Development of a torque vectoring system in hybrid 4wd vehicles to improve vehicle safety and agility

Abstract

In this paper, a new method for vehicle torque vectoring (TV) with the difference in torques between the left and right sides is introduced. This chassis control system can help the vehicle follow the driver's intended line without vehicle deceleration. Targeting a hybrid four wheel drive (4WD) vehicle with an active differential in rear axle and in-wheel motors (IWMs) in front axle, a TV system based on a vehicle bicycle model is developed. Especially, a new yaw rate reference smoothly varying between safety mode and sport mode aims to enhance both cornering safety and agility. To properly combine these two modes, a weighting factor based on steering command is designed. Also, to track the reference accurately, an integral sliding mode controller (SMC) is introduced in this paper, which has the advantage of reducing yaw rate error during steady state cornering. Lastly, a torque distribution method based on modeling of both active differential and IWM is developed to generate the correct yaw moment. Also, it reflects the actuator characteristics, such as response time, torque capacity, and torque direction. The performance of the proposed TV system is evaluated using a vehicle dynamic software, and a comparative study is also conducted.