Traction control of an electric formula student racing car

This article describes the design of a traction control system in an electric Formula Student vehicle. In many race applications the accelerator pedal is difficult to control for an in-experienced driver, especially in the case of electric vehicles, where a large torque is available from standstill. A 3-DOF driveline model is used in combination with a 7-DOF vehicle model and a non-linear tyre model based on 10 parameters. The driveline and tyre model are validated by measurements. These models are used to design a suitable traction control system. This system consists of an open-loop part, which uses the longitudinal and lateral acceleration to calculate a torque limit via a driver provided friction estimation. The feed-back part of the controller regulates the slip-ratio of the rear-wheels. The traction control system is first implemented in the vehicle model and later in an electric Formula Student vehicle. A comparison is made between the vehicle with and without traction control. The vehicle with traction control performs significantly better in terms of longitudinal acceleration and shows a better driveability in terms of lateral acceleration. INTRODUCTION Electric vehicles are becoming more popular, since fuel consumption and emissions are more important issues these days. Many electric vehicle use inboard motors connected to the wheels via drive-shafts and a fixed reduction. Electric motors are able to deliver a high torque from standstill and often have the possibility to deliver very high peak torques for a short amount of time. This can lead to traction problems and dangerous situations, especially at higher speeds. The objective of this research is to design a traction control system to enhance the traction of an electric rearwheel driven Formula Student vehicle with one central motor as in Figure 1. The empty car weight is approximately 245 kg and the motor is able to produce 85 kW which results in 1200 Nm on the rear axle. The system should be able to:  Operate at all speeds, even at standstill.  Enhance traction during cornering.  Deal with the flexible driveline and possible resonances caused by this flexibility. Traction control is defined as a system to maximise the utilisation of the tyres by controlling the drive torque applied by the motor. Since the lateral tyre force strongly depends on the longitudinal force applied to the tyres, traction control can improve the stability of the vehicle [1]. Electric motors are able to deliver high torques at low speeds and therefore the need for traction control is even more present. Figure 2, which shows the friction Figure 1: URE07 Slip ratio κ F ri ct io n co effi ci en t μ Traction control area Longitudinal friction