Patent Publication Number: US-10330115-B2

Title: Adjusting mechanism for centrifugal compressors

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 105140766 filed in Taiwan, R.O.C. on Dec. 9, 2016, the entire contents of which are hereby incorporated by reference. 
     TECHNICAL FIELD 
     The disclosure relates to an adjusting mechanism. 
     BACKGROUND 
     The conventional method of controlling the capacity of a centrifugal chiller is primarily to regulate the rotating speed and/or the opening of an inlet guide vane at a suction inlet of the centrifugal compressor to respond to the load variations, thereby adjusting the capacity of the centrifugal chiller. 
     SUMMARY 
     One embodiment of the disclosure provides an adjusting mechanism adaptive to a main body of a centrifugal compressor. The adjusting mechanism comprises a diffuser channel width adjusting assembly and a gas bypass assembly. The diffuser channel width adjusting assembly comprises a width adjusting annular plate and a first valve stem to adjust the width of the diffuser channel. The width adjusting annular plate is configured for being movably disposed in a diffuser channel of the main body. The first valve stem is connected to the width adjusting annular plate, and is configured for driving the width adjusting annular plate to move so as to adjust the width of the diffuser channel. The gas bypass assembly comprises a gas bypass valve and a second valve stem. The gas bypass valve is configured for being movably disposed in a gas bypass passage of the main body. The second valve stem is connected to the gas bypass valve, and is configured for driving the gas bypass valve to move so as to adjust the opening of the gas bypass port. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only and thus are not intending to limit the present disclosure and wherein: 
         FIG. 1  is a perspective and partial cross-sectional view of a centrifugal compressor in accordance with one embodiment of the disclosure; 
         FIG. 2  is a partial exploded view of the centrifugal compressor in  FIG. 1 ; 
         FIG. 3  is a planar view of a first box cam and a second box cam in  FIG. 2 ; 
         FIG. 4  is a partial cross-sectional view of the centrifugal compressor in  FIG. 1 ; 
         FIG. 5  to  FIG. 10  show the operation of the centrifugal compressor in  FIG. 1 ; and 
         FIG. 11  is a perspective and partial cross-sectional view of a diffuser channel width adjusting assembly and a drive shaft in accordance with the embodiment of the disclosure in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing. 
     Please refer to  FIG. 1  to  FIG. 4 .  FIG. 1  is a perspective and partial cross-sectional view of a centrifugal compressor in accordance with one embodiment of the disclosure.  FIG. 2  is a partial exploded view of the centrifugal compressor in  FIG. 1 .  FIG. 3  is a planar view of a first box cam and a second box cam in  FIG. 2 .  FIG. 4  is a partial cross-sectional view of the centrifugal compressor in  FIG. 1 . 
     As shown in  FIG. 1 ,  FIG. 2  and  FIG. 4 , a centrifugal compressor  1  includes an adjusting mechanism  10  and a main body  20 . The main body  20  has a diffuser channel  22 , a volute  23  and a gas bypass passage  24 . The diffuser channel  22  and the gas bypass passage  24  are connected to the volute  23 , and one side of the gas bypass passage  24  has a gas bypass port  26 . The gas bypass port  26  is connected to an inlet chamber  25  of the main body  20 . 
     The adjusting mechanism  10  includes a drive shaft  100 , a diffuser channel width adjusting assembly  200 , a gas bypass assembly  300  and an actuator  400 . 
     The drive shaft  100  is rotatably disposed in the main body  20 . The diffuser channel width adjusting assembly  200  includes a first box cam  210 , a width adjusting annular plate  220  and a first valve stem  230 . The first box cam  210  is disposed on the drive shaft  100  and has a first cam groove  211 . A distance between a part of the first cam groove  211  and an axis A of the drive shaft  100  is different from a distance between another part of the first cam groove  211  and the axis A of the drive shaft  100 . 
     As shown in  FIG. 3 , in this embodiment, a distance L 1  between a part of the first cam groove  211  on the positive Y-direction side relative to the axis A and the axis A is less than a distance L 3  between another part of the first cam groove  211  on the negative Z-direction side relative to the axis A and the axis A. Also, the distance L 3  is equal to a distance L 4  between another part of the first cam groove  211  on the negative Y-direction side relative to the axis A and the axis A. However, the present disclosure is not limited thereto. In other embodiments, the path of the first cam groove may be adjusted according to actual requirements. 
     As shown in  FIG. 2  and  FIG. 4 , the width adjusting annular plate  220  is movably disposed at the diffuser channel  22  of the main body  20 . One end of the first valve stem  230  is slidably located in the first cam groove  211 , and the other end of the first valve stem  230  is connected to the width adjusting annular plate  220  in order to drive the width adjusting annular plate  220  to move, thereby adjusting a width D 1  of the diffuser channel  22 . 
     In this embodiment, the diffuser channel width adjusting assembly  200  further includes a shaft bearing  240  and two shaft bearing fixing rings  250  and  260 . The shaft bearing  240  is, for example, a linear bearing. The shaft bearing  240  is disposed on the main body  20 . The shaft bearing fixing rings  250  and  260  are disposed on the main body  20 . The shaft bearing  240  is located between and pressed by the two shaft bearing fixing rings  250  and  260 . The first valve stem  230  penetrates through the shaft bearing  240  and the two shaft bearing fixing rings  250  and  260 , so that the smoothness of linear movement of the first valve stem  230  is improved by the shaft bearing  240 . 
     As shown in  FIG. 2  and  FIG. 4 , the gas bypass assembly  300  includes a second box cam  310 , a gas bypass valve  320  and a second valve stem  330 . The second box cam  310  is disposed on the drive shaft  100  and has a second cam groove  311 . A distance between a part of the second cam groove  311  and the axis A of the drive shaft  100  is different from a distance between another part of the second cam groove  311  and the axis A of the drive shaft  100 . As shown in  FIG. 3 , in this embodiment, the distance L 1  between a part of the second cam groove  311  on the positive Y-direction side relative to the axis A and the axis A is equal to a distance L 2  between another part of the second cam groove  311  on the negative Z-direction side relative to the axis A and the axis A. Also, the distance L 2  is less than the distance L 4  between a part of the second cam groove  311  on the negative Y-direction side relative to the axis A and the axis A. However, the present disclosure is not limited thereto. In other embodiments, the path of the first cam groove may be adjusted according to actual requirements. 
     As shown in  FIG. 2  and  FIG. 4 , the gas bypass valve  320  is movably disposed in the gas bypass passage  24  of the main body  20 . One end of the second valve stem  330  is slidably located in second cam groove  311 , and the other end of the second valve stem  330  is connected to the gas bypass valve  320  in order to drive the gas bypass valve  320  to move, thereby opening or closing the gas bypass port  26 . 
     In this embodiment, the gas bypass assembly  300  further includes a fixed base  340 , a compression spring  350 , an airtight gasket  360  and a fixing nut  370 . The fixed base  340  is fixed in the main body  20 . The second valve stem  330  is slidably disposed on the fixed base  340 , and the gas bypass valve  320  is located on a side of the fixed base  340  close to the drive shaft  100  in order to close the gas bypass port  26 . The fixing nut  370  is located on a side of the gas bypass valve  320  close to the drive shaft  100 . The airtight gasket  360  is located between and pressed by the fixing nut  370  and the gas bypass valve  320 . Therefore, the gas bypass valve  320  is able to seal the gas bypass port  26  via the airtight gasket  360 . 
     The compression spring  350  is located between and pressed by the fixed base  340  and the gas bypass valve  320 , and the compression spring  350  constantly forces the gas bypass valve  320  to seal the gas bypass port  26 . 
     The actuator  400  is, for example, a motor. The drive shaft  100  is connected to the actuator  400 , so that the actuator  400  is able to drive the drive shaft  100  to rotate either clockwise or counterclockwise. 
     Please refer to  FIG. 3  to  FIG. 10 .  FIG. 5  to  FIG. 10  show the operation of the centrifugal compressor in  FIG. 1 . As shown in  FIG. 3  and  FIG. 4 , the drive shaft  100  is at a start position, and the drive shaft  100  is at a first rotation angle (such as around 0 degree) while it is at the start position. In such a case, one end of the first valve stem  230  and one end of the second valve stem  330  are respectively guided by the first cam groove  211  and the second cam groove  311 , and a distance from the position of one end of the first valve stem  230  located in the first cam groove  211  to the axis A of the drive shaft  100  is equal to a distance from the position of one end of the second valve stem  330  located in the second cam groove  311  to the axis A of the drive shaft  100 . As a result, the first valve stem  230  is able to drive the width adjusting annular plate  220  to move to a position relatively close to the drive shaft  100 . As shown in  FIG. 4 , the width of the diffuser channel  22  has a first width D 1 . The first width D 1  is, for example, 7 millimeters (mm). The second valve stem  330  is able to drive the gas bypass valve  320  to move to a position relatively close to the drive shaft  100  in order to seal the gas bypass port  26 . 
     Then, as shown in  FIG. 5  and  FIG. 6 , when the drive shaft  100  is rotated to a second rotation angle (such as around 90 degrees) along a direction of arrow a, one end of the first valve stem  230  and one end of the second valve stem  330  are respectively guided by the first cam groove  211  and the second cam groove  311 , the distance from the position of one end of the first valve stem  230  located in the first cam groove  211  to the axis A of the drive shaft  100  becomes greater (L 3 &gt;L 1 , as shown in  FIG. 3 ), and the distance from the position of one end of the second valve stem  330  located in the second cam groove  311  to the axis A of the drive shaft  100  remains the same (L 2 =L 1 , as shown in  FIG. 3 ). As a result, the first valve stem  230  is able to drive the width adjusting annular plate  220  to move to a position relatively away from the drive shaft  100 . As shown in  FIG. 6 , the diffuser channel  22  has a second width D 2 . The second width D 2  is, for example, 3 mm. The second valve stem  330  keeps the gas bypass valve  320  at the position relatively close to the drive shaft  100 , and the gas bypass port  26  is remained closed. 
     Then, as shown in  FIG. 7  and  FIG. 8 , when the drive shaft  100  is kept rotating along the direction of arrow a to a third rotation angle (such as around 180 degrees), one end of the first valve stem  230  and one end of the second valve stem  330  are respectively guided by the first cam groove  211  and the second cam groove  311 , the distance from the position of one end of the first valve stem  230  located in the first cam groove  211  to the axis A of the drive shaft  100  remains the same (L 3 =L 4 , as shown in  FIG. 3 ), and the distance from the position of one end of the second valve stem  330  located in the second cam groove  311  to the axis A of the drive shaft  100  becomes greater (L 4 &gt;L 2 , as shown in  FIG. 3 ). As a result, the diffuser channel  22  is kept in the second width D 2 . The second valve stem  330  is able to drive the gas bypass valve  320  to move to a position relatively away from the drive shaft  100  in order to open the gas bypass port  26 . 
     Then, as shown in  FIG. 9  and  FIG. 10 , when the drive shaft  100  is kept rotating along the direction of arrow a to a fourth rotation angle (such as around 270 degrees), one end of the first valve stem  230  and one end of the second valve stem  330  are respectively guided by the first cam groove  211  and the second cam groove  311 , the distance from the position of one end of the first valve stem  230  located in the first cam groove  211  to the axis A of the drive shaft  100  remains the same (L 4 =L 3 , as shown in  FIG. 3 ), and the distance from the position of one end of the second valve stem  330  located in the second cam groove  311  to the axis A of the drive shaft  100  becomes smaller (L 2 &lt;L 4 , as shown in  FIG. 3 ). As a result, the diffuser channel  22  is kept in the second width D 2 . The second valve stem  330  is able to drive the gas bypass valve  320  to move to the position relatively close to the drive shaft  100  in order to close the gas bypass port  26 . 
     It is noted that if the drive shaft  100  is kept rotating along the direction of arrow a, the drive shaft  100  will be back to the condition as it is at the first rotation angle (such as around 0 degree). 
     As the aforementioned operation as discussed, while the drive shaft  100  is rotated within a first rotation angle range (e.g. 0 degree to 90 degrees), the distance from the position of one end of the first valve stem  230  located in the first cam groove  211  to the axis A of the drive shaft  100  varies; while the drive shaft  100  is rotated within a second rotation angle range (e.g. 90 degrees to 180 degrees) which is different from the first rotation angle range, the distance from the position of one end of the first valve stem  230  located in the first cam groove  211  to the axis A of the drive shaft  100  is fixed. 
     In addition, while the drive shaft  100  is rotated within the first rotation angle range (e.g. 0 degree to 90 degrees), the distance from the position of one end of the second valve stem  330  located in the second cam groove  311  to the axis A of the drive shaft  100  is fixed; while the drive shaft  100  is rotated within the second rotation angle range (e.g. 90 degrees to 180 degrees) which is different from the first rotation angle range, the distance from the position of one end of the second valve stem  330  located in the second cam groove  311  to the axis A of the drive shaft  100  varies. 
     According to the embodiment as described above, the combination of controlling the width of the diffuser channel  22  and controlling the gas bypass port  26  is favorable for expanding the operating envelope of the centrifugal compressor  1  and preventing surge. Taking a 200USRT single-stage R134a refrigerant centrifugal compressor for example, its rated rotational speed is 23,000 rpm, and its predetermined pressure ratio (Pr) is 2.58. Given the condition that the pressure ratio is 2.2 and the rotational speed is 20,460 rpm when in actual operation. If the width of the diffuser channel  22  is 7 mm, the velocity of the refrigerant gas flow through the diffuser channel  22  is reduced when the mass flow rate of the refrigerant gas of the centrifugal compressor  1  is less than 3.7 kg/s. However, if the width of the diffuser channel  22  is reduced from 7 mm to 3 mm, the velocity of the refrigerant gas flow is able to maintain the stable operation of the centrifugal compressor  1  until the mass flow rate is less than 3.15 kg/s, which means that the operating envelope of the centrifugal compressor  1  is expanded. The phrase “operating envelope of the centrifugal compressor” means a range of the mass flow rate of the refrigerant gas flowing in the centrifugal compressor that can maintain the stable operation of the centrifugal compressor. When the width is reduced from 7 mm to 3 mm while the centrifugal compressor  1  is operated at the same pressure ratio and the same rotational speed, the mass flow rate of the refrigerant gas of the centrifugal compressor is dropped from 3.7 kg/s to 3.15 kg/s without stalling the centrifugal compressor  1 ; that is, the refrigeration capacity is reduced by 24.4 refrigeration tons, and the percentage of operating envelope is raised by 12.2%, which clearly shows that the adjustment of the width of the diffuser channel  22  having significant effect on reducing the operating capacity of the centrifugal compressor  1  but without stalling the centrifugal compressor  1 . The operating capacity of the centrifugal compressor  1  can be further reduced when the adjustment of the width of the diffuser channel  22  is cooperated with the control of the gas bypass port  26 . As a result, the operating envelope of the centrifugal compressor  1  is further expanded. 
     In addition, by the design of the coupling mechanism, the width of the diffuser channel and the opening of the gas bypass port are able to be adjusted simultaneously by one actuator and one drive shaft. 
     Furthermore, the design of the diffuser channel width adjusting mechanism and the gas bypass valve opening adjusting mechanism coupled in the centrifugal compressor has positive effect on adjusting capacity and expanding the operating envelope for preventing the compressor surge. 
     Moreover, the adjusting mechanism is favorable for simplifying the piping of the centrifugal chiller, reducing the complexity of controlling the centrifugal chiller, and reducing the piping cost of the centrifugal chiller. 
     In the aforementioned embodiment, although the drive shaft  100  and the second valve stem  330  are driven by the second box cam  310  which has the second cam groove  311 , but the present disclosure is not limited thereto. In other embodiments, the drive shaft  100  and the second valve stem  330  may be driven by a gear and rack assembly. 
     Please refer to  FIG. 11 .  FIG. 11  is a perspective and partial cross-sectional view of a diffuser channel width adjusting assembly and a drive shaft in accordance with the embodiment of the disclosure. 
     In this embodiment, the diffuser channel width adjusting assembly  200  further includes a plurality of support rods  270 . One end of each support rod  270  is connected to the width adjusting annular plate  220 , and the other end of each support rod  270  is movably disposed on main body  20 . The movement of the width adjusting annular plate  220  is in a smooth manner when the width adjusting annular plate  220  is pushed by the first valve stem  230  and the support rods  270  together. 
     According to the adjusting mechanism for the centrifugal compressor as described above, through the combination of controlling the width of the diffuser channel and the opening of the gas bypass port, the velocity of the refrigerant gas flow is raised by reducing the width of the diffuser channel while the centrifugal compressor is operated at the same pressure ratio and rotational speed, thereby preventing the compressor surge caused by the decreasing of refrigerant gas flow. As a result, the operating envelope of the centrifugal compressor is expanded. 
     The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical applications, to thereby enable others skilled in the art to best utilize the disclosure and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalents.