MechanicalSystemsandSignalProcessingMechanicalSystemsandSignalProcessing22(2008)10081015AbstractARTICLEINPRESS/locate/jnlabr/ymssp0888-3270/$-seefrontmatterr2007ElsevierLtd.Allrightsreserved.doi:10.1016/j.ymssp.2007.09.016C3Correspondingauthor.Tel./fax:+8645186418318.E-mailaddresses:(S.Li),(W.Bao).Asmagneticfluidsshowhighersaturationmagnetizationswhentheyareexposedtomagneticfields,theyarewidelyappliedintheareasofsealing,bearing,grinding,speaker,damperandsoon1,2.Investigationsin35showedthatthemagneticfieldstrengthinfluencedtheviscosityofmagneticfluidswhenmagneticfluidswereexposedtoamagneticfield.Theapplicationofmagneticfluidsinanelectricmotorwasalsostudiedin6becauseofthehighermagneticpermeabilityofmagneticfluids.Theapplicationofmagneticfluidsinhydraulicservo-valveswasstudiedrecentlyin7.Hydraulicservo-valvesarethenecessarycomponentsinhydrauliccontrolsystems.Thecharacteristicsofhydraulicservo-valvessignificantlyinfluencetheperformanceofhydrauliccontrolsystems.Astheelectro-mechanicalmechanisminhydraulicservo-valves,torquemotorsareusedtostrokethevalvesfromelectricsignals.Ifthedynamiccharacteristicsofatorquemotorcanbemodified,theperformanceofahydraulicservo-valvecanbeimproved.Theaimofthispaperistoinvestigatetheinfluenceofmagneticfluidsonthedynamiccharacteristicsofahydraulicservo-valvetorquemotor.Asakindoffunctionalmaterials,magneticfluidsarefilledintotheworkinggapsofahydraulicservo-valvetorquemotorinthispaper.Forcesonthetorquemotorduetomagneticfluidsarestudied.Thedynamicmathematicalmodelsofthetorquemotorwithmagneticfluidsareintroduced.Afterthatthedynamiccharacteristicsofthetorquemotorwithmagneticfluidsareanalyzedandtested.Analysisandexperimentalresultsarecomparedwiththeresultswhenmagneticfluidsarenotappliedinthemotor.r2007ElsevierLtd.Allrightsreserved.Keywords:Magneticfluids；Hydraulicservo-valve；Torquemotor；Hydrauliccontrolsystems1.IntroductionInfluenceofmagneticfluidsonthedynamiccharacteristicsofahydraulicservo-valvetorquemotorSongjingLia,C3,WenBaobaDepartmentofFluidControlandAutomation,HarbinInstituteofTechnology,Box3040,ScienceandTechnologyPark,150001Harbin,ChinabSchoolofEnergyScienceandEngineering,HarbinInstituteofTechnology,Box458,150001Harbin,ChinaReceived13December2006；receivedinrevisedform27September2007；accepted27September2007Availableonline6October2007ARTICLEINPRESS12g,xlengthofgapatneutral,displacementoftheendofarmatureS.Li,W.Bao/MechanicalSystemsandSignalProcessing22(2008)100810151009HmagneticfieldstrengthhthicknessofmagneticfluidssurroundingarmatureJainertiaofarmatureKamechanicaltorsionspringconstantofspringpipeKm,KtmagneticspringconstantandtorqueconstantoftorquemotorK0m,K0tmagneticspringconstantofmagneticfluid,torqueconstantofmagneticfluidMssaturationmagnetizationofmagneticfluidM0magnetomotiveforceduetopermanentmagnetNcturnsofcoilTdoutputtorqueoftorquemotorTploadtorqueduetospringpipeTLloadtorqueofarmatureNomenclaturearadiusofarmaturefrompivottocenterofpolefaceAgareanormaltofluxpathinairgapAmfworkingareaofdampingforceonarmatureduetomagneticfluidBaviscousdampingcoefficientofmechanicalarmaturemountingandloadF,Fdampingforceduetomagneticfluid,resistanceduetomagneticfluidSelf-excitedhigh-frequencynoiseandpressureoscillationsappearveryfrequentlyintheflowfieldofaflappernozzleorajetpipeservo-valveduetocavitationsandshear-layerinstabilitiesiftheconstructionparameterswerenotselectedcorrectly,asshownin8.Theself-excitedpressureoscillationsmayirritatetheoscillationsofthetorquemotorarmatureandthespoolofaservo-valvesothattheservo-valvemayloseitsstability.Asmagneticfluidshaveahighersaturationmagnetizationandalargerviscositywhentheyareexposedtomagneticfields,magneticfluidscanbefilledintotheworkinggapsofahydraulicservo-valvetorquemotortointroducedampingintothemotorandtheservo-valve.Inthispaper,theapplicationofmagneticfluidsinahydraulicservo-valvetorquemotorisintroduced.Mathematicalmodelsforforcesduetomagneticfluidsonthetorquemotorarestudied.Dynamiccharacteristicsofahydraulicservo-valvetorquemotoraresimulatedandtestedwhenmagneticfluidsareappliedinthemotor.2.Constructionofahydraulicservo-valvetorquemotorwithmagneticfluidsTheconstructionofahydraulicservo-valveandtorquemotorwithmagneticfluidsisshowninFig.1.TheequivalentmagneticcircuitofthetorquemotorisshowninFig.2.Ahydraulicservo-valvecanusuallybedividedintothevalvepart,theflappernozzlepartandthetorquemotor.Thevalvepartincludesaspoolandavalvebody.Theflappernozzlepartincludesaflapperandtwonozzles.Thetorquemotorusuallyconsistsofcores,anarmaturesupportedbyaspringpipe,twocoilsandtwopermanentmagnets.Theflapperandthearmatureareconnectedwitheachotherandthereforenamedarmatureflappergroupsometimes.Tmf1loadtorqueduetoviscosityofmagneticfluidTmf2loadtorqueduetosaturationmagnetizationofmagneticfluidZ0viscosityofmagneticfluidintheabsenceofamagneticfieldZmfviscosityofmagneticfluidexposedtoamagneticfieldyrotationangleofarmatureo0rotationspeedofarmatureDidifferencecurrentofcoilsDp1,Dp2stressonarmatureduetomagneticfluidsingaps1and2ARTICLEINPRESSS.Li,W.Bao/MechanicalSystemsandSignalProcessing22(2008)100810151010NSMagneticfluidsPermanentmagnetArmatureSpringpipeCoreQLQLValvebodyFeedbackrodSpoolFlapperNozzleTherearefourworkinggapsbetweenthecoresandthearmaturewheremagneticfluidscanbefilledinto.Asahydraulicservo-valvetorquemotorworksunderthecooperationbetweenthepermanentmagnetsandtheelectricmagnets,therearealwaysmagneticfieldsduetothepermanentmagnetsinsidetheworkinggapsofthetorquemotor,eveniftheelectricpowerofthetorquemotoristurnedoff.Thereforemagneticfluidswillalwaysstayinsidetheworkinggapsaftertheyareapplied.Astherotationangleofthearmatureissmall,magneticfluidscanhardlybescatteredoutfromthegapswhenthearmaturerotates.Whenthepowerofthecoilsisturnedoff,thetorquemotorwillstayatthemiddlepositionundertheworkingofthepermanentmagnets.Ifthefourworkinggapsarealmostthesameindimension,thedistributionsofmagneticfieldswillbethesameinthefourworkinggaps.Theoretically,therewillnotbeanyoutputtorquefromthemotorbecausethetorquebalanceisachievedatthistime.Thenthehydraulicservo-valvewillworkatthemiddleposition.Iftheelectricpowerofthecoilsisturnedon,thetorquemotorwillworkunderthecooperationbetweentheelectromagnetsandthepermanentmagnets.AsshowninFig.2,themagneticfluxdensitiesintheworkinggaps1and3willbeincreasedandbecomelargerthanthoseintheothertwoworkinggaps2and4.Therewillbeanoutputtorquesuppliedbythetorquemotortotheservo-valve.Thetorquemotorarmaturewillrotateanddrivetheflaptointroduceapressuredifferencetobothsidesofthespool.ThespoolwillmovetoanewpositionuntiltheoutputtorqueofthemotorequalsthesumoftheloadtorquefromthespringpipeandtheReturnPSSupplyPSSupplyFig.1.Constructionofahydraulicservo-valvewithmagneticfluids.NSNSNS1234g+xgxaFig.2.Torquemotorequivalentmagneticcircuit.feedbacktorquefromthefeedbackrodduetothemovementofthespool.Thedisplacementofthespoolisproportionaltotheinputelectriccurrentofthetorquemotor.Asmagneticfluidsshowahighersaturationmagnetizationandlargerviscositywhentheyareexposedtothemagneticfieldsinsidetheworkinggapsofthetorquemotor,largedampingforcesorresistancewillbeexertedonthetorquemotorarmatureduetothespecialpropertiesofmagneticfluids.Thedampingforcesorresistancewillbehelpfultoimprovethedynamicperformance,especiallythestability,ofthetorquemotorandtheservo-valve.3.ForcesduetomagneticfluidsTheworkingstateofmagneticfluidsinsidetheairgapsofatorquemotorareshowninFig.3.Itcanbeseenthatthecross-sectionofthearmatureissurroundedbymagneticfluidsentirely.Thereforethereareforcesworkingontheupsideanddownsidesurfacesofthearmatureduetothesaturationmagnetizationofmagneticfluids.Andtherearedampingforcesworkingontheleftsideandrightsideofthearmatureduetotheviscosityofmagn