Capability Analysis of Fault-Tolerant Control With Differential Braking for Steer-by-Wire Failure

This study proposes a fault-tolerant control strategy to solve the performance degradation problem due to kingpin offset, especially the negative kingpin offset condition, when steering torque failure occurs in a Steer-by-Wire (SbW) system. Previous studies overlooked kingpin offset, particularly negative offset, and lacked methods for practical control under such conditions. To this end, differential-braking experiments were conducted using an experimental vehicle with a negative kingpin offset to verify the vehicle model. Using the validated model, offline optimization was conducted to identify the control inputs that maximize yaw rate across varying offset and speed conditions, revealing limitations of the conventional approach. Based on this analysis, differential-braking distribution guidelines for each kingpin offset were derived, and a torque distribution controller that reflects kingpin offset was proposed by utilizing the steady-state yaw rate gain of the front and rear wheel differential braking. The proposed strategy was evaluated through open- and closed-loop tests in the full vehicle model and IPG CarMaker simulation environment. The evaluation results showed that the conventional strategy had problems such as performance degradation and unintended vehicle turning under some kingpin offset conditions; however, the proposed strategy showed improved and consistent turning performance within the tested kingpin offset range (-30 to +30 mm). The control error and control effort were reduced over the entire tested kingpin offset conditions compared with that of the conventional strategy.