An Investigation of Longitudinal Tyre Force Observation for Slip Control System Development

Abstract

Longitudinal tyre force is needed in the feedback control systems for enhancing the decelerating and accelerating properties of road vehicles. There lacks means for its direct measurement. This paper presents a longitudinal tyre force observer, designed on wheel rotating dynamics using the conventional linear control systems theory with wheel speed and drive/brake torque. The observer is formulated firstly in continuous-time and then converted to an implementable form in discrete-time for compatibility with digital electronic control units (ECUs). The effectiveness and applicability of the observer are investigated using numerical simulations and road testing of an 8 × 4 Volvo truck with each wheel equipped with an ECU consisting of, in C-code, a robust slip control system, a tyre-road friction estimator, a brake pressure observer and the longitudinal tyre force observer for application in an intelligent brake system. The robustness of the observer to parametric uncertainties, e.g., the inertia of moment, effective radius, and brake gain of the wheel, is also examined.