汽车制动系统外文翻译.docx

汽车制动系统外文翻译.docx

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汽车制动系统外文翻译

河南理工大学万方科技学院

毕业设计（论文）附录

中英文文献翻译

姓名：

王奎

所在院系：

机械与动力工程系

专业班级：

机械设计08-3班

学号：

05

指导教师：

赵武

原文标题：

AutomobileBrakeSystem

2012年5月25日

AutomobileBrakeSystem

Thebrakingsystemisthemostimportantsystemincars.Ifthebrakesfail,theresultcanbedisastrous.Brakesareactuallyenergyconversiondevices,whichconvertthekineticenergy（momentum）ofthevehicleintothermalenergy（heat）.Whensteppingonthebrakes,thedrivercommandsastoppingforcetentimesaspowerfulastheforcethatputsthecarinmotion.Thebrakingsystemcanexertthousandsofpoundsofpressureoneachofthefourbrakes.

Twocompleteindependentbrakingsystemsareusedonthecar.Theyaretheservicebrakeandtheparkingbrake.

Theservicebrakeactstoslow,stop,orholdthevehicleduringnormaldriving.Theyarefoot-operatedbythedriverdepressingandreleasingthebrakepedal.Theprimarypurposeofthebrakeistoholdthevehiclestationarywhileitisunattended.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.

Basically,allcarbrakesarefrictionbrakes.Whenthedriverappliesthebrake,thecontroldeviceforcesbrakeshoes,orpads,againsttherotatingbrakedrumordisksatwheel.Frictionbetweentheshoesorpadsandthedrumsordisksthenslowsorstopsthewheelsothatthecarisbraked.

Inmostmodernbrakesystems,thereisafluid-filledcylinder,calledmastercylinder,whichcontainstwoseparatesections,thereisapistonineachsectionandbothpistonsareconnectedtoabrakepedalinthedriver’scompartment.Whenthebrakeispusheddown,brakefluidissentfromthemastercylindertothewheels.

Atthewheels,thefluidpushesshoes,orpads,againstrevolvingdrumsordisks.Thefrictionbetweenthestationaryshoes,orpads,andtherevolvingdrumsordisksslowsandstopsthem.Thisslowsorstopstherevolvingwheels,which,inturn,sloworstopthecar.

Thebrakefluidreservoirisontopofthemastercylinder.Mostcarstodayhaveatransparentrreservoirsothatyoucanseethelevelwithoutopeningthecover.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.

Brakes-whatdotheydo?

Brakesaredesignedtoslowdownyourvehiclebutprobablynotbythemeansthatyouthink.Thecommonmisconceptionisthatbrakessqueezeagainstadrumordisc,andthepressureofthesqueezingactioniswhatslowsyoudown.Thisinfactisonlypartoftheequation.Brakesareessentiallyamechanismtochangeenergytypes.Whenyou'retravellingatspeed,yourvehiclehaskineticenergy.Whenyouapplythebrakes,thepadsorshoesthatpressagainstthebrakedrumorrotorconvertthatenergyintothermalenergyviafriction.Thecoolingofthebrakesdissipatestheheatandthevehicleslowsdown.It'stheFirstLawofThermodynamics,sometimesknownasthelawofconservationofenergy.Thisstatesthatenergycannotbecreatednordestroyed,itcanonlybeconvertedfromoneformtoanother.Inthecaseofbrakes,itisconvertedfromkineticenergytothermalenergy.

Angularforce.Becauseoftheconfigurationofthebrakepadsandrotorinadiscbrake,thelocationofthepointofcontactwherethefrictionisgeneratedalsoprovidesamechanicalmomenttoresisttheturningmotionoftherotor.

Thermodynamics,brakefadeanddrilledrotors.

Ifyourideamotorbikeordrivearacecar,you'reprobablyfamiliarwiththetermbrakefade,usedtodescribewhathappenstobrakeswhentheygettoohot.Agoodexampleiscomingdownamountainpassusingyourbrakesratherthanyourenginetoslowyoudown.Asyoustarttocomedownthepass,thebrakesonyourvehicleheatup,slowingyoudown.Butifyoukeepusingthem,therotorsordrumsstayhotandgetnochancetocooloff.Atsomepointtheycan'tabsorbanymoreheatsothebrakepadsheatupinstead.Ineverybrakepadthereisthefrictionmaterialthatisheldtogetherwithsomesortofresinandoncethisstartstogettoohot,theresinstartstovapourise,formingagas.Becausethegascan'tstaybetweenthepadandtherotor,itformsathinlayerbetweenthetwowhilsttryingtoescape.Thepadslosecontactwiththerotor,reducingtheamountoffrictionandvoila.Completebrakefade.

Thetypicalremedyforthiswouldbetogetthevehicletoastopandwaitforafewminutes.Asthebrakecomponentscooldown,theirabilitytoabsorbheatreturnsandthenexttimeyouusethebrakes,theyseemtoworkjustfine.Thistypeofbrakefadewasmorecommoninoldervehicles.Newervehiclestendtohavelessoutgassingfromthebrakepadcompoundsbuttheystillsufferbrakefade.Sowhy?

It'sstilltodowiththepadsgettingtoohot.Withnewerbrakepadcompounds,thepadstransferheatintothecalipersoncetherotorsaretoohot,andthebrakefluidstartstoboilformingbubblesinit.Becauseairiscompressible（brakefluidisn't）whenyousteponthebrakes,theairbubblescompressinsteadofthefluidtransferringthemotiontothebrakecalipers.Voila.Modernbrakefade.

Sohowdotheengineersdesignbrakestoreduceoreliminatebrakefade?

Foroldervehicles,yougivethatvapourisedgassomewheretogo.Fornewervehicles,youfindsomewaytocooltherotorsoffmoreeffectively.Eitherwayyouendupwithcross-drilledorgroovedbrakerotors.Whilegroovingthesurfacemayreducethespecificheatcapacityoftherotor,itseffectisnegligibleinthegrandschemeofthings.However,underheavybrakingonceeverythingishotandtheresinisvapourising,thegroovesgivethegassomewheretogo,sothepadcancontinuetocontacttherotor,allowingyoutostop.

Thewholeunderstandingoftheconversionofenergyiscriticalinunderstandinghowandwhybrakesdowhattheydo,andwhytheyaredesignedthewaytheyare.Ifyou'veeverwatchedFormula1racing,you'llseethefrontwheelshavehugescoopsinsidethewheelpointingtothefront（seethepictureabove）.ThisistoductairtothebrakecomponentstohelpthemcooloffbecauseinF1racing,thebrakesareusedviciouslyeveryfewsecondsandspendalotoftheirtimetryingtostayhot.Withoutsomeformofcoolingassistance,thebrakeswouldbefineforthefirstfewcornersbutthenwouldfadeandbecomenearuselessbyhalfwayaroundthetrack.

Rotortechnology.

Ifabrakerotorwasasinglecastchunkofsteel,itwouldhaveterribleheatdissipationpropertiesandleavenowhereforthevapourise