Abstract:
A compressor has at least three-rotors. A first compression path between first inlet and outlet ports is associated with interaction of the first and second rotors. A second compression path between second inlet and outlet ports is associated with interaction of the first and third rotors. At least partial independence of the ports permits the first and second inlet ports to be at a different pressure or the first and second outlet ports to be at a different pressure. Fully or partially separate circuits in a refrigeration or air conditioning system may be associated with the first and second compression paths.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     (1) Field of the Invention  
         [0002]     The invention relates to compressors, and more particularly to screw-type compressors.  
         [0003]     (2) Description of the Related Art  
         [0004]     Screw-type compressors are commonly used in air conditioning and refrigeration applications. In such a compressor, intermeshed male and female lobed rotors or screws are rotated about their axes to pump the working fluid (refrigerant) from a low pressure inlet end to a high pressure outlet end. During rotation, sequential lobes of the male rotor serve as pistons driving refrigerant downstream and compressing it within the space (compression pocket) between an adjacent pair of female rotor lobes and the housing. Likewise sequential lobes of the female rotor produce compression of refrigerant within a male rotor compression pocket between an adjacent pair of male rotor lobes and the housing. In one implementation, the male rotor is coaxial with an electric driving motor and is supported by bearings on inlet and outlet sides of its lobed working portion. There may be multiple female rotors engaged to a given male rotor or vice versa. With such a compressor, male and female compression pockets may also have multiple inlet and outlet ports.  
         [0005]     When a compression pocket is exposed to an inlet port, the refrigerant enters the pocket essentially at suction pressure. As the pocket continues to rotate, at some point during its rotation, the pocket is no longer in communication with the inlet port and the flow of refrigerant to the pocket is cut off. Typically the inlet port geometry is arranged in such a way that the flow of refrigerant is cut off at the time in the cycle when the pocket volume reaches its maximum value. Typically the inlet port geometry is such that both male and female compression pockets are cut off at the same time. The inlet port is typically a combination of an axial port and a radial port. After the inlet port is closed, the refrigerant is compressed as the pockets continue to rotate and their volume is reduced. At some point during the rotation, each compression pocket intersects the associated outlet port and the closed compression process terminates. Typically outlet port geometry is such that both male and female pockets are exposed to the outlet port at the same time. As with the inlet port, the outlet port is normally a combination of an axial port and a radial port. By combining axial and radial ports into one design configuration, the overall combined port area is increased, minimizing throttling losses associated with pressure drop through a finite port opening area. In an exemplary three-rotor configuration, the inlet and outlet ports are respectively formed at common inlet and outlet plenums.  
         [0006]     The compressor may be designed and sized for its intended use (e.g., to provide a given compression or volume index and operate at a given flow at a given speed or combination thereof). Different compressors or at least different components (rotors, motors, and the like) may be required for different uses.  
       SUMMARY OF THE INVENTION  
       [0007]     One aspect of the invention involves an apparatus comprising: a first rotor enmeshed with second rotors. The rotors are held within a housing for rotation about respective first, second, and third axes. The housing has: a first surface cooperating with the first and second rotors to define a first inlet port; a second surface cooperating with the first and second rotors to define a first outlet port; a third surface cooperating with the first and third rotors to define a second inlet port; and a third surface cooperating with the first and third rotors to define a second outlet port. Either the first and second inlet ports are at a different pressure or the first and second outlet ports are at a different pressure.  
         [0008]     In various implementations, the apparatus may further include: a first condenser; a first evaporator; and one or more first conduits coupling the first condenser and the first evaporator to the housing to define a first flowpath from the first outlet port through the first evaporator and first condenser and to the first inlet port. The apparatus may further include: a second condenser; a second evaporator; and one or more second conduits coupling the second condenser and the second evaporator to the housing to define a second flowpath from the second outlet port through the second evaporator and second condenser and to the second inlet port.  
         [0009]     The first outlet port may be at the same pressure as the second inlet port. The apparatus of may further include a first condenser, a first expansion device, and a first evaporator. One or more first conduits may couple the first condenser, the first expansion device and the first evaporator to the housing to define a first flowpath from the second outlet port to the first inlet port. There may be no economizer branches off the first flowpath. There may be an economizer heat exchanger having a first leg along the first flowpath and a second leg, in heat exchange relation with the first leg. The second leg may be along a diversion flowpath from a location along the first flowpath between the first condenser and the first leg to join a second flowpath from the first outlet port to the second inlet port.  
         [0010]     Either the first and second inlet ports may form a common inlet port or the first and second outlet ports may form a common outlet port. Either the first and second inlet ports may be at like pressure or the first and second outlet ports may be at like pressure. The first rotor may be a male rotor and the second and third rotors may be female rotors  
         [0011]     Another aspect of the invention involves an apparatus comprising a first rotor enmeshed with second and third rotors. The rotors are held within a housing for rotation about respective first, second, and third axes. Means cooperate with the first, second, and third rotors for providing: a first volume index associated with interaction of the first and second rotors when the first rotor is driven in the first direction; and a second volume index associated with interaction of the first and third rotors when the first rotor is driven in the first direction. The second volume index is different from the first volume index.  
         [0012]     In various implementations, the apparatus may be combined with first and second refrigerant flows along non intersecting first and second flowpaths through the apparatus. T he apparatus may be combined with first and second refrigerant flows along first and second flowpaths through the apparatus intersecting at a suction side of the apparatus. The apparatus may be combined with first and second refrigerant flows along first and second flowpaths through the apparatus intersecting at a discharge side of the apparatus.  
         [0013]     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a partial semi-schematic longitudinal cutaway sectional view of a compressor.  
         [0015]      FIG. 2  is a schematic view of a first system including a compressor according to principles of the invention.  
         [0016]      FIG. 3  is a schematic view of a second system including a compressor according to principles of the invention.  
         [0017]      FIG. 4  is a schematic view of a third system including a compressor according to principles of the invention.  
         [0018]      FIG. 5  is a schematic view of a fourth system including a compressor according to principles of the invention.  
         [0019]      FIG. 6  is a schematic view of a fifth system including a compressor according to principles of the invention. 
     
    
       [0020]     Like reference numbers and designations in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0021]      FIG. 1  shows a compressor  20  having a housing assembly  22  containing a motor  24  driving rotors  26 ,  27  and  28  having respective central longitudinal axes  500 ,  501  and  502 . In the exemplary embodiment, the male rotor  26  is centrally positioned within the compressor and has a male lobed body or working portion  30  enmeshed with female lobed body or working portion  34 ;  35  of each female rotor  27 ;  28 . Each rotor includes shaft portions (e.g., stubs  39 ,  40 ,  41 , and  42 ,  43 , 44  unitarily formed with the associated working portion) extending from first and second ends of the associated working portion. Each of these shaft stubs is mounted to the housing by one or more bearing assemblies  50  for rotation about the associated rotor axis.  
         [0022]     In the exemplary embodiment, the motor  24  is an electric motor having a rotor and a stator. A portion of the first shaft stub  39  of the male rotor  26  extends within the stator and is secured thereto so as to permit the motor  24  to drive the male rotor  26  about the axis  500 . When so driven in an operative first direction about the axis  500 , the male rotor drives the female rotors in opposite directions about their axes  501  and  502 .  
         [0023]     Surfaces of the housing combine with the enmeshed rotor bodies to define inlet and outlet ports to a two pairs of compression pockets: a first pair of male and female compression pockets formed by the housing, male rotor, and the first female rotor; and a second pair of male and female compression pockets formed by the housing, male rotor and the second female rotor. In each pair, one such pocket is located between a pair of adjacent lobes of each rotor associated rotor. Depending on the implementation, the ports may be radial, axial, or a hybrid of the two.  FIG. 1  shows first and second radial inlet ports  46  and  47  and first and second radial outlet ports  48  and  49 . The resulting enmeshed rotation of the rotor working portions tends to drive fluid from a first (inlet/suction) end to a second (outlet/discharge) end while compressing such fluid. This defines a downstream direction.  
         [0024]     According to the invention, the compression paths associated with two compression pockets do not meet at one or both of the inlet and outlet ends. In the exemplary embodiment, separate first and second inlet plenums  61  and  62  are respectively associated with the first and second pairs of compression pockets as are first and second outlet plenums  63  and  64 . This may be achieved by a simple modification of the housing (e.g. a modification of an actual housing or a modification of the functional design thereof) of a conventional compressor to bifurcate one or both of an initially common suction port and an initially common discharge port. This modification may leave other components (e.g., rotors, motors, and the like) unchanged. More drastic modifications and clean sheet designs are also possible. Reuse of existing designs for varied applications can produce a variety of efficiencies (e.g., economies of scale).  
         [0025]      FIG. 2  shows a system  100  wherein the compressor  20  drives first and second independent refrigerant flows along first and second circuits/flowpaths  102  and  104 . The first and second flowpaths each proceed downstream from the associated discharge plenum through a discharge conduit  106 ; 108  to a condenser  110 ; 112 . From the condenser, the flowpaths proceed through an intermediate conduit  114 ; 116  in which a thermostatic expansion valve (TXV)  118 ; 120  is located to an evaporator  122 ; 124 . From the evaporator, the flowpaths proceed through a suction/return conduit  126 ; 128  to the associated inlet plenum. In normal operation, the first and second flowpaths are separate (except for incidental leakage). Such a configuration may allow one compressor and associated hardware to replace two. This causes certain direct efficiencies and indirect efficiencies (e.g., associating a larger number of uses with a given basic compressor configuration).  
         [0026]     Alternative implementations may involve flowpaths that intersect at one or more individual points or overlap.  FIG. 3  shows a system  150  wherein the compressor  20  drives first and second refrigerant flows along first and second circuits/flowpaths  152  and  154  that have a common upstream length and separate downstream lengths. The outlet plenums may be merged in the housing (e.g., as a single common outlet plenum) or by a T/Y-fitting in the discharge conduit  156 . The combined first and second flowpaths proceed downstream through the discharge conduit to a single common condenser  158 . From the condenser, the combined flowpaths proceed through the trunk of an intermediate conduit  160  which has a T/Y-fitting to separate into a first and second branches to separate the flowpaths. A TXV  162 ; 164  is located in each branch and the associated flowpath proceeds downstream therefrom to an evaporator  166 ; 168 . From the evaporator, the flowpaths proceed through a suction/return conduit  170 ; 172  to the associated inlet plenum.  
         [0027]      FIG. 4  shows a system  200  that may be constructed similarly to the system  150  but has first and second circuits/flowpaths  202  and  204  that have a common downstream length with a common evaporator  206  and separate upstream lengths with separate condensers  208  and  210  and TXVs  212  and  214 .  
         [0028]      FIG. 5  shows a system  250  that has a single flowpath  252  in which the two compression paths are in series. The flowpath proceeds downstream from the first outlet plenum through a conduit  254  to the second inlet plenum. From the second outlet plenum, the flowpath proceeds through a discharge conduit  256  to a condenser  258 . From the condenser, the flowpath proceeds through an intermediate conduit  260  in which a TXV  262  is located to an evaporator  264 . From the evaporator, the flowpath proceed through a suction/return conduit  266  to the first inlet plenum.  
         [0029]     In a variation on the basic two-stage system of  FIG. 5 ,  FIG. 6  shows a system  300  that has a flowpath  302  providing a selective diversion along a diversion path  304  passing within an ecomomizer heat exchanger (HE)  306 . A discharge conduit  308 , condenser  310 , TXV  312 , evaporator  314 , and suction/return conduit  316  may be similar to corresponding elements of the system  250 . The intermediate conduit  318  includes a portion  320  within the HE. A diversion conduit  322  branches from the intermediate conduit between the condenser and HE to define the diversion path  304 . The diversion conduit includes a portion  324  within the HE in heat exchange relation (e.g., parallel flow, counterflow, or crossflow) with the portion  320 . A diversion TXV  326  is located in the diversion conduit to control the diversion flow. The diversion conduit joins the conduit  334  that feedsback from the first outlet plenum to the second inlet plenum.  
         [0030]     One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, additional features may be included as are known in the art or are subsequently developed. Accordingly, other embodiments are within the scope of the following claims.