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Designofanactiveexhaustattenuatingvalveforinternalcombustionengines.R.Boonen,P.SasKULeuven,DepartmentofMechanicalEngineering,Celestijnenlaan300B,B3001,Heverlee,Belgiumemailrene.boonenmech.kuleuven.ac.beAbstractAnactivesilencertoattenuateinternalcombustionengineexhaustnoiseisdeveloped.Thesilencerconsistsofanelectricallycontrolledvalveconnectedtoabuffervolume.Thepulsatingflowfromtheengineisbufferedinthevolumeandthevalveresistanceiscontinuouslycontrolledsuchthatonlythemeanflowpassestotheatmosphere.Thisflowisfreeoffluctuationsandconsequentlyfreeofsound.Thedesignoftheactivesilenceriscarriedoutusingelectricalanalogcircuits.First,theinteractionbetweentheactivesilencerandtheenginewillbestudiedusingananalogcircuitincludingthecombustionengineandalinearizedactivesilencer.Then,adetailedvalvemodelisbuiltinaseparateelectricalanalogcircuit.Itincludestheelectrical,themechanicalandtheflowdynamicpropertiesoftheactuatorvalve.Theactuatorvalveconceptisthensimulated,fromwhichaprototypecanbeconstructed.Theactivesilencerhasbeentestedonacoldenginesimulator.Thisdevicegeneratesrealisticexhaustnoisewiththeassociatedgasflowusingcompressedair.Thesilencercanattenuatepulsationsfromenginesatverylowrevolutionspeed,withoutpassiveelementspreconnectedbetweentheengineandtheactivesilencer.Thisisnotpossibleusingloudspeakerbasedactivesilencers.1IntroductionTheinternalcombustionenginehasfounditswayintoabroadspectrumofapplications,whereintransportationhasfarthelargestshare.Thesuccessoftheinternalcombustionenginehasalsocreatedproblemsassociatedwithit,suchasairpollutionandenvironmentalnoise.Duringthepastdecades,legislationhascomeforwardwhichstringentlyreducesairpollutants,greenhousegasesandnoiseemission.Today,thenoiseemissionlimitsaresetto74dBAforcarsand80dBAforheavyvehicles1.Forcars,theemissionofCO2islimitedto190g/kmEUIIIdirective,andwillbefurtherreducedto170g/kmEUIVin2003and140g/kmEUVin2008.Althoughthesedirectivesarenotrelatedatfirstsight,theydohavetheirimplicationsontheexhaustsystemdevelopment.Itwillbenecessarytodevelopexhaustsystemswithminimumbackpressuretotheengine,tomaximizeengineefficiencyandthiswithoutlossofnoiseattenuationperformance.Awayouttothisproblemistodevelopactiveexhaustsystems.Muchresearchonactivenoisecancellationinductsiscarriedoutintherecentyearsandnumerouspatentshavebeengenerated.Loudspeakersystemsaresuccessfullyappliedandcommercialavailableinventilationchannels2.Loudspeakersystemsarealsodevelopedforstationarydieselengines,forexamplebyDetroitDieselCorporation3andtheKEBAAISTMsystem.Forcars,activeloudspeakersystemsaredevelopedforsixormorecylinderengines4.Forfourcylinderengines,loudspeakersystemssufferfromproblemsasthelowsoundgeneratingefficiencyandreliabilityintheextremeconditionsofanengineexhaust.Applyingacontrollablevalveintheexhaustductisamorerobustconcept.Therestrictingelementofthevalvecanbesmallandrigidlyconstructed.Itcanbeexposedtotheexhaustgasdirectly.Theresistanceofthevalveiscontinuouslyvariablebyapplyinganexternalsignal.Itisassumedthatthevalveispurelyresistive,itisntcapabletostoreenergyfromthegasflow.Asconsequenceofthegasflow,thevalvegeneratesapressuredropoverit.Activenoisecancellationisachieved,whenthevolumevelocitybehindthevalveiskeptconstant.Infigure1,thefirstgraphdemonstrateshowthesoundpressureinfluencesthefluidflowviathevalveresistancecharacteristic.Thesecondgraphdemonstrateshowtheoppositefluctuatingflowisgeneratedfromthemeanpressuredropoverthevalvebyvary33Figure1Basicprincipleusingavalvetocontroltheflowthroughaduct.ThesymbolsinthefiguremeanQ0ismeanfluidflow,qisflowfluctuation,p0ismeanpressure,∆pisthepressurefluctuation,Kisthevalveconstantwhichexpressestherelationbetweenpressureandflow,kisthevariationonK.ingthevalveresistance.Superpositionofbotheffectsresultsinaconstantvolumeflow,showninthethirdgraph.Basedonthisconcept,anoiseattenuatingdeviceisdevelopedbyLEAUniversityofPoitiers,France5,6,usingabutterflyvalve,andistestedonaninternalcombustionenginetestrig.Thetestrigconsistsofan1350cm3fourcylindercarengineequippedwithanhydraulicbrake.Intheexhaustlinetwopassivemufflersarepreconnectedtotheactuatorvalve.Ascontrolstrategy,axLMSfeedforwardandafeedbackcontrolsystemaretested.Inthefeedforwardcase,thethreefirstharmonicsarereducedby20to30dB.Inthefeedbackcase,thefirstharmonicisreducedby20dB,thesecondharmonicby5dB.Theresearchworkpresentedinthispaperaimstodevelopanactiveexhaustsilencerbasedonavalveconcept,capabletohandletheacousticalpowerofthepressurepulsationoftheengineexhaustwithouttherequirementtoinstallsilencerspriortotheactivedevice.Thegeneratedbackpressuremustbelow.Aftertheactivedevice,asmallpassivesilencercanbeinstalledtoattenuatethehighfrequencynoise.2Developmentoftheactivesilencer2.1PrincipleTheoretically,insertinganactivevalveintheflowofavolumevelocitysource,likeacombustionengine,hasnoeffectifnocapacitiveelementsarepresentbetweenthesourceandthevalve.Thevolumevelocitysourceforcesaprescribedflowthroughtheexhaustsystem,whateverthepressurebecomesinit.Capacitiveelementscanbeintroducedusingductsorvolumes.Whenthevalveisinsertedinanexhaustductofanenginewithoutadditionalcapacitiveelements,ahighbackpressurewillbegeneratedoronlyalownoiseattenuationwillresult.Themostsimplesystemabletocontrolofavolumevelocitysourceusingacontrolledvalveispresentedinfigure2.Theengineactsasavolumevelocitysource.Attheexhaust,avolumewithcapacityCandaregulatingvalvewithvariableresistanceRtisconnected.Thetranslationofthephysicalsystemresultsintheelectricalequivalentcircuit7showninfigure2below.TheimpedanceZistheimpedanceofthetailpipeandtheopenairradiator.TheflowfromthesourcewillsplitoverthecapacitorCandthetimedependentresistorRt.Now,thecontrollerhastovarythevalveresistanceduringtime,suchthatthefluctuatingflowthroughtheresistancebecomeszero.Figure2Themostsimpleschemeofanactivecontrolvalveonaninternalcombustionengine,approximatedasavolumevelocitysource.ThevariationofthevalveresistanceisobtainedfromtheelectricalequivalentcircuitUB1CintegraldisplayICdtIRRtZ1Differentiating1resultsinIC1CdIRdtRtIRdRtdtZdIRdt2ConstantflowthroughthevalveopeningimpliesdIRdt03ThecontrollerhastovarythevalveresistanceduringtimeaccordingRtR0integraldisplay1CICIRdt434PROCEEDINGSOFISMA2002VOLUMEIwhereinR0istheinitialvalveresistance.ThesameresultcanbeachievedbyacontrollerwhichminimizesthepressureUZafterthevalvedUZdtZdIRdt05Thissimpleconsiderationhastwoimportantconsequences.First,bybalancingthevolumevalvecombination,itisalwayspossibletocontroltheflowofanyvolumevelocitysource.Second,theresistanceR0canbechosenfreelywiththeonlyrestrictionthattheresistanceRtremainsalwayspositive.TheresistanceR0canbeoptimizedtoobtainminimumbackpressuretotheengine,resultinginahigherengineefficiency.2.2ElectricalequivalentmodelfortheengineandthesilencerThesimplemodel,presentedinfigure2,looksnotveryrealisticforanengineexhaustsystem,thereforethemodelwillbeexpanded.Thevolumevelocitysourcewillbereplacedbyanenginemodel,andaductisconnectedbetweentheengineandtheactivesilencer.Atailpipeisconnectedbehindthesilencer.Theresultingcircuitispresentedinfigure3.Theleftpartofthecircuitistheenginemodel.Thefourvariablecapacitorsrepresentthefourenginecylinders,whosvolumevariessinusoidalbetweenmaximumanddeadvolume.Theuppersetofswitchresistorsrepresenttheintakevalves,thelowersettheexhaustvalves.Theswitchesareactuatedinthesamesequenceasthecamshaftoperatestheenginevalves.Thefourshorttransmissionlinesbehindtheexhaustvalveresistorsrepresentthefourexhaustconduitsbetweenthecylinderportsandtheexhaustmanifoldjunction.TheintakesideisconnectedtoavoltagesourceUBrepresentingtheatmosphericpressureandequals100kV.Thecombustionissimulatedbychargingthecylindercapacitorbyapulsingcurrentsourceparalleloverthecapacitor.Thechargetimepointcorrespondstotheignitiontimepoint.Therightpartrepresentstheactiveexhaustsystem.ThesilencerisconnectedtotheengineviatheductrepresentedbythetransmissionlineT.ThecapacitorCrepresentsthebuffervolumeandthevariableresistorRtthecontrolvalve.ThetransmissionlineTtrepresentsthetailpipeandtheresistorinductorcombinationRaandLacorrespondstothesphericalradiatorimpedance.Insimulation,acollocatedfeedbackcontrollerconductsthecontrolvalveFigure3Electricalanalogcircuitforaninternalcombustionengineequippedwithanactivenoisecontrolvalve.resistance.Thiscontrollerisonlyneededtodeterminetheactivesilencerproperties.Inpractice,othercontrolstrategiesmustbeappliedtohandlethetimedelaybetweenthevalveactionanditseffectintheerrorsensor.Inprinciple,thebackpressuretotheenginecanbesettoanydesiredvaluebychoosingtheappropriatebuffervolumecapacitorC.Inpractice,itwillresultinacompromisebetweenavailablespacefortheactivesilencerandacceptablebackpressure.Figure4Simulatedindicatordiagramfromthecircuitpresentedinfigure3.2.3SimulationresultsIntheelectricalcircuitoffigure3,theengineparametersofa2000cm3engineareintroduced.Theductshaveadiameterof60mm.Theductbetweentheengineandthesilenceris500mmlong,thetailpipe700mmlong.Thebackpressureissetto10kPa,resultinginabuffervolumeof12dm3.Theinitialactuatorvalveresistanceissetto200kΩ1Ω1Pas/m3.Thefeedbackcontrolgainissetto108.Infigure4,thesimulatedengineindicatordiagramACTIVENOISECONTROL35Figure5Simulatedtailpipeabsolutepressure.Thecontrollerstartsat0.2s.ispresented.Actually,thisdiagramhasnophysicalsignificance,itisanisothermalsimulation.Onlythepressureattheexhaustvalveopeningtimepointmusthaveitscorrectvalue,whichisdeterministicfortheexhaustnoise.Theexhaustpressureinthetailpipeisdisplayedinfigure5.Thecontrollerisactivatedat0.2s.Activatingthecontrollerat0.2sdoesnoteffectthegasflowfromtheengine,asindicatedinfigure6.Theenginebehavesasavolumevelocitysource.Infigure7,theabsolutebackpressuretotheengineisdisplayed.Afterthetransientswitchingonthecontroller,thebackpressurereturnstothepresettedvalueof10kPa.Figure6Simulatedgasflowthroughtheexhaustmanifold.2.4Electricalanalogmodelfortheactuatorvalve.Theconstructionoftheactuatorvalveispresentedinfigure8.Thevalvehasaconicalheadandisdrivenbyavoicecoilinapermanentmagneticcircuit.TheFigure7Simulatedabsolutebackpressuretotheengine.Thecontrollerstartsat0.2s.valvehasamonotonicincreasingvalveresistanceintermsofheaddisplacement.Thisresistanceispresentedinfigure10.Thisisanadvantagecomparedtoforexampleabutterflyvalve,whichhasasignreversalinitsresistancecharacteristicderivativeintermsofpositionangle.Figure8Schemeofthevoicecoildrivenactuatorvalve.Figure9Detailedelectricalanalogcircuitforthevoicecoildrivenactuatorvalvepresentedinfigure10.Figure9presentstheelectricalanalogcircuitoftheactuatorvalvepresentedinfigure8.Thiscircuitistypicalfortheconstructionofthisvalve.Anotherconstruction,forinstanceabutterflyvalve,wouldresultinatotallydifferentelectricalanalogcircuit.36PROCEEDINGSOFISMA2002VOLUMEI
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