JPH0860205A - Production of tappet for internal combustion engine - Google Patents

Abstract

PURPOSE: To increase the tissue density at both top and bottom ends where large stresses act on a tappet and to enhance the strength and wear resistance of these parts. CONSTITUTION: The powder P of a metallic material packed into the die hole 22 of a die 21 is compressed by a lower punch 23 and upper punch 25 having small-diameter parts 24, 26 meeting the shape of the tappet to be molded, by which the green compact having the shape of the desired tappet is molded. The green compact is sintered. The tappet is molded at the tissue density of the region proximate to the upper and lower punches made larger than in the intermediate region by the relative friction resistance among the powder particles at the time of compression molding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a tappet, which is applied to a direct-acting valve operating mechanism of an internal combustion engine, by sintering. And a method for manufacturing a tappet with improved strength and wear resistance.

[0002]

2. Description of the Related Art A direct acting valve operating mechanism for an internal combustion engine is generally constructed as shown in FIG. Inside the guide hole (02) formed in the cylinder head (01), a tappet (having a substantially H-shaped cross section formed by a cylindrical peripheral wall (03a) and a disc-shaped top wall (03b) ( 03) is fitted so as to be slidable in the axial direction.

In the center of the peripheral wall (03a) of the tappet (03),
The stem (04a) of the engine valve (04) is arranged with its shaft end abutting against the center of the lower surface of the top wall (03b) of the tappet (03). Near the shaft end of the stem (04a), the spring bearing (05)
Are fixed by a pair of cotters (06), and the engine valve (04) is moved upward by a valve spring (07) that is compressed between the lower surface of the spring receiver (05) and the cylinder head (01). Is being urged towards. A disc-shaped shim (08) is attached to a holding hole formed in the upper surface of the upper wall (03b), and a rotating cam (09) is in contact with the upper surface of the shim (08).

When the cam (09) rotates, the engine valve (0
4) is driven up and down via the shim (08) and the tappet (03) to open and close the intake or exhaust port formed in the cylinder head (01).

[0005]

[Problems to be Solved by the Invention] The above-mentioned tappet (03)
Is usually formed by cold forging a mild steel material such as low carbon steel. An unbalanced load of the load (F) is applied to the tappet (03) in the initial stage of pressing by the rotary cam (09). Due to the bending moment at this time, large stresses (F ₁ ) and (F ₂ ) that compress in the lateral direction from the cylinder head (01) act on the upper and lower ends of the tappet (03).

Therefore, the upper and lower ends of the tappet (03) are required to have high compressive strength and wear resistance. However, it is difficult to locally increase the strength, etc. of the upper and lower edges by the conventional means of manufacturing the tappet (03) with a mild steel material suitable for cold forging. I can only get things.

To cope with this problem, cold forging can be considered using a material having a high strength such as high carbon steel or high chromium steel as a material for the tappet, but these materials are hard. Therefore, there is a problem that the moldability is poor and the quality is not stable due to cracks in the product.

The present invention solves these problems in the prior art and provides a method for manufacturing a tappet for an internal combustion engine, which can increase the strength of the upper and lower ends of the tappet by a simple means. To aim.

[0009]

According to the present invention, the above-mentioned problems are solved by filling a required amount of powder of a metal material into a die hole having an inner diameter matching the outer diameter of a tappet in a die, , A lower punch for forming the body portion on the lower surface side of the tappet and an upper punch for forming the upper surface side of the tappet are compressed to form a green compact having substantially the same shape as the tappet to be manufactured. Is solved by sintering.

[0010]

When the powder filled in the die cavity is compressed by the upper and lower punches, the frictional resistance between the powders causes the regions close to the opposing end faces of the upper and lower punches to be compressed more strongly than the intermediate region. In the green compact, the density at both upper and lower ends is higher than that at the middle part. Therefore, the tappet formed by sintering has high density at the upper and lower ends thereof, and the strength is increased.

[0011]

FIG. 1 is a schematic sectional view showing the main part of a compression molding machine for carrying out the method of the present invention.

The die (21) is provided with a die hole (22) having a diameter matching the outer diameter of the tappet to be formed, and the lower punch (23).
Is slidably inserted in the axial direction. Lower punch (2
The upper end of 3) is a small diameter portion (24) to form a cylindrical body of the tappet.

An upper punch (2) arranged above the die (21)
5) has the same diameter as the lower punch (23) and is coaxial with the die (21)
Is moved in the axial direction between a position separated from above and a position inserted into the mold hole (22). The lower end of the upper punch (25) is a small-diameter portion (26) having a short size so as to form a holding hole for attaching a shim on the upper surface of the tappet.

In order to compression-mold the tappet, first, the lower punch (23) is lowered to a required height in the die hole (22), and the upper punch (25) is raised to lower the lower punch.
A required amount of powder (P) of a metal material is filled in the die cavity (22) including the annular groove between the small diameter portion (24) and the die cavity (22) in (24).

Then, as shown in FIG. 1, the upper punch (2
5) is lowered and the lower punch (23) is raised to compress the powder (P), and the wall surface of the die hole (22), the upper end portion (24) of the lower punch (23), and the upper punch (25 In the space formed by the lower end portion (26) of (1), a green compact (27) having substantially the same shape as the shape of the tappet to be manufactured is molded.

The compacted green body (27) after molding has a top wall portion (27a) and a body portion which are close to the opposite end faces of the upper and lower punches (23) and (25) due to mutual frictional resistance during compression. The upper and lower end portions of (27b) have a high density, and the middle portion of the body portion (27b) has a low density.

The shaped green compact (27) is extracted from the die (21) and then sintered to obtain a tappet in which the upper and lower ends of the body portion (27b) have a high density.

Therefore, the strength and wear resistance of the upper and lower end portions of the tappet, which are subjected to a large stress during the operation of the engine, are significantly increased.

In the above-described embodiment, the upper punch (2) is formed in order to form the holding hole for attaching the shim on the upper surface of the tappet.
Although the small diameter portion (26) is provided at the lower end portion of 5), the lower surface of the upper punch (25) may be a flat surface when manufacturing a tappet without a holding hole.

[0020]

【The invention's effect】

(a) During operation of the engine, the upper and lower end portions of the tappet, which generate a large amount of stress, have a high density, so that the strength and wear resistance of that portion are increased.

(B) In order to increase the density of the required portion by utilizing the frictional resistance between the powders in the compression molding of the powders, the strength is made by using a material having poor formability as in the conventional cold forging method. Therefore, it is possible to easily and inexpensively manufacture a tapette having a desired density distribution.

(C) Since the middle part of the body has a low density and a large porosity, the oil retaining effect is high and the wear resistance is improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a compression molding machine for carrying out the method of the present invention and a procedure for molding a green compact by the compression molding machine.

FIG. 2 is a sectional view showing a main part of a direct-acting valve operating mechanism of an internal combustion engine.

[Explanation of symbols]

 (21) Die (22) Mold hole (23) Lower punch (24) Lower punch small diameter portion (25) Upper punch (26) Upper punch small diameter portion (27) Green compact (27a) Top wall portion (27b) Body (P) powder

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location F01L 1/14 G

Claims (1)

[Claims] 1. A lower punch for forming a body portion on the lower surface side of a tappet after filling a required amount of powder of a metal material into a die hole having an inner diameter matching the outer diameter of the tappet in a die. And a top punch for forming the upper surface of the tappet, to form a green compact having substantially the same shape as the tappet to be manufactured, and sinter the green compact. Manufacturing method.