A lumped-parameter model of tire-terrain interactions for off-road vehicles

摘要

The inclusion of various electronic control units in modern vehicles, such as the anti-lock brake systems, the traction control systems, and the electronic stability control have improved vehicle performance and stability. Design and tuning of such control units requires large amounts of trial and error modifications as well as experiments. Therefore the need for accurate and computationally efficient models has increased to meet the demands of vehicle handling simulations for designing various control units. Tire-terrain model forms the center piece of such vehicle model development.This thesis aims at developing a discrete, lumped-parameter, physical model for capturing transient interactions between a deformable tire and a deformable terrain. Specifically, the model accounts for the radial and the tangential deformation in the tire as well as the normal and the tangential deformation of terrain. Furthermore, the model captures onset and loss of contact, localized stick and slip phases for each of the discrete elements of the tire. The model also characterize events that triggers generic transitions between the different phases of the tire elements. Moreover, special emphasis have been placed on establishing internal mathematical consistency of the formulation and energetic consistency of the model. The thesis presents detailed analysis of two instances of tire-terrain interactions under steady state condition. The thesis further presents the application of a non-linear regression technique for identification of the seven model parameters and, inselected cases additional unknown kinematic variables. Specifically, the model is fit to experimental load-deflection, grossthrust, and net-pull data demonstrating good quantitative agreement.The thesis further includes the preliminary efforts to extend the planar contact model to capture interactions in the lateral direction. Specifically, a method to uniquely resolve the time evolution of internal state variable during slip is presented. Furthermore, the issue of the motion of the contact points at the onset of contact is also addressed with some unanswered questions.