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Modeling of a Sport Utility Vehicle as it moves on two wheels studied in this paper. Our major purpose concentrated on developing a general criterion to specify rollover threshold. First, model of vehicle as it sustained on two wheels derived that its results used to develop rollover threshold of Sport Utility Vehicles. In addition, these results could be valuable to design new controllers, which are able to prevent rollover at the best state of vehicle dynamics. After vehicle modeling, appropriate model for tire forces and moments picked up from the most related and available references. Then validation accomplished as final part of modeling section. Stability of presented model studied as an important part of this paper. In order to specify rollover threshold as vehicle moves on two wheels, steady-state equations of motion used and based on steady state analyses a new criterion proposed. Next, by designing some maneuvers, simulations accomplished to show applicability of proposed criterion at different situations. As conclusion, presented criterion is more implementable and efficient than other proposed model for rollover threshold and can prospect rollover threshold at various steering angles and longitudinal speeds as model inputs.

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In this paper, an active caster mechanism has been introduced for the purpose of vehicle handling enhancement. To this end, a 9-DOF nonlinear vehicle model, consisting of steering system dynamic equations, derived by using Kane dynamics method, and Magic Formula tyre model, is used for the simulation purposes. The effect of caster angle variations on the steady state response of the vehicle, was investigated in the next step. Based on the knowledge, extracted by the mentioned approach, a fuzzy logic controller (FLC) is designed for controlling caster angle. According to the yaw rate error, between actual and desired values, and the vehicle lateral acceleration, the controller produces the required caster angle in order to reach to stable state of the vehicle. The desired vehicle dynamics motion is assumed in the form of the steady motion of the bicycle model. Also the variation of caster angle was limited in a conventional range. During some critical maneuvers, the performance of the caster angle controller was tested and compared with the uncontrolled vehicle. Simulation results show that the caster variation control has a high capability to enhance vehicle handling dynamics.