790043 AFundamental Consideration onShiftMechanism of Automatic Transmission YoshioShindoandHiroshiIto ToyotaMotor Co.,Ltd.(Japan) Tomo-oIshihara Univ.ofTokyo(Japan) ITISCONSIDERED tobeusefulfortheimprove mentofproductivity ofautomatic transmissions toapplymanycommonelements tothoseof variousvehicles. Forthispurpose,itis desirable touseexclusively plateclutches applicable toawiderangeoftorquecapacity astheengaging elements, thatmayalsoresult intheimprovement ofreliability. However, thesubstitution ofplateclutches forbrake bandscausessuchadifficult problem,that theuseofoverrunning clutchesisessentially requiredtohaveagoodshiftqualityinthe widerangesofdrivingconditions. Itresults inanincrease ofweight. Theobjectofthispaperistopropose anewshiftmechanism whichmaysolvetheabove problem. Thenewshiftmechanism ischaracter izedbythemountingofanoverrunning clutch onthe input memberandbytherefinement of shiftcontrolmethodforabettershiftquality. Intherefinement ofthecontrolmethod,the theoretical analysis ontheshiftcharacteristicshasbeenmadeundertheconsideration ofthevibration systemofvehicle. SHIFTMECHANISM Generally, variouselements suchasplate clutches, brakebands,overrunning clutches, coneclutches, etc.areusedastheengaging elements intheshiftmechanism ofautomatic transmissions. Toapplyanautomatic trans missiontovariousvehicles withawiderange ofenginetorquecapacity,itisdesirable to useexclusively plateclutches becauseofits adaptability toawiderangeoftorquecapacity. However, inthecasewhereplateclutches are exclusively usedastheengaging elements (whatiscalled'clutch-to-clutch shiftmecha nism'),itisdifficult tocontrolthetiming ofengagement and/ordisengagement ofplate clutches suitablytothewiderangesofvehicle speedandthrottle openingvariations. To avoidthisdifficulty, anoverrunning clutch ABSTRACT Anewshiftmechanism forautomatic trans missions wasdesigned byconsidering acompact designandabettershiftquality, whichused exclusively plateclutches astheengaging elements oftheplanetary reaction members. Thenewshiftmechanism isusefulforthree orfour-speed automatic transmissions. Inthis design, ashiftcontrolmethodforthenew mechanism andtheeffectofthevibration systemofvehicle ontheshiftqualitywere investigated boththeoretically andexperimen tally.Asresultsofthestudy,itwasclarified thatthenewshiftmechanism showsabetter shiftquality, andthattheshiftcharacter isticsareremarkably affected bythevibration systemofvehicle,especially thetorsional vibration ofrearaxles,theaxlewind-upand thefore-and-aft vibration ofengine. Thenewshiftmechanism hasbeensuccess fullyappliedtoaToyotafour-speed automatic transmission withoverdrive. 219 0096-736X/80/8801-0219$02.50 Copyright ©1980SocietyofAutomotiwe Engineers, Inc. Downloaded from SAE International by University of New South Wales, Sunday, September 16, 2018220 hasbeenusedasthereaction member(whatis called'overrunning clutch-to-clutch shift mechanism' ),thoughithasadisadvantage ofa littleincrease ofweightandaxiallength duetothenecessity ofanadditional clutch fortheenginebraking. Thenewshiftmechanism wasdesignedto overcome theabovedisadvantage. Inorderto simplify theexplanation astothenewshift mechanism, two-speed typemodelsareused. InFig.1,(A),(B)and(C)showconventional shiftmechanisms. Ontheotherhand,(D) showsthenewshiftmechanism consisting ofasingleplanetary gearset,twoclutches, andanoverrunning clutchsetonplanetary inputmember. Thefeatureofthisshiftmechan ismisthattheringgearmemberisdetached fromtheturbine memberbytheoverrunning clutchduringthepower-off upshiftandalso thepower-on downshift andthereforeitis easytocontrolthetimingofengagement and disengagement ofclutches. Thisnewshift mechanism ismoreadvantageous tothethree orfour-speed automatic transmission (See Appendix A). Fig.2showsacontrolmethodforthe newshiftmechanism. Inthemethod, ashift valveforcontrolling thehydraulic pressure appliedtotheclutches andtwotimingvalves forcontrolling thetimingofengagement and disengagement ofclutches areused. FUNDAMENTAL EQUA