Dynamic Characteristics Analysis And Robust Control Of Tractor-semitrailer

With growing logistics demand in China, tractor-semitrailer as a major commercial vehicle models play a dominant role in road large-scale freight transportation, the usage increase continuously. This trend will inevitably demand tractor-semitrailer higher system performance. There are many issues resolved insufficiently such as overload, non-uniform standards, unreasonable matching of semitrailer and tractor system, low level freight, the low level of tractor-semitrailer performance. The existence of theses objective factors increases driving safety issues when tractor-semitrailer is in the conditions of high-speed cornering, corner braking, avoidancing of emergency and suddenly interference. Therefore, researching dynamics of tractor-semitrailer system deeply, mastering motion characteristics, analysizing effect to the performance with major parameters changing of vehicle system, effective controling of tractor-semitrailer to improve active safety driving in bad driving and complex conditions, etc., have become a important topic in the handling and stability research fields of tractor-semitrailer.Based on the vehicle system dynamics, the kinematic characteristics of tractor-semitrailer has been analysized by using computer simulation technology, the matching of traction saddle's structural parameters and the handling stability properties of tractor-semitrailer has been researched by using quantitative analysis method too. The study which aimed at driving lateral stability and robust control strategy of tractor-semitrailer can provides new mean or method for explore tracking control problem of the tractor-semitrailer traveling along the planned route. Specific contents are as follows:1. Through synthetical analyzing of vehicle system dynamics, simplified linear models of tractor-semitrailer with respect to the vehicle reference frame and the road reference frame have been developed. The 6-DOF model which keeps freedom degree of body roll in the vehicle reference frame has been used to analyze the vehicle lateral handling response, since the roll tractor-semitrailer stability requirements are considered. For the straight or nearly straight line movement purpose, the road reference frame is further introduced to describe the tracking error of the tractor-semitrailer relative to the road line, which is propitious to directly analyze response characteristics of the vehicle lateral displacement and provides the analyzed model to the robust controller designing under disturbance.2. The parameters quantitative analysis is studied on the model of tractor-semitrailer, the saddle parameters which have significant influence on handling stability of tractor-semitrailer is investigated in detail, these jobs provides reference to saddle parameters matching and optimizing. The results show that in the commonly driving conditions, the performances of a unit tractor semi-trailer are not determined by the parameters of the traction saddle, it means that these parameter values do not require have high precision, since the saddle model can express as interaction force in the motion equations of tractor-semitrailer in this paper. The unstable characteristic of lateral error is showed by open-loop dynamic response, which provides preliminary conditions to robust controller designing for tractor-semitrailer.3. There are some uncertainies associated with the tractor-semitrailer system when which is in driving conditions with interference factors. H∞loop-shaping robust control is a simple effective method to deal with these problems and can ensure the vehicle system having strong robust, furthermore driving active safety ability of tractor-semitrailer can be increased. The robust control problem of uncertain system is analyzed in the paper through describing the model to generalized form.The H∞robust controller designing procedure incorporate uses the normalized left coprime factorization method and small gain principle, which obtaines robust stability. A researching simple case initially provides the proof that this method can make the system have good robust performance and closed-loop system has good robust stability.4. Tracking control problem of tractor-semitrailer traveling along the planned route is researched and the design process of H∞loop-shaping robust controller is given in detail too. Base on the tractor-semitrailer general dynamics model, the look-ahead lateral offset is choosen as controlling plant whose transfer function is obtained too, then the singular valur curve can be plotted. Through pre and/or post-compensation of the plant adjusting, high order controller with respect to vehicle model is designed at all. Then, by comparing error bound of model order reduction methods, balanced model truncation for normalized coprime factors is adopted to reduce the order of the controller. The controller which has been reduced order has the advantages of little calculation and easy realization, etc, futhermore the final performance lossing of the controller has kept in the extent allowed. Aiming at complex driving conditions, the simulation rout is designed and the performance of this reduced controller is evaluated by the lane tracking control simulations of tractor-semitrailer. The results show that the controller can make the tractor-semitrailer stable robust under perturbed conditions and can guarantee the yawing vehicle back to the lane.The changing of speed, look-ahead distance, interference and other conditions effected on the output dynamics of vehicle are analyzed at last, which can provide judgment to re-looping-shaping.5. By comparing the curves of open-loop characteristic, the unit feedback control and the H∞loop shaping robust control, the control results of tractor-semitrailer's dynamic characteristics are analyzed. Furthermore, the results verify that H∞loop shaping controller has good control effect for open-loop stable system.H∞loop shaping robust control is applied to the tractor-semitrailer line tracking control in the paper, which is a further extended application of robust control technology in the field of automotive electronic control. The computer simulation results show that the control method is practical and effective, so this application of the control technology has a great significance for the practical feasibility and the engineering applications.