Abstract:
Embodiments of the invention relate generally to electromagnetic devices and, more particularly, to the compression of stator core laminations using wire rope members and to stator cores and electromagnetic devices employing such wire rope members. In one embodiment, the invention includes: affixing a first end of a wire rope member to a first flange plate disposed adjacent a first end of a plurality of stator laminations; affixing a second end of the wire rope member to a second flange plate disposed adjacent a second end of the plurality of stator laminations; tensioning at least one of the first end or the second end of the wire rope member against at least one of the first flange plate and the second flange plate to exert a compressive force against the first flange plate, the second flange plate, and the plurality of stator laminations.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Stator cores of electromagnetic machines are made up of many thin steel laminations stacked together to form a large cylindrical body. Each lamination comprises a segment of a circular cross-section making up the cylindrical body. Maintaining the integrity of these thin laminations as a stator core requires inward compression exerted from either end of the stacked laminations. 
         [0002]    In known machines, this compressive force is imparted by a plurality of rigid key bars extending from one end of the stator to the other. Typically, the laminations include dovetail slots or similar features that correspond to a compatible dovetail or similar feature on the key bars. Individual components of the stator core are stacked at either end of the stator and compressive force applied to the stator core by torquing a nut at either or both end of each of the key bars. Typically, each lamination is placed onto an assembly frame or system of rails and a compressive force applied following the installation of each lamination or after a few laminations have been installed. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    In one embodiment, the invention provides a method of exerting a compressive force to components of a stator core of an electromagnetic machine, the method comprising: affixing a first end of a wire rope member to a first flange plate disposed adjacent a first end of a plurality of stator laminations; affixing a second end of the wire rope member to a second flange plate disposed adjacent a second end of the plurality of stator laminations; tensioning at least one of the first end or the second end of the wire rope member against at least one of the first flange plate and the second flange plate to exert a compressive force against the first flange plate, the second flange plate, and the plurality of stator laminations. 
         [0004]    In another embodiment, the invention provides a stator core for an electromagnetic device, the stator core comprising: a plurality of stacked stator laminations; at least one flange member adjacent a first end of the plurality of stacked stator laminations; and a wire rope member attached to the at least one flange member, the at least one wire rope member, upon tensioning, exerting a compressive force against the at least one flange member. 
         [0005]    In still another embodiment, the invention provides an electromagnetic device comprising: a plurality of stacked stator laminations; at least one flange member adjacent a first end of the plurality of stacked stator laminations; and a wire rope member attached to the at least one flange member, the at least one wire rope member, upon tensioning, exerting a compressive force against the at least one flange member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which: 
           [0007]      FIG. 1  shows an axial cross-sectional view of a stator core according to an embodiment of the invention. 
           [0008]      FIG. 2  shows a radial cross-sectional view of a stator core according to an embodiment of the invention. 
           [0009]      FIGS. 3-4  show detailed radial cross-sectional views of portions of stator cores according to other embodiments of the invention. 
           [0010]      FIG. 5  shows a schematic view of a portion of a wire rope member used in some embodiments of the invention. 
           [0011]      FIGS. 6-7  show schematic cross-sectional views of wire rope members used in some embodiments of the invention. 
           [0012]      FIG. 8  shows a cross-sectional side view of a wire rope member and attachment device used in some embodiments of the invention. 
           [0013]      FIG. 9  shows a top view of  FIG. 8 . 
           [0014]      FIG. 10  shows a flow diagram of a method according to an embodiment of the invention. 
       
    
    
       [0015]    It is noted that the drawings of the invention are not to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements among the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Embodiments of the present invention comprise methods for the assembly of stator cores using flexible wire rope rather than rigid key bars, as well as systems for the assembly of such stator cores and stator cores assembled according to such methods or using such systems. 
         [0017]    Turning now to the drawings,  FIG. 1  shows a schematic side view of a stator core  100  according to one embodiment of the invention. Here, stator core  100  comprises a plurality  10  of stacked laminations A, B, C . . . X disposed between a pair of flange plates  20 , 22 . Typically, laminations A, B, C . . . X comprise thin insulated steel plates, which may number in the hundreds or thousands, depending on the application to which the stator core  100  will be put. Flange plates  20 ,  22  are typically comprised of steel or aluminum, although other materials may be used. 
         [0018]    A plurality of wire rope members  30 A through  30 H extend from the first flange plate  20  to the second flange plate  22 . Wire rope members may include any number of materials, including, for example, solid metal wires, twisted or braided metal wires, polyethylene fibers, nylon fibers, etc. In some embodiments of the invention, the wire rope members comprise wire rope made up of a plurality of braided metal strands surrounding a solid or braided metal core. Other materials are possible, of course, and the term “wire rope member,” as used herein, is intended to refer broadly to a flexible wire capable of imparting a compressive force to a plurality of stacked laminations. 
         [0019]      FIG. 2  shows a cross-sectional view of the stator core  100  of  FIG. 1  taken along the plane of lamination A. As can be seen in  FIG. 2 , lamination A includes a plurality of segments A1 through A8. Although lamination A is shown as comprising eight segments in  FIG. 2 , one skilled in the art will recognize that any number of segments may be employed. When assembled, segments A1 through A8 form a central bore  12  having a plurality of slots  14  for containing stator windings (not shown). 
         [0020]    A plurality of wire rope members  30 A through  30 P are disposed around lamination A. As shown in  FIG. 2 , each segment of lamination A includes two wire rope members along its outer surface, although this is not essential. Any number of wire rope members may be employed, with any portion of the total number of wire rope members being disposed adjacent each of the segments of lamination A. 
         [0021]      FIG. 3  shows a detailed view of a portion of segments A1, A2 according to another embodiment of the invention. Here, segment A1, representative of each of the segments, includes channels  16 A,  16 B into which wire rope members  30 A,  30 B, respectively, may be disposed. In some embodiments, channels  16 A,  16 B include openings greater than the diameters of wire rope member  30 A,  30 B, respectively. In other embodiments, channels  16 A,  16 B include openings larger than the diameters of wire rope members  30 A,  30 B, respectively, such that wire rope members  30 A,  30 B may be threaded through adjacently stacked laminations of the stator core. 
         [0022]    In other embodiments, such as that shown in  FIG. 4 , the wire rope members  30 A,  30 C may be threaded through axial holes  26 A,  26 C, respectively, in segments A1 and A2. The placement of axial holes  26 A,  26 C may be matched to create uniform compressive stress in the stator core. One skilled in the art will recognize that some embodiments of the invention may include features of both  FIG. 3  and  FIG. 4 . 
         [0023]    Embodiments of the invention, such as those shown in  FIGS. 1-4 , may be useful in the assembly of stator core  100  ( FIG. 1 ). For example, pre-stress in the wire rope members may be adjusted during various stages of the assembly of a stator core and/or during the subsequent installation of the stator core in a supporting frame. Such adjustment of the tension may aid in the stacking of stator core laminations and/or movement of the assembled stator core. 
         [0024]      FIGS. 5-6  show views of wire rope members according to various embodiments of the invention.  FIG. 5  shows a side view of a wire rope member  30  comprising a plurality of braided wire strands  31 - 36 .  FIG. 6  shows a radial cross-sectional view of wire rope member  30 , showing wire strands  31 - 36  disposed about a central wire strand  37 . In some embodiments, strands  31 - 36  may include flattened rather than rounded surfaces to improve contact friction. 
         [0025]      FIG. 7  shows a radial cross-sectional view of wire rope member  30  including an optional insulating layer  38 . Insulating layer  38  may include any number of materials, including, for example, rubbers, vinyls, polypropylene, polyethylene, epoxies, polyethylene, etc. Insulating layer  38  reduces fretting of wire strands  31 - 36 , which might otherwise occur upon contact with flange plates  20 ,  22  or the laminations of the stator core. It should be noted that insulating layer  38  may be affixed to wire rope member  30  or, in some embodiments of the invention, may surround wire rope member  30 , such that wire rope member  30  may be threaded into and through insulating layer  38 . 
         [0026]      FIG. 8  shows a cross-sectional side view of flange plate  20  according to an embodiment of the invention. For the sake of simplicity, the interaction of wire rope members and flange plate  20  will be described with respect to wire rope member  30 H only. Flange plate  20  includes a conically-shaped passage  40 H through which wire rope member  30 H may be passed. Passage  40 H may include a locking mechanism for securing wire rope member  30 H within passage  40 H. As shown in  FIG. 8 , such a locking mechanism includes a plurality of wedge-shaped members  42 H,  44 H adapted to compress and secure wire rope member  30 H within passage  40 H. Wedge-shaped member  42 H,  44 H include a first surface for contacting wire rope member  30 H and a second member for contacting a wall of passage  40 H. Wedge-shaped members  42 H,  44 H, as their name suggests, include a narrower end and a wider end. Wire rope member  30 H may be tensioned within passage  40 H by drawing wire rope member  30 H through passage  40 H, i.e., from the narrower end toward the wider end of wedge-shaped member  42 H,  44 H. 
         [0027]      FIG. 9  shows a top view of a portion of flange plate  20  including passage  40 H. Here, three wedge-shaped members  42 H,  44 H,  46 H restrain wire rope member  30 H within passage  40 H. 
         [0028]    Stator cores employing wire rope members as described above provide a number of advantages over conventional key bar stator cores. Wire rope, for example, has a higher breaking strength, typically greater than 250 ksi, than key bars. As a consequence, a greater compressive force may be exerted upon stacked laminations than is possible using key bars. 
         [0029]    Wire rope members may also be secured and tensioned using any number of devices and techniques. For example, various devices are commercially available for tensioning wire rope members. Such devices may be employed to tension wire rope members from either or both ends of the stator core by drawing the wire rope members away from the flange plates and the laminations along a longitudinal axis of the stator core. 
         [0030]    In addition, the use of wire ropes permits pre-assembly of a plurality of laminations and their segments, which is not possible using key bars to compress the stator core. Such pre-assembly can greatly reduce assembly time and costs. 
         [0031]      FIG. 10  shows a flow diagram of a method according to an embodiment of the invention. At S 1 , a wire rope member is affixed to a first flange plate adjacent a first end of a plurality of stacked stator laminations. At S 2 , the wire rope member may optionally be inserted into a channel along each of the plurality of stacked stator laminations. At S 3  the wire rope member is affixed to a second flange plate adjacent a second end of the plurality of stacked stator laminations. At S 4 , the wire rope member is tensioned against at least one of the first flange plate and the second flange plate, thereby applying a compressive force against the plurality of stacked stator laminations. 
         [0032]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0033]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any related or incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.