Potential of electric wheel motors as new chassis actuators for vehicle manoeuvring

Abstract

The stability and yaw control systems in today's vehicles are increasingly appreciated for active safety. They use individual wheel braking to obtain an extra yaw moment. Adding individual traction, e.g. through electric wheel motors, would increase the available extra yaw moment. The present work investigates the manoeuvrability potential of such a concept. A passenger car employing electric wheel motors at the rear axle is compared with the same vehicle using only brake intervention. The potential, or ultimate limits, are investigated for two driving situations. The time delay in yaw speed change when entering a curve is estimated. A reduction of some 10-30 per cent is found, the highest gains being at low longitudinal speed. For pure lateral translation, the maximum initial lateral acceleration is estimated and a 40 per cent increase is predicted. The investigation is based on mathematical analysis employing a modified version of the common bicycle model. The feasibility of introducing these solutions in series-produced vehicles is discussed briefly. Cost aspects are not considered in any great detail, but it is emphasized that such aspects must be weighed not only against improved manoeuvrability but also against reduced environmental impact and improved longitudinal driveability, all of which are attainable with electric propulsion.