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1、UNIT4IntroductiontoDriveTrainPartITechnicalandPracticalReadingPassageADriveTrain(I)Thedrivetrainservestwofunctions:ittransmitspowerfromtheenginetothedrivewheels,anditvariestheamountoftorque.“Power”isthespeedatwhichworkisperformed.“Torque”istwistingforce.Thedriv
2、etrainincludes:transmissionthatisconnectedtothebackoftheengineandsendsthepowerfromtheenginetothedrivewheels;driveshaftthattransmitsthepowerfromtransmissiontodifferential;anddifferentialthatsendsthepowertothetwowheelaxles.Seefigure4-1.Figure4-1Sometypesofdrivetr
3、ainlayoutsusea“transaxle”,whichissimplyacombinationofthetransmissionandthedifferential.Theseareusuallyfoundonfrontwheeldrivecars,butarealsousedonrear-enginecars.Seefigure4-2.Figure4-2FrontwheeldrivelayoutTransmissionTypeTherearetwotypesoftransmissions:manualand
4、automatic.Ifyouhaveamanualtransmission,youhavetoshiftthegearsyourself,usuallywithasticklocatedonyourconsoleandtheclutchpedal.Ifyouhaveanautomatictransmission,themechanismchangeswithoutanyhelpfromyou.Thisisaccomplishedthroughasystemthatworksbyoilpressure.Eachshi
5、ftofthegearsiscontrolledbyashiftvalve;andthegearchangesdependonspeed,theroad,andloadconditions.Bothmanualtransmission(withitsclutch)andautomatictransmission(plusitstorqueconverter)accomplishexactlythesamething,buttheydoitintotallydifferentways.Seefigure4-3.Figu
6、re4-3ManualTransmissionManualtransmissionsusuallyhavefourorfivespeeds,andoftenhave“overdrive”,whichmeansthattheoutputshaftcanturnfasterthantheinputshaftforfueleconomyonthehighway.Ingeneral,transmissionswithmorespeedsprovidebetterfueleconomyandsmoothershifting,b
7、uttheycostmoretomanufacture,sosmallsub-compactcarswilloftenhaveoptional4speedtransmissions,whilemoreupscalecarswillhave5or6speedtransmissions.Seefigure4-4.Figure4-4AutomaticTransmissionThemodernautomatictransmissionisbyfarthemostcomplicatedmechanicalcomponentin
8、today’sautomobile. Automatictransmissionscontainmechanicalsystems,hydraulicsystems,electricalsystemsandcomputercontrols,allworkingtogetherinperfectharmony.Allautomatictransm
