Ball bearing

Abstract

To provide a ball bearing capable of suppressing fatigue breakdown of an outer ring due to repeated elastic deformation.SOLUTION: A ball bearing 1 comprises a deformable outer ring 2, a deformable inner ring 3 installed inside the outer ring 2, and a plurality of spherical rolling elements 4 provided between the outer ring 2 and the inner ring 3. At least one of an outer peripheral surface 11 and an inner peripheral surface 12 of the outer ring 2 is provided with a surface layer 5. The surface layer 5 has compressive residual stress. The compressive residual stress in the surface layer 5 has been imparted by shot-peening.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a ball bearing, and more particularly to a ball bearing used in a strain wave gear device. [Background technology]

[0002] As a reducer, a wave gear device that can obtain a high reduction ratio is known. Some wave gear devices have a wave generator with an elliptical outer circumferential surface. The wave generator has an elliptical cam and a ball bearing provided on the outer circumferential surface of the elliptical cam. The ball bearing of the wave gear device is thin-walled, and the thin outer and inner rings are deformable. In the wave gear device, the outer ring elastically deforms in the radial direction in response to the elliptical shape of the outer circumferential surface of the elliptical cam as the elliptical cam rotates, performing wave motion.

[0003] The elastic deformation caused by this wave motion generates stress in the outer ring. This stress is tensile stress in the portion deforming toward the major axis, and compressive stress in the portion deforming toward the minor axis. As such, as the elliptical cam rotates, the outer ring is repeatedly subjected to tensile and compressive stresses, which may cause fatigue failure of the outer ring (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-026834 A Summary of the Invention [Problem to be solved by the invention]

[0005] For this reason, in the ball bearings of conventional strain wave gear devices, there is a demand for an outer ring structure that will not break due to fatigue even when subjected to repeated elastic deformation.

[0006] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide a ball bearing that can suppress fatigue damage to the outer ring due to repeated elastic deformation. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the ball bearing of the present invention comprises a deformable outer ring, a deformable inner ring installed inside the outer ring, and a plurality of spherical rolling elements provided between the inner ring and the outer ring, at least one of the outer peripheral surface and the inner peripheral surface of the outer ring is provided with a surface layer, the surface layer having compressive residual stress, and the compressive residual stress of the surface layer is imparted by shot peening. Effect of the Invention

[0008] According to the ball bearing of the present invention, fatigue damage to the outer ring caused by repeated elastic deformation can be suppressed. [Brief description of the drawings]

[0009] [Figure 1] 1 is a diagram showing a cross section taken along a plane perpendicular to the axis of a ball bearing according to an embodiment of the present invention. [Diagram 2] 1 is a diagram showing a cross section of a ball bearing taken along a plane including an axis of an outer ring; [Diagram 3] FIG. 2 is a perspective view showing a cut-away portion of the outer ring. [Figure 4] FIG. 1 is a diagram showing an example of a strain wave gear device provided with ball bearings. [Diagram 5] FIG. 11 is a cross-sectional view of an outer ring provided with a surface layer according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0011] Fig. 1 is a diagram showing a cross section of a ball bearing 1 according to an embodiment of the present invention, taken along a plane perpendicular to the axis x. Fig. 2 is a diagram showing a cross section of the ball bearing 1, taken along a plane including the axis x of the outer ring 2, and Fig. 3 is a perspective view showing a cutaway portion of the outer ring 2. Note that Fig. 2 shows only one side of the cross section of the outer ring relative to the axis x. The axis x is the axis of the ball bearing 1. In the drawings, not all of the components are labeled with reference symbols, and reference symbols may be omitted as appropriate.

[0012] As shown in Figures 1 to 3, ball bearing 1 comprises a deformable outer ring 2, a deformable inner ring 3 installed inside outer ring 2, and a plurality of spherical rolling elements 4 provided between outer ring 2 and inner ring 3. At least one of outer peripheral surface 11 and inner peripheral surface 12 of outer ring 2 is provided with a surface layer 5. Surface layer 5 has compressive residual stress. The compressive residual stress of surface layer 5 is imparted by shot peening. The configuration of ball bearing 1 will be specifically described below.

[0013] The ball bearing according to the present invention is applicable to wave gearings, including wave gearings, and is used in wave gearings. FIG. 4 is a diagram showing a wave gearing 100 as an example of a wave gearing provided with a ball bearing 1. The ball bearing 1 constitutes a part of a wave generator 101 of the wave gearing 100. In the wave generator 101, an elliptical cam 102 is fitted to an inner ring 3 of the ball bearing 1. The wave generator 101 is fitted to a cup-shaped flexspline 103, and the flexspline 103 is fitted to a circular spline 104. In the wave gearing 100, the cam 102 rotates, and the inner ring 3 of the ball bearing 1 rotates together with the cam 102. As the elliptical inner ring 3 rotates, each part of the outer ring 2 deforms in the radial direction via the rolling elements 4, and at least a part of the outer ring 2 located on the major axis comes into contact with the flexspline 103, and the outer circumferential surface of the flexspline 103 performs wave motion. The teeth 103a located in the long axis direction of this wave-motion flexspline 103 mesh with the teeth 104a of the circular spline 104, and due to the difference in the number of teeth of the teeth 103a of the flexspline 103 and the number of teeth of the teeth 104a of the circular spline 104, the circular spline 104 rotates relative to the flexspline 103, and the flexspline 103 or the circular spline 104 rotates at a slower speed relative to the rotation of the cam 102.

[0014] As described above, the ball bearing 1 has the outer ring 2, the inner ring 3, and the rolling elements 4, and also has a cage 6 that holds the rolling elements 4, as shown in FIG.

[0015] The inner ring 3 has the same configuration as the inner ring of a conventionally known thin-walled ball bearing used in a strain wave gear device, and is a thin-walled inner ring, which is a cylindrical or approximately cylindrical flexible or elastic member with its central axis or approximate central axis being axis x, as shown in Fig. 1. When an elliptical cam 102 is fitted onto the inner ring 3, the inner ring 3 deforms into an elliptical cylinder or approximately elliptical cylinder with its central axis or approximate central axis being axis x, as shown in Fig. 4.

[0016] The outer ring 2 has the same configuration as the outer ring of a conventionally known thin-walled ball bearing used in a strain wave gear device, and is a thin-walled outer ring, and is a cylindrical flexible or elastic member around the axis x as shown in Figs. 1 to 3. As described above, at least one of the outer peripheral surface 11 and the inner peripheral surface 12 of the outer ring 2 is provided with a surface layer 5. The outer peripheral surface 11 is a cylindrical surface facing the outside (hereinafter also referred to as the outer peripheral side) in the radial direction (direction of the radial line r) of the outer ring 2, and the inner peripheral surface 12 is a cylindrical surface facing the inside (hereinafter also referred to as the inner peripheral side) in the radial direction of the outer ring 2. In addition, as shown in Figs. 2 and 3, the inner peripheral surface 12 of the outer ring 2 is formed with a raceway groove 13 in which the rolling elements 4 roll.

[0017] 2 and 3 show a specific example of the outer ring 2. In this specific example, surface layer 5a and surface layer 5b are formed on the outer peripheral surface 11 and inner peripheral surface 12 of the outer ring 2, respectively. As shown in FIGS. 2 and 3, compressive residual stress is imparted to the outer ring 2 from the outer peripheral surface 11 to a predetermined depth toward the inner peripheral side, and a cylindrical portion of a predetermined thickness to which this compressive residual stress is imparted forms the surface layer 5a. In this way, the surface layer 5a extends from the outer peripheral surface 11 toward the inner peripheral side, and the outer peripheral surface 11 has the surface layer 5a. Also, as shown in FIG. 2, compressive residual stress is imparted to the outer ring 2 from the inner peripheral surface 12 to a predetermined depth toward the outer peripheral side, and a cylindrical portion of a predetermined thickness to which this compressive residual stress is imparted forms the surface layer 5b. In this way, the surface layer 5b extends from the inner peripheral surface 12 toward the outer peripheral side, and the inner peripheral surface 12 has the surface layer 5b.

[0018] Specifically, for example, as shown in FIG. 2, the surface layer 5a of the outer peripheral surface 11 extends toward the inner peripheral side from the outer peripheral surface 11 to a radial position (position p1) or near position p1, and the radial thickness (thickness t1) of the surface layer 5a is uniform or approximately uniform.

[0019] Specifically, for example, as shown in Fig. 2, the surface layer 5b of the inner peripheral surface 12 spreads outward from the inner peripheral surface 12 and the actuation groove 14 to a position (position p2) or the vicinity of position p2 in the radial direction. Thus, the radial thickness (thickness t2) of the surface layer 5b is uniform or approximately uniform on the inner peripheral surface 12, and the thickness on the raceway groove 13 is smaller than the thickness on the inner peripheral surface 12. Depending on position p2, the surface layer 5b is formed on the inner peripheral side of the entire raceway groove 13, or on the inner peripheral side of a portion of the raceway groove 13. In this example, as shown in Figs. 2 and 3, the surface layer 5b is formed on the inner peripheral side near both ends of the raceway groove 13 that are connected to the inner peripheral surfaces 5b on both sides. As shown in FIG. 5, the surface layer 5b has a uniform or approximately uniform thickness from the inner circumferential surface 12 and the raceway groove 13, and the radial thickness t2 of the surface layer 5b may be uniform or approximately uniform over the entire inner circumferential surface 12 and the raceway groove 13.

[0020] The thicknesses t1 and t2 of the surface layers 5a and 5b are, for example, less than 100 μm. The thicknesses t1 and t2 of the surface layers 5a and 5b are, for example, less than 50 μm. The thicknesses t1 and t2 of the surface layers 5a and 5b are determined, for example, by a ratio to the radial distance between the outer peripheral surface 11 and the inner peripheral surface 12 (the thickness of the outer ring 2). The maximum absolute value of the compressive residual stress of the surface layers 5a and 5b is, for example, 1000 MPa or more.

[0021] As described above, the compressive residual stress in the surface layers 5a, 5b is imparted by shot peening on the outer peripheral surface 11 and the inner peripheral surface 12 of the outer ring 2. This shot peening is, for example, WPC treatment (registered trademark). This shot peening is also, for example, α treatment (registered trademark). The shot peening that imparts the compressive residual stress to the surface layers 5a, 5b may be another treatment.

[0022] In shot peening, for example, the average particle size of the particles (shot) colliding with the outer ring 2 is 149 μm to 20 μm. Also, for example, the ejection speed of the shot is 100 m / sec to 200 m / sec.

[0023] As described above, the outer ring 2 of the ball bearing 1 according to an embodiment of the present invention has surface layers 5a, 5b having compressive residual stress on the outer peripheral surface 11 and the inner peripheral surface 12, respectively. As a result, the ball bearing 1 can suppress fatigue damage to the outer ring 2 caused by repeated elastic deformation in the strain wave gear device 100. In particular, when the compressive residual stress of the surface layers 5a, 5b is imparted by WPC treatment (registered trademark) or α treatment (registered trademark), fatigue damage to the outer ring 2 caused by repeated elastic deformation in the strain wave gear device 100 can be further suppressed.

[0024] In the above-described specific example of outer ring 2, outer peripheral surface 11 and inner peripheral surface 12 have surface layer 5a and surface layer 5b, respectively. However, ball bearing 1 may be one in which outer peripheral surface 11 has surface layer 5a and inner peripheral surface 12 does not have surface layer 5b, or alternatively, ball bearing 1 may be one in which inner peripheral surface 12 has surface layer 5b and outer peripheral surface 11 does not have surface layer 5a.

[0025] Although the present invention has been described above through the above embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It is clear to those skilled in the art that various modifications or improvements can be made to the above embodiments. It is clear from the claims that such modifications or improvements can also be included in the technical scope of the present invention.

[0026] The above-described embodiments are intended to facilitate understanding of the present invention, and are not intended to limit the present invention. Moreover, the above-described embodiments do not limit the use of the present invention, and the present invention may include anything as its use. The components of the above-described embodiments, as well as their arrangement, materials, conditions, shapes, sizes, etc., are not limited to those exemplified, and can be changed as appropriate. For example, the present invention includes differences that occur in the implementation of manufacturing tolerances, etc. Furthermore, the components shown in different embodiments can be partially replaced or combined with each other within a range that is not technically contradictory. Furthermore, each configuration can be appropriately and selectively combined so as to achieve at least a part of the above-described problems and effects. [Explanation of symbols]

[0027] 1 ball bearing, 2 outer ring, 3 inner ring, 4 rolling element, 5 surface layer, 6 cage, 11 outer peripheral surface, 12 inner peripheral surface, 13 raceway groove, 100... wave gear device, 101... wave generator, 102... cam, 103... flexspline, 103a... teeth, 104... circular spline, 104a... teeth, p1, p2 position, r radius line, t1, t2 thickness, x axis line

Claims

1. A deformable outer ring; a deformable inner ring disposed inside the outer ring; a plurality of spherical rolling elements provided between the inner ring and the outer ring, at least one of the outer peripheral surface and the inner peripheral surface of the outer ring is provided with a surface layer, the surface layer has a compressive residual stress, The compressive residual stress in the surface layer is imparted by shot peening. ball bearings.

2. The shot peening is a WPC treatment (registered trademark); 2. A ball bearing according to claim 1.

3. The shot peening is α treatment (registered trademark); 2. A ball bearing according to claim 1.

4. The thickness of the surface layer is less than 100 μm.

2. A ball bearing according to claim 1.

5. The thickness of the surface layer is less than 50 μm.

5. A ball bearing according to claim 4.

6. The maximum absolute value of the compressive residual stress of the surface layer is 1000 MPa or more; 2. A ball bearing according to claim 1.

7. Used in strain wave gear devices, 2. A ball bearing according to claim 1.

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