Rotor Assembly Manufacturing Technique and Resultant Structure

Abstract

A rotor fabrication method is provided, along with the resultant rotor assembly. The rotor uses pre-fabricated conductive rotor bars in which the ends have been shaped and sized to fit within corresponding end cap receptacles. After assembly, the structure is compressed, thereby achieving mechanical and electrical coupling between the conductive rotor bars and the end caps. Locking members disposed at either end of the assembly maintain the desired level of axial compressive force on the structure.

What is claimed is: 
     
         1 . A rotor assembly mounted to a rotor shaft, said rotor assembly comprising:
 a plurality of lamination discs, each of said plurality of lamination discs comprising a plurality of slots, said plurality of lamination discs assembled into a stack, and said plurality of slots of said plurality of lamination discs co-aligned within said stack;   a plurality of conductive rotor bars extending through said stack and through said plurality of slots, wherein a first end region of each of said plurality of conductive rotor bars extends out of a first end surface of said stack, wherein a second end region of each of said plurality of conductive rotor bars extends out of a second end surface of said stack, and wherein said first end region and said second end region of each of said plurality of conductive rotor bars is tapered;   a first end cap disposed on said rotor shaft, said first end cap comprising a first plurality of receptacles corresponding to said plurality of conductive rotor bars, wherein each receptacle of said first plurality of receptacles receives said first end region of each corresponding conductive rotor bar of said plurality of conductive rotor bars, and wherein each receptacle of said first plurality of receptacles is mechanically and electrically coupled to said first end region of each corresponding conductive rotor bar of said plurality of conductive rotor bars;   a second end cap disposed on said rotor shaft, said second end cap comprising a second plurality of receptacles corresponding to said plurality of conductive rotor bars, wherein each receptacle of said second plurality of receptacles receives said second end region of each corresponding conductive rotor bar of said plurality of conductive rotor bars, and wherein each receptacle of said second plurality of receptacles is mechanically and electrically coupled to said second end region of each corresponding conductive rotor bar of said plurality of conductive rotor bars;   a first locking member disposed on said rotor shaft, said first locking member configured to apply a first axial compressive force on said first end cap to maintain said first end region of each conductive rotor bar of said plurality of conductive rotor bars within each corresponding receptacle of said first plurality of receptacles; and   a second locking member disposed on said rotor shaft, said second locking member configured to apply a second axial compressive force on said second end cap to maintain said second end region of each conductive rotor bar of said plurality of conductive rotor bars within each corresponding receptacle of said second plurality of receptacles.   
     
     
         2 . The rotor assembly of  claim 1 , wherein at least two surfaces of said first end region of each of said plurality of conductive rotor bars are tapered, and wherein at least two surfaces of said second end region of each of said plurality of conductive rotor bars are tapered. 
     
     
         3 . The rotor assembly of  claim 1 , said first end region of each of said plurality of conductive rotor bars comprising at least one arcuate surface, and said second end region of each of said plurality of conductive rotor bars comprising at least one arcuate surface. 
     
     
         4 . The rotor assembly of  claim 1 , said first plurality of receptacles extending away from an inner first surface of said first end cap and towards said first end surface of said stack, and said second plurality of receptacles extending away from an inner second surface of said second end cap and towards said second end surface of said stack. 
     
     
         5 . The rotor assembly of  claim 1 , said first plurality of receptacles extending between an inner first surface of said first end cap and an outer first surface of said first end cap, and said second plurality of receptacles extending between an inner second surface of said second end cap and an outer second surface of said second end cap. 
     
     
         6 . The rotor assembly of  claim 1 , wherein a first portion of said first end region of each of said plurality of conductive rotor bars extends completely through said first end cap, and wherein a second portion of said second end region of each of said plurality of conductive rotor bars extends completely through said second end cap. 
     
     
         7 . The rotor assembly of  claim 6 , wherein said first portion of said first end region of each of said plurality of conductive rotor bars is mechanically deformed and expanded within each corresponding receptacle of said first plurality of receptacles, and wherein said second portion of said second end region of each of said plurality of conductive rotor bars is mechanically deformed and expanded within each corresponding receptacle of said second plurality of receptacles. 
     
     
         8 . The rotor assembly of  claim 6 , wherein said first portion of said first end region of each of said plurality of conductive rotor bars is welded to each corresponding receptacle of said first plurality of receptacles, and wherein said second portion of said second end region of each of said plurality of conductive rotor bars is welded to each corresponding receptacle of said second plurality of receptacles. 
     
     
         9 . The rotor assembly of  claim 1 , wherein each of said plurality of lamination discs and said first end cap and said second end cap is further comprised of a first feature, wherein said rotor shaft is further comprised of a second feature, wherein said first feature is complementary to said second feature, and wherein said first feature and said second feature maintain alignment of each of said plurality of lamination discs and said first end cap and said second end cap. 
     
     
         10 . The rotor assembly of  claim 1 , wherein said first locking member is comprised of a first retaining nut, and wherein said second locking member is comprised of a second retaining nut. 
     
     
         11 . The rotor assembly of  claim 1 , further comprising a first spacer and a second spacer, said first spacer disposed between said first end surface of said stack and said first end cap, said second spacer disposed between said second end surface of said stack and said second end cap, wherein said first spacer and said second spacer limit compressibility and deformation of said plurality of conductive rotor bars. 
     
     
         12 . The rotor assembly of  claim 1 , further comprising a plurality of alignment locking pins, each of said plurality of lamination discs further comprising a plurality of alignment holes, said plurality of alignment holes of said plurality of lamination discs co-aligned within said stack, said plurality of alignment locking pins disposed within said stack, and wherein said plurality of alignment locking pins extend through said stack and through said plurality of alignment holes. 
     
     
         13 . The rotor assembly of  claim 12 , wherein a first end portion of each of said plurality of alignment locking pins extends out of said first end surface of said stack and is disposed within a complementary end cap aperture of said first end cap, and wherein a second end portion of each of said plurality of alignment locking pins extends out of said second end surface of said stack and is disposed within a complementary end cap aperture of said second end cap. 
     
     
         14 . The rotor assembly of  claim 1 , further comprising a first disc spring and a second disc spring, said first disc spring disposed between an outer end surface of said first end cap and said first locking member, said first disc spring maintaining said first axial compressive force on said first end cap, said second disc spring disposed between an outer end surface of said second end cap and said second locking member, said second disc spring maintaining said second axial compressive force on said second end cap. 
     
     
         15 . The rotor assembly of  claim 1 , wherein a first circumferential portion of said first end cap is removed and a first portion of said first end region of each of said plurality of conductive rotor bars is exposed via a first machining process, wherein said first portion of said first end region of each of said plurality of conductive rotor bars is welded to said circumferential portion of said first end cap, wherein a second circumferential portion of said second end cap is removed and a second portion of said second end region of each of said plurality of conductive rotor bars is exposed via a second machining process, wherein said second portion of said second end region of each of said plurality of conductive rotor bars is welded to said circumferential portion of said second end cap. 
     
     
         16 . The rotor assembly of  claim 15 , further comprising a first containment ring interference fit to said first circumferential portion of said first end cap, and a second containment ring interference fit to said second circumferential portion of said second end cap. 
     
     
         17 . The rotor assembly of  claim 16 , said first containment ring and said second containment ring fabricated from a material selected from the group consisting of a stainless steel, a beryllium copper alloy, and a metal matrix composite. 
     
     
         18 . The rotor assembly of  claim 1 , said plurality of conductive rotor bars, said first end cap and said second end cap each fabricated from a material selected from the group consisting of oxygen-free electrolytic (OFE) copper, non-OFE copper and aluminum. 
     
     
         19 . A method of fabricating a rotor assembly for an electric motor, comprising:
 assembling a lamination stack, wherein said lamination stack is comprised of a plurality of lamination discs, wherein each of said lamination discs is comprised of a plurality of slots, said plurality of slots of said plurality of lamination discs co-aligned within said lamination stack, and wherein each of said lamination discs is further comprised of a central bore;   inserting a plurality of conductive rotor bars into said plurality of slots corresponding to said lamination stack, wherein a first end region of each of said plurality of conductive rotor bars extends beyond a first end surface of said lamination stack, and wherein a second end region of each of said plurality of conductive rotor bars extends beyond a second end surface of said lamination stack, and wherein said first end region and said second end region of each of said plurality of conductive rotor bars is tapered;   locating a rotor shaft within said central bore of said lamination stack;   mounting a first end cap onto said rotor shaft and adjacent to said first end surface of said lamination stack, said first end cap comprising a first plurality of receptacles corresponding to said plurality of conductive rotor bars;   inserting said first end region of each conductive rotor bar of said plurality of conductive rotor bars into a corresponding receptacle of said first plurality of receptacles, wherein each receptacle of said first plurality of receptacles is mechanically and electrically coupled to said first end region of each corresponding conductive rotor bar of said plurality of conductive rotor bars;   mounting a second end cap onto said rotor shaft and adjacent to said second end surface of said lamination stack, said second end cap comprising a second plurality of receptacles corresponding to said plurality of conductive rotor bars;   inserting said second end region of each conductive rotor bar of said plurality of conductive rotor bars into a corresponding receptacle of said second plurality of receptacles, wherein each receptacle of said second plurality of receptacles is mechanically and electrically coupled to said second end region of each corresponding conductive rotor bar of said plurality of conductive rotor bars;   mounting a first locking member onto said rotor shaft and adjacent to said first end cap, wherein said first locking member applies a first axial compressive force on said first end cap to maintain said first end region of each conductive rotor bar of said plurality of conductive rotor bars within each corresponding receptacle of said first plurality of receptacles; and   mounting a second locking member onto said rotor shaft and adjacent to said second end cap, wherein said second locking member applies a second axial compressive force on said second end cap to maintain said second end region of each conductive rotor bar of said plurality of conductive rotor bars within each corresponding receptacle of said second plurality of receptacles.   
     
     
         20 . The method of  claim 19 , further comprising:
 tapering at least two surfaces of said first end region of each of said plurality of conductive rotor bars; and   tapering at least two surfaces of said second end region of each of said plurality of conductive rotor bars.   
     
     
         21 . The method of  claim 19 , further comprising:
 arcuately shaping at least one surface of said first end region of each of said plurality of conductive rotor bars; and   arcuately shaping at least one surface of said second end region of each of said plurality of conductive rotor bars.   
     
     
         22 . The method of  claim 19 , said first plurality of receptacles extending completely through said first end cap and said second plurality of receptacles extending completely through said second end cap, wherein said step of inserting said first end region of each conductive rotor bar of said plurality of conductive rotor bars into said corresponding receptacle of said first plurality of receptacles further comprises mechanically deforming and expanding a first portion of said first end region of each of said plurality of conductive rotor bars within each corresponding receptacle of said first plurality of receptacles, and wherein said step of inserting said second end region of each conductive rotor bar of said plurality of conductive rotor bars into said corresponding receptacle of said second plurality of receptacles further comprises mechanically deforming and expanding a second portion of said second end region of each of said plurality of conductive rotor bars within each corresponding receptacle of said second plurality of receptacles. 
     
     
         23 . The method of  claim 19 , said first plurality of receptacles extending completely through said first end cap and said second plurality of receptacles extending completely through said second end cap, the method further comprising:
 welding said first end region of each conductive rotor bar of said plurality of conductive rotor bars into said corresponding receptacle of said first plurality of receptacles; and   welding said second end region of each conductive rotor bar of said plurality of conductive rotor bars into said corresponding receptacle of said second plurality of receptacles.   
     
     
         24 . The method of  claim 19 , further comprising:
 fabricating a first feature on each of said plurality of lamination discs and said first end cap and said second end cap;   fabricating a second feature on said rotor shaft, wherein said first feature is complementary to said second feature; and   aligning said first feature of each of said plurality of lamination discs and said first end cap and said second end cap with said second feature of said rotor shaft, wherein said aligning step maintains alignment between each of said plurality of lamination discs, said first end cap and said second end cap.   
     
     
         25 . The method of  claim 19 , further comprising:
 mounting a first spacer onto said rotor shaft and locating said first spacer between said first end surface of said stack and said first end cap; and   mounting a second spacer onto said rotor shaft and locating said second spacer between said second end surface of said stack and said second end cap, wherein said first spacer and said second spacer limit compressibility and deformation of said plurality of conductive rotor bars.   
     
     
         26 . The method of  claim 19 , further comprising:
 fabricating a plurality of alignment holes within each of said plurality of lamination discs; and   inserting a plurality of alignment locking pins through said lamination stack and through said plurality of alignment holes.   
     
     
         27 . The method of  claim 26 , further comprising:
 inserting a first end portion of each of said plurality of alignment locking pins into a corresponding complementary end cap aperture of said first end cap; and   inserting a second end portion of each of said plurality of alignment locking pins into a corresponding complementary end cap aperture of said second end cap.   
     
     
         28 . The method of  claim 19 , further comprising:
 positioning a first disc spring between an outer end surface of said first end cap and said first locking member, said first disc spring maintaining said first axial compressive force on said first end cap; and   positioning a second disc spring between an outer end surface of said second end cap and said second locking member, said second disc spring maintaining said second axial compressive force on said second end cap.   
     
     
         29 . The method of  claim 19 , further comprising:
 machining said first end cap to remove a first circumferential portion of said first end cap, wherein said step of machining said first end cap exposes a first portion of said first end region of each of said plurality of conductive rotor bars;   welding said first portion of said first end region of each of said plurality of conductive rotor bars to said first circumferential portion of said first end cap;   machining said second end cap to remove a second circumferential portion of said second end cap, wherein said step of machining said second end cap exposes a second portion of said second end region of each of said plurality of conductive rotor bars; and   welding said second portion of said second end region of each of said plurality of conductive rotor bars to said second circumferential portion of said second end cap.   
     
     
         30 . The method of  claim 29 , further comprising:
 fitting a first containment ring around said first end cap, wherein said first containment ring encircles said first portion of said first end region of each of said plurality of conductive rotor bars, and wherein said first containment ring is positioned where said first circumferential portion of said first end cap was removed during said step of machining said first end cap; and   fitting a second containment ring around said second end cap, wherein said second containment ring encircles said second portion of said second end region of each of said plurality of conductive rotor bars, and wherein said second containment ring is positioned where said second circumferential portion of said second end cap was removed during said step of machining said second end cap.   
     
     
         31 . The method of  claim 30 , further comprising fabricating said first containment ring and said second containment ring from a material selected from the group consisting of a stainless steel, a beryllium copper alloy, or a metal matrix composite. 
     
     
         32 . The method of  claim 19 , further comprising fabricating said plurality of conductive rotor bars from a material selected from the group consisting of oxygen-free electrolytic (OFE) copper, non-OFE copper and aluminum. 
     
     
         33 . The method of  claim 19 , further comprising fabricating said first end cap and said second end cap from a material selected from the group consisting of oxygen-free electrolytic (OFE) copper, non-OFE copper and aluminum.