Rolling bearing and vehicular driving unit

Abstract

To provide a rolling bearing which can suppress an 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). The hardness on the rolling surface of at least any one of the inner ring, the outer ring, and the rolling element is 62.5 HRC or more and 67 HRC or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6023422 Summary of the Invention [Problem to be solved by the invention]

[0004] 2. Description of the Related Art Vehicle drive units used in electrically powered vehicles such as EVs (Electric Vehicles) and HEVs (Hybrid Electric Vehicles) will be required to become increasingly efficient in the future due to consideration of environmental issues such as the need to achieve carbon neutrality.

[0005] A vehicle drive unit has multiple rotating shafts, each of which is supported by a rolling bearing. In order to increase efficiency, the viscosity of the lubricating oil is reduced, the amount of oil is reduced, the number of oil pumps is reduced, etc., which can result in poor lubrication between the raceways and the rolling elements.

[0006] As vehicle drive units are made smaller to improve efficiency, the size of the bearings that support the rotating shaft is reduced. Also, to improve efficiency, the output of the drive source (motor, etc.) of the vehicle drive unit is increased. As a result, the load on the rolling bearings becomes even greater.

[0007] The mechanical component described in Patent Document 1 is tempered at 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 progress.

[0008] The present invention has been made in consideration of the problems of the conventional techniques as described above. More specifically, the present invention provides a rolling bearing capable of suppressing the generation and growth of cracks on the rolling surface even in the case of poor lubrication. [Means for solving the problem]

[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 hardness of the rolling surface 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. Effect of the Invention

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

[0011] [Figure 1] 1 is a cross-sectional view of a rolling bearing 100. FIG. [Diagram 2] 10 is a cross-sectional view of a rolling bearing 100 according to a modified example. [Diagram 3] 3A to 3C are manufacturing process diagrams of the rolling bearing 100. [Figure 4] 2 is a cross-sectional view of a vehicle drive unit 200. FIG. [Diagram 5] 11 is a cross-sectional view of a vehicle drive unit 200 according to a modified example. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The details of the embodiment of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are given the same reference symbols, and duplicated explanations will not be repeated. The rolling bearing according to the embodiment is referred to as a rolling bearing 100, and the 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] Fig. 1 is a cross-sectional view of a rolling bearing 100. As shown in Fig. 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.

[0015] The inner ring 10 has a circular shape extending in the circumferential direction and has 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 opposite surface of 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 end in the axial direction 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 end in the axial direction 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 opposite surface of 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 a 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 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 shape extending in the circumferential direction and has 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 opposite surface of 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 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 to 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 a 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 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 therebetween in the radial direction (so that the raceway surface 20ca faces the raceway surface 10da with a gap therebetween 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 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 may be 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 such that the interval between two adjacent rolling elements 30 in the circumferential direction falls within a certain range.

[0026] The inner ring 10, the outer ring 20, and the rolling elements 30 are made of hardened and tempered steel. The steel constituting the inner ring 10, the outer ring 20, and the rolling elements 30 is, for example, high carbon chromium bearing steel as specified by the JIS standard. The steel constituting the inner ring 10, the outer ring 20, and the rolling elements 30 is, for example, SUJ2 or SUJ3 as specified by the JIS standard.

[0027] The hardness of the rolling surfaces 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). The hardness of the rolling surfaces of the inner ring 10, the outer ring 20, and the rolling elements 30 is measured in accordance with the Vickers hardness testing 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, with the position being regarded as the surface layer of the rolling surface. The hardness on 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.

[0028] 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 2 volume percent or more and 10 volume percent or less. The amount of retained austenite in 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 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 measured according to a method defined in the JIS standard.

[0029] No nitriding treatment has been performed on the surfaces of the inner ring 10, the outer ring 20, and the rolling elements 30. From another perspective, if the nitrogen concentration of the rolling surface surface layer of the inner ring 10, the outer ring 20, and the 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 of the rolling surface surface layer is less than 0.01 mass percent. The above nitrogen concentration is measured using an EPMA (Electron Probe Micro Analyzer) by performing a line analysis in the depth direction from the rolling surface in a cross section perpendicular to the rolling surface, thereby measuring the average value of the nitrogen concentration up to a position 10 μm deep from the rolling surface.

[0030] 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, for example, 5.0×10 14 m -2 Above 1.0×10 17 m -2 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 preferably 5.0×10 14 m -2 Above 1.0×10 16 m -2 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 more preferably 5·0×10 14 m -2 Above 1.0×10 15 m -2 The dislocation densities 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 are measured on the rolling surfaces using a cobalt tube type X-ray diffraction device.

[0031] <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 10 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 10 volume percent or less.

[0032] In the above example, the dislocation density of the retained austenite in the rolling surface layers of the inner ring 10, the outer ring 20, and the rolling element 30 is 5.0×10 14 m -2 Above 1.0×10 17 m -2 The following case has been described. In the case where the dislocation density of the retained austenite in the surface layer of the rolling surface 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 1.0×10 17 m -2 In the above example, 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. However, it is sufficient that the nitrogen concentration in the rolling surface surface layer 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.

[0033] 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.

[0034] (Method of manufacturing rolling bearing 100) A method for manufacturing the rolling bearing 100 will now be described.

[0035] Fig. 3 is a manufacturing process diagram of the rolling bearing 100. As shown in Fig. 3, the manufacturing method of the rolling bearing 100 includes a preparation step S1, a quenching step S2, a cooling step S3, a tempering step S4, a post-treatment step S5, and an assembly step S6.

[0036] In the preparation step S1, a workpiece is prepared. The workpiece is preferably made of high carbon chromium bearing steel (e.g., SUJ2, SUJ3) as specified by the JIS standard. The workpiece for the inner ring 10 and the outer ring 20 is ring-shaped, and the workpiece for the rolling element 30 is spherical.

[0037] The quenching step S2 is performed after the preparation step S1. The quenching step S2 is a step of quenching the workpiece from a temperature equal to or higher than the A1 transformation point to a temperature of M S This is performed by cooling the steel to a temperature below the 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 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 martensite formation in the steel progresses and the amount of retained austenite in the steel decreases.

[0038] The tempering step S4 is performed after the cooling step S3. The tempering step S4 is performed by heating and holding the workpiece at a temperature lower than the A1 transformation point. The heating temperature in the tempering step S4 is, for example, 180°C.

[0039] The post-processing step S5 is performed after the tempering step S4. In the post-processing step S5, the surface of the workpiece is machined (grinded, polished). As a result, the inner ring 10, the outer ring 20, and the rolling elements 30 are formed. The assembly step S6 is performed after the post-processing step S5. In the assembly step S6, the inner ring 10, the outer ring 20, and the rolling elements 30 are assembled together with the cage 40 to form the rolling bearing 100 having the structure shown in FIG. 1.

[0040] (Configuration of vehicle drive unit 200) The configuration of the vehicle drive unit 200 will be described below.

[0041] 4 is a cross-sectional view of the vehicle drive unit 200. As shown in FIG.

[0042] 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.

[0043] The reducer 120 has 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 a rolling bearing 130 are, for example, deep groove ball bearings.

[0044] The rotation of the rotating shaft 112 is transmitted to the rotating shaft 121, so that the rotating shaft 121 rotates 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.

[0045] 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. The gears 125 and 126 are attached to the rotating shaft 122 and rotate together with the rotating shaft 122. The gear 125 is meshed with the gear 124. Therefore, the rotating shaft 122 rotates as the rotation of the rotating shaft 121 is transmitted by the gears 124 and 125. The gear ratio of the 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.

[0046] 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 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.

[0047] 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 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. It is preferable that 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 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.

[0048] 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 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 130.

[0049] 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 inner ring, outer ring and rolling surfaces of 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 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.

[0050] At least one of the rolling bearing 114 and the rolling bearing 128 is preferably the rolling bearing 100 .

[0051] <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.

[0052] (Effect of Rolling Bearing 100) The effects of the rolling bearing 100 will be described below.

[0053] When the rolling bearing 100 is used under poor lubrication conditions, the oil film thickness on the rolling surfaces of the inner ring 10, the outer ring 20, and the 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 hardness of the rolling surfaces 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 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 contact occurs between the rolling surface of the inner ring 10 (outer ring 20) and the rolling surface of the rolling elements 30, surface damage (generation and growth of cracks) due to plastic deformation is unlikely to occur.

[0054] 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 down the progression of residual stress due to plastic deformation. Therefore, the rolling bearing 100 also improves the rolling fatigue life.

[0055] 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.

[0056] 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. Also, 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, so that resistance to stress concentration due to shoulder riding and edge hitting is improved.

[0057] 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. When the amount of retained austenite in the rolling surface layers of the inner ring 10 and the outer ring 20 is 2 volume percent or more and 10 volume percent or less, dimensional changes over time in the inner ring 10 and the outer ring 20 that are associated with 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.

[0058] Also, suppressing dimensional changes over time of the inner ring 10 and the outer ring 20 associated with the decomposition of retained austenite allows the rolling bearing 100 to continue rolling stably. Furthermore, suppressing dimensional changes over time of the inner ring 10 and the outer ring 20 associated with 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.

[0059] Furthermore, in the rolling bearing 100, the hardness of the rolling surfaces 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), 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 the outer ring 20 is small.

[0060] 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 a decrease in the dislocation density of martensite is unlikely to occur 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 high dislocation density, and the dislocation density of the retained austenite surrounded by the dislocation density is also high.

[0061] The volume expansion of the retained austenite that 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 1.0×10 17 m -2 By satisfying the following, dimensional changes over time of the inner ring 10 and the outer ring 20 due to decomposition of retained austenite can be further suppressed.

[0062] 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 with the refinement of the crystal grains, further improving surface damage caused by plastic deformation, rolling fatigue life, and foreign matter resistance. Also, 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 and SUJ3, general steel can be used for the inner ring 10, outer ring 20, and rolling elements 30, making it possible to reduce the cost of the rolling bearing 100.

[0063] (Effects of the vehicle drive unit 200) The effects of the vehicle drive unit 200 will be described below.

[0064] Since 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.

[0065] On the other hand, because the rotation 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 that applied to the rolling bearing 128, and the rolling bearing 129 is more likely to be poorly lubricated (the oil film thickness is more likely to be smaller) than the rolling bearing 128. As a result, metal contact is 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 likely to occur on the rolling surfaces of the inner ring, outer ring, and rolling elements.

[0066] In vehicle drive unit 200, the hardness of the rolling surfaces of the inner ring, outer ring and rolling elements of rolling bearing 129 is greater than the hardness of the rolling surfaces of the inner ring, outer ring and rolling elements of rolling bearing 129, and the amount of retained austenite in the surface layers of the rolling surfaces of the inner ring and outer ring of rolling bearing 128 is less than the amount of retained austenite in the surface layers of the rolling surfaces of the inner ring and outer ring of rolling bearing 129. Therefore, it is possible to suppress surface damage to the rolling surfaces of the inner ring, outer ring and rolling elements of rolling bearing 129 while suppressing dimensional changes over time in the inner ring and outer ring of rolling bearing 128.

[0067] (Additional Note) This embodiment includes the following configuration.

[0068] <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 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.

[0069] <Appendix 2> 2. The rolling bearing according to claim 1, wherein an amount of retained austenite in a surface layer of a rolling surface of at least one of the inner ring and the outer ring is 2 volume percent or more and 10 volume percent or less.

[0070] <Appendix 3> 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 5.0×10 14 m -2 Above 1.0×10 17 m -2 3. A rolling bearing according to claim 1 or 2, wherein:

[0071] <Appendix 4> 4. The rolling bearing according to claim 1, wherein a nitrogen concentration in a rolling surface layer of at least one of the inner ring and the outer ring is less than 0.01 mass percent.

[0072] <Appendix 5> A first rotation axis; A second rotating shaft having a rotation speed slower than that of the first rotating shaft; a first rolling bearing supporting the first rotating shaft; a second rolling bearing supporting the second rotating shaft; The first rolling bearing has a first inner ring, a first outer ring, and a first rolling element made of hardened and tempered steel, each of the first inner ring, the first outer ring, and the first rolling element has a first rolling surface; the second rolling bearing has a second inner ring, a second outer ring, and a second rolling element made of hardened and tempered steel, each of the second inner ring, the second outer ring, and the second rolling element has a second rolling surface; the hardness of the second rolling surface is greater than the hardness of the first rolling surface, A vehicle drive unit, wherein the first rolling bearing is the rolling bearing according to any one of Supplementary Note 1 to Supplementary Note 4.

[0073] <Appendix 6> 6. The vehicle drive unit according to claim 5, wherein an amount of retained austenite in a surface layer of a rolling surface of the first inner ring and the first outer ring is smaller than an amount of retained austenite in a surface layer of a rolling surface of the second inner ring and the second outer ring.

[0074] <Appendix 7> 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 being one of the plurality of rotating shafts having the slowest rotation speed, and a second rotating shaft being 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 element of at least one of the plurality of rolling bearings supporting the second rotating shaft having a hardness of 760 Hv or more and 900 Hv or less on the rolling surface.

[0075] <Appendix 8> 8. The vehicle drive unit according to claim 7, wherein an amount of retained austenite in a 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 10 volume percent or less.

[0076] <Appendix 9> In 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, the dislocation density of the retained austenite in the rolling surface layer is 5.0×10 14 m -2 Above 1.0×10 17 m -2 9. A vehicle drive unit according to claim 7 or 8, wherein:

[0077] <Appendix 10> 10. The vehicle drive unit according to any one of Appendix 7 to Appendix 9, wherein a nitrogen concentration in a 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 0.01 mass percent or more.

[0078] Although the embodiment of the present invention has been described above, the above-mentioned embodiment can be modified in various ways. The scope of the present invention is not limited to the above-mentioned embodiment. 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. [Explanation of symbols]

[0079] 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

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 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.

2. 2. The rolling bearing according to claim 1, wherein an amount of retained austenite in a surface layer of a rolling surface of at least one of the inner ring and the outer ring is 2 volume percent or more and 10 volume percent or less.

3. The dislocation density of the retained austenite in the rolling 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 2. The rolling bearing according to claim 1 , wherein:

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

5. A first rotation axis; A second rotating shaft having a rotation speed slower than that of the first rotating shaft; a first rolling bearing supporting the first rotating shaft; a second rolling bearing supporting the second rotating shaft; The first rolling bearing has a first inner ring, a first outer ring, and a first rolling element made of hardened and tempered steel, each of the first inner ring, the first outer ring, and the first rolling element has a first rolling surface; the second rolling bearing has a second inner ring, a second outer ring, and a second rolling element made of hardened and tempered steel, Each of the second inner ring, the second outer ring, and the second rolling element has a second rolling surface, The hardness of the second rolling surface is greater than the hardness of the first rolling surface, The vehicle drive unit, wherein the first rolling bearing is the rolling bearing according to any one of claims 1 to 4.

6. 6. The vehicle drive unit according to claim 5, wherein an amount of retained austenite in a surface layer of the rolling surface of the first inner ring and the first outer ring is smaller than an amount of retained austenite in a surface layer of the rolling surface of the second inner ring and the second outer ring.

7. 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 vehicle drive unit, 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 is designated as a second rotating shaft, and 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.

8. 8. The vehicle drive unit according to claim 7, wherein an amount of retained austenite in a 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 10 volume percent or less.

9. In 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, the dislocation density of the retained austenite in the rolling surface layer is 5.0×10 １４ m －２ Above 1.0 x 10 １７ m －２ 8. A drive unit for a vehicle according to claim 7, wherein:

10. 10. The vehicle drive unit according to claim 7, wherein a nitrogen concentration in a 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 0.01 mass percent or more.

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