Abstract:
A rotor may include a planar lamination having permanent magnets arranged therein, and an inner edge defining an opening configured to receive a driveshaft. The planar lamination may include a driveshaft key, and a relief notch and scallop disposed on each side of the driveshaft key. The relief notch and scallop may distribute stress imparted to the driveshaft key and reduce deformation due to centrifugal loads during rotation of the rotor. The relief notches may be next to the driveshaft key. The relief notches may be sandwiched between the scallops. The inner edge may include additional scallops.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to a permanent magnet electric machine rotor. 
       BACKGROUND 
       [0002]    Hybrid and electric vehicles use an electric machine to provide motive force. Hybrid vehicles may use internal combustion engines and electric machines to propel the vehicle. Electric machines may also be used to recharge vehicle batteries. 
         [0003]    Electric machines typically employ a rotor and a stator to produce torque. Electric current flows through windings of the stator to produce a magnetic field. The magnetic field generated by the stator may cooperate with permanent magnets affixed to the rotor to generate torque. In some arrangements, the permanent magnets may be arranged in V-shaped pairs. Moreover, torque generation may induce stresses within the rotor. 
       SUMMARY 
       [0004]    A rotor may include a planar lamination having permanent magnets arranged therein, and an inner edge defining an opening configured to receive a driveshaft. The planar lamination may include a driveshaft key and a relief notch and scallop disposed on each side of the driveshaft key to distribute stress imparted to the driveshaft key and deformation of the rotor due to centrifugal loads during rotation of the rotor. The relief notches may be next to the driveshaft key. The relief notches may be sandwiched between the scallops. The inner edge may further include additional scallops. The inner edge may further include another driveshaft key disposed opposite the driveshaft key. Each of the scallops may have an ovoid shape. Each of the scallops may have an elliptical shape. 
         [0005]    An electric machine includes a stator and a rotor. The rotor may be surrounded by the stator and include an inner surface defining a driveshaft opening having a key, a pair of relief notches disposed about the key so as to sandwich the key therebetween, and a pair of scallops disposed about the relief notches so as to sandwich the relief notches therebetween such that the scallops distribute stress imparted to the key during rotation of the rotor. The inner surface may further include additional scallops. The inner surface further may include another driveshaft key disposed opposite the driveshaft key. Each of the scallops may an ovoid shape. Each of the scallops may have an elliptical shape. 
         [0006]    An electric machine may include a planar lamination having permanent magnets arranged therein, and an edge defining a driveshaft key, a pair of relief notches straddling the driveshaft key, and a pair of scallops straddling the relief notches to distribute stress imparted to the driveshaft key during rotation of the rotor. The edge may further define additional scallops. The edge may further define another driveshaft key disposed opposite the driveshaft key. Each of the scallops may have an ovoid shape. Each of the scallops may have an elliptical shape. 
         [0007]    An electric may include a rotor having permanent magnets arranged therein, and a surface defining a driveshaft slot, and a pair of scallops straddling and spaced from the driveshaft slot to distribute stress imparted to the driveshaft slot during rotation of the rotor. The surface may further define additional scallops. The surface may further define another driveshaft key disposed opposite the driveshaft key. Each of the scallops may have an ovoid shape. Each of the scallops may have an elliptical shape. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1A  is a plan view of a lamination of a rotor of an electric machine. 
           [0009]      FIG. 1B  is a side view of a rotor having stacked laminations. 
           [0010]      FIG. 2  is a contour plot of von Mises stress distribution of a baseline lamination layer. 
           [0011]      FIG. 3  is a plan view of a lamination having a set of relief notches and a plurality of scallops along the periphery of the inner diameter of the rotor. 
           [0012]      FIG. 4  is a plan view of an excerpt of a lamination layer along View A of  FIG. 2 . 
           [0013]      FIG. 5  a plan view of a drive shaft having a key sized to fit into a keyhole of the rotor. 
           [0014]      FIG. 6  is a plan view of an external rotor configured to surround an internal stator having a key sized to form to a drive ring keyhole. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments may take various and alternative forms. The figures are not necessarily to scale; some features could 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. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
         [0016]    Electric machines typically employ a rotor and a stator to produce torque. Electric current flows through windings of the stator to produce a magnetic field. The magnetic field generated by the stator may cooperate with permanent magnets affixed to the rotor to generate torque. Electric machines have many configurations. One configuration may include the rotor disposed externally, allowing the rotor to rotate about the stator. The rotor may be directly attached to drive a device. For instance, an electric machine with an external rotor may apply torques directly to fan blades or vehicle wheels. The external rotor may also supply energy to a drive chassis or shaft surrounding the rotor to collect torques produced by the rotation of the rotor. 
         [0017]    Another configuration may dispose the rotor internally, allowing the rotor to rotate within the stator. A driveshaft may cooperate with the rotor to transfer torques generated to external devices. For instance, the driveshaft may translate torques produced by the rotor to a drivetrain of a vehicle. The transfer of torque, in both circumstances, may cause uneven or improperly distributed stresses throughout the rotor. Centrifugal loads may cause ovoid deformation of the driveshaft opening or rotor laminations. Each lamination may individually experience this uneven stress distribution or deformation. A pair of relief notches may relieve stresses near the point of energy transfer between the drive shaft and rotor. The relief notches may have many shapes. A smoothed or rounded shape may be preferred. A set of relief notches located about the energy transfer section may reduce uneven stress distributions, but those uneven distributions may be reduced further. The addition of scallops, indentations or, dimples about the drive shaft hole of the rotor may further reduce acute, high-stress areas. The scallops may be evenly or sporadically distributed about the surface, edge, or inner or outer diameter of the rotor. Each may be a curved, smooth, or rigid shape. For example, ten scallops may be evenly distributed about the inner or outer diameter of the rotor. The scallops may have similar ovoid shapes or alternating shapes (e.g., right-angled, ovoid, right-angled, ovoid). 
         [0018]    Referring now to  FIG. 1A , a planar lamination  10  for a rotor is shown. The lamination  10  may define a plurality of portions  11  for each of the alternating magnetic poles  16  formed by permanent magnets  15 . The magnetic poles may be arranged such that each adjacent portion  11  is a dissimilar magnetic pole.  FIG. 1A  depicts an eight-pole rotor. It is well known in the art that an electric machine may have various numbers of poles. The lamination  10  may define a plurality of pockets or cavities  12  adapted to hold permanent magnets  15 . The permanent magnets may form the magnetic poles  16  of the rotor. Between each of the pockets  12  a bridge  25  may provide structural support. The center of the lamination  10  may define a circular central opening or inner edge  14  for accommodating a driveshaft with a keyway that may receive a driveshaft key  30 . The permanent magnets may also be arranged in varying orientations. As shown in  FIG. 1A , the pockets or cavities  12 , which hold permanent magnets, are arranged with a V-shape  18 . Referring now to  FIG. 1B , a plurality of laminations  10  are stacked to form a rotor  8 . The laminations may be skewed to improve torque output of the motor, and the laminations may be grouped into sections that are skewed relative to other sections. A central opening or hole  14  is provided axially along the rotor to engage an output shaft to transfer torque from the rotation of the rotor. A number of mass reduction cavities  27  are provided to reduce the overall mass of the rotor. 
         [0019]    A keyed feature, drive key or driveshaft key  30  is provided on an inner surface of the center opening  14  to engage a powertrain output shaft and transfer torque from the electric machine. One or more relief notches  32  may be provided adjacent to the keyed feature  30 . The shape of the cutout near the keyed feature  30  is optimized in attempt to achieve a more a uniform stress distribution at the feature. Generally, the geometry is smoothed and sharp edges are removed. While small relief notches near the keyed feature  30  limit the weakening effect on the lamination  10  and reduces oval deformation, larger relief notches have a benefit of providing a smoother stress distribution near the keyed feature  30  and a lower overall stress level. 
         [0020]      FIG. 2  is a contour plot of von Mises stress for a portion of the rotor lamination layer  10  under load during operation of the electric machine. The darker regions indicate higher levels of stress. It may be advantageous to manage the stress associated with loads upon the keyed feature  30  because one of the highest stress levels in the lamination is frequently found to be near the keyed feature  30 . In the example provided, the maximum stress encountered at the stress relief notches  32  is about 99% of the overall maximum stress in the lamination layer  10 . As can be seen from the stress contour depicted in  FIG. 2 , a non-uniform stress distribution, or stress riser, is experienced adjacent the keyed feature  30 . While different shapes of the relief notches  32  may be employed, redistribution of stresses caused by loads upon the keyed feature  30  may be limited using local features. While relief notches  32  improve the stress distribution of the lamination, the relief notches  32  introduces a weak point in the rotor structure that causes oval rotor deformation under centrifugal loads. 
         [0021]      FIG. 3  is a sectional plan view of a portion of the lamination  10 . Scallops  34  may be implemented to balance oval deformation of the rotor under stress and reduce the specific stress on the relief notches  32 . The relief notches  32  may sandwich the drive key or drive slot  30 . A pair of scallops  34  may sandwich the relief notches  32 . The scallops  34  may be evenly spaced along the periphery of the generally annular inner diameter of the lamination  10  and coincide with adjacent laminations. The scallops  34  may have a generally elliptical shape  36 . The major axis  38  of the scallops  34  may be sized to fit ten scallops  34  along the periphery of the inner diameter of the central opening  14 . Section A, as shown in  FIG. 4 , discloses a typical scallop  34 . 
         [0022]      FIG. 4  depicts an example of a scallop  34 . Although a generally elliptical shape is shown, the scallop may take any shape or partial shape. For example, the scallop may be an ovoid, rectangular, or triangular shape. The smooth elliptical pattern may provide an even stress distribution under high torsional stresses and mechanical deformation. One of the preferred lengths of the major axis is 11.0 mm for an opening  14  having an inner diameter of 58 mm. One of the preferred lengths of the minor axis  40  for a similar opening is 0.72 mm. The minor axis  40  would have a cut-depth  42  from the periphery of the opening  14  of 0.30 mm. 
         [0023]    Now referring to  FIG. 5 , in one embodiment the drive key  30  may also disposed on the drive shaft  50  with a corresponding keyway or key slot  31  defined by the rotor lamination  10 . In a similar fashion, regardless of whether the drive key is on the drive shaft or rotor, scallops  34  may be defined along the periphery of opening  14 . Although the drive key  30  is preferably disposed on the inner diameter of the rotor  14 , as shown in  FIG. 3 , it is not required. The scallops  34  may be applied to many different types of electric machines. 
         [0024]    Now referring to  FIG. 6 , an external rotor rotor  8  is shown to indicate the versatility of the disclosure. The scallops may be located on an inner or outer surface of the rotor depending on the electric machines construction. An external rotor surrounds a stator (not shown) having coil windings. The external rotor  8  may have permanent magnets  15  positioned to form magnetic poles. The exterior rotor  8  may have a drive key  30  similar to the interior rotor  8  as discussed above. The external rotor  8  may have a set of relief notches  32  and a plurality of scallops  34  along the periphery of the outer diameter of the rotor  8 . 
         [0025]    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 disclosure. As previously described, the features of various embodiments may be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics may be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes may include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.