Ball bearings and bearing devices

Abstract

To realize a bearing that can be used under high-speed rotation conditions. [Solution] The ball bearing has a ball diameter Da of the ball 5, a bearing outer diameter D, a bearing inner diameter d, and a pitch circle diameter PCD, and the minimum axial thickness t of the annular portion 11 at the bottom of the pocket 12 is 15% to 30% of the ball diameter Da, the bearing inner diameter d is 25 mm to 55 mm, the bearing outer diameter D is 50 mm to 90 mm, the bearing width H is 10 mm to 20 mm, the ball diameter Da is 7 / 32 inches or less, and the ratio of the value defined as 1 / 2 the difference between the pitch circle diameter PCD and the bearing inner diameter d to the bearing inner diameter d is 10% to 20%.

Description

[Technical Field]

[0001] The present invention relates to a ball bearing and a bearing device. [Background technology]

[0002] For example, in various vehicles such as automobiles and construction machinery, as well as various industrial machines, many bearings are used in the rotating shafts of transmissions (speed-up / down gears) equipped with drive motors. The bearings used in these devices generally rotate at higher speeds than the bearings used to support shafts in general devices. Furthermore, with the recent spread of electric vehicles (EVs) and hybrid cars (HEVs), there is a demand for bearings that can handle even higher speeds.

[0003] For example, Patent Document 1 describes that in a ball bearing using a crown-type cage with a ring portion and a pocket, making the axial width of the thinnest part of the bottom thickness of the pocket 20% or more of the diameter of the ball has the effect of preventing skidding, heat generation, seizure, and damage to the cage during high-speed rotation, and reducing the agitation resistance of the lubricating oil. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-207699 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, the shape of the cage is improved to make the ball bearing compatible with higher speeds. However, there are cases where the improvement in the shape of the cage as described in Patent Document 1 alone is not enough to accommodate higher speeds, and there is a demand for ball bearings that can accommodate even higher speeds.

[0006] Therefore, an object of the present invention is to apply the bearing to conditions of higher speed rotation.

Means for Solving the Problems

[0007] In order to solve the above problems, the present invention includes an inner ring, an outer ring, balls disposed between the inner ring and the outer ring, and a cage for holding the balls along the circumferential direction. The cage includes an annular portion and a plurality of pairs of cantilevered holding claws extending on one axial side of the annular portion. In a ball bearing in which pockets for accommodating the balls are formed between each pair of the holding claws, the ball diameter Da of the balls, the bearing outer diameter D defined by the maximum outer diameter of the outer ring, the bearing inner diameter d defined by the minimum inner diameter of the inner ring, the outer ring groove bottom diameter D0, the inner ring groove bottom diameter d0, and the pitch circle diameter PCD = {D0 + d0 - gr1} / 2 calculated from the radial internal clearance median value gr1, the minimum wall thickness t of the cage in the axial direction is 15% or more and 30% or less of the ball diameter Da, the bearing inner diameter d is 25 mm or more and 55 mm or less, the bearing outer diameter D is 50 mm or more and 90 mm or less, the bearing width H of the inner ring and the outer ring in the axial direction is 10 mm or more and 20 mm or less, and the ratio of the value defined by half of the difference between the pitch circle diameter PCD and the bearing inner diameter d to the bearing inner diameter d is 10% or more and 20% or less. A ball bearing is adopted (Configuration 1).

[0008] In Configuration 1, a configuration can be adopted in which the ratio of the difference between the outer ring inner diameter D1 defined by the minimum inner diameter of the outer ring and the inner ring outer diameter d1 defined by the maximum outer diameter of the inner ring to the difference between the bearing outer diameter D and the bearing inner diameter d is 15% or more and 25% or less (Configuration 2).

[0009] In Configuration 1 or Configuration 2, a configuration can be adopted in which the ratio of the distance C from the bearing end face to the end face on the other axial side of the annular portion to the bearing width H is 20% or more and 30% or less (Configuration 3).

[0010] In any one of Configurations 1 to 3, a configuration can be adopted in which the pitch circle diameter PCD and the ball diameter Da satisfy 112 < PCD × Da < 384, and as the pitch pitch P of the balls in the bearing circumferential direction, 20 < P × Da / 2 < 34 (Configuration 4).

[0011] In any one of configurations 1 to 4, the end face on the other axial side of the annular portion may be a flat surface with no recesses over the entire area (configuration 5).

[0012] Furthermore, in any one of Configurations 1 to 5, a configuration can be adopted in which the material of the cage contains nylon resin (Configuration 6).

[0013] In any one of the configurations 1 to 6, the dmn value is the pitch circle diameter PCD×n, where n is the rotation speed (min -1 ) can be used at least intermittently when the dmn value specified in the above is within the range of motor use conditions and is 650,000 or more (Configuration 7).

[0014] In addition, in any one of configurations 1 to 6, a configuration can be adopted in which the ball diameter Da is 7 / 32 inches or less (configuration 8).

[0015] A bearing device using the ball bearing according to any one of configurations 1 to 8 can be employed to rotatably support the rotary shaft of a drive motor (configuration 9). [Effects of the Invention]

[0016] According to the present invention, a bearing that can be used under conditions of higher speed rotation can be realized. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a front view showing an embodiment of the present invention. [Figure 2A] II-II cross section of Figure 1 [Figure 2B] Enlarged view of the main part of Figure 2A [Figure 3] Enlarged view of the main part of Figure 2A [Figure 4] Enlarged perspective view of the main part of the cage [Figure 5] Enlarged plan view of the cage [Figure 6] FIG. 10 is a longitudinal cross-sectional view showing another embodiment. [Figure 7]FIG. 10 is a longitudinal cross-sectional view showing yet another embodiment. [Figure 8] FIG. 10 is a longitudinal cross-sectional view showing yet another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] A rolling bearing 1 according to an embodiment of the present invention will now be described with reference to the drawings. The rolling bearing 1 is a ball bearing, and as shown in FIGS. 1 to 3, comprises an inner ring 3, an outer ring 2, a plurality of rolling elements 5 arranged between the inner ring 3 and the outer ring 2, and a cage 10 that holds the rolling elements 5 in the circumferential direction. In this embodiment, spherical elements (steel balls) are used as the rolling elements 5, and these will be referred to hereinafter as balls 5. This ball-bearing type rolling bearing 1 will be referred to hereinafter simply as bearing 1. The direction along the bearing center axis of bearing 1 will be referred to simply as the "axial direction," the direction perpendicular to the axial direction will be referred to simply as the "radial direction," and the circumferential direction around the bearing center axis will be referred to simply as the "circumferential direction."

[0019] The inner ring 3 is annular, and a rotating shaft (not shown) is fixed to its inner diameter portion 3b, rotating circumferentially together with the rotating shaft. The outer ring 2 is also annular, and is attached to a fixed member (not shown), such as a housing or gear, that bears the load from the rotating shaft. In this way, the bearing 1 supports the rotating shaft rotatably relative to the fixed member. Examples of the rotating shaft include the rotating shaft of a drive motor equipped in an electric vehicle or other electric transportation device, or the rotating shaft of a reducer or speed increaser equipped in such electric transportation device. The bearing center axis of the bearing 1 and the rotation center axis of the rotating shaft are set coaxially.

[0020] When the bearing 1 is assembled, an appropriate lubricant such as grease is sealed in the bearing internal space. During use, a lubricant (lubricating oil) is supplied from the outside into the bearing internal space through an opening at the axial end of the bearing internal space.

[0021] The lubricating oil that lubricates devices such as drive motors and transmissions contains gear wear powder, clutch wear powder, and other foreign matter depending on the device in which bearing 1 is installed. It is desirable for these foreign matter to be captured somewhere rather than floating in the lubricating oil. For this reason, an appropriate seal member (not shown) is often attached to the opening at the axial end of the bearing's internal space.

[0022] The cage 10 is a crown-shaped cage molded from engineering plastic and reinforced fiber. As shown in Figures 4 and 5, the cage 10 has a continuous annular portion 11 and multiple column portions 13 protruding from the annular portion 11 toward one axial side. Pairs of column portions 13, 13 are arranged in parallel along the circumferential direction and are spaced at regular intervals along the circumferential direction. The spaces between the column portions 13, 13, each consisting of a pair, form recessed pockets 12 that hold the balls 5. The pockets 12 are arranged in parallel at regular intervals along the circumferential direction on one axial side of the annular portion 11. The outer and inner diameter surfaces of the cage 10 are curved surfaces (cylindrical surfaces) without any steps. The outer and inner diameter surfaces of the cage 10 are connected at the pockets 12.

[0023] The tip of the column portion 13 is a retaining claw 14. The retaining claws 14, 14 on both sides of the pocket 12 are curved in a direction approaching each other. In the embodiment, a recess 15 recessed toward the annular portion 11 is formed between circumferentially adjacent pockets 12, but adjacent column portions 13, 13 may be connected to each other without removing weight by providing such a recess 15. The balls 5 held by the pocket 12 revolve between the raceway groove 3a of the inner ring 3 and the raceway groove 2a of the outer ring 2 while being held by the pocket 12.

[0024] The pocket 12 is surrounded by the inner surfaces of the columnar portions 13, 13 on both circumferential sides of the pocket center a and the surface on one axial side of the annular portion 11, and these surfaces hold the ball 5. The surface of the pocket 12 facing the ball 5 is a concave spherical surface 16.

[0025] Also, as shown in the upper part of Fig. 2A and Fig. 3, in the cross-section passing through the pocket center a and including the bearing center line o (referred to as the axial cross-section / see Fig. 3), the diameter of the spherical surface 16 is HP. Also, in the cross-section passing through the pocket center a and perpendicular to the bearing center line o (referred to as the axial perpendicular cross-section / see Fig. 1), the diameter of the spherical surface 16 is also HP. Furthermore, in the cross-section passing through the pocket center a and perpendicular to the radial line of the bearing passing through the pocket center a (referred to as the circumferential cross-section / see Fig. 5), the diameter of the spherical surface 16 is also HP. Note that in Fig. 5, for easier understanding, the cross-section of the cage 10 which is originally cylindrical in plan view is described in a planar shape by expanding it horizontally. Also, when a recess such as an oil sump is provided in a part of the pocket 12, the part excluding the location of the recess becomes the spherical surface 16. Hereinafter, the diameter HP of the spherical surface 16 of the pocket 12 is referred to as the pocket diameter HP.

[0026] The ball diameter Da defined by the diameter of the ball 5 and the pocket diameter HP are usually set such that Da < HP. Here, the pocket center a and the center of the ball 5 (ball center) coincide in design.

[0027] Here, as shown in Fig. 2, the maximum outer diameter of the outer ring 2 (outer diameter of the maximum diameter part) is defined as the bearing outer diameter D, the minimum inner diameter of the inner ring 3 (inner diameter of the minimum diameter part) is defined as the bearing inner diameter d, and the pitch circle diameter is defined as PCD. The pitch circle diameter PCD can be calculated from the following formula. Pitch circle diameter PCD = {D0 + d0 - gr1} / 2 D0: Outer ring groove bottom diameter d0: Inner ring groove bottom diameter gr1: Radial internal clearance median value

[0028] The radial internal clearance median value gr1 is obtained by applying a measuring element in the radial direction at the center of the width of the raceway ring that is not fixed in the ball top state, and subtracting the elastic deformation amount of the rolling element and the raceway ring due to the measuring load from the movement amount of the raceway ring that is not fixed. Here, the ball top state refers to the state where the ball is located at the 12 o'clock direction of the clock. As shown in Table 1, the measuring load is changed for each bearing inner diameter size. Also, the elastic deformation amount of the rolling element and the raceway ring can be calculated, for example, from Hertz's formula.

Table 1

[0029] The inner diameter of the outer ring 2 (the inner diameter of the smallest diameter part excluding the raceway grooves 2a) is defined as the outer ring inner diameter D1, and the outer diameter of the inner ring 3 (the outer diameter of the largest diameter part excluding the raceway grooves 3a) is defined as the inner ring outer diameter d1. Furthermore, the radial distance between the outer diameter surface 2b of the outer ring 2 and the inner diameter surface 3b of the inner ring, i.e., half the distance between the bearing outer diameter D and the bearing inner diameter d, is defined as the bearing cross-sectional height b (= (Dd) / 2). The axial width of the cage 10, i.e., the axial distance from the back surface (end face) 11a on the other axial side of the annular portion 11 of the cage 10 to the tips of the retention claws 14, is defined as the axial width HB.

[0030] As shown in FIG. 3, the axial width of the outer ring 2 and the inner ring 3 is defined as the bearing width H, the axial distance from the end faces 2c and 3c on the other axial side of the outer ring 2 and the inner ring 3 to the back surface 11a on the other axial side of the annular portion 11 of the cage 10 is defined as the other-side clearance length c, the radial thickness of the outer ring 2 is defined as t2, The radial thickness of the inner ring 3 is defined as t3, and the radial distance between the inner diameter of the outer ring 2 (the inner diameter at the smallest diameter part excluding the raceway groove 2a) and the outer diameter of the inner ring 3 (the outer diameter at the largest diameter part excluding the raceway groove 3a) is defined as e (= (D1 - d1) / 2).

[0031] 5, the minimum axial thickness of the annular portion 11 at the bottom of the pocket 12 of the cage 10 is defined as t. This minimum thickness t is the distance to the back surface 11a at point f, where the spherical surface 16 of the pocket 12 is closest to the back surface 11a of the annular portion 11, in the circumferential cross section of the pocket 12 shown in FIG. 5. This point f is also the point where the spherical surface 16 of the pocket 12 is closest to the back surface 11a of the annular portion 11 in the axial cross section shown in FIG.

[0032] Here, the bearing 1 adopts the specifications of requirements 1 to 6 shown in configuration 1 below.

[0033] (Configuration 1) Requirement 1: The minimum axial thickness t of the annular portion 11 at the bottom of the pocket 12 is 15% or more and 30% or less of the ball diameter Da. Requirement 2: The bearing inner diameter d is between 25 mm and 55 mm. Requirement 3: The bearing outer diameter D is 50 mm or more and 90 mm or less. Requirement 4: The axial bearing width H of the inner ring 3 and the outer ring 2 is 10 mm or more and 20 mm or less. Requirement 5: The ball diameter Da is 7 / 32 inches or less. Requirement 6: The ratio of the value defined as 1 / 2 of the difference between the pitch circle diameter PCD and the bearing bore diameter d to the bearing bore diameter d is between 10% and 20%. By setting the bearing specifications, including the cage shape, according to requirements 1 to 6, it was possible to reduce torque and suppress cage deformation during high-speed rotation more than before, making it possible to operate at even higher speeds.

[0034] Regarding the relationship between the pitch circle diameter PCD and the ball diameter Da, a smaller ball diameter Da is generally preferable for reducing centrifugal force. When comparing bearings under similar load conditions, a smaller ball diameter Da and a larger number of balls 5 results in lower agitation resistance and lower torque than a larger ball diameter Da and a smaller number of balls 5. For this reason, the ratio of the value defined as half the difference between the pitch circle diameter PCD and the bearing bore diameter d to the bearing bore diameter d is set to 10% to 20% (Requirement 6). A ratio of 13% to 17% is preferable for this requirement. In particular, when oil flows within a bearing device (bearing unit) equipped with a bearing, moving the back surface 11a of the cage 10 and the balls 5 away from the end faces 2c and 3c of the bearing 1 reduces obstructions and facilitates oil inflow. Furthermore, a smaller ball diameter Da reduces agitation resistance when oil enters the bearing's internal space, reducing rolling torque and contributing to a low-torque effect. Furthermore, since the pitch circle diameter PCD is close to the bearing inner diameter d, the torque is reduced.

[0035] Requirement 6 allows the axial width HB of the cage 10 to be small. However, if the axial width HB of the cage 10 is small, there is a high possibility that the cage 10 cannot be molded during manufacturing (for example, due to insufficient strength of the annular portion 11 or the column portion 13) or that the rigidity of the entire cage 10 will be insufficient. To avoid such concerns, the minimum thickness t at the bottom of the pocket 12 of the cage 10 is set to be 15% to 30% of the ball diameter Da (Requirement 1).

[0036] The above effect is most pronounced when the ball diameter Da is 7 / 32 inch or less (Requirement 5); for example, the ball diameter Da may be 3 / 16 inch. In the embodiment, the addition of Requirement 5 as Configuration 1 produces a significant effect, but the desired effect has also been confirmed in configurations that do not include Requirement 5, i.e., configurations in which the ball diameter Da exceeds 7 / 32 inch. Furthermore, the minimum wall thickness t is set to 15% to 30% of the ball diameter Da (Requirement 1), and more preferably 18% to 25%. Furthermore, the bearing size can be set to any value within the following ranges: bearing inner diameter d is 25 mm to 55 mm (Requirement 2), bearing outer diameter D is 50 mm to 90 mm (Requirement 3), and bearing width H is 10 mm to 20 mm (Requirement 4).

[0037] Furthermore, further effects can be expected by adopting the following configuration 2 in addition to configuration 1.

[0038] (Configuration 2) Requirement 7: The ratio of the difference between the outer ring inner diameter D1 and the inner ring outer diameter d1 to the difference between the bearing outer diameter D and the bearing inner diameter d is 15% or more and 25% or less. The ratio specified in Requirement 7 is between 15% and 25%, but more preferably between 17% and 21%.

[0039] Furthermore, in an embodiment that includes configuration 1 or an embodiment that adds configuration 2 to configuration 1, employing the following configuration 3 will provide even better results.

[0040] (Configuration 3) Requirement 8: The ratio of the distance C from the bearing end face to the end face 11a on the other axial side of the annular portion 11 to the bearing width H is 20% or more and 30% or less. The ratio specified in Requirement 8 is 20% or more and 30% or less, but more preferably 24% or more and 28% or less.

[0041] In addition, in the aspect provided with Configuration 1, or in the aspect in which Configuration 2 or Configuration 3 or both are added to Configuration 1, if the following Configuration 4 is adopted, better results can be obtained.

[0042] (Configuration 4) Requirement 9: The pitch circle diameter PCD and the ball diameter Da satisfy 112 < PCD × Da < 384 ··· (Equation 1) and Requirement 10: Taking the pitch distance of the balls 5 in the circumferential direction of the bearing as P, 20 < P × Da / 2 < 34 ··· (Equation 2) is satisfied.

[0043] As in (Equation 1), by setting 112 < PCD × Da < 384, the rolling torque of the bearing due to the bearing specifications (bearing dimensions) can be set within the low torque range. Also, as in (Equation 2), by setting 20 < P × Da / 2 < 34, the stirring torque of the oil due to the oil inflow into the bearing can be set within the low torque range. By satisfying both ranges of (Equation 1) and (Equation 2), the torque of the bearing can be significantly reduced.

[0044] In addition, in the aspect provided with Configuration 1, or in the aspect in which a single or a plurality of configurations selected from Configurations 2 to 4 are added to Configuration 1, if the following Configuration 5 is adopted, better results can be obtained.

[0045] (Configuration 5) Requirement 11: The back surface 11a on the other axial side of the annular portion 11 of the cage 10 is a flat surface without any thinning over the entire area. By not removing any weight from the back surface 11a of the annular portion 11 of the retainer 10, the rigidity of the retainer 10 is prevented from decreasing, and deformation due to centrifugal force during high-speed rotation is suppressed, allowing the retainer to accommodate higher speeds.

[0046] Furthermore, in each of the above aspects, even better results can be obtained by adopting the following configuration 6.

[0047] (Configuration 6) Requirement 12: The material of the cage 10 contains nylon resin (polyamide). Examples of polyamides that can be used include 66, 46, 9T, and 10T. Engineering plastics may also be used as the material for the cage 10. Polyphenylene sulfide is particularly suitable as an engineering plastic. Furthermore, if the cage 10 is made of a composite of these materials and reinforcing fibers, it will be able to handle higher speeds.

[0048] Furthermore, in the ball bearings of the above-described embodiments, better effects can be achieved under the conditions of the following configuration 7.

[0049] (Configuration 7) Requirement 13: dmn value = pitch circle diameter PCD × n (Equation 3) where n is the rotation speed (min -1 ) The dmn value specified in the above must be within the range of motor use conditions and be 650,000 or more, and the motor can be used continuously or at least intermittently.

[0050] Generally, the design load of bearings for supporting motor shafts is not particularly large, and the bearing size is often limited to the range of configuration 1. For this reason, if a ball bearing according to any of the above embodiments is used to form a bearing device that rotatably supports the rotating shaft of a drive motor, it will be possible to meet the demand for higher speeds.

[0051] Although steel is generally used as the material for the balls 5, ceramics may also be used. Examples of ceramics include nitride ceramics (Si3N4). Using ceramics for the balls 5 reduces the centrifugal force acting on the balls 5, reducing the contact pressure acting on the raceway grooves 2a of the outer ring 2. Furthermore, by suppressing centrifugal deformation of the cage 10, operation at higher speeds is possible.

[0052] 6 to 8 show another embodiment.

[0053] 6 and 7 each have a groove 2d formed around the entire circumferential direction on the outer diameter portion of the outer ring 2, with an O-ring 20 attached to the groove 2d. The O-ring 20 abuts against the housing (not shown), suppressing vibration and noise between the housing and the outer ring 2 and also helping to prevent creep between the housing and the outer ring 2. The number of grooves 2d and O-rings 20 can be one as shown in FIG. 6, or two as shown in FIG. 7, and the number can be determined as needed.

[0054] Figure 8 shows a case where the thickness of the outer ring 2 is set thinner than in the above-described embodiments. In Figure 8, the position of the pitch circle diameter PCD within the range of the bearing cross-sectional height b is closer to the center of the width of the bearing cross-sectional height b (the center in the radial direction). Even in such an embodiment, the effects of the present invention can be expected as long as it includes the above-described configuration 1, or the configuration 1 plus any configuration selected from configurations 2 to 7.

[0055] Table 2 shows a comparison between the examples of the bearing 1 of the present invention and the conventional examples. In Table 2, the torque reduction effect of the bearings 1 of Examples 1 to 3 and the bearings 1 of Conventional Examples 1 to 3 is verified.

[0056] [Table 2]

[0057] Examples 1 to 3 all satisfy Configuration 1 (Requirements 1 to 6), Configuration 2 (Requirement 7), Configuration 3 (Requirement 8), and Configuration 4 (Requirements 9 and 10), and a predetermined torque reduction effect can be confirmed in comparison with Conventional Examples 1 to 3. This effect is useful for a bearing 1 that supports a shaft that rotates at high speed, such as the rotating shaft of a drive motor. In Conventional Examples 1 to 3, such a torque reduction effect could not be confirmed.

[0058] In the above embodiment, the rotating shaft supported by the bearing 1 is exemplified as the rotating shaft of a drive motor equipped in an electric transport device such as an electric vehicle, or the rotating shaft of a reducer or speed increaser equipped in such electric transport device, but the bearing 1 of the present invention and a bearing device using the bearing 1 can also be applied to supporting parts of rotating shafts in various other types of transport devices, industrial machinery, etc. For example, the bearing can be applied to rotating parts of shafts in power transmission paths in various types of transport devices, constant velocity joints, propeller shafts, turbochargers, transmissions, and wheel bearings, or supporting parts of rotating shafts in various machine tools, generators, etc.

[0059] 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. [Explanation of symbols]

[0060] 1. Bearings 2 outer ring 3. Inner circle 5 balls (rolling elements) 10 Cage 11 Annular part 11a End face 12 pockets 16 Spherical

Claims

1. The bearing comprises an inner ring (3), an outer ring (2), balls (5) disposed between the inner ring (3) and the outer ring (2), and a cage (10) that holds the balls (5) in a circumferential direction, The cage (10) comprises a circular ring portion (11) and a plurality of pairs of cantilever-shaped retaining claws (14) extending axially from the circular ring portion (11) to one side, and a pocket (12) for accommodating the ball (5) is formed between each pair of the retaining claws (14). The ball diameter Da of the ball (5), the bearing outer diameter D defined by the maximum outer diameter of the outer ring (2), the bearing inner diameter d defined by the minimum inner diameter of the inner ring (3), and the outer ring groove bottom diameter D ０ , inner ring groove bottom diameter d ０ , radial internal clearance median value gr １ is calculated by Pitch circle diameter PCD = {D ０ +d ０ -gr １ } / 2, a ball bearing in which the minimum axial wall thickness t of the retainer (10) is 15% to 30% of the ball diameter Da, the bearing inner diameter d is 25 mm to 55 mm, the bearing outer diameter D is 50 mm to 90 mm, the bearing width H of the inner ring (3) and the outer ring (2) in the axial direction is 10 mm to 20 mm, and the ratio of a value defined as 1 / 2 of the difference between the pitch circle diameter PCD and the bearing inner diameter d to the bearing inner diameter d is 10% to 20%.

2. 2. A ball bearing according to claim 1, wherein the ratio of the difference between an outer ring inner diameter D1 defined by the minimum inner diameter of the outer ring (2) and an inner ring outer diameter d1 defined by the maximum outer diameter of the inner ring (3) to the difference between the bearing outer diameter D and the bearing inner diameter d is 15% or more and 25% or less.

3. 2. A ball bearing according to claim 1, wherein the ratio of the distance C from the bearing end face to the other axial end face (11a) of the annular portion (11) to the bearing width H is 20% or more and 30% or less.

4. The pitch circle diameter PCD and the ball diameter Da are 112<PCD×Da<384 and the pitch distance P of the balls (5) in the circumferential direction of the bearing is: 20<P×Da / 2<34 2. The ball bearing according to claim 1, wherein:

5. 2. The ball bearing according to claim 1, wherein the end face (11a) on the other axial side of the annular portion (11) is a flat surface with no recesses over the entire area.

6. 2. The ball bearing according to claim 1, wherein the material of the cage (10) includes nylon resin.

7. dmn value = pitch circle diameter PCD x n where n: rotation speed (min －１ ) 2. A ball bearing according to claim 1, wherein the dmn value defined by the formula (1) is within the range of motor use conditions and is 650,000 or more, and the ball bearing can be used at least intermittently.

8. 2. A ball bearing according to claim 1, wherein the ball diameter Da is 7 / 32 inches or less.

9. A bearing device that uses a ball bearing according to any one of claims 1 to 8 and rotatably supports a rotary shaft of a drive motor.

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