鼓式制动器外文文献及翻译.docx

鼓式制动器外文文献及翻译.docx

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鼓式制动器外文文献及翻译

鼓式制动器-外文文献及翻译

Drumbrake

Adrumbrakewiththedrumremovedasusedontherearwheelofacarortruck.Notethatinthisinstallation,acable-operatedparkingbrakeusestheserviceshoes.

Adrumbrakeisabrakeinwhichthefrictioniscausedbyasetofshoesorpadsthatpressagainstarotatingdrum-shapedpartcalledabrakedrum.

Theterm"drumbrake"usuallymeansabrakeinwhichshoespressontheinnersurfaceofthedrum.Whenshoespressontheoutsideofthedrum,itisusuallycalledaclaspbrake.Wherethedrumispinchedbetweentwoshoes,similartoaconventionaldiskbrake,itissometimescalleda"pinchdrumbrake",althoughsuchbrakesarerelativelyrare.Arelatedtypeofbrakeusesaflexiblebeltor"band"wrappingaroundtheoutsideofadrum,calledabandbrake.

History

Adrumbrakeattherearwheelofamotorbike

KawasakiW800

Themodernautomobiledrumbrakewasinventedin1902byLouisRenault,thoughaless-sophisticateddrumbrakehadbeenusedbyMaybachayearearlier.Inthefirstdrumbrakes,theshoesweremechanicallyoperatedwithleversandrodsorcables.Fromthemid-1930stheshoeswereoperatedwithoilpressureinasmallwheelcylinderandpistons（asinthepicture）,thoughsomevehiclescontinuedwithpurely-mechanicalsystemsfordecades.Somedesignshavetwowheelcylinders.

Theshoesindrumbrakesaresubjecttowearandthebrakesneededtobeadjustedregularlyuntiltheintroductionofself-adjustingdrumbrakesinthe1950s.Inthe1960sand1970sbrakedrumsonthefrontwheelsofcarsweregraduallyreplacedwithdiscbrakesandnowpracticallyallcarsusediscbrakesonthefrontwheels,withmanyofferingdiscbrakesonallwheels.However,drumbrakesarestilloftenusedforhandbrakesasithasprovenverydifficulttodesignadiscbrakesuitableforholdingacarwhenitisnotinuse.Moreover,itisveryeasytofitadrumhandbrakeinsideadiscbrakesothatoneunitservesasbothservicebrakeandhandbrake.

Earlytypebrakeshoescontainedasbestos.Whenworkingonbrakesystemsofoldercars,caremustbetakennottoinhaleanydustpresentinthebrakeassembly.TheUnitedStatesFederalGovernmentbegantoregulateasbestosproduction,andbrakemanufacturershadtoswitchtonon-asbestoslinings.Ownersinitiallycomplainedofpoorbrakingwiththereplacements;however,technologyeventuallyadvancedtocompensate.Amajorityofdaily-drivenoldervehicleshavebeenfittedwithasbestos-freelinings.Manyothercountriesalsolimittheuseofasbestosinbrakes.Earlyautomotivebrakesystems,aftertheeraofhandleversofcourse,usedadrumdesignatallfourwheels.Theywerecalleddrumbrakesbecausethecomponentswerehousedinarounddrumthatrotatedalongwiththewheel.Insidewasasetofshoesthat,whenthebrakepedalwaspressed,wouldforcetheshoesagainstthedrumandslowthewheel.Fluidwasusedtotransferthemovementofthebrakepedalintothemovementofthebrakeshoes,whiletheshoesthemselvesweremadeofaheat-resistantfrictionmaterialsimilartothatusedonclutchplates.Thisbasicdesignprovedcapableundermostcircumstances,butithadonemajorflaw.Underhighbrakingconditions,likedescendingasteephillwithaheavyloadorrepeatedhigh-speedslowdowns,drumbrakeswouldoftenfadeandloseeffectiveness.Usuallythisfadingwastheresultoftoomuchheatbuild-upwithinthedrum.Rememberthattheprincipleofbrakinginvolvesturningkineticenergy（wheelmovement）intothermalenergy（heat）.Forthisreason,drumbrakescanonlyoperateaslongastheycanabsorbtheheatgeneratedbyslowingavehicle'swheels.Oncethebrakecomponentsthemselvesbecomesaturatedwithheat,theylosetheabilitytohaltavehicle,whichcanbesomewhatdisconcertingtothevehicle'soperator.

Self-applyingcharacteristic

Drumbrakeshaveanatural"self-applying"characteristic.[1]Therotationofthedrumcandrageitherorbothoftheshoesintothefrictionsurface,causingthebrakestobiteharder,whichincreasestheforceholdingthemtogether.Thisincreasesthestoppingpowerwithoutanyadditionaleffortbeingexpendedbythedriver,butitdoesmakeitharderforthedrivertomodulatethebrake'ssensitivity.Italsomakesthebrakemoresensitivetobrakefade,asadecreaseinbrakefrictionalsoreducestheamountofbrakeassist.

Discbrakesexhibitnoself-applyingeffectbecausethehydraulicpressureactingonthepadsisperpendiculartothedirectionofrotationofthedisc.Discbrakesystemsusuallyhaveservoassistance（"BrakeBooster"）tolessenthedriver'spedaleffort,butsomediscbrakedcars（notablyracecars）andsmallerbrakesformotorcycles,etc.,donotneedtouseservos.

Note:

Inmostdesigns,the"selfapplying"effectonlyoccursononeshoe.Whilethisshoeisfurtherforcedintothedrumsurfacebyamomentduetofriction,theoppositeeffectishappeningontheothershoe.Thefrictionforceistryingtorotateitawayfromthedrum.Theforcesaredifferentoneachbrakeshoeresultinginoneshoewearingfaster.Itispossibletodesignatwo-shoedrumbrakewherebothshoesareself-applying（havingseparateactuatorsandpivotedatoppositeends）,buttheseareveryuncommoninpractice.

Drumbrakedesigns

Renderingofadrumbrake

Drumbrakesaretypicallydescribedaseitherleading/trailingortwinleading.[1]

Reardrumbrakesaretypicallyofaleading/trailingdesign（ForNonServoSystems）,or[Primary/Secondary]（ForDuoServoSystems）theshoesbeingmovedbyasingledouble-actinghydrauliccylinderandhingedatthesamepoint.[1]Inthisdesign,oneofthebrakeshoeswillalwaysexperiencetheself-applyingeffect,irrespectiveofwhetherthevehicleismovingforwardsorbackwards.[1]Thisisparticularlyusefulontherearbrakes,wherethefootbrake（handbrakeorparkingbrake）mustexertenoughforcetostopthevehiclefromtravellingbackwardsandholditonaslope.Providedthecontactareaofthebrakeshoesislargeenough,whichisn'talwaysthecase,theself-applyingeffectcansecurelyholdavehiclewhentheweightistransferredtotherearbrakesduetotheinclineofaslopeorthereversedirectionofmotion.Afurtheradvantageofusingasinglehydrauliccylinderontherearisthattheoppositepivotmaybemadeintheformofadoublelobedcamthatisrotatedbytheactionoftheparkingbrakesystem.

Frontdrumbrakesmaybeofeitherdesigninpractice,butthetwinleadingdesignismoreeffective.[1]Thisdesignusestwoactuatingcylindersarrangedsothatbothshoeswillutilizetheself-applyingcharacteristicwhenthevehicleismovingforwards.[1]Thebrakeshoespivotatoppositepointstoeachother.[1]Thisgivesthemaximumpossiblebrakingwhenmovingforwards,butisnotsoeffectivewhenthevehicleistravelinginreverse.[1]

Theoptimumarrangementoftwinleadingfrontbrakeswithleading/trailingbrakesontherearallowsformorebrakingforcetobedeployedatthefrontofthevehiclewhenitismovingforwards,withlessattherear.Thishelpstopreventtherearwheelslockingup,butstillprovidesadequatebrakingattherearwhenitisneeded.[1]

Thebrakedrumitselfisfrequentlymadeofcastiron,althoughsomevehicleshaveusedaluminumdrums,particularlyforfront-wheelapplications.Aluminumconductsheatbetterthancastiron,whichimprovesheatdissipationandreducesfade.Aluminumdrumsarealsolighterthanirondrums,whichreducesunsprungweight.Becausealuminumwearsmoreeasilythaniron,aluminumdrumswillfrequentlyhaveanironorsteellinerontheinnersurfaceofthedrum,bondedorrivetedtothealuminumoutershell.

Advantages

Drumbrakesareusedinmostheavydutytrucks,somemediumandlightdutytrucks,andfewcars,dirtbikes,andATV's.Drumbrakesareoftenappliedtotherearwheelssincemostofthestoppingforceisgeneratedbythefrontbrakesofthevehicleandthereforetheheatgeneratedintherearissignificantlyless.Drumbrakesallowsimpleincorporationofaparkingbrake.Drumbrakesarealsooccasionallyfittedastheparking（andemergency）brakeevenwhentherearwheelsusediskbrakesasthemainbrakes.Inthissituation,asmalldrumisusuallyfittedwithinoraspartofthebrakediskalsoknownasabanksiabrake.

Inhybridvehicleapplications,wearonbrakingsystemsisgreatlyreducedbyenergyrecoveringmotor-generators（seeregenerativebraking）,sosomehybridvehiclessuchastheGMCYukonhybridandToyotaPrius（exceptthethirdgeneration）usedrumbrakes.

Discbrakesrelyonpliabilityofcalipersealsandslightrunouttoreleasepads,leadingtodrag,fuelmileageloss,anddiscscoring.Drumbrakereturnspringsgivemorepositiveactionand,adjustedcorrectly,oftenhavelessdragwhenreleased.

Certainheavierdutydrumbrakesystemscompensateforloadwhendeterminingwheelcylinderpressure;afeatureunavailablewhendisksareemployed.OnesuchvehicleistheJeepComanche.TheComanchecanautomaticallysendmorepressuretothereardrumsdependingonthesizeoftheload,whereasthiswouldnotbepossiblewithdisks.

Duetothefactthatadrumbrakesfrictioncontactareaisatthecircumferenceofthebrake,adrumbrakecanprovidemorebrakingforcethananequaldiameterdiscbrake.Theincreasedfrictioncontactareaofdrumbrakeshoesonthedrumallowsdrumbrakeshoestolastlongerthandiscbrakepadsusedinabrakesystemofsimilardimensionsandbrakingforce.Drumbrakesretainheatandaremorecomplexthandiscbrakesbutareoftentimesthemoreeconomicalandpowerfulbraketypetouseinrearbrakeapplicationsduetothelowheatgenerationofrearbrakes,adrumbrakesselfapplyingnature,largefrict