Screw compressor and refrigeration apparatus

Abstract

A screw compressor includes a screw rotor, a plurality of gate rotors, a casing with a cylindrical wall, and an adjustment mechanism to adjust a pressure of a fluid in the casing. A plurality of compression chambers are formed inside the cylindrical wall by the screw rotor and the gates. The plurality of compression chambers include a first compression chamber in which the fluid introduced into the casing with a suction pressure is compressed to a pressure higher than the suction pressure, and a second compression chamber to which the fluid compressed in the first compression chamber is sent via an intermediate pressure space. The adjustment mechanism adjusts an intermediate pressure, which is a pressure of the fluid in the intermediate pressure space, in a two-stage operation in which the fluid is compressed in the first compression chamber and the second compression chamber.

1 . A screw compressor comprising:
 a screw rotor;   a plurality of gate rotors having gates that mesh with the screw rotor;   a casing into which the screw rotor is rotatably inserted, the casing having a cylindrical wall through which the gates penetrate; and   an adjustment mechanism configured to adjust a pressure of a fluid in the casing,   a plurality of compression chambers being formed inside the cylindrical wall by the screw rotor and the gates,   the plurality of compression chambers include
 a first compression chamber in which the fluid introduced into the casing with a suction pressure is compressed to a pressure higher than the suction pressure, and 
 a second compression chamber to which the fluid compressed in the first compression chamber is sent via an intermediate pressure space, and 
   the adjustment mechanism being configured to adjust an intermediate pressure, which is a pressure of the fluid in the intermediate pressure space, in a two-stage operation in which the fluid is compressed in the first compression chamber and the second compression chamber.   
     
     
         2 . The screw compressor of  claim 1 , wherein
 the adjustment mechanism includes a valve movable to an opposing region located in a rotor space surrounded by the gate rotors and the screw rotor, and   the valve changes timing at which the second compression chamber is fully closed, by changing a position of the valve in the opposing region.   
     
     
         3 . The screw compressor of  claim 2 , wherein
 the valve changes a volume of the second compression chamber at start of a compression phase for the fluid in the second compression chamber by changing the timing at which the second compression chamber is fully closed.   
     
     
         4 . The screw compressor of  claim 2 , wherein
 the valve switches between
 a single-stage operation in which the fluid is compressed in the first compression chamber out of the first compression chamber and the second compression chamber and 
 the two-stage operation. 
   
     
     
         5 . The screw compressor of  claim 4 , wherein
 the valve
 is movable to a separation position apart from the rotor space, and 
 when located at the separation position, the valve maintains a state in which the intermediate pressure space communicates with an outside of the screw compressor. 
   
     
     
         6 . The screw compressor of  claim 5 , further comprising:
 inside the casing, a first passage and a second passage communicate with the intermediate pressure space, and   the valve
 when located in the opposing region, allows the fluid to be sent from the intermediate pressure space to the second compression chamber via the first passage, and allows the fluid which has not entered the second compression chamber because the second compression chamber is fully closed to be sent to the intermediate pressure space via the second passage, and 
 when located at the separation position, allows the fluid in the intermediate pressure space to be sent to the outside of the screw compressor via the first passage, and allows the fluid in the intermediate pressure space to be sent to the outside of the screw compressor via the second passage. 
   
     
     
         7 . The screw compressor of  claim 5 , wherein
 the two-stage operation is performed when the valve is located in the opposing region,   the intermediate pressure is adjusted by changing the position of the valve in the opposing region, and   the single-stage operation is performed when the valve is located at the separation position.   
     
     
         8 . The screw compressor of  claim 2 , wherein
 the position of the valve is continuously changeable such that the timing at which the second compression chamber is fully closed is continuously adjustable.   
     
     
         9 . The screw compressor of  claim 6 , wherein
 the first passage and the second passage are located on one side in a movement direction of the valve with respect to the separation position, and   the one side in the movement direction indicates a direction toward the opposing region in the movement direction of the valve from the separation position.   
     
     
         10 . The screw compressor of  claim 6 , wherein
 the valve includes an end surface toward one side in the movement direction of the valve, and the second passage is disposed so as to face the end surface, and   the one side in the movement direction indicates a direction toward the opposing region in the movement direction of the valve from the separation position.   
     
     
         11 . The screw compressor of  claim 6 , wherein
 the first passage includes a first opening communicating with the second compression chamber,   the second passage includes a second opening communicating with the second compression chamber, and   the second opening is located at a position lower than the first opening.   
     
     
         12 . The screw compressor of  claim 6 , wherein
 the second passage extends along an axis of the valve.   
     
     
         13 . A refrigeration apparatus including the screw compressor of  claim 1 .