Estimation of the tire-road friction coefficient andstability control of the vehicle by steering right and theleft tires independently

Abstract

ESTIMATION OF THE TIRE-ROAD FRICTION COEFFICIENT AND STABILITY CONTROL OF THE VEHICLE BY STEERING RIGHT AND THE LEFT TIRES INDEPENDENTLY Over the last two decades, the automotive industries have been aiming to develop more advanced driving assisting systems (ADAS) such as anti-lock braking system (ABS), electronic stability control system (ESC), and lane keeping assist system (LKA) to improve safety of the ground vehicles for saving lives and preventing injuries. Most of the ADAS systems are utilizing longitudinal and lateral tire forces to realize the desired handling characteristics and improve the stability of the vehicle. The utilized tire forces are dependent on the surface friction and the tire loads. The surface friction is the most important mechanism for generating the tire forces. The saturation limits of the forces vary on di erent road surfaces which have di erent coe cients of surface friction, and it has a negative impact on the performance of the active safety systems which have a control structure assuming a constant coe cient of surface friction. For example, these systems can not provide enough tire forces to stabilize the vehicle on icy roads because of the reduced saturation limits. Therefore, it is crucial to know or estimate the coe cients of the friction of the road surfaces to improve the performance of the active safety system. In the rst part of the thesis, the estimation methods for the coe cients of the surface friction are investigated and a new estimation technique based on the active independent steering control system (AISCS) that has independent front tire steering capability was proposed. The second part of this thesis focuses on enhancing the performance of the in troduced AISCS system. After investigating the bene ts of the AISCS, two new control structures were proposed to improve its yaw-rate performance. The rst one is based on the inverse Pacejka tire model to determine the required steering angles for both tires. The second one uses tire forces as feedback and combines a conventional yaw controller with disturbance observers to calculate required steering angles. Keywords: Estimation of tire-road friction coe cient, tire model, simulation, Control system, Vehicle yaw stability, Active steering control, Independent steering, Disturbance observer