Patent ID: 6903476

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 3L pieces of stator pole and stator windings of three-phase each wound around each stator pole, each of said stator poles having a plurality 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 an 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 condition of 0.3≦{(Nr/π)(Ws+Wr)/(Ds+Dr)}≦0.5 is established in which L is an integer not less than 1, Nr is L(3 n±1), n is an integer not less than 1, Ds is an inner diameter of the stator, Dr is an outer diameter of the rotor, Ws is a width of the stator pole tooth, and Wr is a width of the rotor tooth.