US Patent 7525228 Three-phase opposite rotating motor and fan

A three-phase opposite rotating motor of a fan comprises a stator having a three-phase coil set without a core, a first rotor and a second rotor. The number of the poles of the first rotor is unequal to the number of the poles of the second rotor. The ratio of the number of solenoids of the three-phase coil set and the number of the first poles of the first rotor is 3:4, and the ratio of the number of solenoids of the three-phase coil set and the number of the second poles of the second rotor is 3:2, to ensure the motor works normally in an opposite rotating operation.