JPH06307439A - Rolling bearing device for electrically driven motor - Google Patents

Abstract

PURPOSE:To facilitate working for applying proper pre-load on a plural line ball bearing for supporting rotatably a hub. CONSTITUTION:A hub 12 is supported rotatably around a fixed shaft 15 by a plural line ball bearing. Directions and angles of contact angle of a plurality of balls 19, 19 arranged in plural lines respectively are uniformalized each other. Pre-load is applied on respective balls 19, 19 by magnetic suction force acted between a rotator 13 fixed on the hub 12 and a stator 14 fixed on a housing 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION An electric motor incorporating a rolling bearing device according to the present invention is incorporated into, for example, a video tape recorder (VTR), a hard disk drive (HDD), a laser beam printer (LBP), etc. Used to drive rotation.

[0002]

2. Description of the Related Art For example, an electric motor is used to rotate a capstan of a VTR, a disk of an HDD, and a polygon mirror of an LBP. The rotating shaft of the electric motor used for such a precision rotating portion is supported by a plurality of sets of ball bearings in order to prevent whirling motion (motion in a direction perpendicular to the shaft) and axial runout, and Appropriate preload is applied to the plurality of sets of ball bearings.

FIG. 12 shows an electric motor which has been conventionally considered to be used for rotationally driving a capstan or the like of a VTR, which is described in Japanese Utility Model Laid-Open No. 64-16163. The cylindrical housing 1 is supported and fixed to a VTR board or the like by a support plate 2 fixed to the outer peripheral surface thereof. Then, the rotary shaft 7 is provided inside the housing 1.
Are rotatably supported by a pair of ball bearings 3, 3. Each ball bearing 3, 3 has an inner ring 4, 4 having an inner ring raceway on its outer peripheral surface, and an outer ring 5, having an outer ring raceway on its inner peripheral surface,
5 and a plurality of balls 6, 6 rotatably provided between the inner ring raceway and the outer ring raceway.

The outer rings 5, 5 are the housing 1
It is fitted and fixed inside. On the other hand, one of the inner rings 4, 4 (for example, the upper side in FIG. 12) is loosely fitted on the outer peripheral surface of the rotating shaft 7. Then, the compression spring 8 is sandwiched between the end surfaces of the inner rings 4 and 4 to give elastic force in a direction in which the inner rings 4 and 4 are separated from each other, and the ball bearings 3 and 3 are
An appropriate preload is applied according to the elasticity of the compression spring 8.

Further, one end of the housing 1 (see FIG. 12)
The stator 9 is fixed to the outer peripheral surface of the rotor 10, and the inner peripheral surface of the rotor 10 fixed to one end of the rotating shaft 7 is opposed to the outer peripheral surface of the stator 9. Therefore, by energizing the stator 9, the rotary shaft 7 can be driven to rotate.

[0006]

However, in the case of an electric motor incorporating the above-described rolling bearing device, the following problems occur. First, as a first problem, due to the provision of the compression spring 8, the rolling bearing device portion is increased in size and the weight is increased accordingly. Electric motors for VTRs and HDDs are becoming extremely small and lightweight, and it is not preferable to increase the size by such a compression spring 8.

Further, since one inner ring 4 is loosely fitted on the outer peripheral surface of the rotary shaft 7 so that the preload can be applied by the compression spring 8, the inner peripheral surface of the inner ring 4 and the rotary shaft 7 are loosely fitted to each other. It is inevitable that rattling will occur, albeit slightly, between the outer peripheral surface. Such rattling is not preferable because it causes the rotating shaft 7 to move around, or causes vibrations due to the rotation.

On the other hand, for example, with the inner ring 4 loosely fitted on the rotary shaft 7 in a state in which a proper preload is applied to the balls 6, 6,
There is also a method of fixing to the rotating shaft 7 with an adhesive, but it takes time and effort to degrease the coated surface of the adhesive, and the inner ring 4 is kept in an appropriate position until the adhesive solidifies. Therefore, the manufacturing work of the rolling bearing device becomes troublesome.

The rolling bearing device for an electric motor according to the present invention comprises:
It was invented in view of the circumstances as described above.

[0010]

A rolling bearing device for an electric motor according to the present invention includes a fixed member, a rotating member, a rotor supported and fixed on the rotating member, and a fixed and supported axial direction on the fixed member. Corresponding to an inner ring having a stator in which an end face and an axial end face of the rotor are opposed to each other, fixed to one of the fixed member and the rotating member concentrically with the rotor and the stator, and having double row inner ring raceways on its outer peripheral surface On the other side of the member, the fixed member and the rotating member, an outer ring equivalent member fixed concentrically with the inner ring equivalent member, and forming a double row outer ring raceway opposed to each inner ring raceway on its inner peripheral surface, A plurality of rolling elements are provided between the inner ring raceway and each outer ring raceway so as to be rollable. Then, by the force based on the magnetic force acting between the rotor and the stator, an appropriate preload is applied to each rolling element existing between the double row inner ring raceway and the outer ring raceway.

[0011]

When the electric motor incorporating the rolling bearing device of the present invention constructed as described above is used, the rotor and the rotary member supporting and fixing the rotor are rotated by energizing the stator. The rotary member is rotatably supported by the double-row rolling bearing with respect to the fixed member, and a plurality of rolling elements constituting the rolling bearing are always given a proper preload by a force based on a magnetic force. ing. Therefore, whirling motion and axial motion are less likely to occur with the rotation of the rotating member.

Moreover, in order to apply the appropriate preload,
Since the force based on the magnetic force acting between the rotor and the stator originally incorporated in the electric motor is used, the electric motor incorporating the rolling bearing device of the present invention becomes large in size or heavy in weight. There is nothing to do.

[0013]

1 and 2 show a first embodiment of the present invention. The housing 11, which is a fixing member, is formed into a disc shape by die casting of aluminum alloy or the like. The hub 12, which is a rotating member that rotates with respect to the housing 11, is also formed into an annular shape by die casting of an aluminum alloy. And
On one surface of the hub 12 facing the housing 11, one side surface of the hub 12, which is made of a permanent magnet, supports and fixes a ring-shaped rotor 13 in which magnetic poles alternately change in the circumferential direction.

A stator 14 constituted by including a yoke made of a magnetic material is supported and fixed on one surface of the housing 11 facing the rotor 13. The stator 14 and the rotor 13 are opposed to each other at their axial end faces (vertical direction in FIGS. 1 and 2). Therefore, a force is applied between the stator 14 and the rotor 13 in the direction of pulling the hub 12 downward in FIG. 1 based on the magnetic attraction force of the permanent magnets forming the rotor 13. .

At the center of the housing 11, the base end of the fixed shaft 15 (lower end in FIG. 1) which is a member corresponding to the inner ring.
Are fixed by fitting, and the fixed shaft 15 is supported concentrically with the rotor 13 and the stator 14. This fixed shaft 15
On the outer peripheral surface of, double-row inner ring raceways 16, 16 are provided.

On the other hand, a base end portion (upper end portion in FIG. 1) of a cylindrical outer ring 17 is fitted and fixed to a central portion of the hub 12, and the outer ring 17 is provided around the fixed shaft 15 and the fixed shaft. I support it concentrically with 15. Double row outer ring raceways 18, 18 are formed on the inner peripheral surface of the outer ring 17, and the outer ring raceways 18, 18 are formed.
And the inner ring raceways 16, 16 face each other. The pitches of the double-row outer ring raceways 18, 18 and the pitches of the double-row inner ring raceways 16, 16 are substantially equal to each other.

A plurality of balls 19, 19 are provided between the inner ring raceways 16, 16 and the outer ring raceways 18, 18 so as to be rotatable. The plurality of balls 19 and 19 are attached to the rotor 13 and the stator 14 described above.
Appropriate preload is applied by the pulling force based on the magnetic attraction force between and. That is, the double-row inner ring raceways 16 and 16 and the outer ring raceway 1 formed at substantially equal pitches from each other.
Balls 19 and 19 of which outer diameter is selected are provided between 8 and 18,
The outer ring 17 is axially moved through the hub 12 (see FIGS.
Elastically displacing the above balls 19, 1
9 to the inner ring raceways 16 and 16 and the outer ring raceways 18 and 18,
At the same time, the balls 19 and 19 are brought into contact with each other with a contact angle in a direction shown by a chain line in FIG. Incidentally, 21 and 21 are seal rings.

When using the electric motor incorporating the rolling bearing device of the present invention constructed as described above, the stator 1 is used.
By energizing the rotor 4, the rotor 13 and the rotor 1
The hub 12 that supports and fixes 3 is rotated. This hub 12
Is rotatably supported on the housing 11 by a double-row rolling bearing consisting of a fixed shaft 15, an outer ring 17, and a plurality of balls 19, 19. The plurality of balls 19, 19 have a magnetic attraction. A proper preload is always applied by the elastic tensile force based on the force. Therefore, whirling motion and axial motion are less likely to occur with the rotation of the hub 12.

Moreover, in order to apply the above-mentioned proper preload,
Since the pulling force based on the magnetic attraction force, which originally works between the rotor 13 and the stator 14 incorporated in the electric motor, is used, the electric motor incorporating the rolling bearing device becomes large in size or weight. It doesn't get bulky.

Next, FIG. 3 shows a second embodiment of the present invention. In the case of this embodiment, one inner ring raceway 16 is formed on the outer peripheral surface of the base half portion (lower half portion of FIG. 3) of the fixed shaft 15a, and the front half portion (upper half portion of FIG. 3) of this fixed shaft 15a. On the outer peripheral surface of the inner ring 20 fitted and fixed on the outer peripheral surface, the other inner ring raceway 16
Is formed. In the case of this embodiment, the fixed shaft 15a and the inner ring 20 constitute an inner ring equivalent member. Thus, the inner ring raceway 1 on the outer peripheral surface of the member corresponding to the inner ring composed of the two members 15a and 20
The pitches of 6 and 16 can be adjusted by applying a large force to the inner ring 20 in the axial direction (vertical direction in FIG. 3).

Therefore, in the case of this embodiment, the inner ring 2 is
By adjusting the fixed position of 0, the preload applied to the balls 19, 19 is made uniform, or the preload applied to the balls 19, 19 in one row is adjusted according to the load applied to the hub 12. It becomes possible to make an adjustment such that the preload applied to the balls 19 of the other row is made larger. Other configurations and operations are similar to those of the above-described first embodiment.

Next, FIG. 4 shows a third embodiment of the present invention. In the case of this embodiment, a pair of outer rings 2 independent from each other
By abutting the end faces of 2 and 22 against each other, a member corresponding to the outer ring is formed by forming the outer ring raceways 18 and 18 in multiple rows on the inner peripheral surface. On the other hand, the inner rings 20, 20 each having a width dimension smaller than that of the outer rings 22, 22 are fixed shafts 1.
The outer peripheral surface of 5b is fitted and fixed. No inner ring raceway is formed on the outer peripheral surface of the fixed shaft 15b. That is, in the case of the present embodiment, the fixed shaft 15b and the inner rings 20, 20 constitute a member corresponding to the inner ring.

In the case of this embodiment, the pitch of the inner ring raceways 16, 16 can be adjusted by applying a large axial force to the inner rings 20, 20. Therefore, in the case of the present embodiment, by adjusting the fixing positions of the inner rings 20, 20, the preload applied to the balls 19, 19 is made uniform,
Alternatively, the preload applied to the balls 19, 19 in one row can be adjusted to be larger than the preload applied to the balls 19, 19 in the other row. In the case of the present embodiment, one side (see FIG.
The radial displacement of the outer ring 22 (below) of the outer ring 22 is prevented by the frictional force at the abutting portion between the end surface of the one outer ring 22 and the end surface of the other outer ring 22. Other configurations and operations are similar to those of the above-described first embodiment.

Next, FIG. 5 shows a fourth embodiment of the present invention. In the case of the present embodiment, unlike the above-described first to third embodiments, the base end portion of the rotary shaft 23 is fitted and fixed to the center portion of the hub 12. A rolling bearing device is provided between the outer peripheral surface of the rotary shaft 23 and the inner peripheral surface of the cylindrical portion 24 formed at the center of the housing 11, and the rotary shaft 23 and the hub 12 are attached to the housing 11. , Rotatably supported.

In order to form the rolling bearing device, a pair of inner rings 20, 20 are externally fitted and fixed on the outer peripheral surface of the rotary shaft 23, and a pair of outer rings 22, 22 are formed on the outer peripheral surface of the cylindrical portion 24.
Is fixed internally. The end faces of the outer rings 22, 22 are abutted against the flange portion 25 formed on the inner peripheral surface of the intermediate portion of the cylindrical portion 24. Therefore, the positions of the outer rings 22, 22 are immovable. However, by adjusting the fixed position of the inner rings 20, 20, the preload applied to the balls 19, 19 is made uniform, or the preload applied to the balls 19, 19 of one row is adjusted to the other row. It is possible to make an adjustment such that the preload applied to the balls 19 is increased. Other configurations and operations are similar to those of the first embodiment described above.

Next, FIG. 6 shows a fifth embodiment of the present invention. In the case of the present embodiment, the end faces of the inner rings 20, 20 fitted and fixed to the outer peripheral surface of the rotary shaft 23 are butted against each other. Therefore, the positions of these inner rings 20, 20 are immovable. However,
By adjusting the fixed position of the outer rings 22, 22 inside the cylindrical portion 24, the preload applied to the balls 19, 19 is made uniform, or the preload applied to the balls 19, 19 in one row is adjusted. ,
It is possible to make an adjustment such that the preload applied to the balls 19 of the other row is made larger. Other configurations and operations are
This is similar to the fourth embodiment described above.

Next, FIG. 7 shows a sixth embodiment of the present invention.
In the case of the present embodiment, both the fixed positions of the inner rings 20, 20 and the fixed positions of the outer rings 22, 22 are adjustable. Other configurations and actions are similar to those of the above-mentioned fourth to fifth embodiments.

Next, FIG. 8 shows a seventh embodiment of the present invention. In the case of the present embodiment, by extending the rotary shaft 23 in the above-described sixth embodiment, a capstan 26 which is incorporated in a VTR or the like to feed a tape at a predetermined speed is constituted.

Next, a method for adjusting the contact angle of the rolling bearing device to a desired value in the state of being incorporated in the rolling bearing device will be described. FIG. 9 shows the first example. When adjusting the contact angle of the rolling bearing device as shown in FIG. 3, the end of the fixed shaft 15a (the left end in FIG. 9) is held by the holder 27 and one end surface of the outer ring 17 (the left end in FIG. 9) is held. The vibration exciter 28 is abutted against the surface, and vibration is applied to the rolling bearing device through the outer ring 17. Also, the outer ring 1
A vibration sensor 29 is abutted on the other end surface (right end surface in FIG. 9) of 7 to freely measure the resonance frequency or the vibration characteristic of the rolling bearing device.

The resonance frequency (or vibration characteristic) of the rolling bearing device detected by the vibration sensor 29 is detected by the amplifier 30.
And the fast Fourier transform (FFT)
m) and the FFT converter 31 and the controller 32
Are typing in. The controller 32 has the fixed shaft 15a.
The pushing device 33 for pushing the inner ring 20 into the first half portion (right half portion in FIG. 9) is controlled. In the case of the first example shown in FIG. 9, a hydraulic cylinder is used as the pushing device 33. The controller 32 controls the amount or pressure of the pressure oil sent to the pushing device 33 to adjust the force for pushing the inner ring 20 by the pushing arm 34 of the pushing device 33.

In manufacturing the rolling bearing device, when the inner ring 20 is pushed into the first half portion to adjust the contact angles of the balls 19, 19 to proper values, the outer ring 17 is moved by the vibrator 28. In addition to applying vibration to the outer ring 17, the pressing arm 35 elastically presses the outer ring 17 in the axial direction (left and right direction in FIG. 9). The pressing arm 35 includes an air cylinder 36 and a spring 37.
And gives elasticity. And this pressing arm 35
The tip portion of the axially presses the outer ring 17 in the same direction as the elastic force based on the magnetic attraction force acting between the rotor 13 and the stator 14 in the same direction.

When the contact angle adjustment work is performed,
While the outer ring 17 is thus vibrated and the outer ring 17 is axially pressed, the vibration sensor 29 measures the resonance frequency (or vibration characteristic) of the rolling bearing device.
The pressure oil is sent to the pushing device 33, and the pushing arm 3
By pressing the inner ring 20 with 4, the inner ring 20 is press-fitted into the first half of the fixed shaft 15a.

The above resonance frequency (or vibration characteristic)
In a state in which the frequency substantially matches the preset frequency (or vibration characteristic), the feeding of the pressure oil into the pushing device 33 is stopped, and the press-fitting operation is completed. In this state, the rolling bearing device with proper preload is completed.

It is conventionally known that there is a certain relationship between the resonance frequency or vibration characteristic of the rolling bearing device and the contact angle of the balls 19, 19. Therefore, the resonance frequency or the vibration characteristic of the rolling bearing device having the same structure as the rolling bearing device to be manufactured and having an appropriate contact angle is measured in advance, and the measured value is stored in the controller 32. If set, the pressure oil supply to the pushing device 33 is stopped when the contact angle of the balls 19, 19 forming the rolling bearing device has reached an appropriate value. Since the work of giving the proper contact angle to the balls 19, 19 of the rolling bearing device for setting the resonance frequency or the vibration characteristic only needs to be performed once, even if the work for giving the proper contact angle is troublesome. It does not hinder the efficiency of manufacturing work.

As the pushing device 33 for pushing the inner ring 20, an air cylinder or a feed screw device can be used in addition to the hydraulic cylinder as shown.

Next, FIG. 10 shows a method of adjusting the displacement amount of the inner ring 20 with respect to the front half portion (right half portion of FIG. 10) of the fixed shaft 15a so that the contact angles of the balls 19 and 19 are made appropriate values. The 2nd example is shown. The holder 38 holding the base end portion (the left end portion in FIG. 10) of the fixed shaft 15a is rotatably supported by a gas bearing 39. The holder 38 and the fixed shaft 15a are rotationally driven via a belt 40 by an electric motor (not shown). The outer ring 17 provided around the fixed shaft 15a is provided with an appropriate detent so as not to rotate with the rotation of the fixed shaft 15a. However, the detent has a structure that does not suppress the vibration of the rolling bearing device.
Then, the probe 42 of the vibration sensor 41 is abutted against the outer peripheral surface of the outer ring 17.

When manufacturing the rolling bearing device, the fixed shaft 15 is used.
When the inner ring 20 is pushed into the first half of a and the contact angles of the balls 19, 19 are set to appropriate values, the vibration sensor 41 analyzes the vibration characteristics of the rolling bearing device, that is, the sound of the rolling bearing device. Alternatively, pressure oil is fed into the pushing device 33 while performing frequency analysis of vibration. At this time, the outer ring 17 is elastically pressed by the pressing arms 35, 35 as in the case of the first example shown in FIG. Then, the inner ring 20 is pressed by the pushing arm 34, so that the inner ring 20 is press-fitted into the first half portion of the fixed shaft 15a. Then, when the vibration characteristics substantially match the preset characteristics, the feeding of the pressure oil into the pushing device 33 is stopped, and the press-fitting operation is completed.

It has been conventionally known that there is a fixed relationship between the vibration characteristic of the rolling bearing device and the contact angle. Therefore, the vibration characteristics of the rolling bearing device having the same structure as that of the rolling bearing device to be manufactured and the contact angle of the balls 19, 19 being an appropriate value are analyzed in advance, and this analysis data is set in the controller 32. Balls 1 that make up the rolling bearing device
When the contact angles of 9 and 19 have reached appropriate values, the supply of pressure oil to the pushing device 33 is stopped.

Next, FIG. 11 shows a method of adjusting the amount of displacement of the inner rings 20, 20 with respect to the rotating shaft 23 so that the contact angles of the balls 19, 19 are set to proper values. The tip end portion of the pressing arm 35 presses the outer ring 17 with an elastic force commensurate with the magnetic attraction force between the rotor 13 and the stator 14 based on the weight of the weight 43. Balls 19 constituting the rolling bearing device,
When a proper contact angle is given to the outer ring 17, the pair of pressing devices 44a and 44b are alternately operated to thereby generate the outer ring 17
Then, a load of a predetermined magnitude is applied in the axial direction (left and right direction in FIG. 11) to displace the outer ring 17 in the axial direction, and the displacement sensor 45 measures the displacement amount of the outer ring 17. The measurement value of the displacement sensor 45 is input to the controller 46,
The controller 46 determines the play amount in the axial direction of the rolling bearing device based on the measured value. Obtaining the play amount from the displacement amount when a predetermined load is applied to the outer ring 17 can be easily performed by a conventionally known technique.

Further, the controller 46 is provided with the pushing device 3
3 is actuated to press one inner ring 20 in the axial direction by the difference between the actual play amount thus obtained and the play amount required to obtain a proper contact angle. After pressing the inner ring 20 in the axial direction, the contact angles of the balls 19, 19 become appropriate values. In the case of this example, the length of pressing the inner ring 20 is strictly regulated.

In the case of the rolling bearing device for an electric motor of the present invention, the inner ring raceways 16 and 16 and the outer ring raceways 18 and 1, respectively.
Generally, the curvatures of the balls 8 are equal to each other, and the diameters of the balls 19 and 19 are equal to each other.
And the outer ring raceways 18 and 18 have different curvatures,
Alternatively, the balls 19, 19 in each row may have different diameters. By varying the curvature and the diameter of the balls, it is possible to apply substantially the same load to the balls 19 in each row, or to apply a large load to one row, and It is also possible to increase the diameter of the balls 19 forming the row to increase the load capacity of this one row.

Although not shown, as a method of adjusting the contact angle of the rolling bearing device to a desired value in a state of being incorporated in the rolling bearing device, a rotating member other than the three examples described above is used. The loss torque during rotation of the outer ring 17 (first to second examples), 22 (third to fourth examples) and the inner ring 20 (fifth to seventh examples) was measured, and this loss torque was set in advance. It is also possible to adopt a method in which the press-fitting work is completed in a state that almost coincides with.

[0043]

Since the rolling bearing device for an electric motor according to the present invention is constructed and operates as described above, it does not require extra parts or machining, and can be manufactured in a small size, light weight and at a low cost, and it is precise and stable. It is possible to obtain an electric motor that makes a rotating motion.

[Brief description of drawings]

FIG. 1 is a sectional view of an electric motor showing a first embodiment of the present invention.

FIG. 2 is an enlarged view of part A in FIG.

FIG. 3 is a view similar to FIG. 2, showing a second embodiment of the present invention.

FIG. 4 is a view similar to FIG. 2, showing a third embodiment of the present invention.

FIG. 5 is a view similar to FIG. 2, showing a fourth embodiment of the present invention.

FIG. 6 is a view similar to FIG. 2, showing a fifth embodiment of the present invention.

FIG. 7 is a view similar to FIG. 2, showing a sixth embodiment of the present invention.

FIG. 8 is a sectional view of an electric motor showing a seventh embodiment of the present invention.

FIG. 9 is a cross-sectional view showing a first example of a method for providing an appropriate contact angle.

FIG. 10 is a sectional view showing the second example.

FIG. 11 is a sectional view showing the third example.

FIG. 12 is a cross-sectional view of an electric motor incorporating a conventional rolling bearing device.

[Explanation of symbols]

 1 Housing 2 Support Plate 3 Ball Bearing 4 Inner Ring 5 Outer Ring 6 Ball 7 Rotating Shaft 8 Compression Spring 9 Stator 10 Rotor 11 Housing 12 Hub 13 Rotor 14 Stator 15, 15a, 15b Fixed Shaft 16 Inner Ring Orbit 17 Outer Ring 18 Outer Ring Orbit 19 Ball 20 Inner ring 21 Seal ring 22 Outer ring 23 Rotating shaft 24 Cylindrical part 25 Collar part 26 Capstan 27 Holding tool 28 Vibrator 29 Vibration sensor 30 Amplifier 31 FFT converter 32 Controller 33 Pushing device 34 Pushing arm 35 Pushing arm 36 Air cylinder 37 Spring 38 Holding tool 39 Gas bearing 40 Belt 41 Vibration sensor 42 Measuring element 43 Weights 44a, 44b Pressing device 45 Displacement sensor 46 Controller

Claims (1)

[Claims] 1. A fixed member, a rotating member, a rotor supported and fixed on the rotating member, and a stator supported and fixed on the fixed member, the axial end surface of which faces the axial end surface of the rotor. An inner ring equivalent member fixed to one of the fixed member and the rotating member concentrically with the rotor and the stator and having a double row of inner ring raceways on the outer peripheral surface thereof, and to the other of the fixed member and the rotating member, An outer ring equivalent member that is fixed concentrically with the inner ring equivalent member and has a double row outer ring raceway formed on its inner peripheral surface to face each inner ring raceway, and a plurality of each between the inner ring raceway and each outer ring raceway, A rolling element provided so as to be freely rollable, and by a force based on a magnetic force acting between the rotor and the stator, it is suitable for each rolling element existing between the double row inner ring raceway and the outer ring raceway. Electric motor with preload Rolling bearing device for motors.