JP2022169996A - thrust ball bearing - Google Patents

Abstract

To provide a thrust ball bearing capable of improving rolling fatigue life.SOLUTION: A thrust ball bearing has a raceway disk made of steel. The raceway disk has a raceway surface. Arithmetic average roughness of the raceway surface is equal to or lower than 0.1 μm, and a maximum value of compressive residual stress in a circumferential direction applied to the raceway disk in a region at a distance up to 100 μm from the raceway surface is 700 MPa or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to thrust ball bearings.

It is difficult to improve the surface roughness of the raceway surface of the washer of a thrust ball bearing by superfinishing. Therefore, in the raceway washer of the thrust ball bearing, surface-originating flaking is likely to occur due to poor lubrication on the raceway surface. When flaking originates from the surface, the service life of the washer tends to be shorter than when flaking originates from the inside. As a measure for suppressing the surface-originating flaking on the raceway surface of the bearing washer of a thrust ball bearing, it is conceivable to apply compressive residual stress to the raceway surface of the bearing washer of the thrust ball bearing.

For example, Japanese Patent Laying-Open No. 2002-147557 (Patent Document 1) describes a thrust ball bearing. The thrust ball bearing described in Patent Document 1 has a bearing washer made of steel. The bearing washer has a raceway surface. Compressive residual stress is imparted to the raceway surface of the bearing washer by performing shot peening.

JP-A-2002-147557

In shot peening, the raceway surface of the washer of the thrust ball bearing is processed many times. Therefore, in the thrust ball bearing described in Patent Document 1, the retained austenite in the steel on the raceway surface of the bearing washer undergoes deformation-induced transformation, and the amount of retained austenite in the steel on the raceway surface of the bearing washer decreases.

Retained austenite in the steel on the raceway surface of the raceway washer of the thrust ball bearing has the effect of suppressing early flaking caused by inclusion of foreign matter such as metal wear powder. Therefore, in the thrust ball bearing disclosed in Patent Literature 1, the amount of retained austenite in the steel on the raceway surface of the bearing washer is reduced, and as a result, premature flaking may occur due to the inclusion of foreign matter.

The shot peening process increases the surface roughness of the raceway surface of the washer of the thrust ball bearing. Further, as described above, it is difficult to improve the surface roughness of the raceway surface of the raceway washer of the thrust ball bearing by performing superfinishing. Therefore, in the thrust ball bearing described in Patent Document 1, although compressive residual stress is applied to the raceway surface of the washer, the surface roughness of the raceway surface of the washer increases, and poor lubrication tends to occur. Insufficient suppression of origin-type peeling.

The present invention has been made in view of the problems of the prior art as described above. More specifically, the present invention provides a thrust ball bearing capable of improving rolling contact fatigue life.

The thrust ball bearing of the present invention has a bearing washer made of steel. The bearing washer has a raceway surface. The arithmetic mean roughness of the raceway surface is 0.1 μm or less. The maximum value of the circumferential compressive residual stress applied to the bearing washer in the area up to 100 μm from the raceway surface is 700 MPa or more.

In the above thrust ball bearing, the raceway surface may be burnished. In the above thrust ball bearing, the raceway surface may be carbonitrided.

In the above thrust ball bearing, the amount of retained austenite in the steel on the raceway surface may be 10% by volume or more.

In the above thrust ball bearing, the maximum value of radial compressive residual stress applied to the washer in a region up to 100 μm from the raceway surface may be 1000 MPa or more.

The above thrust ball bearing may be used for a hydraulic continuously variable transmission (HST: Hydro-Static Transmission).

According to the thrust ball bearing of the present invention, rolling contact fatigue life can be improved.

2 is a cross-sectional view of thrust ball bearing 100. FIG. 4A to 4C are process diagrams showing a method of manufacturing the shaft washer 10. FIG.

Details of embodiments of the present invention will be described with reference to the drawings. In the drawings below, the same or corresponding parts are denoted by the same reference numerals, and redundant description will not be repeated.

(Configuration of Thrust Ball Bearing According to Embodiment)
The configuration of the thrust ball bearing (hereinafter referred to as "thrust ball bearing 100") according to the embodiment will be described below. Thrust ball bearing 100 is, for example, a thrust ball bearing for a hydraulic continuously variable transmission. However, the thrust ball bearing 100 may be a thrust ball bearing used for other purposes.

FIG. 1 is a cross-sectional view of a thrust ball bearing 100. FIG. As shown in FIG. 1 , the thrust ball bearing 100 has a shaft washer 10 , a housing washer 20 , rolling elements 30 and a retainer 40 . A central axis of the shaft washer 10 is defined as a central axis A1. The center axis of the housing washer 20 is defined as a center axis A2. The central axis A1 and the central axis A2 are on the same straight line. A direction along the central axis A1 (the central axis A2) is defined as an axial direction. Let the direction along the circumference centering on central axis A1 (central axis A2) be a circumferential direction. A direction passing through the central axis A1 (the central axis A2) and orthogonal to the central axis A1 (the central axis A2) is defined as a radial direction.

The shaft washer 10 is annular. The shaft washer 10 has an inner peripheral surface 10a, an outer peripheral surface 10b, a first end surface 10c, and a second end surface 10d. The shaft washer 10 is made of steel. More specifically, the shaft washer 10 is made of hardened and tempered steel. The steel forming the shaft washer 10 is, for example, high carbon chromium bearing steel specified in the JIS standard (JIS G 4805:2008). The surface of the shaft washer 10 (the inner peripheral surface 10a, the outer peripheral surface 10b, the first end surface 10c and the second end surface 10d) may be carbonitrided.

The inner peripheral surface 10a faces the central axis A1 side. The inner peripheral surface 10a extends along the circumferential direction. The shaft washer 10 is fitted to the shaft (not shown) at the inner peripheral surface 10a. The outer peripheral surface 10b faces away from the central axis A1. That is, the outer peripheral surface 10b is the opposite surface of the inner peripheral surface 10a in the radial direction. The outer peripheral surface 10b extends along the circumferential direction.

The first end surface 10c forms an end surface of the shaft washer 10 in the axial direction. The first end surface 10c continues to one end of the inner peripheral surface 10a in the axial direction and one end of the outer peripheral surface 10b in the axial direction. The second end face 10d forms an end face of the shaft washer 10 in the axial direction. The second end face 10d is the opposite face of the first end face 10c in the axial direction. The second end surface 10d continues to the other end of the inner peripheral surface 10a in the axial direction and the other end of the outer peripheral surface 10b in the axial direction.

A raceway groove 10da is formed in the second end face 10d. The raceway groove 10da extends along the circumferential direction. The second end surface 10d is recessed toward the first end surface 10c in the raceway groove 10da. In a cross-sectional view passing through the central axis A1 and parallel to the central axis A1, the raceway groove 10da has, for example, a partial arc shape. The rolling elements 30 come into contact with the surfaces of the raceway grooves 10da. That is, the surface of the raceway groove 10da is the raceway surface of the shaft washer 10. As shown in FIG.

The arithmetic mean roughness (Ra) of the raceway surface of the shaft washer 10 is 0.1 μm or less. The arithmetic mean roughness of the raceway surface of the shaft washer 10 is measured according to the JIS standard (JIS B 0601:2001).

The raceway surface of the shaft washer 10 is subjected to burnishing. The maximum value of the circumferential compressive residual stress applied to the shaft washer 10 in the region up to 100 μm from the raceway surface is 700 MPa or more. The maximum value of the circumferential compressive residual stress applied to shaft washer 10 in a region up to 100 μm from the raceway surface may be 800 MPa or more.

The circumferential compressive residual stress applied to the shaft washer 10 at a distance of 200 μm from the raceway surface may be, for example, 300 MPa or less. That is, the compressive residual stress applied to the raceway surface side of the shaft washer 10 has a distribution with a peak on the raceway surface or very close to the raceway surface due to the burnishing process.

The maximum value of the radial compressive residual stress applied to shaft washer 10 in a region up to 100 μm from the raceway surface may be 1000 MPa or more. The radial compressive residual stress applied to the shaft washer 10 at a distance of 200 μm from the raceway surface may be 500 MPa or less. The residual stress applied to the raceway surface side of the shaft washer 10 is measured by an X-ray diffraction method.

The amount of retained austenite in the steel on the raceway surface of the shaft washer 10 is preferably 10% by volume or more. The amount of retained austenite in the steel on the raceway surface of the shaft washer 10 is measured by an X-ray diffraction method. More specifically, by comparing the integrated intensity of the diffraction peak of austenite on the surface of shaft washer 10 and the integrated intensity of the diffraction peak of phases other than austenite on the surface of shaft washer 10, the The amount of retained austenite in the steel on the raceway surface is measured.

The housing washer 20 is annular. The housing washer 20 has an inner peripheral surface 20a, an outer peripheral surface 20b, a first end surface 20c, and a second end surface 20d. The housing washer 20 is made of steel. More specifically, the housing washer 20 is made of hardened and tempered steel. The steel forming the housing bearing washer 20 is, for example, high carbon chromium bearing steel specified in the JIS standard. The steel forming the housing washer 20 may be different from the steel forming the shaft washer 10 . The surfaces of the housing bearing washer 20 (the inner peripheral surface 20a, the outer peripheral surface 20b, the first end surface 20c and the second end surface 20d) may be carbonitrided.

The inner peripheral surface 20a faces the central axis A2 side. The inner peripheral surface 20a extends along the circumferential direction. The housing washer 20 is fitted to a housing (not shown). The outer peripheral surface 20b faces away from the central axis A2. That is, the outer peripheral surface 20b is the opposite surface of the inner peripheral surface 20a in the radial direction. The outer peripheral surface 20b extends along the circumferential direction.

The first end face 20c forms an end face of the housing raceway washer 20 in the axial direction. The first end surface 20c continues to one end of the inner peripheral surface 20a in the axial direction and one end of the outer peripheral surface 20b in the axial direction. The second end surface 20d forms an end surface of the housing washer 20 in the axial direction. The second end surface 20d is the opposite surface of the first end surface 20c in the axial direction. The second end surface 20d continues to the other end of the inner peripheral surface 20a in the axial direction and the other end of the outer peripheral surface 20b in the axial direction. The second end face 20d faces the second end face 10d with a gap therebetween in the axial direction.

A raceway groove 20da is formed in the second end face 20d. The raceway groove 20da extends along the circumferential direction. The second end surface 20d is recessed toward the first end surface 20c in the raceway groove 20da. In a cross-sectional view passing through the central axis A2 and parallel to the central axis A2, the raceway groove 20da has, for example, a partial circular arc shape. The rolling elements 30 come into contact with the surfaces of the raceway grooves 20da. That is, the surface of the raceway groove 20da is the raceway surface of the housing raceway washer 20. As shown in FIG. The raceway groove 20da faces the raceway groove 10da with a gap therebetween in the axial direction.

The arithmetic average roughness (Ra) of the raceway surface of the housing raceway washer 20 is 0.1 μm or less. The arithmetic mean roughness of the raceway surface of the housing washer 20 is measured by the same method as the arithmetic mean roughness of the raceway surface of the shaft washer 10 .

The raceway surface of the housing raceway washer 20 is subjected to burnishing. The compressive residual stress applied to the raceway surface side of the housing washer 20 has a distribution with a peak on the raceway surface or very close to the raceway surface.

More specifically, the maximum value of the circumferential compressive residual stress applied to housing washer 20 in a region up to 100 μm from the raceway surface is 700 MPa or more. The maximum value of the circumferential compressive residual stress applied to housing washer 20 in a region up to 100 μm from the raceway surface may be 800 MPa or more. The circumferential compressive residual stress applied to housing washer 20 at a position 200 μm from the raceway surface may be 300 MPa or less.

The maximum value of the radial compressive residual stress applied to the housing raceway washer 20 in a region up to 100 μm from the raceway surface may be 1000 MPa or more. The radial compressive residual stress applied to the housing washer 20 at a distance of 200 μm from the raceway surface may be 500 MPa or less.

The residual stress applied to the raceway surface side of the housing washer 20 is measured by the same method as the residual stress applied to the raceway surface side of the shaft washer 10 . The amount of retained austenite in the steel on the raceway surface of the housing washer 20 is preferably 10% by volume or more. The amount of retained austenite in the steel on the raceway surface of the housing washer 20 is measured by the same method as for the amount of retained austenite in the steel on the raceway surface of the shaft washer 10 .

The rolling elements 30 are spherical. That is, the rolling elements 30 are balls. The rolling element 30 is arranged between the second end surface 10d and the second end surface 20d. More specifically, the rolling elements 30 are in contact with the surface of the raceway groove 10da (the raceway surface of the shaft washer 10) and the raceway groove 20da (the raceway surface of the housing raceway washer 20). The number of rolling elements 30 is plural. A plurality of rolling elements 30 are arranged along the circumferential direction.

The rolling elements 30 are made of steel, for example. The steel forming the rolling elements 30 may be the same as the steel forming the shaft washer 10 and the housing washer 20. can be different.

The retainer 40 is annular. The retainer 40 is arranged between the second end face 10d and the second end face 20d. A plurality of rolling elements 30 are held by a retainer 40 . Thereby, the interval between the two rolling elements 30 adjacent in the circumferential direction is kept within a certain range.

<Manufacturing method of bearing washer>
FIG. 2 is a process diagram showing a method of manufacturing the shaft washer 10. As shown in FIG. As shown in FIG. 2, the method for manufacturing the shaft washer 10 includes a preparation step S1, a carbonitriding step S2, a quenching step S3, a tempering step S4, a working step S5, and a burnishing step S6. have. The carbonitriding step S2 is performed after the preparation step S1. The hardening step S3 is performed after the carbonitriding step S2. The tempering step S4 is performed after the hardening step S3. The working step S5 is performed after the tempering step S4. The burnishing process S6 is performed after the process S5. Note that the carbonitriding step S2 may not be performed.

In the preparation step S1, a member to be processed is prepared. The member to be processed is a member that becomes the shaft washer 10 through the carbonitriding process S2, the quenching process S3, the tempering process S4, the working process S5, and the burnishing process S6. The member to be processed is formed by forging or the like so as to have a shape similar to that of the shaft washer 10 .

In the carbonitriding step S2, carbonitriding is performed on the surface of the member to be processed. More specifically, in the carbonitriding step S2, the member to be processed is held at a temperature equal to or higher than the A1 transformation point in _an atmospheric gas containing a carbon source and a nitrogen source (for example, mixed gas of RX gas and ammonia gas). It is done by

In the quenching step S3, the member to be processed is quenched. More specifically, the quenching step _S3 is performed by holding the member to be processed at a temperature equal to or higher than the A1 transformation _point and then rapidly cooling it to a temperature equal to or lower than the M2 transformation point. In the tempering step S4, the member to be processed is tempered. More specifically, it is carried out by holding the member to be processed at _a temperature below the A1 transformation point.

In the processing step S5, machining (grinding, polishing, etc.) is performed on the member to be processed. As a result, the shape of the member to be processed approximately matches the shape of the shaft washer 10 .

In the burnishing step S6, burnishing is performed on a surface of the surface of the member to be processed, which will be the second end face 10d. The burnishing process is performed by pressing a burnishing tool against the second end surface 10d of the surface of the member to be processed while rotating the member to be processed around the central axis. Note that the burnishing process may be performed on at least a portion of the shaft washer 10 that will be the raceway surface.

As described above, the shaft washer 10 having the structure shown in FIG. 1 is manufactured. The housing washer 20 is also manufactured by the same method as the shaft washer 10 .

(Effect of thrust ball bearing 100)
The effects of the thrust ball bearing 100 will be described below.

The raceway surfaces of the bearing washers (the shaft washer 10 and the housing washer 20) of the thrust ball bearing 100 are subjected to burnishing. As a result, a compressive residual stress with a maximum value of 700 MPa or more in the circumferential direction is applied to a region up to 100 μm from the raceway surface of the bearing washer of thrust ball bearing 100 . This compressive residual stress suppresses crack propagation in the depth direction from the raceway surface, thereby suppressing the occurrence of surface-originating flaking on the raceway surface of the raceway washer of thrust ball bearing 100 .

It is difficult to superfinish the raceway surface of the raceway washer of a thrust ball bearing to obtain a surface roughness equivalent to that of the raceway surface of the raceway ring of a radial ball bearing. When residual stress is applied to the raceway surface of the washer of a thrust ball bearing by shot peening, the shot peening process increases the surface roughness. It is necessary to perform superfinishing after shot peening.

Residual stress is applied to the raceway surface of the washer of the thrust ball bearing 100 by burnishing. When burnishing is performed, the surface roughness is less than when superfinishing is performed. Therefore, the surface roughness of the raceway surface of the thrust ball bearing 100 is reduced as compared with the case where superfinishing is performed after applying compressive residual stress by shot peening. More specifically, the surface roughness of the raceway surface of the washer of the thrust ball bearing 100 can be reduced to 0.1 μm or less. Therefore, in the thrust ball bearing 100, it is possible to ensure a good lubricating state on the raceway surface of the raceway washer, and the occurrence of surface-originating flaking on the raceway surface of the raceway washer is suppressed.

When shot peening is performed, the same location on the raceway surface of the raceway washer is subjected to processing many times. On the other hand, when burnishing is performed, the number of times the same portion on the raceway surface of the bearing washer is subjected to the machining is several times at most. Therefore, in the thrust ball bearing 100, stress-induced transformation of the retained austenite on the raceway surface of the bearing washer is difficult to occur, and the amount of retained austenite on the raceway surface of the bearing washer can be secured. As a result, in the thrust ball bearing 100, it is possible to suppress the occurrence of premature flaking due to the entrapment of foreign matter on the raceway surface of the bearing washer. As described above, according to the thrust ball bearing 100, it is possible to improve the rolling contact fatigue life.

Although the embodiment of the present invention has been described as above, it is also possible to modify the above-described embodiment in various ways. Also, the scope of the present invention is not limited to the embodiments described above. The scope of the present invention is indicated by the scope of claims, and is intended to include all changes within the meaning and scope of equivalence to the scope of claims.

The above embodiments are particularly advantageously applied to thrust ball bearings for hydraulic continuously variable transmissions and other applications.

100 thrust ball bearing 10 shaft washer 10a inner peripheral surface 10b outer peripheral surface 10c first end face 10d second end face 10da raceway groove 20 housing washer 20a inner peripheral surface 20b outer peripheral surface 20c first first end face End face 20d Second end face 20da Raceway groove 30 Rolling element 40 Cage A1, A2 Center shaft S1 Preparation process S2 Carbonitriding process S3 Quenching process S4 Tempering process S5 Processing process S6 Burnishing process process.

Claims (6)

A thrust ball bearing,
Equipped with a steel bearing washer,
The bearing washer has a raceway surface,
The arithmetic mean roughness of the raceway surface is 0.1 μm or less,
A thrust ball bearing, wherein a maximum value of circumferential compressive residual stress applied to the bearing washer in a region up to 100 μm from the raceway surface is 700 MPa or more. 2. The thrust ball bearing according to claim 1, wherein said raceway surface is subjected to burnishing. 3. The thrust ball bearing according to claim 1, wherein the raceway surface is carbonitrided. The thrust ball bearing according to any one of claims 1 to 3, wherein the amount of retained austenite in the steel in the raceway surface is 10% by volume or more. The maximum value of the radial compressive residual stress applied to the bearing washer in a region up to 100 μm from the raceway surface is 1000 MPa or more, according to any one of claims 1 to 4. thrust ball bearing. The thrust ball bearing according to any one of claims 1 to 5, wherein the thrust ball bearing is for a hydraulic continuously variable transmission.

Images