Hydrodynamic bearing

Details Hydrodynamic bearing Hydrodynamic bearing

1999-01-11

2001-03-06

Marmor, Charles A (Department: 3681)

Bearings

Rotary bearing

Fluid bearing

C384S124000, C384S135000

Reexamination Certificate

active

06196722

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a hydrodynamic bearing employing a dynamic-pressure hydraulic bearing for use in a disk recording device which is adapted to record and reproduce signals on a magnetic disk while rotating the magnetic disk, a rotary head for a video tape recorder which is rotated at a high speed, and the like.
BACKGROUND OF THE INVENTION
In recent years, recording apparatuses using disks and the like have increased in memory capacity and data transfer speed. This, in turn, has required a disk rotating device for use in such a recording apparatus to be capable of high-speed and high-precision rotation. To this end, a hydrodynamic bearing having a central shaft supported at its opposite ends as disclosed in U.S. Pat. No. 5,504,637 is used in a rotary main shaft of the recording apparatus.
A conventional hydrodynamic bearing will hereinafter be described with reference to
FIGS. 7 and 8
.
FIG. 7
illustrates a recording device employing the hydrodynamic bearing.
A sleeve
30
provided in the center of a hub
29
is rotatably fitted around a stationary shaft
22
having one end fixed to a lower casing
21
. Disks
35
A,
35
B,
35
C,
35
D as recording media are attached to the hub
29
as being spaced from each other by spacers
36
A,
36
B,
36
C.
A flange member
24
is attached to the other end of the stationary shaft
22
by an upper shaft
28
as being fitted in a step portion
30
A of the sleeve
30
. The upper shaft
28
has a male thread, which is threaded in the other end of the stationary shaft
22
so that the flange member
24
is press-fitted to the other end of the stationary shaft
22
.
A thrust plate
27
which is opposed to an upper face of the flange member
24
and an outer circumference of the upper shaft
28
is fixed in a recessed portion
29
A of the hub
29
.
One set or, typically, two sets of herringbone grooves
23
A,
23
B are provided in at least one of an outer circumferential portion of the stationary shaft
22
and an inner circumferential portion of the sleeve
30
. An inner spiral groove
26
is provided in either one of a surface of the step portion
30
A of the sleeve
30
and a face of the flange member
24
which are opposed to each other, and an outer spiral groove
25
is provided in at least one of opposed faces of the flange member
24
and the thrust plate
27
. These grooves
23
A,
23
B,
25
,
26
and an oil pit
30
B are filled with a lubricant
31
.
A motor rotor
33
is fixed to the hub
29
, and a motor stator
32
is fixed to the lower casing
21
. Further, an upper casing
34
is attached to the upper shaft
28
.
In the conventional hydrodynamic bearing, the motor rotor
33
starts co-rotating with the hub
29
, the sleeve
30
, the thrust plate
27
, the disks
35
A,
35
B,
35
C,
35
D and the spacers
36
A,
36
B,
36
C, when the motor stator
32
is energized to develop a rotating magnetic field.
At this time, the herringbone grooves
23
A,
23
B collect the lubricant
31
to generate a pressure by pumping action, and the outer spiral groove
25
and the inner spiral groove
26
also collect the lubricant
31
. The pressure thus generated causes the hub
29
to rotate in a completely non-contacting state with respect to the stationary shaft
22
.
However, the aforesaid arrangement has the following drawbacks.
Since the inner diameter D
2
of the thrust plate
27
is slightly greater than the inner diameter D
1
of a bearing portion of the sleeve
30
as shown in
FIG. 8
, the lubricant
31
filled in the herringbone grooves
23
A,
23
B flows out through the step portion
30
A and scatters over the thrust plate
27
as indicated by
31
A due to a centrifugal force exerted thereon during high speed rotation.
Further, when air which is dissolved into the lubricant through air-liquid interfaces
38
A,
38
B during the rotation is accumulated in the oil pit
30
B and the like and grows into bubbles
37
A,
37
B,
37
C,
37
D, the air-liquid interfaces
38
A,
38
B are bulged, so that the lubricant
31
flows out from the upper side as indicated by
31
A and
31
B, and from the lower side as indicated by
31
C in FIG.
8
. This results in depletion of the lubricant
31
in the herringbone grooves
23
A,
23
B, the outer spiral groove
25
and the inner spiral groove
26
.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a hydrodynamic bearing which is free from the flow-out of a lubricant from a bearing portion thereof and is highly reliable.
The hydrodynamic bearing according to the present invention is characterized in that lower and upper end portions of a stationary shaft are properly spaced from a sleeve and a thrust plate, respectively, and that an air channel is provided inside the stationary shaft with one end thereof opening to a space defined by an outer circumferential portion of the stationary shaft and the sleeve between radial grooves and thrust grooves and with the other end thereof communicating with the outside.
In accordance with the present invention, the lubricant is prevented from flowing out from two open sides of the stationary shaft around the upper and lower end portions thereof, and air bubbles accumulated in the space between the stationary shaft and the sleeve during rotation are expelled through the air channel to the outside. Therefore, the hydrodynamic bearing has a highly reliable construction which is free from the flow-out of the lubricant from the bearing portion thereof.
In accordance with claim
1
of the present invention, there is provided a hydrodynamic bearing which comprises: a stationary shaft fixed at one end thereof to a lower casing and having a flange member and an upper shaft portion adjacent to the other end thereof; a sleeve having a bearing bore in which the stationary shaft is inserted; and a thrust plate fixed to the sleeve and having a face opposed to a plane face of the flange member and an inner circumferential portion opposed to an outer circumferential portion of the upper shaft portion; wherein radial hydrodynamic grooves are provided in at least one of an outer circumferential portion of the stationary shaft and an inner circumferential portion of the sleeve which are opposed to each other; wherein an outer thrust hydrodynamic groove is provided in at least one of the opposed faces of the flange member and the thrust plate; wherein an outer diameter of the upper shaft portion and a diameter of the inner circumferential portion of the thrust plate are smaller than a diameter of the bearing bore of the sleeve; wherein the stationary shaft has a tapered portion provided on a side thereof opposite across the radial hydrodynamic grooves from the flange member and having a progressively decreasing diameter apart from the flange member; wherein the radial hydrodynamic grooves and the outer thrust hydrodynamic groove are filled with a lubricant; and wherein an air channel is provided inside the stationary shaft with one end thereof opening on an outer circumferential portion of the stationary shaft intermediate the flange member and the radial hydrodynamic grooves and with the other end thereof communicating with the outside.
In accordance with claim
2
of the present invention, there is provided a hydrodynamic bearing which has substantially the same construction as the hydrodynamic bearing according to claim
1
, except that the upper shaft portion of the stationary shaft has a tapered portion which is opposed to the inner circumferential portion of the thrust plate and has a progressively decreasing diameter as it extends apart from the flange member, instead of the arrangement that the outer diameter of the upper shaft portion and the diameter of the inner circumferential portion of the thrust plate are smaller than the diameter of the bearing bore of the sleeve.
In accordance with claim
3
of the present invention, the hydrodynamic bearing according to claim
1
or
2
is characterized in that the upper face, outer circumferential surface and lower face of the flange member are closely adjacent to the t

Affiliated with

Also associated with

Rating

Hydrodynamic bearing does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Hydrodynamic bearing, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydrodynamic bearing will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2547649