Multi-rotor helical screw compressor with unloading

Abstract

A compressor with rotor unloading is presented. The compressor having a housing for supporting a multi-rotor configuration (e.g., a male rotor and two axially aligned female rotors) and a drive motor. A discharge disk is mounted at the discharge end of the male rotor. The length of the male rotor is slightly longer than the length of the female rotors, thereby providing axial clearance between the female rotors and the discharge disk. Lubrication is leaked (or flashed) through these clearances to upper bearings. The motor is supported in the compressor housing. Evaporated refrigerant from the evaporator is inducted into the compressor. The vapor phase refrigerant is compressed by the compressor. The compressed vapor phase refrigerant is then presented to a condenser, condensing the refrigerant to the liquid phase. Thereafter, liquid phase refrigerant is delivered through an expansion valve to the evaporator. The motor, bearings and the compression process itself are cooled and lubricated by the oil in the vapor refrigerant. The unloading is accomplished by allowing selective axial movement of the female rotors of the compressor to effectively reduce/prevent compression at that rotor. The axial movement is actuated by a stepper motor. The expansion valve is actuated and the female rotors are unloaded (i.e., the stepper motors are driven) in response to microprocessor control. Accordingly, the above describes a complete cycle which can be capacity varied.