SCREW COMPRESSOR

Abstract: A screw compressor in which a pair of screw rotors (12) and (13) supported by bearings and accommodated in a casing (11)act to compress a gas and in which a slide valve (22) dis­ posed between an inner wall of the casing and the pair of screw rotors is capable of moving axially while maintaining a small gap between itself and the outer peripheries of the screw rotors, the rate of gas flow bypassed to an inlet port (17) during compression being regulated by axially moving the slide valve. The screw compressor has: a side cover (18) in which bearings for supporting the pair of screw rotors on the discharge side and a slide valve driving hydraulic means are incorporated and which is disposed on the discharge side of the screw rotors; a discharge axial port (19) formed in the side cover; and at least one projection (24) continuous with an opening edge of the discharge axial port and in contact with a semi-circular surface of the slide valve facing in the radial direction thereof, the projection acting to limit the radial movement of the slide valve while the slide valve is moving in contact with the top end of the projection.

Description: The invention relates to a screw compressor comprising a pair of screw rotors, supported by bearings and accommodated in a casing to compress a gas, a slide valve disposed between an inner wall of said casing and above said pair of screw rotors so as to move axially while maintaining a small gap between at least one arcuate surface thereof and the outer peripheries of said screw rotors, the rate of gas flow bypassed to an inlet port during compression being regulated by axially moving said slide valve, a side cover in which bearings for supporting said pair of screw rotors on the discharge side of said screw rotors; a discharge axial port formed in said side cover. Such a screw compressor as described in the DE-A-35 05 919 has a first slide valve for controlling the capacity of the compressor, a further slide valve for carrying the set displacement ratio, a plate attached to the end portion at the discharge side and having axial ports for each set displacement ratio, and discharge ports which constitute an empty space. The first slide valve is semi-circular in shape. Because of this semi-circular shape, it is virtually impossible to limit rotation of the valve without reducing the upper and lower gaps to zero and thereby preclude functioning of the compressor. Likewise, the further slide valve is hollowed out in the area of the discharge port where the plate cannot therefore serve to restrict the rotation of the first slide valve. This shows that the radial movement of the first slide valve cannot limit a radial movement of the second slide valve. Therefore the object of the present invention is to provide a screw compressor which has an improved workability and accuracy and is capable of preventing the slide valve from contacting the screw rotors by limiting the radial movement of the slide valve. To this end the present invention provides a screw compressor of the generic kind having two projections continuous with an opening edge of said discharge axial port and in contact with two arcuate surfaces of said slide valve facing in the radial direction thereof for limiting the radial movement of said slide valve while said slide valve is moving in contact with the top ends of the said projections. Advantageously, the two arcuate surfaces of the slide valve are semi-circular. Conveniently, the slide valve is disposed above the pair of screw rotors while the projections are formed so as to be continuous with the opening edge of the axial discharge port and to support the slide valve from below. Preferably, the positions of the projections are between the slide-valve-driving hydraulic means and a guide surface formed by an inner arcuate surface of the casing facing the slide valve. With the screw compressor according to the invention, the slide valve is prevented from contacting the screw rotors by effectively limiting the radial movement of the slide valve. Furtheron, the screw compressor has an improved workability and accuracy. The invention is further explained by means of drawings in which Fig. 1 is a longitudinal section of the screw compressor and Fig. 2 is the section A-A of fig. 1. As shown is Figs. 1 and 2, a pair of male and female rotors 12 and 13, which rotate in engagement with each other to compress a gas, and a rotor driving electric motor 14 are accommodated in a casing 11. A shaft 12a of the male rotor 12 and a shaft 13a of the female rotor 13 are supported by bearings 15a and 15b, respectively, and the shaft 12a of the male rotor 12 is directly coupled to the output shaft of the electric motor 14. The interior of the casing 11 is provided with a slide valve 22 which can move axially while maintaining small gaps between itself and the outer peripheral surfaces of the male and female rotors 12 and 13, a hydraulic drive cylinder 23 for moving the slide valve 22, and a piston 23a. The slide valve 22 is connected to the left end of a rod 23b extending from the piston 23a in the hydraulic drive cylinder 23. Projections 24, which limit the movement of the slide valve 22 in the radial direction, are formed on a discharge-side side cover 18 so as to be continuous with the edge of a discharge axial port 19 and in contact with two semi-circular or arcuate surfaces of the slide valve 22, so that the slide valve 22 moves while being guided by the top ends of the projections 24. A cover 30 is attached and fixed to the end surface of the casing 11 on the discharge side by means of bolts 31, thereby covering the side cover 18. The discharge axial port 19 opens through a discharge port 20 to a discharge chamber 32. An oil separating demister 33 is disposed in the discharge chamber 32 between the discharge axial port 19 and a discharge coupling opening 21, to separate the oil contained in the discharged gas. An oil reservoir portion 34 is formed by extending a casing wall in a lower portion of the casing 11 outside the pair of screw rotors 12 and 13 which are encircled by the casing. The oil reservoir portion 34 communicates with a bottom portion of the discharge chamber 32 through a channel 35. An inlet opening 16 which has a strainer is formed through a motor cover 36 disposed on the casing 11 on the side of the electric motor. A power supply connection terminal portion 37 is disposed on an upper portion of the casing 11. The inlet side of a condenser 25 is connected to the discharge coupling port 21 of the screw compressor by a piping. The inlet side of an expansion valve 26 is connected to the condenser 25 by a piping and its outlet side is connected to an evaporator 27 by a piping. The outlet of the evaporator 27 is connected by piping to the inlet opening 16 of the screw compressor. The male rotor 12 and female rotor 13 are rotated in engagement with each other by the operation of the electric motor 14, thereby compressing a gas which has been drawn through the inlet opening 16 into an inlet port 17. The compressed gas is discharged through the discharge axial port 19 formed in the discharge-side cover 18 to the discharge port 20, and is thereafter sent to the discharge coupling opening 21 and is supplied under pressure to the condenser 25 through the piping. In the condenser 25, the gas is cooled and liquefied by heat exchange with air or water. The liquefied refrigerant is expanded in the expansion valve 26 under reduced pressure to form a low-pressure, low-temperature saturated refrigerant gas, and is then supplied to the evaporator 27. This gas acts to cool air or water in the evaporator 27 during the heat exchange with the air or water. The refrigerant gas which has cooled the air or water is again drawn through the inlet opening 16 to the screw compressor, thus completing a refrigeration cycle. When a rod chamber 38 of the drive cylinder 23 is supplied with a hydraulic fluid (not shown), the slide valve 22 moves to the right as viewed in Fig. 1, thereby increasing the flow rate of bypassed gas to the inlet port 17 during compression. When a head chamber 39 of the drive cylinder 23 is supplied with the hydraulic fluid, the slide valve moves to the left (to the position indicated in Fig. 1), thereby reducing the flow rate of the bypassed gas to the inlet opening 17 during compression. The slide valve 22 moves in the axial direction while being guided by the projections 24. That is, the movement of the slide valve 22 in the radial direction is limited by the projections 24 so that the slide valve 22 does not come into contact with the outer peripheral surfaces of the male rotor 12 and the female rotor 13, thereby preventing wear on the pair of rotors and, hence, a reduction in performance and the generation of abnormal noise. In addition, it is possible to form the projections 24 to a high degree of accuracy, since they can be formed by simply working the surface of the cover instead of by forming a groove therein. A compressor of the 30- to 60-HP class in accordance with this embodiment was manufactured as a trial. It was confirmed that the compressor could prevent a reduction in performance of 3 to 5% and also enabled a reduction in the level of noise by 3 to 5 dB (A scale). As described above, the present invention provides an arrangement in which projections 24 for limiting the movement of a slide valve 22 in the radial direction are formed in a side cover 18 having a discharge axial port 19 so that the slide valve 22 moves while being guided by the projections 24. The present invention thereby makes it possible to overcome the difficulty with respect to the workability and the accuracy and positively prevent the slide valve 22 from contacting the screw rotors 12, 13, thereby eliminating the possibility of reduction in performance and the generation of abnormal noise. The slide valve 22 is connected to the piston 23a by the rod 23b and is guided by an inner arcuate surface 40 of the casing 11, and the radial movement of the slide valve 22 is limited by the projections 24 which upwardly extend between the guide surface consisting of the arcuate surface of the casing 11 and the slide valve driving means consisting of the piston 23a and the cylinder 23, thereby enabling a compact construction around the sliding valve 22 and, hence, reducing the overall size of the screw compressor.

Claims: A screw compressor comprising a pair of screw rotors (12 and 13), supported by bearings (15a) and accommodated in a casing (11) to compress a gas, a slide valve (22) disposed between an inner wall of said casing (11) and above said pair of screw rotors (12, 13) so as to move axially while maintaining a small gap between at least one arcuate surface thereof and the outer peripheries of said screw rotors (12, 13), the rate of gas flow bypassed to an inlet port (17) during compression being regulated by axially moving said slide valve (22), a side cover (18) in which bearings (15b) for supporting said pair of screw rotors (12, 13) on the discharge side and a slide-valve-driving hydraulic means (23, 23a, 23b) are incorporated and which is disposed on the discharge side of said screw rotors (12, 13); a discharge axial port (19) formed in said side cover (18); characterized by two projections (24) continuous with an opening edge of said discharge axial port (19) and in contact with two arcuate surfaces of said slide valve (22) facing in the radial direction thereof for limiting the radial movement of said slide valve (22) while said slide valve (22) is moving in contact with the top ends of the said projections (24). A screw compressor according to claim 1, characterized in that the two arcuate surfaces of said slide valve (22) are semi-circular. A screw compressor according to claim 1 or 2, characterized in that said slide valve (22) is disposed above said pair of screw rotors (12, 13) and wherein said projections (24) are formed so as to be continuous with said opening edge of said axial discharge port (19) and to support said slide valve (22) from below. A screw compressor according to claim 3, characterized in that the positions of said projections (24) are between said slide-valve-driving hydraulic means (23, 23a, 23b) and a guide surface formed by an inner arcuate surface of said casing (11) facing said slide valve (22).

Inventors: IZUSHI, MINETOSHI, NAGATA, KIMIO, NOZAWA, SHIGEKAZU
Applicants: HITACHI, LTD.
Application year: 1987
Main classification: F04C18
IPC codes: F04C18, F04C28