Ball bearing

A ball bearing is provided which includes a cage circular annular portion and a seal member. 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. 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.

TECHNICAL FIELD

The present invention relates to a ball bearing.

BACKGROUND ART

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 Japanese Patent No. 3035766 is known. Such a cage 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 PCT International Publication No. WO2016/143786 is sometimes used. In this ball bearing, 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.

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)×the number of rotations n (min−1)) value exceeds 2 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.

SUMMARY OF THE INVENTION

In order to achieve the above object, the present 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. 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. 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. 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.

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 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.

The outer-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 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.

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.

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 are configured to come into sliding contact with the other of the outer ring groove shoulders. 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 order to achieve the above object, 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. 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. 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. 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

In order to achieve the above object, 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. 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. 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. Each of the cage claw portions has an axial length larger than an axial width of the outer ring raceway groove, and 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. 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 section 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.

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 each of the root-side guided surfaces has, on a side thereof most remote 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 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.

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.

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 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 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, 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.

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 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.

DETAILED DESCRIPTION OF THE INVENTION

FIG.1illustrates a ball bearing1according to the first embodiment of the present invention. The ball bearing1includes an inner ring2; an outer ring3arranged radially outwardly of, and coaxially with, the inner ring2; a plurality of balls5disposed in an annular space4between the inner ring2and the outer ring3so as to be circumferentially spaced apart from each other; an annular seal member6closing one of the end openings of the annular space4on both axial sides thereof; and a resin cage7made of resin (hereinafter simply referred to as the “cage7”) that keeps the circumferential distances between the balls5. The ball bearing1is a sealed ball bearing including the seal member6.

Formed on the outer periphery of the inner ring2are an inner ring raceway groove8with which the balls5come into rolling contact; a pair of inner ring groove shoulders9located axially outwardly of the inner ring raceway groove8; and a sliding recess10located axially outwardly of one of the inner ring groove shoulders9. The inner ring raceway groove8is a circular arc groove having a concave circular arc-shaped cross section along the surfaces of the balls5, and extends circumferentially at the axial central portion of the outer periphery of the inner ring2. The pair of inner ring groove shoulders9are bank-shaped portions circumferentially extending on both axial sides of the inner ring raceway groove8. The sliding recess10is a circumferentially extending recess adjacent to the axially outer side of the one inner ring groove shoulder9. The seal member6has, at the radially inner end thereof, a seal lip11in sliding contact with the inner surface of the sliding recess10. In the shown example, the portion of the inner surface of the sliding recess10with which the seal lip11is 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 ring3are an outer ring raceway groove12with which the balls5come into rolling contact; a pair of outer ring groove shoulders13located axially outwardly of the outer ring raceway groove12; and a seal fixing groove14located axially outwardly of one of the outer ring groove shoulders13. The outer ring raceway groove12is a circular arc groove having a concave circular arc-shaped cross section along the surfaces of the balls5, and extends circumferentially at the axial central portion of the inner periphery of the outer ring3. The pair of outer ring groove shoulders13are bank-shaped portions circumferentially extending on both axial sides of the outer ring raceway groove12. The seal fixing groove14is a circumferentially extending groove adjacent to the axially outer side of the one outer ring groove shoulder13. The seal member6has, on the radially outer edge thereof, a fitted portion15fitted in, and fixed to, the seal fixing groove14.

The balls5are radially sandwiched between the outer ring raceway groove12and the inner ring raceway groove8. The outer ring raceway groove12and the inner ring raceway groove8have an axial width dimension larger than half of the diameter of each ball5. The balls5are steel balls. Instead, however, ceramic balls may be used as the balls5.

As illustrated inFIG.4, the seal member6is an annular member comprising an annular metal core16, and a rubber part17bonded to the surface of the metal core16by vulcanization of a rubber material (such as nitrile rubber or acrylic rubber). The seal member6includes a fitted portion15fitted in the seal fixing groove14; a circular annular plate portion18extending radially inwardly from the fitted portion15; and a seal lip11kept in sliding contact with the inner surface of the sliding recess10. The metal core16includes a circular annular plate-shaped flange portion19; and a cylindrical portion20bent axially inwardly along the radially outer edge of the flange portion19. The flange portion19is embedded in the circular annular plate portion18of the seal member6. The cylindrical portion20is embedded in the fitted portion15of the seal member6.

As illustrated inFIG.1, the seal member6is disposed only in one of the end openings of the annular space4on both axial sides thereof. In other words, the axial end of the annular space4on the opposite side (left side inFIG.1) from the axial end of the annular space4on its side closed by the seal member6(right side inFIG.1) is not provided with an additional seal member6, and is thus open so that lubricating oil supplied from outside enters the annular space4through this opening.

The cage7includes a cage circular annular portion21extending in the circumferential direction and adjacent to the area through which the balls5pass; and cage claw portions22axially extending from the cage circular annular portion21each between the corresponding circumferentially adjacent balls5. The cage circular annular portion21and the cage claw portions22are seamlessly and integrally formed of a resin composition. The resin composition forming the cage circular annular portion21and the cage claw portions22may 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 cage7is preferably formed by injection molding. The cage circular annular portion21extends circumferentially through the space between the seal member6and the space through which the balls5pass.

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 46 (PA46), polyamide 66 (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 portion22has cantilevered structure of which one axial end is a fixed end fixed to the cage circular annular portion21, and the other axial end is a free end. The cage claw portion22has an axial length larger than the radius of each ball5. The cage claw portion22has a uniform radial thickness in the axial direction, that is, the radial thickness does not change in the axial direction.

As illustrated inFIGS.2and4, the cage claw portion22has, in its radially outer surface23, an outer-diameter-side axial groove24axially extending from the distal end of the cage claw portion22toward the cage circular annular portion21. Also, the cage claw portion22has, in its radially inner surface25, an inner-diameter-side axial groove26axially extending from the distal end of the cage claw portion22toward the cage circular annular portion21. As illustrated inFIG.2, the outer-diameter-side axial groove24and the inner-diameter-side axial groove26have a width equal to, or larger than, half of the circumferential width of the distal end of the cage claw portion22. Due to the outer-diameter-side axial groove24and the inner-diameter-side axial groove26, the cross section of the cage claw portion22perpendicular 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 portion22has the same H shape when the cage claw portion22is axially seen from its distal end side, the outer-diameter-side axial groove24and the inner-diameter-side axial groove26are open to the distal end of the cage claw portion22.

The cage claw portion22has circumferentially opposed surfaces27circumferentially opposed to the corresponding balls5, respectively. The portions of the circumferentially opposed surfaces27which circumferentially support the balls5are flat surfaces extending such that when the cage claw portion22is moved radially outwardly by a centrifugal force, the circumferentially opposed surfaces27do not interfere with the balls5. In the shown example, the circumferentially opposed surfaces27are flat surfaces extending parallel to the imaginary straight line connecting the center of the cage circular annular portion21and the center of the cage claw portion22to each other (flat surfaces extending such that the cage claw portion22has 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 portion21is also the center of the inner ring2or the center of the outer ring3. The center of the cage claw portion22is equally spaced apart from the circumferentially opposed surfaces27of the cage claw portion22on both circumferential sides thereof, when seen in the axial direction.

The distance between each circumferentially adjacent pair of cage claw portions22(i.e., the distance between the circumferentially opposed surfaces27of each circumferentially adjacent pair of cage claw portions22that are circumferentially opposed to each other via the ball) is preferably 1.02 to 1.11 times the diameter of the ball5on the pitch circle of the balls5, because this reduces vibration of the cage7.

As illustrated inFIGS.3and5, the portion of each circumferentially opposed surface27that circumferentially supports the ball5extends 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 ball5. The cage circular annular portion21has axially opposed surfaces28axially opposed to the respective balls5. Each circumferentially opposed surface27and the corresponding axially opposed surface28are 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 surface27and the axially opposed surface28to each other is a single rounded curved surface (part-cylindrical surface having a constant radius of curvature).

As illustrated inFIG.4, the axial end of the outer-diameter-side axial groove24of each cage claw portion22closer to the cage circular annular portion21rises to the outer periphery of the cage circular annular portion21to form a concave circular arc-shaped cross section, and the axial end of the inner-diameter-side axial groove26of the cage claw portion22closer to the cage circular annular portion21also rises to the inner periphery of the cage circular annular portion21. The cage circular annular portion21has, on its inner periphery, a cage guided surface29configured to be guided by the one inner ring groove shoulder9of the inner ring2on its outer periphery while being in sliding contact therewith. The cage guided surface29is a circular annular surface configured to come into direct sliding contact with the one inner ring groove shoulder9. By setting the sliding gap between the cage guided surface29and the one inner ring groove shoulder9to 0.22 mm or less, vibration of the cage7can be reduced. The portion of the inner-diameter-side axial groove26rising to the inner periphery of the cage circular annular portion21is open to the cage guided surface29.

As illustrated inFIGS.6and7, the seal lip11includes, on its radially inner edge, a plurality of protrusions30kept in sliding contact with the sliding recess10of the inner ring2on its outer periphery, while being circumferentially spaced apart from each other. The protrusions30extend in the direction perpendicular to the circumferential direction. As illustrated inFIG.7, the protrusions30have a convex circular arc-shaped cross section.

As illustrated inFIG.8, ball bearings1as described above are usable as bearings of an electric vehicle transmission32that reduces rotation of electric motors31of an electric vehicle such as a battery electric vehicle (EV) or a hybrid electric vehicle (HEV). The bearings of the electric vehicle transmission32rotate 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)×the number of rotations (min−1)) value exceeds 2 million.

The transmission ofFIG.8includes stators33and rotors34of the electric motors31; a rotary shaft35coupled to the rotors34, ball bearings1rotatably supporting the rotary shaft35; a second rotary shaft36and a third rotary shaft37both arranged parallel to the rotary shaft35; a first gear train38that transmits rotation of the rotary shaft35to the second rotary shaft36; and a second gear train39that transmits rotation of the second rotary shaft36to the third rotary shaft37. The stators33are annular stationary members, and the rotors34as the rotary members are disposed inside the respective stators33. When the stators33are energized, the rotors34rotate due to the electromagnetic forces acting between the stators33and the rotors34, and the rotation of the rotors34is inputted/transmitted to the rotary shaft35.

In this ball bearing1, since, as illustrated inFIG.5, each cage claw portion22has an H-shaped cross section due to the outer-diameter-side axial groove24in the radially outer surface23of the cage claw portion22and the inner-diameter-side axial groove26in the radially inner surface25of the cage claw portion22, it is possible to reduce the mass of the cage claw portions22while ensuring the moment of inertia of area of the cage claw portions22(while making the cage claw portions22less 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 portion21, and flexural deformation of the cage claw portions22per se toward the radially outer side due to the centrifugal forces which the cage claw portions22receive. It has become clear from data analysis by the inventors that the deformation amount by which the cage claw portions22formed with the outer-diameter-side axial grooves24and the inner-diameter-side axial grooves26are deformed by a centrifugal force can be reduced to at least 77% or less compared to the cage claw portions22that are not formed with the outer-diameter-side axial grooves24and the inner-diameter-side axial grooves26.

Also, in this ball bearing1, since, as illustrated inFIG.2, the portions of the circumferentially opposed surfaces27of each cage claw portion22that circumferentially support the balls5are flat surfaces extending parallel to the imaginary straight line connecting the center of the cage circular annular portion21and the center of the cage claw portion22to each other, when the cage claw portion22is moved radially outwardly by the centrifugal force applied to the cage claw portion22, it is possible to prevent the circumferentially opposed surfaces27of the cage claw portion22from interfering with the balls5. Also, since the shear resistance of lubricating oil generated between the circumferentially opposed surfaces27of the cage claw portions22and the balls5decreases, it is also possible to reduce the heat generation in the ball bearing1.

Also, in this ball bearing1, since, as illustrated inFIG.5, the circumferentially opposed surfaces27of each cage claw portion22are connected to the respective axially opposed surfaces28via 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 portion22while keeping a small mass of the axial distal end portion of the cage claw portion22. Therefore, it is possible to effectively reduce deflection of the cage claw portion22due to the centrifugal force applied to the cage claw portion22.

Also, in this ball bearing1, since, as illustrated inFIG.4, the axial end of the outer-diameter-side axial groove24of each cage claw portion22closer to the cage circular annular portion21rises 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 portion22while keeping a small mass of the axial distal end portion of the cage claw portion22. Also, since the axial end of the inner-diameter-side axial groove26of the cage claw portion22closer to the cage circular annular portion21also rises to the inner periphery of the cage circular annular portion21, it is possible to more effectively ensure the cross-sectional area of the axial root portion of the cage claw portion22. Therefore, it is possible to effectively reduce deflection of the cage claw portion22due to the centrifugal force applied to the cage claw portion22.

Also, in this ball bearing1, since, as illustrated inFIG.4, the cage circular annular portion21has, on its inner periphery, a cage guided surface29configured to be guided while coming into sliding contact with the outer periphery of the inner ring2, the cage7can be radially positioned by the sliding contact between the cage guided surface29of the cage circular annular portion21on its inner periphery and the outer periphery of the inner ring2.

FIGS.9to16illustrate a ball bearing1according to the second embodiment of the present 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 inFIG.10, the portions of the circumferentially opposed surfaces27of each cage claw portion22which circumferentially support the balls5are flat surfaces extending parallel to the imaginary straight line connecting the center of the cage circular annular portion21and the center of the cage claw portion22to each other when seen in the axial direction such that when the cage claw portion22is moved radially outwardly by a centrifugal force, the circumferentially opposed surfaces27do not interfere with the balls5.

As illustrated in11, the portions of the circumferentially opposed surfaces27that circumferentially support the balls5have no circumferential inclination, and extend straight in the axial direction when seen in the radial direction so that when supporting the balls5, no axial component force is generated.

As illustrated inFIG.12, each cage claw portion22is tapered such that the radial thickness gradually decreases from its end closer to the cage circular annular portion21toward its end remoter from the cage circular annular portion21(i.e., from its root toward its distal end). The cage circular annular portion21has an axial thickness substantially equal to the axial distance between the balls5and the seal member6(specifically, 95% or more and less than 100% of the axial distance between the balls5and the seal member6). The cage circular annular portion21has a cage-side sliding contact surface40that is axially opposed to the seal member6and comes into sliding contact with the seal member6. The seal member6has a seal-side sliding contact surface41that comes into sliding contact with the cage-side sliding contact surface40.

As illustrated inFIG.13, a plurality of axial protrusions42are formed on the cage-side sliding contact surface40at constant pitches in the circumferential direction. The cross section of each axial protrusion42along the circumferential direction has an axially convex circular arc shape. The axial protrusion42has an axial height set to 5% or less of the circumferential width dimension of the axial protrusion42. InFIG.13, the axial height of the axial protrusion42is exaggeratedly shown so that the axial protrusion42can be seen clearly. On the other hand, the seal-side sliding contact surface41is a circular annular flat surface extending in the direction perpendicular to the axial direction, and is formed with no axial protrusions42.

As illustrated inFIG.12, the axial protrusions42are disposed at positions where the axial protrusions42overlap with the pitch circle of the balls5(imaginary circle connecting the centers of the balls5), or disposed radially outwardly of the pitch circle of the balls5. The language “the axial protrusions42are disposed at positions where the axial protrusions42overlap with the pitch circle of the balls5” refers to the positional relationship where the imaginary cylindrical surface passing through the pitch circle of the balls5passes through the axial protrusions42. The language “the axial protrusions42are disposed radially outwardly of the pitch circle of the balls5” refers to the positional relationship where the entire axial protrusions42are entirely located radially outwardly of the imaginary cylindrical surface passing through the pitch circle of the balls5. In the shown example, the axial protrusions42are disposed radially outwardly of the pitch circle of the balls5.

As illustrated inFIGS.12and15, the axial protrusions42each have a parallel apex portion43, a first inclined apex portion44and a second inclined apex portion45. The parallel apex portion43is a portion of the axial protrusion42having an axially circular arc convex shape in cross sections along the circumferential direction whose apex height is radially uniform. The first inclined apex portion44is a portion of the axial protrusion42having 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 portion43. The second inclined apex portion45is a portion of the axial protrusion42having 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 portion43. As illustrated inFIG.12, the cross sections of the first and second inclined apex portions44and45perpendicular to the circumferential direction have a rounded shape smoothly connected to the parallel apex portion43.

As illustrated inFIG.16, the cage guided surface29is a circular annular surface that comes into direct sliding contact with the one inner ring groove shoulder9. As illustrated inFIG.17, the cage guided surface29may be a circular annular surface formed with a plurality of radially inwardly protruding protrusions46having a convex circular arc shape, and circumferentially spaced apart from each other. In this case, by setting the sliding gap between the inner ring2and each protrusion46to 0.2 mm or less, vibration of the cage7can be reduced.

As illustrated inFIG.12, the inner-diameter-side axial groove26of the radially inner surface25of each cage claw portion22axially extends through the radially inner surface25and the cage guided surface29. As illustrated inFIG.10, the inner-diameter-side axial groove26has a width equal to, or larger than, half of the circumferential width of the distal end of the cage claw portion22.

As illustrated inFIG.12, the cage circular annular portion21has a chamfer47which extends obliquely in a cross section perpendicular to the circumferential direction, to connect the cage-side sliding contact surface40and the cage guided surface29to each other. Due to the formation of the chamfer47, the radially inner edge of the cage circular annular portion21has an axial width equal to, or smaller than, half of the axial width of the portion of the cage circular annular portion21having the largest axial width. Also, the cage circular annular portion21has a chamfer48obliquely extending in a cross section perpendicular to the circumferential direction, to connect the cage-side sliding contact surface40and the outer peripheral surface of the cage circular annular portion21to each other.

The outer-diameter-side axial groove24of the radially outer surface23of each cage claw portion22is shaped such that, from the distal end of the cage claw portion22toward the cage circular annular portion21, the position of the groove bottom gradually changes radially outwardly. As illustrated inFIGS.11and14, the outer-diameter-side axial groove24has a width equal to, or larger than, half of the circumferential width of the distal end of the cage claw portion22. Also, the cage circular annular portion21has, in its outer periphery, axial cutouts49at positions corresponding to the respective outer-diameter-side axial grooves24.

As illustrated inFIGS.11and14, each cage claw portion22includes claw tip oil passages50formed on both circumferential sides of the distal end portion of the radially outer surface23(i.e., formed in the shoulders of the outer-diameter-side axial groove24on both sides thereof), and circumferentially extending through the respective shoulders of the outer-diameter-side axial groove24. The claw tip oil passages50are stepped cutouts rising from the side remoter from the cage circular annular portion21toward the side closer to the cage circular annular portion21. By forming the claw tip oil passages50, it is possible to improve lubricating performance for the balls5.

In this ball bearing1, since, as illustrated inFIG.13, a plurality of axial protrusions42whose cross sections along the circumferential direction have an axially convex circular arc shape are formed on the cage-side sliding contact surface40at constant pitches in the circumferential direction, oil films due to the wedge film effect are formed between the seal-side sliding contact surface41and the respective axial protrusions42. Due to the oil films, the lubrication condition between the seal-side sliding contact surface41and the axial protrusions42becomes fluid lubrication condition, thus making it possible to markedly reduce the contact resistance between the cage7and the seal member6. Therefore, it is possible to prevent abnormal heat generation due to the sliding resistance of the contact portions of the cage7and the seal member6.

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 10−5to 10−6mm) 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 10−3to 10−1mm) 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 bearing1, since, as illustrated inFIG.12, the cage circular annular portion21is disposed to come into sliding contact with the seal member6, it is possible to increase the axial thickness of the cage circular annular portion21, and thus increase the rigidity of the cage circular annular portion21. Therefore, even during high-speed rotation, it is possible to reduce torsional deformation of the cage circular annular portion21due to the centrifugal forces that the cage claw portions22receive, and reduce radially outward inclination of the cage claw portions22.

Also, this ball bearing1requires 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 member6, and having open ends on both axial sides has to be used instead), too.

Also, in this bearing1, since, as illustrated inFIG.11, the portion of each circumferentially opposed surface27of each cage claw portion22that circumferentially supports the ball5is a straight portion having no circumferential inclination, and extending straight in the axial direction, when the ball5is supported by the cage claw portion22, no axial component force is generated at the cage claw portion22. Therefore, it is possible to prevent the cage7from being axially pressed hard against the seal member6, and effectively reduce the sliding resistance of the contact portions of the cage7and the seal member6.

Also, in this ball bearing1, since, as illustrated inFIG.12, the axial protrusions42, each including the parallel apex portion43and the first inclined apex portion44, are used, while the bearing is rotating at a low speed and the centrifugal forces which the cage claw portions22receive are relatively small, oil films due to the wedge film effect can be formed between the seal-side sliding contact surface41and the parallel apex portions43of the respective axial protrusions42. Also, while the bearing is rotating at a high speed and the centrifugal forces which the cage claw portions22receive are relatively large, an oil film due to the wedge film effect can be formed between the seal-side sliding contact surface41, and the parallel apex portion43and the first inclined apex portion44of each axial protrusion42with torsional deformation of the cage circular annular portion21relatively 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 cage7and the seal member6.

Also, in this ball bearing1, since, as illustrated inFIG.12, the cross section of each first inclined apex portion44perpendicular to the circumferential direction has a rounded shape, and the first inclined apex portion44and the parallel apex portion43are smoothly connected to each other, when, with torsional deformation of the cage circular annular portion21relatively large, an oil film due to the wedge film effect is formed between the seal-side sliding contact surface41, and the parallel apex portion43and the first inclined apex portion44, the oil film can be formed stably.

Also, in this ball bearing1, since, as illustrated inFIG.12, the inner-diameter-side axial grooves26(radially inner oil grooves) are disposed in the inner periphery of the cage7, lubricating oil supplied into the space radially inside of the cage claw portions22is introduced, through the inner-diameter-side axial grooves26, into the space between the cage circular annular portion21and the seal member6. Therefore, it is possible to sufficiently lubricate the portions of the bearing between the seal-side sliding contact surface41and the axial protrusions42, and effectively form oil films due to wedge films.

Also, in this ball bearing1, since, as illustrated inFIG.12, a cage circular annular portion21is used which has a chamfer47obliquely extending, in a cross section perpendicular to the circumferential direction, to connect the cage-side sliding contact surface40and the cage guided surface29to each other, lubricating oil introduced into the space between the cage circular annular portion21and the seal member6through the inner-diameter-side axial grooves26from the radially inner areas of the cage claw portions22can be smoothly fed along the chamfer47and led onto the cage-side sliding contact surface40, by a centrifugal force.

Also, in this ball bearing1, since, as illustrated inFIG.12, the axial protrusions42are disposed at positions where the axial protrusions42overlap with the pitch circle of the balls5, or disposed radially outwardly of the pitch circle of the balls5, when the centrifugal forces applied to the cage claw portions22cause torsional deformation of the cage circular annular portion21in the direction in which the cage claw portions22are inclined radially outward, it is possible to prevent, due to the torsional deformation, the cage-side sliding contact surface40and the seal-side sliding contact surface41from coming into contact with each other at a position displaced radially outwardly of the axial protrusions42.

Also, in this ball bearing1, since, as illustrated inFIG.12, the position of the bottom of the outer-diameter-side axial groove24(radially outer oil groove) of each cage claw portion22gradually changes radially outwardly from the distal end of the cage claw portion22toward the cage circular annular portion21, lubricating oil supplied into the outer-diameter-side axial groove24is moved from the distal end of the cage claw portion22toward the cage circular annular portion21by the pumping action, and is introduced into the space between the cage circular annular portion21and the seal member6. Therefore, it is possible to sufficiently lubricate the portions of the bearing between the seal-side sliding contact surface41and the axial protrusions42, and effectively form oil films due to wedge films.

Also, in this ball bearing1, since the axial end of the annular space4opposite from the axial end thereof closed by the seal member6is open, it is possible to sufficiently lubricate the portions of the bearing between the seal-side sliding contact surface41and the axial protrusions42, and reliably form oil films due to wedge films.

FIG.18illustrates a ball bearing1according to the third embodiment of the present invention. The third embodiment is different from the second embodiment in that the axial protrusions42are disposed on, of the cage-side sliding contact surface40and the seal-side sliding contact surface41, the cage-side sliding contact surface40in the second embodiment, and the seal-side sliding contact surface41in 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 inFIG.19, a plurality of axial protrusions42are formed on the seal-side sliding contact surface41at constant pitches in the circumferential direction. The axial protrusions42are formed, with a mold, on the rubber part17of the seal member6. The cross section of each axial protrusion42along the circumferential direction has an axially convex circular arc shape. The axial protrusion42has an axial height set to 5% or less of the circumferential width dimension of the axial protrusion42. InFIG.19, the axial height of the axial protrusion42is exaggeratedly shown so that the axial protrusion42can be seen clearly. On the other hand, the cage-side sliding contact surface40is a circular annular flat surface extending in the direction perpendicular to the axial direction, and is formed with no axial protrusions42.

As illustrated inFIG.18, the axial protrusions42are disposed at positions where the axial protrusions42overlap with the pitch circle of the balls5(imaginary circle connecting the centers of the balls5), or disposed radially outwardly of the pitch circle of the balls5.

As illustrated inFIGS.18and20, the axial protrusions42each have a parallel apex portion43, a first inclined apex portion44and a second inclined apex portion45. The parallel apex portion43is a portion of the axial protrusion42having an axially circular arc convex shape in cross-sections along the circumferential direction whose apex height is radially uniform. The first inclined apex portion44is a portion of the axial protrusion42having 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 portion43. The second inclined apex portion45is a portion of the axial protrusion42having 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 portion43. As illustrated inFIG.12, the cross sections of the first and second inclined apex portions44and45perpendicular to the circumferential direction have a rounded shape smoothly connected to the parallel apex portion43.

In this ball bearing1, since, as illustrated inFIG.19, a plurality of axial protrusions42whose cross sections along the circumferential direction have an axially convex circular arc shape are formed on the seal-side sliding contact surface41at constant pitches in the circumferential direction, oil films due to the wedge film effect are formed between the cage-side sliding contact surface40and the respective axial protrusions42. Due to the oil films, the lubrication condition between the cage-side sliding contact surface40and the axial protrusions42becomes the fluid lubrication condition, thus making it possible to markedly reduce the contact resistance between the cage7and the seal member6. Therefore, it is possible to prevent abnormal heat generation due to the sliding resistance of the contact portions of the cage7and the seal member6.

Also, in this ball bearing1, since, as illustrated inFIG.18, axial protrusions42each including the parallel apex portion43and the first inclined apex portion44, are used, while the bearing is rotating at a low speed, and the centrifugal forces which the cage claw portions22receive are relatively small, oil films due to the wedge film effect can be formed between the cage-side sliding contact surface40and the parallel apex portions43of the respective axial protrusions42. Also, while the bearing is rotating at a high speed, and the centrifugal forces which the cage claw portions22receive are relatively large, an oil film due to the wedge film effect can be formed between the cage-side sliding contact surface40, and the parallel apex portion43and the first inclined apex portion44of each axial protrusion42with torsional deformation of the cage circular annular portion21relatively 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 cage7and the seal member6.

Also, in this ball bearing1, since, as illustrated inFIG.18, the cross section of each first inclined apex portion44perpendicular to the circumferential direction has a rounded shape, and thus the first inclined apex portion44and the parallel apex portion43are smoothly connected to each other, when, with torsional deformation of the cage circular annular portion21relatively large, an oil film due to the wedge film effect is formed between the cage-side sliding contact surface40, and the parallel apex portion43and the first inclined apex portion44, the oil film can be formed stably.

Also, in this ball bearing1, since, as illustrated inFIG.18, the inner-diameter-side axial grooves26are disposed in the inner periphery of the cage7, lubricating oil supplied to the space of the bearing radially inside the cage claw portions22is introduced, through the inner-diameter-side axial grooves26, into the space between the cage circular annular portion21and the seal member6. Therefore, it is possible to sufficiently lubricate the portions of the bearing between the cage-side sliding contact surface40and the axial protrusions42, 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.

FIGS.21to26illustrate a ball bearing1according to the fourth embodiment of the present invention. The fourth embodiment is different from the third embodiment in that a seal member61is added and also the cage7has 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 inFIG.21, a seal member6is disposed at one of the end openings of the annular space4on both axial sides thereof, and a seal member61is disposed on the other end opening, too. Lubricant is sealed in the portion of the annular space4between the seal members6and61.

As illustrated inFIGS.22and23, each cage claw portion22has circumferentially opposed surfaces27circumferentially opposed to the corresponding balls5, respectively. The portions of the circumferentially opposed surfaces27which circumferentially support the balls5are flat surfaces extending such that when the cage claw portion22is moved radially outwardly by a centrifugal force, the circumferentially opposed surfaces27do not interfere with the balls5. As illustrated inFIG.22, the circumferentially opposed surfaces27are flat surfaces inclined to gradually approach, in the radially inward direction, the imaginary straight line connecting the center of the cage circular annular portion21and the center of the cage claw portion22to each other (flat surfaces extending such that the circumferential width of the cage claw portion22gradually decreases in the radially inward direction), when seen in the axial direction.

As illustrated inFIG.24, the cage circular annular portion21includes a step62radially outwardly rising from the level of the radially outer surface portions of the cage claw portions22at their roots. Due to the formation of the step62, when lubricant sealed in the annular space4is moved toward the cage circular annular portion21along the outer-diameter-side axial grooves24, the lubricant can be partially stopped by the step62, and returned to the balls5.

As illustrated inFIG.25, each circumferentially opposed surface27and the corresponding axially opposed surface28are connected together via a composite rounded curved surface. In the shown example, the curved surface connecting the circumferentially opposed surface27and the axially opposed surface28to each other is constituted by a distal-end-side rounded surface portion63connected to the circumferentially opposed surface27, and having a part-cylindrical shape with a radius of curvature R2smaller than the radius R1of the ball5; a root-side rounded surface portion64connected to the axially opposed surface28, and having a part-cylindrical shape with a radius of curvature R3larger than the radius R1of the ball5; and an intermediate rounded surface portion65smoothly connecting the distal-end-side rounded surface portion63and the root-side rounded surface portion64to each other.

This ball bearing1is the same in operation and effects as the third embodiment.

FIGS.27to31illustrate a ball bearing1according to the fifth embodiment of the present invention. The fifth embodiment is the same as the second embodiment (shown inFIGS.9to17) except that the claw tip oil passages50are 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.

FIGS.32to37illustrate a ball bearing1according to the sixth embodiment of the present 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 portion22has a cantilevered structure of which one axial end is a fixed end fixed to the cage circular annular portion21, and the other axial end is a free end. The cage claw portion22has an axial length larger than the axial width of the outer ring raceway groove12. The cage claw portion22has a radial thickness which is uniform, i.e., does not change, in the axial direction.

As illustrated inFIGS.32and37, a root-side guided surface51that comes into sliding contact with the one outer ring groove shoulder13is formed at the portion of the radially outer surface of the cage circular annular portion21corresponding to the root of each cage claw portion22. Also, a distal-end-side guided surface52that comes into sliding contact with the other outer ring groove shoulder13is formed on the radially outer surface of the axial end portion of the cage claw portion22on its distal end side.

As illustrated inFIG.36, the root-side guided surface51has, 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 portion21. The distal-end-side guided surface52also has, in cross sections along the circumferential direction, a radially outwardly protruding circular arc shape (seeFIG.37). The root-side guided surface51and the distal-end-side guided surface52have the same shape in cross sections along the circumferential direction. The radii of curvature of each of the root-side guided surface51and the distal-end-side guided surface52in cross sections along the circumferential direction can be set to smaller than ½ of the radius of the inner diameter of the outer ring groove shoulder13, and larger than 1/10 of the radius of the inner diameter of the outer ring groove shoulder13.

As illustrated inFIG.37, in this embodiment, the root-side guided surface51and the distal-end-side guided surface52are continuous surfaces continuously connected together straight in the axial direction in order that no recess is formed between the root-side guided surface51and the distal-end-side guided surface52.

As illustrated inFIG.34, the root-side guided surface51has, on its side remoter from the cage claw portion22, an axial end edge53chamfered into a rounded shape. The language “chamfered into a rounded shape” means, as illustrated inFIG.35, forming a corner having a convex circular arc-shaped cross section perpendicular to the circumferential direction. As illustrated inFIG.34, the distal-end-side guided surface52also has, on its side remote from the cage circular annular portion21, an axial end edge54chamfered into the same rounded shape.

In this ball bearing1, since, as illustrated inFIG.36, each of the root-side guided surfaces51has, 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 shoulder13and the root-side guided surfaces51. Due to the oil films, the lubrication condition between the one outer ring groove shoulder13and the root-side guided surfaces51becomes the fluid lubrication condition, thus making it possible to markedly reduce the contact resistance between the cage7and the outer ring3. Since, as with the root-side guided surfaces51, each of the distal-end-side guided surfaces52, shown inFIG.32, 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 shoulder13(outer ring groove shoulder13on the left side) and the distal-end-side guided surfaces52. Due to the oil films, the lubrication condition between the other outer ring groove shoulder13and the distal-end-side guided surfaces52becomes the fluid lubrication condition, thus making it possible to markedly reduce the contact resistance between the cage7and the outer ring3. Therefore, it is possible to prevent abnormal heat generation due to the sliding resistance of the contact portions of the cage7and the outer ring3.

Also, in this ball bearing1, since, as illustrated inFIG.32, the one outer ring groove shoulder13(outer ring groove shoulder13on the right side) supports the cage circular annular portion21from the radially outer side, and the other outer ring groove shoulder13(outer ring groove shoulder13on the left side) supports the axial ends of the cage claw portions22on their distal end sides from the radially outer side, flexural deformation of the cage claw portions22toward 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 portion21, and flexural deformation of the cage claw portions22per se toward the radially outer side, due to the centrifugal forces which the cage claw portions22receive.

Also, in this ball bearing1, since, as illustrated inFIG.34, the axial end edges53of the root-side guided surfaces51on their sides remoter from the cage claw portions22, and the axial end edges54of the distal-end-side guided surfaces52on their sides remoter from the cage circular annular portion21are 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 shoulder13(outer ring groove shoulder13on the right side) and the root-side guided surfaces51shown inFIG.32, and oil films due to the wedge film effect can be effectively formed between the other outer ring groove shoulder13(outer ring groove shoulder13on the left side) and the distal-end-side guided surfaces52, too.

Also, in this ball bearing1, since, as illustrated inFIG.33, the portions of the circumferentially opposed surfaces27of each cage claw portion22which circumferentially support the balls5are flat surfaces extending parallel to the imaginary straight line connecting the center of the cage circular annular portion21and the center of the cage claw portion22to each other, when the cage claw portion22is moved radially outwardly by the centrifugal force applied to the cage claw portion22, it is possible to prevent the circumferentially opposed surfaces27of the cage claw portion22from interfering with the balls5. Also, since the shear resistance of lubricating oil generated between the circumferentially opposed surfaces27of the cage claw portion22and the balls5is reduced, it is also possible to reduce the heat generation in the ball bearing1.

Also, in this ball bearing1, since the axial end of the annular space4opposite from the axial end thereof closed by the seal member6is open, it is possible to sufficiently lubricate the root-side guided surfaces51and the distal-end-side guided surfaces52, and reliably form oil films due to wedge films.

FIGS.38to41illustrate a ball bearing1according to the seventh embodiment of the present invention. The seventh embodiment is different from the sixth embodiment only in that oil reservoir grooves55are 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 inFIGS.38and40, each cage claw portion22has, in its radially inner surface, an oil reservoir groove55axially extending from the distal end of the cage claw portion22toward the cage circular annular portion21. As illustrated inFIG.38, the oil reservoir groove55rises to the radially inner surface of the cage7at the position radially opposed to the inner ring groove shoulder9closer to the cage circular annular portion21. In other words, the oil reservoir groove55does not axially extend through the cage7. The oil reservoir groove55may, however, axially extend through the radially inner surface of the cage7.

As illustrated inFIGS.39and41, the oil reservoir groove55is formed in the circumferential center of the radially inner surface of the cage claw portion22. The oil reservoir groove55has a semicircular sectional shape. The oil reservoir groove55may instead have a triangular sectional shape or a quadrangular sectional shape.

In the ball bearing1of this embodiment, lubricating oil radially outwardly scattered by a centrifugal force can be stored in the oil reservoir grooves55, and supplied to the inner ring2.

The ball bearing1of this embodiment is the same in operation and effects as the bearing of the sixth embodiment.

FIGS.42to45illustrate a ball bearing1according to the eighth embodiment of the present invention. The eighth embodiment is different from the seventh embodiment (shown inFIGS.38to41) only in that relief recesses56are 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 inFIG.45, The relief recesses56are each formed in the portion of the radially outer surface of a respective one of the cage claw portion22between the root-side guided surface51and the distal-end-side guided surface52. That is, the radially outer surface of the cage claw portion22is a stepped surface in which first the root-side guided surface51, then the relief recess56and then the distal-end-side guided surface52are arranged in the axial direction.

As illustrated inFIGS.42and43, the relief recess56has an axial width wider than the axial width of the outer ring raceway groove12, and extends in the circumferential direction. As illustrated inFIG.42, the relief recess56is arranged to cover the entire axial width of the outer ring raceway groove12. That is, the end of the relief recess56closer to the root-side guided surface51is located at a position displaced toward the one outer ring groove shoulder13(outer ring groove shoulder13closer to the cage circular annular portion21) from the boundary between the one outer ring groove shoulder13and the outer ring raceway groove12. Also, the end of the relief recess56closer to the distal-end-side guided surface52is located at a position displaced toward the other outer ring groove shoulder13(outer ring groove shoulder13remoter from the cage circular annular portion21) from the boundary between the other outer ring groove shoulder13and the outer ring raceway groove12. Both axial ends of the relief recess56rise while being inclined to the root-side guided surface51and the distal-end-side guided surface52, respectively.

As illustrated inFIG.43, the relief recess56is a portion recessed relative to the root-side guided surface51(or the distal-end-side guided surface52) so as to have an inner surface at a position retracted radially inwardly relative to the root-side guided surface51(or the distal-end-side guided surface52). In the shown example, the inner surface of the relief groove56is a flat surface extending in the direction perpendicular to the radial direction.

In this ball bearing1, since, as illustrated inFIG.42, the relief recesses56are formed between the root-side guided surfaces51and the respective distal-end-side guided surfaces52, it is possible to prevent each of the boundaries between the outer ring raceway groove12and the respective outer ring groove shoulders13from coming into sliding contact with the radially outer surface of the cage circular annular portion21or the radially outer surfaces of the cage claw portions22. Therefore, it is possible to prevent the radially outer surface of the cage circular annular portion21and the radially outer surfaces of the cage claw portions22from becoming worn locally at the positions corresponding to the boundaries between the outer ring raceway groove12and the outer ring groove shoulders13.

The ball bearing1of this embodiment is the same in operation and effects as the sixth and seventh embodiments.

FIGS.46and47illustrate a ball bearing1according to the ninth embodiment of the present invention. The ninth embodiment corresponds to the combination of the sixth embodiment (ofFIGS.32to37) and the sliding contact structure of the cage7and the seal member6in the second embodiment (sliding contact structure of the cage-side sliding contact surface40and the seal-side sliding contact surface41inFIG.12). 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.

FIGS.48and49illustrate a ball bearing1according to the tenth embodiment of the present invention. The tenth embodiment corresponds to the combination of the sixth embodiment (ofFIGS.32to37) and the sliding contact structure of the cage7and the seal member6in the third embodiment (sliding contact structure of the cage-side sliding contact surface40and the seal-side sliding contact surface41inFIG.18). 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 bearing1, 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 bearing1lubricated by grease, i.e., a ball bearing1in 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.

The above-described embodiments are mere examples in every respect, and the present invention is not limited thereto. The scope of the present invention is indicated not by the above description but by the claims, and should be understood to include all modifications within the scope and meaning equivalent to the scope of the claims.

DESCRIPTION OF REFERENCE NUMERALS