JPH07190060A - Dynamic pressure bearing device - Google Patents

Abstract

PURPOSE:To prevent the reduction in bearing performance by a temperature change. CONSTITUTION:A cylindrical covering member 13 is integrally molded on the inner circumferential surface side of a cylindrical sleeve 10. The thermal expansion coefficient of the covering member 13 is set higher than the thermal expansion coefficients of the sleeve 10 and a shaft 2. Thus, even when the temperature rises to lower the viscosity of a magnetic fluid 11, the covering member 13 is thermally expanded larger than the sleeve 10 and shaft 2, whereby the space of the gap G is minimized, and the radial dynamic pressure is increased. Since the viscosity of the magnetic fluid 11 is high at a low temperature although the gap G is increased, a fixed dynamic pressure can be provided. The gap G is regulated by the difference in thermal expansion coefficient between the covering member 13 and the sleeve 10 and shaft 2, the change of dynamic pressure generated in the magnetic fluid 11 by temperature change can be eliminated to suppress the reduction in bearing performance.

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 containing a magnetic fluid.

[0002]

2. Description of the Related Art FIG. 2 is a sectional view of one side of a conventional hard disk drive, in which a base portion of a shaft 2 is fixed to a central portion of a main body casing 1 on the stator side. A motor coil 3 is arranged on the upper surface side of the main body casing 1. A pair of thrust bearings 4a and 4b are fixed to the tip end side of the shaft 2 along the axial direction. The thrust bearings 4a and 4b are made of magnetic material. The rotor-side hub 5 is made of a non-magnetic aluminum alloy and is arranged so that the shaft 2 is inserted therethrough. Hub 5
A motor magnet 6 corresponding to the motor coil 3 and a back yoke 7 made of a magnetic material are disposed on the inner peripheral surface side of the lower part of the. Inside the upper part of the hub 5, cylindrical yokes 8a and 8b are arranged along the axial direction of the shaft 2,
A ring-shaped permanent magnet 9 is provided between the two yokes 8a and 8b. A cylindrical sleeve 10 is arranged on the inner peripheral surfaces of the yokes 8a and 8b and the permanent magnet 9.
That is, the sleeve 10 is fixed by the yokes 8a and 8b and the permanent magnet 9.

Here, the magnetic fluid 11 is contained in the gap G formed between the outer peripheral surface of the shaft 2, the lower surface of the upper thrust bearing 4a, the upper surface of the lower thrust bearing 4b, and the inner peripheral surface of the sleeve 10. It is enclosed. The magnetic flux of the permanent magnet 9 forms a magnetic circuit 12 by the yoke 8b, the thrust bearing 4b, the shaft 2, the thrust bearing 4a, and the yoke 8a.
2, the thrust bearings 4a and 4b and the yoke 8a,
A magnetic field is formed between the magnetic fluid 8b and the magnetic field 8b to seal the magnetic fluid 11.

Further, the outer peripheral surface of the shaft 2 and / or the inner peripheral surface of the sleeve 10 are subjected to surface processing such as grooves so that dynamic pressure is generated in the magnetic fluid 11 by rotation of a rotor such as the sleeve 10. Has been done. Sleeve 10
The upper and lower surfaces of the bearing, the lower surface of the thrust bearing 4a, and the upper surface of the thrust bearing 4b are also subjected to surface processing such as grooves so that dynamic pressure is generated in the magnetic fluid 11 by the rotation of the sleeve 10. When the rotor such as the sleeve 10 rotates, the magnetic fluid sealed in the gap G between the inner peripheral surface of the shaft 2 and the outer peripheral surface of the sleeve 10 and the gap between the upper and lower surfaces of the sleeve 10 and the thrust bearings 4a, 4b. A dynamic pressure is generated in the shaft 11, and the dynamic pressure is generated in the shaft 2, the thrust bearings 4a and 4b, and the sleeve 10.
Act on each. At this time, the radial load of the sleeve 10 is supported by the shaft 2, and the thrust load is supported by the shaft 2 via the thrust bearings 4a and 4b.

[0005]

By the way, since the sleeve 10 and the shaft 2 are made of the same material, the sleeve 10 and the shaft 2 expand at the same coefficient of thermal expansion due to the temperature rise and fall, and the gap G itself does not largely change. However, since the viscosity of the magnetic fluid 11 is high at low temperature and lower than it at high temperature, the dynamic pressure generated in the magnetic fluid 11 is decreased at high temperature. Therefore, there is a problem that the bearing performance deteriorates due to the temperature change.

The present invention has been made to solve the above-mentioned conventional drawbacks, and an object thereof is to provide a dynamic pressure bearing device capable of preventing the deterioration of the bearing performance due to the temperature change. .

[0007]

Therefore, in the dynamic pressure bearing device of the present invention, the magnetic fluid 11 is enclosed in the gap G formed between the shaft 2 and the sleeve 10, and the sleeve 1
0 is equipped with magnetic yokes 8a and 8b, and a permanent magnet 9 for constituting a magnetic circuit 12 formed through the yokes 8a and 8b and the shaft 2 is provided, and is formed by the magnetic circuit 12. In the dynamic pressure bearing device, the magnetic fluid 11 is sealed in the gap G by a magnetic field, and the covering member 13 is attached to the inner peripheral surface of the sleeve 10 facing the gap G. The thermal expansion coefficient is set to be larger than the thermal expansion coefficients of the sleeve 10 and the shaft 2.

[0008]

In the above dynamic pressure bearing device, when the temperature rises, the coefficient of thermal expansion of the covering member 13 provided on the inner peripheral surface of the sleeve 10 is larger than that of the sleeve 10 and the shaft 2. 13 thermally expands more than the sleeve 10 and the shaft 2. Therefore, the gap G with the shaft 2 becomes small, and even if the viscosity of the magnetic fluid 11 becomes low at high temperature, dynamic pressure is likely to be generated in the magnetic fluid 11, and the dynamic pressure in the radial direction becomes large. Therefore, it is possible to prevent deterioration of the bearing performance due to temperature change.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, specific embodiments of the dynamic pressure bearing device of the present invention will be described in detail with reference to the drawings. Since the overall structure of the dynamic pressure bearing device is substantially the same as that of the conventional example shown in FIG. 2, elements exhibiting the same function are designated by the same reference numerals, and the description thereof will be omitted.

FIG. 1 is a sectional view of the essential portion of the present invention. The present invention is characterized by integrally forming a plastic covering member 13 on the inner peripheral surface side of a sleeve 10. The covering member 13 is formed in a cylindrical shape, and the thermal expansion coefficient of the plastic is set to be larger than the thermal expansion coefficients of the sleeve 10 and the shaft 2.

Therefore, even if the temperature rises and the viscosity of the magnetic fluid 11 decreases, the covering member 13 thermally expands more than the sleeve 10 and the shaft 2, so that the gap G becomes smaller and the dynamic pressure in the radial direction becomes smaller. It becomes big. Further, at low temperature, a constant dynamic pressure can be obtained because the magnetic fluid 11 has a high viscosity although the gap G is large. In this way, the gap G is adjusted by the difference in the coefficient of thermal expansion between the covering member 13, the sleeve 10 and the shaft 2, and the change in the dynamic pressure of the magnetic fluid 11 caused by the temperature change can be eliminated to suppress the deterioration of the bearing performance. it can. Sleeve 1
The groove processing that is performed so that a dynamic pressure is generated in the magnetic fluid 11 when rotating at 0 may be performed on the shaft 2 and / or the covering member 13 side, or both.

In this embodiment, as shown in FIG. 1, the shaft 2 has a round bar shape, and the sleeve 10 and the covering member 13 have a cylindrical shape. However, the shape is not limited to these. . For example, the bearing portion of the shaft 2 is formed in a spherical shape, and the inner peripheral surface of the sleeve 10 is formed in a concave shape corresponding to the spherical portion. The covering member 13 having a concave inner peripheral surface corresponding to the spherical portion may be integrally formed inside the sleeve 10. Alternatively, the sleeve 10 is formed into a cylindrical shape as in the case of FIG. 1, and a sleeve 13 is provided with a covering member 13 on the inner peripheral surface of which the inner peripheral surface is concave so as to correspond to the spherical portion of the shaft 2. 1
It may be integrally formed on the inside of 0.

[0013]

As described above, in the dynamic pressure bearing device of the present invention, when the temperature rises, the coefficient of thermal expansion of the covering member provided on the inner peripheral surface of the sleeve is larger than that of the sleeve and the shaft. The covering member thermally expands more than the sleeve and the shaft. Therefore, the gap with the shaft becomes small, and even if the viscosity of the magnetic fluid becomes low at high temperature, dynamic pressure is easily generated in the magnetic fluid, and the dynamic pressure in the radial direction becomes large. Therefore, it is possible to prevent deterioration of the bearing performance due to temperature change.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of an embodiment of a dynamic pressure bearing device of the present invention.

FIG. 2 is a one-sided sectional view of a conventional dynamic pressure bearing device.

[Explanation of symbols]

 2 shaft 4a thrust bearing 4b thrust bearing 8a yoke 8b yoke 9 permanent magnet 10 sleeve 11 magnetic fluid 12 magnetic circuit 13 coating member G gaff

Claims (1)

[Claims] 1. A magnetic fluid (11) is enclosed in a gap (G) formed between a shaft (2) and a sleeve (10), and a magnetic material yoke (8) is provided in the sleeve (10).
a) (8b) is mounted, and the yokes (8a) (8b) are
A magnetic circuit (1 formed via a shaft (2) and the like.
The dynamic pressure bearing device is provided with a permanent magnet (9) for constituting 2), and the magnetic fluid (11) is sealed in the gap (G) by the magnetic field formed by the magnetic circuit (12). And attaching a covering member (13) to the inner peripheral surface of the sleeve (10) facing the gap (G),
The coefficient of thermal expansion of the covering member (13) is determined by the sleeve (1
0) and the coefficient of thermal expansion of the shaft (2) are set to be larger than that.