变速器英文版文献Word格式.docx
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变速器英文版文献Word格式.docx
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),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"
)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
Non-synchronoustransmissions
Therearecommercialapplicationsengineeredwithdesignstakingintoaccountthatthegearshiftingwillbedonebyanexperiencedoperator.Theyareamanualtransmission,butareknownasnon-synchronizedtransmissions.Dependentoncountryofoperation,manylocal,regional,andnationallawsgoverntheoperationofthesetypesofvehicles(seeCommercialDriver'
sLicense).Thisclassmayincludecommercial,military,agricultural,orengineeringvehicles.Someofthesemayusecombinationsoftypesformulti-p
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