JP2948735B2 - Dynamic pressure bearing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic bearing device.

[0002]

2. Description of the Related Art Conventionally, a spindle motor for driving a disk, for example, is known as a driving device for a rotating body having a dynamic pressure bearing device. FIG. 4 shows this motor.

[0003] The spindle motor shown in FIG. 4 is a so-called center shaft rotating type, and in order to avoid complicating the drawing,
Only the right half from the center line is shown.

In FIG. 1, reference numeral 1 denotes a frame as a motor housing, which is a fixing member, and a cylindrical bearing holder 1a is integrally formed on the frame 1 so as to stand upright. That is, the bearing holder 1
The frame 1 including a has a concave shape with one end closed and the other open. A stator core 6 is fixed to the outer peripheral surface of the bearing holder 1a, and a coil 5 is wound around the stator core 6.

A radial slide bearing (for example, metal) 2 made of, for example, the same system as SUS or made of a copper alloy is fitted and fixed to the inner periphery of the bearing holder 1a. For example, a central shaft 3 as a rotation shaft made of SUS is inserted and arranged. At least one of the outer peripheral surface of the center shaft 3 and the inner peripheral surface of the radial slide bearing 2 is formed with a dynamic pressure generating groove having a herringbone shape or the like. 2 is filled with, for example, a magnetic fluid 14 as a bearing fluid. In other words, the radial movement of the center shaft 3 between the center shaft 3 and the inner peripheral surface of the radial sliding bearing 2 suppresses the deflection in the radial direction, and the center shaft 3 rotates in the radial sliding bearing 2.

A thrust plate 1b that forms the bottom of the recess of the frame 1 is provided at a position facing the end surface 3a of the center shaft 3 on the frame closing side (the lower side in the figure). The thrust plate 1b and the end face 3a of the center shaft 3 on the frame closing side.
A dynamic pressure generating groove is formed in at least one of
The above-described magnetic fluid 14 is filled in a sliding portion (a gap between the end face 3a of the central shaft 3 on the frame closing side and the upper end face of the thrust plate 1b facing the end face 3a). That is, a thrust dynamic pressure toward the frame opening side with respect to the central shaft 3 is generated between the frame closed side end surface 3a of the central shaft 3 and the upper end surface of the thrust plate 1b.

Further, a magnetic attraction toward the frame closing side with respect to the center shaft 3 is generated on the center shaft 3 by a known method or the like for shifting the magnetic centers of the stator core 6 and the drive magnet 7. ing. Therefore, the balance and the runout in the thrust direction are suppressed by the magnetic attraction force and the thrust dynamic pressure, and the thrust plate 1b is rotated.

A hub 4 shaped to cover the core 6, the coil 5 and the like is fitted and fixed to an end of the center shaft 3 on the frame opening side (upper side in the figure). A disc (not shown) is mounted on the outer peripheral surface of the hub 4.
A drive magnet 7 is provided at a position facing the core 6 on the inner periphery.
Has been fixed.

A magnetic fluid seal 8 is disposed in the middle of the passage 10 communicating between the inside and outside of the bearing holder 1a, that is, at the upper end of the bearing holder 1a in the figure (the position above the radial sliding bearing 2 on the open side of the frame). Have been. The magnetic fluid seal 8 includes a magnet 8b and pole pieces 8a, 8a provided so as to sandwich the magnet 8b in the axial direction to form a magnetic path. The magnetic fluid 9 can be held between the outer peripheral surface of the shaft 3 and the magnetic fluid 9. Therefore,
The magnetic fluid seal 8 prevents the magnetic fluid 14 filled in the holder 1a containing the magnetic fluid filled in the sliding portion from leaking outward from the bearing portion and from the outside. It is attempted to prevent dust and the like from entering the bearing portion.

[0010] When a predetermined drive voltage is applied to the coil 5 from a power supply means (not shown) external to the motor via the flexible substrate 15, the hub 4 on which the disk is mounted rotates. Reference numeral 13 denotes a stopper for the central shaft 3.

[0011]

However, the above motor has the following problems. That is, the thickness of the bearing holder 1a is relatively thicker than that of the radial sliding bearing 2, the coefficient of linear expansion of the bearing holder 1a is larger than that of the radial sliding bearing 2, and Since the entire outer peripheral surface is fixed by the inner peripheral surface of the bearing holder 1a, the radial sliding bearing 2 receives a large thermal stress from the bearing holder 1a due to an environmental temperature change, and the central shaft 3 The bearing gap between the radial slide bearing 2 and the radial slide bearing 2 is smaller than when the radial slide bearing 2 is not fixed to the bearing holder 1a.
It expands at high temperatures, while it narrows at low temperatures.

Here, when the bearing gap is widened at a high temperature, the dynamic pressure decreases, while when it is narrowed at a low temperature, the bearing loss increases, which is problematic.

Accordingly, an object of the present invention is to provide a dynamic pressure bearing device in which fluctuations in dynamic pressure and bearing loss due to changes in environmental temperature are reduced.

[0014]

According to a first aspect of the present invention, there is provided a hydrodynamic bearing device in which a bearing fluid is filled between a shaft rotatably fitted to a bearing and a bearing. In a hydrodynamic bearing device configured to generate a dynamic pressure in a bearing fluid, a relief portion is provided on a bearing fixing surface of a member for fixing the bearing, and the magnetic bearing is thermally expanded due to volumetric magnetostriction.
In the direction of canceling, so that the coefficient of linear expansion
Iron-based alloy that is smaller than the linear expansion coefficient of the member that fixes the bearing
It is made of gold .

According to a second aspect of the present invention, in order to achieve the above object, in addition to the first means, a bearing at a position corresponding to a radial direction of a bearing fixing surface formed by providing a relief portion is provided. It is characterized in that the inner peripheral surface is not used as a bearing surface.

[0016]

According to a third aspect of the present invention, in order to achieve the above object, in addition to the above-mentioned second means, the hydrodynamic bearing device includes an iron-based alloy,
VAR or SUPER-INVAR.

[0018]

According to the dynamic pressure bearing device of the first and second means, the relief portion provided on the bearing fixing surface of the bearing fixing member deforms when the environmental temperature changes. Absorbs thermal stress and forms the bearing
Ferrous alloys move in a direction where volume magnetostriction counteracts thermal expansion.
Work, so that the coefficient of linear expansion is smaller than that of the shaft
And the bearing clearance is reduced at high temperatures, while at low temperatures
Is expanded, so that thermal stress acting on the bearing from the bearing fixing member is reduced.

According to the dynamic pressure bearing device of the third and fourth means, the bearing is made of, for example, INVAR or SUPE.
It is formed from an iron-based alloy such as R-INVAR. This iron-based alloy works in a direction in which volume magnetostriction cancels thermal expansion.
As a result, the coefficient of linear expansion is smaller than the coefficient of linear expansion of the shaft, so that the bearing gap is narrowed at high temperatures, while it is widened at low temperatures.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. 1A to 1F are views of a bearing, a bearing fixing member, and a shaft of a hydrodynamic bearing device according to a first embodiment of the present invention, as viewed from an axial direction.

The example shown in FIGS. 1A and 1D shows the inner peripheral surface (bearing fixing surface) of the bearing holder 11a (41a).
The escape portion 11b (41) recessed along the axial direction
b) is provided at three places in the circumferential direction, and 3
FIG. 1 shows an example in which the radial sliding bearing 2 is fixed by a line contact portion 11aa (a surface contact is possible in the case of 41aa).
The examples shown in (b) and (e) show the bearing holder 21a.
On the inner peripheral surface of (51a), four relief portions 21b (51b) recessed along the axial direction are provided in four places in the circumferential direction, and four line contact portions 21aa (51aa) along the axial direction are provided. 1 (c) and 1 (f) show an example in which the radial slide bearing 2 is fixed by contact with the inner surface of the bearing holder 31a (61a) along the axial direction. The recessed relief portions 31b (61b) are provided at six locations in the circumferential direction, and the line contact portions 31 at six locations along the axial direction are provided.
Examples in which the radial sliding bearing 2 is fixed by aa (in 61aa, surface contact is also possible) are shown.

As described above, in this embodiment, the relief portions 11b to 11b are provided on the bearing fixing surfaces of the bearing holder portions 11a to 61a.
61b, the escape portion 11b
61b, the bearing holders 11a to 61a themselves are deformed to absorb thermal stress when the environmental temperature changes, and the thermal stress acting on the radial sliding bearing 2 from the bearing holders 11a to 61a is reduced. It can be reduced. Therefore, fluctuations in dynamic pressure and bearing loss due to environmental temperature changes can be reduced as compared with the case where the entire outer peripheral surface of the radial sliding bearing 2 is fixed by the bearing holder.

FIG. 2 is a cross-sectional view showing only a main part of a bearing and a bearing fixing member of a hydrodynamic bearing device according to a second embodiment of the present invention.

In the example shown in FIG. 2 (a), a relief portion 71b as an annular groove recessed along the circumferential direction is formed on the inner peripheral surface (bearing fixing surface) of the bearing holder portion 71a in the axial direction. 2B, the radial sliding bearing 2 is fixed by three surface contact portions 71aa along the circumferential direction, and the example shown in FIG. 2B shows the inner peripheral surface of the bearing holder portion 81a. In the axial direction, two relief portions 81b as annular grooves are provided along the circumferential direction (the lower relief portions 81b are cutouts opened to the lower side in the figure). An example in which the radial slide bearing 2 is fixed by two surface contact portions 81aa along the direction is shown.

As described above, it is needless to say that the same effect as that of the first embodiment can be obtained even if the configuration of the escape portion is changed from the configuration along the axial direction to the configuration along the circumferential direction. Absent.

FIG. 3 is a cross-sectional view showing only a main part of a bearing and a bearing fixing member of a hydrodynamic bearing device according to a third embodiment of the present invention. Is an improvement of the example shown in FIG.

That is, in the third embodiment, 2
The annular recess 2a and the chamfered portions 2b, 2b, 3b are formed on the inner peripheral surface of the radial sliding bearing 2 at positions corresponding to the radial direction of the three bearing fixing surfaces 71aa formed by providing the relief portions 71b at the locations. 2b is formed.

If it is assumed that the inner peripheral surface of the radial sliding bearing 2 is affected by the thermal stress from the bearing holder 71a, the position of the inner peripheral surface of the radial sliding bearing 2 that is affected is fixed by the bearing. Although it is considered that the position corresponds to the radial direction of the surface 71aa, in the present embodiment, the concave portion 2a and the chamfered portions 2b, 2b are formed at the position and are not used as bearing surfaces. 2 does not adversely affect the bearing gap between the central shaft 3 and the radial sliding bearing 2 even if the inner peripheral surface of the bearing 2 is affected by the thermal stress from the bearing holder 71a. Example effects can be further enhanced.

It goes without saying that the configuration shown in the first embodiment may be combined with the configuration shown in the second and third embodiments.

By the way, the radial sliding bearing 2 in the above embodiment acts in a direction in which volume magnetostriction cancels out thermal expansion, so that the linear expansion coefficient becomes smaller than the linear expansion coefficient of the center shaft 3 and the bearing holder, for example, INVAR. Alternatively, when it is formed from an iron-based alloy such as SUPER-INVAR, fluctuations in dynamic pressure and bearing loss due to a change in environmental temperature can be significantly reduced as compared with the above embodiment.

That is, the radial sliding bearing 2 is made of, for example, SUPER-INVAR (32% Ni-5% Co-F).
e), the SUPER-INVAR has a characteristic that the volume magnetostriction acts in a direction to cancel the thermal expansion, and its linear expansion coefficient is determined by the line of the central shaft 3 (SUS) and the line of the bearing holder (SUS). Since the expansion coefficient is 0.1 ppm, which is smaller than 15 ppm, the bearing gap is narrowed at a high temperature, and widened at a low temperature. Moreover, as described in the previous embodiment, a relief portion is provided on the bearing fixing surface of the bearing holder portion to reduce the thermal stress acting on the radial slide bearing 2 from the bearing holder portion, so that the bearing can be narrowed at high temperatures. In such a case, the bearing gap that has been widened or the bearing gap that has been widened at a low temperature is prevented from occurring. That is, the decrease in the dynamic pressure at high temperature is almost eliminated, while the increase in bearing loss at low temperature is suppressed. Therefore, the fluctuation of the dynamic pressure and the bearing loss due to the environmental temperature change is smaller than that of the previous embodiment. Drastically,
It is possible to decrease. However, when the radial sliding bearing 2 is formed by SUPER-INVAR and the entire outer peripheral surface of the radial sliding bearing 2 is fixed by the bearing holder, the bearing gap narrowed at high temperature by the SUPER-INVAR is removed from the bearing holder. It is expanded by the thermal stress acting on the radial sliding bearing 2, and the SUPER-
The bearing gap widened at a low temperature by INVAR is narrowed by thermal stress acting on the radial sliding bearing 2 from the bearing holder.

The radial sliding bearing 2 is a SUPER
A similar effect can be obtained by forming INVAR (36% Ni-Fe) instead of INVAR (32% Ni-5% Co-Fe).

The material for forming the radial sliding bearing 2 is not limited to the above-mentioned INVAR and SUPER-INVAR, but the volume magnetostriction acts in a direction to cancel the thermal expansion. Other iron-based alloys may be used as long as they are smaller than the linear expansion coefficient of the bearing holder.

The radial sliding bearing 2 is a so-called powder which is obtained by solidifying SUPER-INVAR powder by applying pressure and then firing and solidifying the powder surface at a high temperature of, for example, about 800 to 900 ° C. to such an extent that the powder surface is melted. The radial sliding bearing 2 is formed by a metallurgical method, so that the radial sliding bearing 2 can be formed easily and its dimensional accuracy can be obtained with high accuracy.

Further, the radial plain bearing 2 is made of SUPER
After kneading the INVAR powder with a binder made of polyethylene resin, injection molding is performed into a mold having a predetermined shape to produce an intermediate, and the intermediate is baked and solidified at a high temperature of, for example, 1000 ° C. or more. The same effect as the molding by the powder metallurgy method can be obtained even by molding by the metal injection molding method.

Although the invention made by the inventor has been specifically described based on the embodiments, the present invention is not limited to the above-described embodiments, and can be variously modified without departing from the gist thereof. Needless to say, for example, in the above-described embodiment, an example of application to a center shaft rotation type motor has been described, but it is needless to say that the invention can be applied to a center shaft fixed type motor.

In the above embodiment, an example of a hydrodynamic bearing device applied to a spindle motor for driving a magnetic disk has been described. However, the present hydrodynamic bearing device is similarly applicable to other motors. It goes without saying that it can be applied.

[0038]

As described above, according to the present invention, first, according to the dynamic pressure bearing device of the second invention, Rutotomoni the escape portion is provided in the bearing fixing surface of the bearing fixing member, the bearing, the volume magnetostriction thermal expansion To
Work in the direction of the cancellation, so that the coefficient of linear expansion is the linear expansion of the shaft
Since the bearing fixing member is formed from an iron-based alloy having a smaller coefficient than the coefficient , the bearing fixing member itself deforms and absorbs thermal stress when the environmental temperature changes, so that the thermal stress acting on the bearing from the bearing fixing member is reduced. And when the bearing clearance is high temperature
It is narrowed in the meantime, while widened at low temperatures . Therefore, the fluctuation of the dynamic pressure and the bearing loss due to the environmental temperature change is smaller than when the entire bearing outer peripheral surface is fixed by the bearing fixing member.
It can be reduced.

According to the dynamic bearing device of the third invention,
In addition to the second invention, the bearing is made of INVAR or SUPE
Since the bearing gap is formed from an iron-based alloy such as R-INVAR, the bearing gap is narrowed at a high temperature, and is widened at a low temperature. In addition, since the thermal stress acting on the bearing from the bearing fixing member can be reduced, the fluctuation of the dynamic pressure and the bearing loss due to the environmental temperature change can be significantly reduced as compared with the first and second inventions.

[Brief description of the drawings]

FIG. 1 is a view of a bearing, a bearing fixing member, and a shaft of a dynamic pressure bearing device according to a first embodiment of the present invention, as viewed from an axial direction.

FIG. 2 is a cross-sectional view showing only a main part of a bearing and a bearing fixing member of a hydrodynamic bearing device according to a second embodiment of the present invention.

FIG. 3 is a transverse sectional view showing only a main part of a bearing and a bearing fixing member of a hydrodynamic bearing device according to a third embodiment of the present invention.

FIG. 4 is a cross-sectional view of a spindle motor for driving a magnetic disk to which a dynamic pressure bearing device according to the related art is applied.

[Explanation of symbols]

2 Bearing 2a, 2b Bearing inner peripheral surface not used as a bearing surface 3 Shaft 11a, 21a, 31a, 41a-81a Bearing fixing member 11b, 21b, 31b, 41b-81b Relief portion 11aa-81aa Formed by providing relief portion Bearing fixing surface

──────────────────────────────────────────────────続 き Continued on the front page (56) References JP-A 6-44364 (JP, U) JP-A 57-171424 (JP, U) (58) Fields surveyed (Int. Cl. ⁶ , DB name) F16C 35/02 F16C 17/02 F16C 17/22

Claims (3)

(57) [Claims] 1. A dynamic pressure bearing device in which a bearing fluid is filled between a shaft and a bearing which are relatively rotatably fitted, and a dynamic pressure is generated in the bearing fluid. The relief part is provided on the bearing fixing surface of the member to be
At the same time, the bearing operates in the direction where volume magnetostriction cancels thermal expansion.
A member that fixes the shaft and the bearing,
Formed from an iron-based alloy that has a smaller coefficient of linear expansion than
A dynamic pressure bearing device. 2. The dynamic pressure bearing device according to claim 1, wherein a bearing inner peripheral surface at a position corresponding to a radial direction of the bearing fixing surface formed by providing the relief portion is not used as a bearing surface. Characteristic hydrodynamic bearing device. 3. The dynamic pressure bearing device according to claim 2, wherein the iron-based alloy is INVAR or SUPER-INVAR.
A dynamic pressure bearing device, characterized in that: