Research On Nonlinear Modeling Method Of Commercial Vehicle Steering System

In the commercial vehicle steering system, there exists a large amount of friction andclearance sections. The friction and clearance sections make great contributions to thenonlinear characteristics of commercial vehicles. That plays an important role in themodeling and simulation of the commercial vehicle steering system. Therefore, the nonlinearcharacteristics of commercial vehicle steering system have to be focused on during themodeling process on account of the higher demand for the accuracy of the model simulation.And it’s meaningful to build up an accelerated model of commercial vehicle steering system,which reflects the nonlinear characteristics.This research was from the cooperation projects of Jilin University and corporation.The main work of the research is to put forward a proper method about modeling ofcommercial vehicle steering system, and eventually finish model building. In the process ofmodeling, the thesis put up the models of friction and clearance firstly. Base on that, themodel of the steering system was built. What’s more, the parameter identification methodswere designed in order to get the parameters needed. To verify the accuracy of the modelestablished in this paper, the model was tested under several working conditions. In themeantime, the same working conditions were applied to the former steering system modeland real vehicle test. The work can be done by comparison of the tests results. The maincontents of this paper are summarized as follows:1. The structure of the commercial vehicle steering system was studied at the beginning.On the basis of reflecting its characteristics in movement, the steering system structure wassimplified by means of ignoring some detail components of minimal impact. The sketch mapshowing the structure of commercial vehicle steering systems was established. Taking thestructure of commercial vehicle steering system, together with the advantages anddisadvantages of the classical models into account, this paper made out the modelingmechanism. Namely, in aspect of dynamics, the inertia, elastic and damping factor ofsteering wheel and column were taken into consideration, as well as the link of the leftsteering wheel and the right. Furthermore, this paper paid much attention to the dry frictionand gap sections in the steering system.2. The models of friction and gap in steering system were built. On the one hand, theanalysis program was presented, aiming at description of frictions which exist in different parts of steering system. The program was based on the classical Karnoop friction model.Following that, critical speed threshold was set, which divided the friction into static frictionstage and dynamic friction stage. In this way, the progress of zero relative velocity detectioncan be left out while reducing the handover procedure. On the other hand, the clearanceexisting in the steering system was converted equivalently to the gap between the nut and therocker gear at the output end of the steering gear.3. The steering system was divided into three parts, which were assemblies of thesteering wheel and steering column, steering gear-related components and the kingpintogether with the steering trapezoid. The dynamics differential equations of the various partsof the steering system were established. According to the equation expressions, Simulinkprogram was built progressively. Then each part of the subsystem block was packaged andnamed. Finally the overall Simulink model of the steering system can be made afterconnecting the various the subsystems.4.The acquisition method of the parameters in the model was determined, whichincluded consulting related resources, test measurements, establishing fitting equationmodels and so on. After the required parameters were acquired, the values were edited intothe M-file of Simulink model for use.5. The Simulink model was operated under some typical test conditions. Then the sametest conditions were applied to the original steering system model ignoring the nonlinearcharacteristics. The contribution the nonlinear characteristics made can be seen bycomparison of the both results. In order to verify the accuracy of the model, the simulationresult was compared with that of real-vehicle tests.