Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-05-18
2001-10-23
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C384S123000
Reexamination Certificate
active
06307293
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor, and in particular, to a motor having a hydrodynamic bearing structure which makes use of a lubricating fluid between adjacent surfaces of a rotary member and a stationary member, the motor being adapted to rotate a data storage media such as a hard disk in a hard disk drive.
2. Background Information
Conventionally, there has been known and used a motor equipped with a hydrodynamic bearing device which uses fluid pressure created between a shaft body and a sleeve structure in order to rotatably support the shaft body and the sleeve structure such that one of them is rotatable relative to the other. An example of such a motor is described in detail below with reference to FIG.
1
.
FIG. 1
is a longitudinal sectional view schematically showing structure of a prior art motor
150
equipped with a bearing device using dynamic pressure of a fluid lubricant. As illustrated in
FIG. 1
, the conventional motor
150
equipped with a bearing configuration using hydrodynamic pressure has a cylindrical shaft housing
151
for rotatably supporting a rotary shaft
154
, and the cylindrical shaft housing
151
has a large diameter base portion
151
a
. The outer peripheral surface of a lower portion of the large diameter base portion
151
a
is fixedly fitted in a circular engaging hole
152
a
of a base plate
152
of a recording medium drive device. The base portion
151
a
is integrally formed with an annular ring-shaped plate portion
151
b
. The annular ring-shaped plate portion
151
b
is further integrally formed with a small diameter sleeve portion
151
c
that is coaxially aligned with the base portion
151
a
and located above the base portion
151
a
. Further, a thrust cover
153
is fixedly engaged with an inner recessed surface of the base portion
151
a
adjacent to the lower end thereof, thereby blocking and sealing a disk shaped internal space defined within the base portion
151
a.
In this way, a shaft supporting structure is thus formed with the use of the cylindrical shaft housing
151
and the thrust cover
153
. The rotary shaft
154
is supported in a vertical orientation within the sleeve portion
151
c
of the cylindrical shaft housing
151
by a fluid lubricant
155
, such as lubricating oil, that fills a clearance gap formed between surfaces of the rotary shaft
154
and the sleeve portion
151
c
due to liquid capillary action. The surfaces of the rotary shaft
154
and adjacent surfaces of the sleeve portion
151
c
serve as upper and lower radial bearings
170
and
171
using dynamic pressure of the lubricant
155
to support the rotary shaft
154
within the sleeve portion
151
c
such that the rotary shaft
154
is freely and relatively rotatable within the sleeve portion
151
c.
A ring-shaped thrust plate
156
is fixedly fitted to a lower end of the rotary shaft
154
and is positioned in the disk shaped internal space that is defined within the base portion
151
a
. A clearance gap defined in the disk shaped internal space between the surfaces of the ring-shaped thrust plate
156
and the inner surface of the base portion
151
a
, the inner surfaces of the annular ring-shaped plate portion
151
b
and an upper surface of the thrust cover
153
is filled with lubricant
155
retained therein by capillary action. Upper and lower surfaces of the ring-shaped thrust plate
156
and adjacent surfaces of the base portion
151
a
, the plate portion
151
b
and thrust cover
153
serve as upper and lower thrust bearings allowing the annular ring-shaped thrust plate
156
to rotate freely within the cylindrical shaft housing
151
in combination with the dynamic pressure of the lubricant
155
. In this manner, with the use of upper and lower hydrodynamic radial bearings
170
and
171
and upper and lower hydrodynamic thrust bearings, a hydrodynamic fluid bearing structure is formed which makes use of the hydrodynamic pressure of the fluid lubricant
155
during the relative rotation between the rotary shaft
154
(with the thrust plate
156
) and the cylindrical shaft housing
151
.
An annular groove
157
is formed at approximately a middle portion of the rotary shaft
154
separating the upper and lower radial bearings
170
and
171
. The annular groove
157
is surrounded by an adjacent portion of the inner surface of the sleeve portion
151
c
forming an annular air space
159
that communicates with atmosphere outside the motor via a breather hole
158
formed on the sleeve portion
151
c.
Herringbone grooves
160
a
and
160
b
are formed on lower and upper surfaces, respectively, of the thrust plate
156
. Herringbone grooves
160
c
and
160
d
are formed on inner surfaces of the sleeve portion
151
b
below and above the annular air space
159
, respectively. In response to rotation of the rotary shaft
154
, radial load supporting pressure and thrust load supporting pressure are generated in the lubricant
155
in and about the herringbone grooves
160
a
,
160
b
,
160
c
and
160
d.
A stator
161
formed with coil windings (not shown) around a stator core (not shown) is fixed on an outer surface of the sleeve portion
151
c
. A cup-like rotor hub
162
is formed with an outmost enclosure wall
162
a
that encircles the stator
161
. The upper end of the rotary shaft
154
extends into a center hole formed in the cup-like rotor hub
162
such that the rotary shaft
162
is engaged and fixed to the cup-like rotor hub
162
. A rotor magnet
163
is secured on an internal surface of the outmost enclosure wall
162
a
of the rotor hub
162
such that the rotor magnet
163
radially faces the stator
161
with a predetermined clearance space maintained therebetween thereby forming a rotation driving structure.
When using the above-described conventional hydrodynamic fluid bearing assembly having upper and lower radial hydrodynamic bearings and upper and lower hydrodynamic thrust bearings, the ring-shaped thrust plate
156
is used in the hydrodynamic thrust bearing structure. In order to ensure a stabilized support for the rotary shaft
154
in the axial direction and thereby minimize possible vibrations in that direction, both upper and lower surfaces of the thrust plate
156
must be used to form upper and lower thrust bearings. However, there is a problem associated with using both upper and lower surfaces of the thrust plate as bearings in that bearing losses due to, for instance, fluid friction, may be large and as a result the electric efficiency of the motor may be low.
When a hydrodynamic bearing motor
150
described above is to be installed in a thin hard disk drive (HDD) whose thickness is, for example, less than 5 mm, the sleeve portion
151
c
, the rotary shaft
154
, the stator
161
and the rotary magnet
163
somehow have to be made shorter in the vertical direction, as viewed in FIG.
1
. When a hydrodynamic bearing motor
150
is used in such a thin and low-noise hard disk drive with the motor being provided with both upper and lower radial hydrodynamic bearings, upper and lower thrust hydrodynamic bearings provided on upper and lower sides of a thrust plate
156
, the rotary shaft
154
and the thrust plate
156
may be supported stably with minimal axial vibrations. Although the thrust hydrodynamic bearings on both sides of the thrust plate may ensure stability of the rotary shaft
154
in the axial direction, the grooves
160
a
and
160
b
generate large viscous resistance against the flow of the lubricant
155
resulting in bearing loss making the motor electrically inefficient.
Also known is a hydrodynamic bearing motor in which no thrust plate
156
is employed. Instead a thrust bearing is formed on an end surface of a rotary shaft. In this case, although bearing loss is small and the motor is relatively electrically efficient, the motor requires some kind of axial movement prevention mechanism to prevent movement of the rotary shaft in the axial direction, since the rotary shaft does not have a projection such as a thrust plate for r
Judge James
Nidec Corporation
Perez Guillermo
Ramirez Nestor
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