US Patent 7737591 Coaxial twin variable field permanent magnetic dynamoelectric machine

A coaxial twin variable field permanent magnetic dynamoelectric machine comprising first and second stators displaced from each other and first and second permanent magnet rotors. The rotors comprising hydraulic actuators mounted within the rotors for axially displacing the outer and inner surfaces of the first and second rotors, respectively, with the inner and outer surfaces of the first and second stators, respectively, in order to change magnetic flux interaction between the first stator and rotor and the second stator and rotor. Both stators have magnetic shields covering outer and inner surfaces of the first and second stators, respectively. The first axial hydraulic actuator displaces the first rotor outer surface within the second stator magnetic shield and the second axial hydraulic actuator displaces the second rotor inner surface over the first stator magnetic shield with reduced first rotor-second stator and second rotor-first stator magnetic flux interaction.