Rotor for permanent magnet rotary machine
A permanent magnet rotary machine comprises a rotor comprising a rotor core and a plurality of permanent magnet segments embedded in the rotor core and a stator having a plurality of coils and disposed to define a gap with the rotor, or a permanent magnet rotary machine comprises a rotor comprising a rotor core and a plurality of permanent magnet segments mounted on the surface of the rotor core and a stator having a plurality of coils and disposed to define a gap with the rotor. In the rotor, each permanent magnet segment is an assembly of divided permanent magnet pieces, the coercive force near the surface of the magnet piece is higher than that in the interior of the magnet piece, and the assembly allows for electrical conduction between the magnet pieces.
1. In connection with a permanent magnet rotary machine comprising a rotor comprising a rotor core and a plurality of permanent magnet segments embedded in the rotor core and a stator having a plurality of coils, the rotor and the stator being disposed to define a gap therebetween, or a permanent magnet rotary machine comprising a rotor comprising a rotor core and a plurality of permanent magnet segments mounted on the surface of the rotor core and a stator having a plurality of coils, the rotor and the stator being disposed to define a gap therebetween,
the rotor wherein each of said permanent magnet segments is an assembly of two or more divided permanent magnet pieces, each of the divided permanent magnet pieces has a coercive force at a surface and an interior, the coercive force near the surface of the magnet piece is higher than that in the interior of the magnet piece, and the assembly allows for electrical conduction between the magnet pieces in the absence of an insulating layer capable of complete electrical insulation between the magnet pieces.
2. In connection with a permanent magnet rotary machine comprising a rotor comprising a rotor core and a plurality of permanent magnet segments embedded in the rotor core and a stator having a plurality of coils, the rotor and the stator being disposed to define a gap therebetween, or a permanent magnet rotary machine comprising a rotor comprising a rotor core and a plurality of permanent magnet segments mounted on the surface of the rotor core and a stator having a plurality of coils, the rotor and the stator being disposed to define a gap therebetween,
the rotor wherein each of said permanent magnet segments is an assembly of two or more divided permanent magnet pieces, each of the divided permanent magnet pieces has heat resistance at a surface and an interior, the heat resistance near the surface of the magnet piece is higher than that in the interior of the magnet piece, and the assembly allows for electrical conduction between the magnet pieces in the absence of an insulating layer capable of complete electrical insulation between the magnet pieces.
3. The rotor of claim 1 wherein the magnet pieces are of a sintered Nd base rare earth magnet.
4. The rotor of claim 3 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.
5. The rotor of claim 3 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 mainly via grain boundaries.
6. The rotor of claim 4 wherein the step of letting Dy or Tb diffuse from the surface toward the interior of the sintered Nd base rare earth magnet piece includes applying a Dy or Tb oxide powder, a Dy or Tb fluoride powder or a Dy or Tb-containing alloy powder to surfaces of the magnet piece, then holding the magnet piece at a high temperature sufficient to diffuse Dy or Tb.
7. The rotor of claim 1 wherein each of said permanent magnet segments is constructed by assembling divided permanent magnet pieces into an assembly without insulating treatment.
8. The rotor of claim 7 wherein the magnet pieces have a surface roughness Ry in the range of 50S to 0.8S.