Abstract:
An electrical machine comprising a rotor ( 26 ) mounted on a shaft ( 29 ) for rotation therewith and defining an axis of rotation, and a stator ( 54 ) disposed coaxially with and in opposition to the rotor ( 26 ). The electrical machine further comprises a housing ( 22, 24 ) enclosing the stator ( 54 ) and the rotor ( 26 ), the housing ( 22, 24 ) having a first axial end with a wall with an inner surface and an outer surface and a second axial end with a wall with an inner surface and an outer surface. The electrical machine also includes a first cooling tube ( 80 ′) having a first end and a second end and an embedded portion thereof embedded between the first inner surface and the first outer surface of end wall ( 81 ). A second cooling tube ( 82 ′) has a first end and a second end and an embedded portion thereof embedded between said inner surface and said outer surface of the wall ( 83 ) of the second axial end. The first end ( 226 ) of the first cooling tube and the first end ( 228 ) of the second cooling tube ( 82 ′) are fluidically coupled together to permit fluid flow in parallel between the first cooling tube ( 80 ′) and the second cooling tube ( 82 ′).

Description:
RELATED APPLICATIONS 
     The present invention is also related to U.S. patent application Ser. No. 09/634,411 entitled “Liquid-Cooled Electrical Machine With Integral Bypass” incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to electrical machines, and more particularly to cooling of electrical machines. 
     DESCRIPTION OF THE RELATED ART 
     Ways are continually sought to increase the electrical output of automotive alternators. With increased electrical output comes additional heat generated in the various electrical components of the alternator. In addition, friction in the bearings which support the rotor shaft of the alternator also generates heat. Because heat generated in an alternator is frequently the factor which limits the electrical output of the alternator, effective cooling of the alternator is very important. 
     Circulating liquid within an alternator has been recognized as one means for providing cooling. A liquid cooling design which provides effective cooling and which can support demands for ever-reducing package size of the alternator can be particularly advantageous. 
     SUMMARY OF THE INVENTION 
     The present invention provides an electrical machine comprising a rotor mounted on a shaft for rotation therewith and defining an axis of rotation, and a stator disposed coaxially with and in opposition to the rotor. The electrical machine further comprises a housing enclosing the stator and the rotor, the housing having a first axial end with a wall with an inner surface and an outer surface and a second axial end with a wall with an inner surface and an outer surface. The electrical machine also includes a first cooling tube having a first end and a second end and an embedded portion thereof embedded between the first inner surface and the first outer surface. A second cooling tube having a first end and a second end and an embedded portion thereof embedded between said inner surface and said outer surface of the wall of the second axial end. The first end of the first cooling tube and the first end of the second cooling tube are fluidically coupled together to permit fluid flow in parallel between the first cooling tube and the second cooling tube. 
     Designs according to the present invention are advantageous in that they can provide effective cooling of an electrical machine while also supporting packaging-efficient electrical machine designs. 
     Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an alternator  20  according to one embodiment of the present invention. 
     FIG. 2 is a cross-sectional view of alternator  20  taken along a plane parallel to the axis of rotation of alternator  20 . 
     FIG. 3 is a perspective view of rotor  26  of alternator  20 . 
     FIG. 4 is a cross-sectional view of alternator  20  taken along line  4 — 4  of FIG.  2 . 
     FIG. 5 is a cross-sectional view of alternator  20  taken along line  5 — 5  of FIG.  2 . 
     FIG. 6 is a perspective view of a second embodiment of the invention. 
     FIG. 7 is a rotated perspective view of the second embodiment shown in FIG.  6 . 
     FIG. 8 is a partially exploded view of the second embodiment shown in FIG.  6 . 
     FIG. 9 is a perspective of one housing portion having an inlet according to the present invention. 
     FIG. 10 is a partially cutaway perspective view of a portion of the housing of FIG.  10 . 
     FIG. 11 is a perspective view of second embodiment of an inlet according to the present invention. 
     FIG. 12 is a partial cross-sectional view through the inlet of FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Refer first to FIGS. 1-3, an alternator  20  includes a front housing portion  22  and a rear housing portion  24  which are suitably bolted or otherwise attached together. Front housing portion  22  and rear housing portion  24  are preferably metallic. Included within front housing portion  22  and rear housing portion  24  is a rotor  26 . Those skilled in the art will recognize rotor  26  as being generally of the “claw-pole” variety. A plurality of permanent magnets  28  are disposed within rotor  26  in order to enhance the electrical output of alternator  20 . 
     Rotor  26  includes a shaft  29  having two slip rings  30  and  32  which are means for providing electrical power from a voltage regulator (not shown in the particular sectioning employed in FIG. 2) to a field coil  34  disposed within rotor  26 . Also coupled to shaft  29  is a pulley  36 , or other means for rotating rotor  26 . Shaft  29  is rotatably supported by a front bearing  50 , itself supported by front housing portion  22 , and a rear bearing  52 , rotatably supported by rear housing portion  24 . 
     A stator  54  is disposed in opposition to rotor  26 . Stator  54  includes a ferromagnetic stator core  56 , on which stator windings  58  are wound. The end turns  60  of stator windings  58  on one axial side of stator core  56  are substantially enclosed in a groove  62  in front housing  22 . The end turns  64  of stator winding  58  on the other axial side of stator core  56  are substantially enclosed in a groove  66  in rear housing  24 . Preferably, end turns  60  and  64  are encapsulated in a highly thermally conductive compound in order to facilitate heat transfer away from stator windings  58 . 
     A rectifier  70 , coupled to stator windings  58  in order to rectify the alternating current output generated in stator windings  58  by the operation of alternator  20 , is mounted to rear housing  24 . Rectifier  70  includes a negative rectifier plate  72 , which forms the common connection for the cathodes of the “negative” diodes  72 A. Rectifier  70  also includes a positive rectifier plate  74 , which forms the common connection for the anodes of the “positive” diodes  74 A. Negative rectifier plate  72  and positive rectifier plate  74  are electrically insulated from one another. A plastic cover  76  covers the rear of alternator  20 , including rectifier  70 . Electrical connectors  77  and  78  provide the required electrical connections to and from alternator  20 . As those connections are conventional, they are not described in detail here. 
     Front housing portion  22  also includes cooling tube  80 , and rear housing portion  24  includes cooling tube  82 . Cooling tubes  80  and  82  are preferably metallic, in order to assure good heat transfer from housing portions  22  and  24  to cooling tubes  80  and  82 , respectively. Cooling tubes  80  and  82  are preferably die-cast into their respective axial end walls  81 ,  83  of housing portions  22  and  24 . Of course, if cooling tubes  80  and  82  are included within housing portions  22  and  24  by die casting, the material comprising cooling tubes  80  and  82  must have a higher melting temperature than the material comprising housing portions  22  and  24 , in order to allow cooling tubes  80  and  82  to be die-cast therein. 
     The ends of cooling tube  80  emerge from front housing portion  22 , and the ends of cooling tube  82  emerge from rear housing  24 . End  84  of cooling tube  80  forms an inlet into which cooling fluid can be introduced into alternator  20 . End  86  of cooling tube  82  forms an outlet from which cooling fluid exits from alternator  20 . The remaining two ends of cooling tube  80  and cooling tube  82  are coupled together by a “cross-over” formed by flexible tube  88  and two clamps  90  and  92 . Cooling fluid can thus flow into inlet end  84  of cooling tube  80 , through the length of cooling tube  80 , through the “cross-over” into cooling tube  82 , through the length of cooling tube  82 , and out the outlet end  86  of cooling tube  82 . Inlet end  84  and outlet end  86  are coupled to a source of cooling fluid such as the cooling system of a motor vehicle engine. 
     Referring now to FIG. 4, it can be seen that cooling tube  80  is formed substantially as a circular loop until points  100  and  102 , where cooling tube  80  begins to emerge from front housing portion  22 . 
     Referring now additionally to FIG. 5, it can be seen that cooling tube  82  is also formed in a substantially circular loop until points  104  and  106 , where cooling tube  82  begins to emerge from rear housing portion  22 . 
     The design disclosed herein is particularly effective for cooling alternator  20 , for a number of reasons. First, end turns  60  and  64  of stator  54  are substantially enclosed by grooves  62  and  66  in the housing of alternator  20 . Because the housing is cooled by cooling tubes  80  and  82 , heat generated in stator windings  58  is effectively conducted away from those windings. Second, front housing portion  22  presents a large, substantially flat surface  108  to rotor  26  across a small air gap  110 . Air gap  110  is preferably about 0.5 millimeters wide. Because front housing portion  22  is cooled by cooling tube  80 , the large, flat surface  108  across small air gap  110  provides for substantial heat transfer away from rotor  26 , including heat generated in field coil  34 . Rear housing portion  24  presents a similar large, substantially flat surface  112  to rotor  26  across a small air gap  114 . Air gap  114  is preferably about 0.5 millimeters wide. Third, with bearings  50  and  52  mounted in housing portions  22  and  24  and in proximity with cooling tubes  80  and  82 , heat generated in bearings  50  and  52  due to rotation of shaft  29  is effectively conducted away. 
     The design disclosed herein provides the cooling advantages described immediately above, while also contributing to alternator  20  having a short axial length. It can be seen that the axial alignment of cooling tube  80 , end turns  60  and bearing  50 , as well as the axial alignment of cooling tube  82 , end turns  64  and bearing  52  cause alternator  20  to have the short axial length. This is very much an advantage in packaging alternator  20  in a vehicle. 
     Referring now to FIGS. 6 and 7, a second embodiment having parallel flow as opposed to the serial flow described above is illustrated. In the following description the same reference numerals that are used above in the first embodiment are primed for the same components in FIG.  6 . In this embodiment, a fluid interface  220  is used for coupling fluids to alternator  20 ′. When fluid enters alternator  20 ′ through fluid interface  220 , fluid travels through cooling tube  80 ′ and cooling tube  82 ′ simultaneously. The fluid then exits fluid interface  220  from both cooling tube  80 ′ and cooling tube  82 ′. Fluid interface  220  has an inlet  222  and an outlet  224 . In the preferred embodiment, inlet  222  and outlet  224  are coupled to the cooling system of an automotive vehicle. As will be further described below, it is preferred to have a minimal pressure drop across the alternator. Therefore, providing a parallel flow as in FIGS. 6 and 7 versus a series flow reduces the pressure drop by as much as  70  percent. In the preferred embodiment, inlet  222  and outlet  224  are located on the same housing  22 ′. However, those skilled in the art would recognize that inlet  222  and outlet  224  may also be located on housing  24 ′. 
     To achieve the parallel flow the cooling tube  80 ′ has a first end  226  fluidically and mechanically coupled to first end  228  of second cooling tube  82 ′. First end  226  and first end  228  are fluidically coupled to inlet  222 . Second end  230  of first cooling tube  80 ′ is fluidically and mechanically coupled to second end  232  of second cooling tube  82 ′. Second end  230  and second end  232  are fluidically coupled to outlet  224 . 
     An inlet hose interface  234  may be coupled to inlet  222 . An outlet hose interface  236  is preferably coupled to outlet  224 . Both inlet hose interface  234  and outlet hose interface  236  are mechanically coupled to the respective inlet  222  and outlet  224 . The mechanical coupling may be fixed or may be rotatable to provide convenient assembly. Also, by locating the inlet  222  and the outlet  224  on the same housing, the ease of assembly during manufacture of the vehicle is increased in the ever shrinking underhood environment. 
     Referring now to FIG. 8, a partial exploded view of alternator  20 ′ is illustrated. As can be seen, fluid interface  220  has a first flange  238  coupled adjacent to first end  226  and second end  230 . A second flange  240  is positioned adjacent first end  228  and second end  232  of second cooling tube  82 ′. As is illustrated, each flange  238 ,  240  has nearly a “figure 8” shape. At least one of the flanges  238  and  240  preferably have a seal channel  242  formed therein. Seal channel  242  is sized to receive a seal  244  at least partially therein. Seal  244  provides a seal between first flange  238  and second flange  240  to prevent fluid leakage therebetween. These skilled in the art will recognize various types of seals and gaskets may be used. 
     To conserve material a common wall  246  is preferably located between first end  226  and second end  230  of first cooling tube  80 ′. 
     Referring now to FIGS. 9 and 10, a third embodiment of the present invention is illustrated. In this embodiment the same reference numerals used in the second embodiment will be used for the same components. In this embodiment, the common wall  246  between inlet  222  and outlet  224  has a port  248  formed therethrough. Port  248  is sized to allow fluid to pass directly through common wall  246  from inlet  222  and outlet  224 . By allowing fluid to pass directly between inlet  222  and outlet  224 , the fluid resistance of the alternator is reduced. Moreoever, the amount of fluid traveling through first cooling tube  80 ′ and second cooling tube  82 ′ is sufficient to cool the alternator. Thus, because the pressure drop across the alternator is reduced, a bypass manifold with its associated hoses and connection is not required. 
     Preferably, inlet  222 , outlet  224  and port  248  are colinear along line  250 . However, those skilled in the art will recognize that a non-colinear alignment may be used with the risk of increasing the pressure drop across the alternator. 
     The diameter D of port  248  may be varied to increase or decrease the pressure drop across the alternator. The amount of pressure increase or decrease across the alternator will vary depending on the particular vehicle configuration and cooling system flow requirements. 
     Referring now to FIGS. 11 and 12, a second embodiment of an alternative fluid interface  220 ′ is illustrated. Fluid interface  220 ′ in this embodiment includes an inlet T-shaped portion  260  and an outlet T-shaped portion  262 . Inlet T-shaped portion  260  is coupled to first end  226 ′ of first cooling tube  80 ″ and first end  228 ′ of second cooling tube  82 ″. Outlet T-shaped portion  262  is coupled to second end  230 ′ of first cooling tube  80 ″ and second end  232 ′ of second cooling tube  82 ″. Preferably, a flange  264  extends between first end  226 ′ and second end  230 ′ of first cooling tube  80 ″. A second flange  266  preferably extends between first end  228 ′ and second end  232 ′ of second cooling tube  82 ″. 
     As is best illustrated in FIG. 12, first cooling tube  80 ″ has a receiving portion  268  that extends into inlet T  260  that inlet T-shaped portion  260  may be received thereon. Also, second cooling tube  82 ″ has a receiving portion  270  extending therefrom. Receiving portion  270  also extends inward into inlet T  260  so that inlet T is receiving thereon. A plurality of fields  272  such as O-rings are positioned between inlet T-shaped portion  260  and receiving portions  268 ,  270 . Seals  272  prevent fluid leakage between the T-shaped portion  260  out of the fluid path. 
     Although FIG. 12 only illustrates a cross-sectional view through first T-shaped portion  260 , second T-shaped portion  262  is also configured in a similar manner. 
     Inlet T-shaped portion  260  has an inlet end  261  for receiving fluid from the coolant path of the automotive vehicle. Outlet T-shaped portion  262  has an outlet end  263  for returning coolant to the coolant path of the automotive vehicle. In this embodiment similar to the prior embodiment, coolant enters inlet end  261  and travels through first coolant tube  80 ″ and second coolant tube  82 ″ in parallel so that coolant circulates therethrough and exits simultaneously through outlet end  263 . 
     Other embodiments may be formed as would be evident to those skilled in the art. For example, the inlet  222  and outlet  224  may be located on alternate housing portions. Further, port  248  may be located in a different housing portion than inlet  222  and outlet  224 . 
     Various other modifications and variations will no doubt occur to those skilled in the arts to which this invention pertains. Such variations which generally rely on the teachings through which this disclosure has advanced the art are properly considered within the scope of this invention. This disclosure should thus be considered illustrative, not limiting; the scope of the invention is instead defined by the following claims.