Abstract:
A refrigeration circuit includes a scroll compressor, a condenser and an evaporator connected in a closed loop. A liquid injection system takes liquid refrigerant from the refrigerant circuit and injects it into a suction line leading to the compressor to cool the refrigerant in the refrigeration circuit. An electronic control unit operates a controllable valve based on a temperature reading received from a discharge gas temperature sensor. The controllable valve can be an electronic expansion valve or a solenoid valve.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to scroll-type machines. More particularly, the present invention relates to hermetic scroll compressors incorporating a fluid injection system where the fluid injection system injects the fluid into the suction line of the compressor when a temperature limit is exceeded. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Refrigeration and air conditioning systems generally include a compressor, a condenser, an expansion valve or an equivalent and an evaporator. These components are coupled in sequence in a continuous flow path. A working fluid flows through the system and alternates between a liquid phase and a vapor or gaseous phase. 
     A variety of compressor types have been used in refrigeration systems, including but not limited to reciprocating compressors, screw compressors and rotary compressors. Rotary type compressors can include the various vane type compressors as well as scroll machines. Scroll machines or scroll compressors are constructed using two scroll members with each scroll member having an end plate and a spiral wrap. The scroll members are mounted so that they may engage in relative orbiting motion with respect to each other. During this orbiting movement, the spiral wraps define a successive series of enclosed spaces or crescent shaped pockets, each of which progressively decrease in size as it moves inwardly from a radial outer position at a relatively low suction pressure to a central position at a relatively high discharge pressure. The compressed gas exits from the enclosed space at the central position through a discharge passage formed through the end plate of one of the scroll members. 
     In the normal refrigeration cycle, vapor is drawn into a compressor where it is compressed to a higher pressure. The compressed vapor is cooled and condensed in a condenser into a high pressure liquid which is then expanded, typically through an expansion valve, to a lower pressure and caused to evaporate in an evaporator to thereby draw in heat and thus provide the desired cooling effect. The expanded, relatively low pressure vapor exiting the evaporator is once again drawn into the compressor and the cycle starts anew. The action of compressing the lower pressure vapor imparts work onto the higher pressure vapor and results in a significant increase in the vapor temperature. While a substantial portion of this heat caused by the compression process and the evaporating process is subsequently rejected to the atmosphere during the condensation process, a portion of the heat is transferred to the compressor components. Depending upon the specific refrigerant vapor compressed and on the pressure conditions of operation, this heat transfer can cause the temperature of the compressor components to rise to levels which may cause the compressor to overheat, resulting in degradation of the compressor&#39;s performance and lubrication and possible damage to the compressor. 
     In order to overcome overheating problems, various methods have been developed for injecting gaseous or liquid refrigerant under pressure into the closed pockets of the scroll compressor. One known prior art method of injecting the liquid refrigerant from the refrigerant cycle into the enclosed pockets is to inject the liquid refrigerant using an injection fitting which has an opening which is positioned in alignment with a suction inlet defined by one of the scroll members. The injected liquid is sucked into the closed pockets to cool the compressed gas. This method is described in Assignee&#39;s U.S. Pat. No. 5,076,067; the disclosure of which is incorporated herein by reference. Another known prior art method of liquid injection is to injert the liquid refrigerant from the refrigeration cycle directly into one or more of the closed pockets through an intermediate pressurized biasing chamber which is in communication with one or more of the closed pockets. The injected liquid cools the compressed gas in the closed pockets. This method is described in Assignee&#39;s U.S. Pat. Nos. 5,329,788 and 5,447,420; the disclosures of which are incorporated herein by reference. Another known prior art method of liquid injection is to inject the liquid refrigerant from the refrigeration cycle directly into one or more of the closed pockets through a passage extending through one of the scroll members and opening into one or more of the closed pockets at a position which is as close as possible to the central portion of the scroll member or as close as possible to the actual discharge. This method is described in Assignee&#39;s U.S. Pat. No. 5,469,816; the disclosure of which is incorporated herein by reference. 
     Each of these prior art systems offer advantages and disadvantages even though they perform successfully in the refrigeration compressors. The injection into the suction inlet of the scroll members offers simplicity but it also requires an additional fitting which extends through the hermetic shell. The systems that inject directly into one or more of the closed pockets are able to more accurately control the temperature but they require additional machining of the scroll members as well as requiring an additional fitting which extends through the hermetic shell of the scroll compressor. 
     The present invention overcomes these disadvantages by providing a simple yet effective method for injecting liquid refrigerant into the pockets formed by the scroll members to reduce the temperature of the compressed gas. The present invention uses a temperature sensing device on the top cap of the hermetic shell to sense the temperature of the discharge gas. When the discharge gas temperature exceeds a specified limit, an electronic control will open a device to inject a certain quantity of liquid refrigerant into the suction line of the scroll compressor. The injecting device can be an electronic expansion valve, a pulsing (pulse width modulator) valve or any other known method of having a controllable opening of a fluid passage. The method of the present invention provides an effective low cost liquid injection system which only requires simple modifications of the scroll compressor and the refrigeration system. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
     FIG. 1 is a vertical sectional view of a scroll compressor which incorporates the liquid injection system in accordance with the present invention; 
     FIG. 2 is a schematic diagram of a refrigeration system incorporating the liquid injection system in accordance with the present invention; and 
     FIG. 3 is a schematic diagram of a refrigeration system incorporating a liquid injection system in accordance with another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     Referring now to the drawings in which like reference numerals designate like or corresponding parts through the several views, there is shown in FIG. 1 a scroll compressor which incorporates the liquid injection system in accordance with the present invention and which is identified generally by reference numeral  10 . 
     Scroll compressor  10  comprises a generally cylindrical hermetic shell  12  having welded at the upper end thereof a cap  14  and at the lower end thereof a base  16  having plurality of mounting feet (not shown) integrally formed therewith. Cap  14  is provided with a refrigerant discharge fitting  18  which may have the usual discharge valve therein (not shown). Other major elements affixed to hermetic shell  12  include a transversely extending partition  20  which is welded about its periphery at the same point cap  14  is welded to hermetic shell  12 , an inlet fitting  22 , a main bearing housing  24  which is suitably secured to hermetic shell  12  and a lower bearing housing  26  having a plurality of radially outwardly extending legs each of which is suitably secured to hermetic shell  12 . A motor stator  28  which is generally square in cross-section but with the corners rounded off its press fit into hermetic shell  12 . The flats between the rounded corners on stator  28  provide passageways between stator  28  and hermetic shell  12  which facilitate the return flow of the lubricant from the top of hermetic shell  12  to its bottom. 
     A drive shaft or crankshaft  30  having an eccentric crank pin  32  at the upper end thereof is rotatably journaled in a bearing  34  in main bearing housing  24  and in a bearing  36  in lower bearing housing  26 . Crankshaft  30  has at the lower end thereof a relatively large diameter concentric bore  38  which communicates with a radially outwardly located small diameter bore  40  extending upwardly therefrom to the top of crankshaft  30 . Disposed within bore  38  is a stirrer  42 . The lower portion of the interior hermetic shell  12  is filled with lubricating oil and bores  38  and  40  act as a pump to pump the lubricating oil up crankshaft  30  and ultimately to all of the various portions of compressor  10  which require lubrication. 
     Crankshaft  30  is rotatably driven by an electric motor which includes motor stator  28  having windings  44  passing therethrough and a motor rotor  46  pressed fitted onto crankshaft  30  and having upper and lower counterweights  48  and  50 , respectively. A motor protector  52 , of the usual type, is provided in close proximity to motor windings  44  so that if the motor exceeds its normal temperature range, motor protector  52  will de-energize the motor. 
     The upper surface of main bearing housing  24  is provided with an annular flat thrust bearing surfaces  54  on which is disposed an orbiting scroll member  56 . Scroll member  56  comprises an end plate  58  having the usual spiral valve or wrap  60  on the upper surface thereof and an annular flat thrust surface  62  on the lower surface thereof. Projecting downwardly from the lower surface is a cylindrical hub  64  having a journal bearing  66  therein and in which is rotatively disposed a drive bushing  68  having an inner bore within which crank pin  32  is drivingly disposed. Crank pin  32  has a flat on one surface (not shown) which drivingly engages a flat surface in a portion of the inner bore of drive bushing  68  to provide a radially compliant drive arrangement such as shown in Assignee&#39;s U.S. Pat. No. 4,877,382, the disclosure of which is incorporated herein by reference. 
     Wrap  60  meshes with a non-orbiting scroll wrap  72  forming part of a non-orbiting scroll member  74 . During orbital movement of orbiting scroll member  56  with respect to non-orbiting scroll member  74  moving pockets of fluid are created which are compressed as the pockets move from a radially outer position to a central position of scroll members  56  and  74 . Non-orbiting scroll member  74  is mounted to main bearing housing  24  in any desired manner which will provide limited axial movement of non-orbiting scroll member  74 . The specific manner of such mounting is not critical to the present invention. 
     Non-orbiting scroll member  74  has a centrally disposed discharge port  76  which is in fluid communication via an opening  78  in partition  20  with a discharge muffler  80  defined by cap  14  and partition  20 . Fluid compressed by the moving pockets between scroll wraps  60  and  72  discharges into discharge muffler  80  through discharge port  76  and opening  78 . Non-orbiting scroll member  74  has in the upper surface thereof an annular recess  82  having parallel coaxial sidewalls within which is sealing disposed for relative axial movement an annular seal assembly  84  which serves to isolate the bottom of annular recess  82  so that it can be placed in fluid communication with a source of intermediate fluid pressure by means of a passageway  86 . Non-orbiting scroll member  74  is thus axially biased against orbiting scroll member  56  by the forces created by discharge pressure acting on the central portion of non-orbiting scroll member  74  and the forces created by intermediate fluid pressure acting on the bottom of annular recess  82 . This axial pressure biasing, as well as the various techniques for supporting non-orbiting scroll member  74  for limited axial movement are disclosed in much greater detail in Assignee&#39;s aforementioned U.S. Pat. No. 4,877,382. 
     Relative rotation of scroll members  56  and  74  is prevent by the usual Oldham Coupling  99  having a pair of key slidably disposed in diametrically opposing slots in non-orbiting scroll member  74  and a second pair of keys slidably disposed in diametrically opposed slots in orbiting scroll member  56 . 
     Compressor  10  is preferably of the “low side” type in which suction gas entering hermetic shell  12  is allowed, in part, to assist in cooling the motor. So long as there is an adequate flow of returning suction gas, the motor will remain within the desired temperature limits. When this flow ceases, however, the loss of cooling will cause motor protector  52  to trip and shut compressor  10  down. 
     The scroll compressor, as thus broadly described, is either known in the art or it is the subject matter of other pending applications for patent by Applicant&#39;s assignee. The details of construction which incorporate the principles of the present invention are those which deal with a unique fluid injection system illustrated in FIG.  2  and identified generally by reference numeral  100 . Fluid injection system  100  is used to inject liquid refrigerant for cooling purposes. 
     Liquid injection system  100  is illustrated in conjunction with a refrigeration circuit  102 . Refrigeration circuit  102  comprises compressor  10  and a gas discharge line  104  connected to discharge fitting  18  for supplying high pressure refrigerant to a condenser  106 . A liquid conduit  108  extends, from condenser  106  and branches into a normal flow line  110  and a liquid injection line  112 . Completing the general operation of refrigeration circuit  102 , line  110  communicates condensed relatively high pressure liquid refrigerant to an expansion valve  114  where it is expanded into relatively low pressure liquid and vapor. A fluid line  116  communicates the low pressure liquid and vapor to an evaporator  118  where the liquid evaporates, thereby absorbing heat and providing the desired cooling effect. Finally a return gas line on suction line  120  delivers the low pressure refrigerant vapor from evaporator  118  to suction inlet fitting  22  of compressor  10 . 
     In order to provide cooling to compressor  10 , liquid injection line  112  acts to extract a portion of the relatively high pressure liquid refrigerant from refrigeration circuit  102 . A restrictor  122  is provided to restrict the amount of liquid extracted to an amount adequate to cool compressor  10  under high load operation. In the preferred embodiment, restrictor  122  is a precalibrated capillary tube. It should be understood however that restrictor  122  may also be a calibrated orifice, an adjustable screw type restriction on any other restriction known in the art. This extracted liquid is then communicated by a fluid line  124  through an electronic expansion valve  126  to suction line  120  where the liquid is injected into compressor  10  through suction inlet fitting  22  to effect cooling. Valve  126  is controlled by an electronic control unit  128  which is in communication with valve  126  and a temperature sensor  130  attached to the top cap  14 . While temperature sensor  130  is illustrated as being attached to top cap  14 , it is within the scope of the present invention to utilize other discharge temperature sensing devices known in the art such as temperature sensor  130 ′ located on gas discharge line  104 . Upon sensing a temperature in excess of a predetermined limit, control unit  128  opens electronic expansion valve  126  to inject a specified quantity of liquid refrigerant into suction line  120  of refrigeration circuit  102 . The amount of liquid refrigerant that is injected is controlled by the opening of electronic expansion valve  126 . The further that electronic expansion valve  126  is opened, the more liquid refrigerant is injected. Temperature sensor  130  working with electronic control unit  128  monitors the discharge temperature and controls valve  126  in such a manner than the discharge temperature is brought back into acceptable limits. 
     Thus, the present invention provides a unique liquid injection system that is low cost, efficient and able to be incorporated into a refrigeration system without extensive modifications being made to the compressor itself. 
     Referring now to FIG. 3, a liquid injection system  200  in accordance with another embodiment of the present invention is illustrated. Liquid injection system  200  is also illustrated in conjunction with refrigeration circuit  102 . Refrigeration circuit  102  comprises compressor  10 . Gas discharge line  104  connected to discharge fitting  18 , condenser  106  liquid conduit  108 , normal flow line  110 , liquid injection line  112 , expansion valve  114 , fluid line  116 , evaporator  118  and return gas line on suction line  120  connected to suction inlet fitting  22 . 
     Liquid injection line  112  acts to extract a portion of the relatively high pressure liquid refrigerant from refrigerant circuit  102 . Restrictor  122  is provided to restrict the amount of liquid extracted to an amount adequate to cool compressor  10  under high load operation. This extracted liquid is then communicated by fluid line  124  through a pulse width modulated solenoid valve  226  to suction line  120  where the liquid is injected into compressor  10  through suction inlet fitting  22  to effect cooling. Thus, liquid injection system  200  is the same as liquid injection system  100  except that electronic expansion valve  126  is replaced by pulse width modulated solenoid valve  226 . Solenoid valve  226  is controlled by electronic control unit  128  which is in communication with solenoid valve  226  and temperature sensor  130  attached to top cap  14  or temperature sensor  130 ′ attached to gas discharge line  104 . Upon sensing a temperature in excess of a pre-determined limit, electronic control unit  128  sends a pulse width modulated signal to solenoid valve  226  to inject a specified quantity of liquid refrigerant into suction line  120  of refrigeration circuit  102 . The amount of liquid refrigerant that is injected is controlled by the pulse width modulated signal which controls the opening time for solenoid valve  226 . Temperature sensor  130  working with electronic control unit  128  monitors the discharge temperature and controls solenoid valve  226  in such a manner that the discharge temperature is brought back into acceptable limits. 
     While FIGS. 2 and 3 illustrate electronic expansion valve  126  and solenoid valve  226 , respectively, it is within the scope of the present invention to utilize any other known type of controllable valve in place of valve  126  or solenoid valve  226  if desired. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.