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外文翻译--制动系统.doc

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外文翻译--制动系统.doc

英文原文BrakesystemsWeallknowthatpushingdownonthebrakepedalslowsacartoastop.ButhowdoesthishappenHowdoesyourcartransmittheforcefromyourlegtoitswheelsHowdoesitmultiplytheforcesothatitisenoughtostopsomethingasbigasacarWhenyoudepressyourbrakepedal,yourcartransmitstheforcefromyourfoottoitsbrakesthroughafluid.Sincetheactualbrakesrequireamuchgreaterforcethanyoucouldapplywithyourleg,yourcarmustalsomultiplytheforceofyourfoot.ItdoesthisintwowaysMechanicaladvantageleverageHydraulicforcemultiplicationThebrakestransmittheforcetothetiresusingfriction,andthetirestransmitthatforcetotheroadusingfrictionalso.Beforewebeginourdiscussiononthecomponentsofthebrakesystem,wellcoverthesethreeprinciplesLeverageHydraulicsFrictionLeverageandHydraulicsInthefigurebelow,aforceFisbeingappliedtotheleftendofthelever.Theleftendoftheleveristwiceaslong2XastherightendX.Therefore,ontherightendoftheleveraforceof2Fisavailable,butitactsthroughhalfofthedistanceYthattheleftendmoves2Y.Changingtherelativelengthsoftheleftandrightendsoftheleverchangesthemultipliers.ThebasicideabehindanyhydraulicsystemisverysimpleForceappliedatonepointistransmittedtoanotherpointusinganincompressiblefluid,almostalwaysanoilofsomesort.Mostbrakesystemsalsomultiplytheforceintheprocess.HereyoucanseethesimplestpossiblehydraulicsystemYourbrowserdoesnotsupportJavaScriptoritisdisabled.SimplehydraulicsystemInthefigureabove,twopistonsshowninredarefitintotwoglasscylindersfilledwithoilshowninlightblueandconnectedtooneanotherwithanoilfilledpipe.Ifyouapplyadownwardforcetoonepistontheleftone,inthisdrawing,thentheforceistransmittedtothesecondpistonthroughtheoilinthepipe.Sinceoilisincompressible,theefficiencyisverygoodalmostalloftheappliedforceappearsatthesecondpiston.Thegreatthingabouthydraulicsystemsisthatthepipeconnectingthetwocylinderscanbeanylengthandshape,allowingittosnakethroughallsortsofthingsseparatingthetwopistons.Thepipecanalsofork,sothatonemastercylindercandrivemorethanoneslavecylinderifdesired,asshowninhereYourbrowserdoesnotsupportJavaScriptoritisdisabled.MastercylinderwithtwoslavesTheotherneatthingaboutahydraulicsystemisthatitmakesforcemultiplicationordivisionfairlyeasy.IfyouhavereadHowaBlockandTackleWorksorHowGearRatiosWork,thenyouknowthattradingforcefordistanceisverycommoninmechanicalsystems.Inahydraulicsystem,allyouhavetodoischangethesizeofonepistonandcylinderrelativetotheother,asshownhereYourbrowserdoesnotsupportJavaScriptoritisdisabled.HydraulicmultiplicationTodeterminethemultiplicationfactorinthefigureabove,startbylookingatthesizeofthepistons.Assumethatthepistonontheleftis2inches5.08cmindiameter1inch/2.54cmradius,whilethepistonontherightis6inches15.24cmindiameter3inch/7.62cmradius.TheareaofthetwopistonsisPir2.Theareaoftheleftpistonistherefore3.14,whiletheareaofthepistonontherightis28.26.Thepistonontherightisninetimeslargerthanthepistonontheleft.Thismeansthatanyforceappliedtothelefthandpistonwillcomeoutninetimesgreaterontherighthandpiston.So,ifyouapplya100pounddownwardforcetotheleftpiston,a900poundupwardforcewillappearontheright.Theonlycatchisthatyouwillhavetodepresstheleftpiston9inches22.86cmtoraisetherightpiston1inch2.54cm.ASimpleBrakeSystemBeforewegetintoallthepartsofanactualcarbrakesystem,letslookatasimplifiedsystemYourbrowserdoesnotsupportJavaScriptoritisdisabled.AsimplebrakesystemYoucanseethatthedistancefromthepedaltothepivotisfourtimesthedistancefromthecylindertothepivot,sotheforceatthepedalwillbeincreasedbyafactoroffourbeforeitistransmittedtothecylinder.Youcanalsoseethatthediameterofthebrakecylinderisthreetimesthediameterofthepedalcylinder.Thisfurthermultipliestheforcebynine.Alltogether,thissystemincreasestheforceofyourfootbyafactorof36.Ifyouput10poundsofforceonthepedal,360pounds162kgwillbegeneratedatthewheelsqueezingthebrakepads.Thereareacoupleofproblemswiththissimplesystem.WhatifwehavealeakIfitisaslowleak,eventuallytherewillnotbeenoughfluidlefttofillthebrakecylinder,andthebrakeswillnotfunction.Ifitisamajorleak,thenthefirsttimeyouapplythebrakesallofthefluidwillsquirtouttheleakandyouwillhavecompletebrakefailure.DrumbrakesworkonthesameprincipleasdiscbrakesShoespressagainstaspinningsurface.Inthissystem,thatsurfaceiscalledadrum.Figure1.Locationofdrumbrakes.Seemoredrumbrakepictures.Manycarshavedrumbrakesontherearwheelsanddiscbrakesonthefront.Drumbrakeshavemorepartsthandiscbrakesandarehardertoservice,buttheyarelessexpensivetomanufacture,andtheyeasilyincorporateanemergencybrakemechanism.InthiseditionofHowStuffWorks,wewilllearnexactlyhowadrumbrakesystemworks,examinetheemergencybrakesetupandfindoutwhatkindofservicingdrumbrakesneed.Figure2.Drumbrakewithdruminplace

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