Nonlinear Dynamics Of Active Chassises Of Ground Vehicles

This dissertation presents a systematical study on dynamic modeling and dynamic characteristics of vehicle active chassis, including modeling vehicle active chassis for nonlinear dynamic simulation, modeling delayed dynamic system, effect of discontinuous on active vehicle suspensions equipped with "ON/OFF" control strategies, effect of time delay on active vehicle suspensions equipped with "LQ" control strategies, effect of time delay on four wheel steering equipped with all kinds of control strategies. It aims at modeling more contained four-wheel steering vehicles, presenting a good method to estimate the physical parameters and time delay in the feedback and analysis some nonlinear complications effecting on vehicle dynamic characteristics.Based on the mathematical and mechanic models, the paper analyzes heave motion, lateral motion and longitudinal motion. And then a nonlinear dynamic model often degrees of freedom for four-wheel steering vehicles, which features the surge, sway, heave, yaw, pitch and roll of vehicle body, as well as four rotational degrees of freedom of four wheels, is presented herein to lay a foundation for dynamic simulation. In the model, the effects of vehicle suspension, four wheel steering system, aerodynamics and nonlinearity of tires are taken into account. The dynamic performance of vehicle with all nonlinear features coupled in various maneuvers is investigated.In chapter three, The dissertation presents an approach based on the genetic algorithms to estimate the system parameters and time delays in the feedback simultaneously. The minimization of residual error of system equation is regarded as objective functions. And unknown system parameter and time delays are used as optimized variables so that the genetic algorithms are used to estimate the system parameters and time delays. In the case of many system parameters to be estimated, it is suggested to estimate a part of system parameters through an open-loop experiment and then the time delays and remaining parameters through a closed-loop experiment. The approach is illustrated by two examples of numerical simulation. Due to the global optimum in a parallel, random and blind way, the approach works for both linear and nonlinear systems with time delays. However, the author's recent research shows that the controlled system with time delays identifiability is dependent on the following aspects: system model selection, the identifying methods' competence, and experimental data quality. Firstly, the dissertation discusses the influences of the model selection on the system identifiability. Then, the dissertation analyzes the selected identification method. If unknown parameters are excessively sensitive to the noise, the selected method is not global identifiability.Finally, the dissertation points out that the experimental data quality is very important.In chapter four, the paper applies the theories of Floquent and Filippnov to treat the effect of active vehicle suspensions equipped with "ON/OFF" control strategies. It is shown that how change in the excitation frequency leads to change of Floquet multipliers of periodic solutions. Then, the paper analyzes the possible discontinuous bifurcation of the system under various combinations of feedback gain. In addition, The effect of time delay on the dynamic performance of the model is discussed though the use of numerical simulations in the frequency domain and time domain, respectively.In chapter five, effect of time delay on active vehicle suspensions equipped with "LQ" control strategies is investigated. Firstly, Based on the generalized Sturm criterion, developed by Chinese mathematicians Zaihua WANG and Haiyan FfU for the delay-independent stability analysis, this dissertation investigates the delay-independent stability of active vehicle suspensions equipped with "LQ". The basic steps are as follows. The first step is, according to Routh-Hurwitz, to derive the sufficient and necessary conditions for the delay-independent stability of the active vehicle suspen...