车辆工程-汽车专业英语课件-汽车基础知识部分-Chapter-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Chapter5BrakingSystems

5.1OverviewofBrakingSystems

kinetic[kai'netik]a.(运)动的，动力（学）的caliper['kælipə]n.卡钳，测径器；v.用卡钳测量magnetize['mæɡnitaiz]vt.吸引；使磁化vi.磁化；受磁retarder[ri'tɑ:də]n.缓凝剂；减速器；阻滞剂；迟缩剂hydraulic[hai'drɔ:lik]adj.液压的；水力的；水力学的compartment[kəm'pɑ:tmənt]n.隔间；区划；卧车上的小客房vt.分隔；划分booster['bu:stə]n.升压机；支持者；扩爆器deceleration['di:ֽselə'reiʃən]n.减速acceleration[əkֽselə'reiʃən]n.加速，促进；加速度Chapter5BrakingSystems

5.1OverviewofBrakingSystemsservicebrakesystem行车制动系统parkingbrakesystem驻车制动系统retarderbrakingsystem缓速制动系统brakepedal制动踏板vacuumbooster真空助力器mastercylinder主缸brakeline制动管路Chapter5BrakingSystems

5.1OverviewofBrakingSystemsdrumbrake鼓式制动器discbrake盘式制动器brakeshoe制动蹄brakedrum制动鼓wheelcylinder轮缸frictionlining摩擦衬片brakecaliper制动钳Brakefluid制动液checkvalve单向阀Chapter5BrakingSystems

5.1OverviewofBrakingSystemsThebrakingsystemisveryimportanttoacar.Ifyourbrakesdon’tworkproperly,theresultcanbedisastrous.Brakesareactuallyenergyconversiondevices,whichconvertthekineticenergyofthevehicleintothermalenergy.Chapter5BrakingSystems

5.1OverviewofBrakingSystemsTherearethreekindsofbrakingsystems:servicebrakesystem,parkingbrakesystemandadditionalretarderbrakingsystem.Theservicebrakesystemisthemainbrakingsystemusedtoslowdownorevenstopthecarthat’srunningatahighspeedandguaranteethesafetyofpassengers.Itisfoot-operatedbythedriverdepressingandreleasingthebrakepedal.Aparkingbrakesystemcanpreventtheautoslippingawayfromitsparkingplace,evenifitisparkedonasteepslope.Itisalsocalledthehandbrake.Chapter5BrakingSystems

5.1OverviewofBrakingSystemsThebrakingsystemiscomposedofthebrakeanditscontrolmechanisms.Ahydraulicbrakesystemmainlyconsistsofthebrakepedal,thevacuumbooster,themastercylinder,thebrakelineandthebrake,asshowninFig.5-1.Toincreasesafety,mostmoderncarbrakingsystemsarebrokenintotwocircuits,withtwowheelsoneachcircuit.Fig.5-1HydraulicbrakingsystemChapter5BrakingSystems

5.1OverviewofBrakingSystemsTherearetwomaintypesofbrakes:drumbrakeanddiscbrake.Basically,allcarbrakesarefrictionbrakes.Whenthedriverappliesthebrake,thecontroldeviceforcesbrakeshoesorpadsagainsttherotatingbrakedrumsordiscsatwheels.Frictionbetweentheshoesorpadsandthedrumsordiscsthenslowsorstopsthewheelssothatthecarisbraked.Chapter5BrakingSystems

5.2Brakes

1.DrumBrakeAdrumbrakeisusuallycomposedofthebrakebackingplate,thewheelcylinder,thebrakeshoes,thebrakedrumandthebrakeclearanceadjustingmechanisms,asshowninFig.5-2.Itusesaninternalexpandingbrakeshoewiththeliningattached,workingwithintheconfinesofarotatingbrakesurfacecalledabrakedrum.Thebrakeshoediameterisexpandedtocontactthebrakesurfacebyahydrauliccylinderthatisreferredtoasawheelcylinder.Withdrumbrake,thefluidisforcedintothewheelcylinderwhichpushesthebrakeshowsoutsothatthefrictionliningsarepressedagainstthedrum,andcausethewheeltostop(Fig.5-3).Chapter5BrakingSystems

5.2Brakes

Fig.5-2DrumBrakeChapter5BrakingSystems

5.2Brakes

Fig.5-3PrincipleofDrumBrakeChapter5BrakingSystems

5.2Brakes2.DiscBrakeThemainpartsofadiscbrakeincludethebrakecylinder,thebrakediscandthebrakecalipers.Thediscbrakeisalotlikethebrakesonabicycle.Bicyclebrakeshaveacaliper,whichsqueezesthebrakepadsagainstthewheel.Inadiscbrake,thebrakepadssqueezetherotorinsteadofthewheel,andtheforceistransmittedhydraulicallyinsteadofthroughacable.Frictionbetweenthepadsandthediscslowsthediscdown(Fig.5-4and5-5).Chapter5BrakingSystems

5.2Brakes

Fig.5-4DiscBrakeFig.5-5PrincipleofDiscBrakeChapter5BrakingSystems

5.3BrakeTransmissions

1.MasterCylinderInthemodernbrakingsystem,themastercylinderispower-assistedbytheengine.Themastercylinderislocatedintheenginecompartmentonthefirewall,directlyinfrontofthedriver’sseat.Atypicalmastercylinderhasactuallytwocompletelyseparatemastercylindersinonehousing,eachhandlingtwowheels.Thatistosay,ifonesidefails,youwillstillbeabletostopthecar.2.BrakeFluidBrakefluidisspecialoilthathasspecificproperties.Itisdesignedtowithstandcoldtemperatureswithoutthickeningaswellasveryhightemperatureswithoutboiling.Ifthebrakefluidboils,itwouldcauseyoutohaveaspongypedalandthecarwouldbehardtostop.Chapter5BrakingSystems

5.3BrakeTransmissions

3.BoosterThepowerbrakebooster（Fig.5-6）ismountedonthefirewalldirectlybehindthemastercylinderand,alongwiththemastercylinder,isdirectlyconnectedwiththebrakepedal.Itspurposeistoamplifytheavailablefootpressureappliedtothebrakepedalsothattheamountoffootpressurerequiredtostopeventhelargestvehicleisminimal.Fig.5-6BoosterChapter5BrakingSystems

5.4Anti-lockbrakingsystemsAnanti-lockbrakingsystem(commonlyknownasABS)isasystemonmotorvehicleswhichpreventsthewheelsfromlockingwhilebraking.Itsfunctionistopreventwheelfromlockingwhenapplyingpromptbraking,thebiggestadhesiveforcebetweenthetireandthegroundandthehighsideforcecoefficientcanimprovebrakedecelerationandshortenbrakingdistancethusensuringtravelstability.TherearefourmaincomponentstoanABSsystem:speedsensors,pump,valvesandcontroller(Fig.5-7).Chapter5BrakingSystems

5.4Anti-lockbrakingsystemsFig.5-7Anti-lockbrakingsystemscomponentsChapter5BrakingSystems

5.4Anti-lockbrakingsystems1.Components

SpeedSensors.Thespeedsensorsarelocatedateachwheelandprovidethespeedreferencetothecontrolunit.Thespeedsensorsarepermanentlymagnetizedinductivesensorsthatreadpulsesfromatoothwheeloneachhub.Avoltagesignalisgeneratedaseachtoothpassesthroughthemagneticfield.Thesensorsarereplaceable.Thetoothwheelsareintegralwiththewheelhubsandarereplacedwiththecompletehub.Chapter5BrakingSystems

5.4Anti-lockbrakingsystemsControlUnit.Thecontrolunitcontainsallthesignalconditioningcircuitryandtheoutputcircuits.Theoutputcircuitscontrolthehydraulicunittoadjustthelinepressuretoeachcaliper.Theunitislocatedunderthedashpanelontheleftside,abovetheglovecompartmentandintheforwardpositionoftheelectronicboxintheenginecompartment.Ifaproblemissensed,thecontrolunitwilllighttheinstrumentpanelwarninglamp.Chapter5BrakingSystems

5.4Anti-lockbrakingsystemsPumpandValves.Thehydraulicunit(Fig5-9),alsoknownashydraulicactuator,locatedintheenginecompartmentcontainsvalvesandapump.Thevalveshave3positions:pressurebuild-up,pressureholdandpressuredrop.Asthetireslocks,thecontrolunitinformsthevalvetoholdthepressure.Ifthetireremainslocked,thecontrolunitwillallowthevalvetodropthepressureuntilthetirestartstoturn.Thecontrolunitwillallowthevalvetostartbuildingpressuretostartthecycleoveragain.Chapter5BrakingSystems

5.4Anti-lockbrakingsystemsThepumpreturnsthebrakefluidtakenfromthewheelcylinderwhilethepressureislowered.Thepumpisdesignedtomaintainseparationofthe2brakingcircuits.Duringoperationoftheanti-locksystem,apulsingmaybefeltatthebrakepedalandaclickingheardfromthehydraulicunit.ThisisnormalandinformstheoperatorthattheABSisinthefunctioningmode.Chapter5BrakingSystems

5.4Anti-lockbrakingsystems2.OperatingprincipleTherearemanydifferentvariationsandcontrolalgorithmsforABSsystem.Wewilldiscusshowoneofthesimplersystemsworks.Thecontrollermonitorsthespeedsensorsatalltimes.Itislookingfordecelerationsinthewheelthatareoutoftheordinary.Rightbeforeawheellocksup,itwillexperiencearapiddeceleration.Ifleftunchecked,thewheelwouldstopmuchmorequicklythananycarcould.Itmighttakeacarfivesecondstostopfrom60mph(96.6kph)underidealconditions,butawheelthatlocksupcouldstopspinninginlessthanasecond.Fig.5-7Anti-lockBrakingSystemsChapter5BrakingSystems

5.4Anti-lockbrakingsystemsTheABScontrollerknowsthatsucharapiddecelerationisimpossible,soitreducesthepressuretothatbrakeuntilitseesaacceleration,thenitincreasesthepressureuntilitseesthedecelerationagain.Itcandothisveryquickly,beforethetirecanactuallysignificantlychangespeed.Theresultisthatthetireslowsdownatthesamerateasthecar,withthebrakeskeepingthetiresverynearthepointatwhichtheywillstarttolockup.Thisgivesthesystemmaximumbrakingpower.WhentheABSsystemisinoperationyouwillfeelapulsinginthebrakepedal;thiscomesfromtherapidopeningandclosingofthevalves.SomeABSsystemscancycleupto15timespersecond.Chapter5BrakingSystems

5.4Anti-lockbrakingsystems3.TypesofAnti-lockBrakesAnti-lockbrakingsystemsusedifferentschemesdependingonthetypeofbrakesinuse.Wewillrefertothembythenumberofchannels—thatis,howmanyvalvesthatareindividuallycontrolled—andthenumberofspeedsensors.

Four-channel,four-sensorABS.Thisisthebestscheme.Thereisaspeedsensoronallfourwheelsandaseparatevalveforallfourwheels.Withthissetup,thecontrollermonitorseachwheelindividuallytomakesureitisachievingmaximumbrakingforce.Chapter5BrakingSystems

5.4Anti-lockbrakingsystemsThree-channel,three-sensorABS.Thisscheme,commonlyfoundonpickuptruckswithfour-wheelABS,hasaspeedsensorandavalveforeachofthefrontwheels,withonevalveandonesensorforbothrearwheels.Thespeedsensorfortherearwheelsislocatedintherearaxle.Thissystemprovidesindividualcontrolofthefrontwheels,sotheycanbothachievemaximumbrakingforce.Therearwheels,however,aremonitoredtogether;theybothhavetostarttolockupbeforetheABSwillactivateontherear.Withthissystem,itispossiblethatoneoftherearwheelswilllockduringastop,reducingbrakeeffectiveness.Chapter5BrakingSystems

5.4Anti-lockbrakingsystems

One-channel,one-sensorABS.Thissystemiscommonlyfoundonpickuptruckswithrear-wheelABS.ithasonevalve,whichcontrolsbothrearwheels,andonespeedsensor,locatedintherearaxle.Thissystemoperatesinthesamemannerastherearendofathree-channelsystem.TherearwheelsaremonitoredtogetherandtheybothhavetostarttolockupbeforetheABSkicksin.Inthissystemitisalsopossiblethatoneoftherearwheelswilllock,reducingbrakeeffectiveness.Thissystemiseasytoidentify.UsuallytherewillbeonebrakelinegoingthroughaT-fittingtobothrearwheels.Youcanlocatethespeedsensorbylookingforanelectricalconnectionnearthedifferentialontherear-axlehousing.Chapter5BrakingSystems

5.5TractorandTruckAirABSNewWordsandPhrasesdepict[diˈpikt]v.描绘，描述tandem[ˈtændəm]n.串联plumb[plʌm]v.使竖直，使垂直tandem-axle串联桥，双驱动桥servicebrake行车制动（器）servicebrakechamber行车制动气室straighttruck无挂车货车ABSbrakemodulatorABS制动压力调节器relayvalve继动阀inserieswith与…串联，与…相连Chapter5BrakingSystems

5.5TractorandTruckAirABSAnABSelectroniccontrolunit(ECU)istheelectronicmodulethatcontrolstheairABSsystem.Variablereluctance-typespeedsensorsareusedtomeasureindividualwheelspeedsatbothfrontwheelsandatleasttwooftherearwheelsontandem-axletrucks.ElectricallycontrolledABSvalvesareusedtocontroltheairsuppliedtotheservicebrakechamberstopreventwheellockup.TheelectricalandpneumaticlayoutforastraighttruckABSapplicationisshowninFigure5-10．Chapter5BrakingSystems

5.5TractorandTruckAirABSChapter5BrakingSystems

5.5TractorandTruckAirABSFigure5-11Four-channelABSwithATC（ATC—automatictractioncontrol）Chapter5BrakingSystems

5.5TractorandTruckAirABSWheel-speedsensorsaretypicallyinstalledineachofthetwofront(steer)axlewheelends.Truckswithtandemrearaxlesoftenonlyhavewheel-speedsensorsinoneoftherearaxles(Figure5-11).Thetworearsensorsareinstalledatthewheelendsoftheforward-rearaxleorrear-rearaxle,dependingonthetruck'srearsuspensiontype.Thisfour-sensorfour-ABSvalvesystemshowninFigure5-11isknownasafour-channelABSsystem.Othertruckswithtan