JP2002349549A - Hydrodynamic bearing motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exclude air bubbles, apt to stagnate at the central part of a bearing, to the external part of a bearing to obtain a stable shaft support force, and improve durability and reliability. SOLUTION: The dynamic pressure generating groove of a thrust bearing part forms a pumping type spiral groove rows which are disposed in a juxtaposition state in a circumferential direction and where peak of a dynamic pressure is generated at the central part of a thrust plate. A region where no dynamic pressure generating groove is formed is provided such that the distribution shape of a dynamic pressure generated by the spiral groove is not axisynmmetricality.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrodynamic bearing motor provided with a thrust hydrodynamic bearing capable of easily removing air bubbles which may stay near the center of the bearing.

[0002]

2. Description of the Related Art In a motor such as a spindle motor for driving a recording disk such as a hard disk, a bearing means for supporting an axial load acting on a rotor is provided between two axially opposed planes when the rotor rotates. A thrust dynamic pressure bearing which generates a dynamic pressure in a fluid such as oil to be held and uses this as a load supporting pressure is used.

A dynamic pressure generating groove formed to generate a dynamic pressure in the conventional thrust dynamic pressure bearing is a so-called pump which induces a dynamic pressure acting radially inward on oil when the rotor rotates. It is an in-type spiral groove. Due to this spiral groove, a pressure peak at which the dynamic pressure is maximized appears near the center of the bearing, and the pressure decreases as going outward in the radial direction. The dynamic pressure bearing supports the load acting on the rotor at the pressure peak.

The spiral groove has a higher dynamic pressure generation efficiency than a herringbone groove formed by combining a pair of spiral grooves, and can reduce the diameter of the thrust dynamic pressure bearing itself. The peripheral speed can be reduced, and bearing loss can be reduced.

[0005]

However, for example, when air bubbles exist in a portion where a spiral groove is formed, the air bubbles move from the higher side to the lower side according to the pressure gradient. In the radially outer part of the bearing, if a communication hole communicating with the outside of the bearing is provided, it is possible to discharge bubbles to the outside of the bearing. Since it is formed symmetrically, the pressure gradient near the center is slight, and there is a phenomenon that bubbles existing near the center are hard to be removed.

When air bubbles stay near the center of the bearing as described above, the air bubbles have a larger coefficient of thermal expansion than oil, so that the volume increases due to fluctuations in the temperature and pressure of the external environment of the bearing.
Oil flows out of the bearing. Further, even under a low pressure environment, the bubbles expand to cause a similar phenomenon. Due to the outflow of oil, problems such as a decrease in bearing rigidity due to a decrease in the oil holding amount and a decrease in durability and reliability due to early exhaustion of oil occur.

The present invention relates to a thrust dynamic pressure bearing that generates dynamic pressure by a pump-in type spiral groove.
With a simple configuration, it is possible to obtain stable shaft support force by eliminating bubbles that easily stay in the center of the bearing outside the bearing, and easily remove bubbles mixed in oil, It is an object of the present invention to provide a hydrodynamic bearing motor having excellent durability and reliability.

[0008]

According to the present invention, there is provided a hydrodynamic bearing motor comprising: a disk-shaped thrust plate; a counter plate opposed to a plane portion of the thrust plate via a gap in the axial direction; A dynamic pressure bearing motor including a thrust dynamic pressure bearing having oil retained in an axial gap defined between the counter plate and a dynamic pressure generating groove for inducing dynamic pressure on the oil. The dynamic pressure generating groove is a pump-in type spiral groove array that is arranged in parallel in the circumferential direction and generates a pressure peak of the dynamic pressure at the center of the thrust plate. A region in which a dynamic pressure generating groove is not formed is provided in a part of the spiral groove array so that the distribution shape of the dynamic pressure generated is not axially symmetric (claim 1).

In this configuration, by providing an area where the dynamic pressure grooves are not formed in a part of the dynamic pressure groove row formed in the circumferential direction in the dynamic pressure bearing portion, the pressure distribution of the dynamic pressure generated in the bearing portion can be increased or decreased. Occurs. Bubbles mixed into the oil move from a higher pressure to a lower pressure, and are discharged from the bearing through a region where the pressure is lower and a region where the dynamic pressure groove is not formed as compared with a region where the dynamic pressure groove is formed. It will be.

As described above, it is possible to reliably and easily remove air bubbles mixed in the oil, so that the oil can be smoothly moved toward the center of the bearing by the pump-in type spiral groove, Since a stable shaft supporting force can be obtained and oil outflow due to air bubbles is prevented, reliability and durability of the bearing can be improved.

The spiral groove can be formed by electrolytic processing having a relatively large degree of freedom in processing the shape of the dynamic pressure generating groove to be formed.

Further, the region where the dynamic pressure groove is not formed is
By forming a plurality of grooves at equal intervals in the circumferential direction (claim 2), the regions where the dynamic pressure grooves are formed are also positioned at equal intervals in the circumferential direction, and the regions with high dynamic pressure are also positioned at equal intervals in the circumferential direction. Therefore, the stability of the shaft support is not lost. That is,
Air bubbles can be discharged from the bearing portion, and stable rotation of the motor can be obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a sectional view showing an embodiment in which the hydrodynamic bearing motor according to the present invention is applied to a spindle motor for driving a recording disk such as a hard disk, and FIG. 2 is a sectional view of the spindle motor shown in FIG. FIG. 3 is a plan view of a counter plate showing a spiral groove formed in a lower thrust bearing portion.
FIG. 4 is a partially enlarged cross-sectional view showing a configuration around a thrust plate in the spindle motor shown in FIG.

In FIG. 1, a shaft 2 and a disk-shaped thrust plate 4 protruding radially outward and coaxially from an outer peripheral surface of a lower end portion of the shaft 2 are integrally formed. The upper end of the shaft 2 has a tapered inclined surface in which the outer diameter of the shaft 2 gradually decreases upward.
Annular groove 2a is formed. A second annular groove 2 having a pair of inclined surfaces which are inclined toward an axially central portion of the shaft 2 at an axially intermediate portion of an outer peripheral surface of the shaft 2.
b is formed. Thrust plate 4 of shaft 2
The end opposite to the end on the side is a cup-shaped rotor hub 6.
Attached to A rotor magnet 8 is mounted on the inner peripheral surface of the rotor hub 6.

The shaft 2 has a fixed cylindrical sleeve 10
It is inserted into a through hole provided in the inside. At one end of the through hole, a step portion is provided which cooperates with the thrust plate 4 to constitute an upper thrust bearing portion which will be described in detail later. Further, the opening of the sleeve 10 on the side where the step portion of the through hole is formed is closed by a counter plate 12 which constitutes a lower thrust bearing portion described later in detail in cooperation with the lower surface of the thrust plate 4. The upper opening of the through hole of the sleeve 10 is open to the outside at a tapered seal S1 defined between the shaft 2 and the inclined surface of the first annular groove 2a. The outer peripheral portion of the sleeve 10 is mounted in an annular cylindrical wall 16 a provided on the bracket 16.
A stator 18 is attached to an outer peripheral portion of the cylindrical wall 16a,
It faces the rotor magnet 8 in the radial direction.

The inner peripheral surface of the through hole of the sleeve 10 radially opposes the second annular groove 2 b formed on the outer peripheral surface of the shaft 2, and the inner peripheral surface of the through hole of the sleeve 10 and the inner surface of the shaft 2. A gap enlarging portion 20 is provided in which a minute gap in the radial direction between the outer circumferential surface and the outer circumferential surface is enlarged. The sleeve 10 is provided with a first ventilation hole 10a extending in the radial direction to open the gap enlarged portion 20 to the outside of the bearing. The air taken in through the first ventilation 10a is held in the gap expanding portion 20.

Oil is held between the outer peripheral surface of the shaft 2 and the inner peripheral surface of the through hole of the sleeve 10 at the upper and lower portions in the axial direction of the gap enlarging portion 20, so that the upper radial bearing portion 22 and the lower radial bearing are respectively provided. The unit 24 is configured. The portion defining the upper radial bearing portion 22 between the inner peripheral surface of the through hole of the sleeve 10 and the outer peripheral surface of the shaft 2 has a central position (bending of the groove) as a dynamic pressure generating groove on the inner peripheral surface of the sleeve 10. (A portion position) is provided at an intermediate position in the axial direction of the upper radial bearing portion 22. The herringbone groove 22a is provided in an axially symmetric shape and formed by the herringbone groove 22a when the motor rotates. A dynamic pressure is generated in the oil held in the upper radial bearing portion 22 from both ends (upper and lower sides in the axial direction) of the herringbone groove 22a toward the bent portion of the groove. That is, the upper radial bearing portion 22 is configured such that a pressure peak occurs at an intermediate position in the axial direction and the pressure is lowest at both ends.

The portion defining the lower radial bearing portion 24 between the inner peripheral surface of the through hole of the sleeve 10 and the outer peripheral surface of the shaft 2 is formed on the inner peripheral surface of the sleeve 10 as a dynamic pressure generating groove. An axially asymmetric herringbone groove 24a formed so that the position (the position of the bent portion of the groove) is deviated downward from the lower radial bearing portion 24 is provided. Bone groove 2
4a generates a dynamic pressure acting on the oil held in the lower radial bearing portion 24 from both ends (upper and lower sides) of the herringbone groove 24a toward the bent portion of the groove. That is, the lower radial bearing portion 24 is configured such that a pressure peak occurs near the lower end portion in the axial direction and the pressure is lowest at the upper end portion.

A first tapered seal S1 is located above the upper radial bearing portion 22, and a radial dimension of a gap between the inner peripheral surface of the through hole of the sleeve 10 and the outer peripheral surface of the shaft 2 is determined. It gradually expands as it goes upward in the axial direction. A second annular groove 2b having a pair of inclined surfaces on the outer peripheral surface of the shaft 2 is located between the lower side of the upper radial bearing portion 22 and the upper side of the lower radial bearing portion 24. The gap expanding portion 20 defined between the pair of inclined surfaces of the annular groove 2b and the inner peripheral surface of the through hole of the sleeve 10
The gap size gradually decreases in the axial direction from the opening of the first ventilation hole 10a on the inner peripheral surface of the through hole of the sleeve 10 to the second tapered seal S2 and the third tapered seal S3, respectively. Is defined. In the first, second, and third tapered seal portions S1, S2, and S3, the internal pressure and the external pressure of the oil held in the upper and lower radial bearing portions 22, 24 are balanced to form a gas-liquid interface. It is formed.

If the oil retained in the upper radial bearing portion 22 decreases due to long-term use, the gas-liquid interface between oil and air on the first tapered seal S1 side and the second tapered seal S2 The pressure due to the surface tension of the air acting on the gas-liquid interface between the oil on the side and the air acts so as to be equal, and these gas-liquid interfaces move to the upper radial bearing portion 22 side. Therefore, the oil held in the first and second tapered seals S1 and S2 is replenished to the upper radial bearing portion 22.

Between the upper surface of the thrust plate 4 and the lower surface of the step portion of the sleeve 10 which faces in the axial direction, oil is held continuously by the lower radial bearing portion, and the step portion of the sleeve 10 is formed. A pump-in type spiral groove 26a is formed on the lower surface as a dynamic pressure generating groove, and an upper thrust bearing 26 is formed.

Oil is held between the lower surface of the thrust plate 4 and the upper surface of the counter plate 12 which faces the thrust plate 4 in the axial direction.
The upper thrust bearing 2
6, a pump-in type spiral groove 28a is formed to form a lower thrust bearing portion 28.

When the motor rotates, the spiral groove 26
a, 28a, the upper and lower thrust bearings 26
A dynamic pressure is generated in the oil held in the and 28 so as to increase the pressure inward in the radial direction.

In the oil held by the upper thrust bearing portion 26, a dynamic pressure acting radially inwardly is generated by the spiral groove 26a when the motor rotates, but the shaft 2 is located on the rotation center side of the thrust plate 4. To be located
The radially inward action on the oil by the spiral groove 26 a is prevented by the shaft 2. However, the lower radial bearing portion 24 adjacent to the upper thrust bearing portion 26 is formed with an axially unbalanced herringbone groove 24a so as to generate a pressure peak near the lower end portion in the axial direction. Since oil is continuously held between the portion 24 and the upper thrust bearing portion 26, the dynamic pressure acting on the oil near the boundary between the lower radial bearing portion 24 and the upper thrust bearing portion 26 Pressure peak occurs. Therefore, the lower radial bearing portion 24 and the upper thrust bearing portion 26 cooperate to generate a dynamic pressure required to support the shaft 2 and the thrust plate 4 rotating together with the rotor hub 6.

Further, in the lower thrust bearing portion 28, a pressure peak of dynamic pressure acting on the oil is generated near the axis of the shaft 2 due to the radially inward action on the oil by the spiral groove 28a, and the spiral groove 28a Is a dynamic pressure generating groove array formed in the circumferential direction, the distribution shape is generally symmetric with respect to the axis. However, when the pressure peak of the dynamic pressure becomes substantially symmetrical with respect to the axis, the bubbles remaining near the center of the lower thrust bearing portion 28 cannot move to the outer peripheral side of the low-pressure bearing, and stay there. Will continue. For this reason, as shown in FIG.
A region 28b where a dynamic pressure generating groove is not formed is formed in the dynamic pressure generating groove row composed of a.

In these regions 28b, no dynamic pressure is induced even when the rotating shaft 12 rotates. That is, from the side where the region 28b is located, there is no action to positively press the oil inward in the radial direction, so that the distribution shape of the dynamic pressure of the lower thrust bearing portion 28 is asymmetric with respect to the axis.

As a result, the balance of the circumferential dynamic pressure in the lower thrust bearing portion 28 is lost, and a region where the pressure is partially increased is generated. If bubbles exist in the oil, the bubbles are sent from the high pressure region formed by the spiral groove 28a to the region 28b where the lower dynamic pressure generating groove is not formed, and further reduced in pressure. The thrust plate 12b is sequentially transferred to the outer peripheral portion thereof and is removed from the lower thrust bearing portion 28.

In this case, by arranging the regions 28b in which the dynamic pressure generating grooves are not formed at equal intervals in the circumferential direction, the regions where the dynamic pressure for supporting the rotating shaft portion 12 is high are also arranged at equal intervals in the circumferential direction. Therefore, even if the low pressure region 28b is formed in the lower thrust bearing portion 28, the shaft support of the rotating shaft portion 12 does not become unstable.

As shown in FIG. 3, the sleeve 10 is provided on the outer peripheral surface of the thrust plate 4 from the upper surface side of the thrust plate 4 constituting the upper thrust bearing portion 26 toward the center in the thickness direction of the thrust plate 4. The tapered inclined surface and the lower thrust bearing portion 28 in which the dimension of the radial gap defined between the stepped portion and the inner peripheral surface is increased.
The radial dimension of the radial gap defined between the lower surface of the thrust plate 4 and the inner peripheral surface of the step provided on the sleeve 10 increases toward the center in the thickness direction of the thrust plate 4. A third annular groove 4a having a substantially V-shaped cross section constituted by a tapered inclined surface is provided. The pair of inclined surfaces defining the third annular groove 4a are inclined at substantially the same inclination angle from the upper surface and the lower surface of the thrust plate 4 toward the substantially central portion in the thickness direction of the thrust plate 4, respectively. I have.

The sleeve 10 is provided with a plurality of second ventilation holes 10 b extending in the radial direction so as to open on the inner peripheral surface of the step portion of the sleeve 10 and the outer peripheral surface of the sleeve 10. The two ventilation holes 10b are connected by an annular groove 16a1 formed on the inner peripheral surface of an annular cylindrical wall 16a provided on the bracket 16 over the entire circumference. The sleeve 1 is connected to the annular groove 16a1.
0 is provided with a notch 10b1 in the axial direction in a part of the outer peripheral surface thereof, and the notch 10b1 and the annular groove 16a1 are provided.
And outside air is taken in and held in a pair of tapered spaces defined between the third annular groove 4a and the inner peripheral surface of the step provided in the sleeve 10 through the second ventilation hole 10b. I have. The gas-liquid interface between the oil held by the upper thrust bearing portion 26 and the lower thrust bearing portion 28 and the outside air is:
It is formed in a pair of tapered spaces defined between the third annular groove 4a and the inner peripheral surface of the step of the sleeve 10. In other words, a pair of tapered spaces defined between the third annular groove 4a and the inner peripheral surface of the step of the sleeve 10 are formed by the fourth tapered seal S4 and the fifth tapered seal S5, respectively. Is specified.

As described above, the third annular groove 4a provided on the outer peripheral surface of the thrust plate 4 is constituted by a pair of inclined surfaces having substantially the same inclination angle, so that the fourth and fifth annular grooves are formed. The taper seals S4 and S5 also have substantially the same taper angle and seal length (dimensions of a region that exhibits a sealing function).
have. Further, a third tapered seal S3 which is an end of the oil held by the lower radial bearing portion 24 in which the oil is held continuously by the upper thrust bearing portion 26.
Has a shape that can be balanced so that the oil held in the fourth and fifth tapered seals S4 and S5 and the internal pressure of the oil become equal. Therefore, the oil retained on the outer peripheral portion of the thrust plate 4
Are separated so as to be substantially uniform through a substantially central portion in the thickness direction of the lower bearing, and therefore function as a buffer oil for oil held by the lower radial bearing portion 22, the upper thrust bearing portion 26, and the lower thrust bearing portion 28. There is no imbalance in the amount of oil.

Next, the discharge of air bubbles from each bearing will be described. The upper radial bearing portion 22 has an upper radial bearing portion 22 at a substantially central portion in the axial direction of the herringbone groove 22a.
Is provided with a bent portion where a dynamic pressure peak is generated. Therefore, when the motor rotates, the air bubbles mixed in the oil held in the upper radial bearing portion 22 are substantially centered in the axial direction of the bearing with the highest pressure. From the portion to the axially opposite ends of the bearing with low pressure, and is opened to the outside air from the gas-liquid interface formed in the first and second tapered seals S1, S2.

An axially unbalanced herringbone groove 24a formed in the lower radial bearing portion 24 is provided between the lower radial bearing portion 24 and the upper thrust bearing portion 26 in which oil is continuously held. Pump-in type spiral groove 2 formed in the upper thrust bearing 26
6a, a pressure peak is generated in the vicinity of the boundary between the two bearing portions, and the pressure decreases toward the radially enlarged portion 18 and the breathing hole 34 side. Therefore, the lower radial bearing portion 24 and the upper thrust bearing portion Bubbles mixed into the oil held by the oil through the gas-liquid interface formed in the third and fourth tapered seal portions S3 and S4 having low pressure from near the boundary between these bearing portions having the highest pressure. Open to the open air.

Further, in the lower thrust bearing portion 28, although a pressure peak of the dynamic pressure occurs near a substantially central portion of the bearing portion, the distribution is asymmetric with respect to the axis. For this reason, as described above, the bubbles staying in the vicinity of the center of the bearing also move to the outer peripheral side of the bearing through the low-pressure region 26b, and thereafter the gas-liquid formed in the fourth tapered seal portion S4 having the lowest pressure. Open to the outside air through the interface.

Although the embodiment of the present invention has been described above, the present invention is not limited to such an embodiment, and various modifications and corrections can be made without departing from the scope of the invention.

For example, in FIG. 2, four regions 28b in which the dynamic pressure generating groove is not formed in the lower thrust bearing portion 28 are formed, but the region 28b is formed in a range in which the generated dynamic pressure does not decrease more than necessary. Any number that can be formed at equal intervals in the direction may be used.

The upper and lower radial bearings 22,
The herringbone grooves 22a and 24a formed in the upper and lower spiral thrust bearing portions 26 and 28 are formed by electrolytic processing so that a groove pattern having a desired shape can be easily formed. Although it can be obtained, it can also be formed by a processing method such as ball rolling and coining.

[0038]

According to the hydrodynamic bearing motor according to the first aspect of the present invention, it is possible to reliably eliminate bubbles existing at the center of the bearing, which are difficult to eliminate, and to obtain a stable shaft supporting force. In addition to this, the outflow of oil due to air bubbles is prevented, so that the reliability and durability of the bearing can be improved.

In the hydrodynamic bearing motor according to the second aspect of the present invention, air bubbles can be discharged from the bearing portion without losing the stability of the shaft support, and stable rotation of the motor can be obtained. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a schematic configuration when a hydrodynamic bearing motor of the present invention is applied as a spindle motor.

FIG. 2 is a plan view of a counter plate showing a spiral groove formed in a lower thrust bearing portion of the spindle motor of FIG. 1;

FIG. 3 is a partially enlarged cross-sectional view showing a configuration around a thrust plate of the spindle motor shown in FIG. 1 in an enlarged manner.

[Explanation of symbols]

 4 Thrust plate 12 Counter plate 26, 28 Thrust bearing portion 26a, 28a Spiral groove 28b Area where dynamic pressure groove is not formed

Claims (2)

[Claims] 1. A disc-shaped thrust plate, a counter plate opposed to a plane portion of the thrust plate via a gap in an axial direction, and an axial gap defined between the thrust plate and the counter plate. A hydrodynamic bearing motor including a thrust hydrodynamic bearing having oil held therein and a hydrodynamic groove for inducing dynamic pressure with respect to the oil, wherein the hydrodynamic groove is formed in a circumferential direction. , And a pump-in type spiral groove array that generates a dynamic pressure peak at the center of the thrust plate, and the distribution shape of the dynamic pressure generated by the spiral groove is not axially symmetric. A dynamic pressure bearing motor characterized in that a region in which a dynamic pressure generating groove is not formed is provided in a part of the spiral groove row. 2. A region where the dynamic pressure generating groove is not formed,
2. The hydrodynamic bearing motor according to claim 1, wherein a plurality of the bearings are formed at equal intervals in a circumferential direction.