Sport Utility Vehicle (SUV) sales are increasing globally, even surpassing sedan vehicle sales worldwide. Their increasing popularity is termed a continuous trend that is expected to last. SUVs are known to offer a higher ground clearance which makes them more susceptible to rollover and directional instability during emergency manoeuvres. This dissertation proposes an integrated controller which controls two vehicle states, namely yaw-rate and side-slip angle to improve handling while reducing rollover propensity and improving rollover stability. The control system employs brake based torque vectoring to control the vehicle states, torque vectoring control improves lateral stability by maintaining consistent handling characteristics over all driving conditions and the lateral stability is maintained whilst adhering to a rollover index. The desired vehicle states are obtained from a reference linear two degree of freedom model with tyre characteristics obtained from the linear region of the tyre. A coordinated control strategy is investigated with respect to Direct Yaw Moment Control (DYC) acting on a vehicle through individual brake torques. Two types of controllers are investigated, namely a Linear Quadratic Regulator (LQR) and a Linear Model Predictive Controller (LMPC). It is shown that yaw rate control together with side-slip angle control and the inclusion of a roll index limit allows for better vehicle handling. Simulation tests are done using Simulink/ADAMS and verified experimentally with a SUV undergoing evasive manoeuvres where the vehicle is near its performance limit. The vehicle managed to be successfully navigated through manoeuvres not possible prior to yaw rate and side-slip angle control, with a notable decrease in the vehicle roll.
Dissertation (MEng)--University of Pretoria, 2018.