Abstract:
A compressor includes a male rotor ( 26 ) having a screw-type boy portion ( 30 ) extending from a first end ( 31 ) to a second end ( 32 ) and held within a housing assembly for rotation about a first rotor axis ( 500 ). A female rotor ( 27, 28 ) has a screw-type female body portion ( 33, 34 ) meshed with the male body portion and extending from a first end ( 35, 36 ) to a second end ( 37, 38 ) and held within the housing assembly for rotation about a second rotor axis ( 501, 502 ). An end seal ( 120 ) has a first surface ( 126 ) engaging the female body portion first end and being asymmetric around the second axis.

Description:
This is the 35 USC 371 National Stage Application of PCT/US2004/033421 which is a continuation-in-part of U.S. patent application Ser. No. 10/956,897, filed Sep. 30, 2004 now U.S. Pat. No. 7,121,814. 

   BACKGROUND OF THE INVENTION 
   (1) Field of the Invention 
   The invention relates to compressors. More particularly, the invention relates to sealing of economized screw-type compressors. 
   (2) Description of the Related Art 
   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 between an adjacent pair of female rotor lobes and the housing. Likewise sequential lobes of the female rotor produce compression of refrigerant within a space between an adjacent pair of male rotor lobes and the housing. The interlobe spaces of the male and female rotors in which compression occurs form compression pockets (alternatively described as male and female portions of a common compression pocket joined at a mesh zone). 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. 
   When one of the interlobe spaces is exposed to an inlet port, the refrigerant enters the space essentially at suction pressure. As the rotors continues to rotate, at some point during the rotation the space is no longer in communication with the inlet port and the flow of refrigerant to the space is cut off. After the inlet port is closed, the refrigerant is compressed as the rotors continue to rotate. At some point during the rotation, each space intersects the associated outlet port and the closed compression process terminates. The inlet port and the outlet port may each be radial, axial, or a hybrid combination of an axial port and a radial port. 
   As the refrigerant is compressed along a compression path between the inlet and outlet ports, sealing between the rotors and housing is desirable for efficient operation. To increase the mass flow in a screw compressor an economizer is used. Typical economizer ports are located along the rotor length, positioned to become exposed to the compression pockets just after such pockets are shut off from the associated suction ports. At this location the refrigerant gas trapped within the rotors is near suction pressure. Connecting gas at a pressure above suction to the economizer ports allows for a quantity of gas to flow into the compressor. Furthermore, the feeding of gas into the rotors after suction is cut off increases the pressure of the trapped gas in the rotors. This reduces the amount of work required by the compressor. Also the economizer flow is above suction pressure, so the power for a given total refrigerant mass flow is reduced. 
   The suction port for a screw compressor can be axial, radial or a combination of both. The radial suction port cutoff is defined by the bore surrounding the rotor. The axial port is closed by the meshing of the screw rotors. Typical designs with both axial and radial suction ports require that the axial port be closed before or at the same time the radial port is closed. 
   To make the compressor more compact, shorter screw rotors are desirable. Also, using multiple female rotors about a single male rotor or multiple male rotors about a single female rotor may result in a shorter rotor set. By shortening the length of the rotors, the compression path gets shorter, which minimizes the opportunity and time required/available to inject economizer flow into the rotors. 
   Nevertheless, there remains room for improvement in the art. 
   SUMMARY OF THE INVENTION 
   To reduce the length of the rotors, but increase the length of the compression process, the radial suction port needs to be closed off sooner. However, by reducing the radial suction, the rotors would not mesh in time to close off the axial suction port. It would be desirable to close off the axial suction port to allow for a shorter radial suction port. Advantageously this would only close off a portion of the axial suction port to avoid having the economizer flow leak back to suction and to still allow for an axial suction flow component. 
   One aspect of the invention is a compressor having a housing assembly containing male and female rotors. The male rotor has a screw-type male body portion extending from a first end to a second end and held within the housing assembly for rotation about a first rotor axis. The female rotor has a screw-type female body portion enmeshed with the male body portion. The female body portion extends from a first end to a second end and is held within the housing assembly for rotation about a second rotor axis. An end seal has a first surface engaging the female rotor body portion first end and being asymmetric around the second axis. 
   In various implementations, the end seal may include a full-annulus base portion encircling the second rotor axis and a second portion bearing the first surface. The first surface may be essentially an annular segment of an extent between 30° and 270°. The first surface may be of only partial circumferential extent. The first surface may seal 1/12 to ¾ of a lobe-swept area of said female body portion first end. The first surface may seal ¼ to ½ of the lobe-swept area. A motor may be coupled to the male rotor to drive the male rotor at least in a first direction about the first rotor axis. The male rotor and motor may be coaxial. The motor may be an electric motor having a rotor and a stator and the male rotor may have a shaft portion extending into and secured to the motor&#39;s rotor. The end seal may be essentially unitarily formed of steel. A number of threaded fasteners may secure the end seal to the housing assembly. 
   Another aspect of the invention involves a compressor having a housing assembly, enmeshed male and female rotors, and suction and discharge plenums. The male and female rotor body portions may cooperate with the housing to define at least a first compression path between the suction plenum and the discharge plenum. An economizer port is at an intermediate location along the first compression path. The compressor includes means for resisting leakage from the economizer port to the suction plenum while still permitting an axial flow component from the suction plenum. 
   The means may comprise a rotor end seal with a circumferentially non-constant rotor engagement face. The rotor end seal may include a full-annulus base portion encircling the second rotor axis and a second portion bearing the rotor engagement face. The rotor engagement face may be essentially an annular segment of an extent between 30° and 270°. The means may comprise a rotor end seal with a rotor engagement face of only partial circumferential extent. A second female rotor may have a screw-type female lobed body portion and may mesh with the male lobed body portion. 
   Another aspect of the invention involves a method for remanufacturing a compressor or engineering or reengineering a configuration of such compressor from a baseline condition to a second condition. The method includes providing an axial seal for sealing with a female rotor first end. The axial seal has a sealing surface asymmetric around a female rotor axis. The axial seal either replaces a baseline seal having a sealing surface symmetric around such axis or is located where there is no axial seal in the baseline condition. The compressor may include an economizer port. 
   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 
       FIG. 1  is a longitudinal sectional view of a compressor according to principles of the invention. 
       FIG. 2  is an enlarged view of a suction plenum area of the compressor of  FIG. 1 . 
       FIG. 3  is a transverse sectional view of the compressor of  FIG. 1  taken along line  3 - 3 . 
       FIG. 4  is a view of the projected housing interior surface along rotors of the compressor of  FIG. 1 . 
       FIG. 5  is a view of a female rotor suction seal of the compressor of  FIG. 1 . 
   

   Like reference numbers and designations in the various drawings indicate like elements. 
   DETAILED DESCRIPTION 
     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  extending between a first end  31  and a second end  32 . The working portion  30  is enmeshed with female lobed body or working portions  33  and  34  of each female rotor  27  and  28 . The working portions  33  and  34  have respective first ends  35  and  36  and second ends  37  and  38 . Each rotor includes shaft portions (e.g., stubs  39 ,  40 ,  41 , and  42 ,  43 ,  44  unitarily formed with the associated working portion) extending from the 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. 
   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 an opposite second direction about their axes  501  and  502 . 
   Surfaces of the housing combine with the enmeshed rotor bodies to define inlet and outlet ports to two pairs of compression pockets compressing and driving refrigerant from a suction (inlet) plenum  60  to a discharge (outlet) plenum  62 . A first pair of male and female compression pockets is formed by the housing, male rotor, and the first female rotor. A second pair of male and female compression pockets is 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 inlet ports  66  and  67 . The exemplary inlet ports  66  and  67  are hybrid having a radial component admitting a radial inlet flow component  510  and an axial component emitting an axial inlet flow component  512  ( FIG. 2 ). 
     FIG. 3  shows the housing interior surface as including circular cylindrical portions  70 ,  71 , and  72  in close facing/sealing relationship with the apexes of the lobes of the respective working portions  30 ,  33 , and  34 . The portions  70  and  71  meet at a pair of opposed mesh zones  74  and the portions  70  and  72  meet at a pair of opposed mesh zones  75 . The housing interior surface further includes portions cooperating to define the suction and discharge ports, with portion  78  for the port  66  and  79  for the port  67  shown. The compressor further includes economizer ports  80  positioned at an intermediate stage of the compression process (e.g., the first half of the process such that the economizer port is exposed to the compression pocket(s) only after the start of the compression has occurred and is closed off from such pocket(s) before ½ of the compression has occurred). 
     FIG. 4  shows a projection of the interior surface portions  70 ,  71 , and  72  atop the rotor lobes. These surfaces are shown as having first and second edges  90  and  91  along the associated male and female rotors for each suction port and first and second edges  92  and  93  along the associated male and female rotors for each discharge port. A perimeter  94  defines a closed aperture associated with each economizer port  80  and penetrating the surface  70 . There is a leakage path from each economizer port  80  back to the associated suction port.  FIG. 4  shows this leakage path  98  as extending to intact circumferential portions  100  of the adjacent surface  70  and  102  or  104  of the adjacent surface  71  or  72 . 
     FIG. 5  shows a female rotor suction seal  120 . The exemplary seal  120  is essentially unitarily formed of a metal alloy (e.g., steel). The exemplary seal  120  has a base or mounting portion  122  formed as a full annulus ring of rectangular radial section having an upstream end or face  124  and a downstream end or face  126  and having inboard and outboard surfaces  128  and  130  therebetween. A sealing portion  140  extends from the downstream face  126  and is formed having a trunk  142  and a main body  144 . In the exemplary implementation, both the trunk and the main body are annular segments. The trunk extends between first and second circumferential ends  146  and  148  and the main body extends between first and second circumferential ends  150  and  152 . In the exemplary implementation, the main body ends project slightly circumferentially beyond the trunk ends. In the exemplary implementation, trunk inboard and outboard surfaces are formed as continuation of the base inboard and outboard surfaces. The main body inboard and outboard surfaces  154  and  156  project respectively inward and outward relative to the base portion inboard and outboard surfaces. The main body  144  has a downstream surface  158 . 
   The main body downstream surface  158  (rotor engagement face) has a radial and circumferential extent sufficient to seal the interlobe spaces along the associated leakage path  98  (e.g., along the portions  102 ;  104  and along a remaining lobe pocket area in communication with those portions  102 ;  104  (e.g., as shown in  FIG. 4 ). The exemplary surface  158  forms a first surface being essentially an annular segment of an extent between 30° and 270°. This surface may seal an exemplary 1/12 to ¾, more narrowly, ¼ to ½, of a lobe-swept area of the female body portion first end  35 . As is further shown in  FIG. 3 , the exemplary main body outboard surface  156  is at essentially equal radius to the lobes of the associated female rotor and the inboard surface  154  is in close radial position to the adjacent shaft stub (e.g., preferably at least at or below the radius of the interlobe troughs). In the exemplary implementation, the seal  120  has longitudinal apertures  160  for accommodating fasteners  162  (e.g., screws) to secure the seal within the housing.  FIG. 2  shows the seal base portion  122  mounted in a seal compartment  170  with the upstream face  124  at least partially abutting a base face  172  of a compartment and the outboard surface  130  at least partially abutting a sidewall surface  174  of the compartment. The downstream face  158  of the main body  144  is in close facing or lubricated contacting relation with the rotor body end face  35  and the overlapping portion of the male rotor body face  31 . 
   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, when applied as a reengineering or remanufacturing of an existing compressor, details of the existing compressor may influence or dictate details of the particular implementation. Accordingly, other embodiments are within the scope of the following claims.