Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
1999-06-16
2001-07-24
Estremsky, Sherry (Department: 3681)
Bearings
Rotary bearing
Fluid bearing
C384S124000
Reexamination Certificate
active
06264368
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to spindle motors for use in information, audio and video equipment and more particularly to a fluid bearing motor fit for use in a magnetic disk unit, an optical disk unit or the like.
As a conventional fluid bearing motor, there is a fluid bearing motor for a magnetic disk as shown in
FIG. 9
, for example.
In this fluid bearing motor, a thrust collar
51
is fixed to the outer peripheral surface
50
a
of a shaft member
50
, and a thrust fluid bearing portion
100
is formed among the outer peripheral surface
50
a,
an undersurface
51
b
of the thrust collar
51
and an upper surface
52
b
of a sleeve
52
which faces the undersurface
51
b.
Further, a radial fluid bearing portion
200
is formed under the thrust collar
51
and between the outer peripheral surface
50
a
of the shaft member
50
and an inner peripheral surface
52
c
of the sleeve
52
.
In
FIG. 9
, reference numeral
53
denotes a stator,
54
indicates a rotor magnet, and
55
defines a back yoke.
However, bubbles may remain in the thrust fluid bearing portion
100
of such a fluid bearing motor when a lubricating fluid is poured into the thrust fluid bearing portion
100
and may also be mixed with the lubricating fluid in the thrust fluid bearing portion
200
due to the repetition of starting and stopping the operation. When the temperature of the lubricating fluid rises in such a state that the bubbles have thus been mixed therein, the lubricating fluid may be forced out through the bearing gaps because of the expansion of air, to thereby occur a problem that the reliability of the fluid bearing motor is deteriorated.
Moreover, the lubricating fluid tends to scatter because of the high-speed rotation or otherwise to become easily exhausted from the thrust fluid bearing portion as it evaporates during long-term use. Another problem is that the thrust fluid bearing may often seize during long-term use.
Method for solving the foregoing problems is suggested in the Japanese Patent Unexamined Publication No. Hei. 8-163820. The invention taught by the publication No. Hei. 8-163820 is such that, as shown in
FIG. 10
, a groove
60
is formed circumferentially in the outer peripheral face of a thrust collar
51
in such a way as to form a true circular contour
60
a
which is eccentric with respect to the thrust collar
51
as well as a shaft member
50
in order to make the shallow portion of the groove
60
or a portion without the groove
60
a reservoir
61
for storing a lubricating fluid while making the deep portion of the groove
60
an air chamber
62
by varying the volume of the diametric space between the thrust collar
51
and the inner peripheral face of a sleeve
52
. Further, providing a fluid channel
63
for communicating the air chamber
62
with the atmosphere causes the bubbles mixed with the lubricating fluid in the bearing gap to be gathered in the air chamber
62
before being discharged outside through the fluid channel
63
.
Further, an oil supply channel
64
similar in structure to the fluid channel
6
.
3
communicates with the reservoir position opposite to the air chamber
62
(if the groove
60
is shallow or otherwise non-existent). In this conventional fluid bearing motor, it is intended to prevent the lubricating fluid from being exhausted from the thrust fluid bearing portion by supplying the lubricating fluid from the reservoir
61
via the oil supply channel
64
to the inner diameter side of the thrust fluid bearing portion.
The contour of the outer peripheral face of the thrust collar
51
and the contour of the inner peripheral face
52
a
of the sleeve
52
diametrically opposite to the outer peripheral face thereto as disclosed in the Japanese Patent Unexamined Publication No. Hei. 8-163820 are true circles in both cases.
Although the oil supply channel
64
is allowed to communicate with the reservoir
61
in the device of the Japanese Patent Unexamined Publication No. Hei. 8-163820, the present inventors found by experiment that the existence of the oil supply channel
64
resulted in weakening the generation of a wedge film itself and instead of supplying the lubricating fluid from the reservoir
61
onto the inner diameter side of the thrust fluid bearing portion the oil supply chambers causes bubbles to be readily discharged into the lubricating fluid bearing within the reservoir as the air flowed backward under the influence of the oil supply channel
64
which was opened to an area where the negative pressure passing the pressure peak of the wedge film is generated, that is, opened close to the area where the cavitation occurs. Since the bubbles thus discharged revolve in the eccentric groove
60
formed in the outer peripheral face of the thrust collar as the fluid revolves, there develops a problem of slightly moving the rotational axis during the revolution of the bubbles.
It was also found from the results of observation above that in such an arrangement as to provide the reservoir and the air chamber by forming the true circle eccentrically with reference to the rotational center, the rotational axis was slightly moved. In other words, the rotational center was forced to move in one direction by the pressure generated by the wedge effect of the reservoir portion having only the narrow gap as the speed increased even though no bubbles were generated; the problem in this case is that an unfavorable influence resulting therefrom becomes conspicuous during the high-speed rotational operation in particular.
When applied to magnetic disk units, fluid bearing motors are required to have higher rotational accuracy with the progress of developing-high-speed disk units and attaining improved surface recording density. Consequently, even slight movement of the rotational axis during the high-speed rotational operation becomes increasingly problematical and in addition to improvement in reliability and durability, it is urgently necessary to solve the foregoing problems.
SUMMARY OF THE INVENTION
An object of the present invention in view of the foregoing problems is to provide a fluid bearing motor capable of securing an air chamber for quickly discharging bubbles which are mixed with a fluid in a thrust fluid bearing portion and a reservoir for providing a lubricating fluid bearing for the thrust fluid bearing portion and offering higher rotational accuracy.
In order to accomplish the object above, a fluid bearing motor according to the present invention comprises a shaft member and a sleeve as a mating member cooperating with the shaft member, wherein the shaft member has a thrust collar extending in a diametric direction; thrust fluid bearings are formed among both sides of the thrust collar and the mating member; a reservoir for storing a lubricating fluid and an air chamber with air existing therein are formed between the outer peripheral face of the thrust collar and the mating member along the circumferential direction; and the air chamber communicates with the atmosphere via a fluid channel, and is characterized in that the whole or part of a circumferentially-directed contour of at least one of the outer peripheral face of the thrust collar and the face of the mating member is formed so that a gap between the outer peripheral face of the thrust collar and the face of the mating member varies in the circumferential direction and that a relatively small gap portion out of the gap between the outer peripheral face of the thrust collar and the face of the mating member is formed as the reservoir, whereas a relatively large gap portion out of the gap therebetween is formed as the air chamber.
The aforementioned “the whole or part of one of the faces” also includes a case where not only part of the circumferentially-directed but also part of the axially-directed contour in the circumferential direction is varied (also inclusive of a case where a groove is formed in the outer peripheral face of the thrust collar).
According to the present invention, part or the whole of the circumferentially-direct
Sakatani Ikunori
Tanaka Katsuhiko
Uemura Kazuhiro
Estremsky Sherry
NSK Ltd.
Pang Roger
Sughrue Mion Zinn Macpeak & Seas, PLLC
LandOfFree
Fluid bearing motor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fluid bearing motor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fluid bearing motor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2450227