JP2000224799A - Spindle motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spindle motor capable of preventing magnetic fluid from being splashed to the outside, and suppressing reduction in the seal performance of a magnetic fluid seal means. SOLUTION: This spindle motor is provided with a stationary shaft 2, a rotor hub 4 rotatably supported by the stationary shaft 2 through ball bearings 6, 8, a rotor magnet 20 attached to the rotor hub 4, a stator 22 disposed so as to face the rotor magnet 20, and a magnetic fluid seal means 40 sealing a gap between the stationary shaft 2 and the rotor hub 4. The magnetic fluid seal means 40 involves a holding magnet 42 and a pole piece 44 formed on its one end, the rotor hub 4 has a step so as to meet the pole piece 44, and the magnetic fluid of the magnetic fluid seal means 40 is held between the side surface of the step and the pole piece 44.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle motor having magnetic fluid sealing means.

[0002]

2. Description of the Related Art For example, a spindle motor for rotating a magnetic disk such as a hard disk has a stationary shaft and a rotor hub on which the magnetic disk is mounted. The rotor hub is rotatably supported on the stationary shaft via bearing means. ing. The stationary shaft is fixed to the base member of the disk drive via a mounting bracket or directly. A rotor magnet is mounted on the rotor hub, and a stator is disposed to face the rotor magnet.

In such a spindle motor, a magnetic fluid sealing means is provided outside the bearing means in order to prevent grease from scattering from the bearing means. FIG.
FIG. 5 is an enlarged sectional view showing a magnetic fluid sealing means and its vicinity in a conventional spindle motor. In this conventional spindle motor, a pair of ball bearings 204 (only one is shown in FIG. 5) is provided on a stationary shaft 202 as a bearing means. , The rotor hub 206 is rotatably supported. The magnetic fluid sealing means 208 is disposed axially outside one of the ball bearings 204. This magnetic fluid sealing means 2
Reference numeral 08 includes an annular holding magnet 210 for magnetically holding a magnetic fluid, and a pair of pole pieces 212 and 214 disposed on both end surfaces of the holding magnet 210. Pole piece 2
12, 214 are mounted on the annular holder 216. A shoulder 218 is provided on the inner peripheral portion of the rotor hub 206, and the annular holder 216 is mounted so as to abut the shoulder 218. The inner peripheral portions of the pair of pole pieces 212 and 214 project radially inward from the holding magnet 210, and the magnetic fluid 220 flows between the inner peripheral surface of the outer pole piece 212 and the outer peripheral surface of the stationary shaft 202. Is filled.

[0004]

However, the conventional spindle motor has the following problems to be solved. When the rotation of the rotor hub 202 becomes faster,
A centrifugal force acts on the magnetic fluid 220, and the centrifugal force causes the magnetic fluid 220 to move radially outward along the surface of the pole piece 212. If such a tendency increases, the magnetic fluid 220 may flow along the surface of the pole piece 212 and scatter outside.

Further, the movement by centrifugal force tends to be large for particles having a large specific gravity, ie, iron particles, contained in the magnetic fluid. When the iron particles move due to such a tendency, the oil component of the magnetic fluid is transferred to the stationary shaft. The holding force of the magnetic fluid 220 on the surface of the magnetic fluid 220 is weakened, whereby the sealing layer of the magnetic fluid 220 between the stationary shaft 202 and the pole piece 212 is easily broken, and the sealing performance by the magnetic fluid 220 is reduced.

An object of the present invention is to provide a spindle motor capable of preventing a magnetic fluid from scattering to the outside and suppressing a decrease in sealing performance of a magnetic fluid sealing means.

[0007]

SUMMARY OF THE INVENTION The present invention provides a stationary shaft, a rotor hub rotatably supported on the stationary shaft via bearing means, a rotor magnet mounted on the rotor hub, and a rotor magnet opposed to the rotor magnet. A magnetic fluid sealing means for sealing a gap between the stationary shaft and the rotor hub, the magnetic fluid sealing means being supported by the stationary shaft, A magnetic fluid for sealing a gap between a shaft and the rotor hub, a holding magnet for magnetically holding the magnetic fluid, and a pole piece provided on one end surface of the holding magnet; An outer peripheral portion of the piece protrudes radially outward beyond the holding magnet, and the magnetic fluid is provided between the outer peripheral portion of the pole piece and the rotor housing. And the rotor hub has an axial surface corresponding to the pole piece of the magnetic fluid sealing means and an outer peripheral surface of the pole piece radially opposed to an outer peripheral surface of the pole piece. An annular step portion having an annular bottom surface continuously formed is provided, and most of the magnetic flux from the holding magnet of the magnetic fluid sealing means passes between the pole piece and the bottom surface of the step portion. The peripheral surface of the step portion prevents the magnetic fluid from flowing radially outward due to centrifugal force, and the magnetic fluid is mainly held between the bottom surface of the step portion and the pole piece. It is characterized by the following.

According to the present invention, the magnetic fluid sealing means is provided on the stationary shaft, and the rotor hub is provided with an annular step corresponding to the pole piece of the magnetic fluid sealing means. Is configured to flow between the pole piece and the bottom surface of the step portion of the rotor hub. Therefore, the magnetic fluid filled between the pole piece and the rotor hub is mainly held magnetically between the bottom surface of the step portion and the pole piece, thereby increasing the seal width by the magnetic fluid. As a result, the sealing force can be increased, and the sealing performance can be improved. In addition, the rotation of the rotor hub tends to cause the magnetic fluid to flow radially outward,
Since the peripheral surface of the annular step portion of the rotor hub is formed continuously from the bottom surface and extends in the axial direction, the peripheral surface of the step portion prevents this flow of the magnetic fluid, so that the magnetic fluid can rotate even during rotation. Mainly, magnetically held between the bottom surface of the step and the pole piece, a stable sealing force can be obtained. In the present invention, an outer diameter of the pole piece is set to be larger than an inner diameter of the bottom surface of the step portion and smaller than an outer diameter of the bottom surface.

According to the present invention, since the outer diameter of the pole piece is set as described above, the outer peripheral portion of the pole piece is spaced apart from the bottom surface of the annular step in the axial direction. It will overlap.

In the present invention, a gap between the pole piece and the bottom surface of the step portion is set to be smaller than a gap between an outer peripheral surface of the pole piece and the peripheral surface of the step portion. It is characterized by having.

According to the present invention, the gap between the pole piece and the bottom surface of the annular step portion of the rotor hub is smaller than the gap between the outer peripheral surface of the pole piece and the peripheral surface of the step portion.
Most of the magnetic flux from the holding magnet flows between the pole piece and the bottom surface of the annular step, and the magnetic fluid is mainly held magnetically in this gap.

In the present invention, the pole piece of the magnetic fluid sealing means is formed with a taper which is inclined radially outward toward the inside in the axial direction.

According to the present invention, since the taper is formed on the outer peripheral surface of the pole piece, the magnetic fluid flowing between the outer peripheral surface of the pole piece and the peripheral surface of the annular step portion by the action of the taper is formed. In this method, a force for returning to the original sealing state is applied, whereby the outflow of the magnetic fluid is suppressed, and a stable seal can be obtained for a long period of time.

The present invention also provides a stationary shaft, a rotor hub rotatably supported on the stationary shaft via bearing means,
A spindle motor comprising: a rotor magnet mounted on the rotor hub, a stator disposed to face the rotor magnet, and magnetic fluid sealing means for sealing a gap between the stationary shaft and the rotor hub. The magnetic fluid sealing means is supported by the rotor hub, and includes a magnetic fluid for sealing a gap between the stationary shaft and the rotor hub, a holding magnet for magnetically holding the magnetic fluid, and one of the holding magnets. A pole piece provided on the end face, and a filling member provided at a corner of the holding magnet and the pole piece, wherein an inner peripheral portion of the pole piece extends radially inward beyond the filling member. Projecting, the magnetic fluid is filled between an inner peripheral portion of the pole piece and the stationary shaft, and the magnetic fluid is In correspondence with the pole piece of the tool, a peripheral surface radially opposed to the inner peripheral surface of the pole piece and an annular bottom surface axially opposed to the inner peripheral portion of the pole piece were continuously formed. An annular step is provided, and most of the magnetic flux from the holding magnet of the magnetic fluid sealing means flows between the pole piece and the bottom surface of the step, and the inner peripheral surface of the filling member is formed of the magnetic material. The magnetic fluid is prevented from flowing outward in the radial direction due to the centrifugal force of the fluid, and the magnetic fluid is mainly held between the bottom surface of the step portion and the pole piece.

According to the present invention, the magnetic fluid sealing means is provided on the rotor hub, and the stationary shaft is provided with an annular step corresponding to the pole piece of the magnetic fluid sealing means. Most of the magnetic flux of the stationary shaft is configured to flow between the pole piece and the bottom surface of the step portion of the stationary shaft. Therefore, the magnetic fluid filled between the pole piece and the stationary shaft is mainly held magnetically between the bottom surface of the step portion and the pole piece, thereby increasing the seal width by the magnetic fluid and sealing. The force can be increased, and the sealing performance can be improved.
Also, the rotation of the rotor hub tends to cause the magnetic fluid to flow outward in the radial direction, but since the inner peripheral surface of the filling member provided in the magnetic fluid sealing means extends in the axial direction, the inner peripheral surface of the filling member Block this flow of ferrofluid,
The magnetic fluid is magnetically held mainly between the bottom surface of the step and the pole piece even during rotation, and a stable sealing force can be obtained. In the present invention, the inside diameter of the pole piece is set to be larger than the inside diameter of the bottom surface of the step portion, and smaller than the outside diameter of the bottom surface.

According to the present invention, since the inside diameter of the pole piece is set as described above, the inner peripheral portion of the pole piece is spaced apart from the bottom surface of the annular step portion in the axial direction. It will overlap.

In the present invention, the gap between the pole piece and the bottom surface of the step portion is set smaller than the gap between the inner peripheral surface of the pole piece and the peripheral surface of the step portion. It is characterized by being.

According to the present invention, the gap between the pole piece and the bottom surface of the annular step portion of the rotor hub is smaller than the gap between the inner peripheral surface of the pole piece and the peripheral surface of the step portion.
Most of the magnetic flux from the holding magnet flows between the pole piece and the bottom surface of the annular step, and the magnetic fluid is mainly held magnetically in this gap.

Further, according to the present invention, on the outer peripheral surface of the stationary shaft facing the filling member of the magnetic fluid sealing means,
A taper is formed which is inclined inward in the radial direction toward inward in the axial direction.

According to the present invention, since the taper is formed on the outer peripheral surface of the stationary shaft, the magnetic fluid flowing between the inner peripheral surface of the filling member and the outer peripheral surface of the stationary shaft is formed by the action of the taper. In this method, a force for returning to the original sealing state is applied, whereby the outflow of the magnetic fluid is suppressed, and a stable seal can be obtained for a long period of time.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a spindle motor according to the present invention will be described below with reference to FIGS. FIG. 1 is a sectional view showing a first embodiment of a spindle motor according to the present invention, and FIG. 2 is a partially enlarged sectional view showing a magnetic fluid sealing means and its vicinity in the spindle motor of FIG. .

Referring to FIG. 1, the illustrated spindle motor includes a stationary shaft 2 and a rotor hub 4 rotatable with respect to the stationary shaft 2. The stationary shaft 2 as a stationary member has its lower end portion fixed by a fixing screw (not shown).
The disk drive is fixed to a base plate (not shown). Instead of directly fixing the stationary shaft 2 to the base plate, the stationary shaft 2 may be mounted on a mounting bracket, and the mounting bracket may be mounted on a base plate of a disk drive.

In the vicinity of both ends of the stationary shaft 2, an axial direction (FIG. 1)
A pair of ball bearings 6, 8
(Constituting bearing means) is provided, and the rotor hub 4 is rotatably supported via the pair of ball bearings 6 and 8. In this embodiment, the rotor hub 4 includes a hollow cylindrical hub body 10, and a sleeve-shaped yoke 12 is mounted on the inner peripheral surface of the hub body 10. York 1
At one end (the upper end in FIG. 1) of the second shaft 2, there is provided an annular support projection 14 projecting inward in the radial direction, and the annular support projection 14 and one end of the stationary shaft 2 (the upper end in FIG. 1).
One of the ball bearings 6 is attached to the vicinity. Also,
An annular support ring 16 is mounted on the inner peripheral surface of the other end (the lower end in FIG. 1) of the yoke 12, and the annular support ring 16 and the vicinity of the other end of the stationary shaft 2 (the lower end in FIG. 1). The other ball bearing 8 is mounted between them. For example, the hub body 10 is formed from a non-magnetic material aluminum,
The yoke 12 is formed from a magnetic material, iron.

An annular flange 18 is provided at the lower end of the hub body 10 so as to protrude outward in the radial direction. A magnetic disk (not shown) such as a hard disk as a recording disk is provided on the upper surface of the annular flange 18. A plurality of sheets are placed via spacers (not shown). An annular rotor magnet 20 is mounted on an axially intermediate portion of the yoke 12, that is, on an inner peripheral surface of a portion between the pair of ball bearings 6 and 8.
A stator 22 is provided to face the rotor magnet 20. The stator 22 has a stator core 24 formed by laminating a plurality of core plates, and a coil 26 wound around the stator core 24 as required. That is, it is fixed to a portion between the pair of ball bearings 6 and 8. With this configuration, when a driving current is supplied to the coil 24, the stator core 24 is excited, and the mutual magnetic action between the excited stator core 24 and the rotor magnet 20 causes the rotor hub 4 (and the magnetic disk mounted on the rotor hub 4). ) Is driven to rotate in a predetermined direction.

In this spindle motor, a labyrinth seal means 28 is disposed outside (the lower side in FIG. 1) the other ball bearing 10 in the axial direction of the motor.
The labyrinth seal means 28 has a labyrinth member 30 disposed axially outside the other ball bearing 8.
The labyrinth member 30 is fixed to the other end of the stationary shaft 2, extends radially outward beyond the ball bearing 8, and has an annular portion protruding axially inward toward the support ring 16 on the outer peripheral portion thereof. A protrusion 32 is provided. The labyrinth means 28 includes an annular recess 34 provided on the outer surface of the support ring 16 and an inner flange 36 provided on the inner periphery thereof. The annular projection 32 of the labyrinth member 30 is received in the annular recess 34 of the support ring 16, and the inner flange 36 extends radially inward between the ball bearing 8 and the labyrinth member 30 toward the stationary shaft 2. I have. With this configuration, the labyrinth member 30 and the support ring 16 cooperate with each other to define a labyrinth passage, and the labyrinth means 28 prevents grease and the like from the ball bearings 8 from scattering outside. can do.

A magnetic fluid sealing means 40 is provided outside one of the ball bearings 6 (upper side in FIG. 1) in the axial direction of the motor. Magnetic fluid sealing means 40
Is an annular holding magnet 42 and a pair of pole pieces 44, 4 provided on both end surfaces of the holding magnet 42.
6 and an annular holder 48 for holding them, and the pair of pole pieces 44, 46 project radially outward beyond the holding magnet 42. In this embodiment, an annular holder 48 is mounted on the stationary shaft 2, and a magnetic fluid 47 is filled between one pole piece 44 and the yoke 14 (see FIG. 2). The magnetic fluid sealing means 40 and the configuration related thereto will be described later in detail.

A cap member 50 is disposed further outside the magnetic fluid sealing means 40 in the axial direction of the motor. The cap member 54 is formed of an annular thin plate, the outer peripheral portion of which is attached to the inner peripheral portion of the hub body 10 by an adhesive, and the inner peripheral portion extends to near the outer peripheral surface of the stationary shaft 2, and the magnetic fluid sealing means 40 outside. As shown in FIG. 1, an annular space exists between the cap member 50 and the magnetic fluid sealing means 40, and even if the magnetic fluid 47 of the magnetic fluid sealing means 40 scatters, Is trapped in this annular space, and the magnetic fluid 47 can be prevented from flying outside.

Next, referring mainly to FIG. 2, the magnetic fluid sealing means 40 and its related structure will be described. The annular holder 48 of the illustrated magnetic fluid sealing means 40 has a substantially L-shaped cross section, and has an annular portion 52 and a support portion 54 provided at the lower end of the annular portion 52. Project radially outward. This annular holder 48 is formed from a non-magnetic material. Inner pole piece 46, holding magnet 42 and outer pole piece 4
4 are mounted so as to be placed on the support portion 54 of the annular holder 48 in this order. One end of the stationary shaft 2 has a somewhat smaller outer diameter than the other portions, and thus, a shoulder 56 is formed at one end thereof. Annular holder 4
8 is mounted on the stationary shaft 2 such that the support portion 54 comes into contact with the shoulder 56 of the stationary shaft 2, and the magnetic fluid sealing means 40 is attached to the stationary shaft 2 by mounting in this manner. An adhesive 58 is applied over the inner peripheral portions of the stationary shaft 2, the annular holder 48 and the outer pole piece 44,
These are securely fixed by the adhesive 58.

In this embodiment, the outer pole piece 4
4. In other words, corresponding to the pole piece 44 filled with the magnetic fluid 47, the annular step 6 is formed on the inner peripheral surface of the rotor hub 4, in this embodiment, the inner peripheral surface of the annular support projection 14 of the yoke 12.
0 is formed. The annular step portion 60 is formed by making the inner diameter of one end of the annular support projection 14 somewhat larger than that of the other portion, and radially opposes the outer peripheral surface of the pole piece 44 in which the magnetic fluid 47 is held. Peripheral surface 64
And an annular bottom surface 62 facing the outer periphery of the pole piece 44 in the axial direction.
Are continuously formed.

In connection with the step portion 60, the structure is further as follows. The outer diameter of the outer pole piece 44 is set larger than the inner diameter of the bottom surface 62 of the annular stepped portion 60 and smaller than the outer diameter of the bottom surface 62 (see FIG. 2). Since it is set as above, the outer pole piece 4
The outer peripheral end of 4 extends into the annular stepped portion 60, and the inner end surface thereof is positioned so as to be opposed to the bottom surface 62 of the stepped portion 60 at an interval in the axial direction. And pole piece 4
The gap between the inner end face of the step 4 and the bottom surface 62 of the step 60 is smaller than the gap between the outer peripheral surface of the pole piece 44 and the peripheral surface 64 of the step 60. Further, the outer peripheral portion of the inner pole piece 46 extends to the vicinity of the inner peripheral surface of the annular support protrusion 14 on the inner side in the axial direction of the step portion 60. The holding magnet 42 is magnetized in the axial direction, for example, the outer pole piece 4.
4 is magnetized to the N pole (or S pole), and the side contacting the inner pole piece 46 is magnetized to the S pole (or N pole). With this configuration, the magnetic flux from the holding magnet 42 flows through the outer pole piece 44, and most of the magnetic flux passes from the inner end surface of the pole piece 44 through the bottom surface 62 of the step portion 60 of the yoke 12 And a part of the remaining magnetic flux from the outer peripheral surface of the pole piece 44 to the yoke 12 through the peripheral surface 64 of the step 60, and these magnetic fluxes pass from the yoke 12 through the inner pole piece 46 to the holding magnet 42. And the magnetic fluid sealing means 4
With respect to 0, such a magnetic flux flow magnetic circuit is formed.

The magnetic fluid 47 of the magnetic fluid sealing means 40
Is a step portion 60 between the outer pole piece 44 and the yoke 12.
Is filled in the gap. When the magnetic fluid 47 is filled in this way, most of the magnetic flux flows through between the pole piece 44 and the bottom surface 62 of the step portion 60 of the yoke 12, so that the filled magnetic fluid 47 becomes, as shown in FIG. Mainly, it is magnetically held between the outer peripheral portion of the inner end surface of the pole piece 44 and the bottom surface 62 of the step portion 60. When the magnetic fluid 47 is held between the outer peripheral surface of the pole piece 44 and the inner peripheral surface of the yoke 12, the pole piece 44
Is thin, the width of the seal layer of the magnetic fluid 47 is also small, and it is difficult to secure a sufficient sealing force. On the other hand, when the magnetic fluid 47 is held between the inner end surface of the pole piece 44 and the bottom surface 62 of the step portion 60 as described above, as understood from FIG. Outer peripheral portion of inner end face and bottom surface 62 of stepped portion 60
The magnetic fluid 4
7, the width of the seal layer can be increased, and thereby a sufficient sealing force can be obtained.

In addition, with this configuration,
It is possible to prevent a reduction in sealing force when the rotor hub 4 rotates. That is, when the rotor hub 4 rotates, the magnetic fluid 47 tends to flow radially outward due to centrifugal force.
Extends continuously from the bottom surface 62 in the axial direction, so that even if the magnetic fluid 47 flows radially outward along the bottom surface 62 of the step portion 60, the outer surface of the magnetic fluid 47 To the magnetic fluid 47.
Is mainly the pole piece 44 and the bottom surface 6 of the step portion 60.
2 is held. In particular, particles having a large specific gravity, ie, iron particles, contained in the magnetic fluid 47 tend to flow due to centrifugal force.
As a result, the flow of the iron particles in the magnetic fluid 47 is suppressed, and the flow of the iron particles in the magnetic fluid 47 is suppressed.

When the rotor hub 4 rotates at high speed, the generated centrifugal force also increases, and the magnetic fluid 47
May flow somewhat axially outward along the peripheral surface 64 of the lens. In such a case, in order to prevent the magnetic fluid 47 flowing outward in the axial direction from flowing out, the magnetic fluid 47 can be configured as shown in FIG. 3, for example. In the following description, members that are substantially the same as those in FIGS. 1 and 2 are given the same numbers, and descriptions thereof are omitted.

Referring to FIG. 3, in the second embodiment, pole piece 4 outside magnetic fluid sealing means 40A is provided.
The outer peripheral surface of 4A has an axial direction (vertical direction in FIG. 3).
A taper 72 is provided which is inclined radially outward toward the inside. The magnetic fluid sealing means 40A is provided to face the hub main body 10A of the rotor hub 4A, and the hub main body 10A is made of a nonmagnetic material such as aluminum. When the portion facing the magnetic fluid sealing means 40A is made of a non-magnetic material as described above, a sleeve member 74 made of a magnetic material is attached to a predetermined portion of the hub body 10A. Also, the sleeve member 74
An annular step 76 is provided at a predetermined position corresponding to the outer pole piece 44A, and the annular step 76 has a continuously formed bottom surface 78 and a peripheral surface 80. Other configurations of this embodiment are substantially the same as those of the first embodiment shown in FIGS.

In the second embodiment, the configuration of the outer pole piece 44A and the annular stepped portion 76 of the sleeve member 74 is substantially the same as that of the first embodiment. Is the sleeve member 74
, And the outer peripheral portion of the inner end face thereof is located opposite the bottom surface 78 of the stepped portion 76, and the pole piece 44.
A distance between the inner end surface of the pole piece 44A and the bottom surface 78 of the stepped portion 76 is determined by the outer peripheral surface of the pole piece 44A and the
It is set smaller than the interval with 0. The outer peripheral portion of the inner pole piece 46 extends to the vicinity of the inner peripheral surface of the sleeve member 74 on the inner side in the axial direction of the stepped portion 76. With this configuration, the holding magnet 4
2 flows through the outer pole piece 44A, and most of the magnetic flux passes from the inner end face of the pole piece 44A through the bottom surface 78 of the step portion 76 of the sleeve member 74 to the yoke 1A.
Flow to 2.

In the second embodiment, most of the magnetic flux from the holding magnet 42 flows between the pole piece 44A and the bottom surface 78 of the step portion 76 of the sleeve member 74. The outer peripheral portion of the inner end surface of the piece 44A and the bottom surface 78 of the stepped portion 76
, And the same effect as described above is achieved. In addition, the rotor hub 4 rotates to rotate the magnetic fluid 47.
Even if the fluid flows radially outward due to the centrifugal force, the peripheral surface 80 of the stepped portion 76 continuously extends in the axial direction from the bottom surface 78, so that the flowed magnetic fluid 47
Radially outward flow is prevented by the peripheral surface 80 of
The magnetic fluid 47 is mainly held between the pole piece 44A and the bottom surface 78 of the stepped portion 76.

When the rotor hub 4A rotates at a high speed,
The generated centrifugal force also increases, and the magnetic fluid 47 tends to flow outward in the axial direction along the peripheral surface 80 of the annular stepped portion 76 as shown in FIG. In such a case, a part of the magnetic fluid 47 is held between the outer peripheral surface of the pole piece 44A and the peripheral surface 80 of the stepped portion 76,
Due to the taper 72 of the pole piece 44A, the gap between the outer peripheral surface and the peripheral surface 80 of the annular step portion 76 is received inward in the axial direction and is gradually reduced. The force to do so acts,
Thereby, the outflow of the magnetic fluid 47 to the outside can be effectively prevented. The force due to this surface tension is
When the rotation of the rotor 4A stops, the magnetic fluid 47 acts to return to the original sealing state, and thus a stable seal can be secured for a long period of time.

In the first and second embodiments, the magnetic fluid sealing means 40 (40A) is attached to the stationary shaft 2. Instead, as shown in FIGS. 4 and 5, the magnetic fluid sealing means 40 (40A) is attached to the rotor hub. It may be.

Referring to FIG. 4 showing a part of a third embodiment of the spindle motor, in this embodiment, the magnetic fluid sealing means 102 includes an annular holding magnet 104 and two end faces of the holding magnet 104. It has a pair of pole pieces 106, 108 provided and an annular holder 110 for holding them, and their basic configuration is the magnetic fluid sealing means 40 (40) in the first and second embodiments.
Substantially the same as A). The magnetic fluid sealing means 102 in this embodiment further includes an annular filling member 111, which is radially inside the holding magnet 104 and has a pair of pole pieces 106 and 108.
It is provided between them. The filling member 111 is formed from a non-magnetic material, for example, a non-magnetic metal or a synthetic resin. With this configuration, the filling member 111 is located at the corner between the outer pole piece 106 and the holding magnet 104, and prevents the magnetic fluid 117 from being magnetically held on the surface of the holding magnet 104.

The magnetic fluid sealing means 102 is mounted on, for example, a hub body 112 (or yoke) of a rotor hub.
A shoulder 114 is formed at a predetermined portion of the hub body 112,
The magnetic fluid sealing means 102 is mounted on the hub body 112 so that the annular holder 110 abuts on the shoulder 114,
It is fixed to the hub body 112 by the adhesive 116. In this connection, an annular step 120 is provided at one end of the stationary shaft 118 corresponding to the pole piece 106 outside the magnetic fluid sealing means 102. The annular step portion 120 is formed by making the outer diameter of one end of the stationary shaft 118 somewhat smaller than the other portion, and has a circumferential surface 124 radially opposed to the outer circumferential surface of the pole piece 106;
An inner peripheral portion of the pole piece 106 has an annular bottom surface 122 opposed in the axial direction.
Are continuously formed.

In connection with the annular step 120,
It is configured as follows. The inside diameter of the outer pole piece 106 in which the magnetic fluid 117 is held is set to be larger than the inside diameter of the bottom surface 122 of the annular step 120 and smaller than the outside diameter. Because of this setting, the inner peripheral end of the outer pole piece 106 extends into the annular step 120 of the stationary shaft 118, and the inner end face thereof faces the step 12.
0 is located opposite the bottom surface 122. Then, the inner end surface of the pole piece 106 and the bottom surface 122 of the step portion 120 are formed.
Is set smaller than the interval between the inner peripheral surface of the pole piece 106 and the peripheral surface 124 of the step portion 120. Further, the inner peripheral portion of the inner pole piece 108 is located on the inner side of the stationary portion 1 in the axial direction of the step portion 120.
18 extend to the vicinity of the outer peripheral surface. The holding magnet 104 is magnetized in the axial direction in the same manner as described above. With this configuration, also in the third embodiment, the magnetic flux from the holding magnet 104 flows through the outer pole piece 106, and most of the magnetic flux flows from the inner end face of the pole piece 106 to the bottom surface of the step 120. The magnetic flux from the stationary shaft 118 passes through the inner pole piece 108 to the holding magnet 104 through the stationary shaft 118. Accordingly, as shown in FIG. 4, the magnetic fluid 117 filled in the gap between the outer pole piece 106 and the annular step 120 of the stationary shaft 118 mainly includes the inner peripheral portion of the inner end face of the pole piece 106 The sealing layer width of the magnetic fluid 47 is increased by magnetically held between the bottom surface 122 of the step portion 120 and the overlapping portion between the inner end surface of the pole piece 106 and the bottom surface 122 of the step portion 120. And a sufficient sealing force can be obtained.

In addition, with this configuration,
When the hub body 112 rotates, the magnetic fluid 117 tends to flow radially outward due to centrifugal force. However, the inner peripheral surface of the filling member 111 is continuously moved in the axial direction from the inner end surface of the pole piece 106 (FIG. 4). When the magnetic fluid 117 flows along the inner end surface of the pole piece 108 to the filling member 111, the magnetic fluid 117 is prevented from flowing outward in the radial direction by the filling member 111. The outflow of the fluid 117 to the outside is prevented, and the magnetic fluid 117 is mainly
Is held between the inner end face and the bottom surface 122 of the step 120, and the same effects as described above are achieved.

When the magnetic fluid sealing means 102 is mounted on the rotor hub, the same taper as described above is applied to the stationary shaft 11 so that the flowing magnetic fluid 117 returns to the original sealing state.
8 can be formed. That is, by forming a taper inclining radially inward toward the axial direction on the outer peripheral surface of the stationary shaft 118 facing the carpet member 111 of the magnetic fluid sealing means 102, the same as described above. The effect is achieved.

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

For example, in the illustrated embodiment, the holding magnet 42 and a pair of pole pieces 44, 46 on both sides thereof are provided.
The present invention has been described by applying the present invention to a spindle motor having a magnetic fluid sealing means 40 having a magnetic fluid sealing means having the magnetic fluid sealing means provided with a pole piece on one end surface of a holding magnet. Can be applied to

Further, for example, in the illustrated embodiment, the description has been made by applying the present invention to a spindle motor in which the magnetic fluid sealing means 40 is provided outside one of the ball bearings 6. However, the present invention is not limited to this. The present invention can be similarly applied to a case where a magnetic fluid sealing means is provided outside the bearing 8.

According to the spindle motor of the first aspect of the present invention, the magnetic fluid is mainly held magnetically between the bottom surface of the annular step portion of the rotor hub and the pole piece.
The sealing performance can be improved by increasing the sealing width by the magnetic fluid. Further, since the peripheral surface of the step portion of the rotor hub prevents the magnetic fluid from flowing outward in the radial direction, a stable sealing force can be obtained.

According to the spindle motor of the second aspect of the present invention, the outer peripheral portion of the pole piece is axially opposed to the bottom surface of the annular step portion and is spaced apart from the bottom surface of the annular step portion. Can be held.

According to the spindle motor of the third aspect of the present invention, most of the magnetic flux from the holding magnet flows between the pole piece and the bottom surface of the annular step, and the magnetic fluid is mainly used as the magnetic fluid. Magnetically held in the gap.

According to the spindle motor of the fourth aspect of the present invention, the magnetic fluid flowing between the outer peripheral surface of the pole piece and the peripheral surface of the step portion of the rotor hub returns to the original sealed state by surface tension. An effort is exerted to suppress the outflow of the magnetic fluid, and a stable seal can be obtained for a long period of time.

According to the spindle motor of the fifth aspect of the present invention, the magnetic fluid is mainly held magnetically between the bottom surface of the annular step portion of the stationary shaft and the pole piece. The sealing performance can be improved by increasing the width. Further, since the inner peripheral surface of the filling member of the magnetic fluid sealing means prevents the magnetic fluid from flowing outward in the radial direction, a stable sealing force can be obtained.

According to the spindle motor of the present invention, the inner peripheral portion of the pole piece overlaps the bottom surface of the annular step portion so as to be opposed to the bottom surface of the annular step portion in the axial direction with a gap therebetween. Can hold a magnetic fluid.

Further, according to the spindle motor of the present invention, most of the magnetic flux from the holding magnet flows between the pole piece and the bottom surface of the annular step, and the magnetic fluid mainly becomes Magnetically held in the gap.

Further, according to the spindle motor of the present invention, the magnetic fluid flowing between the inner peripheral surface of the filling member and the outer peripheral surface of the stationary shaft returns to the original sealed state by surface tension. An effort is exerted to suppress the outflow of the magnetic fluid, and a stable seal can be obtained for a long period of time.

[Brief description of the drawings]

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

FIG. 2 is a partially enlarged sectional view showing a magnetic fluid sealing means and its vicinity in the spindle motor of FIG. 1 in an enlarged manner.

FIG. 3 is a partially enlarged sectional view showing a magnetic fluid sealing means and its vicinity in a second embodiment of the spindle motor according to the present invention;

FIG. 4 is a partially enlarged sectional view showing a magnetic fluid sealing means and its vicinity in a third embodiment of a spindle motor according to the present invention;

FIG. 5 is a partially enlarged sectional view showing a part of a conventional spindle motor in an enlarged manner.

[Explanation of symbols]

 2,118 Static shaft 4,4A Rotor hub 6,8 Ball bearing 10,10A, 112 Hub main body 12 Yoke 20 Rotor magnet 22 Stator 40,40A, 102 Magnetic fluid sealing means 42,104 Holding magnet 44,46,44A, 106, 108 Pole piece 47,117 Magnetic fluid 48,110 Annular holder 60,76,120 Step 72 Taper 74 Sleeve member 111 Filling member

Claims (8)

[Claims] 1. A stationary shaft, a rotor hub rotatably supported on the stationary shaft via bearing means, a rotor magnet mounted on the rotor hub, and a stator disposed to face the rotor magnet. A spindle motor comprising magnetic fluid sealing means for sealing a gap between the stationary shaft and the rotor hub, wherein the magnetic fluid sealing means is supported by the stationary shaft and closes a gap between the stationary shaft and the rotor hub. A magnetic fluid for sealing, a holding magnet for magnetically holding the magnetic fluid, and a pole piece provided on one end surface of the holding magnet, and an outer peripheral portion of the pole piece is provided with the holding magnet. Projecting radially outward beyond, and the magnetic fluid is filled between the outer peripheral portion of the pole piece and the rotor hub, The rotor hub has a peripheral surface radially opposed to the outer peripheral surface of the pole piece and an annular bottom surface axially opposed to the outer peripheral portion of the pole piece corresponding to the pole piece of the magnetic fluid sealing means. An annular step portion is formed, and most of the magnetic flux from the holding magnet of the magnetic fluid sealing means flows between the pole piece and the bottom surface of the step portion, and a peripheral surface of the step portion. A spindle motor for preventing a magnetic fluid from flowing radially outward due to centrifugal force, wherein the magnetic fluid is mainly held between the bottom surface of the step portion and the pole piece. 2. The spindle motor according to claim 1, wherein an outer diameter of the pole piece is set to be larger than an inner diameter of the bottom surface of the step portion and smaller than an outer diameter of the bottom surface. 3. A gap between the pole piece and the bottom surface of the step portion is set to be smaller than a gap between an outer peripheral surface of the pole piece and the peripheral surface of the step portion. The spindle motor according to claim 1 or 2, wherein: 4. A taper which is formed on an outer peripheral surface of the pole piece of the magnetic fluid sealing means and is inclined inward in an axial direction and outward in a radial direction. The spindle motor according to any one of the above. 5. A stationary shaft, a rotor hub rotatably supported on the stationary shaft via bearing means, a rotor magnet mounted on the rotor hub, and a stator disposed to face the rotor magnet. A spindle motor comprising magnetic fluid sealing means for sealing a gap between the stationary shaft and the rotor hub, wherein the magnetic fluid sealing means is supported by the rotor hub;
A magnetic fluid for sealing a gap between the stationary shaft and the rotor hub, a holding magnet for magnetically holding the magnetic fluid, a pole piece provided on one end surface of the holding magnet, and the holding magnet And a filling member provided at a corner of the pole piece, wherein an inner peripheral portion of the pole piece projects radially inward beyond the filling member, and the magnetic fluid is an inner peripheral portion of the pole piece. A portion between the stationary shaft and the stationary shaft, wherein the stationary shaft has a peripheral surface radially opposed to an inner peripheral surface of the pole piece corresponding to the pole piece of the magnetic fluid sealing means and the pole. An annular step is formed on the inner periphery of the piece so as to continuously form an annular bottom surface facing in the axial direction, and most of the magnetic flux from the holding magnet of the magnetic fluid sealing means is supplied to the port. Flow between the tool piece and the bottom surface of the step portion, the inner peripheral surface of the filling member prevents the magnetic fluid from flowing radially outward due to centrifugal force, and the magnetic fluid is mainly provided in the step portion. A spindle motor held between the bottom surface and the pole piece. 6. The spindle motor according to claim 5, wherein an inner diameter of the pole piece is set to be larger than an inner diameter of the bottom surface of the step portion and smaller than an outer diameter of the bottom surface. 7. A gap between the pole piece and the bottom surface of the step portion is set to be smaller than a gap between an inner peripheral surface of the pole piece and the peripheral surface of the step portion. 7. The spindle motor according to claim 5, wherein: 8. A taper is formed on an outer peripheral surface of the stationary shaft of the magnetic fluid sealing means facing the filling member, the taper being inclined radially inward toward the inside in the axial direction. A spindle motor according to any one of claims 5 to 7.