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外文翻译--液压与气压传动的特点及发展应用概况.doc

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外文翻译--液压与气压传动的特点及发展应用概况.doc

TheFeaturesandDevelopmentHistoryandApplicationofHydraulicandPneumaticTransmutation1.Theadvantagesofhydraulictransmission1Ahydraulicsystemcanproducehigherpowerthanelectricalequipmentunderthesamevolume.Thehydraulicequipmentsystemhassmallervolume,light,highpowerconsistencyandcompactconfigurationatagivenpower.Thevolumeandweightofahydraulicmotorareabout12ofanelectricmotor.2Hydraulicequipmenthasagoodworkingstability.Itisbecauseoflight,lessinertia,quickresponsethehydraulicequipmentcanrealizeceleritystartup,brakeandfrequentchangeinmotiondirection.3Thehydraulictransmissioncanreachawiderangeofspeedregulationwiththerangeof12000,andthespeedcanalsoberegulatedduringtheworkprocessing.4Thehydraulictransmissioncaneasilyrealizeautomationandthepressure,flowrateandtheflowdirectioncanberegulatedandcontrolled.Ifwecombineitwithelectric,electronorpneumaticcontrolsystems,amorecomplextransmissionsystemwithremotecontrolcanberealized.5Thehydraulicsystemcanprotectfromoverloadeasily,whichcannotbedonebyelectricityormachineequipment.6Becauseofstandardization,series,andallpurposeapplicationthehydraulicsystemiseasierindesign,fabricationandapplication.7Thehydraulicsystemiseasierthanmachineequipmentindoinglinemotion.2.Theshortagesofhydraulictransmission1Leak.Oilleaksareinevitablebecauseofthelossinfluidflowresistance.Somoreenergylossexistsinahydraulictransmission.2Workingtemperature.Theworkingtemperaturehasstrongeffectontheworkingpropertyofahydraulicsystembecauseoftheviscositytemperaturecharacterofhydraulicoil.Itissuitableforworkinginapropertemperature.3Cost.Thecostishighbecauseoftheneedsinhighprecisionfabricateforhydraulicelements.4Itisdifficulttofindthereasonsoffault.3.Theadvantagesofpneumatictransmission1Theaircanbeobtainedandexpelledfromtheatmosphere.Itcannotbringpollutiontotheenvironment.2Itisoflowviscosityandlowerpressurelossinpipes.Thepressureairisconvenientforconvergencesupplyandremotetransportation.3Itisoflowworkingpressureusually0.30.8MPa.Avowersmaterialandfabricateprecisionisrequiredforthepneumatictransmissionelements.4Thepneumatictransmissionhasasimpleservicing.Theairpipeisnoteasytobejammed.5Safety.Thepneumaticsystemcanprotectfromoverloadeasily.4.Theshortcomesofpneumatictransmission1Itisbecauseofaircompressibility.Theworkingstabilitiesforpneumatictransmissionsystemarepoorerthanthoseofhydraulictransmissionsystem.2Becauseoflowerworkingpressureandsmallsizeinconfiguration,thepushforceofpneumatictransmissionisusuallyverylower.3Lowertransmissionefficiency.Tosumup,thestrongpointsofhydraulicandpneumatictransmissionhavetakenthemainadvantages,andtheshortageshavebeenovercomeandimprovedbytechnicalrenovation.ThefundamentallawunderlyingthewholescienceofhydraulicswasdiscoveredbyBlasiePascal,aFrenchphysicist,intheseventeenthcentury.Butitwasnotuntiltheendofthe18centurythatmanfoundwaystomakethesnuglyfittingpartsrequiredinhydraulicsystemsandothermodernequipment.Sincethenprogresshasbeenrapid.Hydraulictransmissionhasbeenexperiencingtheprocessasbelow.The17thand18thcenturieswereaproductiveperiodinthedevelopmentofhydraulictheory.Torricellistudiedfluidmotionintheearly17thcentury.Lateinthatcentury,SirIsaacNewtonconductedstudiesonviscosityandtheresistanceofsubmergedbodiesinamovingfluid.Thekeyachievementsoftheperiodoccurredinthemiddleofthe18thcenturywhenDanielBulliondevelopedthetheoryoftransmissionofenergyinfluidstreamsandBlaséPascal,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.Especiallyinrecentyearshydraulicandpneumatictransmissioniscombinedcloselywiththesensorandmicroelectricitytechnology.Ithasbeenemergingamountsofnewvalvessuchashydraulicelectricityproportionalvalves,digitalvalves,hydraulicandelectrohydraulicservocylindersandtheintegrativeelements,whichwillleadthehydraulicandpneumatictechnologytothedevelopmentofhigherpressure,higherspeed,largerpower,lowerenergywastageandnoise,longevityandhighintegration.ComputeraideddesignCADandtestCATandpracticalcontroltechnologyusedinhydraulicandpneumaticsystemwillbethetrend.Nowadaystheapplicationofhydraulictransmissionsystemhasbecomeoneoftheimportantindicationsofindustrylevelforacountry.Indevelopedcountries,95ofengineeringmachine,90ofnumericalcontrolcenterandmorethan95ofautomationassemblylinesusethehydraulictransmissionsystem.液压与气压传动的特点及发展应用概况1.液压传动有以下优点1)在同等体积下,液压装置毕电气装置产生更高的动力。再同等功率下,液压装置体积小,重量轻,功率密度大,结构紧凑。液压马达的体积和重量只有同等功率电动机的12左右。2)液压装置工作比较平稳。由于重量轻、惯性小、反应快,液压装置易于实现快速启动、制动和频繁的换向。3)液压装置能在大范围内实现无级调速(调速范围可达2000),它还可以在运行过程中进行调速。4)液压传动易于自动化,它对液体压力、流量或流动方向易于进行调节或控制。当将液压控制和电气控制、电子控制或气动控制结合起来使用时,整个传动装置能实现复杂的顺序动作,也能方便的实现远程控制。5)液压装置易于实现过载保护,这是电气传动装置和机械传动装置无法办到的。6)由于液压元件已经实现了标准化、系列化和通用化,液压系统的设计、制造和使用都比较方便。7)用液压传动实现直线运动远比用机械传动简单。2.液压传动的缺点1)由于流体流动的阻力损失和泄露是不可避免的,所以液压传动在工作过程中常有较多的能量损失。2)工作性能易受温度变化的影响,因此不宜在很高或很低的温度下工作。3)为了减少泄漏,液压元件的制造精度要求较高,因而价格较贵。4)液压传动出现故障时不易找出原因。3.气压传动的优点1)空气可以从大气中取得,同时,用过的空气可直接排放到大气中去,处理方便,万一空气管路有泄漏,除引起部分功率损失外,不知产生不利于工作的严重影响,也不会污染环境。2)空气粘度很小,在管道中的压力损失较小,因此压缩空气便于集中供应和远距离输送。3)因压缩空气的工作压力较低(一般为0.30.8Mpa),因此,对气动元件的材料和制造精度上的要求较低。4)气动系统维护简单,管道不易堵塞。5)使用安全,并且便于实现过载保护。4.气压传动的缺点1)由于空气具有可压缩的特性,因此运动速度的平稳性不如液压传动。2)因为工作压力较低和结构尺寸不宜过大,因而气压传动装置的总推力一般不可能很大。3)传动效率低。

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