Electromagnetic servo drive for power steering

Claim 1

An electromagnetic servo device comprising: an input shaft; an output shaft; an electric motor for producing assistive torque to be applied to said output shaft; detecting means for detecting a phase difference between said input and output shafts and for producing a phase difference signal corresponding to the magnitude and direction of said phase difference; and motor control means for driving said electric motor and for controlling the rotational speed of said electric motor, said motor control means comprising, a first circuit means, coupled to said detecting means for producing a phase difference magnitude signal and a phase difference direction signal corresponding to the magnitude and direction of said phase difference detected by said detecting means, feedback circuit means for generating a rotational speed feedback signal corresponding to the rotational speed of said motor, said rotational speed feedback signal being generated by subtracting an armature current signal corresponding to the armature current from a voltage signal corresponding to the armature voltage and for feeding back said rotational speed feedback signal for combination with said phase difference magnitude signal, a second circuit means, coupled to said first circuit means, said feedback circuit means, and said electric motor, for receiving said phase difference magnitude and direction signals and said rotational speed feedback signal, and for producing a driving pulse for said electric motor, said driving pulse having a voltage polarity which is a function of said phase difference direction signal and a mean voltage level which is a function of the combination of said phase difference magnitude signal and said rotational speed feedback signal.