变速器英文版文献

Transmission(mechanics)Atransmissionorgearboxprovidesspeedandtorqueconversionsfromarotatingpowersourcetoanotherdeviceusinggearratios.InBritishEnglishthetermtransmissionreferstothewholedrivetrain,includinggearbox,clutch,propshaft(forrear-wheeldrive),differentialandfinaldriveshafts.Themostcommonuseisinmotorvehicles,wherethetransmissionadaptstheoutputoftheinternalcombustionenginetothedrivewheels.Suchenginesneedtooperateatarelativelyhighrotationalspeed,whichisinappropriateforstarting,stopping,andslowertravel.Thetransmissionreducesthehigherenginespeedtotheslowerwheelspeed,increasingtorqueintheprocess.Transmissionsarealsousedonpedalbicycles,fixedmachines,andanywhereelserotationalspeedandtorqueneedstobeadapted.Often,atransmissionwillhavemultiplegearratios(orsimplygears),withtheabilitytoswitchbetweenthemasspeedvaries.Thisswitchingmaybedonemanually(bytheoperator),orautomatically.Directional(forwardandreverse)controlmayalsobeprovided.Single-ratiotransmissionsalsoexist,whichsimplychangethespeedandtorque(andsometimesdirection)ofmotoroutput.Inmotorvehicleapplications,thetransmissionwillgenerallybeconnectedtothecrankshaftoftheengine.Theoutputofthetransmissionistransmittedviadriveshafttooneormoredifferentials,whichinturndrivethewheels.Whileadifferentialmayalsoprovidegearreduction,itsprimarypurposeistochangethedirectionofrotation.Conventionalgear/belttransmissionsarenottheonlymechanismforspeed/torqueadaptation.Alternativemechanismsincludetorqueconvertersandpowertransformation(e.g.,diesel-electrictransmission,hydraulicdrivesystem,etc.).Hybridconfigurationsalsoexist.ExplanationEarlytransmissionsincludedtheright-angledrivesandothergearinginwindmills,horse-powereddevices,andsteamengines,insupportofpumping,milling,andhoisting.Mostmoderngearboxesareusedtoincreasetorquewhilereducingthespeedofaprimemoveroutputshaft(e.g.amotorcrankshaft).Thismeansthattheoutputshaftofagearboxwillrotateatslowerratethantheinputshaft,andthisreductioninspeedwillproduceamechanicaladvantage,causinganincreaseintorque.Agearboxcanbesetuptodotheoppositeandprovideanincreaseinshaftspeedwithareductionoftorque.Someofthesimplestgearboxesmerelychangethephysicaldirectioninwhichpoweristransmitted.Manytypicalautomobiletransmissionsincludetheabilitytoselectoneofseveraldifferentgearratios.Inthiscase,mostofthegearratios(oftensimplycalledgears)areusedtoslowdowntheoutputspeedoftheengineandincreasetorque.However,thehighestgearsmaybeoverdrivetypesthatincreasetheoutputspeed.UsesGearboxeshavefounduseinawidevarietyofdifferent—oftenstationary—applications,suchaswindturbines.Transmissionsarealsousedinagricultural,industrial,construction,miningandautomotiveequipment.Inadditiontoordinarytransmissionequippedwithgears,suchequipmentmakesextensiveuseofthehydrostaticdriveandelectricaladjustable-speeddrives.SimpleThesimplesttransmissions,oftencalledgearboxestoreflecttheirsimplicity(althoughcomplexsystemsarealsocalledgearboxesinthevernacular),providegearreduction(or,morerarely,anincreaseinspeed),sometimesinconjunctionwitharight-anglechangeindirectionoftheshaft(typicallyinhelicopters,seepicture).TheseareoftenusedonPTO-poweredagriculturalequipment,sincetheaxialPTOshaftisatoddswiththeusualneedforthedrivenshaft,whichiseithervertical(aswithrotarymowers),orhorizontallyextendingfromonesideoftheimplementtoanother(aswithmanurespreaders,flailmowers,andforagewagons).Morecomplexequipment,suchassilagechoppersandsnowblowers,havedriveswithoutputsinmorethanonedirection.Thegearboxinawindturbineconvertstheslow,high-torquerotationoftheturbineintomuchfasterrotationoftheelectricalgenerator.ThesearemuchlargerandmorecomplicatedthanthePTOgearboxesinfarmequipment.Theyweighseveraltonsandtypicallycontainthreestagestoachieveanoverallgearratiofrom40:1toover100:1,dependingonthesizeoftheturbine.(Foraerodynamicandstructuralreasons,largerturbineshavetoturnmoreslowly,butthegeneratorsallhavetorotateatsimilarspeedsofseveralthousandrpm.)Thefirststageofthegearboxisusuallyaplanetarygear,forcompactness,andtodistributetheenormoustorqueoftheturbineovermoreteethofthelow-speedshaft.Durabilityofthesegearboxeshasbeenaseriousproblemforalongtime.Regardlessofwheretheyareused,thesesimpletransmissionsallshareanimportantfeature:thegearratiocannotbechangedduringuse.Itisfixedatthetimethetransmissionisconstructed.Fortransmissiontypesthatovercomethisissue,seeContinuouslyVariableTransmission,alsoknownasCVT.Multi-ratiosystemsManyapplicationsrequiretheavailabilityofmultiplegearratios.Often,thisistoeasethestartingandstoppingofamechanicalsystem,thoughanotherimportantneedisthatofmaintaininggoodfuelefficiency.AutomotivebasicsTheneedforatransmissioninanautomobileisaconsequenceofthecharacteristicsoftheinternalcombustionengine.Enginestypicallyoperateoverarangeof600toabout7000revolutionsperminute(thoughthisvaries,andistypicallylessfordieselengines),whilethecar'swheelsrotatebetween0rpmandaround1800rpm.Furthermore,theengineprovidesitshighesttorqueoutputsapproximatelyinthemiddleofitsrange,whileoftenthegreatesttorqueisrequiredwhenthevehicleismovingfromrestor