Design of a Hierarchical Lane-Keeping Assist Control for a Steer-by-Wire Vehicle

The steer-by-wire (SBW) system has great potential in conjunction with advanced driver assistance systems (ADAS), due to the mechanical disconnection between the steering wheel and tires. However, the collaboration between the upper-level ADAS controller and the lower-level SBW controller needs to be addressed urgently. In this paper, a hierarchical lane-keeping assist (LKA) algorithm is proposed to concurrently optimize trajectory tracking performance and alleviate human-machine conflicts. Firstly, a vehicle dynamics model, a path following model and an SBW system model are developed for the lanekeeping and haptic feedback tasks. Then, linear time-varying (LTV) model predictive control (MPC) is designed to track the desired path and guarantee vehicle safety under the constraints of key states and controlled steering input in the upper-level controller. In the lower-level SBW controller, a torque overlay steering torque control based on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">℞</sub> theory is developed to provide haptic feedback and track the commands from the upper-level controller. Finally, typical scenarios are given and the proposed strategies are validated using a CarSim & Simulink co-simulation platform as well as hardware-in-loop (HIL) bench. The results demonstrate that the proposed control scheme can improve the tracking performance while providing a driverfriendly interface.