基于碰撞安全性的轎車車身結構輕量化設計

基于碰撞安全性的轎車車身結構輕量化設計,基于,碰撞,安全性,轎車,車身,結構,量化,設計 密 級 分類號 編 號 成 績 本科生畢業(yè)設計 (論文) 外 文 翻 譯 原 文 標 題 A Lightweight Optimization Method of Vehicle Body Structure Design 譯 文 標 題 車身結構輕量化優(yōu)化設計方法 作者所在系別 機電工程學院 作者所在專業(yè) 車輛工程 作者所在班級 B13141 作 者 姓 名 宋志鵬 作 者 學 號 201322251 指導教師姓名 許文娟 指導教師職稱 講師 完 成 時 間 2017 年 3 月 譯文標題 車身結構輕量化優(yōu)化設計方法 原文標題 A Lightweight Optimization Method of Vehicle Body Structure Design 作 者 Zhixiang Li 原文出處 Proceedings of the FISITA 2012 World Automotive Congress 摘要：輕量化車身可以有效減少排放污染物，提高防撞性能和動態(tài)性能。輕量級指數(shù)與車身質量成比例，與扭轉剛度成反比，用于評估車身結構的輕度度。可以根據(jù)增加的扭轉剛度和減小質量降低輕量級指數(shù)。車身剛度的計算是一個線性過程，可以通過有限元分析高精度模擬。在本文中，通過使用CAE分析軟件研究了車身的扭轉剛度。模擬后，根據(jù)車身質量和扭轉剛度計算輕量級指數(shù)。為了改善輕質指數(shù)，應優(yōu)化車身結構，以改善扭轉剛度和減輕體重。當考慮燃料經濟性時，車輛的重量起到顯著的作用，因此，車輛的車體結構是減輕重量的主要焦點。然而，車身結構在支撐其他車輛部件，在碰撞情況下保護乘客和整體車輛性能方面發(fā)揮重要作用。 關鍵詞：輕量化 扭轉剛度 地形優(yōu)化 靈敏度分析 1前言 車身質量是車輛整體的主要組成部分，通常是帳戶占整個質量的30％以上。 汽車重量直接影響車輛被動安全性能NVH性能，廢氣排放和車輛處理性能具有國家汽車排放法規(guī)和安全法規(guī)越來越嚴格，對汽車的要求重量變得更加嚴格，如何設計汽車產品來滿足所有法律在規(guī)章制度的前提下，盡量減少體質，成為其中之一汽車行業(yè)的主要研究方向。 輕型車身設計方法，采用先進的生產技術，創(chuàng)新材料和優(yōu)化設計技術優(yōu)化車身初步設計的結構，以達到目標設計性能最佳車身結構質量[2]。 當一輛汽車在路上行駛時，它會持續(xù)一個各種不均勻路面的載荷，這些載荷可分為彎曲載荷和它們是扭轉載荷，而車輛結構上的扭轉載荷更嚴重可能導致門變形，密封條脫落，體結構局部變形或即使是局部裂縫，所以車身扭轉剛度是最基本和最重要的一表現(xiàn)車身結構。 在本文中，使用有限元分析研究了車身的扭轉剛度，得到優(yōu)化部件規(guī)格和結構，以改善車身扭轉剛度并減少體重。 可以使用模擬分析來分析車身的扭轉剛度和實驗分析，仿真分析采用有限元法建立實際扭轉剛度實驗模型，然后計算其剛度計算。 目前電腦的性能可以及時有效地進行計算出一個高度詳細的有限元汽車車身模型，具有滿意的精度。 謝謝到CAE方法它將節(jié)省大量的測試成本，及時指導車身的設計結構，提出優(yōu)化方法; 有限元法已經成為在車身特性設計和分析過程中不可或缺的[3]。 在結構優(yōu)化過程中，首先，敏感性分析應該是對的以設計變量的靈敏度來確定目標[4]然后根據(jù)靈敏度修改設計變量以獲得最佳設計目標與約束條件。 設計變量的靈敏度與A輕量級優(yōu)化方法相關其目標函數(shù)是由客觀因素的變化來衡量的單位設計變量的變化，靈敏度分析是opti的基礎可以根據(jù)敏感度進行結構分析，優(yōu)化結構分析，這將節(jié)省大量的計算時間并改進優(yōu)化因此，在工業(yè)中期望提供一種改進的輕型汽車車身結構，特別是車身框架，其保持所需的強度，剛度和穩(wěn)定性特性，以滿足乘客安全和車輛性能標準。此外，身體結構應當可使用現(xiàn)有技術和材料制造，以實現(xiàn)減輕重量而不增加成本。此外，主體結構應該能夠減少總成分，以進一步降低成本和制造時間。 2靈敏度分析的基本理論 從結構分析可以分為動態(tài)分析和靜態(tài)分析兩個方面，結構敏感性分析也可以分為動力敏感性分析和靜態(tài)敏感性分析。動態(tài)靈敏度分析包括特征值靈敏度分析，傳遞函數(shù)靈敏度分析和動態(tài)響應敏感性分析。靜態(tài)敏感性分析可以是壓力，位移等。對于車輛，靈敏度分析是指車身剛度強度，自由模式和敏感性分析的應變能，部分結構參數(shù)包括材料厚度和橫截面轉動慣量[5 |。有兩種計算靈敏度的方法，推導方法和伴隨結構的方法。直接推導法，是親由胡力構成R.Kapoor M.P，然后由許多人開發(fā)和推廣人們在廣泛的領域。直接推導法具有明顯的物理意義概念，簡單的數(shù)學理論方便計算可擴展從一階敏感度到高階靈敏度，因此是廣泛的在工業(yè)領域[6]。 3 BIW扭轉剛度分析 汽車BIW的有限元模型由769 862組成元素包括三角形元素和四邊形元素重量為371.2公斤。為了比較車輛扭轉剛度試驗過程中的有限元分析模型需要使用直徑為50 mm的梁單元進行模擬測試設備如圖有限元邊界條件分析模型如圖1所示。 3，左右后方的震動塔都很硬點被限制在X，翻譯DOF左右前方震動吸收塔受限于X方向DOF。負載被施加到兩個前沖擊塔的中心在垂直方向這是平等的，但與相反的方向。負載通過公式F = M / L獲得，其中M是測試扭矩值，L是左右前沖擊中心之間的距離塔。剛度結果與施加的扭矩無關，但對于目的是與試驗結果進行比較，施加的扭矩為4000 Nm，進行試驗過程如圖1所示。 4。導出左右負載點的Z方向位移使用公式計算扭轉剛度值，扭轉剛度K如下： M施加扭矩; ts Z大號和AZ尺是負載點的Z方向位移;L是負載點之間的距離。輕量級指標[7]，是評估的關鍵因素之一車身結構的性能，通過車身扭轉剛度和質量計算該越少越好輕體重指數(shù)與車身質量成正比，反之亦然與扭轉剛度成比例因此減輕輕量級的指標最多有效的方法是增加扭轉剛度，同時減少體重，車身輕量級指數(shù)計算公式如下。在公式中：M是體重; K是扭轉剛度; A是車身項目區(qū)（軸距x胎面）。通過有限元軟件的分析計算，剛度車身如表1所示，主體Z方向的輪廓顯示如下圖。 5，根據(jù)圖車身的位移改變了總之，符合預期的負載情況。 4 BIW結構剛度靈敏度分析與優(yōu)化 根據(jù)敏感性分析，各種零件的影響相關性能可以判斷，靈敏度更大意味著部件厚度更多重要的是相應的屬性，因此關鍵組件可以確定并優(yōu)化。部件的主要特點包括結構。形狀，厚度，材料性能，加工性等，用于線性分析如扭轉剛度材料的非線性特性不會影響扭轉剛度性能，部件的結構形狀和尺寸是扭轉剛度的主要因素。車身扭轉剛度主要取決于連接器部件屬性和車身com幾何特性部分厚度和部分厚度是確定幾何的因素之一部件的特點，是影響扭轉剛度的主要因素之一。 通過有限元分析，部件厚度對扭轉的影響剛度可以方便地研究。在本文中，50部分的車身（包括對稱部分）設置靈敏度分析，在分析中只有一面的對稱分量被選擇用于分析最后39厚靈敏度分析中選擇變量。選擇的組件顯示在剛度靈敏度優(yōu)化分析中，將最小質量設置為優(yōu)化目標和左載荷點的Z位移為約束條件部件厚度相對于扭轉剛度和整個車輛質量的敏感度。較大的靈敏度對此有較大的影響目標性能和目標性能可以通過增強來有效增加厚度，同一部分可能對扭轉剛度有很大的影響車輛質量，當增加厚度以提高扭轉剛度也將導致車輛質量的提高這種類型的零件不適合通過增加厚度來優(yōu)化扭轉剛度。不同部件對扭轉剛度和質量的貢獻是多樣的如何選擇合適部件用于厚度優(yōu)化，以提高扭轉剛度，而不會影響體重是指優(yōu)化效率的問題，這可以通過扭轉剛度靈敏度和質量的比較來表示靈敏度，一部分的比較靈敏度相對于其他部分較大的手段，改變其厚度可以提高扭轉剛度，但較少增強車輛質量比其他人比較靈敏度優(yōu)化效率。 為了提高扭轉剛度和減少車輛質量，最終優(yōu)化可以采取措施來增加部件厚度較大的部件比較靈敏度，減少組件的厚度比較靈敏度。零件量規(guī)根據(jù)圖1進行了優(yōu)化。 9，扭轉剛度為重量相對于原始模型，扭轉剛度增加38 Nm /度整體重量減少3.1公斤輕量級指數(shù)下降0.061。 5車身結構優(yōu)化 車身結構優(yōu)化，優(yōu)化鈑金結構肋結構的分布和尺寸可用于優(yōu)化零件強度和剛度，同時減輕重量，為片材提供優(yōu)化方金屬零件設計。在設計領域，車身優(yōu)化決定了最佳由元素節(jié)點擾動引起的位置和優(yōu)化參數(shù)質量和體積對車身優(yōu)化中的元素變化不敏感因此，質量和體積不被設定為約束或目標車身優(yōu)化。優(yōu)化過程中有三個組成部分，即設計變量，目標函數(shù)和約束，設計變量是在優(yōu)化過程中改變的參數(shù)，以提高每個形式目標，它們是目標函數(shù)的變量，約束是對設計的限制，它們是設計變量和其他要求表現(xiàn)[8]。 6結論 靈敏度分析方法可以有效地分析各部分的影響衡量要求的性能，并可以輕松識別關鍵部件進一步優(yōu)化。測量優(yōu)化和靈敏度分析技術基本的輕量化設計方法，首先，靈敏度分析決定了關鍵零件，然后測量和車身優(yōu)化優(yōu)化車身結構 參考文獻 ［1］Car body assembling method and body structure of a vehicle .2002.11.26 ［2］Vehicle construction .2001.05.29 ［3］Floor structure of a vehicle .2000.03.21 ［4］Floor assembly for a passenger car and method of making same .999.08.31 ［5］Method of manufacturing a passenger compartment from a cylindrical tube 1997.09.36 ［6］Vehicle frame components exhibiting enhanced energy absorption, an alloy and a method for their manufacture .9986.06.18 ［7］Push-fit connecting joint .997.01.14 附錄： 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 withhigh precision. In this paper, the torsion stiffness of a vehicle body was studied by using CAE analysis software. After sim-ulation, 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. Keywords: Body structure Lightweight collision Sensi-tivity analysis 1Foreword Body mass is a major component of the whole mass of a vehicle, usually accounts for more than 30 % of the whole mass. Automotive weight directly influences vehicle passive safety performance NVH performance, exhaust emissions and vehicle handling perfonnance. With the national vehicle emission regulations and safety regulations more and more stringent, the requirement for automotive weight become stricter, and how to design automotive products to meet all laws and regulations on the premise of with minimize body mass, has become one of the main research directions of the automotive industry. The lightweight vehicle body design method, which is using advanced production technology, innovative materials and optimal design technique to optimize body structure of the initial design to meet the target design performance with optimal mass of the body structure [2]. When a car is traveling on the road, it will bears a variety of loads from uneven road, these loads can be divided into bending load and torsion load, while torsion loads on the structure of a vehicle are more serious, they may cause door deformation, sealing strips off, local deformation of body structure or even local cracks, so body torsion rigidity is one of the most basic and important performance of thebodystructure. In this paper, using finite element analysis opti-mization method, the torsion rigidity of a car body was studied to get optimized parts gauge and structure to improve body torsion stiffness and reduce body mass. Torsion stiffness of vehicle body can be analyzed using the simulation analysis and experimental analysis, simulation analysis is use finite element method to build model of actual torsion stiffness experiment,and then calculate its stiffness by compute. The performance of current computer can be timely and effectively cal-culate a highly detailed finite element car body model with satisfied accuracy. Thanks to CAE methodit will save much of the test cost, timely guide the design of the body structure, and propose optimization approach; finite element method has become indispensable in the process of design and analysis of car body property [3]. During the structural optimization, at first, sensitivity analysis should be con-ducted to determine the sensitivity of the design variables to the objective [4], and then modify design variables according to the sensitivity to gain optimal design goal with constraints condition. The sensitivities of design variables are relative to A Lightweight Optimization Method the objective function, which are measured by the change of objective caused by the change of unit design variables, sensitivity analysis is the basis of the opti-mization analysis, optimization of structure can be carried out based on sensitivity analysis, which will save a lot of computing time and improve the optimization。 2 Basic Theory of Sensitivity Analysis The structural analysis can be divided into two aspects of dynamic analysis and static analysis, the structure sensitivity analysis can also be divided into dynamicsensitivity analysis and static sensitivity analysis. Dynamic sensitivity analysis including eigenvalue sensitivity analysis, transfer function sensitivity analysis and dynamic response sensitivity analysis. The static sensitivity analysis can be stress, displacement and so on. For the carthe sensitivity analysis refers to body stiffness strength, free mode and sensitivity analysis of the strain energy, part structural parameters including material thicknessand cross-sectional moment of inertia [5|. There are two types of method to calculate sensitivity, derivation method and the accompanying structure method. Direct derivation method, which was pro-posed by Fox. R. L and Kapoor M. P, and then developed and promoted by many people in a wide range of areas. Direct derivation method has clear physicalconcept, simple mathematical theory convenient to calculate and can be extended from the first-order sensitivity to the high-order sensitivity, therefore, it is widely utilized in industry areas [6]. 3 BIW Torsion Stiffness Analyses Finite element model of a car BIW is shown in Fig. 1，which consists of 769 862 elements including triangular elements and quadrilateral elements, the overall weight is 371.2 kg. In order to compare with the vehicle torsion stiffness test process, finite element analysis model required to use beam element with diameter of 50 mm to simulate the test equipment such as Fig. 2. The boundary conditions of finite element analysis model is shown in Fig. 3, both the left and the right rear shock towers hard point are constrained at Z translation DOFthe left and the right front shock absorber towers are constrained at X direction DOF. The loads are applied to the center of both front shock towers in the vertical directionwhich are equal but with opposite direction. The load is obtained by the formula F = M/L, where M is the test torque value, L is distance between the center of right and left front shock tower. The stiffness result has nothing to do with the imposed torque, but for the purpose of compare with test result, the applied torque is 4,000 Nm, the test process is shown in Fig. 4. The Z direction displacements of the left and right load point are exported to compute torsion stiffness value, torsion stiffness K, is calculated using formula as follows: M is imposed torque; ts ZL are Z direction displacement of load points; L is the distance between load points. The lightweight index [7], which is one of the key factors to evaluate the performance of body structure, is calculated by body torsion stiffness and massthe less the better. Light weight index is proportional to body mass and the inversely proportional to torsion stiffnesstherefore to reduce the lightweight index the most effective way is increase the torsion stiffness while reducing body mass, body lightweight index is calculated as follows formula. e formula: M is the body mass; K , is torsion stiffness; A is body project area (wheelbase x tread). Through analysis and calculation with finite element software, the stiffness of the body is shown in Table 1，the contours display of body Z direction is shown in Fig. 5, according to the figurethe displacement of the body is changed continu-ously, in line with the expected load case. 4 BIW Structure Stiffness Sensitivity Analysis and Optimize According to sensitivity analysis, the influence of various parts gauge to relevant performance can be judged, the sensitivity greater means the part thickness is more important for lhe corresponding property, therefore, key components can be determined and then optimized. The main features of the parts including structure. shape, thickness, material properties, processability and so on, for linear analysis such as torsion stiffness nonlinear characteristics of the material does not affect the torsion stiffness performance, the structure shape and size of the parts is the main factors of torsion stiffness. The body torsion stiffness mainly depends on connector section properties and geometric characteristics of vehicle body com-ponents, and part thickness is one of the factors that determine the geometric characteristics of parts, so it is one of the main factors affecting the torsion stiff-ness. By finite element analysis, the affection of parts thicknesses on the torsion stiffness can be studied conveniently. In this paper, 50 parts of the body (including symmetrical parts) are setup for sensitivity analysis, in the analysis, only one side of the symmetrical components are selected for analyzefinally 39 thickness variables are chose in sensitivity analysis. Components which are chose show in Fig. 6. In the stiffness sensitivity optimization analysis, the minimum mass is set as the optimization objective and Z displacement of left load point as constraints, the sensitivities of parts thickness relative to torsion stiffness and whole vehicle mass are shown in Figs. 7 and 8. Sensitivities which are larger have more impact on the target performance, and target property can be effectively increase by enhance thickness, the same part may has great influence on both torsion stiffness and vehicle mass, when increase the thickness to improve the torsion stiffness will also result in the improve of vehicle masssuch types of parts are not suitable for optimizing torsion stiffness by increasing the thickness. The contribution of different parts to the torsion stiffness and mass are diversehow to choose suitable parts for thickness optimization to improve torsion stiffness while does not influence much on body weight is refer to the problem of optimization efficiency, which can be expressed by the compare of torsion stiffness sensitivity and mass sensitivity, the compare sensitivity of a part is larger means relative to other parts, changing its thickness can improve torsion stiffness but less enhance vehicle mass than others. The comparison sensitivity optimization efficiency is shown in Fig. 9. In order to improve torsion stiffness and decrease vehicle mass, the final optimi-zation measures can be taken to is increase the thickness of parts which have larger comparison sensitivity, and decrease thickness of components which have less comparison sensitivity. Parts gauge are optimized according to Fig. 9, and torsion stiffness is recal-culated in Table 2，in relative to original model,the torsion stiffness increase 38 Nm/degreeand whole weight reduce 3.1 kg lightweight index decrease 0.061. 5 Coat Rack Topography Optimization Topography optimization, which is optimize sheet metal structure by optimizing the distribution and size of rib structure, can be utilized to optimize parts strength and stiffness while reducing weight, supplying a optimization method for sheet metal part design. In the design area, topography optimization determines the best position and optimized parameters of ribs by elements nodes perturbation, since mass and volume are not sensitive to element change in topography optimiza-tion, therefore, the mass and volume do not set as constraints or objective in topography optimization. There are three components in optimization process, namely the design variables, objective function and constraints, design variables are parameters that changed during the optimization process to improve the per-formance objective, they are the variables in objective function, and constraints are limitation to design, they are the requirements of design variables and other pert. 6 Conclusion The sensitivity analysis method can effectively analyze the influence of each part gauge to required performance, and can easily identify the key components for further optimization. Gauge optimization and sensitivity analysis technology are basic method for lightweight design, at first, sensitivity analysis determines the key parts, and then gauge and topography optimization optimize References References ［1］Car body assembling method and body structure of a vehicle .2002.11.26 ［2］Vehicle construction .2001.05.29 ［3］Floor structure of a vehicle .2000.03.21 ［4］Floor assembly for a passenger car and method of making same .999.08.31 ［5］Method of manufacturing a passenger compartment from a cylindrical tube 1997.09.36 ［6］Vehicle frame components exhibiting enhanced energy absorption, an alloy and a method for their manufacture .9986.06.18 ［7］Push-fit connecting joint .997.01.14 13 指 導 教 師 評 語 外文翻譯成績： 指導教師簽字： 年 月 日 注：1. 指導教師對譯文進行評閱時應注意以下幾個方面：①翻譯的外文文獻與畢業(yè)設計（論文）的主題是否高度相關，并作為外文參考文獻列入畢業(yè)設計（論文）的參考文獻；②翻譯的外文文獻字數(shù)是否達到規(guī)定數(shù)量（3 000字以上）；③譯文語言是否準確、通順、具有參考價值。 2. 外文原文應以附件的方式置于譯文之后。