汽車制動(dòng)系統(tǒng)-英文文獻(xiàn)及翻譯

BrakesystemsWeallknowthatpushingdownonthebrakepedalslowsacartoastop.Buthowdoesthishappen?Howdoesyourcartransmittheforcefromyourlegtoitswheels?Howdoesitmultiplytheforcesothatitisenoughtostopsomethingasbigasacar?BrakeImageGallery

Layoutoftypicalbrakesystem.

Seemorebrakeimages.Whenyoudepressyourbrakepedal,yourcartransmitstheforcefromyourfoottoitsbrakesthroughafluid.Sincetheactualbrakesrequireamuchgreaterforcethanyoucouldapplywithyourleg,yourcarmustalsomultiplytheforceofyourfoot.Itdoesthisintwoways:Mechanicaladvantage(leverage)HydraulicforcemultiplicationThebrakestransmittheforcetothetiresusingfriction,andthetirestransmitthatforcetotheroadusingfrictionalso.Beforewebeginourdiscussiononthecomponentsofthebrakesystem,we'llcoverthesethreeprinciples:LeverageHydraulicsFrictionLeverageandHydraulicsInthefigurebelow,aforceFisbeingappliedtotheleftendofthelever.Theleftendoftheleveristwiceaslong(2X)astherightend(X).Therefore,ontherightendoftheleveraforceof2Fisavailable,butitactsthroughhalfofthedistance(Y)thattheleftendmoves(2Y).Changingtherelativelengthsoftheleftandrightendsoftheleverchangesthemultipliers.

Thepedalisdesignedinsuchawaythatitcanmultiplytheforcefromyourlegseveraltimesbeforeanyforceiseventransmittedtothebrakefluid.Thebasicideabehindanyhydraulicsystemisverysimple:Forceappliedatonepointistransmittedtoanotherpointusinganincompressiblefluid,almostalwaysanoilofsomesort.Mostbrakesystemsalsomultiplytheforceintheprocess.Hereyoucanseethesimplestpossiblehydraulicsystem:YourbrowserdoesnotsupportJavaScriptoritisdisabled.

SimplehydraulicsystemInthefigureabove,twopistons(showninred)arefitintotwoglasscylindersfilledwithoil(showninlightblue)andconnectedtooneanotherwithanoil-filledpipe.Ifyouapplyadownwardforcetoonepiston(theleftone,inthisdrawing),thentheforceistransmittedtothesecondpistonthroughtheoilinthepipe.Sinceoilisincompressible,theefficiencyisverygood--almostalloftheappliedforceappearsatthesecondpiston.Thegreatthingabouthydraulicsystemsisthatthepipeconnectingthetwocylinderscanbeanylengthandshape,allowingittosnakethroughallsortsofthingsseparatingthetwo

Figure1.Locationofdrumbrakes.

Seemoredrumbrakepictures.Manycarshavedrumbrakesontherearwheelsanddiscbrakesonthefront.Drumbrakeshavemorepartsthandiscbrakesandarehardertoservice,buttheyarelessexpensivetomanufacture,andtheyeasilyincorporateanemergencybrakemechanism.InthiseditionofHowStuffWorks,wewilllearnexactlyhowadrumbrakesystemworks,examinetheemergencybrakesetupandfindoutwhatkindofservicingdrumbrakesneed.

Figure2.Drumbrakewithdruminplace

Figure3.DrumbrakewithoutdruminplaceLet'sstartwiththebasics.TheDrumBrakeThedrumbrakemaylookcomplicated,anditcanbeprettyintimidatingwhenyouopenoneup.Let'sbreakitdownandexplainwhateachpiecedoes.Figure4.PartsofadrumbrakeLikethediscbrake,thedrumbrakehastwobrakeshoesandapiston.Butthedrumbrakealsohasanadjustermechanism,anemergencybrakemechanismandlotsofsprings.First,thebasics:Figure5showsonlythepartsthatprovidestoppingpower.YourbrowserdoesnotsupportJavaScriptoritisdisabled.

Figure5.DrumbrakeinoperationWhenyouhitthebrakepedal,thepistonpushesthebrakeshoesagainstthedrum.That'sprettystraightforward,butwhydoweneedallofthosesprings?Thisiswhereitgetsalittlemorecomplicated.Manydrumbrakesareself-actuating.Figure5showsthatasthebrakeshoescontactthedrum,thereisakindofwedgingaction,whichhastheeffectofpressingtheshoesintothedrumwithmoreforce.Theextrabrakingforceprovidedbythewedgingactionallowsdrumbrakestouseasmallerpistonthandiscbrakes.But,becauseofthewedgingaction,theshoesmustbepulledawayfromthedrumwhenthebrakesarereleased.Thisisthereasonforsomeofthesprings.Otherspringshelpholdthebrakeshoesinplaceandreturntheadjusterarmafteritactuates.BrakeAdjusterForthedrumbrakestofunctioncorrectly,thebrakeshoesmustremainclosetothedrumwithouttouchingit.Iftheygettoofarawayfromthedrum(astheshoesweardown,forinstance),thepistonwillrequiremorefluidtotravelthatdistance,andyourbrakepedalwillsinkclosertothefloorwhenyouapplythebrakes.Thisiswhymostdrumbrakeshaveanautomaticadjuster.

Figure6.AdjustermechanismNowlet'saddinthepartsoftheadjustermechanism.Theadjusterusestheself-actuationprinciplewediscussedabove.YourbrowserdoesnotsupportJavaScriptoritisdisabled.

Figure7.DrumbrakeadjusterinoperationInFigure7,youcanseethatasthepadwearsdown,morespacewillformbetweentheshoeandthedrum.Eachtimethecarstopswhileinreverse,theshoeispulledtightagainstthedrum.Whenthegapgetsbigenough,theadjustingleverrocksenoughtoadvancetheadjustergearbyonetooth.Theadjusterhasthreadsonit,likeabolt,sothatitunscrewsalittlebitwhenitturns,lengtheningtofillinthegap.Whenthebrakeshoeswearalittlemore,theadjustercanadvanceagain,soitalwayskeepstheshoesclosetothedrum.Somecarshaveanadjusterthatisactuatedwhentheemergencybrakeisapplied.Thistypeofadjustercancomeoutofadjustmentiftheemergencybrakeisnotusedforlongperiodsoftime.Soifyouhavethistypeofadjuster,youshouldapplyyouremergencybrakeatleastonceaweek.ServicingThemostcommonservicerequiredfordrumbrakesischangingthebrakeshoes.Somedrumbrakesprovideaninspectionholeonthebackside,whereyoucanseehowmuchmaterialisleftontheshoe.Brakeshoesshouldbereplacedwhenthefrictionmaterialhasworndowntowithin1/32inch(0.8mm)oftherivets.Ifthefrictionmaterialisbondedtothebackingplate(norivets),thentheshoesshouldbereplacedwhentheyhaveonly1/16inch(1.6mm)ofmaterialleft.

PhotocourtesyofalocalAutoZonestore

Figure9.BrakeshoeJustasindiscbrakes,deepscoressometimesgetwornintobrakedrums.Ifaworn-outbrakeshoeisusedfortoolong,therivetsthatholdthefrictionmaterialtothebackingcanweargroovesintothedrum.Abadlyscoreddrumcansometimesberepairedbyrefinishing.Wherediscbrakeshaveaminimumallowablethickness,drumbrakeshaveamaximumallowablediameter.Sincethecontactsurfaceistheinsideofthedrum,asyouremovematerialfromthedrumbrakethediametergetsbigger.Figure10.Brakedrum制動(dòng)系統(tǒng)眾所周知，踩下制動(dòng)踏板可以使汽車減速至停止。但這是如何產(chǎn)生的呢？汽車是如何將力從你的腿傳遞到車輪的呢？汽車是如何將力放大到足夠大以致可以將像汽車一樣大的東西制動(dòng)的呢？制動(dòng)系統(tǒng)組件當(dāng)你踩下制動(dòng)踏板的時(shí)候，汽車通過液體把力從腳傳遞到制動(dòng)器。因?yàn)橹苿?dòng)器需要的真正力量比你的腿能提供的要大的多，所以汽車必須放大腳產(chǎn)生的力有兩種方式：機(jī)械杠桿作用液力放大制動(dòng)器通過摩擦把力傳遞給輪胎，并且輪胎也是通過摩擦把力傳遞給路面的。在我們討論制動(dòng)系統(tǒng)的組成之前，先來介紹以下三條原則：杠桿液力摩擦力杠桿和液力在下面的圖中，一個(gè)力F加在杠桿的左端。左端的杠桿長度（2X）是右端（X）的兩倍。因此杠桿右端可施加的力為2F，但是右端移動(dòng)的距離(Y)是左端距離(2Y)的一半。改變杠桿的左端和右端的長度可以改變放大系數(shù)。任何液壓系統(tǒng)背后的基本原理都是非常簡單的：作用在某一點(diǎn)力通過通常是油一類的不可壓縮的液體傳遞到另一點(diǎn)。大多數(shù)的制動(dòng)系統(tǒng)也在這個(gè)過程中放大力。下面的是最簡單的液壓系統(tǒng)：簡單液壓系統(tǒng)在上圖中，兩個(gè)活塞放在兩個(gè)充滿油的玻璃液壓缸中并且由充滿油的管道相連。如果在一個(gè)活塞上施加一個(gè)向下的力，那么力將通過管道中的油傳遞到第二個(gè)活塞。因?yàn)橛鸵菏遣豢蓧嚎s的，所以傳遞效率很好，大部分的作用力都傳遞到了另一個(gè)活塞。液壓系統(tǒng)的好處連接兩液壓缸的管道可以是任何長度和形狀，這樣就可以使管道彎曲的通過兩活塞之間的各種部件。管道也可以是分叉的，如果有需要的話，這樣一個(gè)主缸可以驅(qū)動(dòng)數(shù)個(gè)副缸。如下圖所示：帶有兩個(gè)副缸的主缸液壓系統(tǒng)的另一個(gè)好處是產(chǎn)生放大（或者縮?。┝ο喈?dāng)?shù)厝菀住Ｈ绻阋蛔x過滑車設(shè)備工作原理或者齒輪齒數(shù)比原理，那么你就會(huì)知道在機(jī)械系統(tǒng)中把力轉(zhuǎn)化為距離處理是很常見的。在液壓系統(tǒng)中，我們所要做的就是相對(duì)地改變一組活塞和液壓缸的尺寸。如下圖所示：液壓增力原理為了確定上圖中的放大因子，先由觀察活塞的尺寸開始。假設(shè)左邊活塞的直徑為2英尺（5.08cm而右邊的直徑為6英尺（15.24cm）。兩個(gè)活塞的面積是Pi*r2。因此左面活塞的面積是3.14，而右面的面積是28.26。右面活塞的面積是左邊的九倍大。這就意味著無論在左面的活塞上施加多大的力，在右面的活塞上就會(huì)輸出九倍于左面的力。所以，如果在左邊活塞上施加100磅向下的力，那么在右面活塞上將產(chǎn)生900磅向上的力。唯一的補(bǔ)償是左面的活塞要移動(dòng)9英尺（22.86cm）來使右面提升1英尺（2.54cm）一個(gè)簡單的制動(dòng)系統(tǒng)在我們深入了解一個(gè)真實(shí)的制動(dòng)系統(tǒng)的各部分之前，讓我們先來看一個(gè)簡化的系統(tǒng)：我們可以看到踏板到樞軸的距離是液壓缸到樞軸距離的4倍，所以施加在踏板上的力在傳遞到液壓缸之前將被增加4倍。我們還可以看到制動(dòng)缸的直徑是踏板缸直徑的3倍。這就將力進(jìn)一步放大了九倍。最終這個(gè)系統(tǒng)將腿上的力增加了36倍。所以，如果在踏板上施加10磅的力，將在擠壓制動(dòng)帶的輪上產(chǎn)生369磅（162kg）的力。下面是這種簡單系統(tǒng)所存在的問題。要是系統(tǒng)有泄漏該怎么辦呢？如果是輕微泄漏，最終將會(huì)沒有足夠的油使制動(dòng)缸充滿，并且制動(dòng)器將停止工作。如果是嚴(yán)重泄漏，那么在你制動(dòng)的第一時(shí)間，所有的油液將從泄露處噴射而出，并且制動(dòng)系統(tǒng)將徹底地不起作用。鼓式制動(dòng)器的工作原理和盤式制動(dòng)器是一樣的：制動(dòng)面接觸一個(gè)磨砂的表面。在這個(gè)系統(tǒng)中，那個(gè)表面稱作制動(dòng)鼓圖1.制動(dòng)鼓的位置許多汽車的后輪安裝鼓式制動(dòng)器，而盤式制動(dòng)器安裝在前面。鼓式制動(dòng)器比盤式制動(dòng)器有更多的零件并且更難檢修。但是制造成本相對(duì)便宜，還有鼓式制動(dòng)器容易組裝一個(gè)緊急使用的制動(dòng)裝置。在本版本的HowStuffWorks中，我們將詳盡了解鼓式制動(dòng)系統(tǒng)是如何工作的?？疾炀o急制動(dòng)系統(tǒng)的組成，并且找到鼓式制動(dòng)器需要何種檢修工作。圖2.有鼓的鼓式制動(dòng)器圖3.未安裝鼓的鼓式制動(dòng)器讓我們基礎(chǔ)開始：鼓式制動(dòng)器鼓式制動(dòng)器可能看起來比較復(fù)雜，它可以是很復(fù)雜的，當(dāng)你打開一個(gè)的時(shí)候。讓我們拆開它，并解釋每一塊的作用。圖4.鼓式制動(dòng)器的組成如盤式制動(dòng)器，鼓式制動(dòng)器有兩個(gè)制動(dòng)蹄和一個(gè)活塞。但是鼓式制動(dòng)器也有一個(gè)調(diào)節(jié)機(jī)制，緊急剎車機(jī)制和大量的彈簧。首先，基礎(chǔ)知識(shí)：圖5顯示只有部分提供的制動(dòng)力。圖5.工作狀態(tài)下的鼓式制動(dòng)器當(dāng)你踩下剎車踏板時(shí)，活塞推動(dòng)緊靠著鼓的制動(dòng)蹄。這是很簡單的，但為什