Variable displacement compressor

Claim 1

A hermetic rotary refrigerant compressor for use in a refrigeration system including refrigerant condensing means for condensing high pressure gaseous refrigerant from said compressor, an expansion device, and evaporator means wherein liquid refrigerant vaporizes and absorbs heat of evaporization comprising: a hermetic casing adapted to contain a high pressure refrigerant gas; a rotary compressor positioned in said casing and comprising means including a cylindrical wall member and upper and lower end plates forming the axial walls of an annular compression cylinder, spaced suction and discharge ports communicating with said cylinder; means connecting said suction port to the evaporator; means connecting said discharge port through a discharge valve to said casing; a rotor extending axially between said plates being eccentrically rotatable within said cylinder with the peripheral surface of said rotor arranged to move progressively into sealing relation with successive portions of said cylindrical wall of said annular cylinder to divide said cylinder between a suction side and a compression side; a motor having a shaft thereon for driving said rotor within said cylinder; a radially disposed vane slidably maintained in a slot in said wall member between said ports being biased against said rotor to divide said cylinder into low and high pressure sides within said cylinder; pressure relief means including channel means formed in one of said end plates, said channel being arranged and dimensioned so that a portion thereof is exposed to said cylinder to form a passageway on said low pressure side of said cylinder; valve means including a valve in said channel and valve actuating means responsive to discharged refrigerant pressure in said casing being operable for moving said valve from a sealing position flush with the axial wall of said cylinder to an open position in said channel by a force varying with the difference in pressure between the suction and discharge pressures for allowing a portion of said refrigerant being compressed in said cylinder by said rotor to flow through said passageway from the compression side of the peripheral surface of said rotor to the suction side of the peripheral surface of said rotor when the pressure of refrigerant in said casing is greater than a predetermined pressure so that refrigerant pressure at said discharge port is maintained within said predetermined pressure.