JP2000063860A - Fluid bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fluid bearing having a low temperature dependency of a bearing torque and suppressed evaporation loss even after a long service by packing a monoester-based lubricating fluid into the gap of a fluid bearing. SOLUTION: The monoester oil based oil (M-816 or M-816+DOS) used as a base oil for a fluid bearing has a high viscosity index and a low viscosity, so that it can provide a low bearing torque over a wide temperature range and has reduced tendency toward spattering even when the fluid bearing is rotated at a high speed. It is desirable that the monoester is used in combination with other esters such as dioctyl sebacate(DOS) having a cloud point of 0 deg.C or below, for it has a limited service temperature range because of its lowered fluidity at a low temperature. The monoester based fluid shows low evaporation loss with the lapse of time and is excellent in totality as a lubricating fluid for the fluid bearing of a spindle motor.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art FIG. 3 shows an example of a conventional magnetic disk spindle motor. The motor includes a housing 100,
The sleeve 102, which is a supporting member, the rotating shaft 104, the hub 106, which is a rotating member, and the rotor / stator 108 are included, and the rotating member 106 is supported by the supporting member 102 via the radial fluid bearing 110 and the thrust fluid bearing 112. Further, in order to prevent the rotating shaft 104 and the hub 106 from falling off during the transportation of the motor, the sleeve 102 and the rotating member 106 have retaining portions 114 and 1 respectively.
16 are formed. The radial fluid bearing portion 110a and the thrust fluid bearing portion 112a are filled with a lubricating fluid 120 so as to generate a sufficient dynamic pressure on the rotary shaft 104 when the rotary shaft 104 rotates.

The fluid bearing is required to have a property of suppressing a change in power consumption of the spindle motor over a wide operating temperature range from a low temperature to a high temperature, that is, a temperature dependency of the bearing torque is small. Therefore, the lubricating fluid is required to have a low viscosity and a small change in viscosity in the operating temperature range. Further, in recent magnetic disk devices and the like, along with the increase in recording density, high followability and high speed of rotation are required.

In recent years, as a lubricating fluid used in the fluid bearing to satisfy the above requirements, for example, a lubricating fluid using a fluorocarbon oil or other fluorine oil as a base oil,
Alternatively, for example, studies have been conducted on a lubricating fluid using a synthetic hydrocarbon oil such as an olefin polymerized oil as a base oil.

[0005]

As described above, the fluid bearing for the spindle motor is required to have a small temperature dependency in the bearing torque, but at the same time, the fluid bearing generated by the centrifugal force applied to the fluid bearing at the time of high speed rotation is It is also required to reduce or prevent the scattering of the lubricating fluid, and to reduce the evaporation loss of the lubricating fluid itself from the fluid bearing in order to obtain excellent durability for a long time.

On the other hand, for example, fluorine oil used as a lubricating fluid has a small temperature dependence of its viscosity, but has a relatively large evaporation loss, and its specific gravity is 1.8, which is usually used in spindle motors and the like. It is about twice as much as the lubricating fluid used, and has a problem that the lubricating fluid is likely to be scattered at high speed rotation. In addition, synthetic hydrocarbon oils can easily reduce the evaporation loss and have a specific gravity as small as about 0.82, so it is relatively easy to reduce or prevent the scattering, but the viscosity is temperature-dependent. Therefore, it is difficult to obtain a stable bearing torque in the entire operating temperature range.

The present invention has the following required characteristics.
The above-mentioned spindle is intended to provide a fluid bearing in which there is little change in bearing torque even when ambient temperature changes, scattering of lubricating fluid is small even at high speed rotation, and evaporation loss of lubricating fluid is small during long-term use. A fluid bearing suitable for a motor and a combination of lubricating fluids used therein are provided.

[0008]

In order to solve the above problems, in a fluid bearing according to the present invention, a bearing surface provided on a fixed member and a bearing surface provided on a rotating member face each other with a bearing gap therebetween. However, it is a hydrodynamic bearing in which a groove for dynamic pressure generation is provided on at least one of the bearing surfaces, and a lubricating fluid exists in the bearing gap, and the base oil in the lubricating fluid is composed mainly of monoester. It is characterized by doing.

Further, in order to achieve the above object, the base oil in the lubricating fluid is based on the main component monoester.
An ester different from the monoester and having a cloud point of less than 0 ° C. may be mixed at a mixing ratio of 50 wt% or less.

[0010]

In the fluid bearing according to the present invention, monoester oil is used as the base oil. The monoester oil has a large viscosity index, and therefore the temperature dependence of the viscosity is small. Furthermore,
The viscosity itself shows a small value, and when used as a lubricating fluid in a fluid bearing, a low bearing torque can be stably obtained in a wide operating temperature range. Also, the specific gravity of monoester oil is about 0.9, which is smaller than that of fluoro oil,
It is also possible to reduce the scattering of the lubricating fluid when the fluid bearing rotates at a high speed.

On the other hand, the monoester oil has the property that it becomes cloudy due to white turbidity at a low temperature, and at the same time, the fluidity is lowered, and the use temperature range on the low temperature side is limited. For example, in the monoester oil according to the embodiment of the present invention, when the above-mentioned clouding temperature generally called a cloud point exists between 0 ° C. and + 5 ° C., use on the low temperature side required in the magnetic disk device. It may be difficult to use the fluid bearing in the temperature range of 5 ° C.

To solve the above problems, as a method of enabling the use of the fluid bearing at a lower temperature side, other esters having a cloud point of 0 ° C. or lower with respect to monoester oil, such as dioctyl sebacate ( Dioctyi Sebacate: Below D
OS. ) Is preferably mixed. However, D
The viscosity of OS is larger than that of monoester oil, and excessive mixing of DOS causes an increase in viscosity of the lubricating fluid itself, that is, an increase in bearing torque. Therefore, it is preferable that the mixing amount be 50% or less.

[0013]

Examples Regarding the lubricating fluid used for the fluid bearing according to the present invention, various characteristics of the lubricating fluid using the fluorine oil as the base oil and the lubricating fluid using the synthetic hydrocarbon oil as the base oil described in the prior art The evaluation result of will be described.

In the following characteristic evaluation, MB-816 (one of trade names in the Unistark M series manufactured by NOF CORPORATION) was used as a monoester oil, and a lubricating oil containing fluorine oil was used as a base oil. Oil is described as lubricating fluid A, and lubricating oil using synthetic hydrocarbon oil as base oil is described as lubricating fluid B. Furthermore, DOS for MB-816
At the same time, the evaluation of the lubricating fluid containing 20 wt% was also performed.

FIG. 1 shows the evaluation results of the torque test for the above-mentioned four types of lubricating fluids. In the torque evaluation, the spindle motor shown in FIG. 3 described in the prior art was used to evaluate the temperature dependence of the bearing torque of each lubricating fluid during use. As shown in the figure, the bearing torque in each lubricating fluid decreases as the operating temperature rises, but both the bearing torque and the temperature dependence of the bearing torque are MB-816, MB-816 plus DOS, Lubricating fluid A and lubricating fluid B increase in this order, especially 5 ° C to 3
At 0 ° C., the lubricating fluid B shows a very large bearing torque with respect to other lubricating fluids.

MB-816 and MB-816 to which DOS is added show bearing torques smaller than those of the other lubricating fluids A and B by about 1 to 2 gf.cm in all temperature ranges evaluated further. . As described above, it is possible to reduce the bearing torque by using the monoester oil as the base oil for the lubricating fluid.

FIG. 2 shows the evaluation results regarding the evaporation loss in the above-mentioned four types of lubricating fluids. For each lubricating fluid,
The evaporation loss tends to increase with the passage of time, and the evaporation loss increases in the order of lubricating fluid B, MB-816 plus DOS, MB-816, and lubricating fluid A. It shows a tendency of weight loss due to evaporation about twice as much as the lubricating fluid. MB-816 plus DOS and MB-816 show slightly higher evaporation loss for lubricating fluid B.

As described above, from the evaluation results of the bearing torque and the evaporation loss in the operating temperature range, MB
-816 and MB-816 to which DOS is added is a lubricating fluid using a fluorine oil represented by a lubricating fluid A as a base oil and a lubricating fluid using a synthetic hydrocarbon oil represented by a lubricating fluid B as a base oil. It is clear that they are comprehensively superior to both fluids as lubricating fluids used in spindle motor fluid bearings.

In addition, in the characteristic evaluation of the lubricating oil according to this example, the case where DOS was used as the ester for addition having a cloud point of 0 ° C. or lower was shown, but dioctyl adipate was used as the ester for addition. (Dioctyl Adipate: DO below
It has been confirmed that similar results are obtained when A) or a hindered polyol ester is used. That is, in an actual fluid bearing, DOS, depending on the characteristics required as the fluid bearing, for example, the allowable bearing torque, the temperature dependence of the bearing torque, the evaporation loss, and the like.
It is preferable to appropriately select the addition ester from among the esters having a cloud point of 0 ° C. or lower, such as DOA or hindered polyol ester.

Further, the ester used for these additions, in the range that does not increase the bearing torque of the fluid bearing,
It is preferable to appropriately change the addition amount according to the characteristics of the monoester oil used as the base oil. Furthermore, the ester used for these additions is not limited to the addition of a single ester such as DOS described above, and a plurality of esters may be combined.

In actual use, the monoester oil may be hydrolyzed by water supplied from the air or the like. Since the carboxylic acid generated by the decomposition of perhydrogen has a high possibility of corroding metals, it is preferable to add an antioxidant or an acid catcher to the monoester oil used as the lubricating fluid. Furthermore, the lubricating fluid may be made conductive by adding a conductive substance to the ester oil.

[0022]

According to the present invention, even if the ambient temperature changes, the bearing torque changes little, the scattering of the lubricating fluid is small even at high speed rotation, and the evaporation loss of the lubricating fluid is small during long-term use. It is possible to provide a fluid bearing suitable for a spindle motor and a combination of lubricating fluids used therein.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a relationship between a service temperature of a lubricating fluid and a bearing torque.

FIG. 2 is an explanatory diagram regarding evaporation loss for each lubricating fluid.

FIG. 3 is a schematic vertical sectional view of a hydrodynamic bearing device.

[Explanation of symbols]

100: Housing 102: Sleeve 104: rotation axis 106: hub 108: rotor / stator 110: Radial fluid bearing 112: Thrust fluid bearing 114, 116: retaining members 120: Lubricating fluid

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F16C 33/10 F16C 33/10 Z // C10N 20:00 30:00 40:02 (72) Inventor Tanaka Katsuhiko 1-5-50 Shinmei Kugenuma, Fujisawa-shi, Kanagawa NSK Ltd. (72) Inventor Michiharu Nakano 1-5-50 Kumei, Kugenuma, Fujisawa-shi, Kanagawa F-Term (reference) 3J011 AA07 AA08 BA02 CA02 JA02 KA02 KA03 MA22 4H104 BB32A BB34A BC09A EA04A LA04 LA20 PA01 PA04

Claims (2)

[Claims] 1. A bearing surface provided on a fixed member and a bearing surface provided on a rotating member face each other with a bearing gap therebetween, and a groove for generating a dynamic pressure is provided on at least one of the bearing surfaces. A hydrodynamic bearing provided and in which a lubricating fluid exists in the bearing gap, wherein the base oil in the lubricating fluid contains a monoester as a main component. 2. The base oil in the lubricating fluid further comprises an ester which is different from the monoester and has a cloud point of less than 0.degree. The fluid bearing according to claim 1, wherein the fluid bearing is mixed at a mixing ratio.