Patent Publication Number: US-2015076955-A1

Title: Dual-out stator lamination for outer rotor motor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an electric motor for use in a machine. More specifically, the present invention concerns a dual-out stator lamination which is particularly suitable for use in a helically wound stator. 
     2. Discussion of the Prior Art 
     Those of ordinary skill in the art will appreciate that electric motors are used in a variety of applications, including, but not limited to, vertical- or horizontal-axis washing machines, electric bicycles, and electric scooters. Fans, generators, and exercise equipment may also use electric motors. 
     Dual-out stator laminations are often employed in motors in an effort to reduce scrap. However, motors having a stator formed of a dual-out lamination traditionally have undesirable performance limitations. 
     SUMMARY 
     According to one aspect of the present invention, a stator formed of a dual-out stator lamination is provided. The stator comprises a generally annular core including a plurality of arcuately spaced apart teeth. Each of the teeth includes a generally radially extending leg and a head extending generally arcuately relative to the leg to present opposite head ends spaced from the leg. The head presents a tooth head height measured in at least a substantially radial direction. Each adjacent pair of the heads is spaced apart by a generally arcuate slot opening distance defined between the adjacent ends of the pair of heads. The ratio of each tooth head height to each adjacent slot opening distance is at least about twenty-eight hundredths (0.28). 
     According to another aspect of the present invention, a method of manufacturing stator cores for use in electric motors is provided. The method comprises the following steps: (a) forming a nested pair of stator laminations from an elongated metal strip, with yokes of the laminations extending at least substantially parallel to one another and each tooth of each lamination being at least partly positioned between an adjacent pair of teeth of the other lamination, wherein each of the teeth includes an elongated leg and a generally transverse head projecting from the leg to present opposite head ends spaced from the leg, wherein the head presents a tooth head height measured in a direction substantially parallel to the leg; (b) separating the stator laminations from each other; and (c) arranging the laminations into separate stator cores, such that a generally arcuate slot opening distance is defined between each adjacent pair of heads, with the ratio of each tooth head height to each adjacent slot opening distance being at least about twenty-eight hundredths (0.28). 
     This summary is provided to introduce a selection of concepts in a simplified form. These concepts are further described below in the detailed description of the preferred embodiments. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
     Various other aspects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments and the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Preferred embodiments of the present invention are described in detail below with reference to the attached drawing figures, wherein: 
         FIG. 1  is a top perspective view of an electric motor constructed in accordance with a first preferred embodiment of the present invention, particularly illustrating the rotor of the motor; 
         FIG. 2  is a partially sectioned top perspective view of the motor of  FIG. 1 , illustrating both the rotor and the stator; 
         FIG. 3  is a perspective view of a pair of dual-out stator laminations in the process of being separated; 
         FIG. 4  is a top view of the stator laminations of  FIG. 3 ; 
         FIG. 5  is a perspective view of the stator core of  FIG. 2  near the completion of its formation using one of the stator laminations of  FIGS. 3 and 4 ; 
         FIG. 6  is a top perspective view of a portion of the stator core of  FIG. 5 , particularly illustrating the preferred tooth geometry; 
         FIG. 7  is a top perspective view of a portion of the stator, particularly illustrating the wire retention wings and the wedge-retaining structures; 
         FIG. 8  is a side view of the stator portion of  FIG. 7 ; 
         FIG. 9  is a top view of the stator portion taken along line  9 - 9  of  FIG. 8 ; 
         FIG. 10  is a side cross-sectional view of the stator portion taken along line  10 - 10  of  FIG. 8 , particularly illustrating the continuity of the overmolding; 
         FIG. 11  is a cross-sectional view of the stator portion taken along line  11 - 11  of  FIG. 8 ; 
         FIG. 12  is a top perspective view of a portion of the stator, particularly illustrating the wedges and the wedge-retaining structures; 
         FIG. 13  is a side view of the stator portion of  FIG. 12 ; 
         FIG. 14  is a top view of the stator portion of  FIGS. 12 and 13 ; 
         FIG. 15  is a cross-sectional view of a portion of the stator portion taken along line  15 - 15  of  FIG. 14 ; 
         FIG. 16  is a cross-sectional view of the stator portion taken along line  16 - 16  of  FIG. 13 ; 
         FIG. 17  is a front perspective view of the stator wedge depicted as part of the first preferred embodiment of the present invention; 
         FIG. 18  is a rear perspective view of the wedge shown specifically in  FIG. 17 ; 
         FIG. 19  is a front perspective view of a portion of a stator constructed in accordance with a second preferred embodiment of the present invention, particularly illustrating a second preferred wedge embodiment; 
         FIG. 20  is a front view of the stator portion of  FIG. 19 ; 
         FIG. 21  is a cross-sectional view of the stator portion taken along line  21 - 21  of  FIG. 20 ; 
         FIG. 22  is front perspective view of the stator wedge shown in  FIGS. 19-21 ; 
         FIG. 23  is a rear perspective view of the wedge shown specifically in  FIG. 22 ; 
         FIG. 24  is a front perspective view of a portion of a stator constructed in accordance with a third preferred embodiment of the present invention, particularly illustrating a third preferred wedge embodiment; 
         FIG. 25  is a top view of the stator portion of  FIG. 24 ; 
         FIG. 26  is a front perspective view of a portion of a stator constructed in accordance with a fourth preferred embodiment of the present invention, particularly illustrating a fourth preferred wedge embodiment; and 
         FIG. 27  is a top view of the stator portion of  FIG. 26 . 
     
    
    
     The drawing figures do not limit the present invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the preferred embodiments. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is susceptible of embodiment in many different forms. While the drawings illustrate, and the specification describes, certain preferred embodiments of the invention, it is to be understood that such disclosure is by way of example only. There is no intent to limit the principles of the present invention to the particular disclosed embodiments. 
     Turning initially to  FIGS. 1 and 2 , a motor  10  is provided. In a preferred embodiment, as illustrated, the motor  10  broadly includes a rotor  12  and a stator  14  spaced partially inside the rotor  12  so that a circumferentially extending gap  16  is defined between the rotor  12  and the stator  14 . 
     As will be discussed in more detail below, the motor  10  is preferably a brushless permanent magnet (BPM) direct drive motor, although it is permissible within the scope of some aspects of the present invention for an alternative motor type to be used. 
     The stator  14  preferably comprises a generally annular core  18  and a plurality of wire coils  20  wound around the core  18 . According to some aspects of the present invention, the core may be arcuately or circumferentially continuous or discontinuous or comprise a plurality of interconnected arcuate sections, although a preferred continuously helically wound embodiment will be described in greater detail below. 
     The core  18  preferably includes a plurality of arcuately spaced apart, radially extending teeth  22 . As will be discussed in more detail below, the teeth  22  are preferably of a laminated design and are shaped in accordance with geometric constraints that are also discussed in greater detail below. It should be understood, however, that it is within the scope of some aspects of the present invention for integrally formed (i.e., a single integral body forming each tooth rather than a stack of laminations) teeth to be provided or for any one or more of a wide variety of tooth shapes to be used. 
     The coils  20  preferably comprise electrically conductive wiring  24 . The wiring preferably comprises aluminum wiring, although copper or another electrically conductive material could also be used without departing from the scope of the present invention. It is noted that the coils  20  and the wiring  24  are shown schematically in the illustrations. 
     Preferably, the stator  14  is configured to be wound using a fly or shed stator winding process. However, it is permissible for an alternately wound stator to be provided without departing from the scope of some aspects of the present invention. 
     As shown in  FIGS. 2 ,  10 , and others, in a preferred embodiment, the stator core  18  is electrically insulated by means of overmolding  26 . As will be discussed in greater detail below, the overmolding  26  preferably covers substantially the entire core  18 . 
     The overmolding  26  preferably comprises a synthetic resin material and most preferably comprises polyethylene, although any one or more at least substantially electrically insulative materials may be used without departing from the scope of the present invention. It is also permissible according to some aspects of the present invention for insulation to be provided additionally or exclusively by one or more discrete insulative structures (e.g. non-conductive tabs or overlays) and/or by at least partial coating of the core with an electrically insulative coating. Such a coating might, for instance, be a powder coating such as Scotchcast™ Electrical Resin 5555, available from 3M′. 
     As best shown in  FIG. 2 , the overmolding  26  preferably defines wire routing structure  28  and stator mounting structure  30 . As best shown in  FIGS. 2 and 10 , the wire routing structure  28  preferably comprises concentric inner and outer annular-shaped walls  32  and  34 , respectively, projecting axially relative to the core  28 . It is permissible, however, for alternate wire routing structures to be defined. The walls might be non-concentric, for instance, or routing might be achieved via hooks and portals rather than the preferred walls. Furthermore, according to some aspects of the present invention, the wire routing structure might be partially or entirely discrete from the overmolding. 
     The stator mounting structure  30  preferably comprises a plurality of arcuately spaced apart fastener-receiving tabs  36 . As shown in  FIG. 2 , in a preferred embodiment, three such tabs  36  are provided and are evenly spaced apart. A fastener-receiving opening  38  is provided in each of the tabs  36 . Fasteners (not shown) inserted through the fastener-receiving openings  38  may be used to fix the stator  14  to the machine, with the mounting structure  30  thus supporting the stator  14  thereon. It is permissible according to some aspects of the present invention, however, for alternatively designed or defined stator mounting structure to be present. The mounting structure might include clips for instance, rather than requiring the use of discrete fasteners; or it might be partially or entirely discrete from the overmolding. 
     As best shown in  FIGS. 1 and 2 , the rotor  12  preferably includes a rotor can  40  that includes a radially projecting spoked base  42 . The rotor can  40  further includes a circumferentially extending outer support wall  44  and a discontinuous, circumferentially extending inner support wall  46 . The inner wall  46  preferably comprises a plurality of substantially rectangular columns  48  (one shown in  FIG. 2 ) that are preferably formed during the molding of the rotor can  40 . 
     In the illustrated embodiment, both of the support walls  44 , 46  project axially upwardly from the base  42 , with the base  42  and the support walls  44 , 46  thus defining a channel  50  therebetween. An annular top wall  52  extends between the inner and outer support walls  44 , 46  to enclose the channel  50 , with the exception of a plurality of windows  54  (one shown in part in  FIG. 2 ), each of which is bounded by a pair of the columns  48 , the base  42 , and the top wall  52 . 
     In the illustrated preferred embodiment, the base  42  of the rotor can  40  also preferably includes a plurality of ventilation slots  56  and ventilation apertures  58 . It is also preferable that a plurality of support ribs  60  are formed as part of the base  42 . In addition to functioning as structural supports, at least a portion of the ribs  60  may also be configured in such a manner as to provide cooling assistance for the motor  10  by disturbing nearby air. 
     The rotor can  40  of the first preferred embodiment preferably comprises a plastic material such as polypropylene, although any one or more of a variety of other materials may be used without departing from the scope of the present invention. It is also permissible and in some instances preferred that the material of the rotor can include reinforcing fibers such as glass fibers, although use of other reinforcement techniques or use of no additional reinforcement is within the scope of the present invention. 
     As best shown in  FIG. 2 , the rotor  12  preferably includes a plurality of arcuately spaced apart magnets  62  positioned in the windows  54 . The magnets  62  are preferably permanent magnets. Most preferably, the magnets  62  comprise ferrite. Although high grade ferrite magnets may be used, lower grade magnets are also permissible. For instance, grade six (6) ferrite magnets are permissible and, according to some aspects of the present invention, preferred. 
     The rotor  12  also preferably includes a backing ring  64  extending circumferentially outside the magnets  62 . The backing ring  64  preferably comprises iron, although other suitable materials may be used. 
     Preferably, as best shown in  FIG. 1 , the base  42  is configured for connection of the rotor can  40  to a rotatable shaft (not shown) via a coupler  66 . Preferably, such engagement is effected by the interaction of the splines on the shaft and inner splines  68  on the coupler  66 , although other engagement mechanisms fall within the scope of the present invention. For instance, interference screws, press fits, or adhesives could all be used, either singly or in combination. 
     The coupler  66  also engages the base  42  of the rotor can  40 , such that the rotor can  40 , the coupler  66 , and the shaft preferably all rotate together about a single axis of rotation. Although a single axis of rotation is preferable, it is with the scope of the present invention for multiple axes of rotation to be defined. 
     Additional details of an exemplary rotor can be found in U.S. Pat. No. 8,482,176, assigned of record to the assignee of the present invention and hereby incorporated herein by reference in its entirety. 
     It is noted that, in addition to the permissible variations described above, certain more significant rotor variations may be permissible without departing from the scope of the present invention. The rotor might be an inner rotor, for instance, or be a spoked rotor in which the magnets are alternately circumferentially arranged with pole pieces. Such a spoked rotor is described in more detail in U.S. patent application Ser. No. 13/911,882, filed Jun. 6, 2013, assigned of record to the assignee of the present invention and hereby incorporated herein by reference in its entirety. 
     Stator Formation and Tooth Shapes 
     As noted previously, in a preferred embodiment, the stator  14  includes a helically wound stator core  18 , best shown in  FIG. 5 . The core  18  is preferably formed from a dual-out stator lamination  70 , a nested pair of which is illustrated in  FIGS. 3 and 4 . Each lamination  70  preferably includes a yoke portion  72  and a plurality of spaced apart tooth portions  74 . As shown, the nested pair of laminations  70  is preferably formed from an elongated metal strip  76 , with each of the yoke portions  72  extending at least substantially parallel to one another and with each of the tooth portions  74  being at least partly positioned between an adjacent pair of tooth portions  74  of the other lamination  70 . 
     Preferably, the laminations  70  are punched at least substantially simultaneously from the metal strip  76 , although alternative methods of defining the laminations are permissible according to certain aspects of the present invention. Non-simultaneous punching may also be permissible. 
     As will be discussed in further detail below, each tooth portion  74  preferably includes an elongated leg portion  78  having circumferentially opposed sides  80  and  82  and defining a radially outermost end  84 . Each leg portion  78  preferably has a substantially straight, rectangular shape, although non-straight leg portions or segmented leg portions are permissible according to some aspects of the present invention. 
     Each tooth portion  74  preferably further includes a generally transverse head portion  86  projecting generally arcuately from the radially outermost end  84  of the respective leg portion  78  to present opposite head portion ends  88  and  90  spaced from the leg portion  78 . However, it is possible for the positioning of the head portions  86  relative to the leg portions  78  to vary from the exemplary arrangement described above. For instance, the head portions might suitably be positioned adjacent a radially innermost end of the leg portions if an inner rotor motor is desired. 
     As illustrated, during fabrication of the laminations, the head portion ends  88  and  90  of each tooth portion  74  of one of the laminations  70  are preferably positioned immediately adjacent the opposed sides  80 , 82  of the leg portions  78  of the adjacent pair of tooth portions  74  of the other lamination  70 . In this manner, scrap from the strip  76  is at least substantially minimized after the punching process (or other lamination-defining process) is complete. 
     After the laminations  70  have been defined, the laminations  70  are separated from each other, and each is arranged into a separate stator core such as the stator core  18 . Preferably, such arrangement is via helical winding, wherein the lamination  70  is continuously coiled upon itself to define a plurality of layers  92 . That is, the yoke portion  72  preferably defines a continuous helical coil upon completion of the fabrication process, while each of the tooth portions  74  are brought into axial alignment with others of the tooth portions. 
     As best shown in  FIG. 6 , a plurality of spaced apart notch portions  94  are formed in the yoke portion  72 . The notch portions  94  preferably facilitating bending of the lamination  70  into the annular shape as required during the coiling process. It is permissible, however, for slits or other means of facilitating bending to be provided in addition to or as an alternative to notches of the sort shown in  FIG. 6  and others. Furthermore, the lamination  70  may alternatively be formed of a sufficiently flexible material to eliminate the need for notches, slits, or other structure for facilitating bending of the lamination. 
     Preferably, separation of the laminations  70  and the winding of each lamination  70  to form a core, such as the core  18 , occurs at least substantially simultaneously. For instance, an aft end of a first lamination  70  might still be engaged with the aft end of a second lamination  70  in the strip  76 , while the fore end of the first lamination  70 , having already been separated from the fore end of the second lamination  70 , is being helically wound. 
     Although a helically wound core  18  as described above is preferred, it is permissible according to some aspects of the present invention for any of a variety of alternative dual-out laminated stator formation techniques to be used. For instance, the core might include a plurality of discrete, stacked dual-out laminations. 
     As best shown in  FIGS. 5 and 6 , after assembly of the core  18 , the yoke portions  72  align to collectively define a yoke  96  having notches  98  defined therein. Furthermore, as also illustrated in  FIGS. 5 and 6 , the tooth portions  74  align to collectively define a plurality of teeth  22  (previously introduced). In keeping with the above, the leg portions  78  define legs  100  each having circumferentially opposed sides  102 , 104  and defining a radially outermost end  106 . Each leg  100  preferably has a substantially straight, rectangular shape, although non-straight legs or segmented legs are permissible according to some aspects of the present invention. The head portions  86  define generally transverse heads  108  projecting generally arcuately from the radially outermost ends  106  of the corresponding legs  100  to present opposite head ends  110  and  112  spaced from the legs  100 . However, as for the head portions  86 , it is of course possible for the positioning of the heads  108  relative to the legs  100  to vary from the exemplary arrangement described above. For instance, the heads might suitably be positioned adjacent a radially innermost end of the legs if an inner rotor motor is desired. 
     As best shown in  FIGS. 5 and 6 , a plurality of slots  114  are preferably defined by the teeth  22 . As shown in  FIG. 6 , an associated generally arcuate slot opening  116  having a generally circumferential dimension referred to herein as a slot opening distance  118  is preferably defined between each adjacent pair of heads  108 . More particularly, each slot opening  116  is preferably defined between adjacent head ends  110  and  112  on adjacent teeth  22 . 
     Preferably, the teeth  22  are evenly spaced apart, such that the slot opening distances  118  are uniform. According to some aspects of the present invention, however, non-uniform spacing is permissible. 
     The previously mentioned coils  20  are preferably received in the slots  114 . 
     In a preferred embodiment, the stator  14  includes twenty-seven (27) teeth  22  defining twenty-seven (27) slots  114  therebetween, while the rotor  12  defines thirty (30) poles. However, it is permissible according to some aspects of the present invention for alternate slot-pole ratios and/or numbers to be used. 
     Preferably, each tooth head  108  presents an at least substantially continuous, curved radially outermost face  120 . The outermost faces  120  preferably cooperatively present the outer radial periphery of the core  18 , with the periphery thus being discontinuous. Each tooth head  108  further preferably presents a discontinuous, generally flat radially innermost face  122  extending on either side of the respective leg  100 . 
     As noted previously, the overmolding  26  preferably covers at least substantially the entire core  18 . Most preferably, at least part of the radially outermost face  120  of each tooth  22  is devoid of the overmolding  26  and thereby exposed. Thus, the aforementioned gap  16  (see  FIG. 2 ) is defined at least substantially by the teeth  22  (or more particularly, the outermost faces  120 ) and the rotor  12 . 
     In a preferred embodiment and as illustrated in  FIG. 6 , each tooth head  108  defines a tooth head height  124  measured in at least a substantially radial direction. Preferably, the tooth head height  124  is at least substantially constant between the head ends  110  and  112 , with minor variations being inherent due to the preferred curvature of the outermost face  120  in contrast to the flatness of the innermost face  122 , 
     Each tooth head  108  also preferably presents a tooth head width  126  defined between the head ends  110  and  112  (see  FIG. 6 ). 
     As is readily understood by those of ordinary skill in the art, electric motor design often requires a balancing of desired motor cost, motor performance, and motor envelope (i.e., the space designated for the motor in or on the machine). Magnet quality, wiring material, core height, coil turns, and other parameters may be varied to achieve an optimal balance, with variations in each parameter generally resulting in both positive and negative consequences. 
     In the preferred embodiment, for instance, the slots  114  are large enough to enable use of a high number of turns in the coils  20 , which in turn enables use of lower-cost aluminum wiring  24  rather than higher-cost copper wiring. However, high-speed efficiency requirements were initially unmet when large slots and aluminum wiring as described above were tested with an at least substantially conventional motor design. 
     Fortunately, it was determined that certain variations in tooth shape could be implemented to unexpectedly provide critical benefits. More particularly, such variations were found to result in a surprising decrease in cogging and increase in inductance and stator reactance. Demagnetization capability was also improved. More particularly, improved performance characteristics were achieved when the ratio of each tooth head height  124  to each adjacent slot opening distance  118  was at least about twenty-eight hundredths (0.28) and when the ratio of each tooth head width  126  to each adjacent slot opening distance  118  was less than about one and thirty-one hundredths (1.31). 
     Although any dimensional characteristics meeting the above requirements may be suitable, in a preferred embodiment, a core  18  having an axial height of twenty-eight (28) mm, an inner diameter of ninety and five tenths (90.5) mm, and an outer diameter of two hundred eight-four (284) mm is provided. The coils  20  preferably comprise one hundred forty-eight (148) turns of Number Eighteen (#18.0) aluminum wiring  24 . The motor  10  includes twenty-seven (27) slots and thirty (30) poles. Each tooth  22  has a tooth head width  126  of fifteen and ninety thousandths (15.090) mm and a tooth head height  124  of six and one hundred seventy-seven thousandths (6.177) mm. The slot opening distance  118  is preferably seventeen and fifty-four thousandths (17.054) mm. 
     Wire Retention Wings 
     As best shown in  FIGS. 7-9  and  11 , the overmolding  26  preferably defines a plurality of wire retention wings  128 . More particularly, a pair of wire retention wings  128  preferably extends at least substantially circumferentially outwardly relative to each of the teeth  22 . It is noted, however, that it is permissible according to some aspects of the present invention for one or more of the wings to be discrete from the overmolding. Furthermore, axially extending components of the wings may be additionally provided without departing from the scope of the present invention. 
     Preferably, each of the wings  128  comprises a wall  130  projecting circumferentially outwardly from one of the head ends  110 , 112  of the teeth  22 . As best shown in  FIGS. 7 ,  9 , and  11 , it is preferable that each wing  128  extends from one of the head ends  110 , 112  immediately adjacent the outermost face  120  of the corresponding tooth  22 . 
     In a preferred embodiment, each of the wings  128  presents a generally radial wing height  132 . Preferably, the wing height  132  is less than the previously discussed tooth head height  124 . The walls  130  preferably restrict radially outward shifting of the wiring  24  of the coils  20 , with the relative dimensioning (more particularly, the height  132 ) of the wings  128  and their positioning adjacent the outermost faces  120  maximizing the space available for the coils  20  and the wiring  24 . (As will be readily understood by those of ordinary skill in the art, although the schematic nature of the coil illustrations shows symmetrical, well defined coils, wiring could feasibly extend radially outwardly at the outer layers of the coils so as to fill the currently illustrated space between the coils and the wings.) 
     In a preferred embodiment, each tooth  22  presents opposite, axially spaced apart endmost surfaces  134  and  136 . Each of the wire retention wings  128  preferably extends at least substantially continuously between the endmost surfaces  134  and  136  of the teeth  22 . However, it is permissible according to some aspects of the present invention for discontinuous extension to occur for one or more wings. 
     As illustrated, the wings  128  are preferably arranged in pairs, with the wings  128  of each pair extending toward one another from adjacent ones of the teeth  22 . Preferably, the wings  128  of the each pair are circumferentially spaced from one another by an axially extending opening or gap  138 . The gap  138  preferably enables access of equipment during fly or shed winding of the stator  14 . It is permissible according to some aspects of the present invention, however, for the wings to extend such that the gap is too small for such access or such that the wings of each pair contact or circumferentially overlap each other. 
     Tooth-Stabilizing Wedges 
     In a preferred embodiment, as illustrated in FIGS.  2  and  12 - 18 , a plurality of stator wedges  140  are provided. Each wedge  140  is received within a corresponding one of the slot openings  116  defined between the head ends  110 , 112  of the teeth  22  and is preferably compressibly retained in the slot opening  116  by a pair of wedge-retaining structures  142 . More particularly, the wedges  140  and the wedge-retaining structures  142  are configured to be resiliently compressed to thereby maintain a force against the teeth  22 , which reduces tooth movement (e.g., vibration) and consequently noise. Furthermore, radial and axial movement of the wedges  140  relative to the core  18  is at least substantially prevented. 
     As best shown in  FIGS. 7 ,  8 ,  12 ,  13 , and  15 , the wedge-retaining structures  142  are preferably at least in part fixed relative to the core  18  and most preferably each comprises a pair of the walls  130  previously discussed in relation to the wire retention wings  128 . It is permissible according to some aspects of the present invention, however, for the walls to function in a manner exclusive of wire retention. 
     As also discussed above in relation to wire retention, the walls  130  preferably extend generally circumferentially from respective ones of the head ends  110 , 112  so as to project into corresponding ones of the slot openings  116 . Furthermore, the wedge-retaining structures  142 , including the walls  130 , are preferably defined by the aforementioned overmolding  26 . It is permissible according to some aspects of the present invention, however, for the wedge-retaining structures to be alternately defined. For instance, the wedge-retaining structures might be fixed to the core in another manner (e.g., if the stator is not provided with the overmolding). 
     Each wall  130  preferably presents a first axial wall end  144 , an axially opposite second wall end  146 , and a pair of wall surfaces  148 , 150  extending between the walls ends  144 , 146  and facing generally radially opposite directions. 
     As discussed previously with respect to the preferred wire retention function, the walls  130  are preferably spaced apart from each other to define an axially extending opening or gap  138  therebetween. In a preferred embodiment and as best illustrated in  FIGS. 2 ,  7 ,  8 ,  12 ,  13 , and  15 , the walls  130  preferably further define a constricted region  152  of the gap  138 . As will be discussed in greater detail below, however, it is permissible according to some aspects of the present invention for the gap to be devoid of a constricted region. 
     Each wall  130  further preferably presents a pair of axially oppositely facing shoulders  154 , 156  defined along the gap  138  at opposite ends of the constricted region  152 . However, according to some aspects of the present invention, the walls might suitably be devoid of shoulders or include alternately positioned shoulders. 
     The wedges  140  are preferably dimensioned and configured to move axially into corresponding ones of the gaps  138 , as illustrated in  FIGS. 12 and 13 . 
     As best shown in  FIGS. 17 and 18 , each wedge  140  preferably includes a first axial wedge end  158  and an axially opposite second wedge end  160 . Furthermore, each wedge  140  preferably includes a first locking plate  162  adjacent the first axial wedge end  156 , a second locking plate  164  axially and radially spaced relative to the first locking plate  162 , and a third locking plate  166  adjacent the second axial wedge end  160  and in at least substantial radial alignment with the first locking plate  162 . That is, three (3) axially and radially staggered locking plates  162 , 164 , 166  are preferably provided. It is permissible, however, for more or fewer locking plates to be provided without departing from the scope of the present invention. 
     The first locking plate  162  preferably presents a first pair of wedge surfaces  168 , 170  that face generally radially opposite directions. The second locking plate  164  preferably presents a second pair of wedge surfaces  172 , 174  that face generally radially opposite directions. The third locking plate  166  preferably presents a third pair of wedge surfaces  176 , 178  that face generally radially opposite directions. 
     The locking plates  162 , 164 , 166  are each preferably rectangular in shape, although any one or more of a variety of shapes may be used without departing from the scope of the present invention. Circular plates might be used, for instance, or a combinations of triangular plates and rectangular plates could be provided. As illustrated, size variations between the plates  162 , 164 , 166  are also permissible, although it is preferred that the first and third plates  162  and  166 , respectively, are at least substantially identical in size. 
     As best shown in  FIGS. 17 and 18 , each of the plates  162 , 164 , 166  is preferably mounted on a generally axially extending bar  180 , which preferably bisects the surfaces  168 ,  174 , and  176 . 
     Although the bar  180  preferably presents a constant, generally rectangular cross-section along at least a substantial portion of its length, the bar  180  preferably includes projections  182 , 184  that extend generally circumferentially on either side of the rectangular portions of the bar  180 . 
     As best illustrated in  FIGS. 14 and 16 , during and after insertion of each wedge  140  into the corresponding slot opening  116 , the wedge surface  168  of the first locking plate  162  preferably engages the wall surface  150  of each of the adjacent walls  130 . Similarly, the wedge surface  174  of the second locking plate  164  preferably engages the wall surface  148  of each of the adjacent walls  130 , and the wedge surface  176  of the third locking plate  166  preferably engages the wall surface  150  of each of the adjacent walls  130 . 
     Furthermore, as best shown in  FIG. 15 , the projections  182 , 184  preferably engage corresponding ones of the shoulders  154 , 156  to restrict relative axial movement between the wedge-retaining structure  142  and the corresponding wedge  140 . More particularly, each of the projections  182 , 184  preferably has a circumferential dimension greater than that of the constricted region  152  of the gap  138  such that, absent the application of a significant axial force, the projections  182 , 184  cannot pass axially through the constricted region  152 . 
     Preferably, the wedges  140  are at least substantially symmetric along a transverse (i.e., generally circumferential) axis, such that insertion into the gap  138  may be led by either the first axial wedge end  158  or the second axial wedge end  160 . Such symmetry provides advantageous flexibility during assembly of the stator  14 . 
     A second preferred embodiment of the present invention is illustrated in  FIGS. 19-23 . It is initially noted that, with certain exceptions to be discussed in detail below, many of the elements of the second preferred embodiment are the same as or very similar to those described in detail above in relation to the first preferred embodiment. Therefore, for the sake of brevity and clarity, redundant descriptions and numbering will be generally avoided here. Unless otherwise specified, the detailed descriptions of the elements presented above with respect to the first preferred embodiment should therefore be understood to apply at least generally to the second preferred embodiment, as well. 
     As best shown in  FIGS. 19-21 , in a second preferred embodiment, a stator  210  including, among other things, a core  212 , a plurality of wedges  214 , and a plurality of wedge-retaining structures  216  is provided. The wedge retaining structures  216  preferably include walls  218  defining first and second axial wall ends  220  and  222 , respectively, and a gap  224  configured to receive corresponding ones of the wedges  214 . However, in contrast to the walls  130  of the first preferred embodiment, the walls  218  of the second preferred embodiment preferably do not define a constricted region of the gap  224 . Such a region could be defined, however, without departing from the scope of the present invention. 
     In a similar manner to the wedges  140  of the first preferred embodiment, the wedges  214  of the second preferred embodiment also preferably include a plurality of locking plates arranged along a bar. More particularly, as best shown in  FIGS. 22 and 23 , a first locking plate  226 , a second locking plate  228 , a third locking plate  230 , a fourth locking plate  232 , and a fifth locking plate  234  are preferably mounted in a radially and axially sequentially staggered manner along a bar  236 . 
     As best shown in  FIGS. 22 and 23 , each wedge  214  preferably presents a first axial wedge end  238  and an axially opposite second wedge end  240 . Each wedge  214  preferably further includes a catch  242  adjacent the first wedge end  238 . The catch  242  preferably includes a pair of tabs  244 , 246 , each of which extends in a generally circumferentially outward direction. The catch  242  is preferably configured to latchingly engage the first wall ends  220  of the corresponding walls  218  via engagement of the tabs  244 , 246  with respective ones of the first wall ends  220 . 
     Preferably, each of the wedges  214  further includes an end plate  248  adjacent the second wedge end  240 . The end plate  248  extends at least substantially perpendicularly to the locking plates  226 , 228 , 230 , 232 , 234  and is preferably configured to engage the second wall ends  222  of the corresponding walls  218 . 
     Although the end plate  248  and the catch  242  are preferred components of each of the wedges  214 , it is noted that other means of retaining each wedge relative to the core may be used without departing from the scope of some aspects of the present invention. 
     A third preferred embodiment of the present invention is illustrated in  FIGS. 24 and 25 . It is initially noted that, with certain exceptions to be discussed in detail below, many of the elements of the third preferred embodiment are the same as or very similar to those described in detail above in relation to the first and second preferred embodiments. Therefore, for the sake of brevity and clarity, redundant descriptions and numbering will be generally avoided here. Unless otherwise specified, the detailed descriptions of the elements presented above with respect to the first and second preferred embodiments should therefore be understood to apply at least generally to the third preferred embodiment, as well. 
     As shown in  FIGS. 24 and 25 , in a third preferred embodiment, a stator  310  including, among other things, a core  312 , a plurality of wedges  314 , and a plurality of wedge-retaining structures  316  is provided. The wedge retaining structures  316  each preferably include first and second walls  318   a , 318   b , respectively. The wedge-retaining structures  316  further preferably define an axially extending gap  320  configured to receive corresponding ones of the wedges  314 . 
     Like the walls  218  of the second preferred embodiment, the walls  318   a , 318   b  of the third preferred embodiment preferably do not define a constricted region of the gap  320 . Such a region could be defined, however, without departing from the scope of the present invention. 
     The stator  310  preferably further comprises a plurality of hinges  322 . Each hinge  322  preferably intercouples one of the wedge-retaining structures  316  and a corresponding one of the wedges  314 . Each of the wedges  314  is thus swingable back and forth between an open position, in which the gap  320  is at least substantially unobstructed in a generally radial direction, and an operational position in which the respective wedge  314  spans the gap  320 . Furthermore, when in the operational position, each wedge  314  is compressibly retained between adjacent ones of the wedge-retaining structures  316 . The open and operational positions, as well as an intermediate position, are illustrated in both of  FIGS. 24 and 25 . 
     In a preferred embodiment, each hinge  322  intercouples one of the wedges  314  with just the corresponding first wall  318   a . As will be discussed in greater detail below, however, alternative hinging configurations are permissible without departing from the scope of some aspects of the present invention. Hinges might be associated with both walls of each wedge-retaining structure, for instance, with the wedges themselves comprising a plurality of segments each corresponding to one of the hinges. The coupling might also alternatively be between each wedge and the second wall or be with the first wall for some wedges and the second wall for other wedges. 
     Preferably, each wedge  314  and the corresponding second wall  318   b  cooperatively define complemental locking structure  324  for retaining the respective wedge  314  in the operational position. More particularly, as shown in  FIGS. 24 and 25 , each wedge  314  preferably includes an axially extending catch  326  configured to latchingly engage the wall  318   b  via a generally circumferentially extending tab  328 . Preferably, the catch  326  extends at least substantially along the entire axial length of the wedge  314  and engages the wall  318   b  along at least substantially its entire axial length. It is permissible, however, for any one or more of a variety of locking mechanisms to be used without departing from the scope of the present invention. A catch might be provided on the wall rather than on the wedge, for instance, or multiple catches might be provided. A single catch extending only along a portion of the axial lengths of the corresponding wedge and wall might be provided, a hook and loop structure might be used, or adhesives might act as or complement the locking structure. 
     Preferably, the stator  310  includes electrically insulative overmolding  330  molded over at least a portion of the core  312 . The overmolding  330  preferably defines both the wedge-retaining structures  316  and, in contrast to the first and second preferred embodiments, the wedges  314  themselves. The overmolding  330  also preferably defines the hinges  322  through presentation of radially thinned regions. However, it is permissible according to some aspects of the present invention for the wedges, hinges, and/or wedge-retaining structures to be discretely formed. 
     A fourth preferred embodiment of the present invention is illustrated in  FIGS. 26 and 27 . It is initially noted that, with certain exceptions to be discussed in detail below, many of the elements of the fourth preferred embodiment of the present invention are the same as or very similar to those described in detail above in relation to the first, second, and third preferred embodiments. Therefore, for the sake of brevity and clarity, redundant descriptions and numbering will be generally avoided here. Unless otherwise specified, the detailed descriptions of the elements presented above with respect to the first, second, and third preferred embodiments should therefore be understood to apply at least generally to the fourth preferred embodiment, as well. 
     As shown in  FIGS. 26 and 27 , in a fourth preferred embodiment, a stator  410  including a plurality of wedges  412  and a plurality of wedge-retaining structures  414  is provided. The wedge retaining structures  414  each preferably include first and second walls  418   a , 418   b , respectively. The wedge-retaining structures  414  further preferably define an axially extending gap  418  configured to receive corresponding ones of the wedges  412 . 
     Like the walls  218  of the second preferred embodiment and the walls  318   a , 318   b  of the third preferred embodiment, the walls  416   a , 416   b  of the fourth preferred embodiment preferably do not define a constricted region of the gap  418 . Such a region could be defined, however, without departing from the scope of the present invention. 
     Each wedge  412  preferably includes a pair of panels  420   a , 420   b  hingedly coupled to respective ones of the walls  416   a , 416   b  via hinges  422   a , 422   b  and cooperatively spanning the gap  418  when the respective wedge  412  is in an operational position. The panels  420   a , 420   b  are compressibly retained between adjacent ones of the wedge-retaining structures  414  when in the operational position. 
     As shown in  FIGS. 26 and 27 , the panels  420   a , 420   b  are also moveable to an open position, in which the gap  418  is at least substantially unobstructed in a generally radial direction, and through intermediate positions between the open and operational positions 
     Preferably, when in the operational position, each of the panels  420   a , 420   b  spans at least substantially the entirety of the respective gap  418  in a generally axial direction and about half of the gap  418  in a generally circumferential. However, it is permissible according to some aspects of the present invention for non-equal spans to be provided by the panels. It is also permissible for the panels to each span at least substantially the entirety of the gap, with the panels thus overlapping each other. Still further, the panels might be alternately oriented so as to each span half of the gap in a generally axial direction and at least substantially the entirety of the gap in a generally circumferential direction. Furthermore, more than two panels might be provided, with equal or non-equal spanning being provided by the more than two panels in any of a variety of manners, including but not limited to those described above. It is also within the scope of some aspect of the present invention for multi-panel embodiments to be provided in which the panels are hingedly interconnected with only one wall of each wedge-retaining structure. 
     Preferably, the panels  420   a , 420   b  of each wedge  412  cooperatively define complemental locking structure  424  for retaining the panels  420   a , 420   b  (and thus the wedge  412 ) in the operational position. More particularly, as shown in  FIGS. 26 and 27 , each panel  420   a  preferably includes a rounded projection  426  extending continuously axially along at least substantially the entire length thereof. Each panel  420   b  preferably includes a complementary rounded groove  428  extending continuously axially along at least substantially the entire length thereof. The projections  426  are latchingly received in the grooves  428  when the panels  420   a , 420   b  are pivotably shifted into the operational position. 
     Although the above-described locking structure  424  is preferred, it is within the scope of the present invention for any one or more of a variety of locking structures to be used. These include but are not limited to variations in continuity, number, and form based on those discussed above with respect to the third preferred embodiment. 
     Although the above description presents features of preferred embodiments of the present invention, other preferred embodiments may also be created in keeping with the principles of the invention. Furthermore, these other preferred embodiments may in some instances be realized through a combination of features compatible for use together despite having been presented independently as part of separate embodiments in the above description. 
     The preferred forms of the invention described above are to be used as illustration only and should not be utilized in a limiting sense in interpreting the scope of the present invention. Obvious modifications to the exemplary embodiments, as hereinabove set forth, could be readily made by those skilled in the art without departing from the spirit of the present invention. 
     The inventor hereby states his intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of the present invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention set forth in the following claims.