Research On Structural Optimization Design And Forming Test Of A Novel Seat Bracket For A Pure Electric Bus

Pure electric buses have become a mainstream means of transportation in our daily travels due to their many advantages such as pollution-free,low noise and comfortable ride.However,due to the low specific energy and overweighted batteries,the bus is heavy and have a short duration of endurance.In addition,there is a lack of systematic theoretical basis and streamlined solutions in the process of R&D and manufacturing of parts.Therefore,in order to reduce energy consumption,improve endurance,reduce production costs,and develop a streamlined R&D program,it is necessary to conduct lightweight research on pure electric buses.The bus seat is an important component of the interior of the vehicle,and the number is large.The seat bracket is the main source of seat quality,and directly determines the carrying capacity of the seat.The structural performance of the seat directly affects the safety and comfort of the passengers.In the traditional design process of seat bracket,there are often more redundant designs,resulting in a cumbersome structure that cannot meet the lightweight design concept.Therefore,this paper combined two lightweight methods: using lightweight materials and optimizing structural design.Based on the performance advantages of hotstamping ultra-high strength steel,a new type of seat bracket was proposed.Firstly,the finite element analysis of the static and dynamic characteristics of the proposed new seat bracket was carried out,including the static analysis,modal analysis and harmonic response analysis of the structure,and the structural optimization was carried out based on the analysis results.In addition,the structurally optimized seat bracket was subjected to fatigue analysis based on quasi-static method and random vibration fatigue analysis based on frequency domain method.Finally,the hot stamping test and the stiffness check test of the novel seat bracket were carried out,which enabled the structure to achieve significant weight reduction under the premise of meeting the performance requirements.It has important guiding significance for the lightweight research of pure electric buses.The main research contents and conclusions of this paper are as follows:(1)First,the finite element modeling process and its key points of the novel seat bracket of the pure electric bus were elaborated.According to the relevant technical standards,based on the four typical combined working conditions of the bus seat bracket,the static analysis of the initial design structure was carried out.The results show that the initial design of the seat bracket has a high safety factor and a small deformation,there is thus a large lightweight space.Therefore,based on the variable density method and static analysis results,the structure was topologically optimized.Subsequently,the static analysis,modal analysis and harmonic response analysis of the optimized seat bracket were carried out to investigate the static and dynamic characteristics of the structure.These results show that under the static load of four working conditions,the bottom of the sidewall of the main frame has a large bending deformation.The low-order natural frequency of the structure is low,and there is a frequency interval overlapping with the external excitation.The structure will resonate under the external excitation of 14.817 Hz.Therefore,the stiffness of the structure was further optimized by the method of setting reinforcements.The static analysis and modal analysis of the optimized structure were carried out.These results show that the safety factor of the structure is higher and the deformation is smaller under the static load of the four working conditions.The loworder natural frequency of the structure is greatly improved,avoiding the frequency range of the external excitation.Both the static and dynamic structural performance of the seat bracket meet the requirements of use.(2)Combined with the theory of structural fatigue analysis,based on the quasi-static method,the Brown-Miller algorithm was used to analyze the fatigue of the seat bracket under typical dangerous conditions.This result proves that the structure meets the infinite life design requirements under all the four typical combined conditions.In addition,based on the frequency domain method,the Dirlik algorithm was used to analyze the random vibration fatigue of the seat bracket.This result shows that the dynamic stress produced by y-direction excitation is the main reason of random vibration fatigue of the structure,and the novel seat bracket has high fatigue life in all three directions.(3)Based on the final design of the novel seat bracket,a hot-stamping die was developed and an indirect hot stamping test of the components of the seat bracket was carried out.Taking the main frame of the seat bracket as an example,the die structure and process of the hot stamping test were introduced in detail,and the typical positions of the formed part were selected for microstructure and mechanical properties analysis.The test results show that the martensite transformation of the main frame in the hot stamping process is sufficient,and the mechanical properties of the formed parts are good.Finally,the static-stiffness check test under the working condition 1 was carried out on the overall structure of the welded seat bracket.The results show that the final design of the novel seat bracket meets the requirements of use,which verifies the rationality of the structural design and the accuracy of the finite element analysis results.The purpose of this paper is to provide an integrated solution for the seat brackets of pure electric buses through the above research,including initial structural design,static and dynamic structural performance analysis,structural optimization,design of hot-stamping die structure and forming process,and testing verification of structural performance.This work provides a reference for realizing the lightweight of pure electric bus body.