Trw Limited

Michael E Behr

Thomas Joseph Wand

Philip A Gaubis

Philip Q Guest, Jr

James L Graves

Kenneth P Wozniak

An electronic control system for a steering system having an electric motor coupled to the steering system for providing power assist. The steering system is of the rack and pinion type having an input gear coupled to the steering wheel and a pinion gear in meshing engagement with the rack. Two torsion sensors are coupled across the input and pinion gears and generate analog output signals. When no input torque is applied to the steering wheel, the output signals from the two torsion sensors are equal. When input torque is applied to the steering wheel, the signals from the torsion sensors vary substantially linearly in opposite directions. An electronic control unit controls operation of the electric power assist motor in accordance with the output signal from one of the torsion sensors. Failsafe circuitry is provided for monitoring the outputs of the redundant torsion sensors to insure proper control of the electric power assist motor. The failsafe circuitry provides (i) a sensor-to-sensor check to insure the output voltage of one sensor is consistent with the output voltage of the other sensor, (ii) a sensor limit check to insure that the output voltage from each sensor does not exceed a predetermined limit, (iii) a sensor direction check to insure that the signal being used to drive the electric power assist motor, as derived from one sensor, will drive the motor in the same direction sensed by the other sensor, and (iv) an excess assist check to insure that the signal used to drive the electric assist motor, as derived from one sensor, will not cause the motor to provide a greater amount of assist than an amount requested, as detected by the other sensor.

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Brighton, MI, United States of America

Michael E Behr