A Lightweight Optimization Method of Vehicle Body Structure Design

Abstract

Lightweight body is effective for reducing the concentration of pollutant in emissions, improving crashworthiness performance and dynamic performance. Lightweight Index, which is proportional to body mass and inversely proportional to torsion stiffness, is used to evaluate the lightweight degree of body structure. Lightweight index can be reduced according to increasing torsion stiffness and reducing mass. The calculation of body stiffness is a linear process, which can be simulated by finite element analysis with high precision. In this paper, the torsion stiffness of a vehicle body was studied by using CAE analysis software. After simulation, the lightweight index was calculated according to body mass and torsion stiffness. For the purpose of improving lightweight index, body structure should be optimized to improve torsion stiffness and decrease body weight. At first, using sensitivity analysis, this paper studied the influence of 50 main parts’ gauge to torsion stiffness and body weight, these parts thickness were set as variables in optimization. Then, after optimization, by comparing sensitivities of torsion stiffness and body weight, this paper identified key parts of a car body, according to optimizing the gauges of parts, the body weight decreased 3.1 kg, while torsion stiffness increased 38 Nm/deg. Comparing with part thickness, part structure has greater affection to the stiffness property, topography optimization can be used to optimize the design of part structure and shape. In this paper, coat rack structure was studied, through topography optimization to find the best optimized structure with manufacturing requirement. Vehicle parts are designed not only considering stiffness performance, but also taking into account strength, crashworthiness, NVH performance and so on, only body torsion stiffness for study has limitation. Topography optimization can only find optimal part structure, however, manufacturing costs and feasibility should be considered. In this paper, CAE software tools were used to perform sensitivity analysis and optimization, parts gauges were set as variables to optimize body stiffness and weight, and topography optimization was used to optimize rib structure and position of coat rack, which gave a simple way to lightweight body design and optimize.