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1、UNIT4IntroductiontoDriveTrainPartITechnicalandPracticalReadingPassageADriveTrain(I)Thedrivetrainservestwofunctions:ittransmitspowerfromtheenginetothedrivewheels,anditvariestheamountoftorque.“Power”isthespeedatwhichworkisperformed.“Torque”istwistingforce.Thedrivetrainincludes:transmissiontha
2、tisconnectedtothebackoftheengineandsendsthepowerfromtheenginetothedrivewheels;driveshaftthattransmitsthepowerfromtransmissiontodifferential;anddifferentialthatsendsthepowertothetwowheelaxles.Seefigure4-1.Figure4-1Sometypesofdrivetrainlayoutsusea“transaxle”,whichissimplyacombinationofthetran
3、smissionandthedifferential.Theseareusuallyfoundonfrontwheeldrivecars,butarealsousedonrear-enginecars.Seefigure4-2.Figure4-2FrontwheeldrivelayoutTransmissionTypeTherearetwotypesoftransmissions:manualandautomatic.Ifyouhaveamanualtransmission,youhavetoshiftthegearsyourself,usuallywithastickloc
4、atedonyourconsoleandtheclutchpedal.Ifyouhaveanautomatictransmission,themechanismchangeswithoutanyhelpfromyou.Thisisaccomplishedthroughasystemthatworksbyoilpressure.Eachshiftofthegearsiscontrolledbyashiftvalve;andthegearchangesdependonspeed,theroad,andloadconditions.Bothmanualtransmission(wi
5、thitsclutch)andautomatictransmission(plusitstorqueconverter)accomplishexactlythesamething,buttheydoitintotallydifferentways.Seefigure4-3.Figure4-3ManualTransmissionManualtransmissionsusuallyhavefourorfivespeeds,andoftenhave“overdrive”,whichmeansthattheoutputshaftcanturnfasterthantheinputsha
6、ftforfueleconomyonthehighway.Ingeneral,transmissionswithmorespeedsprovidebetterfueleconomyandsmoothershifting,buttheycostmoretomanufacture,sosmallsub-compactcarswilloftenhaveoptional4speedtransmissions,whilemoreupscalecarswillhave5or6speedtransmissions.Seefigure4-4.Figure4-4AutomaticTransmi
7、ssionThemodernautomatictransmissionisbyfarthemostcomplicatedmechanicalcomponentintoday’sautomobile. Automatictransmissionscontainmechanicalsystems,hydraulicsystems,electricalsystemsandcomputercontrols,allworkingtogetherinperfectharmony.Allautomatictransm
