Rolling bearing assembly having magnet to prevent brittle flaking

A rolling bearing assembly according to the present invention includes an inner ring, an outer ring, a plurality of rolling elements interposed between the inner and outer rings, and a magnet provided to cause magnetic attraction between the rolling elements and at least one of the inner and outer rings. With the magnetic attraction, it is possible to avoid any collision between the rolling elements and the inner and outer rings, thereby preventing brittle flaking from occurring in the rolling bearing assembly.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority from Japanese Patent Application No. 2005-79931, filed on Mar. 18, 2005, the content of which is hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates generally to bearings and automotive accessories. More particularly, the invention relates to a rolling bearing assembly for use in an automotive accessory, which includes a magnet to prevent the surfaces of rolling elements and the raceway surfaces of inner and outer rings thereof from brittle flaking.

2. Description of the Related Art

In recent years, rolling bearings of automotive accessories, such as an alternator and an air conditioning compressor driven by an engine in an automobile, have come to be used under severe operating conditions (for example, high temperature and vibration), resulting in a new type of bearing damage, called “brittle flaking”.

Brittle flaking may occur at any area of the surfaces of the rolling elements and the raceway surfaces of the inner and outer rings of the rolling bearing. Further, brittle flaking has a feature that the time period from the start to finish thereof is very short, for example, only about 0.1 to 1% of that of a general rolling contact fatigue.

Up to now, the mechanism of brittle flaking has been not made clear. Accordingly, only temporary expedients that are not based on sound scientific grounds have been employed to solve the problem of brittle flaking, in other words, no fundamental solution to the problem has been provided.

According to the results of a rolling bearing reliability test, among the accessories of an automobile, occurrence rate of brittle flaking was highest in the alternator. As is well known in the art, the alternator had the highest speed increasing ratio with respect to the engine and a large rotational inertia, and thus had the largest equivalent inertia which is proportional to the second power of the speed increasing ratio. Further, occurrence rate of brittle flaking was high in the accessories when those were driven by the engine via a Poly-V belt, with which the belt tension was set tight as is well known in the art. Furthermore, occurrence rate of brittle flaking was high in the accessories when there was provided an autotensioner in the belt drive system to prevent slack of the belt via which the engine drove the accessories.

One theory explains, based on the fact that the hydrogen content in grease included in rolling bearings damaged due to brittle flaking is high, the mechanism of brittle flaking such that the hydrogen generated due to decomposition of the grease diffuses into the rolling elements and the outer ring, thereby causing the surfaces thereof to flake. (With regard to the theory, a further reference can be made to: 1) Minoru Umemoto, Sanyo Technical Report, Vol. 11, No. 1 (2004), “Nanocrystallization by Heavy Deformation and White Etching Area in Bearing Steels”; 2) K. Tamada and H. Tanaka, Wear 199 (1996), “Occurrence of Brittle Flaking on Bearings Used for Automotive Electrical Instruments and Auxiliary Devices”; and 3) Japanese Patent First Publication No. 2002-227854.)

Further, according to the theory, a new type of grease has been developed which includes an additive to form electrical insulation films on raceway surfaces of rolling bearings, thereby preventing brittle flaking from occurring. By means of the new grease, a certain decrease in occurrence rate of brittle flaking has been achieved; however, it is still impossible to completely prevent occurrence of brittle flaking only by the help of the grease. Indeed, in some cases, brittle flaking occurred even with the insulation films formed on the raceway surfaces of the rolling bearings. Moreover, on the surfaces damaged by brittle flaking, the evidence of a plastic deformation was found.

Accordingly, though grease does have influence on the occurrence of brittle flaking, it may not be effective to solve the problem of brittle flaking by developing a newer type of grease aiming to form insulation films on raceway surfaces of rolling bearings.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentioned circumstances.

The inventors of the present invention have found that the phenomenon of brittle flaking can be reproduced via a rotational fluctuation test as illustrated inFIG. 9.

In the test, an automotive alternator was driven by a motor, which simulated a four-cylinder automotive engine, via a belt. The motor was so controlled to apply a rotation ripple that had an average rotational fluctuation rate of 2% and a frequency being equal to two times of the rotational speed of the motor. For example, when the rotational speed of the motor was 600 rpm (i.e., 600/60=10 Hz), the frequency of the rotation ripple was 20 Hz. The change in rotational speed of the motor with time is shown inFIG. 10. Additionally, the belt tension was set to 300 to 500 N, which corresponds to the average belt tension of a belt drive system in an ordinary automobile.

The inventors have further found that an indentation was formed through the test on a raceway surface of a rolling bearing of the alternator, as shown inFIG. 11. Since no load greater than the yield stress of the raceway surface was imposed thereon during the test, it was normally impossible to result in such an indentation. Accordingly, the inventors have hypothesized that a lubrication failure occurred during the test on the raceway surface, which further caused the indentation thereon.

According to Elastohydrodynamic Lubrication (EHL) theory, when there is a difference in rotational speed between a rolling element and the inner or outer ring of a rolling bearing, an elastohydrodynamic lubrication film will be developed between the surface of the rolling element and the raceway surface of the inner or outer ring, thereby preventing plastic deformation of the two members.

In normal operating conditions of the rolling bearing of the above-tested alternator, elastohydrodynamic lubrication films were formed between the surfaces of the rolling elements and the raceway surfaces of the inner and outer rings. Further, as shown inFIG. 12, the thickness of the elastohydrodynamic lubrication films increased with the rotational speed of the alternator (i.e., the rotational speed of the inner ring of the rolling bearing).

However, in certain abnormal operating conditions of the rolling bearing, for example, in a condition where the rolling elements have the same rotational speed as the inner or outer ring, the elastohydrodynamic lubrication films formed between the surfaces of the rolling elements and the raceway surface of the inner or outer ring would be broken down. Further, if one of the rolling elements collided against the inner or outer ring without the elastohydrodynamic lubrication film therebetween, the collision would result in a plastic deformation (i.e., an indentation) on the surface of the rolling element and/or the raceway surface of the inner or outer ring. The plastic deformation would further give rise to brittle flaking of the plastically-deformed surface.

Based on the above hypothesis, the inventors have considered that occurrence of brittle flaking in a rolling bearing can be prevented by avoiding any collision between the rolling elements and the inner and outer rings in absence of elastohydrodynamic lubrication films therebetween. The inventors have further considered that a magnet can be used to cause magnetic attraction between the rolling elements and at least one of the inner and outer rings, thereby avoiding any collision between the rolling elements and the inner and outer rings.

It is, therefore, a primary object of the present invention to provide a rolling bearing assembly for use in an automotive accessory, which includes a magnet to prevent the surfaces of rolling elements and the raceway surfaces of inner and outer rings thereof from brittle flaking.

According to the present invention, a rolling bearing assembly includes an inner ring, an outer ring, a plurality of rolling elements interposed between the inner and outer rings, and a magnet provided to cause magnetic attraction between the rolling elements and at least one of the inner and outer rings.

With such a configuration, it becomes possible to avoid any collision between the rolling elements and the inner and outer rings by means of the magnetic attraction, thereby preventing brittle flaking from occurring in the rolling bearing assembly.

In the above rolling bearing assembly, the rolling elements may each have a ball shape.

In one embodiment of the present invention, the rolling bearing assembly further includes a lubricant and a seal interposed between the inner and outer rings to keep the lubricant from escaping out of the rolling bearing assembly. Moreover, all the inner and outer rings and rolling elements are made of a magnetic material, and the seal includes a metal core that works as the magnet to cause magnetic attraction between the rolling elements and the inner and outer rings.

In another embodiment of the present invention, the inner ring is made of a magnetic material, and the rolling elements work as the magnet to cause magnetic attraction between the rolling elements and the inner ring.

In yet another embodiment of the present invention, the outer ring is made of a magnetic material, and the rolling elements work as the magnet to cause magnetic attraction between the rolling elements and the outer ring.

In yet another embodiment of the present invention, the rolling elements are made of a magnetic material, and the inner ring works as the magnet to cause magnetic attraction between the rolling elements and the inner ring.

In yet another embodiment of the present invention, the rolling elements are made of a magnetic material, and the outer ring works as the magnet to cause magnetic attraction between the rolling elements and the outer ring.

In yet another embodiment of the present invention, the rolling bearing assembly is employed in an automotive accessory to support a shaft of the accessory.

The automotive accessory may include a plate-shaped bearing retainer that is made of a magnetic material and has first and second side faces disposed perpendicular to the axial direction of the accessory. Further, all the inner and outer rings and rolling elements may be made of a magnetic material and mounted to the first side face of the bearing retainer, and the magnet may have a ring shape and be mounted to the second side face of the same to cause magnetic attraction between the rolling elements and the inner and outer rings.

Otherwise, the outer ring and rolling elements may be made of a magnetic material, and the automotive accessory may include a hollow cylindrical bearing box that is made of a magnetic material and extends in the axial direction of the accessory. Further, the inner and outer rings and rolling elements may be mounted in the bearing box, and the magnet may have a ring shape and be mounted on the outer surface of the bearing box to cause magnetic attraction between the rolling elements and the outer ring.

The automotive accessory may be an automotive alternator.

The automotive accessory may be driven by an automotive engine in a serpentine belt drive system. Further, the automotive engine may drive four or more automotive accessories in the serpentine belt drive system.

The automotive accessory may be driven by an automotive engine in a belt drive system that includes an autotensioner.

The automotive accessory may be driven by an automotive engine via a Poly-V belt.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will be described hereinafter with reference toFIGS. 1-8.

It should be noted that, for the sake of clarity and understanding, identical components having identical functions in different embodiments of the invention have been marked, where possible, with the same reference numerals in each of the figures.

First Embodiment

FIGS. 1 and 2show the overall structure of a rolling bearing assembly3according to the first embodiment of the present invention.FIG. 3shows the overall structure of an automotive alternator200in which the rolling bearing assembly3is incorporated.FIG. 4shows the overall configuration of a serpentine belt drive system100for an automobile, in which the alternator200is incorporated.

As shown inFIG. 4, in the serpentine belt drive system100, an internal combustion engine drives six automotive accessories (or auxiliary machines) via a belt108.

Specifically, in the serpentine belt drive system100, a pulley101is mounted on a crank shaft (C/S) of the engine; a pulley102is mounted on a rotary shaft of an air conditioning compressor (A/C); a pulley103is mounted on a rotary shaft of the automotive alternator200(ALT); a pulley104is mounted on a rotary shaft of an idler (Idler); a pulley105is mounted on a rotary shaft of an oil pump for power steering (P/S); a pulley106is mounted on a rotary shaft of a water pump (W/P); and a pulley107is mounted on a rotary shaft of an autotensioner (A/T). The pulleys101-107are connected together via the belt108, so that rotating power can be transmitted from the engine to the six accessories.

Each of the accessories has a given gear ratio with respect to the engine. For example, the diameter ratio between the pulley101of the engine and the pulley103of the automotive alternator200is set to 3.3, so that the automotive alternator200has a speed increasing ratio of 3.3 with respect to the engine. The belt108is a Poly-V belt with six grooves. The autotensioner is of torsion spring type and provided on the slack side of the pulley101of the engine. The belt tension on the slack side of the pulley101is kept constant by the autotensioner at, for example, 400 N.

Referring toFIG. 3, the automotive alternator200includes a stator1, which includes a three-phase stator winding1a,and a rotor2that includes a field winding2bfor creating a rotating magnetic field for the stator winding1a.

The rolling bearing assembly3is provided on the front-side (i.e., the pulley-side) of the rotor2. On the rear-side (i.e., the opposite side to the pulley) of the rotor2, there is provided another rolling bearing assembly3athat has the same structure as the front-side rolling bearing assembly3. The rolling bearing assemblies3and3atogether support a shaft2cof the rotor2(i.e., the rotary shaft of the automotive alternator200).

A front-side housing4and a rear-side housing4aare provided to accommodate the stator1and rotor2. In addition, the stator1is supported by the front-side housing4.

A plate-shaped bearing retainer5is fixed to the front-side housing4by means of a screw51, thereby retaining the front-side rolling bearing assembly3. On the other hand, a hollow cylindrical bearing box41is provided which retains therein the rear-side rolling bearing assembly3a.

A knurled bolt42is provided to fix the bearing box41to the rear-side housing4a.

A rectifier6is also fixed to the rear-side housing4avia the knurled bolt42. The rectifier6is electrically connected to the stator winding la and configured to convert a three-phase AC power outputted from the stator winding1ato a DC power.

Brushes8and slip rings2atogether form an excitation mechanism by which field current is supplied to the field winding2bwhile the rotor2is rotating.

A voltage regulator9is provided to regulate an output voltage of the automotive alternator200by controlling the field current supply to the field winding2b.

In addition, through supplying the field current to the field winding2b,the shaft2cof the rotor2is magnetized.

Referring now toFIGS. 1 and 2, the rolling bearing assembly3includes an inner ring31, an outer ring32, a plurality of rolling elements33, a cage34, and a pair of seals35.

The rolling elements33are interposed between the inner and outer rings31and32and retained by the cage34. In the present embodiment, the rolling elements33each have a ball shape. In other words, the rolling bearing assembly3comprises a ball bearing.

The seals5are respectively provided at opposite axial ends of the rolling bearing assembly3. The seals5work to keep grease, which is filled in the interior of the rolling bearing assembly3as lubricant, from escaping out of the rolling bearing assembly3. Each of the seals5includes a metal core36to secure rigidity thereof.

In the present embodiment, the metal core36of one of the seals35(for example, the left-side seal35inFIGS. 1 and 2) is made of a magnet, and the inner and outer rings31and32and the rolling elements33are made of a magnetic material.

With such a configuration, the magnet (i.e., the metal core36) magnetizes the inner and outer rings31and32and the rolling elements33, thereby causing magnetic attraction between the rolling elements33and the inner and outer rings31and32. The magnetic attraction further enables the rolling elements33to keep constant radial and axial distances with the inner and outer rings31and32.

Having described the overall structure of the rolling bearing assembly3according to the present embodiment, advantages thereof will be described with reference toFIGS. 7A-8B.

FIGS. 7A and 7Billustrate a collision of one of the balls33(i.e., the rolling elements33) against the inner ring31in the radial direction with an initial speed V0.

Suppose that the ball33has the same rotational speed as the inner ring31. Further, suppose that the metal core36is not made of a magnet, in other words, there is no magnet provided in the rolling bearing assembly3. Then, there would be no elastohydrodynamic lubrication film between the ball33and the inner ring31, and thus the collision would result in plastic deformation on the surface of the ball33and the raceway surface of the inner ring31.

Let X represent the moving distance of the center of the ball33from an initial position thereof in the radial direction. The initial position of the center of the ball33here represents the position thereof at which the ball33makes first contact with the inner ring31. Further, let m represent the mass of the moving body. For example, when the ball33collides against the inner ring31by itself, m represents the mass of the ball33. Otherwise, when the ball33collides against the inner ring31along with the outer ring32and the alternator housings4and4a,m represents the sum of the masses of the ball33, outer ring32, and alternator housings4and4a.

Referring toFIGS. 8A and 8B, let X1represent the amount of plastic deformation of the ball33during the collision. Similarly, let X2represent the amount of plastic deformation of the inner ring31during the collision. Then, the total plastic deformation X of the two members is equal to X1+X2.

Further, let r represent the radius of the ball33; let R1represent the curvature radius of the raceway surface of the inner ring31before the collision; let R2represent the minimum radius of the raceway of the inner ring31before the collision; let a and b respectively represent the major and minor radiuses of the contact ellipse between the ball33and the inner ring31after the plastic deformation; let Rc1and Rc2respectively represent the curvature radiuses of the interface of the ball33and the inner ring31on first and second reference planes after the plastic deformation. Here, the first reference plane is, as shown inFIGS. 7A and 8A, defined to include thereon the axis of the inner ring31and the center of the ball33. On the other hand, the second reference plane is, as shown inFIGS. 7B and 8B, defined to extend perpendicular to the axis of the inner ring31through the center of the ball33.

Then, since the materials of the ball33and the inner ring31have substantially the same hardness, the parameters X1, X2, and X has the following relationship:

Further, through an approximate computation based on the assumption that a is less than both r and R1and b is less than both r and R2, the fowling geometric relationships can be obtained:

It should be noted that the above relationships can also be applicable to a collision of the ball33against the outer ring32, through substituting −R2for R2.

As can be seen from the above equations2A-3B, the contact ellipse (represented by a and b) and the interface (represented by Rc1and Rc2) between the ball33and the inner ring31change with the total plastic deformation X.

The total plastic deformation X can be determined as follows. Let P represent the contact pressure at the interface between the inner ring31and the ball33, then the force of restitution of the inner ring31is equal to Pπab. Accordingly, the equation of motion for the moving body can be expressed as:
m{umlaut over (X)}=−Pπab(4)

In addition, according to a research by Hutchings, the contact pressure P can be determined by the following equation:
P=C′Y  (5),
where, Y is the yield stress of the inner ring31, and C′ is a constant.

For a plastic deformation of a ball, the constant C′ is about 3. In other cases, for example, in a research paper by Taper, the constant C′ is about 2.8 regardless of the material of the plastically-deformed body.

Through incorporating the equations2A and2B into the equation 4, the equation of motion for the moving body can be rewritten as follows:

The above equation 6 represents a simple harmonic motion. The solution of the equation 6 with the initial condition that {umlaut over (X)}=0 and {dot over (X)}=V0when t=0 can be expressed as:

The loading time tp, which is the time period from the start to finish of the collision, is one fourth of the frequency of the simple harmonic motion represented by the equation 6. Accordingly, the loading time tpcan be expressed as:

Using the above-described equation 7, it is possible to determine the total plastic deformation X at any time instant t(0<t<tp). Further, using the equations2A and2B, it is possible to determine the contact ellipse between the ball33and the inner ring31at that time instant. After the loading time tp, the ball33will rebound from the inner ring31, as to which description is omitted here.

In a conventional rolling bearing, a collision of one of the rolling elements against the inner or outer ring without an elastohydrodynamic lubrication film therebetween will result in a plastic deformation on the surface of the rolling bearing and/or the raceway surface of the inner or outer ring. Further, the plastic deformation will cause brittle flaking of the plastically-deformed surface.

In comparison, in the rolling bearing assembly3according to the present embodiment, the metal core36of one of the seals35is made of a magnet, which causes magnetic attraction between the rolling elements33and the inner and outer rings31and32. The magnetic attraction further enables the rolling elements33to keep constant radial and axial distances with the inner and outer rings31and32, thereby avoiding any collision therebetween. Consequently, occurrence of brittle flaking in the rolling bearing assembly3is prevented.

In addition, when a conventional rolling bearing is used in the automotive alternator200, the field current supply to the field winding2bof the rotor2may magnetize the inner ring of the rolling bearing as well as the shaft2cof the rotor2. However, the magnetomotive force of the field winding2bis generally not large enough to cause magnetic attraction between the inner ring and the rolling elements, and thus it is difficult to avoid any collision between the rolling elements and the inner and outer rings.

The rolling bearing assembly3according to the present embodiment is advantageous especially in the following cases.

1) When employed in an automotive accessory, which has a large inertia and a large speed increasing ratio with respect to the engine driving it, such as the automotive alternator200. The automotive accessory accordingly has a large equivalent inertia, so that it is easy for the automotive accessory to behave unstably. The unstable behavior of the automotive accessory may induce a collision between the components of a rolling bearing employed therein, thereby causing brittle flaking to occur in the rolling bearing.

2) When used in a serpentine belt drive system, such as the one shown inFIG. 4. In a serpentine belt drive system, a plurality of rotating machines are connected together via a single belt. Consequently, it is easy for rotation of the machines to become unstable. Moreover, the probability of occurrence of resonances among the machines and the belt is high. The rotational and vibrational instabilities in the serpentine belt drive system may induce a collision between the components of a rolling bearing used therein, thereby causing brittle flaking to occur in the rolling bearing. Especially, when the serpentine belt drive system includes five or more rotating machines, it is easier for brittle flaking to occur.

3) When used in a belt drive system that includes an autotensioner. The autotensioner generally works to keep the belt tension of the belt drive system constant. However, when an excessive transient variation occurs in the tension of the belt, the autotensioner may impose an impulsive load on the rotating machines of the belt drive system, thereby inducing a collision between the components of a rolling bearing employed in one of the rotating machines.

4) When used in a belt drive system in which a Poly-V belt is employed. With the Poly-V belt, the belt tension is generally set tight, thus imposing high load on the shafts of rotating machines of the belt drive system. The high load may induce a collision between the components of a rolling bearing employed in one of the rotating machines, thereby causing brittle flaking to occur in the rolling bearing.

Second Embodiment

This embodiment provides a rolling bearing assembly3b1that has almost the same structure as the rolling bearing assembly3according to the first embodiment. Accordingly, only the differences in structure therebetween will be described below.

In the rolling bearing assembly3of the first embodiment, the metal core36of one of the seals35is made of a magnet, and all the inner ring31, outer ring32, and rolling elements33are made of a magnetic material.

In comparison, in the rolling bearing assembly3b1of the present embodiment, all the rolling elements33are made of a magnet, and only the inner ring31is made of a magnetic material.

With such a configuration, magnetic attraction is caused between the rolling elements33and the inner ring31, thereby avoiding any collision between the rolling elements33and the inner and outer rings31and32.

Third Embodiment

This embodiment provides a rolling bearing assembly3b2that has almost the same structure as the rolling bearing assembly3according to the first embodiment. Accordingly, only the differences in structure therebetween will be described below.

In the rolling bearing assembly3of the first embodiment, the metal core36of one of the seals35is made of a magnet, and all the inner ring31, outer ring32, and rolling elements33are made of a magnetic material.

In comparison, in the rolling bearing assembly3b2of the present embodiment, all the rolling elements33are made of a magnet, and only the outer ring32is made of a magnetic material.

With such a configuration, magnetic attraction is caused between the rolling elements33and the outer ring32, thereby avoiding any collision between the rolling elements33and the inner and outer rings31and32.

Fourth Embodiment

This embodiment provides a rolling bearing assembly3b3that has almost the same structure as the rolling bearing assembly3according to the first embodiment. Accordingly, only the differences in structure therebetween will be described below.

In the rolling bearing assembly3of the first embodiment, the metal core36of one of the seals35is made of a magnet, and all the inner ring31, outer ring32, and rolling elements33are made of a magnetic material.

In comparison, in the rolling bearing assembly3b3of the present embodiment, the inner ring31is made of a magnet, and all the rolling elements33are made of a magnetic material.

With such a configuration, magnetic attraction is caused between the inner ring31and the rolling elements33, thereby avoiding any collision between the rolling elements33and the inner and outer rings31and32.

Fifth Embodiment

This embodiment provides a rolling bearing assembly3b4that has almost the same structure as the rolling bearing assembly3according to the first embodiment. Accordingly, only the differences in structure therebetween will be described below.

In the rolling bearing assembly3of the first embodiment, the metal core36of one of the seals35is made of a magnet, and all the inner ring31, outer ring32, and rolling elements33are made of a magnetic material.

In comparison, in the rolling bearing assembly3b4of the present embodiment, the outer ring32is made of a magnet, and all the rolling elements33are made of a magnetic material.

With such a configuration, magnetic attraction is caused between the outer ring32and the rolling elements33, thereby avoiding any collision between the rolling elements33and the inner and outer rings31and32.

Sixth Embodiment

This embodiment provides a rolling bearing assembly3b5that has almost the same structure as the rolling bearing assembly3according to the first embodiment. Accordingly, only the differences in structure therebetween will be described below.

In the first embodiment, the rolling bearing assembly3includes the inner and outer rings31and32, the rolling elements33, the cage34, and the seals35. Further, the metal core36of one of the seals35is made of a magnet, and all the inner ring31, outer ring32, and rolling elements33are made of a magnetic material.

In the present embodiment, the rolling bearing assembly3b5includes a magnet55in addition to the inner and outer rings31and32, the rolling elements33, the cage34, and the seals35.

The magnet55has, as shown inFIG. 5, a ring shape and is mounted to the plate-shaped bearing retainer5. More specifically, the bearing retainer5has opposite side faces that are perpendicular to the shaft2cof the rotor2. To one of the side faces, the magnet55is mounted; to the other, all other components of the rolling bearing assembly3b5are mounted.

Further, the inner and outer rings31and32and rolling elements33of the rolling bearing assembly3b5are made of a magnetic material. Moreover, the bearing retainer5is also made of a magnetic material.

With such a configuration, the magnet55magnetizes the inner and outer rings31and32and the rolling elements33, thereby causing magnetic attraction between the rolling elements33and the inner and outer rings31and32.

The magnetic attraction enables the rolling elements33to keep constant radial and axial distances with the inner and outer rings31and32, thereby avoiding any collision therebetween.

Seventh Embodiment

This embodiment provides a rolling bearing assembly3b6that has almost the same structure as the rolling bearing assembly3according to the first embodiment. Accordingly, only the differences in structure therebetween will be described below.

In the first embodiment, the rolling bearing assembly3includes the inner and outer rings31and32, the rolling elements33, the cage34, and the seals35. Further, the metal core36of one of the seals35is made of a magnet, and all the inner ring31, outer ring32, and rolling elements33are made of a magnetic material.

In the present embodiment, the rolling bearing assembly3b6includes a magnet45in addition to the inner and outer rings31and32, the rolling elements33, the cage34, and the seals35.

The magnet45has, as shown inFIG. 6, a ring shape and is mounted on the outer surface of the bearing box41in which all other components of the rolling bearing assembly3b6are mounted.

Further, the outer ring32and rolling elements33of the rolling bearing assembly3b6are made of a magnetic material. Moreover, the bearing box41is also made of a magnetic material.

With such a configuration, the magnet45magnetizes the outer ring32and the rolling elements33, thereby causing magnetic attraction between the outer ring32and the rolling elements33. The magnetic attraction makes it possible to avoid any collision between the rolling elements33and the inner and outer rings31and32.

While the above particular embodiments of the invention have been shown and described, it will be understood by those who practice the invention and those skilled in the art that various modifications, changes, and improvements may be made to the invention without departing from the spirit of the disclosed concept.

For example, in the previous embodiments, the rolling elements33each have a ball shape. However, the rolling elements33may have other shapes, such as a cylindrical shape.

Moreover, in the previous embodiments, the rolling bearing assemblies are employed in an automotive alternator. However, the rolling bearing assemblies may also be employed in any other rotary machines.

Such modifications, changes, and improvements within the skill of the art are intended to be covered by the appended claims.