Abstract:
A method for manufacturing a laminated stator core for an electric motor includes providing a plurality of generally planar laminations, forming a plurality of notches into the lamination, and finally forming a plurality of interlock tabs. The notches extend outward from the interlock tabs to an outside diameter of the lamination to create a void in the back iron area of the interlock tabs to reduce the flux leakage.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to electric motors and more particularly to stator core interlocks that allow minimal flux leakage.  
           [0002]    Electric motors can vary from small, fractional motors that are found, for example, in washing machines, refrigerators and air conditioners, to large industrial motors that are found, for example, in manufacturing equipment, compressors, fans and the like. A typical motor includes a rotating central portion known as a rotor and a stationary outer portion referred to as a stator. Both the stator and rotor are contained, at least partially within a housing that carries the motor. A stator core is typically formed from a plurality of stacked plates or laminations. The laminations which are generally formed from metal, may be punched or pressed and subsequently stacked one on top of another to form the stator core. Due to the possible asymmetries in the lamination material, the laminations can be rotated so that the stator core, upon final assembly, forms a straight rather than lopsided stack. The laminations are interlocked with one another to form a rigid stator core structure and to prevent the laminations from shifting relative to one another.  
           [0003]    In one known interlocking arrangement, each lamination has a dimple or a recess punched into the surface which forms a corresponding projection on the opposite side of the lamination. The laminations are then stacked one on top of the other with the projections from one lamination engaging and residing within the recess in the next adjacent lamination. In this nested arrangement, the laminations are aligned with one another by engagement of the projections and recesses. This is a common and accepted method for interlocking laminations. However, the common and accepted method does not reduce the flux leakage.  
           [0004]    Therefore, it would be desirable to provide a method for a stator core interlocking arrangement that is cost effective as well as effective in reducing the flux leakage.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    In one embodiment, a stator lamination includes a plurality of notches and interlock tabs. The notches extend outward from the interlock tabs to an outer diameter of the lamination to create a void in a back iron area of the interlock tabs. The laminations are stacked to form a stator core. The stack defines at least one inner lamination having laminations positioned adjacent to both sides of the laminations. Each lamination has notches extending outward from an outside edge of the interlock tabs to the outer diameter of the stator lamination, thus creating a void in the back iron area of the stator lamination adjacent the interlocking tabs. The notch impinges upon the interlock tabs along the length of the stator core, interrupting the flux path through the iron towards the outer diameter of the interlock. Since the flux path is interrupted, the flux is significantly less likely to link the conductive interlocks, and thereby reduces the current flow through the interlocks.  
           [0006]    In yet another embodiment, a method for manufacturing a laminated stator core for an electric motor includes forming a plurality of notches and tabs in the interlock laminations. More particularly, the method includes providing a plurality of generally planar laminations, each lamination having an axis substantially perpendicular to the lamination plane, forming a plurality of notches in the lamination, and forming a plurality of interlock tabs. The laminations are stacked to form a stator core. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is an exploded, perspective view of an exemplary motor, illustrating a stator having a core formed in accordance with one embodiment of the present invention;  
         [0008]    [0008]FIG. 2 is a top view of the stator core shown in FIG. 1;  
         [0009]    [0009]FIG. 3 is an enlarged view of a notch area shown in FIG. 2;  
         [0010]    [0010]FIG. 4 is an enlarged view of an alternative embodiment of the notch area shown in FIG. 2;  
         [0011]    [0011]FIG. 5 is an enlarged view of a further alternative embodiment of the notch area shown in FIG. 2;  
         [0012]    [0012]FIG. 6 is an enlarged view of a still further embodiment of the notch area shown in FIG. 2; and  
         [0013]    [0013]FIG. 7 is a side view of the stator core shown in FIG. 1.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    [0014]FIG. 1 is an exploded, perspective view of an exemplary motor  10 , illustrated in accordance with the principles of the present invention. Motor  10  is enclosed within a housing  12  and includes a rotor  14  and a stator  16 . Stator  16  is mounted to and at least partially within housing  12 . Stator  16  includes a longitudinal axis  18 , there-through. Rotor  14  is positioned at least partially within stator  16  and includes a longitudinal axis  20  collinear with stator axis  18 .  
         [0015]    Rotor  14  is positioned within stator  16  such that a gap (not shown) extends therebetween. The gap is sufficiently large to permit rotor  14  to freely rotate within stator  16  without contacting stator  16 . In addition, the gap is sufficiently small such that a magnetic field which is created in stator  16  can in turn induce an electric current in rotor  14  which generates an opposing magnetic field. Interaction between these two magnetic fields is converted to mechanical energy and results in rotation of rotor  14 . As the gap between rotor  14  and stator  16  increases, the rotor current inducement decreases. Thus, the size of the gap between the rotor  14  and stator  16  must be determined by balancing the need to maintain space between rotor  14  and stator  16  while maintaining rotor  14  and stator  16  sufficiently close to reduce and preferably minimize field losses.  
         [0016]    Rotor  14  includes a rotor core  22  and stator  16  includes a stator core  24  formed from a plurality of plates or laminations  26  stacked together. Laminations  26  are secured relative to one another by an interlocking system. The interlocking system prevents the laminations  26  from rotating, shifting and separating from each other, and thus maintains stator core  24  as a unitary member during motor fabrication.  
         [0017]    [0017]FIG. 2 is a top view of the stator core shown in FIG. 1. Stator core  24  (shown in FIG. 1) includes a plurality of teeth  28  defining a plurality of slots  30 . Teeth  28  are formed at an inner edge  32  of each lamination  26 . Teeth  28  are formed integral with the lamination outer or ring portion  36 . Slots  30  are configured to receive and secure conducting elements (not shown) therein. Stator core lamination  26  defines an outer diameter  40  and an inner diameter  42  of stator core  24 . A group of notches or openings  50  are punched into lamination  26  prior to punching a plurality of stator interlock tabs  52 . Interlock tabs  52  include an outside edge  54 , an inside edge  56 , an axis of symmetry  58  and have an oval shape. Notches  50  are oriented such that they extend outward from outside edge  54  of interlock tab  52  to an outside diameter  60  of stator lamination  26 . Interlock tabs  52  are partially punched through lamination  26 . In the exemplary embodiment, there are six notches  50  and six interlock tabs  52 . When stator core  24  is assembled, each interlock tab  52  enhances the engagement between the laminations, to prevent shifting therebetween. FIGS. 3 through 6 (described below) explain the lamination interlocking arrangement in detail.  
         [0018]    [0018]FIG. 3 is an enlarged view of a notch area  62  (shown in FIG. 2). A stator lamination  64  includes an interlock tab  72 . Interlock tab  72  has an outside edge  74 , an inside edge  76  and an axis of symmetry  78 . A notch  80  extends outward from outside edge  74  of interlock tab  72  to an outside diameter  82  (also numbered as  60  in FIG. 2) of stator lamination  26  shown in FIG. 2. Notch  80  is fully punched through lamination  26 . Interlock tab  72  is partially punched through lamination  26 . Notch  80  has an axis of symmetry  84  that substantially coincides with axis of symmetry  78  of tab  72 . There are six notches  80  and six partially punched interlock tabs  72 .  
         [0019]    [0019]FIG. 4 is an enlarged view of an alternative embodiment of notch area  62  (shown in FIG. 2). A stator lamination  90  includes a notch  92  punched at an angle α. Notch  92  extends outward from an outside edge  94  of interlock tab  96 , at angle α, to an outside diameter  98  of stator lamination  90 . An inside edge  100  of interlock tab  96  is substantially parallel to outside edge  94 . An axis of symmetry  102  of interlock tab  92  does not coincide with an axis of symmetry  104  of notch  92 . Instead, axis of symmetry  102  is positioned at angle α with respect to axis of symmetry  104 .  
         [0020]    [0020]FIG. 5 is an enlarged view of a further alternative embodiment of notch area  62  (shown in FIG. 2). A stator lamination  110  includes a notch  120 . An axis of symmetry  124  of notch  120  is substantially parallel to an axis of symmetry  128  of an interlock tab  130 . Notch  120  is punched at a perpendicular angle to an axis of symmetry  132  of interlock tab  130 . Axis of symmetry  132  is perpendicular to both axes  124  and  128 . Furthermore, axis of symmetry  124  does not coincide with axis of symmetry  128 . Instead axis of symmetry  124  is located a pre-determined distance “D” from axis of symmetry  128 . The stator lamination arrangement in this embodiment provides substantial surface area of interlock tabs for more robust mechanical engagement than other embodiments.  
         [0021]    [0021]FIG. 6 is an enlarged view of a still further embodiment of notch area  62  (shown in FIG. 2). A stator lamination  140  includes a partially punched interlock tab  152 . Notch  50  (shown in FIG. 2) is not punched. Additionally, interlock tab  152  extends inward from an outside diameter  154  of stator lamination  140 .  
         [0022]    [0022]FIG. 7 is a side view  160  of stator core  24  shown in FIG. 1. Each lamination of stator core  24  includes at least two interlock tabs. Interlock tabs are stacked on top of each other to lock adjacent laminations together. For example, a lamination  162  has a corresponding interlock tab  192 . Similarly laminations  164 ,  166 ,  168 ,  170 ,  172 ,  174 , and  176  have corresponding interlock tabs  194 ,  196 ,  198 ,  200 ,  202 ,  204 , and  206  respectively. For example, one end lamination  178  receives interlock tab  206  (also shown as number  52  in FIG. 2) of adjacent lamination  176 . Similarly, interlock tab  192  of lamination  162  is received by adjacent lamination  164 . Since lamination  178  is the end lamination of stator core  24 , lamination  178  does not include a punched tab, but instead has a flat surface  220 . Thus, lamination  178  receives interlock tabs  206  of adjacent lamination  176 .  
         [0023]    In the exemplary embodiment, there are at least two interlock tabs per lamination. Interlock tab  192  of lamination  162  is received by lamination  164 . Interlock tab  194  of lamination  164  is received by lamination  166 . The upper surface  222  (shown as  36  in FIG. 2) of lamination  162  (shown as  26  in FIG. 2) is substantially flat and substantially parallel to a second surface  224  of lamination  162 . End lamination  178  has a flat surface  220  and an upper surface  228 , both surfaces substantially parallel. End lamination  178  receives interlock tabs  206  of adjacent lamination  176 . There are no interlock tabs on end lamination  178 .  
         [0024]    End laminations  162  and  178  are formed such that they are engaged by only one adjacent lamination  164  and  176  respectively. On the other side, interior laminations  164 ,  166 ,  168 ,  170 ,  172 , and  174  engage two adjacent laminations, one at the top and other at the bottom.  
         [0025]    The embodiments described above relate specifically to stator lamination arrangements in detail. However, the lamination arrangements are equally applicable to rotor lamination, interlock transformer lamination, ballast lamination, automobile and other ignition coils and various other commercially available electrical devices that utilize lamination arrangements.  
         [0026]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.