Patent Publication Number: US-7588430-B2

Title: Screw compressor

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a screw compressor having a slide valve for adjusting a volume of discharged gas. 
   2. Description of the Related Art 
   A screw compressor having a slide valve to adjust the volume of discharged gas has heretofore been known publicly. 
   It is preferable for the slide valve to be superior in its operation responsivity so that the screw compressor can discharge compressed gas without excess or deficiency in the amount of the gas required in accordance with a change in the amount of consumption of the compressed gas discharged. However, in case of the slide valve being actuated by an ordinary type of a hydraulic cylinder and in case of the hydraulic cylinder being a single hydraulic cylinder, the operation of the slide valve becomes slow and the responsivity in operation, i.e., the responsivity in volume control, of the slide valve is poor. 
   For improving the responsivity it is necessary to increase the power for actuating the slide valve. The power may be increased by enlarging the diameter of a piston in the hydraulic cylinder or by using pressurizing means for increasing the oil pressure. However, in view of the structure of the screw compressor, a limit is in many cases encountered in increasing the diameter of the piston. Further, the addition of pressurizing means for increasing the oil pressure leads to a more complicated configuration of equipment concerned. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to eliminate the above-mentioned conventional problems related to responsivity of a slide valve. 
   First, a screw compressor according to the present invention comprises a pair of screw rotors, a slide valve disposed in parallel with the axis of the screw rotor, and a plurality of hydraulic cylinders for moving the slide valve forward and backward, the plural hydraulic cylinders imparting, in synchronization with each other, a driving force to the slide valve in the same direction. Preferably, the plural hydraulic cylinders comprise a first hydraulic cylinder disposed on a suction side of the slide valve and a second hydraulic cylinder disposed on a discharge side of the slide valve. It is also preferable that the plural hydraulic cylinders comprise a first hydraulic cylinder disposed on a suction side of the slide valve and a second hydraulic cylinder connected in series with the first hydraulic cylinder. 
   In the screw compressor according to the present invention, the slide valve can be operated quickly and its responsivity in volume control can be improved without increasing the diameter of a piston in each hydraulic cylinder or without complicating the equipment concerned. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram schematically showing an entire configuration of a screw compressor according to the present invention; and 
       FIG. 2  is a diagram schematically showing an entire configuration of another screw compressor according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the present invention will be described in detail hereinunder with reference to the accompanying drawings.  FIG. 1  shows a screw compressor  1  according to an embodiment of the present invention. 
   The screw compressor  1  includes a pair of female and male screw rotors  12 , i.e., a female rotor F and a male rotor M, accommodated rotatably within a casing  11  and meshing with each other. The screw compressor  1  further includes a slide valve  13  in parallel with the axes of the screw rotors  12 . The slide valve  13  is accommodated in the interior of the casing  11  in such a manner that the axis of the slide valve  13  is parallel to the axes of the screw rotors  12 . With such a configuration, the slide valve  13  can move forward and backward in directions parallel to the axes of the screw rotors  12 . 
   A suction port  14  is formed on one side of the casing  11 , a discharge port  15  is formed on the other side of the casing  11 , and a rotor chamber  16  is formed between the suction port  14  and the discharge port  15 . The screw rotors  12  are accommodated in the rotor chamber  16 . A rotor shaft  17  projecting from the suction side of the male rotor M is rotated by a motor (not shown). Further, the screw rotors  12  are rotated by a motor (not shown) through the rotor shaft  17 . 
   In  FIG. 1 , an upper portion with respect to a dot-dash line is a vertical cross section of the portion where the male rotor M is positioned, while a lower portion with respect to the dot-dash line is a vertical cross section of the portion where the female rotor F is positioned. In  FIG. 1 , the male rotor M and the female rotor F are depicted conceptually so that the difference between the two can be understood. In other words, the present invention is not limited at all to the illustrated shape. As to a rotor shaft and a bearing for supporting the female rotor F, their illustrations are omitted because they are not related to the essence of the present invention. 
   A valve operating space  18  which is opened to the rotor chamber  16  is formed in adjacency to the rotor chamber  16 . The slide valve  13  is accommodated within the valve operating space  18 . A surface S 1  of the slide valve  13  which surface is opposed in proximity to the screw rotors  12  extends to both sides of an intermeshing portion of both female rotor F and male rotor M and is formed in a shape constituting a part of a wall surface of the rotor chamber  16 . Likewise, a surface S 2  which is opposed in proximity to the screw rotors  12  extends to both sides of the intermeshing portion of both female rotor F and male rotor M. A stopper  19  formed in a shape constituting a part of the wall surface of the rotor chamber  16  is provided projectingly on the suction side of the valve operating space  18 . Though not shown, the suction port  14  actually extends to a lower portion of the rotor shaft  17  and a space portion  18   a  formed on the suction side of the valve operating space  18  is open to the lower extended portion of the suction port  14  without going through the rotor chamber  16 . 
   A piston  21  and a piston rod  22  are provided on the suction side of the slide valve  13 . A first hydraulic cylinder  23  adapted to extend and contract in parallel with the axes of the screw rotors  12  is provided. A piston  24  and a piston rod  25  are provided on the discharge side of the slide valve  13 . A second hydraulic cylinder  26  adapted to extend and contract in parallel with the axes of the screw rotors  12  is provided. The piston rod  22  is connected to an end on the suction side of the slide valve  13 , while the piston rod  25  is connected to an end on the discharge side of the slide valve  13 . 
   On the other hand, the first hydraulic cylinder  23  and the second hydraulic cylinder  26  are connected to an oil pressure source  34  and an oil tank  35  by piping through flow control valves  31  and  32  with check valves and further through a four-port three-way selector valve  33 . That is, a hydraulic circuit is configured by the first and second hydraulic cylinders  23 ,  26 , flow control valve  31  with check valve, flow control valve  32  with check valve, four-port three-way selector valve  33 , oil pressure source  34 , oil tank  35 , and pipes for connection of those components. In  FIG. 1 , a part of the piping is not shown in order to make the drawing more clear. Actually, X-marked portions are in communication with each other and so are the Y-marked portions. 
   As shown in  FIG. 1 , an intra-cylinder space I formed on the right side of the piston  21  and an intra-cylinder space II formed on the right side of the piston  24 , on which an oil pressure acts when the slide valve  13  operates to the discharge side, i.e., leftward in  FIG. 1 , are in communication with each other by piping. Likewise, an intra-cylinder space III formed on the left side of the piston  21  and an intra-cylinder space IV formed on the left side of the piston  24 , on which an oil pressure acts when the slide valve  13  operates to the suction side, i.e., rightward in  FIG. 1 , are in communication with each other by piping. That is, for the first and second hydraulic cylinders  23 ,  26 , in order to impart a driving force to the slide valve  13  in the same direction and in synchronization with each other, the intra-cylinder spaces positioned in the same direction are in communication with each other. In this way the piston rod  22  of the first hydraulic cylinder  23  and the piston rod  25  of the second hydraulic cylinder  26  are operated in the same direction in synchronization with each other. 
   When the slide valve  13  lies in its position indicated by a solid line in  FIG. 1 , that is, when the slide valve  13  is in abutment against the stopper  19 , there is no gap between the slide valve  13  and the stopper  19  and the screw compressor  1  is in a state of loaded operation (full load operation). In this state, the total amount of gas sucked from the suction port  14  into the screw rotors  12  is compressed and discharged from the discharge port  15 . The gas discharged amount of compressed in this state becomes maximum. Insofar as the four-port three-way selector valve  33  is in its state shown in  FIG. 1 , the state of this load operation is maintained. 
   When a flow path is changed by the four-port three-way selector valve  33 , the oil pressure source  34  comes into communication with the intra-cylinder spaces I and II and the oil tank  35  comes into communication with the intra-cylinder spaces III and IV, whereupon the piston  21  and piston rod  22  of the first hydraulic cylinder  23  and the piston  24  and piston rod  25  of the second hydraulic cylinder  26  operate in synchronization with each other and the slide valve  13  moves to the discharge side, i.e., leftward. As a result, a gap is formed between the slide valve  13  and the stopper  19 , the screw compressor  1  shifts to a state of unloaded operation (partial loaded operation or minimum loaded operation), and the volume of discharged gas is adjusted. In the partial loaded operation, a part of gas which has been sucked from the suction port  14  into the screw rotors  12  returns from the gap between the slide valve  13  and the stopper  19  to the suction port  14  through the space potion  18   a  formed on the suction side of the valve operating space  18 . The remaining part except the aforesaid part of the sucked gas is compressed and discharged from the discharge port  15 . When the slide valve  13  lies in its position indicated by a dash-double dot line in  FIG. 1 , the screw compressor  1  assumes a state of minimum loaded operation which is an ultimate state of unloaded operation. At this time, most of the gas sucked from the suction port  14  into the screw rotors  12  returns from the gap between the slide valve  13  and the stopper  19  to the suction port  14  through the space portion  18   a  formed on the suction side of the valve operating space  18 . The minimum loaded operation may be also called merely no-load operation because it is close to a no-load condition. 
   Thereafter, the flow path is changed by the four-port three-way selector valve  33  for adjusting the volume of discharged gas and the oil pressure source  34  comes into communication with the intra-cylinder spaces III and IV, while the oil tank  35  comes into communication with the intra-cylinder spaces I and II. As a result, the piston  21  and piston rod  22  of the first hydraulic cylinder  23  and the piston  24  and the piston rod  25  of the second hydraulic cylinder  26  operate in synchronization with each other and the slide valve  13  moves to the suction side, i.e., rightward. Consequently, the gap between the slide valve  13  and the stopper  19  vanishes and the foregoing state of loaded operation is formed. 
   Thus, the screw compressor  1  is provided with the first and second hydraulic cylinders  23 ,  26  which are adapted to operate in synchronization with each other to impart a driving force in the same direction to the slide valve  13 . Accordingly, there is no such structural problem as that occurring in case of using only a single hydraulic cylinder and increasing the diameter of its piston, nor is there any fear of complication of equipment caused by the addition of pressurizing means for increasing the oil pressure. Moreover, it is possible to strengthen the driving force for the slide valve  13  to quicken the operation of the same valve and improve the responsivity in volume control. 
   Further, in the screw compressor  1 , since the slide valve  13  is positioned between the first and second hydraulic cylinders  23 ,  26  and is supported on both sides thereof, it is difficult to displace the slide valve  13  in a direction orthogonal to the axis of the first hydraulic cylinder  23  and hence in a direction orthogonal to the axis of the second hydraulic cylinder  26 . Consequently, the slide valve  13  is prevented from coming into contact to an abnormal extent with the side wall which surrounds the slide valve  13  sideways or with the screw rotors  12 . 
     FIG. 2  shows a screw compressor  2  according to another embodiment of the present invention. In  FIG. 2 , portions common to the screw compressor  1  described above are identified by the same reference numerals as in  FIG. 1  and explanations thereof will here be omitted. In the screw compressor  2 , a second hydraulic cylinder  26  is connected in series with a bottom side, i.e., the right-hand side in  FIG. 2 , of a first hydraulic cylinder  23 . 
   According to this configuration, like the above configuration, there is no fear for a problem that occurring in case of increasing a diameter of its piston or increasing oil pressure, and it is possible to strengthen the driving force for the slide valve  13  to quicken the operation of the same valve and improve the responsivity in volume control. Besides, since the first and second hydraulic cylinders  23 ,  26  are connected in series with each other, oil pressure pipes associated with both hydraulic cylinders are easily laid in a compact manner. 
   In the present invention the number of plural hydraulic cylinders for actuating the slide valve  13  is not limited to two. Regarding on which of suction side and discharge side each hydraulic cylinder is to be disposed, no limitation is made, either. Thus, it is not always necessary to dispose the first hydraulic cylinder  23  on the suction side of the slide valve  13 .