Ball bearing

Details Ball bearing Ball bearing

2001-10-16

2002-11-05

Bucci, David A. (Department: 3682)

Bearings

Rotary bearing

Antifriction bearing

C384S513000, C384S450000

Reexamination Certificate

active

06474872

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a ball bearing for supporting a spindle which is incorporated into a hard disk drive unit (HDD), a video tape recorder (VTR), or a digital audio tape recorder (DAT) and can be rotated at a high speed.
For example, in the case of an HDD to be incorporated into a computer, such a drive motor as shown in
FIG. 1
is incorporated into the HDD and is used to drive and rotate a spindle
1
which is used to drive the HDD. Between the outer peripheral surface of the spindle
1
and the inner peripheral surface of a housing
2
, there are interposed a pair of ball bearings
3
,
3
. Each of the bearings has such a structure as shown in detail in FIG.
2
. The ball bearings
3
,
3
support the spindle
1
on the inside of the housing
2
in such a manner that the spindle
1
can be rotated freely. Each of the ball bearings
3
,
3
comprises a steel-made inner race
5
, a steel-made outer race
7
and a plurality of steel-made balls
8
,
8
. The steel-made inner race
5
has an inner race raceway
4
formed on the outer peripheral surface thereof. The steel-made outer race
7
has an outer race raceway
6
formed on the inner peripheral surface thereof. The plurality of steel-made balls
8
,
8
are rotatably interposed between the inner race and outer race raceways
4
and
6
. A retainer
9
rotatably retains these balls
8
,
8
. While the balls
8
,
8
are assembled to the drive motor, they are given preloads to thereby prevent them from playing when the spindle
1
is rotated.
In the case of the above-structured ball bearing
3
to be incorporated into the rotation support portion of the HDD, in view of the fact that it is used in the house interior, the ball bearing
3
is requested to be able to minimize the noises that are produced while it is in operation. In addition, at the same time, due to the enhanced density (increased storage capacity) and reduced size of the HDD in recent years, the ball bearing is requested to be able to minimize vibrations such as NRRO (Rotation asynchronous vibration). On the other hand, due to spread of OA equipment such as a notebook computer, in order to prevent trouble caused by impact loads that could be generated when the OA equipment is dropped because of wrong handling, the ball bearing
3
is further requested to be strong (impact-resistant) against the impact loads.
In order to enhance the impact resistance of the ball bearing
3
for this purpose, conventionally, there is known a technique to reduce the ratio of the radiuses of curvature of the inner race raceway
4
and outer race raceway
6
to the radiuses of curvature of the rolling surfaces of the respective balls
8
,
8
. (That is, there is known a technique to set the ratio of the radiuses of curvature of the inner race raceway
4
and outer race raceway
6
to the radiuses of the outside diameters of the respective balls
8
,
8
slightly larger than 0.5).
Namely, the ratio of the radiuses of curvature of the inner race raceway
4
and outer race raceway
6
to the radiuses of curvature of the rolling surfaces of the respective balls
8
,
8
are reduced. Contact ellipses existing on the contact portions between the raceways
4
,
6
and balls
8
,
8
are therefore increased in size, to thereby lower the surface pressures of these contact portions. Accordingly, even the above impact loads are not be able to produce such impressions in the raceways
4
,
6
that give rise to the above-mentioned vibrations.
However, a test conducted by the inventors et al. shows that, in case where the ratio of the radiuses of curvature of the inner race raceway
4
and outer race raceway
6
to the radiuses of curvature of the rolling surfaces of the respective balls
8
,
8
, is reduced, the rotation torque of the ball bearing
3
is increased. At that time, as a result of this, not only the power consumption of the OA equipment incorporating such ball bearing
3
therein is increased but also the ball bearing
3
is not be able to offer sufficient impact resistance. In other words, our test shows that, in case where the above-mentioned ratio of the radiuses of curvature is reduced, the static load rating increases but the impact resistance cannot be always enhanced. For example, when the inventors et al. conducted a drop test in conformity to a case where compact OA equipment is dropped, in the case of the ball bearing with the radius of curvature ratio reduced, the acoustics of the ball bearing were degraded. It is believed that such degraded acoustics were caused by the impressions formed after the OA equipment was dropped down onto the floor.
Specifically, as to the reason why such impressions were produced, the inventors believed as follows. In the case of the ball bearing
3
with the radius of curvature ratio reduced, the rolling surfaces of the balls
8
,
8
are easy to run onto the shoulders of the inner race raceway
4
and outer race raceway
6
due to the impact load applied to the ball bearing
3
. Further, in case where the rolling surfaces of the balls
8
,
8
run onto the raceway shoulders, impressions are produced on the rolling surfaces of the balls
8
,
8
due to excessive surface pressures caused by edge loads.
SUMMARY OF THE INVENTION
In view of the above, the inventors conceived that, by increasing the above-mentioned radius of curvature ratio as well as by reducing an interior geometric clearance, there can be realized a ball bearing
3
having a following feature. That is, in the ball bearing
3
, the rolling surfaces of the balls
8
,
8
can be made hard to run onto the shoulders of the inner race raceway
4
and outer race raceway
6
, the impact resistance thereof is enhanced.
That is, it is an object of the invention to provide such improved ball bearing.
In attaining the above object, according to the invention, there is provided a ball bearing which comprises an inner race
5
, an outer race
7
and a plurality of balls
8
,
8
. The inner race
5
includes on the outer peripheral surface thereof an inner race raceway
4
having an arc-shaped section. The outer race
7
includes on the inner peripheral surface thereof an outer race raceway
6
having an arc-shaped section. The plurality of balls
8
,
8
are rollably interposed between the inner race raceway
4
and outer race raceway
6
, and a retainer
9
for holding the balls
8
,
8
in such a manner that they are able to roll freely.
Especially, according to a first aspect of the invention, there is provided a ball bearing
3
, wherein the ratio r
i
/D
8
of the radius of curvature r
i
of the inner race raceway
4
to the outside diameter D
8
of the balls
8
,
8
is set in the range of 0.51~0.54 (this is, in the range from 0.51 to 0.54 with both inclusive). Also, the ratio r
e
/D
8
of the radius of curvature of the outer race raceway
6
to the outside diameter D
8
of the balls
8
,
8
is set in the range of 0.54~0.56 (this is, in the range from 0.54 to 0.56 with both inclusive). Further, the interior geometric clearance c is set at 13 &mgr;m or less.
By the way, the interior geometric clearance c is a value that can be obtained by subtracting the diameter D
4
of the inner race raceway
4
and the double of the diameter D
8
of the balls
8
,
8
from the diameter D
6
of the outer race raceway
6
(that is, D
6
−D
4
−2D
8
). The above-mentioned value (13 &mgr;m or less) is effective especially in a miniature ball bearing in which the inside diameter R
5
of the inner race
5
is 2.6 mm or less, and the diameter D
8
of the balls
8
,
8
is 2 mm or less.
Note that in the specification, as shown in
FIG. 2
, the diameter D
6
of the outer race raceway
6
means the largest diameter of the outer race raceway
6
that is defined at the deepest position of the arc-shaped section thereof. Further, the diameter D
4
is the smallest diameter of the inner race raceway
4
that is defined at the deepest position of the arc-shaped section thereof.
Also, according to a second aspect of the invention, there is provided a ball bearing

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