汽車專業(yè)英語(yǔ)讀譯教程 第3版 課件 12-U7TA Overview of Emission Control Systems

UNIT7

EMISSIONCONTROLSYSTEMS

TEXTA

OverviewofEmissionControlSystems

PROFESSIONALENGLISHUNIT7

EMISSIONCONTROLSYSTEMS

TEXTA

OverviewofEmissionControlSystems

PCVSystem

EGRSystem

EvaporativeControlSystem

AirInjection

CatalyticConverterPROFESSIONALENGLISH本次課學(xué)習(xí)目標(biāo)掌握排放控制系統(tǒng)的組成掌握排放控制系統(tǒng)的原理掌握有關(guān)的英文專業(yè)術(shù)語(yǔ)了解翻譯技巧—重復(fù)NEWWORDSdilute[dai'lju:t]v.沖淡,變淡,變?nèi)?稀釋crossover['kr?s?ouv?]n.轉(zhuǎn)線路,天橋,交叉channel['t∫?nl]n.海峽，水道，信道，頻道，通道route[ru:t]n.路線,路程,通道；v.發(fā)送lean（out）[li:n]v.貧化，變瘦thermal['θ?:m?l]a.熱的,熱量的transducer[tr?nz'dju:s?]n.傳感器，變頻器，變換器orifice['?rifis]n.孔，口，節(jié)流孔linear['lini?]a.線的,直線的,線性的potentiometer[p??ten∫i'?mit?]n.電位計(jì),電勢(shì)計(jì)fume[fju:m]n.(濃烈或難聞的)煙,氣體；v.用煙熏,冒煙,發(fā)怒prohibit[pr?'hibit]v.禁止,阻止adhere[?d'hi?]v.粘附,膠著,堅(jiān)持pop[p?p]n.砰的一聲,爆裂聲,流行樂(lè)曲,流行藝術(shù)a.流行的,熱門的,通俗的v.發(fā)出爆裂聲,爆開,射擊,突然出現(xiàn)diverter[dai'v?:t?]n.分流器，換向器，分流閥divert[di'v?:t]v.轉(zhuǎn)移,轉(zhuǎn)向catalytic[?k?t?'litik]a.催化的muffler['m?fl?]n.消聲器NEWWORDSpellet['pelit]n.小球honeycomb['h?nikoum]n.蜂房，蜂巢platinum['pl?tin?m]n.白金,鉑palladium[p?'leidi?m]n.鈀catalyst['k?t?list]n.催化劑render['rend?]v.致使，表演，實(shí)施NEWWORDS

PHRASESANDEXPRESSIONS

脈寬調(diào)制pulsewidthmodulationEGR閥位置（EVP）傳感器EGRvalveposition(EVP)sensor錐形端taperedtip通氣孔bleedport背壓backpressure大節(jié)氣門開度（簡(jiǎn)寫為WOT）wide-openthrottle廢氣再循環(huán)閥EGRvalve節(jié)氣門開度throttleopening在最壞的情況下atworst空氣噴射airinjection催化轉(zhuǎn)換器catalyticconverter空氣泵airpump分流閥divertervalve清污閥purgevalve與…一道（同時(shí)），以及，除…之外（還）alongwith活性炭罐charcoalcanister

PHRASESANDEXPRESSIONS

Tominimizepollutionoftheatmospherefromincompletelyburnedandevaporatinggasesandtomaintaingooddriveabilityandfueleconomy,anumberofemissioncontrolsystemsareusedonallvehicles.Theyincludepositivecrankcaseventilation(PCV)system，evaporativeemissioncontrol(EVAP)system，exhaustgasrecirculation(EGR)system，airinjection(AIR)systemandthree-waycatalyticconverter(TWC)system.PCVSystemThepurposeofthepositivecrankcaseventilation(PCV)systemistotakethevaporsproducedinthecrankcaseandpistonblow-by,andredirectthemintotheair/fuelintakesystemtobeburnedduringcombustion.Thesevaporsdilutetheair/fuelmixture,theyhavetobecarefullycontrolledandmeteredsoasnottoaffecttheperformanceoftheengine.Thisisthejobofthepositivecrankcaseventilation(PCV)valve.

OverviewofEmissionControlSystems

Atidle,whentheair/fuelmixtureisverycritical,justalittleofthevaporsareallowedintotheintakesystem.Athighspeedwhenthemixtureislesscriticalandthepressuresintheenginearegreater,moreofthevaporsareallowedintotheintakesystem[1].Whenthevalveorthesystemisclogged,vaporswillbackupintotheairfilterhousingoratworst,theexcesspressurewillpushpastsealsandcreateengineoilleaks[2].Ifthewrongvalveisusedorthesystemhasairleaks,theenginewillidlerough,oratworstengineoilwillbesuckedoutoftheengine.EGRSystemExhaustgasrecirculation(EGR)systemsreducetheamountofoxidesofnitrogenproducedduringthecombustionprocess.TheEGRsystemdilutestheair/fuelmixturewithcontrolledamountsofexhaustgas.Sinceexhaustgasdoesnotburn,thisreducesthepeakcombustiontemperatures.

OverviewofEmissionControlSystems

OverviewofEmissionControlSystems

Atlowercombustiontemperatures,verylittleofthenitrogenintheairwillcombinewithoxygentoformNOX.Mostofthenitrogenissimplycarriedoutwiththeexhaustgases.Fordriveability,itisdesirabletohavetheEGRvalveopening(andtheamountofgasflow)proportionaltothethrottleopening.DriveabilityisalsoimprovedbyshuttingofftheEGRwhentheengineisstartedupcold,atidle,andatfullthrottle.SincetheNOXcontrolrequirementsvaryondifferentengines,thereareseveraldifferentsystemswithvariouscontrolstoprovidethesefunctions.EGRValvesMostofthesesystemsuseavacuum-operatedEGRvalvetoregulatetheexhaustgasflowintotheintakemanifold.Exhaustcrossoverpassagesundertheintakemanifoldchanneltheexhaustgastothevalve.(Somein-lineenginesroutetheexhaustgastothevalvethroughanexternaltube.)TypicalmountingoftheEGRvalveiseitherona

plateunderthecarburetorordirectlyonthemanifold.

OverviewofEmissionControlSystems

TheEGRvalveisavacuum-operated,flowcontrolvalve.OpeningtheEGRvalvebycontrolvacuumatthediaphragm,allowsexhaustgasestoflowthroughthevalveandintotheintakemanifold.Here,theexhaustgasmixeswiththeair/fuelmixture.Theeffectistodiluteorleanoutthemixture,sothatitstillburnscompletelybutwithareductionincombustionchambertemperatures.

TherearealsovariousdesignsofEGRvalves.ThepositivebackpressureEGRvalvehasableedportandvalvepositionedinthecenterofthediaphragm.Alightspringholdsthisbleedvalveopen,andanexhaustpassageisconnectedfromthelowerendofthetaperedvalvethroughthestemtothebleedvalve.Whentheengineisrunning,exhaustpressureisappliedtothebleedvalve.Atlowenginespeeds,exhaustpressureisnothighenoughtoclosethebleedvalve.Ifcontrolvacuumissuppliedtothediaphragmchamber,thevacuumisbledoffthroughthebleedport,andthevalveremainsclosed.

（略）

OverviewofEmissionControlSystems

InanegativebackpressureEGRvalve,anormallyclosedbleedportispositionedinthecenterofthediaphragm.Anexhaustpassageisconnectedfromthelowerendofthetaperedvalvethroughthestemtothebleedvalve.Whentheengineisrunningatlowerspeeds,thereisahigh-pressurepulseintheexhaustsystem.However,betweenthesehigh-pressurepulsestherearelow-pressurepulses.Astheenginespeedincreases,morecylinderfiringsoccurinagiventime,andthehigh-pressurepulsesbecomeclosertogetherintheexhaustsystem.（略）

AdigitalEGRvalvecontainsuptothreeelectricsolenoidsthatareoperateddirectlybythePCM.Eachsolenoidcontainsamovableplungerwithataperedtipthatseatsinanorifice.Whenanysolenoidisenergized,theplungerisliftedandexhaustgasisallowedtorecirculatethroughtheorificeintotheintakemanifold.Thesolenoidsandorificesaredifferentsizes.ThePCMcanoperateone,two,orthreesolenoidstosupplytheamountofexhaustrecirculationrequiredtoprovideoptimum

controlofNOxemissions.Fig.7-2AelectronicEGRsystem

OverviewofEmissionControlSystems

Fig.7-2AelectronicEGRsystem

OverviewofEmissionControlSystems

InternalExhaustGasRecirculation(EGR)EGRreducesthelevelsofoxidesofnitrogen(nitricoxideNO,andsmallquantitiesofnitrogendioxideNO2,collectivelyreferredtoasNOX)inengineexhaustgasesatpartload.TheaimofaninternalEGRsystemistocontroltherecirculationofexhaustgaswithouttheuseofexternalpipeworkontheengine.Inaconventionalplenumthrottledengine,atpartthrottlethereisapressuredifferentialbetweentheinletandexhaustports.Towardstheendoftheexhauststrokeonafourstrokeengine,theinletvalveopensandaperiodfollowswheninletandexhaustvalvesareopensimultaneously.Duringthisvalveoverlapperiod,theinletportdepressioncausesresidualexhaustgasinthecombustionchambertoflowbackintotheinletport.Theresultantpressuredropinthecombustionchambercausesgasesintheexhaustporttoflowbackintothecombustionchamber.Theseresidualexhaustgasesdilutetheincomingair/fuelcharge.

OverviewofEmissionControlSystems

OverviewofEmissionControlSystems

Thisdilutionofthechargereducesthepeakcombustiontemperaturesandpressures,whichreducestheamountofNOXintheexhaustgases.Excessdilutioncanleadtoincompleteorunstablecombustionwhichresultsinanincreaseinhydrocarbon(HC)levels.Theoptimumamountofdilutionvarieswithenginespeedandload.Conventionally,thedilutionrequirementsforoptimizedrunningconditionsareachievedbyusinganexternalEGRsystemwhichrecirculatesmeteredquantitiesofexhaustgasbyexternalpipesandacontrolvalve.EvaporativeControlSystem

Gasolineevaporatesquiteeasily.Inthepasttheseevaporativeemissionswereventedintotheatmosphere.20%ofallHCemissionsfromtheautomobilearefromthegastank.In1970legislationwaspassed,prohibitingventingofgastankfumesintotheatmosphere.Anevaporativecontrolsystemwasdevelopedtoeliminatethissourceofpollution.Thefunctionofthefuelevaporativecontrolsystemistotrapandstoreevaporativeemissionsfromthegastankandcarburetor.

OverviewofEmissionControlSystems

Acharcoalcanisterisusedtotrapthefuelvapors.Thefuelvaporsadheretothecharcoal,untiltheengineisstarted,andenginevacuumcanbeusedtodrawthevaporsintotheengine,sothattheycanbeburnedalongwiththefuel/airmixture.Thissystemrequirestheuseofasealedgastankfillercap.Thiscapissoimportanttotheoperationofthesystemthatatestofthecapisnowbeingintegratedintomanystateemissioninspectionprograms.Pre-1970carsreleasedfuelvaporsintotheatmospherethroughtheuseofaventedgascap.Todaywiththeuseofsealedcaps,redesignedgastanksareused.Thetankhastohavethespaceforthevaporstocollectsothattheycanthenbeventedtothecharcoalcanister.Apurgevalveisusedtocontrolthevaporflowintotheengine.Thepurgevalveisoperatedbyenginevacuum.Onecommonproblemwiththissystemisthatthepurgevalvegoesbadandenginevacuumdrawsfueldirectlyintotheintakesystem[3].Thisenrichesthefuelmixtureandwillfoulthesparkplugs.

OverviewofEmissionControlSystems

Mostcharcoalcanistershaveafilterthatshouldbereplacedperiodically.Thissystemshouldbecheckedwhenfuelmileagedrops.Insomeengines,thepowertraincontrolmodule(PCM)allowsintakemanifoldvacuumtodrawvaporsintothecombustionchambersduringcertainoperatingconditions.Alloftheseenginesuseadutycyclepurgesystem.ThePCMcontrolsthevaporflowbyoperatingthedutycycleEVAPpurgesolenoid(Fig.7-3).Fig.7-3AnECM-controlledEVAPsystem

OverviewofEmissionControlSystems

OverviewofEmissionControlSystems

AirInjectionSincenointernalcombustionengineis100%efficient,therewillalwaysbesomeunburnedfuelintheexhaust.Thisincreaseshydrocarbonemissions.Toeliminatethissourceofemissionsanairinjectionsystemwascreated.Combustionrequiresfuel,oxygenandheat.Withoutanyoneofthethree,combustioncannotoccur.Insidetheexhaustmanifoldthereissufficientheattosupportcombustion,ifweintroducesomeoxygenthatanyunburnedfuelwillignite.Thiscombustionwillnotproduceanypower,butitwillreduceexcessivehydrocarbonemissions.Unlikeinthecombustionchamber,thiscombustionisuncontrolled,soifthefuelcontentoftheexhaustisexcessive,explosions,whichsoundlikepopping,willoccur.Therearetimeswhenundernormalconditions,suchasdeceleration,whenthefuelcontentisexcessive[4].Undertheseconditionswewouldwanttoshutofftheairinjectionsystem.a)coldmodeFig.7-4Airmanagementsystemoperation

OverviewofEmissionControlSystems

b)wormmodeFig.7-4Airmanagementsystemoperation

OverviewofEmissionControlSystems

OverviewofEmissionControlSystems

Thisisaccomplishedthroughtheuseofadivertervalve,whichinsteadofshuttingtheairpumpoff,divertstheairawayfromtheexhaustmanifold.Sinceallofthisisdoneafterthecombustionprocessiscomplete,thisisoneemissioncontrolthathasnoeffectonengineperformance.LaterversionsoftheairinjectionsystemareunderECMcontrol(Fig.7-4).Whentheengineiscold,theECMenergizesacontrolsolenoid.Thisallowsairtoflowtoanairswitchingvalve.Theairswitchingvalveisenergizedtodirectairtotheexhaustports.Onawarmengine,orin"closedloop"mode,theECMde-energizestheairswitchingvalve,directingairbetweenthebedsofthecatalyticconverter.ThisprovidesextraoxygenfortheoxidizingcatalysttodecreaseHCandCOlevels,whilekeepingoxygenlevelslowinthefirstbedoftheconverter.Thisenablesthereducingcatalysttoeffectivelydecreasethelevelsofoxidesofnitrogen(NOX).CatalyticConverterAutomotiveemissionsarecontrolledinthreeways.Oneistopromotemorecompletecombustionsothattherearefewerby-products.Thesecondistoreintroduceexcessivehydrocarbonsbackintotheengin