JP2001140864A - Fluid dynamic pressure bearing and spindle motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve the proper distribution and smooth flow of a lubricant and to prevent accidents such as seizure in a fluid dynamic pressure bearing having a flanged shaft constituted of a ring member formed with thrust dynamic pressure grooves on the upper face and the lower face and radial dynamic pressure grooves on the outer periphery respectively and a columnar member pressed into the ring member. SOLUTION: This fluid dynamic pressure bearing comprises the flanged shaft 1 constituted of the ring member 3 formed with the thrust dynamic pressure grooves G2 on the upper face and the lower face and the radial dynamic pressure grooves G1 on the outer periphery respectively and a columnar member 2 pressed into the ring member 3, a sleeve 4 rotatably coupled with the flanged shaft 1, and an annular cover member 5 functioning as a thrust pressing member. Three pairs or more vertical through-holes Q for lubricant reservoir are formed at uniform intervals in the peripheral direction on the inner periphery of the ring member 3 or on the outer periphery of the columnar member 2 kept in contact with the inner periphery of the ring member 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a ring member having thrust dynamic pressure grooves formed on its upper and lower surfaces and a radial dynamic pressure groove formed on its outer peripheral surface, respectively, and a cylindrical member press-fitted into the ring member. A fluid dynamic pressure bearing having a flanged shaft and a sleeve into which the flanged shaft is rotatably fitted, in other words, one ring member is used as a thrust dynamic pressure bearing member and a radial dynamic pressure bearing member. The present invention relates to a fluid dynamic pressure bearing that is also used as a fluid dynamic pressure bearing suitable for a thin small spindle motor.

[0002]

2. Description of the Related Art A conventional fluid dynamic pressure bearing shown in FIG. 6 is a fluid dynamic pressure bearing having a flanged shaft, and has a flange formed by press-fitting a ring member 3 as a thrust member into a cylindrical member 2. A shaft 1, a stepped cylindrical sleeve 4 into which the flanged shaft 1 is rotatably fitted,
And an annular lid member 5 which also functions as a thrust holding member. The disk-shaped minute gaps RS1, RS2, RV2 and the annular gaps RR, RV1 formed between these bearing components are filled with lubricating oil. The tapered minute gap S formed between the outer peripheral surface on the upper side of the cylindrical member 2 and the inner peripheral surface of the annular lid member 5 functions so as to prevent the lubricating oil from leaking to the outside by utilizing capillary action and surface tension. Capillary seal A radial dynamic pressure groove G1 such as a herringbone groove is formed on the lower outer peripheral surface of the cylindrical member 2, and a spiral thrust dynamic pressure groove G2 such as a herringbone groove is formed on the upper and lower surfaces of the ring member 3, respectively. ing.

The disc-shaped minute gaps RS1 and RS2 function as a first thrust bearing gap and a second thrust bearing gap, respectively, and the annular minute gap RR functions as a radial bearing gap. The distance between these bearing gaps depends on the size of the hydrodynamic bearing, the number of revolutions, and the viscosity coefficient of the lubricating oil.
m to several hundred μm. The interval between the annular minute gap RV1 functioning as a lubricating oil reservoir and the disc-shaped minute gap RV2 is about several times the bearing gap.

In the conventional fluid dynamic pressure bearing shown in FIG. 6, the thrust dynamic pressure bearing portion and the radial dynamic pressure bearing portion are adjacent to each other.
It is divided up and down in the direction of the rotation axis. Therefore, the lubricating oil reservoir in the thrust dynamic pressure bearing portion is occupied by the annular minute gap RV1, and the lubricating oil reservoir in the radial dynamic pressure bearing portion is occupied by the disk-shaped minute gap RV2. Therefore, during rotation of the bearing, the lubricating oil flows in the direction of the arrow, and the distribution and flow of the lubricating oil are theoretically properly performed. However, it is not always appropriate in an actual device.

[0005] With the rapid spread of portable electronic devices, there has been a demand for downsizing and weight reduction of a spindle motor as a rotary drive source thereof. As a result, fluid dynamic pressure bearings widely used for spindle motor bearings have been required to be further reduced in size and weight. Therefore, as shown in FIG.
A fluid dynamic pressure bearing in which the minute gap RR between the inner peripheral surface of the cylindrical member 2 and the inner peripheral surface of the
In other words, a fluid dynamic bearing has been proposed in which the ring member 3 functions as both a thrust dynamic pressure bearing portion and a radial dynamic pressure bearing portion.

However, in the fluid dynamic pressure bearing shown in FIG. 5, the disc-shaped minute gap RR formed between the lower end surface of the cylindrical member 2 and the bottom surface of the sleeve 4 serves as a lubricating oil reservoir. Therefore, it is necessary to appropriately distribute and supply the lubricating oil to the thrust dynamic pressure bearing portion and the radial dynamic pressure bearing portion from the disk-shaped minute gap RR, which is the only shared lubricating oil reservoir, Therefore, it is very difficult to supply the lubricating oil necessary for generating the dynamic pressure.

Further, in the fluid dynamic pressure bearing shown in FIG. 5, the dynamic pressure distribution is such that thrust dynamic pressure is generated on the upper and lower surfaces of the ring member 3 as shown in FIG. Dynamic pressure is generated. For this reason, the boundary C1 between the first thrust bearing gap RS1 and the radial bearing gap RR, the boundary C2 between the first thrust bearing gap RS2 and the radial bearing gap RR, and the disc-shaped minute gap RV
In this case, a negative pressure (atmospheric pressure or lower) is generated, and bubbles are easily generated. There is also a problem that these bubbles hinder the smooth flow of the lubricating oil. That is, if small bubbles collect, they become large bubbles. If the bubbles grow to a size that exceeds the gap of the minute gap, or otherwise close to it, the flow of lubricating oil will be hindered and will not function as a dynamic pressure bearing,
In some cases, an accident such as burn-in may occur.

Therefore, in the conventional fluid dynamic pressure bearing, various methods for solving the problem relating to the bubble have been developed or proposed. For example, if the method disclosed in Japanese Patent Application Laid-Open No. H10-339320 is applied to the conventional fluid dynamic pressure bearing shown in FIG. 6, an annular minute gap RV1 which is a lubricating oil reservoir is provided with a large space in the axial center. (First lubricating oil reservoir) and adjacent upper and lower portions are formed as relatively small spaces (second lubricating oil reservoir), whereby air bubbles are retained in the first lubricating oil reservoir. It is. However, this method cannot be applied to the fluid dynamic pressure bearing of FIG. 5 in which the annular minute gap RR becomes a radial bearing gap.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a ring member having thrust dynamic pressure grooves formed on the upper and lower surfaces and a radial dynamic pressure groove formed on the outer peripheral surface, respectively. A fluid dynamic pressure bearing having, as basic constituent members, a flanged shaft composed of a cylindrical member and a sleeve in which the flanged shaft is rotatably fitted;
In other words, in a fluid dynamic bearing in which one ring member is used as both a thrust dynamic bearing member and a radial dynamic bearing member, proper distribution and smooth flow of lubricating oil are performed to prevent accidents such as seizure. That is.

[0010]

In order to solve the above-mentioned problems, a thrust dynamic pressure groove is formed on an upper surface and a lower surface thereof, and a radial dynamic pressure groove is formed on an outer peripheral surface of the ring member. In a fluid dynamic pressure bearing having a flanged shaft made of a cylindrical member and a sleeve on which the flanged shaft is rotatably fitted as a basic constituent member, the inner peripheral surface of the ring member or its vicinity, or Three or more pairs of longitudinal through holes for lubricating oil storage were formed at equal intervals in the circumferential direction on the outer peripheral surface of the cylindrical member that was in contact with the inner peripheral surface of the ring.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fluid dynamic pressure bearing according to an embodiment of the present invention has a flange including a ring member 3 and a cylindrical member 2 as shown in a longitudinal sectional view of FIG. It comprises a shaft 1, a sleeve 4 for receiving the flanged shaft 1, and an annular lid member 5 which also functions as a thrust holding member. A spiral thrust dynamic pressure groove G2 such as a herringbone groove shown in FIG. 8 is formed on the upper and lower surfaces of the ring member 3 by pressing or etching, and a herringbone groove shown in FIG. Is formed by rolling or the like. Further, disc-shaped minute gaps RS1 and RS2 formed between these bearing components, substantially disc-shaped minute gaps RV,
Lubricating oil is injected and filled into the annular minute gap RR and the plurality of pairs of vertical through holes Q by a vacuum injection method.

The disc-shaped minute gaps RS1 and RS2 function as a first thrust bearing gap and a second thrust bearing, respectively, and the annular minute gap RR functions as a radial bearing gap. The spacing between these bearing gaps depends on the size of the fluid dynamic pressure bearing, the number of revolutions, and the viscosity coefficient of the lubricating oil.
To several hundred μm. The interval between the annular minute gap RR functioning as a lubricating oil reservoir and the substantially disc-shaped minute gap RV is:
It is about several times the bearing clearance.

The plurality of pairs of vertical through holes Q function as lubricating oil reservoirs for supplying lubricating oil to both the thrust dynamic pressure bearing portion and the radial dynamic pressure bearing portion. The inner diameter of these vertical through-holes Q is several hundred μm to several mm, depending on the size of the fluid dynamic pressure bearing, the number of rotations, and the viscosity coefficient of the lubricating oil.

A plurality of pairs of vertical through holes Q are formed in the inner peripheral surface (including the vicinity of the inner peripheral surface) of the ring member 3 as shown in FIG.
As shown in (1), they are formed at equal intervals in the circumferential direction on the outer peripheral surface of the cylindrical member 2 which is in contact with the ring member 3. The vertical through hole Q is shown in FIG.
In FIG. 4, three to six vertical through holes Q are formed by a drill or the like.

The number of formed vertical through holes Q is determined in consideration of the capacity and flow of the lubricating oil reservoir, but the number of rotations must also be considered. That is, by providing the vertical through holes Q, the center of gravity of the flanged shaft 1 in the circumferential direction changes periodically according to the number of the vertical through holes Q. If this change coincides with a harmonic generated based on the rotational speed of the fluid dynamic bearing, the fluid dynamic bearing will cause undesirable vibration. In order to prevent this undesired vibration, the number of the vertical through holes Q is set to three or more.

In the fluid dynamic bearing of FIG. 1 configured as described above, the lubricating oil filled in the vertical through hole Q is pulled by the thrust dynamic pressure generated by rotation and the radial dynamic pressure, and moves in the direction of the arrow. Then, lubricating oil is supplied to the thrust bearing gap and the radial bearing gap. Similarly, the lubricating oil filled in the substantially disk-shaped bearing gap RV is also pulled by the thrust dynamic pressure and the radial dynamic pressure generated by the rotation and moves in the direction of the arrow, and the lubricating oil fills the thrust bearing gap and the radial bearing gap. Supply.

As described above, the lubricating oil filled in the plurality of pairs of the vertical through holes Q and the substantially disk-shaped bearing gaps RV provides the thrust bearing gaps RS1 and RS2 and the radial bearing gaps R during rotation.
Continue to supply the required amount of lubricating oil to R. Therefore, the boundary portion C1 between the first thrust bearing gap RS1 and the radial bearing gap RR where a negative pressure is easily generated, and the first thrust bearing gap RS
No negative pressure was generated because the lubricating oil was not interrupted even at the boundary C2 between the radial bearing clearance RR and the radial bearing gap RR. For this reason, no bubbles are generated in any of the minute gaps RS1, RS2, RR, RV and the vertical through hole Q.

Next, the spindle motor according to the present invention comprises:
The rotor is rotatably supported on the stator by the fluid dynamic bearing described above. That is, with reference to the longitudinal sectional view of one embodiment of FIG. 2, the spindle motor according to the present invention is cup-shaped by the fluid dynamic pressure bearing according to claim 1 which is erected on the motor substrate 9. The hub 6 is rotatably supported. More specifically, the cup-shaped hub 6 as the rotor component is coaxially fixed to the end of the columnar member 2. A rotor magnet 7, which is also a rotor component, is attached to the inner peripheral surface of the cup-shaped hub 6. The rotor magnet 7 is a multi-pole magnetized annular permanent magnet. A stator coil 8, which is a stator constituent member, is annularly mounted on the outer peripheral surface of the sleeve 4 of the fluid dynamic bearing, facing and close to the rotor magnet 7. The motor board 9 also forms a part of the stator component.

[0019]

The present invention relates to a fluid dynamic bearing in which one ring member is used for both a thrust dynamic pressure bearing member and a radial dynamic pressure bearing member, wherein an inner peripheral surface of the ring member or an inner surface of the ring member is provided. 3 on the outer peripheral surface of the cylindrical member contacting the peripheral surface
More than one pair of longitudinal through holes for lubricating oil reservoirs are formed at equal intervals in the circumferential direction, so that the lubricating oil is properly distributed to the thrust dynamic pressure bearing and radial dynamic pressure bearing, and the minute gap including the bearing gap and the lubrication The fluid including the oil reservoir flows smoothly. Accordingly, the occurrence of air bubbles was prevented to prevent an accident such as seizure, and the fluid dynamic bearing was able to maintain smooth rotation and extend the life.

According to the present invention, a fluid dynamic bearing using one ring member as both a thrust dynamic pressure bearing member and a radial dynamic pressure bearing member, and a spindle motor employing the fluid dynamic pressure bearing as a bearing The size and thickness of the device could be reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of one embodiment of a fluid dynamic bearing according to the present invention, in which a minute gap is exaggerated.

FIG. 2 is a longitudinal sectional view of one embodiment of a spindle motor according to the present invention.

FIG. 3 is a cross-sectional view of a shaft 1 in which a vertical through hole is formed in a ring member 3;

FIG. 4 is a shaft 1 in which a vertical through hole is formed in a cylindrical member 2.
FIG.

FIG. 5 is a longitudinal sectional view of an example of a conventional fluid dynamic bearing in which a minute gap is exaggeratedly shown.

FIG. 6 is a longitudinal sectional view of another example of a conventional fluid dynamic bearing in which a minute gap is exaggeratedly shown.

FIG. 7 is a perspective view showing an example of a radial dynamic pressure groove.

FIG. 8 is a plan view showing an example of a thrust dynamic pressure groove.

FIG. 9 is a pressure distribution diagram showing a dynamic pressure distribution of a fluid dynamic bearing in which both a thrust dynamic pressure groove and a radial dynamic pressure groove are formed on a ring member.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Shaft with flange 2 Column member 3 Ring member 4 Sleeve 5 Annular lid member 6 Cup-shaped hub 7 Rotor magnet 8 Stator coil 9 Motor board G1 Radial dynamic pressure groove G2 Thrust dynamic pressure groove Q Vertical through hole RS1, RS2 As a thrust bearing gap Micro gaps that function RR Micro gaps that function as radial bearing gaps RV, RV1, RV2 Micro gaps that function as lubricating oil reservoirs S Tapered micro gaps (capillary seals)

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiromitsu Goto 1-8-8 Nakase, Mihama-ku, Chiba-shi, Chiba F-term (reference) in Seiko Instruments Inc. DD01 DD02 DD03 DD16 GG01 GG03 GG12 GG15 KK10

Claims (2)

[Claims] 1. A flanged shaft comprising: a ring member having thrust dynamic pressure grooves formed on its upper and lower surfaces and radial dynamic pressure grooves formed on its outer peripheral surface; and a cylindrical member press-fitted into the ring member. In a fluid dynamic pressure bearing configured with a sleeve on which a flanged shaft is rotatably fitted as a basic constituent member, an inner peripheral surface of the ring member or an outer peripheral surface of the cylindrical member contacting an inner peripheral surface of the ring member. A fluid dynamic bearing in which three or more pairs of longitudinal through holes for a lubricating oil reservoir are formed at equal intervals in a circumferential direction. 2. A spindle motor in which a rotor is rotatably supported on a stator by the fluid dynamic bearing of claim 1.