Steer-by-wire system safety aspects

Sammanfattning: This thesis research the system safety aspects of a Steer-by-Wire system by studying how a driver handles faults in the system. To start with, identification of risks in the SbW system was performed, followed by identification of potential faults with the help of a HAZOP study. Furthermore, an assessment of risk severity and controllability was performed by the use of the ISO26262 standard and its ASIL classification scheme, as well as the safety analysis FMEA. A steering feel model, with the possibility to simulate the faults from the risk assessment research, were implemented in Simulink and CarMaker. A vehicle model as well as a test scenario were built for both country road driving and highway driving. An experimental study was done using a Logitech G29 steering wheel where six test subjects were involved. To analyse the experiment results and evaluate the severity of the system faults, both subjective evaluation criteria and objective evaluation criteria were introduced in this study. A trend of severity was seen in the majority of the evaluation criteria, showing the signal delay and reduction in steering gear ratio as the two most severe faults. Finally, some examples of mitigation strategies, such as the use of redundancy, was discussed.