附录附录A.ManualTransmissionIt’snosecretthatcarswithmanualtransmissionsareusuallymorefuntodrivethantheautomatic-equippedcounterparts.Ifyouhaveevenapassinginterestintheactofdriving,thenchancesareyoualsoappreciateafine-shiftingmanualgearbox.Buthowdoesamanualtransmissionactuallywork?Ahistoryhowsthatmanualtransmissionsprecededautomaticsbyseveraldecades.Infact，upuntilGeneralMotorsofferedanautomaticin1938,allcarswereoftheshift-it-yourselfvariety.Whileit’slogicalformanytypesoftoday’svehiclestobeequippedwithanautomatic――suchasafull-sizesedan,SUVorpickup――thefactremainsthatnothingismoreofathrilltodrivethanatautlysuspendedsportsedan,snortcoupeortwo-sealerequippedwithaprecise-shiftingfive-orsix-speedgearbox．Weknowwhicntypesorcarshavemanualtrannies.Nowlet’stakealookathowtheywork.Fromthemostbasicfour-speedmanualinacarfromthe’60stothemosthigh-techsix-speedoneinacaroftoday,theprinciplesofamanualgearboxarethesame.Thedrivermustshiftfromgeartogear.Normally,amanualtransmissionboltstoaclutchhousing(orbellhousing）,inturn,boltstothebackoftheengine.Ifthevehiclehasfront-wheeldrive,thetransmissionstillattachestotheengineinasimilarfashionbutisusuallyreferredtoasatransaxle.Thisisbecausethetransmission,differentialanddriveaxlesareonecompleteunit.Inafront-wheel-drivecar,thetransmissionalsoservesaspartofthefrontaxleforthefrontwheels.Intheremainingtext,atransmissionandatransaxlewillbothbereferredtousingthetermtransmission.Thefunctionofanytransmissionistransferringenginepowertothedriveshaftandrearwheels(oraxlehalfshaftsandfrontwheelsinafront-wheel-drivevehicle).Gearsinsidethetransmissionchangethevehicle’sdrive-wheelspeedandtorqueinrelationtoenginespeedandtorque．Lower(numericallyhigher)gearratiosserveastorquemultipliersandhelptheenginetodevelopenoughpowertoacceleratefromastandstill.Initially,powerandtorquefromtheenginecomesintothefrontofthetransmissionsandrotatesthemaindrivegear(orinputshaft),whichmesheswiththeclusterorcountershaftgear――aseriesofgearsforgedintoonepiecethatresemblesaclusterofgears.Thecluster-gearassemblyrotatesanytimetheclutchisengagedtoarunningengine，whetherornotthetransmissionisingearorinneutral.Therearetwobasictypesofmanualtransmissions.Thesliding-geartypeandtheconstant-meshdesign.Withthebasic――andnowobsolete――sliding-geartype，nothingisturninginsidethetransmissioncaseexceptthemaindrivegearandclustergearwhenthetransisinneutral.Inordertomeshthegearsandapplyenginepowertomovethevehicle,thedriverpressestheclutchpedalandmovestheshifterhandle,whichinturnmovestheshiftlinkageandforkstoslideagearalongthemainshaft,whichismounteddirectlyabovethecluster.Oncethegearsaremeshed,theclutchpedalisreleasedandtheengine’spowerissenttothedrivewheels.Therecanbeseveralgearsonthemainshaftofdifferentdiametersandtoothcounts,andthetransmissionshiftlinkageisdesignedsothedriverhastounmeshonegearbeforebeingabletomeshanother.Withtheseoldertransmissions,gearclashisaproblembecausethegearsareallrotatingatdifferentspeeds.Allmoderntransmissionsareoftheconstant-meshtype,whichstillusesasimilargeararrangementasthesliding-geartype.However，allthemainshaftgearsareinconstantmeshwiththeclustergears.Thisispossiblebecausethegearsonthemainshaftarenotsplinedtotheshaft,butarefreetorotateonit.Withaconstant-meshgearbox,themaindrivegear,clustergearandallthemainshaftgearsarealwaysturning,evenwhenthetransmissionisi...
