外文翻譯---應(yīng)用計(jì)算機(jī)輔助工程設(shè)計(jì)重型卡車車架

1、<p>　　應(yīng)用計(jì)算機(jī)輔助工程設(shè)計(jì)重型卡車車架</p><p>　　Carlos Cosme, Amir Ghasemi and Jimmy Gandevia</p><p>　　Western Star Trucks, Inc.</p><p><b>　　摘要：</b></p><p>　　近年來(lái)，重型卡車

2、市場(chǎng)變得非常的注重重量和降低成本。這對(duì)設(shè)計(jì)工程師是重大挑戰(zhàn)，因?yàn)檫@些車輛被用在各種各樣的公路環(huán)境，從高速公路到嚴(yán)重的越野環(huán)境。目前的挑戰(zhàn)是在不犧牲耐用性和性能降低的前提下滿足質(zhì)量和成本。本文論述了運(yùn)用計(jì)算機(jī)集成、計(jì)算機(jī)輔助設(shè)計(jì)和工程軟件代碼（Pro / Engineer，ADAMS軟件和ANSYS）來(lái)輔助設(shè)計(jì)更改車架。</p><p>　　特別是，本文集中論述了一個(gè)ADAMS多體動(dòng)力學(xué)模型，一個(gè)完整的卡車和拖車來(lái)

3、模擬車輛的側(cè)翻穩(wěn)定性，平順性，和耐久性載荷。該模型包括一個(gè)采用靈活的框架模型模態(tài)綜合模式，探討了有限元分析程序。之間的多體仿真鏈接與有限元程序也可以用來(lái)傳輸、加載應(yīng)力分析有限元模型。所有代碼之間緊密連結(jié)，確保新的設(shè)計(jì)并行計(jì)算可快速用于設(shè)計(jì)和分析。一個(gè)說(shuō)明這是如何已被使用的技術(shù)詳細(xì)的個(gè)案研究也包括在內(nèi)。</p><p><b>　　簡(jiǎn)介</b></p><p>　　最

4、近，重卡行業(yè)經(jīng)歷了汽車降低成本和重量的大發(fā)展。這一直是卡車制造商的主要挑戰(zhàn)，在不犧牲耐用性和性能的前提下，尋找好的方式來(lái)優(yōu)化他們的汽車設(shè)計(jì)。 由于車架是車輛系統(tǒng)的重要組成部分，它經(jīng)常被用于完善。本文概述了電腦輔助工程（CAE）分析更改車架以及這些變化會(huì)如何影響車輛性能。重型卡車的車架是該車輛的骨干，上面集成了主要的卡車組成系統(tǒng)，如車軸，懸架，動(dòng)力總成，駕駛室。典型的結(jié)構(gòu)框架是梯形框架，中間交叉幾根橫梁。縱梁的斷面尺寸變化很大，根

5、據(jù)在卡車上的受力而定。而且，需要考慮各種因素：重量，復(fù)雜性和成本。這些變化將取決于橫梁的作用和位置。請(qǐng)參考圖1插圖，一輛卡車的車架。然而，橫梁布置的變化帶來(lái)的影響還無(wú)法看出來(lái)。例如，如果橫梁的抗扭剛度降低，對(duì)汽車的側(cè)傾穩(wěn)定性和耐久性的影響是怎么的呢？設(shè)計(jì)工程師們需要對(duì)這些類型的問(wèn)題給出答案以指導(dǎo)他們的工作。特別是，及時(shí)的設(shè)計(jì)和分析程序是必需的，這樣新的設(shè)計(jì)可以快速評(píng)估。</p><p>　　圖1重型載貨汽車車架&

6、lt;/p><p><b>　　計(jì)算機(jī)輔助工程</b></p><p>　　在過(guò)去的二十年中汽車自動(dòng)化設(shè)計(jì)工具CAE得到了巨大的發(fā)展。這項(xiàng)技術(shù)的已被很多汽車制造商采用以改善汽車設(shè)計(jì)來(lái)滿足快速增長(zhǎng)的市場(chǎng)要求。當(dāng)今的結(jié)構(gòu)設(shè)計(jì)通常是使用兩個(gè)CAE工具：有限元分析（FEA）和多體系統(tǒng)（MSS），結(jié)合CAD提高設(shè)計(jì)和分析。</p><p>　　在過(guò)去十五年里

7、，CAD系統(tǒng)已取代繪圖板作為首選設(shè)計(jì)方法。它們使設(shè)計(jì)師和工程師能夠快速畫出卡車零部件，汽車真實(shí)模型和設(shè)計(jì)圖紙。先進(jìn)的CAD系統(tǒng)功能豐富，如參數(shù)化實(shí)體建模和大型裝配管理。他們已經(jīng)發(fā)展成為主要的數(shù)據(jù)庫(kù)，為工程信息尤其是CAD系統(tǒng)提供下游CAE應(yīng)用的重要數(shù)據(jù)。</p><p>　　工程師通常使用有限元分析研究結(jié)構(gòu)構(gòu)件的強(qiáng)度。典型的有限元分析的重點(diǎn)是結(jié)構(gòu)應(yīng)力，撓度和自然頻率。首先對(duì)通常被稱為網(wǎng)格的離散結(jié)構(gòu)進(jìn)行分析。該網(wǎng)格

8、是由節(jié)點(diǎn)和元素組成，而且經(jīng)常從CAD創(chuàng)建幾何系統(tǒng)。這些節(jié)點(diǎn)代表位移計(jì)算的結(jié)構(gòu)。他們定義的局部質(zhì)量，剛度和阻尼性能結(jié)構(gòu)。有關(guān)這些數(shù)量方程，可以自動(dòng)開發(fā)節(jié)點(diǎn)位移。其他投入，如邊界條件，載荷和材料特性，必須是由用戶定義。所有這些效果都需要小心的判斷和對(duì)有意義的結(jié)果進(jìn)行認(rèn)真的分析。結(jié)果后處理包括圖像變形負(fù)載結(jié)構(gòu)，彩色應(yīng)力輪廓，振型動(dòng)畫。</p><p>　　MSS多體系統(tǒng)仿真方法研究了運(yùn)動(dòng)部件和組件，并經(jīng)常用來(lái)研究車輛暫

9、?；蜍囕v的操作和動(dòng)態(tài)響應(yīng)。一個(gè)典型的完整的車型MSS將剛體組成（車輪，車軸，車架，發(fā)動(dòng)機(jī)，駕駛室）模擬成關(guān)節(jié)連接和理想化力元。 MSS代碼自動(dòng)發(fā)展非線性微分方程和代數(shù)方程定義模型中的物體運(yùn)動(dòng)。該方程在數(shù)值上集成剛體位移，速度，加速度和受力。結(jié)果以圖形和動(dòng)畫顯示該系統(tǒng)的運(yùn)動(dòng)。至于有限元分析，CAD數(shù)據(jù)經(jīng)常使用MSS的發(fā)展模式。CAD幾何數(shù)據(jù)是用于建立MSS的布局模式，如接頭和力量元素的位置。CAD實(shí)體模型數(shù)據(jù)也可以用來(lái)估計(jì)每個(gè)剛體的位置，

10、質(zhì)心和慣性特性。作用在剛體上的力可以用作MSS的輸入負(fù)載，有限元分析確定該剛體的結(jié)構(gòu)應(yīng)力。CAE技術(shù)在本文所討論的工具包括基與CAD的Pro / Engineer，ANSYS進(jìn)行有限元分析，以及基于ADAMS的MSS。下面的討論引用的是某型卡車的車架有限元分析。</p><p><b>　　CAE重型汽車建模</b></p><p>　　如上所述，在目前提供的CAD與

11、CAE工具提供了大量的整合。盡管如此，這些工具是非常粗略的分析，仍然需要努力分析重型卡車和卡車車架。為了充分了解車架影響汽車操縱的變化，滾動(dòng)穩(wěn)定性，平順性和持久性，需要一個(gè)詳細(xì)的MSS模型，可以模擬所有這些影響。使用ADAMS軟件代碼，建立了WesterStar卡車的模型。圖二展示了在ADAMS環(huán)境下的模型。</p><p>　　圖2 ADAMS的MSS的模型</p><p>　　該模型包

12、括以下幾個(gè)特點(diǎn)：?100剛體?180力元?45共同元素?415度-的自由度 固定的機(jī)構(gòu)包括車架，駕駛室，車橋，車輪，發(fā)動(dòng)機(jī)，引擎蓋，散熱器，鋼板彈簧，懸掛臂，傳動(dòng)軸。對(duì)于許多質(zhì)量屬性這些機(jī)構(gòu)采用簡(jiǎn)化的實(shí)體模型。受力的元素包括線性和非線性襯套，橡膠隔震支座模型元素，如駕駛室和發(fā)動(dòng)機(jī)的座椅。非線性單分力用于模擬空氣彈簧和減震器。這些元素的數(shù)據(jù)來(lái)自供應(yīng)商執(zhí)行的部件測(cè)試。轉(zhuǎn)動(dòng)關(guān)節(jié)和球形接頭是用來(lái)連接點(diǎn)模型，如輪轂軸承和扭矩桿支

13、點(diǎn)。Pro / Engineer的組件是用來(lái)確定這些元素的幾何位置。</p><p>　　由于重卡行業(yè)提供各種各樣的車輛布局，為便于進(jìn)行修改參數(shù)，卡車的許多子系統(tǒng)的被分開。例如，前橋組件（車輪，車軸，鋼板彈簧和減震器）被鏈接到一個(gè)變量界定前橋縱向位置。使用這種技術(shù)，不同的汽車型號(hào)，通過(guò)改變這個(gè)變量前軸位置可快速開發(fā)。這一程序是復(fù)制以下組件：后懸掛，駕駛室，發(fā)動(dòng)機(jī)，引擎蓋。輪胎與路面接觸處理內(nèi)置在ADAMS輪胎程序

14、，包括處理模型和輪胎耐用性。在ADAMS路面輸入作為一個(gè)類似三角形有限元網(wǎng)格。自定義軟件程序，然后翻譯成兩個(gè)文件的ADAMS的網(wǎng)格，以確定輪胎/路面相互作用力，圖形查看在后面處理成動(dòng)畫。這些文件存儲(chǔ)在一個(gè)共同的目錄，便于檢索。自定義控制算法開發(fā)，以控制車輛行駛速度，轉(zhuǎn)向，傳動(dòng)扭矩。這些功能可以快速修改，以執(zhí)行不同的車輛如滾筒穩(wěn)定，高速行車變化，或耐久性顛簸類似的試驗(yàn)場(chǎng)。模擬運(yùn)行后，受力和扭矩作用在車架上的數(shù)據(jù)寫入數(shù)據(jù)文件。一個(gè)定制軟件程

15、序然后用來(lái)提取特定的負(fù)載時(shí)間步驟，并將其寫入一個(gè)ANSYS加載文件。該加載文件然后讀入ANSYS和應(yīng)用到有限元模型的車架。然后，車架計(jì)算使用慣性釋放的解決方案?？傊撃Ｐ褪褂枚ㄖ栖浖绦蚺c含代碼的CAD和CAE，評(píng)定一個(gè)定制環(huán)境耐用</p><p>　　這種模態(tài)疊加方法的優(yōu)點(diǎn)很多，包括：?框架是由一個(gè)單一的模態(tài)中性文件。因此，很容易重復(fù)使用其他型號(hào)的MSS。這些文件可以存儲(chǔ)在共同目下方便以后使用。在MSS的模

16、型中被表示為一個(gè)單一靈活的組織，并沒(méi)有大量的剛體。這使得它更容易操作。</p><p>　　?每個(gè)彈性體模式可將一個(gè)自由度仿真。使前面的方法添加更多的自由度，因?yàn)樗麄兪褂昧舜罅康膭傂詸C(jī)構(gòu)和上述每個(gè)自由度。?線性靈活的特點(diǎn)，框架模型更為確切，因?yàn)樗鼈兪腔谝粋€(gè)完整的有限元模型，而不是一個(gè)剛體集合和力量的元素。這使得它更容易調(diào)整模型與模態(tài)試驗(yàn)結(jié)果一致。?阻尼影像于一個(gè)模式的基礎(chǔ)。因此，阻尼從模態(tài)測(cè)試的結(jié)果可以很容

17、易地添加，從而提高精確度。?一個(gè)模擬模態(tài)參與，可跟蹤的應(yīng)變能的貢獻(xiàn)為基礎(chǔ)。模式不能夠作出重大作用，以提高計(jì)算效率。?模擬結(jié)果的可視化的改善，因?yàn)橛邢拊W(wǎng)格的存在，在環(huán)境中的MSS可用于觀看畫面變形動(dòng)畫。?對(duì)MSS的負(fù)荷轉(zhuǎn)移回到原來(lái)的有限元分析應(yīng)力分析模型進(jìn)行了改進(jìn)，因?yàn)樨?fù)載與有限元網(wǎng)格節(jié)點(diǎn)。</p><p>　　雖然，這種方法具有許多優(yōu)點(diǎn)，它仍然需要費(fèi)時(shí)實(shí)施。例如，并非所有整合和力量的元素都支持直接連接。倒

18、是這些都必須先連接到無(wú)質(zhì)量剛體，然后被鎖定在使用固定的網(wǎng)格節(jié)點(diǎn)，對(duì)自由度添加無(wú)質(zhì)量剛體。由于車架可以有36個(gè)或更多的MSS模型的連接點(diǎn)，它非常費(fèi)時(shí)，所以使用靈活的框架。另外，如果現(xiàn)有的靈活的框架，需要取代新的設(shè)計(jì)更改，更多的建模努力是必要的，潛在的引進(jìn)建模錯(cuò)誤是可能的。為了克服這一困難，自定義程序被集成在開發(fā)一個(gè)靈活的車架。該過(guò)程開始于一個(gè)剛性框架。該模型的副本作出了一系列宏程序執(zhí)行任務(wù)的副本：?閱讀柔性體模態(tài)中性文件和位置在該車型的

19、彈性體。?創(chuàng)建并連接每個(gè)無(wú)質(zhì)量剛體節(jié)點(diǎn)力和約束應(yīng)用于彈性體。?修改所有連接到現(xiàn)有的剛體框架，以便它們連接到適當(dāng)?shù)臒o(wú)質(zhì)量剛體。?刪除以前的剛體代表框架。有限元網(wǎng)格建模 </p><p>　　為了這些方法有效地開展工作，車架的有限元模型必須易于創(chuàng)建和修改反映由設(shè)計(jì)師所需的變更。該方法在這里一開始就采用Pro / Engineer的實(shí)體模型，如圖1所示。每個(gè)組件的實(shí)體模型建立專門有限元分析網(wǎng)格劃分，因此，簡(jiǎn)化了

20、實(shí)際的設(shè)計(jì)版本。有限元網(wǎng)格是創(chuàng)建一個(gè)附加模塊為Pro /ENGINEE。它包含的功能有簡(jiǎn)化有限元網(wǎng)格劃分，如自動(dòng)確定中板地點(diǎn)，殼單元，應(yīng)用全局和局部網(wǎng)格控制，并確定元素屬性。同時(shí)建立內(nèi)部的Pro / ENGINEER環(huán)境網(wǎng)格有許多優(yōu)點(diǎn)。例如，更改實(shí)體模型自動(dòng)反映在網(wǎng)格。因此，改變的軌道幾何形狀或位置交叉成員可以迅速網(wǎng)狀和出口到ANSYS。驗(yàn)證框架靈活性 為了建立靈活的精度模型，進(jìn)行模態(tài)試驗(yàn)。同一個(gè)ANSYS有限元模型，在建成

21、使用過(guò)程中，將所述以上特征值和特征向量的計(jì)算進(jìn)行比較?？梢钥闯?，在表1中，有限元模型很好地和試驗(yàn)的結(jié)果吻合。ADAMS模態(tài)頻率也符合良好的測(cè)試數(shù)據(jù)，并為確認(rèn)靈活的框架提供了一個(gè)準(zhǔn)確的代表性結(jié)構(gòu)。注意只有模式在高達(dá)56赫茲時(shí)提取模態(tài)測(cè)試數(shù)據(jù)。但測(cè)試并沒(méi)有包含足夠的測(cè)量點(diǎn)、要清楚界定模式形狀。該框架模型納入整車MSS的模型使用上述程序。然后計(jì)</p><p><b>　　結(jié)論</b></p

22、><p>　　在這份文件中提出的項(xiàng)目的目的是制定一個(gè)過(guò)程，設(shè)計(jì)變更到卡車可快速評(píng)估框架，使得并發(fā)設(shè)計(jì)和分析成為可能。如上所述，這個(gè)目標(biāo)已經(jīng)實(shí)現(xiàn)，結(jié)合當(dāng)前電腦輔助設(shè)計(jì)及工程代碼自定義軟件程序。該工藝充分利用了每個(gè)代碼的優(yōu)勢(shì)，創(chuàng)造高逼真度的環(huán)境，其中微妙的設(shè)計(jì)變更影響卡車框架可以衡量車輛性能和耐久性的要求。設(shè)計(jì)方案可以快速評(píng)估并反饋給設(shè)計(jì)師，雖然仍然有可能做出改變。雖然這個(gè)過(guò)程能成功使用，在許多地方可以進(jìn)一步增強(qiáng)提出，

23、將成為未來(lái)發(fā)展的重點(diǎn)。這些包括：1、仿真結(jié)果驗(yàn)證使用全車試驗(yàn)數(shù)據(jù)。這將用于了解模擬的弱點(diǎn)，并調(diào)整模型的參數(shù)。由于模擬精度改善，該模型將提供更好的數(shù)據(jù)組件優(yōu)化。2、柔性使用模態(tài)綜合技術(shù)將被添加到其他結(jié)構(gòu)如駕駛室/臥鋪和拖車。這兩個(gè)靈活性為這些結(jié)構(gòu)在平順性和耐久性上發(fā)揮了重要作用。3、新的CAE技術(shù)，如疲勞分析會(huì)被添加。最近幾年計(jì)算機(jī)輔助工程代碼顯著提高疲勞壽命估算，現(xiàn)在是可能的估計(jì)疲勞損傷，該結(jié)構(gòu)在多體仿真中使用全時(shí)程負(fù)載。疲勞壽命

24、輪廓可以被看作有限元模型，正如現(xiàn)在強(qiáng)調(diào)輪廓。這項(xiàng)技術(shù)大大提高了耐久性分析和發(fā)展一個(gè)虛擬試驗(yàn)場(chǎng)。</p><p><b>　　致謝</b></p><p>　　我們要感謝西方星卡車的管理團(tuán)隊(duì)，他們?yōu)镃AE技術(shù)的研究提供大力支持。我們還要謝謝肯美利，唐摩爾，鮑勃和馬克他們對(duì)文件認(rèn)真審查。參考文獻(xiàn)</p><p>　　1. “Mechanics

25、of Heavy-Duty Trucks and Truck Combinations” ,UMTRI Course Notes, July, 1995.</p><p>　　2. Stasa, Frank L., “Applied Finite Element Analysis for Engineers”, CBS College Publishing, 1985.</p><p>　

26、　3. Ottarsson, Gisli, “Modal Flexibility Method in ADAMS/FLEX”, Mechanical Dynamics, Inc., March, 1998.</p><p>　　4. “Using ADAMS/FLEX”, Mechanical Dynamics, Inc.,1997.</p><p>　　5. “ADAMS/Finite

27、Element Analysis Reference Manual”, Mechanical Dynamics, Inc. , November 15,1994.</p><p>　　6. “Pro/MESH and Pro/FEM Post, User’s Guide”, Parametric Technology Corporation, 1997.</p><p>　　7. “AN

28、SYS Structural Analysis Guide”, Analysis, Inc.,1994.</p><p>　　8. Gillespie, Thomas D., “Fundamentals of Vehicle Dynamics”, Society of Automotive Engineers, Inc.,1992.</p><p>　　9. Gobessi, Mark a

29、nd Arnold, Wes, “The Application of Bonded Aluminum Sandwich Construction Technology to Achieve a Lightweight, Low Cost Automotive Structure”, SAE paper 982279.</p><p>　　1999-01-3760</p><p>　　Ap

30、plication of Computer Aided Engineering in the Design of Heavy-Duty Truck Frames</p><p>　　Carlos Cosme, Amir Ghasemi and Jimmy Gandevia</p><p>　　Western Star Trucks, Inc.</p><p>　　C

31、opyright © 1999 Society of Automotive Engineers, Inc.</p><p><b>　　ABSTRACT</b></p><p>　　In recent years the heavy-duty Class 8 truck market has become very focused on weight and

32、 cost reduction. This represents a major challenge for design engineers since these vehicles are used in a wide variety of vocations from highway line haul to logging in severe off-road environments.</p><p>

33、　　The challenge is to meet the weight and cost</p><p>　　reduction goals without sacrificing durability and performance. This paper discusses the integration of computer aided design and engineering software

34、codes (Pro/Engineer,</p><p>　　ADAMS, and ANSYS) to simulate the effect of design changes to the truck frame .In particular, this paper discuses the development of an ADAMS multi-body dynamics model of a full

35、 truck and trailer to simulate vehicle handling, roll stability, ride performance, and durability loading. The model includes a flexible frame model using a component mode synthesis</p><p>　　approach with mo

36、des imported from a finite element analysis program. The link between the multi-body simulation and the finite element code is also used to transfer</p><p>　　loads back to the finite element model for stress

37、 analysis. Tight links between all the codes ensures that new design iterations can be quickly evaluated for concurrent</p><p>　　design and analysis. A detailed case study showing how this technology has bee

38、n used is also included.</p><p>　　INTRODUCTION</p><p>　　Recently the heavy truck industry has experienced a large push to develop vehicles with reduced cost and weight. This has been a major cha

39、llenge for truck manufacturers</p><p>　　as they look for ways to optimize their vehicle designs without sacrificing durability or performance.</p><p>　　Since the truck frame is a major component

40、 in the vehicle system, it is often identified for refinement. This paper outlines a computer aided engineering (CAE) procedure for analyzing changes to the truck frame and how these changes affect vehicle performance .T

41、he frame of a heavy truck is the backbone of the vehicle and integrates the main truck component systems such as the axles, suspension, power train, cab, and trailer.</p><p>　　The typical frame is a ladder s

42、tructure consisting of two C channel rails connected by cross-members. The frame</p><p>　　rails vary greatly in length and cross-sectional dimensions depending on the truck application. Likewise, the</p&g

43、t;<p>　　cross-members vary in design, weight, complexity, and cost. These variations will depend upon the cross-member purpose and location. Refer to Figure 1 for an illustration</p><p>　　of a truck f

44、rame. However, the effects of changes to the frame and cross-members are not well understood.</p><p>　　For example, if the torsional stiffness of a suspension cross-member is lowered, what is the effect on t

45、he vehicle’s</p><p>　　roll stability, handling, ride, and durability? Design engineers require answers to these types of questions to guide them in their work. In particular, a concurrent design and analysis

46、 procedure is required so that new</p><p>　　designs can be quickly evaluated.</p><p>　　Figure 1. Class 8 Heavy-Duty Truck Frame</p><p>　　COMPUTER AIDED ENGINEERING</p><p&

47、gt;　　In the last twenty years there has been an enormous growth in the development of CAE tools for automotive design. Much of this technology has been adopted by the truck industry as truck manufacturers look to improve

48、 their designs in a rapidly growing market. Today structural design is typically performed using two CAE tools: finite</p><p>　　element analysis (FEA), and multi-body system simulation (MSS). These are combi

49、ned with computer aided design (CAD) software to improve design and analysis</p><p>　　communication.</p><p>　　CAD – In the last fifteen years CAD systems have replaced drawing boards as the meth

50、od of choice for design. They enable designers and engineers to quickly</p><p>　　create realistic models of truck components, vehicle assemblies, and design drawings for manufacturing.</p><p>　　

51、Advanced CAD systems are rich in features such as parametric solid model and large assembly management. They have evolved to become major databases for engineering information. In particular , CAD systems provide importa

52、nt data for downstream CAE applications.</p><p>　　FEA – Finite element analysis is usually used by engineers to study the strength of structural components.</p><p>　　Typical FEA activity is focu

53、sed on analyzing structural stresses, deflections, and natural frequencies. The analysis begins with a discretized representation of a structure</p><p>　　known as a mesh. The mesh is composed of nodes and el

54、ements and is often created with geometry from a CAD system. The nodes represent points on the structure where displacements are calculated. The elements are bounded by sets of nodes and enclose areas or volumes. They de

55、fine the local mass, stiffness, and damping properties of the structure. Equations relating these quantities</p><p>　　to the nodal displacements are automatically developed by the software codes. Other input

56、s, such as boundary conditions, applied loads, and material properties, must be defined by the user. Each of these quantities requires careful judgement for meaningful results to be achieved. Results post-processing in

57、cludes images of deformed structures under load, coloured stress contours, and mode shape animations.</p><p>　　MSS – Multi-body system simulation is used to study the motion of components and assemblies and

58、is often used to study a vehicle suspension or a vehicle’s handling and ride response. A typical MSS model of a full vehicle will be composed of rigid bodies (wheels, axles, frame , engine, cab, and trailer) connected by

59、 idealized joints and</p><p>　　force elements. The MSS code automatically develops the non-linear differential and algebraic equations that define the motion of the bodies in the model. The equations are nu

60、merically integrated to produce time histories of rigid body displacements, velocities, accelerations, and forces. Results are viewed as graphs and animations of</p><p>　　the system motion. As with FEA, CAD

61、data is often used to develop a MSS model. Geometry data from a CAD assembly is used to establish the layout of the MSS model such as the location of joints and force elements. CAD solid model data is also used to estima

62、te the location of the center-of-mass and the inertial properties of each rigid body. Forces acting on a rigid body from a MSS can be used as input loads to a finite element analysis to determine the structural stresses

63、in that rigid body.</p><p>　　The CAE tools discussed in this paper include Pro/Engineer for CAD, ANSYS for FEA, and ADAMS for MSS. The following discussion references the specific capabilities of these codes

64、 in developing a customized environment for the engineering analysis of truck frames.</p><p>　　CAE CUSTOMIZATION FOR HEAVY TRUCK</p><p><b>　　MODELLING</b></p><p>　　As de

65、scribed above, the current offering of CAD and CAE tools provide a great deal of integration. Nonetheless,</p><p>　　these tools are very general in scope and a significant customization effort is required fo

66、r the analysis of heavy duty trucks and truck frames. To fully understand how changes to the truck frame impact vehicle handling, roll</p><p>　　stability, ride, and durability requires a detailed MSS model

67、that can simulate all these effects. Using the</p><p>　　ADAMS software code such a model was developed at</p><p>　　Western Star Trucks. Refer to Figure 2 for a view of the model in the ADAMS env

68、ironment.</p><p>　　Figure 2. ADAMS MSS Model</p><p>　　The model includes the following characteristics:</p><p>　　? 100 rigid bodies</p><p>　　? 180 force elements</p&

69、gt;<p>　　? 45 joint elements</p><p>　　? 415 degrees-of-freedom</p><p>　　The rigid bodies include the frame, cab, axles, wheels ,engine, hood, radiator, leaf springs, suspension arms, driv

70、e shafts, and the trailer. Mass properties for many of</p><p>　　these bodies were estimated using simplified solid models in Pro/Engineer. The force elements include linear and non-linear bush ielements that

71、 model rubber isolators, such as the cab and engine mounts. Non-linear single component forces are used to model air springs and shock absorbers. Property data for these elements are derived from tests performed by compo

72、nent suppliers. Revolute joints and</p><p>　　spherical joints are used to model connection points, such as wheel bearings and torque rod pivots, respectively. Pro/Engineer assemblies are used to determine th

73、e geometric location of these elements.</p><p>　　Since the heavy truck industry offers a wide variety of vehicle layouts, the locations of many of the truck’s subsystems were made parametric for easy modific

74、ation. For example, the front axle subassembly(wheels, axles, leaf springs, and shock absorbers) were linked to a variable defining the longitudinal position of the front axle. Using</p><p>　　this technique,

75、 truck models with different front axle positions can be quickly developed by changing the value of this variable. This procedure was duplicated for the following</p><p>　　subassemblies: rear suspension, cab

76、 ,engine ,hood, and fifth wheel and trailer .Tire to road contact is handled with the ADAMS built-in tire routines and includes models for tire handling and durability forces. In ADAMS road profiles are represented</p

77、><p>　　as a mesh of triangles similar to a finite element mesh. The geometry and mesh for the road profiles are generated with Pro/Engineer. A custom software program is</p><p>　　then used to trans

78、late the mesh into two files for ADAMS :a road file format for the solver to determine the tire/road interaction forces, and a graphics format to view the road</p><p>　　during post-processing animation. Thes

79、e files are stored in a common directory for easy retrieval. Custom control algorithms were developed to control vehicle speed, steering, and drive torque. These functions</p><p>　　can be quickly modified to

80、 execute different vehicle maneuvers such as roll stability, a high speed lane change, or durability bumps similar to a proving ground.</p><p>　　After the simulations are run, the forces and torques acting o

81、n the frame are written to data files. A custom software program is then used to extract the loads at specific</p><p>　　time steps and write them to an ANSYS load file. The load file is then read into ANSYS

82、and applied to a finite element model of the frame. The frame stresses are then calculated using an inertial relief solution.</p><p>　　In summary, the model uses custom software routines and the existing lin

83、ks between the CAD and CAE codes to create a custom environment for evaluating the performance and durability of a heavy-duty truck. However, the model assumes that the truck frame is a rigid, under formable body. In rea

84、lity, the truck frame contains a great deal</p><p>　　of flexibility which can impact vehicle performance and stability. As a result, these effects must be captured in the multi-body system simulation.</p&

85、gt;<p>　　CAE SOLUTION FOR FRAME FLEXIBILITY</p><p>　　PREVIOUS TECHNIQUES – In the past, several techniques have been employed to capture frame flexibility in a MSS model. Three popular methods are: bu

86、shings,</p><p>　　mass beam elements, and FEA super element reduction. In the first method the frame is divided into two or more rigid bodies connected together with force elements having bushing-like propert

87、ies: stiffness and damping in three translational directions and three rotational directions. The bushing properties are adjusted to give the overall frame bending and torsional stiffness. </p><p>　　As can b

88、e expected, this method is cumbersome to use, and if properly tuned, it will be capable of capturing only the fundamental bending and torsional modes of the frame. In the second method the frame is divided into a large n

89、umber of rigid bodies interconnected by massless beam elements. This is similar to the bushing method but many more rigid bodies are usually used, and they are connected with massless beam elements whose equations (Timos

90、henko beam theory) are better suited to modelling</p><p>　　truck frame rails and cross-members. Nonetheless, it istime consuming to build a frame with this method and careful tuning of the beam elements is s

91、till required to capture the frame’s flexural response. The third method is the most accurate of the three methods and is based on a finite element representation of the frame. In this method the finite element model is

92、reduced</p><p>　　to a super element representation with the overall stiffness and mass properties condensed to a set of master nodes. The reduced model is checked against the original finite element model to

93、 ensure that the important frame dynamics are still captured. It is then imported into the MSS environment where the super elements and</p><p>　　master nodes are converted to an equivalent representation of

94、rigid bodies and force elements. Although this method is based on a finite element solution, it can still be difficult to achieve accurate results. For example, care must be taken in selecting the master nodes to ensure

95、that the mass and stiffness condensation process is accurate.</p><p>　　All the methods described above are difficult to use for creating an accurate flexible model of a truck frame. In general, they are only

96、 capable of capturing the basic frame response: the first few bending and torsional</p><p>　　modes and the gross frame stiffness. If each method is to work, a significant effort is required to tune its prope

97、rties to match some reference, such as static deflection testing,</p><p>　　modal testing, or finite element simulation results. Consequently, neither method is suitable for use in a concurrent design and ana

98、lysis environment - it would simply take too long to make changes to the model, and it would not have adequate spatial resolution to capture subtle design changes to the frame.</p><p>　　COMPONENT MODE SYNTHE

99、SIS TECHNIQUE –</p><p>　　Recent advances in the integration of FEA and MSS have overcome the difficulties in the methods described above .It is now possible to use a finite element model directly in a multi-

100、body simulation using a modal superposition technique known as component mode synthesis (CMS).Using modal superposition, the deformation of a structure can be described by the contribution of each of its modes. Normally,