Research On The Lightweight Design And Performance Matching Method Of Novel Architecture Electric Vehicle Chassis Frame

With the vigorous development of the automobile industry and the rapid growth of automobile production,natural,energy and environmental issues have become particularly prominent.Energy conservation and environmental protection are the eternal themes of today's economic society and the development of the automobile industry.In order to meet the requirements of improving the living environment and reducing the emission of harmful substances,the lightweight technology of automobiles has emerged as one of the important means of reducing pollution and energy saving of automobiles.At the same time,in order to promote the green and coordinated development of automobiles and society as soon as possible,the popularization of pure electric cars is also imperative.However,the current research and development of pure electric vehicles are mainly focused on the battery and electronic control system,and the structural design is less involved,especially the research on the chassis and frame structure of the new architecture electric vehicle is scarcer.In addition,most of the current pure electric vehicles are modified based on the structure of fuel vehicles,and the performance distribution between the passenger compartment and the chassis frame is not yet clear.In addition,the continuous application and development of new materials in the structure of the vehicle are therefore aimed at electric vehicles.The research on the performance distribution of the passenger compartment and the chassis frame and the forward lightweight design method of the chassis frame is imminent.This paper takes a novel electric vehicle as the benchmark model,and analyzes the performance of the first-order mode and the bending and torsional stiffness(basic NVH performance)of the integrated system of the passenger compartment and the chassis frame module(referred to as the "coupling system")in-depth research is carried out with integrated matching,collision energy decomposition and energy flow transmission path,structural multi-working condition joint topology optimization,improved design variable screening method,improved multi-objective particle swarm optimization and multi-attribute decision-making method,etc.,and finally the chassis is optimized The lightweight design plan of the frame structure,and the prototype trial production and test verification of the lightweight chassis frame structure.The main research content of the thesis is summarized as follows:Firstly,establish the finite element model of the chassis frame of the benchmark vehicle,the finite element model of the coupling system,and the finite element model of the whole vehicle.The basic NVH performance of the coupling system is calculated and compared with the corresponding data of the benchmark vehicle,thereby verifying the validity of the finite element model of the coupling system;then the structural crashworthiness of the chassis frame of the standard vehicle is analyzed under the frontal and side impact conditions,and the structural crashworthiness index is extracted.Finally,the design goals of the chassis frame to be developed are determined according to the basic NVH performance and crashworthiness of the benchmark vehicle.Secondly,a simple rectangular cross-section hollow thin-walled tube structure is proposed to simulate the passenger compartment,chassis frame module and its integrated coupling system respectively,and it is concluded that the passenger compartment,chassis frame module and coupling system are meet the parallel spring relationship under bending and torsion conditions;in the first-order bending mode,the frequency of the coupling system is approximately equal to the difference between the frequency of the passenger compartment and the chassis frame;in the first-order torsion mode,the passenger compartment,the chassis frame and the coupling system meet the polynomial relationship;at the same time,verify the effectiveness of the performance index decomposition method on the benchmark vehicle.Then the energy transmission path and energy index decomposition method during the collision process are studied,and the specific energy absorption and energy absorption ratio of the chassis frame were calculated.Finally,based on the chassis frame energy index of the benchmark vehicle,the chassis frame to be developed was determined Energy design goals.Then,the method of combining equivalent static load and inertial release is selected,and the average value of the local collision force including the peak value during the collision is introduced into the topology optimization.According to the variable density method and the compromise planning method,the chassis frame is subjected to a variety of collision conditions.Under the joint topology optimization design,the conceptual design model of the chassis frame and the complete vehicle model are established.Then the vehicle to be developed is calculated and analyzed and compared with the design goal.The result shows that the initial structure of the chassis frame has a slight gap in the crashworthiness index.Therefore,the multi-objective optimization design of the chassis frame structure is considered.Subsequently,a fully parametric model of the chassis frame of the electric vehicle with a new architecture is established,and the final design variables are screened out using the TOPSIS method based on the entropy weight method.The extrusion forming process parameters of aluminum alloy chassis frame parts are introduced as constraints.The support vector regression model is used to establish a proxy model of stiffness and modal performance indicators,and the RBF model is used to establish a proxy model of crashworthiness indicators.An improved multi-objective particle swarm optimization algorithm is proposed to optimize the chassis frame model and obtain the Pareto frontier solution.A method combining game theory and grey relational analysis is put forward to sort the Pareto frontier solutions and get the optimal design plan.Finally,a comparative analysis of the basic NVH performance and structural crashworthiness of the optimized chassis frame before and after the optimization shows that the performance of the optimized chassis frame meets the design goal requirements,and the weight reduction rate reaches 12.16% compared with the initial model;at the same time;It is calculated that the integrated and assembled mass of the chassis frame structure and the carbon fiber composite passenger compartment optimized by the project team is 218 kg,which is a 30.5% weight reduction compared with the body-in-white mass of the same size steel structure of 314 kg.Finally,the basic NVH performance test and frontal crash test of the lightweight chassis frame samples are performed.The results show that the simulation calculation results are consistent with the test values,which verifies that the lightweight chassis frame design method are feasible and effective.