JPH0240476B2 - RENKETSUBONOJIKUKEBUNOKUMITATEHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of assembling a bearing portion of a connecting rod that is subjected to repeated impacts, such as a connecting rod of an internal combustion engine or a reciprocating compressor.

(Prior Art) In the case of a connecting rod for an internal combustion engine, the upper part is connected to the piston and the lower part is connected to the crank. The upper and lower connecting parts are subject to repeated loads from inertia caused by the reciprocating movement of the piston and explosive pressure within the cylinder, so the bearing fitting surface (hereinafter referred to as the fitting surface) of the bearing fitting part of the connecting rod is It is always subject to load fluctuations as a result. In recent years, the output rate of the engine has improved,
As engine speed increases and explosion pressure increases, fluctuating loads are becoming larger, but it is often difficult to change the shape and dimensions of bearings, and this fluctuating load is extremely large and If this occurs frequently, so-called fretting corrosion occurs between the fitting surface and the outer peripheral surface of the bearing. When fretting corrosion occurs, cracks and damage to the main body often occur due to it. The fretting corrosion is thought to be caused by relative slippage between the fitting surface of the connecting rod and the outer peripheral surface of the bearing.

Generally, it is thought that the occurrence of fretting corrosion is controlled by the relative sliding amount and surface pressure between two objects at the contact surface, and there is a
If the surface pressure is small, fretting corrosion will not occur even if the relative slip amount is large, but if the surface pressure is large, fretting corrosion will occur even if the relative slip amount is small.

In order to prevent the occurrence of fretting corrosion, it has been thought to harden the surface of the bearing fitting part, and methods of surface hardening by nitriding the surface, rolling finishing, etc. are known.

(Problems to be Solved by the Invention) In the case of the nitriding method in which the bearing fitting part of the connecting rod body is surface hardened, the connecting rod is deformed, and it is difficult to correct it and apply it immediately. In some cases, the drawback was that careful application testing was required before implementation, such as adjusting roll dimensions and roll pressure for each type of engine. On the other hand, regarding the fit condition between the bearing and the bearing fitting part of the connecting rod, if the interference is increased too much to prevent relative slippage, the surface pressure on the fitting surface will increase and tensile stress will be generated inside. When the strength of the connecting rod body is reduced and the tightening is loosened, the fitting becomes loose, resulting in a problem that the fitting condition becomes poor.

(Means for Solving the Problems) The present invention intentionally roughens the bearing fitting surface of the connecting rod main body to prevent relative slippage, which is a cause of fretting corrosion, and at the same time, to harden the fitting surface. This invention relates to a method for assembling a bearing portion of a connecting rod, in which shot peening is applied as described above, and then a bearing is fitted. The inventors have conducted intensive research to solve the above problem, and as a result they have arrived at this invention.The inventors have developed a method to prevent relative slippage due to the protrusion formed on the fitting surface biting into the outer peripheral surface of the bearing. I got to thinking.

The gist of the first invention is that, when assembling a connecting rod, the bearing fitting surface of the connecting rod main body is machined and finished to have a radius larger than the standard diameter by δ, and then the fitting surface is subjected to shot peening, and then A method for assembling a bearing portion of a connecting rod, which comprises tapering the end of the mating surface after processing at an inclination angle of about 1° over 2 to 3 mm, and then fitting a bearing to the mating surface. The gist of the second invention is that when assembling the connecting rod, the fitting surface of the connecting rod main body has a radius δ from the standard diameter.
After machining and finishing the mating surface to a larger size, the end of the mating surface is
A connecting rod bearing characterized in that it is tapered over ~3 mm at an inclination angle of about 1°, then shot peening is applied to the fitting surface, and a bearing is fitted to the processed fitting surface. How to assemble the parts. Here, δ is the amount of change in the inner diameter of the bearing fitting surface that must be adjusted in order to apply shot peening, which is 10 to 20μ
(microns).

(Function) The present invention roughens the fitting surface of the bearing fitting part of the connecting rod by shot peening the bearing fitting surface of the connecting rod main body to prevent relative sliding with the bearing, and also prevents relative sliding with the bearing. It also takes advantage of surface hardening, which is a feature of

Normally, the mating surface of the connecting rod is machined to a surface roughness of 4 to 6 microns, and the bearing is mated as is (the inner diameter of the bearing mating part at this time is hereinafter referred to as the standard diameter). In the present invention, before applying shot peening to the mating surface, the mating surface is finished by increasing the radius by δ and then the bearing is mated, so that the protrusion on the mating surface touches the outer peripheral surface of the bearing. Since it is possible to prevent relative sliding of the fitting portion by being partially pushed in, it is possible to prevent fretting corrosion from occurring.

The inventors predicted that shot peening would cause the surface to become depressed and the inner diameter of the mating surface to expand, but contrary to expectations, the results of the experiment showed that shot peening would cause the inner diameter of the mating surface to expand. It was found that the difference in roughness before and after was reduced.

Therefore, if the bearing is inserted as is without enlarging the diameter of the fitting surface before shot peening, the compressive stress generated in the bearing will increase.

The tensile stress generated on the fitting surface of the connecting rod body increases.

Bearings with a two-part cylindrical shape, such as the large end of the connecting rod, require bolts 5 to fasten the large end cap 12 (see Figure 1) that holds the bearing down to the connecting rod 1. Since the distance becomes larger, the tightening force of the bolt required to fit the bearing increases. As a result, the net fastening force of the bolt against the fluctuating load acting on the big end of the connecting rod becomes small, and the margin for fastening the big end cap 12 against the fluctuating load decreases.

In order to prevent this, the tightening force of the bolt can be increased, but this requires increasing the size of the bolt, which leads to an increase in the weight of the large end. This has the opposite effect to the general idea that the weight of moving parts such as connecting rods should be reduced as much as possible.

Therefore, in the present invention, by finishing the inner radius of the fitting surface to be larger than the standard diameter by δ, the above-mentioned problems are removed, and proper bearing fitting conditions are satisfied. Relative slippage between the mating surface and the outer periphery of the bearing can be suppressed. In other words, the minute protrusions on the fitting surface dig into the outer circumferential surface of the bearing.

Furthermore, when shot peening is applied to a smooth bearing fitting surface, protrusions are formed at the ends of the fitting surface, and the ends have a larger bulge than the center. If the bearing is fitted into the fitting part in this state, only this protruding part will come into contact with the bearing, and the entire intermediate surface that should be in close contact will not be in close contact, resulting in a poor fitting condition, which will cause relative slippage. To this end, by chamfering the region of the protrusion at the end, a fitted state with uniform surface pressure can be obtained. This may be done by removing the protrusion after the shot peening process, or by chamfering the end portion in advance before the shot peening process to prevent the protrusion from becoming a protrusion.

(Example) To explain an example of the present invention with the drawings, FIGS. 1A and 1B are a front view and a sectional view taken along the line A-A of a connecting rod of an engine as an example of a connecting rod. The connecting rod 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 a bolt 5. 6 is a connecting knob pin.
In the present invention, before fitting the bearing 2 or the bearing 3 to the connecting rod main body 1, shot peening is applied to the fitting surfaces 8, 9 of the connecting rod main body 1 by forcefully spraying steel powder onto the bare surface. Figure 3 shows the surface roughness of the fitting surface before and after shot peening after about 30 minutes.
The surface C before processing has an average roughness of 4 to 6 μm, whereas the surface D after processing has an average roughness of 20 to 25 μm, making the surface rough like a satin finish. At this time, the inner diameter of the mating surface is
14~21μ smaller. At this time, the minute protrusions on the surface bite into the outer peripheral surface of the bearing (Actually measured 1 to 4μ)
Considering this, fretting corrosion can be reliably prevented by making the inner diameter 10 to 20 μ larger than the standard radius before shot peening. When a bearing is fitted to such a fitting surface, the minute protrusions formed on the fitting surface bite into the outer circumferential surface of the bearing, eliminating relative slippage, ensuring good adhesion and reducing the amount of relative slippage even when external force is applied. No fretting corrosion occurs. Figure 2 shows the relationship between shot time and hardness. The horizontal axis shows the shot peening time (minutes), and the vertical axis shows the hardness Hv, and shows the results of measuring changes in the internal hardness of the material. The A line shows the hardness 0.1mm inside the surface, the B line shows the hardness 0.2mm, and the C line shows the hardness 0.3mm.
mm, and the hardness is even lower further inside, and the closer to the surface, the higher the hardness. Regarding the shot time, the hardness increases suddenly from about 20 minutes, and tends to gradually increase until about 30 minutes. Furthermore, it has been confirmed through experiments that the dimension of the finished surface of the fitting surface subjected to shot peening increases by δ in radius due to the difference in roughness described above. When a bearing is fitted into a fitting surface whose diameter has been reduced by 2δ due to the increased dimension of the finished surface by δ, the apparent interference between the connecting rod body 1 and the bearing or bushing increases, so the connecting rod body This has the disadvantage that the tensile stress applied to the fitting surface of No. 1 increases, which actually reduces the strength. In order to improve this, it is important to enlarge the bearing fitting surface of the connecting rod body 1 by δ in advance in consideration of the final finished dimensions of the shot peening.

Example 1 In the assembly method of the first invention, the connecting rod body 1
The fitting surfaces 8 and 9 of are finished in advance to have an inner diameter 2δ larger than the standard diameter. Thereafter, in the shot peened state shown in FIG. 4, the end of the fitting surface is tapered inward over 2 to 3 mm at an inclination angle of approximately 1° (FIG. 7). By fitting the bearing 2 in this manner, the effect of shot peening can be improved, and the bearing fitting surface 8 can be completely brought into close contact as shown in FIG. As a result, fretting corrosion was sufficiently prevented.

Example 2 Next, in an embodiment according to the assembly method of the second invention, the fitting surfaces 8 and 9 of the connecting rod main body 1 are finished in advance to have an inner diameter larger than the standard diameter by 2δ. Thereafter, the edges are chamfered to about 2 to 3 mm and shot peened. Although the connecting rod large end 11 is split into two, the condition of the fitting surface 9 is almost the same as that of the fitting surface 8. In this case, as mentioned above, the finish of the fitting surface is enlarged by the radius δ, but since the diameter has been enlarged in advance, the bearing is fitted and the bolt 5 is enlarged.
Appropriate tightening margin can be obtained even when tightened with
Problems such as poor tightening of the two parts 1 and the mating surfaces do not occur. However, if the end portions are not chamfered, a phenomenon occurs in which the end portions of the fitting surface 8 (or 9) protrude inward as shown in FIG. 4. Although the protruding portion 7 differs slightly depending on the size of the shot powder and the strength of the shot, the bearing fitting portion 1 in this state is
When the bearing 2 (or 3) is fitted into the bearing 0 (or 11), the condition becomes as shown in Fig. 5, and the surfaces between the protrusions do not fit together, and even after careful shot peening, the bearing fitting surface 8 ( or 9), the effect will not be sufficient. For this purpose, the end of the bearing fitting surface of the main body before shot peening is tapered inward by 2 to 3 mm at an inclination angle of about 1°, as shown in Fig. 6, to reduce the angle. I'll keep it. The situation shown in FIG. 5 will not occur. As a result, a sufficient effect of preventing fretting corrosion was obtained.

(Effects of the Invention) As explained in detail above, the present invention involves finish-machining the bearing fitting surface to have a radius larger than usual by about δ before fitting the connecting rod to the bearing, and subjecting it to shot peening for about 30 minutes. When a bearing is fitted onto this bearing fitting surface after the bearing has been fitted, the unevenness is formed on the fitting surface. Slippage is prevented, the bearing fits perfectly onto the mating surface, and as a result of being roughened by shot peening, the mating surface is hardened, leaving compressive residual stress on the inner surface and increasing fatigue strength. Therefore, it has the effect of effectively suppressing the occurrence of fretting corrosion. In particular, by machining the inner diameter of the fitting surface of the bearing fitting part slightly larger in advance in consideration of the diameter reduction effect of shot peening, it is possible to obtain an extremely good fitting condition of the bearing. Protrusion 7 created at the end due to shot peening of the mating surface
This is an effective method of chamfering to obtain an extremely good fitting condition even in parts as shown in FIG. 8.

[Brief explanation of drawings]

Figure 1 A and B are a front view showing an example of a connecting rod, and a sectional view taken along the line A-A in Figure A, Figure 2 is a chart showing the relationship between shot time and surface hardness, and Figure 3 is a surface roughness diagram. Fig. 4 is a partial sectional view of the connecting rod showing the fitting surface after shot peening, Fig. 5 is a sectional view showing the bearing fitting part, Fig. 6,
Figure 7 is a sectional view showing an example of machining of a bearing fitting part, Figure 6 is an example of edge machining before shot peening, Figure 7 is an example of edge machining after shot peening, and Figure 8 is an example of bearing fitting. FIG. 1... Connection rod body, 2, 3... Bearing, 5... Bolt, 6... Knock pin, 7... Projection, 8, 9
... Bearing fitting surface, 10, 11 ... Bearing fitting part, 1
2...Large end cap.

Claims (1)

[Scope of Claims] 1. When assembling the connecting rod, the bearing fitting surface of the connecting rod main body is processed and finished to have a radius larger than the standard diameter by δ, and then the fitting surface is subjected to shot peening processing, and then the processing is performed. 2 to 3 mm from the end of the rear mating surface
1. A method for assembling a bearing portion of a connecting rod, the method comprising tapering the connecting rod at an inclination angle of about 1°, and then fitting a bearing to the fitting surface. 2. When assembling the connecting rod, the bearing fitting surface of the connecting rod main body is machined and finished to have a radius larger than the standard diameter by δ, and then the end of the fitting surface is cut by approximately 2 to 3 mm.
A method for assembling a bearing portion of a connecting rod, characterized by performing taper processing at an inclination angle of 1°, then subjecting the fitting surface to shot peening processing, and fitting a bearing to the processed fitting surface. .