1 汽车专业英语课件-汽车基础知识部分修改后-section 1汽车专业英语2版ppt课件--20180227Chapter 5 Braking System

学习内容,本节课学习内容、目标和重点难点,学习目标,难点重点,Chapter5BrakingSystems,1.掌握制动系统的基本组成、类型、ABS系统主要零件的英文名称2.提高翻译技巧，能较熟练翻译课文,1.重点是英文专业术语记忆2.难点是生词偏多、ABS控制原理原理,Chapter5BrakingSystems5.1OverviewofBrakingSystems,Chapter5BrakingSystems5.1OverviewofBrakingSystems,Chapter5BrakingSystems5.1OverviewofBrakingSystems,Chapter5BrakingSystems5.1OverviewofBrakingSystems,Thebrakingsystemisveryimportanttoacar.Ifyourbrakesdontworkproperly,theresultcanbedisastrous.Brakesareactuallyenergyconversiondevices,whichconvertthekineticenergyofthevehicleintothermalenergy.,Chapter5BrakingSystems5.1OverviewofBrakingSystems,Therearethreekindsofbrakingsystems:servicebrakesystem,parkingbrakesystemandadditionalretarderbrakingsystem.Theservicebrakesystemisthemainbrakingsystemusedtoslowdownorevenstopthecarthatsrunningatahighspeedandguaranteethesafetyofpassengers.Itisfoot-operatedbythedriverdepressingandreleasingthebrakepedal.Aparkingbrakesystemcanpreventtheautoslippingawayfromitsparkingplace,evenifitisparkedonasteepslope.Itisalsocalledthehandbrake.,Chapter5BrakingSystems5.1OverviewofBrakingSystems,Thebrakingsystemiscomposedofthebrakeanditscontrolmechanisms.Ahydraulicbrakesystemmainlyconsistsofthebrakepedal,thevacuumbooster,themastercylinder,thebrakelineandthebrake,asshowninFig.5-1.Toincreasesafety,mostmoderncarbrakingsystemsarebrokenintotwocircuits,withtwowheelsoneachcircuit.,Fig.5-1Hydraulicbrakingsystem,Chapter5BrakingSystems5.1OverviewofBrakingSystems,Therearetwomaintypesofbrakes:drumbrakeanddiscbrake.Basically,allcarbrakesarefrictionbrakes.Whenthedriverappliesthebrake,thecontroldeviceforcesbrakeshoesorpadsagainsttherotatingbrakedrumsordiscsatwheels.Frictionbetweentheshoesorpadsandthedrumsordiscsthenslowsorstopsthewheelssothatthecarisbraked.,Chapter5BrakingSystems5.2Brakes,1.DrumBrakeAdrumbrakeisusuallycomposedofthebrakebackingplate,thewheelcylinder,thebrakeshoes,thebrakedrumandthebrakeclearanceadjustingmechanisms,asshowninFig.5-2.Itusesaninternalexpandingbrakeshoewiththeliningattached,workingwithintheconfinesofarotatingbrakesurfacecalledabrakedrum.Thebrakeshoediameterisexpandedtocontactthebrakesurfacebyahydrauliccylinderthatisreferredtoasawheelcylinder.Withdrumbrake,thefluidisforcedintothewheelcylinderwhichpushesthebrakeshowsoutsothatthefrictionliningsarepressedagainstthedrum,andcausethewheeltostop(Fig.5-3).,Chapter5BrakingSystems5.2Brakes,Fig.5-2DrumBrake,Chapter5BrakingSystems5.2Brakes,Fig.5-3PrincipleofDrumBrake,Chapter5BrakingSystems5.2Brakes,2.DiscBrakeThemainpartsofadiscbrakeincludethebrakecylinder,thebrakediscandthebrakecalipers.Thediscbrakeisalotlikethebrakesonabicycle.Bicyclebrakeshaveacaliper,whichsqueezesthebrakepadsagainstthewheel.Inadiscbrake,thebrakepadssqueezetherotorinsteadofthewheel,andtheforceistransmittedhydraulicallyinsteadofthroughacable.Frictionbetweenthepadsandthediscslowsthediscdown(Fig.5-4and5-5).,Chapter5BrakingSystems5.2Brakes,Fig.5-4DiscBrakeFig.5-5PrincipleofDiscBrake,Chapter5BrakingSystems5.3BrakeTransmissions,1.MasterCylinderInthemodernbrakingsystem,themastercylinderispower-assistedbytheengine.Themastercylinderislocatedintheenginecompartmentonthefirewall,directlyinfrontofthedriversseat.Atypicalmastercylinderhasactuallytwocompletelyseparatemastercylindersinonehousing,eachhandlingtwowheels.Thatistosay,ifonesidefails,youwillstillbeabletostopthecar.2.BrakeFluidBrakefluidisspecialoilthathasspecificproperties.Itisdesignedtowithstandcoldtemperatureswithoutthickeningaswellasveryhightemperatureswithoutboiling.Ifthebrakefluidboils,itwouldcauseyoutohaveaspongypedalandthecarwouldbehardtostop.,Chapter5BrakingSystems5.3BrakeTransmissions,3.BoosterThepowerbrakebooster（Fig.5-6）ismountedonthefirewalldirectlybehindthemastercylinderand,alongwiththemastercylinder,isdirectlyconnectedwiththebrakepedal.Itspurposeistoamplifytheavailablefootpressureappliedtothebrakepedalsothattheamountoffootpressurerequiredtostopeventhelargestvehicleisminimal.,Fig.5-6Booster,Chapter5BrakingSystems5.4Anti-lockbrakingsystems,Ananti-lockbrakingsystem(commonlyknownasABS)isasystemonmotorvehicleswhichpreventsthewheelsfromlockingwhilebraking.Itsfunctionistopreventwheelfromlockingwhenapplyingpromptbraking,thebiggestadhesiveforcebetweenthetireandthegroundandthehighsideforcecoefficientcanimprovebrakedecelerationandshortenbrakingdistancethusensuringtravelstability.TherearefourmaincomponentstoanABSsystem:speedsensors,pump,valvesandcontroller(Fig.5-7).,Chapter5BrakingSystems5.4Anti-lockbrakingsystems,Fig.5-7Anti-lockbrakingsystemscomponents,Chapter5BrakingSystems5.4Anti-lockbrakingsystems,1.ComponentsSpeedSensors.Thespeedsensorsarelocatedateachwheelandprovidethespeedreferencetothecontrolunit.Thespeedsensorsarepermanentlymagnetizedinductivesensorsthatreadpulsesfromatoothwheeloneachhub.Avoltagesignalisgeneratedaseachtoothpassesthroughthemagneticfield.Thesensorsarereplaceable.Thetoothwheelsareintegralwiththewheelhubsandarereplacedwiththecompletehub.,Chapter5BrakingSystems5.4Anti-lockbrakingsystems,ControlUnit.Thecontrolunitcontainsallthesignalconditioningcircuitryandtheoutputcircuits.Theoutputcircuitscontrolthehydraulicunittoadjustthelinepressuretoeachcaliper.Theunitislocatedunderthedashpanelontheleftside,abovetheglovecompartmentandintheforwardpositionoftheelectronicboxintheenginecompartment.Ifaproblemissensed,thecontrolunitwilllighttheinstrumentpanelwarninglamp.,Chapter5BrakingSystems5.4Anti-lockbrakingsystems,PumpandValves.Thehydraulicunit(Fig5-9),alsoknownashydraulicactuator,locatedintheenginecompartmentcontainsvalvesandapump.Thevalveshave3positions:pressurebuild-up,pressureholdandpressuredrop.Asthetireslocks,thecontrolunitinformsthevalvetoholdthepressure.Ifthetireremainslocked,thecontrolunitwillallowthevalvetodropthepressureuntilthetirestartstoturn.Thecontrolunitwillallowthevalvetostartbuildingpressuretostartthecycleoveragain.,Chapter5BrakingSystems5.4Anti-lockbrakingsystems,Thepumpreturnsthebrakefluidtakenfromthewheelcylinderwhilethepressureislowered.Thepumpisdesignedtomaintainseparationofthe2brakingcircuits.Duringoperationoftheanti-locksystem,apulsingmaybefeltatthebrakepedalandaclickingheardfromthehydraulicunit.ThisisnormalandinformstheoperatorthattheABSisinthefunctioningmode.,Chapter5BrakingSystems5.4Anti-lockbrakingsystems,2.OperatingprincipleTherearemanydifferentvariationsandcontrolalgorithmsforABSsystem.Wewilldiscusshowoneofthesimplersystemsworks.Thecontrollermonitorsthespeedsensorsatalltimes.Itislookingfordecelerationsinthewheelthatareoutoftheordinary.Rightbeforeawheellocksup,itwillexperiencearapiddeceleration.Ifleftunchecked,thewheelwouldstopmuchmorequicklythananycarcould.Itmighttakeacarfivesecondstostopfrom60mph(96.6kph)underidealconditions,butawheelthatlocksupcouldstopspinninginlessthanasecond.,Fig.5-7Anti-lockBrakingSystems,Chapter5BrakingSystems5.4Anti-lockbrakingsystems,TheABScontrollerknowsthatsucharapiddecelerationisimpossible,soitreducesthepressuretothatbrakeuntilitseesaacceleration,thenitincreasesthepressureuntilitseesthedecelerationagain.Itcandothisveryquickly,beforethetirecanactuallysignificantlychangespeed.Theresultisthatthetireslowsdownatthesamerateasthecar,withthebrakeskeepingthetiresverynearthepointatwhichtheywillstarttolockup.Thisgivesthesystemmaximumbrakingpower.WhentheABSsystemisinoperationyouwillfeelapulsinginthebrakepedal;thiscomesfromtherapidopeningandclosingofthevalves.SomeABSsystemscancycleupto15timespersecond.,Chapter5BrakingSystems5.4Anti-lockbrakingsystems,3.TypesofAnti-lockBrakesAnti-lockbrakingsystemsusedifferentschemesdependingonthetypeofbrakesinuse.Wewillrefertothembythenumberofchannelsthatis,howmanyvalvesthatareindividuallycontrolledandthenumberofspeedsensors.Four-channel,four-sensorABS.Thisisthebestscheme.Thereisaspeedsensoronallfourwheelsandaseparatevalveforallfourwheels.Withthissetup,thecontrollermonitorseachwheelindividuallytomakesureitisachievingmaximumbrakingforce.,Chapter5BrakingSystems5.4Anti-lockbrakingsystems,Three-channel,three-sensorABS.Thisscheme,commonlyfoundonpickuptruckswithfour-wheelABS,hasaspeedsensorandavalveforeachofthefrontwheels,withonevalveandonesensorforbothrearwheels.Thespeedsensorfortherearwheelsislocatedintherearaxle.Thissystemprovidesindividualcontrolofthefrontwheels,sotheycanbothachievemaximumbrakingforce.Therearwheels,however,aremonitoredtogether;theybothhavetostarttolockupbeforetheABSwillactivateontherear.Withthissystem,itispossiblethatoneoftherearwheelswilllockduringastop,reducingbrakeeffectiveness.,Chapter5BrakingSystems5.4Anti-lockbrakingsystems,One-channel,one-sensorABS.Thissystemiscommonlyfoundonpickuptruckswithrear-wheelABS.ithasonevalve,whichcontrolsbothrearwheels,andonespeedsensor,locatedintherearaxle.Thissystemoperatesinthesamemannerastherearendofathree-channelsystem.TherearwheelsaremonitoredtogetherandtheybothhavetostarttolockupbeforetheABSkicksin.Inthissystemitisalsopossiblethatoneoftherearwheelswilllock,reducingbrakeeffectiveness.Thissystemiseasytoidentify.UsuallytherewillbeonebrakelinegoingthroughaT-fittingtobothrearwheels.Youcanlocatethespeedsensorbylookingforanelectricalconnectionnearthedifferentialontherear-axlehousing.,Chapter5BrakingSystems5.5TractorandTruckAirABS,NewWordsandPhrases,Chapter5BrakingSystems5.5TractorandTruckAirABS,AnABSelectroniccontrolunit(ECU)istheelectronicmodulethatcontrolstheairABSsystem.Variablereluctance-typespeedsensorsareusedtomeasureindividualwheelspeedsatbothfrontwheelsandatleasttwooftherearwheelsontandem-axletrucks.ElectricallycontrolledABSvalvesareusedtocontroltheairsuppliedtotheservicebrakechamberstopreventwheellockup.TheelectricalandpneumaticlayoutforastraighttruckABSapplicationisshowninFigure5-10,Chapter5BrakingSystems5.5TractorandTruckAirABS,Chapter5BrakingSystems5.5TractorandTruckAirABS,Figure5-11Four-channelABSwithATC（ATCautomatictractioncontrol）,Chapter5BrakingSystems5.5TractorandTruckAirABS,Wheel-speedsensorsaretypicallyinstalledineachofthetwofront(steer)axlewheelends.Truckswithtandemrearaxlesoftenonlyhavewheel-speedsensorsinoneoftherearaxles(Figure5-11).Thetworearsensorsareinstalledatthewheelendsoftheforward-rearaxleorrear-rearaxle,dependingonthetrucksrearsuspensiontype.Thisfour-sensorfour-ABSvalvesystemshowninFigure5-11isknownasafour-channelABSsystem.Othertruckswithtandemrearaxlesmayhavesensorsineachoftherear-axlewheelendsforatotalofsixsensorsandsixABSvalves;th