Abstract
Three criteria are important when designing a suspension for a passenger vehicle: safety, handling and comfort. A vehicle suspension is always a compromise between these three subjects. Here, active suspension components like active roll control systems (ARC) can give the suspension system different characteristics in different driving situations to provide a better compromise.
ARC systems can actively influence the roll movement of a vehicle. This is done by actuators which control the preload of the anti-roll bars (ARB). The actuators can be placed between the two halves of the stabiliser as rotational or, instead of the ARB links, as linear actuators. Up to now these actuators are usually hydraulically driven. Hence CO2 emissions get more and more important, the most promising systems for the future are electromechanical active roll control systems (eARC). The engineering objective is the control of such a system.
The first task of eARC systems is to control the roll angle during cornering. For that, a set point value of the roll angle is defined based on the actual lateral acceleration. The curve is designed to give a good directional stability. As there are two actuators (one at the front and one at the rear axle), there is one remaining degree of freedom in setting the torque ratio between front and rear. This is used for shifting the roll distribution in such a way to stabilise the vehicle in evasive manoeuvres, based on a calculated target yaw rate.
A simulation environment was established to analyse the eARC performance. Hereby also a different accuracy of the actuator modelling was considered. The modelling covers not only simple first order systems. But it comprises also complex systems, that have a complete electro motor modelled with torsion of the sway bars and with current and torque limitation. Then the effects of the eARC system were evaluated with respect to comfort on bad roads, the steering feel when doing lane changes and the driving stability in evasive situations. Also a Ford prototype vehicle was built up to analyse the eARC behaviour in practice
KEYWORDS : Control design, active systems, vehicle suspension, active anti-roll bars, target yaw rate