Quantitative High Speed Stability Assessment of a Sports Utility Vehicle and Classification of Wind Gust Profiles

The automotive trends of vehicles with lower aerodynamic drag and more powerful drivetrains have increased the concern of stability issues at high speeds, since more streamlined bodies show greater sensitivity to crosswinds. This is especially important for high vehicles, such as sports utility vehicles. In addition, the competitiveness in the automotive industry requires faster development times and, thus, a need to evaluate the high speed stability performance in an early design phase, preferable using simulation tools. The accuracy of these simulation tools partly relies on realistic boundary conditions for the wind and quantitative measures for assessing stability without the subjective evaluation of experienced drivers. Hence, this study employed an on-road experimental measurements setup to define relevant wind conditions and to find an objective methodology to evaluate high speed stability. The paper is focusing in detail on the events in proximity to the drivers' subjective triggers of instability. Wind direction and magnitude, vehicle motion response, driver steering input along with the subjective event triggering were measured for several aerodynamic configurations during different conditions of the natural wind. A statistical approach was utilized to analyze the correlation between the vehicle response and subjective triggers together with the wind conditions. A correlation was established between the subjective triggers and a rapid change in lateral acceleration and yaw rate response. The paper also proposes a set of crosswind gust profiles of interest for driving stability, combining results from previous research and the experimental data of the natural wind obtained in this study. These findings can be used as objective measures for virtually assessing stability performance and as realistic boundary conditions. The study also shows that some aerodynamic configurations were less sensitive than others in equivalent wind conditions, and that subjective instability triggers were avoided to a higher extent for these better performing configurations.