Abstract:
The invention provides a structural member for a vehicle transmission formed with an annular recess in fluid communication with a fluid source and at least partially enclosing and defining an interior space of the transmission. An interior component, such as a motor/generator, is located in the interior space. The annular recess directs cooling fluid provided from the fluid source onto the interior component. The end cover includes structure defining a flow passage in fluid communication with a fluid source and also defining an annular recess in fluid communication with the flow passage. The flow passage and the annular recess are cooperatively configured for directing fluid provided from the fluid source onto an interior component in the interior space for cooling the interior component. Preferably, the interior component is an electric motor/generator that includes a stator having electric windings. The fluid is directed from the annulus onto the electric windings.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims the benefit of U.S. Provisional Application No. 60/591,748, filed Jul. 28, 2004, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This invention relates to cooling of a motor/generator in a hybrid electromechanical vehicular transmission. 
     BACKGROUND OF THE INVENTION 
     A hybrid electromechanical vehicular transmission utilizes interactive planetary gear arrangements that are operatively connected to an engine and two motor/generators. Selective utilization of torque transfer devices enables power transfer via the planetary gear arrangements from the engine and/or motor/generators to the output member of the transmission. 
     A power transmission in an electromechanical transmission is described in commonly owned U.S. Provisional Application No. 60/590,427 entitled Electrically Variable Transmission with Selective Fixed Ratio Operation, filed Jul. 22, 2004, and hereby incorporated by reference in its entirety. 
     Motor/generators in an electromechanical transmission are typically cooled by directing transmission fluid from a fluid source such as a pump to the motor/generators. A cooling system that requires a minimum of added machining and assembly steps, added components and minimal or no increase in pump capacity is desirable. 
     SUMMARY OF THE INVENTION 
     Novel transmission structure is provided to permit efficient cooling of motor/generators. A motor cooling system is provided using transmission components adjacent to the motor/generators such that a minimum of added machining, assembly steps, added components and minimal or no increase in pump capacity is required. 
     A transmission that has an interior component (i.e., a motor/generator) and a fluid source (such as a pump) is provided with a structural member formed with an annular recess. The annular recess is in fluid communication with the fluid source. The structural member partially encloses and defines an interior space of the transmission. The interior component is located in the interior space. The annular recess is cooperatively configured for directing fluid provided from the fluid source onto the interior component to cool the interior component. 
     Within the scope of the invention, the structural member may be an end cover. The end cover may be formed with another annular recess that also directs fluid provided from the fluid source onto the interior component. Optionally, the end cover may define a flow passage in fluid communication with both the fluid source and the annual recess. A ring-shaped sleeve formed with circumferentially-spaced radial openings may be provided that fits within the end cover adjacent the first annular recess such that fluid from the fluid source flows through the circumferentially-spaced radial openings for cooling the interior component. The circumferentially-spaced openings may be configured such that fluid is provided in the form of a mist so that wear on the interior component is minimized. For instance, the openings may be nozzle shaped (tapered) so that the fluid is ejected in a mist form. A deflector may also be positioned between the structural member and the interior component so that fluid directed from the annular recess is deflected by the deflector, slowing the fluid prior to contact with the interior component. 
     The interior component may be an electric motor/generator having a stator with stator windings. The structural member may be an annular stator support connected to an end cover. The annular stator support may define the circumferentially-spaced radial openings in fluid communication with the annular recess for allowing fluids to flow from the fluid source to the stator windings. 
     A motor cooling system for an electromechanical transmission having a first motor/generator includes a fluid source for providing fluid and a structural member formed with an annular recess as described above. 
     A method of cooling a motor/generator in an electromechanical transmission having a fluid source includes providing a structural member formed with an annular recess that is in fluid communication between the fluid source and the motor/generator. The structural member at least partially encloses the motor/generator. The method further includes directing fluid from the fluid source through the annular recess to the motor/generator to cool the motor/generator. Optionally, the structural member may also define a flow passage in fluid communication between the fluid source and the annular recess. In that case, the method may include directing fluid from the fluid source through the flow passage to the annular recess. 
     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 cross-sectional illustration in fragmentary view of a first embodiment of a hybrid electrical/mechanical transmission; 
         FIG. 2  is a schematic cross-sectional illustration in fragmentary view of the transmission of  FIG. 1  including an end cover and a motor cooling system; 
         FIG. 3  is a schematic partially cross-sectional illustration in fragmentary view of a portion of the motor cooling system of  FIG. 2 ; and 
         FIG. 4  is a schematic partially cross-sectional illustration in fragmentary view of a second embodiment of a hybrid electrical/mechanical transmission. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIRST EXEMPLARY EMBODIMENT 
     Motor Cooling System 
     Referring to the drawings wherein like reference numbers refer to like components,  FIG. 1  shows a vehicle  10  having an electromechanical transmission  11 . An input shaft  12  is disposed about a center axis  14  and is operable for transferring power from an engine (not shown) to the transmission  11 . A main shaft  16  is longitudinally disposed and rotatable about the center axis  14  and is engageable with the input shaft  12 . The engagement of one or more of a plurality of clutches such as clutch  15  interconnects one or more of a plurality of planetary gear sets such as planetary gear set  17  to transfer power at varying ratios to an output member  18 . Two electric motor/generators  20 A and  20 B are coaxially oriented about the center axis  14 . Each motor/generator  20 A,  20 B is selectively operatively connectable to a member of one of the planetary gear sets to provide a range of continuously variable speed ratios between the input shaft  12  and the output member  18 , as will be readily understood by those skilled in the art. Each of the motor/generators  20 A,  20 B includes a respective generally ring-shaped stator  22 A,  22 B and a generally ring-shaped rotor  24 A,  24 B, respectively, rotatable with respect to the respective stator  22 A,  22 B. An end cover  26  is mounted with respect to the main shaft  16 . The end cover  26  partially encases the motor/generators  20 A,  20 B within and partially defines an interior space  28 . The end cover  26  cooperates with a first portion  30  of a housing member (i.e., an upper portion of a transmission case) and a second portion  32  of the housing member (i.e., a lower portion of the transmission case) to further encase the motors/generators  20 A,  20 B within the interior space  28 . An O-ring  33  helps to seal the interface between the end cover  26  and the first and second portions  30 ,  32  of the housing member. 
     Referring now to  FIG. 2 , the end cover  26  is formed with first and second annular recesses  34 ,  36 , respectively. Furthermore, a first flow passage  38  is bored through the end cover  26  to create a fluid communication between the first annular recess  34  and a second flow passage  40  formed in the first portion  30  of the housing member. A valve body  42  is in fluid communication with a fluid source such as a pump (not shown) and is capable of delivering pressurized fluid via the second flow passage  40  to the first flow passage  38  from which the fluid flows to the first annular recess  34 . For illustrative purposes, the valve body  42  is shown directly adjacent to the second flow passage  40  in housing cavity  43 ; however, the valve body  42  may be more remotely located and connected via hydraulic passages to the second flow passage  40 . Additionally, the fluid source or pump may be located anywhere on the vehicle and fluidly connected with the valve body  42 , as will be understood by those skilled in the art. 
     As may be better viewed in  FIG. 3 , a ring-shaped sleeve  44 A is press fit to an inner surface  45  of the end cover  26 . The ring-shaped sleeve  44 A includes a plurality of circumferentially-spaced radial openings  46 A that permit fluid communication between the first annular recess  34  and the interior space  28 . Specifically, the circumferentially-spaced radial openings  46 A direct fluid onto first end (i.e., left side) stator windings  48 B of the stator  22 B to cool the windings  48 B. The circumferentially-spaced radial openings  46 A may be designed to present the fluid in the form of a mist over the stator windings  48 B to prevent wear associated with high velocity fluid spray (e.g., by varying the diameter of the openings or by tapering the openings). Alternatively, nozzles may be fit within the radially-spaced openings  46 A and configured to present the fluid in the form of a mist. Yet another alternative is to connect a deflector  49  to the end cover  26  or to the ring shaped sleeve  44 A to deflect fluid flowing from the circumferentially-spaced radial openings  46 A, thereby slowing the velocity of the fluid prior to the fluid contacting the windings  48 B. The deflector  49  may be a steel flange. A single, ring-shaped deflector may be used or separate deflectors  49  may be placed under each respective circumferentially-spaced radial opening  46 A. 
     Referring again to  FIG. 2 , the second annular recess  36  is in fluid communication with the second flow passage  40 . Furthermore, a second set of circumferentially-spaced radial openings  46 B are formed in the end cover  26  such that they are in fluid communication with the second annular recess  36 . Pressurized fluid from the fluid source flows from the valve body  42  through the second flow passage  40  and the second annular recess  36  to the circumferentially-spaced radial openings  46 B and onto the second end (i.e., right side) stator windings  50 B for cooling thereof. As with the first set of circumferentially-spaced radial openings  46 A, the second set of circumferentially-spaced radial openings  46 B may be configured to supply fluid to the second end stator winding  50 B in the form of a mist. 
     A center support  54  is rigidly supported with respect to the main shaft  16  about the center axis  14  and supports the stator  22 A as described below. A third flow passage  56  is formed within the center support  54  and is in fluid communication with the valve body  42  through a fourth flow passage  58  formed in the first portion  30  of the transmission case. Cooling fluid is supplied to first end (i.e., left side) stator windings  48 A of the stator  22 A via the third and fourth flow passages  56 ,  58 . A drilled bore  55  in the center support  54  intersects an annular cavity  57 . An annular plate  59  having an orifice  61  is press fit into the cavity  57 . Fluid flows from the third passage  56 , into the bore  55 , into the cavity  57  and through the orifice  61  to cool the first end stator windings  448 A. The center support  54  is formed with a third annular recess  60  which is in fluid communication with a third set of circumferentially-spaced radial openings  62  which are also formed in the center support  54 . Cooling fluid is supplied to second end (i.e., right side) stator windings  50 A of the stator  22 A from the valve body  42  via a fifth flow passage  64  in fluid communication with the third annular recess  60  and through the third set of circumferentially-spaced radial openings  62 . 
     Referring to  FIGS. 2–3 , a motor cooling system  66  for the motor/generator  20 B includes the end cover  26  having the first flow passage  38  and being formed with first and second annular recesses  34 ,  36 , respectively. Furthermore, the motor cooling system  66  may include the ring-shaped sleeve  44 A having the first set of circumferentially-spaced radial openings  46 A for cooling the left side stator windings  48 B. The motor cooling system  66  may also include the second set of radially-spaced openings  46 B formed in the end cover  26  to provide fluid communication between the second annular recess  36  and the right side stator windings  50 B for cooling thereof via fluid provided from a fluid source. 
     Stator Support and Motor/Generator Packaging Module 
     Referring to  FIG. 2 , the stator  22 B includes a plurality of segmented portions (one portion shown) spaced about an inner surface  68  of the end cover  26 . Those skilled in the art will readily understand the segmented nature of the stator  22 B. The inner surface  68  of the end cover  26  may be provided with slots coordinating with extensions on the segmented portions of the stator  22 B for fixedly connecting the segments to the end cover  26 . 
     A first rotor hub  70 B is rotatably supported by the end cover  26  at a bearing  72 B and is welded to the main shaft  16 . The rotor  24 B is rigidly connected to the first rotor hub  70 B and is rotatable therewith with respect to the end cover  26 . A gap  74 B is achieved between the stator  22 B and the rotor  24 B and is controlled by the radial dimensions of the rotor  24 B and the stator  22 B and the distance between an exterior surface  76  of the first rotor hub  70 B and the inner surface  68  of the end cover  26 . Because the rotor hub  70 B is mounted at the shaft bearing  72 B and is supported by the end cover  26  which also forms the inner surface  68 , variability in the gap  74 B due to build tolerances is minimized (i.e., the dimensions of one element, the end cover  26 , influence the positioning and dimensional play at both ends (the exterior surface  76  of the first rotor hub  70 B and the inner surface  68  of the end cover  26 ) of the space in which the motor/generator  20 B is packaged). 
     The stator  22 A includes a plurality of segmented portions spaced about an inner surface  78  of the center support member  54 . The inner surface  78  of the center support member  54  may be provided with slots coordinating with extensions on the segmented portions of the stator  22 A for fixedly connecting the segments to the center support member  54 . 
     A second rotor hub  70 A consists of welded outer portion  71  and inner portion  73 . The rotor  24 A is rigidly connected to the second rotor hub  70 A and is rotatable therewith with respect to the center support  54 . The second rotor hub  70 A is partially supported by the center support  54  at bearing  72 A. A gap  74 A is achieved between the stator  22 A and the rotor  24 A and is controlled by the radial dimensions of the rotor  24 A and the stator  22 A and the distance between an outer surface  80  of the second rotor hub  70 A and the inner surface  78  of the center support member  54 . Because the second rotor hub  70 A is supported by the center support member  54 , the dimensions of one component (the center support member  54 ) influence the positioning and dimensional play at both ends (i.e., the inner side  78  of the center support member  54  and the exterior surface  80  of the rotor hub  70 A) of the space in which the motor/generator  20 A is packaged. 
     Support of the rotor  24 B is further provided by bearing  75 B, disposed between the shaft  16  and the rotor hub  70 A, because the weight of the motor  20 B and rotor hub  70 B are distributed to the shaft  16  since the rotor hub  70 B is welded to the shaft  16 . Likewise, support of the rotor  24 A is further provided by shaft bearing  75 A disposed between the rotor hub  70 A and the center support  54 . Thus, support of the rotors  24 A,  24 B is cantilevered, rather than provided on either side of each rotor, as is typically done. The rotors  24 A and  24 B are both grounded or steadied by a common member, the shaft  16 . Rotor  24 B is steadied by the shaft  16  because the rotor hub  70 B is welded to it. Rotor  24 A is steadied by the shaft  16  via the shaft bearing  75 B. By supporting the rotors  24 A,  24 B at a common member (the shaft  16 ), unintended run out between the rotors  24 A,  24 B is minimized. 
     Because for each motor/generator  20 A and  20 B, the rotor  24 A,  24 B and stator  22 A,  22 B are supported by a common member (the center support  54  and end cover  26 , respectively) the invention allows each motor/generator  20 A,  20 B to be easily prepackaged as a module prior to attachment with the transmission  11 . The motor/generator module  82  for motor/generator  20 B includes the end cover  26  having the stator  22 B fit at the inner surface  68 . The rotor  24 B is rigidly connected to the rotor hub  70 B, which is then fit to the end cover  26  at the bearing  72 B. The entire module  82  (end cover  26 , stator  22 B, rotor  24 B, bearing  72 B and rotor hub  70 B) may then be piloted on to the shaft  16  and welded thereto as a unit. Similarly, the motor/generator module  84  for motor/generator  20 A includes the center support  54  having stator  22 A fit at the inner surface  78 . The rotor  24 A is rigidly connected to the rotor hub  70 A, which is then fit to the center support  54  at bearing  72 A and bearing  75 A. The entire module  84  (which includes center support  54 , stator  22 A, rotor  24 A and rotor hub  70 A) may then be piloted on to the shaft  16  over bearing  75 B as a unit. 
     The end cover  26  as well as the center support  54  may be iron. By forming these components from iron, magnetivity of the motor/generators  20 A and  20 B is increased as the iron in the end cover  26  and the center support  54  (which will be disposed both above the stators and below the rotors) supplements the magnets in the respective motor/generators  20 B,  20 A to increase torque capacity. 
     SECOND EXEMPLARY EMBODIMENT 
     Motor Cooling System 
     Referring to  FIG. 4 , a vehicle  10 ′ includes an electro-mechanical transmission  11 ′. An input shaft  12 ′ is disposed about a center axis  14 ′ and is operable for transferring power from an engine (not shown) to the transmission  11 ′. A main shaft  16 ′ is longitudinally disposed and rotatable about the center axis  14 ′ and is engagable with the input shaft  12 ′. The engagement of one or more of a plurality of clutches such as clutch  15 ′ interconnects one or more of a plurality of planetary gear sets such as planetary gear set  17 ′ to transfer power at varying ratios to an output member (not shown, but situated similarly to output member  18  of  FIG. 1 ). Two electric motor/generators  20 A′ and  20 B′ are coaxially oriented about the center axis  14 ′. Each motor/generator  20 A′,  20 B′ is selectively operatively connectable to a member of one of the planetary gear sets to provide a range of continuously variable speed ratios between the input shaft  12 ′ and the output member, as will be readily understood by those skilled in the art. Each of the motor/generators  20 A′,  20 B′ includes a generally ring-shaped stator  22 A′,  22 B′ and a generally ring-shaped rotor  24 A′,  24 B′, respectively, rotatable with respect to the respective stator  22 A′,  22 B′. An end cover  26 ′ is mounted with respect to the main shaft  16 ′. The end cover  26 ′ partially encases the motor/generators  20 A′,  20 B′ within and partially defines an interior space  28 ′. The end cover  26 ′ includes a first annular stator support  86 A′. The stator support  86 A′ is bolted to the end cover  26 ′ with bolt  87  and cooperates with a first portion  30 ′ of a housing member (i.e., an upper portion of a transmission case) and a second portion  32 ′ of the housing member (i.e., a lower portion of the transmission case) to further encase the motors/generators  20 A′,  20 B′ within the interior space  28 ′. The first annular stator support  86 A′ is formed with a notched portion  89  which aids in positioning the stator  22 B′. The stator  22 B′ is held in position against the notched portion  87  to prevent movement of the stator  22 B′ due to magnetic forces. 
     The first annular stator support  86 A′ is formed with an annular recess  36 ′. Furthermore, flow passage  40 ′ is formed in the first portion  30 ′ of the housing member. A valve body  42 ′ is in fluid communication with a fluid source such as a pump (not shown) and is capable of delivering pressurized fluid via the flow passage  40 ′ to the annular recess  36 ′. For illustrative purposes, the valve body  42 ′ is shown directly adjacent to the flow passage  40 ′; however, the valve body  42 ′ may be more remotely located and connected via hydraulic passages to the flow passage  40 ′. An o-ring  33 ′ is disposed between the first portion of the housing  30 ′ and the first annular stator support  86 A′ to help prevent leakage of fluid from a space formed between the annular recess  36 ′ and the first portion  30 ′ of the housing. Additionally, the fluid source or pump may be located anywhere on the vehicle and fluidly connected with the valve body  42 ′, as will be understood by those skilled in the art. 
     A plurality of circumferentially-spaced radial openings  46 A′ are formed in first the annular stator support  86 A′ to permit fluid communication between the annular recess  36 ′ and the interior space  28 ′. Specifically, the circumferentially-spaced radial openings  46 A′ direct fluid onto first end (i.e., left side) stator windings  48 B′ of the stator  22 B′ to cool the windings  48 B′. The circumferentially-spaced radial openings  46 A′ may be designed to present the fluid in the form of a mist over the stator windings  48 B′ to prevent wear associated with high velocity fluid spray (e.g., by varying the diameter of the openings or by tapering the openings). Alternatively, nozzles may be fit within the radially-spaced openings  46 A′ and configured to present the fluid in the form of a mist. Yet another alternative is to connect a deflector to the end cover  26 ′ or to the first annular stator support  86 A′, positioned adjacent to the circumferentially-spaced radial openings  46 A′ similarly to the positioning of deflector  49  of  FIG. 3 , to deflect fluid flowing from the circumferentially-spaced radial openings  46 A′, thereby slowing the velocity of the fluid prior to the fluid contacting the windings  48 B′. The deflector may be a steel flange. A single, ring-shaped deflector may be used or a separate deflector may be placed under each respective circumferentially-spaced radial opening  46 A′. 
     A second set of circumferentially-spaced radial openings  46 B′ are formed in the first annular stator support  86 A′ such that they are in fluid communication with the annular recess  36 ′. Pressurized fluid from the fluid source flows from the valve body  42 ′ through the flow passage  40 ′ and the annular recess  36 ′ to the circumferentially-spaced radial openings  46 B′ and onto the second end (i.e., right side) stator windings  50 B′ for cooling thereof. As with the first set of circumferentially-spaced radial openings  46 A′, the second set of circumferentially-spaced radial openings  46 B′ may be configured to supply fluid to the second end stator winding  50 B′ in the form of a mist. 
     A center support  54 ′ is rigidly supported with respect to the main shaft  16 ′ about the center axis  14 ′. A second annular stator support  86 B′ is welded to a support element  88  which in turn is bolted to the center support  54 ′ via  90 A and  90 B. Bolt  90 A also connects both the support element  88  and the second annular stator support  86 B′ to the first portion  30 ′ of the housing member. Alternatively, the second annular stator support  86 B′ and the support element  88  may be formed as a unitary component. A fourth flow passage  58 ′ and a fifth flow passage  64 ′ are formed in the first portion  30 ′ of the transmission case in fluid communication with the valve body  42 ′. Sixth and seventh flow passages  65 ,  67  are formed in the second annular stator support  86 B′ in fluid communication with the fourth and fifth flow passages  58 ′,  64 ′, respectively. First and second ring-shaped sleeves or annular spray rings  44 B,  44 C are press-fit against an inner surface  94  of the first portion  30 ′ of the housing member. A third set  62 ′ and a fourth set  96  of circumferentially-spaced radial openings are formed in the respective annular spray rings  44 C,  44 B, such that they are in fluid communication with the seventh and sixth flow passages  67 ,  65 , respectively, of the second annular stator support  86 B′. Cooling fluid is supplied to first end (i.e., left side) stator windings  48 A′ of the stator  22 A′ via the fourth and sixth flow passages  58 ′ and the fourth set of circumferentially-spaced radial openings  96 . Cooling fluid is supplied to second end (i.e., right side) stator windings  50 A′ of the stator  22 A′ from the valve body  42  via a fifth flow passage  64 ′ in fluid communication with the seventh flow passage  67  through the third set of circumferentially-spaced radial openings  62 ′. 
     A motor cooling system  66 ′ for the motor/generator  20 B′ includes the second annular stator support  86 B′ having the sixth and seventh flow passages  65 ,  67 . Furthermore, the motor cooling system  66 ′ may include the ring-shaped sleeves  44 B,  44 C having the fourth and third sets of radially-spaced openings  96 ,  62 ′ for cooling the left side and right side stator windings  48 A′,  50 A′, respectively. 
     To assemble the motor/generator  20 A′ within the transmission  11 ′, the support element  88  is bolted to the center support  54 ′. The second annular stator support  86 B′ is press fit against the inner surface  94  of the first portion  30 ′ of the housing member in the interior cavity space  28 ′. The ring sleeves  44 B,  44 C are press fit against the second annular stator support  86 B′. The stator  22 A′ is then press fit against the inner surface  97 B′ of the second annular stator support  86 B′ between the spray rings  44 B,  44 C. 
     Stator Support and Motor/Generator Packaging Module 
     Referring to  FIG. 4 , the stator  22 B′ includes a plurality of segmented portions spaced about an inner surface  97 B of the first annular stator support  86 A′. The inner surface  97 B may be provided with slots coordinating with extensions on the segmented portions of the stator  22 B′ for fixedly connecting the segments to the annular stator support  86 A′. 
     A first rotor hub  70 B′ is rotatably supported by the end cover  26 ′ at a bearing  72 B′ and is welded to the main shaft  16 ′. The rotor  24 B′ is rigidly connected to the first rotor hub  70 B′ and is rotatable therewith with respect to the end cover  26 ′. A gap  74 B′ is achieved between the stator  22 B′ and the rotor  24 B′ and is controlled by the radial dimensions of the rotor  24 B′ and the stator  22 B′ and the distance between an exterior surface  76 ′ of the first rotor hub  70 B′ and the inner surface  97 B of the annular stator support  86 A′. Because the rotor hub  70 B′ is mounted at the shaft bearing  72 B′ which is supported by the end cover  26 ′, and because the end cover  26 ′ also supports the annular stator support  86 A′ which forms the inner surface  97 B, variability in the gap  74 B′ due to build tolerances is minimized. 
     The stator  22 A′ includes a plurality of segmented portions spaced about an inner surface  97 A of the second annular stator support  86 B′. The inner surface  97 A may be provided with slots coordinating with extensions on the segmented portions of the stator  22 A′ for fixedly connecting the segments to the annular stator support  86 B′. 
     The rotor  24 A′ is rigidly connected to a second rotor hub  70 A′ and is rotatable therewith with respect to the center support  54 ′. The second rotor hub  70 A′ is partially supported by the center support  54 ′ at bearing  72 A′. A gap  74 A′ is achieved between the stator  22 A′ and the rotor  24 A′ and is controlled by the radial dimensions of the rotor  24 A′ and the stator  22 A′ and the distance between an outer surface  80 ′ of the second rotor hub  70 A and an inner surface  97 A of the annular stator support  86 B′. 
     Support of the rotor  24 B′ is further provided by bearing  72 C via a rotor flange  99 B welded to the rotor hub  70 B′. Likewise, support of the rotor  24 A′ is further provided by bearing  72 D via a rotor flange  99 A welded to the rotor hub  70 A′. Bearing  72 D is support by separate structure, as shown in  FIG. 4 . Support of the rotor  24 A′ is further provided by shaft bearing  75 A′ disposed between the rotor hub  70 A′ and the center support  54 ′. 
     Because for each motor/generator  20 A′ and  20 B′, the rotor  24 A′,  24 B′ and stator  22 A′,  22 B′ are supported by a common member (the center support  54 ′ and end cover  26 ′, respectively) the invention allows each motor/generator  20 A′,  20 B′ to be easily prepackaged as a module prior to attachment with the transmission  11 . The motor/generator module  82 ′ for motor/generator  20 B′ includes the end cover  26 ′ and the first annular stator support  86 A′ having the stator  22 B′ fit at the inner surface  97 B. The rotor  24 B′ is rigidly connected to the rotor hub  70 B′, which is then fit to the end cover  26 ′ at the bearing  72 B′. The entire module  82 ′ (end cover  26 ′, stator  22 B′, rotor  24 B′, rotor hub  70 B′ and rotor flange  99 B) may then be piloted on to the shaft  16 ′ and welded thereto as a unit. Similarly, the motor/generator module  84 ′ for motor/generator  20 A′ includes the center support  54 ′ and the second annular stator support  86 B′ having stator  22 A′ fit at the inner surface  97 A. The rotor  24 A′ is rigidly connected to the rotor hub  70 A′, which is then fit to the center support  54 ′ at bearing  72 A′. The entire module  84 ′ (which includes center support  54 ′, bearing  72 D, bearing  72 A′, the annular stator support  86 A′, stator  22 A′, ring-shaped sleeves  44 B,  44 C, rotor  24 A′, rotor hub  70 A′ and rotor flange  99 A) may then be piloted on to the shaft  16  as a unit. 
     The end cover  26 ′ as well as the center support  54 ′ may be iron. By forming these components from iron, magnetivity of the motor/generators  20 A′ and  20 B′ is increased as the iron in the end cover  26 ′ and the center support  54 ′ (which will be disposed both above the stators and below the rotors) supplements the magnets in the respective motor/generators  20 B′,  20 A′ to increase torque capacity. 
     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.