Crown-shaped retainer and ball bearing using the same

Abstract

To provide a resin-made crown-shaped retainer which exhibits low deformation due to centrifugal force during rotation and is suppressed from being damaged during ball incorporation.SOLUTION: An annular portion 5 of a retainer 4 is formed of a first resin with carbon fibers blended in PA9T, and a claw portion 6b is formed of a second resin with glass fibers blended in PA66, respectively. The blending ratio of the carbon fibers in the first resin and the blending ratio of the glass fibers in the second resin are adjusted such that the claw portion 6b has a smaller flexural modulus than that of the annular portion 5. Thus, even during high-speed rotation, deformation of the retainer 4 due to centrifugal force is suppressed, strong contact with the ball is avoided to reduce heat generation, and stress applied to the retainer 4 during ball incorporation is reduced, thereby preventing damage to the claw portion 6b.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a resin crown cage and a ball bearing using the crown cage. [Background technology]

[0002] In the technical field of electric vehicles, there is a movement to increase the rotation speed of electric motors while making them smaller and lighter to increase the output density of the motors as a means of reducing electricity costs and improving driving performance. However, when trying to increase the speed of electric motors, the centrifugal force acting on the internal parts of the rolling bearings that support the rotating shaft to which the rotation of the motor is input increases with the increase in rotation speed, and the resulting increased deformation of the internal parts makes them more susceptible to various problems.

[0003] In particular, in a ball bearing (see, for example, Patent Document 1) incorporating a resin crown-shaped cage (hereinafter also simply referred to as a "cage"), the inner surface of the pocket of the cage has a spherical shape that holds the balls, which are the rolling elements, and the dmn value (ball pitch circle diameter dm (mm) × rotation speed n (min -1 When used under high load conditions, the cage is easily deformed by centrifugal force. The deformed cage's inner pockets come into contact with the balls, generating heat, which can lead to seizure and other problems that can cause the bearing to fail.

[0004] On the other hand, if a resin that is less likely to deform is used to form the retainer in order to suppress heat generation in the ball bearing, there is a risk that the claws protruding from the tips of the cantilever-shaped columns that form the pockets will crack or chip when the balls are inserted into the pockets of the retainer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3035766 Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a resin crown cage which is less deformed by centrifugal force during rotation and which is less susceptible to damage when balls are assembled, and a ball bearing incorporating such a crown cage. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides a resin crown cage comprising an annular portion and a number of column portions extending from the annular portion at equal intervals in the circumferential direction to one side in the axial direction, and a pocket formed by the annular portion and the column portions adjacent to each other in the circumferential direction for accommodating balls of a ball bearing, and the column portions have a pair of claw portions opposed to each other in the circumferential direction protruding to one side in the axial direction from the axial tip of a column portion main body continuing from the annular portion, wherein the annular portion and the claw portions are formed from different types of resin, each of which is made by blending a reinforcing material with a base resin, and the bending elastic modulus of the claw portions is smaller than the bending elastic modulus of the annular portion (structure 1).

[0008] In the crown cage of configuration 1 described above, by making the annular portion highly rigid, deformation due to centrifugal force during rotation is reduced, and even when the cage is rotated at high speed while assembled into a ball bearing, strong contact with the balls is not made and heat generation can be suppressed. Moreover, when the balls are assembled, the claw portion, which has a lower rigidity than the annular portion, deforms naturally, so that large stress is not applied to the cage and damage to the claw portion can be prevented.

[0009] Here, the reinforcing material of the annular portion and the claw portion may be fibrous (Configuration 2). Specifically, for example, the reinforcing material of the annular portion may be carbon fiber, and the reinforcing material of the claw portion may be glass fiber (Configuration 3).

[0010] In any of the above configurations 1 to 3, the base resin of the annular portion may be polyamide 9T, and the base resin of the claw portion may be polyamide 66 (configuration 4).

[0011] In addition, in any of the above configurations 1 to 4, the column body can be configured so that the entire column body is formed from the same resin as the annular portion (configuration 5), or both circumferential side portions of the column body are formed from the same resin as the claw portions (configuration 6).

[0012] In any of the above configurations 1 to 6, the flexural modulus of the annular portion is preferably 7.8 GPa or more (configuration 7).In the configuration 3, the blending ratio of carbon fiber in the resin forming the annular portion is preferably 7.5 wt% or more (configuration 8).

[0013] In any of the above configurations 1 to 8, the flexural modulus of the claw portion is preferably 19.6 GPa or less (configuration 9).In the configuration 3, the blending rate of glass fiber in the resin forming the claw portion is preferably 65 wt% or less (configuration 10).

[0014] The present invention also provides a ball bearing comprising an outer ring, an inner ring arranged radially inward of the outer ring, a plurality of balls arranged to roll freely between the outer ring and the inner ring, and a resin crown cage for holding the plurality of balls, wherein the crown cage employs any one of the above configurations 1 to 10 (configuration 11). Effect of the Invention

[0015] As described above, in this invention, the annular portion and the claw portion of the crown-shaped cage of a ball bearing are formed from different types of resin, each of which is made by mixing a reinforcing material with a base resin, and the flexural modulus of the claw portion is made smaller than the flexural modulus of the annular portion.This reduces deformation due to centrifugal force during high-speed rotation and reduces heat generation due to contact with the balls, and also reduces the stress on the cage when the balls are installed, preventing damage to the claw portion. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a front sectional view of a ball bearing according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a perspective view showing the difference in the types of resins used to form the various parts of the cage shown in FIG. [Diagram 3] FIG. 2 is a perspective view showing a schematic diagram of different types of resins forming the various parts of the modified example of the cage shown in FIG. [Figure 4] Graph showing an example of the relationship between the reinforcement compounding ratio of a resin and the flexural modulus DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As shown in Fig. 1, this ball bearing is a deep groove ball bearing including an outer ring 1 with a raceway surface 1a formed on its inner peripheral surface, an inner ring 2 arranged radially inside the outer ring 1 and with a raceway surface 2a formed on its outer peripheral surface, a plurality of balls 3 arranged to roll freely between the raceway surface 1a of the outer ring 1 and the raceway surface 2a of the inner ring 2, and a resin crown cage 4 that holds the plurality of balls 3 at equal intervals so that they can roll freely,

[0018] Here, the central axes (not shown) of the outer ring 1, the inner ring 2 and the cage 4 are arranged coaxially and correspond to the bearing central axis, which is the design center of rotation of the ball bearing. Hereinafter, the central axis of the cage 4 will be simply referred to as the "central axis."

[0019] The axial direction refers to the direction along the central axis, one axial side is the right side in Fig. 1, and the other axial side is the left side in Fig. 1. The radial direction refers to the direction perpendicular to the central axis. The radially outward direction refers to the direction moving away from the central axis in the radial direction, and the radially inward direction refers to the direction moving closer to the central axis in the radial direction. The circumferential direction refers to the direction along the circumference that goes around the central axis.

[0020] 1 and 2, the cage 4 is composed of an annular portion 5 extending in the circumferential direction and a number of pillar portions 6 extending from the annular portion 5 at equal intervals in the circumferential direction to one side in the axial direction, and pockets 7 for accommodating the balls 3 are formed between adjacent pillar portions 6 in the circumferential direction. The pockets 7 are spaces that open to the radially outer side, the radially inner side, and one axial side, and the same number of pockets 7 are formed as the pillar portions 6.

[0021] The column portion 6 of the cage 4 has a column body 6a that is continuous with the annular portion 5, and from the axial tip of the column body 6a, a pair of claw portions 6b that face each other in the circumferential direction protrude to one side in the axial direction.

[0022] Moreover, the inner surface of the pocket 7 is spherical so as to embrace the ball 3, and the openings on the radially outer side, the radially inner side, and one axial side are sized not to pass the ball 3. Therefore, when assembling the ball bearing, the ball 3 is stored in the pocket 7 by pressing the pillar portions 6 of the cage 4 from the other axial side against the ball 3 arranged between the raceway surface 1a of the outer ring 1 and the raceway surface 2a of the inner ring 2, thereby elastically deforming the pillar portions 6 (mainly the claw portions 6b), so that the opening on one axial side of the pocket 7 expands in the circumferential direction, allowing the ball 3 to enter the pocket 7.

[0023] Here, the retainer 4 is formed of two types of resin (a first resin and a second resin), and in FIG. 2, for the sake of explanation, the portion formed of the first resin and the portion formed of the second resin are separated by imaginary lines, and the portion formed of the second resin is shown with a dot pattern (the same applies to FIG. 3 described below).

[0024] 2, in the cage 4, the annular portion 5 and the column body 6a of the column portion 6 are formed from a first resin, and a pair of claw portions 6b of the column portion 6 are formed from a second resin. The cage 4 is formed by a typical two-color molding method, in which the first resin is formed first and then the second resin.

[0025] In addition, while FIG. 2 shows an example in which the entire pillar body 6a of the pillar 6 is formed from the first resin, as in a modified example shown in FIG. 3, only the circumferential center portion of the pillar body 6a may be formed from the first resin, and both circumferential side portions may be formed from the second resin.

[0026] Both the first and second resins are made by blending a fibrous reinforcing material into a base resin, with the first resin being made of polyamide 9T (PA9T) as the base resin blended with carbon fiber as a reinforcing material, and the second resin being made of polyamide 66 (PA66) as the base resin blended with glass fiber as a reinforcing material. The reasons for the above-mentioned composition of the first and second resins and the blending ratio of the reinforcing material in each resin are explained below.

[0027] First, the inventors of this invention focused on the flexural modulus of a typical resin crown cage and investigated the relationship between deformation due to centrifugal force during rotation and deformation during ball installation. The flexural modulus is a value that indicates the resistance to deformation due to bending load, and is defined in JIS K7171 (2022) and ISO178 (2019). As a result of the investigation, they found that if the flexural modulus of the annular portion is 7.8 GPa or more, strong contact between the cage and the balls during high-speed rotation can be avoided, and if the flexural modulus of the claw portion is 19.6 GPa or less, damage is unlikely to occur during ball installation.

[0028] However, since measuring the flexural modulus of the annular part and claw part of a small crown-shaped cage is extremely time-consuming, we considered using the reinforcement blending ratio as a substitute for the flexural modulus in a resin in which a reinforcement is blended into the base resin, and investigated the correlation between the two. Note that the reinforcement blending ratio in a resin can be calculated by using a thermogravimetric differential thermal analyzer (TG-DTA) or similar to thermally decompose a test piece and burn off the base resin, then measuring the weight of the residue and calculating it as the ratio of the weight of the residue to the weight of the test piece before thermal decomposition.

[0029] As an example of the results of the above investigation, Figure 4 shows the relationship between the compounding ratio of the reinforcing material and the flexural modulus of a resin in which the base resin is made of the common cage material polyphenylene sulfide (PPS) or polyamide resin, and carbon fiber or glass fiber is compounded as the reinforcing material. Figure 4 shows that the behavior of the flexural modulus differs greatly depending on the type of reinforcing material, and that while it is easier to increase the flexural modulus with carbon fiber than with glass fiber, there is a high correlation between the compounding ratio and the flexural modulus of each reinforcing material.

[0030] Therefore, in this embodiment, the first resin forming the annular portion 5 is PA9T blended with carbon fiber, and the second resin forming the claw portion 6b is PA66 blended with glass fiber. Since the bending modulus of the annular portion 5 is preferably 7.8 GPa or more as described above, the blending rate of carbon fiber in the first resin is set to 7.5 wt% or more from the regression line A shown by a solid line in FIG. 4. On the other hand, since the bending modulus of the claw portion 6b is preferably 19.6 GPa or less as described above, the blending rate of glass fiber in the second resin is set to 65 wt% or less from the regression line B shown by a dashed line in FIG. 4. The blending rate of the reinforcing material in each resin is actually set so that the bending modulus of the claw portion 6b is smaller than the bending modulus of the annular portion 5 within the above range.

[0031] As the base resin for the first resin and the second resin, in addition to the above-mentioned PPS and polyamide resins, polyether ether ketone (PEEK), polyimide, etc. can be used. In addition, in order to respond to the recent green transformation (GX), bioplastics and biodegradable plastics can also be used.

[0032] In the ball bearing of this embodiment, the annular portion 5 and the claw portion 6b of the retainer 4 are formed from the first resin and the second resin, respectively, as described above. Therefore, heat generation due to contact between the retainer 4 and the balls 3 is small even during high-speed rotation. In addition, the balls 3 can be fitted efficiently during assembly, making it less likely for the retainer 4 to crack or chip, and the bearing can be used stably for a long period of time.

[0033] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0034] For example, the types of base resin and reinforcing material in the first resin forming the annular portion of the retainer and the second resin forming the claw portion, and the reinforcing material mixing ratio are not limited to those in the embodiment, and can be modified in various ways as long as the condition that the bending modulus of the claw portion is smaller than the bending modulus of the annular portion is satisfied.

[0035] Furthermore, the present invention is not limited to deep groove ball bearings as in the above-described embodiments, but can also be applied to angular contact ball bearings incorporating a crown cage. [Explanation of symbols]

[0036] 1 Outer ring 2. Inner Circle 3. Ball 4 Cage 5 Circular ring 6 Pillar section 6a Pillar body 6b Claw part 7 Pocket

Claims

1. A resin crown cage (4) comprising an annular portion (5) and a plurality of column portions (6) extending from the annular portion (5) at equal intervals in the circumferential direction to one side in the axial direction, the cage comprising pockets (7) formed by the annular portion (5) and the column portions (6) adjacent to each other in the circumferential direction for accommodating balls (3) of a ball bearing, the column portions (6) having a pair of claw portions (6b) opposed to each other in the circumferential direction protruding from axial tips of column portion bodies (6a) continuing to the annular portion (5) in the axial direction to one side in the axial direction, The annular portion (5) and the claw portion (6b) are formed from different types of resins, each of which is a base resin mixed with a reinforcing material, The cage (4) is characterized in that the flexural modulus of the claw portion (6b) is smaller than the flexural modulus of the annular portion (5).

2. 2. The cage according to claim 1, wherein the reinforcing material of said annular portion and said claw portion is fibrous.

3. 3. The cage according to claim 2, wherein the reinforcing material of said annular portion is carbon fiber, and the reinforcing material of said claw portion is glass fiber.

4. 4. The cage according to claim 1, wherein the base resin of said annular portion is polyamide 9T, and the base resin of said claw portion is polyamide 66.

5. 4. The cage according to claim 1, wherein the column body (6a) is entirely made of the same resin as the annular portion (5).

6. 4. The cage according to claim 1, wherein both circumferential side portions of said column body (6a) are formed from the same resin as said claw portions (6b).

7. 4. The cage according to claim 1, wherein the annular portion has a flexural modulus of elasticity of 7.8 GPa or more.

8. 4. The cage according to claim 3, wherein the resin forming said annular portion (5) contains carbon fiber at a blending rate of 7.5 wt % or more.

9. 4. The cage according to claim 1, wherein the claw portion has a flexural modulus of elasticity of 19.6 GPa or less.

10. 4. The cage according to claim 3, wherein the resin forming said claw portion (6b) contains glass fiber at a content of 65 wt % or less.

11. 4. A ball bearing comprising an outer ring (1), an inner ring (2) arranged radially inside the outer ring, a plurality of balls (3) arranged to roll freely between the outer ring (1) and the inner ring (2), and a resin crown-shaped cage (4) for holding the plurality of balls (3), wherein the crown-shaped cage (4) is as defined in any one of claims 1 to 3.

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