Rolling bearings

Abstract

A rolling bearing 1 is equipped with an outer race 1A, an inner race 1B and a plurality of rolling elements. The outer race 1A includes a first outer race 10 and a second outer race 20. The first inner race 1B includes a first inner race 30 and a second inner race 40. The grain flow 111 of the steel constituting the first outer race 10 extends along a first rolling surface 511 in a cross-section which includes a center axis R, the grain flow 211 of the steel constituting the second outer race 20 extends along a second rolling surface 512 in said cross-section, the grain flow 311 of the steel constituting the first inner race 30 extends along a third rolling surface 513 in said cross-section, and the grain flow 411 of the steel constituting the second inner race 40 extends along a fourth rolling surface 514 in said cross-section.

Description

Technical Field

[0001] The present invention relates to a rolling bearing. This application claims priority based on Japanese Application No. 2019-177931 filed on September 27, 2019, and incorporates all the descriptions described in the above Japanese application.

Background Art

[0002] A rolling bearing in which rolling elements are arranged on a single raceway and has two sets of rolling surfaces facing each other is known (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above rolling bearing, it is preferable to have sufficient durability. Therefore, one of the objectives is to provide a rolling bearing with improved durability.

Means for Solving the Problems

[0005] A rolling bearing according to this disclosure comprises a steel outer ring, a steel inner ring disposed on the inner circumference side of the outer ring, and a plurality of rolling elements arranged to be rotatable on the inner surface of the outer ring and the outer surface of the inner ring. The outer ring includes a first outer ring having an annular first racing surface that constitutes the inner surface of the outer ring, and a second outer ring having a common central axis with the first racing surface and an annular second racing surface that constitutes the inner surface of the outer ring, and being arranged alongside the first outer ring in the first axial direction which is the direction in which the central axis of the first racing surface extends, and fixed to the first outer ring. The inner ring includes a first inner ring having a central axis common to the first racing surface, facing the second racing surface, and having an annular third racing surface that constitutes the outer circumferential surface of the inner ring, and a second inner ring having a central axis common to the first racing surface, facing the first racing surface, and having an annular fourth racing surface that constitutes the outer circumferential surface of the inner ring, with a line segment connecting it to the first racing surface in a cross section including the central axis of the first racing surface intersecting a line segment connecting the second racing surface and the third racing surface, and being positioned alongside the first inner ring in the first axial direction and fixed to the first inner ring. In a cross section including the central axis of the first racing surface, the forging lines of the steel constituting the first outer ring extend along the first racing surface, the forging lines of the steel constituting the second outer ring extend along the second racing surface, the forging lines of the steel constituting the first inner ring extend along the third racing surface, and the forging lines of the steel constituting the second inner ring extend along the fourth racing surface. [Effects of the Invention]

[0006] According to the rolling bearing described above, durability can be improved. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic plan view showing the structure of a rolling bearing in Embodiment 1. [Figure 2] Figure 2 is a schematic perspective view showing the structure of a rolling bearing in Embodiment 1. [Figure 3] Figure 3 is a schematic perspective view showing the structure of a rolling bearing with the first outer ring and first inner ring removed. [Figure 4] Figure 4 is a schematic cross-sectional view showing the structure of a rolling bearing in Embodiment 1. [Figure 5] Figure 5 is a schematic cross-sectional view showing the structure of a rolling bearing in Embodiment 1. [Figure 6] Figure 6 is a schematic diagram showing the flow lines in the outer and inner rings. [Figure 7] Figure 7 is a schematic cross-sectional view showing the structure of a rolling bearing in Embodiment 1. [Figure 8] Figure 8 is a schematic cross-sectional view showing the structure of a rolling bearing in Embodiment 1. [Figure 9] Figure 9 is a schematic cross-sectional view showing the usage state of the rolling bearing in Embodiment 1. [Figure 10] Figure 10 is a schematic perspective view showing a first modified example of the rolling bearing in Embodiment 1. [Figure 11] Figure 11 is a schematic perspective view showing a second modified example of the rolling bearing in Embodiment 1. [Figure 12] Figure 12 is a schematic cross-sectional view showing the structure of a rolling bearing in Embodiment 2. [Figure 13] Figure 13 is a schematic cross-sectional view showing the structure of a rolling bearing in Embodiment 3. [Figure 14] Figure 14 is a schematic cross-sectional view showing the structure of a rolling bearing in Embodiment 4. [Figure 15] Figure 15 is a schematic perspective view showing the structure of a rolling bearing in Embodiment 5. [Figure 16] Figure 16 is a schematic perspective view showing the structure of the rolling bearing in Embodiment 5. [Figure 17] Figure 17 is a schematic cross-sectional view showing the structure of a rolling bearing in Embodiment 5. [Figure 18] Figure 18 is a schematic cross-sectional enlargement view showing the structure of the rolling bearing in Embodiment 5. [Figure 19] Figure 19 is a schematic, enlarged cross-sectional perspective view showing the structure of the rolling bearing in Embodiment 5. [Figure 20] Figure 20 is a schematic perspective view showing a modified example of the rolling bearing in Embodiment 5. [Figure 21]FIG. 21 is a schematic perspective view showing a modified example of the rolling bearing in Embodiment 5.

Embodiments for Carrying Out the Invention

[0008] [Summary of Embodiment] First, embodiments of the present disclosure will be listed and described. The rolling bearing of the present disclosure includes a steel outer ring, a steel inner ring disposed on the inner peripheral side of the outer ring, and a plurality of rolling elements that are rotatably disposed on the inner peripheral surface of the outer ring and the outer peripheral surface of the inner ring. The outer ring includes a first outer ring having an annular first rolling surface that constitutes the inner peripheral surface of the outer ring, and a second outer ring having an annular second rolling surface that constitutes the inner peripheral surface of the outer ring, having a common central axis with the first rolling surface, arranged side by side with the first outer ring in the first axial direction which is the direction in which the central axis of the first rolling surface extends, and fixed to the first outer ring. The inner ring includes a first inner ring having an annular third rolling surface that has a common central axis with the first rolling surface, faces the second rolling surface, and constitutes the outer peripheral surface of the inner ring, and a second inner ring having an annular fourth rolling surface that has a common central axis with the first rolling surface, faces the first rolling surface, and in a cross-section including the central axis of the first rolling surface, a line segment connecting the first rolling surface intersects a line segment connecting the second rolling surface and the third rolling surface, and constitutes the outer peripheral surface of the inner ring, arranged side by side with the first inner ring in the first axial direction and fixed to the first inner ring. In a cross-section including the central axis of the first rolling surface, the forging streamline of the steel constituting the first outer ring extends along the first rolling surface, the forging streamline of the steel constituting the second outer ring extends along the second rolling surface, the forging streamline of the steel constituting the first inner ring extends along the third rolling surface, and the forging streamline of the steel constituting the second inner ring extends along the fourth rolling surface.

[0009] [[ID=1】4]]The inventors of the present invention studied measures to improve the durability of the rolling bearing. In the rolling bearing disclosed in Patent Document 1, grinding of the rolling surface is performed to improve the dimensional accuracy of the rolling surface. When such grinding of the rolling surface is performed, the ends of the forging streamlines of the steel may be exposed on the rolling surface. In such a case, although the dimensional accuracy of the rolling surface is improved, it has been found that the durability of the inner ring and the outer ring decreases because the rolling element contacts the ends of the forging streamlines of the steel.

[0010] In the rolling bearing of the present disclosure, in a cross section including the central axis of the first rolling surface, the forged streamline of the steel constituting the first outer ring, the second outer ring, the first inner ring, and the second inner ring extends along the first rolling surface, the second rolling surface, the third rolling surface, and the fourth rolling surface, respectively. By extending the forged streamline of the steel along the first rolling surface, the second rolling surface, the third rolling surface, and the fourth rolling surface, it is possible to suppress the contact of the rolling elements with the ends of the forged streamline of the steel. As a result, the durability of the inner and outer rings can be improved. Thus, according to the rolling bearing of the present disclosure, the durability can be improved.

[0011] In the above rolling bearing, the rolling elements may include the first roller and the second roller. The first roller and the second roller may be alternately arranged in the circumferential direction. The central axis of the first roller and the central axis of the second roller may intersect. The first roller may be arranged to be rollable on the first rolling surface and the fourth rolling surface. The second roller may be arranged to be rollable on the second rolling surface and the third rolling surface. By including the first roller and the second roller as described above, a rolling bearing suitable for supporting loads applied in a plurality of directions can be obtained.

[0012] In the above rolling bearing, the rolling elements may be balls. The rolling elements may be arranged to be rollable on the first rolling surface, the second rolling surface, the third rolling surface, and the fourth rolling surface. By doing so, the rotational resistance of the rolling bearing can be reduced.

[0013] In the rolling bearing described above, the first outer ring may include a first part having a disc-like annular shape, a second part having a cylindrical shape, extending from the inner edge of the first part such that its inner diameter decreases as it moves away from the first part in the first axial direction, and having an annular inner surface, and a third part having a cylindrical shape, connected to the end of the second part opposite to the first part in the first axial direction, and extending along the first axial direction. The second outer ring may include a fourth part having a disc-like annular shape, fixed to the first part such that their main surfaces are in contact, a fifth part having a cylindrical shape, extending from the inner edge of the fourth part in the first axial direction opposite to the second part, with its inner diameter decreasing as it moves away from the fourth part, and having an annular inner surface, and a sixth part having a cylindrical shape, connected to the end of the fifth part opposite to the fourth part in the first axial direction, and extending along the first axial direction opposite to the third part. The first inner ring may include a seventh portion having a disc-ring shape, an eighth portion having a cylindrical shape, extending from the outer edge of the seventh portion in the first axial direction such that its outer diameter increases as it moves away from the seventh portion, and having an annular outer surface, and a ninth portion having a cylindrical shape, connected to the end of the eighth portion opposite to the seventh portion in the first axial direction, and extending along the first axial direction. The second inner ring may include a tenth portion having a disc-ring shape, fixed to the seventh portion so that their main surfaces are in contact, an eleventh portion having a cylindrical shape, extending from the outer edge of the tenth portion in the first axial direction opposite to the eighth portion, and extending in the same direction as it moves away from the tenth portion, with an annular outer surface, and a twelfth portion having a cylindrical shape, connected to the end of the eleventh portion opposite to the tenth portion in the first axial direction, and extending along the first axial direction opposite to the ninth portion. The inner surface of the second portion may include a first running surface. The inner surface of the fifth part may include a second turning surface. The outer surface of the eighth part may include a third turning surface. The outer surface of the eleventh part may include a fourth turning surface.

[0014] The first outer ring, second outer ring, first inner ring, and second inner ring, having this configuration, can be easily manufactured, for example, by press-forming steel plates. Therefore, the manufacturing cost of rolling bearings can be reduced.

[0015] In the above rolling bearing, the effective contact length L1 where the outer surface of the first roller contacts the first racing surface and the first racing surface, and the effective contact length L2 where the outer surface of the first roller contacts the fourth racing surface, in a cross-section including the central axis of the first roller, may be 0.5 to 0.9 times the axial length of the first roller. In a cross-section including the central axis of the second roller, the effective contact length L3 where the outer surface of the second roller contacts the second racing surface and the effective contact length L4 where the outer surface of the second roller contacts the third racing surface, may be 0.5 to 0.9 times the axial length of the second roller. By having the effective contact lengths L1 and L2 within the above ranges, the frictional force between the first roller and the first and fourth racing surfaces can be reduced. By having the effective contact lengths L3 and L4 within the above ranges, the frictional force between the second roller and the second and third racing surfaces can be reduced. Therefore, the increase in rotational torque due to the first and second rollers can be suppressed.

[0016] In the rolling bearing described above, in a cross-section including the central axis of the first racing surface, the main surface on the side of the first part that contacts the fourth part and the first racing surface may be connected by a curved first region. The main surface on the side of the fourth part that contacts the first part and the second racing surface may be connected by a curved second region. An annular space may be formed surrounded by the first region, the second region and the rolling elements.

[0017] The annular space described above can be filled with lubricant. Therefore, the risk of oil film breakdown between the first roller and the first racing surface, and between the second roller and the second racing surface, can be reduced.

[0018] In the rolling bearing described above, in a cross-section including the central axis of the first racing surface, the first racing surface and the inner circumferential surface of the third portion may be connected by a curved third region. The third racing surface and the inner circumferential surface of the ninth portion may be connected by a curved fourth region. By including such a third region in the first outer ring, it is possible to reduce the concentration of stress caused by contact between the third region and the rolling elements. Similarly, by including such a fourth region in the first inner ring, it is possible to reduce the concentration of stress caused by contact between the fourth region and the rolling elements.

[0019] In the rolling bearing described above, the thickness of the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, eleventh, and twelfth sections in the cross-section including the central axis of the first racing surface may be less than 0.5 times the diameter of the rolling element. This makes it possible to lighten the first outer ring, second outer ring, first inner ring, and second inner ring.

[0020] In the rolling bearing described above, the inner surface of the third portion and the outer surface of the ninth portion may be arranged to face each other. The inner surface of the sixth portion and the outer surface of the twelfth portion may be arranged to face each other. In a cross-section including the central axis of the first rolling surface, the radial distance between the third portion and the ninth portion may be smaller than the thickness of the third portion, and the radial distance between the sixth portion and the twelfth portion may be smaller than the thickness of the sixth portion. By doing so, it is possible to reduce the entry of foreign matter into the space surrounded by the first outer ring, the second outer ring, the first inner ring and the second inner ring through the gap formed between the third portion and the ninth portion and the gap formed between the sixth portion and the twelfth portion.

[0021] In the rolling bearing described above, in the cross-section including the central axis of the first racing surface, the lengths of the third and ninth portions in the first axial direction are greater than 1.5 times the thickness of the third portion, and the lengths of the sixth and twelfth portions in the first axial direction may be greater than 1.5 times the thickness of the sixth portion. By doing so, when attaching and fixing the first outer ring, second outer ring, first inner ring, and second inner ring of the rolling bearing to other members, the outer circumferential surface of the third portion, the outer circumferential surface of the sixth portion, the inner circumferential surface of the ninth portion, and the inner circumferential surface of the twelfth portion serve as reference surfaces, making attachment easier.

[0022] In the rolling bearing described above, the first outer ring is positioned at the end of the third portion opposite to the second portion in the first axial direction, and may further include a labyrinth portion that is bent radially inward of the third portion and faces the ninth portion at a distance smaller than the radial distance between the third portion and the ninth portion. Including such a labyrinth portion further reduces the entry of foreign matter into the space surrounded by the first outer ring, the second outer ring, the first inner ring, and the second inner ring through the gap formed between the third portion and the ninth portion.

[0023] In the rolling bearing described above, the first inner ring is positioned at the end of the ninth portion opposite to the eighth portion in the first axial direction, and may further include a labyrinth portion that is bent radially outward from the ninth portion and faces the third portion at a distance smaller than the radial distance between the third portion and the ninth portion. Including such a labyrinth portion further reduces the entry of foreign matter into the space surrounded by the first outer ring, the second outer ring, the first inner ring and the second inner ring through the gap formed between the third portion and the ninth portion.

[0024] In the above rolling bearing, the first outer ring includes a first portion having a disc-like annular shape, and the inner surface of the first portion may include a first racing surface. The second outer ring includes a fourth portion fixed to the first portion so that its main surfaces are in contact with each other, and the inner surface of the fourth portion may include a second racing surface. The first inner ring includes a seventh portion having a disc-like annular shape, and the outer surface of the seventh portion may include a third racing surface. The second inner ring includes a tenth portion having a disc-like annular shape and fixed to the seventh portion so that its main surfaces are in contact with each other, and the outer surface of the tenth portion may include a fourth racing surface. By including racing surfaces on the inner surfaces of the disc-like annular portions of the first and second outer rings, and racing surfaces on the outer surfaces of the disc-like annular portions of the first and second inner rings, a thin rolling bearing can be obtained.

[0025] In the above-described rolling bearing, the surface of the first outer ring and the surface of the first inner ring may be formed flat without any protruding portions in the first axial direction. The surface of the second outer ring and the surface of the second inner ring may also be formed flat without any protruding portions in the first axial direction. By making the surface of the rolling bearing flat, an even thinner rolling bearing can be obtained. In addition, because there are no protruding portions, processing to avoid interference with protruding portions is not required in the mating part to which the rolling bearing is attached. For this reason, it is very convenient when attaching the rolling bearing.

[0026] [Specific examples of embodiments] Next, an example of a specific embodiment of the rolling bearing of this disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are given the same reference numerals and their descriptions will not be repeated.

[0027] (Embodiment 1) Figure 1 is a schematic plan view showing the structure of a rolling bearing in one embodiment of the present disclosure. The Z-axis direction in Figure 1 is along the first axial direction, which is the direction in which the central axis R of the rolling bearing extends. Referring to Figures 1 to 3, the rolling bearing 1 in Embodiment 1 comprises an outer ring 1A, an inner ring 1B, and a plurality of rollers 1C as rolling elements. The outer ring 1A and the inner ring 1B are made of steel. The inner ring 1B is arranged on the inner circumference side of the outer ring 1A. In this embodiment, the outer ring 1A and the inner ring 1B are made of steel plates processed into a predetermined shape. In this embodiment, the steel constituting the outer ring 1A and the inner ring 1B is, for example, SCM415 as specified in the JIS standard.

[0028] Figure 4 is a cross-sectional view of the rolling bearing 1 when cut along AA in Figure 1. Figure 4 is a cross-sectional view including the central axis of the first roller, which will be described later. Figure 5 is a cross-sectional view showing an enlarged view of the area around the first roller in Figure 4. Referring to Figures 2 and 4, the outer ring 1A includes an annular first outer ring 10 and an annular second outer ring 20. In this embodiment, the first outer ring 10 and the second outer ring 20 have the same shape. Referring to Figures 4 and 5, the first outer ring 10 includes a first part 15, a second part 16, and a third part 17. In this embodiment, the first part 15, the second part 16, and the third part 17 have the same thickness T1. The first part 15 has a disc-like annular shape. The first part 15 has a central axis common to the central axis R of the rolling bearing 1. The second part 16 has a cylindrical shape. The external shape of the second part 16 is frustoconical. The second part 16 extends from the inner edge of the first part 15 such that its inner diameter decreases as it moves away from the first part 15 in the Z-axis direction. The second part 16 has an annular inner surface 16A. The inner surface 16A has a common central axis with the central axis R of the rolling bearing 1. The third part 17 has a cylindrical shape. The third part 17 has a common central axis with the central axis R of the rolling bearing 1. The third part 17 is connected to the end of the second part 16 opposite to the first part 15 in the Z-axis direction and extends along the Z-axis direction.

[0029] The inner circumferential surface 16A includes an annular first surface 161 as a first region, an annular second surface 162, and an annular third surface 163 as a third region. In this embodiment, the first surface 161, the second surface 162, and the third surface 163 share a common central axis with the central axis R of the rolling bearing 1. The first surface 161 connects the surface 15A of the first portion 15 that contacts the fourth portion 25 with the second surface 162. In this embodiment, in a cross-section including the central axis R, the first surface 161 has a curved shape. In a cross-section including the central axis R, the second surface 162 has a flat shape. The third surface 163 connects the second surface 162 with the inner circumferential surface 17A of the third portion 17. In this embodiment, in a cross-section including the central axis R, the third surface 163 has a curved shape. In this embodiment, the length T2 of the third portion 17 in the Z-axis direction in the cross-section including the central axis R is greater than 1.5 times the thickness T1 of the third portion 17. Preferably, the length T2 of the third portion 17 in the Z-axis direction is 5 times or less the thickness T1 of the third portion 17. In this embodiment, the thickness T1 of the third portion 17 is, for example, about 1 mm.

[0030] Referring to Figures 2 and 4, the first part 15 has multiple mounting holes 11 that penetrate in the thickness direction (Z-axis direction) and are formed at equal intervals in the circumferential direction (six in this embodiment). The first part 15 has projections 13 and through holes 12 formed in the circumferential direction between adjacent mounting holes 11. Multiple projections 13 that protrude from the surface 15A of the first part 15 in the thickness direction (Z-axis direction) are formed at equal intervals in the circumferential direction (six in this embodiment). Multiple through holes 12 that penetrate in the thickness direction (Z-axis direction) are formed at equal intervals in the circumferential direction (six in this embodiment).

[0031] Referring to Figures 4 and 5, the second outer ring 20 is positioned alongside the first outer ring 10 in the Z-axis direction and is fixed to the first outer ring 10. The second outer ring 20 includes a fourth portion 25, a fifth portion 26, and a sixth portion 27. In this embodiment, the fourth portion 25, the fifth portion 26, and the sixth portion 27 have the same thickness T3. In this embodiment, thickness T3 and thickness T1 coincide. The fourth portion 25 has a disc-like annular shape. One surface 25A of the fourth portion 25 is in contact with the surface 15A of the first portion 15. The fourth portion 25 has a common central axis R with the central axis of the rolling bearing 1. The fifth portion 26 has a cylindrical shape. The outer shape of the fifth portion 26 is frustoconical. The fifth portion 26 extends from the inner edge of the fourth portion 25 such that its inner diameter decreases as it moves away from the fourth portion 25 in the Z-axis direction. The fifth part 26 extends in the Z-axis direction opposite to the second part 16. The fifth part 26 has an annular inner surface 26A. The inner surface 26A has a common central axis with the central axis R of the rolling bearing 1. The sixth part 27 has a cylindrical shape. The sixth part 27 has a common central axis with the central axis R of the rolling bearing 1. The sixth part 27 is connected to the end of the fifth part 26 in the Z-axis direction opposite to the fourth part 25 and extends in the Z-axis direction opposite to the third part 17.

[0032] The inner circumferential surface 26A includes an annular fourth surface 261 as a second region, an annular fifth surface 262, and an annular sixth surface 263. The fourth surface 261, the fifth surface 262, and the sixth surface 263 share a common central axis with the central axis R of the rolling bearing 1. The fourth surface 261 connects the surface 25A of the fourth portion 25 and the fifth surface 262. In a cross-section including the central axis R, the fourth surface 261 has a curved shape. In a cross-section including the central axis R, the fifth surface 262 has a flat shape. The sixth surface 263 connects the fifth surface 262 and the inner circumferential surface 27A of the sixth portion 27. In a cross-section including the central axis R, the sixth surface 263 has a curved shape. In this embodiment, the length T4 of the sixth portion 27 in the Z-axis direction in the cross-section including the central axis R is greater than 1.5 times the thickness T3 of the sixth portion 27. Preferably, the length T4 of the sixth portion 27 in the Z-axis direction is 5 times or less the thickness T3 of the sixth portion 27. In this embodiment, the thickness T3 of the sixth portion 27 is, for example, about 1 mm.

[0033] Referring to Figures 3 and 4, the fourth portion 25 has multiple mounting holes 21 that penetrate in the thickness direction (Z-axis direction) and are formed at equal intervals in the circumferential direction (six in this embodiment). The fourth portion 25 has through holes 23 and protrusions 22 formed in the circumferential direction between adjacent mounting holes 21. Multiple through holes 23 that penetrate in the thickness direction (Z-axis direction) are formed at equal intervals in the circumferential direction (six in this embodiment). The through holes 23 have a shape corresponding to the protrusions 13. Multiple protrusions 22 that project from the surface 25A of the fourth portion 25 in the thickness direction (Z-axis direction) are formed at equal intervals in the circumferential direction (six in this embodiment). The protrusions 22 have a shape corresponding to the through holes 12.

[0034] Referring to Figure 2, the inner ring 1B includes an annular first inner ring 30 and an annular second inner ring 40. In this embodiment, the first inner ring 30 and the second inner ring 40 have the same shape. Referring to Figures 4 and 5, the first inner ring 30 includes a seventh portion 35, an eighth portion 36, and a ninth portion 37. In this embodiment, the seventh portion 35, the eighth portion 36, and the ninth portion 37 have the same thickness T5. In this embodiment, thickness T5 and thickness T1 are the same. The seventh portion 35 has a disc-like annular shape. The seventh portion 35 has a central axis common to the central axis R of the rolling bearing 1. The eighth portion 36 has a cylindrical shape. The outer shape of the eighth portion 36 is frustoconical. The eighth portion 36 extends from the outer edge of the seventh portion 35 such that its outer diameter increases as it moves away from the seventh portion 35 in the Z-axis direction. The eighth part 36 has an annular outer surface 36A. The outer surface 36A has a common central axis with the central axis R of the rolling bearing 1. The ninth part 37 has a cylindrical shape. The ninth part 37 has a common central axis with the central axis R of the rolling bearing 1. The ninth part 37 is connected to the end of the eighth part 36 opposite to the seventh part 35 in the Z-axis direction and extends along the Z-axis direction.

[0035] The outer circumferential surface 36A includes an annular seventh surface 361, an annular eighth surface 362, and an annular ninth surface 363 as a fourth region. The seventh surface 361, the eighth surface 362, and the ninth surface 363 share a common central axis R with the central axis of the rolling bearing 1. The seventh surface 361 connects the surface 35A of the seventh portion 35 that contacts the tenth portion 45 with the eighth surface 362. In a cross-section including the central axis R, the seventh surface 361 has a curved shape. In a cross-section including the central axis R, the eighth surface 362 has a flat shape. The eighth surface 362 faces the fifth surface 262. In this embodiment, the eighth surface 362 and the fifth surface 262 are arranged parallel to each other in a cross-section including the central axis R. The ninth surface 363 connects the eighth surface 362 and the outer circumferential surface 37A of the ninth portion 37. In a cross-section including the central axis R, the ninth surface 363 has a curved shape. In this embodiment, the length T6 of the ninth portion 37 in the Z-axis direction in the cross-section including the central axis R is greater than 1.5 times the thickness T5 of the ninth portion 37. Preferably, the length T6 of the ninth portion 37 in the Z-axis direction is 5 times or less the thickness T5 of the ninth portion 37. In this embodiment, the thickness T5 of the ninth portion 37 is, for example, about 1 mm. In this embodiment, the radial distance S1 between the third portion 17 and the ninth portion 37 in the cross-section including the central axis R is smaller than the thickness T1 of the third portion 17 and the thickness T5 of the ninth portion 37.

[0036] Referring to Figures 2 and 4, the seventh portion 35 has multiple mounting holes 31 that penetrate in the thickness direction (Z-axis direction) and are formed at equal intervals in the circumferential direction (six in this embodiment). The seventh portion 35 has projections 33 and through holes 32 formed in the circumferential direction between adjacent mounting holes 31. Multiple projections 33 that protrude in the thickness direction (Z-axis direction) are formed at equal intervals in the circumferential direction (six in this embodiment) from the surface 35A of the seventh portion 35. Multiple through holes 32 that penetrate in the thickness direction (Z-axis direction) are formed at equal intervals in the circumferential direction (six in this embodiment).

[0037] Referring to Figures 4 and 5, the second inner ring 40 is positioned alongside the first inner ring 30 in the Z-axis direction and is fixed to the first inner ring 30. The second inner ring 40 includes a tenth portion 45, an eleventh portion 46, and a twelfth portion 47. In this embodiment, the tenth portion 45, the eleventh portion 46, and the twelfth portion 47 have the same thickness T7. In this embodiment, thickness T7 and thickness T1 coincide. The tenth portion 45 has a disc-like annular shape. The surface 35A of the seventh portion and one surface 45A of the tenth portion 45 are in contact. The tenth portion 45 has a common central axis with the central axis R of the rolling bearing 1. The eleventh portion 46 has a cylindrical shape. The outer shape of the eleventh portion 46 is frustoconical. The 11th portion 46 extends from the outer edge of the 10th portion 45 such that its outer diameter increases as it moves away from the 10th portion 45 in the Z-axis direction. The 11th portion 46 extends in the Z-axis direction opposite to the 8th portion 36. The 11th portion 46 has an annular outer surface 46A. The outer surface 46A has a common central axis with the central axis R of the rolling bearing 1. The 12th portion 47 has a cylindrical shape. The 12th portion 47 has a common central axis with the central axis R of the rolling bearing 1. The 12th portion 47 is connected to the end of the 11th portion 46 in the Z-axis direction opposite to the 10th portion 45 and extends in the Z-axis direction opposite to the 9th portion 37.

[0038] The outer circumferential surface 46A includes an annular tenth surface 461, an annular eleventh surface 462, and an annular twelfth surface 463. The tenth surface 461, the eleventh surface 462, and the twelfth surface 463 share a common central axis with the central axis R of the rolling bearing 1. The tenth surface 461 connects the surface 45A on the side of the tenth portion 45 that contacts the seventh portion 35 with the eleventh surface 462. In the cross-section including the central axis R, the tenth surface 461 has a curved shape. In the cross-section including the central axis R, the eleventh surface 462 has a flat shape. The eleventh surface 462 faces the second surface 162. In this embodiment, the eleventh surface 462 and the second surface 162 are arranged parallel to each other in the cross-section including the central axis R. In a cross-section including the central axis R, the line segment V1 connecting the second surface 162 and the eleventh surface 462 intersects (is perpendicular to) the line segment V2 connecting the fifth surface 262 and the eighth surface 362. The twelfth surface 463 connects the eleventh surface 462 and the outer circumferential surface 47A of the twelfth portion 47. In a cross-section including the central axis R, the twelfth surface 463 has a curved shape. In this embodiment, the length T8 of the twelfth portion 47 in the Z-axis direction in a cross-section including the central axis R is greater than 1.5 times the thickness T7 of the twelfth portion 47. Preferably, the length T8 of the twelfth portion 47 in the Z-axis direction is 5 times or less the thickness T7 of the twelfth portion 47. In this embodiment, the thickness T1 of the twelfth portion 47 is, for example, about 1 mm. In this embodiment, the radial distance S2 between the sixth portion 27 and the twelfth portion 47 in a cross-section including the central axis R is smaller than the thickness T3 of the sixth portion 27 and the thickness T7 of the twelfth portion 47.

[0039] Referring to Figures 3 and 4, the tenth portion 45 has multiple mounting holes 41 that penetrate in the thickness direction (Z-axis direction) and are formed at equal intervals in the circumferential direction. The tenth portion 45 has through holes 43 and protrusions 42 that are arranged circumferentially between adjacent mounting holes 41 in the circumferential direction. Multiple through holes 43 that penetrate in the thickness direction (Z-axis direction) are formed at equal intervals in the circumferential direction (six in this embodiment). The through holes 43 have a shape corresponding to the protrusions 33. Multiple protrusions 42 that project from the surface 45A of the tenth portion 45 in the thickness direction (Z-axis direction) are formed at equal intervals in the circumferential direction (six in this embodiment). The protrusions 42 have a shape corresponding to the through holes 32.

[0040] Figure 6 shows the forging lines in a cross-section when the rolling bearing 1 is cut at AA in Figure 1. Referring to Figure 6, in the first outer ring 10, forging lines 111 of the steel constituting the first outer ring 10 extend along the surface 15A of the first part 15, the inner circumferential surface 16A of the second part 16, and the inner circumferential surface 17A of the third part 17. Forging lines 111 also extend along the first surface 161, the second surface 162, and the third surface 163 of the inner circumferential surface 16A. In this embodiment, the forging lines 111 extend parallel to the second surface 162. In the second outer ring 20, forging lines 211 of the steel constituting the second outer ring 20 extend along the surface 25A of the fourth part 25, the inner circumferential surface 26A of the fifth part 26, and the inner circumferential surface 27A of the sixth part 27. The forging lines 211 extend along the fourth surface 261, the fifth surface 262, and the sixth surface 263 of the inner circumferential surface 26A. In this embodiment, the forging lines 211 extend parallel to the fifth surface 262. In the first inner ring 30, the forging lines 311 of the steel constituting the first inner ring 30 extend along the surface 35A of the seventh portion 35, the outer circumferential surface 36A of the eighth portion 36, and the outer circumferential surface 37A of the ninth portion 37. The forging lines 311 extend along the seventh surface 361, the eighth surface 362, and the ninth surface 363 of the outer circumferential surface 36A. In this embodiment, the forging lines 311 extend parallel to the eighth surface 362. In the second inner ring 40, forging lines 411 of the steel constituting the second inner ring 40 extend along the surface 45A of the tenth portion 45, the outer circumferential surface 46A of the eleventh portion 46, and the outer circumferential surface 47A of the twelfth portion 47. Forging lines 411 also extend along the tenth surface 461, the eleventh surface 462, and the twelfth surface 463 of the outer circumferential surface 46A. In this embodiment, the forging lines 411 extend parallel to the eleventh surface 462.

[0041] Referring to Figure 3, each roller 1C includes a plurality of first rollers 51 and a plurality of second rollers 52. In this embodiment, the first rollers 51 and second rollers 52 are made of steel. In this embodiment, the first rollers 51 and second rollers 52 are, for example, SUJ2 as specified in the JIS standard. In this embodiment, each roller 1C includes 27 first rollers 51 and 27 second rollers 52. The first rollers 51 and second rollers 52 have a cylindrical shape. The first rollers 51 and second rollers 52 are arranged alternately in the circumferential direction. Referring to Figure 5, each first roller 51 is arranged to roll while in contact with the second surface 162 and the eleventh surface 462 at its outer circumferential surface 51A. The second surface 162 constitutes the first rolling surface 511. The eleventh surface 462 constitutes the fourth rolling surface 514. The first and fourth rolling surfaces 511 and 514 share a common central axis with the central axis R of the rolling bearing 1. One end face 51B of the first roller 51 in the axial direction faces the eighth surface 362. The other end face 51C of the first roller 51 in the axial direction contacts the fifth surface 262. In this embodiment, an annular space M1 is formed surrounded by the first surface 161, the fourth surface 261, and the first roller 51.

[0042] Figure 7 is a cross-sectional view of the rolling bearing 1 when cut at BB in Figure 1. Figure 7 is a cross-section including the central axis of the second roller 52, which will be described later. Figure 8 is an enlarged cross-sectional view showing the area around the second roller in Figure 7. Referring to Figures 7 and 8, the second roller 52 is arranged to roll while in contact with the fifth surface 262 and the eighth surface 362 at its outer circumferential surface 52A. The fifth surface 262 constitutes the second racing surface 512. The eighth surface 362 constitutes the third racing surface 513. The second racing surface 512 and the third racing surface 513 share a common central axis with the central axis R of the rolling bearing 1. One end face 52B of the second roller 52 in the axial direction is in contact with the second surface 162. The other end face 52C of the second roller 52 in the axial direction is opposite to the eleventh surface 462. In this embodiment, an annular space M2 is formed surrounded by the first surface 161, the fourth surface 261, and the second roller 52 (see Figure 8). Referring to Figures 4 and 7, the central axis P of the first roller 51 and the central axis Q of the second roller 52 intersect (are perpendicular). Here, the state in which the central axis P of the first roller 51 and the central axis Q of the second roller 52 intersect means that when the rolling bearing 1 rotates, the central axis P of the first roller 51 and the central axis Q of the second roller 52 intersect (are perpendicular) when the centers of gravity of the first roller 51 and the second roller 52 pass through a predetermined point.

[0043] Referring to Figures 5 and 8, in this embodiment, in a cross-section including the central axis R, the thickness T1 of the first part 15, the second part 16, and the third part 17 is less than 0.5 times the diameter U1 of the first roller 51 and the diameter R1 of the second roller. The thickness T3 of the fourth part 25, the fifth part 26, and the sixth part 27 is less than 0.5 times the diameter U1 of the first roller 51 and the diameter R1 of the second roller. The thickness T5 of the seventh part 35, the eighth part 36, and the ninth part 37 is less than 0.5 times the diameter U1 of the first roller 51 and the diameter R1 of the second roller. The thickness T7 of the tenth part 45, the eleventh part 46, and the twelfth part 47 is less than 0.5 times the diameter U1 of the first roller 51 and the diameter R1 of the second roller. In a cross-section including the central axis R, the effective contact length L1 where the outer circumferential surface 51A of the first roller 51 contacts the second surface 162, and the effective contact length L2 where the outer circumferential surface 51A contacts the eleventh surface 462, are between 0.5 and 0.9 times the axial length U2 of the first roller 51. In a cross-section including the central axis R, the effective contact length L3 where the outer circumferential surface 52A of the second roller 52 contacts the fifth surface 262, and the effective contact length L4 where the outer circumferential surface 52A contacts the eighth surface 362, are between 0.5 and 0.9 times the axial length R2 of the second roller 52.

[0044] Next, the manufacturing method of the rolling bearing 1 in this embodiment will be described. First, a first steel plate, a second steel plate, a third steel plate, and a fourth steel plate, each having a flat plate shape, are prepared. Next, the first steel plate, the second steel plate, the third steel plate, and the fourth steel plate are each subjected to press working. In this way, the first outer ring 10, the second outer ring 20, the first inner ring 30, and the second inner ring 40, having the shapes shown in Figures 2 and 3, are formed. Next, referring to Figure 4, known heat treatments are performed on the inner circumferential surface 16A of the second part 16, the inner circumferential surface 26A of the fifth part 26, the inner circumferential surface 36A of the eighth part 36, and the inner circumferential surface 46A of the eleventh part 46. More specifically, carburizing, carbonitriding, and quenching and tempering are performed. By performing such treatments, the hardness of the inner circumferential surfaces 16A, 26A, 36A, and 46A can be improved. In this embodiment, grinding is not performed on the inner circumferential surfaces 16A, 26A, 36A, and 46A. Next, the second inner ring 40 is attached to the first inner ring 30 to form the inner ring 1B. More specifically, the protrusion 33 is fitted into the through hole 43, and the protrusion 42 is fitted into the through hole 32. The inner ring 1B and the second outer ring 20, formed in this manner, are attached to the jig. At this time, the outer circumferential surface 47A of the 12th portion 47 and the inner circumferential surface 27A of the 6th portion 27 are attached to face each other (see Figure 5). Next, the first roller 51 and the second roller 52 are arranged alternately in the space surrounded by the inner ring 1B and the second outer ring 20. Next, the first outer ring 10 is attached to the second outer ring 20, forming the outer ring 1A. More specifically, the projection 13 is fitted into the through hole 23, and the projection 22 is fitted into the through hole 12.

[0045] Next, an example of how to use the rolling bearing 1 in this embodiment will be described. Referring to Figure 9, the first outer ring 10 and the second outer ring 20 are fixed to an annular first member 71. The first member 71 has a plurality of screw holes 71A formed at equal intervals in the circumferential direction, surrounded by a wall surface having a helical screw groove. The screw holes 71A have a shape corresponding to the mounting holes 11 and 21. The positions in which the screw holes 71A are formed coincide with the positions in which the mounting holes 11 and 21 are formed, and fixing bolts 73 are screwed in. The first inner ring 30 and the second inner ring 40 are fixed to an annular second member 72. The second member 72 has a plurality of screw holes 72A formed at equal intervals in the circumferential direction, surrounded by a wall surface having a helical screw groove. The screw holes 72A have a shape corresponding to the mounting holes 31 and 41. The positions in which the screw holes 72A are formed coincide with the positions in which the mounting holes 31 and 41 are formed, and fixing bolts 74 are screwed in. With the rolling bearing 1 installed in this manner, the second member 72 is supported by the first member 71 so that it can rotate in the circumferential direction.

[0046] In this embodiment of the rolling bearing 1, the forging lines of the steel constituting the first outer ring 10, the second outer ring 20, the first inner ring 30, and the second inner ring 40 extend along the first, second, third, and fourth rolling surfaces 511, 512, 513, and 514, respectively, in a cross-section including the central axis R. That is, the forging lines on the first, second, third, and fourth rolling surfaces 511, 512, 513, and 514 are formed continuously without breaks. As a result, contact between the first roller 51 and the second roller 52 and the ends of the forging lines of the steel can be suppressed. Therefore, the durability of the inner ring 1B and the outer ring 1A can be improved. Thus, the rolling bearing 1 in this embodiment has improved durability.

[0047] In the above embodiment, the forging lines 111, 211, 311, and 411 of the steel are formed continuously along the third surface 163, the sixth surface 263, the ninth surface 363, and the twelfth surface 463. By adopting this configuration, it is possible to suppress the reduction in rigidity of the first outer ring 10, the second outer ring 20, the first inner ring 30, and the second inner ring 40 when attaching them to other members. Furthermore, the forging lines 111, 211, 311, and 411 of the steel are formed continuously along the first surface 161, the fourth surface 261, the seventh surface 361, and the tenth surface 461. By adopting this configuration, the bending strength of the first outer ring 10, second outer ring 20, first inner ring 30, and second inner ring 40 can be improved when the first rolling surface 511, second rolling surface 512, third rolling surface 513, and fourth rolling surface 514 are loaded by the first roller 51 and second roller 52.

[0048] In the above embodiment, the first outer ring 10 includes a first portion 15, a second portion 16, and a third portion 17. The second outer ring 20 includes a fourth portion 25, a fifth portion 26, and a sixth portion 27. The first inner ring 30 includes a seventh portion 35, an eighth portion 36, and a ninth portion 37. The second inner ring 40 includes a tenth portion 45, an eleventh portion 46, and a twelfth portion 47. The inner circumferential surface 16A of the second portion 16 includes a first turning surface 511. The inner circumferential surface 26A of the fifth portion 26 includes a second turning surface 512. The inner circumferential surface 36A of the eighth portion 36 includes a third turning surface 513. The inner circumferential surface 46A of the eleventh portion 46 includes a fourth turning surface 514. The first outer ring 10 and the second outer ring 20, having this configuration, can be easily formed, for example, by press forming. Therefore, the manufacturing cost of the rolling bearing 1 can be reduced.

[0049] In the above embodiment, an annular space M1 is formed surrounded by the first surface 161, the fourth surface 261 and the first roller 51, and an annular space M2 is formed surrounded by the first surface 161, the fourth surface 261 and the second roller 52. Lubricant can be held in the annular spaces M1 and M2 as described above. Therefore, the risk of oil film breakdown between the first roller 51 and the first racing surface 511 and between the second roller 52 and the second racing surface 512 can be reduced.

[0050] In the above embodiment, in the cross-section including the central axis R, the thickness T1 of the first part 15, the second part 16, and the third part 17 is less than 0.5 times the diameter U1 of the first roller 51 and the diameter R1 of the second roller. The thickness T3 of the fourth part 25, the fifth part 26, and the sixth part 27 is less than 0.5 times the diameter U1 of the first roller 51 and the diameter R1 of the second roller. The thickness T5 of the seventh part 35, the eighth part 36, and the ninth part 37 is less than 0.5 times the diameter U1 of the first roller 51 and the diameter R1 of the second roller. The thickness T7 of the tenth part 45, the eleventh part 46, and the twelfth part 47 is less than 0.5 times the diameter U1 of the first roller 51 and the diameter R1 of the second roller. By adopting such a configuration, the first outer ring 10, the second outer ring 20, the first inner ring 30, and the second inner ring 40 can be made lighter.

[0051] In the above embodiment, in a cross-section including the central axis R, the radial distance S1 between the third portion 17 and the ninth portion 37 is smaller than the thickness T1 of the third portion 17 and the thickness T5 of the ninth portion 37. In a cross-section including the central axis R, the radial distance S2 between the sixth portion 27 and the twelfth portion 47 is smaller than the thickness T3 of the sixth portion 27 and the thickness T7 of the twelfth portion 47. By setting the distances S1 and S2 within the above range, it is possible to reduce the entry of foreign matter into the space surrounded by the first outer ring 10, the second outer ring 20, the first inner ring 30, and the second inner ring 40 through the gap formed between the third portion 17 and the ninth portion 37 and the gap formed between the sixth portion 27 and the twelfth portion 47.

[0052] In the above embodiment, in the cross-section including the central axis R, the length T2 of the third portion 17 in the Z-axis direction is greater than 1.5 times the thickness T1 of the third portion 17. The length T4 of the sixth portion 27 in the Z-axis direction is greater than 1.5 times the thickness T3 of the sixth portion 27. The length T6 of the ninth portion 37 in the Z-axis direction is greater than 1.5 times the thickness T5 of the ninth portion 37. The length T8 of the twelfth portion 47 in the Z-axis direction is greater than 1.5 times the thickness T7 of the twelfth portion. By adopting such a configuration, when attaching and fixing the first outer ring 10, the second outer ring 20, the first inner ring 30, and the second inner ring 40 to other members, the outer circumferential surface 17B of the third portion 17, the outer circumferential surface 27B of the sixth portion 27, the inner circumferential surface 37B of the ninth portion 37, and the inner circumferential surface 47B of the twelfth portion 47 serve as reference surfaces, making attachment easier.

[0053] In the above embodiment, in the cross-section including the central axis R, the third surface 163 and the sixth surface 263 have a curved shape and a pseudo-crowning shape. By adopting such a configuration, it is possible to reduce the so-called edge load, which is the concentration of stress (contact stress at the end of the raceway) caused by the contact between the third surface 163 and the first roller 51. Similarly, it is possible to reduce the so-called edge load, which is the concentration of stress (contact stress at the end of the raceway) caused by the contact between the sixth surface 263 and the second roller 52. As a result, the life of the rolling bearing 1 can be extended.

[0054] In the above embodiment, in a cross-section including the central axis R, the effective contact length L1 where the outer circumferential surface 52B of the first roller 51 contacts the second surface 162, and the effective contact length L2 where the outer circumferential surface 51B of the first roller 51 contacts the eleventh surface 462, are 0.5 to 0.9 times the axial length U2 of the first roller 51. The effective contact length L3 where the outer circumferential surface 52B of the second roller 52 contacts the fifth surface 262, and the effective contact length L4 where the outer circumferential surface 52B of the second roller 52 contacts the eighth surface 362, are 0.5 to 0.9 times the axial length R2 of the second roller 52. By having the effective contact lengths L1 and L2 within the above ranges, the frictional force between the first roller 51 and the first and fourth rolling surfaces 511 and 514 can be reduced. By having effective contact lengths L3 and L4 within the above range, the frictional force between the second roller 52 and the second and third rolling surfaces 512 and 513 can be reduced. Therefore, the increase in rotational torque due to the first and second rollers 51 and 52 can be suppressed.

[0055] In the above embodiment, the case in which steel first rollers 51 and second rollers 52 are used as rolling elements has been described, but the invention is not limited to this, and the first rollers 51 and second rollers 52 made of ceramic (for example, alumina or silicon nitride) or resin may also be used. By using such rollers, the weight of the rolling bearing 1 can be reduced. In addition, in the above embodiment, the case in which the outer ring 1A is fixed and the inner ring 1B is rotated has been described, but the invention is not limited to this, and a configuration in which the inner ring 1B is fixed and the outer ring 1A is rotated may also be adopted.

[0056] (Variation 1) Next, a first modified example of the rolling bearing 1 in Embodiment 1 will be described. Figure 10 is a perspective view corresponding to the state in which the first outer ring 10 and the first inner ring 30 of the rolling bearing 1 in Figure 2 have been removed. Referring to Figure 10, in this modified example, in addition to the structure in Embodiment 1, a separator 53 is arranged between the first roller 51 and the second roller 52 in the circumferential direction. By arranging the separator 53 in this way, the first roller 51 and the second roller 52 can be kept at a predetermined distance.

[0057] (Modification 2) Figure 11 is a perspective view corresponding to the state in which the first outer ring 10 and the first inner ring 30 of the rolling bearing 1 in Figure 2 have been removed. Referring to Figure 11, in this modified example, in addition to the structure in Embodiment 1 described above, a cage 54 is arranged to hold a plurality of first rollers 51 and a plurality of second rollers 52 at predetermined intervals. The cage 54 in this modified example has an annular shape. The cage 54 has a plurality of through holes 54A formed at equal intervals in the circumferential direction, each having a shape corresponding to the first rollers 51 and the second rollers 52. The plurality of first rollers 51 and the plurality of second rollers 52 are each held in the through holes 54A.

[0058] (Embodiment 2) Next, Embodiment 2 of the rolling bearing 1 of this disclosure will be described. The rolling bearing 1 in Embodiment 2 has basically the same structure as the rolling bearing 1 of Embodiment 1 and provides the same effects. However, Embodiment 2 differs from Embodiment 1 in that the first outer ring 10 and the second outer ring 20 include a labyrinth section. The differences from Embodiment 1 will be mainly described below.

[0059] Referring to Figure 12, the first outer ring 10 in this embodiment further includes a first labyrinth portion 18. The first labyrinth portion 18 is connected to the end of the third portion 17 opposite to the second portion 16 in the Z-axis direction and is arranged to bend radially inward of the third portion 17. The first labyrinth portion 18 has a disc shape. One surface 18A of the first labyrinth portion 18 in the Z-axis direction and the end surface 37C of the ninth portion 37 opposite to the eighth portion 36 in the Z-axis direction are positioned to face each other with a small gap between them. The distance S3 in the Z-axis direction between the first labyrinth portion 18 and the ninth portion 37 in a cross-section including the central axis R is smaller than the radial distance S1 (see Figure 5) between the third portion 17 and the ninth portion 37. In this embodiment, the distance S3 is, for example, about 0.2 mm.

[0060] The second outer ring 20 further includes a second labyrinth section 28 and a bent section 29. The second labyrinth section 28 is connected to the end of the sixth section 27 opposite to the fifth section 26 in the Z-axis direction and is arranged to bend radially inward of the sixth section 27. The second labyrinth section 28 has a disc-like shape. One face 28A of the second labyrinth section 28 in the Z-axis direction and the end face 47B of the twelfth section 47 opposite to the eleventh section 46 in the Z-axis direction are positioned to face each other with a small gap between them. The distance S4 in the Z-axis direction between the second labyrinth section 28 and the twelfth section 47 in a cross section including the central axis R is smaller than the radial distance S2 (see Figure 5) between the sixth section 27 and the twelfth section 47. In this embodiment, the distance S4 is, for example, about 0.2 mm.

[0061] The second outer ring 20 includes a bent portion 29. The bent portion 29 has an annular shape. The bent portion 29 is a region where the outer circumference of the fourth portion 25 is bent in the Z-axis direction on the opposite side from the fifth portion 26. By adopting this configuration, the assembly of the rolling bearing 1 is made easier.

[0062] The rolling bearing 1 of the second embodiment described above can also improve durability in the same way as the first embodiment.

[0063] In the above embodiment, the first outer ring 10 includes a first labyrinth portion 18. The second outer ring 20 includes a second labyrinth portion 28. By including the first labyrinth portion 18 and the second labyrinth portion 28 in this way, it is possible to further reduce the entry of foreign matter into the space surrounded by the first outer ring 10, the second outer ring 20, the first inner ring 30, and the second inner ring 40 through the gap formed between the third portion 17 and the ninth portion 37 and the gap formed between the sixth portion 27 and the twelfth portion 47.

[0064] (Embodiment 3) Next, Embodiment 3 of the rolling bearing 1 of this disclosure will be described. The rolling bearing 1 in Embodiment 3 has basically the same structure as the rolling bearing 1 in Embodiment 2 and provides the same effects. However, Embodiment 3 differs from Embodiment 2 in that the first inner ring 30 and the second inner ring 40 include a labyrinth section. The differences from Embodiment 2 will be mainly described below.

[0065] Referring to Figure 13, the first inner ring 30 in this embodiment includes a first labyrinth portion 38. The first labyrinth portion 38 is connected to the end of the ninth portion 37 opposite to the eighth portion 36 in the Z-axis direction and is arranged to bend radially outward from the ninth portion 37. The first labyrinth portion 38 has a disc shape. One surface 38A of the first labyrinth portion 38 in the Z-axis direction and the end surface 17C of the third portion 17 opposite to the second portion 16 in the Z-axis direction are positioned to face each other with a small gap between them. The distance S5 in the Z-axis direction between the first labyrinth portion 38 and the third portion 17 in a cross-section including the central axis R is smaller than the radial distance S1 (see Figure 5) between the third portion 17 and the ninth portion 37. In this embodiment, the distance S5 is, for example, about 0.2 mm.

[0066] The second inner ring 40 includes a second labyrinth section 28. The second labyrinth section 28 is connected to the end of the 12th section 47 opposite to the 11th section 46 in the Z-axis direction and is positioned to bend radially outward from the 12th section 47. The second labyrinth section 28 has a disc-like shape. One surface 48A of the second labyrinth section 28 in the Z-axis direction and the end surface 27B of the 6th section 27 opposite to the 5th section 26 in the Z-axis direction are positioned to face each other with a small gap between them. The distance S6 in the Z-axis direction between the second labyrinth section 28 and the 6th section 27 in a cross-section including the central axis R is smaller than the radial distance S2 (see Figure 5) between the 6th section 27 and the 12th section 47. In this embodiment, the distance S6 is, for example, about 0.2 mm.

[0067] The rolling bearing 1 of the second embodiment described above can also improve durability in the same way as the first embodiment.

[0068] In the above embodiment, the first inner ring 30 includes a first labyrinth portion 38. The second inner ring 40 includes a second labyrinth portion 48. By including the first labyrinth portion 38 and the second labyrinth portion 48 in this way, it is possible to further reduce the entry of foreign matter into the space surrounded by the first outer ring 10, the second outer ring 20, the first inner ring 30, and the second inner ring 40 through the gap formed between the third portion 17 and the ninth portion 37 and the gap formed between the sixth portion 27 and the twelfth portion 47.

[0069] (Embodiment 4) Next, Embodiment 4 of the rolling bearing 1 of this disclosure will be described. The rolling bearing 1 in Embodiment 4 has basically the same structure as the rolling bearing 1 of Embodiment 1 and provides the same effects. However, Embodiment 4 differs from Embodiment 1 in that it uses balls as rolling elements. The differences from Embodiment 1 will be mainly described below.

[0070] Referring to Figure 14, the inner circumferential surface 16A of the second portion 16 in the first outer ring 10 includes a first surface 161, a second surface 162, and a third surface 163. In a cross-section including the central axis R, the second surface 162 has an arc shape with a larger radius of curvature than the surface of the ball 55. In a cross-section including the central axis R, the outer circumferential surface 16B of the second portion 16 has an arc shape. The inner circumferential surface 26A of the fifth portion 26 in the second outer ring 20 includes a fourth surface 261, a fifth surface 262, and a sixth surface 263. In a cross-section including the central axis R, the fifth surface 262 has an arc shape with a larger radius of curvature than the surface of the ball 55. In a cross-section including the central axis R, the outer circumferential surface 26B of the fifth portion 26 has an arc shape. The inner circumferential surface 36A of the eighth portion 36 of the first inner ring 30 includes the seventh surface 361, the eighth surface 362, and the ninth surface 363. In a cross-section including the central axis R, the eighth surface 362 has an arc shape with a larger radius of curvature than the surface of the ball 55. In a cross-section including the central axis R, the inner circumferential surface 36B of the eighth portion 36 has an arc shape. The inner circumferential surface 46A of the eleventh portion 46 of the second inner ring 40 includes the tenth surface 461, the eleventh surface 462, and the twelfth surface 463. In a cross-section including the central axis R, the eleventh surface 462 has an arc shape with a larger radius of curvature than the surface of the ball 55. In a cross-section including the central axis R, the inner circumferential surface 46B of the eleventh portion 46 has an arc shape. The balls 55, acting as rolling elements, are arranged to roll while in contact with the second surface 162, the fifth surface 262, the eighth surface 362, and the eleventh surface 462 on their outer circumferential surface 55A. In addition, the four rolling surfaces may be formed to have a Gothic arch shape in the cross-section including the rotating shaft G. By employing balls 55 as rolling elements, the rotational resistance of the rolling bearing 1 can be reduced.

[0071] In the above embodiment 4, by using balls 55 as rolling elements, the rotational resistance of the rolling bearing 1 can be reduced.

[0072] (Embodiment 5) Next, Embodiment 5 of the rolling bearing 1 of this disclosure will be described. The rolling bearing 1 in Embodiment 5 has basically the same structure as the rolling bearing 1 of Embodiment 1 and provides the same effects. However, Embodiment 5 differs from Embodiment 1 in that the outer ring and inner ring do not have portions that protrude in the direction along the central axis R, and the outer shape of the rolling bearing is formed to be flat. The differences from Embodiment 1 will be mainly described below.

[0073] Referring to Figure 15, the outer ring 1A of the rolling bearing 1 is composed of a first outer ring 10 and a second outer ring 20. The inner ring 1B is composed of a first inner ring 30 and a second inner ring 40. Figure 16 shows the rolling bearing 1 from Figure 15 with the first outer ring 10 and the first inner ring 30 removed. Referring to Figure 16, a plurality of balls 55, which are rolling elements, are inserted between the second outer ring 20 and the second inner ring 40. As shown in Figure 15, the surfaces of the first outer ring 10 and the first inner ring 30 are flat and do not have any protruding portions that project in the direction of the central axis R. In addition to the mounting hole 11, through hole 12, and protrusion 13 described, the first outer ring 10 has two small through holes 150. The small through holes 150 are holes that penetrate in the thickness direction of the first outer ring 10. The small through-hole 150 is formed at a position corresponding to the small through-hole 250 of the second outer ring 20. The hole formed by the communication between the small through-holes 150 and 250 penetrates the rolling bearing 1 in the thickness direction. The small through-holes 150 and 250 can be used for positioning when mounting the rolling bearing 1 to a mating part. That is, by inserting a pin (not shown) into the two small through-holes 150 and 250 and fixing the pin at a predetermined position on the mating part, the rolling bearing 1 can be positioned relative to the mating part. Similarly, in addition to the mounting hole 31, through-hole 32, and projection 33 described, the first inner ring 30 has two small through-holes 350 formed therein. The small through-holes 350 are holes that penetrate the first inner ring 30 in the thickness direction. The small through-holes 350 are formed at a position corresponding to the small through-hole 450 of the second inner ring 40. The hole formed by the interconnected small through-holes 350 and 450 penetrates the rolling bearing 1 in the thickness direction. The small through-holes 350 and 450, like the small through-holes 150 and 250, can be used for positioning when attaching the rolling bearing 1 to a mating part.

[0074] Figure 17 is a cross-sectional view of the rolling bearing 1 according to Embodiment 5. The first outer ring 10 and the second outer ring 20 are fixed together by the through hole 12 of the first outer ring 10 and the projection 22 of the second outer ring 20 fitting together. One of the main surfaces of the first outer ring 10, surface 15A, and one of the main surfaces of the second outer ring 20, surface 25A, are in contact and fixed together. Although not shown in Figure 17, the first inner ring 30 and the second inner ring 40 are similarly fixed together by the through hole 32 of the first inner ring 30 and the projection 42 of the second inner ring 40 fitting together. One of the main surfaces of the first inner ring 30, surface 35A, and one of the main surfaces of the second outer ring 40, surface 45A, are in contact and fixed together. Surface 15B of the first outer ring 10 and surface 35B of the first inner ring are flat and do not have projections in the direction of the central axis R. The surface 25B of the second outer ring 20 and the surface 45B of the second inner ring 40 are flat and do not have any protrusions in the direction of the central axis R.

[0075] Referring to Figures 15, 16, and 17, the first outer ring 10 includes a first annular disc portion 15, the inner surface of which includes a first turning surface 511 on which the ball 55 rolls. The second outer ring 20 includes a fourth annular disc portion 25, the inner surface of which includes a second turning surface 512 on which the ball 55 rolls. The first inner ring 30 includes a seventh annular disc portion 35, the outer surface of which includes a third turning surface 513 on which the ball 55 rolls. The fourth inner ring 40 includes a tenth annular disc portion 45, the outer surface of which includes a fourth turning surface 514 on which the ball 55 rolls.

[0076] Figure 18 is a partially enlarged view of Figure 17, schematically showing the forging lines of the outer and inner rings. Referring to Figure 18, in the first outer ring 10, forging lines 111 of the steel constituting the first outer ring 10 extend along the surfaces 15A, 15B of the first section 15 and the first rolling surface 511. Similarly, in the second outer ring 20, forging lines 211 of the steel constituting the second outer ring 20 extend along the surfaces 25A, 25B of the fourth section 25 and the second rolling surface 512. In the first inner ring 30, forging lines 311 of the steel constituting the first inner ring 30 extend along the surfaces 35A, 35B of the seventh section 35 and the third rolling surface 513. In the second inner ring 40, forging lines 411 of the steel constituting the second inner ring 40 extend along the surfaces 45A and 45B of the tenth portion 45 and the fourth turning surface 514. Such a configuration can be created, for example, by manufacturing the shape of the outer ring or inner ring by press working, and then manufacturing the turning surface by known plastic working, such as coining.

[0077] Referring to Figures 17 and 18, in the cross-section of the rolling bearing 1 including the central axis R, the spacing of the grain lines near the rolling surfaces 511, 512, 513, and 514 is narrower than the spacing of the grain lines in the rest of the outer and inner rings (the main parts of the outer and inner rings). In other words, the spacing of the grain lines in the steel constituting the first outer ring 10, second outer ring 20, first inner ring 30, and second inner ring 40 at the locations of the rolling surfaces 511, 512, 513, and 514 is narrower than in the rest of the structure. This configuration suggests that the size of the crystal grains near the rolling surfaces 511, 512, 513, and 514 (the parts where the grain lines are closely spaced) is smaller than in the rest of the structure. Figure 19 is an enlarged cross-sectional perspective view of the rolling bearing 1 with the first inner ring 30 and a portion of the ball 55 removed, schematically showing the grain lines. Referring to Figure 19, the ends of the grain lines are not exposed on the rolling surfaces 511 and 512. With this configuration, the rolling elements do not come into contact with the ends of the grain lines on the rolling surface, resulting in improved strength of the rolling surface and a thinner, more durable rolling bearing.

[0078] Figures 20 and 21 show modified examples of Embodiment 5. Figure 20 is a diagram showing the rolling bearing 1 with the first outer ring 10 and the first inner ring 30 removed. Figure 21 is an enlarged cross-sectional perspective view showing the rolling bearing 1 with the first inner ring 30, the first roller 51 and part of the second roller 52 removed, schematically showing the forging lines. The modified examples of Figures 20 and 21 differ from Embodiment 5 in that the rolling elements are the first roller 51 and the second roller 52. Referring to Figure 21, the first outer ring 10 includes a disc-shaped annular first portion 15, and the inner circumferential surface of the first portion 15 includes a first racing surface 511. The second outer ring 20 includes a disc-shaped annular fourth portion 25 fixed to the first portion 15, and the inner circumferential surface of the fourth portion 25 includes a second racing surface 512. The second inner ring 40 has a disc-shaped annular tenth portion 45, the outer circumferential surface of the tenth portion includes a fourth racing surface 514. The first inner ring 30 is not shown, but it is in contact with and fixed to the second inner ring 40 at its main surface. The third inner ring 30 has an annular seventh portion 35, the outer circumferential surface of the seventh portion 35 includes a third racing surface 513. Referring to Figures 20 and 21, the first roller 51 is rotatably positioned on the first racing surface 511 and the fourth racing surface 514, in contact with its outer circumferential surface 51A. The second roller 52 is rotatably positioned on the second racing surface 512 and the third racing surface 513, in contact with its outer circumferential surface 52A.

[0079] Referring to Figure 21, in a cross-section including the central axis R (Figure 20) of the rolling bearing 1, the forging lines 111 of the steel constituting the first outer ring 10 extend along the surfaces 15A, 15B of the first portion 15 and the first rolling surface 511. The forging lines 211 of the steel constituting the second outer ring 20 extend along the surfaces 25A, 25B of the fourth portion 25 and the second rolling surface 512. The forging lines 411 of the steel constituting the second inner ring 40 extend along the surfaces 45A, 45B of the tenth portion 45 and the fourth rolling surface 514. The first inner ring 30 is not shown, but is similar.

[0080] The embodiments disclosed herein should be understood to be illustrative in all respects and not restrictive in any way. The scope of the invention is defined by the claims and not by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of symbols]

[0081] 1 Rolling bearing, 1A Outer ring, 1B Inner ring, 1C Roller, 10 First outer ring, 11,21,31,41 Mounting holes, 12,23,32,43,54A Through holes, 13,22,33,42 Projections, 15 First part, 15A,18A,25A,28A,35A,38A,45A,48A Surface, 16 Second part, 16A,17A,26A,27A,36A,36B,37B,46A,46B,47B Inner surface, 16B,17B,26B,27B,36A,37A,46A,47A,51A,51B,52A,52B,55A Outer surface, 17 Part 3, 17C, 27B, 37C, 47B, 51B, 51C, 52B, 52C End face, 18, 38 First labyrinth section, 20 Second outer ring, 25 Part 4, 26 Part 5, 27 Part 6, 28, 48 Second labyrinth section, 29 Bent section, 30 First inner ring, 35 Part 7, 36 Part 8, 37 Part 9, 40 Second inner ring, 45 Part 10, 46 Part 11, 47 Part 12, 51 First roller, 52 Second roller, 53 Separator, 54 Retainer, 55 Ball, 71 First member, 71A, 72A Screw hole, 72 Second member, 73, 74 Fixing bolt, 111, 211, 311, 411 Forging line, 150, 250, 350, 450 Small through-hole, 161 first face, 162 second face, 163 third face, 261 fourth face, 262 fifth face, 263 sixth face, 361 seventh face, 362 eighth face, 363 ninth face, 461 tenth face, 462 eleventh face, 463 twelfth face, 511 first turning surface, 512 second turning surface, 513 third turning surface, 514 fourth turning surface.

Claims

1. A steel outer ring, A steel inner ring is positioned on the inner circumference side of the outer ring, The system comprises a plurality of rolling elements arranged to be rotatable on the inner circumferential surface of the outer ring and the outer circumferential surface of the inner ring, The aforementioned outer ring is A first outer ring having an annular first running surface that constitutes the inner circumferential surface of the outer ring, The second outer ring has a central axis common to the first racing surface and an annular second racing surface that constitutes the inner circumferential surface of the outer ring, and is arranged alongside the first outer ring in the first axial direction which is the direction in which the central axis of the first racing surface extends, and is fixed to the first outer ring, and has the same shape as the first outer ring, The aforementioned inner ring is A first inner ring having a central axis common to the first turning surface, facing the second turning surface and having an annular third turning surface that constitutes the outer circumferential surface of the inner ring, A second inner ring having a common central axis with the first turning surface, facing the first turning surface, and having a line segment connecting it to the first turning surface in a cross-section including the central axis of the first turning surface, intersecting the line segment connecting the second turning surface and the third turning surface, and having an annular fourth turning surface that constitutes the outer circumferential surface of the inner ring, and being arranged alongside the first inner ring in the first axial direction and fixed to the first inner ring, and having the same shape as the first inner ring, In a cross-section including the central axis of the first rolling surface, the forging lines of the steel constituting the first outer ring extend along the first rolling surface, the forging lines of the steel constituting the second outer ring extend along the second rolling surface, the forging lines of the steel constituting the first inner ring extend along the third rolling surface, and the forging lines of the steel constituting the second inner ring extend along the fourth rolling surface. The first outer ring is, A first part having a disc-ring shape, A second portion having a cylindrical shape, extending from the inner edge of the first portion such that its inner diameter decreases as it moves away from the first portion in the first axial direction, and having an annular inner circumferential surface, It includes a third portion having a cylindrical shape, connected to the end of the second portion opposite to the first portion in the first axial direction, and extending along the first axial direction, The second outer ring is, A fourth portion having a disc-like annular shape and fixed to the first portion such that its main surfaces are in contact with each other, A fifth portion having a cylindrical shape, extending from the inner edge of the fourth portion in the direction opposite to the second portion in the first axial direction, with its inner diameter decreasing as it moves away from the fourth portion, and having an annular inner surface, It includes a sixth portion having a cylindrical shape, connected to the end of the fifth portion opposite to the fourth portion in the first axial direction, and extending in the first axial direction opposite to the third portion, The aforementioned first inner ring is, A seventh part having a disc-like ring shape, Having a cylindrical shape, the eighth portion extends from the outer edge of the seventh portion such that its outer diameter increases as it moves away from the seventh portion in the first axial direction, and has an annular outer surface, It includes a ninth portion having a cylindrical shape, connected to the end of the eighth portion opposite to the seventh portion in the first axial direction, and extending along the first axial direction, The aforementioned second inner ring is A disc-shaped annular portion, a tenth portion fixed to the seventh portion such that its main surfaces are in contact with each other, Having a cylindrical shape, the 11th portion extends from the outer edge of the 10th portion in the direction opposite to the 8th portion in the first axial direction, and its outer diameter increases as it moves away from the 10th portion, and has an annular outer surface, It includes a cylindrical shape, a twelfth portion connected to the end of the eleventh portion opposite to the tenth portion in the first axial direction, and extending in the first axial direction opposite to the ninth portion, The inner circumferential surface of the second portion includes the first running surface, The inner circumferential surface of the fifth portion includes the second running surface, The outer circumferential surface of the eighth portion includes the third running surface, The outer circumferential surface of the 11th portion includes the fourth running surface, The inner circumferential surface of the third portion and the outer circumferential surface of the ninth portion are arranged to face each other. The inner circumferential surface of the sixth portion and the outer circumferential surface of the twelfth portion are arranged to face each other. In a cross-section including the central axis of the first rolling surface, the radial distance between the third portion and the ninth portion is less than the thickness of the third portion, and the radial distance between the sixth portion and the twelfth portion is less than the thickness of the sixth portion. Rolling bearings.

2. The rolling element includes a first roller and a second roller, The first roller and the second roller are arranged alternately in the circumferential direction. The central axis of the first roller and the central axis of the second roller intersect, The first roller is arranged to be rotatable on the first and fourth rolling surfaces, The rolling bearing according to claim 1, wherein the second roller is arranged to be rotatable on the second and third rolling surfaces.

3. The aforementioned rolling element is a ball, The rolling bearing according to claim 1, wherein the rolling elements are arranged to be rotatable on the first, second, third, and fourth rolling surfaces.

4. In a cross-section including the central axis of the first roller, the effective contact length L is the length at which the outer surface of the first roller and the first rolling surface come into contact. １ and the effective contact length L of the outer surface of the first roller and the fourth rolling surface that come into contact. ２ The length of the first roller in the axial direction is 0.5 times or more and 0.9 times or less. In a cross-section including the central axis of the second roller, the effective contact length L is the contact length between the outer surface of the second roller and the second rolling surface. ３ and the effective contact length L of the outer circumferential surface of the second roller and the third rolling surface that come into contact. ４ The rolling bearing according to claim 2, wherein the length of the second roller in the axial direction is 0.5 times or more and 0.9 times or less.

5. In a cross-section including the central axis of the first turning surface, the main surface on the side of the first portion that contacts the fourth portion and the first turning surface are connected by a curved first region. The main surface of the fourth portion that is in contact with the first portion and the second running surface are connected by a curved second region. A rolling bearing according to claim 1, wherein an annular space is formed surrounded by the first region, the second region, and the rolling elements.

6. The rolling bearing according to claim 1, wherein in a cross-section including the central axis of the first rolling surface, the first rolling surface and the inner circumferential surface of the third portion are connected by a curved third region, and the third rolling surface and the outer circumferential surface of the ninth portion are connected by a curved fourth region.

7. The rolling bearing according to claim 1, wherein in a cross-section including the central axis of the first rolling surface, the thickness of the first portion, second portion, third portion, fourth portion, fifth portion, sixth portion, seventh portion, eighth portion, ninth portion, tenth portion, eleventh portion and twelfth portion is less than 0.5 times the diameter of the rolling element.

8. The rolling bearing according to claim 1, wherein in a cross-section including the central axis of the first rolling surface, the lengths of the third portion and the ninth portion in the first axial direction are greater than 1.5 times the thickness of the third portion, and the lengths of the sixth portion and the twelfth portion in the first axial direction are greater than 1.5 times the thickness of the sixth portion.

9. The rolling bearing according to claim 1, wherein the first outer ring is positioned at the end of the third portion opposite to the second portion in the first axial direction, and further includes a labyrinth portion that is bent radially inward of the third portion and faces the ninth portion at a distance smaller than the radial distance between the third portion and the ninth portion.

10. The rolling bearing according to claim 1, wherein the first inner ring is positioned at the end of the ninth portion opposite to the eighth portion in the first axial direction, and further includes a labyrinth portion that is bent radially outward from the ninth portion and faces the third portion at a distance smaller than the radial distance between the third portion and the ninth portion.

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