JP2001124069A - Fluid bearing spindle motor - Google Patents

Abstract

(57) [Object] To provide a fluid bearing spindle motor which is free from fluctuation of a floating amount of a sleeve and seizure due to poor inflow of a lubricating fluid. In a fluid bearing spindle motor in which a shaft (2) and a sleeve (3) are driven to rotate relative to each other, an outer peripheral surface (4Ag) of a thrust plate (4A) and a sleeve inner peripheral surface (3) opposed thereto.
The gap (annular space) C between the thrust plate 4A and the inner surface of the thrust plate 4A is continuously narrowed from the axial center toward both end surfaces. The lubricating fluid in the annular space C collects in a narrow gap due to surface tension. On the other hand, the bubbles collect in the larger gap. That is, the smaller one of the annular gaps C forms the oil reservoir 10, and the larger one forms the air chamber 11. During high-speed rotation, centrifugal force acts and the lubricating fluid flows toward the oil reservoir 10. Thus, the lubricating fluid without bubbles is held in the oil reservoir 10 both at rest and during rotation, and is supplied smoothly to the bearing gap.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
In connection with the fluid bearing spindle motor for video equipment,
The present invention relates to a fluid bearing spindle motor that can supply a lubricating fluid smoothly to a rotating thrust fluid bearing to ensure stable floating.

[0002]

2. Description of the Related Art As a conventional hydrodynamic bearing spindle motor, for example, there is one for a hard disk drive (HDD) shown in FIG. The fluid bearing is a base 1
A shaft 2 of a fixed member and a sleeve 3 of a rotating member surrounding the shaft 2. The shaft 2 has a radial receiving surface 2r on an outer peripheral surface 2g, and a flange-like thrust plate 4 integrally fixed by bonding or press-fitting near an upper end portion thereof, and upper and lower end surfaces of the thrust plate 4 A thrust receiving surface 4 s is provided on the (plane), and a thrust fluid bearing S is formed between the thrust receiving surface 4 s and the sleeve 3. Also, between the radial receiving surface 2r on the outer periphery of the shaft and the sleeve 3,
A radial fluid bearing R is formed. Sleeve 3 is
The rotor 2 is rotatably levitated and supported by the shaft 2 via the thrust fluid bearing S and the radial fluid bearing R, and is rotationally driven integrally with the hub 8 by a motor M having a rotor 6 and a stator 7 opposed thereto. You.

[0003]

In the conventional hydrodynamic bearing spindle motor, when a lubricating fluid is injected into the thrust hydrodynamic bearing S and the radial hydrodynamic bearing R, the outer peripheral surface 4g of the thrust plate 4 and the mating sleeve 3 are connected to each other. In some cases, bubbles may be mixed into the annular space C between them. When the air bubbles are present in the vicinity of the bearing gap of the thrust fluid bearing S, the smooth flow of the lubricating fluid held in the annular space C into the bearing gap during rotation is impeded, and as a result, the floating amount of the sleeve 3 There was a risk of instability in operation due to fluctuations in the surface and seizure due to a sudden decrease in the flying height.

[0004] In the prior art, the lubricating fluid near both ends of the outer peripheral surface 4g of the thrust plate 4 is blown outward by centrifugal force when rotated at a high speed because the gap of the annular space C is wide. Inflow of the lubricating fluid into the bearing S is hindered, and as a result, there is a possibility that instability of the operation due to fluctuations in the floating amount of the sleeve 3 and seizure due to a sudden decrease in the floating amount may similarly occur.

Accordingly, the present invention has been made in view of such an unsolved problem of the prior art, and has a fluid bearing spindle which is free from fluctuations in the floating amount of the sleeve and seizure due to poor inflow of the lubricating fluid. It aims to provide a motor.

[0006]

In order to achieve the above object, the present invention according to claim 1 comprises a shaft having a radial receiving surface and a flange-like thrust plate on an outer peripheral surface, a sleeve surrounding the shaft, and A thrust fluid bearing is provided between at least one of both end faces of the thrust plate and the sleeve, and a radial fluid bearing is provided between the shaft and the sleeve, so that the shaft and the sleeve rotate relative to each other. In the driven fluid bearing spindle motor, a gap (annular space) between the outer peripheral surface of the thrust plate and the inner peripheral surface of the sleeve facing the thrust plate extends from near the axial center of the thrust plate to both end surfaces. It is characterized by being continuously narrowed.

[0007] Since the annular space between the outer peripheral surface of the thrust plate and the inner peripheral surface of the sleeve is configured as described above, the lubricating fluid in the annular space collects in the narrower space due to surface tension. On the other hand, the bubbles collect in the larger gap. In other words, the narrow one forms the oil reservoir, and the wide one forms the air chamber. In this way, the air bubbles mixed into the lubricating fluid are automatically separated and collected in the air chamber communicating with the outside air, and the lubricating fluid is always held near the both end surfaces of the outer peripheral surface of the thrust plate without air bubbles.

Further, since the outer peripheral surface of the thrust plate continuously increases in diameter toward both end surfaces, when a centrifugal force acts during high-speed rotation, the lubricating fluid is discharged toward both end surfaces. Therefore, the flow of the lubricating fluid into the oil reservoir portion is not hindered regardless of whether it is stationary or rotating, and the lubricating fluid is always kept in a state where bubbles are not mixed, and the thrust is kept constant. Supply of the lubricating fluid to the fluid bearing S is performed smoothly.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a hydrodynamic spindle motor according to the present invention. Since the overall configuration of the spindle motor is the same as that shown in FIG. 3, the same parts as those in the related art are denoted by the same reference numerals, and redundant description will be omitted.

First, the structure will be described. The thrust plate 4A of this embodiment is fixed to the outer peripheral surface 2g of the fixed shaft 2 by means such as press-fitting, shrink-fitting, bonding, and welding. Of course, the thrust plate 4A may be integrally formed with the shaft 2, but in that case, the processing cost is increased. The outer peripheral surface 4Ag of the thrust plate 4A has the smallest diameter at the central portion in the axial direction, and the diameter continuously increases from there toward the both end surfaces 4As. A lateral hole 4Aa for venting air is provided in the portion having the minimum diameter, and communicates with the vertical hole 4Ab on the inner surface of the thrust plate to be released to the outside air.

On the other hand, the sleeve 3 has a through hole 3 at its center.
a, and has cylindrical stepped recesses 3b and 3c communicating with the through hole 3a at the upper end. The shaft 2 is inserted into the through-hole 3a of the sleeve and stands upright on the base 1, and the thrust plate 4A is housed in the recess 3b. A donut plate-shaped cover plate 5 is fitted and fixed in the concave portion 3c at the upper end of the sleeve, and the lower surface of the cover plate 5 contacts the upper end surface of the thrust plate 4A in the stopped state, so that the sleeve 3 and the hub 8 are stopped. Is supported by the shaft 2. The upper end of the shaft 2 projects outside the cover plate 5.

Thus, the outer peripheral surface 4Ag of the thrust plate 4A is in contact with the cylindrical inner peripheral surface 3b of the recess 3b of the sleeve 3.
n and a gap C between the 4Ag and 3bn.
Exists. The clearance C has a maximum C at the center in the axial direction.
a _max, both end faces 4s, they become narrower continuously toward 4s, both end faces 4s, the minimum C _min at 4s portion. The minimum clearance C _min defines an oil reservoir 10 that serves as a lubricating fluid reservoir. Retention of the lubricating fluid in the oil reservoir 10 is to be done by the surface tension of the fluid, the minimum clearance C _min portion of the gap may have narrower, specifically preferably 0.3mm or less.

On the other hand, the maximum gap _Cmax defines an air chamber 11 in which bubbles collect, and the air vent holes 4Aa, 4Ab
It communicates with the outside air through. Note that only one air vent hole 4Aa, 4Ab communicating with the air chamber 11 may be provided.
Even if two or more are provided, they are functionally the same, and the processing cost is increased, which is disadvantageous. Thrust plate 4A
A thrust receiving surface 4s on the upper end surface of the cover plate 5 faces a thrust bearing surface 5s on the lower surface of the cover plate 5, and at least one of the corresponding thrust receiving surface 3s and thrust bearing surface 5s has a spiral or herringbone shape. It has a dynamic pressure generating groove. Further, a thrust receiving surface 4s at a lower end surface of the thrust plate 4A faces a thrust bearing surface 3s which is a plane of a concave portion 3b formed in the sleeve 3, and
At least one of the thrust receiving surface 4s and the thrust bearing surface 3s is provided with a spiral or herringbone dynamic pressure generating groove, but the thrust movement on the lower end surface side of the thrust plate 4A which is not always subjected to an axial load. The pressure generating groove may be omitted. Thus, the thrust fluid bearing portion S is configured.

On the other hand, the radial receiving surface 2 of the outer peripheral surface 2 g of the shaft 2
r is formed in a pair at the top and bottom with an interval in the axial direction, and a radial bearing surface 3r facing the radial receiving surface 2r is formed on the inner diameter surface of the sleeve 3, and the radial receiving surface 2r and the radial bearing surface facing each other are formed. 3r, a radial fluid bearing portion R is provided with a herringbone-shaped dynamic pressure generating groove m, for example. However, the radial fluid bearing R may be configured as a three-arc bearing without a radial dynamic pressure generating groove.

A large number of magnetic disks (not shown) are mounted on the outer peripheral surface of the hub 8 which is integrally fixed to the outer periphery of the sleeve 3 rotatably supported via the fluid bearing portion. The rotation is driven by a motor M including a stator 7 fixed to the outer periphery of the base 1 and a rotor magnet 6 fixed to the inner diameter surface of the hub 8. Although not shown, a control board for controlling a current flowing through the coil of the stator 7 is provided on the base 1.

Next, the operation will be described. Oil and oil are formed in an annular space C formed between the outer peripheral surface 4Ag of the thrust plate 4A and the inner peripheral surface 3bn of the sleeve 3 and continuously narrowing from near the center in the axial direction toward both end surfaces 4s, 4s. grease, when supplying lubricating fluid such as a magnetic fluid, by the action of the surface tension of the lubricating fluid collects in the oil reservoir 10 of the gap at both ends which is the minimum unit C _min of clearance. On the other hand, the bubbles gather toward the air chamber 11, which is the maximum portion _Cmax of the gap,
The air is released to the outside air through the air vent holes 4Aa and 4Ab.

When the coil of the stator 7 is energized and the hub 8 rotates together with the sleeve 3, the lubricating fluid present in the annular space C is supplied to the oil reservoirs 10 at the narrow ends by a centrifugal force. Sent out. Therefore, the lubricating fluid containing no air bubbles is always held near the bearing clearance of the thrust fluid bearing S. Then, the lubricating fluid flows from the oil reservoir 10 toward the center of the thrust plate 4A due to the pumping action of the groove for generating the dynamic pressure of the thrust fluid bearing S during rotation, so that the axial dynamic pressure is formed. At the same time, the dynamic pressure in the radial direction is generated in the radial bearing clearance between the radial receiving surface 9 and the radial bearing surface 10 by the pumping action of the groove for generating the dynamic pressure of the radial fluid bearing R. As a result, the sleeve 3 and the hub 8 float, and the shaft 2, the thrust plate 4A
Rotates while being supported in a non-contact manner.

Therefore, according to the present embodiment, even during high-speed rotation, the supply of the lubricating fluid to the bearing gap of the thrust fluid bearing S is smoothly performed without being hindered as in the conventional case, and thus, it is a conventional problem. In addition, fluctuations in the floating amount of the sleeve and seizure due to poor flow of the lubricating fluid can be prevented. FIG. 2 shows a second embodiment of the present invention.

In this case, the shape of the inner peripheral surface 3bn of the sleeve 3 facing the outer peripheral surface 4Ag of the thrust plate 4A is not cylindrical but has a minimum diameter near the axial center and is continuous toward both end surfaces. The first point is that
Is different from that of the embodiment. Moreover, the gap C between the opposing surfaces 4g and 3bn is maximum near the center in the axial direction, and is gradually reduced toward both ends.
The reason for forming the gap by changing the gap interval in this way is that when the gap between the outer peripheral surface 4Ag of the thrust plate 4A and the inner peripheral surface 3bn of the partner 3 is a parallel gap, the lubricating fluid is formed by the surface tension due to the surface tension. This is because there is no function of collecting air bubbles in a narrow side, so that bubbles mixed in the lubricating fluid cannot be separated and collected.

As a result of forming the shape of the gap C as described above, the lubricating fluid is delivered toward both end surfaces 4s, 4s of the thrust plate 4A whose diameter increases due to the centrifugal force acting during rotation, and the thrust fluid bearing S is held in the vicinity of the bearing gap without bubbles, so that even at higher speeds than in the first embodiment, the centrifugal force can be used effectively, and the lubricating fluid flows into the bearing gap. The inflow is not hindered.

The outer peripheral surface 4A of the thrust plate 4A
If the minimum diameter (the central portion in the axial direction) of the inner peripheral surface 3bn of the sleeve 3 opposed to g is designed to be slightly larger than the maximum diameter (both ends) of the outer peripheral surface of the thrust plate 4A, assembly becomes easy. Other configurations, operations, and effects are the same as those of the first embodiment. In each of the above embodiments, the case where the axial shape of the outer peripheral surface 4Ag of the thrust plate 4A is linearly changed is shown. The same applies to the axial shape of the inner peripheral surface 3bn of the sleeve 3 on the opposite side in the second embodiment.

Further, in each of the above embodiments, a circumferential groove is provided on the circumference near the axial center of the outer peripheral surface 4Ag of the thrust plate 4A to increase the space volume of the air chamber for collecting bubbles. You can also do so. In each of the above embodiments, the outer peripheral surface 4Ag of the thrust plate 4A is provided.
Near the center in the axial direction of the inner sleeve 3bn
In the above description, the gap C between them is constant without changing in the circumferential direction. However, also in this regard, the gap C
A circumferential groove having a shape that changes in the circumferential direction, for example, a bottom surface that is substantially elliptical when viewed from above or a polygonal shape such as a triangle or a square is provided, and a wide portion of the circumferential gap is used as an air chamber, and air bubbles are formed. The trapping function can be enhanced.

As for the herringbone groove pattern for generating dynamic pressure formed in the thrust fluid bearing S, a completely symmetric or slightly asymmetric groove pattern in which the flow in the bearing gap is balanced in the radial direction. preferable.
If the lubricating fluid flows in the opposite direction, that is, inward, the lubricating fluid held in the reservoir 10 portion of the annular space on the outer peripheral portion of the thrust plate 4A is not preferable because the lubricating fluid may gradually disappear over a long period of rotation.

In each of the above embodiments, one cover plate 5 is used.
The scattering of the lubricating fluid may be more reliably prevented. Further, the fluid bearing spindle motors of the above embodiments are all of the type having a fixed shaft, but the present invention is also applicable to a case of a rotating shaft type.

[0025]

As described above, according to the hydrodynamic bearing spindle motor of the present invention, in the thrust plate constituting the hydrodynamic bearing, lubrication is applied to the narrower gap between the outer peripheral surface and the sleeve as the mating member. The fluid is collected, and the bubbles are separated and collected in a wider portion of the gap, so that the lubricating fluid containing no bubbles is always smoothly supplied to the bearing gap of the rotating thrust fluid bearing portion. As a result, it is possible to prevent the seizure phenomenon caused by the fluctuation of the flying height or the sudden decrease of the flying height.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is a sectional view showing an outline of a conventional hydrodynamic bearing spindle motor.

[Explanation of symbols]

 2 Shaft 2g Shaft outer circumferential surface 3 Sleeve 3bn Sleeve inner circumferential surface 4 Thrust plate 4A Thrust plate 4s Thrust receiving surface 4Ag Thrust plate outer circumferential surface S Thrust fluid bearing R Radial fluid bearing C Clearance 10 Oil reservoir 11 Air chamber 4Aa Air vent hole 4Ab Air vent M motor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3J011 AA07 BA02 BA09 CA02 JA02 KA04 MA03 MA24 5H605 BB05 BB19 CC04 EB03 EB06 EB28 5H607 BB07 BB09 BB14 CC01 CC05 FF12 GG01 GG02 GG12 GG28

Claims (1)

[Claims] 1. A shaft having a radial receiving surface and a flange-shaped thrust plate on an outer peripheral surface, and a sleeve surrounding the shaft, and a thrust fluid is provided between at least one of both end surfaces of the thrust plate and the sleeve. A fluid bearing spindle motor comprising a bearing and a radial fluid bearing between the shaft and the sleeve, wherein the shaft and the sleeve are driven to rotate relative to each other, wherein an outer peripheral surface of the thrust plate and a sleeve facing the outer surface of the thrust plate; A fluid bearing spindle motor, wherein a gap between the peripheral surface and the peripheral surface is continuously narrowed from near the axial center of the thrust plate toward both end surfaces.