畢業(yè)設(shè)計(jì)(論 文)任務(wù)書課題名稱 輕型貨車（5+1）擋變速器設(shè)計(jì)（直接操縱、全部采用同步器換擋）系 別 汽車工程系專 業(yè) 班 級(jí) 學(xué) 號(hào)姓 名 指導(dǎo)教師 年 02 月 13 日教研室主任 年 02 月 13 日系 主 任 年 02 月 13 日年 2 月 13 日一、課題的主要內(nèi)容和基本要求：參數(shù):發(fā)動(dòng)機(jī) : =220 ； 車速： =90 ；額定轉(zhuǎn)速：n= 3200 max?M?NmaxVhK/RPM； 車輪滾動(dòng)半徑：R 01= 0.366 m ；汽車總質(zhì)量：4490 Kg ；爬坡度：30﹪ ；主減速比：i 0= 5.83 ；要求:采用中間軸式、全同步器換擋。本次設(shè)計(jì)要求：對(duì)各擋齒輪的接觸強(qiáng)度、彎曲應(yīng)力及軸的強(qiáng)度、剛度進(jìn)行校核計(jì)算。設(shè)計(jì)工作量:1、集資料、進(jìn)行方案論證、結(jié)構(gòu)分析，確定合理的結(jié)構(gòu)方案。2、選擇正確的參數(shù)，對(duì)變速器的強(qiáng)度及剛度進(jìn)行校核計(jì)算。3、三維建模，變速器結(jié)構(gòu)圖；繪 CAD 圖（A1）一張。4、設(shè)計(jì)中的計(jì)算要求編程，上機(jī)計(jì)算，打印程序、結(jié)果。5、英譯中大于 5000 字符（折合中文約大于 3000 字） 。 6、設(shè)計(jì)說明書應(yīng)包括：目錄、中、英文摘要、設(shè)計(jì)說明、方案論證、計(jì)算過程、結(jié)論、畢業(yè)設(shè)計(jì)完成情況的自我評(píng)價(jià)及其它說明。要求大于 1.2 萬字。二、進(jìn)度計(jì)劃與應(yīng)完成的工作：第四周：進(jìn)行方案論證。第五、六周：齒輪設(shè)計(jì)與校核（含編程計(jì)算）及各軸傳動(dòng)方案確定與各軸的定位。第七、八周：軸尺寸的確定，軸承、花鍵的選擇，軸及花鍵的校核，同步器的設(shè)計(jì)。第九、十、十一、十二周：完成三維設(shè)計(jì)數(shù)模及設(shè)計(jì)圖紙。第十三、十四周：整理完成說明書；進(jìn)行外文翻譯；檢查圖紙及設(shè)計(jì)說明書，訂正錯(cuò)誤。為答辯做好充分準(zhǔn)備。三、完成期限：2012、05、18四、主要參考文獻(xiàn)、資料：汽車構(gòu)造、汽車?yán)碚?、汽車設(shè)計(jì)、機(jī)械零件、材料力學(xué)，現(xiàn)代汽車設(shè)計(jì)手冊(cè)、機(jī)械零件設(shè)計(jì)手冊(cè)、汽車底盤圖冊(cè) 畢業(yè)設(shè)計(jì)（論文）說明書課題名稱：輕型貨車（5+1）擋變速器設(shè)計(jì)（直接操縱、全部采用同步器換擋）系 別： 汽車與交通學(xué)院 專 業(yè)：班 級(jí)：學(xué) 號(hào)：姓 名：指導(dǎo)教師：年 5 月 18 日摘 要本次輕型貨車變速器的設(shè)計(jì)，主要目的是檢驗(yàn)大學(xué)四年的學(xué)習(xí)成果。文中闡述了變速器的功用與設(shè)計(jì)要求，對(duì)該變速器進(jìn)行了了大量的調(diào)查研究，并進(jìn)行了初步的方案論證，根據(jù)設(shè)計(jì)要求選用中間軸式五檔變速器，其優(yōu)點(diǎn)：最高擋采用直接擋，傳遞扭矩效率高，齒輪和軸承磨損小，噪音小。中間軸采用旋轉(zhuǎn)式，中間軸上的全部斜齒輪的螺旋方向一律取為右旋，第一、第二軸上的斜齒輪取左旋。五個(gè)前進(jìn)擋和倒擋均采用鎖環(huán)式慣性同步器換擋，保證迅速、省力、無沖擊、無噪音換擋，與操作熟練程度無關(guān)，從而提高了加速性、經(jīng)濟(jì)性和行駛安全性。根據(jù)輕型貨車的要求，操縱機(jī)構(gòu)選用直接操縱。本文說明并論證了變速器主要參數(shù)的確定，齒輪幾何參數(shù)的計(jì)算、列表、齒輪材料的選擇、齒輪的強(qiáng)度計(jì)算、強(qiáng)度校核，軸的設(shè)計(jì)及強(qiáng)度剛度校核，軸的材料選擇，軸承的選擇，花鍵的選擇以及簡(jiǎn)單介紹了變速器的拆裝順序和對(duì)本次設(shè)計(jì)做出總結(jié)。關(guān)鍵詞：輕型貨車；變速器設(shè)計(jì)；中間軸式；倒擋ABSTRACTThe design of this light truck transmission, the main purpose is to test the results of four years of study in the university. This design explained the function of the function and design requirements, had the transmission a large number of surveys and studies, and conducted a preliminary studies program. According to the design requirement to choose a intermediate bearing type five gear transmission and its advantages are: the high grade adopts the direct, it is high in efficiency to transmit the torsion , the wearing and tearing of gears and axles is light .the intermediate shaft with rotary, The middle of all the helical gear shaft be taken as the right-hand screw direction, the first and second helical gear to take left. The five gears and reverse gear all use lock ring type inertia synchronizer shifted gears and ensure rapid, labor-saving, non-impact, noise-free transmission ,and operation of proficiency has nothing to do so as to enhance the car’s acceleration economy and road safety. According to the design requirements of the light truck ,the manipulation agencies use direct control. Noted and demonstrated that the transmission parameters, the calculations and the list of gear geometry parameters ,the gear material selection ,gear strength and strength check, the design of the shaft and stiffness and strength check ,shaft material selection, bearing selection, spline options .And briefly introduce the transmission disassembly sequence, as well as a summary of this design.KEY WORD: light truck；transmission design；intermediate bearing type；the reverse gear shaft 畢業(yè)設(shè)計(jì)（論文）附件資料課題名稱：輕型貨車（5+1）擋變速器設(shè)計(jì)（直接操縱、全部采用同步器換擋）系 別： 汽車與交通學(xué)院 專 業(yè)：班 級(jí)：學(xué) 號(hào)：姓 名：指導(dǎo)教師：目 錄第 1章 外文翻譯 .11.1中文譯文 .11.1.1設(shè)計(jì)構(gòu)思11.1.2歷史21.2英文原文 .41.2.1 Designs51.2.2 History5第 2章 方案論證 .82.1變速器的類型選擇 .82.1.1結(jié)構(gòu)工藝性82.1.2變速器的徑向尺寸92.1.3變速器齒輪的壽命92.1.4變速器的傳動(dòng)效率92.2倒擋的型式及布置方案 .92.3換擋的結(jié)構(gòu)型式及齒輪的安排 112.3.1換擋的結(jié)構(gòu)型式.112.3.2齒輪的安排.111第 1 章 外文翻譯1.1 中文譯文運(yùn)動(dòng)型多用途車運(yùn)動(dòng)型多用途車是一款裝有輕型貨車地盤的與旅行車相同的在市場(chǎng)上交易的交通工具。它常常裝備有四輪驅(qū)動(dòng)，是為了擁有越野能力以及符合其他的一些要求或者是在崎嶇路面行駛的能力。并不是所有的四輪驅(qū)動(dòng)的車輛都叫做 SUV。SUV 是包括具有拖拉性能的搭載乘客的敞篷小型載貨汽車以及具有貨運(yùn)空間的小型貨車或者加大的轎車。由于 SUV被考慮成為輕型載貨汽車和輕運(yùn)貨車共同享用一個(gè)技術(shù)平臺(tái)，在美國政策和能源保護(hù)法以及空氣潔凈法令這兩部法律條例下，與乘用車相比較它們被管理得比較松。從 2004年開始，美國環(huán)境保護(hù)局（EPA）開始像其他車輛一樣嚴(yán)格控制 SUV的尾氣排放標(biāo)準(zhǔn)。這個(gè)條款并不是適用于所有的國家地區(qū)。在北美之外的其他地區(qū)“越野車輛” ，“四輪驅(qū)動(dòng)”僅僅是用牌子來形容像“吉普” 、 “蘭德·路華”這樣子的車。然而，并不是所有的具有四輪驅(qū)動(dòng)能力的乘用車就是 SUV。越野車主要是為了越野使用而設(shè)計(jì)的一大類車輛。然而，SUV 的特征并不是為了普通大眾和媒體而設(shè)計(jì)制造的。盡管一些SUV擁有越野的能力，但是它們通常僅僅是扮演次要的角色，而且，這些 SUV通常沒有在兩輪驅(qū)動(dòng)與四輪驅(qū)動(dòng)高速檔的傳動(dòng)裝置的和四輪驅(qū)動(dòng)低速檔傳動(dòng)裝置的能力。當(dāng)汽車生產(chǎn)商出售 SUV時(shí)，利用廣告和給 SUV命名的方式來宣傳 SUV高超的技藝時(shí)，越來越多的 SUV在道路上和城市地區(qū)行駛。SUV在 90年代末和本世紀(jì)初大受歡迎，但是由于油價(jià)的上漲和經(jīng)濟(jì)的衰退 SUV的銷售額開始下降。傳統(tǒng)的卡車底盤的 SUV逐步的被交叉型的 SUV代替。交叉型的 SUV是一類使用更輕的汽車質(zhì)量和更好的燃油效率的汽車平臺(tái)，作為對(duì)運(yùn)動(dòng)型多用途車的許多苛刻要求的回復(fù)。1.1.1 設(shè)計(jì)構(gòu)思盡管 SUV的設(shè)計(jì)構(gòu)思多樣化，但是它擁有歷史上中型乘用車的與輕型貨車相似的框架車身和底盤。早期的 SUV主要是雙門型的和汽車頂部能夠移動(dòng)的。然而，根據(jù)消費(fèi)者的需求，SUV 市場(chǎng)向著四門型發(fā)展。到 2002年所有的全雙門型的 SUV已經(jīng)被市場(chǎng)淘汰。只有吉普牧馬人保留了全雙門型，盡管它仍然加入了四車門的變形體。全雙門型 SUV大部分都是遺留模型，并且后的設(shè)計(jì)流程，雙門型 SUV的銷售額不能夠保證它2的從新設(shè)計(jì)。在 2010年，隨著路虎覽勝和美人奴的發(fā)布，雙門型的 SUV的銷售有所增強(qiáng)， ，盡管這兩款車都是單片式車身汽車。大部分的 SUV都設(shè)計(jì)有發(fā)動(dòng)機(jī)室、結(jié)合乘客與貨物的載貨艙以及專用的汽車車尾行李箱，如旅行車的車身。大部分的中等運(yùn)動(dòng)型多用途車和全尺寸的 SUV都有三排的座位，以及在最后一排座位后面的載貨區(qū)。貨物柵欄通常調(diào)整到使其適應(yīng)載貨區(qū)以便在突發(fā)事件突然減速或者碰撞事件時(shí)用來保護(hù)無抵押貨物以免被損壞。盡管 SUV的設(shè)計(jì)多樣化，傳統(tǒng)意義上的 SUV是一種與輕型卡車擁有類似的框架和底盤的中型客運(yùn)車類，大多數(shù)的 SUV配備發(fā)送機(jī)艙，并兼具客運(yùn)與貨運(yùn)的車廂，并沒有專門一個(gè)專門的主干機(jī)構(gòu)，例如旅行車的車體。許多的中型和全尺寸的 SUV擁有三排座位以及在最后一排后面直接擁有貨物區(qū)域。SUV 以高離地間隙、方方正正的車體以及高 H點(diǎn)著稱。由于這種車身的高重心，可以使這種車型更容易翻轉(zhuǎn)。SUV 的車體最近變得更有空氣動(dòng)力，但是這種絕對(duì)形的尺寸和重量能保持小的耗油量。1.1.2 歷史1）起源最早的長軸距貨車式 SUV是雪弗蘭的 Carryall 郊區(qū)（1935） ，嘎斯-61（1938） ，威利斯吉普旅行車（1948） ，Pobeda M-72(嘎斯-M20/1955)，其中俄羅斯的引用信貸肯能是 SUV的第一個(gè)現(xiàn)代的 SUV，國際收割機(jī) Travelall(1953)，蘭德路華（路虎）系列二 109（1958）以及國際收割機(jī)考特 80（1961） 。其次是更加“現(xiàn)代”的吉普瓦貢爾（1963） ，國際收割機(jī)童軍二（1971） ，福特野馬（1966） ，豐田陸地巡航艦 FJ-55(1968)，雪弗蘭開拓者/GMC Jimmy(1969)，以及蘭德 路華（路虎）Range Rover(1970)。這實(shí)?際術(shù)語“運(yùn)動(dòng)型多用途車”直到二十世紀(jì)八十年代才收到人們的歡迎。許多這樣子的汽車在旅行車的年代被推向市場(chǎng)。根據(jù)在福特汽車博物館的運(yùn)輸館長 Robert Casey的介紹，現(xiàn)代理解這個(gè)術(shù)語吉普的切諾基才是真正的運(yùn)動(dòng)型多用途車。這是向市區(qū)的家庭推出用來代替?zhèn)鹘y(tǒng)汽車的一款 SUV（尤其是旅行車，在那時(shí)候相當(dāng)受歡迎的一類車型） 。這款吉普的切諾基擁有四輪驅(qū)動(dòng)系統(tǒng)在一個(gè)相當(dāng)容易操作的尺寸的空間里（與全尺寸的瓦格尼相比較） ，以及豪華舒適的內(nèi)部裝飾，就相當(dāng)于一輛旅行車。擁有引進(jìn)的更豪華的車型和更加強(qiáng)大的 4.0排量的發(fā)動(dòng)機(jī)，盡管汽油的價(jià)格上漲，切諾基的銷售額還是增加了，并且這個(gè)術(shù)語“運(yùn)動(dòng)型多用途車”首次被國家的出版社使用。成功的來臨使緊湊型的吉普-切諾基汽車改變了卡車的行業(yè)。在二十世紀(jì)七十年代公司燃油經(jīng)濟(jì)性標(biāo)準(zhǔn)（CAPE）被批準(zhǔn)通過，這是用來控制乘用車的燃油性的。汽車制造商通過銷售 SUV這種車輛來逃避這個(gè)標(biāo)準(zhǔn)。在過去的 25年里 SUV在誠實(shí)里得到了普及特別是在過去的十年里。因此，現(xiàn)代的 SUV擁有豪華車的3特點(diǎn)，并且一些交叉車模型還采用了降低懸架的高度以便使其適應(yīng)道路的行駛。Keith Bradsher解釋說為了增加 SUV的生產(chǎn)銷售，AMC 汽車公司對(duì)美國環(huán)境保護(hù)局（EPA）進(jìn)行了游說，讓其在 SUV的生產(chǎn)上放棄《美國空氣清潔法》 。隨后美國環(huán)境保護(hù)局指定 AMC公司的緊湊型的切諾基汽車就是一款輕型卡車， ，該公司能夠向每一個(gè)司機(jī)出售這款車。AMC 公司新型車型的成功影響了官方對(duì)立法的制定，導(dǎo)致了 SUV的熱潮，而當(dāng)時(shí)其他的汽車生產(chǎn)商通過向市場(chǎng)推廣他們自己的車型回應(yīng)切諾基搶走他們常規(guī)汽車的銷售額。2)普及在二十世紀(jì)末和二十一世紀(jì)初 SUV在美國、加拿大、和澳大利亞大受歡迎。美國的汽車制造商每銷售一輛 SUV就可以賺到 10000美元的利潤，而他們只是失去了在銷售小型汽車的幾百美元的利潤。例如：每銷售一輛福特 Excursion就可以凈賺 18000美元，而當(dāng)他們銷售一輛福克斯時(shí)他們卻沒有虧損除非買方選擇選項(xiàng)，這就導(dǎo)致了底特律的三大汽車制造商主要集中于生產(chǎn) SUV.小型汽車的銷售主要靠價(jià)格便宜和符合聯(lián)邦的平均燃用經(jīng)濟(jì)性標(biāo)準(zhǔn)來吸引年輕的買者。在美國和加拿大的相對(duì)比較高工資的汽車工會(huì)（汽車工人聯(lián)合會(huì)（UAW）和加拿大汽車工人工會(huì)（CAW） ） ，與低工資的在屬于美國工會(huì)的公司，像日本豐田公司，使美國汽車生產(chǎn)商制造小型汽車沒有利潤可賺。例如：在阿靈頓，德克薩斯州的美國通用汽車公司生產(chǎn)后輪驅(qū)動(dòng)的汽車，比如雪弗蘭-隨想曲、別克-路尊、凱迪拉克- Fleetwood Brougham被轉(zhuǎn)換成卡車和 SUV產(chǎn)品，終止了全尺寸家庭旅行車的生產(chǎn)和全面終止生產(chǎn)全尺寸車。由于美國三大汽車公司戰(zhàn)略決策的改變，許多長時(shí)間運(yùn)行的汽車比如：Ford Taurus、Buick Century和 Pontiac Grand Pix在產(chǎn)品的特點(diǎn)和外觀上（更倚重的快速的銷售而不是優(yōu)惠折扣價(jià)的刺激手段）將競(jìng)爭(zhēng)對(duì)手遠(yuǎn)遠(yuǎn)的平拋在了后面，有些已經(jīng)被停止使用。高速公路保險(xiǎn)協(xié)會(huì)的汽車碰撞試驗(yàn)表露 SUV探險(xiǎn)者碰撞福特?？怂沟膫Τ潭取Ｙ徺I者主要是被 SUV大的車身空間、較高的懸架高度和感知的安全性。全尺寸的SUV常常提供有自己的產(chǎn)品特征，比如：三排座椅有效的代替了全尺寸旅行車和小型貨車。貨車常常被看成是過時(shí)的。此外，全尺寸 SUV比傳統(tǒng)的汽車擁有較大的牽引能力，并且能夠拖拉拖車或者旅行拖車和船。增加了汽車的離地凈高度在下大雪的時(shí)候可以很好的行駛。正是二十世紀(jì)九十年代低的燃油價(jià)格很好的促進(jìn)了運(yùn)營成本的降低。SUV的外觀真正的說明了它們的普及，尤其是在女性之間，她們?cè)诿绹鴺?gòu)成了 SUV一半以上的擁有者。在美國 SUV是女性選擇的最受歡迎的汽車之一。社會(huì)科學(xué)家通過大受歡迎的民間傳說比如都市傳奇來舉例說明為什么市場(chǎng)能夠利用 SUV提供的力量和安全感覺吸引人們的眼球。比如：流行的故事包括母親通過與持械搶劫者斗爭(zhēng)來拯救家庭和其他通過奪取越野汽車的事件。在澳大利亞，SUV 銷售額的增加是因?yàn)?SUV比轎車有更加低的進(jìn)口稅，這樣與其他相同類型的箱式進(jìn)口轎車先比他們花費(fèi)更少的錢就可以買到 SUV。然而，這間隙將會(huì)逐4漸的減小，在 2010年汽車的進(jìn)口關(guān)稅降低了 5%已經(jīng)和 SUV相稱。由于原油價(jià)格的提高和經(jīng)濟(jì)的衰退，在 2000中期年代 SUV和其他輕型貨車的銷售額開始下降。在 2008年的 6月美國通用公司宣布計(jì)劃建立四個(gè)卡車和 SUV的工廠，包括 Oshawa Truck Assembly。由于緊隨而來的燃油價(jià)格的提高，公司將會(huì)減少大型車輛的引進(jìn)。在二十世紀(jì)中后期公司的經(jīng)營模式主要集中于 SUV和輕型卡車，以生產(chǎn)燃油經(jīng)濟(jì)的緊湊型車型和中型車因銷售額的下降而被底特律三大汽車制造商責(zé)備。與他們的競(jìng)爭(zhēng)者日本汽車公司相比這三大巨頭是比較慢才能適應(yīng)生產(chǎn)小型汽車去適應(yīng)生產(chǎn)發(fā)展的要求，這是由于這些不能夠轉(zhuǎn)變的生產(chǎn)設(shè)備，使其對(duì)生產(chǎn)小型車沒有利潤。1.2 英文原文Sport utility vehicleA sport utility vehicle (SUV) is a generic marketing term for a vehicle similar to a station wagon, but built on a light-truck chassis. It is usually equipped with four-wheel drive for on- or off-road ability, and with some pretension or ability to be used as an off-road vehicle. Not all four-wheel-drive vehicles are termed as SUV. Some SUVs include the towing capacity of a pickup truck with the passenger-carrying space of a minivan or large sedan. Since SUVs are considered light trucks and often share the same platform with pick-up trucks, they were regulated less strictly than passenger cars under the two laws in the United States, the Energy Policy and Conservation Act for fuel economy, and the Clean Air Act for emissions. Starting in 2004, the United States Environmental Protection Agency (EPA) began to hold sport utility vehicles to the same tailpipe emissions standards as cars.The term is not used in all countries, and outside North America the terms “off-road vehicle“, “four-wheel drive“ or “four-by-four“ (abbreviated to “4WD“ or “4x4“) or simply use of the brand name to describe the vehicle like “Jeep“ or “Land Rover“ are more common. However, not all SUVs have four-wheel drive capabilities. Conversely, not all four-wheel-drive passenger vehicles are SUVs. Off-road vehicle is a broad class of vehicles, built primarily for off-road use. However, this distinction is often not made by the general public and the media. Although some SUVs have off-road capabilities, they often play only a secondary role, and SUVs often do not have the ability to switch among two-wheel and four-wheel-drive high gearing and four-wheel-drive low gearing. While auto makers tout an SUV's off-road prowess with advertising and naming, the daily use of SUVs is largely on paved roads and in urban areas.Popular in the late-1990s and early-2000s, SUVs sales have since declined due to high oil prices and a declining economy. The traditional truck-based SUV is gradually being 5supplanted by the crossover SUV, which uses an automobile platform for lighter weight and better fuel efficiency, as a response to much of the criticism of sport utility vehicles.1.2.1 DesignsAlthough designs vary, SUVs have historically been mid-size passenger vehicles with a body-on-frame chassis similar to that found on light trucks. Early SUVs were mostly two-door models, and were available with removable tops. However, consumer demand pushed the SUV market towards four doors, by 2002 all full-size two-door SUVs were gone from the market. Only the Jeep Wrangler remained as a two-door SUV, although it was also joined by a four-door variant. Two-door SUVs were mostly carry-over models, and their sales were not viable enough to warrant a redesign at the end of their design cycle. Two-door SUV models increased in the 2010s with the release of the Range Rover Evoque and the Nissan Murano convertible, although both vehicles are unibody.Most SUVs are designed with an engine compartment, a combined passenger and cargo compartment, and no dedicated trunk such as in a station wagon body. Most mid-size and full-size SUVs have three rows of seats with a cargo area directly behind the last row of seats. Cargo barriers are often fitted to the cargo area to protect the vehicles occupants from injury from unsecured cargo in the event of sudden deceleration or collision.SUVs are known for high ground clearance, upright, boxy body, and high H-point. This can make them more likely to roll over due to their high center of gravity. Bodies of SUVs have recently become more aerodynamic, but the sheer size and weight keeps their fuel economy poor.1.2.2 History1）OriginsEarly SUVs were descendants from commercial and military vehicles such as the World War II Jeep nd Land Rover. SUVs have been popular for many years with rural buyers due to their off-road capabilities.The earliest examples of longer-wheelbase wagon-type SUVs were the Chevrolet Carryall Suburban (1935, RWD only), GAZ-61 (1938, 4x4), Willys Jeep Wagon (1948), Pobeda M-72 (GAZ-M20/1955), which Russian references credit as possibly being the first modern SUV (with unitary body rather than body-on-frame), International Harvester Travelall (1953), Land Rover Series II 109 (1958), and the International Harvester Scout 80 (1961). These were followed by the more 'modern' Jeep Wagoneer (1963), International Harvester 6Scout II (1971), Ford Bronco (1966), Toyota Land Cruiser FJ-55 (1968), the Chevrolet Blazer / GMC Jimmy (1969), and the Land Rover Range Rover (1970). The actual term “sport utility vehicle“ did not come into wide popular usage until the late 1980s; many of these vehicles were marketed during their era as station wagons.According to the transportation curator at the Henry Ford Museum, Robert Casey, the Jeep Cherokee (XJ) was the first true sport utility vehicle in the modern understanding of the term. Marketed to urban families as a substitute for a traditional car (and especially station wagons, which were still fairly popular at the time), the Chrerokee had four-wheel drive in a more manageable size (compared to the full-size Wagoneer), as well as a plush interior resembling a station wagon. With the introduction of more luxurious models and a much more powerful 4-liter engine, sales of the Cherokee increased even higher as the price of gasoline fell, and the term “sport utility vehicle“ began to be used in the national press for the first time. “The advent and immediate success of AMC/Jeep's compact four-door Cherokee turned the truck industry upside down.“ The corporate average fuel economy (CAFE) standard was ratified in the 1970s to regulate the fuel economy of passenger vehicles. Car manufacturers evaded the regulation by selling SUVs as work vehicles. The popularity of SUV increased among urban drivers in the last 25 years, and particularly in the last decade. Consequently, modern SUVs are available with luxury vehicle features, and some crossover models adopt lower ride heights to accommodate on-road driving.Keith Bradsher explained the rise of the SUV with American Motors' (AMC) lobbying the United States Environmental Protection Agency (EPA) for a waiver of the United States Clean Air Act. The EPA subsequently designated AMC's compact Cherokee as a “l(fā)ight truck“, and the company marketed the vehicle to everyday drivers. AMC's effort to affect rulemaking changing the official definition of their new model then led to the SUV boom when other auto makers marketed their own models in response to the Cherokee taking sales from their regular cars. 2）PopularitySUVs became popular in the United States, Canada, and Australia in the 1990s and early-2000s. U.S. automakers could enjoy profit margins of $10,000 per SUV, while losing a few hundred dollars on a compact car. For example, the Ford Excursion could net the company $18,000, while they could not break even with the Ford Focus unless the buyer chose options, leading Detroit's big three automakers to focus on SUVs over small cars.Small cars were sold mainly to attract young buyers with inexpensive options and to increase their fleet average fuel economies to meet federal standards. The relatively high wages of unionized auto workers in the U.S. and Canada (members of the UAW and CAW, 7respectively), compared to the low wages of non-union workers at non-U.S. companies like Toyota, made it unprofitable for the U.S. auto makers to build small cars. For example, the General Motors factory in Arlington, Texas where rear-wheel-drive cars were built, such as the Chevrolet Caprice, Buick Roadmaster, and Cadillac Fleetwood Brougham was converted to truck and SUV production, putting an end to full-size family station wagon and overall terminating production of rear-wheel drive full-size cars. Due to the shift in the Big Three's strategy, many long-running cars like the Ford Taurus, Buick Century and Pontiac Grand Prix fell behind their Japanese competitors in features and image (relying more on fleet sales instead of retail and/or heavy incentive discounts); some were discontinued. Buyers were drawn to SUVs' large cabins, higher ride height, and perceived safety. Full-size SUVs often offered features such as three-row seating, to effectively replace full-size station wagons and minivans. Wagons were seen as old-fashioned. Additionally, full-size SUVs have greater towing capabilities than conventional cars, and can haul trailers, travel trailers (caravans) and boats. Increased ground clearance is useful in climates with heavy snowfall. The very low oil prices of the 1990s helped to keep down running costs. The SUV's image of utility may partly explain its popularity, not least among some women, who constitute more than half of SUV drivers in the U.S. The SUV was one of the most popular choices of vehicle for female drivers in the U.S. Social scientists have drawn on popular folklore such as urban legends to illustrate how marketers have been able to capitalize on the feelings of strength and security offered by SUVs. Popular tales include narratives where mothers save the family from armed robbery and other incidents by taking the automobile off road, for example.In Australia, SUV sales were helped by the fact that SUVs had much lower import duty than passengers cars did, so that they cost less than similarly equipped imported sedans. However, this gap was gradually narrowed, and in January 2010 the import duty on cars was lowered to match the 5 percent duty on SUVs. Sales of SUVs and other light trucks fell in the mid-2000s because of high oil prices and declining economy. In June 2008, General Motors announced plans to close four truck and SUV plants, including the Oshawa Truck Assembly. The company cited decreased sales of large vehicles in the wake of rising fuel prices. The business model of focusing on SUVs and light trucks, at the expense of more fuel-efficient compact and midsized cars, is blamed for declining sales and profits among Detroit's Big Three automakers since the mid-late 2000s. The Big Three were slower to adapt than their Japanese rivals in producing small cars to meet growing demand due to inflexible manufacturing facilities, which made it unprofitable to build small cars. 8第 2 章 方案論證2.1 變速器的類型選擇現(xiàn)代汽車多采用三軸式變速器，而發(fā)動(dòng)機(jī)前置前輪驅(qū)動(dòng)的轎車，若變速器的傳動(dòng)比小，則采用二軸式變速器。如圖 1-1和 1-2分別為兩軸式和三軸式變速器的示意圖。在設(shè)計(jì)時(shí)，究竟采用哪一種方案，除了汽車總布置的要求外，主要考慮以下四個(gè)方面：圖 2-1 兩軸式變速器示意圖圖 2-2 三軸式變速器示意圖92.1.1 結(jié)構(gòu)工藝性兩軸式變速器輸出軸與主減速器主動(dòng)齒輪做成一體，當(dāng)發(fā)動(dòng)機(jī)縱置時(shí)，主減速器可用螺旋圓錐齒輪或雙曲面齒輪，而發(fā)動(dòng)機(jī)橫置時(shí)用圓柱齒輪，因而簡(jiǎn)化了制造工藝。2.1.2 變速器的徑向尺寸兩軸式變速器的前進(jìn)擋均為一堆齒輪副，而三軸式變速器則有兩隊(duì)齒輪副。因此，對(duì)于相同的傳動(dòng)比要求，三軸式變速器的徑向尺寸可以比兩軸式變速器小得多。2.1.3 變速器齒輪的壽命 兩軸式變速器的低檔齒輪副大小相差懸殊，小齒輪工作循環(huán)次數(shù)比大齒輪要高得多，因此，小齒輪工作壽命比大齒輪要短。三軸式變速器的各前進(jìn)檔均為常嚙合齒輪傳動(dòng)，大小齒輪的徑向尺寸相差較小，因此壽命比較接近。在直接檔時(shí)，齒輪只是空轉(zhuǎn)，不影響齒輪壽命。2.1.4 變速器的傳動(dòng)效率兩軸式變速器，雖然可以有等于 1的傳動(dòng)比，但是仍要有一對(duì)齒輪傳動(dòng)，因而有功率損失。而三軸式變速器，可以將輸入軸和輸出軸直接相連，得到直接檔，因而傳動(dòng)效率高，磨損小，噪聲也較小。 轎車，尤其是微型汽車，采用兩軸式變速器比較多，這樣可將變速器和主傳動(dòng)器組成一個(gè)整體，使傳動(dòng)系的結(jié)構(gòu)緊湊，汽車得到較大的有效空間，便于汽車的總體布置。因此，近年來在歐洲的轎車中采用得比較多。而中、重型載貨汽車則多采用三軸式變速器。這次設(shè)計(jì)的變速器是輕型貨車使用，所以采用三軸式變速器2.2 倒擋的型式及布置方案與前進(jìn)擋位比較，倒擋使用率不高，而且都是在停車狀態(tài)下實(shí)現(xiàn)換擋，故多數(shù)方案均采用直齒滑動(dòng)齒輪方式換倒擋。為實(shí)現(xiàn)倒檔傳動(dòng)，有些方案利用在中間軸和第二軸上的齒輪傳動(dòng)路線中加入一個(gè)中間傳動(dòng)齒輪的方案；也有利用兩個(gè)聯(lián)體齒輪的方案。前者雖然結(jié)構(gòu)簡(jiǎn)單，但是中間傳動(dòng)齒輪的輪齒是在最不利的正、負(fù)交替對(duì)稱變化的彎10曲應(yīng)力狀態(tài)下工作；而后者是在較為有利的單向循環(huán)彎曲應(yīng)力狀態(tài)下工作，并使倒檔傳動(dòng)比略有增加。也有少數(shù)變速器采用結(jié)構(gòu)復(fù)雜和使成本增加的嚙合套或同步器方案換入倒檔。常見的倒擋結(jié)構(gòu)方案有以下幾種：方案 1.（如圖 2-3a）所示）在前進(jìn)檔的傳動(dòng)路線中，加入一個(gè)傳動(dòng)，使結(jié)構(gòu)簡(jiǎn)單，但齒輪處于正負(fù)交替對(duì)稱變化的彎曲應(yīng)力狀態(tài)下工作。此方案廣泛用于轎車和輕型貨車的四檔全同步器式變速器中。方案 2.（如圖 2-3b）所示）此方案的優(yōu)點(diǎn)是換倒擋時(shí)利用了中間軸上一檔齒輪，因而縮短了中間軸的長度，但換檔時(shí)要求有兩對(duì)齒輪同時(shí)進(jìn)入嚙合，致使換檔困難。某些輕型貨車四檔變速器采用此方案。方案 3.（如圖 2-3c）所示）此方案能獲得較大的倒檔傳動(dòng)比，突出的缺點(diǎn)是換檔程序不合理。方案 4.（如圖 2-3d）所示）此方案針對(duì)前者的缺點(diǎn)作了修改，因而經(jīng)常在貨車變速器中使用。方案 5.（如圖 2-3e）所示）此方案中，將中間軸上一檔和倒檔齒輪做成一體，將其齒體、寬加大，因而縮短了一些長度。方案 6.（如圖 2-3f）所示）此方案中，采用了全部齒輪副均為常嚙合齒輪，換檔方便。方案 7.（如圖 2-3g）所示）為了充分利用空間，縮短變速器軸向長度，有些貨車采用此方案，其缺點(diǎn)是一檔和倒檔得各用一根變速器撥叉軸，使變速器上蓋中的操縱機(jī)構(gòu)復(fù)雜一些，一般3、4、5、6、7 五種方案用于五檔變速器。根據(jù)需要此次設(shè)計(jì)用 f方案。換擋更輕松方便。11圖 2-3 倒檔布置方案2.3 換擋的結(jié)構(gòu)型式及齒輪的安排2.3.1 換擋的結(jié)構(gòu)型式變速器換擋結(jié)構(gòu)型式有直齒滑動(dòng)齒輪，嚙合套和同步器換擋三種。1) 滑動(dòng)齒輪換擋通常是采用滑動(dòng)直齒輪換檔，但也有采用滑動(dòng)斜齒輪換檔的。滑動(dòng)直齒輪換檔的優(yōu)點(diǎn)是結(jié)構(gòu)簡(jiǎn)單、緊湊、容易制造。缺點(diǎn)是換檔時(shí)齒端面承受很大的沖擊會(huì)導(dǎo)致齒輪過早損壞，并且直齒輪工作噪聲大，所以這種換檔方式一般僅用在一檔和倒檔上。2) 嚙合套換擋用嚙合套換檔，可以將結(jié)構(gòu)為某傳動(dòng)比的一對(duì)齒輪，制造成常嚙合的斜齒輪。用嚙合套換檔，因同時(shí)承受換檔沖擊載荷的接合齒齒數(shù)多，而輪齒又不參與換檔，因此它們都不會(huì)過早損壞，但是不能消除換檔沖擊，所以仍要求駕駛員有熟練的操作技術(shù)。此外，因增設(shè)了嚙合套和常嚙合齒輪，使變速器的軸向尺寸和旋轉(zhuǎn)部分的總慣量增大。因此，這種換檔方法目前只在某些要求不高的檔位及重型貨車變速器上使用。這是因?yàn)橹匦拓涇嚈n位間的公比較小，要求換檔手感強(qiáng)，而且在這種車型上又不宜使用同步器（壽命太短，維修不便） 。3) 同步器換擋現(xiàn)在大多數(shù)汽車的變速器都采用同步器換檔。使用同步器能保證迅速、無沖擊、12無噪聲換擋，與操作技術(shù)熟練程度無關(guān)，從而提高了汽車的加速性、經(jīng)濟(jì)性和行駛安全性。同上述兩種換檔方法相比，雖然它有結(jié)構(gòu)復(fù)雜、制造精度要求高、軸向尺寸大、同步環(huán)使用壽命短等缺點(diǎn)，但仍然得到廣泛應(yīng)用。近年來，由于同步器廣泛使用，壽命問題已得到基本解決。上述三種換擋方案，可同時(shí)用在同一變速器中的不同檔位上，一般倒檔和一檔采用結(jié)構(gòu)較簡(jiǎn)單的滑動(dòng)直齒輪或嚙合套的形式，對(duì)于常用的高檔位則采用同步器或嚙合套。本次設(shè)計(jì)的變速器將采用全部同步器變速器。2.3.2 齒輪的安排各齒輪副的相對(duì)位置，對(duì)于整個(gè)變速器的結(jié)構(gòu)布置有很大的影響。各檔位的安排，應(yīng)考慮以下四個(gè)方面的要求：1) 整車總布置根據(jù)整車的總布置，對(duì)變速器輸入軸與輸出軸的相對(duì)位置和變速器的輪廓形狀以及換擋機(jī)構(gòu)提出要求。2) 駕駛員的使用習(xí)慣有人認(rèn)為人們習(xí)慣于按檔的高低順序，由左到右或由右到左排列來換擋，如圖 2-4b和 c。但是也有人認(rèn)為應(yīng)該將常用檔放在中間位置，而將不常用的低檔放在兩邊，如圖 2-5e。值得注意的是倒檔，雖然它是平常換擋序列之外的一個(gè)特殊檔位，然而卻是決定序列組合方案的重要環(huán)節(jié)。例如在四檔變速器中采用的基本序列組合方案有三種，見圖 2-4。其中 b和 c是倒檔與序列不結(jié)合的方案，即掛檔時(shí)，需先換位再掛倒檔。五檔變速器采用的基本方案有五種，如圖 2-5所示。其中 a和 d是倒檔與序列相結(jié)合的方案。按習(xí)慣，倒檔最好與序列不結(jié)合。否則，從安全考慮，將倒檔與一檔放在一起較好。在五檔變速器中，倒檔與序列結(jié)合與不結(jié)合兩者比較，前者在結(jié)構(gòu)上可省去一個(gè)撥叉和一根變速滑桿，見圖 1-5a；后者如布置適當(dāng)，則可使變速器的軸向長度縮短。13圖 2-4 四擋變速器擋位序列組合的三種方案圖 2-5 五擋變速器擋位序列組合的五種方案根據(jù)以上的要求，本次設(shè)計(jì)的檔擋位布置方案如圖 2-6所示。14圖 2-6 傳動(dòng)方案3) 提高平均傳動(dòng)效率為提高平均傳動(dòng)效率，在三軸式變速器中，普遍采用具有直接擋的傳動(dòng)方案，并盡可能地將使用時(shí)間最多的檔位設(shè)計(jì)成直接擋。4) 改善齒輪受載狀況各檔齒輪在變速器中的位置安排，應(yīng)考慮齒輪的受載狀況。承受載荷大的低檔齒輪，一般安置在離軸承較近的地方，以減小軸的變形，使齒輪的重疊系數(shù)不致下降過多。變速器齒輪主要是因接觸應(yīng)力過高而造成表面點(diǎn)蝕損壞，因此將高檔齒輪安排在離兩支承較遠(yuǎn)處較好。該處因軸的變形而引起齒輪的偏轉(zhuǎn)角較小，故齒輪的偏載也小。本次設(shè)計(jì)傳動(dòng)方案如圖 1-6傳動(dòng)方案 傳動(dòng)路線：Ⅰ檔：一軸→1→2→中間軸→12→11→9、11 齒輪間的同步器→二軸→輸出Ⅱ檔：一軸→1→2→中間軸→8→7→5、7 齒輪間的同步器→二軸→輸出Ⅲ檔：一軸→1→2→中間軸→6→5→5、7 齒輪間的同步器→二軸→輸出Ⅳ檔：一軸→1→2→中間軸→4→3→1、3 齒輪間的同步器→二軸→輸出Ⅴ檔：一軸→1→1、3 齒輪間的同步器→二軸→輸出R檔：一軸→1→2→中間軸→13→10→9→9、11 齒輪間的同步器→二軸→輸出圖 2-7 傳動(dòng)方案15