Research On Hydro-pneumatic Suspension And Electro-hydraulic Servo Steering System In Heavy Wheeled Vehicles

Currently, there are still some problems to be solved in the hydro-pneumatic suspension and electro-hydraulic servo steering system of heavy wheeled vehicles. The urgent problems are described as follows:simultaneous movements of the vehicles in the body posture adjustment with hydro-pneumatic suspension can not be achieved, the majority of vehicles with hydro-pneumatic suspension are designed without taking into account road-friendliness and ride comfort comprehensively and the performance of the electro-hydraulic steering system with proportional valve is not satisfactory. The applications and development of the chassis in the heavy wheeled vehicles are seriously restricted by these problems. This paper focused on these three issues and the further study was carried out for the certain type of Zoomlion7-axles all-terrain crane. The main contents are as follows:In chapter1, on the basis of referring to a large number of domestic and international associated literatures about hydro-pneumatic suspension and electro-hydraulic control steering system, the body posture adjustment of the hydro-pneumatic suspension, integrated performance optimization of ride comfort and road-friendliness and electro-hydraulic control steering system were summarized. Their problems were pointed out. The related research background and significance of this subject was expounded and the main research work was proposed.In chapter2, every function of the commonly used interconnected hydro-pneumatic suspension in heavy wheeled vehicles was analyzed and the asynchrony mechanism was discussed. Based on flow control valve and pressure tracking valve, an improved interconnected hydro-pneumatic suspension was presented and lifting" synchronization of the system was realized. The key element pressure tracking valve of the synchronization system was designed. The mathematic model and simulation model of the pressure tracking valve were established and the effects of the various parameters on the performance of the pressure tracking valve were analyzed. The experimental research on the pressure tracking valve was performed and the model was verified correctly. The simulation and experiment were achieved on the one-axle condition of synchronized lifting system. The lifting synchronization experiment of the actual vehicle was performed and the synchronous effect was well. The improved synchronization system could meet the demand of high performance completely in the heavy wheeled vehicles.In chapter3, the ride comfort and road-friendliness of the hydro-pneumatic suspension were analyzed and optimized. Based on the whole vehicle7-DOFs dynamic model, road spectrum model and hydraulic system model in the hydro-pneumatic suspension were established. With the application of the ADAMS, AMESim and Simulink, the simulation model of the whole vehicle, hydraulic parts of hydro-pneumatic suspension and road spectrum was established and the co-simulation analysis was carried out. The effects of the main stiffness and damping parameters of the hydro-pneumatic suspension on ride comfort and road-friendliness were discussed. With the normalized processing of the ride comfort and road-friendliness, the appropriate configuration parameters of better ride comfort and road-friendliness were achieved by the genetic algorithm.In chapter4, according to the characteristics of heavy wheeled vehicle steering system, the electro-hydraulic servo steering system with servo-proportional valve was designed. The function, mode and working principle of the system were produced. The mathematic model of the steering mechanism was established and its kinematic and dynamic model were analyzed and simplified. Then the mathematic model of the hydraulic control system was established. These mathematic models could be combined as a valve-controlled two steering cylinders model. The simplified linear analysis of the combined model was achieved and the effects of main parameters on the tracking error of the electro-hydraulic servo steering system were discussed. The results show that the tracking error varies with the position of the steering system. The minimum tracking error appears at extreme left steering position while the maximum tracking error appears at extreme right steering position.In chapter5, the co-simulation of the electro-hydraulic servo steering system was analyzed. The simulation model of the mechanical parts including steering mechanism, tire and road was established based on ADAMS. The simulation model of the hydraulic parts was established based on AMESim. AMESim was set as master software and co-simulation analysis was achieved. The simulation results show that the tracking error varies with the position of the steering system. The minimum tracking error appears at extreme left steering position while the maximum tracking error appears at extreme right steering position. It is consistent with the theoretical analysis. The effects of the parameters of supply pressure, gain of the proportion link, area and leakage of the steering cylinder, frequency response, dead zone and hysteresis of the servo-proportional valve, length and diameter of the pipe and load on the performance of electro-hydraulic servo steering system were discussed. A kind of variable-gain control strategy was proposed. The simulation results show that this control strategy can effectively suppress the variation of the tracking error with steering position and the tracking error tends to be constant.In chapter6, experimental studies of the electro-hydraulic servo steering system were carried out, and the test bench and test scheme were introduced. The data acquisition system was designed based on LabVIEW. Firstly, the static experimental analysis based on test bench was carried out and effects of the parameters of supply pressure and gain of proportion link on the performance of the electro-hydraulic servo steering system were investigated. Tests on the unloaded and loaded conditions were carried out and the experimental results were consistent with the theoretical analysis and simulation analysis. Then, the static tests of a certain type of Zoomlion7-axles all-terrain crane on the unloaded and loaded conditions were carried out. Finally, the driving tests of the vehicle were also achieved. The performance of the electro-hydraulic servo steering system is good in all test conditions. It is verified that the designed electro-hydraulic servo steering system with servo-proportional valve is reasonable and effective.In chapter7, the major work of the study was summarized. The conclusions and innovations of the study were elaborated and the future study of the hydro-pneumatic suspension and electro-hydraulic servo steering system in heavy wheeled vehicles was also prospected.