JP3341014B2 - Shims used in valve trains for internal combustion engines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tappet of a valve train for an internal combustion engine and to selectively improving the strength of a shim fitted in a gap provided between cams.

More specifically, the present invention relates to a shim in which the strength of the portion where the shim and the cam come into contact is selectively improved by giving the tissue structure of the shim a specific distribution in its volume density.

[0003]

2. Description of the Related Art A valve operating mechanism of an internal combustion engine mainly includes an engine valve, a valve spring for closing the valve, a valve spring retainer for transmitting the force of the valve spring to the valve, a valve cotter for receiving the valve spring, and opening and closing of the valve. A tappet that accommodates a rocker arm or the like to be driven and transmits reciprocating motion to a valve following a cam, and a rotating cam.

[0004] A gap is provided between the cam and the tappet to cope with changes over time due to thermal expansion and friction. A sheet metal for adjusting the valve is fitted in this gap. This sheet metal is called a shim. In some cases, a metal tip different from or similar to the tappet is fitted to a portion where the tappet contacts the top of the engine valve. in this case,
The chip may be referred to as an inner shim, and the shim fitted into the gap may be referred to as an outer shim to distinguish them. The present invention relates to an outer shim.

[0005] In the valve operating mechanism, a cam provided on a camshaft presses the valve through a shim regularly to open and close the valve accurately in accordance with the rotation. Therefore, a concentrated load is periodically and repeatedly applied to the surface where the shim contacts the cam, and as a result, stress is generated inside the shim.

Although we do not wish to be bound by theory, we will describe the loads and stresses on the shims. The cyclic compression load applied to the shim by the cam varies depending on the rotation speed, but is on average 100 to 200 kg / mm ² .

The allowable stress of the shim is 100 to 150 kg / mm ²
It is. When the shim is repeatedly subjected to the cam's compressive load, the largest stress is first generated at the point where the shim and the cam come into contact, and this is caused by the deformation inside the shim in the form of a deformed sponge whose maximum diameter is shifted upward. To the tappet that accommodates the shim, and in some cases, a longitudinal strain occurs at the point where the shim and the cam come into contact.

Therefore, it is not always necessary to make the entire shim uniform in terms of metal and solid structural structures and practically, and even the strength of the portion where the shim and the cam come into contact is sufficiently maintained. It can be understood that it is only necessary.

However, there have been no reports on the research and development of shims from the above-mentioned viewpoints. Also,
There is no report on a method which does not require a restriction that each part must be uniformly densified in a compression molding step which is an important condition when producing a shim by a sintering method.

[0010]

The problem to be solved by the present invention is that the prior art has made it possible to increase the strength of the part where the shim comes into contact with the cam by making it stronger than the other parts.
That is, the wear resistance of the portion could not be selectively improved.

Another problem to be solved by the present invention is that, in producing a shim by the conventional sintering method, it is possible to overcome the restrictions imposed by the conditions of the molding method or the processing method and to broaden the range of options. It was not.

A further problem to be solved by the present invention is:
The following will be clarified one by one.

[0013]

The means for solving the above-mentioned problems is to reduce the volume density in the direction perpendicular to the axis of the shim as the part where the shim and the cam come into contact is the largest and the outer diameter side of the shim. The distribution is to decrease continuously.

The shim of the present invention is characterized by having a distribution in the volume density of the shim made of powder metallurgy metal. Therefore, the shim made of powder metallurgy metal will be described below .

In the powder metallurgy method, (a) a material having a high melting point and which cannot be dissolved can be molded, (b) the shape is close to a finished product, the yield is good, the process is greatly simplified, and (c) productivity is high and energy is saved. In recent years, it has been widely used for automotive parts for reasons such as accuracy.

The powder metallurgical metal used in the present invention is mainly Fe-based, Al-based or Ti-based. As the Fe-based, Mo-Ni-Cu-Cr steel, Mo-Cr-Ni steel, etc., as the Al-based, Al-Fe-Si, Al-Si, etc., and as the Ti-based, Ti-V
-Al and the like are exemplified.

As specific examples, C 0.5%, Si 0.85%, Mn
0.20%, Ni 1.0%, Cr 17.0%, Mo8.0%, CaF 2 1.0%
And Fe Bal. And C 0.7-1.3%, Nb 0.5-1.0%, Ni 4.0
%, Cr 1.0 to 3.0%, Mo 5 to 8%, Co 1.0%, CaF ₂ ≦ 1.0
% And Fe Bal. Etc. as Fe-based, 11.7% of Si and Al Ba
l., Si 10-20%, Fe 5-10%, V, Cu, Mo and Al Ba
l., etc. are exemplified as Al-based.

In the present invention, the metal powder is 0.1 to 0.000
When it is desired to increase the hardness in the range of 1 mm, it is appropriately selected in the range of 0.1 to 5 μm or submicron.

The metal powder must be evaluated by comprehensively judging various conditions such as particle size, particle size distribution, particle size, powder particle size, powder apparent density, powder compressibility and moldability.

The method for producing the metal powder used in the present invention should be selected in consideration of the raw material metal to be used, the physical properties of the sintered metal to be produced, and the like, and is not particularly limited. For example, in the case of an Al alloy having excellent wear resistance, for example, an Al-Si alloy containing a large amount of Si, a Ti alloy, or a Co alloy containing Cr, W, and Fe, it is preferable to produce the alloy by rapid solidification.

After the production of the metal powder, these raw metal powders are mixed in an appropriate ratio. For example, Al 70-90
%, Fe 5-10%, Si 10-20% and other trace amounts of V, Mo, Cu, Al
−33Cu−7Mg, Al−6Zn−3Mg, Al−5.6Zn−2.5Mg−1.6Cu
Mix powders with a mixing design of -0.3Cr, Al-10.7Zn-0.9Mg-0.4Zr, etc. In the powder mixing process, products such as Cu, Ni, C, etc.
Sintering accelerators such as Cu and Fe-P, and lubricants such as zinc stearate are added according to the situation.

After the powder mixing step, the powder is pressed into a predetermined shape. After pressing, sintering is performed using a normal sintering method such as hot isostatic pressing (HIP), hot isostatic pressing sintering, pseudo-HIP method, or injection molding. In the sintering, the lubricant is volatilized or decomposed and removed by preheating at about 500 ° C. in a continuous furnace to which a protective atmosphere gas has been supplied, and then sintering is performed at 1100 to 1200 ° C.

It is well understood by those skilled in the art that after sintering, post-processing or post-processing according to the purpose is carried out. For example, to improve dimensional accuracy, sizing, hot forging, etc., to improve strength, roll processing, heat treatment, etc., to improve wear resistance, infiltration, impregnation, oil impregnation, surface treatment, etc.
In order to enhance the rust prevention effect, impregnation, oil impregnation, surface treatment and the like are appropriately selected and performed.

It is known that the strength of an iron-based sintered metal is proportional to the density to a certain extent and then becomes constant. (“Steel Handbook 5”, Maruzen P.513, Fig. 221) In other words, for iron-based sintered metal, the tensile strength (kgf / mm ² ) up to a density of 6.2 to 6.8 (g / cm ³ ) Proportionally, the same 6.8 (g / c
m ³ ) Above, it becomes almost constant. Therefore, in the present invention, it is preferable to design the maximum density portion of the shim at 6.8 to 7.1 g / cm ³ and the minimum density portion at 6.6 to 6.8 g / cm ³ .

Using the above-described metal powder, the volume density in the direction perpendicular to the axis of the shim is substantially trapezoidal, where the portion where the shim and the cam come into contact is maximum, and decreases continuously toward the outer diameter side of the shim. The method of distributing in a curve is as follows: (1) The male mold (lower punch) of the compression molding die is divided into two parts, and after filling the material powder, it is temporarily compressed at, for example, 5 ton / cm ² and then, for example, 6 ton / cm 2 how to the compressed ^2, (2) compression mold of the male (lower punch) and 2 into two cavities, first the material powder was filled into the first cavity, for example, 5 t / cm ² And then the male mold is lowered, the second cavity is filled with the remaining material components, the male mold is raised, and fully compressed at, for example, 6 tons / cm ² , and (3) preformed. A green compact having a trapezoidal cross section is placed in a compression mold of a predetermined shape, and compression-molded with a predetermined compression force. There are three methods of law.

The shim of the present invention produced by the above-described method has a certain amount of pores, and thus has an appropriate oil retaining effect. Incidentally, the oil retaining effect of the shim referred to in the present invention is obtained by mixing Sn powder, graphite, and the like with Cu powder, and pressing and producing the oil. The oil content is 18 vol.
It does not mean more than%.

Hereinafter, the present invention will be described by way of examples.

[Example 1] Mixing ratio and particle size of used metal components Component mixing ratio (%) Particle size (μm) Fe 84.2 2 Mo 5.0 2 Cr 3.0 2 Ni 4.0 2 Nb 0.8 2 C 1.0 2 Co 1.0 2 CaF ₂ 1.0 2

Each component was mixed. At that time, a small amount of zinc stearate was added as a lubricant. After mixing each ingredient,
A male mold of a predetermined compression mold defining a cavity in the shape of a shim is divided into two parts, and all the components are filled in a cavity having an inverted convex shape, and the resultant is first pre-compressed at 5 ton / cm ² and then 6 ton / cm ^2. Final compression.

After the completion of the compression molding, the lubricant was preheated to 500 ° C. in a continuous furnace in which argon gas was fed into the chamber to volatilize and remove the lubricant, and then sintered at 1200 ° C.

The sintered shim was measured by ultrasonic attenuation measurement.
As a result of measuring the volume density distribution perpendicular to the shim axis,
The portion where the shim comes into contact with the cam was a substantially trapezoidal curve at the top.

[0035]

Example 2 A pre-compacted green compact having the same material components as in Example 1 and having a trapezoidal cross section of approximately 1/3 of the upper and lower bottoms was produced. After inserting this preliminary compact into the cavity of the compression molding die, it was compression molded at 6 tons / cm ² . After the completion of the compression molding, sintering was performed under the same conditions as in Example 1.

The surface density (%) of the sintered shim in the direction perpendicular to the axis of the shim was measured by ultrasonic attenuation measurement. As a result, the center of the shim was 98%, and the right and left end faces were almost uniformly distributed at 95%. I knew I was doing it.

[0037]

According to the present invention, the following effects can be obtained: In the conventional powder metallurgy method, there is a restriction that each part must be uniformly densified in a compression molding process after mixing the metal powder, but the present invention is not limited thereto.
The range of choices expands depending on the manufacturing conditions.

B. By adjusting the strength of the portion where the shim and the cam come into contact with each other, it is not necessary to impart excessive physical properties to the entire shim, leading to a reduction in cost.

C. Since the manufacturing method is simplified, the cost is reduced.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F01L 1/20 B22F 7/08 C22C 33/02

Claims (1)

(57) [Claims] 1. A powder metallurgical metal shim fitted in a gap provided between a tappet and a cam of a valve train for an internal combustion engine, wherein the shim and the cam have a volume density in a direction perpendicular to an axis of the shim. The shim is characterized by having a trapezoidal curved distribution that continuously decreases toward the outer diameter side of the shim, with a portion contacting with the upper bottom .