Control allocation for all wheel drive sports cars with rear wheel steering

Abstract

The increasing demands for driving comfort and driving dynamics lead to the introduction of a variety of control systems in modern vehicles. So far, these systems are working in peaceful coexistence and do not use potential synergies. This paper presents a modular control allocation, which combines lateral torque distribution at the rear axle, longitudinal torque distribution, and rear wheel steering. The previous investigations of torque vectoring mostly neglected the secondary yaw torque, which is a result of the dependency between lateral and longitudinal forces at the tyres. An increase in longitudinal forces leads to a decrease in lateral forces and, therefore, results in a yaw torque. A comprehensive vehicle and tyre model is used to analyze this secondary effect for different vehicle states and requested yaw torque. The investigation shows that the influence of the secondary yaw torque varies heavily depending on the vehicle state and the requested yaw torque. Especially, for stabilizing torque requests at high lateral acceleration, the secondary effect is significant and should not be neglected. The investigation shows that an optimal distribution for each yaw torque request exists and that results in maximum lateral forces and thereby maximum lateral acceleration. These results are used within the paper’s modular control allocation. A model-based reference generator delivers desirable yaw rates and side slip angles, which are transferred into necessary lateral forces at the wheels by the control allocation unit. This force-based approach enables modular expandability and usability across multiple vehicles. The proposed controller shows that using the available systems in conjunction helps to increase driving performance and the vehicles stability at the same time.