An integrated vehicle velocity and tyre-road friction estimation based on a half-car model

Knowledge of tyre-road friction force is important in many vehicle control systems such as torque vectoring, differential braking and stability control systems. However, tyre friction forces and the factors affecting the friction forces cannot be directly measured by commonly used vehicle sensors. Therefore, an accurate estimation of the friction forces and friction index is crucial for a successful vehicle control design. Although a large number of friction estimation algorithms have been developed, those algorithms mainly focus on a single direction, either longitudinal or lateral, but cannot estimate the tyre friction in a combined condition. This paper presents an integrated friction estimation algorithm based on a half-car vehicle model that can simultaneously estimate the combined friction condition along the longitudinal and lateral directions with some basic measurements. The algorithm consists of a number of estimations for vehicle roll angle, tyre friction forces, vehicle longitudinal and lateral velocities, and tyre-ground friction index. The proposed algorithm has been verified with actual vehicle test results. The test results demonstrate that the algorithm has a fairly good fidelity for estimation of tyre friction forces, vehicle velocities and road-friction conditions that is described quantitatively by a tyre-road friction index.