Increasing Performance of Differential Braking as Steering Backup Using Combined Slip Effects

Redundancies provide essential fail-operationality and are commonly utilized in design of Steer-by-Wire systems. Operationality of steering rack actuators can therefore be increased using differential braking as additional redundancy level. Research in this field has shown boundaries for lateral control to be mitigated compared to conventional steering systems. This paper focuses on performance increases by driveline torque and stability control, both yielding effects of combined longitudinal and lateral tire slip during cornering. Coping with the tradeoff between under- and oversteer whilst increasing performance was the major aim during controller design. For vehicle prototype testing a model following control scheme for differential braking was derived and implemented. Measurements on a low friction proving ground in suitable driving maneuvers were carried out subsequently. The results show new boundaries of vehicle dynamics and address variations of steering kinematics parameters as well as driveline configurations. Investigated interactions of longitudinal and lateral tire slip in the field of differential braking brings up promising potential to increase cornering ability in the fallback level for steering rack actuators.