Abstract:
A substantially hollow cylindrical stator core having a longitudinal axis includes a plurality of winding slots longitudinally parallel with the longitudinal axis each having first and second ends wherein the slots taper progressively larger closer to the ends of the slots.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure is related to stators for induction motors. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0003]    An electric-powered induction motor transforms electric power to mechanical power by inducing rotating magnetic fields between a static element, i.e., a stator, and a rotatable element, i.e., a rotor. The rotating magnetic fields induce torque on a shaft of the rotor. Known stators can induce current flows through conductor bars on the rotor that are parallel to an axis of the motor. 
         [0004]    A known rotor for an induction motor includes a stack of steel sheets assembled onto a rotatable shaft and a plurality of conducting bars fabricated from conductive material, e.g., copper or aluminum. The conducting bars are preferably connected at both axial ends of the rotors using shorting rings. The rotatable shaft of the rotor is mounted on bearing surfaces on end caps of a case containing the induction motor. Known rotor fabrication methods include assembling the stack of steel laminated sections, and then inserting the shorting bars and the conducting bars. Known methods for inserting the shorting bars and the conducting bars on the rotor include placing the rotor in a die cast mold and injecting molten material into open spaces formed in the rotor and open spaces between the die cast mold and the rotor. 
         [0005]    Known stators for induction motors include a stator core and electrical wire windings. Known stator cores are cylindrically shaped devices constructed from laminated steel sheets. An inner circumference of a known stator core includes a plurality of radially-oriented slots into which electrical wire windings are installed. Known electrical wiring windings include strands of insulated wire that are woven or otherwise arranged into a plurality of coil groups, with each coil group providing a single pole of a single phase of motor operation. The insulated wire that is fabricated from suitable conductive material, e.g., copper or aluminum. The quantity of radially-oriented slots in the stator core is determined based upon the quantity of phases and poles of the electrical wiring windings for the induction motor. Thus, a three phase, two-pole induction motor will have electrical wiring windings that are configured as six coil groups, with the coil groups configured in six slots or a quantity of slots that is a multiple of six. Current flow through the electrical wire windings is used to generate the rotating magnetic fields that act on a rotor to induce torque on a shaft of the rotor. 
         [0006]    Known parameters associated with induction motors include packaging size, mass, amount of materials used, e.g., the insulated wire, including amount of excess material that is used, and power density. The amount of excess material that is used in a stator includes that amount of material in the electrical wiring windings that is necessary for wrapping around, folding back or otherwise connecting individual strands of the insulated wire at one or both ends of the stator core and does not directly contribute to generating rotating magnetic fields in the stator. 
       SUMMARY 
       [0007]    A substantially hollow cylindrical stator core having a longitudinal axis includes a plurality of winding slots longitudinally parallel with the longitudinal axis each having first and second ends wherein the slots taper progressively larger closer to the ends of the slots. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0009]      FIG. 1  schematically illustrates a fragmentary perspective view of a portion of a stator for an induction motor in accordance with the present disclosure; 
           [0010]      FIG. 2  schematically illustrates a side view of a stator core in accordance with the present disclosure; 
           [0011]      FIG. 3  schematically illustrates a front view of a stator core in accordance with the present disclosure; 
           [0012]      FIG. 4  schematically illustrates a fragmentary cutaway front view of the stator in accordance with the present disclosure; and 
           [0013]      FIG. 5  schematically illustrates a fragmentary cutaway top view of the stator including adjacent radially-oriented inwardly projecting teeth forming a tapered aperture in accordance with the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,  FIG. 1  schematically illustrates a fragmentary perspective view of a portion of a stator  10  for an induction motor. The induction motor can be any induction motor, with one application including an induction motor for use on a powertrain system for a motor vehicle. The stator  10  includes a hollow cylindrical stator core  11  and electrical wire windings  50  that are assembled into the stator core  11 . As shown, the electrical wire windings  50  are fabricated using a plurality of insulated electric cables  52  that are arranged into a plurality of coil groups, with each coil group providing a single pole of a single phase of motor operation. The electrical wire windings  50  are arranged in any suitable winding pattern, including, e.g., a lap winding pattern and a concentric winding pattern, and installed into winding slots  18  formed in the stator core  11 . The slots  18  are rectangularly-shaped conduits for the insulated electric cables  52 . Electric power leads from each coil group are electrically connected to any suitable electric power source, including, e.g., a high-voltage battery and an inverter device. In one embodiment each of the insulated electric cables  52  is a single-strand copper wire that is fabricated from copper or aluminum and preformed into a shape that facilitates insertion into one of the slots  18  of the stator core  11 . In one embodiment, the insulated electric cables  52  are solid copper bars having a cross-section that is approximately square, having dimensions of about 3 mm (⅛ in), and referred to as bar pin wires. The insulated electric cables  52  preferably have an electrical insulative coating that is a glossy translucent elastomeric coating preferably applied in a dip process. Each of the insulated electric cables  52  emerges from a radially-oriented tapered aperture  28  formed at an end of one of the slots  18 . Each insulated electric cable  52  is bent to fold back and connect to another of the insulated electric cables  52 , preferably by an electric welding process as part of forming one of the coil groups. As is appreciated, the magnitude of allowable or achievable bending of each of the insulated electric cables  52  is determined by magnitude of tapering of the apertures  28  of the slots  18 . The stator  10  is inserted into any housing suitable for mounting and fixturing the stator  10 . The stator  10  is configured to accommodate an inserted rotor assembly having a shaft portion, which rotates within the housing in response to electric power signals originating from the electric power source. 
         [0015]      FIG. 2  schematically illustrates a side view of the stator core  11 . The stator core  11  includes an assembled laminate stack  13  that has been fabricated using a plurality of flat steel plies  12  oriented on a longitudinal axis  15 . The flat steel plies  12  are preferably stamped using a fine blanking process and are electrically insulated. Each of the flat steel plies  12  is a flat annular-shaped element. The assembled laminate stack  13  forms a plurality of radially-oriented, inwardly opening slots  18  each having a longitudinal axis that is parallel to the longitudinal axis  15 . The assembled laminate stack  13  includes first and second ends  14  and  16 , respectively that are perpendicular to the longitudinal axis  15 . An end element  20  is assembled onto one end  14  of the assembled laminate stack  13 . It is appreciated that the end element  20  may be assembled onto one end  14 , or alternatively, there may be first and second end elements assembled onto the first and second ends  14 ,  16  respectively of the assembled laminate stack  13 . 
         [0016]      FIG. 3  schematically illustrates a front view of the stator core  11  and  FIG. 4  schematically illustrates a fragmentary cutaway front view of the stator core  11 .  FIG. 3  schematically illustrates a front view of the stator core  11  including details of one of the flat steel plies  12 . Each of the flat steel plies  12  includes a plurality of radially-oriented inwardly projecting teeth  19 , with contiguous pairs of the teeth  19  forming an inwardly opening aperture  17  oriented radial to the longitudinal axis  15 . The inwardly opening apertures  17  are depicted as having rectangular cross-sections, and may be any suitable shape for accommodating the electrical wire windings  50 . As is appreciated, the flat steel plies  12  are assembled in a laminated fashion to form the assembled laminate stack  13  using any suitable fabricating method. The radially-oriented inwardly opening apertures  17  are aligned to form the corresponding inwardly opening slots  18  and preferably extend parallel to the longitudinal axis  15 . The insulated electric cables  52  are inserted into the inwardly opening slots  18 . 
         [0017]      FIG. 5  schematically illustrates a fragmentary cutaway top view of the stator  10  including the assembled laminate stack  13  and the end element  20 , which is coaxial with the assembled laminate stack  13  and includes an outer surface  22  and an inner surface  24 . The inner surface  24  of the end element  20  is mounted contiguous to one of the ends  14 ,  16  of the assembled laminate stack  13 . The end element  20  has a plurality of radially-oriented inwardly projecting teeth  29 . The radially-oriented inwardly projecting teeth  29  correspond to the radially-oriented inwardly projecting teeth  19  of the assembled laminate stack  13 . Contiguous pairs of the radially-oriented inwardly projecting teeth  29  form radially-oriented inwardly opening tapered apertures  28  that conform to the inwardly opening apertures  17  and the associated inwardly opening slots  18  of the assembled laminate stack  13 . Each of the radially-oriented inwardly projecting teeth  29  includes a cross-sectional area that expands from the outer surface  22  to the inner surface  24  of the end element  20  relative to the longitudinal axis  15 . As such, the radially-oriented inwardly opening tapered apertures  28  each taper, or diminish in cross-sectional area from the outer surface  22  to the inner surface  24  of the end element  20 . In one embodiment, the reduction in cross-sectional area in each tapered aperture  28  from the outer surface  22  to the inner surface  24  is formed using a plurality of discrete steps  33  and corresponding plateaus  35  in each of the inwardly projecting teeth  29 . The discrete steps  33  and corresponding plateaus  35  are formed using a plurality of plies having apertures that decrease in their respective open areas. Alternatively, the reduction in open area of the tapered apertures  28  from the outer surface  22  to the inner surface  24  is formed by machining a continuous chamfer or radius into the end element  20  when the end element is formed as a unitary piece. A single one of the insulated electric cables  52  is shown passing through one of the inwardly opening slots  18  and the tapered aperture  28 . 
         [0018]    The single insulated electric cable  52  includes a first portion  521  contained in the inwardly opening slot  18  of the stator core  11 , a bend portion  522  contained within the tapered aperture  28 , and an exterior portion  523  that is exterior to the stator core  11 . In one embodiment the insulated electric cables  52  are preformed into a shape that facilitates insertion into the slots  18  in the assembled laminate stack  13  with the exterior portion  523  that is exterior to the stator core  11  welded to another of the insulated electric cables  52  at its exterior portion  523  that is exterior to the stator core  11 . The exterior portion  523  of each of the insulated cables  52  includes material that is necessary for wrapping around or folding back to electrically and mechanically connect with other insulated electric cables  52 . It is appreciated that the radially-oriented inwardly opening tapered apertures  28  facilitate use of a greater angle for the bend portions  522  of the insulated electric cables  52  than achievable with a no-tapered aperture, thus reducing length and corresponding amount of wire used to form the insulated electric cables  52  of the electrical wire windings  50  and reducing packaging size of an associated electric motor. It is appreciated that the features of the end elements  20  including radially-oriented inwardly projecting teeth  29  and corresponding radially-oriented inwardly opening tapered apertures  28  may be fabricated directly in a end of the assembled laminate stack  13  of the stator core  11 . 
         [0019]    The disclosure has described certain preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.