Ball bearing

Abstract

To provide a bearing that can respond to high-speed rotation by suppressing a heat generation amount of the entire ball bearing.SOLUTION: A ball bearing includes: an inner member 3; an outer member 4; an inner raceway groove 3a formed in the inner member 3 and having an arc cross section; an outer raceway groove 4a formed in the outer member 4 and having an arc cross section; a plurality of balls 5 disposed between the inner raceway groove 3a and the outer raceway groove 4a; and a cage 10 that holds the balls 5. Each of a curvature radius Ri of the inner raceway groove 3a and a curvature radius Ro of the outer raceway groove 4a is set to 108% or larger and 114% or smaller of a radius Rb of the ball 5. Surface hardness of at least the inner raceway groove 3a of the inner member 3 is set to 60 HRC or larger, and a retained austenite amount of the inner member 3 is set to 10% or smaller.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a ball bearing that can be used for high speed rotation. [Background technology]

[0002] For example, many bearings are used in devices equipped with electric motors in various vehicles such as automobiles and construction machines, as well as in various industrial machines, etc. The bearings used in these devices are generally used under high-speed conditions compared to bearings used to support shafts in general equipment.

[0003] Furthermore, in recent years, especially in electric vehicles, there has been a trend to increase the rotational speed of electric motors to make them smaller and lighter in order to increase the output density of the motor as a means of improving fuel economy and driving performance. As the maximum rotational speed of bearings increases with the speed of electric motors, the centrifugal force acting on the internal components of the bearing increases and the contact pressure changes. For this reason, under the harsh operating conditions expected in the future, the contact pressure, sliding, and friction between the balls and the inner ring and the balls and the outer ring increase, which may cause the bearings to heat up and burn out, resulting in a malfunction.

[0004] Patent Document 1 discloses a technology for a long-life ball bearing intended for use at high speeds with a dmn value of 2 million or more. In this ball bearing, the radius of curvature of the raceway grooves, which are arc-shaped in cross section and formed on the outer peripheral surface of the inner ring, is set to 105% to 120% of the radius of the balls, while the radius of curvature of the raceway grooves, which are arc-shaped in cross section and formed on the inner peripheral surface of the outer ring, is set to 101% to 106% of the radius of the balls. This is said to reduce the amount of heat generated by the inner ring and bring the amount of heat generated by the outer ring closer to that of the inner ring, thereby suppressing the amount of heat generated by the entire ball bearing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2000 / 037813 Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Document 1, the radius of curvature of the raceway groove of the inner ring is increased, and the radius of curvature of the raceway groove of the outer ring is made smaller relative to the radius of curvature of the raceway groove of the inner ring. However, when the radius of curvature of the raceway groove of the outer ring is reduced, the contact ellipse between the ball and the raceway groove becomes larger, which tends to increase differential slip and spin slip in the high-speed rotation range. For this reason, it may not be applicable to applications that require high-speed rotation (such as electric vehicles).

[0007] SUMMARY OF THE PRESENTING EMBODIMENT An object of the present invention is to suppress the amount of heat generated by the entire ball bearing and to provide a bearing capable of handling high speed rotation. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a ball bearing comprising an inner member and an outer member, an inner raceway groove having an arc-shaped cross section formed in the inner member, an outer raceway groove having an arc-shaped cross section formed in the outer member, a plurality of balls arranged between the inner raceway groove and the outer raceway groove, and a cage for holding the balls, wherein the radius of curvature of the inner raceway groove and the radius of curvature of the outer raceway groove are each 108% or more and 114% or less of the radius of the balls, and at least the surface hardness of the inner raceway groove of the inner member is 60 HRC or more, and the amount of retained austenite in the inner member is 10% or less (structure 1).

[0009] Here, the radii of curvature of the inner raceway groove and the outer raceway groove may be specified for the entire circumferential area of ​​the raceway groove, but it is preferable to specify at least 80% of the entire axial area of ​​the groove excluding both ends. The measurement may be performed using a contact type shape measuring machine, or may be performed using an optical method on the cross section of the member.

[0010] In addition, the measurement of retained austenite should be performed on the cross section of the component using a method such as X-ray measurement. The measurement point should be 0.2 mm or more from the surface of the cross section of the component to avoid variations in the surface layer.

[0011] The surface hardness should be measured at any point on the surface if the entire component has been hardened. If the surface has been strengthened by nitriding or other methods, it is desirable to measure the surface hardness at a position about 0.1 mm from the raceway groove on the cross section of the component.

[0012] In configuration 1, a configuration can be adopted in which nitrogen is dissolved in the inner member, so that at least the surface of the inner raceway groove of the inner member has a hardness of 60 HRC or more (configuration 2).

[0013] In configuration 2, a configuration can be adopted in which the depth of solid solution of nitrogen in the inner raceway groove is 0.05 mm or more from the surface of the inner raceway groove (configuration 3).

[0014] In configuration 1, a configuration may be adopted in which at least the surface of the outer raceway groove of the outer member has a hardness of 60 HRC or more (configuration 4). This configuration 4 may also be adopted in an embodiment in which configuration 2 is added to configuration 1, or an embodiment in which configurations 2 and 3 are added to configuration 1.

[0015] In an embodiment including configuration 4, a configuration can be adopted in which the outer member is subjected to a deep cooling treatment (subzero treatment) to reduce the amount of retained austenite to 10% or less, and the hardness of at least the surface of the outer raceway groove of the outer member is 60 HRC or more (configuration 5). Configuration 5 can also be adopted in each of the above-mentioned embodiments including configuration 4.

[0016] In addition, in an embodiment having configuration 4, a configuration can be adopted in which the outer member is subjected to a nitriding treatment to dissolve nitrogen in a solid solution at least 0.05 mm from the surface of the outer raceway groove of the outer member, and the surface hardness of the outer raceway groove is 58 HRC or more (configuration 6). Configuration 6 can also be adopted in each of the above-mentioned embodiments including configuration 4.

[0017] In an embodiment having configuration 6, a configuration in which the amount of retained austenite in the outer member is set to 3% or more can be adopted (configuration 7).

[0018] In each of the above-mentioned aspects combining elements selected from among configuration 1 to configuration 7, a configuration can be adopted in which the material of the inner member and the outer member is any one of bearing steel, case-hardened steel, SKH4 material, and M50 material (configuration 8).

[0019] In each of the above-mentioned embodiments combining elements selected from the embodiments 1 to 7, a configuration can be adopted in which stress concentration due to hoop stress on the inner member is alleviated by subjecting the shoulder portion of the inner member to continuous grinding (Configuration 9). This configuration 9 can also be adopted in each of the above-mentioned embodiments including the configuration 8. Effect of the Invention

[0020] The present invention provides a bearing capable of high speed rotation by suppressing the amount of heat generated by the entire ball bearing. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is an enlarged longitudinal sectional view of a main portion of an embodiment of the present invention, showing a state before a retainer and a seal member are attached; [Diagram 2] FIG. 13 is an enlarged longitudinal sectional view of the main part of the embodiment, showing a state after the retainer and the seal member are attached. [Diagram 3] A cross-sectional view showing the contact area between the inner ring and the rolling element. [Figure 4] Graph showing occurrence of differential slip [Diagram 5] Graph showing changes in contact stress DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] An embodiment of the present invention will be described with reference to the drawings. A rolling bearing 1 of this embodiment is used to support 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 an electric transport device.

[0023] As shown in Figures 1 and 2, the rolling bearing 1 (hereinafter simply referred to as bearing 1) is a ball bearing comprising an inner member 3 and an outer member 4 which constitute a raceway, an inner raceway groove 3a having an arc-shaped cross section formed in the inner member 3, an outer raceway groove 4a having an arc-shaped cross section formed in the outer member 4, a plurality of rolling elements 5 arranged between the inner raceway groove 3a and the outer raceway groove 4a, and a cage 10 which holds the rolling elements 5.

[0024] Here, balls (steel balls) are used as the rolling elements 5, and will be referred to as balls 5 below. The inner raceway groove 3a and the outer raceway groove 4a each have an arc-shaped cross section of a single radius in any longitudinal section including the axis. Hereinafter, the direction along the bearing center axis of the bearing 1 will be referred to as the "bearing axial direction" or simply the "axial direction", the direction perpendicular to the axial direction will be referred to as the "bearing radial direction" or simply the "radial direction", and the circumferential direction around the bearing center axis will be referred to as the "bearing circumferential direction" or simply the "circumferential direction". The radius of the arc of the inner raceway groove 3a and the outer raceway groove 4a will be referred to as the radius of curvature.

[0025] The cage 10 is a crown-shaped cage molded from engineering plastic. The cage 10 is preferably made of a resin material that is resistant to deformation due to centrifugal force, for example, polyamide resin with added reinforcing fibers. However, the material and type of the cage 10 can be changed as appropriate depending on the specifications of the bearing 1.

[0026] The cage 10 has an annular base 12 and a number of pillars 13 protruding from the base 12 in the axial direction. The outer diameter surface of the base 12 is a curved surface (cylindrical surface) without any steps. The pillars 13, 13 adjacent in the circumferential direction form pockets 11 that hold the balls 5 in the circumferential direction. The outer diameter surface and the inner diameter surface of the cage 10 communicate with each other at the pockets 11. The tips of the pillars 13 form retention claws 14, and the adjacent retention claws 14, 14 are curved in a direction approaching each other to form the concave pockets 11. The balls 5 revolve between the inner raceway groove 3a and the outer raceway groove 4a while being held in the pockets 11.

[0027] The inner member 3 (referred to as the inner ring 3 in this embodiment) has a rotating shaft (not shown) fixed to its inner diameter portion 3b, and rotates in the circumferential direction together with the rotating shaft. The outer member 4 (referred to as the outer ring 4 in this embodiment) is attached to a fixed member such as a housing (not shown). In this way, the bearing 1 supports the rotating shaft so that it can rotate freely with respect to the fixed member. The rotating shaft referred to here may be, for example, a rotating shaft of a drive motor equipped in an electric transport device such as an electric vehicle, or a rotating shaft of a reducer or a speed increaser equipped in such an electric transport device. The bearing center axis of the bearing 1 and the rotating center axis of the rotating shaft are set coaxially. When the bearing 1 is assembled, an appropriate lubricant such as grease is sealed in the bearing internal space.

[0028] 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 the bearing 1 is installed. It is undesirable for these foreign matter to enter the bearing internal space. For this reason, a seal member 20 is attached to the opening at the axial end of the bearing internal space. In this embodiment, the seal member 20 is provided at both axial ends of the bearing internal space, but depending on the specifications, there may be an embodiment in which the seal member 20 is provided only at the end on one of the axial sides, or an embodiment in which the seal member 20 is not provided.

[0029] As shown in Fig. 2, the seal member 20 includes a metal core 21 and an elastic portion 22 fixed integrally to the core 21. The core 21 is an annular member formed to have an L-shaped cross section over the entire circumference in the circumferential direction. In this embodiment, the core 21 is formed as a pressed product. The elastic portion 22 is made of rubber and is vulcanization bonded to the core 21. The vulcanization bonding can be performed, for example, by placing the core 21 in a mold and vulcanizing a vulcanized rubber material.

[0030] The elastic portion 22 of the seal member 20 includes a fitting portion 23 that protrudes radially outward on the outer diameter side, a main body portion 25 that covers the core metal 21, and a seal lip 24 that protrudes radially inward like a tongue from the main body portion 25. A seal groove 8 is formed around the entire circumference on the inner circumference of the axial end portion of the outer ring 4. The seal member 20 is fixed to the outer ring 4 by fitting the fitting portion 23 into the seal groove 8.

[0031] A seal sliding portion 9 that slides circumferentially against the seal lip 24 is formed on the outer periphery of the inner ring 3. The seal sliding portion 9 is in the form of a groove extending over the entire circumference, but may also be in the form of a cylindrical surface extending over the entire circumference. An interference is set between the head of the seal lip 24 and the seal sliding portion 9. When the seal member 20 is attached in the predetermined position shown in FIG. 2, the seal lip 24 is pressed against the seal sliding portion 9 by the interference, and generates a tension force of the seal lip 24 by causing deformation of the rubber-like elasticity. An attachment error, manufacturing error, etc. of the seal member 20 is absorbed by a change in the degree of bending of the seal lip 24. It is also possible to adopt a configuration in which the seal member 20 is reversed inside and outside and the seal lip 24 is arranged on the outer ring 4 side.

[0032] In general, in ball bearings, slippage due to microscopic peripheral speed differences that arise geometrically at the rolling contact area between the balls 5 and the raceway is unavoidable. Slippage at the rolling contact area between the balls 5 and the raceway includes differential slippage, spin slippage, and gyroscopic slippage. When the bearing 1 is operated at high speed, excessive differential slippage, spin slippage, and gyroscopic slippage can increase resistance and cause heat generation, and may even lead to oil film rupture and bearing damage due to temperature rise, especially under severe operating conditions. For this reason, heat generation in the bearing has traditionally been suppressed by increasing the amount of oil supplied, suppressing the oil temperature, and cooling the machine used.

[0033] In this regard, the above-mentioned Patent Document 1 adopts a method of enlarging the radius of curvature of the raceway grooves of the inner and outer raceways to reduce the contact ellipse in order to suppress slippage that causes heat generation. However, JIS (Japanese Industrial Standards) B1518 suggests that when the radius of curvature Ri of the raceway groove 3a of the inner raceway 3 exceeds 104% of the radius Rb of the balls 5, and when the radius of curvature Ro of the raceway groove 4a of the outer raceway 4 exceeds 106% of the radius Rb of the balls 5, the rated load of the bearing 1 becomes small, and caution is required. However, Patent Document 1 does not take this into consideration.

[0034] Therefore, in the present invention, the radius of curvature Ri of the inner raceway groove 3a and the radius of curvature Ro of the outer raceway groove 4a are each set to 108% or more and 114% or less of the radius Rb of the balls 5, and the surface hardness of at least the inner raceway groove 3a of the inner ring 3 is set to 60 HRC or more.

[0035] In Fig. 1, the center of the radius of curvature Ri of the inner raceway groove 3a is indicated by ci, the center of the radius of curvature Ro of the outer raceway groove 4a is indicated by co, and the center of the ball 5 is indicated by c. By design, the center c of the ball 5 is located on the pitch circle of the bearing 1. Also, in Fig. 2, the symbol H indicates a hardening layer (hardening treated part) that makes the material hardness 60HRC or more.

[0036] There are various methods for making the surface hardness of the inner raceway groove 3a 60HRC or more, but it is preferable to adopt a method of dissolving nitrogen in the metal constituting the inner ring 3, for example. The depth w1 (see FIG. 2) at which the hardness is made 60HRC or more is preferably 0.05mm or more from the surface of the inner raceway groove 3a. Note that the entire inner ring 3 may have a hardness of 60HRC or more.

[0037] HRC is a number obtained by the Rockwell hardness test specified in JIS Z 2245 (2021) or ISO 6508-1: 2016. The larger the two-digit number, the harder the material is. In other words, 60HRC or higher indicates that the material is the same as or harder than 60HRC.

[0038] Alternatively, the hardness may be measured by measuring the Vickers hardness, which is a numerical value obtained by a Vickers hardness test specified in JIS Z 2244-1 (2020) or ISO 6507-1: 2018, and the Rockwell hardness may be obtained using a conversion table with Rockwell hardness.

[0039] An example of a method for dissolving nitrogen is nitriding. Nitriding is a process in which nitrogen is dissolved in solid solution and then quenching is performed. This has the advantage that quenching can be performed with low distortion. The nitrogen solid solution depth (treatment depth w1) is preferably at least 0.05 mm or more from the surface of the inner raceway groove 3a.

[0040] Cryogenic treatment may also be used to make the surface hardness of the inner raceway groove 3a 60HRC or more. Cryogenic treatment is a process in which metal immediately after quenching is cooled to 0°C or less using dry ice or the like. Cryogenic treatment is expected to have the effects of increasing the hardness of the metal, making the metal hardness uniform, and increasing the wear resistance. Another possible method for making the surface hardness of the inner raceway groove 3a 60HRC or more is to make the amount of retained austenite in the material of the inner ring 3 10% or less. These methods may also be combined to ensure a surface hardness of 60HRC or more.

[0041] The outer ring 4 may have a similar structure. That is, the hardness of at least the surface of the outer raceway groove 4a of the outer ring 4 is set to 60HRC or higher. The entire outer ring 4 may have a hardness of 60HRC or higher.

[0042] Even if the surface hardness of at least the outer raceway groove 4a in the outer ring 4 is 60HRC or less, heat resistance treatment by high-temperature tempering may be adopted instead of or in addition to the above-mentioned deep freezing treatment or nitriding treatment, as long as there is no problem with the contact surface pressure within the range of use of the bearing.

[0043] Materials for the inner ring 3 and the outer ring 4 may be selected from, for example, bearing steel, case hardening steel, high speed tool steel (SKH4 material) which has higher high temperature hardness than bearing steel, and M50 material which has higher strength, slower crack propagation speed, and smaller dimensional change. These materials are particularly preferred for the inner ring 3.

[0044] In general, it is believed that the larger the radius of curvature Ri of the inner raceway groove 3a and the radius of curvature Ro of the outer raceway groove 4a, the smaller the major axis L1 and minor axis L2 of the contact ellipse between the balls 5 and the inner ring 3 and between the balls 5 and the outer ring 4, and the more effectively the differential slippage that causes heat generation during high-speed operation of the bearing 1 can be suppressed. Figure 3 shows an example of the contact ellipse between the balls 5 and the inner ring 3.

[0045] Moreover, Figure 4 shows the relationship between the ratio (%) of the raceway groove curvature radius (corresponding to the curvature radius Ri and the curvature radius Ro) to the radius Rb of the balls 5 and the occurrence of differential slip. Hereinafter, the ratio of the raceway groove curvature radius (corresponding to the curvature radius Ri and the curvature radius Ro) to the radius Rb of the balls 5, (Ri / Rb) x 100 (%) or (Ro / Rb) x 100 (%), will be referred to as the radius ratio (%). As shown in Figure 4, the occurrence of differential slip decreases as the radius ratio (%) increases, and it can be seen that the occurrence of differential slip is effectively suppressed when the radius ratio (%) is 108 (%) or more (see area A in Figure 4).

[0046] In Fig. 5, the contact stress σ / σ0 is plotted on the vertical axis and the radius ratio (%) on the horizontal axis, making it possible to determine the effect of the raceway groove curvature radius on the contact stress, i.e., whether or not indentations occur due to excessive surface pressure. For the conventional HCR58 raceway, it is determined that there is a concern that indentations will occur due to excessive surface pressure if the line where the correction coefficient h0=1.0 for the static load rating C0 is exceeded upwards, and for the HCR60 raceway of this invention, it is determined that there is a concern that indentations will occur due to excessive surface pressure if the line where the correction coefficient h0=1.2 for the static load rating C0 is exceeded upwards. Here, σ: internal contact stress, σ0: internal contact stress due to static load rating C0.

[0047] The static load rating C0 is the non-rotating load at which the raceway of bearing 1 can maintain normal rotation without undergoing plastic deformation when bearing 1 is mounted on the shaft, and is also known as the basic static load rating. The correction coefficient h0 is used to correct the static load rating C0 by multiplying it by a coefficient depending on the hardness of the material, since the static load rating C0 changes if the material and hardness of the raceway changes. In other words, the static load rating C0 (basic static load rating) of bearing 1 is related to the hardness of the raceway surface, and it can be said that the higher the hardness, the higher the resistance to indentation.

[0048] As shown in Fig. 5, when the radius ratio (%) on the horizontal axis exceeds 106%, in the conventional HCR58 raceway, the contact stress σ / σ0 exceeds the line of correction coefficient h0 = 1.0 upwards, and there is a concern that the occurrence of indentations due to excessive surface pressure may occur. For this reason, in the case of HCR58, it was necessary to suppress the radius ratio (%) to 106% or less. However, in the case of the 60HRC raceway of the present invention, the radius ratio (%) on the horizontal axis does not exceed the line of correction coefficient h0 = 1.2 until it reaches 114%. For this reason, at least for raceways of 60HRC or more, the occurrence of indentations can be effectively suppressed by setting the radius ratio (%) to 114% or less (see region B in Fig. 5).

[0049] For the reasons above, the surface hardness of the inner raceway groove 3a and the outer raceway groove 4a is set to 60HRC or more to suppress the occurrence of indentations. This makes it possible to maintain a sufficient basic static load rating up to the region where the radius ratio (%) is 114% or less. Therefore, even if the raceway groove radius of curvature (corresponding to the radius of curvature Ri and the radius of curvature Ro) is set large, damage caused by indentations can be prevented, and improved hardness is expected to improve the bearing life. Furthermore, by increasing the raceway groove radius of curvature (corresponding to the radius of curvature Ri and the radius of curvature Ro), the allowable axial load of the bearing 1 can be increased.

[0050] Also, by subjecting the steel material of the inner ring 3 and the outer ring 4 to deep freezing treatment, the hardness and resistance to indentation can be improved. Furthermore, deep freezing treatment improves dimensional stability. Since it is necessary to prevent negative clearance caused by the temperature difference between the inner ring 3 and the outer ring 4 for high speed rotation bearings 1, deep freezing treatment, which can maintain high dimensional accuracy, is particularly effective. However, since heat resistance treatment by high temperature tempering reduces hardness, high temperature tempering is considered undesirable for the inner ring 3.

[0051] Furthermore, by subjecting the steel material of the inner ring 3 or the outer ring 4 to nitriding treatment, nitrogen is dissolved in the steel surface, improving the surface hardness, heat resistance, and wear resistance. This makes it possible to prevent damage due to heat generation and slippage associated with high-speed rotation. In particular, when subjecting the outer ring 4 to nitriding treatment, it is preferable that nitrogen is dissolved at least 0.05 mm from the surface of the outer raceway groove 4a of the outer ring 4, and the surface hardness of the outer raceway groove 4a is at least 58HRC or more. Furthermore, by subjecting the outer ring 4 to deep freezing treatment, the amount of retained austenite is reduced to a minimum of about 5%, improving the hardness, wear resistance, and indentation resistance. Note that if the amount of retained austenite is 10% or less, the surface hardness can be 60HRC or more. In either of the above-mentioned embodiments in which nitriding treatment is performed and deep freezing treatment is performed, it is desirable that the amount of retained austenite in the inner ring 3 or the outer ring 4 is 3% or more. The steel material that can be subjected to the nitriding treatment may be a bearing steel or a case-hardened steel having a higher tensile strength than the bearing steel. These bearing steels and case-hardened steels may be carburized and then further nitrided.

[0052] It is possible to employ a configuration in which stress concentration due to hoop stress on the inner ring 3 is alleviated by continuously grinding the shoulder portion 7 of the inner ring 3 all around. In other words, by smoothing the surface of the shoulder portion 7 of the inner ring 3, stress concentration due to hoop stress caused by high-speed rotation can be alleviated.

[0053] When using balls (steel balls) as the balls 5, it is desirable that the relationship between the hardness of the balls (steel ball hardness) and the surface hardness (inner ring hardness) of at least the inner raceway groove 3a of the inner ring 3 is such that the steel ball hardness is greater than the inner ring hardness. Also, it is desirable that the relationship between the surface hardness (inner ring hardness) of at least the inner raceway groove 3a of the inner ring 3 and the surface hardness (outer ring hardness) of at least the outer raceway groove 4a of the outer ring 4 is such that the inner ring hardness is greater than or equal to the outer ring hardness.

[0054] Furthermore, in terms of the relationship between the radius of curvature (radius of curvature Ri) of the inner raceway groove 3a and the radius of curvature (radius of curvature Ro) of the outer raceway groove 4a, by making the radius of curvature Ri of the inner raceway groove 3a ≧ the radius of curvature Ro of the outer raceway groove 4a, a better thermal condition can be ensured.

[0055] With the above-mentioned configuration, the bearing 1 of the present invention can be used under high speed conditions where the dmn value is 1 million or more at the maximum rotation speed. dmn=dm×n dm: rolling element pitch diameter (mm) n: rotation speed (rpm) In consideration of deformation during high speed operation, the cage 10 is preferably the above-mentioned crown cage.

[0056] Although the shaft to which the bearing 1 of the present invention is attached is exemplified by the rotating shaft of a drive motor of an electric transport device such as an electric vehicle, or the rotating shaft of a reducer or speed increaser of such an electric transport device, the bearing 1 of the present invention can also be applied to the support parts of rotating shafts in various transport devices, industrial machines, etc. For example, the bearing 1 can be applied to the rotating parts of shafts of power transmission paths in various transport devices, constant velocity joints, propeller shafts, turbochargers, transmissions, and wheel bearings, or the support parts of rotating shafts in various machine tools, generators, etc. Also, as in this embodiment, the inner member 3 may be configured as an inner ring or a shaft. Also, as in this embodiment, the outer member 4 may be configured as an outer ring or a housing.

[0057] Furthermore, the bearing 1 of the present invention can be applied to angular contact ball bearings and other ball bearings in general that use balls as the rolling elements 5, in addition to the deep groove ball bearing of this embodiment.

[0058] 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. [Explanation of symbols]

[0059] 1. Bearings (ball bearings) 3 Inner member (inner ring) 3a Inner raceway groove 4 Outer member (outer ring) 4a Outer raceway groove 5 balls (rolling elements) 7 Shoulder 10 Cage Rb radius Ri,Ro radius of curvature

Claims

1. An inner member (3) and an outer member (4), An inner raceway groove (3a) having an arc-shaped cross section formed in the inner member (3); An outer raceway groove (4a) having an arc-shaped cross section formed in the outer member (4); a plurality of balls (5) disposed between the inner raceway groove (3a) and the outer raceway groove (4a); A cage (10) for holding the balls (5), a radius of curvature (Ri) of the inner raceway groove (3a) and a radius of curvature (Ro) of the outer raceway groove (4a) are each 108% or more and 114% or less of a radius (Rb) of the ball (5), the hardness of at least the surface of the inner raceway groove (3a) of the inner member (3) is 60 HRC or more, and the amount of retained austenite in the inner member (3) is 10% or less.

2. 2. The ball bearing according to claim 1, characterized in that nitrogen is dissolved in the inner member (3) so that the hardness of at least the surface of the inner raceway groove (3a) of the inner member (3) is 60 HRC or more.

3. 3. A ball bearing according to claim 2, wherein the depth of solid solution of nitrogen in said inner raceway groove (3a) is 0.05 mm or more from the surface of said inner raceway groove (3a).

4. 2. A ball bearing according to claim 1, wherein the surface hardness of at least the outer raceway groove (4a) of the outer member (4) is 60 HRC or more.

5. 5. A ball bearing according to claim 4, characterized in that the outer member (4) is subjected to deep cooling treatment to reduce the amount of retained austenite to 10% or less, and the surface hardness of at least the outer raceway groove (4a) of the outer member (4) is 60 HRC or more.

6. 5. A ball bearing according to claim 4, characterized in that the outer member (4) is subjected to a nitriding treatment to dissolve nitrogen in a solid solution at least 0.05 mm deep from the surface of the outer raceway groove (4a) of the outer member (4), and the hardness of the surface of the outer raceway groove (4a) is 58 HRC or higher.

7. 7. A ball bearing according to claim 6, characterized in that the amount of retained austenite in said outer member (4) is 3% or more.

8. The ball bearing according to any one of claims 1 to 7, characterized in that the material of the inner member (3) and the outer member (4) is any one of bearing steel, case-hardened steel, SKH4 material, and M50 material.

9. The ball bearing according to any one of claims 1 to 7, characterized in that stress concentration due to hoop stress on the inner member (3) is alleviated by subjecting the shoulder portion (7) of the inner member (3) to continuous grinding processing around the entire circumference.

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