VALVE SYSTEM FOR A MULTI-CYLINDER ENGINE

Abstract

A valve system includes: a cam shaft including a shaft section and a plurality of cam element sections; and a plurality of operation members that moves the cam element sections in an axial direction. The plurality of operation members include a common operation member that is provided in common between end face cams opposed to each other of the cam element sections of two cylinders disposed adjacent to each other and continuous in ignition order and that engages with the respective end face cams when both the cam element sections are close to each other, and individual operation members that are individually provided for end face cams opposed to each other of the cam element sections of two cylinders disposed adjacent to each other and discontinuous in ignition order and end face cams located at opposite ends of a cylinder row and that engage with the respective end face cams.

Description

TECHNICAL FIELD

The present invention relates to a valve system for a multi-cylinder engine for a vehicle or the like and, more particularly, to a valve system capable of switching a cam for opening and closing a valve, and belongs to a technical field of a valve system for an engine.

BACKGROUND ART

As a valve system for a multi-cylinder engine, there is known a valve system that includes, for one valve of each cylinder, a plurality of cams having different shapes of nose sections and selects a cam for opening and closing the valve out of the cams to make it possible to switch valve opening amounts, valve opening and closing periods, and the like of intake and exhaust valves according to an operation state of the engine.

For example, Patent Literature 1 discloses a valve system including a cam shaft including a shaft section and a cylindrical cam element section movably spline-fitted on the shaft section in an axial direction. In the valve system, on the outer circumference of the cam element section, a plurality of adjacent cams having different shapes of nose sections are provided for one valve. The valve system moves the cam element section in the axial direction to thereby switch a cam that opens and closes the valve.

Specifically, in the valve system disclosed in Patent Literature 1, a plurality of cam element sections are provided to correspond to cylinders of a multi-cylinder engine. End face cams are formed on both end faces of the cam element section. The valve system disclosed in the literature includes operation members retractably provided with respect to opposing positions of the end face cams. The operation members are driven by an actuator to project and engage with the end face cams when projecting. Consequently, the cam element section is moved in the axial direction and the cam is switched.

Incidentally, in the valve system disclosed in Patent Literature 1, the end face cams are provided on both the end faces of the cam element section in order to move the cam element section to both sides in the axial direction of the shaft section. The valve system includes the operation member for each of the end face cams on both the sides. Therefore, two operation members are necessary for one cam element section. The number of components increases.

As measures against this problem, in order to reduce the number of components of the operation members, it is conceivable to adopt a method of disposing a single operation member between cylinders adjacent to each other, projecting the operation member to between opposed end face cams of two cam element sections disposed closer to each other, and engaging the operation member with the respective end face cams to thereby separate both the cam element sections in the axial direction and switch a cam.

However, with this method, there is a problem in that, between two cylinders disposed adjacent to each other and discontinuous in ignition order, a period in which the operation member can be projected to between the opposed end face cams decreases and, in particular, during high-speed rotation of an engine, it is difficult to switch the cam. A reason why the period in which the operation member can be projected decreases is explained below using a four-cylinder engine as an example.

For example, in a four-cylinder engine in which first, second, third, and fourth cylinders are disposed in this order, when ignition order is the order of the third cylinder, the fourth cylinder, the second cylinder, and the first cylinder, the second and third cylinders are adjacent to each other but are discontinuous in the ignition order. In order to move a cam element section while a valve is closed, lift sections of end face cams are disposed to overlap a projecting position of an operation member (overlap the operation member after projection in axial direction view) when nose sections do not open and close the valve. That is, both of the lift sections and reference planes (parts that are not the lift sections) of the end face cams are set on the basis of phases of the nose sections.

Since the second and third cylinders are discontinuous in the ignition order, the phases of the nose sections of two end face cams opposed between these cylinders are not in a continuous relation. As a result, an angle range in which two reference planes of the two end face cams overlap is divided into two ranges, which are respectively narrow angle ranges.

Incidentally, between the cylinders adjacent to each other, timing when the operation members can be projected is limited to time when each of the reference planes of the opposed two end face cams overlaps the projecting position of the operation member. On the other hand, as explained above, when the adjacent cylinders are discontinuous in the ignition order, compared with when the cylinders are continuous in the ignition order, an angle range in which the two reference planes overlap is narrow. Therefore, between the cylinders discontinuous in the ignition order, a period in which the operation member can be projected is short.

Moreover, during high-speed rotation of the engine, since rotating speed of a cam shaft is high, the period in which the operation member can be projected is shorter. As a result, depending on projection speed of the operation member, even if it is attempted to project the operation member to between the two reference planes, the projection is late. It is difficult to switch a cam section.

CITATION LIST

Patent Literature

Patent Literature 1: United States Patent Publication No. 2011/0226205A1

SUMMARY OF INVENTION

The present invention has been devised in order to solve the problems and it is an object of the present invention to obtain, while reducing the number of components to attain compactness of an engine, a valve system for the engine capable of easily performing switching operation for cams during high-speed rotation of the engine.

In order to solve the problems, the present invention relates to a valve system provided in a multi-cylinder engine including at least a pair of cylinders disposed adjacent to each other and discontinuous in ignition order and at least a pair of cylinders disposed adjacent to each other and continuous in ignition order. The valve system includes: a cam shaft including a shaft section extending in a cylinder row direction and a plurality of cam element sections provided respectively in the cylinders and fit in the shaft section to be capable of rotating integrally with the shaft section and moving in an axial direction; and an operation mechanism that moves the plurality of cam element sections in the axial direction with respect to the shaft section. Each of the cam element sections includes, for each one valve of the cylinders, two cam sections which include a common base circle, have differently shaped nose sections, and adjacent to each other in the axial direction. End face cams are respectively provided at both end portions in the axial direction of each of the cam element sections. The operation mechanism includes a plurality of operation members driven by an actuator to be movable between an actuation position where the operation members rush into positions opposed to the end face cams of the plurality of cam element sections in the axial direction and a retracting position where the operation members retract from opposing positions of the end face cams, wherein the operation mechanism engages the operation members, which have moved to the actuation position, with the end face cams and moves the cam element sections in the axial direction to thereby switch the cam section that opens and closes valves of the cylinders. The plurality of operation members include: a common operation member that is provided in common between the end face cams opposed to each other of the cam element sections of two cylinders disposed adjacent to each other and continuous in ignition order and that engages with the respective end face cams when both the cam element sections are close to each other; and individual operation members that are individually provided for the end face cams opposed to each other of the cam element sections of two cylinders disposed adjacent to each other and discontinuous in ignition order and the end face cams located at opposite ends of the cylinder row and that engage with the respective end face cams.

With the valve system for the multi-cylinder engine according to the present invention, it is possible to easily perform the switching operation for the cams during the high-speed rotation of the engine while reducing the number of components to attain compactness of the engine.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view showing the schematic configuration of an exhaust-side valve system according to a first embodiment of the present invention.

FIG. 2 is a front view of the valve system in an x-direction arrow view in FIG. 1.

FIG. 3 is an enlarged sectional view taken along line y-y in FIG. 1.

FIG. 4 is a side view showing a state in which a cam section that opens and closes a valve is switched from a state of FIG. 1.

FIG. 5 is a perspective view of a cam element section alone.

FIG. 6 is a side view of the cam element section alone.

FIG. 7 is a front view of a cam element section in a z-direction arrow view in FIG. 6.

FIG. 8 is a rear view of the cam element section in a w-direction arrow view in FIG. 6.

FIG. 9 is a main part development view developed along the circumference of an end face cam in order to show an angle range in which a second operation member (a pin section of a second operation device) can project.

FIG. 10 is an operation explanatory diagram for showing operation in moving the cam element section with the second operation member.

FIG. 11 is an element development view for showing an angle range in which movement of the second operation member to an actuation position is regulated.

FIG. 12 is a main part development view developed along the circumference of the end face cam in order to show an angle range in which a third operation member (a pin section of a third operation device) can project.

FIG. 13 is an operation explanatory diagram for showing operation in moving the cam element section with the third operation member.

FIG. 14 is a main part development diagram for showing an angle range in which movement of the third operation member to the actuation position is regulated.

FIGS. 15A and 15B are main part development diagrams developed along the circumference of the end face cam in order to show an angle range in which the operation member can project when the cam element section is moved from a second position to a first position.

FIG. 16 is a side view showing the schematic configuration of an exhaust-side valve system according to a second embodiment of the present invention.

FIG. 17 is a front view of the valve system in an x-direction arrow view in FIG. 16.

FIG. 18 is a side view showing a state in which a cam section that opens and closes a valve is switched from a state of FIG. 16.

FIG. 19 is a perspective view of a cam element section alone

FIG. 20 is a side view of a cam element section of a first cylinder or a fourth cylinder.

FIGS. 21A and 21B are front views of the cam element section shown in FIG. 20.

FIG. 22 is a side view of a cam element section of a second cylinder or a third cylinder.

FIGS. 23A and 23B are front views of the cam element section shown in FIG. 22.

DESCRIPTION OF EMBODIMENTS

First Embodiment

A first embodiment of the present invention is explained below using, as an example, a valve system of a four-cylinder four-valve DOHC engine in which two intake valves and two exhaust valves are provided for one cylinder.

FIG. 1 shows the configuration on an exhaust side of a valve system according to the first embodiment. A not-shown cylinder head includes eight exhaust valves A . . . A in total, two each for each of first to fourth cylinders 1₁ to 1₄, and return springs B . . . B that urge the exhaust valves A . . . A in a closing direction. The valve system includes a cam shaft 2 provided in an upper part of the cylinder head as a shaft for opening and closing the exhaust valves A . . . A and an operation mechanism 30 provided above the cam shaft 2.

The cam shaft 2 presses the exhaust valves A . . . A via rocker arms C . . . C to thereby open and close the exhaust valves A . . . A resisting urging force of the return springs B . . . B. The cam shaft 2 is rotatably supported by bearing sections F . . . F including vertical wall sections D . . . D provided in respective center positions of the cylinders 1₁ to 1₄ in the cylinder head and cap members E . . . E attached to upper parts of the vertical wall sections D . . . D. The cam shaft 2 is driven to rotate by a not-shown crankshaft via a chain.

The cam shaft 2 includes a shaft section 10 and first to fourth cam element sections 20₁ to 20₄ spline-fit in the shaft section 10 and capable of rotating integrally with the shaft section 10 and moving in an axial direction. The cam element sections 20₁ to 20₄ are disposed in a row on the shaft section 10 to correspond to the cylinders 1₁ to 1₄.

The operation mechanism 30 includes six operation devices 30₁ to 30₆ of an electromagnetic type that move the cam element sections 20₁ to 20₄ along the shaft section 10. With the side of the first cylinder 1₁ located on one side of the cylinder row set as the front, in order from the front, the first operation device 30₁ is disposed in a front end position of the cylinder row, the second operation device 30₂ is disposed in a position between the first and second cylinders 1₁, 1₂, the third and fourth operation devices 30₃, 30₄ are disposed in a position between the second and third cylinders 1₂, 1₃, the fifth operation device 30₅ is disposed in a position between the third and fourth cylinders 1₃, 1₄, and the sixth operation device 30₆ is disposed in a rear end position of the cylinder row.

The operation devices 30₁ to 30₆ of the operation mechanism 30 include main bodies 31 incorporating electromagnetic actuators and pin sections 32 functioning as operation members that move, with energization to the electromagnetic actuators, from a retracting position where the pin sections 32 retract in the main bodies 31 to an actuation position where the pin sections 32 project from the main bodies 31. As shown in FIG. 2, the first operation device 30₁ (the second, third, fifth, and sixth operation devices 30₂, 30₃, 30₅, and 30₆ as well) is disposed on substantially the opposite side of a cam follower C′ in the rocker arm C across the cam shaft 2. The fourth operation device 30₄ is disposed on the near side in the rotating direction X at a predetermined angle (e.g., about 30°) with respect to the other operation devices.

The operation devices 30₁ to 30₆ are respectively disposed such that the pin sections 32 are directed to the axis of the cam shaft 2. In the case of this embodiment, the operation devices 30₁ to 30₆ are respectively attached to pedestal sections G . . . G integrally formed in cap members E . . . E of the bearing sections F . . . F.

As shown in FIG. 1, the pin sections 32 of the first, third, fourth, and sixth operation devices 30₁, 30₃, 30₄, and 30₆ are formed in a cylindrical shape. On the other hand, the pin sections 32 of the second and fifth operation devices 30₂, 30₅ are formed in a stepped shape and include small-diameter sections 32a, large-diameter sections 32b, and medium-diameter sections 32c in order from the distal end side.

In order to determine, in predetermined two places, positions in the axial direction of the cam element sections 20₁ to 20₄ moved by the operation devices 30₁ to 30₆, as shown in FIG. 3 using the first and second cam element sections 20₁, 20₂ as an example, detent mechanisms 40 are respectively provided in fitting sections of the shaft section 10 and the cam element sections 20₁ to 20₄.

The detent mechanism 40 includes a hole 41 drilled in the radial direction from the outer circumferential surface of the shaft section 10, a spring 42 housed in the hole 41, a detent ball 43 disposed in an opening section of the hole 41 and urged to jump out from the outer circumferential surface of the shaft section 10 to the outer side in the radial direction by the spring 42, and circumferential grooves 44₁, 44₂ provided in two places adjacent to each other in the axial direction on the inner circumferential surfaces of each of the cam element sections 20₁ to 20₄. When the detent ball 43 engages with one circumferential groove 44₁, the cam element sections 20₁ to 20₄ are positioned in the first position shown in FIG. 1. When the detent ball 43 engages with the other circumferential groove 44₂, the cam element sections 20₁ to 20₄ are positioned in the second position shown in FIG. 4.

As shown in FIG. 1, when all of the first to fourth cam element sections 20₁ to 20₄ are present in the first position, the first cam element section 20₁ is disposed in the rear, the second cam element section 20₂ is disposed in the front, the third cam element section 20₃ is disposed in the rear, and the fourth cam element section 20₄ is disposed in the front. Therefore, opposed end faces of the first and second cam element sections 20₁, 20₂ are close to each other, opposed end faces of the second and third cam element sections 20₂, 20₃ are separated from each other, and opposed end faces of the third and fourth cam element sections 20₃, 20₄ are close to each other.

As shown in FIG. 4, when all of the first to fourth cam element sections 20₁ to 20₄ are present in the second position, the first cam element section 20₁ is located in the front, the second cam element section 20₂ is located in the rear, the third cam element section 20₃ is located in the front, and the fourth cam element section 20₄ is located in the rear. Therefore, the opposed end faces of the first and second cam element sections 20₁, 20₂ are separated from each other, the opposed end faces of the second and third cam element sections 20₂, 20₃ are close to each other, and the opposed end faces of the third and fourth cam element sections 20₃, 20₄ are separated from each other.

Next, the configuration of the cam element sections 20₁ to 20₄ is explained more in detail using the first cam element 20₁ as an example with reference to FIG. 5 to FIG. 8.

The cam element section 20₁ (20₂ to 20₄) is formed in a cylindrical shape. The outer circumferential surface in the intermediate section of the cam element section 20₁ is formed as a journal section 21 supported by the bearing section E Actuating sections 22, 22 for the two exhaust valves A, A of the cylinder are provided on both the front and rear sides of the journal section 21. In the actuating sections 22, 22, a first cam section 22₁ having a small lift amount for, for example, low-speed engine rotation time and a second cam section 22₂ with a large lift amount for, for example, high-speed engine rotation time are provided adjacent to each other.

As shown in FIG. 7 and FIG. 8, the first cam section 22₁ and the second cam section 22₂ respectively include nose sections b₁, b₂ having different lift amounts. The nose sections b₁, b₂ are provided on a common base circle a with phases thereof aligned. The first cam section 22₁ and the second cam section 22₂ are respectively provided with order of arrangement in the front-rear direction and phases of the nose sections b₁, b₂ matched in the actuating sections 22, 22 in the two places. Note that the common base circle a means that base circle diameters of base circles a of the first cam section 22₁ and the second cam section 22₂ are the same.

As shown in FIG. 1 and FIG. 4, in the first cam element section 20₁ and the third cam element section 20₃, the first cam section 22₁ is disposed in the front and the second cam section 22₂ is disposed in the rear. In the second cam element section 20₂ and the fourth cam element section 20₄, the second cam section 22₂ is disposed in the front and the first cam section 22₁ is disposed in the rear.

When the cam element sections 20₁ to 20₄ are positioned in the first position on the shaft section 10 by the detent mechanism 40, as shown in FIG. 1, in all the cam element sections 20₁ to 20₄, the two first cam sections 22₁, 22₁ are set to be located to correspond to the cam followers C′, C′ (see FIG. 2) of the two rocker arms C, C of the corresponding cylinder. When the cam element sections 20₁ to 20₄ are positioned in the second position on the shaft section 10, as shown in FIG. 4, the second cam sections 22₂, 22₂ are set to be located to correspond to the cam followers C′, C′.

In the engine according to this embodiment, ignition order (combustion order) of the cylinders is set as the third cylinder 1₃→the fourth cylinder 1₄→the second cylinder 1₂→the first cylinder 1₁. Therefore, the first to fourth cam element sections 20₁ to 20₄ are spline-fit in the shaft section 10 with a phase difference of 90° from each other such that the nose sections b₁, b₂ of the first cam section 22₁ or the second cam section 22₂ of each of the cam element sections 20₁ to 20₄ press the cam followers C′, C′ of the cylinders in order according to the ignition order every time the cam shaft 2 rotates 90°.

Further, end face cams 23, 23 are respectively provided at both front and rear end portions (both end portions in the axial direction) of the cam element sections 20₁ to 20₄.

Each of the end face cams 23, 23 at both the front and rear end portions includes, as shown in FIG. 5 to FIG. 8, a reference plane c formed along a surface orthogonal to the axis of the cam element section 20₁ (20₂ to 20₄) and lift sections d symmetrically projecting to the front or the rear in the axial direction from the reference plane c. As shown in FIG. 7 and FIG. 8, the lift sections d are formed such that a lift amount in the axial direction from the reference plane c (lift amount zero) gradually increases in a predetermined angle range α (e.g., about 120° from a lift start position e to a lift end position f. Specifically, the lift amount of the lift sections d is set to be larger on the forward side in a rotating direction X of the cam shaft 2 in the predetermined angle range α and return to zero in the lift end position f.

As explained above, the cam element sections 20₁ to 20₄ are spline-fit in the shaft section 10 with the predetermined phase difference from each other according to the ignition order of the cylinders 1₁ to 1₄. Accordingly, the end face cams 23, 23 opposed to each other of the cam element sections 20₁ to 20₄ are also opposed having a phase difference from each other.

The pin section 32 of the second operation device 30₂ is equivalent to a “common operation member” in claims. The pin section 32 is disposed between the end face cams 23, 23 opposed to each other of the cam element sections 20₁, 20₂ of the first cylinder 1₁ and the second cylinder 1₂ disposed adjacent to each other and continuous in ignition order. The pin section 32 of the second operation device 30₂ moves (projects) to the actuation position when the cam element sections 20₁, 20₂ are present in the first position to thereby move the cam element sections 20₁, 20₂ to the second position.

The pin section 32 of the fifth operation device 30₅ is equivalent to the “common operation member” in claims. The pin section 32 is disposed between the end face cams 23, 23 opposed to each other of the cam element sections 20₃, 20₄ of the third cylinder 1₃ and the fourth cylinder 1₄ disposed adjacent to each other and continuous in ignition order. The pin section 32 of the fifth operation device 30₅ moves (projects) to the actuation position when the cam element sections 20₃, 20₄ are present in the first position to thereby move the cam element sections 20₃, 20₄ to the second position.

Specifically, the pin section 32 of the second operation device 30₂ or the fifth operation device 30₅ moves to the actuation position when the two cam element sections corresponding to the pin section 32 are in a state (the first position) in which the two cam element sections are close to each other and the reference planes c of the end face cams 23, 23 opposed to each other of both the cam element sections are respectively in positions where the reference planes c overlap a projecting position of the pin section 32 (overlap the pin section 32 after the projection in axial direction view). The pin section 32 moved to the actuation position engages with the end face cams 23, 23 in order according to the rotation of the cam shaft 2 to thereby move the two cam element sections located close to each other in a direction in which the cam element sections are separated from each other.

That is, the first and second cam element sections 20₁, 20₂ located close to each other are separated from each other by the pin section 32 of the second operation device 30₂. The third and fourth cam element sections 20₃, 20₄ located close to each other are separated from each other by the pin section 32 of the fifth operation device 30₅. As a result, all of the first to fourth cam element sections 20₁ to 20₄ move from the first position shown in FIG. 1 to the second position shown in FIG. 4.

On the other hand, the pin sections 32 . . . 32 of the operation devices other than the second and fifth operation devices 30₂, 30₅, that is, the first, third, fourth, and sixth operation devices 30₁, 30₃, 30₄, and 30₆ are equivalent to “individual operation members” in claims. That is, the pin section 32 of the first operation device 30₁ is a pin section exclusive for the end face cam 23 (the end face cam 23 on the front side of the cam element section 20₁) located at the end portion on one side of the cylinder row. The pin section 32 of the sixth operation device 30₆ is a pin section exclusive for the end face cam 23 (the end face cam 23 on the rear side of the cam element section 20₄) located at the end portion on the other side of the cylinder row. The pin section 32 of the third operation device 30₃ is a pin section exclusive for one (the cam 23 on the front side) of the end face cams 23, 23 opposed to each other of the cam element sections 20₂, 20₃ of the second cylinder 1₂ and the third cylinder 1₃ disposed adjacent to each other and discontinuous in ignition order. The pin section 32 of the fourth operation device 30₄ is a pin section exclusive for the other (the cam 23 on the rear side) of the end face cams 23, 23. The pin sections 32 . . . 32 of the first, third, fourth, and sixth operation devices 30₁, 30₃, 30₄, and 30₆ move (project) to the actuation position when the cam element sections 20₁ to 20₄ are present in the second position to thereby individually move the cam element sections 20₁ to 20₄ to the first position.

Specifically, in a state in which the first cam element section 20₁ is present in the second position closer to the front, the pin section 32 of the first operation device 30₁ moves to the actuation position opposed to the end face cam 23 on the front side of the first cam element section 20₁ in the axial direction and engages with the end face cam 23 according to the rotation of the cam shaft 2 to thereby move the first cam element section 20₁ to the first position closer to the rear as shown in FIG. 1. Similarly, in a state in which the second cam element section 20₂ is present in the second position closer to the rear, the pin section 32 of the third operation device 30₃ moves to the actuation position opposed to the end face cam 23 on the rear side of the second cam element section 20₂ in the axial direction and engages with the end face cam 23 according to the rotation of the cam shaft 2 to thereby move the second cam element section 20₂ to the first position closer to the front.

Similarly, the third cam element section 20₃ and the fourth cam element section 20₄ are moved to the first position respectively by the pin sections 32, 32 of the fourth and sixth operation devices 30₄, 30₆. Consequently, all of the cam element sections 20₁ to 20₄ present in the second position move to the first position.

The movement (the projection) of the pin sections 32 of the operation devices 30₁ to 30₆ to the actuation position is performed at timing described below. That is, the projection of the pin sections 32 (the individual operation members) in the first, third, fourth, and sixth operation devices 30₁, 30₃, 30₄, and 30₆ is performed at timing when the reference planes c of the end face cams 23 corresponding to the pin sections 32 overlap projecting positions of the pin sections 32 (overlap the pin sections 32 after the projection in axial direction view). On the other hand, the projection of the pin sections 32 (the common operation members) in the second and fifth operation devices 30₂, 30₅ is performed at timing when both the reference planes c, c of the two end face cams 23, 23 opposed to each other overlap projecting positions of the pin sections 32.

The movement of the cam element sections 20₁ to 20₄ involved in the movement (the projection) of the pin sections 32 to the actuation position has to be performed at timing when the cam follower C′ of the rocker arm C is in contact with the portion of the base circle a of the first cam section 22₁ or the second cam section 22₂, that is, when the cylinder is in a stroke other than an exhaust stroke.

Therefore, in order to satisfy these conditions of the actuation timing, as shown in FIG. 7 and FIG. 8, with respect to the vertexes of the nose sections b₁, b₂ of the first and second cam sections 22₁, 22₂, a lift start position (a start position of the lift sections d) e of the end face cam 23 is set in a position a predetermined angle apart in the forward side in the rotating direction X and a lift end position (an end position of the lift sections d) f of the end face cam 23 is set in a position a predetermined angle apart in the backward side in the rotating direction X, whereby the nose section b₁, b₂ of the first and second cam sections 22₁, 22₂ and the lift sections d of the end face cam 23 are in a positional relation in which the nose sections b₁, b₂ and the lift sections d overlap. In this case, according to a positional relation between the cam follower C′ of the rocker arm C shown in FIG. 2 and the pin sections 32 of the operation devices 30₁ to 30₆, the cam element sections 20₁ to 20₄ move immediately after the end of the exhaust stroke.

Further, as shown in FIG. 5 to FIG. 8, in the cam element section 20₁, a first return cam 50 and a second return cam 51 that push back the pin sections 32, 32 of the first and second operation devices 30₁, 30₂ from the actuation position to the retracting position to thereby regulate the movement of the pin sections 32, 32 from the retracting position to the actuation position are provided. The first return cam 50 is provided to be located to correspond to a front portion of the cam element section 20₁, that is, the first operation device 30₁. The second return cam 51 is provided to be located to correspond to a rear portion of the cam element section 20₁, that is, the second operation device 30₂.

The first return cam 50 includes, as shown in FIG. 5 to FIG. 7, a first reference plane 50a formed in a substantially cylindrical shape, a first slope section 50b and a first regulating section 50c formed to project in the radial direction at one end portion of the first reference plane 50a, and a first attaching section 50d (FIG. 6) formed at the other end portion of the first reference plane 50a. The first return cam 50 is attached to the front portion of the first cam element section 20₁ via a first attaching section 50d.

Similarly, the second return cam 51 includes, as shown in FIG. 5, FIG. 6, and FIG. 8, a second reference plane 51a formed in a substantially cylindrical shape, a second slope section 51b and a second regulating section 51c formed to project in the radial direction at one end portion of the second reference plane 51a, and a second attaching section 51d (FIG. 6) formed at the other end portion of the second reference plane 51a. The second return cam 51 is attached to a rear portion of the first cam element section 20₁ via the second attaching section 51d.

In a state in which the first return cam 50 is attached to the first cam element section 20₁, the first slope section 50b is formed such that a lift amount with respect to the reference plane 50a gradually increases from zero starting from the vicinity of an end position f of the end face cam 23 and is connected to the first regulating section 50c in an end position 50e of the first slope section 50b. The first regulating section 50c is formed to be contiguous to the backward side in the rotating direction X with respect to the first slope section 50b and have a fixed radius and is formed to return to the reference plane 50a in the vicinity of the start position e of the end face cam 23.

The radius of the first reference plane 50a is set to a value for preventing the pin section 32 of the first operation device 30₁ present in the actuation position indicated by a chain line in FIG. 7 and the first reference plane 50a from coming into contact with each other. The radius of the first regulating section 50c is set to a radius substantially the same as the outer circumferential surface of the end face cam 23 and is set to a value for preventing the pin section 32 of the first operation device 30₁ present in the retracting position and the first regulating section 50c from coming into contact with each other.

Axial direction positions of the first slope section 50b and the first regulating section 50c are set such that the first slope section 50b and the first regulating section 50c are located to be opposed to the pin section 32 of the first operation device 30₁ when the first cam element section 20₁ is present in the first position and such that the first slope section 50b and the first regulating section 50c are not located to be opposed to the pin section 32 of the first operation device 30₁ when the first cam element section 20₁ is present in the second position.

The same applies to the shape of the second return cam 51. That is, in a state in which the second return cam 51 is attached to the first cam element section 20₁, the second slope section 51b is formed such that a lift amount with respect to the reference plane 51a gradually increases from zero starting from the vicinity of the end position f of the end face cam 23 and is connected to the second regulating section 51c in an end position 51e of the second slope section. The second regulating section 51c is formed to be contiguous to the forward side in the rotating direction X with respect to the second slope section 51b and have a fixed radius and is formed to return to the reference plane 51a in the vicinity of the start position e of the end face cam 23.

The radius of the second reference plane 51a is set to a value for preventing the pin section 32 of the second operation device 30₂ present in the actuation position indicated by a chain line in FIG. 8 and the second reference plane 51a from coming into contact with each other. The radius of the second regulating section 51c is set to a radius slightly smaller than the outer circumferential surface of the end face cam 23 and is set to a value for preventing a small-diameter section 32a of the pin section 32 of the second operation device 30₂ present in the retracting position and the second regulating section 51c from coming into contact with each other. Note that the large-diameter portion 32b of the pin section 32 does not come into contact with the outer circumferential surface of the end face cam 23 when the pin section 32 is in the retracting position.

Axial direction positions of the second slope section 51b and the second regulating section 51c are set such that the second slope section 51b and the second regulating section 51c are located to be opposed to the pin section 32 of the second operation device 30₂ when the first cam element section 20₁ is present in the second position and such that the second slope section 51b and the second regulating section 51c are not located to be opposed to the pin section 32 of the second operation device 30₂ when the first cam element section 20₁ is present in the first position.

The first return cam 50 is disposed to correspond to the first, third, fourth, and sixth operation devices 30₁, 30₃, 30₄, and 30₆ including the cylindrical pin sections 32 . . . 32 and is configured such that the first slope section 50b and the first regulating section 50c act on the pin sections 32 . . . 32 of the operation devices after cam element sections 20₁ to 20₄ end movement from the second position to the first position with the operation devices 30₁, 30₃, 30₄, and 30₆.

That is, as shown in FIG. 1, the first return cam 50 is attached to the front portion of the first cam element section 20₁, a rear portion of the second cam element section 20₂, a front portion of the third cam element section 20₃, and a rear portion of the fourth cam element section 20₄. Consequently, in a state in which the cam element sections 20₁ to 20₄ are present in the first position, movement of the pin sections 32 . . . 32 of the first, third, fourth, and sixth operation devices 30₁, 30₃, 30₄, and 30₆ to the actuation position is regulated over a predetermined angle range by the first return cam 50.

The second return cam 51 is disposed to correspond to the second and fifth operation devices 30₂, 30₅ including the stepped-shape pin sections 32, 32 and is configured such that the second slope section 51b and the second regulating section 51c act on the pin sections 32, 32 of the operation devices 30₂, 30₅ after the cam element sections 20₁ to 20₄ end movement from the first position to the second position with the operation devices 30₂, 30₅.

The second return cam 51 is attached to only the cam element section that moves later in moving order of the two cam element sections to be moved by the second and fifth operation devices 30₂, 30₅ in the separating direction (from the first position to the second position).

That is, in the case of this embodiment, according to the ignition order, the cam element sections 20₁ to 20₄ are moved in the order of the second cylinder 1₂→the first cylinder 1₁→the third cylinder 1₃→the fourth cylinder 1₄ to switch a cam section that opens and closes the exhaust valves A of the cylinders 1₁ to 1₄. Therefore, the first cam element section 20₁ is later in moving order of the first cam element section 20₁ and the second cam element section 20₂ moved in the separating direction by the pin section 32 (the common operation member) of the second operation device 30₂. The fourth cam element 20₄ is later in moving order of the third cam element section 20₃ and the fourth cam element section 20₄ moved in the separating direction by the pin section 32 (the common operation member) of the fifth operation device 30₅. Therefore, the second return cam 51 (the second slope section 51b and the second regulating section 51c) that pushes back the pin sections 32 of the second and fifth operation devices 30₂, 30₅ is attached to the rear portion of the first cam element section 20₁ and a front section of the forth cam element section 20₄ as shown in FIG. 4. Consequently, in a state in which the cam element sections 20₁ to 20₄ are present in the second position, movement of the pin sections 32 of the second and fifth operation devices 30₂, 30₅ to the actuation position is regulated over a predetermined angle range by the second return cam 51.

Next, the operation of the valve system in the first embodiment is explained.

First, as shown in FIG. 1, for example, when the first to fourth cam element sections 20₁ to 20₄ are present in the first position during low-speed rotation of the engine, in all the cam element sections 20₁ to 20₄, the first cam sections 22₁, 22₁ having a small lift amount in the actuating sections 22, 22 at both the ends are located to correspond to the cam followers C′, C′ of the rocker arms C, C. According to the rotation of the cam shaft 2, in the ignition order explained above, the exhaust valves A . . . A of the cylinders 1₁ to 1₄ open at a relatively small valve opening amount during the exhaust stroke.

From this state, for example, when the cam section is switched to increase the valve opening amount of the exhaust valves A . . . A according to an increase in engine speed, the second and fifth operation devices 30₂, 30₅ are energized to move the respective pin sections 32, 32 from the retracting position to the actuation position.

That is, first, the pin section 32 of the second operation device 30₂ rushes into between the opposed end face cams 23, 23 of the first and second cam element members 20₁, 20₂ present in the first position and in a state in which the end face cams 23, 23 are close to each other. The pin section 32 engages with the end face cams 23, 23. At this point, as shown in FIG. 9, the pin section 32 is rushes into an angle range R1 in which the reference planes c, c, a lift amount of which is zero, in the end face cams 23, 23 of the first and second cam element sections 20₁, 20₂ are opposed to each other. In other words, the pin section 32 is rushed into between the end face cams 23, 23 at timing when the portion of the angle range R1 in which the reference planes c, c are opposed to each other is located below the pin section 32.

After the exhaust stroke of the second cylinder 1₂ shown in (a) of FIG. 10 ends, the lift start position e of the end face cam 23 on the front side of the second cam element section 20₂ indicated by a solid line reaches the position of the pin section 32 of the second operation device 30₂. Thereafter, as shown in (b) of FIG. 10, according to the rotation of the cam shaft 2, the pin section 32 pushes the second cam element section 20₂ rearward while being in slide contact with the lift sections d of the end face cam 23 and moves the second cam element section 20₂ to the second position.

After the lift start position e of the end face cam 23 of the second cam element section 20₂ reaches the position of the pin section 32, when the cam shaft 2 rotates 90° and the exhaust stroke of the first cylinder 1₁ ends, subsequently, the lift start position e of the end face cam 23 on the rear side of the first cam element section 20₁ indicated by a chain line reaches the position of the pin section 32. Thereafter, as shown in (c) in FIG. 10, according to the rotation of the cam shaft 2, the pin section 32 pushes the first cam element section 20₁ forward while being in slide contact with the lift sections d of the end face cam 23 and moves the first cam element section 20₁ to the second position.

When the movement of the first cam element section 20₁ to the second position is completed, as shown in (d) of FIG. 10, the slope section 51b of the second return cam 51 attached to the rear portion of the first cam element section 20₁ is located to be opposed to the small-diameter section 32a of the pin section 32 of the second operation device 30₂. Thereafter, when the energization to the second operation device 30₂ is released, as shown in (e) of FIG. 10, according to the rotation of the cam shaft 2, the small-diameter section 32a of the pin section 32 is forcibly pushed back to the retracting position while being in slide contact with the slopes section 51b.

In the state in which the first cam element section 20₁ is present in the second position, in an angle range Q1 shown in FIG. 11, the second regulating section 51c of the second return cam 51 attached to the first cam element section 20₁ is disposed in a position opposed to the small-diameter section 32a of the pin section 32 of the second operation device 30₂. Consequently, the movement of the pin section 32 of the second operation device 30₂ to the actuation position is regulated over the predetermined angle range Q1.

Subsequently, the pin section 32 of the fifth operation device 30₅ rushes into between the opposed end face cams 23, 23 of the third and fourth cam element sections 20₃, 20₄ present in the first position and in a state in which the end face cams 23, 23 are close to each other. The pin section 32 engages with the end face cams 23, 23. Consequently, as in the case of the first and second cam element sections 20₁, 20₂, first, the pin section 32 moves the third cam element section 20₃ to the second position and subsequently moves the fourth cam element section 20₄ to the second position. Therefore, the pin section 32 is forcibly pushed back to the retracting position by the second return cam 51 attached to the fourth cam element section 20₄.

In a state in which the forth cam element section 20₄ is present in the second position, the movement of the pin section 32 of the fifth operation device 30₅ to the actuation position is regulated over a predetermined angle range by the second regulating section 51c of the second return cam 51 attached to a front portion of the fourth cam element section 20₄.

Consequently, all of the first to fourth cam element sections 20₁ to 20₄ move from the first position to the second position. As shown in FIG. 4, in all of the first to fourth cam element sections 20₁ to 20₄, the second cam sections 22₂, 22₂ are located to correspond to the cam followers C′, C′ of the rocker arms C, C and the exhaust valves A . . . A of the cylinders 1₁ to 1₄ open at a relatively large valve opening amount during the exhaust stroke.

Moreover, in the state in which the cam element sections 20₁ to 20₄ are present in the second position, the movement to the actuation position of the pin sections 32, 32 of the second and fifth operation devices 30₂, 30₅ used for moving the cam element sections 20₁ to 20₄ from the first position to the second position is regulated in the predetermined angle range.

On the other hand, when a state in which the second cam sections 22₂ . . . 22₂ having a large lift amount of the cam element sections 20₁ to 20₄ shown in FIG. 4 are located to correspond to the cam followers C′, C′ of the rocker arms C . . . C is switched to, according to, for example, a decrease in engine speed, a state in which the first cam sections 22₁ . . . 22₁ having a small lift amount shown in FIG. 1 are located to correspond to the cam followers C′, C′, the first, third, fourth, and sixth operation devices 30₁, 30₃, 30₄, and 30₆ are energized to move the pin sections 32 . . . 32 of the operation devices 30₁, 30₃, 30₄, and 30₆ from the retracting position to the actuation position.

That is, first, as shown in FIG. 12, the pin section 32 of the third operation device 30₃ is rushed into an angle range R2 corresponding to the reference plane c of the end face cam 23 on the rear side of the second cam element section 20₂ present in the second position. In other words, the pin section 32 is rushed into an opposing position of the end face cam 23 at timing when the portion of the angle range R2 corresponding to the reference plane c is located below the pin section 32.

After the exhaust stroke of the second cylinder 1₂ shown in (a) of FIG. 13 ends, the lift start position e of the end face cam 23 on the rear side of the second cam element section 20₂ reaches the position of the pin section 32 of the third operation device 30₃. Thereafter, according to the rotation of the cam shaft 2, as shown in (b) of FIG. 13, the pin section 32 pushes the second cam element section 20₂ forward while being in slide contact with the lift sections d of the end face cam 23 and moves the second cam element section 20₂ to the first position.

When the movement of the second cam element section 20₂ to the first position is completed, as shown in (c) of FIG. 13, the slope section 50b of the first return cam 50 attached to the rear portion of the second cam element section 20₂ is located to be opposed to the pin section 32 of the third operation device 30₃. Thereafter, when the energization to the third operation device 30₃ is released, as shown in (d) of FIG. 13, according to the rotation of the cam shaft 2, the pin section 32 is forcibly pushed back to the retracting position while being in slide contact with the slope section 50b.

In a state in which the second cam element section 20₂ is present in the first position, in an angle range Q2 shown in FIG. 14, the first regulating section 50c of the first return cam 50 attached to the second cam element section 20₂ is disposed in a position opposed to the pin section 32 of the third operation device 30₃. Consequently, the movement of the pin section 32 of the third operation device 30₃ to the actuation position is regulated over the predetermined angle range Q2.

Subsequently, the first cam element section 20₁ is pushed rearward by the first operation device 30₁ and moves to the first position. Then, the pin section 32 of the first operation device 30₁ is pushed back to the retracting position by the first return cam 50 attached to the front portion of the first cam element section 20₁ present in the first position. The movement to the actuation position is regulated over the predetermined angle range.

Subsequently, the third cam element section 20₃ is pushed rearward by the fourth operation device 30₄ and moves to the first position. Then, the pin section 32 of the fourth operation device 30₄ is pushed back to the retracting position by the first return cam 50 attached to the front portion of the third cam element section 20₃ present in the first position. The movement to the actuation position is regulated over the predetermined angle range.

Subsequently, the fourth cam element section 20₄ is pushed forward by the sixth operation device 30₆ and moves to the first position. Then, the pin section 32 of the sixth operation device 30₆ is pushed back to the retracting position by the first return cam 50 attached to the rear portion of the fourth cam element section 20₄ present in the first position. The movement to the actuation position is regulated over the predetermined angle range.

Consequently, all of the first to fourth cam element sections 20₁ to 20₄ move from the second position to the first position. As shown in FIG. 1, in all of the first to fourth cam element sections 20₁ to 20₄, the first cam sections 22₁, 22₁ return to the state in which the first cam sections 22₁, 22₁ are located to correspond to the cam followers C′, C′ of the rocker arms C, C.

Moreover, in a state in which the cam element sections 20₁ to 20₄ move from the second position to the first position, the movement to the actuation position of the pin sections 32 . . . 32 of the first, third, fourth, and sixth operation devices 30₁, 30₃, 30₄, and 30₆ used for moving the cam element sections 20₁ to 20₄ from the second position to the first position is regulated over the predetermined angle range.

As explained above, according to the first embodiment, the second operation device 30₂ is disposed in the position between the first and second cylinders 1₁, 1₂ disposed adjacent to each other and continuous in ignition order. The first and second cam element sections 20₁, 20₂ can be moved in the separating direction (from the first position to the second position) by projecting the second operation device 30₂ when the first and second cam element sections 20₁, 20₂ are close to each other (present in the first position). Similarly, the fifth operation device 30₅ is disposed in the position between the third and fourth cylinders 1₃, 1₄ disposed adjacent to each other and continuous in ignition order. The third and fourth cam element sections 20₃, 20₄ can be moved in the separating direction (from the first position to the second position) by projecting the fifth operation device 30₅ when the third and fourth cam element sections 20₃, 20₄ are close to each other (present in the first position).

That is, cam element sections located close to each other can be separated and moved in the axial direction by disposing a single operation device in the position between two cylinders disposed adjacent to each other and continuous in ignition order. Therefore, it is possible to reduce the number of components of the operation device compared with when two operation devices are disposed in the position between cylinders.

The third and fourth operation devices 30₃, 30₄ are respectively disposed to correspond to the end face cams 23, 23 opposed to each other of the cam element sections 20₂, 20₃ of the second and third cylinders 1₂, 1₃ disposed to adjacent to each other and discontinuous in ignition order. The cam element sections 20₂, 20₃ can be respectively moved in the axial direction by respectively projecting the pin sections 32, 32 from the operation devices 30₃, 30₄ and engaging the pin sections 32, 32 with the end face cams 23, 23.

As shown in FIG. 15A, when a single operation device is disposed in the position between two cylinders disposed adjacent to each other and discontinuous in ignition order, timing when the pin section 32 can be projected is two divided narrow angle ranges R3, R3 in which the reference planes c, c of the both the opposed end face cams 23, 23 overlap. However, in this embodiment, as shown in FIG. 15B, dedicated operation devices (the third and fourth operation devices 30₃, 30₄) are respectively disposed in the end face cams 23, 23 opposed to each other between two cylinders (the second and third cylinders 1₂, 1₃) disposed to adjacent to each other and discontinuous in ignition order. Therefore, timing when the pin section 32 can be projected from the operation devices 30₃, 30₄ is not limited to the angle range in which the reference planes c, c of both the end face cams 23, 23 overlap and is the angle range R2 (see FIG. 12) of the reference planes c of the respective end face cams 23.

That is, by disposing two operation devices in the position between two cylinders disposed adjacent to each other and discontinuous in ignition order, the angle range in which the pin sections 32, 32 can be projected can be expanded compared with when the single operation device is disposed. Therefore, it is possible to properly move the pin sections 32, 32 and perform switching operation for the cam sections even during high-speed rotation of the engine without increasing projection speed of the pin section 32 by, for example, increasing the size of an actuator.

In the first embodiment, after the cam element sections 20₁ to 20₄ located to correspond to the pin section 32 moved to the actuation position are finished to be moved in the axial direction by the pin section 32, the pin section 32 can be pushed back to the retracting position by the first slope section 50b or the second slope section 51b provided in the cam element section. That is, while the cam shaft 2 rotates once, it is possible to surely move the pin sections 32 . . . 32 to the retracting position while surely performing the movement of the cam element sections 20₁ to 20₄.

Incidentally, when the cam element sections 20₁ to 20₄ are present in the first position, if the pin sections 32 . . . 32 of the first, third, fourth, and sixth operation devices 30₁, 30₃, 30₄, and 30₆ move to the actuation position, when the cam element sections 20₁ to 20₄ move to the second position, the pin sections 32 . . . 32 and the lift sections d . . . d of the end face cams 23 . . . 23 interfere with each other, leading to a switching failure of the cam sections. Similarly, when the cam element sections 20₁ to 20₄ are present in the second position, if the pin section 32, 32 of the second and fifth operation devices 30₂, 30₅ move to the actuation position, the pins 32, 32 interfere with the end face cams 23 . . . 23 of the cam element sections 20₁ to 20₄, which move to the first position, leading to a switching failure of the cam sections.

However, in the state in which the cam element sections 20₁ to 20₄ are present in the first position, the movement of the pin sections 32 . . . 32 of the first, third, fourth, and sixth operation devices 30₁, 30₃, 30₄, and 30₆ to the actuation position is regulated over the predetermined angle range by the first regulating section 50c formed to be contiguous to the first slope section 50b. Similarly, in the state in which the cam element sections 20₁ to 20₄ are present in the second position, the movement of the pin sections 32, 32 of the second and fifth operation devices 30₂, 30₅ to the actuation position is regulated over the predetermined angle range by the second regulating section 51c formed to be contiguous to the second slope section 51b.

That is, the movement of the pin sections 32 . . . 32 of the operation devices 30₁ to 30₆ to the actuation position due to a malfunction or the like is prevented. Consequently, interference of the pin sections 32 . . . 32 and the end face cams 23 . . . 23 of the cam element sections 20₁ to 20₄ is prevented. Therefore, it is possible to prevent occurrence of a switching failure of the cam sections and improve robustness of the valve system.

The second return cam 51 corresponding to the second operation device 30₂ disposed between the two cylinders 1₁, 1₂ disposed adjacent to each other and continuous in ignition order is provided only in the first cam element section 20₁ that moves later in moving order of the two cam element sections 20₁, 20₂ to be moved in the separating direction by the pin section 32 of the second operation device 30₂. Similarly, the second return cam 51 corresponding to the fifth operation device 30₅ disposed between the two cylinders 1₃, 1₄ disposed adjacent to each other and continuous in ignition order is provided only in the fourth cam element section 20₄ that moves later in moving order of the two cam element sections 20₃, 20₄ to be moved in the separating direction by the pin section 32 of the fifth operation device 30₅. Consequently, after the two sets of the cam element sections 20₁, 20₂ and 20₃, 20₄ disposed adjacent to each other are respectively properly moved in the separating direction, it is possible to push back the pin sections 32, 32 to the retracting position and prevent the movement of the pin sections 32, 32 to the actuation position over the predetermined angle range.

That is, with the valve system for the multi-cylinder engine according to the present invention, it is possible to easily perform the switching operation for the cams during high-speed rotation of the engine while reducing the number of components to attain compactness of the engine.

Second Embodiment

As in the first embodiment, the configuration on an exhaust side of a valve system of a four-cylinder four-valve DOHC engine is explained. The configurations of the first to fourth cam element sections 20₁ to 20₄ and the six operation devices 30₁ to 30₆ (the operation mechanism 30) of the electromagnetic type are different from the configurations in the first embodiment. The other configurations are the same.

FIG. 16 shows the configuration on the exhaust side of the valve system according to the second embodiment. The valve system includes the cam shaft 2 and the operation mechanism 30. The cam shaft 2 includes the shaft section 10 and the first to fourth cam element sections 20₁ to 20₄ spline-fit in the shaft section 10 and capable of rotating integrally with the shaft section 10 and moving in an axial direction. The operation mechanism 30 includes the six operation devices 30₁ to 30₆ of the electromagnetic type that move the cam element sections 20₁ to 20₄ along the shaft section 10.

The operation devices 30₁ to 30₆ include the main bodies 31 incorporating the electromagnetic actuators, the substantially cylindrical pin sections 32 (operation members) capable of projecting from the main bodies 31 during energization to the electromagnetic actuators, and return springs (not shown in the figure) that press and urge the pin sections 32 to main bodies 31 side. In a state in which the electromagnetic actuators are not energized, as indicated by a dotted line in FIG. 17, the pin sections 32 are retained in the upward retracting position by urging force of the return springs. On the other hand, when the electromagnetic actuators are energized, as indicated by a solid line in FIG. 17, the pin sections 32 project downward resisting the return springs and move to the actuation position.

As shown in FIG. 17, the operation devices 30₁ to 30₆ are disposed such that the pin section 32 is directed to the axis of the cam shaft 2 on the opposite side of the cam follower C′ in the rocker arm C across the cam shaft 2. In the case of this embodiment, the operation devices 30₁ to 30₆ are attached to, in the same direction, a cylinder head cover G that covers the cam shaft 2 from above.

Energization to the operation devices 30₁ to 30₆ is performed according to an energization instruction to the operation devices 30₁ to 30₆ by a not-shown computer in a predetermined engine rotation angle period on the basis of a detection signal from a not-shown engine rotation angle sensor.

As shown in FIG. 16, when all of the first to fourth cam element sections 20₁ to 20₄ are present in the first position, the first cam element section 20₁ is disposed in the rear, the second cam element section 20₂ is disposed in the front, the third cam element section 20₃ is disposed in the rear, and the fourth cam element section 20₄ is disposed in the front. Therefore, the opposed end faces of the first and second cam element sections 20₁, 20₂ are close to each other. The opposed end faces of the second and third cam element sections 20₂, 20₃ are separated from each other. The opposed end faces of the third and fourth cam element sections 20₃, 20₄ are close to each other.

As shown in FIG. 18, when all of the first to fourth cam element sections 20₁ to 20₄ are present in the second position, the first cam element section 20₁ is located in the front, the second cam element section 20₂ is located in the rear, the third cam element section 20₃ is located in the front, and the fourth cam element section 20₄ is located in the rear. Therefore, the opposed end faces of the first and second cam element sections 20₁, 20₂ are separated from each other. The opposed end faces of the second and third cam element sections 20₂, 20₃ are close to each other. The opposed end faces of the third and fourth cam element sections 20₃, 20₄ are separated from each other.

Next, the configuration of the cam element sections 20₁ to 20₄ is explained more in detail using the first cam element section 20₁ and the second cam element section 20₂ as an example with reference to FIG. 19 to FIG. 23B.

The cam element section 20₁ (20₂ to 20₄) is formed in a cylindrical shape. The outer circumferential surface in the intermediate section of the cam element section 20₁ is formed as the journal section 21 supported by the bearing section F. The actuating sections 22, 22 for the two exhaust valves A, A of the cylinder are provided on both the front and rear sides of the journal section 21. In the actuation sections 22, 22, as shown in FIG. 19, the first cam section 22₁ having a large lift amount for, for example, high-speed engine rotation time and the second cam section 22₂ having a small lift amount for, for example, low-speed engine rotation time are provided adjacent to each other.

As shown in FIG. 21B, the first cam section 22₁ and the second cam section 22₂ respectively include the nose sections b₁, b₂ having different lift amounts. The nose sections b₁, b₂ are provided on the common base circle a with a slight phase difference. The first cam section 22₁ and the second cam section 22₂ are respectively provided with order of arrangement in the front-rear direction and phases of the nose sections b₁, b₂ matched in the actuating sections 22, 22 in the two places. Note that the common base circle a means that base circle diameters of the base circles a of the first cam section 22₁ and the second cam section 22₂ are the same.

As shown in FIG. 16 and FIG. 18, in the first cam element section 20₁ and the third cam element section 20₃, the first cam section 22₁ is disposed in the front and the second cam section 22₂ is disposed in the rear. In the second cam element section 20₂ and the fourth cam element section 20₄, the second cam section 22₂ is disposed in the front and the first cam section 22₁ is disposed in the rear.

The cam element sections 20₁ to 20₄ are set such that, when the cam element sections 20₁ to 20₄ are positioned in the first position on the shaft section 10 by a detent mechanism (not shown in the figure), as shown in FIG. 16, in all of the cam element sections 20₁ to 20₄, the two first cam sections 22₁, 22₁ are located to correspond to the cam followers C′, C′ (see FIG. 17) of the two rocker arms C, C of the corresponding one of the cylinders 1₁ to 1₄, and, when the cam element sections 20₁ to 20₄ are positioned in the second position on the shaft section 10, as shown in FIG. 18, the second cam sections 22₂, 22₂ are located to correspond to the cam followers C′, C′.

In the engine according to this embodiment, ignition order of the cylinders is set as the third cylinder 1₃→the fourth cylinder 1₄→the second cylinder 1₂→the first cylinder 1₁. The first to fourth cam element sections 20₁ to 20₄ are spline-fit in the shaft section 10 with a phase difference of 90° from each other such that the nose sections b₁, b₂ of the first cam section 22₁ or the second cam section 22₂ of each of the cam element sections 20₁ to 20₄ press the cam followers C′, C′ of the cylinders in order according to the ignition order every time the cam shaft 2 rotates 90°.

Further, the end face cams 23, 23 are respectively provided at both front and rear end portions (both end portions in the axial direction) of each of the cam element sections 20₁ to 20₄.

Each of the end face cams 23, 23 at both the front and rear end portions includes, as shown in FIG. 20 to FIG. 22, a reference plane 23a formed along a surface orthogonal to the axis of the cam element section 20₁ (20₂ to 20₄) and lift sections 23b respectively projecting to the front or the rear in the axial direction from the reference plane 23a. As shown in FIGS. 21A-B and FIGS. 23A-B, the lift sections 23b are formed such that a lift amount in the axial direction from the reference plane 23a (lift amount zero) gradually increases in the predetermined angle range α (e.g., about 120°) from the lift start position e to the lift end position f. Specifically, the lift amount of the lift sections 23b is set to be larger on the forward side in a rotating direction X of the cam shaft 2 and return to zero in the lift end position f or a slope end position g explained below.

Further, as explained above, the cam element sections 20₁ to 20₄ are spline-fit in the shaft section 10 with the predetermined phase difference from each other according to the ignition order of the cylinders 1₁ to 1₄. Accordingly, the end face cams 23, 23 opposed to each other of the cam element sections 20₁ to 20₄ are also opposed having a phase difference from each other. In this embodiment, as indicated by signs Z1, Z2 in FIG. 16, in the two first and second cam element sections 20₁, 20₂ and the two third and fourth cam element sections 20₃, 20₄ adjacent to each other, the lift sections 23b, 23b of the end face cams 23, 23 opposed to each other are provided in phases different from each other. At least a part of the lift sections 23b, 23b overlap in the axial direction when the two cam element sections 20₁ to 20₄ are close to each other.

The pin section 32 of the second operation device 30₂ is a common operation member disposed between the end face cams 23, 23 opposed to each other of the cam element sections 20₁, 20₂ of the first cylinder 1₁ and the second cylinder 1₂ disposed adjacent to each other and continuous in ignition order. Similarly, the pin section 32 of the fifth operation device 30₅ is a common operation member disposed between the end face cams 23, 23 opposed to each other of the cam element sections 20₃, 20₄ of the third cylinder 1₃ and the fourth cylinder 1₄ disposed adjacent to each other and continuous in ignition order.

Specifically, the pin section 32 of the second operation device 30₂ or the fifth operation device 30₅ moves to the actuation position when the two cam element sections (20₁ and 20₂ or 20₃ and 20₄) corresponding to the pin section 32 are close to each other and projects between the end face cams 23, 23 opposed to each of both the cam element sections. The pin section 32 moved to the actuation position engages with the end face cams 23, 23 in order according to the rotation of the cam shaft 2 to thereby move the two cam element sections, which are close to each other, in a direction in which the two cam element sections are separated from each other.

Consequently, the first and second cam element sections 20₁, 20₂ move from the first position shown in FIG. 16 where the first and second cam element sections 20₁, 20₂ are close to each other to the second position shown in FIG. 18 where the first and second cam element sections 20₁, 20₂ are separated from each other. The third and fourth cam element sections 20₃, 20₄ also move from the first position shown in FIG. 16 where the third and fourth cam element sections 20₃, 20₄ are close to each other to the second position shown in FIG. 18 where the third and fourth cam element sections 20₃, 20₄ are separated from each other.

On the other hand, the pin sections 32 . . . 32 of the operation devices other than the second and fifth operation devices 30₂, 30₅, that is, the first, third, fourth, and sixth operation devices 30₁, 30₃, 30₄, and 30₆ are individual operation members respectively exclusively provided in the end face cams 23, 23 opposed each other of the cam element sections 20₂, 20₃ of the second cylinder 1₂ and the third cylinder 1₃ disposed adjacent to each other and discontinuous in ignition order, the end face cam 23 (the end face cam 23 on the front side of the cam element section 20₁) located at the front end portion of the cylinder row, and the end face cam 23 (the end face cam 23 on the rear side of the cam element section 20₄) located at the rear end portion of the cylinder row.

Specifically, in a state in which the first cam element section 20₁ is present in the second position closer to the front, the pin section 32 of the first operation device 30₁ moves to the actuation position opposed to the end face cam 23 on the front side of the first cam element section 20₁ in the axial direction and engages with the end face cam 23 according to the rotation of the cam shaft 2 to thereby move the first cam element section 20₁ to the first position closer to the rear as shown in FIG. 18. Similarly, in a state in which the third cam element section 20₃ is present in the second position closer to the front, the pin section 32 of the fourth operation device 30₄ moves to the actuation position opposed to the end face cam 23 on the front side of the third cam element section 20₃ in the axial direction and engages with the end face cam 23 according to the rotation of the cam shaft 2 to thereby move the third cam element section 20₃ to the first position closer to the rear.

In a state in which the second cam element section 20₂ is present in the second position closer to the rear, the pin section 32 of the third operation device 30₃ moves to the actuation position opposed to the end face cam 23 on the rear side of the second cam element section 20₂ in the axial direction and engages with the end face cam 23 to thereby move the second cam element section 20₂ to the first position closer to the front. Similarly, in a state in which the fourth cam element section 20₄ is present in the second position closer to the rear, the pin section 32 of the sixth operation device 30₆ moves to the actuation position opposed to the end face cam 23 on the rear side of the fourth cam element section 20₄ in the axial direction and engages with the end face cam 23 to thereby move the fourth cam element section 20₄ to the first position closer to the front.

The movement (the projection) of the pin sections 32 of the operation devices 30₁ to 30₆ is performed at timing explained below. That is, the projection of the pin sections 32 (the individual operation members) in the first and fourth operation devices 30₁, 30₄ is performed at timing when the reference planes 23a of the end face cams 23 on the front side of the first and third cam element sections 20₁, 20₃ overlap projecting positions of the pin sections 32 (overlap the pin sections 32 after the projection in axial direction view). Similarly, the projection of the pin sections 32 (the individual operation members) in the third and sixth operation devices 30₃, 30₆ is performed at timing when the reference planes 23a of the end face cams 23 on the rear side of the second and fourth cam element sections 20₂, 20₄ overlap the projecting positions of the pin section 32.

On the other hand, the projection of the pin section 32 (the common operation member) in the second operation device 30₂ is performed at timing when both the reference planes 23a, 23a of the two end face cams 23, 23 opposed to each other of the first and second cam element sections 20₁, 20₂ overlap a projecting position of the pin section 32. Similarly, the projection of the pin section 32 (the common operation member) in the fifth operation device 30₅ is performed at timing when both the reference planes 23a, 23a of the two end face cams 23, 23 opposed to each other of the third and fourth cam element sections 20₃, 20₄ overlap the projecting position of the pin section 32.

The movement of the cam element sections 20₁ to 20₄ involved in the movement (the projection) of the pin sections 32 to the actuation position has to be performed at timing when the cam follower C′ of the rocker arm C is in contact with the base circle a of the first cam section 22₁ or the second cam section 22₂, that is, when the cylinder is in a stroke other than the exhaust stroke.

Therefore, in order to satisfy these conditions of actuation timing, in this embodiment, as shown in FIGS. 21A-B and FIGS. 23A-B, the lift start position (the start position of the lift sections 23b) e of the end face cam 23 is set in a position overlapping the nose sections b₁, b₂ of the first and second cam sections 22₁, 22₂ or a position in the vicinity on the forward side in the rotating direction X of the nose sections b₁, b₂. The lift end position (the end position of the lift sections 23b) f of the end face cam 23 is set in a position at the predetermined angle α on the backward side in the rotating direction X from the lift start position e. The lift sections 23b of the end face cam 23 are formed such that the angle α from the lift start position e of the end face cam 23 to the lift end position f of the end face cam 23 on the backward side in the rotating direction X is smaller than 180 degrees. In this case, according to a positional relation between the cam follower C′ of the rocker arm C and the pin sections 32 of the operation devices 30₁ to 30₆ shown in FIG. 17, the cam element sections 20₁ to 20₄ move immediately after the end of the exhaust stroke.

However, even if the nose sections b₁, b₂ of the first and second cam sections 22₁, 22₂ and the lift sections 23b of the end face cam 23 are provided in the positional relation explained above, when the pin sections 32 of the operation devices 30₁ to 30₆ project at unintended timing because of an actuation failure or the like, it is likely that the pin sections 32 and the lift sections 23b engage carelessly. Therefore, in this embodiment, slope sections 23c for forcibly retracing (pushing back) the pin sections 32, which move to the actuation position, to the retracting position are integrally provided in the end face cams 23 of the cam element sections 20₁ to 20₄.

Places where the slop sections 23c should actually be provided change according to conditions such as order of switching of the cam sections 22 of the cam element sections 20₁ to 20₄ and the number of arranged operation devices 30. In this embodiment, the slope sections 23c are respectively provided at both the front and rear ends of the first cam element section 20₁, the rear end of the second cam element section 20₂, the front end of the third cam element section 20₃, and both the front and rear ends of the fourth cam element section 20₄. On the other hand, the slope sections 23c are not provided at the front end of the second cam element section 20₂ and the rear end of the third cam element section 20₃.

That is, in the case of this embodiment, according to the ignition order, the cam element sections 20₁ to 20₄ are moved in the order of the third cylinder 1₃→the fourth cylinder 1₄→the second cylinder 1₂→the first cylinder 1₁ to switch a cam section that opens and closes the exhaust valves A of the cylinders 1₁ to 1₄. Therefore, the first cam element section 20₁ is later in moving order of the first cam element section 20₁ and the second cam element section 20₂ moved in the separating direction by the pin section 32 (the common operation member) of the second operation device 30₂. The fourth cam element 20₄ is later in moving order of the third cam element section 20₃ and the fourth cam element section 20₄ moved in the separating direction by the pin section 32 (the common operation member) of the fifth operation device 30₅. Therefore, the slope section 23c that pushes back the pin sections 32 of the second operation device 30₂ is provided only at the rear end of the first cam element section 20₁ that is later in the moving order. The slope section 23c is not provided at the front end of the second cam element section 20₂ that is earlier in the moving order. The slope section 23c that pushes back the pin section 32 of the fifth operation device 30₅ is provided only at the front end of the fourth cam element section 20₄ that is later in the moving order. The slope section 23c is not provided at the rear end of the third cam element section 20₃ that is earlier in the moving order.

As shown in FIGS. 20 to 23B, the slope section 23c is formed to further project in the axial direction than the lift section 23b on the end face of the end face cam 23. The slope section 23c is provided over a predetermined angle range further on a rotation delay side (the opposite direction of the arrow X) than the lift end position f of the end face cam 23, more specifically, an angle range from the lift end position (a slope start position) f to the slope end position g. The external circumferential surface of the slope section 23c is formed as a cam surface, a lift amount (a radius) of which in the radial direction gradually increases toward the rotation delay side. The lift amount of the cam surface is set such that the cam surface in the slope start position f is slightly lower than the distal end portion of the pin section 32 present in the actuation position and the cam surface in the slope end position g is slightly lower than the distal end portion of the pin section 32 present in the retracting position.

The slope section 23c having the cam surface of such a shape can retract the pin section 32 from the actuation position to the retracting position by coming into slide contact with the distal end portion of the pin section 32 after the movement of the cam element sections 20₁ to 20₄ by the lift section 23b ends. Note that, as explained above, the cam surface in the slope end position g is lower than the distal end portion of the pin section 32 present in the retracting position. However, the pin section 32 is pushed back to the retracting position away from the cam surface by inertial force applied to the pin section 32 in the period from the slope start position f to the slope end position g and the magnetic force of the electromagnetic actuator.

Further, reverse-rotation-time return slope sections 23d for forcibly pushing back the pin sections 32, which move to the actuation position, to the retracting position when the cam shaft 2 reversely rotates are integrally provided on the end face cams 23 of the cam element sections 20₁ to 20₄.

The reverse-rotation-time return slope sections 23d are provided together with the slope sections 23c on the end face cams 23 on which the slope sections 23c are provided among the end face cams 23, 23 at both the ends of the cam element sections 20₁ to 20₄. In the case of this embodiment, the reverse-rotation-time return slope sections 23d are respectively provided at both the front and rear ends of the first cam element section 20₁, the rear end of the second cam element section 20₂, the front end of the third cam element section 20₃, and both the front and rear ends of the fourth cam element section 20₄.

The slope sections 23c and the reverse-rotation-time return slope sections 23d are provided such that, when the adjacent cam element sections are close to each other, the end face cams 23, 23 opposed to each other, in particular, the slope sections 23c and the reverse-rotation-time return slope sections 23d of the end face cams 23 and the lift sections 23b of the other end face cams 23 opposed to the end face cams 23 do not interfere with each other.

Next, the operation of the valve system in the second embodiment is explained.

First, as shown in FIG. 16, for example, when the first to fourth cam element sections 20₁ to 20₄ are present in the first position during high-speed rotation of the engine, in all of the cam element sections 20₁ to 20₄, the first cam sections 22₁, 22₁ having a large lift amount in the actuating sections 22, 22 at both the ends are located to correspond to the cam followers C′, C′ of the rocker arms C, C. According to the rotation of the cam shaft 2, in the ignition order explained above, the exhaust valves A . . . A of the cylinders 1₁ to 1₄ open at a relatively large valve opening amount during the exhaust stroke.

From this state, for example, when the cam section is switched to decrease the valve opening amount of the exhaust valves A . . . A according to a decrease in engine speed, the second and fifth operation devices 30₂, 30₅ are energized to move the respective pin sections 32, 32 from the retracting position to the actuation position.

That is, first, the pin section 32 of the fifth operation device 30₅ rushes into between the opposed end face cams 23, 23 of the third and fourth cam element members 20₃, 20₄ present in the first position and in a state in which the end face cams 23, 23 are close to each other. The pin section 32 engages with the end face cams 23, 23. At this point, the pin section 32 is rushes into an angle range in which the reference planes 23a, 23a, a lift amount of which is zero, in the end face cams 23, 23 of the third and fourth cam element sections 20₃, 20₄ are opposed to each other. In other words, the pin section 32 is rushed into between the end face cams 23, 23 at timing when the portion of the angle range in which the reference planes 23a, 23a are opposed to each other is located below the pin section 32.

After the exhaust stroke of the third cylinder 1₃ ends, the lift start position e of the end face cam 23 on the rear side of the third cam element section 20₃ reaches the position of the pin section 32 of the fifth operation device 30₅. Thereafter, according to the rotation of the cam shaft 2, the pin section 32 pushes the third cam element section 20₃ forward while being in slide contact with the lift sections 23b of the end face cam 23 and moves the third cam element section 20₃ to the second position.

After the lift start position e of the end face cam 23 of the third cam element section 20₃ reaches the position of the pin section 32, when the cam shaft 2 rotates 90° and the exhaust stroke of the fourth cylinder 1₄ ends, subsequently, the lift start position e of the end face cam 23 on the rear side of the fourth cam element section 20₄ reaches the position of the pin section 32. Thereafter, according to the rotation of the cam shaft 2, the pin section 32 pushes the fourth cam element section 20₄ rearward while being in slide contact with the lift sections 23b of the end face cam 23 and moves the fourth cam element section 20₄ to the second position.

Thereafter, the energization to the electromagnetic actuator of the fifth operation device 30₅ is stopped, the distal end face of the pin section 32 is pushed up while being in slide contact with the cam surface of the slope section 23c, and the pin section 32 is forcibly pushed back to the retracting position. Thereafter, the pin section 32 is retained in the retracting position by urging force of the return spring.

Subsequently, the pin section 32 of the second operation device 30₂ rushes into between the opposed end face cams 23, 23 of the first and second cam element sections 20₁, 20₂ present in the first position and in a state in which the end face cams 23, 23 are close to each other. The pin section 32 engages with the end face cams 23, 23. At this point, the pin section 32 is rushes into an angle range in which the reference planes 23a, 23a, a lift amount of which is zero, in the end face cams 23, 23 of the first and second cam element sections 20₁, 20₂ are opposed to each other.

After the exhaust stroke of the second cylinder 1₂ ends, the lift start position e of the end face cam 23 on the front side of the second cam element section 20₂ reaches the position of the pin section 32 of the second operation device 30₂. Thereafter, according to the rotation of the cam shaft 2, the pin section 32 pushes the second cam element section 20₂ rearward while being in slide contact with the lift sections 23b of the end face cam 23 and moves the second cam element section 20₂ to the second position.

After the lift start position e of the end face cam 23 of the second cam element section 20₂ reaches the position of the pin section 32, when the cam shaft 2 rotates 90° and the exhaust stroke of the first cylinder 1₁ ends, subsequently, the lift start position e of the end face cam 23 on the front side of the first cam element section 20₁ reaches the position of the pin section 32. Thereafter, according to the rotation of the cam shaft 2, the pin section 32 pushes the first cam element section 20₁ forward while being in slide contact with the lift sections 23b of the end face cam 23 and moves the first cam element section 20₁ to the second position.

Further, the energization to the electromagnetic actuator of the second operation device 30₂ is stopped, the distal end face of the pin section 32 is pushed up while being in slide contact with the cam surface of the slope section 23c, and the pin section 32 is forcibly pushed back to the retracting position. Thereafter, the pin section 32 is retained in the retracting position by urging force of the return spring.

Consequently, all of the first to fourth cam element sections 20₁ to 20₄ move from the first position to the second position. As shown in FIG. 18, in all of the first to fourth cam element sections 20₁ to 20₄, the second cam sections 22₂, 22₂ are located to correspond to the cam followers C′, C′ of the rocker arms C, C and the exhaust valves A . . . A of the cylinders 1₁ to 1₄ open at a relatively small valve opening amount during the exhaust stroke.

On the other hand, when a state in which the second cam sections 22₂ . . . 22₂ having a small lift amount of the cam element sections 20₁ to 20₄ shown in FIG. 18 are located to correspond to the cam followers C′, C′ of the rocker arms C . . . C is switched to, according to, for example, an increase in engine speed, a state in which the first cam sections 22₁ . . . 22₁ having a large lift amount shown in FIG. 16 are located to correspond to the cam followers C′, C′, the first, third, fourth, and sixth operation devices 30₁, 30₃, 30₄, and 30₆ are energized to move the pin sections 32 . . . 32 of the operation devices 30₁, 30₃, 30₄, and 30₆ from the retracting position to the actuation position.

That is, first, the pin section 32 of the fourth operation device 30₄ is rushed into an angle range corresponding to the reference plane 23a of the end face cam 23 on the front side of the third cam element section 20₃. In other words, the pin section 32 is rushed into an opposing position of the end face cam 23 at timing when the portion of the angle range corresponding to the reference plane 23a is located below the pin section 32.

After the exhaust stroke of the third cylinder 1₃ ends, the lift start position e of the end face cam 23 on the rear side of the third cam element section 20₃ reaches the position of the rushed-in pin section 32 of the fourth operation device 30₄. Thereafter, according to the rotation of the cam shaft 2, the pin section 32 pushes the third cam element section 20₃ rearward while being in slide contact with the lift sections 23b of the end face cam 23 and moves the third cam element section 20₃ to the first position.

After the lift start position e of the end face cam 23 of the third cam element section 20₃ reaches the position of the pin section 32 of the fourth operation device 30₄, when the cam shaft 2 rotates 90° and the exhaust stroke of the third cylinder 1₃ ends, subsequently, the pin section 32 of the sixth operation device 30₆ is rushed into an angle range corresponding to the reference plane 23a of the end face cam 23 on the rear side of the fourth cam element section 20₄ present in the second position and engages with the end face cam 23.

After the exhaust stroke of the fourth cylinder 1₄ ends, the lift start position e of the end face cam 23 on the rear side of the fourth cam element section 20₄ reaches the position of the rushed-in pin section 32 of the sixth operation device 30₆. Thereafter, according to the rotation of the cam shaft 2, the pin section 32 pushes the fourth cam element section 20₄ forward while being in slide contact with the lift sections 23b of the end face cam 23 and moves the fourth cam element section 20₄ to the first position.

Thereafter, when the slope section 23c of the end face cam 23 of the fourth cam element section 20₄ is absent below the pin section 32 of the fifth operation device 30₅, the pin section 32 is capable of moving in the actuation position.

Subsequently, the pin section 32 of the third operation device 30₃ is rushed into an angle range corresponding to the reference plane 23a of the end face cam 23 on the rear side of the second cam element section 20₂ present in the second position. According to the rotation of the cam shaft 2, the pin section 32 pushes the second cam element section 20₂ forward while being in slide contact with the lift sections 23b of the end face cam 23 and moves the second cam element section 20₂ to the first position.

Substantially in parallel to the movement of the second cam element section 20₂, the pin section 32 of the first operation device 30₁ is rushed into an angle range corresponding to the reference plane 23a of the end face cam 23 on the front side of the first cam element section 20₁ present in the second position.

Further, after the lift start position e of the end face cam 23 of the second cam element section 20₂ reaches the position of the pin section 32 of the third operation device 30₃, when the cam shaft 2 rotates 90° and the exhaust stroke of the first cylinder 1₁ ends, the lift start position e of the end face cam 23 on the front side of the first cam element section 20₁ reaches the position of the pin section 32 of the first operation device 30₁. Then, according to the rotation of the cam shaft 2, the pin section 32 pushes the first cam element section 20₁ rearward while being in slide contact with the lift section 23b of the end face cam 23 and moves the first cam element section 20₁ to the first position.

Consequently, all of the first to fourth cam element sections 20₁ to 20₄ move from the second position to the first position. As shown in FIG. 16, in all of the first to fourth cam element sections 20₁ to 20₄, the first cam sections 22₁ . . . 22₁ return to the state in which the first cam sections 22₁ . . . 22₁ are located to correspond to the cam followers C′, C′ of the rocker arms C, C.

As explained above, according to the second embodiment, the four cam element sections 20₁ to 20₄ respectively provided in the four cylinders 1₁ to 1₄ are operated by the six operation devices 30₁ to 30₆. The cam section 22 that opens and closes the exhaust valves A . . . A is switched between the first cam sections 22₁ . . . 22₁ having a large lift amount and the second cam sections 22₂ . . . 22₂ having a small lift amount.

According to the second embodiment, the cam element sections 20₁ to 20₄ include the slope sections 23c formed over the predetermined angle range from the lift end position f of the lift sections 23b of the end face cams 23, with which the pin sections 32 engage, toward the rotation delay side. The slope sections 23c push back the pin sections 32 from the actuation position to the retracting position by coming into slide contact with the pin sections 32 after the movement by the end face cams 23 ends. Therefore, it is possible to surely push back, with the slope sections 23c, the pin sections 32 present in the actuation position toward the retracting position. Moreover, the slope sections 23c act after the movement of the cam element sections 20₁ to 20₄ by the pin section 32 ends. Therefore, it is possible to quickly push back the pin sections 32 to the retracting position while surely performing the movement of the cam element sections 20₁ to 20₄. Consequently, even when the cam is continuously switched, it is possible to instantaneously continuously perform the switching operation for the cam sections 22₁, 22₂.

Further, according to the second embodiment, in the two cam element sections adjacent to each other, the lift sections 23b, 23b of the end face cams 23, 23 opposed to each other are provided to be in different phases from each other. When the lift sections 23b, 23b are close to each other, at least a part of the lift sections 23b, 23b overlap in the axial direction. Therefore, it is possible to attain compactness in the axial direction of the cam shaft 2 and compactness of the engine.

Note that the above explanation is explanation concerning the cam shaft on the exhaust side. However, a cam shaft on the intake side can also be configured completely the same. Consequently, the action and effects explained above are obtained concerning an intake side as well.

In the embodiments, in the cam element sections 20₁ to 20₄, the lift amount of the first cam section 22₁ and the lift amount of the second cam section 22₂ are set different. However, it is also possible to provide a normal nose section in one cam section and form the entire other cam section only with a base circle without providing a nose section (set the lift amount of the nose section to zero). In this case, it is possible to stop opening and closing of a valve using the other cam section. Such valve stop operation is suitable, for example, when reduced cylinder operation is performed using low-load of the engine.

In the embodiments, the example is explained in which the present invention is applied to the four-cylinder four-valve DOHC engine. However, not only this, but the present invention is applicable to various multi-cylinder engines including at least a pair of cylinders disposed adjacent to each other and continuous in ignition order and at least a pair of cylinders disposed adjacent to each other and discontinuous in ignition order.

For example, in an in-line five-cylinder engine, when ignition order is the order of a first cylinder, a second cylinder, a fourth cylinder, a fifth cylinder, and a third cylinder, a pair of cylinders disposed adjacent to each other and continuous in ignition order is two sets of the first and second cylinders and the four and fifth cylinders. A pair of cylinders disposed adjacent to each other and discontinuous in ignition order is two sets of the second and third cylinders and the third and fourth cylinders.

Note that the present invention is not limited to those explained in the embodiments various modifications and alternations are also possible without departing from the spirit and the scope of the present invention described in claims.

Finally, the characteristic configurations disclosed in the embodiments and action and effects based on the characteristic configurations are collectively explained.

The embodiments relate to a valve system provided in a multi-cylinder engine including at least a pair of cylinders disposed adjacent to each other and discontinuous in ignition order and at least a pair of cylinders disposed adjacent to each other and continuous in ignition order. The valve system includes: a cam shaft including a shaft section extending in a cylinder row direction and a plurality of cam element sections provided respectively in the cylinders and fit in the shaft section to be capable of rotating integrally with the shaft section and moving in an axial direction; and an operation mechanism that moves the plurality of cam element sections in the axial direction with respect to the shaft section. Each of the cam element sections includes, for each one valve of the cylinders, two cam sections which include a common base circle, have differently shaped nose sections, and are adjacent to each other in the axial direction. End face cams are respectively provided at both end portions in the axial direction of each of the cam element sections. The operation mechanism includes a plurality of operation members driven by an actuator to be movable between an actuation position where the operation members rush into positions opposed to the end face cams of the plurality of cam element sections in the axial direction and a retracting position where the operation members retract from opposing positions of the end face cams, wherein the operation mechanism engages the operation members, which have moved to the actuation position, with the end face cams and moves the cam element sections in the axial direction to thereby switch the cam section that opens and closes valves of the cylinders. The plurality of operation members include: a common operation member that is provided in common between the end face cams opposed to each other of the cam element sections of two cylinders disposed adjacent to each other and continuous in ignition order and that engages with the respective end face cams when both the cam element sections are close to each other; and individual operation members that are individually provided for the end face cams opposed to each other of the cam element sections of two cylinders disposed adjacent to each other and discontinuous in ignition order and the end face cams located at opposite ends of the cylinder row and that engage with the respective end face cams.

The “cam section” includes a cam section, the shape of a nose section of which coincides with the base circle (a lift amount of which is zero).

With this configuration, a single operation member (the common operation member) is disposed in the position between two cylinders disposed to be adjacent to each other and continuous in ignition order and, when cam element sections corresponding to the two cylinders are close to each other, the operation member is rushed into between end face cams opposed to each other, whereby it is possible to move the cam element sections in the axial direction to be separated from each other. That is, the cam element sections corresponding to the cylinders disposed adjacent to each other and continuous in ignition order can be moved by the single operation member. Therefore, compared with when an operation member is provided for each of end face cams, it is possible to reduce the number of components.

Operation members (individual operation members) are provided for each of end face cams opposed to each other of cam element sections of two cylinders disposed adjacent to each other and discontinuous in ignition order and the operation members are rushed into the end face cams respectively corresponding to the operation members and engaged with the end face cams, whereby it is possible to independently move the cam element sections in the axial direction. Consequently, compared with when cam element sections corresponding to cylinders disposed adjacent to each other and discontinuous in ignition order are moved by a single operation member, it is possible to expand a period in which the operation members can be projected. As a result, even during high-speed rotation of the engine, it is possible to sufficiently secure the period in which the operation members can be projected. Therefore, it is possible to properly perform switching operation for the cam sections without increasing projection speed of the operation members by, for example, increasing the size of an actuator that drives the operation members.

In the valve system, preferably, the multi-cylinder engine is an in-line four-cylinder engine, and the ignition order is set in the order of a third cylinder, a fourth cylinder, a second cylinder, and a first cylinder.

The ignition order is not limited to the case in which ignition is started from the first cylinder and includes the case in which ignition is started from any one cylinder among the second to fourth cylinders.

With this configuration, common operation members are respectively disposed in positions between the first and second cylinders disposed adjacent to each other and continuous in ignition order and between the third and fourth cylinders and individual operation members are respectively disposed in inter-cylinder positions other than the positions and end portion positions of a cylinder row, whereby it is possible to configure the valve system with six operation members. That is, compared with when operation members are provided for each of the end face cams (in this case, eight operation members are necessary), it is possible to reduce the number of operation members.

With the disposition pattern explained above, the individual operation members are disposed for each of the opposed end face cams between the second and third cylinders disposed adjacent to each other and discontinuous in ignition order. Therefore, it is possible to expand the period in which the operation members can be projected. Therefore, even during high-speed rotation of the engine, it is possible to properly perform the switching operation for the cam sections.

In the valve system, preferably, the cam element section includes a slope section that comes into slide contact with the operation member located in the actuation position and pushes back the operation member to the retracting position after the movement of the cam element section in the axial direction by the operation member ends. The slope section corresponding to the common operation member is provided only in the cam element section that moves later in moving order of the two cam element sections to be moved in a separating direction by the common operation member.

With this configuration, the operation member present in the actuation position can be forcibly pushed back to the retracting position by the slop section provided in the cam element section after the movement of the cam element section in the axial direction by the operation member ends. That is, after the movement of the cam element section is surely performed, it is possible to surely move the operation member to the retracting position. Consequently, even when the switching operation for the cam sections is continuously performed, it is possible to surely prevent interference of the operation member and the cam element section. Therefore, it is possible to continuously perform the switching operation for the cam sections.

In particular, for the common operation member disposed between the two cylinders disposed adjacent to each other and continuous in ignition order, the slope section is provided only in the cam element section that moves later in moving order of the two cam element sections to be moved in the separating direction by the common operation member. Therefore, after both the cam element sections adjacent to each other are respectively properly moved in the separating direction, it is possible to push back the common operation member to the retracting position.

In the valve system, preferably, the cam element section includes: a slope section that comes into slide contact with the operation member located in the actuation position and pushes back the operation member to the retracting position after the movement of the cam element section in the axial direction by the operation member ends; and a regulating section that is formed to be contiguous to the slope section and regulates movement of the operation member, which has been pushed back to the retracting position, to the actuation position. The slope section and the regulating section corresponding to the common operation member are provided only in the cam element section that moves later in moving order of the two cam element sections to be moved in the separating direction by the common operation member.

With this configuration, the movement of the operation member to the actuation position can be prevented by the regulating section formed to be contiguous to the slope section. Therefore, it is possible to prevent the operation member present in the retracting position from moving to the actuation position because of, for example, a malfunction of the actuator. Consequently, it is possible to prevent interference of the operation member and the cam element section and improve robustness of the valve system.

For the common operation member disposed between the two cylinders disposed adjacent to each other and continuous in ignition order, the slope section and the regulating section are provided only in the cam element section that moves later in moving order of the two cam element sections to be moved in the separating direction by the common operation member. Therefore, after the both the cam element sections adjacent to each other are respectively properly moved in the separating direction, it is possible to properly push the common operation member to the retracting position and prevent movement of the common operation member to the actuation position.

INDUSTRIAL APPLICABILITY

As explained above, according to the present invention, in the valve system for the multi-cylinder engine, it is possible to easily perform switching operation for the cams during high-speed rotation of the engine while reducing the number of components to attain compactness of the engine. Therefore, there is possibility that the present invention is suitably used in the technical field of manufacturing of the engine of this type.

Claims

1. A valve system provided in a multi-cylinder engine including at least a pair of cylinders disposed adjacent to each other and discontinuous in ignition order and at least a pair of cylinders disposed adjacent to each other and continuous in ignition order, the valve system comprising:a cam shaft including a shaft section extending in a cylinder row direction and a plurality of cam element sections provided respectively in the cylinders and fit in the shaft section to be capable of rotating integrally with the shaft section and moving in an axial direction; andan operation mechanism that moves the plurality of cam element sections in the axial direction with respect to the shaft section, whereineach of the cam element sections includes, for each one valve of the cylinders, two cam sections which include a common base circle, have differently shaped nose sections and are adjacent to each other in the axial direction,end face cams are respectively provided at both end portions in the axial direction of each of the cam element sections,the operation mechanism includes a plurality of operation members driven by an actuator to be movable between an actuation position where the operation members rush into positions opposed to the end face cams of the plurality of cam element sections in the axial direction and a retracting position where the operation members retract from opposing positions of the end face cams, the operation mechanism engaging the operation members, which have moved to the actuation position, with the end face cams and moving the cam element sections in the axial direction to thereby switch the cam section that opens and closes valves of the cylinders,the plurality of operation members include: a common operation member that is provided in common between the end face cams opposed to each other of the cam element sections of two cylinders disposed adjacent to each other and continuous in ignition order and that engages with the respective end face cams when both the cam element sections are close to each other; andindividual operation members that are individually provided for the end face cams opposed to each other of the cam element sections of two cylinders disposed adjacent to each other and discontinuous in ignition order and the end face cams located at opposite ends of the cylinder row and that engage with the respective end face cams.

2. The valve system for a multi-cylinder engine according to claim 1, wherein the multi-cylinder engine is an in-line four-cylinder engine, andthe ignition order is set in order of a third cylinder, a fourth cylinder, a second cylinder, and a first cylinder.

3. The valve system for a multi-cylinder engine according to claim 1, wherein the cam element section includes a slope section that comes into slide contact with the operation member located in the actuation position and pushes back the operation member to the retracting position after the movement of the cam element section in the axial direction by the operation member ends, andthe slope section corresponding to the common operation member is provided only in the cam element section that moves later in moving order of the two cam element sections to be moved in a separating direction by the common operation member.

4. The valve system for a multi-cylinder engine according to claim 1, wherein the cam element section includes: a slope section that comes into slide contact with the operation member located in the actuation position and pushes back the operation member to the retracting position after the movement of the cam element section in the axial direction by the operation member ends; and a regulating section that is formed to be contiguous to the slope section and regulates movement of the operation member, which has been pushed back to the retracting position, to the actuation position, andthe slope section and the regulating section corresponding to the common operation member are provided only in the cam element section that moves later in moving order of the two cam element sections to be moved in the separating direction by the common operation member.