Abstract:
A hydraulic circuit for a vehicle powertrain includes a first line for carrying fluid to a torque converter, a second line for carrying fluid from the torque converter, a third line for carrying fluid to a balance dam and an electric motor, and a fourth line for supplying actuating pressure to a clutch, said lines being coaxial.

Description:
[0001]    This application is a continuation-in-part of pending U.S. application Ser. No. 13/271,044, filed Oct. 11, 2011. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates to the powertrain of hybrid electric vehicles, particularly to a hydraulic circuit that supplies fluid to a torque converter, balance dam and motor and actuating pressure to a clutch. 
       BACKGROUND 
       [0003]    Hybrid electric vehicles (HEVs) have both an internal combustion engine and an electric motor which can alternately or in combination be used to propel the vehicle. A variety of different drive trains are used in hybrid vehicles. The present application relates to a parallel configuration in which the engine is connected to the motor by a disconnect clutch with the motor driving the torque converter input of an automatic hydraulic transmission. The hydraulic transmission has an output which is connected to a differential coupled to the two driven wheels of the vehicle. This parallel hybrid electric vehicle drive chain power flow arrangement is known in the art. 
         [0004]    A problem facing HEV designers is how to cool the disconnect clutch and the rotor and stator portions of the electric motor. Various air and liquid based cooling systems have been proposed; however, most systems are costly and pose packaging problems when trying to convert a non-hybrid vehicle to a hybrid operation. A need exists to package the disconnect clutch, motor, torque converter and automatic transmission in a compact manner so that a conventional vehicle can be reconfigured as a hybrid at a relatively low cost and with little or no vehicle body modifications. 
       SUMMARY 
       [0005]    A hydraulic circuit for a vehicle powertrain includes a first line for carrying fluid to a torque converter, a second line for carrying fluid from the torque converter, a third line for carrying fluid to a balance dam and an electric motor, and a fourth line for supplying actuating pressure to a clutch, said lines being coaxial. 
         [0006]    The present invention relates to a novel hybrid electric vehicle as well as a number of novel components and subcomponents specifically adapted to reorient the disconnect clutch and the electric motor within the wet side of the automatic transmission. This is done without changing the conventional power flow in which the engine, disconnect clutch, motor, torque converter, transmission are connected in series. 
         [0007]    Rather than connect the torque converter directly to the engine as is typically done in a non-hybrid vehicle, a drive shell is provided which connects the engine to the input side of the disconnect clutch which is has been relocated into the automatic transmission housing. The drive shell forms an annular cavity of sufficient size to contain the torque converter freely therein. The motor is also located in the automatic transmission wet zone preferably circumaxially surrounding the disconnect clutch. The rotor of the motor is connected to the disconnect clutch output. The disconnect clutch output and the rotor are both coupled to the rotor shaft which is connected to input turbine of the torque converter. The torque converter stator and the output turbine are connected to a tubular stator shaft and a transmission input shaft respectively. The transmission input shaft, the stator shaft, the rotor shaft and the disconnect clutch hub are all concentric with one another and accessible through an annular opening in the front side of the automatic transmission housing. 
         [0008]    The torque converter and the drive shell are removably mountable on the front of the transmission housing similar to a conventional torque converter. Rather than attaching the torque converter to the engine mounting plate, a drive shell is attached to the mounting plate. The torque converter is free to rotate relative to the drive shell within the drive shell cavity, resulting in a compact and axially short motor/transmission assembly. By locating the disconnect clutch and motor coaxially in the front portion of the wet zone of the automatic transmission, the transmission hydraulic fluid pump, associated pump and plumbing system can cool the disconnect clutch and the rotor and stator portions of the electric motor with relatively little increase in axial length. 
         [0009]    The torque converter, while generally similar to a conventional torque converter, is uniquely adapted in order to practice the invention. Since the torque converter is not attached to the engine mounting plate, no mounting studs are provided on the shell of the torque converter. Rather, a central axially bearing member is provided which cooperates with an engine mounting plate provided with a corresponding bearing member in order to radially support the torque converter and limit axially movement in the forward direction. Within the torque converter is a rearward facing thrust bearing member which cooperates with the free end of the transmission input shaft to limit the axial movement of the torque converter in the rearward direction. 
         [0010]    The transmission housing is preferably also uniquely adapted in order to practice the present invention. The transmission housing includes a wet housing which partially defines an enclosed wet zone and a torque converter housing, adapted to be affixed to the wet housing on one side and to the engine block on the other. The torque converter housing has a rear wall which forms a boundary between the wet cavity and the dry cavity in which the torque converter and drive shell are oriented. The rear wall defines an annular bore which cooperates with the disconnect clutch input hub to support the input hub and the rotor shaft along with the associated rotor portion of the motor and the disconnect clutch output hub. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic illustration of a hybrid electric vehicle having a parallel-flow design; 
           [0012]      FIG. 2  is a simplified schematic illustration of the disconnect clutch and motor reoriented in the present invention; 
           [0013]      FIG. 3  is a simplified cross-sectional view of an automatic motor/transmission assembly of the present invention; 
           [0014]      FIG. 4   a  is a more detailed cross-sectional side elevation view of an automatic motor/transmission assembly of the present invention; 
           [0015]      FIG. 4   b  is a stick diagram of the motor/transmission assembly of  FIG. 4   a;    
           [0016]      FIG. 4   c  is a clutch application schedule for each of the six forward gears and reverse; 
           [0017]      FIG. 5  is an enlarged view of the cross-section of the torque converter in its cooperation with the disconnect clutch and motor; 
           [0018]      FIG. 6  is an enlarged view of the disconnect clutch and electric motor; 
           [0019]      FIG. 7  is an enlarged view of the engine output on the mounting plate torque converter and the transmission input shaft showing their axial orientation; 
           [0020]      FIG. 8  is a perspective view of a mounting plate used to practice the present invention; 
           [0021]      FIG. 9  is a perspective view of a torque converter used to practice the present invention; 
           [0022]      FIG. 10  is a perspective view of a drive shell; 
           [0023]      FIG. 11  is a view of an alternative embodiment of the drive shell with a torque inverter entrapped therein; 
           [0024]      FIG. 12  is side cross-sectional view of the portion of the vehicle powertrain located above the central axis; 
           [0025]      FIG. 13  is top view of a terminal block assembly; 
           [0026]      FIG. 14  is side cross-sectional view of a portion of the vehicle powertrain located below the central axis; 
           [0027]      FIG. 15  is side cross-sectional view above the central axis of vehicle powertrain showing a torsion damper located between the engine and torque converter. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIG. 1  illustrates a hybrid electric vehicle  10  schematically shown with a parallel type hybrid electric drive train. The hybrid electric vehicle is provided with an engine  12  having a rotary output which is connected to a disconnect clutch  14  which drives an electric motor  16 . The output of the electric motor is connected to the input of torque converter  18 , the output of which is connected to the input shaft of automatic transmission  20 . In a conventional manner, the automatic transmission is connected to the driven wheels,  22 ,  22 ′ by a differential  24 . In the schematic illustration, hybrid electric vehicle  10  is provided with a pair of non-driven wheels, however, alternatively, a transfer case and a second differential can be utilized in order to positively drive all of the vehicle&#39;s wheels. The engine, disconnect clutch, motor, torque converter and the automatic transmission are connected sequentially in series, as illustrated in  FIG. 1 . 
         [0029]    Motor/transmission assembly  26 , in hybrid electric vehicle  10 ′, schematically illustrated in  FIG. 2 , repackages the drive components while maintaining the same power flow, as shown in  FIG. 1 . Engine  12  is mechanically connected to the input side above disconnect clutch  14  via a drive shell  28  which forms an annular chamber sufficiently large to extend about torque converter  18 . The output of disconnect clutch  14  is connected to electric motor  16  which, in turn, is connected to the Impeller “I” of torque converter  18 . The use of the drive shell  28  enables the disconnect clutch and motor to be positioned within the wet side of the automatic transmission housing. Turbine “T” is attached to the output of torque converter  18  which is connected to the input shaft of the automatic transmission in a conventional manner. The invention can be practiced with a wide variety of automatic transmissions. The preferred embodiment of the transmissions described herein is a six-speed, three planetary gear set, five clutch design; alternative transmission structures having fewer or greater speeds and different mechanical configurations can likewise be benefited from the present invention. 
         [0030]    A more detailed, yet quite simplified illustration of the motor/transmission assembly  26  is shown in  FIG. 3 . The engine is provided with a crank shaft output flange  30  which is bolted to mounting plate  32  in a conventional manner. The mounting plate  32 , rather than attaching to the shell of the torque converter, is affixed to the drive shell  28  which has sufficient diameter to encircle the torque converter and connect to the input hub  34  of disconnect clutch  14 . The output of the disconnect clutch is affixed to the rotor “R” portion of motor  16  and in turn, is connected to rotor shaft  36 . The rotor shaft  36  is coaxially nested within the disconnect clutch input hub  34  and extends to an annular opening in the wall portion of the transmission housing defining the wet zone of the transmission. Rotor shaft  36  is connected to the impeller “I” of torque converter  18 , which in turn drives turbine T connected to transmission input shaft  38 . Coaxially spaced between the inside diameter of rotor shaft  36  and the periphery of the transmission input shaft  38  is a stator shaft  40  which is fixed relative to the transmission housing and supports stator element S located within torque converter  18 . 
         [0031]    Preferably, the case of the motor/transmission assembly is made up of a wet housing  42  which partially defines the enclosed wet zone cavity, and a torque converter housing  44  which is adapted to be affixed to the wet housing  42  and to the engine block  46 . The torque converter housing  44  is preferably provided with rear wall  48  having an annular axial opening  50  on the transmission centerline. Rear wall  48  forms a physical boundary between the wet zone cavity and a dry cavity in the transmission housing. The torque converter  18  and drive shell  28  are located in the dry zone as shown. Rear wall  48  cooperates with disconnect clutch input hub  34  which in turn supports motor rotor shaft  36  and the associated rotor portion R of motor  16 . 
         [0032]    The motor/transmission assembly is provided with pump P for hydraulic fluid oriented within the wet zone of the transmission housing and driven by the rotor shaft  36 . Pump P provides pressurized hydraulic fluid to operate the clutches and brakes within the transmission drive train as well as operating the disconnect clutch and provides cooling for the clutches and motor  16 . Similarly, the disconnect clutch and motor share a common sump  52  for transmission fluid as well as a common pump screen  54 . Automatic transmission  20  is provided with an output shaft  56 .  FIG. 4   a  is a cross-sectional side elevational view of the motor/transmission assembly  26 . Once again, the present invention can be utilized with a number of different transmission gear train configurations and is not limited to the disclosed six-speed, three planetary gear set transmission. 
         [0033]    The preferred embodiment of the multi-speed transmission shown in  FIG. 4   a  is more easily understood with reference to the stick diagram of  FIG. 4   b . The input from the engine drives mounting plate  32  which is fastened to drive shell  28  connected to input hub  34  of disconnect clutch  14 . The output side of disconnect clutch  14  is connected to the rotor portion of motor  16 , which in turn is attached to rotor shaft  36 . Coaxially oriented within rotor shaft  36  is a fixed stator shaft  40  which is mounted to the transmission case, and the transmission input shaft  38 . The torque converter impeller I drives torque converter turbine T which is connected to transmission input shaft  38 . The torque converter  18  is further provided with a stator S mounted on the stator shaft  40 , by way of a one-way clutch  56 . In the preferred embodiment illustrated, torque converter  18  is further provided with a lock up clutch  58  which locks the turbine to the impeller in a well known manner. 
         [0034]    The gear set of the planetary automatic transmission  20  is made up of three planetary stages; plan  1 , plan  2  and plan  3 , which are coaxially aligned and axially spaced as shown. Each planetary gear set has a sun, a ring and a series of plant gears supported on a planet carrier. The sun, ring and planet carrier members can be interconnected via a series of five clutches and brakes. For example, in first gear, clutch A and brake D are engaged as illustrated in clutch application table in  FIG. 4   c . The transmission input shaft  38  is connected to the ring of planetary gear set Plan  1 . The sun is fixed and the planet carrier is connected via clutch A to the sun of planetary gear set  3 . With clutch D engaged, the planet carrier of planetary gear set  3  is fixed causing the ring gear of planetary gear set  3  to drive the transmission output shaft  56 . In order to shift to the second gear, brake D is released and brake C is simultaneously engaged to cause a change in the transmission gear ratio. Each shift, either up or down, is achieved by releasing one clutch or brake and engaging another. Similarly, the shift from first reverse is done by a single clutch release, a simultaneous engagement of another clutch. 
         [0035]    Planetary gear sets  2  and  3  share a common planet element as well as a common ring gear. Planetary gear sets  1  and  2  are traditional, simple planetary gear sets, while planetary gear set  3  is a compound planetary gear set having a pair of inter-meshed planets, one engaging the sun and one engaging the ring. In the embodiment illustrated in  FIG. 4   b , the compound planet arrangement enables the third planetary gear set to use a smaller sun and accordingly, obtain a higher gear reduction ratio. Again, the planetary gear set is described merely to illustrate the preferred embodiment, however, the invention can be practiced with a wide variety of automatic transmission structures. 
         [0036]      FIG. 5  is a cross-sectional view illustrating an alternative drive shell arrangement  62  which is designed to accommodate a smaller diameter mounting plate  64 . Output flange  30  of the engine crank shaft is attached to mounting plate  64  by a series of bolts extending through an array of holes in the mounting plate spaced from the mounting plate center. The outer peripheral edge of mounting plate  64  is provided with a ring gear  66  for cooperation with the pinion gear of the starter motor. Inboard of the periphery of the mounting plate is a series of holes sized to receive threaded fasteners for connecting the drive shell  62  to the mounting plate  64 . In the embodiment illustrated, the drive shell  62  is provided with threaded studs  108  which project through an array of holes in the mounting plate  64  to receive nuts to securely affix the drive shell to the mounting plate. Nuts alternatively could be welded to the mounting plate to receive bolts passing through the apertures in the mounting plate. The mounting plate alternatively may also include a dual mass damper (not shown) in order to reduce torque fluctuations. 
         [0037]    Unlike a conventional automatic transmission vehicle, the torque converter  18  is not bolted to the engine mounting plate, rather it is free to rotate within the annular cavity defined by the drive shell  62  and mounting plate  64 . The rearward end of the drive shell forms a tubular drive shell outlet member  68  which is connected to disconnect clutch input hub  34 . Rearward refers to the direction toward the transmission output shaft  56  which would be to the rear of a vehicle in a traditional rear wheel drive front engine vehicle, however, the terms, “rearward” and “forward” are used for simplicity and explanation purposes. They do not necessarily refer to the front and rear of the vehicle as would not be the case if installed transversely in a front wheel drive vehicle. The forward side of the torque converter  18  is free of studs typically used to attach to the mounting plate. 
         [0038]    Preferably, the drive shell tubular output hub  68  is provided with an internal spline to axially cooperate with a complimentary external spline on disconnect clutch input hub  34 . Disconnect clutch  14  has a series of inter-leaved plates alternatively connected to the input hub  34  and output hub  70 . A disconnect hub ring shape piston  72  cooperates within a corresponding cavity formed in the disconnect clutch output hub  70  and is axially shiftable between an extended locked position when the hydraulic signal advancing the disconnect clutch piston  72  is received, and a retracted position when the signal is not present. Affixed to the outer periphery of the disconnect clutch output hub  70  is the rotor R. Disconnect clutch output hub  70  and rotor R are both mounted on and secured to rotor shaft  36 . Rotor shaft  36  is provided with external spline sized to cooperate with a complimentary internal spline on the torque converter input hub  74  which drives impeller I. Torque converter  18  is further provided with a stator S mounted on a stator hub  76  and an output turbine T which is connected to turbine output hub  78  via a torsional damper  82  illustrated in  FIG. 5 . Turbine output hub  78  is provided with an internal spline cooperating with transmission input shaft  38 . Stator hub  76  is mounted on stator shaft  40  which is affixed to and extends out of the transmission housing. In the embodiment illustrated, the stator is mounted on a one-way clutch center in a conventional manner. 
         [0039]    The torque converter  18  and drive shell  62  together mate with the four different coaxial aligned members in the transmission and slide on and off during installation like a conventional torque converter in an automatic transmission, simply having one additional coaxial member, the tubular output  68  of the drive shell  62 . Accordingly, the use of the drive shell takes very little additional axial space in the motor/transmission assembly. The addition of the disconnect clutch  14  and motor  16  to the transmission, however, does take some additional axial space inside of the transmission housing. As shown in  FIG. 6 , the motor is oriented coaxially with the disconnect clutch mounted inside of motor rotor R. Motor stator S is securely affixed to the transmission housing by a series of annularly spaced apart bolts which extend through the stator laminate stack. The motor rotor R is mounted to the outer periphery of the disconnect clutch output hub  70  supported on rotor shaft  36 . 
         [0040]    The rotor shaft  36  is radially located by a roller bearing  80  interposed between the rotor shaft  36  and disconnect input clutch hub  34 . The outside diameter of the disconnect clutch input hub is supported upon a wall  48  in the transmission housing by way of a bearing  84 . Bearing  84  is designed to take an axial load as well as the radially load inserted by the rotor disconnect clutch output hub assembly. A disconnect clutch output hub  70  is further axially constrained by thrust bearings  86  and  88 . Additionally, a circumaxial roller bearing  90  is interposed between the disconnect clutch output hub  70  and stator shaft  40  to axially locate rotor shaft  36  and the associated disconnect clutch and rotor. 
         [0041]    The disconnect clutch output hub  70  is provided with internal coolant passageways  92  which feed transmission fluid through the disconnect clutch output hub into the rotor R. As fluid passes through and exits the rotating rotor R, it strikes the windings of stator S to remove excess heat from stator windings and the associated stator laminate stack. As illustrated in  FIG. 6 , disconnect clutch output hub  70  is also provided with an output spline  94  for driving pump P. 
         [0042]    Since the torque converter  18  is no longer affixed to the engine mounting plate, it is necessary to axially and radially constrain the torque converter. The torque converter  18  is pivotally supported on the engine mounting plates  32  and  64  in  FIGS. 3 and 5 . The engine mounting plates  32 ,  64  are provided with an axially mounted first bearing member  96  which cooperates with a mating second bearing member on the torque converter  18 . As illustrated in  FIG. 7 , the first bearing member in the preferred embodiment is provided by a roller bearing  96  supported in a bearing cup  98  affixed to the mounting plate on the transmission centerline. The corresponding second bearing member is provided by a stub shaft  100  which is affixed to the shell of torque converter  18 . The stub shaft provides radial support for the torque converter while bearing  96  further provides an axial stop for the torque converter in the forward direction. To limit rearward movement of the torque converter, the torque converter is provided with a thrust bearing  102  on the axial center line of the shell interior facing rearward for engaging the end region of the transmission input shaft  38 . Of course, alternative structures can be utilized such as placing the stub shaft on the mounting plate and the roller bearing on the torque converter shell. 
         [0043]    The motor/transmission assembly  26 , as previously described, uses a number of subcomponents which are independently novel.  FIG. 8  is a perspective view of the mounting plate  64  formed of a circular disc provided with a centrally axially aligned first bearing member, roller bearing  96 , mounted in bearing cup  98 . The disc is provided with two circular arrays of mounting holes, an array adjacent the center to attach to the crankshaft of the engine and an array adjacent the periphery to attach to the drive shell  28 . 
         [0044]    Torque converter  18 , illustrated in  FIG. 9 , is similarly novel. The torque converter outer shell is not provided with the conventional mounting studs, rather it is provided with a central axial second bearing member, which in this case is provided by a stub shaft  100 . Other axial central bearing members could alternatively be used provided that they cooperate with a corresponding bearing structure on the mounting plate to bear radial loads and provide a positive forward stop for torque converter movement. The torque converter has an annular rearward facing tubular outlet hub  68  which connects to rotor shaft  36 , and a rearward facing thrust bearing  102  on the centerline inside of the shell as show in  FIG. 7  to abut the end of transmission input shaft  38 . 
         [0045]      FIG. 10  illustrates a perspective view of a drive shell  28 . The drive shell is an annular member having an outer peripheral structure sufficiently large to freely surround the torque converter. The forward edge of the drive shell  28  is provided with a series of spaced apart fasteners  104  for cooperation with the mounting plate  32 . The rearward end of the drive shell forms a tubular output  68  which preferably has a splined internal diameter for engaging a corresponding spline on the disconnect clutch input hub  34 . The spaced apart fasteners  104  illustrated are a series of weld studs, however weld nuts could also be used to cooperate with bolts passed through corresponding apertures in the mounting plate. 
         [0046]      FIG. 11  illustrates an alternative drive shell embodiment  62  as previously illustrated in  FIG. 5 . In order to accommodate a small diameter mounting plate and a relatively large torque converter, the drive shell is provided with a series of inwardly projecting radial members  106  supporting fasteners The illustrated fasteners are provided by studs  108  located at the diameter of the array of holes in the mounting plate which is significantly less than the diameter of the torque converter. As a result, the inwardly projecting members  106  entrap the torque converter  18  inside the large annular cavity formed within the drive shell  62  creating the illustrated drive shell torque converter sub assembly. 
         [0047]    Referring to  FIG. 12 , disconnect clutch  14  further includes a blocker ring  110 , secured against axial displacement relative to output hub  70 ; a balance dam  112 , also secured against axial displacement relative to output hub  70 ; a return spring  114 , contacting piston  72  and balance dam  112  at opposite ends of the spring; and a sealed hydraulic cylinder  116 , in which the piston moves subject to the force of spring  114  and a pressure force. A hydraulic passage  118  carries actuating pressure from an outlet port  120  of a pump housing  122  through an axial passage  123  to the portion of cylinder  116  located behind piston  72 . When pressure in passage  118  is high, piston  72  moves axially leftward against the force of spring  114  forcing the friction plates and spacer plates of clutch  14  unto mutually frictional contact, thereby engaging clutch  14 . 
         [0048]    An axial hydraulic passage  124  carries fluid from pump housing  122  through passage  126  to the portion of cylinder  116  that is located between piston  72  and balance dam  112 . Hydraulic passage  124  also carries fluid from pump housing  122  through radial passage  92  to the rotor R and stator S of motor  16 . Passage  92  communicates with passages  128 , which direct fluid across the width of motor  16  and onto the surfaces of rotor R. Fluid exiting the rotor flows radially outward at opposite axial sides due to centrifugal force and onto the surface of the stator S. This fluid, which carries heat away from the motor  16 , flows downward though an opening  129  (shown in  FIG. 14 ) in the housing  42  and returns to the sump  52 . 
         [0049]    Hydraulic fluid that fills the torque converter  18  is carried from pump P through radial passage  130  and axial passage  132 , which is located in an annular space between stator shaft  40  and the transmission input shaft  38 . The forward end of passage  132  communicates through a radial passage  134  with the toroidal chamber of the torque converter, which is surrounded by the shroud  136  and contains the impeller I, turbine T and stator S. Hydraulic fluid exiting torque converter  18  is carried through an axial passage  138  formed in the transmission input shaft  38  and extending along axis  140 . 
         [0050]    As  FIG. 12  shows, the motor&#39;s stator S is secured by a series of bolts  150  to the transmission case  42 , which is formed with an opening  152 . Each bolt  150  passes though a hole formed in the stator S, and the threaded shank of each bolt engages a threaded hole formed in the casing  42 . Close dimensional tolerances are established among the lower surface  153  of stator S, the centerline through the hole in stator S and bolts  150 , and the location of axis  140 . In this way the distance between axis  140  and the lower surface  153  of stator S is established within a close dimensional tolerance in order to establish and maintain a narrow air gap between the motor&#39;s stator S and rotor R. 
         [0051]    A terminal assembly  154 , seated on a mounting surface  156  that surrounds the opening  152 , includes a block  157  that contains electric terminals  158  including at least one high voltage terminal that is electrically connected to the windings within laminates  160  of the motor&#39;s stator S. Each terminal  158  is connected by a bolt  162 , whose shank passes through a plate  164 , which is secured by bolts  166  to the transmission case  42 . Each bolt  162  also electrically connects and secures each terminal  158  to a receptacle  168 , which engages a conductor  170  connected to the stator S. Both receptacle  168  and conductor are elastically flexible in flexure such that their connection to stator S is completed and maintained without substantially altering the distance between surface  153  and axis  140 . 
         [0052]    The terminal block assembly  154  is preferably located at an angular location relative to axis  140  that places the terminals  158  at a lateral side of the transmission case  42 , rather than at the higher elevation shown in  FIG. 12 . Preferably the terminals  158  are directed along axis  140 , although not necessarily parallel to the axis, and the receptacles of the terminals face rearward, as  FIG. 13  shows. 
         [0053]    The rotor R of motor  16  is secured to output hub  70  such that an air gap located between the stator&#39;s reference surface  153  and the radial outer surface  176  of the rotor is established. 
         [0054]    As  FIG. 14  shows housing  44  is secured by a series of bolts  177  to the transmission housing  42 . The pump&#39;s centering plate P is guided into its correct position, both radial and axial, due to contact between surface  178  on the pump&#39;s centering plate P and a pilot surface  180  on the transmission housing  42 . Similarly pump housing  122  is guide into its correct position, due to contact between surface  182  on the pump centering plate P and a surface  184  on the pump housing  122 . At the rearward end, the outer surface of stator shaft  40  contacts the radial inner surface of pump centering plate P, and at the forward end the outer surface of stator shaft  40  contacts the radial inner surface of the torque converter input hub  74 . 
         [0055]    The axial and radial location of bearing  84  is established by its contact with the rear wall  48  of housing  44 . The axial and radial location of clutch input hub  34  is established by its contact with bearing  84 . The position of the forward end of rotor shaft  36  is established by its contact with roller bearing  80 , and the position of the rearward end of rotor shaft  36  is established by its contact with the inner surface of pump housing  122 . 
         [0056]    The position of the forward end of output hub  70  and rotor R is established by contact between the outer surface of rotor shaft  36  and the inner surface of output hub  70 . The axial and radial location of bearing  190  is established by its contact with the pump housing  122 . The position of the rearward end of output hub  70  and rotor R are established by contact between bearing  190  and the output hub  70 . 
         [0057]    In this way the radial position of the radial outer surface  176  of the rotor R of motor  16  is located such that the air gap parallel to a radius extending from axis  140  and located between the stator&#39;s reference surface  153  and the radial outer surface  176  of the rotor is preferably about 122 mm. 
         [0058]      FIG. 15  shows a torsion damper  196  located in a power path between the engine  12  and the drive shell  28 ,  62 . Engine  12  is connected through crankshaft flange  30  to an input of damper  196 , and a series of bolts  108 , spaced mutually around axis  140 , connect the output of damper  196  to drive shell  28 ,  62 . Damper  196  attenuates torsional vibrations produced by the engine. The outer peripheral edge of damper  196  is provided with a ring gear  66 , which is engaged by a pinion gear driven in rotation by a starter motor. 
         [0059]      FIG. 15  shows damper  196  arranged in series with damper  82  between engine  12  and transmission input shaft  38 . The presence of damper  196  in the powertrain may eliminate need for torsion damper  82 , which is located in a torque delivery path of torque converter  18  between the impeller shroud  136  and the turbine hub  78 . When damper  82  is eliminated, the axial dimension of the torque converter  18  and drive shell  28 ,  62  can be reduced. 
         [0060]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0061]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.