Research On Dynamic Characteristics,Fatigue Reliability And Robustness Optimization Of The Heavy Duty Tractor

Heavy duty tractor,as an important transportation equipment,has been widely applied in various fields such as logistics,construction and transportation.With the continuous improvement of manufacturing technology and user needs,heavy duty tractor is increasingly developing towards higher load,higher efficiency,higher reliability and high speed and light weight to meet various performance requirements and ensure the safe and reliable operation of the system.Heavy duty tractor is one of the main indexes to measure the land transportation capacity of a country.Its structural design performance directly reflects the level of national manufacturing.How to quickly and effectively develop new products with excellent performance,strong competitive,safe and reliable structure and light weight has become an important issue for automotive research and development personnel.The existing methods of vehicle system design mainly include that real vehicle experimental design,virtual prototype technology,lumped parameter mathematical model and finite element method.Although the experimental test method can accurately and effectively reflect the dynamic responses of various parts in the vehicle system,and predict the fatigue life of the structure through fatigue acceleration test,this method takes a lot of manpower,material and financial resources.The long experimental test period can not meet the current high efficient design requirements.Virtual prototype technology is a comprehensive and multidisciplinary technology.The core content is to establish solid model,mechanical model and simulation analysis.It can be very convenient to analyze the statics,kinematics and dynamics analysis on mechanical systems,which can effectively improve the design cycle of the product.But the virtual prototype model cannot be directly used for fatigue damage analysis and light weight research in vehicle systems.The lumped parameter mathematical model is a high abstraction of the research object.It have the advantages of diverse research methods,low research cost,and short research period.However,the research results of the method is greatly influenced by factors such as the degree of simplification of the model and the selection of the model parameters.The finite element simulation analysis technique is a powerful numerical calculation method,which can effectively simulate the dynamic characteristics of a very large and complex model.The simulation model and the dynamic response results can be used directly for the fatigue damage research and optimization design of the structure.It has been widely applied in industries and research of various countries,and plays a huge role in the development of a large number of high-tech products.Therefore,this paper taks a new type of heavy duty tractor as the research object,taking into account the influence of the components of the suspension,the cab,the fuel tank,and the load block on the vehicle system,the dynamic simulation model of the whole vehicle system is established by using the substructure modeling method.The typical road load spectrums of the whole vehicle system are obtained through the test method of heavy duty tractor.Based on the modal synthesis method and the transient dynamic analysis method,the inherent characteristics and dynamic characteristics of vehicle system are studied.Based on the dynamic responses of the whole vehicle system,the cumulative fatigue damage and reliability of the whole vehicle system are studied by using the multi axis random fatigue life analysis method and the input of the load power spectrum density of the axle head.Finally,the cumulative fatigue damage value of the dangerous parts of the heavy tractor frame is treated as the quality characteristic index.Based on the robustness optimization method,the robust and lightweight structure design of the heavy duty tractor is used to improve the anti-interference ability of the vehicle system.The main work carried out is as follows:1.Aiming at the structure of a heavy duty tractor,a complete dynamic simulation model of heavy duty tractor is built by substructure modeling method.Based on the modal synthesis method and modal analysis method,the inherent characteristics of the vehicle system based on the substructure method and the traditional modeling method are compared.In addition,a detailed experimental test scheme is made for the heavy duty tractor system.The typical road test is carried out with the real vehicle structure.Then,the representative excitation load spectrums are obtained,which lays the foundation for the dynamic characteristics analysis,fatigue damage analysis and structural robust optimization of the whole vehicle system.2.Based on the reduced dynamic simulation model of the heavy duty tractor,the dynamic characteristics of the vehicle system are studied by using the modal synthesis method and the transient dynamic analysis method.The effects of damping and modal truncation number on the dynamic response of the system are discussed.By comparing the dynamic response simulation results of the system with the experimental results,the validity of the vehicle's reduced dynamics simulation model based on the substructure modeling method is verified.It also provides an important basis for the selection of system parameters.3.Based on the engine crankshaft,a simplified dynamic analysis model of flexible shaft rotor is established,and the inherent characteristic of the rotor system is solved by modal synthesis method.The oil film pressure distribution of the sliding bearing is obtained by using the short bearing approximation theory,and the calculated bearing load of the bearing to the rotor system is acted on the elastic rotor system.In this paper,the nonlinear dynamic characteristics of the rotor system of the sliding bearing are analyzed,and the influence of the disk offset and speed on the dynamic characteristics of the rotor system is discussed,which lays a certain foundation for the study of the dynamic characteristics of the crankshaft rotor.In addition,the corresponding dynamic simulation model is established for the battery parts in a heavy duty tractor system.The simulation model and the transient dynamic analysis method are used to study the inherent and dynamic response of the structure,and the results are compared with the experimental results.4.Taking the whole vehicle system as the research object,using the multi axis random fatigue life analysis method,the cumulative fatigue damage characteristics of the whole vehicle system are studied using the input excitation of power spectrum density of the test signal.The influences of deadweight and channel correlation factor on cumulative fatigue damage and the influence of different evaluation locations are discussed.According to the probability life of the vulnerable parts of the system,the probability life prediction model of the multi site damage structure is established by using the system reliability modeling method,and the deterministic life of the vehicle system under the different reliability and the life of the specified reliability is obtained.5.In view of the frame structure of heavy duty tractor,the influence of the factors such as the size fluctuation,the difference of material performance and the difference of driver's driving behavior on the cumulative fatigue damage of the structure is considered,and the system robustness optimization method is adopted to optimize the stability of the vehicle's frame structure.The anti-interference ability is improved and the lightweight of the structure is realized for the optimized frame structure.