Research On Nonlinear Dynamic Characteristics Of Full Vehicle & Automotive Steering And Control Simulation

Actually, most of the vehicle dynamic systems belong to nonlinear system. A far-ranging applying foreground shows itself to us that lots of problems derived from automobile engineering can be solved by nonlinear vibration and its control theoretics. Nonlinear dynamic characteristic is regarded as a norm to appraise capability of vehicle, so, a whole and a local vibration and control issues of the independent suspension vehicle are discussed through establishing high dimension nonlinear dynamic model of a automobile.Nonlinear dynamic responses of whole vehicle were calculated during it turned under the condition that inputting supposed turning angle, As the same time, the influence to dynamic model was analyzed by comparing different torsion loaded to four wheels and different parameters of suspension and tire. LuGre friction model sufficiently depicted nonlinear speciality of tire. A series of results including rolling and yaw angular accelerations, centroid acceleration and the friction of tires were calculated in detail.Based on research of characteristic of vehicle high dimension and complex dynamics model via time-delay perturbation of four wheels, chaotic and periodic vibration behavior of whole vehicle model were found. Primarily, according to idiographic 7 D.O.F. and high dimension nonlinear dynamic system, the method of global bifurcation, frequency chart and Poincare maps were used simultaneously in the study. Strange hyper-chaotic attractors of each dimension were obtained. Lyapunov exponents chart calculated result implied the hyper-chaotic characteristic and unstable range of nonlinear system. Numerical value study indicated that in the special range of bifurcation parameter, system exist chaos, hyper-chaos, 1/3 sub-harmonic and so on. From bifurcation diagram, the system existed converse vibration which was from period to chaotic.Nonlinear compelled oscillation characters of independent suspension automotive steering were investigated using an improved incremental harmonic balanced method. Periodic results and its components of frequency were obtained, simultaneously avoiding large matrix reversion operation time after time. Going with it, concreted operational format of transfer matrix, based on 4 order RK method, was established. By this method that mentioned above, bifurcation form and chaotic area occurred to us, Floquent theory was successfully applied to resolve the stability and bifurcation problems of the nonlinear system. After that, influence of clearance and coulomb friction to the vibration of system was analyzed. In this part, another aspect is to study the self-exited vibration form of nonlinear steering system. Using analytical method approximately, critical speed of vehicle was accounted. A evident circumscription between stable range and unstable range could be gotten. Limit cycle amplitude and its stability after Hopf bifurcation is discussed at full length. Synchronously, it was pointed out that this belongs to the phenomenon of loosing stability of balanceable point and giving birth to stable limit cycle at this time. i.e. hyper-critical Hopf bifurcation. Next, influence of clearance and coulomb friction to the Hopf bifurcation of system was analyzedIn this thesis, a new type of hydro-control unit, i.e. magneto-rheological damper was used to reduce the nonlinear oscillation of automobile steering. Damper force altered through regulating the voltage which was acted on the two sides of the damper. This was the reason why amplitude of limit cycle could be reduced in the range of unstable vehicle speed. It was the destination of bifurcation control. Thinking over the inaccurate nonlinear oscillation model and the uncertainty parameters of nonlinear system, an adaptive neural network sliding mode variable structure controller was designed in this research. By estimating the maximum of unknown function, outputs of the nonlinear system vs. time were calculated in detail when disturbance acted on system. Control system was approved convergent in the whole research area and robust to disturbance and dynamic characters of unknown model using Lyapunov stability analysis method.Numerical simulations in the paper make sure the veracity and effectivity of model and theory. The results have strong engineer value practically and have important instructional significance to vehicle landscape orientation dynamic control, prediction of turning dynamics and abrasion of tire, vehicle vertical dynamic design and chaotic dynamic control. At the same time, It can direct nonlinear dynamic control of steering system and avoid its oscillation.