Hydrodynamic bearing and motor having the same

Details Hydrodynamic bearing and motor having the same Hydrodynamic bearing and motor having the same

2000-05-12

2002-04-02

Hannon, Thomas R. (Department: 3682)

Bearings

Rotary bearing

Fluid bearing

C384S100000, C384S114000

Reexamination Certificate

active

06364532

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a hydrodynamic bearing for a motor and the motor having the same, which is used for a data processing apparatus such as a data storing apparatus having a disk drive, or a printer, or, for an entertainment apparatus having a disk drive for recording or reproducing images or sounds, or the like.
BACKGROUND OF THE INVENTION
In recent years, under the circumstance that the reduction of size and weight, high density recording, high speed data processing and the like are required in a data processing apparatus or in an entertainment apparatus, the improvement of the performance of a motor (small spindle motor in this occasion) used for the apparatus is also required.
In regard to the improvement of the performance of the motor, the reduction of the rotational runout of the rotor of the motor, the reduction of the noise and the improvement on the durability of the motor are mostly required, for which the improvement of the performance of a bearing used for the motor is also required.
The runout of the rotor and the noise of the motor are caused by the magnetic attraction and repulsion between the rotor magnet and the stator of the motor. That is, the rotating shaft of the rotor radially vibrates and bumps against the bearing of the rotor when the rotor is rotated. A conventional motor having a bearing whose bearing is made of sintered oleo-metal can hardly reduce the runout and the noise of the motor to a sufficiently low level.
For the improvement on the above problems, a hydrodynamic bearing has been developed, and the bearing is now being put into practical use. The hydrodynamic bearing comprises, which denotes the dimension from the turning point
163
to the end thereof in the second side. That is, the second herringbone pattern
157
is asymmetrical.
An oil reserving groove
159
is formed on the inner wall of the sleeve
155
. The oil reserving groove
159
is located at the position which corresponds to the intermediate portion between the first herringbone pattern
156
and the second herringbone pattern
157
of the rotating shaft
154
. A through-hole
160
is formed through the wall of the sleeve
155
in such a manner that the through-hole
160
radially extends from the oil reserving groove
159
to the outside of the sleeve
155
.
In the above conventional structure, the dynamic pressure of the oil
161
, which is generated at the herringbone pattern
157
when the shaft
154
is rotated, forms a stream of the oil
161
, which flows toward the second side (i.e., the side where the shaft end
162
is located) since the width-E is larger than the width-F, which causes the occurrence of air bubbles in the oil
161
since air comes into the space in the sleeve
155
from the through-hole
160
. Then the air bubbles further push the oil
161
outward from the space in the sleeve
155
, which result in the shortage of oil
161
and causes the increase of the runout of the shaft
154
and the damage on the durability of the motor having the bearing.
FIG. 16
is a partially schematic sectional view showing another example of the structure of the hydrodynamic bearing. This type of bearing, which is also known in general, is disclosed in Japanese Utility Model Publication No.2560501.
In
FIG. 16
, a rotating shaft
164
is rotatably supported by a sleeve
165
. A thrust bearing plate
168
is fixed to the sleeve
165
and supports one end of the shaft
164
. Oil
169
is filled in the space formed with the sleeve
165
, the rotating shaft
164
and the thrust bearing plate
168
. On the outer wall of the rotating shaft
164
, a first herringbone pattern
167
and a second herringbone pattern
166
are formed. The first herringbone pattern
167
is located at a first side (i.e., the side where the thrust bearing plate
168
is located). The second herringbone pattern
166
is located at a second side (i.e., the side opposite the first side). for example, a cylindrical rotating shaft and a sleeve, and, a fluid (oil, in most cases) is filled in a space formed with the sleeve and the rotating shaft which is inserted into the sleeve. A herringbone pattern is formed either on the shaft or on the sleeve. In the above structure, when the rotor is rotated, the rotating shaft is supported by the dynamic pressure of the fluid, which is generated at the herringbone pattern.
The hydrodynamic bearing has advantages that the size of the bearing can be reduced since the mechanical components and portions of the bearing share relatively small space comparing with that in the other bearings. Also, since the rotating shaft is supported by the sleeve via the fluid, the noise of the motor can be reduced, and the motor having the bearing is durable against shock. Also, since the load on the rotating shaft is supported by the whole circumference of the shaft (which generates an integral effect), the runout of the shaft is reduced. As is described above, the hydrodynamic bearing is structurally superior for the spindle motor.
In the hydrodynamic bearing, the structure disclosed in Japanese Non-Examined Patent Publication H6-137320 is known in general. The structure disclosed in the publication is described hereinafter with reference to
FIG. 15
which is a partially schematic sectional view showing the structure of the bearing.
In
FIG. 15
, a rotating shaft
154
is rotatably supported by a sleeve
155
. A thrust bearing plate
158
, which is fixed to the sleeve
155
, supports one end of the shaft
154
. Oil
161
is filled in the space formed with the sleeve
155
, the shaft
154
and the thrust bearing plate
158
. On the outer wall of the shaft
154
, a first herringbone pattern
156
and a second herringbone pattern
157
are formed. The first herringbone pattern
156
is located at a first side (i.e., at the side where the thrust bearing plate
158
is located). The second herringbone pattern
157
is located at a second side (i.e., the side opposite the first side).
In the second herringbone pattern
157
, width-E, which denotes the dimension from the turning point
163
of the pattern
157
to the end thereof in the first side, is larger than width-F
In the second herringbone pattern
166
, width-G, which denotes the dimension from the turning point of the pattern
166
to the end thereof in the second side, is larger than width-H which denotes the dimension from the turning point of the pattern
166
to the end thereof in the first side.
Also, in the first herringbone pattern
167
, width-I, which denotes the dimension from the turning point of the pattern
167
to the end thereof in the second side, is larger than width-J which denotes the dimension from the turning point of the pattern
167
to the end thereof in the first side. That is, both patterns
166
and
167
are respectively asymmetrical.
Also, two through-holes
170
and
171
are formed through the thrust bearing plate
168
.
In the above structure, the oil
169
flows outside from both through-holes
170
and
171
, such that the oil
169
has to be refilled for the continuous operation of the motor having this type of bearing. That is, the bearing is not suitable for continuous long time operation.
When the through-holes
170
and
171
are closed for preventing the leakage of the oil
169
, the pressure around the thrust bearing plate
168
becomes high and air bubbles occur there, such that the shaft
164
enters into a state of unstable floating relative to the thrust bearing plate
168
, which results in a serious problem, for instance, that the disk of a disk drive touches the pickup head of the disk drive when such a bearing is used for the spindle motor of the disk drive, due to the axial runout of the rotating shaft.
SUMMARY OF THE INVENTION
The object of the present invention is to address the problems in the conventional hydrodynamic bearing and to provide a durable hydrodynamic bearing in which the uniform and stable thickness of the oil film for the hydrodynamic bearing is realized for reducing both radial and axial runout of the rotating shaft. Another object

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