Dynamic pressure bearing device

Details Dynamic pressure bearing device Dynamic pressure bearing device

2002-12-24

2004-10-19

Hannon, Thomas R. (Department: 3682)

Bearings

Rotary bearing

Fluid bearing

C384S279000

Reexamination Certificate

active

06805489

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dynamic pressure bearing device in which a dynamic pressure is generated by a lubricating fluid to support a shaft member or a bearing member one of which is relatively rotated.
2. Description of the Related Art
In recent years, various types of dynamic pressure bearing devices have been proposed or a device rotating various types of rotary bodies such as a polygon mirror, a magnetic disk and an optical disk. In such a dynamic pressure bearing device, the outer peripheral face of a shaft member and the inner peripheral face of a bearing member face each other via a minute gap. One of the faces is armed with a dynamic pressure generating part. A lubricating fluid such as air or oil in the minute gap is pressurized by a pumping operation at the dynamic pressure generating part during rotation. Either the shaft member or the bearing member is relatively rotatably supported by the dynamic pressure of the lubricating fluid.
Some dynamic pressure bearing devices are provided with grooves in a herringbone or spiral shape as a means for generating dynamic pressure. On the other hand, especially for journal bearing devices, step-formed and dynamic pressure bearing devices without using herringbone or spiral dynamic pressure generating grooves have been proposed.
FIG.
26
(A) is a transverse cross-sectional view of a conventional taper-formed dynamic pressure bearing device, and FIG.
26
(B) is an explanatory development view of a dynamic pressure generation part which is formed in the dynamic pressure bearing device shown in FIG.
26
(A). In the dynamic pressure bearing device
30
′ shown in the figure, five dynamic pressure generating parts
31
′ are formed along a circumferential direction on the inner peripheral face of a bearing sleeve
15
′ (bearing member) which encloses a rotation shaft
21
(shaft member) via a minute gap
32
′. Each of the dynamic pressure generating parts
31
′ is composed of a protruded part
37
′ which is formed so as to make the radial dimension of the minute gap
32
′ the narrowest, a recessed isolation groove
38
which is formed of a depth of 23 &mgr;m over about 7.5° of the circular angle, and a tapered part
36
′ which makes the radial dimension of the minute gap
32
′ continuously vary about 6 &mgr;m between the recessed isolation groove
38
and the protruded part
37
′. When the rotation shaft
21
is rotated in the direction of arrow “r”, the lubricating fluid such as air or oil is pressurized to generate a desired dynamic pressure in the minute gap
32
′ formed between the rotation shaft
21
and the bearing sleeve
15
′.
However, the dynamic pressure bearing device
30
′ provided with the recessed isolation grooves
38
for canceling negative pressure has a low rigidity, which causes the following problems. First, the deflection of the rotation shaft
21
is liable to occur when disturbances are applied to the shaft
21
at a low speed rotation. In addition, since the rotation speed required to float by the dynamic pressure is high, a metal-to-metal contact occurs between the rotation shaft
21
and the bearing sleeve
15
′ at a low speed rotation of about 5000 rpm, which may cause abrasion. Accordingly, the long life of the dynamic pressure bearing device
30
′ cannot be attained.
In order to solve such problems, it may be inconceivable to make the gap between the rotation shaft
21
and the bearing sleeve
15
′ narrower by strictly controlling the dimensional tolerances of the rotation shaft
21
and the bearing sleeve
15
′. However, such a countermeasure is unfavorable because the components' cost and assembling cost are increased. It is also conceivable to make the diameter of the rotation shaft
21
larger to increase its peripheral velocity, but it is also unfavorable because such a countermeasure causes an increase in cost. It is also conceivable that a high abrasion resistance material is used for the rotation shaft
21
and the bearing sleeve
15
′, but it also causes an increase in the cost of the components.
Further, when the recessed isolation grooves
38
are provided, the contraction percentage of the lubricating fluid in the minute gap
32
′ becomes so large that the lubricating fluid is unable to get into the small gap
32
′ and may leak out in the axial direction.
The recessed isolation grooves
38
are preferable to be formed as deep and narrow as possible to obtain satisfactory dynamic pressure characteristics and normally formed with a depth of 20 &mgr;m or more. Accordingly, the cutting work is performed to form deep and narrow grooves in the manufacturing process of the dynamic pressure bearing device
30
′. The reason is that it is difficult to form deep and narrow recessed isolation grooves
38
by another method. Accordingly, the conventional dynamic pressure bearing device
30
′ requires an additional production process different from the normal manufacturing process. Workability of cutting the work is not satisfactory for a dynamic pressure bearing device. This means the cutting work is not suitable to make a deep and narrow recessed isolation grooves for a dynamic pressure bearing device, although only a simple deep and narrow recessed isolation groove can be formed by cutting work. Therefore, much caution and slow handling are required to form a satisfactory isolation groove for a dynamic pressure bearing device, which resulting in reduced productivity due to low efficiency.
SUMMARY OF THE INVENTION
In view of the problems described above, it is an advantage of the present invention to provide a dynamic pressure bearing device capable of generating satisfactory dynamic pressure even if the recessed isolation grooves are not formed.
In order to achieve the above advantage, according to the present invention, there is provided a dynamic pressure bearing device including a plurality of dynamic pressure generation parts on a peripheral face either of a shaft member or a bearing member. The dynamic pressure generation parts are respectively formed in a circumferential direction at equal angular intervals and extended in an axial direction so as to form a protruded part which makes the dimension of a minute gap the smallest and a recessed part which makes the dimension of the minute gap the largest. The dynamic pressure bearing device also includes a perfect circle part formed on the peripheral face at least on a shaft end side at a region which is adjacent to the dynamic pressure generation part where the protruded part and the recessed part are formed. The dimension of the minute gap in the perfect circle part is set to be the same as that in the protruded part.
The dynamic pressure bearing device according to the present invention is provided with the protruded part and the recessed part, but is not provided with a conventional recessed separation groove. Accordingly, the shaft member or the bearing member produced by, for example, a sintered mold body does not require the recessed separation groove by means of cutting work and therefore productivity of the dynamic pressure bearing device can be improved. In addition, since the recessed separation groove is not formed, the leakage of the lubricating fluid in the axial direction can be restrained.
In accordance with an embodiment of the present invention, the region which is adjacent to the dynamic pressure generation parts on the shaft end side is formed in the perfect circle part. Therefore, the rigidity in the center direction can be made larger and the deflection is hard to occur even when disturbances are applied at a low speed rotation. In addition, since the speed of rotation by which floating begins due to the dynamic pressure can be made lower, a metal-to-metal contact is hard to occur between the shaft member and the bearing member even at a low speed rotation, and hence the life of the dynamic pressure bearing device can be made longer.

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