Study On Key Techniques Of Conceptual Design For Automotive Body Structure

With the rapid development of the auto industry in our country, China has become a large country for automobile production, but we are far from automotive power due to the lack of independent research and development capability. The research and development of automotive body occupies a dominant position in R&D system, and it is the most important breakout and core competitiveness to further improve of our independent research and development capability. As the important manifestations of the R&D level, body R&D cycle, body quality, body weight and cost are the most important goals of the automakers. In order to shorten the R&D cycle of the body, improve body quality, lower body weight and cost, CE (Concurrent Engineering) has been used in body R&D rapidly and widely, and the concept phase of vehicle development is pivotal to the success of CE implementation. In the traditional body R&D system, the structural engineers are difficult to build a detailed body model due to insufficient information, they can only do some exploratory work, blindly, apparently; without the detailed body model, CAE engineers can not carry out effective analysis and optimization. The structural engineers can not get enough help from CAE engineers, and CAE engineers are wasting their time waiting for detailed body model. There are no effective communications between each department, and it is hard to consider the subsequent work in the concept phase of vehicle development. Actually, the serial pattern is set.As to the existent problems in the concept phase of vehicle development, in line with"early start"and"multi-control"in CE, we have to carry out effective analysis and optimization in the concept phase of vehicle development, enhance the communications between each department, and emphasize the optimization of the overall goals. When we achieve the concurrent engineering in the body R&D, then we can shorten the R&D cycle of the body, improve the body quality, and lower the body weight and cost. In the concept phase of body development, there are some aspects completed in this dissertation: the optimization of parameters in conceptual body model, the generation and optimization of key cross-section, the optimization of key joint, fatigue analysis of vehicle body and so on. The main innovative points of this dissertation are given as follows:(1) In the concept phase of vehicle development, proposes a conceptual FEA model of vehicle body based on actual joints (ZJ as an abbreviation). According to body key-section property database, body actual joint database and the size of body packing, the conceptual body model is maken of actual joints, beam elements and large-size shell elements. The equivalent thickness of body key-sections and the thickness of reinforcements in actual joints are taken as variables, and then find out the most important variables to torsion stiffness and joints strength as design variables through the sensitivity analysis. Sampling points of ZJ are obtained by using Latin Hypercube experimental design method, and then build the approximate models of torsion stiffness and strength by using moving least square response surface approximate method. Using sequential quadratic programming method, optimizes the design variables of the body, it lightens the weight of body in meeting the requirements of torsion stiffness and body strength. An example to prove, ZJ is easy-to-build, convenient-to-modify and meeting the engineering precision.(2) Proposes a design-oriented generation and optimization method for body key cross-section. According to the dimension constrains of automotive body styling, interior space and packing in conceptual design phase, taking into account the shape constrains of the formability of pressed metal sheets, the method comes from the behavior of ant colony. Using grid idea, the method disperses the feasible design domain of into a number of discrete nodes, which control the shape of cross-section. Based on ant colony optimization algorithm, establishes the relevant mathematical models and corresponding program. An application is proved that this method is suitable for automotive engineering.(3) In the concept phase of vehicle development, proposes a method for rapid optimization of T-type joint in automotive body. According to the structural characteristics of T-type joint, the joint is divided into seven parts: three branch regions, three transitional regions and a body region, then establishes seven corresponding hexahedrons as each region's control body, through the position changes of hexahedral vertexes to implement the corresponding changes in the size of the structure. First, extracts the boundary loads of joint from the body stiffness and strength models, then sampling points of joint model are obtained by using Latin Hypercube experimental design method, and builds the approximate models by using moving least-squares response surface approximate method. Using sequential quadratic programming method, optimizes the overall size of each branch region and the thickness of each part, and the changes of the body region depend on the changes of the branch regions. It lightens the weight of joint in meeting the requirements of stiffness and strength.(4) In the concept phase of vehicle development, above the basis of ZJ and virtual proving ground, establishes a durability analysis model including the vehicle suspension and tires for the first time. The model takes into account the structure and materia nonlinear characteristic, and it can obtain the dynamic stress-strain time history of the automotive body based on virtual road. Taken the upper C-joint of a new car as an example, the fatigue life analysis and modification design of T-type joint structure are performed with strain-life method, and the feasibility and validity of the analysis is proved by the road test later.