Integrated Steering and Differential Braking for Emergency Collision Avoidance in Autonomous Vehicles

Controlling the lateral dynamics of an autonomous vehicle confronting a sudden obstacle requires optimal use of tires' force capacities. In these situations, autonomous steering may not be able to respond fast enough to prevent collision or instability. This paper presents an integrated controller for autonomous vehicles, capable of suitably reacting to emergency situations when a sudden obstacle appears on the road. The proposed controller employs differential braking conservatively when needed, to produce an additional yaw moment, thereby improving a vehicle's lateral agility and responsiveness without endangering vehicle stability. A longitudinal controller is also designed to track a desired longitudinal velocity. Model predictive control (MPC) method is used for developing a combined path planning and tracking controller with a hierarchical structure that prioritizes (1) collision avoidance, (2) vehicle stability, and (3) path tracking. The effectiveness of the proposed integrated MPC controller is evaluated by simulating an experimentally validated CarSim model to demonstrate the controller's capability in preventing instability and collisions.