JP2025005760A - Rolling bearing and vehicle drive unit - Google Patents

Abstract

To provide a rolling bearing which can suppress occurrence and development of a crack on a rolling surface even in poor lubrication.SOLUTION: A rolling bearing (100) supports a rotation shaft of a vehicular driving unit. The rolling bearing includes an inner ring (10), an outer ring (20), and a rolling element (30) which are subject to hardening and tempering and are made of steel. Each of the inner ring, the outer ring, and the rolling element has a rolling surface (10da, 20ca, 30a). Dislocation density of retained austenite on a rolling surface layer of at least one of the inner ring and the outer ring is 5.0×1014 m-2 or more and 1.0×1017 m-2 or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a rolling bearing and a vehicle drive unit.

Japanese Patent No. 6023422 (Patent Document 1) describes a mechanical part. The mechanical part described in Patent Document 1 is a raceway or rolling element that constitutes a rolling bearing. The mechanical part described in Patent Document 1 is formed by introducing nitrogen into the surface, performing quenching, and then performing tempering at high temperature.

Patent No. 6023422

In the future, vehicle drive units used in electric vehicles such as EVs (Electric Vehicles) and HEVs (Hybrid Electric Vehicles) will be required to be increasingly efficient due to environmental concerns, such as the need to achieve carbon neutrality.

A vehicle drive unit has multiple rotating shafts, each of which is supported by a rolling bearing. To improve efficiency, the viscosity of the lubricating oil can be reduced, the amount of oil can be reduced, and the oil pump can be reduced, which can result in poor lubrication between the raceways and the rolling elements.

As vehicle drive units become smaller to improve efficiency, the size of the bearings that support the rotating shaft becomes smaller. Also, to improve efficiency, the output of the drive source (motor, etc.) of the vehicle drive unit is increased and the rotation speed is increased. As a result, the load on the rolling bearings becomes even greater.

The mechanical parts described in Patent Document 1 are tempered at high temperatures, which reduces the hardness in the immediate vicinity of the surface. Therefore, when a rolling bearing made of the mechanical parts described in Patent Document 1 is used under the above-mentioned conditions, cracks may occur on the rolling surfaces (raceway surfaces, rolling contact surfaces) and these cracks may propagate.

The present invention has been made in consideration of the problems of the conventional technology as described above. More specifically, the present invention provides a rolling bearing that can suppress the occurrence and progression of cracks on the rolling surface even in poor lubrication.

The rolling bearing of the present invention is a rolling bearing that supports a rotating shaft of a vehicle drive unit. The rolling bearing includes an inner ring, an outer ring, and rolling elements made of quenched and tempered steel. The inner ring, the outer ring, and the rolling elements each have a rolling surface. The dislocation density of retained austenite in a surface layer of the rolling surface of at least one of the inner ring and the outer ring is 5.0×10 ¹⁴ m ^-2 or more and 1.0×10 ¹⁷ m ^-2 or less.

The rolling bearing of the present invention can suppress the occurrence and progression of cracks on the rolling surface even in cases of poor lubrication.

FIG. 2 is a cross-sectional view of the rolling bearing 100. 10 is a cross-sectional view of a rolling bearing 100 according to a modified example. FIG. 3A to 3C are manufacturing process diagrams of the rolling bearing 100. 2 is a cross-sectional view of a vehicle drive unit 200. FIG. 11 is a cross-sectional view of a vehicle drive unit 200 according to a modified example. FIG.

Details of an embodiment of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts will be given the same reference symbols, and duplicate descriptions will not be repeated. The rolling bearing according to the embodiment will be referred to as rolling bearing 100, and the vehicle drive unit according to the embodiment will be referred to as vehicle drive unit 200.

(Configuration of rolling bearing 100)
The configuration of the rolling bearing 100 will be described below.

Figure 1 is a cross-sectional view of a rolling bearing 100. As shown in Figure 1, the rolling bearing 100 is, for example, a deep groove ball bearing. The rolling bearing 100 has an inner ring 10, an outer ring 20, a plurality of rolling elements 30, and a cage 40. The central axis of the inner ring 10 is defined as the central axis A. The direction of the central axis A is defined as the axial direction. The direction passing through the central axis A and perpendicular to the central axis A is defined as the radial direction. The direction along the circumference centered on the central axis A when viewed along the axial direction is defined as the circumferential direction.

The inner ring 10 is annular and extends in the circumferential direction. The inner ring 10 has a first width surface 10a, a second width surface 10b, an inner diameter surface 10c, and an outer diameter surface 10d.

The first width surface 10a and the second width surface 10b are end surfaces of the inner ring 10 in the axial direction. The first width surface 10a faces one side in the axial direction (the right side in FIG. 1), and the second width surface 10b faces the other side in the axial direction (the left side in FIG. 1). The second width surface 10b is the opposite surface of the first width surface 10a in the axial direction.

The inner diameter surface 10c and the outer diameter surface 10d extend in the circumferential direction. One end and the other end in the axial direction of the inner diameter surface 10c are connected to the first width surface 10a and the second width surface 10b, respectively. One end and the other end in the axial direction of the outer diameter surface 10d are connected to the first width surface 10a and the second width surface 10b, respectively. The inner diameter surface 10c faces inward in the radial direction. The outer diameter surface 10d faces outward in the radial direction. The outer diameter surface 10d is the opposite surface of the inner diameter surface 10c in the radial direction.

The outer diameter surface 10d has a raceway surface 10da. The raceway surface 10da is the portion of the outer diameter surface 10d that contacts the rolling elements 30. In a cross-sectional view perpendicular to the circumferential direction, the raceway surface 10da is recessed toward the inner diameter surface 10c. In a cross-sectional view perpendicular to the circumferential direction, the raceway surface 10da is partially arc-shaped. The raceway surface 10da extends in the circumferential direction and is located in the center of the outer diameter surface 10d in the axial direction.

The outer ring 20 is annular and extends in the circumferential direction. The outer ring 20 has a first width surface 20a, a second width surface 20b, an inner diameter surface 20c, and an outer diameter surface 20d.

The first width surface 20a and the second width surface 20b are end surfaces of the outer ring 20 in the axial direction. The first width surface 20a faces one side in the axial direction (the right side in FIG. 1), and the second width surface 20b faces the other side in the axial direction (the left side in FIG. 1). The second width surface 20b is the opposite surface of the first width surface 20a in the axial direction.

The inner diameter surface 20c and the outer diameter surface 20d extend in the circumferential direction. One end and the other end in the axial direction of the inner diameter surface 20c are connected to the first width surface 20a and the second width surface 20b, respectively. One end and the other end in the axial direction of the outer diameter surface 20d are connected to the first width surface 20a and the second width surface 20b, respectively. The inner diameter surface 20c faces inward in the radial direction. The outer diameter surface 20d faces outward in the radial direction. The outer diameter surface 20d is the opposite surface of the inner diameter surface 20c in the radial direction.

The inner diameter surface 20c has a raceway surface 20ca. The raceway surface 20ca is the portion of the inner diameter surface 20c that contacts the rolling elements 30. In a cross-sectional view perpendicular to the circumferential direction, the raceway surface 20ca is recessed toward the outer diameter surface 20d. In a cross-sectional view perpendicular to the circumferential direction, the raceway surface 20ca is partially arc-shaped. The raceway surface 20ca extends in the circumferential direction and is located in the center of the inner diameter surface 20c in the axial direction.

The outer ring 20 is disposed radially outside the inner ring 10 so that the inner diameter surface 20c and the outer diameter surface 10d face each other with a gap in the radial direction (so that the raceway surface 20ca faces the raceway surface 10da with a gap in the radial direction).

The rolling element 30 is disposed between the raceway surface 10da and the raceway surface 20ca. The rolling element 30 is spherical. The rolling element 30 has a surface 30a. The rolling element 30 contacts the raceway surface 10da and the raceway surface 20ca at the surface 30a. The raceway surface 10da, the raceway surface 20ca, and the surface 30a are sometimes referred to as rolling surfaces.

The retainer 40 is disposed between the outer diameter surface 10d and the inner diameter surface 20c. The retainer 40 holds a number of rolling elements 30 so that the distance between two adjacent rolling elements 30 in the circumferential direction is within a certain range.

The inner ring 10, outer ring 20, and rolling elements 30 are made of steel that has been quenched and tempered. The steel that constitutes the inner ring 10, outer ring 20, and rolling elements 30 is, for example, high carbon chromium bearing steel as specified by the JIS standard. The steel that constitutes the inner ring 10, outer ring 20, and rolling elements 30 is, for example, SUJ2 or SUJ3 as specified by the JIS standard, 52100 as specified by the ASTMA295 standard, 100Cr as specified by the DIN standard, or GCr5 or GCr15 as specified by the GB standard.

The hardness of the rolling surfaces of the inner ring 10, the outer ring 20, and the rolling elements 30 is preferably 760 Hv or more and 900 Hv or less (62.5 HRC or more and 67 HRC or less). The hardness of the rolling surfaces of the inner ring 10, the outer ring 20, and the rolling elements 30 is measured according to the Vickers hardness test method defined in the JIS standard. The hardness of the rolling surfaces of the inner ring 10, the outer ring 20, and the rolling elements 30 is measured at a position 50 μm deep from the rolling surface in a cross section perpendicular to the rolling surface, which is regarded as the surface layer of the rolling surface. The hardness of the rolling surface may be determined by measuring the Vickers hardness at positions on a cross section perpendicular to the rolling surface that are 50 μm, 150 μm, 250 μm, 350 μm, and 450 μm away from the rolling surface in the depth direction, and estimating the Vickers hardness at a position that is 0 μm away from the rolling surface in the depth direction from an approximation formula (linear or exponential) that is determined based on the Vickers hardness measured at these five points.

The amount of retained austenite in the rolling surface layer of the inner ring 10, outer ring 20, and rolling element 30 is preferably 2 volume percent or more and 12 volume percent or less. The amount of retained austenite in the inner ring 10, outer ring 20, and rolling element 30 is measured by X-ray diffraction at a position 50 μm deep from the rolling surface in a cross section perpendicular to the rolling surface. The grain size number of the prior austenite grains in the rolling surface surface layer of the inner ring 10, outer ring 20, and rolling element 30 is preferably 9 or more. The grain size number of the prior austenite grains in the rolling surface surface layer of the inner ring 10, outer ring 20, and rolling element 30 is measured according to the method specified in the JIS standard.

The surfaces of the inner ring 10, outer ring 20, and rolling element 30 are not subjected to nitriding treatment. From another perspective, if the nitrogen concentration of the rolling surface surface layer of the inner ring 10, outer ring 20, and rolling element 30 is defined as the average nitrogen concentration in the region from the rolling surface to a depth of 10 μm, the nitrogen concentration of the rolling surface surface layer is less than 0.01 mass percent. The above nitrogen concentration is measured by performing a line analysis in the depth direction from the rolling surface using an EPMA (Electron Probe Micro Analyzer) in a cross section perpendicular to the rolling surface, and the average value of the nitrogen concentration up to a position 10 μm deep from the rolling surface.

The dislocation density of the retained austenite in the rolling surface surface layers of the inner ring 10, the outer ring 20, and the rolling elements 30 is 5.0×10 ¹⁴ m ^-2 or more and 1.0×10 ¹⁷ m ^-2 or less. The dislocation density of the retained austenite in the rolling surface surface layers of the inner ring 10, the outer ring 20, and the rolling elements 30 is preferably 5.0×10 ¹⁴ m ^-2 or more and 1.0×10 ¹⁶ m ^-2 or less, and more preferably 5.0×10 ¹⁴ m ^-2 or more and 1.0×10 ¹⁵ m ^-2 or less.

The dislocation density of the retained austenite in the rolling surface layer of the inner ring 10, the outer ring 20, and the rolling element 30 is measured on the rolling surface using a cobalt tube type X-ray diffractometer. More specifically, the X-ray profile is measured using a cobalt tube type X-ray diffractometer, and the half-width obtained from the X-ray profile is separated into crystallite size and strain, and the Williamson-Hall equation is applied to calculate the dislocation density of the retained austenite in the rolling surface surface layer. The dislocation density of the retained austenite is calculated using the strain obtained by Rietveld analysis of the peaks of the X-ray profile corresponding to the (111), (200), (220), (311), and (222) planes. The measurement accuracy of the dislocation density is improved by using the Rietveld analysis, and the device constant is taken into account when the Rietveld analysis is performed. The measurement position may be any point on the surface of the rolling surfaces of the inner ring 10, the outer ring 20, and the rolling element 30, or any point up to 50 μm in depth from the rolling surface in a cross section perpendicular to the rolling surface.

<Modification>
In the above example, a case has been described in which the hardness of the rolling surfaces of the inner ring 10, the outer ring 20, and the rolling elements 30 is 62.5 HRC or more and 67 HRC or less, but it is sufficient that the hardness of the rolling surfaces of at least any of the inner ring 10, the outer ring 20, and the rolling elements 30 is 760 Hv or more and 900 Hv or less (62.5 HRC or more and 67 HRC or less). In the above example, a case has been described in which the amount of retained austenite in the rolling surface surface layers of the inner ring 10, the outer ring 20, and the rolling elements 30 is 2 volume percent or more and 12 volume percent or less, but it is sufficient that the amount of retained austenite in the rolling surface surface layers of at least any of the inner ring 10, the outer ring 20, and the rolling elements 30 is 2 volume percent or more and 12 volume percent or less.

In the above example, a case has been described in which the dislocation density of the retained austenite in the rolling surface surface layers of the inner ring 10, the outer ring 20, and the rolling elements 30 is 5.0×10 ¹⁴ m ^-2 or more and 1.0×10 ¹⁷ m ^-2 or less, but it is sufficient that the dislocation density of the retained austenite in the rolling surface surface layers of at least any of the inner ring 10, the outer ring 20, and the rolling elements 30 is 5.0×10 ¹⁴ m ^-2 or more and 1.0×10 ¹⁷ m ^-2 or less. In the above example, a case has been described in which the nitrogen concentration in the rolling surface surface layers of the inner ring 10, the outer ring 20, and the rolling elements 30 is less than 0.01 mass percent, but it is sufficient that the nitrogen concentration in the rolling surface surface layers of at least any of the inner ring 10, the outer ring 20, and the rolling elements 30 is less than 0.01 mass percent.

Figure 2 is a cross-sectional view of a rolling bearing 100 according to a modified example. As shown in Figure 2, the rolling bearing 100 may be a tapered roller bearing.

(Method of manufacturing the rolling bearing 100)
A method for manufacturing the rolling bearing 100 will now be described.

Figure 3 is a manufacturing process diagram of the rolling bearing 100. As shown in Figure 3, the manufacturing method of the rolling bearing 100 includes a preparation process S1, a quenching process S2, a cooling process S3, a tempering process S4, a post-treatment process S5, and an assembly process S6.

In the preparation step S1, the workpiece to be processed is prepared. The workpiece is preferably made of high carbon chromium bearing steel (e.g., SUJ2, SUJ3) as specified by the JIS standard. The workpieces for the inner ring 10 and the outer ring 20 are ring-shaped, and the workpieces for the rolling elements 30 are spherical.

The quenching step S2 is performed after the preparation step S1. The quenching step S2 is performed by cooling the workpiece from a temperature equal to or higher than the _A1 transformation point to a temperature equal to or lower than the _M2S transformation point. The cooling step S3 is performed after the quenching step S2. The cooling step S3 is a sub-zero treatment or a cryo-treatment. In the sub-zero treatment, the workpiece is cooled to a temperature equal to or higher than -99°C and equal to or lower than 0°C. In the cryo-treatment, the workpiece is cooled to a temperature equal to or lower than -100°C. By performing the sub-zero treatment and the cryo-treatment, the transformation into martensite in the steel progresses and the amount of retained austenite in the steel decreases.

The tempering step S4 is performed after the cooling step S3. The tempering step S4 is performed by heating and holding the processed member at a temperature lower than the _A1 transformation point. The heating temperature in the tempering step S4 is, for example, 180°C.

The post-processing step S5 is carried out after the tempering step S4. In the post-processing step S5, the surface of the workpiece is machined (grinded, polished). This results in the inner ring 10, outer ring 20, and rolling elements 30. The assembly step S6 is carried out after the post-processing step S5. In the assembly step S6, the inner ring 10, outer ring 20, and rolling elements 30 are assembled together with the cage 40 to form the rolling bearing 100 having the structure shown in FIG. 1.

(Configuration of vehicle drive unit 200)
The configuration of the vehicle drive unit 200 will be described below.

Figure 4 is a cross-sectional view of the vehicle drive unit 200. As shown in Figure 4, the vehicle drive unit 200 has a motor 110 and a reduction gear 120.

The motor 110 has a motor body 111, a rotating shaft 112, a motor housing 113, and a rolling bearing 114. The motor body 111 rotates the rotating shaft 112 around the central axis of the rotating shaft 112. The motor body 111 is disposed inside the motor housing 113. The rotating shaft 112 is supported by the rolling bearing 114 so as to be rotatable around the central axis of the rotating shaft 112. The rolling bearing 114 is, for example, a deep groove ball bearing.

The reducer 120 has rotating shafts 121, 122, and 123, gears 124, 125, 126, and 127, and rolling bearings 128, 129, and 130. The rolling bearings 128, 129, and 130 are, for example, deep groove ball bearings.

The rotation of the rotating shaft 112 is transmitted to the rotating shaft 121, causing the rotating shaft 121 to rotate around the central axis of the rotating shaft 112. The rotating shaft 121 is supported by a rolling bearing 128 so as to be rotatable around the central axis of the rotating shaft 121. The gear 124 is attached to the rotating shaft 121 and rotates together with the rotating shaft 121.

The rotating shaft 122 is supported by a rolling bearing 129 so as to be rotatable around the central axis of the rotating shaft 122. Gears 125 and 126 are attached to the rotating shaft 122 and rotate together with the rotating shaft 122. Gear 125 is meshed with gear 124. Therefore, the rotating shaft 122 rotates as the rotation of the rotating shaft 121 is transmitted by gears 124 and 125. The gear ratio of gears 124 and 125 is adjusted so that the rotation speed of the rotating shaft 122 is smaller than the rotation speed of the rotating shaft 121.

The rotating shaft 123 is supported by a rolling bearing 130 so as to be rotatable around the central axis of the rotating shaft 123. The gear 127 is attached to the rotating shaft 123 and rotates together with the rotating shaft 123. The gear 127 is meshed with the gear 126. Therefore, the rotating shaft 123 rotates as the rotation of the rotating shaft 122 is transmitted by the gears 126 and 127. The gear ratio of the gears 126 and 127 is adjusted so that the rotation speed of the rotating shaft 123 is smaller than the rotation speed of the rotating shaft 122.

The hardness of the rolling surfaces of the inner and outer rings and rolling elements of rolling bearing 128 is less than the hardness of the rolling surfaces of the inner and outer rings and rolling elements of rolling bearing 129. The amount of retained austenite in the rolling surface surface layers of the inner and outer rings of rolling bearing 128 is less than the amount of retained austenite in the rolling surface surface layers of the inner and outer rings of rolling bearing 129. It is preferable that the dislocation density of the retained austenite in the rolling surface surface layers of the inner and outer rings of rolling bearing 128 is greater than the dislocation density of the retained austenite in the rolling surface surface layers of the inner and outer rings of rolling bearing 129.

The hardness of the rolling surfaces of the inner and outer rings and rolling elements of rolling bearing 129 is preferably smaller than the hardness of the rolling surfaces of the inner and outer rings and rolling elements of rolling bearing 130. The amount of retained austenite in the rolling surface surface layers of the inner and outer rings of rolling bearing 129 is preferably smaller than the amount of retained austenite in the rolling surface surface layers of the inner and outer rings of rolling bearing 130. The dislocation density of the retained austenite in the rolling surface surface layers of the inner and outer rings of rolling bearing 129 is preferably greater than the dislocation density of the retained austenite in the rolling surface surface layers of the inner and outer rings of rolling bearing 130.

The hardness of the rolling surfaces of the inner and outer rings and rolling elements of rolling bearing 114 is preferably smaller than the hardness of the rolling surfaces of the inner and outer rings and rolling elements of rolling bearing 129. The amount of retained austenite in the rolling surface surface layers of the inner and outer rings of rolling bearing 114 is preferably smaller than the amount of retained austenite in the rolling surface surface layers of the inner and outer rings of rolling bearing 129. The dislocation density of the retained austenite in the rolling surface surface layers of the inner and outer rings of rolling bearing 114 is preferably greater than the dislocation density of the retained austenite in the rolling surface surface layers of the inner and outer rings of rolling bearing 129.

It is preferable that at least one of the rolling bearings 114 and 128 is the rolling bearing 100.

<Modification>
Fig. 5 is a cross-sectional view of a modified vehicle drive unit 200. As shown in Fig. 5, the rolling bearing 129 and the rolling bearing 130 may be tapered roller bearings.

(Effects of the rolling bearing 100)
The effects of the rolling bearing 100 will be described below.

When the rolling bearing 100 is used under poor lubrication conditions, the oil film thickness on the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30 becomes small, and metal contact may occur between the rolling surface of the inner ring 10 (outer ring 20) and the rolling surface of the rolling elements 30. In the rolling bearing 100, the dislocation density of the retained austenite in the surface layers of the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30 is 5.0×10 ¹⁴ m ^-2 or more and 1.0×10 ¹⁷ m ^-2 or less, so that the hardness of the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30 is 760 Hv or more and 900 Hv or less (62.5 HRC or more and 67 HRC or less). That is, in the rolling bearing 100, plastic deformation is unlikely to occur on the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30. Therefore, in the rolling bearing 100, even if metal contact occurs between the rolling surface of the inner ring 10 (outer ring 20) and the rolling surface of the rolling element 30, surface damage (the occurrence and propagation of cracks) caused by plastic deformation is unlikely to occur.

The fact that plastic deformation is less likely to occur on the rolling surfaces of the inner ring 10, the outer ring 20, and the rolling elements 30 means that plastic deformation directly below the rolling surfaces of the inner ring 10, the outer ring 20, and the rolling elements 30 is smaller, and the progression of residual stress due to plastic deformation is slowed down. Therefore, the rolling bearing 100 also improves the rolling fatigue life.

In the rolling bearing 100, the hardness of the rolling surfaces of the inner ring 10, outer ring 20, and rolling element 30 is high, so that indentations caused by foreign matter are less likely to form at the contact area between the rolling surface of the inner ring 10 (outer ring 20) and the rolling surface of the rolling element 30. In this way, the rolling bearing 100 also improves resistance to foreign matter.

In the rolling bearing 100 (i.e., when it is a deep groove ball bearing), stress concentration due to shoulder riding may occur when a large axial load is applied. In addition, in the rolling bearing 100 according to the modified example (i.e., when it is a tapered roller bearing), stress concentration due to edge hitting may occur on the rolling surface. As described above, in the rolling bearing 100 and the rolling bearing 100 according to the modified example, the hardness of the rolling surfaces of the inner ring 10, the outer ring 20, and the rolling elements 30 is high and plastic deformation is unlikely to occur, improving resistance to stress concentration due to shoulder riding and edge hitting.

When the rolling bearing 100 is used at high temperatures, the residual austenite in the inner ring 10 and the outer ring 20 decomposes, causing dimensional changes in the inner ring 10 and the outer ring 20 over time. If the amount of residual austenite in the rolling surface layers of the inner ring 10 and the outer ring 20 is 2 volume percent or more and 12 volume percent or less, the dimensional changes in the inner ring 10 and the outer ring 20 over time that are caused by the decomposition of the residual austenite are suppressed. This eliminates the need for an excessively tight fit with the rotating shaft or housing, making it possible to suppress cracking of the inner ring 10 and the outer ring 20.

In addition, by suppressing dimensional changes over time of the inner ring 10 and outer ring 20 due to the decomposition of retained austenite, the rolling bearing 100 can continue to roll stably. Furthermore, by suppressing dimensional changes over time of the inner ring 10 and outer ring 20 due to the decomposition of retained austenite, creep between the rotating shaft and the inner ring 10 is also suppressed, making it possible to maintain optimal tooth contact of the gear attached to the rotating shaft and ensuring quietness of the vehicle drive unit.

In addition, in the rolling bearing 100, the hardness of the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30 is 760 Hv or more and 900 Hv or less (62.5 HRC or more and 67 HRC or less), so foreign matter resistance is maintained even if the amount of retained austenite on the surface layers of the rolling surfaces of the inner ring 10 and outer ring 20 is small.

In the rolling bearing 100, the cooling step S3 is performed when the inner ring 10, the outer ring 20, and the rolling elements 30 are formed, so that the dislocation density of the martensite is less likely to decrease in the tempering step S4. As a result, in the inner ring 10, the outer ring 20, and the rolling elements 30, the retained austenite is surrounded by martensite with a high dislocation density, and the dislocation density of the retained austenite surrounded by the dislocation density is also high.

Since the volume expansion associated with decomposition of retained austenite, which is surrounded by martensite with a high dislocation density, is restrained by the surrounding martensite with a high dislocation density, even if the retained austenite decomposes during high temperature use, the dimensional change associated with the decomposition is small. In this way, by setting the dislocation density of the retained austenite in the rolling surface surface layers of the inner ring 10, outer ring 20, and rolling elements 30 to be 5.0 x ¹⁰¹⁴ m ^-2 or more and 1.0 x ¹⁰¹⁷ m ^-2 or less, the dimensional change over time of the inner ring 10 and outer ring 20 associated with the decomposition of retained austenite is further suppressed.

It is known that metal materials are strengthened by increasing the dislocation density through processing. However, when processing strengthening is performed, it becomes necessary to perform special processing in addition to the processing process of normal rolling bearings, which increases production energy and complicates the process. On the other hand, in the inner ring 10, the outer ring 20, and the rolling element 30, the dislocation density of the retained austenite increases by heat treatment (cooling step S3) to 5.0×10 ¹⁴ m ^-2 or more and 1.0×10 ¹⁷ m ^-2 or less, and a strengthening effect similar to that of processing is obtained. In addition, precipitation strengthening and grain refinement strengthening using special materials and special heat treatment also cause an increase in production energy. Furthermore, imparting residual compressive stress to the rolling surface by special processing also requires the introduction of a special process, which causes the process to become complicated.

When the grain size number of the prior austenite grains in the rolling surface layer of the inner ring 10, outer ring 20, and rolling element 30 is 9 or more, the hardness of the rolling surfaces of the inner ring 10, outer ring 20, and rolling element 30 increases with the refinement of the crystal grains, and thus the surface damage caused by plastic deformation, rolling fatigue life, and foreign matter resistance are further improved. In addition, when the steel constituting the inner ring 10, outer ring 20, and rolling element 30 is a high carbon chromium bearing steel as specified in the JIS standard such as SUJ2 or SUJ3, general steel can be used for the inner ring 10, outer ring 20, and rolling element 30, so that the cost of the rolling bearing 100 can be reduced.

(Effects of the vehicle drive unit 200)
The effects of the vehicle drive unit 200 will be described below.

Because the rotation speed of the rotating shaft 121 is greater than that of the rotating shaft 122, the rolling bearing 128 supporting the rotating shaft 121 is more likely to become hotter than the rolling bearing 129 supporting the rotating shaft 122. In other words, the inner and outer rings of the rolling bearing 128 are more likely to experience dimensional changes over time than the rolling bearing 129.

On the other hand, because the rotational speed of the rotating shaft 121 is greater than that of the rotating shaft 122, the load applied to the rolling bearing 129 is greater than the load applied to the rolling bearing 128, and the rolling bearing 129 is more likely to be poorly lubricated than the rolling bearing 128 (the oil film thickness is more likely to be smaller). As a result, metal contact is more likely to occur between the rolling surface of the inner ring (outer ring) and the rolling surfaces of the rolling elements. In other words, in the rolling bearing 129, surface damage is more likely to occur on the rolling surfaces of the inner ring, outer ring, and rolling elements.

In the vehicle drive unit 200, the hardness of the rolling surfaces of the inner and outer rings and rolling elements of the rolling bearing 129 is greater than the hardness of the rolling surfaces of the inner and outer rings and rolling elements of the rolling bearing 129, and the amount of retained austenite in the surface layers of the rolling surfaces of the inner and outer rings of the rolling bearing 128 is less than the amount of retained austenite in the surface layers of the rolling surfaces of the inner and outer rings of the rolling bearing 129. This makes it possible to suppress surface damage to the rolling surfaces of the inner and outer rings and rolling elements of the rolling bearing 129 while suppressing dimensional changes over time in the inner and outer rings of the rolling bearing 128.

In the above, deep groove ball bearings and tapered roller bearings are shown as examples of rolling bearings used in the vehicle drive unit 200, but the rolling bearings used in the vehicle drive unit 200 are not limited to these. The rolling bearings used in the vehicle drive unit 200 may be, for example, cylindrical roller bearings, angular ball bearings, tandem type double row angular ball bearings, etc., or may be rolling bearings with some of the shapes improved (for example, tapered roller bearings with the inner ring rib omitted). In other words, rolling bearings in general can be applied to the vehicle drive unit 200 regardless of their shape.

In the above, an integrated drive type unit of a motor shaft and a reducer composed of three parallel shafts is shown as an example of the vehicle drive unit 200, but the vehicle drive unit 200 may have a four-shaft configuration, may be a reducer with a variable speed gear, or may be a drive unit with a planetary gear. In other words, there are no particular limitations on the structure of the vehicle drive unit 200, and it may be any unit to which the rolling bearing of the present application can be applied.

(Additional Note)
This embodiment includes the following configuration.

<Appendix 1>
A rolling bearing for supporting a rotating shaft of a vehicle drive unit, comprising:
The bearing is provided with an inner ring, an outer ring and rolling elements made of hardened and tempered steel,
Each of the inner ring, the outer ring, and the rolling elements has a rolling surface,
A rolling bearing, wherein a dislocation density of retained austenite in a surface layer of a rolling surface of at least one of the inner ring and the outer ring is 5.0×10 ¹⁴ m ^-2 or more and 1.0×10 ¹⁷ m ^-2 or less.

<Appendix 2>
2. The rolling bearing according to claim 1, wherein an amount of retained austenite in the rolling surface layer of at least one of the inner ring and the outer ring is 2 volume percent or more and 12 volume percent or less.

<Appendix 3>
3. The rolling bearing according to claim 1, wherein the hardness of the rolling surfaces of at least any of the inner ring, the outer ring and the rolling elements is 760 Hv or more and 900 Hv or less.

<Appendix 4>
4. The rolling bearing according to claim 1, wherein a nitrogen concentration in the rolling surface surface layer of at least one of the inner ring and the outer ring is less than 0.01 mass percent.

<Appendix 5>
A plurality of rotation axes;
A plurality of rolling bearings;
Each of the plurality of rolling bearings has an inner ring, an outer ring, and rolling elements made of hardened and tempered steel,
Each of the inner ring, the outer ring, and the front rolling element has a rolling surface,
Each of the plurality of rotating shafts is supported by each of the plurality of rolling bearings,
a first rotating shaft is one of the plurality of rotating shafts having the slowest rotation speed, and a second rotating shaft is another of the plurality of rotating shafts other than the first rotating shaft, and at least one of the outer ring, the inner ring and the rolling elements of at least one of the plurality of rolling bearings supporting the second rotating shaft has a dislocation density of retained austenite in a rolling surface layer of 5.0 x 10 ¹⁴ m ^-2 or more and 1.0 x 10 ¹⁷ m ^-2 or less.

<Appendix 6>
6. The vehicle drive unit described in Appendix 5, wherein an amount of retained austenite in a surface layer of the rolling surface of at least one of the outer ring, the inner ring, and the rolling element of at least one of the plurality of rolling bearings supporting the second rotating shaft is 2 volume percent or more and 12 volume percent or less.

<Appendix 7>
7. The vehicle drive unit according to claim 5, wherein at least one of the outer ring, the inner ring, and the rolling element of at least one of the plurality of rolling bearings supporting the second rotating shaft has a hardness of 760 Hv or more and 900 Hv or less on the rolling surface.

<Appendix 8>
8. The vehicle drive unit according to claim 5, wherein a nitrogen concentration in a surface layer of the rolling surface of at least one of the outer ring, the inner ring, and the rolling element of at least one of the plurality of rolling bearings supporting the second rotating shaft is less than 0.01 mass percent.

Although the embodiment of the present invention has been described above, the above-mentioned embodiment can be modified in various ways. Furthermore, the scope of the present invention is not limited to the above-mentioned embodiment. The scope of the present invention is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

100 rolling bearing, 10 inner ring, 10a first width surface, 10b second width surface, 10c inner diameter surface, 10d outer diameter surface, 10da raceway surface, 20 outer ring, 20a first width surface, 20b second width surface, 20c inner diameter surface, 20ca raceway surface, 20d outer diameter surface, 30 rolling element, 30a surface, 40 retainer, 110 motor, 111 motor body, 112 rotating shaft, 113 motor housing, 114 rolling bearing, 120 reducer, 121, 122, 123 rotating shaft, 124, 125, 126, 127 gear, 128, 129, 130 rolling bearing, 200 vehicle drive unit, A central shaft, S1 preparation process, S2 hardening process, S3 Cooling process, S4 tempering process, S5 post-treatment process, S6 assembly process.

Claims (8)

A rolling bearing for supporting a rotating shaft of a vehicle drive unit, comprising:
The bearing is provided with an inner ring, an outer ring and rolling elements made of hardened and tempered steel,
Each of the inner ring, the outer ring, and the rolling elements has a rolling surface,
A rolling bearing, wherein a dislocation density of retained austenite in a surface layer of a rolling surface of at least one of the inner ring and the outer ring is 5.0×10 ¹⁴ m ^-2 or more and 1.0×10 ¹⁷ m ^-2 or less. The rolling bearing according to claim 1, wherein the amount of retained austenite in the rolling surface layer of at least one of the inner ring and the outer ring is 2 volume percent or more and 12 volume percent or less. The rolling bearing according to claim 1, wherein the hardness of the rolling surfaces of at least one of the inner ring, the outer ring, and the rolling elements is 760 Hv or more and 900 Hv or less. The rolling bearing according to any one of claims 1 to 3, wherein the nitrogen concentration in the rolling surface layer of at least one of the inner ring and the outer ring is less than 0.01 mass percent. A plurality of rotation axes;
A plurality of rolling bearings;
Each of the plurality of rolling bearings has an inner ring, an outer ring, and rolling elements made of hardened and tempered steel,
Each of the inner ring, the outer ring, and the front rolling element has a rolling surface,
Each of the plurality of rotating shafts is supported by each of the plurality of rolling bearings,
a first rotating shaft is one of the plurality of rotating shafts having the slowest rotation speed, and a second rotating shaft is another of the plurality of rotating shafts other than the first rotating shaft, and at least one of the outer ring, the inner ring and the rolling elements of at least one of the plurality of rolling bearings supporting the second rotating shaft has a dislocation density of retained austenite in a rolling surface layer of 5.0 x 10 ¹⁴ m ^-2 or more and 1.0 x 10 ¹⁷ m ^-2 or less. The vehicle drive unit according to claim 5, wherein the amount of retained austenite in the rolling surface layer of at least one of the outer ring, the inner ring, and the rolling element of at least one of the plurality of rolling bearings supporting the second rotating shaft is 2 volume percent or more and 12 volume percent or less. The vehicle drive unit according to claim 5, wherein the hardness of the rolling surface of at least one of the outer ring, the inner ring, and the rolling element of at least one of the plurality of rolling bearings supporting the second rotating shaft is 760 Hv or more and 900 Hv or less. A vehicle drive unit according to any one of claims 5 to 7, wherein the nitrogen concentration in the rolling surface layer of at least one of the outer ring, the inner ring, and the rolling element of at least one of the plurality of rolling bearings supporting the second rotating shaft is less than 0.01 mass percent.

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