Hermetic scroll compressor with pressure differential control means for a back-pressure chamber

Claim 1

A hermetic scroll compressor having: a hermetic housing; a frame fixed in said housing; and a motor-driven compressor unit mounted in said housing, said motor-driven compressor unit having a scroll compressor section and an electric motor section which are drivingly connected to each other through a rotary shaft supported by a bearing carried by said frame, said scroll compressor section including a stationary scroll member and an orbiting scroll member each having an end plate and a spiral wrap protruding uprightly from one side of said end plate and said scroll members being assembled together such that their wraps mesh with each other so as to form closed compression chambers between said wraps, said orbiting scroll member engaging with an eccentric shaft portion formed on one end of said rotary shaft, means provided between the orbiting scroll member and the stationary scroll member for preventing a rotation of said orbiting scroll member about its own axis, said stationary scroll member being respectively provided at its central and peripheral portions with a discharge port and a suction port, the orbiting movement of said orbiting scroll member causing a movement of said compression chambers towards a center of said stationary scroll member while progressively decreasing the volumes of said compression chambers thereby compressing a gas confined in the compression chambers until the gas is discharged through said discharge port into a space in said hermetic housing and then to an outside of said compressor through a passage so that a high pressure is maintained in said space in said hermetic housing, said compressor section further having a back-pressure chamber defined between said orbiting scroll member and said frame to which is introduced an intermediate pressure of the gas in a course of compression so as to produce an axial thrust force which tends to press said orbiting scroll member onto said stationary scroll member, said compressor section further having a lubricating means adapted to supply a lubricating oil to bearings by a pressure differential between the high pressure maintained in said space and said hermetic housing and the pressure in said back-pressure chamber, and wherein a control valve means is provided which is adapted to establish a communication between said back pressure chamber and said suction chamber when the pressure differential between the pressure in said discharge chamber and the pressure in said back-pressure chamber is below a predetermined positive level.