| Currently, tractor-semitrailer as a major combination model of tractor-trailer,becomes more and more popular and plays a dominant role in road freighttransportation. However, a number of general reasons lead to the bad performance andeven worse accident situation about tractor-semitrailers in our country. First, becauseof the independent production and management mode, the matching oftractor-semitrailers is often ignored, so it is difficult to ensure vehicles'integratedsecurity. Second, domestic safety evaluation criteria system for the tractor-semitraileris not perfectly constructed and operated, thus how to estimate the performance andevaluate the security of the vehicles is still unsolved. Last but not the least, theoutdated detection technology restraints the development of the articulated vehicles.Therefore, deeply researching dynamics characteristic and improve the handingstability of tractor-semitrailer by whatever means are always important topics andurgent problems to be solved at present.In view to dynamic characteristics, driving stability regions and active securitycontrol of tractor-semitrailer, the aim of this paper is to master the essence of stabilitymechanism and nonlinear dynamic characteristics of tractor-semitrailer, and solve theengineering problems such as handing stability detecting, stability regions estimationas well as the stability control in critical steering and severe environment fortractor-semitrailer. Specific contents are as following:1) Based on system dynamics theory, multi-degree-of-freedom tractor-semitrailerdynamic model is derived, then vehicle dynamic responses and instability form andcharacteristics in different loads and steering conditions are analyzed by quantitativeand qualitative means. Applying advanced GPS and inertial measurement technology,detecting equipment for tractor-semitrailer handing stability is integrated anddeveloped, and vehicle in typical conditions is tested with the detecting equipment.According to the research object, the derived tractor-semitrailer dynamic model isreasonably simplified and its reliability is verified by vehicle tests.2) Though introducing related dynamic characteristics of tractor-semitrailer,vehicle steering stability mechanisms from the view of equilibrium points, balanceregions as well as energy conversion in different steering modes are quantitatively analysis, then the balance and energy conversion principles of tractor-semitrailer andtractor single unit are comparatively studied and the effect and influence of semitraileron tractor and the cooperative motion of whole vehicle are discussed.3) According to bifurcation theory and center manifold theorem, Jacobian matrixof tractor-semitrailer dynamic system with magic formula is indicated, then thesaddle-node bifurcation characteristic in critical of stable steering and the variation ofvehicle system's equilibrium points and bifurcation forms with external disturbanceare analyzed. Based on chaos theory, the question of whether 4 DOFtractor-semitrailer model happens chaotic motion during unsteady steering ispreliminary invested.4) Applying the analysis method on stability regions of single vehicle proposedby John, quadratic Lyapunov energy function of tractor-semitrailer with three timestyre model is derived and boundary conditions of energy function is defined byLagrange rules, then the stability regions are obtained according to Lyapunov theorem.Though analyzing the deficiency of the conversional algorithm, an improved methodbased on perfect vehicle dynamic model and energy conversion is proposed. Bycontrast of the stability regions estimated by conversional and improved method, andcombined with the results of vehicle test and simulation, the accuracy of the improvedalgorithm is analyzed.5) Considering the uncertainty of tyre and external disturbance, linear fractionaltransformation model of tractor-semitrailer is derived. According to robust controltheory, based on H∞loop-shaping and H∞norm index of expected state output, thedesign process of MIMO H∞feed-forward and back-forward synthetic controller withstrategy of active front wheel steering and saddle direct yaw moment is presented indetail. Vehicle hangding stability with and without control in wind disturbance andcritical steering conditions are simulated, then the control effect for eliminating thewind disturbance and the uncertainty of vehicle and improving the trackingperformance of tractor-semitrailer are discussed. |
