JP2002188633A - Fluid bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluid bearing device which implements easy working, low working cost, excellent manufacturability, and high reliability in which unstable vibration is suppressed. SOLUTION: A spindle motor is provided with a shaft 13 having a flange part 15 integrally formed and a sleeve 12 facing the shaft 13 through a fluid bearing clearance, wherein the shaft 13 is made up of a copper alloy or an aluminum alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information device,
For hydrodynamic bearing devices used in video equipment, office machines, etc.
In particular, the present invention relates to a hydrodynamic bearing device most suitable for a magnetic disk device (hereinafter, referred to as an HDD), an optical disk device, and the like.

[0002]

2. Description of the Related Art As a hydrodynamic bearing device used for the above-mentioned applications, for example, there is an HDD spindle motor as shown in FIG. This spindle motor is
The shaft 103 is provided with a shaft 103 to which the shaft 04 is attached, and the sleeve 102 is fixed to the cylindrical portion 101a of the base 101.

More specifically, a cylindrical sleeve 102 is provided inside a cylindrical portion 101a erected on a base 101.
Are interpolated, and these are integrally fixed.
The sleeve 102 has a double structure in which an inner sleeve 102A and an outer sleeve 102B are integrally fixed. That is, the outer sleeve 102B has a cylindrical shape having a bottom plate 102Ba, and is inserted inside the cylindrical portion 101a. The cylindrical inner sleeve 102A is inserted into the outer sleeve 102B and fixed to the inner peripheral surface.

[0004] Such a sleeve 102 (inner sleeve 1)
02A), the shaft 103 is rotatably inserted.
A hydrodynamic bearing is interposed between the sleeve 03 and the sleeve 102. An inverted cup-shaped hub 104 is provided at the upper end of the shaft 103.
Are attached integrally, and at the lower end of the shaft 103,
A disk-shaped flange portion 105 is provided. Note that the shaft 103 and the flange portion 105 are formed by one member integrally formed.

[0005] Both flat surfaces of the flange portion 105 are formed as thrust receiving surfaces 105s, 105s of the thrust fluid bearing S. The lower end surface of the inner sleeve 102A, which is the mating member, faces the upper thrust receiving surface 105s via the fluid bearing clearance of the thrust fluid bearing S, and the lower end surface of the inner sleeve 102A faces the thrust bearing of the thrust fluid bearing S. The surface is 102As.

The lower thrust receiving surface 105s includes:
The upper surface of the bottom plate 102Ba of the outer sleeve 102B, which is the mating member, faces through the fluid bearing clearance of the thrust fluid bearing S, and the upper surface of the bottom plate 102Ba faces the thrust fluid bearing S.
Thrust bearing surface 102Bs. The thrust receiving surfaces 105s, 105s and the thrust bearing surface 1
At least one of 02As and 102Bs has a herringbone or spiral dynamic pressure generating groove (not shown).
, The thrust fluid bearing S is configured.

On the other hand, a pair of radial receiving surfaces 103r, 103r are formed on the outer peripheral surface of the shaft 103 at an interval vertically. Also, on the inner peripheral surface of the inner sleeve 102A,
Radial fluid bearing R on radial receiving surfaces 103r, 103r
Radial bearing surface 10 facing through the fluid bearing clearance of
2r and 102r are formed. Then, the radial receiving surfaces 103r, 103r and the radial bearing surfaces 102r, 102r
The radial fluid bearings R, R are provided with at least one of the grooves 2r and 2 herringbone-shaped or spiral-shaped grooves 107 for generating dynamic pressure.

A stator 108 is fixed to the outer peripheral surface of the outer sleeve 102B, and the driving motor M is formed facing the rotor magnet 109 fixed to the lower side of the inner peripheral surface of the hub 104 via a gap. The drive motor M rotates the shaft 103 and the hub 104 integrally. When the shaft 103 rotates, a dynamic pressure is generated in a small amount of lubricant filled in the fluid bearing clearances of the respective fluid bearings S and R by the pumping action of the respective dynamic pressure generating grooves of the thrust fluid bearing S and the radial fluid bearing R. do it,
The shaft 103 does not contact the inner peripheral surface of the inner sleeve 102A and the upper surface of the bottom plate 102Ba of the outer sleeve 102B and is supported.

[0009] Like this spindle motor, the shaft 103
When the shaft 103 and the flange 105 are integrally formed, the center hole 11 is formed in the end face of the shaft 103 in order to accurately grind the outer peripheral surface of the shaft 103 serving as the fluid bearing surface.
0 must be provided.

[0010]

In recent years, HDDs have been required to have higher recording densities, and the width of tracks for recording information has become narrower. Therefore, the use of fluid bearings with high rotational accuracy has been studied. ing. Further, HDDs mounted on portable devices such as notebook computers are required to be thinner and have excellent portability (800
There is a demand for a hydrodynamic bearing device having a shock resistance of G or more and a high reliability (it is unlikely to generate unstable vibration).

Therefore, in the above-described spindle motor, the height of the apparatus is reduced to make it thinner, and the use of a member in which the flange portion 105 and the shaft 103 are integrally formed is used to improve the impact resistance. (If the flange portion 105 and the shaft 103 are formed as separate members, the fixing strength thereof becomes a problem.) However, since this shaft 103 is usually made of a hard-to-cut material such as martensitic stainless steel or austenitic stainless steel,
The production of 03 required a step of subjecting a round bar material to cutting and heat treatment, followed by finish grinding and superfinishing. The superfinishing performed after the finish grinding is necessary to secure the end surface runout accuracy of the flange portion 105 and the surface roughness required for the fluid bearing surface.

As described above, since a large number of processing steps are required to manufacture the shaft 103, it is not easy to secure the dimensional accuracy required for the fluid dynamic bearing. In addition, processing costs are increased, and there is a problem in mass productivity. Further, in order to finish-grind the shaft 103 integrated with the flange portion 105 with high accuracy using a grinding machine, it is necessary to provide a center hole 110 on the end face of the shaft 103 (see FIG. 2).

With such a center hole 110, when the spindle motor is filled with the lubricant, air bubbles tend to remain in the center hole 110, and as a result, air bubbles tend to remain inside the spindle motor. Become. Then, unstable vibration is likely to occur during rotation of the spindle motor (the fluctuation NRRO of the rotation asynchronous component increases), and there is a problem that reliability is poor.

Therefore, the present invention solves the above-mentioned problems of the conventional hydrodynamic bearing device, and facilitates machining of the shaft.
Provided is a highly reliable hydrodynamic bearing device which is low in processing cost and excellent in mass productivity and hardly causes unstable vibration.

[0015]

In order to solve the above-mentioned problems, the present invention has the following arrangement. That is, a hydrodynamic bearing device of the present invention is a hydrodynamic bearing device including a shaft having a flange portion formed integrally, and a mating member facing the shaft via a hydrodynamic bearing clearance, wherein the shaft is made of copper. It is characterized by being composed of an alloy or an aluminum alloy.

Since the shaft is made of a copper alloy or an aluminum alloy having excellent workability, it can be easily machined with necessary dimensional accuracy without performing finish grinding and super-finishing required for stainless steel. Can be. Further, since a large number of processing steps are not required for manufacturing the shaft, the processing cost is low and the mass productivity is excellent. Further, since no finish grinding is required, it is not necessary to provide a center hole in the end face of the shaft. Therefore, when the lubricant is filled in the hydrodynamic bearing device, air bubbles are unlikely to remain inside, so that unstable vibration is less likely to occur during rotation of the hydrodynamic bearing device, and the reliability is high.

A plating or diamond-like carbon film (at least one of the two opposing surfaces facing each other via the fluid bearing clearance, ie, at least one of the fluid bearing surfaces formed on the shaft and the mating member). (DLC film). Then, the hardness of the fluid bearing surface is improved, and the slidability at the time of starting and stopping the fluid bearing device is improved, so that damage due to contact between the fluid bearing surfaces is less likely to occur.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a hydrodynamic bearing device according to the present invention will be described in detail with reference to the drawings. FIG.
1 is a longitudinal sectional view of a spindle motor for an HDD, which is one embodiment of a hydrodynamic bearing device according to the present invention. First, the structure of the spindle motor will be described. In the following description, terms indicating directions such as up and down mean the respective directions in FIG. 1 for convenience of explanation unless otherwise specified.

This spindle motor comprises a shaft 13 to which a hub 14 is attached, and a sleeve 12 fixed to a cylindrical portion 11a of a base 11. The shaft 13 is rotatably inserted into the sleeve 12, and a radial fluid bearing R is interposed between the shaft 13 and the sleeve 12. A flange 15 is integrally provided at one end of the shaft 13, and a thrust fluid bearing S is provided between both surfaces of the flange 15 and the sleeve 12 facing the flange. The sleeve 12 corresponds to a mating member which is a constituent element of the present invention.

The sleeve 12 (an outer sleeve 12 described later)
A stator 18 is fixed to the outer peripheral surface of B), and a driving motor M is formed so as to face the rotor magnet 19 fixed to the inner peripheral surface of the hub 14 via a gap. When the hub 14 and the shaft 13 are integrally rotated by the drive motor M, the shaft 13 is rotatably supported on the sleeve 12 by the thrust fluid bearing S and the radial fluid bearing R. I have.

Next, the structure of the spindle motor of this embodiment as described above will be described in more detail. Base 11
A cylindrical sleeve 12 is inserted inside a cylindrical portion 11a provided upright at a central portion of the cylindrical portion 11a, and these are integrally fixed. This sleeve 12 is the inner sleeve 1
2A and the outer sleeve 12B have a double structure fixed integrally. That is, the outer sleeve 12B is
The cylindrical portion 11 has a cylindrical shape having Ba, and the lower surface of the bottom plate 12Ba is substantially the same height as the lower surface of the base 11.
a.

Then, the cylindrical inner sleeve 12A is
It is inserted into the outer sleeve 12B and fixed to the inner peripheral surface.
The shaft 1 is attached to the sleeve 12 (the inner sleeve 12A).
3 is rotatably inserted. Upper end 1 of this shaft 13
3a has a smaller diameter than the other portion,
The shaft 13 and the hub 14 are integrally fixed by press-fitting 3a into a hole provided at the center of a shallow inverted cup-shaped hub 14. The upper end surface 13 of the large-diameter other portion formed at the boundary between the small-diameter upper end portion 13a and the large-diameter other portion.
b, the lower surface of the hub 14 is in contact with the shaft 13 and the hub 1.
4 is fixed with sufficient strength to ensure sufficient impact resistance.

At the lower end of the shaft 13 projecting from the lower end of the sleeve 12, a disk-shaped flange portion 15 is provided. Since the flange portion 15 is formed integrally with the shaft 13, that is, since a member in which the flange portion 15 and the shaft 13 are formed integrally is used, a separate shaft and the flange portion are connected. As compared with the case where the fixing is performed by press fitting or the like, the shock resistance is excellent, and there is no need to worry about the fixing strength.

The upper plane of the flange 15 is
It faces the lower end surface of the inner sleeve 12A. The lower flat surface of the flange portion 15 is the bottom plate 1 of the outer sleeve 12B.
It faces the upper surface of 2Ba. Both upper and lower planes of the flange portion 15 are thrust receiving surfaces 15s, 15s. The lower end surface of the inner sleeve 12A faces the upper thrust receiving surface 15s via the fluid bearing clearance of the thrust fluid bearing S, and faces the lower thrust receiving surface 15s via the fluid bearing clearance of the thrust fluid bearing S. And the upper surface of the bottom plate 12Ba, the thrust bearing surfaces 12As and 12Bs, respectively.
At least one of the opposed thrust receiving surfaces 15s, 15s and the thrust bearing surfaces 12s, 12Bs is provided with, for example, a herringbone-shaped groove for generating dynamic pressure (not shown) to constitute a thrust fluid bearing S. ing.

The groove for generating dynamic pressure is connected to the flange 15
The processing method provided on both planes (thrust receiving surfaces 15s, 15s) is not particularly limited, and examples thereof include plastic working, cutting, and etching. Since the flange portion 15 is made of a copper alloy or an aluminum alloy having a low hardness as described later, plastic working by coining is easy. The coining process is a method of engraving the groove for generating dynamic pressure by pressing a mold against the flange portion 15 using a press or the like, so that it is excellent in mass productivity and low in cost as compared with the etching process.

On the other hand, a pair of radial receiving surfaces 13r, 13r are formed on the outer peripheral surface of the shaft 13 at intervals in the axial direction, and the radial receiving surfaces 13r, 13r are provided with a fluid of the radial fluid bearing R. Radial bearing surfaces 12r, 12r facing each other via a bearing clearance are formed on the inner peripheral surface of the inner sleeve 12A. And the radial bearing surface 12
The radial fluid bearings R, R are provided with dynamic pressure generating grooves 17, 17 in the shape of a generally U-shaped herringbone at r, 12r.

The dynamic pressure generating grooves 17, 17 may be provided on the radial receiving surfaces 13r, 13r, or may be provided on both the radial receiving surfaces 13r, 13r and the radial bearing surfaces 12r, 12r. However, it is preferable to provide the fluid bearing surface of a member made of a material having a low hardness because the opposing surface is less likely to be damaged. The processing method for providing the dynamic pressure generating groove 17 is not particularly limited, and the same conventional method as in the case of the dynamic pressure generating groove provided on both planes of the flange portion 15 is employed.

When the dynamic pressure generating groove 17 is formed on the radial bearing surface 12r, that is, on the inner peripheral surface of the inner sleeve 12A, the dynamic pressure generating groove 17 is formed by plastic working such as ball rolling or cutting with a cutting tool which is excellent in mass productivity. 17 can be processed, which is preferable. Ball rolling is a rolling jig that holds a plurality of steel balls in a hollow outer cylinder fitted to the outer circumference of the shaft,
This is a method of processing by pushing it into a sleeve.

That is, after the inner sleeve 12A is cut on a lathe, the rolling jig is pushed into the inner sleeve 12A and relatively moved while slowly rotating the main shaft of the lathe forward and reverse, thereby forming a herringbone shape on the inner peripheral surface. (Substantially letter-shaped) groove processing is performed, and then, finishing processing such as finish cutting or ball threading for removing a raised portion around the groove is performed as necessary. Of course, instead of using a lathe, a rolling device may be pressed into the fixed inner sleeve 12A while rotating the rolling jig forward and backward in the left and right directions to form a herringbone groove.

The one of the two dynamic pressure generating grooves 17, 17 located on the outside air side has an inward asymmetric groove pattern whose groove length is slightly shorter on the inner side than on the outside air side. It is preferable for the following reasons. In other words, since the pressure that pushes the lubricant in from the outside air side to the inside acts as the shaft 13 rotates (pump-in), the lubricant in the fluid bearing clearance of the radial fluid bearing R is centrifuged by the rotation of the shaft 13. It is prevented from being scattered to the outside by the force.

This will be described in more detail. The dynamic pressure generating groove 17 is composed of a plurality of substantially rectangular grooves arranged at predetermined intervals along the circumferential direction of the shaft 13. 2
Of the dynamic pressure generating grooves 17 provided at the two locations, the dynamic pressure generating groove 17 located on the outside air side (the upper dynamic pressure generating groove 17 in FIG. 1) has an axially asymmetric pattern. Shape. The other dynamic pressure generating groove 17 (FIG. 1)
In (2), the pattern of the lower dynamic pressure generating groove 17) is made symmetrical in the axial direction.

That is, in the dynamic pressure generating groove 17 located on the outside air side, the width from the bent portion to the end on the outside air side of the axial width of the substantially U-shaped groove is set to the inside from the bent portion. Shall be larger than the width up to the end. In the present embodiment, the outside air side is the side of the shaft 13 facing the outside air of the spindle motor (upward in FIG. 1), that is, the side opposite to the side on which the thrust fluid bearing S is provided. Is meant. The inside means the side opposite to the outside air side, that is, the side on which the thrust fluid bearing S is provided.

Further, in order to reduce bubbles from being caught in the lubricant in the fluid bearing clearances of the thrust fluid bearing S and the radial fluid bearing R during rotation, it is necessary to provide the thrust fluid bearing S and the radial fluid bearing R with dynamic fluid. It is desirable that the pressure generation groove has a groove angle (an angle formed with respect to the rotation direction) of 30 ° or less, preferably 25 ° or less, and the number of grooves is 10 or more, preferably 12 or more.

In particular, when the bearing width of the herringbone-shaped dynamic pressure generating groove 17 provided on the radial fluid bearing R (the axial width of the dynamic pressure generating groove 17) is smaller than the shaft diameter, the groove angle is reduced. It is desirable that the angle is 25 ° or less, and the number of grooves is 12 or more, preferably 16 or more. When air bubbles are caught in the lubricant, unstable vibration during rotation is caused, and rotation accuracy is likely to be deteriorated.

The upper and lower two radial fluid bearings R, R
The inner peripheral surface of the inner sleeve 12A sandwiched between
Or the inner circumferential surface of the inner sleeve 12A and the outer circumferential surface of the shaft 13) may be formed from a tapered circumferential groove whose clearance decreases toward the bearing clearance of the radial fluid bearing R. May be provided. By doing so, even if the spindle motor is thinned, a large bearing span, which is the distance between the points of action of the radial fluid bearings R, R, can be taken large, so that the spindle motor has excellent resistance to moment loads. In addition, the escape groove,
Since the clearance is greater than the bearing clearance of the radial fluid bearing R, the fluid friction of the lubricant is reduced. Therefore, the spindle motor has low bearing torque and low power consumption.

Further, the axial position of the rotor magnet 19 and the stator 18 constituting the drive motor M is slightly shifted so that an attractive force acts in the axial direction, so that the load is mainly shared on the lower end side of the inner sleeve 12A. By designing the effective area of the thrust receiving surface 15s on the lower surface side of the flange portion 15 to be smaller than the effective area of the thrust receiving surface 15s on the upper surface side (designing the effective bearing diameter to be smaller), The bearing torque on the load side may be reduced. Then, the power consumption of the spindle motor can be reduced.

A drive motor M is used to mount a hub 14 and a shaft 1 on which a magnetic disk (not shown), which is a rotating body, is mounted on the outer periphery.
3 and the thrust fluid bearing S
Further, due to the pumping action of the respective dynamic pressure generating grooves of the radial fluid bearing R, a dynamic pressure is generated in the lubricant filled in the fluid bearing clearances of the respective fluid bearings S, R, and the shaft 13 becomes the sleeve 12 (the inner sleeve). 12A and the upper surface of the bottom plate 12Ba). Since the magnetic disk is screwed with a clamp member, the magnetic disk is fixed with sufficient strength to ensure sufficient impact resistance.

In the spindle motor of this embodiment, the shaft 13 is made of a copper alloy or an aluminum alloy.
Since copper alloys and aluminum alloys have good workability, there is no need to perform finish grinding and superfinishing as in the case of stainless steel, and the shaft 13 can be formed with good dimensional accuracy only by cutting with a lathe or the like. It is easy to process. Since a large number of processing steps are not required for manufacturing the shaft 13, the processing cost is low and the mass productivity is excellent.

This will be described in more detail. Since stainless steel is a difficult-to-cut material, it needs to be cut using a carbide cutting tool or the like. However, since the required dimensional accuracy cannot be ensured by this cutting alone, the necessary dimensional accuracy has been ensured by performing finish grinding. Also,
Even if the finish grinding is performed, the surface roughness of the fluid bearing surface required for the fluid bearing of 0.4 Ry cannot be ensured, so the super-finishing is further performed. As described above, in the case of stainless steel, many processing steps are required, so that the processing cost is high, and it is not easy to secure required dimensional accuracy and surface roughness, so that there is a problem in mass productivity.

On the other hand, in the case of a copper alloy or an aluminum alloy, since the workability is good, it is possible to perform both cutting and finishing (finish cutting) by using a lathe provided with a diamond tool or the like. It is. That is, by this processing, variation in the outer diameter dimension of the shaft 13 is small, and good dimensional accuracy with a roundness of 1 μm or less can be secured. In addition, the surface roughness of the thrust fluid bearing surface and the radial fluid bearing surface is reduced to 0.4R required for the fluid bearing.
It can be processed to y or less (preferably 0.3 Ry or less).

As described above, in the case of a copper alloy or an aluminum alloy, the number of processing steps is small, and the required dimensional accuracy and surface roughness can be easily secured. Therefore, the processing cost is low and the mass productivity is excellent. In the case of a copper alloy or an aluminum alloy, finishing can be performed by cutting, and finish grinding is not required. Therefore, a center hole necessary for grinding using a grinding machine or the like is provided on the end face of the shaft 13. No need to provide. Axis 1
Since there is no center hole in the end face of No. 3, air bubbles hardly remain in the spindle motor when the spindle motor is filled with the lubricant. Therefore, the spindle motor hardly generates unstable vibration during rotation and has high reliability.

It should be noted that even a small amount of residual air bubbles may cause unstable vibration. Therefore, in order to further ensure the deaeration of the air bubbles, a lubricant which has been previously vacuum degassed or a lubricant may be used. After the injection, the spindle motor may be held under vacuum to perform deaeration. When aging is performed for a short time (at least one minute or more) at a predetermined number of revolutions after the completion of assembling and before use of the spindle motor, the self-discharge function of the dynamic pressure generating groove removes residual air bubbles. It is more reliable and preferable.

The copper alloy and aluminum alloy used have a Vickers hardness Hv of 100 or more, preferably 150 or more. With such copper alloys and aluminum alloys,
Even if the opposing fluid bearing surfaces come into contact with each other during handling or at the beginning of rotation, the fluid bearing surfaces are not easily damaged. Examples of such a copper alloy include beryllium copper, manganese silicide-based high-strength brass, aluminum bronze, and the like. Examples of the aluminum alloy include a silicon-containing aluminum alloy, a ceramic-containing aluminum alloy, and a carbon fiber-containing aluminum alloy. Is raised.

Of course, in order to reduce damage to the fluid bearing surface, a surface treatment with plating, a DLC film, or an alumite is applied to the fluid bearing surface as required to harden the surface, and the sliding property at the time of starting and stopping is reduced. May be improved (but
Anodized aluminum alloy only). In addition, axis 1
When the length of the shaft 13 is long, a so-called Swiss type lathe in which the main shaft can move in the axial direction is preferable as the precision lathe used for the machining of No. 3. When the length of the shaft 13 is short, a precision lathe with a fixed spindle may be used. When using a lathe for bar processing, which is cut from a round bar material, the length of the round bar material should be about 1 m or less in order to suppress the generation of vibration due to high-speed rotation and secure dimensional accuracy. Is preferred.

The present embodiment is an example of the present invention, and the present invention is not limited to the present embodiment. For example, the spindle motor may be a sleeve fixed-shaft rotating type or a shaft fixed-sleeve rotating type. Further, the structure of the fluid bearing, the pattern of the groove for generating dynamic pressure, the detailed structure of the spindle motor, and the like are not limited to the present embodiment, and if necessary, if the object of the present invention can be achieved. It can be changed as appropriate.

For example, the groove for generating dynamic pressure is not limited to a herringbone shape or a spiral shape, but may be any groove pattern as long as it functions as a hydrodynamic bearing.
In addition, according to the material and the required precision, the method of processing the groove may be chemical etching, electrolytic etching, plastic processing, cutting,
Laser processing, ion beam processing, shot blast, and the like can be applied.

Further, the position of the flange portion 15 provided on the shaft 13 is not limited to the shaft end but may be near the shaft end, or may be at the center of the shaft or in the vicinity thereof. Further, the upper and lower surfaces of the flange portion 15 are flat, but may be conical surfaces or spherical surfaces. Further, a lubricant reservoir having a clearance gradually narrowing toward the fluid bearing clearance of the thrust fluid bearing S may be provided between the outer peripheral surface of the inner sleeve 12A and the inner peripheral surface of the outer sleeve 12B. . The opening of the lubricant reservoir communicating with the fluid bearing clearance of the thrust fluid bearing S may be formed to be substantially equal to or slightly larger than the fluid bearing clearance of the thrust fluid bearing S.

Then, the lubricant injected into the spindle motor fills the respective fluid bearing clearances of the thrust fluid bearing S and the radial fluid bearing R by the action of surface tension, and excess lubricant passes through the opening. It accumulates in the lubricant reservoir and is retained by capillary action based on surface tension. Therefore, even if the injection amount of the lubricant is excessive, there is no problem because the excess lubricant is stored in the lubricant reservoir. Further, even if the spindle motor is inverted during transportation or handling, the lubricant in the lubricant reservoir does not flow out.

Further, if the lubricant retained in the fluid bearing clearance gradually evaporates or scatters and runs short over a long period of operation, the lubricant pool will be filled with a capillary phenomenon due to surface tension. The retained lubricant is sucked into the narrower gap in accordance with the lack thereof, and is replenished until the lubricant is filled in each fluid bearing clearance. That is, as the lubricant in each fluid bearing clearance decreases, the fluid bearing clearance is sucked into the fluid bearing clearance having a small clearance via the opening by capillary action, and is stabilized at a position where the surface tension of the inner surface of the lubricant reservoir is balanced. Thus, the lubricant is automatically replenished by the reduced amount of the lubricant. Therefore, even in long-term use,
Lubricant in each fluid bearing clearance is less likely to be depleted.

Further, an air passage communicating with the outside air may be provided in a portion where the clearance of the lubricant reservoir is wider. Then, the lubricant is sucked into the narrow gap by the surface tension, while the air bubbles entrained at the time of assembling or filling with the lubricant are separated into the wide gap and discharged through the air passage. Therefore, since a lubricant having no air bubbles is automatically and surely supplied to each fluid bearing clearance, the reliability is high and the durability is excellent even when used for a long time.

Further, in the spindle motor of the present embodiment, the sleeve 12 has the inner sleeve 12A and the outer sleeve 12A.
B, and a bottom plate 12Ba which is a member that forms the thrust fluid bearing S facing the lower plane of the flange portion 15 and is integral with the outer sleeve 12B. However, instead of such a configuration, the sleeve 12 is formed of one member, and a portion of the bottom plate 12Ba, which is a member that forms the thrust fluid bearing S in opposition to the lower flat surface of the flange portion 15, is externally formed. It goes without saying that a configuration separate from the sleeve 12B may be used at all.

Further, a through hole for injecting a lubricant may be provided in the bottom plate 12Ba. Further, the sleeve 12
The material of the shaft is not particularly limited. In addition to the same copper alloy and aluminum alloy as the shaft 13, stainless steel, sintered metal, oil-impregnated sintered metal, plastic, ceramic usually used for members constituting the spindle motor are used. Etc. can be used.

However, if the sleeve 12 and the shaft 13 are made of the same kind of copper alloy or aluminum alloy, the linear expansion coefficients are almost equal, so that even when the ambient temperature changes, the sleeve 12 and the shaft 1 are not changed.
3 is hardly changed in the radial direction, and a copper alloy or an aluminum alloy is preferable because it is easy to process. Furthermore, if the shaft 13 is made of an aluminum alloy and the sleeve 12 is made of a copper alloy, the linear expansion coefficient of the aluminum alloy is slightly large, so that the clearance in the radial direction becomes small at high temperatures, so that a decrease in rigidity can be prevented.

The material of the sleeve 12 is preferably selected to have a lower hardness than the shaft 13 in order to avoid gold. Furthermore, in the present embodiment, the spindle motor has been described as an example of the hydrodynamic bearing device. However, the present invention can be applied to various other hydrodynamic bearing devices.

[0055]

As described above, in the hydrodynamic bearing device of the present invention, since the shaft is made of a copper alloy or an aluminum alloy, the shaft can be easily machined, the machining cost is low, and mass production is excellent. Unstable vibration hardly occurs and high reliability.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a spindle motor which is an embodiment of a hydrodynamic bearing device according to the present invention.

FIG. 2 is a longitudinal sectional view of a conventional spindle motor.

[Explanation of symbols]

 12 Sleeve 12A Inner sleeve 12B Outer sleeve 13 Shaft 15 Flange R Radial fluid bearing S Thrust fluid bearing

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Katsuhiko Tanaka 1-5-50 Kugenuma Shinmei, Fujisawa-shi, Kanagawa F-term in NSK Ltd. (reference) 5H607 AA00 BB01 BB09 BB14 BB17 BB25 CC01 DD16 GG01 GG02 GG09 GG12 GG15

Claims (1)

[Claims] 1. A hydrodynamic bearing device comprising: a shaft having an integrally formed flange portion; and a mating member facing the shaft via a fluid bearing clearance, wherein the shaft is made of a copper alloy or an aluminum alloy. A hydrodynamic bearing device characterized by comprising.