Motor

Details Motor Motor

2002-04-17

2004-05-11

Lam, Thanh (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S06700R

Reexamination Certificate

active

06734590

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor for driving magnetic disks such as a spindle motor used in the hard disk drive device of the computer.
2. Description of the Related Art
Recently, the field of the hard disk drive device has been making steady progress in increasing capacity thereof. In order to optimize such a progress in increasing capacity, there is a growing need for higher rotational speed for the motor used in the hard disk drive device. As a bearing for such a motor, a ball bearing has been generally used so far. However, in order to optimize the need for higher rotational speed, application of fluid dynamic bearings has been introduced.
As an example of the motor used in the hard disk drive device and comprising a fluid dynamic bearing, there is shown in
FIG. 20
a spindle motor for driving magnetic disks. The spindle motor
1
for driving magnetic disks (hereinafter, referred to as a spindle motor) is provided with a magnet
5
on the rotor
4
so as to face toward the stator
3
provided on the flange
2
.
The flange
2
generally comprises a flange body
6
for holding the stator
3
, and a sleeve
7
to be press-fitted into the hole (sleeve fitting hole
6
a
) formed on the flange body
6
.
The sleeve
7
generally comprises a cylindrical sleeve body
9
and a disk-shaped counter plate
11
.
The sleeve body
9
comprises a hole (no reference numeral is assigned) extending from one side (the upper side in
FIG. 20
) to the other side (the lower side in
FIG. 20
) for inserting a shaft
12
therein, and the hole is constructed of a hole formed on one side (hereinafter, referred to as a sleeve hole)
7
a
and an annular stepped portion
8
formed concentrically and in communication with the sleeve hole
7
a
via a step.
As shown in FIG.
21
and
FIG. 22
, the annular stepped portion
8
comprises an annular hole
8
a
having a larger inner diameter in comparison with the sleeve hole
7
a
and formed in communication with the sleeve hole
7
a
via a step (hereinafter, referred to as a medium diameter annular hole), and an annular hole having a larger inner diameter in comparison with the medium diameter annular hole
8
a
and formed in communication with the medium diameter annular hole
8
a
via a step hereinafter, referred to as large diameter annular hole). The large diameter annular hole
8
b
opens at one end (the lower side in
FIG. 21
) of the sleeve body
9
. The counter plate
11
is disposed at the large diameter annular hole
8
b
, and the counter plate
11
and the sleeve body
9
are hermetically connected by welding or the like.
The shaft
12
comprises a shaft body
12
a
, and an annular body
10
fitted on one end (the lower portion in
FIG. 20
) of the shaft body
12
a
. The annular body
10
of the shaft
12
is disposed in the medium diameter annular hole
8
a
and the shaft body
12
a
of the shaft
12
is inserted into the sleeve hole
7
a.
As described above, the annular body
10
of the shaft
12
is disposed in the medium annular hole
8
a
and the shaft body
12
a
of the shaft
12
is inserted into the sleeve hole
7
a
, and the sleeve
7
constitutes a fluid dynamic bearing
13
with the shaft
12
. Though oil
14
is generally used as a fluid for the fluid dynamic bearing
13
, it may be constructed to use gas such as air.
In other words, a plurality of rows of groves
15
are formed on the inner wall (sleeve hole
7
a
) of the sleeve body
9
, and a plurality of rows of grooves (not shown) are formed on the end portion of the annular body
10
that touches the stepped wall surface of the medium annular hole
8
a
of the sleeve body
9
and the portion of the upper surface of the counter plate
11
that touches the annular body
10
. Oil
14
is filled and reserved in the gap between the sleeve
7
including the grooves
15
and the shaft
12
, and in the grooves that are not shown in the figure. The inner peripheral surface of the annular body
10
is formed with a fluid circulating groove
10
a
so as to facilitate circulation of the fluid. The annular body
10
slightly projects toward the counter plate
11
with respect to the shaft
12
, so as to facilitate inflow and outflow of fluid from and to the fluid circulating groove
10
a.
The annular body
10
of the shaft
12
is disposed at the medium diameter annular hole
8
a
, that is, between the wall surface of the medium diameter annular hole
8
a
that faces in the axial direction (the upper side in
FIG. 20
) and the counter plate
11
, so that the axial movement (vertical movement in
FIG. 20
) of the shaft
12
is controlled via the annular body
10
.
The dynamic pressure generated by the pumping action in association with rotation of the shaft
12
forces a fluid layer to be formed between the sleeve
7
and the shaft
12
, and the shaft
12
that touched the counter plate
11
as shown in
FIG. 21
during the rest time rises from the counter plate
11
as shown in
FIG. 22
, so that the shaft
12
can rotate with respect to the sleeve
7
via the fluid layer. The fluid dynamic bearing
13
forms a fluid layer by the dynamic pressure and forms a gap between the shaft
12
and the counter plate
11
to support a thrust load of the shaft
12
as described above [in other words, the counter plate
11
supports a thrust load applied downwardly of the shaft
12
(in the direction of the arrow D in FIG.
20
), and the ceiling wall of the medium diameter annular hole portion
8
a
supports a thrust load applied upwardly of the shaft
12
(annular body
10
) (in the direction of the arrow U in FIG.
20
)], and a radial load of the shaft
12
is supported by the portion of the sleeve
7
where the sleeve hole
7
a
is formed.
Referring now to FIG.
21
and
FIG. 22
, the operation of the fluid dynamic bearing of the related art will be described.
FIG. 22
shows a state in which the
12
is rotated and the dynamic pressure of a fluid is generated.
In
FIG. 22
, when the spindle motor
1
is actuated and the shaft
12
starts rotating, the dynamic pressure is generated and thus a fluid layer is formed in the gap formed between the inner diameter surface of the sleeve
7
that is a fixed body and the outer peripheral surface of the shaft
12
that is a rotating body, between the stepped end surface (annular stepped portion
8
) of the sleeve
7
and the opposing end surface of the annual body
10
, between the wall surface of the medium diameter annular hole
8
a
of the sleeve
7
and the outer diameter surface of the annular body
10
, and between the upper surface
11
a
(inner end surface) of the counter plate
11
that is fitted into the sleeve
7
and the end surface
10
b
of the annular body
10
and the end surface
12
b
of the shaft body
12
a
, so that the rotating portion can rotate without touching the stationary portion, thereby forming a fluid dynamic bearing.
In
FIG. 22
, G07 designates an axial distance of the gap formed between the end surface
10
b
of the annular body
10
and the upper surface
11
a
of the counter plate
11
when the rotor
4
(shaft
12
) is rotated at a specified rotational speed.
FIG. 21
shows that state of the end portion of the shaft when the spindle motor
1
is oriented in such a manner that the counter plate
11
faces downward when the rotation of the shaft
12
is stopped and remained at rest.
In
FIG. 21
, loads of the hub
32
, the yolk
41
, and the magnet
5
assembled to the shaft
12
shown in
FIG. 20
are applied downward, and thus the shaft
12
on which the annular body
10
is fitted moves downward, whereby the end surface
10
b
of the annular body
10
touches the upper surface
11
a
of the counter plate
11
via a thin fluid layer. Since the fluid layer interposed between the upper surface
11
a
of the counter plate
11
and the end surface
10
b
of the annular body
10
is extremely thin, a gap G17 between the upper surface
11
a
of the counter plate
11
and the end surface
10
b
of the annular body
10
becomes extremely small value, or otherwis

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