. A space defined by the inclined section 37X and the inner circumferential surface of the rotor accommodation portion 33A functions as a wedge-shaped advance limiting groove 37A. The depth of the advance limiting groove 37A decreases toward the trailing end. An advance limiting roller 38 is partly located in the advance limiting recess 37. The advance limiting roller 38 extends along the axial direction of the intake camshaft 25 and functions as an advance limiting engagement member. An advance limiting spring 39, which is a leaf spring, is located in the advance limiting recess 37, and is located on the leading side with respect to the rotation direction of the intake camshaft 25 compared to the advance limiting roller 38. The advance limiting spring 39 is provided in a compressed state and functions as an advance limiting elastic member. The advance limiting roller 38 is always urged toward the trailing side with respect to the rotation direction of the intake camshaft 25 by the advance limiting spring 39. The advance limiting roller 38 is engaged with the advance limiting groove 37A and thus functions as a wedge, thereby limiting relative rotation of the rotor 35 in the phase advancing direction with respect to the sprocket 33. The engagement refers to a state in which the advance limiting roller 38 simultaneously contacts the inclined section 37X of the advance limiting recess 37 and the inner circumferential surface of the rotor accommodation portion 33A. The advance limiting groove 37A, the advance limiting roller 38, and the advance limiting spring 39 form an advance limiting mechanism (or advance limiting means) .

The other of the pair of recesses, which is located on the trailing side with respect to the rotation direction of the intake camshaft 25 (on the left side in Fig. 5) , functions as a retard limiting recess 41 that limits relative rotation of the rotor 35 in a direction retarding the rotational phase with respect to the sprocket 33. An inclined section 41X is formed in a leading portion of the retard limiting recess 41 with respect to the rotation direction. The inclined section 41X approaches the inner circumferential surface of the rotor accommodation portion 33A toward the leading end (front end) with respect to the rotation direction. A space defined by the inclined section 41X and the inner circumferential surface of the rotor accommodation portion 33A functions as a wedge- shaped retard limiting groove 41A. The depth of the retard limiting groove 41A decreases toward the leading end. A retard limiting roller 42 is partly located in the retard limiting recess 41. The retard limiting roller 42 extends along the axial direction of the intake camshaft 25 and functions as a retard limiting engagement member. A retard limiting spring 43 is located in the retard limiting recess 41 and is located on the trailing side with respect to the rotation direction of the intake camshaft 25 compared to the retard limiting roller 42. The retard limiting spring 43 is provided in a compressed state and functions as a retard limiting elastic member. The retard limiting roller 42 is always urged toward the leading side with respect to the rotation direction of the intake camshaft 25 by the retard limiting spring 43. The retard limiting roller 42 is engaged with the retard limiting groove 41A and thus functions as a wedge, thereby limiting relative rotation of the rotor 35 in the phase retarding direction with respect to the sprocket 33. The engagement refers to a state in which the retard limiting roller 42 simultaneously contacts the inclined section 41X of the retard limiting recess 41 and the inner circumferential surface of the rotor accommodation portion 33A. The retard limiting groove 41A, the retard limiting roller 42, and the retard limiting spring 43 form a retard limiting mechanism (or retard limiting means) .

The engagement of the advance limiting roller 38 and the advance limiting groove 37A, and the engagement of the retard limiting roller 42 and the retard limiting groove 41A limit relative rotation of the rotor 35 in the phase advancing direction and the phase retarding direction, so that the rotor 35 rotates integrally with the sprocket 33.

To rotate the rotor 35 relative to the sprocket 33 in the phase advancing direction or the phase retarding direction, the advance limiting roller 38 or the retard limiting roller 42 needs to be temporarily disengaged.

In this respect, a rotation lever 44 is located in a portion of the rotor 35 that is in the vicinity of the cover

40 (left side in Fig. 4) . The rotation lever 44 functions as a limit releasing member. The rotation lever 44 includes a cylindrical boss 44A and a sectorial projection 44B that is formed integrally with the outer circumference surface of the boss 44A. The rotation lever 44 is permitted to rotate about the axis L of the intake camshaft 25. A part of the advance limiting roller 38 extends out from the advance limiting recess 37 toward the cover 40, and a part of the retard limiting roller 42 extends out from the retard limiting recess

41 toward the cover 40. The projection 44B of the rotation lever 44 is located between the exposed portion of the advance limiting roller 38 and the exposed portion of the retard limiting roller 42, and is held between the rollers 38, 42.

When the rotation lever 44 rotates in the phase advancing direction relative to the rotor 35, the projection 44B presses the advance limiting roller 38 against the advance limiting spring 39. Accordingly, the advance limiting roller 38 is disengaged from the advance limiting groove 37A, and the rotor 35 is permitted to rotate in the phase advancing direction. Contrastingly, when the rotation lever 44 rotates in the phase retarding direction relative to the rotor 35, the projection 44B presses the retard limiting roller 42 against the retard limiting spring 43. Accordingly, the retard limiting roller 42 is disengaged from the retard limiting groove 41A, and the rotor 35 is permitted to rotate in the phase retarding direction.

To engage the advance limiting roller 38 and the retard limiting roller 42 after the rollers 38, 42 are disengaged by the rotation lever 44, torque fluctuation accompanying rotation of the intake camshaft 25 is used. As shown in Fig. 3, due to compression reaction force of the valve spring 23, the in-cylinder pressure, and friction force, rotation of the intake camshaft 25 creates periodical torque fluctuation having positive torque and negative torque. Positive torque is generated mainly by compressing the valve spring 23 when intake valve 21 is open, and is used to retarding rotation (rotational phase) of the intake camshaft 25 (the rotor 35) relative to the crankshaft 16 (the sprocket 33) . In contrast, negative torque is generated mainly by releasing compressive reaction force stored in the valve spring 23 when intake valve 21 is closed, and is used to advancing rotation (rotational phase) of the intake camshaft 25 (the rotor 35) relative to the crankshaft 16 (the sprocket 33) .

Further, as shown in Figs. 4 and 5, a linear actuator 45, a plunger 46, and a moving direction changing mechanism are provided as a driving mechanism (or driving means) that rotates the rotation lever 44 and the rotor 35 relative to each other. The linear actuator 45 is located in a position away from the rotor 35 with respect to the axial direction of the intake camshaft 25. The linear actuator 45 is fixed to a portion of a timing chain cover 48 of the engine 11 that corresponds to the axis L of the intake camshaft 25. The linear actuator 45 may be provided elsewhere.

The linear actuator 45 includes a case 47, an electric motor 49 accommodated in the case 47, and a movable member 51. The movable member 51 selectively projects from and retracts into the case 47 to approach and moves away from the intake camshaft 25. The electric motor 49 and the movable member 51 are coupled to a transmission mechanism 52. The transmission mechanism 52 converts rotation of an output shaft 49A of the electric motor 49 into linear reciprocation and transmits it to the movable member 51.

The plunger 46 is arranged coaxial with the intake camshaft 25. An end of the plunger 46 corresponding to the linear actuator 45 (left end as viewed in Fig. 4) is located in the movable member 51. The end of the plunger 46 is coupled to the movable member 51 with a bearing 53. The bearing 53 transmits reciprocation of the movable member 51 to the plunger 46, but does not transmit rotation of the plunger 46 to the movable member 51. An end of the plunger 46 corresponding to the rotor 35 (right end as viewed in Fig. 4) is received by the boss 44A of the rotation lever 44. Helical splines 54, 55 are formed on the inner circumferential surface of the boss 44A and the outer circumferential surface of the plunger 46 respectively. The tooth trace of each of the helical splines 54, 55 is intersecting the axial direction of the intake camshaft 25 at a predetermined angle. The helical spline 55 of the plunger 46 is meshed with the helical spline 54 of the rotation lever 44. The moving direction changing mechanism includes the helical splines 54, 55.

The variable valve timing apparatus 32 according to the first embodiment is configured as described above. Operation of the variable valve timing apparatus 32 will now be described.

Fig. 5 illustrates a state in which the advance limiting roller 38 is engaged with the advance limiting groove 37A, and the retard limiting roller 42 is engaged with the retard limiting groove 41A. In this state, the engagement of the rollers 38, 42 limits relative rotation of the rotor 35 in the phase advancing direction and the phase retarding direction, and causes the rotor 35 to rotate integrally with the sprocket 33. The projection 44B is held between the advance limiting roller 38 and the retard limiting roller 42. Therefore, the rotation lever 44 and the plunger 46 rotate integrally with the rotor 35 and the sprocket 33.

To advance the phase of the rotor 35 relative to the sprocket 33 in the above described state, electricity to the electric motor 49 in the linear actuator 45 is controlled to rotate the output shaft 49A in a predetermined direction. Rotation of the output shaft 49A is transmitted to the movable member 51 by means of the mechanism 52, so that the movable member 51 projects from or retracts into the case 47. The movement of the movable member 51 is transmitted to the rotating plunger 46 and moves the plunger 46 linearly. The linear movement is transmitted to the rotation lever 44 by means of the helical splines 55, 54. During the transmission, the rotation lever 44 receives torsional force, which causes the rotation lever 44 to rotate clockwise relative to the rotor 35 as viewed in Fig. 6. In response to the relative rotation, the projection 44B presses the advance limiting roller 38 while compressing the advance limiting spring 39.

Accordingly, the advance limiting roller 38 is disengaged from the advance limiting groove 37A, and the rotor 35 is permitted to rotate in the phase advancing direction relative to the sprocket 33. Then, negative torque in the torque fluctuation causes the intake camshaft 25 and the rotor 35 to rotate in the phase advancing direction relative to the sprocket 33. The relative rotation is stopped when the advance limiting roller 38 is engaged with the advance limiting groove 37A again. When the rotation lever 44 is rotated in the phase advancing direction and the advance limiting spring 39 is compressed, the retard limiting spring 43 in the retard limiting recess 41 is expanded, and the retard limiting roller 42 keeps being engaged with the retard limiting groove 41A. Therefore, positive torque in the torque fluctuation does not cause the rotor 35 to rotate in the phase retarding direction. The rotation lever 44 rotates only in the phase advancing direction.

To retard the phase of the rotor 35 relative to the sprocket 33, electricity to the electric motor 49 in the linear actuator 45 is controlled to rotate the output shaft 49A in the direction opposite to the direction for advancing the phase. Rotation of the output shaft 49A is transmitted to the movable member 51 by means of the mechanism 52, so that the movable member 51 moves in the direction opposite to the moving direction for advancing the phase. The movement of the movable member 51 is transmitted to the rotating plunger 46 and moves the plunger 46 linearly. The linear movement is transmitted to the rotation lever 44 by means of the helical splines 55, 54. During the transmission, the rotation lever 44 receives torsional force the direction of which is opposite to the torsional force generated when advancing the phase. This causes the rotation lever 44 to rotate counterclockwise relative to the rotor 35 as viewed in Fig. 7. In response to the relative rotation, the projection 44B presses the retard limiting roller 42 while compressing the retard limiting spring 43. Accordingly, the retard limiting roller 42 is disengaged from the retard limiting groove 41A, and the rotor 35 is permitted to rotate in the phase retarding direction relative to the sprocket 33. Then, positive torque in the torque fluctuation causes the intake camshaft 25 and the rotor 35 to rotate in the phase retarding direction relative to the sprocket 33. The relative rotation is stopped when the retard limiting roller 42 is engaged with the retard limiting groove 41A again.

When the rotation lever 44 is rotated in the phase retarding direction and the retard limiting spring 43 is compressed, the advance limiting spring 39 in the advance limiting recess 37 is expanded, and the advance limiting roller 38 keeps being engaged with the advance limiting groove 37A. Therefore, negative torque in the torque fluctuation does not cause the rotor 35 to rotate in the phase advancing direction. The rotation lever 44 rotates only in the phase retarding direction.

The first embodiment described above provides the following advantages.

(1) The advance limiting groove 37A, the advance limiting roller 38, and the advance limiting spring 39 are provided between the rotor accommodation portion 33A of the sprocket 33 and the rotor 35, as well as the retard limiting groove 41A, the retard limiting roller 42, and the retard limiting spring 43. Also, the rotation lever 44 is provided coaxial with the rotor 35.

Thus, engagement of the advance limiting roller 38 with the advance limiting groove 37A limits relative rotation of the rotor 35 in the phase advancing direction with respect to the sprocket 33. Also, by rotating the rotation lever 44 in the phase advancing direction relative to the rotor 35, the advance limiting roller 38 is disengaged from the advance limiting groove 37A. Therefore, by using negative torque of the intake camshaft 25, the rotor 35 can be rotated in the phase advancing direction so that the valve timing of the intake valves 21 is advanced with respect to rotation of the crankshaft 16. Likewise, engagement of the retard limiting roller 42 with the retard limiting groove 41A limits relative rotation of the rotor 35 in the phase retarding direction with respect to the sprocket 33. Also, by rotating the rotation lever 44 in the phase retarding direction relative to the rotor 35, the retard limiting roller 42 is disengaged from the retard limiting groove 41A. Therefore, by using positive torque of ^• the intake camshaft 25, the rotor 35 can be rotated in the phase retarding direction so that the valve timing of the intake valves 21 is retarded with respect to rotation of the crankshaft 16.

(2) The advance limiting spring 39, which urges the advance limiting roller 38 toward the trailing side with respect to the rotation direction of the intake camshaft 25, is provided between the rotor accommodation portion 33A and the rotor 35. Also, the retard limiting spring 43, which urges the retard limiting roller 42 toward the leading side with respect to the rotation direction, is provided between the rotor accommodation portion 33A and the rotor 35.

Therefore, when the rotation lever 44 does not permit relative rotation, the advance limiting spring 39 reliably causes the advance limiting roller 38 to be engaged with the advance limiting groove 37A, and the retard limiting spring 43 reliably causes the retard limiting roller 42 to be engaged with the retard limiting groove 41A.

When rotating the rotation lever 44 in the phase advancing direction to disengage the advance limiting roller 38 from the advance limiting groove 37A, the retard limiting roller 42 is kept engaged with the retard limiting groove 41A. Accordingly, the rotor 35 is rotated only in the phase advancing direction by the torque fluctuation of the intake camshaft 25.

Contrastingly, when rotating the rotation lever 44 in the phase retarding direction to disengage the retard limiting roller 42 from the retard limiting groove 41A, the advance limiting roller 38 is kept engaged with the advance limiting groove 37A. Accordingly, the rotor 35 is rotated only in the phase retarding direction by the torque fluctuation of the intake camshaft 25.

(3) The rotation lever 44 is formed by the boss 44A and the projection 44B, and the projection 44B is located between the advance limiting roller 38 and the retard limiting roller 42.

Thus, when the rotation lever 44 is not actuated by the linear actuator 45, the projection 44B is held between the advance limiting roller 38 engaged with the advance limiting groove 37A and the retard limiting roller 42 engaged with the retard limiting groove 4IA, thereby limiting relative rotation of the rotor 35 with respect to the rotation lever 44, so that the rotation lever 44 rotates integrally with the rotor 35.

When the rotation lever 44 is actuated by the linear actuator 45, the advance limiting roller 38 is pressed by the rotation lever 44 so as to be disengaged from the advance limiting groove 37A. Alternatively, the retard limiting roller 42 is pressed by the rotation lever 44 so as to be disengaged from the retard limiting groove 41A. The disengagement permits the rotor 35 to be ready for being rotated by using the torque fluctuation of the intake camshaft 25.

(4) To actuate the rotation lever 44, the linear actuator 45 is provided at a position spaced from the end of the intake camshaft 25 with respect to the axial direction of the intake camshaft 25, and the linear actuator 45 is used to move the plunger 46 in the axial direction. The plunger 45 and the rotation lever 44 are meshed with each other by means of the helical splines 54, 55.

Thus, by operating the linear actuator 45 to move the plunger 46 in the axial direction, torsional force is generated in the rotation lever 44 by means of the helical splines 54, 55, and the rotation lever 44 is rotated relative to the rotor 35. The relative rotation ensures the advantages (D to (3) .

(5) In relation to the advantage (4), the rotation lever 44 is actuated simply by driving the linear actuator 45 fixed to the timing chain cover 48. Driving of the linear actuator 45 is executed independently from rotation of the intake camshaft 25. Unlike the examples described in the background section, the first embodiment does not use a configuration in which an electromagnetic coil is attached to a portion that rotates with the intake camshaft 25 so that the coil rotates integrally with the portion, and electricity is supplied to the electromagnetic coil from a non-rotating portion. Therefore, no slip ring is needed between the rotating portion and the non-rotating portion to supply electricity to the electromagnetic coil. As a result, no wear of slip rings and parts contacting slip rings occurs. Further, since no electromagnetic coil is rotated with the intake camshaft 25, the weight of the rotating components is prevented from increasing, which reduces the driving force for rotating the intake camshaft 25. Since a portion of the driving force of the crankshaft 16 that is used for rotating the intake camshaft 25 is reduced, the fuel economy of the engine 11 is improved. (6) The movable member 51 and the plunger 46 are coupled to each other with the bearing 53. This permits movement of the movable member 51 in the axial direction to be transmitted to the plunger 46 via the bearing 53. Also, rotation of the plunger 46 is blocked by the bearing 53 and is not transmitted to the movable member 51.

(7) A variable valve timing apparatus that varies valve timing using hydraulic pressure cannot reliably change the valve timing when the hydraulic pressure is insufficient, for example, when the engine is being cranked or the temperature of the engine is low. In the first embodiment, the linear actuator 45, which has the electric motor 49 as a driving source, is used for rotating the rotation lever 44, which is directly related to change of valve timing. Therefore, even when the engine is being cranked or when the temperature of the engine is relatively low, the valve timing is reliably varied compared to a case where the hydraulic pressure is used.

(8) Torque fluctuation of the intake camshaft 25 is used for rotating the rotor 35, relative rotation of which is permitted by the rotation lever 44, until the advance limiting roller 38 limits the phase advancing operation or until the retard limiting roller 42 limits the phase retarding operation. Therefore, no extra means for rotating the rotor 35 needs to be provided.

A second embodiment of the present invention will hereafter be described with reference to Figs. 8 and 9.

The second embodiment is different from the first embodiment in the configuration of a moving direction converting mechanism that changes linear movement of the plunger 46 into rotation and transmits the rotation to the rotation lever 44. The moving direction converting mechanism of the second embodiment has a helical groove 61 formed in the inner circumferential surface of the boss 44A of the rotation lever 44 and an engagement projection 62 that projects from the outer circumferential surface of the plunger 46 and is engaged with the groove 61. The groove 61 intersects the generatrix of the inner circumferential surface of the boss 44A at a specific angle. As the engagement projection 62, a pin may be press fitted into the outer circumferential surface of the plunger 46. In this case, the exposed portion of the pin functions as the engagement projection 62. Other than these differences, the second embodiment is the same as the first embodiment. Therefore, like or the same reference numerals are given to those components that are like or the same as the corresponding components of the first embodiment and detailed explanations are omitted.

According to the second embodiment, the variable valve timing apparatus 32 operates basically in the same manner as the first embodiment. The operation of the second embodiment is different from that of the first embodiment in the manner in which linear movement of the plunger 46 is converted into rotation and transmitted to the rotation lever 44 when the linear actuator 45 operates.

That is, when the plunger 46 is moved in the axial direction of the intake camshaft 25 as the linear actuator 45 operates, the engagement projection 62 of the plunger 46 is moved in the same direction, accordingly. This shifts a portion that contacts the groove 61. Since the groove 61 is helical, shifting of the contacting portion generates torsional force in the rotation lever 44 so that the rotation lever 44 rotates relative to the rotor 35. If the relative rotation is in the phase advancing direction, the advance limiting roller 38 is disengaged from the advance limiting groove 37A. This permits the rotor 35 to rotate in the phase advancing direction. Further, if the relative rotation is in the phase retarding direction, the retard limiting roller 42 is disengaged from the retard limiting groove 41A. This permits the rotor 35 to rotate in the phase retarding direction.

Therefore, the second embodiment provides the same advantages as the above described advantages (1) to (8) .

The present invention may be embodied in the following forms.

The first embodiment may be modified in such a manner that the boss 44A of the rotation lever 44 is inserted into the plunger 46. In this case, the outer circumferential surface of the boss 44A and the circumferential surface of the plunger 46 are meshed with each other by means of helical splines.

In the second embodiment, the positions of the helical groove 61 and the engagement projection 62 on the outer circumferential surface of the boss 44A and the outer circumferential surface of the plunger 46 may be interchanged. In this case, the helical groove 61 is provided on the outer circumferential surface of the plunger 46, and the engagement projection 62 is provided on the inner circumferential surface of the boss 44A, so that the engagement projection 62 is engaged with the groove 61. In this case, linear movement of the plunger 46 can be converted into rotation and transmitted to the rotation lever 44 as in the second embodiment.

The second embodiment may be modified in such a manner that the boss 44A of the rotation lever 44 is inserted into the plunger 46. In this case, the helical groove 61 is provided in one of the outer circumferential surface of the boss 44A and the inner circumferential surface of the plunger 46, and the engagement projection 62 is provided on the other.

As long as the linear actuator 45 is separated from the rotor 35 along the axial direction of the intake camshaft 25, the position of the linear actuator 45 may be changed as necessary. For example, the linear actuator 45 may be arranged in such a manner that the output shaft 49A of the electric motor 49 intersects the axis L of the camshaft.

A hydraulic actuator may be used as a linear actuator.

The present invention may be applied to an internal combustion engine in which the sprocket 33 is replaced by a timing pulley that is rotated relative to a camshaft, and rotation of the crankshaft 16 is transmitted to the timing pulley with the timing belt.

Instead of controlling the intake valves 21 or in addition to controlling the intake valves 21, the variable valve timing apparatus according to the present invention may be used to vary the valve timing of the exhaust valves 22.

Claims

1. A variable valve timing apparatus for an internal combustion engine, including: a driving member provided on a camshaft for driving an engine valve, the driving member rotating relative to the camshaft and being coupled to a crankshaft; a driven member provided on the camshaft so as to rotate integrally with the camshaft; an advance limiting mechanism for limiting rotation of the driven member in a phase advancing direction relative to the driving member; a retard limiting mechanism for limiting rotation of the driven member in a phase retarding direction relative to the driving member; a limit releasing member that rotates to release the limitation by the advance limiting mechanism or the limitation by the retard limiting mechanism; and a driving mechanism for rotating the limit releasing member, wherein, in a state in which the limitation by the advance limiting mechanism or the retard limiting mechanism on the driven member has been released by the limit releasing member, the driven member is rotated relative to the driving member to a position where the limitation by the advance limiting mechanism or the retard limiting mechanism is imposed by using torque fluctuation accompanying rotation of the camshaft, so that actuation timing of the engine valve in relation to rotation of the crankshaft is changed, the apparatus being characterized in that the driving mechanism including: an actuator that is located in a position away from the driven member with respect to an axial direction of the camshaft; a plunger that is driven by the actuator so as to move along the axial direction of the camshaft; and a moving direction converting mechanism that changes linear movement of the plunger along the axial direction of the camshaft into rotation and transmits the rotation to the limit releasing member.

2. The apparatus according to claim 1, characterized in that the advance limiting mechanism includes: a wedge-shaped advance limiting groove provided between the driving member and the driven member, wherein the depth of the advance limiting groove decreases toward a rear end with respect to the rotation direction of the camshaft; and an advance limiting engagement member that is engaged with the advance limiting groove so as to limit relative rotation of the driven member in the phase advancing direction, wherein the retard limiting mechanism includes: a wedge-shaped retard limiting groove provided between the driving member and the driven member, wherein the depth of the retard limiting groove decreases toward a front end with respect to the rotation direction of the camshaft; and a retard limiting engagement member that is engaged with the retard limiting groove so as to limit relative rotation of the driven member in the phase retarding direction.

3. The apparatus according to claim 2, characterized in that the advance limiting mechanism further includes an advance limiting elastic member that urges the advance limiting engagement member toward the trailing side with respect to the rotation direction of the camshaft, and wherein the retard limiting mechanism further includes a retard limiting elastic member that urges the retard limiting engagement member toward the leading side with respect to the rotation direction of the camshaft.

4. The apparatus according to claim 2 or 3, characterized in that a part of the limit releasing member is located between the advance limiting engagement member and the retard limiting engagement member.

5. The apparatus according to any one of claims 1 to 4, characterized in that the limit releasing member includes a boss that permits insertion of the plunger, and wherein the moving direction converting mechanism includes helical splines formed on an outer circumferential surface of the plunger and an inner circumferential surface of the boss, respectively, the helical splines being meshed with each other.

6. The apparatus according to any one of claims 1 to 4, characterized in that the limit releasing member includes a boss that permits insertion of the plunger, and wherein the moving direction converting mechanism includes a helical groove formed in one of an inner circumferential surface of the boss and an outer circumferential surface of the plunger and an engagement projection provided on the other, the engagement projection being engaged with the helical groove.

7. The apparatus according to any one of claims 1 to 6, characterized in that the actuator includes an electric motor.