Abstract:
The eccentric on the crankshaft of a rotary compressor, as well as the roller that surrounds the crankshaft, is replaced by an elliptical cam that acts as a double eccentric. In this manner, the elliptical cam provides for proper balancing of the crankshaft and other components of the compressor, while eliminating the need to use counterweights. Specifically, the elliptical cam is symmetrical, resulting in equal forces acting on opposing sides of the elliptical cam. This allows the elliptical cam to maintain its balance throughout its rotation, even when operating at a high rate of revolution.

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. 61/246,319, filed Sep. 28, 2009, titled ROTARY COMPRESSOR, the disclosure of which is expressly incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to compressors and, particularly, to rotary compressors. 
         [0004]    2. Description of the Related Art 
         [0005]    In a rotary compressor, the compression mechanism includes an eccentric positioned within a cylindrical compression chamber. A vane extending from the cylindrical wall of the compression chamber contacts a roller positioned around the eccentric and divides the compression chamber into compression and suction pockets. As the eccentric and, correspondingly, the roller move through the compression chamber, the compression pocket decreases in volume to compress a working fluid contained therein. At the same time, the suction pocket is increasing in volume and drawing working fluid into the suction pocket. As the eccentric and roller continue to rotate, the portion of the roller contacting the wall of the compression chamber passes by the vane. When this occurs, the suction pocket becomes the compression pocket. 
         [0006]    Due to the rotation of the eccentric through the compression mechanism, a counterweight must be used to keep the crankshaft and other components of the compressor in balance. However, as the size of the rotary compressor increases, the size of the eccentric and its corresponding counterweight also increase. Additionally, in order to obtain proper balance, two counterweights may be used. For example, in some rotary compressors, a first counterweight is positioned at the end of the crankshaft opposite the eccentric and on the same side as the eccentric, while a second counterweight is position between the eccentric and the first counterweight on the opposite side of the crankshaft as the eccentric and the first counterweight. In order for the second counterweight to effectively balance the system, the mass-eccentricity of the second counterweight must be equal to the sum of the mass-eccentricities of the first counterweight and the eccentric and the roller. Thus, as rotary compressors increase in volume, i.e., provide compression in the range of 5 to 10 tons, the eccentrics and corresponding counterweights also increase in size. As a result, the size of the counterweights make both the design and assembly of such a compressor increasingly difficult. For example, the height of the compressor must be increased to provide room for the counterweights and the counterweight attachments must be made stronger to accommodate increased centrifugal forces. 
       SUMMARY 
       [0007]    The present invention relates to compressors and, particularly, to rotary compressors. In one exemplary embodiment, the eccentric on the crankshaft of a rotary compressor, as well as the roller that surrounds the eccentric, is replaced by an elongated, preferably elliptical, cam that acts as a double eccentric. In this manner, the elliptical cam provides for inherent balancing of the crankshaft and other components of the compressor, eliminating the need to use counterweights. Specifically, the elliptical cam is symmetrical, resulting in equal inertial forces acting on opposing sides of the elliptical cam. This allows the elliptical cam to maintain its balance throughout its rotation, even when operating at a high rate of revolution. Additionally, because pressure forces from the compression pockets are equal and opposite in direction, bearing loads are reduced which allows for the use of a smaller bearing. This, in turn, reduces the viscous frictional losses associated with shearing of oil in the bearings, which increases mechanical efficiency. 
         [0008]    Advantageously, eliminating the use of counterweights in the rotary compressor of the present invention decreases the overall height and size of the compressor. Additionally, it allows for the rotary compressor to be utilized to compress larger volumes of working fluid and also eliminates the need to provide a roller surrounding an eccentric on the crankshaft. 
         [0009]    In another exemplary embodiment, the present invention includes an open suction pressure channel that extends along an inner surface of the compression mechanism of the compressor to draw suction pressure working fluid into the opposing working pockets defined by the elliptical cam. In another exemplary embodiment, a cross passage is formed through the elliptical cam to draw suction pressure working fluid into the opposing working pockets defined by the elliptical cam. By utilizing the open suction pressure channel and/or the cross passage of the present invention, a single suction port may be provided in the compression mechanism to draw suction pressure working fluid into both working pockets of the compression mechanism. 
         [0010]    Additionally, in one exemplary embodiment, the outboard journal bearing is eliminated and the crankshaft of the compressor includes only a single journal bearing, i.e., the main bearing, which is positioned between the cylinder and the motor. Elimination of the outboard journal reduces the viscous friction losses of the compressor and increases mechanical efficiency. Also, because the outboard journal consists of precisely machined surfaces, its elimination reduces the cost of manufacturing the compressor. 
         [0011]    In one form thereof, the present invention provides a rotary compressor having an outer hermetic housing, a motor and a cylinder having an inner cylindrical surface including a plurality of slots formed therein, the inner cylindrical surface defining a substantially cylindrical bore. A crankshaft includes an elongate cam, either integral therewith or attached thereto, which is rotatably disposed within the cylinder block such that the outer surface of the elongate cam contacts the inner cylindrical surface of the cylinder block at two circumferentially spaced positions to form a pair of working pockets. First and second vanes are positioned at least partially within the slots in the cylinder block and biased inwardly to contact the outer surface of the elongate cam. An outboard thrust bearing is positioned adjacent the cylinder block and a main bearing positioned adjacent the cylinder block at an axial end thereof and at least partially defining a discharge port in fluid communication with the working pockets at certain rotation angles of the elongate cam. A suction pressure inlet is in communication with the working pockets at certain angles of rotation of the cam to supply suction pressure working fluid into the working pockets. 
         [0012]    In another form thereof, the present invention provides a rotary compressor having an outer hermetic housing, a motor and a cylinder having an inner cylindrical surface including a plurality of slots, the inner cylindrical surface defining a substantially cylindrical bore. A crankshaft having an elongate cam thereon is rotatably disposed within the cylinder block such that the outer surface of the cam contacts the inner surface of the cylinder block at two circumferentially spaced positions to form a pair of working pockets. First and second vanes at least partially positioned within the slots are biased inwardly to contact the outer surface of the elongate cam. An outboard thrust bearing is positioned adjacent the cylinder block and defines a suction pressure passage therein, the suction pressure passage in simultaneous fluid communication with each of the working pockets at certain rotation angles of the cam to draw suction pressure working fluid from a suction pressure inlet to both of the working pockets. A main bearing is provided adjacent the cylinder and at least partially defines a discharge port in fluid communication with the working pockets at certain rotation angles of the elongate cam. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The above-mentioned and other features and advantages 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 an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0014]      FIG. 1  is a perspective view of a rotary compressor in accordance with an embodiment of the present invention; 
           [0015]      FIG. 2  is a plan view thereof; 
           [0016]      FIG. 3  is a sectional view thereof taken along one A-A of  FIG. 2  and viewed in the direction of the arrows, wherein the section is taken through the suction port; 
           [0017]      FIG. 4  is a sectional view thereof taken through the vanes; 
           [0018]      FIG. 5  is a sectional view thereof taken through the discharge ports; 
           [0019]      FIG. 6  is a transverse sectional view of the compressor taken through the cylinder; 
           [0020]      FIG. 7  is a perspective view of the outboard thrust bearing showing the suction panel 
           [0021]      FIG. 8  is a perspective view of the main bearing; 
           [0022]      FIG. 9  is a perspective view of an alternative crankshaft and cam design; and 
           [0023]      FIG. 10  is a sectional view of the alternate embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]      FIG. 1  illustrates the rotary compressor  10  forming one embodiment of the present invention. Compressor  10  includes an outer hermetic housing  12  including center portion  14  to which upper and lower caps  16  and  18  are connected, such as by welding. A conventional suction accumulator  20  having inlet  22  and outlet suction line  24  is connected to the center portion  14  of compressor  10  by means of mounting strap  26 . Compressed refrigerant is discharged from high pressure housing  12  through discharge line  28 . Compressor  10  may be a component of a heating and/or cooling circuit and functions to compress the working fluid, such as a refrigerant, which may be a hydrofluorocarbon, chlorofluorocarbon, hydrochlorofluorocarbon, or carbon dioxide refrigerant, for example. 
         [0025]    Turning now to  FIGS. 3-5 , motor  30  and compression mechanism  32  are mounted within hermetic housing  12 . Oil sump  41  ( FIG. 3 ) is formed in the lower portion of hermetic housing  12 . The motor includes stator  34  and rotor  36 . Compression mechanism  32  comprises a cylinder  34  that is rigidly connected to the inner surface  35  of housing center section  14 , a main bearing  36  fastened to cylinder  34  by means of a plurality of screws  38  and an outboard thrust bearing  40  connected to cylinder  34  by means of a plurality of screws  42 . Suction line  24  extends through the center section  14  of housing  12  and is sealably joined to cylinder block  34  in communication with suction port  44  which opens into the wall of cylinder bore  50 . 
         [0026]    An elongate cam  46 , which is preferably elliptical, is preferably integrally connected with crankshaft  14 , although alternatively it may be a separate element connected by any suitable means. Shaft  64  is rotationally secured to rotor  28  and, as shown in  FIG. 6 , cam  46  is in sealing engagement with the bore  50  of cylinder  34 . 
         [0027]    Extending through elliptical cam  46  and up through shaft  48  is oil passage  52 . Oil paddle  54  extends from oil passage  52  of elliptical cam  46  and is configured to draw oil upward and into passageway  52  that is in combination with passages  56  in elliptical cam  46 . Passages  56  extend through elliptical cam  46  and direct oil into main bearing  36  between elliptical cam  46  and rotor  28  of motor  30 . In order to advance the oil further along the journal surface of crankshaft  48  and substantially entirely along main bearing  36 , the journal surface of crankshaft  48  may include a spiral groove (not shown). Alternatively, passages  56  may extend into crankshaft  48  and exit crankshaft  48  at a point above main bearing  36  allowing oil exiting passages  56  to pass along the journal surface and through main bearing  36 . For example, passages  56  may be in fluid communication with radial discharge passages (not shown) that are positioned above or within main bearing  36 . Alternatively, oil passage  52  may extend through the entire length of crankshaft  48  as shown. Oil passage  92  extends from the oil passage  52  of crankshaft  48  to the outboard thrust bearing surface of thrust bearing  40 . 
         [0028]    Referring to  FIG. 6 , slots  58  are formed in cylinder block  34  and have vanes  60  positioned therein. Springs  62  bias vanes  60  radially inwardly toward the center of cylinder  34  during start-up of the compressor. After start-up, discharge pressure working fluid is used to bias vanes  60  radially inwardly. Cylinder  34  includes an inner cylindrical surface defining cylinder bore  50  for rotation of elliptical cam  46  therein. 
         [0029]    By utilizing elliptical cam  46 , the need for a roller is eliminated. As a result, any potential wear that may occur between the contact surfaces of the roller and an eccentric is also eliminated. Additionally, elliptical cam  46  is symmetrical and provides for proper balancing of crankshaft  48  and the other rotating components of the compressor while eliminating the need to use counterweights. As a result, the overall height of the compressor utilizing elliptical cam  46  may be reduced. 
         [0030]    As indicated above, vanes  60  are biased toward the center of cylinder bore  50  where they contact exterior surface  66  of elliptical cam  46 . Vanes  60  may be coated with a ceramic or other material to lessen the friction generated between vanes  60  and the exterior surface  66  of cam  46 . The contact of the outer surface  66  of elliptical cam  46  with the inner cylindrical surface of bore  50  at two circumferentially spaced positions and the biasing of vanes  60  against surface  66  forms two working pockets  68  that are defined by vanes  60 , elliptical cam  46  and cylinder  34 . 
         [0031]    Referring to  FIGS. 3-5 , working pockets  68  are sealed on opposite axial sides thereof by outboard bearing  40  and main bearing  36 . Outboard bearing  40  includes thrust surfaces  70 ,  71  upon which elliptical cam  46  is supported. During rotation of crankshaft  48 , elliptical cam  46  bears against and rotates on thrust surfaces  70 ,  71 . The surface of elliptical cam  46  that contacts surfaces  70 ,  71  as well as surfaces  70 ,  71  and thrust surface  72  ( FIG. 8 ) of main bearing  36  are finely machined surfaces that cooperate to seal working pockets  68 . 
         [0032]    As shown in  FIGS. 3 and 7 , outboard bearing  40  includes suction pressure channel  74  formed therein. Channel  74  extends around oil passage  76  formed by boss  73  in outboard bearing  40  and is formed as an open channel that is in fluid communication with bore  50  in cylinder  34 . 
         [0033]    Referring to  FIG. 6 , as elliptical cam  46  moves in a clockwise direction, the volume of working pockets  68  is increased and suction pressure working fluid is drawn into working pockets  68 . Specifically, suction pressure working fluid passes through suction port  44  in block  34  to enter the proximal working pocket  68  and suction pressure channel  74 . In order to equalize the pressure in working pockets  68 , suction pressure working fluid is drawn through suction pressure channel  74 , passing under elliptical cam  46 , around aerodynamically shaped diverters  78 , to enter distal working pocket  68 . By utilizing a single suction port  44  to draw suction pressure working fluid into compression mechanism  32 , the cost of machining and assembling compression mechanism  32  is reduced. The tapered portions  78  forming the diverters are aligned with the longitudinal axis of slot  74  to thereby smooth the flow of suction fluid around boss  73 . 
         [0034]    As elliptical cam  46  continues to rotate, the portions of cam  46  contacting cylindrical surface  50  pass vanes  60 . At this point, the volume of working pockets  68  begins to decrease, increasing the pressure of the working fluid contained within pockets  68 . As the volume of working pockets  68  continues to decrease with the rotation of elliptical cam  46 , working fluid within working pockets  68  reaches a pressure substantially equal to discharge pressure. Once that pressure has been reached, flapper valves  82  open and the working fluid is discharged through discharge ports  80  ( FIG. 5 ) in cylinder  34  and main bearing  36 . Flapper valves  82 , which are positioned above ports  80 , allow for discharge pressure working fluid to flow into the interior of housing  12  but operate in a known manner to prevent discharge pressure working fluid from reentering ports  80  once discharged. Also shown are valve retainers  84  and muffler  86 . Discharge pressure working fluid flows past motor  30  and out discharge line  28 . 
         [0035]    In addition to, or alternatively to, suction pressure channel  74  in outboard bearing  40 , main bearing  36  may be provided with a suction pressure channel  88  that extends between working pockets  68  and around boss  90  ( FIG. 8 ). 
         [0036]    With reference to  FIGS. 9 and 10 , an alternative embodiment is disclosed. In this embodiment, cross passages  94  extending through elliptical cam  96  of crankshaft  98  allow for suction pressure working fluid received through suction port  44  to pass between working pockets  68 . Specifically, such pressure working fluid as received through suction port  44  enters the proximal working pocket  68  and then passes through cross passages  94  into the distal working pocket  68 . As shown in  FIG. 10 , cross passages  94  are oriented at a slight angle relative to the major chord of the ellipse defined by elliptical cam  96  so that cross passages  94  are never in fluid communication with the discharge side of the contact points between cam  96  and bore  50 . Passages  94  and suction pressure channel  70  may possibly be used in conjunction with one another or, alternatively, employed separately. For example, in one embodiment, suction pressure channel  74  is present and passages  94  are absent. In another alternative embodiment, passages  94  are present and suction pressure channel  74  is absent. 
         [0037]    In addition to the benefits described above, the use of elongate cam  46  also eliminates the need for an outboard journal bearing. In a typical rotary compressor, the outboard journal extends around the oil paddle and through an opening in the outboard bearing. The interaction of the journal with the portion of the outboard bearing that defines the opening prevents off-centered movement of the crankshaft and eccentric during rotation of the crankshaft. By utilizing the elliptical cam of the embodiment of the present invention, the interaction of opposing pressure forces on exterior surface  66  of cam  46  substantially eliminates the need for an outboard journal on crankshaft  48 . By eliminating the need for this journal, which must be formed as a highly machined surface, the need to create a correspondingly highly machined journal and outboard bearing  40  is also eliminated. As a result, the cost of manufacturing a rotary compressor in accordance with this embodiment of the invention is substantially reduced. 
         [0038]    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.