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EP-4737752-A1 - ROLLING BEARING AND DRIVE UNIT FOR VEHICLE

EP4737752A1EP 4737752 A1EP4737752 A1EP 4737752A1EP-4737752-A1

Abstract

A rolling bearing (100) supports a rotation shaft of a vehicle drive unit. The rolling bearing includes an inner ring (10), an outer ring (20), and a rolling element (30) which are made of steel subjected to quenching and tempering. Each of the inner ring, the outer ring, and the rolling element has a rolling surface (10da, 20ca, 30a). A dislocation density of retained austenite at a rolling surface superficial layer of at least one of the inner ring and the outer ring is 2.5×10 14 m -2 or more and 1.0×10 17 m -2 or less.

Inventors

  • MATSUDA, Ryuutarou
  • KAWAI, TAKASHI

Assignees

  • NTN Corporation

Dates

Publication Date
20260506
Application Date
20240531

Claims (20)

  1. A rolling bearing that supports a rotation shaft of a vehicle drive unit, the rolling bearing comprising: an inner ring, an outer ring, and a rolling element which are made of steel subjected to quenching and tempering, wherein each of the inner ring, the outer ring, and the rolling element has a rolling surface, and a dislocation density of retained austenite at a rolling surface superficial layer of at least one of the inner ring and the outer ring is 2.5×10 14 m -2 or more and 1.0×10 17 m -2 or less.
  2. The rolling bearing according to claim 1, wherein a hardness at the rolling surface of at least one of the inner ring, the outer ring, and the rolling element is 800 Hv or more and 1245 Hv or less.
  3. The rolling bearing according to claim 1, wherein a nitrogen concentration at the rolling surface superficial layer of the at least one of the inner ring and the outer ring is 0.25 mass percent or more.
  4. The rolling bearing according to claim 1, wherein the dislocation density of retained austenite at the rolling surface superficial layer of the at least one of the inner ring and the outer ring is 3.5×10 14 m -2 or more and 1.0×10 17 m -2 or less.
  5. The rolling bearing according to claim 4, wherein a hardness at the rolling surface of at least one of the inner ring, the outer ring, and the rolling element is 760 Hv or more and 940 Hv or less.
  6. The rolling bearing according to claim 4, wherein a nitrogen concentration at the rolling surface superficial layer of the at least one of the inner ring and the outer ring is 0.03 mass percent or more and 0.25 mass percent or less.
  7. The rolling bearing according to any one of claims 1 to 6, wherein an amount of retained austenite at the rolling surface superficial layer of the at least one of the inner ring and the outer ring is 5 volume percent or more and 30 volume percent or less.
  8. The rolling bearing according to claim 1, wherein the dislocation density of retained austenite at the rolling surface superficial layer of the at least one of the inner ring and the outer ring is 5.0×10 14 m -2 or more and 1.0×10 17 m -2 or less.
  9. The rolling bearing according to claim 8, wherein an amount of retained austenite at the rolling surface superficial layer of the at least one of the inner ring and the outer ring is 2 volume percent or more and 12 volume percent or less.
  10. The rolling bearing according to claim 8, wherein a hardness at the rolling surface of at least one of the inner ring, the outer ring, and the rolling element is 760 Hv or more and 900 Hv or less.
  11. The rolling bearing according to any one of claims 8 to 10, wherein a nitrogen concentration at the rolling surface superficial layer of the at least one of the inner ring and the outer ring is less than 0.01 mass percent.
  12. A vehicle drive unit comprising: a plurality of rotation shafts; and a plurality of rolling bearings, wherein each of the plurality of rolling bearings has an inner ring, an outer ring, and a rolling element which are made of steel subjected to quenching and tempering, each of the inner ring, the outer ring, and the rolling element has a rolling surface, the plurality of rotation shafts are respectively supported by the plurality of rolling bearings, and when one of the plurality of rotation shafts having a lowest rotation speed is defined as a first rotation shaft, and the plurality of rotation shafts other than the first rotation shaft are defined as second rotation shafts, a dislocation density of retained austenite at a rolling surface superficial 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 that support the second rotation shafts is 2.5×10 14 m -2 or more and 1.0×10 17 m -2 or less.
  13. The vehicle drive unit according to claim 12, wherein a hardness at the rolling surface of the at least one of the outer ring, the inner ring, and the rolling element of the at least one of the plurality of rolling bearings that support the second rotation shafts is 800 Hv or more and 1245 Hv or less.
  14. The vehicle drive unit according to claim 12, wherein a nitrogen concentration at the rolling surface superficial layer of the at least one of the outer ring, the inner ring, and the rolling element of the at least one of the plurality of rolling bearings that support the second rotation shafts is 0.25 mass percent or more.
  15. The vehicle drive unit according to claim 12, wherein the dislocation density of retained austenite at the rolling surface superficial layer of the at least one of the outer ring, the inner ring, and the rolling element of the at least one of the plurality of rolling bearings that support the second rotation shafts is 3.5×10 14 m -2 or more and 1.0×10 17 m -2 or less.
  16. The vehicle drive unit according to claim 15, wherein a hardness at the rolling surface of the at least one of the outer ring, the inner ring, and the rolling element of the at least one of the plurality of rolling bearings that support the second rotation shafts is 760 Hv or more and 940 Hv or less.
  17. The vehicle drive unit according to claim 15, wherein a nitrogen concentration at the rolling surface superficial layer of the at least one of the outer ring, the inner ring, and the rolling element of the at least one of the plurality of rolling bearings that support the second rotation shafts is 0.03 mass percent or more and 0.25 mass percent or less.
  18. The vehicle drive unit according to any one of claims 12 to 17, wherein an amount of retained austenite at the rolling surface superficial layer of the at least one of the outer ring, the inner ring, and the rolling element of the at least one of the plurality of rolling bearings that support the second rotation shafts is 5 volume percent or more and 30 volume percent or less.
  19. The vehicle drive unit according to claim 12, wherein the dislocation density of retained austenite at the rolling surface superficial layer of the at least one of the outer ring, the inner ring, and the rolling element of the at least one of the plurality of rolling bearings that support the second rotation shafts is 5.0×10 14 m -2 or more and 1.0×10 17 m -2 or less.
  20. The vehicle drive unit according to claim 19, wherein an amount of retained austenite at the rolling surface superficial layer of the at least one of the outer ring, the inner ring, and the rolling element of the at least one of the plurality of rolling bearings that support the second rotation shafts is 2 volume percent or more and 12 volume percent or less.

Description

TECHNICAL FIELD The present invention relates to a rolling bearing and a vehicle drive unit. BACKGROUND ART Japanese Patent No. 6023422 (PTL 1) describes a mechanical component. The mechanical component described in PTL 1 is a bearing ring or a rolling element constituting a rolling bearing. The mechanical component described in PTL 1 is formed by introducing nitrogen into a surface, performing quenching, and thereafter performing tempering at a high temperature. CITATION LIST PATENT LITERATURE PTL 1: Japanese Patent No. 6023422 SUMMARY OF INVENTION TECHNICAL PROBLEM Vehicle drive units used in electrically powered vehicles such as electric vehicles (EVs) and hybrid electric vehicles (HEVs) will be required to have a higher efficiency in the future in consideration of environmental issues such as realization of carbon neutrality. A vehicle drive unit has a plurality of rotation shafts, and each of the plurality of rotation shafts is supported by a rolling bearing. In order to achieve a higher efficiency, measures such as reducing the viscosity of a lubricating oil, reducing the amount of the oil, and reducing the number of oil pumps are taken, which may result in poor lubrication between a bearing ring and a rolling element. As the vehicle drive unit is downsized in order to achieve a higher efficiency, the bearing that supports the rotation shaft has a smaller size. Further, in order to achieve a higher efficiency, an output of a drive source (such as a motor) of the vehicle drive unit is increased, and a rotation speed is increased. As a result, a load on the rolling bearing further increases. In the mechanical component described in PTL 1, tempering at a high temperature is performed, and a hardness in the very vicinity of the surface decreases. Accordingly, when a rolling bearing constituted by the mechanical component described in PTL 1 is used under conditions as described above, a crack may be formed in a rolling surface (a raceway surface, a rolling contact surface) and the crack may develop. The present invention has been made in view of the problems of the conventional technique as described above. More specifically, the present invention provides a rolling bearing capable of suppressing formation and development of a crack in a rolling surface even in the case of poor lubrication. SOLUTION TO PROBLEM A rolling bearing of the present invention is a rolling bearing that supports a rotation shaft of a vehicle drive unit. The rolling bearing includes an inner ring, an outer ring, and a rolling element which are made of steel subjected to quenching and tempering. Each of the inner ring, the outer ring, and the rolling element has a rolling surface. A dislocation density of retained austenite at a rolling surface superficial layer of at least one of the inner ring and the outer ring is 2.5×1014 m-2 or more and 1.0×1017 m-2 or less. ADVANTAGEOUS EFFECTS OF INVENTION According to the rolling bearing of the present invention, it is possible to suppress formation and development of a crack in the rolling surface even in the case of poor lubrication. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a cross sectional view of a rolling bearing 100.Fig. 2 is a cross sectional view of rolling bearing 100 according to a modification.Fig. 3 is a diagram of a process for manufacturing rolling bearing 100.Fig. 4 is a cross sectional view of a vehicle drive unit 200.Fig. 5 is a cross sectional view of vehicle drive unit 200 according to a modification. DESCRIPTION OF EMBODIMENTS Details of an embodiment of the present invention will be described with reference to the drawings. In the drawings below, identical or corresponding parts will be designated by the same reference numerals, and redundant description will not be repeated. A rolling bearing according to the embodiment is referred to as a rolling bearing 100, and a vehicle drive unit according to the embodiment is referred to as a vehicle drive unit 200. (Configuration of Rolling Bearing 100) Hereinafter, a configuration of rolling bearing 100 will be described. Fig. 1 is a cross sectional view of rolling bearing 100. As shown in Fig. 1, rolling bearing 100 is a deep groove ball bearing, for example. Rolling bearing 100 has an inner ring 10, an outer ring 20, a plurality of rolling elements 30, and a cage 40. A central axis of inner ring 10 is defined as a central axis A. A direction of central axis A is defined as an axial direction. A direction which passes through central axis A and is orthogonal to central axis A is defined as a radial direction. A direction along a circumference centered on central axis A when viewed along the axial direction is defined as a circumferential direction. Inner ring 10 has an annular shape extending in the circumferential direction. Inner ring 10 has a first width surface 10a, a second width surface 10b, an inner diameter surface 10c, and an outer diameter surface 10d. First width surface 10a and second width surface 10b are end surfac