學(xué)習(xí)內(nèi)容本節(jié)課學(xué)習(xí)內(nèi)容、目標(biāo)和重點(diǎn)難點(diǎn)學(xué)習(xí)目標(biāo)難點(diǎn)重點(diǎn)Chapter5BrakingSystems

1.掌握制動(dòng)系統(tǒng)的基本組成、類型、ABS系統(tǒng)主要零件的英文名稱2.提高翻譯技巧，能較熟練翻譯課文1.重點(diǎn)是英文專業(yè)術(shù)語(yǔ)記憶2.難點(diǎn)是生詞偏多、ABS控制原理原理Chapter5BrakingSystems

5.1OverviewofBrakingSystems

kinetic[kai'netik]a.(運(yùn))動(dòng)的，動(dòng)力（學(xué)）的caliper['k?lip?]n.卡鉗，測(cè)徑器；v.用卡鉗測(cè)量magnetize['m?ɡnitaiz]vt.吸引；使磁化vi.磁化；受磁retarder[ri'tɑ:d?]n.緩凝劑；減速器；阻滯劑；遲縮劑hydraulic[hai'dr?:lik]adj.液壓的；水力的；水力學(xué)的compartment[k?m'pɑ:tm?nt]n.隔間；區(qū)劃；臥車(chē)上的小客房vt.分隔；劃分booster['bu:st?]n.升壓機(jī)；支持者；擴(kuò)爆器deceleration['di:?sel?'rei??n]n.減速acceleration[?k?sel?'rei??n]n.加速，促進(jìn)；加速度Chapter5BrakingSystems

5.1OverviewofBrakingSystemsservicebrakesystem行車(chē)制動(dòng)系統(tǒng)parkingbrakesystem駐車(chē)制動(dòng)系統(tǒng)retarderbrakingsystem緩速制動(dòng)系統(tǒng)brakepedal制動(dòng)踏板vacuumbooster真空助力器mastercylinder主缸brakeline制動(dòng)管路Chapter5BrakingSystems

5.1OverviewofBrakingSystemsdrumbrake鼓式制動(dòng)器discbrake盤(pán)式制動(dòng)器brakeshoe制動(dòng)蹄brakedrum制動(dòng)鼓wheelcylinder輪缸frictionlining摩擦襯片brakecaliper制動(dòng)鉗Brakefluid制動(dòng)液checkvalve單向閥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[di?pikt]v.描繪，描述tandem[?t?nd?m]n.串聯(lián)plumb[pl?m]v.使豎直，使垂直tandem-axle串聯(lián)橋，雙驅(qū)動(dòng)橋servicebrake行車(chē)制動(dòng)（器）servicebrakechamber行車(chē)制動(dòng)氣室straighttruck無(wú)掛車(chē)貨車(chē)ABSbrakemodulatorABS制動(dòng)壓力調(diào)節(jié)器relayvalve繼動(dòng)閥inserieswith與…串聯(lián)，與…相連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