汽车专业英语课件-与汽车专业英语读译教程2版配套汽车专业英语读译教程2版课件、参考译文17-U10TA

UNIT10BRAKINGSYSTEMSTEXTABasicBrakingSystemandABS,PROFESSIONALENGLISH,UNIT8BasicBrakingSystemandABSTEXTABasicoperatingprincipleofthehydraulicsystemDiscbrakesDrumbrakesABSComponentsOperatingprincipleTypesofAnti-LockBrakes,本次课学习内容,本次课学习目标,掌握制动系统的有关英文专业词汇掌握制动系统主要部件工作原理训练快速阅读能力，提高阅读速度,NEWWORDS,PHRASESANDEXPRESSIONS,BasicBrakingSystemandABSInordertoreducethespeedofthevehicle，thebrakeshavetoconvertthekineticenergystoredinthevehicletoheatenergy.Abrakingsystemconsistsofanenergy-supplyingdevice，acontroldevice，atransmissiondeviceandthebrake.Today，therearethreetypesofbrakingsystemsinuse:servicebrakingsystem，parkingbrakingsystemandadditionalretarderbrakingsystem.Theservicebrakingsystemandtheparkingbrakingsystemhaveseparatecontrolandtransmissiondevices.Theservicebrakingsystemisnormallyfoot-operated，whiletheparkingbrakingsystemishand-operated.BasicoperatingprincipleofthehydraulicsystemHydraulicsystemsareusedtoactuatethebrakesofallsmallcars.Thesystemtransportsthepowerrequiredtoforcethefrictionalsurfacesofthebrakingsystemtogetherfromthepedaltotheindividualbrakeunitsateachwheel.,Themastercylinderconsistsofafluidreservoirandadoublecylinderandpistonassembly.Doubletypemastercylindersaredesignedtoseparatethefrontandrearbrakingsystemshydraulicallyincaseofaleak.Steellinescarrythebrakefluidtoapointonthevehicleframeneareachofthevehicleswheels.Thefluidisthencarriedtothecalipersandwheelcylindersbyflexibletubesinordertoallowforsuspensionandsteeringmovements.Thehydraulicsystemoperatesasfollows:Whenatrest，theentiresystem，fromthepiston(s)inthemastercylindertothoseinthewheelcylindersorcalipers，isfullofbrakefluid.Uponapplicationofthebrakepedal，fluidtrappedinfrontofthemastercylinderpiston(s)isforcedthroughthelinestothewheelcylinders.Here，itforcesthepistonsoutward，inthecaseofdrumbrakes，andinwardtowardthedisc，inthecaseofdiscbrakes.Themotionofthepistonsisopposedbyreturnspringsmountedoutsidethecylindersindrumbrakes，andbyspringseals，indiscbrakes.,Uponreleaseofthebrakepedal，aspringlocatedinsidethemastercylinderimmediatelyreturnsthemastercylinderpistonstothenormalposition.Thepistonscontaincheckvalvesandthemastercylinderhascompensatingportsdrilledinit.Theseareuncoveredasthepistonsreachtheirnormalposition.Thepistoncheckvalvesallowfluidtoflowtowardthewheelcylindersorcalipersasthepistonswithdraw.Then，asthereturnspringsforcethebrakepadsorshoesintothereleasedposition，theexcessfluidreservoirsthroughthecompensatingports.Itisduringthetimethepedalisinthereleasedpositionthatanyfluidthathasleakedoutofthesystemwillbereplacedthroughthecompensatingports1.Dualcircuitmastercylindersemploytwopistons，locatedonebehindtheother，inthecylinder.Theprimarypistonisactuateddirectlybymechanicallinkagefromthebrakepedalthroughthepowerbooster.Thesecondarypistonisactuatedbyfluidtrappedbetweenthetwopistons.,Ifaleakdevelopsinfrontofthesecondarypiston，itmovesforwarduntilitbottomsagainstthefrontofthemastercylinder，andthefluidtrappedbetweenthepistonswilloperatetherearbrakes.Iftherearbrakesdevelopaleak，theprimarypistonwillmoveforwarduntildirectcontactwiththesecondarypistontakesplace，anditwillforcethesecondarypistontoactuatethefrontbrakes.Ineithercase，thebrakepedalmovesfartherwhenthebrakesareapplied，andlessbrakingpowerisavailable.Discbrakes（自学）Insteadofthetraditionalexpandingbrakesthatpressoutwardagainstacirculardrum，discbrakesystemsutilizeadisc(rotor)withbrakepadspositionedoneithersideofit.Brakingeffectisachievedinamannersimilartothewayyouwouldsqueezeaspinningphonographrecordbetweenyourfingers.Thedisc(rotor)isacastingwithcoolingfinsbetweenthetwobrakingsurfaces.,Thisenablesairtocirculatebetweenthebrakingsurfacesmakingthemlesssensitivetoheatbuildupandmoreresistanttofade.Dirtandwaterdonotaffectbrakingactionsincecontaminantsarethrownoffbythecentrifugalactionoftherotororscrapedoffbythepads.Also，theequalclampingactionofthetwobrakepadstendstoensureuniform，straightlinestops.Discbrakesareinherentlyself-adjusting.Therearethreegeneraltypesofdiscbrake:fixedcaliper，floatingcaliperandslidingcaliper.Thefixedcaliperdesignusestwopistonsmountedoneithersideoftherotor(ineachsideofthecaliper).Thecaliperismountedrigidlyanddoesnotmove.Theslidingandfloatingdesignsarequitesimilar.Infact，thesetwotypesareoftenlumpedtogether.Inbothdesigns，thepadontheinsideoftherotorismovedintocontactwiththerotorbyhydraulicforce.Thecaliper，whichisnotheldinafixedposition，movesslightly，bringingtheoutsidepadintocontactwiththerotor.,Drumbrakes（自学）Drumbrakesemploytwobrakeshoesmountedonastationarybackingplate.Theseshoesarepositionedinsideacirculardrumwhichrotateswiththewheelassembly.Theshoesareheldinplacebysprings.Thisallowsthemtoslidetowardthedrums(whentheyareapplied)whilekeepingtheliningsanddrumsinalignment.Theshoesareactuatedbyawheelcylinderwhichismountedatthetopofthebackingplate.Whenthebrakesareapplied，hydraulicpressureforcesthewheelcylindersactuatinglinksoutward.Sincetheselinksbeardirectlyagainstthetopofthebrakeshoes，thetopsoftheshoesarethenforcedagainsttheinnersideofthedrum.Thisactionforcesthebottomsofthetwoshoestocontactthebrakedrumbyrotatingtheentireassemblyslightly(knownasservoaction).Whenpressurewithinthewheelcylinderisrelaxed，returnspringspulltheshoesbackawayfromthedrum.,ABSStoppingacarinahurryonaslipperyroadcanbeverychallenging.Anti-lockbrakingsystems(ABS)takealotofthechallengeoutofthissometimesnerve-wrackingevent.Infact，onslipperysurfaces，evenprofessionaldriverscantstopasquicklywithoutABSasanaveragedrivercanwithABS.TherearefourmaincomponentstoanABSsystem:speedsensors，pump，valvesandcontroller(Fig.10-1).,Fig.10-1Maincomponentsofanti-lockbrakingsystem,ComponentsSpeedSensorsThespeedsensorsarelocatedateachwheelandprovidethespeedreferencetothecontrolunit.Thespeedsensorsarepermanentlymagnetizedinductivesensorsthatreadpulsesfromatoothwheeloneachhub.Avoltagesignalisgeneratedaseachtoothpassesthroughthemagneticfield.Thesensorsarereplaceable.Thetoothwheelsareintegralwiththewheelhubsandarereplacedwiththecompletehub.ControlUnitThecontrolunitcontainsallthesignalconditioningcircuitryandtheoutputcircuits.Theoutputcircuitscontrolthehydraulicunittoadjustthelinepressuretoeachcaliper.Theunitislocatedunderthedashpanelontheleftside，abovetheglovecompartmentandintheforwardpositionoftheelectronicboxintheenginecompartment.Ifaproblemissensed，thecontrolunitwilllighttheinstrumentpanelwarninglamp.,PumpandValvesThehydraulicunit(Fig.10-2)，alsoknownashydraulicactuator，locatedintheenginecompartmentcontainsvalvesandapump.Thevalveshave3positions;pressurebuild-up，pressureholdandpressuredrop.Asthetireslocks，thecontrolunitinformsthevalvetoholdthepressure.Ifthetireremainslocked，thecontrolunitwillallowthevalvetodropthepressureuntilthetirestartstoturn.Thecontrolunitwillallowthevalvetostartbuildingpressuretostartthecycleoveragain.,1.Hydrauliccontrolunit2.Valverelay3.Motorrelay4.Cover5.ABScontrolunitFig.10-2Hydraulicunitoftheanti-lockbrakesystem,Thepumpreturnsthebrakefluidtakenfromthewheelcylinderwhilethepressureislowered.Thepumpisdesignedtomaintainseparationofthe2brakingcircuits.Duringoperationoftheanti-locksystem，apulsingmaybefeltatthebrakepedalandaclickingheardfromthehydraulicunit.ThisisnormalandinformstheoperatorthattheABSisinthefunctioningmode.OperatingprincipleTherearemanydifferentvariationsandcontrolalgorithmsforABSsystems.Wewilldiscusshowoneofthesimplersystemsworks.Thecontrollermonitorsthespeedsensorsatalltimes.Itislookingfordecelerationsinthewheelthatareoutoftheordinary.Rightbeforeawheellocksup，itwillexperiencearapiddeceleration.Ifleftunchecked，thewheelwouldstopmuchmorequicklythananycarcould.Itmighttakeacarfivesecondstostopfrom60mph(96.6kph)underidealconditions，butawheelthatlocksupcouldstopspinninginlessthanasecond.,TheABScontrollerknowsthatsucharapiddecelerationisimpossible，soitreducesthepressuretothatbrakeuntilitseesaacceleration，thenitincreasesthepressureuntilitseesthedecelerationagain.Itcandothisveryquickly，beforethetirecanactuallysignificantlychangespeed.Theresultisthatthetireslowsdownatthesamerateasthecar，withthebrakeskeepingthetiresverynearthepointatwhichtheywillstarttolockup2.Thisgivesthesystemmaximumbrakingpower.WhentheABSsystemisinoperationyouwillfeelapulsinginthebrakepedal;thiscomesfromtherapidopeningandclosingofthevalves.SomeABSsystemscancycleupto15timespersecond.TypesofAnti-LockBrakesAnti-lockbrakingsystemsusedifferentschemesdependingonthetypeofbrakesinuse.Wewillrefertothembythenumberofchannels-thatis，howmanyvalvesthatareindividuallycontrolled-andthenumberofspeedsensors.,Four-channel，four-sensorABS-Thisisthebestscheme.Thereisaspeedsensoronallfourwheelsandaseparatevalveforallfourwheels.Withthissetup，thecontrollermonitorseachwheelindividuallytomakesureitisachievingmaximumbrakingforce.Three-channel，three-sensorABS-Thisscheme，commonlyfoundonpickuptruckswithfour-wheelABS，hasaspeedsensorandavalveforeachofthefrontwheels，withonevalveandonesensorforbothrearwheels.Thespeedsensorfortherearwheelsislocatedintherearaxle.Thissystemprovidesindividualcontrolofthefrontwheels，sotheycanboth