Research On Top-down Design Of The Pure Electric Midibus Body Structure Driven By CAE Analysis

Along with the rapid development of high-speed train, the long-distance highway passenger transportation is being replaced gradually. On the contrary, the mid-short distance midibus transport market is full of vitality. After a lot of work on relevant information and market research, I found that the market share of the 6 to 8 meters midibus grows year by year, and as a global energy and environmental crisis spreading, the pure electric vehicle, because of its many advantages, has become the research focus. However, the domestic research and development of the pure electric bus structure is still currently in the initial stage, mainly obtained by substituting the powertrain and local modification based on the traditional bus structure, and the unscientific design leads to high body structure mass, which has violated the lightweight design concept.According to the current situation of pure electric bus’ s R&D and market demand, taken integral body structure of 7 meters pure electric midibus as design object, this paper, combining with the design principles and methods for bus structure, conducts a research on top-down design of the pure electric midibus body structure driven by CAE analysis, and meanwhile based on this, a bottom platform is further extracted and established with applying to both integral and separate frame body structure of 7 meters pure electric midibus.The main contents of this paper as follows:A preliminary design of body structure scheme is carried out under the scientific arrangement of power system to prepare for the subsequent research in this paper. Firstly, a reference model is established according to the 2d drawings of 7 meters fuel midibus offered by a bus enterprise. And via analysis of its basic performance, the reference data is obtained to determine the target performance level of this topic. Secondly, considering the flexible layout characteristic of pure electric bus power system, the layout space and its quality are caculated through formula with related power battery technical parameters, and the powertrain layout design is completed preliminary. Based on this, the initial wire frame model is built, and then according to the actual steel cross section library and bus project experience, the initial finite element model is established. Finally, the research direction in the next phase of the design is indicated through comparative analysis between the initial body structural basic performance and target level.A multistage design for performance improvement of the structure is conducted through applying a series of bus structural design principles and methods aim to obtain the satisfying body structure project. The first stage is the bar parameter improvement design by bar internal force analysis. A new bar orientation scheme is made by analyzing the internal force and stress components of high and low stress bar. Hence, not only the internal force distribution is improved reasonably but also the effect of lightweight is remarkable. And the second stage is performance complementary design based on bending stiffness matching method. By multistep matching design, the bending stiffness of the vehicle is significantly increased, and the other performances are improved too. Besides, an up and down bending stiffness matching design idea is proposed preliminary, and the third stage is conducted based on the idea. After that, a conclusion is acheived accordingly that the impact of continuing to strengthen the upper structure for the vehicle bending stiffness improvement is on the decrease when the upper and lower bending stiffness ratio increases to a certain value. Eventually, a pure electric midibus integral body structure meeting various performance targets is obtained. On this basis, the active diagonal brace of battery door is designed by applying local topology optimization method. The supplementary design significantly increases the vehicle stiffness, makes the structure become more safe and reliable and can provides an alternative scheme for future engineering application. Besides, through the vehicle performance comparison of the traditional layout and topology optimization design, the superiority of topology optimization method is verified. Lastly, the beam element finite element model is intelligently converted to 3D geometrical model by using CAE to CAD model intelligent conversion program. Some processing work such as bar offset, weld spacing of joint and joint cut are conducted subsequently, which lays a good foundation for the subsequent engineering design.A kind of original bottom platform used for 7 meters pure electric midibus is further extracted and established based on the above design results, which is featured by its universal frock, novel structure and scientific design and aim to achieve the design goal of shortening product development cycle, reducing the production cost and solving the problem of electric bus lightweight. First of all,the multi-objective topology optimization method is selected by compareing two different methods and findind the limitation of single-objective topology optimization. And the preliminary design of bottom platform is built based on the frame development mode of separate frame body. Then, the bottom structure is improved in view of its strength and stiffness, and importing the improvement design into integral body structure to analyze and verify its performance and conduct adaptive matching design. Finally, the new truss type bottom platform which applies to both integral and separate frame body structure of 7 meters pure electric midibus is achieved.This topic follows the technological development trend closely, meets the demand of bus market and provides clear thinking and effective means for scientific research and development of pure electric bus, the developed product can be applied in engineering applications in a way.