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1、设计巴巴工作室www.88doc88.comAutomobileTransmissionsandPowerSteeringAutomobiles,trucks,buses,andtractorsalldependontransmissionstodeliverpowerfromtheenginetothewheels,Thegasolineanddieselenginesthatpowerthesevehiclescannotbeconnecteddirectlytothewheels,becausetheeng
2、inesmustkeepturningatacertainseedtokeepfromstalling.Also,differentamountoftorque(turningforce)mustbedeliveredtothewheelsatdifferenttimes.Alargeamountofforceisneededtogetacarmovingfromastandstill.Lessforceisneededtokeepthecarmovingonceitisrolling.Goingupahillo
3、fdrivingathighspeedrequiresstillotheramountofforce.Itisthejobofthetransmissiontodelivertheparticularamountofforcethatisneeded.Thetransmissionalsoallowsamotorvehicletobackup-----gasolineanddieselenginescanruninonlyonedirection,butthetransmissioncanreversethedi
4、rectionoftheforce.Andwhenacarstops,thetransmissionletstheenginekeeprunningwithoutmovingthewheels.Theheartofanytransmission——evenanautomaticone—isasetofgears.Gearsdonotchangethepowerofanengine,buttheycanincreasethetorquebydecreasingthespeed.Theycanalsoincrease
5、thespeedbydecreasingthetorque.Theautomobiletransmissionusesaseriesofgearswhichenablestheenginetocontinuetooperateatmaximumefficiencywhenthevehicle’sspeedisaltered.Settinganautomobileinmotionrequiresalargeamountofpowertoovercometheinertiaofthevehicle’sweight.T
6、hisprocessrequireshighenginespeed,neededforhighpower,andagradualincreaseinavehicle’sspeedtoavoidajerkystart.Todothis,alowgearratioisallowsthecrankshafttorevolveseveraltimesinordertoturntherealaxleonce.Thelowgearratioisusedforstarting,climbingsteepslops,andoth
7、ersituationsinwhichmaximumpowerisrequired.Aspowerneedsarereduced,asecond,highergearratioisusedwhichrotatestherearaxlewithfewerrevolutionsofthecrankshaft.Asthecar’sspeedincreases,successivelyhighergearratiosareuseduntilthedrivefromtheenginetotherearwheelspasse
8、sthroughthetransmissionwithoutreduction.Twoprincipletypesoftransmissionareused,manualandautomatic.Themanualtransmissionsystempermitsthedrivertoselectthedesiredgearratiobymanipulatingashif
