JP2002147444A - Fluid bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluid bearing device eliminating any possibility of the deformation of a flange part in fixing the flange part to a shaft even if thinning the flange part and any possibility of falling of the flange part from the shaft in applying a large impact thereto, and scarcely causing the unstable vibration caused by effects of bubbles. SOLUTION: This fluid bearing device is provided with the shaft 13 having the flange part 15 in one end, sleeves 12 opposed to each other in the shaft 13 via a fluid bearing clearance of a radial fluid bearing R, and counter plates 16 opposed to each other in one plane of the flange part 15 via a fluid bearing clearance of a thrust fluid bearing S. The flange part 15 is fixed to the shaft 13 by a hollow screw 20 screwed with a through hole 13f or a hollow pin 20c fitted around it with the shaft 13 set to a hollow shaft having the through hole 13h.

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 HDD), an optical disk device, and the like.

[0002]

2. Description of the Related Art An example of such a hydrodynamic bearing device under development is a spindle motor for an HDD as shown in FIG. A cylindrical sleeve 2 is inserted inside a cylindrical portion 1a erected on a base 1 of the spindle motor, and these are integrally fixed. And
The shaft 3 is rotatably inserted into the sleeve 2, and a hydrodynamic bearing is interposed between the shaft 3 and the sleeve 2.

[0003] An inverted cup-shaped hub 4 is integrally attached to the upper end of the shaft 3, and a disk-shaped flange portion 5 is fixed to the lower end of the shaft 3 by press-fitting. Both flat surfaces of the flange portion 5 are thrust receiving surfaces 5s, 5s of the thrust fluid bearing S. The lower end surface of the sleeve 2 is opposed to the thrust receiving surface 5s on the upper surface via a thrust fluid bearing clearance, and the lower end surface of the sleeve 2 is the thrust bearing surface 2s of the thrust fluid bearing S.

A counter plate 6 as a mating member is arranged below the flange 5 and is fixed to the base 1. The upper surface of the counter plate 6 faces the thrust receiving surface 5s on the lower surface side of the flange portion 5 with a thrust fluid bearing clearance interposed therebetween, and serves as a thrust bearing surface 6s of the thrust fluid bearing S. The thrust receiving surface 5s,
At least one of the 5s and the thrust bearing surfaces 2s and 6s is provided with a herringbone-shaped or spiral-shaped groove (not shown) for generating a dynamic pressure, thereby forming a thrust fluid bearing S.

[0005] Further, a pair of radial receiving surfaces 3r, 3r are formed on the outer peripheral surface of the shaft 3 at an interval vertically. A radial receiving surface 3 is provided on the inner peripheral surface of the sleeve 2.
Radial bearing surfaces 2r, 2r are formed so as to oppose r, 3r via a radial fluid bearing clearance. At least one of the radial receiving surfaces 3r, 3r and the radial bearing surfaces 2r, 2r is provided with a herringbone-shaped or spiral-shaped groove 7 for generating dynamic pressure, so that the radial fluid bearings R,
R is configured.

A stator 8 is fixed to the outer peripheral surface of the cylindrical portion 1a, and a driving motor M is formed facing the rotor magnet 9 fixed below the inner peripheral surface of the hub 4 via a gap. The shaft 3 and the hub 4 are integrally rotated by the drive motor M. Axis 3
Rotates, a dynamic pressure is generated in a small amount of lubricant filled in the fluid bearing clearances of the fluid bearings S and R by the pumping action of the dynamic pressure generating grooves of the thrust fluid bearing S and the radial fluid bearing R. The shaft 3 is not in contact with the sleeve 2 and the counter plate 6 and is supported.

[0007]

The HDD mounted on a portable device such as a notebook personal computer is required to be thinner and lighter and to have an improved recording density. Therefore, adoption of a fluid bearing is being studied. However, in the configuration in which the flange portion 5 is fixed to the shaft 3 by press-fitting as described above, if the flange portion 5 is further thinned to make the spindle motor thinner, the flange portion 5 is formed on the lower surface of the flange portion 5 by the press load during press-fitting. The thrust receiving surface 5s is deformed and the thrust receiving surface 5s
There is a fear that the flatness of the sample may be reduced.

When the pressing load at the time of press-fitting is reduced in order to avoid deformation of the thrust receiving surface 5s, the fixing strength of the flange portion 5 to the shaft 3 is reduced, and when a large impact is applied, the flange portion 5 However, there was a risk of falling off the shaft 3. Furthermore, in the above-described fluid bearing device, generally, after inserting the shaft member into the sleeve, the lubricant is injected, and then the counter plate is attached. Therefore, air bubbles are generated in the space between the counter plate and the flange portion during assembly. There was a possibility that the air bubbles would remain in the bearing clearance and its vicinity due to being trapped. And if the air bubbles remain, the air bubbles expand due to changes in atmospheric pressure and temperature during use,
As a result, the spindle motor may generate unstable vibration during rotation.

Accordingly, the present invention solves the problems of the hydrodynamic bearing device under development as described above, and even if the flange portion is thinned, the flange portion may be deformed when the flange portion is fixed to the shaft. It is another object of the present invention to provide a hydrodynamic bearing device which does not have a possibility of causing the flange portion to fall off the shaft when a large impact is applied, and is less likely to generate unstable vibration due to the influence of bubbles.

[0010]

According to a first aspect of the present invention, there is provided a hydrodynamic bearing device comprising: a shaft having a flange at one end; and a thrust fluid on at least one plane of the flange. And a mating member facing through a fluid bearing clearance of the bearing, wherein the shaft is a hollow shaft having a through hole opened at both end surfaces of the shaft, and the flange portion is It is fixed to the shaft by a hollow screw screwed into the through hole or a hollow pin fitted into the through hole.

As described above, since the flange portion is fixed to the shaft by the hollow screw screwed into the through hole of the shaft or the hollow pin fitted into the through hole, even if the flange portion is made thin, There is no fear that the flange portion will be deformed when the flange portion and the shaft are fixed, and that there will be no risk that the flange portion will fall off the shaft when a large impact is applied. Furthermore, since the shaft is a hollow shaft having through holes opened at both end surfaces of the shaft, a lubricant can be injected into the hydrodynamic bearing device from the through hole after assembling the hydrodynamic bearing device. (For example, a method in which a lubricant is injected by inserting a dispenser into the through-hole), the injection of the lubricant is easy, and the risk of bubbles being trapped in the lubricant can be reduced. In addition, even if bubbles are accidentally entrapped inside and the bubbles expand due to a change in atmospheric pressure or a change in operating temperature, the expanded bubbles are discharged to the outside through the through-holes. Less likely to occur.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the hydrodynamic bearing device according to the present invention will be described in detail with reference to the drawings. (First Embodiment) FIG. 1 is a sectional view of a spindle motor for an HDD, which is a first embodiment of a hydrodynamic bearing device according to the present invention.

First, the structure of the spindle motor will be described. This spindle motor includes a shaft 13 to which a hub 14 is fixed, and a sleeve 12 through which the shaft 13 is inserted. A radial fluid bearing R is interposed between the shaft 13 and the sleeve 12. . Also, at one end of the shaft 13,
A flange portion 15 is provided, and a thrust fluid bearing S is provided between both flat surfaces of the flange portion 15 and the sleeve 12 and the counter plate 16 opposed thereto. The sleeve 12 and the counter plate 16
Corresponds to a mating member which is a constituent element of the present invention.

The base 11 to which the sleeve 12 is fixed
A stator 18 is fixed to the outer peripheral surface of the cylindrical portion 11a, 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 sleeve 12 having a cylindrical shape with a flange is inserted inside a cylindrical portion 11a provided upright at a central portion of the cylindrical portion, and is integrally fixed by the flange 12f. As a result, a lubricant reservoir 22 having an annular clearance is formed between the outer peripheral surface of the sleeve 12 and the inner peripheral surface of the cylindrical portion 11a. The structure of the lubricant reservoir 22 will be described later in more detail.

A hollow shaft 13 provided with a through hole 13 is rotatably inserted into the sleeve 12.
A female screw 13f is formed on the inner peripheral surface of 3h. The material of the shaft 13 is not particularly limited as long as it is a material having high hardness and excellent corrosion resistance. For example, a martensitic stainless steel or an austenitic stainless steel is subjected to a heat treatment to form a surface. A hardened material or a copper alloy or aluminum alloy having high hardness may be used. In addition, there may be mentioned those obtained by performing surface treatment with plating or a diamond-like carbon (DLC) film to harden the surface.

The upper end portion 13a of the shaft 13 has a smaller diameter than the other portion. The small upper end portion 13a is press-fitted into a hole provided in the center of a shallow inverted cup-shaped hub 14 so that the shaft 13 has a smaller diameter. And the hub 14 are integrally fixed. Since the lower surface of the hub 14 abuts on the upper end surface 13b of the large-diameter other portion formed at the boundary between the small-diameter upper end portion 13a and the large-diameter other portion, the shaft 13 and the hub 14 are sufficiently separated from each other. With sufficient strength to ensure high impact resistance.

A disk-shaped flange 15 is fixed to the lower end of the shaft 13 projecting from the lower end of the sleeve 12. That is, the flange portion 15 is attached to the shaft 13 by a set screw 20 having a through hole 20a screwed into a female screw 13f provided on the inner peripheral surface of the through hole 13h of the shaft 13. When the flange portion 15 is attached by screwing, sufficient fastening strength is secured. Unlike the case where the flange portion 15 is attached by press fitting, no large load is applied to the flange portion 15 so that there is no deformation, and the shaft 13 and the flange 13 are not attached. The portion 15 has sufficient strength to ensure sufficient impact resistance.

The shape of the head 20b of the set screw 20 is not limited to the flat head shown in the drawing, but may be a round head such as a round screw or a countersunk head such as a countersunk screw. May be changed. The lower surface of the flange portion 15 faces the upper surface of the counter plate 16 attached to the central portion of the base 11, and the opposing surfaces are in contact when the spindle motor is stopped. The upper surface of the flange portion 15 faces the lower end surface of the sleeve 12.

The central portion of the counter plate 16 (the shaft 13
(Located immediately below) is provided with a concave portion 16a for accommodating the head portion 20b of the set screw 20. Then set screw 2
It is not necessary to attach the “0” in a state of being immersed in the flange portion 15, and the processing of the flange portion 15 becomes easy. When the set screw 20 for fixing the flange portion 15 is attached in a form in which the head portion 20b is immersed, the concave portion 16a does not need to be provided.

Both upper and lower planes of the flange portion 15 are thrust receiving surfaces 15s, 15s. The lower end surface of the sleeve 12 facing the upper surface thrust receiving surface 15s via the thrust fluid bearing clearance, and the lower surface thrust receiving surface 15s
s is opposed to the upper surface of the counter plate 16 via the thrust fluid bearing clearance, respectively.
2s and 16s, and the opposing thrust receiving surfaces 15
and at least one of the thrust bearing surfaces 12s and 16s is provided with a dynamic pressure generating groove (not shown) having a herringbone shape, a spiral shape, or the like.
Is composed.

The groove for generating dynamic pressure is connected to the flange 15
The processing method provided on both flat surfaces (thrust receiving surfaces 15s, 15s) is not particularly limited, and examples thereof include plastic working, cutting, and etching. The coining process, which is plastic working, is a method of stamping the dynamic pressure generating groove by pressing a mold against the flange portion 15 using a press or the like. Cost.

On the other hand, a pair of upper and lower radial receiving surfaces 13r, 13r are formed on the outer peripheral surface of the shaft 13 at an interval in the axial direction, and the radial receiving surfaces 13r, 13r are provided with radial fluid bearing clearances. And opposed radial bearing surfaces 12r, 12r are formed on the inner peripheral surface of the sleeve 12. A radial fluid bearing R is provided on at least one of the radial receiving surface 13r and the radial bearing surface 12r, for example, with a U-shaped herringbone-shaped groove 17 for generating dynamic pressure. The processing method for providing the dynamic pressure generating groove 17 is not particularly limited, and is not particularly limited.
The same conventional method as described above 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 sleeve 12, 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. Is preferred because it can be processed. Ball rolling is a method in which a rolling jig in which a plurality of steel balls are held in a hollow outer cylinder fitted to the outer periphery of a shaft is pressed into a sleeve.

That is, after the sleeve 12 is cut on a lathe, the rolling jig is relatively moved with respect to the sleeve 12 while slowly rotating the main shaft of the lathe forward and backward, so that a herringbone shape is formed on the inner peripheral surface. Is performed, and thereafter, finish machining such as finish cutting or ball-through to remove a bulge around the groove is performed as necessary. Of course, instead of using a lathe, the rolling jig may be pressed into the fixed sleeve 12 while rotating the rolling jig forward and backward in the left and right directions to form a herringbone groove.

Groove 1 for generating dynamic pressure of this radial fluid bearing R
It is preferable that 7 is an inward asymmetric groove pattern in which the groove length is slightly shorter on the inner side than on the outer side for the following reasons. In other words, the pressure that pushes the lubricant from the outside air side to the opposite side acts with the rotation of the shaft 13 (pump-in), so that the centrifugal force caused by the rotation of the shaft 13 causes the inside of the fluid bearing clearance of the radial fluid bearing R to move. Lubricant is prevented from scattering to the outside.

This will be described in further detail. The dynamic pressure generating groove 17 is constituted by a plurality of substantially rectangular grooves arranged at predetermined intervals along the circumferential direction of the shaft 13. .
Of the dynamic pressure generating grooves 17, 17 provided at two locations, the dynamic pressure generating groove 17 (the upper dynamic pressure generating groove 17 in FIG. 1) located on the outside air side has a pattern in the axial direction. The shape is asymmetric. Then, the pattern of the other dynamic pressure generating groove 17 (the lower dynamic pressure generating groove 17 in FIG. 1) is changed to
The shape is symmetrical in the axial direction.

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

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.

Further, in order to reduce the torque of the spindle motor, the inner peripheral surface of the sleeve 12 (the outer peripheral surface of the shaft 13 or the inner peripheral surface of the sleeve 12 may be interposed between the upper and lower radial fluid bearings R, R). The clearance groove 21 may be a tapered peripheral groove whose clearance becomes narrower toward the bearing clearance of the radial fluid bearing R on both the surface and the outer peripheral surface of the shaft 13).

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

Next, the structure of the lubricant reservoir 22 will be described. An annular clearance is interposed between the outer peripheral surface of the sleeve 12 and the inner peripheral surface of the cylindrical portion 11a, and the annular clearance forms a lubricant reservoir 22. The inner peripheral surface of the cylindrical portion 11a forming the inner surface of the lubricant reservoir 22 is formed as a tapered surface 24, whereby the clearance of the lubricant reservoir 22 gradually decreases toward the lower thrust fluid bearing S.

However, the tapered surface 24 is not always formed on the inner peripheral surface of the cylindrical portion 11a, but may be formed on the outer peripheral surface of the sleeve 12, or the outer peripheral surface of the sleeve 12 and the inner peripheral surface of the cylindrical portion 11a. May be formed on both.
The tapered surface 24 may be tapered to the position where the counter plate 16 is located. Further, at the lower end of the lubricant reservoir 22, the outer peripheral surface 1 of the flange portion 15 is provided.
A lubricant supply passage 25 is provided which opens toward an annular clearance formed between the inner peripheral surface of the cylindrical portion 11a which is a member facing the lubricant supply passage 5a.

The opening of the lubricant supply passage 25 communicating with the fluid bearing clearance of the thrust fluid bearing S in close proximity
Is approximately equal to the fluid bearing clearance of the thrust fluid bearing S,
Alternatively, the lubricant is slightly larger, so that the lubricant is easily introduced from the lubricant supply passage 25 to the fluid bearing clearance of the thrust fluid bearing S by a capillary phenomenon based on the surface tension.

In the present embodiment, the entire lower portion of the lubricant reservoir 22 having an annular clearance forms a lubricant supply passage 25 (that is, the lubricant supply passage 25 has an annular clearance shape). A slit-shaped lubricant supply passage 25 may be provided at one position in the lower part of the agent reservoir 22 (that is, in the other portions, the outer peripheral surface of the sleeve 12 and the inner peripheral surface of the cylindrical portion 11a are in contact with each other. And a slit-shaped lubricant supply passage 25 may be provided at a plurality of locations.

In the present embodiment, the cylindrical portion 11
The entirety of the inner peripheral surface of the a
A part of the tapered surface 24 is a lubricant supply passage 25, and the tapered surface 24 is directly communicated with an annular gap formed between the outer peripheral surface 15a of the flange portion 15 and the inner peripheral surface of the cylindrical portion 11a. Let me. However, the upper portion of the inner peripheral surface of the cylindrical portion 11a is a tapered surface 24, and the lower portion is a surface parallel to the outer peripheral surface of the sleeve 12, and an annular clearance formed by this parallel surface forms the lubricant supply passage 25. Such a structure may be adopted.

On the upper part of such a lubricant reservoir 22,
An air vent hole 23 communicating with the outside air is open. The air vent hole 23 extends vertically from the top of the lubricant reservoir 22 and opens at the upper end surface of the sleeve 12. of course,
The air vent hole 23 may be provided so as to form an axial slit on the surface of the cylindrical portion 11a that fits with the sleeve 12.

Further, a corner at the upper end (outside air side) of the inner peripheral surface of the sleeve 12 is chamfered. This allows
The uppermost end (outside air side) of the clearance formed between the outer peripheral surface of the shaft 13 and the inner peripheral surface of the sleeve 12 has a tapered shape in which the clearance gradually increases upward (outside air side). Has become. At this time, the angle formed by the tapered shape, that is, the angle formed between the inclined surface of the chamfered portion and the outer peripheral surface of the shaft 13 is defined as α.

The angle α formed by the tapered shape is
Is larger than the angle formed between the outer peripheral surface of the sleeve 12 (that is, the tapered surface 24) and the inner peripheral surface of the cylindrical portion 11a (hereinafter, referred to as the inclination angle of the tapered surface 24). With such a configuration, since the surface tension acts strongly on the narrower gap, the lubricant is more strongly sucked into the lubricant reservoir 22 than the tapered gap of the chamfered portion, The liquid level of the lubricant located at the chamfered portion can be lowered and can be maintained below the chamfered portion.

Further, the volume of the lubricant reservoir 22 is
Of the gap formed between the outer peripheral surface of the sleeve 3 and the inner peripheral surface of the sleeve 12 is a tapered portion at the uppermost portion (that is, the inclined surface of the chamfered portion and the shaft 13).
If the volume of the outer peripheral surface is larger than that of the portion facing the inclined surface (the portion surrounded by the inclined surface), excess lubricant is retained in the lubricant reservoir 22.

Therefore, even if the injection amount of the lubricant is excessive or insufficient, the possibility that the lubricant is scattered to the outside or the lubricant in each fluid bearing clearance is depleted during a long-term use is reduced. Therefore, the long-term reliability of the spindle motor is excellent. In order to sufficiently exhibit the above-described effects, it is preferable that the inclination angle of the tapered surface 24 is 0 ° or more and less than 45 °, and the angle α formed by the tapered shape is 45 ° or more. In particular, the inclination angle of the tapered surface 24 is set to 10 °
When the following conditions are satisfied, the above-mentioned effect is more sufficiently exhibited. In addition, in order to suction and hold the excess lubricant in the lubricant reservoir 22 by surface tension, in practice, the angle α formed by the tapered shape is set to be larger than the inclination angle of the tapered surface 24 by 15 ° or more. preferable.

If the bearing span, which is the distance between the two radial fluid bearings R, is to be widened within the determined apparatus height, the outer peripheral surface of the shaft 13 and the inner peripheral surface of the sleeve 12 must be separated. The length of the tapered portion of the gap formed between them, that is, the axial width of the inclined surface of the chamfered portion needs to be smaller. On the other hand, since it is necessary to retain as much excess lubricant as possible in the lubricant reservoir 22, the angle α formed by the tapered shape is set to 4 °.
It is desirable that the width of the inclined surface in the axial direction be 5 mm or more and 1 mm or less, preferably 0.5 mm or less. further,
In order to increase the long-term reliability, it is necessary to secure a sufficient amount of the lubricant that can be held in the lubricant reservoir 22. Therefore, the axial width of the tapered surface 24 is set to 2 times the axial width of the inclined surface.
It is preferable that the number be twice or more.

The width of the widest part (radial width) of the tapered shape of the chamfered part is the widest part.
Is larger than the width (radial width) of the widest part of the lubricant reservoir 22, and is held by the lubricant level located in the chamfered portion and the lubricant reservoir 22. The liquid level of the lubricant is at a position where the surface tension is balanced. Accordingly, the liquid level of the lubricant located in the chamfered portion can be maintained below the chamfered portion, and the lubricant is prevented from scattering from the chamfered portion to the outside with the rotation.

In this embodiment, the inclined surface is provided on the inner peripheral surface of the sleeve 12 (that is, the chamfered portion is provided on the inner peripheral surface of the sleeve 12).
It may be provided on the outer peripheral surface of the shaft 13 or the sleeve 12
And the outer peripheral surface of the shaft 13 may be provided. When the inclined surface is provided on the outer peripheral surface of the shaft 13, the inclined surface is provided on the outermost air side portion among the portions facing the inner peripheral surface of the sleeve 12.

An oil repellent (having a property of repelling a lubricant) is applied to the inclined surface of the chamfered portion of the sleeve 12 and a portion of the outer peripheral surface of the shaft 13 facing the inclined surface. When the oil repellent treatment is performed, the lubricant is repelled to the portion subjected to the oil repellent treatment, and the lubricant leaks outside the part (the chamfered part or the like) when the spindle motor is stationary or rotating. Can be more effectively prevented.

Next, a method of injecting a lubricant into the spindle motor will be described. The lubricant is injected into the spindle motor after the entire assembly is completed.
3 through a through hole 13h using a dispenser or the like. As described above, since the lubricant can be injected from the through hole 13h of the shaft 13, the injection operation of the lubricant is easy.
Further, the lubricant injected from the through hole 13h gradually spreads and fills each fluid bearing clearance through the through hole 20a of the set screw 20 by utilizing the surface tension.
When the lubricant is injected, inside the device (in each fluid bearing clearance)
Air bubbles are less likely to get caught in the air. Further, air bubbles remaining in the bearing clearance and in the vicinity thereof are formed in the through hole 1 of the shaft 13.
Since it is discharged to the outside from 3h through the through hole 20a of the set screw 20, there is little possibility that unstable vibration will occur even if a change in air pressure or a change in operating temperature occurs. In addition, the through hole 13h
Even when a bolt for fixing the magnetic disk mounted on the hub 14 is screwed into the female screw 13f formed on the inner peripheral surface of the hub, the through hole 13h communicates with the outside via the screw clearance. . In addition, in order to ensure the deaeration of air bubbles, if necessary, use a lubricant that has been vacuum degassed in advance, or fill the lubricant while injecting the lubricant into the vacuum tank after pouring the lubricant. It may be.

The injected lubricant fills the respective fluid bearing clearances of the thrust fluid bearing S and the radial fluid bearing R by surface tension, and excess lubricant is supplied to the lubricant supply passage 2.
5 and is accumulated in the lubricant reservoir 22 and is held on the tapered surface 24 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 22. Further, even if the spindle motor is inverted during transportation or handling, the lubricant in the lubricant reservoir 22 does not flow out. The through hole 13 of the shaft 13 is
An absorbing member made of a porous member may be provided inside the through hole 13h of the shaft 13 so that the excess lubricant that has oozed out on the inner peripheral surface of the shaft 13 does not flow out during transportation or rotation. .

Further, since the size of the clearance of the lubricant reservoir 22 becomes narrower toward the lower lubricant supply passage 25 due to the tapered surface 24, the lubricant scattered by the external impact does not flow out. Are naturally collected in the lubricant supply passage 25 having a narrow clearance in the lubricant reservoir 22. The air bubbles collected on the upper portion (the larger gap) of the lubricant reservoir 22 are discharged to the outside through the air vent hole 23.

The drive motor M drives the hub 14 and the shaft 1 for mounting a magnetic disk (not shown), which is a rotating body, on the outer periphery.
3 and the thrust fluid bearing S
Further, due to the pumping action of each dynamic pressure generating groove of the radial fluid bearing R, a dynamic pressure is generated in the lubricant filled in the fluid bearing clearance of each fluid bearing S, R, so that the shaft 13 becomes the sleeve 12 and the counter plate. No contact with 16 and it is supported. Since the magnetic disk is screwed with a clamp member, the magnetic disk is fixed with sufficient strength to ensure sufficient impact resistance.

If the lubricant retained in the clearance of the fluid bearing gradually evaporates or scatters and runs short over a long period of operation, the lubricant is retained in the lubricant reservoir 22 by capillary action based on the surface tension. The lubricated lubricant is sucked into the narrower gap while being guided by the tapered surface 24 according to the shortage, and is replenished until the lubricant is filled in the fluid bearing clearance. That is, as the lubricant in the fluid bearing clearance decreases, the lubricant is sucked by the capillary bearing via the lubricant supply passage 25 into the fluid bearing clearance having a smaller clearance, and the surface tension of the tapered surface 24 of the lubricant reservoir 22 is balanced. And stabilized. Thus, the lubricant is automatically replenished by the reduced amount of the lubricant.

As described above, in the spindle motor of the present embodiment, since the annular clearance of the lubricant reservoir 22 is tapered, the lubricant is sucked toward the narrower clearance by the surface tension, while the residual air bubbles that are entrained during the assembly are removed. Is separated and discharged to the larger gap. Accordingly, a lubricant having no air bubbles is automatically and reliably replenished to each of the fluid bearing clearances, and is constantly filled with the lubricant. Even when the lubricant is used for a long time, the reliability is high and the durability is excellent.

Therefore, even if the amount of the injected lubricant is too small or small, there is little possibility that the lubricant will be scattered to the outside or the lubricant in the fluid bearing clearance will be depleted during a long-term use. In the vicinity of the shaft 13 of the flange portion 15,
A communication hole 15b communicating the space with the through hole 13h is provided. The air bubbles collected in the space between the sleeve 12 and the shaft 13 during the rotation of the spindle motor move to the space between the flange portion 15 and the counter plate 16 through the flow hole 15b, and pass through the through hole 13h of the shaft 13 Is discharged to the outside. In addition, using a vacuum-degassed lubricant or putting the spindle motor in a vacuum chamber after injecting the lubricant,
When the number of bubbles entrained in the lubricant is reduced in advance, the flow hole 15b may be omitted.

(Second Embodiment) Next, a spindle motor according to a second embodiment will be described with reference to the sectional view of FIG. The description of the same parts as those of the spindle motor of the first embodiment will be omitted, and only different parts will be described. In FIG. 2, the same or corresponding parts as those in FIG. 1 are denoted by the same reference numerals as those in FIG.

In this spindle motor, a shaft 13 is integrated with a base 11, and a sleeve 12 supported on a fixed shaft 13 through a radial fluid bearing R and a thrust fluid bearing S rotates together with a hub 14. That is, it is a spindle motor of a shaft fixed type and a sleeve rotating type.
A shaft 13 is provided upright at the center of the base 11, and this shaft 1
3 is fixed to the base 11 by press fitting. The shaft 13 is a hollow shaft having through holes 13h opened at both end surfaces.

The shaft 13 is rotatably inserted into a cylindrical sleeve 12, and this sleeve 12 is fixed by press-fitting to the center of an inverted cup-shaped hub 14 on which an unillustrated magnetic disk is mounted on the outer periphery. I have. Also, sleeve 1
Reference numeral 2 denotes a double structure in which the inner sleeve 12A and the outer sleeve 12B are integrally fixed, and the shaft 13 is inserted through the inner sleeve 12A. That is, the outer sleeve 12B
Is a cylindrical body having a top plate 12Ba, and an outer sleeve 12B
Are integrally fixed to the hub 14. The inner sleeve 12A is a cylindrical body having a flange 12Af, and the flange 12Af is fixed to an inner peripheral surface at a lower portion of the outer sleeve 12B, whereby an outer peripheral surface of the inner sleeve 12A and an inner peripheral surface of the outer sleeve 12B are formed. Between them, an annular clearance forming the lubricant reservoir 22 is formed. An air vent hole 23 communicating with the outside air is provided at the lower end of the lubricant reservoir 22. The air vent hole 23 is provided in the lubricant reservoir 2.
2 extends vertically downward from the lower end thereof, and opens to the lower end surface of the inner sleeve 12A. Of course, the air vent hole 23 may be provided so as to form a slit in the axial direction on the fitting surface of the outer sleeve 12B with the inner sleeve 12A. The structure of the lubricant reservoir 22 will be described later in more detail.

Shaft 1 protruding from the upper end of inner sleeve 12A
A disk-shaped flange portion 15 is fixed to the upper end of 3. The flange portion 15 is provided with a pin 20 having a through hole 20d bonded in a state fitted into the through hole 13h of the shaft 13.
c, it is attached to the shaft 13. When the flange portion 15 is attached with the pin 20c, sufficient fastening strength is secured, and unlike the case where the flange portion 15 is attached by press fitting, no large load is applied to the flange portion 15 so that there is no deformation, and the shaft 13 and the flange 13 are not attached. The portion 15 has sufficient strength to ensure sufficient impact resistance. In addition,
A set screw may be used instead of the pin 20c. When a set screw is used, the gap formed between the hole in which the set screw is inserted and the screw thread of the set screw is also filled with the adhesive, so that the bonding area increases and the pin 20c is used. The fixing strength can be significantly improved as compared with the case.

The base 11 is provided with an annular cylindrical portion 11a radially outward of the shaft 13.
The lower portion of the sleeve 12 is disposed between the shaft a and the shaft 13. The upper surface of the flange portion 15 is the top plate 1 of the outer sleeve 12B which is one of the mating members and corresponds to the counter plate.
2Ba is opposed to the lower surface, and both opposing surfaces are in contact with each other when stopped. The lower surface of the flange portion 15 faces the upper end surface of the inner sleeve 12A, which is the other member.

Both upper and lower planes of the flange portion 15 are thrust receiving surfaces 15s, 15s. Then, the top plate 12B of the outer sleeve 12B facing the thrust receiving surface 15s on the upper surface side
The upper surface of the inner sleeve 12A opposed to the lower surface of the inner sleeve 12A and the thrust receiving surface 15s on the lower surface side is the thrust bearing surface 1 respectively.
2Bs and 12As. In addition, thrust receiving surface 1
At least one of the 5s, 15s and the thrust bearing surfaces 12As, 12Bs is provided with, for example, a herringbone-shaped groove (not shown) for generating dynamic pressure, so that the thrust fluid bearing S
Is composed.

On the other hand, a pair of radial receiving surfaces 13r, 13r are formed on the outer peripheral surface of the shaft 13 at an interval in the axial direction, and a radial bearing surface 12r facing the radial receiving surfaces 13r, 13r. , 12r is the inner sleeve 1
2A is formed on the inner peripheral surface of the radial bearing surface 12A.
For example, radial fluid bearings R, R are provided with r-shaped and herringbone-shaped herringbone-shaped grooves 17 for generating dynamic pressure. The grooves 17 for generating dynamic pressure
May be provided on the radial receiving surface 13r, or may be provided on both the radial bearing surface 12r and the radial receiving surface 13r.

Further, in order to reduce the torque of the spindle motor, the inner peripheral surface of the inner sleeve 12A (or the outer peripheral surface of the shaft 13 or the inner peripheral surface of the inner sleeve 12A) sandwiched between the upper and lower two radial fluid bearings R, R. And the outer peripheral surface of the shaft 13), there is provided a relief groove 21 composed of a tapered peripheral groove whose clearance decreases toward the bearing clearance of the radial fluid bearing R.

Further, the inner peripheral surface of the outer sleeve 12B forming the inner surface of the lubricant reservoir 22 is formed as a tapered surface 24, so that the lubricant reservoir 22 is disposed on the upper thrust fluid bearing S (the outer peripheral surface of the flange portion 15). The width (gap) gradually decreases toward the gap (gap between 15a and the inner peripheral surface of the outer sleeve 12B opposed thereto). However, the tapered surface 24 is not necessarily formed on the inner peripheral surface of the outer sleeve 12B, and may be formed on the outer peripheral surface of the inner sleeve 12A. Alternatively, the outer peripheral surface of the inner sleeve 12A and the inner peripheral surface of the outer sleeve 12B may be formed. May be formed on both.

In the case of the sleeve rotation type, when the tapered surface 24 is formed on the outer peripheral surface of the inner sleeve 12A, the lubricant held in the lubricant reservoir 22 is directed toward a lubricant supply passage 25 having a narrow clearance, which will be described later. It is suitable for high-speed rotation because it is pushed by centrifugal force. And the lubricant pool 22
The portion communicating with the thrust fluid bearing S in the upper part of the thrust fluid bearing S is substantially equal to the bearing clearance of the thrust fluid bearing S,
Alternatively, the lubricant supply passage 25 has a slightly larger clearance so that the lubricant can be easily introduced into the bearing clearance by capillary action based on surface tension.

The injection of the lubricant into the spindle motor is performed by using a dispenser or the like from the through hole 13h of the shaft 13 after assembling the whole. Since the lubricant can be injected from the through-hole 13h in this manner, the operation of injecting the lubricant is easy, and at that time, there is little possibility that bubbles are trapped inside. Further, since the air bubbles remaining in the bearing clearance and its vicinity are discharged from the through hole 13h of the shaft 13 to the outside through the through hole 20d of the pin 20c, unstable vibration occurs even if a change in atmospheric pressure or a change in the use temperature occurs. Less likely to occur. The injected lubricant fills the bearing clearances of the thrust fluid bearing S and the radial fluid bearing R by surface tension via the through hole 20d of the pin 20c, and excess lubricant is stored in the lubricant reservoir 22. It accumulates and is held on its tapered surface 24 by capillary action based on surface tension. Therefore, even if the spindle motor is inverted during transportation or handling, the lubricant in the lubricant reservoir 22 does not flow out.

Further, since the size of the clearance of the lubricant reservoir 22 is reduced toward the upper lubricant supply passage 25 by the tapered surface 24, the lubricant scattered by the external impact does not flow out as long as it does not flow out. Are naturally collected in the lubricant supply passage 25 having a narrow clearance in the lubricant reservoir 22. Since the air vent hole 23 communicating with the outside air is provided at the lower end of the lubricant reservoir 22 as described above, the air bubbles collected at the lower end of the lubricant reservoir 22 (the one with the larger clearance) pass through the air vent hole 23. Is discharged outside.

A stator 18 is fixed to the outer periphery of the cylindrical portion 11a of the base 11, 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. . The drive motor M drives the hub 14.
When the shaft and the sleeve 12 are integrally driven to rotate, the lubrication filled in the bearing clearances of the 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. When dynamic pressure is generated in the agent, the sleeve 12 is not in contact with the shaft 13 and the flange portion 15 and is supported. When a centrifugal force acts upon the rotation, the lubricant in the lubricant reservoir 22 rises along the tapered surface 24 and reaches and is held by the lubricant supply passage 25 having a narrow clearance. Then, the lubricant is reliably supplied from the lubricant supply passage 25 to the bearing clearance by capillary action. Further, even if there are bubbles remaining in the bearing clearance, the bubbles are immediately released to the outside air via the air vent hole 23 opened in the lubricant reservoir 22. As in the case of the first embodiment, the excess lubricant that has oozed into the inner peripheral surface of the through-hole 13h of the shaft 13 due to the injection of the lubricant does not flow out during transportation or rotation.
An absorbing member made of a porous member may be provided inside the through hole 13h of the shaft 13.

If the lubricant retained in the bearing clearance gradually evaporates or scatters and runs short over a long period of operation, the lubricant is retained in the lubricant reservoir 22 by capillary action based on surface tension. The lubricating oil is sucked into the narrower gap while being guided by the tapered surface 24 according to the shortage, and is replenished until the lubricant is filled in the bearing gap. That is, as the lubricant in the bearing clearance decreases, the lubricant is sucked by the capillary phenomenon through the lubricant supply passage 25 into the bearing clearance having a small clearance, and is stabilized at a position where the surface tension of the tapered surface 24 of the lubricant reservoir 22 is balanced. I do. Thus, the lubricant is automatically replenished by the reduced amount of the lubricant.

Note that the first and second embodiments show examples of the present invention, and the present invention is not limited to these embodiments. For example, the flange portion 15 provided on the shaft 13 is not limited to the shaft end but may be near the shaft end.
Further, the thrust fluid bearing S is not necessarily required to have the flange portion 15.
It is not necessary to provide on both sides. That is, the thrust fluid bearing S is provided only on the side of the sleeve 12 on the upper surface, and the axial positions of the rotor magnet 19 and the stator 18 constituting the drive motor M are slightly shifted so that the axial attraction force is applied. The magnetic suction force generated by the motor M may be used to suction upward.

Further, the radial fluid bearings R need not always be provided at a plurality of locations, but may be provided at one location. Further, the structure of the fluid bearing, the structure of the air vent hole 23, the lubricant reservoir 22, the lubricant supply passage 25, the pattern of the groove for generating the dynamic pressure, the detailed structure of the spindle motor, and the like are limited to the present embodiment. Rather, it can be changed as needed as long as the object of the present invention can be achieved.

For example, the tapered surface 24 forming the lubricant reservoir 22 may have various curved surfaces as long as the lubricant reservoir 22 has a shape in which the clearance gradually narrows toward the fluid bearing clearance. Further, 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, the processing method of the groove may be etching,
Electrolytic etching, plastic processing, cutting, laser processing, ion beam processing, shot blast, and the like can be applied.

Further, the materials of the members constituting the spindle motor such as the shaft 13 and the sleeve 12 are not particularly limited, and metals (stainless steel, copper alloy, Materials such as aluminum alloys), sintered metals, sintered oil-impregnated metals, plastics, and ceramics can be used without any problems. That is,
It may be a combination of stainless steel or copper alloy,
A combination of dissimilar metals such as iron and copper alloy, iron and aluminum alloy, or a combination of metal and plastic may be used. Of course, a surface treatment such as plating or a DLC film (diamond-like carbon coating) may be applied to the fluid bearing surface as necessary to improve the slidability at the time of starting and stopping.

When the shaft 13 and the sleeve 12 are made of a combination of copper alloys having different hardnesses, for example, the shaft 13 is made of a combination of high hardness beryllium copper or aluminum bronze, and the sleeve 12 is made of lead bronze or phosphor bronze. The dynamics and the cutting workability can be satisfied. In this case, it is preferable to provide a groove for generating a fluid shunt on the fluid bearing surface of lead bronze or phosphor bronze having a low hardness because the mating member is less likely to be damaged.

Further, the material of the base 11 is not particularly limited, and may be an aluminum die cast, an aluminum forged product,
In addition to metals such as magnesium alloys, it is also possible to use plastics which are usually difficult to caulk. Further, in the present embodiment, the spindle motor has been described as an example of the hydrodynamic bearing device, but the present invention can be applied to other various hydrodynamic bearing devices.

[0074]

As described above, in the hydrodynamic bearing device of the present invention, the flange portion is fixed to the shaft by a hollow screw screwed into the through hole of the shaft or a hollow pin fitted into the through hole. Therefore, even when the flange portion is made thin, there is no possibility that the flange portion will be deformed when the flange portion is fixed to the shaft, and there is no possibility that the flange portion will fall off the shaft when a large impact is applied. .

Further, since the shaft is a hollow shaft having through holes opened at both end surfaces of the shaft, after assembling the hydrodynamic bearing device, a lubricant is injected into the hydrodynamic bearing device from the through hole after the assembling of the hydrodynamic bearing device. (Eg, a method of injecting a lubricant by inserting a dispenser into the through-hole), it is easy to inject the lubricant, and it is possible to reduce the risk of air bubbles being caught in the interior. In addition, even if bubbles are accidentally entrapped inside and the bubbles expand due to a change in atmospheric pressure or a change in operating temperature, the expanded bubbles are discharged to the outside through the through-holes. Less likely to occur.

[Brief description of the drawings]

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

FIG. 2 is a sectional view of a spindle motor which is a second embodiment of the hydrodynamic bearing device according to the present invention.

FIG. 3 is a sectional view of a conventional spindle motor.

[Explanation of symbols]

 Reference Signs List 12 sleeve 13 shaft 13h through hole 15 flange portion 16 counter plate 20 set screw 20a through hole 20c pin 20d through hole R radial fluid bearing S thrust fluid bearing

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Ikuki Sakatani 1-5-150 Kugenuma Shinmei, Fujisawa-shi, Kanagawa F-term in NSK Ltd. (reference) 3J011 AA04 AA20 BA02 BA06 CA02 JA02 KA04 MA21 3J017 AA02 BA01 DA01 DB01 5H019 AA06 CC04 DD01 FF03 5H605 BB05 BB10 BB19 CC04 EB02 EB06 5H607 AA04 AA12 BB01 BB07 BB09 BB14 BB17 BB25 CC01 DD04 DD16 GG01 GG02 GG09 GG15

Claims (1)

[Claims] 1. A fluid bearing device comprising: a shaft having a flange portion at one end; and a mating member facing at least one plane of the flange portion via a fluid bearing clearance of a thrust fluid bearing. A hollow shaft having a through-hole opening at both end surfaces of the shaft, wherein the flange portion is fixed to the shaft with a hollow screw screwed into the through-hole or a hollow pin fitted into the through-hole. A hydrodynamic bearing device.