Patent Publication Number: US-2023136725-A1

Title: Overlapped end caps for stator core

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 16/862,641, filed Apr. 30, 2020, which claims benefit of U.S. Provisional Patent Application No. 62/948,683, filed Dec. 16, 2019, and entitled OVERLAPPED END CAPS FOR STATOR CORE, the entire disclosure of each of which is hereby incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a stator for use in an electric motor. More particularly, the present invention concerns electrical insulation for a stator core for use in the stator of an electric motor. 
     2. Discussion of the Prior Art 
     Electric motors often include a stator core and insulation associated with the stator core. For instance, electrically insulative end caps may be provided to overlie portions of the teeth of the stator core. Liners, such as those formed of Mylar, are often used to insulate portions of the teeth that are not fully insulated by the end caps. 
     Winding of stator cores often provides numerous challenges. Due to the presence of numerous structures in the vicinity of winding slots, for instance, catching of wires during the winding process may occur, leading to poor coil consistency, wire damage, and/or lost time due to the need for corrective efforts. 
     SUMMARY 
     According to one aspect of the present invention, a set of interchangeably configurable end caps is provided for electrically insulating a variety of stator cores. The stator cores include at least a first stator core presenting a first axial stack height and a second stator core presenting a second axial stack height that is different than the first axial stack height. The set of end caps comprises a first first-type end cap including an axially extending first first-type skirt having an axial first first-type skirt length, a first second-type end cap including an axially extending first second-type skirt having an axial first second-type skirt length, and a second second-type end cap including an axially extending second second-type skirt having an axial second second-type skirt length that is different than the first second-type skirt length. The first and second second-type end caps are interchangeably pairable with the first first-type end cap, with the first and second second-type skirts configured to extend toward the first first-type skirt, such that a first cumulative axial extent as cooperatively presented by the paired first first-type skirt and first second-type skirt is different than a second cumulative axial extent as cooperatively presented by the paired first first-type skirt and second second-type skirt. The first cumulative axial extent corresponds to the first axial stack height and the second cumulative axial extent corresponds to the second axial stack height. 
     According to another aspect of the present invention a stator is provided. The stator comprises a generally toroidal core presenting axially opposed first and second core faces, a first end cap fitted to the core, a second end cap fitted to the core, and wiring wound about the core. The end caps extend toward each other and between the upper and lower core faces to at least in part encompass the core. The end caps are at least in part disposed between the wiring and the core. The end caps cooperatively define an axially extending trough receiving at least a portion of the wiring. The end caps cooperatively define a generally radially projecting, generally axially extending wire barrier defining a generally circumferential margin of the trough. The wire barrier includes axially opposed ends, wherein the first end cap defines a first one of the ends and the second end cap defines a second one of the ends. Each of the ends forms a respective rounded winding ramp configured to smoothly guide wiring into the trough during wiring of the core. 
     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 a fully assembled stator according to a preferred embodiment of the present invention, with a coil and a pair of end caps removed from one of the stator teeth; 
         FIG.  2    is a bottom perspective view of the stator of  FIG.  1   ; 
         FIG.  3    is a perspective view of the core and end caps of the stator of  FIGS.  1  and  2   , in a straight configuration and prior to winding; 
         FIG.  4    is a second perspective view of the core and end caps of  FIG.  3   ; 
         FIG.  5    is an enlarged, exploded perspective view of a portion of the core and end caps as shown in  FIG.  3   , particularly illustrating the relationship between a single tooth and its associated upper and lower end caps; 
         FIG.  6    is an enlarged perspective view of an upper end cap; 
         FIG.  7    is an alternative perspective view of the upper end cap of  FIG.  6   ; 
         FIG.  8    is another perspective view of the upper end cap of  FIGS.  6  and  7   ; 
         FIG.  9    is yet another perspective view of the upper end cap of  FIGS.  6 - 8   ; 
         FIG.  10    is still another perspective view of the upper end cap of  FIGS.  6 - 9   ; 
         FIG.  11    is an enlarged perspective view of a lower end cap; 
         FIG.  12    is an alternative perspective view of the lower end cap of  FIG.  11   ; 
         FIG.  13    is another alternative perspective view of the lower end cap of  FIGS.  11  and  12   ; 
         FIG.  14    is an enlarged perspective view of an engaged pair of upper and lower end caps; 
         FIG.  15    is an alternative perspective view of the engaged pair of upper and lower end caps of  FIG.  14   ; 
         FIG.  16    is a side view of a single tooth and the engaged pair of upper and lower end caps of  FIGS.  14  and  15   ; 
         FIG.  17    is a cross-sectional view of the single stator tooth and the engaged pair of upper and lower end caps of  FIG.  16   , taken along line  17 - 17  of  FIG.  16   ; 
         FIG.  18    is an additional cross-sectional view of the single stator tooth and the engaged pair of upper and lower end caps of  FIG.  16   , taken along line  18 - 18  of  FIG.  16   ; 
         FIG.  19    is a bottom view of a single stator tooth and a lower end cap; 
         FIG.  20    is a cross-sectional view of a single stator tooth and both upper and lower end caps, taken along line  20 - 20  of  FIG.  19   ; 
         FIG.  21    is a side view of the upper end caps of a set of interchangeably pairable end caps; and 
         FIG.  22    is a side view of the lower end caps of the set of interchangeably pairable end caps. 
     
    
    
     The drawing figures do not limit the present invention to the specific embodiments disclosed and described herein. While the drawings do not necessarily provide exact dimensions or tolerances for the illustrated structures or components, the drawings are to scale with respect to the relationships between the components of the structures illustrated in the drawings. 
     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. 
     Furthermore, unless specified or made clear, the directional references made herein with regard to the present invention and/or associated components (e.g., top, bottom, upper, lower, inner, outer, etc.) are used solely for the sake of convenience and should be understood only in relation to each other. For instance, a component might in practice be oriented such that faces referred to as “top” and “bottom” are sideways, angled, inverted, etc. relative to the chosen frame of reference. 
     Motor Overview 
     In a preferred embodiment of the present invention, a motor is provided. The motor preferably includes a stator  10  and a rotor 
     (not shown) rotatable about an axis. The motor further preferably includes a housing (not shown) defining a motor chamber (not shown). The stator  10  and the rotor are at least substantially received in the motor chamber. 
     In an assembled form (see  FIGS.  1  and  2   ), the stator  10  preferably includes a generally toroidal stator core  12  and a plurality of coils  14  wound about the stator core  12 . The stator core  12  is preferably a laminated stator core, although it is permissible for the stator core to be non-laminated. The stator core  12  preferably comprises a ferromagnetic material such as steel, although use of any one or more electrically conductive materials is permissible without departing from the scope of the present invention. 
     In the assembled form, the stator core  12  preferably includes a plurality of arcuately spaced apart teeth  16 . In a preferred embodiment, each of the teeth  16  includes a generally circumferentially extending yoke  18 , a generally radial arm  20  extending from the yoke  18  and having an outer end  22   a  adjacent the yoke  18 , and a crown  24  extending generally circumferentially from an inner end  22   b  of the arm  22 . 
     The stator  10  preferably at least substantially circumscribes the rotor, such that the motor is an inner rotor motor. Certain aspects of the present invention are applicable to dual rotor or outer rotor motors, however. 
     Each yoke  18  preferably engages a pair of adjacent yokes  18 , such that the yokes  18  cooperatively present an outer circumferential stator core face  26 . The crowns  24  cooperatively present a discontinuous inner circumferential stator core face  28  configured to face the rotor. 
     Each tooth  16  preferably presents an upper tooth face  30 , a lower tooth face  32 , and two side tooth faces  34 . The upper tooth faces  30  each preferably include a crown portion  30   a , an arm portion  30   b , and a yoke portion  30   c . The lower tooth faces  32  each preferably include a crown portion  32   a , an arm portion  32   b , and a yoke portion  32   c . The side tooth faces  34  each preferably include a crown portion  34   a , an arm portion  34   b , and a yoke portion  34   c.    
     The teeth  16  (or, more particularly, the upper tooth faces  30 ) preferably cooperatively present an upper stator core face  36 . Similarly, the teeth  16  (or, more particularly, the lower tooth faces  32 ) preferably cooperatively present a lower stator core face  38 . 
     It is permissible according to some aspects of the present invention for the stator core to be alternatively configured, however. Among other things, for instance, the stator core could comprise a plurality of interconnected multi-tooth segments, comprise one or more helically wound laminations, or comprise stacked annular laminations each formed from a single punched strip. 
     As will be discussed in greater detail below, the stator core  12  is preferably electrically insulated by means of upper and lower (or, alternatively described, lead end and opposite lead end, or first-type and second-type) electrically insulative end caps  40  and  42 , respectively. As will be apparent from the detailed discussions below, the end caps  40  and  42  preferably provide all necessary insulation for the stator core  12 . That is, it is preferable that no other insulation is provided to the core  12  beyond the end caps  40  and  42 . For instance, the stator  10  is preferably devoid of insulative inserts or liners (such as those comprising Mylar or paper), powder coating, and/or additional insulative overlayments including but not limited to overmolding. 
     The coils  14  are preferably wound about the arms  20  of the teeth  16 . More particularly, a slot  44  is defined between each adjacent pair of teeth  16 . In greater detail, the slot  44  is preferably defined between each adjacent pair of teeth  16  by the proximate side faces  34  (including respective crown, arm, and yoke portions  34   a ,  34   b , and  34   c  thereof) of the teeth  16 . The coils  14  are preferably wound about the teeth  16  and through the slots  44  (on the outside of the end caps  40  and  42 , as will be discussed in greater detail below) so as to circumscribe or loop about respective ones of the arms  20 . The end caps  40  and  42  are thus disposed between the core  12  and the coils  14 . 
     The coils  14  preferably comprise electrically conductive wiring or wires  46 . The wiring  46  is preferably wound multiple times about each tooth  16  to form a plurality of turns or loops. In greater detail, the coils  14  preferably loop around and circumscribe the upper tooth face  30 , the lower tooth face  32 , and the two side tooth faces  34  of each tooth  16 . More particularly, the coils  14  loop around the arm portions  30   b ,  32   b , and  34   c  of the respective upper, lower, and side tooth faces  30 ,  32 , and  34  of each tooth  16 . 
     The wiring  46  is preferably formed of copper or aluminum, although any one or more of a variety of electrically conductive materials or a combination thereof may be used within the ambit of the present invention. Furthermore, the wiring  46  may be coated or uncoated. 
     As is customary, the wiring  46  is wound around the teeth  16  in a particular manner according to the configuration and desired performance characteristics of the motor. 
     The stator core  12  is preferably initially provided in a straight configuration (see  FIGS.  3  and  4   ). That is, the teeth  16  are disposed in a straight line prior to winding. As will be discussed in greater detail below, the end caps  40  and  42  are then slid onto respective ones of the teeth  16 . The coils  14  are then preferably wound using a “chain wound” technique. The stator  10  is then curved into its final toroidal form. However, it is noted that alternative winding techniques, including those applied on an already toroidal core, fall within the scope of the present invention. 
     As noted previously, the stator core  12  is preferably insulated by means of a plurality of end caps  40  and  42  fitted over portions of the teeth  16 . Each end cap  40  or  42  preferably comprises an at least substantially electrically insulative material. For instance, a plastic or synthetic resin material may be used. Other materials having suitable electrically insulative properties are permissible, however. 
     In a preferred embodiment, each end cap  40  and  42  provides both a physical and electrical barrier between the coils  14  and the stator core  12 . More particularly, as will be discussed in greater detail below, a pair of upper and lower end caps  40  and  42  are fitted over opposite axial sides (corresponding to upper and lower stator core faces  36  and  38 , or alternatively stated, to the upper and lower tooth faces  30  and  32 ) of a corresponding tooth  16 . The end caps  40  and  42  extend axially toward one another and overlap one another at an overlapped region  48  so as to in part encompass the tooth  16  via full (that is, continuous) encirclement of the arm  20 . At least partial overlayment of the upper end cap  40  along the crown portion  30   a  and the yoke portion  30   c  of the upper tooth face  30 , as well as partial overlayment of the lower end cap  42  along the crown portion  32   a  and the yoke portion  32   c  of the lower tooth face  32 , are also preferably achieved. 
     Fitting of the end caps  40  and  42  onto the teeth  16  is preferably via a friction fit, although other fit types (e.g., slip) fall within the scope of some aspects of the present invention. 
     As will be discussed in greater detail below, engagement of each upper end cap  40  with its corresponding lower end cap  42  in the overlapped region  48  is preferably via a slip fit, although it is again permissible according to some aspects of the present invention for other fit types (e.g., friction or tight, permanently secured with adhesive or welding, etc.) to be used. 
     Upper, Lead End, or First-Type End Caps 
     Turning now to the general structure of the upper (alternatively, lead end or first-type) end caps  40 , each upper end cap  40  includes a top  50  and an axially downwardly extending upper skirt  52 . Each top  50  includes a top crown portion  54 , a top arm portion  56 , and a top yoke portion  58 . Each upper skirt  52  includes an upper skirt crown portion  60 , an upper skirt arm portion  62 , and an upper skirt yoke portion  64 . 
     As will be discussed in greater detail below, the top crown portion  54  corresponds to and is most preferably configured to fully overlie the upper crown portion  30   a  of the upper face  30  of the corresponding tooth  16 . The top arm portion  56  corresponds to and is most preferably configured to fully overlie the upper arm portion  30   b  of the upper face  30  of the corresponding tooth  16 . The top yoke portion  58  corresponds to and is most preferably configured to shield at least part of the upper yoke portion  30   c  of the upper face  30  of the corresponding tooth  16 . 
     As will also be discussed in greater detail below, each upper skirt  52  preferably extends along both of the tangentially or circumferentially spaced apart side faces  34  of the corresponding tooth  16  so as to fully overlie the upper portions of the crown, arm, and yoke portions  34   a ,  34   b , and  34   c , respectively, of the side faces  34 . 
     Each top crown portion  54  preferably includes a generally radially and circumferentially extending crown overlayment  66  and an axially upwardly extending crown retaining wall  68  projecting from the crown overlayment  66  for restricting radially inward movement of the coils  14 . 
     Each top arm portion  56  preferably includes a generally radially and circumferentially extending upper arm overlayment  70 . 
     Each top yoke portion  58  preferably includes an upper wire management structure  72  and a support structure  74 . The support structure  74  preferably includes a plurality of brackets  76  that engage the yoke portion  30   c  of the upper face  30  and extend axially upwardly to a portion of the upper wire management structure  72 . 
     The upper wire management structure  72  of each lead end or upper end cap  40  facilitates routing of wiring  46 , including lead ends (not shown) thereof. More particularly, the upper wire management structure  72  preferably includes an axially upwardly and tangentially extending upper retaining wall  78  projecting from an outer end of the corresponding arm overlayment  70 , near the end  22   a  of the corresponding arm  20 . The retaining wall  78  is most preferably disposed radially inwardly of the brackets  76 . The upper wire management structure  72  additionally includes a floor  80  extending generally orthogonally from the retaining wall  78  and supported by the brackets  76 , a pair of hooks  82  extending axially upwardly from tangentially (or circumferentially) opposed ends of the floor  80 , and a fastener shield  84  projecting axially upwardly and downwardly from the arcuate center of the floor  80 . The downwardly projecting portion of the fastener shield  84  is preferably disposed between a pair of the brackets  76 . The upper wire management structure  72  further preferably includes a two-part outer barrier  86  extending generally orthogonally from a radially outer edge of the floor  80 . 
     Each upper skirt  52  preferably extends axially from the corresponding top  50 , toward a corresponding one of the lower end caps  42 , so as to present an upper skirt length L_us (see  FIG.  20   ). 
     Each upper skirt  52  includes a pair of tangentially or circumferentially spaced apart upper skirt sides  88 , each of which extends along a respective one of the side faces  34  of the corresponding tooth  16 . More particularly, each upper skirt side  88  includes an upper skirt crown portion side  60   a , an upper skirt arm portion side  62   a , and an upper skirt yoke portion side  64   a , each of which extends along and overlies the corresponding crown, arm, and yoke portions  34   a ,  34   b , and  34   c  of the corresponding side face  34 . 
     Each upper skirt  52  includes an upper main portion  90  and an upper overlappable portion  92  disposed axially below the upper main portion  90 . The functionality of the upper overlappable portion  92  will be discussed in greater detail below. 
     Each upper main portion  90  defines a pair of tangentially or circumferentially innermost upper main portion faces  94   a  (each associated with a respective one of the upper skirt sides  88 ) and a pair of tangentially or circumferentially outermost upper main portion faces  94   b  (also each associated with one of the upper skirt sides  88 ). 
     Similarly, each upper overlappable portion  92  defines a pair of tangentially or circumferentially innermost upper overlappable portion faces  96   a  (each associated with a respective one of the upper skirt sides  88 ) and a pair of tangentially or circumferentially outermost upper overlappable portion faces  96   b  (also each associated with one of the upper skirt sides  88 ). 
     As will be discussed in greater detail below, the innermost upper overlappable portion faces  96   a  are preferably disposed tangentially or circumferentially outward of the corresponding innermost upper main portion faces  94   a . The corresponding outermost upper overlappable portion faces  96   b  and outermost upper main portion faces  94   b , however, are preferably coplanar with one another. 
     Each upper skirt  52  also preferably cooperates with the upper wire management structure  72  of the top yoke portion  58  to define a pair of upper wire barrier portions  98 . More particularly, the upper retaining wall  78  and the upper skirt yoke portions  64   a  of each side  88  cooperatively present a pair of tangentially or circumferentially outermost edges  100 . Each upper wire barrier portion  98  preferably extends axially along the upper skirt  52  and a portion of the upper retaining wall  78 , adjacent the corresponding edge  100 , and projects radially inwardly. 
     Preferably, each set of corresponding upper skirt crown portion sides  60   a , upper skirt arm portions sides  62   a , upper skirt yoke portion sides  64   a , upper retaining walls  78 , and upper wire barrier portions  98  cooperatively defines an upper wire trough portion  102  through which wiring  46  is wound and in which a part of the corresponding coil  14  is disposed. (Each slot  44  thus preferably includes a pair of the upper wire trough portions  102 .) Each upper wire barrier portion  98  preferably at least in part defines a tangential or circumferential margin of the aforementioned trough portion  102 . 
     The upper wire barrier portions  98  each include an upper end  104 . The end  104  is preferably rounded or smoothed in some manner, as opposed to presenting a squared, jagged, or otherwise rough or abruptly edged form. This feature will be discussed in greater detail below. 
     Lower, Opposite Lead End, or Second-Type End Caps 
     Turning now to the general structure of the lower (alternatively, opposite lead end or second-type) end caps  42 , each lower end cap  42  includes a bottom  106  and an axially upwardly extending lower skirt  108 . Each bottom  106  includes a bottom crown portion  110 , a bottom arm portion  112 , and a bottom yoke portion  114 . Each lower skirt  108  includes a lower skirt crown portion  116 , a lower skirt arm portion  118 , and a lower skirt yoke portion  120 . 
     As will be discussed in greater detail below, the bottom crown portion  110  corresponds to and is most preferably configured to fully overlie the lower crown portion  32   a  of the lower face  32  of the corresponding tooth  16 . The bottom arm portion  112  corresponds to and is most preferably configured to fully overlie the lower arm portion  32   b  of the lower face  32  of the corresponding tooth  16 . The bottom yoke portion  114  corresponds to and is most preferably configured to shield at least part of the lower yoke portion  32   c  of the lower face  32  of the corresponding tooth  16 . 
     As will also be discussed in greater detail below, each lower skirt  108  preferably extends along both of the tangentially or circumferentially spaced apart side faces  34  of the corresponding tooth  16  so as to fully overlie the lower portions of the crown, arm, and yoke portions  34   a ,  34   b , and  34   c , respectively, of the side faces  34 . 
     Each bottom crown portion  110  preferably includes a generally radially and circumferentially extending crown underlayment  122  and an axially downwardly extending retaining wall  124  projecting from the crown underlayment  122  for restricting radially inward movement of the coils  14 . 
     Each bottom arm portion  112  preferably includes a generally radially and circumferentially extending lower arm underlayment  126 . 
     Each bottom yoke portion  114  preferably includes a lower wire management structure  128 , a support structure  130 , and a yoke underlayment  132 . The support structure  130  preferably includes a plurality of brackets  134  that engage the yoke underlayment  132  and extend axially downwardly therefrom, adjacent and radially outside the lower wire management structure  128 . 
     The lower wire management structure  128  of each opposite lead end or lower end cap  42  facilitates routing of wiring  46 . More particularly, the lower wire management structure  128  preferably includes an axially downwardly and tangentially extending lower retaining wall  136  projecting from an outer end of the corresponding arm underlayment  126 , adjacent the outer end  22   a  of the arm  20 . The retaining wall  136  is most preferably disposed radially inwardly of the brackets  134 . 
     The lower wire management structure  128  additionally includes a fastener shield  138  projecting axially downwardly the arcuate center of the yoke underlayment  132 . The fastener shield  138  is preferably disposed between a pair of the brackets  134 . 
     Each lower skirt  108  preferably extends axially upwardly from the corresponding bottom  106 , toward a corresponding one of the upper end caps  40 , so as to present a lower skirt length L_ls (see  FIG.  20   ). 
     Each lower skirt  108  includes a pair of tangentially or circumferentially spaced apart lower skirt sides  140 , each of which extends along a respective one of the side faces  34  of the corresponding tooth  16 . More particularly, each lower skirt side  140  includes a lower skirt crown portion side  116   a , a lower skirt arm portion side  118   a , and a lower skirt yoke portion side  120   a , each of which extends along and overlies the corresponding crown, arm, and yoke portions  34   a ,  34   b , and  34   c  of the corresponding side face  34 . 
     Each lower skirt  108  includes a lower main portion  142  and a lower overlappable portion  144  disposed axially below the lower main portion  142 . The functionality of the lower overlappable portion  144  will be discussed in greater detail below. 
     Each lower main portion  142  defines a pair of tangentially or circumferentially innermost lower main portion faces  146   a  (each associated with a respective one of the lower skirt sides  140 ) and tangentially or circumferentially outermost lower main portion faces  146   b  (also each associated with one of the lower skirt sides  140 ). 
     Similarly, each lower overlappable portion  144  defines a pair of tangentially or circumferentially innermost lower overlappable portion faces  148   a  (each associated with a respective one of the lower skirt sides  140 ) and tangentially or circumferentially outermost lower overlappable portion faces  148   b  (also each associated with one of the lower skirt sides  140 ). 
     As will be discussed in greater detail below, the outermost lower overlappable portion faces  148   b  are preferably disposed tangentially or circumferentially inward of the corresponding outermost lower main portion faces  146   b . The corresponding innermost lower overlappable portion faces  148   a  and innermost lower main portion faces  146   a , however, are preferably co-planar with one another. 
     Each lower skirt  108  also preferably cooperates with the lower wire management structure  128  of the bottom yoke portion  114  to define a pair of lower wire barrier portions  150 . More particularly, the lower retaining wall  136  and the lower skirt yoke portions  120   a  of each side  140  cooperatively present a pair of tangentially or circumferentially outermost edges  152 . Each lower wire barrier portion  150  preferably extends axially along the lower skirt  108  and a portion of the lower retaining wall  136 , adjacent the corresponding edge  152 , and projects radially inwardly. 
     Preferably, each set of corresponding lower skirt crown portion sides  116   a , lower skirt arm portion sides  118   a , lower skirt yoke portion sides  120   a , lower retaining walls  136 , and lower wire barrier portions  150  cooperatively defines a lower wire trough portion  154  through which wiring  46  is wound and in which a part of the corresponding coil  14  is disposed. (Each slot  44  thus preferably includes a pair of the lower wire trough portions  154 .) Each lower wire barrier portion  150  preferably at least in part defines a tangential or circumferential margin of the aforementioned trough portion  154 . 
     The lower wire barrier portions  150  each include a lower end  156 . The end  156  is preferably rounded or smoothed in some manner, as opposed to presenting a squared, jagged, or otherwise rough or abruptly edged form. This feature will be discussed in greater detail below. 
     End Cap Overlapping Interengagement 
     In a preferred embodiment, corresponding ones of the upper and lower end caps  40  and  42  extend toward one another or, alternatively stated, toward the lower and upper stator core faces  38  and  36 , respectively. Furthermore, the end caps  40  and  42  preferably engage one another at a juncture  157  such that the arm  20  of the corresponding tooth  16  is fully covered by the end caps  40  and  42  cooperatively. That is, paired end caps  40  and  42  preferably cooperatively extend continuously axially along the core and leave no surface (or, more specifically, in a preferred embodiment, no metal) of the corresponding arm  20  exposed. Stated in yet another way, the paired end caps  40  and  42  cooperatively form an axially continuous arm covering devoid of gaps or openings. 
     More particularly, for each pair of end caps  40  and  42 , the upper overlappable portion  92  of the upper skirt  52  and the lower overlappable portion  144  of the lower skirt  108  at least in part overlap or overlie one another such that the previously mentioned overlapped region  48  is defined at the juncture  157 . In the illustrated embodiment, for instance, the upper overlappable portion  92  overlies the lower overlappable portion  144 . In greater detail still as best shown in  FIGS.  17  and  18   , a recess  158  is defined between the side faces  34  of each tooth  16  and the inner tangential faces  96   a  of the upper overlappable portion  92 . The lower overlappable portion  144  is at least in part received in the recess  158 . 
     In some instances, the entireties of either of both of the upper and lower overlappable portions  92  and  144 , respectively, may be included in (i.e., define) the overlapped region  48 . In other instances, however, only a small portion of either or both of the upper and lower overlappable portions  92  and  144  may be included in (i.e., define) the overlapped region  48 . 
     More particularly, it is noted that, in assembled or paired form as when secured on a tooth  16 , a paired set of end caps  40  and  42  cooperatively present an actual cumulative end cap axial extent or length L_ec (see  FIG.  20   ) defined between the crown and arm overlayments  66  and  70 , respectively, and the crown, arm, and yoke underlayments  122 ,  126 , and  132 , respectively. The stator core  12  presents an actual axial stack height H_sc-a (see  FIGS.  1  and  2   ) defined between the upper and lower core faces  36  and  38 . After assembly of the stator  12 , the actual cumulative end cap axial extent or length L_ec is most preferably equal to or only slightly larger than the actual axial stack height H_sc-a to facilitate axial coverage of the core  12  as described above. 
     As is conventional, the stator core  12  is preferably specified with a nominal (i.e., designed, intended, etc.) axial stack height and a tolerance associated therewith. As will be readily understood by those of ordinary skill in the art, the tolerance may be based on, among other things, expected manufacturing capabilities and overall motor precision requirements. The nominal stack height plus or minus to the tolerance provides maximum and minimum allowable stack heights, respectively, associated with the given stator core. 
     The upper and lower overlappable portions  92  and  144  preferably each present respective axial extents or lengths L_uop and L_lop, respectively (see  FIG.  17   ). The upper and lower skirt lengths L_us and L_ls and the upper and lower overlappable portion lengths L_uop and L_lop are designed to accommodate the aforementioned allowable variations in actual axial stack height H_sc-a. For a stator core  12  having an actual axial stack height H_sc-a equal to the maximum allowable stack height, for instance, an axial dimension L_or (see  FIGS.  15 ,  17 , and  20   ) of the overlapping region  48  will be minimized as the end caps  40  and  42  shift axially away from each other. In contrast, for a stator core  12  having an actual axial stack height H_sc-a equal to the minimum allowable stack height, the axial dimension L_or of the overlapping region  48  will be maximized as the end caps  40  and  42  move axially toward each other. 
     In this manner, axially continuous insulation of the teeth  16  is achieved in a simple and robust manner for all stator cores  12  falling within allowable manufacturing tolerances, without any changes being made to the provided end caps  40  and  42  and without the provision of additional insulative means. Such a design is highly advantageous. For instance, conventional upper and lower end caps remain axially spaced from one another even after assembly, such that an axially extending exposed portion of the corresponding tooth remains. To rectify this exposure, liners are conventionally first inserted between each pair of teeth so as to line the tooth sides. The end caps are then placed on the teeth and, in theory, smoothly over the top of the liners. In practice, the additional step of placing the liners is cumbersome and inefficient. Furthermore, deformation (for instance, smashing, crinkling, and so on) of the liners frequently occurs as the tightly fitted, generally rigid end caps are forcefully placed on the corresponding teeth. Thus, omission of such liners (as in the present design, in which liners are entirely unnecessary and would be both redundant and obstructive) results in significant time and cost savings, as well as improved and more reliable motor insulation. 
     End Cap Interchangeability 
     In addition to accommodating axial stack height tolerances and eliminating the need for liners or other insulative means, the end caps  40  and  42  of the present invention are also easily interchangeable with other end caps of their type (i.e, upper or lead end, vs. lower or opposite lead end) having differing axial skirt lengths but maintaining identical tops  50  and bottoms  106 , respectively. 
     For instance, consider a set of six (6) stator cores designated herein as Stator Cores A, B, C, D, E, and F, each having a different nominal and actual axial stack height. Additionally, with reference to  FIGS.  21  and  22   , consider a set  210  of interchangeably configurable end caps including both upper end caps  212  and lower end caps  214 . More particularly, as shown in  FIG.  21   , the set  210  includes two (2) upper end caps  212 , designated herein as Upper End Caps A and B, and having different upper skirt lengths L_us-a and L_us-b, respectively. Furthermore, as shown in  FIG.  22   , the set  210  includes three (3) lower end caps  214 , designated herein as Lower End Caps A, B, and C, and having different lower skirt lengths L_ls-a, L_ls-b, and L_ls-c, respectively. 
     Pairing of Upper End Cap A with Lower End Cap A would result in a first cumulative axial extent that is different than that which would result from pairing of upper End Cap A with Lower End Cap B or Lower End Cap C. Pairing of Upper End Cap B with each of the Lower End Caps A-C would result in three (3) axial extents that are also distinct from one another and also distinct from the three (3) axial extents associated with Upper End Cap A. 
     Thus, in this example, a set of five (5) total end caps are interchangeably configurable (more specifically, pairable) to define six (6) distinct cumulative axial extents. Careful selection of the individual skirt lengths to ensure that these six (6) distinct cumulative axial extents corresponds to the six (6) distinct nominal axial stack heights of the Stator Cores A-F leads to the ability to efficiently and effectively insulate a given tooth of all six (6) Stator Cores A-F using a single set of five (5) end caps comprising two (2) Upper End Caps and three (3) Lower End Caps. 
     As will be readily apparent to those of ordinary skill in the art, absent the interchangeable pairability of the present invention, a set of twelve (12) end caps comprising six (6) upper end caps and six (6) lower end caps would instead be necessary. 
     Of course, provided appropriate skirt length selections, any number of combinations of upper and lower end caps may be interchangeably made to facilitate any number of axial stack heights. Furthermore, it is permissible according to some aspects of the present invention for more than one combination to produce a given cumulative axial extent. 
     Rounded Wire Barrier 
     As noted previously, each upper end cap  40  preferably presents a pair of upper wire barrier portions  98 . Likewise, each lower end cap  42  preferably presents a pair of lower wire barrier portions  150 . When a corresponding pair of upper and lower end caps  40  and  42  are in a paired configured, as when placed over a corresponding tooth  16 , each upper wire barrier portion  98  aligns with a corresponding one of the lower wire barrier portions  150  such that they cooperatively form a generally radially projecting, axially extending wire barrier  160 . 
     The wire barrier  160  is preferably substantially continuous between the ends  104  and  156 , although a small inner discontinuity  162  (see  FIG.  14   ) and a small outer discontinuity  164  (see  FIGS.  14  and  16   ) may be present at or near the juncture  157 . More particularly, an upper notch  166  is preferably formed in a tangentially outer portion of the upper wire barrier portion  98 . A lower notch  168  is preferably formed in a tangentially inner portion of the lower wire barrier portion  150 . A lower barrier projection  170  is received in the upper notch  166 , and an upper barrier projection  172  is received in the lower notch  168 . Portions of the upper notch  166  not filled by the lower barrier projection  170  constitute the outer discontinuity  164 , and portions of the lower notch  168  not filled by the upper barrier projection  172  constitute the inner discontinuity  162 . 
     Such discontinuities  162  and  164  will increase in size for actual axial stack heights that are nearer a maximum axial stack height, or, alternatively stated, as the size of the overlapped region  48  decreases. However, an axial dimension of any inner discontinuity  162  is preferably less than twenty five percent (25%) of the cumulative axial extent L_ec of the end caps  40  and  42 , more preferably less than ten percent (10%) of the cumulative axial extent L_ec, and most preferably less than about five percent (5%) of the cumulative axial extent L_ec. Likewise, an axial dimension of any outer discontinuity  164  is preferably less than twenty five percent (25%) of the cumulative axial extent L_ec of the end caps  40  and  42 , more preferably less than ten percent (10%) of the cumulative axial extent L_ec, and most preferably less than about five percent (5%) of the cumulative axial extent L_ec. 
     For present purposes, a wire barrier  160  associated with an inner discontinuity  162  having an axial extent that is less than ten (10%) of the cumulative axial extent of the cumulative axial extent L_ec shall be understood to be substantially axially continuous. Such an inner discontinuity  162  will be understood by those in the art to be small enough to not have detrimental effects of the wiring  46  during winding, nor on the coils  14  after winding. 
     Preferably, the aforementioned upper and lower wire trough portions  102  and  154  cooperatively define an axially extending trough  174  through which wiring  46  is wound and in which a part of the corresponding coil  14  is disposed. Each slot  44  thus preferably includes a pair of troughs  174 , with each of the troughs  174  in a given slot  44  being associated with a different tooth  16 . 
     Each wire barrier  160  defines a tangential or circumferential outer margin of the corresponding trough  174 . The corresponding upper and lower skirt arm portions  62  and  118  are each spaced generally tangentially inwardly from respective ones of the wire barriers  160  to define a tangential or circumferential inner margin of each trough  174 . The corresponding upper and lower skirt yoke portions  64  and  120 , along with portions of each of the upper and lower wire retaining walls  78  and  136 , cooperatively define a radially outer margin of each trough  174 . The corresponding upper and lower skirt crown portions  60  and  116 , along with portions of each of the retaining walls  68  and  124  of the top and bottom crown portions  54  and  110 , cooperatively define a radially inner margin of each trough  174 . 
     As briefly noted above, the upper and lower wire barrier portions  98  and  150  present respective upper and lower ends  104  and  156 . As also noted above, the ends  104  and  156  are each preferably strategically rounded, smoothed, or chamfered in some manner, as opposed to presenting a squared, jagged, or otherwise rough or abruptly edged form. That is, in a broad sense, the ends  104  and  156  are shaped so as to facilitate unobstructed and simplified winding while also guiding wiring  46  into the aforementioned wiring trough  174 . Each of the ends  104  and  156  therefore forms a respective winding ramp  176  or  178  configured to smoothly guide wiring  46  into the trough  174  during wiring of the core  12 . 
     In the illustrated embodiment, for instance (and as shown in  FIGS.  8 ,  10 ,  11   , and others), each end  104  and  156  is in the form of a quartered cone  180  having a radiused base  182  and smoothed top  184 . This in contrast to a conventional squared end, which may lead to snagging, catching, and/or misdirection of the wire during winding. 
     Each wire barrier  160  preferably extends axially upwardly beyond the corresponding upper arm overlayment  70  and axially downwardly beyond the corresponding arm underlayment  126 . 
     More particularly, each upper wire barrier portion  98  extends axially upwardly along the upper retaining wall  78 , past the upper arm overlayment  70 . Preferably, the upper wire barrier portion  98  extends along only a portion of the axial extent of the upper retaining wall  78  beyond the upper arm overlayment  70 . Most preferably, the upper wire barrier portion  98  extends axially along about half of the axial extent of the upper retaining wall  78  beyond the upper arm overlayment  70 . 
     Similarly, each lower wire barrier portion  150  extends axially downwardly along the lower retaining wall  136 , past the lower arm underlayment  126 . Preferably, the lower wire barrier portion  150  extends along only a portion of the axial extent of the lower retaining wall  136  beyond the lower arm underlayment  126 . Most preferably, the lower wire barrier portion  98  extends axially along about half of the axial extent of the lower retaining wall  136  beyond the lower arm underlayment  126 . 
     Even more particularly, each rounded upper end  104  (or, alternatively, upper ramp  176 ) preferably extends axially upwardly along the upper retaining wall  78 , past the upper arm overlayment  70 . Preferably, the end  104  (or, alternatively, the ramp  176 ) extends along only a portion of the axial extent of the upper retaining wall  78  beyond the upper arm overlayment  70 . Most preferably, the end  104  (or, alternatively, the ramp  176 ) extends axially along about half of the axial extent of the upper retaining wall  78  beyond the upper arm overlayment  70 . 
     Similarly, each rounded lower end  156  (or, alternatively, lower ramp  178 ) extends axially downwardly along the lower retaining wall  136 , past the lower arm underlayment  126 . Preferably, the lower end  156  (or, alternatively, the lower ramp  178 ) extends along only a portion of the axial extent of the lower retaining wall  136  beyond the lower arm underlayment  126 . Most preferably, the lower end  156  (or, alternatively, the lower ramp  178 ) extends axially along about half of the axial extent of the lower retaining wall  136  beyond the lower arm underlayment  126 . 
     The preferred axial extents as described in detail above, in combination with the rounded features also described above, facilitate smooth, even winding of the coils  14  with minimal snagging and other errors, inconsistencies, and imperfections associated with conventional end cap designs. 
     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 inventors hereby state their intent to rely on the Doctrine of Equivalents to determine and access 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.