Abstract:
Power capacitors for AC motors are mounted diametrically on associated transmissions. The power capacitors are in one embodiment annular and in another embodiment, arcuate. By having power capacitors mounted on transmission housings diametrically, cooling of the power capacitors is facilitated for both air and liquid cooling.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed to power capacitors for AC motors mounted diametrically on associated transmissions. More particularly, the present invention relates to power capacitors for AC motors mounted diametrically on associated transmissions used to drive automotive vehicles. 
       BACKGROUND OF THE INVENTION 
       [0002]    In configuring automotive vehicles, efficient use of space is an important consideration. This is because various components of automotive vehicles frequently compete for space within the envelope defined by vehicle bodies. The judicious use of space is a consideration not only during assembly of automotive vehicles, but also during maintenance of vehicles. In addition, consuming less space for essential automotive components allows the designer to increase space for optional components and for cabin capacity. While adjusting or decreasing space consumption of one component may not appear to have substantial design effects, cumulative space adjustments and decreased space consumption for several components can result in more efficient use of total space within a vehicle and enhanced design flexibility. 
         [0003]    In voltage source inverter arrangements, capacitors are used as energy storage devices providing power buffers to maintain relatively smooth dc link voltages. Typically, capacitance volume accounts for a significant portion of the total volume required by voltage source inverter packaging. Such capacitors are frequently electrolytic or film capacitors. These capacitors are manufactured by winding a thin film to increase the total amount surface area of the film. In the prior art, such capacitors are usually wound tightly around their center to produce enclosed or solid cylinders of different heights and diameters. 
         [0004]    In order to reduce loses and EMI, which results from the transmission of power between an electric drive (inverters and capacitors) and an electric motor, it is often desirable to minimize transmission distance between electric drives and motors. In order to minimize distance, the electric drive can be integrated into a common package with a motor. In many hybrid vehicles, the motor(s) are integrated into the mechanical transmission (or gearbox) of the vehicle. Hence, one such embodiment of the system could incorporate the inverter in a container attached externally to the transmission housing so that it is located in close proximity to the electric motor. 
         [0005]    A drawback to attaching the electric drive in its enclosed container to the outside of the transmission is the difficulty in packaging the volume of the inverter into the space and form factor allotted. Since the capacitance required by the electric drive comprises a significant volume of the electric drive relocating the capacitance will decrease the volume of the remaining drive components, and thus make the system much simpler to package. 
       SUMMARY OF THE INVENTION 
       [0006]    An alternating current electric motor drive assembly comprises an AC electric motor with an output shaft coupled to a transmission, wherein the transmission has a power capacitor diametrically mounted thereon and electrically connected to windings of the motor. 
         [0007]    In one aspect of the drive assembly, the power capacitor is annular. 
         [0008]    In another aspect of the drive assembly, the power capacitor is arcuate with a gap between ends of the power capacitor. 
         [0009]    In another aspect of the drive assembly, the motor is a traction motor for an automotive vehicle. 
         [0010]    In still another aspect, the power capacitor is cooled by circulating liquid which transfers heat from the power capacitor to a radiator or is cooled by air flowing over the power capacitor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Various other features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views, and wherein: 
           [0012]      FIG. 1  is a schematic view of a hybrid automotive vehicle utilizing an AC electric traction motor having power capacitor diametrically mounted on an associated transmission; 
           [0013]      FIG. 2  is a schematic illustration of a fuel cell powered vehicle having an AC electric tractor motor driving the vehicle through a transmission having a power capacitor diametrically mounted thereon; 
           [0014]      FIG. 3  is a side view of a motor-transmission combination of  FIGS. 1 and 2  with an annular power capacitor diametrically mounted thereon in accordance with a first embodiment of the invention; 
           [0015]      FIG. 4  is a front view of  FIG. 3 ; 
           [0016]      FIG. 5  is a side view of a motor-transmission combination having a capacitor on the transmission at another location; 
           [0017]      FIG. 6  is a side view of a motor-transmission combination having a capacitor of increased axial length mounted diametrically thereon; 
           [0018]      FIG. 7  is a side view of a transmission with an arcuate power capacitor mounted diametrically thereon in accordance with another embodiment of the present invention, and 
           [0019]      FIG. 8  is a front view of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Referring now to  FIG. 1  there is shown a vehicle  10  with a hybrid drive  12  comprising an internal combustion engine  14  and an alternating current (AC) motor  16 . The internal combustion engine  14  and AC motor  16  drive wheels  18  through a transmission  20 , which is integral with the AC motor. A power splitter  22  connected to the IC engine  14  via a shaft  23  drives an electric generator  24  to charge a battery  26  (which may be configured as a bank of batteries) when the internal combustion engine  14  is running. The electric generator  24  can under selected circumstances power the electric motor  16  to run simultaneously with the internal combustion engine  14 . The battery  26  and the electric generator  24  deliver DC current to an inverter  30  that is illustrated as axially mounted and integral with the AC motor  16 . According to the present invention, a power capacitor  32  is mounted on the transmission  20 . Preferably, the power capacitor  32  is diametrically mounted on the transmission  20  to form a drive assembly  33  comprised of the AC motor  16 , the transmission  20 , the inverter  30  and the capacitor  32 . The term “diametrically mounted” means mounted around the diameter of the transmission. By positioning the power capacitor  32  on the transmission  20  diametrically, the power capacitor is available for air cooling or water/glycol cooling utilizing a heat exchanger  34  coupled to the vehicle radiator  35  which cools the IC engine  14 . In an alternative embodiment, the motor  16  also serves ad the generator. 
         [0021]    Referring now to  FIG. 2 ,  FIG. 2  is similar to  FIG. 1  with the exception that the vehicle  10 ′ is powered by a fuel cell  40  that both charges the battery  26  and provides direct current to the inverter  30  of the drive assembly  33 ′. The drive assembly  33 ′ is configured similarly to the drive assembly  33  of  FIG. 1 , wherein an axial mounted inverter  30  converts direct current from the fuel cell  40  into AC and wherein the power capacitor  32 ′ is mounted diametrically on the transmission  20 . The motor  16  is preferably integral with the transmission  20  and disposed within a housing enclosing the transmission. As in  FIG. 1 , the power capacitor  32  is air or liquid cooled. 
         [0022]    Referring now to  FIGS. 3-6  in which a first embodiment of the invention is shown, the power capacitor  32  is configured an annular capacitor that is mounted around the housing  50  of the transmission  20 . Preferably, the annular power capacitor  32  is on the first stage  52  in close axial relation to the motor  16 . As is seen in  FIG. 5 , the annular power capacitor  32 ′ may be mounted around any convenient diameter of the transmission housing  50 . As is seen in  FIG. 6 , the capacitor  32 ′ may be as long as the transmission  20 , and in further embodiments, not illustrated, the capacitor  32 ′ may occupy any portion of the axial length of the transmission or may be packaged such that it is longer than the transmission  20 . 
         [0023]    As is seen in  FIGS. 7 and 8 , where a second embodiment  32 ′″ of the capacitor is shown, the capacitor  32 ′″ is arcuate having ends  60  and  62  separated by a gap  64 . Preferably, in this embodiment the capacitor  32 ′″ is oriented so that the gap  64  is at the bottom of the transmission housing  50 , however in further embodiments, the gap  64  may be oriented at the top of the transmission housing  50  or laterally with respect to the transmission housing. The power capacitor  32 ′″ in the illustrated configuration has an arcuate extent of 270°, but may have other arcuate extents. The capacitor  32 ″ is shown with a single circular extent, but the capacitor may be divided into a plurality of arcuate sections. 
         [0024]    By packaging the capacitors  32 ,  32 ′,  32 ″ and  32 ′″ is illustrated in  FIGS. 3-8 , the amount of capacitance may be increased as a result of the large surface area available. Accordingly, the reliability of the entire drive systems  33 - 33 ′″ is increased. Since the voltage of the capacitors  32 - 32 ′″ is substantially DC, the capacitors themselves may serve as a shield against undesirable electromagnetic interference. 
         [0025]    Placing the capacitors  32 - 32 ′″ on the outer surfaces of the transmission housings  50 , rather than inside the transmission housings, facilitates cooling of the capacitors by either air cooling arrangements, or by cooling with water/glycol circulated directly through a radiator  35  or through a heat exchanger  34  as shown in  FIGS. 1 and 2 . 
         [0026]    Internal temperatures of transmissions  20  can exceed capacitor ratings. By arranging power capacitors  32 - 33 ′″ as illustrated, the capacitors have a large surface area to volume ratio which allows the capacitors to more easily reject heat and to operate in a lower temperature environment. Cooler capacitor temperatures reduce capacitance derating due to temperature. In addition, improved EMI shielding may result by placing the power capacitor diametrically around the transmission housing  50 . 
         [0027]    Placing the capacitors  32 - 33 ′″ on the outside diameter of the transmission housing  50  provides a very large surface area within the capacitor, resulting in a large capacitance value. Inverter/AC motor systems with large bulk capacitance, as provided by the arrangements of  FIGS. 3-8 , have enhanced reliability, reducing the need for other filtering components and resulting in cost and space savings. 
         [0028]    By positioning the capacitors  32 - 32 ′″ as illustrated in  FIGS. 3-8 , available space within the body of a vehicle may be utilized more efficiently making it easier to package other components such as the inverter  30  in the vehicle. 
         [0029]    From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing form the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.