JP2001208069A - Spindle motor with liquid bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spindle motor with liquid bearing in which static electricity is hard to be charged in a carried disc, power consumption is low, and reliability for prolonged operation is high. SOLUTION: As a lubricating liquid for the spindle motor with liquid bearing comprising of a shaft 3 and a sleeve 2 relatively rotatable against the shaft through a radial liquid bearing R and a thrust liquid bearing S, such lubricating oil has been used to which at least 0.1 to 10 percent weight of antistat and 0.1 to 5 percent weight of oxidation inhibitor have been added. By controlling the amount of such additives as to give electroconductivity to the lubricating liquid and to prevent oxidization of the same, an increase of viscosity and a restraint of evaporation loss can be achieved with properties of electroconductivity and oxidation resistance being granted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid bearing spindle motor for office machines, information equipment, audio / video equipment, and more particularly to a fluid bearing spindle motor most suitable for mounting on a magnetic disk device, an optical disk device, or the like. .

[0002]

2. Description of the Related Art Conventionally, as a fluid bearing spindle motor for a magnetic disk drive, for example, a sleeve fixed type in which a shaft is rotatably inserted through a sleeve fixed to a base, a shaft rotating type, and a fluid bearing spindle motor fixed to a base. A shaft fixed type in which a sleeve is rotatably supported on an erect shaft and a sleeve rotating type is known. In the former, a hub on which a plurality of magnetic disks are mounted is integrally attached to a shaft which is a rotating member, whereas in the latter, it is integrally attached to an outer periphery of a sleeve which is a rotating member. .

In both types, a thrust fluid bearing and a radial fluid bearing are interposed between a fixed member fixed to the base and a rotating member on the other side thereof. The lubricating fluid is injected between the bearing gaps. Then, the rotating member is rotationally driven by a motor including a stator disposed on the fixed member side and a rotor magnet disposed on the rotating member side. When the rotating member rotates, dynamic pressure is generated in the lubricating fluid in the clearance between the bearings by the pumping action of the dynamic pressure generating grooves provided in the thrust fluid bearing and the radial fluid bearing, respectively. It is not in contact with the fixing member via the membrane and is supported in a floating state.

In this manner, data is read and written by the magnetic head while the magnetic disk mounted on the hub is rotated at a constant rotation speed by the fluid bearing spindle motor. As the lubricating fluid, a non-conductive synthetic hydrocarbon oil such as α-olefin oil conventionally used for oil-impregnated bearings has been used.

[0005]

However, during the rated rotation of the rotating member of the spindle motor, the rotating member of the spindle motor comes into non-contact with the fixed member due to the interposition of the fluid film of the non-conductive lubricating fluid. It is charged as it is. Therefore, in the case of a magnetic disk device that uses a floating magnetic head for recording and reproduction as a magnetic head and reads and writes data on a rotating magnetic disk, a small gap is formed between the floating magnetic head and the static electricity charged on the disk. It is found that the magnetic head is damaged by the discharge.

In the case of a high-speed rotating or portable magnetic disk drive, there is a demand for a spindle motor which consumes low power and has excellent reliability even when used for a long time.
Therefore, the present invention has been made in view of such unresolved problems and market requirements of the conventional technology, and it is difficult for a mounted disk to be charged with static electricity, and the power consumption is small and the reliability of long-term operation is reduced. It is an object of the present invention to provide a hydrodynamic bearing spindle motor with high performance.

[0007]

In order to achieve the above object, the present invention according to the first aspect provides a fluid bearing having a shaft and a sleeve which rotates relative to the shaft via a fluid bearing portion. In a spindle motor, at least 0.1 to 10% by weight of an antistatic agent and 0.1 to 5% by weight of an antioxidant
The fluid bearing portion is lubricated with the added lubricating fluid.

In the fluid bearing spindle motor of the present invention, the antistatic agent is added to the lubricating fluid such as oil in a regulated amount within the range of 0.1 to 10% by weight. cm or less, and increase in viscosity can be suppressed. If the amount of the antistatic agent is less than 0.1% by weight, the required conductivity cannot be secured, and the electrostatic charging of the disk cannot be prevented. On the other hand, if the addition amount exceeds 10% by weight, the viscosity of the lubricating fluid becomes too high, causing an increase in the torque of the spindle motor.

Further, by adding the antioxidant in an amount of 0.1 to 5% by weight, oxidation of the lubricating fluid can be prevented and evaporation can be suppressed. If the amount of the antioxidant is less than 0.1% by weight, the effect of suppressing the evaporation of the lubricating fluid is small. On the other hand, if the addition amount exceeds 5% by weight, the viscosity of the lubricating fluid increases,
This causes an increase in torque.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of an embodiment of a fluid bearing spindle motor for an HDD, which is of a shaft rotation type and a sleeve fixed type. First, the structure will be described. A sleeve 2 is fixed to a base 1. The sleeve 2
A shaft 3 is rotatably inserted into the shaft 3, and a hub 4 is integrally attached to an upper end of the shaft 3. A plurality of magnetic disks, not shown, are mounted on the outer peripheral surface of the shallow inverted cup-shaped hub 4 at intervals in the axial direction.

A shaft 3 extending downward through the sleeve 2
A disk-shaped thrust plate 6 is fixed to the lower end of the plate by means such as press-fitting, bonding, and screwing. On the other hand, a cover plate 7 is attached to the lower surface of the base 1 so as to face the thrust plate 6. Both upper and lower planes of the last plate 6 are formed as a thrust receiving surface 6s, and the lower surface of the sleeve 2 facing the upper surface thrust receiving surface 6s and the upper surface of the cover plate 7 facing the lower surface thrust receiving surface 6s are Thrust bearing surfaces 2s and 7s respectively
It has been. A thrust fluid bearing portion S is provided on at least one of the opposed thrust receiving surface and the thrust bearing surface, for example, with a herringbone-shaped or spiral-shaped groove for generating dynamic pressure (not shown). In the stopped state, the lower thrust receiving surface 6s and the thrust bearing surface 7
is in contact with s.

A pair of radial receiving surfaces 3r are formed vertically on the outer peripheral surface of the shaft 3 with an interval in the axial direction, and a radial bearing surface 2r facing the radial receiving surface 3r is formed on the inner peripheral surface of the sleeve 2. Radial receiving surface 3r
The radial fluid bearing portion R is provided with at least one of the radial bearing surface 2r and a groove m for generating a dynamic pressure in a herringbone shape, for example.

The shaft 3 and the hub 4 are integrally formed by a motor M composed of a stator 9 fixed to the outer periphery of the base 1 and a rotor magnet 10 fixed to the inner diameter surface of the hub 4 as a rotating body. Is driven to rotate. A predetermined amount of lubricating fluid is injected into the radial fluid bearing portion R and the thrust fluid bearing portion S in advance. The lubricating fluid is obtained by adding at least 0.1 to 10% by weight of an antistatic agent and 0.1 to 5% by weight of an antioxidant to lubricating oil.

As lubricating oils, for example, DOA, DOD
Including diesters such as N, DOS, DOZ, and DIDA, TMP (trimethylol / propane ester), PMP
Examples thereof include ET (pentaurethritol ester), aromatic ester, complex ester, and carbonate ester. These may be used alone or in combination of two or more to obtain a desired viscosity. In addition,
When a carbonate ester is blended and used, the boundary lubrication of the bearing surface is improved, and the start / stop durability is improved.

[0015] The kinematic viscosity of the oil used is 4 in order to reduce the bearing torque at low temperatures and to secure the rigidity at high temperatures.
The kinematic viscosity at 0 ° C. is desirably 20 × 10 ⁻⁶ m ² / s (20 cSt) or less. If the kinematic viscosity is higher than this, the bearing torque increases as the number of rotations of the spindle motor increases, and accordingly, the diameter of the shaft 3 constituting the fluid bearing portion must be reduced (for example, less than 2 mm). 2) Therefore, the strength and rigidity required for a fluid bearing cannot be secured.

Examples of the antistatic agent include glycerin fatty acid ester, polyoxyethylene alkylphenyl ether, polyoxyethylene alkylamine fatty acid amide,
Those selected from alkyl phosphates, alkyl ammonium salts, alkyl benzyl ammonium salts, betaine imidazolinium betain acetate, stearic acid amide, aromatic phosphate, aliphatic phosphate and the like are desirable.

In the present invention, an antistatic agent selected from these is added to the above lubricating oil in a range of 0.1 to 10% by weight. By restricting the amount of addition to such a range, the volume resistivity of the lubricating fluid can be reduced to 3000 MΩ · cm or less, and the conductivity can be ensured, and the viscosity can be prevented from becoming too high. As the antioxidant, an amine antioxidant, a phenolic antioxidant, and the like are desirable. The antioxidant selected from these is added to the lubricating oil in 0.1%.
Addition within the range of 5% by weight can suppress oxidation of the lubricating fluid and reduce evaporation loss when left at high temperature.

Since the antistatic agent and the antioxidant used here have high viscosities, if they are added in large amounts, the viscosity of the lubricating fluid will increase and the bearing torque will increase. Therefore, in order to keep the viscosity of the lubricating fluid low, it is necessary to limit the upper limit of the amount to be added. Therefore, in the present invention, the additive amount of these additives is 10% by weight or less, preferably 5% by weight or less for an antistatic agent, and 5% by weight or less, preferably 3% by weight or less for an antioxidant. .

If the extreme pressure additive is further added to the above lubricating oil in an amount of 0.1 to 3% by weight or less in order to improve the boundary lubricating property, the start / stop durability of the hydrodynamic bearing is reduced. It is preferable because it improves. Next, the operation will be described. In the hydrodynamic spindle motor shown in FIG.
Then, the shaft 3 and the hub 4 can be integrally rotated by energizing through a motor drive control circuit (not shown). Then, a dynamic pressure is generated in the lubricating fluid filled in each of the bearing clearances of the thrust fluid bearing portion S and the radial fluid bearing portion R by a pumping action of a dynamic pressure generating groove, and the shaft 3 and the hub 4 are sleeved. 2 and cover plate 7
And rotate while being supported in a floating state. Thus, while the magnetic disk mounted on the hub 4 is rotated at a constant rotation speed, data can be read and written by the magnetic head.

When a floating magnetic head for recording and reproduction is used as the magnetic head, static electricity generated on the magnetic disk during the rated rotation of the spindle motor shown in FIG. 1 is restricted to a volume resistivity of 3000 MΩ · cm or less. It has been found that static elimination is performed through the conductive lubricating fluid of the part. Therefore, when a lubricating fluid having a volume resistivity of 3000 MΩ · cm or less is used, the static electricity is discharged via the conductive lubricating fluid held in the bearing gap of the fluid bearing portion. Not at all.

In addition, even in the case of high-speed rotation, since the viscosity of the lubricating fluid is kept low, the bearing torque is small, so that the operation can be performed with low power consumption. Moreover, lubricating fluids include
An antioxidant is added by regulating the addition amount so as not to increase the viscosity, so that the oxidation of the lubricating fluid is suppressed and the deterioration is prevented, and the evaporation loss when left at high temperature is small, so Even if used, the reliability of the spindle motor is maintained.

FIGS. 2 and 3 show the effect of adding an antistatic agent and an antioxidant whose addition amount is regulated to the lubricating fluid for lubricating the fluid bearing portion in the fluid bearing spindle motor of the present invention. It shows the result of the experiment performed for this purpose. FIG. 2 shows the relationship between the added amount of the antistatic agent and the specific volume resistance of the lubricating fluid, and FIG. 3 shows the relationship between the added amount of the antioxidant and the evaporation loss of the lubricating fluid. A diester oil was used as the lubricating oil, and the antistatic agent A and the antistatic agent B selected from those exemplified above were compared and studied. The antioxidant was obtained by adding 2% by weight of the antioxidant selected from those exemplified above to the diester oil and the diester oil only when left at a high temperature of 120 ° C. for a long time. The evaporation loss of was compared and studied.

FIG. 2 shows that the addition of 0.1 to 10% by weight of the antistatic agent makes the volume resistivity of the lubricating fluid 300
It can be seen that it can be suppressed to 0 MΩ · cm or less. Also, from FIG. 3, it is apparent from FIG. 3 that when 2% by weight of the antioxidant is added, the evaporation loss hardly increases even when left at a high temperature for more than 120 hours, whereas in the case where no antioxidant is added, the evaporation loss rapidly increases after 80 hours. It can be seen that it increases.

In the above embodiment, the description has been given of the case of the hydrodynamic bearing spindle motor of the shaft rotation, sleeve fixed type. However, the present invention is not limited to this, and the present invention is applied to a hydrodynamic bearing spindle motor of the sleeve rotation, shaft fixed type. Is similarly applicable.

[0025]

As described above, according to the first aspect of the present invention, since the lubricating fluid in which the antistatic agent and the antioxidant are added with their addition amounts being regulated is used, the load of the mounted object is reduced. It is possible to provide a fluid bearing spindle motor that can prevent electrification, has low torque and low power consumption, has little evaporation of lubricating fluid, and has high reliability for long-term operation.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of one embodiment of a hydrodynamic bearing spindle motor according to the present invention.

FIG. 2 is a diagram showing a relationship between an added amount of an antistatic agent in a lubricating fluid and a volume resistivity value.

FIG. 3 is a diagram showing the relationship between the presence or absence of an oxidizing agent in a lubricating fluid and the evaporation loss.

[Explanation of symbols]

 2 Sleeve 3 Shaft 4 Hub M Motor R Radial fluid bearing S Thrust fluid bearing

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C10N 30:10 C10N 30:10 40:02 40:02 40:18 40:18 (72) Inventor Denpo Kotsutsu 1-5-50 Kugenuma Shinmei, Fujisawa-shi, Kanagawa F-term (reference) in NSK Ltd. 3J011 JA02 KA04 MA22 4H104 BB05C BB33A BB34A BB34C BB36A BB37A BE02C BE07C BE11C BH03C CB14C CE19C LA05 A14 CC05 CC03 CC04 CC05 EB06 EB30 FF13 GG21 5H607 AA12 BB01 BB07 BB09 BB14 BB17 DD01 DD03 DD08 GG09 GG12 KK01 KK10

Claims (1)

[Claims] 1. A fluid bearing spindle motor comprising a shaft and a sleeve which rotates relative to the shaft via a fluid bearing portion, wherein at least 0.1 to 10% by weight of an antistatic agent and 0% by weight of an antioxidant. A fluid bearing spindle motor, wherein the fluid bearing portion is lubricated with a lubricating fluid added at 1 to 5% by weight.