JP2000262004A - Spindle motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a spindle motor, which can eliminate the change of a preliminary pressure applied between bearings caused by the difference in thermal linear expansion coefficients, and furthermore eliminate the lowering of the rigidity of bearing parts, while the flexibility of selection of the material for a rotary part is not impaired. SOLUTION: A bracket 6 on which a stator 7 is attached and a shaft 1 is erected, a rotor hub 2 which has magnets 8 facing the stator 7, a hole part 2a in which the shaft 1 is placed and a bearing holder 5a which has a thermal expansion coefficient substantially equal to that of the shaft 1 and is attached to an inner circumference 2b of the hole part 2a, so as to extend in the axial direction of the shaft 1 and bearings 3 and 4, whose inner rings are fixed to the outer circumference of the shaft 1 and whose outer rings are fixed to the inner circumference 2b of the hole part 2a, are provided. An outer ring 3b of a bearing 3 is fixed to the inner circumference 2b of the hole part 2a with the bearing holder 5a therebetween.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle motor in which a stationary portion and a rotating portion are rotatably connected via a plurality of bearings, and in particular, the magnitude of preload applied between bearings fluctuates due to a temperature change. The present invention relates to a spindle motor that prevents the occurrence of such a problem.

[0002]

2. Description of the Related Art Conventionally, in a magnetic disk device such as a hard disk device, a spindle motor is used as a disk rotating means. FIG. 3 is a schematic sectional view showing a conventional spindle motor. As shown in FIG. 3, the conventional spindle motor has a stationary part, a rotating part, and two bearings that rotatably connect the stationary part and the rotating part. In the stationary portion, a shaft 1 made of an iron-based metal such as stainless steel is provided upright at the center of the bracket 6, and a stator 7 is provided on the bracket 6 around the shaft 1.

The shaft 1 has two bearings 3 and 4 made of an iron-based metal such as stainless steel.
Are fitted apart from each other in the axial direction of the shaft 1. The bearings 3, 4 include inner rings 3a, 4a and outer rings 3b, 4b, and ball bearings 3c, 4c therebetween.

Further, in the rotating part, a cylindrical rotor hub 2 made of aluminum or an aluminum alloy and having a hole 2a in the center is supported by a bearing 3, and a shaft 1 is provided.
Are arranged so as to be rotatable around the center. This rotor hub 2 has its inner surface at both ends in the longitudinal direction cut out and this portion is thinner, and forms a stepped receiving surface 2c with respect to the inner peripheral surface 2b at the center. A magnet 8 is fixed to the lower end of the rotor hub 2 so as to face the stator 7.

[0005] The inner ring 3a of the bearing 3 is bonded and fixed to the outer peripheral surface of the shaft 1. Similarly, the inner ring 4a of the bearing 4 is fixed to the shaft 1
The outer ring 3b of the bearing 3 and the outer ring 4b of the bearing 4 are bonded and fixed to the upper and lower stepped receiving surfaces 2c of the rotor hub 2, respectively. The inner ring 3a of the bearing 3 and the inner ring 4a of the bearing 4 are fixed to the shaft 1 in a state where a preload is applied in a direction away from each other in the axial direction. That is, for example, the shaft 1 is heated, and the rotor hub 2 is heated.
At room temperature, the shaft 1 and the rotor hub 2 are positioned, and the inner rings 3a, 4a of the bearings 3, 4 are bonded and fixed to the shaft 1, and the outer rings 3b, 4b are fixed to the rotor hub 2 by bonding. Thereby, when the temperature of the shaft 1 and the rotor hub 2 becomes the same, the outer rings 3b,
A preload is generated in the direction away from each other via 4b and ball bearings 3c, 4c.

In the conventional spindle motor constructed as described above, when an electric current is applied to the stator 7, the spindle hub 2 provided with the magnet 8 rotates about the shaft 1 via the bearings 3 and 4. At this time, since the preload is applied between the bearings, the vibration of the bearings is prevented, and the rigidity of the bearing portion including the shaft 1, the bearing 3, the bearing 4, and the rotor hub 2 is maintained.

[0007]

However, in the above-mentioned conventional spindle motor, the material of the rotor hub 2 (aluminum-based metal) is higher than the material of the shaft 1 (iron-based metal) in the coefficient of linear thermal expansion (coefficient of linear thermal expansion). When the temperature decreases, the shrinkage of the rotor hub 2 is larger than the shrinkage of the shaft 1, so that the preload between the inner rings 3a and 4a of the bearing decreases, and the bearing vibrates when the rotating part rotates. There is a point.

Similarly, when the temperature decreases, the rigidity of the bearing portion composed of the shaft 1, the bearing 3, the bearing 4, and the rotor hub 2 decreases, so that the natural frequency of the bearing portion decreases, and the bearing is mounted on the spindle motor. There is a drawback in that it approaches the magnitude of the natural frequency of another part such as a magnetic disk and induces resonance with the bearing part, causing vibration and noise.

On the other hand, when the temperature rises, the rotor hub 2 expands more than the shaft 1, so that the outer races 3b, 4b fixed to the rotor hub 2 move largely outward in the axial direction, and There is a problem that the preload increases excessively.

Therefore, motors which solve the above-mentioned problems caused by the difference in the coefficient of thermal expansion are disclosed in Japanese Utility Model Laid-Open No. 4-64962 and Japanese Patent Laid-Open No. 2-240888.

In the motor disclosed in Japanese Utility Model Laid-Open No. 4-64962, a rotating shaft (shaft) and a spindle hub (corresponding to a rotor hub) are fixed via two bearings. The inner ring part of which is fixed to the outer peripheral surface of the rotating shaft, the outer ring part of the bearing is fixed to the spindle hub, and the materials of the spindle hub and the rotating shaft have the same coefficient of thermal expansion as the bearing. It is.

On the other hand, in the spindle motor disclosed in JP-A-2-240888, a bush made of a material substantially equal to the coefficient of thermal expansion of an outer ring of a bearing is pressed into an inner peripheral surface of a spindle hub (corresponding to a rotor hub). The outer ring of the bearing is fixed to the bush, and an urging member for pressing the bush in the shaft direction is provided between the bush and the spindle hub.

However, in the motor disclosed in Japanese Utility Model Laid-Open No. 4-64962, since the bearings, shafts and spindle hubs have the same coefficient of thermal expansion, it is possible to prevent a change in preload between bearings. However, for example, in order to reduce the weight of the rotating portion including the spindle hub, an aluminum-based metal cannot be adopted as the material of the spindle hub, and there is a problem that the degree of freedom in selecting the material is low.

Further, in the spindle motor disclosed in Japanese Patent Application Laid-Open No. 2-240888, it is possible to absorb the difference in the thermal expansion of the bearing in the radial direction, but to absorb the difference in the thermal expansion of the bearing in the axial direction. Can not do.

The present invention has been made in view of such a problem, and the magnitude of the preload applied beforehand between bearings due to the difference in the linear thermal expansion coefficient without impairing the degree of freedom in selecting the material of the rotating part. It is an object of the present invention to provide a spindle motor capable of preventing a change in the rigidity of the bearing portion and preventing a decrease in rigidity of the bearing portion.

[0016]

According to the present invention, there is provided a spindle motor comprising: a shaft; a pair of bearings including an inner ring, an outer ring, and a ball bearing fitted to the shaft;
A rotor hub rotatably provided with respect to the shaft via the bearing; and a rotor hub provided between the inner ring and the rotor hub of at least one of the bearings, being fixed to an inner surface of the rotor hub, and A bearing holder made of a material having substantially the same linear thermal expansion coefficient.

In this spindle motor, the bearing holder can be provided between both outer rings of the pair of bearings and the rotor hub. In the rotor hub, a portion between the pair of bearings protrudes toward the shaft, and an outer ring of the bearing is disposed outside the protruding portion of the rotor hub with an interval between the outer rings regulated by the protruding portion. It can be configured to be.

Further, the bearing holder may be configured to be bent so as to come into contact with the side surface and the inner surface of the protruding portion, and the pair of inner rings may be connected via the ball bearing and the outer ring. It can be fixed to the shaft in a state where preload is applied in a direction away from each other.

Still further, the bearing holder has a cylindrical shape, and has a cylindrical portion which comes into contact with an inner surface of a protruding portion of the rotor hub, and an outer flange which comes into contact with both end surfaces of the protruding portion on the bearing side. Can be configured.

In the present invention, at least one outer race of the bearing has a coefficient of thermal expansion substantially equal to that of the shaft and is fixed to a bearing holder fixed to the inner surface of the rotor hub. When the shaft and rotor hub have different coefficients of linear thermal expansion, such as when the rotor hub is formed from an aluminum alloy, the temperature decreases,
Even if the rotor hub contracts relatively largely with respect to the shaft, the shaft and the bearing holder have substantially the same linear thermal expansion coefficient, so that the mutual distance between the outer races fixed to the bearing holder is prevented from being reduced. As described above, in the present invention, the deformation of the rotor hub is absorbed, the interval between the bearings is kept constant, and a decrease in the preload between the bearings can be prevented. On the other hand, if the temperature rises,
Although the rotor hub tends to expand relatively with respect to the shaft, since at least one bearing is fixed to the bearing holder, a deforming force acts on the rotor hub in a direction to separate the outer rings of the bearings from each other. Again, it is mitigated by the bearing holder, which can prevent an excessive increase in preload.

Further, the bearing holder is formed in a cylindrical shape, and has a cylindrical portion which comes into contact with the inner surface of the protruding portion of the rotor hub, and an outer flange which comes into contact with both end surfaces of the protruding portion on the bearing side. Accordingly, the adjacent outer ring is supported only by the bearing holder having substantially the same linear thermal expansion coefficient as the shaft, so that it is possible to more reliably prevent a change in the interval between the outer rings when the temperature changes, and The effect of preventing the change in the magnitude of the preload during the period can be further improved.

As described above, in the present invention, it is possible to prevent a change in preload caused by a difference in linear thermal expansion coefficient due to a difference in material between the rotor hub and the shaft, so that there is an advantage that the degree of freedom in selecting a material is high. Therefore, both the rigidity of the bearing portion and the preload can be achieved.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a spindle motor according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a schematic sectional view showing a spindle motor according to a first embodiment of the present invention.

As shown in FIG. 1, in the spindle motor according to the first embodiment of the present invention, a stationary part, a rotating part, and two bearings for rotatably connecting the stationary part and the rotating part are provided. have. In the stationary part, the bracket 6
And a bracket 6 made of an iron-based metal such as stainless steel.
And a stator 7 mounted on a bracket 6. Similarly to the shaft 1, two bearings 3 and 4 made of an iron-based metal such as stainless steel are provided on the outer peripheral surface of the shaft 1 so as to be spaced apart in the axial direction. Further, in the rotating portion, a magnet 8 facing the stator 7 and a rotor hub 2 provided with the magnet 8 at a lower portion and having a hole 2a at the center are provided. The material of the rotor hub 2 is aluminum or an aluminum alloy, and a part of the hole 2a has a selectively reduced inner diameter, and two stepped receiving surfaces 2c are formed. A bearing holder 5a made of an iron-based metal like the shaft 1 is selectively provided so as to extend from the stepped receiving surface 2c above the hole 2a to the inner peripheral surface 2b.

The inner ring 3a of the bearing 3 is bonded and fixed to the outer peripheral surface of the shaft 1. Similarly, the inner ring 4a of the bearing 4 is
The outer ring 3b of the bearing 3 has an end surface and a side surface on the outer side in the axial direction abutting against a receiving surface of the bearing holder 5, and the outer ring 4b of the bearing 4 has an end surface on the outer side in the axial direction. Is brought into contact with the stepped receiving surface 2c of the rotor hub 2, and in the same manner as before, the inner ring 3a of the bearing 3 and the inner ring 4a of the bearing 4 are applied with a preload in a direction in which they are separated from each other in the axial direction. Is held. Thus, the stationary part and the rotating part are rotatably connected via the bearings 3 and 4.

In the thus constructed spindle motor of this embodiment, when an electric current is applied to the stator 7, the spindle hub 2 provided with the magnet 8 is provided with the bearings 3 and 4.
Through the shaft 1 via the shaft. At this time, since the preload is applied between the bearings, the vibration of the bearings is prevented, and the rigidity of the bearing portion including the shaft 1, the bearing 3, the bearing 4, the bearing holder 5, and the rotor hub 2 is maintained.

At this time, when the temperature decreases, the rotor hub 2 having a large coefficient of linear thermal expansion contracts relatively largely with respect to the shaft 1, and deforms in a direction in which the outer rings of the bearings 3 and 4 approach each other. However, since the bearing 3 is held by the bearing holder 5a which does not shrink relatively to the shaft 1, the deformation of the bearings 3 and 4 in the direction in which the outer rings approach each other is absorbed. The distance from the bearing 4 is maintained. Thus, a decrease in the preload between the bearings can be prevented.

On the other hand, when the temperature rises, the rotor hub 2
The bearing 3 is held by the bearing holder 5a and is not in contact with the rotor hub 2, and the bearing holder 5a separates the outer rings of the bearings 3 and 4 from each other. In order to reduce the deformation of the preload, an excessive increase in the preload can be prevented.

As described above, in the present embodiment, the material of the rotor hub does not need to be the same as the material of the shaft. In addition to preventing a change in the magnitude of the preload, a reduction in the rigidity of the bearing portion can be prevented. Therefore, it is possible to maintain the state where the preload is applied to the bearings 3 and 4 with respect to a temperature change in a wider range than in the related art.

FIG. 2 is a schematic sectional view showing a spindle motor according to a second embodiment of the present invention. In the present embodiment, the configuration of the connecting portion between the stationary unit and the rotating unit is changed.
As shown in FIG. 2, in the spindle motor according to the second embodiment of the present invention, the stationary portion and the bearing have the same configuration as the spindle motor according to the first embodiment of the present invention.

On the other hand, in the rotating part, a magnet 8 facing the stator 7 and a rotor hub 2 provided with the magnet 8 in the lower part and having a hole 2a in the center are provided. The material of the rotor hub 2 is aluminum or an aluminum alloy, and a part of the hole 2a has a selectively reduced inner diameter, and two stepped receiving surfaces 2c are formed. The bearing holder 5b includes the shaft 1
It is made of an iron-based metal, has a cylindrical shape, and has a flange shape with both ends extending outward. The bearing holder 5b is provided with the rotor hub 2 at the center of the outer peripheral surface.
The flanges at both ends are supported and fixed on the stepped receiving surface 2c above the hole 2a and the stepped receiving surface 2c below, respectively.

The inner race 3a of the bearing 3 is bonded and fixed to the outer peripheral surface of the shaft 1. Similarly, the inner race 4a of the bearing 4 is
The outer ring 3b of the bearing 3 and the outer ring 4b of the bearing 4 have their outer end faces and side faces in the axial direction abutting against the receiving faces at both ends of the bearing holder 5b. And the inner ring 4a of the bearing 4 are fixed by an adhesive in a state where a preload is applied in a direction to be separated from each other in the axial direction. Thus, the stationary part and the rotating part are rotatably connected via the bearings 3 and 4.

In the spindle motor of the second embodiment according to the present invention thus constructed, the outer races 3b and 4b are both held by an integral bearing holder 5b, unlike the spindle motor of the first embodiment. . For this reason, even if the temperature changes, the bearings 3 and 4 are not affected by the rotor hub 2 at all and compared with the spindle motor of the first embodiment.
Can further improve the effect of preventing a change in relative position. Therefore, the effect of preventing a change in preload between bearings and a change in rigidity of the bearing portion can be further improved.

Although two bearings are provided in the above embodiment, three or more bearings may be provided. Further, in the above embodiment, the stator is provided in the stationary part and the magnet is provided in the rotating part. However, in the present invention, the magnet may be provided in the stationary part and the stator may be provided in the rotating part. Good.

In the above embodiment, the linear thermal expansion coefficients of the shaft and the bearing holder are smaller than the linear thermal expansion coefficient of the rotor hub. However, the same effect can be obtained even if the magnitude relation of the linear thermal expansion coefficients is reversed. Obtainable. Further, in this embodiment, the material of the shaft and the bearing holder is stainless steel. However, in the present invention, other materials may be used as long as the linear thermal expansion coefficients are substantially equal, or a combination of different materials may be used.

[0036]

As described in detail above, according to the present invention,
It is possible to prevent a change in the magnitude of the preload applied in advance between the bearings due to the difference in the coefficient of linear thermal expansion, and to prevent a decrease in the rigidity of the bearing portion. Therefore, it is possible to maintain a state in which a preload is applied between the bearings with respect to a temperature change in a wider range than in the related art.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a spindle motor according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view showing a spindle motor according to a second embodiment of the present invention.

FIG. 3 is a schematic sectional view showing a conventional spindle motor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1; Shaft 2; Rotor hub 3, 4; Bearing 3a, 4a; Inner ring 3b, 4b; Outer ring 5a, 5b; Bearing holder 6; Bracket 7; Stator 8;

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) JK13 JK17 JK19

Claims (6)

[Claims] A shaft, a pair of bearings including an inner ring, an outer ring, and a ball bearing fitted to the shaft; a rotor hub rotatably provided on the shaft via the bearing; A bearing holder, which is provided between the inner ring of the bearings and the rotor hub and is fixed to the inner surface of the rotor hub and is made of a material having a coefficient of linear thermal expansion substantially equal to that of the shaft. Spindle motor. 2. The spindle motor according to claim 1, wherein the bearing holder is provided between both outer rings of the pair of bearings and the rotor hub. 3. The rotor hub has a portion between the pair of bearings protruding toward the shaft, and an outer ring of the bearing is provided outside the protrusion of the rotor hub such that a distance between the outer rings is regulated by the protrusion. The spindle motor according to claim 1, wherein the spindle motor is disposed. 4. The spindle motor according to claim 1, wherein the bearing holder is bent so as to contact a side surface and an inner surface of the protrusion. 5. The system according to claim 1, wherein the pair of inner races is fixed to the shaft with a preload applied in a direction away from each other via the ball bearing and the outer race. The spindle motor according to any one of claims 1 to 4. 6. The bearing holder has a cylindrical shape, and has a cylindrical portion that contacts an inner surface of a protruding portion of the rotor hub, and an outer flange that contacts both end surfaces of the protruding portion on the bearing side. The spindle motor according to any one of claims 2 to 5, wherein