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AT08 valve body circuit.pdf

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AT08 VALVE BODY CIRCUIT
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88 TOYOTA Technical Training 1. Describe the function of pressure control valves in the valve body as they apply to: w Slippage w Upshifting w Downshifting w Lubrication 2. Describe the function of shift control valves in the valve body as they apply to: w Line pressure distribution w Downshifting w Upshifting 3. Describe the function of timing (sequencing) valves in the valve body as they apply to: w Manual second gear downshift quality w Manual low gear shift quality w Reverse gear engagement quality w Automatic upshift and downshift engagement 4. Describe the function of pressure modulating valves in the valve body as they apply to: w Manual second gear downshift quality w Manual low gear shift quality w Control of line at cruise speed 5. Explain the effect that throttle pressure and governor pressure have on the shift valves and clutch application. 6. Describe the effect of the shift solenoids on the position of the shift valves in each of the following gear ranges: w First gear w Second gear w Third gear w Fourth gear Section 8 VALVE BODY CIRCUITS Lesson Objectives:VALVE BODY CIRCUITS Automatic Transmissions - Course 262 89 Thevalvebodyconsistsofanuppervalvebody,alowervalvebodyand amanualvalvebody.Thetwobodyhalvesareseparatedbyaseparator platewhichcontainsopeningsthatcontroltheflowoffluidbetween valvecircuits.Thevalvescontainedthereincontrolfluidpressureand switchfluidfromonepassagetoanother.Hydrauliccircuitsextendto thetransmissionhousingandareconnectedeitherbydirectmounting orthroughoiltubepassages. Thevalvesareaprecisionfittotheboreinthebody,andtheirposition isdeterminedbyabalancebetweenspringtensionandhydraulic pressure.Hydraulicpressurewithinthevalvebodywillvarybasedon throttlepositionorpressuremodulatingvalves.Inthecaseofa non-ECTtransmission,pressurealsovariesbasedonvehiclespeed throughthegovernorvalve. Inordertounderstandwhatthemanyvalvesdointhevalvebody,they havebeenseparatedbyfunctionaslistedbelow: w Pressurecontrolvalves w Hydrauliccontrolvalves w Timing(Sequencing)valves w Pressuremodulatingvalves Pressurecontrolvalvesregulatepressurewithinthetransmission. Hydraulicpressureisnecessarytoapplytheclutches,brakes,and bandsthatholdplanetarygearcomponentsofthetransmission.There aretimeswhenhighpressureisnecessaryandothertimeswhenitis lessimportant.Theprimaryconcernwithhighpressureisthatengine powerislostandexcessiveheatisgenerated.Heatbreaksdownthe transmissionfluidandrobsitofitsproperties.Ontheotherhand,fuel economyisimportanttoachieve,sobyregulatingpressure,lessloadis placedontheengine. Thisvalveadjuststhepressurefromtheoilpumptoallthehydraulic circuitsinthetransmission.Thepurposeofthevalveistoreduce engineloadandpowerloss.Ifpressureremainedhigh,itwouldcause hardshiftingandwouldcreatemoreheatwhichwouldbeaproblemfor fluidlife,andadditionalenginepowerislostjustturningthepump.By reducingpressure,lesspowerisrequiredtorotatethepumpandless heatisgenerated. Theamountofpressurehasadirecteffectontheholdingforceof clutchesandbrakes.Itshouldbehighwhenacceleratingthevehiclein firstorreversegear.Asthevehiclepicksupspeed,lessholdingforceis needed,andtherefore,pressureisdecreased. Theoutputofthevalveiscalledthe“linepressure,“thehighestoil pressureanywhereinthetransmission.Linepressureisshowninthe colorredatalltimesinToyotapublications. Pressure Control Valves Primary Regulator ValveSection 8 90 TOYOTA Technical Training Thepositionoftheprimaryregulatorvalveisdeterminedbythrottle pressure,linepressureandspringtension.Springtensionpushesthe valveupforhigherlinepressure.Linepressureisroutedtothetopof thevalveandcountersspringtensiontoreducelinepressure.The overalleffectisabalancebetweenlinepressureandspringtension. Primary Regulator Valve Atthebaseofthevalve,throttlepressureisappliedtopushthevalve upward,increasinglinepressure.Thegreaterthethrottleopening,the greaterlinepressurebecomesasthepressureregulatorvalvebleedsoff lesspressure.VALVE BODY CIRCUITS Automatic Transmissions - Course 262 91 Linepressureisalsoincreasedwhenreversegearisselected.Line pressurefromthemanualvalveisdirectedtothebottomofthevalve pushingitupward,increasinglinepressurebyasmuchas50%. Primary Regulator Valve in R-Range Thisvalveregulatestheconverterpressureandlubricationpressure. Springtensionpushesthevalveupwardtoincreaseconverterpressure. Converterpressureactsonthetopofthevvalvetocreateaalance betweenitandspringtension.Inaddition,insomeapplicatioSection 8 92 TOYOTA Technical Training Thisvalvepreventsexcessivepressureinthecircuittotheoilcooler. Thecircuitisalowpressuresystemwhichroutesoilthroughtheoil coolerinthetankoftheradiatorandbacktothesumpofthe transmission.Thevalveisspringloadedintheclosedposition.When pressureexceedsthespringrate,excesspressureisrelieved. Oil Cooler By-Pass Valve and Pressure Relief Valve Thisvalveregulatestheoilpumppressuresothatitdoesnotrise aboveapredeterminedmaximumvalue.Acalibratedspring-isusedto controlthepressurebyholdingthevalveagainstitsseat. Oil Cooler By-Pass Valve Pressure Relief ValveVALVE BODY CIRCUITS Automatic Transmissions - Course 262 93Section 8 94 TOYOTA Technical Training Thisvalveisfoundonallnon-ECTtransmissions.Itismountedonthe outputshaftofrear-wheeldrivetransmissionsorisdrivenfromthe drivegearonthedifferentialdrivepinion/outputshaftonfront-wheel drivetransmissions.Itbalancesthelinepressureroutedfromthe manualvalveandthecentrifugalforceofthegovernorweightsto producehydraulicpressureinproportiontovehiclespeed.Thegreater thespeedoftheoutputshaft,thegreaterthegovernorpressure. Thepartswhichmakeupthegovernorincludeaninnerweightandan outerweightmountedtothegovernorbody.Bothweightsarehingedat theiraxispoint.Thecalibratedspringspushtheouterweightsin towardthecenterofthegovernor.Theleverendsoftheinnerweights pushdownonthegovernorvalve.Thegovernorvalveislocatedinthe centerofthegovernorbodyandispushedupwardbygovernorpressure throughadrilledpassageinthevalve. Below10mph,centrifugalforceislowandlinepressureentering throughthedrilledpassageinthevalvetothebaseofthevalvepushes thevalveupward,blockingthelinepressurepassageandopeningthe drainatthetopland. Governor Valve Line pressure to the base of the valve moves it upward, opening the drain pport. Centrifugal force does not begin to push the valve down until approximately 10 mph. Governor ValveVALVE BODY CIRCUITS Automatic Transmissions - Course 262 95 Asthegovernorturns,thecentrifugalforceoftheinnerandouter weightsalongwiththespringcausetheweightstoopenoutward.As theweightsmoveoutward,thegovernorvalveispusheddownwardby theleveroftheinnerweights.Thegovernorvalvepositionisbalanced betweencentrifugalforceactingontheleveratthetopofthevalveand governorpressureatthebaseofthevalve.Thebalanceofthesetwo forcesbecomesthegovernorpressureatthatvehiclespeed. Astherpmincreases(middleandhighspeed)theouterweight movementislimitedbythestopperofthegovernorbody.Increased governorpressureactingonthebaseofthevalveworksagainstspring tension.Withincreasedrpmsthecentrifugalforceoftheinnerweight andspringtensionplacesadditionalforcetopushthevalvedown. Governorpressurewillremainat0psiuntilapproximately10mph. Forspecificgovernorpressures,besuretochecktheappropriaterepair manualwhichwillgiveapressureandvehiclespeedrelationship. GovernorpressureshowninToyotapublicationsisalwaysgreen. Governor Valve Governor pressure increases as weights move outward by centrifugal forceSection 8 96 TOYOTA Technical Training Thethrottlevalveproducesthrottlepressureinresponsetothrottle openingangle.Whentheacceleratorpedalisdepressed,thedownshift plugispushedupwardviathethrottlecableandthrottlecam.The throttlevalvethereforemovesupwardbymeansofthespring,opening thepressurepassageandmodifyinglinepressuretothrottlepressure. ThrottlepressureshowninToyotapublicationsisalwaysblue. Thisthrottlepressurealsoactsonthethrottlevalve,pushingitdown againstthespringtension.Thethrottlevalvesuppliesthrottle pressuretoeachshiftvalveandactsinoppositiontogovernor pressure. Throttlepressurealsoaffectslinepressureeitherdirectlyorthrough throttlemodulatorpressure.Hydraulicpressureaffectedbythrottle openingisdirectedtothebaseofthepressureregulatorvalveto increaselinepressurewhenenginetorqueisincreased.Additionalline pressureservestoprovideadditionalholdingforceattheholding devicestopreventslippage. Throttle Valve Throttle pressure is provided to each shift valve to counter governor pressure. Throttle ValvesVALVE BODY CIRCUITS Automatic Transmissions - Course 262 97 Shiftcontrolvalvesareresponsiblefordirectingfluidtodifferent passagesinthetransmission.Theycanbemanuallycontrolled, solenoidcontrolled,orhydraulicallycontrolled.Theyblockhydraulic passageswhileotherlandsofthevalveopenpassages. Thisvalvedirectslinepressuretovariouspassagesinthevalvebody. Itislinkedtothedriver’sselectorleverandshiftsthetransmission intoandoutoftheP,R,N,D,2andLrangesasdirectedbythedriver. Asthevalvemovestotheright,itexposespassagestolinepressure whichwilldeterminethegearselected.Thevariouspositionsofthe valvearemaintainedbyadetentmechanismwhichalsoprovides feedbacktothedriver. Manual Valve Directs line pressure to various passages in the valve body. Shift Control Valves Manual ValveSection 8 98 TOYOTA Technical Training Thisvalvecontrolsshiftingbetweenfirstandsecondgearsbasedon governorandthrottlepressures.Thevalveisheldinpositionbya calibratedspringlocatedbetweenthelowcoastshiftvalveandthe1-2 shiftvalve.Whengovernorpressureislowbutthrottlepressureis high,thisvalveispusheddownbythrottlepressureandspring tension.Infirstgeartheforwardclutch(Cl)isappliedthroughthe manualvalve,andtheone-wayclutchNo.2(F2)isholding.Line pressureisblockedbythevalvefromthesecondbrake(B2)andthe transmissionisheldinfirstgear. Asvehiclespeedbecomesgreater,governorpressureincreasesand overcomesthrottlepressureandspringtensionatthe1-2shiftvalve. Thevalveispushedupbygovernorpressure,andthecircuittothe secondbrakepistonopens,causingthetransmissiontoshifttosecond gear.Whentheshiftvalvemovesup,itcoversthethrottlepressure passage;thusthedownshifttofirstgeardependsonspringtensionand governorpressureonly.Thisoccurswhencoastingtoastop.The downshiftoccurswhenspringtensionovercomesgovernorpressure. Thishappensatsuchalowspeedthatitishardlynoticeable. Forceddownshiftsfromsecondtofirstgearoccurswhenthedownshift plugatthebaseofthethrottlevalveopenstoallowdetentregulator pressuretoactonthetopofthe1-2shiftvalve.Thisforcestheshift valvedown,whichopensthesecondbrakepistontoadrainandthe downshiftoccursasthesecondbrakereleases. WhentheselectorisplacedintheLrange,lowmodulatorpressureis appliedtothetopofthelowcoastshiftvalve,holdingthe1-2shift valveinthefirstgearposition. 1-2 Shift Valve Controls line pressure to the 2nd brake (B2) and the 2-3 shift valve 1-2 Shift ValveVALVE BODY CIRCUITS Automatic Transmissions - Course 262 99 Thisvalvecontrolsshiftingbetweensecondandthirdgearsbasedon throttleandgovernorpressures.Thevalveispositionedbyacalibrated springlocatedbetweentheintermediateshiftvalveandthe2-3shift valve.Whengovernorpressureislowbutthrottlepressureishigh, suchasunderacceleration,thisvalveispusheddownbythrottle pressureandspringtension,holdingthetransmissioninsecondgear. Whengovernorpressureriseswithincreasedvehiclespeed,thisvalve ismovedupwardagainstthrottlepressureandspringtensionopening thepassagetothedirectclutch(C2)pistonandcausingashiftinto thirdgear.Asvehiclespeeddecreaseswiththesameorincreased throttleposition,throttlepressureatthetopofthe2-3shiftvalve causesthevalvetomovedownward,closingthepassagetothedirect clutch(C2).Thepressureinthedirectclutchdrainsandthe transmissionisdownshiftedintosecondgear. Intheeventthattheacceleratorisdepressedatornearfullthrottle, thedetentpressureactsonthe2-3shiftvalvetopermitquicker downshiftingtosecondgear.Asthethrottleisopenedwider,thecamat thebaseofthethrottlevalvepushesthedetentvalveupward.This allowsdetentpressuretoassistthrottlepressureatthetopofthe2-3 shiftvalvepushingdownonthevalve,resultinginfastervalve movement. Inaddition,takenotethatthelinepressurewhichappliesthedirect clutch(C2)comesthroughthe1-2shiftvalve.Soifthis1-2shiftvalve isstuck,therecanbenothirdgearbecausethedirectclutchcannotbe applied. Whenthegearselectorisplacedinthe2-range,linepressurefromthe manualvalveactsontheintermediateshiftvalve.The2-3shiftvalve descends,causingadownshiftintosecondgearandpreventingan upshifttothirdgear.Also,linepressurepassagesthroughthesecond modulatorvalveand1-2shiftvalveandactsonthesecondcoastbrake toeffectenginebraking. 2-3 Shift Valve Controls line pressure to the direct clutch (C2). This line pressure comes through the 1-2 shift valve in the second gear position. 2-3 Shift ValveSection 8 100 TOYOTA Technical Training Thisvalvecontrolsshiftingbetweenthirdandfourthgearsbasedon governorandthrottlepressures.Thevalveisheldinpositionbya calibratedspringlocatedatthetopofthe3-4coastshiftvalvewhich transfersthetensionandholdsthe3-4shiftvalvedown.Linepressure controlledbythe3-4shiftvalvecomesfromtheoilpumpdirectly. Wheneverthepumpisturning,pressureispresentthroughthe3-4 shiftvalvetoeithertheoverdrivedirectclutchortheoverdrivebrake. Whentheoverdrivedirectclutchisapplied,theoverdriveunitisin directdrive.Whentheoverdrivebrakeisapplied,theoverdriveu
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