Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-06-16
2001-06-12
Waks, Joseph (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C384S107000
Reexamination Certificate
active
06246136
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to a motor. More specifically, the present invention relates to a motor such as a spindle motor having hydrodynamic beatings, the spindle motor adapted to be provided in a disk-driving device for rotationally driving a data storage media such as a hard disk. The present invention also relates to a method for manufacturing the motor.
2. Background Information
FIG. 1
is a cross sectional view of a spindle motor (an electric motor), provided with hydrodynamic bearings that make use of the dynamic pressure of a lubricating fluid, for driving at least one data storage medium such as hard disk. The spindle motor depicted in
FIG. 1
is described in detail in co-pending application Ser. No. 09/267,621, filed Mar. 15, 1999, now U.S. Pat. No. 6,066,903. The content of and disclosure in U.S. Pat. No. 6,066,903 is hereby incorporated by reference in its entirety.
The spindle motor depicted in
FIG. 1
includes a stationary shaft
12
fixed to a base
10
and a rotor
11
rotatably supported by the stationary shaft
12
via hydrodynamic bearings. A lower end of the stationary shaft
12
is fixedly fitted in a coupling bore of a base
10
(base portion).
The stationary shaft
12
includes two main components: a stationary shaft portion
12
a
which extends rigidly upward from the base
10
; and a stationary thrust plate
12
b
which is an annular plate member fixedly and coaxially fitted to an upper portion of the stationary shaft portion
12
a.
The rotor
11
includes a rotary sleeve
18
that fits over the outer periphery of the stationary shaft
12
with a gap defined between opposing surfaces of the stationary shaft
12
and of the rotary sleeve
18
. The rotary sleeve
18
includes a cylindrical rotor hub
18
a
and an annular rotary thrust plate
18
b
fixedly fitted into a portion of the rotary sleeve
18
.
A hard disk (not shown) of a hard disk drive is carried on an outer peripheral portion of a cylindrical surface of the cylindrical rotor hub
18
a.
The rotary thrust plate
18
b
is fixedly fitted in a large inner diameter portion
18
a
4
to partially define a thrust bearing gap
20
around the stationary thrust plate
12
b
. The thrust bearing gap
20
is defined between the opposing surfaces of the stationary and rotary thrust plates
12
b
and
18
b
and between the surfaces of the stationary thrust plate
12
b
and the side and bottom surfaces of a recess formed within a middle inner diameter portion
18
a
3
of the rotary sleeve
18
. Above the rotary thrust plate
18
b
in the large inner diameter portion
18
a
4
, an annular plate-shaped seal member
22
is fixedly fitted in place.
The radially inner portion of the surface which partially defines the upper portion of the thrust gap
20
, specifically, the radially inner portion of the bottom or lower inclined surface
100
of the rotary thrust plate
18
b
, is tapered such that the lower inclined surface
100
of the rotary thrust plate
18
b
is inclined upward toward the center of the stationary shaft
12
. As a result, an air space
29
defined between the lower inclined surface
100
of the rotary thrust plate
18
b
and the upper flat surface of the stationary thrust plate
12
b
progressively increases toward the center of the stationary shaft
12
to form a tapered seal of an upper thrust bearing
40
.
A radially inner portion of the surface of the rotary sleeve
18
is formed with a tapered surface
20
a
that is inclined downward toward the radially inner direction thereby defining a tapered seal of a lower thrust bearing
42
.
Lubricant
44
is provided as needed in the gap between the stationary shaft
12
and the rotary sleeve
18
, in particular in the regions depicted in FIG.
1
. The lubricant
44
is retained at each respective position by the above described tapered seals, and in particular as a result of the surface tension created on the surface of the lubricant
44
.
The effects of surface tension in the lubricant
44
cause formation of a meniscus in each exposed portion of the lubricant
44
, for example between the lower inclined surface
100
and the adjacent surface of the stationary thrust plate
12
b
. The meniscus, in effect, defines an interface between the lubricant
44
and air. There are upper and lower interfaces defined by the meniscus of the lubricant
44
in the annular gaps between the walls defining the thrust bearing gap
20
and the surfaces of the stationary thrust plate
12
b
. The upper and lower interfaces face radially inward at the air space
29
and first oil separating space
32
. An annular oil-free space
46
is defined at an inner periphery from the lower interface (lower meniscus) of the lubricant
44
at the first oil separating space
32
.
On an inner peripheral surface of the stationary thrust plate
12
b
, an axial groove is formed. When the stationary thrust plate
12
b
is fixedly fitted on the stationary shaft portion
12
a
, the axial groove defines a breathing bore
48
between the outer peripheral surface of the stationary shaft portion
12
a
and the inner peripheral surface of the stationary thrust plate
12
b
. The breathing bore
48
connects the annular oil free space
46
to the air outside of the spindle motor via the annular space
31
, a gap between the outer peripheral surface of the stationary shaft portion
12
a
and the inner peripheral surfaces of the rotary thrust plate
18
b
, the lubricant catching groove
30
, and a gap between the outer peripheral surface of the stationary shaft portion
12
a
and the seal member
22
. The breathing bore
48
has a cross sectional size that is large enough so as not to be closed by the lubricant
44
due to surface tension. The breathing bore
48
can be formed at a plurality of positions of the stationary thrust plate
12
b.
An upper radial bearing
56
and a lower radial bearing
58
are formed by herringbone groove portions
54
and
55
, respectively, of the inner peripheral surface of the journal portion
18
a
1
and the portions of the outer peripheral surface of the stationary shaft member
12
a
that face the herringbone grooves
54
and
55
. The upper radial bearing
56
is located immediately beneath the first oil separating space
32
. The lower radial bearing
58
is located between the air space
28
and a second oil separating space
62
.
An air communication or conduit bore
64
is formed inside the stationary shaft portion
12
a
. The bore
64
includes a lower opening
64
a
which is open to the lubricant
44
in the lower radial bearing
58
, and the bore
64
includes an upper opening
64
b
which is open to the second oil separating space
62
. The lower opening
64
a
is disposed in the proximity of a boundary between the lower radial bearing
58
and the air space
28
. The upper opening
64
b
is disposed in the proximity of a boundary between the upper portion and the lower portion of the second oil separating space
62
.
The spindle motor described above is typically assembled by first inserting a lower portion of the stationary shaft portion
12
a
into the rotary sleeve
18
such that, for instance, only the portion of the shaft portion
12
a
below the upper opening
64
b
is inserted into the rotary sleeve
18
. Lubricant, such as the lubricant
44
, is applied to the portion of the shaft portion
12
a
proximate the upper opening
64
b
. Thereafter, the shaft portion
12
a
is lowered into the rotary sleeve
18
thereby drawing and spreading the lubricant down into the portions of the rotary sleeve
18
which subsequently form the radial hydrodynamic bearings
56
and
58
and the lower thrust bearing
42
. Lubricant
44
is also applied to the upper surface of the thrust plate
12
b
after completely inserting the thrust plate
12
b
and shaft
12
into the rotary sleeve
18
. Next, the rotary thrust plate
18
b
is fitted to the opening of the rotary sleeve
18
above the thrust plate
12
b
. The rotary thrust plate
18
b
and the rotary sleeve
18
are adhered to one another by, for in
Nidec Corporation
Shinjyu Intellectual Property Firm
Waks Joseph
LandOfFree
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