PI Front Steering and PI Rear Steering Control with Tire Workload Analysis

The main contribution of this paper it to show that a proportional-integral active front steering control and a proportional-integral active rear steering control from the yaw rate tracking error can set arbitrary steady state values for lateral speed and yaw rate at any longitudinal speed. The proposed control system can: (i) assign real stable eigenvalues, without lateral speed measurements, for any value of longitudinal speed; (ii) set steady state responses to driver constant inputs to zero lateral speed for any value of longitudinal speed without additional steady state tire workload if the yaw rate reference for the controlled vehicle is equal to the uncontrolled one. The controlled system shows the advantages of both active front and rear steering control: higher controllability, enlarged bandwidth for the yaw rate dynamics, suppressed resonances, new stable cornering manoeuvres, enlarged stability regions and improved manoeuvrability; in addition comfort is improved since the phase lag between lateral acceleration and yaw rate is reduced. Several simulations are carried out on a standard small SUV CarSim^reg car model to confirm the analysis and to explore the robustness with respect to unmodelled dynamics such as pitch, roll and nonlinear combined lateral and longitudinal tire forces according to combined slip theory.