Patent Publication Number: US-2021190070-A1

Title: Compressor Having Capacity Modulation Assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/154,844, filed on Oct. 9, 2018, which claims the benefit of U.S. Provisional Application No. 62/672,700, filed on May 17, 2018. The entire disclosures of the above applications are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a compressor having a capacity modulation assembly. 
     BACKGROUND 
     This section provides background information related to the present disclosure and is not necessarily prior art. 
     A climate-control system such as, for example, a heat-pump system, a refrigeration system, or an air conditioning system, may include a fluid circuit having an outdoor heat exchanger, an indoor heat exchanger, an expansion device disposed between the indoor and outdoor heat exchangers, and one or more compressors circulating a working fluid (e.g., refrigerant or carbon dioxide) between the indoor and outdoor heat exchangers. Efficient and reliable operation of the one or more compressors is desirable to ensure that the climate-control system in which the one or more compressors are installed is capable of effectively and efficiently providing a cooling and/or heating effect on demand. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     The present disclosure provides a compressor that may include a first scroll, a second scroll, an axial biasing chamber, a first valve, and a second valve. The first scroll may include a first end plate and a first spiral wrap extending from the first end plate. The second scroll may include a second end plate and a second spiral wrap extending from the second end plate. The first and second spiral wraps mesh with each other and form a plurality of compression pockets therebetween. The compression pockets include a suction-pressure compression pocket, a discharge-pressure compression pocket at a higher pressure than the suction-pressure pocket, and a plurality of intermediate-pressure compression pockets at respective pressures between the pressures of the suction and discharge compression pockets. The second end plate includes an outer port and an inner port. The outer port is disposed radially outward relative to the inner port. The outer port may be open to (i.e., in fluid communication with) a first one of the intermediate-pressure compression pockets. The inner port may be open to (i.e., in fluid communication with) a second one of the intermediate-pressure compression pockets. The axial biasing chamber may be disposed axially between the second end plate and a component. The component may partially define the axial biasing chamber. Working fluid disposed within the axial biasing chamber may axially bias the second scroll toward the first scroll. The first valve may be movable between a first position allowing fluid communication between the inner port and the axial biasing chamber and a second position preventing fluid communication between the inner port and the axial biasing chamber. The second valve may be movable between a first position allowing fluid communication between the outer port and the axial biasing chamber and a second position preventing fluid communication between the outer port and the axial biasing chamber. 
     In some configurations, the component could be a floating seal assembly, a component of a shell assembly (e.g., an end cap or a transversely extending partition separating a suction-pressure region from a discharge chamber), a bearing housing, etc. 
     In some configurations of the compressor of any one or more of the above paragraphs, the first scroll is an orbiting scroll, and the second scroll is a non-orbiting scroll. 
     In some configurations of the compressor of any one or more of the above paragraphs, the first valve is in the first position when the second valve is in the second position. 
     In some configurations of the compressor of any one or more of the above paragraphs, the first valve is in the second position when the second valve is in the first position. 
     In some configurations of the compressor of any one or more of the above paragraphs, the compressor includes a capacity modulation assembly configured to switch the compressor between a first capacity mode and a second capacity mode that is lower than the first capacity mode. 
     In some configurations of the compressor of any one or more of the above paragraphs, when the compressor is in the first capacity mode, the first valve is in the second position and the second valve is in the first position. 
     In some configurations of the compressor of any one or more of the above paragraphs, when the compressor is in the second capacity mode, the first valve is in the first position and the second valve is in the second position. 
     In some configurations of the compressor of any one or more of the above paragraphs, the second end plate includes one or more modulation ports in fluid communication with one or more of the intermediate-pressure compression pockets. 
     In some configurations of the compressor of any one or more of the above paragraphs, the capacity modulation assembly could include a vapor-injection system for injecting working fluid into one of more of the modulation ports. 
     In some configurations of the compressor of any one or more of the above paragraphs, the one or more modulation ports may be in fluid communication with a suction-pressure region of the compressor when the compressor is in the second capacity mode. 
     In some configurations of the compressor of any one or more of the above paragraphs, the capacity modulation assembly includes a valve ring disposed between the component and the second end plate and is movable relative to the component and the second end plate between a first position in which the valve ring blocks fluid communication between the one or more modulation ports and the suction-pressure region and a second position in which the valve ring is spaced apart from the second end plate to allow fluid communication between the one or more modulation ports and the suction-pressure region. 
     In some configurations of the compressor of any one or more of the above paragraphs, the capacity modulation assembly includes a lift ring at least partially disposed within an annular recess in the valve ring. The lift ring and the valve ring may cooperate to define a modulation control chamber that is in selective fluid communication with the suction-pressure region and in selective fluid communication with the axial biasing chamber. 
     In some configurations of the compressor of any one or more of the above paragraphs, the axial biasing chamber is disposed axially between the valve ring and the component. 
     In some configurations of the compressor of any one or more of the above paragraphs, the first and second valves are mounted to the valve ring. The first and second valves are movable with the valve ring and are movable relative to the valve ring. 
     In some configurations of the compressor of any one or more of the above paragraphs, the first and second valves are in contact with the component during at least a portion of a movement of the valve ring toward its second position. Further movement of the valve ring into its second position forces the first valve into its first position and forces the second valve into its second position. 
     In some configurations of the compressor of any one or more of the above paragraphs, movement of the valve ring toward its first position allows movement of the first valve toward its second position and movement of the second valve toward its first position. A spring may bias the first valve toward its second position. 
     In some configurations of the compressor of any one or more of the above paragraphs, a pressure differential between the outer port and the axial biasing chamber moves the second valve into its first position as the valve ring moves toward its first position. 
     In some configurations of the compressor of any one or more of the above paragraphs, the first valve is fluidly connected to the inner port by a first tube that extends partially around an outer periphery of the second end plate. The second valve may be fluidly connected to the outer port by a second tube that extends partially around the outer periphery of the second end plate. 
     The present disclosure also provides a compressor that may include a first scroll, a second scroll, and an axial biasing chamber. The first scroll may include a first end plate and a first spiral wrap extending from the first end plate. The second scroll may include a second end plate and a second spiral wrap extending from the second end plate. The first and second spiral wraps mesh with each other and form a plurality of compression pockets therebetween. The compression pockets include a suction-pressure compression pocket, a discharge-pressure compression pocket at a higher pressure than the suction-pressure pocket, and a plurality of intermediate-pressure compression pockets at respective pressures between the pressures of the suction and discharge compression pockets. The axial biasing chamber may be disposed axially between the second end plate and a component. The component may partially define the axial biasing chamber. Working fluid disposed within the axial biasing chamber may axially bias the second scroll toward the first scroll. The second end plate includes an outer port and an inner port. The outer port is disposed radially outward relative to the inner port. The outer port may be open to (i.e., in fluid communication with) a first one of the intermediate-pressure compression pockets and may be in selective fluid communication with the axial biasing chamber. The inner port may be open to (i.e., in fluid communication with) a second one of the intermediate-pressure compression pockets and may be in selective fluid communication with the axial biasing chamber. 
     In some configurations of the compressor of the above paragraph, the compressor includes a first valve movable between a first position allowing fluid communication between the inner port and the axial biasing chamber and a second position preventing fluid communication between the inner port and the axial biasing chamber. 
     In some configurations of the compressor of any one or more of the above paragraphs, the compressor includes a second valve movable between a first position allowing fluid communication between the outer port and the axial biasing chamber and a second position preventing fluid communication between the outer port and the axial biasing chamber. 
     In some configurations of the compressor of any one or more of the above paragraphs, the first valve is in the first position when the second valve is in the second position. The first valve is in the second position when the second valve is in the first position. 
     In some configurations of the compressor of any one or more of the above paragraphs, the first valve is fluidly connected to the inner port by a first tube that extends partially around an outer periphery of the second end plate. The second valve may be fluidly connected to the outer port by a second tube that extends partially around the outer periphery of the second end plate. 
     In some configurations of the compressor of any one or more of the above paragraphs, the compressor includes a capacity modulation assembly configured to switch the compressor between a first capacity mode and a second capacity mode that is lower than the first capacity mode. 
     In some configurations of the compressor of any one or more of the above paragraphs, when the compressor is in the first capacity mode, the inner port is fluidly isolated from the axial biasing chamber and the outer port is in fluid communication with the axial biasing chamber. 
     In some configurations of the compressor of any one or more of the above paragraphs, when the compressor is in the second capacity mode, the outer port is fluidly isolated from the axial biasing chamber and the inner port is in fluid communication with the axial biasing chamber. 
     In some configurations of the compressor of any one or more of the above paragraphs, the second end plate includes one or more modulation ports in fluid communication with one or more of the intermediate-pressure compression pockets. 
     In some configurations of the compressor of any one or more of the above paragraphs, the capacity modulation assembly could include a vapor-injection system for injecting working fluid into one of more of the modulation ports. 
     In some configurations of the compressor of any one or more of the above paragraphs, the one or more modulation ports may be in fluid communication with a suction-pressure region of the compressor when the compressor is in the second capacity mode. 
     In some configurations of the compressor of any one or more of the above paragraphs, the capacity modulation assembly includes a valve ring disposed between the component and the second end plate and is movable relative to the component and the second end plate between a first position in which the valve ring blocks fluid communication between the one or more modulation ports and the suction-pressure region and a second position in which the valve ring is spaced apart from the second end plate to allow fluid communication between the one or more modulation ports and the suction-pressure region. 
     In some configurations of the compressor of any one or more of the above paragraphs, the capacity modulation assembly includes a lift ring at least partially disposed within an annular recess in the valve ring. The lift ring and the valve ring may cooperate to define a modulation control chamber that is in selective fluid communication with the suction-pressure region and in selective fluid communication with the axial biasing chamber. 
     In some configurations of the compressor of any one or more of the above paragraphs, movement of the valve ring toward its first position provides clearance between the component and the first and second valves, and wherein a spring biases the first valve toward its second position. 
     In some configurations of the compressor of any one or more of the above paragraphs, a pressure differential between the outer port and the axial biasing chamber moves the second valve into its first position as the valve ring moves toward its first position. 
     In some configurations of the compressor of any one or more of the above paragraphs, the axial biasing chamber is disposed axially between the valve ring and the component. 
     In some configurations of the compressor of any one or more of the above paragraphs, the component could be a floating seal assembly, a component of a shell assembly (e.g., an end cap or a transversely extending partition separating a suction-pressure region from a discharge chamber), a bearing housing, etc. 
     In some configurations of the compressor of any one or more of the above paragraphs, the first scroll is an orbiting scroll, and the second scroll is a non-orbiting scroll. 
     In some configurations of the compressor of any one or more of the above paragraphs, the compressor may include a valve assembly in communication with the axial biasing chamber. The valve assembly may include a valve member movable between a first position providing fluid communication between the outer port and the axial biasing chamber and a second position providing fluid communication between the inner port and the axial biasing chamber. 
     In some configurations of the compressor of any one or more of the above paragraphs, the valve member includes a first aperture and a second aperture. When the valve member is in the first position, communication between the inner port and the first aperture is blocked and the second aperture is in communication with the outer port. When the valve member is in the second position, communication between the outer port and the second aperture is blocked and the first aperture is in communication with the inner port. 
     In some configurations of the compressor of any one or more of the above paragraphs, the compressor may include a capacity modulation assembly configured to switch the compressor between a first capacity mode and a second capacity mode that is lower than the first capacity mode. When the compressor is in the first capacity mode, the inner port is fluidly isolated from the axial biasing chamber and the outer port is in fluid communication with the axial biasing chamber. When the compressor is in the second capacity mode, the outer port is fluidly isolated from the axial biasing chamber and the inner port is in fluid communication with the axial biasing chamber. 
     In some configurations of the compressor of any one or more of the above paragraphs, the second end plate includes one or more modulation ports in fluid communication with one or more of the intermediate-pressure compression pockets. The one or more modulation ports are in fluid communication with a suction-pressure region of the compressor when the compressor is in the second capacity mode. The capacity modulation assembly includes a valve ring disposed between the component and the second end plate and is movable relative to the component and the second end plate between a first position in which the valve ring blocks fluid communication between the one or more modulation ports and the suction-pressure region and a second position in which the valve ring is spaced apart from the second end plate to allow fluid communication between the one or more modulation ports and the suction-pressure region. The capacity modulation assembly includes a lift ring at least partially disposed within an annular recess in the valve ring. The lift ring and the valve ring cooperate to define a modulation control chamber that is in selective fluid communication with the suction-pressure region and in selective fluid communication with the axial biasing chamber. 
     In some configurations of the compressor of any one or more of the above paragraphs, the valve member includes a third aperture and a fourth aperture, wherein the third aperture is in fluid communication with the first aperture. When the valve member is in the first position: the first aperture and the third aperture are blocked from fluid communication with the axial biasing chamber and the modulation control chamber, the second aperture provides fluid communication between the outer port and the axial biasing chamber, and the fourth aperture provides fluid communication between the suction-pressure region and the modulation control chamber. 
     In some configurations of the compressor of any one or more of the above paragraphs, when the valve member is in the second position: the first aperture and the third aperture are in fluid communication with the axial biasing chamber and the modulation control chamber, fluid communication is blocked between the second aperture and the outer port and between the second aperture and the axial biasing chamber, fluid communication is blocked between the fourth aperture and the suction-pressure region and between the fourth aperture and the modulation control chamber, and fluid communication between suction-pressure region and the modulation control chamber is blocked. 
     In some configurations of the compressor of any one or more of the above paragraphs, the valve assembly is a MEMS microvalve. 
     The present disclosure also provides a compressor that may include a first scroll, a second scroll, an axial biasing chamber, and a valve assembly. The first scroll includes a first end plate and a first spiral wrap extending from the first end plate. The second scroll includes a second end plate and a second spiral wrap extending from the second end plate. The first and second spiral wraps mesh with each other and form a plurality of compression pockets therebetween. The axial biasing chamber may be disposed axially between the second end plate and a floating seal assembly. The floating seal assembly at least partially defines the axial biasing chamber. The valve assembly is in communication with the axial biasing chamber and is movable between a first position providing fluid communication between a first pressure region and the axial biasing chamber and a second position providing fluid communication between a second pressure region and the axial biasing chamber. The second pressure region may be at a higher pressure than the first pressure region. 
     In some configurations, the first pressure region is a first intermediate-pressure compression pocket defined by the first and second spiral wraps, wherein the second pressure region is a second intermediate-pressure compression pocket defined by the first and second spiral wraps, and wherein the second intermediate-pressure compression pocket is disposed radially inward relative to the first intermediate-pressure compression pocket. 
     In some configurations, the first pressure region is a suction-pressure region. 
     In some configurations, the second pressure region is a discharge-pressure region. In some configurations, the discharge-pressure region is a discharge passage extending through the second end plate. In other configurations, the discharge-pressure region could be a discharge chamber (discharge muffler), or an innermost pocket defined by the first and second spiral wraps, for example. 
     In some configurations of the compressor of any one or more of the above paragraphs, the second end plate includes a first passage and a second passage, wherein the first passage is open to a discharge passage and is in fluid communication with the valve assembly, and wherein the second passage is open to the axial biasing chamber and is in fluid communication with the valve assembly. 
     In some configurations of the compressor of any one or more of the above paragraphs, the valve assembly provides fluid communication between the first passage and the second passage when the valve assembly is in the second position. 
     In some configurations of the compressor of any one or more of the above paragraphs, the valve assembly provides fluid communication between the second passage and the suction-pressure region when the valve assembly is in the first position. 
     In some configurations of the compressor of any one or more of the above paragraphs, the valve assembly includes a valve member movable between the first position and the second position. The valve member includes a first aperture and a second aperture. When the valve member is in the first position, communication between the first passage and the first aperture is blocked and the second aperture is in communication with the suction-pressure region. When the valve member is in the second position, communication between the suction-pressure region and the second aperture is blocked and the first aperture is in communication with the first passage. 
     In some configurations of the compressor of any one or more of the above paragraphs, the valve assembly is a MEMS microvalve. 
     In some configurations of the compressor of any one or more of the above paragraphs, the compressor may include a control module controlling operation of the valve assembly. The control module may pulse-width-modulate the valve assembly between the first and second positions to achieve a desired fluid pressure within the axial biasing chamber. The desired fluid pressure may be determined based on compressor operating conditions (e.g., suction and discharge pressures or temperatures) and/or operating conditions (e.g., condensing and evaporating temperatures or pressures) of a climate-control system in which the compressor is installed. 
     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 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a cross-sectional view of a compressor having a capacity modulation assembly according to the principles of the present disclosure; 
         FIG. 2  is a bottom view of a non-orbiting scroll of the compressor of  FIG. 1 ; 
         FIG. 3  is a partial cross-sectional view of the compressor taken along line  3 - 3  of  FIG. 2 ; 
         FIG. 4  is an exploded view of the non-orbiting scroll and capacity modulation assembly; 
         FIG. 5  is a perspective view of a portion of the compressor; 
         FIG. 6  is a cross-sectional view of a portion of the compressor in a full-capacity mode; 
         FIG. 7  is another cross-sectional view of a portion of the compressor in the full-capacity mode; 
         FIG. 8  is a cross-sectional view of a portion of the compressor in a reduced-capacity mode; 
         FIG. 9  is another cross-sectional view of a portion of the compressor in the reduced-capacity mode; 
         FIG. 10  is a perspective view of a portion of another compressor according to the principles of the present disclosure; 
         FIG. 11  is a cross-sectional view of an alternative non-orbiting scroll and a valve assembly in a first position according to the principles of the present disclosure; 
         FIG. 12  is a cross-sectional view of the non-orbiting scroll and valve assembly of  FIG. 11  in a second position according to the principles of the present disclosure; 
         FIG. 13  is a cross-sectional view of another alternative non-orbiting scroll and an alternative valve assembly in a first position according to the principles of the present disclosure; 
         FIG. 14  is a cross-sectional view of the non-orbiting scroll and valve assembly of  FIG. 13  in a second position according to the principles of the present disclosure; 
         FIG. 15  is a cross-sectional view of yet another alternative non-orbiting scroll, an alternative valve assembly, and an alternative capacity modulation assembly in a first position according to the principles of the present disclosure; 
         FIG. 16  is a cross-sectional view of the non-orbiting scroll, valve assembly and capacity modulation assembly of  FIG. 15  in a second position according to the principles of the present disclosure; 
         FIG. 17  is an exploded view of the valve assembly of  FIGS. 15 and 16 ; 
         FIG. 18  is a cross-sectional view of the valve assembly of  FIG. 17  in the first position; 
         FIG. 19  is another cross-sectional view of the valve assembly of  FIG. 17  in the first position; 
         FIG. 20  is yet another cross-sectional view of the valve assembly of  FIG. 17  in the first position; 
         FIG. 21  is a cross-sectional view of the valve assembly of  FIG. 17  in the second position; 
         FIG. 22  is another cross-sectional view of the valve assembly of  FIG. 17  in the second position; and 
         FIG. 23  is yet another cross-sectional view of the valve assembly of  FIG. 17  in the second position. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     With reference to  FIG. 1 , a compressor  10  is provided that may include a hermetic shell assembly  12 , a first bearing housing assembly  14 , a second bearing housing assembly  15 , a motor assembly  16 , a compression mechanism  18 , a floating seal assembly  20 , and a capacity modulation assembly  28 . The shell assembly  12  may house the bearing housing assemblies  14 ,  15 , the motor assembly  16 , the compression mechanism  18 , the seal assembly  20 , and the capacity modulation assembly  28 . 
     The shell assembly  12  forms a compressor housing and may include a cylindrical shell  29 , an end cap  32  at the upper end thereof, a transversely extending partition  34 , and a base  36  at a lower end thereof. The end cap  32  and partition  34  may generally define a discharge chamber  38 . The discharge chamber  38  may generally form a discharge muffler for compressor  10 . While the compressor  10  is illustrated as including the discharge chamber  38 , the present disclosure applies equally to direct discharge configurations. A discharge fitting  39  may be attached to the shell assembly  12  at an opening in the end cap  32 . A suction gas inlet fitting (not shown) may be attached to the shell assembly  12  at another opening. The partition  34  may include a discharge passage  44  therethrough providing communication between the compression mechanism  18  and the discharge chamber  38 . 
     The first bearing housing assembly  14  may be affixed to the shell  29  and may include a main bearing housing  46  and a first bearing  48  disposed therein. The main bearing housing  46  may house the bearing  48  therein and may define an annular flat thrust bearing surface  54  on an axial end surface thereof. The second bearing housing assembly  15  may be affixed to the shell  29  and may include a lower bearing housing  47  and a second bearing  49  disposed therein. 
     The motor assembly  16  may generally include a motor stator  58 , a rotor  60 , and a driveshaft  62 . The motor stator  58  may be press fit into the shell  29 . The driveshaft  62  may be rotatably driven by the rotor  60  and may be rotatably supported within the bearing  48 . The rotor  60  may be press fit on the driveshaft  62 . The driveshaft  62  may include an eccentric crankpin  64 . 
     The compression mechanism  18  may include a first scroll (e.g., an orbiting scroll  68 ) and a second scroll (e.g., a non-orbiting scroll  70 ). The orbiting scroll  68  may include an end plate  72  having a spiral wrap  74  on the upper surface thereof and an annular flat thrust surface  76  on the lower surface. The thrust surface  76  may interface with the annular flat thrust bearing surface  54  on the main bearing housing  46 . A cylindrical hub  78  may project downwardly from the thrust surface  76  and may have a drive bushing  80  rotatably disposed therein. The drive bushing  80  may include an inner bore in which the crank pin  64  is drivingly disposed. A flat surface of the crankpin  64  may drivingly engage a flat surface in a portion of the inner bore of the drive bushing  80  to provide a radially compliant driving arrangement. An Oldham coupling  82  may be engaged with the orbiting and non-orbiting scrolls  68 ,  70  or the orbiting scroll  68  and the main bearing housing  46  to prevent relative rotation therebetween. 
     The non-orbiting scroll  70  may include an end plate  84  defining a discharge passage  92  and having a spiral wrap  86  extending from a first side thereof. The non-orbiting scroll  70  may be attached to the bearing housing  46  via fasteners and sleeve guides that allow for a limited amount of axial movement of the non-orbiting scroll  70  relative to the orbiting scroll  68  and the bearing housing  46 . The spiral wraps  74 ,  86  may be meshingly engaged with one another and define pockets  94 ,  96 ,  97 ,  98 ,  99 ,  100 ,  102 ,  104 . It is understood that the pockets  94 ,  96 ,  98 ,  100 ,  102 ,  104  change throughout compressor operation. 
     A first pocket (pocket  94  in  FIG. 1 ) may define a suction pocket in communication with a suction-pressure region (suction chamber)  106  of the compressor  10  operating at a suction pressure. A second pocket (pocket  104  in  FIG. 1 ) may define a discharge pocket in communication with a discharge pressure region (e.g., discharge chamber  38 ) of the compressor  10  operating at a discharge pressure via the discharge passage  92 . Pockets intermediate the first and second pockets (pockets  96 ,  97 ,  98 ,  99 ,  100 ,  102  in  FIG. 1 ) may form intermediate compression pockets operating at intermediate pressures between the suction pressure and the discharge pressure. 
     As shown in  FIG. 4 , the end plate  84  of the non-orbiting scroll  70  may include a raised central boss  108  and an annular groove  110  encircling the central boss  108 . The discharge passage  92  may extend through the central boss  108 . As shown in  FIGS. 2, 4 and 6 , the end plate  84  may also include a plurality of modulation passages or ports (e.g., one or more first modulation ports  112 , one or more second modulation ports  114 , one or more third modulation ports  116 , and one or more fourth modulation ports  118 ), one or more first variable-volume-ratio (VVR) passages or ports  120 , one or more second VVR passages or ports  122 , an outer intermediate-cavity-pressure (ICP) passage or port  124 , and an inner ICP passage or port  126 . As shown in  FIG. 6 , the modulation ports  112 ,  114 ,  116 ,  118  may extend entirely through first and second opposing axially facing sides of the end plate  84  and are in selective fluid communication with respective intermediate pressure pockets (e.g., pockets  96 ,  97 ,  98 ,  99 ). The first and second modulation ports  112 ,  114  may be disposed radially outward relative to the third and fourth modulation ports  116 ,  118 . The first and second VVR ports  120 ,  122  may be disposed radially inward relative to the third and fourth modulation ports  116 ,  118 . As shown in  FIG. 6 , the first and second VVR ports  120 ,  122  may extend through the end plate  84  (e.g., through the first axially facing side of the end plate  84  and through the central boss  108 . As shown in  FIG. 6 , the first and second VVR ports  120 ,  122  may be in selective fluid communication with respective intermediate pressure pockets (e.g., pockets  100 ,  102  disposed radially between pocket  104  and pockets  96 ,  97 ,  98 ,  99 ). 
     As shown in  FIG. 2 , the outer ICP port  124  may include an axially extending portion  128  and a radially extending portion  130 , and the inner ICP port  126  may include an axially extending portion  132  and a radially extending portion  134 . As shown in  FIG. 3 , the axially extending portions  128 ,  132  of the ICP ports  124 ,  126  extend through the first axially facing side of the end plate  84  and extend only partially through the axial thickness of the end plate  84 . As shown in  FIG. 3 , the axially extending portions  128 ,  132  are in selective fluid communication with respective intermediate pressure pockets (e.g., any of pockets  96 ,  97 ,  98 ,  99 ,  100 ,  102 ). The radially extending portions  130 ,  134  of the ICP ports  124 ,  126  extend radially from upper axial ends of the respective axially extending portions  128 ,  132  and through a radially peripheral surface  136  of the end plate  84 , as shown in  FIGS. 2 and 4 . 
     As shown in  FIG. 6 , a hub  138  may be mounted to the second axially facing side of the end plate  84 . The hub  138  may include a pair of feet or flange portions  140  ( FIGS. 4 and 7 ) and a cylindrical body portion  142  ( FIGS. 4, 6, and 7 ) extending axially from the flange portions  140 . The hub  138  may be fixedly attached to the end plate  84  by fasteners  139  ( FIG. 4 ) that extend through apertures in the flange portions  140  and into apertures  141  in the end plate  84 . An annular seal  143  ( FIGS. 4 and 6 ) is disposed in the annular groove  110  in the end plate  84  and sealingly engages the end plate  84  and the hub  138 . A discharge passage  144  extends axially through the body portion  142  and is in fluid communication with the discharge chamber  38  via the discharge passage  44  in the partition  34 . The discharge passage  144  is also in selective fluid communication with the discharge passage  92  in the end plate  84 . 
     As shown in  FIG. 6 , a VVR valve  146  (e.g., an annular disk) may be disposed within the discharge passage  144  of the hub  138  and may be movable therein between a closed position and an open position. In the closed position (shown in  FIG. 6 ), the VVR valve  146  contacts the central boss  108  of the end plate  84  to restrict or prevent fluid communication between the VVR ports  120 ,  122  and the discharge passages  144 ,  44 . In the open position, the VVR valve  146  is spaced apart from the central boss  108  to allow fluid communication between the VVR ports  120 ,  122  and the discharge passages  144 ,  44 . A spring  148  biases the VVR valve  146  toward the closed position. The VVR valve is moved into the open position when the pressure of fluid within the compression pockets that are in communication with the VVR ports  120 ,  122  is higher than the pressure of fluid in the discharge chamber  38 . 
     As shown in  FIG. 6 , a discharge valve assembly  150  may also be disposed within the discharge passage  144  of the hub  138 . The discharge valve assembly  150  may be a one-way valve that allows fluid flow from the discharge passage  92  and/or VVR ports  120 ,  122  to the discharge chamber  38  and restricts or prevents fluid flow from the discharge chamber  38  back into the compression mechanism  18 . 
     As shown in  FIGS. 4 and 6 , the capacity modulation assembly  28  may include a seal plate  152 , a valve ring  154 , a lift ring  156 , a modulation control valve  158 , a first ICP valve  206 , and a second ICP valve  210 . As will be described in more detail below, the capacity modulation assembly  28  is operable to switch the compressor  10  between a first capacity mode (e.g., a full-capacity mode;  FIGS. 6 and 7 ) and a second capacity mode (e.g., a reduced-capacity mode;  FIGS. 8 and 9 ). In the full-capacity mode, fluid communication between the modulation ports  112 ,  114 ,  116 ,  118  and the suction-pressure region  106  is prevented. In the reduced-capacity mode, the modulation ports  112 ,  114 ,  116 ,  118  are allowed to fluidly communicate with the suction-pressure region  106  to vent intermediate-pressure working fluid from intermediate compression pockets (e.g., pockets  96 ,  97 ,  98 ,  99 ) to the suction-pressure region  106 . 
     The seal plate  152  may include an annular ring  160  having a pair of flange portions  162  that extend axially downward and radially outward from the annular ring  160 . As shown in  FIG. 6 , the seal plate  152  may encircle the cylindrical body portion  142  of the hub  138 . That is, the body portion  142  may extend through the central aperture of the ring  160  of the seal plate  152 . The flange portions  140  of the hub  138  may extend underneath the annular ring  160  (e.g., between the end plate  84  and the annular ring  160 ) and between the flange portions  162  of the seal plate  152 . The seal plate  152  may be fixedly attached to the valve ring  154  (e.g., by fasteners  164  ( FIG. 4 ) that extend through apertures  165  in the annular ring  160  and into the valve ring  154 ). The seal plate  152  may be considered a part of the valve ring  154  and/or the seal plate  152  may be integrally formed with the valve ring  154 . 
     As will be described in more detail below, the seal plate  152  is movable with the valve ring  154  in an axial direction (i.e., a direction along or parallel to a rotational axis of the driveshaft  62 ) relative to the end plate  84  between a first position ( FIG. 6 ) and a second position ( FIG. 8 ). In the first position ( FIG. 6 ), the flange portions  162  of the seal plate  152  contact the end plate  84  and close off the modulation ports  112 ,  114 ,  116 ,  118  to prevent fluid communication between the modulation ports  112 ,  114 ,  116 ,  118  and the suction-pressure region  106 . In the second position ( FIG. 8 ), the flange portions  162  of the seal plate  152  are spaced apart from the end plate  84  to open the modulation ports  112 ,  114 ,  116 ,  118  to allow fluid communication between the modulation ports  112 ,  114 ,  116 ,  118  and the suction-pressure region  106 . 
     As shown in  FIGS. 4 and 6 , the valve ring  154  may be an annular body having a stepped central opening  166  extending therethrough and through which the hub  138  extends. In other words, the valve ring  154  encircles the cylindrical body portion  142  of the hub  138 . As shown in  FIG. 4 , the valve ring  154  may include an outer peripheral surface  168  having a plurality of key features  170  (e.g., generally rectangular blocks) that extend radially outward and axially downward from the outer peripheral surface  168 . The key features  170  may be slidably received in keyways  172  (e.g., generally rectangular recesses; shown in  FIG. 4 ) formed in the outer periphery of the end plate  84  (see  FIG. 5 ). The key features  170  and keyways  172  allow for axial movement of the valve ring  154  relative to the non-orbiting scroll  70  while restricting or preventing rotation of the valve ring  154  relative to the non-orbiting scroll  70 . 
     As shown in  FIGS. 6-8 , the central opening  166  of the valve ring  154  is defined by a plurality of steps in the valve ring  154  that form a plurality of annular recesses. For instance, a first annular recess  174  may be formed proximate a lower axial end of the valve ring  154  and may receive the ring  160  of the seal plate  152 . A second annular recess  176  may encircle the first annular recess  174  and may be defined by inner and outer lower annular rims  178 ,  180  of the valve ring  154 . The inner lower rim  178  separates the first and second annular recesses  174 ,  176  from each other. The lift ring  156  is partially received in the second annular recess  176 . A third annular recess  182  is disposed axially above the first annular recess  174  and receives an annular seal  184  that sealingly engages the hub  138  and the valve ring  154 . A fourth annular recess  186  may be disposed axially above the third annular recess  182  and may be defined by an axially upper rim  188  of the valve ring  154 . The fourth annular recess  186  may receive a portion of the floating seal assembly  20 . 
     As shown in  FIGS. 4 and 6 , the lift ring  156  may include an annular body  190  and a plurality of posts or protrusions  192  extending axially downward from the body  190 . As shown in  FIG. 6 , the annular body  190  may be received within the second annular recess  176  of the valve ring  154 . The annular body  190  may include inner and outer annular seals (e.g., O-rings)  194 ,  196 . The inner annular seal  194  may sealingly engage an inner diametrical surface of the annular body  190  and the inner lower rim  178  of the valve ring  154 . The outer annular seal  196  may sealingly engage an outer diametrical surface of the annular body  190  and the outer lower rim  180  of the valve ring  154 . The protrusions  192  may contact the end plate  84  and axially separate the annular body  190  from the end plate  84 . The lift ring  156  remains stationary relative to the end plate  84  while the valve ring  154  and the seal plate  152  move axially relative to the end plate  84 . 
     As shown in  FIGS. 6 and 8 , the annular body  190  of the lift ring  156  may cooperate with the valve ring  154  to define a modulation control chamber  198 . That is, the modulation control chamber  198  is defined by and disposed axially between opposing axially facing surfaces of the annular body  190  and the valve ring  154 . The valve ring  154  includes a first control passage  200  that extends from the modulation control chamber  198  to the modulation control valve  158  and fluidly communicates with the modulation control chamber  198  and the modulation control valve  158 . 
     As shown in  FIGS. 6-9 , the floating seal assembly  20  may be an annular member encircling the hub  138 . For example, the floating seal assembly  20  may include first and second disks  191 ,  193  that are fixed to each other and annular lip seals  195 ,  197  that extend from the disks  191 ,  193 . The floating seal assembly  20  may be sealingly engaged with the partition  34 , the hub  138 , and the valve ring  154 . In this manner, the floating seal assembly  20  fluidly separates the suction-pressure region  106  from the discharge chamber  38 . In some configurations, the floating seal assembly  20  could be a one-piece floating seal. 
     During steady-state operation of the compressor  10 , the floating seal assembly  20  may be a stationary component. The floating seal assembly  20  is partially received in the fourth annular recess  186  of the valve ring  154  and cooperates with the hub  138 , the annular seal  184  and the valve ring  154  to define an axial biasing chamber  202  ( FIGS. 6-9 ). The axial biasing chamber  202  is axially between and defined by the floating seal assembly  20  and an axially facing surface  207  of the valve ring  154 . The valve ring  154  includes a second control passage  201  that extends from the axial biasing chamber  202  to the modulation control valve  158  and fluidly communicates with the axial biasing chamber  202  and the modulation control valve  158 . 
     The axial biasing chamber  202  is in selective fluid communication with one of the outer and inner ICP ports  124 ,  126  ( FIGS. 2 and 3 ). That is, the inner ICP port  126  is in selective fluid communication with the axial biasing chamber  202  during the reduced-capacity mode via a first tube  204  ( FIGS. 5  and  9 ), and the first ICP valve  206  ( FIG. 9 ); and the outer ICP port  124  is in selective fluid communication with the axial biasing chamber  202  during the full-capacity mode via a second tube  208  ( FIGS. 5 and 7 ) and the second ICP valve  210  ( FIG. 7 ). Intermediate-pressure working fluid in the axial biasing chamber  202  (supplied by one of the ICP ports  124 ,  126 ) biases the non-orbiting scroll  70  in an axial direction (a direction along or parallel to the rotational axis of the driveshaft  62 ) toward the orbiting scroll  68  to provide proper axial sealing between the scrolls  68 ,  70  (i.e., sealing between tips of the spiral wrap  74  of the orbiting scroll  68  against the end plate  84  of the non-orbiting scroll  70  and sealing between tips of the spiral wrap  86  of the non-orbiting scroll  70  against the end plate  72  of the orbiting scroll  68 ). 
     As shown in  FIG. 2 , the radially extending portion  134  of the inner ICP port  126  is fluidly coupled with a first fitting  212  that is fixedly attached to the end plate  84 . As shown in  FIG. 5 , the first fitting  212  is fluidly coupled with the first tube  204 . As shown in  FIG. 5 , the first tube  204  extends partially around the outer peripheries of the end plate  84  and the valve ring  154  and is fluidly coupled with a second fitting  214  that is fixedly attached to the valve ring  154 . The first tube  204  may be flexible and/or stretchable to allow for movement of the valve ring  154  relative to the non-orbiting scroll  70 . As shown in  FIG. 7 , the second fitting  214  is in fluid communication with a first radially extending passage  216  in the valve ring  154 . As shown in  FIG. 7 , the first ICP valve  206  is disposed in an aperture  218  formed in the axially facing surface  207  of the valve ring  154  (the axially facing surface  207  partially defines the axial biasing chamber  202 ). The aperture  218  extends from the first radially extending passage  216  to the axial biasing chamber  202 . As will be described in more detail below, the first ICP valve  206  controls fluid communication between the inner ICP port  126  and the axial biasing chamber  202 . 
     As shown in  FIG. 2 , the radially extending portion  130  of the outer ICP port  124  is fluidly coupled with a third fitting  220  that is fixedly attached to the end plate  84 . As shown in  FIG. 5 , the third fitting  220  is fluidly coupled with the second tube  208 . As shown in  FIG. 5 , the second tube  208  extends partially around the outer peripheries of the end plate  84  and the valve ring  154  and is fluidly coupled with a fourth fitting  222  that is fixedly attached to the valve ring  154 . The second tube  208  may be flexible and/or stretchable to allow for movement of the valve ring  154  relative to the non-orbiting scroll  70 . As shown in  FIG. 7 , the fourth fitting  222  is in fluid communication with a second radially extending passage  224  in the valve ring  154 . As shown in  FIG. 7 , the second ICP valve  210  is disposed in an aperture  225  formed in the axially facing surface  207  the valve ring  154 . The aperture  225  extends from the second radially extending passage  224  to the axial biasing chamber  202 . As will be described in more detail below, the second ICP valve  210  controls fluid communication between the outer ICP port  124  and the axial biasing chamber  202 . 
     In some configurations, the first ICP valve  206  could be a Schrader valve, for example. In some configurations, as shown in  FIGS. 7 and 9 , the first ICP valve  206  may include a valve member  226 , a bushing  228 , and a spring  230 . The valve member  226  may include a disk portion  232  and a cylindrical stem portion  234  extending axially upward from the disk portion  232  (i.e., axially toward the floating seal assembly  20 ). The disk portion  232  has a larger diameter than the stem portion  234 . The bushing  228  may be fixedly received in the aperture  218  in the valve ring  154  and may include a central aperture  229  through which the stem portion  234  is reciprocatingly received. The distal axial end of the stem portion  234  may protrude into the axial biasing chamber  202 . The disk portion  232  may be movably disposed between the lower axial end of the bushing  228  and the spring  230 . The valve member  226  is axially movable relative to the bushing  228  and the valve ring  154  between a closed position ( FIG. 7 ) and an open position ( FIG. 9 ). The spring  230  may contact the valve ring  154  and the disk portion  232  to bias the valve member  226  toward the closed position. 
     When the first ICP valve  206  is in the closed position ( FIG. 7 ), the disk portion  232  contacts the bushing  228  and prevents fluid flow through the first ICP valve  206  to prevent fluid communication between the inner ICP port  126  and the axial biasing chamber  202 . When the first ICP valve  206  is in the open position ( FIG. 9 ), the disk portion  232  is axially separated from the bushing  228  to allow fluid flow through the first ICP valve  206  (e.g., through the central aperture  229  of the bushing  228  (e.g., between the outer diametrical surface of the stem portion  234  and the inner diametrical surface of the central aperture  229  of the bushing  228 )) to allow fluid communication between the inner ICP port  126  and the axial biasing chamber  202 . 
     The second ICP valve  210  is a valve member including disk portion  236  and a cylindrical stem portion  238  extending axially downward from the disk portion  236  (i.e., axially away from the floating seal assembly  20 ). The disk portion  236  has a larger diameter than the stem portion  238 . The stem portion  238  may be reciprocatingly received in the aperture  225  in the valve ring  154  to allow the second ICP valve  210  to move between an open position ( FIG. 7 ) and a closed position ( FIG. 9 ). As will be described below, the second ICP valve  210  is in the open position when the first ICP valve  206  is in the closed position (as shown in  FIG. 7 ), and the second ICP valve  210  is in the closed position when the first ICP valve  206  is in the open position (as shown in  FIG. 9 ). 
     When the second ICP valve  210  is in the open position ( FIG. 7 ), the disk portion  236  is spaced apart from a recessed axially-facing surface  240  of the valve ring  154  to allow fluid flow through the second ICP valve  210  (e.g., through the aperture  225  (e.g., between the outer diametrical surface of the stem portion  238  and the inner diametrical surface of the aperture  225 )) to allow fluid communication between the outer ICP port  124  and the axial biasing chamber  202 . When the second ICP valve  210  is in the closed position ( FIG. 9 ), the disk portion  236  is in contact with the surface  240  of the valve ring  154  to prevent fluid flow through the second ICP valve  210  to prevent fluid communication between the outer ICP port  124  and the axial biasing chamber  202 . 
     The modulation control valve  158  may include a solenoid-operated three-way valve and may be in fluid communication with the suction-pressure region  106  and the first and second control passages  200 ,  201  in the valve ring  154 . During operation of the compressor  10 , the modulation control valve  158  may be operable to switch the compressor  10  between a first mode (e.g., a full-capacity mode) and a second mode (e.g., a reduced-capacity mode).  FIGS. 6 and 8  schematically illustrate operation of the modulation control valve  158 . 
     When the compressor  10  is in the full-capacity mode ( FIGS. 6 and 7 ), the modulation control valve  158  may provide fluid communication between the modulation control chamber  198  and the suction-pressure region  106  via the first control passage  200 , thereby lowering the fluid pressure within the modulation control chamber  198  to suction pressure. With the fluid pressure within the modulation control chamber  198  at or near suction pressure, the relatively higher fluid pressure within the axial biasing chamber  202  (e.g., an intermediate pressure) will force the valve ring  154  and seal plate  152  axially downward relative to the end plate  84  (i.e., away from the floating seal assembly  20 ) such that the seal plate  152  is in contact with the end plate  84  and closes the modulation ports  112 ,  114 ,  116 ,  118  (i.e., to prevent fluid communication between the modulation ports  112 ,  114 ,  116 ,  118  and the suction-pressure region  106 ), as shown in  FIG. 6 . 
     When the compressor  10  is in the reduced-capacity mode ( FIGS. 8 and 9 ), the modulation control valve  158  may provide fluid communication between the modulation control chamber  198  and the axial biasing chamber  202  via the second control passage  201 , thereby raising the fluid pressure within the modulation control chamber  198  to the same or similar intermediate pressure as the axial biasing chamber  202 . With the fluid pressure within the modulation control chamber  198  at the same intermediate pressure as the axial biasing chamber  202 , the fluid pressure within the modulation control chamber  198  and the fluid pressure in the modulation ports  112 ,  114 ,  116 ,  118  will force the valve ring  154  and seal plate  152  axially upward relative to the end plate  84  (i.e., toward the floating seal assembly  20 ) such that the seal plate  152  is spaced apart from the end plate  84  to open the modulation ports  112 ,  114 ,  116 ,  118  (i.e., to allow fluid communication between the modulation ports  112 ,  114 ,  116 ,  118  and the suction-pressure region  106 ), as shown in  FIG. 8 . 
     As shown in  FIG. 7 , in the full-capacity mode, the floating seal assembly  20  is spaced axially apart from the axially facing surface  207  of the valve ring  154  is axially spaced sufficiently far apart from the floating seal assembly  20  to provide clearance to: (a) allow the spring  230  of the first ICP valve  206  to force the valve member  226  of the first ICP valve  206  axially upward into the closed position (thereby preventing fluid communication between the inner ICP port  126  and the axial biasing chamber  202 ); and (b) allow fluid pressure in the second radially extending passage  224  to force the second ICP valve  210  axially upward into the open position (i.e., a pressure differential between the outer ICP port  124  and the axial biasing chamber  202  may move the second ICP valve  210  into the open position as the valve ring  154  moves into the position shown in  FIG. 7 , thereby allowing working fluid from the outer ICP port  124  to flow into the axial biasing chamber  202 ). 
     As shown in  FIG. 9 , in the reduced-capacity mode, the valve ring  154  and seal plate  152  are moved axially upward toward the floating seal assembly  20 , thereby reducing or eliminating the axial space between the floating seal assembly  20  and the axially facing surface  207  of the valve ring  154 . Therefore, as the valve ring  154  and seal plate  152  are moved axially upward toward the floating seal assembly  20 , the floating seal assembly  20  contacts and forces the valve member  226  of the first ICP valve  206  and the valve member of the second ICP valve  210  further into their respective apertures  218 ,  225  in the valve ring  154 , thereby opening the first ICP valve  206  (to allow working fluid from the inner ICP port  126  to flow into the axial biasing chamber  202 ) and closing the second ICP valve  210  (to prevent fluid communication between the axial biasing chamber and the outer ICP port  124 ). 
     Accordingly, the axial biasing chamber  202  receives working fluid from the outer ICP port  124  when the compressor  10  is operating in the full-capacity mode, and the axial biasing chamber  202  receives working fluid from the inner ICP port  126  when the compressor  10  is operating in the reduced-capacity mode. As shown in  FIG. 3 , the inner ICP port  126  may be open to (i.e., in direct fluid communication with) one of the compression pockets (such as one of the intermediate-pressure pockets  98 ,  100 , for example) that is radially inward relative to the compression pocket to which the outer ICP port  124  is open (i.e., the compression pocket with which the outer ICP port  124  is in direct fluid communication). Therefore, for any given set of operating conditions, the compression pocket to which the inner ICP port  126  is open may be at a higher pressure than the compression pocket to which the outer ICP port  124  is open. 
     By switching which one of the ICP ports  124 ,  126  supplies working fluid to the axial biasing chamber  202  when the compressor  10  is switched between the full-capacity and reduced-capacity modes, the capacity modulation assembly  28  of the present disclosure can supply working fluid of a more preferred pressure to the axial biasing chamber  202  in both the full-capacity and reduced-capacity modes. That is, while the pressure of the working fluid supplied by the outer ICP port  124  may be appropriate while the compressor is in the full-capacity mode, the pressure of the working fluid at the outer ICP port  124  is lower during the reduced-capacity mode (due to venting of working fluid to the suction-pressure region  106  through modulation ports  112 ,  114 ,  116 ,  118  during the reduced-capacity mode) than it is during the full-capacity mode. To compensate for that reduction in fluid pressure, the second ICP valve  210  closes and the first ICP valve  206  opens in the reduced-capacity mode so that working fluid from the inner ICP port  126  is supplied to the axial biasing chamber during the reduced-capacity mode. In this manner, working fluid of an appropriately high pressure can be supplied to the axial biasing chamber  202  during the reduced-capacity mode to adequately bias the non-orbiting scroll  70  axially toward the orbiting scroll  68  to ensure appropriate sealing between the tips of spiral wraps  74 ,  86  and end plates  84 ,  72 , respectively. 
     Supplying working fluid to the axial biasing chamber  202  from the outer ICP port  124  (rather than from the inner ICP port  126 ) in the full-capacity mode ensures that the pressure of working fluid in the axial biasing chamber  202  is not too high in the full-capacity mode, which ensures that the scrolls  70 ,  68  are not over-clamped against each other. Over-clamping the scrolls  70 ,  68  against each other (i.e., biasing the non-orbiting scroll  70  axially toward the orbiting scroll  68  with too much force) would introduce an unduly high friction load between the scrolls  68 ,  70 , which would result in increased wear, increased power consumption and efficiency losses. Therefore, the operation of the ICP valves  206 ,  210  described above minimizes wear and improves efficiency of the compressor  10  in the full-capacity and reduced-capacity modes. 
     While the capacity modulation assembly  28  is described above as an assembly that selectively allows venting of modulation ports in the end plate to the suction-pressure region, in some configurations, the capacity modulation assembly  28  could additionally or alternatively include a vapor-injection system that selectively injects working fluid into one or more intermediate-pressure compression pockets to boost the capacity of the compressor. One or more passages in one of both of the end plates  72 ,  84  may be provided through which the working fluid may be injected into the one or more intermediate-pressure compression pockets. One or more valves may be provided to control the flow of working fluid into the one or more intermediate-pressure compression pockets. 
     With reference to  FIG. 10 , a compressor  310  is provided. The structure and function of the compressor  310  may be similar or identical to that of the compressor  10  described above, apart from the differences described below. Like the compressor  10 , the compressor  310  may include first and second tubes  204 ,  208  to provide fluid communication between the ICP ports  124 ,  126  and the axial biasing chamber  202 . However, instead of having ICP valves  206 ,  210  mounted to the valve ring  154  to control fluid communication between the ICP ports  124 ,  126  and the axial biasing chamber  202  (as in the compressor  10 ), the compressor  310  may include first and second ICP valves  312 ,  314  disposed on the first and second tubes  204 ,  208 , respectively. The first and second ICP valves  312 ,  314  may be solenoid valves, for example, and may be controlled by a controller (e.g., processing circuitry). When the compressor  310  is operating in the reduced-capacity mode, the controller may: (a) move the first ICP valve  312  to an open position to allow fluid flow from the inner ICP port  126  to the axial biasing chamber  202 , and (b) move the second ICP valve  314  to a closed position to restrict or prevent fluid flow between the outer ICP port  124  and the axial biasing chamber  202 . When the compressor  310  is operating in the full-capacity mode, the controller may: (a) move the second ICP valve  314  to an open position to allow fluid flow from the outer ICP port  124  to the axial biasing chamber  202 , and (b) move the first ICP valve  312  to a closed position to restrict or prevent fluid flow between the inner ICP port  126  and the axial biasing chamber  202 . 
     With reference to  FIGS. 11 and 12 , an alternative non-orbiting scroll  370  and a valve assembly  372  are provided. The non-orbiting scroll  370  and valve assembly  372  could be incorporated into the compressor  10  instead of the non-orbiting scroll  70  and capacity modulation assembly  28 . 
     The non-orbiting scroll may include an end plate  384  defining a discharge passage  392  and having a spiral wrap  386  extending from a first side thereof. The non-orbiting scroll  370  may be attached to the bearing housing  46  via fasteners and sleeve guides that allow for a limited amount of axial movement of the non-orbiting scroll  370  relative to the orbiting scroll  68  and the bearing housing  46 . The spiral wrap  386  may be meshingly engaged with the spiral wrap  74  of the orbiting scroll  68  and the spiral wraps  74 ,  386  define pockets (e.g., similar or identical to pockets  94 ,  96 ,  97 ,  98 ,  99 ,  100 ,  102 ,  104  described above). 
     An annular recess  393  may be formed in the end plate  384  of the non-orbiting scroll  370 . An annular floating seal assembly  320  (similar or identical to the floating seal  20  described above) may be received within the annular recess  393 . The floating seal assembly  20  may be sealingly engaged with the partition  34  and inner and outer diametrical surfaces  394 ,  395  that define the recess  393 . In this manner, the floating seal assembly  320  fluidly separates the suction-pressure region  106  of the compressor  10  from the discharge chamber  38  of the compressor  10 . An axial biasing chamber  402  is axially between and defined by the floating seal assembly  320  and an axially facing surface  396  of the end plate  384 . 
     The end plate  384  may include a first passage  404  and a second passage  406 . In some configurations, the first and second passages  404 ,  406  may extend radially through a portion of the end plate  384 . One end of the first passage  404  may be open to and in fluid communication with the discharge passage  392 . The other end of the first passage  404  may be fluidly coupled with the valve assembly  372 . One end of the second passage  406  may be open to and in fluid communication with the axial biasing chamber  402 . The other end of the second passage  406  may be fluidly coupled with the valve assembly  372 . 
     The valve assembly  372  may include a valve body  408  and a valve member  410 . The valve member  410  is movable relative to the valve body  408  between a first position ( FIG. 11 ) and a second position ( FIG. 12 ). When the valve member  410  is in the first position, the valve assembly  372  provides fluid communication between the axial biasing chamber  402  and the suction-pressure region  106  of the compressor  10 . When the valve member  410  is in the second position, the valve assembly  372  provides fluid communication between the axial biasing chamber  402  and the discharge passage  392  (i.e., a discharge-pressure region). 
     The valve body  408  may include a first body member  412  and a second body member  414 . The first body member  412  may be mounted to the end plate  384  and may include first, second and third apertures  416 ,  418 ,  420  and a recess  422 . The first aperture  416  may be fluidly connected to the second passage  406  in the end plate  384 . The second aperture  418  may be fluidly connected to the first passage  404  in the end plate  384 . The third aperture  420  may be open to and in fluid communication with the suction-pressure region  106 . The recess  422  in the first body member  412  may movably receive the valve member  410 . 
     The second body member  414  may include a communication passage  424 . The communication passage  424  may be: (a) in constant fluid communication with the first aperture  416  of the first body member  412 , (b) in selective fluid communication with second aperture  418  of the first body member  412 , and (c) in selective fluid communication with the third aperture  420  of the first body member  412 . 
     The valve member  410  is disposed within the recess  422  in the first body member  412  and is movable within the recess  422  between the first and second positions. The valve member  410  may include a first aperture  426  and a second aperture  428 . 
     When the valve member  410  is in the first position ( FIG. 11 ): (a) the valve member  410  blocks fluid communication between the second aperture  418  of the first body member  412  and the communication passage  424  in the second body member  414 , thereby blocking fluid communication between the discharge passage  392  and the axial biasing chamber  402 ; and (b) the second aperture  428  in the valve member  410  provides fluid communication between the third aperture  420  of the first body member  412  and the communication passage  424  of the second body member  414 , thereby providing fluid communication between the suction-pressure region  106  and the axial biasing chamber  402 . 
     When the valve member  410  is in the second position ( FIG. 12 ): (a) the valve member  410  blocks fluid communication between the third aperture  420  of the first body member  412  and the communication passage  424  in the second body member  414 , thereby blocking fluid communication between the suction-pressure region  106  and the axial biasing chamber  402 ; and (b) the first aperture  426  in the valve member  410  provides fluid communication between the second aperture  418  of the first body member  412  and the communication passage  424  of the second body member  414 , thereby providing fluid communication between the discharge passage  392  and the axial biasing chamber  402 . 
     In some configurations, the valve assembly  372  may be a MEMS (micro-electro-mechanical systems) valve assembly. For example, the valve member  410  may include silicon ribs (or other resistive elements). A flow of electrical current through the silicon ribs causes the silicon ribs to expand (due to thermal expansion), which results in linear displacement of the valve member  410 . 
     The valve assembly  372  may include a control module  430  having processing circuitry for controlling movement of the valve member  410  between the first and second positions. The valve assembly  372  may be in communication with pressure sensors (or the valve assembly  372  may have built-in pressure sensing capability) to detect pressures of working fluid within the suction-pressure region  106 , the axial biasing chamber  402 , and the discharge passage  392 . The control module  430  may control movement of the valve member  410  based on the values of such pressures (and/or based on additional or alternative operating parameters) to maintain optimum pressures within the axial biasing chamber  402  to provide optimum the force biasing non-orbiting scroll  370  toward the orbiting scroll  68  at various operating conditions in the operating envelope of the compressor  10 . The valve assembly  372  may also function as a high-pressure cutout device or pressure-relief valve to vent the axial biasing chamber  402  to the suction-pressure region  106  if pressure within the axial biasing chamber  402  raises above a predetermined threshold. 
     At initial startup of the compressor  10 , the control module  430  may position the valve member  410  at the second position ( FIG. 12 ) so that discharge-pressure working fluid is communicated to the axial biasing chamber  402  to provide sufficient initial axial loading of the non-orbiting scroll  370  against the orbiting scroll  68 . 
     During operation of the compressor  10 , the control module  430  may receive signals from sensors measuring suction and discharge pressures (or pressures within the suction-pressure region  106  and discharge passage  392 ) and reference a lookup table stored in the memory of the control module  430  to determine a desired or ideal pressure value for the axial biasing chamber  402  for a given set of suction and discharge pressures. The control module  430  could pulse the valve member  410  between the first and second positions to achieve the ideal pressure value. After achieving the desired pressure in the axial biasing chamber  402 , the control module  430  may move the valve member  410  to a third position (e.g., downward relative to the second position shown in  FIG. 12 ) in which both of the apertures  426 ,  428  in the valve member  410  are blocked from fluid communication with both of the apertures  418 ,  420  in the valve body  408  to prevent fluid communication between the axial biasing chamber  402  and the suction-pressure region  106  and between the axial biasing chamber  402  and the discharge passage  392 . Thereafter, the control module  430  could move or pulse (e.g., pulse-width-modulate) the valve member  410  among any of the first, second and third positions, as appropriate. 
     In some configurations, during shutdown of the compressor  10 , the control module  430  may position the valve member  410  in the first position ( FIG. 11 ) so that suction-pressure working fluid is communicated to the axial biasing chamber  402  to allow the floating seal assembly  320  to drop down further into the recess  393  and allow discharge gas in the discharge chamber  38  to flow into the suction-pressure region  106  to prevent reverse rotation of the orbiting scroll  68 . 
     While the valve body  408  is described above as having the first and second body members  412 ,  414 , in some configurations, the valve body  408  could be a one-piece valve body. Furthermore, while the valve assembly  372  is described above as a MEMS valve assembly, in some configurations, the valve assembly  372  could be any other type of valve assembly, such as a solenoid, piezoelectric, or stepper valve, for example (i.e., the valve member  410  could be actuated by a solenoid, piezoelectric, or stepper actuator). 
     With reference to  FIGS. 13 and 14 , another alternative non-orbiting scroll  570  and valve assembly  572  are provided. The non-orbiting scroll  570  and valve assembly  572  could be incorporated into the compressor  10  instead of the non-orbiting scroll  70  and capacity modulation assembly  28  and instead of the non-orbiting scroll  370  and valve assembly  372 . 
     The structure and function of the non-orbiting scroll  570  and valve assembly  572  may be similar or identical to that of the non-orbiting scroll  370  and valve assembly  372 , apart from exceptions noted below. Therefore, at least some similar features will not be described again in detail. 
     Like the non-orbiting scroll  370 , the non-orbiting scroll  570  may include an end plate  584 , a spiral wrap  586 , and a recess  593  in the end plate  584  in which a floating seal assembly  520  is received to define an axial biasing chamber  602 . The floating seal assembly  520  may be similar or identical to the floating seal assembly  20 ,  320 . The end plate  584  may include a passage  606  (like the passage  406 ) that is open to and in fluid communication with the axial basing chamber  604  at one end and fluidly connected to the valve assembly  572  at the other end. 
     Instead of the first passage  404 , the end plate  584  may include may include an outer ICP passage or port  605  and an inner ICP passage or port  607 . One end of the outer port  605  may be open to and in fluid communication with a first intermediate-pressure compression pocket  598  (e.g. like pocket  98  described above) and the other end of the outer port  605  may be fluidly connected to the valve assembly  572 . One end of the inner port  607  may be open to and in fluid communication with a second intermediate-pressure compression pocket  600  (e.g. like pocket  100  described above) that is disposed radially inward relative to the first intermediate-pressure pocket  598  and is at an intermediate pressure that is higher than the pressure of pocket  598 . The other end of the inner port  607  may be fluidly connected to the valve assembly  572 . 
     The valve assembly  572  may include a valve body  508  and a valve member  510 . The valve member  510  is movable relative to the valve body  508  between a first position ( FIG. 13 ) and a second position ( FIG. 14 ). When the valve member  510  is in the first position, the valve assembly  572  provides fluid communication between the axial biasing chamber  502  and the first intermediate-pressure pocket  598 . When the valve member  510  is in the second position, the valve assembly  572  provides fluid communication between the axial biasing chamber  502  and the second intermediate-pressure pocket  600 . 
     The valve body  508  may include a first body member  512  and a second body member  514 . The first body member  512  may be mounted to the end plate  584  and may include first, second and third apertures  516 ,  518 ,  520  and a recess  522 . The first aperture  516  may be fluidly connected to the passage  606  in the end plate  584 . The second aperture  518  may be fluidly connected to the inner port  607  in the end plate  584 . The third aperture  520  may be open to and in fluid communication with the outer port  605  in the end plate  584 . The recess  522  in the first body member  512  may movably receive the valve member  510 . 
     The second body member  514  may include a communication passage  524 . The communication passage  524  may be: (a) in constant fluid communication with the first aperture  516  of the first body member  512 , (b) in selective fluid communication with second aperture  518  of the first body member  512 , and (c) in selective fluid communication with the third aperture  520  of the first body member  512 . 
     The valve member  510  is disposed within the recess  522  in the first body member  512  and is movable within the recess  522  between the first and second positions. The valve member  510  may include a first aperture  526  and a second aperture  528 . 
     When the valve member  510  is in the first position ( FIG. 13 ): (a) the valve member  510  blocks fluid communication between the second aperture  518  of the first body member  512  and the communication passage  524  in the second body member  514 , thereby blocking fluid communication between the second intermediate-pressure pocket  600  and the axial biasing chamber  602 ; and (b) the second aperture  528  in the valve member  510  provides fluid communication between the third aperture  520  of the first body member  512  and the communication passage  524  of the second body member  514 , thereby providing fluid communication between the first intermediate-pressure pocket  598  and the axial biasing chamber  402 . 
     When the valve member  510  is in the second position ( FIG. 14 ): (a) the valve member  510  blocks fluid communication between the third aperture  520  of the first body member  512  and the communication passage  524  in the second body member  514 , thereby blocking fluid communication between the first intermediate-pressure pocket  598  and the axial biasing chamber  502 ; and (b) the first aperture  526  in the valve member  510  provides fluid communication between the second aperture  518  of the first body member  512  and the communication passage  524  of the second body member  514 , thereby providing fluid communication between the second intermediate-pressure pocket  600  and the axial biasing chamber  602 . 
     In some configurations, the valve assembly  572  may be a MEMS (micro-electro-mechanical systems) valve assembly and may include a control module  530  having processing circuitry for controlling movement of the valve member  510  between the first and second positions. The control module  530  may control the valve member  510  in the same or a similar manner as described above with respect to the control module  430  and valve member  410 . In some configurations, the valve assembly  572  could be any other type of valve assembly, such as a solenoid, piezoelectric, or stepper valve, for example (i.e., the valve member  510  could be actuated by a solenoid, piezoelectric, or stepper actuator). 
     With reference to  FIGS. 15-23 , another alternative non-orbiting scroll  770 , valve assembly  772 , and capacity modulation system  728  are provided. The non-orbiting scroll  770 , valve assembly  772  and capacity modulation system  728  could be incorporated into the compressor  10  instead of the non-orbiting scroll  70 ,  310 , ICP valves  206 ,  210 ,  312 ,  314 , modulation control valve  158 , and capacity modulation assembly  28  and instead of the non-orbiting scroll  370  and valve assembly  372 . That is, the valve assembly  772  can replace the ICP valves  206 ,  210 ,  312 ,  314  and the modulation control valve  158 . 
     The structure and function of the non-orbiting scroll  770  and capacity modulation system  728  may be similar to that of the non-orbiting scroll  70  and capacity modulation system  28 . Therefore, at least some similar features will not be described again in detail. 
     The non-orbiting scroll  770  may include an end plate  784  and a spiral wrap  786 . The spiral wrap  786  may be meshingly engaged with the spiral wrap  74  of the orbiting scroll  68  and the spiral wraps  74 ,  786  define pockets (e.g., similar or identical to pockets  94 ,  96 ,  97 ,  98 ,  99 ,  100 ,  102 ,  104  described above). 
     The end plate  784  may include one or more modulation passages or ports  812 ,  814 . The modulation ports  812 ,  814  may be open to and in fluid communication with respective intermediate-pressure pockets  96 - 102 . The end plate  784  may also include an outer ICP passage or port  824 , and an inner ICP passage or port  826  (shown schematically in  FIGS. 15 and 16 ). The inner port  826  is disposed radially inward relative to the outer port  824  and is in fluid communication with a second one of the intermediate-pressure pockets (e.g., like  96 - 102 ). 
     One end of the outer port  824  may be open to and in fluid communication with a first intermediate-pressure compression pocket  798  (e.g. like pocket  98 ) and the other end of the outer port  824  may be fluidly connected to the valve assembly  772 . One end of the inner port  826  may be open to and in fluid communication with a second intermediate-pressure compression pocket  800  (e.g. like pocket  100  described above) that is disposed radially inward relative to the first intermediate-pressure pocket  798  and is at an intermediate pressure that is higher than the pressure of pocket  798 . The other end of the inner port  826  may be fluidly connected to the valve assembly  772 . 
     The capacity modulation assembly  728  may include a valve ring  854  (e.g., similar to the valve ring  154 ) and a lift ring  856  (e.g., similar or identical to the lift ring  156 ). The valve ring  854  may encircle and sealingly engage a central annular hub  788  of the end plate  784 . The lift ring  856  may be received within an annular recess  876  formed in the valve ring  854  and may include a plurality of posts or protrusions (not shown; e.g., like protrusions  192 ) that contact the end plate  384 . 
     The lift ring  856  may cooperate with the valve ring  854  to define a modulation control chamber  898  (e.g., like modulation control chamber  198 ). That is, the modulation control chamber  898  is defined by and disposed axially between opposing axially facing surfaces of the lift ring  856  and the valve ring  854 . A first control passage  900  (shown schematically in  FIGS. 15 and 16 ) may extend through a portion of the valve ring  854 , for example, and may extend from the modulation control chamber  898  to the valve assembly  772 . The first control passage  900  fluidly communicates with the modulation control chamber  898  and the valve assembly  772 . 
     An annular floating seal  820  (similar or identical to the floating seal  120 ,  320 ) may be disposed radially between the hub  788  of the end plate  784  and an annular rim  855  of the valve ring  854 . The floating seal  820  may sealingly engage the hub  788  and the rim  855 . The floating seal  820 , the end plate  784 , and the valve ring  854  cooperate to form an axial biasing chamber  902 . 
     A second control passage  904  (shown schematically in  FIGS. 15 and 16 ) may extend through a portion of the valve ring  854 , for example, and may extend from the axial biasing chamber  902  to the valve assembly  772 . The second control passage  904  fluidly communicates with the biasing chamber  902  and the valve assembly  772 . 
     The valve ring  854  may be movable relative to the end plate  784  between a first position ( FIG. 15 ) and a second position ( FIG. 16 ). In the first position, the valve ring  854  axially abuts the end plate  784  and blocks fluid communication between the modulation ports  812 ,  814  and the suction-pressure region  106  of the compressor  10 . The valve ring  854  is axially movable relative to the end plate  784  and floating seal  820  from the first position to the second position such that, in the second position ( FIG. 16 ), the modulation ports  812 ,  814  are allowed to fluidly communicate with the suction-pressure region  106 . 
     As shown in  FIGS. 17-23 , the valve assembly  772  may include a valve body  910  and a valve member  912  that is movable relative to the valve body  910  between a first position ( FIGS. 15 and 18-20 ) and a second position (FIGS.  16  and  21 - 23 ). As shown in  FIG. 15 , when the valve member  912  is in the first position, the valve member  912 : (a) provides fluid communication between the outer port  824  and the axial biasing chamber  902 , (b) blocks fluid communication between the inner port  826  and the axial biasing chamber  902 , (c) provides fluid communication between the modulation control chamber  898  and the suction-pressure region  106 , and (d) blocks fluid communication between the axial biasing chamber  902  and the modulation control chamber  898 . As shown in  FIG. 16 , when the valve member  912  is in the second position, the valve member  912 : (a) allows fluid communication between the axial biasing chamber  902 , the modulation control chamber  898 , and the inner port  826 , (b) blocks fluid communication between the outer port  824  and the axial biasing chamber  902 , and (c) blocks fluid communication between the modulation control chamber  898  and the suction-pressure region  106 . Moving the valve member  912  to the first position ( FIGS. 18-20 ) moves the valve ring  854  to the first position ( FIG. 15 ), which allows the compressor  10  to operate at full capacity. Moving the valve member  912  to the second position ( FIGS. 21-23 ) moves the valve ring  854  to the second position ( FIG. 16 ), which allows the compressor  10  to operate at a reduced capacity. 
     As shown in  FIG. 17 , the valve body  910  may include a cavity  914  in which the valve member  912  is movably disposed. A lid or cap  915  may enclose the valve member  912  within the cavity  914 . The valve body  910  may include a first opening  916 , a second opening  918 , a third opening  920 , a fourth opening  922 , and a fifth opening  924 . The openings  916 ,  918 ,  920 ,  922 ,  924  extend through walls of the valve body  910  to the cavity  914 . First and second recesses  926 ,  928  may be formed in an interior wall of the valve body  910  (e.g., an interior wall defining the cavity  914 ). The first recess  926  is open to and in communication with the fourth opening  922 . The second recess  928  is open to and in communication with the fifth opening  924 . 
     The first opening  916  in the valve body  910  may be fluidly connected (either directly or via a conduit or connector) to the inner port  826  in the end plate  784 . The second opening  918  in the valve body  910  may be fluidly connected (either directly or via a conduit or connector) to the outer port  824  in the end plate  784 . The third opening  920  in the valve body  910  may be open to in in fluid communication with the suction-pressure region  106  of the compressor  10 . The fourth opening  922  in the valve body  910  may be fluidly connected (e.g., via a conduit or connector) to the axial biasing chamber  902 . The fifth opening  924  in the valve body  910  may be fluidly connected (e.g., via a conduit or connector) to the modulation control chamber  898 . 
     As shown in  FIGS. 17-23 , the valve member  912  may include a first aperture  930 , a second aperture  932 , a third aperture  934 , and a fourth aperture  936 . A fifth aperture  938  ( FIGS. 18 and 21 ) may fluidly connect the first aperture  930  with the third aperture  934 . 
     As shown in  FIGS. 18-20 , when the valve member  912  is in the first position: (a) the first aperture  930  in the valve member  912  is blocked from fluid communication with the first opening  916  in the valve body  910 , and the first and third apertures  930 ,  934  in the valve member  912  are blocked from fluid communication with the first and second recesses  926 ,  928  and the fourth and fifth openings  922 ,  924  in the valve body  910  (as shown in  FIG. 18 ), thereby blocking fluid communication among the inner port  826 , the axial biasing chamber  902  and the modulation control chamber  898 ; (b) the second aperture  932  in the valve member  912  is in fluid communication with the second and fourth openings  918 ,  922  in the valve body  910  (as shown in  FIG. 19 ), thereby providing fluid communication between the outer port  824  and the axial biasing chamber  902 ; (c) the fourth aperture  936  in the valve member  912  is in fluid communication with the third and fifth openings  920 ,  924  in the valve body  910 , thereby providing fluid communication between the modulation control chamber  898  and the suction-pressure region  106 . By venting the modulation control chamber  898  to the suction-pressure region  106 , intermediate-pressure fluid in the axial biasing chamber  902  forces the valve ring  854  axially against the end plate  784 , to close off fluid communication between the modulation ports  812 ,  814  and the suction-pressure region  106  (as shown in  FIG. 15 ). 
     As shown in  FIGS. 21-23 , when the valve member  912  is in the second position: (a) the first aperture  930  in the valve member  912  is in fluid communication with the first opening  916  in the valve body  910 , and the first and third apertures  930 ,  934  in the valve member  912  are in fluid communication with the first and second recesses  926 ,  928  and the fourth and fifth openings  922 ,  924  in the valve body  910  (as shown in  FIG. 21 ), thereby allowing fluid communication among the inner port  826 , the axial biasing chamber  902  and the modulation control chamber  898 ; (b) the second aperture  932  in the valve member  912  is blocked from fluid communication with the second and fourth openings  918 ,  922  in the valve body  910  (as shown in  FIG. 22 ), thereby blocking fluid communication between the outer port  824  and the axial biasing chamber  902 ; (c) the fourth aperture  936  in the valve member  912  is blocked from fluid communication with the third and fifth openings  920 ,  924  in the valve body  910 , thereby blocking fluid communication between the modulation control chamber  898  and the suction-pressure region  106 . By providing intermediate-pressure fluid from the inner port  826  to the modulation control chamber  898 , the intermediate-pressure fluid in the modulation control chamber  898  forces the valve ring  854  axially away from the end plate  784  (toward the floating seal  820 ), to open the modulation ports  812 ,  814  to allow fluid communication between the modulation ports  812 ,  814  and the suction-pressure region  106  (as shown in  FIG. 16 ). 
     In some configurations, the valve assembly  772  may be a MEMS (micro-electro-mechanical systems) valve assembly and may include a control module having processing circuitry for controlling movement of the valve member  912  between the first and second positions. In some configurations, the valve assembly  772  could be any other type of valve assembly, such as a solenoid, piezoelectric, or stepper valve, for example (i.e., the valve member  912  could be actuated by a solenoid, piezoelectric, or stepper actuator). 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.