MTTE-Based traction control for directional stability on mixed-μ roads

This paper presents a traction control approach for an electric vehicle with two independently driven wheels based on maximum transmissible torque estimation (MTTE) [1]. This extends the work on MTTE in order to maintain directional stability for straight line acceleration over mixed-μ roads. We derive the controller equations from equations of motion of the vehicle and show for the first time that the maximum transmissible torque estimation to each wheel is dependent on the estimation of friction torque of both wheels. The performance of the traction controller is verified through simulation on a high fidelity vehicle model using Dymola. A control strategy is proposed for straight line driving and is compared to independent MTTE control. A split-μ road simulation shows that the proposed controller maintains vehicle directional stability whereas an independent control strategy results in the vehicle spinning off the road. Additionally, in terms of practical implementation, it was found that controller update rates of less than 75 Hz may lead to torque response instability, and that carcass compliance in the tyre model may cause torque oscillations when changing from a lowto high-μ road.