TheFeaturesandDevelopmentHistoryandApplicationofHydraulicandPneumaticTransmutation1.Theadvantagesofhydraulictransmission1)Ahydraulicsystemcanproducehigherpowerthanelectricalequipmentunderthesamevolume.Thehydraulicequipmentsystemhassmallervolume,light,highpowerconsistencyandcompactconfigurationatagivenpower.Thevolumeandweightofahydraulicmotorareabout12%ofanelectricmotor.2)Hydraulicequipmenthasagoodworkingstability.Itisbecauseoflight,lessinertia,quickresponse:thehydraulicequipmentcanrealizeceleritystart-up,brakeandfrequentchangeinmotiondirection.3)Thehydraulictransmissioncanreachawiderangeofspeedregulation(withtherangeof1:2000),andthespeedcanalsoberegulatedduringtheworkprocessing.4)Thehydraulictransmissioncaneasilyrealizeautomationandthepressure,flowrateandtheflowdirectioncanberegulatedandcontrolled.Ifwecombineitwithelectric,electronorpneumaticcontrolsystems,amorecomplextransmissionsystemwithremotecontrolcanberealized.5)Thehydraulicsystemcanprotectfromover-loadeasily,whichcannotbedonebyelectricityormachineequipment.6)Becauseofstandardization,series,andall-purposeapplication；thehydraulicsystemiseasierindesign,fabricationandapplication.7)Thehydraulicsystemiseasierthanmachineequipmentindoinglinemotion.2.Theshortagesofhydraulictransmission1)Leak.Oilleaksareinevitablebecauseofthelossinfluidflowresistance.Somoreenergylossexistsinahydraulictransmission.2)Workingtemperature.Theworkingtemperaturehasstrongeffectontheworkingpropertyofahydraulicsystembecauseoftheviscosity-temperaturecharacterofhydraulicoil.Itissuitableforworkinginapropertemperature.3)Cost.Thecostishighbecauseoftheneedsinhighprecisionfabricateforhydraulicelements.4)Itisdifficulttofindthereasonsoffault.3.Theadvantagesofpneumatictransmission1)Theaircanbeobtainedandexpelledfromtheatmosphere.Itcannotbringpollutiontotheenvironment.2)Itisoflowviscosityandlowerpressurelossinpipes.Thepressureairisconvenientforconvergencesupplyandremotetransportation.3)Itisoflowworkingpressure(usually0.3-0.8MPa).Avowersmaterialandfabricateprecisionisrequiredforthepneumatictransmissionelements.4)Thepneumatictransmissionhasasimpleservicing.Theairpipeisnoteasytobejammed.5)Safety.Thepneumaticsystemcanprotectfromover-loadeasily.4.Theshortcomesofpneumatictransmission1)Itisbecauseofaircompressibility.Theworkingstabilitiesforpneumatictransmissionsystemarepoorerthanthoseofhydraulictransmissionsystem.2)Becauseoflowerworkingpressureandsmallsizeinconfiguration,thepushforceofpneumatictransmissionisusuallyverylower.3)Lowertransmissionefficiency.Tosumup,thestrong-pointsofhydraulicandpneumatictransmissionhavetakenthemainadvantages,andtheshortageshavebeenovercomeandimprovedbytechnicalrenovation.ThefundamentallawunderlyingthewholescienceofhydraulicswasdiscoveredbyBlasiePascal,aFrenchphysicist,intheseventeenthcentury.Butitwasnotuntiltheendofthe18centurythatmanfoundwaystomakethesnuglyfittingpartsrequiredinhydraulicsystemsandothermodernequipment.Sincethenprogresshasbeenrapid.Hydraulictransmissionhasbeenexperiencingtheprocessasbelow.The17thand18thcenturieswereaproductiveperiodinthedevelopmentofhydraulictheory.Torricellistudiedfluidmotionintheearly17thcentury.Lateinthatcentury,SirIsaacNewtonconductedstudiesonviscosityandtheresistanceofsubmergedbodiesinamovingfluid.Thekeyachievementsoftheperiodoccurredinthemiddleofthe18thcenturywhenDanielBulliondevelopedthetheoryoftransmissionofenergyinfluidstreamsandBlasPascal,ataboutthesametime,establishedtheprincipleofhydrostaticpressuretransmission.Thisprinciplewasfirstusedinthelatterpartofthe18thcentury.ThefirsthydraulicpressuremachinewasmanufacturedbyEnglandinthelate18thcentury.ThefundamentalsoffluidtheorywereestablishedbytheaboveworkandrefinementswereaddedbyNavierwhoderivedthemathematicsofmotioninliquidsincludingequationsforfluidflowwithfriction.Thiswasearlyinthe19thcentury.ItwasfollowedbytheworkofStokes,whoindependentlydiscoveredthesameequationsandfurtherextendedtheworkofNavicert.Recentlyhydraulicandpneumaticpressuretransmissiontechnologyhasbeendevelopedwithalargescalepetrolicindustryinthe19thcentury,andthebarbettedisplacewasthefirstonesuccessfulusinghydraulicequipment,andthenhydraulicmachinetool.InWorldWarImanynewmachinesbasedontheprinciplesofhydraulicshadbeenused.Thegreatautomotiveindustyintroducedhydraulicbrakesintheearlythirtiesandhydraulictransmissionsinthelatethirties.Thetractorindustrybeganusinghydraulicsin1940toincreasetheflexibilityandutilityoffarmequipment.InWorldWarIIbecauseofthedemandtransmissionandcontrolequipmentsinfastreaction,precisionactionandhighoutputpowersboosteddevelopmentinhydraulictheology.AftertheWar,thehydraulicdevelopmentturnedintocivilindustry,suchasmachinetool,engineering,metallurgy,plasticmachine,farmmachine,vehicleandwatercraft.Inmorerecentyears,theroleofleadershipinhydraulicpowerapplicationhasbeentakenoverlargelybysomeofthelargeearthmovingandconstructionequipmentmanufacturers.Thetotalpowerinvolvedisoftengreaterthanthatrequiredineventhelargestaircraftsystems.Withthedevelopmentofhigherautomationofhydraulicmachinesandincreasinguseofhydraulicandpneumaticelements,thescaledelementsandintegratedhydraulicsystemwithminiaturizationisinevitable.Especiallyinrecentyearshydraulicandpneumatictransmissioniscombinedcloselywiththesensorandmicro-electricitytechnology.Ithasbeenemergingamountsofnewvalvessuchashydraulic-electricityproportionalvalves,digitalvalves,hydraulicandelectro-hydraulicservocylindersandtheintegrativeelements,whichwillleadthehydraulicandpneumatictechnologytothedevelopmentofhigherpressure,higherspeed,largerpower,lowerenergywastageandnoise,longevityandhighintegration.Computeraideddesign(CAD)andtest(CAT)andpracticalcontroltechnologyusedinhydraulicandpneumaticsystemwillbethetrend.Nowadaystheapplicationofhydraulictransmissionsystemhasbecomeoneoftheimportantindicationsofindustrylevelforacountry.Indevelopedcountries,95%ofengineeringmachine,90%ofnumericalcontrolcenterandmorethan95%ofautomationassemblylinesusethehydraulictransmissionsystem.液壓與氣壓傳動的特點及發(fā)展應用概況1.液壓傳動有以下優(yōu)點1）在同等體積下，液壓裝置畢電氣裝置產生更高的動力。再同等功率下，液壓裝置體積小，重量輕，功率密度大，結構緊湊。液壓馬達的體積和重量只有同等功率電動機的12%左右。2）液壓裝置工作比較平穩(wěn)。由于重量輕、慣性小、反應快，液壓裝置易于實現快速啟動、制動和頻繁的換向。3）液壓裝置能在大