| Because of bad working environment, poor road conditions and larger load weight for loader, causing loader's vibration phenomenon to be serious while it is driving on some bumpy roads. The phenomenon of loader vibration not only adversely affects the structure of the vehicle, but also limits to the loader's development of high-speed and efficient. With increasing demands of engineering vehicle's ride comfort, safety, comfort and high-efficiency for customer, the vibration problems are also got more and more attention while loader is driving. Loader ride comfort, vibration research of engine and tire need dynamic characteristic analysis, modal analysis of vehicle structure is also based on vibration dynamic analysis category. In oder to minimize the impact of vibration on the loader, improve vehicle structure reliability and ride comfort, it is necessary to study the loader structure system, analyze the dynamic characteristics of vehicle structure system in the process of driving.The structure system research of this paper was subsidized by the national natural science foundation "Study on the Key Technologies of Powertrain Load Spectrum of Wheeled Vehicle"(No:50805065). This paper makes multibody dynamics analysis of structure system in the process of driving based on 80 wheel loader. Oil cylinder dynamic model was established, and the influence factors of oil cylinder stiffness and damping characteristics were analyzed. Loader structure system dynamics model was established according to the basic theory of multi-body dynamics, multibody dynamics analysis of structure system in different conditions of driving were carried out. The finite element model of structure system was found, and modal analysis of vehicle structure was implemented.Driving stability system is added on the working device hydraulic system, the dynamic characteristics of the loader are analyzed by using the established structure system dynamics model. At last, this chaper studys vibration performance of driving stability system for loader structure system.The main works and contents of this paper are as follows:(1) Chaper 1 elaborates the background and significance of the paper. Then the history and trend of the experimental and theoretical research on multi-body dynamics of engineering vehicle were summarized. Some existing problems in the process of driving were described. Combining the development situation of engineering vehicles, this chapter presents the basic research methods and main work contents of this paper.(2) Oil cylinder driving force formulas are obtained while driving through the force analysis of working device. The hydraulic system principle of loader working device was analyzed, and oil cylinder dynamic model was established. The dynamic characteristics parameters which affecting arm oil cylinder and bucket cylinder parameters were analyzed, and the dynamic characteristics influence factors of load weight, road characteristics, working device lifting height, oil cylinder hydraulic oil leakage and hydraulic oil itself characteristics for oil cylinder were studied. This chapter lays a foundation for loader structure system model establishment and the multi-body dynamics analysis.(3) This chapter explains the method of selecting loader tire model to determine the corresponding parameters of the tire model, the establishment of the tire dynamic model.3D equivalent volume road model was established basing on the roughness theory of road. The establishment methods of oil cylinder mechanical model and engine incentive model were discussed. And this chapter studys the establishing methods of virtual prototyping model for loader structure system, including three-dimensional entity model establishment, data file conversion, structure system topology constraint relation, corresponding movement and constraints setting, etc. Finally, tire model and 3D equivalent volume road model were added on structure system, and structure system dynamics model of the loader was established.(4) By identifying the related simulation parameters of the structure system, aiming at driving conditions, the whole vehicle structural dynamics model was set up. By selecting some different driving conditions, this paper emphasis on the multi-body dynamics analysis of structural systems for the loader which is loaded and unloaded conditions with high-speed. Kinematic characteristics and dynamic characteristics of the key components were obtained, and the dynamic loads characteristics of the hinge points were analyzed. In three typical driving conditions, dynamic characteristics of the loader structure system were analyzed. The influence of driving speed, road characteristics, working device lifting height on the loader's structure dynamics characteristics and driving performance were studied. For oil cylinder's support characteristics, the features of the elastic oil cylinder and rigid oil cylinder were analyzed and compared. Simplified model of the whole vehicle structure and the virtual prototype models were compared and analyzed, the dynamic influence of random road characteristics and the working device suspension structure on loader structure system were studied. Research shows that the whole vehicle structure system dynamics simulation model can better simulate the dynamic characteristics of the loader in driving conditions, the analysis results closer to the engineering practice. (5) According to the Finite Element Method, the structure system finite element model of loader was established. Modal analysis of the whole vehicle structure system was accomplished by using the finite element software, inherent frequency and vibration mode of structure system were obtained in loaded and unloaded conditions. The vehicle's driving performance was evaluated and analyzed from surface roughness incentive, tire incentive, engine incentive, etc. It's meaningful to study the strength, reliability and vibration attenuation of structure system by the research of modal analysis.(6) In order to solve some problems while loader is driving on bumpy roads, a set of stability system is added to hydraulic system of working device. Stiffness and damping characteristics of driving stability system were calculated, and the loader structural system which was added on the stability system was analyzed by using the theory of multi-body dynamics. The vibration isolation characteristic of structure system which was added to driving stability system was studied. Driving stability system damping effect on the structure system was analyzed by comparing the calculated results. Driving stability system analysis provides certain basis in order to reduce vibration and shocks of structure system from road incentive and improve the driving stability and the reliability of structure system.Finally, the main research of this paper was summarized, and the further research direction was pointed out.In this paper, according to the particularity of driving conditions for wheel loader, structure system model was established by using multi-body dynamics, finite element method, etc. Dynamic characteristics of loader structural system were analyzed. In the process of driving the dynamic characteristics of structural system were described, the results were evaluated and analyzed. The research of this paper provides certain theoretical basis so as to improve rideability and structure reliability for wheel loader. |
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