制动器外文翻译 制动器 精品.docx

制动器外文翻译 制动器 精品.docx

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制动器外文翻译制动器精品

本科生毕业设计（论文）外文翻译

毕业设计（论文）题目：

几种典型的制动器的对比分析与设计

外文题目：

THEBRAKEBIBLE

译文题目：

制动器

学生姓名：

专业：

车辆工程

指导教师姓名：

评阅日期：

THEBRAKEBIBLE

Brakes-whatdotheydo?

Thesimpleanswer:

theyslowyoudown.

Thecomplexanswer:

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,itwouldhaveterribleheatdissipationpropertiesandleavenowhereforthevapourisedgastogo.Becauseofthis,brakerotorsaretypicallymodifiedwithallmannerofextradesignfeaturestohelpthemcooldownasquicklyaspossibleaswellasdissapateanygasfrombetweenthepadsandrotors.Thediagramhereshowssomeexamplesofrotortypeswiththevariousmodificationthatcanbedonetothemtohelpthemcreatemorefriction,dispersemoreheatmorequickly,andventilategas.Fromlefttoright.

1:

Basicbrakerotor.2:

Groovedrotor-thegroovesgivemorebiteandthusmorefrictionastheypassbetweenthebrakepadsTheyalsoallowgastoventfrombetweenthepadsandtherotor.3:

Grooved,drilledrotor-thedrilledholesagaingivemorebite,butalsoallowaircurrents（eddies）toblowthroughthebrakedisctoassistcoolingandventilatinggas.4:

Dualventilatedrotors-sameasbeforebutnowwithtworotorsinsteadofone,andwithvanesinbetweenthemtogenerateavortexwhichwillcooltherotorsevenfurtherwhilsttryingtoactually'suck'anygasawayfromthepads.

Animportantnoteaboutdrilledrotors:

Drilledrotorsaretypicallyonlyfound（andtobeusedon）racecars.Thedrillingweakenstherotorsandtypicallyresultsinmicrofracturestotherotor.Onracecarsthisisn'taproblem-thebrakesarechangedaftereachraceorweekend.Butonaroadcar,thiscaneventuallyleadtobrakerotorfailure-notwhatyouwant.Ionlymentionthisbecauseofalotofperformancesupplierswillsupplyyouwithdrilledrotorsforstreetcarswithoutmentioningthislittlefact.

Bigrotors.

Howdoesallthisapplytobiggerbrakerotors-acommonsportscarupgrade?

Sportscarsandracebikestypicallyhavemuchbiggerdiscsorrotorsthanyouraveragefamilycar.Abiggerrotorhasmorematerialinitsoitcanabsorbmoreheat.Morematerialalsomeansalargersurfaceareaforthepadstogeneratefrictionwith,andbetterheatdissipation.Largerrotorsalsoputthepointofcontactwiththepadsfurtherawayfromtheaxleofrotation.Thisprovidesalargermechanicaladvantagetoresisttheturningoftherotoritself.Tobestillustratehowthisworks,imagineaspinningsteeldisconanaxleinfrontofyou.Ifyouclampedyourthumbseithersideofthediscclosetothemiddle,yourthumbswouldheatupveryquicklyandyou'dneedtopushprettyhardtogeneratethefrictionrequiredtoslowthediscdown.Nowimaginedoingthesamethingbutclampingyourthumbstogetherclosetotheouterrimofthedisc.Thediscwillstopspinningmuchmorequicklyandyourthumbswon'tgetashot.That,inanutshellexplainsthewholeprinciplebehindwhybiggerrotors=betterstoppingpower.

Thedifferenttypesofbrake.

Allbrakesworkbyfriction.Frictioncausesheatwhichispartofthekineticenergyconversionprocess.Howtheycreatefrictionisdowntothevariousdesigns.

Bicyclewheelbrakes

IthoughtI'dcoverthesebecausethey'reaboutthemostbasictypeoffunctioningbrakethatyoucansee,watchworking,andunderstand.Theconstructionisverysimpleandout-in-the-open.Apairofrubberblocksareattachedtoapairofcaliperswhicharepivotedontheframe.Whenyoupullthebrakecable,thepadsarepressedagainstthesideorinneredgeofthebicyclewheelrim.Therubbercreatesfriction,whichcreatesheat,whichisthetransferofkineticenergythatslowsyoudown.There'sonlyreallytwotypesofbicyclebrake-thoseonwhicheachbrakeshoesharesthesamepivotpoint,andthosewithtwopivotpoints.Ifyoucanlookatabicyclebrakeandnotunderstandwhat'sgoingon,therestofthispageisgoingtocauseyouabitofaheadache.

Drumbrakes-singleleadingedge

Thenext,morecomplicatedtypeofbrakeisadrumbrake.Theconcepthereissimple.Twosemicircularbrakeshoessitinsideaspinningdrumwhichisattachedtothewheel.Whenyouapplythebrakes,theshoesareexpandedoutwardstopressagainsttheinsideofthedrum.Thiscreatesfriction,whichcreatesheat,whichtransferskineticenergy,whichslowsyoudown.Theexamplebelowshowsasimplemodel.Theactuatorinthiscaseistheblueellipticalobject.Asthatistwisted,itforcesagainstthebrakeshoesandinturnforcesthemtoexpandoutwards.Thereturnspringiswhatpullstheshoesbackawayfromthesurfaceofthebrakedrumwhenthebrakesarereleased.Seethelatersectionformoreinformationonactuatortypes.

The"singleleadingedge"referstothenumberofpartsofthebrakeshoewhichactuallycontactthespinningdrum.Becausethebrakeshoepivotsatoneend,simplegeometrymeansthattheentirebrakepadcannotcontactthebrakedrum.Theleadingedgeisthetermgiventothepartofthebrakepadwhichdoescontactthedrum,andinthecaseofasingleleadingedgesystem,it'sthepartofthepadclosesttotheactuator.Thisdiagram（right）showswhathappensasthebrakesareapplied.Theshoesarepressedoutwardsandthepartofthebrakepadwhichfirstcontactsthedrumistheleadingedge.Theactionofthedrumspinningactuallyhelpstodrawthebrakepadoutwardsbecauseoffriction,whichcausesthebrakesto"bite".Thetrailingedgeofthebrakeshoemakesvirtuallynocontactwiththedrumatall.Thissimplegeometryexplainswhyit'sreallydifficulttostopavehicler