Patent Publication Number: US-11397034-B2

Title: Unloading system for variable speed compressor

Description:
BACKGROUND 
     Embodiments of the disclosure relate generally to air conditioning and refrigeration systems, and more particularly, to a valve for use with a variable speed compressor. 
     Refrigerant systems are utilized in many air conditioning and heat pump applications for cooling and/or heating air provided to an environment. The cooling or heating load of the environment may vary with ambient conditions. occupancy level, other changes in sensible and latent load demands, and as the temperature and/or humidity set points are adjusted by an occupant of the environment. 
     A compressor is used to compress a working fluid (i e, the refrigerant) from initial (suction) conditions to compressed (discharge) conditions. In some refrigerant systems, a single compressor is utilized to compress the refrigerant and move the refrigerant through the cycle connecting indoor and outdoor heat exchangers in a closed loop. However, under many circumstances, it is desirable to have the ability to vary the capacity, or amount of cooling or heating provided by the refrigerant system. 
     Use of a variable speed compressor is known to improve the efficiency of a refrigerant system. By driving the compressor at a higher or lower speed, the amount of refrigerant that is compressed per unit of time changes, and thus the system capacity can be adjusted. Often the compressor need not operate at full speed, such as when the cooling load on the refrigerant system is relatively low for example. Under such circumstances, it may be desirable to reduce the compressor speed, and thus the overall energy consumption of the refrigerant system. 
     In a variable speed compressor, the amount of unloading available is determined by the slowest speed limit at which the compressor can operate reliably. The speed of the variable speed compressor is commonly controlled by a variable frequency drive; however, the variable frequency drive does not provide a mechanism for further unloading the compressor due to thermal and mechanical limitations of the compressor at minimum speed. Accordingly, further unloading of a compressor beyond the lower limit set speed of operation is desirable. 
     BRIEF DESCRIPTION 
     According to an embodiment, a variable speed compressor includes a housing assembly having a suction port and an inlet port, a motor disposed within the housing assembly, and at least one rotatable element mounted within the housing assembly. The at least one rotatable element is driven by the motor about an axis of rotation. The variable speed compression additionally includes an unloading system having at least one valve. The unloading system is selectively operable to supplement an unloading of the variable speed compressor defined by an operational speed of the variable speed compressor. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the at least one valve is positioned within an opening formed in the housing assembly. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the at least one valve is aligned with a working portion of the at least one rotatable element. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the at least one valve includes a plurality of valves spaced about a periphery of the housing assembly. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the plurality of valves are arranged within a plane oriented substantially perpendicular to the axis of rotation. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the at least one valve further comprises a valve body having a first end and a second end, a central bore formed in the valve body, an inlet opening formed at the first end, the inlet opening being arranged in fluid communication with the central bore, and an outlet opening formed in a side of the valve body, the outlet opening being arranged in fluid communication with the central bore. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the at least one valve is positioned such that an outlet opening is aligned with a fluid flow path defined between an interior surface of the housing assembly and an exterior of the at least one rotatable element. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the at least one rotatable element includes at least one lobe and the inlet opening is arranged in fluid communication with the at least one lobe. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the at least one valve further comprises a movable member disposed within the central bore, the movable member being movable between a first position and a second position. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the at least one valve is a poppet valve. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the movable member is arranged in the first position when the unloading system is non-operational. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments when the movable member is in the first position, the movable member seals both the inlet opening and the outlet opening. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the movable member is arranged in the second position when the unloading system is operational. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments when the movable member is in the second position, the inlet opening and the outlet opening are fluidly coupled. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the unloading system further comprises a drive mechanism configured to move the movable member between the first position and the second position. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the drive mechanism includes a solenoid. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments when the drive mechanism is inactive, the movable member is configured to automatically transform from the second position to the first position. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the movable member is configured to automatically transform from the second position to the first position via gravity. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments comprising a biasing member disposed between the movable member and the valve body, wherein a biasing force of the biasing member is configured to automatically transform the movable member from the second position to the first position. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the at least one rotatable element includes a male screw rotor and a female screw rotor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG. 1  is a perspective view of an example of a compressor; 
         FIG. 2  is a cross-sectional view of the compressor of  FIG. 1  taken along line X-X according to an embodiment; 
         FIG. 3  is a detailed cross-sectional view of a valve of an unloading system of a compressor in a first position according to an embodiment; 
         FIG. 4  is a detailed cross-sectional view of a valve of an unloading system of a compressor in a first position according to an embodiment; 
         FIG. 5  is a detailed cross-sectional view of a valve of an unloading system of a compressor in a first position according to an embodiment; and 
         FIG. 6  is a detailed cross-sectional view of a valve of an unloading system of a compressor in a first position according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
     The term “about” is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof. 
     Referring now to  FIGS. 1 and 2 , a perspective and cross-sectional view of an example of a screw compressor, commonly used in refrigerant systems, is illustrated. The compressor  20  includes a housing assembly  22  defining at least one inlet or suction port  24  and at least one outlet or discharge port  26  with a fluid flow path there between. To drive a flow, the compressor  20  includes a plurality of lobed rotors  28 ,  30  driven by one or more motors  32 . In an embodiment, the rotor  28  is a male rotor having a male-lobed working portion  34  and shaft portions  36  and  38  protruding from opposite ends of the working portion  32 . Similarly, the compressor includes at least one female rotor  30  having a female-lobed working portion  40  enmeshed with the working portion  34  of the male rotor  28 . The female rotor  30  additionally includes shaft portions  42  and  44  protruding from opposite ends of the working portion  40 . The shaft portions  36 ,  38 ,  42 ,  44  are supported by appropriate bearings  46  for rotation of the rotors  28 ,  30  about respective axes A and B. 
     In the illustrated, non-limiting embodiment, the motor  32  is an electric motor, such as an induction, permanent magnet (PM), or switch reluctance motor for example, and includes a rotor and a stator. A shaft portion  38  of one of the rotors  28  is coupled to and driven by the motor  32  about its axis A. As a result, when the shaft portion  38 , and therefore the screw rotor  28  is driven in a first direction about its axis A by the motor  32 , the rotor  28  drives the other rotor  30  in a second, opposite direction about its axis B via the intermeshing engagement therewith. 
     During operation, a low pressure working fluid, such as refrigerant for example, enters the compressor  20  via the inlet  24 , and travels through the housing  22  along a fluid flow path. At the rotors  28 ,  30 , the low pressure working fluid enters the compression pockets formed between the lobes of the male and female working portions  34 ,  40 . As the rotors  28 ,  30  rotate about their respective axes A, B, the volume of the compression pockets gradually reduces, thereby compressing the fluid contained within the pocket as the pocket translates between lobes over the length of the working portion  34 ,  40 , toward the discharge outlet  26 . High pressure working fluid is discharged into a discharge chamber  48  arranged adjacent a downstream end of the rotors  28 ,  30  and is provided to a component (not shown) located downstream of the compressor  20  via the outlet or discharge port  26 . 
     As best shown in  FIG. 2 , the compressor  20  may additionally include an unloading system  50 . The unloading system  50  includes at least one valve  52  arranged in fluid communication with a portion of the fluid flow path of the compressor  20 . In the illustrated, non-limiting embodiment, the unloading system  50  includes only a single valve  52 . However, in other embodiments, the unloading system  50  may include a plurality of valves  52 . The valves  52  may be substantially identical, or alternatively, may be different. Further, in embodiments including multiple valves  52 , the plurality of valves  52  may be spaced about the periphery housing assembly  22 . In an embodiment, each of the plurality of valves  52  is centered about a plane oriented generally perpendicular to the axes A, B of the rotors  28 ,  30 . However, embodiments where one or more of the valves  52  is offset from another of the valves  28 ,  30  is also within the scope of the disclosure. 
     With reference to  FIGS. 3-6 , an example of a valve  52  of the unloading system  50  is illustrated in more detail. In an embodiment, the valve  52  includes a valve body or housing  54  positioned within an opening  56  formed in a portion of the housing assembly  22  generally adjacent a central portion of the rotors. However, it should be understood that in other embodiments, the valve body  54  may be integrally formed as a portion or feature of the housing assembly  22  of the compressor  20 . As shown, a first, interior end  58  of the valve body  54  is positioned radially outward of the lobes of the working body  34  of an adjacent rotor  28 . A central bore  60  formed in the valve body  54  extends through the interior end  58  to define an inlet opening  62 . In an embodiment, an outlet opening  64  is formed in an upstream side  66  of the valve body  54 . The valve  52  is positioned such that the outlet opening  64  is aligned with the portion of the fluid flow path defined between an interior surface  68  of the housing assembly  22  and an outer periphery of the working body  34  of an adjacent screw rotor  28 . It should be understood that a valve body  54  having another configuration of one or both of the inlet and outlet openings  62 ,  64  is also within the scope of the disclosure. 
     A movable member  70 , such as a poppet, piston, or plunger for example, is located within the central bore  60  of the valve body  54 . The movable member  70  is configured to translate within the central bore  60  between a first, closed position ( FIG. 3 ) and a second, open position ( FIG. 5 ). In the first position, the movable member  70  is located adjacent the interior end  58  of the valve body  54  such that the movable member  70  blocks at least one of the outlet opening  64  and the inlet opening  62 . In the illustrated, non-limiting embodiment, when in the first position, the movable member  70  seals both the outlet opening  64  and the inlet opening  62 . In the second position, the movable member  70  is generally located adjacent a second, opposite end  72  of the valve body  54 . In the second position, the outlet opening  64  and the inlet opening  62  are at least partially arranged in fluid communication with one another such that the fluid at the one or more lobes aligned with the inlet opening  62  may recirculate to an upstream portion of the lobes or working portion  34  via the outlet opening  64 . 
     In an embodiment, the movable member  70  is operably coupled to a drive mechanism, illustrated schematically at  74 , such as a solenoid for example. The drive mechanism  74  may be embedded within the valve body  54 , the housing assembly  22 , or alternatively, may be located external to the compressor  20 . The drive mechanism  74  is operable to move the movable member  70  within the valve body  54  between the first position and the second position. In embodiments where the drive mechanism  74  is a solenoid, the solenoid may be selectively energized. When the solenoid is energized, the magnetic field generated may attract the material of the movable member  70 , causing the movable member  70  to translate within the central bore  60  between the first position and the second position. Upon removing the power provided to the solenoid, the magnetic field is eliminated. 
     In an embodiment, the movable member  70  is configured to automatically translate from the second position back to the first position. This automatic translation may occur due to gravity. Alternatively, a biasing member  76  may be disposed between the movable member  70  and an end of the central bore  60 . When the movable member  70  is moved into the second position via the drive mechanism  74 , kinetic energy is stored in the biasing member  76 , such as via compression of the biasing member  76 . Upon removal of power from the solenoid, and therefore the force opposing the biasing force of the biasing member  76 , the biasing force will bias the movable member  70  back to the first position, to seal at least one of the outlet opening  64  and the inlet opening  62 . However, it should be understood that embodiments where the drive mechanism  74  is operable to translate the moveable member  70  from the first position to the second position and from the second position to the first position are also within the scope of the disclosure. 
     During normal operation of the compressor  20 , the one or more valves  52  of the unloading system  50  are typically in the first, closed position, such that one or both of the inlet opening  62  and the outlet opening  64  are sealed. In the closed position, the unloading of the compressor  20  is limited by the speed of operation of the compressor  20 . To achieve additional unloading when the compressor  20  is already at a lower limit speed of operation, one or more of the valves  52  of the unloading system  50  are opened, i.e. the movable member  70  is translated from the first position to the second position. As a result, the overall fluid flow through the compressor  20  is reduced. It should be understood that in embodiments where the unloading system  50  included a plurality of valves  52 , the amount of additional unloading achieved may be customized by operating a desired portion of the valves  52 . When additional loading of the compressor  20  is required, the open valves  52  are closed by transitioning the movable members  70  from the second position to the first position. Further, it should be understood that the additional unloading achieved via operation of the valves  52  of the unloading system  50  is not limited to use when the compressor  20  is at a lower limit speed of operation. 
     A compressor  20  having an unloading system  50  as illustrated and described herein allows additional unloading of the compressor  20  beyond the current limits defined by the minimum speed. This additional unloading allows for greater operational efficiency at low load conditions while still allowing the compressor to meet full load requirements when needed. 
     While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.