Ball bearing

Abstract

The present invention avoids, during an operation of a ball bearing including a crown-shaped resin retainer, interference between the resin retainer and a bearing ring while suppressing a load on the resin retainer due to lag of progressing balls. When a pocket diameter on a circumferential cut surface of the resin retainer (4) is dc, a pocket diameter on a radial cut surface of the resin retainer (4) is dr, and a diameter of the ball (3) is Da, Da < dr < 1.07 Da ≤ dc is satisfied.

Description

ball bearing

[0001] The present invention relates to a ball bearing, and more particularly to a ball bearing having a cage formed in a crown shape from resin.

[0002] Conventionally, ball bearings for high-speed rotation have employed crown-shaped resin cages that are relatively lightweight and have excellent self-lubricating properties (see, for example, Patent Documents 1 and 2).

[0003] A crown-shaped resin cage houses balls in pockets that are open on the inner and outer periphery and on one axial side of the cage. Generally, the resin surface that forms the pockets is spherical. The diameter of the spheres in the spherical surface is set larger than the diameter of the balls to provide pocket clearance between the resin cage and the balls.

[0004] JP 2007-263280 A JP 2011-117609 A

[0005] However, the load and lubrication conditions imposed on ball bearings are becoming stricter every year. If the lead / lag of the balls during ball bearing rotation becomes larger than the pocket clearance, the lead balls will press hard against the column sections of the crown-shaped resin cage, and the column sections will press hard against the lagging balls, placing a load on the resin cage. While it is possible to avoid such loads by increasing the spherical diameter of the pocket shape and setting a larger pocket clearance, this also increases the amount by which the resin cage can move freely radially relative to the balls, reducing the radial clearance between the resin cage and the raceway ring, which can easily cause interference between the two.

[0006] In view of the above background, the problem to be solved by this invention is to suppress the load on the resin cage due to the advance / delay of the balls when a ball bearing having a crown-shaped resin cage is in operation, while avoiding interference between the resin cage and the raceway rings.

[0007] In order to solve the above problems, the present invention employs Configuration 1, which is a ball bearing comprising an inner ring, an outer ring, a plurality of balls arranged between the inner ring and the outer ring, and a resin cage that houses the balls in a plurality of pockets that open to one axial side, wherein when the pocket diameter on a circumferential cross section of the resin cage is dc, the pocket diameter on a radial cross section of the resin cage is dr, and the diameter of the balls is Da, the ball bearing is characterized in that Da < dr < 1.07 Da ≦ dc is satisfied.

[0008] According to the above configuration 1, since 1.07 Da≦dc is satisfied, the pocket clearance is unlikely to become insufficient in the circumferential direction in response to the advance / delay of the balls when the ball bearing is in operation, and the load on the crown-shaped resin cage can be suppressed. In addition, since Da<dr<1.07 Da is satisfied, the pocket clearance is not too large in the radial direction relative to the balls, and interference with the raceways (inner ring, outer ring) due to radial movement of the resin cage can be avoided.

[0009] In the above configuration 1, configuration 2 can be adopted in which the bearing is operated under usage conditions that satisfy the following: when the basic dynamic load rating is C and the dynamic equivalent load is P, the value of the radial load (C / P) is 0.17 or less, the value of the axial load (C / P) is 0.30 or less, and the value of the misalignment of the relative inclination between the inner ring and the outer ring is 1 / 300 (mm / mm) or less.

[0010] According to the above configuration 2, the lead / lag of the balls does not become larger than the pocket clearance, and it is possible to prevent the lead / lag of the balls from generating a load on the resin cage.

[0011] In the above configuration 1 or 2, a configuration 3 can be adopted in which the resin cage is formed from a thermoplastic engineering plastic or a thermosetting engineering plastic.

[0012] In the above configuration 1 or 2, a configuration 4 can be adopted in which the resin cage is formed of a fiber reinforced resin.

[0013] As described above, by adopting the above-mentioned configuration 1, the present invention can suppress the load on the resin cage due to the advance / delay of the balls when operating a ball bearing equipped with a crown-shaped resin cage, while avoiding interference between the resin cage and the raceway.

[0014] 1. A partial cross-sectional view showing a circumferential cross section of a resin cage according to an embodiment of the present invention, developed. A cross-sectional view showing a ball bearing equipped with the resin cage of FIG. 1. A partial perspective view of a pocket of FIG. 1. A graph showing the relationship between the lead / lag of balls and the pocket shape in a ball bearing according to an embodiment. A graph showing the relationship between the radial movement of the resin cage and the pocket shape in a ball bearing according to an embodiment.

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A ball bearing according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0016] The ball bearing shown in Figures 1 to 3 (hereinafter simply referred to as "this ball bearing") comprises an inner ring 1, an outer ring 2, a plurality of balls 3 arranged between the inner ring 1 and the outer ring 2, and a crown-shaped resin cage 4 that holds these balls 3.

[0017] Hereinafter, the direction along the bearing center axis (not shown, same below) of this ball bearing will be referred to as the "axial direction," the direction perpendicular to the bearing center axis will be referred to as the "radial direction," and the circumferential direction going around the center axis will be referred to as the "circumferential direction."

[0018] The inner ring 1 and the outer ring 2 are single-row raceway rings for radial bearings, each having a raceway groove 1a, 2a along the circumferential direction. The raceway groove 1a, 2a has a radial groove depth relative to the outer diameter surface of the corresponding inner ring 1 or the inner diameter surface of the corresponding outer ring 2.

[0019] The resin retainer 4 is an annular resin part that forms pockets 4a at equal intervals in the circumferential direction, and is composed of a circular ring portion 4b that is continuous around the entire circumference, and multiple pillar portions 4c, 4c that extend cantilever-like from the circular ring portion 4b to one side in the axial direction.

[0020] The pocket 4a is made up of an annular portion 4b and a plurality of pillar portions 4c extending cantilever-like from the annular portion 4b toward one axial side, and is a portion formed between adjacent pillar portions 4c in the circumferential direction to accommodate the balls 3. The pocket 4a is open on the inner periphery, outer periphery, and one axial side surface of the resin cage 4. The opening on one axial side of the pocket 4a is an opening for passing the balls 3 between the circumferentially adjacent pillar portions 4c and 4c to place them in the pocket 4a.

[0021] The entire resin cage 4 is formed seamlessly by injection molding of resin. For example, a thermoplastic engineering plastic, a thermosetting engineering plastic, or a fiber-reinforced resin can be used as the resin.

[0022] Here, the engineering plastic may be at least one of a thermoplastic resin and a thermosetting resin, and may be either a crystalline resin or an amorphous resin. The synthetic resin may be primarily composed of a thermosetting resin or a thermoplastic resin, with other thermosetting resins, thermoplastic resins, rubber, glass fiber (GF), carbon fiber, carbon black, graphite, or the like added as appropriate. For example, the engineering plastic may be a resin having a heat resistance of 100°C or higher and a tensile strength of 40 MPa or higher. The fiber-reinforced resin is a composite material in which a matrix resin is used as the base material and fibers serving as a reinforcing material are mixed in a predetermined ratio. Examples of such reinforcing materials include carbon fiber and glass fiber.

[0023] A radial gap δi is provided between the resin cage 4 and the outer diameter surface of the inner ring 1. A radial gap δo is provided between the resin cage 4 and the inner diameter surface of the outer ring 2. The gaps δi and δo are set to have the same dimensions.

[0024] The resin cage 4 is provided in a rolling element guided form that is guided by the balls 3 .

[0025] Fig. 1 shows a circumferential cross section of the resin cage 4 near the pocket 4a, developed into a plane, particularly showing the state in which the balls 3 are most biased to one circumferential side in a circumferential cross section including the geometric center of the pocket 4a and the center of the balls 3. Fig. 2 shows a radial cross section of this ball bearing and resin cage 4, particularly showing a radial cross section including the geometric center of the pocket 4a and the center of the balls 3. Fig. 3 shows a perspective view of one half of the pocket 4a, circumferentially divided, viewed from one axial side and radially outward. Here, the circumferential cross section refers to a cross section on an imaginary cylindrical surface along the circumferential direction. The radial cross section refers to a cross section on an imaginary plane perpendicular to the bearing center axis. The geometric center of the pocket 4a refers to the intersection of an imaginary plane that bisects the pocket 4a in the circumferential direction, an imaginary plane that bisects the axial depth of the pocket 4a and is perpendicular to the bearing center axis, and an imaginary cylindrical surface that bisects the radial length of the pocket 4a.

[0026] Of the resin cage 4, the resin surface portions that form the pockets 4a are resin surface portions that allow contact with the balls 3 when the ball bearing rotates. In other words, the resin surface portions that form the pockets 4a are made of resin surface portions that, by contact with the balls 3, restrict the range within which the resin cage 4 can freely move in the circumferential, axial, and radial directions relative to the plurality of balls 3. For example, if a recess such as an oil groove that cannot come into contact with the balls is formed in a column portion or the like to hold or guide lubricant between the balls and the resin cage, that recessed resin surface portion does not fall under the category of a resin surface portion that forms a pocket.

[0027] A pocket gap is set between the resin surface portion that forms the pocket 4a and the ball 3. The pocket gap is provided in the circumferential direction, the radial direction, and the axial direction based on the geometric shape of the resin surface portion that forms the pocket 4a and the diameter of the ball 3.

[0028] The resin surface portion forming the pocket 4 a is not spherical with the center of sphere located at the geometric center of the pocket 4 a. As shown in Fig. 3, the resin surface portion forming the pocket 4 a has a curvature in the direction of arrow A extending from the tip end of the column portion 4 c toward the bottom of the pocket 4 a, and a curvature in the direction of arrow B extending from the outer periphery to the inner periphery of the resin cage 4, with the curvature in the direction of arrow B being set smaller than the curvature in the direction of arrow A.

[0029] Here, as shown in Fig. 1, the pocket diameter in the circumferential cross section of the resin cage 4 is dc, and as shown in Fig. 2, the pocket diameter in the radial cross section of the resin cage 4 is dr, and the diameter of the balls 3 is Da. The pocket diameters dc and dr are diameters based on the curved shape of the resin surface portion forming the pocket 4a in the corresponding circumferential cross section (see Fig. 1) or radial cross section (see Fig. 2), and correspond to a dimension obtained by doubling the radius of curvature of the curved shape.

[0030] In order to provide a pocket gap between the resin cage 4 and the balls 3, the relationship between the diameter Da of the balls 3 and the pocket diameters dc and dr (see Figures 1 and 2) is set to satisfy Da < dc and Da < dr.

[0031] In order to suppress the load on the resin cage 4 caused by the advance / delay of the balls 3 that occurs when this ball bearing rotates, the relationship between the diameter Da of the balls 3 and the pocket diameter dc is set to satisfy 1.07Da≦dc.

[0032] In this numerical analysis model of a ball bearing, typical conditions for use of a ball bearing were assumed, and the amount of lead and lag of ball 3 that occurs when ball 3 revolves in the circumferential direction under those conditions was calculated. Also, various ratios of pocket diameter dc to diameter Da of ball 3 were set, and the size of the pocket clearance in the circumferential cross section of resin cage 4 (see pocket clearance δ in Figure 1) was calculated for each ratio. A graph based on these calculation results is shown in Figure 4.

[0033] The advance or delay of ball 3 (see Figures 1 and 2 below as appropriate) occurs when the orbital speed of ball 3 changes in accordance with changes in the contact angle between ball 3 and raceway grooves 1a, 2a. The contact angle changes depending on the magnitude of the load acting on the contact point between ball 3 and raceway grooves 1a, 2a and the magnitude of the tilt misalignment between inner ring 1 and outer ring 2.

[0034] The operating conditions for the numerical analysis described above were as follows: where C is the basic dynamic load rating of this ball bearing and P is the dynamic equivalent load, the radial load (C / P) value was 0.17, the axial load (C / P) value was 0.30, and the relative misalignment between the inner ring 1 and the outer ring 2 was 1 / 300 (mm / mm). The maximum lead / lag amount of ball 3 that occurred under these operating conditions was approximately 0.8 mm circumferentially on both the lead and lag sides. The maximum lead / lag amount of ball 3 is shown by the horizontal dashed line in Figure 4.

[0035] When the amount of lead / lag of the balls 3 is less than the pocket clearance in the circumferential cross section of the resin cage 4, the lead / lag balls 3 and the column portion 4c of the resin cage 4 do not press against each other strongly, and no load is generated on the resin cage 4 due to the lead / lag of the balls 3.

[0036] As can be seen from Figure 4, the size of the pocket clearance in the circumferential cross section of the resin cage 4 is equal to the amount of lead / lag of the balls 3 when 1.07Da = dc, and is greater than the amount of lead / lag of the balls 3 when 1.07Da < dc. Therefore, it can be seen that satisfying 1.07Da ≤ dc is effective in suppressing the load on the resin cage 4 due to the lead / lag of the balls 3, whereas satisfying 1.07Da > dc makes it impossible to suppress such load.

[0037] When the aforementioned radial load (C / P) value is less than 0.17, the axial load (C / P) value is less than 0.30, and the tilt misalignment value is less than 1 / 300 (mm / mm), the lead / lag of the balls 3 will be less than the maximum value shown in Figure 4. Therefore, as long as this ball bearing is operated under conditions where the radial load (C / P) value is 0.17 or less, the axial load (C / P) value is 0.30 or less, and the relative tilt misalignment value between the inner ring and the outer ring is 1 / 300 (mm / mm) or less, no load will be generated on the resin cage 4 due to lead / lag of the balls 3.

[0038] In order to avoid interference between the resin cage 4 and the inner ring 1 and outer ring 2 by making the amount by which the resin cage 4 can freely move radially relative to the multiple balls 3 (hereinafter simply referred to as the "radial movement amount of the resin cage 4") smaller than the gaps δi and δo, the relationship between the diameter Da of the balls 3 and the pocket diameter dr is set to satisfy dr < 1.07 Da.

[0039] In the above-mentioned numerical analysis model, various ratios of the pocket diameter dr to the diameter Da of the balls 3 were set, and the radial movement of the resin cage 4 was calculated for each ratio. A graph based on these calculation results is shown in Figure 5.

[0040] The amount of radial movement of the resin cage 4 is affected by the relative size of the pocket diameter dr and the diameter Da of the balls 3. As the pocket diameter dr increases relative to the diameter Da of the balls 3, the amount of radial movement of the resin cage 4 increases. If the amount of radial movement of the resin cage 4 is smaller than the gaps δi and δo, no interference occurs between the resin cage 4 and the inner ring 1 or outer ring 2. The dimensions of the gaps δi and δo are indicated by horizontal dashed lines in Figure 5.

[0041] 5, the amount of radial movement of the resin cage 4 is equivalent to the gaps δi and δo when 1.07 Da = dr, and is smaller than the gaps δi and δo when dr < 1.07 Da. Therefore, it can be seen that if dr < 1.07 Da is satisfied, interference between the resin cage 4 and the inner ring 1 and outer ring 2 can be avoided, but if dr ≥ 1.07 Da is satisfied, such interference cannot be avoided.

[0042] As described above, this ball bearing comprises an inner ring 1, an outer ring 2, a plurality of balls 3 arranged between the inner ring 1 and the outer ring 2, and a resin cage 4 that houses the balls 3 in a plurality of pockets 4a that open to one axial side. In particular, when the pocket diameter on a circumferential cross section of the resin cage 4 is dc, the pocket diameter on a radial cross section of the resin cage 4 is dr, and the diameter of the balls 3 is Da, the relationship Da < dr < 1.07Da ≦ dc is satisfied. As a result, when the ball bearing is in operation, the pocket clearance is unlikely to be insufficient circumferentially to accommodate the lead and lag of the balls 3, and the pocket clearance is not too large radially relative to the balls 3. As a result, it is possible to suppress the load on the crown-shaped resin cage 4 due to the lead and lag of the balls 3, while avoiding interference between the resin cage 4 and the raceways (inner ring 1, outer ring 2).

[0043] Furthermore, when this ball bearing is operated under conditions that satisfy the following conditions, where C is the basic dynamic load rating and P is the dynamic equivalent load, the radial load (C / P) value is 0.17 or less, the axial load (C / P) value is 0.30 or less, and the relative inclination misalignment value between the inner ring and the outer ring is 1 / 300 (mm / mm) or less, the lead / lag of the balls 3 does not become larger than the pocket clearance, so that it is possible to prevent load from being generated on the resin cage 4 due to lead / lag of the balls 3.

[0044] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0045] REFERENCE SIGNS LIST 1 Inner ring 2 Outer ring 3 Ball 4 Resin cage 4a Pocket 4b Annular portion 4c Bar portion Da Diameter of ball dc Pocket diameter in circumferential cross section of resin cage dr Pocket diameter in radial cross section of resin cage

Claims

1. A ball bearing comprising an inner ring, an outer ring, a number of balls arranged between the inner ring and the outer ring, and a plastic cage which houses the balls in a number of pockets which open to one axial side, wherein the pocket diameter on a circumferential cut surface of the plastic cage is dc, the pocket diameter on a radial cut surface of the plastic cage is dr, and the diameter of the balls is Da, wherein Da < dr < 1.07Da ≦ dc is satisfied.

2. A ball bearing as claimed in claim 1, which is operated under the following operating conditions: when the basic dynamic load rating is C and the dynamic equivalent load is P, the radial load (C / P) value is 0.17 or less, the axial load (C / P) value is 0.30 or less, and the relative inclination misalignment value between the inner ring and the outer ring is 1 / 300 (mm / mm) or less.

3. A ball bearing according to claim 1 or 2, wherein the resin cage is made of a thermoplastic engineering plastic or a thermosetting engineering plastic.

4. A ball bearing according to claim 1 or 2, wherein the resin cage is formed from a fiber-reinforced resin.

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