Patent Document

FIELD OF THE INVENTION 
     The present invention is related to scroll-type machinery. More particularly, the present invention is directed towards capacity modulation of scroll-type compressors. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Scroll machines are becoming more and more popular for use as compressors in refrigeration systems as well as air conditioning and heat pump applications. The popularity of scroll machinery is primarily due to their capability for extremely efficient operation. Generally, these machines incorporate a pair of intermeshed spiral wraps, one of which is caused to orbit with respect to the other so as to define one or more moving chambers which progressively decrease in size as they travel from an outer suction port towards a center discharge port. An electric motor is normally provided which operates to drive the scroll members via a suitable drive shaft. During normal operation, these scroll machines are designed to have a fixed compression ratio. 
     Air conditioning and refrigeration systems experience a wide range of loading requirements. Using a fixed compression ratio compressor to meet this wide range of loading requirements can present various problems to the designer of the system. One method of adapting the fixed compression ratio compressors to the wide range of loading requirements is to incorporate a capacity modulation system into the compressor. Capacity modulation has proven to be a desirable feature to incorporate into the air conditioning and refrigeration compressors in order to better accommodate the wide range of loading to which the systems may be subjected. Many different approaches have been utilized for providing this capacity modulation feature. These prior art systems have ranged from control of the suction inlet to bypassing compressed discharge gas directly back into the suction area of the compressor. With scroll-type compressors, capacity modulation has often been accomplished via a delayed suction approach which comprises providing ports at various positions along the route of the compression chambers which, when opened, allow the compression chambers formed between the intermeshing scroll wraps to communicate with the suction gas supply, thus delaying the point at which compression of the suction gas begins. This delayed suction method of capacity modulation actually reduces the compression ratio of the compressor. While such systems are effective at reducing the capacity of the compressor, they are only capable of providing a predetermined or stepped amount of compressor unloading. The amount of unloading or the size of the step is dependent upon the positioning of the unloading ports along the wraps or the compression process. While it is possible to provide multiple stepped unloading by incorporating a plurality of unloading ports at different locations along the compression process, this approach becomes more and more costly as the number of ports is increased and it requires additional space to accommodate the separate controls for opening and closing each individual on each set of ports. 
     The present invention, however, overcomes these deficiencies by enabling an infinitely variable capacity modulation system which has the capability of modulating the capacity from 100% of full capacity down to virtually zero capacity utilizing only a single set of controls. Further, the system of the present invention enables the operating efficiency of the compressor and/or refrigeration system to be maximized for any degree of compressor unloading desired. 
     In the present invention, compressor unloading is accomplished by cyclically effecting axial separation of the two scroll members during the operating cycle of the compressor. More specifically, the present invention provides an arrangement wherein one scroll member is moved axially with respect to the other scroll member by a solenoid valve which operates in a pulsed width modulation mode. The pulsed width modulation operating mode for the solenoid valve provides a leakage path across the tips of the wraps from the higher compression pockets defined by the intermeshing scroll wraps to the lower compression pockets and ultimately back to suction. By controlling the pulse width modulation frequency and thus the relative time between sealing and unsealing of the scroll wrap tips, infinite degrees of compressor unloading can be achieved with a single control system. Further, by sensing various conditions within the refrigeration system, the duration of compressor loading and unloading for each cycle can be selected for a given capacity such that overall system efficiency is maximized. 
     The various embodiments of the present invention detailed below provide a wide variety of arrangements by which one scroll member may be axially reciprocated with respect to the other to accommodate a full range of compressor unloading. The ability to provide a full range of capacity modulation with a single control system as well as the ability to select the duration of loaded and unloaded operation cooperate to provide an extremely efficient system at a relatively low cost. 
     Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings which illustrate the best mode presently contemplated for carrying out the present invention: 
         FIG. 1  is a section view of a scroll-type refrigeration compressor in accordance with the present invention operating at full capacity; 
         FIG. 2  is a section view of the scroll-type refrigeration compressor shown in  FIG. 1  operating at a reduced capacity; 
         FIG. 3  is a detailed view of the ring and biasing arrangement taken in the direction of arrows  3 — 3  shown in  FIG. 2 ; 
         FIG. 4  is a section view of a scroll-type refrigeration compressor in accordance with another embodiment of the present invention operating at full capacity; 
         FIG. 5  is a section view of a scroll-type refrigeration compressor in accordance with another embodiment of the present invention; 
         FIG. 6  is a top section view of the compressor shown in  FIG. 5 ; 
         FIG. 7  is an enlarged section view of the piston assembly shown in  FIG. 5 ; 
         FIG. 8  is a top view of the discharge fitting shown in  FIG. 7 ; 
         FIG. 9  is an elevational view of the biasing spring shown in  FIG. 5 ; 
         FIG. 10  is a side view of the non-orbiting scroll member shown in  FIG. 5 ; 
         FIG. 11  is a cross sectional top view of the non-orbiting scroll member shown in  FIG. 10 ; 
         FIG. 12  is an enlarged sectional view of the injection fitting shown in  FIG. 5 ; 
         FIG. 13  is an end view of the fitting showing in  FIG. 12 ; 
         FIG. 14  is a schematic diagram of a refrigerant system utilizing the capacity control system in accordance with the present invention; 
         FIG. 15  is a schematic diagram of a refrigerant system in accordance with another embodiment of the present invention; and 
         FIG. 16  is a graph showing the capacity of the compressor using the capacity control system in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views, there is shown in  FIG. 1  a scroll compressor which includes the unique capacity control system in accordance with the present invention and which is designated generally by the reference numeral  10 . Scroll compressor  10  is generally of the type described in Assignee&#39;s U.S. Pat. No. 5,102,316, the disclosure of which is incorporated herein by reference. Scroll compressor  10  comprises an outer shell  12  within which is disposed a driving motor including a stator  14  and a rotor  16 , a crankshaft  18  to which rotor  16  is secured, an upper bearing housing  20  and a lower bearing housing (not shown) for rotatably supporting crankshaft  18  and a compressor assembly  24 . 
     Compressor assembly  24  includes an orbiting scroll member  26  supported on upper bearing housing  20  and drivingly connected to crankshaft  18  via a crankpin  28  and a drive bushing  30 . A non-orbiting scroll member  32  is positioned in meshing engagement with orbiting scroll member  26  and is axially movably secured to upper bearing housing  20  by means of a plurality of bolts  34  and associated sleeve members  36 . An Oldham coupling  38  is provided which cooperates with scroll members  26  and  32  to prevent relative rotation therebetween. A partition plate  40  is provided adjacent the upper end of shell  12  and serves to divide the interior of shell  12  into a discharge chamber  42  at the upper end thereof and a suction chamber  44  at the lower end thereof. 
     In operation, as orbiting scroll member  26  orbits with respect to non-orbiting scroll member  32 , suction gas is drawn into suction chamber  44  of shell  12  via a suction fitting  46 . From suction chamber  44 , suction gas is sucked into compressor  24  through an inlet  48  provided in non-orbiting scroll member  32 . The intermeshing scroll wraps provided on scroll members  26  and  32  define moving pockets of gas which progressively decrease in size as they move radially inwardly as a result of the orbiting motion of scroll member  26  thus compressing the suction gas entering via inlet  48 . The compressed gas is then discharged into discharge chamber  42  through a hub  50  provided in scroll member  32  and a passage  52  formed in partition  40 . A pressure responsive discharge valve  54  is preferably provided seated within hub  50 . 
     Non-orbiting scroll member  32  is also provided with an annular recess  56  formed in the upper surface thereof. A floating seal  58  is disposed within recess  56  and is biased by intermediate pressurized gas against partition  40  to seal suction chamber  44  from discharge chamber  42 . A passage  60  extends through non-orbiting scroll member  32  to supply the intermediate pressurized gas to recess  56 . 
     A capacity control system  66  is shown in association with compressor  10 . Control system  66  includes a discharge fitting  68 , a piston  70 , a shell fitting  72 , a three-way solenoid valve  74 , a control module  76  and a sensor array  78  having one or more appropriate sensors. Discharge fitting  68  is threadingly received or otherwise secured within hub  50 . Discharge fitting  68  defines an internal cavity  80  and a plurality of discharge passages  82 . Discharge valve  54  is disposed within cavity  80 . Thus, pressurized gas overcomes the biasing load of discharge valve  54  to open discharge valve  54  and allowing the pressurized gas to flow into cavity  80 , through passages  82  and into discharge chamber  42 . 
     Referring now to  FIGS. 1 and 3 , discharge fitting  68  is assembled to piston  70  by first aligning a plurality of tabs  84  on discharge fitting  68  with a matching plurality of slots  86  formed in piston  70 . Discharge fitting  68  is then rotated to the position shown in  FIG. 3  to misalign tabs  84  with slots  86 . An alignment pin  88  maintains the misalignment between tabs  84  and slots  86  while a coil spring  90  biases the two components together. 
     Shell fitting  72  is sealingly secured to shell  12  and slidingly receives piston  70 . Piston  70  and shell fitting  72  define a pressure chamber  92 . Pressure chamber  92  is fluidically connected to solenoid  74  by a tube  94 . Solenoid valve  74  is also in fluid communication with discharge chamber  42  through a tube  96  and it is in fluid communication with suction fitting  46  and thus suction chamber  44  through a tube  98 . A seal  100  is located between piston  70  and shell fitting  72 . The combination of piston  70 , seal  100  and shell fitting  72  provides a self-centering sealing system to provide accurate alignment between piston  70  and shell fitting  72 . 
     In order to bias non-orbiting scroll member  32  into sealing engagement with orbiting scroll member  26  for normal full load operation as shown in  FIG. 1 , solenoid valve  74  is deactivated (or it is actuated) by control module  76  to the position shown in FIG.  1 . In this position, discharge chamber  42  is in direct communication with chamber  92  through tube  96 , solenoid valve  74  and tube  94 . The pressurized fluid at discharge pressure within chambers  42  and  92  will act against opposite sides of piston  70  thus allowing for the normal biasing of non-orbiting scroll member  32  towards orbiting scroll member  26  as shown in  FIG. 1  to sealingly engage the axial ends of each scroll member with the respective end plate of the opposite scroll member. The axial sealing of the two scroll members  26  and  32  causes compressor  24  to operate at 100% capacity. 
     In order to unload compressor  24 , solenoid valve  74  will be actuated (or it is deactuated) by control module  76  to the position shown in FIG.  2 . In this position, suction chamber  44  is in direct communication with chamber  92  through suction fitting  46 , tube  98 , solenoid valve  74  and tube  94 . With the discharge pressure pressurized fluid released to suction from chamber  92 , the pressure differences on opposite sides of piston  70  will move non-orbiting scroll member  32  upward as shown in  FIG. 2  to separate the axial ends of the tips of each scroll member with its respective end plate to create a gap  102  which allows the higher pressurized pockets to bleed to the lower pressurized pockets and eventually to suction chamber  44 . A wave spring  104  which is illustrated in  FIG. 9  maintains the sealing relationship between floating seal  58  and partition  40  during the modulation of non-orbiting scroll member  32 . The creation of gap  102  will substantially eliminate continued compression of the suction gas. When this unloading occurs, discharge valve  54  will move to its closed position thereby preventing the backflow of high pressurized fluid from discharge chamber  42  or the downstream refrigeration system. When compression of the suction gas is to be resumed, solenoid valve  74  will be deactuated (or it will be actuated) to the position shown in  FIG. 1  in which fluid communication between chamber  92  and discharge chamber  42  is again created. This again allows fluid at discharge pressure to react against piston  70  to axially engage scroll members  26  and  32 . The axial sealing engagement recreates the compressing action of compressor  24 . 
     Control module  76  is in communication with sensor array  78  to provide the required information for control module  76  to determine the degree of unloading required for the particular conditions of the refrigeration system including scroll compressor  10  existing at that time. Based upon this information, control module  76  will operate solenoid valve  74  in a pulsed width modulation mode to alternately place chamber  92  in communication with discharge chamber  42  and suction chamber  44 . The frequency with which solenoid  74  is operated in the pulsed width modulation mode will determine the percent capacity of operation of compressor  24 . As the sensed conditions change, control module  76  will vary the frequency of operation for solenoid valve  74  and thus the relative time periods at which compressor  24  is operated in a loaded and unloaded condition. The varying of the frequency of operation of solenoid valve  74  can cause the operation of compressor between fully loaded or 100% capacity and completely unloaded or 0% capacity or at any of an infinite number of settings in between in response to system demands. 
     Referring now to  FIG. 4 , there is shown a unique capacity control system in accordance with another embodiment of the present invention which is designated generally as reference numeral  166 . Capacity control system  166  is also shown in association with compressor  10 . Capacity control system  166  is similar to capacity control system  66  but it uses a two-way solenoid valve  174  instead of three-way solenoid valve  74 . Control system  166  includes discharge fitting  68 , a piston  170 , shell fitting  72 , solenoid valve  174 , control module  76  and sensor array  78 . 
     Piston  170  is identical to piston  70  with the exception that piston  170  defines a passageway  106  and an orifice  108  which extend between pressure chamber  92  and discharge chamber  42 . The incorporation of passageway  106  and orifice  108  allows the use of two-way solenoid  174  instead of three-way solenoid  74  and the elimination of tube  96 . By eliminating tube  96 , the fitting and hole through shell  12  is also eliminated. Seal  100  is located between piston  170  and seal fitting  72  to provide for the self-aligning sealing system for piston  170  and fitting  72 . 
     Solenoid  174  operates in a manner similar to solenoid  74 . Pressure chamber  92  is fluidically connected to solenoid  174  by tube  94 . Solenoid valve  174  is also in fluid communication with suction fitting  46  and thus suction chamber  44  by tube  98 . 
     In order to bias non-orbiting scroll member  32  into sealing engagement with orbiting scroll member  26  for normal full load operation, solenoid valve  174  is deactivated (or it is activated) by control module  76  to block fluid flow between tube  94  and tube  98 . In this position, chamber  92  is in communication with discharge chamber  42  through passageway  106  and orifice  108 . The pressurized fluid at discharge pressure within chambers  42  and  92  will act against opposite sides of piston  170  thus allowing for the normal biasing of non-orbiting scroll member  32  towards orbiting scroll member  26  to sealingly engage the axial ends of each scroll member with the respective end plate of the opposite scroll member. The axial sealing of the two scroll members  26  and  32  causes compressor  24  to operate at 100% capacity. 
     In order to unload compressor  24 , solenoid valve  174  will be actuated (or it will be deactuated) by control module  76  to the position shown in FIG.  4 . In this position, suction chamber  44  is in direct communication with chamber  92  through suction fitting  46 , tube  98 , solenoid valve  174  and tube  94 . With the discharge pressure pressurized fluid released to suction from chamber  92 , the pressure differences on opposite sides of piston  170  will move non-orbiting scroll member  32  upward to separate the axial end of the tips of each scroll member with its respective end plate and the higher pressurized pockets will bleed to the lower pressurized pockets and eventually to suction chamber  44 . Orifice  108  is incorporated to control the flow of discharge gas between discharge chamber  42  and chamber  92 . Thus, when chamber  92  is connected to the suction side of the compressor, the pressure difference on opposite sides of piston  170  will be created. Wave spring  104  is also incorporated in this embodiment to maintain the sealing relationship between floating seal  58  and partition  40  during modulation of non-orbiting scroll member  32 . When gap  102  is created the continued compression of the suction gas will be eliminated. When this unloading occurs, discharge valve  54  will move to its closed position thereby preventing the backflow of high pressurized fluid from discharge chamber  42  on the downstream refrigeration system. When compression of the suction gas is to be resumed, solenoid valve  174  will be deactuated (or it will be actuated) to again block fluid flow between tubes  94  and  98  allowing chamber  92  to be pressurized by discharge chamber  42  through passageway  106  and orifice  108 . Similar to the embodiment shown in  FIGS. 1-3 , control module  76  is in communication with sensor array  78  to provide the required information for control module  76  to determine the degree of unloading required and thus the frequency with which solenoid valve  174  is operated in the pulsed width modulation mode. 
     Referring now to  FIG. 5 , there is shown a scroll compressor which includes a unique capacity control system in accordance with another embodiment of the present invention and which is designated generally by the reference numeral  210 . 
     Scroll compressor  210  comprises an outer shell  212  within which is disposed a driving motor including a stator  214  and a rotor  216 , a crankshaft  218  to which rotor  216  is secured, an upper bearing housing  220  and a lower bearing housing  222  for rotatably supporting crankshaft  218  and a compressor assembly  224 . 
     Compressor assembly  224  includes an orbiting scroll member  226  supported on upper bearing housing  220  and drivingly connected to crankshaft  218  via a crankpin  228  and a drive bushing  230 . A non-orbiting scroll member  232  is positioned in meshing engagement with orbiting scroll member  226  and is axially movably secured to upper bearing housing  220  by means of a plurality of bolts (not shown) and associated sleeve members (not shown). An Oldham coupling  238  is provided which cooperates with scroll members  226  and  232  to prevent relative rotation therebetween. A partition plate  240  is provided adjacent the upper end of shell  212  and serves to divide the interior of shell  212  into a discharge chamber  242  at the upper end thereof and a suction chamber  244  at the lower end thereof. 
     In operation, as orbiting scroll member  226  orbits with respect to scroll member  232 , suction gas is drawn into suction chamber  244  of shell  212  via a suction fitting  246 . From suction chamber  244 , suction gas is sucked into compressor  224  through an inlet  248  provided in non-orbiting scroll member  232 . The intermeshing scroll wraps provided on scroll members  226  and  232  define moving pockets of gas which progressively decrease in size as they move radially inwardly as a result of the orbiting motion of scroll member  226  thus compressing the suction gas entering via inlet  248 . The compressed gas is then discharged into discharge chamber  242  via a discharge port  250  provided in scroll member  236  and a passage  252  formed in partition  240 . A pressure responsive discharge valve  254  is preferably provided seated within discharge port  250 . 
     Non-orbiting scroll member  232  is also provided with an annular recess  256  formed in the upper surface thereof. A floating seal  258  is disposed within recess  256  and is biased by intermediate pressurized gas against partition  240  to seal suction chamber  244  from discharge chamber  242 . A passage  260  extends through non-orbiting scroll member  232  to supply the intermediate pressurized gas to recess  256 . 
     A capacity control system  226  is shown in association with compressor  210 . Control system  266  includes a discharge fitting  268 , a piston  270 , a shell fitting  272 , solenoid valve  174 , control module  76  and sensor array  78  having one or more appropriate sensors. Discharge fitting  268  is threadingly received or otherwise secured within discharge port  250 . Discharge fitting  268  defines an internal cavity  280  and a plurality of discharge passages  282 . Discharge valve  254  is disposed below fitting  268  and below cavity  280 . Thus, pressurized gas overcomes the biasing load of discharge valve  254  to open discharge valve  254  and allowing the pressurized gas to flow into cavity  280 , through passages  282  and into discharge chamber  242 . 
     Referring now to  FIGS. 5 ,  7  and  8 , the assembly of discharge fitting  268  and piston  270  is shown in greater detail. Discharge fitting  268  defines an annular flange  284 . Seated against flange  284  is a lip seal  286  and a floating retainer  288 . Piston  270  is press fit or otherwise secured to discharge fitting  268  and piston  270  defines an annular flange  290  which sandwiches seal  286  and retainer  288  between flange  290  and flange  284 . Discharge fitting  268  defines passageway  106  and orifice  108  which extends through discharge fitting  268  to fluidically connect discharge chamber  242  with a pressure chamber  292  defined by discharge fitting  268 , piston  270 , seal  286 , retainer  288  and shell  212 . Shell fitting  272  is secured within a bore defined by shell  212  and slidingly receives the assembly of discharge fitting  268 , piston  270 , seal  286  and retainer  288 . Pressure chamber  292  is fluidically connected to solenoid  174  by tube  94  and with suction fitting  246  and thus suction chamber  244  through tube  98  in a manner similar to that described above for control system  166 . The combination of piston  270 , seal  286  and floating retainer  288  provides a self-centering sealing system to provide accurate alignment with the internal bore of shell fitting  272 . Seal  286  and floating retainer  288  include sufficient radial compliance such that any misalignment between the internal bore of fitting  272  and the internal bore of discharge port  250  within which discharge fitting  268  is secured is accommodated by seal  286  and floating retainer  288 . 
     In order to bias non-orbiting scroll member  232  into sealing engagement with orbiting scroll member  226  for normal full load operation, solenoid valve  174  is deactivated (or it is activated) by control module  76  to block fluid flow between tube  94  and tube  98 . In this position, chamber  292  is in communication with discharge chamber  242  through passageway  106  and orifice  108 . The pressurized fluid at discharge pressure within chambers  242  and  292  will act against opposite sides of piston  270  thus allowing for the normal biasing of non-orbiting scroll member  232  towards orbiting scroll member  226  to sealingly engage the axial ends of each scroll member with the respective end plate of the opposite scroll member. The axial sealing of the two scroll members  226  and  232  causes compressor  224  to operate at 100% capacity. 
     In order to unload compressor  224 , solenoid valve  174  will be actuated (or it will be deactuated) by control module  76  to the position shown in FIG.  4 . In this position, suction chamber  244  is in direct communication with chamber  292  through suction fitting  246 , tube  98 , solenoid valve  174  and tube  94 . With the discharge pressure pressurized fluid released to suction from chamber  292 , the pressure difference on opposite sides of piston  270  will move non-orbiting scroll member  232  upward to separate the axial end of the tips of each scroll member with its respective end plate and the higher pressurized pockets will bleed to the lower pressurized pockets and eventually to suction chamber  244 . Orifice  108  is incorporated to control the flow of discharge gas between discharge chamber  242  and chamber  292 . Thus, when chamber  292  is connected to the suction side of the compressor, the pressure difference on opposite sides of piston  270  will be created. Wave spring  104  is also incorporated in this embodiment to maintain the sealing relationship between floating seal  258  and partition  240  during modulation of non-orbiting scroll member  232 . When gap  102  is created the continued compression of the suction gas will be eliminated. When this unloading occurs, discharge valve  254  will move to its closed position thereby preventing the backflow of high pressurized fluid from discharge chamber  242  on the downstream refrigeration system. When compression of the suction gas is to be resumed, solenoid valve  174  will be deactuated (or it will be actuated) to again block fluid flow between tubes  94  and  98  allowing chamber  292  to be pressurized by discharge chamber  242  through passageway  106  and orifice  108 . Similar to the embodiment shown in  FIGS. 1-3 , control module  76  is in communication with sensor array  78  to provide the required information for control module  76  to determine the degree of unloading required and thus the frequency with which solenoid valve  174  is operated in the pulsed width modulation mode. 
     Referring now to  FIGS. 6 ,  10  and  11 , the fluid injection system for compressor  210  is shown in greater detail. Compressor  210  includes the capability of having fluid injected into the intermediate pressurized moving chambers at a point intermediate suction chamber  244  and discharge chamber  242 . A fluid injection fitting  310  extends through shell  212  and is fluidically connected to an injection tube  312  which is in turn fluidically connected to an injection fitting  314  secured to non-orbiting scroll member  232 . Non-orbiting scroll member  232  defines a pair of radial passages  316  each of which extend between injection fitting  314  and a pair of axial passages  318 . Axial passages  318  are open to the moving chambers on opposite sides of non-orbiting scroll member  232  of compressor  224  to inject the fluid into these moving chambers as required by a control system as is well known in the art. 
     Referring now to  FIGS. 12 and 13 , fitting  310  is shown in greater detail. Fitting  310  comprises an internal portion  320 , and an external portion  322 . Internal portion  320  includes an L-shaped passage  324  which sealingly receives injection tube  312  at one end. External portion  322  extends from the outside of shell  212  to the inside of shell  212  where it is unitary or integral with internal portion  320 . A welding or brazing attachment  326  secures and seals fitting  310  to shell  212 . External portion  322  defines a bore  330  which is an extension of L-shaped passage  324 . External portion  322  also defines a cylindrical bore  332  to which the tubing of the refrigeration system is secured. 
       FIG. 14  illustrates a vapor injection system which provides the fluid for the fluid injection system of compressor  210 . Compressor  210  is shown in a refrigeration system which includes a condenser  350 , a first expansion valve or throttle  352 , a flash tank or an economizer  354 , a second expansion valve or throttle  356 , an evaporator  358  and a series of piping  360  interconnecting the components as shown in FIG.  14 . Compressor  210  is operated by the motor to compress the refrigerant gas. The compressed gas is then liquified by condenser  350 . The liquified refrigerant passes through expansion valve  352  and expands in flash tank  354  where it is separated into gas and liquid. The gaseous refrigerant further passes through piping  362  to be introduced into compressor  210  through fitting  310 . On the other hand, the remaining liquid refrigerant further expands in expansion valve  356 , is then vaporized in evaporator  358  and is again taken into compressor  210 . 
     The incorporation of flash tank  354  and the remainder of the vapor injection system, allows the capacity of the compressor to increase above the fixed capacity of compressor  210 . Typically, at standard air conditioning conditions, the capacity of the compressor can be increased by approximately 20% to provide a compressor with 120% of its capacity as shown in the graph in FIG.  16 . In order to be able to control the capacity of compressor  210 , a solenoid valve  364  is positioned within piping  362 . The amount of percent increase in the capacity of compressor  210  can be controlled by operating solenoid valve  364  in a pulse width modulation mode. Solenoid valve  364  when operated in a pulse width modulation mode in combination with capacity control system  266  of compressor  210  allows the capacity of compressor  210  to be positioned anywhere along the line shown in FIG.  16 . 
       FIG. 15  illustrates a refrigerant system schematic in accordance with another embodiment of the present invention. The refrigerant system shown in  FIG. 15  is the same as the refrigerant system shown in  FIG. 14  except that flash tank  354  has been replaced by a heat exchanger  354 ′. Compressor  210  is operated by the motor to compress the refrigerant gas. The compressed gas is then liquified by condenser  350 . The liquified refrigerant is then routed to the liquid side of heat exchanger  354 ′ while a second portion of the liquified refrigerant passes through expansion valve  352  and then is routed to the vapor side of heat exchanger  354 ′ in a gas and liquid state. The portion of refrigerant passing through expansion valve  352  is heated by the portion of refrigerant passing directly through heat exchanger to provide the vapor for injecting into compressor  210 . This gaseous refrigerant then passes through piping  362  to be introduced into compressor  210  through fitting  310 . On the other hand, the liquid refrigerant passing directly through heat exchanger  354 ′ expands in expansion valve  356  and is then vaporized in evaporator  358  to again be taken into the suction side of compressor  210 . Similar to the system shown in  FIG. 14 , solenoid valve  364  is positioned within piping  362  to allow the capacity of compressor  210  to be positioned anywhere along the line shown in  FIG. 16  when used in combination with capacity control system  266 . 
     While the above detailed description describes the preferred embodiment of the present invention, it should be understood that the present invention is susceptible to modification, variation and alteration without deviating from the scope and fair meaning of the subjoined claims.

Technology Category: f