JP2001289242A - Fluid bearing spindle motor - Google Patents

Abstract

(57) [Summary] [PROBLEMS] A low-cost hydrodynamic bearing spindle that has high ability to withstand moment loads such as swinging even in limited height dimensions, is strong against external impacts, and has excellent reliability. Provide a motor. A shaft (13) having a thrust plate (15) at one end, a sleeve (12) opposed to the shaft (13) via a bearing clearance of a radial fluid bearing (R), and a thrust plate (15).
A fluid bearing spindle motor provided with a sleeve 12 and a counter plate 16 which face each other through the bearing gap of the thrust fluid bearing S with the two flat surfaces 15s, 15s.
The thrust plate 15 has a thickness of 1.5 mm or less, grooves for generating dynamic pressure with a depth of 12 μm or less are provided on both flat surfaces 15 s and 15 s by coining, and is fixed to the shaft 13 by press-fitting. The configuration was adopted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information device,
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid bearing spindle motor for video equipment and office machines, and more particularly to a fluid bearing spindle motor most suitable for a magnetic disk drive (HDD), a fan motor, and the like used in a notebook computer or the like.

[0002]

2. Description of the Related Art As a conventional fluid bearing spindle motor of this type, for example, there is a spindle motor for HDD as shown in FIG. In this device, a sleeve 2 made of free-cutting brass is fixed to a cylindrical portion 1a erected on a base 1, and a shaft 3 made of stainless steel is rotatably inserted through the sleeve 2. An inverted cup-shaped hub 4 is integrally attached to the upper end of the shaft 3, and a hydrodynamic bearing is interposed between the shaft 3 and the sleeve 2.

That is, a disc-shaped thrust plate 5 made of stainless steel is fixed to the lower end of the shaft 3 by press-fitting, and both planes of the thrust plate 5 are thrust receiving surfaces 5s, 5s of the thrust fluid bearing S. ing. The lower end surface of the sleeve 2, which is one of the mating members, is opposed to the thrust receiving surface 5s on the upper surface side, and the lower end surface of the sleeve 2 is the thrust bearing surface 2s of the thrust fluid bearing S.

[0004] Below the thrust plate 5, a counter plate 6 made of free-cutting brass, which is the other counterpart member, is arranged and fixed to the base 1. The upper surface of the counter plate 6 faces the thrust receiving surface 5 s on the lower surface side of the thrust plate 5 and serves as a thrust bearing surface 6 s of the thrust fluid bearing S. Thrust receiving surface 5
and at least both thrust receiving surfaces 5s and 5s of the thrust bearing surfaces 2s and 6s are provided with herringbone or spiral grooves (not shown) for generating dynamic pressure formed by etching. The bearing S is configured.

[0005] Further, a pair of radial receiving surfaces 3r are formed on the outer peripheral surface of the shaft 3 at an interval vertically. Further, a radial bearing surface 2r is formed on the inner peripheral surface of the sleeve 2 so as to face the radial receiving surface 3r. Further, at least one of the radial receiving surface 3r and the radial bearing surface 2r is provided with, for example, a herringbone-shaped groove 7 for generating dynamic pressure, thereby forming a radial fluid bearing R.

A stator 8 is provided on the outer periphery of the cylindrical portion 1a.
The drive motor M is opposed to the rotor magnet 9 fixed below the inner peripheral surface of the hub 4 via a gap.
Are formed, and the shaft 3 and the hub 4 are integrally driven to rotate. When the shaft 3 rotates, a dynamic pressure is generated in the lubricant between the bearings of the fluid bearings S and R by the pumping action of the grooves for generating the dynamic pressure of the thrust fluid bearing S and the radial fluid bearing R. Is sleeve 2 and counter plate 6
Non-contact and supported.

[0007]

In recent HDDs for notebook computers, thin HDDs (having a height dimension of, for example, 9.
(Limited to 5 mm or less) as well as strength against external impact that may act during swinging during transportation or handling. In addition, it is also required to be low cost and excellent in durability.

Further, in order to increase the ability to withstand the moment load acting on the fluid bearing during the swing, it is necessary to design a large bearing span of a plurality of radial bearings, but the height dimension of the HDD is limited. Therefore, it is necessary to reduce the thickness of the thrust plate. However, in the case where the thrust plate is fixed to the shaft by press-fitting, it is necessary to provide a pull-out load that can withstand an external impact of 1000 G, while a stress greater than the yield stress of the material of the thrust plate is generated during press-fitting. Therefore, even if the thrust plate is made of stainless steel, the thickness must be 2 mm or more, and the bearing span cannot be designed large with this thickness. It was difficult to improve my ability to endure.

In addition, when a groove for generating a dynamic pressure is formed in a thrust plate, there is a problem that processing by etching is expensive. Therefore, the present invention solves the problems of the conventional hydrodynamic bearing spindle motor as described above, and has a high ability to withstand moment loads such as swinging even in a limited height dimension, and has a high resistance to external impact. It is an object of the present invention to provide a low cost hydrodynamic spindle motor that is strong (excellent in shock resistance) and excellent in reliability.

[0010]

In order to solve the above-mentioned problems, the present invention has the following arrangement. In other words, the fluid bearing spindle motor of the present invention has a shaft having a flange at one end, a sleeve facing the shaft via a radial fluid bearing clearance, and a sleeve facing both surfaces of the flange and an axial fluid bearing clearance. In the fluid bearing spindle motor provided with the mating member, the flange portion,
It is characterized in that grooves for dynamic pressure generation having a thickness of 1.5 mm or less and a depth of 12 μm or less are provided on the both planes by coining, and are fixed to the shaft by press fitting.

In the hydrodynamic bearing spindle motor of the present invention, since the thickness of the flange portion is 1.5 mm or less, the bearing span of the radial hydrodynamic bearing can be designed to be large even in a limited height dimension. High ability to withstand moment loads such as swinging. If the thickness of the flange portion exceeds 1.5 mm, the bearing span cannot be designed to be large, and the ability to withstand a moment load during swing or the like is not sufficient.

Further, the grooves for generating dynamic pressure provided on the both planes of the flange portion have a depth of 12 μm or less and are provided by coining as a plastic working method.
The variation in the depth of the groove is small. If an attempt is made to provide a groove having a depth exceeding 12 μm, the variation in the depth tends to increase. Furthermore, if the coining process is used, the grooves can be simultaneously formed on the two planes, so that mass production is excellent and the cost is low.

If the fixing portion between the shaft and the flange portion is reinforced by an adhesive means such as an adhesive, it is possible to apply a detachment load that can withstand a strong external impact.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a fluid bearing spindle motor according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing one embodiment of a fluid bearing spindle motor of the present invention, and FIG. 2 is an enlarged sectional view of a fixed portion between a shaft 13 and a thrust plate 15 of the fluid bearing spindle motor of FIG. .

A cylindrical sleeve 11 with a flange is provided inside a cylindrical portion 11a erected at the center of the base 11.
Are interpolated and are integrally fixed by the flange. The sleeve 12 can be made of a copper alloy such as free-cutting brass, a lead bronze casting, phosphor bronze, or aluminum bronze. A shaft 13 is inserted through the sleeve 12, and the shaft 13 has a concave portion on the upper surface, and a female screw 13f is formed on an inner peripheral surface of the concave portion. The recess and the female screw 13f may not be provided. The material of the shaft 13 is not particularly limited as long as it is a material having high hardness and excellent corrosion resistance. For example, a martensitic stainless steel or an austenitic stainless steel is subjected to a heat treatment to harden the surface. What was done, or plating or D
One obtained by performing a surface treatment with an LC (diamond-like carbon) film and hardening the surface.

The upper end 13a of the shaft 13 has a diameter smaller than that of the other portion, and the small-diameter upper end 13a is press-fitted into a hole provided at the center of a shallow inverted cup-shaped hub 14 to thereby form the shaft 13a. And the hub 14 are integrally fixed. Since the lower surface of the hub 14 is in contact with the upper end surface 13b of the large-diameter other portion formed at the boundary between the small-diameter upper end portion 13a and the large-diameter other portion, the shaft 13 and the hub 14 have sufficient resistance. Secured with sufficient strength to ensure impact.

A disk-shaped thrust plate 15 (having a thickness of 15 mm or less) made of copper alloy, stainless steel, or the like is fixed to the lower end of the shaft 13 projecting from the lower end of the sleeve 12. That is, the lower end portion 13c of the shaft 13 has a smaller diameter than the other portion similarly to the upper end portion 13a, and the lower end portion 13c having the small diameter is press-fitted into a hole 15a provided in the central portion of the thrust plate 15, thereby obtaining the shaft. 13 and the thrust plate 15 are integrally fixed (see FIG. 2). In addition, the thrust plate 15 corresponds to a flange portion which is a constituent element of the present invention.

In addition to the upper surface of the thrust plate 15 being in contact with the lower end surface 13d of the large-diameter other portion formed at the boundary between the small-diameter lower end portion 13c and the large-diameter other portion,
Since an adhesive 30 (not shown in FIG. 1) is interposed at this joint portion, the shaft 13 and the thrust plate 15 are fixed to each other with strength (peeling load) sufficient to secure sufficient impact resistance. Is done.

The thickness of the thrust plate 15 is 1.
If it is less than 5 mm, it is difficult to keep the end face runout of the thrust plate 15 required for bearing performance to within 3 μm by simply press-fitting the thrust plate 15 into the shaft 13, but as described above, the thrust is applied to the lower end face 13 d. Plate 15
The upper surface of the thrust plate 15
Can be within 3 μm.

Such shaft 13 and thrust plate 15
The structure of the joint portion with will be described in more detail with reference to FIG. The small-diameter lower end portion 13c of the shaft 13 has a tip (lower end) having a smaller diameter in two steps. That is, the lower end portion 13c is divided into three stages, and has a gradually decreasing diameter in a downward direction. Hereinafter, each step of the lower end portion 13c divided into three steps will be referred to as a step 13 from the upper side.
e, step 13f, and step 13g.

The lower end 13c of the shaft 13 is press-fitted into a hole 15a provided at the center of the thrust plate 15, but as shown in FIG. 2, only the largest diameter step 13e of the lower end 13c is provided. It is in a press fit form. In addition,
The height of the step 13 e is about half the thickness of the thrust plate 15. A portion of the inner peripheral surface of the hole 15a of the thrust plate 15 that is not in contact with the step 13e (ie, a portion facing the step 13f and the step 13g) is provided with an epoxy adhesive 30. It is bonded to the lower end 13c to reinforce the fixation between the shaft 13 and the thrust plate 15. That is, the adhesive 30 is interposed in a gap formed between the outer peripheral surface of the step portion 13f and the inner peripheral surface of the hole 15a of the thrust plate 15, and the shaft 13 and the thrust plate 15
And are glued. The gap formed between the outer peripheral surface of the step 13g and the inner peripheral surface of the hole 15a is
Is flowing into the adhesive pool. The type of the adhesive is not particularly limited, but an epoxy-based adhesive is preferable from the viewpoint of high adhesive strength and oil resistance.

As described above, in the hydrodynamic spindle motor of this embodiment, the thickness of the thrust plate 15 is 1.5 mm.
Because of the following, the bearing span between the radial fluid bearings R, R can be designed to be large even though the height of the device is limited, so that the ability to withstand a moment load during rocking or the like is high. However, if the thickness of the thrust plate 15 is 2.0 mm or less, the thrust plate 15 may not be able to secure a withdrawal load that satisfies impact resistance only by press-fitting the thrust plate 15 into the shaft 13. That is, even if the interference is increased beyond the yield stress of the material of the thrust plate 15 (stainless steel, copper alloy, or the like), the release load cannot be increased only by press-fitting.

If the interference between the thrust plate 15 and the shaft 13 exceeds 10 μm, the thrust plate 15
May be deformed at the time of press-fitting.
This deformation is caused by the fact that the central portion of the thrust plate 15 (the portion provided with the hole 15a for press-fitting the shaft 13) is approximately 3 μm
Therefore, both flat surfaces (receiving surfaces 15s, 15s of the thrust fluid bearing S described later) are curved.

Therefore, in the present embodiment, the lower end 13c (see FIG. 2) of the above structure is press-fitted into the hole 15a of the thrust plate 15 with a margin of 10 μm or less, and the joint is bonded with an adhesive 30. Thus, the required pull-out load was secured without causing the above-mentioned problems. The interference is 10 μm
As described below, the deformation of the thrust plate 15
μm or less.

The lower surface of the thrust plate 15 is opposed to the upper surface of the counter plate 16 attached to the base 11, and the opposing surfaces are in contact with each other when stopped. In addition,
The counter plate 16 can be made of a copper alloy such as free-cutting brass, a lead bronze casting, phosphor bronze, or aluminum bronze. Both upper and lower planes of the thrust plate 15 are formed as thrust receiving surfaces 15s. Then, the thrust receiving surface 15 on the upper surface side
The upper surface of the counter plate 16, which is the mating member facing the lower end surface of the sleeve 12 and the lower surface side thrust receiving surface 15s, is the thrust bearing surfaces 12s and 16s, respectively, and the thrust receiving surface 15s is formed. ,
For example, a thrust fluid bearing S, which is an axial fluid bearing, is provided at 15s with a herringbone-shaped groove (not shown) for generating dynamic pressure.

The grooves for generating dynamic pressure on both planes (thrust receiving surfaces 15s, 15s) of the thrust plate 15 are provided by coining as plastic working.
The coining process is a method of engraving the groove by pressing a mold against the thrust plate 15 using a press or the like, and therefore is superior in mass productivity and lower in cost as compared with the etching process.

In the case where grooves for generating a dynamic pressure having a depth of, for example, 12 μm are formed on both planes of the thrust plate 15 by such coining processing, when the thickness of the thrust plate 15 exceeds 2.0 mm, the mold is not used. The grooves cannot be provided unless the pressing load is increased to increase the upsetting amount. If the upsetting amount is large, the variation in the depth of the groove tends to be large, and the variation may exceed 4 μm. However, the thickness of the thrust plate 15 is 1.5 mm
If it is below, the upsetting amount may be small, so that the variation in the depth of the groove can be suppressed to 4 μm or less. further,
When the thickness of the thrust plate 15 is set to 1 mm or less, the upsetting amount can be further reduced, so that the variation in the depth of the groove can be suppressed to 3 μm or less, which is more preferable. In terms of the performance of the hydrodynamic bearing, at least the variation in the depth of the groove is 4 μm.
m, the thickness of the thrust plate 15 is preferably 1.5 mm or less.

On the other hand, a pair of upper and lower radial receiving surfaces 13r are formed on the outer peripheral surface of the shaft 13 at an interval in the axial direction, and a radial bearing surface 12r facing the radial receiving surface 13r is The radial fluid bearing R is formed on the inner peripheral surface, and is provided with, for example, a U-shaped herringbone-shaped groove 17 for generating dynamic pressure on the radial bearing surface 12r. If the groove 17 for generating dynamic pressure of the radial fluid bearing R is formed into an inward asymmetric groove pattern in which the groove length is slightly shorter on the inner side than on the outer side, the lubricant in the bearing gap is exposed to the outside during rotation. Outflow phenomenon can be prevented.

Groove processing on the inner peripheral surface of the sleeve 12 is as follows.
This is because the grooves are formed by plastic working such as ball rolling which is excellent in mass productivity. Ball rolling is a method in which a rolling jig in which a plurality of steel balls are held in a hollow outer cylinder fitted to the outer periphery of a shaft is pressed into a sleeve. That is, after the sleeve is cut on a lathe, the rolling jig is pressed into the sleeve while slowly rotating the main spindle of the lathe forward and backward to form a herringbone-shaped groove on the inner peripheral surface. After that, finish machining such as finish cutting or ball threading for removing a raised portion around the groove is performed as necessary. Of course, instead of using a lathe, the rolling jig may be pressed into a fixed sleeve while rotating the rolling jig forward and backward in the left and right directions to form a herringbone groove.

The groove 17 for generating dynamic pressure may be provided on the radial receiving surface 13r, or may be provided on both the radial bearing surface 12r and the radial receiving surface 13r. In order to reduce the torque of the spindle motor, the inner peripheral surface of the sleeve 12 (or the outer peripheral surface of the shaft 13 or the inner peripheral surface of the sleeve 12 and the outer peripheral surface of the shaft 13) is sandwiched between the upper and lower radial fluid bearings R, R. And a clearance groove 21 formed of a tapered peripheral groove having a narrower clearance toward the bearing clearance of the radial fluid bearing R.

Further, the outer peripheral surface of the sleeve 12 and the cylindrical portion 1
An annular gap is interposed between the inner peripheral surface 1a and the inner peripheral surface, and the gap forms a lubricant reservoir 22. Above the lubricant reservoir 22, an air vent hole 23 communicating with the outside air is opened. The air vent hole 23 extends vertically from the top of the lubricant reservoir 22 and opens at the upper end surface of the sleeve 12. Of course, the air vent hole 23 may be provided so as to form an axial slit on the surface of the cylindrical portion 11a that fits with the sleeve 12.

The inner peripheral surface of the cylindrical portion 11a forming the inner surface of the lubricant reservoir 22 is formed as a tapered surface 24 having a narrower gap toward the lower thrust fluid bearing S.
The tapered surface 24 may be tapered to the position where the counter plate 16 is located. However, the tapered surface 24 is not always formed on the inner peripheral surface of the cylindrical portion 11a, and may be formed on the outer peripheral surface of the sleeve 12, or both the outer peripheral surface of the sleeve 12 and the inner peripheral surface of the cylindrical portion 11a. May be formed.

A portion of the lower portion of the lubricant reservoir 22 which communicates with the fluid bearing in the vicinity thereof is provided with a lubricant supply passage 25 having a clearance substantially equal to or slightly larger than the bearing clearance.
Therefore, the lubricant is easily introduced into the bearing gap by capillary action based on the surface tension. The injection of the lubricant into the spindle motor is performed through a through hole 26 formed in the center of the counter plate 16 and having a through hole in the thickness direction after the entire assembly is assembled. The injected lubricant fills the bearing clearances of the thrust fluid bearing S and the radial fluid bearing R by the surface tension, and the excess lubricant is accumulated in the lubricant reservoir 22, and the tapered surface 24 has a capillary based on the surface tension. Maintained by the phenomenon. Therefore, even if the spindle motor is inverted during transportation or handling, the lubricant in the lubricant reservoir 22 does not flow out.

Further, since the size of the gap of the lubricant reservoir 22 becomes narrower toward the lower lubricant supply passage 25 due to the tapered surface 24, the lubricant scattered by the external impact does not flow out. Are naturally collected in the lubricant supply passage 25 having a narrow gap in the lubricant reservoir 22. After the lubricant is injected into the spindle motor, the ball 27 is pressed into the through hole 26 to seal the through hole 26. The ball 27 may be a cylindrical member or the like.

By assembling the spindle motor in this way, there is little air bubble remaining in the bearing clearance. In addition, in order to more reliably deaerate bubbles, the spindle motor may be put into a vacuum chamber and deaerated after the lubricant is injected as necessary. In order to prevent the ball 27 press-fitted from falling off due to an external impact and prevent oil from leaking from the clearance of the ball press-fitting portion, a sheet member or an adhesive seal member is adhered to the outside of the counter plate 16 after the ball 27 is press-fitted. (Not shown). However, since the through hole 26 does not necessarily need to be sealed in terms of the performance of the fluid bearing, it may be used for venting air after it is used as a lubricant inlet.

A stator 18 is fixed to the outer periphery of the cylindrical portion 11a of the base 11, and a driving motor M is formed facing the rotor magnet 19 fixed to the inner peripheral surface of the hub 14 via a gap. . When the drive motor M rotates the hub 14 and the shaft 13 on which a magnetic disk (not shown), which is a rotating body, is mounted on the outer periphery, integrally, the respective dynamic pressures of the thrust fluid bearing S and the radial fluid bearing R are generated. The dynamic pressure is generated in the lubricant filled in the bearing clearance of each fluid bearing S, R by the pumping action of the groove for
Is not in contact with the sleeve 12 and the counter plate 16 and is supported. Since the magnetic disk is screwed with a clamp member, the magnetic disk is fixed with sufficient strength to ensure sufficient impact resistance.

Even if there are bubbles remaining in the bearing gap due to the rotation, the bubbles are immediately discharged to the outside air via the air vent hole 23 opened in the lubricant reservoir 22. If the lubricant held in the bearing gap gradually evaporates or scatters and runs short over a long period of operation, the lubricant pool 2
The lubricant retained in the space 2 by capillary action based on the surface tension is sucked into the narrower gap while being guided by the tapered surface 24 according to the shortage, and supplied until the lubricant is filled in the bearing gap. Is done. That is, as the lubricant in the bearing gap decreases, the lubricant is sucked by the capillary action in the narrow bearing gap via the lubricant supply passage 25, and is stabilized at a position where the surface tension of the tapered surface 24 of the lubricant reservoir 22 is balanced. I do. Thus, the lubricant is automatically replenished by the reduced amount of the lubricant.

As described above, in the spindle motor of the present embodiment, since the gap of the lubricant reservoir 22 is tapered,
Lubricant is sucked into the narrower space by surface tension, while
The residual air bubbles entrained during assembly are separated and discharged to the larger gap. Accordingly, a lubricant having no bubbles is automatically and reliably supplied to each bearing gap, communicates with the lubricant reservoir 22, and is always filled with the lubricant. Excellent in nature.

The present embodiment is an example of the present invention, and the present invention is not limited to the present embodiment. For example, the structure of the fluid bearing, the structure of the air vent hole 23 and the structure of the through hole 26, the presence or absence, the groove pattern for generating the dynamic pressure, the detailed structure of the spindle motor, and the like are not limited to the present embodiment. It can be changed as needed.

[0040]

As described above, the hydrodynamic bearing spindle motor of the present invention has a high ability to withstand a moment load such as swinging even with a limited height, and is strong against external impact (impact resistance). Excellent in reliability), and has excellent reliability and low cost.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a fluid bearing spindle motor of the present invention.

FIG. 2 is a partially enlarged sectional view of the hydrodynamic spindle motor of FIG. 1;

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

[Explanation of symbols]

 12 sleeve 13 shaft 15 thrust plate 16 counter plate R radial fluid bearing S thrust fluid bearing

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukio Higuchi 1-50-50 Kugenuma Shinmei, Fujisawa City, Kanagawa Prefecture Nippon Seiko Co., Ltd. (72) Inventor Nobuyuki Hagiwara 1-50-50 Kugenuma Shinmei, Fujisawa City, Kanagawa Prefecture F-term in NSK Ltd. (reference) 3J011 AA04 BA02 CA02 DA02 KA04 5H607 BB01 BB14 BB17 CC01 DD03 FF04 FF12 GG01 GG02 GG12 GG15 GG25 JJ06 KK10

Claims (1)

[Claims] 1. A shaft having a flange at one end, and a sleeve opposed to the shaft via a radial fluid bearing gap.
In a fluid dynamic bearing spindle motor including both flat surfaces of the flange portion and a mating member opposed via an axial fluid bearing gap, the flange portion has a thickness of 1.5 mm.
A hydrodynamic bearing spindle motor wherein a groove for generating a dynamic pressure having a depth of 12 μm or less is provided on each of the two planes by coining, and is fixed to the shaft by press-fitting.