Abstract:
In sealed compressors, in one form of the invention, the compressor housing and the compression mechanism are assembled to one another without fasteners. As a result, the time required to install and tighten the fasteners is eliminated, lessen the time required to assemble the compressor. Further, such a fastenerless assembly requires less parts and machining, further reducing the cost of the compressor. Additionally, in one form of the invention, the compression mechanism includes two bearings mounted to the compressor housing and a cylinder block reciprocatingly driven between the bearings by an eccentric member of the crankshaft. Typically, the cylinder block of existing compressors is rigidly mounted to the compressor housing and does not reciprocate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit under Title 35, U.S.C. § 119(e) of U.S. Provisional Patent Application Ser. No. 60/729,681, entitled COMPRESSOR, filed on Oct. 24, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to compressors and, in particular, compressors for refrigeration systems.  
         [0004]     2. Description of the Related Art  
         [0005]     Known compressors commonly have a three-part housing including a generally cylindrical main housing and end caps mounted to opposite ends of the main housing. The housing defines an interior space in which a compressor mechanism is mounted. Positive displacement rotary compressor mechanisms commonly include a crankshaft driven by a motor and an eccentric driven by the crankshaft. The eccentric rotates within a cylinder bore of a compressor mechanism cylinder block to compress refrigerant in a refrigeration system. Commonly, the compressor mechanism is fastened to the compressor housing through a plurality of fasteners. Often, a significant amount of time is required to machine and install the fasteners therein. An improvement over the forgoing is discussed below.  
       SUMMARY OF THE INVENTION  
       [0006]     In sealed compressors, in one form of the invention, the compressor housing and the compression mechanism are assembled to one another without fasteners. As a result, the time required to install and tighten the fasteners is eliminated, which lessens the time required to assemble the compressor. Further, such a fastenerless assembly requires fewer parts and machining, further reducing the cost of the compressor. Additionally, in one form of the invention, the compression mechanism includes two bearings mounted to the compressor housing and a cylinder block reciprocatingly driven between the bearings by an eccentric member of the crankshaft. Typically, the cylinder block of existing compressors is rigidly mounted to the compressor housing and does not reciprocate.  
         [0007]     In one form of the invention, the compressor includes a cylinder block that is mounted to, and reciprocatingly movable with respect to, a bearing mounted to a compressor housing. In one embodiment, an eccentric is positioned within a cylinder bore of the cylinder block and is driven by a rotating crankshaft. In this embodiment, the cylinder block is mounted to the bearing such that it can translate with respect to the bearing along an axis. The eccentric reciprocatingly drives the cylinder block back and forth along this axis as it rotates within the cylinder bore. In another embodiment, the bearing and a second bearing define a muffler chamber that encompasses the cylinder block. In operation, compressed refrigerant discharged from the cylinder bore of the cylinder block enters the muffler chamber wherein unwanted noise is dampened therein.  
         [0008]     In another form of the invention, a bearing is positioned within and, without fasteners, substantially rigidly mounted to a compressor housing. In one embodiment, the peripheral edge of the bearing is positioned within a recess defined by inner surfaces of first and second housing portions. During assembly, in this embodiment, the housing portions are pressed together and welded. The sides of the recess are compressed against the bearing and, as a result, the bearing is firmly contained within the recess and thereby substantially rigidly mounted to the compressor housing.  
         [0009]     In one form thereof, the present invention provide a compressor mechanism, including a shaft including an eccentric, a bearing, the shaft rotatably supported by the bearing, and a cylinder block, the cylinder block defining a cylinder bore extending therethrough, the eccentric positioned in the cylinder bore, wherein rotation of the shaft and the eccentric results in reciprocating translation of the cylinder block with respect to the bearing.  
         [0010]     In another form thereof, the present invention provides a compressor, including a housing including a first portion and a second portion, a compressor mechanism mounted within the housing, and a bearing compressed between the first second portions of the housing, the compressor mechanism mounted to the bearing, whereby the bearing is mounted to the housing solely by the compression between the first portion and the second portion of the housing.  
         [0011]     In another form thereof, the present invention provides a method of assembling a compressor including the steps of mounting a compressor assembly to a bearing, positioning the bearing within a housing having first and second housing portions, and pressing the first and second housing portions against the bearing to mount the bearing within the housing without the need for fasteners. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The above-mentioned and other features of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:  
         [0013]      FIG. 1  is a longitudinal cross-sectional view of a single cylinder compressor in accordance with an embodiment of the present invention;  
         [0014]      FIG. 2  is a cross-sectional, partial view of the compressor of  FIG. 1  with parts of the compressor removed;  
         [0015]      FIG. 3  is a transverse cross-sectional view of the compressor of  FIG. 1  taken along line  3 - 3  of  FIG. 1  with parts of the compressor removed;  
         [0016]      FIG. 4  is a perspective view of the compressor mechanism assembly of  FIG. 1 ;  
         [0017]      FIG. 5  is an exploded view of the compressor mechanism assembly of  FIG. 1 ;  
         [0018]      FIG. 6  is a second perspective view of the compressor mechanism assembly of  FIG. 1 ;  
         [0019]      FIG. 7  is a plan view of the leaf valve of the compressor of  FIG. 1 ;  
         [0020]      FIG. 8A  is an elevation view of the valve retainer of the compressor of  FIG. 1 ;  
         [0021]      FIG. 8B  is a plan view of the valve retainer of  FIG. 8A ;  
         [0022]      FIG. 9  is a plan view of the impeller of the compressor of  FIG. 1 ;  
         [0023]      FIG. 10A  is a plan view of the shaft plug of the compressor of  FIG. 1 ;  
         [0024]      FIG. 10B  is a cross-sectional view of the shaft plug of  FIG. 10A  taken along line  10 B- 10 B of  FIG. 10A ;  
         [0025]      FIG. 11  is a longitudinal cross-sectional view of a twin-cylinder compressor in accordance with an embodiment of the present invention;  
         [0026]      FIG. 12  is a cross-sectional, partial view of the twin-cylinder compressor of  FIG. 11  with parts of the compressor removed;  
         [0027]      FIG. 13  is a transverse cross-sectional view of the compressor of  FIG. 11  taken along line  13 - 13  of  FIG. 11  with parts of the compressor removed;  
         [0028]      FIG. 14A  is an end view of the compressor mechanism of  FIG. 1  with parts removed illustrating the eccentric in its top-dead-center (TDC) position;  
         [0029]      FIG. 14B  is an end view of the compressor mechanism of  FIG. 14A  illustrating the eccentric rotated 90 degrees from its TDC position;  
         [0030]      FIG. 14C  is an end view of the compressor mechanism of  FIG. 14A  illustrating the eccentric in its bottom-dead-center (BDC) position; and  
         [0031]      FIG. 14D  is an end view of the compressor mechanism of  FIG. 14A  illustrating the eccentric rotated 90 degrees from its BDC position.  
         [0032]     Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent exemplary embodiments of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain the present invention. The exemplifications set out herein illustrate exemplary embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     
    
     DETAILED DESCRIPTION  
       [0033]     Referring to  FIG. 1 , single-cylinder compressor  20  is shown which includes cylindrical main housing  22 , bottom cap  24  secured to a lower end  28  of housing  22 , and top cap  30  secured to an upper end  32  of housing  22 , each by a welding, brazing, or other suitable operation to thereby define an enclosed hermetic housing in which compressor mechanism  34  of compressor  20  is disposed. Compressor  20 , in this embodiment, is a vertical compressor and includes base  26  secured to bottom cap  24  to support the compressor in an upright position.  
         [0034]     Compressor mechanism  34  includes shaft  35 , reciprocating cylinder block  36 , eccentric  38  operatively engaged with shaft  35  and positioned within cylinder bore  37  of cylinder block  36 , lower bearing  40  and upper bearing  42 . In one exemplary embodiment, cylinder block  36  is mounted between and substantially surrounded by lower bearing  40  and upper bearing  42 . As illustrated in  FIG. 3 , eccentric  38  includes aperture  39 . Aperture  39  includes substantially cylindrical portion  31  and substantially flat portion  33  which are tightly interfitted with similar, corresponding geometries on shaft  35 . Due to corresponding and operatively engaged flat portions, shaft  35  and eccentric  38  are keyed together and the rotational motion of shaft  35  is transmitted to eccentric  38  during operation of the compressor.  
         [0035]     In operation, shaft  35  is rotated by electric motor  68 . Electric motor  68  includes rotor  64  affixed to shaft  35  and is positioned within stator  70 . Windings  72  of stator  70 , when energized by an electric source, create a rotating magnetic field which turns rotor  64 . In the present embodiment, windings  72  are energized from an outside electrical source through electrical connector  71 . Stator  70  includes outer substantially flat surfaces (not shown) which allow refrigerant to pass from suction inlet  74  in housing  22  through gaps (not shown) between the substantially flat sides of stator  70  and housing  22 .  
         [0036]     As illustrated in  FIGS. 1 and 3 , compressor mechanism  34  further includes guide members, such as dowels  44 , and bearing rollers  46 . Dowels  44  extend through, and are tightly interfitted with, apertures  48  of upper bearing  42  and apertures  50  of lower bearing  40  such that dowels  44  hold bearings  40  and  42  together prior to their placement into the compressor housing. Bearing rollers  46  may be substantially concentrically interfitted over dowels  44  and positioned between upper bearing  42  and lower bearing  40 . Bearing rollers  46 , along with dowels  44 , are positioned within guide recesses  52  ( FIG. 3 ) of cylinder block  36 , which define the relative reciprocal movement of cylinder block  36  with respect to bearings  40  and  42 , as discussed in detail further below. Guide recesses  52  may be subtantially linear, although other configurations may also be utilized.  
         [0037]     Referring to  FIGS. 1, 3 , and  14 A- 14 D, eccentric  38  is positioned within cylinder bore  37  and constantly engages a portion thereof. Eccentric  38  can directly or indirectly engage cylinder bore  37 , e.g, by way of a bushing, roller, et cetera between eccentric  38  and cylinder bore  37 . Eccentric  38 , in this embodiment, is substantially circular but is eccentrically positioned on shaft  35 . Cylinder bore  37 , in this embodiment, includes two substantially semicircular wall portions  41  and substantially straight walls  43 . Substantially straight walls  43  are substantially parallel to each other and define a dimension therebetween that is approximately the same size as, but slightly larger than, the diameter of circular eccentric  38 . In another way, at any rotational position of eccentric  38  within cylinder bore  37 , eccentric  38  is in sealing contact with straight walls  43 . Semicircular portions  41  each define a diameter that is the same size or slightly larger than the diameter of eccentric  38  and substantially equal to the above-mentioned dimension between side walls  43 . The centers of semicircular portions  41  are substantially co-linear with the mid-line between walls  43  wherein portions  41  and  43  define, essentially, an elongate cavity having rounded ends.  
         [0038]     As eccentric  38  is rotated by shaft  35 , eccentric  38  will typically bear against one of walls  43  of cylinder block  36  and reciprocatingly translate cylinder block  36  along axis  53  ( FIG. 14A ) defined by guide recesses  52 . More specifically, when eccentric  38  is in the position illustrated in  FIG. 14B , cylinder block  36  has been translated along axis  53  from its centered position illustrated in  FIG. 14A  to accommodate the eccentricity of eccentric  38 . When eccentric  38  is in the position illustrated in  FIG. 14C , cylinder block  36  has been driven back to a centered position as roller  38  is no longer eccentric with respect to the axis. When eccentric  38  is in the position illustrated in  FIG. 14D , eccentric  38  has translated cylinder block  36  in the opposite direction along axis  53  to, once again, accommodate the eccentricity of eccentric  38 . The positions of eccentric  38  illustrated in  FIGS. 14A-14D  occur once during each revolution of shaft  35 . In operation, eccentric  38  continuously cycles through these positions.  
         [0039]     Eccentric  38  further includes suction port  47 , illustrated in phantom in  FIGS. 3 and 14 A- 14 D, in fluid communication with suction port  49  in shaft  35  ( FIG. 1 ). Cylinder block  36  includes two discharge ports  45 , also illustrated in phantom, located on opposite sides of cylinder bore  37 . In operation, when eccentric  38  is in its top-dead-center (TDC) position, as illustrated in  FIG. 14A , chamber  55  is defined by eccentric  38 , upper bearing  42 , lower bearing  40  and one of semicircular portions  41  of cylinder block  36 . In this position, chamber  55  ( FIG. 14A ) is in fluid communication with one of discharge ports  45 , as illustrated in  FIG. 14A . Also, in this position, chamber  55  is in fluid communication with suction port  47  of roller  38 . In operation, refrigerant in the interior plenum of housing  20  flows through suction port  49  of shaft  35  and suction port  47  of roller  38  into chamber  55 .  
         [0040]     When eccentric  38  is in the position illustrated in  FIG. 14B , a second chamber, chamber  57 , is defined by eccentric  38 , upper bearing  42 , lower bearing  40  and the other semicircular portion  41  of cylinder block  36 . In the position illustrated in  FIG. 14B , chambers  55  and  57  are substantially the same size. In this position, suction port  47  is in fluid communication with second chamber  57  wherein chamber  57  represents the suction chamber. As eccentric  38  continues to rotate, the size of chamber  55  continues to decrease and the size of chamber  57  continues to increase. Correspondingly, the pressure of the refrigerant contained in chamber  55  increases until it reaches a level sufficient to resiliently lift the discharge valve covering the discharge port  45  in fluid communication with chamber  55  away from its valve seat, as discussed in further detail below. As eccentric  38  continues to rotate, chamber  55  decreases in size until eccentric  38  is substantially enveloped by portion  41 , as illustrated in  FIG. 14C . In this position, suction inlet  47  is still in fluid communication with second chamber  57  wherein chamber  57  still represents the suction chamber. However, as eccentric  38  continues to rotate past the position illustrated in  FIG. 14C , suction port  47  is placed out of fluid communication with second chamber  57  and is placed into fluid communication with first chamber  55 . As a result, first chamber  55  is, once again, the suction chamber and second chamber  57  is, once again, the discharge chamber. Accordingly, as eccentric  38  moves into the position illustrated in  FIG. 14D , chamber  55  increases in size drawing refrigerant therein and chamber  57  decreases in size compressing the refrigerant contained therein. When eccentric  38  is in the position represented by  FIG. 14D , chambers  55  and  57  are substantially the same size, similar to the position illustrated in  FIG. 14B . As eccentric  38  rotates from the position illustrated in  FIG. 14D  to the position illustrated in  FIG. 14A , second chamber  57  decreases in size compressing the refrigerant contained therein until the discharge valve covering the discharge port  45  in fluid communication with chamber  57  lifts away from its valve seat allowing compressed refrigerant to escape therethrough.  
         [0041]     In another way of describing the above, the first chamber serves as the suction chamber for approximately 180° of revolution of eccentric  38  and as the compression chamber for the remaining approximately 180° of eccentric  38 . Correspondingly, the second chamber serves as the compression chamber for approximately 180° of revolution of eccentric  38  and as the suction chamber for the remaining approximately 180° of eccentric  38 .  
         [0042]     In operation, refrigerant, represented by arrows  73  ( FIG. 1 ), is drawn into the suction chamber through aperture  49  ( FIGS. 14A-14D ) in shaft  35 . Aperture  49  is in fluid communication with elongate aperture  56  extending along the axis of shaft  35  which is in fluid communication with interior plenum  58  of compressor  20 . Refrigerant in gaseous form enters into elongate aperture  56  through impeller  60  ( FIGS. 1 and 9 ). However, refrigerant in liquid form which enters into impeller  60  is centrifuged, or accelerated outwardly, and is substantially prevented from entering into aperture  56 . Impeller  60  is mounted to shaft  35  and includes fan blades  62 , which inhibit liquid refrigerant from entering into aperture  56 . In this embodiment, impeller  60  is mounted to rotor  64  with bolts  66  passing through bolt holes  67 .  
         [0043]     As illustrated in  FIGS. 1 and 2 , upper bearing  42  and lower bearing  40  are captured between housing  22  and bottom cap  24 . In this embodiment, bearings  40  and  42  are compressed between housing  22  and bottom cap  24 . Specifically, housing  22  includes recess  140  formed therein and defining shoulder  142 . Shoulder  142  is positioned adjacent upper bearing  42  to substantially entirely contact upper bearing  42 . Wall portion  144  of housing  22  defines a portion of recess  140  and is configured to engage the outer surface of bottom cap  24 . Additionally, end surface  146  of bottom cap  24  contacts the bottom of lower bearing  40 , pressing it into upper bearing  42 . In this configuration, housing  22  presses upper bearing  42  and lower bearing  40  against end surface  146  of bottom cap  24 . As a result, bearings  40  and  42  are fixed relative to the compressor without the use of fasteners. Such an arrangement reduces the cost of the compressor and decreases the assembly time of the compressor.  
         [0044]     To further secure housing  22  and bottom cap  24  in position, housing  22  and bottom cap  24  may be welded, braised, or connected in another suitable fashion to hold their relative positions therebetween. In one exemplary embodiment, housing  22  and bottom cap  24  are secured together by welding. During the welding process, housing  22  and bottom cap  24  are heated, causing expansion of housing  22  and bottom cap  24 . When housing  22  and bottom cap  24  are securely welded to one another in this expanded condition, the subsequent cooling of housing  22  and bottom cap  24  results in contraction of housing  22  and bottom cap  24 . This contraction presses shoulder  142  of housing  22  toward upper bearing  42  and also presses end surface  146  of bottom end  24  toward lower bearing  40 , compression bearings  40 ,  42  together. In another exemplary embodiment, brazing is used instead of welding to achieve the results described in detail above. As illustrated in  FIG. 1 , lower bearings  40  includes apertures  76  and upper bearing  42  includes apertures  78  to promote fluid communication between lower interior plenum  80  and upper interior plenum  82 .  
         [0045]     As illustrated in  FIG. 1 , oil reservoir  83  is located in the bottom of compressor  20 . Oil reservoir  83  includes oil that precipitates from refrigerant as it passes into the compressor housing through suction port  74 . As illustrated in  FIG. 1 , shaft  35  includes oil impeller  110  affixed thereto. Oil impeller  110  includes an opening  112  which is typically submerged in oil reservoir  83 . As shaft  35  is rotated, oil from oil reservoir  83 , represented by arrows  85 , is drawn into impeller  110  until it reaches aperture  88  in shaft  35 . Thereafter, the oil flows through aperture  88  into oil channel  89  to lubricate the interface between the bearings  40  and  42  and shaft  35 . Referring to  FIG. 1 , oil plug  86  is positioned in shaft  35  to substantially prevent the oil in reservoir  83  from being sucked into suction inlet  49 . However, oil plug  86  includes apertures  84  ( FIGS. 1, 10A  and  10 B) which allow some oil to flow from reservoir  83  into suction inlet  49  to lubricate the moving compressor components.  
         [0046]     As mentioned above, when eccentric  38  is rotated by shaft  35 , cylinder block  36  is reciprocatingly driven along an axis defined by rollers  46  and dowels  44 . The compression chamber between eccentric  38  and cylinder block  36  is in fluid communication with discharge port  45 . Discharge port  45  is in fluid communication with muffler region  92  which is defined by lower bearing  40  and upper bearing  42 . Muffler region  92  defines a volume of space that dampens the acoustic energy of the refrigerant after it has been compressed. Muffler region  92  is in fluid communication with discharge port  94  ( FIG. 2 ) in lower bearing  40 . As illustrated in  FIG. 2 , discharge port  94  is in fluid communication with discharge tube  95  which extends through aperture  96  in lower cap  24 . Discharge tube  95  is welded or braised to lower cap  24  to sealingly engage them together. Refrigerant flowing through discharge tube  95  enters the refrigeration system thereafter. As illustrated in  FIG. 3 , valve assembly  98  covers the discharge port of cylinder block  36 . Discharge valve assembly  98  includes discharge valve  100 , valve stop  102 , and retainer  105  which are mounted to cylinder block  36  through shoulder bolts  104 , as illustrated in  FIGS. 3, 7 ,  8 A and  8 B. Discharge valve  100 , valve stop  102  and retainer  105  include elongate bodies having elongate recesses at the ends thereof through which shoulder bolts  104  pass therethrough. As illustrated in  FIG. 8A , valve stop  102  is arcuate along its length and provides support for discharge valve  100  when it deflects away from the discharge port of cylinder block  36 . Retainer  105 , which bear against heads  107  of shoulder bolts  104 , provides support for valve stop  102  by preventing substantial translation thereof. Discharge valve  100  covers the discharge port of cylinder block  36  until sufficient pressure has been developed in the discharge chamber, thereafter, the leaf valve is flexed away from the discharge port by the compressed refrigerant, as is well known in the art. After sufficient refrigerant has escaped from the discharge chamber, the force applied to the leaf spring will reduce and the leaf spring will return to cover the discharge port of cylinder block  36 . This process is repeated throughout operation of the compressor. A cantilevered leaf valve and valve support are illustrated in  FIG. 5 .  
         [0047]     To balance the rotating components of the compressor, counterweights may be attached thereto. As illustrated in  FIG. 1 , counterweight  114  is affixed to impeller  60  through bolts  66 . Also, counterweight  116  is affixed to the lower end of rotor  64  to balance the rotating weight of the rotor. In addition to adding weights, material can be removed from rotating components to facilitate counterbalancing. For example, as illustrated in  FIGS. 3 and 14 A- 14 D, material has been removed from eccentric  38  to create aperture  117 . To counterbalance reciprocating cylinder block  36  of the present single-cylinder compressor, as illustrated in  FIGS. 1, 4 ,  5  and  6 , plate  118  is operatively engaged with shaft  35  such that plate  118  reciprocates substantially 180° out-of-phase with cylinder block  36 . Plate  118  includes elongate recesses  120  ( FIG. 5 ) for operatively engaging rollers  122  and moves in a manner similar to cylinder block  36  as discussed above. Rollers  122 , like rollers  46 , are positioned over dowels  44  to facilitate relative movement between plate  118  and lower bearing  40  as plate  118  is translated along axis  136 , which is defined by rollers  122  and dowels  44 . Plate  118  is driven by eccentric  119  mounted to shaft  35  which rotates within aperture  123  of plate  118 .  
         [0048]     Similar to cylinder bore  37 , aperture  123 , referring to  FIG. 6 , includes two substantially semicircular portions  132  and two substantially straight walls  134 . Similar to eccentric  38  and cylinder  37 , aperture  123  and second eccentric  119  are constructed such that second eccentric  119  contacts substantially straight walls  134 , in an alternating manner, to drive plate  118  along axis  136 . Referring to  FIGS. 5 and 6 , the position of second eccentric  119  on shaft  35  is maintained by retaining ring  124  which engages shaft  35 , retaining washer  126  and spring washer  128  which is elastically compressed between lower bearing  40  and retaining washer  126 . As illustrated in  FIG. 5 , second eccentric  119  includes aperture  138 . Aperture  138  ( FIG. 5 ) includes a substantially cylindrical portion and a substantially flat portion which are tightly interfitted with similar, corresponding geometries on shaft  35 . Due to corresponding and operatively engaged flat portions, shaft  35  and second eccentric  119  are keyed together and the rotational motion of shaft  35  is transmitted to second eccentric  119  during operation of the compressor. Referring to  FIG. 6 , the position of plate  118  between rollers  122  is maintained by nuts  130  mounted on the ends of dowels  44  to maintain plate  118  against or substantially adjacent to lower bearing  40 . In one embodiment, nuts  130 , which each include an elastic spring member, are snapped onto dowels  44 . In this embodiment, the spring members of nuts  130  can provide a resilient spring force against plate  118 .  
         [0049]     In one embodiment, it is desirable for plate  118  and cylinder block  36  to weigh substantially the same amount, thereby substantially balancing the forces created by plate  118  and roller  38  as they travel in opposite directions. In another way, the mass of plate  118 , when accelerated along axis  136 , generates a force along axis  136 . Similarly, the mass of cylinder block  36 , when accelerated along axis  53 , also generates a force. However, as plate  118  and cylinder block are moving 180° degrees out-of-phase with each other, i.e., they are traveling in opposite directions at substantially the same speed, the forces created by their accelerating masses substantially cancel each other out. As a result, very little vibration results from the accelerating masses of plate  118  and cylinder block  36 . In one embodiment, cylinder block  36  is constructed from aluminum and plate  118  is constructed from steel. As steel is heavier than aluminum, plate  118  is smaller than cylinder block  36 , yet they are substantially the same weight. Such an embodiment is illustrated in  FIGS. 1, 4 ,  5  and  6 .  
         [0050]     In embodiments having two cylinders 180° degrees out of phase with each other, such as the embodiment illustrated in  FIGS. 11-13 , the cylinder blocks substantially counterbalance each other and plate  118  may be unnecessary. Generally, compressor  200 , depicted in  FIGS. 11-13 , operates, substantially, in accordance with the description for compressor  20 , however, some of the differences are described below. Compressor  200  includes compressor mechanism  234  which includes shaft  235 , two cylinder blocks  236 , two eccentrics  238  operatively engaged with shaft  235  and positioned within cylinder bores  237  of cylinder blocks  236 , lower bearing  240  and upper bearing  242 . Compressor mechanism  234  further includes dowels  244  and four bearing rollers  246 . Similar to the above, dowels  244  extend through, and are tightly interfitted with, apertures  248  of upper bearing  242  and apertures  250  of lower bearing  240  such that dowels  244  hold bearings  240  and  242  together prior to their placement into the compressor housing. Bearing rollers  246  are substantially concentrically interfitted over dowels  244  and are positioned between upper bearing  242  and center plate  252  and lower bearing  240  and center plate  252 . Center plate  252 , along with bearings  240  and  242 , separately enclose the compression and discharge chambers within cylinder bores  237 . Further, center plate  252 , along with bearings  240  and  242 , can separately enclose the chambers surrounding cylinder blocks  236  thereby creating two muffler chambers. These muffler chambers operate in a similar manner as the single-cylinder embodiment. In some embodiments, these muffler chambers are in fluid communication. Other embodiments in accordance with the present invention having more than two cylinders are envisioned.  
         [0051]     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.