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本科畢業(yè)論文（設計） 開 題 報 告 論文題目 某貨車車架輕量化設計 - 1 - 1．課題研究的目的和意義 汽車問世百余年來，特別是從汽車產(chǎn)品的大批量生產(chǎn)及汽車工業(yè)的大發(fā)展以來，汽車為世界經(jīng)濟的大發(fā)展、為人類進入現(xiàn)代生活產(chǎn)生了無法估量的巨大影響。今天，在發(fā)達國家，汽車的普及已經(jīng)達到很高的程度，在美國平均每個家庭擁有各種汽車2、3輛；雖然中國的汽車人均擁有量遠低于發(fā)達國家水平，但是由于中國巨大的市場和國際汽車工業(yè)對中國汽車工業(yè)的影響，中國汽車工業(yè)經(jīng)過50年的風雨歷程，已形成一個比較完整的工業(yè)體系。 任何問題都有兩面性，汽車工業(yè)的發(fā)展為人們帶入現(xiàn)代生活的同時也帶來了許多問題[1][2]，例如，一、能源問題，每年汽車的石油消耗量保持在近100億桶，并每年以一定的速度增加，而世界石油資源只能開采幾十年，煤炭資源也只夠開采一百來年，人類面臨著嚴重的能源危機，節(jié)能環(huán)保成為工業(yè)領域不可避免的課題，汽車工業(yè)同樣不可避免。二、環(huán)境問題，汽車每年向大氣排放大約幾億噸的有害氣體，占大氣污染物的60％以上，被認為大氣污染的“頭號殺手”。汽車尾氣中C02、CO、HC是大氣污染的主要有害氣體，特別是C02溫室效應近年來傾向日趨明顯。 汽車作為現(xiàn)代化社會大工業(yè)的產(chǎn)物，在推動人類文明向前躍進并給人類生活帶來了便捷舒適的同時，對大自然生態(tài)環(huán)境的惡化也有著難以推卸的責任。目前世界汽車的保有量超過6億輛，每年新生產(chǎn)的各種汽車約3500萬輛，汽車每年的石油消耗量約占世界每年石油產(chǎn)量的一半以上。隨著人們對環(huán)境保護的日益重視，以緩解石油資源緊缺所帶來的能源危機，節(jié)能環(huán)保技術越來越多為廣大汽車公司所采用，車輛輕量化是降低能量消耗的有效措施之一，資料表明，車重減輕10%，燃油消耗可降低6%-8%[3]。普遍認為客車、貨車的車架骨架質量占整車質量的60%，對于專用車，車架所占的質量比例則更大，因此減小車架質量可為車輛輕量化提供最大的潛力。輕量化還可以減少原材料的消耗，降低車輛的生產(chǎn)成本。 本課題就是在上述背景下提出的，目的在于研究載貨車車架結構使之受力合理，等強度及等壽命設計。對重型車的車架進行以減輕自重為目標的結構優(yōu)化，提出車架的輕量化方案，在保證承載能力的前提下有效降低質量，一定程度上起到節(jié)能的作用。最終達到保證載貨車在性能和功能不受影響或有所提高的情況下，減輕載貨車車架質量。 2．國內外研究現(xiàn)狀 受到能源和環(huán)境保護的壓力，世界汽車工業(yè)很早就開始了輕量化的研究。雖然應用輕金屬、現(xiàn)代復合材料是現(xiàn)代車輛輕量化研究的熱點之一，但是這些新材料應用在主要承載部件上的成本較高，因此在短時間內很難普及[4]。另一方面， 車輛的傳統(tǒng)材料——鋼材，由于其強度高、成本低、工藝成熟，并且是最適于回收循環(huán)利用的材料，因此利用鋼材實現(xiàn)輕量化的可能性備受關注。 1994年,國際鋼鐵協(xié)會成立了由來自全世界18個國家的35個鋼鐵生產(chǎn)企業(yè)組成的ULSAB(Ultra-Light Steel Auto Body)項目組，其目的是在保持性能和不提高成本的同時，有效降低鋼制車身的質量。ULSAB項目于1998年5月完成，其成果是顯著的。ULSAB試制的車身總質量比對比車的平均值降低25%，同時扭轉剛度提高80%，彎曲剛度提高52%，一階模態(tài)頻率提高58%，滿足碰撞安全性要求，同時成本比對比車身造價降低15%[5]。 從1997年5月啟動的ULSAC (Ultra-Light Steel Auto Closures)、ULSAS (Ultra-Light Steel Auto Suspension)和1999年1月啟動的ULSAB_AVC(Advanced Vehicle Concepts)為ULSAB的后續(xù)項目，也在輕量化研究上取得很大成[6~8]。 除了以上提到的國際上著名的四個輕量化項目外，全世界范圍內對基于結構優(yōu)化的輕量化技術也進行了大量的研究。韓國漢陽大學J.K.Shin、K.H.Lee、S.I.Song和G.J.Park應用ULSAB的設計理念和組合鋼板的工藝，對轎車前車門內板進行了結構優(yōu)化，成功地使前車門內板的質量減重8.72%，此技術己在韓國一家汽車企業(yè)中得到應用[9]。 通用汽車公司的R.R.MAYER、密西根大學的N.KIKUCHI和R.A.SCOTT應用拓撲優(yōu)化技術以碰撞過程中最大吸收能量為目標對零件進行優(yōu)化設計。此技術 已應用到一款轎車的后圍結構上[10]。 瑞典Linkoping University的P.O.Marklund和L.Nilsson從碰撞安全性角度對轎車B柱進行了減重研究。研究以B柱變形過程中的最大速度為約束變量，以B柱各段的厚度為優(yōu)化變量，以質量為優(yōu)化目標，實現(xiàn)在不降低安全性能的條件下 減重25%[11]。 美國航天航空局蘭利研究中心的J.Sobieszczanski Sobieski和SGI公司的S. Kodiyalam以及福特汽車公司車輛安全部門的R.Y.Yang共同進行了轎車的BIP (Body In Prime)基于NVH(噪聲、振動、穩(wěn)定性)和碰撞安全性要求下的輕量化研 究，實現(xiàn)了在不降低性能的條件下減重15Kg[12]。 從上面的文獻中,可知國外的汽車結構輕量化研究主要可分為四類: (1) 提出先進的設計理念，發(fā)展先進的制造工藝并通過尺寸參數(shù)優(yōu)化而得到新的輕量結構； (2) 將拓撲優(yōu)化和形狀優(yōu)化引入到結構輕量化過程中； (3) 利用硬件優(yōu)勢，大量考慮動態(tài)過程(如碰撞、振動過程)中的各種約束，對尺寸參數(shù)進行優(yōu)化而得到輕量結構，主要強調安全性； (4) 提出和應用新的現(xiàn)代優(yōu)化算法，并引入到結構輕量化過程中、 國內對基于結構優(yōu)化的車輛輕量化研究開展也很多，在車架的輕量化方面，吉林工業(yè)大學的黃金陵曾經(jīng)在對影響車架結構強度和剛度的因素進行理論分析的基礎上，運用懲罰函數(shù)法得到了汽車車架各梁截面參數(shù)的最佳值[13]。河北工學院的馮國勝曾經(jīng)在有限元分析的基礎上，采用復合形法和罰函數(shù)法對汽車車架結構參數(shù)進行了實例優(yōu)化計算[14]。此外，國內對轎車和客車的結構輕量化做了大量的研究[15~18]。 由國內外的研究現(xiàn)狀可以看出，目前國內外對車輛的輕量化都主要集中在車身上，對車架的輕量化研究也集中在對轎車和客車的研究，真正將輕量化應用到重型車和專用車結構方面的還相當少。對于車架占據(jù)絕大部分質量的專用車輛來說，減小其車架質量可為車輛輕量化提供最大的潛力挖掘空間。 依據(jù)國內外研究現(xiàn)狀，目前對轎車和客車骨架應用有限元法進行靜力分析和模態(tài)分析，并在此基礎上對結構進行分析和改進己是常用的技術手段，但對于一些需求量相對較少，產(chǎn)量不高的重型車和專用車，有限元技術還沒有得到廣泛使用。本文將有限元法引入重型專用車的設計、分析和結構優(yōu)化工作中，既解決企業(yè)設計生產(chǎn)過程中的實際問題，也有較高的應用價值。 3. 本課題的研究內容及技術方案 本文的研究對象為EQ1290W載重汽車車架，論文的任務側重于對車架 的結構有限元分析，完成其輕量化設計研究。主要內容包括： 1. 車架設計 參照EQ1290W載重汽車相關參數(shù)進行車架設計； 2. 車架有限元建模 先在CATIA中建立其三維幾何模型，在此基礎上利用ANSYS建立其有限元模型及邊界條件； 3. 典型工況下車架靜態(tài)分析 根據(jù)實際車架受力情況對車架進行加載,分析各種工況下車架的靜態(tài)強度和剛度,對靜態(tài)性能進行評估； 4. 車架質量的優(yōu)化設計 在滿足強度和剛度的前提下，使其質量盡可能小，并做優(yōu)化后的結構分析，檢驗方案的可行性； 4. 本設計的特色 ANSYS是大型的通用有限元軟件，其功能強大，可靠性好，具有強大的結構分析能力和優(yōu)化設計模塊，因而被國外大多數(shù)汽車公司所采用。 本文將基于ANSYS建立車架結構的實體單元模型，對汽車車架結構進行靜力的研究。首先，對ANSYS進行了簡要的介紹，為車架結構進行有限元分析做好準備工作；其次，以某重型載貨汽車車架結構為研究對象，利用ANSYS建立了車架結構有限元的實體單元模型，對車架建模過程進行了研究；再次，對車架結構的靜態(tài)特性進行深入研究，對車架進行性能分析評價；最后，建立車架結構簡單的梁單元優(yōu)化模型，以車架縱梁截面尺寸作為設計變量，以車架總體積為設計目標，運用ANSYS優(yōu)化模塊對車架結構的輕量化設計進行有益的嘗試。 5. 進度安排 第1周至第3周：搜集資料，寫開題報告； 第4周至第7周：確定車架的基本結構； 第8周至第10周：建立車架的三維實體模型； 第11周至第16周：輕量化設計； 第17周：撰寫說明書； 第18周：準備答辯。 6. 參考文獻 [1]靳福來，汽車輕量化技術現(xiàn)狀，汽車技術，1995，7：56—58 [2]華潤蘭，論汽車輕量化，汽車工程，1994，209(6)：375—383 [3] B.Honf., G.Bremana, Light-weight Body-current Status and Future Challengers, Chenises-German Ultra-Light Symposium, Beijing, 2001, (9):201~207 [4] 馮美斌，汽車輕量化技術中新材料的發(fā)展及應用，汽車工程，2006，28(3)： 213~220 [5] Ultra-Light Steel Auto Body Final Report, Porsche Engineering Services, Inc. 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Song, et al., Automotive Door Design with the ULSAB Concept using Structural Optimization, Struct Multidisc Optim 23:320~327 [10] R.R.Mayer, N.Kikuchi, R.A.Scott, Application of Topological Optimization Techniques to Structural Crashworthiness, International Journal for Numerical Methods inEngineering, Volume 39, Issue 8:1383~1403 [11] P.O.Marklund and L.Nilssom, Oprimization of a car body component subjected to side impact, Struct Multidisc Optim 21:383~392 [12] J.Sobieszczansiki-Sobieski, S.Kodiyalam, R.Y.Yang, Optimization of car body under constraints of noise, vibration, and harshness (NVH)and crash, Struct Multidisc Optim 22:295~306 [13] 黃金陵，汽車車架結構元件參數(shù)的優(yōu)選，汽車技術，1984，(1)：20~21 [14] 馮國勝，汽車車架結構參數(shù)的優(yōu)化設計，汽車技術，1994，(3)：6~11 [15] 桂良進，周長路，范子杰，某型載貨車車架結構輕量化設計，汽車工程， 2003，(4)：403~406 [16] 劉竹清，丁能根，全承載式客車車身結構優(yōu)化設計，機械科學與技術，2004， (1)：68~70 [17] 孟床功，徐寶云，低地板城市電動客車車架結構有限元分柞及其輕量化設 計，機械研究與應用，2004，(3)：51~52 [18] 石琴，基于現(xiàn)代設計理論的車身結構設計方法研究，[博士研究生學位論文] 合肥，合肥工業(yè)大學，2006 開題報告檢查組意見： 組長（簽字）： 年 月 日 - 7 - 本科畢業(yè)論文（設計） 翻譯資料 論文題目 某貨車車架輕量化 - 9 - 汽車設計----車架設計 車架是汽車最基本的臺架，所有的懸架和轉向連接部件都安裝在車架上面。如果汽車車架柔性過大，會使汽車既無法轉向，也無法進行正常操縱。而如果汽車車架結構剛性過大，又會引起不必要的震動傳遞給駕駛員和乘客的座艙室。汽車車架和懸架的結構設計不僅決定了汽車噪聲大小和震動的幅度強度，而且也將影響到汽車的質量和車輛的正常操縱。 汽車制造廠商們在他們生產(chǎn)的汽車上都使用了幾種不同的車架結構。其中，整個七十年代最常使用的是殼體和大梁的分體結構。目前它仍然在大型貨車、小噸位貨車和卡車上應用著。在汽車殼體和大梁的分體結構里，發(fā)動機、傳動裝置、傳動齒輪和車殼都是通過絕緣裝置固定在車身大梁上。車架內部的絕緣裝置是人造橡膠緩沖墊，能夠阻止道路不平和發(fā)動機工作引起的噪音和震動傳到駕駛員和乘客的座艙里。 第二種是汽車車架的單體結構。這種設計到目前為止在現(xiàn)代汽車上是最常用。單體車架按所需的強度來分，設計有輕型結構。在這種汽車結構中大梁作為車架的一部分被直接焊接到殼體上。底盤的重量增加了大梁的強度。傳動齒輪和傳動裝置經(jīng)由大而軟的人造橡膠絕緣墊安裝在單體車架上。絕緣墊減弱了噪聲的傳動和震動。若絕緣墊太軟，將會引起傳動齒輪和傳動裝置位移。這種位移稱為柔量，它會影響到汽車的操縱性能和控制性能。若絕緣墊太硬，則不能起到應有的隔絕噪音和減小震動的作用。汽車制造廠商們精心地設計絕緣墊，把它們裝置在汽車適當?shù)牡胤?，以降低噪聲，緩沖震動的傳送，使汽車便于駕駛，駕駛員和乘客乘坐舒適。絕緣墊的性能隨使用年限發(fā)生變化，當汽車變舊時原先的性能也隨之改變。 第三種結構是把前兩種結構的主要特點結合在一起。它在汽車前艙使用了短車梁，在汽車后艙使用了單體車架。單體部分剛性很大，而短的車梁增強了絕緣作用。 汽車制造廠家們在汽車上選擇那種生產(chǎn)成本低而同時又符合對噪音震動，駕駛操縱性能要求很高的車架結構。老式的大型的車輛、貨車、和卡車通常使用殼體和大梁的分體結構。較新的，較小型的車輛通常使用單體結構的車架。 動力傳動系統(tǒng) 動力傳動系統(tǒng)包括從發(fā)動機直到驅動輪的所有部件。聯(lián)動裝置和后驅動裝置傳送著來自發(fā)動機的扭矩。其它部件則把部件與部件相互連接起來。加速時發(fā)動機的扭矩和制動時的扭矩則加載在懸架部位上。 修理懸架時，很可能需要拆卸傳動系統(tǒng)的各零部件來進行修理。懸架移動時產(chǎn)生的噪音可能來源于傳動系統(tǒng)的零部件。下邊敘述一些不同的傳動裝置系統(tǒng)的基本知識，在進行懸架修理時可供參考。 使用前輪驅動的傳動系統(tǒng)經(jīng)常將聯(lián)動裝置和后輪傳動裝置結合成一個裝置。這個對中置和后置發(fā)動機的汽車也是很適用的。這個裝置稱為轉換軸。它為兩端各帶有一個萬向節(jié)的短半軸，把轉換軸和車輪連接起來。這些軸當懸梁移動和轉向時把動力從后傳動裝置傳送到車輪上。 后傳動裝置里的差速器分流輸入的動力，每個驅動輪上各分一半。這就使驅動輪在轉彎時會以不同的速度轉動。 在前置發(fā)動機后輪驅動的汽車里，聯(lián)動裝置位于駕駛坐艙的前底板下。傳動軸被用來把發(fā)動機動力傳送到后橋上。傳動軸每端各有一個萬向節(jié)。當懸架移動時，萬向節(jié)通過變化著的傳動系統(tǒng)的角度傳送動力。 驅動輪上帶有獨立懸架的汽車中有一個牢固地附加在車身大梁或發(fā)動機上的后傳動裝置。在加速時該裝置在懸架部位上會產(chǎn)生動力，并不產(chǎn)生扭矩。如果剎車裝置安裝在車艙內，卡鉗裝到大梁上而不是懸架上，那么剎車裝置也不會在懸架上產(chǎn)生扭矩。僅用于控制加速和減速扭矩的懸架與必須同時控制懸架力和扭矩的懸架在汽車設計上是完全不相同的。 懸架系統(tǒng) 懸架包括彈簧，避震器和控制連桿裝置。它必須能夠足以支撐車身自重和負載。懸架也應能夠承受發(fā)動機和制動對它的反作用力。懸架系統(tǒng)最重要的作用是使輪胎與路面接觸的時間盡可能的長。在支撐車體和負載時，甚至在高低不平的道路上行駛時更加應如此。這四個輪胎的胎面是車與路面相接觸的唯一的部位。發(fā)動機全部輸出的動力，轉向力和制動力都通過與路面相接觸的輪胎的胎面起作用。每當輪胎不與路面接觸或汽車開始打滑時，汽車的控制力（動力、轉向力、制動力）就會減弱甚至喪失。 車體是靠彈簧支撐著，彈簧可分為螺旋型、鋼板型、扭棒型和充氣型。螺旋型彈簧是現(xiàn)代汽車中應用最為廣泛的類型。螺旋型、扭棒型和充氣型彈簧都需要用連桿和連桿臂以使車輪就位。鋼板彈簧提供了對車體的橫向和縱向控制，以防止汽車車輪在行駛時不必要的位移，它們通常用在載重貨車和卡車上。 懸架系統(tǒng)是隨著客運汽車的發(fā)展而變化和改進著。豪華轎車，特種車輛，小型汽車和輕型卡車的設計目的是截然不同的。現(xiàn)代輪胎的改進不斷地改善了車輛的操作性能，它的改進是與避震器，轉向系統(tǒng)和懸架控制裝置一起同步改進的。 現(xiàn)代汽車在各種操縱條件下都需要輪胎與路面接觸，以便安全、正確地控制并行駛汽車。要想要最大限度的安全駕車，要牢記這四個輪胎必須在任何時間都與路面相接觸。同時需要考慮汽車操縱的靈活性，輪胎的抗耐磨性，汽車駕駛的舒適性和行車的安全性，以達到汽車的有效控制。 懸架系統(tǒng)分為前懸架和后懸架。前懸架的設計已得到了飛速發(fā)展。從較為粗糙的硬軸結構發(fā)展到了現(xiàn)代的輕型、高強度、支撐型獨立懸架結構，并由于增加了連桿裝置而使汽車的性能得到了改善。懸架結構的改進是隨著路況的改善和駕駛員的需要而進行改進的。 大多數(shù)前置發(fā)動機，后輪驅動的汽車都采用一個簡單的從屬性后懸架。但后輪驅動的獨立懸架結構復雜得多，而且成本極高，因而只用于少數(shù)客車上。 對于前置發(fā)動機前輪驅動的車輛，通過把傳動裝置移至前部，后懸架僅用來調節(jié)駕駛控制力和剎車時的反作用。這就導致了簡化的非獨立的懸架機構，半獨立的懸架機構和獨立的后懸架機構的應用，后者大量應用于新型車輛的結構設計上。 轉向系統(tǒng) 汽車駕駛員通過對轉向齒輪的控制汽車前輪的方向?，F(xiàn)代的轉向齒輪有兩個主要的部分組成，轉向桿和齒輪組。轉向桿有一個被支撐的軸，它把駕駛員的方向盤與齒輪組連在了一起。齒輪組可將汽車駕駛員的轉向力增大，以帶動轉向連桿裝置。 后輪驅動汽車的前輪在一個心軸上轉動。心軸是轉向節(jié)的一部分。該轉向節(jié)與帶有球接頭的前懸橫梁相互連接。球接頭在前懸架上下移動時可以進行轉向。前輪驅動的汽車的輪轂在轉向節(jié)里的軸承內的空心軸短軸桿上傳動。 汽車方向盤控制轉向齒輪裝置。它依次通過轉向連桿裝置使轉向節(jié)開始移動?，F(xiàn)在使用兩種轉向齒輪的結構，即齒輪齒條式結構以及循環(huán)球式結構。 現(xiàn)代汽車設計了對速度敏感的轉向結構。因此當汽車慢速行駛時需要較大的力才能使汽車轉向。于是在很多汽車上裝備了助力轉向裝置。 由于助力轉向裝置起了主要作用，所以轉向比降低了，這樣就能夠輕微轉動方向盤使得汽車轉向。助力轉向齒輪類似于標準的轉向齒輪。它有承壓面，液體壓力加在其上，以增加汽車駕駛員的轉向力。齒輪齒條式轉向結構和循環(huán)球齒輪結構都有了動力輔助裝置。 轉向齒輪的動力是由發(fā)動機從動泵提供的。該泵使動力轉向液體流過一個由閥體控制的系統(tǒng)。該控制閥能感知汽車駕駛員的轉向力。把液體壓力加到轉向系統(tǒng)的承壓面上。該液體壓力承接了一些使汽車轉向的力。 現(xiàn)在汽車的轉向桿有很多個部件組成。它被用來分散、抵消汽車碰撞力以保護駕駛員的切身安全。在有些汽車上轉向桿還可以傾斜和伸縮來調節(jié)方向盤的位置使駕駛員感覺更加舒適。為了減少駕駛員汽車被盜的機會，還安裝有一個轉向齒輪的保險鎖。很多汽車還有一個變速器保險鎖。因為處在駕駛員很容易觸及的范圍內，所以轉向桿上還可以帶有變速器換擋控制滑桿，轉向信號開關，前大燈和變光開關，刮水器開關，緊急閃爍器開關和速度控制器。 制動系統(tǒng) 使用中的制動器應能起到制動住車輛的作用。制動器能使汽車滑行時能防止行駛速度過快，在斜坡上制動時能將汽車停在適當?shù)奈恢蒙稀Ｆ噭x車的設計應使駕駛員能調節(jié)制動力以控制汽車。汽車的控制不僅受懸架和轉向系統(tǒng)影響，而且也受汽車剎車影響。制動系統(tǒng)的故障可導致汽車剎車時車輪滑脫。要修理懸梁系統(tǒng)，也可能需要將制動系統(tǒng)的部件拆卸開。為此本文將討論制動系統(tǒng)。 制動系統(tǒng)應給予汽車駕駛員提供均勻平穩(wěn)的制動力。剎車板上所需的力不應太大，而使車輪不至于被瞬間剎死。為滿足這些汽車剎車的要求，對于汽車制動已有了最低限度的剎車標準。 駕駛員通過機械裝置、真空和液壓裝置控制制動力。制動力是隨著附加在汽車剎車板上的踏板力的增加而增加的。這個力通過制動系統(tǒng)的傳遞以把固定的汽車剎車片推壓到轉動的制動器表面上。當它把動能（運動的能量）轉化為熱能（熱）時，就使汽車減速。制動量的最大值就產(chǎn)生于車輪被瞬間閘死而引起的輪胎在路面上滑動之前。所以制動量的最大值取決于輪胎和路面之間的附著力。當輪胎在道路上滑動時，制動效果減弱，汽車的方向控制可能就不起作用了。 前剎車總成的固定構件安裝在前懸架的轉向節(jié)上，在后部，它們被安裝在后橋殼或后心軸總成上，鑄鐵剎車鼓或車盤隨車輪一起轉動。 汽車的制動盤剎車時：汽車制動盤剎車有隨車輪一起轉動的圓盤。它通常被稱為汽車剎車轉子。在固定的卡鉗里的液壓控制的活塞被用來把汽車的剎車片加在轉子的汽車剎車表面上。汽車剎車片和轉子之間的摩擦力的大小會減慢或阻止車輪的轉動。固定的卡鉗殼體使墊圈被壓在轉動的汽車剎車盤上，使之不能轉動。 汽車制動盤剎車墊圈的運動與剎車轉子的表面垂直，這樣會使它們卡在轉子上減慢汽車的車輪運動。卡鉗壓的力與駕駛員加在汽車剎車板上的力成正比。 汽車制動鼓剎車：汽車制動鼓剎車使用帶有摩擦片的固定的內脹式剎車塊。他們被安裝在轉動的汽車剎車鼓內側。汽車剎車鼓緊箍在輪胎總成和轂總成或輪軸法蘭之間。當汽車剎車塊的直徑膨脹至使汽車剎車片與汽車剎車表面相接觸時，汽車剎車塊就減慢了汽車剎車鼓的轉動。它是由液壓操縱的汽車剎車分泵來完成的。來自剎車總泵的流體壓力被施加到汽車剎車分泵上，使剎車分泵膨脹起來。汽車剎車分泵的膨脹使剎車塊通過機械連桿進行移動，把汽車剎車片壓到轉動的剎車鼓上。當汽車剎車鼓的轉動速度減慢時，就起到了制動作用。 英文資料部分 Automobile Design----Frame Designs The vehicle frame is the basic platform to which all suspension and steering linkage parts attach. A vehicle will neither steer nor handle well if the frame is too flexible. A rigid frame structure may pass unnecessary vibrations into the passenger compartment. The frame and suspension design will affect the ride quality, handling, and durability, as well as the levels of both noise and vibration. Manufacturers use several different types of construction on their vehicles. Of these, separate body and frame construction was the most common through the 1970's. It is still used in large vans, pickups, and trucks. In this type of construction, the engine, drive line, running gear, and body mount to the frame through insulators. Insulators are synthetic rubber pads that keep road and engine noise and vibration from going into the passenger compartment. A second type of construction is the unitized body. This, design is by far the most popular in modern vehicles. The unitized design has a lightweight structure with the required strength. Tn this type of construction, the frame is welded into the body as part of the body structure. Body panels add strength to the frame pieces. The running gear and drive line are mounted to the unitized body through large, soft synthetic rubber insulators. The insulators minimize the transfer of noise and vibration. If the insulators are too soft, they will allow too much running gear and drive line movement. This movement, called compliance, affects vehicle handling and control. If the insulators are too hard, they will not insulate noise and vibration as they should. The manufacturer carefully designs the insulators and puts them where they will be in a vehicle with low noise and vibration transmission that still has proper handling and feel. Insulator properties change with age, changing original characteristics as the vehicle becomes older. A third type of construction combines the features of the first and second types. It uses a stub frame from the bulkhead forward and a unitized body from the bulkhead back. The unitized part is very rigid, while the stub frame provides a place for good insulation. Manufacturers select the type of construction .that is most economical to build,' while providing the noise, vibration, and ride and handling characteristics they want in the vehicle. Large older vehicles, vans, and trucks generally use separate body and frame construction. The newer, smaller' vehicles generally use unitized construction. Drive Lines The drive line includes all the parts from the and final drive carry the torque from the engine, the other.? The engine torque during acceleration and the torque during braking place loads on the suspension parts. During suspension repair, it may be essary to disassemble parts of the drive line. Noises produced when the suspension moves may originate from drive line parts. A basic understanding of different drive line assemblies is presented here to give you a working knowledge so that you can do suspension repair. Drive lines with front-wheel drive often combine the transmission and the final drive into one assembly. This is also true of mid-and rear-engine vehicles. The assembly is called a transaxle, Short half-shafts with universal joints at each end connect between the transaxle and the wheels. These shafts carry power from the final drive to the wheels even when the suspension moves and steers. A differential in the final drive splits incoming power, sending half to each drive wheel. This allows the drive wheels to turn at different speeds while rounding corners. The transmission Other parts form the link from one part to while cornering. In front-engine, rear-wheel drive vehicles, the transmission is located under the front floor of the passenger compartment. A drive shaft is used to carry engine power to the rear axle. The drive shaft has a universal joint at each end. It carries power through the changing drive line angles as the suspension moves. A vehicle with independent suspension at the drive wheels has the final drive attached rigidly to the vehicle frame or the engine. This drive arrangement produces forces, without any torques, on the suspension parts during acceleration. If the brakes are mounted inboard so the caliper mounts to a frame piece and not to a suspension, the brake will also not produce a torque on the suspension. A suspension designed to handle only acceleration and braking torques can be designed differently than one that must handle both suspension forces and torques. Suspension Systems The suspension includes springs, shock absorbers, and control linkages. It must be strong enough to support the vehicle body and load. The suspension must also resist engine and brake reactions. The most important job of the suspension is to keep the tires in contact with the road as much of the time as possible. This is done while supporting the vehicle and its load, even while traveling over rough roads. The four tire footprints are the only place the vehicle touches the road. All of the engine power, steering, and braking forces operate through the tire-to-road footprints. Control of the vehicle ( power, steering and braking) is reduced or lost any time a tire does not stay on the road or when skidding begins. The vehicle body is supported by springs. The springs can be of the coil, leaf, torsion bar, or pneumatic type. Coil springs are the most popular design used in the modern automobile. Coil, torsion bar, and pneumatic springs all require links and arms to hold the wheel in position. Leaf springs provide lateral and longitudinal control to prevent unwanted wheel motions.? They are commonly found on vans and trucks. Suspension systems have been changed and refined as the passenger automobile has developed. Design objectives differ between luxury sedans, performance vehicles, small compact vehicles, and light trucks. Tire improvements, along with improvements in shock absorbers, steering systems, and suspension control devices, have continually upgraded vehicle handling characteristics. Tire-to-road contact is needed for safe, positive vehicle control under all operating conditions. Keep in mind that all four tires must stay in contact with the road at all times for maximum vehicle control. Compromises are made in handling response, tire wear, driver comfort, and ride harshness to achieve positive vehicle control. Suspension systems are divided into front suspension and rear suspension. Front suspension designs have developed from relatively rugged solid-axle designs to the modern lightweight, high-strength , strut-type independent designs. These have been upgraded with added linkage. Suspension design improvements have followed improvements in roadways and driver expectations. Most front-engine, rear-wheel-drive vehicles use a simple dependent rear suspension . Rear-wheel-drive independent suspension is much more complex and expensive. As a result, it is only used on a few passenger vehicles. To front-engine, front-wheel-drive vehicles by moving the drive train to the front, only ride control and braking reactions are controlled by the rear suspension. This has led to the use of simplified dependent suspension , semi-independent suspension and independent rear suspension. The latter is used in a larger number of new vehicle designs. Steering Systems The driver controls the direction of the front wheels of the vehicle through the steering gear. Modern steering gears have two major units* a steering column and a gear unit. Tin-steering column has a supported shaft that connects the driver's steering wheel to the gem unit.? The gear unit multiplies the driver's steering effort to move the steering linkage. The front wheels of rear-wheel-drive vehicles rotate on a spindle. The spindle is part ol the steering knuckle . The knuckle is connected to the front suspension members with ball joints. The ball joints allow for steering as the suspension moves up and down. The wheel hubs on front-wheel-drive vehicles rotate on hollow axle stub shafts inside bearings within the steering knuckles. The steering wheel controls the steering gear assembly. This, in turn, moves the knuckle through the steering linkage. Two steering gear designs are in use today, the rack and pinion and recirculating ball. vehicles are designed with responsive steering. As a result, more effort is needed to steer the vehicle when it is moving slowly. Power steering supplies this effort on many vehicles. With power steering doing most of the work, steering ratios are decreased so that the vehicle can be steered with small steering wheel movements. The power steering gear is similar to the standard steering gear. It includes surfaces upon which fluid pressure is applied to aid the driver's steering effort. Both rack and pinion and recirculating ball gears may have power assist. Power for the steering gear is provided by an engine-driven pump. The pump forces power steering fluid through a system controlled by a valve. This control valve can sense the driver's steering effort. It puts fluid pressure against a pressure surface in the steering system.? This fluid pressure takes over some of the effort needed to steer the vehicle. The steering column in the modern vehicle has many parts. It is designed to collapse or fold in a vehicle collision to protect the driver. In some installations, it may be tilted and telescoped to adjust the position of the steering wheel for the comfort of the driver. To reduce the chance of theft, it also has a steering gear lock. On many vehicles, it has a transmission lock. Because it is within easy reach of the driver, the steering column may carry the transmission shift control lever, turn signal switch, headlight and dimmer switches, wiper switch, emergency flasher switch, and speed control. Brake Systems Service brakes must be able to stop the vehicle, prevent excess speed when coasting, and hold the vehicle in position while it is stopped on grades. They are designed so the driver can adjust the braking effort to maintain vehicle control. Vehicle control is influenced by brakes as well as the suspension and steering systems. Faults in the brake system can lead to wheel pull during braking. To repair suspension systems, parts of the brake system may require disassembly.? For these reasons, the brake system will be discussed briefly in this text. The brake system must provide smooth stopping power that can be controlled by the driver. The force required on the brake pedal must not be so high that the wheels cannot be locked. To meet these braking requirements, minimum braking standards have been set for vehicle brakes. The driver controls the braking force through mechanical, vacuum, and hydraulic mechanisms. The amount of braking increases as more force is placed on the brake pedal. This force is transferred through the brake system to push stationary brake linings against the rotating brake surface. This slows the vehicle as it turns kinetic energy (energy of motion) into thermal energy (heat). Maximum braking occurs just before the wheels lock to cause the tires to slide on the road surface. Maximum braking, therefore, depends on the adhesion between the tire and the road surface. When the tire slides on the road, braking effect is reduced and directional control of the vehicle may be lost. The stationary parts of the front brake assemblies are mounted on the steering knuckle of the front suspension. In the rear, they are mounted on the axle housing or the rear spindle assembly. The cast-iron brake drum or disc rotates with the wheel . Disc Brake.? Disc brakes have discs that rotate with the wheel . The brake disc is usually called a brake rotor. A hydraulically operated piston in a stationary caliper is used to force the lining of the brake pad against the braking surface of the rotor. The friction between the lining and rotor is used to slow or stop wheel rotation. The stationary caliper housing keeps the pads from rotating when they are being forced against the rotating brake disc. Disc brake pads move perpendicular to the face of the brake rotor. In this way,? they clamp on the rotor to slow the vehicle motion. The clamping force is proportional to the force the driver puts on the brake pedal. Drum Brakes. Drum brakes use stationary, internal expanding brake shoes with linings. They are mounted inside a rotating brake drum. The brake drum is fastened between the wheel-tire assembly and the hub assembly or the axle flange. The brake shoes slow drum rotation when the diameter of the shoes is expanded to bring the lining in contact with the brake surface. This is done by a hydraulically operated wheel cylinder. Fluid pressure from the master cylinder is forced into the wheel cylinders, expanding them. The expansion of the wheel cylinder moves the brake shoe through mechanical linkage to press the-linings against the rotating brake drum. This provides braking action as it slows the rotation of the drum. ?