Use of Active Rear Steering to Achieve Desired Vehicle Transient Lateral Dynamics

This paper studies the use of active rear steering (4-wheel steering) to change the transient lateral dynamics and body motion of passenger cars in the stable or linear region of the tires. Rear steering systems have been used for several decades to improve low speed turning maneuverability and high speed stability, and various control strategies have been previously published. With a model-based, feed-forward rear steer control strategy, the lateral transient can be influenced separately from the steady-state steering gain. This lateral transient is influenced by many vehicle parameters, but we will look at the influence of active rear steer and various tire types such as all-season, snow, and summer. This study will explore the ability for a rear steering system to change the lateral transient to a step steer input, compared to the effect of changing tire types. While the yaw rate response to a steering input can be dramatically influenced by rear steering, the effect in a dynamic maneuver can feel very unnatural and unpleasant to a human driver. This paper also seeks to define the behavior caused by excessive rear steer calibrations which are subjectively unnatural or unpleasant. A 2017 Cadillac CT6 with factory-equipped active rear steer will be used for driver feedback and to confirm the results predicted by simulation.