Longitudinal control for an all-electric vehicle

The present paper describes a torque controller for a vehicle equipped with 4 electric motors, one at each wheel. The controller is set up to ensure two main functions: braking with anti-skidding and traction control using the electric motor torque as the unique actuator signal source. Unlike the torque generated by classic internal combustion engines, the torque of electric motors is available almost instantaneously. In addition, it can be measured on-line, which means that advanced control techniques can be applied. In order to generate the appropriate anti-skid or anti-slip torque for each wheel, one has to estimate the friction between the wheel and the road. In the first step, the instantaneous friction coefficient and the maximum friction coefficient between the wheel and the road are estimated, without prior knowledge of the road conditions. Next, the approach relies on a feedback sliding mode control scheme to ensure the vehicle is operated in the maximum friction zone in both hard acceleration and braking phases, along with a given reference speed to track. The only variables used in this strategy are the wheel acceleration, the instantaneous torque generated by the electric motors and the chassis acceleration.