Open Differential and locking Differential.docx
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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
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