unitEngineElectronicControl汽车实用英语

Unit4EngineElectronicControlSystemsService第1页/共113页Uponcompletionofthisunit,youshouldbeableto:OverallObjectives•Learnkeytermsaboutengineelectroniccontrolsystemsinthisunit.•Understandtheprocessofinspectionandrepairofengineelectroniccontrolsystems.•Usemaintenancemanualtodealwiththepracticalproblems.第2页/共113页Task4.1EngineControlSystemInspection-发动机控制系统检测Task4.2FuelInjectorReplacement-更换喷油器Task4.3EmissionControlInspection-排放控制检测Task4.4IgnitionSystemInspection-点火系统检测Task4.5DiagnosticProcedures-诊断程序TasksIntroduction第3页/共113页Automotiveenginecontrolsystemsmustsatisfydiverseandoftenconflictingrequirements.Servicingthesesystemsregularlyensurestheautomotiverunningnormallyandmeetingstringentstandards.Thefollowingtasks(e.g.enginecontrolsysteminspection,fuelinjectorreplacement,ignitionsysteminspection,etc.)aretheimportantitemsinengineelectronicsystemservicingtocontrolexhaustemissions,fueleconomyandotherperformanceindicatorsoftheengine.TaskDescription第4页/共113页Task4.1EngineControlSystemInspection第5页/共113页LearningPreparationengineelectronicsystemintakeairflowmeterohmmeterresistanceterminalvoltmeterpositivenegativethrottlepositionsensorknocksensorKeyterms:发动机电控系统进气空气流量计欧姆电阻终端，端子伏特计，电压表正极负极节气门位置传感器爆震传感器第6页/共113页Step1Amaintenancecaseisprovided;Step2Learntheprocessofinspectingtheengineelectronicsystem;Step3Requirestudentstograspthekeytermsinthistask;Step4Trytodescribetheprocessofinspectingtheengineelectronicsystem;Step5Studentsreadrelativematerial;Step6AssessmentPlanandImplement第7页/共113页()1.Theresistanceoftheintakeairflowmeterisrelatedtothetemperature.()2.WheninspectingthevoltageofterminalVGandE2G,youshouldturnofftheignitionswitch.()3.Ifairisblownintotheintakeairflowmeter,thevoltageshouldchangewiththeairflow.()4.Iftheresistanceofthecamshafttimingoilcontrolvalveis7.3Ω,itisok.()5.Whentestingthemovementofthecamshafttimingoilcontrolvalve,terminal2shouldbeconnectedwiththepositiveleadofthebattery.AssessmentandFeedbackTrueorFalse第8页/共113页()6.Thebadreturningthevalvemaybecausedbyentranceofforeignobjects.()7.Thereisaclearancebetweenthethrottlestopscrewandthrottleleveratthethrottleclosedposition.()8.Intheinspectionofthethrottlepositionsensor,theresistancebetweenterminalsVTAandE2shouldchangeinproportiontothethrottleleveropeningvalue.()9.Thewatertemperaturesensorcannotbecheckedinthewater.()10.Iftheresistanceoftheknockcontrolsensoris50kΩat20°C,itshouldbechanged.第9页/共113页AnAirFlowSensor（空气流量传感器）orMassAirflowSensor(MAF)isoneofthecomponentsofanelectronicfuelinjectionsystemofamoderncarortruck.Amassairflowsensorisinstalledinsidetheintakeairductbetweentheaircleanerandtheintakemanifoldoftheengine.Amassairflowsensormeasurestheamountofairenteringtheengine.Oftenanintakeairtemperaturesensor(IAT)isalsoinstalledwithinthemassairflowsensor.Therearefewtypesofairflowsensors,howeverahot-wiretypeisusedthemostinthemoderncars.Let’sseehowitworks.Ahot-wiremassairflowsensor（热线式空气流量计）hasasmallelectricallyheatedwire(hotwire)andasmalltemperaturesensorinstalledclosetothehotwire.Thetemperaturesensormeasuresthetemperatureoftheairnearthehotwire.4.1.1WhatisaMassAirFlowSensor(MAF)第10页/共113页Fig4.1.1MassAirflowSensor(MAF)Fig.4.1.2LocationoftheMAFFig4.1.3Toyotamassairflowsensor(MAF)Fig4.1.4Volkswagenmassairflowsensor第11页/共113页Whentheengineisidling,averylittleairflowspassthehotwire,soittakesverysmallelectricalcurrenttokeepthewirehot.Whenyoupressthegas,thethrottleopensallowingmoreairtoflowoverthehotwire.Thepassingaircoolsthehotwiredown;themoreairflowsoverthewire,themoreelectricalcurrent（电流）isneededtokeepithot.Theamountofthiselectricalcurrentisproportionaltotheamountoftheairflow.第12页/共113页Asmallelectronicchipinstalledinsidetheairflowsensorturnstheamountofthiselectricalcurrentintoadigitalsignalthatissenttotheenginecomputer(ECM).Thecomputerusestheairflowsignal（信号）tocalculatetheproperamountoffuelinjectedintothecylindersinordertokeepanoptimalair/fuelratio.Thisisneededtokeeptheexhaustemissionslowwithoutsacrificingtheengineperformance.Inaddition,thecomputerusestheairflowreadingstodeterminetheshiftpointsoftheautomatictransmission（自动变速器）;soiftheairflowsensordoesn’tworkproperly,theautomatictransmissionmightshiftgearsdifferently.第13页/共113页Problemsofmassairflowsensorsareverycommon.Theairflowsensorusuallygetscontaminatedordamagedwhenabadorimproperlyinstalledairfilterallowssomeunfiltered（未经过滤的）airintotheengineorwhenoilfromanoil-soakedairfiltercontaminatestheairflowsensor.Abadorcontaminatedmassairflowsensorcannotmeasuretheamountofairflowcorrectly.Thiscancausevariousdriveabilityproblemssuchasstalling,especiallywhentheengineiscold,misfiring,lackofpower,pooracceleration,etc.Inaddition,aproblemwiththemassairflowsensorwillcausetheCheckengineorServiceenginelighttocomeon.4.1.2MassAirFlowSensorProblems第14页/共113页The“checkengine”lightcomesonwhenthecomputerhasdetectedafaultinoneoftheengineelectronicsystems.Thisfault（故障）isstoredasatroublecodeandcanberetrievedfromthecomputerwithascantool.Thefollowingtroublecodesareassociatedwithamassairflowsensor:P0100-MassAirFlowCircuitMalfunctionP0101-MassAirFlowCircuitRange/PerformanceP0102-MassAirFlowCircuitLowP0103-MassAirFlowCircuitHighP0104-MassAirFlowCircuitIntermittentThetroublecodesP0171SystemTooLean(Bank1)andP0174SystemTooLean(Bank2)arealsocouldbecausedbyabadorcontaminatedmassairflowsensor.Ifyourcheckenginelightison,haveyourvehicle’scomputerscannedandreadmoreaboutleancodes.第15页/共113页Often,anairflowsensorcanbecheckedwithascantool.Usually,theairflowreadingsofthesensorinquestioniscomparedtothereadingsofaknowngoodsensor.Typically,acontaminatedairflowsensorwillshowdifferentamountfromaknowngoodsensor.Iftheairflowsensorisbad,itwillneedtobereplaced.It’safairlysimplejob,howevertheairflowsensoritselfcouldcostuptoafewhundreddollars.Ifthesensorisjustdirty,yourmechanicmaysuggestcleaningit(cleaningtheairflowsensorisadelicateprocedure)asatemporarysolution—sometimesthiscouldhelpyou.Ifthenewmassairflowsensorisinstalled,makesuretheairfilterisinstalledproperly,asthesandparticlescomingwiththeunfilteredaircandamagetheairflowsensor.第16页/共113页Practice—MaintenanceManualReading1.IntakeairflowmeterSUB-ASSY.(a)Inspecttheintakeairflowmeterresistance.(1)Usinganohmmeter,measure（测量）theresistancebetweenterminalsTHAandE2.EngineControlSystemInspection第17页/共113页HINT:Iftheresistanceisnotasspecified,replacetheintakeairflowmeter.(b)Inspecttheintakeairflowmeteroperation.(1)Connecttheintakeairflowmeterconnector.(2)Turntheignitionswitch（点火开关）toON.(3)Usingavoltmeter,connectthepositive(+)testerprobetoterminalVG,andnegative(–)testerprobetoterminalE2G.(4)Blowairintotheintakeairflowmeter,andcheckthatthevoltagefluctuates.第18页/共113页HINT:Ifoperationisnotasspecified,replacetheintakeairflowmeter.(5)TurntheignitionswitchtoLOCK.(6)Disconnecttheintakeairflowmeterconnector.第19页/共113页2.CamshafttimingoilcontrolvalveASSY(a)Resistanceinspection.(1)Usinganohmmeter,measuretheresistancebetweentheterminals.Resistance:6.9to7.9Ωat20°C(68°F)(b)Movementinspection.(1)Connectthepositive(+)leadfromthebattery（蓄电池）toterminal1andnegative(–)leadtoterminal2,andcheckthemovementofthevalve.NOTICE:Confirmthevalvedoesnotadhere.HINT:Badreturningofthevalve（阀）byentranceofforeignobjectscausessubtlepressureleaktotheadvanceddirection.Then,DTCcanbedetected.第20页/共113页3.ThrottlebodyASSYCheckthrottlebody.(1)Checkthatthrottlevalveshaftisnotrickety.(2)Checkthateachportisnotstoppedup（堵塞）.(3)Checkthatthrottlevalveopensandclosessmoothly.(4)Checkthatthereisnoclearancebetweenthethrottlestopscrewandthrottleleveratthethrottleclosedposition.NOTICE:Donotadjustthethrottlestopscrew.第21页/共113页4.E.F.I.ThrottlePositionSensor(a)Resistanceinspection.(1)Disconnectthethrottlepositionsensorconnector.(2)Usinganohmmeter,measuretheresistancebetweenterminalsVCandE2.Resistance:2.5to6.0kΩ(3)CheckthechangeofresistancebetweenterminalsVTAandE2.Changeofresistance:Theresistancevalue（电阻值）increasesinproportiontothethrottleleveropeningvalue.第22页/共113页第23页/共113页5.E.F.I.EngineCoolantTemperatureSensor(a)Resistanceinspection.(1)Usinganohmmeter,measuretheresistancebetweeneachterminal.Resistance:At20°C(68°F)2.32–2.59kΩAt80°C(176°F)0.310–0.326kΩNOTICE:Incaseofcheckingthewatertemperaturesensor（水温传感器）inthewater,becarefulnottoallowwatertogointotheterminals,andafterchecking,wipeoutthesensor.第24页/共113页6.KnockControlSensor(a)Usinganohmmeter,measuretheresistancebetweenterminals.Resistance:120–280kΩat20°C(68°F)HINT:Iftheresistanceisnotspecified,replacethesensor.HINT:Iftheresistanceisnotspecified,replacethesensor.第25页/共113页7.E.F.I.CircuitOpeningRelay（继电器）ASSY(a)Continuityinspection.(1)Usinganohmmeter,checkthatcontinuityexistsbetweeneachterminal.Specifiedcondition:Betweenterminals1and2ContinuityBetweenterminals3and5Nocontinuity(2)Usinganohmmeter,checkthatcontinuityexistsbetweenterminals3and5whenhebatteryvoltageisappliedacrossterminals1and2.第26页/共113页Task4.2FuelInjectorReplacement第27页/共113页LearningPreparationfuelinjectorcylinderheadcoverventilationhoseretainerconnectorinsertfueldeliverypipetwistKeyterms:喷油器汽缸盖罩通风软管保持架接头，连接器插入燃油分配管扭转，扭曲第28页/共113页Step1Amaintenancecaseisprovided;Step2Learntheprocessofreplacingfuelinjectorviaamaintenancemanual;Step3Requirestudentstograspthekeytermsinthistask;Step4Trytodescribetheprocessofreplacingfuelinjector;Step5Studentsreadrelativematerial;Step6AssessmentPlanandImplement第29页/共113页()1.Whenyoureplacingtheinjectors,youmustpreventthegasolineleakage.()2.Theventilationhoseisconnectedwiththecylinderblock.()3.Theengineisatypeofmulti-pointfuelinjection.()4.Theharnessclampsareusedtofixthewires.()5.AnSSTmustbeadoptedtodisconnectthefueltube.AssessmentandFeedbackTrueorFalse第30页/共113页()6.Thepipeandtheconnectorshouldbekeptveryclean.()7.Thefuelinjectorsshouldberemovedwiththefueldeliverypipe.()8.Theinsulatorinstalledoneachfuelinjectorneedsnottobechanged.()9.Wheninstallingtheinjectortothefueldelivery,youcanapplyalittleengineoilontheO-ring.()10.Theinjectorshouldbepusheddirectlytothefueldeliverypipe.第31页/共113页TheEFI(ElectronicFuelInjection)system（电控燃油喷射系统）usessensorstodetecttheengineconditionandvehiclerunningcondition.AndtheengineECU（电控单元）calculatestheoptimumfuelinjectionvolume,andcausestheinjectorstoinjectthefuel.Fig.4.2.1showsthebasicEFIconfiguration.4.2.1ElectronicFuelInjectionSystem第32页/共113页Fig.4.2.1ElectronicFuelInjectionSystem1-exhaustgasoxygensensor;2-injector;3-fuelpressureregulator;4-coolanttemperaturesensor;5-idlecontrolvalve;6-airflowmeter;7-fueltank;8-fuelpump;9-fuelfilter;10-ECU第33页/共113页TheElectronicFuelInjectionsystemcanbedividedintothreebasicsubsystems:thefueldeliverysystem,theairinductionsystemandtheelectroniccontrolsystem.Thefueldeliverysystemconsistsofthefueltank（油箱）,fuelpump,fuelfilter,fueldeliverypipe(fuelrail),fuelinjector,fuelpressureregulator,andfuelreturnpipe.Someenginesalsohavepulsationdamper.Thefuelistakenfromthefueltankbythefuelpumpandsprayedunderpressurebyaninjector.Thefuelpressureinthefuellinemustberegulatedtomaintainstablefuelinjectionbythepressureregulator.Anyfuelwhichisnotdeliveredtotheintakemanifoldbytheinjector（喷油器）isreturnedtothetankthroughafuelreturnpipe.第34页/共113页Theairinduction（空气供给）systemconsistsoftheaircleaner,airflowmeter,throttlevalve,airintakechamber,intakemanifoldrunner,andintakevalve.Whenthethrottlevalveisopened,airflowsthroughtheaircleaner,throughtheairflowmeter,pastthethrottlevalve,andthroughawelltunedintakemanifoldrunnertotheintakevalve.Airdeliveredtotheengineisafunctionofdriverdemand.Asthethrottlevalveisopenedfurther,moreairisallowedtoentertheenginecylinder.Theelectroniccontrolsystemconsistsofvariousenginesensors,ElectronicControlUnit(ECU),variousactuators.Therearemanysensorssuchasmassairflowsensor,manifoldabsolutepressuresensor,throttlepositionsensor,enginecoolanttemperaturesensor,intakeairtemperaturesensor,crankshaftpositionsensor,camshaftpositionsensor,andexhaustgasoxygensensor,etc.第35页/共113页ThebasicfunctionoftheECUistocontrolthepulsewidthoftheinjector.Inenginemanagementsystems,theECUcontrolsadditionalfunctions,suchasidlespeed（怠速）,ignitiontiming,andfuelpumpoperation.Theactuators（执行元件）containfuelpumprelay,injector,MalfunctionIndicatorLight(MIL),EVAPcanisterpurgesolenoidvalve,airconditionerrelay,coolingfanrelays,idlecontrolvalve,etc.Airenterstheenginethroughtheairinductionsystemwhereitismeasuredbytheairflowmeter.Astheairflowsintothecylinder,fuelismixedintotheairbythefuelinjector.Fuelinjectorsarearrangedintheintakemanifoldbehindeachintakevalve.TheinjectorsareelectricalsolenoidswhichareoperatedbytheECU.TheECUpulsestheinjectorbyswitchingtheinjectorgroundcircuitonandoff.第36页/共113页Whentheinjectoristurnedon,itopens,sprayingatomizedfuelatthebacksideoftheintakevalve.Asfuelissprayedintotheintakeairstreams,itmixeswiththeincomingairandvaporizesduetothelowpressureintheintakemanifold.TheECUsignalstheinjectortodeliverjustenoughfueltoachieveanidealair/fuelratio（空燃比）of14.7:1,oftenreferredtoasstoichiometry.ThepreciseamountoffueldeliveredtotheengineisafunctionofECUcontrol.TheECUdeterminesthebasicinjectionquantitybaseduponmeasuredintakeairvolumeandenginerpm（转速）.Dependingonengineoperatingconditions,injectionquantitywillvary.TheECUmonitorsvariablessuchascoolanttemperature,enginespeed,throttleangleandexhaustoxygencontentandmakesinjectioncorrectionswhichdeterminefinalinjectionquantity.第37页/共113页Afuelinjectorisnothingbutanelectronicallycontrolledvalve.Itissuppliedwithpressurizedfuelbythefuelpumpinyourcar,anditiscapableofopeningandclosingmanytimespersecond.Whentheinjectorisenergized,anelectromagnetmovesaplungerthatopensthevalve,allowingthepressurizedfueltosquirtoutthroughatinynozzle（喷嘴）.Thenozzleisdesignedtoatomizethefuel—tomakeasfineamistaspossiblesothatitcanburneasily.4.2.2Injector第38页/共113页Fig.4.2.2InsideaFuelInjectorFig.4.2.3LocationoftheFuelInjectors第39页/共113页Theamountoffuelsuppliedtotheengineisdeterminedbytheamountoftimethefuelinjectorstaysopen.Thisiscalledthepulsewidth,anditiscontrolledbytheECU.Theinjectorsaremountedintheintakemanifoldsothattheysprayfueldirectlyattheintakevalves.Apipecalledthefuelrailsuppliespressurizedfueltoalloftheinjectors.第40页/共113页Practice—MaintenanceManualReading1.WorkforPreventingGasolinefromSpillingOut2.RemoveCylinderHeadCoverNO.2(a)Removethe2nuts（螺母）,2clipsandcylinderheadcover.FuelInjectorReplacement3.DisconnectVentilationHose(a)Disconnecttheventilationhosefromthecylinderheadcover.第41页/共113页4.DisconnectEngineWire(a)Disconnectthe4fuelinjectorconnectors.(b)Removethe3wireharnessclampsfromtheclampbrackets.5.RemoveEFIFuelPipeClamp(a)RemovetheEFIfuelpipeclamp.第42页/共113页6.DisconnectFuelTubeSUB-ASSY(a)UsinganSST,disconnectthefueltube.(SST=SpecialServiceTool)SST09268–21010(1)AssembletheSSTtotheconnectionasshown.(2)TurntheSST,aligntheretainersinsidetheconnectorwiththeSSTchamferedpartsandinserttheSSTintotheconnector.(3)SlidetheSSTandtheconnectortogethertowardsthefueltubeassembly..第43页/共113页第44页/共113页7.RemoveFuelDeliveryPipeSUB–ASSYRemovethe3boltsandfueldeliverypipe（燃油分配管）togetherwiththe4fuelinjectors.NOTICE:Becarefulnottodropthefuelinjectorswhenremovingthefueldeliverypipe.8.RemoveFuelInjectorASSY(a)Pulloutthe4fuelinjectorsfromthefueldeliverypipe.第45页/共113页9.InstallFuelInjectorASSY(a)Installanewinsulatortoeachfuelinjector.(b)ApplyalightcoatofspindleoilorgasolinetoanewO-ring,andinstallittoeachfuelinjector.NOTICE:Neveruseengine,gearorbrakeoil.第46页/共113页(c)ApplyalightcoatofspindleoilorgasolineontheplacewherethefueldeliverypipetouchesontheO-ring.(d)Whileturningthefuelinjectorclockwiseandcounterclockwise,pushittothefueldeliverypipe.NOTICE:BecarefulnottotwisttheO-ring.Afterinstallingthefuelinjectors,checkthattheyturnsmoothly.Ifthefuelinjectordoesnot,reinstallitwithanewO-ring.第47页/共113页10.InstallFuelDeliveryPipeSUB–ASSY(a)Installthe2spacerstothecylinderhead.(b)Installthefueldeliverypipetogetherwiththe4fuelinjectorswiththe3bolts.Torque:BoltA19N·m(194kgf·cm,14ft·lbf)BoltB9.0N·m(92kgf·cm,80in.·lbf)NOTICE:Becarefulnottodropthefuelinjectorswheninstallingthefueldeliverypipe.Checkthatthefuelinjectorsrotatesmoothlyafterinstallingthefueldeliverypipe.第48页/共113页11.ConnectFuelTubeSUB–ASSY(a)Connectthefueltubetothefueldeliverypipe.NOTICE:Checkifthereisanydamageorforeignobjectsontheconnectedpartofthefueltube.Afterconnecting,checkifthefueltubeandtheconnectoraresecurelyconnectedbypullingthem.12.InstallCylinderHeadCoverNO.2(a)Installthecylinderheadcoverwiththe2nutsand2clips.Torque:7.0N·m(71kgf·cm,62in.·lbf)13.CheckFuelLeak第49页/共113页Task4.3EmissionControlSystemInspection第50页/共113页LearningPreparationemissionair-fuelratiodatamonitoroxygensensorrpmwarmupevaporativevacuumhoseairtightnessfillerpipecharcoalcanisterKeyterms:排放空燃比数据监控氧传感器转速热机蒸发的真空管密封性加油管活性碳罐第51页/共113页Step1Amaintenancecaseisprovided;Step2Learntheprocessofinspectingemissionsystemviaamaintenancemanual;Step3Requirestudentstograspthekeytermsinthistask;Step4Trytodescribetheprocessofinspectingemissionsystem;Step5Studentsreadrelativematerial;Step6AssessmentPlanandImplement第52页/共113页()1.The“O2SENSOROUTPUTVOLTAGE”istestedwhentheenginespeedisat2,500rpm.()2.ItisOKifthevoltagechangesmorethan8timespersecond.()3.Asoundscopeisusedtoinspecttheworkingconditionoftheinjector.()4.WheninspectingEvaporativeEmissionControlSystem,theVSVshouldbeturnedoff.()5.Whencheckingairtightnessinfueltank,youshouldmakesurethattheinternalpressurecanbeheldat6kPafor1minute.AssessmentandFeedbackTrueorFalse第53页/共113页()6.Ifthepurgelineispressurizedat4kpa,thereshouldbeventilationthroughtheEVAPlinehose.()7.Acharcoalcanisterisacontainerfilledwithactivatedcharcoalthattrapsoilvaporsemittedbythefuelsystem.()8.Theenginerunningoutofturnmaybecausedbythecracksorleaksofthehoses.()9.Theheaterresistanceoftheheatedoxygensensorshouldbesomevaluebetween11Ωand16Ω.()10.Thefueltankcapisusuallycheckedbyyourowneyes.第54页/共113页Emissionsofmanyairpollutants（污染）havebeenshowntohavevarietyofnegativeeffectsonpublichealthandthenaturalenvironment.Emissionsthatareprincipalpollutantsofconcerninclude:Hydrocarbons（碳氢化合物）—Aclassofburnedorpartiallyburnedfuel,hydrocarbonsaretoxins.Hydrocarbonsareamajorcontributortosmog,whichcanbeamajorprobleminurbanareas.Prolongedexposuretohydrocarbonscontributestoasthma（哮喘）,liverdisease（肝病）,lungdisease,andcancer.4.3.1PollutantsofEmissions第55页/共113页Carbonmonoxide(CO)—Aproductofincompletecombustion,carbonmonoxidereducestheblood’sabilitytocarryoxygen;overexposure(carbonmonoxidepoisoning)maybefatal.CarbonMonoxidepoisoningisamajorkiller.Nitrogenoxides(NOx)—Generatedwhennitrogenintheairreacts（反应）withoxygenathehightemperatureandpressureinsidetheengine.NOxisaprecursortosmogandacidrain.NOxisamixtureofNO,N2O,andNO2.NO2isextremelyreactive.Itdestroysresistancetorespiratoryinfection.NOxproductionisincreasedwhenanenginerunsatitsmostefficient(i.e.hottest)partofthecycle.第56页/共113页Particulatematter—Sootorsmokemadeupofparticlesinthemicrometresizerange:Particulatemattercausesnegativehealtheffects,includingbutnotlimitedtorespiratorydiseaseandcancer.Sulfuroxide(SOx)—Ageneraltermforoxidesofsulfur,whichareemittedfrommotorvehiclesburningfuelcontainingsulfur.ReducingtheleveloffuelsulfurreducesthelevelofSulfuroxideemittedfromthetailpipe.Refineriesgenerallyfightrequirementstodothisbecauseoftheincreasedcoststothem,ignoringtheincreasedcoststosocietyasawhole.Volatileorganiccompounds(VOCs)—Organiccompoundswhichtypicallyhaveaboilingpointlessthanorequalto250°C;forexamplechlorofluorocarbons(CFCs)andformaldehyde.VolatileorganiccompoundsareasubsectionofHydrocarbonsthatarementionedseparatelybecauseoftheirdangerstopublichealth.第57页/共113页Emissioncontrolsystems（排放控制系统）havebeenincorporatedintoautomobilestopreventpollutionbylimitingtheamountofpartiallyburnedandevaporatedgasesintotheatmosphere.Thesesystemshavebeenefficientinreducingthepollutioncausedbyautomobilestoalargeextent.Automobileswerefirstmanufacturedwithexhaustemissionscontrolsystemsin1966.Sincethentechnologyhasundergoneseveralchangesthathasincreasedthenumberofcarswhichusethistechnology.Theemissionreleasediscalculatedbyquantityreleasedperdistancetraveled.Thetypesofemissionsaretailpipeemissions,lifecycleemissionsandevaporativefuelemissions.4.3.2HowdoesanEngineEmissionControlSystemWorks第58页/共113页CatalyticConverter（催化转化器）Thecatalyticconverterwasdevelopedintheearly70’swhensevereairpollutionwasemanated,butwasn’tmademandatorybytheU.S.governmentuntil1