Method of manufacturing a tappet in an internal combustion engine

Abstract: A tappet (6) in an internal combustion engine comprises a cylindrical body (8) and a cam receiving plate (10) on the top wall of the cylindrical body (8). To manufacture the tappet (6) by forging, light metal material is provided on the surface which has a groove (30) of the cam receiving plate (10), and forged in a die to mold the body (8) and to connect the body (8) with the cam receiving plate (10) by a single step, thereby decreasing the number of mechanical steps and cost.

Description: BACKGROUND OF THE INVENTION The present invention relates to a method of manufacturing a tappet in an internal combustion engine, the tappet having a body which is made of light metal such as Al alloy, and in particular to a method of manufacturing a tappet in an internal combustion engine, the tappet having a cam receiving plate made of wear resistant material at the contact surface with a rotary cam. To lighten a direct acting type valve operating mechanism, tappets made of Al alloy have been widely used instead of conventional steel tappets. Al alloy tappets have lower strength and wear resistance than steel tappets. Therefore, on the upper surface of a tappet which contacts a rotary cam, a cam receiving plate made of wear resistant material is attached. To attach the cam receiving plate on the upper surface of the tappet, there are methods of caulking, brazing and pressing engagement of a projection into a groove. JP-A-4 246 210 (D1) discloses a method of manufacturing a tappet of an internal combustion engine, a body (3) of the tappet being made of light metal, a wear resistant hard cam receiving plate (2) being provided on an upper surface of a top wall of the body (3). The method disclosed in D1 comprises the steps of: providing light metal material on a surface of the cam receiving plate (2) said surface having a groove (30); and forging the light metal material on the cam receiving plate (2) in a die to mould the body (3) and to connect the body (3) with the cam receiving plate (2) at the same time. However, in the conventional methods, two members are separately molded and connected, which increases the number of mechanical steps and cost. For example, in pressing engagement, an Al alloy body and a steel cam receiving plate are separately formed and connected with each other, but it is necessary to improve accuracy in size of the groove and projection which are engaged with each other, which requires a number of mechanical steps and high cost. SUMMARY OF THE INVENTION The object of the present invention is to provide a method of manufacturing a tappet in an internal combustion engine, a body of the tappet being molded and integrally connected with a cam receiving plate, thereby decreasing the number of steps for mechanical processing and cost. The said object is achieved by a method comprising the steps according to claim 1. BRIEF DESCRIPTION OF THE DRAWINGS The features and advantages of the invention will become more apparent from the following description about embodiments with respect to appended drawings wherein: Fig. 1 is a vertical sectioned front view of a direct acting type valve operating mechanism in an internal combustion engine which contains a tappet made by a method according to the present invention; Fig. 2 is sectional views of steps of the first embodiment, (a) being before forging, (b) being after forging. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 1 illustrates a direct acting type valve operating mechanism which contains a tappet according to the present invention. 2 denotes a cam which rotates together with rotation of a crankshaft(not shown). 4 denotes a valve stem of an intake/exhaust valve. 6 denotes a tappet which follows the cam 2 and reciprocates up and down in Fig. 1 to transmit the movement to valve stem 4 of the intake/exhaust valve 4. 12 denotes a cylinder head which guides reciprocating movement of the tappet 6. 14 denotes a valve spring for allowing the intake/exhaust valve to close. 16 denotes a valve spring retainer for transmitting force of the valve spring 14 to the intake/exhaust valve. 18 denotes a pair of cotters which are engaged in an annular groove 20 of the valve stem 4 of the intake/exhaust valve so that the valve spring retainer 16 may be attached around the valve stem 4. The tappet 6 comprises a body 8 and a cam receiving plate 10. The body 8 is molded from Al alloy and comprises a top wall 22 and a cylindrical portion 24. The top wall 22 which is put between the cam 2 and the valve stem 4 is subjected to high compression load, so that a thicker portion 26 in the middle of the lower surface is formed. On the upper surface of the top wall 22, there is formed an annular projection 28 the center of which coincides with the axis of the tappet. The cam receiving plate 10 which needs wear resistance to sliding with rotation of the cam 2 is made of steel and, if necessary, subjected to heat treatment. On the lower surface of the cam receiving plate 10, there is an annular groove 30 at a position corresponding to the annular projection 28 of the body 8. The annular projection 28 of the body 8 is engaged in the annular groove 30, so that the body 8 is connected with the cam receiving plate 10. The present invention relates to a method of manufacturing the tappet 6 as mentioned above. The first embodiment of the method according to the present invention will be described with respect to Fig. 2. In manufacturing, the tappet is inverted. In Fig. 2, 40 denotes a stationary die for molding. 42 and 44 denote moving lower and upper punches. The upper surface of the lower punch 42 is flat, and the lower surface of the upper punch 44 has a recess 44a which fits the thicker portion 26 of the top wall 22 of the body 8. Between the die 40 and the upper punch 44, there is a gap for forming the cylindrical portion 24 of the body 8. As shown in Fig. 2(a), the steel cam receiving plate 10 in which the annular groove 30 was already formed is placed on the lower punch 42 in the die 40 to direct the surface which has the annular groove 30 upwards. On the cam receiving plate 10, there is an inverted intermediate material 45 made of Al alloy for forming the body 8, the intermediate material 45 being shorter than body 8 to be molded and having a thicker top wall 45a. As shown in Fig. 2(b), the upper and lower punches 42 and 44 move simultaneously, or either one of them moves to forge the intermediate material 45. The hard steel cam receiving plate 10 is not plastically deformed, but only Al alloy intermediate material 45 is plastically deformed to decrease thickness of the top wall 45a and to flow into the gap "C", so that the body 8' and the cam receiving plate 10 are integrally combined. The contents of the top wall 45a flow at smaller amount into the gap "C", so that they flow towards and away from the center of the thicker portion 26' owing to the bottom section of the upper punch 44 as shown in the arrows in Fig. 2(b). The annular groove 30 of the cam receiving plate 10 may be preferably formed at a neutral position of material flow that the outer diameter "B" of the annular groove 30 is equal to or slightly smaller than the maximum outer diameter "A" of a thicker portion 26'. Accordingly, in forging, the material of the top wall 22' is closely filled in the annular groove 30, so that larger bonding strength is obtained between the body 8' and the cam receiving plate 10.

Claims: A method of manufacturing a tappet (6) in an internal combustion engine, a body (8) of the tappet (6) being made of light metal, a wear resistant hard cam receiving plate (10) being provided on an upper surface of a top wall (22) of the body (8), a thicker portion (26) being provided in the middle of the top wall (22) of the body (8), the method comprising the steps of: providing light metal material on a surface of the cam receiving plate (10), said surface having a groove (30) ; and forging the light metal material on the cam receiving plate (10) in a die (40) to mold the body (8) and to connect the body (8) with the cam receiving plate (10) at the same time, said groove (30) being formed on the cam receiving plate (10) at a neutral position of flows of contents of the light metal material which moves towards and away from a center of said thicker portion during the step of forging. The method as defined in claim 1 wherein the light metal material comprises a cylindrical intermediate material (45) which is shorter than the body (8) to be molded, the groove (30) comprising an annular groove formed at a position corresponding to an outer circumference of the thicker portion of the top wall (22). The method as defined in claim 1 wherein the forging step comprises cold forging.

Inventors: HARA NOBUO, HARA, NOBUO
Applicants: FUJI VALVE, FUJI OOZX INC.
Application year: 1996
Main classification: F01L1
IPC codes: F01L1, B21D53