A control scheme for automatic path tracking of vehicles subject to wheel slip constraint

We present a control scheme for automatic path tracking of a four-wheeled steering and four-wheeled drive (4WS4WD) vehicle subject to wheel slip constraint. The wheel slip, containing wheel slip ratio in longitudinal direction and slip angle in lateral direction, is a vector that serves as an index to avoid the tire-road friction saturation. Using linearization and singular perturbation theory, a linear and order-reduced design model is obtained, and the wheel slip is replaced by its quasi-steady state for the controller design. We propose a control structure of wheel torque and steering to transform the original tracking problem to a problem of state regulation subject to input constraint. A low-and-high gain technique is applied to construct the constrained controller and to enhance the utilization of the constrained wheel slip. Simulation shows that the new proposed control, scheme subject to wheel slip constraint coordinates well between wheel steering and wheel torque during tracking.