汽車(chē)專(zhuān)業(yè)畢業(yè)設(shè)計(jì)--外文翻譯

1、汽車(chē)的基本機(jī)械機(jī)構(gòu)汽車(chē)工業(yè)是一種迅速發(fā)展的工業(yè)。從十八世紀(jì)后期第一輛汽車(chē)出現(xiàn)在公路上 后，這一工業(yè)便迅猛發(fā)展起來(lái)。如今全世界成千上萬(wàn)的工廠生產(chǎn)著各種各樣的汽 車(chē)。汽車(chē)行業(yè)也匯聚了千千萬(wàn)萬(wàn)的人。汽車(chē)發(fā)動(dòng)機(jī)廣泛地應(yīng)用于配有巨大動(dòng)力的 機(jī)械屮，如農(nóng)業(yè)、建筑業(yè)、制造業(yè)。不同類(lèi)型的小型發(fā)動(dòng)機(jī)也應(yīng)用于植草機(jī)、動(dòng) 力鋸、除雪機(jī)等類(lèi)似的設(shè)備中。汽車(chē)行業(yè)是一個(gè)發(fā)展著的、需求著的行業(yè)，似乎 永遠(yuǎn)找不到它的盡頭和飽和點(diǎn)。汽車(chē)、運(yùn)輸工具、發(fā)動(dòng)機(jī)有著巨大的需求量。這 一行業(yè)同樣需要受過(guò)鍛煉的、有經(jīng)驗(yàn)的精英，來(lái)診斷這些機(jī)動(dòng)車(chē)倆的故障、修理 和更新機(jī)動(dòng)車(chē)的零件、變速器、推動(dòng)軸、差分器、車(chē)軸、操縱系統(tǒng)、剎車(chē)系統(tǒng)、 暫停部件、

2、空調(diào)裝置、發(fā)熱器、機(jī)身以及玻璃制造等。汽車(chē)由五個(gè)基木的機(jī)械機(jī)構(gòu)或部件組成。它們是：（1）發(fā)動(dòng)機(jī)，它是動(dòng)力的源泉，包括燃料、潤(rùn)滑劑、冷卻和電氣系統(tǒng)。（2）框架，它支持發(fā)動(dòng)機(jī)、車(chē)輪、操縱和剎車(chē)系統(tǒng)，以及機(jī)身。（3）傳動(dòng)系，它將來(lái)自發(fā)動(dòng)機(jī)的動(dòng)力（經(jīng)過(guò)離合器、調(diào)速器、傳動(dòng)軸、差分器和車(chē)軸）傳送到車(chē)輪。（4）機(jī)身。（5）機(jī)身附件，它包括加熱器、燈光、擋風(fēng)玻璃擦等等。發(fā)動(dòng)機(jī)是使得汽車(chē)運(yùn)行的動(dòng)力源泉。它通常叫做一個(gè)內(nèi)置的燃燒發(fā)動(dòng)機(jī)， 因?yàn)槠褪窃诎l(fā)動(dòng)機(jī)氣缸或燃燒腔內(nèi)被燃燒的。這是相對(duì)于外置的發(fā)動(dòng)機(jī)而言的 （如蒸汽發(fā)動(dòng)機(jī)），其燃燒發(fā)生在發(fā)動(dòng)機(jī)的外部。發(fā)動(dòng)機(jī)氣缸內(nèi)的汽油的燃燒產(chǎn) 生了動(dòng)力。然后動(dòng)力經(jīng)過(guò)傳動(dòng)系傳送

3、到發(fā)動(dòng)機(jī)再到車(chē)輪，這樣車(chē)輪轉(zhuǎn)動(dòng)，汽車(chē)便 開(kāi)始運(yùn)行。在動(dòng)力產(chǎn)生的過(guò)程中燃料系統(tǒng)起著重要的作用，因?yàn)樗o發(fā)動(dòng)機(jī)氣缸提供汽 油。在每一個(gè)發(fā)動(dòng)機(jī)氣缸里，蒸發(fā)岀來(lái)的汽油和空氣組成的混合體進(jìn)入氣缸，活 塞推進(jìn)氣缸，壓縮混合體，然后電火花點(diǎn)燃?jí)嚎s混合體，這樣活塞被迫向下。當(dāng) 然，在發(fā)動(dòng)機(jī)內(nèi)，活塞沒(méi)有完全推到氣缸外面，而是隨著混合體的燃燒，在氣缸 內(nèi)簡(jiǎn)單地來(lái)回移動(dòng)。在汽車(chē)車(chē)輪能夠轉(zhuǎn)動(dòng)之前，活塞的線性運(yùn)動(dòng)必須轉(zhuǎn)變成旋轉(zhuǎn) 運(yùn)動(dòng)。發(fā)動(dòng)機(jī)機(jī)軸上的連桿和曲柄實(shí)現(xiàn)了這一轉(zhuǎn)變。閥門(mén)將燃燒過(guò)的汽油蒸氣送出氣缸外面，同時(shí)把汽油蒸氣和空氣新鮮可燃混 合氣送入氣缸。當(dāng)他們被關(guān)閉或固定時(shí)（也就是推到端口上），端口被封閉，這 樣氣體不

4、能流通到端口。當(dāng)他們被打開(kāi)時(shí)，氣體可以流通到端口。閥門(mén)是通過(guò)發(fā)動(dòng)凸輪軸上的凸輪被打開(kāi)的。凸輪有一個(gè)最高點(diǎn)，或圓形突出 部分；每次當(dāng)凸輪轉(zhuǎn)動(dòng)時(shí)，突出部分在氣門(mén)挺桿之下，使得挺桿向上。挺桿將這 個(gè)向上的運(yùn)動(dòng)傳動(dòng)到推桿再傳送到搖桿臂。搖桿臂在它的支撐體上轉(zhuǎn)動(dòng)并在閥桿 上推下去，使得閥移到低處，也就是說(shuō)閥被打開(kāi)了。當(dāng)凸輪轉(zhuǎn)動(dòng)得足夠使突出部 分移出挺桿z下時(shí)，承重的閥門(mén)彈簧將閥門(mén)退回到自己的位置。彈簧被彈簧座和 鎖附在閥桿的下端。在發(fā)動(dòng)機(jī)凸輪軸上每個(gè)閥門(mén)都有一個(gè)凸輪（每個(gè)氣缸兩個(gè)凸 輪）。凸輪軸通過(guò)齒輪或鏈條齒和齒條受到機(jī)軸的驅(qū)動(dòng)。如果整個(gè)循環(huán)過(guò)程需耍四次活塞運(yùn)動(dòng)，那么該發(fā)動(dòng)機(jī)就叫做四沖程發(fā)動(dòng)機(jī), 或四

5、行程發(fā)動(dòng)機(jī)。這四個(gè)行程是輸入、壓縮、發(fā)動(dòng)、和排氣。在輸入行程時(shí)，進(jìn)氣閥是被打開(kāi)的，活塞受到機(jī)軸旋轉(zhuǎn)的推動(dòng)，移到下面。 活塞的這個(gè)移動(dòng)引起了氣缸內(nèi)的局部的真空，同時(shí)空氣通過(guò)進(jìn)氣閥推進(jìn)氣缸，以 填補(bǔ)該真空。當(dāng)空氣向氣缸移動(dòng)時(shí)，它必須經(jīng)過(guò)氣化器。那里充滿了汽油蒸氣。 因此當(dāng)活塞在輸入端移至下端時(shí)進(jìn)入氣缸的是空氣和汽油蒸氣的混合體。當(dāng)活塞在進(jìn)口端移到下止點(diǎn)時(shí)，進(jìn)氣閥關(guān)閉。控制著進(jìn)氣閥的凸輪的突出部 分已經(jīng)從閥門(mén)下面移走。因?yàn)榱硪粋€(gè)閥門(mén)也是關(guān)閉的，氣缸的上端被關(guān)閉?，F(xiàn)在， 當(dāng)轉(zhuǎn)動(dòng)著的機(jī)軸將閥門(mén)推上時(shí)，已經(jīng)進(jìn)入氣缸的空氣和汽油蒸氣混合體被壓縮。 直到活塞被推到上止點(diǎn)吋，氣體被壓縮成原來(lái)的七分之一或八分之一

6、。這就類(lèi)似 一加侖的空氣被壓所成一品托。究其原因是由于氣缸內(nèi)部的高壓。在壓縮行程，當(dāng)活塞到達(dá)上止點(diǎn)時(shí)，氣缸火花塞產(chǎn)生一個(gè)電火花?；鸹ㄈ?質(zhì)上是兩個(gè)粗鋼絲電極?；鸹ㄓ牲c(diǎn)火系統(tǒng)產(chǎn)生。它點(diǎn)燃了壓縮的空氣和汽油蒸氣 混合體。由于高壓和高溫，發(fā)生了急劇的燃燒。此時(shí)，活塞頂端向下的壓力達(dá)到 兩噸。這個(gè)巨大的推力使得活塞向下，同時(shí)巨大的沖力通過(guò)連桿和曲柄傳送到機(jī) 軸。在動(dòng)力行程，由于汽油蒸氣的燃燒使得活塞受迫。當(dāng)活塞達(dá)到下止點(diǎn)時(shí)， 排氣閥被打開(kāi)。這吋，活塞又一次被返冋，它推動(dòng)氣缸內(nèi)被燃燒過(guò)的氣體。到活 塞到達(dá)上止點(diǎn)時(shí)，氣缸內(nèi)被燃燒過(guò)的氣體被清除掉。排氣閥關(guān)閉，進(jìn)氣閥開(kāi)啟。 活塞在下一個(gè)輸入行程時(shí)再次被返回

7、。發(fā)動(dòng)機(jī)運(yùn)行時(shí)，這四個(gè)行程持續(xù)地重復(fù)著。離合器是一種摩擦裝置，它用于從從動(dòng)機(jī)構(gòu)中聯(lián)合和拆分驅(qū)動(dòng)力。在汽車(chē)的 應(yīng)用中，它用于與發(fā)動(dòng)機(jī)調(diào)速輪相連，以提供發(fā)動(dòng)機(jī)和手工傳送之間的平滑結(jié)合 和正常脫離。因此隨著發(fā)動(dòng)機(jī)速度的降低，需要漸進(jìn)裝載的應(yīng)用，以獲得一個(gè)合理的和舒 適的啟動(dòng)。在裝配有手工傳動(dòng)的汽車(chē)系統(tǒng)中，這可以通過(guò)一個(gè)機(jī)械離合器獲得成 功。離合器是通過(guò)摩擦獲得運(yùn)行的。離合器的主要裝置是一個(gè)壓力盤(pán)和一個(gè)驅(qū)動(dòng) 板。壓力盤(pán)外加有調(diào)速輪，而驅(qū)動(dòng)板和傳動(dòng)輸入軸相品配。壓力盤(pán)通過(guò)彈力壓住 驅(qū)動(dòng)盤(pán)，這樣扭矩由于發(fā)動(dòng)機(jī)和傳送的輸入軸z間的摩擦力而被傳動(dòng)。汽車(chē)一般裝有干式彈力離合器。之所以稱(chēng)之為干的是因?yàn)閴毫ΡP(pán)和驅(qū)動(dòng)

8、板是 干的，相對(duì)于油式離合器，它是浸泡在油中運(yùn)行的。之所以稱(chēng)之為彈力的是由于 壓力盤(pán)和驅(qū)動(dòng)板是靠彈力相互壓在一起的，同時(shí)在某個(gè)時(shí)刻被釋放到汽車(chē)的齒輪 或剎車(chē)裝置中。除了壓力盤(pán)和驅(qū)動(dòng)盤(pán)，離合器還包含有一個(gè)外殼、釋放桿、釋放轆、壓力彈 簧和一個(gè)控制連接。離合器外殼是一個(gè)鋼鐵沖壓，由螺釘裝載調(diào)速器上。釋放桿 通過(guò)支撐螺釘確保在外売內(nèi)部。釋放桿的外部端被放置在壓力盤(pán)中。這樣的裝置 允許壓力盤(pán)接近或離開(kāi)外殼，并一直隨著調(diào)速盤(pán)而轉(zhuǎn)動(dòng)。沿壓盤(pán)和離合器蓋之間 的圓周均勻分布的彈簧加住壓盤(pán)與飛輪之間的從動(dòng)盤(pán)。彈簧的安裝依賴(lài)于外殼和壓力盤(pán)提供的發(fā)射孔和插槽。為了防治彈簧過(guò)熱, 壓力盤(pán)插槽配有熱的絕緣墊圈。液壓制動(dòng)

9、離合器分離裝置由一個(gè)踏板、分離彈簧、主氣缸、氣力調(diào)壓器、管 道、軟管、分離叉的桿組成。主氣缸供應(yīng)一個(gè)附有杯子的活塞。氣力調(diào)壓器用以 降低踏板力以分離離合器。調(diào)壓器包括內(nèi)置伺服機(jī)構(gòu)的兩個(gè)機(jī)架。機(jī)架供應(yīng)氣力 的、水壓的、伺服的活塞。當(dāng)踏板被推上去的時(shí)候，來(lái)自主氣缸的液壓經(jīng)過(guò)管和 軟管被傳到氣力調(diào)壓器的水壓和伺服活塞上。自動(dòng)離合器理所當(dāng)然被應(yīng)用在美國(guó)和歐洲的汽車(chē)中。美國(guó)發(fā)動(dòng)機(jī)”estick”離 合器消除了踏板物理運(yùn)行的需要。一個(gè)徳國(guó)的汽車(chē)制造者設(shè)計(jì)了一個(gè)自動(dòng)的離合 器系統(tǒng)叫做"hydrak",它由一個(gè)液力飛輪連接著一個(gè)干燥的轉(zhuǎn)盤(pán)。在"e-stick"裝配中，壓

10、力盤(pán)杠桿嚙合離合器盤(pán)而不是分離的。同樣，當(dāng)變速 器的運(yùn)動(dòng)處于正常時(shí)，離合器處于閑置狀態(tài)，直到伺服系統(tǒng)被油壓應(yīng)用到的時(shí)候。 "hydrak"系統(tǒng)只有杠桿正常時(shí)才開(kāi)始運(yùn)行。這激勵(lì)了一個(gè)用以分離離合器轉(zhuǎn)盤(pán)的 調(diào)壓器系統(tǒng)。通過(guò)釋放輪系統(tǒng)建立了水壓離合器部分，當(dāng)后輪的速度大于發(fā)動(dòng)機(jī) 的速度吋，水壓離合器處于工作狀態(tài)。機(jī)械離合器的運(yùn)行由一個(gè)特殊的裝置控制 著，它依賴(lài)于后車(chē)輪是否處于牽引狀態(tài)或被汽車(chē)的推力推動(dòng)。在克萊斯特汽車(chē)和美國(guó)通用汽車(chē)中，用到了一個(gè)不平常的離合器壓盤(pán)系統(tǒng)。 叫做半離心式離合器，壓盤(pán)有六個(gè)圓柱滾輪，它在離心力的作用下向外運(yùn)動(dòng)，直 至觸到外殼。當(dāng)發(fā)動(dòng)機(jī)速度增加時(shí)，滾輪的楔

11、形物自動(dòng)進(jìn)入壓力盤(pán)和外殼之間, 這樣離合器轉(zhuǎn)動(dòng)的越快，施加在壓力盤(pán)上的壓力便越大。變速器是安裝在汽車(chē)發(fā)動(dòng)機(jī)和驅(qū)動(dòng)輪之間某個(gè)點(diǎn)上的控制速度和功率變化 的裝置。它提供了一種方法，該方法使得在行使的每一個(gè)特殊情況下，發(fā)動(dòng)機(jī)每 分鐘的轉(zhuǎn)數(shù)和主動(dòng)輪每分鐘的轉(zhuǎn)數(shù)達(dá)到最好的配合。對(duì)于水平路面，如果沒(méi)有變速器，汽車(chē)可以通過(guò)發(fā)動(dòng)機(jī)的加速和離合器的連 接而啟動(dòng)。然而，這種條件下的啟動(dòng)不僅慢、有噪聲，而且不舒適。此外，它還 將在發(fā)動(dòng)機(jī)和汽車(chē)驅(qū)動(dòng)部分產(chǎn)生一個(gè)巨大的拉伸。這樣為了獲得平滑的啟動(dòng)并且能過(guò)越過(guò)和爬上山坡，必須提供一個(gè)功率比, 用以對(duì)扭矩和發(fā)動(dòng)機(jī)的轉(zhuǎn)動(dòng)力成倍地增加。同樣需要一個(gè)速比以避免高速公路上 過(guò)高的發(fā)動(dòng)

12、機(jī)轉(zhuǎn)速/每分鐘。變速器便是實(shí)現(xiàn)這些功能。變速器需要設(shè)計(jì)的是：改變從發(fā)動(dòng)機(jī)曲軸到傳動(dòng)軸被傳送的扭矩、使汽車(chē)逆 向運(yùn)動(dòng)、當(dāng)長(zhǎng)時(shí)間停車(chē)或靠邊行使時(shí)將發(fā)動(dòng)機(jī)從驅(qū)動(dòng)路線上分離生來(lái)。當(dāng)慣性大、 牽引阻力小的時(shí)候，應(yīng)對(duì)車(chē)輪施加一個(gè)比在一般平路上行使時(shí)還要大的扭矩使汽 車(chē)全負(fù)荷運(yùn)轉(zhuǎn)或全負(fù)荷爬坡。為了配合這些變化的扭矩的需要，用到一個(gè)特殊的 齒輪箱。這樣的齒輪箱叫做固定系數(shù)變速器。由主動(dòng)齒輪和從動(dòng)齒輪組成的齒輪鏈中，主動(dòng)齒輪上的扭矩將增加很多倍, 因?yàn)橹鲃?dòng)齒輪的齒數(shù)大于從動(dòng)齒輪的齒數(shù)。為了滿足變化的操作條件，需要提供不同的扭矩，因此變速器里加入了幾組 不同齒數(shù)比的齒輪。變化。變速器有機(jī)殼、輸入軸和齒輪、輸出軸和

13、齒輪、惰輪軸、回轉(zhuǎn)齒輪、齒輪組 及換檔機(jī)構(gòu)組成。鐵鑄的機(jī)売有一個(gè)上蓋和側(cè)蓋并有用于裝軸的孔。底面和另一側(cè)面提供了用 于裝油和排油的孔。輸入軸是剛鑄的，又主動(dòng)齒輪和輪緣構(gòu)成整體。輸入軸的前端安裝在曲軸的 孔中，而末端在機(jī)身前而的孔中做旋轉(zhuǎn)運(yùn)動(dòng)。輸入軸這樣布置以便只有主動(dòng)齒輪 和齒圈安裝在箱體內(nèi)，而伸出變速器外的軸的花鍵部分用來(lái)支承離合器從動(dòng)盤(pán)轂。 輸出端是用花鍵連接的，并隨著安裝在輸入軸孔中的滾動(dòng)軸承的的前端而休息。 輸出端的另一端在變速器機(jī)身的滾動(dòng)軸承中做旋轉(zhuǎn)運(yùn)動(dòng)。齒輪軸安放著一組不同齒數(shù)比的齒輪。這組齒輪安裝在輪軸上的滾動(dòng)軸承上, 或和軸安裝在一起，即機(jī)身的孔的軸承屮。閑置的軸始終隨著輸入軸

14、而轉(zhuǎn)動(dòng)，因 為它們的齒輪是保持嚙合的。冋轉(zhuǎn)齒輪（單個(gè)齒輪或兩個(gè)齒輪組）由機(jī)身上的孔 確保在軸輪上轉(zhuǎn)動(dòng)。換檔機(jī)構(gòu)被設(shè)計(jì)用以實(shí)現(xiàn)是連接齒輪、使其保持空檔和使其倒檔。沿著輸出 軸齒輪的變換將引起速度的變化。變速器的類(lèi)型依賴(lài)于滑動(dòng)齒輪的個(gè)數(shù)。有兩個(gè) 滑動(dòng)齒輪或同步嚙合套的叫做2范圍，三個(gè)齒輪的叫做3范圍。根據(jù)向前的速 度的大小，由3、4、5速度的變速器。換檔機(jī)構(gòu)安裝在蓋的頂端上。換檔桿安 裝在蓋上或水平支座的托座上。譯文the basic mechanisms of automobilesthe automobile industry is a fast developing industry. fr

15、om the later 18th century when the first automobile was put on road, this industry has developed tremendously. now there are thousands of factories all over the world manufacturing numerous types of automobiles. this industry employs crores of men and women directly and indirectly in allied industri

16、es. the automobile engines are also being used in engine powered machines for agriculture, construction and manufacturing processes. various types of small engines are also being used in lawn movers, power saws, snow removers and similar equipment. the automobile industry is a developing and demandi

17、ng industry which does not find its end or saturation point. there is a great demand for varied types of automotive products, vehicles and engines.there is also a great demand for trained and experienced persons in this industry for diagnosing motor vehicle troubles, repairing and replacing engines

18、components, transmissions, propeller shafts, differentials, axles, steering system components,brake system components, suspension components, air-conditioners, heaters, body and glass work.the automobile consists of five basic mechanisms, or components. these are :(1) the engine, which is the source

19、 of power, including the fuel, lubricating, cooling, and electric systems(2) the frame, which supports the engine, wheels, steering and brake systems, and body(3) the power train, which carries the power from the engine(through the clutch,transmission, drive shaft, differential, and axles)to the car

20、 wheels(4) the car body(5) car-body accessories, including heater ,lights, windshield wipers, and so forththe engine is the source of power that makes the car move. it is usually called an internal combustion engine because gasoline is burned inside the engine cylinders, or combustion chambers. this

21、 is in contrast to external-combustion engines(such as steam engines),where the combustion takes place outside the engine. the burning of gasoline in the engine cylinders produces the power. the power is then carried from the engine through the power train to the car wheels so that the wheels turn a

22、nd the car moves.the fuel system plays a vital part in the power producing process since it supplies the gasoline to the engine cylinders. in each engine cylinder, a mixture of gasoline vapor and air enters the cylinder, the piston pushes up into the cylinder to compress the mixture, and then an ele

23、ctric spark ignites the compressed mixture so that the piston is forced downward. of course, in the engine the piston is not blown completely out of the cylinder, the piston simply moves up and down in the cylinder-up to compress as the mixture burns. the piston straight-line motion must be changed

24、to rotary motion before it can be used to make the car wheels rotate. a connecting rod and a crank on the engine crankshaft make this change.the engine valves get the burned gasoline vapor out of the engine cylinder and bringing fresh changes of gasoline vapor and air into the cylinder. there are tw

25、o openings ,or ports, in the enclosed end of the cylinder .each containing a valve. the valve are accurately machined plugs on long stems- when they are closed, or seated (that is, moved up into the ports), the ports are sealed off and gas cannot pass through the ports. when the valve is open, gas c

26、an pass through the portthe valves are opened by cams on the engine camshaft. the cam has a high point, or lobe; every time the cam rotates, the lobe comes around under the valve lifter and move it upward. the lifter then carries this upward movement through the pushrod to the rocker arm. the rocker

27、 arm pivots on its support and pushes down on the valve stem, causing the valve to move down, that is, to open. after the cam has turned enough to move the lobe out from under the lifter, the heavy valve spring pulls the valve back into its seat. the spring is attached to the upper end of the valve

28、stem by a spring retainer and lock. there is a cam for each valve (two cams per cylinder) on the engine camshaft. the camshaft is driven off the crankshaft by gears or by sprockets and a chain.when the entire cycle of events requires four piston strokes (two crankshaft revolutions), the engine is ca

29、lled a four-stroke-cycle engine, or a four-cycle engine. the four strokes are intake, compression, power, and exhaust.on the intake stroke, the intake valve is open. the piston moves down, pulled by the rotation of the crankshaft. this piston movement creates a partial vacuum in the cylinder, and ai

30、r rushes into the cylinder past the intake valve to "fill upn this vacuum. as the air moves toward the cylinder, it must pass through the carburetor. there it is charged with gasoline vapor. thus, it is a mixture of air and gasoline vapor that rushes into the cylinder as the piston moves down o

31、n theintake stroke.after the piston moves down to the bottom dead center on the intake stroke, the intake valve closes. the lobe on the cam controlling the intake valve has moved out from under the valve lifte匚 since the other valve is also closed, the upper end of the cylinder is sealed. now, as th

32、e piston is pushed up by the rotating crankshaft, the mixture of air and gasoline vapor that has been drawn into the cylinder is compressed.by the time the piston has moved up to the top dead center, the mixture is compressed to a seventh or an eighth of its original volume. that is like taking a ga

33、llon of air and compressing it to a pin匸 the result is high pressure in the cylinde匚about the time the piston reaches the top dead center on the compression stroke, an electric spark occurs at the cylinder spark plug. the spark plug is essentially two heavy wire electrodes; the spark jumps between t

34、hese electrodes. the spark is produced by the ignition system. it ignites, or sets fire to, the compressed air-gasoline-vapor mixture. rapid combustion takes place; high temperatures and pressures result. at this instant, the downward pressure on the top of the piston may amount to as much as 2tons.

35、 this powerful push forces the piston down, and a power impulse is transmitted to the crankshaft through connecting rod and the crank.the piston is forced down by the pressure of the burning gasoline vapor during the power stroke. when the piston reaches the bottom dead center, the exhaust valve ope

36、ns. now, as the piston starts back up again, it forces the burned gases from the cylinder. by the time the piston has reached the top dead center the cylinder is cleared of the burned gases. the exhaust valve closes and the intake valve opens- then ,the piston starts back down again on the next inta

37、ke stroke. the four cycles, or piston strokes, are continuously repeated while the engine is running.the clutchesa clutch is a friction device used to connect and disconnect a driving force from a driven membe匚 in automotive application, it is used in conjunction with an engine flywheel to provide s

38、mooth engagement and disengagement of the engine and manual transmission.since an internal combustion engine develops little power or torque at low rpm, it must gain speed before it will move the vehicle. however, if a rapidly rotating engine is suddenly connected to the drive line of a stationary v

39、ehicle, a violent shock will result.so gradual application of load, along with some slowing of engine speed, is needed to provide reasonable and comfortable starts. in vehicles equipped with a manual transmission, this is accomplished by means of a mechanical clutch.the clutch utilizes friction for

40、its operation. the main parts of the clutch are a pressure plate, and a driven disk. the pressure plate is coupled with the flywheel, while the driven disk is fitted to the transmission input shaft. the pressure plate is pressed to the disk by the springs so that the torque is transmitted owing to f

41、riction forces from the engine to the input shaft of the transmission. smooth engagement is ensured by slipping of the disk before a full pressure is applied.the automobiles are equipped with a dry spring-loaded clutch. the clutch is termed ndryh because the surfaces of the pressure plate and driven

42、 disks are dry incontrast to oil-bath clutches in which the plate and disks operate in a bath of oil. it is called nspring-loadedn because the pressure plate and the driven disk are always pressed to each other by springs and are released only for a time to shift gears or to brake the automobile.in

43、addition to the plate and disk, the clutch includes a cover, release levers, a release yoke, pressure springs and a control linkage. the clutch cover is a steel stamping bolted to the flywheel. the release levers are secured inside the cover on the supporting bolts. the outer ends of the release lev

44、ers are articulated to the pressure plate. such a construction allows the pressure plate to approach the cover or move away from it, all the time rotating with the flywheel. the springs spaced around the circumference between the pressure plate and the clutch cover clamp the drivendisk between the p

45、ressure plate and the flywheel.the springs are installed with the aid of projections and sockets provided on the cover and pressure plate. the pressure plate sockets have thermal-insulation gaskets for protecting the springs against overheating.the clutch release mechanism can be operated either mec

46、hanically or hydraulically. the mechanicallyoperated release mechanism consists of a pedal,a return spring, a shaft with lever, a rod, a release yoke lever, a release yoke, a release ball bearing with support and a clutch release spring. when the clutch pedalis depressed, the rod and shaft with yoke

47、 shift the released bearing and support assembly. the release bearing presses the inner ends of the release levers, the pressure plate is moved away from, the driven disk and the clutch is disengaged. to engage the clutch, the pedal is released, the release bearing thus releasing the release levers

48、so that the pressure plate is forced by its springs towards the flywheel to clamp the driven disk and engage the clutch.the clutch hydraulically-operated release mechanism consists of a clutch pedal, clutch release spring, a main cylinder, a pneumatic booster, pipelines and hoses and a lever of the

49、clutch release yoke shaft. the main cylinder accommodates a piston with a cup. the pneumatic booster serves to decrease the pedal force required to disengage the clutch. the booster includes two housings with the servo diaphragm clamped in between. the housing accommodates pneumatic, hydraulic and s

50、ervo plungers. when the clutch pedal is pushed, the fluid pressure from the main cylinder is transmitted through the pipelines and hoses to the hydraulic and servo plungers of the pneumatic booste 匚the servo arrangement is intended for automatic change of the air pressure in the pneumatic cylinder p

51、roportionally to the force applied to the pedal. the plunger moves with the diaphragm, the outlet valve closes and the inlet valve opens thus admitting the compressed air to the pneumatic plunger piston. the forces created by the pneumatic and hydraulic plungers are added together and are applied th

52、rough the push rod to the release yoke shaft lever, the lever turns the shaft and the release yoke shaft disengaging the clutch. after the clutch pedal is released,the outlet valve opens and the inlet closes. under the action of the springs thepistons return the plungers to the initial position and

53、the air from the cylinder is let out to the atmosphere.automatic clutches were used in certain u.s. and european cars. american motorsne-stickh clutch eliminated the need for physical operation of the clutch pedal. a german car maker engineered an automatic clutch system called mhydrak, which consis

54、ted of a fluid flywheel connected to a single, dry disk clutch.in the ne-stickn set up, the pressure plate levers "engage” the clutch disk rather than "release” them. also, the clutch remains disengaged until a servo unit is applied by oil pressure when the shift lever is placed "in g

55、ear11 with the engine running.the nhydrakn unit also begins operation when the lever is "in gearh. this activates a booster unit, which disengages the clutch disk. the hydraulic clutch parts are bridged over by a free-wheel unit, which goes into action when the speed of the rear wheels is highe

56、r than the speed of the engine. a special device controls ingagement of the mechanical clutch, depending on whether the rear axle is in traction or is pushed by car momentum.a more-or-less unusual clutch pressure plate set-up is used on late model chrysler and american motors cars. called a semi-cen

57、trifugal clutch, the pressure plate has six cylindrical rollers which move outward under centrifugal force until they contact the cover. as engine speed increases, the rollers wedge themselves between the pressure plate and cover so that the faster the clutch rotates, the greater the pressure exerte

58、d on the pressure plate and disk.automobile transmissiona transmission is a speed and power changing device installed at some point between the engine and driving wheel of the vehicle. it provides a means for changing the ratio between engine rpm ( revol utions per minute) and driving wheels rpm to

59、best meet each particular driving situation.given a level road ,an automobile without a transmission could be made to move by accelerating the engine and engaging the clutch. however, a start under these conditions would be slow, noisy and uncomfortable. in addition, it would place a tremendous strain on the engine and driving parts of the automobile.so in order to get smooth starts and have power to pass and climb hills, a power ratio must be provided to multiply the torqu