【正文】 piston back on the third, or power, stroke of the cycle. The fourth stroke, as in the Ottocycle engine, is an exhaust stroke. The efficiency of the diesel engine, which is in general governed by the same factors that control the efficiency of Ottocycle engines, is inherently greater than that of any Ottocycle engine and in actual engines today is slightly more than 40 percent. Diesels are, in general, slowspeed engines with crankshaft speeds of 100 to 750 revolutions per minute (rpm) as pared to 2500 to 5000 rpm for typical Ottocycle engines. Some types of diesel, however, have speeds up to 2020 rpm. Because diesels use pression ratios of 14 or more to 1, they are generally more heavily built than Ottocycle engines, but this disadvantage is counterbalanced by their greater efficiency and the fact that they can be operated on less expensive fuel oils. By suitable design it is possible to operate an Ottocycle or diesel as a twostroke or twocycle engine with a power stroke every other stroke of the piston instead of once every four strokes. The power of a twostroke engine is usually double that of a fourstroke engine of parable size. The general principle of the twostroke engine is to shorten the periods in which fuel is introduced to the bustion chamber and in which the spent gases are exhausted to a small fraction of the duration of a stroke instead of allowing each of these operations to occupy a full stroke. In the simplest type of twostroke engine, the poppet valves are replaced by sleeve 本科 生畢業(yè) 設(shè)計（論文）外文翻譯 5 valves or ports (openings in the cylinderwall that are uncovered by the piston at the end of its outward travel). In the twostroke cycle, the fuel mixture or air is introduced through the intake port when the piston is fully withdrawn from the cylinder. The pression stroke follows, and the charge is ignited when the piston reaches the end of this stroke. The piston then moves outward on the power stroke, uncovering the exhaust port and permitting the gases to escape from the bustion chamber. In the 1950s the German engineer Felix Wankel developed an internalbustion engine of a radically new design, in which the piston and cylinder were replaced by a threecornered rotor turning in a roughly oval chamber. The fuelair mixture is drawn in through an intake port and trapped between one face of the turning rotor and the wall of the oval chamber. The turning of the rotor presses the mixture, which is ignited by a spark plug. The exhaust gases are then expelled through an exhaust port through the action of the turning rotor. The cycle takes place alternately at each face of the rotor, giving three power strokes for each turn of the rotor. Because of the Wankel engine39。在本設(shè)計中將對活塞的加工工藝進(jìn)行設(shè)計，以保證活塞長久穩(wěn)定工作。接下來經(jīng)過計算查表確定活塞各主要工序的切削用量并繪制工序卡片，最后設(shè)計夾具。 關(guān)鍵字： 活塞；工藝路線；加工設(shè)備；切削用量；夾具 任何通過燃料在氣缸中燃燒，使燃油的化學(xué)能轉(zhuǎn)化為機(jī)械能，從而獲得動力的引擎都成為內(nèi)燃機(jī)。是飛機(jī)上很常見的一種發(fā)動機(jī)；而柴油機(jī)是由法籍德國工程師 Rudolf Christian Karl Diesel 命名的。 奧托式發(fā)動機(jī)和柴油機(jī)的基本構(gòu)造都是一樣的。曲軸將活塞的 運動轉(zhuǎn)化成旋轉(zhuǎn)式的運動。這樣能夠使曲軸運動的慣性最小化，達(dá)到平衡的目的。在大多數(shù)發(fā)動機(jī)上，燃料都是通過化油器霧化后通過壓氣機(jī)進(jìn)入進(jìn)氣管道。在上世紀(jì) 80 年代，缸內(nèi)直噴技術(shù)開始用于內(nèi)燃機(jī)領(lǐng)域，從很大程度上代替了傳統(tǒng)的燃油與空氣相混合的技術(shù)。比如奧托式發(fā)動機(jī)的點火系統(tǒng)包括低壓電源 ，即具有變壓性質(zhì)的初級線圈，從而導(dǎo)出直流電。在火花塞末端的兩極間有一個間隙，高壓電流會擊穿這個點火間隙，從而點燃汽缸中的混合氣體。除此之外的還有水冷系統(tǒng)，它是在發(fā)動機(jī)的汽缸中設(shè)有水套來達(dá)到冷卻的目的。汽車發(fā)動機(jī)的啟動要靠一個與曲軸箱嚙合的摩擦片，通過摩擦片的分離才能向外輸出力矩。一般，慣性啟動裝置和爆炸性質(zhì)的裝置都是在飛機(jī)上采用的。接著的行程，就是將混合后的氣體壓縮到燃燒室里。通常，發(fā)動機(jī)的效率是由其壓縮比決定的。理論上，柴油周期相比奧托循環(huán)的區(qū)別在于，它的壓縮過程是等容、等壓的。在壓縮結(jié)束的時候，蒸發(fā)的燃油被噴入汽缸，由于汽缸中的氣體高溫作用而立本科 生畢業(yè) 設(shè)計（論文）外文翻譯 8 即燃燒。柴油機(jī)的效率，跟一般的奧托式發(fā)動機(jī)是受同樣的因素所影響的，但是稍好于奧托式發(fā)動 機(jī)。因為柴油機(jī)的壓縮比高達(dá) 14 或者 15，這使得它們的體積較奧托式大，這個缺點正體現(xiàn)出柴油機(jī)的到效率和高燃油經(jīng)濟(jì)特性。在最簡單的二沖程發(fā)動機(jī)上，排氣門被廢氣管代替了。上世紀(jì) 50 年代，德國機(jī)械師菲利克斯 .王科爾開發(fā)了一種新型的發(fā)動機(jī)。然后， 廢棄就會隨著轉(zhuǎn)子的運動從排氣口排出。在上世紀(jì) 70 年代初期，一條轉(zhuǎn)子發(fā)動機(jī)的生產(chǎn)線在日本落成。 發(fā)動機(jī)采用火花點火的改進(jìn)方式，進(jìn)行分層點火稀薄燃燒，幫助沒有使用廢氣再循環(huán)和催化轉(zhuǎn)換器的發(fā)動機(jī)減小排放量。