| As a large population country,China's car ownership is increasing year by month,and the problem of energy consumption and environmental pollution becomes more and more serious.Although the country vigorously develop high-speed rail and civil aviation industry to solve the people's travel problems,the transportation in annual spring Festival is still the main mode of transport,so vigorously developing the bus industry is still urgent.Since this century,because China's bus industry has entered a high-speed development period,the market competition is increasingly fierce.With the bus running in the process of many groups of dead group injury events,the technical performance of the bus also put forward higher requirements.Bus body structure,as an important part of passenger cars,is not only the installation carrier of various parts,but also the main bearing parts and functional parts of the whole vehicle.Therefore,the performance of its design will directly affect the vehicle's power,economy,comfort and safety,etc.In recent years,with the introduction of CAE technology and the continuous growth of a number of train-bus structure talents,the design of bus body structure has changed from reverse imitation to forward design.The structure of the vehicle can be improved obviously,including the static stiffness characteristic,the modal characteristic,the anti rollover ability and the lightweight level of the car body is improved steadily.The whole bearing body structure becomes the mainstream of the industry.In this background,based on the study of the structure performance of the bus body,through the analysis of the dynamic and static stiffness performance of current body structure,this paper sums up and puts forward a new method for evaluating the body structural properties,which will be applied to the matching design of body structure.The main ideas of this paper is: on the basis of analyzing and summarizing the existing theory and analysis methods of body structure design,the paper improves the evaluation method proposed by the research team,and puts forward a new efficient and feasible evaluation and design method of bus body structural performance(including static stiffness and dynamic stiffness).Combined with many years ' experience in engineering practice,the research results are applied to the body structure design,and the new bus body structure,which takes into account structural mechanics and lightweight,is used to verify the validity and convenience of the evaluation method and design method.According to the above research ideas,this paper mainly completed the following research:(1)This paper presents an evaluation method of the local stiffness contribution coefficient by perfecting and improving the existing evaluation method of local stiffness contribution degree.The evaluation method of the local stiffness contribution coefficient is based on the evaluation method of local stiffness contribution of the vehicle body.The ratio of local module quality to the vehicle quality(i.e.the mass coefficient)is introduced into the stiffness contribution degree evaluation method,and the concept of the stiffness contribution coefficient of the body local module is proposed.At the same time,considering the stiffness contribution of the module and two evaluation indexes of the mass coefficient,a relatively intuitive and normalized method for evaluating the stiffness performance of the body structure is established.The process of evaluation method is summarized and the evaluation process is established,which provides the basis for the evaluation method of body stiffness contribution coefficient to guide the optimization design of bus body structure matching and the application of lightweight materials for body structure.(2)Based on the evaluation method of local stiffness contribution coefficient,the application of body structure matching design method is studied.Firstly,the paper uses the test data of body structure to revise the CAE model,which lays a foundation for the accuracy of the subsequent research work.Taking the body structure of the fully-loaded bus as the research object,the matching design of the stiffness of the body structure which is complementary to the left and the right structure stiffness is first studied to get an optimized body structure.On this basis,the evaluation method of local stiffness contribution coefficient is applied to evaluate the stiffness performance and optimize the structure,in order to build a bus body structure.Then,the stiffness contribution coefficient and structure optimization of the upper and lower structure are further carried out by the body structure.Finally,a new car body structure matching design scheme----Parallel three-truss type full load bus body structure.Co MPared with the initial structure,the flexural stiffness and torsional stiffness of the whole vehicle structure are increased by 84.67% and 94.13% respectively.The first order bending frequency and the first order torsion frequency are increased by 18.22% and 23.35% respectively,and the maximum stress under three typical conditions is decreased by 57.89%.The weight of the structure was reduced by 407 kg,and the light quantity reached 13.59%.The data of case results show that the evaluation method of local stiffness contribution coefficient of body structure has important theoretical significance and engineering application value for body structure matching design.(3)A research on lightweight body structure design method based on evaluation method of local stiffness contribution coefficient.The parallel three-truss type fully loaded bus body structure is studied in this paper.Firstly,the evaluation criterion of local stiffness contribution coefficient is established.Then,the stiffness contribution coefficient and part structure are respectively used to replace different types of lightweight materials,and the properties of various materials are fully utilized and used to make "suitable materials for suitable parts".The paper is divided into four parts to study the comprehensive performance of the vehicle in different parts of body structure replacing different lightweight materials.Based on the analysis structure of the above performance,a kind of body structure containing high strength steel,aluminum alloy and carbon fiber is proposed.Co MPared with the initial structure,the flexural stiffness and torsional stiffness of the whole vehicle are increased by 49.56% and 76.95% respectively.The first order bending frequency and the first order torsion frequency are increased by 28.98% and 42.97% respectively.The maximum stress of three typical conditions is decreased by 42.21%.The maximum deformation is reduced by 36.22%.The weight of the structure is reduced by 1140 kg and the light quantity is 38.06%.The data of case results show that the evaluation method of local stiffness contribution coefficient has important theoretical significance and engineering application value to lightweight design of body structure.(4)This paper presents a method for evaluating the modal contribution of each local structure of the body based on modal analysis.Modal analysis is an important aspect of the structural performance evaluation of bus body.Based on the research and application of the static stiffness evaluation method,this paper puts forward the evaluation method of the local modal contribution degree.By adjusting the structural stiffness of each local module of the body(such as Young's modulus E),the method is used to investigate the influence of the local structure on the change of the modal characteristics of the vehicle structure,so as to establish a new method for the modal evaluation.This method can be used to classify the whole vehicle structure and find the most sensitive body structure area which affects the modal frequency of the vehicle structure,in order to guide the optimization design.A more generalized modal sensitivity analysis method is established,which further extends and deepens the research results of static characteristics,and provides effective technical guidance for engineering technicians to adjust the dynamic performance of the whole vehicle.Through the analysis of the case,the data results show that the method is convenient and effective,which provides important guidance for the structure optimization design of bus body structure based on modal frequency characteristic,and has important theoretical significance and engineering application value. |
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