Centrifugal switch device for induction motor

Electrical generator or motor structure – Dynamoelectric – Rotary

Reexamination Certificate

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Details

C200S08000A

Reexamination Certificate

active

06246135

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a centrifugal switch device, and more particularly to a centrifugal switch device for an induction motor.
2. Description of the Related Art
A common used induction motor usually includes a start circuit for starting the rotation of the motor. The start circuit includes a centrifugal switch for controlling the starting and stopping of the motor, and a capacitor for providing a higher starting force so as to increase the rotational speed of the motor to reach a higher value in a short time. When the rotational speed of the motor reaches 75% of that of its full load, the centrifugal switch is used to cut of connection between the starting motor and the motor so that the rotational speed of the motor will not be increased excessively, and so that the motor is operated at a predetermined normal rotational speed.
A conventional centrifugal switch for an induction motor in accordance with the prior art shown in
FIGS. 1 and 2
comprises a switch contact
8
mounted on a casing
1
of the motor and connecting to a start circuit (not shown) for controlling the rotation of the motor, an elastic strip
7
detachably contacting with the switch contact
8
, a sliding member
6
mounted on a shaft (not shown) of the motor and having a distal end pressing a distal end of the elastic strip
7
, two springs
9
each mounted between the sliding member
6
and the casing
1
, a fan
2
secured on the shaft to rotate therewith, a pressing disk
3
secured in the fan
2
to rotate therewith and slidably mounted on the shaft for urging the sliding member
6
, two urging members
5
pivotally mounted on the fan
2
and each attached to the pressing disk
3
for moving the pressing disk
3
on the shaft relative to the sliding member
6
, and two springs
4
each mounted on the two urging members
5
for pivoting the two urging members
5
.
In operation, the pressing disk
3
is initially pushed toward the sliding member
6
by the two urging members
5
and the two springs
4
to move the sliding member
6
toward the casing
1
to press the elastic strip
7
which then touches the switch contact
8
as shown in
FIG. 1
so that the centrifugal switch device can be disposed in a state of “ON”, thereby allowing the induction motor electrically connecting to a start circuit (not shown) so as to start the induction motor.
When the rotational speed of the induction motor is increased to reach 75% of that of its full load, the urging members
5
is moved from the position as shown in
FIG. 1
to the position as shown in
FIG. 2
by means of the centrifugal force generated by the high speed rotation of the shaft to move the pressing disk
3
away from the sliding member
6
so that the sliding member
6
is moved toward the pressing disk
3
by the restoring force of the springs
9
so as to move the sliding member
6
from the position as shown in
FIG. 1
to the position as shown in
FIG. 2
, thereby detaching the switch contact
8
from the elastic strip
7
so that the centrifugal switch device is disposed in a state of “OFF”, and the start circuit is disconnected. In such a manner, the rotational speed of the induction motor will not be increased due to the power supplied from the centrifugal switch device is cut off so that the induction motor is rotated at a normal speed.
However, heat is easily created by high friction while the sliding member
6
, the elastic strip
7
and the switch contact
8
are in contact with each other during the operation. In addition, the switch is not provided with a registering apparatus for regulating the parts such that they have a tendency of sliding out of position. Further, the parts are easily attached by dirt or dust. Accordingly, the disadvantages will result in poor connection of electricity and destruction of the parts of the motor, thereby increasing difficulties of operation and costs of maintenance.
The closest prior arts of which the applicant is aware are disclosed in U.S. Pat. No. 5,602,436 to Sherman et al.; U.S. Pat. No. 2,555,703 to Restemeier; and U.S. Pat. No. 4,272,660 to Mayer et al.
In the Sherman reference, it discloses a shaft
9
, a flange
25
, a sleeve
17
, a table
30
, a contact
27
, a switch
28
, a spring
34
, and a weight
31
. The table
30
engages the contact
27
of the switch
28
, and the spring
34
biases the table
30
normally away from the contact
27
toward the flange
25
so that the switch
28
is not normally closed. When the rotational rate of the shaft
9
reaches a predetermined speed, the weights
31
pivot outward to move the flange
25
along the sleeve
17
so as to engage the table
30
. The table
30
is then urged downward to depress the contact
27
and actuate the switch
28
to disengage the starting winding so that the switch
28
is actuated at an appropriate speed.
In the Restemeier reference, it discloses a disc
24
which is embossed to provide an annular rim portion
30
which is adapted to engage a button
31
forming a part of a microswitch
32
. When the motor is idle, the coil spring
29
insures that the rim
30
of the disc
24
will be in contact with the button
31
to hold the electrical contacts in engagement with the microswitch, thereby enabling the motor to start rotating. As the speed of the motor increases, the arms
20
and
22
are urged in a radially outward direction by the centrifugal force, and this outward movement of the arms
20
and
22
is translated into axial movement of the disc
24
so that the button
31
is released, the contacts associated with the microswitch are opened, and flow of current to the starting winding of the motor is thereby stopped. However, the disc
24
is secured on a sleeve
27
which is slidably secured on the shaft
17
of the motor to rotate herewith. Therefore, the disc
24
is rotated with the shaft
17
so that the rim portion
30
constantly and continuously contacts with the button
31
during the rotation of the shaft
17
, thereby easily creating high heat due to friction, and thereby easily wearing the button
31
.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, there is provided a centrifugal switch device for an induction motor. The induction motor includes a casing having a side wall, and a shaft rotatably mounted on the casing.
The centrifugal switch device comprises a microswitch mounted on the side wall of the casing and including a push button protruding outward therefrom; a protective cover mounted on the microswitch for encompassing and contacting the push button of the microswitch and the protective cover including a stub protruding therefrom; a sliding member secured to the casing and slidably mounted on the shaft, an extension extending outward from the sliding member to move therewith and including a pressing piece releasably pressing the protective cover for urging the protective cover to press the push button of the microswitch, the pressing piece defining a through hole for receiving the stub of the protective cover; a fan secured on the shaft to rotate therewith; a pressing disk secured in the fan to rotate therewith and slidably mounted on the shaft for detachably urging the sliding member; a pad movably mounted on the shaft and located between the sliding member and the pressing disk; two urging members each pivotally mounted on the fan and each attached to the pressing disk for moving the pressing disk on the shaft relative to the sliding member; and two biasing members each mounted on the two urging members for pivoting the two urging members.
The casing includes two flanges extending outward therefrom and each defining a receiving chamber and a screw bore. The sliding member defines two holes each respectively aligning with the receiving chamber of each of the two flanges of the casing. The centrifugal switch device further comprises two retaining bolts each extending through the hole of the sliding member into the receiving chamber and each screwed into the screw hole of the flange of the casing

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