汽車制動系統(tǒng)-英文文獻及翻譯

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制動系統(tǒng)眾所周知，踩下制動踏板可以使汽車減速至停止。但這是如何產生的呢？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的呢？制動系統(tǒng)組件當你踩下制動踏板的時候，汽車通過液體把力從腳傳遞到制動器。因為制動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生的力有兩種方式：機械杠桿作用液力放大制動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：作用在某一點力通過通常是油一類的不可壓縮的液體傳遞到另一點。大多數(shù)的制動系統(tǒng)也在這個過程中放大力。下面的是最簡單的液壓系統(tǒng)：簡單液壓系統(tǒng)在上圖中，兩個活塞放在兩個充滿油的玻璃液壓缸中并且由充滿油的管道相連。如果在一個活塞上施加一個向下的力，那么力將通過管道中的油傳遞到第二個活塞。因為油液是不可壓縮的，所以傳遞效率很好，大部分的作用力都傳遞到了另一個活塞。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，這樣一個主缸可以驅動數(shù)個副缸。如下圖所示：帶有兩個副缸的主缸液壓系統(tǒng)的另一個好處是產生放大（或者縮小）力相當?shù)厝菀?。如果你一讀過滑車設備工作原理或者齒輪齒數(shù)比原理，那么你就會知道在機械系統(tǒng)中把力轉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生900磅向上的力。唯一的補償是左面的活塞要移動9英尺（22.86cm）來使右面提升1英尺（2.54cm）一個簡單的制動系統(tǒng)在我們深入了解一個真實的制動系統(tǒng)的各部分之前，讓我們先來看一個簡化的系統(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缸的直徑是踏板缸直徑的3倍。這就將力進一步放大了九倍。最終這個系統(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，將在擠壓制動帶的輪上產生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，最終將會沒有足夠的油使制動缸充滿，并且制動器將停止工作。如果是嚴重泄漏，那么在你制動的第一時間，所有的油液將從泄露處噴射而出，并且制動系統(tǒng)將徹底地不起作用。鼓式制動器的工作原理和盤式制動器是一樣的：制動面接觸一個磨砂的表面。在這個系統(tǒng)中，那個表面稱作制動鼓圖1.制動鼓的位置許多汽車的后輪安裝鼓式制動器，而盤式制動器安裝在前面。鼓式制動器比盤式制動器有更多的零件并且更難檢修。但是制造成本相對便宜，還有鼓式制動器容易組裝一個緊急使用的制動裝置。在本版本的HowStuffWorks中，我們將詳盡了解鼓式制動系統(tǒng)是如何工作的?？疾炀o急制動系統(tǒng)的組成，并且找到鼓式制動器需要何種檢修工作。圖2.有鼓的鼓式制動器圖3.未安裝鼓的鼓式制動器讓我們基礎開始：鼓式制動器鼓式制動器可能看起來比較復雜，它可以是很復雜的，當你打開一個的時候。讓我們拆開它，并解釋每一塊的作用。圖4.鼓式制動器的組成如盤式制動器，鼓式制動器有兩個制動蹄和一個活塞。但是鼓式制動器也有一個調節(jié)機制，緊急剎車機制和大量的彈簧。首先，基礎知識：圖5顯示只有部分提供的制動力。圖5.工作狀態(tài)下的鼓式制動器當你踩下剎車踏板時，活塞推動緊靠著鼓的制動蹄。這是很簡單的，但為什