Optimization Design Method Of Vehicle Lightweight Based On Approximate Model

Along with the fast development of automotive industry, the energy tense and environment pressure becomes increasingly serious, which will prevent the development of automotive industry. As an effective energy-saving method, automotive lightweight has already become a crucial research topic. In the near future, it must be one of core competence among car companies. In recent years, many research achievements have been made in the automotive lightweight field. However, many lightweight-related issues need to be studied. Research methods still concentrated on replacing some automobile body parts with low-density materials, such as aluminum, magnesium alloy, composite materials, and so on. These methods almost depend on the empirical design. Therefore, in this paper, based on the predecessor's literature research, an in-depth study about the lightweight, using approximate model technology and optimization method, was conducted, so as to reduce the weight of automobile and achieve aggregative objective (reducing weight and consumes and improving vehicle safety) , under the guarantee of comprehensive performances of automobiles.Main research content and innovation of the paper are as follows:1. Based on moving least square method, a response surface approximate model of automotive front impact was established, and used the different approximate model technology for the different optimized design response to achieve the goal of enhancing optimization efficiency. By contrasting to Kriging response surface, the polynomial response surface is approaching the sampling points in design space, and the fitting accuracy is not high, so it is generally applied to the responses of low non-linear level, while the Kriging model whose fitting accuracy is high, can pass the spatial sampling point accurately, but it is vulnerable to numerical noise which raise the cost of calculation. However, the moving least square response surface model has both merits above, so it is very suitable for the car crash safety optimization of highly non-linear, and numerical noise. And, the model's validity is confirmed by utilizing the model in the automotive lightweight.2. A method of high strength steel plate selection which based on the multi-objective genetic algorithm and approximate model was proposed. Although the application of the light quality materials such as aluminum alloy increases gradually in automotive manufacturing industry, due to the difficulty of processing, forming, and welding results from the good thermal conductivity, and even the higher cost than the steel, aluminum can only be used as vehicle body instead of only part of the iron and steel in the automobile manufacture at present. While the thin high-strength steel has merits of lighter quality, higher strength, as compared to the traditional steels. And it also can improve the performance of vehicle safety. Therefore, the high-strength steel has been widely used as automotive raw materials. Using the high-strength steel plate instead of traditional steel plate, the automobile body weight can be reduced to a greater degree. However, the traditional selection of materials often based on the experiences of engineers, which made the choice of materials in every part of vehicles blind and not optimal. In the paper, the safety of front impact and side impact of vehicles are conducted in deep study by combining the approximate model and the multi-objective genetic algorithm, make the high strength steel plate of front key absorbing parts of the automobile cab and the side parts and its thickness reasonable in disposition. And, the safety of vehicles was improved, and the weight of automotive body was reduced.3. A method of the entire vehicle lightweight optimization design basing on the approximate model and the multi-disciplinary design optimization was proposed. With the most important premise which is to maintain the original performance, the automobile lightweight, not only destinate to reduce the weight, but also ensure the safety, crashworthiness, vibration, comfort, and so on. However, because the traditional model of car design was often taken as a serial design patterns, in which engineers chosed different key points to design and optimize in different stages, the influence of automobile performance was separated about the aerodynamic performance, vibration, noise, crashworthiness, safety, comfort, and the coordination effect which be produced by coupling of various subjects was not used and taken into account. So it always turned out the optimization results were not the overall optimal solution. At the same time, if the lightweight design of automobile takes the effects of safety, vibration, stiffness into account, this is bound to encounter bottleneck of the optimal design (CAE time of single calculation and simulation is too long). It is based on the flaw above-mentioned traditional serial design and CAE simulation time, and the paper propose that the process of the lightweight of automobile is a multi-disciplinary design optimization process, and establish the approximate model of automobile lightweight optimization design by combining the response surface method and multi-disciplinary design optimization method, and solve the problem that the time of optimization is too long one-time. The method was utilized in lightweight design of a certain vehicle successfully.4. A design model of thin-walled beam for lightweight optimization was established based on the reliability of design theory. Thin-walled beam of the body is not only a basic loading part in the body design, but also a main energy-absorption part in frontal impact. Meantime, impact responses of acceleration and impact force of a vehicle and occupant safety at collision depend on the pattern of deformation and energy absorption characteristic of the thin-walled beam. In addition, the poor environment in use leads to higher design requirement of reliability . The traditional process of optimization often ignore the effects of uncertainty of the engineering design, such as geometry size, material properties, loads and boundary conditions and operating environment and so on, which leads to the design failure beyond the constraints and reduces the reliability of the product. In the paper, the thin-walled beam design was regarded as a multi-disciplinary reliability optimization design process of considering the safety, the static load-bearing characteristics and the first-order vibration mode. And this method has been applied to the lightweight optimization design of cap-thin-walled successfully.