Abstract:
Alternating current motors used to drive wheels of hybrid or fuel cell vehicles have capacitors which are mounted diametrically on the motors, i.e., mounted around the diameter of the motors. The capacitors may be annular or arcuate in shape. By so configuring the power capacitors, axial space adjacent to the motors is reduced, providing enhanced design flexibility for automotive vehicles.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed to power capacitors mounted diametrically on electric motors. More particularly, the present invention relates to power capacitors mounted diametrically on AC motors used as traction motors for 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 space within a vehicle and enhanced design flexibility. 
         [0003]    In voltage source inverter arrangements, capacitors are used as voltage 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 an enclosed or solid cylinder 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. Thus, the electric drive in current design may be in the form of a container having both inverter and capacitance circuitry attached to the outside of a motor. The electric drive is thus integrated with the motor by attaching the electric drive configured as a cylinder, to the end of the motor. By attaching the drive to the end of the motor, the axial length is necessarily increased. In many packaging applications, axial space is limited, and by attaching the electric drive to the end of the motor, the electric motor may need to be reduced in axial length, which results in a loss of power and torque output capacity. Since capacitance required by electric drives consumes significant volume, relocating the capacitance decreases the volume of remaining electric drive components, thus decreasing the axial length of electric drive packages on the end of the motor. Since axial length is often a more restrictive dimension of an electrical drive system than width, reducing axial length can have desirable results. 
       SUMMARY OF THE INVENTION 
       [0005]    An alternating current electric motor assembly comprises an alternating current electric motor having a rotor and a drive shaft for rotation around an axis in combination with a stator positioned around the rotor and a power capacitor diametrically mounted with respect to the stator and electrically connected to windings of the motor. 
         [0006]    In another aspect of the assembly, a housing surrounds the outer periphery of the stator and the power capacitor is positioned diametrically on the housing. 
         [0007]    In another aspect of the assembly, the power capacitor is annular. 
         [0008]    In still another aspect of the assembly, the power capacitor is arcuate. 
         [0009]    In still another aspect of the assembly, the motor is a tractor motor for an automotive vehicle. 
         [0010]    In still a further aspect of the assembly, an inverter is axially mounted on the motor with the power capacitor being diametrically mounted on the motor. 
     
     
       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 electric motor with a diametrically mounted capacitor; 
           [0013]      FIG. 2  is a schematic illustration of a fuel cell powered vehicle having an electric motor with a diametrically mounted capacitor. 
           [0014]      FIG. 3  is a side view of an electric motor with a diametrically mounted annular capacitor in accordance with a first embodiment of the invention; 
           [0015]      FIG. 4  is a view taken along line  4 - 4  of  FIG. 3 ; 
           [0016]      FIG. 5  is a side, bottom or top view of an electric motor with a diametrically mounted arcuate capacitor in accordance with the second embodiment of the present invention; 
           [0017]      FIG. 6  is an elevation taken along lines  6 - 6  of  FIG. 5 ; 
           [0018]      FIG. 7  is a top, side view or bottom view of a motor having a capacitor of increased axial length mounted diametrically thereon according to a third embodiment of the invention, and 
           [0019]      FIG. 8  is an elevation taken along lines  8 - 8  of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Referring now to  FIG. 1  there is schematically 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 . A power splitter device  22  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  which is illustrated as axially mounted and integral with the AC motor  16 . Also integral with the AC motor  16  is a power capacitor  32 . In accordance with the present invention, the power capacitor  32  is diametrically mounted on the motor  16  to form a motor assembly  33  comprised of the motor  16 , the inverter  30  and the capacitor  32 . The term diametrically mounted means mounted around the diameter of the motor  16 . 
         [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 a battery  26  and provides direct current to the inverter  30  of the AC motor assembly  33 . The AC motor assembly  33  is configured similarly to the AC motor assembly  33  of  FIG. 1 , wherein an axial mounted inverter  30  turns direct current from the fuel cell  40  into AC and wherein the power capacitor  32  is mounted diametrically on the AC motor  16 . 
         [0022]    Referring now to  FIGS. 3 and 4 , there is shown a first embodiment of the invention wherein the motor assembly  33  shown in  FIGS. 1 and 2  has the inverter  30  mounted on a first end  43  of the AC motor  16  to extend axially with the motor, while the power capacitor  32  is mounted diametrically on the AC motor and connected to the windings of the AC motor. As is seen in  FIG. 4 , the motor  16  has an output shaft  42  which projects from a second end  44  of the AC motor. The output shaft  42  is fixed with respect to an armature  46  of the AC motor, which armature rotates inside of a stator  48 . The stator  48  is surrounded by a housing  50  on which the power capacitor  32  is mounted diametrically. In  FIGS. 3 and 4 , the power capacitor  32  is annular having a circular interior surface  52  in which the motor  16  is received. Preferably, the power capacitor  32  is mounted on the exterior surface of the housing  50 , but it may be configured so as to be positioned within the housing  50 . 
         [0023]    By mounting the power capacitor  32  diametrically on the AC motor  16 , the axial length L of the motor assembly  33  is limited to the length of the AC motor plus the inverter  30 . Thus, the motor assembly  33  consumes less axial space. Since axial space is a more restrictive design dimension, the reduction in axial extent of the motor assembly  33  frees considerable axial space while consuming minimal additional radial space. 
         [0024]    Referring now to  FIGS. 5 and 6 , the motor assembly  33 ′ of a second embodiment has substantially the same structure as the assembly  33  of  FIGS. 1-4 , with the same reference numerals identifying similar structure. In  FIGS. 5 and 6 , the capacitor  32 ′ is arcuate rather than annular, with a gap  55  between the ends  56  and  58  of the capacitor  32 ′. The arc of the capacitor may be 270° instead of 360° or may be another arcuate length. 
         [0025]    Referring now to  FIGS. 7 and 8 , where a third embodiment of the motor assembly  33 ″ is shown, it is seen that the capacitor  32 ″ is axially elongated as compared to the capacitors  32  and  32 ′ of  FIGS. 1-6 . The axial extent of the capacitor  32 ″ is substantially the same as the defined axial length of the motor  16  as shown in  FIG. 7 , however the axial extent can be even longer than the axial length of the motor in either direction. For example, the length of the capacitor  32 ′ may extend over the inverter  30  or over the output shaft  42 . Moreover, the axial length of the capacitor  32 ′ may be greater than that illustrated in  FIGS. 3 and 4 , but not as long as the axial length of the motor  16 . In addition, in the embodiment shown in  FIGS. 7 and 8 , the capacitor  32 ″ may be arcuate like the capacitor  32 ′, rather than annular like the capacitor  32  shown in  FIGS. 3 and 4 . 
         [0026]    By mounting the capacitors  32 ,  32 ′ and  32 ″ on the motor housing  50  as shown in  FIGS. 1-8 , it is possible to increase the amount of capacitance employed as a result of the large surface area available. As a result, the reliability of the motor assemblies  33 ,  33 ′ and  33 ″ of the present invention can be increased. In addition, because the voltage on the capacitors  32 ,  32 ′ and  32 ″ is substantially DC, the capacitors themselves may serve to shield the motor  16  against undesirable electromagnetic interference from other components of the vehicle  10  or from electromagnetic interference exterior to the vehicle. 
         [0027]    Design configurations may locate the inverter  30  remote from the electric motor  16 , however the benefits of diametric mounting locations for the capacitors  32 ,  32 ′ and  32 ″ still provide advantages of reduced axial length and electromagnetic shielding for drive packages comprising motors with just capacitors in integral assembly with the motor  16 . 
         [0028]    An additional design tradeoff, made available by utilizing the diametrically mounted capacitors  32 ,  32 ′ and  32 ″, is an increase in available space for increased axial length of the motors  16 , resulting in increased output power and torque. 
         [0029]    Annular and arcuate capacitor configurations are available from SBE, Inc., SB Electronics Division located in Barre, Vt. 
         [0030]    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.