Adaptive emergency braking control with underestimation of friction coefficient

In this paper, a control scheme for emergency braking maneuvers in automated highway systems and a new online identification scheme to determine the tire-road friction characteristics of the vehicle are presented. The proposed controller determines the required pressure in the master cylinder of the braking system to achieve maximum deceleration during braking, based on the estimation of the tire-road friction characteristics and the overall braking system gain, for the given set of parameter estimates. With persistence of excitation, the identified static map between the tire longitudinal slip and the tire-road friction coefficient is guaranteed to converge to the actual map. When there is no persistence of excitation, and under a proper choice of initial conditions and adaptation gains, the proposed scheme underestimates the maximum coefficient of friction and its corresponding slip, and allows a conservative calculation of the safety critical inter-vehicle spacing.