Driver torque and road reaction force estimation of an Electric Power Assisted Steering using sliding mode observer with unknown inputs

Driver torque and steering reaction force are important information in the designing of EPAS (Electric Power Assisted Steering) system. The driver torque determines the amount of assisted torque and the reaction force can be used to improve the steering feeling and the vehicle stability or introduce a new assist torque control. Since, in practice, they are not usually measureable; a sliding mode observer with unknown inputs is introduced to estimate the driver torque and the road reaction force of an EPAS system by using other measured signals which are normally available. A state space formulation for EPAS system with brushed motor is used for the synthesis of observer with unknown inputs. The proposed observer is applied to state and unknown input estimation of EPAS. Simulation results demonstrate the effectiveness of the proposed observer which improves the EPAS system performance and also reduces system cost and complexity.