液压系统及液压缸-外文翻译

PAGE15液压传动第十讲制动器力流体动力系统的优秀的特性之一是由电源产生，通过适当的控制和指导，并通过电线传输，就可以轻松转换到几乎任何类型的机械运动所需要用到的地方。使用一个合适的驱动装置，可以获得线性（直线）或者是旋转运动。驱动器是一种转换流体动力机械力和运动的装置。缸、马达和涡轮机是最常见的将流体动力系统应用于驱动设备的类型。这一章描述了各种类型的动作汽缸和他们的应用程序、不同类型的流体汽车和使用流体动力系统的涡轮机。汽缸制动汽缸是一种将流体动力转换成线性或直线、力和运动的装置。因为线性运动是沿着一条直线前后移动的往复运动。这种类型的制动器有时被称为一个往复、或线性、电动机。由ram或活塞组成的汽缸在一个圆柱孔内操作。制动汽缸可以安装，以便汽缸被固定在一个固定的结构，ram或活塞被连接到该机制来操作，或者是活塞和ram可能被固定到固定结构，汽缸附加到机械装置来操作。制动汽缸气动和液压系统的设计和操作是类似的。一些变化的ram和活塞式制动汽缸的内容将在后面的段落中描述。冲压式缸术语ram和活塞通常可以互换使用。然而，一个冲压式缸通常被认为是一个截面积活塞杆超过一半的截面积活动元件。在大多数这种类型的制动汽缸中，杆和活动元件各占一半。这种类型的活动元件经常被称为柱塞。冲压式缸主要是用来推动而不是拉。一些应用程序需要ram的一部分在平坦的外部来推动或升降单位操作。其他应用程序需要一些机械装置的附件，如一个U型夹或有眼螺栓。冲压式缸的设计在很多其他方面不同，以满足不同应用程序的要求。单作用千斤顶单作用千斤顶（如图：10-1）试用力只在一个方向。流体定向的汽缸取代ram和他外部的弹性元件，将物体举起放在上面。当流体压力释放后，由于没有规定由流体动力缩回ram。物体的重量或者是一些机械设备，比如一个弹簧，迫使ram回到汽缸。这种流体能量就倒回到容器。单作用冲压式汽缸通常用于液压千斤顶。用于移动飞机的飞行甲板和机库甲板航空母舰的升降机也使用这种类型的汽缸。在这些升降机中，汽缸是水平安装的，通过一系列的电缆和捆运行升降机。流体压力产生ram的外在能量使升降机运行。当从ram中释放出流体压力，升降机的重量迫使ram回到汽缸。反过来，这迫使流体回容器。双作用千斤顶一个双作用冲压式缸如图10-2。在这个汽缸中，两个中风的ram都是由加压流体产生的。它有两个流体端口，每一个都在或是接近汽缸的两端。针对流体压力的封闭端缸扩展ram和应用力。撤销ram和减少力、流体是指向截然相反的汽缸。一个四通换向阀是通常用于控制双作用ram。当阀门定位来扩展ram，加压流体进入端口A，作用于ram的地面，加强ram的外部力量。对于在液压系统中的回流管，或者气动系统中的大气，通过控制阀门，高于ramFluidPowerNAVEDTRA14105CHAPTER10ACTUATORSOneoftheoutstandingfeaturesoffluidpowersystemsisthatforce,generatedbythepowersupply,controlledanddirectedbysuitablevaluing,andtransportedbylines,canbeconvertedwitheasetoalmostanykindofmechanicalmotiondesiredattheveryplaceitisneeded.Eitherlinear(straightline)orrotarymotioncanbeobtainedbyusingasuitableactuatingdevice.Anactuatorisadevicethatconvertsfluidpowerintomechanicalforceandmotion.Cylinders,motors,andturbinesarethemostcommontypesofactuatingdevicesusedinfluidpowersystems.Thischapterdescribesvarioustypesofactuatingcylindersandtheirapplications,differenttypesoffluidmotors,andturbinesusedinfluidpowersystems.CYLINDERSAnactuatingcylinderisadevicethatconvertsfluidpowertolinear,orstraightline,forceandmotion.Sincelinearmotionisaback-and-forthmotionalongastraightline,thistypeofactuatorissometimesreferredtoasareciprocating,orlinear,motor.Thecylinderconsistsofaramorpistonoperatingwithinacylindricalbore.Actuatingcylindersmaybeinstalledsothatthecylinderisanchoredtoastationarystructureandtheramorpistonisattachedtothemechanismtobeoperated,orthepistonorrammaybeanchoredtothestationarystructureandthecylinderattachedtothemechanismtobeoperated.Actuatingcylindersforpneumaticandhydraulicsystemsaresimilarindesignandoperation.Someofthevariationsofram-andpiston-typeactuatingcylindersaredescribedinthefollowingparagraphs.RAM-TYPECYLINDERSThetermsramandpistonareoftenusedinterchangeably.However,aram-typecylinderisusuallyconsideredoneinwhichthecross-sectionalareaofthepistonrodismorethanone-halfthecross-sectionalareaofthemovableelement.Inmostactuatingcylindersofthistype,therodandthemovableelementhaveequalareas.Thistypeofmovableelementisfrequentlyreferredtoasaplunger.Theram-typeactuatorisusedprimarilytopushratherthantopull.Someapplicationsrequiresimplyaflatsurfaceontheexternalpartoftheramforpushingorliftingtheunittobeoperated.Otherapplicationsrequiresomemechanicalmeansofattachment,suchasaclevisoreyebolt.Thedesignofram-typecylindersvariesinmanyotherrespectstosatisfytherequirementsofdifferentapplications.Single-ActingRamThesingle-actingram(fig.10-1)appliesforceinonlyonedirection.Thefluidthatisdirectedintothecylinderdisplacestheramandforcesitoutward,liftingtheobjectplacedonit.Sincethereisnoprovisionforretractingtherambyfluidpower,whenfluidpressureisreleased,eithertheweightoftheobjectorsomemechanicalmeans,suchasaspring,forcestherambackintothecylinder.Thisforcesthefluidbacktothereservoir.Thesingle-actingram-typeactuatingcylinderisoftenusedinthehydraulicjack.Theelevatorsusedtomoveaircrafttoandfromtheflightdeckandhangardeckonaircraftcarriersalsousecylindersofthistype.Intheseelevators,thecylindersareinstalledhorizontallyandoperatetheelevatorthroughaseriesofcablesandsheaves.Fluidpressureforcestheramoutwardandliftstheelevator.Whenfluidpressureisreleasedfromtheram,theweightoftheelevatorforcestherambackintothecylinder.This,inturn,forcesthefluidbackintothereservoir.Double-ActingRamAdouble-actingram-typecylinderisillustratedinfigure10-2.Inthiscylinder,bothstrokesoftheramareproducedbypressurizedfluid.Therearetwofluidports,oneatorneareachendofthecylinder.Fluidunderpressureisdirectedtotheclosedendofthecylindertoextendtheramandapplyforce.Toretracttheramandreducetheforce,fluidisdirectedtotheoppositeendofthecylinder.Afour-waydirectionalcontrolvalveisnormallyusedtocontrolthedouble-actingram.Whenthevalveispositionedtoextendtheram,pressurizedfluidentersportA(fig.10-2),actsonthebottomsurfaceoftheram,andforcestheramoutward.FluidabovetheramlipisfreetoflowoutofportB,throughthecontrolvalve,andtothereturnlineinhydraulicsystemsortotheatmosphereinpneumaticsystems.Normally,thepressureofthefluidisthesameforeitherstrokeoftheram.Recallfromchapter2thatforceisequaltopressuretimesarea(F=PA).Noticethedifferenceoftheareasuponwhichthepressureactsinfigure10-2.Thepressureactsagainstthelargesurfaceareaonthebottomoftheramduringtheextensionstroke,duringwhichtimetheramappliesforce.Sincetheramdoesnotrequirealargeforceduringtheretractionstroke,pressureactingonthesmallareaonthetopsurfaceoftheramlipprovidesthenecessaryforcetoretracttheram.TelescopingRamsFigure10-3showsatelescopingram-typeactuatingcylinder.Aseriesoframsisnestedinthetelescopingassembly.Withtheexceptionofthesmallestram,eachramishollowandservesasthecylinderhousingforthenextsmallerram.Theramassemblyiscontainedinthemaincylinderassembly,whichalsoprovidesthefluidports.Althoughtheassemblyrequiresasmallspacewithalltheramsretracted,thetelescopingactionoftheassemblyprovidesarelativelylongstrokewhentheramsareextended.Anexcellentexampleoftheapplicationofthistypeofcylinderisinthedumptruck.Itisusedtolifttheforwardendofthetruckbedanddumptheload.Duringtheliftingoperation,thegreatestforceisrequiredfortheinitialliftingoftheload.Astheloadisliftedandbeginstodump,therequiredforcebecomeslessandlessuntiltheloadiscompletelydumped.Duringtheraisecycle,pressurizedfluidentersthecylinderthroughportA(fig.10-3)andactsonthebottomsurfaceofallthreerams.Ram1hasalargersurfaceareaand,therefore,providesthegreaterforcefortheinitialload,Asram1reachestheendofitsstrokeandtherequiredforceisdecreased,ram2moves,providingthesmallerforceneededtocontinueraisingtheload.Whenram2completesitsstroke,astillsmallerforceisrequired.Ram3thenmovesoutwardtofinishraisinganddumpingtheload.Sometelescopingram-typecylindersareofthesingle-actingtype.Likethesingle-actingramdiscussedpreviously,thesetelescopingram-typecylindersareretractedbygravityormechanicalforce.Somehydraulicjacksareequippedwithtelescopingrams.Suchjacksareusedtoliftvehicleswithlowclearancestotherequiredheight.Othertypesoftelescopingcylinders,liketheoneillustratedinfigure10-3,areofthedouble-actingtype.Inthistype,fluid