Abstract:
The systems and compressors for use with flammable refrigerants can include features that can reduce or address the generation of sparks or arcs internal or external to the compressor that could ignite the flammable refrigerant. The systems and compressors can also include features that can reduce or address leakage into or out of the hermetic compressor shell which could create a flammable atmosphere that could be ignited if the flammable atmosphere came into contact with an ignition source.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/726,676, filed Nov. 15, 2012, entitled SYSTEMS AND COMPRESSORS USING FLAMMABLE REFRIGERANT, and U.S. Provisional Application No. 61/726,672, filed Nov. 15, 2012, entitled HERMETIC ELECTRICAL FEEDTHROUGH ASSEMBLY FOR A COMPRESSOR, both of which Applications are incorporated by reference herein in their entirety. 
     
    
     BACKGROUND 
       [0002]    The application generally relates to systems and compressors using a flammable refrigerant. 
         [0003]    When using flammable refrigerant in a compressor and vapor compression system, numerous matters have to be addressed for safety and other reasons. Some examples of the matters that have to be addressed include: 1) refrigerant leaks that are external to the compressor, which can result in a flammable state that is a fire or explosion hazard; 2) overcharge of refrigerant that could generate a flammable state if a leak occurred; 3) mechanical failure (possibly from thermal contributions) that could cause a refrigerant leak; and 4) spark or arc generation from any source (such as a loose connection), internal or external to the compressor, which can result in a fire or explosion hazard if a flammable state is present. The determination of a flammable state or atmosphere can be based on specific air (oxygen) and refrigerant (fuel) ratios in the space that contains the refrigerant. 
         [0004]      FIG. 1  shows a top, partial cross-sectional view of a prior art compressor  100 . The compressor  100  has a shell  110  that provides a hermetically sealed environment for electrical and mechanical components inside the shell  110 . To maintain proper operation of the compressor  100 , the integrity of the hermetically sealed environment cannot be breached. Further, when a flammable refrigerant is used in the compressor  100  as the working fluid, any sparking or arcing inside or outside the compressor  100  should be avoided. 
         [0005]    One type of electrical connection into the hermetically sealed environment of the shell  110  can be provided by a power terminal  112 . The power terminal  112  has to maintain the hermetically sealed environment while withstanding the harsh operating conditions associated with the compressor  100 . The power terminal  112  can be located within an aperture in the shell  110 . The power terminal  112  can have a cup-shaped metal collar  126  with a bottom wall. The bottom wall has holes that permit conductor pins  128  to pass through the power terminal  112  to provide the electrical connection through the shell  110 . The collar  126  is sealed in the shell aperture by welding and the pins  128  are sealed within the collar  126  by fused glass insulation. To further stabilize the power terminal  112 , the fused glass insulation surrounding the pins  128  can be covered with epoxy or shielded by ceramic collars. 
         [0006]    A fence  130  can surround and protect the power terminal  112 . A molded plug (not shown) can be configured to couple with the fence  130  and, thereby, make an electrical connection with the pins  128  outside the shell  110 . To accomplish this connection on the outside of the shell, the pins  128  can be provided with a tab (not shown). For example, each pin  128  may include an attached, e.g., welded, 0.250 inch tab that can connect to a 0.250 inch spade connector crimped onto the end of a voltage supply wire or conductor. Plugs, tabs, connectors or wires similar to those used on the outer ends of the pins  128  can be used on the inner end of the pins  128  to accomplish the electrical connection between the electrical components inside the shell  110  and the power terminal  112 . Any of the previously described connections, e.g., pin-tab, tab-connector, connector-wire, can become corroded or loose and result in arcing or sparking that is undesirable when using a flammable refrigerant due to the risk of fire or explosion inside (or outside) of the shell  110 . Further, any of the seals associated with the components of the terminal  112  can deteriorate and provide a leakage path into or out of the shell  110 . 
         [0007]    Therefore, what is needed is one or more systems and/or methods to increase the safety and reliability of a compressor using a flammable refrigerant by reducing or addressing the risks of sparking or arcing internal or external to the compressor and by reducing or addressing the risks associated with leakage into or out of the hermetic compressor shell. 
       SUMMARY 
       [0008]    The present application is directed to a compressor. The compressor includes a shell and a compression mechanism. The shell has an upper portion connected to a lower portion to form an enclosed space. The compression mechanism is positioned in the lower portion of the shell. The compressor also includes a motor connected to the compression mechanism by a shaft to power the compression mechanism. The motor includes a rotor connected to the shaft and a stator to rotate the rotor. The rotor is positioned in the enclosed space of the upper portion of the shell and the stator is positioned outside of the upper portion of the shell. 
         [0009]    The present invention is also directed to a system. The system includes a compressor, a condenser and an evaporator connected in a circuit and circulating a flammable refrigerant. The system additionally includes a motor connected to the compressor to power the compressor. The motor includes a stator and a rotor. The compressor includes a compression mechanism and a shell. The shell has an upper portion connected to a lower portion. The compression mechanism is positioned in the lower portion of the shell. The upper portion of the shell includes a non-magnetic material. The rotor is positioned in the upper portion of the shell and the stator is positioned outside the upper portion of the shell. The stator transmits electromagnetic energy to the rotor. 
         [0010]    One advantage of the present application is the reduction of sources for sparking or arcing near a flammable refrigerant. 
         [0011]    Other features and advantages of the present invention will be apparent from the following, more detailed description of the embodiments, taken in conjunction with the accompanying drawings which show, by way of example, the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  shows a top, partial cross-sectional view of a prior art compressor. 
           [0013]      FIGS. 2 and 3  schematically show embodiments of vapor compression systems. 
           [0014]      FIG. 4  shows an embodiment of a compressor using an embodiment of an electrical feedthrough assembly. 
           [0015]      FIG. 5  shows an embodiment of a compressor using an embodiment of an external stator. 
           [0016]      FIGS. 6 and 7  schematically show partial cross sections of embodiments of the connection between the upper portion and the lower portion of the compressor shell. 
           [0017]      FIG. 8  schematically shows a partial side view of an embodiment of the upper portion of the compressor shell. 
       
    
    
       [0018]    Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
       DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0019]    As shown in  FIGS. 2 and 3 , a vapor compression system  300  includes a compressor  302 , a condenser  304 , and an evaporator  306  (see  FIG. 2 ) or a compressor  302 , a reversing valve  350 , an indoor unit  354  and an outdoor unit  352  (see  FIG. 3 ). The vapor compression system can be included in a heating, ventilation and air conditioning (HVAC) system, refrigeration system, chilled liquid system or other suitable type of system. Some examples of refrigerants that may be used in vapor compression system  300  are: hydrofluorocarbon (HFC) based refrigerants, for example, R-410A, R-407C, R-404A, R-134a and R-32 (a component of R410A and R407C); hydrofluoro olefin (HFO) refrigerants, also known as “unsaturated HFCs,” such as R1234yf; inorganic refrigerants like ammonia (NH3), R-717 and carbon dioxide (CO2), R-744; hydrocarbon (HC) based refrigerants such as propane (R-290), isobutane (R-600a) or propene (R-1270), or any other suitable type of refrigerant. The hydrocarbon based refrigerants may be referred to as “flammable” refrigerants and can have an ASHRAE flammability class of 3. Other types of “flammable” refrigerants can include R-32, ammonia (R-717) and HFO refrigerants, each of which can have an ASHRAE flammability class of 2L. In another embodiment, flammable refrigerant can include any refrigerant classified in ASHRAE flammability class of 3 or ASHRAE flammability class of 2L. 
         [0020]    The vapor compression system  300  can be operated as an air conditioning system, where the evaporator  306  is located inside a structure or indoors, i.e., the evaporator is part of indoor unit  354 , to provide cooling to the air in the structure and the condenser  304  is located outside a structure or outdoors, i.e., the condenser is part of outdoor unit  352 , to discharge heat to the outdoor air. The vapor compression system  300  can also be operated as a heat pump system, i.e., a system that can provide both heating and cooling to the air in the structure, with the inclusion of the reversing valve  350  to control and direct the flow of refrigerant from the compressor  302 . When the heat pump system is operated in an air conditioning mode, the reversing valve  350  is controlled to provide for refrigerant flow as described above for an air conditioning system. However, when the heat pump system is operated in a heating mode, the reversing valve  350  is controlled to provide for the flow of refrigerant in the opposite direction from the air conditioning mode. When operating in the heating mode, the condenser  304  is located inside a structure or indoors, i.e., the condenser is part of indoor unit  354 , to provide heating to the air in the structure and the evaporator  306  is located outside a structure or outdoors, i.e., the evaporator is part of outdoor unit  352 , to absorb heat from the outdoor air. 
         [0021]    Referring back to the operation of the system  300 , whether operated as a heat pump or as an air conditioner, the compressor  302  is driven by the motor  106  that is powered by motor drive  104 . The motor drive  104  receives AC power having a particular fixed line voltage and fixed line frequency from AC power source  102  and provides power to the motor  106  at a preselected voltage and preselected frequency. In another embodiment, the motor  106  can be powered directly from the AC power source  102 . The motor  106  used in the system  300  can be any suitable type of motor that can be powered by a motor drive  104 . The motor  106  can be any suitable type of motor including, but not limited to, an induction motor, a switched reluctance (SR) motor, or an electronically commutated permanent magnet motor (ECM). In another embodiment, the motor  106  can be a DC motor that would connect to a DC power source instead of AC power source  102 . 
         [0022]    Referring back to  FIGS. 2 and 3 , the compressor  302  compresses a refrigerant vapor and delivers the vapor to the condenser  304  through a discharge line (and the reversing valve  350  if configured as a heat pump). The compressor  302  can be suitable type of hermetic or semi-hermetic compressor including, but not limited to, a reciprocating compressor, rotary compressor, screw compressor, swag link compressor, scroll compressor, spool compressor, centrifugal compressor, or turbine compressor. The refrigerant vapor delivered by the compressor  302  to the condenser  304  enters into a heat exchange relationship with a fluid, e.g., air or water, and undergoes a phase change to a refrigerant liquid as a result of the heat exchange relationship with the fluid. The condensed liquid refrigerant from the condenser  304  flows through an expansion device to the evaporator  306 . 
         [0023]    The condensed liquid refrigerant delivered to the evaporator  306  enters into a heat exchange relationship with a fluid, e.g., air or water, and undergoes a phase change to a refrigerant vapor as a result of the heat exchange relationship with the fluid. The vapor refrigerant in the evaporator  306  exits the evaporator  306  and returns to the compressor  302  by a suction line to complete the cycle (and the reversing valve arrangement  350  if configured as a heat pump). In other exemplary embodiments, any suitable configuration of the condenser  304  and the evaporator  306  can be used in the system  300 , provided that the appropriate phase change of the refrigerant in the condenser  304  and evaporator  306  is obtained. For example, if air is used as the fluid to exchange heat with the refrigerant in the condenser or the evaporator, then one or more fans can be used to provide the necessary airflow through the condenser or evaporator. The motors for the one or more fans may be powered directly from the AC power source  102  or a motor drive, including motor drive  104 . 
         [0024]      FIG. 4  shows an embodiment of a hermetic compressor. Compressor  2  may be connected to a refrigeration or heating, ventilation and air conditioning (HVAC) system  300 . The compressor  2  is shown as a reciprocating compressor, but compressor  2  can be any suitable type of hermetic compressor as previously described. The compressor  2  can be connected to evaporator  306  by a suction line that enters the suction port  14  of compressor  2 . The suction port  14  can be in fluid communication with a suction plenum  12 . Refrigerant gas from the evaporator  306  enters the compressor  2  through the suction port  14  and then flows to the suction plenum  12  before being compressed. In one embodiment, the refrigerant gas from the suction port  14  can fill the interior space of the compressor housing before flowing to the suction plenum  12 . 
         [0025]    The compressor  2  can use an electrical motor  18 . As shown in  FIG. 4 , motor  18  is an induction motor having a stator  21  and a rotor  23 , however any other suitable type of electrical motor may be used. A shaft assembly  25  extends through the rotor  23 . The bottom end  29  of the shaft assembly  25  extends into an oil sump  405  and includes a series of apertures  27 . Connected to the shaft assembly  25  below the motor is a compression device. As shown in  FIG. 4 , the compression device can be a piston assembly  31  that has two pistons. A connecting rod  33  is connected to a piston head  34 , which moves back and forth within a cylinder  36 . The cylinder  36  includes a gas inlet port  38  and a gas discharge port  41 . Associated with ports  38 ,  41  are suction valves and discharge valves. The gas inlet port  38  is connected to an intake tube  55 , which is in fluid communication with the suction plenum  12 . 
         [0026]    The motor  18  can be activated by a signal in response to the satisfaction of a predetermined condition, for example, an electrical signal from a thermostat when a preset temperature threshold is reached. While a thermostat is used as an example, it should be known that any type of device or signal may be used to activate the compressor. When the compressor is activated, electricity is supplied to the stator  21 , and the windings in the stator  21  cause the rotor  23  to rotate. Rotation of the rotor  23  causes the shaft assembly  25  to turn. When the shaft assembly  25  is turning, oil sump fluid in the oil sump  405  enters the apertures  27  in the bottom end  29  of the shaft and then moves upward through and along the shaft  25  to lubricate the moving parts of the compressor  2 . 
         [0027]    Rotation of the rotor  23  also causes reciprocating motion of the piston assembly  31 . As the assembly  31  moves to an intake position, the piston head  34  moves away from gas inlet port  38 , the suction valve opens and refrigerant fluid is introduced into an expanding cylinder  36  volume. The gas is pulled from the suction plenum  12  through the intake tube  55  to the gas inlet port  38  where the gas passes through the suction valve and is introduced into the cylinder  36 . When the piston assembly  31  reaches a first end (or top) of its stroke, shown by movement of the piston head  34  to the right side of the cylinder  36  of  FIG. 4 , the suction valve closes. The piston head  34  then compresses the refrigerant gas by reducing the cylinder  36  volume. When the piston assembly  31  moves to a second end (or bottom) of its stroke, shown by movement of piston head  34  to the left side of cylinder  36  of  FIG. 4 , a discharge valve is opened and the compressed refrigerant gas is expelled through the gas discharge port  41 . The compressed refrigerant gas flows from the gas discharge port  41  into a muffler  51  then through an exhaust or discharge tube  53  to exit the compressor  2  into a conduit connected to a condenser. 
         [0028]    The motor  18  can be positioned within the top portion of the compressor  2 , and the piston assembly  31  can be positioned below the motor  18 . The oil sump  405  can be located at the bottom portion of the compressor  2 . In one embodiment, a portion of the piston assembly  31  can be submerged below the oil level in the oil sump  405 . When the compressor is not operating, some of the refrigerant in compressor  2  may condense and fall by force of gravity into the oil sump  405  and mix with the oil in the oil sump  405  or be absorbed into the oil in the oil sump. The oil in the oil sump  405  is used to lubricate the mechanical portions of the compressor  2 , such as shaft assembly  25 . When liquid refrigerant mixes with the oil, the resulting liquid is a less effective lubricant. To avoid this problem, the oil sump fluid is heated with a heater  131  and the refrigerant is evaporated from the oil, leaving oil in the oil sump  405  to lubricate the components. The heater  131  can be positioned within the oil sump and mounted or secured to any suitable structure inside the compressor such as the piston assembly  31  or an interior surface of a compressor shell  39 . 
         [0029]    Power can be provided to the motor  18  and the heater  131 , or any other electrical component inside the compressor shell  39 , by use of an electrical feedthrough assembly  10 . As shown in  FIG. 4 , the electrical feedthrough assembly  10  can be positioned in the top cylindrical portion of the compressor  2 . However, in other embodiments, the electrical feedthrough assembly  10  can be positioned at any suitable location in the compressor shell  39 . 
         [0030]    The feedthrough assembly  10  can be used to provide power, control and/or communication signals to the compressor motor  18  and the heater  131 . The feedthrough assembly  10  can eliminate all inside and outside terminal connections at the compressor shell  39  for the motor  18  and heater  131  by permitting the corresponding power and control conductors or wires to pass through the compressor shell  39  without interruption, i.e., a continuous conductor or wire is used. 
         [0031]      FIG. 5  shows an embodiment of a hybrid semi-hermetic compressor, i.e., the rotor for the motor is inside the shell and the stator and overload protection (OLP) for the motor, along with corresponding electrical connections to a power source, are outside the shell. The hybrid semi-hermetic compressor can be considered a hermetic compressor because the shell for the compressor does not require any seals and can maintain a hermetic environment. Compressor  500  may be connected to a refrigeration or HVAC system  300 . The compressor  500  can have a compression mechanism  502  positioned inside a shell or housing  400  that receives refrigerant gas from a suction inlet  504  that passes or travels through the shell  400 . The compression mechanism  502  then provides compressed refrigerant gas to a discharge outlet  506  that travels or passes through the shell  400 . The compression mechanism  502  can incorporate a compression mechanism from any of the previously described types of compressors, e.g., a reciprocating compressor, a rotary compressor, a screw compressor, a swag link compressor, a scroll compressor, a spool compressor, a centrifugal compressor, or a turbine compressor. The suction inlet  504  can be connected to the evaporator  306  of the HVAC system  300  and the discharge outlet  506  can be connected to the condenser  304  of the HVAC system  300 . 
         [0032]    The suction line  504  of compressor  500  is shown in  FIG. 5  as directly flowing into the compression mechanism  502 . However, in other embodiments, the suction line  504  can be in fluid communication with a suction plenum that can supply the compression mechanism  502 . The suction plenum can be incorporated into the compression mechanism  502  and/or can be in communication with or incorporate all or part of the internal volume of the compressor  500 . In one embodiment, the compressor  500  can include one or more filters, mufflers or other components between the suction inlet  504  and the compression mechanism  502 . In another embodiment, the filters, mufflers or other components can be located upstream from the suction inlet  504  outside of the compressor  500 . The discharge outlet  506  is shown in  FIG. 5  as directly flowing from the compression mechanism  502 . However, in other embodiments, the compressor  500  can include one or more mufflers, oil separators or other components between the compression mechanism  502  and the discharge outlet  506  or downstream from the discharge outlet. 
         [0033]    The compressor  500  can use an electrical motor  510 . As shown in  FIG. 5 , a stator  512  for the motor  510  can be positioned outside of the shell  400  and the rotor  514  for the motor  510  can be positioned within the shell  400 . The motor  510  can be any suitable type of electrical motor that has a stator  512  and a rotor  514 , including, but not limited to, an induction motor, an SR motor, an ECM or a DC motor. The rotor  514  can be connected to a shaft  516  that is used to drive the compression mechanism  502 . In one embodiment, the bottom end of the shaft  516  can extend into an oil sump located in the bottom of the shell  400  to draw lubrication oil for the shaft  516  and compression mechanism  502 . 
         [0034]    The motor  510  can be activated by a signal in response to the satisfaction of a predetermined condition, for example, an electrical signal from a thermostat when a preset temperature threshold is reached. While a thermostat is used as an example, it should be known that any type of device or signal may be used to activate the motor  510  and compressor  500 . When the compressor  500  and motor  510  are activated, electricity is supplied to the stator  512 , and the windings in the stator  512  cause the rotor  514  to rotate. Rotation of the rotor  514  causes the shaft  516  to turn and move or rotate the compression mechanism  502 . 
         [0035]    Since the stator  512  for the motor  510  is located outside of the shell  400 , the stator  512  can be wired to the corresponding power supply for the compressor  500  using any suitable wiring technique without the risk of introducing a spark or arc inside of the compressor shell  400 . The stator  512  and rotor  514  can be positioned in close proximity to one another to permit the efficient transfer of electromagnetic energy between the stator  512  and rotor  514 , i.e., to enable the stator  512  to turn or rotate the rotor  514 . 
         [0036]    The shell  400  can have a first or lower portion  402  that can include the compression mechanism  502  and a second or upper portion  404  that can include the rotor  514 . The upper portion  404  can also include one or more bearings  408  positioned in a gap or space  409  between the top of the rotor  514  and upper portion  404  to prevent the shaft  516  and/or rotor  514  from touching or contacting the top and/or the sides of the upper portion  404 . A gap or space  407  can separate the sides of the rotor  514  and an inner surface of the upper portion  404 . In one embodiment, the gap or space  409  can be in the range of 0.250 to 0.750 inches and the gap or space  407  can be in the range of 0.005 to 0.030 inches. In another embodiment, the upper portion  404  can include one or more bearings positioned in the gap or space  407  between the rotor  514  and upper portion  404  to prevent the rotor  514  from touching or contacting the sides of the upper portion  404 . The upper portion  404  and lower portion  402  can each have a closed end and an open end opposite the closed end with an opening that is circular, elliptical, oval or any other suitable geometric shape. The open end of the upper portion  404  can have a smaller diameter, circumference and/or perimeter than the open end of the lower portion  402 . 
         [0037]    In one embodiment, the outer surface of the upper portion  404  and/or the stator  512  can include guides or other suitable mechanisms, such as tabs and/or depressions, to ensure the proper alignment of the stator  512  relative to the upper portion  404  and rotor  514 . In another embodiment, the inner surface of the upper portion  404  and/or the rotor  514  can include guides or other suitable mechanisms, such as tabs and/or depressions, to ensure the proper alignment and spacing of the rotor  514  relative to the inner surface of the upper portion  404 . Depending on the configuration of the guides or other mechanisms used for positioning the stator  512  and rotor  514  relative to the upper portion  404 , the guides or mechanism can either remain in place or be removed either through manual operation or operation of the motor  510 . In a further embodiment, precision machining of one or more of the stator  512 , the rotor  514  and the upper portion  404  can be performed to provide for the proper alignment of the stator  512  and the rotor  514 . 
         [0038]    In another embodiment as shown in  FIG. 5 , the rotor  514  can have a greater length than the corresponding stator portion, e.g., the stator teeth or projections, to ensure that the rotor  514  and stator  512  are in proper alignment when the stator  512  is mounted outside the upper portion  404 . The rotor  514  can extend past either or both of the upper end and the lower end of the stator  512 . In an alternate embodiment, the rotor  514  can have the same length as the corresponding stator portion. 
         [0039]    A flange or ring portion  410  can be used to connect the upper portion  404  to the lower portion  402 . The upper portion  404  can be hermetically connected to an inner portion of the flange portion  410  and the lower portion  402  can be hermetically connected to an outer portion of the flange portion  410  to provide a hermetically sealed environment within the compressor shell  400 . In one embodiment, the flange portion  410  can be integral and/or continuous with the upper portion  404 , i.e., no joint between the flange portion  410  and the upper portion  404 , while in another embodiment, the flange portion  410  can be integral and/or continuous with the lower portion  402 , i.e., no joint between the flange portion  410  and the lower portion  402 . The flange portion  410  is shown in  FIG. 5  with a generally linear cross-sectional shape extending substantially horizontally between the inner portion and the outer portion of the flange portion  410 . As shown in  FIGS. 6 and 7 , the flange portion  410  could extend at an angle such that the inner portion of the flange portion  410  is at a different elevation than the outer portion of the flange portion  410 . In other embodiments, the flange portion  410  can have other cross sectional shapes besides generally linear, including arch shapes, inverted arch shapes (e.g., horseshoe shape) or other suitable types of shapes and can extend either horizontally or at an angle. In still other embodiments, the cross-sectional shape of the flange portion  410  may be different in different locations to accommodate internal components or equipment in either the upper portion  404  or the lower portion  402 . 
         [0040]    To permit the stator  512  to transmit electromagnetic energy through the upper portion  404  to the rotor  514 , the upper portion  404  can have a relatively thin material thickness. In one embodiment, the thickness for the upper portion can be between 0.02 and 0.1 inches. The material for the upper portion  404  can be any suitable material, including non-magnetic, non-conductive, paramagnetic and/or magnetic materials, that can permit the transfer of electromagnetic energy between the stator  512  and the rotor  514  In one embodiment, the upper portion  404  can be made from one or more of stainless steel (both austenitic and non-austenitic), polymer material(s), ceramic material(s), epoxy material(s), steel, sheet metal, or titanium. In contrast, the lower portion  402  and flange portion  410  can be made from conventional materials such as steel or sheet metal and can have a material thickness between 0.105 and 0.125 inches. However, in another embodiment, the flange portion  410  and/or the lower portion  402  can be made from the same material and/or have the same material thickness as the upper portion  404 . 
         [0041]    In one embodiment, the stator  512  can be press-fit onto the outer surface of the upper portion  404  to securely mount the stator  512  and to help minimize the distance between the stator  512  and the rotor  514 . In another embodiment as shown in  FIG. 8 , the upper portion  404  can be made of a substantially non-magnetic and/or non-conductive material  802  with a plurality of magnetic portions  804  embedded or molded into the non-magnetic material  802  to insulate the magnetic portions  804 . The positions of the magnetic portions  804  in the upper portion  404  can correspond to the location of corresponding teeth or projections from the stator  512  such that when the stator  512  is press-fit onto the upper portion  404  the teeth or projections from the stator  512  contact the magnetic portions  804  of the upper portion  404 . The contact between the magnetic portions  804  of the upper portion  404  and the teeth or projections of the stator  512  can provide a direct path for the electromagnetic energy between the stator  512  and the rotor  514 , i.e., the electromagnetic energy does not need to travel through the upper portion  404 . In a further embodiment, the upper portion  404  can be made of a substantially magnetic material and only those areas of the upper portion  404  that correspond to the teeth or projections of the stator  512  can be surrounded by insulating or non-magnetic material. In still other embodiments, the stator  512  can be mounted using a suitable mounting technique. 
         [0042]    In another embodiment, the stator  512  can be surrounded by an enclosure to provide protection to the stator  512 . The enclosure for the stator  512  may or may not be hermetically sealed and may or may not be connected to the compressor shell  400 . 
         [0043]    In one embodiment, different types of compressor fittings, e.g., non-brazed connections, can be used with compressors  2  and  500 . Some examples of suitable non-brazed compressor fittings can include Rotolock and high Q (high quality) compression fittings. A Rotolock fitting can be a special refrigeration fitting that uses a teflon ring seated against a machined surface enclosed by a threaded fitting. 
         [0044]    In another embodiment, lubricant that minimizes the amount of refrigerant absorbed, which lowers the amount of refrigerant charge required, can be used with compressors  2  and  500 . Compressors  2  or  500  may also include components that do not require lubricant. For example, compressors  2  or  500  may use magnetic or sealed bearings that do not require lubricant. In an additional embodiment, depending on the properties of the refrigerant used by the compressor, the refrigerant itself could be used to lubricate certain components of the compressor. 
         [0045]    In a further embodiment, a low pressure cut-out switch can be used with compressors  2  or  500  to make sure no oxygen enters the compressors  2  or  500  such that a flammable atmosphere or state is created. If the stator is internal to the compressor as shown in  FIG. 4 , an internal line break pressure switch can be used as a low pressure cut-out to disconnect the power to the motor to prevent sparking or arcing near the possible flammable atmosphere. 
         [0046]    In still another embodiment, improved testing procedures can be used to ensure that no leaks are present in the compressor for the avoidance of a flammable atmosphere. Additional testing for leaks can be conducted after the compressor leaves the factory to detect leaks caused by system tubing breaks. 
         [0047]    In yet another embodiment, the internal free volume of the compressor can be reduced by adjusting the configuration of the shell or by the insertion of “filler” such as solid blocks to reduce the amount flammable refrigerant stored in the compressor and to avoid a flammable atmosphere if a leak should occur. 
         [0048]    In one embodiment, an arc detect circuit breaker can be used to eliminate ignition sources and avoid spark generation. A specialized board can be used to detect arcs in the compressor. The specialized control board can include enhanced sensitivities or can identify certain characteristics that are associated with arcs in a flammable refrigerant atmosphere or state. 
         [0049]    In another embodiment, the motor  510  can be a variable speed permanent magnet (PM) motor or a line start PM motor. 
         [0050]    In a further embodiment, the entire motor can be located outside of the compressor shell and a shaft seal can be used to provide the hermetic environment for the compressor shell, i.e., a semi-hermetic compressor. The external motor can have its own housing which can be hermetically sealed. If the external motor is mounted in its own housing, a sensor can be placed in the motor&#39;s housing to detect leaks from the shaft seal. When a leak is detected by the sensor, a control can be put into place to shut down the motor and compressor due to the leak. 
         [0051]    As would be appreciated by those of ordinary skill in the pertinent art, the functions of several elements of the present application may, in alternative embodiments, be carried out by fewer elements, or a single element. Similarly, in some embodiments, any functional element may perform fewer, or different, operations than those described with respect to the illustrated embodiment. Also, functional elements shown as distinct for purposes of illustration may be incorporated within other functional elements, separated in different hardware or distributed in various ways in a particular implementation. Further, relative size and location are merely somewhat schematic and it is understood that not only the same but many other embodiments could have varying depictions. 
         [0052]    All relative descriptions herein such as above, below, left, right, up, and down are with reference to the Figures, and not meant in a limiting sense. Relative descriptions such as inner and inward are with reference to being a direction toward the interior of a compressor shell whereas outer and outward are a direction away from the compressor. The illustrated assemblies can be understood as providing exemplary features of varying detail of certain embodiments, and therefore, components, modules, elements, and/or aspects of the illustrations can be otherwise added to, combined, interconnected, sequenced, separated, interchanged, positioned, and/or rearranged without materially departing from the disclosed systems or methods. Additionally, the shapes and sizes of components are also exemplary and unless otherwise specified, can be altered without materially affecting or limiting the disclosed technology. 
         [0053]    It is important to note that the construction and arrangement of the present application as shown in the various exemplary embodiments is illustrative only. Although only a few embodiments have been described in detail in this application, those who review this application can readily appreciate that many modifications are possible (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 described in the application. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present application. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. In the claims, any means-plus-function clause is intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present application. Accordingly, the present application is not limited to a particular embodiment, but extends to various modifications that nevertheless fall within the scope of the appended claims. 
         [0054]    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 invention, or those unrelated to enabling the invention). 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.