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For the purposes of modeling vehicle response in lateral lane deviation maneuvers, a path follower that utilizes adaptive control has been developed and implemented into vehicle simulation software. The path follower utilizes input-output, model reference adaptive control so that no a priori knowledge of the vehicle system is required. The reference model response is generated by a second order linear dynamic model and represents the desired lateral lane deviation trajectory of the vehicle under the conditions of a single maneuver. The controller utilizes any steering degree of freedom of the vehicle model as the input. Therefore different vehicle model structures can be used without modification of the controller. With its adaptive structure, the vehicle model can be made to follow the desired trajectory by minimizing the error between its trajectory and the trajectory response of the reference model.

This research work was done in an effort to provide a tool for predicting on-center behavior of automobiles using computer simulation. It was discovered through this research effort that steering systems can have nonlinear characteristics that strongly affect the vehicle performance, especially in on-center driving. These nonlinearities must be modeled, characterized and simulated with care in order to predict vehicle performance. This research proposes a nonlinear steering system model that is based on the study of individual steering system components from both a hydraulic rack-and-pinion and a hydraulic recirculating ball power steering system. Included in the model are friction, nonlinear stiffness characeristics of the steering system and nonlinear boost curve shape. In addition, a means by which to characterize the steering system model for each steering system type is provided.

In developing a nonlinear steering system model for vehicle simulation, it was determined that proper inclusion of system friction is necessary to correctly predict steering wheel torque response in on-center driving using simulation models. A method to characterize the inherent friction behavior for a given steering gear has been developed and performed on two types of power steering gears: a recirculating ball gear and a rack-and-pinion gear. During this research it was discovered that levels of static and dynamic friction can differ widely for these two types. Therefore this characterization procedure provides a method to ascertain both static and dynamic friction levels. The results from these tests show that friction levels can depend on steering gear input shaft position, steering gear input angular velocity and steering gear loading conditions.