Sensitivity Analysis toward Differential Braking as Backup Steering Functionality

This paper presents a novel sensitivity analysis framework for differential braking as a backup steering solution in fail-operational Steer-by-Wire systems. The fault-tolerant design approach of Steer-by-Wire and steering systems for highly automated driving relies on the availability of road wheel actuators (RWA). Redundancies are therefore commonly used to ensure fail-operationality. Since its widespread implementation in production vehicles through electronic stability control, the use of differential braking as a cost-effective measure is desirable to increase functional diversity. However, feasible lateral accelerations through this backup solution are limited compared to conventional steering systems and lie close to ordinary driving scenarios. To address this limitation, this work investigates the influence of chassis parameters on differential braking performance. After defining characteristic values and a simulation test plan, a preliminary analysis using a linear single-track model incorporating differential braking is conducted. The most influential vehicle parameters are identified, including the newly derived effect of rear axle cornering stiffness—an aspect not previously quantified in this context. A second, more detailed sensitivity analysis is performed using a characteristic-based dual-track model equipped with representative brake, steering, and chassis subsystems. Parameter variation ranges are derived from distributed data-based sources. The resulting total effects reveal new insights into the sensitivity of chassis design parameters, including scrub radius, steering friction, rear axle cornering stiffness, and coupling effects of suspension and kinematics. The findings provide valuable guidance for future chassis design in fail-operational steering systems and highlight the importance of underexplored parameters in achieving reliable lateral dynamics through differential braking.