Patent Publication Number: US-2013249342-A1

Title: Cantilevered Rotor Magnet Support

Description:
Cross-reference is made to commonly assigned, co-pending U.S. patent application Ser. No. 13/215,296, filed Aug. 23, 2011, titled MAGNETIC ROTOR HAVING INSET BRIDGES TO PROMOTE COOLING. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention concerns a multilayer laminated rotor configuration usable in a rotary electric machine arrangement. 
     2. Description of Related Art 
     U.S. Pat. No. 3,979,821 to Noodleman discloses a permanent magnet rotor lamination having openings adapted to receive pieces of magnet material. Each of these openings has lips or flanges adapted to retain a respective magnet material piece in place. 
     U.S. Pat. No. 5,162,686 to Royer concerns a rotor having magnets held radially in place by extensions of magnetic poles, laminations, or pockets. 
     U.S. Pat. No. 7,436,096 to Guven et al. relates to an electric machine including a rotor with permanent magnets arranged in clusters or groups adjacent an outer rotor perimeter. 
     U.S. Pat. No. 6,340,857 to Nishiyama et al., U.S. Pat. No. 6,525,442 to Koharagi et al., U.S. Pat. No. 6,700,288 to Smith, U.S. Pat. No. 6,703,743 to Kaneko et al., U.S. Pat. No. 6,794,784 to Takahashi et al., U.S. Pat. No. 7,504,754 to Jahns et al., U.S. Pat. No. 7,687,957 to Ochiai et al., U.S. Pat. No. 7,847,456 to Kori et al., U.S. Pat. No. 7,851,958 to Cai et al., U.S. Pat. No. 7,902,710 to Han et al., and U.S. Pat. No. 7,952,249 to Kori et al. may also be of interest. 
     The disclosures of U.S. Pat. Nos. 3,979,821 to Noodleman, 5,162,686 to Royer, and 7,436,096 to Guven et al. are all incorporated herein by reference in their entireties as non-essential subject matter. 
     SUMMARY OF THE INVENTION 
     A multilayer laminated rotor according to this invention is mountable on a shaft for rotation relative to a stator of a rotary electric machine arrangement and has a plurality of laminas joined together to form the rotor with voids for receiving magnets. The rotor has an annular section, extending between a shaft opening for receiving the shaft and a radially outer circumferential rotor surface, which includes an undulating series of the voids in void groups extending from the radially outer circumferential rotor surface inwardly toward the shaft opening and then back toward the radially outer circumferential rotor surface. A pair of distal voids in each void group, together with distal voids of adjacent void groups, define gaps separating adjacent arc sections of the radially outer circumferential rotor surface. 
     The voids may be arranged in a variety of ways, although, in each arrangement, it is intended to have webs disposed between adjacent voids in each of the void groups support portions of the rotor defining the arc sections primarily in a radial direction of the rotor, and to have portions of the rotor defining the arc sections connected to a central rotor portion solely by webs disposed between adjacent voids in each of the void groups. A central permanent magnet received in a central one of the voids in at least one of the void groups, for example, may be wider than other magnets in that void group. Some of the voids in each of the void groups may be interconnected, moreover, and at least one of the webs may be located centrally with respect to at least one of the void groups. None of the webs needs to be located centrally with respect to any of the void groups, however. 
     Although it is contemplated that the voids will have an approximately rectangular configuration in a plan view, other void geometries could be used, and the undulating series of voids mentioned extends circumferentially completely around the rotor. The invention additionally concerns a lamina to be included in a multilayer laminated rotor such as that referred to. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic plan view of an end of a rotor that supports permanent magnets according to the invention. 
         FIG. 2  is an enlarged view of a portion P of a rotor lamina at the end of the rotor shown in  FIG. 1 . 
         FIG. 3  is an enlarged view similar to that of  FIG. 2  but of a lamina with a different magnet receptacle arrangement. 
         FIG. 4  is an enlarged view similar to that of  FIG. 2  but of a lamina with another magnet receptacle arrangement. 
         FIG. 5  is an enlarged view similar to that of  FIG. 2  but of a lamina with still another magnet receptacle arrangement. 
         FIG. 6  is a further enlarged view of a portion Q of the rotor lamina shown in  FIG. 2  without the magnets being shown. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An interior permanent magnet rotor lamina  10  used in production of a multilayer laminated rotor according to the present invention is shown, in plan view, in  FIG. 1 . It will be understood by those of ordinary skill in the art that the lamina  10  shown in  FIG. 1  is an endmost lamina of multiple (e.g., fifty) laminas joined together in a lamination stack to produce the rotor  12  constituting part of a rotary electric machine arrangement, such as a motor, generator, or motor/generator. The laminas may be stamped from sheets of steel or other suitable material. A rotor shaft (not shown) is receivable within a shaft opening  14  of the rotor  12  to impart rotational motion to the rotor. A radially inwardly projecting tooth or key  16  may be used in conjunction with a corresponding recess in the rotor shaft to help secure the rotor  12  against rotation relative to the rotor shaft. 
     Each lamina  10  has an annular section surrounding the shaft opening  14  and extending between that shaft opening  14  and a radially outer circumferential surface of the overall rotor  12 . The annular section is provided with a series  18  of magnet receiving holes, voids, or orifices (hereafter referred to as voids for simplicity) located adjacent a radially outer lamina surface. When the laminas  10  are joined together in a stack to collectively define the rotor  12 , the voids of adjacent laminas align and are located near the radially outer circumferential rotor surface  20 . As will be described in connection with  FIGS. 2-6 , permanent magnets  22  are receivable within the voids. The permanent magnets  22  may be inserted into the voids after the laminas  10  are joined together, or, if desired, the voids may be aligned with the magnets  22  as the laminas  10  are slid over the magnets  22  so that the magnets  22  serve as guides to position the laminas  10  properly during rotor construction. Once a selected number of laminas  10  have been joined together, the magnets  22  have been potted, glued, or otherwise secured in place, and the laminated rotor  12  is completed, the permanent magnets  22  extend axially relative to the rotor  12  through the aligned voids of the stack of laminas  10  to a desired extent. The magnets  22  thereafter remain fixed within the voids to cooperate with windings disposed around poles of a stator, within which the overall rotor  12  is rotatable. 
     As  FIG. 1  shows, the series  18  of voids undulates, and is composed of a multiplicity of void groups  24 . Each void group  24  extends from the radially outer circumferential rotor surface inwardly toward the shaft opening  14  and then back toward the rotor surface  20 . The series  18  extends circumferentially completely around the lamination and, therefore, the rotor including that lamination. In the arrangement illustrated in  FIGS. 1 and 2 , each void group  24  includes a pair of opposite distal voids  26 ,  28 , a pair of opposite proximal voids  30 ,  32 , and a pair of opposite intermediate voids  34 ,  36 . In this particular arrangement, each of the distal voids  26 ,  28  is separated from an adjacent intermediate void  34 ,  36  by a respective web  38 ,  40  of lamina material. Each of the proximal voids  30 ,  32 , however, is separated from its adjacent intermediate void  34 ,  36 , by flanges, nubs or bumps  42 ,  44 , defining partial webs, such that the sets of proximal and adjacent intermediate voids are actually interconnected. The adjacent proximal voids  30 ,  32 , in each void group  24  are separated from each other by a middle web  46  located centrally with respect to that void group. The voids, shown as approximately rectangular in the plan view provided by  FIG. 2 , may include recessed fillets  48  at some or all of their corners for optimal stress concentration properties. Other void geometries, of course, could be used. Certain features of this particular arrangement are more clearly illustrated in the enlarged view provided by  FIG. 6 . 
     Typically, a rotor lamina utilizing a “buried magnet” design will have a continuous radially outer circumferential surface, such that the material of the rotor lamina fully encircles all magnets in the voids of each void group. In each of the embodiments of this invention, however, as will be described, rotor lamina material is removed from or left out of the outer diameter region of the distal voids in each void group. Avoiding the presence of this rotor lamina material has a structural benefit, as it eliminates rotational hoop stresses from the typically thin outer sections of the lamination webs, and instead forces the structural support to be cantilevered. With this configuration, the remaining webs provide support primarily in the radial direction. 
     Referring once again to  FIG. 2 , the series  18  of voids is arranged in such a way that, throughout the rotor  12 , the distal voids  26 ,  28  of adjacent void groups  24  are located next to each other. The distal voids  26 ,  28  in each of the void groups  24 , together with distal voids of adjacent void groups, define gaps  52  separating adjacent arc sections of the radially outer circumferential rotor surface  20 . These adjacent arc sections of the rotor surface  20  are accordingly separated by the gaps  52 , which may be produced by machining away or leaving out rotor material between the adjacent arc sections. Although such a construction leaves the distal voids  26 ,  28  open and exposed, flanges, nubs, bumps, or other protrusions  50  of material at adjacent ends of the rotor surface arc sections and common interior flanges, nubs, bumps, or other protrusions  54  of material located between the distal voids  26 ,  28  help in positioning and retaining magnets  22  within the voids  26 ,  28 . Thus, instead of having support webs fully encircling the permanent magnets, the support web is eliminated from the gaps  52  at the outer diameter region of the rotor. By distributing the gaps  52  around the radially outer circumferential surface  20  of the rotor  12 , a modified rotor lamination geometry resulting in reduced stress and improved performance at high rotational speeds is provided. Absence of rotor material in the gaps  52  has a structural benefit, as such a configuration, again, removes rotational hoop stresses from the typically thin outer sections of the rotor laminations, and instead forces the structural support to be cantilevered. Thus, in the arrangement illustrated in  FIG. 2 , the remaining webs  38 ,  40 , and  46  advantageously provide support primarily in the radial direction, and the added benefit of improved electrical performance, due to a reduction in magnetic leakage pathways, is also provided by the gaps. Different types of void series patterns, of course, can be utilized; such patterns, for example, could be roughly v-shaped, similar to that of the series  18 , roughly u-shaped, or flat. 
       FIG. 3  illustrates an alternative void group arrangement. Here, each void group  124  includes a pair of opposite distal voids  126 ,  128 , a single, v-shaped proximal void  130 , and a pair of opposite intermediate voids  134 ,  136  disposed between the proximal void  130  and the distal voids  126 ,  128 . Each of the distal voids  126 ,  128  is separated from an adjacent intermediate void  134 ,  136  by a respective web  138 ,  140  of lamina material, while the proximal void  130  is separated at opposite ends from its adjacent intermediate voids  134 ,  136  by respective webs  142 ,  144  of lamina material. There is no web separating adjacent magnets  22  received within the v-shaped proximal void  130  in this particular arrangement. In other respects, the arrangement shown in  FIG. 3  is essentially the same as that shown in  FIG. 2 . The voids once again may include recessed fillets  148  at some or all of their corners to optimize stress concentration. 
     Accordingly, the series of voids is configured in the arrangement shown in  FIG. 3  so that, throughout the rotor, the distal voids  126 ,  128  of adjacent void groups  124  are located next to each other. Adjacent arc sections of the rotor surface  120  are separated by gaps  152 , which may be produced by machining away or leaving out rotor material between the adjacent arc sections. Flanges, nubs, bumps, or other protrusions  150  of material at adjacent ends of the rotor surface arc sections and common interior flanges, nubs, bumps, or other protrusions  154  of material located between the distal voids  126 ,  128  help in positioning and retaining magnets  22  within the voids  126 ,  128 . Again, instead of having support webs fully encircling the permanent magnets, the support web is eliminated from the gaps at the outer diameter region of the rotor. By distributing the gaps  152  around the radially outer circumferential surface  120  of the rotor, the rotor lamination geometry results in reduced stress and improved performance at high rotational speeds. As before, absence of rotor material in the gaps  152  has a structural benefit, as such a configuration removes rotational hoop stresses from the typically thin outer sections of the rotor laminations, and instead forces the structural support to be cantilevered. Once again, the remaining webs  138 ,  140 ,  142  and  144  provide support primarily in the radial direction, and improved electrical performance, due to a reduction in magnetic leakage pathways, is provided. 
     Another void group arrangement is shown in  FIG. 4 . The arrangement shown in  FIG. 4  is essentially the same as that shown in  FIG. 3 , except that the single, elongated proximal void  230  shown in  FIG. 4  is rectangular in plan view rather than v-shaped, and can receive a wider unitary magnet  222 . The voids  226 ,  228 ,  234 , and  236  shown in  FIG. 4  are, respectively, essentially identical to the voids  126 ,  128 ,  134 , and  136  shown in  FIG. 3 , and carry magnets  22 . Due to the presence of the elongated void  230 , the void series pattern of  FIG. 4  is best described as roughly u-shaped. Gaps  252  are distributed around the radially outer circumferential rotor surface  220 , and webs  238 ,  240 ,  242 , and  244  provide support primarily in the radial direction. Improved electrical performance due to a reduction in magnetic leakage pathways is again provided. 
     Yet another void group arrangement is shown in  FIG. 5 . The arrangement shown in  FIG. 5  is similar to that shown in  FIG. 4 , except that each of the voids  330 ,  334 , and  336  shown in  FIG. 5  is rectangular and can receive a pair of directly adjacent, contacting magnets  22  or, if desired, a unitary magnet of greater width. Gaps  352  are distributed around the radially outer circumferential rotor surface  320 , and webs  342  and  344  provide support primarily in the radial direction. Improved electrical performance due to a reduction in magnetic leakage pathways is once again provided. 
     The present invention thus provides a rotor lamination geometry that allows for reduced mechanical stress and reduced electromagnetic degradation from magnet support webs. This geometry allows for higher speed, higher performance electric motors and generators. In contrast to conventional laminated rotor designs utilized with buried permanent magnets, with support webs fully encircling the permanent magnets, the modified rotor lamination geometry of this invention reduces stress and improves performance at high rotational speeds. By eliminating a support web from the outer diameter region of the rotor, rotational hoop stresses are removed from the typically thin outer web sections. The structural support is forced to be cantilevered, and the remaining webs provide tensile support primarily in the radial direction of the rotor. The invention can be used with a number of different magnet segments in both flat, v-, and u-orientation shapes, as noted, and only a few examples, which are not intended to be limiting, have been described above. 
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, and the invention should be construed to include everything within the scope of the invention ultimately claimed.