Thrust roller bearing

Abstract

The thrust roller bearing (10) includes a plurality of rollers (11) and a cage (12). Each cage pocket (13) includes a first side surface (31) and a second side surface (32). The rollers and the cage are configured to satisfy the following expression (1). (Y1 + Y2) / X < tan(3×π / 180) (1). Y1 represents the clearance between the first contact point (Q1) of the roller and the first side surface before skew, when the roller skews towards one side, the roller contacts the first side surface at the first contact point (Q1), Y2 represents the clearance between the second contact point (Q2) of the roller and the second side surface before skew, when the roller skews towards the one side, the roller contacts the second side surface at the second contact point (Q2), and X represents the difference between the radius (R1) of the first imaginary circle (K1) passing through the first contact point and the radius (R2) of the second imaginary circle (K2) passing through the second contact point.

Description

Technical Field

[0001] The present invention relates to a thrust roller bearing. Background Art

[0002] A thrust roller bearing can receive an axial load generated between a first member and a second member that rotate relative to each other. In particular, when the rollers of the thrust roller bearing are needle rollers, the size of the thrust roller bearing can be reduced. The thrust roller bearing also has a large load capacity and can handle high-speed rotation. The thrust roller bearing is used not only in transmission devices such as automobiles and industrial construction machinery, but also widely in other rotating devices (see Japanese Unexamined Patent Application Publication No. 2018-66501 (JP2018-66501A)). Summary of the Invention

[0003] When a thrust roller bearing (hereinafter sometimes simply referred to as "bearing") rotates, the rollers roll between the raceway surface of the first member and the raceway surface of the second member. The cylindrical rollers attempt to move linearly along the raceway surface. However, the rollers are accommodated in the pockets of the cage, and the cage regulates the movement of the rollers so that the rollers move in the circumferential direction.

[0004] The pockets of the cage are designed to have an appropriate shape so as not to impede the rotation of the rollers. That is, an appropriate gap is provided between the pockets of the cage and the outer peripheral surface of the rollers. It is desirable to hold the rollers at an ideal position in the pockets of the cage. However, the rollers may be skewed due to the gap. When the rollers are skewed, for example, the rollers may locally contact the pockets of the cage, which may cause an increase in contact pressure and an increase in sliding friction resistance. This increase in sliding friction resistance in the contact portion between the cage and the pockets of the cage hinders the reduction of the torque of the bearing.

[0005] In recent years, in order to improve the rotation efficiency, that is, to reduce the rotational loss, various types of rotating devices have required reducing the torque of the thrust roller bearing. Therefore, it is desirable to minimize the sliding friction resistance in the contact portion between the cage and the pockets of the cage. An object of the present invention is to provide a thrust roller bearing capable of maintaining the reduction of torque.

[0006] One aspect of the present disclosure relates to a thrust roller bearing, the thrust roller bearing comprising: a plurality of rollers; and a retainer. The plurality of rollers are arranged between a first raceway surface and a second raceway surface facing each other. The retainer has a plurality of retainer pockets, each retainer pocket holding the roller such that the central axis of the roller extends in the radial direction. The roller includes a cylindrical outer peripheral surface, a first end surface on the radially outer side, and a second end surface on the radially inner side. The retainer pocket includes an outer surface, an inner surface, a first side surface, and a second side surface, the outer surface having a protrusion capable of contacting the first end surface, the inner surface facing the second end surface, the first side surface on one side and facing the cylindrical outer peripheral surface, and the second side surface on the other side and facing the cylindrical outer peripheral surface. The roller and the retainer are configured to satisfy the following expression (1)

[0007] (Y1 + Y2) / X < tan(3×π / 180) (1)

[0008] where Y1 represents the clearance between the first contact point of the roller and the first side surface before skew, when the roller skews towards one side, the roller contacts the first side surface at the first contact point, Y2 represents the clearance between the second contact point of the roller and the second side surface before skew, when the roller skews towards the one side, the roller contacts the second side surface at the second contact point, and X represents the difference between the radius of a first imaginary circle around the central axis of the retainer and the radius of a second imaginary circle around the central axis of the retainer, the first imaginary circle passing through the first contact point and the second imaginary circle passing through the second contact point.

[0009] The inventors have found through their extensive research on thrust roller bearings that even when the roller skews, as long as the inclination angle of the central axis of the roller with respect to the normal rotation axis of the roller is less than 3×π / 180 radians (less than 3°), the operating torque is still prevented from becoming very large.

[0010] When the thrust roller bearing of the present disclosure rotates, in the case where the first end surface of the roller contacts the protrusion of the retainer pocket due to centrifugal force, each roller rolls on the first raceway surface and the second raceway surface. The roller may skew in the retainer pocket. However, even when the roller skews in the retainer pocket, the inclination angle of the central axis of the roller with respect to the normal rotation axis of the roller is less than 3×π / 180 radians (less than 3°) because the shapes of the roller and the retainer pocket have a relationship that satisfies expression (1). Therefore, even when the roller skews in the retainer pocket, the operating torque of the thrust roller bearing is still prevented from becoming very large. Thus, the reduction of torque is maintained.

[0011] In the thrust roller bearing, the roller may include: a cylindrical portion located at the middle of the roller in the axial direction of the roller, and the cylindrical portion is formed to have a straight generatrix; an outer convex surface portion disposed radially outside the cylindrical portion, and the outer convex surface portion is formed to have an arc-shaped generatrix; and an inner convex surface portion disposed radially inside the cylindrical portion, and the inner convex surface portion is formed to have an arc-shaped generatrix. Each of the first side surface and the second side surface may include: a recessed surface and a flat surface, the recessed surface is disposed at the middle of the cage pocket in the radial direction, and the recessed surface cannot contact the roller, the flat surface is disposed at the radially outer side and the radially inner side in the cage pocket, and the flat surface can contact the roller. A first dimension may be greater than a second dimension. The first dimension is the dimension in the radial direction from the first end face capable of contacting the protrusion to the boundary between the outer convex surface portion and the cylindrical portion. The second dimension is the dimension in the radial direction from the contact point of the protrusion and the first end face to the boundary between the flat surface at the radially outer side and the recessed surface.

[0012] In this case, the first dimension is greater than the second dimension. Therefore, when the roller is skewed, the outer convex surface portion of the roller comes into contact with the flat surface at the radially outer side of the cage pocket. Since the outer convex surface portion is formed to have an arc-shaped generatrix, the roller and the cage contact each other (point contact) in a manner that generates a contact ellipse in the radially outer region of the cage pocket. Therefore, the sliding friction resistance in the contact portion between the roller and the cage is reduced, and a reduction in torque is achieved.

[0013] In the thrust roller bearing, the outer convex surface portion may include a first portion and a second portion, the first portion is adjacent to the cylindrical portion, and the first portion is defined by an arc-shaped generatrix having a first radius of curvature, the second portion is adjacent to the first portion, and the second portion is defined by an arc-shaped generatrix having a second radius of curvature, and the second radius of curvature is smaller than the first radius of curvature. A third dimension may be smaller than the second dimension. The third dimension is the dimension in the radial direction from the first end face capable of contacting the protrusion to the boundary between the first portion and the second portion.

[0014] In this case, the first portion of the outer convex surface portion of the roller contacts the flat surface at the radially outer side of the cage pocket. The radius of curvature of the arc-shaped generatrix of the first portion is greater than the radius of curvature of the arc-shaped generatrix of the second portion. Therefore, a relatively large contact ellipse is generated between the flat surface and the first portion. Therefore, the surface pressure in the contact portion between the roller and the cage is reduced, and wear is suppressed.

[0015] According to the present invention, the operating torque of the thrust roller bearing is prevented from becoming extremely large, and the reduction in torque is maintained. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

[0017] Figure 1 is a cross-sectional view showing an example of a thrust roller bearing;

[0018] Figure 2 is a perspective view of a part of a cage that holds rollers;

[0019] Figure 3 is a view showing the cage pockets and the rollers in a cross-section perpendicular to the central axis of the thrust roller bearing and including the central axis of the rollers;

[0020] Figure 4 is a view of the cage pockets of the cage as viewed from one side in the axial direction;

[0021] Figure 5 is a view of the cage pockets of the cage as viewed from the other side in the axial direction;

[0022] Figure 6 is a cross-sectional view showing the rollers in an inclined state;

[0023] Figure 7 is a cross-sectional view showing the rollers in an inclined state;

[0024] Figure 8 is a view of the cage pockets and the rollers in a cross-section perpendicular to the central axis of the thrust roller bearing and including the central axis of the rollers; and

[0025] Figure 9 is a graph showing the torque ratio of the thrust roller bearing. DETAILED DESCRIPTION

[0026] Description of the Overall Structure of the Thrust Roller Bearing

[0027] Figure 1 is a cross-sectional view showing an example of a thrust roller bearing. Figure 1 The thrust roller bearing 10 (sometimes simply referred to as "bearing 10" hereinafter) shown in includes an annular cage 12 and a plurality of rollers 11. The bearing 10 of the present disclosure further includes: an annular first bearing ring (outer cover washer) 5, which is located on one side of the bearing 10 in the axial direction ( Figure 1 the upper side in ); and an annular second bearing ring (shaft washer) 6, which is located on the other side of the bearing 10 in the axial direction (Figure 1 lower side in

[0028] The first bearing ring 5 and the second bearing ring 6 rotate relative to each other about the central axis C0 of the bearing 10. In the present disclosure, the direction along the central axis C0 of the bearing 10 is referred to as the "axial direction". The axial direction includes directions parallel to the central axis C0. The direction perpendicular to the central axis C0 is the "radial direction about the central axis C0" and is simply referred to as the "radial direction" herein. The circumferential direction about the central axis C0, i.e., the direction of relative rotation, is the "circumferential direction of the bearing 10" and is simply referred to as the "circumferential direction". In the present disclosure, it is assumed that the central axis of the cage 12 matches the central axis C0 of the bearing 10.

[0029] The first bearing ring 5 includes an annular first body 5a and a short cylindrical first rib 5b extending from the radially outer end of the first body 5a toward the other side in the axial direction. The first body 5a has a flat annular first raceway surface 7 on the other side of the first body 5a in the axial direction. The second bearing ring 6 includes an annular second body 6a and a short cylindrical second rib 6b extending from the radially inner end of the second body 6a toward the one side in the axial direction. The second body 6a has a flat annular second raceway surface 8 on the one side of the second body 6a in the axial direction. The cage 12 and the rollers 11 are disposed between the first raceway surface 7 and the second raceway surface 8. When the bearing 10 rotates, the rollers 11 held by the cage 12 roll on the first raceway surface 7 and the second raceway surface 8.

[0030] In the bearing 10, the first bearing ring 5 and the second bearing ring 6 may be omitted. In this case, although not shown in the drawings, a first member included in the device in which the bearing 10 is installed serves as a substitute for the first bearing ring 5, and a second member included in the device serves as a substitute for the second bearing ring 6. The first member has an annular first raceway surface 7, and the second member has an annular second raceway surface 8.

[0031] Figure 2 is a perspective view showing a part of the cage 12 that holds the rollers 11. The cage 12 has a plurality of cage pockets 13. The cage pockets 13 are arranged in a radial pattern about the central axis C0 (see Figure 1 ). The cage 12 includes: an inner annular member 38 disposed on the radially inner side; an outer annular member 39 disposed on the radially outer side; and a plurality of cage bars 40 connecting the inner annular member 38 and the outer annular member 39. The space surrounded by the cage bars 40, the inner annular member 38, and the outer annular member 39 that are adjacent to each other in the circumferential direction is the cage pocket 13.

[0032] Each roller 11 has a cylindrical shape. In Figure 1 and Figure 2 , the roller 11 has a first end face 21 on the radially outer side, a second end face 22 on the radially inner side, and an outer peripheral surface 20 of the roller 11. The roller 11 of the present disclosure may be a needle roller, or may be a cylindrical roller or a long cylindrical roller. A single roller 11 is received in each cage pocket 13. The roller 11 is held in each cage pocket 13 such that the central axis C1 of the roller 11 matches the radial direction.

[0033] As described above, in the bearing 10 of the present disclosure, the rollers 11 are arranged between the first raceway surface 7 and the second raceway surface 8 facing each other. The cage 12 has a plurality of cage pockets 13. Each cage pocket 13 holds the roller 11 such that the central axis C1 of the roller 11 extends in the radial direction. There is an appropriate gap between the outer peripheral surface 20 of the roller 11 and the cage bar 40. The roller 11, the first bearing ring 5, and the second bearing ring 6 are made of steel. Although the cage 12 may be made of metal (steel), the cage 12 of the present disclosure is made of resin, thereby reducing the sliding friction resistance.

[0034] Description of the cage pocket 13 and the roller 11

[0035] The shape of the roller 11 will be further described. Figure 3 Shown are the cage pocket 13 and the roller 11 in a cross-section perpendicular to the central axis C0 of the bearing 10 (see Figure 1 ) and including the central axis C1 of the roller 11. The roller 11 has a cylindrical portion 15 in the middle and outer convex portions 16 and inner convex portions 17 located on the respective sides of the cylindrical portion 15.

[0036] The cylindrical portion 15 is a portion located in the middle of the roller 11 in the axial direction and is formed to have a straight generatrix. The outer peripheral surface 15a of the cylindrical portion 15 has a cylindrical shape parallel to the central axis C1 of the roller 11. The outer convex portion 16 is a portion provided adjacent to the cylindrical portion 15 (specifically, radially outside the cylindrical portion 15) and is formed to have an arcuate generatrix. The outer peripheral surface 16a of the outer convex portion 16 has a shape such that the diameter gradually decreases toward the first end face 21. The inner convex portion 17 is a portion provided adjacent to the cylindrical portion 15 (specifically, radially inside the cylindrical portion 15) and is formed to have an arcuate generatrix. The outer peripheral surface 17a of the inner convex portion 17 has a shape such that the diameter gradually decreases toward the second end face 22.

[0037] The outer peripheral surface 15a of the cylindrical portion 15, the outer peripheral surface 16a of the outer convex portion 16, and the outer peripheral surface 17a of the inner convex portion 17 are included in the outer peripheral surface 20 of the roller 11.

[0038] The convex outer surface 16 is composed of two parts. That is, the convex outer surface 16 has a first part 26 adjacent to the cylindrical part 15 and a second part 27 adjacent to the first part 26. The outer peripheral surface of the first part 26 is formed to have an arc-shaped generatrix with a first radius of curvature r1 in a cross section including the central axis C1 of the roller 11. The outer peripheral surface of the second part 27 is formed to have an arc-shaped generatrix with a second radius of curvature r2 in a cross section including the central axis C1 of the roller 11, and the second radius of curvature r2 is smaller than the first radius of curvature r1. The outer peripheral surface 15a of the cylindrical part 15 and the outer peripheral surface of the first part 26 are connected to each other in a differentiable manner in a cross section including the central axis C1 of the roller 11. The outer peripheral surface of the first part 26 and the outer peripheral surface of the second part 27 are connected to each other in a differentiable manner in a cross section including the central axis C1 of the roller 11.

[0039] The concave inner surface 17 is composed of two parts. That is, the concave inner surface 17 has a third part 28 adjacent to the cylindrical part 15 and a fourth part 29 adjacent to the third part 28. The outer peripheral surface of the third part 28 is formed to have an arc-shaped generatrix with a third radius of curvature r3 in a cross section including the central axis C1 of the roller 11. The outer peripheral surface of the fourth part 29 is formed to have an arc-shaped generatrix with a fourth radius of curvature r4 in a cross section including the central axis C1 of the roller 11, and the fourth radius of curvature r4 is smaller than the third radius of curvature r3. The outer peripheral surface 15a of the cylindrical part 15 and the outer peripheral surface of the third part 28 are connected to each other in a differentiable manner in a cross section including the central axis C1 of the roller 11. The outer peripheral surface of the third part 28 and the outer peripheral surface of the fourth part 29 are connected to each other in a differentiable manner in a cross section including the central axis C1 of the roller 11. In the present embodiment, the first radius of curvature r1 and the third radius of curvature r3 have the same value, and the second radius of curvature r2 and the fourth radius of curvature r4 have the same value.

[0040] Figure 4 The retainer pocket 13 of the retainer 12 is shown as viewed from one side in the axial direction. Figure 5 The retainer pocket 13 of the retainer 12 is shown as viewed from the other side in the axial direction. In Figure 4 and Figure 5 the roller 11 is shown by a hidden contour (double-dot chain line). The retainer pocket 13 is an area surrounded by an outer surface 33, an inner surface 34, and a pair of side surfaces 31, 32.

[0041] The outer surface 33 is configured by the radially inner surface of the outer annular member 39. The outer surface 33 has a protrusion 37, and the protrusion 37 has a curved surface. The protrusion 37 can contact the first end face 21 of the roller 11. The protrusion 37 of the present disclosure has a curved surface conforming to a spherical surface as the contact surface with the roller 11. The radially innermost position of the curved surface of the protrusion 37 is located on an imaginary plane that is at the same distance from the opposing surfaces of the retainer bars 40 adjacent to each other in the circumferential direction. When the bearing 10 rotates, the roller 11 attempts to move radially outward due to centrifugal force. Therefore, the first end face 21 of the roller 11 forms a point contact with the protrusion 37, thereby positioning the roller 11 in the radial direction. The inner surface 34 is constituted by the radially outer surface of the inner annular member 38. The inner surface 34 faces the second end face 22 of the roller 11.

[0042] The first side surface 31 on one side in the circumferential direction is constituted by such a surface of the retainer bar 40 that is located on one side of the roller 11 in the circumferential direction and faces the other side in the circumferential direction. The first side surface 31 faces the outer peripheral surface 20 of the roller 11. The second side surface 32 on the other side in the circumferential direction is constituted by such a surface of the retainer bar 40 that is located on the other side of the roller 11 in the circumferential direction and faces the one side in the circumferential direction. The second side surface 32 faces the outer peripheral surface 20 of the roller 11.

[0043] As Figure 4 shown, a pair of first protrusions 41 are provided in each retainer pocket 13 so as to face each other in the circumferential direction. Each first protrusion 41 is provided at the middle portion of the retainer bar 40 in the radial direction. Each first protrusion 41 is provided on one side of the retainer bar 40 in the axial direction so as to protrude in the circumferential direction. The interval between the pair of first protrusions 41 in the retainer pocket 13 is smaller than the diameter of the roller 11. Therefore, the first protrusions 41 prevent the roller 11 accommodated in the retainer pocket 13 from falling off toward one side in the axial direction.

[0044] As Figure 5 shown, a pair of second protrusions 42 are provided in each retainer pocket 13 so as to face each other in the circumferential direction. Each second protrusion 42 is provided on the radially outer side of the retainer bar 40. Each second protrusion 42 is provided on the other side of the retainer bar 40 in the axial direction so as to protrude in the circumferential direction. The interval between the second protrusions 42 is smaller than the diameter of the roller 11. Therefore, the second protrusions 42 prevent the roller 11 accommodated in the retainer pocket 13 from falling off toward the other side in the axial direction. As Figure 5As shown in the figure, a pair of third protrusions 43 are provided in each retainer pocket 13, facing each other in the circumferential direction. Each third protrusion 43 is provided on the radially inner side of the retainer bar 40. Each third protrusion 43 is provided on the other side of the retainer bar 40 in the axial direction, protruding in the circumferential direction. The interval between the pair of third protrusions 43 is smaller than the diameter of the roller 11. Therefore, the third protrusion 43 prevents the roller 11 accommodated in the retainer pocket 13 from falling off toward the other side in the axial direction.

[0045] Figure 3 The state where the central axis C2 extending in the radial direction of the retainer pocket 13 and the central axis C1 of the roller 11 are matched with each other (hereinafter referred to as the "aligned state") is shown. The central axis C2 of the retainer pocket 13 is a line extending in the radial direction at the radially innermost position including the protrusion 37 on the imaginary plane, and the imaginary plane is positioned at the same distance from the opposing surfaces of the retainer bars 40 adjacent to each other in the circumferential direction. In this state, the roller 11 protrudes beyond the surface on one side of the retainer 12 in the axial direction and also protrudes beyond the surface on the other side of the retainer 12 in the axial direction. In this state, there is a gap between the outer peripheral surface 20 of the roller 11 and each of the side surfaces 31, 32 of the retainer pocket 13. The first side surface 31 on one side in the circumferential direction of the retainer pocket 13 has a recessed surface 35a in the middle and flat surfaces 36a, 36b on the respective sides of the recessed surface 35a. Similarly to the first side surface 31 on one side in the circumferential direction, the second side surface 32 on the other side in the circumferential direction has a recessed surface 35b in the middle and flat surfaces 36c, 36d on the respective sides of the recessed surface 35b. The first side surface 31 and the second side surface 32 have the same structure, and the first side surface 31 on one side in the circumferential direction will be described as an example below.

[0046] The flat surface 36a is a surface that is disposed radially outside in the retainer pocket 13 and can contact the roller 11. The flat surface 36b is a surface that is disposed radially inside in the retainer pocket 13 and can contact the roller 11. The recessed surface 35a is disposed in the middle of the retainer pocket 13 in the radial direction. The recessed surface 35a is a surface that is more recessed than the flat surfaces 36a and 36b and cannot contact the roller 11. The recessed surface 35a includes an outer inclined surface 45, an inner inclined surface 46, and an intermediate surface 47 disposed between the outer inclined surface 45 and the inner inclined surface 46. The outer inclined surface 45 is inclined such that the circumferential width of the retainer pocket 13 gradually increases from the flat surface 36a on the radially outer side. The inner inclined surface 46 is inclined such that the circumferential width of the retainer pocket 13 gradually increases from the flat surface 36b on the radially inner side. In the aligned state, the flat surfaces 36a, 36b, and the intermediate surface 47 are parallel to the central axis C1 of the roller 11. Each of the flat surfaces 36a, 36b except for the second protrusion 42 or the third protrusion 43 is constituted by a surface that is flat in the radial direction and the axial direction (see Figure 4 and Figure 5 ).

[0047] The convex circular portion (round chamfer) 48 is disposed at the boundary B2 between the flat surface 36a on the radially outer side and the recessed surface 35a (outer inclined surface 45). The convex circular portion (round chamfer) 49 is disposed at the boundary B5 between the flat surface 36b on the radially inner side and the recessed surface 35a (inner inclined surface 46). Regarding the circular portions at the boundaries B2, B5, the second side surface 32 on the other side in the circumferential direction has a configuration similar to that of the first side surface 31 on one side in the circumferential direction. That is, the convex circular portion 48 is disposed at the boundary B2 between the flat surface 36c on the radially outer side and the recessed surface 35b, and the convex circular portion 49 is disposed at the boundary B5 between the flat surface 36d on the radially inner side and the recessed surface 35b. The dimensions of the circular portions 48, 49 (i.e., the dimensions of the round chamfers) are, for example, 1 mm or more and 5 mm or less.

[0048] Figure 6 The state in which the central axis C1 of the roller 11 is inclined with respect to the central axis C2 extending in the radial direction of the retainer pocket 13 is shown (hereinafter referred to as the "non-aligned state"). When the roller 11 skews in the retainer pocket 13, the non-aligned state is generated. In the present disclosure, the term "skew" means that the roller 11 is inclined with respect to the normal rotation axis of the roller 11. The normal rotation axis matches the central axis C2 of the retainer pocket 13. When the bearing 10 rotates, the first end face 21 of the roller 11 comes into contact with the protrusion 37 of the retainer pocket 13 due to centrifugal force, and the roller 11 rolls on the first raceway surface 7 and the second raceway surface 8 (see Figure 1 ). AsFigure 6 As shown, when the roller 11 is tilted in the cage pocket 13, in the case where the first end face 21 of the roller 11 contacts the protrusion 37, the outer convex surface portion 16 of the roller 11 contacts the flat surface 36a, and the inner convex surface portion 17 of the roller 11 contacts the flat surface 36d. In this state, the roller 11 is located in the cage pocket 13 and rotates.

[0049] Figure 7 Shows the cage pocket 13 and the roller 11 in a cross section perpendicular to the central axis C0 (see Figure 1 ) of the bearing 10 and including the central axis C1 of the roller 11. Similar to Figure 6 Similarly, Figure 7 Shows a state where the central axis C1 of the roller 11 is inclined with respect to the central axis C2 extending in the radial direction of the cage pocket 13. That is, Figure 7 Shows that the roller 11 has skewed towards one side.

[0050] As described above, each of the outer convex surface portion 16 and the inner convex surface portion 17 is formed to have an arc-shaped generatrix. When the roller 11 is skewed in the cage pocket 13, the outer convex surface portion 16 makes a point contact with the flat surface 36a of the first side surface 31, and the inner convex surface portion 17 makes a point contact with the flat surface 36d of the second side surface 32. As will be further described later, the outer convex surface portion 16 and the inner convex surface portion 17 contact (point contact) the flat surface 36a and the flat surface 36d in a manner that produces a contact ellipse. The first contact point Q1 refers to the contact point between the outer convex surface portion 16 and the flat surface 36a, and the second contact point Q2 refers to the contact point between the inner convex surface portion 17 and the flat surface 36d.

[0051] Figure 8 Shows the cage pocket 13 and the roller 11 in a cross section perpendicular to the central axis C0 (see Figure 1 ) of the bearing 10 and including the central axis C1 of the roller 11. Figure 8 Shows the alignment state (the state before skewing). As Figure 8 Shown, there are predetermined gaps (Y1, Y2) between each of the first side surface 31 and the second side surface 32 of the cage pocket 13 and the outer peripheral surface 20 of the roller 11. The shape (i.e., the gap) of the cage pocket 13 with respect to the shape of the roller 11 is designed to satisfy the following expression (1).

[0052] (Y1 + Y2) / X < tan(3×π / 180) (1)

[0053] In expression (1), Y1, Y2, and X are defined as follows (see Figure 8 ).

[0054] Y1: The clearance between the first contact point Q1 and the first side surface 31 (flat surface 36a) before skew;

[0055] Y2: The clearance between the second contact point Q2 and the second side surface 32 (flat surface 36d) before skew;

[0056] X: The difference between the radius R1 of the first imaginary circle K1 passing through the first contact point Q1 around the central axis C0 of the retainer 12 and the radius R2 of the second imaginary circle K2 passing through the second contact point Q2 around the central axis C0 of the retainer 12.

[0057] That is to say, Y1 represents the clearance between the first contact point Q1 of the roller 11 and the first side surface 31 before skew. When the roller 11 skews towards one side, the roller 11 contacts the first side surface 31 at the first contact point Q1. Y2 represents the clearance between the second contact point Q2 of the roller 11 and the second side surface 32 before skew. When the roller 11 skews towards one side, the roller 11 contacts the second side surface 32 at the second contact point Q2. As Figure 8 shown, the first contact point Q1 for defining Y1 is the position before skew, and the second contact point Q2 for defining Y2 is the position before skew. X is given by the expression "(R1 - R2)".

[0058] When the roller 11 skews towards the other side (i.e., the side opposite to the Figure 7 side shown), the convex outer surface 16 forms a point contact (third contact point Q3) with the flat surface 36c of the second side surface 32, and the convex inner surface 17 forms a point contact (fourth contact point Q4) with the flat surface 36b of the first side surface 31. In the Figure 8 state before skew shown, the clearance between the third contact point Q3 and the second side surface 32 (flat surface 36c) has the same value as Y2, and the clearance between the fourth contact point Q4 and the first side surface 31 (flat surface 36b) has the same value as Y1. The first imaginary circle K1 passes through the third contact point Q3, and the second imaginary circle K2 passes through the fourth contact point Q4.

[0059] Figure 9 is a graph showing the torque ratio (running torque ratio) of the bearing 10. This graph is obtained through experiments. The abscissa of the graph represents the angle β by which the central axis C1 of the roller 11 is inclined with respect to the normal rotation axis of the roller 11 (see Figure 7)。The angle β is an angle (sub-angle) formed by the central axis C2 extending in the radial direction of the retainer pocket 13 and the inclined central axis C1 of the roller 11. The ordinate represents the torque ratio assuming that the rotational resistance of the bearing 10 is "1" when the angle β is 3.5×π / 180 radians (3.5°). As Figure 9 shown, when the angle β becomes greater than 3×π / 180 radians (3°), the torque ratio increases rapidly, that is, the rotational resistance of the bearing 10 increases. On the other hand, when the angle β is less than 3×π / 180 radians (less than 3°), the torque ratio is relatively low, that is, the rotational resistance of the bearing 10 is small.

[0060] As described above, the inventors found through extensive research and experiments that even when the roller 11 is skewed, as long as the angle β is less than 3×π / 180 radians (less than 3°), the operating torque is prevented from becoming very large.

[0061] When the shapes of the roller 11 and the retainer pocket 13 have a relationship that satisfies Expression (1), even when the roller 11 is skewed in the retainer pocket 13 as Figure 7 shown, the angle β is less than 3×π / 180 radians (less than 3°). Therefore, even when the roller 11 is skewed, the operating torque of the bearing 10 is still prevented from becoming very large. Thus, the reduction of the torque is maintained.

[0062] Preferably, Y1 and Y2 are set such that X is as large as possible within the range that satisfies Expression (1). This is because when the moment for skewing the roller 11 is constant, the contact force acting between the roller 11 and the retainer 12 can be reduced by increasing X. Therefore, the sliding friction resistance generated due to the contact between the roller 11 and the retainer 12 is further reduced.

[0063] Referring back to Figure 3 , the dimensions of each part of the roller 11 and the retainer pocket 13 will be described. The first dimension Z1 of the roller 11 defined as follows is larger than the second dimension Z2 of the retainer pocket 13 defined as follows (Z1 > Z2).

[0064] First dimension Z1: The dimension in the radial direction from the first end face 21 of the roller 11 that can contact the protrusion 37 of the retainer pocket 13 to the boundary B1 between the outer convex portion 16 and the cylindrical portion 15.

[0065] Second dimension Z2: The dimension in the radial direction from the contact point P1 between the protrusion 37 of the retainer pocket 13 and the first end face 21 of the roller 11 to the boundary B2 (the boundary B2 is the boundary between the flat surface 36a (36c) on the radially outer side and the recessed surface 35a (35b)).

[0066] As described above, the first dimension Z1 is greater than the second dimension Z2. Therefore, as Figure 6 shown in Figure 6 , when the bearing 10 rotates and the roller 11 tilts in the cage pocket 13, the convex outer surface portion 16 of the roller 11 comes into contact with the flat surface 36a on the radially outer side of the cage pocket 13. As described above, the convex outer surface portion 16 is formed to have an arcuate generatrix. Therefore, the convex outer surface portion 16 of the roller 11 contacts (point contact) the flat surface 36a of the cage pocket 13 in a manner that produces a contact ellipse. This configuration reduces the sliding frictional resistance in the contact portion between the roller 11 and the cage 12 and achieves a reduction in torque.

[0067] For example, although not shown in the figures, when the rotation direction of the bearing 10 is reversed and the roller 11 tilts in a direction opposite to the Figure 6 direction shown in Figure 6 , the convex outer surface portion 16 comes into contact with the opposite flat surface 36c. Also in this case, the convex outer surface portion 16 of the roller 11 contacts (point contact) the flat surface 36c of the cage pocket 13 in a manner that produces a contact ellipse.

[0068] In the present disclosure (see Figure 3 ), a third dimension Z3 defined as follows is less than the second dimension Z2 (Z3 < Z2).

[0069] Third dimension Z3: The dimension in the radial direction from the first end face 21 that can contact the protrusion 37 to the boundary B3 between the first portion 26 and the second portion 27 of the convex outer surface portion 16.

[0070] With this configuration, as Figure 6 shown in Figure 6 , the tilt angle of the roller 11 is very small (less than 3°). Therefore, the first portion 26 of the convex outer surface portion 16 of the roller 11 contacts the flat surface 36a of the cage pocket 13. As described above, the radius of curvature of the arcuate generatrix of the first portion 26 is greater than the radius of curvature of the arcuate generatrix of the second portion 27 (r1 > r2). Therefore, a relatively large contact ellipse is generated between the flat surface 36a and the first portion 26. Accordingly, the specific load in the contact portion between the roller 11 and the cage 12 is reduced, and wear is suppressed. This configuration satisfies "the first dimension Z1 > the second dimension Z2 > the third dimension Z3".

[0071] In the present disclosure (see Figure 3 ), a fourth dimension Z4 of the roller 11 defined as follows is less than a fifth dimension Z5 of the cage pocket 13 defined as follows (Z4 < Z5).

[0072] Fourth dimension Z4: The dimension in the radial direction from the first end face 21 of the roller 11 that can contact the protrusion 37 of the cage pocket 13 to the boundary B4 between the concave inner surface portion 17 and the cylindrical portion 15.

[0073] Fifth dimension Z5: The dimension in the radial direction from the contact point P1 between the projection 37 of the cage pocket 13 and the first end face 21 of the roller 11 to the boundary B5 (the boundary B5 is the boundary between the flat surface 36d on the radially inner side and the recessed surface 35b).

[0074] As described above, the fourth dimension Z4 is smaller than the fifth dimension Z5. Therefore, as Figure 6 shown, when the bearing 10 rotates and the roller 11 tilts in the cage pocket 13, the inner convex surface portion 17 of the roller 11 comes into contact with the flat surface 36d on the radially inner side. As described above, the inner convex surface portion 17 is formed to have an arc-shaped generatrix. Therefore, the inner convex surface portion 17 of the roller 11 contacts (point contact) the flat surface 36d of the cage pocket 13 in a manner that generates a contact ellipse. This configuration reduces the sliding friction resistance in the contact portion between the roller 11 and the cage 12 and achieves a reduction in torque.

[0075] For example, although not shown in the figure, when the rotation direction of the bearing 10 is reversed and the roller 11 tilts in the direction opposite to that Figure 6 shown, the inner convex surface portion 17 comes into contact with the opposite flat surface 36b. Also in this case, the inner convex surface portion 17 of the roller 11 contacts (point contact) the flat surface 36b of the cage pocket 13 in a manner that generates a contact ellipse.

[0076] In the present disclosure (see Figure 3 ), the sixth dimension Z6 defined as follows is larger than the fifth dimension Z5 (Z6>Z5).

[0077] Sixth dimension Z6: The dimension in the radial direction from the first end face 21 that can contact the projection 37 to the boundary B6 between the third portion 28 and the fourth portion 29 of the inner convex surface portion 17.

[0078] With this configuration, as Figure 6 shown, the tilt angle of the roller 11 is very small (less than 3°). Therefore, the third portion 28 of the inner convex surface portion 17 of the roller 11 contacts the flat surface 36d of the cage pocket 13. As described above, the radius of curvature of the arc-shaped generatrix of the third portion 28 is larger than the radius of curvature of the arc-shaped generatrix of the fourth portion 29 (r3>r4). Therefore, a relatively large contact ellipse is generated between the flat surface 36d and the third portion 28. Therefore, the surface pressure in the contact portion between the roller 11 and the cage 12 is reduced, and wear is suppressed. This configuration satisfies "the fourth dimension Z4 < the fifth dimension Z5 < the sixth dimension Z6".

[0079] In Figure 3As described above, the convex circular portion 48 is provided at the boundary B2 between the flat surface 36a on the radially outer side of the retainer pocket 13 and the recessed surface 35a. Therefore, even when the outer convex surface portion 16 of the roller 11 contacts the boundary B2, no edge load is applied. As described above, the convex circular portion 49 is provided at the boundary B5 between the flat surface 36d on the radially inner side of the retainer pocket 13 and the recessed surface 35b. Therefore, even when the inner convex surface portion 17 of the roller 11 contacts the boundary B5, no edge load occurs.

[0080] In Figure 3 According to the configuration in which the first dimension Z1 > the second dimension Z2 and the fourth dimension Z4 < the fifth dimension Z5, when the first end face 21 of the roller 11 contacts the protrusion 37, the cylindrical portion 15 of the roller 11 exists within the radial range of the recessed surface 35a (35b) in the retainer pocket 13. Therefore, as Figure 6 As shown in, when the bearing 10 rotates and the roller 11 tilts in the retainer pocket 13, the outer convex surface portion 16 and the inner convex surface portion 17, both formed with an arcuate generatrix, come into contact with the flat surfaces 36a, 36d on the radially outer side and the radially inner side of the retainer pocket 13. As described above, each of the outer convex surface portion 16 and the inner convex surface portion 17 is formed with an arcuate generatrix. Therefore, the roller 11 and the retainer 12 are in point contact with each other on the radially outer side and the radially inner side in a manner that generates a contact ellipse. This configuration reduces the sliding friction resistance in the contact portion between the roller 11 and the retainer 12 and achieves a reduction in torque.

[0081] As described above, in the thrust roller bearing 10 according to the present disclosure, the sliding friction resistance in the contact portion between the roller 11 and the retainer 12 is reduced. Thereby, a reduction in the torque of the thrust roller bearing 10 is achieved. In addition, an increase in temperature due to the sliding contact between the roller 11 and the retainer 12 is suppressed.

[0082] The embodiments disclosed herein are illustrative rather than restrictive in all respects. The scope of the present invention is not limited to the above embodiments, but includes all variations included in the scope equivalent to the configuration described in the claims.

Claims

1. A thrust roller bearing (10), comprising: A plurality of rollers (11) arranged between a first raceway surface (7) and a second raceway surface (8) facing each other, wherein the first raceway surface (7) is flat and annular, and the second raceway surface (8) is flat and annular; and A cage (12) having a plurality of cage pockets (13), each cage pocket (13) holding the roller (11) such that the central axis (C1) of the roller (11) extends in the radial direction. The roller (11) includes a cylindrical outer peripheral surface (20), a first end surface (21) on the radially outer side, and a second end surface (22) on the radially inner side. The cage pocket (13) includes an outer surface (33), an inner surface (34), a first side surface (31), and a second side surface (32). The outer surface (33) has a protrusion (37) capable of contacting the first end surface (21). The inner surface (34) faces the second end surface (22). The first side surface (31) is on one side and faces the cylindrical outer peripheral surface (20). The second side surface (32) is on the other side and faces the cylindrical outer peripheral surface (20), wherein The roller (11) and the cage (12) are configured to satisfy the following expression (1) (Y1 + Y2) / X < tan(3×π / 180) (1) Where Y1 represents the clearance between the first contact point (Q1) of the roller (11) and the first side surface (31) before skew. When the roller (11) skews towards one side, the roller (11) contacts the first side surface (31) at the first contact point (Q1), Y2 represents the clearance between the second contact point (Q2) of the roller (11) and the second side surface (32) before skew. When the roller (11) skews towards the one side, the roller (11) contacts the second side surface (32) at the second contact point (Q2), and X represents the difference between the radius (R1) of a first imaginary circle (K1) around the central axis (C0) of the cage (12) and the radius (R2) of a second imaginary circle (K2) around the central axis (C0) of the cage (12). The first imaginary circle (K1) passes through the first contact point (Q1), and the second imaginary circle (K2) passes through the second contact point (Q2), Characterized in that: The roller (11) includes a cylindrical portion (15), an outer convex surface portion (16), and an inner convex surface portion (17). The cylindrical portion (15) is located in the middle of the roller (11) in the axial direction of the roller (11), and the cylindrical portion (15) has a straight generatrix. The outer convex surface portion (16) is disposed radially outside the cylindrical portion (15), and the outer convex surface portion (16) has an arc-shaped generatrix. The inner convex surface portion (17) is disposed radially inside the cylindrical portion (15), and the inner convex surface portion (17) has an arc-shaped generatrix. Each of the first side surface (31) and the second side surface (32) includes a recessed surface (35a, 35b) and a flat surface (36a, 36b, 36c, 36d). The recessed surface (35a, 35b) is provided in the middle of the retainer pocket (13) in the radial direction, and the recessed surface (35a, 35b) cannot contact the roller (11). The flat surface (36a, 36b, 36c, 36d) is provided on the radially outer side and the radially inner side of the retainer pocket (13), and the flat surface (36a, 36b, 36c, 36d) can contact the roller (11), and A first dimension (Z1) is greater than a second dimension (Z2). The first dimension (Z1) is the dimension in the radial direction from the first end face (21) that can contact the protrusion (37) to the boundary (B1) between the outer convex surface portion (16) and the cylindrical portion (15). The second dimension (Z2) is the dimension in the radial direction from the contact point (P1) of the protrusion (37) and the first end face (21) to the boundary (B2) between the flat surface (36a, 36c) on the radially outer side and the recessed surface (35a, 35b).

2. The thrust roller bearing (10) according to claim 1, wherein: The outer convex surface portion (16) includes a first portion (26) and a second portion (27). The first portion (26) is adjacent to the cylindrical portion (15), and the first portion (26) is defined by an arc-shaped generatrix having a first radius of curvature (r1). The second portion (27) is adjacent to the first portion (26), and the second portion (27) is defined by an arc-shaped generatrix having a second radius of curvature (r2). The second radius of curvature (r2) is smaller than the first radius of curvature (r1); and A third dimension (Z3) is smaller than the second dimension (Z2). The third dimension (Z3) is the dimension in the radial direction from the first end face (21) that can contact the protrusion (37) to the boundary (B3) between the first portion (26) and the second portion (27).

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