Ball bearings for wave reducers

Abstract

A ball bearing for a wave reduction gear according to the present disclosure has a retainer 36. The retainer 36 has an annular body 40 and a plurality of prongs 42. A space surrounded by a pair of opposing surfaces 42a of a pair of prongs 42 is a pocket 37. The pairs of opposing surfaces 42a have second flat surfaces 46 parallel to first imaginary planes P1, recessed curved surfaces 47 smoothly inclined toward the insides of the pockets 37 from radially inner-side edges 46a of the second flat surfaces 46, first corner curved surface parts 48 connecting first flat surfaces 43 and the second flat surfaces 46, and second corner curved surface parts 49 connecting the first flat surfaces 43 and the recessed curved surfaces 47. Section contour lines L1 of the first corner curved surface parts 48 when the first corner curved surface parts 48 are sectioned by second imaginary planes P2 perpendicular to the first imaginary planes P1 and parallel to a center axis C2, and section contour lines L2 of the second corner curved surface parts 49 when the second corner curved surface parts 49 are sectioned by third imaginary planes P3 perpendicular to the first imaginary planes P1 and parallel to the center axis C2, are circular arcs having a radius smaller than the radius of a plurality of balls 35.

Description

[Technical Field]

[0001] The present invention relates to a ball bearing for a wave reducer. [Background technology]

[0002] FIG. 12 is a diagram showing an example of a wave reducer. The wave reducer shown in FIG. 12 is a conventionally known wave reducer. The wave reducer includes an annular circular spline 80, an annular flexspline 99, and a rotor 89 (see, for example, Patent Document 1). The circular spline 80 has internal teeth 81. The flexspline 99 is provided inside the circular spline 80. The flexspline 99 has external teeth 86 that mesh with the internal teeth 81. The rotor 89 is provided inside the flexspline 99. The number of teeth of the external teeth 86 of the wave reducer is set to be smaller than the number of teeth of the internal teeth 81. The rotating body 89 has a cam 91 and a ball bearing 90. The ball bearing 90 is fitted onto the outside of the cam 91. The ball bearing 90 is also fitted onto the outside of a flexspline 99. The cam 91 has an elliptical shape. This causes the ball bearing 90 and flexspline 99 on the outside thereof to bend in an elliptical shape. As a result, the external teeth 86 of the flexspline 99 partially mesh with the internal teeth 81 of the circular spline 80. In other words, the circular spline 80 and the teeth mesh with each other at a portion S1 of the major axis of the flexspline 99 that bends in an elliptical shape, and are separated from each other at a portion S2 of the minor axis.

[0003] When the cam 91 rotates, the position of the major axis of the ellipse of the flexspline 99 (the position of meshing with the internal teeth 81) moves relative to the circular spline 80. As the cam 91 rotates, the flexspline 99 rotates with the external teeth 86 partially meshing with the internal teeth 81.

[0004] Ball bearing 90 is provided on the outside of cam 91, which has an elliptical shape. Ball bearing 90 has an outer ring 98, an inner ring 92, a plurality of balls 96 arranged in an annular space 95 formed between the outer ring 98 and the inner ring 92, and an annular cage 97 that holds the balls 96. Cage 97 holds the plurality of balls 96. Outer ring 98 is fitted inside flexspline 99. Inner ring 92 is fitted outside cam 91.

[0005] Fig. 13A is a cross-sectional view showing the ball bearing 90 and its surroundings, and Fig. 13B is a view of the cage 97 as seen from the outer periphery. The cage 97 is a so-called crown type. The cage 97 has an annular body 97a and a plurality of horns 97b extending axially from the annular body 97a. In this cage 97, the space surrounded by the annular body 97a and a pair of circumferentially adjacent horns 97b forms pockets 94 that hold balls 96. As shown in Fig. 13A, the inner surface 100 of the pocket 94 is straight in the radial direction. Also, as shown in Fig. 13B, the inner surface 100 of the pocket 94 has a circular shape that fits along the outer peripheral surface of the ball 96. Therefore, the inner surface 100 of the pocket 94 is part of the cylindrical inner peripheral surface. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2016-121724 Summary of the Invention [Problem to be solved by the invention]

[0007] The outer ring 98, inner ring 92, and cage 97 of the ball bearing 90 are perfectly circular before being attached to the cam 91. After being attached to the cam 91, the outer ring 98 and inner ring 92 elastically deform into an ellipse. In contrast, the cage 97 tries to maintain its perfectly circular shape.

[0008] Here, in a ball bearing 90 fitted onto an elliptical cam 91, an inner ring 92 is deformed into an ellipse, and multiple balls 96 are arranged on the ellipse along the inner ring 92. In other words, the centers of the multiple balls 96 are arranged on the ellipse. On the other hand, the cage 97 tries to maintain a perfect circular shape. Therefore, the relative position of the balls 96 located at the minor axis portion S2 relative to the pocket 94 in the radial direction is different from the relative position of the balls 96 located at the major axis portion S1 relative to the pocket 94 in the radial direction. Therefore, the plurality of balls 96 revolve and pass through the major axis portion S1 and the minor axis portion S2, whereby the balls 96 move back and forth in the radial direction relative to the pocket 94. As the balls 96 move back and forth radially relative to the pockets 94, the balls 96 push out the grease remaining between the balls 96 and the pockets 94 to the outside of the pockets 94. In such a ball bearing 90, there is a risk that the pockets 94 of the cage 97 may not be able to sufficiently retain grease. [Means for solving the problem]

[0009] An embodiment according to the present disclosure is a ball bearing for a wave reducer including: a circular spline having internal teeth; a flexspline provided inside the circular spline and having external teeth that mesh with the internal teeth; and a rotor provided inside the flexspline for deflecting the flexspline noncircularly to partially mesh the external teeth with the internal teeth. This ball bearing for a wave reducer includes an inner raceway that is elastically deformable and rotatable integrally with a noncircular cam of the rotor; an outer raceway that is elastically deformable and rotatable integrally with the flexspline; multiple balls provided between the inner and outer raceways; and a cage that has multiple pockets formed in the circumferential direction to accommodate the balls. The cage includes an annular body and multiple tines provided on a first axial side surface of the annular body and extending in the axial direction. The pockets are spaces surrounded by the first side surface and pairs of opposing surfaces of adjacent pairs of tines among the multiple tines. The first side surface has a first plane perpendicular to the central axis of the cage, disposed between the pair of horns and facing the pocket. Each of the pair of opposing surfaces has, between a radially outer outer edge of the opposing surface and a radially inner inner edge of the opposing surface, a second plane parallel to a first imaginary plane that includes the central axis and passes through the circumferential center of the pair of horns, and a concave curved surface portion having a cylindrical concave curved surface parallel to the central axis that smoothly slopes inwardly of the pocket from the radially inner edge of the second plane to the inner edge. The distance between the pair of opposing second planes is greater than the diameter of the balls. The distance between the pair of inner edges is smaller than the diameter of the balls. Each of the pair of opposing surfaces further has a first corner curved surface portion connecting the first plane and the second plane, and a second corner curved surface portion connecting the first plane and the concave curved surface portion. The cross-sectional contour of the first corner curved surface portion when the first corner curved surface portion is cut by a second imaginary plane that is perpendicular to the first imaginary plane and parallel to the central axis, and the cross-sectional contour of the second corner curved surface portion when the second corner curved surface portion is cut by a third imaginary plane that is perpendicular to the first imaginary plane and parallel to the central axis, are arcs with radii smaller than the radii of the plurality of balls. [Effects of the Invention]

[0010] According to the present disclosure, grease can be effectively retained. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing an example of a wave reducer equipped with a ball bearing. [Figure 2] FIG. 2 is a vertical cross-sectional view of the wave reducer. [Figure 3] FIG. 3 is a cross-sectional view of the ball bearing taken along the axial direction. [Figure 4] FIG. 4 is a diagram illustrating the operation of the wave reducer. [Figure 5] FIG. 5 is a perspective view of the cage. [Figure 6] FIG. 6 is a view of the cage as viewed from the outer periphery along the radial direction. [Figure 7] FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. [Figure 8] FIG. 8 is a partial enlarged view of the cage. [Figure 9] FIG. 9 is a cross-sectional view showing the balls and cage located at the short shaft portion. [Figure 10] 10 is a cross-sectional view of the cage taken along a second imaginary plane in FIG. [Figure 11] 11 is a cross-sectional view of the cage taken along a third imaginary plane in FIG. [Figure 12] FIG. 12 is a diagram illustrating an example of a wave reducer. [Figure 13A] FIG. 13A is a cross-sectional view showing a ball bearing and its surroundings. [Figure 13B] FIG. 13B is a view of the cage as viewed from the outer periphery side. DETAILED DESCRIPTION OF THE INVENTION

[0012] First, the contents of the embodiment will be listed and explained. [Outline of the embodiment] (1) An embodiment of the present disclosure is a ball bearing for a wave reducer including: a circular spline having internal teeth; a flexspline provided inside the circular spline and having external teeth that mesh with the internal teeth; and a rotor provided inside the flexspline for deflecting the flexspline noncircularly to partially mesh the external teeth with the internal teeth. This ball bearing for a wave reducer includes an inner raceway that is elastically deformable and rotatable integrally with a noncircular cam of the rotor; an outer raceway that is elastically deformable and rotatable integrally with the flexspline; a plurality of balls provided between the inner and outer raceways; and a cage that has a plurality of pockets formed in the circumferential direction to accommodate the balls. The cage includes an annular body and a plurality of tines that are provided on a first axial side surface of the annular body and extend in the axial direction. The pockets are spaces surrounded by the first side surface and pairs of opposing surfaces of adjacent pairs of tines among the plurality of tines. The first side surface has a first plane perpendicular to the central axis of the cage, disposed between the pair of horns and facing the pocket. Each of the pair of opposing surfaces has, between a radially outer outer edge of the opposing surface and a radially inner inner edge of the opposing surface, a second plane parallel to a first imaginary plane that includes the central axis and passes through the circumferential center of the pair of horns, and a concave curved surface portion having a cylindrical concave curved surface parallel to the central axis that smoothly slopes inwardly of the pocket from the radially inner edge of the second plane to the inner edge. The distance between the pair of opposing second planes is greater than the diameter of the balls. The distance between the pair of inner edges is smaller than the diameter of the balls. Each of the pair of opposing surfaces further has a first corner curved surface portion connecting the first plane and the second plane, and a second corner curved surface portion connecting the first plane and the concave curved surface portion. The cross-sectional contour of the first corner curved surface portion when the first corner curved surface portion is cut by a second imaginary plane that is perpendicular to the first imaginary plane and parallel to the central axis, and the cross-sectional contour of the second corner curved surface portion when the second corner curved surface portion is cut by a third imaginary plane that is perpendicular to the first imaginary plane and parallel to the central axis, are arcs with radii smaller than the radii of the plurality of balls.

[0013] According to the above configuration, the cross-sectional contours of the first and second curved corner portions connecting the annular body and the rim are arcs with radii smaller than the radius of the balls, so the first and second curved corner portions are farther away from the balls than the inner surfaces of the circular pockets in the above conventional example, and therefore the first and second curved corner portions have space for retaining more grease. The concave curved surface portion is smoothly inclined toward the inside of the pocket and protrudes toward the inside of the pocket relative to the second plane, thereby making it possible to properly hold the balls in the pocket. Furthermore, the second corner curved surface portion connecting the first plane and the concave curved surface portion protruding inward of the pocket also protrudes inward of the pocket relative to the first corner curved surface portion. As a result, even if relative reciprocating motion occurs between the ball and the pocket, the second corner curved surface portion protruding inward of the pocket keeps the accumulated grease within the pocket, preventing the grease from leaking out of the space defined by the first corner curved surface portion and the second corner curved surface portion. As a result, the ball bearing for a wave reducer according to the embodiment can effectively retain grease in the cage.

[0014] (2) In the ball bearing for a wave reducer, it is preferable that the radius of the cross-sectional contour of the first corner curved surface portion and the radius of the cross-sectional contour of the second corner curved surface portion are the same. In this case, the first curved corner portion and the second curved corner portion can be connected more smoothly.

[0015] (3) Furthermore, it is preferable that the distance between the pair of inner edges is greater than the following diameter dimension. Diameter dimension: The diameter dimension of the cross section when the ball located on the minor axis of the inner raceway is cut by a fourth imaginary plane including the pair of inner edges, with the inner raceway fixed to the cam and the inner raceway bent into an elliptical shape. In this case, a predetermined clearance can be secured between the balls located on the minor axis and the pair of inner edges.

[0016] [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 5 equipped with a ball bearing 32. Fig. 2 is a longitudinal cross-sectional view of the wave reducer 5. The wave reducer 5 is equipped with a circular spline 10, a flexspline 20, and a rotor 30. The rotor 30 is equipped with a cam 31 and a ball bearing 32.

[0017] 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) of the wave reducer 5.

[0018] 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. The flexspline 20 of this embodiment (see FIG. 2) is a thin-walled, cup-shaped metal member. The flexspline 20 is capable of elastic deformation by a larger amount 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 fewer than the number of teeth of the internal teeth 11 of the circular spline 10. In this embodiment, the number of teeth of the external teeth 21 is two fewer than the number of teeth of the internal teeth 11. This difference in the number of teeth is arbitrary.

[0019] As will be explained later, the cylindrical portion 22 of the flexspline 20 can bend into a non-circular shape (an elliptical shape in this embodiment) by elastically deforming, as shown in FIG. At a portion S1 that forms the major axis of the ellipse, the external teeth 21 and the internal teeth 11 are in a meshed state, and at a portion S2 that forms the minor axis, the external teeth 21 and the internal teeth 11 are in a separated state.

[0020] The rotor 30 is provided radially inside the cylindrical portion 22 of the flexspline 20. The cam 31 is non-circular and has an elliptical shape in this embodiment (see FIG. 1). The ball bearing 32 is fitted onto the outside of the cam 31. The ball bearing 32 is also fitted onto the outside of the cylindrical portion 22 of the flexspline 20.

[0021] FIG. 3 is a cross-sectional view of the ball bearing 32 taken along the axial direction. As shown in Fig. 3, ball bearing 32 has a thin outer raceway ring (hereinafter referred to as outer raceway 33), a thin inner raceway ring (hereinafter referred to as inner raceway 34), a plurality of balls 35, and an annular cage 36. The plurality of balls 35 are arranged between outer raceway 33 and inner raceway 34. Cage 36 has a plurality of pockets 37 spaced apart circumferentially to accommodate balls 35. All of the pockets 37 have the same shape.

[0022] The outer ring 33 and the inner ring 34 are annular members made of metal, such as bearing steel. The outer ring 33 and the inner ring 34 are thin-walled. Therefore, the radial length over which the outer ring 33 and the inner ring 34 can elastically deform is greater than the radial length over which the circular spline 10 can elastically deform. The thickness (maximum thickness) of the outer ring 33 and the inner ring 34 is, for example, greater than or equal to 1 / 7 and less than or equal to 1 / 2 of the diameter of the balls 35. The balls 35 are also made of metal, such as bearing steel. The radial length over which the balls 35 can elastically deform is smaller than the radial length over which the outer ring 33 and the inner ring 34 can elastically deform. The inner peripheral surface of the outer ring 33 is provided with a raceway groove 38 having an arc-shaped cross section. The outer peripheral surface of the inner ring 34 is provided with a raceway groove 39 having an arc-shaped cross section. Each ball 35 rolls in the raceway grooves 38, 39. When viewed from the axial direction, the shapes of the outer ring 33 and the inner ring 34 are circular when the inner ring 34 is not fixed to anything and the outer ring 33 is not fixed to anything, so no force is acting from the circumferential direction.

[0023] The inner ring 34 is fixed to the cam 31 (fitted on the outside of the cam 31). The inner ring 34 and the cam 31 can rotate together. The outer ring 33 is fixed to the cylindrical portion 22 of the flexspline 20 (fitted onto the outside of the cylindrical portion 22). The outer ring 33 and the flexspline 20 can rotate integrally. The outer peripheral contour shape of the cam 31 is elliptical (see FIG. 1). Therefore, when the inner ring 34 is fitted onto the cam 31, the circular inner ring 34 elastically deforms along the outer peripheral contour shape of the cam 31. Therefore, the inner ring 34 becomes elliptical along the shape of the cam 31. The outer ring 33 and the cylindrical portion 22 also elastically deform via the multiple balls 35. The outer ring 33 becomes elliptical along the multiple balls 35.

[0024] 1 and 2, a rotor 30 having a cam 31 and a ball bearing 32 is also called a wave generator. An input shaft (not shown) is attached to the cam 31. As described above, the rotating body 30 can bend 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. In this embodiment, 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] As shown in Figure 1, the flexspline 20 is bent into an elliptical shape by the rotor 30. The external teeth 21 and the internal teeth 11 mesh with each other at a portion S1 of the major axis of this ellipse, and are separated from each other at a portion S2 of the minor axis of this ellipse. The circular spline 10 is fixed. In this state, when the cam 31 is rotated clockwise around the central axis C1 in FIG. 1 (see (A) in FIG. 4), 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] As shown in (B) of Figure 4, when the cam 31 is rotated 180 degrees from the state shown in Figure 1, the flexspline 20 moves in the opposite direction to the rotational direction of the cam 31 (counterclockwise direction) by a distance equivalent to one tooth, which is half the difference in the number of teeth between the external teeth 21 and the internal teeth 11. Then, as shown in FIG. 4C, when the cam 31 is rotated a further 180 degrees from the state shown in FIG. 4B, the flexspline 20 moves in the opposite direction (counterclockwise) to the rotational direction of the cam 31 by a distance equivalent to the difference in the number of teeth between the external teeth 21 and the internal teeth 11, that is, two teeth. In this wave reducer 5, the cam 31 can rotate integrally with an input shaft (not shown), and the flexspline 20 can rotate integrally with an output shaft (not shown), so the input to the cam 31 is reduced in speed by the wave reducer 5, and the rotation of the flexspline 20 is taken out as an output. Note that the cage 36 of the ball bearing 32 is not shown in Figure 4.

[0027] [Regarding the cage] 5 is a perspective view of the cage 36. The cage 36 is a so-called crown-type cage. The cage 36 is made of, for example, resin and is obtained by injection molding. The retainer 36 has an annular body 40 and a plurality of horns 42. The annular body 40 is annular. In FIG. 5, the direction parallel to the central axis C2 of the annular body 40 (retainer 36) and from left to right on the page is called a first direction, and the direction parallel to the central axis C2 and opposite to the first direction is called a second direction. The annular body 40 has a first side surface 40a facing in a first direction.

[0028] The plurality of horns 42 are provided on the first side surface 40a. The plurality of horns 42 are provided at equal intervals in the circumferential direction. The plurality of horns 42 protrude from the first side surface 40a in the first direction and extend in the axial direction. The space surrounded by the first side surface 40a and a pair of opposing surfaces 42a of a pair of adjacent horns 42 among the plurality of horns 42 is the pocket 37. The first side surface 40a has a plurality of first flat surfaces 43. The first flat surfaces 43 are provided between pairs of adjacent horns 42 and face the pocket 37. The first flat surfaces 43 are planes perpendicular to the central axis C2.

[0029] Fig. 6 is a view of the cage 36 as viewed radially from the outer periphery. Fig. 7 is a cross-sectional view taken along line VII-VII in Fig. 6. Fig. 8 is a partially enlarged view of the cage 36. Fig. 7 shows a cross section of a second flat surface 46 and a concave curved surface portion 47, which will be described later.

[0030] As shown in Figures 6 and 8, each of the pair of opposing surfaces 42a has a tip side surface 44, a tip curved surface 45, a second flat surface 46, a concave curved surface portion 47, a first corner curved surface portion 48, and a second corner curved surface portion 49.

[0031] The tip side surface 44 is provided on the tip side of the horn 42. The tip side surface 44 is connected to the tip surface 42b of the horn 42. The second flat surface 46 and the concave curved surface portion 47 are provided between the tip side surface 44 and the annular body 40 (the first flat surface 43 of the annular body 40). The second flat surface 46 is recessed in the circumferential direction with respect to the tip side surface 44. As shown in Fig. 7, the second flat surface 46 is provided in a range from the outer edge 42a1 to the edge portion 46a. The outer edge 42a1 is the radially outer edge of the opposing surface 42a. Circle D is a circle that includes the center of each ball 35 when the balls 35 are placed in the pocket 37, and is a circle that includes the center of each of the multiple balls 35 that are placed between the outer ring 33 and the inner ring 34 in a circular state when viewed from the axial direction. The edge portion 46a is the radially inner edge of the second flat surface 46. The edge portion 46a is also the boundary between the second flat surface 46 and the concave curved surface portion 47.

[0032] The second flat surface 46 is provided on the outer edge 42a1 side of the opposing surface 42a on the radially outer side, and is parallel to the central axis C2 as shown in FIG. The second plane 46 is parallel to the first imaginary plane P1 in Fig. 7. The first imaginary plane P1 is an imaginary plane that includes the central axis C2 and passes through the circumferential centers of the pair of horns 42. In FIG. 7, the first imaginary plane P1 appears as a straight line passing through the central axis C2 and the circumferential centers of the pair of horns 42.

[0033] Therefore, the pair of opposing second planes 46 are parallel to each other. The distance W1 between the pair of opposing second planes 46 is slightly larger than the diameter of the ball 35. The distance W1 is the distance in a direction perpendicular to the first imaginary plane P1.

[0034] As shown in FIG. 7, the concave curved surface portion 47 is provided on the radially inner side of the second flat surface 46. The concave curved surface portion 47 is provided from the radially inner edge 46a of the second plane 46 to the inner edge 42a2. The concave curved surface portion 47 is inclined toward the first imaginary plane P1 as it extends from the edge 46a to the inner edge 42a2. The inner edge 42a2 is the radially inner edge of the opposing surface 42a. The edge 46a of the second plane 46 is also the radially outer edge of the concave curved surface portion 47.

[0035] The concave curved surface portion 47 has a cylindrical inner peripheral surface whose central axis is parallel to the central axis C2. The radius r1 of the inner peripheral surface of the concave curved surface portion 47 is set to a value slightly larger than the radius r0 of the ball 35. 7, the central axes C3 of the inner peripheral surfaces of a pair of opposing concave curved surface portions 47 are set at different points on a circle D. More specifically, the central axis C3 of the inner peripheral surface of one of the concave curved surface portions 47 is located on the circle D closer to the other concave curved surface portion 47 than the first imaginary plane P1 (the circumferential center between the horns 42).

[0036] 7, the concave curved surface portion 47 is provided so as to form a tangent circle with respect to the second plane 46. That is, at the edge portion 46a, the tangent line of the inner circumferential surface of the concave curved surface portion 47 coincides with the second plane 46. Furthermore, the distance in the direction perpendicular to the first imaginary plane P1 between the pair of edge portions 46a of the pair of opposing concave curved surface portions 47 is the same as the distance W1. Therefore, the concave curved surface portion 47 protrudes inward of the pocket 37 (toward the first imaginary plane P1) relative to the second plane . As described above, the opposing surface 42a has the second flat surface 46 and the concave curved surface portion 47 between the outer edge 42a1 and the inner edge 42a2.

[0037] The distance W2 between the pair of opposing inner edges 42a2 is smaller than the diameter of the ball 35. The distance W2 is the distance in a direction perpendicular to the first imaginary plane P1. The distance W2 is smaller than the distance W1. The distance W2 is set to a value that ensures a predetermined clearance between the ball 35 located at the portion S2 (FIG. 1) of the minor axis and the pair of inner edges 42a2. FIG. 9 is a cross-sectional view showing balls 35 and cage 36 located at portion S2 of the minor shaft. 9, an imaginary plane P4 (fourth imaginary plane) is an imaginary plane that includes the pair of inner edges 42a2. The imaginary plane P4 is perpendicular to the first imaginary plane P1 and parallel to the central axis C2.

[0038] The ball bearing 32 is fitted onto the elliptical cam 31. In this state, the inner ring 34 is deformed into an ellipse, and the centers of the balls 35 are arranged on the ellipse. Meanwhile, the cage 36 tries to maintain its circular shape. Therefore, the balls 35 located at the portion S1 of the major axis (FIG. 1) are located radially outward in the pockets 37. Additionally, the balls 35 located in the minor axis portion S2 (FIG. 2) are located radially inward within the pocket 37. Therefore, the balls 35 located in the minor axis portion S2 are closer to the pair of inner edges 42a2 than the balls 35 located in the major axis portion S1. 9, when ball 35 is located at portion S2 of the minor axis, distance W2 is greater than diameter D1 of the cross section of ball 35 on imaginary plane P4. Therefore, a predetermined clearance exists between ball 35 located at portion S2 of the minor axis and the pair of inner edges 42a2.

[0039] 6 and 8, the tip curved surface 45 is provided between the tip side surface 44 and the second flat surface 46 and the concave curved surface portion 47. The tip curved surface 45 connects the tip side surface 44 with the second flat surface 46 and the concave curved surface portion 47 by a smooth concave curved surface. Tip curved surface 45 connects tip side surface 44 and concave curved surface portion 47 with a smooth concave curved surface. As described above, concave curved surface portion 47 is a cylindrical concave curved surface. Therefore, the portion of tip curved surface 45 between tip side surface 44 and concave curved surface portion 47 is spherical with a curvature corresponding to the outer peripheral surface of ball 35.

[0040] As shown in FIG. 6, the first corner curved surface portion 48 is provided between the second plane 46 and (the first plane 43 of) the annular body 40. The first corner curved surface portion 48 smoothly connects the second plane 46 and the first plane 43. The first corner curved surface portion 48 has a cylindrical inner circumferential surface. The center of the inner circumferential surface of the first corner curved surface portion 48 is parallel to the radial direction on the first imaginary plane P1 (FIG. 7).

[0041] The second corner curved surface portion 49 is provided between the concave curved surface portion 47 and (the first flat surface 43 of) the annular body 40. The second corner curved surface portion 49 smoothly connects the concave curved surface portion 47 and the first flat surface 43. As described above, the concave curved surface portion 47 protrudes inward of the pocket 37 (toward the first imaginary plane P1) relative to the second plane 46. Therefore, the second corner curved surface portion 49 also protrudes inward of the pocket 37 relative to the second plane 46 and the first plane 43. Of the inner edge 42a2, an edge 49a of the second corner curved surface portion 49 connects an edge 47a of the concave curved surface portion 47 and the first flat surface 43 by an arc of a predetermined radius.

[0042] FIG. 10 shows a cross section of the cage 36 taken along the second imaginary plane P2 in FIG. 7 is an imaginary plane that is perpendicular to the first imaginary plane P1 and parallel to the central axis C2. The second imaginary plane P2 crosses the second flat surface 46 and the first corner curved surface portion 48 of the horn 42. As described above, the first corner curved surface portion 48 has an inner peripheral surface. In Fig. 10, the cross-sectional contour line L1 of the first corner curved surface portion 48 is an arc of radius r2 that connects the second plane 46 and the first plane 43.

[0043] FIG. 11 shows a cross section of the cage 36 taken along the third imaginary plane P3 in FIG. 7 is an imaginary plane that is perpendicular to the first imaginary plane P1 and parallel to the central axis C2. The third imaginary plane P3 traverses the concave curved surface portion 47 and the second corner curved surface portion 49 of the horn 42. In FIG. 11, the cross-sectional contour line L2 of the second corner curved surface portion 49 is an arc with a radius r3. The second corner curved surface portion 49 is a concave curved surface such that the cross-sectional contour line L2 is an arc of a constant radius r3.

[0044] When the imaginary plane P3 is moved from the edge 46a to the inner edge 42a2, the center of the arc of the cross-sectional contour line L2 is located on an arc at a certain distance in the normal direction of the imaginary plane P1, at the same axial position as the boundary between the concave curved surface portion 47 and the second corner curved surface portion 49. The radius r3 of the cross-sectional contour line L2 of the second corner curved surface portion 49 is the same as the radius r2 of the cross-sectional contour line L1 of the first corner curved surface portion . This allows the first curved corner portion 48 and the second curved corner portion 49 to be connected more smoothly. Furthermore, the radius r2 of the cross-sectional contour line L1 of the first corner curved surface portion 48 and the radius r3 of the cross-sectional contour line L2 of the second corner curved surface portion 49 are smaller than the radius r0 of the ball 35 (half the diameter).

[0045] In the radial range of the imaginary plane P1 from the outer edge 42a1 to the radially inner edge 46a of the second plane 46, the tip curved surface 45 (see FIGS. 6 and 8) on the second imaginary plane P2 is an arc with a radius r4. The center of the arc is on a straight line perpendicular to the imaginary plane P2. In addition, in the radial range of the imaginary plane P1 from the edge 46a of the second plane 46 to the inner edge 42a2, the tip curved surface 45 on the third imaginary plane P3 is an arc with a radius equal to or less than r4. The center of the arc is on a straight line perpendicular to the imaginary plane P2. The radius r4 is slightly larger than the radius r0.

[0046] According to this embodiment, the cross-sectional contour lines L1, L2 of the first corner curved surface portion 48 and the second corner curved surface portion 49 connecting the annular body 40 and the horn 42 are arcs with a radius smaller than the radius r0 of the ball 35, so the first corner curved surface portion 48 and the second corner curved surface portion 49 are farther away from the ball 35 than the inner surface of the circular pocket in the above-mentioned conventional example. Therefore, as shown in FIG. 10, a space K is secured in the first curved corner portion 48 and the second curved corner portion 49 to allow more grease to accumulate. Furthermore, the concave curved surface portion 47 is smoothly inclined toward the inside of the pocket 37 and protrudes toward the inside of the pocket 37 with respect to the second plane. Therefore, the balls 35 in the pocket 37 can be held appropriately. Furthermore, the second corner curved surface portion 49 connecting the first plane 43 and the concave curved surface portion 47 protruding inward of the pocket 37 also protrudes inward of the pocket 37 relative to the first corner curved surface portion 48. As a result, even if relative reciprocating motion occurs between the ball 35 and the pocket 37, the second corner curved surface portion 49 protruding inward of the pocket 37 can keep the accumulated grease within the pocket 37 and prevent the grease from leaking out of the space K. As a result, the grease can be effectively retained.

[0047] Furthermore, when the entire inner surface of the pocket is made cylindrically curved as in the conventional example, the male mold for forming the pocket included in the mold for injection molding the cage is designed to be removed in the radial direction. In this case, since the inner surface of the pocket is cylindrically curved, the male mold will not be removed forcibly. However, if the entire inner surface of the pocket is a cylindrically curved surface, the pocket may not be able to properly hold the balls in the radial direction, and there is a risk that the cage will move slightly in the radial direction relative to the balls. Such micro-movement of the cage must be suppressed because it can impair the stability of the bearing and cause vibrations. In this regard, according to this embodiment, the balls 35 in the pocket 37 can be appropriately held in the radial direction by the concave curved surface portion 47 that protrudes inward of the pocket 37 with respect to the second plane. As a result, the micro-movement of the cage 36 can be suppressed, and the stability of the bearing can be improved while suppressing vibration. In this embodiment, a concave curved surface portion 47 is provided on the radially inner side of the second plane 46, so even if the male mold for forming the pocket 37 is designed to be removed radially, the male mold will not be removed forcefully.

[0048] 〔others〕 The embodiments disclosed herein are illustrative in all respects and are not restrictive. For example, in the present embodiment, the radius r2 of the cross-sectional contour line L1 of the first corner curved surface portion 48 and the radius r3 of the cross-sectional contour line L2 of the second corner curved surface portion 49 are the same. However, the radius r2 of the cross-sectional contour line L1 of the first corner curved surface portion 48 and the radius r3 of the cross-sectional contour line L2 of the second corner curved surface portion 49 may be different as long as they are smaller than the radius r0 of the ball 35.

[0049] The scope of the present invention is not limited to the above-described embodiments, but includes all modifications within the scope of equivalents to the configurations described in the claims. [Explanation of symbols]

[0050] 5 Wave reducer 10 Circular Spline 11 Inner teeth 20 Flexspline 21 Outer teeth 30 Rotating Body 31 Cam 32 Ball bearing 33 Outer ring 34 Inner Circle 35 balls 36 Retainer 37 pockets 40 cyclic bodies 40a First side 42 42a Opposite side 42a1 outer edge 42a2 inner edge 43 1st plane 46 Second plane 46a Edge 47 Concave curved surface part 48 1st corner curved surface part 49 Second corner curved surface part L1 cross section contour line L2 cross section contour line P1 First virtual plane P2 Second virtual plane P3 Third virtual plane P4 virtual plane (fourth virtual plane)

Claims

1. A ball bearing for a wave reducer comprising: a circular spline having internal teeth; a flexspline provided inside the circular spline and having external teeth that mesh with the internal teeth; and a rotor provided inside the flexspline for bending the flexspline non-circularly to partially mesh the external teeth with the internal teeth, the bearing comprises an inner raceway ring that is rotatable integrally with a non-circular cam of the rotating body and is elastically deformable, an outer raceway ring that is rotatable integrally with the flexspline and is elastically deformable, a plurality of balls provided between the inner and outer raceways rings, and a cage that has a plurality of pockets formed in the circumferential direction for accommodating the balls; the cage has an annular body and a plurality of tines provided on a first axial side surface of the annular body and extending in the axial direction, and a space surrounded by the first side surface and a pair of opposing surfaces of a pair of adjacent tines among the plurality of tines is the pocket, the first side surface has a first plane that is provided between the pair of horns and faces the pocket, and is perpendicular to the central axis of the cage; Each of the pair of opposing surfaces has, between a radially outer outer edge of the opposing surface and a radially inner inner edge of the opposing surface, a second plane parallel to a first imaginary plane including the central axis and passing through circumferential centers of the pair of horns; a concave curved surface portion that smoothly slopes inwardly of the pocket from the radially inner edge of the second plane to the inner edge, a distance between the pair of second flat surfaces facing each other is greater than a diameter of the ball; the distance between the pair of inner edges is smaller than the diameter of the ball; Each of the pair of opposing surfaces further comprises: a first curved corner portion connecting the first plane and the second plane; a second corner curved surface portion connecting the first plane and the concave curved surface portion; and A cross-sectional contour of the first corner curved surface portion when the first corner curved surface portion is cut along a second imaginary plane perpendicular to the first imaginary plane and parallel to the central axis, and a cross-sectional contour of the second corner curved surface portion when the second corner curved surface portion is cut along a third imaginary plane perpendicular to the first imaginary plane and parallel to the central axis are arcs having radii smaller than the radii of the plurality of balls. Ball bearings for wave reducers.

2. The radius of the cross-sectional contour of the first curved corner portion is the same as the radius of the cross-sectional contour of the second curved corner portion. The ball bearing for a wave reducer according to claim 1.

3. The distance between the pair of inner edges is greater than the diameter dimension The ball bearing for a wave reducer according to claim 1 or 2. Diameter dimension: The diameter dimension of a cross section of the ball located on the minor axis of the inner raceway, cut by a fourth imaginary plane including the pair of inner edges, when the inner raceway is fixed to the cam and bent into an elliptical shape.

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