JPH03203067A - Spindle motor - Google Patents

Abstract

PURPOSE:To obtain sufficiently stable sealing effect extending over a long period of time by constituting a motor so that two magnetic flux densities acting upon magnetic fluid from an inner pole piece and an outer pole piece become practically equal. CONSTITUTION:The spindle motor is provided with a housing main body 2 and a shaft member 4. A magnetic fluid sealing means 24 is arranged at the outside of a bearing member 10. The means 24 is provided with an annular permanent magnet 26 and a pair of the outer pole piece 28 and the inner pole piece 30 arranged at both the sides of this magnet 26, and these are fitted to the inner circumferential surface of the cylindrical part 8 of the main body 2. Besides, two magnetic fluid layers 32, 34 are formed between a pair of the pole pieces 28, 30 and the member 4. Then, the inner diameter of the pole piece 30 is made smaller than the inner diameter of the pole piece 28. Accordingly the magnetic flux density to flow to the magnetic fluid from the pole piece 30 and the magnetic flux density to flow to the magnetic fluid from the magnetic pole piece 28 become practically equal, and the stable sealing effect can be obtained extending over a long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to improvements in spindle motors equipped with magnetic fluid sealing means.

[Prior art and its drawbacks]

A spindle motor for rotationally driving a recording member such as a general magnetic disk includes a housing body and a hub member that is rotatable relative to the housing body.

In a shaft-rotating type motor, a shaft member is fixed to a housing body, and a hub member is rotatably supported by the shaft member via bearing means.

Further, in a shaft rotating type motor, the shaft member is rotatably supported by the housing body via bearing means, and the hub member is fixed to the thus supported shaft member.

This type of spindle motor further includes magnetic fluid sealing means to prevent grease from splattering from the bearing means. The magnetic fluid sealing means has a pair of pole pieces and a magnetic fluid forming a sealing layer, forming substantially two magnetic sealing layers outside the bearing means.

However, conventional spindle motors have the following problems to be solved.

That is, although the pair of pole pieces are of substantially identical construction, they are spaced apart in a predetermined direction, one of them adjacent to the bearing means and the other of them spaced apart from said bearing means. There is. Therefore, the magnetic flux from the pole piece partially leaks to the outside through the bearing means (so-called shunting through the bearing means). Therefore, the magnetic flux densities acting on the magnetic fluid of a pair of pole pieces are not equal (the magnetic flux density of the pole piece adjacent to the bearing member is larger than the magnetic flux density of the other pole piece), and this imbalance in magnetic flux density is the cause. Therefore, there is a possibility that scattering of the magnetic fluid, damage to the magnetic fluid layer, etc. may occur in a relatively short period of time. The same phenomenon as described above also occurs when another member is placed close to the pair of pole pieces instead of the bearing means.

[Purpose of the invention]

The present invention has been made in view of the above facts, and its main purpose is to provide a spindle motor that can obtain a sufficiently stable magnetic sealing effect over a long period of time with a relatively simple configuration. .

[Summary of the invention]

In the present invention, in a spindle motor with a rotating shaft member or a fixed shaft member, the inner pole piece and the outer pole piece compensate for the asymmetry of magnetic resistance, and the magnetic flux density acting on the magnetic fluid from the inner pole piece is adjusted. The magnetic flux density acting on the magnetic fluid from the outer pole piece is configured to be substantially equal.

In such a spindle motor, the asymmetry of the reluctance caused by the presence of bearing means etc. is compensated as required, and the magnetic flux density in the outer magnetic fluid layer produced by the outer pole piece and the inner one produced by the inner pole piece are compensated as required. The magnetic flux density in the magnetic fluid layer becomes substantially equal. Therefore, two stable magnetic fluid layers are formed over a long period of time, and scattering of the magnetic fluid and damage to the magnetic fluid layer are prevented.

〔Concrete example〕

Further details will be given below with reference to the accompanying drawings.

In FIGS. 1 and 2 showing a first specific example of the spindle motor of the present invention, the illustrated spindle motor includes a housing body 2 and a shaft member 4 that is rotatable with respect to the housing body 2. . The housing body 2 has a bracket part 6 that is attached to a frame (not shown) and a cylindrical part 8 that extends substantially vertically from the bracket part 6 in the up and down direction. It is rotatably supported via a bearing member 10 (constituting bearing means, only one of which is shown in FIGS. 1 and 2), and is rotationally driven, for example, in the direction shown by the arrow (FIG. 1). Hub member 12
is fixed to one end (upper end) of the shaft member 4. The illustrated hub member 12 includes an end wall portion 14 fixed to the shaft member, a cylindrical body portion 16 extending downward from the outer peripheral end of the end wall portion 14, and a flange portion extending radially outward from the lower end of the cylindrical body portion 16. 18, and a plurality of recording members 20 such as magnetic disks are attached to the outer periphery of the cylindrical main body 16 via spacer members 22.

A magnetic fluid sealing means 24 is further provided on the outside of the one (upper) bearing member 10 shown. The MI fluid sealing means 24 includes an annular permanent magnet 26 and a pair of pole pieces 28 disposed on both sides of the annular permanent magnet 26.
and 30, which are attached to the inner peripheral surface of the cylindrical portion 8 of the housing body 2.

Moreover, a magnetic fluid is filled between the pair of pole pieces 28 and 30 and the shaft member 4, and the magnetic fluid substantially forms two magnetic fluid layers 32 and 34. The magnetic fluid layers 32 and 34 are formed in an annular shape on the outer peripheral surface of the shaft member 4 to prevent grease and the like from the bearing means 10 from entering the disk chamber.

In relation to the magnetic fluid sealing means 24, the first specific example is further configured as follows.

Referring principally to FIG.
Lower side in Figures 1 and 2) Inner pole piece 30
has an inner diameter smaller than that of the other (upper side in FIGS. 1 and 2) outer pole piece 28, so that the pole tip of the inner pole piece 30 is located radially inwardly than the pole tip 28 of the outer pole piece 28. Protruding, outer pole piece 2
Gap W between the magnetic pole end surface (inner end surface) of No. 8 and the outer peripheral surface of the shaft member 4
1 is larger than the gap W2 between the magnetic pole end surface (inner end surface) of the inner pole piece 30 and the outer peripheral surface of the shaft member 4.

In the first specific example, the inner pole piece 28 and the outer pole piece 30 are made of a magnetic material such as iron, and have substantially the same thickness.

This configuration has the following advantages. As shown, bearing means 10 is located near the pair of pole pieces 10.
is arranged, a magnetic circuit is generated through this bearing means 10, and a part of the magnetic flux passing through the inner pole piece 30 flows through the bearing means 10 as a shunt. Therefore, as in the embodiment, the pole pieces 28 and 3 are placed on both sides of the permanent magnet 26.
0, the magnetic flux densities from pole pieces 28 and 30 are substantially equal;
Since a part of the magnetic flux flowing through the bearing member 10 is divided and flows through the bearing member 10, the magnetic fluid (magnetic fluid layer 3
4) becomes smaller than the magnetic flux density acting on the magnetic fluid (magnetic fluid layer 32) from the outer pole piece 28, and there is a possibility that a stable sealing effect cannot be obtained. On the other hand, in the first specific example, in order to eliminate the above-mentioned disadvantage, the gap W1 between the magnetic pole end surface (inner end surface) of the outer pole piece 28 and the outer peripheral surface of the shaft member 4 is The gap W2 is set larger than the gap W2 between the end surface (inner end surface) and the outer circumferential surface of the shaft member 4. Therefore, the magnetic flux density acting on the gap between the magnetic pole end surface (inner end surface) of the outer pole piece 28 and the outer peripheral surface of the shaft member 4 is increased, and the imbalance of magnetic resistance due to the presence of the bearing member 10 is caused by the magnetic flux in the gap between the two. The difference in resistance is compensated as required, so that the magnetic flux density flowing from the inner pole piece 30 to the magnetic fluid and the magnetic flux flowing from the outer pole piece 28 to the magnetic fluid are substantially equal, resulting in a stable sealing effect over a long period of time. can get.

FIG. 3 shows a second specific example of the spindle motor. In this second embodiment, improvements are made to the magnetic end faces of the pair of pole pieces in order to compensate for the asymmetry in magnetic resistance. Hereinafter, the same members as those shown in FIGS. 1 and 2 will be described with the same reference numerals.

In FIG. 3, also in the second specific example, the magnetic fluid sealing means 24' includes an annular permanent magnet 26 and a pair of pole pieces 28' and 30' disposed on both sides of the annular permanent magnet 26. . The outer pole piece 28' and the inner pole piece 30' have substantially the same inner diameter and outer diameter, and therefore the distance between the magnetic end surface (inner end surface) of the outer pole piece 28' and the outer circumferential surface of the shaft member 4 is The distance between the magnetic end surface (inner end surface) of the inner pole piece 30'' and the outer circumferential surface of the shaft member 4 is substantially the same, but the outer pole piece 28°
The thickness T1 of the magnetic end of the inner pole piece 30'' is thicker than the thickness T2 of the magnetic end of the inner pole piece 30'', and therefore the inner pole piece 3
The area of the 0° magnetic end face (the face facing the shaft member 4) is smaller than the area of the free end face of the outer pole piece 28'. The other configurations of the second specific example are substantially the same as those of the first specific example.

With this structure, in the second specific example, the magnetic end of the inner pole piece 30' is partially chamfered to have a small area, and the magnetic flux density on the 30° side of the inner pole piece is equal to the magnetic flux flow relative to the area. The ratio is increased so that the reduction in magnetic reluctance due to the bearing member 10 is compensated as required. As a result, the magnetic flux density acting on the magnetic fluid from the inner pole piece 30' and the magnetic flux density acting on the magnetic fluid from the outer pole piece 28' become substantially equal, and as in the first example, a stable sealing effect is achieved. is obtained.

In FIG. 3, only a part of the magnetic end of the inner pole piece 30' is made thinner to locally concentrate the magnetic flux density, but instead of this, for example,
The area of the magnetic end surface is made different by adopting a configuration such as reducing the entire thickness of the pole piece 28' or increasing the thickness of a part of the magnetic end (inner peripheral end) of the outer pole piece 28'. You may also have

FIG. 4 shows a third specific example of the spindle motor. In this third specific example, the magnetic permeability of the pair of pole pieces is made different in order to compensate for the unbalance of magnetic resistance.

In FIG. 4, also in the third embodiment, the magnetic fluid sealing means 24'' includes an annular permanent magnet 26 and a pair of pole pieces 28''' and 30''' disposed on both sides of the annular permanent magnet 26. The outer pole piece 28'" and the inner pole piece 30' have substantially the same inner and outer diameters, and therefore the magnetic end surface (inner end surface) of the outer pole piece 28'" and the shaft member 4 The distance between the outer peripheral surface, the magnetic end surface (inner end surface) of the inner pole piece 30°', and the shaft member 4
The distances from the outer circumferential surfaces of the two are substantially the same, and their thicknesses are also substantially the same throughout, but their materials are different. That is, outer pole piece 28''' is formed from a material with relatively low magnetic permeability, and inner pole piece 30'' is formed from a material with relatively high magnetic permeability.

The other configurations of the third specific example are substantially the same as those of the first specific example.

With this structure, in the third specific example, the magnetic flux density in the gap between the magnetic end surface of the inner pole piece 30'' and the outer circumferential surface of the shaft member 4 is increased due to the material thereof, and the magnetic flux density due to the bearing member 10 is increased. The magnetoresistance imbalance is compensated as required by equalization of the magnetoresistance based on the difference in magnetic permeability,
As a result, the magnetic flux density acting on the magnetic fluid from the inner pole piece 30°' becomes substantially equal to the magnetic flux density acting on the magnetic fluid from the outer pole piece 28°, and as in the first example, A stable sealing effect can be obtained over a period of time.

In the third specific example, the materials of the entire pole pieces 28" and 30 are changed to have different magnetic permeability, but instead of this, the material of only the negative part of the pole pieces may be changed, or the material of the same material may be used. The magnetic permeability may be varied by providing through holes or surface processing (for example, making the surface uneven).

Although specific examples of the spindle motor according to the present invention have been described above, the present invention is not limited to these specific examples, and various modifications and changes can be made without departing from the scope of the present invention.

For example, the air gap between the pole piece and the shaft member in the first specific example, the area of the pole tip surface of the pole piece in the second specific example, and the magnetic permeability of the pole piece in the third specific example are It can be set as appropriate to compensate.

In addition, for example, in the first specific example, differences are made in the air gap between the pole piece and the shaft member, in the second specific example, in the area of the magnetic end face of the pole piece, and in the third specific example, differences are made in the magnetic permeability of the pole piece. Although the unbalance of magnetic resistance is compensated for by using these elements, it is also possible to compensate for the unbalance by combining these elements.

Furthermore, in the first to third specific examples, since the influence of the bearing member is relatively large, the unbalance of the magnetic shunt is explained in relation to the bearing member, but in reality, it is caused by various other members and these. Due to the existence of voids in the component, it is desirable to consider these as well.

Furthermore, for example, in the first to third specific examples, all spindle motors have a rotating shaft member (a form in which the shaft member and the hub member rotate relative to the housing body).
Although the description has been made by applying it to
6776, in which the hub member rotates relative to the shaft member fixed to the housing body). In such a case, the bearing means is interposed between the hub member and the shaft member, the magnetic fluid sealing means is mounted on the shaft member (or the hub member), and the magnetic fluid flows between the pair of magnetic fluid sealing means thus mounted. It is filled between the pole piece and the hub member (or shaft member).

[Brief explanation of drawings]

FIG. 1 is a sectional view showing essential parts of a first specific example of a spindle motor according to the present invention. FIG. 2 is an enlarged sectional view showing a part of the spindle motor of FIG. 1; FIG. 3 is an enlarged sectional view showing a part of a second specific example of the spindle motor according to the present invention. FIG. 4 is an enlarged sectional view showing a part of a third specific example of the spindle motor according to the present invention. Housing body shaft member cylindrical part, bearing member, hub member, recording member 4' and 24''... Magnetic fluid sealing means 28, 28' and 28 pa... Outer pole piece 2 4 8 8 10・ l 2 ・ 20 ・ 24. 30. 30° and 30°'... Inner pole pieces 32 and 34... Magnetic fluid layer

Claims (1)

[Claims] 1. A housing body, a shaft member that is rotatable relative to the housing body, a hub member fixed to the shaft member, and a space between the housing body and the shaft member. a pair of pole pieces, the magnetic fluid sealing means being attached to the housing body or the shaft member; and between the pair of pole pieces and the shaft member or the housing body. In a spindle motor having a magnetic fluid filled with magnetic fluid, the inner pole piece and the outer pole piece compensate for the asymmetry of magnetic resistance, and the magnetic flux density acting on the magnetic fluid from the inner pole piece and the outer pole A spindle motor characterized in that the magnetic flux densities acting on the magnetic fluid from the pieces are substantially equal. 2. The spindle motor according to claim 1, wherein a gap between the outer pole piece and the shaft member or the housing body is smaller than a gap between the inner pole piece and the shaft member or the housing body. 3. The spindle motor according to claim 1, wherein the area of at least the magnetic pole end face of the outer pole piece is larger than the area of the magnetic pole end face of the inner pole piece. 4. The spindle motor according to claim 1, wherein at least a portion of the outer pole piece has a higher magnetic permeability than the inner pole piece. 5. Comprising a shaft member fixed to the housing body, a hub member rotatable relative to the shaft member, and a magnetic fluid sealing means disposed between the shaft member and the hub member. and a spindle motor in which the magnetic fluid sealing means includes a pair of pole pieces attached to the shaft member or the hub member, and a magnetic fluid filled between the pair of pole pieces and the hub member or the shaft member. In the above, the inner pole piece and the outer pole piece compensate for the asymmetry of magnetic resistance and reduce the magnetic flux density acting on the magnetic fluid from the inner pole piece and the magnetic flux density acting on the magnetic fluid from the outer pole piece. A spindle motor characterized in that the spindle motor is configured such that the two are substantially equal to each other. 6. The spindle motor according to claim 5, wherein a gap between the outer pole piece and the shaft member or the hub member is smaller than a gap between the inner pole piece and the shaft member or the hub member. 7. The spindle motor according to claim 5, wherein the area of at least the magnetic pole end face of the outer pole piece is larger than the area of the magnetic pole end face of the inner pole piece. 8. The spindle motor according to claim 5, wherein at least a portion of the outer pole piece has a higher magnetic permeability than the inner pole piece.