汽车制动系统毕业设计外文资料翻译.docx
《汽车制动系统毕业设计外文资料翻译.docx》由会员分享,可在线阅读,更多相关《汽车制动系统毕业设计外文资料翻译.docx(9页珍藏版)》请在冰豆网上搜索。
![汽车制动系统毕业设计外文资料翻译.docx](https://file1.bdocx.com/fileroot1/2023-2/22/3dffea17-1075-4205-bd45-cef69d9e6798/3dffea17-1075-4205-bd45-cef69d9e67981.gif)
汽车制动系统毕业设计外文资料翻译
AutomobileBrakeSystem
Thebrakingsystemisthemostimportantsystemincars.Ifthebrakesfail,theresultcanbedisastrous.Brakesareactuallyenergyconversiondevices,whichconvertthekineticenergy(momentum)ofthevehicleintothermalenergy(heat).Whensteppingonthebrakes,thedrivercommandsastoppingforcetentimesaspowerfulastheforcethatputsthecarinmotion.Thebrakingsystemcanexertthousandsofpoundsofpressureoneachofthefourbrakes.
Twocompleteindependentbrakingsystemsareusedonthecar.Theyaretheservicebrakeandtheparkingbrake.
Theservicebrakeactstoslow,stop,orholdthevehicleduringnormaldriving.Theyarefoot-operatedbythedriverdepressingandreleasingthebrakepedal.Theprimarypurposeoftheparkingbrakeistoholdthevehiclestationarywhileitisunattended.Theparkingbrakeismechanicallyoperatedbywhenaseparateparkingbrakefootpedalorhandleverisset.
Thebrakesystemiscomposedofthefollowingbasiccomponents:
the“mastercylinder”whichislocatedunderthehood,andisdirectlyconnectedtothebrakepedal,convertsdriverfoot’smechanicalpressureintohydraulicpressure.Steel“brakelines”andflexible“brakehoses”connectthemastercylindertothe“slavecylinders”locatedateachwheel.Brakefluid,speciallydesignedtoworkinextremeconditions,fillsthesystem.“Shoes”and“pads”arepushedbytheslavecylinderstocontactthe“drums”and“rotors”thuscausingdrag,which(hopefully)slowsthecar.
Thetypicalbrakesystemconsistsofdiskbrakesinfrontandeitherdiskordrumbrakesintherearconnectedbyasystemoftubesandhosesthatlinkthebrakeateachwheeltothemastercylinder(Figure).
Basically,allcarbrakesarefrictionbrakes.Whenthedriverappliesthebrake,thecontroldeviceforcesbrakeshoes,orpads,againsttherotatingbrakedrumordisksatwheel.Frictionbetweentheshoesorpadsandthedrumsordisksthenslowsorstopsthewheelsothatthecarisbraked.
Inmostmodernbrakesystems(seeFigure15.1),thereisafluid-filledcylinder,calledmastercylinder,whichcontainstwoseparatesections,thereisapistonineachsectionandbothpistonsareconnectedtoabrakepedalinthedriver’scompartment.Whenthebrakeispusheddown,brakefluidissentfromthemastercylindertothewheels.
Atthewheels,thefluidpushesshoes,orpads,againstrevolvingdrumsordisks.Thefrictionbetweenthestationaryshoes,orpads,andtherevolvingdrumsordisksslowsandstopsthem.Thisslowsorstopstherevolvingwheels,which,inturn,sloworstopthecar.
Thebrakefluidreservoirisontopofthemastercylinder.Mostcarstodayhaveatransparentreservoirsothatyoucanseethelevelwithoutopeningthecover.Thebrakefluidlevelwilldropslightlyasthebrakepadswear.Thisisanormalconditionandnocauseforconcern.Iftheleveldropsnoticeablyoverashortperiodoftimeorgoesdowntoabouttwothirdsfull,haveyourbrakescheckedassoonaspossible.Keepthereservoircoveredexceptfortheamountoftimeyouneedtofillitandneverleaveacamofbrakefluiduncovered.Brakefluidmustmaintainaveryhighboilingpoint.Exposuretoairwillcausethefluidtoabsorbmoisturewhichwilllowerthatboilingpoint.
Thebrakefluidtravelsfromthemastercylindertothewheelsthroughaseriesofsteeltubesandreinforcedrubberhoses.Rubberhosesareonlyusedinplacesthatrequireflexibility,suchasatthefrontwheels,whichmoveupanddownaswellassteer.Therestofthesystemusesnon-corrosiveseamlesssteeltubingwithspecialfittingsatallattachmentpoints.Ifasteellinerequiresarepair,thebestprocedureistoreplacethecompeteline.Ifthisisnotpractical,alinecanberepairedusingspecialsplicefittingsthataremadeforbrakesystemrepair.Youmustneverusecoppertubingtorepairabrakesystem.Theyaredangerousandillegal.
Drumbrakes,itconsistsofthebrakedrum,anexpander,pullbacksprings,astationarybackplate,twoshoeswithfrictionlinings,andanchorpins.Thestationarybackplateissecuredtotheflangeoftheaxlehousingortothesteeringknuckle.Thebrakedrumismountedonthewheelhub.Thereisaclearancebetweentheinnersurfaceofthedrumandtheshoelining.Toapplybrakes,thedriverpushespedal,theexpanderexpandstheshoesandpressesthemtothedrum.Frictionbetweenthebrakedrumandthefrictionliningsbrakesthewheelsandthevehiclestops.Toreleasebrakes,thedriverreleasethepedal,thepullbackspringretractstheshoesthuspermittingfreerotationofthewheels.
Diskbrakes,ithasametaldiskinsteadofadrum.Aflatshoe,ordisk-brakepad,islocatedoneachsideofthedisk.Theshoessqueezetherotatingdisktostopthecar.Fluidfromthemastercylinderforcesthepistonstomovein,towardthedisk.Thisactionpushesthefrictionpadstightlyagainstthedisk.Thefrictionbetweentheshoesanddiskslowsandstopsit.Thisprovidesthebrakingaction.Pistonsaremadeofeitherplasticormetal.Therearethreegeneraltypesofdiskbrakes.Theyarethefloating-calipertype,thefixed-calipertype,andthesliding-calipertype.Floating-caliperandsliding-caliperdiskbrakesuseasinglepiston.Fixed-caliperdiskbrakeshaveeithertwoorfourpistons.
Thebrakesystemassembliesareactuatedbymechanical,hydraulicorpneumaticdevices.Themechanicalleverageisusedintheparkingbrakesfittedinallautomobile.Whenthebrakepedalisdepressed,therodpushesthepistonofbrakemastercylinderwhichpressesthefluid.Thefluidflowsthroughthepipelinestothepowerbrakeunitandthentothewheelcylinder.Thefluidpressureexpandsthecylinderpistonsthuspressingtheshoestothedrumordisk.Ifthepedalisreleased,thepistonreturnstotheinitialposition,thepullbackspringsretracttheshoes,thefluidisforcedbacktothemastercylinderandbrakingceases.
Theprimarypurposeoftheparkingbrakeistoholdthevehiclestationarywhileitisunattended.Theparkingbrakeismechanicallyoperatedbythedriverwhenaseparateparkingbrakinghandleverisset.Thehandbrakeisnormallyusedwhenthecarhasalreadystopped.Aleverispulledandtherearbrakesareapproachedandlockedinthe“on”position.Thecarmaynowbeleftwithoutfearofitsrollingaway.Whenthedriverwantstomovethecaragain,hemustpressabuttonbeforethelevercanbereleased.Thehandbrakemustalsobeabletostopthecarintheeventofthefootbrakefailing.Forthisreason,itisseparatefromthefootbrakeusescableorrodsinsteadofthehydraulicsystem.
Anti-lockBrakeSystem
Anti-lockbrakesystemsmakebrakingsaferandmoreconvenient,Anti-lockbrakesystemsmodulatebrakesystemhydraulicpressuretopreventthebrakesfromlockingandthetiresfromskiddingonslipperypavementorduringapanicstop.
Anti-lockbrakesystemshavebeenusedonaircraftforyears,andsomedomesticcarwereofferedwithanearlyformofanti-lockbrakinginlate1990’s.Recently,severalautomakershaveintroducedmoresophisticatedanti-locksystem.InvestigationsinEurope,whereanti-lockbrakingsystemshavebeenavailableforadecade,haveledonemanufacturetostatethatthenumberoftrafficaccidentscouldbereducedbysevenandahalfpercentifallcarshadanti-lockbrakes.Sosomesourcespredictthatallcarswillofferanti-lockbrakestoimprovethesafetyofthecar.
Anti-locksystemsmodulatebrakeapplicationforceseveraltimespersecondtoholdthetiresatacontrolledamountofslip;allsystemsaccomplishthisinbasicallythesameway.Oneormorespeedsensorsgeneratealternatingcurrentsignalwhosefrequencyincreaseswiththewheelrotationalspeed.Anelectroniccontrolunitcontinuouslymonitorsthesesignalsandifthefrequencyofasignaldropstoorapidlyindicatingthatawheelisabouttolock,thecontrolunitinstructsamodulatingdevicetoreducehydraulicpressuretothebrakeattheaffectedwheel.Whensensorsignalsindicatethewheelisagainrotatingnormally,thecontrolunitallowsincreasedhydraulicpressuretothebrake.Thisrelease-applycycleoccursseveraltimepersecondto“pump”thebrakeslikeadrivermightbutatamuchfasterrate.
Inadditiontotheirbasicoperation,anti-locksystemshavetwootherthingsincommon.First,theydonotoperateuntilthebrakesareappliedwithenoughforcetolockornearlylockawheel.Atallothertimes,thesystemstandsreadytofunctionbutdoesnotinterferewithnormalbraking.Second,iftheanti-locksystemfailinanyway,thebrakescontinuetooperatewithoutanti-lockcapability.Awarninglightontheinstrumentpanelalertsthedriverwhenaproblemexistsintheanti-locksystem.
ThecurrentBoschcomponentAnti-lockBrakingSystem(ABSⅡ),isasecondgenerationdesignwildlyusedbyEuropeanautomakerssuchasBWM,Mercedes-BenzandPorsche.ABSⅡsystemconsistsof:
fourwheelspeedsensor,electroniccontrolunitandmodulatorassembly.
Aspeedsensorisfittedateachwheelsendssignalsaboutwheelrotationtocontrolunit.Eachspeedsensorconsistsofasensorunitandagearwheel.Thefrontsensormountstothesteeringknuckleanditsgearwheelispressedontothestubaxlethatrotateswiththewheel.Therearsensormountstherearsuspensionmemberanditsgearwheelispressedontotheaxle.Thesensoritselfisawindingwithamagneticcore.Thecorecreatesamagneticfieldaroundthewinding,andastheteethofthegearwheelmovethroughthisfield,analternatingcurrentisinducedinthewinding.Thecontrolunitmonitorstherateochangeinthisfrequencytodetermineimpendingbrakelockup.
Thecontrolunit