Analysis of Rollover Stability in Consideration of Dynamic Oversteer Tendency

Abstract

"The trends towards increasing popularity of high performance SUVs require a novel assessment of “trade-off” between driving dynamics and rollover stability, which represents a new challenge for chassis design in the concept phase of chassis development. However, the rollover behavior has been typically investigated by means of experimental test maneuvers with prototype vehicles, which require a large amount of resources, such as measuring equipment, outrigger and roof loading. Besides, measurement data with measurement errors do not always provide satisfactory results due to external disturbance factors, e.g. environmental temperature and road surface. By contrast, a simulation environment can rule out the part of the aforementioned disturbance factors by reproducible simulation maneuvers in order to reduce the development expenses and obtain a better understanding of the rollover behavior. Within a cooperation project between Audi AG (Germany) and TU Dresden (Germany) five previous works have focused on the vehicle modeling, model verification, validation, analysis methodology and physical effect chains analysis for rollover behavior. However, a study into existing literature reveals that the interaction between yaw instability and roll instability has not been investigated sufficiently to date. Especially the question arises, to what extent the oversteer tendency (lateral instability) affects the rollover behavior (roll instability). Therefore, this paper aims to analyze the motion couplings between yaw and roll dynamics to explain the interrelation between oversteer tendency and rollover behavior, using the developed nonlinear two-track model with full axle kinematics and compliance, a dynamic steering and a nonlinear tire model. Firstly, a new criterion to describe the dynamical oversteer tendency in the nonlinear limit range of driving dynamics has been defined, which can be regarded as a further development of the traditional definitions of oversteer tendency in the linear range. Secondly, the rollover criticality has been quantified by means of a new maneuver in order to gain a comprehensive comparison between different vehicle configurations. Subsequently, different chassis parameters of the reference vehicle have been varied to investigate the relationship between driving performance and rollover stability. Finally, the results of the study are interpreted and discussed. Through analysis in this paper, the driving dynamics both in the linear and nonlinear range are evaluated to identify the operation principles between dynamical oversteer tendency and the rollover behavior. Summarizing the acquired know-how together, recommendations for design targets in the early phase of chassis development are derived. Newsworthy: 1. A new criterion to describe the dynamical oversteer tendency in the nonlinear limit range of driving dynamics 2. Systematical investigation of the interaction between oversteer tendency and rollover behavior 3. Parameter study to build up the understanding of the nonlinear physical chains of rollover behavior"