JPH112235A - Dynamic pressure fluid bearing device and electric motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply lubrication liquid when the lubrication oil is decreased, to enhance for use for a long time by preventing the decrease of the lubrication oil due to evaporation from occurring as much as possible, and to form a device in a compact state by shortening length in an axial direction as much as possible without damaging performance as a dynamic pressure fluid bearing. SOLUTION: The storage gap opening 40a of a communication hole 40 at the internal part of a fixed sleeve body 12 is opened to a lubrication oil storage gap part 36, and an opening 40b in the vicinity of an interface is opened to the upper end of an upper radial bearing part 28. When lubrication oil 24 with which a gap between a rotary shaft body 20 and a fixed sleeve body 12 or a thrust plate 14 is filled is decreased and an boundary at which outside air fronts on the lubrication oil 24 retreats downward, the opening 40b in the vicinity of the boundary is opened to the outside air side and the lubrication oil storage gap part 36 is communicated with outside air. When the upper radial bearing part 28 side is replenished with the lubrication oil 24 in the lubrication oil storage gap part 36, the boundary is returned and the opening 40b in the vicinity of the boundary is positioned on the lubrication oil 24 side.

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 capable of replenishing a lubricating liquid during long-term use, and a recording medium such as a magnetic disk, a magneto-optical disk, or an optical disk provided with the hydrodynamic bearing device. The present invention relates to an electric motor particularly suitable as a small precision motor for driving.

[0002]

2. Description of the Related Art FIG.
FIG. 2 is a sectional view of a conventional example of a hydrodynamic bearing.

In this hydrodynamic bearing, a pair or a plurality of pairs of spiral grooves c having different directions are formed on either the outer peripheral surface of a rotating shaft a or the inner peripheral surface of a cylindrical bearing b supporting the rotating shaft a. The space between the bearing b and the rotary shaft a is filled with oil d as a working fluid.

The bearing b has a closed-bottom cylindrical shape with a closed bottom, and a flow path e extending in the axial direction is formed inside the peripheral wall. The circulation path e has one end communicating with the outside air and the other end communicating with one end of the spiral groove c. Further, a part of the flow path e and the end of the spiral groove c are filled with oil d which is a working fluid. Even if the entire area of the flow path e is not filled with oil, at least the vicinity of the communication holes f and g and the oil reservoirs h and i and the vicinity of the spiral groove c are filled with oil. It is sufficient if the oils are filled so that the liquid level is high, and these oils are connected to each other. That is, the distribution channel e
The end of the spiral groove c in the bearing b communicates with the atmospheric pressure and also serves as an oil reservoir.

[0005] With the above construction, the atmospheric pressure is constantly applied to the end of the spiral groove c through the communication holes f and g and the oil in the flow path e, the communication hole j and the gap k. . For this reason, if the oil d leaks or evaporates from the end c1 on the upper end opening side of the upper spiral groove c, the shortage is transferred to the oil reservoir i or the flow path via the lower end of the upper spiral groove c. e.

However, if the communication hole j of the flow path e is to be always opened in the gap k above the upper spiral groove c, the axial length of the bearing becomes longer by that amount. Improvements are desired for use in spindle motors and the like for driving recording media, for which there is a strong demand for thinning. Also,
Since the oil d faces the outside air even in the distribution path e, it also causes an increase in the amount of evaporation of the lubricating oil. Therefore, improvement in this point is also desired.

The present invention has been made in view of the above-mentioned problems in the prior art, and has an object to solve the problem when the lubricating fluid is reduced due to evaporation, centrifugal force, impact, or the like. Lubricant is replenished and, of course, the decrease due to evaporation of the lubricating fluid is prevented as much as possible, so that it is suitable for long-term use and its axial length without impairing the performance as a hydrodynamic bearing. It is an object of the present invention to provide a hydrodynamic bearing device capable of minimizing the size as much as possible and making the whole compact and an electric motor provided with the hydrodynamic bearing device.

[0008]

In order to achieve the above object, a hydrodynamic bearing device according to the present invention is characterized in that a lubricating liquid filled in a gap between a shaft body and a bearing body externally fitted to the shaft body is used. A hydrodynamic bearing device in which one of a shaft body and a bearing body is supported so as to be relatively rotatable relative to the other, wherein a gap between the shaft body and the bearing body includes a load supporting portion, and a gap between the load supporting portion. A lubricating fluid storage gap that is larger than the outside air, has a storage gap opening that opens to the lubricating fluid storage gap, and an interface near opening that opens to the lubricating fluid side near the interface position of the lubricating fluid that faces the outside air. And a communication hole for communicating them is provided in the shaft body or the bearing body (Claim 1).

The shaft body may be, for example, substantially cylindrical in its entirety, and has a substantially cylindrical shaft portion and a thrust plate portion projecting radially outward from the shaft portion. You can also. The bearing body may be, for example, a cylinder with a bottom when the entire shaft body has a substantially cylindrical shape, and the shaft body may have a substantially cylindrical shaft portion and a radially outer portion from the shaft portion. In the case where the thrust plate portion is protruded in the axial direction, the cylindrical portion sleeve-fitted to a portion of the shaft portion closer to the base end side than the thrust plate portion and the radially inner portion fitted externally to the thrust plate portion. An annular thrust groove having an opening may be provided.

As the lubricating liquid, various lubricating oils such as spindle oil can be used.

As described above, the entire shaft body has a substantially cylindrical shape, the bearing body has a bottomed cylindrical shape, and one of the tip end surface of the shaft body and the inner bottom surface of the bearing body has the other through the lubricating liquid. When the lubricating liquid is supported in the center direction, the lubricating liquid has an interface facing the outside air only on the base end side of the shaft. On the other hand, the interface between the lubricating liquid filled in the gap between the shaft body and the bearing body, which faces the outside air, may be provided on both one end side and the other end side of the shaft body. For example, both ends of a substantially cylindrical shaft portion are fixed, and a shaft body having a radially outwardly protruding thrust plate portion between both ends of the shaft portion, the base portion of the shaft portion closer to the thrust plate portion than the thrust plate portion. In the case where the cylindrical portion of the bearing body is sleeve-fitted to the portion and the annular thrust groove of the radially inner opening of the bearing body is fitted to the thrust plate portion, the interface facing the outside air of the lubricating liquid is connected to one end of the shaft body. On both sides.

The load supporting portion of the gap between the shaft and the bearing is
It is a portion that supports at least the main radial load and thrust load via the lubricating liquid. It is preferable that a groove for generating dynamic pressure, such as a herringbone groove or a spiral groove, be provided on the outer surface of the shaft body or the inner surface of the bearing body in the load supporting portion.

[0013] The lubricating fluid storage gap in the gap between the shaft body and the bearing body is larger than the gap between the load supporting portions and does not reach the outside air, and may be two or more.

An appropriate radial thickness of the lubricating fluid storage gap is:
It varies depending on the type of the lubricating liquid and the material and condition of the surfaces forming the lubricating liquid storage gap, and an example of a small spindle motor is a thickness of about 50 μm.

Examples of the load support portion include a radial bearing portion in which the shaft body and the bearing body face each other in the radial direction, and a thrust bearing portion in which the shaft body and the bearing body face each other in the axial center direction. The radial bearing part
Typically, it is located at two places spaced apart in the axial direction,
It may be one or three or more. When a plurality of radial bearing portions are provided, the lubricant storage gap portion may be provided between the radial bearing portions (claim 2).

When the lubricating liquid filled in the gap between the shaft and the bearing decreases due to evaporation, centrifugal force, impact, etc.,
The interface of the lubricating liquid facing the outside air recedes, the opening near the interface of the communication hole opens to the outside air side, and the lubricating liquid storage gap communicates with the outside air via the communication hole. Then, the lubricating liquid in the lubricating liquid storage gap is replenished to the load supporting portion side of the gap smaller than the lubricating liquid storage gap, and the interface facing the outside air of the lubricating liquid returns to the original position, and the interface of the communication hole The vicinity opening is located on the lubricating liquid side.

There is an interface between the lubricating liquid and the gas (air or the like) in the lubricating liquid storage gap, and the gas in the lubricating liquid storage gap is continuous with the gas (air or the like) in the communication hole. In the normal case, since the space between the communication hole and the lubricating liquid storage gap and the outside air is blocked by the lubricating liquid, the temperature of the gas in the communication hole and the lubricating liquid storage gap increases due to an increase in the outside air temperature. When expanded, a small amount of gas tends to go out, and conversely, when the temperature of the gas in the communication hole and the lubricating fluid storage gap decreases due to a decrease in outside air temperature and contracts, a small amount of outside air enters the communication hole. Try to enter. The same applies to a case where the outside air pressure is low or a case where the outside pressure is high. Since the opening near the interface of the communication hole opens to the lubricating liquid side near the interface position of the lubricating liquid facing the outside air, the gas flows in such a case through the opening near the interface and is bubbled. That is, the gas moves in the form of bubbles in the lubricating liquid from the communication hole side to the outside air side or vice versa.

The opening near the interface is temporarily opened to the outside air side when the lubricating fluid is reduced, but is always closed at the lubricating liquid side. Is small. Therefore, the evaporation of the lubricating liquid is suppressed to a low level, and a decrease in the lubricating liquid due to the evaporation is prevented as much as possible. In addition, the opening near the interface of the communication hole is opened on the lubricating liquid side near the interface position of the lubricating liquid facing the outside air, and does not require a separate space for the opening. Can be made as short as possible.

It is desirable that the communicating hole has a cross section substantially larger than the lubricating liquid storing gap at least at the opening of the storing gap and at the opening near the interface and the vicinity thereof. The fact that the storage gap opening and the vicinity thereof have a substantially larger cross section than the lubricating liquid storage gap means that, for example, the lubricating fluid is continuous slightly inward of the storage gap opening of the lubricating liquid storage gap and the communication hole. In this case, it refers to a state in which the lubricating liquid tends to move toward the lubricating liquid storage gap due to the surface tension (capillary action) of the lubricating liquid. The same applies to the opening near the interface. The entire communication hole, including the storage gap opening and the opening near the interface, may have a substantially larger cross section than the lubricating liquid storage gap.

The communication hole is desirably provided on a fixed side of the shaft or the bearing in order to avoid impairing the balance of rotation. In order to prevent the lubricating liquid from flowing into the communication hole due to the centrifugal force at the time of rotation, the communication hole is desirably provided in the shaft. The number of communication holes may be two or more.

It should be noted that the hydrodynamic bearing device of the present invention can be used for various types of machinery other than electric motors.

Next, an electric motor according to the present invention includes the above-described hydrodynamic bearing device, and the shaft or the bearing rotates as a part of the rotor. (Claim 4) The electric motor includes a magnetic disk such as a hard disk, a magneto-optical disk, a CD,
The present invention can be used as various motors, in addition to a spindle motor for a recording medium driving device such as an optical disk such as a DVD.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. 1 which shows a schematic sectional view of a spindle motor (electric motor) for driving a hard disk provided with a hydrodynamic bearing device as an example. I will explain it.

The lower end of the substantially cylindrical fixed sleeve 12 is fitted and fixed to the fitting hole of the spindle motor base 10 by, for example, press-fitting or bonding with an adhesive, so that the fixed sleeve 12 is erected. Fixed. The lower end portion of the fixed sleeve body 12 is closed by fixing the thrust receiving plate 14, and the fixed sleeve body 12 and the thrust receiving plate 14 constitute a bearing body.

The fixed sleeve 1 on the upper side of the base 10
A stator core 16 around which a stator coil is wound is fixed to the outer peripheral side of 2.

A rotating shaft 20 whose upper end (base end) is fixed to the center of a bowl-shaped rotor hub 18 and protrudes inward is fitted in the fixed sleeve 12. A cylindrical rotor magnet 2 is provided on the inner peripheral surface of the outer peripheral wall of the rotor hub 18.
2 are fixed inside and are opposed to the stator core 16 with a radial gap therebetween. The rotor includes a rotating shaft body 20, a rotor hub 18, and a rotor magnet 22. Rotor hub 1
A hard disk is fitted and held on the outer peripheral surface of the outer peripheral wall 8.

The gap between the fixed sleeve body 12 and the thrust plate 14 and the rotary shaft body 20 is filled with a lubricating oil 24, and these constitute a hydrodynamic bearing device.

The lower end surface of the substantially cylindrical rotating shaft body 20 is formed on a thrust surface 20a perpendicular to the axial direction, and faces the upper surface of the thrust receiving plate 14 via the lubricating oil 24 in the axial direction. It constitutes the thrust bearing 26 (load support).

The outer periphery of the rotating shaft body 20 is formed with a tapered portion 20b whose upper end portion is reduced in diameter upward, and an annular concave portion 20c whose upper and lower middle portion is opened radially outward. The outer peripheral surface of the rotary shaft body 20 between the tapered portion 20b and the annular concave portion 20c, the outer peripheral surface of the rotary shaft body 20 below the annular concave portion 20c, and the inner peripheral surface of the fixed sleeve body 12 are each interposed with lubricating oil 24. The upper and lower radial bearing portions 28 and 30 (load support portions) are formed by radially facing each other. The inner peripheral portion of the fixed sleeve body 12 in the upper and lower radial bearing portions 28 and 30 is provided with a dynamic force for increasing the pressure of the lubricating liquid 24 toward the axial center of each radial bearing portion during rotation of the rotary shaft body 20. Herringbone grooves 32 and 34 for pressure generation
Is provided.

A lubricating oil storage gap 36 is formed between the annular recess 20 c and the inner peripheral surface of the fixed sleeve 12.
The thickness of the radial gap of the lubricating oil storage gap 36 is about 50 μm
The lubricating oil 24 is larger than the gap (usually about 20 μm) between the upper and lower radial bearing portions 28 and 30 and the thrust bearing portion 26, and the lubricating oil 24 contacts both the bottom surface of the annular concave portion 20c and the inner peripheral surface of the fixed sleeve body 12. Is maintained by the surface tension. The function of the bearing does not necessarily require the presence of the lubricating oil 24 in the lubricating oil storage gap 36, but the presence of the lubricating oil 24 does not impair the function of the bearing.

The interface between the lubricating oil 24 and the outside air is defined by a gap expanding portion 38 in which the gap between the tapered portion 20b of the rotary shaft 20 and the inner peripheral surface of the fixed sleeve body 12 gradually increases upward (outside air). To position. Since the lubricating oil 24 facing this interface is continuous with the lubricating oil 24 located in the lubricating oil storage gap 36, the span of the lubricating oil 24 interface in the gap expanding portion 38 is equal to the gap of the lubricating oil storage gap 36. Since it is kept below a small extent, it prevents migration of the lubricating oil 24 from the interface.

A communication hole 40 is provided inside the fixed sleeve body 12.
Are provided, and the storage gap opening 40 which is one end of the communication hole 40 is provided.
a is open to the lubricating oil storage gap portion 36 on the inner peripheral surface of the fixed sleeve body 12, and an opening 40 b near the interface, which is the other end, is connected to the upper radial bearing portion 28 of the inner peripheral surface of the fixed sleeve body 12.
Open at the top of In the example of FIG. 1, the lubricating oil storage gap 3
6 is a gas portion 4 facing the storage gap opening 40a.
2

The cross section inside the communication hole 40 is the same as the storage gap opening 40.
a and a cross section substantially larger than the lubricating oil storage gap portion 36, including the opening 40b near the interface. That is, for example, when the lubricating oil 24 continues from the lubricating oil storage gap 36 to the communication hole 40 slightly inward through the storage gap opening 40a, the lubricating oil 24 is lubricated by the surface tension (capillary phenomenon) of the lubricating oil 24. An attempt is made to move to the oil storage gap 36 side.

When the lubricating oil 24 filled in the gap between the rotating shaft 20 and the fixed sleeve 12 and the thrust plate 14 is reduced by evaporation, centrifugal force, impact, etc., the interface where the lubricating oil 24 faces the outside air is downward. The opening 40b near the interface of the communication hole 40 opens to the outside air side, and the lubricating oil storage gap 36 communicates with the outside air through the communication hole 40. Then, the lubricating oil 24 in the lubricating oil storage gap 36 is
Replenishment is performed on the upper radial bearing portion 28 side with a smaller gap, and the interface of the lubricating oil 24 facing the outside air moves upward and returns to the original position, and the opening 40b near the interface of the communication hole 40 is positioned on the lubricating oil 24 side. I will be.

The lubricating oil storage gap 36 has an interface between the lubricating oil 24 and air, and the air in the lubricating oil storage gap 36 is continuous with the air in the communication hole 40. In the normal case, the space between the communication hole 40 and the lubricating oil storage gap 36 and the outside air is closed by the lubricating oil 24. When the temperature rises and expands, a small amount of air tends to go out. Conversely, when the temperature of the air in the communication hole 40 and the lubricating oil storage gap 36 decreases due to a decrease in the outside air temperature and contracts, a small amount of air decreases. Outside air attempts to enter the communication hole 40. The same applies to a case where the outside air pressure is low or a case where the outside pressure is high. In such a case, an opening 40b near the interface that opens toward the lubricating oil 24 near the interface position of the lubricating oil 24 facing the outside air
Inlet and outflow of air are performed by bubbling through, and the pressure inside and outside is adjusted.

The opening 40b near the interface is temporarily opened to the outside air when the amount of the lubricating oil 42 is reduced. However, since the opening 40b is always closed on the lubricating oil 24 side, the lubricating oil 2 is viewed from the outside air side.
4 has a small interface with the outside air. Therefore, the evaporation of the lubricating oil 42 is suppressed to a low level, and a decrease in the lubricating oil 24 due to the evaporation is prevented as much as possible.

An opening 40b near the interface of the communication hole 40 is provided.
Is the lubricating oil 24 near the interface position of the lubricating oil 24 facing the outside air.
The hydrodynamic bearing device and the spindle motor can be made as compact as possible by shortening the axial length of the hydrodynamic bearing device and the spindle motor as much as possible.

It should be noted that the vertical positional relationship in the above description of the embodiment is merely for convenience of description based on the drawings, and does not limit the actual use state and the like.

[0039]

According to the hydrodynamic bearing device or the electric motor of the present invention, when the lubricating fluid decreases due to evaporation, centrifugal force, impact, etc., the interface of the lubricating fluid facing the outside air recedes, and the vicinity of the interface of the communication hole is reduced. Since the opening is open to the outside air and the lubricating fluid storage gap communicates with the outside air through the communication hole, the lubricating liquid in the lubricating fluid storage gap is replenished to the load support portion of the gap smaller than the lubricating fluid storage gap. Is done. Therefore, even during long-term use, problems such as unstable rotation of the shaft or sleeve due to lack of lubricating liquid and damage to the load supporting portion can be prevented.

The opening near the interface is temporarily opened to the outside air when the lubricating fluid is reduced. However, since it is always closed on the lubricating fluid side, evaporation of the lubricating fluid is suppressed to a low level. Lubricant reduction is prevented as much as possible.

Further, when the gas inside the communication hole expands or contracts due to a change in temperature or a change in the outside air pressure, the gas flows in and out of the inside and outside through the opening near the interface between the communication hole and the outside. The pressure is adjusted.

Further, the opening near the interface of the communication hole is opened on the lubricating liquid side near the interface position of the lubricating liquid facing the outside air, and does not require a separate space for the opening. The overall length can be reduced by shortening the length in the axial direction as much as possible without loss.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a spindle motor for driving a hard disk provided with a hydrodynamic bearing device.

FIG. 2 is a sectional view of a conventional hydrodynamic bearing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 Fixed sleeve body 14 Thrust plate 20 Rotating shaft body 24 Lubricating oil 28 Upper radial bearing part 36 Lubricating oil storage gap part 40 Communication hole 40a Storage gap opening 40b Opening near interface

Claims (4)

[Claims] 1. One of the shaft and the bearing is rotatably supported on the other of the shaft and the bearing via a lubricating liquid filled in a gap between the shaft and a bearing fitted to the shaft. A hydrodynamic bearing device, comprising a load supporting portion and a lubricating liquid storage gap that is larger than the gap between the load supporting portions and does not face the outside air, in the gap between the shaft body and the bearing body. A communication hole having a storage gap opening that opens to the liquid storage gap portion and an interface near the interface opening to the lubricating liquid side near the interface position of the lubricating liquid facing the outside air, and a communication hole that connects them is formed in the shaft body or the bearing body. A hydrodynamic bearing device characterized by comprising: 2. The hydrodynamic bearing device according to claim 1, comprising a plurality of radial bearing portions, and a lubricating fluid storage gap portion between the radial bearing portions. 3. The hydrodynamic bearing device according to claim 1, wherein at least the opening of the storage gap, the opening near the interface, and the vicinity of the communication hole have a cross section substantially larger than the lubricant storage gap. 4. An electric motor comprising the hydrodynamic bearing device according to claim 1, wherein the shaft or the bearing rotates as a part of a rotor.