Influence of tire parameters on ABS performance

The antilock braking system (ABS) is an active control system, which prevents the wheels from locking-up during severe braking. The ABS control cycle rapidly modulates braking pressure at each wheel mainly based on tire peripheral acceleration. Significant wheel speed oscillations and consequent fast variations of tire longitudinal slip are a consequence, which, in turn, produce a corresponding variation of tire longitudinal force according to the ABS control cycle. Clearly, tire characteristics, namely, tire peak friction (regulating maximum vehicle deceleration), longitudinal stiffness, optimal slip ratio, curvature factor (regulating the position of the peak of µ-slip curve and the subsequent drop), and relaxation length (accounting for tire dynamic response) may significantly influence ABS performance. The aim of the present paper is to evaluate the effect of the main tire parameters on ABS performance. This task is, however, very challenging, since tire characteristics are intrinsically related, and the analysis involves interaction between tires, vehicle, and ABS control logic. A methodology based on the hardware-in-the-loop (HiL) technique is used. This approach was selected to overcome limitations of numerical simulations or difficulties related to the execution of onroad experimental tests (repeatability, costs, etc.). The developed HiL test bench includes all the physical elements of the braking system of a vehicle (comprising the ABS control unit) and a 14 degrees of freedom (dofs) vehicle model, which are synchronized by a real-time board. With the developed HiL test bench, a sensitivity analysis was carried out to assess the influence of tire peak friction, longitudinal stiffness, and relaxation length on ABS performance, evaluated in terms of braking distance, mean longitudinal acceleration, and energy distribution.