Integrated Control of Active Steering and Electronic Differentials in Four Wheel Drive Vehicles

In this paper the integrated control of front and rear active differentials with active front steering is investigated in order to improve dynamics, stability and to reduce the drawbacks of mechanical self-locking differentials. The proposed integrated centralized control feeds back both the yaw rate and the wheel speed measurements to the control inputs which are the front wheel steering angle and the torque transferred by the electronic differentials between the left and the right wheels of both vehicle's axles. The control of the electronic differentials is not only aimed at keeping the wheel speed differences at desired values but it is also integrated with the active steering control ( a PI action from the yaw rate error) to produce a yaw moment ( also depending on the yaw rate error) which improves handling and stability. Several simulations are carried out on a CarSim small SUV model to explore the robustness with respect to unmodelled dynamics such as pitch, roll and nonlinear combined lateral and longitudinal tire forces. In response to sudden direction changes the simulations show reduced oscillations, robustness and enlarged bandwidth for the yaw rate tracking dynamics while new stable maneuvers are allowed especially in critical conditions such as mu-split braking.