JPH11125236A - Sliding bearing and bearing device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a cost of a back plate, and improve press moldability by detecting the number of crystal grain boundaries in an inside surface area of two specific parts from the back plate uppermost surface, and controlling the distribution so that a rate of the grain boundary number of these two areas falls within a specific range. SOLUTION: A sliding bearing for an internal combustion engine is formed by being bent in a semicircular shape by putting a bearing alloy layer joint to a back plate surface composed of a steel plate on the inside. A crystal grain boundary of a back plate is detected in a cross section by etching the back plate for about 20 seconds by nital having the sulfuric acid concentration of 3 to 20%. The distribution of the number of crystal grain boundaries in two areas is controlled in the relationship of (0<=n1 /n2 ×100<=70%) from the detecting number (n1 ) in a surface area of 10 μm from the back plate back face uppemost surface and the detecting number (n2 ) on the inside by 50 μm from the back plate uppermost surface area. Therefore, a preventive measure against a fatigue crack of the back plate by fretting becomes possible from the viewpoint of such crystal grain boundary control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slide bearing and a bearing device for an internal combustion engine. More specifically, the present invention relates to a slide bearing or a connecting rod capable of suppressing fatigue caused by fretting wear of a backing of a slide bearing. The present invention relates to a bearing device that reduces fretting wear and fatigue of a back metal, which leads to breakage of a connecting rod whose rigidity is reduced while using a high-strength material to reduce the weight of the bearing.

[0002]

2. Description of the Related Art Conventionally, from the viewpoint of reducing noise of an engine (internal combustion engine), a hard rubber, a fluororesin or the like is provided between a bearing metal and a bearing housing, and the thickness is 0.5 to 1 m.
It has been proposed to interpose an elastic body of m (Japanese Utility Model Publication No. 60-27220). It has also been proposed to interpose or bake a cushioning material such as synthetic rubber or synthetic resin between the bearing and the housing from the viewpoint of vibration proofing (Japanese Utility Model Application Laid-open No.
146840 and Japanese Utility Model Laid-Open No. 57-71812).

Conventionally, a sliding bearing interposed between a connecting rod and a crankshaft so as to be rotatably fitted thereto has conventionally been made of a back metal such as a semi-circular mild steel plate and an aluminum alloy or kelmet bonded to the inside of a bend thereof. And other bearing alloys as basic elements. Hereinafter, fretting wear will be described mainly with reference to an example of a connecting rod. However, fretting wear occurs in other internal combustion engine parts in the same situation.

Conventionally, as a countermeasure against fretting wear, Japanese Patent Application Laid-Open No. 4-282013 proposes that an epoxy resin coating to which MoS ₂ is added is baked and fixed to either the inner surface of the large end of the connecting rod or the outer surface of the bearing metal. ing. In the case of the resin coating to which MoS ₂ is added according to this publication, a large amount of particles of the MoS ₂ powder fall off from the resin base material due to small slipping or small tapping that occurs between the inner surface of the large end of the connecting rod and the back of the bearing, and The present applicant has found that there is a problem that the peeling is accelerated, and the present applicant discloses in Japanese Patent Application Laid-Open No. Hei 7-293547 that the tensile strength at 150 ° C. between the housing-side surface of the bearing device and the back surface of the housing is 8 kg / mm ^2. that's all,
Provided is a bearing device for an internal combustion engine in which a resin film having a thickness of 5 to 200 μm is interposed.

[0005] In recent years, in order to reduce the weight of the engine, the weight of the moving parts constituting the engine has been reduced. As one of the measures, increasing the material strength and reducing the rigidity of the connecting rod has been studied. I have. In the first place, fretting wear is caused by the occurrence of these small collisions or small slips between the large end of the connecting rod and the back of the bearing under the high load or high rotation operation conditions of the engine. The connecting rod, whose rigidity is low due to its light weight, is easily deformed by itself and easily hits one side.
There is a concern that a crack may be generated from the adhesion as a starting point, or may be broken at once due to a crack damage of the back metal. For this reason, the parts which are easily broken are covered with overlays, but this should be said to be a bitter measure against weight reduction.
In addition, as a countermeasure against fretting fatigue, the strength of the back metal is also improved. Specifically, it is known to increase the carbon content of the back metal steel sheet and increase the degree of skin pass processing after rolling the steel sheet. When a thin iron-based sintered material is used, since the strength is lower than that of a normal forged material, fretting wear or fatigue is also concerned.

In the bearing manufacturing process, kermet manufactured at a sintering temperature of 700 ° C. to 900 ° C. or an aluminum bearing alloy by pressure welding is subjected to diffusion annealing (200 to 600 ° C.) for increasing the adhesion strength between the back metal and the lining. ℃), and the back metal sheet recrystallizes accordingly. The present inventor paid attention to recrystallization of a steel sheet occurring during this annealing, conducted research, and obtained the following knowledge. That is, the crystal of the backed steel sheet after cold rolling has a worked structure elongated in the rolling direction and having a large anisotropy, while the recrystallized structure is relatively isotropic. From another perspective, in the recrystallized structure, the number of crystal grains per length on the back surface is large, so that the direction intersects the back surface at an angle of approximately 90 ° ± 45 ° toward the back surface of the back metal. The number of growing crystal grain boundaries increases. In the following description, this crystal grain boundary is referred to as “intersecting crystal grain boundary”.

After annealing, the bimetallic bearing is pressed into a semicircular shape. According to the knowledge of the present inventors, small cracks occur at the intersecting crystal grain boundaries during the processing and extend along the grain boundaries. However, it was found that the grain boundary structure was weak even if cracking did not occur, and cracking occurred immediately when used under fretting conditions in an actual machine.

[0008]

As described above, a plain bearing with a back metal having crossed grain boundaries is apt to be fatigued under fretting conditions, and in particular, is liable to break a lightweight connecting rod. In contrast, the conventional method of interposing a coating between the backing metal and the connecting rod does not essentially improve the performance of the backing metal. And there is also a risk of cracking at intersecting grain boundaries. Accordingly, an object of the present invention is to provide a preventive measure against fatigue cracking of a back metal due to fretting from the viewpoint of controlling grain boundaries.

[0009]

In order to achieve the above object, a sliding bearing for an internal combustion engine, which is formed into a semi-circular shape with a bearing alloy layer bonded to the surface of a back metal made of a steel plate inside, is formed by nitric acid. For a grain boundary detected in a cross section of the back metal etched with nital having a concentration of 3 to 20% for about 20 seconds, a unit length in the back metal back direction (however, 1
0 μm or more) is determined by the number (n) in the surface region of 10 μm from the outermost surface of the back metal back surface.
₁ ) and the number (n ₂ ) 50 μm inside the outermost surface region, respectively, 0 ≦ n ₁ / n ₂ × 10
An object of the present invention is to provide a sliding bearing for an internal combustion engine, wherein the distribution of the number of grain boundaries is controlled to be 0 ≦ 70%.

The plain bearing according to the present invention is generally made of carbon steel having a C content of 0.05 to 0.2% and a thickness of 0.3 to 0.3%.
It has a bimetal structure in which a bearing alloy layer is adhered to a 5.0 mm, generally 1.3 to 2.3 mm back metal. The material of the back metal is not limited to carbon steel as described above, and various steel materials including alloy steel can be used. Next, as the bearing alloy layer, kelmet, its improved copper alloy, and various aluminum bearing alloys can be used, and there is no particular limitation. In the case of kelmet, a metal-based or resin-based overlay is usually applied to the surface of the bearing alloy layer. Further, a pure metal layer such as Al, Cu, or Ni may be interposed between the bearing alloy layer and the back metal in order to increase the adhesive strength.

Next, the crystal grain boundary which is the most characteristic of the present invention will be described. In the present invention, the starting point of fretting fatigue is reduced by eliminating the crystal grain boundaries in the surface region or by reducing the number of grains from the inside. By the way, it is natural that the bulk of the back metal steel material is an aggregate of crystal grains, but the disappearance of the grain boundaries in the surface region of the present invention is a state in which no grain boundaries are observed when observed under specific etching conditions. However, the present invention is not limited to an amorphous surface state having no grain boundaries in theory. The present invention has found a relationship between crystal grains detected under specific etching conditions and fretting fatigue, and not every crystal grain boundary is a starting point of fretting fatigue. More specifically, the crystal grain boundaries that are somewhat thick and long are fragile, and serve as starting points for cracking due to fretting.

The surface region where the crystal grain boundaries need to be regulated in order to prevent fretting cracks is the region from the outermost surface of the back metal back to a depth of 10 μm. This depth is 10
If it is less than 5 μm, for example, 5 μm, cracking in a shallow surface region less than 5 μm is unlikely to occur, but it becomes fragile during press bending at a large number of crystal boundaries present inside an unregulated area, for example, 8 μm. Is a problem. That is,
When the bimetallic bearing in this state is incorporated into an actual machine and operated, the material is not easily damaged by fretting.
When this occurs in the surface area of μm, this fracture is continued at the above-mentioned crack at the position of 8 μm at the time of press working, and the fracture of the back metal occurs early. In other words, the generation of cracks is delayed at the very beginning of use, but once the cracks occur, the cracks progress rapidly and deeply into the inside. On the other hand, even if the surface region in which the crystal grain boundaries need to be regulated is deeper than 10 μm from the outermost surface of the back metal, not only is there little relation to the suppression of the occurrence of fretting fatigue, but rather brittleness is caused by performing strong processing. Therefore, the regulation of the crystal grain boundary is 1 as described above.
The depth was set to 0 μm. Further, since fretting occurs at any position on the entire circumference of the back metal semicircle, the grain boundary control according to the present invention is performed over this entire circumference.

The control of the number of grain boundaries in the surface region is as follows.
The number of crystal grain boundaries detected per unit length (100 μm or more) in the back metal back surface direction is defined as n ₁ in the surface region 100 μm from the outermost surface of the back metal back surface, and n _{2 in the} inside of the outermost surface region. When expressed as
≦ n ₁ / n ₂ × 100 ≦ 70%. Here, if n ₁ / n ₂ × 100> 70%, there is no effect of suppressing fretting wear. Preferably, 0 ≦ n ₁ / n ₂
× 100 ≦ 30%. The direction of measurement with respect to the back metal rolling direction is arbitrary.

In the present invention, the reason why the etching solution is nital is that ferrite crystal grains, which are basic components of the backed steel sheet, can be clearly expressed. Further, in order to detect the crystal grain boundaries, the etching conditions were set as nital with a nitric acid concentration of 3 to 20% and the etching time was about 20 seconds. Here, if the nitric acid concentration is less than 3%, especially in the case of high-purity low-carbon steel, crystal grain boundaries are unlikely to appear. It becomes difficult to determine the world. The preferred concentration of nitric acid is 5%. Also, if the etching time is shorter than about 20 seconds or longer, the accuracy of discriminating the crystal grain boundaries is lowered.

As generally accepted, a crystal grain is a grain adjacent via a grain boundary triple point, and the boundary between such grains is a grain boundary. If the back metal sheet has a high carbon content and a ferrite + pearlite mixed structure,
Since the grain boundary triple point is formed by ~ 2 ferrite crystal grains and 2 ~ 1 pearlite grains, the number of each grain boundary is measured. On the other hand, fine particles are observed in the surface region, but they are not adjacent to each other via the grain boundary triple point; they are isolated from each other; only two are adjacent to each other; Often exist in a portion corresponding to a grain boundary triple point. These grains do not count the number of grain boundaries. In addition, if the interface is unclear and looks discontinuous; it is ultrafine that cannot be detected at the level of an optical microscope; and if the particle morphology cannot be identified because it is extremely amorphous, the number of grain boundaries is not calculated as a crystal grain.

Next, a method for reducing the number of crystal grain boundaries in the surface region will be described. First, a method in which fine crystal peening is performed on the back metal surface to destroy and deform recrystallization can be employed. In this case, as the shot, it is preferable to project ceramic particles having a diameter of 20 to 300 μm at a high speed of 50 m / sec or more. Since this condition is a stronger condition than shot peening that adjusts the surface stress that is usually performed,
Affects grain boundaries in the surface region. Next, the back metal back surface is heated to a temperature equal to or higher than the transformation point by high-frequency induction heating, and then rapidly cooled, the structure of the surface region becomes a fine martensite structure or a structure in which free ferrite is combined with this structure. Very blurred. The laser irradiation is almost the same as the high-frequency induction heating, but the structure becomes finer due to the higher temperature heating and faster cooling. Further, a method may be used in which a large amount of impurities such as P are implanted into the back metal back surface by ion implantation to disturb the fcc crystal and the crystal grain boundaries.

The sliding bearing according to the present invention is characterized in that V-added S45
It can be preferably used as a connecting rod bearing of high strength and low rigidity such as C and Ti. The back of the back metal may be coated with Sn plating or the like for preventing rust, but depending on the plating, adhesion due to fretting may be promoted, and improvement in fretting fatigue resistance may hardly be expected. Hereinafter, the present invention will be described in more detail with reference to examples.

[0020]

【Example】

Example 1 An alloy powder of Cu-3 wt% Sn-24 wt% Pb was used as a bearing alloy, and a SPCC steel plate (carbon content 0.15 wt%, thickness 1.5 mm) was used as a backing metal, and the bearing alloy 0 was sintered. .2 mm, 1.5 mm for 1.3 mm
mm bimetallic bearing material was prepared. 80 for sintering
Sintering is performed twice at 0 ° C. The back metal is rolled by 13% by intermediate pass and skin pass. Thereafter, it was pressed into a semicircular plain bearing shape. The result of observing the structure on the back side of the back metal in this state under conditions of 5% nital nitrate (room temperature) and an etching time of 20 seconds is shown in FIG.
0 times). In the structure shown in FIG. 1, many crystal grain boundaries are observed on the surface.

Subsequently, spherical ceramic beads having a particle size of 125 to 185 μm were projected onto the back of the back metal at a speed of about 100 m / sec. FIG. 2 shows the resulting tissue at the same location as in FIG. In this structure, 1
The number (n ₁ ) in the surface area of 0 μm was 200 as measured for a length of 1000 μm. Further, n ₁ in the outermost surface region was 50. On the other hand, the number (n ₂ ) 50 μm inside from the outermost surface region was measured for a length of 1000 μm, and was 200. Therefore,
n ₁ / n ₂ × 100 = 25%.

Eight of the above-mentioned plain bearings are mounted on the large end of the connecting rod of a 1600 cc four-cylinder gasoline engine,
It was operated for 100 hours under the condition of full load of 7,800 rpm. As a result of the test, adhesion and cracking due to fretting were not observed.

COMPARATIVE EXAMPLE 1 A similar test was performed on the slide bearings not subjected to the shot blast treatment in Example 1, and as a result, cracks occurred and the bearings were broken.

[0024]

According to the present invention, it is not necessary to increase the strength of the back metal more than necessary as in the prior art, so that the cost of the back metal can be reduced and the press formability can be improved. Further, even a low-rigidity connecting rod can be used without overlaying. Thus, the present invention has a very high practical value.

[Brief description of the drawings]

FIG. 1 is a microstructure photograph of a back surface of a back metal steel plate before shot blasting (at a magnification of 1000).

FIG. 2 is a microstructure photograph of a back surface of a back metal plate after shot blasting (at a magnification of 1000).

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Daisuke Fukuda 3-65 Midorigaoka, Toyota-shi, Aichi Prefecture Inside Daitoyo Kogyo Co., Ltd.

Claims (3)

[Claims] 1. A plain bearing for an internal combustion engine, which is formed by bending a bearing alloy layer bonded to the surface of a back metal made of a steel sheet into a semicircular shape with an inner side thereof being about 20% in nital having a nitric acid concentration of 3 to 20%. Regarding the crystal grain boundaries detected in the cross section of the back metal etched in seconds, the number of crystal grain boundaries detected per unit length (10 μm or more) in the back metal back direction is calculated as the surface area of 10 μm from the outermost surface of the back metal rear face. in the number and (n _1), the number (n ₂₎ in 50μm inward from the backing outermost regions, to represent respectively, that controls the distribution of _{0 ≦ n 1 / n 2 ×} 100 ≦ 70% and the grain boundary number Features a sliding bearing for internal combustion engines. 2. A sliding bearing for an internal combustion engine according to claim _1, wherein said n ₁ / n ₂ is 30% or less. 3. A bearing device for an internal combustion engine, wherein the sliding bearing according to claim 1 is used as a connecting rod bearing.