Patent Publication Number: US-2020300262-A1

Title: Keyless impeller system and method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from and the benefit of U.S. Provisional Application Ser. No. 62/563,968, entitled “KEYLESS IMPELLER SYSTEM AND METHOD,” filed Sep. 27, 2017, and U.S. Provisional Application Ser. No. 62/610,785, entitled “KEYLESS IMPELLER SYSTEM AND METHOD,” filed Dec. 27, 2017, which are hereby incorporated by reference in their entireties for all purposes. 
    
    
     BACKGROUND 
     This application relates generally to vapor compression systems incorporated in air conditioning and refrigeration applications, and, more particularly, to an impeller system for a vapor compression system. 
     Vapor compression systems are utilized in residential, commercial, and industrial environments to control environmental properties, such as temperature and humidity, for occupants of the respective environments. The vapor compression system circulates a working fluid, typically referred to as a refrigerant, which changes phases between vapor, liquid, and combinations thereof in response to being subjected to different temperatures and pressures associated with operation of the vapor compression system. For example, the vapor compression system utilizes a compressor to circulate the refrigerant to a heat exchanger which may transfer heat between the refrigerant and another fluid flowing through the heat exchanger. The compressor includes a shaft that drives rotation of an attached impeller to facilitate circulation of the refrigerant. The impeller is coupled to the shaft via keys, pins, or splines, which may be difficult to machine due to manufacturing tolerances. 
     SUMMARY 
     In one embodiment, a compressor for a heating, ventilating, air conditioning, and refrigeration (HVAC&amp;R) unit, includes an impeller, a shaft configured to rotate the impeller, and a fastener. The impeller includes an opening and does not include keys, splines, pins, or any combination thereof. Then fastener is coupled to an end of the shaft and extends through the opening of the impeller, in which the fastener is configured to stretch in an axial direction relative to the shaft via a tensioner during assembly of the compressor. 
     In another embodiment, a method of coupling an impeller to a shaft for a compressor includes inserting a fastener through an opening of the impeller, in which a first end of the fastener is coupled to a second end of the shaft, coupling a nut to a third end of the fastener such that the nut is disposed against a surface of the impeller, stretching the fastener in an axial direction away from the shaft, and tightening the nut along the fastener while the fastener is in a stretched position. 
     In another embodiment, a system to couple an impeller to a shaft of a compressor includes a fastener configured to couple to an end of the shaft at a first end of the fastener, a nut configured to couple to the fastener at a second end of the fastener, and a tensioner configured to stretch the fastener, in which the tensioner is configured to be disposed against a surface of the impeller. The fastener is a threaded stud, a tie bolt, or any combination thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an embodiment of a building that may utilize a heating, ventilation, air conditioning, and refrigeration (HVAC&amp;R) system in a commercial setting, in accordance with an aspect of the present disclosure; 
         FIG. 2  is a perspective view of a vapor compression system, in accordance with an aspect of the present disclosure; 
         FIG. 3  is a schematic of an embodiment of the vapor compression system of  FIG. 2 , in accordance with an aspect of the present disclosure; 
         FIG. 4  is a schematic of an embodiment of the vapor compression system of  FIG. 2 , in accordance with an aspect of the present disclosure; 
         FIG. 5  is a sectional view of an embodiment of a compressor impeller assembly utilized in the vapor compression system of  FIGS. 2-4 , in accordance with an aspect of the present disclosure; 
         FIG. 6  is a sectional view of an embodiment of a tensioner utilized to couple the impeller of  FIG. 5  to a shaft of a compressor, in accordance with an aspect of the present disclosure; 
         FIG. 7  is a block diagram of an embodiment of a process for coupling the impeller of  FIG. 5  to the compressor shaft, in accordance with an aspect of the present disclosure; and 
         FIG. 8  is a block diagram of an embodiment of a process for stretching a fastener of the impeller system of  FIG. 5  using the tensioner of  FIG. 6 , in accordance with an aspect of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     Embodiments of the present disclosure are directed towards a heating, ventilating, air conditioning, and refrigeration (HVAC&amp;R) system that uses a compressor to circulate refrigerant through a refrigerant loop. The compressor may be coupled to a condenser of the HVAC&amp;R system along the refrigerant loop. The compressor may compress the refrigerant to increase a pressure of the refrigerant and direct the refrigerant to the condenser. The refrigerant may flow towards the condenser of the HVAC&amp;R system where it may transfer heat to a working fluid in the condenser. In some embodiments, the compressor may be a centrifugal compressor and include an impeller that rotates at a relatively high speed to circulate and compress the refrigerant. In a centrifugal compressor, the impeller may impart a centrifugal force on the refrigerant to enable compression of the refrigerant. 
     The impeller of a centrifugal compressor may be coupled to a shaft that is rotated at a high speed by a motor. Typically, the impeller is coupled to the shaft via keys, splines, pins, or a combination thereof, which transfers torque from the shaft to the impeller. Thus, the impeller rotates as the shaft rotates. However, machining the impeller and the shaft to accommodate the keys, splines, or pins may be complex, expensive, and time-consuming. Since the impeller rotates at a high speed, the keys, splines, or pins may be machined such that the rotation of the shaft does not cause excess stress on the impeller. For example, machining the keys, splines, or pins may be precise enough to enable the impeller to couple to the shaft without interference from keys, splines, or pins. As such, there may be difficulties that arise during machining to achieve such precision. In addition, assembly of existing systems may include coupling the impeller onto the shaft while imparting torque onto the shaft, thereby blocking rotation of the shaft. As such, the shaft may be kept in place to facilitate the coupling process, which may further enhance complexity of assembly. 
     In accordance with certain embodiments of the present disclosure, it is now recognized that a new method of coupling the impeller onto the shaft may facilitate assembly of the compressor. That is, a method that does not use keys, splines, or pins to couple the impeller onto the shaft may reduce assembly time and/or costs of fabrication and assembly of the compressor. 
     To this end, embodiments of the present disclosure are directed to a shaft that may thread to a fastener, such that a first end of the fastener is coupled to the shaft. An opening of an impeller may be positioned over a second end of the fastener so that the impeller (e.g., a surface of the impeller) abuts a face of the shaft. A nut may couple to a remaining length of the fastener to clamp the impeller to the shaft. A tensioner (e.g., a hydraulic tensioner) may facilitate securement of the nut to the fastener and apply a predetermined amount of force between the impeller and the shaft. As used herein, a tensioner refers to any device or mechanism configured to apply a force that stretches the fastener in an axial direction defining the fastener and/or the shaft. Although the present disclosure primarily focuses on the use of a hydraulic tensioner, it should be appreciated that other types of devices, such as a mechanical tensioner, an electrical tensioner, another suitable device configured to apply an axial force to the fastener, or any combination thereof, may be utilized to stretch the fastener and enable the nut to be further tightened onto the fastener. In this manner, machined keys, splines, or pins may be eliminated, and torque applied to the shaft may no longer be utilized during assembly to facilitate securing the nut onto the fastener. This method may also enable the impeller to be more aerodynamic. For example, the impeller may include a single opening through a center of the impeller, which may reduce a resistance of the refrigerant flow when compared to impellers that include keys, splines, and/or pins. Furthermore, the absence of keys, splines, and/or pins may reduce the moment of inertia of the assembly to facilitate rotation of the impeller. As such, a higher efficiency of the compressor may be achieved, which may reduce energy costs. 
     Turning now to the drawings,  FIG. 1  is a perspective view of an embodiment of an environment for a heating, ventilation, air conditioning, and refrigeration (HVAC&amp;R) system  10  in a building  12  for a typical commercial setting. The HVAC&amp;R system  10  may include a vapor compression system  14  that supplies a chilled liquid, which may be used to cool the building  12 . The HVAC&amp;R system  10  may also include a boiler  16  to supply warm liquid to heat the building  12  and an air distribution system which circulates air through the building  12 . The air distribution system can also include an air return duct  18 , an air supply duct  20 , and/or an air handler  22 . In some embodiments, the air handler  22  may include a heat exchanger that is connected to the boiler  16  and the vapor compression system  14  by conduits  24 . The heat exchanger in the air handler  22  may receive either heated liquid from the boiler  16  or chilled liquid from the vapor compression system  14 , depending on the mode of operation of the HVAC&amp;R system  10 . The HVAC&amp;R system  10  is shown with a separate air handler on each floor of building  12 , but in other embodiments, the HVAC&amp;R system  10  may include air handlers  22  and/or other components that may be shared between or among floors. 
       FIGS. 2 and 3  are embodiments of the vapor compression system  14  that can be used in the HVAC&amp;R system  10 . The vapor compression system  14  may circulate a refrigerant through a circuit starting with a compressor  32 . The circuit may also include a condenser  34 , an expansion valve(s) or device(s)  36 , and a liquid chiller or an evaporator  38 . The vapor compression system  14  may further include a control panel  40  that has an analog to digital (A/D) converter  42 , a microprocessor  44 , a non-volatile memory  46 , and/or an interface board  48 . 
     Some examples of fluids that may be used as refrigerants in the vapor compression system  14  are hydrofluorocarbon (HFC) based refrigerants, for example, R-410A, R-407, R-134a, hydrofluoro olefin (HFO), “natural” refrigerants like ammonia (NH 3 ), R-717, carbon dioxide (CO 2 ), R-744, or hydrocarbon based refrigerants, water vapor, or any other suitable refrigerant. In some embodiments, the vapor compression system  14  may be configured to efficiently utilize refrigerants having a normal boiling point of about 19 degrees Celsius (66 degrees Fahrenheit) at one atmosphere of pressure, also referred to as low pressure refrigerants, versus a medium pressure refrigerant, such as R-134a. As used herein, “normal boiling point” may refer to a boiling point temperature measured at one atmosphere of pressure. 
     In some embodiments, the vapor compression system  14  may use one or more of a variable speed drive (VSDs)  52 , a motor  50 , the compressor  32 , the condenser  34 , the expansion valve or device  36 , and/or the evaporator  38 . The motor  50  may drive the compressor  32  and may be powered by a variable speed drive (VSD)  52 . The VSD  52  receives alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source, and provides power having a variable voltage and frequency to the motor  50 . In other embodiments, the motor  50  may be powered directly from an AC or direct current (DC) power source. The motor  50  may include any type of electric motor that can be powered by a VSD or directly from an AC or DC power source, such as a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor, or another suitable motor. 
     The compressor  32  compresses a refrigerant vapor and delivers the vapor to the condenser  34  through a discharge passage. In some embodiments, the compressor  32  may be a centrifugal compressor. The refrigerant vapor delivered by the compressor  32  to the condenser  34  may transfer heat to a cooling fluid (e.g., water or air) in the condenser  34 . The refrigerant vapor may condense to a refrigerant liquid in the condenser  34  as a result of thermal heat transfer with the cooling fluid. The liquid refrigerant from the condenser  34  may flow through the expansion device  36  to the evaporator  38 . In the illustrated embodiment of  FIG. 3 , the condenser  34  is water cooled and includes a tube bundle  54  connected to a cooling tower  56 , which supplies the cooling fluid to the condenser. 
     The liquid refrigerant delivered to the evaporator  38  may absorb heat from another cooling fluid, which may or may not be the same cooling fluid used in the condenser  34 . The liquid refrigerant in the evaporator  38  may undergo a phase change from the liquid refrigerant to a refrigerant vapor. As shown in the illustrated embodiment of  FIG. 3 , the evaporator  38  may include a tube bundle  58  having a supply line  60 S and a return line  60 R connected to a cooling load  62 . The cooling fluid of the evaporator  38  (e.g., water, ethylene glycol, calcium chloride brine, sodium chloride brine, or any other suitable fluid) enters the evaporator  38  via return line  60 R and exits the evaporator  38  via supply line  60 S. The evaporator  38  may reduce the temperature of the cooling fluid in the tube bundle  58  via thermal heat transfer with the refrigerant. The tube bundle  58  in the evaporator  38  can include a plurality of tubes and/or a plurality of tube bundles. In any case, the vapor refrigerant exits the evaporator  38  and returns to the compressor  32  by a suction line to complete the cycle. 
       FIG. 4  is a schematic of the vapor compression system  14  with an intermediate circuit  64  incorporated between condenser  34  and the expansion device  36 . The intermediate circuit  64  may have an inlet line  68  that is directly fluidly connected to the condenser  34 . In other embodiments, the inlet line  68  may be indirectly fluidly coupled to the condenser  34 . As shown in the illustrated embodiment of  FIG. 4 , the inlet line  68  includes a first expansion device  66  positioned upstream of an intermediate vessel  70 . In some embodiments, the intermediate vessel  70  may be a flash tank (e.g., a flash intercooler). In other embodiments, the intermediate vessel  70  may be configured as a heat exchanger or a “surface economizer.” In the illustrated embodiment of  FIG. 4 , the intermediate vessel  70  is used as a flash tank, and the first expansion device  66  is configured to lower the pressure of (e.g., expand) the liquid refrigerant received from the condenser  34 . During the expansion process, a portion of the liquid may vaporize, and thus, the intermediate vessel  70  may be used to separate the vapor from the liquid received from the first expansion device  66 . Additionally, the intermediate vessel  70  may provide for further expansion of the liquid refrigerant because of a pressure drop experienced by the liquid refrigerant when entering the intermediate vessel  70  (e.g., due to a rapid increase in volume experienced when entering the intermediate vessel  70 ). The vapor in the intermediate vessel  70  may be drawn by the compressor  32  through a suction line  74  of the compressor  32 . In other embodiments, the vapor in the intermediate vessel may be drawn to an intermediate stage of the compressor  32  (e.g., not the suction stage). The liquid that collects in the intermediate vessel  70  may be at a lower enthalpy than the liquid refrigerant exiting the condenser  34  because of the expansion in the expansion device  66  and/or the intermediate vessel  70 . The liquid from intermediate vessel  70  may then flow in line  72  through a second expansion device  36  to the evaporator  38 . 
     As noted above, a compressor, such as the compressor  32 , may use an impeller to enable the circulation of refrigerant through the vapor compression system  14 . For example, the impeller may contain blades that, during rotation, draw in refrigerant towards the center of the impeller and into the compressor  32 . The impeller may impart centrifugal force on the refrigerant such that a velocity and kinetic energy of the refrigerant increases as the refrigerant flows through a compressor housing. The high velocity refrigerant is directed into a diffuser which may convert the kinetic energy of the refrigerant into pressure, thereby compressing the refrigerant. In some embodiments, the impeller may couple to a rotating shaft of the compressor, such that the shaft drives rotation of the impeller. The present disclosure includes an improved method of securing the impeller to the shaft. For example, the method may include coupling a fastener to one end of the shaft, such as via threads, inserting the fastener into an opening through a center of the impeller, and threading a nut onto the fastener to clamp the shaft and impeller to one another. The method may also include using a tensioner to thread the nut on the fastener and apply a predetermined amount of force between the impeller and the shaft. 
       FIG. 5  is a sectional side view of an embodiment of an impeller assembly  100 . As shown in the illustrated embodiment of  FIG. 5 , the impeller assembly  100  includes an impeller  102 , a shaft  104 , and a fastener  106 . In some embodiments, the shaft  104  and the fastener  106  may each be cylindrical in shape, where the fastener  106  is smaller in diameter when compared to the shaft  104 . The fastener  106  may contain external or male threads on a first end  107  and a second end  109 . On an end  111  of the shaft  104 , there may be a shaft opening  113  with internal or female threads, such that the first end  107  of the fastener  106  may be inserted and threaded into the shaft opening  113 . When the fastener  106  is fully inserted into or threaded onto the shaft  104 , at least a portion  115  of a length of the fastener  106  may be exposed. That is, when the fastener  106  and the shaft  104  are coupled to one another, the second end  107  of the fastener  106  may not be inserted into the shaft opening  113  and remain exposed. 
     The second end  109  of the fastener  106  may be inserted into an opening  117  extending through a center of the impeller  102 . In some embodiments, the impeller  102  may be made from aluminum or an aluminum alloy to increase a strength of the impeller  102  and enable the impeller  102  to withstand operating conditions in the compressor, while maintaining a relatively low weight. The impeller  102  may contain the opening  117  that extends through a body of the impeller  102 , such that the fastener  106  may be disposed within and support the impeller  102 . In some embodiments, the opening  117  may extend through a center of the impeller  102 . The opening  117  may also include sections having different diameters as the opening  117  extends through the impeller  102  along an axis  108 . 
     For example, the opening  117  may include a first diameter portion  118  that may extend for a first length  119  of the impeller. Additionally, the opening  117  may include a second diameter portion  120  of the opening that may extend for a second length  121  of the impeller  102 . The second diameter portion  120  may be of a larger diameter relative to the first diameter portion  118 . A portion of the fastener  106  may be inserted into the first diameter portion  118 . When the fastener  106  is inserted into the opening  117 , a surface  110  of the shaft  104  may contact the impeller  102 . The impeller  102  may contain a lip  125  that acts as an interface between the impeller  102  and the surface  110 . As such, the shaft  104  may be substantially aligned with the impeller  102 . In other words, the shaft  104 , the impeller  102 , and the fastener  106  are all aligned coaxially with one another along the axis  108 . 
     Additionally or alternatively, a friction modifier may be disposed on the surface  110  to enhance a torque capacity of the impeller  102 . For example, a coefficient of friction between the impeller  102  and shaft  104  may increase by disposing a friction modifier material on the surface  110 . In some cases, the coefficient of friction between the impeller  102  and the shaft  104  decreases when a liquid (e.g., water, oil, or a lubricant) is present on the surface  110 . The coefficient of friction may decrease between 1% and 50%, between 5% and 30%, or between 15% and 25% when compared to conditions where liquid is not present on the surface  110  (e.g., dry conditions). Including the friction modifier (e.g., silicon carbide or diamond particles) on the surface  110  may increase the coefficient of friction between the impeller  102  and the shaft  104  when compared to dry conditions, regardless of whether liquid is present on the surface  110 . For example, the friction modifier may act as keys on the surface  110  between the impeller  102  and the shaft  104  to thereby increase the coefficient of friction at the surface  110 . In some embodiments, the friction modifier may be sprayed onto the surface  110  in liquid form and/or in gel form. Additionally or alternatively, the friction modifier may be applied to the surface  110  as a powder using an adhesive. In any case, the friction modifier is compressed at the surface  110  to enhance the coefficient of performance at the surface  110  between the impeller  102  and the shaft  104 . Accordingly, the torque capacity of the impeller  102  is increased. 
     When inserted, a portion of the fastener  106  may extend past the second diameter portion  120  of the opening  117 , such that at least a portion  115  of the threads on the second end  109  of the fastener  106  are accessible through the second diameter portion  120  of the opening  117 . The second diameter portion  120  of the opening  117  may enable a nut  112  and a washer  114  to be disposed over and/or coupled to the second end  109  of the fastener  106 . The transition from the first diameter portion  118  to the second diameter portion  120  may form a mounting surface  116  for the washer  114  and/or the nut  112  against the impeller  102 . The washer  114  may press against the mounting surface  116  the nut  112  and the fastener  106  are secured to one another via threading. Additionally, the nut  112  may clamp down onto the washer  114  to apply a force against the impeller  102  and to secure the impeller  102  onto the shaft  104 . 
     After initial coupling of the components, the fastener  106  may be stretched (e.g., elastically deformed) along the axis  108  in a direction  124  to secure the impeller  102  to the shaft  104  and to apply a predetermined amount of force between the impeller  102  and the shaft  104 . In some embodiments, the fastener  106  and the nut  112  may be designed in a specific manner. For example, stretching the fastener  106  may also stretch the threads of the fastener  106 , such that adjacent threads along the fastener  106  are spaced further from one another upon stretching. Thus, the threads on the fastener  106  and the nut  112  may each contain a non-standard pitch to enable the nut  112  to be threaded onto the fastener  106  when the fastener  106  is stretched. That is, the nut  112  may contain threads to accommodate the increased spacing between adjacent threads of the fastener and to enable the nut  112  to be further tightened onto the fastener  106  when the fastener  106  is in a stretched position. 
     Moreover, the fastener  106  may include a body portion  126  that lacks threads. The body portion  126  may include a smaller diameter than the threaded first and second ends  107 ,  109 , such that during the stretching of the fastener  106 , the tensile stresses produced from stretching are concentrated in the body portion  126 . Concentrating the stress at the body portion  126  avoids stripping the threads at the first and second ends  107 ,  109  of the fastener  106  during stretching. 
     Furthermore, the fastener  106  may contain a neck portion  128  (e.g., a portion of the body portion  126 ) having an increased diameter to maintain contact with a surface within the opening  117  of the impeller  102 . That is, the majority of the body portion  126  of the fastener  106  has a diameter that is less than the diameter of the first diameter portion  118  of the impeller  102 . However, the neck portion  128  may be sized to maintain contact with the walls of the first diameter portion  118  of the opening  117 , such as with a slip fit interface. The neck portion  128  thus ensures that the fastener  106  remains substantially centered in the opening  117  of the impeller  102  during stretching. 
     Furthermore, the fastener  106 , the shaft  104 , the washer  114 , and the nut  112 , may be made from high strength steel, such as a steel alloy. High strength steel may increase strength of the impeller assembly  100  and enable the impeller assembly  100  to withstand the forces that may come from both the stretching of the fastener  106  and the operation of the compressor. The body portion  126  and the neck portion  128  of the fastener  106 ; the material of the fastener  106 , the shaft  104 , the washer  114 , and the nut  112 ; and the non-standard pitch of the fastener  106  and the nut  112  may increase longevity of the fastener  106 , the shaft  104 , the washer  114 , and the nut  112  during the stretching conditions and operating conditions of the compressor. 
       FIG. 6  is a sectional view of an embodiment of a device that may be used to stretch the fastener  106 . As shown in the illustrated embodiment of  FIG. 6 , a tensioner  150  is coupled to the impeller  102  and the fastener  106 . The tensioner  150  may be partially inserted into the opening  117  (e.g., the second diameter portion  120 ) of the impeller  102 . The tensioner  150  may include a shell  152  that contacts the washer  114  when the tensioner  150  is fully inserted over the fastener  106 . As such, the portion  115  of the fastener  106  may be fully inserted into the tensioner  150 . Within the shell  152 , the tensioner  150  may contain a grip  154  that secures onto the second end  109  of the fastener  106  via threads, for example. When the tensioner  150  is positioned against the impeller  102 , the grip  154  may be able to move in an axial direction. For example, the grip  154  may move in the direction  124  and stretch the fastener  106  in the direction  124 . In some embodiments, the tensioner  150  may be a hydraulic tensioner and fluid may be used to move the grip  154  in the direction  124 . For example, a hydraulic fluid source (not pictured) may be coupled to the tensioner  150  at an inlet  151  and supply fluid through the inlet  151  into the tensioner  150  to direct a member  155  in the direction  124  to drive movement of the grip  154  in the direction  124 . 
     Furthermore, the shell  152  may contain a tightening element  156  that attaches to the nut  112  and may be configured to rotate the nut  112  in a circumferential direction  159  about the axis  108 . Accordingly, the tightening element  156  is utilized to thread the nut  112  onto the fastener  106 . For example, as the grip  154  directs (e.g., stretches) the fastener  106  in the direction  124 , the tightening element  156  is rotated in the circumferential direction  159  to tighten the nut  112  on the fastener and drive the washer  114  and the nut  112  in a direction  161 , opposite the direction  124 . To rotate the tightening element  156 , the tightening element  156  may contain a hole  157  which may extend along and/or through the diameter of the tightening element  156 . Additionally, the shell  152  may also contain an access point  158  that enables access to the hole  157  of the tightening element  156 . Accordingly, a tool  160  may be inserted into the hole  157  and act as a lever to enable rotation of the tightening element  156 . As the tightening element  156  rotates in the circumferential direction  159  about the axis  108 , the tightening element  156  may apply a torque onto the nut  112  and likewise rotate the nut  112 . Although  FIG. 6  depicts the tool  160  as an Allen wrench, the tool  160  may be any other component or device that may be inserted into the holes  157  of the tightening element  156 . 
       FIG. 7  is a flow diagram of an embodiment of a method  200  for securely clamping the impeller  102  onto the shaft  104  by stretching the fastener  106  with the tensioner  150 . For example, at block  210 , the impeller  102 , the shaft  104 , the fastener  106 , the washer  114 , and the nut  112  are coupled to one another. Specifically, the first end  107  of the fastener  106  may be inserted into and threaded into the opening  113  of the shaft  104 . Once the first end  107  is inserted, the second end  109  of the fastener  106  remains outside of the shaft  104 . A portion  115  of the second end  109  of the fastener  106 , may be inserted into the opening  117  of the impeller  102  until the surface  110  of the shaft  104  is in contact with the impeller  102 . The washer  114  and the nut  112  may then be coupled to the second end  109  of the fastener  106 . In some embodiments, the washer  114  may be inserted until contacting the mounting surface  116 . The nut  112  may then be threaded onto the fastener  106  until contacting and clamping down on the washer  114 . 
     At block  220 , the fastener  106  is stretched via a tensioner  150 . In some embodiments, the tensioner  150  is a hydraulic tensioner. That is, fluid may be delivered to the tensioner  150 , such as using a fluid source coupled to the inlet  151  of the tensioner  150 . The fluid source may direct fluid to the tensioner  150 , thereby generating pressure that ultimately moves the grip  154  in the direction  124 . When the grip  154  moves in the direction  124 , the grip  154  also stretches the fastener  106  in the direction  124 . As the fastener  106  stretches, the washer  114  and the nut  112 , which are coupled to the fastener  106 , may also move in the direction  124  away from the shaft  104 . That is, the washer  114  may no longer be in contact with the impeller  102  at the mounting surface  116 . As such, the nut  112  may be further tightened onto the fastener  106  by threading the nut  112  with the tightening element  156  until the washer  114  contacts the mounting surface  116  as shown at block  230 . When the fastener  106  is no longer stretched, such as when fluid is released from the tensioner  150  to release pressure within of the tensioner  150 , the fastener  106  will compress in the direction  161  and produce a clamping force to further secure the impeller  102  onto the shaft  104 . As such, a force of between 25,000 pounds per square inch (psi) and 150,000 psi, between 30,000 and 120,000 psi, or between 35,000 and 100,000 psi may be applied between the impeller  102  and the shaft  104 . 
       FIG. 8  is a flow diagram that describes in greater detail an embodiment of a method  270  for stretching the fastener  106  using the tensioner  150  of  FIG. 6 . At block  280 , the tensioner  150  is partially inserted into the opening  117  (e.g., the second diameter portion  120 ) of the impeller  102  until the shell  152  of the tensioner  150  is in contact with the washer  114 . When the tensioner  150  is in contact with the impeller  102 , the grip  154  may be coupled to the fastener  106  and the tightening element  156  may be coupled to the nut  112 . In some embodiments, the tensioner  150  is a hydraulic tensioner and a fluid source may be coupled to the tensioner  150 , such as via inlet  151 . Accordingly, the tensioner  150  and the fluid source are in fluid communication with one another. 
     After coupling the components, the tensioner  150  may stretch the fastener  106 , as shown at block  290 . For example, the grip  154  of the tensioner  150  may move in the direction  124  and thus, apply an axial force to the fastener  106  and direct the fastener  106  in the same direction  124 . In some embodiments, the grip  154  may move due to hydraulic pressure force. That is, fluid may be delivered into the tensioner  150 . The fluid may exert pressure within the tensioner  150  to move the member  155  and thereby the grip  154  in the direction  124 . Since the grip  154  is coupled to the fastener  106 , the grip  154  exerts a tensile force onto the end  109  of the fastener  106 , which stretches the fastener  106  in the direction  124 . By stretching the fastener  106  in the direction  124 , the washer  114  may no longer be in contact with the mounting point  116  of the impeller  102 . 
     Since the washer  114  is no longer in contact with the impeller  102 , the nut  112  located directly adjacent to the washer  114  may be tightened against insert into the impeller  102 . For example, the tightening element  156  may facilitate rotating the nut  112  to further tighten the impeller  102  against the shaft  104 . In some embodiments, the tool  160  may be used to rotate the tightening element  156  in the circumferential direction  159  about the  108  axis, thereby rotating the tightening element  156  as well. Since the tightening element  156  is coupled to the nut  112 , rotation of tightening element  156  may transfer torque to the nut  112  to rotate the nut  112 . The rotation of the nut  112  may then move the nut  112  in the direction  161  opposite the direction  124 , such that the washer  114  moves back into contact with the mounting point  116 . 
     After the nut  112  and the washer  114  are secured against onto the impeller  102 , the stretching of the fastener  106  may be released by removing the tensioner  150  as shown at block  310 . For example, when the tensioner  150  is a hydraulic tensioner, pressure may be released from inside the tensioner  150  by directing fluid back toward the fluid source, for example. When pressure is released, the grip  154  may attempt to revert back to its starting position by moving in the direction  161  opposite the direction  124 . As the grip  154  moves, it compresses the fastener  106  in the direction  161 . This compression further applies a clamping force between the impeller  102  and the shaft  104 , caused by the washer  114  and the nut  112 . After releasing the pressure within the tensioner  150 , the tensioner  150  may be decoupled from the impeller  102 . In some embodiments, the grip  154  may be decoupled from the fastener  106  and/or the tightening element  156  may be decoupled from the nut  112  prior to the removal of the tensioner  150 . After removal of the tensioner  150 , the clamping is maintained between the impeller  102  and the shaft  104  to secure the impeller  102  against the shaft  104  during compressor operation. 
     As set forth above, the present disclosure may provide one or more technical effects useful in the assembly of a compressor of HVAC&amp;R systems. Embodiments of the disclosure may include clamping an impeller onto a shaft using a fastener, a washer, and a nut, and tightening the nut by using a hydraulic tensioner to achieve a predetermined force between the impeller and the shaft. This method for coupling an impeller onto a shaft in a compressor may facilitate assembly of the components. For example, the shaft and the impeller may not undergo precise machining that may have been involved for shafts and impellers that contain keys, splines, and/or pins. Furthermore, the impeller may be more aerodynamic since it may no longer includes the keys, splines, and/or pins. The lack of keys, splines, and/or pins in the assembly may also reduce the moment of inertia of the assembly, which facilitates rotation of the impeller. This reduction in moment of inertia may result in less power required to rotate the shaft and the impeller, which may reduce energy costs. As such, the present disclosure may benefit the fabrication, assembly, and operation of the compressor. The technical effects and technical problems in the specification are examples and are not limiting. It should be noted that the embodiments described in the specification may have other technical effects and can solve other technical problems. 
     While only certain features and embodiments have been illustrated and described, many modifications and changes may occur to those skilled in the art (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters (e.g., temperatures, pressures, etc.), mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described (i.e., those unrelated to the presently contemplated best mode of carrying out the disclosure, or those unrelated to enabling the claimed disclosure). It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.