JPH04351453A - Spindle motor - Google Patents

Abstract

PURPOSE:To suppress eccentricity of the center of rotation according to a change of temperature by fixing a bush member press-fitted to an internal peripheral surface of a yoke member in an intermediate part in an axial direction so as to improve fitting of the yoke member to a hub member. CONSTITUTION:In a free end part of a large diametric part 22a of a yoke member 22, a large internal diametric part 22c of a little larger internal diameter is provided. The external diameter of an upper part 30b above a stepped part provided in almost the central part in an axial direction on the peripheral surface of a bush member 30 is a little smaller than the external diameter of a lower part 30c in a lower side. When the bush member 30 is thus connected to the yoke member 22, the fixing region of both the members is relatively short in the axial direction, and a slight space between both the members at both end parts of the bush member 30 is created. By providing this space, eccentricity of the center of rotation of a rotor hub can be effectively prevented even when the ambient temperature is changed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle motor for rotationally driving a recording member such as a magnetic disk.

0002

[Prior Art] Generally, a spindle motor for rotationally driving a magnetic disk or the like includes a shaft, a rotor hub that is rotatable relative to the shaft, and a pair of bearings that rotatably supports the rotor hub with respect to the shaft. a rotor magnet attached to a rotor hub via a yoke member, and a stator disposed opposite to the rotor magnet. One bearing member rotatably supports one end of the rotor hub via a yoke member (or directly), and the other bearing member rotatably supports the other end of the rotor hub via a bushing member and a yoke member. ing. Further, the recording member is attached to the rotor hub, and the recording member is rotationally driven in a predetermined direction together with the rotor hub by the magnetic action of the rotor magnet and the stator.

0003

In this type of spindle motor, the rotor hub is made of aluminum or an aluminum alloy, and the yoke member is made of a magnetic material such as iron. When the rotor hub and yoke member are fixed together in a relatively long region in the axial direction by means such as shrink fitting, there is a difference in thermal expansion coefficient between the rotor hub and yoke member (aluminum or aluminum alloy is better than iron). thermal stress is generated between the two members due to their thermal expansion coefficient being larger than that of the two members, and thermal expansion and contraction of both members is restricted. At this time, if the bushing member is made of the same magnetic material as the yoke member, such as iron, and is press-fitted into the yoke member over substantially its entire length, thermal stress will also be generated between the yoke member and the bushing member. Due to such thermal stress, a fitting clearance is created between the bushing member and the yoke member, and this clearance may cause the center of rotation of the rotor hub to become eccentric.

The present invention has been made in view of the above facts, and its object is to provide a spindle motor that can improve the fitting between the yoke member and the hub member and suppress eccentricity of the center of rotation due to temperature changes. It is to provide.

[0005]

[Means for Solving the Problems] In the spindle motor of the present invention, the bushing member interposed between the yoke member and the bearing member is press-fitted and fixed to the inner circumferential surface of the yoke member at its axially intermediate portion. There is.

[0006]

[Operation] In such a spindle motor, the bushing member is press-fitted into the yoke member at its axially intermediate portion, so that a slight gap exists between the bushing member and the yoke member at both ends thereof. Therefore, even if the ambient temperature changes and strain occurs due to thermal expansion between the yoke member and the bushing member, most of this strain is absorbed by the gap, and eccentricity of the rotation center of the rotor hub is effectively prevented. Ru.

Furthermore, even if the yoke member is slightly deformed due to a difference in thermal expansion between the rotor hub and the yoke member due to a change in ambient temperature, the effect on the bushing member is extremely small because there is a gap at both ends. This also effectively prevents eccentricity of the rotation center.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a spindle motor according to the present invention will be described below with reference to FIG.

FIG. 1 is a schematic half-sectional view of a brushless motor for driving a hard disk as an embodiment of the present invention.

Reference numeral 10 indicates a shaft, 12 a stator core made of a silicon steel plate which is externally fitted and fixed to the shaft 10, and 14 a stator coil wound around the stator core 12.

Reference numeral 16 denotes a substantially cylindrical rotor hub (peripheral wall portion) made of aluminum. The rotor hub 16 has a large outer diameter section 16a to which a hard disk is fixed to the outer periphery, and a shoulder section 16 that constitutes the upper end of the large outer diameter section 16a in FIG.
b, and the small outer diameter portion 16 located inside and above the shoulder portion 16b.
c, and an outwardly projecting portion 16d projecting outward at the lower end of the large outer diameter portion 16a. The inner diameter of the large outer diameter portion 16a is reduced to an intermediate diameter between the inner diameter of the small outer diameter portion 16c and the inner diameter of the small outer diameter portion 16c at the shoulder portion 16b.

An annular yoke member 22 is disposed on the inner peripheral surface of the rotor hub 16. The yoke member 22 has a cylindrical large diameter part 22a and an upper reduced diameter part 22b provided at one end of the large diameter part 22a, and the upper reduced diameter part 22b is connected to the shoulder part 16b of the rotor hub 16 with a slight gap. It is located inside. An annular rotor magnet 29 is attached to the inner peripheral surface of the intermediate portion of the yoke member 22 . This rotor magnet 29 is arranged opposite to the stator (consisting of stator core 12 and stator coil 14).

The rotor hub 16 is rotatably supported via a pair of bearing members 32 and 34. In the embodiment, one bearing member 34 is attached to the upper end of the rotor hub 16.
is arranged, and the inner ring of the bearing member 34 is connected to the shaft 10.
The outer ring is fixed to the upper reduced diameter portion 2 of the yoke member 22.
2b is supported. The other bearing member 32 is arranged at the lower end of the rotor hub 16, and its inner ring is connected to the shaft 1.
0, and its outer ring supports the free end of the large diameter portion 22a of the yoke member 22 via a bushing member 30, which will be described later.

A frequency generator magnet 24 is fixed to the lower surface of the outwardly extending portion 16d of the rotor hub 16 via a yoke 26. In addition, the shoulder portion 1 of the rotor hub 16
6b is provided with a screw hole 28 for fixing a hard disk fixing clamp (not shown). Further, magnetic fluid sealing means 36 and 38 are provided on the outside of the pair of bearing members 32 and 34, respectively. One of the magnetic fluid sealing means 36 is disposed outside the bearing member 34 and attached to the inner peripheral surface of the small outer diameter portion 16c of the rotor hub 16. The other magnetic fluid sealing means 38 is disposed outside the bearing member 32 and attached to the inner peripheral surface of a holder 40 mounted on the lower surface (outer surface) of the annular bushing member 30. Furthermore, the small outer diameter portion 16c of the rotor hub 16
A cap member 42 for protecting the magnetic fluid sealing means 36 is provided (outside the magnetic fluid sealing means 36).

Next, the rotor hub 16 and the yoke member 22
And the manner of coupling the bushing member 30 will be explained.

The rotor hub 16 is made of aluminum, and the yoke member 22 is made of a ferrous material such as iron. As shown in FIG.
2a is fixed by shrink fit over substantially the entire length in the axial direction (vertical direction in FIG. 1).

The bushing member 30 is made of the same iron-based material as the yoke member 22, and its axial length is substantially the same as the axial length of the outer ring of the bearing member 32. The inner circumferential surface of the bushing member 30 is press-fitted to the outer ring of the bearing member 32 over substantially its entire length.

The outer peripheral surface of the bushing member 30 and the yoke member 2
The inner peripheral surface of No. 2 is fixed as follows. That is, the free end portion (lower end portion in FIG. 1) of the large diameter portion 22a of the yoke member 22 has a large inner diameter portion 2 having a somewhat larger inner diameter than the other portion.
2c is provided. Further, a stepped portion is provided at approximately the center of the outer circumferential surface of the bushing member 30 in the axial direction (vertical direction in FIG. 1), and the outer diameter of the upper portion 30b above the stepped portion in FIG. It is set to be somewhat smaller than the outer diameter of the lower part 30c located below the stepped portion in FIG. With this configuration, when the bushing member 30 and the yoke member 22 are coupled as required, the axially intermediate portion of the bushing member 30 and the inner circumferential surface of the yoke member 22 are brought into contact and fixed, as shown in FIG. The distance between the two fixed regions is relatively short in the axial direction (the length of the fixed region may be about 2 to 5 mm), and there is a slight gap between the two at both ends of the bushing member 30.

Providing such a gap at both ends of the bushing member 30 provides the following advantages. That is, even if a difference in thermal expansion occurs between the yoke member 22 and the bushing member 30 due to a change in ambient temperature, most of the difference in thermal expansion is absorbed by the gap, and the eccentricity of the center of rotation of the rotor hub 16 is effective. is prevented. Furthermore, even if the yoke member 22 is slightly deformed due to a change in ambient temperature (for example, the rotor hub 16
Due to the presence of the gap (due to the difference in thermal expansion between the bushing member 30 and the bushing member 30), the yoke member 22 does not act on the bushing member 30 at both ends thereof, and any adverse effects caused by distortion of the yoke member 22 are also prevented.

In order to more securely fix the yoke member 22 and the bushing member 30, it is preferable to interpose an adhesive layer in the gap between them. When the adhesive layer is interposed in this way, the difference in thermal expansion between the two is absorbed by the elastic deformation of the adhesive.

In the embodiment, the adhesive is applied to the outer circumferential surface of the bushing member 30 and the inner circumferential surface of the free end of the large diameter portion 22a of the yoke member 22, and in this applied state, the bushing member 30 is attached to the yoke member 22. Press-fitted. When press-fitted in this way, as can be easily understood from FIG. 1, the bushing member 30
Since the outer diameter of the distal end in the insertion direction of the yoke member 22 is somewhat smaller and the inner diameter of the large inner diameter portion 22c of the yoke member 22 is somewhat larger, the adhesive is substantially removed from their peripheral surfaces during insertion. Therefore, sufficient adhesive is retained in the gap between the yoke member 22 and the bushing member 30, and the adhesion of the two is ensured.

Although one embodiment of the spindle motor according to the present invention has been described above, the present invention is not limited to this embodiment, and various modifications and changes can be made without departing from the scope of the present invention. be.

For example, in the illustrated embodiment, bearing member 34
Although the rotor hub 16 is supported via the yoke member 22, the rotor hub 16 may be directly supported.

Further, for example, in the illustrated embodiment, only one of the pair of bearing members 32 and 34 supports the rotor hub 16 via the bushing member 30, but the other of them also supports the rotor hub 16 via the bushing member. It can also be configured to support In such a case, the present invention can also be applied in relation to this bush member.

Furthermore, for example, in the illustrated embodiment, stepped portions are provided on the outer circumferential surface of the bushing member 30 and on the inner circumferential surface of the yoke member 22, and the intermediate portion of the bushing member 30 is press-fitted into the yoke member. However, the present invention is not limited to this, and an annular projection may be provided on the outer peripheral surface of the bushing member 30 or the inner peripheral surface of the yoke member 22, and the annular projection may be press-fitted and fixed.

[0026]

In the spindle motor of the present invention, the intermediate portion of the bushing member is press-fitted and fixed to the yoke member, and gaps exist between the two ends of the bushing member. Therefore, even if a difference in thermal expansion occurs between the yoke member and the bushing member due to a change in ambient temperature, this difference in thermal expansion is absorbed by the gap, and even if the yoke member deforms to some extent, the deformation does not have an adverse effect on the bushing member. It will never reach you.

[Brief explanation of drawings]

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

[Explanation of symbols]

10 Shaft 16 Rotor hub 22 Yoke member 29 Rotor magnet 30 Bush member 32, 34 Bearing member

Claims (1)

[Claims] 1. A shaft, a rotor hub rotatable relative to the shaft, a pair of bearing members rotatably supporting the rotor hub with respect to the shaft, and mounted on the rotor hub via a yoke member. A spindle motor comprising a rotor magnet and a stator disposed opposite to the rotor magnet, wherein at least one of the pair of bearing members supports the yoke member via a bush member. A spindle motor characterized in that the member is press-fitted and fixed to the yoke member at an axially intermediate portion thereof.