JPH084751A - Dynamic pressure bearing device - Google Patents

Abstract

PURPOSE:To reliably prevent outside leakage of magnetic fluid by constituting so that a shaft directional magnetic flux density gradient of a space between a magnetic substance, magnetic members and a magnet becomes a unidirectional magnetic flux density gradient to increase toward the bearing side in a dynamic pressure bearing device using the magnetic fluid as lubricating oil. CONSTITUTION:In a dynamic pressure bearing device where magnetic fluid 14 is filled in slidingly movable parts 2 of radial bearings 2 to support a rotary member 3, a magnet 30 magnetized in the shaft direction is arranged in a fixing member 1a on the opening side close to the bearings 2, and magnetic members 31 and 32 are respectively arranged on both opposed end surfaces of the magnet 30. The other rotary member 3 opposed to the magnetic members 31 and 32 and the magnet 30 is formed of a magnetic substance, and by a magnetic circuit formed of the magnetic substance 3, the magnetic members 31 and 32 and the magnet 30, a shaft directional magnetic flux density gradient of a space between the magnetic substance 3, the magnetic member 31 and the magnet 30 is formed so as to have a unidirectional magnetic flux density gradient to increase toward the bearing side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic pressure bearing device, and more particularly to a dynamic pressure bearing device using magnetic fluid as lubricating oil.

[0002]

2. Description of the Related Art Proposals for a dynamic pressure bearing device using a magnetic fluid as a lubricating oil have been made, for example, in Japanese Unexamined Patent Publication No. 62-155327 and Japanese Utility Model Laid-Open No. 62-202526.
FIG. 8 shows an example of a spindle motor for an HDD to which this dynamic pressure bearing device is applied. This spindle motor is a so-called center shaft rotating type and a radial bearing fixed type, and in order to avoid complication of the drawing, only the right half of the center line is shown.

In the figure, reference numeral 1 denotes a frame as a motor housing which is a fixing member, and a cylindrical bearing holder portion 1a is integrally formed on the frame 1 so as to stand upright. That is, the bearing holder part 1
The frame 1 including a has a concave shape with one end closed and the other open. A stator core 6 is fixed to the outer peripheral surface of the bearing holder portion 1a, and a coil 5 is wound around the stator core 6.

Radial slide bearings 2 and 2 are fitted and fixed to the inner circumference of the bearing holder portion 1a, and a central shaft 3 as a rotary shaft is inserted and arranged in the inner circumference of the radial slide bearings 2 and 2. Has been done. At least one of the outer peripheral surface of the central shaft 3 and the inner peripheral surfaces of the radial slide bearings 2, 2 is formed with a dynamic pressure generating groove, such as a herringbone shape, for sliding portions (the central shaft 3 and the radial surface). The magnetic fluid 14 is filled in the space between the plain bearings 2 and 2. That is, the central shaft 3 is prevented from swinging in the radial direction due to the radial dynamic pressure generated between the central shaft 3 and the inner peripheral surfaces of the radial slide bearings 2 and 2, so that the center shaft 3 rotates in the radial slide bearings 2 and 2. There is.

A thrust plate 1b forming the bottom of the recess of the frame 1 is provided at a position facing the end surface 3a of the central shaft 3 on the frame closing side (downward in the figure). This thrust plate 1b and the end surface 3a of the central shaft 3 on the frame closing side
A dynamic pressure generating groove is formed on at least one of the
A magnetic fluid 14 is filled in the sliding portion (the space between the frame closing side end surface 3 a of the central shaft 3 and the upper end surface of the thrust plate 1 b facing the same). That is, a thrust dynamic pressure is generated between the end surface 3a of the central shaft 3 on the frame closing side and the upper end surface of the thrust plate 1b toward the frame opening side with respect to the central shaft 3.

Further, a magnetic attraction force is generated on the central shaft 3 toward the frame closing side with respect to the central shaft 3 by a known method for shifting the magnetic centers of the stator core 6 and the drive magnet 7. ing. Therefore, due to the magnetic attraction force and the thrust dynamic pressure, balance and shake in the thrust direction are suppressed, and the thrust plate 1b is rotated.

A hub 4 shaped so as to cover the core 6, the coil 5 and the like is fitted and fixed to the end of the central shaft 3 on the frame open side (upper side in the figure). A disc (not shown) is mounted on the outer peripheral surface of the hub 4.
A drive magnet 7 is provided at a position facing the core 6 on the inner circumference.
Has been fixed.

A magnetic fluid seal 8 is provided on the way of the passage 10 communicating the inside and outside of the bearing holder portion 1a, that is, at the upper end portion of the bearing holder 1a in the figure (a position above the radial slide bearing 2 on the frame opening side). Has been done. The magnetic fluid seal 8 is composed of a magnet 8b and pole pieces 8a, 8a which are provided so as to sandwich the magnet 8b in the axial direction and form a magnetic path. The magnetic fluid seal 8 is centered on the inner peripheral surfaces of the pole pieces 8a, 8a. The magnetic fluids 9 and 9 can be held between the shaft 3 and the outer peripheral surface thereof. Therefore,
This magnetic fluid seal 8 prevents leakage of the magnetic fluid 14 containing the magnetic fluid filled in the sliding portion and filling the inside of the holder portion 1a from the bearing portion to the outside, and It is intended to prevent dust and the like from entering the inside of the bearing section.

In order to prevent the magnetic fluid 14 from leaking to the frame opening side, as shown in FIG. 9, instead of the magnetic fluid seal 8, the frame opening side of the radial sliding bearing 2 is opened. A magnet 16 magnetized in the axial direction is arranged on the side end surface.
There is also a structure in which the magnetic fluid 14 is held by an open magnetic field of 6.

When a predetermined driving voltage is applied to the coil 5 from a power supply means (not shown) outside the motor through the flexible substrate 12, the hub 4 having the disk mounted thereon is rotated. The reference numeral 11 designates a bearing collar which is disposed so as to abut between the plain bearings 2 and 2.
Indicate the retaining of the central shaft 3, respectively.

[0011]

Here, in the above spindle motor for HDD, since a clean atmosphere is required, the leakage of the magnetic fluid 14 filled in the bearing holder portion 1a is caused. Prevention is an important point,
For example, even if vibration, impact, centrifugal force is applied, or the posture is changed, it is necessary to prevent leakage.

However, the liquid surface position of the magnetic fluid 14 filled in the bearing holder portion 1a is such that the volume change of the magnetic fluid (actually, the air mixed in the inside) due to the atmospheric pressure / temperature change, the component size / injection. When the liquid surface position of the magnetic fluid changes as described above due to variations in the amount of the magnetic fluid, the magnetic fluid leakage prevention structure shown in FIGS. However, there is a problem that the leakage of the magnetic fluid cannot be prevented.

Such a problem is not limited to the central shaft rotating type motor having one end closed and the other being open, and similarly occurs in the central shaft fixed type motor having both open ends. To do.

Therefore, an object of the present invention is to provide a dynamic pressure bearing device in which leakage of magnetic fluid to the outside can be reliably prevented.

[0015]

To achieve the above object, the dynamic pressure bearing device of the first means is a radial bearing which is fixed to either a fixed member or a rotating member and rotatably supports the rotating member. In a dynamic pressure bearing device configured to generate a dynamic pressure in the magnetic fluid filled in the sliding portion of the radial bearing, one of the fixed member or the rotating member on the open side of the radial bearing, A magnet magnetized in the axial direction is provided, and a first magnetic member is provided on the bearing-side end surface of the magnet and a second magnetic member is provided on the open-side end surface.
Magnetic members are provided respectively, and the other rotating member or fixed member facing in the radial direction of the first and second magnetic members and the magnet is a magnetic body, and the magnetic body, the first and second magnetic members, and A magnetic circuit formed by a magnet, the magnetic body and the first magnetic member,
The magnetic flux density gradient in the axial direction of the space between the magnet and the magnet is a unidirectional magnetic flux density gradient increasing toward the bearing side.

In order to achieve the above-mentioned object, the dynamic pressure bearing device of the second means has, in addition to the above-mentioned first means, one of the facing surfaces of the first magnetic member or the magnetic body and the other facing surface. On the other hand, it is inclined in a direction approaching toward the bearing side.

In order to achieve the above-mentioned object, the dynamic pressure bearing device of the third means, in addition to the above-mentioned first means, adjusts the mutual gap between the first and second magnetic members and the magnetic substance to make the magnetic substance. The axial magnetic flux density gradient of the space between the first magnetic member, the magnet, and the second magnetic member is a one-way magnetic flux density gradient increasing toward the bearing side.

In order to achieve the above object, the dynamic pressure bearing device of the fourth means is provided with a means for communicating the inside and the outside with the second magnetic member in addition to the first or third means.

[0019]

According to the hydrodynamic bearing device of the first and third means, the magnetic fluid is changed due to, for example, volume change of the magnetic fluid due to change of atmospheric pressure and temperature, variation of parts size and amount of injected magnetic fluid. Even if the liquid surface position of is changed, the magnetic fluid is favorably held by the magnetic force due to the one-way magnetic flux density gradient increasing toward the bearing side. Also, for example,
Even if an impact / centrifugal force is applied or the posture changes, the magnetic fluid due to the one-way magnetic flux density gradient pulls back the magnetic fluid that is about to leak. In particular, in the hydrodynamic bearing device of the first means, the magnetic fluid is held between the magnetic body and the second magnetic member, and functions as a magnetic fluid seal for sealing.

According to the dynamic pressure bearing device of the second means, the direction in which the facing surface of either the first magnetic member or the magnetic body approaches the bearing surface of the other facing surface. When inclined to, the magnetic flux density gradient in the axial direction of the space between the magnetic body, the first magnetic member, and the magnet becomes
The unidirectional magnetic flux density gradient is increased toward the bearing side.

According to the hydrodynamic bearing device of the fourth means, air may accumulate in the space surrounded by the first and second magnetic members, the magnet, and the magnetic material.
This air is released to the outside by the inside / outside communication means provided in the second magnetic member.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a spindle motor for a HDD, for example, a center shaft rotating type and a fixed radial bearing type, to which a dynamic pressure bearing device according to a first embodiment of the present invention is applied, FIG.
1 is an enlarged view of a main part of FIG. 1, and FIG. 1B is a magnetic flux density distribution diagram of a space between the magnetic body and the first and second magnetic members and the magnet in FIG. The same reference numerals are attached to the same components and those having the same functions, and description thereof will be omitted here to avoid duplication.

In the first embodiment, the central shaft 3 is made of a magnetic material, and the radial slide bearing 2 on the frame opening side is provided.
An annular magnet 30 magnetized in the axial direction is arranged on the more open side. The first magnetic member 31 is provided on the bearing side end surface 30 a of the magnet 30, and the open side end surface 3 is provided.
0b has its inner peripheral surface approaching the outer peripheral surface of the central shaft 3
The magnetic members 32 are disposed respectively, and the non-magnetic member 33 is disposed between the first magnetic member 31 and the radial slide bearing 2 on the frame opening side. The first and second magnetic members 31, 32, the magnet 30, and the non-magnetic member 33 are fitted and fixed to the inner peripheral surface of the bearing holder portion 1a, and the inner peripheral surface of each member with respect to the central axis 3 is fixed. Have been contacted.

Therefore, the first and second magnetic members 31, 32
2A by the magnet 30, the magnet 30 and the central shaft 3.
The magnetic circuit shown in is formed.

The facing surface (inner peripheral surface) 31a of the first magnetic member 31 facing the central axis 3 faces the bearing side (opposite to the open side; downward in the figure) with respect to the outer peripheral surface of the central axis 3. It is an inclined surface that is approaching.

When the inclined surface 31a as described above is formed on the first magnetic member 31, the space between the central shaft 3 and the first magnetic member 31 and the magnet 30 (the central shaft 3, the first magnetic member 31) is formed. , Second magnetic members 31, 32, magnet 30
The magnetic flux density gradient in the axial direction of the space surrounded by
As shown in FIG. 2B, the unidirectional magnetic flux density gradient increases toward the bearing side. In addition, the magnetic flux density of the space between the central axis 3 and the second magnetic member 32 is as shown in FIG.
As shown in (b), the magnetic fluid 14 is retained between the central shaft 3 and the second magnetic member 32 because it becomes larger in a convex shape.

As described above, in the first embodiment, the magnetic circuit is formed by the first and second magnetic members 31 and 32, the magnet 30 and the central shaft 3, and the central shaft 3 of the first magnetic member 31 is formed. The facing surface 31a against the outer peripheral surface of the central shaft 3 so as to approach the bearing side with respect to the outer peripheral surface of the central shaft 3, and the magnetic flux in the axial direction of the space between the central shaft 3 and the first magnetic member 31 and the magnet 30. Since the density gradient is a one-way magnetic flux density gradient increasing toward the bearing side, for example, due to volume change of the magnetic fluid 14 due to atmospheric pressure / temperature change, variation in component size / injection amount of the magnetic fluid 14,
Even if the liquid surface position of the magnetic fluid 14 changes, the magnetic fluid 14 can be satisfactorily held by the magnetic force due to the one-way magnetic flux density gradient increasing toward the bearing side. In addition, even if the magnetic fluid 14 moves in a leaking direction due to, for example, vibration, impact, centrifugal force, or change in posture,
Due to the magnetic force of the one-way magnetic flux density gradient, a relatively large one-way magnetic flux density gradient continues even at a position distant from the first magnetic member 31, so that the leaking magnetic fluid can be pulled back. Has become. Therefore, leakage of the magnetic fluid 14 to the outside can be reliably prevented.

Further, the magnetic fluid 14 can be held between the central shaft 3 and the second magnetic member 32, that is, it can function as a magnetic fluid seal for sealing. It is possible to prevent the magnetic fluid 14 from evaporating and deteriorating.

Incidentally, it is desirable that the one-way magnetic flux density gradient is long in the axial direction and has a steep gradient, and that the holding portion volume for holding the magnetic fluid is also large. Such desired one-way magnetic flux density gradient and magnetic fluid holding portion volume can be easily obtained by changing the inclination of the first magnetic member 31. In addition, in order to satisfy the above, in this embodiment, the axial length of the facing surface 31a of the first magnetic member 31 is 0.5 mm or more.

Further, in order to increase the magnetic flux density in the axial direction of the space between the central shaft 3 and the first magnetic member 31 and the magnet 30, the first magnetic member 31 and the radial slide bearing 2 on the frame open side are provided. Although the non-magnetic member 33 is provided between them, the non-magnetic member 33 may be omitted if the radial plain bearing 2 on the frame opening side is a non-magnetic material.

By the way, in the present embodiment, as described above, since the central shaft 3 and the second magnetic member 32 constitute a magnetic fluid seal for sealing, the magnetic fluid seal makes it possible to use the first magnetic fluid seal. Air may accumulate in the space surrounded by the second magnetic members 31 and 32, the magnet 30, and the central shaft 3. However, there is a problem in that the accumulation of air causes expansion due to the influence of atmospheric pressure, temperature, etc., and the seal pressure resistance decreases.

Therefore, in this embodiment, as shown in FIG.
As shown in FIG. 3, the second magnetic member 32 is provided with a through hole 32a as a means for communicating the inside and the outside, and the through hole 32a allows the accumulated air to escape to the outside. Has become. That is, the seal withstand pressure can be improved.

FIG. 3 is a cross-sectional view of a spindle motor for an HDD, for example, a fixed center shaft type and a radial bearing rotating type, to which a dynamic pressure bearing device according to a second embodiment of the present invention is applied. The same reference numerals are given to the same components and the components that perform the same functions as those described above, and the description thereof is omitted here to avoid duplication.

The motor according to the second embodiment is a fixed central shaft type motor in which the central shaft 22 made of a magnetic material is fixed together with the frame 21. Therefore, in order to prevent leakage of magnetic fluid from both open ends, The first and second magnetic members 31 and 32, the magnet 30 and the non-magnetic member 33 are arranged on the open side of the radial slide bearings 2 and 2, respectively. Further, in order to form a magnetic circuit similar to that of the first embodiment, a member 44 facing the lower first magnetic member 31 in the drawing.
(The hub 54 when the member 44 is not provided) is made of a magnetic material.

It goes without saying that even with this structure, the same effects as those of the first embodiment can be obtained.

FIG. 4 is a cross-sectional view of the main part of a dynamic pressure bearing device showing a third embodiment of the present invention. The difference between the hydrodynamic bearing device of the third embodiment and that of the first and second embodiments is that the first embodiment is different from the first embodiment.
A concave portion 31b is provided on the open side end surface of the magnetic member 31, and the bearing side portion of the magnet 30 is fitted and accommodated in the concave portion 31b.

It is needless to say that even with this structure, the same effects as those of the first and second embodiments can be obtained, and further, there is an advantage that the device can be made compact in the axial direction. .

A notch 32b is formed in the second magnetic member 32 so that the inside and the outside communicate with each other.
Air in the space surrounded by the second magnetic members 31 and 32, the magnet 30, and the central shaft 3 may be released to the outside to improve the seal withstand pressure.

FIG. 5 is a cross-sectional view of the essential parts of a hydrodynamic bearing device showing a fourth embodiment of the present invention. In the hydrodynamic bearing device of the fourth embodiment, the facing surface 41a of the first magnetic member 41 with respect to the central axis 3 is not an inclined surface, and is located at a position facing the first magnetic member 41. An annular magnetic body 35 is fixed to the outer periphery of the central shaft 3. First of this magnetic body 35
The facing surface (outer peripheral surface) 35a of the magnetic member 41 is an inclined surface that approaches the facing surface 41a of the first magnetic member 41 toward the bearing side (downward in the drawing).

Even with this structure, the magnetic body 35 and the first
Since the magnetic flux density gradient in the axial direction of the space between the magnetic member 41 and the magnet 30 can be made a one-way magnetic flux density gradient increasing toward the bearing side, the same effect as in the above embodiment can be obtained.

A gap 32c for communicating the inside and the outside is formed in the second magnetic member 32, and the gap 32c forms the first and second gaps.
Air in a space surrounded by the second magnetic members 41 and 32, the magnet 30, the central shaft 3, and the magnetic body 35 may be released to the outside to improve the seal withstand pressure.

Incidentally, the through hole 32a, the notch 32b,
The sizes of the gaps 32c are the through holes 32a and the notches 3
2b, the magnetic flux density in the gap 32c is set to be half or less of the maximum magnetic flux density between the first magnetic member and the central axis 3 and between the second magnetic member and the central axis 3. There is.

FIG. 6 shows a fifth embodiment of the present invention. (A) is a cross-sectional view of the main part of the hydrodynamic bearing device, (b) is the magnetic body (center axis) in (a). And the first and second magnetic members,
It is a magnetic flux density distribution map of the space between a magnet.

In the hydrodynamic bearing device of the fifth embodiment, the central shaft 3 and the first and second magnetic members 51 and 52 and the central shaft 3 are adjusted by adjusting the gap between them. The magnetic flux density gradient in the space between the second magnetic members 51 and 52 and the magnet 50 is as shown in FIG.
The unidirectional magnetic flux density gradient increases toward the bearing side.

Incidentally, the facing surface 51a of the first magnetic member 51 with respect to the central axis 3 and the central axis 3 of the second magnetic member 52.
The facing surface 52A with respect to is an inclined surface that approaches the outer peripheral surface of the central shaft 3 toward the bearing side.

Even by adjusting the gap as described above, the central shaft 3, the first and second magnetic members 51 and 52, and the magnet 5 are formed.
Since the magnetic flux density gradient in the axial direction of the space between 0 and 0 can be made a one-way magnetic flux density gradient increasing toward the bearing side,
It is possible to obtain the same effect as that of the above embodiment.

It should be noted that the opposed surface 51a of the first magnetic member 51 with respect to the central axis 3 is not inclined, but its axial thickness is reduced, and the second magnetic member 52 becomes the first magnetic member 51. Even if the gap is adjusted so as to approach each other, the central shaft 3, the first and second magnetic members 51 and 52, and the magnet 5
The axial magnetic flux density gradient of the space between 0 and 0 can be a one-way magnetic flux density gradient increasing toward the bearing side. Incidentally, in this case, the magnetic flux density of the space facing the first magnetic member 51 does not become gentle as shown in FIG. 6B but becomes slightly convex.

By the way, in this embodiment, as shown in FIG. 7, since the second magnetic member 52 is provided with the through hole 52a for communicating the inside and the outside, the first and second magnetic members 5 are formed.
Even if air collects in the space surrounded by the magnets 1, 52, the magnet 50, and the central shaft 3, the air can escape to the outside, and the pressure applied to the seal portion can be suppressed. Has become.

The through hole 52a may be replaced with the notch 52b and the gap 52c as shown in FIG.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say, for example, the first and second magnetic members, the magnet, and the non-magnetic member are fixed to the central shaft 3 as members facing them (the upper one in the drawing of the second embodiment is It may be fixed to the central shaft 22 or to the hub 54 in the case of the lower side in the drawing), and a member facing these may be a magnetic body.
Further, a magnetic body may be provided so as to face these existing positions.

Further, in the above embodiment, the dynamic pressure bearing device includes a central shaft rotating type and a radial bearing fixed type (shown in FIGS. 1, 2 and 4 to 7), a central shaft fixed type. Although an example applied to a radial bearing rotary type (shown in FIG. 3) spindle motor is described, a central shaft having a radial bearing outer peripheral surface as a sliding surface, a radial bearing rotary type, and a central shaft. Also, the present invention can be applied to a radial bearing fixed type spindle motor.

Further, in the above embodiment, an example in which the dynamic pressure bearing device is applied to a spindle motor for HDD is described, but it is also applicable to a motor for laser beam printer. The same can be applied to other motors.

[0053]

As described above, according to the dynamic pressure bearing device of the first, second and third inventions, for example, the volume change of the magnetic fluid due to the atmospheric pressure / temperature change and the size of the component / the magnetic fluid to be injected can be prevented. Even if the liquid surface position of the magnetic fluid changes due to variations in the amount and the like, the magnetic fluid is favorably held by the magnetic force due to the one-way magnetic flux density gradient increasing toward the bearing side. Also, for example, even if vibration, shock, centrifugal force is applied, or the posture changes, due to the magnetic force due to the one-way magnetic flux density gradient,
The magnetic fluid that is about to leak is pulled back. Therefore, it is possible to reliably prevent the magnetic fluid from leaking to the outside. Further, according to the hydrodynamic bearing device of the first invention, since the magnetic fluid is held between the magnetic body and the second magnetic member and functions as a magnetic fluid seal for sealing, the evaporation of the magnetic fluid inside the There is a new effect that alteration and the like can be prevented.

According to the dynamic pressure bearing device of the fourth invention,
Air may accumulate in the space surrounded by the first and second magnetic members, the magnet, and the magnetic body. This air is generated by the internal / external communication means provided in the second magnetic member.
Since it escapes to the outside, there is a new effect that the pressure resistance of the seal can be improved.

[Brief description of drawings]

FIG. 1 is a transverse cross-sectional view of a center shaft rotating type and radial bearing fixed type HDD motor to which a dynamic pressure bearing device according to a first embodiment of the present invention is applied.

2 (a) is an enlarged view of a main part of FIG. 1, (b) is (a).
FIG. 3 is a magnetic flux density distribution diagram of a space between a magnetic body therein, first and second magnetic members, and a magnet.

FIG. 3 is a cross-sectional view of a center shaft fixed type and radial bearing rotation type HDD motor to which a dynamic pressure bearing device according to a second embodiment of the present invention is applied.

FIG. 4 is a transverse cross-sectional view of a main part of a hydrodynamic bearing device showing a third embodiment of the present invention.

FIG. 5 is a cross-sectional view of a main part of a dynamic pressure bearing device showing a fourth embodiment of the present invention.

FIG. 6 shows a fifth embodiment of the present invention, (a)
[FIG. 4] is a transverse cross-sectional view of a main part of the dynamic pressure bearing device, and FIG. 6B is a magnetic flux density distribution diagram of a space between the magnetic body in FIG.

FIG. 7 is a transverse cross-sectional view of a main part of a hydrodynamic bearing device showing a sixth embodiment of the present invention.

FIG. 8 is a transverse cross-sectional view of a center shaft rotating type and radial bearing fixed type HDD motor to which a dynamic pressure bearing device according to the related art is applied.

9 is a transverse cross-sectional view showing another example of the magnetic fluid holding structure in FIG.

[Explanation of symbols]

1, 1a, 21, 22 Fixed member 2 Radial bearing 3, 54 Rotating member 14 Magnetic fluid 30, 50 Magnet 30a Magnet bearing side end surface 30b Magnet open side end surface 31, 41, 51 First magnetic member 31a, 41a, 51a First magnetic member facing surface 32,52 Second magnetic member 32a, 32b, 32c, 52a, 52b, 52c Inner / outer communication means 35,44 Magnetic body 35a Magnetic body facing surface

Claims (4)

[Claims] 1. A radial bearing fixed to either a fixed member or a rotating member for rotatably supporting the rotating member, wherein dynamic pressure is generated in a magnetic fluid filled in a sliding portion of the radial bearing. In the dynamic pressure bearing device configured to be tightened, an axially magnetized magnet is provided on either the fixed member or the rotating member on the open side of the radial bearing, and the first end is provided on the bearing side end surface of the magnet. And a second magnetic member on the end face on the open side, and the other rotating member or fixed member facing in the radial direction of the first and second magnetic members and the magnet is a magnetic body. Due to the magnetic circuit formed by the body, the first and second magnetic members, and the magnet, the space between the magnetic body and the first magnetic member and the magnet is reduced. Dynamic pressure bearing device, wherein a magnetic flux density gradient in the direction, and a one-way flux density gradient that increases toward the bearing side. 2. The dynamic pressure bearing device according to claim 1, wherein the facing surface of either the first magnetic member or the magnetic body is
A hydrodynamic bearing device that is inclined toward the bearing side with respect to the other facing surface. 3. The dynamic bearing device according to claim 1, wherein a gap between the first and second magnetic members and the magnetic body is adjusted to adjust the magnetic body and the first magnetic member, the magnet, and the second magnetic member. The magnetic flux density gradient in the axial direction of the space between the magnetic member and
A hydrodynamic bearing device having a unidirectional magnetic flux density gradient increasing toward the bearing side. 4. The hydrodynamic bearing device according to claim 1 or 3, wherein the second magnetic member is provided with means for communicating the inside and the outside.