汽车制动系统英文文献及翻译Word文档下载推荐.docx

汽车制动系统英文文献及翻译Word文档下载推荐.docx

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∙Mechanicaladvantage（leverage）

∙Hydraulicforcemultiplication

Thebrakestransmittheforcetothetiresusingfriction,andthetirestransmitthatforcetotheroadusingfrictionalso.Beforewebeginourdiscussiononthecomponentsofthebrakesystem，we’llcoverthesethreeprinciples:

∙Leverage

∙Hydraulics

∙Friction

LeverageandHydraulics

Inthefigurebelow,aforceFisbeingappliedtotheleftendofthelever.Theleftendoftheleveristwiceaslong（2X）astherightend（X）.Therefore,ontherightendoftheleveraforceof2Fisavailable，butitactsthroughhalfofthedistance（Y）thattheleftendmoves（2Y）。

Changingtherelativelengthsoftheleftandrightendsoftheleverchangesthemultipliers。

Thepedalisdesignedinsuchawaythatitcanmultiplytheforcefromyourlegseveraltimesbeforeanyforceiseventransmittedtothebrakefluid.

Thebasicideabehindanyhydraulicsystemisverysimple:

Forceappliedatonepointistransmittedtoanotherpointusinganincompressiblefluid，almostalwaysanoilofsomesort。

Mostbrakesystemsalsomultiplytheforceintheprocess。

Hereyoucanseethesimplestpossiblehydraulicsystem:

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Simplehydraulicsystem

Inthefigureabove，twopistons（showninred）arefitintotwoglasscylindersfilledwithoil（showninlightblue）andconnectedtooneanotherwithanoil-filledpipe。

Ifyouapplyadownwardforcetoonepiston（theleftone，inthisdrawing），thentheforceistransmittedtothesecondpistonthroughtheoilinthepipe.Sinceoilisincompressible,theefficiencyisverygood——almostalloftheappliedforceappearsatthesecondpiston.Thegreatthingabouthydraulicsystemsisthatthepipeconnectingthetwocylinderscanbeanylengthandshape，allowingittosnakethroughallsortsofthingsseparatingthetwopistons.Thepipecanalsofork,sothatonemastercylindercandrivemorethanoneslavecylinderifdesired，asshowninhere：

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Mastercylinderwithtwoslaves

Theotherneatthingaboutahydraulicsystemisthatitmakesforcemultiplication（ordivision）fairlyeasy。

IfyouhavereadHowaBlockandTackleWorksorHowGearRatiosWork，thenyouknowthattradingforcefordistanceisverycommoninmechanicalsystems.Inahydraulicsystem,allyouhavetodoischangethesizeofonepistonandcylinderrelativetotheother,asshownhere：

Hydraulicmultiplication

Todeterminethemultiplicationfactorinthefigureabove，startbylookingatthesizeofthepistons。

Assumethatthepistonontheleftis2inches（5。

08cm）indiameter（1-inch/2.54cmradius）,whilethepistonontherightis6inches（15.24cm）indiameter（3—inch/7.62cmradius）.TheareaofthetwopistonsisPi*r2.Theareaoftheleftpistonistherefore3。

14,whiletheareaofthepistonontherightis28.26。

Thepistonontherightisninetimeslargerthanthepistonontheleft。

Thismeansthatanyforceappliedtotheleft—handpistonwillcomeoutninetimesgreaterontheright-handpiston。

So,ifyouapplya100-pounddownwardforcetotheleftpiston，a900—poundupwardforcewillappearontheright.Theonlycatchisthatyouwillhavetodepresstheleftpiston9inches（22.86cm）toraisetherightpiston1inch（2。

54cm）.

ASimpleBrakeSystem

Beforewegetintoallthepartsofanactualcarbrakesystem,let’slookatasimplifiedsystem：

Asimplebrakesystem

Youcanseethatthedistancefromthepedaltothepivotisfourtimesthedistancefromthecylindertothepivot，sotheforceatthepedalwillbeincreasedbyafactoroffourbeforeitistransmittedtothecylinder.

Youcanalsoseethatthediameterofthebrakecylinderisthreetimesthediameterofthepedalcylinder.Thisfurthermultipliestheforcebynine。

Alltogether,thissystemincreasestheforceofyourfootbyafactorof36。

Ifyouput10poundsofforceonthepedal,360pounds（162kg）willbegeneratedatthewheelsqueezingthebrakepads。

Thereareacoupleofproblemswiththissimplesystem。

Whatifwehavealeak？

Ifitisaslowleak，eventuallytherewillnotbeenoughfluidlefttofillthebrakecylinder，andthebrakeswillnotfunction.Ifitisamajorleak,thenthefirsttimeyouapplythebrakesallofthefluidwillsquirtouttheleakandyouwillhavecompletebrakefailure。

Drumbrakesworkonthesameprincipleasdiscbrakes：

Shoespressagainstaspinningsurface。

Inthissystem，thatsurfaceiscalledadrum.

Figure1.Locationofdrumbrakes. 

Seemoredrumbrakepictures。

Manycarshavedrumbrakesontherearwheelsanddiscbrakesonthefront。

Drumbrakeshavemorepartsthandiscbrakesandarehardertoservice,buttheyarelessexpensivetomanufacture，andtheyeasilyincorporateanemergencybrakemechanism.

InthiseditionofHowStuffWorks,wewilllearnexactlyhowadrumbrakesystemworks，examinetheemergencybrakesetupandfindoutwhatkindofservicingdrumbrakesneed.

Figure2.Drumbrakewithdruminplace

Figure3.Drumbrakewithoutdruminplace

Let'

sstartwiththebasics。

TheDrumBrake

Thedrumbrakemaylookcomplicated,anditcanbeprettyintimidatingwhenyouopenoneup.Let’sbreakitdownandexplainwhateachpiecedoes。

Figure4.Partsofadrumbrake

Likethediscbrake,thedrumbrakehastwobrakeshoesandapiston。

Butthedrumbrakealsohasanadjustermechanism，anemergencybrakemechanismandlotsofsprings。

First,thebasics:

Figure5showsonlythepartsthatprovidestoppingpower.

Figure5。

Drumbrakeinoperation

Whenyouhitthebrakepedal，thepistonpushesthebrakeshoesagainstthedrum.That’sprettystraightforward，butwhydoweneedallofthosesprings?

Thisiswhereitgetsalittlemorecomplicated.Manydrumbrakesareself-actuating。

Figure5showsthatasthebrakeshoescontactthedrum，thereisakindofwedgingaction,whichhastheeffectofpressingtheshoesintothedrumwithmoreforce。

Theextrabrakingforceprovidedbythewedgingactionallowsdrumbrakestouseasmallerpistonthandiscbrakes.But，becauseofthewedgingaction,theshoesmustbepulledawayfromthedrumwhenthebrakesarereleased.Thisisthereasonforsomeofthesprings.Otherspringshelpholdthebrakeshoesinplaceandreturntheadjusterarmafteritactuates.

BrakeAdjuster

Forthedrumbrakestofunctioncorrectly,thebrakeshoesmustremainclosetothedrumwithouttouchingit。

Iftheygettoofarawayfromthedrum（astheshoesweardown，forinstance）,thepistonwillrequiremorefluidtotravelthatdistance,andyourbrakepedalwillsinkclosertothefloorwhenyouapplythebrakes。

Thisiswhymostdrumbrakeshaveanautomaticadjuster.

Figure6.Adjustermechanism

Nowlet'

saddinthepartsoftheadjustermechanism。

Theadjusterusestheself-actuationprinciplewediscussedabove。

Figure7.Drumbrakeadjusterinoperation

InFigure7，youcanseethatasthepadwearsdown,morespacewillformbetweentheshoeandthedrum。

Eachtimethecarstopswhileinreverse,theshoeispulledtightagainstthedrum.Whenthegapgetsbigenough,theadjustingleverrocksenoughtoadvancetheadjustergearbyonetooth。

Theadjusterhasthreadsonit,likeabolt,sothatitunscrewsalittlebitwhenitturns，lengtheningtofillinthegap。

Whenthebrakeshoeswearalittlemore，theadjustercanadvanceagain，soitalwayskeepstheshoesclosetothedrum。

Somecarshaveanadjusterthatisactuatedwhentheemergencybrakeisapplied.Thistypeofadjustercancomeoutofadjustmentiftheemergencybrakeisnotusedforlongperiodsoftime.Soifyouhavethistypeofadjuster,youshouldapplyyouremergencybrakeatleastonceaweek。

Servicing

Themostcommonservicerequiredfordrumbrakesischangingthebrakeshoes.Somedrumbrakesprovideaninspectionholeonthebackside，whereyoucanseehowmuchmaterialisleftontheshoe。

Brakeshoesshouldbereplacedwhenthefrictionmaterialhasworndowntowithin1/32inch（0。

8mm）oftherivets。

Ifthefrictionmaterialisbondedtothebackingplate（norivets），thentheshoesshouldbereplacedwhentheyhaveonly1/16inch（1.6mm）ofmaterialleft.

PhotocourtesyofalocalAutoZonestore

Figure9.Brakeshoe

Justasindiscbrakes,deepscoressometimesgetwornintobrakedrums。

Ifaworn—outbrakeshoeisusedfortoolong,therivetsthatholdthefrictionmaterialtothebackingcanweargroovesintothedrum.Abadlyscoreddrumcansometimesberepairedbyrefinishing.Wherediscbrakeshaveaminimumallowablethickness，drumbrakeshaveamaximumallowablediameter。

Sincethecontactsurfaceistheinsideofthedrum,asyouremovematerialfromthedrumbrakethediametergetsbigger.

Figure10.Brak