【正文】 r heattreated alloy steel. It must be strong to take the downward force of power strokes without excessive bending. It must be balanced so the engine will run without excessive vibration. Engine Operating Principles Most automobile engines are internal bustion, reciprocating 4stroke gasoline engines, but other types have been used, including the diesel the rotary (Wankel), the 2stroke and the stratified charge. Reciprocating means “up and down” or “back and forth”. It is the up and down action of a piston in the cylinder that produces power in a reciprocating engine. Almost all engines of this type are built upon a cylinders block, or engine block. The block is an iron or aluminum casting that contains engine cylinders and passages called water jackets for coolant circulation. The top of the block is covered with the cylinder head, which forms the bustion chamber. The bottom of the block is covered with an oil pan or oil sump. 天津職業(yè)技術(shù)師范大學(xué) 2021屆本科生畢業(yè)設(shè)計 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 and 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 bearings called rod bearings. Similar bearings, called main bearings, are used to mount the crankshaft in the block. The 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 piston 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 4 stroke engine is also called Otto, who first applied the principle in 1876. In the 4 stroke 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. （ 1） Intake stroke As the piston moves down, the vaporized mixture of fuel and air enters the cylinder through the open intake valve. To obtain the maximum filling of the cylinder the intake valve opens about 10176。after b. d . c. to take advantage of ining mixture. （ 2） 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. （ 3） Power stroke The expanding gases of bustion produces a rise in pressure of the gas to some Mpa, and the piston is forced down in the cylinder. The exhaust valve opens near the bottom of the stroke. （ 4） Exhaust stroke The piston moves back up with the exhaust valve open some 50176。 (5)燃料，機(jī)油，維修的經(jīng)濟(jì)性。 往復(fù)式發(fā)動機(jī) 在這種類型汽車的發(fā)動機(jī)里，活塞在各自的汽缸里往復(fù)運(yùn)動。 （ 4）活塞環(huán)。它包括汽缸體本身和環(huán) 繞在周圍的水套。鋁也是一種金屬，重量比鑄鐵要輕很多，并天津職業(yè)技術(shù)師范大學(xué) 2021屆本科生畢業(yè)設(shè)計 且鋁的導(dǎo)熱速度比鑄鐵的要快。然后給它們涂上一層化學(xué)制劑，把表面上的鋁腐蝕掉。 活塞在氣缸中就像你在騎自行車時的腿。這個銷子用來連接連桿小頭的。通常，連桿蓋上都印有數(shù)字。這將破壞發(fā)動機(jī)。 發(fā)動機(jī)工作原理 大多數(shù)發(fā)動機(jī)是四沖程往復(fù)式內(nèi)部燃燒，但也有的是兩沖程的發(fā)動機(jī)，包括一些柴油機(jī)和一些旋轉(zhuǎn)的機(jī)器。然而，這個直線運(yùn)動必須要變?yōu)檐囕喌仔D(zhuǎn)運(yùn)功。排量表示發(fā)動機(jī)的大小，壓縮比是整個氣缸容積與發(fā)動機(jī)燃燒室容積的比值。 開啟，并有 20176。 打開，允許氣缸內(nèi)的氣體排出，并準(zhǔn)備為下一次進(jìn)氣沖程做準(zhǔn)備。 一個多缸發(fā)動機(jī)有三種布置形