【正文】 NSMost automobile dngines are internal bustion, reciprocating 4stroke gasoline engines, but other types have been used, including the diesel, the rotary ( Wankel ) , the 2srtoke, and stratified charge.Reciprocating means up and down or banck and forth, It is the up and down action of a piston in the cylinder blick, or engine block. The blick is an iron or aluminum casting that contains engine cylinders and passges called water jackets for coolant circulation. The top of the block is covered with the cylinder head. Which forms the bustion chanber. The bottom of the block is covered with an oil pan or oil sump.Power is produced by the linear motion of a piston in a cylinder. However, this linear motion must be changed into rotary motion to turn the wheels of cars of trucks. The piston is attached to the top of a connecting rod by a pin, called a piston pin or wrist pin. The bottom of the connecting rod is attached to the crankshaft. The connecting rod transmits the upanddown motion of the piston to the crankshaft, which changes it into rotary motion.The connecting rod is mounted on the crankshaft with large beaings called rod bearings. Similar bearings, called main bearings, are used to mount the crankshaft in the block. Shown in Fig. 11The diameter of the cylinder is called the engine bore. Displacement and pression ratio are two frequently used engine specifications. Displacement indicates engine size, and pression ratio pares the total cylinder volume to pression chamber volume. The term stroke is used to describe the movement of the iston within the cylinder, as well as the distance of piston travel. Depending on the type of engine the operating cycle may require either two or four strokes to plete. The 4stroke engine is also called Otto cycle engine, in honor of the German engineer, Dr. Nikolaus Otto, who first applied the principle in 1876. In the 4stroke engine, four strokes of the piston in the cylinder are required to plete one full operating cycle. Each stroke is named after the action it performs intake, pression, power, and exhaust in that order, shown in Fig12.Intake stroke As the piston moves down, the vaporized mixture of fuel and air enters the cylinder through open intake valve. To obtain the maximum filling of the cylinder the intake valve opens about 10176。before ., giving 20176。overlap. The inlet valve remains open until some 50176。after . to take advantage of ining mixture.Compression stroke The piston turns up, the intake valve closes, the mixture is pressed within the bustion chamber, while the pressure rise to about 1Mpa, depending on various factors including the pression ratio, throttle opening and engine speed. Near the top of the stroke the mixture is ignited by a spark which bridges the gap of the spark plug. Power stroke The expanding gases of bustion produces a rise in pressure of the gas to some , and the piston is forced down in the cylinder. The exhaust valve opens near the bottom of the stroke.Exhust stroke The piston moves back up with the exhaust valve open some 50176。before ., allowing the pressure within the cylinder to fall and to reduce ‘back’pressure on the piston during the exhaust stroke, and the burned gases are pushed out to prepare for the next intake intake valve usually opens just before the exhaust stroke.This 4stroke cycle is continuously repeared in every as long as the engineremains running.A 2stroke engine also goes through four actions to plete one operating cycle.However, the intake and the pression actions are bined in one seroke, and the power and exhaust actions are bined in the other stroke. The term2stroke cycle or 2stroke is preferred to the term 2cycle, which is really not accurate.In automobile engines, all pistons are attached to a single crankshaft. The more cylinders an engine has, the more power strokes produced for cach revolution. This means that an 8cylinder engine runs more smoothly bdcause the power atrokes are closer together in time and in degrees of engine rotation.The cylinders of multicylinder automotive engines arranged in one of three ways.Inline engines use a single block of 4cylinder and any 6cylinder engines are of this design. The cylinders do not have to be vertical. They can be inclined either side.Vtype engines use two equal bands of cylinders, usually inclined 60degrees or 90degrees from the cach other. Most Vtype engines have 6 or 8 cylinders, although V4 and V12 engines have been built.Horizontally opposed or pancake engines have two equal banks of cylinders 180degreeas apart. These space saving engine designs are often aircooled, and are found in the Chevrolet Carvair, Porsches, Subaus, and Volkswagens. Subaus design is liquid cooled.Latemodel Volkswagen vans use a liquidcooled version of the air cooled VWhorizontally opposed engine.譯文大多數(shù)汽車的發(fā)動(dòng)機(jī)是內(nèi)燃機(jī)，往復(fù)四沖程汽油機(jī)，但是也有使用其它類型的發(fā)動(dòng)機(jī)，包括柴油機(jī)，轉(zhuǎn)子發(fā)動(dòng)機(jī)，二沖程發(fā)動(dòng)機(jī)和分程燃燒發(fā)動(dòng)機(jī)。往復(fù)的意思就是上下運(yùn)動(dòng)或前后運(yùn)動(dòng)，在往復(fù)發(fā)動(dòng)機(jī)中，氣缸中活塞的上下運(yùn)動(dòng)產(chǎn)生發(fā)動(dòng)機(jī)的動(dòng)力，這種類型幾乎所有的發(fā)動(dòng)機(jī)都是依賴氣缸體即發(fā)動(dòng)機(jī)缸體，缸體是鑄鐵或鑄鋁制的，它包括發(fā)動(dòng)機(jī)氣缸和冷卻液循環(huán)用的水套。缸體的頂部是氣缸蓋，它組成了燃燒室，缸體底部是油底殼。氣缸內(nèi)活塞的直線運(yùn)動(dòng)產(chǎn)生動(dòng)力，然而，必須將直線運(yùn)動(dòng)轉(zhuǎn)化成旋轉(zhuǎn)運(yùn)動(dòng)，使汽車車輪轉(zhuǎn)動(dòng)，活塞銷將活塞連接在連桿頂部，連桿底部與曲軸連接，使汽車車輪轉(zhuǎn)動(dòng)，活塞銷將活塞連桿頂部，連桿底剖與曲軸連接，連桿將活塞的往復(fù)運(yùn)動(dòng)傳遞給曲軸，曲軸將其轉(zhuǎn)化為旋轉(zhuǎn)運(yùn)動(dòng)，連桿是用連桿曲軸安裝在曲軸上的，用類似的軸承即主軸承將曲軸固定在缸體內(nèi)。氣缸的直徑稱為發(fā)動(dòng)機(jī)的內(nèi)徑，排量和壓縮比是兩個(gè)常用的發(fā)動(dòng)機(jī)參數(shù)，排量是指發(fā)動(dòng)機(jī)的大小，壓縮比是氣缸總?cè)莘e與燃燒室壓縮容積之比。術(shù)語(yǔ): 沖程是用來(lái)說(shuō)明活塞在氣缸內(nèi)的運(yùn)動(dòng)，也就是活塞行程的距離根據(jù)發(fā)動(dòng)機(jī)類型的需要二沖程或四沖程來(lái)完成一個(gè)工作循環(huán)四沖程發(fā)動(dòng)機(jī)也叫做奧托發(fā)動(dòng)機(jī)，為了紀(jì)念德國(guó)工程師奧托，他是在1876年第一個(gè)應(yīng)用該原理的，在四沖程發(fā)動(dòng)機(jī)中，要求氣缸活塞四沖程來(lái)完成一個(gè)完整的工作循環(huán)，每個(gè)沖程根據(jù)其行為命名分別為: 進(jìn)氣沖程，壓縮沖程，作功沖程和排氣沖程。進(jìn)氣沖程當(dāng)活塞下移時(shí)，霧化后的可燃混合氣通過(guò)打開(kāi)的進(jìn)氣門進(jìn)入氣缸，為了達(dá)到最大的進(jìn)氣量，進(jìn)氣門在活塞到達(dá)上止點(diǎn)前10176。打開(kāi)，使進(jìn)、排氣門有20176。打開(kāi)重疊角，進(jìn)氣門一直打開(kāi)到活塞到達(dá)下止點(diǎn)充分進(jìn)入混合氣之后50176。左右。壓縮沖程活塞開(kāi)始向上移動(dòng)時(shí)，進(jìn)氣門關(guān)閉，混合氣在燃燒室中壓縮，根據(jù)不同因素包括壓縮比，節(jié)氣門開(kāi)度，發(fā)動(dòng)機(jī)轉(zhuǎn)速壓力上升到約1兆帕，接近沖程頂部時(shí)，火花塞產(chǎn)生的電火花擊穿點(diǎn)火間隙點(diǎn)燃可燃混合氣。作功沖程，推動(dòng)活塞下移，接近氣缸底時(shí)，排氣門打開(kāi)。排氣沖程隨著排氣門開(kāi)啟約下止點(diǎn)前50176。，活塞回升，使氣缸內(nèi)壓力下降在排氣沖程，減少對(duì)活塞回壓，派出廢氣，為下一個(gè)進(jìn)氣沖程作準(zhǔn)備，通常情況下，進(jìn)氣門在排氣沖程完成前打開(kāi)。只要發(fā)動(dòng)機(jī)保持運(yùn)轉(zhuǎn)，每個(gè)氣缸內(nèi)四個(gè)沖程循環(huán)連續(xù)不斷地重復(fù)下去。兩沖程發(fā)動(dòng)機(jī)也同樣通過(guò)四行程來(lái)完成，一個(gè)工作循環(huán)但是進(jìn)氣沖程，壓縮沖程合為一個(gè)沖程，作功沖程形成另一個(gè)沖程，術(shù)語(yǔ)兩行程循環(huán)和兩行程就是所謂的術(shù)語(yǔ)雙循環(huán)但實(shí)際上并不太準(zhǔn)確。在所用的汽車