When automobile is at the threat of collisions, steering usually needs a shorter longitudinal distance than braking to avoid collision, especially at a high speed. In emergency steering evasion, the vehicle may be out of the road or colliding with obstacles ahead when the driver’s steering torque is excessive or insufficient. In view of the above problems, this paper presents an emergency steering evasion torque assistance system based on optimized trajectory.
First, a feasible steering evasion area is established which treats the paths of excessive and insufficient steering as boundary conditions in this paper. An optimized trajectory is derived from the lateral acceleration of the vehicle and the time to the adjacent lane as optimization conditions. Second, a two degree of freedom vehicle model is used to represent dynamics of the vehicle. A single input-single output assistance steering torque model is derived by a driver torque model and a dynamics steering equation represented steering system. Third, a model predictive control (MPC) approach based on the mentioned models is used in steering torque assistance system to acquire assistance torque.
In the simulation stage, this paper establishes a driver-in-loop simulation platform based on Automotive Simulation Models (ASM) to acquire the inputs of the drivers and test the performance of the assistance torque controller at different emergency steering evasion conditions. The results show that the method can ensure that the vehicle is driving in feasible steering evasion area, and improve the trajectory tracking accuracy of the vehicle, and the intervention to the driver is minimal in emergency steering evasion.