【作者】 陈晓斌；

【导师】 韩英淳；

【作者基本信息】 吉林大学 ， 车身工程， 2011， 博士

【摘要】 近年来,国内汽车工业迎来了快速发展期,国内汽车保有量逐年稳步增长,然而由此带来的能源消耗及环境保护等问题则日趋紧张,这必将阻碍国内汽车工业的可持续发展。汽车轻量化技术作为汽车降低能耗、减少排放的有效手段已经成为汽车工业发展过程中的一项关键性研究课题,在不久的将来,轻量化将成为国内外各汽车厂商的核心竞争技术之一。车身轻量化作为汽车轻量化技术的有效途径之一,近年来得到广泛应用。国内外很多学者对车身轻量化进行了广泛的研究,取得了诸多成果,如车身结构优化设计,使用低密度材料如铝、镁合金、复合材料等替换以传统钢材制造的零部件以及使用新工艺等。本文在总结前人研究的基础上,使用车身结构优化设计方法对国产某自主研发品牌轿车的轻量化进行了较为系统和深入的研究,在确保汽车综合性能如车身静、动态刚度及车身结构耐撞性能基本不变的前提下,尽可能降低车身重量,达到减重以及节能减排的目的。围绕汽车轻量化这一主题,本文主要开展了以下几方面的研究内容:1.以国产某自主研发轿车为例,介绍了整车开发流程及前期开发过程中有限元数值模拟所涉及的开发内容,同时详细论述了整车有限元建模方法。整车前期开发过程中,一个既能够准确模拟整车结构各种力学特征,又能够使模型计算规模控制在计算机可接受范围内的整车有限元模型是前期开发过程中必不可少的,它为预测整车结构性能及进行结构优化设计提供了支持。基于此,以白车身及动力总成与变速器系统为例,系统阐述了钣金件、焊点、胶连接、MAG焊、螺栓连接等建模方法,同时建立了整车碰撞有限元模型及白车身刚度模型。2.设计并进行了国产某自主研发轿车白车身模态试验。由试验结果分析得到了白车身结构模态频率和振型,获得了白车身的动态特性。引入了Trimmed Body模型概念,详细论述了Trimmed Body有限元建模方法并建立了Trimmed Body模型,并进行了模态及频率响应计算,同时进行了Trimmed Body模态试验,得出了有关整车振动舒适性的频率响应函数,并与有限元计算值进行了模态置信度MAC(Modal Assurance Criterion)分析,分析结果验证了有限元模型的准确性。该方法已成功应用于国产某自主研发轿车的自主研发过程中。3.进行了国产某自主研发轿车白车身的灵敏度分析及优化计算。通过灵敏度计算识别出了对刚度及重量影响较大的零件。在进行优化设计时综合考虑了白车身的动静态刚度,并对静态弯曲、扭转刚度的算法进行了详细的论述。通过优化设计实现了白车身第一阶固有频率提高1.2%、车身质量下降5.4%的目标。4.通过正面碰撞试验的变形时间历程及整车结构变形验证了整车碰撞有限元模型的有效性后,首次将正面碰撞与侧面碰撞的数值仿真联合应用于车身轻量化设计前后的整车结构抗撞性能研究。通过对比正面碰撞试验与轻量化前后B柱及中通道加速度曲线以及轻量化前后侧面碰撞前后车门侵入量、B柱侵入量及侵入速度曲线,验证了本文所研究的车身轻量化结果的可行性,确保了轻量化后整车结构的抗撞性能。同时,本章所引入的侧面碰撞侵入速度限值曲线可为同级别车型开发提供经验上的借鉴。介绍了两种B柱及门槛的结构设计方案,以作为车辆实际结构设计的经验借鉴。5.提出了基于引擎盖刚度与行人头部保护要求的轻量化设计方法。通过综合考虑引擎盖开发过程中刚度及行人保护头部碰撞性能,以前盖内板结构及内板板厚作为设计变量,利用田口试验设计方法进行试验设计,使用Kriging方法建立了引擎盖刚度与行人保护头部碰撞有限元模型的近似数学模型,并基于Kriging模型进行优化。优化后的前盖刚度及行人保护头部碰撞性能得到了显著改善,质量由13.5kg降为12.6kg,减少6.7%,头部HIC值由1373降低至1156,减小15.8%。更多还原

【Abstract】 In recent years, national automobile industry is meeting rapid growth and autos’holding amount is gradually increasing, which makes the problem of energy consumption and environmental protection much more critical and this will obviously obstruct sustainable development of our national automobile industry. As an effective way to reduce energy consumption and emission, automobile lightweight has already become critical research issue. In the near future, it will be one of the core competitiveness among domestic and international auto companies. Car body’s lightweight is one of the effective way of automobile lightweight, which has been widely used for the past few years. It has been deeply studied by many national and international researchers and many achievements have been made, for example, optimal design of car body’s structure, replacing some traditional steel parts by lower density materials such as aluminum and magnesium alloy, composite materials etc., using of new technics and so on. Based on predecessor’s achievements, this paper does systemic and in-depth study on some homemade independent-brand car by use of optimal design of car body’s structure. By ensuring car’s comprehensive performance such as static and dynamic stiffness and safety, the objective of reducing weight and consumption has been achieved.Centering on the issue of lightweight, main researches are showed as follows:1. As far as some homemade car is concerned, development flow of complete vehicle and simulation contents have been introduced in this paper. And it also illustrates finite element modelling method of complete vehicle in detail. In concept phase of developing a car, it is indispensable to have one finite element model of complete vehicle which can not only simulate vehicle’s mechanical performance accurately but also its computational time is acceptable. It can provide some supports for predicting vehicle’s structure performances and conducting optimal design. Concerned on body-in-white(BIW) and powretrain and transmission system, this paper systematically discusses modelling method of sheet metal, spotwelds, glue connection, MAG welding, bolt connection and so on. Then the complete vehicle’s crash finite element model is created.2. Conducting modal test of BIW of this homemade car. From the test frequencies and modes of vibration and dynamic performance have been extracted. The concept of Trimmed Body has been introduced in this paper, then its the modelling method is discoursed in detail and its finite element model is created. After that it calculates the mode and frequency response function(FRF) of Trimmed Body and then its modal test is conducted in order to get the FRF curve of Trimmed Body which is related to vehicle’s vibration and harshness. It also makes Modal Assurance Criterion(MAC) analysis between simulation and test and the result validates accurateness of Trimmed Body’s model. This way of making simulation and test of Trimmed Body has been applied to some homemade car’s development.3. Calculation on sensitivity and optimization of homemade car’s BIW. Through sensitivity analysis Those parts have bigger sensitivity on stiffness and weight are identified through sensitivity analysis. In process of optimization static and dynamic stiffness have been taken into account and algorithm of stiffness has been illustrated specially. After optimization, the objective has been achieved, that is, the first mode of BIW has 1.2 percent increase and mass of BIW has 5.4 percent decrease.4. The complete vehicle’s crash finite element model is validated by crash time history and strutures deformation in 100% frontal impact test. Based on this, it is the first time that this paper parallelly applies simulation of frontal and side impact to study the crashworthiness of the whole car before and after car body’s lightweight. The whole car’s safety performance has been guaranteed through comparison between frontal impact test and simulation of B-pillar and tunnel’s acceleration curve, intrusion displacement of front and rear door and B-pillar and intrusion velocity of B-pillar of side impact before and after optimization. At the same time, this paper introduces some limit velocity curves in side impact simulation and this provides some experience for the other same class cars’development. It also introduces two different structures of B-pillar and threshold. One of this struture can decrease intrusion displacement of B-pillar in side impact.5. A lightweight method has been proposed which takes stiffness and pedestrian head protection of engine hood into account. By considering those factors, this paper takes struture and thickness of inner part of engine hood as design variables. It uses Taguchi design to do DOE and builds approximate mathematical finite element model for stiffness and head protection of engine hood by use of Kriging method. Based on Kriging model, it does optimization. The optimized results shows that stiffness and head protection performance has been improved. Mass of engine hood has 6.7 percent decrease from 13.5 kg to 12.6 kg and HIC value has 15.8 percent decrease from 1373 to 1156.更多还原