Patent Publication Number: US-6709244-B2

Title: Diagnostic system for a compressor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 09/843,492 filed on Apr. 25, 2001, now U.S. Pat. No. 6,457,948. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to capacity modulation of compressors. More particularly, the present invention relates to a diagnostic system for a capacity modulated compressor which is capable of determining if the capacity modulation system is functioning properly. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Capacity modulation is often a desirable feature to incorporate in 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 ranging from controlling of the suction inlet to bypassing discharge gas back to the suction inlet. With scroll-type compressors, capacity modulation has often been accomplished via a delayed suction approach which comprises providing ports at various positions which, when opened, allow the compression chambers formed between the intermeshing scroll wraps to communicate with the suction gas supply thereby delaying the point at which compression of the suction gas begins. This 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 able to provide a predetermined amount of compressor unloading, the amount of unloading being dependant upon the positioning of the unloading ports along the wraps. While it is possible to provide multiple step unloading by incorporating a plurality of such ports at different locations, this approach becomes costly and requires additional space to accommodate the separate controls for opening and closing each set of ports. 
     Other capacity modulation systems overcome these deficiencies in that they enable virtually a continuous range of unloading from 100 percent or full capacity down to virtually zero capacity utilizing only a single set of controls. Further, these systems enable the operating efficiency of the compressor and/or refrigeration system to be maximized for any degree of compressor unloading desired. 
     In these capacity modulation systems, compressor unloading is 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. More specifically, an arrangement is provided wherein one scroll member is moved axially or radially toward and away from the other scroll member in a pulsed fashion to cyclically provide a leakage path across the tips or flanks of the wraps from higher pressure compression pockets defined by the intermeshing scroll wraps to lower pressure pockets and ultimately back to suction. By controlling the relative time between sealing and unsealing of the scroll wrap tips or flanks, virtually any degree 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. For example, if it is desired to operate the compressor at 50 percent capacity, this can be accomplished by operating the compressor alternately in a loaded condition for five seconds and unloaded for five seconds or loaded for seven seconds and unloaded for seven seconds, one or the other of which may provide greater efficiency for the specific operating conditions being encountered. 
     The various capacity modulation systems all have the capability of reducing the capacity of the compressor and all work well within the design limits of the particular system. While the capacity modulation systems function in an acceptable manner, there is a need to be able to determine if and when these systems have stopped functioning properly. 
     The present invention provides a simple low-cost system which is capable of detecting the failure of a capacity modulation system. In a capacity modulation system which opens and closes a fluid passage between two areas of the compressor utilizing a valve, the proper functioning of the system can be accomplished by monitoring the fluid temperature downstream of the valve. If the valve fails, either open or closed, the temperature in the downstream passage will be steady as opposed to fluctuating with the opening and closing of the valve during reduced capacity modulation. Knowing this downstream temperature also allows for the detecting of whether the valve failed in an open or closed position since this temperature would have two different valves for these two failure modes. Another approach is to sense the temperature differential between upstream and downstream of the valve. This temperature value coupled with the temperature error in the room provide effective conformation of these failing modes. 
     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: 
     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; 
     FIG. 2 is a fragmentary section view of a scroll-type refrigeration compressor showing another embodiment of the present invention; 
     FIG. 3 is a view similar to that of FIG. 2, but showing the compressor in an unloaded condition; 
     FIG. 4 is a fragmentary section view of a scroll-type refrigeration compressor showing a further embodiment of the present invention; 
     FIG. 5 is an enlarged view of the valve arrangement incorporated in the embodiment shown in FIG. 4; 
     FIG. 6 is also a fragmentary section view of a scroll-type refrigeration compressor showing another embodiment of the present invention; 
     FIGS. 7 through 15 are all fragmentary section views of refrigeration compressors in accordance with the present invention in which the orbiting scroll member is axially reciprocated to accomplish compressor unloading; 
     FIGS. 16 through 22 are all fragmentary section views of refrigeration compressors in accordance with the present invention in which the non-orbiting scroll member is axially reciprocated to accomplish compressor unloading; 
     FIGS. 23 through 28 are all fragmentary section views of refrigeration compressors in accordance with the present invention in which the scroll members are co-rotating; 
     FIGS. 29 through 30 are both fragmentary section views of additional embodiments of refrigeration compressors all in accordance with the present invention in which the non-orbiting scroll member is reciprocated; 
     FIG. 31 is a section view of yet another embodiment of a scroll-type compressor in accordance with the present invention adapted to be driven by an external power source. 
     FIGS. 32 through 34 are fragmentary section views of additional embodiments of scroll-type compressors in accordance with the present invention; 
     FIG. 34A is an enlarged fragmentary view of the valving arrangement shown in FIG.  34  and enclosed within circle  34 A; 
     FIG. 35 is a fragmentary section view of a further embodiment of a scroll-type compressor in accordance with the present invention; 
     FIG. 36 is also a fragmentary section view of yet a further embodiment of the present invention showing an arrangement for radially unloading of the compressor in accordance with the present invention; 
     FIG. 37 is a section view of the crank pin and drive bushing employed in the embodiment of FIG. 36, the section being taken along lines  37 — 37  thereof; 
     FIG. 38 is a section view of the embodiment shown in FIG. 36, the section being taken along lines  38 — 38  thereof; 
     FIG. 39 is a view similar to that of FIG. 36 but showing the compressor in an unloaded condition; 
     FIG. 40 is a fragmentary section view showing a modified version of the embodiment of FIG. 36, all in accordance with the present invention; 
     FIG. 41 is a fragmentary section view showing a portion of a scroll-type compressor incorporating another embodiment of the radial unloading arrangement of FIG. 36, all in accordance with the present invention; 
     FIG. 42 is a section view similar to that of FIG. 38 but showing the embodiment of FIG. 41; 
     FIG. 43 is a fragmentary section view showing yet another embodiment of the present invention; 
     FIG. 44 is a view of a portion of the embodiment shown in FIG. 43 in an unloaded condition; 
     FIG. 45 is a schematic showing a means for reducing motor power consumption during periods when the compressor is operating in an unloaded condition in accordance with the present invention; and 
     FIG. 46 is a section view of a compressor incorporating both cyclical scroll wrap separation and delayed suction unloading, all in accordance with the present invention. 
    
    
     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 hermetic scroll compressor in accordance with the present invention indicated generally at  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 by reference, and includes an outer shell  12  within which is disposed a driving motor including stator  14  and rotor  16 , a crankshaft  18  to which rotor  16  is secured, upper and lower bearing housings  20 ,  22  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 crank pin  28  and drive bushing  30 . A second non-orbiting scroll member  32  is positioned in meshing engagement with scroll member  26  and 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 between 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 define a discharge chamber  42  at the upper end thereof. 
     In operation, as orbiting scroll member  26  orbits with respect to scroll member  32 , suction gas is drawn into shell  12  via a suction inlet  44  and thence into compressor  24  through an inlet  46  provided in non-orbiting scroll member  32 . The intermeshing wraps provided on scroll members  26  and  32  define moving fluid pockets which progressively decrease in size and move radially inwardly as a result of the orbiting motion of scroll member  26  thus compressing the suction gas entering via inlet  46 . The compressed gas is then discharged into discharge chamber  42  via a discharge port  48  provided in scroll member  32  and a passage  50 . A suitable pressure responsive discharge valve  51  is preferably provided seated within discharge port  48 . 
     Scroll member  32  is also provided with an annular cylindrical recess  52  formed in the upper surface thereof. One end of a generally irregularly shaped cylindrical member  54  within which passage  50  is provided projects into cylinder  52  and divides same into upper and lower chambers  56  and  58 . The other end of cylindrical member  54  is sealingly secured to partition plate  40 . An annular ring  60  is secured to the upper end of scroll member  32  and includes an axially extending flange  62  slidingly engageable with cylinder member  54  to thereby seal off the open upper end of chamber  56 . 
     Cylindrical member  54  includes a passage  64  having one end which opens into upper chamber  56 . A fluid line  66  is connected to the other end of passage  64  and extends outwardly through shell  12  to a solenoid operated valve  68 . A second fluid line  70  extends from valve  68  to a suction line  72  connected to suction inlet  44  and a third fluid line  74  extends from valve  68  to a discharge line  76  extending outwardly from discharge chamber  42 . 
     In order to bias scroll member  32  into sealing engagement with scroll member  26  for normal fully loaded operation, a bleed hole  78  is provided in scroll member  32  communicating between chamber  58  and a compression pocket at an intermediate pressure between suction and discharge pressure. Thus, chamber  58  will be at an intermediate pressure which together with the discharge pressure acting on the upper surface of scroll member  32  in the area of discharge port  48  will exert a biasing force on scroll member urging it axially into sealing engagement with orbiting scroll member  26 . At the same time, solenoid valve  68  will be in a position so as to place upper chamber  56  in fluid communication with suction line  72  via fluid lines  66  and  70 . 
     In order to unload compressor  24 , solenoid valve  68  will be actuated in response to a signal from control module  80  to interrupt fluid communication between lines  66  and  70  and to place fluid line  66  in communication with discharge line  76  thus increasing the pressure within chamber  56  to that of the discharge gas. The biasing force resulting from this discharge pressure will overcome the sealing biasing force thereby causing scroll member  32  to move axially upwardly away from orbiting scroll member  26 . This axial movement will result in the creation of a leakage path between the respective wrap tips and end plates of scroll members  26  and  32  thereby substantially eliminating continued compression of the suction gas. When unloading occurs, discharge valve  51  will move to a closed position thereby preventing the back flow of high pressure fluid from discharge chamber  42  or the downstream system. When compression of the suction gas is to be resumed, solenoid valve  68  will be actuated to a position in which fluid communication between upper chamber  56  and discharge line  76  via lines  66  and  74  is interrupted and upper chamber  56  is placed in communication with suction line  72  via fluid lines  66  and  70  thereby relieving the axially directed separating force. This then allows the cooperative action of the intermediate pressure in chamber  58  and discharge pressure acting in passage  50  to again move scroll member  32  into sealing engagement with scroll member  26 . 
     Preferably, control module  80  will have one or more appropriate sensors  82  connected thereto to provide the required information for control module  80  to determine the degree of unloading required for the particular conditions existing at that time. Based upon this information, control module  80  will send appropriately timed sequential signals to solenoid valve  68  to cause it to alternately place fluid line  66  in communication with discharge line  76  and suction line  72 . For example, if conditions indicate that it is desirable to operate compressor  24  at 50 percent of full capacity, control module  80  may actuate solenoid valve to a position to place fluid line  66  in communication with suction line  72  for a period of say 10 seconds whereupon it is switched to place fluid line  66  in fluid communication with discharge line  76  for a like period of 10 seconds. Continued switching of solenoid valve  68  in this manner will result in compression occurring during only 50 percent of the operating time thus reducing the output of compressor  24  to 50 percent of its full load capacity. As the sensed conditions change, control module will vary the relative time periods at which compressor  24  is operated in a loaded and unloaded condition such that the capacity of compressor  24  may be varied between fully loaded or 100 percent capacity and completely unloaded or 0 percent capacity in response to varying system demands. 
     Control module  80  will also be in communication with a first temperature sensor  81  located to monitor the temperature of fluid within line  66  and a second temperature sensor  83  located to monitor the temperature of fluid within line  74 . Temperature sensor  81  can be used to monitor the status of solenoid valve  68 . When control module  80  continuously loads and unloads compressor  24 , fluid line  66  will continuously be in cyclical communication with suction line  72  and discharge line  76 . The temperature of fluid within discharge line  76  is greater than the temperature of fluid within suction line  72 . Thus, during the operation of solenoid valve  68 , the temperature sensed by temperature sensor  81  will continuously fluctuate. If, during the time that solenoid valve  68  is operating, the temperature monitored by temperature sensor  81  remains constant, a failure of solenoid valve  68  is indicated. In addition, the temperature of the fluid detected by sensor  81  will determine if solenoid valve  68  is open or closed because it is known that the temperature of fluid within discharge line  76  is greater than the temperature of fluid within suction line  72 . 
     As a confirmation to the failure mode detected by sensor  81 , sensor  83  can be included in fluid line  74 . The incorporation of sensor  83  within fluid line  74  gives a direct indication of whether or not sensor  81  is detecting discharge temperatures within discharge line  76  or suction temperatures within suction line  72 . Also, when this temperature valve is coupled with the temperature error in the room, a good confirmation of the failure mode is provided. Optionally, temperature sensor  83  could monitor fluid temperature within fluid line  70  as shown in phantom in FIG.  1 . 
     An alternative to temperature sensor  81  alone or in combination with sensor  83  would be to incorporate a pressure sensor  85  within fluid line  66  that is in communication with control module  80 . The pressure of fluid within discharge line  76  is greater than the pressure of fluid within suction line  72 . Thus, during operation of solenoid valve  68 , the pressure of fluid within line  66  will continuously fluctuate. If during the time that solenoid valve  68  is operating, the pressure monitored by pressure sensor  85  remains constant, a failure of solenoid valve  68  is indicated. In addition, the pressure of the fluid within fluid line  66  detected by sensor  85  will determine if solenoid valve  68  is open or closed because it is known that the pressure of fluid within discharge line  76  is greater than the pressure of fluid within suction line  72 . Typically, the costs associated with pressure sensor  85  are greater than those associated with temperature sensor  81 . 
     FIGS. 2 and 3 show an axial unloading scroll compressor  84  similar to that of FIG. 1 with the primary exception being the arrangement for placing upper chamber  56  In fluid communication, with suction and discharge lines. Accordingly, like portions have been indicated by the same reference numbers. As shown therein, passage  64  has been replaced by a passage  86  provided in annular member  60  which opens at one end into upper chamber  56  and at the other end through a radially outwardly facing sidewall. A flexible fluid line  88  extends from the outer end of passage  86  to a fitting  90  extending through shell  12  with a second line  92  connecting fitting  90  to solenoid valve  68 . As with FIG. 1, solenoid valve  68  has fluid lines  70  and  74  connected to suction line  72  and discharge line  76  and is controlled by control module  80  in response to conditions sensed by sensor  82  to effect movement of non-orbiting scroll member  32  between the positions shown in FIGS. 2 and 3 in the same manner as described above with respect to the embodiment of FIG.  1 . While this embodiment eliminates the need for an extra fitting extending outwardly from the high pressure discharge chamber  42 , it requires that fluid conduit  88  be flexible so as to accommodate axial movement of scroll member  32  and associated annular member  60 . It should also be noted that in this embodiment cylindrical member  54  is sealingly secured to partition plate  40  by means of nut  55  which threadedly engages the upper end thereof. Also in this embodiment, discharge valve  51  has been replaced by a discharge check valve  93  secured to the outer shell. It should be noted that the provision of a check valve some place along the discharge flowpath is highly desirable in order to prevent back flow of compressed gas from the system when the compressor is in an unloaded condition. 
     Temperature sensors  81  and  83  are the same as that described above for FIG. 1 except that temperature sensor  81  monitors the temperature of fluid in fluid line  92  instead of fluid line  66 . Pressure sensor  85  is the same as that described above for FIG. 1 except that pressure sensor  85  monitors the pressure within fluid line  92  instead of fluid line  66 . Optionally, temperature sensor  83  could be located to monitor the fluid temperature within fluid line  70 , if desired. 
     FIGS. 4 and 5 show another embodiment  94  of the present invention in which axial unloading separating pressure fluid is provided directly from the discharge gas exiting the compressor. In this embodiment, a tubular member  96  is suitably secured to partition member  40  and includes a radially outwardly extending flange  98  which is positioned in and separates cylindrical recess into upper and lower chambers  56  and  58 . Tubular member  96  also defines passage  50  for directing compressed discharge gas from port  48  to discharge chamber  42 . An axial extending bore  100  is provided in tubular member which opens outwardly through the upper end thereof and is adapted to receive a fluid conduit  102 . Fluid conduit  102  extends outwardly through the top of shell  12  and is connected to solenoid valve  68 . Solenoid valve  68  also has fluid conduits  70  and  74  connected to respective suction and discharge lines  72 ,  76  and is controlled by module  80  in response to signals from appropriate sensors  82  in the same manner as described above. 
     A valve member  104  is axially movably disposed within bore  100 . Valve member  104  includes a reduced diameter portion  106  operative to place radially extending passages  108  and  110  provided in member  96  in fluid communication when in a first position so as to vent upper chamber  56  to suction and to place radial fluid passage  110  in fluid communication with radial fluid passage  112  when in a second position so as to admit discharge gas from discharge flowpath  50  to upper chamber  56 . A vent passage  113  is also provided which communicates between the bottom of bore  100  and passage  50  to vent gas from the area below valve  104  during operation thereof. A spring  114  is also provided which serves to aid in biasing valve  104  into its second position whereas pressurized discharge fluid entering bore  100  via passage  112  and passage  113  serves to bias valve member  104  into its first position. 
     As shown, valve member  104  and solenoid valve  68  are both in a position for fully loaded operation wherein solenoid valve  68  is in position to place fluid conduit  102  in communication with the suction line  72  and valve member  104  is in a position to vent upper chamber  56  to the interior of shell  12  which is at suction pressure. When it is desired to unload the compressor, solenoid valve  68  will be actuated to a position to place fluid line  102  in communication with fluid line  74  thereby enabling pressurized discharge fluid to act on the upper end of valve member  104 . This pressurized fluid together with spring  114  will cause valve member  104  to move downwardly thereby closing off communication of radial passage  110  with radial passage  108  and opening communication between radial passage  110  and radial passage  112 . Discharge pressure fluid will then flow into upper chamber  56  thus overcoming the intermediate pressure biasing force resulting from the communication of chamber  58  with a compression chamber at intermediate pressure via passage  78  and causing scroll member  32  to move axially upwardly away from orbiting scroll member  26 . It should be noted that the relatively short flowpath for supplying discharge pressure fluid to upper chamber  56  ensures rapid unloading of the compressor. 
     FIG. 6 shows a modified embodiment similar to that of FIGS. 4 and 5 except that solenoid valve  68  is positioned within shell  12 . This embodiment eliminates the need for an additional fluid conduit through the high pressure portion of the shell, requiring only an electrical feed for actuating solenoid valve  68  and monitoring sensors  81 ,  83  or  85 . In all other respects, construction and operation of this embodiment is substantially the same as that described above with respect to the embodiment shown in FIGS. 4 and 5 and accordingly corresponding portions are indicated by the same reference numbers. 
     Temperature sensors  81  and  83  are the same as that described above for FIG. 1 except that temperature sensor  81  monitors the fluid temperature within fluid conduit  102  instead of fluid line  66 . Pressure sensor  85  is the same as that described above for FIG. 1 except that pressure sensor  85  monitors the pressure within fluid conduit  102  instead of fluid line  66 . Optionally, temperature sensor  83  could be located to monitor the fluid temperature within fluid line  70 , if desired. 
     While the previously described embodiments have been directed to unloading arrangements wherein the non-orbiting scroll has been moved axially away from the orbiting scroll, it is also possible to apply these same principles to the orbiting scroll. FIGS. 7 through 15 described below illustrate such a series of embodiments. 
     Referring now to FIG. 7, a scroll compressor  140  is shown which is similar to the scroll compressors described above except that non-orbiting scroll member  142  is non-movably secured to bearing housing  144  and orbiting scroll member  146  is axially movable. It is also noted that compressor  140  is a high side machine, that is, the suction inlet  149  is directly connected to the non-orbiting scroll member  142  and the interior of the shell  12  is at discharge pressure. In this embodiment, orbiting scroll member  146  is axially movable and is biased into engagement with non-orbiting scroll  142  by means of a pressure chamber  148  defined between orbiting scroll member  146  and main bearing housing  144 . An annular recess  150  is provided in main bearing housing  144  in which is disposed a suitable annular resilient seal member  152  which sealingly engages the lower surface of orbiting scroll member  146  so as to prevent fluid communication between chamber  148  and the interior of shell  12  which is at discharge pressure. A second annular seal  154  is provided on main bearing housing  144  surrounding shaft  18  to prevent fluid leakage therealong. A small passage  156  is provided through the end plate of orbiting scroll member  146  to place chamber  148  in fluid communication with a compression chamber at a pressure intermediate suction and discharge pressure. Additionally, a passage  158  in main bearing housing extends outwardly from chamber  148  and has one end of fluid line  160  connected thereto. The other end of fluid line  160  extends outwardly through shell  12  and is connected to solenoid valve  162 . A second fluid line  164  extends between solenoid valve  162  and suction line  148 . 
     In operation, chamber  148  will be supplied with fluid at intermediate pressure to thereby bias orbiting scroll  146  into sealing engagement with non-orbiting scroll  142 . At this time, solenoid valve  162  will be in a position to prevent fluid communication between lines  160  and  164 . In order to unload compressor  140 , solenoid valve  162  is actuated to a position to place line  160  in fluid communication with fluid line  164  thereby venting the intermediate pressure in chamber  148  to suction. The pressure within the compression pockets will then cause orbiting scroll member  146  to move axially downwardly as shown compressing resilient seals  152  and thereby forming a leakage path across the respective wrap tips and associated end plates of the orbiting and non-orbiting scroll members  146 ,  142 . While passage  156  may continue to provide fluid at a pressure somewhat higher than suction pressure to chamber  148 , the relative sizing of passage  158 , fluid lines  160  and  164  and passage  158  will be such that there will be insufficient pressure in chamber  148  to bias orbiting scroll member  146  into sealing engagement with non-orbiting scroll member  142  so long as solenoid valve  162  is in a position to maintain fluid communication between suction line  149  and chamber  148 . Solenoid valve  162  will be cycled between open and closed positions so as to cyclically load and unload compressor  140  in substantially the same manner as described above. 
     In this embodiment and the embodiments in FIGS. 8-10, temperature sensor  81  monitors the temperature of fluid in fluid line  160  and temperature sensor  83  monitors the temperature of fluid in fluid line  164 . The temperature of gas within fluid line  160  will be greater than the temperature of gas within fluid line  164  because of its compression. Also, pressure sensor  85  monitors the pressure within fluid line  160  which is greater than the pressure of fluid within fluid line  164 . The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . 
     FIG. 8 shows a modified version  140   a  of the embodiment of FIG. 7 wherein a plurality of springs  166  are provided. Springs  166  are seated in recesses  168  provided in bearing housing  144   a  and bear against the end plate of orbiting scroll  146  so as to assist in urging orbiting scroll into sealing engagement with non-orbiting scroll  142 . Springs  166  serve primarily to provide an initial biasing force for orbiting scroll member  146  on initial start up of compressor  140   a  but will also assist in providing more rapid loading of compressor  140   a  upon closing of solenoid valve  162  during operation. 
     FIG. 9 shows a further modification  140   b  of the embodiments of FIGS. 7 and 8. In this embodiment shell  12  is provided with a partition member  170  to separate the interior thereof into a high pressure discharge chamber  172  to which discharge port  174  is connected via conduit  176  and a low suction pressure chamber therebelow within which the compressor is disposed. Additionally, in this embodiment shaft seal  154  has been replaced with a second annular seal  178  positioned radially inwardly and concentric with seal  150   b . Thus the area in which crank pin  28  and drive bushing  30  are located will be at suction pressure to thereby avoid any problems associated with providing lubrication thereto from the oil sump which is also at suction pressure. It should be noted that the oil sump in the embodiments of FIGS. 7 and 8 was at discharge pressure and hence do not present any problems with respect to supplying of lubricant to these drive components. 
     The embodiment  140   c  of FIG. 10 is substantially identical to that of FIG. 9 with the exception that in addition to the biasing force resulting from intermediate fluid pressure in chamber  148   b , a plurality of springs  180  are also provided being positioned between orbiting scroll member  156  and main bearing housing  144  and functioning primarily to assist during start up but also to assist in reloading of compressor  140   c  similar to that described above with reference to FIG.  8 . 
     In the embodiment of FIG. 11, non-orbiting scroll member  182  is provided with an annular recess  184  within which an annular ring-shaped piston member  186  is movably disposed. The lower surface of annular piston member  186  bears against a radially outwardly extending portion  187  of end plate  189  of orbiting scroll member  146  and radially inner and outer annular seals  188 ,  190  are provided thereon which sealingly engage radially inner and outer walls of recess  184 . A radially extending passage  192  provided in non-orbiting scroll member  182  communicates with the upper portion of recess  184  and has fluid conduit  194  connected to the outer end thereof. Fluid conduit  194  extends outwardly through shell  12  to solenoid valve  196 . A second fluid conduit  198  connects solenoid valve  196  to suction line  200  whereas a third fluid conduit  202  connects solenoid valve  196  to discharge line  204 . 
     Under normal fully loaded operating conditions, orbiting scroll member  146  will be axially biased into sealing engagement with non-orbiting scroll member  182  by intermediate fluid pressure in chamber  206  admitted thereto via bleed passage  208 . At this time, the area of recess  184  disposed above annular piston member  186  will be vented to suction via solenoid valve  196  and conduits  194  and  198 . When conditions indicate partial unloading of the compressor is desirable, solenoid valve  196  will be actuated to place fluid conduit  194  in fluid communication with discharge line  204  via conduit  202 . The area above annular piston  186  will then be pressurized by fluid at discharge pressure thereby causing orbiting scroll member  146  to be biased axially downwardly as shown. As noted above, cyclical switching of solenoid valve  196  will result in repetitive loading and unloading of the compressor with the degree of unloading being determined by associated sensors and control module (not shown). It should be noted that in this embodiment, the compressor is shown as a high side machine and thus suction inlet  200  is directly connected to the suction inlet of non-orbiting scroll  182 . 
     In this embodiment and the embodiments in FIGS. 12,  13  and  15 , temperature sensor  81  monitors the fluid temperature within fluid line  194  and temperature sensor  83  monitors the fluid temperature within fluid line  202 . Pressure sensor  85  monitors the fluid pressure within fluid line  194 . The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . Optionally, temperature sensor  83  could monitor the fluid temperature within fluid line  198 , if desired. 
     The embodiment  208  of FIG. 12 represents a combination of the axial unloading arrangement of FIG.  11  and the orbiting scroll biasing arrangement of FIG. 9 both described above. Accordingly, elements corresponding to like elements shown in and described with reference to FIGS. 9 and 11 are indicated by the same reference numbers. In this embodiment, the intermediate pressure axial biasing chamber  148   b  for the orbiting scroll is completely separate from the unloading discharge pressure biasing chamber defined by recess  184  and annular piston  186 . 
     In like manner, the embodiment  210  of FIG. 13 represents a combination of the intermediate pressure biasing arrangement of FIG. 8 described above and the axial unloading pressure biasing arrangement of FIG.  11 . Accordingly, corresponding elements have been indicated by the same reference numbers used in these respective figures. 
     FIG. 14 shows an embodiment  212  wherein shell  12  includes an upper chamber  214  at discharge pressure and a lower portion  216  at a pressure intermediate suction and discharge. Accordingly, suction line  234  is directly connected to non-orbiting scroll member  224 . Additionally, a suitable annular seal  225  may be provided between orbiting scroll  222  and non-orbiting scroll  224  around the outer periphery thereof. Orbiting scroll  222  is biased into sealing relationship with non-orbiting scroll  224  by intermediate pressure in chamber  216  supplied via passage  226 . In order to unload compressor  212 , a solenoid valve  228  is provided having a first fluid line  230  extending through shell  12  and being connected to one end of a passage  231  provided in lower bearing housing  233 . A second fluid line  232  is connected between the suction inlet  234  and solenoid valve  228 . When solenoid valve  228  is opened, the intermediate pressure acting on the lower surface of orbiting scroll  222  will be vented to suction via passage  231 , fluid line  230 , solenoid valve  228  and fluid line  232 . Because passage  231 , fluid lines  230  and  232  and solenoid valve  228  will be sized to provide a flow volume greater than that through passage  226  plus the leakage into the area defined between the bearing housing and end plate of orbiting scroll  222 , the biasing force acting on orbiting scroll  222  will be relieved thus allowing the force of the fluid within the compression chamber to move orbiting scroll  222  axially away from non-orbiting scroll  224 . As soon as solenoid valve  228  is closed, leakage flow of intermediate pressure fluid within lower portion  216  of shell  12  combined with flow from passage  226  will quickly restore the biasing force on orbiting scroll  222  whereby full compression will resume. Again, as with each of the above embodiments, cyclical actuation of solenoid valve  228  in response to a signal from a control module (not shown) resulting from appropriate sensed system conditions will result in cyclical loading and unloading of compressor thereby enabling modulation of capacity from 100 percent down to 0 percent capacity. 
     In this embodiment temperature sensor  81  monitors the fluid temperature within fluid line  230 , and temperature sensor  83  monitors the fluid temperature within fluid line  232 . Pressure sensor  85  monitors the fluid pressure within fluid line  230 . The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . 
     FIG. 15 shows an embodiment  236  which combines the features of an intermediate pressure lower shell and biasing arrangement for the orbiting scroll as shown in FIG. 14 with the discharge pressure unloading arrangement of FIG.  11 . Accordingly, corresponding portions thereof are indicated by the same reference numbers. Additionally, as described with reference to FIGS. 8,  10 , and  13 , a plurality of springs  238  are provided being positioned in recess  240  provided in main bearing housing  242  and acting on the lower surface of the end plate of orbiting scroll member  222 . As noted above, springs  238  serve primarily to bias orbiting scroll member  222  into sealing engagement with non-orbiting scroll member  182  during initial start up and also aid in reloading of compressor  236 . Again, full and reduced loading of compressor  236  will be accomplished in the same manner as described above by means of cyclic actuation of solenoid valve  196 . 
     Referring now to FIG. 16, yet another embodiment  244  of the present invention is shown which is generally similar to that of FIG.  1  and includes a shell  12  having a separating plate  246  dividing the interior thereof into a discharge chamber  248  and a lower chamber  250  at suction pressure. A cylindrical member  252  is secured to plate  246  and defines a flow path  254  for conducting compressed fluid from discharge port  256  of axially movable non-orbiting scroll  258 . Non-orbiting scroll  258  has an annular recess provided in the upper surface thereof which is separated into upper and lower chambers  260 ,  262  respectively by a radially outwardly extending annular flange  264  provided on cylindrical member  252 . A passage  266  places lower chamber  262  in fluid communication with a compression pocket at intermediate pressure to provide a biasing force for urging non-orbiting scroll  258  into sealing engagement with orbiting scroll  268 . An annular plate member  269  is secured to non-orbiting scroll  258 , sealingly and slidingly engages tubular member  252  and serves to close off the top of chamber  260 . A pressure responsive discharge check valve  270  is also provided on non-orbiting scroll  258 . 
     A two way solenoid valve  270  is provided being connected to discharge conduit  272  via fluid line  274  and to upper separating chamber  260  via fluid line  276  and passage  278  in tubular member  252 . A vent passage  280  is provided between non-orbiting scroll  258  and plate  269  and extends between separating chamber  260  and the lower interior  250  of shell  12  which is at suction pressure. Vent passage  280  serves to continuously vent separating chamber  260  to suction pressure. When solenoid valve  270  is in a closed position, compressor  244  will be fully loaded as shown. However, when solenoid valve  270  is actuated to an open position by the control module (not shown) in response to selected sensed conditions, separating chamber  260  will become pressurized to substantially discharge pressure thereby overcoming the combined force of discharge pressure and suction pressure acting to bias non-orbiting scroll member  258  toward orbiting scroll member  268 . Thus, non-orbiting scroll member  258  will move axially upwardly as shown thereby unloading compressor  244 . It should be noted that in this embodiment, the size of lines  274  and  276  and passage  278  must be selected relative to the size of vent passage  280  to enable build up of sufficient pressure in separating chamber  260  to effect unloading. Additionally, the relative size of these passages will affect the speed at which compressor  244  may be cycled between loaded and unloaded conditions as well as the volume of discharge gas required to accomplish and maintain unloading. 
     In this embodiment and the embodiment shown in FIG. 17, temperature sensor  81  monitors the temperature of fluid in fluid line  276  and  276 ′, respectively; temperature sensor  83  monitors the temperature of fluid in fluid line  274  and  274 ′, respectively; and pressure sensor  85  monitors the fluid pressure within line  276  and  276 ′, respectively. The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . 
     The embodiment of FIG. 17 is generally similar to that of FIG. 16 described above except that spring biasing members  282  are included in the intermediate pressure chamber. Accordingly, corresponding elements are indicated by the same reference numbers primed. As noted above, springs  280  serve primarily to assist in biasing non-orbiting scroll member  258  into sealing relationship with orbiting scroll member  268  during start up but will also function to assist in reloading compressor  244 . In all other respects, the operation of compressor  244  will be substantially identical to that described with reference to FIGS. 1 and 16 above. 
     Referring now to FIG. 18, a further embodiment of the present invention is shown being indicated generally at  284 . Compressor  284  includes an outer shell  12  having a separating plate  286  dividing the interior thereof into a discharge chamber  290  and a lower chamber  292  at suction pressure. A cylindrical member  294  is suitably secured to plate  286  and slidingly sealingly engages a cylindrical portion of axially movable non-orbiting scroll member  296  so as to define a discharge fluid flow path  298  from discharge port  300 . A pressure responsive discharge check valve  302  is also provided being secured to non-orbiting scroll  296  and operative to prevent back flow of discharge fluid from chamber  290  into the compression chambers. Non-orbiting scroll  296  includes a pair of annular stepped portions  304 ,  306  on its outer periphery which cooperate with complementary portions  308 ,  310  on main bearing housing  312  to define a generally annular separating chamber  314 . Additionally, non-orbiting scroll  296  includes a radially outwardly projecting flange portion  316  which cooperates with a radially inwardly projecting flange portion  318  on main bearing housing  312  to limit axially separating movement of non-orbiting scroll  296 . 
     A solenoid valve  320  is also provided being connected in fluid communication with chamber  314  via passage  322  in main bearing housing  312  and fluid line  324 . Fluid lines  326  and  328  serve to interconnect solenoid valve  320  with discharge line  330  and suction line  332  respectively. 
     Similarly to that described above, when compressor  284  is operating under a normal fully loaded condition as shown, solenoid valve  320  will be in a position to place chamber  314  in fluid communication with suction line  332  via passageway  322  and fluid lines  324  and  328 . Under these conditions, the biasing force resulting from discharge pressure fluid in chamber  290  acting on the upper surface of non-orbiting scroll  296  within flow path  298  will operate to urge non-orbiting scroll  296  into sealing engagement with orbiting scroll  334 . When it is desired to unload compressor  284 , solenoid valve  320  will operate to place chamber  314  in fluid communication with discharge pressure fluid via fluid lines  326 ,  324  and passageway  322 . The resulting pressure in chamber  314  will then operate to overcome the biasing force being exerted on non-orbiting scroll  296  thus causing it to move axially upwardly as shown and out of sealing engagement with orbiting scroll  334  thus unloading compressor  284 . To reload compressor  296 , solenoid valve  320  will operate to vent the discharge pressure fluid in chamber  314  to suction line  332  via passage  322  and fluid lines  324 ,  328  thereby allowing the biasing force acting on non-orbiting scroll  296  to move it axially downwardly back into sealing engagement with orbiting scroll  334 . In like manner, as noted above, operation of solenoid valve  320  will be controlled by a suitable control module (not shown) in response to system conditions sensed by one or more sensors to cyclically load and unload compressor  284  as needed. 
     A further embodiment of the present invention is shown in FIG. 19 being indicated generally at  336  which is similar to the embodiment shown in FIG.  18 . Accordingly, corresponding portions thereof have been indicated by the same reference numbers primed. In this embodiment, lower portion  292 ′ of shell  12 ′ is at intermediate pressure supplied via passage  338  in orbiting scroll  334 ′ which also acts to exert an upwardly directed biasing force thereon. Additionally, ring member  340  which includes stepped portions  308 ′,  310 ′ is separately fabricated and secured to main bearing housing  342 . Ring member  340  also includes a portion  344  which extends into overlying relationship with the end plate of orbiting scroll member  334 ′ and operates to limit upward movement thereof when compressor  336  is in an unloaded condition. Additionally, an internal flexible suction line  346  is provided being connected to suction line  332 ′ and to non-orbiting scroll  296 ′. A check valve  348  is provided at the connection of line  346  with non-orbiting scroll  296 ′ and serves to prevent back flow of fluid under compression when compressor  336  is unloaded. A suction control device  350  is also optionally provided in suction line  332 ′ upstream of the point at which fluid line  328  is connected. Suction control device  350  will be controlled by control module (not shown) and will operate to restrict suction gas flow through suction line  332 ′ so that the reduced pressure downstream thereof will assist in evacuating chamber  314 ′ during transition from unloaded operation to loaded operation or also on initial start up of compressor  336 . In all other respects the operation including the cyclical loading and unloading of compressor  336  will be substantially the same as described above. 
     In FIGS. 18 and 19, temperature sensor  81  monitors the fluid temperature in fluid line  324 , temperature sensor  83  monitors the fluid temperature in fluid line  326  and pressure sensor  85  monitors the fluid pressure within fluid line  324 . The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . Optionally, temperature sensor  83  can monitor the fluid temperature within fluid line  328 , if desired. 
     Yet another embodiment is illustrated in FIG. 20 being indicated generally at  352 . Compressor  352  includes non-orbiting scroll member  354  which is axially movably secured to main bearing housing  356  by means of a plurality of bushings  358  secured in position by fasteners  360 . Bushings  358  and fasteners  360  cooperate to accurately and non-rotatably position non-orbiting scroll  354  while allowing limited axial movement thereof. A separate annular flanged ring  362  is secured to non-orbiting scroll  354  and cooperates with a radially outwardly disposed stationary flanged ring member  364  to define a sealed separating chamber  366  therebetween. Ring member  364  includes a passage  368  to which one end of a fluid line  370  is connected, the other end of which is connected to solenoid valve  372 . Similar to that described above, solenoid valve  372  includes fluid lines  374  and  376  connected to discharge line  378  and suction line  380  respectively. The operation of compressor  352  will be substantially identical to that described above with solenoid valve  372  operating to cyclically place chamber  366  in fluid communication with discharge pressure fluid and suction pressure fluid to thereby cyclically load and unload compressor  352 . 
     FIG. 21 represents yet a further embodiment  382  of the subject invention. Compressor  382  combines the separating chamber arrangement of compressor  352  with the suction gas supply arrangement and intermediate pressure shell of compressor  336  shown in FIG.  19 . Accordingly, corresponding portions thereof are indicated by like numbers double primed and the operation thereof will be substantially the same as described above. 
     In FIGS. 20 and 21, temperature sensor  81  monitors the fluid temperature in fluid line  370  and  370 ″, respectively; temperature sensor  83  monitors the fluid temperature in fluid line  374  and  374 ″, respectively; and pressure sensor  85  monitors the fluid pressure in fluid line  370  and  370 ″, respectively. The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . Optionally, temperature sensor  81  could monitor the fluid temperature within fluid line  376  and  376 ″, respectively, if desired. 
     FIG. 22 shows a further modification of the present invention. Compressor  384  is substantially the same as that shown in FIG. 16 with the exception that compressor  384  includes a two way solenoid valve  386  connected to suction line  388  via fluid conduit  390 , a modified passage arrangement as described below and omits cover member  269  defining upper chamber  260 . Accordingly, portions corresponding to like portions of compressor  244  are indicated by like numbers double primed. Additionally, the mounting arrangement for axially movable non-orbiting scroll  258 ″ is substantially identical to that described with reference to FIG.  20  and hence corresponding portions thereof are indicated by like numbers primed. In this embodiment solenoid valve is also connected to chamber  262 ″ via first fluid line  392 , a second internal flexible fluid line  394  and radially extending passage  396  provided in non-orbiting scroll  258 ″. Additionally, a plurality of separating springs  398  are provided being positioned coaxially with bushings  358 ′ and extending between main bearing housing  400  and the lower surface of non-orbiting scroll  258 ″. 
     Under normal fully loaded operation, non-orbiting scroll  258 ″ will be biased into sealing engagement with orbiting scroll  268 ″ by the combined force resulting from discharge pressure acting on the upper surface of non-orbiting scroll  258 ″ within passage  254 ″ and intermediate pressure fluid within chamber  262 ″ conducted thereto via passage  266 ″. Under these conditions solenoid valve  386  will be in a closed position thereby preventing fluid communication between chamber  262 ″ and suction line  388 . When sensed system conditions indicate it is desired to unload compressor  384 , solenoid valve  386  will open to thereby vent chamber  262 ″ to suction line  388  via passage  396 , and fluid lines  394 ,  392  and  390  thereby relieving the intermediate biasing force on non-orbiting scroll  258 ″. As this biasing force is relieved, the combined force from the fluid under compression between the scroll members and the force exerted by springs  398  will operate to move non-orbiting scroll  258 ″ axially away from and out of sealing engagement with orbiting scroll  268 ″ thereby unloading compressor  384 . Of course, passageway  396 , fluid lines  394 ,  392  and  390 , and solenoid valve  386  must all be sized relative to the size of passage  266 ″ to ensure adequate venting of chamber  262 ″. Cyclical unloading and loading of compressor  384  will be accomplished in substantially the same manner in response to system conditions as described above. 
     In FIG. 22, temperature sensor  81  monitors the fluid temperature in fluid line  392 , temperature sensor  83  monitors the temperature in fluid line  390  and pressure sensor  85  monitors the fluid pressure in fluid line  392 . The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . 
     The present invention is also well suited for application to dual rotating scroll-type compressors. Such embodiments are illustrated in FIGS. 23 through 28. 
     Referring first to FIG. 23, a dual rotating scroll-type compressor is shown being indicated generally at  402 . Compressor  402  includes first and second scroll members  404 ,  406  rotatably supported within an outer shell  408  by upper and lower bearing members  410 ,  412  axially offset from each other. Upper bearing member  410  is formed in a plate member  415  which also serves to define a discharge chamber  414  into which compressed fluid exiting discharge port  416  in upper scroll  404  is directed via passage  418 . A discharge check valve  420  is also provided overlying discharge port  416 . Lower scroll member  406  is supported within and rotatable with a lower housing  422 . An upper housing  424  surrounds upper scroll member  404 , is secured to lower housing  422  and cooperates with lower housing  422  and upper scroll member  404  to define an intermediate pressure biasing chamber  426  and a separating chamber  428 . A fluid passage  430  is provided in upper scroll member  404  extending from a compression pocket at intermediate pressure to biasing chamber  426  to supply fluid pressure thereto which in combination with discharge pressure fluid acting on upper scroll member  404  within passage  418  will serve to bias upper scroll  404  into sealing engagement with lower scroll member  402  during fully loaded operation. 
     A second passage  432  is also provided in upper scroll member  404  extending from separating chamber  428  to an annular recess  434  formed in the outer periphery of an upper cylindrical hub portion  436  of upper scroll  404 . Annular recess  434  is in fluid communication with a passage  438  provided in bearing  410  and extending radially outwardly through plate  415 . 
     A solenoid valve  440  is also provided the operation of which is designed to be controlled by a control module (not shown) in response to system conditions sensed by appropriate sensors (also not shown). Solenoid valve  440  includes a first fluid conduit  442  connected to passage  438 , a second fluid line  444  connected to discharge line  448  and a third fluid line  450  connected to suction line  452 . 
     When compressor  402  is operating under fully loaded conditions, solenoid valve  440  will be in a position to place separating chamber  428  in fluid communication with suction line  452  via passage  432 , recess  434 , passage  438  and fluid lines  442  and  450 . In order to unload compressor  402 , solenoid valve will operate to connect chamber  428  to discharge line  448  thereby pressurizing same to discharge pressure. The force resulting from discharge pressure fluid in chamber  428  will operate to move scroll member  404  axially away from and out of sealing engagement with scroll member  402  thereby unloading the compressor. Cyclic operation of solenoid valve will result in cyclic unloading of compressor  402  in substantially the same manner as discussed above. 
     FIG. 24 illustrates another embodiment of a dual rotating scroll-type compressor  454  in accordance with the present invention. Compressor  454  is substantially identical in construction and operation to compressor  402  with the exception that compressor  454  does not incorporate an intermediate pressure biasing chamber but rather utilizes only discharge pressure to bias the upper axially movable scroll member into sealing engagement with the lower scroll member. Accordingly, corresponding portions thereof are indicated by the same reference numbers primed. 
     A further embodiment of a dual rotating scroll-type compressor  456  is shown in FIG.  25 . Compressor  456  is substantially identical to compressors  402  and  454  with the exception that in place of the intermediate pressure biasing chamber provided in compressor  402 , compressor  456  employs a plurality of springs  458  extending between a radially inwardly extending portion  460  of upper housing  424 ″ and an upper surface of upper scroll member  404 ″. Accordingly, portions corresponding to like portions of compressor  402  are indicated by the same reference numbers double primed. Springs  458  serve to cooperate with the discharge pressure in passage  418 ″ to bias upper scroll member  404 ″ axially into sealing engagement with lower scroll member  402 ″. In all other respects the operation of compressor  456  is substantially identical to that described above. 
     FIG. 26 shows a further embodiment of a dual rotating scroll-type compressor  462 . Compressor  462  is very similar to compressors  402 ,  454 , and  456  except as noted below and accordingly, like portions thereof are indicated by the same reference numbers triple primed. 
     Compressor  462  as shown is mounted in the bottom portion of a hermetic shell  464  and in an inverted position as compared to compressors  402 ,  454  and  456 . A discharge port  466  is provided in scroll member  406 ′″ and serves to discharge compressed fluid to a chamber  468  via check valve  470  from which it is directed to the motor compartment  472  disposed in the upper portion of shell  464  via a passage  474  extending through drive shaft  476 . A driving motor is provided in motor compartment  472  and includes a stator  478  and rotor  480  secured to crankshaft  476 . Axially movable scroll member  404 ′″ is rotatably supported in a cylindrical bearing housing  482  formed in the lower end portion  483  of housing  464  and cooperates therewith to define a discharge pressure biasing chamber  484 . In order to supply discharge pressure fluid to chamber  484 , a passage  486  is provided in main bearing housing  488  which is connected to a second passage  490  in lower housing portion  483 . Passage  490  opens into chamber  484  and thus conducts high pressure discharge fluid from motor compartment  472  to chamber  484  to bias scroll member  404 ′″ into sealing engagement with scroll member  406 ′″ during normal full load operation. A second passage  432  extends through lower housing portion  483  from recess  434 ″ to fluid conduit  442 ′″. It should be noted that chamber  484  could alternatively be pressurized with intermediate pressure fluid by providing a passage through the end plate of scroll  404 ′″ from a compression pocket at a pressure between suction and discharge to chamber  484  thus eliminating the need for passages  486  and  490 . Alternatively, discharge pressure fluid could be provided to chamber  484  by means of a passage through the end plate of scroll  404 ″ extending thereto from the control pocket into which port  466  opens. 
     Operation of compressor  462  will be substantially identical to that of compressor  454  including the cyclical loading and unloading thereof in response to actuation of solenoid valve  440 ′″ as controlled by a control module and associated sensors (not shown). 
     In FIGS. 23-26, temperature sensor  81  monitors the fluid temperature in fluid line  442 - 442 ′″, respectively; temperature sensor  83  monitors the fluid temperature in fluid line  444 - 444 ′″, respectively; and pressure sensor  85  monitors the fluid pressure in fluid line  442 - 442 ′″, respectively. The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . Optionally, temperature sensor  83  could monitor the fluid temperature within fluid line  450 - 450 ′″, respectively, if desired. 
     FIG. 27 is directed to another embodiment of a dual rotating scroll-type compressor  494  in which the lower driving scroll member is axially movable. Compressor  494  includes an outer housing  496  within which upper and lower scroll members  498 ,  500  are rotatably supported. A partition plate  502  is provided which separates the discharge chamber  504  from the lower suction pressure chamber  506  and also includes a cylindrical bearing portion  508  for rotatably supporting upper scroll member  498  by means of cylindrical portion  510 , the interior which also defines a discharge fluid flow path  512  from discharge port  514  past discharge check valve  516  to discharge chamber  504 . Upper scroll member  498  includes an annular cavity  518  which opens outwardly in facing relationship to lower scroll  500 . An annular ring shaped piston member  520  is movably disposed therein and operative to exert a separating force on lower scroll  500  in response to pressurization of the separating chamber  522  disposed above piston member  520 . In order to supply discharge pressure fluid to chamber  522 , a passage  524  is provided in scroll member  498  extending upwardly from chamber  522  through cylindrical portion  510  and opening radially outwardly therefrom into an annular recess  526 . A second passage  528  extends generally radially outwardly through plate  502  and connects to fluid line  530  which in turn is connected to solenoid valve  532 . Solenoid valve  532  also has a fluid line  534  extending therefrom to discharge conduit  536  and another fluid line  538  extending therefrom to suction line  540 . 
     Lower scroll member  500  is rotatably supported via lower bearing  542  and includes an internally splined center hub portion  544  adapted to axially movably receive a complementarily splined drive shaft  546 . An intermediate pressure bleed passage  548  is formed in the end plate of lower scroll member  500  and serves to conduct biasing pressure fluid from an intermediate pressure compression pocket to a biasing chamber  550  therebelow. A plate member  552  is secured to upper scroll  498  and includes an annular recess  554  in which an annular seal  556  is disposed. Seal  556  engages the lower surface of lower scroll  500  so as to seal chamber  550  from the suction pressure chamber  506 . 
     Under fully loaded operation, lower scroll  500  will be biased axially upwardly into sealing engagement with upper scroll  498  due to the force from intermediate pressure fluid in chamber  550 . Under these conditions, solenoid valve will be in a position to place chamber  522  in fluid communication with suction line  540 . When system conditions indicate a lower capacity output is desired, solenoid valve will be actuated to a position to place chamber  522  in fluid communication with discharge line  536  thereby pressurizing chamber  522  and effecting an axial downward movement of piston  520 . Piston  520  in turn will move lower scroll  500  axially downwardly out of sealing engagement with upper scroll  498 . When solenoid valve is cycled back to a position to vent chamber  522  to suction line  540 , the biasing force resulting from intermediate pressure in chamber  550  will return lower scroll member  500  to sealing engagement with upper scroll member  498 . The cyclic operation between loaded and unloaded operation will then be controlled in like manner similar to that described above by a control module and associated sensors. 
     FIG. 28 shows another embodiment of a dual rotating compressor  558  which is substantially the same as that described with reference to FIG. 27 except as noted below. Accordingly, like portions thereof are indicated by the same reference numbers primed. Compressor  558  utilizes discharge pressure fluid supplied to chamber  550 ′ via passage  560  to bias lower scroll member  500 ′ into sealing engagement with upper scroll member  498 ′. Otherwise the operation of compressor  558  is substantially identical to that described above. 
     In FIGS. 27 and 28, temperature sensor  81  monitors the temperature in fluid line  530  and  530 ′, respectively; temperature sensor  83  monitors the temperature in fluid lines  534  and  534 ′, respectively; and pressure sensor  85  monitors the fluid pressure in fluid line  530  and  530 ′, respectively. The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . Optionally, temperature sensor  83  could monitor the temperature within fluid line  538  and  538 ′, respectively, if desired. 
     Another compressor  562  incorporating a further embodiment of the present invention is shown in FIG.  29 . Compressor  562  is similar to compressor  352  shown in FIG. 20 except as noted below and accordingly like portions thereof are indicated by the same reference numbers triple primed. Compressor  562  incorporates a partition plate  564  which forms a part of outer shell  566  and separates the interior thereof into a high pressure discharge chamber  568  and a low pressure suction portion  570 . Partition plate  564  includes a central cylindrical portion  572  which is adapted to sealingly movably receive a cylindrical portion  574  of non-orbiting axially movable scroll member  354 ′″. Cylindrical portion  574  includes a plurality of radial openings  576  which are aligned with openings  578  in portion  572  to define a discharge gas flow path  579  from discharge port  580  past discharge check valve  582  to discharge chamber  568 . A cover plate  584  is secured to cylindrical portion  574  to close off the upper end of passage  579  and also cooperates with cylindrical portion  572  to define an intermediate pressure biasing chamber  586  therebetween. A fluid passage  588  extends from a compression pocket at intermediate pressure to chamber  586  and serves to provide fluid pressure for biasing axially movable scroll member  354 ′″ into sealing engagement with orbiting scroll  590 . The operation including cyclical loading and unloading of compressor  562  is substantially identical to that described with reference to compressor  352  and the other embodiments described above. 
     In FIG. 29 temperature sensor  81  monitors the temperature in fluid line  370 ′″; temperature sensor  83  monitors the temperature in fluid line  374 ′″; and pressure sensor  85  monitors the fluid pressure in fluid line  370 ′″. The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . Optionally, temperature sensor  83  could monitor the fluid temperature within fluid line  376 ′″, if desired. 
     FIG. 30 illustrates a compressor  592  incorporating a further modification of the present invention. Compressor  592  is substantially identical to compressor  562  of FIG. 29 except as noted below and accordingly like portions thereof are indicated by the same reference numbers quadruple primed. Compressor  592  incorporates a two way solenoid valve  594  having a fluid line  596  connected to chamber  586 ′″ and a second fluid line  598  connected to suction line  380 ′″. Additionally, member  362 ′″ and  364 ′″ are omitted and in lieu thereof biasing springs  600  are provided being positioned in coaxial surrounding relationship to bushings  358 ′″. 
     Under fully loaded operating conditions, the biasing force resulting from intermediate fluid pressure in chamber  586 ′″ will bias axially movable non-orbiting scroll  354 ′″ downwardly into sealing engagement with orbiting scroll  590 ′″ in the same manner as discussed above and will overcome the separating force resulting from springs  600 . When conditions indicate unloading is desired, solenoid valve  594  will switch from a closed condition (which prevented venting of chamber  586 ′″ to suction during fully loaded operation) to an open position thereby venting chamber  586 ′″ to suction line  380 ′″ and relieving the biasing force exerted on scroll  354 ′″. As this biasing force is relieved, the force from springs  600  together with the pressure of the fluid under compression will operate to move axially movable scroll member  354 ′″ upwardly out of sealing engagement with orbiting scroll  590 ′″. As before, solenoid valve  594  will be operated in a cyclic manner by control means in response to associated sensors to cyclically load and unload compressor  592  so as to achieve the desired degree of capacity modulation. 
     In FIG. 30 temperature sensor  81  monitors the temperature in fluid line  596 ; temperature sensor  83  monitors the temperature in fluid line  598 ; and pressure sensor  85  monitors the fluid pressure in fluid line  596 . The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . 
     While the previous embodiments have been primarily directed to hermetic motor compressors, the present invention is also well suited for use with compressors employing an external drive such as for example automotive air conditioning system compressors. The use of the present invention in such an environment can eliminate the need for the expensive clutch systems commonly utilized in today&#39;s systems. 
     FIG. 31 illustrates a compressor  602  which is specifically directed for use with an external power source. Compressor  602  is similar in construction to compressor  244  of FIG. 16 except as noted below and accordingly like portions thereof are indicated by the same reference numbers triple primed. 
     Compressor  602  incorporates a three way solenoid valve  604  as opposed to the two way solenoid valve of compressor  244  and hence includes fluid lines  606  connected to discharge line  272 ′″ and a second fluid line  608  connected to suction line  610 . It should be noted that a two way solenoid valve could be used in the same arrangement if desired. Because solenoid valve  604  is designed to directly vent upper chamber  260 ′″ to suction line  610  during unloading, continuously open vent passage  280  provided in compressor  244  is omitted. Drive shaft  612  of compressor  602  extends outwardly of housing  614  through suitable bearing means  616  and sealing means  618  and is adapted to be connected to a suitable external power source such as an automobile engine via a conventional pulley and V-belt arrangement or the like. 
     In operation, the external power source will continuously drive shaft  612  thereby effecting continuous orbital movement of orbiting scroll  268 ′″. When system conditions indicate cooling is required, solenoid valve  604  will be positioned by suitable control means to place chamber  260 ′″ in fluid communication with suction line  610  thereby relieving any separating force resulting therefrom and enabling chamber  262 ′″ which is supplied with intermediate pressure fluid via passage  266 ′″ to generate a biasing force which, with the biasing force resulting from discharge pressure fluid acting on the surface of non-orbiting scroll member  258 ′″ in passage  254 ′″, will bias non-orbiting scroll member  258 ′″ into sealing engagement with orbiting scroll member  268 ′″. When system requirements have been met, compressor  602  will be unloaded by actuation of solenoid valve  604  to a position in which chamber  260 ′″ is placed in fluid communication with discharge line  272 ′″ thereby resulting in the creation of a separating force which will operate to move non-orbiting scroll member axially out of sealing engagement with orbiting scroll member  268 ′″. Cyclic control of compressor  602  may be achieved in the same manner as described above thus eliminating the need for a clutch when such a system is utilized in an automotive application. 
     In FIG. 31 temperature sensor  81  monitors the temperature in fluid line  276 ′″; temperature sensor  83  monitors the temperature in fluid line  606 ; and pressure sensor  85  monitors the fluid pressure in fluid line  276 ′″. The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . Optionally, temperature sensor  83  could monitor the fluid temperature within fluid line  608 , if desired. 
     While the previous embodiments have all been directed to the use of the fluid being compressed to effect unloading of the respective compressors, the present invention may also accomplish such unloading by the use of other types of force generating means to effect axial movement of one or the other of the two scroll members. Embodiments illustrating such arrangements are shown and will be described with reference to FIGS. 32 through 34. 
     Referring first to FIG. 32, there is shown a hermetic compressor  620  which includes a housing  622  having a plate  624  operative to separate the interior thereof into a discharge chamber  626  and a lower portion  628  at suction pressure. A bearing housing  630  is secured within shell  622  and rotatably supports a crankshaft  632  which is drivenly connected to orbiting scroll member  634 . A non-orbiting axially movable scroll member  636  is mounted on bearing housing  630  by means of bushings  638  and fasteners  640  such that scroll member  636  is slidably movable along bushings  638  but is restrained from circumferential or radial movement. Non-orbiting scroll member  636  includes a pressure biasing chamber  642  in the upper surface into which one end of ring shaped flanged member  644  projects. The other end of flanged member  644  is secured to plate  624 . A cylindrical portion  646  of non-orbiting scroll member  636  projects upwardly through ring shaped flanged member  644  into discharge chamber  626  to define a discharge passage  648  extending upwardly from discharge port  650  via discharge check valve  652 . A plurality of circumferentially spaced radial openings  654  are provided adjacent the upper end of portion  646  to place passage  648  in fluid communication with discharge chamber  626 . A cover plate  656  is secured to the upper end of portion  646  and also includes openings  658  therein to allow passage of discharge fluid into discharge chamber  626 . Non-orbiting scroll member  636  also includes a passage  660  extending from a compression pocket at intermediate pressure to biasing chamber  642  whereby intermediate pressure fluid may be supplied to chamber  642  to axially bias non-orbiting scroll member  636  into sealing engagement with orbiting scroll  634  during normal fully loaded operation. Of course, this intermediate pressure biasing force will be aided by discharge pressure acting against the upper surfaces of non-orbiting scroll  636 . 
     In this embodiment, an unloading mechanism  662  is provided which includes a suitable force applying actuator  664  supported on a cylindrical flanged support member  666  which in turn is sealingly secured to a fitting  668  provided on the top of shell  622 . An actuator shaft  670  extends downwardly through member  666  and fitting  668  and has its lower end connected to cover plate  656 . Actuator  664  may be any suitable type force applying capable of exerting a pulling force on non-orbiting scroll  636  such as for example an electrically actuated solenoid, a pneumatic or other fluid actuated piston and cylinder device or any other type of mechanical, magnetic, electromechanical, hydraulic, pneumatic, gas or spring type device. Operation of actuator will be controlled by a suitable control module  672  in response to sensed system conditions sensed by appropriate sensors  674 . 
     As noted above, under fully loaded operating conditions, intermediate pressure fluid in chamber  642  will cooperate with discharge pressure fluid in passage  648  to bias non-orbiting scroll member  636  into sealing engagement with orbiting scroll member  634 . When system conditions indicate unloading is desired, control module  672  will effect operation of actuator  664  to exert a separating force on non-orbiting scroll member  636  thereby moving it out of sealing engagement with orbiting scroll member. When fully loaded operation is to be resumed, actuator  664  will be deactuated thereby enabling the biasing force from intermediate pressure chamber  642  and discharge pressure in passage  648  to again move non-orbiting scroll member  636  into sealing engagement with orbiting scroll member  634 . Actuator  664  will be designed to enable rapid cyclic operation so as to enable cyclical loading and unloading of compressor  620  in the same manner as described above. 
     FIG. 33 shows a modified version of the embodiment of FIG. 32 wherein like portions are indicated by the same reference numbers primed. In this embodiment, actuator  664 ′ is located within housing  622 ′ with actuating connections  676  extending outwardly therefrom. In all other respects, compressor  620 ′ will operate in the same manner as that described above with reference to FIG.  32 . 
     Referring now to FIG. 34, there is shown a hermetic compressor  880  which combines certain features employed in the compressors of FIGS. 4 and 33. Compressor  880  includes an outer shell  882  having a plate  884  which separates the interior thereof into an upper discharge chamber  886  and a lower chamber  888  at suction pressure. A main bearing housing  890  is disposed in lower chamber  888  and serves to rotatably support a drive shaft  892  which is drivenly connected to an orbiting scroll member  894  also supported on main bearing housing  890 . A non-orbiting scroll member  896  is axially movably secured to main bearing housing  890  and includes a cavity at the upper end thereof defined by radially inner and outer cylindrical projections  898 ,  900  respectively. A flanged cylindrically shaped member  902  is sealingly secured to plate  884  and extends downwardly between and movably sealingly engages projections  898  and  900  to divide the cavity into an upper separating chamber  904  and a lower intermediate pressure biasing chamber  906 . A passage  907  in non-orbiting scroll  896  operates to place biasing chamber  906  in fluid communication with a fluid pocket undergoing compression and at a pressure intermediate suction and discharge. The interior of member  902  cooperates with projection  898  to define a discharge gas flowpath  908  extending from discharge port  910  to discharge chamber  886  via discharge check valve  912 . 
     As best seen with reference to FIG. 34A, an axially extending bore  914  is provided in member  902  within which a valve member  916  is axially movably disposed. Valve member  916  includes a reduced diameter portion  918  adjacent the lower end thereof which, when valve member is in a first position, operates to place separating chamber  904  in fluid communication with discharge pressure fluid in passage  908  via radially extending passages  920  and  922  and when in a second position, to place separating chamber  904  in fluid communication with suction pressure fluid in area  888  via radially extending passages  922  and  924 . Additionally, a radial vent passage  926  extends outwardly from the bottom of bore  914  to discharge passage  908  to facilitate movement of valve member  916  therein. 
     As shown, valve member  916  extends axially upwardly through discharge chamber  886  and outwardly through shell  882  and is coupled to a suitable actuator  928  secured to shell  882  and which operates to move it between the first and second positions noted above. A fitting  930  surrounds valve member  916  as it passes through shell  882  and contains suitable seals to prevent fluid leakage from discharge chamber  886 . Actuator  928  may be any suitable device having the ability to reciprocate valve member  916  between the noted first and second positions including, for example, a solenoid or any other electrical, electromechanical, mechanical, pneumatic or hydraulically actuated device. It should also be noted that actuator may, if desired, be mounted within the interior of shell  882 . 
     Under full load operation, intermediate fluid pressure in biasing chamber  906  in cooperation with discharge pressure acting against the surface of non-orbiting scroll member  896  in passage  908  will bias non-orbiting scroll member  896  axially into sealing engagement with orbiting scroll  894 . At this time, valve member  916  will be in a position to place separating chamber  904  in fluid communication with area  888  at suction pressure via passages  922  and  924 . In order to unload compressor  880 , actuator  928  will operate to move valve member  916  to a position in which it places separating chamber  904  in fluid communication with discharge pressure fluid in passage  908  via passages  920  and  922  thereby pressurizing chamber  904 . The force resulting from pressurization of chamber  904  will move non-orbiting scroll out of sealing engagement with orbiting scroll member  894  to thereby unload compressor  880 . In order to reload compressor  880 , actuator  928  operates to enable valve  916  to move back to its initial position in which the discharge pressure in chamber  904  will be vented to area  888  which is at suction pressure via passages  922  and  924  thereby enabling intermediate pressure in chamber  906  and discharge pressure fluid in passage  908  to move non-orbiting scroll back into sealing engagement with orbiting scroll  894 . Cyclical time pulsed actuation of actuator  928  will thus enable the capacity of compressor  880  to be modulated in substantially the same manner as described above. 
     FIG. 35 shows a further variation of the embodiments shown in FIGS. 32 and 33. In this embodiment, compressor  678  includes a non-orbiting scroll  680  which is fixedly mounted to bearing housing  682  and orbiting scroll member  684  is designed to be axially movable. Compressor  678  includes a suitable force applying means  686  in the form of an annular electromagnetic coil secured to bearing housing  682  in a well  688  provided therein in underlying relationship to orbiting scroll member  684 . A suitable magnetically responsive member  690  is positioned within force applying means  686  and bears against the undersurface of orbiting scroll member  684 . In this embodiment, actuation of force applying means  686  operates to exert an axially upwardly directed force on orbiting scroll member  684  thereby urging it into sealing engagement with non-orbiting scroll member  680 . Unloading of compressor  678  is accomplished by deactuating force applying means  686  thus relieving the biasing force generated thereby and allowing the separating force from the fluid under compression to move orbiting scroll member  684  out of sealing engagement with orbiting scroll member  680 . Cyclic time pulsed loading and unloading may be easily accomplished by controlling force applying means  686  in substantially the same manner as described above. 
     It should be noted that while compressor  678  has been described utilizing an electro-magnetic force applying means, other suitable force applying means may be substituted therefor including mechanical, magnetic, electromechanical, hydraulic, pneumatic, gas or mechanical spring type devices. 
     The prior embodiments of the present invention have all been directed to various means for effecting unloading by axial separation of the respective scroll members. However, the present invention also contemplates accomplishing unloading by radial separation of the flank surfaces of the scroll wraps thereby providing a leakage path between the compression pockets. Embodiments illustrating this method of unloading are shown and will be described with reference to FIGS. 36 through 44. 
     Referring now to FIG. 36, a compressor incorporating radially directed unloading is shown being indicated generally at  692 . Compressor  692  is generally similar to the previously described compressors and includes an outer shell  694  having a discharge chamber  696  and lower chamber  698  at suction pressure. A bearing housing  700  is supported within shell  694  and has a non-orbiting scroll member  702  axially movably secured thereto and an orbiting scroll  704  supported thereon which is adapted to be driven by crankshaft  706 . An intermediate pressure biasing chamber  708  is provided at the upper end of non-orbiting scroll member  702  which is supplied with intermediate pressure fluid from a compression pocket via passage  710  to thereby axially bias non-orbiting scroll member into sealing engagement with orbiting scroll member  704 . 
     Bearing housing  700  includes a plurality of substantially identical circumferentially spaced chambers  712  within each of which a piston  714  is movably disposed. Each piston  714  includes a pin  716  projecting axially upwardly therefrom, through opening  718  in the upper surface of bearing housing  700  and into corresponding axially aligned opening  720  provided in non-orbiting scroll member  702 . A spring  722  is provided in each of the openings  720  and extends between a cylindrical spring retainer  724  secured to non-orbiting scroll  702  and the upper end of each of the pins  716  and serves to exert an axially downwardly directed biasing force thereon. As shown, each of the pins  716  includes an upper portion  726  of a first diameter and a lower portion  728  of a greater diameter. Pins  716  are positioned in surrounding relationship to the periphery of orbiting scroll  704 . An annular manifolding assembly  729  is secured to the lower portion of main bearing  700  and closes off the lower end of respective chambers  712 . Manifolding assembly  729  includes an annular passage  731  from which respective axially extending passages  733  open upwardly into each of the chambers  712 . 
     As best seen with reference to FIG. 37, eccentric pin  730  of crankshaft  706  is drivingly connected to orbiting scroll member by means of a bushing  732  rotatably disposed within hub  734  provided on orbiting scroll  704 . Bushing  732  includes a generally oval shaped opening  736  having a flat  738  along one side thereof which is adapted to receive eccentric pin  730  which also includes a flat  740  engageable with flat  738  through which the driving forces are transmitted to orbiting scroll  704 . As shown, opening  736  is sized such that bushing and associated orbiting scroll  704  may move relative to each other such that the orbiting radius through which orbiting scroll moves may be reduced from a maximum at which the flank surfaces of the scroll wraps are in sealing engagement with each other to a minimum distance at which the flank surfaces are spaced from each other. 
     Compressor  692  also includes a three way solenoid valve  742  having a fluid line  744  connected to annular passage  731 , a second fluid line  746  connected to suction line  748  and a third fluid line  750  connected to discharge line  752 . 
     Under fully loaded operation, solenoid valve  742  will be in a position so as to place each of the chambers  712  in fluid communication with suction line  748  via passages  733 , passage  731 , and fluid lines  744  and  746 . Thus, each of the pistons and associated pins will be held in a lowered positioned by springs  722  whereby orbiting scroll member will be free to orbit at its full maximum radius. As axially movable non-orbiting scroll  702  is biased into sealing engagement with orbiting scroll  704  by biasing chamber  708 , compressor  692  will operate at full capacity. In order to unload compressor  692 , solenoid valve will be actuated so as to place discharge line  752  in fluid communication with annular chamber  731  which in turn will pressurize each of the chambers  712  with discharge pressure fluid to urge each of the pistons  714  and associated pins  716  to move axially upwardly to a fully raised position as shown in FIG.  39 . Because the force of the discharge pressure fluid acting on the respective pistons  714  will not be sufficient to overcome the forces urging the orbiting scroll radially outwardly, pins  716  will move upwardly sequentially as the orbiting scroll moves away therefrom. Once all of the pins have moved upwardly, the large diameter portion  728  of pins  716  will be in a position to engage the arcuate cutouts  754  provided around the periphery of orbiting scroll member  704  as best seen with reference to FIG. 38 thereby causing the orbiting radius of orbiting scroll member  704  to be reduced to a minimum at which the flank surfaces thereof are no longer in sealing relationship and the compressor is fully unloaded. It should be noted that the pins  716  will be circumferentially spaced such that at least two adjacent pins will be in engagement with corresponding cutouts  754  throughout the orbit of orbiting scroll member  704 . When loaded operation is to be resumed, solenoid valve will be returned to a position in which chamber  712  is vented to suction line  748  via passages  733 ,  731  and fluid lines  744  and  746  thereby allowing springs  722  to bias each of the pins  716  and associated pistons  714  downwardly to a position in which reduced diameter portion  726  of the respective pins is positioned in radially spaced relationship to cutouts  754  and orbiting scroll  704  is able to resume its full orbital radius and full capacity compression will resume. 
     In FIGS. 36-39 temperature sensor  81  monitors the temperature in fluid line  744 ; temperature sensor  83  monitors the temperature in fluid line  750 ; and pressure sensor  85  monitors the fluid pressure in fluid line  744 . The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . Optionally, temperature sensor  83  could monitor the fluid temperature within fluid line  746 , if desired. 
     FIG. 40 shows a modified version of the embodiment of FIGS. 36 through 39 at  756  wherein a two way solenoid valve  758  is utilized having fluid lines  760  and  762  connected to chamber  712  and discharge line  752 ′ respectively. In this embodiment, each of the chambers  712  includes a passage  764  at the lower end thereof that is in continuous communication with lower portion  698 ′ of shell  694 ′ which is at suction pressure. Thus, each of the chambers  712 ′ will be continuously vented to suction. To unload compressor  756 , solenoid valve is opened thereby placing each of the chambers  712 ′ in fluid communication with discharge pressure fluid from discharge line  752 ′ and biasing each of the pistons  714 ′ into a raised position. The remaining portions of compressor  756  are substantially identical to those of compressor  692  and accordingly are indicated by the same reference numbers primed. Similarly, the operation of compressor  756  will in all other respects be substantially identical to that of compressor  692 . 
     In FIG. 40 temperature sensor  81  monitors the temperature in fluid line  760 ; temperature sensor  83  monitors the temperature in fluid line  762 ; and pressure sensor  85  monitors the fluid pressure in fluid line  760 . The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . 
     A further modification of the embodiments shown in FIGS. 36 through 40 is shown in FIGS. 41 and 42 at  766 . In this embodiment, cutout portions  754  are deleted and two circular openings  768  are provided in lieu thereof. Likewise, only two pins  716 ″ are provided. The diameter of circular openings  768  relative to the reduced diameter portion  726 ″ of pins  714 ″ will be such that there will be a slight clearance therebetween when orbiting scroll member  704 ″ is orbiting at its maximum orbiting radius. When the larger diameter portion  728 ″ of pins  716 ″ are moved into holes  768 , the orbiting radius of orbiting scroll  704 ″ will be reduced to a minimum thus interrupting the sealing relationship between the flank surfaces of the scroll wraps. 
     Additionally, in this embodiment, springs  722  have been replaced by an intermediate pressure biasing arrangement including a passage  770  in scroll member  702 ″ extending from intermediate pressure biasing chamber  708 ″ into the upper end of member  724 ″. Thus, pins  716 ″ will be biased to a lowered position by means of intermediate fluid pressure. In all other respects the construction and operation of compressor  766  will be substantially identical to compressor  692  and hence corresponding portions have been indicated by the same reference numbers used in FIG. 35 double primed. 
     In FIG. 41 temperature sensor  81  monitors the temperature in fluid line  744 ″; temperature sensor  83  monitors the temperature in fluid line  750 ″; and pressure sensor  85  monitors the fluid pressure in fluid line  744 ″. The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . Optionally, temperature sensor  83  could monitor the fluid temperature within fluid line  746 ″, if desired. 
     Another arrangement for radially unloading a scroll-type compressor is shown in FIGS. 43 and 44. Compressor  772  is generally similar in construction to compressor  692  and includes an outer shell  774  having a partition plate  776  dividing the interior thereof into an upper discharge chamber  778  and a lower portion  780  at suction pressure. A main bearing housing is secured within lower portion  780  and includes a first member  782  to which axially movable non-orbiting scroll member  784  is secured by means of bushings  786  and fasteners  788  and which also axially supports orbiting scroll member  790 . A second member  792  of main bearing housing is secured to the lower end of member  782 , rotatably supports a driving crankshaft  794  and together with first portion  782  and orbiting scroll member  790  defines a substantially closed cavity  796 . Orbiting scroll member  790  includes a center hub  797  having a conically shaped outer surface which is adapted to drivingly mate with an eccentric pin  798  provided on crankshaft  794  via a drive bushing  800  disposed therebetween. Pin  798  and drive bushing  800  are substantially identical to that shown in FIG.  37  and allow for variation in the orbiting radius of orbiting scroll member  790  between a maximum at which the flank surfaces of the wraps are in sealing engagement and a minimum at which the flank surfaces of the wraps are spaced apart. 
     Non-orbiting scroll member  784  includes a cavity at the upper end thereof in which a floating seal member  802  is disposed to define an intermediate pressure biasing chamber  804  which is supplied with fluid under compression at a pressure between suction and discharge via passage  806  to thereby axially bias non-orbiting scroll member  784  into sealing engagement with orbiting scroll member  790 . The upper end of floating seal  802  sealingly engages plate  776  and cooperates with non-orbiting scroll member  784  to define a discharge fluid flow path  808  from discharge port  810  to discharge chamber  778  via discharge check valve  812  and opening  814  in plate  776 . 
     A piston member  816  is axially movably disposed within cavity  796  and includes suitable seals to thereby define a sealed separating chamber  818  at the lower end of cavity  796 . A plurality of springs  820  extend from a radially inwardly extending flange portion  822  of member  782  into suitable wells  824  provided in piston member  816  and serve to bias piston member  816  axially downwardly away from hub portion  797 . Additionally, piston member  816  includes a conically shaped radially inwardly facing surface  826  at the upper end thereof which is adapted to engage and is complementary to the outer conical surface of center hub  797 . 
     As shown, a three way solenoid valve  828  is also provided which is connected to separating chamber  818  via fluid line  830 , to suction line  832  via fluid line  834  and to discharge line  836  via fluid line  838 . It should be noted, however, that a two way solenoid valve connected only to suction could be substituted for three way solenoid  828 . In such a case, a bleed hole from the bottom chamber  818  through member  792  opening into area  780  would be required to vent discharge pressure fluid in somewhat similar manner to that described with reference to FIG.  38 . 
     Under full load operation, solenoid valve  828  will be in a position so as to place separating chamber  818  in fluid communication with suction line  832  via fluid lines  830  and  834  thereby maintaining chamber  818  at substantially suction pressure. The action of springs  820  will maintain piston member in its axially lowered position as shown in FIG. 41 at which conical surface  826  thereof will be slightly spaced from the outer conical surface of hub  796  of orbiting scroll member  790 . 
     When unloading is desired, solenoid valve  828  will be actuated to a position to place discharge line  836  in fluid communication with separating chamber  818  via fluid lines  838  and  830  thereby pressurizing chamber  818  to substantially discharge pressure. The biasing force resulting from this pressurization of chamber  818  will operate to move piston  816  axially upwardly overcoming the biasing force of springs  820  and moving conical surface  826  into engagement with the outer conical surface of hub  796  of orbiting scroll member  790 . Continued upward movement of piston  816  to a position as shown in FIG. 44 will result in conical surface  826  reducing the orbiting radius of orbiting scroll member  790  such that the flank surfaces of the wraps thereof are no longer in sealing engagement with the flank surfaces of the non-orbiting scroll member and further compression of fluid ceases. In order to resume compression, solenoid valve is actuated to a position to vent chamber  818  to suction line  832  via fluid lines  830  and  834  thereby enabling springs  820  to bias piston member  816  into its lowered position as shown in FIG.  43 . 
     It should be noted that while compressor  772  has been shown as including springs  820  to bias piston  816  axially downwardly, it may be possible to delete these biasing members in some applications and to rely on the axial component of the force exerted on piston  818  by the engagement of conical surface  826  with the conical surface on hub  796  to cause movement of piston member away from orbiting scroll member  790 . Additionally, solenoid valve  828  is intended to be controlled in a cyclical manner by means of a control module and associated sensors (not shown) in response to varying system conditions in substantially the same manner as described above with respect to the other embodiments. 
     In FIG. 43 temperature sensor  81  monitors the temperature in fluid line  830 ; temperature sensor  83  monitors the temperature in fluid line  838 ; and pressure sensor  85  monitors the fluid pressure in fluid line  830 . The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . Optionally, temperature sensor  83  could monitor the fluid temperature within fluid line  834 , if desired. 
     It should also be noted that the features incorporated in the various embodiments described above should not be viewed as being restricted to use only in that embodiment. Rather, features of one embodiment may be incorporated into another embodiment in addition to or in lieu of the specific features disclosed with respect to that other embodiment. For example, the discharge check valve provided on the outer shell of some of the embodiments may be substituted for the discharge check valve provided adjacent the discharge port in other embodiments or vice versa. Likewise, the suction control module disclosed for use with the embodiment of FIGS. 19 and 21 may also be incorporated into other embodiments. Further, while in many embodiments, the solenoid valve and associated fluid lines have been shown as positioned outside of the shell, they may be located within the shell if desired. 
     In each of the above embodiments, it is intended that the orbiting scroll continue to be driven while the compressor is in an unloaded condition. Obviously, the power required to drive the orbiting scroll member when the compressor is unloaded (no compression taking place) is considerably less than that required when the compressor is fully loaded. Accordingly, it may be desirable to provide additional control means operative to improve motor efficiency during these periods of reduced load operation thereof. 
     Such an embodiment is shown schematically in FIG. 45 which comprises a motor compressor  840  having a solenoid valve  842  connected to discharge line  844  via fluid line  846  and a suction line  848  via fluid line  850  and being operative to selectively place a compressor unloading mechanism in fluid communication with either the suction line or discharge line via fluid line  852 . Solenoid valve  842  is intended to be controlled by a control module  854  via line  855  in response to system conditions sensed by sensors  856 . As thus far described, the system represents a schematic illustration of any of the embodiments described above, it being noted that solenoid valve  842  could be a two way solenoid valve in lieu of the three way solenoid valve arrangement shown. In order to improve efficiency of the driving motor during reduced load operation, a motor control module  858  is also provided which is connected to the compressor motor circuit via line  860  and to control module  854  via line  862 . It is contemplated that motor control module  858  will operate in response to a signal from control module  854  indicating that the compressor is being placed in an unloaded operating condition. In response to this signal, motor control module will operate to vary one or more of the compressor motor operating parameters to thereby improve its efficiency during the period of reduced load. Such operating parameters are intended to include any variably controllable factors which affect motor operating efficiency including voltage reduction or varying the running capacitance of the motor for example. Once control module  854  signals motor control module  858  that the compressor is being returned to fully loaded operation, motor control module will then operate to restore the affected operating parameters to maximize motor efficiency under full load operation. 
     The above described compressor unloading arrangements are particularly well suited to provide a wide range of capacity modulation in a relatively inexpensive and effective manner and to maximize the overall efficiency of the system as compared to prior capacity modulation arrangements. However, under some operating conditions such as those encountered when condenser inlet pressure is at a reduced level, it may be desirable to reduce the compression ratio of the compressor to avoid over-compression of the refrigerant at certain levels of system capacity reduction. 
     FIG. 46 illustrates a compressor  864  which incorporates both the advantages of a cyclical or pulsed unloading as described above with means for reducing the compression ratio of the compressor so as to thereby increase the ability of the compressor to maximize efficiency under any operating conditions. Compressor  864  is substantially identical to compressor  10  shown in and described with reference to FIG. 1 except as noted below and accordingly like portions thereof are indicated by the same reference numbers primed. 
     Compressor  864  includes a pair of ports  866 ,  868  in non-orbiting scroll member  32 ′ which open into compression pockets  870 ,  872  respectively. Ports  866  and  868  communicate with a passage  874  opening outwardly through the outer periphery of non-orbiting scroll member  32 ′ into the lower area  876  of shell  12 ′ which is at suction pressure. Suitable valve means  878  are provided to selectively control communication of ports  866 ,  868  with area  876 . Preferably, ports  866 ,  868  will be located in an area such that they will begin to be in communication with the respective compression pockets prior to the compression pockets being sealed off from the suction fluid supply from area  876 . 
     In operation, when it is determined that a reduction in compressor capacity is desired, a determination will also be made from the system operating conditions if the compressor is operating in an over-compression mode or an under-compression mode. If it is determined that an over-compression mode is present, initial capacity reduction will most efficiently be carried out by opening valve means  878  which will thus place pockets  870 ,  872  in fluid communication with area  876  of compressor  864  which is at suction pressure. The effect of opening valve  878  is thus seen as reducing the operating length of the wraps as compression does not begin until the respective pockets are closed off from the supply of suction gas. As the volume of the pockets when they are closed off when ports  866 ,  868  are open to area  876  is less than if ports  866 ,  868  were closed, the compression ratio of the compressor is reduced. This then will eliminate or at least reduce the level of over-compression. If additional capacity reduction is required after ports  866 ,  868  have been opened, the cyclic pulsed unloading of compressor  864  may be initiated in the same manner as described above. 
     If it is initially determined that the compressor is operating either in an under-compression mode or a point between an under and over-compression mode, reducing the compression ratio thereof will only result in decreased efficiency. Therefore, under these conditions, the cyclic pulsed unloading of compressor  864  will be initiated in the same manner as described above while valve means  878  and hence ports  866 ,  868  remain in a closed position. 
     In this manner, the overall efficiency of the system may be maintained at a high level regardless of the operating conditions being encountered. It should be noted that while FIG. 46 shows the delayed suction method of capacity modulation incorporated with the embodiment of FIG. 1, it may also be utilized in conjunction with any of the other embodiments disclosed herein. Also, while the delayed suction method of capacity modulation illustrated shows only the use of a single step provided by a single set of ports, it is possible to incorporate multiple steps by providing multiple ports any number of which may be opened depending on the system operating conditions. Also, the specific valving and porting arrangement shown should be considered exemplary only as there exist many different arrangements by which capacity modulation may be achieved via a delayed suction approach. Any number of these known delayed suction approaches may be utilized in place of the arrangement shown. It should also be noted that the arrangement for controlling motor efficiency under reduced load conditions as described with reference to FIG. 45 may also be incorporated into the embodiment of FIG.  46 . 
     In FIG. 46 temperature sensor  81  monitors the temperature in fluid line  74 ′; temperature sensor  83  monitors the temperature in fluid line  74 ′; and pressure sensor  85  monitors the fluid pressure in fluid line  66 ′. The function and operation of sensors  81 ,  83  and  85  are the same as that described above for FIG.  1 . Optionally, temperature sensor  83  could monitor the fluid temperature within fluid line  70 ′, 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.