Härtill 4 uppsatser

Diss. (sammanfattning) Göteborg : Chalmers tekniska högskola, 2023

The automotive industry is continuously advancing towards more energy-efficient vehicle designs. Streamlined vehicles have low aerodynamic drag but have the potential to be unstable when exposed to external excitations such as unsteady aerodynamic forces created by the flow of air around them. Before signing off a new vehicle for production, several on-road test scenarios are conducted by professional drivers to evaluate the performance. Finding vehicle instabilities and proposing solutions to problems during late phases of development is challenging and costly. The objective of this thesis is to correlate and predict the driver’s subjective evaluation of high speed straight-line driving stability with measurable quantities in early design phases. In this work, substandard straight-line drivability was investigated on-road using different aerodynamic devices for generating high rear lift and asymmetric aerodynamic forces. These aerodynamic devices were then paired with stabilizers, called side-kicks, which helped to define the flow separation and improved the drivability of the tested vehicle. Vector plots of the mean and standard deviation of lateral acceleration, yaw velocity, steering angle, and steering torque were used to understand vehicle behaviour for the paired configurations and relate to the difference of subjective evaluation of drivability within each pair. The ride diagram was used to separate the presence of transient behaviour and study its impact on subjective evaluation. The qualitative assessment of the resulting trends agreed well with the subjective evaluation of the driver. Following this, experimental trials were conducted in driving simulators and on-road, in order to have an in-depth understanding of drivers’ subjective evaluation and responses to external excitations. Both common and professional test drivers were involved in the study. The results provided insight into the excitation frequencies and amplitudes of interest. From the test data, mathematical models were generated that can predict the drivers’ subjective evaluation after experiencing induced external excitations.