Modeling and control of an adaptive tire-inflation system based on in-tire sensing feedback
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Tire contact area is an important feature that influences the performance of a ground wheeled vehicle, especially on soft terrain. This thesis evaluates a system meant to control tire-surface contact area by inflating and deflating the tire while the vehicle is in motion. The system includes a measurement of the vertical deflection of the tire using ultrasonic distance sensors, from which tire-surface contact area can be inferred from a model basis. In order to validate the concept and determine limits on such a system, a model and simulation of a controlled system has been developed. For the purposes of this study, it is assumed that the tire is operating on a hard (i.e., non-deformable) terrain, the contact area is elliptical, and the tire deflection can be predicted by a 1-D stiffness model. The system was evaluated using three driving scenarios, namely a change in terrain stiffness, changes in vertical applied load, and pressure changes in the tire due to change in temperature. It is shown that inflating and deflating the tire is effective in making up for changes in driving condition. The influence of sensor response characteristics, such as time delay and noise, were also included in the simulation and evaluated. The time delay was estimated based on the time to obtain the deflection based on the period of the wheel spin; the influence of the time delay can be minimized by changing the proportional and integral gains. The results also suggest that the system is actually robust to the influence of noise. Some suggestions for future work on this problem are provided.