Method for assembling rotor for use in IPM rotary machine

A method for assembling a rotor used in connection with an interior permanent magnet (IPM) rotary machine, the rotor having an axis of rotation and comprising a rotor yoke having bores and a plurality of permanent magnet segments disposed in the bores of the rotor yoke, each permanent magnet segment consisting of a plurality of sintered Nd base rare earth magnet pieces, the method comprising the steps of:

• inserting the plurality of magnet pieces in each bore of the rotor yoke, with each of the magnet pieces for each of the magnet segments being kept loose from each other, for axially stacking the magnet pieces in the bore, and
• fixedly securing the stacked magnet pieces in the bore of the rotor yoke, wherein
• each piece of sintered Nd base rare earth magnet has a coercive force profile from the surface toward the interior, which is created by letting Dy or Tb diffuse from the surface toward the interior of the magnet piece, and
• the step of letting Dy or Tb diffuse from the surface toward the interior of the magnet piece includes:
• applying a Dy or Tb oxide powder, a Dy or Tb fluoride powder or Dy or Tb-containing alloy powder to surfaces of the magnet piece, and then
• bolding the magnet piece at a high temperature sufficient to diffuse the Dy or Tb powder applied to the surface of the magnet piece.