Abstract:
A scroll compressor has a biasing chamber which contains a pressurized fluid. The pressurized fluid within the chamber biases the two scroll members together. A rotatable ring is attached to one of the scroll members to open and close a passage leading to this biasing chamber. When the ring opens the passage in one embodiment, this releases the pressurized fluid to remove the load, biasing the two scroll members together. When the biasing load is removed, the two scroll members separate, creating a leakage path between discharge and suction to reduce the capacity of the scroll compressor. When the ring opens the passage in another embodiment, a delayed suction passage is opened to reduce the capacity of the compressor.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to capacity modulation of compressors. More particularly, the present invention relates to the capacity modulation of a scroll compressor by controlling the fluid pressure in a chamber where the fluid pressure in the chamber biases the two scrolls together.  
       BACKGROUND AND SUMMARY OF THE INVENTION  
       [0002]     Capacity modulation is often a desirable feature to incorporate into the compressors of air conditioning and refrigeration systems 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 approaches have ranged from control of the suction inlet of the compressor to bypassing compressed discharge gas back into the suction pressure zone of the compressor. With a scroll-type compressor, capacity modulation has often been accomplished by using a delayed suction approach which comprises providing ports at various positions extending through one of the base plates which, when opened, allow the initially formed compression chambers between the intermeshing scroll wraps to communicate with the suction zone of the compressor. This delays the point at which the sealed compression chambers are formed and, thus, delays the start of compression of the suction gas. This method of capacity modulation has the effect of actually reducing the compression ratio of the compressor. While these delayed suction systems are effective at reducing the capacity of the compressor, they are only able to provide a predetermined amount of compressor unloading with the amount being determined by the position of the unloading ports along the end plate. While it is possible to provide multiple step unloading by incorporating a plurality of unloading ports at different locations, this approach becomes costly and it requires additional space to accommodate the separate controls for opening and closing each set of ports. Even when using multiple unloading ports, it is typically not possible to control the capacity of the compressor between 0% and 100% using this delayed suction technique.  
         [0003]     More recently, compressor unloading and, thus, capacity modulation has been accomplished by cyclically effecting axial or radial separation of the two scroll members for predetermined periods of time during the operating cycle of the compressor. In order to facilitate the axial unloading or axial separation of the two scroll members, a biasing chamber is formed in or adjacent one of the two scroll members; and this biasing chamber is placed in communication with a source of compressed fluid in a pressure chamber or the discharge chamber of the compressor. The fluid in the biasing chamber is cyclically released to the suction area of the compressor to facilitate the unloading of the compressor.  
         [0004]     The continued development of capacity modulated scroll compressors has been directed towards the simplification of the capacity modulation devices in order to lower the costs of the capacity modulated systems, as well as simplifying the overall manufacture, design and development of these capacity modulated systems without sacrificing performance and more preferably increasing the performance and/or reliability of the capacity modulation system.  
         [0005]     The present invention provides the art with a capacity modulated compressor which vents an existing intermediate pressurized chamber cyclically to suction to modulate the capacity of the compressor. The existing intermediate pressurized chamber is utilized in the compressor to bias the two scrolls together as well as to bias a floating seal into contact with a partition or the shell to seal a leakage passage between discharge pressure and the suction pressure zone of the compressor. A sealing system is incorporated into the scroll member defining the intermediate pressurized chamber. The sealing system incorporates a lip seal which improves both the performance and the reliability of the capacity modulation system.  
         [0006]     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  
       [0007]     In the drawings which illustrate the best mode presently contemplated for carrying out the present invention:  
         [0008]      FIG. 1  is a vertical section view of a scroll-type compressor incorporating a capacity modulation system in accordance with the present invention;  
         [0009]      FIG. 2  is a fragmentary view of the compressor of  FIG. 1  showing the capacity modulation system shown in  FIG. 1 :  
         [0010]      FIG. 3  is a plan view of the compressor shown in  FIG. 1  with the top portion of the outer shell removed;  
         [0011]      FIG. 4  is an enlarged view showing a portion of a modified valving ring;  
         [0012]      FIG. 5  is a perspective view of the valving ring incorporated in the compressor of  FIG. 1 ;  
         [0013]      FIG. 6  is a fragmentary section view showing the scroll assembly forming a part of the compressor of  FIG. 1 ;  
         [0014]      FIG. 7  is an enlarged detailed view of the actuating assembly incorporated in the compressor of  FIG. 1 ;  
         [0015]      FIG. 8  is a perspective view of the compressor of  FIG. 1  with portions of the outer shell broken away;  
         [0016]      FIG. 9  is a fragmentary section view of the compressor of  FIG. 1  showing the pressurized fluid supply passages provided in the non-orbiting scroll;  
         [0017]      FIG. 10  is an enlarged section view of the solenoid valve assembly incorporated in the compressor of  FIG. 1 ;  
         [0018]      FIG. 11  is an enlarged view of the sealing system shown in  FIG. 1  with the by-pass port closed;  
         [0019]      FIG. 12  is an enlarged view of the sealing system shown in  FIG. 1  with the by-pass port open;  
         [0020]      FIG. 13  is a fragmentary view of a compressor incorporating a capacity modulation system in accordance with another embodiment of the present invention; and  
         [0021]      FIG. 14  is a fragmentary section view showing the scroll assembly forming a part of the compressor of  FIG. 13 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     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.  
         [0023]     While the present invention is suitable for incorporation in many different types of scroll machines, including hermetic machines, open drive machines and non-hermetic machines, for exemplary purposes it will be described herein incorporated in a hermetic scroll refrigerant motor-compressor  10  of the “low side” type (i.e., where the motor and compressor are cooled by suction gas in the hermetical shell, as illustrated in the vertical section shown in  FIG. 1 ). Generally speaking, compressor  10  comprises a cylindrical hermetic shell  12  which includes at the upper end thereof an end cap  14 . End cap  14  is provided with a refrigerant discharge fitting  16  optionally having the usual discharge valve therein. Other elements affixed to the shell include a transversely extending partition  18  which is welded about its periphery at the same point that end cap  14  is welded to shell  12 , a two-piece main bearing housing  20  which is affixed to shell  12  at a plurality of points in any desirable manner, and a suction gas inlet fitting  22  disposed in communication with the suction pressure zone of compressor  10  inside shell  12 .  
         [0024]     A motor stator  24  is press fit into a frame  26  which is in turn press fit into shell  12 . A crankshaft  28  having an eccentric crank pin  30  at the upper end thereof is rotatably journaled in a bearing  32  in main bearing housing  20  and a second bearing  34  in frame  26 . Crankshaft  28  has at the lower end the usual relatively large diameter oil-pumping concentric bore  36  which communicates with a radially outwardly inclined smaller diameter bore  38  extending upwardly therefrom to the top of crankshaft  28 . The lower portion of the interior shell  12  is filled with lubricating oil in the usual manner and concentric bore  36  at the bottom of crankshaft  28  is the primary pump acting in conjunction with bore  38 , which acts as a secondary pump, to pump lubricating fluid to all the various portions of compressor  10  which require lubrication.  
         [0025]     Crankshaft  28  is rotatively driven by an electric motor including stator  24  having windings  40  passing therethrough, and a rotor  42  press fit on crankshaft  28  and having one or more counterweights  44 . A motor protector  46 , of the usual type, is provided in close proximity to motor windings  40  so that if the motor exceeds its normal temperature range motor protector  46  will de-energize the motor.  
         [0026]     The upper surface of main bearing housing  20  is provided with an annular flat thrust bearing surface  48  on which is disposed an orbiting scroll member  50  comprising an end plate  52  having the usual spiral vane or wrap  54  on the upper surface thereof, an annular flat thrust surface  56  on the lower surface, and projecting downwardly therefrom a cylindrical hub  58  having a journal bearing  60  therein and in which is rotatively disposed a drive bushing  62  having an inner bore in which crank pin  30  is drivingly disposed. Crank pin  30  has a flat on one surface (not shown) which drivingly engages a flat surface in a portion of the inner bore of drive bushing  62  to provide a radially compliant driving arrangement, such as shown in assignee&#39;s U.S. Pat. No. 4,877,382, the disclosure of which is herein incorporated by reference.  
         [0027]     Wrap  54  meshes with a non-orbiting spiral wrap  64  forming a part of a non-orbiting scroll member  66  which is mounted to main bearing housing  20  in any desired manner which will provide limited axial movement of non-orbiting scroll member  66 . The specific manner of such mounting is not relevant to the present inventions. For a more detailed description of the non-orbiting scroll suspension system, see assignee&#39;s U.S. Pat. No. 5,055,010, the disclosure of which is hereby incorporated herein by reference.  
         [0028]     Non-orbiting scroll member  66  has a centrally disposed discharge passageway communicating with an upwardly open recess  72  which is in fluid communication via an opening  74  in partition  18  with a discharge muffler chamber  76  defined by end cap  14  and partition  18 . A pressure relief valve is disposed between the discharge muffler chamber  76  and the interior of shell  12 . The pressure relief valve will open at a specified differential pressure between the discharge and suction pressures to vent pressurized gas from the discharge muffler chamber  76 . Non-orbiting scroll member  66  has in the upper surface thereof an annular recess  80  having parallel coaxial side walls in which is sealingly disposed for relative axial movement an annular floating seal  82  which serves to isolate the bottom of recess  80  from the presence of gas under suction and discharge pressure so that it can be placed in fluid communication with a source of intermediate fluid pressure by means of one or more passageways  84 . Non-orbiting scroll member  66  is thus axially biased against orbiting scroll member  50  by the forces created by discharge pressure acting on the central portion of non-orbiting scroll member  66  and those created by intermediate fluid pressure acting on the bottom of recess  80 . This axial pressure biasing, as well as various techniques for supporting non-orbiting scroll member  66  for limited axial movement, are disclosed in much greater detail in assignee&#39;s aforesaid U.S. Pat. No. 4,877,328.  
         [0029]     Relative rotation of the scroll members is prevented by the usual Oldham coupling comprising a ring  86  having a first pair of keys  88  (one of which is shown) slidably disposed in diametrically opposed slots  90  (one of which is shown) in non-orbiting scroll member  66  and a second pair of keys (not shown) slidably disposed in diametrically opposed slots in orbiting scroll member  50 .  
         [0030]     Referring now to  FIG. 2 . Although the details of construction of floating seal  82  are not part of the present invention, for exemplary purposes floating seal  82  is of a coaxial sandwiched construction and comprises an annular base plate  100  having a plurality of equally spaced upstanding integral projections  102 . Disposed on plate  100  is an annular gasket  106  having a plurality of equally spaced holes which receive projections  102 . On top of gasket  106  is disposed an upper seal plate  110  having a plurality of equally spaced holes which receive projections  102 . Seal plate  110  has disposed about the inner periphery thereof an upwardly projecting planar sealing lip  116 . The assembly is secured together by swaging the ends of each of the projections  102 , as indicated at  118 .  
         [0031]     The overall seal assembly therefore provides three distinct seals; namely, an inside diameter seal at  124 , an outside diameter seal at  128  and a top seal at  130 . Seal  124  is between the inner periphery of gasket  106  and the inside wall of recess  80 . Seal  124  isolates fluid under intermediate pressure in the bottom of recess  80  from fluid under discharge pressure in open recess  72 . Seal  128  is between the outer periphery of gasket  106  and the outer wall of recess  80 , and isolates fluid under intermediate pressure in the bottom of recess  80  from fluid at suction pressure within shell  12 . Seal  130  is between sealing lip  116  and an annular wear ring surrounding opening  74  in partition  18 , and isolates fluid at suction pressure from fluid at discharge pressure across the top of the seal assembly. The details of the construction of floating seal  82  is similar to that described in U.S. Pat. No. 5,156,539, the disclosure of which is hereby incorporated herein by reference.  
         [0032]     The compressor is preferably the “low side” type in which suction gas entering gas inlet fitting  22  is allowed, in part, to escape into shell  12  and assist in cooling the motor. So long as there is an adequate flow of returning suction gas the motor will remain within desired temperature limits. When this flow drops significantly, however, the loss of cooling will eventually cause motor protector  46  to trip and shut the machine down.  
         [0033]     As thus far described, scroll compressor  10  is typical of such scroll-type refrigeration compressors. In operation, suction gas directed to the lower chamber via suction gas inlet fitting  22  is drawn into the moving fluid pockets as orbiting scroll member  50  orbits with respect to non-orbiting scroll member  66 . As the moving fluid pockets move inwardly, this suction gas is compressed and subsequently discharged into discharge muffler chamber  76  via upwardly open recess  72  in non-orbiting scroll member  66  and discharge opening  74  in partition  18 . Compressed refrigerant is then supplied to the refrigeration system via discharge fitting  16 .  
         [0034]     In selecting a refrigeration compressor for a particular application, one would normally choose a compressor having sufficient capacity to provide adequate refrigerant flow for the most adverse operating conditions to be anticipated for that application and may select a slightly larger capacity to provide an extra margin of safety. However, such “worst case” adverse conditions are rarely encountered during actual operation and thus this excess capacity of the compressor results in operation of the compressor under lightly loaded conditions for a high percentage of its operating time. Such operation results in reducing overall operating efficiency of the system. Accordingly, in order to improve the overall operating efficiency under generally encountered operating conditions while still enabling the refrigeration compressor to accommodate the “worse case” operating conditions, compressor  10  is provided with a capacity modulation system. The capacity modulation system allows the compressor to operate at the capacity required to meet the requirements of the system.  
         [0035]     The capacity modulation system includes an annular valving ring  150  movably mounted on non-orbiting scroll member  66 , an actuating assembly  152  supported within shell  12  and a control system  154  for controlling operation of the actuating assembly.  
         [0036]     As best seen with reference to  FIGS. 2 and 5 , valving ring  150  comprises a generally circular shaped main body  156  having a pair of holes  158  and  160  extending therethrough. A pair of T-shaped slots  162  are formed into the inside diameter of main body  156 . T-shaped slots  162  include an axial portion  164  and a circumferential portion  166 . T-shaped slots  162  each accept a pin (not shown) extending from an outer surface  168  of non-orbiting scroll member  66 . Axial portion  164  allows for the assembly of valving ring  150  over the pins and onto non-orbiting scroll member  66 . Circumferential portion  166  restrict the rotational movement of valving ring  150  with respect to non-orbiting scroll member  66 . A flange  170  extend radially outward from main body  156  to support a pin  172  which is utilized to rotate valving ring  150  with respect to non-orbiting scroll member  66  as detailed below.  
         [0037]     Non-orbiting scroll member  66  also includes a pair of diametrically opposed radial passages  192  and  194  opening to the outer surface  168  of non-orbiting scroll member  66 . Passages  192  and  194  extend radially inwardly through the end plate of non-orbiting scroll member  66 . One axially extending passage  84  places the inner end of passage  192  in fluid communication with annular recess  80  while another axially extending passage  84  places the inner end of passage  194  in fluid communication with annular recess  80 .  
         [0038]     As best seen with reference to  FIG. 7 , actuating assembly  152  includes a piston and cylinder assembly  200  and a return spring assembly  202 . Piston and cylinder assembly  200  includes a housing  204  having a bore defining a cylinder  206  extending inwardly from one end thereof and within which a piston  208  is movably disposed. An outer end  210  of piston  208  projects axially outwardly from one end of housing  204  and includes an elongated or oval-shaped opening  212  therein adapted to receive pin  172  forming a part of valving ring  150 . Elongated or oval opening  212  is designed to accommodate the arcuate movement of pin  172  relative to the linear movement of piston end  210  during operation. A depending portion  214  of housing  204  has secured thereto a suitably sized mounting flange  216  which is adapted to enable housing  204  to be secured to a suitable flange member  218  by bolts  220 . Flange  218  is in turn suitably supported within outer shell  12  such as by main bearing housing  20 .  
         [0039]     A passage  222  is provided in depending portion  214  extending upwardly from the lower end thereof and opening into a laterally extending passage  224  which in turn opens into the inner end of cylinder  206 . A second laterally extending passage  226  provided in depending portion  214  opens outwardly through the sidewall thereof and communicates at its inner end with passage  222 . A second relatively small laterally extending passage  228  extends from fluid passage  222  in the opposite direction of fluid passage  224  and opens outwardly through an end wall  230  of housing  204 .  
         [0040]     A pin member  232  is provided upstanding from housing  204  to which is connected one end of a return spring  234  the other end of which is connected to an extended portion of pin  172 . Return spring  234  will be of such a length and strength as to urge valving ring  150  and piston  208  into the position shown in  FIG. 7  when cylinder  206  is fully vented via passage  228 .  
         [0041]     As best seen with reference to  FIGS. 1, 8  and  10 , control system  154  includes a valve body  236  having a radially outwardly extending flange  238  including a conical surface  240  on one side thereof. Valve body  236  is inserted into an opening  242  in outer shell  12  and positioned with conical surface  240  abutting the peripheral edge of opening  242  and then welded to shell  12  with a cylindrical portion  244  projecting outwardly therefrom. Cylindrical portion  244  of valve body  236  includes an enlarged diameter threaded bore  246  extending axially inwardly and opening into a recessed area  248 .  
         [0042]     Valve body  236  includes a housing  250  having a first passage  252  extending downwardly from a substantially flat upper surface  254  and intersecting a second laterally extending passage  256  which opens outwardly into the area of opening  242  in shell  12 . A third passage  258  also extends downwardly from surface  254  and intersects a fourth laterally extending passage  260  which also opens outwardly into recessed area  248  provided in the end portion of valve body  236 .  
         [0043]     A manifold  262  is sealingly secured to surface  254  by means of suitable fasteners and includes fittings for connection of one end of each of fluid lines  264  and  266  so as to place them in sealed fluid communication with respective passages  258  and  252 .  
         [0044]     A solenoid coil assembly  268  is designed to be sealingly secured to valve body  236  and includes an elongated tubular member  270  having a threaded fitting  272  sealingly secured to the open end thereof. Threaded fitting  272  is adapted to be threadedly received within bore  246  and sealed thereto by means of an O-ring  274 . A plunger  276  is movably disposed within tubular member  270  and is biased outwardly therefrom by a spring  278  which bears against a closed end of tubular member  270 . A valve member  280  is provided on the outer end of plunger  276  and cooperates with a valve seat  282  to selectively close off passage  256 . A solenoid coil  284  is positioned on tubular member  270  and secured thereto by means of a nut threaded on the outer end of tubular member  270 .  
         [0045]     In order to supply pressurized fluid to actuating assembly  152 , an axially extending passage  286  extends downwardly from open recess  72  and connects to a generally radially extending passage  288  in non-orbiting scroll member  66 . Passage  288  extends radially and opens outwardly through the circumferential sidewall of non-orbiting scroll member  66  as best seen with reference to  FIG. 11 . The other end of fluid line  264  is sealingly connected to third passage  258  whereby a supply of compressed fluid at discharge pressure may be supplied from open recess  72  to valve body  236 . A circumferentially elongated slot  290  is provided in valving ring  150  suitably positioned so as to enable fluid line  264  to pass therethrough while accommodating the rotational movement of valving ring  150  with respect to non-orbiting scroll member  66 .  
         [0046]     In order to supply pressurized fluid from valve body  236  to actuating piston and cylinder assembly  200 , fluid line  266  extends from valve body  236  and is connected to passage  226  provided in depending portion  214  of housing  204  ( FIG. 7 ).  
         [0047]     Valving ring  150  may be easily assembled to non-orbiting scroll member  66  by merely aligning axial portions  164  of T-shaped slots  162  with the respective pins extending from outer surface  168  of non-orbiting scroll member  66 . Thereafter valving ring  150  is rotated into the desired position with circumferential portions  166  of T-shaped slots  162  cooperating with the respective pins extending from outer surface  168  to control the rotation of valving ring  150  with respect to non-orbiting scroll member  66 . Thereafter, cylinder assembly  200  of actuating assembly  152  may be positioned on mounting flange  218  with piston end  210  receiving pin  172 . One end of spring  234  may then be connected to pin member  232 . Thereafter, the other end of spring  234  may be connected to pin  172  thus completing the assembly process.  
         [0048]     While non-orbiting scroll member  66  is typically secured to main bearing housing  20  by suitable bolts  292  prior to assembly of valving ring  150 , it may in some cases be preferable to assemble this continuous capacity modulation component to non-orbiting scroll member  66  prior to assembly of non-orbiting scroll member  66  to main bearing housing  20 . This may be easily accomplished by merely providing a plurality of suitably positioned arcuate cutouts  294  along the periphery of valving ring  150  as shown in  FIGS. 4 and 5 . These cutouts will afford access to securing bolts  292  with valving ring  150  assembled to non-orbiting scroll member  66 .  
         [0049]     In operation, when system operating conditions as sensed by one or more sensors  296  indicate that full capacity of compressor  10  is required, control module  298  will operate in response to a signal from sensors  296  to energize solenoid coil  284  of solenoid coil assembly  268  thereby causing plunger  276  to be moved out of engagement with valve seat  282  thereby placing passages  256  and  260  in fluid communication. Pressurized fluid at substantially discharge pressure will then be allowed to flow from open recess  72  to cylinder  206  via passages  286 ,  288  fluid line  264 , passages  258 ,  260 ,  256 ,  252  fluid line  266  and passages  226 ,  222  and  224 . This fluid pressure will then cause piston  208  to move outwardly with respect to cylinder  206  thereby rotating valving ring  150  so as to move main body  156  into sealing overlying relationship to passages  192  and  194  as illustrated in  FIG. 11 . This will then prevent intermediate pressurized gas disposed within recess  80  from being exhausted or vented through passages  192  and  194 . Compressor  10  will then operate at its full capacity.  
         [0050]     When the load conditions change to the point that the full capacity of compressor  10  is not required, sensors  296  will provide a signal indicate thereof to controller  298  which in turn will deenergize solenoid coil  284  of solenoid coil assembly  268 . Plunger  276  will then move outwardly from tubular member  270  under the biasing action of spring  278  thereby moving valve member  280  into sealing engagement with seat  282  thus closing off passage  256  and the flow of pressurized fluid therethrough. It is noted that recessed area  248  will be in continuous fluid communication with open recess  72  and hence continuously subject to discharge pressure. This discharge pressure will aid in biasing valve member  280  into fluid tight sealing engagement with valve seat  282  as well as retaining same in such relationship.  
         [0051]     The pressurized gas contained in cylinder  206  will bleed back into the suction zone of compressor  10  via vent passage  228  thereby enabling spring  234  to rotate valving ring  150  back to a position in which passages  192  and  194  are aligned with holes  158  and  160  of valving ring  150  as illustrated in  FIG. 12 . Spring  234  will also move piston  208  inwardly with respect to cylinder  206 . In this position, the intermediate pressure within annular recess  80  will be exhausted or vented through passages  192  and  194  and holes  158  and  160 . The venting of the intermediate pressurized fluid removes the biasing force urging non-orbiting scroll member  66  into sealing engagement with orbiting scroll member  50  to create a leak between the discharge pressure zone and the suction pressure zone. This leak causes the capacity of compressor  10  to move to zero capacity. A spring urges floating seal  82  upwards and maintains the sealing relationship at top seal  130 . Thus, by controlling solenoid coil assembly  268  in a pulsed width modulation mode, the capacity of compressor  10  can be set anywhere between zero capacity and full capacity.  
         [0052]     It should be noted that the speed with which valving ring  150  may be moved between the modulated position and the unmodulated position will be directly related to the relative size of vent passage  228  and the supply lines. In other words, because passage  228  is continuously open to the suction pressure zone of compressor  10 , when solenoid coil  284  of solenoid coil assembly  268  is energized a portion of the pressurized fluid flowing from open recess  72  will be continuously vented to suction pressure. The volume of this fluid will be controlled by the relative sizing of passage  228 . However, as passage  228  is reduced in size, the time required to vent cylinder  206  will increase thus increasing the time required to switch from reduced capacity to full capacity.  
         [0053]     While actuating assembly  152  has been illustrated including piston and cylinder assembly  200  and return spring assembly  202 , it is within the scope of the present invention to utilize a solenoid valve assembly attached directly to pin  172  as actuating assembly  152  and controlling the solenoid valve assembly using PWM (pulse width modulation) or by using direct control to effect the rotation of valving ring  150  if desired.  
         [0054]     Efficient operation of the capacity modulation system of the present invention requires the proper sealing between main body  156  of valving ring  150  and passages  192  and  194  extending into non-orbiting scroll member  66 .  
         [0055]     As best illustrated in  FIGS. 11 and 12 , non-orbiting scroll member  66  defines a counterbore  300  located at the outer end of passages  192  and  194 . Disposed within each counterbore  300  is an annular lip seal  302 . When valving ring  150  is rotated such that main body  156  closes passages  192  and  194  as illustrated in  FIG. 11 , lip seal  302  has a cylindrical portion  304  having a first lip seal that seals against counterbore  300  and annular portion  306  that has a second lip seal that seals against main body  156  of valving ring  150 . Lip seal  302  is a self-actuating seal. Intermediate pressurized fluid within passages  192  and  194  will urge cylindrical portion  304  of lip seal  302  into sealing engagement with counterbore  300 . Also, the intermediate pressurized fluid within passages  192  and  194  will urge annular portion  306  into sealing engagement with main body  156  of valving ring  150 .  
         [0056]     As illustrated in  FIG. 12 , when valving ring  150  is rotated to a position where holes  158  and  160  are aligned with passages  192  and  194 , respectively, intermediate pressurized fluid in passages  192  and  194  and annular recess  80  will be vented to the suction pressure zone of compressor  10 . The diameter of holes  158  and  160  are sized to be the same as the internal diameter formed by annular portion  306  of lip seal  302 . Thus, annular portion  306  never completely loses contact with main body  156  of valving ring  150 . Main body  156  of valving ring  150  retains lip seal  302  within counterbore  300  due to this continued contact.  
         [0057]     Referring now to  FIGS. 13 and 14 , a capacity modulation system in accordance with the present invention is illustrated. The capacity modulation system described above has the capability to modulate the capacity of compressor  10  between zero capacity and full capacity. The capacity control system illustrated in  FIGS. 13 and 14  has the ability to modulate the capacity of compressor  10  between full capacity and a selected reduced capacity.  
         [0058]      FIGS. 13 and 14  illustrate non-orbiting scroll member  66 ′ which is the same as non-orbiting scroll member  66  except that the one or more passageways  84  which extend from a source of intermediate fluid pressure to recess  80  are no longer in communication with radial passages  192  and  194 . Thus, recess  80  is continuously supplied with intermediate pressurized fluid from passageway  84 .  
         [0059]     Non-orbiting scroll member  66 ′ defines a first axially extending passage  196  and a second axially extending passageway  198 . Axially extending passage  196  extends between an intermediate pressurized moving pocket defined by scroll wraps  54  and  64  and radial passage  192 . Axial extending passage  198  extends between an intermediate pressurized moving pocket defined by scroll wraps  54  and  64  and radial passage  194 . Preferably passages  196  and  198  will be oval in shape so as to maximize the size of the opening thereof without having a width greater than the width of wrap  54  of orbiting scroll member  50 .  
         [0060]     In operation, when system operating conditions as sensed by one or more sensors  296  indicate that full capacity of compressor  10  is required, control module  298  will operate in response to a signal from sensors  296  to energize solenoid coil  284  of solenoid coil assembly  268  thereby causing plunger  276  to be moved out of engagement with valve seat  282  thereby placing passages  256  and  260  in fluid communication. Pressurized fluid at substantially discharge pressure will then be allowed to flow from open recess  72  to cylinder  206  via passages  286 ,  288  fluid line  264 , passages  258 ,  260 ,  256 ,  252  fluid line  266  and passages  226 ,  222  and  224 . This fluid pressure will then cause piston  208  to move outwardly with respect to cylinder  206  thereby rotating valving ring  150  so as to move main body  156  into sealing overlying relationship to passages  192  and  194  as illustrated in  FIG. 11 . This will then prevent intermediate pressurized gas disposed within the moving pockets defined by scroll wraps  54  and  64  from being exhausted or vented through passages  192 ,  194 ,  196  and  198 . Compressor  10  will then operate at its full capacity.  
         [0061]     When the load conditions change to the point that the full capacity of compressor  10  is not required, sensors  296  will provide a signal indicate thereof to controller  298  which in turn will deenergize solenoid coil  284  of solenoid coil assembly  268 . Plunger  276  will then move outwardly from tubular member  270  under the biasing action of spring  278  thereby moving valve member  280  into sealing engagement with seat  282  thus closing off passage  256  and the flow of pressurized fluid therethrough. It is noted that recessed area  248  will be in continuous fluid communication with open recess  72  and hence continuously subject to discharge pressure. This discharge pressure will aid in biasing valve member  280  into fluid tight sealing engagement with valve seat  282  as well as retaining same in such relationship.  
         [0062]     The pressurized gas contained in cylinder  206  will bleed back into the suction zone of compressor  10  via vent passage  228  thereby enabling spring  234  to rotate valving ring  150  back to a position in which passages  192  and  194  are aligned with holes  158  and  160  of valving ring  150  as illustrated in  FIG. 12 . Spring  234  will also move piston  208  inwardly with respect to cylinder  206 . In this position, the moving pockets defined by scroll wraps  54  and  64  will be exhausted or vented through passages  192 ,  194 ,  196  and  198  and holes  158  and  160 . The venting of the moving pockets reduces the capacity of compressor  10  by delaying the point at which compression begins by delaying the point at which the sealed chambers are formed. This has the effect of reducing the compression ratio of the compressor by a predetermined amount. The predetermined amount of the reduction of the compression ratio of the compressor can be controlled by the location of axial passages  196  and  198 .  
         [0063]     Passages  196  and  198  may be located so that they are in communication with the respective suction pockets at any point up to 360° inwardly from the point at which the trailing flank surfaces move into sealing engagement. If they are located further inwardly than this, compression of the fluid in the pockets will have begun and hence venting thereof will result in lost work and a reduction in efficiency.  
         [0064]     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.