Automobile English Unit ThreeWord文件下载.docx

Automobile English Unit ThreeWord文件下载.docx

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Thereareseveraldifferentarrangementsofcamshaftsonengines.Themostcommontypecontainsthesingleoverheadcam（SOHC）engine,thedoubleoverheadcam（DOHC）engine,thepushrodengine.

SingleOverheadCams

Thisarrangementdenotesanenginewithonecamperhead.Soifitisanin-line4-cylinderor

in-line6-cylinderengine,itwillhaveonecam;

ifitisaV-6orV-8,itwillhavetwocams（oneforeachhead）.Thecamactuatesrockerarmsthatpressdownonthevalves,openingthem.Springsreturnthevalvestotheirclosedposition.Thesespringshavetobeverystrongbecauseathighenginespeeds,thevalvesarepusheddownveryquickly,anditisthespringsthatkeepthevalvesincontactwiththerockerarms.Ifthespringswerenotstrongenough,thevalvesmightcomeawayfromtherockerarmsandsnapback.Thisisanundesirablesituationthatwouldresultinextrawearonthecamsandrockerarms.

DoubleOverheadCam

Adoubleoverheadcamenginehastwocamsperhead.Soin-lineengineshavetwocams,

andVengineshavefour.Usually,doubleoverheadcamsareusedonengineswithfourormore

valvespercylinder—asinglecamshaftsimplycannotfitenoughcamlobestoactuateallofthose

valves.

Themainreasontousedoubleoverheadcamsistoallowformoreintakeandexhaustvalves.Morevalvesmeanthatintakeandexhaustgasescanflowmorefreelybecausetherearemoreopeningsforthemtoflowthrough.Thisincreasesthepoweroftheengine.

Onsingleanddoubleoverheadcamengines,thecamsaredrivenbythecrankshaft,viaeitherabeltorchaincalledthetimingbeltortimingchain.Thesebeltsandchainsneedtobereplacedoradjustedatregularintervals.Ifatimingbeltbreaks,thecamwillstopspinningandthepistoncouldhittheopenvalves.

PushrodEngines

LikeSOHCandDOHCengines,thevalvesinapushrodenginearelocatedintheheadabovethecylinder.Thekeydifferenceisthatthecamshaftonapushrodengineisinsidetheengineblock,ratherthaninthehead.

Thecamactuateslongrodsthatgoupthroughtheblockandintotheheadtomovetherockers.Theselongrodsaddmasstothesystem,whichincreasestheloadonthevalvesprings.Thiscanlimitthespeedofpushrodengines;

theoverheadcamshaft,whicheliminatesthepushrodfromthesystem,isoneoftheenginetechnologiesthatmadehigherenginespeedspossible.

Thecamshaftinapushrodengineisoftendrivenbygearsorashortchain.Gear-drivesaregenerallylesspronetobreakagethanbeltdrives,whichareoftenfoundinoverheadcamengines.

VariableValveTiming

Thereareacoupleofnovelwaysbywhichcarmakersvarythevalvetiming.Onesystem

usedonsomeHondaenginesiscalledVTEC.VTEC（VariableValveTimingandLiftElectronicControl）isanelectronicandmechanicalsysteminsomeHondaenginesthatallowstheengineto

havemultiplecamshafts.VTECengineshaveanextraintakecamwithitsownrocker,which

followsthiscam.Theprofileonthiscamkeepstheintakevalveopenlongerthantheothercam

profile.Atlowenginespeeds,thisrockerisnotconnectedtoanyvalves.Athighenginespeeds,

apistonlockstheextrarockertothetworockersthatcontrolthetwointakevalves.

Somecarsuseadevicethatcanadvancethevalvetiming.Thisdoesnotkeepthevalvesopenlonger;

instead,itopensthemlaterandclosesthemlater.Thisisdonebyrotatingthecamshaftaheadafewdegrees.Iftheintakevalvesnormallyopenat10degreesbeforetopdeadcenter（TDC）andcloseat190degreesafterTDC,thetotaldurationis200degrees.Theopeningandclosingtimescanbeshiftedusingamechanismthatrotatesthecamaheadalittleasitspins.Sothevalvemightopenat10degreesafterTDCandcloseat210degreesafterTDC.Closingthevalve20degreeslaterisgood,butitwouldbebettertobeabletoincreasethedurationthattheintakevalveisopen.

Severalenginemanufacturersareexperimentingwithsystemsthatwouldallowinfinitevariabilityinvalvetiming.Forexample,imaginethateachvalvehadasolenoidonitthatcouldopenandclosethevalveusingcomputercontrolratherthanrelyingonacamshaft.Withthistypeofsystem,youwouldgetmaximumengineperformanceateveryRPM.Somethingwillbelookedforwardtointhefuture.

NewWords

1.mechanism[]n.机械装置

2.camshaft[]n.凸轮轴

3.lobe[]n.突出部,凸角

4.cam[]n.凸轮

5.linkage[]n.连接，连合

6.sump[]n.油底壳

7.rod[]n.杆,棒

8.lifter[]n.（气门）挺杆

9.subsequent[]a.后来的

10.lag[]n.延迟，落后

11.timing[]v.正时，计时

12.belt[]n.传动带，（机器）皮带

13.chain[]n.链子

14.gear[]v.（使）适合n.齿轮

15.spin[]v.快速旋转；

回旋

16.bottom[]n.底部

17.slam[]v.猛推

18.profile[]n.外形,轮廓

19.scheme[]n.计划，配置；

体制

20.actuate[]vt.驱使

21.press[]v.挤压

22.spring[]n.弹簧

23.interval[]n.间隔

24.mass[]n.（物）质量

25.load[]n.负荷

26.prone[]adj.易于…的；

倾向于…的

27.duration[]n.持续时间

28.silenoid[]n.螺线管

29.dual[]a.对偶的，双的

PhrasesandExpressions

1.valvetrain配气机构

2.overheadcamshaft顶置式凸轮轴

3.valvelifter气门挺杆

4.timingbelt正时皮带

5.timingchain正时链条

6.valvelift气门升程

7.camlobe凸轮的工作部分，凸轮的凸起部

8.singleoverheadcam（SOHC）engine顶置单凸轮轴发动机

9.doubleoverheadcam（DOHC）engine顶置双凸轮轴发动机

10.pushrodengine推杆发动机

11.rockerarm摇臂

12.snapback迅速跳回，很快恢复

13.cylinderhead汽缸盖

14.engineblock发动机汽缸体

15.valvespring气门弹簧

16.variablevalvetiming（VVT）可变气门正时

17.valvetiming配气（相位）正时

NotestoText

1.Atimingbeltortimingchainlinksthecrankshafttothecamshaftsothatthevalvesareinsyncwiththepistons.

曲轴与凸轮轴通过正时皮带或正时链条连接了起来，以便于气门与活塞同步。

insyncwith与…同步。

2.Thecamshaftisgearedtoturnatone-halftherateofthecrankshaft.

凸轮轴转动应与曲轴想配合，其速度是曲轴的一半。

begearedto使适合；

与…配合，

例如：

Educationshouldbegearedtochildren'

sneeds.教育应适合学生们的需要。

3.Asthecamshaftspins,thelobesopenandclosetheintakeandexhaustvalvesintimewiththemotionofthepiston.

当凸轮轴快速旋转时，凸角可随着活塞的运动及时的开启和关闭进、排气门。

4.Itturnsoutthatthereisadirectrelationshipbetweentheshapeofthecamlobesandthewaytheengineperformsindifferentspeedranges.

这证明了凸轮凸角的形状与发动机在不同速度范围内的工况有直接的关系。

turnout证明（是），结果（是），常与to或that连用。

Thingsturnedouttobeexactlyastheprofessorhadforeseen.事情正如教授所预见的那样。

5.Thesespringshavetobeverystrongbecauseathighenginespeeds,thevalvesarepushed

downveryquickly,anditisthespringsthatkeepthevalvesincontactwiththerockerarms.

因为当发动机高转速时，气门被非常快速地推下并且气门弹簧要让气门与摇臂保持接

触，所以气门弹簧必须是强有力的。

itisthespringsthatkeepthevalvesincontactwiththerockerarms.是一个强调句式，强

调thesprings。

Exercises

1.Questionstothetext

（1）Whyisthelobesarethekeypartsofautomobiles？

（2）Whatisthesingleoverheadcam（SOHC）engine？

（3）Whatisthedoubleoverheadcam（DOHC）engine？

（4）Whatisthepushrodengine？

（5）WhatisVTEC？

2.TranslatethefollowingintoChinese

（1）singleoverheadcam（SOHC）engine

（2）doubleoverheadcam（DOHC）engine

（3）pushrodengine

（4）camlobe

（5）variablevalvetiming（VVT）

（6）engineblock

3.TranslatethefollowingintoEnglish

（1）配气机构

（2）摇臂

（3）气门升程

（4）正时皮带

（5）顶置式凸轮轴

（6）气门弹簧

4.TranslatethefollowingsentencesintoCh