Tappet in an internal combustion engine

Abstract

 In a tappet in use for an internal combustion engine, a shim (10) is provided on an upper wall (7) of a tappet body (6) and has a chamfer (106) in the lower circumferential edge of the shim (10). The shim (10) is not engaged on a curved portion of a corner (12) between the side wall (8) and the upper wall (7) of the tappet body (6). Thus, the shim (10) is fitted on the upper wall (7) of the tappet body without a clearance groove, thereby increasing strength and durability.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a tappet in use for a direct acting type valve operating mechanism in an internal combustion engine of a vehicle, and especially to a tappet which has no annular groove on an inner corner between an upper wall and a side wall for supporting a shim.

[0002] Fig. 3 schematically illustrates a direct acting type valve operating mechanism in use for a DOHC type engine.

[0003] A poppet valve 101 is provided in a cylinder head 105 with a pair of cotters 102, a valve spring retainer 103 and a valve spring 104. At the upper end of the valve 101, there is provided a cylindrical tappet body 106 which is closed by an upper wall 107, the lower surface of the upper wall 107 being engaged with the end of a stem of the valve. A recess 109 is formed by an annular side wall 108 projected on the outer circumference of the upper wall 107, a disc-shaped shim 110 for adjusting valve clearance being removably engaged in the recess 109. The valve 101 is opened and closed by pressing a tappet body 116 slidably engaged in the cylinder head 105, by a rotary cam 111 which contacts the upper surface of the shim 110.

[0004] There is formed an annular clearance groove 113 which opens towards the recess 109, on the corner 112 between the side wall 108 and the upper surface of the upper wall 107 of the tappet body 106. The clearance groove 113 is provided to fit the shim 110 on the upper surface of the upper wall 107 and to prevent stress concentration to the corner 112. When the tappet body 106 is molded by cold forging, it is inevitable to form a curved surface 112a on the corner 112 between the upper wall 107 and the side wall 108. Owing to the curved surface 112a, when the shim 110 is fitted in the recess 109, the circumferential edge of the shim 110 is engaged on the curved surface 112a, thereby preventing fitting with the upper wall 107.

[0005] For example, the clearance groove 113 is formed as shown in Figs. 5 and 6. In the method as shown in Fig. 5, the inner circumferential surface of the side wall 108 is cut by the edge of a bite 114 having substantially the same width with that of the clearance groove 113, the edge of the bite 114 is pressed against the corner 113, and the upper surface of the upper wall 107 is continuously finished.

[0006] In the method as shown in Fig. 6, first, the clearance groove 113 is formed by the edge of the bite 114, and the inner circumferential surface of the side wall 108 and the upper surface of the upper wall 107 are simultaneously ground and finished.

[0007] In the conventional tappet, owing to the clearance groove, the lower side wall 108 is thinner, so that the side wall 108 is likely to cause fatigue rupture when the side wall 108 is repeatedly subjected to large lateral load when the engine is operated.

[0008] Further, in the foregoing method of forming the clearance groove, it takes a lot of time to form the groove, thereby decreasing working efficiency. Further, since a thinner bite must be used, wear in the bite 114 becomes faster and the bite 114 must be often replaced, thereby involving disadvantages in cost.

SUMMARY OF THE INVENTION

[0009] According to the present invention, to solve the disadvantages, it is an object to provide a tappet device in an internal combustion engine which increases working efficiency and strength.

[0010] According to the present invention, there is provided a tappet device in an internal combustion engine, the tappet device comprising:

a cylindrical tappet body which is closed by an upper wall, an annular side wall being projected upwards on an outer circumference; and

a shim which is removably fitted in a recess fdormed in the side wall so as to adjust a valve clearance, the shim having a chamfer on a lower circumferential edge.

[0011] The chamfer is formed on the lower circumferential edge, so that the lower circumferential edge of the shim is not engaged with the curved surface of the corner between the side wall and the upper wall of the tappet, thereby fitting the shim on the upper wall of the tappet body.

[0012] It is not necessary to form a clearance groove on the tappet body, thereby preventing stress concentration to the lower portion of the side wall, and decreasing the number of the processing steps to increase efficiency and productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The features and advantages of the invention will become more apparent by the following description with respect to embodiments as shown in the appended drawings wherein:

Fig. 1 is an enlarged vertical sectional view of the main portion of one embodiment according to the present invention;

Fig. 2 is a vertical sectional view of variations of a shim;

Fig. 3 is a central vertical sectional front view of a conventional tappet in a direct acting type valve operating mechanism;

Fig. 4 is an enlarged vertical sectional view of the main portion of a tappet body before forming a clearance groove; and

Fig. 5 is an enlarged vertical sectional view which illustrates how to form the clearance groove; and

Fig. 6 is an enlarged vertical sectional view which illustrates another way to form the clearance groove.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0014] In the following embodiments of the present invention, numerals which does not contain "1" are allotted to the same members as those shown in the conventional device as above.

[0015] In Fig. 1, a shim 10 is molded by powder metallurgy, and has a chamfer 10b on the lower circumferential edge, the chamfer 10b having a concave section 10b. In a tappet body 6, a corner between a side wall 8 and an upper wall 7 is formed as a curved surface as made by cold forging.

[0016] Owing to the chamfer 10b on the lower circumferential edge of the shim 10, no clearance groove in the conventional device is required on the corner 12 of the tappet body 6, but the shim 10 can be fitted on the upper surface of the upper wall 7. Thus, it prevents stress concentration on the corner 12 in the tappet body 6, and needs no process for forming a clearance groove by a bite.

[0017] Fig. 2 (a) to (e) illustrates variations of the chamfer. (a) shows a chamfered portion 10d; (b) shows a right-angled groove; (c) shows a rounded portion 10f; (d) shows a concaved portion 10g; and (e) shows a portion 10h which comprises a right-angle and a rounded portion. The variations achieve similar advantage to one as illustrated in Fig. 1. A chamfer may be formed on the upper circumferential edge 10c, so that the shim 10 can be reversibly used. The shim may be made by punching and then, the chamfer 10b may be made by a lathe etc.

[0018] The foregoings merely relate to embodiments of the present invention. Any modifications and changes may be made by person skilled in the art without departing from the scope of claims wherein:

Claims

1. A tappet device in an internal combustion engine, the device comprising:

a cylindrical tappet body which is closed by an upper wall, an annular side wall being projected upwards on an outer circumference; and

a shim which is removably provided in a recess formed in the side wall so as to adjust a valve clearance, the shim having a chamfer on a lower circumferential edge.

2. A tappet device as defined in claim 1 wherein the shim is formed by powder metallurgy.

Drawing