A control allocation technique to recover from driver-induced oscillations
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The focus of this thesis is the study of driver induced oscillations. When the rear tires of a car are force saturated due to aggressive driver behaviour, high velocity on a slippery road, sudden steering action or heavy braking, rear end of the car tends to lose traction on the road and starts skidding. At the same time, the driver, having the direct steering control over the front two tires, feels a time delay at the response of the rear tires to the steering actions. The delay between the driver's action and the vehicle's response may eventually instigate the swinging of the rear end of the vehicle, which is generally referred to as \fishtailing". In the literature, few studies exist regarding fishtailing motion and in those studies, the theoretical background of this motion is not studied in detail. In this thesis, fishtailing motion dynamics are investigated in detail by employing a non linear vehicle model, and this motion is recreated for a specific vehicle configuration. Then, a control allocation technique is presented to recover from this driverinduced fishtailing motion. The proposed control allocation method helps the vehicle recover from these undesired oscillations by minimizing the phase shift between the commanded and realized forces and moments. The simulation results demonstrate that using the proposed method, it is possible to make the vehicle recover from driver induced oscillations even at high velocities where conventional approaches fail. For the cases of actuator failure, for example loss of tire inflation pressure, an adaptive version of the control allocation is also proposed that can stabilize the vehicle even when the actuator effectiveness is reduced significantly.