Counterweight of reduced size

Details Counterweight of reduced size Counterweight of reduced size

2000-03-27

2001-10-23

Freay, Charles G. (Department: 3746)

Pumps

Motor driven

Electric or magnetic motor

C417S410400, C418S151000, C418S055600, C418S055400, C418S094000, C418S055100

Reexamination Certificate

active

06305914

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to reduction of counterweight size in electric motor driven rotating machinery. Counterweights are used widely in rotating machinery applications to counteract unbalanced forces of eccentrically rotated machinery components. Known counterweights often occupy a substantial amount of space within a rotating machinery extending both radially outward of the rotating shaft and axially along the shaft length. Examples of such rotating machinery for air conditioning and refrigeration application include scroll and rotary vane compressors.
While this invention is equally applicable to both scroll and rotary vane compressor, the application of this idea is illustrated on a scroll compressor. It should be understood that a worker of ordinary skill in the art would recognize the application of this idea to other types of compressors.
Scroll compressors are widely utilized in refrigerant compression applications. In a scroll compressor, a pair of scroll members each have a base and generally spiral wrap extending from the base. The wraps interfit to define compression chambers. One of the two scroll members is driven by a rotating shaft to orbit relative to the other. Because the orbiting scroll is positioned eccentrically on the rotating shaft, the scroll orbiting movement creates force imbalance. Scroll compressors have historically been manufactured with a relatively massive counterweight attached to the shaft or electric motor rotor to counteract this force imbalance and thus minimize scroll compressor vibration.
It is often desirable to reduce the required housing size of scroll compressors. However, the relatively massive counterweight has restricted the ability to reduce the size of the scroll compressor housing.
SUMMARY OF THE INVENTION
In a disclosed embodiment of this invention, the counterweight size is reduced by removing material in the motor rotor which drives the shaft. By removing material at a position circumferentially spaced from the counterweight location, the force which must be offset by the counterweight is reduced. The prior art has sometimes drilled cooling holes through the electric motor rotor. However, these known cooling holes have been symmetrically located around the rotor perimeter. The present invention does not use symmetrically located holes, and thus the prior art is not applicable to this invention.
In one embodiment of this invention, holes are machined to extend axially along the axis of the rotor. The holes may extend entirely through the length of the rotor, or for only a portion of the length. Preferably there are plural holes. The holes are preferably clustered on one side of the rotor, and more preferably over an arc of a relatively small circumferential extent. The holes are preferably located near the rotor bore, such that they have minimal impact on the motor electromagnetic field. Proper hole positioning reduces the counterweight size. In some applications, it may be possible to entirely eliminate the need for the counterweight.
In a second embodiment of this invention, a first portion of the outer periphery of rotor end ring is cut away. This portion is cut away on the side of rotor end ring opposite to the counterweight location. A second portion of the rotor end ring may also be cut away on the same side as the counterweight and receive a relatively small tooth shaped portion of counterweight. In this embodiment, the counterweight tooth fits downwardly into a notch in the outer periphery of the rotor.
In this embodiment, the additional space occupied by the counterweight is reduced by having the above-mentioned modifications to the rotor end rings and the counterweight. This occurs because the first portion of the rotor end ring is removed on the side opposite to the counterweight and the second portion of rotor end ring is filled the counterweight tooth whose density is much higher (typically copper material) than the density of the rotor end ring (typically aluminum material).
In either embodiment, the present invention reduces the space occupied by the counterweight.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.


REFERENCES:
patent: 3952612 (1976-04-01), Kurkowski et al.
patent: 4439118 (1984-03-01), Iimori
patent: 5336060 (1994-08-01), Tomell et al.
patent: 5476369 (1995-12-01), Fowlkes et al.

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