Patent Publication Number: US-2023138965-A1

Title: Screw compressor, refrigeration system, and method for controlling refrigeration system

Description:
BACKGROUND 
     Technical Field 
     This application relates to compressors, and more specifically relates to a screw compressor. 
     Related Art 
     A compressor includes a screw compressor. The screw compressor includes a housing and a female rotor and a male rotor disposed in the housing. There is a compression cavity between the female rotor and the male rotor. During rotation of the female rotor and the male rotor, the compression cavity becomes smaller and smaller, so that the volume of a gas accommodated in the compression cavity becomes smaller, so as to increase the pressure of the gas, thereby realizing compression of the gas. In the screw compressor, there are a plurality of spaced compression cavities between the female rotor and the male rotor, and thus, the compressed gas intermittently discharged from the compression cavities acts on the housing and is delivered downstream, thereby producing airflow induced vibration and noise. 
     SUMMARY 
     According to a first aspect of this application, this application provides a screw compressor. The screw compressor includes a screw compressor housing, a discharge cavity, at least one silencing channel and at least one adjustment piston. The discharge cavity is defined by at least one part of the screw compressor housing, the at least one part of the screw compressor housing defining the discharge cavity forms a wall of the discharge cavity, and at least one hole is provided in the wall of the discharge cavity. The at least one adjustment piston can be inserted into the at least one hole and can move therein. The at least one silencing channel is formed by the at least one hole and the at least one adjustment piston, and the at least one silencing channel is in fluid communication with the discharge cavity. A position of the at least one adjustment piston in the at least one hole determines a silencing length of the at least one silencing channel. 
     According to the screw compressor of the first aspect of this application, the at least one silencing channel is at least two silencing channels, and the at least one adjustment piston is at least two adjustment pistons. The screw compressor further includes an adjustment slider, and the at least two adjustment pistons are connected to the adjustment slider. The adjustment slider and the at least two adjustment pistons are configured such that each of the at least two adjustment pistons can do reciprocating movement in the corresponding silencing channel when the adjustment slider does reciprocating movement relative to the screw compressor housing, thereby changing the silencing length of each of the at least two silencing channels. 
     According to the screw compressor of the first aspect of this application, the at least one silencing channel is at least two silencing channels, and the at least one adjustment piston is at least two adjustment pistons. The at least two adjustment pistons can do reciprocating movement relative to the screw compressor housing independently of each other, thereby changing a silencing length of each of the at least two silencing channels. 
     According to the screw compressor of the first aspect of this application, the at least two adjustment pistons are configured such that each of the at least two silencing channels has a different silencing length at any moment when the at least two adjustment pistons do reciprocating movement relative to the screw compressor housing. 
     According to the screw compressor of the first aspect of this application, the at least one hole is provided with an inlet end and a distal end opposite to the inlet end, and the at least one adjustment piston can be inserted into the at least one hole from the distal end. The distance between a top portion of the at least one adjustment piston and the inlet end is a silencing length. 
     According to the screw compressor of the first aspect of this application, the at least one hole is provided with an inlet end and a distal end opposite to the inlet end, and the at least one adjustment piston can be inserted into the at least one hole from the distal end. Each of the at least one adjustment piston is provided with a recess extending from an end surface of one end of the at least one adjustment piston to the other end, and the distance between a bottom of the recess of the at least one adjustment piston and the inlet end is a silencing length. 
     According to the screw compressor of the first aspect of this application, the screw compressor further includes an adjustment box, and the adjustment box is arranged on an outer side of the screw compressor housing and defines an adjustment cavity. The adjustment slider is disposed in the adjustment box, and divides the adjustment cavity into a first accommodation portion and a second accommodation portion, the first accommodation portion is formed on one side of the adjustment slider close to the screw compressor housing, and the second accommodation portion is formed between the adjustment box and the adjustment slider. 
     According to a second aspect of this application, this application further provides a screw compressor, the screw compressor including a screw compressor housing, a discharge cavity, an adjustment box, an adjustment piston and a silencing channel. The discharge cavity is defined by at least one part of the screw compressor housing, the at least one part of the screw compressor housing defining the discharge cavity forms a wall of the discharge cavity, and a hole is provided in the wall of the discharge cavity. The adjustment box is arranged on the outer side of the screw compressor housing and defines an adjustment cavity, and the adjustment cavity and the hole form a continuous channel. The adjustment piston can be inserted into the continuous channel, and can move therein. The silencing channel is formed by the hole, the adjustment piston and the adjustment box, and the silencing channel is in fluid communication with the discharge cavity. A position of the at least one adjustment piston in the hole and the adjustment cavity determines a silencing length of the silencing channel. 
     According to the screw compressor of the second aspect of this application, the screw compressor further includes at least one plate, and the at least one plate is arranged in the discharge cavity and covers the hole. At least one plate is provided with several perforations so as to make the discharge cavity be in fluid communication with the silencing channel. 
     According to the screw compressor of the second aspect of this application, the adjustment piston is disposed in the adjustment box, and divides the adjustment cavity into a first accommodation portion and a second accommodation portion, the first accommodation portion is formed on one side of the adjustment piston close to the screw compressor housing, and the second accommodation portion is formed between the adjustment box and the adjustment piston. 
     According to a third aspect of this application, this application further provides a refrigeration system, the refrigeration including the screw compressor and a lubricant circuit. The lubricant circuit is connected to the screw compressor. The second accommodation portion communicates with the lubricant circuit in a closable manner, and communicates with an inlet of the screw compressor in a closable manner. The refrigeration system is configured to be capable of supplying a lubricant from the lubricant circuit to the second accommodation portion so as to make the adjustment piston move towards the inlet end, and capable of introducing the lubricant in the second accommodation portion into an inlet of the screw compressor so as to make the adjustment piston move away from the inlet end. 
     The screw compressor of this application can adapt to different compressor operating conditions, reducing noise. 
     Other features, advantages and embodiments of this application may be set forth or become apparent from consideration of the following detailed description, drawings and claims. Furthermore, it is to be understood that both the foregoing summary and the following detailed description are exemplary and intended to provide further explanation without limiting the scope of the claimed application. However, the detailed description and specific examples are only indicative of preferred embodiments of this application. Various changes and modifications within the spirit and scope of this application will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of this application may be better understood by reading the following detailed description with reference to the accompanying drawings, and the same reference numerals indicate the same components throughout the drawings. 
         FIG.  1 A  is a three-dimensional view of a screw compressor from front to rear according to an embodiment of this application; 
         FIG.  1 B  is a cross-sectional view of a screw compressor shown in  FIG.  1 A  along a length direction of the screw compressor and from rear to front; 
         FIG.  1 C  is a cross-sectional view of a screw compressor shown in  FIG.  1 A  along a width direction of the screw compressor and section-cut to a discharge cavity of the screw compressor; 
         FIG.  2    is a cross-sectional view of a first embodiment of a silencing structure shown in  FIG.  1 A ; 
         FIG.  3    is a partial system diagram of a refrigeration system using the screw compressor of this application; 
         FIG.  4    is a flow path diagram of a lubricant in a refrigeration system when an adjustment slider is moved upwards; 
         FIG.  5    is a flow path diagram of a lubricant in a refrigeration system when an adjustment slider is moved downwards; 
         FIG.  6    is a schematic diagram of controlling movement of an adjustment slider and an adjustment piston; 
         FIG.  7    is a schematic diagram of another embodiment of a drive mechanism of driving an adjustment slider and eight adjustment pistons; 
         FIG.  8    is a cross-sectional view of a second embodiment of the silencing structure; 
         FIG.  9    is a cross-sectional view of a third embodiment of the silencing structure; 
         FIG.  10    is a cross-sectional view of a fourth embodiment of the silencing structure; 
         FIG.  11    is a cross-sectional view of a fifth embodiment of the silencing structure; and 
         FIG.  12    is a cross-sectional view of a sixth embodiment of the silencing structure. 
     
    
    
     DETAILED DESCRIPTION 
     Various specific implementations of this application will be described below with reference to the accompanying drawings forming a part of this specification. It should be understood that although directional terms such as “front”, “rear”, “upper”, “lower”, “outer” and “bottom” are used in this application to describe various example structural components and elements of this application, these terms used herein are for convenience of description only, and are determined based on the exemplary orientations shown in the drawings. Since the embodiments disclosed in this application may be disposed in different directions, these directional terms are used for illustration only and should not be regarded as limiting. 
       FIG.  1 A  is a three-dimensional view of a screw compressor  100  from front to rear according to an embodiment of this application;  FIG.  1 B  is a cross-sectional view of a screw compressor  100  shown in  FIG.  1 A  along a length direction of the screw compressor and from rear to front; and  FIG.  1 C  is a cross-sectional view of a screw compressor  100  shown in  FIG.  1 A  along a width direction of the screw compressor and section-cut to a discharge cavity  113  of the screw compressor  100 . As shown in  FIGS.  1 A to  1 C , the screw compressor  100  includes a screw compressor housing  101 . The screw compressor housing  101  defines a rotor cavity  111  and a discharge cavity  113 . The rotor cavity  111  and the discharge cavity  113  communicate with each other via a communication port  112 . 
     Specifically, a pair of rotors are disposed in the rotor cavity  111 . The pair of rotors include a male rotor  121  and a female rotor (not shown). A compression cavity (not shown) is formed between the male rotor  121  and the female rotor, the compression cavity being enclosed by tooth surfaces of the male rotor  121  and the female rotor. The compression cavity can be in fluid communication with the discharge cavity  113  via the communication port  112 . When the screw compressor  100  operates, a gas enters a compression cavity between the male rotor  121  and the female rotor from an inlet of the screw compressor  100  (see  FIG.  3   , i.e., a screw compressor inlet  302 ). As the male rotor  121  and the female rotor rotate, the compression cavity will gradually become smaller and moves towards the communication port  112 . When the compression cavity moves until being in fluid communication with the communication port  112 , the compressed gas in the compression cavity flows into the discharge cavity  113  via the communication port  112 . Intermittently formed compressed fluid temporarily stays in the discharge cavity  113  to form a buffer, thereby forming relatively smooth airflow, flowing out of the screw compressor  100  through an outlet  188  (see  FIG.  3   , i.e., a screw compressor outlet  306 ) of the screw compressor  100  disposed on the discharge cavity  113 . Eight holes  122  are provided in a wall of the discharge cavity  113 , the eight holes  122  are arranged in two rows, and each row includes four holes  122 . The eight holes  122  all extend through the wall of the discharge cavity  113 . 
     As shown in  FIG.  1 A , the screw compressor  100  further includes an adjustment box  132 . The adjustment box  132  is disposed on the screw compressor housing  101  and covers the eight holes  122 . Components provided in the adjustment box  132  can fit with the eight holes  122 , thereby reducing noise produced by the gas discharged from the screw compressor  100 . The adjustment box  132  is provided with a communication port  134  connected with a lubricant system through a connecting pipe  150 . The adjustment box  132 , the components provided in the adjustment box  132  and the holes provided in the wall of the discharge cavity  113  form a silencing structure, and a specific fitting relationship of them will be described in conjunction with  FIG.  2   . 
       FIG.  2    is a cross-sectional view of a first embodiment of a silencing structure shown in  FIG.  1 A , so as to show the fitting relationship between the adjustment box  132 , the components in the adjustment box  132  and the screw compressor housing  101 . As shown in  FIG.  2   , the eight holes  122  are provided in the wall of the discharge cavity  113 . Each of the eight holes  122  extends through the wall of the discharge cavity  113 . The adjustment box  132  includes a substantially rectangular bottom wall  242 , side walls  244  and connecting walls  246 . The side walls  244  surround the bottom wall  242  and extend upwards from a circumferential edge of the bottom wall  242 , and the connecting wall  246  extends outwards from an upper edge of the side wall  244 . The adjustment box  132  is disposed on an outer side of the screw compressor housing  101  and covers the eight holes  122 . The connecting wall  246  abuts against the screw compressor housing  101  and is connected with the outer side of the screw compressor housing  101  by means of connecting components (not shown) or welding or the like. The bottom wall and the side walls  244  of the adjustment box  132  enclose an adjustment cavity  204  together with the screw compressor housing  101 . The adjustment cavity  204  is in fluid communication with the eight holes  122 . 
     The screw compressor  100  further includes an adjustment slider  202  and eight adjustment pistons  222 . Each of the eight adjustment pistons  222  is a cylindrical body connected with an upper surface of the adjustment slider  202 , so that the adjustment slider  202  and the eight adjustment pistons  222  can move together. A shape of each of the eight adjustment pistons  222  matches a corresponding one of the eight holes  122 , so that each of the eight adjustment pistons  222  can be inserted into the corresponding one of the eight holes  122 . The eight adjustment pistons  222  and the eight holes  122  are further configured such that the gas in the discharge cavity  113  does not flow into the adjustment cavity  204  when the eight adjustment pistons  222  move vertically in the eight holes  122 . The eight holes  122  are each provided with an inlet end and a distal end opposite to the inlet end. The inlet end is formed by walls of the eight holes  122 , and is in fluid communication with the discharge cavity  113 . The eight adjustment pistons  222  are inserted into the corresponding holes  122  from the distal end. The eight adjustment pistons  222  and the eight holes  122  form eight silencing channels  288 , respectively. Specifically, one end of the silencing channel  288  is defined by the inlet end, and the other end thereof is defined by top portions of the eight adjustment pistons  222 . When the adjustment pistons  222  moves vertically in the holes  122 , the distance between the inlet end and the top portions of the eight adjustment pistons  222  changes, so that the silencing channels  288  have a different length. When a top surface of the adjustment piston  222  is flush with an inner side of the wall of the hole  122 , the length of the silencing channel  288  is 0. A circumferential size of the adjustment slider  202  is configured to match the side walls  244  of the adjustment box  132 , so that the adjustment cavity  204  is divided by the adjustment slider  202  into a first accommodation portion  231  and a second accommodation portion  232  separated from each other. The first accommodation portion  231  is formed on one side (i.e., an upper side of the adjustment slider  202 ) of the adjustment slider  202  close to the screw compressor housing  101 , and the second accommodation portion  232  is formed between (i.e., a lower side of the adjustment slider  202 ) the adjustment slider  202  and the bottom wall  242  of the adjustment box  132 . 
     The bottom wall  242  of the adjustment box  132  is provided with a communication port  134  for being connected with a pressure source. In an embodiment of this application, the communication port  134  is connected with a lubricant circuit through the connecting pipe  150  (see  FIG.  1 A ), so that a lubricant can flow into the second accommodation portion  232  through the communication port  134 . Pressure in the first accommodation portion  231  is substantially ambient pressure (i.e., one atmospheric pressure). 
     The screw compressor  100  further includes a spring  252  for providing an auxiliary force for upward (i.e., towards the screw compressor housing  101 ) movement of the adjustment slider  202  in the adjustment box  132 , and for limiting the range of downward movement of the adjustment slider  202 . Specifically, one end of the spring  252  is connected with a lower surface of the adjustment slider  202 , and the other end of the spring  252  is connected with the bottom wall  242  of the adjustment box  132 . When the distance between a bottom portion of the adjustment slider  202  and a top portion of the bottom wall  242  is a predetermined distance H, the spring  252  is in a free state, that is, the spring  252  is not compressed or stretched, without exerting a force on the adjustment slider  202 . When the distance between the bottom portion of the adjustment slider  202  and the top portion of the bottom wall  242  is greater than the predetermined distance H, the spring  252  is stretched, exerting a downward (i.e., away from the screw compressor housing  101 ) pulling force on the adjustment slider  202 . When the distance between the bottom portion of the adjustment slider  202  and the top portion of the bottom wall  242  is less than the predetermined distance H, the spring  252  is compressed, exerting an upward (i.e., towards the screw compressor housing  101 ) thrust to the adjustment slider  202 . 
     When the screw compressor  100  operates, a refrigerant is compressed in the screw compressor  100  into a high-temperature and high-pressure gas. The compressed gas enters the discharge cavity  113 , producing an exhaust pulsation with relatively high acoustic energy. The exhaust pulsation not only causes vibration and noise, but also causes a device downstream of the screw compressor  100  in a refrigeration system to form a secondary sound source. 
     The wall of the discharge cavity  113  of the screw compressor  100  of this application is provided with the silencing channels  288 , capable of controlling propagation of the noise at a position closest to a noise-causing position. When an operating frequency, exhaust pressure, exhaust temperature and other parameters of the screw compressor  100  change, a frequency corresponding to peak energy of the exhaust pulsation of the screw compressor  100  is different, and a wavelength corresponding to its peak energy is also different. The length of the silencing channel  288  in the silencing structure of this application can be adjusted, thereby adapting to the peak wavelength under different working conditions, so as to reduce the peak energy of the exhaust pulsation and effectively perform silencing. 
       FIG.  3    shows a partial system diagram of a refrigeration system  300  using a screw compressor  100  of this application. In this embodiment, the lubricant is used as a power source for driving the adjustment slider  202  and the eight adjustment pistons  222  to move. 
     As shown in  FIG.  3   , the refrigeration system  300  includes the screw compressor  100 . The screw compressor  100  includes a screw compressor inlet  302 , a lubricant inlet  304  and a screw compressor outlet  306 . The screw compressor inlet  302  is in fluid communication with the rotor cavity  111  for receiving a refrigerant from an evaporator (not shown) of the refrigeration system  300 . The lubricant inlet  304  is in fluid communication with the rotor cavity  111  for receiving a lubricant from a lubricant separating apparatus  312 . The screw compressor outlet  306  is in fluid communication with the discharge cavity  113  for discharging the compressed refrigerant and lubricant out of the screw compressor  100 . 
     The refrigeration system  300  further includes the lubricant separating apparatus  312 . The lubricant separating apparatus  312  is configured to separate the refrigerant and the lubricant. Specifically, the lubricant separating apparatus  312  includes a lubricant separating apparatus inlet  314 , a lubricant outlet  316  and a refrigerant outlet  318 . The lubricant separating apparatus inlet  314  is connected with the screw compressor outlet  306  through a first channel  322  for receiving compressed refrigerant and lubricant. After the refrigerant and the lubricant pass through the lubricant separating apparatus  312 , the lubricant flows out of the lubricant outlet  316  and the refrigerant flows out of the refrigerant outlet  318 . The lubricant outlet  316  is in fluid communication with the lubricant inlet  304  of the screw compressor through a second channel  324  for introducing the lubricant into the rotor cavity  111  of the screw compressor  100 , thereby lubricating the male rotor  121  and the female rotor. The refrigerant flows from the refrigerant outlet  318  to a condenser (not shown) of the refrigeration system  300 . Thus, the screw compressor  100 , the first channel  322 , the lubricant separating apparatus  312  and the second channel  324  form the lubricant circuit. 
     The refrigeration system  300  further includes a switching apparatus  332 . The switching apparatus  332  includes a first port  326 , a second port  327 , a third port  328 , a switching apparatus first channel  341  and a switching apparatus second channel  342 . The switching apparatus first channel  341  is configured to connect the first port  326  with the third port  328 , and the switching apparatus second channel  342  is configured to connect the second port  327  with the third port  328 . When the switching apparatus  332  is in a first position, the switching apparatus first channel  341  is connected while the switching apparatus second channel  342  is disconnected. When the switching apparatus  332  is in a second position, the switching apparatus first channel  341  is disconnected while the switching apparatus second channel  342  is connected. The first port  326  of the switching apparatus  332  is in fluid communication with the lubricant outlet  316  for introducing a high-pressure lubricant. The second port  327  of the switching apparatus  332  is in fluid communication with the screw compressor inlet  302  for making the high-pressure lubricant flow into the screw compressor  100 . The third port  328  of the switching apparatus  332  is connected with the communication port  134  of the adjustment box  132  through the connecting pipe  150 . The connecting pipe  150  is provided with a solenoid valve  360 . Opening and closing of the solenoid valve  360  can be controlled, thereby controlling connection and disconnection of the connecting pipe  150 . 
     The screw compressor  100  further includes two acoustic sensors  351  and  352 . In this embodiment, the acoustic sensors  351  and  352  are arranged in the first channel  322 . Detection ends (not shown) of the acoustic sensors  351  and  352  are in fluid communication with the first channel  322  so as to detect an exhaust pulsation energy value of the gas discharged from the screw compressor  100 . Those skilled in the art can understand that the two acoustic sensors  351  and  352  are configured to detect the exhaust pulsation energy value of the gas discharged from the screw compressor  100 , and therefore, the detection ends of the two acoustic sensors  351  and  352  can also be disposed in the discharge cavity  113 . 
     The screw compressor  100  further includes a position sensor  355  for detecting the distance between the adjustment slider  202  and the bottom wall  242  of the adjustment box  132 . Since a wall thickness of the screw compressor housing  101 , the distance from the bottom wall  242  of the adjustment box  132  to the screw compressor housing  101  and lengths of the eight adjustment pistons  222  are all fixed and known, the real-time silencing length can be obtained according to the distance between the adjustment slider  202  and the bottom wall  242  of the adjustment box  132  detected by the position sensor  355 . 
     The refrigeration system  300  further includes a controlling apparatus  301 . The controlling apparatus  301  is connected with the acoustic sensors  351  and  352 , the position sensor  355 , the solenoid valve  360  and the switching apparatus  332  in a communicating manner. The controlling apparatus  301  can obtain the exhaust pulsation energy value of the gas discharged from the screw compressor  100  from the acoustic sensors  351  and  352 , thereby working out a target silencing length. The controlling apparatus  301  can obtain the distance between the adjustment slider  202  and the bottom wall  242  of the adjustment box  132  from the position sensor  355 , thereby working out a real-time silencing length. The controlling apparatus  301  can monitor the real-time silencing length, and adjust positions of the eight adjustment pistons  222  according to a relationship between the real-time silencing length and the target silencing length. For example, when the real-time silencing length is less than or greater than the target silencing length, the eight adjustment pistons  222  are moved downwards or upwards. When the real-time silencing length is equal to the target silencing length, the eight adjustment pistons  222  are made to stop moving and kept at current positions. The controlling apparatus  301  can also control opening or closing of the solenoid valve  360  and control the switching apparatus  332  to be in the first position or the second position. 
       FIG.  4    shows a flow path diagram of a lubricant in a refrigeration system  300  when an adjustment slider  202  is moved upwards. Arrows indicate a flow path of the lubricant. As shown in  FIG.  4   , when the adjustment slider  202  needs to move upwards, the controlling apparatus  301  switches the switching apparatus  332  to the first position, so that the first channel  341  is connected while the second channel  342  is disconnected. The controlling apparatus  301  also opens the solenoid valve  360 , so that the connecting pipe  150  is communicated. In this way, the lubricant is divided into two ways after flowing out from the lubricant outlet  316  of the lubricant separating apparatus  312 . One way of lubricant enters the second accommodation portion  232  through the first port  326  and the third port  328  of the switching apparatus  332  and the communication port  134  of the adjustment box  132  in sequence, thereby controlling the movement of the adjustment slider  202  and the eight adjustment pistons  222 . The other way of lubricant flows by following the lubricant circuit. Specifically, the lubricant enters the screw compressor  100  through the second channel  324  from the lubricant inlet  304  of the screw compressor. 
       FIG.  5    shows a flow path diagram of a lubricant in a refrigeration system  300  when an adjustment slider  202  is moved downwards. Arrows indicate a flow path of the lubricant. As shown in  FIG.  5   , when the adjustment slider  202  needs to move downwards, the controlling apparatus  301  switches the switching apparatus  332  to the second position, so that the second channel  342  is connected while the first channel  341  is disconnected. The controlling apparatus  301  also opens the solenoid valve  360 , so that the connecting pipe  150  is communicated. In this way, in addition to the fact that one way of lubricant flows by following the lubricant circuit, the lubricant flowing out from the second accommodation portion  232  enters the screw compressor inlet  302  via the communication port  134 , the third port  328  and the second port  327  of the adjustment box  132  and flows into the screw compressor  100 . 
       FIG.  6    shows a schematic diagram of controlling movement of an adjustment slider  202  and an adjustment piston  222 . As shown in  FIG.  6   , the eight adjustment pistons  222  and the adjustment slider  202  are connected with each other, so that the eight adjustment pistons  222  and the adjustment slider  202  can move together. Movement directions of the eight adjustment pistons  222  and the adjustment slider  202  depend on a pressure difference between upper sides and lower sides of the eight adjustment pistons  222  and the adjustment slider  202 . When the switching apparatus  332  is located in the first position, the second accommodation portion  232  is filled with the high-pressure lubricant, pressure on the lower sides of the eight adjustment pistons  222  and the adjustment slider  202  is greater than that on the upper sides of the eight adjustment pistons  222  and the adjustment slider  202 , and the adjustment slider  202  and the adjustment pistons  222  move upwards, thereby reducing the length of the silencing channels  288 . When the switching apparatus  332  is located in the second position, the second accommodation portion  232  communicates with a low pressure end (i.e., a suction end) of the screw compressor  100 , the lubricant flows out of the second accommodation portion  232 , and the adjustment slider  202  and the adjustment pistons  222  move downwards, thereby increasing the length of the silencing channels  288 . When the silencing length of the silencing channel  288  is equal to the target silencing length, the controlling apparatus  301  closes the solenoid valve  360 , so that the adjustment slider  202  and the adjustment piston  222  are kept at current positions. 
     Thus, the screw compressor  100  of this application can utilize the lubricant circuit in the refrigeration system  300 , and thereby, the length of the silencing channel  288  is controlled by controlling the position of the adjustment piston  222  without requiring an additional drive source. 
     As an example, the peak wavelength of the exhaust pulsation can be calculated by signals collected by the two acoustic sensors  351  and  352 , thereby determining the length of the silencing channel  288 , so as to achieve a silencing effect. Specifically, the detection ends (not shown) of the two acoustic sensors  351  and  352  are disposed in the first channel  322  so as to obtain the exhaust pulsation energy value (for example, autopower spectra, cross-power spectra). Then, spectrum data of the exhaust pulsation energy traveling downstream is obtained by the following equation: 
     
       
         
           
             pi 
             = 
             
               
                 
                   
                     S 
                     11 
                   
                   + 
                   
                     S 
                     12 
                   
                   - 
                   
                     2 
                     ⁢ 
                     
                       C 
                       12 
                     
                     ⁢ 
                     cos 
                     ⁢ 
                     
                       kx 
                       12 
                     
                   
                   + 
                   
                     2 
                     ⁢ 
                     
                       Q 
                       12 
                     
                     ⁢ 
                     sin 
                     ⁢ 
                     
                       kx 
                       12 
                     
                   
                 
                 
                   4 
                   ⁢ 
                   
                     
                       ( 
                       
                         sin 
                         ⁢ 
                         
                           kx 
                           12 
                         
                       
                       ) 
                     
                     2 
                   
                 
               
             
           
         
       
     
     where, S 11  and S 12  are the autopower spectra of signals picked up at the acoustic sensors  351  and  352 , C 12  and Q 12  are the cross-power spectra of the signals picked up at the acoustic sensors  351  and  352 , k is a wave number, x 12  is a center distance between the acoustic sensor  351  and the acoustic sensor  352 , and p i  is the spectrum data of the exhaust pulsation energy. 
     Then, the frequency corresponding to the peak energy is extracted according to the worked out spectrum data p i  of the exhaust pulsation energy, and sound velocity in an exhaust fluid is obtained from operating parameters of the screw compressor  100  (for example, the exhaust pressure, the exhaust temperature), and thereby, the wavelength corresponding to the peak energy can be worked out. The corresponding target silencing length is calculated from this wavelength. The controlling apparatus  301  controls the position of the adjustment piston  222  according to the worked out target silencing length, so that the actual length of the silencing channel  288  is consistent with the target silencing length. 
     In this way, the silencing structure in the screw compressor  100  of this application can effectively reduce the exhaust pulsation in the discharge cavity  113 , and can automatically adapt to different operating conditions to reduce a pulsation with prominent energy. 
     It should be noted that although the wall of the discharge cavity  113  is provided with the eight holes in this application, any number of holes and the number of its correspondingly disposed adjustment pistons are within the protection scope of this application. 
     The eight silencing channels  288  are formed in the silencing structure shown in  FIG.  2    (only four silencing channels are shown in  FIG.  2   , and the other four silencing channels are not shown), and each of the eight silencing channels  288  has a same length, and can be configured to perform silencing on a wavelength band corresponding to the peak energy. Specifically, when sound waves matching the silencing length are transmitted to the inlet end of the silencing channel, most of the sound waves are reflected due to a mismatch of acoustic impedance, and some sound waves are converted into heat energy due to a damping action and absorbed, so that only a small part of the sound waves can further propagate downstream to achieve silencing. As can be seen from  FIG.  1 B , the plurality of silencing channels are arranged in two rows, and are disposed along a travel route of the sound waves (for example, from the communication port  112  to the outlet of the screw compressor  100 ). Compared with only one silencing channel, the plurality of silencing channels disclosed along the travel route of the sound waves in the screw compressor  100  of this application can perform a plurality of silencing on the same wavelength band, thus greatly reducing the noise produced by the gas discharged from the screw compressor  100 . 
       FIG.  7    shows another embodiment of a drive mechanism of driving an adjustment slider  202  and eight adjustment pistons  222 . The silencing structure shown in  FIG.  7    is substantially the same as the silencing structure shown in  FIG.  6   , and the description will not be repeated here. The difference from that shown in  FIG.  6    is that the adjustment slider  202  and the eight adjustment pistons  222  shown in  FIG.  6    take the lubricant as a drive source, while the adjustment slider  202  and the eight adjustment pistons  222  shown in  FIG.  7    take a driving apparatus  701  as a drive source. More specifically, in an embodiment shown in  FIG.  6   , the adjustment box  132  is provided with the communication port  134  for receiving the lubricant, and the movement of the adjustment slider  202  is controlled by controlling the lubricant accommodated in the second accommodation portion  232 , thereby controlling the length of the silencing channel  288 . This control method does not require an external power source, and the length of the silencing channel  288  can be controlled by using the lubricant in the refrigeration system  300 , thereby reducing production cost and operation cost. While in an embodiment shown in  FIG.  7   , the movement of the adjustment slider  202  is controlled by the driving apparatus  701 , thereby controlling the length of the silencing channel  288 . In this control method, there are fewer piping arrangements, and the length of the silencing channel  288  can be directly controlled by the driving apparatus  701 . 
     Specifically, the driving apparatus  701  includes a body  703  and a rod  702 . The rod  702  can extend and retract from the body  703  relative to the body  703 . The adjustment box  132  is provided with a receiving port  710  for receiving the rod  702  of the driving apparatus  701 . The rod  702  extends from the receiving port  710  into the adjustment cavity  204 . A distal end of the rod  702  is connected with the adjustment slider  202 , so that when the rod  702  extends, the eight adjustment pistons  222  move towards the screw compressor housing  101  together with the adjustment slider  202 , so that the length of the silencing channel  288  is reduced. When the rod  702  retracts, the eight adjustment pistons  222  move away from the screw compressor housing  101  together with the adjustment slider  202 , so that the length of the silencing channel  288  is increased. As an example, the driving apparatus  701  is a motor. The controlling apparatus  301  is connected with the driving apparatus  701  in a communicating manner, thereby controlling start and stop of the driving apparatus  701 . 
       FIG.  8    shows a cross-sectional view of a second embodiment of a silencing structure. The similarities between the silencing structure shown in  FIG.  8    and the silencing structure shown in  FIG.  2    will not be repeated here. The difference from that shown in  FIG.  2    is that each of the adjustment pistons  822  shown in  FIG.  8    is provided with a blind hole  882 . In other words, each of the adjustment pistons  822  is provided with a recess extending from one end surface to the other end. A diameter of the recess is slightly less than that of the adjustment piston  822 . The silencing channel  888  is now formed jointly by parts of the eight holes  122  starting from the inlet end with the blind hole  882 . When the adjustment piston  822  moves in the hole  122 , a relatively long silencing length can be provided, thereby adapting to sound waves with a relatively long wavelength. More specifically, in an embodiment of the silencing structure as shown in  FIG.  2   , the length of the silencing channel  288  is determined by the distance from the inlet end to the top portion of the adjustment piston  222 . The silencing structure is suitable for application scenarios where the wall thickness of the screw compressor housing  101  is relatively large, or the target silencing length is relatively short. While in an embodiment of the silencing structure as shown in  FIG.  8   , the silencing channel  888  is determined by the distance from the inlet end to a bottom of the recess of the adjustment piston. The silencing structure is suitable for application scenarios where the wall thickness of the screw compressor housing  101  is relatively small, or the target silencing length is relatively long, so as to reduce noise with a relatively long wavelength. 
     It should be noted that, when the length of the adjustment piston  822  is greater than that of the eight holes  122 , the adjustment piston  822  can protrude inwards relative to an inner wall of the discharge cavity  113 . The length of the silencing channel  888  is now determined by a depth of the blind hole  882  in the adjustment piston  822 . 
       FIG.  9    shows a cross-sectional view of a third embodiment of a silencing structure. The similarities between the silencing structure shown in  FIG.  9    and the silencing structure shown in  FIG.  2    will not be repeated here. The difference from that shown in  FIG.  2    is that lengths of the eight adjustment pistons  922  shown in  FIG.  9    are different. Therefore, lengths of the eight silencing channels  988  are also different. The eight silencing channels  988  with different lengths can perform silencing on sound waves of different wavelengths, respectively, thereby realizing that pulsations of a plurality of frequencies with more prominent energy are reduced simultaneously, so as to widen a silencing range. As an example, the lengths of some of the eight silencing channels  988  in the embodiment shown in  FIG.  9    can be designed to match the wavelength corresponding to the peak energy, thereby reducing noise at the peak energy. While the length of the remaining silencing channels  988  can be designed to match a wavelength near the peak energy, thereby reducing other noise near the peak energy. 
       FIG.  10    shows a cross-sectional view of a fourth embodiment of a silencing structure. As shown in  FIG.  10   , the eight holes  122  are provided in the wall of the discharge cavity  113 . Each of the eight holes  122  extends through the wall of the discharge cavity  113 . The adjustment box  1032  is a cuboid, and eight adjustment cavities  1002  are disposed on the adjustment box. The eight adjustment cavities  1002  extend downwards from one side of the adjustment box  1032 . The eight adjustment cavities  1002  are the same as the eight holes  122  in circumferential size, and are disposed in a one-to-one correspondence with the eight holes  122  so as to form a continuous channel. The eight adjustment pistons  1022  are each disposed in corresponding one of the eight channels, and divide each of the adjustment cavities  1002  into a first accommodation portion  1031  and a second accommodation portion  1033 . The eight silencing channels are now formed by the eight holes  122  starting from the inlet end to the end surfaces of the adjustment pistons  1022 . One side of the adjustment box  1032  opposite to the eight adjustment cavities  1002  is provided with eight communication ports  1034  corresponding to the second accommodation portion  1033  for being connected with the lubricant system so as to control the position of each adjustment piston  1022  in the channel. The eight communication ports  1034  are in fluid communication with the eight adjustment cavities  1002 , respectively. The bottom portion of each adjustment piston  1022  is provided with a protrusion portion, and the protrusion portion serves as a limit for downward movement of each adjustment piston  1022 . The refrigeration system may include a plurality of third channels, a plurality of fourth channels and a plurality of switching apparatuses corresponding to the number of adjustment pistons  1022  so as to control the position of each adjustment piston  1022  in the channels by using the lubricant in the lubricant circuit. A specific control method thereof is similar to that described in  FIG.  3    to  FIG.  5   , and the description will not be repeated here. When the screw compressor  100  operates, the position of each adjustment piston  1022  in the channel can be independently controlled, thereby forming silencing channels with different silencing lengths. The silencing channels of different lengths can perform silencing on the noise of different wavelengths, and thereby, in addition to the wavelength corresponding to the peak energy, silencing can also be performed on wavelengths corresponding to other relatively high energy, broadening a silencing range. 
     The silencing structures shown in  FIG.  2    to  FIG.  10    above are each provided with the silencing channels on the inner wall of the discharge cavity  113 . When the sound waves matching the silencing length are transmitted to the inlet end of the silencing channel, most of the sound waves are reflected due to the fact that the presence of the silencing channels causes an acoustic impedance mismatch, and some sound waves are converted into heat energy due to a damping action and absorbed, so that only a small part of the sound waves can further propagate forwards to achieve silencing. When the silencing length is different, sound waves at more frequency bands can be absorbed, thereby improving a silencing effect. 
     It should be understood that although the eight holes are provided in the wall of the discharge cavity  113  in this application, any number of holes and the number of its correspondingly disposed adjustment pistons are within the protection scope of this application. 
       FIG.  11    shows a cross-sectional view of a fifth embodiment of the silencing structure. As shown in  FIG.  11   , a square hole  1122  is provided in the screw compressor housing  101 . The width of the hole  1122  is approximately the sum of diameters of the eight holes  122  in the embodiment shown in  FIG.  2   . The adjustment cavity  1104  of the adjustment box  132  communicates with the hole  1122  and forms a continuous channel. An adjustment piston  1142  is disposed in the continuous channel and can move in the continuous channel. The silencing channel  1188  is now formed by the hole  1122  starting from the inlet end to the end surface of the adjustment piston  1142 . When the adjustment pistons  1142  move in the continuous channel, different silencing lengths can be formed. 
     A plate  1144  is further disposed in the discharge cavity  113 . The plate  1144  is provided with a several perforations  1110 . The plate  1144  covers the hole  1122  and thereby covers the inlet end of the silencing channel  1188 , so that the sound waves can pass through the several perforations  1110  and enter the channel formed by the adjustment cavity  1104  and the hole  1122 . The perforations  1110  in the plate  1144  and the channels form a silencing structure. When the sound waves matching the silencing length are transmitted to the vicinity of the perforations  1110 , most of the sound waves are reflected due to the fact that the presence of the silencing channels causes an acoustic impedance mismatch, and some sound waves are converted into heat energy due to a damping action and absorbed, so that only a small part of the sound waves can further propagate forwards to achieve silencing. 
       FIG.  12    shows a cross-sectional view of a sixth embodiment of a silencing structure. The embodiment shown in  FIG.  12    is substantially the same as the embodiment shown in  FIG.  11   , and the description will not be repeated here. The difference from the embodiment shown in  FIG.  11    is that the discharge cavity  113  of the embodiment shown in  FIG.  12    is provided with two plates  1242  and  1244 . Several perforations are disposed in each of the two plates  1242  and  1244 . The two plates  1242  and  1244  can move relative to each other, thereby changing alignment area of the several perforations. Aligned parts of the two plates  1242  and  1244  form an additional silencing channel, so that the discharge cavity  113  can communicate with the silencing channel  1188  through the several perforations. By changing the area of the additional silencing channel, the pulsation wavelength mainly silenced by this silencing structure can be changed, thereby matching and reducing the peak energy under different operating conditions. 
     It should be noted that although the two plates are shown in this application, any number of plates are within the protection scope of this application, as long as the additional silencing channel can be formed between the plates. 
     Thus, this application provides a screw compressor, and the length of the silencing channel can be automatically adjusted according to the operating conditions (for example, the operating frequency, the exhaust temperature and the exhaust pressure) of the screw compressor, thereby effectively reducing the peak energy of exhaust pulsation under different operating conditions, reducing the noise. 
     In addition, the silencing structure of this application forms a portion of the silencing channel by providing holes in the inner wall, so that the silencing structure is small in size and compact in layout. This silencing structure does not increase flow resistance of the airflow and is easy to manufacture. 
     Although only some of the features of this application have been illustrated and described herein, various modifications and changes will occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all the above modifications and changes falling within the true spirit and scope of this application.