Study On Conceptual Design Of Car Body Using Stiffness Chain

With market competition bcoming severer, automobile enterprises are urgent toshorten the development cycle to lunch new products. The appearance, performanceand upgrade speed of car body largely determines the competitiveness of automotivebrand for the reason that the life cycle of car body is merely3-5years compared to10years of chassis. Conceptual design phase is a key part in car-body design process, itfinished the design of enveloping space, sections and joints which are hardly modifiedin detailed design phase. As an important indicator for assessing the car-body loadcapacity, stiffness determines the structural arrangement of car body and the structureof key components and parts, therefore car-body stiffness is a critical technical issueto be solved. The study on car-body stiffness distribution and key structures design inconceptual design phase has an important significance for improving vehicleperformance and shortening design cycle.The research is around the issue of car-body stiffness distribution in conceptualdesign phase. A top-down conceptual design process was proposed based on theresearch of several key techniques in car-body conceptual design phase. A modelingmethod of simplified car-body model was put forward to realize rapid design inconceptual design phase. According to the feature that the car-body structuraltopology is closely related to and mutually influences with stiffness distribution, amethod of car-body stiffness chain was proposed using frame structure theory, beamelement concept and transfer matrix method. A simplified car-body wireframe modelwas established and18main sections were defined from Class A surface of a car bodyand the mathematic model of car-body stiffness chain with main sections as nodes wasbuilt. Stiffness optimum distribution was studied based on car-body stiffness chainand the mathematic model of car-body bending stiffness optimum distribution wasbuilt and then solved by genetic algorithm to obtain the equivalent stiffness of mainsections. The rationality of stiffness optimum distribution and the availability ofcar-body stiffness chain were verified by comparing with the CAE analysis ofapproximate benchmarking car, and the mathematic model of car-body stiffness chainwas updated to improve its calculation accuracy. Structural optimization design ofmain sections was studied and a design flow including topology optimization and sizeoptimization was put forward. With the threshold beam for example, a mathematicmodel of its main section was built and then solved so that the main section structure with shape and parameter information were obtained, which lies a foundation for thefollow-up detailed design.This study provides valuable reference for the domestic automotive enterprises tocarry out the top-down conceptual design, and discuss a new idea to improve theindependent research and development level of domestic auto industry.