Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1998-08-10
2001-04-10
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S085000, C310S090000, C310S091000
Reexamination Certificate
active
06215214
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to electric motors and, more particularly, to an electric motor assembly capable of withstanding heavy side loading.
BACKGROUND OF THE INVENTION
Electric motors typically include a housing, a stator, and a rotor assembly. The housing includes a shell and two end shields and houses at least a portion of the rotor assembly. The rotor assembly includes a rotor core and a rotor shaft extending through the core. Some motor types and configurations include components to modify the motor operating characteristics for particular applications. Examples of such motor types are resistance start, reactor start, capacitor start, permanent split capacitor, and capacitor start-capacitor run motors. These different types of motors are characterized by different speed-torque characteristics and may be designed to provide different theoretical maximum efficiencies. For some applications, particularly those where high starting torque is required as in compressor motors, part of the windings in the motor serve as auxiliary or starting windings which are energized during initial excitation of the motor, but which are deenergized as the motor comes up to a predetermined speed. Deenergization of such windings is often accomplished by a centrifugal switch, or other appropriate device.
Electrical components used in some motor configurations include, in addition to the centrifugal switch, at least one capacitor and an overload. These components can be mounted to one of the motor end shields to facilitate access thereto. To provide protection from moisture, dust, and other contaminants, such components are often mounted in a closed “control compartment” in which the subject electrical components are housed.
Compressor motors typically used in today's consumer markets have moved to a direct drive construction. A direct drive construction compressor motor utilizes an end shield on the normal drive end of the motor to structurally support the compressor. The end shield typically includes a flange that accepts the cylinder sleeve, piston, crank, and head that are the basic components of the compressor. This direct integration of the compressor to the motor requires the rotor shaft to withstand unusually high side loading resulting from the compression stroke. Known electric motors that drive compressors typically utilize a stepped shaft configuration to limit shaft deflection and prevent crank bearing failures. Stepped shafts are expensive to manufacture due, at least in part, to the complexity of the shaft.
Accordingly, it would be desirable to provide a capacitor start-capacitor run motor with an inexpensive to fabricate rotor shaft that is capable of handling unusually high side loading. It would also be desirable to have all electronic components of the electric motor enclosed and protected from the external environment. It would further be desirable to provide easy access to at least some of the electrical components mounted to the motor.
SUMMARY OF THE INVENTION
These and other objects may be attained by an electric motor assembly having low cost, high volume production components (e.g., shaft and collar) and a reduced bearing span as compared to known compressor motors. In one embodiment, the assembly includes a motor housing having a shell with first and second ends. A first end shield is mounted to the first shell end and a second end shield is mounted to the second shell end. The first and second end shields include bearing supports having bearings therein. The first end shield further includes a flange for connecting a compressor to the motor.
A stator, including run windings and start windings, is mounted in the housing and includes a bore extending therethrough. A rotor assembly, including a rotor core and a shaft with a substantially uniform diameter, extends through the bore in the stator. The rotor is rotatably mounted in the housing by the bearings in the end shields. A stiffening collar, positioned between the rotor core and the first end shield, surrounds a portion of the rotor shaft. The collar provides support for the shaft against deflection due to heavy side loading.
The electric motor assembly further includes a centrifugal mechanism and a spacer positioned outboard of the motor housing. The spacer is positioned outboard of the motor housing and adjacent the second end shield bearing. The centrifugal mechanism is positioned adjacent the spacer and rotates with the rotor shaft. A retaining ring is positioned on the rotor shaft adjacent the centrifugal mechanism and maintains the centrifugal mechanism in contact with the spacer.
The positioning of the centrifugal mechanism outboard of the housing allows for a reduced bearing span relative to the bearing span of known electric motors. This reduced bearing span provides further support for the rotor shaft against deflection due to heavy loading.
The electric motor assembly also includes a cover attached to the second end shield. The cover and the second end shield form an enclosure housing the centrifugal mechanism. The cover includes first and second capacitor supports and a centrifugal switch. A start capacitor is positioned in the first capacitor support and a run capacitor is positioned in the second capacitor support. The centrifugal switch is electrically connected to the start capacitor and to the run capacitor. The cover further includes snaps for mounting the centrifugal switch to the cover in a position adjacent the centrifugal mechanism. The centrifugal switch includes an actuating lever capable of being actuated by the centrifugal mechanism. When the centrifugal mechanism actuates the actuating lever, the centrifugal switch cuts out the start capacitor which deenergizes the start windings.
The motor assembly also includes an overload and an overload mounting bracket. The overload extends through an opening in the second end shield and the overload mounting bracket is positioned over the overload. The overload bracket includes snaps that engage to the second end shield and maintain the bracket and overload in position.
The electric motor assembly also includes a load washer having a plurality of snaps. The snaps engage the second end shield and maintain the load washer in position on the second end shield.
The above described electric motor assembly is less costly to manufacture because a stepped rotor shaft is not needed. Instead, a rotor shaft of substantially uniform diameter is used, and a stiffening collar is positioned on the shaft for support. Also, electrical components such as the centrifugal switch and overload are held in position by snaps. These snaps allow for quick, easy removal of the components and are inexpensive to manufacture. Also, the snaps are unitary with other components of the assembly thus reducing the number of individual parts required to assemble the motor.
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pa
Fisher Lynn E.
Marks Michael A.
Pape Marc D.
Straley Larry W.
Armstrong Teasdale LLP
Enad Elvin
General Electric Company
Horton Esq. Carl B.
Wasserbauer Esq. Damian
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