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本科畢業(yè)論文（設(shè)計(jì)） 中期檢查報(bào)告 論文題目 某貨車(chē)車(chē)架輕量化設(shè)計(jì) 1．論文工作是否按開(kāi)題報(bào)告預(yù)定的內(nèi)容及進(jìn)度安排進(jìn)行 論文工作按照開(kāi)題報(bào)告預(yù)定內(nèi)容進(jìn)行，車(chē)架設(shè)計(jì)、建模、有限元靜力分析已基本完成，下一步準(zhǔn)備進(jìn)行動(dòng)態(tài)分析，為最后的輕量化設(shè)計(jì)做準(zhǔn)備。 2．目前已完成的研究工作及結(jié)果 （1）參照載重汽車(chē)相關(guān)參數(shù)進(jìn)行車(chē)架設(shè)計(jì)； （2）建立車(chē)架結(jié)構(gòu)的實(shí)體模型； （3）對(duì)車(chē)架結(jié)構(gòu)進(jìn)行靜力分析； 車(chē)架彎曲（滿載）工況， 車(chē)架扭轉(zhuǎn)工況 3．后期擬完成的研究工作及進(jìn)度安排 （1）擬完成的研究工作： 動(dòng)態(tài)分析：包括模態(tài)分析和瞬態(tài)響應(yīng)分析； 車(chē)架輕量化設(shè)計(jì)。 （2）進(jìn)度安排： 第十三周進(jìn)行相關(guān)英文資料的翻譯； 第十四周進(jìn)行動(dòng)態(tài)分析； 第十五周到十六周進(jìn)行輕量化設(shè)計(jì)； 第十七到十八周撰寫(xiě)說(shuō)明書(shū)并準(zhǔn)備答辯。 4．存在的困難與問(wèn)題 （1）在軟件運(yùn)用方面還有些不熟練； （2）多像老師和同學(xué)請(qǐng)教。 5．如期完成全部論文工作的可能性 論文工作進(jìn)展順利，預(yù)計(jì)能夠如期地完成論文工作。 中期報(bào)告檢查組意見(jiàn)：（以下空4~6行文字） 組長(zhǎng)（簽字）： 年 月 日 （此行置于頁(yè)面底部） - 6 - 本科畢業(yè)論文（設(shè)計(jì)） 開(kāi) 題 報(bào) 告 論文題目 某貨車(chē)車(chē)架輕量化設(shè)計(jì) - 1 - 1．課題研究的目的和意義 汽車(chē)問(wèn)世百余年來(lái)，特別是從汽車(chē)產(chǎn)品的大批量生產(chǎn)及汽車(chē)工業(yè)的大發(fā)展以來(lái)，汽車(chē)為世界經(jīng)濟(jì)的大發(fā)展、為人類(lèi)進(jìn)入現(xiàn)代生活產(chǎn)生了無(wú)法估量的巨大影響。今天，在發(fā)達(dá)國(guó)家，汽車(chē)的普及已經(jīng)達(dá)到很高的程度，在美國(guó)平均每個(gè)家庭擁有各種汽車(chē)2、3輛；雖然中國(guó)的汽車(chē)人均擁有量遠(yuǎn)低于發(fā)達(dá)國(guó)家水平，但是由于中國(guó)巨大的市場(chǎng)和國(guó)際汽車(chē)工業(yè)對(duì)中國(guó)汽車(chē)工業(yè)的影響，中國(guó)汽車(chē)工業(yè)經(jīng)過(guò)50年的風(fēng)雨歷程，已形成一個(gè)比較完整的工業(yè)體系。 任何問(wèn)題都有兩面性，汽車(chē)工業(yè)的發(fā)展為人們帶入現(xiàn)代生活的同時(shí)也帶來(lái)了許多問(wèn)題[1][2]，例如，一、能源問(wèn)題，每年汽車(chē)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(kāi)采幾十年，煤炭資源也只夠開(kāi)采一百來(lái)年，人類(lèi)面臨著嚴(yán)重的能源危機(jī)，節(jié)能環(huán)保成為工業(yè)領(lǐng)域不可避免的課題，汽車(chē)工業(yè)同樣不可避免。二、環(huán)境問(wèn)題，汽車(chē)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(rèn)為大氣污染的“頭號(hào)殺手”。汽車(chē)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(yīng)近年來(lái)傾向日趨明顯。 汽車(chē)作為現(xiàn)代化社會(huì)大工業(yè)的產(chǎn)物，在推動(dòng)人類(lèi)文明向前躍進(jìn)并給人類(lèi)生活帶來(lái)了便捷舒適的同時(shí)，對(duì)大自然生態(tài)環(huán)境的惡化也有著難以推卸的責(zé)任。目前世界汽車(chē)的保有量超過(guò)6億輛，每年新生產(chǎn)的各種汽車(chē)約3500萬(wàn)輛，汽車(chē)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(duì)環(huán)境保護(hù)的日益重視，以緩解石油資源緊缺所帶來(lái)的能源危機(jī)，節(jié)能環(huán)保技術(shù)越來(lái)越多為廣大汽車(chē)公司所采用，車(chē)輛輕量化是降低能量消耗的有效措施之一，資料表明，車(chē)重減輕10%，燃油消耗可降低6%-8%[3]。普遍認(rèn)為客車(chē)、貨車(chē)的車(chē)架骨架質(zhì)量占整車(chē)質(zhì)量的60%，對(duì)于專(zhuān)用車(chē)，車(chē)架所占的質(zhì)量比例則更大，因此減小車(chē)架質(zhì)量可為車(chē)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(chē)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(chē)車(chē)架結(jié)構(gòu)使之受力合理，等強(qiáng)度及等壽命設(shè)計(jì)。對(duì)重型車(chē)的車(chē)架進(jìn)行以減輕自重為目標(biāo)的結(jié)構(gòu)優(yōu)化，提出車(chē)架的輕量化方案，在保證承載能力的前提下有效降低質(zhì)量，一定程度上起到節(jié)能的作用。最終達(dá)到保證載貨車(chē)在性能和功能不受影響或有所提高的情況下，減輕載貨車(chē)車(chē)架質(zhì)量。 2．國(guó)內(nèi)外研究現(xiàn)狀 受到能源和環(huán)境保護(hù)的壓力，世界汽車(chē)工業(yè)很早就開(kāi)始了輕量化的研究。雖然應(yīng)用輕金屬、現(xiàn)代復(fù)合材料是現(xiàn)代車(chē)輛輕量化研究的熱點(diǎn)之一，但是這些新材料應(yīng)用在主要承載部件上的成本較高，因此在短時(shí)間內(nèi)很難普及[4]。另一方面， 車(chē)輛的傳統(tǒng)材料——鋼材，由于其強(qiáng)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(shí)現(xiàn)輕量化的可能性備受關(guān)注。 1994年,國(guó)際鋼鐵協(xié)會(huì)成立了由來(lái)自全世界18個(gè)國(guó)家的35個(gè)鋼鐵生產(chǎn)企業(yè)組成的ULSAB(Ultra-Light Steel Auto Body)項(xiàng)目組，其目的是在保持性能和不提高成本的同時(shí)，有效降低鋼制車(chē)身的質(zhì)量。ULSAB項(xiàng)目于1998年5月完成，其成果是顯著的。ULSAB試制的車(chē)身總質(zhì)量比對(duì)比車(chē)的平均值降低25%，同時(shí)扭轉(zhuǎn)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(shí)成本比對(duì)比車(chē)身造價(jià)降低15%[5]。 從1997年5月啟動(dòng)的ULSAC (Ultra-Light Steel Auto Closures)、ULSAS (Ultra-Light Steel Auto Suspension)和1999年1月啟動(dòng)的ULSAB_AVC(Advanced Vehicle Concepts)為ULSAB的后續(xù)項(xiàng)目，也在輕量化研究上取得很大成[6~8]。 除了以上提到的國(guó)際上著名的四個(gè)輕量化項(xiàng)目外，全世界范圍內(nèi)對(duì)基于結(jié)構(gòu)優(yōu)化的輕量化技術(shù)也進(jìn)行了大量的研究。韓國(guó)漢陽(yáng)大學(xué)J.K.Shin、K.H.Lee、S.I.Song和G.J.Park應(yīng)用ULSAB的設(shè)計(jì)理念和組合鋼板的工藝，對(duì)轎車(chē)前車(chē)門(mén)內(nèi)板進(jìn)行了結(jié)構(gòu)優(yōu)化，成功地使前車(chē)門(mén)內(nèi)板的質(zhì)量減重8.72%，此技術(shù)己在韓國(guó)一家汽車(chē)企業(yè)中得到應(yīng)用[9]。 通用汽車(chē)公司的R.R.MAYER、密西根大學(xué)的N.KIKUCHI和R.A.SCOTT應(yīng)用拓?fù)鋬?yōu)化技術(shù)以碰撞過(guò)程中最大吸收能量為目標(biāo)對(duì)零件進(jìn)行優(yōu)化設(shè)計(jì)。此技術(shù) 已應(yīng)用到一款轎車(chē)的后圍結(jié)構(gòu)上[10]。 瑞典Linkoping University的P.O.Marklund和L.Nilsson從碰撞安全性角度對(duì)轎車(chē)B柱進(jìn)行了減重研究。研究以B柱變形過(guò)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(zhì)量為優(yōu)化目標(biāo)，實(shí)現(xiàn)在不降低安全性能的條件下 減重25%[11]。 美國(guó)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(chē)公司車(chē)輛安全部門(mén)的R.Y.Yang共同進(jìn)行了轎車(chē)的BIP (Body In Prime)基于NVH(噪聲、振動(dòng)、穩(wěn)定性)和碰撞安全性要求下的輕量化研 究，實(shí)現(xiàn)了在不降低性能的條件下減重15Kg[12]。 從上面的文獻(xiàn)中,可知國(guó)外的汽車(chē)結(jié)構(gòu)輕量化研究主要可分為四類(lèi): (1) 提出先進(jìn)的設(shè)計(jì)理念，發(fā)展先進(jìn)的制造工藝并通過(guò)尺寸參數(shù)優(yōu)化而得到新的輕量結(jié)構(gòu)； (2) 將拓?fù)鋬?yōu)化和形狀優(yōu)化引入到結(jié)構(gòu)輕量化過(guò)程中； (3) 利用硬件優(yōu)勢(shì)，大量考慮動(dòng)態(tài)過(guò)程(如碰撞、振動(dòng)過(guò)程)中的各種約束，對(duì)尺寸參數(shù)進(jìn)行優(yōu)化而得到輕量結(jié)構(gòu)，主要強(qiáng)調(diào)安全性； (4) 提出和應(yīng)用新的現(xiàn)代優(yōu)化算法，并引入到結(jié)構(gòu)輕量化過(guò)程中、 國(guó)內(nèi)對(duì)基于結(jié)構(gòu)優(yōu)化的車(chē)輛輕量化研究開(kāi)展也很多，在車(chē)架的輕量化方面，吉林工業(yè)大學(xué)的黃金陵曾經(jīng)在對(duì)影響車(chē)架結(jié)構(gòu)強(qiáng)度和剛度的因素進(jìn)行理論分析的基礎(chǔ)上，運(yùn)用懲罰函數(shù)法得到了汽車(chē)車(chē)架各梁截面參數(shù)的最佳值[13]。河北工學(xué)院的馮國(guó)勝曾經(jīng)在有限元分析的基礎(chǔ)上，采用復(fù)合形法和罰函數(shù)法對(duì)汽車(chē)車(chē)架結(jié)構(gòu)參數(shù)進(jìn)行了實(shí)例優(yōu)化計(jì)算[14]。此外，國(guó)內(nèi)對(duì)轎車(chē)和客車(chē)的結(jié)構(gòu)輕量化做了大量的研究[15~18]。 由國(guó)內(nèi)外的研究現(xiàn)狀可以看出，目前國(guó)內(nèi)外對(duì)車(chē)輛的輕量化都主要集中在車(chē)身上，對(duì)車(chē)架的輕量化研究也集中在對(duì)轎車(chē)和客車(chē)的研究，真正將輕量化應(yīng)用到重型車(chē)和專(zhuān)用車(chē)結(jié)構(gòu)方面的還相當(dāng)少。對(duì)于車(chē)架占據(jù)絕大部分質(zhì)量的專(zhuān)用車(chē)輛來(lái)說(shuō)，減小其車(chē)架質(zhì)量可為車(chē)輛輕量化提供最大的潛力挖掘空間。 依據(jù)國(guó)內(nèi)外研究現(xiàn)狀，目前對(duì)轎車(chē)和客車(chē)骨架應(yīng)用有限元法進(jìn)行靜力分析和模態(tài)分析，并在此基礎(chǔ)上對(duì)結(jié)構(gòu)進(jìn)行分析和改進(jìn)己是常用的技術(shù)手段，但對(duì)于一些需求量相對(duì)較少，產(chǎn)量不高的重型車(chē)和專(zhuān)用車(chē)，有限元技術(shù)還沒(méi)有得到廣泛使用。本文將有限元法引入重型專(zhuān)用車(chē)的設(shè)計(jì)、分析和結(jié)構(gòu)優(yōu)化工作中，既解決企業(yè)設(shè)計(jì)生產(chǎn)過(guò)程中的實(shí)際問(wèn)題，也有較高的應(yīng)用價(jià)值。 3. 本課題的研究?jī)?nèi)容及技術(shù)方案 本文的研究對(duì)象為EQ1290W載重汽車(chē)車(chē)架，論文的任務(wù)側(cè)重于對(duì)車(chē)架 的結(jié)構(gòu)有限元分析，完成其輕量化設(shè)計(jì)研究。主要內(nèi)容包括： 1. 車(chē)架設(shè)計(jì) 參照EQ1290W載重汽車(chē)相關(guān)參數(shù)進(jìn)行車(chē)架設(shè)計(jì)； 2. 車(chē)架有限元建模 先在CATIA中建立其三維幾何模型，在此基礎(chǔ)上利用ANSYS建立其有限元模型及邊界條件； 3. 典型工況下車(chē)架靜態(tài)分析 根據(jù)實(shí)際車(chē)架受力情況對(duì)車(chē)架進(jìn)行加載,分析各種工況下車(chē)架的靜態(tài)強(qiáng)度和剛度,對(duì)靜態(tài)性能進(jìn)行評(píng)估； 4. 車(chē)架質(zhì)量的優(yōu)化設(shè)計(jì) 在滿足強(qiáng)度和剛度的前提下，使其質(zhì)量盡可能小，并做優(yōu)化后的結(jié)構(gòu)分析，檢驗(yàn)方案的可行性； 4. 本設(shè)計(jì)的特色 ANSYS是大型的通用有限元軟件，其功能強(qiáng)大，可靠性好，具有強(qiáng)大的結(jié)構(gòu)分析能力和優(yōu)化設(shè)計(jì)模塊，因而被國(guó)外大多數(shù)汽車(chē)公司所采用。 本文將基于ANSYS建立車(chē)架結(jié)構(gòu)的實(shí)體單元模型，對(duì)汽車(chē)車(chē)架結(jié)構(gòu)進(jìn)行靜力的研究。首先，對(duì)ANSYS進(jìn)行了簡(jiǎn)要的介紹，為車(chē)架結(jié)構(gòu)進(jìn)行有限元分析做好準(zhǔn)備工作；其次，以某重型載貨汽車(chē)車(chē)架結(jié)構(gòu)為研究對(duì)象，利用ANSYS建立了車(chē)架結(jié)構(gòu)有限元的實(shí)體單元模型，對(duì)車(chē)架建模過(guò)程進(jìn)行了研究；再次，對(duì)車(chē)架結(jié)構(gòu)的靜態(tài)特性進(jìn)行深入研究，對(duì)車(chē)架進(jìn)行性能分析評(píng)價(jià)；最后，建立車(chē)架結(jié)構(gòu)簡(jiǎn)單的梁?jiǎn)卧獌?yōu)化模型，以車(chē)架縱梁截面尺寸作為設(shè)計(jì)變量，以車(chē)架總體積為設(shè)計(jì)目標(biāo)，運(yùn)用ANSYS優(yōu)化模塊對(duì)車(chē)架結(jié)構(gòu)的輕量化設(shè)計(jì)進(jìn)行有益的嘗試。 5. 進(jìn)度安排 第1周至第3周：搜集資料，寫(xiě)開(kāi)題報(bào)告； 第4周至第7周：確定車(chē)架的基本結(jié)構(gòu)； 第8周至第10周：建立車(chē)架的三維實(shí)體模型； 第11周至第16周：輕量化設(shè)計(jì)； 第17周：撰寫(xiě)說(shuō)明書(shū)； 第18周：準(zhǔn)備答辯。 6. 參考文獻(xiàn) [1]靳福來(lái)，汽車(chē)輕量化技術(shù)現(xiàn)狀，汽車(chē)技術(shù)，1995，7：56—58 [2]華潤(rùn)蘭，論汽車(chē)輕量化，汽車(chē)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(chē)輕量化技術(shù)中新材料的發(fā)展及應(yīng)用，汽車(chē)工程，2006，28(3)： 213~220 [5] Ultra-Light Steel Auto Body Final Report, Porsche Engineering Services, Inc. March 1998 [6] Ultra-Light Steel Auto Closures Final Report, Porsche Engineering Services, Inc. May 2001 [7] Ultra-Light Steel Auto Suspension Final Report, Lotus Engineering Services, Inc. January 2001 [8] ULSAB-Advanced Vehicle Concepts Final Report, Porsche Engineering Services, Inc. June 2001 [9] J.-K. Shin, K.-H. Lee, S.-I. 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(chē)車(chē)架結(jié)構(gòu)元件參數(shù)的優(yōu)選，汽車(chē)技術(shù)，1984，(1)：20~21 [14] 馮國(guó)勝，汽車(chē)車(chē)架結(jié)構(gòu)參數(shù)的優(yōu)化設(shè)計(jì)，汽車(chē)技術(shù)，1994，(3)：6~11 [15] 桂良進(jìn)，周長(zhǎng)路，范子杰，某型載貨車(chē)車(chē)架結(jié)構(gòu)輕量化設(shè)計(jì)，汽車(chē)工程， 2003，(4)：403~406 [16] 劉竹清，丁能根，全承載式客車(chē)車(chē)身結(jié)構(gòu)優(yōu)化設(shè)計(jì)，機(jī)械科學(xué)與技術(shù)，2004， (1)：68~70 [17] 孟床功，徐寶云，低地板城市電動(dòng)客車(chē)車(chē)架結(jié)構(gòu)有限元分柞及其輕量化設(shè) 計(jì)，機(jī)械研究與應(yīng)用，2004，(3)：51~52 [18] 石琴，基于現(xiàn)代設(shè)計(jì)理論的車(chē)身結(jié)構(gòu)設(shè)計(jì)方法研究，[博士研究生學(xué)位論文] 合肥，合肥工業(yè)大學(xué)，2006 開(kāi)題報(bào)告檢查組意見(jiàn)： 組長(zhǎng)（簽字）： 年 月 日 - 7 - 本科畢業(yè)論文（設(shè)計(jì)） 翻譯資料 論文題目 某貨車(chē)車(chē)架輕量化 - 9 - 汽車(chē)設(shè)計(jì)----車(chē)架設(shè)計(jì) 車(chē)架是汽車(chē)最基本的臺(tái)架，所有的懸架和轉(zhuǎn)向連接部件都安裝在車(chē)架上面。如果汽車(chē)車(chē)架柔性過(guò)大，會(huì)使汽車(chē)既無(wú)法轉(zhuǎn)向，也無(wú)法進(jìn)行正常操縱。而如果汽車(chē)車(chē)架結(jié)構(gòu)剛性過(guò)大，又會(huì)引起不必要的震動(dòng)傳遞給駕駛員和乘客的座艙室。汽車(chē)車(chē)架和懸架的結(jié)構(gòu)設(shè)計(jì)不僅決定了汽車(chē)噪聲大小和震動(dòng)的幅度強(qiáng)度，而且也將影響到汽車(chē)的質(zhì)量和車(chē)輛的正常操縱。 汽車(chē)制造廠商們?cè)谒麄兩a(chǎn)的汽車(chē)上都使用了幾種不同的車(chē)架結(jié)構(gòu)。其中，整個(gè)七十年代最常使用的是殼體和大梁的分體結(jié)構(gòu)。目前它仍然在大型貨車(chē)、小噸位貨車(chē)和卡車(chē)上應(yīng)用著。在汽車(chē)殼體和大梁的分體結(jié)構(gòu)里，發(fā)動(dòng)機(jī)、傳動(dòng)裝置、傳動(dòng)齒輪和車(chē)殼都是通過(guò)絕緣裝置固定在車(chē)身大梁上。車(chē)架內(nèi)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(dòng)機(jī)工作引起的噪音和震動(dòng)傳到駕駛員和乘客的座艙里。 第二種是汽車(chē)車(chē)架的單體結(jié)構(gòu)。這種設(shè)計(jì)到目前為止在現(xiàn)代汽車(chē)上是最常用。單體車(chē)架按所需的強(qiáng)度來(lái)分，設(shè)計(jì)有輕型結(jié)構(gòu)。在這種汽車(chē)結(jié)構(gòu)中大梁作為車(chē)架的一部分被直接焊接到殼體上。底盤(pán)的重量增加了大梁的強(qiáng)度。傳動(dòng)齒輪和傳動(dòng)裝置經(jīng)由大而軟的人造橡膠絕緣墊安裝在單體車(chē)架上。絕緣墊減弱了噪聲的傳動(dòng)和震動(dòng)。若絕緣墊太軟，將會(huì)引起傳動(dòng)齒輪和傳動(dòng)裝置位移。這種位移稱(chēng)為柔量，它會(huì)影響到汽車(chē)的操縱性能和控制性能。若絕緣墊太硬，則不能起到應(yīng)有的隔絕噪音和減小震動(dòng)的作用。汽車(chē)制造廠商們精心地設(shè)計(jì)絕緣墊，把它們裝置在汽車(chē)適當(dāng)?shù)牡胤?，以降低噪聲，緩沖震動(dòng)的傳送，使汽車(chē)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(dāng)汽車(chē)變舊時(shí)原先的性能也隨之改變。 第三種結(jié)構(gòu)是把前兩種結(jié)構(gòu)的主要特點(diǎn)結(jié)合在一起。它在汽車(chē)前艙使用了短車(chē)梁，在汽車(chē)后艙使用了單體車(chē)架。單體部分剛性很大，而短的車(chē)梁增強(qiáng)了絕緣作用。 汽車(chē)制造廠家們?cè)谄?chē)上選擇那種生產(chǎn)成本低而同時(shí)又符合對(duì)噪音震動(dòng)，駕駛操縱性能要求很高的車(chē)架結(jié)構(gòu)。老式的大型的車(chē)輛、貨車(chē)、和卡車(chē)通常使用殼體和大梁的分體結(jié)構(gòu)。較新的，較小型的車(chē)輛通常使用單體結(jié)構(gòu)的車(chē)架。 動(dòng)力傳動(dòng)系統(tǒng) 動(dòng)力傳動(dòng)系統(tǒng)包括從發(fā)動(dòng)機(jī)直到驅(qū)動(dòng)輪的所有部件。聯(lián)動(dòng)裝置和后驅(qū)動(dòng)裝置傳送著來(lái)自發(fā)動(dòng)機(jī)的扭矩。其它部件則把部件與部件相互連接起來(lái)。加速時(shí)發(fā)動(dòng)機(jī)的扭矩和制動(dòng)時(shí)的扭矩則加載在懸架部位上。 修理懸架時(shí)，很可能需要拆卸傳動(dòng)系統(tǒng)的各零部件來(lái)進(jìn)行修理。懸架移動(dòng)時(shí)產(chǎn)生的噪音可能來(lái)源于傳動(dòng)系統(tǒng)的零部件。下邊敘述一些不同的傳動(dòng)裝置系統(tǒng)的基本知識(shí)，在進(jìn)行懸架修理時(shí)可供參考。 使用前輪驅(qū)動(dòng)的傳動(dòng)系統(tǒng)經(jīng)常將聯(lián)動(dòng)裝置和后輪傳動(dòng)裝置結(jié)合成一個(gè)裝置。這個(gè)對(duì)中置和后置發(fā)動(dòng)機(jī)的汽車(chē)也是很適用的。這個(gè)裝置稱(chēng)為轉(zhuǎn)換軸。它為兩端各帶有一個(gè)萬(wàn)向節(jié)的短半軸，把轉(zhuǎn)換軸和車(chē)輪連接起來(lái)。這些軸當(dāng)懸梁移動(dòng)和轉(zhuǎn)向時(shí)把動(dòng)力從后傳動(dòng)裝置傳送到車(chē)輪上。 后傳動(dòng)裝置里的差速器分流輸入的動(dòng)力，每個(gè)驅(qū)動(dòng)輪上各分一半。這就使驅(qū)動(dòng)輪在轉(zhuǎn)彎時(shí)會(huì)以不同的速度轉(zhuǎn)動(dòng)。 在前置發(fā)動(dòng)機(jī)后輪驅(qū)動(dòng)的汽車(chē)?yán)?，?lián)動(dòng)裝置位于駕駛坐艙的前底板下。傳動(dòng)軸被用來(lái)把發(fā)動(dòng)機(jī)動(dòng)力傳送到后橋上。傳動(dòng)軸每端各有一個(gè)萬(wàn)向節(jié)。當(dāng)懸架移動(dòng)時(shí)，萬(wàn)向節(jié)通過(guò)變化著的傳動(dòng)系統(tǒng)的角度傳送動(dòng)力。 驅(qū)動(dòng)輪上帶有獨(dú)立懸架的汽車(chē)中有一個(gè)牢固地附加在車(chē)身大梁或發(fā)動(dòng)機(jī)上的后傳動(dòng)裝置。在加速時(shí)該裝置在懸架部位上會(huì)產(chǎn)生動(dòng)力，并不產(chǎn)生扭矩。如果剎車(chē)裝置安裝在車(chē)艙內(nèi)，卡鉗裝到大梁上而不是懸架上，那么剎車(chē)裝置也不會(huì)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(shí)控制懸架力和扭矩的懸架在汽車(chē)設(shè)計(jì)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(chē)身自重和負(fù)載。懸架也應(yīng)能夠承受發(fā)動(dòng)機(jī)和制動(dòng)對(duì)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(shí)間盡可能的長(zhǎng)。在支撐車(chē)體和負(fù)載時(shí)，甚至在高低不平的道路上行駛時(shí)更加應(yīng)如此。這四個(gè)輪胎的胎面是車(chē)與路面相接觸的唯一的部位。發(fā)動(dòng)機(jī)全部輸出的動(dòng)力，轉(zhuǎn)向力和制動(dòng)力都通過(guò)與路面相接觸的輪胎的胎面起作用。每當(dāng)輪胎不與路面接觸或汽車(chē)開(kāi)始打滑時(shí)，汽車(chē)的控制力（動(dòng)力、轉(zhuǎn)向力、制動(dòng)力）就會(huì)減弱甚至喪失。 車(chē)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(chē)中應(yīng)用最為廣泛的類(lèi)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(chē)輪就位。鋼板彈簧提供了對(duì)車(chē)體的橫向和縱向控制，以防止汽車(chē)車(chē)輪在行駛時(shí)不必要的位移，它們通常用在載重貨車(chē)和卡車(chē)上。 懸架系統(tǒng)是隨著客運(yùn)汽車(chē)的發(fā)展而變化和改進(jìn)著。豪華轎車(chē)，特種車(chē)輛，小型汽車(chē)和輕型卡車(chē)的設(shè)計(jì)目的是截然不同的?，F(xiàn)代輪胎的改進(jìn)不斷地改善了車(chē)輛的操作性能，它的改進(jìn)是與避震器，轉(zhuǎn)向系統(tǒng)和懸架控制裝置一起同步改進(jìn)的。 現(xiàn)代汽車(chē)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(chē)。要想要最大限度的安全駕車(chē)，要牢記這四個(gè)輪胎必須在任何時(shí)間都與路面相接觸。同時(shí)需要考慮汽車(chē)操縱的靈活性，輪胎的抗耐磨性，汽車(chē)駕駛的舒適性和行車(chē)的安全性，以達(dá)到汽車(chē)的有效控制。 懸架系統(tǒng)分為前懸架和后懸架。前懸架的設(shè)計(jì)已得到了飛速發(fā)展。從較為粗糙的硬軸結(jié)構(gòu)發(fā)展到了現(xiàn)代的輕型、高強(qiáng)度、支撐型獨(dú)立懸架結(jié)構(gòu)，并由于增加了連桿裝置而使汽車(chē)的性能得到了改善。懸架結(jié)構(gòu)的改進(jìn)是隨著路況的改善和駕駛員的需要而進(jìn)行改進(jìn)的。 大多數(shù)前置發(fā)動(dòng)機(jī)，后輪驅(qū)動(dòng)的汽車(chē)都采用一個(gè)簡(jiǎn)單的從屬性后懸架。但后輪驅(qū)動(dòng)的獨(dú)立懸架結(jié)構(gòu)復(fù)雜得多，而且成本極高，因而只用于少數(shù)客車(chē)上。 對(duì)于前置發(fā)動(dòng)機(jī)前輪驅(qū)動(dòng)的車(chē)輛，通過(guò)把傳動(dòng)裝置移至前部，后懸架僅用來(lái)調(diào)節(jié)駕駛控制力和剎車(chē)時(shí)的反作用。這就導(dǎo)致了簡(jiǎn)化的非獨(dú)立的懸架機(jī)構(gòu)，半獨(dú)立的懸架機(jī)構(gòu)和獨(dú)立的后懸架機(jī)構(gòu)的應(yīng)用，后者大量應(yīng)用于新型車(chē)輛的結(jié)構(gòu)設(shè)計(jì)上。 轉(zhuǎn)向系統(tǒng) 汽車(chē)駕駛員通過(guò)對(duì)轉(zhuǎn)向齒輪的控制汽車(chē)前輪的方向?，F(xiàn)代的轉(zhuǎn)向齒輪有兩個(gè)主要的部分組成，轉(zhuǎn)向桿和齒輪組。轉(zhuǎn)向桿有一個(gè)被支撐的軸，它把駕駛員的方向盤(pán)與齒輪組連在了一起。齒輪組可將汽車(chē)駕駛員的轉(zhuǎn)向力增大，以帶動(dòng)轉(zhuǎn)向連桿裝置。 后輪驅(qū)動(dòng)汽車(chē)的前輪在一個(gè)心軸上轉(zhuǎn)動(dòng)。心軸是轉(zhuǎn)向節(jié)的一部分。該轉(zhuǎn)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(dòng)時(shí)可以進(jìn)行轉(zhuǎn)向。前輪驅(qū)動(dòng)的汽車(chē)的輪轂在轉(zhuǎn)向節(jié)里的軸承內(nèi)的空心軸短軸桿上傳動(dòng)。 汽車(chē)方向盤(pán)控制轉(zhuǎn)向齒輪裝置。它依次通過(guò)轉(zhuǎn)向連桿裝置使轉(zhuǎn)向節(jié)開(kāi)始移動(dòng)。現(xiàn)在使用兩種轉(zhuǎn)向齒輪的結(jié)構(gòu)，即齒輪齒條式結(jié)構(gòu)以及循環(huán)球式結(jié)構(gòu)。 現(xiàn)代汽車(chē)設(shè)計(jì)了對(duì)速度敏感的轉(zhuǎn)向結(jié)構(gòu)。因此當(dāng)汽車(chē)慢速行駛時(shí)需要較大的力才能使汽車(chē)轉(zhuǎn)向。于是在很多汽車(chē)上裝備了助力轉(zhuǎn)向裝置。 由于助力轉(zhuǎn)向裝置起了主要作用，所以轉(zhuǎn)向比降低了，這樣就能夠輕微轉(zhuǎn)動(dòng)方向盤(pán)使得汽車(chē)轉(zhuǎn)向。助力轉(zhuǎn)向齒輪類(lèi)似于標(biāo)準(zhǔn)的轉(zhuǎn)向齒輪。它有承壓面，液體壓力加在其上，以增加汽車(chē)駕駛員的轉(zhuǎn)向力。齒輪齒條式轉(zhuǎn)向結(jié)構(gòu)和循環(huán)球齒輪結(jié)構(gòu)都有了動(dòng)力輔助裝置。 轉(zhuǎn)向齒輪的動(dòng)力是由發(fā)動(dòng)機(jī)從動(dòng)泵提供的。該泵使動(dòng)力轉(zhuǎn)向液體流過(guò)一個(gè)由閥體控制的系統(tǒng)。該控制閥能感知汽車(chē)駕駛員的轉(zhuǎn)向力。把液體壓力加到轉(zhuǎn)向系統(tǒng)的承壓面上。該液體壓力承接了一些使汽車(chē)轉(zhuǎn)向的力。 現(xiàn)在汽車(chē)的轉(zhuǎn)向桿有很多個(gè)部件組成。它被用來(lái)分散、抵消汽車(chē)碰撞力以保護(hù)駕駛員的切身安全。在有些汽車(chē)上轉(zhuǎn)向桿還可以?xún)A斜和伸縮來(lái)調(diào)節(jié)方向盤(pán)的位置使駕駛員感覺(jué)更加舒適。為了減少駕駛員汽車(chē)被盜的機(jī)會(huì)，還安裝有一個(gè)轉(zhuǎn)向齒輪的保險(xiǎn)鎖。很多汽車(chē)還有一個(gè)變速器保險(xiǎn)鎖。因?yàn)樘幵隈{駛員很容易觸及的范圍內(nèi)，所以轉(zhuǎn)向桿上還可以帶有變速器換擋控制滑桿，轉(zhuǎn)向信號(hào)開(kāi)關(guān)，前大燈和變光開(kāi)關(guān)，刮水器開(kāi)關(guān)，緊急閃爍器開(kāi)關(guān)和速度控制器。 制動(dòng)系統(tǒng) 使用中的制動(dòng)器應(yīng)能起到制動(dòng)住車(chē)輛的作用。制動(dòng)器能使汽車(chē)滑行時(shí)能防止行駛速度過(guò)快，在斜坡上制動(dòng)時(shí)能將汽車(chē)停在適當(dāng)?shù)奈恢蒙?。汽?chē)剎車(chē)的設(shè)計(jì)應(yīng)使駕駛員能調(diào)節(jié)制動(dòng)力以控制汽車(chē)。汽車(chē)的控制不僅受懸架和轉(zhuǎn)向系統(tǒng)影響，而且也受汽車(chē)剎車(chē)影響。制動(dòng)系統(tǒng)的故障可導(dǎo)致汽車(chē)剎車(chē)時(shí)車(chē)輪滑脫。要修理懸梁系統(tǒng)，也可能需要將制動(dòng)系統(tǒng)的部件拆卸開(kāi)。為此本文將討論制動(dòng)系統(tǒng)。 制動(dòng)系統(tǒng)應(yīng)給予汽車(chē)駕駛員提供均勻平穩(wěn)的制動(dòng)力。剎車(chē)板上所需的力不應(yīng)太大，而使車(chē)輪不至于被瞬間剎死。為滿足這些汽車(chē)剎車(chē)的要求，對(duì)于汽車(chē)制動(dòng)已有了最低限度的剎車(chē)標(biāo)準(zhǔn)。 駕駛員通過(guò)機(jī)械裝置、真空和液壓裝置控制制動(dòng)力。制動(dòng)力是隨著附加在汽車(chē)剎車(chē)板上的踏板力的增加而增加的。這個(gè)力通過(guò)制動(dòng)系統(tǒng)的傳遞以把固定的汽車(chē)剎車(chē)片推壓到轉(zhuǎn)動(dòng)的制動(dòng)器表面上。當(dāng)它把動(dòng)能（運(yùn)動(dòng)的能量）轉(zhuǎn)化為熱能（熱）時(shí)，就使汽車(chē)減速。制動(dòng)量的最大值就產(chǎn)生于車(chē)輪被瞬間閘死而引起的輪胎在路面上滑動(dòng)之前。所以制動(dòng)量的最大值取決于輪胎和路面之間的附著力。當(dāng)輪胎在道路上滑動(dòng)時(shí)，制動(dòng)效果減弱，汽車(chē)的方向控制可能就不起作用了。 前剎車(chē)總成的固定構(gòu)件安裝在前懸架的轉(zhuǎn)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(chē)鼓或車(chē)盤(pán)隨車(chē)輪一起轉(zhuǎn)動(dòng)。 汽車(chē)的制動(dòng)盤(pán)剎車(chē)時(shí)：汽車(chē)制動(dòng)盤(pán)剎車(chē)有隨車(chē)輪一起轉(zhuǎn)動(dòng)的圓盤(pán)。它通常被稱(chēng)為汽車(chē)剎車(chē)轉(zhuǎn)子。在固定的卡鉗里的液壓控制的活塞被用來(lái)把汽車(chē)的剎車(chē)片加在轉(zhuǎn)子的汽車(chē)剎車(chē)表面上。汽車(chē)剎車(chē)片和轉(zhuǎn)子之間的摩擦力的大小會(huì)減慢或阻止車(chē)輪的轉(zhuǎn)動(dòng)。固定的卡鉗殼體使墊圈被壓在轉(zhuǎn)動(dòng)的汽車(chē)剎車(chē)盤(pán)上，使之不能轉(zhuǎn)動(dòng)。 汽車(chē)制動(dòng)盤(pán)剎車(chē)墊圈的運(yùn)動(dòng)與剎車(chē)轉(zhuǎn)子的表面垂直，這樣會(huì)使它們卡在轉(zhuǎn)子上減慢汽車(chē)的車(chē)輪運(yùn)動(dòng)?？ㄣQ壓的力與駕駛員加在汽車(chē)剎車(chē)板上的力成正比。 汽車(chē)制動(dòng)鼓剎車(chē)：汽車(chē)制動(dòng)鼓剎車(chē)使用帶有摩擦片的固定的內(nèi)脹式剎車(chē)塊。他們被安裝在轉(zhuǎn)動(dòng)的汽車(chē)剎車(chē)鼓內(nèi)側(cè)。汽車(chē)剎車(chē)鼓緊箍在輪胎總成和轂總成或輪軸法蘭之間。當(dāng)汽車(chē)剎車(chē)塊的直徑膨脹至使汽車(chē)剎車(chē)片與汽車(chē)剎車(chē)表面相接觸時(shí)，汽車(chē)剎車(chē)塊就減慢了汽車(chē)剎車(chē)鼓的轉(zhuǎn)動(dòng)。它是由液壓操縱的汽車(chē)剎車(chē)分泵來(lái)完成的。來(lái)自剎車(chē)總泵的流體壓力被施加到汽車(chē)剎車(chē)分泵上，使剎車(chē)分泵膨脹起來(lái)。汽車(chē)剎車(chē)分泵的膨脹使剎車(chē)塊通過(guò)機(jī)械連桿進(jìn)行移動(dòng)，把汽車(chē)剎車(chē)片壓到轉(zhuǎn)動(dòng)的剎車(chē)鼓上。當(dāng)汽車(chē)剎車(chē)鼓的轉(zhuǎn)動(dòng)速度減慢時(shí)，就起到了制動(dòng)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. ?