Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-12-12
2004-09-21
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S090000, C360S099080, C384S504000
Reexamination Certificate
active
06794774
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spindle motor suitable for use in a rotary drive unit, wherein the rotary drive unit is used in office automation equipment such as computers and the like, and in their peripheral equipment as well.
2. Description of the Related Art
As shown in
FIG. 4
, a conventional spindle motor, which serves as a magnetic disk drive component in a hard disk drive unit (one of computer peripheral equipments), has a construction in which: an upright shaft
42
has its base portion fixedly mounted in a base
41
; and, a rotor hub
43
forming a rotating member of the motor is rotatably mounted on the upright shaft
42
through a pair of an upper ball bearing
44
and a lower ball bearing
45
, inner rings
44
a
,
45
a
of which bearings
44
,
45
are axially spaced apart from each other, wherein the inner rings
44
a
and
45
a
belong to the upper ball bearing
44
and the lower ball bearing
45
, respectively, and have conventional steel balls
48
a
and
48
b
interposed between the inner rings
44
a
,
45
a
and their corresponding outer rings
44
b
,
45
b
, respectively; these ball bearing
44
and
45
have their outer rings
44
b
and
45
b
fitted in a sleeve
46
, respectively; the sleeve
46
is fitted in an axial center bore
47
of the rotor hub
43
; and, the ball bearings
44
,
45
have their inner rings
44
a
,
45
a
or their outer rings
44
b
,
45
b
bonded to the upright shaft
42
or to the sleeve
46
using an appropriate adhesive or like fastening means in a condition in which the inner ring
44
a
or the outer ring
44
b
of the upper ball bearing
44
is appropriately pressed from above in a manner such that the balls
48
a
,
48
b
are brought into press-contact with both the inner and the outer rings of these ball bearings
44
,
45
.
When the spindle motor is energized, a temperature of the motor goes up so that its individual components thermally expand at various expansion amounts. The relationship in thermal expansion amount in radial direction of these components of the ball bearings
44
,
45
is as follows: outer rings>inner rings>balls.
Consequently, when the temperature of the spindle motor goes up, a radial space or clearance between the inner ring and the corresponding outer ring in each of the ball bearings
44
,
45
increases. On the other hand, since the balls
48
a
,
48
b
are smaller in thermal expansion amount than the inner and the outer rings, a pre-load applied to each of the balls
48
a
,
48
b
by the inner and the outer rings is reduced, which results in variations in resonant frequency of the motor, and often results in the generation of the resonant vibration of the motor with a structural member to which the motor is mounted.
For example, in case that the conventional motor is used as a drive component of the hard disk drive unit, there is a fear that the conventional motor resonates to the structural member such as a swing arm, a casing and the like to impair the hard disk drive unit in accuracy in data reading and writing operations due to the drive unit's vibration and also to impair the hard disk drive unit in quietness in operation due to noises caused by the drive unit's vibration.
On the other hand, when differences in thermal expansion amount between the inner rings and the outer rings of the ball bearings
44
,
45
further increase, too much play appears between the balls and each of the inner and the outer rings, which causes considerable vibrations in rotation of the rotor hub
43
. Such vibrations of the rotor hub
43
cause a recording surface of the magnetic disk to vibrate in axial direction and considerably impairing the hard disk drive unit in reliability in operation.
Particularly, when the balls
48
a
,
48
b
are made of ceramics in order to improve the hard disk drive unit in reliability, the above-mentioned problem caused by the differences in thermal expansion amount among the individual components of the ball bearings becomes more serious, because the ceramic balls are much less in thermal expansion amount than the conventional steel balls.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a spindle motor, which is capable of keeping high rotation accuracies and having its inner and its outer rings brought into appropriate press-contact with its balls even when a temperature of the motor goes up to permit individual components of the motor to thermally expand at various expansion amounts, and further capable of being free from variations in resonant frequency and also free from vibrations in rotation.
In accordance with a first aspect of the present invention, the above object of the present invention is accomplished by providing:
In a spindle motor comprising: a first upright shaft fixedly mounted on abase; a pair of a first upper ball bearing and a first lower ball bearing both rotatably mounted on the first upright shaft and provided with a plurality of first balls between their first inner rings and their first outer rings; a first sleeve fitted to outer peripheral surfaces of the first outer rings; and, a rotor hub mounted on an outer peripheral surface of the first sleeve so that the rotor hub is rotatably supported on the base, the improvement wherein:
the rotor hub is provided with an axial center bore;
the axial center bore is provided with a pair of large-diameter bore portions in its opposite axial end portions together with a small-diameter bore portion which is axially interposed between the large-diameter bore portions;
an inner diameter of the small-diameter bore portion is smaller than an outer diameter of the first sleeve;
the axial center bore of the rotor hub is fitted to an outer peripheral surface of the first sleeve in an insertion manner through a heating shrinkage fit process, so that the first sleeve is subjected to a radially inwardly exerted pressure applied from outside to the first sleeve to deform resiliently radially inwardly;
whereby a small-diameter portion is formed in the first sleeve to extend radially inwardly between the first outer rings of the first upper ball bearing and the first lower ball bearing.
In the spindle motor of the present invention having the above construction, preferably, an annular groove is formed in an inner peripheral surface of the first sleeve in an axial position in which each of the first outer rings of the ball bearings is brought into contact with the inner peripheral surface of the first sleeve; and, the annular groove is substantially equal in axial width to an outer ring raceway of each of the first outer rings, wherein the outer ring raceway is formed in an inner peripheral surface of each of the outer rings.
In accordance with a second aspect of the present invention, the above object of the present invention is accomplished by providing:
In a spindle motor comprising: a stepped shaft i.e., a two-diameter shaft, provided with a large-diameter portion and a small-diameter portion; a second sleeve which surrounds the stepped shaft and provided with a pair of an upper outer ring raceway and a lower outer ring raceway both arranged parallel to each other in an inner peripheral surface of the second sleeve; an upper row of balls interposed between an upper inner ring raceway and the upper outer ring raceway of the second sleeve, wherein the upper inner ring raceway is formed in an outer peripheral surface of an inner ring which is fitted to the small-diameter portion of the stepped shaft in an insertion manner; a lower row of balls interposed between a lower inner ring raceway and the lower outer ring raceway which is formed in a lower portion of the inner peripheral surface of the second sleeve, wherein the lower inner ring raceway is formed directly in an outer peripheral surface of the large-diameter portion of the stepped shaft; the second sleeve, the balls, the inner ring and the stepped shaft are combined with each other to form a compound bearing assembly, wherein a base portion of the large-diameter portio
Obara Rikuro
Yoshikawa Hiroshi
Gopstein Israel
Minebea Kabushiki-Kaisha
Nguyen Tran
LandOfFree
Spindle 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 Spindle motor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spindle motor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3203795