Abstract:
A compressor includes orbiting and non-orbiting scroll members meshingly engaged to form a series of compression pockets, including first pockets when the orbiting scroll member is in a first position. A first porting in the non-orbiting scroll member communicates with the first pockets during a portion of a compression cycle. The first pockets include a set of radially outermost pockets located radially inward relative to the first porting and isolated from communication with the first porting during the compression cycle. The first porting is aligned with a spiral wrap of the orbiting scroll member at a location radially outward from and directly adjacent the first pockets when the orbiting scroll member is in the first position. Additional porting communicates with each of the compression pockets located radially outward relative to the first pockets when the orbiting scroll member is in the first position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/057,401, filed on May 30, 2008. The entire disclosure of the above application 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 and is not necessarily prior art. 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 compression. 
       SUMMARY 
       [0004]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0005]    A compressor may include a housing and a non-orbiting scroll member supported within the housing and including a first end plate and a first spiral wrap extending from the first end plate. The orbiting scroll member may be supported within the housing and include a second end plate having a second spiral wrap extending therefrom and meshingly engaged with the first spiral wrap to form a series of compression pockets. A first porting may extend through the first end plate and is located radially outward relative to a radially outer surface of the first spiral wrap at least five hundred and forty degrees inward along the first spiral wrap from an outer end thereof. The first porting may be in communication with a first pocket of the series of compression pockets during a portion of a compression cycle of the orbiting and non-orbiting scroll members. The first and second spiral wraps may abut one another to define first modulated capacity pockets when the orbiting scroll member is in a first position. The first modulated capacity pockets may include a set of radially outermost compression pockets located radially inward relative to the first porting and isolated from communication with the first porting during an entirety of the compression cycle. The first porting may align with the second spiral wrap at a location radially outward from and directly adjacent the first modulated capacity pockets when the orbiting scroll member is in the first position. The additional porting may extend through the first end plate and in communication with each of the compression pockets located radially outward relative to the first modulated capacity pockets when the orbiting scroll member is in the first position. 
         [0006]    The compressor porting may have an angular extent of at least twenty degrees. 
         [0007]    The compressor may include a first angular position, which is defined by the abutting of the first and second spiral wrap, defining a starting location of the first porting. 
         [0008]    The compressor may include a second porting extending through the first end plate and located radially inward relative to a radially inner surface of the first spiral wrap at least three hundred and sixty degrees inward along the first spiral from the outer end thereof. The second porting may be in communication with a second of the compression pockets during a portion of the compression cycle. The first and second spiral wraps may abut one another to define second modulated capacity pockets when the orbiting scroll member is in a second position subsequent to the first position. The second modulated capacity pockets including a set of radially outermost compression pockets located radially inward relative to the first and second porting and isolated from communication with the first and second porting during an entirety of the compression cycle. 
         [0009]    The compressor second porting may have an angular extent of at least twenty degrees. 
         [0010]    The compressor second porting may align with the second spiral wrap at a location radially outward from and directly adjacent the second set of radially outermost pockets when the orbiting scroll member is in the second position. 
         [0011]    The compressor second porting may be in communication with the first modulated capacity pockets when the orbiting scroll member is in the first position. 
         [0012]    The compressor second modulated capacity pockets may correspond to the first modulated capacity pockets after displacement of the orbiting scroll member from the first position to the second position. 
         [0013]    The compressor&#39;s additional porting may include a third porting located radially outward relative to the radially outer surface of the first spiral wrap less than five hundred and forty degrees inward along the first spiral from the outer end thereof. 
         [0014]    The compressor&#39;s additional porting may include a fourth porting located radially inward relative to the radially inner surface of the first spiral wrap less than three hundred and sixty degrees inward along the first spiral from the outer end thereof. 
         [0015]    The compressor pressure in the first porting may continuously increasing during the compression cycle. 
         [0016]    The compressor may include a second spiral wrap overlies an entirety of the first porting when the orbiting scroll member is in the first position. 
         [0017]    The compressor first porting may be isolated from communication with the compression pockets by the second spiral wrap when the orbiting scroll member is in the first position. 
         [0018]    The compressor first porting may include a continuous aperture. 
         [0019]    The compressor porting may include a series of discrete apertures. 
         [0020]    The compressor may comprise a valve member in communication with the first porting and the additional porting to selectively provide communication between the compression pockets located radially outward from the first modulated capacity pockets and a bypass location external to the compression pockets. 
         [0021]    The compressor bypass location may include a suction pressure region of the compressor. 
         [0022]    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 
         [0023]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0024]      FIG. 1  is a section view of a compressor according to the present disclosure; 
           [0025]      FIG. 2  is a plan view of a non-orbiting scroll member of the compressor of  FIG. 1 ; 
           [0026]      FIG. 3  is a section view of a non-orbiting scroll, seal assembly, and modulation system of the compressor of  FIG. 1 ; 
           [0027]      FIG. 4  is an additional section view of the non-orbiting scroll, seal assembly, and modulation system of  FIG. 3 ; 
           [0028]      FIG. 5  is a schematic illustration of the orbiting scroll member of  FIG. 1  in one orientation; 
           [0029]      FIG. 6  is a schematic illustration of the orbiting scroll member of  FIG. 1  in another orientation; 
           [0030]      FIG. 7  is a schematic illustration of the orbiting scroll member of  FIG. 1  in another orientation; 
           [0031]      FIG. 8  is a schematic illustration of the orbiting scroll member of  FIG. 1  in another orientation; 
           [0032]      FIG. 9  is a schematic illustration of the orbiting scroll member of  FIG. 1  in another orientation; 
           [0033]      FIG. 10  is a schematic illustration of the orbiting scroll member of  FIG. 1  in another orientation; 
           [0034]      FIG. 11  is a schematic illustration of the orbiting scroll member of  FIG. 1  in another orientation; and 
           [0035]      FIG. 12  is a schematic illustration of an alternate compression mechanism according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION  
       [0036]    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. 
         [0037]    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 . 
         [0038]    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 . 
         [0039]    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 . 
         [0040]    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 . 
         [0041]    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. 
         [0042]    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  11   7  may be engaged with the orbiting and non-orbiting scrolls  104 ,  106  to prevent relative rotation therebetween. 
         [0043]    With additional reference to  FIGS. 2-5 , 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 a series of pockets. The pockets created by spiral wraps  110 ,  120  may change throughout a compression cycle of compression mechanism  18 , as discussed below. End plate  118  may include a first and second porting  148 ,  149  therein, as discussed below. End plate  118  may include first and second porting  148 ,  149  alone or may additionally include a third and fourth porting  150 ,  151 . 
         [0044]    Second porting  149  may be located radially inward relative to first porting  148  and fourth porting  151  may be located radially inward relative to third porting  150 . More specifically, fourth porting  151  may be located radially inward relative to a radially inner surface of spiral wrap  120  and at least three hundred and sixty degrees inward along spiral wrap  120  from an outer end  119  of spiral wrap  120 . Second porting  149  may be located radially outward relative to a radially outer surface of spiral wrap  120  and at least three hundred and sixty degrees inward along spiral wrap  120  from the location  110 - 2  where an outer end  110 - 1  of spiral wrap  110  of orbiting scroll  104  contacts intermittently during a compression cycle, or at least five hundred and forty degrees inward along spiral wrap  120  from outer end  119 . Third porting  150  may be located radially inward along spiral wrap  120  relative to a radially inner surface of spiral wrap  120  and less than three hundred and sixty degrees inward from outer end  119  of spiral wrap  120 . First porting  148  may be located radially outward relative to a radially outer surface of spiral wrap  120  and less than three hundred and sixty degrees inward from location  110 - 2 , or less than five hundred and forty degrees inward along spiral wrap  120  from outer end  119 . 
         [0045]      FIG. 5  illustrates first, second, third, fourth, fifth, and sixth pockets  122 - 1 ,  124 - 1 ,  126 - 1 ,  128 - 1 ,  130 - 1 ,  132 - 1  formed by spiral wraps  110 ,  120 . More specifically,  FIG. 5  illustrates the start of the compression cycle for first and second pockets  122 - 1 ,  124 - 1 . First, second, third and fourth pockets  122 - 1 ,  124 - 1 ,  126 - 1 ,  128 - 1  may form compression pockets and fifth and sixth pockets  130 - 1 ,  132 - 1  may form discharge pockets in communication with a discharge passage  134  in non-orbiting scroll  106 . A recess  176  in orbiting scroll  104  may provide communication between fifth pocket  130 - 1  and discharge passage  134 . 
         [0046]      FIG. 6  illustrates the orbiting scroll  104  in a first position. The first position may generally correspond to approximately eighty degrees of drive shaft rotation relative to  FIG. 5 . First, second, third, fourth, fifth, and sixth pockets  122 - 2 ,  124 - 2 ,  126 - 2 ,  128 - 2 ,  130 - 2 ,  132 - 2  may be formed by the spiral wraps  110 ,  120  when the orbiting scroll  104  is in the first position. In the first position, first, second, third and fourth pockets  122 - 2 ,  124 - 2 ,  126 - 2 ,  128 - 2  may form compression pockets and fifth and sixth pockets  130 - 2 ,  132 - 2  may form discharge pockets. Third and fourth pockets  126 - 2 ,  128 - 2  may form first modulated capacity pockets for compression mechanism  18  relative to second porting  149 . 
         [0047]    The first modulated capacity pockets may generally be defined as the radially outermost compression pockets that are disposed radially inward relative to second porting  149  and isolated from second porting  149  from the time the first modulated capacity pockets are formed until the volume in the first modulated capacity pockets is discharged through discharge passage  134 . Thus, the volume in the first modulated capacity pockets may be isolated from second porting  149  during a remainder of a compression cycle associated therewith, as discussed below. The volume of the first modulated capacity pockets may be at a maximum volume when orbiting scroll  104  is in the first position and may be continuously compressed until being discharged through discharge passage  134 . 
         [0048]    Spiral wrap  110  of orbiting scroll  104  may abut an outer radial surface of spiral wrap  120  at a first location  125 - 2  and may abut the inner radial surface of spiral wrap  120  at a second location  127 - 2  generally opposite the first location  125 - 2  when orbiting scroll  104  is in the first position. Second porting  149  may extend at least twenty degrees along spiral wrap  110  in a rotational direction (R) of drive shaft  80  starting at a first angular position corresponding to the first location  125 - 2  when orbiting scroll  104  is in the first position. Second porting  149  may be sealed by spiral wrap  110  when orbiting scroll  104  is in the first position. A portion of fourth porting  151  may be in communication with third and fourth pockets  126 - 2 ,  128 - 2  when orbiting scroll  104  is in the first position. First porting  148  may be in communication with first pocket  122 - 2  and third porting  150  may be in communication with second pocket  124 - 2  when orbiting scroll  104  is in the first position. 
         [0049]      FIG. 7  illustrates the orbiting scroll  104  in a second position. The second position may generally correspond to approximately one hundred degrees of drive shaft rotation relative to  FIG. 5 . First, second, third, fourth, fifth, and sixth pockets  122 - 3 ,  124 - 3 ,  126 - 3 ,  128 - 3 ,  130 - 3 ,  132 - 3  may be formed by the spiral wraps  110 ,  120  when the orbiting scroll  104  is in the second position. In the second position, first, second, third and fourth pockets  122 - 3 ,  124 - 3 ,  126 - 3 ,  128 - 3  may form compression pockets and fifth and sixth pockets  130 - 3 ,  132 - 3  may form discharge pockets in communication with discharge passage  134  in non-orbiting scroll  106 . Third and fourth pockets  126 - 3 ,  128 - 3  may form second modulated capacity pockets for compression mechanism  18  relative to second and fourth porting  149 ,  151 . 
         [0050]    In the second position, the second modulated capacity pockets may generally be defined as the radially outermost compression pockets that are disposed radially inwardly relative to second and fourth porting  149 ,  151  and isolated from second and fourth porting  149 ,  151  from the time the orbiting scroll  104  is in the second position until the volume in the second modulated capacity pockets is discharged through discharge passage  134 . The second modulated capacity pockets may correspond to the first modulated capacity pockets after compression resulting from orbiting scroll  104  travelling from the first position to the second position. For example, the compression from the first position to the second position may correspond to approximately twenty degrees of rotation of drive shaft  80 . 
         [0051]    Spiral wrap  110  of orbiting scroll  104  may abut an outer radial surface of spiral wrap  120  at a third location  125 - 3  and may abut an inner radial surface of spiral wrap  120  at a fourth location  127 - 3  generally opposite the third location  125 - 3  when orbiting scroll  104  is in the second position. Fourth porting  151  may extend at least twenty degrees along spiral wrap  110  generally opposite a rotational direction (R) of drive shaft  80  starting at a second angular position corresponding to the fourth location  127 - 3  when orbiting scroll  104  is in the second position. Fourth porting  151  may be sealed by spiral wrap  110  when orbiting scroll  104  is in the second position. First porting  148  may be in communication with first pocket  122 - 3  and third porting  150  may be in communication with second pocket  124 - 3  when orbiting scroll  104  is in the second position. 
         [0052]      FIG. 8  illustrates the orbiting scroll  104  in a third position. The third position may generally correspond to approximately three hundred degrees of drive shaft rotation relative to  FIG. 5 . First, second, third and fourth pockets  122 - 4 ,  124 - 4 ,  126 - 4 ,  128 - 4  may be formed by the spiral wraps  110 ,  120  when the orbiting scroll  104  is in the third position. In the third position, first and second pockets  122 - 4 ,  124 - 4  may form compression pockets and third and fourth pockets  126 - 4 ,  128 - 4  may form discharge pockets. Fifth and sixth pockets  130 - 3 ,  132 - 3  shown in  FIG. 7  may be discharged through discharge passage  134  as orbiting scroll  104  travels from the second position to the third position. 
         [0053]    Spiral wrap  110  of orbiting scroll  104  may abut an outer radial surface of spiral wrap  120  at a fifth location  125 - 4  and may abut the inner radial surface of spiral wrap  120  at a sixth location  127 - 4  generally opposite the fifth location  125 - 4  when orbiting scroll  104  is in the third position. First porting  148  may extend at least twenty degrees along spiral wrap  110  in a rotational direction (R) of drive shaft  80  starting at an angular position corresponding to the fifth location  125 - 4  when orbiting scroll  104  is in the third position. First porting  148  may be sealed by spiral wrap  110  when orbiting scroll  104  is in the third position. A portion of third porting  150  may be in communication with first and second pockets  122 - 4 , 124 - 4  when orbiting scroll  104  is in the third position. 
         [0054]      FIG. 9  illustrates the orbiting scroll  104  in a fourth position. The fourth position may generally correspond to approximately three hundred and twenty degrees of drive shaft rotation relative to  FIG. 5 . First, second, third and fourth pockets  122 - 5 ,  124 - 5 ,  126 - 5 ,  128 - 5  may be formed by the spiral wraps  110 ,  120  when the orbiting scroll  104  is in the fourth position. In the fourth position, first and second pockets  122 - 5 ,  124 - 5  may form compression pockets and third and fourth pockets  126 - 5 , 128 - 5 , may form discharge pockets. 
         [0055]    Spiral wrap  110  of orbiting scroll  104  may abut an outer radial surface of spiral wrap  120  at a seventh location  125 - 5  and may abut the an inner radial surface of spiral wrap  120  at a eighth location  127 - 5  generally opposite the seventh location  125 - 5  when orbiting scroll  104  is in the fourth position. Third porting  150  may extend at least twenty degrees along spiral wrap  110  generally opposite a rotational direction (R) of drive shaft  80  starting at an angular position corresponding to the eighth location  127 - 5  when orbiting scroll  104  is in the fourth position. Third porting  150  may be sealed by spiral wrap  110  when orbiting scroll  104  is in the fourth position. 
         [0056]      FIG. 10  generally illustrates the compression of first, second, third and fourth pockets  122 - 5 ,  124 - 5 ,  126 - 5 ,  128 - 5  ( FIG. 9 ) to first, second, third and fourth pockets  122 - 6 ,  124 - 6 ,  126 - 6 ,  128 - 6 .  FIG. 10  generally illustrates the compression resulting from three hundred and sixty degrees of rotation of drive shaft  80  relative to  FIG. 6 . First and second pockets  122 - 6 ,  124 - 6  may become the first modulated capacity pockets in  FIG. 10 . 
         [0057]      FIG. 11  generally illustrates the compression of first, second, third and fourth pockets  122 - 6 ,  124 - 6 ,  126 - 6 ,  128 - 6  ( FIG. 10 ) to first, second, third and fourth pockets  122 - 7 ,  124 - 7 ,  126 - 7 ,  128 - 7 .  FIG. 11  generally illustrates the compression resulting from three hundred and sixty degrees of rotation of drive shaft  80  relative to  FIG. 7 . First and second pockets  122 - 7 ,  124 - 7  may become the second modulated capacity pockets in  FIG. 11 . First and second pockets  122 - 7 , 124 - 7  may be discharged through discharge passage  134  upon further rotation of drive shaft  80  to complete the compression cycle for first and second pockets  122 - 7 ,  124 - 7 . 
         [0058]    Referring back to  FIG. 4 , 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 the pockets formed by the meshing engagement between the spiral wraps  110 ,  120 . 
         [0059]    First, second, third and fourth porting  148 ,  149 ,  150 ,  151  are each shown as continuous openings in  FIGS. 5-11 . However, an alternate first, second, third and fourth porting  148 ′,  149 ′,  150 ′,  151 ′ may each be in the form of a series of discrete openings as seen in  FIG. 12 . 
         [0060]    First, second, third and fourth porting  148 ,  149 ,  150 ,  151  may be placed in second annular recess  145  in communication with four of the pockets formed by the meshing engagement between the spiral wraps  110 ,  120  during a portion of the compression cycle of compression mechanism  18 . Second annular recess  145  may be in communication with different ones of the pockets than first annular recess  144 . More specifically, second annular recess  145  may be in communication with pockets located radially outwardly relative to the pocket 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. 
         [0061]    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. 
         [0062]    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 may include a spring and may be located in second portion  170  and engaged with annular piston  162 . 
         [0063]    Annular piston  162  may be displaceable between first and second positions. In the first position ( FIG. 3 ), annular piston  162  may seal first, second, third and fourth porting  148 ,  149 ,  150 ,  151  from communication with second portion  170  of second annular recess  145 . In the second position ( FIG. 4 ), annular piston  162  may be displaced from first, second, third and fourth porting  148 ,  149 ,  150 ,  151 , providing communication between first, second, third and fourth porting  148 ,  149 ,  150 , 151  and second portion  170  of second annular recess  145 . Therefore, when annular piston  162  is in the second position, first, second, third and fourth porting  148 ,  149 ,  150 ,  151  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 . Additionally, gas may flow from ones of first, second, third, and fourth porting  148 ,  149 ,  150 , to others of first, second, third, and fourth porting  148 ,  149 ,  150 ,  151  operating at a lower pressure. 
         [0064]    As discussed above, second porting  149  may be located radially inward relative to first porting  148  and fourth porting  151  may be located radially inward relative to third porting  150 . Therefore, second and fourth porting  149 , may generally define the modulated capacity of compressor  10  when annular piston  162  is in the second position as discussed above regarding the first and second modulated capacity pockets. First and third porting  148 ,  150  may generally form auxiliary porting to prevent compression in pockets located radially outward from second and fourth porting  149 ,  151  when annular piston  162  is in the second position. 
         [0065]    Pressure source  174  may include a pressure that is greater than an operating pressure of the pockets in communication with first, second, third and fourth porting  148 ,  149 ,  150 ,  151 . 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. 
         [0066]    While first, second, third and fourth porting  148 ,  149 ,  150 ,  151  have been discussed as providing a two-step capacity modulation arrangement, it is understood that similar porting may alternatively be used to provide a three-step capacity modulation arrangement. 
         [0067]    The terms “first”, “second”, etc. are used throughout the description for clarity only and are not intended to limit similar terms in the claims.