Strain-matched hub for motor/generator

Abstract

A strain-matched hub for a motor/generator. The motor/generator preferably includes a cylindrical rotor surrounding a stator, and of larger diameter than a shaft. The hub, formed of a single material, connects the shaft to the rotor assembly, and contains a fastener circle whose expansion is matched to the rotor's expansion, in operation. Like the rotor, the hub's fastener circle expands uniformly around the fastener circle's circumference. Typically, a ring of keystone-shaped metal elements fits the hub to the rotor. The hub attaches to the keystone-shaped elements with a plurality of bolts or other fasteners, and the keystone-shaped elements fit to the rotor. The hub is formed of a single material and contains a plurality of spokes, each spoke positioned along a radius from the center of the hub to the center of a bolt. Each spoke is shaped to fit between two pairs of tangent-joined circles. For each pair of circles, the center of the circle that is formed in part by the inner curve of the hub rim is located radially outside the center of the circle that is formed by the outer curve of the hub's center region.

What is claimed is:  
     
         1 . A method of structuring an electric machine, the method comprising: 
 providing a hollow cylindrical rotor, which is part of a hollow cylindrical rotor assembly, the hollow cylindrical rotor assembly having a plurality of fastener openings; and    connecting the hollow cylindrical rotor assembly to a shaft using a hub that comprises a hub rim connected to a hub center region by a plurality of spokes, the hub rim having a plurality of fastener openings and having the characteristic that an imaginary circle through the hub rim's fastener openings expands substantially uniformly around its circumference as the hub rotates.    
     
     
         2 . A method according to  claim 1 , wherein the step of connecting the hollow cylindrical rotor assembly to the shaft uses a hub having the characteristic that, at any given time during rotation of the hollow cylindrical rotor assembly and the hub, a distance of radial expansion of the hub rim's imaginary circle substantially equals a distance of radial expansion of an imaginary circle through the rotor assembly's fastener openings.  
     
     
         3 . A method according to  claim 2 , the method further comprising: 
 locating the hub outside the axial length of the rotor.    
     
     
         4 . A method according to  claim 3 , in which the hub is made of a plastic material.  
     
     
         5 . A method according to  claim 4 , in which the hub is made of a polyamideimide plastic.  
     
     
         6 . A method according to  claim 5 , the method further comprising: 
 making an interference fit of a ring of keystone-shaped metal elements, that are part of the rotor assembly, to the rotor; and    attaching the hub to the keystone-shaped elements with a plurality of bolts.    
     
     
         7 . A method according to  claim 6 , in which the hub comprises a plurality of spokes, each spoke positioned along a radius from the center of the hub, and shaped to fit between two pairs of tangent-joined circles, each pair of circles including a first circle that is formed in part by the inner curve of the hub rim and a second circle that is formed in part by the outer curve of the hub's center region, the center of the first circle located radially outside the center of the second circle.  
     
     
         8 . A method according to  claim 7 , in which the hub is formed to include one or more stress-relief holes between adjacent bolts.  
     
     
         9 . A method according to  claim 1 , further comprising: 
 positioning a stator, comprising windings, along the axis of a uniform dipole field formed by an array of permanent magnets on the rotor; and    providing current to the windings with an electric commutator.    
     
     
         10 . A method according to  claim 9 , wherein the array of permanent magnets comprises bars of identical permanent magnets assembled in a circle, wherein the bars are dipole elements, each bar of the bars having a vector direction of magnetization that rotates at a rate which is twice that of a vector, rotating about the circle, pointing from the center of the uniform dipole field to the center of the dipole elements.  
     
     
         11 . A method according to  claim 10 , the method further comprising: 
 surrounding the electric machine with an aluminum containment vessel.    
     
     
         12 . A method according to  claim 4 , the method further comprising: 
 positioning a stator, comprising windings, along the axis of a uniform dipole field formed by an array of permanent magnets on the rotor, wherein the array of permanent magnets comprises bars of identical permanent magnets assembled in a circle, wherein the bars are dipole elements, each bar of the bars having a vector direction of magnetization that rotates at a rate which is twice that of a vector, rotating about the circle, pointing from the center of the uniform dipole field to the center of the dipole elements; and    providing current to the windings with an electric commutator.