JPH0874863A - Bearing device - Google Patents

Abstract

PURPOSE: To surely prevent the leakage of a magnetic fluid to the outside, reduce the contamination of the outer part, the generation of dust, and the outgassing, and eliminate the lack of the magnetic fluid in the inner part. CONSTITUTION: This bearing device has a radial bearing 2 fixed to either one of a fixed member and a rotating member to rotatably support the rotating member, and a magnetic fluid 14 filled in the sliding part of the bearing 2. A magnet 30 is provided on either one of the fixed member and the rotating member closer to the opening side from the radial bearing 2, and the other rotating member or fixed member opposed in the radial direction of the magnet is formed into a magnetic body 3. The magnetic flux density gradient in the axial direction of the space between the magnetic body 3 and the magnet 30 is set to a one-directional magnetic flux density gradient increased toward the reversed direction to the opening side by the magnetic circuit formed by the magnetic body 3 and the magnet 30, and a magnetic fluid leakage preventing plate 41 consisting of a nonmagnetic material the circumferential surface of which is adjacent to the magnetic body 3 is provided on the opening side from the magnet 30.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art A bearing device using a magnetic fluid as a lubricating oil has been proposed, for example, in Japanese Patent Application Laid-Open No. 62-155327 and Japanese Utility Model Laid-Open No. 62-202526. FIG. 13 shows an example of a spindle motor for HDD, to which this bearing device is applied. This spindle motor is of the so-called center axis rotation type, and only the right half of the center line is shown in order to avoid complication of the drawing.

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,
The magnetic fluid seal 8 prevents the magnetic fluid 14 filled in the holder 1a containing the magnetic fluid filling the sliding surface from leaking outward from the bearing portion and from the outside. It is designed to prevent dust from entering the bearing.

In order to prevent leakage of the magnetic fluid 14 to the frame opening side, as shown in FIG. 14, instead of the magnetic fluid seal 8, the frame opening of the radial sliding bearing 2 on the frame opening side is performed. 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. Especially when the device is transported by air,
Since the atmospheric pressure and the temperature change drastically, there is a high risk that the magnetic fluid 14 will leak out.

Further, for example, referring to FIG. 14, when the magnetic fluid 14 is about to leak out, a member (for example, a central shaft) in the passage 10 with which the magnetic fluid 14 about to leak out comes into contact. 3, the bearing holder portion 1a, etc.) has a high wettability with the magnetic fluid 14 (easy wetting), the magnetic fluid 14 that is about to leak out is not favorably attracted by the magnet 16, and the magnetic fluid 14 is adhered to the surface of the member. There is also a problem in that the residual gas remains, resulting in an increase in outgas and a shortage of magnetic fluid inside the bearing, resulting in a decrease in reliability.

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

Therefore, the present invention provides a bearing device in which leakage of the magnetic fluid to the outside can be reliably prevented, external pollution and dust generation and outgas can be reduced, and a shortage of the internal magnetic fluid can be eliminated. The purpose is to

[0016]

In order to achieve the above object, the 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 bearing device provided with a magnetic fluid filled in a sliding portion of a radial bearing, a magnet is provided on either the fixed member or the rotating member on the open side of the radial bearing, and the magnet is opposed in the radial direction. The other rotating member or fixed member is made of a magnetic body, and the magnetic circuit formed by this magnetic body and the magnet causes the magnetic flux density gradient in the axial direction of the space between the magnetic body and the magnet to be on the open side. A unidirectional magnetic flux density gradient increasing in the opposite direction is formed, and a peripheral surface of the magnetic body is made of a non-magnetic material on the opening side of the magnet. Formed by providing a magnetic fluid leakage prevention plate approaching.

In order to achieve the above object, in the bearing device of the second means, in addition to the above first means, at least one of the magnetic fluid leakage prevention plate and the magnetic body and at least the surface thereof are provided with a magnet and a magnetic fluid. The material is characterized in that the contact angle with the magnetic fluid is larger than the contact angle.

In order to achieve the above-mentioned object, the bearing device of the third means is, in addition to the above-mentioned first means, the magnetic fluid leakage prevention plate on the open side from the position where the magnetic fluid leakage prevention plate and the magnetic body face each other, and At least one side and at least the surface of the magnetic body are made of a material having a contact angle with the magnetic fluid larger than a contact angle between the magnet and the magnetic fluid.

In order to achieve the above object, the bearing device of the fourth means is, in addition to the above first, second or third means,
An oil absorbing material is provided on the opening side of the magnet in the passage communicating between the bearing portion and the outside.

[0020]

According to the bearing device in the first means, the liquid surface position of the magnetic fluid is changed due to, for example, a change in the volume of the magnetic fluid due to a change in atmospheric pressure and a temperature, a variation in component dimensions and the amount of the magnetic fluid to be injected. Even if it changes, the magnetic fluid is well retained by the magnetic force due to the unidirectional magnetic flux density gradient increasing in the opposite direction to the open side. Further, for example, even if vibration, shock, centrifugal force is applied or the posture is changed, the magnetic fluid that is about to leak is pulled back by the magnetic force due to the one-way magnetic flux density gradient. Further, even if the magnetic fluid should leak out against the attraction force due to the one-way magnetic flux density gradient, the magnetic fluid leakage prevention plate prevents the magnetic fluid from leaking out.

According to the bearing device in the second and third means, the material having a larger contact angle with the magnetic fluid than the contact angle between the magnet and the magnetic fluid is hard to be wetted by the magnetic fluid, which is unlikely to occur. Even if the magnetic fluid is about to leak, the magnetic fluid is repelled by the material and is returned to the original state by the attraction force of the one-way magnetic flux density gradient.

According to the bearing device in the fourth means, even if the magnetic fluid leaks against the attractive force due to the one-way magnetic flux density gradient, the leaked magnetic fluid can be quickly absorbed by the oil absorbing material. It is absorbed by and does not leak out.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a transverse cross-sectional view of a spindle motor for a center axis rotation type HDD, for example, to which a bearing device according to a first embodiment of the present invention is applied, and FIG. 2 is an enlarged view of a main part of FIG. 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.

In the first embodiment, the center shaft 3 and the radial sliding bearing 2 on the frame opening side are made of a magnetic material, and the radial sliding bearing 2 on the frame opening side is on the opening side, that is, the radial opening on the frame opening side. An annular magnet 30 magnetized in the radial direction is arranged on the end surface of the plain bearing 2 on the frame open side. The magnet 30 is held by the radial slide bearing 2 on the frame opening side and the holding member 40 made of a magnetic material fixedly arranged on the outer periphery of the magnet 30, and therefore,
A magnetic circuit is formed by the magnet 30, the central shaft 3, the radial slide bearing 2 on the frame opening side, and the holding member 40.

The surface (inner peripheral surface) 30a of the magnet 30 facing the central axis 3 is an inclined surface that approaches the outer peripheral surface of the central axis 3 in the opposite direction (downward in the drawing) to the open side. ing.

As described above, when the inclined surface 30a is formed on the magnet 30 and a magnetic circuit is formed between the magnet 30 and the central axis 3, the space between the magnet 30 and the central axis 3 and the frame of the magnet 30 are formed. The magnetic flux density distribution in the axial direction of the magnetic fluxes A and B (see FIG. 11) in the space near the open end face is as shown in FIG.

Here, in the present embodiment, the magnetic flux density gradient in the axial direction of the space between the magnet 30 and the central axis 3 takes the range of the section X shown in FIG. That is, the magnetic flux density gradient in the axial direction in the space between the magnet 30 and the central axis 3 is a one-way magnetic flux density gradient that increases in the opposite direction to the open side.

As described above, in the first embodiment, the magnetic circuit formed by the magnet 30, the central shaft 3, the radial slide bearing 2 on the frame opening side, and the holding member 40 serves to connect the central shaft 3 and the magnet 30. Since the magnetic flux density gradient in the axial direction of the space between them is set to a one-way magnetic flux density gradient that increases in the opposite direction on the open side, for example, the volume change of the magnetic fluid 14 due to atmospheric pressure / temperature change and the component size / injection Due to variations in the amount of the magnetic fluid 14, the magnetic fluid 1
Even if the liquid surface position of 4 changes, the magnetism due to the unidirectional magnetic flux density gradient increasing in the opposite direction to the open side (corresponding to the steep unidirectional magnetic flux density gradient shown by the symbol A ′ in FIG. 12) The magnetic fluid 14 is held well by the force. Further, even when the magnetic fluid 14 moves in a direction in which the magnetic fluid 14 leaks, for example, when vibration, shock, or centrifugal force is applied or the posture changes, the one-way magnetic flux density gradient (reference numeral A in FIG. 12).
The magnetic force due to the gradual one-way magnetic flux density gradient indicated by A ′) causes a relatively large one-way magnetic flux density gradient to continue even at a position away from the magnet 30, so that the magnetic fluid that is about to leak is It is supposed to be pulled back.

That is, it is possible to reliably prevent the magnetic fluid 14 from leaking to the outside, so that it is possible to reduce the generation of external pollution and dust and the outgas, and to eliminate the shortage of the magnetic fluid inside. Is possible.

Such a structure is a particularly effective means in the case of, for example, air transportation of the device accompanied by a rapid change in atmospheric pressure and temperature.

Further, the radial slide bearing 2 on the frame opening side as a member for holding the magnet 30 and the holding member 40 are made of a magnetic material, and the central shaft 3 and the magnet 30 form a magnetic circuit. The effect can be further enhanced as compared with a magnetic circuit constituted only by the central shaft 3 and the magnet 30.

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 magnet 30.

By the way, in the first embodiment, as shown in FIG. 2, a magnetic fluid leakage prevention plate 41 is disposed on the open end surface of the magnet 30. The magnetic fluid leakage prevention plate 41 is made of a non-magnetic material, and the inner peripheral surface thereof has
It is driving out to the vicinity of the outer peripheral surface.

Therefore, even if the magnetic fluid 14 should leak out against the attraction force due to the one-way magnetic flux density gradient, the leakage passage is narrowed by the magnetic fluid leakage prevention plate 41, so that the leakage is prevented. The effect of preventing sticking out can be further enhanced.

Further, in the first embodiment, as shown in FIG. 2, the magnetic fluid leakage prevention plate 4 on the open side from the position where the magnetic fluid leakage prevention plate 41 and the central shaft 3 face each other.
Coatings 42, 42 made of a material having a larger contact angle with the magnetic fluid 14 than the contact angle between the magnet 30 and the magnetic fluid 14 are formed on both surfaces of the first and the center shafts 3. As the coatings 42, 42, for example, a polymer material is used, and for example, Teflon, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride having a critical surface tension of 30 dynes / cm (20 ° C.) or less. Etc. are used.

With this structure, the magnetic fluid 1 should be used by any chance.
For example, as a material having a larger contact angle with the magnetic fluid 14 than the contact angle between the magnet 30 and the magnetic fluid 14, even if 4 leaks from the gap between the magnetic fluid leakage prevention plate 41 and the central shaft 3, for example, Since the polymer material 42 is hard to get wet with the magnetic fluid 14, the leaking magnetic fluid 14 is repelled by the polymer material 42 and is returned to the original state by the attraction force of the one-way magnetic flux density gradient. . Therefore, it can be made more effective than the magnetic fluid leakage prevention plate 41.

Instead of the polymer material 42, for example, a coating in which a low energy surface of fluorocarbon or hydrocarbon is oriented on the surface may be used. Further, instead of the polymer material 42, a palm oil coating may be applied. As the oil-repellent coating, for example, Teflon-based resin, or when the magnetic fluid is ester-based, isostearic acid can be used, for example. In addition, the oil-repellent coating itself is used as the magnetic fluid 14.
On the other hand, even if it is hard to get wet, the same effect as described above can be obtained.

FIG. 3 is a transverse cross-sectional view of a spindle motor for a center axis fixed type HDD to which the bearing device according to the second embodiment of the present invention is applied, which is the same as that described in the first embodiment. Those having the same function as those having the same function are denoted by the same reference numerals, and the description thereof will be omitted here to avoid duplication.

The motor of the second embodiment has a central shaft 21a.
Is a fixed center axis motor fixed together with a frame 21 made of a magnetic material.
In order to prevent the leakage of No. 4, the magnet 30 is arranged on the open side of each radial slide bearing 2, 2.
Further, in order to form a magnetic circuit similar to that of the first embodiment,
The central shaft 21 facing the upper magnet 30 in the figure
a and the member 44 (the hub 54 when this member 44 is not provided) facing the lower magnet 30 in FIG.
Each is composed of a magnetic material. Further, a magnetic fluid leakage prevention plate 41 similar to that of the first embodiment is arranged on the open side end surface of the magnet 30, respectively, and a position where the magnetic fluid leakage prevention plate 41 and the central shaft 21a (hub 54) face each other. On the surface of both the magnetic fluid leakage prevention plate 41 and the central shaft 21a (hub 54) on the open side from the first side of the material of which the contact angle with the magnetic fluid 14 is larger than the contact angle between the magnet 30 and the magnetic fluid 14. Coatings 42 and 4 similar to those of the first embodiment
2 is formed.

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 the bearing device showing the third embodiment of the present invention. In the third embodiment,
An annular magnetic body 35 is fixed to the outer circumference of the central shaft 3 at a position facing the magnet 31 without making the facing surface 31a of the magnet 31 facing the central shaft 3 an inclined surface. The surface of the magnetic body 35 facing the magnet 31 (outer peripheral surface)
35a is an inclined surface that approaches the facing surface 31a of the magnet 31 in the opposite direction (downward in the drawing) to the open side.

The magnetic fluid leakage prevention plate 41 and the coating film 42 are provided in the same manner as in the first embodiment. Reference numeral 60 denotes a spacer for axially separating the magnetic fluid leakage prevention plate 41 from the magnet 31.

Even with this structure, the magnet 31,
By the magnetic circuit formed by the magnetic body 35, the central shaft 3, the radial slide bearing 2 on the frame open side, and the holding member 40, the magnetic flux density gradient in the axial direction of the space between the magnetic body 35 and the magnet 31 is Since the unidirectional magnetic flux density gradient can be increased in the opposite direction to the open side as in the first embodiment, the effect produced by forming this unidirectional magnetic flux density gradient can be obtained as in the first embodiment. be able to. Further, the effect produced by providing the magnetic fluid leakage prevention plate 41 and the coating film 42 can be similarly obtained.

FIG. 5 is a cross-sectional view of the main part of a bearing device showing the fourth embodiment of the present invention. The bearing device of the fourth embodiment is different from that of the first embodiment in that the facing surface 32a of the magnet 32 facing the central axis 3 is not an inclined surface, but the surface (rear surface) opposite to the facing surface 32a of the magnet 32. ) 32b,
This is the point where the magnet 32 is inclined so that the thickness in the radial direction increases in the direction opposite to the opening side.

Even with this construction, the magnet 32,
With the magnetic circuit formed by the central shaft 3, the radial slide bearing 2 on the frame open side, and the holding member 40, the magnetic flux density gradient in the axial direction of the space between the central shaft 3 and the magnet 32 is set to that of the first embodiment. Since the unidirectional magnetic flux density gradient can be increased in the opposite direction on the similar opening side, the effect produced by forming this unidirectional magnetic flux density gradient can be obtained as in the first embodiment. Further, the effect produced by providing the magnetic fluid leakage prevention plate 41 and the coating film 42 can be similarly obtained.

FIG. 6 shows a fifth embodiment of the present invention. (A) is a cross-sectional view of the main part of the bearing device, (b) is a magnetization distribution map of the magnet shown in (a). Is.

The bearing device of the fifth embodiment is different from that of the first embodiment in that the facing surface 33a of the magnet 33 facing the central axis 3 is not inclined and the magnetizing strength of the magnet 33 is on the open side. The magnet 33 is magnetized so as to increase in the opposite direction.

Even with this structure, the effect produced by forming the unidirectional magnetic flux density gradient can be obtained similarly to the first embodiment. Further, the magnetic fluid leakage prevention plate 41
Also, the effect produced by providing the coating film 42 can be similarly obtained.

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

In the sixth embodiment, in addition to the magnetic fluid leakage prevention plate 41 and the coating film 42 of the first embodiment, a position on the open side of the magnet 30 in the passage 10 that communicates the bearing portion with the outside is provided. , Oil absorbers 43, 43 are provided. In the present embodiment, the positions of the oil absorbers 43, 43 are set to the open end surface of the magnetic fluid leakage prevention plate 41 and the surface of the central shaft 3 on the open side of the coating 42 (specifically, to the coating 42 on the hub 4). On the other hand, it is adjacent to the wall).

As the oil absorbent 43, for example, a non-woven fabric made of polypropylene or polyester is used.
As shown in FIG. 8, it is composed of an oil absorption layer 43a on the front surface and an adhesive layer 43b on the back surface.

As described above, in the present embodiment, since the oil absorbers 43, 43 are provided on the open side of the magnet 30 in the passage 10 that communicates the bearing portion with the outside, the attraction by the one-way magnetic flux density gradient is obtained. Even if the magnetic fluid 14 leaks out against the force, the leaked magnetic fluid 14 is quickly absorbed by the oil absorbents 43, 43, and does not leak out. ing.
Therefore, the first to fifth embodiments can be made more effective.

Instead of the oil absorbent 43 shown in FIG. 8, a solidifying material made of, for example, a long-chain polyacrylate or a gelling agent may be used, and the oil absorbent 4 shown in FIG.
3, the oil absorption layer 5 on the surface is replaced by the oil absorption layer 5 as shown in FIG.
0a and the adhesive layer 50b on the back surface, an oil absorbent 50 having a solidified layer 50c made of, for example, a long-chain polyacrylate or a gelling agent may be used, and as shown in FIG. You may use the oil absorption material 51 which consists of the oil absorption layer 51a containing the solidifying material, and the adhesive layer 51b.

Incidentally, the oil absorbents 43, 50, 51 are
The present invention can be similarly applied to a bearing device that has only the attraction force due to the one-way magnetic flux density gradient and the magnetic fluid leakage prevention plate 41 and does not have the coating 42.

Although the invention made by the present inventor has been specifically described based on the embodiments, the invention is not limited to the above-mentioned embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say, for example, the magnets 30 to 33 are replaced by the magnets 30 to 33.
It is fixed to the central shaft 3 as a member opposed to the central shaft 2 (in the case of the upper magnet 30 in the drawing of the second embodiment, the central shaft 2
1a may be fixed to the hub 54 in the lower magnet 30 in the drawing), and a magnetic body may be provided so as to face the positions of the magnets 30 to 33.

Further, in the above embodiment, the position where the coating 42 is formed is considered to be the most effective, and the magnetic fluid leakage prevention plate 41 on the open side from the position where the magnetic fluid leakage prevention plate 41 and the central axis 3 face each other. Although the position of the central axis 3 is used, the coating may be applied to other positions. Further, although the coating 42 is formed on both the magnetic fluid leakage prevention plate 41 and the central shaft 3, the effect of the present invention is not hindered if it is formed on at least one of them. Furthermore, without forming the coating film 42, at least one of the magnetic fluid leakage prevention plate 41 and the central shaft 3 has a larger contact angle with the magnetic fluid 14 than the contact angle between the magnets 30 to 33 and the magnetic fluid 14. It may be formed of the following material.

Further, in the above-mentioned embodiment, the application example to the dynamic pressure bearing is described, but it can be similarly applied to other bearings.

Further, in the above embodiment, the bearing device is applied to the spindle motor for HDD, but it is also applicable to the motor for laser beam printer, and further other embodiments. The same can be applied to a motor.

[0059]

As described above, according to the bearing device of the first aspect of the present invention, the magnetic fluid changes due to, for example, the volume change of the magnetic fluid due to the change of the atmospheric pressure and the temperature, and the variation of the component size and the amount of the magnetic fluid to be injected. Even if the liquid surface position of is changed, the magnetic fluid is satisfactorily held by the magnetic force due to the unidirectional magnetic flux density gradient increasing in the opposite direction to the opening side. Also, for example, even if vibration, shock, centrifugal force is applied, or the posture changes,
The magnetic fluid due to the unidirectional magnetic flux density gradient pulls back the magnetic fluid that is about to leak. Further, even if the magnetic fluid should leak out against the attraction force due to the one-way magnetic flux density gradient, the magnetic fluid leakage prevention plate prevents the magnetic fluid from leaking out. That is, it is possible to reliably prevent the magnetic fluid from leaking to the outside, it is possible to reduce the generation of external pollution and dust and the outgas, and it is possible to eliminate the shortage of the magnetic fluid inside.

In particular, according to the bearing devices of the second and third inventions, in addition to the first invention, even if the magnetic fluid is about to leak, the contact angle between the magnetic fluid and the contact angle between the magnet and the magnetic fluid is larger than the contact angle between the magnet and the magnetic fluid. Since the material having a large magnetic field is hard to wet with the magnetic fluid, the magnetic fluid that is about to leak is repelled by the material and is returned to the original state by the attraction force of the one-way magnetic flux density gradient. Therefore, the first invention can be made more effective.

According to the bearing device of the fourth invention,
Alternatively, in addition to the second or third invention, even if the magnetic fluid leaks against the attractive force due to the one-way magnetic flux density gradient, the leaked magnetic fluid is quickly absorbed by the oil absorbing material, Never leak out. Therefore, the first, second, or third invention can be made more effective.

[Brief description of drawings]

FIG. 1 is a transverse cross-sectional view of a center axis rotation type HDD motor to which a bearing device according to a first embodiment of the present invention is applied.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is a cross-sectional view of a center axis fixed type HDD motor to which a 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 bearing device showing a third embodiment of the present invention.

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

FIG. 6 shows a fifth embodiment of the present invention, (a)
[Fig. 3] is a transverse cross-sectional view of the main part of the bearing device, and (b) is a magnetization distribution map of the magnet shown in (a).

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

FIG. 8 is a cross-sectional view of an oil absorbent material showing an example of the oil absorbent material in FIG. 7.

FIG. 9 is a cross-sectional view of an oil absorbent material showing another example of the oil absorbent material.

FIG. 10 is a transverse cross-sectional view of an oil absorbing material showing still another example of the oil absorbing material.

FIG. 11 is an analysis diagram showing magnetic fluxes around the magnets and magnetic bodies of the first to sixth embodiments.

12 is a density distribution diagram of magnetic fluxes indicated by reference characters A and B in FIG.

FIG. 13 is a transverse cross-sectional view of a center axis rotation type HDD motor to which a bearing device according to the related art is applied.

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

[Explanation of symbols]

 1, 1a, 21, 21a Fixed member 2 Radial bearing 3, 54 Rotating member 14 Magnetic fluid 30-33 Magnet 35, 44 Magnetic body 41 Magnetic fluid leak prevention plate 42 Material 43, 50, 51 Oil absorbent material

Claims (4)

[Claims] 1. A bearing device comprising: a radial bearing fixed to either a fixed member or a rotating member to rotatably support the rotating member; and a magnetic fluid filled in a sliding portion of the radial bearing. In the above, a magnet is provided on either the fixed member or the rotary member on the open side of the radial bearing, and the other rotary member or fixed member facing in the radial direction of the magnet is a magnetic body. By the magnetic circuit formed, the magnetic flux density gradient in the axial direction of the space between the magnetic body and the magnet is made a one-way magnetic flux density gradient increasing in the opposite direction of the open side, and A bearing device comprising a magnetic fluid leakage prevention plate, which is made of a non-magnetic material and whose peripheral surface approaches the magnetic body, on the open side. 2. The bearing device according to claim 1, wherein at least one of the magnetic fluid leakage prevention plate and the magnetic body and at least the surface thereof has a larger contact angle with the magnetic fluid than a contact angle between the magnet and the magnetic fluid. Bearing device characterized by being made of the following materials. 3. The bearing device according to claim 1, wherein at least one of the magnetic fluid leakage prevention plate and the magnetic body and at least the surface of the magnetic fluid leakage prevention plate and the magnetic body on the opening side from the position where the magnetic fluid leakage prevention plate and the magnetic body face each other, A bearing device made of a material having a larger contact angle with a magnetic fluid than a contact angle between a magnet and a magnetic fluid. 4. The bearing device according to claim 1, 2 or 3, wherein an oil absorbing material is provided on the opening side of the magnet in the passage that communicates the bearing portion and the outside.