VALVE MECHANISM OF ENGINE

Abstract

A valve mechanism for an engine includes a camshaft, a rocker arm, a synchronization cam that rotates in synchronism with a valve driving cam, and a switch assembly that switches the driving state of an intake valve or an exhaust valve when a cam follower is pressed by the synchronization cam. The synchronization cam presses the cam follower at a time when the intake valve or the exhaust valve is closed. The switch assembly includes a switch unit that switches the driving state when a switch moves, a driver that drives the switch via a transmission, and a positioner including a spring-biased presser that engages with a concave portion of the transmission. The concave portion includes a first concave portion with which the presser engages in a first driving state, and a second concave portion with which the presser engages in a second driving state.

Claims

1-6. (canceled)

7. A valve mechanism for an engine, the valve mechanism comprising: a camshaft including a valve driving cam that drives one of an intake valve and an exhaust valve; a rocker arm that converts a rotation of the valve driving cam into a reciprocal motion and transmits the reciprocal motion to one of the intake valve and the exhaust valve; a synchronization cam that rotates in synchronism with the valve driving cam; and a switch assembly including a cam follower that is pressed and moved by the synchronization cam, and that switches, when the cam follower is pressed by the synchronization cam, a driving state of one of the intake valve and the exhaust valve to a first driving state or a second driving state; wherein the synchronization cam presses the cam follower at a time when one of the intake valve and the exhaust valve is closed; the switch assembly includes: a switch unit that switches the driving state when a switch moves; a driver including a transmission that transmits a motion of the cam follower to the switch, and drives the switch via the transmission in a direction to switch the driving state; and a positioner that includes a presser that engages with a concave portion in the transmission, and positions the transmission at a predetermined position defined by the concave portion; the concave portion includes: a first concave portion with which the presser engages when the transmission moves to a position in the first driving state; and a second concave portion with which the presser engages when the transmission moves to a position in the second driving state; and a positioning interval between the first concave portion and the second concave portion is greater than a moving amount of the transmission when the transmission is driven and moved by the synchronization cam.

8. The valve mechanism according to claim 7, wherein the concave portion has a slope such that an opening width becomes narrower from an opening edge to a bottom; a position to which the transmission is driven and moved by the synchronization cam is a position that the presser abuts against the slope of the concave portion; and the transmission is further moved by a thrust generated when the presser presses against the slope, and reaches a predetermined position defined by the concave portion.

9. The valve mechanism according to claim 8, further comprising a spring having a spring force that biases the presser and is set to a magnitude that causes the transmission to be moved by the thrust to the predetermined position within a time when one of the intake valve and the exhaust valve is closed.

10. The valve mechanism according to claim 7, further comprising a spring having a spring force that biases the presser and is set to a magnitude that generates a position holding force that holds the transmission in the predetermined position defined by the concave portion in a state in which the presser engages with one of the first concave portion and the second concave portion; and the position holding force is set to a magnitude that prevents the first driving state and the second driving state from being switched by a force other than an actuating force generated when the synchronization cam presses the cam follower.

11. The valve mechanism according to claim 7, wherein the driver includes: a pivot shaft that rotates when a pressing force is transmitted from the cam follower; an inverter that alternately switches a direction of the rotation of the pivot shaft between a first side and a second side; and a converter that converts a pivotal motion of the pivot shaft into a reciprocal motion and transmits the reciprocal motion to the switch.

12. The valve mechanism according to claim 11, wherein the pivot shaft includes: a first projection projecting to a first side of a direction perpendicular or substantially perpendicular to an axial direction of the pivot shaft; and a second projection projecting to a second side of the direction perpendicular or substantially perpendicular to the axial direction of the pivot shaft; the inverter includes: a slide pin pressed by the cam follower; a moving member that supports the slide pin movably in a first direction that is a moving direction of the cam follower, and movable in a second direction perpendicular or substantially perpendicular to the first direction; and an actuator that drives the moving member to the first side or the second side of the second direction; the slide pin is disposed between the cam follower and the first projection when the moving member moves to the first side of the second direction, and is disposed between the cam follower and the second projection when the moving member moves to the second side of the second direction; one of the first projection and the second projection that interposes the slide pin between the one projection and the cam follower receives the pressing force, via the slide pin, from the cam follower pressed by the synchronization cam, and causes the pivot shaft to rotate in a direction in which the one projection is pressed; and the other of the first projection and the second projection functions as a cam follower return cam that presses the slide pin toward the camshaft together with the cam follower and returns the cam follower when the slide pin that presses the one projection moves together with the moving member in a direction toward the other projection.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a sectional view of a valve mechanism for an engine according to a first preferred embodiment of the present invention.

[0026] FIG. 2 is a front view of the main elements of the valve mechanism.

[0027] FIG. 3 is a plan view of the main elements of the valve mechanism.

[0028] FIG. 4 is a perspective view of the main elements of the valve mechanism.

[0029] FIG. 5 is a side view of the main elements of the valve mechanism.

[0030] FIG. 6 is a sectional view of rocker arms, which shows a connected state in which a first rocker arm and a second rocker arm are connected.

[0031] FIG. 7 is a sectional view of the rocker arms, which shows a non-connected state in which the first rocker arm and the second rocker arm are not connected.

[0032] FIG. 8 is a sectional view of a driver taken along a line A-A in FIG. 5.

[0033] FIG. 9A is a sectional view of a positioner, which shows a state before the start of movement.

[0034] FIG. 9B is a sectional view of the positioner, which shows a state in which a presser moves across the boundary portion between one concave portion and the other concave portion.

[0035] FIG. 9C is a sectional view of the positioner, which shows a state at the time when the operation of a synchronization cam to press a cam follower ends.

[0036] FIG. 9D is a sectional view of the positioner, which shows a state in which positioning is completed.

[0037] FIG. 10 is an enlarged sectional view of the main elements of the driver.

[0038] FIG. 11 is an enlarged sectional view of the main elements of the driver.

[0039] FIG. 12 is a plan view for explaining the structure of a connecting lever.

[0040] FIG. 13 is a sectional view of the driver taken along the line A-A in FIG. 5.

[0041] FIG. 14 is a sectional view of a switch unit taken along a line B-B in FIG. 5.

[0042] FIG. 15 is a sectional view of the driver taken along the line A-A in FIG. 5.

[0043] FIG. 16 is a sectional view of the switch unit taken along the line B-B in FIG. 5.

[0044] FIG. 17 is a sectional view of the driver taken along the line A-A in FIG. 5.

[0045] FIG. 18 is a sectional view of the switch unit taken along the line B-B in FIG. 5.

[0046] FIG. 19 is a plan view for explaining the structure of a camshaft and a switch unit according to a second preferred embodiment of the present invention, in which a sectional view of a driver is also illustrated.

[0047] FIG. 20 is a plan view for explaining the structure of the camshaft and the switch unit according to the second preferred embodiment of the present invention, in which a sectional view of the driver is also illustrated.

[0048] FIG. 21 is a plan view for explaining the structure of a camshaft and a switch unit according to a third preferred embodiment of the present invention, in which a sectional view of a driver is also illustrated.

[0049] FIG. 22 is a plan view for explaining the structure of the camshaft and the switch unit according to the third preferred embodiment of the present invention, in which a sectional view of the driver is also illustrated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Preferred Embodiment

[0050] A valve mechanism for an engine according to a preferred embodiment of the present invention will now be described in detail with reference to FIGS. 1 to 18.

[0051] A valve mechanism 1 shown in FIG. 1 is provided in, for example, a DOHC-type four-cylinder engine 2 mounted in a vehicle (not shown). The valve mechanism 1 includes switch assemblies 3 that switch between a full cylinder operation state in which four cylinders are operated as usual and a partial cylinder operation state (deactivated state) in which two cylinders of the four cylinders are deactivated.

[0052] The switch assemblies 3 are provided for the two cylinders of the four cylinders, as will be described below in detail. For example, the switch assemblies 3 may be provided for the first cylinder and the fourth cylinder which are located at the two ends of a cylinder train, or for the second cylinder and the third cylinder which are located at the center of the cylinder train.

[0053] As shown in FIG. 1, the switch assemblies 3 according to this preferred embodiment define a portion of the valve mechanism 1 and are respectively provided on one side where an intake valve 4 is located and on the other side where an exhaust valve 5 is located. In the above-described operation states, the valve mechanism 1 converts the rotations of an intake camshaft 7 and an exhaust camshaft 8 provided in a cylinder head 6 into reciprocal motions by rocker arms 9 and drives the intake valves 4 and the exhaust valves 5.

[0054] In the valve mechanism 1, a portion that drives the intake valves 4 and a portion that drives the exhaust valves 5 preferably have the same structure. For this reason, as for elements with the same structure on the side of the intake valves 4 and the side of the exhaust valves 5, the elements on the side of the exhaust valves 5 will be described below. The elements on the side of the intake valves 4 are denoted by the same reference numerals as those on the side of the exhaust valves 5, and a description thereof will be omitted.

[0055] Each of the intake camshaft 7 and the exhaust camshaft 8 includes a camshaft main body 11 rotatably supported in the cylinder head 6, and valve driving cams 12 and synchronization cams 13 which are provided on the camshaft main body 11. Note that the intake camshaft 7 and the exhaust camshaft 8 will simply be referred to as camshafts 14 in general hereinafter.

[0056] The camshaft main body 11 has an elongated rod shape with a circular cross-section. As shown in FIG. 5, the valve driving cam 12 includes a base circle portion 12a and a nose portion 12b. The base circle portion 12a has a shape that defines a portion of a column located on the same axis as the camshaft main body 11, and has a size that sets the valve lift amount of the intake valve 4 or the exhaust valve 5 to zero. The nose portion 12b has a shape that projects, by a predetermined projection amount, from the base circle portion 12a outward in the radial direction so as to have a mountain-shaped cross-section.

[0057] The synchronization cam 13 defines the time when the switch assembly 3 performs a switching operation and powers the switch assembly 3. As shown in FIG. 5, the synchronization cam 13 includes a base circle portion 13a and a nose portion 13b, and is provided at a position adjacent to the valve driving cam 12. The synchronization cam 13 rotates in synchronism with the valve driving cam 12. The base circle portion 13a of the synchronization cam 13 has a shape that defines a portion of a column located on the same axis as the camshaft main body 11. The nose portion 13b of the synchronization cam 13 has a shape that projects, by a predetermined projection amount, from the base circle portion 13a outward in the radial direction so as to have a mountain-shaped cross-section.

[0058] The positional relationship between the valve driving cam 12 and the synchronization cam 13 with respect to the rotation direction of the camshaft 14 is set such that the switch assembly 3 is operated by the synchronization cam 13 at the time when the valve driving cam 12 closes the intake valve 4 or the exhaust valve 5. That is, when the camshaft main body 11 is viewed from the axial direction, as shown in FIG. 5, the positional relationship is set such that the switch assembly 3 is operated by the nose portion 13b at any timing during the period when the base circle portion 12a of the valve driving cam 12 is in contact with the rocker arm 9.

[0059] Two intake valves 4 and two exhaust valves 5 are preferably provided in each cylinder and are movably supported in the cylinder head 6. The two intake valves 4 are located at a predetermined interval in the axial direction of the intake camshaft 7. The two exhaust valves 5 are located at a predetermined interval in the axial direction of the exhaust camshaft 8.

[0060] Each intake valve 4 includes a valve body 4a that opens/closes an intake port 15 of the cylinder head 6, and a valve stem 4b extending from the valve body 4a into a valve chamber 16 of the cylinder head 6. Each exhaust valve 5 includes a valve body 5a that opens/closes an exhaust port 17 of the cylinder head 6, and a valve stem 5b extending from the valve body 5a into the valve chamber 16 of the cylinder head 6. A valve spring 18 that biases the intake valve 4 or the exhaust valve 5 in a closing direction is provided between the cylinder head 6 and each of the distal ends of the valve stems 4b and 5b. A cap-shaped shim 19 is provided at each of the distal ends of the valve stems 4b and 5b.

[0061] The upstream end of the intake port 15 is open to one side of the cylinder head 6. The downstream end of the intake port 15 is open to a combustion chamber 20 of each cylinder. The upstream end of the exhaust port 17 is open to the combustion chamber 20. The downstream end of the exhaust port 17 is open to the other side of the cylinder head 6. A spark plug (not shown) is provided at the center of the combustion chamber 20.

[0062] As shown in FIG. 4, the switch assembly 3 according to this preferred embodiment includes a switch unit 21 including the rocker arm 9 that drives the intake valves 4 or the exhaust valves 5, a driver 23 including a cam follower 22 that is pressed and moved by the above-described synchronization cam 13, a positioner 24 located at the uppermost position in FIG. 4, and the like.

[0063] The switch unit 21 switches the driving state of the intake valves 4 or the exhaust valves 5 by moving a switch 21A (see FIG. 6) that is one of the elements of a valve mechanism system to be described below. The driver 23 includes a transmission 25 defined by a plurality of elements located between the cam follower 22 and the rocker arm 9, as will be described below in detail. The transmission 25 transmits the motion of the cam follower 22. The driver 23 drives the switch 21A that is also one of a plurality of elements of the valve mechanism system in a direction to switch the driving state via the transmission 25.

[0064] As shown in FIGS. 2 to 4, the rocker arm 9 includes a plurality of elements. The plurality of elements include a first rocker arm 27 including a roller 26 in contact with the valve driving cam 12, a second rocker arm 28 located at a position adjacent to the first rocker arm 27 in the axial direction of the camshaft 14, first to third switching pins 31 to 33 (see FIGS. 6 and 7) that selectively connect the first rocker arm 27 and the second rocker arm 28, and the like.

[0065] As shown in FIGS. 1 to 5, the first rocker arm 27 includes a right-side arm portion 27b and a left-side arm portion 27c, which are connected by a connecting portion 27a (see FIG. 5) to define a U shape (see FIG. 2) in a front view. One end of the first rocker arm 27 is swingably supported by a rocker shaft 34. The rocker shaft 34 is attached to a support 35 (see FIG. 1) fixed to the cylinder head 6 in a state in which the rocker shaft 34 is parallel or substantially parallel to the camshaft 14. A swing end of the first rocker arm 27 includes a tubular shaft 36, as shown in FIGS. 6 and 7, and supports the roller 26 via the tubular shaft 36. The axis of the tubular shaft 36 is parallel or substantially parallel to the axis of the rocker shaft 34. The roller 26 is rotatably supported on the tubular shaft 36 by a bearing 37.

[0066] The hollow portion of the tubular shaft 36 extends in the axial direction of the camshaft 14 so as to cross the first rocker arm 27. The first switching pin 31 is movably fitted in the hollow portion. The hollow portion of the tubular shaft 36 will be referred to as a first pin hole 38 hereinafter. In this preferred embodiment, the length of the first switching pin 31 equals the length of the first pin hole 38. However, the length of the first switching pin 31 may be larger or smaller than that of the first pin hole 38 as long as the first switching pin 31 is able to avoid fitting in an adjacent pin hole in a non-connected state to be described below.

[0067] As shown in FIGS. 1 and 2, a return spring 39 is provided between the cylinder head 6 and the connecting portion 27a that connects the right-side arm portion 27b and the left-side arm portion 27c to define a U shape in the front view at a swing end of the first rocker arm 27. The spring 39 biases the first rocker arm 27 in a direction in which the roller 26 is pressed against the valve driving cam 12. For this reason, the first rocker arm 27 is pressed by the valve driving cam 12, thus swinging against the spring force of the spring 39.

[0068] As shown in FIG. 3, the second rocker arm 28 includes a first arm main body 28a and a second arm main body 28b, which are located on both sides of the first rocker arm 27, and a connecting portion 28c that connects swing ends of the first arm main body 28a and the second arm main body 28b. First ends of the first arm main body 28a and the second arm main body 28b are swingably supported by the rocker shaft 34. As shown in FIG. 2, the connecting portion 28c extends in the axial direction of the camshaft 14. Pressing portions 40 that press the shims 19 of the intake valves 4 or the exhaust valves 5 are located at the two ends of the connecting portion 28c in the longitudinal direction. The second rocker arm 28 simultaneously presses the two intake valves 4 or exhaust valves 5 of each cylinder.

[0069] As shown in FIGS. 6 and 7, a second pin hole 41 is located in the intermediate portion of the first arm main body 28a. A third pin hole 42 is located in the intermediate portion of the second arm main body 28b. The second pin hole 41 and the third pin hole 42 extend in the axial direction of the camshaft 14 so as to cross the first arm main body 28a and the second arm main body 28b. The distance between the center line of the second pin hole 41 and the third pin hole 42 and the axis of the rocker shaft 34 matches the distance between the center line of the first pin hole 38 of the first rocker arm 27 and the axis of the rocker shaft 34. That is, the first pin hole 38 and the second pin hole 41 and the third pin hole 42 are located on the same axis in a state in which the swing angle of the first rocker arm 27 and the swing angle of the second rocker arm 28 are set to a predetermined angle. The predetermined angle is an angle obtained when the intake valves 4 or the exhaust valves 5 are closed. For this reason, the second pin hole 41 and the third pin hole 42 are located on the same axis as the first pin hole 38 when the valve lift amount of the intake valves 4 or the exhaust valves 5 becomes zero.

[0070] The hole diameters of the second pin hole 41 and the third pin hole 42 match the hole diameter of the first pin hole 38. The second switching pin 32 is movably fitted in the second pin hole 41, and the second pin hole 41 is provided with a spring 43 that biases the second switching pin 32 toward the first rocker arm 27.

[0071] The third switching pin 33 is movably fitted in the third pin hole 42. The length of the third switching pin 33 equals the length of the third pin hole 42. However, the length of the third switching pin 33 may be larger or smaller than that of the third pin hole 42 as long as the third switching pin 33 is able to avoid fitting in an adjacent pin hole in a non-connected state to be described later. The end of the third switching pin 33 on the opposite side of the first rocker arm 27 faces a pressing member 44 of the driver 23 to be described below. The driver 23 presses the third switching pin 33 toward the first rocker arm 27 using the pressing member 44.

[0072] When the first to third pin holes 38, 41, and 42 are arranged on the same axis in a state in which the pressing member 44 is not pressing the third switching pin 33, the first to third switching pins 31 to 33 are pressed by the spring force of the spring 43 and move to a connecting position, as shown in FIG. 6. The connecting position is a position where the first switching pin 31 and the second switching pin 32 are located across the first rocker arm 27 and the second rocker arm 28.

[0073] When the first switching pin 31 and the second switching pin 32 move to the connecting position, one end of the third switching pin 33 projects from the second arm main body 28b and abuts against the pressing member 44. When the first to third switching pins 31 to 33 move to the connecting position, the first rocker arm 27 and the second rocker arm 28 are connected and integrally swing together. That is, the rotation of the valve driving cam 12 is converted into a reciprocal motion by both the first rocker arm 27 and the second rocker arm 28, and the intake valves 4 or the exhaust valves 5 are driven. In this case, the cylinders including the switch assemblies 3 are set in an operation state. At this time, the third switching pin 33 moves with the swinging of the second rocker arm 28 in a state in which the third switching pin 33 is pressed against the pressing member 44.

[0074] On the other hand, when the pressing member 44 presses the third switching pin 33, the first switching pin 31 and the second switching pin 32 move to a non-connecting position where the first switching pin 31 and the second switching pin 32 are not located across the first rocker arm 27 and the second rocker arm 28, as shown in FIG. 7. When the first and second switching pins 31 and 32 move to the non-connecting position, the connected state between the first rocker arm 27 and the second rocker arm 28 is canceled. In this case, since the first rocker arm 27 and the second rocker arm 28 individually swing, only the first rocker arm 27 is pressed by the valve driving cam 12 and swings, and the second rocker arm 28 does not swing. For this reason, since the intake valves 4 or the exhaust valves 5 are kept in the closed state, the cylinders including the switch assembly 3 are in a deactivated state.

[0075] In this preferred embodiment, the switch 21A that is one of elements of the valve mechanism system from the valve driving cam to the rocker arm includes the first to third switching pins 31 to 33. Additionally, in this preferred embodiment, the operation state in which the first rocker arm 27 and the second rocker arm 28 are connected is the first driving state, and the operation state in which the connected state between the first rocker arm 27 and the second rocker arm 28 is canceled is the second driving state.

[0076] As shown in FIGS. 6 and 7, the pressing member 44 has a columnar shape and is movably fitted in a shaft hole 45 of the support 35 fixed to the cylinder head 6. As shown in FIG. 1, the support 35 includes a base portion 46 that supports the rocker shaft 34, and driver housings 47 projecting from the base portion 46. The driver housings 47 are molded integrally with the base portion 46, or are elements separate from the base portion 46 and attached to the base portion 46. The shaft hole 45 is provided in the base portion 46.

[0077] One end of the pressing member 44, which faces the third switching pin 33, has a disc shape and a predetermined size. The end surface of the one end, which faces the third switching pin 33, is flat such that the third switching pin 33 is able to swing integrally with the second arm main body 28b in a state in which the third switching pin 33 is in contact with the end face. The one end has a size that makes the one end always face the third switching pin 33 that swings integrally with the second arm main body 28b.

[0078] A connecting lever 51 (to be described below) of the driver 23 is pivotally connected to the pressing member 44 via a first connecting pin 52. When the connecting lever 51 swings, the pressing member 44 advances or retreats with respect to the second arm main body 28b. For this reason, the pressing member 44 reciprocally moves between an advance position shown in FIG. 7 and a retreat position shown in FIG. 6.

[0079] The connecting lever 51, which is connected to the pressing member 44, is connected to one end of a pivot shaft 53 to be described below via a driving lever 54. As shown in FIG. 12, the connecting lever 51 is pivotally supported on the base portion 46 (not shown) by a support shaft 55. The support shaft 55 extends through the center of the connecting lever 51 in the longitudinal direction and is fixed to the base portion 46. The axis of the support shaft 55 is parallel or substantially parallel to the axis of the pivot shaft 53.

[0080] One end of the connecting lever 51 is pivotally connected to the pressing member 44 by the first connecting pin 52. For this reason, the above-described switch 21A (third switching pin 33) is operated by the connecting lever 51 via the pressing member 44.

[0081] The other end of the connecting lever 51 is pivotally connected to the pivotal end of the driving lever 54 by a second connecting pin 56. The driving lever 54 is fixed to the pivot shaft 53. The axes of the first connecting pin 52 and the second connecting pin 56 are parallel or substantially parallel to the axes of the pivot shaft 53 and the support shaft 55.

[0082] In FIG. 12, a length L1 of the connecting lever 51 on one end side is the same as a length L2 on the other end side. However, the operation amount of the connecting lever 51 is able to be changed by changing the ratio of the lengths L1 and L2. The length L1 is the distance between the axis of the support shaft 55 and the axis of the first connecting pin 52. The length L2 is the distance between the axis of the support shaft 55 and the axis of the second connecting pin 56.

[0083] Since the pivot shaft 53 is connected to the pressing member 44 via the connecting lever 51 and the driving lever 54 in this manner, when the pivot shaft 53 pivots, the motion of the pivot shaft 53 is transmitted to the pressing member 44. This will be described in detail. When the pivot shaft 53 pivots, the driving lever 54 and the connecting lever 51 swing in synchronism with the pivotal operation of the pivot shaft 53, and the pressing member 44 moves in the axial direction of the camshaft 14 to the advance position or the retreat position. That is, the pivotal motion of the pivot shaft 53 is converted into a reciprocal motion by the driving lever 54 and the connecting lever 51 and transmitted to the above-described switch 21A (third switching pin 33). In this preferred embodiment, a converter 57 includes the connecting lever 51, the driving lever 54, the above-described pressing member 44, and the like.

[0084] The pivot shaft 53 defines a portion of the driver 23. The driver 23 according to this preferred embodiment includes the combination of a plurality of elements including the pivot shaft 53, and is provided at a position adjacent to the rocker arm 9 in the axial direction of the rocker shaft 34, as shown in FIGS. 3 and 4. For the driver 23 shown in FIGS. 2 to 5, only elements that operate are illustrated for easier understanding of the driver 23.

[0085] As shown in FIG. 5, the driver 23 includes the pivot shaft 53 whose one end (the lower end in FIG. 5) is provided with the above-described driving lever 54, an inverter 59 including a moving member 58 located between the pivot shaft 53 and the cam follower 22, the converter 57 including the driving lever 54, and the like.

[0086] The pivot shaft 53 is pivotally supported by a housing 47 in a state in which the pivot shaft 53 extends in a direction (the vertical direction in FIG. 5) perpendicular or substantially perpendicular to both the axial direction (a direction perpendicular to the sheet surface in FIG. 5) of the camshaft 14 and the moving direction (the horizontal direction in FIG. 5) of the cam follower 22. The moving direction of the cam follower 22 will simply be referred to as a first direction, and the axial direction of the camshaft 14 will simply be referred to as a second direction hereinafter. The pivot shaft 53 is located at a position where it faces the cam surface of the synchronization cam 13. A concave member 61 of the positioner 24 to be described below is provided at the other end (the upper end in FIG. 5) of the pivot shaft 53.

[0087] As shown in FIG. 8, a first projection 62 and a second projection 63 are provided at the intermediate portion of the pivot shaft 53 in the axial direction. The first projection 62 projects from the pivot shaft 53 to one side perpendicular or substantially perpendicular to the axial direction. The second projection 63 projects from the pivot shaft 53 in a direction opposite to the first projection 62.

[0088] The pivot shaft 53 is attached to the housing 47 in a state in which the first projection 62 and the second projection 63 extend in the axial direction of the camshaft 14. The first projection 62 and the second projection 63 are housed in a space S in the housing 47. A side surface of each of the first projection 62 and the second projection 63, which faces the camshaft 14, defines a cam surface 65 that comes into contact with a slide pin 64 to be described below. As shown in FIG. 10, the cam surface 65 includes a steep slope portion 65a and a gentle slope portion 65b. The steep slope portion 65a is located on the proximal end side of each of the first and second projections 62 and 63. The gentle slope portion 65b is located on the projecting end side of each of the first and second projections 62 and 63.

[0089] As shown in FIG. 11, the steep slope portion 65a of the first projection 62 and the steep slope portion 65a of the second projection 63 define the inner wall of a concave portion 66 that houses the slide pin 64 to be described below. The concave portion 66 includes the two steep slope portions 65a and a portion of the pivot shaft 53. Referring to FIG. 11, an axis C1 of the pivot shaft 53 and an axis C2 of the slide pin 64 are located on a single plane P. In the state shown in FIG. 11, the first projection 62 and the second projection 63 are located at positions almost symmetric with respect to the plane P. Additionally, in FIGS. 10 and 11, the cam follower 22 is illustrated by a solid line and an alternate long and two short dashed line. The solid line indicates the cam follower 22 that is pressed by the synchronization cam 13 and stops at a pressing end position. The alternate long and two short dashed line indicates the cam follower 22 that stops at a pressing start position before it is pressed by the synchronization cam 13.

[0090] As shown in FIG. 8, the cam follower 22, the moving member 58, and the slide pin 64 are provided between the first projection 62 and the second projection 63 and the synchronization cam 13.

[0091] The cam follower 22 has a columnar shape and is supported by the housing 47 to be movable in the first direction to move closer to or away from the axis of the camshaft 14.

[0092] The cam follower 22 reciprocally moves between the pressing start position (see FIGS. 13 and 17) where one end surface (an end surface facing the synchronization cam 13) is pressed by the nose portion 13b of the synchronization cam 13 and the pressing end position (see FIGS. 8 and 15) where the pressing by the synchronization cam 13 ends. The time when the nose portion 13b of the synchronization cam 13 presses the cam follower 22 is the time when the roller 26 of the first rocker arm 27 contacts the base circle portion 12a of the valve driving cam 12 (the time when the intake valves 4 or the exhaust valves 5 are closed). In other words, this is the time when the driving force to drive the intake valves 4 or the exhaust valves 5 is not transmitted to the first to third switching pins 31 to 33 of the switch assembly 3.

[0093] As shown FIG. 8, the moving member 58 located between the cam follower 22 and the first projection 62 and the second projection 63 has a columnar shape extending along the above-described second direction (the horizontal direction in FIG. 8), and supported by the housing 47 to be movable in the second direction. The above-described pivot shaft 53 is located at a position facing the cam follower 22 across the moving member 58 and supported by the housing 47 to be pivotal about an axis extending in a direction perpendicular or substantially perpendicular to the first direction and the second direction.

[0094] A cylinder hole 67 that is a non-through hole extending in the second direction from one side portion of the housing 47 is provided in the housing 47. The opening of the cylinder hole 67 is closed by a plug 68. The moving member 58 is slidably fitted in the cylinder hole 67. One end of the cam follower 22 faces the central portion of the cylinder hole 67 in the axial direction. In addition, the cylinder hole 67 communicates with the space S in which the first projection 62 and the second projection 63 are housed.

[0095] A first oil passage 71 is connected to a bottom portion 67a located at the deepest position in the cylinder hole 67. In addition, a second oil passage 72 is connected to the vicinity of the plug member 68 in the cylinder hole 67. The first and second oil passages 71 and 72 define a portion of an actuator 73 that drives the moving member 58.

[0096] The actuator 73 includes the inverter 59 together with the above-described moving member 58 and the slide pin 64.

[0097] The actuator 73 drives the moving member 58 by an oil pressure to one side or to the other side in the second direction. The actuator 73 according to this preferred embodiment includes first and second pistons 74 and 75 in the moving member 58, a switching valve 76 connected to the first and second oil passages 71 and 72, a hydraulic pump 77 that supplies an oil pressure to the switching valve 76, and the like. The first piston 74 is provided at one end of the moving member 58. The second piston 75 is provided at the other end of the moving member 58. The switching valve 76 is connected to the cylinder hole 67 via the first and second oil passages 71 and 72. The switching valve 76 is automatically or manually operated and switches between a state in which the oil pressure is supplied to the first piston 74 and a state in which the oil pressure is supplied to the second piston 75.

[0098] The hydraulic pump 77 is driven by the engine 2 or an electric motor (not shown) and discharges hydraulic oil.

[0099] When the oil pressure is applied to the first piston 74, the moving member 58 moves to the side of the plug 68, as shown in FIG. 13. In addition, when the oil pressure is applied to the second piston 75, the moving member 58 moves to the side of the bottom portion 67a of the cylinder hole 67, as shown in FIG. 17. The time when the moving member 58 moves in the second direction in this manner is the time when the cam follower 22 faces the base circle portion 13a of the synchronization cam 13.

[0100] A compression coil spring 78 that biases the moving member 58 to one side of the second direction is provided between the second piston 75 and the plug member 68. The compression coil spring 78 is provided to avoid an uncontrollable state caused by shutoff of the oil pressure supply.

[0101] Two concave grooves 58a are provided at the central portion of the moving member 58 in the longitudinal direction, along with the slide pin 64 to be pressed by the cam follower 22. The concave grooves 58a extend by a predetermined length in the second direction in the outer peripheral portion of the moving member 58. The predetermined length is a length that allows the cam follower 22 to enter the concave groove 58a even if the moving member 58 is located at either of the terminating positions on the side of the bottom portion 67a and on the side of the plug member 68, as shown in FIGS. 8 and 13. The concave grooves 58a are located on one side and the other side in the radial direction of the moving member 58. The bottom surface of each concave groove 58a is preferably flat.

[0102] The slide pin 64 has a columnar shape that is thinner than the cam follower 22 and is supported by the moving member 58 to be movable in the first direction in a state in which the slide pin 64 extends through the central portion of the moving member 58 in the first direction. One end surface of the slide pin 64 always contacts the other end surface of the cam follower 22 when the moving member 58 moves from one end to the other end in the cylinder hole 67.

[0103] The moving member 58 moves to one side (to the side of the bottom portion 67a of the cylinder hole 67) of the second direction, such that the slide pin 64 is disposed between the cam follower 22 and the first projection 62. Additionally, the moving member 58 moves to the other side (to the side of the plug 68) of the second direction, as shown in FIG. 13, such that the slide pin 64 is disposed between the cam follower 22 and the second projection 63. When the cam follower 22 presses the slide pin 64 in a state in which the other end surface of the slide pin 64 faces the first projection 62 or the second projection 63, the first projection 62 or the second projection 63 is pressed by the slide pin 64. The length of the slide pin 64 is a length that makes the slide pin 64 press the first projection 62 or the second projection 63 in a direction to separate from the cam follower 22 when the cam follower 22 is pressed by the synchronization cam 13 and moves to the pressing end position.

[0104] For this reason, of the first projection 62 and the second projection 63, one projection (the first projection 62 indicated by a solid line in FIG. 8) that interposes the slide pin 64 between the one projection and the cam follower 22 receives a pressing force, via the slide pin 64, from the cam follower 22 pressed by the synchronization cam 13. The one projection that receives the pressing force rotates the pivot shaft 53 in the direction in which the one projection is pressed (clockwise in FIG. 8). For this reason, the pivot shaft 53 rotates when the pressing force is transmitted from the cam follower 22.

[0105] The first projection 62 and the second projection 63 swing like a seesaw about the pivot shaft 53. For this reason, one projection (the first projection 62 in FIG. 8) pressed by the slide pin 64 tilts in a direction in which its distal end separates from the cam follower 22. At this time, the other projection (the second projection 63 in FIG. 8) tilts in a direction in which its distal end approaches the cam follower 22.

[0106] That is, the other projection tilts so as to gradually approach the cam follower 22 from the pivot shaft 53 to the distal end. The other projection that tilts in this manner functions as a cam follower return cam 79 when the slide pin 64 that presses the one projection moves together with the moving member 58 in a direction (the direction in which the plug 68 is located in FIG. 8) to move toward the other projection. The cam follower return cam 79 presses the slide pin 64 toward the camshaft 14 together with the cam follower 22, thus returning the cam follower 22. When the other projection functions as the return cam 79, the slide pin 64 comes into contact with the above-described cam surface 65, and the moving direction of the slide pin 64 is changed. This means that the cam surface 65 substantially functions as the cam follower return cam 79.

[0107] When the moving member 58 moves, and the slide pin 64 is pressed by the above-described return cam 79, the slide pin 64 presses the cam follower 22 upward and returns it from the pressing end position to the pressing start position (see FIG. 13).

[0108] The time when the moving member 58 moves is the time when the slide pin 64 is not pressed by the cam follower 22. This is because when the slide pin 64 is pressed by the cam follower 22, the slide pin 64 cannot move to the side of the cam follower 22 along the above-described cam follower return cam 79. For this reason, the moving member 58 waits without moving until two conditions to be described below are satisfied, and moves after the two conditions are satisfied. As the first condition of the two conditions, the oil pressure is applied. As the second condition, the cam follower 22 faces the base circle portion 13a of the synchronization cam 13.

[0109] When the slide pin 64 presses the first projection 62 in a state in which the moving member 58 moves to one side (the side of the bottom portion 67a of the cylinder hole 67) of the second direction, the pivot shaft 53 rotates clockwise in FIG. 8. On the other hand, when the slide pin 64 presses the second projection 63 in a state in which the moving member 58 moves to the other side (the side of the plug member 68) of the second direction, the pivot shaft 53 rotates counterclockwise in FIG. 8. Hence, the inverter 59 alternately switches the rotation direction of the pivot shaft 53 to the one side and the other side.

[0110] When the pivot shaft 53 rotates, the rotation is converted into a reciprocal motion by the above-described converter 57 and transmitted to the third switching pin 33. In other words, the motion of the cam follower 22 is transmitted to the third switching pin 33 via the transmission 25 including the slide pin 64, the pivot shaft 53, the driving lever 54, the connecting lever 51, the pressing member 44, and the like, and the third switching pin 33 is driven in the direction to switch the driving state of the intake valves 4 or the exhaust valves 5.

[0111] The transmission 25 is located at a predetermined position by the positioner 24 to be described below. Here, the predetermined position includes a position (when in the first driving state) where the first rocker arm 27 and the second rocker arm 28 are in the connected state and a position (when in the second driving state) where the first rocker arm 27 and the second rocker arm 28 are in the non-connected state.

[0112] As shown in FIGS. 4 and 5, the positioner 24 includes a concave portion 81 in the concave member 61 of the pivot shaft 53, a presser 82 that engages with the concave portion 81, and a spring 83 that presses the presser 82 against the concave portion 81. The concave member 61 is fixed to the shaft end of the pivot shaft 53 in a state in which the concave member 61 pivots integrally with the pivot shaft 53, and substantially becomes a portion of the pivot shaft 53. For this reason, the concave portion 81 is provided in the pivot shaft 53 (transmission 25). As shown in FIGS. 9A to 9D, the presser 82 and the spring 83 are inserted and held in a non-through hole 84 of the housing 47. The presser 82 according to this preferred embodiment includes a ball. Additionally, the spring 83 according to this preferred embodiment includes a compression coil spring.

[0113] As shown in FIGS. 9A to 9D, the concave portion 81 includes a first concave portion 81a and a second concave portion 81b which are spaced apart by a predetermined angle in the rotation direction of the pivot shaft 53. The presser 82 engages with the first concave portion 81a in a state (a state in which the pivot shaft 53 rotates) in which the transmission 25 moves to the position where the first rocker arm 27 and the second rocker arm 28 are in the connected state. The presser 82 engages with the second concave portion 81b in a state (a state in which the pivot shaft 53 rotates) in which the transmission 25 moves to the position where the first rocker arm 27 and the second rocker arm 28 are in the non-connected state. For this reason, the positioner 24 positions the transmission 25 to the predetermined position defined by the first concave portion 81a or the second concave portion 81b.

[0114] A positioning interval A (see FIG. 9A) between the first concave portion 81a and the second concave portion 81b is larger than the moving amount (the rotation angle of the pivot shaft 53) of the transmission 25 when it is driven and moved by the synchronization cam 13. When the moving amount is represented by, for example, an angle B (an angle made by bisectors shown in FIG. 8) of the pivot shaft 53 driven and rotated by the synchronization cam 13, the positioning interval A=angle B+additional angle .

[0115] Each of the first concave portion 81a and the second concave portion 81b have a slope 85 such that an opening width becomes gradually narrower from the opening edge to the bottom. The pivot shaft 53 is driven by the synchronization cam 13 and rotates until the presser 82 abuts against the slope 85. For this reason, the position to which the pivot shaft 53 (transmission 25) is driven and moved by the synchronization cam 13 is a position where the presser 82 abuts against the slope 85 of the first concave portion 81a or the second concave portion 81b (see FIG. 9C). When the presser 82 presses the slope 85 in this manner, a thrust F acts in a direction (counterclockwise in FIG. 9C) in which the first and second concave portions 81a and 81b further move. Hence, the pivot shaft 53 is further rotated by the thrust F and reaches the predetermined position (see FIG. 9D) defined by the first concave portion 81a or the second concave portion 81b.

[0116] The spring force of the spring 83 that biases the presser 82 is set to a magnitude that allows the transmission 25 to be moved by the above-described thrust F to the predetermined position within the time when the intake valves 4 or the exhaust valves 5 are closed. In addition, the spring force is set to a magnitude that generates a position holding force in a state in which the presser 82 engages with the first concave portion 81a or the second concave portion 81b. The position holding force is a force that holds the pivot shaft 53 (transmission 25) at the predetermined position defined by the concave portion 81. In addition, the position holding force is set to a magnitude that prevents the pivot shaft 53 from being rotated by another force different from an actuating force generated when the synchronization cam 13 presses the cam follower 22. Here, another force can be, for example, the force of the slide pin 64 pressing the first projection 62 or the second projection 63 when the first projection 62 or the second projection 63 functions as the cam follower return cam 79. In addition, a magnitude that prevents the pivot shaft 53 from being rotated is a magnitude that prevents switching between the first driving state and the second driving state. The first driving state is the full cylinder operation state in which the first rocker arm 27 and the second rocker arm 28 are in the connected state. The second driving state is the partial cylinder operation state in which the first rocker arm 27 and the second rocker arm 28 are in the non-connected state.

[0117] The operation of the valve mechanism 1 for the engine 2 will be described next with reference to FIGS. 8, 9A to 9D, and 13 to 18. First, an operation performed when the operation state of the engine 2 is switched from the full cylinder operation state to the partial cylinder operation state by the switch assembly 3 will be described. When the full cylinder operation state is used, the driver 23 of the switch assembly 3 is set in the state shown in FIG. 8. That is, the moving member 58 of the driver 23 is moved to one end side (the side of the bottom portion 67a of the cylinder hole 67) by the oil pressure in the second oil passage 72. In addition, the driving lever 54 and the pivot shaft 53 are rotated clockwise in FIGS. 9A and 14. When the driving lever 54 is thus rotated, the pressing member 44 is located at the retreat position, and the first to third switching pins 31 to 33 are located at the connecting position. In this case, the first rocker arm 27 and the second rocker arm 28 are connected to each other and integrally swing.

[0118] The valve mechanism 1 of the engine 2 starts operating when the rotation of a crankshaft (not shown) is transmitted to the camshaft 14. When the rotation of the crankshaft is transmitted to the camshaft 14, the valve driving cam 12 and the synchronization cam 13 rotate. In the full cylinder operation state, the rotation of the valve driving cam 12 is transmitted from the first rocker arm 27 to the second rocker arm 28 via the first switching pin 31 and the second switching pin 32, and the intake valves 4 or the exhaust valves 5 are driven. At this time, since the cam follower 22 is located at the pressing end position, the synchronization cam 13 slips without pressing the cam follower 22.

[0119] To switch from the full cylinder operation state to the partial cylinder operation state, first, the oil pressure is supplied to the first piston 74 by the actuator 73 manually or automatically at an arbitrary time (see FIG. 13). At this time, the moving member 58 is biased by the oil pressure to the other end side (the left side or the side of the plug 68 in FIG. 13) on the opposite side of the current position in FIG. 13. When the oil pressure thus acts on the moving member 58, the moving member 58 moves to the side of the plug 68 against the spring force of the spring 78, and the slide pin 64 hits the cam surface 65 of the second projection 63 due to this movement. To further move the moving member 58 by the oil pressure from the state in which the slide pin 64 hits the second projection 63, the slide pin 64 needs to rise along the steep slope portion 65a of the cam surface 65 and move in a direction to press the cam follower 22.

[0120] In a case in which the nose portion 13b of the synchronization cam 13 faces the cam follower 22, the movement of the cam follower 22 in the direction to return to the pressing start position is regulated by the synchronization cam 13. For this reason, during the time in which the movement of the cam follower 22 is regulated, even if the oil pressure is applied to the moving member 58, the slide pin 64 never further moves to the side of the plug 68 from the state in which the slide pin 64 hits the second projection 63.

[0121] In a case in which the base circle portion 13a of the synchronization cam 13 faces the cam follower 22 when the synchronization cam 13 rotates from the above state while maintaining the supply of the oil pressure, or in a case in which the base circle portion 13a of the synchronization cam 13 faces the cam follower 22 when the oil pressure is applied to the moving member 58, the cam follower 22 is able to move in the direction to return to the pressing start position. For this reason, in either case, the oil pressure is applied to the moving member 58, and the moving member 58 thus moves in the cylinder hole 67 to the side of the plug 68 against the spring force of the spring 78. In addition, the slide pin 64 is pressed against the steep slope portion 65a and slides, and moves in a direction to approach the synchronization cam 13, as indicated by an alternate long and two short dashed line A in FIG. 10. At this time, the second projection 63 is pressed by the slide pin 64 but never tilts. This is because the presser 82 engages with the first concave portion 81a, as shown in FIG. 9A, and the pivotal movement of the pivot shaft 53 is regulated. Hence, the pressing member 44 is held at the retreat position, and the first to third switching pins 31 to 33 are held at the connecting position.

[0122] When the moving member 58 is further moved by the oil pressure, the slide pin 64 moves to a position indicated by an alternate long and two short dashed line C via a position indicated by an alternate long and two short dashed line B in FIG. 10. Here, the position indicated by the alternate long and two short dashed line B is a position where the slide pin 64 contacts the gentle slope portion 65b, that is, a position where the axis C1 of the pivot shaft 53 and the axis C2 of the slide pin 64 are located on the single plane P. The position indicated by the alternate long and two short dashed line C is a position where the cam follower 22 returns to the pressing start position. For this reason, when the moving member 58 moves in a state in which the cam follower 22 faces the base circle portion 13a of the synchronization cam 13, the cam follower 22 is pressed by the slide pin 64 and returns to the pressing start position, and a state shown in FIG. 13 is obtained.

[0123] Even when the moving member 58 and the slide pin 64 are moving as described above, the camshaft 14 is rotating. Hence, the nose portion 13b of the synchronization cam 13 may press the cam follower 22 in a state in which the slide pin 64 is in contact with the steep slope portion 65a, as indicated by the alternate long and two short dashed line A in FIG. 10. In this case, the slide pin 64 is pressed by the cam follower 22 and slides down on the steep slope portion 65a, and the moving member 58 retreats against the oil pressure.

[0124] Additionally, when the nose portion 13b of the synchronization cam 13 presses the cam follower 22 in a state in which the slide pin 64 moves to the position indicated by the alternate long and two short dashed line B in FIG. 10, the second projection 63 is pressed by the slide pin 64, as shown in FIG. 11, and the pivot shaft 53 rotates counterclockwise in FIG. 11. Then, the distal end of the slide pin 64 retracts into the concave portion 66. At this time, a small gap d1 is formed in the vertical direction of the slide pin 64, and the slide pin 64 never presses the pivot shaft 53. When the base circle portion 13a of the synchronization cam 13 faces the cam follower 22 in this state, the moving member 58 is pressed by the oil pressure and further moves, and the slide pin 64 moves to a position overlapping the gentle slope portion 65b of the second projection 63, as indicated by an alternate long and two short dashed line D in FIG. 11, and presses the cam follower 22 toward the pressing start position.

[0125] The cam follower 22 is returned from the pressing end position to the pressing start position side (FIG. 13) and then pressed again by the nose portion 13b of the synchronization cam 13 that is continuously rotating. The time when the cam follower 22 is pressed by the nose portion 13b of the synchronization cam 13 is the time when the intake valves 4 or the exhaust valves 5 are closed and the time when the first to third switching pins 31 to 33 of the switch assembly 3 are able to move. The cam follower 22 is pressed by the nose portion 13b of the synchronization cam 13 and thus moves to the pressing end position, as shown in FIG. 15.

[0126] When the cam follower 22 moves in this manner, the slide pin 64 presses the second projection 63 to the final position, and the pivot shaft 53 rotates in a direction (counterclockwise in FIG. 15) reverse to that in pressing the first projection 62. When the second projection 63 is pressed by the slide pin 64, and the pivot shaft 53 rotates, the first concave portion 81a and the second concave portion 81b of the positioner 24 move toward the presser 82 along with the rotation of the pivot shaft 53, as shown in FIGS. 9A to 9D. That is, when the pivot shaft 53 in the state shown in FIG. 9A starts rotating, first, as shown in FIG. 9B, the slope 85 of the first concave portion 81a presses the presser 82, and the presser 82 moves across the boundary portion between the first concave portion 81a and the second concave portion 81b. Then, when the pivot shaft 53 further rotates, the presser 82 enters the second concave portion 81b.

[0127] The operation of the synchronization cam 13 to press the cam follower 22 in this case ends before the presser 82 completely engages with the second concave portion 81b, that is, halfway through the engagement. For this reason, as shown in FIG. 9C, the synchronization cam 13 stops pressing the cam follower 22 halfway through the time when the presser 82 is pressing the slope 85 that defines a portion on the side of the opening edge of the second concave portion 81b by the spring force of the spring 83. When the presser 82 thus presses the portion on the side of the opening edge of the second concave portion 81b, the thrust F that further presses the pivot shaft 53 ahead in the rotation direction acts on the pivot shaft 53. As a result, after the operation of the synchronization cam 13 to press the cam follower 22 ends, the pivot shaft 53 is pressed by the above-described thrust F and further advances.

[0128] As shown in FIG. 9D, when the presser 82 completely engages with the second concave portion 81b, the pivot shaft 53 is located at the position defined by the second concave portion 81b. When the pivot shaft 53 is positioned in this manner, the driving lever 54 swings in the same direction, the pressing member 44 moves to the advance position, and simultaneously, the first to third switching pins 31 to 33 move to the non-connecting position, as shown in FIG. 16. At this time, since the first to third switching pins 31 to 33 are in a movable state, they are pressed by the pressing member 44 and smoothly move. As a result, the connected state between the first rocker arm 27 and the second rocker arm 28 is canceled. In this case, only the first rocker arm 27 swings along with the rotation of the valve driving cam 12, and the second rocker arm 28 stops. When the second rocker arm 28 stops, the intake valves 4 or the exhaust valves 5 are held in a closed and stopped state (deactivation state). For this reason, the operation state of the engine 2 is switched by the switch assembly 3 from the full cylinder operation state to the partial cylinder operation state.

[0129] To switch the operation state of the engine 2 from the partial cylinder operation state in which the intake valves 4 or the exhaust valves 5 are deactivated to the full cylinder operation state, the oil pressure is applied to the second oil passage 72 by the actuator 73, as shown in FIG. 17. When the supply of the oil pressure is switched in this manner, the moving member 58 is moved by the oil pressure to the side of the bottom portion 67a of the cylinder hole 67 when the base circle portion 13a of the synchronization cam 13 faces the cam follower 22.

[0130] Along with the movement of the moving member 58, the slide pin 64 slides while being pressed against the tilting first projection 62 and moves in a direction to approach the synchronization cam 13. When the slide pin 64 thus moves, the cam follower 22 is returned from the pressing end position to the pressing start position.

[0131] At this time, since the pivot shaft 53 does not rotate due to the action of the positioner 24, the pressing member 44 is held at the advance position, and the first to third switching pins 31 to 33 are held at the non-connecting position, as shown in FIG. 18.

[0132] When the synchronization cam 13 rotates in a state in which the cam follower 22 is located at the pressing start position (see FIG. 17), the nose portion 13b of the synchronization cam 13 comes into contact with the cam follower 22, and the cam follower 22 is pressed in a direction to the pressing end position. Then, the cam follower 22 moves to the pressing end position shown in FIG. 8. The time when the nose portion 13b of the synchronization cam 13 presses the cam follower 22 is the time when the base circle portion 12a of the valve driving cam 12 is in contact with the roller 26.

[0133] Then, along with the movement of the cam follower 22, the slide pin 64 moves to the same direction as the cam follower 22 and is pressed against the first projection 62. When the first projection 62 shown in FIG. 17 is pressed by the slide pin 64, the pivot shaft 53 rotates clockwise in FIG. 17 from the position shown in FIG. 17 to the position shown in FIG. 8. At this time, the presser 82 exits from the second concave portion 81b and enters the first concave portion 81a. After driving by the synchronization cam 13 ends, the pivot shaft 53 is further rotated by the thrust F that acts when the presser 82 presses the slope 85 of the first concave portion 81a. As a result, the pivot shaft 53 is located at the predetermined position defined by the first concave portion 81a.

[0134] When the pivot shaft 53 thus rotates, the driving lever 54 swings clockwise in FIG. 18 from the position shown in FIG. 18 to the position shown in FIG. 14. The time when the driving lever 54 swings in this manner is the time when the intake valves 4 or the exhaust valves 5 are closed, and the driving force is not transmitted to the first arm main body 28a and the second arm main body 28b (when the movement of the first to third switching pins 31 to 33 is not regulated).

[0135] When the driving lever 54 thus swings, the pressing member 44 moves to the retreat position shown in FIG. 14, and the first to third switching pins 31 to 33 are moved to the connecting position by the spring force of the spring 43.

[0136] When the first to third switching pins 31 to 33 move to the connecting position in this manner, the first rocker arm 27 and the second rocker arm 28 are connected. As a result, the intake valves 4 or the exhaust valves 5 are driven by the valve driving cam 12, and the operation state of the engine 2 shifts to the full cylinder operation state.

[0137] For this reason, according to this preferred embodiment, it is possible to provide the valve mechanism in which a flip phenomenon does not occur since the transmission 25 that changes the driving state reliably operates only in a predetermined operation amount at an appropriate time. Since the flip phenomenon does not occur, the intake valves 4 or the exhaust valves 5 never abruptly close and break, and the first to third switching pins 31 to 33 never break due to an excessive load.

[0138] In the valve mechanism 1 shown in this preferred embodiment, if a manufacturing error of the transmission 25 from the cam follower 22 to the pivot shaft 53 is large, the operation amount generated when the first projection 62 or the second projection 63 is pressed by the slide pin 64 and the pivot shaft 53 rotates may vary. However, in the valve mechanism 1 according to this preferred embodiment, since the positioning interval A between the first concave portion 81a and the second concave portion 81b is larger than the moving amount B of the transmission 25 when it is driven and moved by the synchronization cam 13, the influence of the manufacturing error is small, and the operation amount of the pivot shaft 53 is almost constant. In addition, since the operation amount of the pivot shaft 53 is larger than the operation amount generated when the first projection 62 or the second projection 63 is pressed by the slide pin 64, and the pivot shaft 53 rotates, the height of the nose portion 13b of the synchronization cam 13 is small, and the driver 23 is made compact.

[0139] Each of the first and second concave portions 81a and 81b have the slope 85 such that the opening width becomes gradually narrower from the opening edge to the bottom. The position to which the pivot shaft 53 (transmission 25) is driven and moved by the synchronization cam 13 is the position where the presser 82 abuts against the slope 85 of the first concave portion 81a or the second concave portion 81b. The transmission 25 further moves due to the thrust F that acts when the presser 82 presses the slope 85, and reaches the predetermined position defined by the first concave portion 81a or the second concave portion 81b.

[0140] For this reason, in this preferred embodiment, since the thrust F acts on the transmission 25 when the presser 82 slides while pressing the slope 85 of the concave portion 81, the movement of the transmission 25 is smooth, and switching of the driving state of the intake valves 4 or the exhaust valves 5 is quickly performed. Hence, according to this preferred embodiment, it is possible to provide the valve mechanism with stable responsiveness when switching the driving state.

[0141] The spring force of the spring 83 that biases the presser 82 according to this preferred embodiment is set to a magnitude that allows the transmission 25 to be moved by the thrust F to the predetermined position within the time when the intake valves 4 or the exhaust valves 5 are closed.

[0142] For this reason, according to this preferred embodiment, since the switching operation of the driving state is completed within the time when the intake valves 4 or the exhaust valves 5 are closed, it is possible to provide the valve mechanism which has a high reliability in the switching operation.

[0143] The spring force of the spring 83 that biases the presser 82 according to this preferred embodiment is set to a magnitude that generates a position holding force that holds the transmission 25 at the predetermined position defined by the concave portion 81 in a state in which the presser 82 engages with the first concave portion 81a or the second concave portion 81b. The position holding force is set to a magnitude that prevents the first driving state and the second driving state from being switched by another force other than the actuating force generated when the synchronization cam 13 presses the cam follower 22.

[0144] For this reason, since the position of the transmission 25 is fixed in a state in which the synchronization cam 13 does not press the cam follower 22, an unintended operation of the switch assembly 3 or damage or a fault in the engine 2 caused by the operation of the switch assembly 3 is prevented.

[0145] The driver 23 according to this preferred embodiment includes the pivot shaft 53, the converter 57, and the inverter 59. The pivot shaft 53 rotates when the pressing force is transmitted from the cam follower 22. The inverter 59 alternately switches the direction of rotation of the pivot shaft 53 to one side and the other side. The converter 57 converts the pivotal motion of the pivot shaft 53 into a reciprocal motion and transmits it to one (third switching pin 33) of the elements in the valve mechanism system.

[0146] According to this preferred embodiment, the elements that transmit the pressing force from the synchronization cam 13 to the pivot shaft 53 and the elements of the inverter 59 and the elements in the converter 57 are arranged in the axial direction of the pivot shaft 53. It is therefore possible to provide the valve mechanism in which the driver 23 is compact.

[0147] Of the first projection 62 and the second projection 63 according to this preferred embodiment, one projection that interposes the slide pin 64 between the one projection and the cam follower 22 receives the pressing force, via the slide pin 64, from the cam follower 22 pressed by the synchronization cam 13, and causes the pivot shaft 53 to rotate in the direction in which the one projection is pressed. The other projection functions as the cam follower return cam 79 that presses the slide pin 64 toward the camshaft together with the cam follower 22 and returns the cam follower 22 when the slide pin 64 that presses the one projection moves in a direction to the other projection together with the moving member 58.

[0148] According to this preferred embodiment, the cam follower 22 is returned to the pressing start position using the first and second projections 62 and 63 that convert the reciprocal motion of the cam follower 22 into a pivotal motion. For this reason, since a mechanism exclusively used to return the cam follower 22 to the pressing start position is unnecessary, it is possible to decrease the number of elements and make the driver 23 compact.

Second Preferred Embodiment

[0149] A valve mechanism for an engine according to a preferred embodiment of the present invention is as shown in FIGS. 19 and 20. Elements that are the same as or similar to those described with reference to FIGS. 1 to 18 are denoted by the same reference numerals in FIGS. 19 and 20, and a detailed description thereof will appropriately be omitted. The valve mechanism for an engine according to this preferred embodiment is different from the valve mechanism shown in the first preferred embodiment in the structure of a camshaft 14 and a switch unit 21 of a switch assembly 3, but the rest of the structure is preferably the same as in the first preferred embodiment.

[0150] A valve mechanism 101 shown in FIG. 19 includes a first cam 102 and a second cam 103 having different valve lift amounts for an intake valve 4 or an exhaust valve 5 to switch between two types of driving states. The first cam 102 and the second cam 103 are arranged in the axial direction of the camshaft 14. The second cam 103 is arranged only on one side of the first cam 102 and is in contact with the first cam 102. The first cam 102 and the second cam 103 include base circle portions 102a and 103a, and nose portions 102b and 103b.

[0151] The outer diameter of the base circle portion 102a of the first cam 102 equals the outer diameter of the base circle portion 103a of the second cam 103. The nose portion 102b of the first cam 102 has a shape that generates a larger valve lift amount of the intake valve 4 or the exhaust valve 5 as compared to the nose portion 103b of the second cam 103.

[0152] A rocker arm 9 in the valve mechanism 101 is supported by a rocker shaft 34 to be movable in the axial direction and swingably supported by the rocker shaft 34. A pressing portion 40 that presses the intake valve 4 or the exhaust valve 5 is provided at the swing end of the rocker arm 9. The pressing portion 40 has a predetermined length in the axial direction of the rocker shaft 34. The length of the pressing portion 40 is equal to or longer than the interval (formation pitch) between the first cam 102 and the second cam 103.

[0153] The rocker arm 9 includes a roller 26 that contacts the first cam 102 or the second cam 103 and rotates, and a connecting portion 104 projecting in the axial direction of the rocker shaft 34. The connecting portion 104 is connected to a connecting member 105 of a driver 23. The connecting member 105 is pivotally connected to a driving lever 54 of the driver 23 and movably supported by a housing 47 so as to advance/retreat with respect to the rocker arm 9. A first concave portion 81a and a second concave portion 81b each of which engages with a presser 82 of a positioner 24 are provided in the connecting member 105. The first concave portion 81a and the second concave portion 81b according to this preferred embodiment are provided on one side of the connecting member 105 that translates while being arranged in the moving direction of the connecting member 105. A positioning interval A between the first concave portion 81a and the second concave portion 81b is larger than a moving amount B of a transmission 25 that is driven and moved by a synchronization cam 13.

[0154] As shown in FIG. 19, when a pivot shaft 53 of the driver 23 rotates in one direction, and the connecting member 105 moves to the retreat position shown in FIG. 19, the rocker arm 9 moves to a position corresponding to one cam (the second cam 103 in FIG. 19) of the first cam 102 and the second cam 103. In addition, as shown in FIG. 20, when the pivot shaft 53 rotates in the other direction, and the connecting member 105 moves to the advance position, the rocker arm 9 moves to a position corresponding to the other cam (the first cam 102 in FIG. 20) of the first cam 102 and the second cam 103.

[0155] When the camshaft 14 rotates in a state in which the roller 26 of the rocker arm 9 is in contact with the second cam 103 (see FIG. 19), the rocker arm 9 is pressed by the second cam 103 and swings. On the other hand, when the camshaft 14 rotates in a state in which the roller 26 of the rocker arm 9 is in contact with the first cam 102 (see FIG. 20), the rocker arm 9 is pressed by the first cam 102 and swings. For this reason, when the rocker arm 9 moves from the position where it is pressed by the second cam 103 to the position where it is pressed by the first cam 102, the valve lift amount of the intake valve 4 or the exhaust valve 5 becomes relatively large.

[0156] In this preferred embodiment, a switch 21A that is one element of the valve mechanism system from the valve driving cam to the rocker arm includes the rocker arm 9.

[0157] According to this preferred embodiment, it is possible to provide the valve mechanism for an engine, which correctly switches between a first driving state in which the valve lift amount of the intake valve 4 or the exhaust valve 5 becomes relatively large and a second driving state in which the valve lift amount of the intake valve 4 or the exhaust valve 5 becomes relatively small.

Third Preferred Embodiment

[0158] A valve mechanism for an engine according to a third preferred embodiment of the present invention is shown in FIGS. 21 and 22. Elements that are the same as or similar to those described with reference to FIGS. 1 to 20 are denoted by the same reference numerals in FIGS. 21 and 22, and a detailed description thereof will appropriately be omitted.

[0159] The valve mechanism for an engine shown in this preferred embodiment is different from the valve mechanism shown in the second preferred embodiment in the structure of a camshaft 14 and a switch unit 21 of a switch assembly 3, but the rest of the structure is preferably the same as in the second preferred embodiment.

[0160] A valve mechanism 111 shown in FIG. 21 includes a first cam 102 and a second cam 103 having different valve lift amounts for an intake valve 4 or an exhaust valve 5 to switch between two types of driving states. The first cam 102 and the second cam 103 are arranged in the axial direction of a camshaft main body 11. A nose portion 102b of the first cam 102 has a shape that generates a larger valve lift amount of the intake valve 4 or the exhaust valve 5 as compared to a nose portion 103b of the second cam 103.

[0161] The first cam 102 and the second cam 103 according to this preferred embodiment are attached to the camshaft main body 11 via a tubular slider 112. The slider 112 is fitted on the outer peripheral portion of the camshaft main body 11 by, for example, a spline (not shown) in a state in which the camshaft main body 11 is inserted into the hollow portion. In other words, the slider 112 is supported by the camshaft main body 11 to be movable in the axial direction in a state in which the relative movement in the rotation direction is regulated. The first cam 102 and the second cam 103 are fixed to the slider 112 in a state in which the slider 112 extends through their axes.

[0162] An annular plate-shaped flange 113 is provided at one end of the slider 112 in the axial direction. The flange 113 is located on the same axis as the slider 112. The flange 113 is connected to a connecting member 114 of a driver 23. The connecting member 114 is pivotally connected to a driving lever 54 of the driver 23 and movably supported by a housing 47 so as to advance/retreat with respect to the first cam 102 and the second cam 103.

[0163] A connecting portion 115 is provided at the distal end of the connecting member 114. The connecting portion 115 includes a groove 116 in which the above-described flange 113 is slidably fitted. In addition, a first concave portion 81a and a second concave portion 81b of a positioner 24 are provided in the connecting member 114. The first concave portion 81a and the second concave portion 81b are provided on one side portion of the connecting member that translates while being arranged in the moving direction of the connecting member. A positioning interval A between the first concave portion 81a and the second concave portion 81b is larger than a moving amount B of a transmission 25 that is driven and moved by a synchronization cam 13.

[0164] According to this preferred embodiment, when a pivot shaft 53 of the driver 23 rotates, and the driving lever 54 swings in one direction, the connecting member 114 moves to the retreat position, and the slider 112 and the first cam 102 and the second cam 103 move to one side (the right side in FIG. 21) of the axial direction with respect to the camshaft main body 11, as shown in FIG. 21. When the driving lever 54 swings in a direction reverse to the above direction, the connecting member 114 moves to the advance position, and the slider 112 and the first cam 102 and the second cam 103 move to the other side of the axial direction with respect to the camshaft main body 11, as shown in FIG. 22.

[0165] A rocker arm 9 according to this preferred embodiment is swingably supported by a rocker shaft 34 in a state in which the movement in the axial direction is regulated. A roller 26 that rotates in contact with the first cam 102 or the second cam 103 is provided at the intermediate portion of the rocker arm 9. A pressing portion 40 that presses the intake valve 4 or the exhaust valve 5 is provided at the swing end of the rocker arm 9. The number of intake valves 4 or exhaust valves 5 to be driven by the rocker arm 9 is not limited by the arrangement of the switch unit 21. The rocker arm 9 according to this preferred embodiment may drive one intake valve 4 or exhaust valve 5 per cylinder, or drive two intake valves 4 or exhaust valves 5 per cylinder.

[0166] In this preferred embodiment, a switch 21A that is one element of the valve mechanism system from the valve driving cam to the rocker arm includes the first cam 102 and the second cam 103.

[0167] In the valve mechanism 111 according to this preferred embodiment, when the pivot shaft 53 of the switch assembly 3 rotates in one direction, the roller 26 comes into contact with the second cam 103, and the first cam 102 separates from the roller 26, as shown in FIG. 21. When the camshaft 14 rotates in this state, the rocker arm 9 is pressed by the second cam 103 and swings.

[0168] When the pivot shaft 53 rotates in the other direction, the second cam 103 separates from the roller 26, and the first cam 102 comes into contact with the roller 26, as shown in FIG. 22. When the camshaft 14 rotates in this state, the rocker arm 9 is pressed by the first cam 102 and swings.

[0169] For this reason, according to this preferred embodiment, it is possible to provide the valve mechanism in which the first cam 102 and the second cam 103 move, thus switching the driving state of the intake valve 4 or the exhaust valve 5.

[0170] In the above-described preferred embodiments, an example in which the presser 82 of the positioner 24 includes a ball has been described. However, the presser 82 is not limited to a ball and may be appropriately changed. For example, the presser 82 may have a sectional shape rising in a crescentic shape.

[0171] While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.