Open Differential and locking Differential.docx

Open Differential and locking Differential.docx

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OpenDifferentialandlockingDifferential

OpenDifferential

Anopendifferentialisthemechanismthatreceivesthepowerfromthetransmissionusuallythroughadriveshaftandsplitsthatpowerintwoandsendsittotheleftandrightofthedrivenwheelsandallowsthemtorotateatdifferentspeeds.

 Theopendifferentialoftenreferredtoasjustadifferentialcanalsobeusedtosplitthepowerbetweenthefrontandrearwheelsinaall/fourwheeldrivevehiclesandthentwootherdifferentialscanfurthersplitthepowertotheleftandrightwheels.

 Theabilitytorotatebothdrivenwheelsatdifferentspeedsistheprimaryobjectiveofthedifferential,itseparatesthebothwheelsbyallowingthemtohavetheirownfinalshaftinsteadofonecontinuousshaftbetweenthebothwheels.

 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