Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-03-29
2002-01-29
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S090000, C310S089000, C384S204000
Reexamination Certificate
active
06342739
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a bearing fixing structure for a small-sized motor used as a drive motor in automotive-use electrical equipment, power tools, or the like, as well as to a method of manufacturing the same.
BACKGROUND ART
A conventional small-sized motor has an overall structure as shown in
FIG. 6
(see Japanese Patent Application Laid-Open (kokai) No. 3-234915). Permanent magnets
15
serving as stator magnet poles (generally, two poles) are attached to the inner surface of a motor casing
1
, which is formed of a metallic material into a closed-bottomed cylindrical shape. A cylindrical projection for receiving a bearing
4
(slide bearing) is provided at the center of the bottom portion of the motor casing
1
. A casing cover
8
is fitted into the opening of the motor casing
1
. A projection for receiving a bearing
12
(slide bearing) is provided at the center of the casing cover
8
. Brushes
11
and terminals
9
connected thereto are provided on the casing cover
8
. A core
13
, a winding
14
, and a commutator
10
are attached to a motor shaft
5
to constitute a rotor
16
.
Such a small-sized motor is assembled in the following manner. After one end of the motor shaft
5
of the rotor is inserted in the bearing
4
fitted into the center of the bottom portion of the motor casing
1
, the casing cover
8
carrying the brushes
11
and the terminals
9
is fitted into the opening of the motor casing
1
, while the other end of the motor shaft
5
is inserted into the bearing
12
fixed to the casing cover
8
. During the assembly, a bush
17
fixed to the motor shaft
5
positions the rotor
16
in the thrust direction (axial direction).
Such a small-sized motor sometimes encounters the problem of generation of mechanical vibration caused by a clearance between the motor shaft and the bearings. The applicant of the present application has proposed means for solving the problem of vibration generation, in the above-described Japanese Patent Application Laid-Open No. 3-234915. The proposed means will be described with reference to FIGS.
7
(A) and
7
(B).
FIG.
7
(A) shows a state in which the bearing
4
is press-fitted into a bearing support portion
2
, which is integral with the motor casing
1
. In this state, a relatively large clearance remains between the motor shaft
5
and the bearing
4
, because of limitations in mechanical machining. As shown in FIG.
7
(B), the clearance can be reduced forcedly through an operation of pressing the entirety of the outer circumferential surface of the bearing support portion
2
by use of a pressing jig
6
. When the bearing support portion
2
is pressed, the inner circumferential surface of the bearing
4
comes into contact with the motor shaft
5
. However, when the pressing jig
6
is moved, the bearing
4
produces a restoration force, so that a fine clearance necessary for rotation of the motor shaft is formed.
The above-described measure solves the problems caused by a radial clearance between the motor shaft and the bearing. However, the measure can solve neither a problem which arises when the perpendicularity of the bearing
4
and the bush
17
relative to the motor shaft deteriorates nor a problem which arises when the alignment between two bearings at the opposite ends of the motor shaft becomes incorrect. Further, the measure cannot decrease neither the clearance between the bearing and the bush or the end play with ease.
FIG. 8
shows an example bearing structure which can be used as the bearing
4
of the conventional small-sized motor shown in FIG.
6
.
FIG. 8
shows a lower half of a cross section taken along the center of the motor shaft
5
. In
FIG. 8
, reference numeral
2
denotes a cylindrical bearing support portion which is integrally formed with the metal motor casing
1
to be located at the center of the bottom portion and which is adapted to support the bearing
4
. Since the bearing
4
is press-fitted into the interior of the bearing support portion
2
, no clearance is formed between the outer circumferential surface of the bearing
4
and the inner circumferential surface of the bearing support portion
2
, and therefore the bearing
4
cannot move in the thrust direction relative to the bearing support portion
2
. Movement of the motor shaft
5
in the thrust direction is restricted by means of the bush
17
fixed to the motor shaft
5
.
As shown in FIGS.
9
(A) and
9
(B), the perpendicularity of the contact surface of the bearing
4
and the bush
17
relative to the motor shaft may deteriorate slightly due to insufficient precision arising in parts and assembly. FIG.
9
(B) shows a state in which the rotor rotates by 180 degrees from the position shown in FIG.
9
(A). When the end surface of the bush
17
in contact with an end surface of the bearing
4
cannot maintain a desired level of perpendicularity relative to the motor shaft, the rotor causes run-out, resulting in generation of noise.
Conventionally, the above-described problem is overcome through employment of a measure such that thrust movement of the motor shaft is absorbed by use of a wave washer or the like, or the end play (gap that allows thrust movement of the motor shaft) is reduced. However, use of a wave washer results in an increase in the number of parts, which increases cost. Further, in order to decrease the end play, the dimensional tolerance of each part must be decreased considerably. When the dimensional tolerance is set to a very small value, parts which fail the tolerance are often produced, resulting in an increase in cost. Alternatively, an adjustment washer or washers are provided for at least one of the two bearings, and the thickness of the washer (in the case of a single washer being used) or the number of washers (in the case of plural washers being used) is adjusted in order to reduce the end play. However, this method increases the number of fabrication steps, and is therefore not efficient.
Further, in order to cope with deterioration in the alignment between two bearing at the opposite ends of the motor shaft, it becomes necessary to increase the clearance between the motor shaft and the bearing or to taper the inner surface of the bearing to thereby provide play. However, in this case, when the alignment has not deteriorated, the motor shaft hits the bearing in the radial direction, resulting in generation of noise.
The problems involved in conventional techniques have been described with reference to exemplary cases in which “slide bearings” are used as bearings. However, the same problems arise in cases in which “ball bearings” are used.
FIG. 15
is a partially sectioned side view of a conventional small-sized motor using ball bearings with the rotor and casing cover being removed.
FIG. 16
is a view of the small-sized motor as viewed from the interior of the motor toward the bearing portion. In general, a slight clearance is provided outside a ball bearing
3
. In addition, for fixation of the ball bearing
3
, a bearing attachment
30
is used in order to eliminate the end play of the motor.
However, since fixation of the bearing attachment
30
carrying the ball bearing
3
is performed through caulking of caulking portions
31
formed integrally with the attachment
30
, the bearing attachment
30
itself must be formed to have a relatively large volume and a complicated shape, resulting in an increase in cost.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a bearing fixing structure for a small-sized motor which prevents run-out of a rotor and generation of noise even when the perpendicularity of a bearing and a bush relative to a motor shaft deteriorates slightly, as well as a method of manufacturing such a small-sized motor.
Another object of the present invention is to decrease the end play and the clearance between the bearing and the bush, without use of a special washer such as a wave washer or an adjustment washer and without necessity of decreasing the tolerance of each part to an extreme extent, to thereby reduce
Furuya Kenji
Yui Toshiya
Lam Thanh
Mabuchi Motor Co. Ltd.
McGlew and Tuttle , P.C.
Ramirez Nestor
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