Abstract:
An electric machine includes a stator having slots of substantially rectangular cross section. The slots are subdivided into pairs of slots, with each pair of slots configured with parallel flanks, wherein teeth are formed between the slots and have alternating rectangular and triangular cross sections. Positioned on the teeth of rectangular cross section are tooth coils.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application claims the priority of German Patent Application, Serial No. 103 52 814.8, filed Nov. 12, 2003, pursuant to 35 U.S.C. 119(a)-(d).  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates, in general, to an electric machine, and more particularly to an electric machine having a stator with slots for positioning tooth coils.  
         [0003]     Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.  
         [0004]     Coils of electric machines are positioned in slots, i.e. the coils are prefabricated and then positioned in the slots of the electric machine. Machines are also known having pronounced windings to form tooth coils, whereby each winding surrounds a single tooth. These prefabricated tooth coils are positioned from outside into a star-shaped coil bobbin constructed in the form of a stacked metal sheets and pushed into a stator yoke. It is also possible to fabricate the windings of electric machines in the form of prefabricated coils which are then fed-in wire by wire into the slots of the stator. This is time-consuming and labor intensive.  
         [0005]     Common to all these approaches is also the very complicated manufacture. In addition, these approaches lead to large end windings, and the slot filling factor is relatively low. Especially when a two-part lamination piece is involved, the provision of webs between the stator teeth is required to ensure a mechanical stability of the star-shaped packet. As a consequence, part of the flux which could assist the torque formation is shorted and thus becomes ineffective.  
         [0006]     It would therefore be desirable and advantageous to provide an improved electric machine to obviate prior art shortcomings and to allow easy placement of a winding in the slots.  
       SUMMARY OF THE INVENTION  
       [0007]     According to one aspect of the present invention, an electric machine includes a stator having slots of substantially rectangular cross section, wherein the slots are subdivided into pairs of slots, with each pair of slots configured with parallel flanks, wherein teeth are formed between the slots and have alternating rectangular and triangular cross sections, and tooth coils positioned on the teeth of rectangular cross section.  
         [0008]     As a result of the configuration of the electric machine according to the present invention, the tooth coils can be directly placed onto the teeth that have rectangular cross section, without requiring winding each wire individually and without requiring an axial split of the lamination piece of the stator. The tooth coils can be prefabricated and secured in the slot by a simple casting process and/or provision of slot wedges. The tooth coil is hereby wound around a coil bobbin or forms a separate structure without coil bobbin.  
         [0009]     According to another feature of the present invention, the teeth terminate in tooth heads in the direction of the air gap, which tooth heads are configured to maintain the boundary surface of the air gap equidistant on the side of the stator in the area of the teeth. This is especially of importance when several, e.g. three or four, slots are configured in neighboring relationship with parallel flanks, whereby, in particular when an uneven number of slots with parallel flanks are involved, coil halves of different tooth coils are provided in a slot.  
         [0010]     By positioning the slots at a small angle, e.g. less than 5 degrees, relative to one another, the casting process results in a wedging effect for the tooth coils in the slots to permanently retain the tooth coils in the slots.  
         [0011]     As a result of the greater slot filling degree, the electric power and torque parameters are improved in comparison to conventional electric machines. Moreover, manufacturing times of the electric machines is decreased.  
         [0012]     According to another aspect of the present invention, a method of making a stator includes the steps of blanking lamination pieces to form slots separated by teeth, and packaging the lamination pieces to provide a lamination stack, positioning tooth coils about a first plurality of teeth that have a rectangular cross section, and casting the tooth coils with the lamination stack. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0013]     Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:  
         [0014]      FIG. 1  is a schematic illustration of a lamination piece according to the present invention;  
         [0015]      FIG. 2  is an enlarged detailed view of an encircled area of the lamination piece, marked by Roman number  11  in  FIG. 1 ;  
         [0016]      FIG. 3  is a partly sectional side view of a stator having incorporated the subject matter of the present invention;  
         [0017]      FIG. 4  is a perspective illustration of the stator of  FIG. 3 ;  
         [0018]      FIG. 5  is a perspective illustration of a coil bobbin with phase separator for placement into slots of the stator;  
         [0019]      FIG. 6  is a perspective illustration of a coil bobbin without phase separator;  
         [0020]      FIG. 7  is a schematic illustration of another embodiment of a lamination piece according to the present invention; and  
         [0021]      FIG. 8  is a schematic illustration of still another embodiment of a lamination piece according to the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0022]     Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.  
         [0023]     Turning now to the drawing, and in particular to  FIG. 1 , there is shown a schematic illustration of a lamination piece  1  according to the present invention which together with like lamination pieces forms a lamination stack of a stator  5  ( FIG. 3 ). Each lamination piece  1  has blanked or stamped therein a plurality of slots  7  to define teeth  2 ,  3  about the circumference, such that teeth  2  of generally rectangular alternate with teeth  3  of generally triangular cross section. The lamination piece  1  is subdivided into adjacent pairs of two slots  7 , whereby the two slots  7  have parallel flanks. As shown by way of example, during manufacture, each of the generally rectangular teeth  2  of the lamination stack of lamination pieces  1  is used here for placement of a tooth coil  6  which is attached to the respective tooth  2  in substantially radial direction as indicated by arrow  4 . In other word, each of the two slots  7  contains half of a tooth coil  6 .  
         [0024]      FIG. 2  shows an enlarged detailed view of the area encircled  11  in  FIG. 1  to depict more clearly the parallel flanks of the two slots  7  which bound the generally rectangular tooth  2 . Located adjacent to each of the slots  7  on the flank distal to the tooth  2  are two generally triangular teeth  3  which have no winding. Thus, a generally rectangular tooth  2  is followed by a generally triangular tooth  3 .  
         [0025]     As indicated by dash-dot lines in  FIG. 2 , the slots  7  may also be configured such that the tooth  2 , bounded by the two slots  7 , has a generally trapezoidal configuration, with the flanks  22  and  23  of the tooth  2  defining an angle α.  
         [0026]     When packaging the lamination pieces  1  to a lamination stack, the tooth coils  6  are attached to the rectangular or trapezoidal teeth  2 , and the assembly of lamination stack and tooth coils  6  is then embedded in a casting compound so that the tooth coils  6  are wedged in the slots  7 . Suitably, the slots  7  and thus the teeth  2 ,  3  are configured during the blanking process such that their tooth heads  70  are shaped to provide for a circumferentially continuous air gap at an enveloping radius R. Of course, the slots  7  may have a slot depth or may be generally constructed with geometric dimensions during the blanking operation as to best suit the application at hand.  
         [0027]     As shown in  FIGS. 7 and 8 , each lamination piece  1  may also be subdivided in sections of more than two slots with parallel flanks.  FIG. 8  shows for example sections with three immediately adjacent slots  7 , whereby the center slot, designated here by reference numeral  7   a , contains a coil half of two different tooth coils  6 . Optionally, a phase separator  20 , as shown by way of example in  FIG. 6 , may be provided in order to separate the adjacent coil halves. Suitably, the center slot  7   a  is sized wider than the other slots  7 .  FIG. 7  shows the arrangement of sections with four slots  7  which generally follows the concept of the configuration shown in  FIG. 1 . In other words, each of the slots  7  contains half of a tooth coil  6  only.  
         [0028]     Turning now to  FIGS. 3 and 4 , there are shown an application of the lamination piece  1  of  FIG. 1  for manufacturing a stator  5  which is depicted here on the right-hand half by way of a sectional view. As shown on the left-hand half of  FIG. 3 , the lamination stack is provided with the tooth coils  6  which are attached to the teeth  2  only. The teeth  3  have no windings and merely bear upon the tooth coils  6  (see also  FIG. 4 ). The right-hand side of  FIG. 3  shows the position of the tooth coils  6  in the slots  7 . The slots  7  are suitably sealed by slot wedges  21  which are anchored in complementary recesses  24  ( FIG. 2 ) of the teeth  2 ,  3 . The entire lamination stack with embedded tooth coils  6  through the casting process is fitted in a housing  8  which includes fastening means  9  for attachment to a work machine and may also include cooling channels  10 . The laminate section  1  may also have cutouts  20  at the radially outer edge of the laminate section  1  for engagement by the housing  8 .  
         [0029]     As shown in  FIGS. 5 and 6 , the tooth coils  6  may also be placed on coil bobbins  6 . 1  or  6 . 2  which can be secured to the tooth  2  through material union, form-fitting engagement or friction engagement. The coil bobbin  6 . 1  is here formed with the phase separator  20  to separate adjacent halves of two tooth coils  6  in a same slot, such as center slot  7   a.    
         [0030]     While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.