Abstract:
A capacity control system has a valve which closes off the inlet to one or more of the cylinders in a multicylinder compressor. The valve is motivated by fluid at discharge pressure which reacts against a piston to close the inlet. An orifice is positioned in the flow of the fluid at discharge pressure to control the velocity of the piston to reduce impact loading and improve reliability.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to refrigeration compressors. More particularly, the present invention relates to a reciprocating piston type refrigeration compressor which incorporates capacity modulation by utilization of blocked suction. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Refrigeration and air conditioning systems are commonly operated under a wide range of loading conditions due to changing environmental conditions. In order to effectively and efficiently accomplish the desired cooling under these changing conditions, it is advantageous to incorporate a system which varies the capacity of the refrigeration compressor in the system. 
     A wide variety of systems have been developed in order to accomplish capacity modulation. The various types of unloading and capacity control found in the prior art for refrigeration compressors all have been subject to various drawbacks and/or durability issues. Some of these prior art systems have operated satisfactorily but they have required a substantial amount of external tubing or other components which are subject to damage during shipping and/or possible accidental damage after installation. In addition, the field labor required in the installation and maintenance of these external systems is subject to error which creates problems during actual operation and increases the field labor costs. 
     Other designs for capacity modulation systems are installed during the manufacture of the compressor. These designs have all of the major components internal to the compressor itself except for a single component which is typically the only element to require servicing during the expectable life of the compressor. This single external component is constructed such that it is easily accessible for service while still being positioned to limit the danger of accidental damage. 
     While the prior art internal systems have proven to operate satisfactorily, there is still a need to improve both the reliability and durability of these capacity modulation systems. 
     The present invention provides the art with a capacity modulation system which utilizes a piston for blocking the suction inlet to reduce the capacity of the compressor. The high-pressure gas which is supplied to the piston during activation is throttled in order to reduce the piston impact velocity. The reduction in the piston impact velocity improves the reliability and durability of the piston, the piston seals and the piston seat. 
     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 fragmentary partially sectioned end elevational view of a three-bank radial reciprocating compressor incorporating the capacity modulation system in accordance with the present invention; 
     FIG. 2 is an enlarged cross-sectional view of the internal unloader valve shown in FIG. 1 in a full capacity position; 
     FIG. 3 is an enlarged cross-sectional view of the internal unloader valve shown in FIG. 2 with the unloader valve in a reduced capacity position; 
     FIG. 4 is an enlarged cross-sectional view of an internal unloader valve in accordance with another embodiment of the present invention with the unloader valve in a full capacity position; and 
     FIG. 5 is an enlarged cross-sectional view of the internal unloader valve shown in FIG. 4 with the unloader valve in a reduced capacity position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) 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 throughout the several views, there is shown in FIG. 1 a body or cylinder block portion of a multicylinder refrigeration compressor in accordance with the present invention and which is designated generally by the reference numeral  10 . Compressor  10  illustrates three cylindrical banks  12 ,  14  and  16 . Although only cylindrical banks  14  and  16  are illustrated, it is to be understood that each cylinder bank may contain one, two or more cylinders and that the construction illustrated typifies known commercial practice and is merely illustrative insofar as the compressor itself is concerned. 
     Each cylinder bank  12 ,  14  and  16  defines a compression cylinder  20  within which a piston  22  is slidingly disposed. Cylinder bank  14  is illustrated with a capacity control system  24  while cylinder bank  16  is illustrated without capacity control system  24 . As detailed below, one or more of cylinder banks  12 ,  14  and  16  may include capacity control system  24 . Cylinder bank  16  includes a cylinder head  26  which closes cylinder  20  and which defines a suction chamber  28  and a discharge chamber  30 . A suction valve  32  controls the communication between suction chamber  28  and cylinder  20  and a discharge valve  34  controls the communication between discharge chamber  30  and cylinder  20 . A suction passage  36  extends between suction chamber  28  and a common suction chamber (not shown) of compressor  10  which is in turn open to the inlet of the compressor. Discharge chamber  30  is in communication with the outlet of compressor  10  through a discharge passage (not shown). 
     Referring now to FIGS. 1 and 2, cylinder bank  14  is illustrated incorporating capacity control system  24 . Capacity control system  24  comprises a cylinder head  40 , a control piston assembly  42  and a solenoid valve assembly  44 . Cylinder head  40  closes cylinder  20  and it defines a suction chamber  46  and a discharge chamber  48 . A suction valve  32  controls the communication between suction chamber  46  and cylinder  20  and a discharge valve  34  controls the communication between discharge chamber  48  and cylinder  20 . A suction passage  50  extends between suction chamber  46  and the common suction chamber of compressor  10 . Discharge chamber  30  is in communication with the outlet of compressor  10  through a discharge passage (not shown). Cylinder head  40  defines a discharge pressure passage  52  which extends between discharge chamber  48  and solenoid valve assembly  44 , a suction pressure passage  54  (FIG. 2) which extends between suction chamber  46  and solenoid valve assembly  44  and a control passage  56  which extends between solenoid valve assembly  44  and a control chamber  58  defined by cylinder head  40 . 
     Control piston assembly  42  is slidingly disposed within control chamber  58  and it comprises a valve body or piston  60  and a biasing spring  62 . Piston  60  is slidingly disposed within control chamber  58  with a seal disposed between piston  60  and control chamber  58 . Biasing spring  62  is disposed between piston  60  and cylinder bank  14  with a seal  64  attached to piston  60 . Seal  64  engages cylinder bank  14  to block suction passage  50  when piston assembly  42  is in its closed position. Biasing spring  62  urges piston assembly  42  into an open position. 
     Solenoid valve assembly  44  comprises a valve block  66  and a solenoid valve  68 . Valve block  66  is secured to cylinder head  40  and it defines a discharge control passage  70  in communication with discharge pressure passage  52 , a suction control passage  72  in communication with suction pressure passage  54  and a common control passage  74  in communication with control passage  56 . A discharge valve seat  76  is disposed between discharge control passage  70  and common control passage  74  and a suction valve seat  78  is disposed between suction control passage  72  and common control passage  74 . 
     Solenoid valve  68  includes a solenoid coil  80  and a needle valve  82 . Needle valve  82  is disposed between valve seats  76  and  78  and moves between a first position and a second position. In its first position, communication between discharge control passage  70  and common control passage  74  is blocked but communication between suction control passage  72  and common control passage  74  is permitted. In its second position, communication between discharge control passage  70  and common control passage  74  is permitted but communication between suction control passage  72  and common control passage  74  is prohibited. Needle valve  82  and thus solenoid valve  68  is normally biased into its first position by a biasing member  84  which allows full capacity for compressor  10 . Activation of solenoid coil  80  moves needle valve  82  and thus solenoid valve  68  to its second position which results in operation of compressor  10  at a reduced capacity. 
     Referring now to FIG. 2, capacity control system  24  is illustrated in its full capacity or first position. In this position, solenoid coil  80  is de-energized and needle valve  82  is biased against discharge valve seat  76 . The biasing of needle valve  82  against discharge valve seat  76  closes discharge control passage  70  and opens suction control passage  72 . Thus, control chamber  58  is in communication with the common suction chamber of compressor  10  through common control passage  74 , suction valve seat  78 , suction control passage  72  and suction pressure passage  54 . Fluid at suction pressure reacts against both the upper and lower surfaces of piston  60  and piston  60  is urged away from cylinder bank  14  by biasing spring  62 . The movement of piston  60  away from cylinder bank  14  places suction passage  50  in communication with suction chamber  46  allowing for the free flow of suction gas and the full capacity operation of cylinder bank  14 . 
     Referring now to FIG. 3, capacity control system  24  is illustrated in its reduced capacity or second position. In this position, solenoid coil  80  is energized and needle valve  82  is biased against suction valve seat  78 . The biasing of needle valve  82  against suction valve seat  78  closes suction control passage  72  and opens discharge control passage  70 . Thus, control chamber  58  is in communication with discharge pressure from the outlet of compressor  10  through common control passage  74 , discharge valve seat  76 , discharge control passage  70  and discharge pressure passage  52 . Fluid at discharge pressure reacts against the upper surface of piston  60  to urge piston  60  into engagement with cylinder bank  14  against the force produced by biasing spring  62 . The engagement of piston  60  and seal  64  with cylinder bank  14  closes suction passage  50  which blocks fluid at suction pressure from entering suction chamber  46 . The capacity of cylinder bank  14  is essentially reduced to zero. Discharge control passage  70  is provided with an orifice  90  which limits the flow of fluid at discharge pressure from control passage  70  to control chamber  58 . By limiting the flow of fluid at discharge pressure into control chamber  58 , the velocity of piston  60  is reduced which then diminishes the impact force between piston  60  and cylinder bank  14 . The diminishing of the impact force reduces damage and wear on piston  60 , seal  64  and the seat on cylinder bank  14 . This, in turn, significantly improves the reliability of compressor  10 . 
     In the preferred embodiment, piston  60  has a diameter of approximately one inch and a stroke of approximately 0.310 inches. With these dimensions, the preferred diameter for orifice  90  is between 0.020 inches and 0.060 inches and more preferably between 0.030 inches and 0.050 inches. 
     The above data can be used to calculate the following list of values using well known equations: 
     
       
         
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 “Preferred” 
                   
               
               
                   
                 Piston 
                 Orifice Range 
                 “More Preferred” 
               
               
                   
               
             
             
               
                 Diameter (in) 
                 1.000 
                 0.020 to 0.060 
                 0.030 to 0.050 
               
               
                 Cross-Sectional area 
                 0.785 
                 0.000314 to 
                 0.000707 to 
               
               
                 (in 2 ) 
                   
                 0.00283 
                 0.00196 
               
               
                 Stroke (in) 
                 0.310 
                 Na 
                 Na 
               
               
                 Displacement (in 2 ) 
                 0.243 
                 Na 
                 Na 
               
               
                 Ratio of piston to orifice 
                 Na 
                 50.0:1 to 16.7:1 
                 33.3:1 to 20.0:1 
               
               
                 diameters 
               
               
                 Ratio of piston to orifice 
                 Na 
                 2500:1 to 277:1 
                 1110:1 to 401:1 
               
               
                 diameters 
               
               
                 Ratio of piston displace- 
                 Na 
                 12.2:1 to 4.05:1 
                 8.1:1 to 4.86:1 
               
               
                 ment to orifice diameters 
               
               
                 Ratio of piston displace- 
                 Na 
                 77.4:1 to 85.9:1 
                 344:1 to 124:1 
               
               
                 ment to orifice area 
               
               
                   
               
             
          
         
       
     
     While the present invention is described as having only cylinder bank  14  incorporating capacity control system  24 , it is within the scope of the present invention to include capacity control system  24  on more than one cylinder bank but not all of the cylinder blocks because discharge pressurized fluid is required for the movement of piston  60 . With the present invention having three cylinder banks, the incorporation of one capacity control system allows the capacity of compressor  10  to vary between ⅔ capacity and full capacity. The incorporation of two capacity control systems  24  allows the capacity of compressor  10  to vary between ⅓ capacity and full capacity. 
     Solenoid coil  80  is described as being de-energized to place needle valve  82  in a first position which provides full capacity and as being energized to place needle valve  82  in a second position which provides reduced capacity. It is within the scope of the present invention to operate solenoid coil  80  in a pulsed width modulation mode in order to provide an infinitesimal number of capacities between the fully reduced capacity and the full capacity. In this manner and by incorporating capacity control system  24  on two of the cylinder blocks, the capacity of compressor  10  can be selected at any capacity between ⅓ capacity and full capacity. 
     Referring now to FIGS. 4 and 5, a capacity control system  124  is illustrated. Capacity control system  124  is the same as capacity control system  24  except that orifice  90  has been relocated from discharge control passage  70  to a gasket  92  disposed between cylinder head  40  and valve block  66 . The operation and function of capacity control system  124  is identical to that described above for capacity control system  24 . FIG. 4 illustrates capacity control system  124  at full capacity and FIG. 5 illustrates capacity control system  124  at reduced capacity. 
     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.