Patent Publication Number: US-2013249345-A1

Title: Segmented rotor in a rotor assembly

Description:
TECHNICAL FIELD 
     This disclosure relates to electric machines and, more specifically, to rotors for electric machines. 
     BACKGROUND 
     An electric motor uses electric potential energy to produce mechanical energy through the interaction of magnetic fields and current-carrying conductors. The reverse process, using mechanical energy to produce electrical energy, is accomplished by a generator or dynamo. Other electric machines, such as motor/generators, combine various features of both motors and generators. 
     Electric machines may include an element rotatable about a central axis. The rotatable element, which may be referred to as a rotor, may be coaxial with a static element, which may be referred to as a stator. The electric machine uses relative rotation between the rotor and stator to produce mechanical energy or electrical energy. 
     SUMMARY 
     A rotor assembly is provided. The rotor assembly includes a hub and a rotor core having a first rotor lamination positioned at least partially around the hub. The first rotor lamination is at least partially defined by a first segment and a second segment that are configured to connect or interlock. The first segment includes a projection extending from a first body. The projection is configured to engage with a corresponding notch in the second segment in order to connect the first segment to the second segment. At least one first mounting tab extends from the first body and is configured to engage with a corresponding first groove on an outer periphery of the hub in order to connect the first segment to the hub. 
     The above features and advantages, and other features and advantages, of the present invention are readily apparent from the following detailed description of some of the best modes and other embodiments for carrying out the invention, as defined in the appended claims, when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic, perspective view of a rotor assembly having a hub and rotor core formed from laminations having a plurality of segments per lamination, in accordance with a first embodiment; 
         FIG. 2  is a schematic, fragmentary, top view of the rotor core and hub shown in  FIG. 1 , with other components removed for clarity; 
         FIG. 3  is a schematic, fragmentary, close-up view of portion  3  shown in  FIG. 2 ; 
         FIG. 4  is a schematic, fragmentary, top view of a rotor assembly having a rotor core and hub, in accordance with a second embodiment; and 
         FIG. 5  is a schematic, fragmentary, close-up view of portion  5  shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the Figures, wherein like reference numbers refer to the same or similar components throughout the several views,  FIG. 1  is a schematic, perspective view of a rotor assembly  10  having a rotor core  12  and a hub  14 , according to a first embodiment. The hub  14  is longitudinally disposed around a center axis  16 . An end face  18  of the rotor core  12  is shown in  FIG. 1 . The hub  14  may include inner and outer portions  20 ,  22  that are concentric and connected via spokes  24 . The hub  14  may be a single cylindrical shaft (not shown). The rotor core  12  is positioned at least partially around the hub  14 . As illustrated in  FIG. 1 , the rotor core  12  is formed by stacking a plurality of rotor laminations  26 , such as first rotor lamination  28 . The rotor core  12  is configured to be rotatable within a generally annular stator (not shown). Referring to  FIG. 1 , the assembly  10  may also include a speed and position sensor target  34  and a spline  36  that engages with a component (not shown) for transmitting torque from the assembly  10 . The assembly  10  may also include an end ring, which is not shown for illustrative purposes. 
       FIG. 2  is a schematic top view of a portion of the rotor core  12  and hub  14  shown in  FIG. 1 , with other components removed for clarity. Referring to  FIGS. 1-2 , a plurality of slots  30  may be formed near the outer periphery of the first rotor lamination  28 . The slots  30  may be partially filled with permanent magnets  32  (shown in  FIG. 1 ). The first rotor lamination  28  is formed from a plurality of segments. Referring to  FIGS. 1-2 , a first segment  40  and a second segment  42  are configured to interlock and at least partially define the first rotor lamination  28 . A third segment  44  is configured to interlock with the first segment  40  to further define the first rotor lamination  28 . Employing a first rotor lamination  28  composed of a plurality of segments eliminates the need for a large blank size that is typically required for producing un-segmented rotor laminations. The first, second and third segments  40 ,  42  and  44  may be formed with the same or similar geometry. Alternatively, the first, second and third segments  40 ,  42 ,  44  may be formed having different geometries, for example, different shapes and numbers of slots  30 . 
       FIG. 3  is a schematic close-up view of portion  3  shown in  FIG. 2 , illustrating the interface between the first and second segments  40 ,  42  of the rotor core  12  (shown in  FIG. 1 ). Referring to  FIGS. 2-3 , the first segment  40  includes a projection  46  extending from a first body  48 . The projection  46  is configured to engage with a corresponding notch  50  in the second segment  42  in order to connect the first segment  40  to the second segment  42 . The notch  50  is shaped to correspond to or conform to the projection  46  in order to provide a sufficiently snug fit. 
     The projection  46  may be shaped to provide sufficient hoop strength or stiffness to allow the rotor core  12  (and hub  14 ) to be rotated at higher speeds. Hoop strength and stiffness may be defined as the ability to resist circumferential forces. As the rotor core  12  spins, a component of force in the radial direction is induced due to centrifugal loading  58  (shown in  FIGS. 2-3 ). The components of the rotor core  12  are pulled apart due to the centrifugal loading. Some of the radial loading is carried across the projection  46 , thereby inducing a tangential load  56  (shown in  FIGS. 2-3 ) into the rotor core  12 . The first segment  40  is configured to share the structural or tangential load  56  of the second segment through the projection  46 . 
     The projection  46  is configured to have a shape that provides locking capability, i.e. a shape that locks or holds the first and second segments  40 ,  42  together as the rotor core  12  and hub  14  spin. Referring to  FIG. 3 , in one example, the projection  46  may be defined by a proximal portion  52  and a distal portion  54 , with the distal portion  54  having a width  53  that is greater than the width  55  of the proximal portion  52 . The projection  46  may also be shaped in other ways that provide locking capability. The embodiment shown in  FIGS. 1-3  may be used in applications where the rotor core  12  is moving at high speeds. 
     Referring to  FIGS. 2-3 , the first segment  40  may be connected to the hub  14  through one or more first mounting tabs  60  that extend from the first body  48 . Referring to  FIGS. 2-3 , the first mounting tab  60  is configured to engage with a corresponding first groove  62  on an outer periphery  64  of the hub. The first groove  62  has an internal shape that corresponds to or conforms to the first mounting tab  60  in order to provide a sufficiently snug fit. As shown in  FIGS. 2-3 , the first mounting tab  60  may have a “dovetail” shape. Referring to  FIG. 3 , the first mounting tab  60  may be defined by an end  66  configured to be substantially parallel to the outer periphery  64  of the hub  14  and at least two tips  68  configured to be at least partially rounded and substantially perpendicular relative to the end  66 . 
     Referring to  FIG. 2 , the second segment  42  includes one or more second mounting tabs  70  extending from a second body  72 . Each second mounting tab  70  is configured to engage with a corresponding second groove  74  in the hub  14  in order to connect the second segment  42  to the hub  14 , as shown in  FIG. 2 . 
     Referring to  FIGS. 2-3 , each of the segments  40 ,  42  (and segment  44  shown in  FIGS. 1-2 ) may be defined by a respective outer profile  76 , an inner profile  78  and edges  80 . Referring to  FIGS. 2-3 , the inner profile  78  may be defined by at least one relief  79  that allows for a varying radius to be obtained at the inner profile  78 . Stated differently, the inner profile  78  may be defined by at least abutting portion  82  (which abuts the outer periphery  64  of the hub  14 ) and at least one non-abutting portion  84  (which is spaced from the outer periphery  64  of the hub  14 ). The abutting portion  82  has a larger first radius  86  than the second radius  88  of the non-abutting portion  84 . Referring to  FIG. 3 , the inner profile  78  may be formed with a rounded corner  89  between the relief  79  and the normal edge of the first mounting tab  60  (or second mounting tab  70 ), in order to reduce stress on the rotor core  12 . Referring to  FIG. 3 , the abutting portion  82  may be defined by a width  83 . By way of example only, the width  83  may be 1 mm. 
     Referring to  FIGS. 1-2 , a third segment  44  is configured to interlock with the first segment  40  to further define the first rotor lamination  28 . In the embodiment shown, the first rotor lamination  12  is formed from six segments. However, any numbers of segments may be used to create each of the laminations or layers of the rotor core  12 . Referring to  FIG. 2 , the third segment  44  includes a third projection  92  configured to engage with a corresponding notch  94  in the first segment  40 , thereby connecting the first segment  40  to the third segment  44 . Referring to  FIG. 2 , the third segment  44  includes a third mounting tab  96  configured to engage with a corresponding third groove  98  in the hub  14 , in order to connect the third segment  44  to the hub  14 . 
       FIG. 4  is a fragmentary schematic top view of a rotor assembly  110  according to a second embodiment. Referring to  FIG. 4 , the assembly  110  includes a hub  114  and a rotor core  112  having a first rotor lamination  128 . The assembly  110  shown in  FIG. 4  is similar to the assembly  10  in the first embodiment unless otherwise described. 
     The first rotor lamination  128  is formed from a plurality of segments. Referring to  FIG. 4 , first, second and third segments  140 ,  142 ,  144  are configured to interlock and at least partially define the first rotor lamination  128 .  FIG. 5  is a schematic, fragmentary, close-up view of portion  5  shown in  FIG. 4 , showing the interface between segments  140 ,  142  and the hub  114 . Referring to  FIG. 5 , the first segment  140  includes a projection  146  extending from a first body  148 . The projection  146  is configured to engage with a corresponding notch  150  in the second segment  142  in order to connect the first segment  140  to the second segment  142 . Referring to  FIG. 5 , the second segment  142  includes a protrusion  151  extending from a second body  172  and configured to engage with a corresponding recess  153  in the first segment  140 . 
     Referring to  FIG. 5 , the interlocking of the projection  146  in the first segment  140  with the notch  150  in the second segment  142 , and the protrusion  151  in the second segment  142  with the recess  153  in the first segment  140 , keeps the first and second segments  140 ,  142  from twisting outwards or deflecting when the rotor core  112  (and hub  114 ) is spinning, that is, the interlocking supports the radial loads induced during spinning As the rotor core  112  spins, a component of force in the radial direction is induced due to centrifugal loading  156  (shown in  FIG. 5 ). The components of the rotor core  112  are pulled apart due to the centrifugal loading  156 . Referring to  FIG. 5 , some of the radial loading is carried across the projection  146 . The embodiment shown in  FIGS. 4-5  may be used in applications where the rotor core  112  is moving at low speeds. The number of mounting tabs  60 ,  70 ,  160 ,  170  in either embodiment may be varied depending on the particular application. For example, the number of mounting tabs  60 ,  70 ,  160 ,  170  may be selected based on the stress of the component, i.e., keeping the stress below the yield strength of the material used to form the hub  14  or  114  and first rotor lamination  28  or  128 . 
     Similar to the first embodiment and referring to  FIG. 5 , the first and second segments  140 ,  142  are connected to the hub  114  through respective first and second mounting tabs  160 ,  170  inserted into respective grooves  162 ,  174  in the hub  114 . The second mounting tab  170  attaching the second segment  142  to the hub  114  is positioned sufficiently close to the projection  146  so that the forces acting on the first segment  140  will be transmitted to second segment  142  and then directly into the hub  114 . This minimizes deflection of the first rotor lamination  128 . 
     Referring to  FIGS. 4-5 , each of the segments  140 ,  142 ,  144  may be defined by a respective outer profile  176 , an inner profile  178  and edges  180 . Referring to  FIG. 5 , the projection  146  of the first segment  140  is configured to be inclined relative to the edge  180 , as shown by the angle of incline  181 . In one example, the angle of incline  181  is 30 degrees. 
     Referring to  FIG. 5 , the inner profile  178  may be defined by at least one relief  179  that allows for a varying radius to be obtained at the inner profile  178 . Stated differently, the inner profile  178  may be defined by at least abutting portion  182  (which abuts the outer periphery  164  of the hub  114 ) and at least one non-abutting portion  184  (which is spaced from the outer periphery  164  of the hub  114 ). The abutting portion  182  has a larger first radius  186  than the second radius  188  of the non-abutting portion  184 . Referring to  FIG. 5 , the inner profile  178  may be formed with a rounded corner  189  between the relief  179  and the normal edge of the second mounting tab  170  (or first mounting tab  160 ), in order to reduce stress on the rotor core  112 . 
     The detailed description and the drawings or figures are supportive and descriptive of the invention, but the scope of the invention is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed invention have been described in detail, various alternative designs and embodiments exist for practicing the invention defined in the appended claims.