Abstract:
A stator includes a housing made of magnetically conductive material, a plurality of magnets fixed to the stator housing; and a magnet holder attached to one end of the housing for fixing the magnets to the stator housing. The magnet holder includes a body and a plurality of locking structures extending from the body. Each magnet is locked between two adjacent locking structures. A plurality of cut-outs is formed in the stator housing, and a plurality of projections is formed on the body of the magnet holder and engaged with the cut-outs. Each locking structure includes a wedge-shaped inner end inwardly abutting against respective magnets to prevent the magnets from moving inwardly.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 201310416203.4 filed in The People&#39;s Republic of China on Sep. 12, 2013, the entire contents of which are hereby incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to electric motors and in particular, to permanent magnet stators of electric motors. 
       BACKGROUND OF THE INVENTION 
       [0003]    An electric motor usually comprises a stator and a rotor rotatable relative to the stator. The stator usually comprises a round stator housing and a plurality of arc magnets installed on the inner surface of the stator housing. The magnets are usually adhered to the stator housing via glue, which is complicated and time-consuming especially when the motor has a lot of magnets. Furthermore, when the motor operates at a high temperature for a long time, the glue is subject to faster aging and the magnets may detach from the stator housing. 
       SUMMARY OF THE INVENTION 
       [0004]    Thus there is a desire for a stator with an improved magnet holder which can solve the above problems. 
         [0005]    Accordingly, in one aspect thereof; the present invention provides a stator for an electric motor, comprising: a housing made of magnetically conductive material; a plurality of magnets fixed to the housing; and a magnet holder attached to one end of the housing for fixing the magnets to the housing, the magnet holder comprising a plurality of locking structures, each magnet being locked between two adjacent locking structures. 
         [0006]    Preferably, each locking structure has a pair of concave locking surfaces formed on opposite sides thereof, and each magnet has a pair of side surfaces conforming with corresponding locking surfaces of the magnet holder. 
         [0007]    Preferably, the magnets are arranged in groups of like polarities to form magnetic poles of the stator. 
         [0008]    Preferably, widths of the locking structures located between adjacent magnets with the same polarities are less than widths of the locking structures located between adjacent magnets with opposite polarities. 
         [0009]    Preferably, the magnets are elongate plate shaped magnets. 
         [0010]    Preferably, each magnet has a pair of opposite major surfaces parallel to each other, the major surfaces being perpendicular to a radial direction of the stator. 
         [0011]    Preferably, at least one locating structure is formed between the magnet holder and the housing for locating the magnet holder relative to the housing. 
         [0012]    Preferably, the at least one locating structure comprises a cut-out formed in the housing, and a projection formed on the magnet holder and engaged with the cut-out. 
         [0013]    Preferably, the magnet holder further comprises a body, the locking structures extending from the body and being inserted into the housing. 
         [0014]    Preferably, each locking structure comprises a wedge-shaped inner end inwardly abutting corresponding magnets to prevent the corresponding magnets from moving inwardly. 
         [0015]    Preferably, a flux ring is installed between the magnets and the housing. 
         [0016]    Preferably, a second magnet holder is disposed within the housing, the second magnet holder comprising a plurality of locking structures, and the other ends of the magnets are respectively locked between adjacent locking structures of the second magnet holder. 
         [0017]    Preferably, the magnets are sandwiched between a retaining ring and the housing or flux ring. 
         [0018]    Preferably, the retaining ring has a flange abutting against an end of the magnets. 
         [0019]    Preferably, the magnet holder has a plurality of locking recesses and the retaining ring has a plurality of fingers crimped into corresponding locking recesses of the magnet holder. 
         [0020]    Alternatively, plastic material is injected into the space between the retaining ring and the flux ring to fix the magnets and retaining ring to the flux ring. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Preferred embodiments of the invention will now be described, by way of example only, with reference to figures of the accompanying drawings. In the figures, identical structures, elements or parts that appear in more than one figure are generally labeled with a same reference numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale, The figures are listed below. 
           [0022]      FIG. 1  is a perspective view of a magnet holder according to a first embodiment of the present invention; 
           [0023]      FIG. 2  is an enlarged partial view of the magnet holder of  FIG. 1 ; 
           [0024]      FIG. 3  illustrates a slight modification of the magnet holder of  FIG. 1  viewed from another aspect; 
           [0025]      FIG. 4  illustrates a portion of an assembly of the magnet holder, magnets and a flux ring; 
           [0026]      FIG. 5A  is an exploded view of a flux ring, magnets and magnet holders in accordance with a second embodiment of the present invention; 
           [0027]      FIG. 5B  is an assembled view of the parts of  FIG. 5A ; 
           [0028]      FIG. 6  illustrates the assembled flux ring, magnets and magnet holders of  FIG. 5B , installed within a stator housing; 
           [0029]      FIG. 7A . is an exploded view of a flux ring, magnets and magnet holders in accordance with a third embodiment of the present invention; 
           [0030]      FIG. 7B  is an assembled view of the parts of  FIG. 7A ; 
           [0031]      FIG. 8  illustrates the assembly of  FIG. 7B , viewed from a different angle; 
           [0032]      FIG. 9  illustrates the assembly of  FIG. 8 , installed in a stator housing; 
           [0033]      FIG. 10A  is an exploded view of a flux ring, magnets and magnet holders in accordance with a fourth embodiment of the present invention; 
           [0034]      FIG. 10B  is an assembled view of the parts of  FIG. 10A ; 
           [0035]      FIG. 11  illustrates the assembled flux ring, magnets and magnet holders of  FIG. 10B  installed in a stator housing; and 
           [0036]      FIG. 12  illustrates a stator in accordance with a fifth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0037]    Referring to  FIG. 1 , a magnet holder  10  in accordance with a preferred embodiment of the present invention comprises an annular body  12 , a plurality of locating projections  14 , locking blocks  16  and locking ribs  18 . The annular body  12  comprises a first end surface (upper surface in  FIG. 1 ), a second end surface (lower surface in.  FIG. 1 ) opposite to the first end surface., and a pair of circumferential surfaces respectively connecting inner and outer edges of the first and second end surfaces. The locking blocks  16  and the locking ribs  18  are arranged on the first end surface of the body  12 . In this embodiment, the magnet holder  10  comprises four locking blocks  16  evenly distributed in the circumferential direction of the annular body  12 . Three locking ribs  18  are evenly distributed between each pair of adjacent blocks  16 . Preferably, each block  16  and rib  18  extends perpendicularly from the first end surface of the annular body  12 . 
         [0038]    Referring to  FIG. 2 , the ribs  18  have the same height as the blocks  16  in the axial direction of the body  12  and less width than the blocks  16  in the circumferential direction of the body  12 . Each block/rib  16 / 18  has a pair of concave locking side surfaces  162 / 182  on opposite sides in a circumferential direction of the body  12 . Each block/rib  16 / 18  has a wedge inner end  164 / 184 . The width of the block/rib  16 / 18  reduces gradually in the radial direction of the body  12  from the radial outer end toward the radial inner end while the width of inner end  164 / 184  increases gradually in the radial direction towards the center of the body  12 . 
         [0039]    Magnet holder  10  is shown in  FIG. 3  from the other side to reveal four locating protrusions  13  formed at the second end surfaces of the body  12  and three locating projections  14  respectively extending radially outwardly from three of the four locating protrusions.  FIG. 3  also illustrates optional locating recess  15  formed in the inner surface of locating protrusions  13  and joining with optional grooves formed in the locking. blocks  16 . The locating projections  14  and the recesses  15  cooperatively form a locating structure for locating the ring magnet holder  10  to a round motor housing  90  (shown in  FIGS. 8 ,  10  and  11 ). Understandably, when the body  12  has a non-circle shape, the locating projections  14  and recesses  15  may be omitted. 
         [0040]    Preferably, the magnet holder  10  is integrally made of plastic via molding to form a monolithic structure. 
         [0041]      FIG. 4  illustrates a portion of an assembly of the magnet holder  10 , magnets  20  and a flux ring  30 . During assembly, the magnet holder  10  is pressed into the flux ring  30  from one open end of the flux ring  30  until the first end surface of the body  12  of magnet holder  10  contacts with the end surface of the flux ring  30 . The blocks  16  and ribs  18  are inserted into the open end of the flux ring  30 . The magnets  20  are then pressed into the flux ring  30  from the other open end of the flux ring  30  until the magnets  20  contact with the first end surface of the body  12  of the magnet holder  10 . Each magnet  20  is locked between a pair of adjacent locking surfaces of the blocks/ribs  16 / 18 . In this embodiment, the magnets  20  are elongate plate-shaped magnets. Each magnet  20  comprises a pair of opposite major surfaces parallel to each other and a pair of side surfaces respectively connecting sides of the major surfaces. The major surfaces of the magnet  20  are perpendicular to a radial direction of the stator. The side surfaces of the magnet  20  conform to the corresponding side surfaces of the ribs  18  or blocks  16 . The wedge inner ends  164  and  184  of the blocks  16  and ribs  18  abut against inner edges of the magnets  20  to thereby prevent the magnet  20  moving inwardly. There are four magnets  20  located between each pair of adjacent blocks  16  and the four magnets  20  located between adjacent blocks  16  have the same polarity to cooperatively form a magnetic pole. Adjacent magnetic poles have opposite polarities. In this embodiment, each magnetic pole is comprised of multiple elongate plate shaped magnets, which reduces eddy current losses in the magnets, 
         [0042]      FIGS. 5A ,  5 B and  FIG. 6  illustrate a stator in accordance with a second embodiment of the present invention. The stator  100  comprises a pair of magnet holders  10 ,  40  which are press fitted into opposite open ends  32 ,  34  of the flux ring  30 . Opposite axial end surfaces of the flux ring  30  respectively contact with the first end surfaces  12  of the magnet holders  10 ,  40  and outer surfaces of the blocks  16  and ribs  18  firmly contact with the inner surface of the flux ring  30 . The magnet holder  40  has a structure similar to the magnet holder  10  except that the magnet holder  40  has no locating projections formed on the outer circumferential surface of the annular body. Opposite axial ends of each magnet  20  are locked between adjacent ribs  18  or between adjacent block  16  and rib  18  of the magnet holders  10 ,  40 . The combined magnet holders  10 ,  40 , magnets  20  and flux ring  30  are inserted into a stator housing  90 . The stator housing  90  has a cylindrical configuration with open axial ends. One end of the stator housing  90  defines a plurality of cutouts  92  for receiving the locating projections  14  of the magnet holder  10  to thereby circumferentially locate the magnets with the housing and to prevent the magnet holder  10  from moving relative to the stator housing  90  in axial and circumferential directions of the stator. An end cap (not shown) may be attached to the end of the stator housing  90  to prevent the combined magnet holders  10 ,  40 , magnets  20  and flux ring  30  from withdrawing from the stator housing  90 . 
         [0043]      FIGS. 7A  to  FIG. 9  illustrate a stator  200  in accordance with a third embodiment of the present invention. The stator  200  comprises a magnet holder  10 , a plurality of magnets  20 , a flux ring  30 , a retaining ring  50  and a stator housing  90 . The magnet holder  10  is pressed into one end of the flux ring  30 . The magnets  20  are inserted into the flux ring  30  from the other end of the flux ring  30 . One axial end of each magnet  20  is located between adjacent ribs  16  or between adjacent rib and block  18 . The retaining ring  50  has a flange  52  extending outwardly from one end thereof. The retaining ring  50  is inserted into the flux ring  30  from the other end thereof until the flange  52  contacts with the other end of the flux ring  30 . The outer circumferential surface of the ring  50  presses the magnets  20  outwardly to thereby firmly sandwich the magnets  20  between the retaining ring  50  and the flux ring  30 . The retaining ring  50  may be made of non-magnetically conductive material such as stainless steel. Preferably, the retaining ring  50  has the same height as the magnets  20 . The retaining ring  50  has fingers  54  formed at the other end thereof away from the flange  52 . After the retaining ring  50  is inserted into the flux ring  30 , the fingers  54  are pressed outwardly to be crimped into the corresponding locating recesses  15  of the magnet holder  10  to thereby locate the retaining ring  50  relative to the magnet holder  10  in axial and circumferential directions. The combined magnet holders  10 ,  40 , magnets  20  and flux ring  30  are inserted into a stator housing  90 , as shown in  FIG. 9  to complete the stator. End caps, brush gear and a wound rotor complete the motor. 
         [0044]      FIG. 10A  to  FIG. 11  illustrate a stator  300  in accordance with a fourth embodiment of the present invention. The stator  300  comprises a magnet holder  10 , a plurality of magnets  20 , a flux ring  30 , a retaining ring  60  and a stator housing  90 . The retaining ring  60  is similar to the retaining ring  50  except that the retaining ring  60  has no flange formed at an end thereof. After the combined magnet holder  10 , magnets  20 , flux ring  30  and retaining ring  60  are inserted into the stator housing  90  from one end of the stator housing  90 , plastic material  310  is injected into the space formed between the retaining ring  60  and flux ring  30  from the other end of the stator housing  90 . The magnets  20 , flux ring  30  and retaining ring  60  are therefore fixed to the inner surface of the stator housing  90  via the plastic material  310 . 
         [0045]      FIG. 12  illustrates a stator  400  in accordance with a fifth embodiment of the present invention. In this embodiment, the stator  400  is similar to the stator  100  except that the stator  400  comprises a cylindrical heat dissipation device  95  attached on the stator housing  90 . The heat dissipation device  95  comprises a plurality of fins  97  for increasing heat dissipation surface area of the heat dissipation device  95 . 
         [0046]    In the description and claims of the present application, each of the verbs “comprise”, “include”, “contain” and “have”, and variations thereof, are used in an inclusive sense, to specify the presence of the stated item but not to exclude the presence of additional items. 
         [0047]    Although the invention is described with reference to one or more preferred embodiments, it should be appreciated. by those skilled in the art that various modifications are possible. For example, each magnetic pole may be made of one magnet and locking ribs  16  may be omitted. The flux ring  30  may be omitted when the stator housing  90  has enough thickness. Therefore, the scope of the invention is to be determined by reference to the claims that follow.