GB2121476A

GB2121476A - I.C. engine valve gear with hydraulic clearance adjustment

Info

Publication number: GB2121476A
Application number: GB08314957A
Authority: GB
Inventors: Yoshikazu Ishikawa
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1982-06-04
Filing date: 1983-05-31
Publication date: 1983-12-21
Also published as: JPS58211515A; GB8314957D0; DE3319766A1

Abstract

A cylindrical member (26) which is rotatably received in a transverse hole (26c) in a rocker arm (21), is formed with a tapered radial hole (26a) in which a projecting end (25a) of a plunger (25) of an hydraulic valve clearance adjuster (22) is inserted. <IMAGE>

Description

SPECIFICATION Valve operating mechanism with lash adjuster The present invention relates to a valve operating mechanism having an automatic lash adjuster, such as a hydraulic lash adjuster, for an internal combustion engine.

In a mechanism for operating an intake or exhaust valve of an internal combustion engine, a rocker arm is driven by a camshaft, and swings on a fulcrum in a plane which includes the axis of the valve and is perpendicular to the axis of the camshaft. If the rocker arm is inclined from this plane and swings outside this plane, it causes one-sided contact, one-sided wear of contacting surfaces, faulty valve operation, increase of noise and loss of engine performance.

It is an object of the present invention to provide a valve operating mechanism in which lash adjusting means reliably supports the fulcrum of a rocker arm and prevents the rocker arm from being rotated about its longitudinal line.

According to the present invention, the mechanism for operating a poppet valve of an internal combustion engine comprises a cam, a rocker arm and support means. The cam is capable of rotating. The rocker arm is connected between the cam and the poppet valve. The rocker arm swings on a fulcrum by being driven by the rotational movement of the cam, and by so doing, reciprocates the valve in accordance with the rotational movement of the cam. The support means comprises fulcrum means for supporting the rocker arm swingably and serving as the fulcrum on which the rocker arm swings, and lash adjusting means for supporting the fulcrum means and allowing the fulcrum means to move in a plane in which the rocker arm swings. The fulcrum means is a cylindrical member whose axis is substantially perpendicular to the plane.

Preferably, the rocker arm has a transverse hole and the cylindrical member is rotatably received in the transverse hole. The lash adjusting means comprises a casing fixed in a position and a plunger received in the casing. The plunger has a tapered end portion projecting from the casing.

The axis of the plunger lies in said plane and the plunger is axially movable in said plane. The cylindrical member has a tapered radial hole in which the end portion of the plunger is fitted. The rocker arm has an opening through which the end portion of the plunger is inserted into the tapered radial hole of the cylindrical member.

Fig. 1 is a schematic sectional elevation showing one embodiment of the valve operating mechanism according to the present invention; Fig. 2 is an exploded perspective view showing a main portion of Fig. 1; Figs. 3A, 3B and 3C are, respectively, a front elevation, a side elevation, and a bottom plan view of a rocker arm shown in Fig. 1; and Fig. 4 is a bottom plane view showing another design of the rocker arm.

Figs. 1 to 3 show one embodiment of the present invention. A cylinder head 12 is mounted on and fastened to a cylinder block 11. In the cylinder head 12, there is provided a camshaft 1 3 which is connected with a crankshaft, and is capable of rotating in relation with the crankshaft.

The camshaft 1 3 is formed integrally with cams 14. An intake valve 1 5 for opening and closing an intake port 17 and an exhaust valve 16 for opening and closing an exhaust port 18 are mounted in the cylinder head 12 in such a manner that the intake and exhaust valves 1 5 and 16 can axially reciprocate. The exhaust valve 1 6 and its valve operating mechanism are constructed in the same manner as the intake valve 1 5 and its operating mechanism. A retainer 1 9 is fastened to a stem end 1 5a of the valve 1 5. A valve spring 20 is disposed under compression between the retainer 19 and the cylinder head 12. The valve spring 20 urges the valve 1 5 so that the port 17 is closed by the valve 15.A rocker arm 21 is located above the camshaft 13, and is swingable in a plane which is approximately perpendicular to the axis of the camshaft 13. Driven by the cam 14, the rocker arm 21 reciprocates the valve 15. The rocker arm 21 has a first longitudinal end having a follower 21 a, and a second longitudinal end which is spaced longitudinally from the first end and has a groove 21 b (Fig. 2). The follower 21 a is held in contact with the cam 14. The groove 21 b extends longitudinally of the rocker arm, and receives the stem end 1 5a of the valve 1 5. The lash adjuster 22 pivotally supports the rocker arm 21 at an intermediate portion betwaen the first and second ends. The adjuster 22 includes a fulcrum for the rocking motion of the rocker arm 21.The rocker arm 21 is swingable on the fulcrum in the plane which includes the axis of the valve 1 5 and is approximately perpendicular to the axis of the camshaft 13. In this plane of the rocking motion, the adjuster 22 is movable (up and down in Fig. 1) by force of hydraulic fluid pressure. The adjuster 22 automatically adjusts the valve clearance between the valve stem end 1 5a and the second end of the rocker arm 21 (the bottom of the groove 21 b) at a predetermined value such as zero by slightly shifting the fulcrum of the rocking motion by the aid of the force of the valve spring 20 and the driving force of the cam 1 4. The adjuster 22 comprises a casing 24, a plunger 25 and a cylindrical member 26. The casing 24 is fixed to the cylinder head 12.The plunger 25 is received in the casing 24, and is axially movable in a projecting direction and in a retracting direction. The cylindrical member 26 is supported by the plunger 25. The axis of the cylindrical member 26 is approximately parallel with the axis of the camshaft 13, and approximately perpendicular to the plane in which the rocker arm 21 swings (see Fig. 2). The cylindrical member 26 is rotatably received in a hole 21 c formed in the rocker arm 21 at the intermediate portion. Thus, the cylindrical member 26 serves as the fulcrum for the rocking motion of the rocker arm 21. The cylindrical member 26 is formed with a tapered hole 26a which becomes gradually narrower downwardly.

On the other hand, the plunger 25 has a tapered projecting portion 25a, which is fitted in the tapered hole 26a of the cylindrical member 26. In this way, the cylindrical member 26 is supported by the plunger 25, and functions as the fulcrum for the rocking motion of the rocker arm 21 by supporting the rocker arm 21 swingably in the above-mentioned plane of the rocking motion.

The plunger 25 supports the cylindrical member 26 in such a manner that the cylindrical member 26 (the fulcrum for the rocking motion) can move along the axial direction of the plunger 25 in the plane of the rocking motion. Figs. 3A, 3B and 3C show the rocker arm 21 whose longitudinal extending center line x forms an angle of a with the axis y of the hole 21 c in which the cylindrical member 26 is fitted.

The thus constructed valve operating mechanism is operated as follows: When the camshaft 13 with the cam 14 rotates by being driven by the crankshaft, the rocker arm 21 is driven by the cam 14, and thereby swings on the cylindrical member 26 in the plane which includes the longitudinal line x of the rocker arm 21, and forms the predetermined angle of cy with the axis y of the cylindrical member 26. By so doing, the rocker arm 21 reciprocates the valve 1 5. The rocker arm 21 of this example is of an offset type in which the longitudinal line joining both ends of a rocker arm is not perpendicular to the axis on which the rocker arm swings. In such an offset type rocker arm, its principal axis of inertia is not parallel with the axis on which the rocker arm swings.

Therefore, when the engine is operated at high speeds, the rocker arm 21 receives a torque of considerable magnitude which twists the rocker arm 21 about its longitudinal line as shown by an arrow x in Fig. 3B. According to the present invention, the cylindrical member 26 fitted in the hole 21 c of the rocker arm 21 supports the rocker 21 and protects the rocker arm 21 against such a torque. That is, the engagement between the cylindrical member 26 and the hole 21 c of the rocker arm 21 prevents the rocker arm 21 from rotating about its longitudinal line and falling to an inclined position. Thus, the valve operating mechanism of the present invention can prevent one-sided contact between the cam 14 and the follower portion 21 a and one-sided wear of contacting surfaces, and maintain the correct valve reciprocating action. As a result, the noise of the engine is reduced, and the engine performance is improved.

In this embodiment, the rocker arm 21 is a center-pivoted type, so that this mechanism possesses the advantages of the center-pivoted type rocker arm as contrasted with an end pivoted type rocker arm. Besides, the hydraulic .lash adjuster 22 supports the fulcrum of the rocker arm 21. This arrangement is very advantageous, because the casing 24 of the hydraulic adjuster 22 is not moving but stationary.

Fig. 4 shows another design of a rocker arm. In this case, a longitudinal center line x0 of a rocker arm 31 is perpendicular to an axis y0 of a hole 31 c in which the cylindrical member is received. In this case, too, the rocker arm 31 is operated in the same manner as the rocker arm 21 of the preceding example.

Claims

1. A mechanism for operating a poppet valve of an internal combustion engine, comprising: a rotatable cam, a rocker arm, connected between said cam and said poppet valve, for swinging on a fulcrum by being driven by the rotational movement of said cam, and by so doing, reciprocating said valve in accordance with the rotational movement of said cam, and support means comprising fulcrum means for supporting said rocker arm swingably and serving as the fulcrum on which said rocker arm swings, and lash adjusting means for supporting said fulcrum means and allowing said fulcrum means to move in a plane in which said rocker arm swings, said fulcrum means being a cylindrical member whose axis is substantially perpendicular to said plane.

2. A valve operating mechanism according to Claim 1, wherein said rocker arm has a transverse hole, and said cylindrical member is rotatably received in said hole.

3. A valve operating mechanism according to Claim 2, wherein said lash adjusting means comprises a casing fixed in a position and a plunger received in said casing, said plunger having a tapered end portion projecting from said casing, the axis of said plunger lying in said plane and said plunger being axially movable in said plane, said cylindrical member having a tapered radial hole in which said end portion of said plunger is fitted.

4. A valve operating mechanism according to Claim 3, wherein said rocker arm has an opening through which said end portion of said plunger is inserted into said tapered radial hole of said cylindrical member.

5. A valve operating mechanism according to Claim 4, wherein said rocker arm having a first longitudinal end to be moved by said cam and a second longitudinal end for pushing said valve, the fulcrum of said rocker arm lying between said first and second longitudinal ends.

6. A valve operating mechanism according to Claim 5, wherein said cam and said valve lie on one side of said rocker arm, and'said casing of said lash adjusting means lies on the other side of said rocker arm.

7. A valve operating mechanism according to Claim 6, the angle formed between the axis of said cylindrical member and said plane is not a right angle.

8. A valve operating mechanism according to Claim 6, wherein the angle formed between the axis of said cylindrical member and said plane is a right angle.

9. A valve operating mechanism according to Claim 6, wherein said lash adjusting means is a hydraulic lash adjuster.

10. A valve operating mechanism as hereinbefore described with reference to Figs. 1 to 3, or Fig. 4 of the accompanying drawings.