JP3198694B2 - Shim for internal combustion engine valve train - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve mechanism for an internal combustion engine,
More specifically, the present invention relates to a disk-shaped metal shim attached to the top of a valve lifter and in contact with a cam. In a valve operating mechanism of an internal combustion engine, in particular, a top portion of a valve lifter comes into contact with a cam and reciprocates (opens and closes) a valve by an amount corresponding to a valve lift caused by rotation of the cam. Further, in order to prevent local wear of the top of the lifter due to the cam, usually, the center of the lifter and the center of the cam (width) are offset by about 0.5 to 3 mm to forcibly rotate the head of the lifter. The present application relates to an improvement of a valve lifter in which a fitting-type metal shim is provided on a top surface side of a head component member of the valve lifter, and the shim rotates in contact with a cam.

[0002]

2. Description of the Related Art In a valve lifter of an ordinary gasoline engine, a fitting-type rotatable shim is a steel disc having a diameter of about 25 to 30 mm. The disk-shaped metal shim is supplied with lubricating oil because friction loss occurs due to sliding of the cam. Then, when the shim is manufactured, the surface roughness is made uniform over the entire surface by the finishing.

Generally, friction loss at a sliding portion between a cam and a mating member can be suppressed low by reducing the surface roughness. For example, Japanese Patent Application Laid-Open No. 61-124581 has proposed that a contact surface portion of a rocker arm that comes into contact with a cam is polished and further subjected to a surface smoothing treatment.

[0004]

Performing the surface smoothing treatment in addition to the polishing treatment as proposed results in a remarkable increase in processing time and processing cost. In particular, such a problem is further increased in high-precision surface finishing. On the other hand, between the cam and the shim in the valve mechanism, an increase in friction (friction) has become a problem, especially when the engine is running at a low speed (idle operation). This means that the cam nose will slide slowly when touching the shim,
This is because the lubricating oil film becomes particularly thin and enters a boundary lubrication state.

Conventionally, the surface roughness is uniform on the entire surface of the shim.
However, the actual cam-shim contact surface
Therefore, the lubricating oil film does not have a uniform thickness. It's a sim
This is due to the fact that it is rotating at high speed. This oil slick (most
Small) Thickness distribution on the shim is as follows:
As shown in FIG. First, in the plane of the rotating shim
Is the rotational angular velocity ω as shown in FIG.
In heart O₀= 0 and distance d from the center of the shim₁Then
u₁= D₁ω and distance d from the center of the shim_TwoThen u_Two
= D_Twoω and distance d from the center of the shim_ThreeThen u_Three= D
_Threeω. Where u_ThreeIs u ₁And u_TwoIs the direction
The opposite is true.

Assuming that the rotation speed of the cam is Uc, the average speed at the contact point is as follows: V ₀ = (Uc + u ₀ ) / 2 V ₁ = (Uc + u ₁ ) / 2 V ₂ = (Uc + u ₂ ) / 2 V ₃ = ( Uc + u ₃ ) / 2.

According to the EHL theory, it is widely known that the minimum oil film thickness is proportional to the speed to the 0.7th power.
Therefore, the minimum oil film thickness at each position is h ₀ , h
When _1, h ₂ and _{h 3, h 3 <h 0} <h 1 <h 2
Thus, the thickness distribution shown in FIG. 1 is obtained. Further, a film thickness ratio 状態 (lambda) of the following equation is often used as an index of the lubrication state.

[0008]

(Equation 1)

In the formula, Hmin: minimum oil film thickness (μm) σ ₁ , σ ₂ : cam and shim surface roughness (Ra value, μm) The relationship among the film thickness ratio, lubrication state and friction is shown in Table 1.
It is shown as follows.

[0010]

[Table 1]

The inventor of the present invention has conducted a lubrication analysis on a case where a practical engine is lubricated with a normal engine oil.
m was secured. In the case of this practical engine, when the film thickness ratio is Λ = 1, the surface roughness of the cam and the shim is σ ₁ = σ ₂ = 0.05 μm, and when 膜厚 = 2.5, the surface roughness of the cam and the shim is σ ₁ = σ ₂ = 0.02 μm.
When the film thickness ratio S = 1, the friction is equivalent to that of a roller-rocker. When し て も = 2.5, even if the surface roughness is further improved, the friction is not reduced. In the conventional cam-shim at a practical level, the film pressure ratio Λ was 0.19 at the center of the shim. The conditions in this case are as follows:
Shim surface roughness 0.48μm, cam surface roughness 0.34μ
m, the cam rotation speed is 300 rpm, and 1
0W30 was used.

Thus, the boundary between the cam and the shim is in the boundary lubrication state as seen from Table 1, and the friction increases as the film thickness ratio decreases. Therefore, if the rotational speed is low and the minimum oil film thickness Hmin is small, and the surface roughness at the shim central portion is reduced, the friction can be reduced. on the other hand,
The cam has a contact width and is in contact with the shim at an offset (the distance f between the center line of the shim and the center line of the cam in FIG. 2) to apply a rotational driving force to the shim in the cam advancing direction. In order to prevent local wear of the shim, it is also necessary to increase the shim rotation propulsion force by giving appropriate friction, so that it is not necessary to improve the surface roughness of the shim outside. This is because the minimum oil film thickness increases as the shim rotates more easily.

An object of the present invention is to provide a shim having a shim surface roughness that contributes to promoting the rotation of the shim and capable of reducing friction at the center of the shim.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to provide a disk-shaped metal shim mounted on the top of a valve lifter in an internal combustion engine valve train and rotating in contact with a cam.
This is achieved by a shim for a valve train of an internal combustion engine, characterized in that the surface roughness of the shim is roughened at the periphery compared to the center side of the shim. .

The center portion of the shim for reducing the surface roughness has a center of the shim which is equal to or more than 1/3 of the cam width and equal to or less than the radius width shorter than "1/2 of the cam width offset distance f". Preferably it is.

[0016]

The conventional surface roughness is reduced by reducing the surface roughness on the center side of the disk-shaped metal shim and increasing it on the peripheral side. In this way, the rotation of the shim is promoted, and at the same time, the lubricating oil film thickness on the center side, which tends to cause boundary lubrication, is secured to reduce friction.

In order to make the friction ratio of the lubricating oil film Λ ≧ 1 so that the friction during idling at the center of the shim is equal to or less than the friction corresponding to the roller-rocker, the surface roughness is 0.05 μm to 0.05 μm. It is desirable that the thickness be 07 μm. Also,
At the periphery of the shim, the rotation speed is faster than at the center, and the minimum lubricating oil film thickness is greater than at the center, but nevertheless, the friction to secure the shim rotation is secured, so the surface roughness is reduced. It is desirable that the thickness be 0.1 to 0.12 μm.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the accompanying drawings. The shim according to the present invention is a steel disc fitted into the top surface side of the head component of the valve lifter as before, and its dimensions (diameter and thickness) are the same as before. Then, in the shim 1 according to the present invention, as shown in FIG. 3, the cam contact surfaces are a central part a and a peripheral part b, and the surface roughness σ ₃ of the central part a is the surface roughness σ of the peripheral part b. _It is smaller than ₄ .

In terms of the manufacturing process, a shim is manufactured in a conventional manner, and finally, in order to improve the roughness of the shim central portion a,
A step of polishing only the central portion is added.
Further, after the entire surface of the cam contact surface is finished to the roughness σ ₃ , the roughness of the peripheral portion b may be roughened. Based on the above calculation of the minimum oil film thickness Hmin in a practical engine, the cam surface roughness
Calculating the preferable roughness of the shim central part and the peripheral part, assuming that it is constant at 0.05 Ra, is as follows.

Surface roughness σ ₃ = 0.05 Ra (or about 0.25 Rz) of central part a Surface roughness σ ₄ = 0.1 Ra (or about 0.5 Rz) of peripheral part b And lower limit of central part a The area is an area having a width of “１ ／ of the cam width” around the center of the shim.
This is a region having a radius shorter than “１ ／ offset distance f of cam width”. As an example of the shim roughness, in the case of the shim in the above-mentioned practical engine, 3.2 Rz to 2.0 Rz (0.48 Rz).
9Ra to 0.306Ra).

In the shim according to the present invention in which the surface roughness is changed as described above, the periphery of the shim promotes the rotation of the shim by sliding with the cam, and the shim has a film having a small roughness at the center. Friction can be reduced by increasing the thickness ratio.

[0022]

As described above, the rotation shim of the valve tufter according to the present invention suppresses the increase in friction at low engine speed by making the surface roughness of the shim central part smaller than that of the peripheral part. Can be. This leads to prevention of damage to the cam and also extends the life of the valve train. Further, assuming the same degree of friction as that of the conventional shim, the present invention can be applied to a lubricating oil having a low viscosity (or even when the same oil is used at a high temperature). This will make it difficult to form an oil film with low-viscosity oil, which will lead to an increase in the fraction.However, the surface roughness at the center of the shim is improved and the value of the oil film thickness ratio Λ there is increased to increase the friction. Will not be invited.

[Brief description of the drawings]

FIG. 1 is a graph showing a distribution of a lubricating oil film thickness between a cam and a shim.

FIG. 2 is a schematic plan view of the shim illustrating the rotation of the shim, the rotation speed at a point inside the shim, and the cam position.

FIG. 3 is a schematic sectional view of a shim according to the present invention.

[Explanation of symbols]

1: Shim O: Shim center σ ₃ : Surface roughness of shim central part σ ₄ : Surface roughness of shim peripheral part A ₁ , A ₂ : Outer diameter of shim f: Offset distance

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F01L 1/20 F01L 1/14

Claims (1)

(57) [Claims] 1. A disk-shaped metal shim (1) mounted on the top of a valve lifter in an internal combustion engine valve mechanism and rotating in contact with a cam, the surface roughness of the shim is reduced by:
A shim for a valve train of an internal combustion engine, wherein the shim is roughened at a peripheral portion (b) as compared with a central portion (a) of the shim.