【7A文】航空飞机液压理论英文培训课件.ppt

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HydraulicsAirlineTransitionCourse LessonObjectivesDevelopabasicunderstandingofhydraulictheoryandthephysicsrelatedtohydraulicsFluidPowerLawofConservationofEnergyPascal’sLawHydrostaticParadoxMechanicaladvantageBernoulli’sprincipleTypesofFluidHydraulicSystemComponents FluidPowerTHEORY HydraulicsystemsoperateaccordingtoPascalslaw.ThelawofBlaisePascalsays:'Thepressure,inastatichydraulicfluidinaclosedsystemiseverywherethesame'.However,whenthevelocityoftheflowisconstantonemayapplyPascalsLawaswell.Animation:Whenthemanjumpsonthesmallpiston,heinducesapressureinthesystem.Thispressurealsoworksonthelargepiston:becauseofthelargeareaofthispiston,theforceinducedbythepressureiscapabletoliftthecar.Thepressurecanbecalculatedwiththeformula:where:p=pressure(psi)F=force(pound)A=area(squareinch) FluidPowerForce=energyexerted(F=MA)Pressure=aforcethatisappliedoveragivenarea(usuallyinpsi)Pressure=Force/AreaWork=anytimeaforcecausesanobjecttomoveWork=ForcexDistancePower=theamountofpowerrequiredtoaccomplishagiveamountofworkinacertainperiodoftimePower=(ForcexDistance)/Time LawofConservationofEnergyWeareabletotakeenergyandchangeit’sform,conserveitforlater,andreleaseitatwill.Wegetthesameamountofenergyoutasweputin.Unfortunatelysomeenergyistransformedandlostintoanunusableform.Ex:Rubbingyouhandstogether,takesyourbodiesenergyandreleasesitasthermalenergy.(UnlessyourinNorthDakotainJan.doingthisisusuallyprettyuseless)Thislossofenergyisusuallyreferredtoasinefficiency TwoFormsofEnergyPotential:ExistsinanobjectbecauseofitspositionEx:ArubberbandstretchedoutKinetic:ExistsinanobjectduetoitsmotionEx:ArubberbandafterIhaveletgoofit,asitfliestowardsyourface HydrostaticParadoxParadox:Atruestatementthatdoesnotreadilyappeartobetrue.HydrostaticParadox:Thepressureofafluidatthebottomofthecontainerwillbeeffectedbytheheightofthatcontainerbutnotitsshapeortheamountoffluid. Pascal’sLaw“Pressureinanenclosedcontaineristransmittedequallyandundiminishedtoallpartsofthecontainerandactsatrightanglestotheenclosingwalls. Pascal’sLawPressureexertedonafluidinaclosedcontaineristransmittedequallyandundiminishedtoallpartsofthecontainerandactsatrightanglestotheenclosingwalls.Force MechanicalAdvantageConsiderateeter-totter.Ex:A5lb.weightwitha10ft.armbalancesa50lb.weightwitha1ft.arm.ThesamemaybemaintainedwithahydraulicsystemF1=F2A1A25lbs=50lbs1sq.in.10sq.in. TransmittingPressureF=AxPTransmittingaforcethroughasmalltube.Piston110in.2Piston210in.2Force2=100lbs.Pressure10lbs./in2Force1=100lbs. Bernoulli’sPrincipleBecomestheexchangebetweenkineticenergy(velocity/dynamicpressure)andpotentialenergy(staticpressure)Morekineticenergy(velocity/dynamicpressure)resultsinlesspotentialenergy(staticpressure)whiletotalenergy(totalpressure)remainsconstant SystemComponents SystemComponentsHydraulicReservoir:StoresfluidServesasanexpansionchambertocompensateforheatexpansionApointwherefluidcanpurgeitselfofanyairAlsocontainsstandpipesforaux.useHydraulicPumpsFluidmoversDevelopspressureasresistanceisappliedHydraulicValves:OpensandclosestodirectorrestricttheflowofthefluidAccumulators:Amethodtostorehydraulicfluid(whichisnoncompressible)underpressure SystemComponents(cont)Filters:RemovescontaminantsMicronsareusedtodescribethesizeoftheparticlesthefilterwillcollectFluidLines:UsedtotransferthefluidtotheactuatororfromtheactuatorSeals:Usedtominimizeleakageandlossofsystempressure,alsousedtokeepoutunwantedcontaminantsActuators:UsedtoconvertpressureinthefluidintoworkPTUsPowerTransferUnits:Usedtotransferpowerfromonehydraulicsystemtoanother SystemComponents(cont) ReservoirsNonpressurized:Foamingisbyminimizedrouting,throughswirlingusingcentrifugalforceForloweraltitudeapplicationsPressurized:AsaircraftflyhigherfoamingbecomesmoreofaproblemPressurizingthereservoirminimizesthisproblem. HydraulicReservoirStandpipe:Forlargeraircraftsystems,astandpipeisincorporatedAstandpipeallowsfluidtoflowthroughstandpipefornormaloperationsWhenfluidleveldecreasesbelowthestandpipe,ex:ahydraulicleak,thestandpipecannotdrawanymorefluidLeavingsomefluidleftforprioritysystems HydraulicPumpsHandpumps:UsedforemergencygearextensiononsomeA/CSingleaction–pumpsfluidwithonestroke,onlywhenthehandleisbeingmovedonedirectionDoubleaction–pumpsfluidwithbothstrokesDash8AlternateGearExtensionhandpump HydraulicPumps(cont.)Powerpumps:Constantdisplacement:MovesagivenamountoffluideachtimeitrotatesIfRPMchanges,amountoffluidandpressurechangesSomesortofpressurereliefisrequiredtopreventrupturingalineordamagetothesystemPowerPumps(cont.):Variabledisplacement:Moveavolumeoffluidproportionaltothedemandsofthesystem PumpTypesTheaxialpistonpump Thegearmotor:TwomeshinggearsConstantdisplacementPumpTypes PumpTypesVanePumpfixedoutputVanePumpvariableoutput GerotorPump:ConstantdisplacementPumpTypes Piston-typeHydraulicmotorVariabledisplacementPumpTypes HydraulicActuatorsLineartype:PistoninsideacylinderHydraulicpressureisappliedtoeithersidetoforcethepistontomoveNote:Thesidewhichthepressureisbeingappliedresultsinadifferentamountofforceduetoadifferenceofsurfacearea HydraulicAccumulatorsUsedtostorehydraulicfluidunderpressureSincehydraulicfluidcannotbecompressedwemusthavesomesortofmechanismtoapplypressure,understorage,againstthehydraulicfluidAdiaphragm,inthecasing,separates,containedpressurizedgasfromthehydraulicfluidwhilestillapplyingpressureAshydraulicpressureisapplieditpushesagainstthediaphragm,avalveclosesandthepressureisstoredOncethehydraulicpressureisneeded,thevalveisopenedandthehydraulicpressureisreleased HydraulicAccumulatorsAccumulatorscanbeusedfor:UnfeatheringapropellerAlternatebrakes PTUsUsedtotransferhydraulicpressurefromonesystemtoanother.ThinkofaturbochargeronacarExhaustgasturnsaturbine,whichisconnectedtoanotherturbinetocompressairThePTUuseshydraulicpressurefromonesystemtoturnaturbine,whichisconnectedtoanothersystemtoprovidepressurewithinthatsystem TypesofFluids TypesofFluidsVegetablebase:MIL-H-7644,essentiallycastoroilRubbersealsneededusedoldersystems,unlikelytobeinanymodernsystemsMineralbase:MIL-H-5606Kerosene-typepetroleum/doesn’tmixwellwithwaterGoodlubricatingpropertiesMixeseasilywithadditivestopreventfoamingandcorrosionNeoprenesealsneededDyedredFlammable TypesofFluids(cont.)SyntheticPhosphateEster:MIL-H-8446(Skydrol)Usedonmodernhigh-speedjetaircraftWiderangeofoperatingtemperaturesSusceptibletocontaminationbywaterMustnotbeallowedtodripontoelectricalwiring(breaksdownthewiring)TeflonsealsDyedpurple THEEND