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Structural Design and Evaluation for Improvement of the Roof Strength of a Three-Wheel Vehicle(삼륜차의 루프 강도 향상을 위한 구조 설계 및 평가)
Electric vehicles have gained increasing interests as new research area to reduce the air pollution as well as carbon dioxide. Electric vehicles are able to save energy that wasted during braking and do not need energy to keep engine start. In adittion, mechanical connection between motor and battery is not necessary to electric vehicles so that various type of structure can be applied to electric vehicles. TWVs(Three Wheel Vehicles) are one of the efficient type of vehicle to increase driving distance for their low weight and air resistance, although TWVs are weaker in rollover than FWVs(Four Wheel Vehicles). Rollover can take place by not only severe cornering or lane change but also side collision and flip over by obstacles. In addition, rollover motion of TWVs can be different from that of FWV because of basal plane of TWVs are different from that of FWVs.
This paper is concerned with auto-body frames and roof structures against rollover motion which could take place frequently with TWVs compared to FWVs because of the major difference of the loading between the two motions. Topology optimization is a mathematical approach that optimizes structure satisfying performance targets within a given design space and set of loads and boundary conditions. Topology optimization is utilized for conceptual design and preliminary design of the roof structure for various loading conditions. The roof structure for TWV consists of existing part of FWV and a new part called Cross-bar reinforcement. Material of A pillar and cantrail is DP780, DP980 is for B pillar, SPRC440 is for C pillar, and DP590 is for member structures. Although a test method for regulation of roof strength is with static loading, simulations are carried out for both static and dynamic cases. In the dynamic loading case, rate-dependency of a material needs to be considered for accurate results of FE analysis. In addition, the roof structure is modified into various types for a better result. The roof crush is investigated with various modification of the roof structure to figure out the best modification of the roof structure for TWV. Effects of each design parameters are calculated by using FE analysis. The better result is calculated when all member structures except for rear member are straight than when these are arch shape. Furthermore, rear member of arch shape makes the result better than that of straight shape. This difference is caused by different buckling mode. These result considering the effect of each design parameter can utilized to optimize roof structure.