The variable-geometry suspension system is in the focus of the paper. The advantages of the variable-geometry system are the simple structure, low energy consumption and low cost. During
IntroductionIn recent decades several new researches and development tendencies have evolved [13]. The automotive industry put emphasis on urban mobility and transport, alternative fuels, electrification of the vehicle safety applications in co-operative systems, suitable materials, environment-friendly and efficient manufacturing. In some of these systems the driver is supported by assistance systems to meet the performance specifications. Several important journal and conference papers have been presented in this topic, see e.g. [20], [16].A new possibility in automotive safety control is variable geometry suspension systems. The suspension determines such critical components as the height of the roll center and the half track change. The advantages of the variable geometry suspension are the simple structure, low energy consumption and low cost compared to other mechanical solutions such as an active front wheel steering, see [3,9]. Since various safety and economy properties of the vehicle are determined by the suspension geometry it has significant influence on the control design. The control input of variable geometry systems is camber angles of the front and rear wheels, with which the driver is supported to perform the various vehicle maneuvers, such as a sharp cornering, overtaking or double lane changing. The control system must guarantee various crucial vehicle performances such as trajectory tracking, roll stability and geometry limits.Several papers for various kinematic models of suspension systems have been published. A review of the variable geometry systems was presented by [19]. The control system varied the leverage ratio between the spring/damper unit and the road wheel assembly. A nonlinear model of the McPherson strut suspension system was published by [4]. By using this model the kinematic parameters such as camber, caster and king-pin angles were examined. The kinematic design of a double-wishbone suspension system was examined by [18]. Seeking to meet the performance requirements often leads conflict situations and requires a compromise considering the kinematic and dynamic properties, see [21]. The vehicle handling characteristics based on a variable roll center suspension was proposed by [12]. A rear-suspension active toe control for the enhancement of driv-