Patent ID: 7622875

Claim:
A controller for a motor that has a first rotor and a second rotor, each of which produces a field by a permanent magnet, and an output shaft capable of rotating integrally with the first rotor of the rotors, which are coaxially disposed, said second rotor being capable of relatively rotating with respect to said first rotor, and the strength of a composite field of the fields of the permanent magnets of the rotors being capable of being changed by changing the phase difference between the rotors by the relative rotation of the second rotor, the controller comprising: a phase difference changing driving means that has an actuator that produces a driving force to make said second rotor relatively rotate with respect to said first rotor; and a phase difference controlling means for controlling the phase difference between the rotors to a predetermined phase difference for which the strength of said composite field is lower than a maximum strength thereof via said phase difference changing driving means in the case where a point on a two-axis coordinate plane, whose coordinate axes indicate the torque produced on said output shaft and the rotational velocity of said output shaft, that represents a set of the value of the torque produced on said output shaft and the value of the rotational velocity of said output shaft lies within a preset predetermined region on the two-axis coordinate plane that is in the proximity of and includes the origin of the two-axis coordinate plane.