Deep groove ball bearing

Abstract

Provided is a cage for a deep groove ball bearing, the cage being hard to be broken even under a high-speed rotating environment of an electric vehicle speed reducer and a motor that are used in an environment where a dmn value is 850,000 or more, as in an electric vehicle. The deep groove ball bearing includes the resin cage containing, as a reinforcement material, glass fibers, carbon fibers, or both. The reinforcement material has a number-average fiber length of 100 to 600 μm and a number-average fiber diameter of φ4 to φ18 μm.

Description

deep groove ball bearing

[0001] The present invention relates primarily to a cage for a ball bearing.

[0002] Deep groove ball bearings that support the motors and transmissions of hybrid and fuel cell vehicles use fiber-reinforced resin cages that contain fibers to improve durability. For example, Patent Document 1 proposes the use of a crown cage molded from a nylon resin containing 15 to 35% by weight of glass fiber for rolling bearings for automobile transmissions used in applications where dm·n≧650,000 (dm: pitch circle diameter of rolling elements, n: rotational speed).

[0003] Patent No. 4626183

[0004] In recent years, the spread of EVs has led to the advancement of motor miniaturization, and the motor support and the reducer shaft directly connected to the motor shaft are now being exposed to an even more severe environment, dm·n≧850,000, than the range specified in Patent Document 1. In such a high-speed rotation environment, the strong centrifugal force causes the toe side of the cage to deform in the outer diameter direction, causing constant interference with the rolling elements or outer ring, which can cause the bearing to heat up.

[0005] In addition, the centrifugal force generated by high-speed rotation acts on the steel balls, increasing the stress generated when they come into contact with the cage, raising concerns that this could lead to the cage breaking.

[0006] In view of the above background, the problem to be solved by this invention is to provide a cage for a deep groove ball bearing that avoids constant interference with the steel balls and outer ring due to deformation of the resin cage under high speed rotation.

[0007] In order to solve the above problems, the present invention provides a bearing comprising an inner ring, an outer ring, balls arranged between the inner ring and the outer ring, and a cage having pockets for holding the balls in the circumferential direction, dmn={(D+d) / 2}×n, where D: bearing outer diameter (mm), d: bearing inner diameter (mm), n: rotational speed (min －１In a deep groove ball bearing used in an environment where the dmn value defined in JIS C 2002-2005 is 850,000 or more, the cage is a crown-shaped cage made of resin, and the resin contains glass fiber, carbon fiber, or both as a reinforcing material, and the reinforcing material has a number average fiber length of 100 μm or more and 600 μm or less and a number average fiber diameter of φ4 μm or more and φ18 μm or less (Configuration 1).

[0008] Here, a configuration (configuration 2) can be adopted in which the cage contains 15 mass % or more and 50 mass % or less of the reinforcing material.

[0009] In addition to the configuration 1 or 2, a configuration (configuration 3) can be adopted in which the resin forming the cage is a thermoplastic resin.

[0010] Furthermore, in addition to the configuration 3, a configuration (configuration 4) can be adopted in which the thermoplastic resin is a crystalline resin.

[0011] Furthermore, in addition to the configuration 4, a configuration (configuration 5) can be adopted in which the crystalline resin is polyamide, polyphenylene sulfide, or polyether ether ketone.

[0012] In addition to the configuration 1 or 2, a configuration (configuration 6) can be adopted in which the resin forming the cage is a thermosetting resin.

[0013] Furthermore, in addition to the configuration 6, a configuration (configuration 7) can be adopted in which the thermosetting resin is a phenolic resin.

[0014] The deep groove ball bearings according to these embodiments can be used in electric vehicles, hybrid vehicles, plug-in hybrid vehicles, or fuel cell vehicles.

[0015] While glass fiber and other materials have been used as reinforcing materials, this invention uses glass fiber or carbon fiber with a number-average fiber length of 100 μm to 600 μm and a number-average fiber diameter of φ4 μm to φ18 μm, thereby improving the strength of resin cages containing sufficient amounts of glass fiber or carbon fiber. Specifically, the resin cage can have a Young's modulus of 7 GPa to 22 GPa, which suppresses deformation due to centrifugal force during high-speed rotation and also suppresses deformation upon contact with steel balls, thereby preventing cage breakage. Deep groove ball bearings for electric vehicle reducers and motors, which may be subject to environments of dmn ≥ 850,000, such as those found in electric vehicles, hybrid vehicles, plug-in hybrid vehicles, and fuel cell vehicles, can suppress deformation of the resin cage due to centrifugal force, thereby improving durability and safety in high-speed rotation environments.

[0016] 1B is an axial cross-sectional view showing an example of a deep groove ball bearing according to the present invention; FIG. 1C is an axial cross-sectional view showing the cross-sectional position of the cage in FIG. 1A changed; FIG. 1D is a perspective view of the cage used in FIGS. 1A and 1B; and FIG. 1E is a perspective view showing an example of a gate of the cage.

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A deep groove ball bearing 10 according to an embodiment of the present invention will now be described with reference to the accompanying drawings. This embodiment is directed to a deep groove ball bearing 10 having a resin cage 14 that exhibits high strength due to the inclusion of a predetermined reinforcing material.

[0018] 1A and 1B, deep groove ball bearing 10 includes inner ring 11, outer ring 12, a plurality of balls 13 arranged between inner ring 11 and outer ring 12, and a cage 14 having pockets 19 that hold balls 13 in the circumferential direction. Hereinafter, deep groove ball bearing 10 will be referred to simply as bearing 10. Furthermore, the direction along the bearing center axis of bearing 10 will be referred to as the "bearing axial direction" or simply as the "axial direction," the direction perpendicular to the axial direction will be referred to as the "bearing radial direction" or simply as the "radial direction," and the circumferential direction around the bearing center axis will be referred to as the "bearing circumferential direction" or simply as the "circumferential direction."

[0019] The inner ring 11 has a concave inner ring raceway surface 16 formed on an inner ring outer diameter surface 15. The outer ring 12 has a similarly concave outer ring raceway surface 18 formed on an outer ring inner diameter surface 17 at a position opposite to the inner ring raceway surface 16. The balls 13 are rotatably arranged between the inner ring raceway surface 16 and the outer ring raceway surface 18.

[0020] A rotating shaft (not shown) is fixed to the inner diameter of the inner ring 11, and the inner ring 11 rotates circumferentially together with the rotating shaft. The outer ring 12 is a member (not shown), such as a housing or gear, that is attached to a fixed member that bears the load from the rotating shaft. In this way, the bearing 10 rotatably supports the rotating shaft relative to the fixed member. Examples of the rotating shaft include the rotating shaft of a drive motor included in an electric vehicle or other electric transportation device, or the rotating shaft of a reducer or speed increaser included in such electric transportation device. The bearing center axis of the bearing 10 and the rotation center axis of the rotating shaft are set coaxially.

[0021] FIG. 2 shows a perspective view of the cage 14 alone. The cage 14 is a crown-shaped cage molded from a resin containing a reinforcing material. Conventional reinforcing materials have a fiber length of approximately 1,500 μm. The cage 14 has an annular base 20 and column sections 21, 21 that protrude axially from the base 20 and form a curved surface surrounding the balls 13 as pockets (pockets 19). These column sections 21, each consisting of a pair, form a concave pocket 19. The outer diameter surface of the cage 14 is a curved surface (cylindrical surface) without any steps. The outer diameter surface and inner diameter surface of the cage 14 are connected at the pockets 19.

[0022] The tip of the pillar portion 21 forms a retaining claw. The retaining claws of the pillar portions 21, 21 on both sides of the pocket 19 are curved in a direction approaching each other. Note that, in FIG. 2 , recesses 22 are formed between circumferentially adjacent pockets 19, separating the pillar portions 21, but adjacent pillar portions 21, 21 may also be connected to each other. The balls 13 held by the pockets 19 revolve between the inner ring raceway surface 16 and the outer ring raceway surface 18 while being held by the pockets 19.

[0023] The resin forming the cage 14 can be selected appropriately as needed from thermoplastic resin or thermosetting resin. In the case of thermoplastic resin, a high-strength crystalline resin is preferred because it is less likely to deform due to centrifugal force caused by bearing rotation. Specific examples of crystalline resins that are desirable from the standpoint of strength include polyamide, polyphenylene sulfide, and polyether ether ketone. As a thermosetting resin, for example, a phenolic resin is preferably used.

[0024] The resin forming the cage 14 contains a reinforcing material, which may be glass fiber or carbon fiber, or may contain both of these.

[0025] The reinforcing material must have a number-average fiber length of 100 μm or more and 600 μm or less. This number-average fiber length is the total length of all measured fibers divided by the number of fibers measured. If the fiber length is less than 100 μm, the decrease in strength, expressed as the flexural modulus or Young's modulus, becomes significant. In an expected operating environment where dmn is 850,000 or more, deformation due to centrifugal force may cause the steel balls to be cramped or interference with the outer ring may occur. On the other hand, if the fiber length exceeds 600 μm, the strength may decrease, and the stress caused by interference with the balls 13 accelerated by centrifugal force may cause fatigue failure of the cage 14. Within the above range, deformation is suppressed even in high-speed rotation environments, making the cage 14 less likely to interfere with the balls 13, enabling stable use.

[0026] The standard deviation of the fiber length is preferably not more than 500. The smaller the standard deviation, the fewer irregularly long fibers there are, which is preferable because it increases the reinforcing effect.

[0027] The reinforcing material must have a number-average fiber diameter of φ4 μm or more and φ18 μm or less. This number-average fiber diameter is the sum of the diameters of all measured fibers divided by the number of fibers measured. If the diameter is smaller than φ4 μm, the strength-improving effect as a reinforcing material may be insufficient. On the other hand, if the diameter exceeds φ18 μm, the fiber is too thick and difficult to handle as a reinforcing material.

[0028] The content of the reinforcing material in the resin forming the cage 14 is preferably 15% by mass or more and 50% by mass or less. If the content is less than 15% by mass, there is a high risk that the strength improvement effect will be insufficient even if the reinforcing material is in the above range. On the other hand, if the content exceeds 50% by mass, the resin becomes difficult to handle, and there is a high risk that the gates will become clogged during the manufacture of the cage 14, making it impossible to manufacture.

[0029] FIG. 3 shows an example of the position of the gate 31 provided in the mold when forming the cage 14 by injection molding. In the case of a single-point gate, the gate 31 is provided at a location located on one of the outer peripheries of the pillar portion 21. A resin composition 32 containing the reinforcing material and kneaded with resin is injected through the gate 31 to be molded. Note that this is just one example, and gates may be provided in multiple locations, or may be provided at locations other than the pillar portion 21. The type of gate can be selected as appropriate from among a pin gate, submarine gate, and disk gate.

[0030] The cage 14 manufactured under the above conditions preferably has a Young's modulus of 7 GPa or more and 22 GPa or less. If the Young's modulus is less than 7 GPa, deformation may become significant in an environment where dmn is 850,000 or more. On the other hand, even within the above range, it is not realistic to have a Young's modulus exceeding 22 GPa.

[0031] According to this configuration, dmn={(D+d) / 2}×n, where D: bearing outer diameter (mm), d: bearing inner diameter (mm), n: rotation speed (min －１ ) is 850,000 or more at the maximum rotational speed, deformation of the cage 14 is suppressed, enabling stable application of the bearing 10. In such an environment where dmn is 850,000 or more, the bearing 10 can be used as a bearing that supports the reducer and motor of an electric vehicle, such as an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, or a fuel cell vehicle.

[0032] The present invention will be explained in more detail below using data from actual experiments. First, the materials used will be explained. PA66+GF (a kneaded product of nylon 66 and glass fiber, glass fiber content 25% by mass) PA9T+GF (a kneaded product of nylon 9T and glass fiber, glass fiber content 30% by mass) PA66+CF (a kneaded product of nylon 66 and carbon fiber, carbon fiber content 20% by mass)

[0033] Examples 1 to 3 Using the above materials, cages having the shape shown in FIG. 2 were manufactured by injection molding. Small pieces were cut out from the manufactured cage, and the resin was burned off to recover the contained fibers. At least 30 randomly collected fibers (39 in this example) were identified and photographed. The fiber length and fiber diameter of each photographed fiber were measured. The results are shown in Table 1. In Example 1, the number-average fiber length was 290 μm with a standard deviation of 230 μm. The number-average fiber diameter was 13 μm. In Example 2, the number-average fiber length was 250 μm with a standard deviation of 150 μm. The number-average fiber diameter was 11 μm. In Example 3, the number-average fiber length was 260 μm with a standard deviation of 120 μm. The number-average fiber diameter was 6 μm.

[0034]

[0035] <Measurement of Young's Modulus> Measurement was carried out in accordance with JIS K7161 (ISO527).

[0036] REFERENCE SIGNS LIST 11 Inner ring 12 Outer ring 13 Ball 14 Cage 15 Inner ring outer diameter surface 16 Inner ring raceway surface 17 Outer ring inner diameter surface 18 Outer ring raceway surface 19 Pocket 20 Base 21 Pillar portion 22 Recessed portion 31 Gate 32 Resin composition

Claims

1. A bearing bearing comprising an inner ring (11), an outer ring (12), balls (13) arranged between the inner ring (11) and the outer ring (12), and a cage (14) having pockets (19) for holding the balls (13) in a circumferential direction, dmn={(D+d) / 2}×n, where D: bearing outer diameter (mm), d: bearing inner diameter (mm), n: rotational speed (min －１ ) is 850,000 or more, the cage (14) is a crown-shaped cage made of resin, the resin contains glass fiber, carbon fiber, or both as a reinforcing material, and the reinforcing material has a number average fiber length of 100 μm or more and 600 μm or less, and a number average fiber diameter of φ4 μm or more and φ18 μm or less.

2. The deep groove ball bearing according to claim 1, wherein the retainer contains 15 mass % or more and 50 mass % or less of the reinforcing material.

3. A deep groove ball bearing according to claim 1 or 2, wherein the resin forming the cage is a thermoplastic resin.

4. The deep groove ball bearing according to claim 3, wherein the thermoplastic resin is a crystalline resin.

5. The deep groove ball bearing according to claim 4, wherein the crystalline resin is any one of polyamide, polyphenylene sulfide, and polyether ether ketone.

6. A deep groove ball bearing according to claim 1 or 2, wherein the resin forming the cage is a thermosetting resin.

7. The deep groove ball bearing according to claim 6, wherein the thermosetting resin is a phenolic resin.

8. A vehicle which is an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, or a fuel cell vehicle, using the deep groove ball bearing according to any one of claims 1 to 7.

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