Abstract:
A rotor assembly is provided for a compressor assembly having a housing defining an inlet port, outlet port, and a rotor cavity in communication with the inlet port and outlet port. The rotor assembly includes a rotor body having a plurality of lobes formed thereon and rotatably mountable within the rotor cavity of the housing. The rotor body has a first end, substantially adjacent to the inlet port, and a second end, substantially adjacent to the outlet port, when mounted within the housing. Each of the plurality of lobes has an outer radius that is greater at the first end than at the second end.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to rotor assemblies having a generally tapering shape for use within a supercharger assembly. 
       BACKGROUND OF THE INVENTION 
       [0002]    Roots-type and screw-type positive displacement compressors are employed in industrial and automotive applications. The compressor or supercharger may be operatively connected to an internal combustion engine to increase the amount or volume of intake air communicated to the internal combustion engine thereby increasing the volumetric efficiency thereof. The supercharger typically includes two interleaved and counter-rotating rotors each of which may be formed with a plurality of lobes to convey volumes of intake air from an inlet passage to an outlet passage for subsequent introduction to the internal combustion engine. The efficiency of the supercharger is dependent on the running clearances between each of the two rotors and a housing within which the two rotors are rotatably supported. 
       SUMMARY OF THE INVENTION 
       [0003]    A rotor assembly is provided for a compressor assembly having a housing defining an inlet port, outlet port, and a rotor cavity in communication with the inlet port and outlet port. The rotor assembly includes a rotor body having a plurality of lobes formed thereon and rotatably mountable within the rotor cavity of the housing. The rotor body has a first end, substantially adjacent to the inlet port, and a second end, substantially adjacent to the outlet port, when mounted within the housing. Each of the plurality of lobes has an outer radius that is greater at the first end than at the second end. 
         [0004]    The outer radius may generally taper from the first end to the second end. Alternatively, the outer radius may generally taper from a point between the first and second end to the second end. A compressor assembly incorporating the rotor assembly is also disclosed. 
         [0005]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic perspective view of a supercharger assembly configured for use with an internal combustion engine; 
           [0007]      FIG. 2  is a schematic cross sectional view of the supercharger of  FIG. 1  taken along line  2 - 2  of  FIG. 1 ; 
           [0008]      FIG. 3  is a schematic cross sectional view of the supercharger of  FIG. 1  taken along line  3 - 3  of  FIG. 1 ; and 
           [0009]      FIG. 4  is a sectional drawing illustrating the generally tapering profile of rotors contained within the supercharger assembly of  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0010]    Referring to the drawings wherein like reference numbers correspond to like or similar components throughout the several figures, there is shown in  FIG. 1  a compressor or supercharger assembly, generally indicated at  10 . The supercharger  10  includes a housing  12 . The housing  12  defines an inlet passage  14  configured to induct intake air, represented by arrow  16 , into the supercharger assembly  10 . The housing  12  further defines an outlet passage  18  configured to exhaust or expel the intake air  16  from the supercharger assembly  10 . 
         [0011]    A rotor cavity  20  is defined by the housing  12  and is configured to contain a first and second rotor assembly  22  and  24 , respectively, rotatably disposed therein. The first and second rotor assemblies  22  and  24  are interleaved and counter-rotating. The first rotor assembly  22  includes a plurality of lobes  26  extending radially outward in a clockwise twisting helical shape, as viewed from the inlet passage  14 , while the second rotor assembly  24  includes a plurality of lobes  28  extending radially outward in a counter-clockwise twisting helical shape, as viewed from the inlet passage  14 . The first and second rotor assemblies  22  and  24  have first ends  30  and  32 , respectively, disposed substantially adjacent to the inlet passage  14  and second ends  34  and  38 , respectively, disposed substantially adjacent to the outlet passage  18 . The first and second rotor assemblies  22  and  24  are rotatably supported within the rotor cavity  20  by a respective first and second shaft member  40  and  42 . Those skilled in the art will recognize that the first and second rotor assemblies  22  and  24  may have screw-type lobes formed thereon while remaining within the scope of that which is claimed. 
         [0012]    During operation of the supercharger assembly  10 , the first and second rotor assemblies  22  and  24  cooperate to convey volumes of intake air  16  from the inlet passage  14  to the outlet passage  18 . The temperature of the intake air  16  tends to increase as the intake air  16  is transferred from the inlet passage  14  to the outlet passage  18 , thereby forming a thermal gradient along the longitudinal axis of the first and second rotors  22  and  24  from the respective first ends  30  and  32  to the respective second ends  34  and  38 . As a result, the degree of thermal expansion of the first and second rotor assemblies  22  and  24  will increase from the first ends  30  and  32  and the second ends  34  and  38 , thereby increasing the likelihood of “scuff” at the second ends  34  and  38  of the first and second rotor assemblies  22  and  24 . Scuff is defined as metal transfer as a result of the first and second rotor assemblies  22  and  24  contacting one another or the housing  12 . 
         [0013]    Referring to  FIG. 2  and with continued reference to  FIG. 1 , there is shown a sectional view of the supercharger assembly  10  taken along line  2 - 2  of  FIG. 1 . Each of the plurality of lobes  26  and  28  include a tip portion  44  and  46 , respectively, positioned at the outer extreme of the respective lobes  26  and  28 . The rotor cavity  20 , within which the first and second rotor assemblies  22  and  24  are disposed, is defined by an inner wall  48  of the housing  12 . As illustrated in  FIG. 2 , each of the lobes  26  and  28  have an outer radius, indicated as R 1 , at the first ends  30  and  32  of the respective first and second rotor assemblies  22  and  24 . A gap or clearance, generally indicated as C 1 , is provided between the tip portions  44  and  46  and the inner wall  48 . Referring now to  FIG. 3  and with continued reference to  FIG. 1 , there is shown a sectional view of the supercharger assembly  10  taken along line  3 - 3  of  FIG. 1 . As illustrated in  FIG. 3 , each of the lobes  26  and  28  have an outer radius, indicated as R 2  at the second ends  34  and  38  of the respective first and second rotor assemblies  22  and  24 . A gap or clearance, generally indicated as C 2 , is provided between the tip portions  44  and  46  and the inner wall  48 . In a preferred embodiment, the outer radius of the lobes  26  and  28  generally tapers from the first ends  30  and  32  to the second ends  34  and  38  of the respective first and second rotor assemblies  22  and  24 . That is, the outer radii R 1 , of the lobes  26  and  28 , at the first ends  30  and  32  is greater than the outer radii R 2 , of the lobes  26  and  28 , at the second ends  34  and  38  of the respective first and second rotor assemblies  22  and  24 . As such, the clearance C 1  between the rotor tip portions  44  and  46  and the inner wall  48  at the first ends  30  and  32  of the first and second rotor assembly  22  and  24  is less than the clearance C 2  at the second ends  34  and  38  of the first and second rotor assemblies  22  and  24 . 
         [0014]    Referring to  FIGS. 1 through 3 , in operation, the intake air  16  will heat the first and second rotor assemblies  22  and  24  causing a greater thermal expansion at the second ends  34  and  38  than the first ends  30  and  32 . By providing the first and second rotor assemblies  22  and  24  with a generally tapering shape, the clearance C 1  and C 2  during operation of the supercharger assembly  10  will substantially equalize. The generally tapered shape of the first and second rotor assemblies  22  and  24  enables a smaller or tighter clearance dimension C 1  at the first ends  30  and  32  of the first and second rotor assemblies  22  and  24 , while substantially avoiding the possibility of scuff at the second ends  34  and  38  during operation of the supercharger assembly  10 . The lobes  26  and  28  may taper continuously from the first ends  30  and  32  to the second ends  34  and  38  of the first and second rotor assemblies  22  and  24 . Alternatively, the lobes  26  and  28  may taper from any point between the first and second ends  30 ,  32  and  34 ,  38  to the second ends  34  and  38  of the first and second rotor assemblies  22  and  24 . The lobes  26  and  28  may taper in a generally linear or a curved fashion while remaining within the scope of that which is claimed. 
         [0015]    Referring to  FIG. 4  and with continued reference to  FIGS. 1 through 3 , there is shown a sectional schematic view of the super charger assembly  10 . The swept volume of the first and second rotor assemblies  22  and  24  is delineated by phantom lines and indicated at  50 . The swept volume  50  illustrates first, second, and third profiles  52 ,  54 , and  56 , respectively. The first profile  52  illustrates a rotor shape tapering continuously from the first ends  30  and  32  to the second ends  34  and  38 . The second profile  54  illustrates a rotor shape that generally tapers from a point between the first ends  30  and  32  and the second ends  34  and  38  to the second ends  34  and  38 . Alternately, the third profile  56  illustrates a rotor shape tapering in a generally curved fashion toward the second ends  34  and  38 . 
         [0016]    By tapering the lobes  26  and  28  of the first and second rotor assemblies  22  and  24 , improvements in the efficiency of the supercharger assembly  10  may be achieved such as, for example, increase in the flow of intake air  16 , reduced temperature rise of the intake air  16  flowing through the supercharger assembly  10 , reduced parasitic losses, and improved resistance to scuff. Those skilled in the art will recognize that lobes  26  and  28  having a curved taper to optimally fit the thermal growth pattern of the first and second rotor assemblies  22  and  24  may be may be employed while remaining within the scope of that which is claimed. 
         [0017]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.