JPH0874864A - Bearing device - Google Patents

Abstract

PURPOSE: To surely prevent the leakage of a magnetic fluid to the outer part, and reduce the contamination of the outer part, the generation of dust, and the outgassing. CONSTITUTION: This bearing device has a radial bearing 2 fixed to either one of a fixed member or rotating member to rotatably support the rotating member, and a magnetic fluid 14 filled in the sliding part of the radial 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 to the radial direction of the magnet 30 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 inclined toward the reversed direction to the opening side by the magnetic circuit formed by the magnetic body 3 and the magnet 30, and magnetic fluid absorbing material 43, 43 are provided in positions closer to the opening side from the radial bearing 2 in a passage for allowing a bearing part to communicate with the outer part, which never generally make contact with the magnetic fluid 14.

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. 11 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 the magnetic fluid 14 from leaking to the frame opening side, as shown in FIG. 12, 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. 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.

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 bearing device in which magnetic fluid is reliably prevented from leaking to the outside, and external pollution and dust generation and outgas are reduced.

[0015]

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. The gradient of the unidirectional magnetic flux density increases in the opposite direction, and at the open side of the radial bearing in the passage that connects the bearing and the outside, and A position not in contact normal to the magnetic fluid, formed by providing a magnetic fluid absorbent material.

In order to achieve the above object, the bearing device of the second means has the magnetic fluid absorbing material also having a solidifying function in addition to the first means.

[0017]

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 attractive force due to such a one-way magnetic flux density gradient, it is absorbed by the magnetic fluid absorbing material, and leakage to the outside is prevented.

According to the bearing device in the second means as described above, even if the magnetic fluid leaks out against the attraction force due to the one-way magnetic flux density gradient, the magnetic fluid absorbing material also having a solidifying function promptly accelerates the leakage. It is absorbed and solidified to prevent leakage to the outside.

[0019]

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 central 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 closer to 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 facing surface (inner peripheral surface) 30a of the magnet 30 with respect to the central axis 3 is an inclined surface that approaches the outer peripheral surface of the central axis 3 in the direction opposite to the open side (downward in the figure). 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. 9) in the space near the open-side end surface is as shown in FIG.

Here, in this 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 sliding 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 No. 4 changes, the magnetism due to the unidirectional magnetic flux density gradient increasing in the opposite direction on the open side (approximately corresponding to the steep unidirectional magnetic flux density gradient shown by reference sign A ′ in FIG. 10) 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. 10).
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 surely prevent the magnetic fluid 14 from leaking to the outside, and it is possible to reduce the generation of external pollution and dust and the outgas.

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

Further, the radial sliding bearing 2 on the frame open 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, the passage 10 for communicating the bearing portion with the outside is on the open side of the radial slide bearing 2 and is not normally in contact with the magnetic fluid 14. Position (position on the opening side of the magnet 30 in the passage 10 that communicates the bearing portion and the outside), that is, in the present embodiment, the outer peripheral surface on the open side of the position facing the magnet 30 on the central shaft 3 and this outer peripheral surface. On the wall surface of the hub 4 adjacent to the magnetic fluid absorber 43,
43 are provided.

As the magnetic fluid absorbing material 43, for example, a non-woven fabric made of polypropylene, polyester, polyethylene, polystyrene, nylon, polyurethane, vinyl chloride, etc. is used. As shown in FIG. It is composed of a layer 43a and an adhesive layer 43b on the back surface.

Therefore, even if the magnetic fluid 14 leaks against the attraction force due to the one-way magnetic flux density gradient, the leaked magnetic fluid 14 will be absorbed by the magnetic fluid absorbing material 43,
It is absorbed by 43, and the effect of preventing the magnetic fluid from leaking to the outside can be further enhanced.

FIG. 3 is a 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, magnetic fluid absorbing materials 43, 43 similar to those of the first embodiment are arranged on the open end surface of the magnet 30 and the peripheral surface of the central shaft 21a (hub 54) on the open side of the position facing the magnet 30. Has been done.

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.

Regarding the magnetic fluid absorbing material 43,
Similar to the previous embodiment, they are provided on the open end surface of the magnet 31 and the peripheral surface on the open side of the central shaft 3 (21a) facing the magnet 31, respectively.

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 absorbing material 43 can be similarly obtained.

FIG. 5 is a cross-sectional view of the essential parts of a bearing device showing a 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. The magnetic fluid absorber 43 is provided in the same manner as in the third embodiment.

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 absorbing material 43 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 differs 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. The magnetic fluid absorber 43 is provided in the same manner as in the third embodiment.

Even with this configuration, the effect produced by forming the unidirectional magnetic flux density gradient can be obtained as in the first embodiment. Further, the effect produced by providing the magnetic fluid absorbing material 43 can be similarly obtained.

FIG. 7 is a cross sectional view of a magnetic fluid absorbent material showing another example of the magnetic fluid absorbent material used in the first to fifth embodiments, and FIG. 8 is a magnetic material used in the first to fifth embodiments. It is a cross-sectional view of a magnetic fluid absorbent material showing still another example of the fluid absorbent material.

The magnetic fluid absorbing material 50 shown in FIG. 7 has, for example, a cross-linked polymer of polyacrylic acid resin, N-benzyloxy-carbonyl-L, between the magnetic fluid absorbing layer 50a on the front surface and the adhesive layer 50b on the rear surface. -Valyl-L-valine octadecylamide-related compounds, various cyclic dipeptide derivatized products, N-lauroylglutamic acid dibutylamide, a solidifying layer 50c comprising a gelling agent and the like.

Further, the magnetic fluid absorbing material 51 shown in FIG.
Is composed of a magnetic fluid absorbing layer 51a containing the solidifying material and an adhesive layer 51b.

Magnetic fluid absorbing material 5 having these solidifying functions
If 0, 51 is used instead of the magnetic fluid absorbent 43 of the first to fifth embodiments, even if the magnetic fluid leaks against the attractive force due to the one-way magnetic flux density gradient, the leakage of the magnetic fluid Since the magnetic fluid thus absorbed is quickly absorbed and solidified by the magnetic fluid absorbing materials 50 and 51 having the solidifying function,
The magnetic fluid does not leak to the outside, so that the first to fifth embodiments can be made more effective.

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 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-described embodiment, the magnetic fluid absorbents 43, 50, 51 are arranged at the most effective positions, and the seal is created by the one-way magnetic flux density gradient in the passage 10 communicating the bearing portion and the outside. Although it is set near the structure, that is, near the magnets 30 to 33, it is not limited to this position and the number thereof is not limited.

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

In the above embodiment, an example in which the bearing device is applied to a spindle motor for HDD is described, but it is applied to a polygon mirror motor, an MO motor, etc. of a laser beam printer (LBP). However, the present invention can be applied to other motors as well.

[0051]

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 leaks against the attraction force due to such a one-way magnetic flux density gradient, the magnetic fluid is absorbed by the magnetic fluid absorbing material and is prevented from leaking to the outside. That is, it is possible to reliably prevent the magnetic fluid from leaking to the outside, and it is possible to reduce the generation of external pollution and dust, and the outgas.

According to the bearing device of the second invention, the first
In addition to the invention, even if the magnetic fluid leaks out against the attraction force due to the one-way magnetic flux density gradient, the leaked magnetic fluid is quickly absorbed and solidified by the magnetic fluid absorbent material that also has a solidification function. , Does not leak outside. Therefore, the first 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 cross-sectional view of a magnetic fluid absorbent material showing another example of the magnetic fluid absorbent material used in the first to fifth embodiments.

FIG. 8 is a cross-sectional view of a magnetic fluid absorbent material showing still another example of the magnetic fluid absorbent material used in the first to fifth embodiments.

FIG. 9 is an analysis diagram showing magnetic fluxes around the magnets and magnetic bodies of the first to fifth embodiments.

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

FIG. 11 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.

12 is a transverse 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 10 Passage that connects the bearing portion and the outside 14 Magnetic fluid 30-33 Magnet 35, 44 Magnetic body 43 Magnetic fluid absorbing material 50, 51 Solidification function Combined magnetic fluid absorber

Claims (2)

[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. With 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 On the open side of the radial bearing in the passage communicating with the outside, and at a position not normally in contact with the magnetic fluid,
A bearing device provided with a magnetic fluid absorbing material. 2. The bearing device according to claim 1, wherein the magnetic fluid absorbing material also has a solidifying function.