Patent Document

TECHNICAL FIELD 
     The present invention relates to a liquid-cooled rotor assembly for a compressor or supercharger assembly. 
     BACKGROUND OF THE INVENTION 
     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 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 intake air 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 
     A rotor assembly for a supercharger assembly is provided. The rotor assembly includes at least one lobe defining at least one cavity. The at least one cavity is configured to contain a fluid, such as oil or coolant, operable to cool the at least one lobe. 
     In one embodiment, the rotor assembly includes a rotatable shaft member and the at least one lobe is operatively connected to the shaft member. The shaft member defines a feed passage operable to communicate the fluid to the at least one cavity. The shaft member further defines a return passage operable to exhaust the fluid from the at least one cavity. The feed passage is positioned generally along an axis of rotation of the shaft member, while the return passage is positioned generally adjacent to the outer periphery of the shaft member. A supercharger incorporating the rotor assembly is also disclosed. 
     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 
         FIG. 1  is a schematic perspective view of a supercharger assembly configured for use with an internal combustion engine; 
         FIG. 2  is a perspective view of a first and second rotor assembly for use within the supercharger assembly of  FIG. 1 ; 
         FIG. 3  is a non-planar or revolved cross sectional view, taken along  3 - 3  of  FIG. 2 , of two adjacent lobes of the first rotor assembly; and 
         FIG. 4  is a non-planar or revolved cross sectional view, similar to that of  FIG. 3 , of an alternate embodiment of the first rotor assembly of  FIGS. 1-3 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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 assembly  10  includes a housing  12 . The housing  12  defines an inlet passage  14  configured to induct intake air, represented as arrow  16 , into the supercharger assembly  10 . The housing  12  further defines an outlet passage  18  configured to exhaust the intake air  16  from the supercharger assembly  10 . 
     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 with respect to each other. 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  cooperate to convey intake air  16  from the inlet passage  14  to the outlet passage  18 . The first and second rotor assemblies  22  and  24  are rotatably supported within the rotor cavity  20  by respective first and second shaft member  30  and  32 . 
     During operation of the supercharger assembly  10 , the first and second rotor assemblies  22  and  24  cooperate to convey 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 . As a result, the degree of thermal expansion of the first and second rotor assemblies  22  and  24  will increase during operation of the supercharger assembly  10 , thereby increasing the likelihood of “scuff”. 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 . Scuff occurs when the running clearances, i.e. the clearance dimension between the lobes  26  and  28  and the housing  12  when the supercharger assembly  10  is operating, reaches zero causing an interference condition and material transfer between the first and second rotor assemblies  22  and  24  and the housing  12 . 
     A cooling system  34 , such as a loop or a simple tank, is schematically depicted in  FIG. 1  and is operable to cool or extract heat energy from the lobes  26  and  28  of the first and second rotor assemblies  22  and  24  during the operation of the supercharger assembly  10 . By cooling the lobes  26  and  28 , the thermal expansion of the first and second rotor assemblies  22  and  24  can be minimized thereby reducing the likelihood of scuff. Additionally, the cooling system  34  enables tighter running clearances between the first and second rotor assemblies  22  and  24  and the housing  12  since the dimensional stability of the lobes  26  and  28  during operation of the supercharger assembly  10  is improved. The cooling system  34  includes a source  35  of fluid  36 , such as oil from a gear case (not shown) of the supercharger assembly  10 , or coolant from a liquid-to-air supercharger intercooler (not shown) or the engine (not shown), or a completely separate fluid circuit; however, those skilled in the art will recognize other fluids that may be used within the cooling system  34  while remaining within the scope of that which is claimed. A pump  38  is in fluid communication with the source  35  and is operable to communicate the fluid  36  under pressure to feed passages  40  and  42  defined by respective first and second shaft members  30  and  32  to effect cooling of the first and second rotor assemblies  22  and  24 . Annular grooves  41  and  43  are partially defined by the respective first and second shaft members  30  and  32 . The annular grooves  41  and  43  are operable to return the fluid  36  to the source  35 . 
     Referring to  FIG. 2 , there is shown a perspective view of the first and second rotor assemblies  22  and  24  illustrating in greater detail the generally helical shape of the lobes  26  and  28 . Additionally, the feed passages  40  and  42  and the annular grooves  41  and  43 . 
     The structure and operation of the first and second rotor assemblies  22  and  24  will be discussed in greater detail with reference to  FIG. 3 . Although only the first rotor assembly  22  is shown in  FIG. 3 , it should be understood that the same general structure may be employed with the second rotor assembly  24 . Referring to  FIG. 3  and with continued reference to  FIG. 1 , there is shown a non-planer cross sectional view of the first rotor assembly  22 . The section is taken along  3 - 3  of  FIG. 2  and generally rotates with the helix angle of lobes  26 . The first shaft member  30  is rotatable about an axis of rotation, indicated at A. The feed passage  40  extends generally along the axis of rotation A and is in communication with a generally radially extending passage  42  defined by the first shaft member  30 . The radially extending passage  42  is in communication with a cavity  44  defined by the lobe  26 . Specifically, the cavity  44  is defined by a radially-inner wall  45  of the lobe  26  and a radially-outer wall  47  of the lobe  26 . The cavity  44  extends radially between the radially-inner wall  45  and the radially outer wall  47 . Although only one radially extending passage  42  is shown in  FIG. 3 , it should be understood that each of the cavities  44  defined by lobes  26  are in communication with a respective radially extending passage  42 . The lobes  26  and the first shaft member  30  cooperate to define a generally annular passage  46 . The annular passage  46  extends axially along the first shaft member  30  on an opposing side  49  of the radially-inner wall  45  than the side  51  of the radially-inner wall  45  that the cavity  44  is on, and is in communication with a return passage  48  defined by the first shaft member  30 . The return passage  48  extends generally axially along the outer periphery of the first shaft member  30 . 
     During operation of the supercharger assembly  10  of  FIG. 1 , the cooling system  34  provides fluid  36 , indicated as arrows in  FIG. 3 , to the feed passage  40 . The fluid  36  is forced radially outward, through the radially extending passage  42 , and into the cavity  44 . The fluid  36  is at least partially forced radially outward by the centrifugal forces exerted thereon by the rotation of the first shaft member  30 . Subsequently, the fluid  36  travels the length of the cavities  44  to extract heat energy and thereby cool the lobes  26  of the first rotor assembly  22 . The fluid  36 , having traveled the length of the lobes  26 , is exhausted into the generally annular passage  46  where the fluid is communicated to the return passage  48  for later communication to the cooling system  34 . The annular groove  41  is defined by the first shaft member  30  and is operable to facilitate the exhausting of fluid  36  from the return passage  48 . 
     By cooling the lobes  26  and  28 , the running clearances between the lobes  26  and  28  and the housing  12  may be minimized while reducing the likelihood of scuff. Therefore, the operating efficiency of the supercharger assembly  10  may be increased by maintaining the temperature of lobes  26  and  28  within predetermined limits. It should be understood that with certain configurations of the first rotor assembly  22  and operating speeds of the supercharger assembly  10 , the pump  38  may not be necessary since the feed passage  40  is centrally located along the axis of rotation A of the first shaft member  30 , while the return passage  48  is provided on the outer periphery of the first shaft member  30 . As such, the centrifugal forces exerted on the fluid  36  by the rotation of the first shaft member  30  may be sufficient to enable the pumping of the fluid  36  through the first rotor assembly  22  in lieu of the pump  38 . The first and second rotor assemblies  22  and  24  may have helical-type, screw-type, or straight-type configurations for lobes  26  and  28  while remaining within the scope of that which is claimed. As stated hereinabove, the lobes  26  and  28  of the first and second rotor assemblies  22  and  24  have a generally helical shape; as such, the fluid  36  is pumped through the cavities  44  during rotation of the first and second rotor assemblies  22  and  24 . 
     Referring to  FIG. 4 , there is shown an alternate embodiment of the first rotor assembly  22  of  FIGS. 1 through 3 , generally indicated at  22 A. The first rotor assembly  22 A is similar to the first rotor assembly  22 ; however the cavity  44  is formed by cross drilling lobes  26 A. The cavity  44  is defined by a radially-inner wall  145  of the lobe  26 A and a radially-outer wall  147  of the lobe  26 A. The cavity  44  extends radially between the radially-inner wall  145  and the radially-outer wall  147 . Plugs  50 , such as cup plugs or ball bearings, are mounted to the lobes  26 A and are operable to prevent leakage of fluid  36  from the cavity  44  during operation of the first rotor assembly  22 A. By cross-drilling the lobes  26 A, a conventional, i.e. non liquid-cooled rotor assembly may be adapted to a liquid cooled rotor assembly. Additionally, cavities  44  may be easier to form within certain rotor shapes, such as helix shapes, by cross drilling as opposed to investment casting or other casting methods. 
     In operation of the first rotor assembly  22 A, the fluid  36  is communicated to the feed passage  40  and is subsequently communicated to the cavities  44  via the radially extending passages  42 . As with the first rotor assembly  22  of  FIG. 3 , the fluid  36  travels the length of the cavities  44  to extract heat energy and thereby cool the lobes  26 A of the first rotor assembly  22 A. The fluid  36 , having traveled the length of the lobes  26 A, is exhausted into the return passage  48  for later communication to the cooling system  34  via the annular groove  41 . 
     Although the discussion has focused on the application of the supercharger assembly  10  to an internal combustion engine, those skilled in the art will recognize other applications of the supercharger  10  such as a compressor for industrial application, compressor for fuel cell applications, etc. 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.

Technology Category: f