Jade Axle

Abstract

This enables the use of ball bearings with a large ratio of the ball pitch circle diameter to the ball diameter at high rotational speeds. [Solution] When the pitch circle diameter of ball 3 is D (mm) and the diameter of ball 3 is d (mm), (D / d) ≥ 5 is satisfied, the resin holder 4 is formed of a resin composition having a Young's modulus of 4700 MPa (120°C) or higher, and the number of balls 3 Z (pieces) satisfies (d × Z) / πD ≤ 0.33 with respect to the diameter of ball 3 d (mm) and the pitch circle diameter D (mm) of ball 3.

Description

Technical Field

[0001] This invention relates to ball bearings.

Background Art

[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 electricity costs, the high-speed rotation of electric motors for vehicle driving has been promoted. Along with this, ball bearings that support the rotating shafts of electric motors and ball bearings that support the rotating shafts of speed reducers that decelerate the rotation of 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 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. 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] This ball bearing of Patent Document 1 sets the axial thickness a (mm) of the portion between the pockets of the resin cage (the portion connecting the cage claw portions between the pockets adjacent in the circumferential direction in the cage annular portion) 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, reduces the axial thickness of the portion between the pockets of the resin cage), thereby reducing the weight of the resin cage. As a result, when the ball bearing rotates at high speed, deformation of the resin cage due to the centrifugal force acting on the resin cage is reduced.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Patent No. 6608151 [Overview of the Initiative] [Problems that the invention aims to solve]

[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 may 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 low, 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 a ball bearing where the ratio of the pitch circle diameter of the balls to the diameter of the balls is large, even if the axial thickness a (mm) of the portion between the pockets of the resin cage is set small as in Patent Document 1, during high-speed rotation, the cage ring portion is torsionally deformed by the centrifugal forces acting on the plurality of pairs of cage claw portions extending in a cantilever beam shape from the cage ring portion, and due to the torsional deformation of the cage ring portion, the plurality of pairs of cage claw portions are inclined radially outward respectively. As a result, the pocket forming surfaces of the cage claw portions of the resin cage strongly interfere with the balls, and it has been found that the ball bearing may generate heat.

[0012] The problem to be solved by this invention is to enable a ball bearing where the ratio of the pitch circle diameter of the balls to the diameter of the balls is large to be used at high speed rotation.

Means for Solving the Problem

[0013] To solve the above problem, this invention provides a ball bearing having the following configuration. [Configuration 1] 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 for holding the plurality of balls, The resin cage has a cage ring portion extending in the circumferential direction on one axial side of the plurality of balls, and a plurality of pairs of cage claw portions extending in a cantilever beam shape from the cage ring portion to the other axial side, Between each pair of cage claw portions, a pocket for accommodating each ball is formed, In the ball bearing where the axial minimum thickness a (mm) of the portion between the pockets, which is the portion connecting the cage claw portions adjacent in the circumferential direction among the cage ring portion, satisfies 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, When the pitch circle diameter of the balls is D (mm) and the diameter of the balls is d (mm), (D / d) ≥ 5 is satisfied, The resin cage is formed of a resin composition having a Young's modulus of 4700 MPa (120 °C) or more. The ball bearing is characterized in that the number Z (pieces) of the balls is set so as to satisfy (d×Z) / πD≦0.33 with respect to the diameter d (mm) of the balls and the pitch circle diameter D (mm) of the balls.

[0014] When this configuration is adopted, since a < c is satisfied, the axial thickness of the portion between the pockets of the resin cage is thin and the resin cage is lightweight. Therefore, the magnitude of the centrifugal force acting on the resin cage can be reduced.

[0015] Also, since (d×Z) / πD≦0.33 is satisfied, the number of balls is small and the number of cage claw portions is also small, and thus the ratio of the mass of the cage claw portions in the entire resin cage can be kept small. Therefore, when rotating at high speed, the total of the centrifugal forces acting on each of the cage claw portions holding the plurality of balls is small. In general ball bearings, (d×Z) / πD > 0.50.

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

[0017] Due to the synergistic effect of each of the above configurations, when a centrifugal force acts on the cage claw portion of the resin cage, the torsional deformation of the cage ring portion caused by the force transmitted from the cage claw portion to the cage ring portion can be effectively suppressed, and it is possible to effectively prevent the plurality of pairs of cage claw portions from inclining radially outward due to the torsional deformation of the cage ring portion.

[0018] Therefore, even in a ball bearing that satisfies (D / d)≧5, that is, a ball bearing in which the ratio of the pitch circle diameter of the balls to the diameter of the balls is large (for example, a ball bearing having a relatively low 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) or a ball bearing having a relatively large pitch circle diameter of the balls with respect to the cross-sectional height of the bearing), it is possible to effectively prevent the pocket formation surface of the cage claw portion from strongly interfering with the balls during high-speed rotation.

[0019] [Structure 2] The ball bearing according to Configuration 1, wherein when the pitch circle diameter of the ball is D (mm) and the diameter of the ball is d (mm), (D / d) ≤ 20.1 is satisfied.

[0020] [Structure 3] The ball bearing according to Configuration 1 or 2, wherein the minimum axial thickness a (mm) of the portion between the pockets of the cage ring portion is greater than the axial thickness b (mm) of the portion corresponding to the bottom of the pocket of the cage ring portion.

[0021] When this configuration is adopted, the strength of the cage ring portion can be ensured.

[0022] [Structure 4] The ball bearing according to any one of Configurations 1 to 3, wherein the resin cage is formed of a resin composition in which a fiber reinforcing material is added to any one of a polyamide resin, a polyetheretherketone resin, and a polyphenylene sulfide resin.

[0023] [Structure 5] The ball bearing of each of the above configurations is preferably used as a bearing that supports the rotating shaft of an electric motor for driving an electric vehicle or a bearing that supports the rotating shaft of a speed reducer that decelerates the rotation of the electric motor.

[0024] That is, although the bearings that support the rotating shaft of the electric motor for driving an electric vehicle or the bearings that support the rotating shaft of the speed reducer that decelerates the rotation of the electric motor rotate at a very high speed, the magnitude of the load supported by the bearings itself is very small compared to the basic dynamic rated load of a standard ball bearing (for example, several percent or less). Therefore, it is possible to set the number of balls to be small. Therefore, it is particularly suitable to adopt the ball bearing according to this invention. [Advantages of the Invention]

[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. [Brief explanation of the drawing]

[0026] [Figure 1] A view of a ball bearing according to an embodiment of this invention from the axial direction. [Figure 2] Cross-sectional view along line II-II in Figure 1 [Figure 3] Figure 1 shows the cage of a ball bearing, viewed from the axial direction. [Figure 4] Perspective view of the retainer shown in Figure 3. [Figure 5] Figure 3 shows another example of the retainer shown in Figure 3. [Figure 6] A view from the axial direction of a conventional cage used in standard ball bearings. [Figure 7] This figure shows the relationship between the number of pockets in the retainer and the amount of radial outward displacement of the tip of the retainer claw due to centrifugal deformation of the retainer. [Modes for carrying out the invention]

[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 parallel to the central axis of the outer ring 1 (the central axis of the bearing), the radial direction is perpendicular to the central axis of the outer ring 1, and the circumferential direction is 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 the 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 of 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 removing 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 (7 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 (7 in the figure).

[0036] This ball bearing is characterized by a large ratio of the pitch circle diameter of ball 3 to the diameter of ball 3. Specifically, when the pitch circle diameter of ball 3 shown in Figure 1 is D (mm) and the diameter of 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 ball 3 relative to the cross-sectional height of the bearing. The pitch circle diameter D (mm) of 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 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 ball 3 d (mm) and the pitch circle diameter D (mm) of 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 inch = 7.14375 (mm)), generally, the number of balls 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 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 this case, the pitch circle diameter D = 95.5 (mm), and the diameter of ball 3 d = 11 / 32 inch = 8.73125 (mm)), generally, the number of balls 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 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 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" defined in Japanese Industrial Standard JIS B1513-1995 ( "Diameter series" defined in International Standard ISO15:2011) 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. Note that 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, the 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 certain 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 and a<c 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 these conditions.

[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 driving an electric vehicle such as an EV (battery electric vehicle) or an HEV (hybrid electric vehicle), or a bearing that rotatably supports a rotating 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-1 When used at high rotational speeds of 1.5 million or more, there is a problem that the cage claws 8 may strongly interfere with the balls 3 due to deformation of the cage 4 caused by the centrifugal force acting on the cage 4. This problem is particularly noticeable when using ball bearings at high rotational speeds where the ratio of the pitch circle diameter D of the balls 3 to the diameter d of the balls 3 is large, for example, ball bearings with a relatively low cross-sectional height (radial height from the inner diameter of the inner ring 2 to the outer diameter of the outer ring 1) or ball bearings with a relatively large pitch circle diameter D of the balls 3 relative to the cross-sectional height of the bearing.

[0046] In other words, if the cross-sectional height of the bearing shown in Figure 2 (the radial height from the inner diameter of the inner ring 2 of the ball bearing to the outer diameter of the outer ring 1) is low, the cross-sectional height of the cage 4 positioned between the outer ring 1 and the inner ring 2 will also be lower, resulting in a decrease in the rigidity of the cage ring portion 7 that constitutes the cage 4.

[0047] Furthermore, if the pitch circle diameter D of the balls 3 in the ball bearing shown in Figure 1 is large, the diameter of the cage 4 that holds the balls 3 also increases accordingly, resulting in a greater centrifugal force acting on the cage 4 during high-speed rotation.

[0048] Thus, in the case of a ball bearing where the ratio of the pitch circle diameter D of the ball 3 to the diameter d of the ball 3 is large, specifically, a ball bearing where the pitch circle diameter D (mm) and the diameter d (mm) of the ball 3 satisfy (D / d) ≥ 5, at high-speed rotation, as shown in Figure 4, the centrifugal force acting on each of the multiple pairs of cage claws 8 that extend from the cage ring 7 in a cantilever-like manner causes the cage ring 7 to twist and deform. This torsional deformation of the cage ring 7 causes each of the cage claws 8 to tilt radially outward, resulting in a significant problem where the pocket-forming surface 10 of the cage claws 8 strongly interferes with the ball 3, potentially causing the ball bearing to overheat.

[0049] To address this problem, the ball bearing of the above embodiment sets the minimum axial thickness a (mm) of the portion 11 between the pockets of the cage ring portion 7 shown in FIG. 2 such that a < c with respect to 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. Also, the number Z (pieces) of the balls 3 is set small such that (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. Furthermore, since the cage 4 is formed of a resin composition having a Young's modulus of 4700 MPa (120°C) or more, it is possible to effectively prevent the pocket forming surface 10 of the cage claw portion 8 from strongly interfering with the balls 3 during high-speed rotation.

[0050] That is, the ball bearing of the above embodiment sets the minimum axial thickness a (mm) of the portion 11 between the pockets of the cage ring portion 7 shown in FIG. 2 such that a < c with respect to 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. Therefore, as shown in FIG. 4, the axial thickness of the portion 11 between the pockets of the cage 4 is thin and the cage 4 is lightweight. As a result, the magnitude of the centrifugal force acting on the cage 4 during high-speed rotation can be reduced.

[0051] Also, the number Z (pieces) of the balls 3 is set small such that (d × Z) / πD ≤ 0.33, preferably (d × Z) / πD ≤ 0.27, 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. Therefore, as shown in FIG. 4, the number of the cage claw portions 8 is small, and thus the ratio of the mass of the cage claw portions 8 in the entire cage 4 can be kept small. As a result, the total centrifugal force acting on each cage claw portion 8 during high-speed rotation is small.

[0052] Furthermore, since the cage 4 is formed of a resin composition having a Young's modulus of 4700 MPa (120°C) or more, the torsional rigidity of the cage ring portion 7 shown in FIG. 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 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 the 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 the 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 Z to be small. 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 with 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 present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of symbols]

[0058] 1 Outer ring 2 Inner ring 3 balls 4. Resin retainer 7. Retainer ring section 8 Cage claw part 9 pockets 11 Inter-pocket area a. Axial thickness b. Axial thickness c Axial distance d. Diameter of the ball

Claims

1. Outer ring (1) and, An inner ring (2) is positioned radially inward of the outer ring (1), A plurality of balls (3) are incorporated between the outer ring (1) and the inner ring (2), It has a resin holder (4) that holds the plurality of balls (3), The resin retainer (4) has a retainer ring portion (7) that extends circumferentially on one axial side of the plurality of balls (3), and a plurality of pairs of retainer claw portions (8) that extend cantilever-like from the retainer ring portion (7) to the other axial side, A pocket (9) for housing each of the balls (3) is formed between each pair of retainer claws (8). In a ball bearing in which 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 annular portion (7) to the center of the ball (3), When the pitch circle diameter of the ball (3) is D (mm) and the diameter of the ball (3) is d (mm), the following conditions must be met: (D / d) ≥ 5. The resin retainer (4) is formed from a resin composition having a Young's modulus of 4700 MPa (120°C) or higher. A ball bearing characterized in that the number Z of the balls (3) is set such that (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).

2. The ball bearing according to claim 1, where D (mm) is the pitch circle diameter of the ball (3) and d (mm) is the diameter of the ball (3), and (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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