JP2963619B2 - Dynamic pressure bearing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

In FIG. 1, reference numeral 1 denotes a frame as a motor housing as a fixing member, and a cylindrical bearing holder 1a is integrally formed on the frame 1 so as to stand upright. That is, the bearing holder 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 1a, and a coil 5 is wound around the stator core 6.

[0004] Radial sliding bearings 2 and 2 are fitted and fixed to the inner periphery of the bearing holder 1a, respectively, and a central shaft 3 as a rotating shaft is inserted and arranged in the inner periphery of the radial sliding bearings 2 and 2. Have been. On at least one of the outer peripheral surface of the center shaft 3 and the inner peripheral surfaces of the radial slide bearings 2, for example, a dynamic pressure generating groove having a herringbone shape or the like is formed. The gap between the sliding bearings 2 and 2) is filled with a magnetic fluid. That is, the radial movement of the center shaft 3 between the inner peripheral surfaces of the radial slide bearings 2 and 2 suppresses the deflection in the radial direction, and the center shaft 3 rotates in the radial slide bearings 2 and 2. I have.

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 center shaft 3 on the frame closing side (the lower side in the figure). The thrust plate 1b and the end face 3a of the center shaft 3 on the frame closing side.
A dynamic pressure generating groove is formed in at least one of
The sliding surface (gap between the end face 3a of the central shaft 3 on the frame closing side and the upper end face of the thrust plate 1b facing the end face 3a) is filled with the magnetic fluid. That is, a thrust dynamic pressure toward the frame opening side with respect to the central shaft 3 is generated between the frame closed side end surface 3a of the central shaft 3 and the upper end surface of the thrust plate 1b.

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

A hub 4 shaped to cover the core 6, the coil 5 and the like is fitted and fixed to an end of the center shaft 3 on the frame opening 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 periphery.
Has been fixed.

A magnetic fluid seal 8 is provided in the passage 10 communicating between the inside and outside of the bearing holder 1a, that is, at the upper end of the bearing holder 1a in the figure (the position above the radial sliding bearing 2 on the open side of the frame). Have been. The magnetic fluid seal 8 includes a magnet 8b and pole pieces 8a, 8a provided so as to sandwich the magnet 8b in the axial direction to form a magnetic path. The magnetic fluid 9 can be held between the outer peripheral surface of the shaft 3 and the magnetic fluid 9. Therefore,
The magnetic fluid seal 8 prevents the magnetic fluid 14 filled in the inside of the holder portion 1a containing the magnetic fluid filled in the sliding surface from leaking outward from the bearing portion and from the outside. It is attempted to prevent dust and the like from entering the bearing portion.

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

[0010] When a predetermined drive voltage is applied to the coil 5 from a power supply means (not shown) outside the motor via the flexible substrate 12, the hub 4 on which the disk is mounted rotates. Reference numeral 11 denotes a bearing collar disposed in contact with the slide bearings 2 and 13;
Indicates the retaining of the central shaft 3 respectively.

[0011]

Here, in the above-mentioned spindle motor for the HDD, etc., since a clean atmosphere is required, the leakage of the magnetic fluid 14 filled in the bearing holder 1a occurs. Prevention is an important point,
For example, even if vibration, impact, or centrifugal force is applied, or the posture changes, it is necessary that leakage does not occur.

However, the liquid surface position of the magnetic fluid 14 filled in the bearing holder 1a depends on the change in volume of the magnetic fluid (actually air mixed inside) due to the change in air pressure and temperature, and the dimensions and injection of parts. 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 holding force against the magnetic fluid greatly increases in the magnetic fluid leakage prevention structure shown in FIGS. And the leakage of the magnetic fluid cannot be prevented.

[0013] Such a problem is not limited to the above-described motor of the center shaft rotation type having one end closed and the other opened, but similarly occurs in a center shaft fixed type motor having both ends opened. I do.

An object of the present invention is to provide a dynamic pressure bearing device in which leakage of a magnetic fluid to the outside is reliably prevented.

[0015]

According to a first aspect of the present invention, there is provided a dynamic bearing device which is fixed to one of a fixed member and a rotating member to rotatably support the rotating member. A dynamic pressure bearing device configured to generate a dynamic pressure in a magnetic fluid filled in a sliding surface of the radial bearing, wherein one of a fixed member and a rotating member on an open side of the radial bearing is provided with a magnet. The other rotating member or fixed member facing the magnet in the radial direction is made of a magnetic material, and a magnetic circuit formed by the magnetic material and the magnet forms an axis of a space between the magnetic material and the magnet. The magnetic flux density gradient in one direction is a one-way magnetic flux density gradient that increases in the opposite direction on the open side.

According to a second aspect of the present invention, in order to achieve the above object, in addition to the first means, the dynamic pressure bearing device is configured such that one of the opposing surfaces of the magnet or the magnetic body is open to the other opposing surface. In the direction approaching the opposite direction.

In order to achieve the above object, the dynamic pressure bearing device according to the third means, in addition to the first means, has a structure in which the thickness of the magnet in the radial direction increases in the direction opposite to the open side. The surface opposite to the facing surface of the magnet is inclined.

In order to achieve the above object, the dynamic pressure bearing device of the fourth means increases the magnetizing strength of the magnet in the direction opposite to the open side in addition to the first means.

In order to achieve the above object, the dynamic pressure bearing device of the fifth means is characterized in that the magnet is magnetized in a radial direction in addition to the first means.

In order to achieve the above object, the dynamic pressure bearing device of the sixth means is characterized in that, in addition to the first means, a member holding the magnet is made of a magnetic material.

[0021]

According to the dynamic pressure bearing device of the first and fifth means, for example, a change in the volume of the magnetic fluid due to a change in air pressure or temperature, a variation in the dimensions of parts, an amount of the magnetic fluid to be injected, etc. Even if the liquid surface position changes, the magnetic fluid is favorably held by the magnetic force due to the one-way magnetic flux density gradient that increases in the reverse direction on the open side. Also, even if, for example, vibration, impact, or centrifugal force is applied or the posture changes, the magnetic fluid that is about to leak is pulled back by the magnetic force due to the one-way magnetic flux density gradient.

According to the dynamic pressure bearing device of the second means, the one-way magnetic flux density gradient that increases in the opposite direction on the open side is such that one of the opposing surfaces of the magnet or the magnetic material is connected to the other surface. It is obtained by inclining in the direction approaching the opposite side on the open side with respect to the facing surface.

According to the dynamic pressure bearing device of the third means, the one-way magnetic flux density gradient increasing in the reverse direction on the open side is such that the radial thickness of the magnet is in the reverse direction on the open side. It is obtained by inclining the surface on the opposite side of the facing surface of the magnet in the direction in which the magnet becomes thicker.

According to the dynamic pressure bearing device of the fourth means, the one-way magnetic flux density gradient that increases in the reverse direction on the open side reduces the magnetizing strength of the magnet in the reverse direction on the open side. It is obtained by increasing.

According to the dynamic bearing device of the sixth means, the effect of the first means is further increased by forming a magnetic circuit using the member holding the magnet as a magnetic material.

[0026]

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, of a central shaft rotating type and a fixed radial bearing type, to which a hydrodynamic bearing device according to a first embodiment of the present invention is applied. Identical components and components performing the same function are denoted by the same reference numerals, and description thereof is omitted here to avoid duplication.

In the first embodiment, the central shaft 3 and the radial sliding bearing 2 on the open side of the frame are made of a magnetic material, and the radial sliding bearing 2 on the open side of the radial sliding bearing 2 on the open side of the frame, that is, the radial on the open side of the frame. An annular magnet 30 that is magnetized in the radial direction is disposed on an end surface of the sliding bearing 2 on the frame open side. The magnet 30 is held by the radial sliding bearing 2 on the open side of the frame and the holding member 40 made of a magnetic material fixedly arranged on the outer periphery of the magnet 30.
A magnetic circuit is formed by the magnet 30, the center shaft 3, the radial sliding 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 approaching the outer peripheral surface of the central axis 3 in a direction opposite to the open side (downward in the drawing). ing.

When the above-described inclined surface 30a is formed on the magnet 30 to form a magnetic circuit 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 each of the magnetic fluxes A and B (see FIG. 6) 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 of 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 on the open side.

Reference numeral 41 denotes a stopper made of a non-magnetic material, and reference numerals 42 and 43 denote absorption sheets.

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 open side of the frame, and the holding member 40 connects the central shaft 3 to the magnet 30. Since the magnetic flux density gradient in the axial direction of the space between them is 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 a change in air pressure and temperature, and the dimensions and injection of parts. Due to variations in the amount of the magnetic fluid 14, the magnetic fluid 1
4. Even if the liquid level position of 4 changes, the magnetism due to the one-way magnetic flux density gradient (approximately corresponding to the steep one-way magnetic flux density gradient indicated by A 'in FIG. 7) that increases in the reverse direction on the open side. The force holds the magnetic fluid 14 well. Further, even when, for example, vibration, impact, or centrifugal force is applied, or the posture changes, and the magnetic fluid 14 moves in a leaking direction, the one-way magnetic flux density gradient (the reference sign AA ′ in FIG. 7).
Approximately corresponds to the gentle one-way magnetic flux density gradient indicated by.)
Due to the magnetic force generated by the magnetic fluid, a relatively large magnetic flux density gradient in one direction continues even at a position distant from the magnet 30, so that the magnetic fluid to be leaked is pulled back. Therefore, leakage of the magnetic fluid 14 to the outside is reliably prevented.

Further, the radial sliding bearing 2 and the holding member 40 on the frame opening side as members for holding the magnet 30 are made of a magnetic material, and a magnetic circuit is formed by these, the center shaft 3 and the magnet 30. The effect can be further enhanced as compared with the case where a magnetic circuit is constituted only by the center shaft 3 and the magnet 30.

The one-way magnetic flux density gradient is desirably long in the axial direction and steep, and the volume of the holding portion for holding the magnetic fluid is also desirably large. Such a desired one-way magnetic flux density gradient and the holding volume of the magnetic fluid can be easily obtained by changing the inclination of the magnet 30 and the like.

FIG. 2 is a cross-sectional view of a spindle motor for a HDD of, 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 those having the same functions and the same functions as those described above, and the description thereof will be omitted here to avoid duplication.

The motor of the second embodiment has a center shaft 21a.
Is a central shaft fixed type motor fixed together with a frame 21 made of a magnetic material, and in order to prevent leakage of the magnetic fluid from both open ends, the magnet 30 is placed on the open side from the radial sliding bearings 2, 2. Each is arranged. Further, in order to form a magnetic circuit similar to that of the first embodiment, a central shaft 21a facing the upper magnet 30 in the figure is used.
And the member 4 facing the lower magnet 30 in the figure.
4 (the hub 54 when the member 44 is not provided) is made of a magnetic material.

It is needless to say that the same effect as that of the first embodiment can be obtained even with this configuration.

FIG. 3 is a cross-sectional view of a main part of a hydrodynamic bearing device according to a third embodiment of the present invention. In the third embodiment, an annular magnetic body 35 is fixed to the outer periphery of the center shaft 3 at a position facing the magnet 31 without using the inclined surface 31a facing the center axis 3 of the magnet 31. I have.
The surface (outer peripheral surface) 35a of the magnetic body 35 facing the magnet 31 is an inclined surface that approaches the opposite surface 31a of the magnet 31 in a direction opposite to the open side (downward in the drawing).

Even with this configuration, the magnet 31,
The magnetic circuit formed by the magnetic body 35, the central shaft 3, the radial sliding bearing 2 on the open side of the frame, and the holding member 40 reduces the axial magnetic flux density gradient of the space between the magnetic body 35 and the magnet 31. Since the one-way magnetic flux density gradient can be increased in the reverse direction on the open side as in the first embodiment, the same effect as in the first embodiment can be obtained.

FIG. 4 is a cross-sectional view of a main part of a hydrodynamic bearing device according to a fourth embodiment of the present invention. The difference between the dynamic pressure bearing device of the fourth embodiment and that of the first embodiment is that
The surface (back surface) 3 opposite to the facing surface 32a of the magnet 32 without making the facing surface 32a with respect to the center axis 3
2b is that the magnet 32 is inclined such that the radial thickness of the magnet 32 increases in the opposite direction to the open side.

Even with this configuration, the magnet 32,
The magnetic circuit formed by the center shaft 3, the radial sliding bearing 2 on the open side of the frame, and the holding member 40 reduces the magnetic flux density gradient in the space between the center shaft 3 and the magnet 32 in the axial direction. Since a one-way magnetic flux density gradient that increases in the opposite direction on the same open side can be obtained, the same effect as in the first embodiment can be obtained.

FIGS. 5A and 5B show a fifth embodiment of the present invention, in which FIG. 5A is a cross-sectional view of a main part of a hydrodynamic bearing device, and FIG. 5B is a magnetized magnet shown in FIG. It is a distribution map.

The dynamic pressure bearing device of the fifth embodiment differs from that of the first embodiment in that the surface of the magnet 33 facing the central axis 3 is not inclined and the magnetizing strength of the magnet 33 is reduced. So that it increases in the opposite direction to the open side,
The point is that the magnet 33 is magnetized.

It is needless to say that the same effect as in the first embodiment can be obtained even with this configuration.

Although the invention made by the inventor has been specifically described based on the embodiments, the present invention is not limited to the above-described embodiments, and can be variously modified without departing from the gist thereof. Needless to say, for example, the magnets 30 to 33 are
Is fixed to the center shaft 3 as a member facing the center shaft (in the upper magnet 30 in the drawing of the second embodiment, the center shaft 2
1a, the lower magnet 30 in the figure is fixed to the hub 54), and a magnetic body may be provided at a position where the magnets 30 to 33 are located so as to face each other.

The magnets 30 to 33 may be multi-pole magnets in which the N and S poles are alternately magnetized in the circumferential direction.

Further, in the above embodiment, the dynamic pressure bearing device may be a central shaft rotating type and a radial bearing fixed type (shown in FIGS. 1, 3 to 5) or a central shaft fixed type and a radial bearing rotating type. An example in which the present invention is applied to a type (shown in FIG. 2) spindle motor is described, but a central shaft and a radial bearing rotary type in which the outer peripheral surface of a radial bearing serves as a sliding surface, and a central shaft and a radial bearing It can also be applied to fixed type spindle motors.

In the above-described embodiment, an example is described in which the dynamic bearing device is applied to a spindle motor for an HDD. However, the present invention is also applicable to a motor for a laser beam printer. The same can be applied to other motors.

[0049]

As described above, according to the hydrodynamic bearing devices of the first to sixth aspects of the present invention, the volume change of the magnetic fluid due to, for example, a change in air pressure and temperature, and the variation in the dimensions of parts and the amount of the magnetic fluid to be injected. Thus, even if the liquid surface position of the magnetic fluid changes, the magnetic fluid is favorably held by the magnetic force due to the one-way magnetic flux density gradient that increases in the opposite direction to the open side. Also, even if, for example, vibration, impact, or centrifugal force is applied or the posture changes, the magnetic fluid that is about to leak is pulled back by the magnetic force due to the one-way magnetic flux density gradient. Therefore, it is possible to reliably prevent the leakage of the magnetic fluid to the outside.

In particular, according to the dynamic bearing device of the sixth invention,
Since the magnetic circuit is formed by using the member holding the magnet as a magnetic material, the above effect can be further increased.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a central 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.

FIG. 2 is a cross-sectional view of a central shaft fixed type and radial bearing rotary type HDD motor to which a dynamic pressure bearing device according to a second embodiment of the present invention is applied.

FIG. 3 is a cross-sectional view of a main part of a hydrodynamic bearing device according to a third embodiment of the present invention.

FIG. 4 is a cross-sectional view of a main part of a hydrodynamic bearing device according to a fourth embodiment of the present invention.

FIG. 5 shows a fifth embodiment of the present invention, in which (a)
FIG. 2 is a cross-sectional view of a main part of the dynamic pressure bearing device, and FIG. 2B is a magnetization distribution diagram of the magnet shown in FIG.

FIG. 6 is an analysis diagram showing magnets and magnetic fluxes around a magnetic body of the first to fifth embodiments.

FIG. 7 is a density distribution diagram of magnetic flux represented by reference numerals A and B in FIG.

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

9 is a cross-sectional view illustrating 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 to 33 Magnet 31a to 33a Magnet facing surface 32b Magnet facing surface 35,44 Magnetic body 35a Magnetic body 35a Opposing surface 40 Member for holding magnet

Claims (6)

(57) [Claims] 1. A radial bearing fixed to one of a fixed member and a rotating member and rotatably supporting the rotating member, wherein a dynamic pressure is generated in a magnetic fluid filled in a sliding surface of the radial bearing. In the hydrodynamic bearing device configured to be tightened, a magnet is provided on one of a fixed member and a rotating member on an open side of the radial bearing, and the other rotating member or fixed member facing the magnet in a radial direction is a magnetic material. The magnetic circuit formed by the magnetic material and the magnet causes the magnetic flux density gradient in the axial direction of the space between the magnetic material and the magnet to increase in the one-way magnetic flux increasing in the opposite direction on the open side. A hydrodynamic bearing device characterized by having a density gradient. 2. The dynamic pressure bearing device according to claim 1, wherein one of the opposing surfaces of the magnet and the magnetic body is inclined in a direction approaching the open surface in the opposite direction to the other opposing surface. Hydrodynamic bearing device. 3. The dynamic pressure bearing device according to claim 1, wherein a surface of the magnet opposite to the facing surface of the magnet is inclined in a direction in which a thickness of the magnet in a radial direction increases toward a direction opposite to the open side. Hydrodynamic bearing device. 4. The hydrodynamic bearing device according to claim 1, wherein the magnetizing strength of the magnet is increased in a direction opposite to the open side. 5. The hydrodynamic bearing device according to claim 1, wherein the magnet is magnetized in a radial direction. 6. The dynamic pressure bearing device according to claim 1, wherein the member holding the magnet is made of a magnetic material.