Patent Description:
Ball bearings are often used as bearings supporting rotary shafts of automobiles, industrial machines, etc. Generally, ball bearings include an inner ring; an outer ring arranged radially outwardly of, and coaxially with, the inner ring: a plurality of balls disposed in the annular space between the inner ring and the outer ring; and a cage retaining the balls.

As such a cage, for example, a so-called "crown-shaped" resin cage as disclosed in the below-identified Patent Document <NUM> is known which includes a cage circular annular portion extending circumferentially and adjacent to the space through which the balls pass; and cage claw portions having a cantilevered structure axially extending from the cage circular annular portion each between the corresponding circumferentially adjacent balls. Each cage claw portion has a ball guiding surface opposed to the surface of one of the balls. The ball guiding surface is a concave spherical surface extending along the surface of the ball to hold the ball.

Also, for example, a sealed ball bearing as disclosed in the below-identified Patent Document <NUM> is sometimes used in which the axial end openings of the annular space between the inner ring and the outer ring are closed by annular seal members to prevent foreign matter from entering the ball bearing from the outside of the ball bearing, or to prevent a lubricant (such as lubricating oil or grease) from leaking from the interior of the ball bearing to the exterior.

The document <CIT> discloses a ball bearing according to the preamble of claim <NUM>.

Nowadays, in the field of electric vehicles such as battery electric vehicles (EV) and hybrid electric vehicles (HEV), electric motors are rotated at a higher speed for a reduction in size and weight. A ball bearing supporting a rotary shaft to which rotation of such an electric motor is input is sometime used under the conditions that the dmn (ball pitch circle diameter dm(mm) X the number of rotations n (min-<NUM>)) value exceeds <NUM> million.

The inventors of the present application considered using a crown-shaped cage in a ball bearing supporting a rotary shaft of, e.g., an EV or a HEV that rotates at a high speed.

However, it turned out that if a crown-shaped cage is used in a ball bearing that rotates at a high speed, the centrifugal forces applied to its cantilevered cage claw portions cause (i) torsional deformation of its cage circular annular portion in the direction in which the cage claw portions are inclined toward the radially outer side, and (ii) flexural deformation of the cage claw portions per se toward the radially outer side, and, due to these deformations, the cage claw portions may interfere with the balls. The interference of the cage claw portions with the balls causes heat generation in the ball bearing.

Especially if the bearing using a crown-shaped cage is a sealed ball bearing with a seal member, since, if the cage circular annular portion of the crown-shaped cage comes into contact with the seal member, the sliding resistance of the contact portions thereof may cause abnormal heat generation, the axial width dimension of the cage circular annular portion needs to be reduced to prevent the cage circular annular portion from coming into contact with the seal member. Therefore, it is difficult to increase the rigidity of the cage circular annular portion. As a result, torsional deformation of the cage circular annular portion is likely to occur due to the centrifugal forces applied to the cage claw portions, and thus the cage claw portions are likely to interfere with the balls.

As described above, if a crown-shaped cage is used in a sealed ball bearing, it is difficult to use the sealed ball bearing for a component that rotates at a high speed. Also, if the space for installing the bearing is small and thus the width dimension of the bearing needs to be reduced, it is difficult to prevent the crown-shaped cage from coming into contact with the seal member. Therefore, instead of the sealed ball bearing, an open-type ball bearing including no seal members and having open ends on both axial sides needs to be used in some cases.

It is an object of the present invention to provide a ball bearing in which deformation of a cage made of resin due to a centrifugal force is less likely to occur during high-speed rotation.

In order to achieve the above object, the present invention provides a ball bearing according to claim <NUM>. Another an example not part of the claimed invention provides a ball bearing comprising: an inner ring; an outer ring arranged radially outwardly of, and coaxially with, the inner ring; a plurality of balls disposed in an annular space between the inner ring and the outer ring; and a cage made of resin and retaining the balls, wherein the cage comprises: a cage circular annular portion extending circumferentially adjacent to a space through which the balls pass; and cage claw portions having a cantilevered structure axially extending from the cage circular annular portion, each between a corresponding pair of the balls circumferentially adjacent to each other, characterized in that each of the cage claw portions has: an outer-diameter-side axial groove formed in a radially outer surface of the cage claw portion, and axially extending from a distal end of the cage claw portion toward the cage circular annular portion; and an inner-diameter-side axial groove formed in a radially inner surface of the cage claw portion, and axially extending from the distal end of the cage claw portion toward the cage circular annular portion, wherein due to the outer-diameter-side axial groove and the inner-diameter-side axial groove of each of the cage claw portions, a cross section of the cage claw portions perpendicular to an axial direction has an H shape of which the openings of the letter H face radially outward and radially inward, respectively.

With this arrangement, since each cage claw portion has an H-shaped cross section due to the outer-diameter-side axial groove in the radially outer surface of the cage claw portion and the inner-diameter-side axial groove in the radially inner surface of the cage claw portion, it is possible to reduce the mass of the cage claw portions while ensuring the moment of inertia of area of the cage claw portions (while making the cage claw portions less likely to deform against the bending moment). Therefore, even during high-speed rotation, it is possible to reduce torsional deformation of the cage circular annular portion, and flexural deformation of the cage claw portions per se toward the radially outer side due to the centrifugal forces which the cage claw portions receive.

It is preferable that each of the cage claw portions has an axial length larger than a radius of each of the balls, and each of the cage claw portions has circumferentially opposed surfaces which are circumferentially opposed to the corresponding pair of the balls, respectively, and of which portions configured to circumferentially support the corresponding pair of the balls are flat surfaces extending such that when the cage claw portion is moved radially outwardly by a centrifugal force, the circumferentially opposed surfaces do not interfere with the corresponding pair of the balls.

With this arrangement, since the circumferentially opposed surfaces of each cage claw portion are flat surfaces, when the cage claw portion is moved radially outwardly by the centrifugal force applied to the cage claw portion, the circumferentially opposed surfaces of the cage claw portion do not interfere with the balls. Also, since the shear resistance of lubricating oil generated between the circumferentially opposed surfaces of the cage claw portion and the balls can be reduced, the heat generation in the ball bearing can also be reduced.

It is preferable that the cage circular annular portion has axially opposed surfaces axially opposed to the respective balls, and each of the circumferentially opposed surfaces of the cage claw portions is connected to a corresponding one of the axially opposed surfaces via a curved surface having a concave circular arc-shaped cross section.

With this arrangement, since the circumferentially opposed surfaces of each cage claw portion are connected to the respective axially opposed surfaces via curved surfaces having a concave circular arc-shaped cross section, it is possible to ensure the cross-sectional area of the axial root portion of the cage claw portion while keeping a small mass of the axial distal end portion of the cage claw portion. Therefore, it is possible to effectively reduce deflection of the cage claw portion due to the centrifugal force applied to the cage claw portion.

An axial end of the outer-diameter-side axial groove of each of the cage claw portions closer to the cage circular annular portion preferably rises to an outer periphery of the cage circular annular portion to form a concave circular arc-shaped cross section.

With this arrangement, since the axial end of the outer-diameter-side axial groove of each cage claw portion closer to the cage circular annular portion rises to form a concave circular arc-shaped cross section, it is possible to ensure the cross-sectional area of the axial root portion of the cage claw portion while keeping a small mass of the axial distal end portion of the cage claw portion. Therefore, it is possible to effectively reduce deflection of the cage claw portion due to the centrifugal force applied to the cage claw portion.

The cage circular annular portion preferably has, on an inner periphery of the cage circular annular portion, a cage guided surface configured to be guided while coming into sliding contact with an outer periphery of the inner ring.

With this arrangement, the cage made of resin can be radially positioned by the sliding contact between the cage guided surface of the cage circular annular portion on its inner periphery and the outer periphery of the inner ring.

According to the claimed invention, the ball bearing further comprises an annular seal member closing one axial end opening of the annular space, the cage circular annular portion has a cage-side sliding contact surface axially opposed to the seal member and configured to come into sliding contact with the seal member, the seal member has a seal-side sliding contact surface configured to come into sliding contact with the cage-side sliding contact surface, and a plurality of axial protrusions each having an axially convex circular arc shape in cross sections along a circumferential direction are formed on one of the cage-side sliding contact surface and the seal-side sliding contact surface so as to be disposed at constant pitches in the circumferential direction.

With this arrangement, since a plurality of axial protrusions whose cross sections along the circumferential direction have an axially convex circular arc shape are formed on one of the cage-side sliding contact surface and the seal-side sliding contact surface at constant pitches in the circumferential direction, oil films due to the wedge film effect are formed between the sliding contact surface and the respective axial protrusions. Due to the oil films, the lubrication condition between the sliding contact surface and the axial protrusions becomes fluid lubrication condition, thus making it possible to markedly reduce the contact resistance between the cage and the seal member. Therefore, it is possible to prevent abnormal heat generation due to the sliding resistance of the contact portions of the cage and the seal member. Also, since the cage circular annular portion is disposed to come into sliding contact with the seal member, it is possible to increase the axial thickness of the cage circular annular portion, and thus increase the rigidity of the cage circular annular portion. Therefore, even during high-speed rotation, it is possible to reduce torsional deformation of the cage circular annular portion due to the centrifugal forces that the cage claw portions receive, and reduce inclination of the cage claw portions toward radially outer side.

Each of the axial protrusions preferably includes: a parallel apex portion having an axially convex circular arc-shape in cross sections along the circumferential direction whose apex height is radially uniform; and an inclined apex portion having an axially convex circular-arc shape in cross sections along the circumferential direction whose apex height gradually decreases radially outward from a radially outer end of the parallel apex portion.

With this arrangement, while the bearing is rotating at a low speed and the centrifugal forces which the cage claw portions receive are relatively small, oil films due to the wedge film effect can be formed between the sliding contact surface and the parallel apex portions of the respective axial protrusions. Also, while the bearing is rotating at a high speed and the centrifugal forces which the cage claw portions receive are relatively large, an oil film due to the wedge film effect can be formed between the sliding contact surface, and the parallel apex portion and the inclined apex portion of each axial protrusion with torsional deformation of the cage circular annular portion relatively large. As described above, regardless of the rotation speed of the bearing, oil films due to the wedge film effect can be stably formed between the cage and the seal member.

A cross section of the inclined apex portion of each of the axial protrusions perpendicular to the circumferential direction preferably has a rounded shape smoothly connected to the parallel apex portion.

If such a rounded shape is used, since the inclined apex portion and the parallel apex portion are smoothly connected to each other, when, with torsional deformation of the cage circular annular portion relatively large, an oil film due to the wedge film effect is formed between the sliding contact surface, and the parallel apex portion and the inclined apex portion, the oil film can be formed stably.

The axial protrusions are preferably disposed at positions where the axial protrusions overlap with a pitch circle of the balls, or disposed radially outwardly of the pitch circle.

With this arrangement, when the centrifugal forces applied to the cage claw portions cause torsional deformation of the cage circular annular portion in the direction in which the cage claw portions are inclined radially outward, it is possible to prevent, due to the torsional deformation, the cage-side sliding contact surface and the seal-side sliding contact surface from coming into contact with each other at a position displaced radially outwardly of the axial protrusions.

According to the claimed invention, the outer-diameter-side axial groove of each of the cage claw portions is shaped such that, from the distal end of the cage claw portion toward the cage circular annular portion, a position of a bottom of the outer-diameter-side axial groove gradually changes radially outwardly.

If such a shape is used, since the position of the bottom of the outer-diameter-side axial groove of each cage claw portion gradually changes radially outwardly from the distal end of the cage claw portion toward the cage circular annular portion, lubricating oil supplied into the outer-diameter-side axial groove is moved from the distal end of the cage claw portion toward the cage circular annular portion by the pumping action, and is introduced into the space between the cage circular annular portion and the seal member. Therefore, it is possible to sufficiently lubricate the portions of the bearing between one of the cage-side sliding contact surface and the seal-side sliding contact surface and the axial protrusions, and effectively form oil films due to wedge films.

In another example not claimed, the inner-diameter-side axial groove of each of the cage claw portions is preferably shaped such that, from the distal end of the cage claw portion toward the cage circular annular portion, a position of a bottom of the inner-diameter-side axial groove gradually changes radially inwardly.

It is preferable that an axial end of the annular space opposite from an axial end of the annular space closed by the seal member is not provided with an additional seal member, and is open so that lubricating oil supplied from outside enters the annular space through this opening.

With this arrangement, it is possible to sufficiently lubricate the portions of the bearing between one of the cage-side sliding contact surface and the seal-side sliding contact surface and the axial protrusions, and reliably form oil films due to wedge films.

If each of the cage claw portions has an axial length larger than a radius of each of the balls, and has circumferentially opposed surfaces circumferentially opposed to the corresponding pair of the balls, respectively, portions of the circumferentially opposed surfaces configured to circumferentially support the corresponding pair of the balls are preferably straight portions having no circumferential inclination, and extending straight in the axial direction so that when supporting the corresponding pair of the balls, no axial component forces are generated.

With this arrangement, when each ball is supported by the cage claw portion, no axial component force is generated at the cage claw portion. Therefore, it is possible to prevent the cage from being axially pressed hard against the seal member, and thus effectively reduce the sliding resistance of the contact portions of the cage and the seal member.

If the axial protrusions are formed on the seal-side sliding contact surface, it is preferable that the seal member comprises an annular metal core, and a rubber part bonded to a surface of the metal core by vulcanization, and the axial protrusions are formed of the same material as the rubber part.

With this arrangement, the axial protrusions having high dimensional accuracy can be formed at a low lost.

It is preferable that the inner-diameter-side axial groove of each of the cage claw portions axially extends through the radially inner surface of the cage claw portion and the cage guided surface.

With this arrangement, lubricating oil supplied into the space radially inside of the cage claw portions is introduced, through the inner-diameter-side axial grooves, into the space between the cage circular annular portion and the seal member. Therefore, it is possible to sufficiently lubricate the portions of the bearing between one of the cage-side sliding contact surface and the seal-side sliding contact surface and the axial protrusions, and effectively form oil films due to wedge films.

If the cage circular annular portion has, on an inner periphery of the cage circular annular portion, a cage guided surface configured to be guided while coming into sliding contact with an outer periphery of the inner ring, the cage circular annular portion preferably has a chamfer obliquely extending in a cross section perpendicular to the circumferential direction, to connect the cage-side sliding contact surface and the cage guided surface to each other.

With this arrangement, lubricating oil introduced into the space between the cage circular annular portion and the seal member through the inner-diameter-side axial grooves from the radially inner areas of the cage claw portions can be smoothly fed along the chamfer and led onto the cage-side sliding contact surface by a centrifugal force.

In another example not claimed, the ball bearing may be a ball bearing wherein the outer ring has, on an inner periphery of the outer ring, an outer ring raceway groove with which the balls come into rolling contact, and a pair of outer ring groove shoulders located on both axial sides of the outer ring raceway groove, each of the cage claw portions has an axial length larger than an axial width of the outer ring raceway groove, the cage circular annular portion has, on a radially outer surface of the cage circular annular portion, root-side guided surfaces configured to come into sliding contact with one of the outer ring groove shoulders, the cage claw portions have, respectively, distal-end-side guided surfaces each formed on a radially outer surface of an axial end portion of the cage claw portion on a distal end side thereof, and configured to come into sliding contact with the other of the outer ring groove shoulders, and each of the root-side guided surfaces and the distal-end-side guided surfaces has a radially outwardly protruding circular arc shape in cross sections along the circumferential direction.

With this arrangement, since each of the root-side guided surfaces has, in cross sections along the circumferential direction, a radially outwardly protruding circular arc shape, oil films due to the wedge film effect are formed between the one outer ring groove shoulder and the root-side guided surfaces. Due to the oil films, the lubrication condition between the one outer ring groove shoulder and the root-side guided surfaces becomes the fluid lubrication condition, thus making it possible to markedly reduce the contact resistance between the cage and the outer ring. Since, as with the root-side guided surfaces, each of the distal-end-side guided surfaces also has a radially outwardly protruding circular arc shape in cross sections along the circumferential direction, oil films due to the wedge film effect are formed between the other outer ring groove shoulder and the distal-end-side guided surfaces. Due to the oil films, the lubrication condition between the other outer ring groove shoulder and the distal-end-side guided surfaces becomes the fluid lubrication condition, thus making it possible to markedly reduce the contact resistance between the cage and the outer ring. Therefore, it is possible to prevent abnormal heat generation due to the sliding resistance of the contact portions of the cage and the outer ring. Also, since the one outer ring groove shoulder supports the cage circular annular portion from the radially outer side, and the other outer ring groove shoulder supports the axial ends of the cage claw portions on their distal end sides from the radially outer side, flexural deformation of the cage claw portions toward the radially outer side is less likely to occur. Therefore, even during high-speed rotation, it is possible to reduce torsional deformation of the cage circular annular portion, and flexural deformation of the cage claw portions per se toward the radially outer side due to the centrifugal forces which the cage claw portions receive.

It is preferable that each of the root-side guided surfaces has, on a side thereof remoter from a corresponding one of the cage claw portions, an axial end edge chamfered into a rounded shape, and each of the distal-end-side guided surfaces has, on a side thereof remoter from the cage circular annular portion, an axial end edge chamfered into a rounded shape.

If chamfered into a rounded shape, oil films due to the wedge film effect can be effectively formed between the one outer ring groove shoulder and the root-side guided surfaces, and oil films due to the wedge film effect can be effectively formed between the other outer ring groove shoulder and the distal-end-side guided surfaces, too.

Each of the cage claw portions preferably has a relief recess in a portion of the radially outer surface of the cage claw portion between a corresponding one of the root-side guided surfaces and the distal-end-side guided surface of the cage claw portion, the relief recess having an axial width larger than the axial width of the outer ring raceway groove, and extending in the circumferential direction.

If such relief recesses are formed, it is possible to prevent each of the boundaries between the outer ring raceway groove and the respective outer ring groove shoulders from coming into sliding contact with the radially outer surface of the cage circular annular portion or the radially outer surfaces of the cage claw portions. Therefore, it is possible to prevent the radially outer surface of the cage circular annular portion and the radially outer surfaces of the cage claw portions from becoming worn locally at the positions corresponding to the boundaries between the outer ring raceway groove and the outer ring groove shoulders.

In another example not claimed, the present invention also provides a ball bearing comprising: an inner ring; an outer ring arranged radially outwardly of, and coaxially with, the inner ring; a plurality of balls disposed in an annular space between the inner ring and the outer ring; an annular seal member closing one axial end opening of the annular space; and a cage made of resin and retaining the balls, wherein the cage comprises a cage circular annular portion extending circumferentially through a space axially sandwiched between the seal member and the space through which the balls pass; and cage claw portions having a cantilevered structure extending from the cage circular annular portion, and each located between a corresponding pair of the balls circumferentially adjacent to each other, characterized in that the cage circular annular portion has a cage-side sliding contact surface axially opposed to the seal member and configured to come into sliding contact with the seal member, wherein the seal member has a seal-side sliding contact surface configured to come into sliding contact with the cage-side sliding contact surface, and wherein a plurality of axial protrusions each having an axially convex circular arc shape in cross sections along a circumferential direction are formed on one of the cage-side sliding contact surface and the seal-side sliding contact surface at constant pitches in the circumferential direction.

It is preferable that each of the cage claw portions has an axial length larger than a radius of each of the balls, and each of the cage claw portions has circumferentially opposed surfaces which are circumferentially opposed to the corresponding pair of the balls, respectively, and of which portions configured to circumferentially support the corresponding pair of the balls are straight portions having no circumferential inclination, and extending straight in an axial direction in order that when supporting the corresponding pair of the balls, no axial component forces are generated.

Of the circumferentially opposed surfaces of each of the cage claw portions, the portions configured to circumferentially support the corresponding pair of the balls, preferably extend parallel to an imaginary straight line connecting a center of the cage circular annular portion and a center of the cage claw portion to each other in order that when the cage claw portion is moved radially outwardly by a centrifugal force, the circumferentially opposed surfaces do not interfere with the corresponding pair of the balls.

With this arrangement, when the cage circular annular portion and the cage claw portions are deformed by the centrifugal forces applied to the cage claw portions and the cage claw portions are thus moved radially outwardly, it is possible to prevent the circumferentially opposed surfaces of the cage claw portions from interfering with the balls.

Each of the axial protrusions preferably includes: a parallel apex portion having an axially convex circular arc convex shape in cross sections along the circumferential direction whose apex height is radially uniform; and an inclined apex portion having an axially circular arc convex shape in cross sections along the circumferential direction whose apex height gradually decreases radially outward from a radially outer end of the parallel apex portion.

The cage, which is made of resin, preferably has, in an inner periphery of the cage, inner-diameter-side axial grooves axially extending through radially inner surfaces of the respective cage claw portions and the cage guided surface.

The cage circular annular portion preferably has a chamfer obliquely extending in a cross section perpendicular to the circumferential direction, to connect the cage-side sliding contact surface and the cage guided surface to each other.

Each of the cage claw portions preferably has, in a radially outer surface of the cage claw portion, an outer-diameter-side axial groove axially extending from a distal end of the cage claw portion toward the cage circular annular portion, and shaped such that, from the distal end of the cage claw portion toward the cage circular annular portion, a position of a bottom of the outer-diameter-side axial groove gradually changes radially outwardly.

With this arrangement, since the position of the bottom of the outer-diameter-side axial groove of each cage claw portion gradually changes radially outwardly from the distal end of the cage claw portion toward the cage circular annular portion, lubricating oil supplied into the outer-diameter-side axial groove is moved from the distal end of the cage claw portion toward the cage circular annular portion by the pumping action, and is introduced into the space between the cage circular annular portion and the seal member. Therefore, it is possible to sufficiently lubricate the portions of the bearing between one of the cage-side sliding contact surface and the seal-side sliding contact surface and the axial protrusions, and effectively form oil films due to wedge films.

In another example not claimed, the present invention also provides a ball bearing comprising: an inner ring; an outer ring arranged radially outwardly of, and coaxially with, the inner ring; a plurality of balls disposed in an annular space between the inner ring and the outer ring; and a cage made of resin and retaining the balls, wherein the outer ring has, on an inner periphery of the outer ring, an outer ring raceway groove with which the balls comes into rolling contact, a pair of outer ring groove shoulders located on both axial sides of the outer ring raceway groove, wherein the cage comprises: a cage circular annular portion adjacent to a space through which the balls pass, and extending in a circumferential direction; and cage claw portions having a cantilevered structure axially extending from the cage circular annular portion, and each located between a corresponding pair of the balls circumferentially adjacent to each other, characterized in that each of the cage claw portions has an axial length larger than an axial width of the outer ring raceway groove, wherein the cage circular annular portion has, on a radially outer surface of the cage circular annular portion, root-side guided surfaces configured to come into sliding contact with one of the outer ring groove shoulders, wherein the cage claw portions have, respectively, distal-end-side guided surfaces each formed on a radially outer surface of an axial end portion of the cage claw portion on a distal end side thereof, and configured to come into sliding contact with the other of the outer ring groove shoulders, and wherein each of the root-side guided surfaces and the distal-end-side guided surfaces has a radially outwardly protruding circular arc shape in cross sections along the circumferential direction.

With this arrangement, since each of the root-side guided surfaces has, in cross sections along the circumferential direction, a radially outwardly protruding circular arc shape, oil films due to the wedge film effect are formed between the one outer ring groove shoulder and the root-side guided surfaces. Due to the oil films, the lubrication condition between the one outer ring groove shoulder and the root-side guided surfaces becomes the fluid lubrication condition, thus making it possible to markedly reduce the contact resistance between the cage and the outer ring. Since, as with the root-side guided surfaces, each of the distal-end-side guided surfaces also has a radially outwardly protruding circular arc shape in cross sections along the circumferential direction, oil films due to the wedge film effect are formed between the other outer ring groove shoulder and the distal-end-side guided surfaces. Due to the oil films, the lubrication condition between the other outer ring groove shoulder and the distal-end-side guided surfaces becomes the fluid lubrication condition, thus making it possible to markedly reduce the contact resistance between the cage and the outer ring. Therefore, it is possible to prevent abnormal heat generation due to the sliding resistance of the contact portions of the cage and the outer ring. Also, since the one outer ring groove shoulder supports the cage circular annular portion from the radially outer side, and the other outer ring groove shoulder supports the axial ends of the cage claw portions on their distal end sides from the radially outer side, flexural deformation of the cage claw portion toward the radially outer side is less likely to occur. Therefore, even during high-speed rotation, it is possible to reduce torsional deformation of the cage circular annular portion, and flexural deformation of the cage claw portions per se toward the radially outer side due to the centrifugal forces which the cage claw portions receive.

Each of the cage claw portions preferably has circumferentially opposed surfaces which are circumferentially opposed to the corresponding pair of the balls, respectively, and of which portions configured to circumferentially support the corresponding pair of the balls are flat surfaces extending parallel to an imaginary straight line connecting a center of the cage circular annular portion and a center of the cage claw portion to each other in order that when the cage claw portion is moved radially outwardly by a centrifugal force, the circumferentially opposed surfaces do not interfere with the corresponding pair of the balls.

Each of the cage claw portions preferably has a relief recess in a portion of a radially outer surface of the cage claw portion between a corresponding one of the root-side guided surfaces and the distal-end-side guided surface of the cage claw portion, the relief recess having an axial width larger than the axial width of the outer ring raceway groove, and extending in the circumferential direction.

Each of the cage claw portions preferably has, in the radially inner surface of the cage claw portion, an oil reservoir groove axially extending from a distal end of the cage claw portion toward the cage circular annular portion.

If such oil reservoir grooves are formed, lubricating oil scattered radially outwardly by a centrifugal force can be stored in the oil reservoir grooves, and supplied to the inner ring.

It is preferable that the ball bearing further comprises an annular seal member closing one axial end opening of the annular space, the cage circular annular portion has a cage-side sliding contact surface axially opposed to the seal member and configured to come into sliding contact with the seal member, the seal member has a seal-side sliding contact surface configured to come into sliding contact with the cage-side sliding contact surface, and a plurality of axial protrusions each of which has, in cross sections along the circumferential direction, an axially convex circular arc shape are formed on one of the cage-side sliding contact surface and the seal-side sliding contact surface at constant pitches in the circumferential direction.

With this arrangement, since a plurality of axial protrusions whose cross sections along the circumferential direction have an axially convex circular arc shape are formed on one of the cage-side sliding contact surface and the seal-side sliding contact surface at constant pitches in the circumferential direction, oil films due to the wedge film effect are formed between the sliding contact surface and the respective axial protrusions. Due to the oil films, the lubrication condition between the sliding contact surface and the axial protrusions becomes fluid lubrication condition, thus making it possible to markedly reduce the contact resistance between the cage and the seal member. Therefore, it is possible to prevent abnormal heat generation due to the sliding resistance of the contact portions of the cage and the seal member. Also, since the cage circular annular portion is disposed to come into sliding contact with the seal member, it is possible to increase the axial thickness of the cage circular annular portion, and thus increase the rigidity of the cage circular annular portion. Therefore, even during high-speed rotation, it is possible to reduce torsional deformation of the cage circular annular portion due to the centrifugal forces that the cage claw portions receive.

Each of the axial protrusions preferably comprises: a parallel apex portion having an axially convex circular arc shape in cross sections along the circumferential direction whose apex height is radially uniform; and an inclined apex portion having an axially convex circular arc shape in cross sections along the circumferential direction whose apex height gradually decreases radially outward from a radially outer end of the parallel apex portion.

With this arrangement, it is possible to sufficiently lubricate the root-side guided surfaces and the distal-end-side guided surfaces, and reliably form oil films due to wedge films.

Each of the above ball bearings is particularly suitably used as a bearing of an electric motor of an electric vehicle, or a bearing of an electric vehicle transmission for reducing rotation of the electric motor.

In the ball bearing of the present invention, deformation of the cage made of resin due to a centrifugal force is less likely occur during high-speed rotation.

<FIG> illustrates a ball bearing <NUM> according to the first embodiment which is not part of the claimed invention. The ball bearing <NUM> includes an inner ring <NUM>; an outer ring <NUM> arranged radially outwardly of, and coaxially with, the inner ring <NUM>; a plurality of balls <NUM> disposed in an annular space <NUM> between the inner ring <NUM> and the outer ring <NUM> so as to be circumferentially spaced apart from each other; an annular seal member <NUM> closing one of the end openings of the annular space <NUM> on both axial sides thereof; and a resin cage <NUM> made of resin (hereinafter simply referred to as the "cage <NUM>") that keeps the circumferential distances between the balls <NUM>. The ball bearing <NUM> is a sealed ball bearing including the seal member <NUM>.

Formed on the outer periphery of the inner ring <NUM> are an inner ring raceway groove <NUM> with which the balls <NUM> come into rolling contact; a pair of inner ring groove shoulders <NUM> located axially outwardly of the inner ring raceway groove <NUM>; and a sliding recess <NUM> located axially outwardly of one of the inner ring groove shoulders <NUM>. The inner ring raceway groove <NUM> is a circular arc groove having a concave circular arc-shaped cross section along the surfaces of the balls <NUM>, and extends circumferentially at the axial central portion of the outer periphery of the inner ring <NUM>. The pair of inner ring groove shoulders <NUM> are bank-shaped portions circumferentially extending on both axial sides of the inner ring raceway groove <NUM>. The sliding recess <NUM> is a circumferentially extending recess adjacent to the axially outer side of the one inner ring groove shoulder <NUM>. The seal member <NUM> has, at the radially inner end thereof, a seal lip <NUM> in sliding contact with the inner surface of the sliding recess <NUM>. In the shown example, the portion of the inner surface of the sliding recess 10with which the seal lip <NUM> is in sliding contact is a cylindrical surface portion having a uniform outer diameter along the axial direction.

Formed on the outer periphery of the outer ring <NUM> are an outer ring raceway groove <NUM> with which the balls <NUM> come into rolling contact; a pair of outer ring groove shoulders <NUM> located axially outwardly of the outer ring raceway groove <NUM>; and a seal fixing groove <NUM> located axially outwardly of one of the outer ring groove shoulders <NUM>. The outer ring raceway groove <NUM> is a circular arc groove having a concave circular arc-shaped cross section along the surfaces of the balls <NUM>, and extends circumferentially at the axial central portion of the inner periphery of the outer ring <NUM>. The pair of outer ring groove shoulders <NUM> are bank-shaped portions circumferentially extending on both axial sides of the outer ring raceway groove <NUM>. The seal fixing groove <NUM> is a circumferentially extending groove adjacent to the axially outer side of the one outer ring groove shoulder <NUM>. The seal member <NUM> has, on the radially outer edge thereof, a fitted portion <NUM> fitted in, and fixed to, the seal fixing groove <NUM>.

The balls <NUM> are radially sandwiched between the outer ring raceway groove <NUM> and the inner ring raceway groove <NUM>. The outer ring raceway groove <NUM> and the inner ring raceway groove <NUM> have an axial width dimension larger than half of the diameter of each ball <NUM>. The balls <NUM> are steel balls. Instead, however, ceramic balls may be used as the balls <NUM>.

As illustrated in <FIG>, the seal member <NUM> is an annular member comprising an annular metal core <NUM>, and a rubber part <NUM> bonded to the surface of the metal core <NUM> by vulcanization of a rubber material (such as nitrile rubber or acrylic rubber). The seal member <NUM> includes a fitted portion <NUM> fitted in the seal fixing groove <NUM>; a circular annular plate portion <NUM> extending radially inwardly from the fitted portion <NUM>; and a seal lip <NUM> kept in sliding contact with the inner surface of the sliding recess <NUM>. The metal core <NUM> includes a circular annular plate-shaped flange portion <NUM>; and a cylindrical portion <NUM> bent axially inwardly along the radially outer edge of the flange portion <NUM>. The flange portion <NUM> is embedded in the circular annular plate portion <NUM> of the seal member <NUM>. The cylindrical portion <NUM> is embedded in the fitted portion <NUM> of the seal member <NUM>.

As illustrated in <FIG>, the seal member <NUM> is disposed only in one of the end openings of the annular space <NUM> on both axial sides thereof. In other words, the axial end of the annular space <NUM> on the opposite side (left side in <FIG>) from the axial end of the annular space <NUM> on its side closed by the seal member <NUM> (right side in <FIG>) is not provided with an additional seal member <NUM>, and is thus open so that lubricating oil supplied from outside enters the annular space <NUM> through this opening.

The cage <NUM> includes a cage circular annular portion <NUM> extending in the circumferential direction and adjacent to the area through which the balls <NUM> pass; and cage claw portions <NUM> axially extending from the cage circular annular portion 21each between the corresponding circumferentially adjacent balls <NUM>. The cage circular annular portion <NUM> and the cage claw portions <NUM> are seamlessly and integrally formed of a resin composition. The resin composition forming the cage circular annular portion <NUM> and the cage claw portions <NUM> may be composed of only a resin material, but, here, a resin composition comprising a resin material and a reinforcing fiber material added thereto is used. The cage <NUM> is preferably formed by injection molding. The cage circular annular portion <NUM> extends circumferentially through the space between the seal member <NUM> and the space through which the balls <NUM> pass.

The resin material as the base material of the resin composition may be a polyamide (PA) or a super engineering plastic. As the polyamide, for example, polyamide <NUM> (PA46), polyamide <NUM> (PA66) or polynonamethylene terephthalamide (PA9T) can be used. As the super engineering plastic, for example, polyether ether ketone (PEEK) or polyphenylene sulfide (PPS) can be used. As the reinforcing fiber material added to the resin material, for example, glass fiber, carbon fiber or aramid fiber can be used.

Each cage claw portion <NUM> has cantilevered structure of which one axial end is a fixed end fixed to the cage circular annular portion <NUM>, and the other axial end is a free end. The cage claw portion <NUM> has an axial length larger than the radius of each ball <NUM>. The cage claw portion <NUM> has a uniform radial thickness in the axial direction, that is, the radial thickness does not change in the axial direction.

As illustrated in <FIG> and <FIG>, the cage claw portion <NUM> has, in its radially outer surface <NUM>, an outer-diameter-side axial groove <NUM> axially extending from the distal end of the cage claw portion <NUM> toward the cage circular annular portion <NUM>. Also, the cage claw portion <NUM> has, in its radially inner surface <NUM>, an inner-diameter-side axial groove <NUM> axially extending from the distal end of the cage claw portion <NUM> toward the cage circular annular portion <NUM>. As illustrated in <FIG>, the outer-diameter-side axial groove <NUM> and the inner-diameter-side axial groove <NUM> have a width equal to, or larger than, half of the circumferential width of the distal end of the cage claw portion <NUM>. Due to the outer-diameter-side axial groove <NUM> and the inner-diameter-side axial groove <NUM>, the cross section of the cage claw portion <NUM> perpendicular to the axial direction has an H shape of which the openings of the letter H face radially outward and radially inward, respectively. Also, in order that the cage claw portion <NUM> has the same H shape when the cage claw portion <NUM> is axially seen from its distal end side, the outer-diameter-side axial groove <NUM> and the inner-diameter-side axial groove <NUM> are open to the distal end of the cage claw portion <NUM>.

The cage claw portion <NUM> has circumferentially opposed surfaces <NUM> circumferentially opposed to the corresponding balls <NUM>, respectively. The portions of the circumferentially opposed surfaces <NUM> which circumferentially support the balls <NUM> are flat surfaces extending such that when the cage claw portion <NUM> is moved radially outwardly by a centrifugal force, the circumferentially opposed surfaces <NUM> do not interfere with the balls <NUM>. In the shown example, the circumferentially opposed surfaces <NUM> are flat surfaces extending parallel to the imaginary straight line connecting the center of the cage circular annular portion <NUM> and the center of the cage claw portion <NUM> to each other (flat surfaces extending such that the cage claw portion <NUM> has a uniform circumferential width in the radial direction, i.e., a circumferential width that does not change in the radial direction), when seen in the axial direction. The center of the cage circular annular portion <NUM> is also the center of the inner ring <NUM> or the center of the outer ring <NUM>. The center of the cage claw portion <NUM> is equally spaced apart from the circumferentially opposed surfaces <NUM> of the cage claw portion <NUM> on both circumferential sides thereof, when seen in the axial direction.

The distance between each circumferentially adjacent pair of cage claw portions <NUM> (i.e., the distance between the circumferentially opposed surfaces <NUM> of each circumferentially adjacent pair of cage claw portions <NUM> that are circumferentially opposed to each other via the ball) is preferably <NUM> to <NUM> times the diameter of the ball <NUM> on the pitch circle of the balls <NUM>, because this reduces vibration of the cage <NUM>.

As illustrated in <FIG> and <FIG>, the portion of each circumferentially opposed surface <NUM> that circumferentially supports the ball <NUM> extends straight in the axial direction with no circumferential inclination, when seen in the radial direction so that no axial component force is generated when supporting the ball <NUM>. The cage circular annular portion <NUM> has axially opposed surfaces <NUM> axially opposed to the respective balls <NUM>. Each circumferentially opposed surface <NUM> and the corresponding axially opposed surface <NUM> are connected together via a curved surface having a concave circular arc-shaped cross section. In the shown example, the curved surface connecting the circumferentially opposed surface <NUM> and the axially opposed surface <NUM> to each other is a single rounded curved surface (part-cylindrical surface having a constant radius of curvature).

As illustrated in <FIG>, the axial end of the outer-diameter-side axial groove <NUM> of each cage claw portion <NUM> closer to the cage circular annular portion <NUM> rises to the outer periphery of the cage circular annular portion <NUM> to form a concave circular arc-shaped cross section, and the axial end of the inner-diameter-side axial groove <NUM> of the cage claw portion <NUM> closer to the cage circular annular portion <NUM> also rises to the inner periphery of the cage circular annular portion <NUM>. The cage circular annular portion <NUM> has, on its inner periphery, a cage guided surface <NUM> configured to be guided by the one inner ring groove shoulder <NUM> of the inner ring <NUM> on its outer periphery while being in sliding contact therewith. The cage guided surface <NUM> is a circular annular surface configured to come into direct sliding contact with the one inner ring groove shoulder <NUM>. By setting the sliding gap between the cage guided surface <NUM> and the one inner ring groove shoulder <NUM> to <NUM> or less, vibration of the cage <NUM> can be reduced. The portion of the inner-diameter-side axial groove <NUM> rising to the inner periphery of the cage circular annular portion <NUM> is open to the cage guided surface <NUM>.

As illustrated in <FIG> and <FIG>, the seal lip <NUM> includes, on its radially inner edge, a plurality of protrusions <NUM> kept in sliding contact with the sliding recess <NUM> of the inner ring <NUM> on its outer periphery, while being circumferentially spaced apart from each other. The protrusions <NUM> extend in the direction perpendicular to the circumferential direction. As illustrated in <FIG>, the protrusions <NUM> have a convex circular arc-shaped cross section.

As illustrated in <FIG>, ball bearings <NUM> as described above are usable as bearings of an electric vehicle transmission <NUM> that reduces rotation of electric motors <NUM> of an electric vehicle such as a battery electric vehicle (EV) or a hybrid electric vehicle (HEV). The bearings of the electric vehicle transmission <NUM> rotate at the number of rotations in a low-speed to high-speed wide rotation range while the vehicle is travelling, and are used under the conditions that, while the bearings are rotating at the highest speed, the dmn (ball pitch circle diameter (mm) X the number of rotations (min-<NUM>)) value exceeds <NUM> million.

The transmission of <FIG> includes stators <NUM> and rotors <NUM> of the electric motors <NUM>; a rotary shaft <NUM> coupled to the rotors <NUM>, ball bearings <NUM> rotatably supporting the rotary shaft <NUM>; a second rotary shaft <NUM> and a third rotary shaft <NUM> both arranged parallel to the rotary shaft <NUM>; a first gear train <NUM> that transmits rotation of the rotary shaft <NUM> to the second rotary shaft <NUM>; and a second gear train <NUM> that transmits rotation of the second rotary shaft <NUM> to the third rotary shaft <NUM>. The stators <NUM> are annular stationary members, and the rotors <NUM> as the rotary members are disposed inside the respective stators <NUM>. When the stators <NUM> are energized, the rotors <NUM> rotate due to the electromagnetic forces acting between the stators <NUM> and the rotors <NUM>, and the rotation of the rotors <NUM> is inputted/transmitted to the rotary shaft <NUM>.

In this ball bearing <NUM>, since, as illustrated in <FIG>, each cage claw portion <NUM> has an H-shaped cross section due to the outer-diameter-side axial groove <NUM> in the radially outer surface <NUM> of the cage claw portion <NUM> and the inner-diameter-side axial groove <NUM> in the radially inner surface <NUM> of the cage claw portion <NUM>, it is possible to reduce the mass of the cage claw portions <NUM> while ensuring the moment of inertia of area of the cage claw portions <NUM> (while making the cage claw portions <NUM> less likely to deform against the bending moment). Therefore, even during high-speed rotation, it is possible to reduce torsional deformation of the cage circular annular portion <NUM>, and flexural deformation of the cage claw portions <NUM> per se toward the radially outer side due to the centrifugal forces which the cage claw portions <NUM> receive. It has become clear from data analysis by the inventors that the deformation amount by which the cage claw portions <NUM> formed with the outer-diameter-side axial grooves <NUM> and the inner-diameter-side axial grooves <NUM> are deformed by a centrifugal force can be reduced to at least <NUM>% or less compared to the cage claw portions <NUM> that are not formed with the outer-diameter-side axial grooves <NUM> and the inner-diameter-side axial grooves <NUM>.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, the portions of the circumferentially opposed surfaces <NUM> of each cage claw portion <NUM> that circumferentially support the balls <NUM> are flat surfaces extending parallel to the imaginary straight line connecting the center of the cage circular annular portion <NUM> and the center of the cage claw portion <NUM> to each other, when the cage claw portion <NUM> is moved radially outwardly by the centrifugal force applied to the cage claw portion <NUM>, it is possible to prevent the circumferentially opposed surfaces <NUM> of the cage claw portion <NUM> from interfering with the balls <NUM>. Also, since the shear resistance of lubricating oil generated between the circumferentially opposed surfaces <NUM> of the cage claw portions <NUM> and the balls <NUM> decreases, it is also possible to reduce the heat generation in the ball bearing <NUM>.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, the circumferentially opposed surfaces <NUM> of each cage claw portion <NUM> are connected to the respective axially opposed surfaces <NUM> via curved surfaces having a concave circular arc-shaped cross section, it is possible to ensure the cross-sectional area of the axial root portion of the cage claw portion <NUM> while keeping a small mass of the axial distal end portion of the cage claw portion <NUM>. Therefore, it is possible to effectively reduce deflection of the cage claw portion <NUM> due to the centrifugal force applied to the cage claw portion <NUM>.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, the axial end of the outer-diameter-side axial groove <NUM> of each cage claw portion <NUM> closer to the cage circular annular portion <NUM> rises to form a concave circular arc-shaped cross section, it is possible to ensure the cross-sectional area of the axial root portion of the cage claw portion <NUM> while keeping a small mass of the axial distal end portion of the cage claw portion <NUM>. Also, since the axial end of the inner-diameter-side axial groove <NUM> of the cage claw portion <NUM> closer to the cage circular annular portion <NUM> also rises to the inner periphery of the cage circular annular portion <NUM>, it is possible to more effectively ensure the cross-sectional area of the axial root portion of the cage claw portion <NUM>. Therefore, it is possible to effectively reduce deflection of the cage claw portion <NUM> due to the centrifugal force applied to the cage claw portion <NUM>.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, the cage circular annular portion <NUM> has, on its inner periphery, a cage guided surface <NUM> configured to be guided while coming into sliding contact with the outer periphery of the inner ring <NUM>, the cage <NUM> can be radially positioned by the sliding contact between the cage guided surface <NUM> of the cage circular annular portion <NUM> on its inner periphery and the outer periphery of the inner ring <NUM>.

<FIG> illustrate a ball bearing <NUM> according to the second embodiment which is part of the claimed invention. The elements of the second embodiment corresponding to those of the first embodiment are denoted by the same reference numerals, and their description is omitted.

As illustrated in <FIG>, the portions of the circumferentially opposed surfaces <NUM> of each cage claw portion <NUM> which circumferentially support the balls <NUM> are flat surfaces extending parallel to the imaginary straight line connecting the center of the cage circular annular portion <NUM> and the center of the cage claw portion <NUM> to each other when seen in the axial direction such that when the cage claw portion <NUM> is moved radially outwardly by a centrifugal force, the circumferentially opposed surfaces <NUM> do not interfere with the balls <NUM>.

As illustrated in <NUM>, the portions of the circumferentially opposed surfaces <NUM> that circumferentially support the balls <NUM> have no circumferential inclination, and extend straight in the axial direction when seen in the radial direction so that when supporting the balls <NUM>, no axial component force is generated.

As illustrated in <FIG>, each cage claw portion <NUM> is tapered such that the radial thickness gradually decreases from its end closer to the cage circular annular portion <NUM> toward its end remoter from the cage circular annular portion <NUM> (i.e., from its root toward its distal end). The cage circular annular portion <NUM> has an axial thickness substantially equal to the axial distance between the balls <NUM> and the seal member <NUM> (specifically, <NUM>% or more and less than <NUM>% of the axial distance between the balls <NUM> and the seal member <NUM>). The cage circular annular portion <NUM> has a cage-side sliding contact surface <NUM> that is axially opposed to the seal member <NUM> and comes into sliding contact with the seal member <NUM>. The seal member <NUM> has a seal-side sliding contact surface <NUM> that comes into sliding contact with the cage-side sliding contact surface <NUM>.

As illustrated in <FIG>, a plurality of axial protrusions <NUM> are formed on the cage-side sliding contact surface <NUM> at constant pitches in the circumferential direction. The cross section of each axial protrusion <NUM> along the circumferential direction has an axially convex circular arc shape. The axial protrusion <NUM> has an axial height set to <NUM>% or less of the circumferential width dimension of the axial protrusion <NUM>. In <FIG>, the axial height of the axial protrusion <NUM> is exaggeratedly shown so that the axial protrusion <NUM> can be seen clearly. On the other hand, the seal-side sliding contact surface <NUM> is a circular annular flat surface extending in the direction perpendicular to the axial direction, and is formed with no axial protrusions <NUM>.

As illustrated in <FIG>, the axial protrusions <NUM> are disposed at positions where the axial protrusions <NUM> overlap with the pitch circle of the balls <NUM> (imaginary circle connecting the centers of the balls <NUM>), or disposed radially outwardly of the pitch circle of the balls <NUM>. The language "the axial protrusions <NUM> are disposed at positions where the axial protrusions <NUM> overlap with the pitch circle of the balls <NUM>" refers to the positional relationship where the imaginary cylindrical surface passing through the pitch circle of the balls <NUM> passes through the axial protrusions <NUM>. The language "the axial protrusions <NUM> are disposed radially outwardly of the pitch circle of the balls <NUM>" refers to the positional relationship where the entire axial protrusions <NUM> are entirely located radially outwardly of the imaginary cylindrical surface passing through the pitch circle of the balls <NUM>. In the shown example, the axial protrusions <NUM> are disposed radially outwardly of the pitch circle of the balls <NUM>.

As illustrated in <FIG> and <FIG>, the axial protrusions <NUM> each have a parallel apex portion <NUM>, a first inclined apex portion <NUM> and a second inclined apex portion <NUM>. The parallel apex portion <NUM> is a portion of the axial protrusion <NUM> having an axially circular arc convex shape in cross sections along the circumferential direction whose apex height is radially uniform. The first inclined apex portion <NUM> is a portion of the axial protrusion <NUM> having an axially convex circular arc shape in cross sections along the circumferential direction whose apex height gradually decreases radially outward from the radially outer end of the parallel apex portion <NUM>. The second inclined apex portion <NUM> is a portion of the axial protrusion <NUM> having an axially convex circular arc shape in cross sections along the circumferential direction whose apex height gradually decreases radially inwardly from the radially inner end of the parallel apex portion <NUM>. As illustrated in <FIG>, the cross sections of the first and second inclined apex portions <NUM> and <NUM> perpendicular to the circumferential direction have a rounded shape smoothly connected to the parallel apex portion <NUM>.

As illustrated in <FIG>, the cage guided surface <NUM> is a circular annular surface that comes into direct sliding contact with the one inner ring groove shoulder <NUM>. As illustrated in <FIG>, the cage guided surface <NUM> may be a circular annular surface formed with a plurality of radially inwardly protruding protrusions <NUM> having a convex circular arc shape, and circumferentially spaced apart from each other. In this case, by setting the sliding gap between the inner ring <NUM> and each protrusion <NUM> to <NUM> or less, vibration of the cage <NUM> can be reduced.

As illustrated in <FIG>, the inner-diameter-side axial groove <NUM> of the radially inner surface <NUM> of each cage claw portion <NUM> axially extends through the radially inner surface <NUM> and the cage guided surface <NUM>. As illustrated in <FIG>, the inner-diameter-side axial groove <NUM> has a width equal to, or larger than, half of the circumferential width of the distal end of the cage claw portion <NUM>.

As illustrated in <FIG>, the cage circular annular portion <NUM> has a chamfer <NUM> which extends obliquely in a cross section perpendicular to the circumferential direction, to connect the cage-side sliding contact surface <NUM> and the cage guided surface <NUM> to each other. Due to the formation of the chamfer <NUM>, the radially inner edge of the cage circular annular portion <NUM> has an axial width equal to, or smaller than, half of the axial width of the portion of the cage circular annular portion <NUM> having the largest axial width. Also, the cage circular annular portion <NUM> has a chamfer <NUM> obliquely extending in a cross section perpendicular to the circumferential direction, to connect the cage-side sliding contact surface <NUM> and the outer peripheral surface of the cage circular annular portion <NUM> to each other.

The outer-diameter-side axial groove <NUM> of the radially outer surface <NUM> of each cage claw portion <NUM> is shaped such that, from the distal end of the cage claw portion <NUM> toward the cage circular annular portion <NUM>, the position of the groove bottom gradually changes radially outwardly. As illustrated in <FIG> and <FIG>, the outer-diameter-side axial groove <NUM> has a width equal to, or larger than, half of the circumferential width of the distal end of the cage claw portion <NUM>. Also, the cage circular annular portion <NUM> has, in its outer periphery, axial cutouts <NUM> at positions corresponding to the respective outer-diameter-side axial grooves <NUM>.

As illustrated in <FIG> and <FIG>, each cage claw portion <NUM> includes claw tip oil passages <NUM> formed on both circumferential sides of the distal end portion of the radially outer surface <NUM> (i.e., formed in the shoulders of the outer-diameter-side axial groove <NUM> on both sides thereof), and circumferentially extending through the respective shoulders of the outer-diameter-side axial groove <NUM>. The claw tip oil passages <NUM> are stepped cutouts rising from the side remoter from the cage circular annular portion <NUM> toward the side closer to the cage circular annular portion <NUM>. By forming the claw tip oil passages <NUM>, it is possible to improve lubricating performance for the balls <NUM>.

In this ball bearing <NUM>, since, as illustrated in <FIG>, a plurality of axial protrusions <NUM> whose cross sections along the circumferential direction have an axially convex circular arc shape are formed on the cage-side sliding contact surface <NUM> at constant pitches in the circumferential direction, oil films due to the wedge film effect are formed between the seal-side sliding contact surface <NUM> and the respective axial protrusions <NUM>. Due to the oil films, the lubrication condition between the seal-side sliding contact surface <NUM> and the axial protrusions <NUM> becomes fluid lubrication condition, thus making it possible to markedly reduce the contact resistance between the cage <NUM> and the seal member <NUM>. Therefore, it is possible to prevent abnormal heat generation due to the sliding resistance of the contact portions of the cage <NUM> and the seal member <NUM>.

There are two types of lubrication conditions between sliding contact surfaces, i.e., boundary lubrication condition and fluid lubrication condition. The boundary lubrication condition is the condition in which sliding contact surfaces are lubricated by an oil film comprising several molecular layers (about <NUM>-<NUM> to <NUM>-<NUM> mm) of lubricating oil adsorbed on the sliding contact surfaces, and minute protrusions and recesses of the sliding contact surfaces are in direct contact with each other. The fluid lubrication condition is the condition in which an oil film (e.g., about <NUM>-<NUM> to <NUM>-<NUM> mm) due to the wedge film effect is formed between sliding contact surfaces, and, due to the oil film, the sliding contact surfaces are not in direct contact with each other (i.e., they are in indirect contact with each other via the oil film). Since, when the fluid lubricating condition is generated due to the generation of the wedge film effect, the sliding resistance of the seal member becomes substantially zero, the bearing can be used at a high peripheral speed, which was impossible with conventional seals.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, the cage circular annular portion <NUM> is disposed to come into sliding contact with the seal member <NUM>, it is possible to increase the axial thickness of the cage circular annular portion <NUM>, and thus increase the rigidity of the cage circular annular portion <NUM>. Therefore, even during high-speed rotation, it is possible to reduce torsional deformation of the cage circular annular portion <NUM> due to the centrifugal forces that the cage claw portions <NUM> receive, and reduce radially outward inclination of the cage claw portions <NUM>.

Also, this ball bearing <NUM> requires only a small space for installation, and thus can be installed at a place where the width dimension of a bearing needs to be reduced for installation (i.e., at a place where a bearing with a seal cannot be used, and an open-type ball bearing provided with no seal member <NUM>, and having open ends on both axial sides has to be used instead), too.

Also, in this bearing <NUM>, since, as illustrated in <FIG>, the portion of each circumferentially opposed surface <NUM> of each cage claw portion <NUM> that circumferentially supports the ball <NUM> is a straight portion having no circumferential inclination, and extending straight in the axial direction, when the ball <NUM> is supported by the cage claw portion <NUM>, no axial component force is generated at the cage claw portion <NUM>. Therefore, it is possible to prevent the cage <NUM> from being axially pressed hard against the seal member <NUM>, and effectively reduce the sliding resistance of the contact portions of the cage <NUM> and the seal member <NUM>.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, the axial protrusions <NUM>, each including the parallel apex portion <NUM> and the first inclined apex portion <NUM>, are used, while the bearing is rotating at a low speed and the centrifugal forces which the cage claw portions <NUM> receive are relatively small, oil films due to the wedge film effect can be formed between the seal-side sliding contact surface <NUM> and the parallel apex portions <NUM> of the respective axial protrusions <NUM>. Also, while the bearing is rotating at a high speed and the centrifugal forces which the cage claw portions <NUM> receive are relatively large, an oil film due to the wedge film effect can be formed between the seal-side sliding contact surface <NUM>, and the parallel apex portion <NUM> and the first inclined apex portion <NUM> of each axial protrusion <NUM> with torsional deformation of the cage circular annular portion <NUM> relatively large. As described above, regardless of the rotation speed of the bearing, oil films due to the wedge film effect can be stably formed between the cage <NUM> and the seal member <NUM>.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, the cross section of each first inclined apex portion <NUM> perpendicular to the circumferential direction has a rounded shape, and the first inclined apex portion <NUM> and the parallel apex portion <NUM> are smoothly connected to each other, when, with torsional deformation of the cage circular annular portion <NUM> relatively large, an oil film due to the wedge film effect is formed between the seal-side sliding contact surface <NUM>, and the parallel apex portion <NUM> and the first inclined apex portion <NUM>, the oil film can be formed stably.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, the inner-diameter-side axial grooves <NUM> (radially inner oil grooves) are disposed in the inner periphery of the cage <NUM>, lubricating oil supplied into the space radially inside of the cage claw portions <NUM> is introduced, through the inner-diameter-side axial grooves <NUM>, into the space between the cage circular annular portion <NUM> and the seal member <NUM>. Therefore, it is possible to sufficiently lubricate the portions of the bearing between the seal-side sliding contact surface <NUM> and the axial protrusions <NUM>, and effectively form oil films due to wedge films.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, a cage circular annular portion <NUM> is used which has a chamfer <NUM> obliquely extending, in a cross section perpendicular to the circumferential direction, to connect the cage-side sliding contact surface <NUM> and the cage guided surface <NUM> to each other, lubricating oil introduced into the space between the cage circular annular portion <NUM> and the seal member <NUM> through the inner-diameter-side axial grooves <NUM> from the radially inner areas of the cage claw portions <NUM> can be smoothly fed along the chamfer <NUM> and led onto the cage-side sliding contact surface <NUM>, by a centrifugal force.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, the axial protrusions <NUM> are disposed at positions where the axial protrusions <NUM> overlap with the pitch circle of the balls <NUM>, or disposed radially outwardly of the pitch circle of the balls <NUM>, when the centrifugal forces applied to the cage claw portions <NUM> cause torsional deformation of the cage circular annular portion <NUM> in the direction in which the cage claw portions <NUM> are inclined radially outward, it is possible to prevent, due to the torsional deformation, the cage-side sliding contact surface <NUM> and the seal-side sliding contact surface <NUM> from coming into contact with each other at a position displaced radially outwardly of the axial protrusions <NUM>.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, the position of the bottom of the outer-diameter-side axial groove <NUM> (radially outer oil groove) of each cage claw portion <NUM> gradually changes radially outwardly from the distal end of the cage claw portion <NUM> toward the cage circular annular portion <NUM>, lubricating oil supplied into the outer-diameter-side axial groove <NUM> is moved from the distal end of the cage claw portion <NUM> toward the cage circular annular portion <NUM> by the pumping action, and is introduced into the space between the cage circular annular portion <NUM> and the seal member <NUM>. Therefore, it is possible to sufficiently lubricate the portions of the bearing between the seal-side sliding contact surface <NUM> and the axial protrusions <NUM>, and effectively form oil films due to wedge films.

Also, in this ball bearing <NUM>, since the axial end of the annular space <NUM> opposite from the axial end thereof closed by the seal member <NUM> is open, it is possible to sufficiently lubricate the portions of the bearing between the seal-side sliding contact surface <NUM> and the axial protrusions <NUM>, and reliably form oil films due to wedge films.

<FIG> illustrates a ball bearing <NUM> according to the third embodiment which is part of the claimed invention. The third embodiment is different from the second embodiment in that the axial protrusions <NUM> are disposed on, of the cage-side sliding contact surface <NUM> and the seal-side sliding contact surface <NUM>, the cage-side sliding contact surface <NUM> in the second embodiment, and the seal-side sliding contact surface <NUM> in the third embodiment. Otherwise, this embodiment is structurally the same as the second embodiment, and therefore, the elements of the third embodiment corresponding to those of the second embodiment are denoted by the same reference numerals, and their description is omitted.

As illustrated in <FIG>, a plurality of axial protrusions <NUM> are formed on the seal-side sliding contact surface <NUM> at constant pitches in the circumferential direction. The axial protrusions <NUM> are formed, with a mold, on the rubber part <NUM> of the seal member <NUM>. The cross section of each axial protrusion <NUM> along the circumferential direction has an axially convex circular arc shape. The axial protrusion <NUM> has an axial height set to <NUM>% or less of the circumferential width dimension of the axial protrusion <NUM>. In <FIG>, the axial height of the axial protrusion <NUM> is exaggeratedly shown so that the axial protrusion <NUM> can be seen clearly. On the other hand, the cage-side sliding contact surface <NUM> is a circular annular flat surface extending in the direction perpendicular to the axial direction, and is formed with no axial protrusions <NUM>.

As illustrated in <FIG>, the axial protrusions <NUM> are disposed at positions where the axial protrusions <NUM> overlap with the pitch circle of the balls <NUM> (imaginary circle connecting the centers of the balls <NUM>), or disposed radially outwardly of the pitch circle of the balls <NUM>.

As illustrated in <FIG> and <FIG>, the axial protrusions <NUM> each have a parallel apex portion <NUM>, a first inclined apex portion <NUM> and a second inclined apex portion <NUM>. The parallel apex portion <NUM> is a portion of the axial protrusion <NUM> having an axially circular arc convex shape in crosssections along the circumferential direction whose apex height is radially uniform. The first inclined apex portion <NUM> is a portion of the axial protrusion <NUM> having an axially convex circular arc shape in cross sections along the circumferential direction whose apex height gradually decreases radially outward from the radially outer end of the parallel apex portion <NUM>. The second inclined apex portion <NUM> is a portion of the axial protrusion <NUM> having an axially convex circular arc shape in cross sections along the circumferential direction whose apex height gradually decreases radially inwardly from the radially inner end of the parallel apex portion <NUM>. As illustrated in <FIG>, the cross sections of the first and second inclined apex portions <NUM> and <NUM> perpendicular to the circumferential direction have a rounded shape smoothly connected to the parallel apex portion <NUM>.

In this ball bearing <NUM>, since, as illustrated in <FIG>, a plurality of axial protrusions <NUM> whose cross sections along the circumferential direction have an axially convex circular arc shape are formed on the seal-side sliding contact surface <NUM> at constant pitches in the circumferential direction, oil films due to the wedge film effect are formed between the cage-side sliding contact surface <NUM> and the respective axial protrusions <NUM>. Due to the oil films, the lubrication condition between the cage-side sliding contact surface <NUM> and the axial protrusions <NUM> becomes the fluid lubrication condition, thus making it possible to markedly reduce the contact resistance between the cage <NUM> and the seal member <NUM>. Therefore, it is possible to prevent abnormal heat generation due to the sliding resistance of the contact portions of the cage <NUM> and the seal member <NUM>.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, axial protrusions <NUM> each including the parallel apex portion <NUM> and the first inclined apex portion <NUM>, are used, while the bearing is rotating at a low speed, and the centrifugal forces which the cage claw portions <NUM> receive are relatively small, oil films due to the wedge film effect can be formed between the cage-side sliding contact surface <NUM> and the parallel apex portions <NUM> of the respective axial protrusions <NUM>. Also, while the bearing is rotating at a high speed, and the centrifugal forces which the cage claw portions <NUM> receive are relatively large, an oil film due to the wedge film effect can be formed between the cage-side sliding contact surface <NUM>, and the parallel apex portion <NUM> and the first inclined apex portion <NUM> of each axial protrusion <NUM> with torsional deformation of the cage circular annular portion <NUM> relatively large. In other words, regardless of the rotation speed of the bearing, oil films due to the wedge film effect can be stably formed between the cage <NUM> and the seal member <NUM>.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, the cross section of each first inclined apex portion <NUM> perpendicular to the circumferential direction has a rounded shape, and thus the first inclined apex portion <NUM> and the parallel apex portion <NUM> are smoothly connected to each other, when, with torsional deformation of the cage circular annular portion <NUM> relatively large, an oil film due to the wedge film effect is formed between the cage-side sliding contact surface <NUM>, and the parallel apex portion <NUM> and the first inclined apex portion <NUM>, the oil film can be formed stably.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, the inner-diameter-side axial grooves <NUM> are disposed in the inner periphery of the cage <NUM>, lubricating oil supplied to the space of the bearing radially inside the cage claw portions <NUM> is introduced, through the inner-diameter-side axial grooves <NUM>, into the space between the cage circular annular portion <NUM> and the seal member <NUM>. Therefore, it is possible to sufficiently lubricate the portions of the bearing between the cage-side sliding contact surface <NUM> and the axial protrusions <NUM>, and effectively form oil films due to wedge films.

The other operations and effects are also the same as in the first and second embodiments.

<FIG> illustrate a ball bearing <NUM> according to the fourth embodiment which is part of the claimed invention. The fourth embodiment is different from the third embodiment in that a seal member <NUM> is added and also the cage <NUM> has a partially different shape, but otherwise the fourth embodiment is structurally the same as the third embodiment. Therefore, the elements of the fourth embodiment corresponding to those of the third embodiment are denoted by the same reference numerals, and their description is omitted.

As illustrated in <FIG>, a seal member <NUM> is disposed at one of the end openings of the annular space <NUM> on both axial sides thereof, and a seal member <NUM> is disposed on the other end opening, too. Lubricant is sealed in the portion of the annular space <NUM> between the seal members <NUM> and <NUM>.

As illustrated in <FIG> and <FIG>, each cage claw portion <NUM> has circumferentially opposed surfaces <NUM> circumferentially opposed to the corresponding balls <NUM>, respectively. The portions of the circumferentially opposed surfaces <NUM> which circumferentially support the balls <NUM> are flat surfaces extending such that when the cage claw portion <NUM> is moved radially outwardly by a centrifugal force, the circumferentially opposed surfaces <NUM> do not interfere with the balls <NUM>. As illustrated in <FIG>, the circumferentially opposed surfaces <NUM> are flat surfaces inclined to gradually approach, in the radially inward direction, the imaginary straight line connecting the center of the cage circular annular portion <NUM> and the center of the cage claw portion <NUM> to each other (flat surfaces extending such that the circumferential width of the cage claw portion <NUM> gradually decreases in the radially inward direction), when seen in the axial direction.

As illustrated in <FIG>, the cage circular annular portion <NUM> includes a step <NUM> radially outwardly rising from the level of the radially outer surface portions of the cage claw portions <NUM> at their roots. Due to the formation of the step <NUM>, when lubricant sealed in the annular space <NUM> is moved toward the cage circular annular portion <NUM> along the outer-diameter-side axial grooves <NUM>, the lubricant can be partially stopped by the step <NUM>, and returned to the balls <NUM>.

As illustrated in <FIG>, each circumferentially opposed surface <NUM> and the corresponding axially opposed surface <NUM> are connected together via a composite rounded curved surface. In the shown example, the curved surface connecting the circumferentially opposed surface <NUM> and the axially opposed surface <NUM> to each other is constituted by a distal-end-side rounded surface portion <NUM> connected to the circumferentially opposed surface <NUM>, and having a part-cylindrical shape with a radius of curvature R2 smaller than the radius R1 of the ball <NUM>; a root-side rounded surface portion <NUM> connected to the axially opposed surface <NUM>, and having a part-cylindrical shape with a radius of curvature R3 larger than the radius R1 of the ball <NUM>; and an intermediate rounded surface portion <NUM> smoothly connecting the distal-end-side rounded surface portion <NUM> and the root-side rounded surface portion <NUM> to each other.

This ball bearing <NUM> is the same in operation and effects as the third embodiment.

<FIG> illustrate a ball bearing <NUM> according to the fifth embodiment which is part of the claimed invention. The fifth embodiment is the same as the second embodiment (shown in <FIG>) except that the claw tip oil passages <NUM> are omitted. Therefore, the elements of the fifth embodiment corresponding to those of the second embodiment are denoted by the same reference numerals, and their description is omitted.

<FIG> illustrate a ball bearing <NUM> according to the sixth embodiment which is not part of the claimed invention. The elements of the sixth embodiment corresponding to those of the above embodiments are denoted by the same reference numerals, and their description is omitted.

Each cage claw portion <NUM> has a cantilevered structure of which one axial end is a fixed end fixed to the cage circular annular portion <NUM>, and the other axial end is a free end. The cage claw portion <NUM> has an axial length larger than the axial width of the outer ring raceway groove <NUM>. The cage claw portion <NUM> has a radial thickness which is uniform, i.e., does not change, in the axial direction.

As illustrated in <FIG> and <FIG>, a root-side guided surface <NUM> that comes into sliding contact with the one outer ring groove shoulder <NUM> is formed at the portion of the radially outer surface of the cage circular annular portion <NUM> corresponding to the root of each cage claw portion <NUM>. Also, a distal-end-side guided surface <NUM> that comes into sliding contact with the other outer ring groove shoulder <NUM> is formed on the radially outer surface of the axial end portion of the cage claw portion <NUM> on its distal end side.

As illustrated in <FIG>, the root-side guided surface <NUM> has, in cross sections along the circumferential direction, a radially outwardly protruding circular arc shape. The "radially outwardly protruding" means protruding radially outwardly relative to an imaginary circle concentric with the cage circular annular portion <NUM>. The distal-end-side guided surface <NUM> also has, in cross sections along the circumferential direction, a radially outwardly protruding circular arc shape (see <FIG>). The root-side guided surface <NUM> and the distal-end-side guided surface <NUM> have the same shape in cross sections along the circumferential direction. The radii of curvature of each of the root-side guided surface <NUM> and the distal-end-side guided surface <NUM> in cross sections along the circumferential direction can be set to smaller than <NUM>/<NUM> of the radius of the inner diameter of the outer ring groove shoulder <NUM>, and larger than <NUM>/<NUM> of the radius of the inner diameter of the outer ring groove shoulder <NUM>.

As illustrated in <FIG>, in this embodiment, the root-side guided surface <NUM> and the distal-end-side guided surface <NUM> are continuous surfaces continuously connected together straight in the axial direction in order that no recess is formed between the root-side guided surface <NUM> and the distal-end-side guided surface <NUM>.

As illustrated in <FIG>, the root-side guided surface <NUM> has, on its side remoter from the cage claw portion <NUM>, an axial end edge <NUM> chamfered into a rounded shape. The language "chamfered into a rounded shape" means, as illustrated in <FIG>, forming a corner having a convex circular arc-shaped cross section perpendicular to the circumferential direction. As illustrated in <FIG>, the distal-end-side guided surface <NUM> also has, on its side remote from the cage circular annular portion <NUM>, an axial end edge <NUM> chamfered into the same rounded shape.

In this ball bearing <NUM>, since, as illustrated in <FIG>, each of the root-side guided surfaces <NUM> has, in cross sections along the circumferential direction, a radially outwardly protruding circular arc shape, oil films due to the wedge film effect are formed between the one outer ring groove shoulder <NUM> and the root-side guided surfaces <NUM>. Due to the oil films, the lubrication condition between the one outer ring groove shoulder <NUM> and the root-side guided surfaces <NUM> becomes the fluid lubrication condition, thus making it possible to markedly reduce the contact resistance between the cage <NUM> and the outer ring <NUM>. Since, as with the root-side guided surfaces <NUM>, each of the distal-end-side guided surfaces <NUM>, shown in <FIG>, also has a radially outwardly protruding circular arc shape in cross sections along the circumferential direction, oil films due to the wedge film effect are formed between the other outer ring groove shoulder <NUM> (outer ring groove shoulder <NUM> on the left side) and the distal-end-side guided surfaces <NUM>. Due to the oil films, the lubrication condition between the other outer ring groove shoulder <NUM> and the distal-end-side guided surfaces <NUM> becomes the fluid lubrication condition, thus making it possible to markedly reduce the contact resistance between the cage <NUM> and the outer ring <NUM>. Therefore, it is possible to prevent abnormal heat generation due to the sliding resistance of the contact portions of the cage <NUM> and the outer ring <NUM>.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, the one outer ring groove shoulder <NUM> (outer ring groove shoulder <NUM> on the right side) supports the cage circular annular portion <NUM> from the radially outer side, and the other outer ring groove shoulder <NUM> (outer ring groove shoulder <NUM> on the left side) supports the axial ends of the cage claw portions <NUM> on their distal end sides from the radially outer side, flexural deformation of the cage claw portions <NUM> toward the radially outer side is less likely to occur. Therefore, even during high-speed rotation, it is possible to reduce torsional deformation of the cage circular annular portion <NUM>, and flexural deformation of the cage claw portions <NUM> per se toward the radially outer side, due to the centrifugal forces which the cage claw portions <NUM> receive.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, the axial end edges <NUM> of the root-side guided surfaces <NUM> on their sides remoter from the cage claw portions <NUM>, and the axial end edges <NUM> of the distal-end-side guided surfaces <NUM> on their sides remoter from the cage circular annular portion <NUM> are chamfered into the above-defined rounded shape, oil films due to the wedge film effect can be effectively formed between the one outer ring groove shoulder <NUM> (outer ring groove shoulder <NUM> on the right side) and the root-side guided surfaces <NUM> shown in <FIG>, and oil films due to the wedge film effect can be effectively formed between the other outer ring groove shoulder <NUM> (outer ring groove shoulder <NUM> on the left side) and the distal-end-side guided surfaces <NUM>, too.

Also, in this ball bearing <NUM>, since, as illustrated in <FIG>, the portions of the circumferentially opposed surfaces <NUM> of each cage claw portion <NUM> which circumferentially support the balls <NUM> are flat surfaces extending parallel to the imaginary straight line connecting the center of the cage circular annular portion <NUM> and the center of the cage claw portion <NUM> to each other, when the cage claw portion <NUM> is moved radially outwardly by the centrifugal force applied to the cage claw portion <NUM>, it is possible to prevent the circumferentially opposed surfaces <NUM> of the cage claw portion <NUM> from interfering with the balls <NUM>. Also, since the shear resistance of lubricating oil generated between the circumferentially opposed surfaces <NUM> of the cage claw portion <NUM> and the balls <NUM> is reduced, it is also possible to reduce the heat generation in the ball bearing <NUM>.

Also, in this ball bearing <NUM>, since the axial end of the annular space <NUM> opposite from the axial end thereof closed by the seal member <NUM> is open, it is possible to sufficiently lubricate the root-side guided surfaces <NUM> and the distal-end-side guided surfaces <NUM>, and reliably form oil films due to wedge films.

<FIG> illustrate a ball bearing <NUM> according to the seventh embodiment which is not part of the claimed invention. The seventh embodiment is different from the sixth embodiment only in that oil reservoir grooves <NUM> are added. Otherwise, the seventh embodiment is structurally the same as the sixth embodiment. Therefore, the elements of the seventh embodiment corresponding to those of the sixth embodiment are denoted by the same reference numerals, and their description is omitted.

As illustrated in <FIG> and <FIG>, each cage claw portion <NUM> has, in its radially inner surface, an oil reservoir groove <NUM> axially extending from the distal end of the cage claw portion <NUM> toward the cage circular annular portion <NUM>. As illustrated in <FIG>, the oil reservoir groove <NUM> rises to the radially inner surface of the cage <NUM> at the position radially opposed to the inner ring groove shoulder <NUM> closer to the cage circular annular portion <NUM>. In other words, the oil reservoir groove <NUM> does not axially extend through the cage <NUM>. The oil reservoir groove <NUM> may, however, axially extend through the radially inner surface of the cage <NUM>.

As illustrated in <FIG> and <FIG>, the oil reservoir groove <NUM> is formed in the circumferential center of the radially inner surface of the cage claw portion <NUM>. The oil reservoir groove <NUM> has a semicircular sectional shape. The oil reservoir groove <NUM> may instead have a triangular sectional shape or a quadrangular sectional shape.

In the ball bearing <NUM> of this embodiment, lubricating oil radially outwardly scattered by a centrifugal force can be stored in the oil reservoir grooves <NUM>, and supplied to the inner ring <NUM>.

The ball bearing <NUM> of this embodiment is the same in operation and effects as the bearing of the sixth embodiment.

<FIG> illustrate a ball bearing <NUM> according to the eighth embodiment which is not part of the claimed invention. The eighth embodiment is different from the seventh embodiment (shown in <FIG>) only in that relief recesses <NUM> are added. Otherwise, the eighth embodiment is structurally the same as the seventh embodiment. Therefore, the elements of the eighth embodiment corresponding to those of the seventh embodiment are denoted by the same reference numerals, and their description is omitted.

As illustrated in <FIG>, The relief recesses <NUM> are each formed in the portion of the radially outer surface of a respective one of the cage claw portion <NUM> between the root-side guided surface <NUM> and the distal-end-side guided surface <NUM>. That is, the radially outer surface of the cage claw portion <NUM> is a stepped surface in which first the root-side guided surface <NUM>, then the relief recess <NUM> and then the distal-end-side guided surface <NUM> are arranged in the axial direction.

As illustrated in <FIG> and <FIG>, the relief recess <NUM> has an axial width wider than the axial width of the outer ring raceway groove <NUM>, and extends in the circumferential direction. As illustrated in <FIG>, the relief recess <NUM> is arranged to cover the entire axial width of the outer ring raceway groove <NUM>. That is, the end of the relief recess <NUM> closer to the root-side guided surface <NUM> is located at a position displaced toward the one outer ring groove shoulder <NUM> (outer ring groove shoulder <NUM> closer to the cage circular annular portion <NUM>) from the boundary between the one outer ring groove shoulder <NUM> and the outer ring raceway groove <NUM>. Also, the end of the relief recess <NUM> closer to the distal-end-side guided surface <NUM> is located at a position displaced toward the other outer ring groove shoulder <NUM> (outer ring groove shoulder <NUM> remoter from the cage circular annular portion <NUM>) from the boundary between the other outer ring groove shoulder <NUM> and the outer ring raceway groove <NUM>. Both axial ends of the relief recess <NUM> rise while being inclined to the root-side guided surface <NUM> and the distal-end-side guided surface <NUM>, respectively.

As illustrated in <FIG>, the relief recess <NUM> is a portion recessed relative to the root-side guided surface <NUM> (or the distal-end-side guided surface <NUM>) so as to have an inner surface at a position retracted radially inwardly relative to the root-side guided surface <NUM> (or the distal-end-side guided surface <NUM>). In the shown example, the inner surface of the relief groove <NUM> is a flat surface extending in the direction perpendicular to the radial direction.

In this ball bearing <NUM>, since, as illustrated in <FIG>, the relief recesses <NUM> are formed between the root-side guided surfaces <NUM> and the respective distal-end-side guided surfaces <NUM>, it is possible to prevent each of the boundaries between the outer ring raceway groove <NUM> and the respective outer ring groove shoulders <NUM> from coming into sliding contact with the radially outer surface of the cage circular annular portion <NUM> or the radially outer surfaces of the cage claw portions <NUM>. Therefore, it is possible to prevent the radially outer surface of the cage circular annular portion <NUM> and the radially outer surfaces of the cage claw portions <NUM> from becoming worn locally at the positions corresponding to the boundaries between the outer ring raceway groove <NUM> and the outer ring groove shoulders <NUM>.

The ball bearing <NUM> of this embodiment is the same in operation and effects as the sixth and seventh embodiments.

<FIG> and <FIG> illustrate a ball bearing <NUM> according to the ninth embodiment of the present invention. The ninth embodiment corresponds to the combination of the sixth embodiment (of <FIG>) and the sliding contact structure of the cage <NUM> and the seal member <NUM> in the second embodiment (sliding contact structure of the cage-side sliding contact surface <NUM> and the seal-side sliding contact surface <NUM> in <FIG>). Therefore, the elements of the ninth embodiment corresponding to those of the above relevant embodiments are denoted by the same reference numerals, and their description is omitted.

<FIG> and <FIG> illustrate a ball bearing <NUM> according to the tenth embodiment of the present invention. The tenth embodiment corresponds to the combination of the sixth embodiment (of <FIG>) and the sliding contact structure of the cage <NUM> and the seal member <NUM> in the third embodiment (sliding contact structure of the cage-side sliding contact surface <NUM> and the seal-side sliding contact surface <NUM> in <FIG>). Therefore, the elements of the tenth embodiment corresponding to those of the above relevant embodiments are denoted by the same reference numerals, and their description is omitted.

While, each of the above embodiments exemplifies an oil-lubricated ball bearing <NUM>, in which lubricating oil is used as the lubricant for lubricating the interior of the bearing, the present invention is also applicable to a ball bearing <NUM> lubricated by grease, i.e., a ball bearing <NUM> in which grease is used as the lubricant for lubricating the interior of the bearing. Grease is a semisolid lubricant containing lubricating oil and a thickener dispersed in the lubricating oil.

Claim 1:
A ball bearing comprising:
an inner ring (<NUM>);
an outer ring (<NUM>) arranged radially outwardly of, and coaxially with, the inner ring (<NUM>);
a plurality of balls (<NUM>) disposed in an annular space (<NUM>) between the inner ring (<NUM>) and the outer ring (<NUM>);
an annular seal member (<NUM>) closing one axial end opening of the annular space (<NUM>); and
a cage (<NUM>) made of resin and retaining the balls (<NUM>),
wherein the cage (<NUM>) comprises a cage circular annular portion (<NUM>) extending circumferentially through a space axially sandwiched between the seal member (<NUM>) and the space through which the balls (<NUM>) pass; and
cage claw portions (<NUM>) having a cantilevered structure axially extending from the cage circular annular portion (<NUM>), and each located between a corresponding pair of the balls (<NUM>) circumferentially adjacent to each other,
characterized in that the cage circular annular portion (<NUM>) has a cage-side sliding contact surface (<NUM>) axially opposed to the seal member (<NUM>) and configured to come into sliding contact with the seal member (<NUM>),
wherein the seal member (<NUM>) has a seal-side sliding contact surface (<NUM>) configured to come into sliding contact with the cage-side sliding contact surface (<NUM>),
wherein a plurality of axial protrusions (<NUM>) each having an axially convex circular arc shape in cross sections along a circumferential direction are formed on one of the cage-side sliding contact surface (<NUM>) and the seal-side sliding contact surface (<NUM>) at constant pitches in the circumferential direction, and
characterized in that each of the cage claw portions (<NUM>) has, in a radially outer surface (<NUM>) of the cage claw portion (<NUM>), an outer-diameter-side axial groove (<NUM>) axially extending from a distal end of the cage claw portion (<NUM>) toward the cage circular annular portion (<NUM>), and shaped such that, from the distal end of the cage claw portion (<NUM>) toward the cage circular annular portion (<NUM>), a position of a bottom of the outer-diameter-side axial groove (<NUM>) gradually changes radially outwardly.