Research On The Key Problems Of Forward Conceptual Lightweight Design Of Automotive Body

Automotive body lightweight is an important approach to realize the energy conservation and emission reduction of tranditioanal energy cars,and lift the mileage of new energy cars,thus it has drawn more and more attention and reseach from industry and academia.Conceptual design stage is the previous stage of car-body detailed design,during which the car-body design and optimization should be accomplished under the vehicle performance requirements,and the feasiable design scheme should be provided to the latter detailed design phase.Conceptual design stage has a significant position in the whole development process of car body,and design flaws generated in this phase cannot be remedied in the detailed design phase.Reversal design is the main conventional conceptual design method,in which the product design is seriously enslaved to the benchmark car constraints,thus it is difficult to realize the car-body structural design with optimum vehicle performances.Moreover,the automobile manufacturer cannot form its development platform,process system,and operating mechanism.Forward conceptual design is driven by the optimum vehicle performances,and it can benefit the realization of more thorough car-body lightweight,and promote the realization of technological innovation and the enhancement of ore competitiveness for Chinese domestic brand automobile.This dissertation aims at realizing the forward conceptual design of automotive body,and studing the key problems in the automotive body forward conceptual lightweight design deeply and systematically.After the introduction of research bankground and significance of car-body lightweight,the dissertation elaborates the main approaches of car-body lightweight in detail,concludes the research status of car-body lightweight and conceptual design in both domestic and overseas,and points out the engineering value and theoretical significance of automotive body forward conceptual lightweight design.Then the automobile conceptual structure model is built,a structural analysis method for this model is proposed,a global optimization algorithm is studied,and the cross-sectional iterative refinement optimization method and process for the automotive frame are presented.Lastly,the automotive body conceptual design software system is developed to promote the automotive body forward conceptual lightweight design.The main contents of this dissertation could be summarized as follow:(1)The automotive body simplified model at conceptual design stage is built,and the structural analysis method for this model is proposed.Under the accuracy requirement at the conceptual design stage,the car-body is simplified as a semi-rigid spatial framed structure.An exact structural anlaysis method,i.e.,the transfer stiffness matrix method,which can give both of static and dynamic analyses for this semi-rigid spatial framed structure is proposed.The exact static and dynamic stiffness matrices are derived from the governing differential equations of the rigid beam member,and also the internal joint degrees of freedom for the semi-rigid beam member are reduced.The proposed method is employed to analyze and optimize the car-body sturture in the latter chapters.(2)An improved and intergrated global optimization algorithm is proposed.Allowing that in the tranditional genetic algorithm the penalty parameters in the penalty function method is intractable to set,a penalty-parameterless method is presented to handle constraints.Additionally,the genetic algorithm is parallelized using the parallel computing technique of MATLAB.The proposed parallel and penalty-parameterless genetic algorithm is capable of sloving the optimization problems with continuous variables,discrete variables,single objective,multiple objective,unrestraint,and multiple constraints.Also,the explorative ability,exploitation ability,and the balance between explorative and exploitation of genetic algorithm are raised notably;the convergence performance,global optimization performance,and integration performance are enhanced dramatically as well.(3)The cross-sectional forward conceptual design method and process for car-body frame are presented.Size optimization and shape optimization are carried out for the lightweight design of automotive body frame,in which the exact bending stiffness,torsional stiffness and first-order eigen-frequency are caculacted by the proposed structural analysis method and also four key manufacture constraints are considered.Then the cross-sectional iterative refinement optimization method and process for the automotive frame are proposed based on the cross-sectional size optimization and shape optimization.The iterative refinement optimization proceeds from the wire frame model,goes through four-level optimization,and realizes the detailed cross-sectional design of the car-body frame from scratch.In addition,the material substitution and selection of multi-material design are studied to promote further lightweight design.The cross-sectional design of aluminium alloy thin-walled beam under stiffness requirement is explored as an example.(4)An automotive body conceptual design software system is developed,and the effectiveness of the software is verified.The small and user-friendly software is developed in MATLAB environment with object-oriented software development methodology to realize the car-body conceptual structural analysis method,the refined and intergrated genetic algorithm,and the cross-sectional iterative refinement optimization method proposed in this dissertation.The architecture,submodules,class relationship,interface data format,and output documents of the software are introduced in detail.The software is demonstrated to be capable of promoting the car-body forward conceptual design with benchmark tests on the structural analyses both on a sedan and a bus.