US Patent 7626299 Motor

A motor includes a stator with an annular stator yoke, a stator core having a plurality of inner and outer teeth projecting from the stator yoke toward inside and outside respectively, a plurality of coils wound on the stator core, and an inner rotor and an outer rotor confronting the inner and outer teeth respectively via an air-gap, and having an permanent magnet respectively. The number of slots “S” and the number of poles “P” establish a relation of S:P=3:2N−1, where N is an integer equal to 1 or more, and a case when 2N−1 becomes a multiple of 3 is excluded.