Steering Stability Study Of Three-axle Heavy Vehicle

Steering performance of heavy vehicle has directly effect on vehicle handling stability, agility and use economy. So it is necessary to make deeply research on steering characteristics of heavy vehicle, thus improves its dynamic stability as well as safe driving ability.Currently, the virtual prototyping and dynamic simulation technology have showed the remarkable fruit in car design. However, in domestic, this technique is only used on two-axle vehicles. A great amount of heavy vehicle factories still use the traditional experience-design methods, which are featured by manufacturing physical prototype to check problems in the tests. Generally, various new technologies have to be tested on product directly in this method, which brings high risks in technology innovation and, on certain degree, restricts product creativity.Based on the project of"Study on special vehicle intelligent all-wheel steering system"of Jilin University innovation fund, with the use of three-axle all terrain crane prototype, this paper studied the virtual experiments using large dynamics simulation software ADAMS/Car. Also, in this paper, the mechanics model and control arithmetic of the multi-axle all terrain crane were analyzed to get the simulation results, which laid a solid foundation for field tests and product improvement in order to obtain helpful experiences for study of heavy vehicle's steering stability.Firstly, according to multi-axle steering principles, this paper analyzed the simplified 2-DOF vehicle model and expatiated various common control methods of multi-axle steering. Using the Simulink software, this paper established the open loop proportional control strategy based on zero side-slip angle of mass center, and also, analyzed the full vehicle step input transient response in 6WS and 2WS modes.The simulation results indicats that, compared with 2WS mode, the 6WS mode with the open loop proportional control strategy improved its mobility at low speed as well as handling stability at high speed. Most of the characteristic indexes of 6WS vehicle are better than that of 2WS vehicle at corresponding speed.Sequentially, this paper deeply studied the basic modeling theory of ADAMS, usage of the coordinate's system and the establishing and solving methods for dynamics equation. On the basis of them, this paper systematically introduced the establishing processes of suspension template, steering template, tire template as well as the communicator which transfers information among those templates. Also, three-axle virtual prototype model which includes the suspension, steering, tire body subsystem etc. was established by ADAMS/Car.After having read a great variety of relative references, the author expatiated the application values of co-simulation in multi-axle design processes, summarized the processes of co-simulation with ADAMS/Car and Matlab, and discussed the necessary interface settings between these two softwares to ensure the co-simulation goes successfully. Simulation curves were obtained from the analysis of co-simulation vehicle model both in steady static circular test and in ISO lane change test. Results showed that with control strategy, 6WS model could run according to scheduled course during steady static circular test; however, without control strategy, it had serious side-slip phenomenon. From the ISO lane change test curves, it can be seen that the characteristic indexes of 6WS were far better than 2WS in yaw velocity and lateral acceleration. Also, this simulation results verified the consistency on the qualitative analysis of the Simulink mathematics model and the ADAMS dynamic system. This paper also writed the DCF file according to national standards. The handling stability virtual experiments such as Pylon course slalom test and Steering transient response test were carried out to verify the transient and steady responsive characteristics for multi-wheel steering vehicle. Testing curves are obtained and analyzed to evaluate the steady characteristic of the vehicle model.Finally, in order to test the effects of the control strategy on real vehicle and the characteristics of electro-hydraulic vehicle steering control system, this paper programmed the heavy vehicle steering experiment processes, which included testing methods, measured parameters, the instrumental choice, testing work conditions, data processing as well as the theoretic calculation methods of the testing data. At last, the blueprints of common testing platform were drawn.The above research work indicates that, through the virtual prototyping and dynamic simulation technology which were introduced in this paper, multi-wheel 3-D model of all terrain crane can be built; computer simulation of vehicle test, according with the road testing prescribed by national authority, can be realized. Compared with the traditional formula calculation, the more accurate results are obtained from the reservation of as much as possible the whole-vehicle DOF. Through the simulation analysis for the whole-vehicle dynamic characteristics, most design problems are resolved before the prototype testing. Consequently, the design reliability is increased.