Open Differential and locking DifferentialWord文档格式.docx

Open Differential and locking DifferentialWord文档格式.docx

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Ifthereisavehiclethatisrequiredtoonlytravelinastraightlinethenadifferentialwouldnotberequired,thedriveshaftcouldbeconnectedtoasinglefinalshaft.Theproblemwithasingleshaftisthatitdoesnotallowthevehicletocornerproperly.Theouterwheelsrotatefasterthantheinnerwheelsandthelackofadifferentialdoesnotfacilitatethis.

Arearwheeldrivedifferentialwillbeusedtoexplainacommonconfigurationoftheopendifferentialandhowitoperates.

Thedifferentialmechanismishousedinsideofaround-ishmetalcasingwithanopeningatthefronttoconnectthedriveshaftto.Insideofthiscasingisalsolubricatedasanywhereelsewheremetalrubsonoragainstmetal.

Insideofthecasethedriveshaftrotatesadiscusingteethontheedgeofthedriveshaftandthediscsimilartogears.Thisdisccanbeontheleftortherightsideontheinsideofthecasingandwhicheversideitsonitisattachedtooneofthesunwheels（similarinshapetothediscbutsmaller）.

Theshafttobothwheelshasasunwheelinsideofthecasing. 

Bothsunwheelsareconnectedtoeachotherbytwoormoreplanetgearsandtheplanetgearsrotatefromanextensionoffthemaindisc.Allofthesecomponentsrotateasthevehiclemoves.

Evenwithallofthesecomponentsthedifferentialallowsthetwoshaftstoeachhavehalfofthetorqueandhorsepowerandtheyrotateequallywhenmovinginastraightline.

Whenthevehicleiscorneringtheinnerwheelrotatesslowerandoffersmoreresistance,thiscausestheplanetwheelstorotateonitsownaxisanditincreasesthespeedoftheouterbythesamepercentagethattheinnerwheelslowsdown.

Arearwheeldrivevehicleswillhaveonedifferentialwillhaveonedifferential,afrontwheeldrivevehiclewillalsohaveonedifferentialbutitisusuallyintegratedintothetransmission.Aparttimefourwheeldriveshouldhavetwodifferentialsandafulltimefour/allwheeldrivewouldhavethreedifferentialsbutthecenterdifferentialcouldbeintegratedintothetransmission.

Therehavebeenimprovementstothebasicoropendifferentialwhichwouldbethelimitedslipdifferentialandthelockingdifferential.

LockingDifferential

Thelockingdifferentialfunctionsasaregularoropendifferentialbuthastheabilitytolocktheshaftsleadingtothetwowheelsonanaxletogetherandforcesthemtorotateatthesamespeed.Bothwheelsarethereforeoperatingasifwereonasingleshaft.

Alockingdifferentialisdesignedtobeusedindifficultsituationsduringoffroaddrivingasitisnotconstantlylocked.Thereisaswitchtolockthedifferentialforoffroaddrivingandtounlockitforregularasphaltdriving.Alockingdifferentialshouldneverbelockedoncethevehicleisbeingdrivenonapavedroadanditmaynotberequiredtobelockedonlightoffroading.

Thereasonthedifferentialcan'

tbepermanentlylockedduringregulardrivingisbecausetheleftandrightwheelsonthesameaxlerotatesatdifferentspeedsduringcorneringbecausetheouterwheelhasmoredistancetocoverandalockeddifferentialforcesbothwheelstorotateatthesamespeed.Ifbothofthewheelshaveadequatetractiontheouterwheelwillslipandthisputsastrainonthevehicleorthetransmissionmaybedamaged.

Whendrivingoffroadinlowtractionconditionsthelockingdifferentialworkswellasinmanyoccasionsoneofthewheelsmaynothavemuchtractionandcaneasilyspintogetherwiththewheelwiththegrip.Thegroundinoffroadconditionsusuallyconsistofmud,sand,grassorlooseparticlessuchasgravelsoifawheelhastoslipitcanslipwithoutputtinganypressureonthevehicle.

Itiscommonforadedicatedoffroadvehicletohavethreedifferentialsandallthreecanbelockingdifferentials.Oncethevehicleisanfourwheelorallwheeldrivetherewillnaturallybeadifferentialforthefrontandrearaxlesandthethirddifferentialwillbealongthedriveshaftbetweenthefrontandrearaxlesasthefrontandrearwheelsalsocovervariousdistancesduringcornering.

A4WDvehiclewithoutacenterdifferentialwillbeaparttimefourwheeldriveasthevehiclewillhavetoremainintwowheeldriveforonroaddriving.Ifavehicleisaparttimefourwheeldrivethen4WDshouldonlybeselectedwhenthevehicleisbeingdrivenoffroadasthefrontandrearwheelswillrotateatthesamespeedbecausethedriveshaftwithoutacenterdifferentialistheequivalentofhavingaconstantlylockeddifferential.

Thelockingdifferentialisthesuperioralternativeforoffroadmanoeuvresasbothwheelsspinwithequalforceregardlessofwhichwheelreceivesthepowerandthatwheelcanmovethevehicleoutofastickysituation.Thisisopposedtoalimitedslipdifferentialwhichismainlyusedtodirecttorquetothewheelwiththemosttractiontoachievebetterhandlingandperformanceinonroaddriving.

Alockingdifferentialcanbemechanicalorelectronic.Anelectroniclockingdifferentialmaybeautomaticandlockbothshaftsautomaticallyifthevehiclesensesthatonewheelhasnotractionandunlockthemwithtractionisdetectedatbothwheels.

Lockingdifferential

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Alockingdifferential,diff-lockorlockerisavariationonthestandardautomotivedifferential.Alockingdifferentialmayprovideincreasedtractioncomparedtoastandard,or"

open"

differentialbyrestrictingeachofthetwowheelsonanaxletothesamerotationalspeedwithoutregardtoavailabletractionordifferencesinresistanceseenateachwheel.

Alockingdifferentialisdesignedtoovercomethechieflimitationofastandardopendifferentialbyessentially"

locking"

bothwheelsonanaxletogetherasifonacommonshaft.Thisforcesbothwheelstoturninunison,regardlessofthetraction（orlackthereof）availabletoeitherwheelindividually.

Whenthedifferentialisunlocked（opendifferential）,itallowseachwheeltorotateatdifferentspeeds（suchaswhennegotiatingaturn）,thusavoidingtirescuffing.Anopen（orunlocked）differentialalwaysprovidesthesametorque（rotationalforce）toeachofthetwowheels,onthataxle.Soalthoughthewheelscanrotateatdifferentspeeds,theyapplythesamerotationalforce,evenifoneisentirelystationary,andtheotherspinning.（Equaltorque,unequalrotationalspeed）.

Bycontrast,alockeddifferentialforcesbothleftandrightwheelsonthesameaxletorotateatthesamespeedundernearlyallcircumstances,withoutregardtotractionaldifferencesseenateitherwheel.Therefore,eachwheelcanapplyasmuchrotationalforceasthetractionunderitwillallow,andthetorquesoneachside-shaftwillbeunequal.（Unequaltorque,equalrotationalspeeds）.Exceptionsapplytoautomaticlockers,discussedbelow.

Alockeddifferentialcanprovideasignificanttractionadvantageoveranopendifferential,butonlywhenthetractionundereachwheeldifferssignificantly.

Alltheabovecommentsapplytocentraldifferentialsaswellastothoseineachaxle:

full-timefour-wheel-drivevehicleshavethreedifferentials,oneineachaxle,andacentralonebetweenthefrontandrearaxles.

Contents

[hide]

∙1Types

o1.1Automaticlockers

o1.2Selectablelocker

o1.3Spool

∙2Disadvantages

∙3Alternatives

∙4Applications

∙5References

∙6Seealso

Types

Automaticlockers

Automaticlockerslockandunlockautomaticallywithnodirectinputfromthedriver.Someautomaticlockingdifferentialdesignsensurethatenginepowerisalwaystransmittedtobothwheels,regardlessoftractionconditions,andwill"

unlock"

onlywhenonewheelisrequiredtospinfasterthantheotherduringcornering.Theywillneveralloweitherwheeltospinslowerthanthedifferentialcarrieroraxleasawhole,butwillpermitawheeltobeover-drivenfasterthanthecarrierspeed.Themostcommonexampleofthistypewouldbethefamous"

DetroitLocker,"

alsoknownasthe"

DetroitNo-Spin,"

whichreplacestheentiredifferentialcarrierassembly.Others,sometimesreferredtoas"

lunchboxlockers,"

employthestockdifferentialcarrierandreplaceonlytheinternalspidergearsandshaftswithinterlockingplates.Bothtypesofautomaticlockerswillallowforadegreeofdifferentialwheelspeedwhileturningcornersinconditionsofequaltraction,butwillotherwiselockbothaxleshaftstogetherwhentractionconditionsdemandit.

∙Pros:

Automaticaction,nodriverinteractionnecessary,nostoppingfor（dis-）engagementnecessary

∙Cons:

Increasedtirewearandnoticeableimpactondrivingbehavior.Duringcornering,theautomaticlockerischaracterizedbyheavyundersteerwhichtransitionsinstantlytopoweroversteerwhentractionisexceeded.

Someotherautomaticlockersoperateasanopendifferentialuntilwheelspinisencounteredandthentheylockup.Thisstylegenerallyusesaninternalgovernor