汽车发动机如何工作勘测外文文献翻译中英文翻译外文翻译.docx
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汽车发动机如何工作勘测外文文献翻译中英文翻译外文翻译.docx
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汽车发动机如何工作勘测外文文献翻译中英文翻译外文翻译
HowCarEnginesWork
IntroductiontoHowCarEnginesWork
Haveyoueveropenedthehoodofyourcarandwonderedwhatwasgoingoninthere?
Acarenginecanlooklikeabigconfusingjumbleofmetal,tubesandwirestotheuninitiated.
Youmightwanttoknowwhat'sgoingonsimplyoutofcuriosity.Orperhapsyouarebuyinganewcar,andyouhearthingslike"3.0literV-6"and"dualoverheadcams"and"tunedportfuelinjection."Whatdoesallofthatmean?
Ifyouhaveeverwonderedaboutthiskindofstuff,thenreadon--Inthisarticle,we'lldiscussthebasicideabehindanengineandthengointodetailabouthowallthepiecesfittogether,whatcangowrongandhowtoincreaseperformance.
Thepurposeofagasolinecarengineistoconvertgasolineintomotionsothatyourcarcanmove.Currentlytheeasiestwaytocreatemotionfromgasolineistoburnthegasolineinsideanengine.Therefore,acarengineisaninternalcombustionengine--combustiontakesplaceinternally.
Twothingstonote:
Therearedifferentkindsofinternalcombustionengines.Dieselenginesareoneformandgasturbineenginesareanother.SeealsothearticlesonHEMIengines,rotaryenginesandtwo-strokeengines.Eachhasitsownadvantagesanddisadvantages.
Thereissuchathingasanexternalcombustionengine.Asteamengineinold-fashionedtrainsandsteamboatsisthebestexampleofanexternalcombustionengine.Thefuel(coal,wood,oil,whatever)inasteamengineburnsoutsidetheenginetocreatesteam,andthesteamcreatesmotioninsidetheengine.Internalcombustionisalotmoreefficient(takeslessfuelpermile)thanexternalcombustion,plusaninternalcombustionengineisalotsmallerthananequivalentexternalcombustionengine.Thisexplainswhywedon'tseeanycarsfromFordandGMusingsteamengines
Almostallcarstodayuseareciprocatinginternalcombustionenginebecausethisengineis:
Relativelyefficient(comparedtoanexternalcombustionengine)
Relativelyinexpensive(comparedtoagasturbine)
Relativelyeasytorefuel(comparedtoanelectriccar)
Theseadvantagesbeatanyotherexistingtechnologyformovingacararound.
Tounderstandthebasicideabehindhowareciprocatinginternalcombustionengineworks,itishelpfultohaveagoodmentalimageofhow"internalcombustion"works.OnegoodexampleisanoldRevolutionaryWarcannon.Youhaveprobablyseentheseinmovies,wherethesoldiersloadthecannonwithgunpowderandacannonballandlightit.Thatisinternalcombustion.
Almostallcarscurrentlyusewhatiscalledafour-strokecombustioncycletoconvertgasolineintomotion.Thefour-strokeapproachisalsoknownastheOttocycle,inhonorofNikolausOtto,whoinventeditin1867.Thefourstrokesareillustratedbellow,theyare:
Intakestroke
Compressionstroke
Combustionstroke
Exhauststroke
Thepistonisconnectedtothecrankshaftbyaconnectingrod.Asthecrankshaftrevolves,ithastheeffectof"resettingthecannon."Here'swhathappensastheenginegoesthroughitscycle:
1.Thepistonstartsatthetop,theintakevalveopens,andthepistonmovesdowntolettheenginetakeinacylinder-fullofairandgasoline.Thisistheintakestroke.Onlythetiniestdropofgasolineneedstobemixedintotheairforthistowork.
2.Thenthepistonmovesbackuptocompressthisfuel/airmixture.Compressionmakestheexplosionmorepowerful.
3.Whenthepistonreachesthetopofitsstroke,thesparkplugemitsasparktoignitethegasoline.Thegasolinechargeinthecylinderexplodes,drivingthepistondown.
4.Oncethepistonhitsthebottomofitsstroke,theexhaustvalveopensandtheexhaustleavesthecylindertogooutthetailpipe.
Thentheenginegetsreadyforthenextcircle.
Cylinders,DisplacementandOtherEngineParts
Thecoreoftheengineisthecylinder,withthepistonmovingupanddowninsidethecylinder.Theenginedescribedabovehasonecylinder.Thatistypicalofmostlawnmowers,butmostcarshavemorethanonecylinder(four,sixandeightcylindersarecommon).Inamulti-cylinderengine,thecylindersusuallyarearrangedinoneofthreeways:
inline,Vorflat(alsoknownashorizontallyopposedorboxer),asshowninthefollowingfigures.
Differentconfigurationshavedifferentadvantagesanddisadvantagesintermsofsmoothness,manufacturing-costandshapecharacteristics.Theseadvantagesanddisadvantagesmakethemmoresuitableforcertainvehicles.
Displacement
Thecombustionchamberistheareawherecompressionandcombustiontakeplace.Asthepistonmovesupanddown,youcanseethatthesizeofthecombustionchamberchanges.Ithassomemaximumvolumeaswellasaminimumvolume.ThedifferencebetweenthemaximumandminimumiscalledthedisplacementandismeasuredinlitersorCCs(CubicCentimeters,where1,000cubiccentimetersequalsaliter).
Valves
Theintakeandexhaustvalvesopenatthepropertimetoletinairandfuelandtoletoutexhaust.Notethatbothvalvesareclosedduringcompressionandcombustionsothatthecombustionchamberissealed.
Piston
Apistonisacylindricalpieceofmetalthatmovesupanddowninsidethecylinder.
Pistonrings
Pistonringsprovideaslidingsealbetweentheouteredgeofthepistonandtheinneredgeofthecylinder.Theringsservetwopurposes:
∙Theypreventthefuel/airmixtureandexhaustinthecombustionchamberfromleakingintothesumpduringcompressionandcombustion.
∙Theykeepoilinthesumpfromleakingintothecombustionarea,whereitwouldbeburnedandlost.
Mostcarsthat"burnoil"andhavetohaveaquartaddedevery1,000milesareburningitbecausetheengineisoldandtheringsnolongersealthingsproperly.
Connectingrod
Theconnectingrodconnectsthepistontothecrankshaft.Itcanrotateatbothendssothatitsanglecanchangeasthepistonmovesandthecrankshaftrotates.
Crankshaft
Thecrankshaftturnsthepiston'supanddownmotionintocircularmotion.
Sump
Thesumpsurroundsthecrankshaft.Itcontainssomeamountofoil,whichcollectsinthebottomofthesump(theoilpan).
ValveTrainsandSystems
Thevalvetrainconsistsofthevalvesandamechanismthatopensandclosesthem.Theopeningandclosingsystemiscalledacamshaft.Thecamshafthaslobesonitthatmovethevalvesupanddown。
Mostmodernengineshavewhatarecalledoverheadcams.Thismeansthatthecamshaftislocatedabovethevalves.Thecamsontheshaftactivatethevalvesdirectlyorthroughaveryshortlinkage.Olderenginesusedacamshaftlocatedinthesumpnearthecrankshaft.Thisapproachhasmoremovingpartsandalsocausesmorelagbetweenthecam'sactivationofthevalveandthevalve'ssubsequentmotion.Atimingbeltortimingchainlinksthecrankshafttothecamshaftsothatthevalvesareinsyncwiththepistons.Thecamshaftisgearedtoturnatone-halftherateofthecrankshaft.Manyhigh-performanceengineshavefourvalvespercylinder(twoforintake,twoforexhaust),andthisarrangementrequirestwocamshaftsperbankofcylinders,hencethephrase"dualoverheadcams."
IgnitionandCoolingSystems
Theignitionsystemproducesahigh-voltageelectricalchargeandtransmitsittothesparkplugsviaignitionwires.Thechargefirstflowstoadistributor,whichyoucaneasilyfindunderthehoodofmostcars.Thedistributorhasonewiregoinginthecenterandfour,six,oreightwires(dependingonthenumberofcylinders)comingoutofit.Theseignitionwiressendthechargetoeachsparkplug.Theengineistimedsothatonlyonecylinderreceivesasparkfromthedistributoratatime.Thisapproachprovidesmaximumsmoothness.
CoolingSystem
Thecoolingsysteminmostcarsconsistsoftheradiatorandwaterpump.Watercirculatesthroughpassagesaroundthecylindersandthentravelsthroughtheradiatortocoolitoff.Inafewcars(mostnotablyVolkswagenBeetles),aswellasmostmotorcyclesandlawnmowers,theengineisair-cooledinstead.Air-coolingmakestheenginelighterbuthotter,generallydecreasingenginelifeandoverallperformance.
Air-intakeandStartingSystems
Mostcarsarenormallyaspirated,whichmeansthatairflowsthroughanairfilteranddirectlyintothecylinders.High-performanceenginesareeitherturbochargedorsupercharged,whichmeansthataircomingintotheengineisfirstpressurizedtoincreaseperformance.Theamountofpressurizationiscalledboost.Aturbochargerusesasmallturbineattachedtotheexhaustpipetospinacompressingturbineintheincomingairstream.Asuperchargerisattacheddirectlytotheenginetospinthecompressor.
StartingSystem
Thestartingsystemconsistsofanelectricstartermotorandastartersolenoid.Whenyouturntheignitionkey,thestartermotorspinstheengineafewrevolutionssothatthecombustionprocesscanstart.Ittakesapowerfulmotortospinacoldengine.Thestartermotormustovercome:
∙Alloftheinternalfrictioncausedbythepistonrings
∙Thecompressionpressureofanycylinder(s)thathappenstobeinthecompressionstroke
∙Theenergyneededtoopenandclosevalveswiththecamshaft
∙Allofthe"other"thingsdirectlyattachedtotheengine,likethewaterpump,oilpump,alternator,etc.
Becausesomuchenergyisneededandbecauseacarusesa12-voltelectricalsystem,hundredsofampsofelectricitymustflowintothestartermotor.Thestartersolenoidisessentiallyalargeelectronicswitchthatcanhandlethatmuchcurrent.Whenyouturntheignitionkey,itactivatesthesolenoidtopowerthemotor.
LubricationandFuelSystems
Thelubricationsystemmakessurethateverymovingpartintheenginegetsoilsothatitcanmoveeasil
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