Hydraulic and pneumatic systems_i

2005/2006I.,HydraulicandPneumaticSystems,1,HydraulicandPneumaticSystems,Dr.GyrgyPal,2005/2006I.,HydraulicandPneumaticSystems,2,Powertrain,Mechanicalpowertransmission:GearsBeltdriveFrictiondriveRigidcouplingsClutches,PrimemoverACMotorDCMotorDieselEngineOttoEngine,Powertransmissionsystem,Machine(linearorrotationalmotion),Mi,i,M0,0,F0,v0,Properties:ContinuouslyvariabledriveisdifficultTherelativespatialpositionofprimemoverisfixedIfthemotoriselectrical(DCmotororACmotorwithvariablefrequency),thentherotationalspeedcanbecontinuouslychangedbuttheyareexpensive,2005/2006I.,HydraulicandPneumaticSystems,3,Hydraulicpowertransmission,Hydraulicpowertransmission:Hydro=water,aulos=pipeThemeansofpowertransmissionisaliquid(pneumaticgas),Hydrodynamicpowertransmission:TurbopumpandturbinePowertransmissionbykineticenergyofthefluidStilltherelativespatialpositionisfixedCompactunits,Hydrostaticpowertransmission:PositivedisplacementpumpCreateshighpressureandthroughatransmissionlineandcontrolelementsthispressuredrivesanactuator(linearorrotational)Therelativespatialpositionisarbitrarybutshouldnotbeverylargebecauseoflosses(50m),AcontinuouslyvariabletransmissionispossibleMostofthislecturewillbeabouthydrostaticsystems(incommonlanguageitisalsocalledsimplyhydraulics),2005/2006I.,HydraulicandPneumaticSystems,4,Hydrostaticvshydrodynamicsystems,Roughlyspeaking:P=DpQLargeQ,smallDphydrodynamictransmissionLargeDp,smallQhydrostatictransmission.Butthereisnogeneralrule,dependsonthetask.,Generallylargerthan300kWpowerhydrodynamicismorefavourable.Butforsoftoperation(startingoflargemasses)hydrodynamicisusedforsmallerpowerseither.,Linearmovementagainstlargeforces:hydrostaticLinearmovementandstoppinginexactposition:alsohydrostatic,Powerdensity,PkW,100,200,300,400,Hydrostat.,Hydrodyn.,2005/2006I.,HydraulicandPneumaticSystems,5,Structureofahydrostaticdrive,Aggregate,Controlelements,Actuator,Thesecomponentsandtheirinteractionisthesubjectofthissemester,Valves,determiningthepath,pressure,flowrateoftheworkingfluid,ElementsdoingworkLinearRotationalSwinging,Pump,motorFluidreservoirPressurereliefvalveFilterPiping,2005/2006I.,HydraulicandPneumaticSystems,6,Atypicalhydraulicsystem,1pump2oiltank3flowcontrolvalve4pressurereliefvalve5hydrauliccylinder6directionalcontrolvalve7throttlevalve,2005/2006I.,HydraulicandPneumaticSystems,7,Advantagesofhydrostaticdrives,SimplemethodtocreatelinearmovementsCreationoflargeforcesandtorques,highenergydensityContinuouslyvariablemovementoftheactuatorSimpleturnaroundofthedirectionofthemovement,startingpossibleunderfullloadfromrestLowdelay,smalltimeconstantbecauseoflowinertiaSimpleoverloadprotection(nodamageincaseofoverload)SimplemonitoringofloadbymeasuringpressureArbitrarypositioningofprimemoverandactuatorLargepowerdensity(relativelysmallmassforagivenpowercomparedtoelectricalandmechanicaldrives)Robust(insensitiveagainstenvironmentalinfluences),2005/2006I.,HydraulicandPneumaticSystems,8,Disadvantagesofhydrostaticdrives,Workingfluidisnecessary(leakageproblems,filtering,etc.)Itisnoteconomicforlargedistances,2005/2006I.,HydraulicandPneumaticSystems,9,Hydraulicfluids-tasks,Theyhavethefollowingprimarytasks:Powertransmission(pressureandmotiontransmission)SignaltransmissionforcontrolSecondarytasks:LubricationofrotatingandtranslatingcomponentstoavoidfrictionandwearHeattransport,awayfromthelocationofheatgeneration,usuallyintothereservoirTransportofparticlestothefilterProtectionofsurfacesfromchemicalattack,especiallycorrosion,2005/2006I.,HydraulicandPneumaticSystems,10,Hydraulicfluids-requirements,FunctionalGoodlubricationcharacteristicsViscosityshouldnotdependstronglyontemperatureandpressureGoodheatconductivityLowheatexpansioncoefficientLargeelasticitymodulusEconomicLowpriceSlowagingandthermalandchemicalstabilitylonglifecycle,2005/2006I.,HydraulicandPneumaticSystems,11,Hydraulicfluids-requirements(contd.),SafetyHighflashpointorincertaincasesnotinflammableatallChemicallyneutral(notaggressiveatallagainstallmaterialsittouches)Lowairdissolvingcapability,notinclinedtofoamformationEnvironmentalfriendlinessNoenvironmentalharmNotoxiceffect,2005/2006I.,HydraulicandPneumaticSystems,12,Hydraulicfluidtypes,Water(3%)Mineraloils(75%)Notinflammablefluids(9%)Biologicallydegradablefluids(13%)Electrorheologicalfluids(indevelopment),2005/2006I.,HydraulicandPneumaticSystems,13,Hydraulicfluidtypes(contd.),-Clearwater-WaterwithadditivesOldestfluidbutnowadaysthereisarenaissanceUsedwherethereisanexplosionorfiredangerorhygienicproblem:Foodandpharmaceuticalindustry,textileindustry,mining,1.Water:,Advantages:NoenvironmentalpollutionNodisposaleffortCheapNofireorexplosiondangerAvailableeverywhere4timeslargerheatconductioncoefficientthanmineraloils2timeshighercompressionmodulethanmineraloilsViscositydoesnotdependstronglyontemperature,2005/2006I.,HydraulicandPneumaticSystems,14,Hydraulicfluidtypes(contd.),1.Water:,Disadvantages:BadlubricationcharacteristicsLowviscosity(problemofsealing,buthasgoodsides:lowenergylosses)CorrosiondangerCavitationdanger(relativelyhighvapourpressure)Limitedtemperatureintervalofapplicability(freezing,evaporating),Consequences:needslowtolerancesandverygoodmaterials(plastics,ceramics,stainlesssteel)componentsareexpensive,2005/2006I.,HydraulicandPneumaticSystems,15,Hydraulicfluidtypes(contd.),-Withoutadditives-WithadditivesConventional”use,stationaryhydraulicsAlwaysmixturesofdifferentoils,oftenwithadditivesAdditives:decreasecorrosionincreaselifedurationimprovetemperaturedependenceofviscosityimproveparticletransport,2.Mineraloil:,Advantages:GoodlubricationHighviscosity(goodforsealing,badforlosses)Cheap,Disadvantages:InflammableEnvironmentalpollution,2005/2006I.,HydraulicandPneumaticSystems,16,Hydraulicfluidtypes(contd.),-Containswater-Doesnotcontainwatermines,airplaneproduction,casting,rolling,wherethereisexplosionandfiredangerWater-oilemulsions(oilsynthetic)orwater-freesyntheticliquids,3.Notinflammablefluids:,Disadvantages:Higherdensity,higherlosses,moreinclinationtocavitationLimitedoperationaltemperature55CWorselubricationcharacteristics,reductionofmaximumloadWorsede-aerationcharacteristicsSometimeschemicallyaggressiveagainstsealingmaterials,2005/2006I.,HydraulicandPneumaticSystems,17,Hydraulicfluidtypes(contd.),-Natural-SyntheticEnvironmentalprotection,waterprotectionAgriculturalmachinesMobilehydraulicsCharacteristicssimilartomineraloilsbutmuchmoreexpensive.Ifthetrendcontinuesitsusageexpands,pricewilldrop.,4.Biologicallydegradablefluids:,2005/2006I.,HydraulicandPneumaticSystems,18,Propertiesofhydraulicfluids,Viscosity:well-known,Temperaturedependence,Ubbelohde-Walther:c,m,Kvareconstants,TisinK,log-logscale,Vogel-Cameron:A,B,Careconstants,tisinC,2005/2006I.,HydraulicandPneumaticSystems,19,Propertiesofhydraulicfluids(contd.),Pressuredependenceofviscosity,0,0viscosityatatmosphericpressure,2005/2006I.,HydraulicandPneumaticSystems,20,Propertiesofhydraulicfluids(contd.),Densitydependenceonpressure:likeHookeslaw,KisthecompressibilityKisnotaconstantbutdependsonpressureitselfeffectiveKisalsoinfluencedby:AircontentFlexibilityofthepipe,Temperaturedependenceofdensityissmall,2005/2006I.,HydraulicandPneumaticSystems,21,HydraulicFluids,Suckingairwiththepumphappensbutisbyproperinstallationavoidable.Theoilisquicklyintosolutionduringtheincreasingpressure.Airbubblescometooilmostlysothatwithdecreasingpressuretheairgoesoutofsolution”.-dissolvingcoefficientatnormalpressureAtnormalpressureVa=Vf.Athighpressure,thevolumeofthedissolvedairismuchmorethanthevolumeoftheliquid.Whenthepressuredropstheairleavesthesolutionsuddenlybutthedissolutionhappensgradually.,Aircontentinoilisharmful.,2005/2006I.,HydraulicandPneumaticSystems,22,HydraulicFluids,Sudden,jerkymovements,oscillation,noiseLateswitchingReducedheatconductionAcceleratedagingoftheliquid,disintegrationofoilmoleculesCavitationerosion,Problemswithaircontent:,Kl:liquidcompressibilityVf:volumeofliquidVa0:volumeofgasinnormalstatep0:normalpressurep:punderinvestigation,2005/2006I.,HydraulicandPneumaticSystems,23,HydraulicFluids,Themanufacturerspecifiesthecharacteristicsoftherequiredliquidandthedurationofusage.Beforefillinginthenewoil,therighastobewashedwithoil.Nevermixoldandnewoil!,2005/2006I.,HydraulicandPneumaticSystems,24,Calculationbasics,e)Continuity,b)Pascalsslaw,g)Bernoulliequation,f)Flowresistance,a)Hydrostaticpressure,c)Transmissionofpower,d)Transmissionofpressure,2005/2006I.,HydraulicandPneumaticSystems,25,Calculationbasics,Flowresistance:,2005/2006I.,HydraulicandPneumaticSystems,26,Calculationbasics,laminar,Calculationbasics:,turbulent,Forastraight,stiffpipe:,Ifthetwocrosssectionsarenotthesamethen:,2005/2006I.,HydraulicandPneumaticSystems,27,Calculationbasics,Usuallythefunction=(Re)lookslikethefollowing:,Calculationbasics:,Practically:,2005/2006I.,HydraulicandPneumaticSystems,28,Calculationbasics,Onthisbasiswecandefinetwohydraulicresistances:,Calculationbasics:,Dependsonviscosity,Doesnotdependonviscosity,2005/2006I.,HydraulicandPneumaticSystems,29,Calculationbasics,Foraparallelcircuit:,Forelbows,suddenexpansions,T-pieces,etc.valuesaregivenasafunctionofRe,roughnessandgeometricparameters,Foraseriescircuit:,Threedifferentcoefficientsareusedtoexpresspressureloss:,Gh:Hydraulicadmittance,2005/2006I.,HydraulicandPneumaticSystems,30,Leakagelosses,Leakagelosses:ExternallossesInternallosses,OccuralwayswhencomponentsmoverelativetoeachotherTheyreduceefficiencyIncaseofexternalleakagesthereisenvironmentaldamageandthelostfluidhastoberefilled.Externallossescanbeavoidedbycarefuldesignandmaintenance.Internallossescannotbeavoided.,2005/2006I.,HydraulicandPneumaticSystems,31,Leakagelosses,2005/2006I.,HydraulicandPneumaticSystems,32,Leakagelosses,2005/2006I.,HydraulicandPneumaticSystems,33,Leakagelosses,theeccentricityincreasestheleakageflowbyafactorof2,5ifeincreasestothelimitQLs3m!Becauseofthelargep,therearelargetemperaturedifferencesalongl.Mediumviscosityhastobesubstituted.InadditionthereisaCouetteflowdraggedflow,whichincreasesordecreasestheleakage,2005/2006I.,HydraulicandPneumaticSystems,34,Hydrauliccapacityandinductivity,Allthethingsdiscussedsofarreferredtosteadyprocesses.Inpractice,however,veryoftenunsteadyprocessesareencountered:starting,stopping,changeofload,changeofdirectionofmotion,etc.Inthesecasesthecompressibilityofthefluidandthepipes,andtheinertiaofthefluidhavetobetakenintoconsideration.,Nonlinearfunction.Itcanbelocallylinearizedand:,Hydrauliccapacity:,2005/2006I.,HydraulicandPneumaticSystems,35,Hydrauliccapacityandinductivity,Hydrauliccapacity:,Thecapacityhasthreeparts:,Thecapacitiveflowrate:,Kcompressionmodule,Cpipeisnegligibleifthepipeismadeofmetal,Cpipeisnotnegligibleifthepipeisflexible.,2005/2006I.,HydraulicandPneumaticSystems,36,Hydrauliccapacityandinductivity,Ltotal=Lh+Lsol,whereLsolistheinertiaofsolidparts.,Hydraulicinductivity:,2005/2006I.,HydraulicandPneumaticSystems,37,HydraulicAccumulators,Constructionsandtasksinthehydraulicsystem,Tasks:Thehydropneumaticaccumulatorsperformdifferenttasksinthehydraulicsystems,e.g.:,Constructions,reserveenergystorefluidemergencyoperateforcecompensatingdampmechanicalshocksabsorbpressureoscillationscompensateleakagelossesspringsinvehiclesrecoverofbrakingenergystabilizepressurecompensatevolumetricflowrate(expansionreservoir),Withspring,Withweight,Withgas(hydropneumaticaccumulator),Separatingpartbetweengasandfluid,Piston,Bladder,Membrane,2005/2006I.,HydraulicandPneumaticSystems,38,HydraulicAccumulators,Constructions,Withbladder,Withpiston,Withmembraneaboveweldedbelowscrewed,2005/2006I.,HydraulicandPneumaticSystems,39,HydraulicAccumulators,Workingstatesofhydroaccumulatorswithbladder:,Thisinstallationispracticallyabladderfilledwithgasandplacedinatankmadeoutofsteal.Thebladderisfilledwithcarbondioxide(gaspressure).Atthestartingofthepumpthefluidflowsinthetankandcompressesthegas.Whenrequired(ifthereisahighenoughpressuredifference)thefluidflowsveryquicklybackinthesystem.Requirementsonthesystemside:-locksbothintheTandPlines,controlledreleasevalves,junctureforpressuremanometer(mostlybuiltwiththehydroaccumulatortogether),throwbackvalveinthePline.,Fluidflowsout,Fluidflowsin,Hydroaccumulatorwithpre-stressedbladder,pressureless,withoutpre-stress,2005/2006I.,HydraulicandPneumaticSystems,40,HydraulicAccumulators,Construction,Membrane,Bladder,Piston,2005/2006I.,HydraulicandPneumaticSystems,41,Bigpictures,EndofnormalpresentationBeginningofbigpictures,2005/2006I.,HydraulicandPneumaticSystems,42,HydraulicSystems,2005/2006I.,HydraulicandPneumaticSystems,43,HydraulicSystems,2005/2006I.,HydraulicandPneumaticSystems,44,HydraulicSystems,Continuity,2005/2006I.,HydraulicandPneumaticSystems,45,HydraulicSystems,Pascalslaw,2005/2006I.,HydraulicandPneumaticSystems,46,HydraulicSystems,Bernoulliequation,2005/2006I.,HydraulicandPneumaticSystems,47,HydraulicSystems,Flowresistance,2005/2006I.,HydraulicandPneumaticSystems,48,HydraulicSystems,Visc