Powertrain Calibration 101动力总成与校准(-85)

Powertrain&Calibration101JohnBucknellDaimlerChryslerPowertrainSystemsEngineeringDecember4,2006Powertrain&CalibrationTopicsBackgroundPowertraintermsThermodynamicsMechanicalDesignCombustionArchitectureCylinderFilling&EmptyingAerodynamicsCalibrationSpark&FuelTransients&DrivabilityWhatisaPowertrain?EnginethatconvertsthermalenergytomechanicalworkParticularly,thearchitecturecomprisingallthesubsystemsrequiredtoconvertthisenergytoworkSometimesextendstodrivetrain,whichconnectspowertraintoend-userofpowerCharacteristicsofInternalCombustionHeatEnginesHighenergydensityoffuelleadstohighpowertoweightratio,especiallywhencombustingwithatmosphericoxygenExternalcombustionhaslossesduetomultipleinefficiencies(primarilyheatlossfromcondensingofworkingfluid),internalcombustionhaslessinefficienciesHeatenginesuseworkingfluidswhichisthesimplestofallenergyconversionmethodsReciprocatingInternalCombustionHeatEnginesCharacteristicsSlider-crankmechanismhashighmechanicalefficiency(pistonskirtrubbingissourceof50-60%ofallfiringfriction)Piston-cylindermechanismhashighsingle-stagecompressionratiocapability–leadstohighthermalefficiencycapabilityFairtopoorairpump,limitingpowerpotentialwithoutadditionalmechanismsReciprocatingEngineTermsVc=ClearanceVolumeVd=DisplacementorSweptVolumeVt=TotalVolumeTCorTDC= ToporTopDeadCenterPositionBCorBDC= BottomorBottomDeadCenterPositionCompressionRatio(CR)FurtherexplanationofaspectsofCompressionRatioReciprocatingEnginesMostlayoutscreatedduringsecondWorldWarasaircraftmanufacturersstruggledtomaketheleast-compromisedinstallationThermodynamicsOttoCycleDieselCycleThrottledCycleSuperchargedCycleSource:InternalComb.EngineFund.ThermodynamicTermsMEP

–MeanEffectivePressureAveragecylinderpressureovermeasuringperiodTorqueNormalizedtoEngineDisplacement(VD)BMEP–BrakeMeanEffectivePressure

IMEP–IndicatedMeanEffectivePressure MEPofCompressionandExpansionStrokesPMEP–PumpingMeanEffectivePressure MEPofExhaustandIntakeStrokesFFMEP–FiringFrictionMeanEffectivePressure

BMEP=IMEP–PMEP–FFMEPThermodynamicTermscontinuedWork=Power=Work/UnitTimeSpecificPower

–Powerperunit,typicallydisplacementorweightPressure/VolumeDiagram

–EngineeringtooltographcylinderpressureIndicatedWorkTDCBDCSource:DesignandSimofFourStrokesTDCBDCSource:DesignandSimofFourStrokesPumpingWorkHistoryofInternalCombustion1878NiklausOttobuiltfirstsuccessfulfourstrokeengine1885GottliebDaimlerbuiltfirsthigh-speedfourstrokeengine1878sawSirDougaldClerkcompletefirsttwo-strokeengine(simplifiedbyJosephDayin1891)1891Panhard-LevassorvehiclewithfrontenginebuiltunderDaimlerlicenseEnergyDistributioninPassengerCarEnginesSource:SAE2000-01-2902(Ricardo)Source:AdvancedEngineTechnologyUsingExhaustEnergyHighestexpansionratiorecoversmostthermalenergyTurbinescanrecoverheatenergyleftoverfromgasexchangeEnergycanbeusedtodriveturbo-compressororfedbackintocranktrainSource:InternalComb.EngineFund.SuperchargingIncreasesspecificoutputbyincreasingchargedensityintoreciprocatorManymethodsofimplementation,costusuallyonlylimitingfactorMechanicalDesignTwoValveValvetrainPushrodOHV(Type5)HEMI2-Valve(Type5)SOHC2-Valve(Type2)FourValveValvetrainSOHC4-Valve(Type3)DOHC4-Valve(Type2)DOHC4-Valve(Type1)DesmodromicSpecificPower= f(AirFlow,ThermalEfficiency)Airflowisaneasiervariabletochangethanthermalefficiency90%ofrestrictionofinductionsystemoccursincylinderheadCylinderheadlayoutsthatallowthegreatestairflowwillhavehighestspecificpowerpotentialPeakflowfrompoppetvalveenginesprimarilyafunctionoftotalvalveareaMore/largervalvesequalsgreatervalveareaValvetrainCombustionTermsBrakePower–Powermeasuredbytheabsorber(brake)atthecrankshaftBSFC-BrakeSpecificFuelConsumption FuelMassFlowRate/BrakePower grams/kW-horlbs/hp-hLBTFuelling-LeanBestTorque LeanestFuel/AirtoAchieveBestTorque LBT=0.0780-0.0800FAor0.85-0.9LambdaThermalEnrichment–FueladdedforcoolingduetocomponenttemperaturelimitInjectorPulseWidth-TimeInjectorisOpenCombustionTermscontinuedSparkAdvance–TimingincrankdegreespriortoTDCforstartofcombustionevent(ignition)

MBTSpark–MaximumBrakeTorqueSpark MinimumSparkAdvancetoAchieveBestTorqueBurnRate–SpeedofCombustion Expressedasafractionoftotalheatreleasedversuscrankdegrees

MAP-ManifoldAbsolutePressure AbsolutenotGauge(doesnotreferencebarometer)CombustionTermscontinuedKnock

–Autoignitionofend-gassesincombustionchamber,causingextremeratesofpressurerise.KnockLimitSpark-MaximumSparkAllowedduetoKnock–canbehigherorlowerthanMBTPre-Ignition–Autoignitionofmixturepriortosparktiming,typicallyduetohightemperaturesofcomponentsCombustionStability–Cycletocyclevariationinburnrate,trappedmass,locationofpeakpressure,etc.Thelowerthevariationthebetterthestability.EngineArchitecture

InfluenceonPerformanceIntake&ExhaustManifoldTuningCylinderFilling&EmptyingMomentumPressureWaveAerodynamicsFlowSeparationWallFrictionJunctions&BendsInductionRestrictionExhaustRestriction(Backpressure)CompressionRatioValveEventsIntakeTuning

forWOTPerformanceIntakemanifoldshaveducts(“runners〞)thattuneatfrequenciescorrespondingtoenginespeed,likeanorganpipeLongerrunnerstuneatlowerfrequenciesShorterrunnerstuneathigherfrequenciesTuningincreaseslocalpressureatintakevalvetherebyincreasingflowrateDuctdiameterisatrade-offbetweenvelocityandwallfrictionofpassingchargeExhaustTuning

forWOTPerformanceExhaustmanifoldstunejustasintakemanifoldsdo,butsincenofreshchargeisbeingintroducedasaresult–notasmuchimpactonvolumetricefficiency(~8%maximumforheaders)CatalystperformanceusuallylimitsproductionexhaustsystemsthatflowacceptablywithlittletonotuningTunedHeadersTunedHeadersgenerallydonotappearonproductionenginesduetotheimpairmenttocatalystlight-offperformance(usuallyaminimumof150%additionaldistanceforcold-startexhaustheattobelost).Performancecanbeenhancedby3-8%across60%oftheoperatingrange.MomentumEffectsPressurelossinfluencesdictatethatductdiameterbeaslargeaspossibleforminimumfrictionIncreasingchargemomentumenhancescylinderfillingbyextendinginductionprocesspastunsteadydirectenergytransferofinductionstroke(iepistonmotion)DecreasingductdiameterincreasesavailablekineticenergyforagivenmassfluxThereforeductdiameterisatrade-offbetweenvelocityandwallfrictionofpassingchargePressureWaveEffectsInductionprocessandexhaustblowdownbothcausepressurepulsationsAbruptchangesofincreasedcross-sectioninthepathofapressurewavewillreflectawaveofoppositemagnitudebackdownthepathofthewaveClosed-endedductsreflectpressurewavesdirectly,thereforeawavewillechowithsameamplitudePressureWaveEffectscon’tFrictiondecreasesenergyofpressurewaves,thereforethe1storderreflectionisthestrongest–butupto5thorderhavebeenutilizedtogoodeffectinhighspeedengines(thusactiverunnersinF1inY2K)Plenumsalsoresonateandthroughsuperpositionincreasetheamplitudeofpressurewavesinrunners–smallimpactrelativetorunnergeometryEffectsofIntakeRunnerGeometryTuninginProductionI4EngineAerodynamicsLossesduetopooraerodynamicscanbeequalinmagnitudetothegainsfrompressurewavetuningOftenthedominantfactoryinpoorlyperformingOEcomponentsIfproperlydesigned,flowofasingle-entryintakemanifoldcanapproach98%ofanidealentranceonacylinderheadport(steadystateonaflowbench)Aerodynamicscon’tFlowSeparationLiterallysamephenomenonasstallinwingelements–pressureinfreestreaminsufficientto‘push’flowalongwallofshortsideradiusRecirculationpushesflowawayfromwall,therebyreducingeffectivecross-section:so-called“venacontracta〞Simpleguidelinescanpreventflowseparationinducts–studiesperformedbyNACAinthe1930sempiricallyestablishedthebestductconfigurationsAerodynamicscon’tWallFrictionSurfacefinishofductsneedtobeassmoothaspossibletoprevent‘tripping’offlowonamacrolevelJunctions&BendsEverythingfromyourfluiddynamicstextbookappliesRadiusedinletsandfree-standingpipeoutletsMinimizenumberofbendsAvoid‘S’bendsifatallpossibleInductionRestrictionAircleanerandintakemanifoldsprovidesomeresistancetoincomingchargePowerlossrelatedtorestrictionalmostdirectlyafunctionofratiobetweenmanifoldpressure(plenumpressureupstreamofrunners)andatmosphericExhaustRestrictionCompressionRatioThehighestpossiblecompressionratioisalwaysthedesignpoint,ashigherwillalwaysbemorethermallyefficientwithbetteridlequalityKnocklimitscompressionratiobecauseofcombustionstabilityissuesatlowenginespeedduetonecessarysparkretardMostenginesaredesignedwithhighercompressionthanisbestforlowspeedcombustionstabilitybecauseoftheassociatedpart-loadBSFCbenefitsandhighspeedpowerValveEventsValveeventsdefinehowanenginebreathesallthetime,andsoareanimportantaspectoflowloadaswellashighloadperformanceValveeventsalsoeffectivelydefinecompression&expansionratio,as“compression〞willnotbeginuntilthepiston-cylindermechanismissealed–samewithexpansionValveEventTimingDiagramSpiderPlot-DescribestimingpointsforvalveeventswithrespecttoCrankPositionCamCenterline-PeakValveLiftwithrespecttoTDCinCrankDegreesValveEventsforPowerMaximizeTrappingEfficiencyIntakeclosingthatisbestcompromisebetweencompressionstrokebackflowandinductionmomentum(retardwithincreasingenginespeed)EarlyintakeclosingusefulnesslimitedatlowenginespeedduetoknocklimitEarlyintakeopeningwillimpartsomeexhaustblowdownorpressurewavetuningmomentumtointakechargeMaximizeThermalEfficiencyEarliestintakeclosingtomaximizecompressionratioforbestburnrate(optimumisinstantaneousafterTDC)LatestexhaustopeningtomaximizeexpansionratioforbestuseofheatenergyandlowestEGT(leastthermalprotectionenrichmentbeyondLBT)ValveEventsforPowerMinimizeFlowLossAchievemaximumvalvelift(maxflowusuallyatL/D>0.25-0.3)aslongaspossible(squareliftcurvesareoptimumforpoppetvalves)MinimizeExhaustPumpingWorkEarliestexhaustopeningthatblowsdowncylinderpressuretobackpressurelevelsbeforeexhauststroke(advancewithincreasingenginespeed)Earliestexhaustclosingthatavoidsrecompressionspike(retardwithincreasingenginespeed)EnginePowerandBSFCvsEngineSpeedSummaryComponent’sRelativeImpactonPerformanceCylinderHeadPorts&ValveAreaValveEventsIntakeManifoldRunnerGeometryCompressionRatioExhaustHeaderGeometryExhaustRestrictionAirCleanerRestrictionPowertrainClosingRemarksPowertrainiscompromiseFour-strokeenginesarevolumetricflowratedevices–theonlyroutetomorepowerisincreasedenginespeed,morevalveareaorincreasedchargedensityMorespeed,chargedensityorvalveareaareexpensiveordifficulttodevelop–thereforeminimizinglossesisthemostefficientpathwithinexistingenginearchitecturesHighestaveragepowerduringavehicleaccelerationisfastest–peakpowervaluesdon’twinracesBreakCalibrationWhatisit?Optimizingthecontrolsystem(oncehardwareisfinalized)fordrivability,durability&emissionsIt’sjustsparkandfuel–howhardcoulditbe?KnowledgeofThermodynamics,CombustionandControlTheoryallplayinFortunatelyraceengineshavenoemissionsconstraintsanduseracefuel(usuallyeliminatesanyknock)–thereforearerelativelyeasytocalibrateCalibrationTermsStoichiometry

–ChemicallycorrectratiooffueltoairforcombustionF/A–Fuel/AirRatio Massratioofmixture,adeterminationofrichnessorleanness. Stoichiometry=0.0688-0.0696FALambda–ExcessAirRatio Stoichiometry=1.0LambdaRichF/A–F/AgreaterthanStoichiometry Rich<1.0LambdaLeanF/A–F/AlessthanStoichiometry Lean>1.0LambdaCalibrationTermscontinuedBrakePower–Powermeasuredbytheabsorber(brake)atthecrankshaftBSFC-BrakeSpecificFuelConsumption FuelMassFlowRate/BrakePower grams/kW-horlbs/hp-hLBTFuelling–LeanBestTorque LeanestFuel/AirtoAchieveBestTorque LBT=0.0780-0.0800FAor0.85-0.9LambdaThermalEnrichment–FueladdedforcoolingduetoexhaustcomponenttemperaturelimitInjectorPulseWidth-TimeInjectorisOpenCalibrationTermscontinuedSparkAdvance–TimingincrankdegreespriortoTDCforstartofcombustionevent(ignition)

MBTSpark-MaximumBrakeTorque MinimumSparkAdvancetoAchieveBestTorqueBurnRate–SpeedofCombustion Expressedasafractionoftotalheatreleasedversuscrankdegrees

MAP-ManifoldAbsolutePressure AbsolutenotGauge(whichreferencesbarometer)ControlSystemTypesAlpha-NEngineSpeed&ThrottleAngleSpeed-DensityEngineSpeedandMAP/ACTMAFEngineSpeedandMAFAlpha-NFuelandsparkmapsarebasedonthrottleangle–whichisverynon-linearandrequirescompletemappingofengineGoodthrottleresponseoncedialedinDensitycompensation(altitudeandtemperature)isusuallyabsent–needstoberecalibratedeverytimecargoesoutSpeed-DensityFuelandsparkmapsarebasedonMAP–densityofchargeisastrongfunctionofpressure,correctedbyairtempandcoolanttempthereforeairflowissimpletocalculateLesstime-intensivethanAlpha-N,oncecalibratedisgood–mostcommontypeofcontrolNeedslessmapping–candoWOTlineandmid-mapthencurve-fitairflow(sparkneedsalittlemorein-depthforoptimalcontrol)MAFFuelandsparkmapsarebasedonMAF–airflowmeasureddirectlyMAFsensorisn’tthemostrobustdevicePressurepulsesconfusesignal,eachapplicationhastobemappedwithsecondarydampedMAFsensor(usuallya55gallondruminline)Leastnoisysignalisusuallyataircleaner–soseparatetransportdelaycontrolsneedtobecalibratedfortransientsandleaksneedtobeabsolutelyeliminatedBoostedapplicationsusuallyaddaMAPaswellControlSystemComponentsFuelSystemInjectors,Fuelpump&RegulatorBasicSensorsManifoldAbsolutePressure(MAP)orMassAirFlow(MAF)CrankPosition(Rpm&TDC)CamPosition(Sync)AirChargeTemp(ACT)EngineCoolantTemp(ECT)KnockSensorLamdaSensorFuelSystemInjectorsVolumetricflowratesolenoids,linearrelationshipbetweenpulsewidthandflowforgivenpressuredeltaBatteryoffsetistimenecessarytoopenandclosesolenoid–timeisfixedforanyvoltageDutycycleisinjectorontime–it’llgostaticabove95%Bernoullirelationshipfordifferentpressuredeltas–allowingdifferingflowratesforagiveninjectorHighimpedanceinjectorshavelowerdynamicrangeandloweramperageandthuslessheatincontrollerFuelPump&RegulatorPressureneedstobesufficientlyhightopreventvapourlock(>4bar)andlowenoughthatenginecanidleIn-tankregulationaddsleastheatbuthasline-lossasflowrateincreases,iefuelpressurechangeswithflowManifold-referencedregulationcanhelpinjectorsachievehigherflowratesatelevatedboostorlowerflowsatlowvacuum–makingcalibrationmorecomplicatedBernoulliEffectofFuelPressureSensorsManifoldAbsolutePressure(MAP)Avariable-resistancediaphragmwithperfectvacuumononesideandmanifoldpressureonotherMassAirFlow(MAF)Aheatingelementfollowedbyatemperature-sensitiveelement.HeatedelementismaintainedataconstanttemperatureandbaseduponthemeasureddownstreamtemperaturethemassflowratecanbedeterminedCrankPositionHighresolutionforsparkadvance,less-soforcrankspeedandwithonce-per-revcanindicateTDCCamPositionLowresolutionforsyncronizationforsequentialfuelinjectionandindividualcylindersparkAirChargeTempandEngineCoolantTempThermistorsusedforairdensitycorrectionandstartupenrichmentSensors,contKnockSensorApiezoelectricloadcellthatmeasuresstructuralvibration.Knockisapressurewavethattravelsatlocalsonicvelocityand‘rings’atafrequencythatisafunctionofborediameter(typicallybetween14-18kHz).Whenthestructureoftheengine(typicallytheblock)ishitwiththispressurewaveitringsaswell,butatafrequencythatisafunctionofthestructure(iematerialsandgeometry).AFFTanalysisofdifferentmountingpositions(nodesnotanti-nodes)isnecessarytodeterminethe‘centerfrequency’tolistenforknock(whichismeasuredviain-cylinderpressuremeasurements)withoutpickingupotherstructure-bornenoise.Sensors,contLamdaSensor(EGO)Comparesambientairtoexhaustoxygencontent(partialpressureofoxygen).Sensoroutputisessentiallybinary(onlyindicatesrichorleanofstoichiometry).Wide-bandLamdaSensor(UEGO)Comparespartialpressureofoxygen(lean)andpartialpressureofHmCn,H2&CO(rich)withambient.Givesoutputfrom~0.6to2Lamda.UEGOSchematicEGOSchematicCalibrationGoalsCombustion&ThermodynamicsWork,Power&MeanEffectivePressuresKnock,Pre-IgnitionBurnRateTransientsWallfilmThermalEnrichmentDrivabilityKnockCausesofKnockKnock=f(Time,Temperature,Pressure,Octane)Time–Higherenginespeedsorfasterburnratesreduceknocktendency.Burnratecancomefrommultiplesparksources,morecompactcombustionchambersorincreasedturbulenceTemperature–Reducedcombustiontemperaturesreduceknockthroughreducedchargetemperatures(coolerincomingchargeorreducedresidualburnedgases),increasedevaporativecoolingfromricherF/AmixturesandincreasedcombustionchambercoolingPressure–LowercylinderpressuresreduceknocktendencythroughlowercompressionratioorMAPpressureOctane–Differentfueltypeshavehigherorlowerautoignitiontendencies.OctanevalueisdirectlyrelatedtoknockingtendencyKnockcontinuedEffectsofKnockDisruptsstagnantgasesthatformboundarylayeratedgeofcombustionchamber,increasingheattransfertocomponentsandraisingmeancombustionchambertempthatcanleadtopre-ignitionScoursoilfilmoffcylinderwall,leadingtodryfrictionandincreasedwearofpistonringsShockwavecaninducevibratoryloadsintopistonpin,pistonpinboreandtopland-reducingoilfilmthicknessandacceleratingwearShockwavecanbestrongenoughtostresscomponentstofailureIn-cylinderPressureMeasurementPiezoelectricpressuretransducersdevelopchargewithchangesinpressureInstalledincombustionchamberwallorsparkplugtomeasurefull-cyclepressuresTypicalpressureprobeinstallationPassagedrilledthroughdeckface(avoidingcoolantjacket)CylinderPressureTrace

NoKnockCylinderPressureTrace

KnockLimitorTraceKnock-BestPowerCylinderPressureTrace

SevereDamagingKnockPre-IgnitionEffectsofPre-IgnitionIncreasespeakcylinderpressurebybeginningheatreleasetoosoonIncreasedcylinderpressurealsoincreasesheatloadtocombustionchambercomponents,sustainingthepre-ignition(leadingto‘run-awaypre-ignition’)IncreasesloadsonpistoncrownandpistonpinSustainedpre-ignitionwilltypicallyputaholeinthecenterofthepistoncrownBurnRateBurnRate=f(Spark,DilutionRate/FARatio,ChamberVolumeDistribution,EngineSpeed/MixtureMotion/TurbulentIntensity)SparkClosertoMBTthefastertheburnwithtraceknockthefastestDilutionRate/FARatioLeastdilution(exhaustresidualoranythingunburnable)fastestFARatiobestratearoundLBTChamberVolumeDistributionSmallestchamberwithshortestflamepathbest(multipleignitionsourcesshortenflamepath)EngineSpeed/MixtureMotion/TurbulentIntensityCrankangletimeforcompleteburnnearlyconstantwithincreasingenginespeedindicatingotherfactorsspeedingburnrateMixturemotion-contributedangularmomentumconservedascylindervolumedecreasesduringcompressionstroke,eventuallybreakingdownintovorticesaroundTDCincreasingkineticenergyinchargeTurbulentIntensityameasureoftotalkineticenergyavailabletomoveflamefrontfasterthanlaminarflamespeed.MoreTurbulentIntensityequalsfasterburn.Combustion&ThermodynamicsSummaryPeakSpecificPowerLBTfuellingforbestcompromisebetweenavailableoxygenandchargedensityMBTsparkifpossible,fastburnrateassumedatpeakloadHighestenginespeedtoallowhighestcompressionratioHighestoctanePeakThermalEfficiencyatdesiredloadHighestcompressionratiowillhavebestcombustion,usuallywithhighestexpansionratioforbestuseofthermalenergyMBTsparkwithfastestburnrate10%leanofstoichiometrywillprovidebestcompromisebetweenheatlossesandpumpingwork,butnotusedbecauseofcatalystperformanceimpactsinpasscarsTransientFuellingLiquidfueldoesnotburn,onlyfuelvapourHeatfromsomewheremustbeusedtomakevapour–whichiswhyupto500%morefuelmustbeusedonacoldstarttoprovidesufficien