Comparing rear wheel steering and rear active differential approaches to vehicle yaw control

Abstract

A comparison between two different approaches to vehicle stability control is carried out, employing a robust non-parametric technique in the controller design. In particular, an enhanced internal model control strategy, together with a feedforward action and a suitably generated reference map, is employed for the control of a vehicle equipped either with a rear wheel steering (RWS) system or with a rear active differential (RAD) device. The uncertainty arising from the wide range of operating conditions is described by an additive model set employed in the controller design. Extensive steady state and transient tests simulated with an accurate 14 degrees of freedom nonlinear model of the considered vehicle show that both systems are able to improve handling and safety in normal driving conditions. RAD devices can make the vehicle reach higher lateral acceleration values but they achieve only slight stability improvements against oversteer. On the other hand, 4WS systems can greatly improve both vehicle safety and manoeuvrability in all driving situations, making this device an interesting and powerful stability system.

Keywords:

• vehicle yaw control
• vehicle stability control
• rear active differential
• rear wheel steering

Acknowledgements

This research was supported by funds of Ministero dell'Istruzione dell'Università e della Ricerca under the Projects ‘Advanced control and identification techniques for innovative applications’ and ‘Control of advanced systems of transmission, suspension, steering and braking for the management of the vehicle dynamics’.