Research On Steering Performance Of Multi-axle Steering Vehicle

This doctoral dissertation has been finished on the foundation of the innovation fund of Jilin university,'multi-axle steering system research of special truck'. With the increasing of lifting weight, the whole weight and axle number of large cranes have been increased. The demand of advanced technology becomes higher and higher and the maneuverability of multi-axle struck is becoming more and more important. Multi-axle steering technology is an effective method to improve maneuverability and stability of special large all terrain crane and it becomes the key technology that influences the development of all terrain cranes. Compared to the international homologous heavy industry, we have a great gap in multi-axle steering technology. Nowadays, the hydraulic assistant mechanical steering system is still applied on multi-axle steering system in nation. In some foreign countries, the mechanical and dynamic control steering system has been adopted in multi-axle steering system in the large vehicles. Their maneuverability, reliability, stability have been greatly improved. At present, the theory about multi-axle steering vehicle is very limited. In order to improve our technology about this part, the research of multi-axle steering vehicle seems to be very necessary.According to the above statements, to improve the multi-axle steering performances of multi-axle steering vehicle, this paper has deeply researched the mainly affected factors of it, such as hydro-pneumatic suspension, the stiffness of steering system, the structural parameters of steering linkage, hydraulic power steering system, steering Control Algorithm and so on. According to the characteristics of multi-axle steering system It has provided some beneficial practical and theoretical guide for multi-axle steering technical in our country.The multi-axle steering vehicle dynamic model is the basic of multi-axle steering technology. Based on the existent theories, a linear 2DOF multi-axle steering vehicle model has been presented including the stiffness of steering system, hydraulic power steering system, aerodynamic etc. The consistency of the results demonstrates its correctness and universality. Base on this conclusion, the stability evaluation parameters, including yaw angular velocity gain, sideslip angle gain, side acceleration gain etc. are presented under the steady state cornering test. The formula keeping the sideslip angle zero is obtained. Simulation results give the relationship of yaw angular velocity gain between FWS and MWS. The velocity according to the maximal yaw angular velocity gain is expressed. The affections of structure and performance parameters on the steering characteristics have been analyzed.Based on the linear 2DOF model, another kinetic model of 3-DOF multi-axle steering vehicle which has considered the lean movement of vehicle body has been built according to Lagrange equation. And The transfer function among rolling angle, yaw angular velocity and sideslip angle have been presented using Matlab.Hydro-pneumatic suspension (HPS) system is one of the main factors of effect on the steering performance of multi-axle steering vehicle. Based on the research of effect of double-gas-gambers parameters on the nonlinear characteristics of HPS, the paper deeply discussed the stiffness characteristics of independent and linked HPS and its effect on rolling characteristic of multi-axle steering vehicle. The effects of the parameters of linked HPS system on the steering and rolling characteristics of multi-axle steering vehicle were analyzed. The stiffness transfer characteristic of linked HPS is firstly put forward. The effects of parameters of linked HPS on the steering of multi-axle steering vehicle were simulated. Two new modes of HPS were designed, which is in favor of ride performance and steering performance of multi-axle steering vehicle.The steering linkage of multi-axle steering vehicle is one of mainly affective factors to multi-axle steering characteristics. The steering drag torque of multi-axle steering vehicle is very big and the steering linkage is very long. Therefore, the affection of the stiffness of steering system on the steering characteristics has been simulated. The results of simulation verify the correctness of theory result. Namely, properly reducing the stiffness of steering system properly will help to improve the steering stability of multi-axle steering vehicle.The optimization of steering linkage is an effective method to improve steering characteristics. The optimal steering linkage can avoid the abnormal wear of tire and decrease the force of steering linkage. The force of whole steering linkage becomes more balanced. The steering portability and reliability of the vehicle have been improved. To improve the efficiency and precision of steering linkage optimization, a set of blocking parameter model and optimal program have been developed. During the developing process, a blocking parameter model method is put forward. The parameter modeling and optimization become easier for the steering system. The optimization design of steering linkage of a multi-axle steering all terrain cranes gets a very remarkable effect by this program. By doing so, the work efficiency and the design precision not only are improved greatly, but also the reliability of outputs is improved greatly.The steering system force is the mainly effective factor of reliability and portability of multi-axle steering vehicle. The section mainly aims at the failures of steering system of real struck. A multi-axle steering vehicle virtual prototype including Electrical-hydraulic Controlling System is built. The opening rate formula of valve has deduced and the function of servo-actuated redirector has been simulated. Simulation and test of multi-axle steering system have been done. The test results demonstrate the virtual prototype model′s correctness. Based on it, the effect of hydraulic power steering system on the force of steering system is discussed. According to the working circumstance of multi-axle steering vehicle, the force change of steering system has been simulated under several working conditions. The effect of centre of mass, the lock angle of wheel, the design of steering linkage system, on the force of steering system is analyzed. Because of the unbalanced force of steering system, the mend and optimization of steering system have been done and an effective measure is put forward. The results indicate that the maximal force is reduced to 58%. The reliability of steering system has greatly improved.Because the force of multi-axle steering system is general very big, a deeply research has been done. The method matching the cylinder force with the turning resisting moment is an effective plant for reducing the force of multi-axle steering system.Rear axles dynamic steering control strategy is an effective means to improve the characteristics of multi-axle steering vehicle, security and stability, it also are the popular technical in international range. The multi-axle steering technology derives from 4ws and is more complex, universality than 4ws. Based on the 2-DOF and 3-DOF models, electro-hydraulic proportional control system and H 2 /H∞optimization controller are built. A virtual prototype model of multi-axle steering vehicle including electrical-hydraulic controlling system is presented. The co-simulation of ESYS5 and ADAMS has been done. The characteristics of hydraulic steering system and the performance parameters of multi-axle steering vehicle are analyzed during the dynamic turning process. It is discussed the effect of electro-hydraulic proportional control system on the steering characteristics. Because of the lower turning agile capability of the multi-axle steering vehicle adopting the sideslip angle zero control strategy at high speed turning process, a coefficient method is put forward. When the sideslip angle is not very big, the method can improve the agility of vehicle and lay a foundation for the design of the multi-axle steering vehicle controller. A H 2 /H∞optimal controller of 3-DOF multi-axle steering vehicle is designed by Matlab and H 2 /H∞optimiation theory. The effect of the optimal controller on the steering characteristics of multi-axle steering vehicle is analysis. The simulation results show that the H 2 /H∞optimal controller has better system performance and robust performance. The steering characteristics of multi-axle steering vehicle have been greatly improved and guarantee the security, handling and stability.