汽車專業(yè)英語unit2

PAGEPAGE8UNIT2AUTOMOTIVEENGINE2.1PurposeandLocationsofEnginesThepurposeofanautomotiveengineistosupplythepowerneededtomovethevehicle.Theengineproducesthispowerbyburningfuelinsideit.Becausetheengineburnsfuelinside,orinternally,theengineisknownasaninternalcombustionengine（ICE）.汽車發(fā)動機的功用是汽車行駛提供必需的動力。發(fā)動機通過它內部的燃料燃燒來產生動力。由于發(fā)動機在其內部燃燒燃料，所以發(fā)動機被稱作內燃機。Enginesmaybefueledbygasoline,propane（LPG-liquefiedpetroleumgas）,ordieselfuel.Compressednaturalgas（CNG）mayalsobeusedinsomevehicles.發(fā)動機燃料可以是汽油、丙烷（液化石油汽體）或柴油。壓縮天燃氣也可以用在一些車輛上。befueledby通過…得到燃料Mostautomotiveenginesarelocatedatthefrontofthevehicle.Manyenginesdrivetherearwheels.Thisrequiresalongdriveshaftextendingformthefrontwheelstotherearwheels.Otherenginesdrivethefrontwheels.Intherear-wheel-drivearrangement,theenginesitslongitudinally.Itslongdimensionisfromfronttoback.大多數(shù)汽車發(fā)動機位于汽車前方。許多發(fā)動機由后輪驅動。這需要一根長傳動軸從前輪延伸到后輪。其它發(fā)動機由前輪驅動。在后輪驅動布置中，發(fā)動機縱向放置。它前后尺寸最長。Inthefront-wheel-drivearrangement,theenginesitscrosswise,transversely.Witheitherarrangement,thepoweriscarriedtothedrivewheels（rearorfront）bygearsandshafts.在前輪驅動布置中，發(fā)動機橫向放置。不管哪種放置方式，動力都是通過齒輪和軸傳遞到驅動輪。Crosswise交叉地，橫向的Somecarshavetheenginemountedinbackofthefrontseat.Thisiscalledamid-enginearrangement.Othercarshavebeenbuiltwiththeenginemountedattherear,inbackofrearseat.TheVolkswagen"beetle"isanexampleofrear.一些轎車把發(fā)動機安裝在前排座位的后面，這稱為中置發(fā)動機布置。其它轎車發(fā)動機安裝在車的尾部，也就是后排座的后面。比如：大眾汽車甲殼蟲就是采用這種發(fā)動機后置布置。2.2EngineTypesVariouskindsofenginesareusedinautomotivevehicles.Thetwomajortypesare:機動車輛上采用各種各樣的發(fā)動機，其兩種主要類型為：1.Thepistonengineinwhichpistonsmoveupanddown,orreciprocate,intheenginecylinders.Thisistheengineusedinallcarstoday,exceptforsomemodelsofMazda.活塞發(fā)動機，活塞在其氣缸內上下或往復運動。這就是現(xiàn)今轎車所采用的發(fā)動機形式，除了馬自達的一些型號發(fā)動機。2.TheWankelrotaryengineinwhichrotorsrotate,orspin.TheMazdaMotorCorporationofJapanisthemajormanufacturerofthisengine.汪克爾轉子發(fā)動機，由其轉子回轉。日本馬自達發(fā)動機公司是這類發(fā)動機的主要生產商。Therearetwotypesofpistonengines-sparkignition（SI）andcompressionignition（CI）.Spark-ignitionenginesuseanelectricignitionsystemwithsparkplugs.Electricsparksatthesparkplugsignite,orsetfire,thefuelintheenginecylinders.Thecombustionofthefuelmakestheenginerunandproducepower.Thisisthetypeofengineusedinmostproducepower.Thisisthetypeofengineusedinmostautomotivevehicles.有兩種類型的活塞發(fā)動機：火花點火和壓縮點火?；鸹c火發(fā)動機采用帶有火花塞的電子點火系統(tǒng)?；鸹ㄈ碾娮狱c火點燃發(fā)動機氣缸中的燃料。燃料燃燒使發(fā)動機運轉并產生動力。這是在大多數(shù)產生動力的發(fā)動機所采用的形式，這種類型的發(fā)動機在大部分機動車輛上使用。Thecompression-ignitionenginethedieselusestheheatofcompressiontoignitethefuel.Whenairiscompressed,itgetsveryhot.Inthedieselengine,theairiscompressedsomuchthatitstemperaturegoesupto1,000degreesFahrenheit（538degreesCelsius）orhigher.Thedieselfuelissprayedintothisveryhotairandisignitedbytheheat.Someautomobileshavedieselengines.Manyheavy-dutytrucksandbusesarepoweredbydieselengines.壓縮點火發(fā)動機，柴油機使用壓縮產生的熱量來點燃燃料。當空氣被壓縮時，會變得非常熱。柴油機內空氣壓縮溫度可過1000華氏以上（538攝氏度）。然后柴油被噴射到這種熱空氣中，并被這種熱度點燃。一些汽車上采用柴油機。大多重型卡車和客車由柴油機提供動力。Thereareotherenginesstillintheexperimentalstagethatmightsomedaybecomeimportant.Theseincludegas-turbineengines,steamengines,Stirlingengines,andelectricmotors.還有一些其它的發(fā)動機仍處于實驗階段，總有一天會變得重要。它們包括燃氣渦輪發(fā)動機、蒸汽汽、斯特林（熱氣體）發(fā)動機和電動機。2.3BasicEngineSystemsAspark-ignitionenginerequiresfourbasicsystemstorun.Dieselenginesrequirethreeofthesesystems.Theyarefuelsystem,ignitionsystem（exceptdiesel）,lubricatingsystemandcoolingsystem.Eachperformsabasicjobinmakingtheenginerun.Thesearedescribedbrieflybelow.火花點火發(fā)動機運轉需要4個基本系統(tǒng)。柴油發(fā)動機需要其中的3個。它們是燃料系統(tǒng)，點火系統(tǒng)（除了柴油機），潤滑系統(tǒng)和冷卻系統(tǒng)。其每個系統(tǒng)在使發(fā)動機運轉時完成一個基本工作。簡要介紹如下：2.3.1FuelSystemsThefuelsystemsuppliesgasolineordieselfueltotheengine.Thisfuelismixedwithairtomakeacombustiblemixture（amixturethatwillburn）.Eachcylinderisrepeatedlyfilledwiththemixture.Then,themixtureisignitedandburned,producinghighpressure.Thehighpressuremakesthepistonsmove（orrotorsspin）.Thisturnsshaftsthatrotatethewheels,causingthevehicletomove.燃料系統(tǒng)給發(fā)動機提供汽油或柴油燃料。燃料與空氣混合形成可燃混合氣（一種會燃燒的混合物）。氣缸被反復填充這種混合氣體。然后被點燃、燃燒，產生高壓，推動活塞運動（或轉子旋轉）。這使車軸帶到車輪旋轉，從而使車輛移動。2.3.2IgnitionsystemEverytimethefuelsystemdeliversair/fuelmixturetoacylinder,theignitionsystemfollowsupbydeliveringanelectricspark.Thisignitesthemixturewhichcreatesthehighpressurethatmovesthepistonsandturnsthecarwheels.Theactionisrepeatedmanytimeseachsecondwhiletheengineisrunning.每當燃料系統(tǒng)傳送可燃混合氣給氣缸，點火系統(tǒng)隨后會產生電火花來點燃混合氣，從而產生高壓，使活塞運動和車輪運轉。當發(fā)動機運轉時，每秒鐘這個動作重復多次。Theignitionsystemtakesthelowvoltage,ofthebatteryandbuildsituptoaveryhighvoltage:ashighas47,000voltsinsomesystems.Thishighvoltagejumpsthegapsinthesparkplugs,producingthesparksthatignitetheair/fuelmixtureintheenginecylinders.點火系統(tǒng)把蓄電池的低壓增到高壓，在一些系統(tǒng)中可達到47000伏。高壓擊穿火花塞（兩電極之間）間隙，產生電火花，點燃發(fā)動機氣缸內的可燃混合氣。2.3.3LubricatingsystemTheenginehasmanymovingmetalparts.Ifmetalpartsrubagainsteachother,theywillwearrapidly.Topreventthis,engineshavelubricatingoil.Theoilgetsbetweenthemetalpartssotheyslideontheoil,andnotoneachother.發(fā)動機有許多運動金屬部件。如果金屬部件之間相互磨擦，會加速磨損。為防止這樣，發(fā)動機帶有潤滑油。潤滑油充斥在金屬部件之間，從而使它們在油面上滑動，而不是在其表面。Thelubricatingsystemhasanoilpanatthebottomoftheenginewhichholdsseveralquarts（liters）ofoil.Anoilpump,drivenbytheengine,sendsoilfromthisreservoirthroughtheengine.Aftercirculatingthroughtheengine,theoildropsbackdownintotheoilpan.Theoilpumpcontinuestocirculatetheoilaslongastheengineisrunning.潤滑系統(tǒng)油底殼位于發(fā)動機的底部，它可保存幾夸脫（升）的潤滑油。油泵由發(fā)動機驅動把潤滑油從油底殼送到發(fā)動機各個部件，潤滑油在發(fā)動機內循環(huán)后，回落到油底殼中。只要發(fā)動機不斷運轉，油泵就會連續(xù)循環(huán)潤滑油。夸脫(容量單位=1/4加侖,約1.14升)throughprep，通過，到，各處，各地wentthroughthetunnel.atourthroughFrance.adj.直達的,直通的athroughbus一輛直達的公共汽車；adv，從頭到尾，完全，徹底seeamatterthrough，drovethroughtotheirfinaldestination.2.3.4CoolingsystemWherethereisfire（combustion）,thereisheat.Burningoftheair/fuelmixtureraisesthetemperatureinsidetheenginecylindersseveralthousanddegrees.Someofthisheatproducesthehighpressurethatmovesthepistonstoproducepower.Someoftheheatleavesthecylinderswiththeexhaustgas.Theexhaustgasiswhatisleftaftertheair/fuelmixtureburns.Itisclearedoutofthecylindersaftercombustioniscomplete.有火（燃燒）的地方，就會有熱。可燃混合氣的燃燒會把發(fā)動機氣缸內的溫度提升到幾千攝氏度。其中一部分熱量產生高壓推動活塞運動來產生動力。另外一部分熱量隨著廢氣排出氣缸。廢氣是指可燃混合氣燃燒后殘留的氣體。它在燃燒完成后被排出氣缸。Someoftheheatisremovedbythecirculatingoil.Afterthehotoildropsdownintotheoilpan,theoilgivesupsomeofthisheattotheairpassingundertheoilpan.Therestoftheheatisremovedbythecoolingsystem.還有一部分熱量由循環(huán)潤滑油帶走。灼熱的潤滑油落到油底殼后，會把部分熱量傳給通過油底殼下方的空氣。其余熱量由冷卻系散發(fā)。2.3.5OtherenginesystemsAnenginewillrunwiththefourbasicsystemsdescribedabove—fuel,ignition,lubricating,andcooling.However,threeotherrelatedsystemsarealsonecessary.Thesearetheexhaustsystem,theemission-controlsystem,andthestartingsystem.發(fā)動機運轉需要上述4個基本系統(tǒng)－燃料、點火、潤滑和冷卻。但是，還有另外三個相關系統(tǒng)也是必需的。它們是排放系統(tǒng)、廢氣處理（排氣凈化）系統(tǒng)和起動系統(tǒng)。Theexhaustsystemreducesthenoiseoftheburnedgasesleavingtheenginecylindersandcarriestheseexhaustgasessafelyawayfromthepeopleinthecar.Theemission-controlsystemisrequiredbylawtoreducetheairpollutiontheenginecouldproduce.Thestartingsystemisneededtocranktheengine.Abatteryprovidestheelectricpowertooperatethestartingmotorandtheignitionsystemduringcranking.排放系統(tǒng)功能，一方面減小燃燒廢氣排出氣缸時所產生的噪聲，另一方面把這些廢氣從車中乘客身邊安全帶走。廢氣處理（排放控制）系統(tǒng)是法規(guī)所要求的用來降低發(fā)動機所產生的空氣污染。起動系統(tǒng)用來轉動發(fā)動機曲軸。蓄電池在起動時為開動起動機和點火系統(tǒng)提供電力。Crankn.曲軸曲柄→vt.轉動曲柄Cranking搖動，起動2.4EnergyConversionTheinternalcombustionengineisadeviceusedtoconvertthechemicalenergyofthefuel（gasolineordieselfuel）intoheatenergy,andthentoconvertthisheatenergyintousablemechanicalenergy.Thisisachievedbycombiningtheappropriateamountsofairandfuel,andburningthemixtureinanenclosedcylinderatacontrolledrate.Amovablepistoninthecylinderisforceddownbytheexpandinggasesofcombustion.內燃機是一種把（汽油或柴油）燃料的化學能轉變成熱能，再轉換成可利用的機械能的裝置。這通過混合適量的空氣和燃料，并在密閉的汽缸中按照控制速度燃燒來實現(xiàn)。氣缸中活塞由燃燒氣體膨脹作功來壓下。Enclosevt.裝入，圍繞Enclosedadj.被附上的，封閉的enclosern.外殼，外罩。Anaverageair/fuelratioforgoodcombustionisabout15partsofairto1partoffuelbyweight.Thismeansthatforeverygallonofgasolineburned,theoxygenisabout9,000to10,000gallonsofairisrequired.Airisabout21%oxygenand78%nitrogen.燃燒良好的空燃比，按質量平均大約是15：1。這意味著每加侖汽油完全燃燒所需的空氣質量大約在9000到10000加侖。空氣中氧氣成份點21%，氮氣占78%。air/fuelratio空氣/燃油混合比，即空燃比，可燃混合氣中空氣質量與燃油質量之比。Dieselenginesoperateonamuchwiderair/fuelratio,sinceairintakeisnotregulatedonmostdiesels.Ratiosmayrangefromabout20:1toabout100:1.Thefact,plusthehighcompressionofthediesel,makesitaveryfuelefficientengine.因為進氣量在大多數(shù)內柴油機上不規(guī)則的，柴油機有更寬的空燃比。其范圍大約在20：1到100：1之間。實際上，加上柴油機的高壓縮比，使其成為極其節(jié)約燃油的發(fā)動機。fuelefficient節(jié)約燃油的，燃油經濟性高的Themovablepistoninthecylinderisconnectedtothetopofaconnectingrod.Thebottomoftheconnectingrodisattachedtotheoffsetportionofacrankshaft.Asthepistonisforcedown,thisforceistransferredtothecrankshaft,causingthecrankshafttorotate.Thereciprocating（backandforthorupanddown）movementofthepistonisconvertedtorotary（turning）motionofthecrankshaft,whichsuppliesthepowertodrivethevehicle.氣缸活塞與連桿上端相連。連桿底部則連到曲軸的偏心部。當活塞被壓下時，驅動力被傳遞到曲軸，并帶動曲軸旋轉。活塞的往復運動轉化成曲軸的旋轉運動，從而為驅動車輛提供動力。Theefficiencyoftheinternalcombustion,reciprocatingpistonengineinconvertingthepotentialenergyinfuelintomechanicalenergyisonlyabout33%.Oftheavailableheatenergyinthefuel,aboutone-thirdislostthroughtheexhaustsystemandone-thirdisabsorbedanddissipatedbythecoolingsystem.Oftheremainingone-third,aboutone-halfislostthroughavailableatthevehicle’sdrivewheels.活塞發(fā)動機在轉化燃料的勢能為機械能時的效率大約只有33%。對于燃料的可用熱能，大概有1/3損失在排放系統(tǒng)中，另外1/3被冷卻系統(tǒng)吸收和散發(fā)。在剩余的1/3中，約有一半完全利用在車輛的驅動輪上。Theoverallefficiencyofthedieselengineisconsiderablyhigherthanthatofthegasolineengine.Thereasonsforthisare:thehighercompressionratio,thehigherair/fuelratio,andthehigherheatvalueofthefuel.Theusefulpowerdevelopedatthedrivewheelsbyadieselengineisabout25%ascomparedto15%byagasolineengine.柴油機的總效率明顯高于汽油機。原因在于柴油機的高壓縮比，高空燃比和柴油的高熱值。柴油機傳遞到車輪的有效功率大約在25%，而汽油機只有15%。heatvalue高熱值，單位燃料燃燒時釋放的熱量。ascomparedto同…相比2.5Four-Stroke-CycleGasolineEngineOperationThemovementofthepistonfromitsuppermostposition（TDC,topdeadcenter）toitslowestposition（BDC,bottomdeadcenter）iscalledastroke.Mostautomobileenginesoperateonthefourstroke-cycleprinciple.Aseriesofeventsinvolvingfourstrokesofthepistoncompletesonecycle.Figure2-1.Theseeventsare:（1）theintakestroke,（2）thecompressionstroke,（3）thepowerstroke,and（4）theexhauststroke.Tworevolutionsofthecrankshaftandonerevolutionofthecamshaftarerequiredtocompleteonecycle.從活塞的最上端（上止點）到它的最下端（下止點）的運動過程稱為一個行程。大多數(shù)汽車發(fā)動機根據四沖程原理工作。四個活塞行程完成一個工作周期。這4個行程是進氣行程，壓縮行程，作功行程和排氣行程。同時，需要曲軸轉動兩圈，凸輪軸轉動一圈。Event事件→過程，（內燃機）行程Ontheintakestrokethepistonispulleddowninthecylinderbythecrankshaftandconnectingrod.Duringthistimetheintakevalveisheldopenbythecamshaft.Sincethepistonhasmoveddowninthecylinder,creatingalow-pressurearea（vacuum）,atmosphericpressureforcesamixtureofairandfuelpasttheintakevalveintothecylinder.Atmosphericpressureisapproximately14.7poundspersquareinch（about101.35kilopascals）atsealevel.Pressureinthecylinderduringtheintakestrokeisconsiderablylessthanthis.Thepressuredifferenceistheforcethatcausestheair/fuelmixturetoflowintothecylinder,sincealiquidoragas（vapor）willalwaysflowfromahigh-pressuretoalow-pressurearea.在進氣行程中，活塞在氣缸中被曲軸和連桿拉下。這時，進氣門被凸輪軸開啟。因為活塞在氣缸中向下移動，產生一個低壓區(qū)（真空），大氣壓將可燃混合氣通過進氣門壓入氣缸。大氣壓在海平面上大約為14.7磅/平方英寸(101.35千帕)。進氣行程中氣缸內壓力遠小于大氣壓力。因為液體或氣體（蒸汽）總是從高壓區(qū)流向低壓區(qū)，所以這個壓力差促使可燃混合氣注入汽缸。AsthepistonismovedupbythecrankshaftfromBDC,theintakevalvecloses.Theair/fuelmixtureistrappedinthecylinderabovethepiston.Furtherpistontravelcompressestheair/fuelmixturetoapproximatelyone-eighthofitsoriginalvolume（approximately8:1compressionratio）whenthepistonhasreachedTDC.Thiscompletesthecompressionstroke.當活塞曲軸帶動從下止點向上移時，進氣門關閉。可燃混合氣封在氣缸內活塞的上方。當活塞到達上止點時，可燃混合氣體積由活塞運動壓縮至其原來體積的約1/8（8:1的壓縮比）。這就完成了壓縮行程。WhenthepistonisatornearTDC,theair/fuelmixtureisignited.Theburningoftheair/fuelmixture（combustion）takesplaceatacontrolledrate.Expansionoftheburningmixturecausesarapidriseinpressure.Thisincreasedpressureforcesthepistondownonthepowerstroke,causingthecrankshafttorotate.當活塞移動到上止點附近時，可燃混合氣被點燃?；旌衔锏娜紵凑湛刂扑俣冗M行。燃燒氣體體積膨脹使（氣缸內）壓力迅速上升。在此作功行程中，氣體增壓推動活塞向下移動，帶動曲軸旋轉。Attheendofthepowerstrokethecamshaftopenstheexhaustvalve,andtheexhauststrokebegins.Remainingpressureinthecylinder,andupwardmovementofpiston,forcetheexhaustgasesoutofthecylinder.Attheendoftheexhauststroke,theexhaustvalveclosesandtheintakevalveopens,repeatingtheentirecycleofeventsoverandoveragain.在作功行程結束時，凸輪軸打開排氣門，進入排氣行程。氣缸中剩余壓力和活塞的向上移動把廢氣排出氣缸。排氣行程結束時，排氣門關閉，進氣門打開，反復不斷重復整個沖程循環(huán)周期。overandoveragain反復不斷地Tostarttheengine,somemethodofcrankingtheengineisrequiredtoturnthecrankshaftandcausepistonmovement.Thisisdonebythestartermotorwhentheignitionkeyisinthestartposition.Whensufficientair/fuelmixturehasenteredthecylindersandisignited,thepowerstrokescreateenoughenergytocontinuecrankshaftrotation.Atthepoint,theignitionkeyisreleasedtotherunpositionandthestarterisdisengaged.為了起動發(fā)動機，需要一些起動方法來轉動發(fā)動機曲軸，使活塞（上下）運動。這在點火開關處于起動位置時由起動機來實現(xiàn)。當足量的可燃混合氣進入氣缸并且被點燃，作功行程能產生足夠的熱量來繼續(xù)曲軸旋轉，此時點火開關釋放至運行位置，起動機解除。Sufficientenergyisstoredintheflywheelandotherrotatingpartsonthepowerstroketomovethepistonandrelatedpartsthroughtheotherthreestrokes（exhaust,intake,andcompression）.Theamountofair/fuelmixtureallowedtoenterthecylinderdeterminesthepowerandspeeddevelopedbytheengine.在作功行程中，能量被存儲在飛輪和其它旋轉部件中，并在其它三個行程（排氣、進氣和壓縮）中推動活塞和相關部件。進入氣缸中的可燃混合氣的量決定著該發(fā)動機的功率和轉速。EXERCISEI.Answerthefollowingquestions:1.Whatisthepurposeofanautomotiveengine?Itissupplythepowerneededtomovethevehicle.2.Whatisthedifferencebetweenagasolineengineandadieselengine?Theoverallefficiencyofthedieselengineishigherthanthatofthegasolineengine.P15Gasolineengineissparkignitionanddieselengineiscompressionignition.3.Whatarethebasicsystemstorunasparkignitionenginerequired?Theyarefuelsystem,ignitionsystem,lubricatingsystemandcoolingsystem.4．Listthestrokesofafour-stroke-cyclegasolineeng