Rolling bearing and vehicle drive unit

Abstract

A rolling bearing (100) supports a rotating shaft of a vehicle drive unit. A rolling bearing is provided with a quenched and tempered steel inner ring (10), outer ring (20), and rolling elements (30). The inner ring, the outer ring, and the rolling elements each have a rolling surface (10da, 20ca, 30a). The hardness at the rolling surface of at least one of the inner ring, the outer ring, and the rolling body is 865-1245 Hv.

Description

Technical Field

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

[0002] Japanese Patent No. 6023422 (Patent Document 1) describes a mechanical component. The mechanical component described in Patent Document 1 is a raceway ring or rolling element that constitutes a rolling bearing. The mechanical component described in Patent Document 1 is formed by quenching after nitrogen is introduced into the surface, followed by high-temperature tempering.

[0003] Prior art literature Patent Literature Patent Document 1: Japanese Patent No. 6023422 Summary of the Invention

[0004] Technical problem to be solved by the invention Drive units used in electric vehicles such as EVs (electric vehicles) and HEVs (hybrid electric vehicles) are being increasingly demanded to achieve higher efficiency due to environmental concerns such as achieving carbon neutrality.

[0005] Vehicle drive units have multiple rotating shafts, each supported by a rolling bearing. To improve efficiency, the lubrication between the raceway rings and rolling elements is sometimes lean lubrication by reducing the viscosity of the lubricating oil, reducing the amount of oil, or reducing the number of oil pumps.

[0006] As vehicle drive units become smaller in size to improve efficiency, the bearings supporting the rotating shafts are becoming smaller. Furthermore, to further enhance efficiency, the output of the drive sources (e.g., motors) in vehicle drive units is increasing. As a result, the load on the rolling bearings is further increasing.

[0007] The mechanical component described in Patent Document 1 undergoes high-temperature tempering, which reduces hardness close to the surface. Consequently, when a rolling bearing comprising the mechanical component described in Patent Document 1 is used under these conditions, cracks may develop on the rolling surfaces (raceways, rolling element surfaces), and these cracks may develop.

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

[0009] Technical solutions used to solve technical problems The rolling bearing of the present invention supports the rotating shaft of a vehicle drive unit. The rolling bearing comprises an inner ring, an outer ring, and rolling elements made of quenched and tempered steel. Each of the inner ring, outer ring, and rolling elements has a rolling surface. The hardness of the rolling surface of at least one of the inner ring, outer ring, and rolling element is 865 Hv or higher and 1245 Hv or lower.

[0010] Effects of the Invention According to the rolling bearing of the present invention, the occurrence and growth of cracks on the rolling surface can be suppressed even in the case of lean lubrication. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0012] The details of the embodiments of the present invention will be described with reference to the accompanying drawings. In the following drawings, identical or corresponding parts are denoted by the same reference numerals, and descriptions thereof will not be repeated. The rolling bearing of the embodiment is denoted as rolling bearing 100, and the vehicle drive unit of the embodiment is denoted as vehicle drive unit 200.

[0013] (Structure of Rolling Bearing 100) Next, the structure of the rolling bearing 100 will be described.

[0014] Figure 1 is a cross-sectional view of the rolling bearing 100. Figure 1 As shown, rolling bearing 100 is, for example, a deep groove ball bearing. Rolling bearing 100 includes an inner ring 10, an outer ring 20, multiple rolling elements 30, and a retainer 40. The central axis of inner ring 10 is referred to as central axis A. The direction of central axis A is referred to as the axial direction. Directions passing through and perpendicular to central axis A are referred to as radial directions. The direction along the circumference of a circle centered on central axis A when viewed in the axial direction is referred to as the circumferential direction.

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

[0016] The first wide face 10a and the second wide face 10b are the end faces of the inner ring 10 in the axial direction. The first wide face 10a faces one side in the axial direction ( Figure 1 The second wide surface 10b faces the other side in the axial direction ( Figure 1 The second wide surface 10b is a surface opposite to the first wide surface 10a in the axial direction.

[0017] The inner diameter surface 10c and the outer diameter surface 10d extend circumferentially. One axial end of the inner diameter surface 10c and the other axial end are connected to the first wide surface 10a and the second wide surface 10b, respectively. One axial end of the outer diameter surface 10d and the other axial end are connected to the first wide surface 10a and the second wide surface 10b, respectively. The inner diameter surface 10c faces radially inward. The outer diameter surface 10d faces radially outward. The outer diameter surface 10d is the surface radially opposite to the inner diameter surface 10c.

[0018] The outer diameter surface 10d includes a raceway surface 10da. The raceway surface 10da is the portion of the outer diameter surface 10d that contacts the rolling element 30. When viewed in a cross-section perpendicular to the circumferential direction, the raceway surface 10da is recessed toward the inner diameter surface 10c. When viewed in a cross-section perpendicular to the circumferential direction, the raceway surface 10da has a partial arc shape. The raceway surface 10da, which extends circumferentially, is located at the axial center of the outer diameter surface 10d.

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

[0020] The first wide surface 20a and the second wide surface 20b are end surfaces of the outer ring 20 in the axial direction. The first wide surface 20a faces one side in the axial direction ( Figure 1 The second wide surface 20b faces the other side in the axial direction ( Figure 1 The second wide surface 20b is a surface opposite to the first wide surface 20a in the axial direction.

[0021] The inner diameter surface 20c and the outer diameter surface 20d extend circumferentially. One axial end of the inner diameter surface 20c and the other axial end are connected to the first wide surface 20a and the second wide surface 20b, respectively. One axial end of the outer diameter surface 20d and the other axial end are connected to the first wide surface 20a and the second wide surface 20b, respectively. The inner diameter surface 20c faces radially inward. The outer diameter surface 20d faces radially outward. The outer diameter surface 20d is the surface radially opposite to the inner diameter surface 20c.

[0022] The inner diameter surface 20c includes a raceway surface 20ca. The raceway surface 20ca is the portion of the inner diameter surface 20c that contacts the rolling element 30. The raceway surface 20ca is recessed toward the outer diameter surface 20d when viewed in a cross-section perpendicular to the circumferential direction. The raceway surface 20ca has a partial arc shape when viewed in a cross-section perpendicular to the circumferential direction. The raceway surface 20ca, which extends circumferentially, is located at the axial center of the inner diameter surface 20c.

[0023] The outer ring 20 is arranged radially outside the inner ring 10 such that the inner diameter surface 20 c and the outer diameter surface 10 d face each other with a radial gap therebetween (such that the raceway surface 20 ca and the raceway surface 10 da face each other with a radial gap therebetween).

[0024] The rolling element 30 is disposed between the track surface 10da and the track surface 20ca. The rolling element 30 is spherical. The rolling element 30 has a surface 30a. The rolling element 30 contacts the track surface 10da and the track surface 20ca at the surface 30a. The track surface 10da, the track surface 20ca, and the surface 30a are sometimes referred to as rolling surfaces.

[0025] The retainer 40 is disposed between the outer diameter surface 10d and the inner diameter surface 20c and retains the plurality of rolling elements 30 so that the interval between two circumferentially adjacent rolling elements 30 falls within a certain range.

[0026] The inner ring 10, outer ring 20, and rolling elements 30 are made of quenched and tempered steel. These steels are, for example, high-carbon chromium bearing steel specified in the JIS standard. These steels are, for example, SUJ2 or SUJ3 specified in the JIS standard.

[0027] The hardness of the rolling contact surfaces of the inner ring 10, outer ring 20, and rolling element 30 is 865 Hv to 1245 Hv (66 HRC to 72 HRC). The hardness of the rolling contact surfaces of the inner ring 10, outer ring 20, and rolling element 30 is measured using the Vickers hardness test method specified in JIS standards. The hardness of the rolling contact surfaces of the inner ring 10, outer ring 20, and rolling element 30 is measured at a depth of 50 μm from the rolling contact surface in a cross section perpendicular to the rolling contact surface, with the surface layer of the rolling contact surface considered to be the surface layer. The hardness at the rolling surface can also be calculated as follows: in a cross section perpendicular to the rolling surface, the Vickers hardness is measured at positions at a depth of 50 μm, 150 μm, 250 μm, 350 μm, and 450 μm from the rolling surface, and the Vickers hardness at a position at a depth of 0 μm from the rolling surface is estimated using an approximate formula (linear or exponential) determined based on the Vickers hardness measured at these five points.

[0028] The retained austenite content of the surface layers of the rolling contact surfaces of the inner ring 10, outer ring 20, and rolling element 30 is preferably 5% by volume or greater and 16% by volume or less. The retained austenite content of the surface layers of the rolling contact surfaces of the inner ring 10, outer ring 20, and rolling element 30 is measured by X-ray diffraction at a position 50 μm in the depth direction of the rolling contact surfaces in a cross section perpendicular to the rolling contact surfaces. The grain size of the prior austenite grains of the surface layers of the rolling contact surfaces of the inner ring 10, outer ring 20, and rolling element 30 is preferably 9 or greater. The grain size of the prior austenite grains of the surface layers of the rolling contact surfaces of the inner ring 10, outer ring 20, and rolling element 30 is measured according to the method specified in the JIS standard.

[0029] The surfaces of the inner ring 10, outer ring 20, and rolling element 30 are preferably nitrided. The nitrogen concentration in the surface layer of the rolling contact surface of the inner ring 10, outer ring 20, and rolling element 30 is defined as the average nitrogen concentration in the region extending from the rolling contact surface to a depth of 10 μm. The nitrogen concentration in the surface layer of the rolling contact surface of the inner ring 10, outer ring 20, and rolling element 30 is preferably 0.3 mass% or greater. For example, the nitrogen concentration in the surface layer of the rolling contact surface of the inner ring 10, outer ring 20, and rolling element 30 is 1.0 mass% or less. If the nitrogen concentration in the surface layer of the rolling contact surface exceeds 1.0 mass%, the amount of retained austenite exceeds 16 volume%, reducing the effect of suppressing dimensional change over time. Furthermore, if the nitrogen concentration in the surface layer of the rolling contact surface exceeds 1.0 mass%, the carbon concentration decreases due to decarburization during heat treatment, potentially reducing the hardness of the rolling contact surface. The nitrogen concentration was measured using EPMA (Electron Probe Micro Analyzer) by performing line analysis in the depth direction from the rolling surface in a cross section perpendicular to the rolling surface. The average nitrogen concentration from the rolling surface to a depth of 10 μm was measured.

[0030] The dislocation density of retained austenite in the surface layer of the rolling contact surfaces of the inner ring 10, the outer ring 20, and the rolling element 30 is, for example, 2.5×10 14 m -2 Above and 1.0×10 17 m -2 The dislocation density of retained austenite in the surface layer of the rolling contact surfaces of the inner ring 10, the outer ring 20, and the rolling element 30 is preferably 2.5×10 14 m -2 Above and 1.0×10 16 m -2 The dislocation density of retained austenite in the surface layer of the rolling contact surfaces of the inner ring 10, the outer ring 20, and the rolling element 30 is more preferably 2.5×10 14 m -2 Above and 1.0×10 15 m -2The dislocation density of retained austenite in the surface layers of the rolling contact surfaces of the inner ring 10 , the outer ring 20 , and the rolling elements 30 was measured at the rolling contact surfaces using a cobalt tube-shaped X-ray diffractometer.

[0031] Modifications While the above example describes a case where the hardness of the rolling contact surfaces of the inner ring 10, outer ring 20, and rolling element 30 is 865 Hv to 1245 Hv (66 HRC to 72 HRC), it is sufficient that the hardness of the rolling contact surfaces of at least one of the inner ring 10, outer ring 20, and rolling element 30 is 865 Hv to 1245 Hv (66 HRC to 72 HRC). Furthermore, while the above example describes a case where the retained austenite content of the surface layers of the rolling contact surfaces of the inner ring 10, outer ring 20, and rolling element 30 is 5 volume % to 16 volume %, it is sufficient that the retained austenite content of the surface layers of the rolling contact surfaces of at least one of the inner ring 10, outer ring 20, and rolling element 30 is 5 volume % to 16 volume %, it is sufficient that the retained austenite content of the surface layers of the rolling contact surfaces of at least one of the inner ring 10, outer ring 20, and rolling element 30 is 5 volume % to 16 volume %.

[0032] In the above example, the dislocation density of the retained austenite in the surface layer of the rolling surface of the inner ring 10, the outer ring 20 and the rolling element 30 is 2.5×10 14 m -2 Above and 1.0×10 17 m -2 The following case is described, but as long as the dislocation density of retained austenite in the surface layer of the rolling contact surface 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 and 1.0×10 17 m -2 Furthermore, while the above example illustrates a case where the nitrogen concentration in the rolling surface layers of the inner ring 10, outer ring 20, and rolling element 30 is 0.3 mass% or greater, it suffices to note that the nitrogen concentration in the rolling surface layers of at least any one of the inner ring 10, outer ring 20, and rolling element 30 is 0.3 mass% or greater.

[0033] In the above example, the hardness of the rolling contact surfaces of the inner ring 10, outer ring 20, and rolling element 30 is described as being 865 Hv or higher and 1245 Hv or lower. However, the hardness of the rolling contact surfaces of the inner ring 10, outer ring 20, and rolling element 30 may also be 800 Hv or higher and 940 Hv or lower. In this case, the dislocation density of the retained austenite in the surface layer of the rolling contact surfaces of the inner ring 10, outer ring 20, and rolling element 30 may also be 3.5×10 14 m -2 Above and 1.0×10 17 m -2In this case, the nitrogen concentration of the surface layers of the rolling contact surfaces of the inner ring 10 , the outer ring 20 , and the rolling elements 30 may be 0.1 mass % or more and less than 0.3 mass %.

[0034] Figure 2 1 is a cross-sectional view of a rolling bearing 100 according to a modified example. Figure 2 As shown, the rolling bearing 100 can also be a tapered roller bearing.

[0035] (Method for Manufacturing Rolling Bearing 100) Next, a method for manufacturing the rolling bearing 100 will be described.

[0036] Figure 3 FIG is a manufacturing process diagram of the rolling bearing 100. Figure 3 As shown, the method for manufacturing the rolling bearing 100 includes a preparation step S1 , a nitriding treatment step S2 , a quenching step S3 , a cooling step S4 , a tempering step S5 , a post-treatment step S6 , and an assembly step S7 .

[0037] In the preparation step S1 , the workpiece is prepared. The workpiece is preferably made of high-carbon chromium bearing steel (e.g., SUJ2 or SUJ3) specified in the JIS standard. The workpieces for the inner ring 10 and outer ring 20 are ring-shaped, while the workpiece for the rolling element 30 is spherical.

[0038] Nitriding step S2 is performed after preparatory step S1. Nitriding step S2 is performed by heating and holding the workpiece in an atmosphere containing a nitrogen source (e.g., ammonia). The heating temperature in nitriding step S2 is above the Al transformation point of the steel constituting the heated workpiece. For example, this heating temperature is 800°C or higher. The heating and holding in nitriding step S2 allows nitrogen to penetrate from the surface of the workpiece. Nitriding step S2 is performed so that nitrogen diffuses to the locations where it will become the surfaces of the inner ring 10, outer ring 20, and rolling element 30 after post-treatment step S6.

[0039] Furthermore, nitrogen that has penetrated from the surface of the workpiece reacts with alloying elements (e.g., chromium) in the steel constituting the workpiece to form precipitates. Due to the pinning effect of the precipitates, the prior austenite grains produced during heating in the quenching step S3 are refined, and the martensite grains produced during cooling in the quenching step S3 are also refined.

[0040] The quenching step S3 is performed after the nitriding step S2. The quenching step S3 is performed by cooling the workpiece from a temperature above the A1 transformation point to a temperature of M SThe cooling step S4 is performed at a temperature below the transformation point. The cooling step S4 is performed after the quenching step S3. The cooling step S4 is either ice-cooling or cryogenic treatment. In ice-cooling, the workpiece is cooled to a temperature between -99°C and 0°C. In cryogenic treatment, the workpiece is cooled to a temperature below -100°C. Ice-cooling and cryogenic treatment promote martensite formation in the steel and reduce the amount of retained austenite in the steel.

[0041] The tempering step S5 is performed after the cooling step S4. The tempering step S5 is performed by heating and holding the workpiece at a temperature lower than the A1 transformation point. The heating temperature of the tempering step S5 is, for example, 180°C.

[0042] Post-processing step S6 is performed after tempering step S5. In post-processing step S6, the surface of the workpiece is machined (grinded or polished). This forms the inner ring 10, outer ring 20, and rolling elements 30. Assembly step S7 is performed after post-processing step S6. In assembly step S7, the inner ring 10, outer ring 20, and rolling elements 30 are assembled together with the retainer 40 to form the inner ring 10, outer ring 20, and rolling elements 30. Figure 1 A rolling bearing 100 of the structure shown.

[0043] (Structure of Vehicle Drive Unit 200) Hereinafter, the structure of the vehicle drive unit 200 will be described.

[0044] Figure 4 FIG is a cross-sectional view of the vehicle drive unit 200. Figure 4 As shown, the vehicle drive unit 200 includes a motor 110 and a speed reducer 120 .

[0045] Motor 110 includes a motor body 111, a rotating shaft 112, a motor housing 113, and a rolling bearing 114. Motor body 111 rotates rotating shaft 112 about its central axis. Motor body 111 is disposed within motor housing 113. Rotating shaft 112 is rotatable about its central axis and is supported by rolling bearing 114. Rolling bearing 114 is, for example, a deep groove ball bearing.

[0046] Speed ​​reducer 120 includes rotating shafts 121, 122, and 123, gears 124, 125, 126, and 127, and rolling bearings 128, 129, and 130. Rolling bearings 128, 129, and 130 are, for example, deep groove ball bearings.

[0047] The rotating shaft 121 rotates about the central axis of the rotating shaft 112 by transmitting the rotation of the rotating shaft 112. The rotating shaft 121 is supported by the 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.

[0048] Rotating shaft 122 is supported by rolling bearing 129 so as to be rotatable about its central axis. Gears 125 and 126 are mounted on rotating shaft 122 and rotate together with the rotating shaft 122. Gear 125 meshes with gear 124. Thus, rotating shaft 122 rotates by transmitting the rotation of rotating shaft 121 via gears 124 and 125. The gear ratio between gears 124 and 125 is adjusted so that the rotation speed of rotating shaft 122 is lower than that of rotating shaft 121.

[0049] Rotating shaft 123 is supported by rolling bearing 130 so as to be rotatable about its central axis. Gear 127 is attached to rotating shaft 123 and rotates together with rotating shaft 123. Gear 127 meshes with gear 126. Thus, rotating shaft 123 rotates by transmitting the rotation of rotating shaft 122 via gears 126 and 127. The gear ratio between gears 126 and 127 is adjusted so that the rotation speed of rotating shaft 123 is lower than that of rotating shaft 122.

[0050] The hardness of the inner ring, outer ring, and rolling element rolling surfaces of rolling bearing 128 is lower than that of the inner ring, outer ring, and rolling element rolling surfaces of rolling bearing 129. The amount of retained austenite in the rolling surface layers of the inner and outer rings of rolling bearing 128 is lower than that of the inner and outer rings of rolling bearing 129. The dislocation density of the retained austenite in the rolling surface layers of the inner and outer rings of rolling bearing 128 is preferably higher than that of the retained austenite in the rolling surface layers of the inner and outer rings of rolling bearing 129.

[0051] The hardness of the inner ring, outer ring, and rolling element rolling surfaces of rolling bearing 129 is preferably lower than that of the inner ring, outer ring, and rolling element rolling surfaces of rolling bearing 130. The amount of retained austenite in the rolling surface layers of the inner ring and outer ring of rolling bearing 129 is preferably lower than that of the inner ring and outer ring of rolling bearing 130. The dislocation density of the retained austenite in the rolling surface layers of the inner ring and outer ring of rolling bearing 129 is preferably higher than that of the inner ring and outer ring of rolling bearing 130.

[0052] The hardness of the rolling surfaces of the inner and outer rings and rolling elements of rolling bearing 114 is preferably lower than that of the inner and outer rings and rolling elements of rolling bearing 129. The amount of retained austenite in the rolling surface layers of the inner and outer rings of rolling bearing 114 is preferably lower than that of the inner and outer rings of rolling bearing 129. The dislocation density of the retained austenite in the rolling surface layers of the inner and outer rings of rolling bearing 114 is preferably higher than that of the inner and outer rings of rolling bearing 129.

[0053] It is preferable that at least one of the rolling bearing 129 and the rolling bearing 130 is the rolling bearing 100 , and it is more preferable that the rolling bearing 130 is the rolling bearing 100 .

[0054] Modifications Figure 5 FIG is a cross-sectional view of a modified example of a vehicle drive unit 200. Figure 5 As shown, rolling bearing 129 and rolling bearing 130 may also be tapered roller bearings.

[0055] (Effect of rolling bearing 100) Next, the effects of the rolling bearing 100 will be described.

[0056] When rolling bearing 100 is used under lean lubrication conditions, the oil film thickness on the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30 is thin, potentially leading to metallic contact between the rolling surfaces of the inner ring 10 (outer ring 20) and the rolling elements 30. In rolling bearing 100, the hardness of the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30 is 865 Hv to 1245 Hv (800 Hv to 940 Hv). This means that plastic deformation of the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30 is less likely to occur in rolling bearing 100. Therefore, even if metallic contact occurs between the rolling surfaces of the inner ring 10 (outer ring 20) and the rolling elements 30, surface damage (the initiation and growth of cracks) caused by plastic deformation is less likely to occur.

[0057] Plastic deformation is less likely to occur at the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30. This means that plastic deformation directly below these surfaces is reduced, and the development of residual stress caused by plastic deformation is slowed. Consequently, rolling bearing 100 also improves rolling fatigue life.

[0058] In rolling bearing 100, the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30 have high hardness. Therefore, indentations caused by foreign matter biting into the contact areas between the rolling surfaces of the inner ring 10 (outer ring 20) and the rolling elements 30 are less likely to form. Consequently, rolling bearing 100 also improves foreign matter resistance.

[0059] In rolling bearing 100 (i.e., in the case of a deep groove ball bearing), stress concentration due to shoulder creep can occur when a large axial load is applied. Furthermore, in rolling bearing 100 of a modified example (i.e., in the case of a tapered roller bearing), stress concentration due to edge contact can occur on the rolling surfaces. As described above, the rolling bearing 100 and the modified example rolling bearing 100 have high hardness at the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30, making them less susceptible to plastic deformation. This improves their resistance to stress concentration due to shoulder creep and edge contact.

[0060] When rolling bearing 100 is used at high temperatures, retained austenite in the inner ring 10 and outer ring 20 decomposes, causing dimensional changes over time. When the retained austenite content in the surface layers of the rolling contact surfaces of the inner ring 10 and outer ring 20 is 5% to 16% by volume, the dimensional changes over time associated with the decomposition of retained austenite are suppressed. This eliminates the need for excessively tight fit with the rotating shaft or housing, thus preventing cracking in the inner ring 10 and outer ring 20.

[0061] Furthermore, by suppressing the dimensional changes over time of the inner ring 10 and outer ring 20 associated with the decomposition of retained austenite, the rolling bearing 100 can continue to roll stably. Furthermore, by suppressing the dimensional changes over time of the inner ring 10 and outer ring 20 associated with the decomposition of retained austenite, creep between the rotating shaft and the inner ring 10 is also suppressed. This maintains optimal tooth contact between the gears mounted on the rotating shaft, ensuring the quietness of the vehicle drive unit.

[0062] Furthermore, in the rolling bearing 100, the hardness of the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30 is greater than 865 Hv and less than 1245 Hv (greater than 800 Hv and less than 940 Hv). Therefore, even if the amount of retained austenite in the surface layer of the rolling surfaces of the inner ring 10, outer ring 20, and rolling elements 30 decreases, foreign matter resistance can be maintained.

[0063] In rolling bearing 100, cooling step S4 is performed during the formation of inner ring 10, outer ring 20, and rolling elements 30. Therefore, the reduction in the dislocation density of the martensite during tempering step S5 is less likely to occur. As a result, in inner ring 10, outer ring 20, and rolling elements 30, martensite with a high dislocation density surrounds retained austenite, and the retained austenite surrounded by the dislocation density also has a high dislocation density.

[0064] In retained austenite surrounded by high-dislocation-density martensite, the volume expansion associated with decomposition is restrained by the surrounding high-dislocation-density martensite. Therefore, even if the retained austenite decomposes during high-temperature use, the dimensional change associated with this decomposition is small. In this way, by setting the dislocation density of the retained austenite in the surface layer of the rolling contact surfaces of the inner ring 10 and the outer ring 20 to 2.5×10 14 m -2 Above and 1.0×10 17 m -2 Below (3.5×10 14 m -2 Above and 1.0×10 17 m -2 ), further suppressing the dimensional changes of the inner ring 10 and the outer ring 20 over time that are associated with the decomposition of retained austenite.

[0065] By setting the nitrogen concentration in the surface layers of the rolling contact surfaces of the inner ring 10, outer ring 20, and rolling element 30 to 0.3 mass% or higher (0.1 mass% or higher and less than 0.3 mass%), rolling fatigue life is further improved. When the grain size of the prior austenite grains in the surface layers of the rolling contact surfaces of the inner ring 10, outer ring 20, and rolling element 30 is 9 or higher, the hardness at the rolling contact surfaces of the inner ring 10, outer ring 20, and rolling element 30 increases as the grains become finer. This further improves surface damage caused by plastic deformation, rolling fatigue life, and foreign matter resistance. If the steel constituting the inner ring 10, outer ring 20, and rolling element 30 is high-carbon chromium bearing steel specified in JIS standards, such as SUJ2 or SUJ3, standard steel can be used for the inner ring 10, outer ring 20, and rolling element 30, thereby reducing the cost of the rolling bearing 100.

[0066] (Effects of Vehicle Drive Unit 200) Next, the effects of the vehicle drive unit 200 will be described.

[0067] Because the rotational speed of rotating shaft 121 is greater than that of rotating shaft 122, rolling bearing 128 supporting rotating shaft 121 is more likely to reach a higher temperature than rolling bearing 129 supporting rotating shaft 122. Specifically, the dimensions of the inner and outer rings of rolling bearing 128 are more likely to change over time than those of rolling bearing 129.

[0068] On the other hand, because the rotational speed of rotating shaft 121 is greater than that of rotating shaft 122, the load applied to rolling bearing 129 is greater than that applied to rolling bearing 128. This makes rolling bearing 129 more prone to poor lubrication (oil film thickness tends to be smaller) than rolling bearing 128. As a result, metal contact is more likely to occur between the rolling surfaces of the inner and outer rings and the rolling elements. This means that surface damage to the rolling surfaces of the inner and outer rings and the rolling elements of rolling bearing 129 is more likely to occur.

[0069] In the vehicle drive unit 200, the hardness of the rolling surface of the inner ring, outer ring and rolling element of the rolling bearing 129 is greater than the hardness of the rolling surface of the inner ring, outer ring and rolling element of the rolling bearing 128, and the amount of retained austenite in the rolling surface of the inner ring and outer ring of the rolling bearing 128 is smaller than the amount of retained austenite in the rolling surface of the inner ring and outer ring of the rolling bearing 129. Therefore, while suppressing the time-dependent change in the size of the inner ring and outer ring of the rolling bearing 128, it is possible to suppress surface damage to the rolling surface of the inner ring, outer ring and rolling element of the rolling bearing 129.

[0070] (Note) This embodiment includes the following structures.

[0071] Note 1 A rolling bearing is a rolling bearing that supports the rotating shaft of a vehicle drive unit. Equipped with inner ring, outer ring and rolling elements made of quenched and tempered steel, The inner ring, the outer ring and the rolling element each have a rolling surface. The hardness of at least any one of the inner ring, the outer ring, and the rolling elements at the rolling contact surface is 865 Hv or more and 1245 Hv or less.

[0072] Note 2 In the rolling bearing according to Supplementary Note 1, the amount of retained austenite in the rolling contact surface layer of at least one of the inner ring and the outer ring is 5 volume % or more and 16 volume % or less.

[0073] Note 3 In the rolling bearing according to Supplementary Note 1 or Supplementary Note 2, the dislocation density of retained austenite in the surface layer of the rolling contact surface of at least one of the inner ring and the outer ring is 2.5×10 14 m -2 Above and 1.0×10 17 m -2 the following.

[0074] Note 4 In the rolling bearing according to any one of Supplementary Notes 1 to 3, a nitrogen concentration in a surface layer of the rolling contact surface of at least one of the inner ring and the outer ring is 0.3 mass % or more.

[0075] <Note 5> A vehicle drive unit comprises: a first rotating shaft; a second rotation axis having a rotation speed lower than that of the first rotation axis; a first rolling bearing supporting the first rotating shaft; and a second rolling bearing supporting the second rotating shaft, The first rolling bearing includes a first inner ring, a first outer ring, and a first rolling element made of quenched and tempered steel. The first inner ring, the first outer ring and the first rolling element each have a first rolling surface. The second rolling bearing includes a second inner ring, a second outer ring, and a second rolling element made of quenched and tempered steel. The second inner ring, the second outer ring and the second rolling element each have a second rolling surface. The hardness of the second rolling surface is greater than the hardness of the first rolling surface. The second rolling bearing is the rolling bearing specified in any one of Supplementary Notes 1 to 4.

[0076] <Note 6> In the vehicle drive unit according to Supplementary Note 5, the retained austenite amount of the rolling contact surface layers of the first inner ring and the first outer ring is smaller than the retained austenite amount of the rolling contact surface layers of the second inner ring and the second outer ring.

[0077] <Note 7> A vehicle drive unit includes: a plurality of rotating shafts; and Multiple rolling bearings, Each of the plurality of rolling bearings has an inner ring, an outer ring, and rolling elements made of quenched and tempered steel. The inner ring, the outer ring and the rolling element each have a rolling surface, Each of the plurality of rotating shafts is supported by each of the plurality of rolling bearings. When one of the multiple rotating shafts with the slowest rotation speed is set as the first rotating shaft, and the multiple rotating shafts other than the first rotating shaft are set as the second rotating shaft, the hardness at 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 greater than 865Hv and less than 1245Hv.

[0078] <Note 8> In the vehicle drive unit described in Note 7, the amount of retained austenite in the 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 multiple rolling bearings supporting the second rotating shaft is greater than 5 volume % and less than 16 volume %.

[0079] <Note 9> In the vehicle drive unit according to Supplementary Note 7 or Supplementary Note 8, in at least any 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 retained austenite in the rolling surface layer is 2.5×10 14 m -2 Above and 1.0×10 17 m -2 the following.

[0080] <Note 10> In the vehicle drive unit described in any one of Notes 7 to 9, 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 multiple rolling bearings supporting the second rotating shaft is 0.3 mass % or more.

[0081] <Note 11> A rolling bearing is a rolling bearing that supports the rotating shaft of a vehicle drive unit. Equipped with inner ring, outer ring and rolling elements made of quenched and tempered steel, The inner ring, the outer ring and the rolling element each have a rolling surface. The hardness of at least any one of the inner ring, the outer ring, and the rolling element at the rolling contact surface is 800 Hv or more and 940 Hv or less.

[0082] <Note 12> In the rolling bearing according to Supplementary Note 11, the amount of retained austenite in the rolling contact surface layer of at least one of the inner ring and the outer ring is 5% by volume or more and 16% by volume or less.

[0083] <Note 13> In the rolling bearing according to Supplementary Note 11 or Supplementary Note 12, the dislocation density of retained austenite in the surface layer of the rolling contact surface of at least one of the inner ring and the outer ring is 3.5×10 14 m -2 Above and 1.0×10 17 m -2 the following.

[0084] <Note 14> In the rolling bearing according to any one of Supplementary Notes 11 to 13, the nitrogen concentration in the rolling contact surface layer of at least one of the inner ring and the outer ring is 0.1 mass % or more and less than 0.3 mass %.

[0085] <Note 15> A vehicle drive unit comprises: a first rotating shaft; a second rotation axis having a rotation speed lower than that of the first rotation axis; a first rolling bearing supporting the first rotating shaft; and a second rolling bearing supporting the second rotating shaft, The first rolling bearing includes a first inner ring, a first outer ring, and a first rolling element made of quenched and tempered steel. The first inner ring, the first outer ring and the first rolling element each have a first rolling surface. The second rolling bearing includes a second inner ring, a second outer ring, and a second rolling element made of quenched and tempered steel. The second inner ring, the second outer ring and the second rolling element each have a second rolling surface. The hardness of the second rolling surface is greater than the hardness of the first rolling surface. The second rolling bearing is the rolling bearing specified in any one of Supplementary Notes 11 to 14.

[0086] <Note 16> In the vehicle drive unit according to Supplementary Note 15, the retained austenite amount of the rolling contact surface layers of the first inner ring and the first outer ring is smaller than the retained austenite amount of the rolling contact surface layers of the second inner ring and the second outer ring.

[0087] <Note 17> A vehicle drive unit includes: a plurality of rotating shafts; and Multiple rolling bearings, Each of the plurality of rolling bearings has an inner ring, an outer ring, and rolling elements made of quenched and tempered steel. The inner ring, the outer ring and the rolling element each have a rolling surface. Each of the plurality of rotating shafts is supported by each of the plurality of rolling bearings. When one of the multiple rotating shafts with the slowest rotation speed is set as the first rotating shaft, and the multiple rotating shafts other than the first rotating shaft are set as the second rotating shaft, the hardness at 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 greater than 800Hv and less than 940Hv.

[0088] <Note 18> In the vehicle drive unit described in Note 17, the amount of retained austenite in the 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 multiple rolling bearings supporting the second rotating shaft is greater than 5 volume % and less than 16 volume %.

[0089] <Note 19> In the vehicle drive unit according to Supplementary Note 17 or Supplementary Note 18, in at least any 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 retained austenite in the rolling surface layer is 3.5×10 14 m -2 Above and 1.0×10 17 m -2 the following.

[0090] <Note 20> In the vehicle drive unit described in any one of Notes 17 to 19, the nitrogen concentration in the 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 multiple rolling bearings supporting the second rotating shaft is greater than 0.1 mass% and less than 0.3 mass%.

[0091] As described above, the embodiments of the present invention have been described, but various modifications may be made to the above embodiments. In addition, the scope of the present invention is not limited to the above embodiments. The scope of the present invention is represented by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0092] Explanation of symbols 100 Rolling bearing; 10 Inner ring; 10a First wide face; 10b Second wide face; 10c Inner diameter face; 10d Outer diameter face; 10da Raceway face; 20 Outer ring; 20a First wide face; 20b Second wide face; 20c Inner diameter face; 20ca Raceway face; 20d Outer diameter face; 30 Rolling element; 30a Surface; 40 Cage; 110 Motor; 111 Motor body; 112 Rotating shaft; 113 Motor housing; 114 Rolling bearing; 120 Speed ​​reducer; 121, 122, 123 Rotating shaft; 124, 125, 126, 127 Gear; 128, 129, 130 Rolling bearing; 200 Vehicle drive unit; A Center axis; S1 Preparation process; S2 Nitriding process; S3 Quenching process; S4 Cooling process; S5 Tempering process; S6 post-processing process; S7 assembly process.

Claims

1. A rolling bearing, A rolling bearing for supporting a rotating shaft of a vehicle drive unit, characterized in that: Equipped with inner ring, outer ring and rolling elements made of quenched and tempered steel, The inner ring, the outer ring and the rolling element each have a rolling surface. The hardness of at least any one of the inner ring, the outer ring, and the rolling elements at the rolling contact surface is 865 Hv or more and 1245 Hv or less.

2. The rolling bearing according to claim 1, characterized in that The amount of retained austenite in the rolling contact surface layer of at least one of the inner ring and the outer ring is 5 volume % or more and 16 volume % or less.

3. The rolling bearing according to claim 1 or 2, characterized in that: The dislocation density of retained austenite in the rolling contact surface layer of at least one of the inner ring and the outer ring is 2.5×10 14 m -2 Above and 1.0×10 17 m -2 the following.

4. The rolling bearing according to any one of claims 1 to 3, characterized in that The nitrogen concentration in the rolling contact surface layer of at least one of the inner ring and the outer ring is 0.3 mass % or more.

5. A vehicle drive unit, characterized in that: have: a first rotation axis; a second rotation axis having a rotation speed lower than that of the first rotation axis; a first rolling bearing supporting the first rotating shaft; and a second rolling bearing supporting the second rotating shaft, The first rolling bearing includes a first inner ring, a first outer ring, and a first rolling element made of quenched and tempered steel. The first inner ring, the first outer ring and the first rolling element each have a first rolling surface. The second rolling bearing includes a second inner ring, a second outer ring, and a second rolling element made of quenched and tempered steel. The second inner ring, the second outer ring and the second rolling element each have a second rolling surface. The hardness of the second rolling surface is greater than the hardness of the first rolling surface. The second rolling bearing is the rolling bearing defined in any one of claims 1 to 4 .

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

7. A vehicle drive unit, characterized in that: have: multiple axes of rotation; and Multiple rolling bearings, Each of the plurality of rolling bearings has an inner ring, an outer ring, and rolling elements made of quenched and tempered steel. The inner ring, the outer ring and the rolling element each have a rolling surface. Each of the plurality of rotating shafts is supported by each of the plurality of rolling bearings. When one of the multiple rotating shafts with the slowest rotation speed is set as the first rotating shaft, and the multiple rotating shafts other than the first rotating shaft are set as the second rotating shaft, the hardness at 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 greater than 865Hv and less than 1245Hv.

8. The vehicle drive unit according to claim 7, wherein: In at least any 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 amount of retained austenite in the rolling contact surface layer is 5 volume % or more and 16 volume % or less.

9. The vehicle drive unit according to claim 7 or 8, wherein: 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 retained austenite in the surface layer of the rolling contact surface is 2.5×10 14 m -2 Above and 1.0×10 17 m -2 the following.

10. The vehicle drive unit according to any one of claims 7 to 9, characterized in that: In at least any 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, a nitrogen concentration in a surface layer of a rolling contact surface is 0.3 mass % or more.

11. A rolling bearing, A rolling bearing for supporting a rotating shaft of a vehicle drive unit, characterized in that: Equipped with inner ring, outer ring and rolling elements made of quenched and tempered steel, The inner ring, the outer ring and the rolling element each have a rolling surface. The hardness of at least any one of the inner ring, the outer ring, and the rolling element at the rolling contact surface is 800 Hv or more and 940 Hv or less.

12. The rolling bearing according to claim 11, characterized in that The amount of retained austenite in the rolling contact surface layer of at least one of the inner ring and the outer ring is 5 volume % or more and 16 volume % or less.

13. The rolling bearing according to claim 11, characterized in that The dislocation density of retained austenite in the rolling contact surface layer of at least one of the inner ring and the outer ring is 3.5×10 14 m -2 Above and 1.0×10 17 m -2 the following.

14. The rolling bearing according to claim 11, characterized in that The nitrogen concentration in the rolling contact surface layer of at least one of the inner ring and the outer ring is 0.1 mass % or more and less than 0.3 mass %.

15. A vehicle drive unit, characterized in that: have: a first rotation axis; a second rotation axis having a rotation speed lower than that of the first rotation axis; a first rolling bearing supporting the first rotating shaft; and a second rolling bearing supporting the second rotating shaft, The first rolling bearing includes a first inner ring, a first outer ring, and a first rolling element made of quenched and tempered steel. The first inner ring, the first outer ring and the first rolling element each have a first rolling surface. The second rolling bearing includes a second inner ring, a second outer ring, and a second rolling element made of quenched and tempered steel. The second inner ring, the second outer ring and the second rolling element each have a second rolling surface. The hardness of the second rolling surface is greater than the hardness of the first rolling surface. The second rolling bearing is the rolling bearing defined in any one of claims 11 to 14 .

16. The vehicle drive unit according to claim 15, wherein: The retained austenite amount of the rolling contact surface layers of the first inner ring and the first outer ring is smaller than the retained austenite amount of the rolling contact surface layers of the second inner ring and the second outer ring.

17. A vehicle drive unit, characterized in that: have: multiple axes of rotation; and Multiple rolling bearings, Each of the plurality of rolling bearings has an inner ring, an outer ring, and rolling elements made of quenched and tempered steel. The inner ring, the outer ring and the rolling element each have a rolling surface. Each of the plurality of rotating shafts is supported by each of the plurality of rolling bearings. When one of the multiple rotating shafts with the slowest rotation speed is set as the first rotating shaft, and the multiple rotating shafts other than the first rotating shaft are set as the second rotating shaft, the hardness at 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 greater than 800Hv and less than 940Hv.

18. The vehicle drive unit according to claim 17, wherein: In at least any 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 amount of retained austenite in the rolling contact surface layer is 5 volume % or more and 16 volume % or less.

19. The vehicle drive unit according to claim 17, wherein: 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 retained austenite in the surface layer of the rolling contact surface is 3.5×10 14 m -2 Above and 1.0×10 17 m -2 the following.

20. The vehicle drive unit according to any one of claims 17 to 19, characterized in that: In at least any 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, a nitrogen concentration in a rolling contact surface layer is 0.1 mass % or more and less than 0.3 mass %.

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