机械工程学院毕业设计(论文)外文翻译

上海应用技术学院机械工程学院毕业设计（论文）外文翻译题目学生姓名陈业飞专业机械电子工程学号0710211217班级071021A1指导老师杨征瑞职称督导2011年3月5日1HydraulicmachineryandpumpHydraulicmachineryaremachinesandtoolswhichusefluidpowertodowork.Heavyequipmentisacommonexample.Inthistypeofmachine,high-pressureliquid-calledhydraulicfluid-istransmittedthroughoutthemachinetovarioushydraulicmotorsandhydrauliccylinders.Thefluidiscontrolleddirectlyorautomaticallybycontrolvalvesanddistributedthroughhosesandtubes.Thepopularityofhydraulicmachineryisduetotheverylargeamountofpowerthatcanbetransferredthroughsmalltubesandflexiblehoses,andthehighpowerdensityandwidearrayofactuatorsthatcanmakeuseofthispower.Hydraulicmachineryisoperatedbytheuseofhydraulics,wherealiquidisthepoweringmedium.Pneumatics,ontheotherside,isbasedontheuseofagasasthemediumforpowertransmission,generationandcontrol.HydrauliccircuitsForthehydraulicfluidtodowork,itmustflowtotheactuatorandormotors,thenreturntoareservoir.Thefluidisthenfilteredandre-pumped.Thepathtakenbyhydraulic12fluidiscalledahydrauliccircuitofwhichthereareseveraltypes.Opencentercircuitsusepumpswhichsupplyacontinuousflow.Theflowisreturnedtotankthroughthecontrolvalve'sopencenter;thatis,whenthecontrolvalveiscentered,itprovidesanopenreturnpathtotankandthefluidisnotpumpedtoahighpressure.Otherwise,ifthecontrolvalveisactuateditroutesfluidtoandfromanactuatorandtank.Thefluid'spressurewillrisetomeetanyresistance,sincethepumphasaconstantoutput.Ifthepressurerisestoohigh,fluidreturnstotankthroughapressurereliefvalve.Hydraulicpumpssupplyfluidtothecomponentsinthesystem.Pressureinthesystemdevelopsinreactiontotheload.Hence,apumpratedfor5,000psiiscapableofmaintainingflowagainstaloadof5,000psi.Pumpshaveapowerdensityabouttentimesgreaterthananelectricmotor(byvolume).Theyarepoweredbyanelectricmotororanengine,connectedthroughgears,belts,oraflexibleelastomericcouplingtoreducevibration.Commontypesofhydraulicpumpstohydraulicmachineryapplicationsare;Gearpump:cheap,durable,simple.Lessefficient,becausetheyareconstantdisplacement,andmainlysuitableforpressuresbelow20MPa(3000psi).23Vanepump:cheapandsimple,reliable(especiallying-rotorform).Goodforhigher-flowlow-pressureoutput.Axialpistonpump:manydesignedwithavariabledisplacementmechanism,tovaryoutputflowforautomaticcontrolofpressure.Therearevariousaxialpistonpumpdesigns,includingswashplateandcheckball.Themostcommonistheswashplatepump.Radialpistonpump:Apumpthatisnormallyusedforveryhighpressureatsmallflows.Pistonpumpsaremoreexpensivethangearorvanepumps,butprovidelongerlifeoperatingathigherpressure,withdifficultfluidsandlongercontinuousdutycycles.Pistonpumpsmakeuponehalfofahydrostatictransmission.ControlvalvesDirectionalcontrolvalvesroutethefluidtothedesiredactuator.Theyusuallyconsistofaspoolinsideacastironorsteelhousing.Directionalcontrolvalvesareusuallydesignedtobestackable,withonevalveforeachhydrauliccylinder,andonefluidinputsupplyingallthevalvesinthestack.Thespoolpositionmaybeactuatedbymechanicallevers,hydraulicpilotpressure,orsolenoidswhichpushthespoolleftorright.34Themainvalveblockisusuallyastackofofftheshelfdirectionalcontrolvalveschosenbyflowcapacityandperformance.Somevalvesaredesignedtobeproportional(flowrateproportionaltovalveposition),whileothersmaybesimplyon-off.Thecontrolvalveisoneofthemostexpensiveandsensitivepartsofahydrauliccircuit.Pressurereliefvalvesareusedinseveralplacesinhydraulicmachinery;onthereturncircuittomaintainasmallamountofpressureforbrakes,pilotlines,etc...Onhydrauliccylinders,topreventoverloadingandhydrauliclinerupture.Onthehydraulicreservoir,tomaintainasmallpositivepressurewhichexcludesmoistureandcontamination.Pressurereducingvalvesreducethesupplypressureasneededforvariouscircuits.Checkvalvesareone-wayvalves,allowinganaccumulatortochargeandmaintainitspressureafterthemachineisturnedoff,forexample.Counterbalancevalvesareinfactaspecialtypeofpilotcontrolledcheckvalve.Whereasthecheckvalveisopenorclosed,thecounterbalancevalveactsabitlikeapilotcontrolledflowcontrol.45HydraulicpumptypesGearpumps(withexternalteeth)(fixeddisplacement)aresimpleandeconomicalpumps.Thesweptvolumeorofgearpumpsforhydraulicswillbebetweenabout1cm3(0.001litre)and200cm3(0.2litre).Thesepumpscreatepressurethroughthemeshingofthegearteeth,whichforcesfluidaroundthegearstopressurizetheoutletside.Somegearpumpscanbequitenoisy,comparedtoothertypes,butmoderngearpumpsarehighlyreliableandmuchquieterthanoldermodels.Rotaryvanepumps(fixedandsimpleadjustabledisplacement)havehigherefficienciesthangearpumps,butarealsousedformidpressuresupto180barsingeneral.Sometypesofvanepumpscanchangethecentreofthevanebody,sothatasimpleadjustablepumpisobtained.Theseadjustablevanepumpsareingeneralconstantpressureorconstantpowerpumps:thedisplacementisincreaseduntiltherequiredpressureorpowerisreachedandsubsequentlythedisplacementorsweptvolumeisdecreaseduntilanequilibriumisreached.Screwpumps(fixeddisplacement)areadouble,butclosed.Thismeansthattwoscrewsareusedinonebody.Thepumpsareusedforhighflowsandrelativelylowpressure(max100bar).Theywere56usedonboardshipswheretheconstantpressurehydraulicsystemwasgoingthroughthewholeship,especiallyforthecontrolof,butalsoforthesteeringgearandhelpdrivesystems.Theadvantageofthescrewpumpsisthelowsoundlevelofthesepumps;theefficiencyisnotthathigh.Bentaxispumps,axialpistonpumpsandmotorsusingthebentaxisprinciple,fixedoradjustabledisplacement,existsintwodifferentbasicdesigns.TheThoma-principle(engineerHansThoma,Germany,patent1935)withmax25degreesangleandtheWahlmark-principle(GunnarAxelWahlmark,patent1960)withspherical-shapedpistonsinonepiecewiththepistonrod,pistonrings,andmaximum40degreesbetweenthedriveshaftcenterlineandpistons(VolvoHydraulicsCo.).Thesehavethebestefficiencyofallpumps.Althoughingeneralthelargestdisplacementsareapproximatelyonelitreperrevolution,ifnecessaryatwo-litersweptvolumepumpcanbebuilt.Oftenvariable-displacementpumpsareused,sothattheoilflowcanbeadjustedcarefully.Thesepumpscaningeneralworkwithaworkingpressureofupto350–420barsincontinuouswork.Axialpistonpumpsswashplateprincipleusingtheprinciple(fixedandadjustabledisplacement)haveaqualitythatisalmostthesameasthebentaxis67model.Theyhavetheadvantageofbeingmorecompactindesign.Thepumpsareeasierandmoreeconomicaltomanufacture;thedisadvantageisthattheyaremoresensitivetooilcontamination.Radialpistonpumps(fixeddisplacement)areusedespeciallyforhighpressureandrelativelysmallflows.Pressuresofupto650bararenormal.Infactvariabledisplacementisnotpossible,butsometimesthepumpisdesignedinsuchawaythattheplungerscanbeswitchedoffonebyone,sothatasortofvariabledisplacementpumpisobtained.Peristalticpumpsarenotgenerallyusedforhighpressures.PumpsforopenandclosedsystemsMostpumpsareworkinginopensystems.Thepumpdrawsoilfromareservoirat.Itisveryimportantthatthereisnoatthesuctionsideofthepump.Forthisreasontheconnectionofthesuctionsideofthepumpislargerindiameterthantheconnectionofthepressureside.Incaseoftheuseofmulti-pumpassemblies,thesuctionconnectionofthepumpisoftencombined.Itispreferredtohavefreeflowtothepump(pressureatinletofpumpatleast0.8bars).Thebodyofthepumpisofteninopenconnectionwiththesuctionsideofthepump.Incaseofaclosedsystem,bothsidesofthepumpcanbeathighpressure.78Thereservoirisoftenpressurizedwith6-20barsboostpressure.Forclosedloopsystems,normallyaxialpistonpumpsareused.Becausebothsidesarepressurized,thebodyofthepumpneedsaseparateleakageconnection.MultipumpassemblyInahydraulicinstallation,onepumpcanservemorecylindersandmotors.Theproblemhoweveristhatinthatcaseaconstantpressuresystemisrequiredandthesystemalwaysneedsthefullpower.Itismoreeconomictogiveeachcylinderandmotoritsownpump.Inthatcasemultipumpassembliescanbeused.Gearpumpscanoftenbeobtainedasmultipumps.Thedifferentchambers(sometimesofdifferentsize)aremountedinonebodyorbuilttogether.Alsovanepumpscanoftenbeobtainedasamultipump.Gerotorpumpsareoftensuppliedasmultipumps.Screwpumpscanbebuilttogetherwithagearpumporavanepump.Axialpistonswashplatepumpscanbebuilttogetherwithasecondpumpofthesameorsmallersize,orcanbebuilttogetherwithoneormoregearpumpsorvanepumps(dependingonthesupplier).Axialplungerpumpsofthebentaxisdesigncannotbebuilttogetherwithotherpumps.翻译89液压机械及泵液压机械是机械和工具,它使用流体的力量去做的工作。重型设备是一种常见的例子。在这种类型的机器，高压液-所谓的液压油-是整个传送机各种液压马达和液压缸。流体是直接控制或自动通过控制阀，并通过软管和管分配。液压机械的普及是由于应用非常的大量，可以通过小管和软管转移，高功率密度和广泛的执行机构，可以使这项技术广泛的使用。液压机械是由水力学，其中以液体为介质供电使用。气动，在另一边，是基于一种气体作为动力传输，发电和控制媒介的使用。液压回路对于液压油做的工作，它必须对执行机构的马达，然后返回到一个水库。流体过滤，然后再抽水。由液压油所采取的路径称为一个液压回路，其中有几种类型。开放中心电路用泵的供应源源不断。流返回到油箱，通过控制阀的开放中心，也就是说，当控制阀为中心，它提供了一个开放的返回路径坦克和流体是不是被泵到高的压力。否则，如果控制阀的流体驱动它的路线和从驱动器和坦克。流体的压力将上升，以应付任何反抗，因为该泵具有恒定的输出。如果压力上升过高，流体返回舱通过泄压阀。液压泵液供应系统中的组成部分。发展中的系统压力与负载的反应。因此，5000磅额定泵是维持对5000磅潮流有一个约十倍以上的电动马达（体积比）的功率密度更大的能力。它们均采用了电动马达或引擎，通过齿轮，皮带，弹性联轴器或柔性连接以减少振动。液压泵的常用类型转换为液压机械应用;齿轮泵：便宜，耐用，操作简单。效率较低，因为他们是恒位移，主要用于低于20兆帕（3000磅）的压力下使用。叶片泵：便宜，简单，可靠（特别是在G-转子的形式）。良好的高流量低压力输出。轴向活塞泵：很多人用一个变量的机制设计，来改变输出流量的压力自动控制。有各种轴向活塞泵的设计，包括斜盘。最常见的是活塞泵斜盘：通常是用于一个非常高的压力容器用在小流量泵。活塞泵比齿轮泵或叶片昂贵，但提供更长的运行在更高的生活压力，困难的液体和更长的连续工作周期。活塞泵组成的一个静液压传动的一半。控制阀方向控制阀路由到所需的驱动器的液体。它们通常由一个内部的铸铁或不锈钢外壳阀芯。方向控制阀通常设计成可堆叠每一个阀液压缸和一个液体输入提供所有堆栈中的阀门。阀芯位置可能由机械驱动的杠杆，液压试验压力或螺线管这推动阀芯左或右。主阀块通常是一堆现成的定向控制流量阀的容量和性能选择。有些阀门被设计成比例（流量成比例阀的位置），而其他可能会在过简单。控制阀是液压回路的最昂贵的和敏感的地区之一。泄压阀用于液压机械在几个地方;在回路保持刹车的压力，中试线等少量..对液压缸，防止超载和液压管破裂。对液压水库，以维持一个小的正压力，排除水分和910污染。减压阀减少供应压力，对各种电路的需要。止回阀是单向阀，允许蓄电池充电和维持其压力后机关闭，例如。平衡阀的其实是一种液控单向阀的特殊类型。而单向阀打开或关闭，平衡阀的行为像一个飞行员控制流量控制位。液压泵类型[编辑]齿轮泵齿轮泵（带外齿）（固定位移）既简单又经济的泵。波及体积或液压齿轮泵的排量将由约一立方厘米（0.001升）和二百立方厘米（0.2升）。这些泵创建通过齿轮啮合，这迫使各地的齿轮流体加压出口侧的压力。一些齿轮泵可以很嘈杂，相对于其他类型，但现