Integrated Fault-Tolerant Control Scheme for Steer-by-Wire Systems Based on Steering Motor and Steering Angle Sensor Fault Estimation

In steer-by-wire (SBW) systems, the steering performance is highly dependent on reliable steering angle measurements and steering torque output. Steering motor faults and steering angle sensor faults can both distort the steering response and may compromise vehicle safety. Fault-tolerant control (FTC) is therefore required to maintain steering functionality, and its effectiveness relies on accurate fault estimation. However, these faults can produce similar effects on system outputs under the same operating conditions, making single-fault estimation indistinguishable and degrading estimation accuracy. To address this issue, an integrated FTC scheme for SBW systems based on steering motor and steering angle sensor fault estimation is proposed. First, an improved fast adaptive unknown input observer (IFAUIO) is developed for simultaneous estimation of steering motor faults and steering-angle sensor faults. A differencing operation is introduced into the fast estimation law to suppress steady state estimation errors caused by bias faults, thereby improving fault estimation accuracy. Second, based on the estimated fault information, a high-order control barrier function-based model predictive control (HOCBF-MPC) fault-tolerant controller is developed to maintain steering angle tracking performance and coordinated steering-driving control under fault conditions. Finally, simulation and experimental results demonstrate that the IFAUIO improves the estimation accuracy of steering motor faults and steering angle sensor faults by 20.1 and 80.9%, respectively, compared to the fast adaptive unknown input observer (FAUIO). In addition, the proposed HOCBF-MPC improves steering angle tracking accuracy by 17.0% compared to the conventional MPC-based fault-tolerant controller.