Abstract:
A reciprocating compressor may include a shell, a first cylinder, a plate, a second cylinder, and a piston. The first cylinder may be disposed within the shell and may include a first valve. The plate may be fixed relative to the first cylinder and may include a second valve. The second cylinder may be axially aligned with the first cylinder and may be moveable relative to the first cylinder between first and second positions. The piston may be disposed within the second cylinder and may include a third valve. The piston may reciprocate relative to the first and second cylinders. The piston and the plate may define a first compression chamber therebetween. The piston and the first cylinder may define a second compression chamber therebetween. A fluid-injection passage extending through the first cylinder selectively provides a working fluid from a source to the second compression chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. patent application Ser. No. 14/337,589, filed Jul. 22, 2014, now U.S. Pat. No. 9,476,414, and U.S. Provisional Application No. 61/863,550, filed on Aug. 8, 2013. The entire disclosure of the above applications is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to a variable capacity reciprocating compressor. 
       BACKGROUND 
       [0003]    This section provides background information related to the present disclosure and is not necessarily prior art. 
         [0004]    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 
       [0005]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0006]    In one form, the present disclosure provides a reciprocating compressor that may include a shell, a first cylinder, a plate, a second cylinder, and a piston. The first cylinder may be disposed within the shell and may include a first valve. The plate may be fixed relative to the first cylinder and may include a second valve. The second cylinder may be axially aligned with the first cylinder and may be moveable relative to the first cylinder between first and second positions. The piston may be disposed within the second cylinder and may include a third valve. The piston may reciprocate relative to the first and second cylinders. The piston and the plate may define a first compression chamber therebetween. The piston and the first cylinder may define a second compression chamber therebetween. 
         [0007]    In some embodiments, the third valve may be movable between a first position restricting communication between the first and second compression chambers and a second position allowing communication between the first and second compression chambers. 
         [0008]    In some embodiments, an inner diametric surface of the second cylinder may include an opening extending therethrough and communicating with an interior volume of the shell. 
         [0009]    In some embodiments, the opening in the second cylinder may be isolated from the first compression chamber when the second cylinder is in the first position and may be allowed to communicate with the first compression chamber when the second cylinder is in the second position. 
         [0010]    In some embodiments, motion of the piston toward the plate compresses fluid within the first compression chamber and forces fluid into the second compression chamber. 
         [0011]    In some embodiments, fluid within the first compression chamber may be compressed therein to a first pressure when the second cylinder is in the first position and may be compressed therein to a second pressure when the second cylinder is in the second position. The second pressure may be lower than the first pressure. 
         [0012]    In some embodiments, fluid may be compressed to a first discharge pressure in the second compression chamber when the second cylinder is in the first position and fluid is compressed to a second discharge pressure in the second compression chamber when the second cylinder is in the second position. The second discharge pressure may be lower than the first discharge pressure. 
         [0013]    In some embodiments, the first cylinder may include a fluid-injection passage in communication with the second compression chamber. 
         [0014]    In some embodiments, the reciprocating compressor may include a crankshaft driving the piston. The second cylinder may move between the first and second positions independently of motion of the crankshaft. 
         [0015]    In another form, the present disclosure provides a reciprocating compressor operable in a full-capacity mode and in a reduced-capacity mode. The reciprocating compressor may include first and second cylinders and a piston. The second cylinder may at least partially surround the first cylinder and may be axially movable relative to the first cylinder between a first position corresponding to the full-capacity mode and a second position corresponding to the reduced-capacity mode. The piston may reciprocate within the second cylinder and may reciprocatingly receiving the first cylinder. 
         [0016]    In some embodiments, the first cylinder and the piston may define a compression chamber therebetween. 
         [0017]    In some embodiments, the first cylinder may include a fluid-injection passage in communication with the compression chamber. 
         [0018]    In some embodiments, the reciprocating compressor may include a plate fixed relative to the first cylinder and cooperating with the piston and the second cylinder to define a first compression chamber. The piston and the first cylinder may cooperate to define a second compression chamber therebetween. 
         [0019]    In some embodiments, the piston may include a first valve movable between a first position restricting communication between the first and second compression chambers and a second position allowing communication between the first and second compression chambers. 
         [0020]    In some embodiments, the plate may include a second valve that may close to restrict fluid flow into the first compression chamber when the piston is moving toward the plate and may open to allow fluid flow into the first compression chamber when the piston is moving away from the plate. 
         [0021]    In some embodiments, the first cylinder may include a third valve that closes to restrict fluid flow out of the second compression chamber when the piston is moving toward the plate and opens to allow fluid flow out of the second compression chamber when the piston is moving away from the plate. 
         [0022]    In some embodiments, fluid within the first compression chamber may be compressed therein to a first pressure when the second cylinder is in the first position and may be compressed therein to a second pressure when the second cylinder is in the second position. The second pressure may be lower than the first pressure. 
         [0023]    In some embodiments, an inner diametric surface of the second cylinder may include an opening extending therethrough. 
         [0024]    In some embodiments, the opening in the second cylinder may be isolated from the first compression chamber when the second cylinder is in the first position. The opening may be allowed to communicate with the first compression chamber when the second cylinder is in the second position. 
         [0025]    In some embodiments, the reciprocating compressor may include a crankshaft driving the piston. The second cylinder may move between the first and second positions independently of motion of the crankshaft. 
         [0026]    In some embodiments, the piston may compress fluid to a first discharge pressure when the second cylinder is in the first position and the piston may compress fluid to a second discharge pressure when the second cylinder is in the second position. The second discharge pressure may be lower than the first discharge pressure. 
         [0027]    In another form, the present disclosure provides a compressor including a compression mechanism that may include a piston and a cylinder defining a compression chamber therebetween. The piston may be movable within the cylinder in a first direction to draw working fluid into the compression chamber and movable within the cylinder in a second direction to compressor the working fluid in the compression chamber and discharge compressed working fluid from the compression chamber through a passage. The cylinder including an opening in selective communication with the compression chamber. The compression mechanism may be operable in a full-capacity mode in which communication between the compression chamber and the opening is restricted and in a reduced-capacity mode in which communication between the opening and the compression chamber is allowed during at least a portion of a duration of movement of the piston in the second direction. 
         [0028]    In some embodiments, the compressor may include a shell containing the compression mechanism. In some embodiments, the shell may define a suction-pressure chamber in communication with the opening in the cylinder. In some embodiments, the cylinder may be movable relative to the shell between a first position allowing communication between the opening and the compression chamber and a second position restricting communication between the opening and the compression chamber. 
         [0029]    In some embodiments, the compression mechanism may be a single-stage compression mechanism. 
         [0030]    In some embodiments, the compression mechanism may be a multi-stage compression mechanism. 
         [0031]    In some embodiments, the compression mechanism includes a fluid-injection passage extending through the first cylinder and provides a working fluid from a source. A valve in the fluid-injection passage is moveable between an open position allowing fluid to be injected into the second compression chamber through the fluid-injection passage and a closed position restricting fluid communication between the second compression chamber and the fluid-injection passage. 
         [0032]    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 
         [0033]    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. 
           [0034]      FIG. 1  is a schematic representation of a compressor including a compression mechanism according to the principles of the present disclosure; 
           [0035]      FIG. 2  is a schematic cross-sectional view of a piston-cylinder assembly of the compression mechanism of  FIG. 1  in a full-capacity mode with a piston in a first position; 
           [0036]      FIG. 3  is a schematic cross-sectional view of the piston-cylinder assembly in the full-capacity mode with the piston in a second position; 
           [0037]      FIG. 4  is a schematic cross-sectional view of the piston-cylinder assembly in the full-capacity mode with the piston in a third position; 
           [0038]      FIG. 5  is a schematic cross-sectional view of the piston-cylinder assembly in a reduced-capacity mode with the piston in a first position; 
           [0039]      FIG. 6  is a schematic cross-sectional view of the piston-cylinder assembly in the reduced-capacity mode with the piston in a second position; 
           [0040]      FIG. 7  is a schematic cross-sectional view of the piston-cylinder assembly in the reduced-capacity mode with the piston in a third position; 
           [0041]      FIG. 8  is a schematic cross-sectional view of another piston-cylinder assembly having a fluid-injection passage; and 
           [0042]      FIG. 9  is a schematic cross-sectional view of a compression mechanism having a plurality of piston-cylinder assemblies according to the principles of the present disclosure. 
       
    
    
       [0043]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0044]    Example embodiments will now be described more fully with reference to the accompanying drawings 
         [0045]    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. 
         [0046]    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. 
         [0047]    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. 
         [0048]    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. 
         [0049]    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. 
         [0050]    With reference to  FIGS. 1-7 , a compressor  10  is provided that may include a shell  12 , a motor assembly  14  and one or more compression mechanisms  16 . The shell  12  may be a hermetic shell and may define an interior volume  18  that receives suction-pressure working fluid (e.g., refrigerant) through a suction inlet  20 . The motor assembly  14  may be disposed within the shell  12  and may drivingly engage a crankshaft  22  that is operatively coupled to the compression mechanism  16 . The compression mechanism  16  may draw in working fluid from the interior volume  18  and may discharge compressed working fluid into a discharge muffler  24  and subsequently out of the compressor  10  through a discharge outlet  26 . As will be subsequently described, the compression mechanism  16  may be operable in a full-capacity mode and a reduced-capacity mode. 
         [0051]    The compression mechanism  16  may include a first cylinder  28 , a suction plate  30 , a piston  32 , and a second cylinder  34 . The first cylinder  28  may be fixed relative to the discharge muffler  24  and the shell  12  and may include an outer diametrical surface  36 , an inner diametrical surface  38 , and an axial end wall  40 . The inner diametrical surface  38  and axial end wall  40  may define a conduit  42  in fluid communication with the discharge muffler  24 . The axial end wall  40  may include a discharge passage  44  extending therethrough and in selective communication with the conduit  42 . A first valve member  46  may be movable relative to the axial end wall  40  between an open position ( FIGS. 2 and 4 ) allowing fluid flow through the discharge passage  44  and a closed position ( FIG. 3 ) restricting fluid flow through the discharge passage  44 . The first valve member  46  can be any suitable type of valve. For example, in some embodiments, the first valve member  46  may be actuated by a difference in fluid pressures upstream and downstream of the discharge passage  44 . In some embodiments, the first valve member  46  could be an electromechanically actuated valve, for example. 
         [0052]    The suction plate  30  may be fixed relative to the first cylinder  28  and may be spaced apart and generally parallel to the axial end wall  40 . The suction plate  30  may include an outer circumferential surface  48  and one or more suction passages  50 . The circumferential surface  48  may slidably engage the second cylinder  34 . In some embodiments, a piston ring (not shown) or other sealing member may sealingly engage the circumferential surface  48  and the second cylinder  34 . One or more second valve members  52  may be movable relative to the suction plate  30  between an open position ( FIGS. 2 and 4 ) allowing fluid flow through the suction passages  50  and a closed position ( FIG. 3 ) restricting fluid flow through the suction passages  50 . The second valve member  52  can be any suitable type of valve. For example, in some embodiments, the second valve member  52  may be actuated by a difference in fluid pressures upstream and downstream of the suction passages  50  (i.e., a fluid-pressure differential between the interior volume  18  and the first compression chamber  62 . In some embodiments, the second valve member  52  could be an electromechanically actuated valve, for example. 
         [0053]    The piston  32  may include a base portion  54  and a cup portion  56 . The base portion  54  may be generally parallel to and disposed between the suction plate  30  and the axial end wall  40  of the first cylinder  28 . A circumferential surface  58  of the base portion  54  may slidably engage the second cylinder  34 . The cup portion  56  may extend in an axial direction from the base portion  54  and may reciprocatingly receive the first cylinder  28 . An inner diametrical surface  60  of the cup portion  56  may slidably and sealingly engage the outer diametrical surface  36  of the first cylinder  28 . One or more connecting rods  61  ( FIG. 1 ) may couple the piston  32  to the crankshaft  22  so that rotation of the crankshaft  22  causes corresponding reciprocation of the piston  32  relative to the first and second cylinders  28 ,  34  and the suction plate  30 . 
         [0054]    The base portion  54  of the piston  32 , the suction plate  30  and the second cylinder  34  may cooperate to define a first compression chamber  62 . The base portion  54 , the cup portion  56 , and the axial end wall  40  of the first cylinder  28  may cooperate to define a second compression chamber  64 . The base portion  54  may include one or more intermediate passages  66  and one or more third valve members  68  that are movable relative to the base portion  54  between an open position ( FIG. 3 ) allowing fluid communication between the first and second compression chambers  62 ,  64  and a closed position ( FIGS. 2 and 4 ) restricting fluid communication between the first and second compression chambers  62 ,  64 . The third valve member  68  can be any suitable type of valve. For example, in some embodiments, the third valve member  68  may be actuated by a difference in fluid pressures upstream and downstream of the intermediate passages  66 . 
         [0055]    The second cylinder  34  may at least partially surround the first cylinder  28 , the suction plate  30 , and the piston  32  and may include one or more ports or openings  70  that extend radially through inner and outer diametrical surfaces  72 ,  74  of the second cylinder  34 . The second cylinder  34  may be movable in an axial direction relative to the first cylinder  28 , the suction plate  30 , and the piston  32  between a first position ( FIGS. 2-4 ) corresponding to the full-capacity mode and a second position ( FIGS. 5-7 ) corresponding to the reduced-capacity mode. An actuator  76  ( FIG. 1 ) may be coupled to the second cylinder  34  and may move the second cylinder  34  between the first and second positions. The actuator  76  could be or include any suitable type of actuator or motor, such as a solenoid or a stepper motor, for example, and may move the second cylinder  34  independently of the piston  32  and the crankshaft  22 . A controller (not shown) may control operation of the actuator  76  based on compressor and/or system operating parameters, for example. 
         [0056]    With continued reference to  FIGS. 1-7 , operation of the compressor  10  will be described in detail. As described above, the compression mechanism  16  may be operable in a full-capacity mode ( FIGS. 2-4 ) and a reduced-capacity mode ( FIGS. 5-7 ). In the full-capacity mode, the actuator  76  may position the second cylinder  34  such that the base portion  54  of the piston  32  remains between the suction plate  30  and the openings  70  in the second cylinder  34  during the entire reciprocation stroke of the piston  32  (i.e., travel of the piston  32  between a top-dead-center position ( FIG. 2 ) and a bottom-dead-center position ( FIG. 4 )). That is, in the full-capacity mode, the second cylinder  34  is positioned so that the openings  70  are restricted or prevented from fluidly communicating with the first compression chamber  62  while the piston  32  is reciprocating. In the reduced-capacity mode, the actuator  76  may position the second cylinder  34  such that the base portion  54  of the piston  32  remains between the suction plate  30  and the openings  70  during, at most, only a portion of a reciprocation stroke of the piston  32 . That is, in the reduced-capacity mode, the second cylinder  34  is positioned so that the openings  70  are able to fluidly communicate with the first compression chamber  62  during some or all of the reciprocation stroke of the piston  32 . 
         [0057]    In the full-capacity mode, movement of the piston  32  away from the suction plate  30  (as shown in  FIG. 2 ) may generate a pressure differential between the interior volume  18  and the first compression chamber  62  causing low-pressure working fluid from the interior volume  18  of the shell  12  to be drawn into the first compression chamber  62  through the suction passages  50 . Meanwhile, such movement of the piston  32  toward the axial end wall  40  may compress working fluid within the second compression chamber  64  and force the working fluid out of the second compression chamber  64  and into the conduit  42  through the discharge passage  44 . From the conduit  42 , the compressed working fluid may flow into the discharge muffler  24  and out of the compressor  10  through the discharge outlet  26 . 
         [0058]    After reaching the top-dead-center position, the piston  32  moves back toward the suction plate  30  (as shown in  FIG. 3 ), thereby compressing the working fluid in the first compression chamber  62 , which generates a fluid-pressure differential between the interior volume  18  and the first compression chamber  62  that closes the second valve member  52  and generates another fluid-pressure differential between the first and second compression chambers  62 ,  64  that opens the third valve member  68  to allow working fluid to flow from the first compression chamber  62  into the second compression chamber  64 . In this manner, in the full-capacity mode, the working fluid in the first compression chamber  62  is compressed to an intermediate pressure (while the piston  32  is moving toward the suction plate  30 ) before being drawn into the second compression chamber  64  for subsequent additional compression therein to a higher discharge pressure when the piston  32  moves back away from the suction plate  30 . 
         [0059]    In the reduced-capacity mode, the openings  70  are in fluid communication between the first compression chamber  62  for at least a portion of the stroke of the piston  32  so that working fluid within the first compression chamber  62  can leak to the interior volume  18 . Therefore, the pressure of the fluid within the first compression chamber  62  may be substantially equal to the pressure of the fluid within the interior volume  18  (i.e., suction pressure) as long as the first compression chamber  62  is in communication with the openings  70 . Therefore, in the reduced-capacity mode, the compression mechanism  16  may not begin to compress the working fluid until the base portion  54  of the piston  32  moves between the openings  70  and the suction plate  30  to seal off the first compression chamber  62  from the openings  70  (as shown in  FIG. 7 ). Therefore, when compression of the fluid within the first compression chamber  62  occurs over only a portion of the stroke of the piston  32  (if at all), the pressure of the fluid entering the second compression chamber  64  will be lower than in the full-capacity mode. Therefore, the first valve member  46  will be forced open for a shorter duration (i.e., the first valve member  46  will be open for fewer degrees of crankshaft rotation than in the full-capacity mode) and less discharge-pressure working fluid will be discharged from the second compression chamber  64  into the conduit  42  in the reduced-capacity mode. In the reduced-capacity mode, the actuator  76  may position the second cylinder  34  at any desired position to achieve any desired amount of compression (or lack thereof) in the first compression chamber  62 , which, in turn, controls the final capacity output of the compression mechanism  16 . 
         [0060]    With reference to  FIG. 8 , another compression mechanism  116  is provided that may include a first cylinder  128 , a suction plate  130 , a piston  132 , and a second cylinder  134 . The compression mechanism  116  may be incorporated into the compressor  10  in place of or in addition to the compression mechanism  16  and may be operable in a full-capacity mode and a reduced-capacity mode, as described above. The structure and function of the first cylinder  128 , suction plate  130 , piston  132 , and second cylinder  134  may be similar or identical to that of the first cylinder  28 , suction plate  30 , piston  32 , and second cylinder  34 , respectively, described above, apart from any exceptions described below. As described above, the suction plate  130  and the piston  132  may cooperate to define a first compression chamber  162  therebetween, and the piston  132  and the first cylinder  128  may cooperate to define a second compression chamber  164  therebetween. The second cylinder  134  may be movable relative to the suction plate  130  to control communication between openings  170  in the second cylinder  134  and the first compression chamber  162 , thereby controlling the capacity output of the compression mechanism  116 . 
         [0061]    The first cylinder  128  may include a vertically extending portion  138  having a fluid-injection passage  139  extending therethrough. A check valve  141  may be mounted to the first cylinder  128  and may be movable relative thereto between an open position allowing fluid to be injected into the second compression chamber  164  through the fluid-injection passage  139  and a closed position restricting fluid communication between the second compression chamber  164  and the fluid-injection passage  139 . The fluid-injection passage  139  may receive intermediate-pressure working fluid from an economizer or vapor-injection circuit (not shown), a metered liquid refrigerant supply, and/or oil from an oil separator or sump, for example. Fluid may be injected into the second compression chamber  164  through the fluid-injection passage  139  when the compression mechanism  116  is in the full-capacity mode or in the reduced capacity mode. Injecting intermediate-pressure working fluid into the second compression chamber  164  when the compression mechanism  116  is in the full-capacity mode may result in a capacity output of greater than one-hundred percent. 
         [0062]    With reference to  FIG. 9 , another compression mechanism  216  is provided and may include a plurality of piston-cylinder assemblies  217  operable in a full-capacity mode and a reduced-capacity mode, as described above. Each of the piston-cylinder assemblies  217  may be disposed within a common body  219  and may include a first cylinder  228 , a suction plate  230 , a piston  232 , and a second cylinder  234 . The structure and function of the first cylinder  228 , suction plate  230 , piston  232 , and second cylinder  234  may be generally similar to that of the first cylinder  28 , suction plate  30 , piston  32 , and second cylinder  34 , and therefore, will not be described again in detail. The compression mechanism  216  may be incorporated into the compressor  10 , for example. 
         [0063]    The first cylinders  228  may be integrally formed with the body  219  and each may include a conduit  242  in communication with a common manifold  243  formed in the body  219 . The manifold  243  may include an outlet  245  in communication with a discharge muffler (not shown) and/or an outlet (not shown) of the compressor. The body  219  may be fixed relative to the shell  12 . 
         [0064]    As described above, the suction plate  230  and the piston  232  may cooperate to define a first compression chamber  262  therebetween, and the piston  232  and the first cylinder  228  may cooperate to define a second compression chamber  264  therebetween. The pistons  232  may be driven by a common crankshaft  221 . As described above, the second cylinder  234  may be movable relative to the suction plate  230  to control communication between openings  270  in the second cylinder  234  and the first compression chamber  262 , thereby controlling the capacity output of the compression mechanism  216 . 
         [0065]    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.