汽车换挡原理英文版.docx
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汽车换挡原理英文版.docx
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汽车换挡原理英文版
汽车换挡原理(英文版)
Themaincomponentofatransmissioninacaristhegearbox.Thegearsthatareincargearboxesaremadetoactivateorsetinmotionwhenthegearshiftorthegearselectorisactivated.Thegearboxinthecarwillprovidethedriverwithgearreductionfromamotorthatisinhigh-speedtoamuchslowerspeed,butwithamorepowerfulproductionsystem.
Thecarwillpropelforwardwhenthegearboxconvertsthespeedoftheengineintotorque.Togivethecarthemaximumamountoftorqueandspeeditneeds,eachcategoryofthegearshaveacorrespondinggeardesignedthatworksappropriatelywiththegears.
Mostoftenthegearboxesaredesignedtoincreasethetorquewhilealsoreducingthespeedofthedrive-shaftoftheengineinthecar.Thishappenswhenthedrive-shaftinthegearboxrotatesatamuchslowerspeedthanthedrive-shaftoftheengine.Becauseofthereductioninspeed,thiswillconverttheenergyproducedintospeedthrust,andthiscausesthedrive-shaftofthegearboxtorotateproducingmorepower,whichleadstoincreasedtorque.
Whenitcomestomanualtransmissionsincars,thegearboxdesignismuchsimplerandrequiresthemanualmovementofaslidinggear,whichisthemainshaftofthegearboxandusesashiftertochangegears.Thegearleverandtheshifterareattached,whichallowstheslidinggeartomove.Whentheclutchisactivated,theslidinggearwilldisengageoutoftheexistingpositionandwillslidealongthegearboxtoreengageinalowerorhighergear.
Themostmodernmanualgearboxeswillhaveadiagonalgeardesign,andtheywillsitalongsidethemaingearsofthecar.Thisensuresthattheslidinggeariscoordinatedwiththemaingearsofthecar.Thiscoordinationallowstheslidinggeartoeffortlesslyengagewiththerestofthemaingears.Thiswillpreventthegearsfromconflictingwitheachotherandcausingdamagetothetransmission.
Withautomaticgearboxes,itissimilartoamanualgearboxonlythatthetransmissionsystemwillselecttheappropriategearautomatically.Thedriverwillnothavetoshiftthegears;itwilldoitonitsown.Thereisahydraulicsystemintheautomaticgearbox,anditwilldetectthepressureofthefluidsintheenginetoselectthepropergearforthecar.Withanautomaticgearbox,itwilluseatorqueconverterratherthanaclutch.
Transmission,orgearbox?
Latestblogentry
03/21/201107:
00AM
OnStarforeveryone.
Startingthisspring,OnStarwillbeginsellingtheirOnStarAnywhereproductfor
$299.Essentiallyit'sanOnStar-equippedrearviewmirrorthatyouswapoutforyour
existingmirror.It'sdesignedtoallowaccesstomanyofOnStar'sservicesforeitheramonthlyorannualfee.Becausethemirroritselfincludesaccelerometers,itwillallegedlybeabletodetectacrashandcallOnStarforyou.Inaddition,itprovidesaccesstoemergencyservices,stolenvehiclelocation(ithasbuilt-inGPStoo),
turn-by-turnnavigation(callthem,tellthemwhereyouwanttogo,andOnStarwilldownloaddirectionsintoyourmirror),roadsideassistanceandhands-freecallingvia
bluetoothtoyourphone.
NowI'mambivalentaboutOnStar.FranklyIdon'tseethepoint,andIthinktheirfear-mongeringTVcommercialsarepatronisingandunethical.Butthisatleastproductdoesgetridofthebiggestevil-becauseit'sastandalonedevice,it'snot
hookedintoyourcar'son-boardcomputerorenginemanagementsystem,meaning
it'snotopenforhackingandabuse.Ofcoursethisalsomeansthatifyou'redumbenoughtolockyourkeysinyourcar,GMcan'tunlockitforyou.
Howeverbecauseithasamicinitforthehands-freetelephoneintegration,OnStar
willbeabletolistenintowhateverisgoingoninthecar,whenevertheywant,andtheGPScanbeusedtotrackyouwithoutyouknowing.Bothhavehappenedbefore,andbothwillhappenagain-don'tkidyourselfthatthelawwillprotectyouonthatfront.
Soifyou'redesperateforthementalcrutchthatOnStarprovides,anddon'tmindaconstantGMspyinyourcar,it'syoursshortlyfor$299andarecurringfee.
ThatquestiondependsonwhichsideoftheAtlanticyou'reon.
TotheEuropeans,it'sagearbox.TotheAmericans,it'sa
transmission.Althoughtobetruthful,thetransmissionisthe
entireassemblythatsitsbehindtheflywheelandclutch-the
gearboxisreallyasubsetofthetransmissionifyouwanttosplit
hairs.
Eitherway,thispageaimstodealwiththewholeideaofgetting
thepowerfromyourenginetothegroundinordertomoveyour
car(orbike)forwards.
Manualgearboxes-what,whyandhow?
FromtheFuel&EngineBibleyouknowthatthepistonsdrive
themaincrankinyourenginesothatitspins.Idling,itspins
around900rpm.Atspeeditcanbeanythingupto7,500rpm.You
can'tsimplyconnectasetofwheelstotheendofthecrank
becausethespeedistoohighandtoovariable,andyou'dneedto
stalltheengineeverytimeyouwantedtostandstill.Insteadyou
needtoreducetherevolutionsofthecrankdowntoausable
value.Thisisknownasgearingdown-themechanicalprocess
ofusinginterlockinggearstoreducethenumberofrevolutionsofsomethingthatisspinning.
CheckoutAmericanMuscleforallyouraftermarketMustangparts.
Aquickprimeronhowgearswork
InthiscaseI'mtalkingaboutgearsmeaning'toothedwheel'asopposetogearsasin'mycarhas5gears'.Agear(orcog,orsprocket)initsmostbasicformisaflatcircularobjectthathasteethcutintotheedgeofit.Themostbasictypeofgeariscalledaspurgear,andithasstraight-cutteeth,wheretheangleoftheteethisparalleltotheaxisofthegear.Widergearsandthosethatarecutforsmoothermeshingareoftencutwiththeteethatanangle,andthesearecalledhelicalgears.Becauseoftheangleofcut,helicalgearteethhaveamuchmoregradualengagementwitheachother,andassuchtheyoperatealotmoresmoothlyandquietlythanspurgears.Gearboxesforcarsandmotorbikesalmostalwaysusehelicalgearsbecauseofthis.Asideeffectofhelicalgearsisthatiftheteetharecutatthecorrectangle-45degrees-apairofgearscanbemeshedtogetherperpendiculartoeachother.Thisisausefulmethodofchangingthedirectionofmovementorthrustinamechanicalsystem.Anothermethodwouldbetousebevelgears.
Thenumberofteethcutintotheedgeofageardeterminesitsscalarrelativetoothergearsinamechanicalsystem.Forexample,ifyoumeshtogethera20-toothgearanda10-tooth
gear,thendrivethe20-toothgearforonerotation,itwillcausethe10-toothgeartoturntwice.Gearratiosarecalculatedbydivindingthenumberofteethontheoutputgearbythenumberofteethontheinputgear.Sothegearratiohereisoutput/input,10/20=1/2=1:
2.Gearratiosareoftensimplifiedtorepresentthenumberoftimestheoutputgearhastoturnonce.Inthisexample,1:
2is0.5:
1-"pointfivetoone".Meaningtheinput
gearhastospinhalfarevolutiontodrivetheoutputgearonce.Thisisknownasgearingup.
Gearingdownisexactlythesameonlytheinputgearisnowtheonewiththeleastnumberofteeth.Inthiscase,drivingthe10-toothgearastheinputgeargivesusoutput/inputof20/10=2/1=2:
1-"twotoone".Meaningtheinputgearhastospin
twicetodrivetheoutputgearonce.
Bymeshingmanygearstogetherofdifferentsizes,youcancreateamechanicalsystemtogearuporgeardownthenumberofrotationsveryquickly.Asafinalexample,imagineaninputgearwith10teeth,asecondarygearwith20teethandafinalgearwith30teeth.Fromtheinputgeartothesecondarygear,theratiois20/10=2:
1.Fromthesecondgeartothefinalgear,theratiois30/20=1.5:
1.Thetotalgearratioforthissystemis(2*
1.5):
1,or3:
1.ie.toturntheoutputgearonce,theinputgearhastoturnthreetimes.
Thisalsoneatlyshowshowyoucandothecalculationandmissthemiddlegearratios-ultimatelyyouneedtheratioofinputtooutput.Inthisexample,thefinaloutputis30andtheoriginalinputis10.30/10=3/1=3:
1.
Collectionsofhelicalgearsinagearboxarewhatgivethegearingdownofthespeedoftheenginecranktothefinalspeedoftheoutputshaftfromthegearbox.Thetablebelowshowssomeexamplegearratiosfora5-speedmanualgearbox(inthiscaseaSubaruImpreza).
RPMofgearboxoutputshaftGearRatiowhentheengineisat3000rpm
1st3.166:
1947
2nd1.882:
11594
3rd1.296:
12314
4th0.972:
13086
5th0.738:
14065
Finaldrive-calculatingspeedfromgearboxratios.It's
importanttonotethatinalmostallvehiclesthereisalsoafinalreductiongear.Thisisalsocalledafinaldriveorarear-orfront-axlegearreductionandit'sdoneinthedifferentialwithasmallpiniongearandalargeringgear(seethesectionondifferentialslowerdownthepage).IntheSubaruexampleabove,itis4.444:
1.Thisisthefinalreductionfromtheoutputshaftofthegearboxtothedriveshaftscomingoutofthedifferentialtothewheels.Sousingtheexampleabove,in5thgear,at3000rpm,thegearboxoutputshaftspinsat4065rpm.Thisgoesthrougha4.444:
1reductioninthedifferentialtogiveawheeldriveshaftrotationof914rpm.ForaSubaru,assumeawheelandtyrecomboof205/55R16givingacircumferenceof1.985mor6.512ft(seeTheWheel&TyreBible).Eachminute,thewheel
spins914timesmeaningitmovesthecar(914x6.512ft)=5951ftalongtheground,or1.127miles.Inanhour,that's(60minutesx1.127miles)=67.62.Inotherwords,knowingthe
gearboxratiosandtyresizes,youcanfigureoutthatat3000rpm,thiscarwillbedoing67mphin5thgear.
Makingthosegearsworktoget
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