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This work presents a theoretical study on a linear 3-DOF vehicle handling model which, incorporates driver's operation and vehicle suspension derivatives. The model is constructed to investigate the performance of vehicles with conventional front steering system and vehicles with actively controlled front wheel steering system as well. The control strategy of the Active Front Steering (AFS) control is based on the optimal control theory using LQR technique. The vehicle model excitation is a simulation of the aerodynamic forces and moments generated on a passenger car when overtaking a truck. Results are showing a comparison between the performance of the vehicle with conventional steering system and the vehicle with Active Front Steering (AFS) system. A significant improvement with the AFS optimal system is achieved in the vehicle response especially for lateral deviation error.

The directional stability properties of passenger cars under high speed, straight running conditions form a major contributory factor in overall subjective ratings of vehicle handling, comfort and driveability. The aim of the paper is to investigate the links between straight running properties under random wind loading and vehicle design parameters. A linear, three degree of freedom vehicle model was selected, to which a simple driver model could be incorporated as necessary. The wind loading excitation was modeled using a quasi-static approach, involving a randomly varying side wind with statistical properties taken from existing literature. The response properties of the vehicle with and without driver were characterized by performance indices such as root mean square values of vehicle motions. Finally, these results were analyzed to search for correlation between the performance indices and vehicle chassis design features such as tires, steering system and suspension kinematics.