Abstract
KEYWORDS – Friction estimation, real time identification, model based estimation, ABS, wheel slip.
ABSTRACT Tire-road friction characteristics are essential elements of contemporary active safety systems and vehicle dynamics controls, such as anti-lock braking system (ABS) or stability control systems (SCS). The scope of this work is to devise a mathematical algorithm that in real time will be able to calculate the tire-road friction characteristics during each vehicle operating mode; decelerating, driving/accelerating and stationary/low-speed. The core of this algorithm is the calculation of the tire-road friction coefficient based on the measured wheel slip and the estimation of the wheel slip value that corresponds to the peak value of the tire-road adhesion coefficient curve and the rate of change of the wheel slip. The algorithm is divided in three fundamentals modes, using real time measurements, such as speed over ground and estimation parameters, such as the brake torque, rotational inertia etc. For the stationary/low speed mode the algorithm incorporates an appropriate tyre model and measurements of the steering wheel torque in order to calculate the wheel slip and the tire-road interaction characteristics. Overall, the aim of real time tire-road friction identification method is to be able to identify the current and the maximum value of the tire-road friction coefficient.