Variable inner volume ratio-type inverter screw compressor

Abstract

Regulating compression capability to a load is performed by an inverter ( 15 ) that regulates revolution number of an electric motor ( 11 ). This makes unload control in capability regulation unnecessary, preventing operational efficiency from lowering. Further, a capacity control valve for capacity control is eliminated for a simplified valve control mechanism. Regulating a variable inner volume ratio achieves the highest compressor efficiency corresponding to operating condition (capability). When a low inner volume ratio command is issued, a slide valve ( 19 ) is moved by a compression section controller ( 27 ) in an axial direction toward the electric motor ( 11 ). This advances completion time of a compression step to advance discharge of a compressed gas. When a high inner volume ratio command is issued, the slide valve ( 19 ) is moved in an axial direction toward a piston ( 25 ), which delays time of completion of compression step to delay discharge of a compressed gas.

1 . A variable inner volume ratio-mode inverter screw compressor comprising: 
 a variable inner volume ratio valve changing completion time of a compression step in a screw compression section to make inner volume ratio variable;    an electric motor rotationally driving the screw compression section; and    an inverter controlling rotational frequency of the electric motor corresponding to a load.    
   
   
       2 . The variable inner volume ratio-mode inverter screw compressor as set forth in  claim 1 , comprising: 
 a control section controlling an opening degree of the variable inner volume ratio valve based on suction side pressure and discharge side pressure of the screw compression section and rotational frequency of the electric motor.