JP2002054628A - Dynamic pressure fluid bearing device and spindle motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dynamic pressure fluid bearing device and spindle motor capable of effectively preventing leak and scatter of lubricant and stably performing lubrication even under elevated temperature. SOLUTION: Linear expansion coefficients of a sleeve member 12 and a rotation shaft 22 are maintained high in comparison with that of a hub 20 including an outer circumference side annular part 20a. A linear expansion coefficient of an inner circumference side annular part forming member 24 is maintained high in comparison with those of the sleeve member 12 and the rotation shaft 22. Accordingly, clearances of a first interface retention part 26 and a second interface retention part 48 decrease when temperature rises. The linear expansion coefficients of the sleeve member 12 and the rotation shaft 22 are maintained in a same level to reduce clearance changes at an upper and a lower radial bearing parts 32, 34 and a thrust bearing part 46 when temperature rises.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrodynamic bearing device, and more particularly, to a hydrodynamic bearing device capable of effectively preventing the leakage of lubricating fluid even when the temperature rises, and a hydrodynamic bearing device. It relates to a spindle motor.

[0002]

2. Description of the Related Art In a hydrodynamic bearing device shown in FIG. 3 and a spindle motor provided with the hydrodynamic bearing device, a sleeve member a and lubricating oil are supplied by the sleeve member a. A rotating shaft b rotatably supported through the inner circumferential side annular portion forming member c, and
The hub d including the outer peripheral side annular portion d1 is made of a ferrous material of the same system having a similar linear expansion coefficient to suppress a change in the gap between the upper and lower radial bearing portions ef and the thrust bearing portion g when the temperature changes. Stainless steel). Note that the spindle motor is a motor that rotationally drives with a recording medium such as various recording disks mounted thereon.

The interface between the lubricating oil and the inner peripheral side annular portion forming member c
Tapered lower interface holding portion h between the sleeve member a and the outer peripheral side annular portion d1 and the tapered upper interface holding portion i between the sleeve member a and the tapered intermediate portion communicating with the outside air through the radial communication hole j. In the interface holding portion k · l, the lubricating oil is held by the surface tension, and the lubricating oil necessary for the upper and lower radial bearing portions ef and the thrust bearing portion g is maintained. Each of the interface holding portions h, i, k, and l is located at the end of the gap between the bearing portions e, f, and g, and is formed so as to gradually expand from the side where the filled lubricant is located toward the outside air. Have been.

However, at high temperatures, the bearing gap changes due to the slightly different linear expansion coefficients of the parts, and the viscosity of the lubricating oil decreases drastically (the viscosity decreases by half at a temperature rise of only about 10 ° C.). The balance position of the generated pressure designed for each hydrodynamic bearing device moves, and accordingly, the interface position of the lubricating oil may move significantly. In addition, since the surface tension of the lubricating oil is also drastically reduced, the lubricating oil holding force at each interface holding portion is reduced, and there is a possibility that the lubricating oil flows out and scatters from the lower interface holding portion h and the upper interface holding portion i to the outside.
Therefore, the lubricating oil required for the bearing may be insufficient and seizure may occur, or the lubricating oil may scatter or evaporate and adhere to recording media such as various recording disks to cause a reading error.

The present invention has been made in view of the above-mentioned problems in the prior art, and an object of the present invention is to effectively prevent leakage and scattering of a lubricating liquid even when a temperature rises. An object of the present invention is to provide a hydrodynamic bearing device capable of performing stable and stable lubrication and a spindle motor provided with the hydrodynamic bearing device.

[0006]

Means for Solving the Problems (1) A hydrodynamic bearing device according to the present invention includes a fixed portion, a rotating portion, and a lubricating liquid filled in a gap between the fixed portion and the rotating portion. On the other hand, the rotating portion is rotatably supported via the lubricating liquid, and has a boundary holding portion over the entire circumference at a part of a gap between the fixed portion and the rotating portion, and the lubricating liquid is disposed between the fixed portion and the rotating air. The interface holding portion is formed on the interface holding portion over the entire circumference, and the interface holding portion is formed such that the gap between the fixed portion and the rotating portion gradually increases from the side where the filled lubricant is located toward the outside air. A hydrodynamic bearing device comprising: a member that forms at least an interface holding part of the fixed part and the rotating part, so that a gap between the fixed part and the rotating part in the interface holding part decreases with an increase in temperature. Among them, at least the coefficient of linear expansion of the members constituting the interface holding part is selected. It is characterized by that.

In this hydrodynamic bearing device, the temperature of the gap between the fixed part and the rotating part in the interface holding part increases (for example, when the temperature rises above normal temperature) by selecting the linear expansion coefficients of the fixed part and the rotating part. ). Even when the surface tension that generates the holding force of the lubricating liquid at the interface holding part decreases with the temperature rise, the gap between the fixed part and the rotating part at the interface holding part is reduced, so that the lubricating liquid is held by the interface holding part. The reduction in force is at least suppressed and leakage of lubricating fluid is prevented.

When two or more interface holding portions are present in the hydrodynamic bearing device of the present invention, the gap between the fixed portion and the rotating portion in at least one of the interface holding portions is reduced so as to increase with temperature.
What is necessary is that the linear expansion coefficient of at least the member forming the interface holding portion of the fixed portion and the member forming the interface holding portion of the rotating portion are selected.

Linear expansion of at least a member constituting the interface holding portion of the fixed portion and at least a member forming the interface holding portion of the rotating portion so that the gap between the fixed portion and the rotating portion in the interface holding portion decreases with an increase in temperature. Selecting the coefficient means that, for example, when one of the fixed part and the rotating part in the interface holding part is located radially inward and the other is located radially outward, at least the interface holding part of the fixed part is formed. Of the members constituting the interface holding portion of the rotating member and the rotating member, it is appropriate to select such that the linear expansion coefficient of the member located radially outward is smaller than the member located radially inward. I do. However, it is not necessary that both the fixed portion and the rotating portion are made of two or more members.

[0010] The hydrodynamic bearing device of the present invention can be used for various types of machinery other than electric motors.

(1-1) The above hydrodynamic bearing device has two or more interface holding portions, and the lubricating liquid filled in the gap between the fixed portion and the rotating portion forms an interface over the entire circumference at each interface. The holding part has a gap between the fixed part and the rotating part in at least two interface holding parts, which decreases with an increase in temperature.
The linear expansion coefficient of the member of the fixed portion and the member of the rotating portion may be selected. For example, as a case where such a configuration can be applied to two interface holding portions, a case where the gap between the two interface holding portions gradually increases in the opposite direction in the axial direction or in the same direction. In addition, for example, when the gap of one interface holding portion is gradually expanded in the axial direction and the gap of the other interface holding portion is gradually expanded inward in the radial direction, the gap between the fixed portion and the rotating portion is only the former. The coefficient of linear expansion of the member of the fixed portion and the member of the rotating portion may be selected so as to decrease with increasing temperature.

(1-2) The above hydrodynamic bearing device is a hydrodynamic bearing for generating a dynamic pressure in a lubricating liquid at a portion where a fixed portion and a rotating portion are opposed to each other so as to rotatably support the rotating portion with respect to the fixed portion. The absolute value of the rate of change due to the temperature rise in the gap between the fixed part and the rotating part in the dynamic pressure bearing part is smaller than the reduction rate due to the temperature rise in the gap between the fixed part and the rotating part in the interface holding part. Is preferred. (The absolute value of the rate of change due to temperature rise in the gap between the fixed part and the rotating part in the dynamic pressure bearing is
It is almost 0, or the reduction ratio due to the temperature rise of the gap between the fixed portion and the rotating portion in the interface holding portion is, for example, 1/1000 or more or 1/100 or more, 1/2 or less, 1/3 or less, 1/4 or less, 1/10 or less, or 1/100
It can be: )

[0013] Even if the surface tension for generating the holding force of the lubricating liquid in the interface holding portion decreases with the temperature rise, the gap between the fixed portion and the rotating portion in the interface holding portion is reduced, so that the lubrication by the interface holding portion is reduced. A decrease in the holding power of the liquid is suppressed at least, and leakage of the lubricating liquid is prevented. The gap between the fixed part and the rotating part in the dynamic pressure bearing part is smaller than that of the interface holding part, and the absolute value of the rate of change in the temperature rise is the temperature of the gap between the fixed part and the rotating part in the interface holding part. Since it is smaller than the reduction ratio due to the rise, it can be maintained almost constant, and the pressure balance in the dynamic pressure bearing portion can be maintained.

(1-3) A fixed portion, a rotating portion, and a lubricant filled in a gap between the fixed portion and the rotating portion, wherein the rotating portion is rotatably supported by the fixed portion via the lubricant. As an example of the hydrodynamic bearing device thus formed, one of a fixed portion and a rotating portion has a shaft body and the other has a sleeve body, and the shaft body has a shape perpendicular to the shaft portion and the shaft portion. (In general, two axial thrust portions spaced apart from each other in the axial direction), and the sleeve body has a sleeve portion fitted to the shaft portion of the shaft body. A sleeve-side thrust portion axially opposed to the shaft-side thrust portion of the shaft body (generally, two sleeve-side thrust portions opposed to the two shaft-side thrust portions, respectively); There is a case in which the gap between the shaft body and the sleeve body is filled with lubricating liquid. Kill. In this case, a radial bearing portion (one or more radial bearing portions) in which the shaft portion and the sleeve portion face each other in the radial direction, and a thrust bearing in which the shaft-side thrust portion faces the sleeve-side thrust portion in the axial direction. In a portion (generally, two thrust bearing portions), a main dynamic pressure for supporting one of the shaft body and the sleeve body so as to be rotatable relative to the other can be generated in the lubricating liquid. It is desirable to provide a dynamic pressure generating groove such as a herringbone groove in a sleeve portion or a shaft portion of the radial bearing portion, and a herringbone groove or a sleeve side thrust portion or a shaft side thrust portion in the thrust bearing portion. It is desirable to provide a dynamic pressure generating groove such as a spiral groove.

The shaft portion and the shaft-side thrust portion constituting the shaft body are:
They may be formed integrally or may be formed by combining separate components. Normally, the shaft portion has a substantially cylindrical outer peripheral surface that is rotationally symmetric with respect to the axis,
The shaft-side thrust portion generally has a surface that is perpendicular to the axis and is rotationally symmetric. Further, the sleeve portion and the sleeve-side thrust portion constituting the sleeve body may be integrally formed, or may be formed by combining separate components. Normally, the sleeve portion has a substantially cylindrical inner peripheral surface that is rotationally symmetric with respect to the axis, and the sleeve-side thrust portion is usually perpendicular and rotationally symmetric with respect to the axis. Has a surface to make.

The gap between the fixed portion and the rotating portion has, for example, two ends, and at least at both ends, the space between the fixed portion and the rotating portion is substantially open to the outside over the entire circumference. . In this case, near each end or near each end, an interface holding portion is provided, an interface over the entire circumference of the lubricating liquid is located at each interface holding portion, and the lubricating liquid is substantially continuous in a gap between both interfaces. State. As the lubricating liquid, various lubricating oils such as spindle oil can be used.

The gap between the fixed part and the rotating part has one end substantially open to the outside over the entire circumference between the fixed part and the rotating part, and the other part substantially closes, for example, the shaft inside. It can also be done.

The sleeve may be fixed and the shaft may rotate as a rotary shaft. In addition, the shaft may be fixed and the sleeve may rotate as a rotary sleeve.

(1-4) In the hydrodynamic bearing device as described in (1-3), the inner peripheral side annular portion having, as a part of the shaft, an outer peripheral surface facing a part of the inner peripheral surface of the sleeve body. A portion forming member is provided, and an interface holding portion is formed between the outer peripheral surface of the inner peripheral side annular portion forming member and the inner peripheral surface of the sleeve body facing the inner peripheral side forming member, and the inner peripheral side annular portion forming member is more stranded than the sleeve body. By using a material having a large expansion coefficient, the gap between the shaft body and the sleeve body in the interface holding portion can be reduced with an increase in temperature.

In this hydrodynamic bearing device, when the gap between the fixed portion and the rotating portion in the interface holding portion is formed so as to gradually increase toward one side in the axial direction, the outer peripheral surface of the inner peripheral side annular portion forming member is formed. The inner peripheral surface of the sleeve body is inclined inward in the radial direction toward the one axial direction, and the inner peripheral surface of the sleeve body opposed to the outer peripheral surface of the inner peripheral side annular portion forming member is not inclined in the axial direction or toward one axial direction. It is preferable to incline radially inward smaller than the outer peripheral surface of the inner peripheral side annular portion forming member. This is to prevent a tendency that the lubricating liquid tends to leak outside due to centrifugal force when the rotating part rotates.

In this case, as described in the above (1-2),
It is preferable that the absolute value of the rate of change of the gap between the fixed part and the rotating part in the dynamic pressure bearing part due to temperature rise is smaller than the reduction rate due to the temperature rise in the gap between the fixed part and the rotating part in the interface holding part. For example, of the shaft portion and the sleeve portion, at least a member including a radially opposed portion in the radial bearing portion has the same or approximate linear expansion coefficient, so that a gap between the radial bearing portions due to a temperature rise is obtained. It is desirable to suppress the change of.

(1-5) Further, in the hydrodynamic bearing device as described in (1-3), the inner peripheral surface having an outer peripheral surface facing a part of the inner peripheral surface of the sleeve body as a part of the shaft body. A side annular portion forming member is provided, and one interface holding portion is formed between the outer peripheral surface of the inner peripheral side annular portion forming member and the inner peripheral surface of the sleeve body opposed thereto, and as another part of the shaft, An outer peripheral side annular portion forming member having an inner peripheral surface facing a part of an outer peripheral surface of the sleeve body; and the one side between the inner peripheral surface of the outer peripheral side annular portion forming member and the outer peripheral surface of the sleeve body facing the same. Forming another interface holding portion different from the interface holding portion, the lubricating liquid filled in the gap between the shaft body and the sleeve body has at least two interfaces over the entire circumference, and each of the interface holding portions And the inner peripheral side annular portion forming member is made of a material having a larger linear expansion coefficient than the sleeve body. And forming a,
By forming the outer peripheral side annular portion forming member from a material having a smaller linear expansion coefficient than that of the sleeve body, the gap between the shaft body and the sleeve body in the two interface holding portions can be reduced with an increase in temperature.

In the hydrodynamic bearing device, even when the gap between the fixed portion and the rotating portion in each interface holding portion is formed so as to gradually expand in any of the axial directions, the inner peripheral side annular portion forming member The inclination of the inner peripheral surface of the outer peripheral surface and the sleeve body opposed thereto and the inclination of the inner peripheral surface of the part of the outer peripheral surface of the sleeve body and the outer peripheral side annular portion forming member opposed thereto are caused by centrifugal force during rotation of the rotating part. In order to prevent the lubricating liquid from easily leaking to the outside, it is preferable to adopt the same configuration as described above.

In this case as well, as in the case of (1-5), the absolute value of the rate of change due to the temperature rise in the gap between the fixed part and the rotating part in the dynamic pressure bearing part is the same as that of the fixed part in each interface holding part. It is preferable that the ratio be smaller than the reduction ratio due to a rise in the temperature of the gap between the portions.

(1-6) In the above hydrodynamic bearing device,
In order to prevent a decrease in the viscosity and surface tension of the lubricating liquid due to a rise in temperature as much as possible, heat generated due to the rotation of the rotating part is released to the outside through a fixed part (for example, a sleeve or a shaft) in contact with the lubricating liquid. Thereby, it is preferable to suppress the temperature rise. For this purpose, it is desirable to increase the thermal conductivity of the fixing portion as much as possible so that heat can easily escape to the outside (directly to the outside or through another member having a large thermal conductivity as much as possible).

For this purpose, for example, the sleeve or the shaft constitutes at least a part of the fixing portion, and the thermal conductivity of the sleeve or the shaft is 60 kcal / m · h · ° C. or more. it can. As described above, by using a material whose thermal conductivity is about three times that of the conventionally used stainless steel, the difference between the temperature of the lubricating liquid and the external temperature is made larger than that of the conventional one (for example, to about one third). It is possible to reduce. Examples of a material having such thermal conductivity and capable of forming a groove for generating a dynamic pressure include aluminum nitride (AlN), brass, and an Al alloy.

(1-7) In the hydrodynamic bearing device according to (1-4), the shaft member and the inner peripheral side annular portion constitute a dynamic pressure bearing portion between the sleeve member and the sleeve member. A sleeve, which forms at least a part of the fixing portion, and has a thermal conductivity of 60 kcal / m · m.
h · ° C or higher, the sleeve body is made of aluminum nitride,
The shaft member is made of alumina (Al ₂ O ₃ ) or martensitic stainless steel, and the inner ring member is made of an aluminum alloy or a magnesium alloy. The outer peripheral surface and the inner peripheral surface of the sleeve body opposed thereto reduce the gap of the interface holding part, and realize a high thermal conductivity as described in (1-6), and further reduce the weight compared to the conventional one be able to.

(1-8) Further, in the hydrodynamic bearing device according to (1-5), the shaft member may include a shaft member forming a hydrodynamic bearing portion between the sleeve member and the inner peripheral annular portion. A sleeve member constituting at least a part of the fixed portion, the sleeve body having a thermal conductivity of 60 kcal / m · h · ° C. or more, The side annular portion forming member is made of a titanium alloy, the sleeve body is made of brass, the shaft member is made of austenitic or martensitic stainless steel, and the inner peripheral side annular portion forming member is made of an aluminum alloy or a magnesium alloy. Due to the temperature rise, the gap between the interface holding portion due to the outer peripheral surface of the inner peripheral side annular portion forming member and the inner peripheral surface of the sleeve body opposed thereto is reduced, and a part of the outer peripheral surface of the sleeve body and the outer peripheral side annular surface opposed thereto Of the part forming members Reduction of the gap surface holding portion by the surface, and (1-6) to achieve a high thermal conductivity, such as described, can be further lighter than conventional.

(1-9) Materials which can be selectively used in various combinations as parts in the hydrodynamic bearing device of the present invention, such as a sleeve body, a shaft member, an inner peripheral side annular portion forming member, and an outer peripheral side annular portion forming member. Are listed in Table 1.

[0030]

[Table 1]

(2) A spindle motor according to the present invention includes the above-described hydrodynamic bearing device, and the shaft or the sleeve rotates integrally with the rotor.

The sleeve body may be fixed, and the shaft body may rotate as a rotary shaft body.
The sleeve body may rotate as a rotating sleeve body.

This spindle motor is, for example, a magnetic disk such as a hard disk, a magneto-optical disk, a CD-R
OM, CD-R, CD-RW, DVD-ROM, DVD
-It can be used as a spindle motor for driving a recording medium such as an optical disc such as a RAM, particularly a disc-shaped recording medium.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A spindle motor provided with a hydrodynamic bearing device as an embodiment of the present invention will be described with reference to FIG. Note that the spindle motor of the present embodiment is used for mounting and driving a hard disk as a recording medium to rotate.

The bracket 10 has a cylindrical support cylinder 10a at the center and an annular concave portion formed on the outer peripheral side of the support cylinder 10a. A sleeve member 12 having a substantially cylindrical shape is coaxially fitted and fixed inside the support cylinder portion 10a, and a stator core 16 around which a stator coil 14 is wound is fixedly fitted outside. A cover member 17 for sealing the lower opening is fixed to the lower surface of the sleeve member 12. On the lower surface of the bracket 10, the support cylinder 1
A sealing plate 18 for sealing the lower opening of Oa is fixed.

The sleeve member 12 includes a substantially bowl-shaped hub 2.
A rotating shaft 22 protruding downward at the center of 0 is fitted rotatably via lubricating oil. Rotating shaft 22
An inner peripheral side annular portion forming member 24 is externally fitted and fixed to a lower end reduced diameter portion 22a provided on an outer peripheral portion of a lower end of the lower end and protrudes radially outward. Outer overhang portion 2 of inner peripheral side annular portion forming member 24
4 a is located in the lower end enlarged diameter portion 12 a provided at the lower end of the inner periphery of the sleeve member 12. Inner circumference side annular portion forming member 2
4 is formed on an inclined surface that is reduced in diameter downward, and the gap between the fixed portion and the rotating portion gradually decreases in the radial direction relative to the inner peripheral surface of the lower end enlarged diameter portion 12a of the sleeve member 12. The enlarged first interface holding unit 26 is configured. The upper surface of the cover member 17, the rotating shaft 22, and the inner peripheral side annular portion forming member 24
Are separated by an axial gap.

Upper and lower herringbone grooves 28 and 30 for generating dynamic pressure are provided on the upper and lower portions of the inner peripheral surface of the substantially cylindrical surface of the sleeve member 12, respectively. The upper and lower radial bearing portions 32 and 34 are configured with lubricating oil therebetween. Both herringbone-shaped grooves 28 on the inner peripheral surface of the sleeve member 12
The portion between 30 is an intermediate enlarged portion 36 whose upper and lower ends are formed on inclined surfaces, and the gap between the outer peripheral surface of the rotating shaft 22 is enlarged. An intermediate interface holding portion 3 is provided between the vertically inclined surface of the intermediate enlarged portion 36 and the outer peripheral surface of the rotating shaft 22.
8.40. Further, a first radial communication hole 42a is opened in a part of the intermediate enlarged portion 36, and the sleeve member 1 is formed.
Notch and support member 10 provided on the outer peripheral surface of
A communication with an axial communication hole 42b formed with the inner peripheral surface of the a allows release of bubbles in the lubricating oil from the intermediate interface holding portions 38 and 40. Further, a second radial communication hole 42c formed by the cover member 17 and a radial notch provided on the lower end surface of the sleeve member 12 communicates with the axial communication hole 42b.
The release of air bubbles in the lubricating oil from the first interface holding portion 26 is enabled.

The upper end surface of the sleeve member 12 is an annular sleeve-side thrust portion 12c perpendicular to the axial direction, and a pump-in type spiral groove 44 for generating dynamic pressure is formed in the sleeve-side thrust portion 12c. And a shaft-side thrust portion 20b formed on the lower surface of the inner peripheral portion of the hub 20.
A thrust bearing portion 46 is formed between the two through a lubricating oil.

The herringbone-shaped groove 28 in the upper radial bearing portion 32 is formed by biasing the bent portion upward, and the spiral groove 44 in the thrust bearing portion 46 is of a pump-in type, so that it is generated in lubricating oil during rotation. The fluid pressure is highest at the upper portion of the upper radial bearing portion 32 and at the radially inner portion of the thrust bearing portion 46, and is lower at the lower portion of the upper radial bearing portion 32 and the radially outer portion of the thrust bearing portion 46. Become. The herringbone-shaped groove 3 in the lower radial bearing portion 34
Since 0 is formed vertically symmetrically, the fluid pressure generated in the lubricating oil at the time of rotation becomes highest at the axial center and decreases toward both ends. Bubbles that can be included in the lubricating liquid move to a lower fluid pressure generated during rotation.

An outer peripheral annular portion 20 protruding annularly downward from the outer peripheral portion of the axial thrust portion 20b of the hub 20.
a is provided (the hub 20 is an outer peripheral side annular portion forming member). An upper end reduced diameter portion 12b is provided at an outer peripheral upper end portion of the sleeve member 12, and a lower end portion of the outer peripheral side annular portion 20a is inserted between the upper end reduced diameter portion 12b and an upper end portion of the support tubular portion 10a. It is in a state. Upper end reduced diameter portion 12b
Is formed on an inclined surface whose diameter is reduced downward, and the gap between the rotating portion and the fixed portion gradually expands downward relative to the inner circumferential surface of the outer annular portion 20a in the radial direction. The holding unit 48 is configured. The lower portion of the second interface holding portion 48 communicates with a gap formed by the upper end reduced diameter portion 12b of the sleeve member 12 and the inner peripheral surface of the outer peripheral side annular portion 20a, so that air bubbles in the lubricating oil can be released therefrom. Close. In this hydrodynamic bearing device, the rotating shaft 22, the inner peripheral side annular portion forming member 24
At least the outer annular portion 20a and the inner portion of the hub 20 constitute a shaft.

Outer projecting portion 2 of inner circumferential side annular portion forming member 24
4a, an outer peripheral surface of the rotary shaft 22, an axial thrust portion 20b, and an inner peripheral surface of the outer annular portion 20a;
Upper surface and outer peripheral surface of lower end enlarged diameter portion 12a, sleeve member 12
Of the interfaces of the lubricating oil filled between the inner peripheral surface, the sleeve-side thrust portion 12c, and the outer peripheral surface of the upper-end reduced-diameter portion 12b, the lower interface is the first interface holding portion 26 and the upper and lower interfaces of the intermediate portion. Are held by surface tension in the intermediate interface holding portions 38 and 40, and the upper interface is held in the second interface holding portion 48, respectively, whereby the upper and lower radial bearing portions 32 and 34 and the thrust bearing portion 46 are required. Lubricating oil is maintained.

A cylindrical rotor magnet 50 is internally fixed to the outer peripheral wall of the hub 20 and faces the stator core 16 and the stator coil 14 with a radial gap therebetween.
The drive current flowing through the stator coil 14 is commutated according to the position of the magnetic pole of the rotor magnet 50, so that the hub 2
The rotating portion including the rotating shaft 22 and the inner peripheral side annular portion forming member 24 is rotationally driven with respect to the fixed portion including the sleeve member 12, the bracket 10, and the like.

In this spindle motor, the hub 20 including the outer annular portion 20a is made of a titanium alloy, the sleeve member 12 is made of brass, the rotating shaft 22 is made of austenitic or martensitic stainless steel, and the inner annular portion forming member 2 is formed.
Reference numeral 4 is made of an aluminum alloy or a magnesium alloy.

These linear expansion coefficients are determined by the outer annular portion 20.
a sleeve member 12 and the rotating shaft 2
2 is larger, and the inner peripheral side annular portion forming member 24 is larger than the sleeve member 12 and the rotating shaft 22. for that reason,
When the temperature rises, each of the gaps between the first interface holding section 26 and the second interface holding section 48 is reduced, and a decrease in the holding power of the lubricating oil by the interface holding sections is suppressed, and leakage of the lubricating oil is suppressed. Is prevented.

On the other hand, since the linear expansion coefficients of the sleeve member 12 and the rotary shaft 22 are substantially the same, even if the temperature rises, the clearance between the upper and lower radial bearing portions 32 and 34 and the thrust bearing portion 46 is larger than that of the two interface holding portions. Is small, and the pressure balance of the lubricating fluid is maintained.

The sleeve member 12 has a thermal conductivity of 60.
Since the temperature is as high as kcal / m · h · ° C. or more, heat generated due to the rotation of the rotating shaft 22 and the hub 20 easily escapes to the outside through the sleeve member 12 and the bracket 10 in contact with the lubricating oil. Therefore, a decrease in the viscosity and surface tension of the lubricating oil due to a rise in temperature is prevented as much as possible. The sleeve member 12
Can be made of, for example, an aluminum alloy or a magnesium alloy, and it is preferable to use a material having as high a thermal conductivity as possible.

By using the above materials, the spindle motor as a whole is lighter than the conventional one.

FIG. 2 is a sectional view of a spindle motor having a hydrodynamic bearing device according to another embodiment of the present invention. The difference between FIG. 2 and FIG.
The upper part of a substantially cylindrical outer circumferential portion forming member 62 is externally fitted and fixed to the outer circumferential portion of the axial thrust portion 60a, and the lower portion of the outer circumferential portion forming member 62 is fixed to the outer circumferential portion 62.
a. Outer peripheral side annular portion forming member 62
Is made of a titanium alloy, and the hub 60 can be made of, for example, martensitic stainless steel. By forming the hub 60 and the outer peripheral side annular portion 62a as separate bodies, the material of the hub 60 is selected separately from the outer peripheral side annular portion 62a in consideration of the relationship with a disk which is externally fixed to the hub 60 and driven to rotate. can do.

[0049]

According to the hydrodynamic bearing device and the spindle motor of the present invention, even if the surface tension for generating the holding force of the lubricating liquid at the interface holding portion decreases with the temperature rise, the fixed portion at the interface holding portion can be used. By reducing the gap between the rotating parts, a decrease in the holding force of the lubricating liquid by the interface holding part is suppressed at least, and leakage of the lubricating liquid is prevented.
For this reason, even in a high-speed type hydrodynamic bearing device such as a hydrodynamic bearing device of a spindle motor for driving a hard disk having a rotation speed exceeding 10,000 rpm, poor lubrication due to insufficient lubrication, occurrence of seizure, leakage or scattering, etc. External contamination is prevented and lubrication can be performed stably.

In the hydrodynamic bearing device according to the fourth aspect,
The gap between the fixed part and the rotating part in the dynamic pressure bearing part is smaller than the interface holding part, and the absolute value of the rate of change in the temperature rise is the reduction rate due to the temperature rise in the gap between the fixed part and the rotating part in the interface holding part. Therefore, it can be maintained almost constant, and the pressure balance in the dynamic pressure bearing portion can be maintained.

In the hydrodynamic bearing device according to any one of the eighth to eleventh aspects, the heat generated due to the rotation of the rotating part easily escapes to the outside through the fixed part in contact with the lubricating liquid. The lowering of the tension is prevented as much as possible,
Poor lubrication and leakage of lubricating fluid are prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view of a spindle motor.

FIG. 2 is a sectional view of another spindle motor.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Bracket 10a Support cylinder part 12 Sleeve member 12a Lower end enlarged diameter part 12b Upper end reduced diameter part 12c Sleeve side thrust part 14 Stator coil 16 Stator core 17 Cover member 18 Sealing plate 20 Hub 20a Outer peripheral side annular part 20b Shaft side thrust part 22 Rotating shaft 22a Lower diameter reduction part 24 Inner peripheral side annular part forming member 24a Outer projection part 26 First interface holding part 28 Upper herringbone-shaped groove 30 Lower herringbone-shaped groove 32 Upper radial bearing part 34 Lower radial bearing part 36 Middle expansion Diameter part 38 Intermediate interface holding part 40 Intermediate interface holding part 42a First radial communication hole 42b Axial communication hole 42c Second radial communication hole 44 Spiral groove 46 Thrust bearing part 48 Second interface holding part 50 Rotor magnet 60 Hub 60a Shaft side thrust portion 62 Outer circumference side annular portion forming member 62 a Outer side annular part

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[Procedure amendment]

[Submission date] August 23, 2000 (2008.2
3)

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

[Procedure amendment 3]

[Document name to be amended] Drawing

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

FIG. 2

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Claims (11)

[Claims] 1. A fixed part, a rotating part, and a lubricant filled in a gap between the fixed part and the rotating part, wherein the rotating part is rotatably supported by the fixed part via the lubricant. A part of the gap between the fixed part and the rotating part has an interface holding part over the entire circumference, and the lubricating liquid has an interface with the outside air over the entire circumference at the interface holding part; The holding unit is a hydrodynamic bearing device in which a gap between the fixed unit and the rotating unit is formed so as to gradually expand from the side where the filled lubricating liquid is located to the outside air side. A hydrodynamic bearing device, wherein a linear expansion coefficient of a member of the fixed portion and a member of the rotating portion is selected so that a gap between the fixed portion and the rotating portion decreases with an increase in temperature. 2. An interface holding portion at two or more locations,
The lubricating liquid filled in the gap between the fixed part and the rotating part has an interface around the entire circumference in each interface holding part, and the gap between the fixed part and the rotating part in at least two interface holding parts is reduced as the temperature rises. 2. The hydrodynamic bearing device according to claim 1, wherein the linear expansion coefficients of the fixed member and the rotating member are selected. 3. A dynamic pressure bearing portion for generating a dynamic pressure in a lubricating liquid for supporting the rotating portion rotatably with respect to the fixed portion at a portion where the fixed portion and the rotating portion are opposed to each other. 3. The hydrodynamic bearing device according to claim 1, wherein an absolute value of a rate of change due to a temperature rise in the gap between the rotating part and the rotating part is smaller than a reduction rate due to a temperature rise in the gap between the fixed part and the rotating part in the interface holding part. 4. A shaft member is provided on one of the fixed portion and the rotating portion,
The other has a sleeve body, and the shaft body has a shaft portion and a shaft-side thrust portion perpendicular to the shaft portion, and the sleeve body is sleeve-fitted to the shaft portion of the shaft body. A combined sleeve portion and a sleeve-side thrust portion axially opposed to the shaft-side thrust portion of the shaft body, wherein a lubricating liquid is provided in a gap between the shaft body and the sleeve body; In a radial bearing portion in which a portion faces in a radial direction, and in a thrust bearing portion in which the shaft-side thrust portion faces the sleeve-side thrust portion in an axial direction, the other is rotatable relative to one of the shaft body and the sleeve body. The hydrodynamic bearing device according to any one of claims 1 to 3, wherein a main dynamic pressure supported by the lubricating fluid is generated in the lubricating liquid. 5. An inner peripheral side annular portion forming member having an outer peripheral surface facing a part of an inner peripheral surface of a sleeve body is provided as a part of a shaft body, and an outer peripheral surface of the inner peripheral side annular portion forming member is provided. By forming an interface holding portion between the inner peripheral surfaces of the sleeve body opposed thereto and forming the inner circumferential side annular portion forming member from a material having a larger linear expansion coefficient than the sleeve body, a shaft body in the interface holding portion is formed. 5. The hydrodynamic bearing device according to claim 4, wherein a gap between the sleeve member and the sleeve body decreases with an increase in temperature. 6. An inner peripheral side annular portion forming member having an outer peripheral surface facing a part of an inner peripheral surface of a sleeve body is provided as a part of the shaft body, and an outer peripheral surface of the inner peripheral side annular portion forming member is provided. An outer peripheral side annular portion having one interface holding portion formed between the inner peripheral surfaces of the sleeve body opposed thereto and having, as another part of the shaft, an inner peripheral surface facing a part of the outer peripheral surface of the sleeve body. A forming member is provided, and between the inner peripheral surface of the outer peripheral side annular portion forming member and the outer peripheral surface of the sleeve body opposed thereto, another interface holding portion different from the one interface holding portion is formed. The lubricating liquid filled in the gap with the sleeve body has at least two interfaces over the entire circumference, and each of the two interfaces is located in each of the interface holding portions. While being formed of a material having a larger linear expansion coefficient than the body,
6. The gap between the shaft body and the sleeve body in the two interface holding portions is reduced with a rise in temperature by forming the outer peripheral side annular portion forming member from a material having a smaller linear expansion coefficient than the sleeve body. Hydrodynamic bearing device. 7. A sleeve or a shaft constitutes at least a part of the fixing portion, and the thermal conductivity of the sleeve or the shaft is 6 or less.
7. The temperature is at least 0 kcal / m · h · ° C.
The hydrodynamic bearing device according to any one of the preceding claims. 8. The hydrodynamic bearing device according to claim 7, wherein the sleeve body or the shaft body is made of an aluminum alloy. 9. A shaft body comprising a shaft member constituting a dynamic pressure bearing portion with a sleeve body and an inner peripheral side annular portion forming member, wherein the sleeve body forms at least a part of a fixed portion. And the thermal conductivity of the sleeve body is 60 kcal / h.
m. ° C or higher, the sleeve body is made of aluminum nitride,
The hydrodynamic bearing device according to claim 5, wherein the shaft member is made of alumina or martensitic stainless steel, and the inner peripheral side annular portion forming member is made of an aluminum alloy or a magnesium alloy. 10. A shaft body comprising: a shaft member constituting a dynamic pressure bearing portion with a sleeve body; an inner peripheral side annular portion forming member; and an outer peripheral side annular portion forming member. At least a part of the fixing portion is formed, and the heat transfer heat conductivity of the sleeve body is 60 kcal / h. m. ° C or more, the outer peripheral side annular portion forming member is made of titanium alloy, the sleeve body is made of brass, the shaft member is made of austenitic or martensitic stainless steel, and the inner peripheral side annular portion forming member is made of aluminum alloy or magnesium alloy. 7. The hydrodynamic bearing device according to claim 6, wherein: 11. A spindle motor comprising the hydrodynamic bearing device according to claim 1, wherein the shaft or the sleeve rotates integrally with the rotor.