Controller for motor

A controller for a motor having a first rotor and a second rotor that produce fields by permanent magnets, and an output shaft that can be integrally rotated with the first rotor of the two rotors, wherein the two rotors and the output shaft are coaxially provided, the second rotor is provided such that the second rotor can be relatively rotated with respect to the first rotor, and the phase difference between the two rotors is changed by the relative rotation of the second rotor so as to change the intensity of a resultant field obtained by combining the fields of the permanent magnets of the rotors, the controller for a motor comprising:

• a phase difference changing driving means which has a hydraulic chamber whose volume changes as the second rotor relatively rotates and which causes the second rotor to rotate relatively to the first rotor by a pressure of hydraulic oil charged in the hydraulic chamber;
• a cleaning need determining means which determines whether the hydraulic chamber needs to be cleaned;
• and
• a cleaning phase difference controlling means which controls the phase difference changing driving means such that the second rotor relatively rotates in the forward direction and the reverse direction alternately with respect to the first rotor in the case where the cleaning need determining means determines that cleaning is necessary.