應(yīng)用計算機(jī)輔助工程設(shè)計重型卡車車架 外文翻譯

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1、應(yīng)用計算機(jī)輔助工程設(shè)計重型卡車車架 Carlos Cosme, Amir Ghasemi and Jimmy Gandevia Western Star Trucks, Inc. 摘要： 近年來，重型卡車市場變得非常的注重重量和降低成本。這對設(shè)計工程師是重大挑戰(zhàn)，因為這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。本文論述了運用計算機(jī)集成、計算機(jī)輔助設(shè)計和工程軟件代碼（Pro / Engineer，ADAMS軟件和ANSYS）來輔助設(shè)計更改車架。 特別是，本文集中論述了一個ADAMS多體動力學(xué)模型，一個完整的卡

2、車和拖車來模擬車輛的側(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)計并行計算可快速用于設(shè)計和分析。一個說明這是如何 已被使用的技術(shù)詳細(xì)的個案研究也包括在內(nèi)。 簡介 最近，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，尋找好的方式來優(yōu)化他們的汽車設(shè)計。 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如何影響

3、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?？v梁的斷面尺寸變化很大，根據(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。請參考圖1插圖，一輛卡車的車架。然而，橫梁布置的變化帶來的影響還無法看出來。例如，如果橫梁的抗扭剛度降低，對汽車的側(cè)傾穩(wěn)定性和耐久性的影響是怎么的呢？設(shè)計工程師們需要對這些類型的問題給出答案以指導(dǎo)他們的工作。特別是，及時的設(shè)計和分析程序是必需的，這樣新的設(shè)計可以快速評估。 圖1重型載貨汽車車架 計算機(jī)輔助工程 在

4、過去的二十年中汽車自動化設(shè)計工具CAE得到了巨大的發(fā)展。這項技術(shù)的已被很多汽車制造商采用以改善汽車設(shè)計來滿足快速增長的市場要求。當(dāng)今的結(jié)構(gòu)設(shè)計通常是使用兩個CAE工具：有限元分析（FEA）和多體系統(tǒng)（MSS），結(jié)合CAD提高設(shè)計和分析。 在過去十五年里，CAD系統(tǒng)已取代繪圖板作為首選設(shè)計方法。它們使設(shè)計師和工程師能夠快速畫出卡車零部件，汽車真實模型和設(shè)計圖紙。先進(jìn)的CAD系統(tǒng)功能豐富，如參數(shù)化實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，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)。 工程師通常使用有限元分析研究結(jié)構(gòu)構(gòu)件的強度。典型的有限元分析的重點是結(jié)構(gòu)應(yīng)力，撓度和自然

5、頻率。首先對通常被稱為網(wǎng)格的離散結(jié)構(gòu)進(jìn)行分析。該網(wǎng)格是由節(jié)點和元素組成，而且經(jīng)常從CAD創(chuàng)建幾何系統(tǒng)。這些節(jié)點代表位移計算的結(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，可以自動開發(fā)節(jié)點位移。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，振型動畫。 MSS多體系統(tǒng)仿真方法研究了運動部件和組件，并經(jīng)常用來研究車輛暫?；蜍囕v的操作和動態(tài)響應(yīng)。一個典型的完整的車型MSS將剛體組成（車輪，車軸，車架，發(fā)動機(jī)，駕駛室）模擬成關(guān)節(jié)連接和理想化力元。 MSS代碼自動發(fā)展非線

6、性微分方程和代數(shù)方程定義模型中的物體運動。該方程在數(shù)值上集成剛體位移，速度，加速度和受力。結(jié)果以圖形和動畫顯示該系統(tǒng)的運動。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實體模型數(shù)據(jù)也可以用來估計每個剛體的位置，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。 CAE重型汽車建模 如上所述，在目前提供的

7、CAD與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，滾動穩(wěn)定性，平順性和持久性，需要一個詳細(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。 圖2 ADAMS的MSS的模型 該模型包括以下幾個特點： ?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)動機(jī)，引擎蓋，散熱器，鋼板彈簧，懸掛臂，傳動軸。對于許多質(zhì)量屬性這些機(jī)構(gòu)采用簡化的實體模

8、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)來自供應(yīng)商執(zhí)行的部件測試。轉(zhuǎn)動關(guān)節(jié)和球形接頭是用來連接點模型，如輪轂軸承和扭矩桿支點。Pro / Engineer的組件是用來確定這些元素的幾何位置。 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）被鏈接到一個變量界定前橋縱向位置。使用這種技術(shù)，不同的汽車型號，通過改變這個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)動機(jī)，引擎蓋。輪胎與路面接觸處理內(nèi)置在

9、ADAMS輪胎程序，包括處理模型和輪胎耐用性。在ADAMS路面輸入作為一個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畫。這些文件存儲在一個共同的目錄，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場。模擬運行后，受力和扭矩作用在車架上的數(shù)據(jù)寫入數(shù)據(jù)文件。一個定制軟件程序然后用來提取特定的負(fù)載時間步驟，并將其寫入一個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，車架計算使用慣

10、性釋放的解決方案。總之，該模型使用定制軟件程序與含代碼的CAD和CAE，評定一個定制環(huán)境耐用的重型卡車。但是，模型假設(shè)車架是剛性的。在現(xiàn)實中，卡車車架包含了大量的靈活性，會影響車輛性能及穩(wěn)定。因此，這些影響必須捕獲到多體系統(tǒng)仿真。 CAE解決方案的框架靈活性 前人技法 - 在過去，一些技術(shù)已經(jīng)使用捕捉畫面靈活性的MSS的模型。流行的三種方法是：軸套無質(zhì)量的梁單元，超單元和有限元分析。第一種方法車架分為兩種更為嚴(yán)格的機(jī)構(gòu)或以剛性元素連接在一起有套管式的車架：剛性和三個阻尼方向。套管性能調(diào)整總體車架彎曲和扭轉(zhuǎn)剛度。隨著可以預(yù)計，這種方法使用起來很麻煩，如果適當(dāng)調(diào)整，這將是唯一的能夠捕捉

11、基本彎曲和扭轉(zhuǎn)的框架模式。第二種方法的框車架分為剛體無質(zhì)量的梁互聯(lián)元素。這是類似于套管的方法，但許多更為嚴(yán)格的機(jī)構(gòu)通常使用，而且它們的連接用的是無質(zhì)量的梁單元的方程（Timoshenko梁理論），更適合貨車車架縱梁和交叉的橫梁。然而，用此方法建立一個車架很費時，詳細(xì)的梁單元的調(diào)整仍需捕獲彎曲響應(yīng)。第三種方法是最準(zhǔn)確的，并且是基于有限元的代表性框架。在此方法中的有限元模型，減少到具有代表性的總體剛度超單元和質(zhì)量屬性濃縮到一個主集節(jié)點。減少的模型是檢查原有限元模型，以確保重要動態(tài)參數(shù)的捕獲。導(dǎo)入MSS的環(huán)境下，超單元和主節(jié)點轉(zhuǎn)換為等價表示剛性機(jī)構(gòu)和力量的元素。雖然這種方法是在有限元解的基礎(chǔ)上，它仍

12、然可以實現(xiàn)難以精確的結(jié)果。例如，必須選擇主節(jié)點，以確保質(zhì)量和剛度冷凝過程的準(zhǔn)確。上述所有方法很難用于創(chuàng)建一個卡車精確靈活的車架。在一般情況下，他們只是捕捉基本響應(yīng)：最初的幾個彎扭、總的框架模式和剛度。在工作中需要很大的努力來調(diào)整其屬性，配合一些諸如靜撓度測試的參考，模態(tài)測試，或有限元模擬結(jié)果。因此，無論一個方法是同時使用合適的設(shè)計和分析環(huán)境 ，它只會對模型進(jìn)行修改，并沒有足夠的空間分辨捕捉微妙的設(shè)計改變。模態(tài)綜合技術(shù) - 在有限元分析和MSS整合最新進(jìn)展克服了上述方法的困難?，F(xiàn)在可以用有限元模型，直接在多體仿真采用模態(tài)疊加，作為模態(tài)綜合（CMS）的知名技術(shù)。利用模態(tài)疊加，一個結(jié)構(gòu)變形可以說是由

13、它的每一個貢獻(xiàn)模式。通常，一個模式是非常大的數(shù)目，需要準(zhǔn)確地捕捉點的變形。 約束應(yīng)用到結(jié)構(gòu)。發(fā)達(dá)國家解決了這個問題。它結(jié)合了正常模式與約束模式。這些約束模式或靜態(tài)形狀，捕捉到關(guān)鍵領(lǐng)域變形而不必維持正常模式結(jié)構(gòu)。因此，他們在計算上更有效率。CMS的程序代碼采用的是在ADAMS基于對克雷格-班普頓修改后的版本方法。這種方法的結(jié)構(gòu)被認(rèn)為是有約束和接口點力量應(yīng)用，并且每個接口點最多可以有六個自由度：三個平移和三個旋轉(zhuǎn)。該結(jié)構(gòu)的議案，然后用一個兩套組合模式：約束接口點的模式和固定接口的正常模式。第一種 約束模式是計算每個自由度的一個接口點，它描述的靜態(tài)形狀是對這種結(jié)構(gòu)的自由度給出一個單位偏斜

14、度，同時保持所有自由度的其他接口點固定。此過程反復(fù) 所有的接口模式。由于約束模式是靜態(tài)的形狀，其頻率的信息是未知的。固定接口正常模式代表了整個結(jié)構(gòu)的正常模式，對自由度的所有接口點是固定的。在這種形式下，克雷格.班普頓模式不適合集成理想的多體方程。例如，添加剛體約束模式，可在ADAMS非線性剛體上作用。此外，約束模式可能包含高頻率，很??難解決。Adams可以解決這些在處理克雷格-班普頓模式的問題。它標(biāo)識剛體模式使它們很容易禁用。它還增加頻率信息的約束模式，這是設(shè)置的寶貴積分參數(shù)。正交化后，修改設(shè)置存在的模式：正常模式，無約束結(jié)構(gòu)（如類似的模式在特征值計算的有限元分析運行一個典型）和界面的自由

15、度。所有的模態(tài)計算，上述是在ANSYS的環(huán)境中進(jìn)行的。為了計算模式，用戶選擇的節(jié)點代表接口點在受力和限制進(jìn)入的框架，然后運行宏，執(zhí)行適當(dāng)?shù)腁NSYS命令。正常模式包括在計算時傳遞到宏參數(shù)。最后一組的方式寫入到一個模態(tài)中性文件，可讀取ADAMS。 這種模態(tài)疊加方法的優(yōu)點很多，包括： ?框架是由一個單一的模態(tài)中性文件。因此，很容易重復(fù)使用其他型號的MSS。這些文件可以存儲在共同目下方便以后使用。在MSS的模型中被表示為一個單一靈活的組織，并沒有大量的剛體。這使得它更容易操作。 ?每個彈性體模式可將一個自由度仿真。使前面的方法添加更多的自由度，因為他們使用了大量的剛性機(jī)構(gòu)和上述每個自由度。

16、?線性靈活的特點，框架模型更為確切，因為它們是基于一個完整的有限元模型，而不是一個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)試驗結(jié)果一致。 ?阻尼影像于一個模式的基礎(chǔ)。因此，阻尼從模態(tài)測試的結(jié)果可以很容易地添加，從而提高精確度。 ?一個模擬模態(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，以提高計算效率。 ?模擬結(jié)果的可視化的改善，因為有限元網(wǎng)格的存在，在環(huán)境中的MSS可用于觀看畫面變形動畫。 ?對MSS的負(fù)荷轉(zhuǎn)移回到原來的有限元分析應(yīng)力分析模型進(jìn)行了改進(jìn)，因為負(fù)載與有限元網(wǎng)格節(jié)點。 雖然，這種方法具有許多優(yōu)點，它仍然需要費時實施。例如，并非所有整合和力量的元素都

17、支持直接連接。倒是這些都必須先連接到無質(zhì)量剛體，然后被鎖定在使用固定的網(wǎng)格節(jié)點，對自由度添加無質(zhì)量剛體。由于車架可以有36個或更多的MSS模型的連接點，它非常費時，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)計更改，更多的建模努力是必要的，潛在的引進(jìn)建模錯誤是可能的。為了克服這一困難，自定義程序被集成在開發(fā)一個靈活的車架。該過程開始于一個剛性框架。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彈性體。 ?創(chuàng)建并連接每個無質(zhì)量剛體節(jié)點力和約束應(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質(zhì)量剛體。 ?刪除

18、以前的剛體代表框架。 有限元網(wǎng)格建模 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)計師所需的變更。該方法在這里一開始就采用Pro / Engineer的實體模型，如圖1所示。每個組件的實體模型建立專門有限元分析網(wǎng)格劃分，因此，簡化了實際的設(shè)計版本。有限元網(wǎng)格是創(chuàng)建一個附加模塊為Pro /ENGINEE。它包含的功能有簡化有限元網(wǎng)格劃分，如自動確定中板地點，殼單元，應(yīng)用全局和局部網(wǎng)格控制，并確定元素屬性。同時建立內(nèi)部的Pro / ENGINEER環(huán)境網(wǎng)格有許多優(yōu)點。例如，更改實體模型自動反映在網(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ANSY

19、S。 驗證框架靈活性 為了建立靈活的精度模型，進(jìn)行模態(tài)試驗。同一個ANSYS有限元模型，在建成使用過程中，將所述以上特征值和特征向量的計算進(jìn)行比較?？梢钥闯?，在表1中，有限元模型很好地和試驗的結(jié)果吻合。ADAMS模態(tài)頻率也符合良好的測試數(shù)據(jù)，并為確認(rèn)靈活的框架提供了一個準(zhǔn)確的代表性結(jié)構(gòu)。注意只有模式在高達(dá)56赫茲時提取模態(tài)測試數(shù)據(jù)。但測試并沒有包含足夠的測量點、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。然后計算和比較以模態(tài)的卡車類似的測試數(shù)據(jù)配置。見表2，一個典型的卡車的動力由模型很好的表示出來。 結(jié)論 在這份文件中提出的項目的目的是制定一個過程，設(shè)計

20、變更到卡車可快速評估框架，使得并發(fā)設(shè)計和分析成為可能。如上所述，這個目標(biāo)已經(jīng)實現(xiàn)，結(jié)合當(dāng)前 電腦輔助設(shè)計及工程代碼自定義軟件程序。該工藝充分利用了每個代碼的優(yōu)勢，創(chuàng)造高逼真度的環(huán)境，其中微妙的設(shè)計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)計方案可以快速評估并反饋給設(shè)計師，雖然仍然有可能做出改變。雖然這個過程能成功使用，在許多地方可以進(jìn)一步增強提出，將成為未來發(fā)展的重點。這些包括： 1、仿真結(jié)果驗證使用全車試驗數(shù)據(jù)。這將用于了解模擬的弱點，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。這兩個靈活

21、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)，如疲勞分析會被添加。最近幾年計算機(jī)輔助工程代碼顯著提高疲勞壽命估算，現(xiàn)在是可能的估計疲勞損傷，該結(jié)構(gòu)在多體仿真中使用全時程負(fù)載。疲勞壽命輪廓可以被看作有限元模型，正如現(xiàn)在強調(diào)輪廓。這項技術(shù) 大大提高了耐久性分析和發(fā)展一個虛擬試驗場。 致謝 我們要感謝西方星卡車的管理團(tuán)隊，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，鮑勃和馬克他們對文件認(rèn)真審查。 參考文獻(xiàn) 1. “Mechanics of Heavy-Duty Trucks and Truck Combinations” ,UMTRI Cours

22、e Notes, July, 1995. 2. Stasa, Frank L., “Applied Finite Element Analysis for Engineers”, CBS College Publishing, 1985. 3. Ottarsson, Gisli, “Modal Flexibility Method in ADAMS/FLEX”, Mechanical Dynamics, Inc., March, 1998. 4. “Using ADAMS/FLEX”, Mechanical Dynamics, Inc.,1997. 5. “ADAMS/Finite E

23、lement Analysis Reference Manual”, Mechanical Dynamics, Inc. , November 15,1994. 6. “Pro/MESH and Pro/FEM Post, User’s Guide”, Parametric Technology Corporation, 1997. 7. “ANSYS Structural Analysis Guide”, Analysis, Inc.,1994. 8. Gillespie, Thomas D., “Fundamentals of Vehicle Dynamics”, Society

24、of Automotive Engineers, Inc.,1992. 9. Gobessi, Mark and Arnold, Wes, “The Application of Bonded Aluminum Sandwich Construction Technology to Achieve a Lightweight, Low Cost Automotive Structure”, SAE paper 982279. 1999-01-3760 Application of Computer Aided Engineering in the Design of Heavy-

25、Duty Truck Frames Carlos Cosme, Amir Ghasemi and Jimmy Gandevia Western Star Trucks, Inc. Copyright 1999 Society of Automotive Engineers, Inc. 18 ABSTRACT In recent years the heavy-duty Class 8 truck market has become very focused on weight and cost reduction. This represents a major chal

26、lenge 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. The challenge is to meet the weight and cost reduction goals without sacrificing durability and performance. This paper discusses the integrati

27、on of computer aided design and engineering software codes (Pro/Engineer, 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 truck and trailer to simulate vehicle handling,

28、 roll stability, ride performance, and durability loading. The model includes a flexible frame model using a component mode synthesis approach with modes imported from a finite element analysis program. The link between the multi-body simulation and the finite element code is also used to transfer

29、 loads back to the finite element model for stress analysis. Tight links between all the codes ensures that new design iterations can be quickly evaluated for concurrent design and analysis. A detailed case study showing how this technology has been used is also included. INTRODUCTION Recently th

30、e heavy truck industry has experienced a large push to develop vehicles with reduced cost and weight. This has been a major challenge for truck manufacturers as they look for ways to optimize their vehicle designs without sacrificing durability or performance. Since the truck frame is a major comp

31、onent 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 .The frame of a heavy truck is the backbone of the vehicle and integrates the

32、 main truck component systems such as the axles, suspension, power train, cab, and trailer. The typical frame is a ladder structure consisting of two C channel rails connected by cross-members. The frame rails vary greatly in length and cross-sectional dimensions depending on the truck application

33、. Likewise, the 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 of a truck frame. However, the effects of changes to the frame and cross-members are not well understood. For

34、example, if the torsional stiffness of a suspension cross-member is lowered, what is the effect on the vehicle’s 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

35、procedure is required so that new designs can be quickly evaluated. Figure 1. Class 8 Heavy-Duty Truck Frame COMPUTER AIDED ENGINEERING 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

36、 by the truck industry as truck manufacturers look to improve their designs in a rapidly growing market. Today structural design is typically performed using two CAE tools: finite element analysis (FEA), and multi-body system simulation (MSS). These are combined with computer aided design (CAD) sof

37、tware to improve design and analysis communication. CAD – In the last fifteen years CAD systems have replaced drawing boards as the method of choice for design. They enable designers and engineers to quickly create realistic models of truck components, vehicle assemblies, and design drawings for

38、manufacturing. 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 important data for downstream CAE applications. FEA – Finite element a

39、nalysis is usually used by engineers to study the strength of structural components. Typical FEA activity is focused on analyzing structural stresses, deflections, and natural frequencies. The analysis begins with a discretized representation of a structure known as a mesh. The mesh is composed of

40、 nodes and elements 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 define the local mass, stiffness, and damping properties of the struc

41、ture. Equations relating these quantities to the nodal displacements are automatically developed by the software codes. Other inputs, such as boundary conditions, applied loads, and material properties, must be defined by the user. Each of these quantities requires careful judgement for meaningfu

42、l results to be achieved. Results post-processing includes images of deformed structures under load, coloured stress contours, and mode shape animations. MSS – Multi-body system simulation is used to study the motion of components and assemblies and is often used to study a vehicle suspension or a

43、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 idealized joints and force elements. The MSS code automatically develops the non-linear differential and algebraic equations t

44、hat define the motion of the bodies in the model. The equations are numerically integrated to produce time histories of rigid body displacements, velocities, accelerations, and forces. Results are viewed as graphs and animations of the system motion. As with FEA, CAD data is often used to develop a

45、 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 estimate the location of the center-of-mass and the inertial properties of each rigid body. Forces acting on a rigid

46、body from a MSS can be used as input loads to a finite element analysis to determine the structural stresses in that rigid body. 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 the

47、se codes in developing a customized environment for the engineering analysis of truck frames. CAE CUSTOMIZATION FOR HEAVY TRUCK MODELLING As described above, the current offering of CAD and CAE tools provide a great deal of integration. Nonetheless, these tools are very general in scope and a si

48、gnificant customization effort is required for the analysis of heavy duty trucks and truck frames. To fully understand how changes to the truck frame impact vehicle handling, roll stability, ride, and durability requires a detailed MSS model that can simulate all these effects. Using the ADAMS so

49、ftware code such a model was developed at Western Star Trucks. Refer to Figure 2 for a view of the model in the ADAMS environment. Figure 2. ADAMS MSS Model The model includes the following characteristics: ? 100 rigid bodies ? 180 force elements ? 45 joint elements ? 415 degrees-of-fre

50、edom The rigid bodies include the frame, cab, axles, wheels ,engine, hood, radiator, leaf springs, suspension arms, drive shafts, and the trailer. Mass properties for many of these bodies were estimated using simplified solid models in Pro/Engineer. The force elements include linear and non-linear

51、 bush ielements that 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 component suppliers. Revolute joints and spherical joints are us

52、ed to model connection points, such as wheel bearings and torque rod pivots, respectively. Pro/Engineer assemblies are used to determine the geometric location of these elements. Since the heavy truck industry offers a wide variety of vehicle layouts, the locations of many of the truck’s subsystems

53、 were made parametric for easy modification. 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 this technique, truck models with different front axle positions can be quickl

54、y developed by changing the value of this variable. This procedure was duplicated for the following subassemblies: rear suspension, cab ,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 durabil

55、ity forces. In ADAMS road profiles are represented 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 then used to translate the mesh into two files for ADAMS :a road file format for the

56、 solver to determine the tire/road interaction forces, and a graphics format to view the road during post-processing animation. These files are stored in a common directory for easy retrieval. Custom control algorithms were developed to control vehicle speed, steering, and drive torque. These funct

57、ions can be quickly modified to execute different vehicle maneuvers such as roll stability, a high speed lane change, or durability bumps similar to a proving ground. After the simulations are run, the forces and torques acting on the frame are written to data files. A custom software program is t

58、hen used to extract the loads at specific time steps and write them to an ANSYS load file. The load file is then read into ANSYS and applied to a finite element model of the frame. The frame stresses are then calculated using an inertial relief solution. In summary, the model uses custom software

59、routines and the existing links 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 reality, the truck frame contains a great deal of fle

60、xibility which can impact vehicle performance and stability. As a result, these effects must be captured in the multi-body system simulation. CAE SOLUTION FOR FRAME FLEXIBILITY PREVIOUS TECHNIQUES – In the past, several techniques have been employed to capture frame flexibility in a MSS model. Thr

61、ee popular methods are: bushings, 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 properties: stiffness and damping in three translational directions and three rota

62、tional directions. The bushing properties are adjusted to give the overall frame bending and torsional stiffness. As can be 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 secon

63、d method the frame is divided into a large number 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 (Timoshenko beam theory) are better suited

64、 to modelling 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 still required to capture the frame’s flexural response. The third method is the most accurate of the three methods and is based on a fini

65、te element representation of the frame. In this method the finite element model is reduced 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 ensure that the i

66、mportant frame dynamics are still captured. It is then imported into the MSS environment where the super elements and master nodes are converted to an equivalent representation of 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 that the mass and stiffness condensation process is accurate. All the methods described above are