Abstract:
A compressor includes first and second scroll members, a piston and a control valve. The first scroll member includes an end plate defining a capacity modulation passage. The first and second scroll members form a suction pocket, an intermediate compression pocket and a discharge pocket. The capacity modulation passage is in communication with the first intermediate compression pocket. The piston is supported on the first scroll member and partially defines a modulation control chamber. The control valve is in communication with the control chamber and selectively provides communication between the control chamber and one of the first and second pressure sources to displace the piston between a closed position and an open position. The piston isolates the capacity modulation passage from communication with the suction pressure region when in the closed position and provides communication between the capacity modulation passage and the suction pressure region when in the open position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/909,303 filed on Oct. 21, 2010, which is a continuation of U.S. patent application Ser. No. 12/474,806 filed on May 29, 2009, which claims the benefit of U.S. Provisional Application No. 61/057,470, filed on May 30, 2008. The entire disclosure of each of the above applications is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to compressors, and more specifically to compressors having capacity modulation systems. 
       BACKGROUND 
       [0003]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0004]    Scroll compressors include a variety of capacity modulation mechanisms to vary operating capacity of a compressor. The capacity modulation mechanisms may include fluid passages extending through a scroll member to selectively provide fluid communication between compression pockets and another pressure region of the compressor. 
       SUMMARY 
       [0005]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0006]    A compressor may include a housing, a first scroll member, a second scroll member, a piston and a control valve. The housing may define a suction pressure region. The first scroll member may be supported within the housing and may include a first end plate defining a capacity modulation passage and having a first spiral wrap extending from the first end plate. The second scroll member may be supported within the housing and may include a second end plate having a second spiral wrap extending therefrom and meshingly engaged with the first spiral wrap to form a suction pocket, a first intermediate compression pocket and a discharge pocket. The capacity modulation passage may be in communication with the first intermediate compression pocket. The piston may be supported on the first scroll member and may partially define a modulation control chamber. The control valve may be in communication with the control chamber and with first and second pressure sources. The control valve may selectively provide communication between the control chamber and one of the first and second pressure sources to displace the piston between a closed position and an open position. The piston may isolate the capacity modulation passage from communication with the suction pressure region when in the closed position and may provide communication between the capacity modulation passage and the suction pressure region when in the open position. 
         [0007]    The compressor may additionally include a seal engaged with the first scroll member. The seal and the first scroll member may at least partially define a biasing chamber in communication with a second intermediate compression pocket formed by the first and second spiral wraps. The control valve may be in communication with the biasing chamber and the biasing chamber may form the first pressure source. The control valve may be in communication with the suction pressure region and the suction pressure region may form the second pressure source. The piston may include an annular body at a location axially between the first end plate and the seal. The piston may be spaced axially from the seal and at least a portion of the seal may overlap the piston in a radial direction. The first end plate may define a biasing passage extending from the second intermediate compression pocket to the biasing chamber and located radially inward relative to an inner radial surface of the annular body of the piston. 
         [0008]    The piston may be displaceable axially outward relative to the first end plate to provide the open and closed positions. The piston may include an annular body. The first scroll member may define a hub extending from the first end plate and through an inner circumferential wall of the piston. The hub may surround a discharge passage in the first end plate in communication with the discharge pocket. The piston may be forced against the first end plate to isolate the capacity modulation passage from communication with the suction pressure region when in the closed position and may be offset from the first end plate to provide communication between the capacity modulation passage and the suction pressure region when in the open position. 
         [0009]    The control valve may be operable in a pulse width modulation capacity mode to operate the compressor at an intermediate capacity between full capacity and zero capacity. The compressor may additionally include a seal engaged with the first scroll member. The seal and the first scroll member may at least partially define a biasing chamber in communication with a second intermediate compression pocket formed by the first and second spiral wraps. The piston may include an end surface facing the biasing chamber and pressurized fluid within the biasing chamber may bias the piston to the closed position. A portion of the piston may be in communication with the biasing chamber when the piston is in the open position and when the piston is in the closed position. 
         [0010]    In another arrangement, a compressor may include a housing, a first scroll member, a second scroll member, a seal, a piston and a control valve. The housing may define a suction pressure region. The first scroll member may be supported within the housing and may include a first end plate defining a capacity modulation passage and a biasing passage and having a first spiral wrap extending from the first end plate. The second scroll member may be supported within the housing and may include a second end plate having a second spiral wrap extending therefrom and meshingly engaged with the first spiral wrap to form a suction pocket, a first intermediate compression pocket, a second intermediate compression pocket and a discharge pocket. The capacity modulation passage may be in communication with the first intermediate compression pocket and the biasing passage may be in communication with the second intermediate compression pocket. The seal may be engaged with the first scroll member. The seal and the first scroll member may at least partially define a biasing chamber in communication with the second intermediate compression pocket via the biasing passage. The piston may be supported on the first scroll member and may partially define a modulation control chamber. The control valve may be in communication with the control chamber and with the suction pressure region and the biasing chamber. The control valve may selectively provide communication between the control chamber and one of the suction pressure region and the biasing chamber to displace the piston between a closed position and an open position. The piston may isolate the capacity modulation passage from communication with the suction pressure region when in the closed position and may provide communication between the capacity modulation passage and the suction pressure region when in the open position. 
         [0011]    The piston may include an end surface facing the biasing chamber. Pressurized fluid within the biasing chamber may bias the piston to the closed position. 
         [0012]    In another arrangement, a compressor may include a housing, a first scroll member, a second scroll member, a seal, a piston and a control valve. The housing may define a suction pressure region. The first scroll member may be supported within the housing and may include a first end plate defining a capacity modulation passage and a biasing passage and having a first spiral wrap extending from the first end plate. The second scroll member may be supported within the housing and may include a second end plate having a second spiral wrap extending therefrom and meshingly engaged with the first spiral wrap to form a suction pocket, a first intermediate compression pocket, a second intermediate compression pocket and a discharge pocket. The capacity modulation passage may be in communication with the first intermediate compression pocket and the biasing passage may be in communication with the second intermediate compression pocket. The seal may be engaged with the first scroll member. The seal and the first scroll member may at least partially define a biasing chamber in communication with the second intermediate compression pocket via the biasing passage. The piston may be supported on the first scroll member and may partially define a modulation control chamber. The piston may include an end surface facing and in communication with the biasing chamber. The control valve may be in communication with the control chamber and with first and second pressure sources and may selectively provide communication between said control chamber and one of said first and second pressure sources to displace said piston between a closed position and an open position, said piston isolating said capacity modulation passage from communication with said suction pressure region when in the closed position and provide communication between the capacity modulation passage and the suction pressure region when in the open position. 
         [0013]    A portion of the piston may be in communication with the biasing chamber when the piston is in the open position and when the piston is in the closed position. The control valve may be operable in a pulse width modulation capacity mode to operate the compressor at an intermediate capacity between full capacity and zero capacity. One of the first and second pressure sources may include the suction pressure region of the compressor. 
         [0014]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0015]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0016]      FIG. 1  is a section view of a compressor according to the present disclosure; 
           [0017]      FIG. 2  is a plan view of a non-orbiting scroll member of the compressor of  FIG. 1 ; 
           [0018]      FIG. 3  is a section view of a non-orbiting scroll, seal assembly, and modulation system of the compressor of  FIG. 1 ; 
           [0019]      FIG. 4  is an additional section view of the non-orbiting scroll, seal assembly, and modulation system of  FIG. 3 ; 
           [0020]      FIG. 5  is a section view of an alternate non-orbiting scroll, seal assembly, and modulation system according to the present disclosure; 
           [0021]      FIG. 6  is an additional section view of the non-orbiting scroll, seal assembly, and modulation system of  FIG. 5 ; 
           [0022]      FIG. 7  is a section view of an alternate non-orbiting scroll, seal assembly, and modulation system according to the present disclosure; 
           [0023]      FIG. 8  is an additional section view of the non-orbiting scroll, seal assembly, and modulation system of  FIG. 7 ; 
           [0024]      FIG. 9  is a section view of an alternate non-orbiting scroll, seal assembly, and modulation system according to the present disclosure; 
           [0025]      FIG. 10  is an additional section view of the non-orbiting scroll, seal assembly, and modulation system of  FIG. 9 ; 
           [0026]      FIG. 11  is a fragmentary section view of an alternate compressor according to the present disclosure; 
           [0027]      FIG. 12  is an additional fragmentary section view of the compressor of  FIG. 11 ; 
           [0028]      FIG. 13  is a fragmentary section view of an alternate compressor according to the present disclosure; 
           [0029]      FIG. 14  is an additional fragmentary section view of the compressor of  FIG. 13 ; and 
           [0030]      FIG. 15  is a plan view of the main bearing housing of the compressor of  FIG. 13 . 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
         [0032]    The present teachings are suitable for incorporation in many different types of scroll and rotary compressors, including hermetic machines, open drive machines and non-hermetic machines. For exemplary purposes, a compressor  10  is shown as a hermetic scroll refrigerant-compressor of the low-side type, i.e., where the motor and compressor are cooled by suction gas in the hermetic shell, as illustrated in the vertical section shown in  FIG. 1 . 
         [0033]    With reference to  FIG. 1 , compressor  10  may include a hermetic shell assembly  12 , a main bearing housing assembly  14 , a motor assembly  16 , a compression mechanism  18 , a seal assembly  20 , a refrigerant discharge fitting  22 , a discharge valve assembly  24 , a suction gas inlet fitting  26 , and a modulation assembly  27 . Shell assembly  12  may house main bearing housing assembly  14 , motor assembly  16 , and compression mechanism  18 . 
         [0034]    Shell assembly  12  may generally form a compressor housing and may include a cylindrical shell  28 , an end cap  30  at the upper end thereof, a transversely extending partition  32 , and a base  34  at a lower end thereof. End cap  30  and partition  32  may generally define a discharge chamber  36 . Discharge chamber  36  may generally form a discharge muffler for compressor  10 . Refrigerant discharge fitting  22  may be attached to shell assembly  12  at opening  38  in end cap  30 . Discharge valve assembly  24  may be located within discharge fitting  22  and may generally prevent a reverse flow condition. Suction gas inlet fitting  26  may be attached to shell assembly  12  at opening  40 . Partition  32  may include a discharge passage  46  therethrough providing communication between compression mechanism  18  and discharge chamber  36 . 
         [0035]    Main bearing housing assembly  14  may be affixed to shell  28  at a plurality of points in any desirable manner, such as staking. Main bearing housing assembly  14  may include a main bearing housing  52 , a first bearing  54  disposed therein, bushings  55 , and fasteners  57 . Main bearing housing  52  may include a central body portion  56  having a series of arms  58  extending radially outwardly therefrom. Central body portion  56  may include first and second portions  60 ,  62  having an opening  64  extending therethrough. Second portion  62  may house first bearing  54  therein. First portion  60  may define an annular flat thrust bearing surface  66  on an axial end surface thereof. Arm  58  may include apertures  70  extending therethrough and receiving fasteners  57 . 
         [0036]    Motor assembly  16  may generally include a motor stator  76 , a rotor  78 , and a drive shaft  80 . Windings  82  may pass through stator  76 . Motor stator  76  may be press fit into shell  28 . Drive shaft  80  may be rotatably driven by rotor  78 . Rotor  78  may be press fit on drive shaft  80 . Drive shaft  80  may include an eccentric crank pin  84  having a flat  86  thereon. 
         [0037]    Compression mechanism  18  may generally include an orbiting scroll  104  and a non-orbiting scroll  106 . Orbiting scroll  104  may include an end plate  108  having a spiral vane or wrap  110  on the upper surface thereof and an annular flat thrust surface  112  on the lower surface. Thrust surface  112  may interface with annular flat thrust bearing surface  66  on main bearing housing  52 . A cylindrical hub  114  may project downwardly from thrust surface  112  and may have a drive bushing  116  rotatively disposed therein. Drive bushing  116  may include an inner bore in which crank pin  84  is drivingly disposed. Crank pin flat  86  may drivingly engage a flat surface in a portion of the inner bore of drive bushing  116  to provide a radially compliant driving arrangement. An Oldham coupling  117  may be engaged with the orbiting and non-orbiting scrolls  104 ,  106  to prevent relative rotation therebetween. 
         [0038]    With additional reference to  FIGS. 2-4 , non-orbiting scroll  106  may include an end plate  118  having a spiral wrap  120  on a lower surface thereof, a series of radially outwardly extending flanged portions  121 , and an annular ring  123 . Spiral wrap  120  may form a meshing engagement with wrap  110  of orbiting scroll  104 , thereby creating an inlet pocket  122 , intermediate pockets  124 ,  126 ,  128 ,  130 , and an outlet pocket  132 . Non-orbiting scroll  106  may be axially displaceable relative to main bearing housing assembly  14 , shell assembly  12 , and orbiting scroll  104 . Non-orbiting scroll  106  may include a discharge passage  134  in communication with outlet pocket  132  and upwardly open recess  136  which may be in fluid communication with discharge chamber  36  via discharge passage  46  in partition  32 . 
         [0039]    Flanged portions  121  may include openings  137  therethrough. Opening  137  may receive bushings  55  therein and bushings  55  may receive fasteners  57 . Fasteners  57  may be engaged with main bearing housing  52  and bushings  55  may generally form a guide for axial displacement of non-orbiting scroll  106 . Fasteners  57  may additionally prevent rotation of non-orbiting scroll  106  relative to main bearing housing assembly  14 . 
         [0040]    Non-orbiting scroll  106  may include an annular recess  138  in the upper surface thereof defined by parallel coaxial inner and outer side walls  140 ,  142 . Annular ring  123  may be disposed within annular recess  138  and may separate annular recess  138  into first and second annular recesses  144 ,  145 . First and second annular recesses  144 ,  145  may be isolated from one another. First annular recess  144  may provide for axial biasing of non-orbiting scroll  106  relative to orbiting scroll  104 , as discussed below. More specifically, a passage  146  may extend through end plate  118  of non-orbiting scroll  106 , placing first annular recess  144  in fluid communication with one of intermediate pockets  124 ,  126 ,  128 ,  130 . While passage  146  is shown extending into intermediate pocket  126 , it is understood that passage  146  may alternatively be placed in communication with any of the other intermediate pockets  124 ,  128 ,  130 . 
         [0041]    Additional passages  148 ,  150  may extend through end plate  118 , placing second annular recess  145  in communication with two of intermediate fluid pockets  124 ,  128 ,  130 . Second annular recess  145  may be in communication with different ones of intermediate fluid pockets  124 ,  126 ,  128 ,  130  than first annular recess  144 . More specifically, second annular recess  145  may be in communication with intermediate fluid pockets  124 ,  126 ,  128 ,  130  located radially outwardly relative to the intermediate fluid pocket  124 ,  126 ,  128 ,  130  in communication with the first annular recess  144 . Therefore, first annular recess  144  may operate at a pressure greater than an operating pressure of second annular recess  145 . First and second radial passages  152 ,  154  may extend into second annular recess  145  and may cooperate with modulation assembly  27  as discussed below. 
         [0042]    Seal assembly  20  may include a floating seal located within first annular recess  144 . Seal assembly  20  may be axially displaceable relative to shell assembly  12  and non-orbiting scroll  106  to provide for axial displacement of non-orbiting scroll  106  while maintaining a sealed engagement with partition  32  to isolate discharge and suction pressure regions of compressor  10  from one another. More specifically, pressure within first annular recess  144  may urge seal assembly  20  into engagement with partition  32  during normal compressor operation. 
         [0043]    Modulation assembly  27  may include a piston assembly  156 , a valve assembly  158 , and a biasing member  160 . The piston assembly  156  may include an annular piston  162  and first and second annular seals  164 ,  166 . Annular piston  162  may be located in second annular recess  145  and first and second annular seals  164 ,  166  may be engaged with inner and outer side walls  140 ,  142  to separate second annular recess  145  into first and second portions  168 ,  170  that are isolated from one another. First portion  168  may be in communication with first radial passage  152  and second portion  170  may be in communication with second radial passage  154 . Valve assembly  158  may include a valve member  172  in communication with a pressure source  174  and with first radial passage  152 , and therefore first portion  168 . Biasing member  160  may include a spring and may be located in second portion  170  and engaged with annular piston  162 . 
         [0044]    Annular piston  162  may be displaceable between first and second positions. In the first position ( FIG. 3 ), annular piston  162  may seal passages  148 ,  150  from communication with second portion  170  of second annular recess  145 . In the second position ( FIG. 4 ), annular piston  162  may be displaced from passages  148 ,  150 , providing communication between passages  148 ,  150  and second portion  170  of second annular recess  145 . Therefore, when annular piston  162  is in the second position, passages  148 ,  150  may be in communication with a suction pressure region of compressor  10  via second radial passage  154  providing a reduced capacity operating mode for compressor  10 . 
         [0045]    Pressure source  174  may include a pressure that is greater than an operating pressure of intermediate pockets  124 ,  126 ,  128 ,  130 . Valve member  172  may provide communication between pressure source  174  and first portion  168  of second annular recess  145  to displace annular piston  162  to the first position. Valve member  172  may prevent communication between pressure source  174  and first portion  168  of second annular recess  145  to displace annular piston  162  to the second position. Valve member  172  may additionally vent first portion  168  to the suction pressure region of compressor  10  to displace annular piston  162  to the second position. Biasing member  160  may generally bias annular piston  162  toward the second position. 
         [0046]    With reference to  FIGS. 5 and 6 , an alternate non-orbiting scroll  306  and modulation assembly  227  are shown. Non-orbiting scroll  306  may be generally similar to non-orbiting scroll  106 . Therefore, it is understood that the description of non-orbiting scroll  106  applies equally to non-orbiting scroll  306  with the exceptions indicated below. Further, it is understood that non-orbiting scroll  306  and modulation assembly  227  may be incorporated into a compressor such as compressor  10  in place of non-orbiting scroll  106  and modulation assembly  27 . 
         [0047]    Non-orbiting scroll  306  may include a passage  376  extending between and providing communication between first annular recess  344  and first portion  368  of second annular recess  345 . Modulation assembly  227  may include a valve assembly  358  having a valve member  372  located in radial passage  352 . Valve member  372  may be displaceable between first and second positions to displace annular piston  362  between first and second positions. The first and second positions of annular piston  362  and corresponding capacity reduction may be generally similar to that discussed above for modulation assembly  27 . Therefore, for simplicity, the description will not be repeated with the understanding that the above description applies equally to the modulation assembly  227 . 
         [0048]    Valve member  372  may provide communication between the first and second annular recesses  344 ,  345  when valve member  372  is in the first position ( FIG. 5 ). Since first annular recess  344  operates at a higher pressure than second annular recess  345 , annular piston  362  may be displaced (or held) in the first position. Valve member  372  may be displaced to the second position and vent first portion  368  of second annular recess  345  to suction pressure in order to displace annual piston  362  to the second position ( FIG. 6 ). In the second position, valve member  372  may seal passage  376  to isolate first and second annular recesses  344 ,  345  from one another. When first and second annular recesses  344 ,  345  are isolated from one another, biasing member  360  may urge annular piston  362  to the second position where passages  348 ,  350  are in communication with a suction pressure region. 
         [0049]    With reference to  FIGS. 7 and 8 , an alternate non-orbiting scroll  506  and modulation assembly  427  are shown. Non-orbiting scroll  506  may be generally similar to non-orbiting scroll  106 . Therefore, it is understood that the description of non-orbiting scroll  106  applies equally to non-orbiting scroll  506  with the exceptions indicated below. Further, it is understood that non-orbiting scroll  506  and modulation assembly  427  may be incorporated into a compressor such as compressor  10  in place of non-orbiting scroll  106  and modulation assembly  27 . 
         [0050]    Non-orbiting scroll  506  may include passages  576  extending through annular ring  523  and providing communication between first annular recess  544  and first portion  568  of second annular recess  545 . Second portion  570  of second annular recess  545  may be isolated from intermediate pockets. Radial passage  552  may be in communication with a suction pressure region and radial passage  554  may be in communication with modulation assembly  427 . Modulation assembly  427  may be generally similar to modulation assembly  27 . Therefore, it is understood that the description of modulation assembly  27  applies to modulation assembly  427  with the exceptions noted below. 
         [0051]    Modulation assembly  427  may include a valve assembly  558  including a valve member  572  in communication with radial passage  554 , a pressure source  574  and the suction pressure region. Pressure source  574  may include a pressure that is greater than an operating pressure within first annular recess  544 . Valve member  572  may provide communication between pressure source  574  and second portion  570  of second annular recess  545  to bias annular piston  562  into a first position ( FIG. 7 ). Annular piston  562  may seal passage  576  when in the first position to prevent fluid communication between first annular recess  544  and the first portion  568  of second annular recess  545  when in the first position. 
         [0052]    Valve member  572  may vent second portion  570  of second annular recess  545  to a suction pressure region and biasing member  560  may act on annular piston  562  to displace annular piston  562  to a second position ( FIG. 8 ). Annular piston  562  may be displaced from passage  576  when in the second position. Passage  576  may therefore provide communication between first annular recess  544  and a suction pressure region when annular piston  562  is in the second position. Providing communication between the first annular recess  544  and the suction pressure region may remove the axial biasing force that normally urges non-orbiting scroll  506  toward an orbiting scroll (not shown) providing a reduced compressor operating capacity by providing clearance between the non-orbiting scroll end plate and the orbiting scroll wrap, as well as the non-orbiting scroll wrap and the orbiting scroll end plate. The capacity is reduced to zero when the axial biasing force is removed and the axial clearance exists between the orbiting and non-orbiting scrolls. In order to modulate the compressor to a desired capacity between about 0% to 100%, the piston may be actuated in a pulse width modulation manner to achieve a desired capacity. The scrolls will switch between a generally sealed state and an un-sealed state to provide a desired output capacity. 
         [0053]    With reference to  FIGS. 9 and 10 , an alternate non-orbiting scroll  706  and modulation assembly  627  are shown. Non-orbiting scroll  706  may be generally similar to non-orbiting scroll  106 . Therefore, it is understood that the description of non-orbiting scroll  106  applies equally to non-orbiting scroll  706  with the exceptions indicated below. Further, it is understood that non-orbiting scroll  706  and modulation assembly  627  may be incorporated into a compressor such as compressor  10  in place of non-orbiting scroll  106  and modulation assembly  27 . 
         [0054]    Non-orbiting scroll  706  may include a radial passage  754  extending between and in communication with second portion  770  of second annular recess  745  and a discharge pressure region (rather than a suction pressure region shown in  FIGS. 3 and 4  for second radial passage  154 ). Pressure source  774  may include a pressure that is greater than an operating pressure of second portion  770  of second annular recess  745 . Valve member  772  may provide communication between pressure source  774  and first portion  768  of second annular recess  745  to displace annular piston  762  to the first position ( FIG. 9 ). 
         [0055]    Valve member  772  may prevent communication between pressure source  774  and first portion  768  of second annular recess  745  to displace annular piston  762  to the second position ( FIG. 10 ). Valve member  772  may additionally vent first portion  768  to a suction pressure region to displace annular piston  762  to the second position. Biasing member  760  may generally bias annular piston  762  toward the second position. The second position of annular piston  762  may provide communication between second portion  770  of second annular recess  745 , and therefore passages  748 ,  750 , and a discharge pressure region to provide a change in a compression volume ratio for the compressor. 
         [0056]    With reference to  FIGS. 11 and 12 , an alternate main bearing housing assembly  814 , compression mechanism  818 , and a capacity adjustment assembly  827  are illustrated. Capacity adjustment assembly  827  may include a modulation assembly. Main bearing housing assembly  814  and compression mechanism  818  may be generally similar to main bearing housing assembly  14  and compression mechanism  18 . Therefore, for simplicity, it is understood that the description of main bearing housing assembly  14  and compression mechanism  18  above applies equally to main bearing housing assembly  814  and compression mechanism  818  with the exceptions indicated below. Further, it is understood that main bearing housing assembly  814 , compression mechanism  818 , and capacity adjustment assembly  827  may be incorporated into a compressor similar to compressor  10  in place of main bearing housing assembly  14 , compression mechanism  18 , and modulation assembly  27 . 
         [0057]    Main bearing housing assembly  814  may include main bearing housing  852 . Main bearing housing  852  may include an annular passage  853  that forms an annular recess extending into thrust bearing surface  866 . First radial passages  952  may extend radially through first portion  860  and into annular passage  853 , providing communication between annular passage  853  and a suction pressure region. A second radial passage  954  may extend radially through first portion  860  and into annular passage  853  and may be in communication with capacity adjustment assembly  827 , as discussed below. 
         [0058]    Compression mechanism  818  may include orbiting scroll  904  and non-orbiting scroll  906 . Orbiting scroll  904  may include first and second passages  948 ,  950  extending through end plate  908  and providing communication between two of intermediate fluid pockets  924 ,  926 ,  928 ,  930  and annular passage  853 . Non-orbiting scroll  906  may include a single annular recess  944  having seal assembly  920  disposed therein. Passage  946  may provide communication between annular recess  944  and one of intermediate fluid pockets  924 ,  926 ,  928 ,  930 . The intermediate fluid pocket  924 ,  926 ,  928 ,  930  in communication annular recess  944  may be different than the two of intermediate fluid pockets  924 ,  926 ,  928 ,  930  in communication with annular passage  853 . More specifically, the intermediate fluid pocket  924 ,  926 ,  928 ,  930  in communication annular recess  944  may be located radially inwardly relative to and operate at a pressure greater than the two of intermediate fluid pockets  924 ,  926 ,  928 ,  930  in communication with annular passage  853 . 
         [0059]    Capacity adjustment assembly  827  may include a piston assembly  956 , a valve assembly  958 , and a biasing member  960 . The piston assembly  956  may include an annular piston  962  located in annular passage  853 . Annular piston  962  may be displaceable between first and second positions. In the first position ( FIG. 11 ), annular piston  962  may isolate first and second passages  948 ,  950  from first radial passage  952 . In the second position, ( FIG. 12 ), annular piston  962  may be displaced to provide communication between first and second passages  948 ,  950  and first radial passage  952 . In the second position, first and second passages  948 ,  950  may be in communication with a suction pressure region via first radial passage  952  providing a reduced capacity operating mode. In both the first and second positions, annular piston  962  may isolate first and second radial passages  952 ,  954  from one another and may additionally isolate first and second passages  948 ,  950  from second radial passage  954 . 
         [0060]    Valve assembly  958  may include a valve member  972  in communication with a pressure source  974  and with second radial passage  954 . Biasing member  960  may include a spring and may be located in annular passage  853  and engaged with annular piston  962 . Valve assembly  958  may displace annular piston  962  between the first and second positions. Valve member  972  may provide communication between pressure source  974  and second radial passage  954  to bias annular piston to the first position. The pressure source may include a pressure that is greater than an operating pressure of intermediate pockets  924 ,  926 ,  928 ,  930 . Valve member  972  may prevent communication between pressure source  974  and second radial passage  954  and may vent second radial passage to a suction pressure region to allow annular piston  962  to be displaced to the second position. Biasing member  960  may generally bias annular piston  962  to the second position when second radial passage  954  is vented to suction pressure. 
         [0061]    With reference to  FIGS. 13-15 , an alternate main bearing housing assembly  1014 , compression mechanism  1018  and a capacity adjustment assembly  1027  are illustrated. Capacity adjustment assembly  1027  may include a vapor injection assembly. Main bearing housing assembly  1014  and compression mechanism  1018  may be generally similar to main bearing housing assembly  14  and compression mechanism  18 . Therefore, for simplicity, it is understood that the description of main bearing housing assembly  14  and compression mechanism  18  above applies equally to main bearing housing assembly  1014  and compression mechanism  1018  with the exceptions indicated below. Further, it is understood that main bearing housing assembly  1014 , compression mechanism  1018 , and capacity adjustment assembly  1027  may be incorporated into a compressor similar to compressor  10  in place of main bearing housing assembly  14 , compression mechanism  18 , and modulation assembly  27 . 
         [0062]    Main bearing housing assembly  1014  may include main bearing housing  1052 . Main bearing housing  1052  may include first and second recesses  1053 ,  1054  extending axially into thrust bearing surface  1066 . A first passage  1152  may extend through main bearing housing  1052  radially inward from an actuation control port  1154  to first recess  1053  and a second passage  1153  may extend through main bearing housing  1052  radially inward from actuation control port  1154  to second recess  1054 . A third passage  1155  may extend through main bearing housing  1052  radially inward from an injection port  1158  to first recess  1053  and a fourth passage  1157  may extend through main bearing housing  1052  radially inward from injection port  1158  to second recess  1054 . 
         [0063]    Compression mechanism  1018  may include orbiting scroll  1104  and non-orbiting scroll  1106 . Orbiting scroll  1104  may include first and second passages  1148 ,  1150  extending through end plate  1108 . First passage  1148  may provide communication between one of intermediate fluid pockets  1124 ,  1126 ,  1128 ,  1130 ,  1132  and first recess  1053 . Second passage  1150  may provide communication between another one of intermediate fluid pockets  1124 ,  1126 ,  1128 ,  1130 ,  1132  and second recess  1054 . Non-orbiting scroll  1106  may include a single annular recess  1144  having seal assembly  1120  disposed therein. Passage  1146  may provide communication between annular recess  1144  and one of intermediate fluid pockets  1124 ,  1126 ,  1128 ,  1130 ,  1132 . 
         [0064]    The intermediate fluid pocket  1124 ,  1126 ,  1128 ,  1130 ,  1132  in communication annular recess  1144  may be different than the two of intermediate fluid pockets  1124 ,  1126 ,  1128 ,  1130 ,  1132  in communication with first and second recesses  1053 ,  1054 . More specifically, the intermediate fluid pocket  1124 ,  1126 ,  1128 ,  1130 ,  1132  in communication annular recess  1144  may be located radially inwardly relative to and operate at a pressure greater than the two of intermediate fluid pockets  1124 ,  1126 ,  1128 ,  1130 ,  1132  in communication with first and second recesses  1053 ,  1054 . 
         [0065]    Capacity adjustment assembly  1027  may include a piston assembly  1156 , a vapor source  1159 , and an actuation mechanism  1160 . The piston assembly  1156  may include first and second pistons  1162 ,  1163 . First piston  1162  may be located in first recess  1053  and second piston  1163  may be located in second recess  1054 . Actuation mechanism  1160  may include a valve in communication with first and second pressure sources and actuation control port  1154 . The first pressure source may include a fluid operating at a pressure greater than the operating pressure provided by first and second passages  1148 ,  1150 , such as discharge pressure. The second pressure source may include a fluid operating at a pressure less than the operating pressure provided by first and second passages  1148 ,  1150 , such as suction pressure. Actuation mechanism  1160  may selectively displace first and second pistons  1162 ,  1163  from a first position ( FIG. 13 ) to a second position ( FIG. 14 ). 
         [0066]    First piston  1162  may isolate first passage  1148  from communication with actuation control port  1154  and second piston  1163  may isolate second passage  1150  from communication with actuation control port  1154  when in the first and second positions. Additionally, first and second pistons  1162 ,  1163  may isolate actuation control port  1154  from communication with injection port  1158  when in the first and second positions. 
         [0067]    During operation, the first and second pistons  1162 ,  1163  may be in the first position during normal compressor operation. Normal compressor operation may include a full operating capacity for the compressor. First and second pistons  1162 ,  1163  may be in the first position ( FIG. 13 ) when actuation mechanism  1160  provides the first pressure source to first and second recesses  1053 ,  1054  to isolate first and second passages  1148 ,  1150  from communication with vapor source  1159 . When increased capacity is desired, first and second pistons  1162 ,  1163  may be displaced to the second position ( FIG. 14 ) by placing first and second recesses  1053 ,  1054  in communication with the second pressure source. In the second position, vapor source  1159  injects vapor into the compression mechanism  1018  via first and second passages  1148 ,  1150 . 
         [0068]    The terms “first”, “second”, etc. are used throughout the description for clarity only and are not intended to limit similar terms in the claims.