Development and analysis of active rear axle steering for 8x8 combat vehicle
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This thesis proposes and compares multiple vehicle dynamics controllers using rear axle steering of an 8x8 combat vehicle. The controllers are assessed on ability to increase maneuverability at low speed, increase stability at higher speeds, avoiding rollover and ability to dampen the effects of external disturbances. The two controllers that are proposed to improve the lateral vehicle dynamics include a feed-forward Zero Side Slip (ZSS) controller which steers the rear axle based on the vehicle speed, and a Linear Quadratic Regulator (LQR) controller that monitors the steering angle and compares the vehicle yaw rate and sideslip angle to the desired values calculated at steady state. These controllers are evaluated by performing simulations using a previously validated 8x8 combat vehicle as a TruckSim© full vehicle model. The controllers are developed in MATLAB/Simulink and are applied in co-simulation with TruckSim©. The simulation events to evaluate the controller performance include a 15-meter constant step slalom, modified J-turn, FMVSS 126 ESC and NATO double lane-change. These simulations are performed in between 20 km/h and 80 km/h over low friction (μ =0.35) and high friction (μ=0.85) surfaces. The rollover prevention capabilities of the controllers are evaluated using a fishhook maneuver over a high friction surface and damping of external disturbances will be tested using a crosswind simulation. The ZSS controller is a very responsive controller that increases the maneuverability at low speed and increases the stability at higher speeds. The responsiveness results in oversteering at mid range speeds and low lateral displacement during FMVSS 126 ESC. The LQR controller, as designed, is not applicable to improve low speed maneuverability but improves the lateral stability at high speed while achieving a respectable lateral displacement during the FMVSS 126 ESC maneuver. Both the ZSS and LQR controllers reduce the lateral accelerations at high speeds. The LQR controller also dampens the external disturbances applied during a cross wind simulation.