Screw compressor

Abstract

In a screw compressor, on a bearing side relative to a discharge port of a compression chamber in a casing, an intermediate-pressure chamber to which an intermediate-pressure coolant is supplied from outside of the casing is provided in a high-pressure space surrounded by an outer cylinder and an intermediate cylinder of the casing and communicating with the discharge port, and the intermediate-pressure coolant has a temperature and a pressure that are lower than those of a coolant in the high-pressure space and higher than a coolant in a low-pressure space on a motor side relative to the discharge port in the casing. The intermediate-pressure chamber and the low-pressure space communicate with each other.

1 . A screw compressor comprising:
 a casing including an outer cylinder, an intermediate cylinder, and an inner cylinder which have cylindrical shapes and which are connected in a radial direction and arranged in a nested structure in this order from an outer side;   a screw shaft rotatably provided in an axial direction in the inner cylinder;   a screw rotor having a plurality of helical screw grooves extending in the axial direction around an outer circumference thereof, the screw rotor being fixed to the screw shaft;   a motor to which the screw shaft is connected;   a pair of gate rotors which rotate with teeth thereof meshed with the screw grooves and which form a compression chamber for compressing a coolant, together with the screw rotor; and   a bearing and a bearing housing which are provided inside the inner cylinder on a side opposite to the motor in the axial direction, the bearing rotatably supporting the screw shaft, and the bearing housing storing the bearing, wherein   on the bearing side relative to a discharge port of the compression chamber in the casing, an intermediate-pressure chamber to which an intermediate-pressure coolant is supplied from outside of the casing is provided in a high-pressure space surrounded by the outer cylinder and the intermediate cylinder of the casing and communicating with the discharge port,   the intermediate-pressure coolant has a temperature and a pressure that are lower than those of a coolant in the high-pressure space and higher than those of a coolant in a low-pressure space on the motor side relative to the discharge port in the casing, and   the intermediate-pressure chamber and the low-pressure space communicate with each other.   
     
     
         2 . The screw compressor according to  claim 1 , further comprising
 two semi-cylindrical slide valve storage grooves protruding radially outward from an inner circumferential surface of the inner cylinder and extending in the axial direction;   slide valves which are provided in the respective slide valve storage grooves and which adjust a compression ratio of the coolant or adjust a compression capacity for the coolant, wherein   the intermediate-pressure chamber is provided at a position that is not adjacent to the slide valves.   
     
     
         3 . The screw compressor according to  claim 1 , wherein
 the intermediate-pressure chamber is provided at a circumferential-direction position between the two slide valves and on a radially outer side relative to the slide valves.   
     
     
         4 . The screw compressor according to  claim 1 , wherein
 in a coolant circuit circulating from the screw compressor through an external condenser and an external evaporator to the screw compressor, the intermediate-pressure coolant is branched from a coolant circuit part leading from the condenser to the evaporator, so as to be supplied to the intermediate-pressure chamber.   
     
     
         5 . The screw compressor according to  claim 1 , wherein
 the bearing housing has an annular first groove recessed in the axial direction toward the motor side,   the intermediate-pressure chamber and the first groove communicate with each other via a communication path,   the inner cylinder has a second groove recessed radially outward and extending in the axial direction so as to communicate with the low-pressure space, and   the first groove and the second groove communicate with each other in the radial direction.   
     
     
         6 . The screw compressor according to  claim 1 , wherein
 two fixation legs for fixation are provided to an outer circumferential surface of the outer cylinder, and   the intermediate-pressure chamber is provided at a part other than a radially inner side between the two fixation legs.   
     
     
         7 . The screw compressor according to  claim 1 , wherein
 the intermediate-pressure chambers are respectively provided at symmetric positions with respect to a center axis of the casing.   
     
     
         8 . The screw compressor according to  claim 2 , wherein
 the intermediate-pressure chamber is provided at a circumferential-direction position between the two slide valves and on a radially outer side relative to the slide valves.   
     
     
         9 . The screw compressor according to  claim 2 , wherein
 in a coolant circuit circulating from the screw compressor through an external condenser and an external evaporator to the screw compressor, the intermediate-pressure coolant is branched from a coolant circuit part leading from the condenser to the evaporator, so as to be supplied to the intermediate-pressure chamber.   
     
     
         10 . The screw compressor according to  claim 3 , wherein
 in a coolant circuit circulating from the screw compressor through an external condenser and an external evaporator to the screw compressor, the intermediate-pressure coolant is branched from a coolant circuit part leading from the condenser to the evaporator, so as to be supplied to the intermediate-pressure chamber.   
     
     
         11 . The screw compressor according to  claim 2 , wherein
 the bearing housing has an annular first groove recessed in the axial direction toward the motor side,   the intermediate-pressure chamber and the first groove communicate with each other via a communication path,   the inner cylinder has a second groove recessed radially outward and extending in the axial direction so as to communicate with the low-pressure space, and   the first groove and the second groove communicate with each other in the radial direction.   
     
     
         12 . The screw compressor according to  claim 3 , wherein
 the bearing housing has an annular first groove recessed in the axial direction toward the motor side,   the intermediate-pressure chamber and the first groove communicate with each other via a communication path,   the inner cylinder has a second groove recessed radially outward and extending in the axial direction so as to communicate with the low-pressure space, and   the first groove and the second groove communicate with each other in the radial direction.   
     
     
         13 . The screw compressor according to  claim 4 , wherein
 the bearing housing has an annular first groove recessed in the axial direction toward the motor side,   the intermediate-pressure chamber and the first groove communicate with each other via a communication path,   the inner cylinder has a second groove recessed radially outward and extending in the axial direction so as to communicate with the low-pressure space, and   the first groove and the second groove communicate with each other in the radial direction.   
     
     
         14 . The screw compressor according to  claim 2 , wherein
 two fixation legs for fixation are provided to an outer circumferential surface of the outer cylinder, and   the intermediate-pressure chamber is provided at a part other than a radially inner side between the two fixation legs.   
     
     
         15 . The screw compressor according to  claim 3 , wherein
 two fixation legs for fixation are provided to an outer circumferential surface of the outer cylinder, and   the intermediate-pressure chamber is provided at a part other than a radially inner side between the two fixation legs.   
     
     
         16 . The screw compressor according to  claim 4 , wherein
 two fixation legs for fixation are provided to an outer circumferential surface of the outer cylinder, and   the intermediate-pressure chamber is provided at a part other than a radially inner side between the two fixation legs.   
     
     
         17 . The screw compressor according to  claim 5 , wherein
 two fixation legs for fixation are provided to an outer circumferential surface of the outer cylinder, and   the intermediate-pressure chamber is provided at a part other than a radially inner side between the two fixation legs.   
     
     
         18 . The screw compressor according to  claim 2 , wherein
 the intermediate-pressure chambers are respectively provided at symmetric positions with respect to a center axis of the casing.   
     
     
         19 . The screw compressor according to  claim 3 , wherein
 the intermediate-pressure chambers are respectively provided at symmetric positions with respect to a center axis of the casing.   
     
     
         20 . The screw compressor according to  claim 4 , wherein
 the intermediate-pressure chambers are respectively provided at symmetric positions with respect to a center axis of the casing.