A Fail-Operational Assessment for Controllability and Comfortability of Steer-by-Wire Systems

This paper describes a fail-operational evaluation of the controllability and comfortability for the safety architecture development of steer-by-wire (SbW) systems. According to the functional safety requirement, it is demanded that Steer-by-Wire systems shall continue to function and not misbehave after a failure by the intended fail tolerant sub-system. Most recently, developing Steer-by-Wire Systems are well advanced in fail-operational design utilizing the redundant systems, principally using Sensor voting or ECU switching functions. The system can sustainably keep the lateral motion of vehicle even though a failure is detected while driving. During such events, the controllability assessment is used to determine the fault-tolerant time interval (FTTI), including failure detection and the safe state transition time. Furthermore, typically highly automated vehicles will be controlled without the human driver's input or reaction; this study considers test assessment containing the controllability for the driver and the comfortability for the passenger. The evaluation is accomplished by the comprehensive methodological approach composed of questionnaire jury ratings, vehicle behaviors, and physiological measures. The results can be applied to determine the requirements of SbW systems.