Abstract:
The need for specialized tooling which was previously required to accurately place the first layer of turns in a precision winding of a rotor having an even number of layers of turns is eliminated by providing self-fixturing wire-guiding features in corners of slots in the rotor which receive the winding, thereby facilitating the manufacture or repair of precision-wound rotors. In some exemplary embodiments, the self-fixturing wire-guiding features are provided by configuring the corners of the slots to include a chamfer or shoulder. In other exemplary embodiments, a specially shaped slot liner inserted into the slots includes a corner spacer which provides the self-fixturing wire-guiding feature.

Description:
TECHNICAL FIELD 
     This invention relates to a precision-wound rotor for a high speed dynamoelectric machine, and more particularly to a structure and a method for facilitating the manufacture of such a rotor. 
     BACKGROUND 
     Many dynamoelectric machines, including certain types of electric motors or generators, utilize a rotating member, which is known as a rotor, having a winding formed from layers of turns of wire wound about a rotor core of magnetic material. Rotors which provide superior performance and compact physical size can be produced by precision-winding the turns of wire about the rotor core. 
     In such precision-wound rotors, as shown in FIG. 1, the turns of wire  1 - 23  are precisely positioned within generally planar, overlapping layers  144 , 146 , 147  of the winding  118  in a side-by-side fashion with each turn in a given layer closely abutting an adjacent turn in that layer. The turns are preferably offset by one-half wire diameter in adjacent layers, so that each turn of wire will rest in a groove  148  formed between adjacent turns of wire in the preceding and any subsequent layers of the winding  118 . 
     The precision-wound winding is generally contained in a slot  116  or channel of the rotor core  102 . Ideally, as shown in FIG. 1, the winding  118  is formed in such a manner that the outer turns of wire  1 , 8 , 16 , 23  in the radially innermost and outermost layers  160 , 162 , and the outer turns in alternating intermediate layers, bear simultaneously against a wall  132 , 134  of the slot  116  and/or one of more adjacent turns of wire in the winding  118 , to form a densely packed structure. 
     In such a densely packed structure, the space occupied by the turns is minimized and remains highly consistent from one rotor to another, thereby allowing such precision-wound rotors to be physically smaller and more tightly toleranced than non-precision-wound rotors. Precision-wound rotors are also inherently more structurally self-supporting due to the interlocking nature of the turns within the slot  116 , thereby allowing a precision wound rotor to operate safely at high rotational speed without fear of centrifugal forces causing the turns to shift, in contrast to non-precision-wound rotors in which shifting of the turns is known to occur. 
     Where cooling fluid is pumped through the winding  118 , precision-winding provides superior heat transfer, thereby allowing wire size and/or coolant flow to safely be reduced without fear of the winding overheating. This improved heat transfer results from the turbulent fluid flow which occurs in the small interstices  156  which are formed between adjacent turns of the precision wound rotor. In non-precision-wound rotors, the interstices are larger, thereby causing laminar instead of turbulent fluid flow, which results in lower heat removal capability and the need for larger wire sizes and/or coolant flow rates in order to maintain acceptable temperatures in the winding. Commonly assigned U.S. Pat. Nos. 4,583,696 and 4,603,274 to Mosher are illustrative of precision-wound rotors as described above. 
     For precision-wound rotors having an odd number of layers of turns, as illustrated in FIG. 1, the tightly wound winding  118  supported by walls  132 , 134  of the slot  116  as described above, may be readily manufactured with minimal difficulty due to the fact that the first and last layers  160 , 162  can be configured to extend entirely across the width W 2  of the slot  116  in the core  102 . However, as illustrated in FIGS. 2 and 3 where the winding  118  includes an even number of layers having each turn nested in a groove  148  formed by turns in an adjacent layer as described above, either the innermost layer  160  or the outermost layer  162  of the turns will not extend entirely across the width W 2  of the slot  116 , and will thus not be fully supported by the slot walls  132 , 134 . 
     Stated another way, for the desired nesting of turns to occur in adjacent layers of turns, the turns in one layer of each pair of adjacent layers of the winding  118  must be offset by one-half wire diameter from the turns in the other layer of the pair of layers. For a slot  116  having parallel walls  132 , 134 , this means that if one member of the pair of layers has n turns of wire, the adjacent member of the pair of layers must have either n+1 or n−1 turns. Therefore, if the slot  116  has a width W 2  equal to (n+1)×(the wire diameter D), either the innermost  160  or outermost  162  layer of the winding  118  will have only n turns, and thus will not extend entirely across the slot  116 , or be supported by the walls  132 , 134 . 
     If the outermost layer  162  has only n turns, additional structure or winding retaining means may be required to preclude shifting of the turns as the result of centrifugal forces acting on the turns incident with rotation of the rotor. It would appear to be preferable, therefore, to have the innermost layer contain only n turns, as depicted in FIG. 3, since an overlying layer of n+1 turns, which extends entirely across the slot  116  will trap the innermost layer against the bottom surface  130  of the slot, thereby precluding movement. However, with the innermost layer  160  having only n turns, and not extending entirely across the slot width, some means of fixturing the innermost layer during fabrication of the winding must be provided to ensure that the subsequent layers having n+1 turns will fit properly within the slot width and simultaneously nest within the grooves between adjacent turns in the innermost layer of turns. Such fixturing increases the difficulty and cost of manufacturing the precision-wound rotor. The inconvenience and cost of providing such fixturing becomes even more acute with respect to repair or re-manufacturing of a damaged rotor in need of having the winding  118  replaced. Repair or re-manufacturing operations are often preferably carried out at repair centers or depots remote from the facility in which the rotor was originally manufactured. If special fixturing is required for precision winding, duplicate sets of such fixturing will need to be maintained at every remote repair or re-manufacturing facility. In many instances, the cost of maintaining and utilizing such duplicate fixturing at the remote sites will be so prohibitively high that damaged rotors will have to be shipped back to the initial manufacturing facility for repair, or worse yet, simply discarded and replaced with a new rotor, thus greatly increasing the cost of ownership of the dynamoelectric machine. 
     Accordingly, it is an object of my invention to provide a precision-wound rotor having an even number of layers of turns which is self-fixturing, and may thus be more readily manufactured at low cost without specialized fixturing or tooling. It is also an object of my invention to provide such a rotor in a form which may be readily repaired by re-winding the rotor at a remote repair facility or depot, without the use of specialized fixturing. 
     SUMMARY 
     My invention accomplishes these objects in a precision-wound rotor through inclusion of a self-fixturing wire-guiding feature, such as a shoulder or a chamfer, in the corners of slots in the rotor core which contain the precision-wound winding. 
     Specifically, the precision-wound rotor of my invention includes a magnetic core having a slot therein for receipt of a winding having a first layer of n turns of wire and a second layer of n+1 turns of wire. The slot includes a generally planar bottom surface thereof, and sidewalls intersecting with the bottom surface to form corners of the slot. The sidewalls are disposed equidistant from a slot centerline bisecting and extending perpendicularly outward from the bottom surface of the slot. A self-fixturing wire-guiding feature is provided for centering a first and a second layer of the winding about the slot centerline within the slot in such a manner that when the first layer is formed by winding the turns of the first layer in a side-by-side fashion across the bottom surface of the slot, with each of the turns tightly abutting a radially outer surface of an adjacent turn in the first layer, each pair of adjacent turns in the first layer defines a groove extending parallel to the turns of wire for receipt therein of a turn of wire in the second layer of turns. 
     According to one aspect of my invention, the wire from which the turns of the winding are formed has a diameter D, and the self-fixturing wire-guiding feature includes a spacer at each corner of the slot having a width substantially equal to about one-half of the wire diameter D extending along the bottom surface of the slot, and a height extending along the sidewall of the slot substantially equal to about the wire diameter D. 
     According to another aspect of my invention, the wire used to form the turns of the winding has a diameter substantially equal to about D and the sidewalls are configured to define a width W. of the bottom surface of the slot which is substantially equal to about the number of turns n times the wire diameter D, and a second width W 2  of the slot substantially equal to about (n+1) times D beginning at a distance substantially equal to about D along the sidewall from the corner of the slot. 
     In some embodiments of my invention, the self-fixturing wire-guiding feature of my invention is provided by configuring the corners of the slot itself to include a chamfer or a shoulder as defined above. In other embodiments of my invention, the self-fixturing wire-guiding feature is provided by a specially shaped slot liner which is inserted into the slot prior to precision winding of the turns therein. 
     The self-fixturing wire-guiding features of my invention, thus eliminate the need for special fixturing during either the initial manufacture or subsequent repair and rewinding of a precision-wound rotor. As a result, the cost of initially acquiring, and the long term cost associated with ownership of a dynamoelectric machine having a precision-wound rotor according to my invention are substantially reduced. Other objects, aspects, and advantages of my invention will become readily apparent upon consideration of the following drawings and detailed descriptions of preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For all drawing figures included herewith, including those labeled as prior art, like reference numerals have been used to indicate similar elements or features in the interest of clarity of explanation. 
     FIGS. 1-3 are schematic cross-sectional representations of layers of turns of wire in a winding of prior precision-wound rotors which illustrate the problems solved by my invention; 
     FIG. 4 is an exploded isometric view of a precision-wound rotor according to my invention; 
     FIG. 5 is an isometric illustration of a precision wound core assembly of the rotor of FIG. 4, 
     FIGS. 6-8 are schematic cross-sectional representations taken along line  6 — 6  of FIG. 5, illustrating three alternate embodiments of self-fixturing wire-guiding features provided by my invention to facilitate fabrication of the precision winding. 
    
    
     DESCRIPTION OF THE INVENTION 
     FIG. 4 depicts an exploded three-dimensional view of a precision-wound rotor  100 , according to my invention, for a dynamoelectric machine. The rotor  100  includes a precision wound core assembly  102  which is inserted into an elongated slot  104  in a shaft  106  of the rotor  100 . The core assembly  102  is secured within the shaft  106  by a cylindrical sleeve or can  108  which is installed over the shaft  106  and core assembly  102  with an interference fit, by a process such as shrink fitting, thereby completing fabrication of the precision-wound rotor  100 . 
     As shown in FIG. 5, the precision wound core assembly  102  has a longitudinal axis  110  and axially spaced core ends  112   a,   112   b.  Each of the axially spaced core ends  112   a,   112   b  is fitted respectively with a winding end support  114   a,   114   b  of an electrically insulative material. The core assembly  102  includes a slot or channel  116  extending in a generally longitudinal direction completely around the core assembly  102 , for receipt therein of a winding  118 . Specifically, the core assembly  102  includes a central generally cylindrical shaped magnetic core  120  of typical laminated construction which defines two oppositely opening and longitudinally oriented portions  122 , 124  of the slot  116 , thereby resulting in the magnetic core  102  having a generally H-shaped cross section. Each of the winding end supports  114   a,   114   b  respectively defines a transverse portion  126 , 128  of the slot  116  which extend across each winding support  114   a,   114   b  in alignment with the longitudinally oriented portions  122 , 124  of the slot  116  to jointly define the entire slot or channel  116  for receipt therein of the winding  118 . 
     As shown in FIG. 6, the winding  118  includes a plurality of turns of wire having a diameter D wound in a generally longitudinal direction about the core  102 , to form a first layer  144  having n turns of wire and a second layer  146  having n+1 turns of wire. Specifically, for the exemplary embodiment depicted in FIG. 6, the first layer includes turns  1  through  7 , such that n equals 7, and the second layer includes turns  8  through  15 , such that (n+1) equals 8. 
     As shown in FIGS. 5 and 6, the slot  116  includes a generally planar bottom surface  130  thereof and first and second sidewalls  132 , 134  intersecting with the bottom surface  130  to respectively form corners  136 , 138  of the slot  116 . The sidewalls  132 , 134  are disposed equidistant from a slot centerline  140  which bisects and extends perpendicularly outward from the bottom surface  130 . The corners  136 , 138  of the slot  116  are configured with a chamfer  142  which provides a self-fixturing wire-guiding means for centering the first and second layers  144 , 146  of the winding  118  about the slot centerline  140 , such that when the first layer  144  is formed by winding turns  1 - 7  of the first layer  144  in a side by side fashion across the bottom surface  130  of the slot  116 , with each of the turns  1 - 7  tightly abutting a radially outer surface of an adjacent turn of the first layer  144 , each pair of adjacent turns in the first layer  144  defines a groove  148  extending parallel to the turns of wire  1 - 7  in the first layer  144  for receipt therein of a turn of wire  8 - 15  in the second layer  146  of turns. As shown in FIGS. 7 and 8, the self-fixturing wire-guiding means for centering the first and second layers  144 , 146  of the winding about the slot centerline  140  may alternatively be provided by either configuring the corners  136 , 138  of the walls  132 , 136  of the slot  116  to form a shoulder  150 , rather than the chamfer  142 , or a slot liner  152  of electrically insulating material having integrally formed corner spacers  154  may be inserted into the slot  116 . 
     Regardless of the particular corner treatment selected, the chamfer  142 , the shoulder  150 , or the spacer  154 , should preferably have a width substantially equal to about ½ of the wire diameter D extending along the bottom surface  130  and a height extending along the sidewalls  132 , 134  of the slot  116  which is substantially equal to about the wire diameter D. Stated another way, where the wire used to fabricate the winding has a diameter of D and the numeral n refers to the number of turns in the first layer  144  of the winding  118 . The sidewalls  132 , 134  are preferably configured to define a width W 1  at the bottom surface  130  of substantially about n times D, and a width W 2  of the slot  116  substantially equal to about (n+1) times D beginning at a distance substantially equal to about D from the corners  136 , 138  formed by the intersection of the sidewalls  132 , 134  and the bottom surface  130 . 
     From the foregoing description, those skilled in the art will readily recognize that the self-fixturing wire-guiding features of my invention provide the means for fabricating a precision-wound rotor in a straight-forward, low cost manner, without the need for special fixturing. Specifically, my invention allows a precision wound electrical winding to be installed in a rotor by a two step process. In the first step, the first layer  144  of turns is wound across the bottom surface  130 , starting with a first turn  1  disposed in simultaneous contact with one of the chamfers  142 , shoulders  150 , or spacers  154 , etc., at the intersection of a first sidewall  132  and the bottom surface  130 , and continuing with subsequent turns  2 - 7  each wound in a manner to tightly abut the previous turn across the bottom surface until the 7th turn is wound adjacent the second sidewall  134 . The second layer  146  is then wound back across the first layer  144  starting with a first turn  8  of the second layer  146  adjacent the sidewall  134 , and winding each subsequent turn  9 - 15  of the second layer in such a manner that each turn closely abuts a radially outer surface of the previous turn in the second layer  146  and simultaneously resides in a groove  148  formed between adjacent turns of the first layer  144 , until turn  15  of the second layer is wound adjacent to the first sidewall  132 . Subsequent layers of turns  147 , 149  are wound in the same fashion as the second layer  146  of turns, with each turn in each subsequent layer of turns closely abutting a radially outer surface of the previous turn in that layer and simultaneously residing in a groove  148  formed between adjacent turns of wire in the preceding layer. 
     For windings having an even number of layers of turns, my invention thus results in both the innermost  160  and outermost layers  162  of turns being fully supported by the sidewalls  132 , 134  of the slot  116  as illustrated by turns  1 ,  7 ,  23 , and  30  in FIGS. 6-8. Intermediate layers are either tightly contained within the sidewalls  132 , 134  of the slot  116 , as illustrated by turns  8  and  15  in FIGS. 6-8, or are tightly nested and contained within grooves formed by layers of turns extending entirely across the slot as illustrated by the layer of turns  16 - 22  in FIGS. 6-8. Because the turns are so tightly nested, interstices  156  formed between the individual turns are of minimal cross-section and therefore promote maximum fluid velocities of coolant flowing through the interstices leading to turbulent flow conditions and optimum heat transfer from the winding to the cooling fluids. 
     Those skilled in the art will further recognize that the procedure for fabricating the winding  118  described above, and the advantages gained through the practice of my invention, are the same for a rotor which is being repaired as for a new rotor completing initial manufacture. No additional tooling is required to rewind the rotor, and the self-fixturing wire-guiding means of my invention ensure that the precision winding of a rotor which has been repaired will be essentially identical in all respects with a newly manufactured rotor. The only additional steps required to repair or rewind a rotor are removal of the sleeve  105  and the core assembly  102  from the rotor  100 , and stripping off the old winding  118  prior to installing a new winding. Once the core assembly  102  has been rewound, it may be reinstalled in the shaft  106  and the sleeve  105  replaced to complete assembly of the precision-wound rotor  100  in the same manner as during original manufacture. 
     From the foregoing description, those skilled in the art will readily recognize that the self-fixturing wire-guiding features of my invention thus overcome problems encountered in prior precision-wound rotors which required specialized fixturing for their manufacture, or additional structural support for the winding, and in particular for precision-wound rotors having an even number of layers of turns. Those skilled in the art will further recognize that although I have described my invention herein with respect to certain specific embodiments and applications thereof, many other embodiments and applications of my invention are possible within the scope of my invention as described in the appended claims. For instance, although I have made numerous references herein to applications of my invention in a rotor of a dynamoelectric machine, my invention is by no means limited to use only in the rotor of such machines. My invention may be used with equal efficacy in stationary portions of dynamoelectric machines such as in stator windings of such machines. Furthermore, I wish to specifically point out that certain commonly used elements and features of dynamoelectric machine rotor manufacture have been purposely omitted from the illustrations of the exemplary embodiments described herein for purposes of clarity in describing the invention. For example, a slot liner of non-electrically conductive material would typically be included between the winding  118  and slot  116  in an actual rotor construction. It is contemplated that such additional structures or features would be included in a rotor built according to my invention. 
     It is understood, therefore, that the spirit and scope of the appended claims should not be limited to the specific embodiments described and depicted herein.