CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is claims priority to Chinese Patent Application No. 200910259884.1, filed Dec. 16, 2009 and Chinese Patent Application No. 200920293410.4, filed Dec. 16, 2009, which are both hereby incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to an assembling method for a stator, and specifically to a method for assembling a laminated stator of a motor and a stator produced by the method. 
       BACKGROUND 
       [0003]    Referring to  FIG. 10 , a conventional monolithic iron stator core  2  for a brushless permanent magnet motor includes an annular hub  3  having a central circular hole  4  and a plurality of stator teeth  5  extending radially outward from the hub. Each adjacent pair of stator teeth  5  defines a slot  6  for receiving wire (not shown) wound around the corresponding teeth. Each tooth  5  includes a free end or tip  7  having an arcuate outer surface  8 . In the illustrated core  2 , the arcuate surface  8  of each stator tooth  5  is concentric with the circular hole  4 . There is a narrow gap  9  between each adjacent pair of free end  7  of the stator teeth  5 . During assembly of the stator, a winding needle (not shown) passes through the gaps  9  as it winds electrically conductive wires around each tooth  5  to form stator windings. 
         [0004]    Due to the width of the winding needle, the narrow gap  9  must not be made too narrow. Yet, the gap  9  should not be too wide. If the gap  9  is too wide this will have an undesirable impact on performance of the motor. Therefore, the conventional monolithic stator core  2  has the following disadvantages: It is difficult to wind stator windings around the teeth  5 ; there is a low slot fill factor; and there is low utilization of material. 
         [0005]    Although a high slot fill factor can be achieved by conventional segmented stator structures, the assembling process after wire winding is complicated because the multiple stator segments have to be assembled together to form the stator core and numerous wire connections may be needed to connect the stator windings. 
         [0006]    A variety of structures have been proposed to solve the problems associated with a conventional monolithic stator cores. For example, in the stator structures disclosed in U.S. Pat. No. 6,583,530 B2, U.S. Pat. No. 6,404,095 B1, and U.S. Pat. No. 6,400,059 B1, each tooth is wound individually while it is separate from the rest of the stator, and then the teeth are connected to segmented stator yokes after the windings are already on the teeth and assembled to form a stator using interlocking structures on the teeth. The assembly process for these stators is complicated, adding to manufacturing costs. 
         [0007]    U.S. Pat. No. 6,781,278 B2 discloses another example of a stator structure. Wire is wound around electrically insulating tooth rings to form the stator windings. Then a stator tooth is inserted into each tooth ring and secured to the stator body by means of a positioning pin to form the stator. This stator structure is difficult to assemble because all the teeth have to be inserted into corresponding slot structures in the stator body to assemble the stator and the positioning pins have to be inserted into a notch formed between the stator body and each tooth. 
         [0008]    In the stator structures disclosed in US 2009/0183357 A1 and U.S. Pat. No. 7,538,467 B2, two initially separate stator magnetic yoke modules made from a moldable magnetic powder material are joined to form a stator core. After the yoke modules are joined, stator windings are wound around the teeth of the stator core. The yoke modules are configured and combined in such a way to produce a stator core that is skewed to reduce cogging. This stator core is costly to assemble and does not solve any of the problems arising from the difficulty in passing a winding needle through the relatively narrow gaps between the free ends of adjacent stator teeth to wind the stator windings around the teeth. 
         [0009]    In the stator structures disclosed in U.S. Pat. No. 7,679,255, WO 2004/098023 A1, and WO 2006/018346 A1, the stator is formed by disposing multiple modules adjacent one another in an axial direction and combining them to form a stator core. Each module is formed from a moldable soft magnetic powder iron composite and includes a ring-shaped magnetic yoke and poles extending radially from the yoke. Each module includes a fraction of the total number of poles and the stator windings can be wound around the poles before the modules are combined. 
         [0010]    The present invention is directed to overcoming one or more of the problems set forth above. 
       SUMMARY 
       [0011]    In one aspect, the present invention includes an assembling method comprising the steps of: a) providing a plurality of lamination stacks, each of which comprises an annular portion having a central axis and a plurality of teeth arranged along the periphery of the annular portion, wherein each lamination has a same number of teeth; b) fixing the plurality of lamination stacks in sequence coaxially such that the plurality of lamination stacks are separated from each other by a predetermined axial distance; c) winding the teeth in such a way that the teeth belonging to a same phase of the stator are wound with a single continuous wire; and d) rotating the plurality of lamination stacks about a common central axis to a predetermined position, meshing the plurality of lamination stacks so that the annular portions of the plurality of lamination stacks are stacked adjacent one another along the axial direction, and the teeth of the plurality of laminations form teeth staggered along the periphery of the annular portions in such a manner that between adjacent teeth of one of the lamination stacks there is provided one tooth of each of other lamination stack. 
         [0012]    According to the assembling method of the present invention, because the plurality of lamination stacks are fixed coaxially and separated from each other at a predetermined axial distance before winding, the space between the teeth on each lamination stack is relatively wide and this makes it much easier to carry out the winding process. A single continuous long wire can be used to wind all the teeth of the stator belonging to the same phase. As a result, the disadvantages of numerous wire connections, of the possibility of loosening of joints, eccentricity of the assembled stator, and vibration and noises of the motor can be reduced. 
         [0013]    In one embodiment of the method, step a) comprises providing notches on the annular portion of each lamination stack, the notches being located between adjacent teeth on the periphery of the lamination stack for receiving root portions of teeth of another lamination stack. The notches can facilitate aligning the plurality of lamination stacks with one another as they are being meshed such that the meshing process can be completed smoothly. 
         [0014]    Preferably, step a) comprises integrally forming the teeth with the annular portion of the associated lamination. The integrally forming process suitably involves molding, cutting, or other suitable methods for making a single unitary body including an annular portion and teeth. In this way, the number of steps needed to produce laminations can be reduced. 
         [0015]    Preferably, step a) comprises forming the teeth by stacking a plurality of tooth portions having the same shape. In a specific embodiment, the plurality of tooth portions include the tooth portions extending from the annular portions of the laminations and additional separate tooth portions, which can be obtained by cutting or punching, such that the plurality of tooth portions are consistent in terms of shape, material and size favorable to forming the stator teeth. 
         [0016]    Preferably, the tooth portions of a lamination stack are fixedly connected to each other by locking, riveting, or adhering to form the stator tooth. 
         [0017]    Preferably, the tooth portions are aligned with positioning pins. Positioning holes for inserting positioning pins are preferably provided at root portions of the teeth portions. 
         [0018]    Preferably, step a) comprises insulating the stator teeth from the wire wound around the teeth to form the stator windings. For example, each tooth can be enclosed in an insulating case such that all portions of each tooth are covered by the insulating casings except for the root portion and the end portion. When a single tooth is formed by stacking a plurality of tooth portions, the insulating casings can be provided with positioning pins for aligning the plurality of tooth portions. 
         [0019]    In a specific embodiment, the number of the lamination stacks is two. 
         [0020]    In another aspect, the present invention further provides a laminated stator obtained by the above assembling method. In other words, a laminated stator for a motor is provided that is formed by meshing a plurality of lamination stacks, each of which comprises an annular portion having a central axis and a plurality of teeth arranged along the periphery of the annular portion, and each of which has a same teeth number, wherein the annular portions of the plurality of lamination stacks are stacked axially, characterized in that, in such a stator, the teeth of the plurality of lamination stacks are staggered along the periphery of the annular portions in such a manner that between adjacent teeth of one of the lamination stacks there is provided one tooth of each of other lamination stacks, and all teeth belonging to a same phase of the stator are wound with a single continuous wire. In practice, the stator may be an inner or outer stator. 
         [0021]    Another aspect of the invention is a stator for an electric motor. The stator includes first and second lamination stacks. Each lamination stack has: (a) a first group of stator laminations including an annular portion having a central axis and a plurality of tooth portions extending from a periphery of the annular portion; and (b) a second group of stator laminations including only tooth portions positioned to correspond with the tooth portions of said first group of stator laminations. The tooth portions of the first and second groups of lamination collectively form a plurality of stator teeth for each of the first and second lamination stacks. The annular portions of the first and second stacks are axially adjacent one another. The teeth of the first and second lamination stacks are intermeshed with one another. 
         [0022]    Another aspect of the invention is a method for making a laminated stator of an electric motor. The method includes arranging a plurality of stator laminations into lamination stacks spaced axially from one another. Each lamination stack includes (a) a first group of stator laminations having an annular portion having a central axis and a plurality of tooth portions extending from a periphery of the annular portion; and (b) a second group of stator laminations that have only tooth portions positioned to correspond with the tooth portions of said first group of stator laminations. The tooth portions of the first and second groups of laminations collectively form a plurality of stator teeth. Stator windings are wound around selected subsets of the plurality of teeth while the lamination stacks are spaced axially from one another. The lamination stacks are meshed with one another so that the annular portions of the lamination stacks are axially adjacent one another and the plurality of teeth of each lamination stack are intermeshed with the plurality of another of the lamination stacks. 
         [0023]    Other objects and features will in part be apparent and in part pointed out hereinafter 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a perspective view of a group of stator laminations including an annular portion having a central axis and a plurality of teeth extending from a periphery of the annular portion; 
           [0025]      FIG. 2  is a perspective of a lamination stack formed by combining the group of laminations illustrated in  FIG. 1  with another group of laminations that form only teeth; 
           [0026]      FIG. 3  is a perspective view of an electrically insulating disk supporting a plurality of casings for insulating the stator teeth from the stator windings; 
           [0027]      FIG. 4  is a perspective view of an electrically insulating cap that can be used with one of the insulating casings shown in  FIG. 3 ; 
           [0028]      FIG. 5  is a perspective view of the lamination stack shown in Fig. having with its teeth insulated by the casings of  FIG. 3  and a plurality of the caps shown in  FIG. 4 ; 
           [0029]      FIG. 6  is a cross-sectional view of the insulated lamination stack taken in a plane including line A-A on  FIG. 5 ; 
           [0030]      FIG. 7  is a perspective view of a plurality of coaxially fixed lamination stacks; 
           [0031]      FIGS. 8   a - 8   e  are perspectives illustrating steps of a process in which stator windings are wound around the teeth of the lamination stacks; 
           [0032]      FIG. 9  is a perspective view of a stator according to one embodiment of the invention; and 
           [0033]      FIG. 10  is a perspective view of a monolithic stator structure in prior art. 
       
    
    
       [0034]    Corresponding reference characters indicate corresponding parts throughout the drawings. 
       DETAILED DESCRIPTION 
       [0035]      FIG. 1  shows a group, generally designated by  10 , of one or more laminations having a collective thickness smaller than that of a conventional stator. Each lamination in the group  10  has a hub or annular portion  11  and tooth portions, each generally designated by  12 , arranged equi-angularly along the annular portion. Because those skilled in the art are already familiar with laminated stators it is not necessary to complicate the drawings by showing individual laminations in each view. An opening  11   a  (e.g., a generally circular opening) is positioned within the annular portion  11  and aligned with an imaginary central axis. 
         [0036]    As illustrated in  FIG. 1  each tooth portion  12  is generally T-shaped and has a tooth root portion  121 , a tooth body portion  122  and a tooth end portion  123  that is spaced radially from a periphery of the annular portion  11 . The tooth end portion  123  has an arcuate outer surface. The T-shaped configuration of the tooth portion  12  helps prevent wire slipping from the tooth as will be apparent to those skilled in the art. The arcuate surfaces of the tooth end portions  123  of the teeth lie on a common imaginary circle that is concentric with the central axis and opening  11   a . Preferably, the tooth portions  12  for this group  10  of laminations are integral with the annular portion  11 . As an example, each lamination in the group  10  suitably has twelve identical tooth portions  12 . A positioning hole  13  is provided in the tooth root portion  121  of each tooth portion  12 . Optionally, a notch  14  is positioned centrally between two adjacent teeth portions  12  on the periphery of the annular portion  11  (i.e., at a predetermined position) for reasons that will become apparent. It is conceivable that each lamination in the group  10  can be obtained by starting with a lamination having twenty-four tooth portions (or more broadly, twice as many tooth portions as the number of tooth portions for the laminations in the group  10 ), punching the lamination at each tooth root region to obtain the positioning hole  13 , then cutting or otherwise removing alternating tooth portions to form the notches  14  and obtain the lamination  10  as shown in  FIG. 1 . The tooth portions removed in this process are suitably retained and will be referred to herein as tooth portion only laminations  12 ′. 
         [0037]    As shown in  FIG. 2 , a lamination stack  1  can be obtained by stacking one or more tooth portion only laminations  12 ′ onto the tooth portions  12  of the laminations in the group  10  shown in  FIG. 1 . The tooth portions  12 ′ and  12  can be connected to one another by any suitable methods such as adhering, riveting, or interlocking. The tooth portions  12 ′ and  12  of the first and second groups of laminations are stacked to constitute a single stator tooth  15 . Thus, the lamination stack  1  includes the annular portion(s)  11  of the laminations in the first group and the tooth  15  formed by the tooth portions  12  of the laminations in the first group and the tooth portion only laminations  12 ′ in the second group. Because of the additional laminations  12 ′ in each tooth  15 , the axial thickness of each tooth is greater than the thickness of the annular portion of the lamination stack  1 . It is noted, the stator tooth  15  may also be formed integrally instead of being formed by a plurality of stacked laminations without departing from the scope of the present invention. Those skilled in the art can conceive that the stator tooth  15  can be integrally formed with the annular portion  11  of the thin sheet  10 , for example by molding, or an integrally formed tooth can be connected to the annular portion  11  by an interlocking structure. The tooth portions  12 ′ and  12  of each group of laminations are identical in shape so contours of the tooth portions can be aligned during stacking. 
         [0038]      FIGS. 3 and 4  show electrical insulation  20  used for each tooth  15  of the lamination stack  1  shown in  FIG. 2 , and  FIG. 5  shows a stator of the invention equipped with the insulation  20 . The insulation  20  suitably includes a disk  21  for insulating an axially-facing surface of the annular portion  11  and insulating casings  22  along the periphery of the disk  21 . The disk  21  has notches  211  disposed centrally between adjacent insulating casings  22  on the periphery of the disk to align with the notches  14  of the lamination stack  1 . Each insulating case  22  is composed of a recess  221  substantially defining a space for receiving a tooth  15  and a cap  222  for covering the opening of the recess and covering an axially-facing side of a tooth  15  received in the recess. The recess  221  can be sized and shaped to receive a tooth  15  by loose or tight fit. Preferably, the opposing sides  2211 ,  2212  of the each casing  22  clamp the tooth  15  and the cap  222  engages a tooth portion  12 ′ stacked at one end of the tooth and connects with the opposing sides  2211 ,  2212  by snap connection, so as to form an insulating casing  22  that insulates the tooth from the stator windings. The insulating casing  22  and disk  21  are suitably connected to the annular portion  11  of the lamination stack  10 , including the tooth  15 , by conventional means. At the edges of the two opposite sides  2211 ,  2212  of the casings adjacent the annular portion  11  of the lamination stack  10 , laterally extending flanges  241 ,  242  are provided for abutting the periphery of the annular portion  11  to ensure insulation of the stator windings from the annular portion of the lamination stack  10 . In the illustrated embodiment, bottom sides  2213  of the casings  22  are connected to the disk  21  or are integrally formed with the disk  21 . It is noted that the disk  21  can be omitted (e.g., when the lamination is not used as an end lamination of the stator). 
         [0039]      FIG. 4  shows the cap  222  of the insulating casing  22  has a substantially identical shape as the axially-facing side of the tooth  15 . A positioning pin  23  extends from the cap  222  at a position corresponding to the position of the positioning hole  13  of the tooth portions  12 ,  12 ′ of the lamination stack  10 . The positioning pin  23  is suitably fixed to a side of the cap  222  facing the tooth  15  by conventional means. It is conceivable that the positioning pin  23  can alternatively be integrally formed with the cap  222 . After the tooth  15  is placed within the recess  221  of the insulating casing  22 , the side of the cap  222  having the positioning pin  23  is arranged to face the un-insulated axially-facing side of the tooth  15 , and the positioning pin  23  is aligned with the positioning hole  13  at the tooth root portion  121  of the tooth  15 . Then the positioning pin  23  is inserted into the positioning hole  13  until the cap  222  abuts the tooth  15  as shown in  FIGS. 5 and 6 . Once the cap is secured to the tooth  15  in this manner, the tooth is insulated from the wire to form the stator windings. The insulating casing  22  may additionally function to align the tooth portions  12  of the laminations stack  10  and the tooth only lamination portions  12 ′ stacked to form the teeth  15 . Those skilled in the art can conceive of other structures and methods for insulating the teeth from the wire, e.g., by applying an electrically insulating coating or insulation paper on each surface of the tooth  15  contacted by wire. In another embodiment, the positioning pin can be arranged on the bottom side  2213  of the casing  22  instead of on the cap  222 . 
         [0040]    The assembling method of the stator according to the present invention will be described in detail in terms of an example of an integral stator formed from two identical stacks  1 ,  1 ′ of laminations as illustrated in  FIG. 2 . 
         [0041]    First, two structurally identical lamination stacks  1 ,  1 ′ are insulated with insulation  20 , respectively, so each stack is substantially identical to the insulated stack in  FIG. 5 . Then, the insulated lamination stacks  1 ,  1 ′ are mounted on a wire-winding fixture  301  such that the two lamination stacks are coaxial with one another and spaced axially from one another, as illustrated in  FIG. 7 . 
         [0042]    Next, winding begins. All the teeth  15  of each stack  1 ,  1 ′ are categorized as belonging to X, Y, or Z phase (taking three-phase stator as an example) before winding. Referring to  FIGS. 8   a - 8   d , a single long continuous wire is wound around each tooth  15  belonging to the same phase. As illustrated in  FIG. 8   a  the wire is wound clockwise around a first tooth  151  of the lamination stack  1  belonging to the X-phase to form the stator windings for this tooth. Then, the continuous wire is wound counter-clockwise around a first tooth  151 ′ of the other lamination stack  1 ′ of the X-phase to form the stator windings for this tooth ( FIG. 8   b ). Next, after jumping over two teeth of the lamination stack  1 ′ ( FIG. 8   c ), the same continuous wire is wound around a second tooth  152  of the lamination stack  1  of the X-phase, then around a second tooth  152 ′ of the lamination  1 ′, etc. These steps are repeated until the same continuous wire is wound around all the teeth of the lamination stacks  1 ,  1 ′ belonging to the same phase X to form a complete set of X phase stator windings. During winding, segments L ( FIG. 8   c ) of the wire skipping over teeth of the other phases are preferably arranged on the insulated lower end surface of the lamination  1  or the insulated upper end surface of the lamination  1 ′ to prevent interference from these segments L when the laminations  1 ,  1 ′ are meshed. Then, a substantially similar winding process is carried out for teeth belonging to each additional phase (e.g., for the Y-phase and Z-phase in the case of a three phase stator). The stator structure according to the present invention can be wound with wire more conveniently than the conventional stator structure because the spaces between the teeth  15  of each stack of laminations  1 ,  1 ′ is much wider than the gaps  9  between the teeth  6  of the conventional stator  2  in  FIG. 10  and the space for the winding needle to pass between adjacent teeth is more than doubled. In addition, because a single continuous wire is used to form the windings on all of the teeth for a particular phase, the number of wire connections is greatly reduced. 
         [0043]    To mesh the laminations stacks  1 ,  1 ′ after winding to form a stator  30 , one of the laminations is rotated to align each tooth of the lamination stack  1 ′ with a notch  14  of the other lamination stack  1  and vice versa and the lamination stacks are moved into axially abutting relation with one another, as indicated by the arrows on  FIG. 8   d , so the teeth of the lamination stacks are intermeshed with one another. Then the lamination stacks  1 ,  1 ′ are secured to one another to retain them in position relative to one another. When intermeshed, each tooth  15  of the first lamination stack  1  is between two adjacent teeth of the second lamination stack  1 ′ and vice versa. Also, the tooth root portions  121  of the part of the teeth  15  formed from the tooth only lamination portions  12 ′ are received in the notches  14  of the other lamination stack  1  or F. The stacks  1 ,  1 ′ are suitably axially spaced from one another during the winding process by a predetermined distance selected so a segment of wire  303  ( FIG. 8   d ) extending from a tooth  15  on the first stack  1  to a tooth  15  on the second stack  1 ′ is the correct length to bridge across one tooth for each additional phase of the stator (e.g., to bridge across two teeth in a three phase stator) in the finished stator  30 . This facilitates using a single continuous wire to wind all the teeth of the same phase because it automatically results in the wire segment  303  having the proper length to bridge across the teeth of the other phases without producing unnecessary slack in the wire segment Although the lamination stacks  1 ,  1 ′ are rotated relative to one another after winding, it is also possible to rotationally fix the laminations stacks  1 ,  1 ′ before winding and then mesh the laminations stacks  1 ,  1 ′ with one another without rotating them after winding without departing from the scope of the invention. 
         [0044]    As shown in  FIGS. 8   e  and  9 , in the stator  30  formed by meshing the lamination stacks  1 ,  1 ′ the annular portions  11  of each stack are stacked axially adjacent one another and the teeth  15  of the laminations extend radially from the peripheries of the annular portions. For aesthetics, the jumper wire segments L on the end surface of the stator can be tightened and bundled (not shown). Finally, the assembled stator  30  is removed from the wire-winding fixture  301  as shown in  FIG. 9 . 
         [0045]    Although the example provided above merely shows a stator composed of two lamination stacks, those skilled in the art will appreciate that the stator of the present invention is not limited to those formed by stacking just two lamination stacks. For example, the stator can be formed by stacking three, four, or more lamination stacks. 
         [0046]    When the stator is assembled by stacking three lamination stacks, for instance, the axial thickness of the teeth of each lamination stack is approximately three times the thickness of the annular portion of the respective lamination stack, wherein the axial length of the teeth of the upper lamination extending downward from its annular portion is 2h, the length of the teeth of the middle lamination extending upward and downward from its annular portion each are h, and the length of the teeth of lower lamination extending upward from its annular portion is 2h. In this case, each of the three lamination stacks has two toothless positions (e.g., where notches are formed to receive tooth root portions of the other lamination stacks) between its adjacent teeth. Winding is performed in such a manner that jumper wire does not exist on the axially-facing surfaces of the middle lamination stack, and all the teeth belonging to the same phase are wound with a single wire. After all the teeth belonging to different phases are wound with wire, the three lamination stacks are stacked axially adjacent one another to form a stator with a tooth thickness of 3h. 
         [0047]    When a stator is assembled from a plurality of lamination stacks, those skilled in the art will appreciate how to modify the structure of insulation means or insulation casing according to assembling or winding requirements. In addition, the teeth number of each lamination stack is not limited to the number shown in the figures and modification also can be made to the annular portion, the tooth portions  12 ,  12 ′, or thickness or shape of the tooth portions  12 ,  12 ′ of each lamination without departing from the scope of the present invention. 
         [0048]    The method of winding as shown in  FIGS. 8   a - 8   d  and described above is illustrative only. Modifications can be made by those skilled in the art according to structural parameters such as lamination number and tooth number. 
         [0049]    Although the figures show an inner stator structure, the present invention can be applied to outer stator structures as well. 
         [0050]    As illustrated by the description provided above, the stator structure produced according to the present invention has many advantages such as convenient wire winding, high slot fill factor and fewer wire connections. Accordingly, the stator structure is particularly suitable for aluminum wire. Thus, in one embodiment, the stator windings comprise aluminum. 
         [0051]    It should apparent for those skilled in the art that various changes and modifications can be made to the stator structure of the present invention without departing from the scope of the disclosure. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the description and practice disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.
A laminated stator and a method for making a laminated stator of an electric motor. The method includes arranging a plurality of stator laminations into lamination stacks spaced axially from one another, each lamination stack including a first group of stator laminations including an annular portion and a plurality of tooth portions extending from a periphery of the annular portion, and a second group of stator laminations including only tooth portions positioned to correspond with the tooth portions of said first group. The method further includes winding stator windings around selected subsets of the plurality of teeth while the lamination stacks are spaced axially and meshing the lamination stacks with one another so the annular portions of the lamination stacks are axially adjacent one another and the plurality of teeth are intermeshed with the plurality of another stack.