Small-size motor

Details Small-size motor Small-size motor

2000-03-16

2002-01-15

Nguyen, Tran (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S06700R, C360S098080, C360S099050, C360S098070

Reexamination Certificate

active

06339273

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a small-size motor which is suitable for rotating CD, DVD, MD, or CD-ROM, DVD-ROM, and other various types of information recording discs (referred to simply as “discs”), and applicable to other various uses.
An example of a disc drive motor is shown in FIG.
8
. As shown, a motor
60
is generally composed of a stator section
64
and a rotor section
65
. The stator section
64
includes a base board
64
a
, a sintered oil-contained bearing
64
b
fastened to the base board
64
a
, a stator core
64
c
which is fastened to the outer circumferential face of the sintered oil-contained bearing
64
b
while being arranged coaxially with the bearing, and a coil winding
64
d
wound around protruding poles of the stator core
64
c.
The rotor section
65
includes a rotary shaft
65
b
rotatably supported with the aid of the sintered oil-contained bearing
64
b
, a cup-shaped rotor case
65
c
which is coupled to the rotary shaft
65
b
so as to rotate together with the latter, and an annular rotor magnet
65
d
fastened to the inner circumferential face of the rotor case
65
c.
A thick, annular boss
67
with a disc-like flange
67
a
formed therearound is fitted into the central portion of the rotor case
65
c
. The rotary shaft
65
b
is press-fitted into a center hole of the annular boss
67
. With this structure, the rotor case
65
c
is coupled to the rotary shaft
65
b
with the annular boss
67
intervening therebetween, whereby the rotor case and the rotary shaft are rotated together.
A tapered portion
67
b
is formed around the lower end of the center hole of the annular boss
67
. The tapered portion
67
b
is formed so as to assist the press-fitting of the rotary shaft
65
b
into the center hole of the annular boss
67
.
A chucking mechanism
63
is provided around a portion of the rotary shaft
65
b
, which is extended above the upper face of the rotor case
65
c
.The chucking mechanism
63
is generally formed with a fitting member
68
to be fitted into the center hole of the disc, clamping members
69
provided at a plurality of locations on the outer circumferential face of the fitting member
68
, and a plurality of urging members
70
for radially urging the clamping members
69
respectively.
Some recent technical requirements are to thin the motor and to improve a shock resistance of the motor. This necessitates increase of a coupling force of the rotary shaft
65
b
to the annular boss
67
.
A possible approach to increase the coupling force of the rotary shaft
65
b
with the annular boss
67
is to increase a length &agr; of the center hole of the annular boss
67
as viewed in the axial direction as shown in FIG.
9
. However, this coupling-force increasing approach is defective in that if the length &agr; of the center hole of the annular boss
67
is increased, it is impossible to thin the motor.
Another possible approach to increase the coupling force is that the inside diameter of the center hole of the annular boss
67
is selected to be smaller than the outside diameter of the rotary shaft
65
b
, and an overlap width of press-fitting of the rotary shaft to the boss is increased. However, this approach is defective in that it is difficult to secure the perpendicularity of the rotary shaft to the boss at the time of the press fitting, and it will cause the perpendicularity of the boss to degrade.
A further possible approach is that a groove is formed around the outer circumferential face of the rotary shaft
65
b
where it is in contact with the center hole of the annular boss
67
, and is filled with adhesive, whereby the rotary shaft
65
b
is bonded to the center hole of the annular boss
67
. However, this approach is defective in that the workability is impaired, and the coupling force of the rotary shaft
65
b
to the annular boss
67
varies depending on a variation of the amount of adhesive.
The coupling of the rotary shaft
65
b
with the annular boss
67
by welding also suffers from problems of cost increase and limitation of a kind of material that may be used.
Generally, a sintered oil-contained bearing is used for the bearing of the motor. As shown in
FIG. 8
, the sintered oil-contained bearing
64
b
is impregnated with lubricant oil. The lubricant oil fills a gap between the inner circumferential face of the sintered oil-contained bearing
64
b
and the outer circumferential face of the rotary shaft
65
b
. With presence of the lubricant oil, the rotary shaft
65
b
is smoothly rotatable. The lubricant oil in the gap oozes from the upper end of the sintered oil-contained bearing
64
b
. In the thinned motor, the exuded lubricant oil is likely to reach the lower end of the boss
67
. When the oil reaches the lower end of the boss
67
, part of the lubricant oil is radially splashed along the end face of the boss
67
by a centrifugal force generated.
The splashing of the lubricant oil results in reduction of the amount of the lubricant oil in the gap, and hence in reduction of the lifetime of the bearing. Further, the splashed oil soils related parts of the motor. A gap between the upper end of the sintered oil-contained bearing
64
b
and the end face of the annular boss
67
may be increased so as to prevent the lubricant oil oozing from the upper end of the sintered oil-contained bearing
64
b
from reaching the boss
67
. In this case, a dimension of the motor in the axial direction is increased. This fact makes it impossible to thin the motor.
SUMMARY OF THE INVENTION
The present invention is made to solve the problems of the related techniques, and has a first object to provide a small-size motor which is capable of improving the perpendicularity of the boss to a shaft to achieve the thinning of the motor.
The invention has a second object to provide a small-size motor which, to thin the motor, prevents the splashing of the lubricant oil and impregnates again the sintered oil-contained bearing with the oozing lubricant oil.
In order to achieve the above objects, according to the present invention, there is provided a motor comprising:
a boss having a center hole; and
a shaft press-fitted into the center hole, a diameter of which is A,
wherein a tapered portion is formed around one end of the shaft, which is inserted to the center hole, such that a dimension in the extending direction of the shaft is R; and
wherein the boss includes a cylindrical recess formed concentrically with the center hole on one end face thereof facing a side from which the shaft is inserted such that a dimension in the extending direction of the center hole thereof is larger than R, and such that a diameter thereof is A<B≦1.05A.
Preferably, the cylindrical recess includes a first side wall linearly extending from the end face of the boss and a second side wall subsequent to the first side wall, which is tapered inwardly in order to serve as an insertion guide member against which the tapered portion of the shaft is to be abutted when the shaft is inserted into the center hole.
With this structure, the perpendicularity of the shaft to the boss is secured when the shaft is press-fitted into the boss, without increasing the axial length of the center hole of the boss, whereby motor may be thinned.
Preferably, a caulking member is provided on at least one end face of the boss so as to surround the center hole, which is to be compressed onto the shaft inserted into the center hole.
When comparing the motor structure in which the shaft is simply press-fitted into the center hole of the boss, a coupling force of the shaft with the boss may be increased without increasing the axial length of the center hole of the boss. Therefore, thinning of the motor and improvement of the motor shock resistance are both achieved.
According to the present invention, there is also provided a motor comprising:
a boss having a center hole;
a shaft press-fitted into the center hole;
a sintered bearing for supporting the shaft, in which lubricant oil is contained;
a holder for holding the bearing; and
a wall membe

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