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1、天津職業(yè)技術(shù)師范大學(xué)2012屆本科生畢業(yè)設(shè)計(jì) Engine Fundamentals Automobiles have been operated successfully by electric motors ,steam engines ,and internal combustion engines .The internal combustion engine burns fuel within its cylinders and converts the expanding force of the burning fuel ,or combustion, into a

2、rotary force used to propel the vehicle. There are several types of internal combustion engines: two-and four-cycle reciprocating piston engines ,gas turbine engines .However ,four-cycle reciprocating engines have been refined to such a degree that they have almost complete dominance of the automot

3、ive field .Engines of other types are described in Chapter 18 ,Diesel and Other Engines. Many things are demanded of an engine used to propel an automobile. Some of the requirements are: （1）Ease of starting. （2）Reliability. （3）Power. （4）Responsiveness. （5）Economy in fuel ,oil ,and ,repairs. （

4、6）Ease of handling. （7）Quiet operation. Some of these factors conflict .For example ,a great amount of power can be had from an engine of sufficient size, but a super-size engines is not economical to operate .Therefore ,all automobile engines are a compromise in order to obtain the desirable comb

5、ination of performance and economy. Engine fuels Internal combustion engines can be made to operate on almost anything that can be converted into a combustible gas, such as wood ,coal, alcohol, vegetable oils, mineral oils, etc. However, because of convenience, a variety of petroleum products are

6、 commonly used as fuel :gasoline, kerosene ,fuel oil ,liquefied petroleum gas (LP-Gas) ect. What kerosene ,fuel oil ,or LP-Gas is used it is necessary to alter the design of the engine to achieve efficient operation. Engine Deign Gasoline engines used in automotive vehicles are of two basic types

7、:four-cycle engines and two-cycle engines .Either type may be water-cooled ,or air-cooled .Four- ,six-, and eight-cylinder engines are common However, three-, five-, ten- ,and twelve-cylinder engine are available. Almost all automobile engines have more than one cylinder. These cylinders can be ar

8、ranged in an inline ,opposed ,or V-type configuration. Engines for other purpose ,such as aviation, are arranged as radial, inverted inline ,inverted V, and X-shaped configurations. Reciprocating Engines In the typical automobile engine, a piston reciprocates (moves back and forth) within each cyl

9、inder. Each piston is connected to the crankshaft by means of a link known as a connecting rod. Other types of reciprocating engines substitutes an eccentric, an inclined plate ,or a cam mechanism for the crankshaft .The piston engine has no crankshaft or connecting rods. Engine Components The ty

10、pical automotive engine is made up of several essential components. These components are designed to provide efficient and reliable engine operation .The basic components in a four-cycle automotive engine include the following: （1）Cylinder block. （2）Crankshaft. （3）Pitons. （4）Piston rings. （5）Co

11、nnecting rods. （6）Piston pin. （7）Cylinder head. （8）Valve train(includes valves and valve operating mechanism). Engine construction Cylinder Block The cylinder block is cast in one piece. Usually, this is the largest and the most complicated single piece of metal in the automobile. The

12、cylinder block is a complicated casting made of gray iron (cast iron ) or aluminum. It contains the cylinders and the water jackets that surround them. To make the cylinder block, a sand form called a mold is made. Then molten metal is poured into the mold. When the metal has cooled the sand mold is

13、 broken up and removed. This leaves the tough cylinder-block casting. The casting. The casting is then cleaned and machined to make the finished block. Cylinder blocks for diesel engines are very similar to those for spark-ignition engines. The basic difference is that the diesel-engine cylinder b

14、lock is heavier and stronger. This is because of the higher pressures developed in the diesel-engine cylinders. Several engines have aluminum cylinder blocks. Aluminum is relatively light metal, weighing much less than cast iron. also ,aluminum conducts heat more rapidly than cast soft to use as cy

15、linder wall material. It wears too rapidly. Therefore, aluminum cylinder blocks must have cast-iron cylinder liners or be cast from an aluminum alloy that has silicon particles in it. Some manufactures make an aluminum cylinder block that does not have cylinder liners, or sleeves. Instead ,the alu

16、minum is loaded with silicon particles. Silicon is a very hard material. After the cylinder block is cast, the cylinders are honed. Then they are treated with a chemical that etches eats away, the surface aluminum. This leaves only the silicon particles exposed. the pist. The cylinder block is cast

17、 in one piece. Usually, this is the largest and the most complicated single piece of metal in the automobile. The cylinder block is a complicated casting made of gray iron (cast iron ) or aluminum. It contains the cylinders and the water jackets that surround them. To make the cylinder block, a san

18、d form called a mold is made. Then molten metal is poured into the mold. When the metal has cooled the sand mold is broken up and removed. This leaves the tough cylinder-block casting. The casting. The casting is then cleaned and machined to make the finished block. Cylinder blocks for diesel engi

19、nes are very similar to those for spark-ignition engines. The basic difference is that the diesel-engine cylinder block is heavier and stronger. This is because of the higher pressures developed in the diesel-engine cylinders. Several engines have aluminum cylinder blocks. Aluminum is relatively li

20、ght metal, weighing much less than cast iron. also ,aluminum conducts heat more rapidly than cast soft to use as cylinder wall material. It wears too rapidly. Therefore, aluminum cylinder blocks must have cast-iron cylinder liners or be cast from an aluminum alloy that has silicon particles in it.

21、 Some manufactures make an aluminum cylinder block that does not have cylinder liners, or sleeves. Instead ,the aluminum is loaded with silicon particles. Silicon is a very hard material. After the cylinder block is cast, the cylinders are honed. Then they are treated with a chemical that etches eat

22、s away, the surface aluminum. This leaves only the silicon particles exposed. the piston and rings slide on the silicon with minimum wear. Piston The piston converts the potential energy of the fuel into the kinetic energy that turns the crankshaft. The piston is a cylindrical shaped ho

23、llow part that moves up and down inside the engine’s cylinder. It has grooves around its perimeter near the top where the ring are placed. The piston fits snugly in the cylinder. It has grooves around its perimeter near the top where the rings are placed. The piston fits snugly in the cylinder. The

24、pistons ate used to ensure a snug “air tight” fit. The piston in your engine’s cylinder are similar to your legs when you ride a bicycle. Think of your legs as pistons; they go up and down on the pedals, providing power. Pedals are like the connecting rods; they are “attached” to your legs. The ped

25、als are attached to the bicycle crank which is like the crank shaft, because it turns the wheels. To reverse this, the pistons (legs) are attached to the connecting rods ( pedals ) which are attached to the crankshaft (the bicycle rank). The power from the combustion in the cylinders powers the fr

26、om the combustion rods to turn the crankshaft. Connecting rod： The connecting rod shown in is made of forged high strength steel. It transmits force and motion from the piston to the crank pin on the crankshaft. A steel piston pin, or “wrist pin”, connects the small end of the connecting rod. Some

27、 rods have a lock bolt in the small end. As the piston moves up and down in the cylinder, the pin rocks back and forth in the hole, or bore, in the piston. The big end of the connecting rod is attached to a crank pin by a rod bearing cap. Connecting rod and rod-bearing caps are assembled during man

28、ufacture. Then the hold for the bearing is bored with the cap in place. This is called line-bring. It make each rod and its cap a matched set. Usually, the same number is stamped on the rod and cap. This prevents the caps setting mixed during engine service. If the caps are mixed, the bearing bore w

29、ill not be round. An engine assembled with the rod bearing caps switched will probably lock the crankshaft. If the crankshaft turns, the bearing will probably have improper clearance and early bearing failure will result. Another reason for keeping the cap and rod matched is to prevent engine unbal

30、ance and unwanted vibration. All connecting rods in an engine must be as light as possible. But they must all weigh the same. If one rod is heavier than the other, the engine will vibrate. This could damage the engine. Crankshaft The crankshaft then main rotating member, or shaft , in the engine.

31、It has crank-pins, to which the connecting rod from the pistons are attached . During the power strokes, the connecting rods force the crank-pins and therefore the crankshaft to rotate. The reciprocating motion of the pistons is changed to rotary motion as the crankshaft spins. This rotary motion is

32、 transmitted through the power train to the car wheels. The crankshaft is a strong, one-piece casting, or forging, or heat-treated 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 vibra

33、tion. Engine Operating Principles Most automobile engines are internal combustion, reciprocating 4-stroke gasoline engines, but other types have been used, including the diesel the rotary (Wankel), the 2-stroke and the stratified charge. Reciprocating means “up and down” or “back and forth”. It

34、 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 coola

35、nt circulation. The top of the block is covered with the cylinder head, which forms the combustion chamber. 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 motio

36、n 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 up-and-down motion of the piston to the crankshaft, which change

37、s 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 compression ratio are two

38、 frequently used engine specifications. Displacement indicates engine size, and compression ratio compares the total cylinder volume to compression 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. Dependi

39、ng on the type of engine the operating cycle may require either two or four strokes to complete. 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 complete one full operating cycle. Eac

40、h stroke is named after the action it performs intake, compression, 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 o

41、pens about 10before t. d. c., giving 20overlap. The inlet valve remains open until some 50after b. d . c. to take advantage of incoming mixture. （2）Compression stroke The piston turns up, the intake valve closes, the mixture is compressed within the combustion chamber, while the pressure rise to a

42、bout 1Mpa depending on various factors including the compression 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 combustion produces a rise in pressure of the gas

43、 to some 3.5 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 50before b. d. c. , allowing the pressure within the cylinder to fall and to reduce ‘back’ piston dur

44、ing the exhaust stroke, and burned gases are pushed out to prepare for the next intake stroke. The intake valve usually opens just before the exhaust stroke. This 4 stroke cycle is continuously repeated in every cylinder as long as the engine remains running. A 2 stroke engine also goes through fo

45、ur actions to complete one operating cycle. However, the intake and the compression actions are combined in one stroke, and the power and exhaust actions are combined in the other stroke. The term 2 stroke cycle or 2 stroke is preferred to the term 2 cycle, which is really not accurate. In automobi

46、le engines, all pistons are attached to a single crankshaft. The more cylinders an engine has he more power stroke produced for each revolution. This means that an 8-cylinder engine runs more smoothly because the power strokes are closer together in time and in degrees of engine rotation. The cylin

47、ders of multi cylinder automotive engines are arranged in one of three ways. (1) Inline engines use a single block of cylinder. Most 4 cylinder and any 6 cylinder engines are of this design. The cylinders do not have to be vertical. They can be inclined to either side. (2) V-type engines use two

48、equal banks of cylinders, usually inclined 60 degrees or 90 degrees from the each other. Most V-type engines have 6 or 8 cylinders, although V 4 and V 12 engines have been built. (3) Horizontally opposed or pancake engines have two equal banks of cylinders 180degrees apart. These space saving engin

49、e designs are often air cooled, and are found in the Chevrolet Carver, Porsches, Subaru’ s, and Volkswagens. Subaru’s design is liquid cooled. Late-model Volkswagen vans use a liquid cooled version of the air cooled VW horizontally opposed engine. 發(fā)動(dòng)機(jī)基本原理 汽車已經(jīng)工作的非常成功通過電子馬達(dá)，蒸汽機(jī)，和內(nèi)

50、燃機(jī)，內(nèi)燃機(jī)在氣缸里燃燒并且將燃料燃燒發(fā)出的膨脹力轉(zhuǎn)換或旋轉(zhuǎn)力用來推動(dòng)汽車。 內(nèi)燃機(jī)有好幾種類型：兩沖程或四沖程的活塞發(fā)動(dòng)機(jī)，渦輪發(fā)動(dòng)機(jī)，自由活塞的發(fā)動(dòng)機(jī)。然而，四沖程的發(fā)動(dòng)機(jī)改進(jìn)的程度如此之高。已經(jīng)幾乎統(tǒng)治壟斷了汽車的領(lǐng)域，其它類型的發(fā)動(dòng)機(jī)，如柴油機(jī)在以后再敘述。 發(fā)動(dòng)機(jī)上的許多東西都是有要求，它們常用于推動(dòng)發(fā)動(dòng)機(jī)，許多的要求如下： （1）容易起動(dòng)性能： (2)可靠性。 (3)動(dòng)力性。 (4)靈敏性。 (5)燃料，機(jī)油，維修的經(jīng)濟(jì)性。 (6)輕便的操縱性。 (7)安全的工作性能。 有些性能是互相沖突的，例如，很大的動(dòng)力需要以尺寸是足夠大的發(fā)動(dòng)機(jī)上獲得，但是這么大的尺寸的發(fā)

51、動(dòng)機(jī)工作時(shí)經(jīng)濟(jì)性不好，因此，所有汽車的發(fā)動(dòng)機(jī)都是為獲的滿意的性能和經(jīng)濟(jì)性。 發(fā)動(dòng)機(jī)的燃料 內(nèi)燃機(jī)能被制造或依靠幾乎任務(wù)東西運(yùn)行的，只要這些東西能轉(zhuǎn)換或燃料的氣體。例如木材，煤礦，酒精，植物油，礦物油等，燃而，因?yàn)檫m合方便，各種各樣的石油產(chǎn)品被用來作為燃料，汽油，煤油，液化氣等當(dāng)煤油，燃油或液化氣被使用時(shí)，必須改變發(fā)動(dòng)機(jī)的設(shè)計(jì)從而獲得較高的效率。 發(fā)動(dòng)機(jī)的設(shè)計(jì) 用于車輛上的汽油發(fā)動(dòng)機(jī)有兩種基本類型，四沖程發(fā)動(dòng)機(jī)任何其中一種類型都應(yīng)是水冷或風(fēng)冷，四缸六缸和八缸的發(fā)動(dòng)機(jī)都是普通常見的燃而三缸五缸十缸的發(fā)動(dòng)機(jī)都是可以利用的 幾乎所有汽車的發(fā)動(dòng)機(jī)的汽缸都不少于一個(gè)。這些汽缸都被設(shè)計(jì)或線性排列對(duì)

52、置或V型的結(jié)構(gòu)，其它途徑的發(fā)動(dòng)機(jī)例如航空應(yīng)用的都被設(shè)計(jì)成輻射狀的倒置反轉(zhuǎn)的V型的結(jié)構(gòu)。 往復(fù)式發(fā)動(dòng)機(jī) 在這種類型汽車的發(fā)動(dòng)機(jī)里，活塞在各自的汽缸里往復(fù)運(yùn)動(dòng)。每個(gè)活塞通過連桿被連接在曲軸上。 其它類型往復(fù)式發(fā)動(dòng)機(jī)的的代表是離心的，有斜向的盤子，或在曲軸上有一個(gè)凸輪機(jī)構(gòu)。自由活塞的發(fā)動(dòng)機(jī)沒有曲軸或連桿。 發(fā)動(dòng)機(jī)的部件 典型的汽車的發(fā)動(dòng)機(jī)是由許多必須的部件組成的，這些部件被設(shè)計(jì)成用來提供發(fā)動(dòng)機(jī)運(yùn)行的可靠性和高效率性。四缸汽車發(fā)動(dòng)機(jī)的基本部件包括： （1）汽缸體。 （2）曲軸。 （3）活塞。 （4）活塞環(huán)。 （5）連桿。 （6）活塞銷。 （7）汽缸蓋。 （8）氣閥結(jié)構(gòu)。

53、 發(fā)動(dòng)機(jī)結(jié)構(gòu) 汽缸體 汽缸體是鑄造成而成一體的。通常，這是發(fā)動(dòng)機(jī)上最大，最復(fù)雜的鐵制的部件。 汽缸體是用灰鑄鐵或鋁鑄造成的。它包括汽缸體本身和環(huán)繞在周圍的水套。要做汽缸體需要一個(gè)沙模模型，然后將金屬溶液倒入模型中。當(dāng)金屬溶液冷卻后，將模型打破拿走，只剩下了一個(gè)粗糙的汽缸體。然后將它清潔機(jī)加工，最后完成一個(gè)汽缸體。 柴油機(jī)用的發(fā)動(dòng)機(jī)與汽油機(jī)用的非常相似。最根本的不同是柴油機(jī)的比汽油機(jī)的更加堅(jiān)固更沉。這是因?yàn)椴裼蜋C(jī)產(chǎn)生的氣缸壓力更大。 有許多發(fā)動(dòng)機(jī)用的是鋁制的氣缸。鋁也是一種金屬，重量比鑄鐵要輕很多，并且鋁的

54、導(dǎo)熱速度比鑄鐵的要快。這就是說它發(fā)生爆燃的可能性要小。然而，鋁作為汽缸體材料來說較軟，鋁的磨損也非?？臁Ｒ虼?，鋁制氣缸要有氣缸襯套，因此在鋁中加入硅粒子形成鋁合金。 一些制造商制造的鋁制氣缸也沒有氣缸。他在鋁中加入了硅粒子。硅是非常硬的材料。氣缸在鑄造后，要進(jìn)行研磨。然后給它們涂上一層化學(xué)制劑，把表面上的鋁腐蝕掉。這樣只剩下硅存在表面。此時(shí)，活塞和環(huán)磨損最小。 活塞 活塞將化學(xué)能轉(zhuǎn)變?yōu)閯?dòng)能傳給曲軸?；钊且粋€(gè)圓柱狀放在氣缸內(nèi)的物體?；钊敳坑蟹胖没钊h(huán)的活塞環(huán)槽?；钊梢愿线m的放在氣缸中。活塞環(huán)用來保持氣缸的氣密性。 活塞在氣缸中就像你在騎自行車時(shí)的腿。認(rèn)為你的腿和活塞一樣；當(dāng)上下踏

55、腳踏板時(shí)可以產(chǎn)生動(dòng)力。腳踏板就像連桿；它連著你的腿。踏板連著自行車的軸，這個(gè)軸類似于曲軸因?yàn)樗灿脕眚?qū)動(dòng)車輪。 反過來，活塞與連桿連著，連桿連在曲軸上。動(dòng)力從氣缸燃燒產(chǎn)生，推動(dòng)活塞并帶動(dòng)曲軸旋轉(zhuǎn)。 連桿 連桿通過軸瓦與曲軸聯(lián)在一起。鋼制的活塞銷將連桿和活塞連在一起。這個(gè)銷子用來連接連桿小頭的。一些連桿在連桿小頭用鎖銷。隨著活塞在氣缸內(nèi)上下運(yùn)動(dòng)，銷在孔內(nèi)來回運(yùn)動(dòng)。連桿大端用軸瓦與曲軸相連。 連桿和連桿軸瓦的間隙是在制造中造好的。裝軸瓦時(shí)必須使軸瓦上的小孔與連桿上的對(duì)準(zhǔn)。這叫直線銷。它用在每個(gè)連桿和它的配合偶件上。通常，連桿蓋上都印有數(shù)字。這可以防止在發(fā)動(dòng)機(jī)維修時(shí)裝錯(cuò)。如果連桿蓋混淆，軸承

56、將運(yùn)轉(zhuǎn)不良。發(fā)動(dòng)機(jī)在運(yùn)轉(zhuǎn)時(shí)可能發(fā)生曲軸抱死。如果曲軸旋轉(zhuǎn)，軸瓦可能由于間隙不符合要求而發(fā)生過早磨損或失效。 另一個(gè)保持連桿蓋順序的原因時(shí)防止發(fā)動(dòng)機(jī)在運(yùn)轉(zhuǎn)時(shí)不平穩(wěn)，從而產(chǎn)生不必要的振動(dòng)。發(fā)動(dòng)機(jī)內(nèi)所有的曲軸重量必須盡可能一致，但不是必須相等。如果一個(gè)連桿比另一個(gè)輕發(fā)動(dòng)機(jī)會(huì)出現(xiàn)振動(dòng)。這將破壞發(fā)動(dòng)機(jī)。 曲軸 它有連桿軸頸，用來傳遞活塞傳來的動(dòng)力。在做功行程中，連桿推動(dòng)連桿軸頸，因此曲軸旋轉(zhuǎn)。在活塞的往復(fù)運(yùn)動(dòng)中將往復(fù)運(yùn)動(dòng)轉(zhuǎn)變?yōu)榍S的旋轉(zhuǎn)運(yùn)動(dòng)。旋轉(zhuǎn)運(yùn)動(dòng)通過傳動(dòng)系將動(dòng)力傳給車輪。 曲軸非常堅(jiān)硬，它是一塊合金經(jīng)過鍛造、熱加工而成的。它必須非常堅(jiān)硬，以承受做功行程的力而不發(fā)生彎曲。它必須要平衡以避免發(fā)動(dòng)

57、機(jī)發(fā)生不必要的振動(dòng)。 發(fā)動(dòng)機(jī)工作原理 大多數(shù)發(fā)動(dòng)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(dòng)機(jī)，包括一些柴油機(jī)和一些旋轉(zhuǎn)的機(jī)器。 往復(fù)移動(dòng)就是說“上上下下”或者說“里里外外”的移動(dòng)。氣缸中的活塞是上上下下的移動(dòng)的，它使往復(fù)循環(huán)的發(fā)動(dòng)機(jī)產(chǎn)生動(dòng)力。大多數(shù)發(fā)動(dòng)機(jī)是依靠汽缸體或者說發(fā)動(dòng)機(jī)體。機(jī)體是用鐵或鋁鑄造成的，里面包含著氣缸和水套，水套是為了冷卻水在里面循環(huán)。機(jī)體上部蓋有氣缸蓋，它是燃燒室的一部分。機(jī)體底部蓋有油底殼或者叫集油器。 動(dòng)力是由氣缸內(nèi)活塞底直線運(yùn)動(dòng)而產(chǎn)生底。然而，這個(gè)直線運(yùn)動(dòng)必須要變?yōu)檐囕喌仔D(zhuǎn)運(yùn)功。活塞上連著一個(gè)銷子，叫活塞銷。下面連著連桿。連桿將活塞底上下直線運(yùn)動(dòng)變

58、為旋轉(zhuǎn)運(yùn)動(dòng)。連桿通過一個(gè)叫連桿軸承的零件裝在曲軸上。和軸承類似，也叫主軸承備用來將曲軸裝在機(jī)體上。 氣缸的直徑叫做發(fā)動(dòng)機(jī)的內(nèi)徑。發(fā)動(dòng)機(jī)排量和壓縮比是發(fā)動(dòng)機(jī)兩個(gè)常用的參數(shù)。排量表示發(fā)動(dòng)機(jī)的大小，壓縮比是整個(gè)氣缸容積與發(fā)動(dòng)機(jī)燃燒室容積的比值。 術(shù)語中的“沖程”是用來描述活塞在氣缸內(nèi)的運(yùn)動(dòng)狀態(tài)的，和活塞通過的行程一樣。根據(jù)發(fā)動(dòng)機(jī)的型號(hào)，一個(gè)工作循環(huán)需要兩個(gè)或四個(gè)沖程來完成。四沖程發(fā)動(dòng)機(jī)也叫奧托發(fā)動(dòng)機(jī)，是為了紀(jì)念德國工程師，奧托先生，他在1876年第一次提出了這個(gè)理論。在四沖程發(fā)動(dòng)機(jī)中，活塞需要在一個(gè)工作循環(huán)完成四個(gè)沖程。每個(gè)沖程用它們的運(yùn)動(dòng)狀態(tài)來命名，按順序進(jìn)氣、壓縮、做功、排氣。 （1）進(jìn)氣

59、沖程 隨著活塞向下移動(dòng)，可燃油氣混合氣通過開啟的進(jìn)氣門進(jìn)入氣缸。為了使混合氣能充滿氣缸，進(jìn)氣門要在上止點(diǎn)前10開啟，并有20的重疊角。進(jìn)氣門直到下止點(diǎn)后50才開啟，以利用進(jìn)氣慣性。 （2）壓縮沖程 活塞向上運(yùn)動(dòng)，進(jìn)氣門關(guān)閉，混合氣被壓縮在燃燒室內(nèi)，壓力迅速上升到MPa，這是和壓縮比，節(jié)氣門開啟度和發(fā)動(dòng)機(jī)轉(zhuǎn)速等有關(guān)。在活塞接近上止點(diǎn)時(shí)，混合氣被擊穿火花塞間隙的火花點(diǎn)燃。 （3）做功沖程 混合氣燃燒膨脹產(chǎn)生的壓力使氣壓上升到3.5MPa，氣缸內(nèi)的活塞開始被推動(dòng)，排氣門在接近下止點(diǎn)時(shí)打開。 （4）排氣沖程 活塞向下運(yùn)動(dòng)，排氣門在上止點(diǎn)前50打開，允許氣缸內(nèi)的氣體排出，并準(zhǔn)備為下一次進(jìn)氣

60、沖程做準(zhǔn)備。進(jìn)氣門經(jīng)常在排氣行程前一點(diǎn)打開。 只要發(fā)動(dòng)機(jī)運(yùn)轉(zhuǎn)，氣缸的四個(gè)沖程就周而復(fù)始的不停重復(fù)。 一個(gè)兩沖程的發(fā)動(dòng)機(jī)也是通過四個(gè)動(dòng)作來完成一個(gè)工作循環(huán)的。然而，進(jìn)氣和壓縮兩個(gè)動(dòng)作被合并為一個(gè)沖程，做功和排氣被合并為一個(gè)沖程。 在汽車發(fā)動(dòng)機(jī)中，所有的活塞共用一個(gè)曲軸。發(fā)動(dòng)機(jī)的氣缸越多，每轉(zhuǎn)的做功行程就越長(zhǎng)。這也就是說一個(gè)8缸發(fā)動(dòng)機(jī)運(yùn)轉(zhuǎn)的更加平穩(wěn)，因?yàn)槊總€(gè)缸的做功沖程在一個(gè)工作循環(huán)內(nèi)間隔的時(shí)間就越短。 一個(gè)多缸發(fā)動(dòng)機(jī)有三種布置形式。 （1）直列式。大多數(shù)4缸和六缸發(fā)動(dòng)機(jī)用這種設(shè)計(jì)方案。 （2）V型氣缸量列同樣的氣缸，彼此相差60度或90度。大多數(shù)V型發(fā)動(dòng)機(jī)有6缸或8缸，但也有4缸機(jī)和12缸機(jī)也用這種排列。 （3）兩列氣缸彼此相差180度成臥式。這種發(fā)動(dòng)機(jī)通常是風(fēng)冷的，在保時(shí)捷、大眾等車型上長(zhǎng)見到，但也有用水冷的。