JPH0874525A - Tappet for internal combustion engine and manufacture thereof - Google Patents

Abstract

PURPOSE: To improve the strength of a too wall center part with which the shaft end of an engine valve is brought in contact, by making the density of the center part of the top wall with which the shaft end of the engine valve is to be brought in contact in a tappet main body composed of the top wall and a cylindrical body part higher than the density of the other part. CONSTITUTION: A tappet main body 1 is composed of a top wall 2 and a cylindrical body part 3, and a bottom provided holding hole 4 into which a shim for adjusting the valve clearance is to be fitted is formed on the upper surface of the top wall 2. A round recessed part 5 is formed on the upper surface center of the top wall 2, and a downward projecting part 6 is formed on the lower surface center, and the projecting part 6 is to be brought in contact with the shaft end of an engine valve 7. The tappet main body 1 is formed by the powder metallurgy method, namely, the sintering, and the projecting part 6 with which the engine valve 7 is to be brought in contact has the density higher than that of the other part. Since the strength of the center part of the too wall with which the shaft end of the engine valve to be brought in contact is increased, the compressive strength resistance of the part is enhanced, and the generations of a recess and abrasion are restrained to the minimum extent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tappet used in a direct acting valve operating mechanism in an internal combustion engine and a method for manufacturing the tappet.

[0002]

2. Description of the Related Art Many of the tappets of this type are made of relatively inexpensive iron. To manufacture this tappet, conventionally, a mild steel material such as low carbon steel is cold-forged to almost the final shape of the tappet. After molding, it is carburized or heat treated to provide the required mechanical strength and wear resistance, and then each part is machined to finish.

[0003]

A tappet used in a direct-acting type valve operating mechanism is usually designed so that the shaft end of the engine valve abuts on the lower surface center of the top wall of the tappet. In the inside, a high compressive load repeatedly acts on the central portion of the lower surface of the top wall. Therefore, a dent or a wear mark is likely to occur in the central portion of the lower surface of the top wall, and in order to prevent this, it is necessary to increase the mechanical strength, particularly the compression resistance strength of that portion.

However, it is difficult for the tappet formed by the cold forging using the above-mentioned mild steel material and the subsequent carburizing treatment or heat treatment to locally greatly improve the strength of the central portion of the top wall.

In order to solve this, it is conceivable to increase the addition amount of hard elements such as carbon and chromium in the composition of the raw material, and perform cold forging and heat treatment to strengthen the entire tappet. In this case, not only the moldability deteriorates and the quality becomes unstable, but also the quality becomes excessive and the cost increases.

The present invention has been made to solve the above-mentioned problems, and the strength of the central portion of the top wall with which the shaft end of the engine valve abuts can be greatly improved by a simple means. It is an object to provide a tappet for an engine and a manufacturing method thereof.

[0007]

SUMMARY OF THE INVENTION According to the present invention, the above-mentioned problems can be solved by changing the density of the central portion of the top wall, which is in contact with the axial end of the engine valve, in the tappet body including the top wall and the cylindrical body. It is solved by making the density higher than that of.

Further, the tappet has a gap for forming a body of the tappet body and a hole for forming a top wall in the die,
After filling the required amount of raw material powder, by compressing this raw material powder with an upper punch having a downward circular convex portion in the center of the lower surface, a green compact having substantially the same shape as the tappet body to be produced is formed. It is manufactured by sintering a green compact.

At this time, the central portion of the raw material powder filled in the holes is simultaneously compressed from above and below by the convex portion of the upper punch and the lower punch provided in the mold so as to face the convex portion. Is good.

[0010]

Since the central portion of the top wall of the tappet body, which is in contact with the shaft end of the engine valve, has a high density, the hardness of that portion is increased, and the compression strength and wear resistance are improved.

[0011]

FIG. 1 is a vertical sectional front view showing an embodiment of the tappet of the present invention.

The tappet body (1) comprises a top wall (2) and a cylindrical body (3) hanging downwardly from the top wall (2).
A bottomed holding hole (4) for fitting a shim (not shown) for valve clearance adjustment is formed on the upper surface of the. A circular recess (5) is formed in the center of the upper surface of the top wall (2), and a downward bulge (6) is also formed in the center of the lower surface.
Engages with the shaft end of the engine valve (7).

The tappet body (1) is formed by powder metallurgy, that is, sintering, and the bulging portion (6) with which the engine valve (7) contacts has a higher density than other portions.

FIG. 2 shows a procedure for molding a green compact for producing the tappet body (1). First, the molding device will be briefly described. (8) is a mold, (9) is a cylindrical first lower punch that slides up and down along the inner peripheral surface of the mold (8), (1)
0) is a second punch which is slidably fitted in the first lower punch (9).
The lower punch, (11) is a cylindrical first upper punch that can be inserted into the mold (8), and (12) is the second upper punch that is slidably fitted in the first upper punch (11). It is an upper punch.

A circular recess (10a) is formed in the center of the lower surface of the second lower punch (10).

A downward circular protrusion 12a is formed in the center of the lower surface of the second upper punch 12.

The radial dimension of the annular gap (13) formed between the die (8) and the second lower punch (10) is determined by the body (3) of the tappet body (1) to be manufactured. ) Is set equal to the wall thickness.

In order to mold a green compact using this apparatus, first, as shown in FIG. 2 (A), the first lower punch (9) is slightly lowered, and the first and second upper punches ( 11) (12) is raised, the gap (13) in the mold (8) and the second
The required amount of raw material powder (14) is filled in the holes in the upper part of the lower punch (10). As the raw material powder (14), an inexpensive Fe-C based powder material is preferable.

Then, as shown in FIG. 2B, the first and second lower punches 9 and 10 are raised, and at the same time, the first and second lower punches 9 and 10 are raised.
Lower the upper punches (11) (12) to compress the raw material powder (14),
A green compact (15) having substantially the same shape as the tappet body (1) to be manufactured is molded. At this time, due to the downward circular projection (12a) in the center of the lower surface of the second upper punch (12), the raw material powder (1
The center of the upper surface of 4) is strongly compressed, so the green compact (1
As for the density of 5), the central portion of the top wall (15a) corresponding to the top wall (2) of the tappet body (1) has a higher density than the other portions.

When the green compact (15) is taken out from the mold (8) and sintered and necessary parts are machined, only the bulging part (6) has a high density as shown in FIG. The tappet body (1) having high hardness and high compression strength can be easily obtained.

In this way, when the tappet body (1) is manufactured by the powder metallurgy method, the mixing amount of the hardening element such as carbon can be appropriately adjusted at the stage of the raw material, and the machine required for the tappet. The mechanical strength and the like can be easily increased without the conventional cold forging and the subsequent carburizing treatment.

FIG. 3 shows another embodiment for molding a green compact as described above. In this embodiment, a guide hole (10b) penetrating on the central axis of the second lower punch (10) similar to the above.
A third lower punch (16) having a diameter substantially the same as that of the convex portion (12a) of the second upper punch (12) is slidably fitted in the inside, and the central portion of the filled raw material powder is The convex portion (12a) of the second upper punch (12) and the third lower punch (16) simultaneously compress.

By doing so, the compressibility of the central portion of the top wall (15a) in the green compact (15) is further increased, so that the density of that portion is made denser and stronger than the embodiment shown in FIG. Greatly improved.

The present invention is not limited to the above embodiment. For example, in FIG. 2 and FIG. 3, the first and second lower punches (9) and (10) are integrated with the die (8) so as to be immobile, and the filled raw material powder (14) is 2 Upper punch (11) (1
2) only (the third lower punch (16) also rises in FIG. 3)
You may make it compress by.

[0025]

According to the present invention, the following effects can be obtained. (a) Since the strength of the central portion of the top wall with which the shaft end of the engine valve abuts increases, the compression resistance strength of that portion increases,
Occurrence of dents and wear can be minimized.

(B) According to the methods described in claims 2 and 3, it is possible to easily manufacture the tappet body in which the central portion of the top wall has a locally high density.

[Brief description of drawings]

FIG. 1 is a central vertical sectional front view showing an embodiment of a tappet of the present invention.

FIG. 2 shows a manufacturing procedure of a tappet of the present invention, (A) is
FIG. 3B is a vertical cross-sectional view showing a step of filling the die with the raw material powder, and FIG. 6B is a step of forming the green compact by compressing the raw material powder with the upper and lower punches.

FIG. 3 is a longitudinal sectional view showing a state in which a green compact has been formed by another manufacturing procedure.

[Explanation of symbols]

 (1) Tappet body (2) Top wall (3) Body (4) Holding hole (5) Recess (6) Bulging part (7) Engine valve (8) Mold (9) First lower punch (10) Second lower punch (10a) Recessed portion (10b) Guide hole (11) First upper punch (12) Second upper punch (12a) Convex portion (13) Gap (14) Raw powder (15) Green compact (15a) ) Top wall (16) Third lower punch

Claims (3)

[Claims] 1. A tappet body comprising a top wall and a cylindrical body, wherein a central portion of the top wall with which a shaft end of an engine valve abuts has a higher density than other portions. Tappet for internal combustion engine. 2. A raw material powder is filled into a gap for forming a body portion of a tappet body and a hole for forming a top wall in a die, and then the raw material powder is downwardly rounded at the center of a circular convex portion. A method for producing a tappet for an internal combustion engine, comprising: forming a green compact having substantially the same shape as a tappet body to be produced by compressing the green compact with an upper punch, and sintering the green compact. 3. The central portion of the raw material powder filled in the holes is simultaneously compressed from above and below by the convex portion of the upper punch and the lower punch provided in the mold so as to face the convex portion. The method for manufacturing a tappet for an internal combustion engine according to claim 2, wherein