On the Impact of the Maximum Available Tire-Road Friction Coefficient Awareness in a Brake-Based Torque Vectoring System

Tire-road interaction is one of the main concerns in the design of control strategies for active/semi-active differentials oriented to improve handling performances of a vehicle. In particular, the knowledge of the friction coefficient at the tire-road interface is crucial for achieving the best performance in any working condition. State observers and estimators have been developed at the purpose, based on the measurements traditionally carried out on board vehicle (steer angle, lateral acceleration, yaw rate, wheels speed). However, until today, the problem of tire-road friction coefficient estimation (and especially of its maximum value) has not completely been solved. Thus, active control systems developed so far rely on a driver manual selection of the road adherence condition (anyway characterized by a rough and imprecise quality) or on a conservative tuning of the control logic in order to ensure vehicle safety among different tire-road friction coefficients. The drawback is that a conservative tuning obviously penalizes the overall performances. A new technology (Pirelli Cyber™ Tire) claims to be able to measure, among the others, tire-road contact forces and friction coefficient. An enhancement of the performances of present control systems is expected by including this additional information into the control strategies. In particular, the present paper investigates the improvements that Cyber™ Tire would bring into a Brake Torque Vectoring control strategy (BTV). The research has been developed using validated numerical models and carrying out a series of test-runs, ad hoc designed to show the key-points of the work. Results have been systematically presented and commented. In order to assess the robustness of the control system to measurement errors/noise and sensor delays, an emulator of the Cyber™ Tire measurement system (based on experiments on a prototype) has been introduced into the vehicle model.