Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-01-14
2001-04-10
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S043000, C310S090000, C310S07500D, C029S596000
Reexamination Certificate
active
06215209
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a small-sized motor equipped with a worm gear reducer used to drive, for example, electric equipment of an automobile, such as a power window apparatus, as well as to a method of manufacturing the same.
BACKGROUND ART
Conventionally, the position with respect to the thrust direction of the shaft of a small-sized motor equipped with a worm gear reducer is fixed, for example, as shown in
FIG. 8
(Japanese Patent Publication (kokoku) No. 60-11536/1985). Reference numeral
1
denotes a motor body; reference numeral
6
denotes a worm coupled with a motor shaft
4
; and reference numeral
7
denotes a worm wheel engaged with the worm
6
. As shown in
FIG. 8
, an adjustment screw
43
is attached to a gear case
17
at a position corresponding to a front end portion of the motor shaft
4
. After thrust is adjusted by means of the adjustment screw
43
, the adjustment screw
43
is fixed by means of a nut
44
. In thrust adjustment, the motor is rotated, while a specially machined front end of the adjustment screw
43
is brought in contact with the end of the motor shaft
4
. While a no-load current of the motor is being observed, the adjustment screw
43
is positioned where the no-load current assumes a value as small as possible and the motor shaft
4
has no play in the thrust direction. The adjustment screw
43
is fixed in the position by means of tightening the nut
44
. Such a manner of fixation of the motor shaft
4
with respect to the thrust direction requires skill in fixing the adjustment screw
43
and the nut
44
together, thus consuming much time.
Japanese Patent Publication (kokoku) No. 60-11536/1985 also discloses a technique for positioning with respect to the thrust direction by use of a spacer to be heated through electromagnetic induction. In addition to a shaft insertion hole, a square hole is provided. The spacer is inserted through the square hole and toward the front end portion of the shaft. The front end portion of the shaft is brought into direct contact with the spacer and is heated through electromagnetic induction. The front end portion of the shaft is then pressed against the softened spacer to thereby be positioned with respect to the thrust direction.
Since this positioning mechanism requires formation of the square hole in addition to the shaft insertion hole, an associated gap may allow entry of water from the outside. Also, frictional heat generated through shaft rotation during motor operation or heat generated from windings and a commutator during motor operation is transmitted to the spacer through the shaft, potentially re-softening the spacer. Further, since the spacer by itself bears a radial force and a thrust force, wear or breakage of the spacer is likely to cresent a problem.
Other conventional techniques for fixing a motor shaft with respect to the thrust direction include the following. As shown in
FIG. 9
, resin
46
is injected into a cavity portion located between a gear case
17
and a motor shaft
4
through an injection inlet
45
extending between the cavity portion and the exterior of the gear case
17
, thereby fixing the position of the motor shaft
4
with respect to the thrust direction (Japanese Patent Publication (kokoku) No. 61-56701/1986). Similarly, as shown in
FIG. 10
, the resin
46
is injected into a cavity portion located between the gear case
17
and a bearing holder
22
equipped with a bearing device (radial bearing
5
and steel ball
9
) for the motor shaft
4
, through the injection inlet
45
extending between the cavity portion and the exterior of the gear case
17
, thereby fixing the position of the motor shaft
4
with respect to the thrust direction (Japanese Patent Publication (kokoku) No. 7-106044/1995).
Such resin-injection practice requires labor and time for curing of the applied resin. Also, deformation, such as shrinkage, or time-course change of the resin causes a decrease in adhesion between the resin and the gear case with a resultant formation of a gap between the resin and the gear case at an injection inlet portion. Water may enter the gear case through the gap from the outside.
A certain kind of resin may require control of injection pressure or injection temperature. In the case of a resin that requires mixture and reaction of two components before use, a mixing process requires labor, and resin control must be performed before and after the mixing process. In addition, at the time of resin injection, the amount of resin to be injected must be controlled or adjusted, and care must be taken in order to prevent mixing of bubbles into the resin. In a configuration where resin to be used directly supports a motor shaft, a problem may arise due to wear or breakage of the resin caused by a thrust of the motor shaft.
DISCLOSURE OF THE INVENTION
An object of the present invention is to solve the above problems and to provide a small-sized motor equipped with a worm reducer capable of being easily assembled, enabling accurate fixation of the position of a motor shaft with respect to the thrust direction, and capable of preventing entry of water from the outside to thereby avoid potential quality-related troubles and impart high reliability as well as to provide a method of manufacturing the motor.
To achieve the above object, the present invention provides a small-sized motor equipped with a worm reducer and a method of manufacturing the same, in which a cavity portion
10
for receiving a front end of a motor shaft
4
is formed in a gear case
17
, which accommodates a worm
6
connected to the motor shaft
4
and a worm wheel
7
engaged with the worm
6
, such that the cavity portion
10
does not communicate with the exterior of the gear case
17
. In the cavity portion
10
are disposed a bearing holder
22
including a radial bearing
5
and a thrust bearing for the motor shaft
4
, and a spacer
30
formed of a metallic-fiber-contraining resin, which is located on the side of the bearing holder
22
opposite the motor shaft
4
and is disposed between the bearing holder
22
and the gear case
17
. The spacer
30
is softened through electromagnetic induction heating.
The present invention further provides a small-sized motor equipped with a worm reducer and a method of manufacturing the same, characterized in that a metallic spacer to be heated through electromagnetic induction is used as the spacer
30
in place of a resin spacer and that a protrusion
33
abutting the spacer
30
is formed on the inside of the gear case
33
and is crushed after being softened through application of heat transmitted from the abutting heated spacer
30
.
Thrust adjustment for the motor shaft
4
is performed through application of thrust to the motor shaft
4
after the resin spacer is softened through induction heating effected electromagnetically from outside the gear case, or after the gear case protrusion
33
, which is in contact with the metallic spacer, is softened through application of heat transmitted from the metallic spacer heated through induction heating effected electromagnetically from outside the gear case.
As described above, except for reception of the bearing holder
22
, the gear case cavity portion
10
does not communicate with the exterior thereof through, for example, a through-hole, thereby maintaining positional accuracy of the motor shaft
4
with respect to the thrust direction and preventing movement of the motor shaft
4
with respect to the thrust direction.
The present invention is applicable to an actuator operated by a small-sized motor equipped with a worm reducer and to a method of manufacturing the actuator. The actuator comprises an actuator box
40
which accommodates and supports the small-sized motor equipped with a worm reducer. The actuator box
40
includes a spacer holder portion
44
, which is formed on the inner wail of the actuator box
40
at a position corresponding to the front end portion of the shaft of a small-sized motor
1
supported within the actuator box
40
. A metallic-fiber-containing
Mabuchi Motor Co. Ltd.
McGlew and Tuttle , P.C.
Mullins Burton
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