| With the development of world economy and the progress of technology,higher requirements are put forward for off-road capability of vehicle for complex unstructured terrain.The wheeled off-road vehicle with independent hydraulic transmission has the advantages of balanced driving force,good mobility,high energy transfer efficiency and flexible layout,being widely used in transportation work under complex traffic conditions.Under the environment that the core components are still dependent on imports,it is of great practical and theoretical significance to carry out research on the overall performance of the walking system,and to strive to improve the performance of vehicle driving and steering.This paper comes from the national key research and development program “The key technologies of the walking device in the narrow area and the complex terrain”(No.:2016YFC0802904),and the school-enterprise cooperation project “Design and development of unmanned single degree of freedom articulated four wheeled off-road vehicle-Rabbit”.Engine of off-road vehicle walking system,hydraulic transmission system and energy transfer relationship between wheel and ground are analyzed,and the key issues are researched by the combination of theoretical modeling,simulation analysis and experimental verification.Review the domestic and foreign wheeled off-road vehicles and the research status of hydraulic driving system and analyze the optimized space and deficiency of the existing research by reading relevant papers extensively.I Considering the research background and conditions of the four wheeled off-road vehicle which supports the papers,the research contents of this paper are determined and corresponding results are obtained.Introduce the design scheme of the walking system and analyze the composition and principle of the driving system in detail,and compare the dynamic characteristics of the flow and pressure in the two transmission schemes,taking the independent research and development of four wheeled off-road vehicle as research object.The matching principle and the realization method of the speed sensitive control of variable pump are studied basing on the engine variable pump four wheel motor drive system.According to load characteristics of interaction between tire and rigid pavement,the kinematics and dynamics models of typical conditions including straight-line driving,front wheel steering and four wheel steering are established.The analysis results show that the change of the center of gravity in the longitudinal direction has a direct influence on the driving force of the front and rear wheels of the four wheeled off-road vehicle.When the flow of four wheel motors is the same and the center of gravity close to the rear wheels,the front wheels are dragged,that is,the front wheel motors provide driving force.During steering,the effect of automatic speed difference of the scheme of low speed with motors on the opposite angles and the scheme of medium speed with motors on the same side is better relatively.The two schemes can be composite applied by On-off solenoid valve.The system pressure of four wheel steering is less than front wheel steering under the same steering radius.AMESim and LMS Virtual.Lab Motion are used to build the hydraulic driving system of the four wheeled off-road vehicle and the multi-body dynamics model to implement 1D+3D joint simulation.The correctness of matching control between engine and variable pump is verified by simulating the conditions of straight-line driving and climbing.The advantages and disadvantages of automatic speed difference are compared by simulating the front wheel steering conditions of combinations of one of the two schemes and low,medium or high speed gear.System pressures are compared by simulating the four wheel steering and the front wheel steering conditions.Front and rear wheel driving forces are compared by adding load to change the position of the longitudinal center of gravity of off-road vehicle.The independent research and development of four wheeled off-road vehicle is used as experimental vehicle.According to the typical conditions in the simulation research,the experimental scheme is designed on the basis of theoretical analysis.The correctness of the theoretical analysis and the accuracy of the simulation research are verified by the analysis of pump speed and pressure difference of each motor under steady state and the comparison between experimental data and simulation results.Furthermore it lays the foundation for the walking system optimization of the four wheeled off-road vehicle and the research and development of next generation of prototype. |
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