Rolling bearing and drive unit for vehicle

Abstract

A rolling bearing (100) supports a rotating shaft of a drive unit for a vehicle. The rolling bearing comprises an inner ring (10), an outer ring (20), and a rolling element (30) which are made of quenched and tempered steel. The inner ring, the outer ring, and the rolling element respectively have rolling surfaces (10da, 20ca, 30a). The dislocation density of retained austenite in a surface layer of at least one of the rolling surfaces of the inner ring and the outer ring is 2.5 × 1014m-2 or more and 1.0 × 1017m-2 or less.

Description

Rolling bearing and vehicle drive unit

[0001] The present invention relates to a rolling bearing and a vehicle drive unit.

[0002] Japanese Patent No. 6023422 (Patent Document 1) describes a mechanical component. The mechanical component described in Patent Document 1 is a raceway or a rolling element that constitutes a rolling bearing. The mechanical component described in Patent Document 1 is formed by introducing nitrogen into the surface, performing quenching, and then performing tempering at a high temperature.

[0003] Patent No. 6023422

[0004] BACKGROUND ART Vehicle drive units used in electrically powered vehicles such as EVs (Electric Vehicles) and HEVs (Hybrid Electric Vehicles) will be required to have increasingly high efficiency in the future due to consideration of environmental issues such as the realization of carbon neutrality.

[0005] A vehicle drive unit has multiple rotating shafts, each supported by a rolling bearing. To improve efficiency, the lubrication between the bearing rings and the rolling elements can be poor due to factors such as lowering the viscosity of the lubricating oil, reducing the amount of oil, and eliminating the need for an oil pump.

[0006] As vehicle drive units become smaller to improve efficiency, the size of the bearings that support the rotating shaft becomes smaller. Furthermore, to achieve higher efficiency, the output of the drive source (e.g., motor) of the vehicle drive unit increases and the rotation speed increases. As a result, the load on the rolling bearings becomes even greater.

[0007] The mechanical component described in Patent Document 1 is tempered at a high temperature, which reduces the hardness in the immediate vicinity of the surface. Therefore, when a rolling bearing formed from the mechanical component 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 the cracks may propagate.

[0008] The present invention has been made in view of the above-mentioned problems of the conventional art. More specifically, the present invention provides a rolling bearing that can suppress the occurrence and growth of cracks on the rolling surface even in poor lubrication conditions.

[0009] 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 the retained austenite in the surface layer of the rolling surface of at least one of the inner ring and the outer ring is 2.5 × 10 １４ m －２ Above 1.0 x 10 １７ m －２ The following is the result.

[0010] According to the rolling bearing of the present invention, even in cases of poor lubrication, the occurrence and growth of cracks on the rolling surfaces can be suppressed.

[0011] 1 is a cross-sectional view of a rolling bearing 100; 2 is a cross-sectional view of a rolling bearing 100 according to a modified example; 3 is a manufacturing process diagram of the rolling bearing 100; 4 is a cross-sectional view of a vehicle drive unit 200; and 5 is a cross-sectional view of a vehicle drive unit 200 according to a modified example.

[0012] The 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 are designated by the same reference numerals, and redundant description will not be repeated. A rolling bearing according to the embodiment is referred to as a rolling bearing 100, and a vehicle drive unit according to the embodiment is referred to as a vehicle drive unit 200.

[0013] (Configuration of Rolling Bearing 100) The configuration of the rolling bearing 100 will be described below.

[0014] 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 of a circle centered on the central axis A when viewed along the axial direction is defined as the circumferential direction.

[0015] The inner ring 10 has a circular ring shape extending in the circumferential direction and includes a first width surface 10a, a second width surface 10b, an inner diameter surface 10c, and an outer diameter surface 10d.

[0016] 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 surface opposite the first width surface 10a in the axial direction.

[0017] The inner diameter surface 10c and the outer diameter surface 10d extend in the circumferential direction. One end and the other axial end of the inner diameter surface 10c are continuous with the first width surface 10a and the second width surface 10b, respectively. One end and the other axial end of the outer diameter surface 10d are continuous with 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 surface opposite the inner diameter surface 10c in the radial direction.

[0018] 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 section perpendicular to the circumferential direction, the raceway surface 10da is recessed toward the inner diameter surface 10c. In a cross section perpendicular to the circumferential direction, the raceway surface 10da has a partial arc shape. 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.

[0019] The outer ring 20 has a circular ring shape extending in the circumferential direction and includes a first width surface 20a, a second width surface 20b, an inner diameter surface 20c, and an outer diameter surface 20d.

[0020] 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 surface opposite the first width surface 20a in the axial direction.

[0021] The inner diameter surface 20c and the outer diameter surface 20d extend in the circumferential direction. One end and the other axial end of the inner diameter surface 20c are continuous with the first width surface 20a and the second width surface 20b, respectively. One end and the other axial end of the outer diameter surface 20d are continuous with 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 surface opposite the inner diameter surface 20c in the radial direction.

[0022] 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 has a partial arc shape. 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.

[0023] The outer ring 20 is arranged 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).

[0024] 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 surface 30a of the rolling element 30 contacts the raceway surface 10da and the raceway surface 20ca. The raceway surface 10da, the raceway surface 20ca, and the surface 30a are sometimes referred to as rolling surfaces.

[0025] The cage 40 is disposed between the outer diameter surface 10d and the inner diameter surface 20c. The cage 40 holds the rolling elements 30 so that the interval between two adjacent rolling elements 30 in the circumferential direction is within a certain range.

[0026] The inner ring 10, outer ring 20, and rolling elements 30 are made of quenched and tempered steel. The steel constituting the inner ring 10, outer ring 20, and rolling elements 30 is, for example, a high-carbon chromium bearing steel as specified in the JIS standard. The steel constituting the inner ring 10, outer ring 20, and rolling elements 30 is, for example, SUJ2 or SUJ3 as specified in the JIS standard, 52100 as specified in the ASTM A295 standard, 100Cr as specified in the DIN standard, or GCr5 or GCr15 as specified in the GB standard.

[0027] The hardness of the rolling surfaces of the inner ring 10, the outer ring 20, and the rolling elements 30 is preferably 800 Hv or more and 1245 Hv or less, and more preferably 865 Hv or more and 1245 Hv or less. The hardness of the rolling surfaces of the inner ring 10, the outer ring 20, and the rolling elements 30 may be 760 Hv or more and 940 Hv or less, or may be 800 Hv or more and 940 Hv or less.

[0028] The hardness of the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30 is measured in accordance with the Vickers hardness testing method defined in JIS standards. The hardness of the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30 is measured at a position 50 μm deep from the rolling surface in a cross section perpendicular to the rolling surface, with the position being considered to be the surface layer of the rolling surface. The hardness at 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 0 μm away from the rolling surface in the depth direction from an approximation formula (linear or exponential) determined based on the Vickers hardness measured at these five points.

[0029] The amount of retained austenite in the rolling surface surface layers of the inner ring 10, outer ring 20, and rolling elements 30 is preferably 5 volume percent or more and 30 volume percent or more, and more preferably 5 volume percent or more and 16 volume percent or less. The amount of retained austenite in the rolling surface surface layers of the inner ring 10, outer ring 20, and rolling elements 30 may be 2 volume percent or more and 12 volume percent or less. The amount of retained austenite in the rolling surface surface layers of the inner ring 10, outer ring 20, and rolling elements 30 is measured by X-ray diffraction at a position 50 μm away 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 layers of the inner ring 10, outer ring 20, and rolling elements 30 is preferably 9 or more. The grain size numbers of the prior austenite grains in the surface layers of the rolling surfaces of the inner ring 10, the outer ring 20 and the rolling elements 30 are measured according to the method defined in the JIS standard.

[0030] The surfaces of the inner ring 10, outer ring 20, and rolling elements 30 are preferably subjected to nitriding treatment. The nitrogen concentration in the rolling surface surface layer of the inner ring 10, outer ring 20, and rolling elements 30 is defined as the average nitrogen concentration in a region from the rolling surface to a depth of 10 μm. The nitrogen concentration in the rolling surface surface layer of the inner ring 10, outer ring 20, and rolling elements 30 is preferably 0.25 mass percent or more. The nitrogen concentration in the rolling surface surface layer of the inner ring 10, outer ring 20, and rolling elements 30 is, for example, 1.0 mass percent or less. If the nitrogen concentration in the rolling surface surface layer exceeds 1.0 mass percent, the amount of retained austenite exceeds 16 volume percent, reducing the effect of suppressing secular dimensional change. Furthermore, if the nitrogen concentration in the rolling surface surface layer exceeds 1.0 mass percent, the carbon concentration will decrease due to decarburization during heat treatment, raising concerns about a reduction in the hardness of the rolling surface. The nitrogen concentration in the rolling surface surface layers of the inner ring 10, outer ring 20, and rolling elements 30 may be 0.03 mass percent or more and 0.25 mass percent or less. The above nitrogen concentration is measured as the average value of the nitrogen concentration up to a position 10 μm deep from the rolling surface by performing a linear analysis in the depth direction from the rolling surface using an EPMA (Electron Probe Micro Analyzer) on a cross section perpendicular to the rolling surface. The surfaces of the inner ring 10, outer ring 20, and rolling elements 30 do not need to be subjected to nitriding treatment. From another perspective, the nitrogen concentration in the rolling surface surface layers of the inner ring 10, outer ring 20, and rolling elements 30 may be less than 0.01 mass percent.

[0031] 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 2.5 × 10 １４ m －２ Above 1.0 x 10 １７ m －２ The dislocation density of the retained austenite in the rolling surface layers of the inner ring 10, the outer ring 20, and the rolling elements 30 is preferably 2.5 × 10 １４ m －２ Above 1.0 x 10 １６ m －２ More preferably, it is 2.5 × 10 １４ m －２ Above 5.0 x 10 １５ m－２ It is particularly preferably 2.5 × 10 １４ m －２ Above 1.0 x 10 １５ m －２ The dislocation density of the retained austenite in the rolling surface layers of the inner ring 10, the outer ring 20, and the rolling elements 30 is 3.5 × 10 １４ m －２ Above 1.0 x 10 １７ m －２ It may be 3.5 × 10 or less. １４ m －２ Above 1.0 x 10 １６ m －２ It may be 3.5 × 10 or less. １４ m －２ Above 5.0 x 10 １５ m －２ The dislocation density of the retained austenite in the rolling surface layers of the inner ring 10, the outer ring 20, and the rolling elements 30 may be 5.0 × 10 or less. １４ m －２ Above 1.0 x 10 １７ m －２ Below, 5.0 x 10 １４ m －２ Above 1.0 x 10 １６ m －２ Less than or equal to 5.0 x 10 １４ m －２ Above 1.0 x 10 １５ m －２ It may be the following:

[0032] 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 measured on the rolling surfaces using a cobalt tube X-ray diffractometer. More specifically, the X-ray profile is measured using the cobalt tube 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 strain obtained by Rietveld analysis of the peaks in the X-ray profile corresponding to the (111), (200), (220), (311), and (222) planes. The use of Rietveld analysis increases the accuracy of dislocation density measurement, and the instrument constants are taken into account when performing the Rietveld analysis. The measurement position may be any point on the surface of the rolling surfaces of the inner ring 10, outer ring 20 and rolling elements 30, or any point up to 50 μm in depth from the rolling surface in a cross section perpendicular to the rolling surface.

[0033] <Modifications> In the above, an example 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 800 Hv or more and 1245 Hv or less (760 Hv or more and 940 Hv or less), but it is sufficient that the hardness of the rolling surfaces of at least one of the inner ring 10, the outer ring 20, and the rolling elements 30 is 800 Hv or more and 1245 Hv or less (760 Hv or more and 940 Hv or less). Also, in the above, an example 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 5 volume percent or more and 30 volume percent or less, but it is sufficient that the amount of retained austenite in the rolling surface surface layers of at least one of the inner ring 10, the outer ring 20, and the rolling elements 30 is 5 volume percent or more and 30 volume percent or less.

[0034] In the above, 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 2.5×10 １４ m －２ Above 1.0 x 10 １７ m －２ Below (3.5 x 10 １４ m －２Above 1.0 x 10 １７ m －２ hereinafter), an example was described in which the dislocation density of the retained austenite in the rolling surface surface layer of at least one of the inner ring 10, the outer ring 20, and the rolling element 30 is 2.5 × 10 １４ m －２ Above 1.0 x 10 １７ m －２ Below (3.5 x 10 １４ m －２ Above 1.0 x 10 １７ m －２ Furthermore, although the above description has been given of the case where the nitrogen concentration in the rolling surface surface layers of the inner ring 10, the outer ring 20, and the rolling elements 30 is 0.25 mass percent or more (0.03 mass percent or more and 0.25 mass percent or less), it is sufficient that the nitrogen concentration in the rolling surface surface layer of at least one of the inner ring 10, the outer ring 20, and the rolling elements 30 is 0.25 mass percent or more (0.03 mass percent or more and 0.25 mass percent or less).

[0035] In the above example, the case where the amount of retained austenite in the rolling surface surface layers of the inner ring 10, outer ring 20, and rolling elements 30 is 2 volume percent or more and 12 volume percent or less has been described, but it is sufficient that the amount of retained austenite in the rolling surface surface layer of at least one of the inner ring 10, outer ring 20, and rolling elements 30 is 2 volume percent or more and 12 volume percent or less. Also, in the above example, 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 is 5.0 × 10 １４ m －２ Above 1.0 x 10 １７ m －２ The following case has been described, but the dislocation density of the retained austenite in the rolling surface surface layer of at least one of the inner ring 10, the outer ring 20, and the rolling element 30 is 5.0 × 10 １４ m －２ Above 1.0 x 10 １７ m －２In the above example, the case where 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 has been described, but it is sufficient that the nitrogen concentration in the rolling surface surface layer of at least one of the inner ring 10, the outer ring 20, and the rolling elements 30 is less than 0.01 mass percent.

[0036] Fig. 2 is a cross-sectional view of a modified rolling bearing 100. As shown in Fig. 2, the rolling bearing 100 may be a tapered roller bearing.

[0037] (Method of Manufacturing Rolling Bearing 100) A method of manufacturing the rolling bearing 100 will now be described.

[0038] 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 step S1, a nitriding step S2, a quenching step S3, a cooling step S4, a tempering step S5, a post-treatment step S6, and an assembly step S7. However, if the nitrogen concentration in the rolling surface layer of the inner ring 10, outer ring 20, and rolling element 30 is to be less than 0.01 mass percent, the nitriding step S2 is not performed.

[0039] In the preparation step S1, workpieces are prepared. The workpieces are preferably made of high-carbon chromium bearing steel (e.g., SUJ2 or SUJ3) as specified in 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.

[0040] The nitriding step S2 is carried out after the preparation step S1. The nitriding step S2 is carried out by heating and holding the workpiece in an atmospheric gas containing a nitrogen source (e.g., ammonia gas). The heating temperature in the nitriding step S2 is set to a value equal to the A content of the steel constituting the workpiece. １ The temperature is equal to or higher than the transformation point. This heating temperature is, for example, 800°C or higher. By maintaining the temperature in the nitriding treatment step S2, nitrogen penetrates from the surface of the workpiece. The nitriding treatment step S2 is carried out so that nitrogen diffuses to positions that will become the surfaces of the inner ring 10, the outer ring 20, and the rolling elements 30 after the post-treatment step S6.

[0041] The nitrogen that penetrates through the surface of the workpiece reacts with alloy elements (e.g., chromium) in the steel that constitutes the workpiece to form precipitates. The pinning effect of the precipitates refines the prior austenite grains that are formed during heating in the quenching step S3, and refines the martensite grains that are formed during cooling in the quenching step S3.

[0042] The quenching step S3 is performed after the nitriding treatment step S2. １ From temperatures above the transformation point Ｓ This is done by cooling to a temperature below the transformation point. The cooling step S4 is done after the quenching step S3. The cooling step S4 is a sub-zero treatment or a cryo-treatment. In the sub-zero treatment, the workpiece is cooled to a temperature of -99°C or higher and 0°C or lower. In the cryo-treatment, the workpiece is cooled to a temperature of -100°C or lower. 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.

[0043] The tempering step S5 is performed after the cooling step S4. １ The tempering step S5 is performed by heating and holding the material at a temperature below the transformation point. The heating temperature in the tempering step S5 is, for example, 180°C.

[0044] The post-processing step S6 is performed after the tempering step S5. In the post-processing step S6, the surface of the workpiece is machined (grinded and polished). This results in the inner ring 10, outer ring 20, and rolling elements 30. The assembly step S7 is performed after the post-processing step S6. In the assembly step S7, 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 .

[0045] (Configuration of Vehicle Drive Unit 200) The configuration of vehicle drive unit 200 will be described below.

[0046] 4 is a cross-sectional view of the vehicle drive unit 200. As shown in FIG. 4, the vehicle drive unit 200 has a motor 110 and a reducer 120.

[0047] 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 about 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 about the central axis of the rotating shaft 112. The rolling bearing 114 is, for example, a deep groove ball bearing.

[0048] The reducer 120 includes a rotating shaft 121, a rotating shaft 122, and a rotating shaft 123, a gear 124, a gear 125, a gear 126, and a gear 127, and a rolling bearing 128, a rolling bearing 129, and a rolling bearing 130. The rolling bearings 128, 129, and 130 are, for example, deep groove ball bearings.

[0049] The rotation of the rotating shaft 112 is transmitted to the rotating shaft 121, causing the rotating shaft 121 to rotate about the central axis of the rotating shaft 112. The rotating shaft 121 is supported by a rolling bearing 128 so as to be rotatable about 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.

[0050] 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 rotation of the rotating shaft 121 is transmitted to the rotating shaft 122 by gears 124 and 125, and the rotating shaft 122 rotates. The gear ratio between gears 124 and 125 is adjusted so that the rotation speed of the rotating shaft 122 is lower than the rotation speed of the rotating shaft 121.

[0051] 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 rotation of the rotating shaft 122 is transmitted to the rotating shaft 123 by the gears 126 and 127, and the rotating shaft 123 rotates. The gear ratio between 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.

[0052] The hardness of the rolling surfaces of the inner ring, outer ring, and rolling elements of rolling bearing 128 is smaller than the hardness of the inner ring, outer ring, and rolling surfaces of the rolling elements of rolling bearing 129. The amount of retained austenite in the rolling surface surface layers of the inner ring and outer ring of rolling bearing 128 is smaller than the amount of retained austenite in the rolling surface surface layers of the inner ring and outer ring of rolling bearing 129. The dislocation density of the retained austenite in the rolling surface surface layers of the inner ring and outer ring of rolling bearing 128 is preferably larger than the dislocation density of the retained austenite in the rolling surface surface layers of the inner ring and outer ring of rolling bearing 129.

[0053] The hardness of the rolling surfaces of the inner ring, outer ring, and rolling elements of rolling bearing 129 is preferably smaller than the hardness of the rolling surfaces of the inner ring, outer ring, and rolling elements of rolling bearing 130. The amount of retained austenite in the rolling surface surface layers of the inner ring and outer ring of rolling bearing 129 is preferably smaller than the amount of retained austenite in the rolling surface surface layers of the inner ring and outer ring of rolling bearing 130. The dislocation density of the retained austenite in the rolling surface surface layers of the inner ring and outer ring of rolling bearing 129 is preferably greater than the dislocation density of the retained austenite in the rolling surface surface layers of the inner ring and outer ring of rolling bearing 130.

[0054] The hardness of the rolling surfaces of the inner ring, outer ring, and rolling elements of rolling bearing 114 is preferably smaller than the hardness of the rolling surfaces of the inner ring, outer ring, and rolling elements of rolling bearing 129. The amount of retained austenite in the rolling surface surface layers of the inner ring and outer ring of rolling bearing 114 is preferably smaller than the amount of retained austenite in the rolling surface surface layers of the inner ring and outer ring of rolling bearing 129. The dislocation density of the retained austenite in the rolling surface surface layers of the inner ring and outer ring of rolling bearing 114 is preferably greater than the dislocation density of the retained austenite in the rolling surface surface layers of the inner ring and outer ring of rolling bearing 129.

[0055] At least one of the rolling bearing 129 and the rolling bearing 130 is preferably the rolling bearing 100, and it is more preferable that the rolling bearing 130 is the rolling bearing 100. At least one of the rolling bearing 114 and the rolling bearing 128 may be the rolling bearing 100.

[0056] <Modification> Fig. 5 is a cross-sectional view of a modification of a vehicle drive unit 200. As shown in Fig. 5, the rolling bearings 129 and 130 may be tapered roller bearings.

[0057] (Effects of the Rolling Bearing 100) The effects of the rolling bearing 100 will be described below.

[0058] 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 decreases, and metal-to-metal contact may occur between the rolling surfaces of the inner ring 10 (outer ring 20) and the rolling surfaces 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 2.5×10 １４ m －２ Above 1.0 x 10 １７ m －２ Below (3.5 x 10 １４ m －２ Above 1.0 x 10 １７ m －２800 Hv or less (760 Hv or more and 940 Hv or less), the hardness of the rolling surfaces of the inner ring 10, the outer ring 20, and the rolling elements 30 is 800 Hv or more and 1245 Hv or less (760 Hv or more and 940 Hv or less). In other words, in the rolling bearing 100, plastic deformation is unlikely to occur on the rolling surfaces of the inner ring 10, the outer ring 20, and the rolling elements 30. Therefore, in the rolling bearing 100, even if metal-to-metal contact occurs between the rolling surfaces of the inner ring 10 (outer ring 20) and the rolling surfaces of the rolling elements 30, surface damage (the occurrence and propagation of cracks) due to plastic deformation is unlikely to occur.

[0059] 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 reduced, slowing the progression of residual stress due to plastic deformation. As a result, the rolling bearing 100 also improves the rolling fatigue life.

[0060] In the rolling bearing 100, the hardness of the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30 is high, so that indentations due to foreign matter getting caught are less likely to be formed at the contact areas between the rolling surfaces of the inner ring 10 (outer ring 20) and the rolling surfaces of the rolling elements 30. In this way, the rolling bearing 100 also has improved foreign matter resistance.

[0061] In the rolling bearing 100 (i.e., when it is a deep groove ball bearing), stress concentration due to shoulder riding can occur when a large axial load is applied. Furthermore, in the rolling bearing 100 according to the modified example (i.e., when it is a tapered roller bearing), stress concentration due to edge strike can occur on the rolling surfaces. 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, outer ring 20, and rolling elements 30 is high and plastic deformation is less likely to occur, thereby improving resistance to stress concentration due to shoulder riding and edge strike.

[0062] When the rolling bearing 100 is used at high temperatures, the retained austenite in the inner ring 10 and the outer ring 20 decomposes, causing dimensional changes over time in the inner ring 10 and the outer ring 20. If the amount of retained austenite in the rolling surface surface layers of the inner ring 10 and the outer ring 20 is 5 volume percent or more and 30 volume percent or less (2 volume percent or more and 12 volume percent or less), dimensional changes over time in the inner ring 10 and the outer ring 20 due to the decomposition of retained austenite are suppressed. This eliminates the need for an excessively tight fit with respect to the rotating shaft or housing, making it possible to suppress cracking of the inner ring 10 and the outer ring 20.

[0063] Furthermore, suppressing dimensional changes over time of the inner ring 10 and the outer ring 20 that accompany the decomposition of retained austenite enables the rolling bearing 100 to continue rolling stably. Furthermore, suppressing dimensional changes over time of the inner ring 10 and the outer ring 20 that accompany the decomposition of retained austenite also suppresses creep between the rotating shaft and the inner ring 10, making it possible to maintain optimal tooth contact of the gear attached to the rotating shaft and ensuring quietness of the vehicle drive unit.

[0064] 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 800 Hv or more and 1245 Hv or less (760 Hv or more and 940 Hv 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, outer ring 20, and rolling elements 30 is small.

[0065] In the rolling bearing 100, the cooling step S4 is performed when the inner ring 10, the outer ring 20, and the rolling elements 30 are formed, and therefore a decrease in the dislocation density of martensite is unlikely to occur in the tempering step S5. 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 also becomes high.

[0066] The volume expansion of the retained austenite, which is surrounded by martensite with a high dislocation density, due to decomposition is restricted by the surrounding martensite with a high dislocation density, so even if the retained austenite decomposes due to high-temperature use, the dimensional change due to the decomposition is small. １４ m －２ Above 1.0 x 10 １７ m －２ Below (3.5 x 10 １４ m －２ Above 1.0 x 10 １７ m －２ Dimensional changes over time of the inner ring 10 and the outer ring 20 due to decomposition of the retained austenite are further suppressed by setting the dislocation density of the retained austenite in the surface layers of the rolling surfaces of the inner ring 10, the outer ring 20, and the rolling elements 30 to 5.0 × 10 １４ m －２ Above 1.0 x 10 １７ m －２ The same applies to the following cases:

[0067] It is known that metal materials are strengthened by increasing the dislocation density when they are processed. However, when processing strengthening is performed, special processing is required in addition to the normal processing steps for rolling bearings, which increases the production energy and complicates the process. On the other hand, in the inner ring 10, outer ring 20, and rolling elements 30, the dislocation density of the retained austenite increases by heat treatment (cooling step S4) to 2.5 × 10 １４ m －２ Above 1.0 x 10 １７ m －２ Below (3.5 x 10 １４ m －２ Above 1.0 x 10 １７ m －２) and obtains the same strengthening effect as processing. Note that precipitation strengthening and grain refinement strengthening using special materials and special heat treatments also cause an increase in production energy. Furthermore, applying residual compressive stress to the rolling surfaces by special processing also requires the introduction of special processes, which causes the process to become more complicated. This means that 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 Above 1.0 x 10 １７ m －２ The same applies to the following cases:

[0068] By making the nitrogen concentration in the rolling surface surface layers of the inner ring 10, outer ring 20, and rolling elements 30 0.25 mass percent or more (0.03 mass percent or more and 0.25 mass percent or less), rolling fatigue life is further improved. When the grain size number of the prior austenite grains in the rolling surface surface layers of the inner ring 10, outer ring 20, and rolling elements 30 is 9 or more, the hardness of the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30 increases as the crystal grains become finer, further improving surface damage due to plastic deformation, rolling fatigue life, and foreign matter resistance. When the steel constituting the inner ring 10, outer ring 20, and rolling elements 30 is a high-carbon chromium bearing steel specified in JIS standards such as SUJ2 or SUJ3, ordinary steel can be used for the inner ring 10, outer ring 20, and rolling elements 30, thereby reducing the cost of the rolling bearing 100.

[0069] (Effects of Vehicle Drive Unit 200) The effects of vehicle drive unit 200 will be described below.

[0070] Because the rotation speed of the rotating shaft 121 is greater than the rotation speed of the rotating shaft 122, the rolling bearing 128 supporting the rotating shaft 121 is more likely to reach a higher temperature 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.

[0071] On the other hand, because the rotational speed of rotating shaft 121 is greater than the rotational speed of rotating shaft 122, the load applied to rolling bearing 129 is greater than the load applied to rolling bearing 128, and rolling bearing 129 is more likely to be poorly lubricated (the oil film thickness is more likely to be smaller) than rolling bearing 128. As a result, metal-to-metal contact is more likely to occur between the rolling surfaces of the inner ring (outer ring) and the rolling surfaces of the rolling elements. In other words, rolling bearing 129 is more likely to suffer surface damage on the rolling surfaces of the inner ring, outer ring, and rolling elements.

[0072] In vehicle drive unit 200, the hardness of the surface layers of the rolling surfaces of the inner and outer rings and rolling elements of rolling bearing 129 is greater than the hardness of the surface layers of the rolling surfaces of the inner and outer rings and rolling elements of rolling bearing 128, and the amount of retained austenite in the surface layers of the rolling surfaces of the inner and outer rings of 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 rolling bearing 129. Therefore, it is possible to suppress dimensional changes over time in the inner and outer rings of rolling bearing 128 while also suppressing surface damage to the rolling surfaces of the inner and outer rings and rolling elements of rolling bearing 129.

[0073] In the above, deep groove ball bearings and tapered roller bearings have been shown as examples of rolling bearings used in vehicle drive unit 200, but the rolling bearings used in vehicle drive unit 200 are not limited to these. The rolling bearings used in vehicle drive unit 200 may be, for example, cylindrical roller bearings, angular contact ball bearings, tandem double-row angular contact ball bearings, etc., or may be rolling bearings with a modified shape (for example, a tapered roller bearing with the inner ring small flange omitted). In other words, rolling bearings in general can be applied to vehicle drive unit 200, regardless of their shape.

[0074] In the above, an integrated drive unit with a motor shaft and a reducer configured with three parallel shafts has been shown as an example of vehicle drive unit 200, but vehicle drive unit 200 may also have a four-shaft configuration, may be a reducer with a speed change gear, or may be a drive unit with a planetary gear. In other words, there are no particular limitations on the structure of vehicle drive unit 200, as long as the rolling bearing of the present application can be applied.

[0075] (Additional Note) This embodiment includes the following configuration.

[0076] <Supplementary Note 1> A rolling bearing supporting a rotating shaft of a vehicle drive unit, comprising an inner ring, an outer ring, and rolling elements made of quenched and tempered steel, wherein the inner ring, the outer ring, and the rolling elements each have a rolling surface, and 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 2.5 × 10 １４ m －２ Above 1.0 x 10 １７ m －２ Below is a rolling bearing.

[0077] <Appendix 2> The rolling bearing according to Appendix 1, wherein the hardness of the rolling surfaces of at least any of the inner ring, the outer ring, and the rolling elements is 800 Hv or more and 1245 Hv or less.

[0078] <Appendix 3> The rolling bearing according to appendix 1 or 2, wherein the nitrogen concentration in the rolling surface surface layer of at least one of the inner ring and the outer ring is 0.25 mass percent or more.

[0079] <Supplementary Note 4> The dislocation density of retained austenite in the rolling surface surface layer of at least one of the inner ring and the outer ring is 3.5×10 １４ m －２ Above 1.0 x 10 １７ m －２ 4. The rolling bearing according to claim 1, wherein:

[0080] <Appendix 5> The rolling bearing according to appendix 4, 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 940 Hv or less.

[0081] <Appendix 6> The rolling bearing according to Appendix 4 or Appendix 5, wherein the nitrogen concentration in the rolling surface surface layer of at least one of the inner ring and the outer ring is 0.03 mass percent or more and 0.25 mass percent or less.

[0082] <Appendix 7> The rolling bearing according to any one of Appendices 1 to 6, wherein the amount of retained austenite in the rolling surface surface layer of at least one of the inner ring and the outer ring is 5 volume percent or more and 30 volume percent or less.

[0083] <Appendix 8> The dislocation density of retained austenite in the rolling surface surface layer of at least one of the inner ring and the outer ring is 5.0 × 10 １４ m －２ Above 1.0 x 10 １７ m －２ Attachment 1: A rolling bearing according to claim 1,

[0084] <Appendix 9> The rolling bearing according to Appendix 8, wherein the amount of retained austenite in the rolling surface 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.

[0085] <Appendix 10> The rolling bearing according to appendix 8 or 9, 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.

[0086] <Appendix 11> The rolling bearing according to any one of Appendices 8 to 10, wherein the 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.

[0087] <Supplementary Note 12> A rolling bearing system is provided, comprising: a plurality of rotating shafts; and a plurality of rolling bearings, each of the plurality of rolling bearings having an inner ring, an outer ring, and rolling elements made of quenched and tempered steel, each of the inner ring, the outer ring, and the front rolling element having a rolling surface, each of the plurality of rotating shafts being supported by a respective one of the plurality of rolling bearings, wherein, when one of the plurality of rotating shafts having the slowest rotation speed is designated as a first rotating shaft and the plurality of rotating shafts other than the first rotating shaft are designated as second rotating shafts, the dislocation density of retained austenite in a surface layer of a rolling surface of at least any 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 2.5×10 １４ m －２Above 1.0 x 10 １７ m －２ A vehicle drive unit as follows:

[0088] <Supplementary Note 13> The vehicle drive unit according to Supplementary Note 12, 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 800 Hv or more and 1245 Hv or less on the rolling surface.

[0089] <Supplementary Note 14> The vehicle drive unit according to Supplementary Note 12 or Supplementary Note 13, 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 0.25 mass percent or more.

[0090] <Supplementary Note 15> The dislocation density of retained austenite in the rolling surface 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 3.5 × 10 １４ m －２ Above 1.0 x 10 １７ m －２ 15. A vehicle drive unit according to any one of appendices 12 to 14, wherein:

[0091] <Supplementary Note 16> The vehicle drive unit according to Supplementary Note 15, 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 940 Hv or less on the rolling surface.

[0092] <Supplementary Note 17> The vehicle drive unit according to Supplementary Note 15 or Supplementary Note 16, 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 0.03 mass percent or more and 0.25 mass percent or more.

[0093] <Supplementary Note 18> The vehicle drive unit according to any one of Supplementary Note 12 to Supplementary Note 17, 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 5 volume percent or more and 30 volume percent or less.

[0094] <Supplementary Note 19> The dislocation density of retained austenite in the rolling surface 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 5.0 × 10 １４ m －２ Above 1.0 x 10 １７ m －２ 13. A vehicle drive unit as described in appendix 12, wherein:

[0095] <Supplementary Note 20> The vehicle drive unit according to Supplementary Note 19, 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.

[0096] <Supplementary Note 21> The vehicle drive unit according to Supplementary Note 19 or Supplementary Note 20, 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.

[0097] <Supplementary Note 22> The vehicle drive unit according to any one of Supplementary Note 19 to Supplementary Note 21, 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.

[0098] Although the embodiments of the present invention have been described above, the above-described embodiments can be modified in various ways. Furthermore, the scope of the present invention is not limited to the above-described embodiments. The scope of the present invention is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0099] 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 nitriding treatment process, S3 Quenching process, S4 cooling process, S5 tempering process, S6 post-treatment process, S7 assembly process.

Claims

1. A rolling bearing that supports a rotating shaft of a vehicle drive unit, comprising 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 having a rolling surface, and the dislocation density of the retained austenite in the rolling surface surface layer of at least one of the inner ring and the outer ring is 2.5 x 10 １４ m －２ Above 1.0 x 10 １７ m －２ Below is a rolling bearing.

2. A rolling bearing as set forth in 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 800 Hv or more and 1245 Hv or less.

3. A rolling bearing as set forth in claim 1, wherein the nitrogen concentration in the rolling surface layer of at least one of the inner ring and the outer ring is 0.25 mass percent or more.

4. The dislocation density of the retained austenite in the surface layer of the rolling surface of at least one of the inner ring and the outer ring is 3.5×10 １４ m －２ Above 1.0 x 10 １７ m －２ 2. The rolling bearing according to claim 1 , wherein:

5. A rolling bearing as set forth in claim 4, 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 940 Hv or less.

6. A rolling bearing as set forth in claim 4, wherein the nitrogen concentration in the rolling surface layer of at least one of the inner ring and the outer ring is 0.03 mass percent or more and 0.25 mass percent or less.

7. A rolling bearing as claimed in any one of claims 1 to 6, wherein the amount of retained austenite in the rolling surface layer of at least one of the inner ring and the outer ring is 5 volume percent or more and 30 volume percent or less.

8. The dislocation density of the retained austenite in the surface layer of the rolling surface of at least one of the inner ring and the outer ring is 5.0 x 10 １４ m －２ Above 1.0 x 10 １７ m －２ 2. The rolling bearing according to claim 1 , wherein:

9. A rolling bearing according to claim 8, 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.

10. A rolling bearing as set forth in claim 8, 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.

11. A rolling bearing as claimed in any one of claims 8 to 10, 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.

12. A bearing comprising a plurality of rotating shafts and a plurality of rolling bearings, each of the plurality of rolling bearings having an inner ring, an outer ring and rolling elements made of quenched and tempered steel, each of the inner ring, the outer ring and the front rolling elements having a rolling surface, each of the plurality of rotating shafts being supported by each of the plurality of rolling bearings, wherein one of the plurality of rotating shafts having the slowest rotation speed is designated as a first rotating shaft and the plurality of rotating shafts other than the first rotating shaft are designated as second rotating shafts, the dislocation density of retained austenite in the surface layer of the rolling surface of at least any 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 is 2.5×10 １４ m －２ Above 1.0 x 10 １７ m －２ A drive unit for a vehicle, comprising:

13. A vehicle drive unit as described in claim 12, 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 800 Hv or more and 1245 Hv or less.

14. A vehicle drive unit as described in claim 12, wherein the nitrogen concentration in the rolling surface 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 0.25 mass percent or more.

15. The dislocation density of the 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 3.5×10 １４ m －２ Above 1.0 x 10 １７ m －２ 13. A drive unit for a vehicle according to claim 12, wherein:

16. A vehicle drive unit as described in claim 15, 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 940 Hv or less.

17. A vehicle drive unit as described in claim 15, wherein the nitrogen concentration in the rolling surface surface layer of at least one of the outer ring, the inner ring, and the rolling element of at least one of the multiple rolling bearings supporting the second rotating shaft is 0.03 mass percent or more and 0.25 mass percent or more.

18. A vehicle drive unit as described in any one of claims 12 to 17, 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 multiple rolling bearings supporting the second rotating shaft is 5 volume percent or more and 30 volume percent or less.

19. The dislocation density of the 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 5.0×10 １４ m －２ Above 1.0 x 10 １７ m －２ 13. A drive unit for a vehicle according to claim 12, wherein:

20. A vehicle drive unit as described in claim 19, 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 multiple rolling bearings supporting the second rotating shaft is 2 volume percent or more and 12 volume percent or less.

21. A vehicle drive unit as described in claim 19, 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 multiple rolling bearings supporting the second rotating shaft is 760 Hv or more and 900 Hv or less.

22. A vehicle drive unit as claimed in any one of claims 19 to 21, 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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