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AT02 torque converter.pdf

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AT02 TORQUE CONVERTER
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6 TOYOTA Technical Training 1. Describethefunctionofthetorqueconverter. 2. Identifythethreemajorcomponentsofthetorqueconverterthat contributetothemultiplicationoftorque. 3 Describetheoperationofeachmajortorqueconvertercomponent. 4. Describetheoperationofthelock-upmechanismofthetorque converter. 5. Distinguishbetweenvortexflowandrotaryflowinatorque converter. 6. Identifytwosymptomsofafailedstatorone-wayclutch. 7. Determinewhenreplacementorserviceoftheconverteris appropriate. Section 2 TORQUE CONVERTER Lesson ObjectivesTORQUE CONVERTER Automatic Transmissions - Course 262 7 Thetorqueconverterismountedontheinputsideofthetransmission geartrainandconnectedtoadriveplate.Thedriveplate,orflexplate asitissometimesreferredto,isusedtoconnecttheconvertertothe crankshaftflywheelflangeoftheengine.Theringgear,whichthe startermotorengagestoturntheengine,isattachedtothedriveplate. Torque Converter Transmits engine torqueto the transmissioninput shaft. Roleofthe torqueconverter: w Multipliestorquegeneratedbytheengine. w Servesasanautomaticclutchwhichtransmitsenginetorquetothe transmission. w Absorbstorsionalvibrationoftheengineanddrivetrain. w Smoothesoutenginerotation. w Drivestheoilpumpofthehydrauliccontrolsystem. Thetorqueconverterisfilledwithautomatictransmissionfluid,and transmitstheenginetorquetothetransmission.Thetorqueconverter caneithermultiplythetorquegeneratedbytheengineorfunctionasa fluidcoupling. Thetorqueconverteralsoservesastheengineflywheeltosmoothout enginerotationasitsinertiahelpstomaintaincrankshaftrotation betweenpistonpowerpulses.Ittendstoabsorbtorsionvibrationfrom theengineanddrivetrainthroughthefluidmediumsincethereisno directmechanicalconnectionthroughtheconverter. Inaddition,therearhubofthetorqueconverterbodydrivesthe transmissionoilpump,providingavolumeoffluidtothehydraulic system.Thepumpturnsanytimetheenginerotates,whichisanSECTION 2 8 TOYOTA Technical Training importantconsiderationwhenavehicleistowed.Ifthevehicleistowed withthedrivewheelsonthegroundandtheengineisnotrunning,the axlesdrivethetransmissionoutputshaftandintermediateshafton bearingsthatreceivenolubrication.Thereisagreatpotentialfor damageifthevehicleistowedforalongdistanceoratgreaterthanlow speeds. Thetorqueconverter’sthreemajorcomponentsare;thepumpimpeller, turbinerunnerandthestator.Thepumpimpellerisfrequently referredtoassimplytheimpellerandtheturbinerunnerisreferredto astheturbine. Theimpellerisintegratedwiththetorqueconvertercase,andmany curvedvanesthatareradiallymountedinside.Aguideringisinstalled ontheinneredgesofthevanestoprovideapathforsmoothfluidflow. Torque Converter - Impeller The vanes of the stator catch the fluid as it leaves the turbine and redirects it back to the impeller. Whentheimpellerisdrivenbytheenginecrankshaft,thefluidinthe impellerrotateswithit.Whentheimpellerspeedincreases,centrifugal forcecausesthefluidtoflowoutwardtowardtheturbine. Torque Converter Components Pump ImpellerTORQUE CONVERTER Automatic Transmissions - Course 262 9 Theturbineislocatedinsidetheconvertercasebutisnotconnectedto it.Theinputshaftofthetransmissionisattachedbysplinestothe turbinehubwhentheconverterismountedtothetransmission.Many cuppedvanesareattachedtotheturbine.Thecurvatureofthevanesis oppositefromthatoftheimpellervanes.Thereforewhenthefluidis thrustfromtheimpeller,itiscaughtinthecuppedvanesoftheturbine andtorqueistransferredtothetransmissioninputshaft,turningitin thesamedirectionastheenginecrankshaft. Torque Converter - Turbine Fluid is caught in the cupped vanes of the turbine and torque is transferred to the input shaft. Beforemovingontothenextcomponentofthetorqueconverterwe needtoexaminethefluidcouplingwhosecomponentswehavejust described.Whenautomatictransmissionsfirstcameonthescenein thelate1930s,theonlycomponentsweretheimpellerandtheturbine. Thisprovidedameansoftransferringtorquefromtheenginetothe transmissionandalsoallowedthevehicletobestoppedingearwhile theenginerunsatidle.However,thoseearlyfluidcouplingshadone thingincommon;accelerationwaspoor.Theenginewouldlaboruntil thevehiclepickedupspeed.Theproblemoccurredbecausethevanes ontheimpellerandturbinearecurvedintheoppositedirectiontoone another.Fluidcomingoffoftheturbineisthrustagainsttheimpeller inadirectionoppositetoenginerotation. Noticetheillustrationofthetorqueconverterstatoronthefollowing page;thearrowdrawnwiththedashedlinesrepresentsthepathof fluidifthestatorwerenotthere,suchasinafluidcoupling.Notonlyis enginehorsepowerconsumedtopumpthefluidinitially,butnowitalso hastoovercometheforceofthefluidcomingfromtheturbine.The statorwasintroducedtothedesigntoovercomethecounterproductive forceoffluidcomingfromtheturbineopposingenginerotation.Itnot onlyovercomestheproblembutalsohastheaddedbenefitof increasingtorquetotheimpeller. Turbine Runner Fluid CouplingSECTION 2 10 TOYOTA Technical Training Thestatorislocatedbetweentheimpellerandtheturbine.Itis mountedonthestatorreactionshaftwhichisfixedtothetransmission case.Thevanesofthestatorcatchthefluidasitleavestheturbine runnerandredirectsitsothatitstrikesthebackofthevanesofthe impeller,givingtheimpelleranaddedboostortorque.Thebenefitof thisaddedtorquecanbeasgreatas30%to50%. Torque Converter - Stator The vanes of the stator catch the fluid as it leaves the turbine and redirects it back to the impeller Theone-wayclutchallowsthestatortorotateinthesamedirectionas theenginecrankshaft.However,ifthestatorattemptstorotateinthe oppositedirection,theone-wayclutchlocksthestatortopreventit fromrotating.Thereforethestatorisrotatedorlockeddependingon thedirectionfromwhichthefluidstrikesagainstthevanes. StatorTORQUE CONVERTER Automatic Transmissions - Course 262 11 Nowthatwe’velookedatthepartswhichmakeupthetorque converter,let’slookatthephenomenonoffluidflowwithinthetorque converter.Whentheimpellerisdrivenbytheenginecrankshaft,the fluidintheimpellerrotatesinthesamedirection.Whentheimpeller speedincreases,centrifugalforcecausesthefluidtoflowoutwardfrom thecenteroftheimpellerandflowsalongthevanesurfacesofthe impeller.Astheimpellerspeedrisesfurther,thefluidisforcedout awayfromtheimpellertowardtheturbine.Thefluidstrikesthevanes oftheturbinecausingtheturbinetobeginrotatinginthesame directionastheimpeller. Afterthefluiddissipatesitsenergyagainstthevanesoftheturbine,it flowsinwardalongthevanesoftheturbine.Whenitreachesthe interioroftheturbine,theturbine’scurvedinnersurfacedirectsthe fluidatthevanesofthestator,andthecyclebeginsagain. Stator Operation The stator one-way clutch locks the stator counterclockwise and freewheels clockwise. Converter OperationSECTION 2 12 TOYOTA Technical Training We’vealreadymentionedthattheimpellercausesthefluidtoflowto theturbineandtransferstorquethroughthefluidmediumandthen passesthestatorandbacktotheimpeller.Buttherearetimeswhen thisflowisquickerandmorepowerfulthanatothertimes,andthere aretimeswhenthisflowisalmostnonexistent. Therearetwotypesoffluidflowwithintheconverter:oneisvortex flow,andtheotherisrotaryflow.Intheillustrationoftheconverter fluidflowbelow,vortexflowisaspiralingflowwhichcontinuesaslong asthereisadifferenceinspeedbetweentheimpellerandtheturbine. Rotaryflowisfluidflowwhichcirculateswiththeconverterbody rotation. Converter Fluid Flow Vortex flow is strongest when the difference in impeller and turbine speed is the greatest Theflowisstrongerwhenthedifferenceinspeedbetweentheimpeller andtheturbineisgreat,aswhenthevehicleisacceleratingfor example.Thisiscalledhighvortex.Duringthistimetheflowoffluid leavingtheturbinestrikesthefrontofthevanesofthestatorandlocks itonthestatorreactionshaft,preventingitfromrotatinginthe counterclockwisedirection.Thefluidpassingthroughthestatoris redirectedbytheshapeofthevanesandstrikesthebackofthevanes oftheimpellerresultinginanincreaseintorqueoverthatwhichis providedbytheengine.Withoutthestator,thereturningfluidwould interferewithnormalimpellerrotation,reducingitseverely. Converter Fluid Flow Vortex and Rotary FlowTORQUE CONVERTER Automatic Transmissions - Course 262 13 Fluid Flow While Vehicle is Accelerating Impeller turning much faster than turbine. Duringtimesoflowvortexflowthefluidcomingfromtheturbine strikestheconvexbackofthevaneratherthantheconcavefaceofthe vane.Thiscausestheone-wayclutchtoreleaseandthestator freewheelsonthereactionshaft.Atthispointthereislittleneedfor torquemultiplication. Astherotatingspeedoftheimpellerandtheturbinebecomecloser,the vortexflowdecreasesandthefluidbeginstocirculatewiththeimpeller andturbine.Thisflowisreferredtoasrotaryflow.Rotaryflowisthe flowoffluidinsidethetorqueconverterinthesamedirectionastorque converterrotation.Thisflowisgreatwhenthedifferenceinspeed betweentheimpellerandturbineissmall,aswhenthevehicleisbeing drivenataconstantspeed.Thisiscalledthecouplingpointofthe torqueconverter.Atthecouplingpoint,likethelowvortex,thestator mustfreewheelintheclockwisedirection.Shouldthestatorfailto freewheel,itwouldimpedetheflowoffluidandtendtoslowthe vehicle. Fluid Flow While Vehicle is Cruising Impeller and Turbine at almost same speedSECTION 2 14 TOYOTA Technical Training Nowthatweunderstandtheoperationofthestator,let’sexaminewhat wouldhappenifthestatorwastomalfunction.First,ifthestatorwas tolock-upinbothdirections,atperiodsofhighvortexthestatorwould functionjustperfectly.Thefluidwouldberedirected,hitthebackside oftheimpellervanesandmultiplytorqueandperformanceatlowend wouldbejustfine.But,astheimpellerandturbinereachthecoupling point,thefluidwouldhitthebackofthestatorvanesanddisruptthe flowoffluid.Thiswouldhindertheflowoffluidandcausefluidto bounceoffthevanesinadirectionthatwouldopposetheflowfromthe impellertotheturbine.Thiswouldcausetheconvertertoworkagainst itselfandcauseperformanceattopendtobepoor.Continuedoperation atthiscouplingpointwouldcausethefluidtooverheatandcanalso affecttheoperatingtemperatureoftheengine. Atypicalscenariomightbethatthecustomeroperatesthevehicle aroundtownonsurfacestreetsandthereisnoindicationofaproblem. Howeverwhenthevehicleisdrivenontheexpresswayforany appreciabledistance,theengineoverheatsanddoesnothavethetop endperformanceitoncehad. Second,ifthestatorwastofree-wheelinbothdirections,thefluidfrom theturbinehittingthevanesofthestatorwouldcauseittoturn backwardsandwouldnotredirectthefluidandstriketheimpeller vanesintheoppositedirectionofenginerotation,ineffect,reducing thetorqueconvertertoafluidcouplingwithnobenefitoftorque multiplication.Performanceonthelowerendwouldbepoor, accelerationwouldbesluggish.However,topendperformancewhen thestatorfreewheelswouldbenormal. Thetorqueconverterisasealedunitand,assuch,itisnotserviceable. However,ifcontaminationisfoundinthetransmissionthenitwillalso befoundinthetorqueconverter.Ifthecontaminationintheconverter isnotdealtwith,itwillcontaminatetheoverhauledtransmissionand causeacome-back.Sofornon-lock-upconverters,flushtheconverter offthevehiclewithspecializedequipment.Flushingtheconverterwith specializedequipmentisnotrecommendedforlock-upconvertersasit maydeterioratetheclutchmaterial.Ifcontaminationexistsanditisa lock-upconverter,replacementisrequired. Converter Diagnosis ServiceTORQUE CONVERTER Automatic Transmissions - Course 262 15 Therearetwowaystotestatorqueconverter.Thefirstmethodof testingiswhileitisinthevehicle;thisiscalledatorqueconverterstall test.Thesecondtestmethodiswhiletheconverterisonthebench,and specialtoolsareusedtodeterminetheconditionofthestatorone-way clutch. Inordertobenchtesttheconverter,thestatorone-wayclutchmust lockinonedirectionandfreewheelintheother.Twospecialservice toolsareusedtoperformthetest:thestatorstopperandtheone-way clutchtesttoolhandle.Refertothevehiclerepairmanualunderthe headingof“TorqueConverterandDrivePlate“fortheappropriatetool setbecausethereareseveraldifferenttoolsets.Thetoolsetnumberis listedbeforethetoolnumberinthetextoftherepairmanual. Sincetheone-wayclutchissubjecttogreaterloadwhileinthevehicle (whileonthebenchisonlysubjecttotheloadyoucanplacebyhand), finaldeterminationismadewhenitisinthevehicle.Youneedtobe familiarwiththesymptomsofthetestdrive,customercomplaintand theconditionoftheholdingdevicesinthetransmissionupon disassembly.Allthisinformationisimportanttodeterminethe conditionoftheconverter. Bench Testing the Torque Converter Place the converter on its side and use the stator stopper which locks the stator to the converter case while the test tool handle is turned clockwise and then counterclockwise. Torque Converter Testing Bench TestingSECTION 2 16 TOYOTA Technical Training Thetermstallistheconditionwheretheimpellermovesbutthe turbinedoesnot.Thegreatestamountofstallhappenswhenthepump impellerisdrivenatthemaximumspeedpossiblewithoutmovingthe turbine.Theenginespeedatwhichthisoccursiscalledthetorque converterstallspeed. Beforestalltestingatorqueconverter,considerthecustomercomplaint andyourtestdrivesymptoms.Thesymptomsdiscussedpreviously regardingpoortopendperformanceorpooraccelerationmayalready pointtothetorqueconverterastheproblem.Aroadtestofthevehicle’s accelerationandforceddownshiftwillindicateaslippingstatorif accelerationispoor.Poortopendperformancew
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