外文翻译--汽车发动机.doc

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1、译文题目： Automobile engine 汽车发动机 AUTOMOTIVE ENGINE1 Engine Classification and Overall MechanicsThe automobile engines can be classified according to: (1) cycles, (2) cooling system, (3) fuel system, (4) ignition method, (5) valve arrangement, (6) cylinder arrangement, (7) engine speed. Engines used in

2、automobiles are the internal combustion heat engines. The burning of gasoline inside the engine produces high pressure in the engine combustion chamber. This high pressure force piston to move, the movement is carried by connecting rods to the engine crankshaft. The crankshaft is thus made to rotate

3、: the rotary motion is carried through the power train to the car wheels so that they rotate and the car moves. The engine requires four basic systems to run (Fig. 2-1). Diesel engines require three of these systems. They are fuel system, ignition system (except diesel), lubricating system and cooli

4、ng system. However, three other related systems are also necessary. These are the exhaust system, the emission-control system, and the starting system. Each performs a basic job in making the engine run. Fig. 2-1 The engine construction2EngineOperating PrinciplesFig. 2-2 Engine termsThe term “stroke

5、” is used to describe the movement of the piston within the cylinder. The movement of the piston from its uppermost position (TDC, top dead center) to its lowest position (BDC, bottom dead center) is called a stroke. The operating cycle may require either two or four strokes to complete. Most automo

6、bile engines operate on the four stroke cycle (Fig. 2-2).In four-stroke engine, four strokes of the piston in the cylinder are required to complete one full operating cycle. Each stroke is named after the action. It performs intake, compression, power, and exhaust in that order (Fig. 2-3). Intake st

7、roke Compression stroke Power stroke Exhaust strokeFig. 2-3 Four-stroke-cycle gasoline engine1. The intake strokeThe intake stroke begins with the piston near the top of its travel. As the piston begins its descent, the exhaust valve closes fully, the intake valve opens and the volume of the combust

8、ion chamber begins to increase, creating a vacuum. As the piston descends, an air/fuel mixture is drawn from the carburetor into the cylinder through the intake manifold. The intake stroke ends with the intake valve close just after the piston has begun its upstroke.2. Compression strokeAs the pisto

9、n is moved up by the crankshaft from BDC, the intake valve closes. The air/fuel mixture is trapped in the cylinder above the piston. Future piston travel compresses the air/fuel mixture to approximately one-eighth of its original volume (approximately 8:1 compression ratio) when the piston has reach

10、ed TDC. This completes the compression stroke.3. Power strokeAs the piston reaches TDC on the compression stroke, an electric spark is produced at the spark plug. The ignition system delivers a high-voltage surge of electricity to the spark plug to produce the spark. The spark ignites, or sets fire

11、to, the air/fuel mixture. It now begins to burn very rapidly, and the cylinder pressure increases to as much as 3-5MPa or even more. This terrific push against the piston forces it downward, and a powerful impulse is transmitted through the connecting rod to the crankpin on the crankshaft. The crank

12、shaft is rotated as the piston is pushed down by the pressure above it.4. Exhaust strokeAt the end of the power stroke the camshaft opens the exhaust valve, and the exhaust stroke begins. Remaining pressure in the cylinder, and upward movement of the piston, force the exhaust gases out of the cylind

13、er. At the end of the exhaust stroke, the exhaust valve closes and the intake valve opens, repeating the entire cycle of events over and over again.3 Engine Block and Cylinder Head3.1 Engine Block The engine block is the basic frame of the engine. All other engine parts either fit inside it or faste

14、n to it. It holds the cylinders, water jackets and oil galleries (Fig. 2-4). The engine block also holds the crankshaft, which fastens to the bottom of the block. The camshaft also fits in the block, except on overhead-cam engines. In most cars, this block is made of gray iron, or an alloy (mixture)

15、 of gray iron and other metals, such as nickel or chromium. Engine blocks are castings.Fig. 2-4 V6 engine blockSome 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. Therefore, the cylinders in

16、most aluminum engines are lined with iron or steel sleeves. These sleeves are called cylinder sleeves. Some engine blocks are made entirely of aluminum.3.2 Cylinder SleevesCylinder sleeves are used in engine blocks to provide a hard wearing material for pistons and piston rings. The block can be mad

17、e of one kind of iron that is light and easy to cast while the sleeves uses another that is better able to stand up wear and tear. There are two main types of sleeves: dry and wet (Fig. 2-5).Dry sleeve Wet sleeveFig. 2-5 Cylinder sleeve3.3 Cylinder Head The cylinder head fastens to the top of the bl

18、ock, just as a roof fits over a house. The underside forms the combustion chamber with the top of the piston. In-line engine of light vehicles have just one cylinder head for all cylinders; larger in-line engines can have two or more. Just as with engine blocks, cylinder heads can be made of cast ir

19、on or aluminum alloy. The cylinder head carries the valves, valve springs and the rockers on the rocker shaft, this part of valve gear being worked by the pushrods. Sometimes the camshaft is fitted directly into the cylinder head and operates on the valves without rockers. This is called an overhead

20、 camshaft arrangement.3.4 Gasket The cylinder 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. Gaskets are also used to seal joins be

21、tween the other parts, such as between the oil pan, manifolds, or water pump and the blocks.3.5 Oil Pan The oil pan is usually formed of pressed steel. The oil pan and the lower part of cylinder block together are called the crankcase; they enclose, or encase, the crankshaft. The oil pump in the lub

22、ricating system draws oil from the oil pan and sends it to all working parts in the engine. The oil drains off and run down into the pan. Thus, there is a constant circulation of oil between the pan and the working parts of the engine. 4 Piston Assembly, pistonrings , Thepistonpin ,Connecting Rods,

23、Crankshafts And Flywheel4.1 Piston Piston rings and the piston pin are together called the piston assembly (Fig. 2-6).Fig. 2-6 Piston, piston rings and connecting rodThepistonisanimportantpartofafour-strokecycleengine.Mostpistonsaremadefromcastaluminum.Thepiston,throughtheconnectingrod,transferstoth

24、ecrankshafttheforcecreatedbytheburningfuelmixture.Thisforceturnsthecrankshaft.Towithstandtheheatofthecombustionchamber,thepistonmustbestrong.Italsomustbelight,sinceittravelsathighspeedsasitmovesupanddowninsidethecylinder.Thepistonishollow.Itisthickatthetopwhereittakesthebruntoftheheatandtheexpansion

25、force.Itisthinatthebottom,wherethereislessheat.Thetoppartofthepistonisthehead,orcrown.Thethinpartistheskirt.Mostpistonshavethreeringgroovesatthetop.Thesectionsbetweentheringgroovesarecalledringlands.4.2 pistonringspistonringsfitintoringgroovesnearthetopofthepiston.Insimplestterms,pistonringsarethin,

26、circularpiecesofmetalthatfitintogroovesinthetopsofthepistons.Inmodernengines,eachpistonhasthreerings.(Pistoninolderenginessometimeshadfourrings,orevenfive.)Theinsidesurfaceoftheringfitsinthegrooveonthepiston.Theringsoutsidesurfacepressesagainstthecylinderwalls.Ringsprovidetheneededsealbetweenthepist

27、onandthecylinderwalls.Thatis,onlytheringscontactthecylinderwalls.Thetoptworingsaretokeepthegasesinthecylinderandarecalledcompressionrings.Theloweronepreventstheoilsplashedontothecylinderborefromenteringthecombustionchamber,andiscalledanoilring.4.3 ThepistonpinThepistonpinholdstogetherthepistonandthe

28、connectingrod.Thispinfitsintothepistonpinholesandintoaholeinthetopendoftheconnectingrod.Thetopendoftherodismuchsmallerthantheendthatfitsonthecrankshaft.Thissmallendfitsinsidethebottomofthepiston.Thepistonpinfitsthroughonesideofthepiston,throughthesmallendoftherod,andthenthroughtheothersideofthepisto

29、n.Itholdstherodfirmlyinplaceinthecenterofthepiston.Pinsaremadeofhigh-strengthsteelandhaveahollowcenter.Manypinsarechrome-platedtohelpthemwearbetter.Apistonpinfitsintoaroundholeinthepiston.Thepistonpinjoinsthepistontotheconnectingrod.Thethickpartofthepistonthatholdsthepistonpinisthepinboss.4.4 Connec

30、ting RodsTheconnectingrodlittleendisconnectedtothepistonpin.Abushmadefromasoftmetal,suchasbronze,isusedforthisjoint.Thelowerendoftheconnectingrodfitsthecrankshaftjournal.Thisiscalledthebigend.Forthisbig-endbearing,steel-backedleadortinshellbearingsareused.Thesearethesameasthoseusedforthemainbearings

31、.Thesplitofthebigendissometimesatanangle,sothatitissmallenoughtobewithdrawnthroughthecylinderbore.Theconnectingrodismadefromforgedalloysteel.4.5 CrankshaftsThe crankshaft is regarded as the “backbone” of the engine (Fig. 2-7). Thecrankshaft,inconjunctionwiththeconnectingrod,convertsthereciprocatingm

32、otionofthepistontotherotarymotionneededtodrivethevehicle.Itisusuallymadefromcar-bonsteelwhichisalloyedwithasmallproportionofnickel.Themainbearingjournalsfitintothecylinderblockandthebigendjournalsalignwiththeconnectingrods.Attherearendofthecrankshaftisattachedtheflywheel,andatthefrontendarethedrivin

33、gwheelsforthetiminggears,fan,coolingwaterandalternator.Thethrowofthecrankshaft,i.e.thedistancebetweenthemainjournalandthebigendcenters,controlsthelengthofthestroke.Thestrokeisdoublethethrow,andthestrokelengthisthedistancethatthepistontravelsfromTDCtoBDCandviceversa.Fig. 2-7 The crankshaft4.6 Flywhee

34、lTheflywheelismadefromcarbonsteel.Itfitsontotherearofthecrankshaft.Aswellaskeepingtheenginerotatingbetweenpowerstrokesitalsocarriestheclutch,whichtransmitsthedrivetothegearbox,andhasthestarterringgeararounditscircumference.Thereisonlyoneworkingstrokeinfoursoaflywheelisneededtodrivethecrankshaftdurin

35、gthetimethattheengineisperformingthenon-powerstrokes.5 Valve System Fig. 2-8 Parts of the valve trainThe valve operating assembly includes the lifters or cam followers, pushrods, rocker arms and shafts or pivot, valve and springs etc. The purpose of this to open and close the intake and exhaust port

36、s that lead to the combustion chambers as required (Fig. 2-8). Valve mechanisms vary depending on the camshaft location. When the camshaft is positioned in the engine block, valve lifters are mounted in the openings above the camshaft. Pushrods are connected from each valve lifter to a pivoted rocke

37、r arm mounted above each valve. A lobe on the camshaft is positioned directly below each valve lifter. A typical camshaft drive has a sprocket bolted to the end of the camshaft, and a matching sprocket is attached to the end of the crankshaft. Those two sprockets may be meshed together or surrounded

38、 a steel chain to have the camshaft drive. When the lower part of the camshaft lobe is rotating under the valve lifter, the valve spring holds the valve closed.汽车发动机1发动机的分类和整体力学汽车发动机可根据如下因素进行分类：（1）循环系统，（2）冷却系统，（3）燃油系统，（4）点火方式，（5）气门布置，（6）气缸排列，（7）发动机转速。用于汽车的发动机是内燃机。汽油在发动机内部燃烧，产生的高压力使活塞移动，这一运动通过连杆传递到曲轴

39、，使它旋转。动力通过动力总成传递到车轮，从而带动汽车前进。发动机需要四个基本系统来运行（图2-1）。柴油发动机需要其中的三个基本系统来运行。它们是燃油系统、点火系统（柴油除外）、润滑系统和冷却系统。然而，其他三个相关系统也是必要的。这些是排气系统，排放控制系统，启动系统。每个系统执行一项基本工作，使发动机正常运行。图2-1发动机结构2发动机工作原理“冲程”一词是用来形容汽缸内活塞的运动。活塞从最高位置（TDC，上止点）运动到其最低位置（BDC上，下止点）的运动过程被称为一个冲程。做功周期可能需要两个或四冲程来完成。大多数汽车发动机为四冲程循环（图2-2）。 图2-2发动机简图在四冲程发动机中，

40、活塞在汽缸内的动作都需要完成一个完整的运行周期。每个行程按所完成的动作命名。分别是进气，压缩，做功，和排气（图2-3）。 进气冲程 压缩冲程 做功冲程 排气冲程图2-3四冲程循环汽油发动机1、进气冲程进气冲程开始运动到活塞行程的顶端附近。当活塞开始下降，排气门完全关闭，打开进气门，创造一个真空，燃烧室里进气量开始增加。当活塞下降，空气/燃料混合物从化油器通过进气歧管进入气缸。活塞已经开始上行后，进气行程结束进气门即将关闭。2、压缩行程当活塞通过曲轴从BDC位置开始移动，进气门关闭。在汽缸中活塞上面的空气/燃料混合物被压缩。活塞行程压缩空气/燃料混合物约为原体积的1/8（大约8:1的压缩比）时，

41、这时候活塞已经达到TDC的八分之一。这就完成了压缩冲程。3、做功冲程在压缩冲程中当活塞到达TDC时，火花塞产生电火花。点火系统提供给火花塞一个高压脉冲使产生火花。火花点燃（放火）空气/燃料混合物，开始迅速燃烧，气缸压力增加多达3-5MPa。这压力推动活塞下降，并通过连杆曲轴的曲柄销传送到一个强大的冲动。活塞上面的压力推动它从而使曲轴旋转。4、排气冲程在动力冲程结束时，凸轮轴打开排气门，排气冲程开始。活塞向上运动，气缸内的压力迫使废气排出气缸。在排气冲程结束时，排气门关闭进气打开，一遍又一遍地重复整个循环。3发动机缸体和缸盖3.1发动机缸体发动机缸体是发动机的基本框架。所有其他发动机零部件装进或

42、拧紧在缸体上。它拥有冷却回路、润滑油道（图2-4），发动机缸体，还拥有曲轴，机油底壳。除了顶置凸轮发动机外，凸轮轴也属于这部分。在大多数汽车中，此缸体是由灰铸铁和其他金属，如镍或铬，合金（混合物）铸造成的。 图2-4 V6发动机缸体有些发动机缸体，尤其是那些小型车使用铸铝，这种金属比铸铁轻得多。然而，铁的耐磨性比铝好。因此，在大多数铝制发动机汽缸内衬有铁或钢材质的套管。这些轴套叫做气缸套。一些发动机缸体完全由铝做成。3.2气缸套气缸套用于发动机缸体内，用来防止活塞和活塞环对缸体的磨损。缸体可以由一种既轻也易于成型的金属制成，而缸套则用来承受活塞跟活塞环的磨损。有两种主要类型的缸套：干缸套和湿缸

43、套（图2-5）。干缸套 湿缸套图2-5缸套3.3缸盖气缸盖是缸体的顶部，相当于一所房子的屋顶与活塞顶部形成燃烧室。直列式轻型车辆的发动机气缸只有一个缸盖;较大的直列式发动机可以有两个或两个以上。正如发动机缸体，缸盖也可由铸铁或铝合金制成。气缸盖携带阀门，气门弹簧，摇臂轴，摇臂，推动气门齿轮工作的推杆。有时，凸轮轴直接安装在缸盖上，不用摇臂控制气门工作。这被称为顶置凸轮轴布置。3.4垫片缸盖与高强度钢螺栓连接缸体。缸体和头部之间的联合，必须不透气，使燃烧的混合物不能泄漏。这是通过使用气缸盖垫片实现。密封垫片还可以用于连接的其他部分，如油底壳，歧管，或水泵和缸体之间。3.5油底壳油底壳通常由钢冲压

44、形成。油底壳和缸体下部一同被叫做曲轴箱;它们把曲轴封闭起来。润滑系统中的油泵，抽出油底壳中的油，并把它传送到发动机的所有工作部件。机油流出再通过管道流回油底壳。因此，机油要在发动机的工作部件不断地循环流动。4活塞，活塞环，活塞销，连杆，曲轴和飞轮4.1活塞活塞、活塞环和活塞销在一起称为活塞总成（图2-6）。活塞是四冲程发动机的重要部件。大多数活塞由铸铝制成。活塞，通过连杆，与曲轴相连并将燃烧混合气产生的力传给曲轴。这种力量使曲轴转动。 图2-6活塞，活塞环和连杆为了经得住燃烧室的高温，活塞必须有足够的强度。同时活塞必须很轻，因为它在气缸内以很高的速度上下移动。活塞是空心的。活塞顶部厚，承受着高

45、温燃气的带有冲击性的高压力。底部薄，在那里热量少。活塞的顶部是活塞头或者活塞顶。薄的部分是裙部。大多数活塞的顶部有3个活塞环槽。活塞环槽之间的部分称为环带。 4.2 活塞环活塞环装在活塞顶部附近的活塞环槽里。简单地讲，活塞环就是装在活塞顶部的凹槽里的薄，圆的金属。 现代的发动机，每个活塞有3 道环。(在更旧的发动机里活塞有4道环甚至5道环。)这些环的内表面和活塞上的凹槽相配合。环的外表面推挤气缸壁。环为活塞和气缸壁之间提供了必要的密封。活塞与汽缸壁不接触，只有环与气缸壁接触。最顶的两道保证活塞与气缸壁间密封的环叫做气环。底下的一道防止机油飞溅到缸筒从而窜入燃烧室的环叫做油环。4.3活塞销活塞销

46、把活塞和连杆连接在一起。这个销装在活塞销座孔和连杆小头衬套孔内。连杆的小头比安装在曲轴的大头小得多。小头装在活塞的底部。活塞销贯穿活塞，把连杆小头与活塞连在一起，并将连杆保持在活塞中心的适当位置处。销由高强度的钢做成并且是空心的。很多销都是镀铬的以使他们更加耐磨。活塞销装在活塞的环形的孔里。活塞销把活塞和连杆连接起来。用来支撑活塞销的活塞厚的部分称为活塞销凸台。4.4连杆 连杆小头连接着活塞销。轴瓦由软金属制成，例如青铜常被用于这种连接。在连杆大头安装曲柄轴颈。这被称为连杆大头。对连杆大头轴承来说，使用的是铅的钢背或锡的轴瓦式轴承。这些轴承与那些被用作主要轴承的轴承相同。大头的裂口有时有一个角度，以便足够小通过气缸。连杆由锻造的合金钢制成。4.5曲轴曲轴被视为发动机