Ball bearing and wave motion decelerator

Abstract

To provide a technique that can obtain a ball bearing in which a retainer is easily formed.SOLUTION: A ball bearing 32 according to the present disclosure comprises an outer ring 33, an inner ring 34, a plurality of balls 35, and a retainer 36. The retainer 36 comprises: an annular body 50; and a plurality of columns 52 extended in an axial direction from a side surface 50a of the annular body 50, and defining a plurality of pockets P. The plurality of columns 52 include a plurality of first columns 54 arranged in a circumferential direction along an inner peripheral surface 33a, and a plurality of second columns 56 arranged along an outer peripheral surface 34a so as to correspond to circumferential positions of the plurality of first columns 54. The plurality of second columns 56 are arranged at a predetermined interval in a radial direction with respect to the plurality of first columns 54. The plurality of first columns 54 each comprise an outer surface part 60 opposed to the inner peripheral surface 33a, and a first protrusion 62 protruding to an outer ring raceway groove 40 from the outer surface part 60. The plurality of second columns 56 each comprise an inner surface part 64 opposed to the outer peripheral surface 34a, and a second protrusion 66 protruding to an inner ring raceway groove from the inner surface part 64.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a ball bearing and a wave reducer. [Background technology]

[0002] Patent Document 1 discloses a wave reducer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-200112 Summary of the Invention [Problem to be solved by the invention]

[0004] The wave reducer uses a ball bearing. This ball bearing is provided between the flexspline and an elliptical cam. The ball bearing is fitted onto the cam and the flexspline. The ball bearing has an outer ring, an inner ring, a plurality of balls interposed between the outer ring and the inner ring, and an annular cage that holds the plurality of balls. Before the ball bearing is installed in the wave reducer, the contours of the inner ring, outer ring, and cage are perfectly circular when viewed in the axial direction. Once the ball bearing is installed in the wave reducer, that is, once the ball bearing is fitted onto the cam, the contours of the inner ring and outer ring are elastically deformed to become elliptical. In contrast, the contour of the cage is not affected by the deformation of the inner ring and outer ring, and remains perfectly circular.

[0005] The outer ring is deformed into an elliptical shape in accordance with the elliptical shape of the cam. Here, the total number of balls in the ball bearing used in the wave reducer is greater than the total number of balls in a general ball bearing, so that backlash between the inner and outer rings is suppressed and the elliptical shape of the cam is appropriately reflected in the outer ring.

[0006] Fig. 7 is a diagram showing an example of a cage for a ball bearing used in the above-mentioned conventional wave reducer. As shown in Fig. 7, cage 90 has pockets 99. Pockets 99 have a shape that follows an imaginary cylindrical surface. The central axis of the imaginary cylindrical surface is parallel to the central axis of cage 90. In this case, the minimum dimension E on the opening side of a pair of adjacent posts 91 is smaller than the diameter d of balls 95, and when the rolling bearing is assembled, the axial movement of cage 90 is limited by balls 95, so that cage 90 will not fall off the rolling bearing.

[0007] As described above, the total number of balls in a ball bearing for a wave reducer is greater than the total number of balls in a general ball bearing. For this reason, the distance between adjacent pairs of balls among the plurality of balls is relatively narrow, and it may be necessary to make the thickness of the pillar 91 in the circumferential direction extremely thin.

[0008] In such thin-walled portions of the pillar, the fluidity of the resin is not good, so measures to prevent underfill may be required. Furthermore, if there are thin-walled portions in the pillars, there is a risk that the thin-walled portions may break when the retainer is released from the mold during molding, and measures may be required to prevent breakage.

[0009] As described above, forming a cage with thin-walled portions requires measures to prevent undercutting and fracture, which has led to the problem that it is not easy to form a cage for a ball bearing used in a wave reducer. Therefore, an object of the present disclosure is to provide a ball bearing having a cage that is easy to form, and a wave reducer including this ball bearing. [Means for solving the problem]

[0010] A ball bearing according to an embodiment of the present disclosure includes an outer ring having an outer ring raceway groove on its inner peripheral surface, an inner ring having an inner ring raceway groove on its outer peripheral surface, multiple balls interposed between the inner ring raceway groove and the outer ring raceway groove, and a resin cage having multiple pockets for holding the multiple balls. The cage includes an annular body disposed between the inner and outer rings and axially adjacent to the multiple balls, and multiple pillars extending axially from a side surface of the annular body facing the multiple balls and defining the multiple pockets. The multiple pillars include multiple first pillars arranged circumferentially along the inner peripheral surface and multiple second pillars arranged along the outer peripheral surface corresponding to the circumferential positions of the multiple first pillars. The multiple second pillars are arranged at predetermined radial intervals relative to the multiple first pillars. Each of the multiple first pillars has an outer surface facing the inner peripheral surface and a first protrusion protruding from the outer surface into the outer ring raceway groove. Each of the plurality of second pillars has an inner surface portion facing the outer circumferential surface, and a second projection protruding from the inner surface portion into the inner ring raceway groove. [Effects of the Invention]

[0011] According to the present disclosure, a ball bearing in which the retainer is easily formed can be obtained. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing an example of a wave reducer according to this embodiment. [Figure 2] FIG. 2 is a cross section taken along a plane including the central axis of the wave reducer. [Figure 3] FIG. 3 is a cross-sectional view showing a part of a ball bearing. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 5 is a perspective view of the cage. [Figure 6] FIG. 6 is a front view of the cage. [Figure 7] FIG. 7 is a diagram showing an example of a cage for a ball bearing used in a wave reducer. DETAILED DESCRIPTION OF THE INVENTION

[0013] First, the contents of the embodiment will be listed and explained. [Outline of the embodiment]

[0014] (1) A ball bearing according to an embodiment of the present disclosure includes an outer ring having an outer ring raceway groove on its inner peripheral surface, an inner ring having an inner ring raceway groove on its outer peripheral surface, multiple balls interposed between the inner ring raceway groove and the outer ring raceway groove, and a resin cage having multiple pockets for holding the multiple balls. The cage includes an annular body disposed between the inner and outer rings and axially adjacent to the multiple balls, and multiple pillars extending axially from a side surface of the annular body facing the multiple balls and defining the multiple pockets. The multiple pillars include multiple first pillars arranged circumferentially along the inner peripheral surface and multiple second pillars arranged along the outer peripheral surface corresponding to the circumferential positions of the multiple first pillars. The multiple second pillars are arranged at predetermined radial intervals relative to the multiple first pillars. Each of the multiple first pillars has an outer surface facing the inner peripheral surface and a first protrusion protruding from the outer surface into the outer ring raceway groove. Each of the plurality of second pillars has an inner surface portion facing the outer circumferential surface, and a second projection protruding from the inner surface portion into the inner ring raceway groove. According to the above configuration, the multiple pockets are formed by multiple first pillars and multiple second pillars arranged along the inner surface of the outer ring and the outer surface of the inner ring, so that the portions where adjacent pairs of balls are closest to each other can be positioned in the space between the first pillar and the second pillar at the same circumferential position. As a result, it is not necessary to provide thin-walled portions on the plurality of pillars, and the cage can be easily formed. In this embodiment, the pockets are formed by multiple pillars extending along the axial direction, so the movement of the cage along the axial direction is not limited by the multiple balls. However, the first and second protrusions on the first and second pillars limit the movement of the cage along the axial direction relative to the inner and outer rings.

[0015] (2) In the ball bearing of (1) above, when the center axis of the retainer and the center axis of the inner and outer rings are aligned, there may be a predetermined gap between the outer surface portion and the inner peripheral surface, and between the inner surface portion and the outer peripheral surface, and the tip of the first protrusion may be located within the outer ring raceway groove, and the tip of the second protrusion may be located within the inner ring raceway groove. In this case, whether the contour shape of the ball bearing is a perfect circle or an ellipse, the first protrusion engages with the outer ring raceway groove and the second protrusion engages with the inner ring raceway groove, restricting movement of the cage along the axial direction.

[0016] (3) In the ball bearing of (1) above, the radial thickness of the plurality of first posts may be greater than the radial thickness of the plurality of second posts. When a ball bearing elastically deforms, the stress acting on each part tends to be greater on the radially outer parts than on the radially inner parts. As a result, the stress acting on the multiple first posts is greater than the stress acting on the multiple second posts, which could result in the amount of deformation of the multiple first posts being greater than the amount of deformation of the multiple second posts. In contrast, in this embodiment, the radial thickness of the first pillar is made larger than the radial thickness of the second pillar, thereby increasing the rigidity of the first pillar. As a result, even if a difference in stress acts between the first pillar and the second pillar, the amount of deformation of the first pillar can be suppressed, and the amount of deformation of the first pillar and the amount of deformation of the second pillar can be balanced.

[0017] (4) In the ball bearing of (3) above, the inner peripheral surface of the inner ring may include an outer fitting surface that fits onto the outer peripheral surface of a cam of a wave reducer. In this case, the ball bearing of this embodiment can be used as a ball bearing fitted onto the cam of the wave reducer.

[0018] (5) From another perspective, the present embodiment is a wave reducer. This wave reducer includes a cam and a ball bearing fitted and fixed to the outer circumferential surface of the cam. The ball bearing is the ball bearing described in (1) above.

[0019] [Details of the embodiment] Preferred embodiments will now be described with reference to the drawings. [Configuration of the wave reducer] Fig. 1 is a diagram showing an example of a wave reducer according to this embodiment. Fig. 2 is a cross-sectional view of the wave reducer. Fig. 2 is a cross-section taken along a plane including a central axis C1 of the wave reducer 1. The wave reducer 1 includes a circular spline 10, a flexspline 20, and a rotor 30. The rotor 30 includes a cam 31 and a ball bearing 32.

[0020] The circular spline 10 is an annular member (metal member) that is more rigid than the flexspline 20. The circular spline 10 has internal teeth 11 on its inner circumferential surface. The inner circumferential surface is a circular (perfect circle) surface centered on the central axis C1. The circular spline 10 is fixed to a casing (not shown) to which the wave reducer 1 is fixed.

[0021] The flexspline 20 is provided radially inside the circular spline 10. The flexspline 20 has external teeth 21 on its outer circumferential surface. The external teeth 21 partially mesh with the internal teeth 11. As shown in Fig. 2, the flexspline 20 of this embodiment is a thin-walled, cup-shaped metal member. The flexspline 20 has a larger amount of elastic deformation than the circular spline 10. The flexspline 20 has a cylindrical portion 22 and a bottom portion 23. The external teeth 21 are provided on the outer peripheral surface of the cylindrical portion 22. An output shaft (not shown) is attached to the bottom portion 23. The number of teeth of the external teeth 21 of the flexspline 20 is smaller than the number of teeth of the internal teeth 11 of the circular spline 10.

[0022] 1, the cylindrical portion 22 of the flexspline 20 is elastically deformed into a non-circular shape. The contour shape of the cylindrical portion 22 is elliptical. In FIG. 1, in the portion S1 of the flexspline 20 that forms the long axis of the ellipse, the external teeth 21 and the internal teeth 11 are in a state of meshing with each other, and in the short axis portion S2 that forms the short axis, the external teeth 21 and the internal teeth 11 are in a state of separation.

[0023] The rotor 30 is provided radially inside the cylindrical portion 22 of the flexspline 20 . The cam 31 has a non-circular contour shape. In this embodiment, the contour shape of the cam 31 is elliptical (see FIG. 1). The ball bearing 32 is fitted onto the outer peripheral surface 31a of the cam 31. The ball bearing 32 is also fitted onto the inner peripheral surface of the cylindrical portion 22 of the flexspline 20. Therefore, the ball bearing 32 is interposed between the cam 31 and the flexspline 20. The ball bearing 32 supports the cam 31 and the flexspline 20 so that they can rotate relative to each other. The ball bearing 32 is provided so as to be elastically deformable to the same extent as the flexspline 20. As a result, the ball bearing 32 and the flexspline 20 fitted onto the outside of the cam 31 are elastically deformed into an elliptical shape in accordance with the contour shape of the cam 31.

[0024] In other words, the rotor 30 elastically deforms the flexspline 20 into an elliptical shape. As a result, the external teeth 21 of the flexspline 20 partially mesh with the internal teeth 11 of the circular spline 10. The external teeth 21 and the internal teeth 11 mesh with each other at two locations 180 degrees apart around the central axis of the circular spline 10.

[0025] 1, the circular spline 10 is in a fixed state. In this state, when the cam 31 is rotated clockwise around the central axis C1, the position of the long axis portion S1 of the flexspline 20 moves (changes) clockwise. The meshing portion between the external teeth 21 and the internal teeth 11 moves (changes) following the movement of the long axis portion S1 of the flexspline 20.

[0026] At this time, since the number of teeth of the external teeth 21 is different from the number of teeth of the internal teeth 11, when the meshing portion between the external teeth 21 and the internal teeth 11 moves, the flexspline 20 rotates relative to the circular spline 10. When the cam 31 is rotated 180 degrees from the state shown in FIG. 1, the flexspline 20 moves in the direction opposite to the rotation direction of the cam 31 (counterclockwise) by a distance equivalent to half the difference in the number of teeth between the external teeth 21 and the internal teeth 11. As a result, the rotation of the cam 31 is decelerated and transmitted to the flexspline 20.

[0027] An input shaft (not shown) is attached to the cam 31 so as to be rotatable together with the cam 31. As described above, the flexspline 20 can rotate integrally with the output shaft (not shown). Therefore, the rotation given to the input shaft is reduced in speed by the wave reducer 1 and transmitted to the output shaft.

[0028] [About ball bearings] Fig. 3 is a cross-sectional view showing a part of the ball bearing 32. Fig. 4 is a cross-sectional view taken along the line IV-IV in Fig. 3. Fig. 3 shows a cross section along a plane perpendicular to the central axis C1. As shown in FIGS. 3 and 4, the ball bearing 32 includes an outer ring 33, an inner ring , a plurality of balls 35, and a cage .

[0029] The outer ring 33 is an annular member made of a metal such as bearing steel. The outer ring 33 is thin-walled, which allows the outer ring 33 to have elastic deformation to the extent that it can deform according to the contour shape of the cam 31. The inner peripheral surface 33 a of the outer ring 33 has an outer ring raceway groove 40 and a peripheral surface portion 42 . The peripheral surface portion 42 is a cylindrical surface centered on the central axis C1. The outer ring raceway groove 40 is an annular groove recessed radially into the peripheral surface portion 42. The cross section of the outer ring raceway groove 40 along the axial direction is a smooth arc shape.

[0030] The inner ring 34 is disposed concentrically on the inner periphery of the outer ring 33. Like the outer ring 33, the inner ring 34 is an annular member made of a metal such as bearing steel. The inner ring 34 has a thin wall. This allows the inner ring 34 to have elastic deformability to the extent that it can deform in accordance with the contour shape of the cam 31. The outer peripheral surface 34 a of the inner ring 34 has an inner ring raceway groove 44 and a peripheral surface portion 46 . The peripheral surface portion 46 is a cylindrical surface centered on the central axis C1. The inner ring raceway groove 44 is an annular groove that is recessed radially into the peripheral surface portion 46. The cross section of the inner ring raceway groove 44 along the axial direction is a smooth arc shape. The inner ring raceway groove 44 and the outer ring raceway groove 40 face each other.

[0031] The plurality of balls 35 are members made of metal such as bearing steel. The plurality of balls 35 are interposed between the outer ring raceway groove 40 and the inner ring raceway groove 44. The plurality of balls 35 roll in the outer ring raceway groove 40 and the inner ring raceway groove 44. Therefore, the outer ring 33 and the inner ring 34 can rotate relative to each other due to the plurality of balls 35. The movement of the balls 35 in the axial direction is restricted by the outer ring raceway groove 40 and the inner ring raceway groove 44 .

[0032] The outer ring 33 and the inner ring 34 are circular in a free state in which no external force is acting on them. The inner peripheral surface 34 b of the inner ring 34 is an external fitting surface that fits onto the outer peripheral surface 31 a of the cam 31 . When the ball bearing 32 is fitted onto the outer peripheral surface 31 a of the cam 31 , the outer ring 33 and the inner ring 34 are elastically deformed into an elliptical shape in accordance with the contour shape of the cam 31 .

[0033] The cage 36 is an annular member that holds a plurality of balls 35 at equal intervals in the circumferential direction. The cage 36 has a plurality of pockets P that hold a plurality of balls 35. The plurality of pockets P are provided at equal intervals in the circumferential direction. The cage 36 is made of resin and is formed by injection molding.

[0034] [Regarding the cage] Fig. 5 is a perspective view of the cage 36. Fig. 6 is a front view of the cage. The cage 36 includes an annular body 50 and a plurality of pillars 52. The plurality of pillars 52 are provided on a side surface 50a of the annular body 50.

[0035] In the following description, the direction parallel to the central axis C2 of the annular body 50 (retainer 36) is referred to as the axial direction. The direction parallel to the central axis C2 and toward which the side surface 50a faces is referred to as the first axial direction, and the opposite direction is referred to as the second axial direction. Furthermore, the direction perpendicular to the central axis C2 is referred to as the "radial direction," and the direction along a circle centered on the central axis C2 is referred to as the "circumferential direction." FIG. 6 is a view of the cage 36 as seen from the first axial direction side.

[0036] The annular body 50 is disposed in the annular space between the outer ring 33 and the inner ring 34 (see FIGS. 3 and 4). The annular body 50 is disposed on the second axial side of the plurality of balls 35. The annular body 50 is disposed adjacent to the plurality of balls 35. Therefore, the side surface 50a of the annular body 50 faces the plurality of balls 35 and can slide against the plurality of balls 35.

[0037] As shown in FIG. 5, a plurality of pillars 52 extend from the side surface 50a in the first axial direction. The tips of the plurality of pillars 52 protrude further toward the first axial direction than the side surfaces of the outer ring 33 and the inner ring 34 on the first axial direction side (see FIG. 4).

[0038] The plurality of pillars 52 includes a plurality of first pillars 54 and a plurality of second pillars 56 . 3 and 4, the multiple first pillars 54 are arranged at equal intervals in the circumferential direction along the inner peripheral surface 33a of the outer ring 33. The multiple first pillars 54 extend so as to pass between pairs of adjacent balls 35 (FIG. 3).

[0039] 5, the multiple first pillars 54 have a substantially quadrangular prism shape. The cross section of the multiple first pillars 54 has a shape that tapers from the outside to the inside in the radial direction. Each of the plurality of first pillars 54 has a first radial side surface 54a, a second radial side surface 54b, and a pair of circumferential side surfaces 54c.

[0040] The first radial side surface 54a is one of the side surfaces of the first pillar 54 that faces the outer periphery. The second radial side surface 54b is one of the side surfaces of the first pillar 54 that faces the inner periphery. The pair of circumferential side surfaces 54c are side surfaces of the first pillar 54 that face in the circumferential direction. The first radial side surface 54a, the second radial side surface 54b, and the pair of circumferential side surfaces 54c are surfaces that are substantially parallel to the axial direction.

[0041] When the first pillar 54 is viewed in cross section, the first radial side surface 54a is a convex arc surface that is flush with the outer circumferential surface 50b of the annular body 50. In addition, when the first column 54 is viewed in cross section, the second radial side surface 54b is a concave arc surface. The circumferential position of the arc center of the second radial side surface 54b coincides with the circumferential position of the arc center of the first radial side surface 54a. The arc length of the second radial side surface 54b is shorter than the arc length of the first radial side surface 54a.

[0042] When the first pillar 54 is viewed in cross section, the pair of circumferential side surfaces 54c are inclined from the radially outer side to the radially inner side so as to approach a straight line passing through the arc center of the first radial side surface 54a and the central axis C2. The pair of circumferential side surfaces 54c also have a concave arc surface shape.

[0043] 6, a concave curved surface portion 54d is provided between the pair of circumferential side surfaces 54c and the side surface 50a. The concave curved surface portion 54d smoothly connects the pair of circumferential side surfaces 54c and the side surface 50a. The first radial side surface 54a also has an outer surface portion 60 and a first protrusion 62. The first protrusion 62 will be described later.

[0044] 3 and 5, the second pillars 56 are arranged at equal intervals in the circumferential direction along the outer peripheral surface 34a of the inner ring 34. The second pillars 56 extend so as to pass between pairs of adjacent balls 35 (FIG. 3). Furthermore, the multiple second pillars 56 are arranged to correspond to the circumferential positions of the multiple first pillars 54. In other words, the circumferential positions of the multiple second pillars 56 are the same as the circumferential positions of the multiple first pillars 54. Therefore, the circumferential center of the second pillar 56 is located on a straight line passing through the circumferential center of the first pillar 54 and the central axis C2. The second pillars 56 are arranged at predetermined intervals in the radial direction relative to the first pillars.

[0045] 5, the second pillars 56 have a substantially rectangular pillar shape. The cross section of the second pillars 56 has a shape that tapers from the inside to the outside in the radial direction. Each of the second pillars 56 has a third radial side surface 56a, a fourth radial side surface 56b, and a pair of circumferential side surfaces 56c.

[0046] The third radial side surface 56a is one of the side surfaces of the second pillar 56 that faces the inner periphery. The fourth radial side surface 56b is one of the side surfaces of the second pillar 56 that faces the outer periphery. The pair of circumferential side surfaces 56c are side surfaces of the second pillar 56 that face in the circumferential direction. The third radial side surface 56a, the fourth radial side surface 56b, and the pair of circumferential side surfaces 56c are surfaces that are substantially parallel to the axial direction.

[0047] When the second pillar 56 is viewed in cross section, the third radial side surface 56a is a concave arc surface that is flush with the inner circumferential surface 50c of the annular body 50. Furthermore, when the second column 56 is viewed in cross section, the fourth radial side surface 56b is a convex arc surface. The circumferential position of the arc center of the fourth radial side surface 56b coincides with the circumferential position of the arc center of the third radial side surface 56a. The circumferential position of the arc center of the fourth radial side surface 56b also coincides with the circumferential position of the arc center of the first radial side surface 54a. The arc length of the fourth radial side surface 56b is shorter than the arc length of the third radial side surface 56a.

[0048] When the second pillar 56 is viewed in cross section, the pair of circumferential side surfaces 56c are inclined from the radially inner side to the radially outer side so as to approach a center line that passes through the center of the third radial side surface 56a and the central axis C2. The pair of circumferential side surfaces 56c also have a concave arcuate surface shape.

[0049] 6, a concave curved surface portion 56d is provided between the pair of circumferential side surfaces 56c and the side surface 50a. The concave curved surface portion 56d smoothly connects the pair of circumferential side surfaces 56c and the side surface 50a. The third radial side surface 56a has an inner surface portion 64 and a second protrusion 66. The second protrusion 66 will be described later.

[0050] The pillars 52, together with the annular body 50, define a plurality of pockets P. A pocket P is a space for holding one ball 35. As shown in FIG. 3, the pocket P is defined by a pair of first pillars 54 adjacent to each other among the plurality of pillars 52 and a pair of second pillars 56 corresponding to the pair of first pillars 54. The pair of first pillars 54 have another pair of circumferential side surfaces 54c that face each other in the circumferential direction. The pair of second pillars 56 have another pair of circumferential side surfaces 56c that face each other in the circumferential direction. The pocket P is a space surrounded by another pair of circumferential side surfaces 54c, another pair of circumferential side surfaces 56c, and the side surface 50a. Therefore, the circumferential side surfaces 54c, 56c and the side surface 50a serve as sliding contact surfaces with which the balls 35 slide.

[0051] As shown in FIG. 3, the other pair of circumferential side surfaces 54c and the other pair of circumferential side surfaces 56c have a concave arcuate surface shape that follows an imaginary cylindrical surface S whose central axis is parallel to the axial direction. This imaginary cylindrical surface S has a diameter larger than the diameter of the ball 35. Therefore, a predetermined clearance is provided between the other pair of circumferential side surfaces 54c and the outer surface of the ball 35, and between the other pair of circumferential side surfaces 56c and the outer surface of the ball 35.

[0052] The specified clearance is set to a value such that when the outer ring 33 and the inner ring 34 elastically deform into an elliptical shape, the multiple balls 35 do not come into contact with the other pair of circumferential side surfaces 54c and the other pair of circumferential side surfaces 56c. As a result, even if the outer ring 33 and the inner ring 34 are elastically deformed into an elliptical shape, the contour shape of the cage 36 remains a perfect circle, and the plurality of balls 35 can be properly held in the circumferential direction.

[0053] As shown in FIG. 4, the radial thickness T1 of the first pillar 54 is greater than the radial thickness T2 of the second pillar 56. When the ball bearing 32 elastically deforms, the load on the cage 36 is greatest near the position of the major axis. As described above, even if the outer ring 33 and the inner ring 34 elastically deform into an elliptical shape, the contour shape of the cage 36 remains perfectly circular. Therefore, the deformation of the outer ring 33 and the inner ring 34 causes the balls 35 to move, increasing the PCD near the position of the major axis. As a result, the load on the cage 36 is greatest near the position of the major axis. For this reason, the stress acting on the first columns 54 located on the outer periphery is greater than the stress acting on the second columns 56 located on the inner periphery, and there is a risk that the amount of deformation of the multiple first columns 54 will be greater than the amount of deformation of the multiple second columns 56. In contrast to this, in this embodiment, the radial thickness dimension T1 of the first pillar 54 is made larger than the radial thickness dimension T2 of the second pillar 56, thereby increasing the rigidity of the first pillar 54. As a result, even if a difference in stress acts between the first pillar 54 and the second pillar 56 when the ball bearing 32 elastically deforms, the amount of deformation of the first pillar 54 can be suppressed, and the amounts of deformation of the first pillar 54 and the second pillar 56 can be balanced.

[0054] As described above, the first radial side surface 54 a of the first pillar 54 has the outer surface portion 60 and the first protrusion 62 . The outer surface portion 60 is flush with the outer peripheral surface 50b of the annular body 50 and has an arcuate surface shape with the same curvature as the outer peripheral surface 50b. The outer surface portion 60 faces the inner peripheral surface 33a. The first protrusion 62 is a protrusion having a spherical surface. The diameter (circumferential dimension) of the first protrusion 62 is smaller than the circumferential dimension of the outer surface portion 60. The first protrusion 62 protrudes radially outward from the outer surface portion 60. 3 and 4, the first protrusion 62 protrudes from the outer surface portion 60 into the outer ring raceway groove 40. In other words, the first protrusion 62 is provided at a position on the first radial side surface 54a corresponding to the outer ring raceway groove 40. As a result, the first protrusion 62 engages with the outer ring raceway groove 40 and restricts axial movement of the cage 36 relative to the outer ring 33 and the inner ring 34.

[0055] As described above, the third radial side surface 56 a of the second pillar 56 has the inner surface portion 64 and the second protrusion 66 . The inner surface portion 64 is flush with the inner peripheral surface 50c of the annular body 50 and has an arcuate surface shape with the same curvature as the inner peripheral surface 50c. The inner surface portion 64 faces the outer peripheral surface 34a. The second protrusion 66 is a protrusion having a spherical surface. The diameter of the second protrusion 66 is smaller than the circumferential dimension of the inner surface portion 64. The second protrusion 66 protrudes radially inward from the inner surface portion 64. 3 and 4, the second protrusion 66 protrudes from the inner surface portion 64 into the inner ring raceway groove 44. In other words, the second protrusion 66 is provided at a position on the third radial side surface 56a corresponding to the inner ring raceway groove 44. As a result, the second protrusion 66 engages with the inner ring raceway groove 44 and restricts axial movement of the cage 36 relative to the outer ring 33 and the inner ring 34.

[0056] According to the above configuration, the multiple pockets P are formed by multiple first pillars 54 and multiple second pillars 56 arranged along the inner surface 33a of the outer ring 33 and the outer surface 34a of the inner ring 34, so that the portions of adjacent pairs of balls 35 that are closest to each other can be positioned in the space between the first pillars 54 and second pillars 56 at the same circumferential position (Figure 3). As a result, it is not necessary to provide thin-walled portions to the plurality of pillars 52, and the retainer 36 can be easily formed.

[0057] That is, the first radial side surface 54a, the second radial side surface 54b, and the pair of circumferential side surfaces 54c of the first pillar 54 are surfaces that are substantially parallel to the axial direction. In addition, the third radial side surface 56a, the fourth radial side surface 56b, and the pair of circumferential side surfaces 56c of the second pillar 56 are surfaces that are substantially parallel to the axial direction. Therefore, when the retainer 36 is injection molded, even if a mold that can be removed in the axial direction is used, it can be easily formed without being forced to be removed. The outer surface portion 60 and the inner surface portion 64 are provided with a first protrusion 62 and a second protrusion 66, but since these first protrusions 62 and second protrusions 66 have a low protrusion height and a spherical surface, they can be easily formed without being forced out even when a mold that is punched in the axial direction is used.

[0058] Furthermore, since there is no need to provide a thin portion and the cage 36 is easily formed, it is possible to use a resin material containing glass fiber or carbon fiber as the material for the cage 36. This makes it possible to increase the strength of the cage 36.

[0059] In this embodiment, the pocket P is formed by multiple pillars 52 extending along the axial direction, so the movement of the cage 36 along the axial direction is not restricted by the multiple balls 35. However, the first protrusions 62 and second protrusions 66 provided on the first pillars 54 and second pillars 56 restrict the movement of the cage 36 along the axial direction relative to the inner and outer rings 33, 34.

[0060] Furthermore, because the first protrusions 62 and the second protrusions 66 have spherical surfaces, when the first posts 54 and the second posts 56 are inserted between the inner and outer rings 33, 34 to assemble the cage 36 to the inner and outer rings 33, 34, the first protrusions 62 and the second protrusions 66 are smoothly inserted between the inner and outer rings 33, 34, gradually elastically deforming the first posts 54 and the second posts 56. When the first protrusions 62 and the second protrusions 66 reach the raceway grooves 40, 44, the first protrusions 62 and the second protrusions 66 engage with the raceway grooves 40, 44.

[0061] 3 and 4 show a state in which the central axis C1 of the outer ring 33 and the inner ring 34 and the central axis C2 of the cage 36 are aligned. In this way, when the central axis C2 of the retainer 36 and the central axis C1 of the inner and outer rings 33 and 34 are aligned, there is a predetermined gap between the outer surface portion 60 and the peripheral surface portion 42, and between the inner surface portion 64 and the peripheral surface portion 46. Further, a tip 62a of the first projection 62 is positioned within the outer ring raceway groove 40. Between the tip 62a and the outer ring raceway groove 40, a slight gap is provided in the radial direction. Similarly, a tip 66a of the second projection 66 is positioned within the inner ring raceway groove 44. Between the tip 66a and the inner ring raceway groove 44, a slight gap is provided in the radial direction.

[0062] In this case, whether the shape of ball bearing 32 is a perfect circle or an ellipse, first protrusion 62 engages with outer ring raceway groove 40, and second protrusion 66 engages with inner ring raceway groove 44. In other words, whether the shape of ball bearing 32 is a perfect circle or an ellipse, first protrusion 62 and second protrusion 66 have interference with inner and outer rings 33, 34. Therefore, whether the contour shape of the ball bearing 32 is a perfect circle or an ellipse, the movement of the cage 36 along the axial direction relative to the inner and outer rings 33, 34 is restricted. In particular, when the contour shape of the ball bearing 32 is elliptical, the interference between the first projections 62 and the second projections 66 and the inner and outer rings 33, 34 increases, and the movement of the cage 36 in the axial direction is more reliably restricted.

[0063] 〔others〕 It should be noted that the embodiments disclosed herein are to be considered as illustrative in all respects and not restrictive. For example, in the above embodiment, the other pair of circumferential side surfaces 54c and the other pair of circumferential side surfaces 56c that constitute the pocket P have concave arc surface shapes that follow the imaginary cylindrical surface S. However, the other pair of circumferential side surfaces 54c and the other pair of circumferential side surfaces 56c may be simply flat surfaces that make point contact with the balls 35, rather than concave arc surfaces.

[0064] In the above embodiment, the first protrusion 62 and the second protrusion 66 have spherical surfaces. However, the second protrusion 66 and the second protrusion 66 may be frustum-shaped protrusions as long as they protrude from the outer surface portion 60 and the inner surface portion 64, or may have a convex rounded surface other than a spherical surface.

[0065] The scope of the present invention is defined by the claims, not by the meaning described above, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof. [Explanation of symbols]

[0066] 1 Wave reducer 31 Cam 31a Outer surface 32 Ball bearing 33 Outer ring 33a Inner surface 34 Inner Circle 34a Outer surface 34b Inner surface 35 balls 36 Retainer 40 Outer ring raceway groove 44 Inner ring raceway groove 50 cyclic bodies 50a side 52 pillars 54 Pillar 1 54a 1st radial side 56 Pillar 2 56a 3rd radial side 60 External part 62 1st protrusion 62a tip 64 inner surface 66 2nd protrusion 66a tip

Claims

1. an outer ring having an outer ring raceway groove on its inner peripheral surface; an inner ring having an inner ring raceway groove on its outer peripheral surface; a plurality of balls interposed between the inner ring raceway groove and the outer ring raceway groove; a resin cage having a plurality of pockets for holding the plurality of balls; The retainer is an annular body disposed between the inner and outer rings and axially adjacent to the plurality of balls; a plurality of posts extending axially from a side of the annular body facing the plurality of balls and defining the plurality of pockets; The plurality of pillars a plurality of first pillars arranged in a circumferential direction along the inner circumferential surface; a plurality of second pillars arranged along the outer circumferential surface in a manner corresponding to the circumferential positions of the plurality of first pillars, the second pillars are arranged at predetermined intervals in the radial direction relative to the first pillars, each of the plurality of first pillars has an outer surface portion facing the inner circumferential surface and a first projection protruding from the outer surface portion into the outer ring raceway groove; Each of the plurality of second pillars has an inner surface portion facing the outer circumferential surface, and a second protrusion protruding from the inner surface portion into the inner ring raceway groove. ball bearings.

2. When the central axis of the cage and the central axes of the inner and outer rings are aligned, there are predetermined gaps between the outer surface portion and the inner peripheral surface and between the inner surface portion and the outer peripheral surface, and the tip of the first protrusion is located in the outer ring raceway groove, and the tip of the second protrusion is located in the inner ring raceway groove.

2. The ball bearing according to claim 1.

3. The thickness dimension of the first pillars in the radial direction is greater than the thickness dimension of the second pillars in the radial direction.

2. The ball bearing according to claim 1.

4. The inner peripheral surface of the inner ring includes an outer fitting surface that fits onto the outer peripheral surface of the cam of the wave reducer. A ball bearing according to any one of claims 1 to 3.

5. Cam and a ball bearing fitted and fixed to the outer peripheral surface of the cam, The ball bearing is a ball bearing according to claim 1. Wave reducer.

Images