JP2003156036A - Dynamic pressure fluid bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dynamic pressure fluid bearing device in which bubbles generated in a lower thrust space can be discharged rapidly. SOLUTION: In the dynamic pressure fluid bearing device comprising a stationary member having an air vent hole 33 penetrating a shaft 3 with a first access port 33a located above a thrust plate 32 and a second access port 33b located therebelow, and a rotary member having surfaces facing each other via a first radial space on the outer circumferential surface of the thrust plate 32 and a thrust space on the upper surface and a second radial space on the outer circumferential surface of the shaft, and having a thrust shaft bearing dynamic pressure generating groove and a radial bearing dynamic pressure generation groove, the short radial space 34 comprises a small space 34c surrounded by the surface with the radial bearing dynamic pressure generating groove formed therein and an air vent space 34a around the first access port, and the space in the radial direction of the air vent space 34a is widest at the phase of the first access port 33a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrodynamic bearing device, and can be suitably used particularly for a bearing of a spindle motor for rotating a recording medium such as a hard disk of a computer.

[0002]

2. Description of the Related Art There is a so-called hydrodynamic bearing device as a bearing means for rotatably supporting a rotating member with respect to a stationary member such as a relationship between a rotor and a shaft. In this, a pair of thrust plates are arranged above and below the shaft, and the inner surface of the rotor is opposed to the shaft outer peripheral surface between these thrust plates and the axial inner surfaces of both thrust plates through a radial gap and a thrust gap, respectively. The gap is filled with lubricating oil, and a dynamic pressure generating groove for generating a dynamic pressure in the lubricating oil during rotation is formed at a predetermined position on the surface forming the gap.

In such a bearing device, the bubbles in the lubricating oil cause leakage of the lubricating oil, and therefore it is necessary to discharge the bubbles to the atmosphere before the bubbles greatly grow. Therefore, the radial bearing portion is vertically separated by providing an air vent gap called a gas interposition portion that is not filled with lubricating oil in the axial center of the radial gap described above, and a communication hole for communicating the air vent gap with the outside air is provided. The structure formed in the above is proposed (Japanese Patent Laid-Open No. 2000-354349). In this configuration, there is only one point where the dynamic pressure of the lubricating oil held above and below the gas intervening part reaches the maximum from one gas-liquid interface to the other gas-liquid interface, and there is a point where it becomes minimum. Instead, the bubbles are automatically vented to the atmosphere where the pressure is minimal. Thus, in the hydrodynamic bearing device, the rotor can be held in a non-contact manner with the shaft due to the dynamic pressure effect during rotation, and the bubbles in the lubricating oil are discharged by the above configuration.

[0004]

However, since the dynamic pressure effect does not occur when the rotor is not rotating, the rotor freely moves within the above-mentioned gap when an impact is applied from the outside. Normally, the radial gap that the shaft outer surface faces is as small as a few μm,
The thrust gap that the upper surface (or lower surface) of the thrust plate faces is as wide as several tens of μm. Therefore, when the rotor abruptly moves in the thrust direction due to the impact, the pressure decreases due to the squeeze effect at the portion of the upper and lower thrust bearing portions where the gap widens, and bubbles are generated.

That is, when vibrating in the thrust direction, the dynamic pressure change ΔP of the hill (the portion having no groove) on the inner diameter side where the lubricating oil flow resistance is the largest and the gap is smallest increases. When the thrust gap expands, the fluctuation pressure P decreases by ΔP from the static pressure P ₀ before vibration (P = P ₀ −ΔP), and when P becomes a certain value or less, the air dissolved in the oil vaporizes. It becomes a small bubble. The bubbles are pushed to a groove with a low pressure due to an increase in the fluctuation pressure P when the thrust gap is narrowed (P = P ₀ + ΔP), and are accumulated there in a stable state with a small total surface area and a small energy. Go to As a result, the bubbles grow large and in some cases occupy a main part of the bearing portion in a ring shape to discharge the oil to the outside. Further, if the air bubbles are rotated while remaining in the bearing portion, a normal lubrication function is not generated, which causes serious damage such as a seizure phenomenon. Therefore, the subject of this invention is
It is an object of the present invention to provide a hydrodynamic bearing device in which bubbles in lubricating oil are quickly discharged.

[0006]

In order to solve the problem, the hydrodynamic bearing device of the present invention has a shaft and a disk-shaped thrust plate fixed to the lower part of the shaft so as to project radially. A stationary member formed with an air vent hole that penetrates the inside of the shaft and communicates with the outer peripheral surface of the shaft above the thrust plate, and a second entrance that communicates with the outside below.
A cylindrical inner surface that faces the outer peripheral surface of the thrust plate with a first radial gap, and a cylindrical inner surface that faces the upper surface of the thrust plate with a thrust gap and the outer peripheral surface of the shaft that face the outer peripheral surface with a second radial gap. And a lubricating oil held in the three gaps, and at least one of the upper surface of the thrust plate and the thrust inner surface has a boundary between the thrust gap and the second radial gap during rotation. A thrust bearing dynamic pressure generating groove for sending lubricating oil toward is formed in at least one of the outer peripheral surface of the shaft and the radial inner peripheral surface at a position lower than the first inlet / outlet and the thrust gap and the second radial during rotation. In a hydrodynamic bearing device in which a radial bearing dynamic pressure generating groove for sending lubricating oil toward the boundary of the gap is formed, the second radial gap is the radial A cylindrical minute gap surrounded by the surface on which the bearing dynamic pressure generating groove is formed and the surface facing the groove and filled with the lubricating oil, the outer peripheral surface of the shaft including the periphery of the first inlet and outlet, and the radial inside facing the shaft. It is composed of a cylindrical air vent gap having a gas-liquid interface between the lubricating oil and air, which is surrounded by the peripheral surface and lower than the first inlet / outlet, and the radial gap of the air vent gap is the phase in which the first inlet / outlet is formed. It is characterized by being formed most widely in.

In a bearing device in which a pair of thrust plates are fixed to the upper and lower sides of a shaft and thrust bearing portions are provided above and below, and a radial bearing portion is provided between them, a lower thrust bearing portion is provided below the radial bearing portion. To position. In such a positional relationship, the upper surface of the lower thrust plate that constitutes the lower thrust bearing portion and the thrust inner surface of the rotating member that faces the lower thrust plate are in contact with each other due to gravity when stationary, so the thrust gap Part of the lubricating oil to be retained in the first radial gap moves to the outer periphery of the lower thrust plate, and a gas-liquid interface is formed there. The gas-liquid interface has a gas phase on the lower side in the direction of gravity and a liquid phase on the upper side. Therefore, in this state, it is difficult to guide the air bubbles generated by the vibration as described above against the buoyancy so as to discharge from the air-liquid interface on the outer circumference of the thrust plate to the outside air.

Therefore, in the present invention, the bubbles are moved to the second radial gap above the lower thrust gap by leaving the buoyancy to be discharged to the outside through the air vent hole from the first inlet / outlet. At this time, the lubricating oil collects on the side of the narrow gap due to the surface tension, while the bubbles in the liquid try to move to the side of the wide gap opposite to the liquid while growing by coalescing. Therefore, according to the configuration of the present invention, the lubricating oil collects in the minute gap in the second radial gap, and the bubbles move to the air venting gap wider than the minute gap with the minimum resistance due to the effect of the surface tension on the action of the buoyancy. , Move quickly to the widest entrance / exit and enter the air vent hole. As a result, the lubricating oil rarely blows out from the air vent hole.

Bubbles generated in the upper thrust bearing portion are usually formed because the gas-liquid interface formed in the radial gap on the outer periphery of the upper thrust plate becomes the vapor phase upward in the direction of gravity and the liquid phase downward. Just leave it to buoyancy to escape to the atmosphere. Therefore, for the sake of convenience, the operation of the present invention has been described based on the structure having the upper and lower thrust bearing portions, but the feature of the present invention is applied to the bearing device in which the lower thrust bearing portion is located below the radial bearing portion. It is general.

As means for making the radial gap of the air vent gap widest in the phase in which the first inlet / outlet is formed, there is a means for eccentricizing the portion of the shaft corresponding to the air vent gap with respect to the rotary member. . According to this aspect, the radial interval of the gap can be partially widened without changing the wall thickness of the shaft. Therefore, the mechanical strength of the shaft can be made substantially uniform.

As another means for forming the radial gap of the air vent gap to be widest in the phase in which the first inlet / outlet is formed, a portion of the shaft corresponding to the air vent gap is orthogonal to the diameter line passing through the first inlet / outlet. There are some that are flatly divided along a plane. According to this aspect, it is possible to easily manufacture the shaft in which the radial gap is partially wide.

As still another means, it is preferable to gradually increase the radial distance of the air venting gap over one round in the circumferential direction starting from the edge of the first entrance / exit. When there are two air bubbles of equal size on both sides of the phase of the first inlet / outlet, in the configuration where the radial intervals of the air bleeding gaps are uniform, whichever one does not remove the lubricating oil sandwiched between those air bubbles Bubbles cannot reach the first entrance / exit, and may enter the first entrance / exit together with the lubricating oil. Therefore, by gradually increasing the radial interval in the circumferential direction once, the movement path of the bubbles is made one-way, and the congestion of the movement of the bubbles can be prevented.

Further, in the above construction in which the radial gap is widest in the vicinity of the first entrance / exit, the preferable construction is 1 of the radial inner peripheral surface forming the air vent gap.
Alternatively, an axial groove that straddles the gas-liquid interface is provided at two or more locations, and the lower end surface of the groove is inclined so that it becomes shallower as it approaches the minute gap. As described above, the bubbles in the lubricating oil try to move toward a large space. At this time, it is desirable that the lubricating oil entrained in the bubbles returns to the minute gap as soon as possible so as not to flow into the air vent hole. Therefore, an axial groove is provided at a key point in the circumferential direction, and bubbles are ruptured there, and the lubricating oil that is raised by the bubbles is caused to flow to the inclined lower end surface of the groove and returned to the minute gap, The lubricating oil was prevented from accumulating in the groove.

As another means for preventing the lubricating oil from flowing into the air vent hole, the air vent hole is located at an eccentric position with respect to the center of the outer diameter of the shaft so that the thickness of the shaft on the first inlet / outlet side becomes thicker. Can be formed. With this configuration,
This is because it is possible to secure a long radial path from the first inlet / outlet to the center of the air vent hole, and to provide a large resistance force to the inflow of lubricating oil.

As another means for preventing the lubricating oil from flowing into the air vent hole, an oil repellent agent is applied to the outer peripheral surface of the shaft facing the air vent gap, or a portion of the shaft corresponding to the air vent gap is repelled. It may be covered with a tube made of an oily material. With this configuration, the contact angle of the outer peripheral surface of the shaft facing the air bleeding gap with respect to the oil increases, and the surface side of the shaft is in the vapor phase and the surface opposite to it is the lubricating oil.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1 With respect to a first embodiment of a hydrodynamic bearing device of the present invention,
A case where the present invention is applied to a spindle motor for driving a recording disk will be described with reference to FIGS. FIG. 1 shows a spindle motor for driving a recording disk (hereinafter referred to as “motor”).
2) is an enlarged view of part A in FIG. 1, and FIG. 3 is a partial cross-sectional view in the radial direction.

As shown in FIG. 1, the motor 1 includes a bracket 2 having a through hole formed therein, and a shaft 3 fixed by fitting one end of the bracket 2 into the through hole of the bracket 2 by tightening.
A rotor 4 which rotates around the shaft 3, and a lubricating oil 10 which is filled in a predetermined bearing portion described later.

The rotor 4 includes a sleeve 5 loosely fitted to the shaft 3 through a predetermined radial gap described later, a hub 6 fixed to the outer periphery of the upper half of the sleeve 5, and a cover 7 fixed to the upper end of the sleeve 5. Become. The upper half of the sleeve 5 projects radially outward, and the hub 6 hangs downward from there to the vicinity of the bracket 2 to form a storage space for the stator 8 with the outer periphery of the lower half of the sleeve 5, and It projects outward in the radial direction. A recording disk (not shown) is placed on the outer periphery and the protruding portion of the hub 6, and a magnet 9 is fixed to the inner peripheral surface. The stator 8 is fixed to the bracket 2 so as to face the magnet 9.

A disk-shaped upper thrust plate 31 and a lower thrust plate 32, which project outward in the radial direction, are attached to the upper and lower parts of the shaft 3, and the inner diameter of the sleeve 5 is the shaft 3 and the upper and lower thrust plates 31. , 32 are relatively large at the portions corresponding to the upper and lower thrust plates 31, 32, and are small between the upper and lower thrust plates 31, 32. The lower surface of the upper thrust plate 31 and the upper surface of the lower thrust plate 32 have a thrust inner surface and a thrust gap 31 formed in the horizontal direction between the small diameter portion and the large diameter portion of the sleeve 5.
The thrust force from the sleeve 5 is received, and they face each other via a and 32a. Also, the upper thrust plate 3 is attached to the sleeve 5.
1 and the lower thrust plate 32 lower surface, the thrust gap 3
Upper counter plate 5 so as to face each other via 1b and 32b
1 and the lower counter plate 52 are attached, and the upper and lower thrust plates 31, 32 receive a thrust force in a direction opposite to the thrust force via the upper and lower counter plates 51, 52.

The shaft 3 has an air vent hole 33 penetrating therethrough.
The first entrance / exit 33a is provided substantially in the middle of the upper and lower thrust plates 31, 32, and the second entrance / exit 3
3b is provided below the lower thrust plate 32 and communicates with the outside.

The radial gap between the outer peripheral surface of the shaft 3 and the upper and lower thrust plates 31, 32 and the inner peripheral surface of the sleeve 5 is
Depends on the axial position. That is, as shown in the enlarged view of the lower half of FIG. 2, the first radial gap 31c between the outer peripheral surfaces of the upper and lower thrust plates 31, 32 and the inner peripheral surface of the sleeve 5,
32c is large enough to retain the lubricating oil. In addition, the second radial gap 34 between the outer peripheral surface of the shaft 3 and the inner peripheral surface of the sleeve 5 between the upper and lower thrust plates 31 and 32 is a gap between the outer periphery of the upper and lower thrust plates 31 and 32 at the central portion where the first doorway 33a is located. The air vent gap 34a is wider than 31b and 32b, and conversely, the minute gaps 34b and 34c are narrow near the upper and lower thrust plates 31 and 32.

In this embodiment, in order to make the width of the second radial gap 34 different in the axial position as described above, the outer diameter of the shaft 3 corresponding to the air vent gap 34a is set to the minute gaps 34b and 34c.
It is narrower than the part corresponding to. However, the outer diameters of the shafts 3 at the upper and lower ends of the air bleeding gap 34a gradually increase as they move away from the first inlet / outlet 33a, and the minute gap 34
It is connected to the portion corresponding to b and 34c. Further, in this embodiment, the radial gap of the air vent gap 34a is the widest in the phase of the first inlet / outlet port 33a as shown in FIG. This configuration is possible by making the axially intermediate portion of the shaft 3 eccentric with respect to the sleeve 5.

The lubricating oil 10 is continuously filled in the first radial gap 32c, the thrust gap 32a and the minute gap 34c in the lower portion of the shaft 3, and a gas-liquid interface is formed at the lower end of the air venting gap 34a. Further, also in the upper part of the shaft 3, the first radial gap 31c, the thrust gap 31a and the minute gap 34b are continuously filled, and the air vent gap 34
A gas-liquid interface is formed at the upper end of a. However, in the stationary state, the upper surface of the thrust plate 32 and the thrust inner surface of the sleeve 5 facing the upper surface are in contact with each other due to gravity,
A part of the lubricating oil 10 to be retained in the thrust gap 32a has moved to the first radial gap 32c. Therefore, another gas-liquid interface different from the gas-liquid interface is formed there.

Spiral grooves 31d and 32d (31d is not shown) are formed on the thrust inner surfaces of the thrust plates 31 and 32 facing the thrust gaps 31a and 32a.
However, on the outer peripheral surface facing the minute gaps 34b, 34c of the shaft 3, there are herringbone-shaped grooves 35, 36 (35
(Not shown in the figure) is formed, and dynamic pressure is generated in the lubricating oil by these grooves during rotation, and the rotor 4 is kept in non-contact with the shaft 3.

When the motor 1 receives an axial impact, the rotor 4
When is swung upward, the thrust gap 32a, which was closed in a stationary state, suddenly opens, and bubbles may be generated there. This bubble B moves to the minute gap 34c by buoyancy. At this time, the lubricating oil collects on the side of the narrow gap due to the surface tension, while the bubbles B in the liquid try to move to the side of the wide gap opposite to the liquid while growing together. Therefore,
The lubricating oil 10 collects in the narrow minute gap 34c, while the action of the surface tension and the action of the buoyancy of the bubbles B synergize to rise toward the wide air vent gap 34a with the minimum resistance, and pass through the gas-liquid interface to the air vent gap 34a. Enter and move quickly to the widest first entrance / exit 33a,
The air is discharged from a through the air vent hole 33. As a result, the lubricating oil 10 is rarely ejected from the air vent hole.

When the rotor 4 swings downward due to the continued vibration of the motor 1, air bubbles are also generated in the thrust gap 31a. In this bubble, the gas-liquid interface formed in the first radial gap 31c moves upward in the gravity direction. Since the liquid phase becomes the liquid phase on the lower side, the buoyancy normally leaves the atmosphere.

In this embodiment, the air venting gap 34
The portion corresponding to the air venting gap 34a of the shaft 3 is only eccentric with respect to the sleeve 5 in order to form the widest radial spacing of a in the phase in which the first inlet / outlet port 33a is formed. Therefore, the thickness of the shaft 3 does not change, and the shaft 3
The mechanical strength of is almost uniform.

-Embodiment 2- The second embodiment of the present invention exemplifies another means for forming the radial clearance of the air venting gap 34a in FIGS. 1 and 2 to be the widest in the phase in which the first inlet / outlet 33a is formed. To do. In this embodiment, as shown as a radial cross-sectional view in FIG. 4, a portion of the shaft 3 corresponding to the air vent gap 34a is flatly divided along a plane P orthogonal to a diameter line passing through the first inlet / outlet 33a. did. The other points are the same as those of the first embodiment. With this configuration, it is possible to easily manufacture the shaft in which the air gaps 34a have a partially wide radial gap.

-Embodiment 3- The third embodiment of the present invention provides yet another means for forming the radial clearance of the air venting gap 34a in FIGS. 1 and 2 to be the widest in the phase in which the first doorway 33a is formed. It is an example.

As shown in FIG. 5 as a radial cross-sectional view, in the structure in which the radial intervals of the air venting gap 34a are uniform in the circumferential direction, two bubbles B1 of balanced size on both sides of the phase of the first inlet / outlet 33a, When B2 is present, neither of the bubbles B1 and B2 can reach the first entrance and exit and the traffic jams for a while unless the lubricating oil 10 sandwiched between the bubbles B1 and B2 is removed. If the traffic jam is prolonged, the lubricating oil 10 may enter the first entrance 33a.

Therefore, in this embodiment, as shown in FIG. 6, starting from the edge of the first inlet / outlet port 33a, the wall thickness of the shaft 3 is gradually reduced in the circumferential direction (counterclockwise in the drawing) to reduce the diameter of the air bleeding gap 34a. The direction interval was gradually increased in the circumferential direction once. The other points are the same as those of the first embodiment. As a result, the movement path of the bubbles becomes one-way, and the bubbles swirl around the shaft 3 rapidly, reach the gas-liquid interface in the meantime, burst, and join the air venting gap 34a.

Fourth Embodiment The fourth embodiment of the present invention exemplifies a means for promptly returning the lubricating oil, which is entrained by bubbles and has entered the air vent gap, to the minute gap. As described in detail in the first embodiment, the bubbles in the lubricating oil 10 tend to move toward a wide space. Lubricating oil 10 taken in by bubbles at this time
However, it is desirable to return to the minute gap 34c as soon as possible so as not to flow into the air vent hole 33 together with the bubbles.

Therefore, as shown in FIG. 7 and FIG. 8 as a radial sectional view and an axial sectional view, respectively, at one or more locations (3 in FIG. 7) on the inner peripheral surface of the sleeve 5 forming the air vent gap 34c. (A location), an axial groove 53 straddling the gas-liquid interface is provided, and the lower end surface 53a of the groove 53 is provided with a minute gap 34.
It was inclined so that it becomes shallower as it approaches c. The other points are the same as those of the second embodiment. With this configuration, the bubbles burst in the groove 53 and merge into the air bleeding gap 34c, while the lubricating oil 10 that rises along with the bubble flows down the lower end surface 53a of the groove 53 and the minute gap 34c.
Promptly return to. The lubricating oil 10 does not collect in the groove 53.

Embodiment 5 The fifth embodiment of the present invention exemplifies another means for preventing the lubricating oil from flowing into the air vent hole. In this embodiment, as shown in FIG. 9 and FIG. 10 as a radial sectional view and an axial sectional view, respectively, an air vent hole 33 is formed.
Was formed at an eccentric position with respect to the center of the outer diameter of the shaft 3 so that the thickness of the shaft 3 on the side of the first inlet / outlet 33a is thicker than the thickness on the opposite side in the radial direction. The other points are the same as those of the second embodiment. With this configuration, a long radial path from the first inlet / outlet port 33a to the center of the air vent hole 33 can be secured, a large resistance force can be imparted to the inflow of the lubricating oil, and the leakage of the lubricating oil can be prevented. it can.

-Embodiment 6- The sixth embodiment of the present invention exemplifies yet another means for preventing the lubricating oil from flowing into the air vent hole. In this embodiment, the shape of each member of the motor 1 may be any of the above-mentioned five embodiments. Therefore, for convenience, FIG. 11 shows a sectional view in the axial direction of a main part corresponding to the shape of the first embodiment for description. Here, the air vent gap 34a
An oil repellent 37 (for example, a fluorine-based one) is applied to the outer peripheral surface of the shaft 3 that faces the. With this configuration, the contact angle of the outer peripheral surface of the shaft 3 facing the air venting gap 34a with respect to oil is increased, the gas phase is on the surface side, and the lubricating oil 10 is on the inner peripheral surface side of the sleeve 5 facing it.

-Seventh Embodiment- This is an example of the sixth embodiment. That is, instead of the oil repellent agent 37 in the sixth embodiment, a tube 38 made of an oil repellent material is covered on a portion corresponding to the air vent gap 34a as shown in FIG. 12 (a), and as shown in FIG. 12 (b). It was heat-shrinked and fixed. First entrance / exit 3 for tube 38
The hole 38a was previously formed at a position corresponding to 3a. With this configuration, as in the sixth embodiment, the contact angle of the outer peripheral surface of the shaft 3 facing the air venting gap 34a with respect to oil is large, the surface side is in the gas phase, and the lubricating oil is provided on the inner peripheral surface side of the sleeve 5 facing the surface. 10 will come closer.

[0037]

As described above, since the hydrodynamic bearing device of the present invention is constructed so that the bubbles in the lubricating oil are quickly discharged, the leakage of the lubricating oil and the seizure of the bearing portion are prevented.

[Brief description of drawings]

FIG. 1 is an axial sectional view of a main part of a recording disk driving spindle motor to which a hydrodynamic bearing device of a first embodiment is applied.

FIG. 2 is an enlarged view of part A in FIG.

FIG. 3 is a partial radial cross-sectional view of FIG.

FIG. 4 is a partial radial cross-sectional view showing the movement of bubbles in a hydrodynamic bearing device.

FIG. 5 is a partial radial cross-sectional view of a hydrodynamic bearing device of a second embodiment.

FIG. 6 is a partial radial cross-sectional view of a hydrodynamic bearing device of a third embodiment.

FIG. 7 is a partial radial cross-sectional view of a hydrodynamic bearing device of a fourth embodiment.

FIG. 8 is a partial axial sectional view of a hydrodynamic bearing device of a fourth embodiment.

FIG. 9 is a partial radial cross-sectional view of a hydrodynamic bearing device of a fifth embodiment.

FIG. 10 is a partial axial sectional view of a hydrodynamic bearing device of a fifth embodiment.

FIG. 11 is a partial axial sectional view of a hydrodynamic bearing device of a sixth embodiment.

FIG. 12 is a partial axial sectional view of a hydrodynamic bearing device of a seventh embodiment, (a) showing a manufacturing process of the shaft, and (b) showing a completed state of the shaft.

[Explanation of symbols]

1 motor 2 bracket 3 axes 4 rotor 5 sleeve 6 hubs 7 cover 8 stator 9 magnets 10 Lubricating oil 31, 32 Thrust plate 51,52 counter plate 33a First doorway 33b Second doorway 31a, 32a, 31b, 32b Thrust gap 31c, 32c First radial gap 34 Second radial gap 34a Air venting gap 34c Micro gap 53 groove

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[Procedure amendment]

[Submission date] November 26, 2001 (2001.11.
26)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Title of invention

[Correction method] Change

[Correction content]

Title: Hydrodynamic bearing device

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Claims (8)

[Claims] 1. A first entrance / exit that has a shaft and a disk-shaped thrust plate fixed to the lower part of the shaft so as to project in the radial direction, and penetrates the inside of the shaft and leads to the shaft outer peripheral surface above the thrust plate. A stationary member having an air vent hole in which a second inlet / outlet opening to the outside is located, a cylindrical inner surface facing the outer peripheral surface of the thrust plate through a first radial gap, and a thrust gap on the upper surface of the thrust plate. A thrust member having a radial inner peripheral surface opposed to the thrust inner surface and a shaft outer peripheral surface via a second radial gap, and a lubricating oil held in the three gaps. A thrust bearing dynamic pressure generating groove that sends lubricating oil toward the boundary between the thrust gap and the second radial gap during rotation is formed on at least one of the upper surface of the shaft and the inner surface of the thrust, and the outer peripheral surface of the shaft and the At least one of the radial inner peripheral surfaces, at a position lower than the first inlet / outlet, a radial bearing dynamic pressure generating groove for sending lubricating oil toward the boundary between the thrust gap and the second radial gap during rotation is formed. In the bearing device, the second radial gap is surrounded by a surface on which the radial bearing dynamic pressure generating groove is formed and a surface opposite to the surface, and a cylindrical minute gap filled with the lubricating oil, and the first inlet / outlet. It is surrounded by the shaft outer peripheral surface including the periphery and the radial inner peripheral surface facing it, and is composed of a cylindrical air vent gap having a gas-liquid interface between the lubricating oil and air at a position lower than the first inlet / outlet. A hydrodynamic bearing device characterized in that the radial interval is widest in the phase in which the first inlet / outlet is formed. 2. A portion of the shaft corresponding to the air vent gap is eccentric with respect to the rotating member, so that the radial gap of the air vent gap is formed to be widest in the phase in which the first inlet / outlet is formed. The hydrodynamic bearing device according to claim 1. 3. A portion of the shaft corresponding to the air vent gap has a shape that is flatly divided along a plane orthogonal to a diameter line passing through the first inlet / outlet, whereby the radial gap of the air vent gap is 2. The hydrodynamic bearing device according to claim 1, wherein the hydrodynamic bearing device is formed in the widest phase in which the entrance and exit are formed. 4. The hydrodynamic bearing device according to claim 1, wherein the radial clearance of the air venting clearance is gradually increased over the entire circumference in the circumferential direction starting from the edge of the first inlet / outlet. 5. An axial groove that straddles the gas-liquid interface is provided at one or more locations on the radial inner peripheral surface forming the air vent gap, and the lower end surface of the groove becomes shallower as it approaches the minute gap. The hydrodynamic bearing device according to any one of claims 1 to 4, which is inclined so as to be. 6. The dynamic pressure according to claim 2, wherein the air vent hole is formed at an eccentric position with respect to the center of the outer diameter of the shaft so that the thickness of the shaft on the first inlet / outlet side becomes thicker. Hydrodynamic bearing device. 7. A hydrodynamic bearing device according to claim 1, wherein an oil repellent agent is applied to an outer peripheral surface of the shaft facing the air venting gap. 8. A portion of the shaft corresponding to the air vent gap is covered with a tube made of an oil repellent material.
5. A hydrodynamic bearing device according to any one of 1.