Modeling and sensorless optimal controller design for an electric power assist steering system

This paper considers the analysis and design of a double-pinion type electric power assist steering (EPAS) control system. A simplified model of the augmented steering assembly-electric motor system is arrived at using Lagrangian dynamics. In contrast to the state of the art, the paper presents three advances. First, a state-space approach is used rather than an input-output model. The state-space formulation for the system model is obtained with the motor column angular position and the steering column torque as outputs. Secondly, LQG techniques are employed to arrive at an optimal controller for the EPAS system. The selection of weighting coefficients for the LQR is discussed. Finally, the authors present a control strategy that eliminates the steering column torque sensor, a critical component in existing EPAS controller designs. The proposed control strategy presents an opportunity to improve EPAS system performance and also reduce system cost and complexity.