JP2002174241A - Fluid bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin type fluid bearing device having excellent moment proof stress important for realizing excellent portablility, low power consumption, high reliability and extremely small influence of air bubbles left inside a bearing. SOLUTION: In a spindle motor provided with a shaft 13 having a flange part 15 and a sleeve 12 facing to the shaft 13 via fluid bearing clearance, two radial fluid bearings R and R are provided across the flange part 15 between an outer peripheral surface of the shaft 13 and the sleeve 12 facing to the shaft 13, a thrust fluid bearing S is provided among both planes of the flange part 15 and the sleeve 12 facing to the planes, a lubricant reservoir 22 for holding lubricant is provided so as to be communicated with the fluid bearing clearance, the lubricant reservoir 22 is formed into a shape for gradually narrowing clearance toward the fluid bearing clearance and an air vent 23 communicating with outside air is provided in a wider clearance part of the lubricant reservoir 22.

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 conventional hydrodynamic bearing device used for the above applications, for example, an HDD having a thrust hydrodynamic bearing S and a radial hydrodynamic bearing R as shown in FIG.
There is a spindle motor for This is the base 101
A cylindrical housing 100 having a bottom plate 100a is inserted inside a cylindrical portion 101a standing upright, and these are integrally fixed. And the housing 1
A sleeve 102 having a cylindrical shape is inserted into the inner peripheral surface of 00 and is integrally fixed thereto.

Further, a shaft 103 is rotatably inserted through the sleeve 102. At the upper end of this shaft 103,
An inverted cup-shaped hub 104 is integrally attached, and a disc-shaped flange portion 105 is integrally formed at a lower end of the shaft 103. Both flat surfaces of the flange portion 105 are connected to the thrust receiving surfaces 105s, 1 of the thrust fluid bearing S.
05s. And the upper thrust receiving surface 10
5s, the lower end surface of the sleeve 102, which is the mating member, is opposed via the fluid bearing clearance of the thrust fluid bearing S, and the lower end surface of the sleeve 102 is the thrust bearing surface 102s of the thrust fluid bearing S.

On the lower thrust receiving surface 105s,
The upper surface of the bottom plate 100a of the housing 100, which is the mating member, opposes through the fluid bearing clearance of the thrust fluid bearing S, and the upper surface of the bottom plate 100a is the thrust bearing surface 100s of the thrust fluid bearing S. The thrust receiving surfaces 105s, 105s and the thrust bearing surface 102
s and 100s are provided with a herringbone-shaped or spiral-shaped groove for generating dynamic pressure (not shown) to constitute a thrust fluid bearing S.

[0005] Further, a pair of radial receiving surfaces 103r, 103r are formed on the outer peripheral surface of the shaft 103 at an interval above and below. Further, on the inner peripheral surface of the sleeve 102, the radial bearing surfaces 103r, 103r are opposed to the radial bearing surfaces 103r via the fluid bearing clearance of the radial fluid bearing R.
r 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 herringbone-shaped or spiral-shaped dynamic pressure generating grooves 107, 107.

In order to reduce the torque of the spindle motor, the inner peripheral surface of the sleeve 102 (the outer peripheral surface of the shaft 103 or the inner peripheral surface of the sleeve 102 may be interposed between the upper and lower radial fluid bearings R, R). Surface and the outer peripheral surface of the shaft 103).
Is provided. A stator 108 is fixed to the outer peripheral surface of the cylindrical portion 101a, and a driving motor M is formed to face the rotor magnet 109 fixed below the inner peripheral surface of the hub 104 via a gap. The shaft 103 and the hub 104 are integrally driven to rotate by the drive motor M.

When the shaft 103 rotates, a small amount of lubricant filled in the fluid bearing clearances of the fluid bearings S and R is pumped by the pumping action of the dynamic pressure generating grooves of the thrust fluid bearing S and the radial fluid bearing R. When pressure is generated, the shaft 103 comes into non-contact with the inner peripheral surface of the sleeve 102 and the upper surface of the bottom plate 100a and is supported.

[0008]

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. Furthermore, HDDs mounted on portable devices such as notebook personal computers are required to be thinner, and a hydrodynamic bearing device with low power consumption, excellent portability, and high reliability is required.

However, in the above-mentioned conventional spindle motor, since the flange portion 105 is provided at one end of the shaft 103, if the height of the device is reduced for thinning, the radial fluid bearing is smaller than the height of the device. There is a problem that the bearing span, which is the distance between the points of application of R, R, becomes small, and the proof stress against moment load (hereinafter referred to as moment proof stress) decreases.

Therefore, when the apparatus is swung by transportation or the like, the bearings may come into contact with each other and may be damaged. In other words, when the bearing is carried while rotating, the gyro moment acts on the rotating body when swinging, and a large moment load acts on the bearing, so that the bearing surfaces may come into contact with each other and be damaged. Also, if the bearing span is small, it is difficult to reduce the bearing torque while securing the required moment resistance, which has been an obstacle to practical application from the viewpoint of power consumption.

Further, the filling of the spindle motor with the lubricant is usually performed simultaneously with the assembly of the spindle motor. That is, the bottom plate 100 of the housing 100
a. A suitable amount of lubricant is injected in advance on a.
03 is inserted. After that, when the sleeve 102 is pressed into the inner peripheral surface of the housing 100, the lubricant is filled in each fluid bearing clearance.

Therefore, since the lubrication of the fluid bearing is performed only by the fluid bearing clearance and a very small amount of lubricant held in the vicinity thereof, in a long-term use, the lubricant is evaporated and scattered in the fluid bearing clearance. There is a problem that the lubricant gradually decreases and is liable to be depleted, eventually causing seizure, and the reliability of the spindle motor is poor.

Further, when filling the lubricant, the shaft 103
Center hole 111 and relief groove 110 necessary for machining
Air bubbles tended to remain. If air bubbles remain in the clearance of the fluid bearing or in the space near the bearing, there is a problem that the rotation of the bearing is likely to be unstable (NRRO, which is the fluctuation of the rotation asynchronous component during rotation, increases).

Accordingly, the present invention solves the problems of the conventional hydrodynamic bearing device as described above, and is excellent in moment resistance, which is important for realizing excellent portability, with low power consumption and reliability. It is an object of the present invention to provide a thin hydrodynamic bearing device which is high and has a very small influence of bubbles remaining inside the bearing.

[0015]

In order to solve the above-mentioned problems, the present invention has the following arrangement. That is, a hydrodynamic bearing device according to the present invention is a hydrodynamic bearing device including a shaft having a flange portion and a mating member facing the shaft via a hydrodynamic bearing clearance. A plurality of radial fluid bearings are provided between the mating member and the flange portion, and a thrust fluid bearing is provided between both flat surfaces of the flange portion and the mating member opposed thereto, and a lubricant is provided. The retained lubricant reservoir is provided in communication with the fluid bearing clearance, the lubricant reservoir is formed to have a shape in which the clearance is gradually narrowed toward the fluid bearing clearance, and further, the lubricant reservoir has a wider clearance. A vent hole communicating with the outside air is provided.

If the radial fluid bearing is provided so as to sandwich the flange portion, the bearing span of the radial fluid bearing can be increased even when the height of the device is restricted. Have excellent moment resistance, low bearing torque and low power consumption. Further, when the shape of the lubricant reservoir is tapered as described above, the lubricant injected into the hydrodynamic bearing device is held in the lubricant reservoir by surface tension, and the fluid is discharged from the lubricant reservoir. It is automatically supplied to the bearing clearance. Therefore, even if the hydrodynamic bearing device is used for a long period of time, the possibility that the lubricant in the hydrodynamic bearing clearance is depleted is small, and thus the hydrodynamic bearing device has high reliability.

Even if air bubbles remain inside the hydrodynamic bearing device (the space between the hydrodynamic bearing clearance and the vicinity thereof), lubricant collects in a narrower portion of the lubricant pool due to surface tension, and the air bubbles become The air bubbles are discharged to the outside air from the ventilation holes because the air bubbles are collected on a wider side of the lubricant reservoir. Therefore, rotation of the fluid bearing is less likely to be unstable.

[0018]

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 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. This spindle motor is composed of 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 outer peripheral surface of the shaft 13 and the sleeve 12. Have been. A flange portion 15 is integrally formed near the center of the shaft 13, and a thrust fluid bearing S is provided between both surfaces of the flange portion 15 and the sleeve 12 facing the flange portion.
The sleeve 12 corresponds to a mating member which is a constituent element of the present invention.

The base 11 to which the sleeve 12 is attached
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 cylindrical sleeve 12 is inserted inside a cylindrical portion 11a erected at the center of the body, and both are integrally fixed. This sleeve 12 is the first sleeve 1
2A and the second sleeve 12B are integrally fixed.

More specifically, the first sleeve 12A has a cup shape having a hole at the center of the bottom plate, and the lower portion (the side having the bottom plate) is inserted inside the cylindrical portion 11a. The second sleeve 12B has a ring shape,
It is inserted into the upper end of 2A and is fixed to the inner peripheral surface of the first sleeve 12A. That is, the sleeve 12 composed of the first sleeve 12A and the second sleeve 12B has a cylindrical shape, and has inwardly projecting portions 28 and 29 at both upper and lower ends.

The shaft 13 is rotatably inserted through the sleeve 12. In the vicinity of the center of the shaft 13, a disk-shaped flange portion 15 is integrally formed. That is, the shaft 13 includes a shaft portion above the flange portion 15 (hereinafter referred to as an upper shaft portion) and the flange portion 15.
And a shaft portion below the flange portion 15 (hereinafter referred to as a shaft lower portion).

In this embodiment, the shaft 13 and the flange portion 15 are integrally formed by one member. However, the separate flange portion and the shaft are connected to each other by a conventional fixing method such as bonding or welding. May be used. 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. Examples of the hardened material include a hardened material, a hardened surface obtained by performing surface treatment with plating or a diamond-like carbon (DLC) film, and a copper alloy having high hardness.

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 at 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.

The inner peripheral surface of the sleeve 12 into which the shaft 13 is inserted has a shape corresponding to the shaft 13 having the above-described shape, and has a shape facing the shaft 13 via a fluid bearing clearance. ing. That is, the outer peripheral surface of the upper shaft and the inner peripheral surface of the upper protrusion 29 (second sleeve 12B) face each other, and the outer peripheral surface of the lower shaft and the inner peripheral surface of the lower protrusion 28 face each other. ing.

The flange portion 15 is housed in a concave portion formed between the upper and lower projecting portions 28 and 29, and the upper flat surface of the flange portion 15 and the lower surface of the upper projecting portion 29 face each other. The lower surface of the part 15 and the lower protrusion 28
Are opposed to each other. The lower flat surface of the flange portion 15 and the upper surface of the lower protruding portion 28 are in contact when the spindle motor is stopped.

Both upper and lower planes of the flange portion 15 are thrust receiving surfaces 15s, 15s. And, the upper surface of the lower protruding portion 28 which faces the lower thrust receiving surface 15s via the fluid bearing clearance of the thrust fluid bearing S,
The lower surface of the upper protruding portion 29 which faces the upper thrust receiving surface 15s via the fluid bearing clearance of the thrust fluid bearing S is defined as thrust bearing surfaces 28s and 29s, respectively, and the opposing thrust receiving surfaces 15s, 15s and 15s are formed. At least one of the thrust bearing surfaces 28s and 29s is provided with, for example, a herringbone-shaped groove (not shown) for generating a dynamic pressure to constitute the thrust fluid bearing S.

In particular, the herringbone-shaped dynamic pressure generating grooves provided on the thrust receiving surface 15s are slightly radially outwardly shorter than the groove length on the outer circumference side from the top of the groove. It is preferable to have a simple asymmetric groove pattern. Then, the pumping action generated by the rotation drive,
Since the outer side is smaller than the inner side than the groove top,
The lubricant is sent from the center toward the outer periphery.

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. In the coining process, which is plastic working, the die is placed on the flange 1 using a press or the like.
Since the groove for dynamic pressure generation is stamped by pressing the groove 5, the mass production is excellent and the cost is low as compared with the etching process.

On the other hand, a pair of radial receiving surfaces 13r, 13r are formed on the outer peripheral surfaces of the lower shaft portion and the upper shaft portion, and the radial bearing surfaces 13r, 13r have a fluid bearing clearance of a radial fluid bearing R. The radial bearing surfaces 12r, 12r facing each other are formed on the inner peripheral surface of the lower protruding portion 28 and the inner peripheral surface of the upper protruding portion 29. The radial fluid bearings R, R are provided with the herringbone-shaped dynamic pressure generating grooves 17, 17 in a substantially U-shape on the radial bearing surfaces 12r, 12r. However, 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.

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. You. In this spindle motor, as described above, the two radial fluid bearings R, R are arranged at an interval vertically above and below the flange portion 15. For this reason, even when the spindle motor is reduced in thickness, the bearing span, which is the distance between the points of action of the radial fluid bearings R, R, can be made large, so that the spindle motor is excellent in moment resistance. Therefore, such a spindle motor has low bearing torque and low power consumption. In addition,
The number of the radial fluid bearings R is not limited to two, but may be three or more as long as they are arranged above and below the flange portion 15 with the flange portion 15 interposed therebetween.

The radial bearing surface 12r, that is, the projection 2
It is preferable to form the dynamic pressure generating grooves 17 on the inner peripheral surfaces of the grooves 8 and 29 because the dynamic pressure generating grooves 17 can be formed by plastic working such as ball rolling or cutting with a cutting tool, which is excellent in mass productivity. 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 into the sleeve 12.

That is, after the sleeve 12 is cut on a lathe, the rolling jig is pushed into the sleeve 12 and relatively moved while slowly rotating the main spindle of the lathe forward and backward, so that the inner periphery of the protruding portions 28 and 29 is rotated. A herringbone-shaped (substantially U-shaped) groove is formed on the surface, and then a finishing process such as finish cutting or ball-through is performed as necessary, to remove a raised portion around the groove. Of course not on a lathe,
The rolling jig may be pressed into the fixed sleeve 12 while rotating the rolling jig right and left forward and reverse to form a herringbone-shaped groove.

Also, grooves 1 for generating dynamic pressure are provided at two locations.
7 and 17 are inwardly asymmetric groove patterns in which the groove length is slightly shorter on the inner side than on the outside air side, that is, the axis of a plurality of substantially V-shaped grooves constituting the dynamic pressure generation groove 17 It is preferable that the width from the bent portion to the outside air end of the width in the direction is larger than the width from the bent portion to the inner end portion for the following reasons.

That is, a pressure is applied to push the lubricant in from the outside air side to the inside with the rotation of the shaft 13 (pump-in), so that the lubricant in the fluid bearing clearance of the radial fluid bearing R is rotated by the rotation of the shaft 13. Is prevented from being scattered to the outside due to the centrifugal force associated therewith. In the present embodiment, the outside air side means a side of the shaft 13 facing the outside air of the spindle motor (upward in FIG. 1). The inside means the side opposite to the outside air 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.

Next, the lubricant reservoir 22 for retaining the lubricant is provided.
Will be described. Outer peripheral surface of flange portion 15 and inner peripheral surface of sleeve 12 opposed thereto (portion of the concave portion)
And an annular clearance is interposed therebetween, and the annular clearance forms a lubricant reservoir 22. The outer peripheral surface of the flange portion 15 forming the inner surface of the lubricant reservoir 22 is formed as a tapered surface 24 tapering from the center in the thickness direction of the flange portion 15 to the upper and lower planes. Has a tapered shape in which the center is the widest and the clearance gradually narrows toward the upper and lower ends.

However, the tapered surface 24 is not always formed on the outer peripheral surface side of the flange portion 15, and
2 may be formed on the inner peripheral surface side, or the flange portion 1
5 may be formed on both the outer peripheral surface side and the inner peripheral surface side of the sleeve 12. However, in consideration of the centrifugal force acting on the lubricant during rotation, it is preferable to provide it on the outer peripheral surface side (the rotating member side) of the flange portion 15.

Further, at both upper and lower ends of the lubricant reservoir 22,
A lubricant supply passage 25 is provided which communicates with the fluid bearing clearances of the thrust fluid bearing S and the radial fluid bearing R.
The opening of the lubricant supply passage 25 is substantially equal to or slightly larger than the fluid bearing clearance, and the lubricant flows from the lubricant supply passage 25 to the fluid bearing clearance by capillary action based on surface tension. It is easy to be introduced.

In the present embodiment, the lubricant reservoir 22 is provided on the entire outer circumferential surface of the flange portion 15 in the circumferential direction (that is, the lubricant reservoir 22 has an annular clearance shape). One or more of the outer circumferential surfaces may be provided in a slit shape (that is, the other portions do not have a tapered clearance, and the outer circumferential surface of the flange portion 15 and the inner circumferential surface of the sleeve 12 may not be provided). Are parallel).

In the present embodiment, the entire outer circumferential surface of the flange portion 15 in the vertical direction is a tapered surface 24, and a part of the tapered surface 24 of the lubricant reservoir 22 is used as the lubricant supply passage 2.
5, the tapered surface 24 is directly connected to the fluid bearing clearance. However, the vertical center of the outer peripheral surface of the flange portion 15 is a tapered surface 24, and the upper and lower ends are surfaces parallel to the inner peripheral surface of the sleeve 12, and an annular clearance formed by the parallel surface is a lubricant supply passage 25. May be configured.

At the center of the lubricant reservoir 22 in the vertical direction (the portion having the widest clearance), a ventilation hole 23 communicating with the outside air is provided.
Is open. The ventilation hole 23 extends horizontally from the inner peripheral surface of the sleeve 12 (the vertical center of the lubricant reservoir 22),
It is open on the outer peripheral surface of the sleeve 12. The ventilation holes 23 may be provided in the shaft 13 instead of the sleeve 12. That is, the flange portion 15 may be provided so as to extend horizontally from the outer peripheral surface (the vertical center of the lubricant reservoir 22), bend upward in the middle, and open to the upper end surface of the shaft 13.

On the other hand, a second ventilation hole 30 for discharging the remaining air bubbles is opened at the lower end face 13d of the shaft 13. The ventilation hole 30 is provided continuously with a screw hole 13c provided on the upper end surface of the shaft 13, and communicates with the outside air. A filter 13e made of a porous member is provided below the screw hole 13c. When a magnetic disk, which will be described later, is screwed into the screw hole 13c, the air hole 30c is provided.
Foreign matter or the like is prevented from entering the inside of the spindle motor through the motor.

The screw hole 13c for screwing the magnetic disk is not provided at the upper end surface of the shaft 13 but at the hub 14
May be provided on the upper surface. In that case, the vent hole 30 is
3 is provided. The lower end surface 13d of the shaft 13 is
The gap between the base 11 and the upper surface may be a tapered surface that gradually narrows from the center toward the outer periphery. Then, since the tapered clearance acts as a lubricant reservoir, that is, has the same effect as the lubricant reservoir 22, the lubricant is automatically supplied from the clearance to the thrust fluid bearing S.

Next, a method of injecting a lubricant into the spindle motor will be described. The injection of the lubricant into the spindle motor is performed from the ventilation hole 23 using a dispenser or the like. That is, when a lubricant is injected into the lubricant reservoir 22 by inserting an injection needle or the like of a dispenser into the ventilation hole 23, the lubricant is accumulated in the lubricant reservoir 22 by the surface tension.
The bubbles collect in the narrower gap, and in the wider gap.
The lubricant gradually spreads and fills from the fluid bearing clearance of the thrust fluid bearing S to the fluid bearing clearance of the radial fluid bearing R. Therefore, when the lubricant is injected, the inside of the device (in the fluid bearing clearance and inside thereof) is filled. (In the vicinity) is less likely to be trapped.

Therefore, even when the lubricant is injected in the atmosphere, entrapment of air bubbles can be prevented. Of course, the lubricant may be injected in a vacuum, or after the injection, the spindle motor may be put in a vacuum chamber and deaerated. Further, in order to more reliably deaerate bubbles, a lubricant which has been previously vacuum degassed may be used, if necessary. 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.

Providing such a vacuum degassing step or aging step during the manufacturing process of the spindle motor is very effective for removing the remaining air bubbles, but depending on the rotational performance required for the spindle motor, May be omitted from one or both. In addition, when the shaft 13 and the base 11 have a through hole at the center thereof, the lubricant may be injected into the spindle motor from the through hole.

When the inner peripheral surfaces of the ventilation holes 23 and 30 are subjected to an oil-repellent treatment such as applying an oil-repellent (having a property of repelling a lubricant), the portions subjected to the oil-repellent treatment are treated. Since the lubricant is repelled, it is possible to effectively prevent the lubricant from flowing out of the ventilation holes 23 and 30 to the outside during transportation of the spindle motor or the like. The injected lubricant fills each of the fluid bearing clearances of the thrust fluid bearing S and the radial fluid bearing R by the surface tension, and excess lubricant is accumulated in the lubricant reservoir 22 via the lubricant supply passage 25, and the surface tension is reduced. Is held on the tapered surface 24 by capillary action based on 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.

Further, since the size of the clearance of the lubricant reservoir 22 is reduced toward the upper and lower lubricant supply passages 25 by 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 at the center of the lubricant reservoir 22 in the up-down direction (a wide gap portion) are discharged to the outside through the ventilation holes 23. As described above, since air bubbles hardly remain inside the apparatus (in the fluid bearing clearance and its vicinity), the rotation of the spindle motor is less likely to be unstable.

Further, outside the radial fluid bearings R, R (the side opposite to the side on which the thrust fluid bearing S is provided).
Is provided with a taper seal 27 for preventing the lubricant from flowing out and scattering from the fluid bearing clearances of the radial fluid bearings R, R by surface tension and centrifugal force. That is, on the outer peripheral surface of the shaft 13, the outer portion of the radial fluid bearings R, R (in the case of the upper radial fluid bearing R,
The lower portion of the radial fluid bearing R has a tapered surface, and the clearance formed between the shaft 13 and the sleeve 12 gradually increases toward the fluid bearing clearance of the radial fluid bearings R, R. It has a tapered shape that becomes narrower.

By providing such a tapered clearance in communication with the fluid bearing clearance, the lubricant in the fluid bearing clearance is less likely to flow out and scatter. That is, lubricant is collected toward the fluid bearing clearance by surface tension when the spindle motor is at rest and by centrifugal force when the spindle motor is rotating.

When the drive motor M integrally rotates the hub 14 and the shaft 13 on which the magnetic disk (not shown) as a rotating body is mounted on the outer periphery, the thrust fluid bearing S and the radial fluid bearing R Due to the pumping action of the respective dynamic pressure generating grooves, dynamic pressure is generated in the lubricant filled in the fluid bearing clearances of the respective fluid bearings S and R, and the shaft 13 is not in contact with the sleeve 12 and is supported. Since the magnetic disk is screwed into a screw hole 13c provided on the upper end surface of the shaft 13 with a clamp member, the magnetic disk is fixed with sufficient strength to ensure sufficient impact resistance.

If the lubricant held in each fluid bearing clearance gradually evaporates or scatters and runs short over a long period of time, the lubricant pool 22 will be filled with capillary action due to surface tension. The retained lubricant is sucked into the narrower gap while being guided by the tapered surface 24 according to the shortage, and is supplied until the lubricant is filled in each fluid bearing clearance. That is, as the amount of the lubricant in the fluid bearing clearance decreases, the lubricant is sucked by the capillary phenomenon through the lubricant supply passage 25 into the fluid bearing clearance having a small clearance, and the lubricant reservoir 22 is formed.
At a position where the surface tension of the tapered surface 24 is balanced.
Thus, the lubricant is automatically replenished by the reduced amount of the lubricant.

As described above, in the spindle motor according to the present embodiment, since the annular clearance of the lubricant reservoir 22 is tapered, the lubricant is sucked into 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. Therefore, a lubricant having no air bubbles is automatically and reliably supplied to each fluid bearing clearance, and is always filled with the lubricant. Thus, even when used for a long period of time, the reliability is high and the durability is excellent.

Further, even if the amount of the injected lubricant is too small or small, there is little possibility that the lubricant is scattered to the outside or the lubricant in each fluid bearing clearance is depleted in a long-term use. In the spindle motor according to the present embodiment, a portion (fluid bearing portion) including the sleeve 12, the shaft 13, and the flange portion 15 may have an integrated unit structure. Since such a fluid bearing unit can be incorporated into the spindle motor at one time, manufacture and assembly of the spindle motor are easy.

The fluid bearing unit is manufactured in advance by a bearing manufacturer (assembly and injection of lubricant),
Since it can be completed into a spindle motor by a spindle motor manufacturer, there is an advantage that it is easy to share production. (Second Embodiment) FIG. 2 is a longitudinal sectional view of an HDD spindle motor which is another embodiment of the hydrodynamic bearing device according to the present invention.

First, the structure of the spindle motor of this embodiment will be described. The spindle motor of this embodiment is different from the spindle motor of the first embodiment in that a shaft 13 is fixed to a base 11, and a sleeve 12 supported on the fixed shaft 13 via a fluid bearing rotates together with a hub 14. That is, a spindle motor of a shaft fixed-sleeve rotating type.

However, the description of the same parts as those in the first embodiment will be omitted, and only different parts will be described. In FIG. 2, the same or corresponding parts as in FIG. 1 are denoted by the same reference numerals as in FIG. A shaft 13 is provided upright at the center of the base 11. A flange 15 is integrally formed near the center of the shaft 13. The shaft 13 is rotatably inserted into a cylindrical sleeve 12, and the sleeve 12 is inserted into a center portion of an inverted cup-shaped hub 14 on which a magnetic disk (not shown) is mounted on an outer peripheral portion by a conventional method such as press fitting. It is fixed by fixing means. The configuration of the sleeve 12 is the same as in the first embodiment.

An annular clearance is interposed between the outer peripheral surface of the flange portion 15 and the inner peripheral surface of the sleeve 12 opposed thereto, and the annular clearance forms a lubricant reservoir 22. The configuration of the lubricant reservoir 22 is the same as in the first embodiment. At the center of the lubricant reservoir 22 in the vertical direction (the portion having the widest clearance), a ventilation hole 23 communicating with the outside air is provided.
Is open. The vent hole 23 extends horizontally from the outer peripheral surface of the flange portion 15 (the center in the vertical direction of the lubricant reservoir 22), bends downward in the middle, and opens at the lower end surface of the shaft 13.

The ventilation holes 23 may be provided on the sleeve 12 side. That is, the sleeve 12 may be provided so as to extend horizontally from the inner peripheral surface (the vertical center of the lubricant reservoir 22), bend in the middle, and open at the upper end surface or lower end surface or the outer peripheral surface of the sleeve 12. In addition, when the opening of the ventilation hole 23 is covered with a gas-permeable filter made of a porous member or the like, it is possible to prevent foreign substances from entering the inside of the apparatus from the outside. This filter may be provided so as to fill the inside of the ventilation hole 23.

Further, outside the radial fluid bearings R, R (the side opposite to the side on which the thrust fluid bearing S is provided)
Is provided with the same taper seal 27 as in the first embodiment. Other configurations and actions of the spindle motor,
The effects are the same as in the first embodiment.

Each embodiment shows an example of the present invention, and the present invention is not limited to these embodiments. For example, the structure of the fluid bearing, the vent holes 23,
The structure of the lubricant reservoir 22, the lubricant supply passage 25, the detailed structure of the spindle motor, and the like are not limited to each embodiment, and may be appropriately changed as needed if the object of the present invention can be achieved. It is possible to

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, chemical etching, electrolytic etching, plastic processing, cutting, laser processing, ion beam processing, shot blast, and the like can be applied to the groove according to the material and the required accuracy.

Further, the material of the members constituting the spindle motor such as the shaft 13 and the sleeve 12 is not particularly limited, and metals (stainless steel, copper alloy, and the like) usually used for the members constituting the spindle motor are not limited. 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.

Furthermore, in each of the embodiments, 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.

[0069]

As described above, the hydrodynamic bearing device of the present invention has excellent moment resistance, which is important for realizing excellent portability, low power consumption and high reliability, and remains inside the bearing. The effect of the generated bubbles is extremely small.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a spindle motor according to a first embodiment.

FIG. 2 is a longitudinal sectional view of a spindle motor according to a second embodiment.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Base 12 Sleeve 12A First sleeve 12B Second sleeve 13 Shaft 15 Flange part 17 Groove for generating dynamic pressure 22 Lubricant reservoir 23 Vent R Radial fluid bearing S Thrust fluid bearing

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takenobu Otsubo 1-5-50 Kugenuma Shinmei 1-chome, Fujisawa-shi, Kanagawa Nippon Seiko Co., Ltd. No. N-Seiko Co., Ltd. F-term (reference) 3J011 AA04 BA06 CA02 JA02 KA04 LA05 MA03

Claims (1)

[Claims] 1. A fluid bearing device comprising: a shaft having a flange portion; and a mating member facing the shaft via a fluid bearing clearance, wherein the outer peripheral surface of the shaft and the mating member facing the shaft are connected to each other. A plurality of radial fluid bearings are provided between the flange portions, a thrust fluid bearing is provided between both flat surfaces of the flange portions and the opposing member facing the flange portions, and a lubricant reservoir for holding a lubricant. Is provided so as to communicate with the fluid bearing clearance, the lubricant reservoir is formed in such a shape that the clearance gradually narrows toward the fluid bearing clearance. A hydrodynamic bearing device, characterized in that a vent hole is provided.