Integrated differential braking and electric power steering control for advanced lane change assist systems

Abstract

This dissertation describes the design and verification of control algorithm for advanced lane change assist systems (ALCA) with integrated control of differential braking and electric power steering (EPS) system. The ALCA system can warn a potential rear side crashes and prevent collisions in lane change maneuvers with active intervention when there is an upcoming vehicle with potential risk to the rear in the next lane. The objective of the proposed control algorithm of ALCA system is to minimize the unexpected control input of EPS and to make maximum use of differential brake effort. An enhanced LCA warning algorithm is developed with additional information of estimated past trajectory of subject vehicle. The upper controller of the ALCA determines the control on/off decision, the desired yaw rate for collision avoidance, and the strategic control input distribution. The key strategy of this integrated control algorithm is to use the maximum tire road friction of the differential brake force and to operate with smaller control effort of the EPS only when lacking in the amount of yaw rate moment by the electronic stability control (ESC), which is intended for minimizing driver annoyance and control intervention. The lower controller decides the control input of an advanced ESC and EPS system. A rear/side radar and front camera are adopted as environmental sensors. The rear/side radar is used to detect object vehicles at the rear and side area of the subject vehicle. The camera is used to get lane information about front road. Advanced ESC and EPS are adopted as actuators to execute automatic control for collision avoidance. A control algorithm for differential brake is implemented to generate yaw rate using advanced ESC and steering angle control algorithm is developed to compensate deficit yaw rate using EPS. A control algorithm for differential brake consists of upper and lower level controller. A target wheel cylinder pressure is calculated with feedforward and feedback controller in the upper level controller. A target current of valves and motor are determined in the lower level controller. Finally the ALCA system is implemented in a real vehicle and tested in both steering control only case and integrated control case. It is shown that the proposed strategy can intervene appropriately and verify the effectiveness of collision avoidance in dangerous lane change situation and about 20% decrease of EPS control input can be achieved by the proposed algorithm.