Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-11-05
2004-03-23
Ponomarenko, Nicholas (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S06800R, C310S06800R
Reexamination Certificate
active
06710478
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention pertains to a centrifugal actuator of an electric motor that has been modified to reduce noise produced by the operation of the actuator. More specifically, the present invention pertains to a centrifugal actuator comprising a damper sleeve that mounts the actuator to the shaft of an electric motor and permits limited rotational movement of the actuator relative to the shaft to reduce the transmission of acceleration pulses from the shaft to the actuator and thereby reduce chattering of the centrifugal actuator.
(2) Description of the Related Art
Electric motors having stators with separate start windings and run windings typically employ centrifugal actuators to control the energization of the two windings. The start windings are energized during startup of the motor, or when the speed of the motor falls below a specified operating speed, so as to create a rotating magnetic field in the motor stator and to apply sufficient torque to the motor rotor for starting purposes. However, once the motor has accelerated to a desired operating speed, or to a predetermined percentage of the desired operating speed, the rotor is able to follow the alternations of the magnetic field created by the run windings and the start windings are no longer needed. At this point In the motor's operation the centrifugal actuator automatically switches over energization of the start windings to the run windings.
Usually, the start windings are not intended for continuous use and may fail if not de-energized during normal operation of the motor. Conventionally, a switch referred to as a motor starting switch is provided on the motor for energizing the start windings only during startup of the motor and for de-energizing the start windings once the motor has attained its desired operating speed. A centrifugal actuator is typically employed in switching the motor windings between their start windings and run windings. The centrifugal actuator is mounted on the motor shaft for rotation with the shaft, and is responsive to the speed of the motor shaft for switching the motor start switch between the start windings and the run windings, and visa versa.
A typical centrifugal actuator is disclosed in the U.S. Patent of Hildebrandt, U.S. Pat. No. 3,609,421, which issued on Sep. 28, 1971, and is incorporated herein by reference. Basically, the centrifugal actuator includes a main body that is mounted on the electric motor shaft for rotation with the shaft. An actuator sleeve is mounted on the main body for axially reciprocating movement of the actuator sleeve over the main body between first and second positions of the actuator sleeve relative to the motor shaft. The sleeve has an annular flange that projects radially outwardly from the sleeve. The centrifugal actuator is positioned on the shaft so that the annular flange of the actuator sleeve is positioned adjacented to the start switch of the motor that completes the circuits through the start windings and the run windings of the motor. In the operation of the actuator sleeve to be explained, the switch completes a circuit through the start windings or the run windings of the motor in response to the actuator sleeve moving between its respective first and second axially displaced positions on the motor shaft
The actuator sleeve and its annular flange are biased by a pair of springs on the actuator toward the first position of the sleeve relative to the shaft. The springs extend transversely across opposite sides of the motor shaft and the actuator body and are connected between a pair of levers mounted on the actuator body on opposite sides of the motor shaft. The levers are mounted on the actuator body for pivoting movement of the levers relative to the body. Each of the levers is formed as a bell crank having one end connected to the actuator sleeve and the opposite end connected to a weight. Each of the levers has an intermediate portion that is mounted for pivoting movement on the actuator body. The pair of springs exert a biasing force on the levers pulling the weighted ends of the levers radially inwardly, and thereby bias the actuator sleeve toward its first position relative to the actuator body and the motor shaft.
On startup of the electric motor the switch of the motor is in position to complete a circuit through the start windings of the motor. The run windings circuit is open. Thus, the circuit through the start windings causes initial rotation of the motor shaft. When rotation of the shaft and the centrifugal actuator reaches a predetermined speed, the centrifugal force exerted on the weighted ends of the actuator levers causes the weighted ends to move radially outwardly against the bias of the pair of springs. This in turn causes the opposite ends of the levers that engage with the actuator sleeve to move the sleeve from its first axial position relative to the shaft to its second axial position relative to the shaft. This movement of the sleeve causes the sleeve annular flange to switch the motor switch from its position closing the circuit through the start windings to its position closing the circuit through the run windings where the start windings circuit is opened. When the speed of rotation of the shaft falls below the predetermined speed the pair of springs pull the weighted ends of the levers radially Inwardly, thereby causing the opposite ends of the levers to move the actuator sleeve from its second position relative to the shaft to its first position relative to the shaft. This in turn causes the sleeve annular flange to switch the motor switch from its position closing the circuit of the run windings back to its position closing the circuit of the start windings.
The construction of the centrifugal actuator described above is typical among prior art centrifugal actuators. Most actuators basically employ an actuator sleeve and a pair of lever arms mounted on the main body of the actuator for movement relative to the main body and the motor shaft However, this simplified and inexpensive construction of the typical centrifugal actuator has its disadvantages. The actuator main body has a center bore that is mounted in tight engagement around the motor shaft. Because the motor rotor on the shaft is basically rotated by rotating magnetic fields created in the windings of the motor stator, the rotor and the motor shaft are continuously subjected to a series of torque pulses that rotate the rotor and the motor shaft. These torque pulses are transmitted from the motor shaft through the tight engagement of the actuator main body on the shaft to the component parts of the actuator, i.e., the actuator sleeve and the actuator weighted levers. The series of torque pulses often produce a clicking or chattering noise in the component parts of the centrifugal actuator that is very undesirable in certain applications of the electric motors, in particular where the electric motors are used In home appliances.
The prior art solution to reducing the vibration-induced clicking or chattering, noise of the centrifugal actuator was to mount the centrifugal actuator in a friction fit on the motor shaft that allowed some relative movement between the actuator and shaft. This would reduce the transmitted vibration due to the torque pulses of the motor that would produce the noise in the component parts of the actuator. However, it was still necessary for the centrifugal actuator to rotate with the motor shaft in order for it to function properly in switching between the start and run windings of the motor. Therefore, a pair of annular grooves were machined in the motor shaft adjacent to the opposite ends of the centrifugal actuator. A lubricated caring was assembled into one of the grooves at one side of the actuator and the actuator was provided with serrations that extended radially inwardly into the other groove on the opposite side of the actuator. The centrifugal actuator would be mounted on the motor shaft between the pair of groves with the c-ring and serrations mounted
Lewis William R.
Newberg Barry M.
Emerson Electric Co.
Mohandesi Iraj A.
Thompson & Coburn LLP
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