Ball bearing

Abstract

When the pitch circle diameter of balls (3) is D (mm) and the diameter of the balls (3) is d (mm), (D / d) ≥ 5 is satisfied. A resin cage (4) is formed of a resin composition having a Young's modulus of 4700 MPa or more at 120 °C, and the number Z of the balls (3) satisfies (d×Z) / πD ≤ 0.33 with respect to the diameter d (mm) of the balls (3) and the pitch circle diameter D (mm) of the balls (3).

Description

Ball bearing

[0001] This invention relates to a ball bearing.

[0002] In recent years, in the field of electric vehicles such as EVs (battery electric vehicles) and HEVs (hybrid electric vehicles), in order to improve the electricity consumption, the high-speed rotation of the electric motors for vehicle running has been promoted. Along with this, ball bearings that support the rotating shafts of these electric motors and ball bearings that support the rotating shafts of speed reducers that decelerate the rotation of these electric motors are also required to be suitable for high-speed rotation.

[0003] Therefore, the applicant of the present application has already proposed the ball bearing of Patent Document 1 as a ball bearing suitable for high-speed rotation.

[0004] The ball bearing of Patent Document 1 has an outer ring, an inner ring disposed radially inside the outer ring, a plurality of balls incorporated between the outer ring and the inner ring, and a resin cage that holds the plurality of balls. The resin cage has a cage annular portion that extends in the circumferential direction on one axial side of the plurality of balls, and a plurality of pairs of cage claw portions that extend in a cantilever beam shape from the cage annular portion to the other axial side. Between each pair of cage claw portions, a pocket for accommodating each ball is formed.

[0005] In this ball bearing of Patent Document 1, the axial thickness a (mm) of the portion between the pockets of the resin cage (the portion connecting the cage claw portions between the circumferentially adjacent pockets in the cage annular portion) is set so as to satisfy a < c with respect to the axial distance c (mm) from the side surface on one axial side of the cage annular portion to the center of the ball (that is, the axial thickness of the portion between the pockets of the resin cage is made small). Thereby, the weight of the resin cage is reduced, and thus, when the ball bearing rotates at high speed, the deformation of the resin cage due to the centrifugal force acting on the resin cage is reduced.

[0006] Japanese Patent No. 6608151

[0007] The inventors of the present invention considered using ball bearings with a relatively low cross-sectional height (radial height from the inner diameter of the inner ring to the outer diameter of the outer ring) or ball bearings with a relatively large pitch circle diameter relative to the cross-sectional height, that is, ball bearings with a large ratio of the pitch circle diameter to the diameter of the balls, as bearings to support the rotating shaft of an electric motor for driving an electric vehicle or a bearing to support the rotating shaft of a reduction gear that reduces the rotation of the electric motor.

[0008] As a result of this study, it was found that in the case of ball bearings where the ratio of the ball pitch circle diameter to the ball diameter is large, even if the axial thickness a (mm) of the inter-pocket portion of the resin cage is set small, as in Patent Document 1, this alone is not sufficient to suppress the deformation of the resin cage due to centrifugal force during high-speed rotation, and there is a risk that the cage claws of the resin cage will strongly interfere with the balls.

[0009] In other words, if the cross-sectional height of the bearing (the radial height from the inner diameter of the inner ring to the outer diameter of the outer ring of the ball bearing) is low, the cross-sectional height of the resin cage positioned between the outer and inner rings will also be lower, resulting in a lower rigidity of the cage ring portion that makes up the resin cage.

[0010] Furthermore, if the pitch circle diameter of the ball bearings is large, the diameter of the resin cage that holds the balls will also be larger, resulting in a greater centrifugal force acting on the resin cage during high-speed rotation.

[0011] Therefore, in the case of ball bearings where the ratio of the ball pitch circle diameter to the ball diameter is large, even if the axial thickness a (mm) of the inter-pocket portion of the resin cage is set small, as in Patent Document 1, it has been found that at high-speed rotation, the centrifugal force acting on each of the multiple pairs of cage claws extending from the cage ring in a cantilever-like manner causes the cage ring to twist and deform. This twisting deformation of the cage ring causes each of the multiple pairs of cage claws to tilt radially outward, and as a result, the pocket-forming surfaces of the cage claws of the resin cage strongly interfere with the balls, which may cause the ball bearing to overheat.

[0012] The problem this invention aims to solve is to enable the use of ball bearings with a large ratio of the ball pitch circle diameter to the ball diameter at high rotational speeds.

[0013] To solve the above problems, this invention provides a ball bearing having the following configuration: [Configuration 1] An outer ring, an inner ring disposed radially inward of the outer ring, a plurality of balls incorporated between the outer ring and the inner ring, and a resin cage that holds the plurality of balls, wherein the resin cage has a cage ring portion extending circumferentially on one axial side of the plurality of balls, and a plurality of pairs of cage claw portions extending cantilever-like from the cage ring portion to the other axial side, a pocket for housing each ball is formed between each pair of cage claw portions, and the minimum axial thickness a (mm) of the inter-pocket portion, which is the portion of the cage ring portion that connects the cage claw portions between adjacent pockets in the circumferential direction, is set such that a < c with respect to the axial distance c (mm) from the side surface on one axial side of the cage ring portion to the center of the ball, and when the pitch circle diameter of the ball is D (mm) and the diameter of the ball is d (mm), (D / d) ≥ 5 is satisfied. The aforementioned resin cage is formed from a resin composition having a Young's modulus of 4700 MPa (120°C) or higher, and the ball bearing is characterized in that the number of balls Z is set such that (d × Z) / πD ≤ 0.33 with respect to the diameter of the ball d (mm) and the pitch circle diameter D (mm) of the ball.

[0014] By adopting this configuration, a < c is satisfied, so the axial thickness of the inter-pocket portion of the resin retainer is thin, and the resin retainer is lightweight. Therefore, the magnitude of the centrifugal force acting on the resin retainer can be reduced.

[0015] Furthermore, since (d × Z) / πD ≤ 0.33 is satisfied, the number of balls is small, and the number of cage claws is also small, which allows the ratio of the mass of the cage claws to the total mass of the resin cage to be kept small. As a result, the sum of the centrifugal forces acting on each cage claw holding multiple balls is small during high-speed rotation. For reference, in general ball bearings, (d × Z) / πD > 0.50.

[0016] Furthermore, since the resin retainer is formed from a resin composition having a Young's modulus of 4700 MPa (120°C) or higher, the torsional rigidity of the retainer ring portion of the resin retainer is sufficiently large.

[0017] The synergistic effect of the above configurations effectively suppresses torsional deformation of the retainer ring portion caused by the force transmitted from the retainer claw portion to the retainer ring portion when centrifugal force acts on the retainer claw portion of the resin retainer, and effectively prevents multiple pairs of retainer claw portions from tilting radially outward due to the torsional deformation of the retainer ring portion.

[0018] Therefore, even with ball bearings that satisfy (D / d) ≥ 5, that is, ball bearings with a large ratio of the ball's pitch circle diameter to the ball's diameter (for example, ball bearings with a relatively low cross-sectional height (radial height from the inner diameter of the inner ring to the outer diameter of the outer ring) or ball bearings with a relatively large ball's pitch circle diameter relative to the cross-sectional height), it is possible to effectively prevent the pocket-forming surface of the cage claws from strongly interfering with the balls during high-speed rotation.

[0019] [Configuration 2] A ball bearing according to Configuration 1, where D (mm) is the pitch circle diameter of the ball and d (mm) is the diameter of the ball, and (D / d) ≤ 20.1.

[0020] [Configuration 3] The ball bearing according to Configuration 1 or 2, wherein the minimum axial thickness a (mm) of the inter-pocket portion of the cage ring is such that a > b (mm) is greater than or equal to the axial thickness b (mm) of the portion of the cage ring corresponding to the bottom of the pocket.

[0021] This configuration ensures the strength of the retainer ring.

[0022] [Configuration 4] The ball bearing according to any one of Configurations 1 to 3, wherein the resin cage is formed of a resin composition obtained by adding a fiber reinforcing material to a resin material which is one of polyamide resin, polyetheretherketone resin, or polyphenylene sulfide resin.

[0023] [Configuration 5] The ball bearings in each of the above configurations are preferably used as bearings to support the rotating shaft of an electric motor for driving an electric vehicle, or as bearings to support the rotating shaft of a reduction gear that reduces the rotation of the electric motor.

[0024] In other words, although the bearings supporting the rotating shaft of the electric motor used for driving an electric vehicle, or the bearings supporting the rotating shaft of the reduction gear that reduces the rotation of the electric motor, rotate at very high speeds, the magnitude of the load supported by the bearings themselves is very small (for example, a few percent or less) compared to the basic dynamic load rating of a standard ball bearing, making it possible to set a smaller number of balls. For this reason, the ball bearing according to this invention is particularly preferable.

[0025] The ball bearing of this invention can effectively suppress torsional deformation of the cage ring portion caused by the force transmitted from the cage claw portion to the cage ring portion when centrifugal force acts on the cage claw portion of the resin cage, and can effectively prevent multiple pairs of cage claw portions from tilting radially outward due to the torsional deformation of the cage ring portion. Therefore, even in ball bearings that satisfy (D / d) ≥ 5, that is, ball bearings with a large ratio of the pitch circle diameter of the balls to the diameter of the balls (for example, ball bearings with a relatively low cross-sectional height or ball bearings with a relatively large pitch circle diameter of the balls relative to the cross-sectional height of the bearing), it is possible to effectively prevent the pocket-forming surface of the cage claw portion from strongly interfering with the balls during high-speed rotation.

[0026] Figure 1 shows a cross-sectional view of a ball bearing according to an embodiment of this invention along the line II-II in Figure 1, a view of the cage of the ball bearing shown in Figure 1 from the axial direction, a perspective view of the cage shown in Figure 3, another example of the cage shown in Figure 3, a conventional cage used in a standard ball bearing viewed from the axial direction, and a figure showing the relationship between the number of pockets in the cage and the amount of radial outward displacement of the tip of the cage claw due to centrifugal deformation of the cage.

[0027] Figure 1 shows a ball bearing according to an embodiment of the present invention. This ball bearing comprises an outer ring 1, an inner ring 2 coaxially provided radially inward of the outer ring 1, a plurality of balls 3 assembled between the outer ring 1 and the inner ring 2 at a constant interval in the circumferential direction, and a resin cage 4 (hereinafter simply referred to as "cage 4") that holds the plurality of balls 3.

[0028] The axial direction is the direction parallel to the central axis of the outer ring 1 (the central axis of the bearing), the radial direction is the direction perpendicular to the central axis of the outer ring 1, and the circumferential direction is the direction along the circumference that revolves around the central axis of the outer ring 1.

[0029] As shown in Figure 2, an outer ring raceway groove 5 is formed on the inner circumference of the outer ring 1, on which the ball 3 rolls and makes contact. The outer ring raceway groove 5 is a groove with a circular arc cross-section that extends circumferentially on the inner circumference of the outer ring 1. The outer diameter of the outer ring 1 is set to be between 60 mm and 130 mm.

[0030] An inner ring raceway groove 6 is formed on the outer circumference of the inner ring 2, into which the ball 3 rolls and makes contact. The inner ring raceway groove 6 is a groove with a circular arc cross-section that extends circumferentially around the outer circumference of the inner ring 2. The inner diameter of the inner ring 2 is set to be between 40 mm and 90 mm.

[0031] Ball 3 is in rolling contact with the outer ring raceway groove 5 and the inner ring raceway groove 6. The outer ring raceway groove 5 is formed symmetrically with respect to the axial center of the outer ring 1, and the inner ring raceway groove 6 is also formed symmetrically with respect to the axial center of the inner ring 2. This ball bearing is a deep groove ball bearing.

[0032] The retainer 4 has a retainer ring portion 7 that extends circumferentially on one axial side (right side in the figure) of the ball 3, and a plurality of retainer claw portions 8 that extend circumferentially from the retainer ring portion 7 to the other axial side (left side in the figure) between adjacent balls 3. Each retainer claw portion 8 is formed in a cantilever shape with one end on the axial side (right side in the figure) fixed to the retainer ring portion 7 and the other end on the axial side (left side in the figure) being a free end. The retainer ring portion 7 and each retainer claw portion 8 are formed seamlessly as a single unit from a resin composition in which a fiber reinforcement material is added to a resin material.

[0033] Polyamide resin (PA), polyetheretherketone resin (PEEK), and polyphenylene sulfide resin (PPS) can be used as the resin material constituting the resin composition. For polyamide resin (PA), polyamide 46 (PA46), polyamide 66 (PA66), polynonameethylene terephthalamide (PA9T), etc., can be used. As the fiber reinforcing material added to the resin material, glass fiber, carbon fiber, aramid fiber, etc., can be used. The fiber reinforcing material is blended in a proportion accounting for 10 to 50% by weight of the resin composition forming the retainer 4. The blending ratio of the fiber reinforcing material can be measured by eliminating the resin material contained in the retainer 4 using the method described in Japanese Industrial Standard JIS K7120:1987 "Thermogravimetric Analysis Method for Plastics".

[0034] The resin composition used to form the retainer 4 has a Young's modulus (modulus of elasticity) of 4700 MPa or higher at a temperature of 120°C. The Young's modulus can be measured by a ring compression test using the annular portion obtained by machining the retainer 4 as a test specimen, in accordance with the description in Hitachi Review, Vol. 34, No. 5, "Derivation of a simplified calculation formula for the deflection of an annular ring subjected to compressive load and its experimental method." Alternatively, the Young's modulus can be measured by measuring the natural frequency (resonance frequency) of the same test specimen.

[0035] As shown in Figure 1, multiple pairs (seven pairs in the figure) of retainer claws 8 are provided to correspond to multiple balls 3. The number of pairs of retainer claws 8 is the same as the number of balls 3 (seven in the figure).

[0036] This ball bearing is characterized by a large ratio of the pitch circle diameter of a ball 3 to the diameter of a ball 3. Specifically, when the pitch circle diameter of a ball 3 shown in Figure 1 is D (mm) and the diameter of a ball 3 shown in Figure 2 is d (mm), the bearing satisfies (D / d) ≥ 5.0, preferably (D / d) ≥ 7.0, and more preferably (D / d) ≥ 8.0. Examples of such ball bearings include the ball bearing shown in Figure 2, which has a low cross-sectional height (radial height from the inner diameter of the inner ring 2 to the outer diameter of the outer ring 1), and the ball bearing, which has a large pitch circle diameter D of a ball 3 relative to the cross-sectional height of the bearing. The pitch circle diameter D (mm) of a ball 3 is the diameter of a virtual circle connecting the centers of multiple balls 3 arranged in a circumferential direction. The size of the pitch circle diameter D (mm) is equal to the midpoint between the outer diameter of the outer ring 1 and the inner diameter of the inner ring 2. Furthermore, the pitch circle diameter D (mm) and the diameter d (mm) of a ball 3 are set to satisfy (D / d) ≤ 20.1. Furthermore, ((Axial width dimension of outer ring 1) / D) ≤ 0.29 is specified.

[0037] Furthermore, the distance between the centers of adjacent balls 3 in the circumferential direction, as shown in Figure 1, is set to be greater than the distance between the centers of adjacent balls 3 in the circumferential direction estimated from the Japanese Industrial Standard JIS B1518:2013 "Rolling bearings - Dynamic load rating and rated life" and catalogs issued by bearing manufacturers (for example, "Rolling Bearing General Catalog CAT. No. 2202-XI / J Issued March 6, 2014" issued by NTN Corporation). Specifically, the number of balls 3 Z (pieces) is set such that (d × Z) / πD ≤ 0.33, preferably (d × Z) / πD ≤ 0.27, and more preferably (d × Z) / πD ≤ 0.21, with respect to the diameter of the ball 3 d (mm) and the pitch circle diameter D (mm) of the ball 3. Here, (d × Z) / πD represents the ratio of the diameter d of ball 3 to the arc length (πD / Z) along the pitch circle connecting the centers of adjacent balls 3 in the circumferential direction.

[0038] For example, in the case of a standard ball bearing with an outer ring 1 having an outer diameter of 90 mm and an inner ring 2 having an inner diameter of 65 mm (specifically, a ball bearing with designation number 6913; in this case, the pitch circle diameter D = 77.5 mm, and the diameter of ball 3 d = 9 / 32 inches = 7.14375 mm), generally, the number of balls 3 Z is 19, and (d × Z) / πD = 0.557. When applying this invention to a ball bearing having the same dimensions, as shown in Figure 5, the number of balls 3 Z can be 11 or less ((d × Z) / πD ≤ 0.33), preferably 9 or less ((d × Z) / πD ≤ 0.27), and more preferably 7 or less ((d × Z) / πD ≤ 0.21), as shown in Figure 3.

[0039] Similarly, in the case of a standard ball bearing with an outer ring 1 having an outer diameter of 110 mm and an inner ring 2 having an inner diameter of 80 mm (specifically, a ball bearing with designation number 6916, in which case the pitch circle diameter D = 95.5 (mm) and the diameter of ball 3 d = 11 / 32 inches = 8.73125 (mm)), generally the number of balls 3 Z is 19, and (d × Z) / πD = 0.553. When applying this invention to a ball bearing having the same dimensions, the number of balls 3 Z can be 11 or less ((d × Z) / πD ≤ 0.33), preferably 9 or less ((d × Z) / πD ≤ 0.27), and more preferably 7 or less ((d × Z) / πD ≤ 0.21).

[0040] Furthermore, in the case of a standard ball bearing with an outer ring 1 having an outer diameter of 62 mm and an inner ring 2 having an inner diameter of 40 mm (specifically, a ball bearing with designation number 6908; in this case, the pitch circle diameter D = 51 mm and the diameter of the ball 3 d = 1 / 4 inch = 6.35 mm), the number of balls 3 Z is generally 14. When applying this invention to a ball bearing having the same dimensions, the number of balls 3 Z can be 8 or less ((d × Z) / πD ≤ 0.33), preferably 6 or less ((d × Z) / πD ≤ 0.27), and more preferably 5 or less ((d × Z) / πD ≤ 0.21).

[0041] As described above, this invention can be applied, for example, to ball bearings in which the "diameter series" ( "Diameter series" defined in International Standard ISO15:2011) defined in Japanese Industrial Standard JIS B1513-1995 is any one of 8, 9, 0, 1 (preferably any one of 8, 9, 0, and 9 in each of the above examples), and the inner diameter of the inner ring 2 is 40 mm or more and 90 mm or less. Incidentally, the size of (d×Z) / πD of a standard ball bearing as shown in FIG. 6 is larger than 0.50 and is generally about 0.55.

[0042] As shown in FIGS. 3 and 4, between each pair of cage claw portions 8, a pocket 9 for accommodating balls 3 (see FIG. 3) is formed. As shown in FIG. 4, the pocket forming surface 10 (the inner surface of the pocket 9) of the cage claw portion 8 is a concave spherical surface along the surface of the ball 3.

[0043] As shown in FIG. 4, among the cage ring portions 7, a between-pocket portion 11, which is a portion connecting the cage claw portions 8 between circumferentially adjacent pockets 9, is formed in a flat plate shape extending in the circumferential direction with a constant axial thickness.

[0044] As shown in FIGS. 2 and 4, the side surface on the other axial side (the left side in the figure) of the between-pocket portion 11 of the cage ring portion 7 is a plane perpendicular to the axial direction. As shown in FIG. 2, the minimum axial thickness a (mm) of the between-pocket portion 11 of the cage ring portion 7 satisfies a>b with respect to the axial thickness b (mm) of the portion corresponding to the bottom of the pocket 9 of the cage ring portion 7 and the axial distance c (mm) from the side surface on one axial side (the right side in the figure) of the cage ring portion 7 to the center of the ball 3, and is set to a size that satisfies a<c.

[0045] The above ball bearing can be used as a bearing that rotatably supports a rotor shaft, which is a rotational output shaft of an electric motor for running an electric vehicle such as an EV (battery electric vehicle) or an HEV (hybrid electric vehicle), or as a bearing that rotatably supports a rotational shaft of a speed reducer that decelerates the rotation output from the electric motor. The ball bearing used in this application has a dmn value (pitch circle diameter D (mm) of the ball 3 × rotational speed n (min －１When used at high speeds such that the number of

[0046] That is, when the cross-sectional height of the bearing shown in FIG. 2 (the radial height from the inner diameter of the inner ring 2 to the outer diameter of the outer ring 1 of the ball bearing) is low, the cross-sectional height of the cage 4 disposed between the outer ring 1 and the inner ring 2 also becomes low accordingly, so that the rigidity of the cage ring portion 7 constituting the cage 4 becomes low.

[0047] Also, when the pitch circle diameter D of the balls 3 of the ball bearing shown in FIG. 1 is large, the diameter of the cage 4 that holds the balls 3 also becomes large accordingly, so that the centrifugal force acting on the cage 4 during high-speed rotation becomes large.

[0048] As described above, in the case of a ball bearing in which the ratio of the pitch circle diameter D of the balls 3 to the diameter d of the balls 3 is large, specifically, a ball bearing in which the pitch circle diameter D (mm) of the balls 3 and the diameter d (mm) of the balls 3 satisfy (D / d) ≧ 5, during high-speed rotation, as shown in FIG. 4, the cage ring portion 7 is torsionally deformed by the centrifugal force acting on each of the plurality of pairs of cage claw portions 8 extending in a cantilever beam shape from the cage ring portion 7. Due to the torsional deformation of the cage ring portion 7, the cage claw portions 8 are inclined radially outward, and as a result, the pocket forming surface 10 of the cage claw portions 8 strongly interferes with the balls 3, and there is a problem that the ball bearing may generate heat.

[0049] To address this problem, the ball bearing of the above embodiment is configured such that the minimum axial thickness a (mm) of the inter-pocket portion 11 of the cage ring portion 7 shown in Figure 2 satisfies a < c with respect to the axial distance c (mm) from the side surface on one axial side (right side in the figure) of the cage ring portion 7 to the center of the ball 3, and the number of balls 3 Z (pieces) is set small enough to satisfy (d × Z) / πD ≤ 0.33 with respect to the diameter d (mm) of the ball 3 and the pitch circle diameter D (mm) of the ball 3, and furthermore, the cage 4 is formed of a resin composition having a Young's modulus of 4700 MPa (120°C) or higher, so that it is possible to effectively prevent the pocket forming surface 10 of the cage claw portion 8 from strongly interfering with the ball 3 during high-speed rotation.

[0050] In other words, in the ball bearing of the above embodiment, the minimum axial thickness a (mm) of the inter-pocket portion 11 of the cage ring portion 7 shown in Figure 2 is set such that a < c with respect to the axial distance c (mm) from the side surface on one axial side (right side in the figure) of the cage ring portion 7 to the center of the ball 3. As a result, as shown in Figure 4, the axial thickness of the inter-pocket portion 11 of the cage 4 is thin, and the cage 4 is lightweight. Therefore, the magnitude of the centrifugal force acting on the cage 4 during high-speed rotation can be reduced.

[0051] Furthermore, the number of balls 3 Z is set small so as to satisfy (d × Z) / πD ≤ 0.33, preferably (d × Z) / πD ≤ 0.27, and more preferably (d × Z) / πD ≤ 0.21 with respect to the diameter d (mm) of the balls 3 and the pitch circle diameter D (mm) of the balls 3. As a result, as shown in Figure 4, the number of retainer claws 8 is small, and this makes it possible to keep the ratio of the mass of the retainer claws 8 to the total mass of the retainer 4 small. Therefore, the sum of the centrifugal forces acting on each retainer claw 8 is small when rotating at high speed.

[0052] Furthermore, since the retainer 4 is formed from a resin composition having a Young's modulus of 4700 MPa (120°C) or higher, the torsional rigidity of the retainer ring portion 7 shown in Figure 4 is sufficiently large.

[0053] The synergistic effect of the above configurations effectively suppresses the torsional deformation of the retainer ring portion 7 caused by the force transmitted from the retainer claw portion 8 to the retainer ring portion 7 when centrifugal force acts on the retainer claw portion 8 of the retainer 4 shown in Figure 4. This effectively prevents the multiple pairs of retainer claw portions 8 from tilting radially outward due to the torsional deformation of the retainer ring portion 7.

[0054] Therefore, even with ball bearings that satisfy (D / d) ≥ 5, that is, ball bearings where the ratio of the pitch circle diameter of the ball 3 to the diameter d of the ball 3 is large (for example, ball bearings with a relatively low cross-sectional height, or ball bearings where the pitch circle diameter of the ball 3 is relatively large relative to the cross-sectional height of the bearing), it is possible to effectively prevent the pocket forming surface 10 of the cage claw portion 8 from strongly interfering with the ball 3 during high-speed rotation.

[0055] The ball bearing of this embodiment is particularly suitable for use as a bearing to support the rotor shaft of an electric motor used for driving an electric vehicle, or as a bearing to support the rotating shaft of a reduction gear that reduces the rotation of that electric motor. That is, although the bearing supporting the rotor shaft of an electric motor used for driving an electric vehicle, or the bearing supporting the rotating shaft of a reduction gear that reduces the rotation of that electric motor, rotates at very high speeds, the magnitude of the load supported by the bearing itself is very small (for example, a few percent or less) compared to the basic dynamic load rating of a standard ball bearing, so it is possible to set the number of balls 3 Z to a small number. For this reason, the ball bearing according to this embodiment is particularly suitable.

[0056] Figure 7 shows the results of an analysis of the relationship between the number of balls 3 Z (= number of pockets 9) and the amount of radial outward displacement of the tip of the cage claw portion 8 due to centrifugal deformation of the cage 4. The solid curve in the figure represents the amount of radial outward displacement of the tip of the cage claw portion 8 when a ball bearing having a cage 4 made of a resin composition with a Young's modulus of 4700 MPa (120°C) is operated at a high rotational speed where the dmn value is 1.5 million. The dashed horizontal line in the figure represents the threshold at which the pocket forming surface 10 of the cage claw portion 8 interferes with the balls 3. From these analysis results, it can be understood that by setting a small number of balls 3 Z (= number of pockets 9), the amount of radial outward displacement of the tip of the cage claw portion 8 due to centrifugal deformation of the cage 4 can be suppressed, and strong interference between the cage claw portion 8 and the balls 3 during high-speed rotation can be prevented. Although not shown in the diagram, when the Young's modulus is small, the radial displacement of the cage 4 increases, making it easier for the cage 4 to interfere with the ball 3. Therefore, the number of pockets 9 corresponding to the threshold at which the cage 4 interferes with the ball 3 decreases. If the number of pockets 9 is too small, the surface pressure applied to the ball 3 increases, raising concerns about a decrease in bearing life. For this reason, it is preferable to set the number of pockets 9 to at least 3, preferably 5 or more.

[0057] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope of equivalents of the claims are intended.

[0058] 1 Outer ring 2 Inner ring 3 Ball 4 Resin retainer 7 Retainer ring portion 8 Retainer claw portion 9 Pocket 11 Inter-pocket portion a Axial thickness b Axial thickness c Axial distance d Ball diameter

Claims

1. The device comprises an outer ring (1), an inner ring (2) positioned radially inward of the outer ring (1), a plurality of balls (3) incorporated between the outer ring (1) and the inner ring (2), and a resin retainer (4) that holds the plurality of balls (3), wherein the resin retainer (4) has a retainer annular portion (7) extending circumferentially on one axial side of the plurality of balls (3), and a plurality of pairs of retainer claw portions (8) extending cantilever-like from the retainer annular portion (7) to the other axial side, and a pocket (9) for housing each of the balls (3) is formed between each pair of retainer claw portions (8). In a ball bearing, the minimum axial thickness a (mm) of the inter-pocket portion (11), which is the portion connecting the cage claw portions (8) between adjacent pockets (9) in the circumferential direction, is set such that a < c with respect to the axial distance c (mm) from the side surface on one axial side of the cage ring portion (7) to the center of the ball (3), and when the pitch circle diameter of the ball (3) is D (mm) and the diameter of the ball (3) is d (mm), (D / d) ≥ 5 is satisfied, the resin cage (4) is formed of a resin composition having a Young's modulus of 4700 MPa (120°C) or more, and the number of balls (3) Z (pieces) is set such that (d × Z) / πD ≤ 0.33 with respect to the diameter d (mm) of the ball (3) and the pitch circle diameter D (mm) of the ball (3).

2. The ball bearing according to claim 1, wherein when the pitch circle diameter of the ball (3) is D (mm) and the diameter of the ball (3) is d (mm), (D / d) ≤ 20.

1.

3. The ball bearing according to claim 1 or 2, wherein the minimum axial thickness a (mm) of the inter-pocket portion (11) of the retainer ring portion (7) satisfies a > b with respect to the axial thickness b (mm) of the portion of the retainer ring portion (7) corresponding to the bottom of the pocket (9).

4. The ball bearing according to claim 1 or 2, wherein the resin retainer (4) is formed of a resin composition obtained by adding a fiber reinforcing material to a resin material which is one of polyamide resin, polyetheretherketone resin, or polyphenylene sulfide resin.

5. The ball bearing according to claim 1 or 2, used as a bearing for supporting the rotating shaft of an electric motor for driving an electric vehicle, or as a bearing for supporting the rotating shaft of a reduction gear that reduces the rotation of the electric motor.

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