Study on Driver-Dependent Stabilization Capabilities for Safe Chassis Control with Steer By Wire

Steer-by-wire actuators represent a transformative advancement in chassis control, opening up new potential for optimizing driving behavior across the entire range of driving dynamics - including driver-dependent automatic countersteering in critical driving situations. However, from a functional safety perspective, the increased potential also introduces new risks with respect to possible system failures. To mitigate these risks, sophisticated monitoring functions are essential to ensure vehicle controllability at all times. Current research approaches for monitoring functions use safe driving envelopes. This set of safe driving states is often found by open-loop simulations, which provide a phase portrait of the nonlinear system under control and from which stability limits can be derived. However, it remains open how these open-loop stability limits correspond to the stabilization capability of a real human driver in the loop. And secondly, how these closed-loop stability limits might change depending on the driving skill. To answer these questions, the paper presents the results of a subject study conducted in a semi-dynamic driving simulator with 52 participants. The study investigated the stabilization behavior of drivers after a sudden and unexpected disturbance. The disturbance leads to oversteering of the vehicle with varying criticality, allowing an analysis of the driver's behavior over a wide range of the phase portrait of side slip angle and its derivative. Based on this data, the stabilization performance of groups of drivers with different skill levels, from novice to expert, is compared to each other and to the model-based open-loop limits. The results show that the open-loop stability limits provide a good estimate for novice drivers and therefore represent a conservative envelope for functional safety approaches. At the same time average and expert drivers are able to push the limits further, which enables chassis controllers to safely adapt functionalities to the driver skills.