OSCILLATING CAM AND DYNAMIC VALVE MECHANISM OF INTERNAL COMBUSTION ENGINE

Abstract

 A rocking cam includes a cam surface having a base circle portion and a lift portion, and is disposed so as to make reciprocating motion, in which a width of a contact surface of the base circle portion is formed smaller than a width of a contact surface of the lift portion.

Description

Technical Field

[0001] The present invention relates to a rocking cam, which includes a cam surface having a base circle portion and a lift portion, and which is disposed so as to make reciprocating motion, and relates to a valve mechanism for an internal combustion engine, which is provided with the rocking cam.

Related Art

[0002] Conventionally, this type of valve mechanism for an internal combustion engine has: a camshaft rotated by a crankshaft; a rotating cam provided to the camshaft; a rocking cam rocked by the rotating cam for reciprocating motion; and a rocker arm partly coming into contact with a cam surface of the rocking cam. When the rocking cam is rocked, the cam surface thereof allows the rocker arm to be rocked. This motion by the rocker arm presses an intake or exhaust valve to open/close the valve (See Patent Document 1).
Patent Document 1: JP-A-H7-063023

Disclosure of the Invention

Problem to be Solved by the Invention

[0003] However, in such a conventional valve mechanism that the cam surface of the rocking cam has a base circle portion, a lift portion and a ramp portion for connecting therebetween, the cam surface requires a certain width to secure strength enough to withstand a large force acting on the cam surface. This results in an increase in weight of the rocking cam on its distal end side, causing an increase in inertia force of the rocking cam which makes reciprocating motion. Accordingly, other parts associated with the rocking cam also need to secure certain strength, causing increases in weight of the parts as well as in size of the entire system. This creates additional problem with an increase in wear and the like on a contact portion of the rocking cam.

[0004] In the view of the above, the present invention has been made in order to solve the above-mentioned problems of the prior art. Accordingly, it is an object of the present invention to provide a rocking cam and a valve mechanism for an internal combustion engine, which can achieve reductions in size and weight as well as in wear and the like on a contact portion of the rocking cam.

Means for Solving the Problem

[0005] In order to attain the above object, the invention as described in Claim 1 provides a rocking cam including a cam surface having a base circle portion and a lift portion, and disposed so as to make reciprocating motion, in which a width of a contact surface of the base circle portion is formed smaller than a width of a contact surface of the lift portion.

[0006] The invention as described in Claim 2 provides a valve mechanism for an internal combustion engine, having: a camshaft rotated by a crankshaft of the internal combustion engine; a rotating cam provided to the camshaft; a rocking shaft provided in parallel to the camshaft; and a rocking cam supported with the rocking shaft and freely rockable by the rotating cam and capable of varying a lift amount of an intake valve or an exhaust valve of the internal combustion engine, in which the rocking cam includes a cam surface having a base circle portion and a lift portion, and is disposed so as to make reciprocating motion, and a width of a contact surface of the base circle portion is formed smaller than a width of a contact surface of the lift portion.

[0007] The invention as described in Claim 3 provides the valve mechanism for an internal combustion engine according to Claim 2, in which the rocking cam is provided with a movable rotating cam abutment portion that comes into contact with the rotating cam to transmit a drive force from the rotating cam to the rocking cam, and provided with a guide portion for guiding the rotating cam abutment portion in a certain direction; the drive force from the rotating cam is inputted to the guide portion via the rotating cam abutment portion so that the rocking cam is rocked; a variable abutment portion mechanism is provided for making a relative distance between the rotating cam abutment portion and a center axis of the rocking shaft variable by making the rotating cam abutment portion movable along the guide portion; and a lift amount of each valve is made variable by thus making the relative distance variable.

Effect of the Invention

[0008] According to the invention as described in Claim 1, the rocking cam includes the cam surface having the base circle portion and the lift portion, and is disposed so as to make reciprocating motion, in which the width of the contact surface of the base circle portion is formed smaller than the width of the contact surface of the lift portion. Therefore, weight of the rocking cam can be reduced. This results in a reduction in inertia force of the rocking cam at the time of rocking movement, as well as in a reduction in weight of parts associated with the rocking cam.

[0009] According to the invention as described in Claims 2 and 3, the valve mechanism for an internal combustion engine, which is capable of changing the lift amount of the intake valve or the exhaust valve of the internal combustion engine, is provided with the rocking cam having the base circle portion and the lift portion, with the width of the contact surface of the base circle portion being formed smaller than the width of the contact surface of the lift portion. This allows this variable valve mechanism to provide the above-mentioned effects.

Brief Description of the Drawings

[0010] 

FIG. 1 is a longitudinal sectional view of the main portion of the variable valve mechanism for the internal combustion engine according to Embodiment 1 of the present invention when the maximum lift amount is required, illustrating the state in which the intake valve is closed.

FIG. 2 is a longitudinal sectional view of the main portion of the variable valve mechanism for the internal combustion engine according to Embodiment 1 of the present invention when the maximum lift amount is required, illustrating the state in which the intake valve is open.

FIG. 3 is a longitudinal sectional view of the main portion of the variable valve mechanism for the internal combustion engine according to Embodiment 1 of the present invention when the minimum lift amount is required, illustrating the state in which the intake valve is closed.

FIG. 4 is a longitudinal sectional view of the main portion of the variable valve mechanism for the internal combustion engine according to Embodiment 1 of the present invention when the minimum lift amount is required, illustrating the state in which the intake valve is open.

FIGs. 5(a) and 5(b) are views showing a rocking cam according to Embodiment 1 of the present invention, of which FIG. 5 (a) is a front view, and FIG. 5(b) is a bottom view.

FIG. 6 is a longitudinal sectional view of the main portion of the variable valve mechanism for the internal combustion engine according to Embodiment 2 of the present invention when the maximum lift amount is required, illustrating the state in which the intake valve is closed.

FIG. 7 is a longitudinal sectional view of the main portion of the variable valve mechanism for the internal combustion engine according to Embodiment 2 of the present invention when the minimum lift amount is required, illustrating the state in which the intake valve is closed.

FIGs. 8(a) and 8(b) are views showing a rocking cam according to Embodiment 2 of the present invention, of which FIG. 8 (a) is a front view, and FIG. 8(b) is a bottom view.

FIG. 9 is a longitudinal sectional view of the main portion of the variable valve mechanism for the internal combustion engine according to Embodiment 3 of the present invention when the maximum lift amount is required, illustrating the state in which the intake valve is closed.

FIGs. 10(a) and 10(b) are views showing a rocking cam according to Embodiment 3 of the present invention, of which FIG. 10 (a) is a front view, and FIG. 10(b) is a bottom view.

FIG. 11 is a perspective view of a rocking cam according to Embodiment 3, viewed obliquely from below.

FIG. 12 is a longitudinal sectional view of the main portion of variable valve mechanism for an internal combustion engine according to Embodiment 4 of the present invention, illustrating a state in which the intake valve is closed.

FIGs. 13(a) and 13(b) are views showing a rocking cam according to Embodiment 4 of the present invention, of which FIG. 13 (a) is a front view, and FIG. 13(b) is a bottom view.

FIG. 14 is a longitudinal sectional view of the main portion of variable valve mechanism for an internal combustion engine according to Embodiment 5 of the present invention, illustrating a state in which the intake valve is closed.

FIGs. 15(a) and 15(b) are views showing a rocking cam according to Embodiment 5 of the present invention, of which FIG. 15 (a) is a front view, and FIG. 15(b) is a bottom view.

Best Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment 1 of the Invention]

[0012] FIGs. 1 through 5 illustrate Embodiment 1 of the present invention.

[0013] First, the construction will be described. In FIG. 1, reference numeral 1 denotes a variable valve mechanism for an intake valve 11 of an internal combustion gasoline engine. The variable valve mechanism 1 has a camshaft 2 rotated by a crankshaft (not shown) of the internal combustion engine, a rotating cam 3 provided to the camshaft 2, a rocking shaft 4 provided in parallel to the camshaft 2, a rocking cam 5 supported on the rocking shaft 4 and adapted to rock by the rotating cam 3, and a rocker arm 6 that is rocked in synchronization with the rocking cam 5 to open/close the intake valve 11.

[0014] It should be noted that the construction of the variable valve mechanism 1 is the same between the intake valve 11 and exhaust valve of the gasoline engine. Accordingly, Embodiment 1 focuses on the mechanism on the intake valve 11 side, and the description of the mechanism on the exhaust valve side is omitted.

[0015] As shown in FIG. 1, the camshaft 2 is arranged with its longitudinal direction extending toward the front and back (i.e. in the direction perpendicular to the plane) of FIG. 1. The camshaft 2 is rotated about a center axis O1 at a half rotational speed of that of the crankshaft of the internal combustion engine.

[0016] Further, the rotating cam 3 is fixed onto the outer peripheral surface of the camshaft 2 and, as shown in FIG. 1, the outer peripheral portion thereof is configured with a base surface 3a that is arc-shaped in plan view, and a nose surface 3b projecting from the base surface 3a.

[0017] Further, a center axis O2 of the rocking shaft 4 is arranged in parallel to the center axis O1 of the camshaft 2.

[0018] The rocking cam 5 is in fitting engagement with the outer peripheral surface of the rocking shaft 4, and is supported so as to be rockable about the center axis O2 of the rocking shaft 4. A cam surface 5a for rocking the rocker arm 6 is formed in the lower end portion of the rocking cam 5.

[0019] As shown in FIGs. 1 through 5, in the cam surface 5a, there are formed an arc-shaped base circle portion 5c around the center axis O2, a lift portion 5d for rocking the rocker arm 6, and a ramp portion 5e connecting between the lift portion 5d and the base circle portion 5c.

[0020] Further, as shown in FIG. 5, a width L1 of a contact surface of the base circle portion 5c is formed smaller than a width L2 of a contact surface of the lift portion 5d.

[0021] Further, a guide portion 5b as an elongate through-hole is formed at the longitudinally middle portion of the rocking cam 5. A roller shaft 7, which has a center axis O3 in parallel to the center axis O2 of a rocking shaft 4, is movably inserted through the guide portion 5b. Provided to the roller shaft 7 is a roller 8 as a "rotating cam abutting portion" that contacts and operates in synchronization with a base surface 3a or a nose surface 3b of the rotating cam 3, for transmitting the drive force from the rotating cam 3 to the rocking cam 5.

[0022] Further, the guide portion 5b is formed in the shape of an elongate hole so as to guide the roller shaft 7 along its longitudinal direction over a predetermined distance, and the guiding direction at this time is inclined with respect to the radial direction of the camshaft 2.

[0023] Further, as shown in FIG. 1, the roller 8 is formed in a circular shape, and is arranged on the outer peripheral surface of the roller shaft 7 so that the center axis of the roller 8 becomes the same as the center axis O3 of the roller shaft 7. The outer peripheral surface of the roller 8 is capable of rolling on the base surface 3a and nose surface 3b of the rocking cam 3.

[0024] In such manner, "the rotating cam abutment portion" which abuts the rotating cam 3 is formed in the shape of a roller to rotate on the rotating cam 3 face. This reduces loss of the drive force transmitted from the rotating cam 3 to "the rotating cam abutment portion."

[0025] Incidentally, "the rotating cam abutment portion" is the roller 8 which rotates on the rotating cam 3 face, but is not limited to this. The rotating cam abutment portion may be the one which slides on the rotating cam 3 face, as long as the drive force from the rotating cam 3 is transmitted to the rocking cam 5.

[0026] Further, a spring 15 for urging the rocking cam 5 toward the rotating cam 3 side is in fitting engagement with the rocking shaft 4. Thus, the rocking cam 5 is urged toward the rotating cam 3 side by the urging force of the spring 15, so that the outer peripheral surface of the roller 8 is in constant contact with the base surface 3a or nose surface 3b of the rotating cam 3.

[0027] Furthermore, the variable valve mechanism 1 is provided with "a variable abutment portion mechanism" for making the relative distance between the roller 8 and the center axis O2 of the rocking shaft 4 variable.

[0028] "The variable abutment portion mechanism" has a drive shaft 9 fixedly provided onto the rocking shaft 4, and an arm 10 whose one end portion 10a is connected to the roller shaft 7 and whose other end portion 10b is connected to the drive shaft 9.

[0029] The drive shaft 9 is provided to the rocking shaft 4 in such a manner that a center axis O4 thereof is located in parallel and eccentrically to the center axis O2 of the rocking shaft 4.

[0030] Further, an actuator (not shown) for rotating the rocking shaft 4 within a predetermined angle range about the center axis O2 is connected to one end portion of the rocking shaft 4. Connected to the actuator is control means (not shown) for controlling the angle of the actuator according to the operational state of the internal combustion engine.

[0031] Thus, when the rocking shaft 4 turns by a predetermined angle, the drive shaft 9 turns by a predetermined angle about the center axis O2 of the rocking shaft 4, whereby the position of the center axis O4 changes relative to the center axis O2 of the rocking shaft 4.

[0032] The arm 10 is capable of keeping the distance between the center axis O3 of the roller shaft 7 and the center axis O4 of the drive shaft 9 constant. A through-hole 10c, with which the roller shaft 7 is fitted, is formed at the one end portion 10a of the arm 10, and an insertion portion 10d, into which the drive shaft 9 is inserted and which is partially open, is formed at the other end portion 10b thereof. Accordingly, the roller shaft 7 is rotatably fitted with the through-hole 10c at the one end portion 10a, and the drive shaft 9 is rotatably fitted with the insertion portion 10d at the other end portion 10b and mounted in place with a pin 16 so as to prevent dislodging thereof.

[0033] Thus, when the rocking shaft 4 is rotated by a predetermined angle by the actuator, the drive shaft 9 provided to the rocking shaft 4 is turned by a predetermined angle about the center axis O2 of the rocking shaft 4, and the roller shaft 7 is operated in synchronization with this turning movement through the arm 10. The roller shaft 7 can be thus moved within the guide portion 5b while keeping the distance between the center axis O3 of the roller shaft 7 and the center axis O4 of the drive shaft 9 constant with the arm 10, whereby the relative distance between the center axis O2 of the rocking shaft 4 and the roller 8 can be made variable.

[0034] Further, the rocker arm 6 is disposed below the rocking cam 5 while being rockably supported on the rocker arm shaft 12.

[0035] Although the rocker arm 6 is rockably supported with the rocker arm shaft 12, the configuration is not limited to this. The rocker arm 6 may be rockably supported with a spherical pivot, hydraulic lash adjuster, or the like.

[0036] Further, a valve pressing portion 6a is formed at the distal end portion of the rocker arm 6 for pressing on the upper surface of a shim 23 fitted on an intake valve 11 which will be described later.

[0037] A roller 14 is rotatably provided to the roller shaft 13, and the outer peripheral surface of the roller 14 is capable of rolling on the cam surface 5a of the rocking cam 5.

[0038] Further, a spring 17 for urging the rocker arm 6 toward the rocking cam 5 side is in fitting engagement with the rocker arm shaft 12. Thus, the rocker arm 6 is urged toward the rocking cam 5 side by means of the spring 17, so that the outer peripheral surface of the roller 14 is in constant contact with the cam surface 5a of the rocking cam 5.

[0039] Further, the intake valve 11 pressed by the valve pressing portion 6a is arranged below the valve pressing portion 6a of the rocker arm 6 so as to be vertically movable.

[0040] The intake valve 11 has a collet 20 and an upper retainer 21 that are provided in its upper portion. A valve spring 22 is arranged below the upper retainer 21. The intake valve 11 is urged toward the rocker arm 6 side by the urging force of the valve spring 22. Further, the shim 23 is fitted on the upper end portion of the intake valve 11.

[0041] Accordingly, the intake valve 11 can be vertically moved by rocking the rocker arm 6 in synchronization with the rocking motion of the rocking cam 5. Thus, by making the relative distance between the center axis O2 of the rocking cam 4 and the roller 8 variable to adjust the rocking start position of the rocking cam 5, the lift amount and the maximum lift timing of the intake valve 11 can be adjusted and made variable through the rocker arm 6.

[0042] Operation of the variable valve mechanism 1 constructed as above will next be described.

[0043] First, detailed description will be made on the operation of the variable valve mechanism 1 for an internal combustion engine when the maximum lift amount is required, with reference to FIGs. 1 and 2.

[0044] Here, FIG. 1 is a longitudinal sectional view of the main portion of variable valve mechanism 1 of the internal combustion engine according to Embodiment 1 of the present invention when the maximum lift amount is required, illustrating the state in which the intake valve 11 is closed. FIG. 2 is a longitudinal sectional view of the main portion of the variable valve mechanism 1 of the internal combustion engine according to Embodiment 2 of the present invention when the maximum lift amount is required, illustrating the state in which the intake valve is open.

[0045] First, as shown in FIG. 1, the roller shaft 7 is moved to the rotating cam 3-side end portion of the guide portion 5b, thereby changing the relative distance between the center axis O2 of the rocking shaft 4 and the roller 8. That is, the rocking shaft 4 is turned by a predetermined angle by the actuator, causing the drive shaft 9 to move in the circumferential direction of the rocking shaft 4. Thus, the roller shaft 7 is operated in synchronization with this movement via the arm 10 so as to be moved to the rotating cam 3-side end portion of the guide portion 5b, whereby the relative distance between the center axis O2 of the rocking shaft 4 and the roller 8 changes.

[0046] Further, as shown in FIG. 1, while the roller 8 provided to the rocking cam 5 is in contact with the base surface 3a of the rotating cam 3, the rocking cam 5 is not rocked to the intake valve 11 side, the rocker arm 6 is urged to the rocking cam 5 side by the urging force of the spring 17, and also the intake valve 11 is urged to the rocker arm 6 side by the urging force of the valve spring 22. Thus, the lift of the intake valve 11 does not occur and the intake valve 11 is brought into a closed state.

[0047] In this state, the roller 14 is located at the position corresponding to the base circle portion 5c of the cam surface 5a of the rocking cam 5. Since no large abutment force acts between the roller 14 and the base circle portion 5c in the valve closure state, a sufficient durability can be secured even through the width L1 of the base circle portion 5c is small.

[0048] Then, when the rotating cam 3 is rotated via the camshaft 2 due to the rotation of the crankshaft of the internal combustion engine, as shown in FIG. 2, the roller 8 is pressed on by the nose surface 3b. As the roller 8 is further pressed, the rocking cam 5 is pressed via the roller shaft 7, causing the rocking cam 5 to rock counterclockwise in FIG. 1 against the urging force of the spring 15.

[0049] Through the rocking movement of the rocking cam 5, the portion of the cam surface 5a of the rocking cam 5 which presses the roller 14 changes from the base circle portion 5c to the lift portion 5d via the ramp portion 5e, and the rocker arm 6 is turned via the roller shaft 13 to the intake valve 11 side. In this way, a relative distance M between the center axis O2 of the rocking shaft 4 and the roller 14 in contact with the cam surface 5a of the rocking cam 5 as shown in FIG. 1 is largely changed to a relative distance N between the center axis O2 of the rocking shaft 4 and the roller 14 in contact with the cam surface 5a of the rocking cam 5 as shown in FIG. 2. The rocker arm 6 thus undergoes large rocking movement to the intake valve 6 side.

[0050] Then, the valve pressing portion 6a formed at the distal end portion of the rocker arm 6 that has thus undergone large rocking movement to the intake valve 11 side presses on the upper surface of the shim 23 to push down the intake valve 11 by a large distance. As described above, by moving the roller shaft 7 to the end portion of the guide portion 5b in the rotating cam 3 side to make the relative distance between the center axis O2 of the rocking shaft 4 and the roller 8 variable, the relative distance between the center axis O2 of the rocking shaft 4 and the roller 14 in contact with the cam surface 5a of the rocking cam 5 can be largely changed, whereby the intake valve 11 can be pushed down by a large distance to bring the intake valve 11 into an open state at the maximum lift amount.

[0051] In the case where the intake valve 11 is opened in this way, the width L2 of the lift portion 5d is made large because a large reaction force acts on the cam surface 5a of the rocking cam 5, thereby making it possible to secure strength.

[0052] Next, detailed description will be made on the operation of the variable valve mechanism 1 of the internal combustion engine when the minimum lift amount is required, with reference to FIG. 3 and 4.

[0053] Here, FIG. 3 is a longitudinal sectional view of the main portion of the variable valve mechanism for the internal combustion engine according to Embodiment 1 of the present invention when the minimum lift amount is required, illustrating the state in which the intake valve is closed. FIG. 4 is a longitudinal sectional view of the main portion of the variable valve mechanism for the internal combustion engine according to Embodiment 1 of the present invention when the minimum lift amount is required, illustrating the state in which the intake valve is open.

[0054] First, as shown in FIG. 3, in the state as shown in FIG. 1 where the roller shaft 7 is retained at the rotating cam 3-side end portion, the roller shaft 7 is moved to the rocking shaft 4-side end portion of the guide portion 5b, thereby changing the relative distance between the center axis O2 of the rocking shaft 4 and the roller 8.

[0055] That is, the rocking shaft 4 is turned within a predetermined angle range by the actuator, causing the drive shaft 9 to move in the circumferential direction of the rocking shaft 4. Accordingly, the roller shaft 7 is operated in synchronization with this movement via the arm 10 so that the roller shaft 7 is moved to the rocking shaft 4-side end portion of the guide portion 5b from the state where it is retained at the rotating cam 3-side end portion, whereby the relative distance between the center axis O2 of the rocking shaft 4 and the roller 8 decreases. Then, the rocking cam 5 turns from the position as shown in FIG. 1 to the position as shown in FIG. 3 due to the urging force of the spring 15.

[0056] Further, as shown in FIG. 3, while the roller 8 provided to the rocking cam 5 is in contact with the base surface 3a of the rotating cam 3, the rocking cam 5 is not rocked to the intake valve 11 side, the rocker arm 6 is urged to the rocking cam 5 side by the urging force of the spring 17, and also the intake valve 11 is urged to the rocker arm 6 side by the urging force of the valve spring 22. Thus, the lift of the intake valve 11 does not occur and the intake valve 11 is brought into a closed state.

[0057] When the rotating cam 3 is rotated via the camshaft 2 due to the rotation of the crankshaft of the internal combustion engine, as shown in FIG. 4, the roller 8 is pressed on by the nose surface 3b, and the rocking cam 5 is pressed via the roller shaft 7, causing the rocking cam 5 to rock counterclockwise in FIG. 3 against the urging force of the spring 15.

[0058] As the rocking cam 5 is further rocked, the roller 14 in contact with the rocking shaft 4-side distal end portion of the cam surface 5a of the rocking cam 5 is pushed down to the intake valve 11 side by using the range of the cam surface 5a from the rocking shaft 4-side distal end portion to the center portion thereof, whereby the rocker arm 6 is rocked to the intake valve 11 side via the roller shaft 13. In this way, a relative distance P between the center axis O2 of the rocking shaft 4 and the roller 14 in contact with the cam surface 5a of the rocking cam 5 as shown in FIG. 3 undergoes a small change to become a relative distance Q between the center axis O2 of the rocking shaft 4 and the roller 14 in contact with the cam surface 5a of the rocking cam 5 as shown in FIG. 4. The rocker arm 6 thus undergoes small rocking movement to the intake valve side.

[0059] Then, the valve pressing portion 6a formed at the distal end portion of the rocker arm 6 that has thus undergone small rocking movement to the intake valve 11 side presses on the upper surface of the shim 23 to push down the intake valve 11 by a small distance. In this way, by moving the roller shaft 7 to the rocking shaft 4-side end portion of the guide portion 5b to make the relative distance between the center axis O2 of the rocking shaft 4 and the roller 8 variable, the relative distance between the center axis O2 of the rocking shaft 4 and the roller 14 in contact with the cam surface 5a of the rocking cam 5 can be subjected to a small change to push down the intake valve 11 by a small distance, whereby, in Embodiment 1, the intake valve 11 can be brought into an open state at the minimum lift amount.

[0060] Further, although the width L1 of the base circle portion 5c is small, since no large load acts on this portion, a requisite strength can be secured for the base circle portion 5c. Because a large load acts on the lift portion 5d, the width L2 thereof is made larger to secure a requisite strength.

[0061] Weight of the rocking cam 5 can be reduced because of the small width L1 of the base circle portion 5c. This results in a reduction in inertia force of the rocking cam 5 at the time of rocking movement, as well as in a reduction in weight of parts associated with the rocking cam 5 (e.g. spring 15). This allows the whole system to be smaller while reducing wear on a contact portion of the cam surface 5a.

[0062] Particularly, the base circle portion 5c is formed in a position apart from the center axis O2, and therefore can more contribute to the reduced inertia force.

[0063] In the variable valve mechanism 1 of the internal combustion engine constructed as described above, the rocking cam 5 is provided with the roller 8 or the rotating cam abutment portion that comes into contact with the rotating cam 3 to transmit the drive force from the rotating cam to the rocking cam 5. The valve mechanism 1 is provided with the variable abutment portion mechanism for making the relative distance between the roller 8 and the center axis O2 of the rocking shaft 4 variable by making the roller 8 movable; the lift amount or the like of each valve is made variable by thus making the relative distance variable, whereby the structure can be simplified to achieve low-cost construction.

[0064] Further, the load from the rotating cam 3 is input to the roller 8, and the load is directly transmitted from the roller 8 to the guide portion 5a of the rocking cam 5. Then, the load is transmitted from the rocking cam 5 to the intake valve 11 via the rocker arm 6. Thus, no large load acts on the arm 10 that supports the roller 8, and since the arm 10 serves the sole function of moving the roller 8 along the guide portion 5a, not so large strength is required for the arm 10.

[Embodiment 2 of the Invention]

[0065] FIGs. 6 through 8 illustrate Embodiment 2 of the present invention. FIG. 6 is a longitudinal sectional view of the main portion of the variable valve mechanism for the internal combustion engine when the maximum lift amount is required, illustrating the state in which the intake valve is closed. FIG. 7 is a longitudinal sectional view of the main portion of the variable valve mechanism for the internal combustion engine when the minimum lift amount is required, illustrating the state in which the intake valve is closed.

[0066] In Embodiment 2, the rocker arm 6 which opens and closes an intake valve 11 as in Embodiment 1 is not provided, but a rocking cam 5 directly moves the intake valve 11 upward and downward to open and close the intake valve 11.

[0067] As shown in FIGs. 6 through 8, the rocking cam 5 is formed in the shape of a comma-shaped bead. The rocking cam 5 is fitted on the peripheral surface of a rocking shaft 4 and supported so as to be rockable about the center axis O2 of the rocking shaft 4.

[0068] More specifically, as shown in FIG. 8, the rocking cam 5 includes a cam surface 5a having a base circle portion 5c, a lift portion 5d and a ramp portion 5e. A width L1 of a contact surface of the base circle portion 5c is formed smaller than a width L2 of a contact surface of the lift portion 5d. Further, the bottom end of the rocking cam 5 is formed with a cam surface 5a. The cam surface 5a is curved toward the intake valve 11 to form a projection, and depresses a lifter 26 of the intake valve 11 to vertically move the intake valve 11. The upper portion of the cam surface 5a is formed with a guide portion 5b, along which a roller shaft 7 having a roller 8 slides.

[0069] The roller shaft 7 is connected to one end portion 10a of an arm 10 connected to a drive shaft 9. A roller 8 rotatably supported with the roller shaft 7 comes into contact with a rotating cam 3.

[0070] The rocking shaft 4 is provided with a spring (not shown) for urging the rocking cam 5 toward the rotating cam 3. The rocking cam 5 is thereby urged toward the rotating cam 3 by the urging force of the spring, so that the peripheral surface of the roller shaft 7 is normally in contact with the guide portion 5b, and the peripheral surface of the roller 8 is normally in contact with a base surface 3a or a nose surface 3b of the rotating cam 3.

[0071] There is provided, below the cam surface 5a of the rocking cam 5, the lifter 26 attached on the intake valve 11. Thus, the swinging motion of the rocking cam 5 directly moves the intake valve 11 upward and downward.

[0072] Thus, when the rocking shaft 4 is rotated by a predetermined angle by the actuator, the drive shaft 9 provided to the rocking shaft 4 is turned by a predetermined angle about the center axis O2 of the rocking shaft 4, and the roller shaft 7 is operated in synchronization with this turning movement through the arm 10. The roller shaft 7 can be thus moved within the guide portion 5b while keeping the distance between the center axis O3 of the roller shaft 7 and the center axis O4 of the drive shaft 9 constant with the arm 10, whereby the relative distance between the center axis O2 of the rocking shaft 4 and the roller 8 can be made variable. Therefore, the lift amount and the maximum lift timing of the intake valve 11 can be adjusted and made variable.

[0073] As shown in FIG. 6, when the roller shaft 7 is displaced to the distal end portion of the guide portion 5b so that the relative distance between the center axis O2 of the rocking shaft 4 and the roller 8 is made variable, the intake valve 11 is depressed with the cam surface 5a of the rocking cam 5 by a larger amount. A maximum lift amount is thus obtained in Embodiment 2.

[0074]  As shown in FIG. 7, when the roller shaft 7 is displaced to the rocking shaft 4 side of the guide portion 5b so that the relative distance between the center axis O2 of the rocking shaft 4 and the roller 8 is made variable, the intake valve 11 is depressed with the cam surface 5a of the rocking cam 5 by a smaller amount. A minimum lift amount is thus obtained in Embodiment 2.

[0075] Further, although the width L1 of the base circle portion 5c is small, as in the Embodiment described above, since no large load acts on this portion, a requisite strength can be secured for the base circle portion 5c. Because a large load acts on the lift portion 5d, the width L2 thereof is made larger to secure a requisite strength.

[0076] Weight of the rocking cam 5 can be reduced because of the small width L1 of the base circle portion 5c. This results in a reduction in inertia force of the rocking cam 5 at the time of rocking movement, as well as in a reduction in weight of parts associated with the rocking cam 5 (e.g. spring 15). This allows the whole system to be smaller while reducing wear on a contact portion of the cam surface 5a.

[0077] Otherwise, Embodiment 2 is of the same construction and operation as Embodiment 1 of the present invention, so repetitive description will not be repeated.

[Embodiment 3 of the Invention]

[0078] FIGs. 9 through 11 are longitudinal sectional views of the main portion of valve mechanism for an internal combustion engine according to Embodiment 3 of the present invention, illustrating a state in which the intake valve is closed.

[0079] In Embodiment 3, a rocker arm 6 has a roller 14 that comes into contact with a cam surface 5a of a rocking cam 5, a roller arm 6c for supporting the roller 14, which is operated in synchronization with the rocking motion of the rocking cam 5, and a rocker arm main body 6d that rocks in synchronization with the roller arm 6c to vertically move an intake valve 11.

[0080] A leaf spring 28 is used to urge the roller arm 6c to the rocking cam 5 side to bring the roller 14 and the cam surface 5a of the rocking cam 5 into contact with each other.

[0081] As shown in FIG. 10, as in the Embodiments described above, the cam surface 5a has a base circle portion 5c, a lift portion 5d, and a ramp portion 5e, and a width L1 of the base circle portion 5c is formed smaller than a width L2 of the lift portion 5d.

[0082] Further, the roller arm 6c is freely movable to a predetermined position. By changing the contact position between the roller 14 provided to the roller arm 6c and the cam surface 5a of the rocking cam 5, the life amount of each valve or the like can be adjusted.

[0083] Specifically, as shown in FIG. 9, an eccentric shaft 29 is fixedly provided to the rocker arm shaft 12 in such a manner that a center axis O7 thereof is located in parallel and eccentrically to the center axis O5 of the rocker arm shaft 12. The roller arm 6c of the rocker arm 6 is rotatably locked onto the eccentric shaft 29 by means of the leaf spring 28.

[0084] The roller arm 6c has an engaging portion 6e formed at its one end. The engaging portion 6e engages with the outer peripheral surface of the eccentric shaft 29, and is so shaped as to be capable of sliding on the outer peripheral surface of the eccentric shaft 29. Formed at a position adjacent to the engaging portion 6e is a fitting engagement portion 6f with which the leaf spring 28 for integrally locking the roller arm 6c and the eccentric shaft 29 in place is brought into fitting engagement so as to prevent dislodging thereof. Further, a through-hole 6g, with which the roller shaft 13 supporting the roller 14 that slides on the cam surface 5a of the rocking cam 5 is brought into fitting engagement, is formed at the other end of the roller arm 6c. Formed below the through-hole 6g is a pressing portion 6h for pressing the rocker arm main body 6d to the intake valve 11 side when the roller arm 6c rocks to the intake valve 11 side in synchronization with the rocking motion of the rocking cam 5.

[0085] Further, the rocker arm main body 6d of the rocker arm 6 is rockably supported and arranged on the rocker arm shaft 12, and has the valve pressing portion 6a formed at is distal end portion. The valve pressing portion 6a presses on the upper surface of the shim 23 fitted on the intake valve 11. Further, a contact surface 6i with which a distal end portion 28b of the leaf spring 28, which will be described later, comes into contact is formed above the valve pressing portion 6a, and a guide portion 6j pressed on by the pressing portion 6h formed in the rocker arm 6c is formed above the contact surface 6i.

[0086] Further, the leaf spring 28 is formed into a predetermined configuration by bending a planar spring at several locations. More specifically, the leaf spring 28 is formed in a configuration allowing fitting engagement with the fitting engagement portion 6f of the roller arm 6c and with the eccentric shaft 29, and has formed therein a locking portion 28a for integrally locking the roller arm 6c and the eccentric shaft 29 onto each other. Further, the distal end portion 28b of the leaf spring 28 on the roller arm 6c side extends to the roller 14 side and comes into contact with the contact surface 6i formed in the rocker arm main body 6d.

[0087] Further, the leaf spring 28 is formed in such a configuration as to urge the roller arm 6c and the rocker arm main body 6d so as to spread out from each other when the roller arm 6c and the eccentric shaft 29 are integrally locked onto each other by the locking portion 28a.

[0088] Further, a predetermined clearance A is provided between a pressing portion 6h of the roller arm 6c and a guide portion 6j of the rocker arm main body 6d.

[0089] Thus, since the roller arm 6c is integrally locked onto the eccentric shaft 29 by the leaf spring 28 so that the roller arm 6c can slide on the outer peripheral surface of the eccentric shaft 29, when the rocking cam 5 is rocked, the roller arm 6c is caused via the roller 14 and the roller shaft 13 to rock to the intake valve 11 side against the urging force of the leaf spring 28. Further, as the rocker arm 6c is rocked to the intake valve 11 side, the pressing portion 6h of the roller arm 6c presses on the guide portion 6j of the rocker arm main body 6d, causing the rocker arm main body 6d to rock to the intake valve 11 side, thereby making it possible to open and close the intake valve 11.

[0090] Further, the roller arm 6c is urged to the rocking cam 5 side by the leaf spring 28, so the outer peripheral surface of the roller 14 provided to the roller arm 6c is held in constant contact with the cam surface 5a of the rocking cam 5.

[0091] Further, an actuator (not shown) for rotating the rocker arm shaft 12 within a predetermined angle range about the center axis O5 is connected to one end portion of the rocker arm shaft 12. Connected to the actuator is control means (not shown) for controlling the angle of the actuator according to the operational state of the internal combustion engine.

[0092] Thus, when the rocker arm shaft 12 is rotated by a predetermined angle by the actuator, the eccentric shaft 29 provided to the rocker arm shaft 12 is turned by a predetermined angle about the center axis O5 of the rocker arm shaft 12. Further, when the eccentric shaft 29 is turned by the predetermined angle, the roller arm 6c operating in synchronization therewith is moved, for example, from the position indicated by the solid line in FIG. 9 to a predetermined position indicated by the chain double-dashed line in FIG. 9. Then, once the roller arm 6c has been moved to the predetermined position, the contact point where the cam surface 5a of the rocking cam 5 and the roller 14 provided to the roller arm 6c come into contact with each other changes. The rocking amount of the rocker arm main body 6d can be thus changed, which makes it possible to adjust the lift amount or the like of the intake valve 11 that is vertically moved by the rocker arm 6.

[0093] Further, even in the case where a predetermined clearance is not provided between the valve pressing portion 6a of the rocker arm main body 6d and the intake valve 11, the predetermined clearance (A) provided between the pressing portion 6h and the guide portion 6j allows the intake valve 11 to be reliably opened/closed even when, due to a rise in the temperature of the internal combustion engine, the intake valve 11 undergoes thermal expansion to cause upward jumping of the valve.

[0094] Also with the valve mechanism 1 for an internal combustion engine constructed as described above, in which the lift amount or the like of each valve can be adjusted by making the roller arm 6c be movable to the predetermined position and changing the contact position between the roller 14 provided to the roller arm 6c and the cam surface 5a of the rocking cam 5, the roller arm 6c is urged toward the rocking cam 5 side by the leaf spring 28. Accordingly, when the roller arm 6c has been moved to the predetermined position and the contact position between the roller 14 and the cam surface 5a changes, the roller 14 of the rocker arm 6 and the cam surface 5a of the rocking cam 5 constantly come into contact with each other, thereby making it possible to prevent adhesive wear.

[0095] Further, although the width L1 of the base circle portion 5c is small, as in the Embodiments described above, since no large load acts on this portion, a requisite strength can be secured for the base circle portion 5c. Because a large load acts on the lift portion 5d, the width L2 thereof is made larger to secure a requisite strength.

[0096] Weight of the rocking cam 5 can be reduced because of the small width L1 of the base circle portion 5c. This results in a reduction in inertia force of the rocking cam 5 at the time of rocking movement, as well as in a reduction in weight of parts associated with the rocking cam 5 (e.g. spring 15).

[0097]  Particularly, the base circle portion 5c is formed in a position apart from the center axis O2, and therefore can more contribute to the reduced inertia force.

[0098] Otherwise, Embodiment 3 is of the same construction and operation as Embodiment 1 of the present invention, so repetitive description will not be repeated.

[0099] Otherwise, Embodiment 3 is of the same construction and operation as Embodiment 1 of the present invention, so repetitive description will not be repeated.

[Embodiment 4 of the Invention]

[0100] FIGs. 12 and 13 are longitudinal sectional views of the main portion of a valve mechanism for an internal combustion engine according to Embodiment 4 of the present invention, illustrating a state in which the intake valve is closed.

[0101] The valve mechanism 1 for an internal combustion engine according to Embodiment 4 is capable of adjusting the lift amount or the like of each valve by making the rocking shaft 4 movable to a predetermined position.

[0102] Specifically, as shown in FIG. 12, a roller 33 is arranged on the outer peripheral surface of the rocking shaft 4. The roller 33 is in contact with a guide portion 19a formed in the cylinder head main body 19 for guiding the rocking shaft 4 to a predetermined position. Further, the rocking shaft 4 is provided to the cylinder head main body 19 such that, when the rocking cam 5 is pressed by a control cam 34 that will be described next, the rocking shaft 4 can move in synchronization with the rocking cam 12 within a range from a position indicated by the solid line in FIG. 12 to that indicated by the chain double-dashed line in FIG. 12.

[0103] The control cam 34 is fixed onto the outer peripheral surface of a control shaft 35 provided in parallel to the camshaft 2. Further, the outer peripheral portion of the control cam 34 contacts the rocking cam 5 and is formed in a configuration allowing the rocking shaft 4 to be guided to a predetermined position by rotating the control cam 34 in a predetermined angle.

[0104] As shown in FIG. 13, the cam surface 5a of the rocking cam 5 has a base circle portion 5c, a lift portion 5d, and a ramp portion 5e, and a width L1 of the base circle portion 5c is formed smaller than a width L2 of the lift portion 5d.

[0105] Further, an actuator (not shown) for rotating the control shaft 35 within a predetermined angle range about a center axis O8 of the control shaft 35 is connected to one end portion of the control shaft 35. Connected to the actuator is control means (not shown) for controlling the angle of the actuator according to the operational state of the internal combustion engine.

[0106] Further, the rocker arm 6, which makes reciprocating motion while rocking within a predetermined range in synchronization with the rocking cam 5, is of the same construction as that of Embodiment 1. That is, the rocker arm 6 has the valve pressing portion 6a formed therein, is provided with the roller shaft 13 and the roller 14, and is rockably supported on the rocker arm shaft 12.

[0107] Further, as in Embodiment 1, the rocker arm shaft 12 is provided with the torsion spring 17 as a spring member for bringing the roller 14 and the cam surface 5a into constant contact with each other.

[0108] Thus, when the control shaft 35 is turned by a predetermined angle by the actuator, the control cam 34 is rotated by a predetermined angle about the center axis O8 of the control shaft 35. When the control cam 34 is rotated by the predetermined angle, by the control cam 34, the roller 33 is caused via the rocking cam 5 to slide on the guide portion 19a of the cylinder head main body 19 so as to be moved, for example, from the position indicated by the solid line in FIG. 12 to a predetermined position indicated by the chain double-dashed line in FIG. 12. Then, as the rocking shaft 4 is moved, the position of the cam surface 5a of the rocking cam 5 changes. The rocking amount of the rocker arm 6 can be thus changed, which makes it possible to adjust the lift amount or the like of the intake valve 11 that is vertically moved by the rocker arm 6.

[0109] Also with the valve mechanism 1 constructed as described above, which makes the lift amount or the like of each valve variable by moving the rocking shaft 4 to a predetermined position, the rocker arm 6 is urged to the rocking cam 5 side by the torsion spring 17, so even when the rocking shaft 4 has been moved to the predetermined position, and the position of the cam surface 5a of the rocking cam 5 changes, the roller 14 of the rocker arm 6 and the cam surface 5a of the rocking cam 5 constantly come into contact with each other. Adhesive wear can be thus prevented.

[0110] Further, although the width L1 of the base circle portion 5c is small, as in the Embodiments described above, since no large load acts on this portion, a requisite strength can be secured for the base circle portion 5c. Because a large load acts on the lift portion 5d, the width L2 thereof is made larger to secure a requisite strength.

[0111] Weight of the rocking cam 5 can be reduced because of the small width L1 of the base circle portion 5c. This results in a reduction in inertia force of the rocking cam 5 at the time of rocking movement, as well as in a reduction in weight of parts associated with the rocking cam 5 (e.g. spring 15).

[0112] Particularly, the base circle portion 5c, formed in a position apart from the center axis O2, can more contribute to the reduced inertia force.

[0113] Otherwise, Embodiment 4 is of the same construction and operation as Embodiment 1 of the present invention, so repetitive description will not be repeated.

[Embodiment 5 of the Invention]

[0114] FIGs. 14 and 15 are longitudinal sectional views of the main portion of a valve mechanism for an internal combustion engine according to Embodiment 5 of the present invention, illustrating a state in which the intake valve is closed.

[0115] Embodiment 5 provides the valve mechanism 1 for an internal combustion engine in which the rotating cam 3 has a tapered configuration, and the contact position between the outer peripheral portion of the rotating cam 3 and the rocking cam 5 is changed by moving the rotating cam 3 in the direction of the center axis O1 of the camshaft 2, thereby making it possible to adjust the lift amount or the like of each valve.

[0116] Specifically, as shown in FIG. 14, the rotating cam 3 is fixed onto the outer peripheral surface of the camshaft 2. The outer peripheral portion of the rotating cam 3 is constructed with the base surface 3a that is arc-shaped in plan view, and the nose surface 3b projecting from the base surface 3a. The base surface 3a and the nose surface 3b are formed in the tapered configuration in the direction of the center axis O1 (in the direction perpendicular to the sheet plane) of FIG. 14.

[0117] Further, an actuator (not shown) for moving the camshaft 2 within a predetermined range in the direction of the center axis O1 is connected to one end portion of the camshaft 2. Connected to the actuator is control means (not shown) for controlling the angle of the actuator according to the operational state of the internal combustion engine.

[0118] Further, the outer peripheral surface of the roller 8 provided to the rocking cam 5 rocked by the rotating cam 3 is capable of sliding on the base surface 3a and base surface 3b of the rotating cam 3 formed in the tapered configuration.

[0119] Further, as shown in FIG. 15, the cam surface 5a of the rocking cam 5 has a base circle portion 5c, a lift portion 5d, and a ramp portion 5e, and a width L1 of the base circle portion 5c is formed smaller than a width L2 of the lift portion 5d.

[0120] Further, the rocker arm 6, which makes reciprocating motion while rocking within a predetermined range in synchronization with the rocking cam 5, is of the same construction as that of Embodiment 4. That is, the rocker arm 6 has the valve pressing portion 6a formed therein, is provided with the roller shaft 13 and the roller 14, and is rockably supported on the rocker arm shaft 12.

[0121] Further, as in Embodiment 4, the rocker arm shaft 12 is provided with the torsion spring 17 for bringing the roller 14 and the cam surface 5a into constant contact with each other.

[0122] Thus, when the camshaft 2 moves within a predetermined range in the direction of the center axis O1 by the actuator, the rotating cam 3 moves within a predetermine range in the direction of the center axis O1 of the camshaft 2. Since the rotating cam 3 is formed in the tapered configuration, when the rotating cam 3 is moved with the predetermined range, the rocking cam 5 is caused via the roller shaft 7 and the roller 8 to move, for example, from the position indicated by the solid line in FIG. 14 to a predetermined position indicated by the double-dashed chain line in FIG. 14. Then, when the rocking cam 5 has been moved to the predetermined position, the position of the cam surface 5a of the rocking cam 5 changes. Therefore, the rocking amount of the rocker arm 6 can be changed, which makes it possible to adjust the lift amount or the like of the intake valve 11 that is vertically moved by the rocker arm 6.

[0123] Also with the valve mechanism 1 constructed as described above, in which the rotating cam 3 is tapered, and the lift amount or the like of each valve variable is made variable by moving the rotating cam 3 in the direction of the center axis O1 of the camshaft 2 and changing the contact position between the outer peripheral portion of the rotating cam 3 and the rocking cam 5, the rocker arm 6 is urged to the rocking cam 5 side by the torsion spring 17, so even when the rocking shaft 4 has been moved to the predetermined position, and the position of the cam surface 5a of the rocking cam 5 changes, the roller 14 of the rocker arm 6 and the cam surface 5a of the rocking cam 5 constantly come into contact with each other. Adhesive wear can be thus prevented.

[0124] Further, although the width L1 of the base circle portion 5c is small, as in the Embodiments described above, since no large load acts on this portion, a requisite strength can be secured for the base circle portion 5c. Because a large load acts on the lift portion 5d, the width L2 thereof is made larger to secure a requisite strength.

[0125] Weight of the rocking cam 5 can be reduced because of the small width L1 of the base circle portion 5c. This results in a reduction in inertia force of the rocking cam 5 at the time of rocking movement, as well as in a reduction in weight of parts associated with the rocking cam 5 (e.g. spring 15).

[0126] Particularly, the base circle portion 5c is formed in a position apart from the center axis O2, and therefore can more contribute to the reduced inertia force.

[0127] Otherwise, Embodiment 5 is of the same construction and operation as Embodiment 1 of the present invention, so repetitive description will not be repeated.

[0128] It should be noted that while, in the Embodiments described above, the present invention is applied to the variable valve mechanism 1 provided with the rocking cam 5, the present invention is not limited to this construction. The present invention may also be applied to any valve mechanism incapable of changing the lift amount or the like.

Description of Reference Numerals and Symbols

[0129] 

1:

variable valve mechanism

2:

camshaft

3:

rotating cam

4:

rocking shaft

5:

rocking cam

5a:

cam surface

5b:

guide portion

5c:

base circle portion

5d:

lift portion

5e:

ramp portion

6:

rocker arm

7:

roller shaft

8:

roller (rotating cam abutting portion)

9:

drive shaft

10:

arm (variable abutment portion mechanism)

L1:

width of base circle portion

L2:

width of lift portion

Claims

1. A rocking cam comprising a cam surface having a base circle portion and a lift portion, and disposed so as to make reciprocating motion,
wherein a width of a contact surface of the base circle portion is formed smaller than a width of a contact surface of the lift portion.

2. A valve mechanism for an internal combustion engine, having: a camshaft rotated by a crankshaft of the internal combustion engine; a rotating cam provided to the camshaft; a rocking shaft provided in parallel to the camshaft; and a rocking cam supported with the rocking shaft and freely rockable by the rotating cam, and capable of varying a lift amount of an intake valve or an exhaust valve of the internal combustion engine, wherein the rocking cam includes a cam surface having a base circle portion and a lift portion, and is disposed so as to make reciprocating motion; and
a width of a contact surface of the base circle portion is formed smaller than a width of a contact surface of the lift portion.

3. The valve mechanism for an internal combustion engine according to Claim 2,
wherein the rocking cam is provided with a movable rotating cam abutment portion that comes into contact with the rotating cam to transmit a drive force from the rotating cam to the rocking cam, and provided with a guide portion for guiding the rotating cam abutment portion in a certain direction; the drive force from the rotating cam is inputted to the guide portion via the rotating cam abutment portion so that the rocking cam is rocked;
a variable abutment portion mechanism is provided for making a relative distance between the rotating cam abutment portion and a center axis of the rocking shaft variable by making the rotating cam abutment portion movable along the guide portion; and a lift amount of each valve is made variable by thus making the relative distance variable.

Drawing