JPH08266007A - Motor with dynamic pressure bearing device - Google Patents

Abstract

PURPOSE: To obtain a dynamic pressure bearing device excellent in lubricating ability, sealing ability, and life reliability by causing the base oil solvent of lubricating fluid to contain a poly-α-olefin hydride(PAO) and polyol ester. CONSTITUTION: The inner circumferential surfaces of the radial sliding bearings 24, 24 of a stator set 2 face the peripheral surface of a rotational shaft 31 slidably through the medium of a specified bearing lubricant A, and have radial- direction pressure sliding surfaces. Besides, the tip parts of the rotational shaft 31 face thrust receiving plates 25 for covering the lower end side bearing holders 22 slidably through the medium of the bearing lubricating fluid A and have thrust-direction pressure sliding surfaces. Besides, the bearing lubricating fluid A is also used as magnetic fluid for sealing, and a lubricating fluid formation having a base oil solvent containing poly-α-olefin hydride and polyol eslter is used. As the result, it becomes possible to improve physical properties such as viscosity, evaporation, high-temperature gelling, etc., and to enhance the lubricating ability, sealing ability, and life reliability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic pressure bearing device for rotatably supporting a rotary member and a fixed member by a dynamic pressure of a bearing fluid, and a motor using the same.

[0002]

2. Description of the Related Art In recent years, a dynamic pressure bearing using a magnetic lubricating fluid has been proposed for various devices, particularly for devices such as a motor for driving various rotary plates such as a polygon mirror, a magnetic disk and an optical disk at high speed. . That is, a magnetic fluid is a colloidal solution in which ferromagnetic fine particles are stably dispersed in a liquid dispersion solvent, and because the liquid itself has apparently strong magnetism, it is usually used as a sealing in combination with a ball bearing. However, a dynamic pressure bearing using a magnetic lubricating fluid is considered to be promising because it is superior to the ball bearing in high-speed rotation stability and quietness. The proposal of a dynamic pressure bearing using a magnetic fluid has been made under such a background, for example, Japanese Patent Laid-Open No. 60-88223.
The publication discloses a device in which one fluid is used as both a lubricating fluid for generating a dynamic pressure and a magnetic fluid for magnetic sealing.

However, in such a device,
The magnetic fluid composition is required to have both a low evaporation property as a seal and a low viscosity property for reducing a bearing loss. Therefore, it is necessary to actually obtain a characteristic of the magnetic fluid composition that can be adapted to it. The current situation is that it is not possible. That is, the bearing portion receives a much larger shearing force than the seal portion and is exposed to a high temperature, and at the time of starting and stopping, the metals may come into contact with each other and wear to contact the active metal surface.
Although the magnetic fluid composition is used with the greatest advantage that "high airtightness can be obtained even at high speed (-10-6 Toor)", it functions as a lubricating fluid (low wear characteristics) and life characteristics (low wear characteristics). Those having both sufficient evaporating property and high temperature resistance) have not yet been developed (from PETROTECH Vol. 13, No. 12 (1989)). Thus, there is a demand for a lubricating fluid composition for a dynamic pressure bearing device that covers not only the sealability but also the lubricity and life characteristics.

[0004]

More specifically, the characteristics that the lubricating fluid composition should have in order to use both the lubricating fluid for generating dynamic pressure and the fluid for magnetic sealing as one fluid are as follows: 1) It has a low viscosity of 100 CP or less (27 ° C.), 2) it has a saturation magnetization of 50 Gauss or more, 3) it has a low evaporation property that can maintain the sealing property, and 4) there is no high temperature gelation or oxidation. In addition, it has stability that can suppress it, 5) suppresses the activity of metal generated by contact and wear, etc., but a magnetic fluid satisfying such good characteristics has not yet been obtained. . Above all, the phenomenon of so-called gelation, which loses fluidity as a life characteristic of the magnetic lubricating fluid, as described in 4) above, is particularly likely to occur at the time of high temperature use and is an important problem to be solved.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a motor having a dynamic pressure bearing device which satisfies the above characteristics and is excellent in lubricity, sealability and life reliability.

[0006]

In order to achieve the above object, a motor having a hydrodynamic bearing device according to a first aspect of the present invention has magnetic particles between the hydrodynamic surfaces of a shaft body and a bearing body which are arranged to face each other. A fluid dynamic bearing device is provided which interposes a lubricating fluid dispersed in a base oil solvent and rotatably supports the shaft body and the bearing body shaft by the dynamic pressure generated in the lubricating fluid. Then, in the motor using the dynamic pressure bearing device, the rotor having the other one of the drive coil and the drive magnet is rotatably supported by the dynamic pressure bearing device to the stator having one of the drive coil and the drive magnet, The base oil solvent of the lubricating fluid used in the hydrodynamic bearing device is poly-
It has a structure containing an α-olefin hydride (PAO) and a polyol ester.

The poly-α-olefin hydride in the above invention is obtained, for example, by hydrogenating a polymer obtained by polymerizing 1-decene, isobutylene or the like with a Lewis acid or the like. These have a number average molecular weight of 20.
Some have a number average molecular weight of about 400 from the viewpoint of evaporation characteristics and the like. Although the hydrogenation does not have to be performed completely, it is likely to deteriorate when the degree of hydrogenation is low.

As the polyol ester, for example, a polyhydric alcohol such as neopentyl glycol (NPG), trimethylolpropane (TMP) or pentaerythritol (PE) and a long-chain or branched fatty acid having 5 to 18 carbon atoms are used. And various trimethylolpropane mixed esters in which R (R is an alkyl group) of CH ₃ CH ₂ —C— (CH ₂ OOCR) ₃ is changed within the range of C5 to C20 are used. To be More specifically, valeric acid, a mixed trimethylolpropane ester of heptanoic acid (manufactured by Nippon Steel Chemical Co., Ltd .; trade name HATCOL 2915, 2925, 2937, etc.) and trimethylolpropane with decanoic acid and heptanoic acid Mixed ester oil (manufactured by Nippon Steel Chemical Co., Ltd .; HATCOL29)
38).

Further, the invention of claim 3 is configured such that an anti-gelling agent is added to the base oil solvent according to the invention of claim 1 or claim 2.

As the gelling inhibitor, for example, an antioxidant is used as in claim 4, and in the case of the antioxidant, a phenol type, amine type or peroxide which functions as a free radical chain reaction terminator is used. One or more antioxidants selected from the group consisting of sulfur-based antioxidants that act as decomposers can be used as a mixture, and amine-based and phenol-based antioxidants are preferably used in combination. It is preferable. Considering the solubility in the base oil solvent, etc., the compounding amount thereof is preferably 1 to 10 parts by weight of the amine-based antioxidant and 1 to 10 parts by weight of the phenol-based antioxidant with respect to 100 parts by weight of the base oil solvent. When used alone, 1 to 10 parts by weight of amine antioxidant is suitable. Phenolic antioxidants are effective only when used in combination.

As the phenolic antioxidant,
2,6-di-t-butyl-phenol (trade name; ethyl 701, Irganox L108 etc.), 4,4'-methylenebis (2,6-di-t-butyl-phenol) (trade name; ethyl 702, Irganox L109 etc.),
2,6-di-t-butyl-4-ethylphenol (trade name: ethyl 724, etc.) and 2,6-di-t-4-n-butylphenol (trade name: ethyl 744, etc.) are adopted. . From the viewpoint of evaporation characteristics and compatibility with the base material,
4,4'-methylenebis (2,6-di-t-butylphenol) is preferred.

Alkyldiphenylamine (trade name; Irganox L01,
L57, L06 etc.) and phenyl-α-naphthylamine (trade name; Irganox L05 etc.) are adopted. From the viewpoint of evaporation properties and compatibility with the base material, alkyldiphenylamine is preferable.

Further, the invention of claim 5 has a constitution in which a viscosity temperature index improver is added to the base oil solvent according to the invention of claim 1 or claim 2.

As the viscosity temperature index improver, there are polymethacrylate type compounds having the following compositions.

Embedded image

The average molecular weight of this product is from 20,000 to
Although it is 1,500,000, the average molecular weight is 20,000 to 5 in view of the relationship between the effect of improving the viscosity index and the shear stability.
Those in the range of 50,000, for example, Sanyo Kasei Co., Ltd .; In addition, since these polymers are difficult to handle in production and blending, they are generally diluted with low-viscosity mineral oils, but low-viscosity mineral oils have drawbacks such as evaporation and dispersion stability. ,
It is preferred to utilize poly-α-olefin hydride as the diluent.

Further, as the viscosity temperature index improver,
There is a polybutene type (polyisobutylene type) having the following composition, and for example, Tetrat manufactured by Nippon Petrochemical Co., Ltd. is used.

Embedded image Although the average molecular weight of this product is 5,000 to 300,000, it is preferable to use a poly-α-olefin hydride as the diluent for the same reason as above.

On the other hand, the invention of claim 6 has a constitution in which a metal deactivator is added to the base oil solvent according to the invention of claim 1 or claim 2.

Typical examples of the metal deactivator include benzotriazole and its derivatives, but also imidazoline and pyrimidine derivatives. Many of these are effective in compounds having at least an N-CN bond, and have an action of forming an inactive film on the metal surface and an antioxidant action.

Other than this, there are compounds having an N--C--S bond, but due to their solubility in the substrate and volatility,
For example, manufactured by Ciba Geigy; Leomet 38, 39, SB
Benzotriazole derivatives such as T are used.

According to a seventh aspect of the present invention, in the dynamic pressure bearing device according to the first aspect, the dynamic pressure bearing portion for generating a dynamic pressure in the lubricating fluid and the outflow of the lubricating fluid from the dynamic pressure bearing portion are prevented. And a seal portion that operates so that the dynamic pressure bearing portion and the seal portion communicate with each other, and the same lubricating fluid continuously flows from the dynamic pressure bearing portion that communicates with the seal portion to the seal portion. It is configured to be filled in.

The blending ratio of the entire lubricating fluid in the present invention is 30 to 90 parts by weight of poly-α-olefin hydride,
5 to 70 parts by weight of polyol ester oil, antioxidant 10
˜20 parts by weight, 10 to 20 parts by weight of metal deactivator, and 25 to 35 parts by weight of magnetic fine particles are preferable, the viscosity is 100 cp or less, and the saturation magnetization is 150 gauss or more. When the amount of magnetic fine particles is 25 parts by weight or less, the amount is less than 150 gauss, and when it is 35 parts by weight or more, the viscosity is affected.

[0022]

According to the means according to the inventions of claims 1 and 2, a base oil satisfying physical properties such as viscosity, evaporation and high temperature gelation can be obtained. By adding an anti-gelling agent (antioxidant), a viscosity temperature index improver, and a metal deactivator as in the invention of 6, the high temperature gelation property and the viscosity property are further improved.

Further, as in the invention described in claim 7, for a motor having a dynamic pressure bearing device in which one fluid serves both as a lubricating fluid for generating a dynamic pressure and a magnetic fluid for a magnetic seal, The above-mentioned effects are satisfactorily exhibited.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment in which the present invention is applied to an HDD spindle motor will be described in detail below with reference to the drawings.

First, the HDD spindle motor shown in FIG. 1 has a stator set 2 as a fixing member assembled to the frame 1 side, and a rotation assembled to the stator set 2 from the upper side in the figure in a laminated manner. The rotor set 3 as a member. Of these, the stator core 21 that constitutes the stator set 2 is fitted to the outer peripheral portion of a substantially cylindrical bearing holder 22 that is erected at a substantially central position of the frame 1, and the salient pole portion of the stator core 21 concerned. The winding wire 23 is wound around.

A pair of integrally formed radial slide bearings 24, 24 are provided on the inner peripheral portion of the bearing holder 22 so as to be separated from each other by a predetermined distance in the axial direction. A rotary shaft 31 is rotatably supported. That is, the inner peripheral surfaces of the both radial plain bearings 24, 24 are different from the outer peripheral surface of the rotating shaft 31.
The bearings are slidably opposed to each other through a predetermined bearing lubricating fluid A, and the inner peripheral surface of each radial sliding bearing 24 and the outer peripheral surface of the rotating shaft 31 constitute a dynamic sliding surface in the radial direction. . The bearing lubricating fluid A is composed of the magnetic fluid composition according to the present invention, and its structure will be described later.

Further, the tip end portion (lower side portion in the drawing) of the rotary shaft 31 passes through the bearing lubricating fluid A similar to the above to the thrust receiving plate 25 covering the opening portion on the lower end side in the drawing of the bearing holder 22. Are slidably opposed to each other, and the tip end surface of the rotary shaft 31 and the receiving surface of the thrust receiving plate 25 form a dynamic pressure sliding surface in the thrust direction. Hereinafter, both the radial direction bearing portion and the thrust direction bearing portion will be collectively referred to as a dynamic pressure bearing portion.

On the other hand, a retaining plate 32 made of a collar-shaped magnet is fixed to the tip portion (lower portion in the figure) of the rotating shaft 31, and the rotor set 3 is entirely covered by the stator set 2 by the retaining plate 32. It is designed not to fall off the side.

Further, the bearing lubricating fluid A in this embodiment is
It also serves as a magnetic fluid for sealing the bearing lubricating fluid A. That is, a seal portion is provided in the upper end opening of the bearing holder 22 so as to communicate with the above-mentioned dynamic pressure bearing portion, and from the dynamic pressure bearing portion to the seal portion, that is, from the bottom of the bearing holder 22 to the upper end. The same bearing lubricating fluid A is continuously filled near the opening. A seal magnet 26 magnetized in the radial direction is annularly attached to the seal portion along the inner peripheral wall of the seal portion, and the magnetic attraction of the seal magnet 26 causes the bearing lubricating fluid A to flow. The bearing lubricating fluid A is retained and is prevented from flowing out to the outside.

Further, a hub 33 constituting the rotor set 3 is fixed to the base end portion (upper end portion in the drawing) of the rotary shaft 31 so as to rotate integrally therewith. This hub 33
It is formed of a substantially cylindrical body for mounting a plurality of magnetic disks 34 on its outer peripheral portion, and has a back yoke 35 at the lower end edge in the figure.
The drive magnet 36 is mounted in a ring shape via the.
The drive magnet 36 is closely arranged so as to face the outer peripheral end surface of the stator core 21 in an annular shape.

At this time, the central portion of the hub 33 is disposed so as to face the seal body 26 in the axial direction, and a pair of magnet bodies 33a mounted on the facing wall surfaces of these.
The rotor set 3 including the rotating shaft 31 and the hub 33 is configured to receive a predetermined pressing force in the thrust direction toward the thrust receiving plate 25 by the attraction force between the shafts 26a and 26a.

Next, examples of the magnetic fluid composition constituting the bearing lubricating fluid A used in the dynamic pressure bearing device according to the present invention will be described.

In each of the examples of the present invention, Mn-Zn ferrite obtained by the coprecipitation method was used as the magnetic fine particles. 200 g of manganese chloride, 220 g of zinc chloride and 520 g of iron trichloride were dissolved in 10 liters of water, the temperature of the water-soluble solution was kept at 95 ° C., 6N sodium hydroxide was added dropwise with stirring to adjust the pH of the aqueous solution to 11, After the colloid of Mn-Zn ferrite was generated, the liquid temperature was set to 80 ° C,
While continuing to stir, add 10 parts of sodium oleate.
% Solution 2 l was added. After cooling the solution to room temperature, 3
An aqueous hydrochloric acid solution of N was added to adjust the pH to 6. The agglomerated colloidal particles were thoroughly washed with water and then dehydrated and dried to obtain Mn-Zn ferrite fine particles coated with oleic acid.

Then, the Mn coated with the above oleic acid was used.
14.8 g of -Zn ferrite was taken, 15 g of the following base oil solvent was added, and the mixture was sufficiently stirred and dispersed, and then the undispersed substance was removed by centrifugation. Further, a base oil was added so that the specific gravity became 1.16 to obtain a fluid. The fluid thus obtained has a ferrite concentration of 35 wt% and a saturation magnetization of 25.
It was 0 gauss.

Further, Mn-Zn as the above magnetic fine particles
As a base oil solvent for dispersing ferrite, poly-α-olefin hydride [C30 to C40] (manufactured by Nippon Steel Chemical Co., Ltd .; Synflude 401), mixed trimethylolpropane ester of valeric acid and heptanoic acid ( HATCOL2937 manufactured by Nippon Steel Chemical Co., Ltd., diisodecyl adipate oil (manufactured by Nippon Steel Chemical Co., Ltd .; HATCOL)
2910), a trimellitic acid trioctyl ester oil (manufactured by Nippon Steel Chemical Co., Ltd .; HATCOL 2920), an antioxidant (alkyldiphenylamine / trade name; Irganox L57), a viscosity index improver (OSW).
ALD BOLL; OLICAT-M) and a metal deactivator (manufactured by Ciba-Geigy; Rheomet 39) were used. And the lubricating fluid compositions of Examples 1 to 5 and Comparative Examples 1 to 4 were prepared by variously changing the ratio of each element in the base oil solvent as shown in Table 1 below.

[0036]

[Table 1] It should be noted that “Bal” in Table 1 represents that all the rest other than the numerically displayed ones are themselves.

Each lubricating fluid composition thus obtained was put in a petri dish, and the dispersion stability of the magnetic fine particles was evaluated by confirming the appearance such as precipitation, aggregation, separation, etc.
The evaporation amount was compared by the weight reduction in time, and further the gelling time when the temperature was left at 140 ° C. was compared. Regarding the viscosity, the viscosity at 25 ° C. and the viscosity temperature index were compared. Table 2 shows the evaluation results.

[0038]

[Table 2] In Table 2, for each sample of Examples 1 and 2 of the present invention, dispersion stability, viscosity, evaporation amount, viscosity temperature index, and
The characteristics of the high temperature gelation time show favorable values,
Particularly, it was found that the sample according to Example 2 in which the amount of the polyol ester was increased within the range of 70 wt% had a very high high-temperature gelation time, and thus was excellent in high-temperature stability.

On the other hand, 70% of polyol ester was used.
In Comparative Example 1 in which the content of the fine particles was more than wt%, it was impossible to disperse the magnetic fine particles. Further, in Comparative Example 2 in which the polyol ester was not mixed, although it was possible to disperse, gelation occurred in a short time at high temperature.

Further, in Comparative Examples 3 and 4 in which an ester other than the polyol ester was used, the viscosity characteristics and the evaporation characteristics were poor.

In the sample according to Example 3 in which the metal deactivator was removed from the sample of Example 2 described above, the respective properties also showed good values, but the high temperature gelation time was slightly decreased, It was then found that the addition of a metal deactivator makes it possible to extend the high temperature gelation time.

The samples according to Example 4 in which the viscosity temperature index improver was removed from the samples of Example 3 also showed good values for each property, but of course the viscosity properties slightly decreased. Therefore, it was found that the viscosity characteristics can be improved by adding the viscosity temperature index improver.

Further, in the sample according to Example 5 in which the antioxidant was removed from the sample of Example 4 described above, the characteristics showed relatively good values, but the high temperature gelation time was considerably reduced. It was then found that the addition of an antioxidant can significantly extend the high temperature gelation time.

The invention made by the present invention has been specifically described based on the embodiments, but the present invention is not limited to the above, and various modifications can be made without departing from the scope of the invention. There is no end. For example, as the magnetic fine particles, Ni-Zn ferrite or magnetite can be used similarly in addition to Mn-Zn ferrite.
Further, as the surfactant, any other higher fatty acid can be adopted. Further, as the gelling agent, for example, amine-based, phenol-based, or sulfur-based ones other than the antioxidant can be similarly employed.

[0045]

As described above, the motor using the dynamic pressure bearing device according to the invention of claim 1 and the invention of claim 2 is
By using a lubricating fluid composition having a base oil solvent containing a poly-α-olefin hydride and a polyol ester, physical properties such as viscosity, evaporation and high temperature gelation are improved. With a unique structure, good characteristics can be obtained. Especially, the feasibility and reliability of a motor using a dynamic pressure bearing device in which one fluid is used as both the lubricating fluid for generating dynamic pressure and the fluid for magnetic sealing. It is possible to improve the sex.

Further, as in the inventions of claims 3 to 6, by adding an anti-gelling agent, a viscosity temperature index improver and a metal deactivator, the properties such as viscosity and high temperature gelation are further improved. Therefore, it is possible to further improve the feasibility and reliability of the motor using the dynamic pressure bearing device.

Further, according to the invention of claim 7, for a motor having a dynamic pressure bearing device in which one fluid serves both as a lubricating fluid for generating a dynamic pressure and a magnetic fluid for a magnetic seal, Since the above-described action is exhibited well, it is possible to improve the feasibility and reliability of the motor having the dynamic pressure bearing device of the configuration.

[Brief description of drawings]

FIG. 1 is a half cross-sectional explanatory view showing an HDD motor having a dynamic pressure bearing device according to an embodiment of the present invention.

[Explanation of symbols]

 A bearing lubricating fluid (magnetic fluid composition) 2 stator set (fixed member) 3 rotor set (rotating member) 22 bearing holder 26 seal magnet 23 drive coil 31 rotating shaft 36 drive magnet

Claims (7)

[Claims] 1. A lubricating fluid, in which magnetic particles are dispersed in a base oil solvent, is interposed between the dynamic pressure surfaces of a shaft body and a bearing body which are arranged so as to face each other, and the dynamic pressure generated in the lubricating fluid is applied. A dynamic pressure bearing device for rotatably supporting the shaft body and the bearing body shaft relative to each other is provided, wherein the dynamic pressure bearing device provides a stator having one of a drive coil and a drive magnet. On the other hand, in a motor using a hydrodynamic bearing device that rotatably supports a rotor equipped with the other one, in the base oil solvent of the lubricating fluid used in the hydrodynamic bearing device, poly-α-olefin hydrogen is used. A motor using a dynamic pressure bearing device, which contains a compound (PAO) and a polyol ester. 2. A motor using a dynamic pressure bearing device according to claim 1, wherein the blending ratio of the polyol ester is less than 70%. 3. A motor using a hydrodynamic bearing device according to claim 1, wherein an anti-gelling agent is added to the base oil solvent. 4. A motor using a dynamic pressure bearing device, wherein the gelation inhibitor according to claim 3 is an antioxidant. 5. A motor using a dynamic pressure bearing device according to claim 1, wherein a predetermined amount of a viscosity index improver is added to the base oil solvent. 6. A motor using a hydrodynamic bearing device according to claim 1, wherein a predetermined amount of a metal deactivator is added to the base oil solvent. 7. The dynamic pressure bearing device according to claim 1, further comprising a dynamic pressure bearing portion for generating a dynamic pressure in the lubricating fluid, and a seal portion for preventing the lubricating fluid from flowing out from the dynamic pressure bearing portion. The dynamic pressure bearing portion and the seal portion are provided so as to communicate with each other, and the same lubricating fluid is continuously filled from the dynamic pressure bearing portion that communicates with the seal portion to the seal portion. A motor using a dynamic bearing device.