JPS5838264B2 - Machining method of pivot part of cast iron Rocker arm - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for machining a pivot portion of a cast iron rocker arm.

Among the rocker arms of internal combustion engines, the swing arm type rocker arm is used to open and close the valve 5 of the cylinder by swinging by a rotating cam 4 with the pivot portion 2 of the rocker arm 1 as a fulcrum, as shown in Fig. 1. ing.

Since the pivot portion 2 of the rocker arm 1 slides on the adjuster 3 having a spherical surface, which is a mating part, it is required that the dimensional accuracy and radius of the radius R be good.

Even if this rocker arm is made by precision casting, the roundness and R shape of the pivot portion cannot be sufficiently accurate.

Therefore, it is possible to hot coin the cast rough shape to satisfy the required precision of the pivot part, but when the deformability of cast iron is small, the coining will be large because the dimensional error of the cast rough shape is large. Otherwise, the tensile stress in the casing increased, causing cracks in the product.

However, the Rotsuka arm is made of a material that emphasizes wear resistance.
Since the hardness is as high as Hv≧400, it is obtained by grinding, but the disadvantage is that productivity is very low because the finishing accuracy of the pivot part is strict and the grindstone used for grinding is very small. has.

The present invention is intended to solve the above-mentioned drawbacks, and by making the pivot part of the rough section obtained by casting into a special shape, the amount of coining due to the R dimension error is small, and the tensile stress is reduced. As a result, even if the deformability of the cast iron rough section is small, hot coining can be performed within the range of the deformability.

That is, in the present invention, the roughly shaped rocker arm is made of cast iron with low deformability, and in this case, the shape of the pivot portion is larger than the R dimension of the product, and the R center position is eccentric from the R center position of the product, and the bottom part is It is characterized by hot coining at 450° C. or higher at the pivot portion of the rough section.

As the cast iron to which the processing method of the present invention can be applied, those used as materials for rocker arms of conventional swing arm systems can be used, such as alloy cast iron such as high chromium cast iron.

Regarding the deformability of the cast iron rough shape material, one that can be deformed at a temperature of 450° C. or higher and has an elongation rate of 3% or higher, for example, is used.

The rough shape of the pivot part is 1 to 5 times larger than the product R dimension.
The R center position is preferably eccentric by 1.5 to 30 times the R center position of the product.

Hot coining is performed at a temperature of 450°C or higher, preferably 750°C or higher.
It is carried out at 1100°C, and for example, when the material is high chromium cast iron, it is carried out at 900 to 1000°C.

Hereinafter, the present invention will be specifically explained based on Examples.

The product dimensions of the pivot part in the example are R as shown in FIG. 7.
5 shows how to make a rocker arm having a curved surface with R center position eccentricity E of 2.6.

High chromium cast iron (Fe-3%C-30
%Cr (% is a weight factor) is used to make a roughly shaped Rotsuka arm by precision casting.

In this case, the dimensional accuracy of the pivot part by precision casting is R7
．． 5±0.15 with a maximum variation of 0.3.

High chromium cast iron has almost no tensile elongation at room temperature, but shows elongation at high temperatures, elongating by 4 to 7 at 900'C.

In this example, the shape of the pivot part of the rough profile is made such that the bottom part 2F and the entrance part 22 are relieved as shown in FIG. 3, the width to be coined is limited to the necessary range, and the R
It was cast to a size of 9.85±0.15 (R10 in FIG. 3).

The pivot portion having such a shape was hot-coined at a temperature of 900° C. or higher to produce a pivot portion having a curved surface of predetermined dimensions as shown in FIG. 4.

Next, in order to explain the present invention more clearly, FIG. 5 is shown.

Figure (I) on the left side of Figure 5 shows the dimensional change when the pivot part shape is cast with the same R dimension as the product by the conventional method and coined to correct the casting error. The master diagram is a diagram obtained by using the method of the present invention.

As shown in Figure 5 (I), when casting is performed with the same R dimension as the product dimension, and the R of the rough profile is small, the coining allowance at the entrance part a becomes large and the circumferential tensile stress at the end face increases, causing cracking. When the R dimension of the rough shaped material is large, the coining allowance of the bottom C becomes a dog because it is machined so that the curved surface of the part indicated by the symbol b near the end surface comes into contact with it, resulting in cracks at the bottom.

Note that the hatched area indicated by symbol A in the figure indicates the coining amount when the R dimension is a dog, and the hatched area indicated by symbol B indicates the coining amount when the R dimension is small.

In contrast to the above, when the method of the present invention is used, the bottom part 21 is made into a relief shape as shown in FIG. The coining distance is small both when the input is large and when the input is small, and good coining can be performed without tensile stress being applied to the bottom portion 21 and the entrance portion 22.

In addition, in the figure, S indicates the R center position, d indicates the dimensional variation, the P punch center locus, and the arrow indicates the coining direction.

As mentioned above, when using the method of the present invention, by setting the shape of the pivot part of the rough section to a specific shape, finishing processing by coining can be easily performed without any particular selection of cast iron materials, resulting in higher accuracy than before. It has the advantage that rocker arms can be easily produced without requiring a large number of man-hours.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of a swing arm type rocker arm, Fig. 2 is a cross-sectional view showing the product dimensions of the pivot part of the rocker arm, Fig. 3 is a cross-sectional view of the pivot part of a rough section according to the present invention, and Fig. 4 5 is a cross-sectional view showing a pivot portion finished by the method of the present invention, and FIG. 5 is an enlarged cross-sectional view of the pivot portion showing the difference in coining allowance between the conventional method and the method of the present invention. In the diagram: 1... Locker arm, 2... Pivot position, 3... Adjuster, 4...
Cam, 5... Valve, 21... Bottom of pivot part, 22... Inlet part of pivot part.

Claims (1)

[Claims] 1. The shape of the pivot part of the rough shape material of the rosoka arm made of cast iron with low deformability is set to be larger than the R dimension of the product and R
The center position is eccentric from the R center of the product, and the bottom part is relieved, and the pivot part of this rough profile is set at 450 mm.
A method for processing a pivot part of a cast iron rock arm, which is characterized by coining at a temperature of °C or higher.