JPS59124570A - Processing method for connecting rod bearings - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of machining a bearing portion of a connecting rod to which shocks are repeatedly applied, such as a connecting rod of an internal combustion engine or a reciprocating compressor.

In the case of a connecting rod for an internal combustion engine, the upper end connects to the piston and the lower end connects to the crank. Since the connecting portion is subjected to repeated loads due to inertia caused by the reciprocating movement of the piston and explosion pressure within the cylinder, load fluctuations such as tensile force and compressive force are always applied to the inner surface of the bearing fitting portion of the connecting rod body. In recent years, the output rate of engines has improved, and as the engine speed increases and the explosion pressure increases, the fluctuating load increases.However, in many cases, the dimensions and shape of the bearing cannot be changed, and this fluctuating load Because the fretting is so large and so frequent, relative slippage occurs between the inner surface of the connecting rod body and the outer circumferential surface of the bearing, resulting in so-called fretting corrosion (annealing). When fretting corrosion occurs, it often causes cracks and damage to the main body.

To prevent fretting corrosion,
Conventionally, it has been considered to harden the surface of the bearing fitting part.
Methods of hardening the surface by nitriding the surface or rolling finishing are known, but the nitriding method causes deformation of the connecting rod, which is difficult to correct and difficult to apply immediately. This method had the disadvantage of requiring careful application testing before implementation, such as adjusting roll dimensions and roll pressure for each type of engine. On the other hand, there is a problem in that when the interference between the bearing and the connecting rod is increased, the internal pressure in the tensile direction applied to the inner surface increases and the strength is reduced, and when the interference is loosened, the fit becomes poor.

The present invention applies shot peening as a means of suppressing the occurrence of fretting corrosion by intentionally roughening the surface and increasing the friction coefficient of the fitting part, and then processing when fitting the bearing. It is an invention about law. FIGS. 1(A) and 1(B) are a front view and a side view of the connecting rod of the engine. The connecting rod main body 1 has a cylindrical bearing 2 at one end through which a piston pin passes, and a two-part cylindrical bearing 3 at the other end through which a crank pin passes. The connecting rod main body 1 is divided into two parts at the bearing 3, and is joined by ports 1 to 5. 6 is a knock bottle for joining. In the present invention, before fitting the bearing 2 or the bearing 3 to the connecting rod main body 1, the fitting surface of the connecting rod main body 1 is shot peened by strongly spraying (shot peening) steel powder onto the bare surface. Peening increases the hardness of the scalp and makes the surface rough.

Figure 2 shows the relationship between shot time and hardness.
The horizontal axis shows the shot peening processing time (minutes), and the vertical axis shows the hardness Hv, showing the results of measuring the internal hardness change of vJFj. The line is 0.2mm.

The C line is 0.3 mm, and the hardness is even smaller inside the line, and the harder it is closer to the surface. Regarding the shot time, the hardness increases rapidly from about 20 minutes, and tends to gradually increase until about 309 minutes. After about 30 minutes of shot peening, the surface becomes rough like a satin finish. When a bearing is fitted into such a bearing portion, the friction between the bearing metal and the bearing metal is strong, and the degree of adhesion is good and fretting corrosion does not occur.

Figure 3 shows the surface roughness before and after shot peening after about 30 minutes.
It has been experimentally confirmed that the surface roughness after machining is roughly i20 to 25μ compared to μ, and that the apparent internal dimension eventually increases by δ. When a bearing is inserted into a cylindrical surface whose internal dimensions have been reduced by δ, it is thought that the interference between the main body 1 and the bearing or bushing increases, and the internal pressure in the tensile direction applied to the inner surface of the main body 1 increases, which in turn increases the strength. It had the disadvantage of lowering the This improvement can be achieved by expanding the diameter of the cylindrical surface of the main body 1 by δ in advance, taking into consideration the final finished dimensions of shot peening.

Further, when the bearing portion of the connecting rod main body 1 is subjected to shot peening, an etch on the bearing FM6 surface protrudes inward as shown in FIG. 4.

This protrusion 7 may vary slightly depending on the size of the shot powder and the strength of the shot, but when the bearing 2 or 3 is fitted into the bearing fitting part in this state, the state will be as shown in Fig. 5. As a result, the two sides do not fit together, and even if shot peening is applied, a sufficient effect cannot be obtained on the mating surfaces. Therefore, it is effective if the etch of the bearing fitting portion of the main body before shot peening is inwardly 2-b as shown in FIG. 6 to reduce the angle at an inclination angle of about 1°. Unless the etching is removed and shot peening is performed, the phenomenon shown in FIG. 4 will not occur, and the effect of shot peening can be achieved because no protrusion 7 is generated in the etching on the bearing fitting surface.

In addition, in the state shown in Fig. 4 where shot peening was performed without using the method shown in Fig. 6, 2
It is also possible to taper the corners over ~3 mm with an inclination angle of approximately 1° (Figure 7). By doing so, when the bearing 2 or 3 is fitted, the shot peening effect can be improved, and the bearing fitting portion can be brought into a completely tight contact state as shown in FIG.

As explained in detail above, the present invention is such that the surface of the bearing fitting portion is enlarged in diameter by δ culm than usual before the bearing fitting of the connecting rod.
When a bearing is fitted into this bearing fitting part after being shot peened for about 0 minutes, the surface of the bearing fitting part is hardened and leaves a residual compressive force on the inner surface, increasing the fatigue strength. Since the grooves are formed, the coefficient of friction increases after the bearing is fitted, and the bearing is completely fitted into the bearing fitting part1, which has the effect of suppressing the occurrence of fretting. In particular, by enlarging the diameter of the bearing fitting part while taking into account the shot peening effect, an extremely good bearing fitting condition can be obtained, and furthermore, it is possible to obtain an extremely good fitting condition of the bearing, and to further reduce the protrusion of the etch caused by the peening of the bearing fitting part. It is an effective method to obtain an extremely good fit even in parts by performing a corner cutting process on the portion 7 as shown in FIG.

[Brief explanation of the drawing]

Figure 1 (a) and (b) are front views showing an example of a connecting rod and (
b) A cross-sectional view taken along the line A-A in the figure, Figure 2 is a chart showing the relationship between shot time and surface hardness, Figure 3 is an enlarged cross-sectional view showing surface roughness, and Figure 4 is the fit after shot peening. Fig. 5 is a partial sectional view of the connecting rod without showing the mating surface; Fig. 5 is a sectional view showing the bearing fitting part; 2 Figs. 6 and 7 show processing examples of the bearing fitting part; 1-
6 is a sectional view showing an example of etching processing before shot peening, FIG. 7 is an example of etching processing after shot peening, and FIG. 8 is a sectional view showing a fitted state of the bearing. DESCRIPTION OF SYMBOLS 1... Connecting rod main body, 2... Bearing, 3... Half bearing, 5... Bolt, 6... Dowel pin, 7... Projection part. Patent applicant's agent name: Patent attorney Kaku 1) Kato' (ro) '/9, Ntopi 12〉2°〃口1＠En(Ima)date 3 Tsuritate 7 Figure 4 Figure 4 Figure 51 Figure 61 ψ1'

Claims (3)

[Claims] (1) In the processing method where the bearing fitting part of the connecting rod body is shot peened before the bearing is fitted, and then the bearing is fitted, the inner surface of the bearing fitting part is tightened before the bearing is fitted.
A method of processing connecting rod bearings that is characterized by expanding the diameter by taking into account the final finished dimensions of shot peening, and then subjecting it to shot peening. (2) The method for processing a connecting rod bearing according to claim 1, wherein the etching on the inner surface of the bearing fitting portion before shot peening is inwardly carved by 2 to 3+ nm and tapered at an inclination angle of 1°. (3) The method for processing a connecting rod bearing according to claim 1, wherein the etching on the inner surface of the bearing portion before shot peening is tapered inward at an inclination angle of about 1° over a range of 2 to 311ffi.