Patent ID: 7339292

Claim:
A multi-polar rotary machine comprising: a stator; a cylindrical outer rotor arranged concentrically with the stator and with an air gap therebetween; said stator having two splitted stator elements and a ring shaped permanent magnet held between the stator elements and magnetized so as to form N and S poles in the axial direction of the stator, a plurality of small stator teeth A and Ā separated in the axial direction of the stator from each other and formed on the outer peripheral surface of one of the splitted stator elements, a plurality of small stator teeth B and B separated in the axial direction of the stator from each other and formed on the outer peripheral surface of the other of the spliffed stator elements, and stator windings for A phase and B phase wound around the stator elements, respectively; said rotor having a plurality of small rotor teeth formed on the inner peripheral surface thereof similar in number to the small stator teeth; said small stator teeth A , Ā, B and B being circumferentially shifted from said small rotor teeth by a ¼ pitch of the small stator teeth, respectively, wherein each of said stator and said rotor is formed of pressed powder consisting of soft magnetic material, and of resin and/or inorganic material; and wherein a ratio of thickness of the small stator teeth Ā or in the axial direction of the stator to a thickness of the small stator teeth A in the axial direction is set to 0.5 to 0.8 so as to equalize substantially in mean permeance both small stator teeth A and Ā to each other, and wherein a ratio of a thickness of the small stator teeth B in the axial direction of the stator to a thickness of the small stator teeth B in the axial direction of the stator is set to 0.5 to 0.8 so as to equalize substantially in mean permeance both small stator teeth B and B to each other.