汽車專業(yè)英語U1L5(發(fā)動機部分)

Unit1One.TheFuelsystemThefuelsystemhasthejobofstoringandsupplyingaclear,continuous,adequateamountofair-fuelmixtureundersufficientpressuretothecylinder,andalsosupplyingacombustiblemixtureofairandfueltotheengine.Fuelsupplysystem

(燃油供給系統(tǒng))1．TheConventionalFuelSystemTheconventionalfuelsystemconsistsoffueltank,fuelpump,fuelfilter,carburetor,airfilter,intakemanifold,exhaustmanifold,andfuellines（Fig.5-1）（1）TheFuelTank：Thefueltankstoresasupplyoffuel.（2）TheFuelLines：油管Thefuellinescarrythefuelfromthetanktothecarburetor.（3）TheFuelPump：燃油泵Thefuelpumpmovesfuelfromthetanktothecarburetor.（4）TheFuelFilter：

燃油濾清器Thefuelfilterremovesimpuritiesfromthefuel.（5）TheCarburetor：化油器Thecarburetorisameteringdevicethatmixesfuelwithairinthecorrectproportionanddeliversthismixturetotheintakemanifold,wheretheair-fuelmixtureisdeliveredtothevariouscombustionchambers.化油器carburetor2．TheOperatingConditionIncertainoperatingconditions,thefuelrequirementdiffersgreatlyfromthebasicfuelinjectionquantitysothatcorrectiveisrequiredinmixtureformation.（1）ColdStart：Duringacoldstart,additionalfuelmustbeinjectedduringcranking.Thisisduetothelowturbulenceatcrankingspeedscausingpoormixtureofthefuelparticleswiththeair.（2）Warmup：Thewarmupphasefollowsthecoldstart.Theengineneedsextrafuel,becausesomeofthefuelstillcondensesonthecoldcylinderwalls.3）Acceleration：Ifthethrottleisopenedabruptly,theair-fuelmixtureismomentarilyleaned-off,andashortperiodofmixtureenrichmentisneededtoensuregoodtransitionalresponse.（4）PartLoad：Duringpartloadoperation,achievingmaximumfueleconomyandobservingtheemissionvaluesarethecrucialfactors.（5）FullLoad：Theair-fuelmixturemustbeenrichedcomparedtowhichatpartloadwhentheenginedeliversmaximumpoweratfullload.（6）Idling：Theengineidlespeedprincipallydeterminesthefuelconsumptionatidles.3.TheElectronicFuelInjectionSystemThecarburetorsendsthecorrectair-fuelmixturetotheengine.However,thecarburetorisamechanicaldevicethatisneithertotallyaccuratenorparticularlyfastinrespondingtochangingenginerequirements.So,notallcarshavecarburetors.Fuelinjectionsystemsareusedonmanymoderncars.Fuelinjectionsystemshavemanyadvantagesovercarburetors.Forexample,theyprovidemoreexactfuelcontrol.Thus,theycanbettermatchair-fuelratiostochangingtheengineconditions.Theyalsoprovidebettereconomyandemissioncontrol.Furthermore,fuelinjectionsystemdonotneedmanypartsascarburetorhave.ThefuelinjectionsystemsusedinautomobilesareportfuelinjectionandThrottleBodyInjection（TBI）.PortfuelinjectioniscalledMultiplePointInjection（MPI）.ThrottlebodyinjectionisalsocalledSinglePointInjection（SPI）.Today,themostadvancedfuelinjectiontechnologyisFuelStratifiedInjection（FSI）.ElectronicFuelInjectionsystemcanbedividedintothreebasicsub-systems.Theyarefueldeliverysystem,airinductionsystem,andelectroniccontrolsystem（1）TheFuelDeliverySystemThefueldeliverysystemconsistsoffueltank,fuelpump,fuelfilter,fueldeliverypipe,injector,fuelpressureregulatorandfuelreturnpipe（Fig.5-2）.①TheFuelDeliveryPipe：Thefueldeliverypipeisdesignedtoholdtheinjectorinplaceontheintakemanifold.Thepulsationdamperandthefuelpressureregulatoraremountedtothefueldeliverypipe.②TheInjector：Theinjectorsaresmallon/offvalvescontrolledbyanelectricsignal,whicharemountedintheintakemanifoldsothattheysprayfueldirectlyattheintakevalves.Two.TheExhaustSystemTheexhaustsystemcarriesexhaustgasesfromtheengine’scombustionchambertotheatmosphereandreducesenginenoise.Exhaustgasesleaveinapipe,startfromtheexhaustmanifold,travelingthroughacatalyticconverterandamufflerbeforeexitingthroughthetailpipe.Thebasisoftheproblemgasesare：hydrocarbons（unburned）,carbonmonoxide,nitrogenoxides,sulfurdioxide.Exhaustsystemconsistsoftailpipe,mainmuffler,centerexhaustpipe,secondmuffler,frontexhaustpipe,exhaustmanifold,catalyticconverter,etc（Fig.5-3）.1．TheTailPipeThetailpipeisalongmetaltubeattachedtothemuffler.Itsticksoutunderthebodyofacar,producedattherear,inordertodischargetheexhaustgasesfromthemuffleroftheengineintotheairoutsidethecar.1．TheTailPipe2．TheMainMufflerExhaustgasesleavetheengineunderextremelyhighpressure.Ifthesegasesescapeddirectlyfromtheengine,thenoisewouldbetremendous.Forthisreason,thepressureofthegasesisreducedwhentheypassthroughthemuffler,sotheygooutofthetailpipequietly.It’sconnectedbetweenthetailpipeandthecenterexhaustpipe.3．TheCatalyticConverterThecatalyticconverterisusuallylocatedintheengineexhaustpipe,intheclosestproximitytotheexhaustmanifold.Itisnowacompulsorycomponentofallvehicles.Itconvertsharmfulpollutantscontainedintheexhaustgasintoharmlessemissions..4．TheExhaustManifoldandCylinderHeadTheexhaustmanifoldisapipethatconductsth