外文翻譯內(nèi)燃機(jī)

1、畢業(yè)設(shè)計(jì)(論文)外文資料翻譯系部： 機(jī)械工程系 專 業(yè)： 機(jī)械工程及自動(dòng)化 姓 名： 學(xué) 號(hào)： 外文出處：-1.html 附 件： 1.外文資料翻譯譯文；2.外文原文。 指導(dǎo)教師評(píng)語： 此翻譯文章簡單介紹了內(nèi)燃機(jī)的原理，詳細(xì)描述了內(nèi)燃機(jī)各零部件在內(nèi)燃機(jī)工作時(shí)所起到的作用，翻譯用詞比較準(zhǔn)確，文筆也較為通順，為在以后工作中接觸英文資料打下了基礎(chǔ)。 簽名： 年 月 日注：請(qǐng)將該封面與附件裝訂成冊(cè)。附件1：外文資料翻譯譯文內(nèi)燃機(jī)我們知道，無論是汽油發(fā)動(dòng)機(jī)還是柴油發(fā)動(dòng)機(jī)，它們都屬于內(nèi)燃機(jī)，都是燃燒燃料后通過推動(dòng)氣缸內(nèi)活塞作往返運(yùn)動(dòng)來將燃料中的化學(xué)能量轉(zhuǎn)換成為驅(qū)動(dòng)車輛前進(jìn)的機(jī)械能量，因此兩者的工作原理大體

2、是相同的。作為日常使用的燃料本身，柴油的能量密度最高，比液化天然氣高出近1倍，比汽油高出10%以上。與汽油相比，柴油不易揮發(fā)，著火點(diǎn)較高，不易因偶然情況被點(diǎn)燃或發(fā)生爆炸。由于兩者揮發(fā)性和燃點(diǎn)的不同，導(dǎo)致使用這兩種燃料的發(fā)動(dòng)機(jī)有不同的點(diǎn)火方式。汽油發(fā)動(dòng)機(jī)的特點(diǎn)：體積小、重量輕、起動(dòng)性好。汽油發(fā)動(dòng)機(jī)中，油氣混合氣進(jìn)入氣缸后，在壓縮接近終了時(shí)由火花塞點(diǎn)燃。因此，汽油發(fā)動(dòng)機(jī)需要一套控制何時(shí)讓火花塞工作的點(diǎn)火系統(tǒng)，此系統(tǒng)必須精確控制火花塞放電的時(shí)刻和火花能量的大小，才能保證汽油機(jī)的工作正常，汽油機(jī)的燃料供給系和點(diǎn)火系是汽油機(jī)上發(fā)生故障比例較高的部位。此外，由于汽油的燃點(diǎn)較低，汽油機(jī)的壓縮比就不能太高，以

3、免油氣自燃，因此其熱效率和經(jīng)濟(jì)性較柴油機(jī)為差。汽油機(jī)的優(yōu)點(diǎn)在于其體積小、重量輕、價(jià)格便宜；起動(dòng)性好，最大功率時(shí)的轉(zhuǎn)速高；工作中振動(dòng)及噪聲小，因此，在載客汽車，特別是轎車中，汽油機(jī)得到了廣泛的應(yīng)用，特別是在我們國家目前生產(chǎn)的絕大多數(shù)轎車，都是采用汽油發(fā)動(dòng)機(jī)作為自己的動(dòng)力系統(tǒng)。傳統(tǒng)柴油發(fā)動(dòng)機(jī)的特點(diǎn)：熱效率和經(jīng)濟(jì)性較好。柴油機(jī)采用壓縮空氣的辦法提高空氣溫度，使空氣溫度超過柴油的自燃燃點(diǎn)，這時(shí)再噴入柴油、柴油噴霧和空氣混合的同時(shí)自己點(diǎn)火燃燒。因此，柴油發(fā)動(dòng)機(jī)無需點(diǎn)火系。同時(shí)，柴油機(jī)的供油系統(tǒng)也相對(duì)簡單，因此柴油發(fā)動(dòng)機(jī)的可靠性要比汽油發(fā)動(dòng)機(jī)的好。由于不受爆燃的限制以及柴油自燃的需要，柴油機(jī)壓縮比很高。熱

4、效率和經(jīng)濟(jì)性都要好于汽油機(jī)，同時(shí)在相同功率的情況下，柴油機(jī)的扭矩大，最大功率時(shí)的轉(zhuǎn)速低，適合于載貨汽車的使用。但柴油機(jī)由于工作壓力大，要求各有關(guān)零件具有較高的結(jié)構(gòu)強(qiáng)度和剛度，所以柴油機(jī)比較笨重，體積較大；柴油機(jī)的噴油泵與噴嘴制造精度要求高，所以成本較高；另外，柴油機(jī)工作粗暴，振動(dòng)噪聲大；柴油不易蒸發(fā)，冬季冷車時(shí)起動(dòng)困難。由于上述特點(diǎn)，以前柴油發(fā)動(dòng)機(jī)一般用于大、中型載重貨車上。小型高速柴油發(fā)動(dòng)機(jī)的新發(fā)展：排放已經(jīng)達(dá)到歐洲iii號(hào)的標(biāo)準(zhǔn)。傳統(tǒng)上，柴油發(fā)動(dòng)機(jī)由于比較笨重，升功率指標(biāo)不如汽油機(jī)(轉(zhuǎn)速較低)，噪聲、振動(dòng)較高，炭煙與顆粒(pm)排放比較嚴(yán)重，所以一直以來很少受到轎車的青睞。但隨著近年來柴油

5、機(jī)技術(shù)的進(jìn)步，特別是小型高速柴油發(fā)動(dòng)機(jī)的新發(fā)展，一批先進(jìn)的技術(shù)，例如電控直噴、共軌、渦輪增壓、中冷等技術(shù)得以在小型柴油發(fā)動(dòng)機(jī)上應(yīng)用，使原來柴油發(fā)動(dòng)機(jī)存在的缺點(diǎn)得到了較好的解決，而柴油機(jī)在節(jié)能與co2排放方面的優(yōu)勢(shì)，則是包括汽油機(jī)在內(nèi)的所有熱力發(fā)動(dòng)機(jī)無法取代的，因此，先進(jìn)的小型高速柴油發(fā)動(dòng)機(jī)，其排放已經(jīng)達(dá)到歐洲iii號(hào)的標(biāo)準(zhǔn)，成為“綠色發(fā)動(dòng)機(jī)”，目前已經(jīng)成為歐美許多新轎車的動(dòng)力裝置，可以預(yù)見，我國將出現(xiàn)越來越多的柴油轎車。內(nèi)燃機(jī)是一種熱力發(fā)動(dòng)機(jī)。通?？砂慈加玫娜剂蟻矸钟校浩蜋C(jī)、煤氣機(jī)等幾類。因?yàn)槠蜋C(jī)輕便、噪音低以及環(huán)保性，它贏得了公眾較好的口碑，因此其有機(jī)在國民經(jīng)濟(jì)和國防工程上得到了較為廣泛

6、的應(yīng)用。內(nèi)燃機(jī)傳熱在很大程度上主宰著汽油機(jī)的經(jīng)濟(jì)性、可靠性以及其他各項(xiàng)重要的技術(shù)經(jīng)濟(jì)指標(biāo)。在汽油機(jī)負(fù)載日益增強(qiáng)的今天，研究汽油機(jī)熱負(fù)荷問題已經(jīng)是非常緊迫的任務(wù)了。汽油機(jī)向高強(qiáng)化方向的發(fā)展使其零部件的機(jī)械負(fù)荷和熱負(fù)荷不斷增大，而汽油機(jī)的的汽缸套是氣體壓縮、燃燒和膨脹的空間，并為活塞起導(dǎo)向作用，它的不正常變形將破壞活塞與缸套間的正常間隙，導(dǎo)致工作過程的惡化。因而，如何降低汽油機(jī)的熱負(fù)荷，則是提高其整機(jī)性能的重要研究課題。 發(fā)動(dòng)機(jī)：發(fā)動(dòng)機(jī)充當(dāng)動(dòng)力裝置。內(nèi)燃機(jī)是最常見的：它通過在發(fā)動(dòng)機(jī)汽缸里面燃燒一種液體燃料獲得動(dòng)力。發(fā)動(dòng)機(jī)有兩種類型:汽油機(jī) (也叫做一個(gè)火花- 點(diǎn)火發(fā)動(dòng)機(jī))和柴油機(jī)(也被稱為一個(gè)壓縮

7、- 點(diǎn)火發(fā)動(dòng)機(jī))。這兩種發(fā)動(dòng)機(jī)都叫做熱機(jī)；燃料在氣缸內(nèi)燃燒產(chǎn)生的高溫高壓氣體推動(dòng)曲軸旋轉(zhuǎn)而傳遞動(dòng)力。車身：汽車車身是由窗子，門，一個(gè)發(fā)動(dòng)機(jī)罩和一個(gè)行李艙蓋建成的一個(gè)金屬板殼。它給發(fā)動(dòng)機(jī)，乘客和貨物提供一種保護(hù)。車身的設(shè)計(jì)應(yīng)使得乘客安全和舒適。車身的外表使得汽車具有吸引人的，五彩繽紛的和現(xiàn)代的外表。底盤：底盤是汽車上主要操作系統(tǒng)組成的一個(gè)總成。底盤包括傳動(dòng)系，懸掛，轉(zhuǎn)向，以及剎車系統(tǒng)。傳動(dòng)系統(tǒng) - 把動(dòng)力運(yùn)送到車輪。主要零部件是離合器，變速器，傳動(dòng)軸，主減速器，和差速器。懸掛 - 吸收路面震動(dòng)。轉(zhuǎn)向 - 控制運(yùn)動(dòng)的方向。剎車 使車輛減速。電氣設(shè)備：電系統(tǒng)為點(diǎn)火，喇叭，燈光，發(fā)熱器和起動(dòng)器提供電。

8、通過循環(huán)充電來維持電量。這條電路由電池，交流發(fā)電機(jī)(或者發(fā)電機(jī))組成。蓄電池儲(chǔ)存電。交流發(fā)電機(jī)把發(fā)動(dòng)機(jī)的機(jī)械能換成電能并給電池再充電。氣缸體：氣缸體是發(fā)動(dòng)機(jī)的基本框架。發(fā)動(dòng)機(jī)的其他零件都安裝在它里面或者固定在它上。缸體里有氣缸，水套和油道。曲軸也固定在氣缸體底部。除了頂置凸輪(ohc)發(fā)動(dòng)機(jī)以外，凸輪軸都安裝在氣缸體里面。在大多數(shù)汽車?yán)?，氣缸體由灰鑄鐵或者一種灰鑄鐵和其他金屬的合金(混合物)做成，例如鎳或鉻。氣缸體是鑄件。 有些氣缸體，特別是在小汽車?yán)锏哪切?，都是由鋁做成的。這種金屬比鑄鐵輕得多。但是，鑄鐵的耐磨性比鋁好。因此，在大多數(shù)鋁制發(fā)動(dòng)機(jī)的氣缸內(nèi)鑲有鑄鐵或者鋼的軸套。這些軸套叫做氣缸套

9、。而有些氣缸體完全由鋁做成。氣缸蓋：氣缸蓋固定在氣缸體的頂上，正像屋頂套在一所房子上面一樣。氣缸蓋下面與活塞頂上的空間形成燃燒室。最常見的氣缸蓋類型是半球形，楔形和準(zhǔn)半球形。這三種說法都是指燃燒室的形狀。氣缸蓋攜帶閥門，氣門彈簧和在搖臂桿上的搖臂，這部分的氣門傳動(dòng)機(jī)構(gòu)通過推桿工作。有時(shí)，凸輪軸直接安裝在氣缸蓋上并且不用搖臂控制閥門工作。這被叫為頂置凸輪軸裝置。像氣缸體一樣，氣缸蓋是由鑄鐵或者鋁合金制成。襯墊：氣缸蓋與氣缸體用高強(qiáng)度的鋼螺栓縛連結(jié)。氣缸體和氣缸蓋之間的連接必須密封以便沒有燃燒的混合氣體泄漏。這通過使用氣缸蓋襯墊實(shí)現(xiàn)。這是一個(gè)夾層襯墊，即在兩片銅之間放一片石棉，這兩種材料都能禁得住

10、在發(fā)動(dòng)機(jī)內(nèi)的高溫和高壓。油底殼：油底殼通常由鋼沖壓形成。油底殼和氣缸體的下半部分一同被叫做曲軸箱；他們把曲軸封閉起來。潤滑系統(tǒng)中的機(jī)油泵從油底殼抽取油并把油輸送到發(fā)動(dòng)機(jī)內(nèi)全部正在工作的部分。機(jī)油流出后又流回油底殼。因而在油底殼和發(fā)動(dòng)機(jī)工作零件之間有機(jī)油不斷流動(dòng)循環(huán)。進(jìn)氣配氣定時(shí)：如果進(jìn)口門在進(jìn)氣行程的上止點(diǎn)打開并且在這次行程的下止點(diǎn)關(guān)閉，它將有180的開度。氣門在180轉(zhuǎn)角內(nèi)完全打開。然而氣門達(dá)到全開位置需要一定時(shí)間，完全關(guān)閉也需要一定時(shí)間。因此閥門在上止點(diǎn)(btdc)之前被打開，在下止點(diǎn)(abdc)之后關(guān)閉。排氣配氣定時(shí)： 如果排氣門在排氣行程的下止點(diǎn)打開并且在這次行程的上止點(diǎn)關(guān)閉，它將有1

11、80的持續(xù)。但是像進(jìn)氣門一樣，排氣門需要時(shí)間到達(dá)充分打開和關(guān)閉的位置。因此排氣門在下止點(diǎn)之前打開，在上止點(diǎn)之后關(guān)閉。 氣門重疊：進(jìn)氣門在上止點(diǎn)前17打開，排氣門在上止點(diǎn)后17關(guān)閉。 因此，有34的一段時(shí)期，兩個(gè)閥門都是開的：(17+ 17= 34)。這時(shí)期被稱為氣門重疊。排氣門的關(guān)閉和進(jìn)氣門的開啟重疊。在這個(gè)時(shí)候，新的混合氣推動(dòng)燃燒后的廢氣從排氣門排出。在渦輪增壓發(fā)動(dòng)機(jī)上氣門重疊角被保持在一個(gè)最小值。這就防止廢氣倒流入進(jìn)氣管。 配氣機(jī)構(gòu)：那些打開和關(guān)閉氣門的氣門傳動(dòng)是為了協(xié)調(diào)四沖程的工作循環(huán)(使他們各自上下移動(dòng))。這些閥門運(yùn)動(dòng)必須正好在合適的時(shí)刻進(jìn)行。每個(gè)閥門的開啟由凸輪軸控制。頂置凸輪軸氣閥

12、傳動(dòng)：凸輪是一在軸上的蛋形的金屬，通過曲軸協(xié)調(diào)旋轉(zhuǎn)。那金屬軸叫凸輪軸，在發(fā)動(dòng)機(jī)里的每個(gè)氣門一般有各自的凸輪。當(dāng)凸輪軸旋轉(zhuǎn)時(shí)，凸輪凸起的或者高點(diǎn)的位置，推動(dòng)氣門座。這行動(dòng)強(qiáng)迫閥門向下移動(dòng)。這過程能使進(jìn)氣門在進(jìn)氣行程打開，或者排氣門在排氣行程打開。 因?yàn)橥馆嗇S繼續(xù)旋轉(zhuǎn)，凸輪軸上的凸起部分離開氣門裝置。當(dāng)這發(fā)生時(shí)，氣門彈簧緊緊地關(guān)閉氣門口，叫做氣門座?，F(xiàn)代汽車發(fā)動(dòng)機(jī)里的閥門位于發(fā)動(dòng)機(jī)頂上的汽缸蓋。這被稱為頂置氣門(ohv)結(jié)構(gòu)。另外，當(dāng)凸輪軸位于汽缸蓋上面時(shí)，這種方式被稱為是頂置凸輪軸(ohc)結(jié)構(gòu)。一些高性能發(fā)動(dòng)機(jī)有兩個(gè)單獨(dú)的凸輪軸，分別負(fù)責(zé)開關(guān)進(jìn)氣門和排氣門。這些發(fā)動(dòng)機(jī)被稱為雙頂置凸輪軸(doh

13、c)發(fā)動(dòng)機(jī)。推桿氣閥傳動(dòng)：凸輪軸也裝在發(fā)動(dòng)機(jī)底部的氣缸體內(nèi)。為了將凸輪的運(yùn)動(dòng)傳給氣門需要一些附屬裝置。在這種布置中，凸輪凸角推動(dòng)凸輪挺桿。當(dāng)凸輪的凸角在凸輪挺桿下出現(xiàn)時(shí)，它推動(dòng)凸輪挺桿向上運(yùn)動(dòng)(離開凸輪軸)。凸輪挺桿推動(dòng)控制搖臂的推桿。搖臂以通過它的中心為軸而旋轉(zhuǎn)。當(dāng)搖臂的一側(cè)上升，其另一側(cè)下降，正如一塊蹺蹺板一樣。搖臂向下移動(dòng)的那一邊推動(dòng)氣門桿以打開氣門。 因?yàn)橥茥U氣閥傳動(dòng)有另外的部分，所以很難以高速運(yùn)轉(zhuǎn)。推桿發(fā)動(dòng)機(jī)一般在低速運(yùn)轉(zhuǎn)，從而產(chǎn)生比相同大小的頂置凸輪軸較少功率。(記住，功率反映了工作能力。) 氣門間隙：當(dāng)發(fā)動(dòng)機(jī)處于壓縮行程和做功行程時(shí)，閥門必須緊緊地關(guān)閉以產(chǎn)生一個(gè)不透氣的氣封，以防

14、止氣體逃離燃燒室。如果閥門不完全關(guān)閉，發(fā)動(dòng)機(jī)將不能發(fā)揮全部動(dòng)力。此外氣門頭易于被通過的熱氣體燃燒，這有可能使活塞頻繁沖擊打開的氣門，使發(fā)動(dòng)機(jī)嚴(yán)重?fù)p壞。 所以閥門能完全關(guān)閉，氣門間隙在操作機(jī)構(gòu)內(nèi)是必須的。這意味著操作機(jī)構(gòu)必須離閥門足夠遠(yuǎn)以允許閥門通過氣門彈簧使其完全關(guān)閉。但是，如果間隙太大，將引起金屬輕敲的噪音。凸輪軸驅(qū)動(dòng)機(jī)構(gòu)：在四行程循環(huán)時(shí)，每凸輪必須旋轉(zhuǎn)打開一閥門。記住，一個(gè)循環(huán)相當(dāng)于曲軸旋轉(zhuǎn)兩次。因此，凸輪軸必須以曲軸正好一半的速度旋轉(zhuǎn)。這用2：1的傳動(dòng)比完成。齒輪連接到凸輪軸的齒數(shù)是齒輪連接到曲軸的兩倍。齒輪連結(jié)有三種方式：（1）皮帶傳動(dòng)齒型帶能被使用。這樣的帶是由合成橡膠做成并且用內(nèi)部

15、的鋼或者玻璃纖維絞合加強(qiáng)。皮帶上有齒，或者槽以嚙合并且驅(qū)動(dòng)傳動(dòng)齒輪上的齒。皮帶一般與頂置凸輪閥門傳動(dòng)一起被用在發(fā)動(dòng)機(jī)上。（2）鏈傳動(dòng)在一些發(fā)動(dòng)機(jī)上，金屬鏈被用來連結(jié)曲軸和凸輪軸齒輪。大多數(shù)推桿發(fā)動(dòng)機(jī)和一些頂置凸輪軸發(fā)動(dòng)機(jī)都有鏈。（3）齒輪傳動(dòng)凸輪軸和曲軸齒輪可能被直接連結(jié)，或者相嚙合。這類操作聯(lián)動(dòng)通常被用在更老的六氣缸，直列發(fā)動(dòng)機(jī)上。凸輪軸被鏈或者帶驅(qū)動(dòng)，使其朝著曲軸相同的方向轉(zhuǎn)動(dòng)。但是凸輪軸被曲軸齒輪直接驅(qū)動(dòng)，其將在相反方向上轉(zhuǎn)動(dòng)。正時(shí)皮帶被使用，因?yàn)樗麄兓ㄙM(fèi)少于鏈子，而且噪音少。一條典型的正時(shí)皮帶由用玻璃纖維加強(qiáng)的氯丁橡膠(合成橡膠)做成的。附件2：外文原文belong enginewe

16、know that both gasoline engines or diesel engines, they all belong engine. all from the burning of fuel through the cylinder piston made from the campaign to promote the fuel conversion of chemical energy into mechanical energy driving the vehicle forward. so the working principle is generally the s

17、ame.daily use as fuel itself, the highest energy density of diesel, liquefied natural gas nearly doubled over, more than 10% higher than gasoline. compared with conventional gasoline, diesel not volatile, higher ignition point, the situation was not due to accidental fire or explosion. because of th

18、e volatile and, if different, resulting in the use of two different fuels the engine ignition.gasoline engine features : small size, light weight, good start.gasoline engines, the gas mixture into the cylinder, close to the end of the compression ignited by the spark plug. therefore, the need for a

19、gasoline engine when to control the spark plug ignition system. this system requires an accurate control of spark plugs and spark discharge energy of the moment, be able to ensure the normal gasoline engine. gasoline engine fuel supply system and ignition system is a high proportion of the gasoline

20、engine fault location. in addition, the gasoline ignited lower gasoline engine compression ratio can not be too high so as to avoid spontaneous combustion of oil and gas. therefore the thermal efficiency and economy worse than diesel.the advantage lies in its small gasoline engine, light weight, low

21、 price; start good, the speed at maximum power; small vibration and noise work, therefore, passenger motor vehicles, particularly cars, has been widely used in gasoline engines. especially in the vast majority of our countrys current production cars, as their gasoline engines are used on the power s

22、ystem.the conventional diesel engine thermal efficiency and economy better characteristics :diesel use of compressed air and improve air temperature, air temperature over the spontaneous ignition of diesel. then again injected into diesel, hybrid diesel spray at the same time their ignition and comb

23、ustion air. therefore, no diesel engine ignition system. meanwhile, the engine oil system is relatively simple and therefore the reliability of diesel engines than gasoline engines as good.from injuries caused by spontaneous combustion due to the restrictions and the need for diesel engine with a hi

24、gh compression ratio. thermal efficiency and economy must be better than the gasoline engine, while the power in the same circumstances, the engine torque, maximum power at low speed, suitable for use in the truck.however, due to work pressure diesel called on the structural components with high str

25、ength and stiffness. so diesel relatively bulky size; diesel fuel pump with the nozzle to create high-precision, high costs; in addition, the engine crude, large vibration and noise; diesel easy evaporation in winter when cold starting problems.because of these features, previously used in diesel en

26、gines, medium radial truck.the new development : small high-speed diesel engine emission standards has been achieved in euc22 rope iii.traditionally, due to relatively heavy diesel engine or gasoline engine power as indicators (low speed), noise, vibration higher. smoke and carbon particles (pm) emi

27、ssions is fairly serious, very little has been favored by car.but with the advances in technology in recent years diesel, especially small high-speed diesel engine is a new development of a number of advanced technologies, for example, electronic control di, common rail, turbo-charged, in the cold l

28、ight of technology, such as the use of diesel engines. the shortcomings of the original diesel engine to be a better solution. and the diesel engines advantages in energy and co2 emissions. including the gasoline engine is no way to replace all heat engines, advanced high-speed small diesel engines.

29、 the european iii emission standards has been achieved, the green engine that many cars in europe and the united states has now become the new power plant, it can be predicted that china will see an increasing number of diesel cars.ice is a heat engine. usually can burn the fuel used to be in : gaso

30、line engine, gas and other types of aircraft. because the gasoline engine light, low noise and environmental protection, it won the public good reputation, therefore organic in its national economy and national defense projects has been more widely used. engine heat transfer to a large extent the ke

31、y to the economic gasoline engine, reliability and other important technical and economic indicators. the gasoline engine load increasing today, the research gasoline engine heat load problems is very urgent task. high gasoline engine to enhance the development direction of its mechanical parts load

32、 and thermal load is increasing, and the gasoline engine and the cylinder sets of gas compression, combustion and expansion of the space, and to orient the pistons, its not normal deformation of the cylinder and piston damage the normal clearance, resulting in the deterioration process. therefore, h

33、ow to reduce the gasoline engine heat load, it is to enhance its overall performance an important research topic. enginethe engine acts as the power unit. the internal combustion engine is most common: this obtains its power by burning a liquid fuel inside the engine cylinder. there are two types of

34、 engine :gasoline(also called a spark-ignition engine) and diesel(also called a compression-ignition engine).both engines are called heat engines; the burning fuel generates heat which causes the gas inside the cylinder to increase its pressure and supply power to rotate a shaft connected to the tra

35、nsmission.bodyan automobile body is a sheet metal shell with windows, doors, a hood, and a trunk deck built into it. it provides a protective covering for the engine, passengers, and cargo. the body is designed to keep passengers safe and comfortable. the body styling provides an attractive, colorfu

36、l, modern appearance for the vehicle.chassisthe chassis is an assembly of those systems that are the major operating part of a vehicle. the chassis includes the transmission, suspension, steering, and brake systems.transmission systems conveys the drive to the wheels. the main components are clutch,

37、 gearbox, driveshaft, final drive, and differential.suspension absorbs the road shocks.steering controls the direction of the movement.brake slows down the vehicle.electrical equipmentthe electrical system supplies electricity for the ignition, horn, lights, heater, and starter. the electricity leve

38、l is maintained by a charging circuit. this circuit consists of the battery, alternator (or generator). the battery stores electricity. the alternator changes the engines mechanical energy into electrical energy and recharges the battery.engine blockthe engine block is the basic frame of the engine.

39、 all other engine parts either fit inside it or fasten to it. it holds the cylinders, water jackets, and oil galleries.the engine block also holds the crankshaft, which fastens to the bottom of the block. the camshaft also fits inside the block, except on overhead-cam engines (ohc). in most cars, th

40、is block is made of gray iron, or an alloy (mixture) of gray iron and other metals, such as nickel or chromium. engine blocks are castings. some engine blocks, especially those in smaller cars, are made of cast aluminum. this metal is much lighter than iron. however, iron wears better than aluminum.

41、 therefore, the cylinders in most aluminum engines are lined with iron or steel sleeves. these sleeves are called cylinder sleeves. some engine blocks are made entirely of aluminum.cylinder headthe cylinder head fastens to the top of the block, just as a roof fits over a house. the underside forms t

42、he combustion chamber with the top of the piston. the most common cylinder head types are the hemi, wedge, and semi-hemi.all three of these terms refer to the shape of the engines combustion chamber. the cylinder head carries the valves, valve springs and the rockers on the rocker shaft, this part o

43、f the valve gear being worked by the push-rods. sometimes the camshaft is fitted directly into the cylinder head and operates on the valves without rockers. this is called an overhead camshaft arrangement. like the cylinder block, the head is made from either cast iron or aluminum alloy.gasketthe cy

44、linder head is attached to the block with high-tensile steel studs. the joint between the block and the head must be gas-tight so that none of the burning mixture can escape. this is achieved by using cylinder head gasket. this is a sandwich gasket, i.e. a sheet of asbestos between two sheets of cop

45、per, both these materials being able to withstand the high temperature and pressures within the engine.oil pan or sumpthe oil pan is usually formed of pressed steel. the oil pan and the lower part of the cylinder block together are called the crankcase; they enclose, or encase, the crankshaft. the o

46、il pump in the lubricating system draws oil from the oil pan and sends it to all working parts in the engine. the oil drains off and runs down into the pan. thus, there is constant circulation of oil between the pan and the working parts of the engine.inlet valve timingif the inlet valve opened at t

47、dc of the intake stroke and closed at bdc of that stroke, it would have a duration of 180.it would have remained open for half of a complete 360 revolution, or 180. however, it takes some time for the valve to open to its full position. it also takes time for it to close tightly. therefore the valve

48、 is opened before tdc (btdc) and closed after bdc (abdc).exhaust valve timingif the exhaust valve opened at bdc at the beginning of the exhaust stroke and closed at tdc at the end of the exhaust stroke, it would have a duration of 180. but like the inlet valve, the exhaust valve needs time to reach

49、the full-open position, it also needs time to reach the full-closed position. so the exhaust valve opens before bdc and closes after tdc.valve overlapthe intake opens at 17 btdc and the exhaust closes at 17 atdc. thus, for a period of 34, both of the valves are open: (17 + 17 =34). this period of ti

50、me is known as valve overlap. the closing of the exhaust valve laps over the opening of the intake valve. during this time, the first of the new mixture pushes the last of the burned gases out the exhaust valve. valve overlap is held to a minimum on turbo-charged engines. this prevents the intake ch

51、arge from being blown out the exhaust.valve operationto coordinate the four-stroke cycle, a group of parts called the valve train opens and closes the valves (moves them down and up, respectively). these valve movements must take place at exactly the right moments. the opening of each valve is contr

52、olled by a camshaft.overhead camshaft (ohc) valve trainthe cam is an egg-shaped piece of metal on a shaft that rotates in coordination with the crankshaft. the metal shaft, called the camshaft, typically has individual cams for each valve in the engine. as the camshaft rotates, the lobe, or high spo

53、t of the cam, pushes against parts connected to the stem of the valve. this action forces the valve to move downward. this action could open an inlet valve for an intake stroke, or open an exhaust valve for an exhaust stroke.as the camshaft continues to rotate, the high spot moves way from the valve

54、 mechanism. as this occurs, valve springs pull the valve tightly closed against its opening, called the valve seat.valves in modern car engines are located in the cylinder head at the top of the engine. this is known as an overhead valve (ohv) configuration. in addition, when the camshaft is located

55、 over the cylinder head, the arrangement is known as an overhead camshaft (ohc) design. some high-performance engines have two separate camshafts, one for each set of inlet and exhaust valves. these engines are known as dual overhead camshaft (dohc) engines.push-rod valve trainthe camshaft also can

56、be located in the lower part of the engine, within the engine block. to transfer the motion of the cam upward to the valve, additional parts are needed.in this arrangement, the cam lobes push against round metal cylinders called cam follower. as the lobe of the cam comes up under the cam follower, i

57、t pushes the cam follower upward (away from the camshaft). the cam follower rides against a push rod, which pushes against a rocker arm. the rocker arm pivots on a shaft through its center. as one side of the rocker arm moves up, the other side moves down, just like a seesaw. the downward-moving sid

58、e of the rocker arm pushes on the valve stem to open the valve.because a push-rod valve train has additional parts, it is more difficult to run at high speeds. push-rod engines typically run at slower speeds and, consequently, produce less horsepower than overhead-camshaft designs of equal size. (remember, power is the rate at which work is