Patent ID: 7145278

Claim:
A permanent magnet type three-phase stepping motor comprising a stator and a rotor said rotor arranged concentrically with the stator with an air gap therebetween, said stator having three stator poles and stator windings of three-phase each wound around each stator pole, each of said stator poles having m pieces of stator pole teeth, said rotor having two split rotor elements and a permanent magnet held between the two split rotor elements and magnetized to form N and S poles in the axial direction thereof, and a plurality (Nr) of small rotor teeth formed at a regular pitch on an outer peripheral surface of each of said two split rotor elements, said two split rotor elements being circumferentially shifted from each other by a ½ pitch of the small rotor teeth; wherein a pitch of the stator pole teeth is smaller than the pitch of the small rotor teeth, m is an integer equal to (Nr±2 k )/3, Nr is 3n±1, wherein n is an integer not less than 1, and k is an integer not less than 1 and not more than 4.