变速器英文版文献.docx

变速器英文版文献.docx

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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（orsimply"gears"）,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.

Explanation

Earlytransmissionsincludedtheright-angledrivesandothergearinginwindmills,horse-powereddevices,andsteamengines,insupportofpumping,milling,andhoisting.

Mostmoderngearboxesareusedtoincreasetorquewhilereducingthespeedofaprimemoveroutputshaft（e.g.amotorcrankshaft）.Thismeansthattheoutputshaftofagearboxwillrotateatslowerratethantheinputshaft,andthisreductioninspeedwillproduceamechanicaladvantage,causinganincreaseintorque.Agearboxcanbesetuptodotheoppositeandprovideanincreaseinshaftspeedwithareductionoftorque.Someofthesimplestgearboxesmerelychangethephysicaldirectioninwhichpoweristransmitted.

Manytypicalautomobiletransmissionsincludetheabilitytoselectoneofseveraldifferentgearratios.Inthiscase,mostofthegearratios（oftensimplycalled"gears"）areusedtoslowdowntheoutputspeedoftheengineandincreasetorque.However,thehighestgearsmaybe"overdrive"typesthatincreasetheoutputspeed.

Uses

Gearboxeshavefounduseinawidevarietyofdifferent—oftenstationary—applications,suchaswindturbines.

Transmissionsarealsousedinagricultural,industrial,construction,miningandautomotiveequipment.Inadditiontoordinarytransmissionequippedwithgears,suchequipmentmakesextensiveuseofthehydrostaticdriveandelectricaladjustable-speeddrives.

Simple

Thesimplesttransmissions,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-ratiosystems

Manyapplicationsrequiretheavailabilityofmultiplegearratios.Often,thisistoeasethestartingandstoppingofamechanicalsystem,thoughanotherimportantneedisthatofmaintaininggoodfuelefficiency.

Automotivebasics

Theneedforatransmissioninanautomobileisaconsequenceofthecharacteristicsoftheinternalcombustionengine.Enginestypicallyoperateoverarangeof600toabout7000revolutionsperminute（thoughthisvaries,andistypicallylessfordieselengines）,whilethecar'swheelsrotatebetween0rpmandaround1800rpm.

Furthermore,theengineprovidesitshighesttorqueoutputsapproximatelyinthemiddleofitsrange,whileoftenthegreatesttorqueisrequiredwhenthevehicleismovingfromrestortravelingslowly.Therefore,asystemthattransformstheengine'soutputsothatitcansupplyhightorqueatlowspeeds,butalsooperateathighwayspeedswiththemotorstilloperatingwithinitslimits,isrequired.Transmissionsperformthistransformation.

Manytransmissionsandgearsusedinautomotiveandtruckapplicationsarecontainedinacastironcase,thoughmorefrequentlyaluminiumisusedforlowerweightespeciallyincars.Thereareusuallythreeshafts:

amainshaft,acountershaft,andanidlershaft.

Themainshaftextendsoutsidethecaseinbothdirections:

theinputshafttowardstheengine,andtheoutputshafttowardstherearaxle（onrearwheeldrivecars-frontwheeldrivesgenerallyhavetheengineandtransmissionmountedtransversely,thedifferentialbeingpartofthetransmissionassembly.）Theshaftissuspendedbythemainbearings,andissplittowardstheinputend.Atthepointofthesplit,apilotbearingholdstheshaftstogether.Thegearsandclutchesrideonthemainshaft,thegearsbeingfreetoturnrelativetothemainshaftexceptwhenengagedbytheclutches.

Typesofautomobiletransmissionsincludemanual,automaticorsemi-automatictransmission.

Manual

Mainarticle:

Manualtransmission

Manualtransmissioncomeintwobasictypes:

asimplebutruggedsliding-meshorunsynchronized/non-synchronoussystem,wherestraight-cutspurgearsetsarespinningfreely,andmustbesynchronizedbytheoperatormatchingenginerevstoroadspeed,toavoidnoisyanddamaging"gearclash",andthenowcommonconstant-meshgearboxeswhichcanincludenon-synchronised,orsynchronized/synchromeshsystems,wherediagonalcuthelical（andsometimesdouble-helical）gearsetsareconstantly"meshed"together,andadogclutchisusedforchanginggears.Onsynchromeshboxes,frictionconesor"synchro-rings"areusedinadditiontothedogclutch.

Theformertypeiscommonlyfoundinmanyformsofracingcars,olderheavy-dutytrucks,andsomeagriculturalequipment.

ManualtransmissionsarethemostcommontypeoutsideNorthAmericaandAustralia.Theyarecheaper,lighter,usuallygivebetterperformance,andfuelefficiency（althoughthelatestsophisticatedautomatictransmissionsmayyieldresultsslightlybetterthantheonesyieldedbymanualtransmissions）.Itiscustomaryfornewdriverstolearn,andbetested,onacarwithamanualgearchange.InMalaysia,DenmarkandPolandallcarsusedfortesting（andbecauseofthat,virtuallyallthoseusedforinstructionaswell）haveamanualtransmission.InJapan,thePhilippines,Germany,Italy,Israel,theNetherlands,Belgium,NewZealand,Austria,Bulgaria,theUK,Ireland,Sweden,Estonia,France,Spain,Switzerland,theAustralianstatesofVictoriaandQueensland,FinlandandLithuania,atestpassusinganautomaticcardoesnotentitlethedrivertouseamanualcaronthepublicroad;atestwithamanualcarisrequired.ManualtransmissionsaremuchmorecommonthanautomatictransmissionsinAsia,Africa,SouthAmericaandEurope.

Mostmanualtransmissionsincludebothsynchronizedandunsynchronizedgearing,suchasareversegearandalow-speed"grannygear",bothofwhichcanonlybeshiftedintowhenstopped.Shiftingfromgrannygeartoalowsynchronizedgearisgenerallyavailablewhileinmotion,whileshiftingoutofreversetoanyothergeartypicallyrequiresthevehicletobestopped.

Non-synchronous

Mainarticle:

Non-synchronoustransmissions

Therearecommercialapplicationsengineeredwithdesignstakingintoaccountthatthegearshiftingwillbedonebyanexperiencedoperator.Theyareamanualtransmission,butareknownasnon-synchronizedtransmissions.Dependentoncountryofoperation,manylocal,regional,andnationallawsgoverntheoperationofthesetypesofvehicles（seeCommercialDriver'sLicense）.Thisclassmayincludecommercial,military,agricultural,orengineeringvehicles.Someofthesemayusecombinationsoftypesformulti-p