汽车专业英语读译教程 第3版 课件 3-U2TB Valve Systems

UNIT2

ENGINEMECHANICAL

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ValveSystemsPROFESSIONALENGLISH

UNIT2

ENGINEMECHANICAL

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ValveSystems

OperationofValveSystem

VVT—Toyota'sContinuouslyVariableValveTiming

VTEC—HondaVariableValveTimingandLiftElectronicControl

MIVEC—MitsubishiInnovativeValvetimingElectronicControl

ElectronicValveControlSystem

SmartValves本次课学习内容本次课学习目标掌握可变气门定时机构主要部件的英文名称掌握可变气门定时机构的基本原理掌握常用术语（phrasesandexpressions）了解相关术语（relatedterms）NEWWORDSbump[bʌmp]n.撞击，（因撞击而起的）肿块；v.碰，撞，颠簸cam[kæm]n.凸轮lobe[loub]n.凸起integral['intigrəl]a.完整的，整体的，积分的stem[stem]n.杆，茎powertrain['pauətrein]n.动力系统，动力装置，传动系统dyno['dainou]n.=dynamometer测功机，测力计breathe[bri:ð]v.呼吸，发出certification[ֽsə:tifi'kei∫ən]n.证明，鉴定，检验证明书compromise['kɔmprəmaiz]v.&n.妥协，折衷NEWWORDSessence['esns]n.基本，本质，实质，精华，要素pulley['puli]n.滑轮，带轮helical['helikəl]a.螺旋状的spline[splain]n.花键，方栓spool[spu:l]n.线轴，卷轴；滑阀；线圈mpg

=milepergallon（英里/加仑）actuator['æktjueitə]n.执行器，执行元件strategy['strætiʤi]n.策略，谋略flexibility[ֽfleksə'biliti]n.灵活性，柔性，适应性eager['i:gə]v.渴望着，热心于multiplex['mʌtipleks]a.多元的，多重的，多样的；n.多路传输，多路通信NEWWORDSnominal['nɔminl]a.有名无实的；极微小的；标定的，额

定的bus[bʌs]n.总线innovation[inou'vei∫ən]v.改进，革新，创新，新发明（技术，方法）residual[ri'zidjuəl]a.剩余的，残余的

PHRASESANDEXPRESSIONScamlobe凸轮的凸起部分valvestem气门杆variablevalvetiming（VVT）可变气门定时inessence本质上，实质上spoolvalve滑阀electronicvalvecontrol(EVC)电子式气门控制centralizedsystem集中系统distributedsystem分布系统camlessengine无凸轮发动机smartvalve智能气门OperationofValveSystemYouhaveseenthattheintakevalvemustbeopenedfortheintakestroke,bothvalvesmustremainclosedduringthecompressionandpowerstrokes,andtheexhaustvalveopensduringtheexhauststroke.Thedesignermustdesignadevicetoopenandclosethevalvesatthepropertimes.Theshaftwillhaveanegg-shapedbumpcalledacamlobe.Thecamlobeismachinedasanintegralpartoftheshaft.Thisshaftiscalledacamshaft.Thedistancethevalvewillberaised,howlongitwillstayopen,andhowfastitopensandclosescanallbecontrolledbytheheightandshapeofthelobe[1].

ValveSystems

ValveSystemsAsyouwillseelater,itisimpracticaltohavethecamlobecontacttheendofthevalvestemitself.Youhaveplacedthecamshaftsomedistanceabovetheendofthevalvestem.Whenthecamshaftisturn,thelobeswillnoteventouchthevalvestem.Thelifterisinstalledbetweenthecamlobeandthevalvestem.Theupperendridesonthelobeandthelowerendalmosttouchesthevalvestem.Thelifterslidesupanddowninaholeboredintheheadmetalthatseparatesthevalvestemfromthecamshaft[2].Rememberthatfourstrokesofthepistonrequiretworevolutionsofthecrankshaft.ValveSystemsYoucansaythatforeverytworevolutionsofthecrankshaft,thecamshaftmustturnonce.Ifyouarespeakingofthespeedofthecamshaft,youcansaythatthecamshaftmustturnatone-halfcrankshaftspeed.Youhavedevelopedamethodofopeningandclosingthevalves.Thenextproblemishowandatwhatspeedtoturnthecamshafts.Eachvalvemustbeopenforonestroke.Theintakevalveisopenduringtheintakestrokeandremainsclosedduringthecompression,power,andexhauststrokes.Thiswouldindicatethatthecamlobemustturnfastenoughtoraisethevalveeveryfourthstroke.Youcanseethatittakesonecompleterevolutionofthecamlobeforeveryfourstrokesofthepiston.

ValveSystemsIfthecrankshaftisturningandthecamshaftmustturnatone-halfcrankshaftspeed,itseemslogicaltousethespinningcrankshafttoturnthecamshaft.Oneverysimplewaytodrivethecamshaftwouldbebymeansofgearsandabelt.Onegearisfastenedontheendofthecrankshaft,andtheotherisfastenedontheendofthecamshaft.Thesmallercrankshaftgeardrivesthelargercamshaftgearthroughthebelt.If,forinstance,thesmallgearonthecrankshafthas10teethandthelargegearonthecamshafthas20teeth,thecrankshaftwillturnthecamshaftatexactlyone-halfcrankshaftspeed.ValveSystemsVVT-Toyota'sContinuouslyVariableValveTimingThemostsignificantandsatisfyingchangestotheLexusGSlineareintheareaofpowertrain.InthecaseoftheGS300,Lexusbreathesnewlifeintolastyear's3.0Linlinesix,byintroducingVVT—continuouslyvariablevalvetimingsystem.Onthedyno,VVTshowsupasonlyfiveadditionalhorsepowerand10lb-ftoftorque.Butinthecaritmeansfueleconomyimprovementsof1.6mpg,smootheridle,CaliforniaTLEV(transitionallow-emissionsvehicle)certificationandzero-to-60mphahalfsecondquicker.ToyotaeliminatesthecompromiseofconventionalvalvetimingwiththeintroductionofVVT.Bycontinuouslyvaryingintakevalvetiming(upto60crankangledegrees),Toyotaoptimizeslow-tomid-speedtorque,improvesfueleconomyandlowersemissionswithouthavinganegativeimpactonidle.

Inessence,thesystemcontrolsvalveoverlap,whichmeansitcaneliminateitcompletelyforaglasssmoothidle,ormaximizeittoboostvolumetricefficiencyandreducepumpinglosses—thistranslatesintopower,economyandcleanerrunningatallenginespeeds.

ValveSystemsValveSystemsTheheartofthesystemistheintakecampulley,whichconsistsofaninnerandoutersection.Theinnerportionisfixedtothecamshaftandnestsinsidethebelt-drivenouterpulleyviahelicalsplinegears.Anelectronicallycontrolledhydraulicpistonmovesthepulleyhalvesrelativetooneanother,causingthecamportiontorotatewithintheouterpulley.Thisrotationadvancesorretardsintakevalvetiming.AspoolvalvereactingtosignalsfromtheECUcontrolshydraulicpressure.VTEC-HondaVariableValveTimingandLiftElectronicControl

Bydesigningahighervalvelift,widervalve-timing,andlargervalvediameter,itispossibletoobtainahighervolumetricefficiencytocopewithhigheroutputenginespeeds.TheVTECisusedtoimprovevolumetricefficiencyfromlowenginespeedtohighenginespeed.WithVTEC,thevalvetimingandliftcanbeadjustedatlowenginerotationtoincreasetorqueandpreventairfrombeingforcedbackthroughtheintake.ValveSystemsValveSystemsVTECLayoutInFig.2-3thestructureoftheVTECisshown.Theenginehasoneextracamprofileandrockerarm(midrockerarm)forhighenginespeed.Thecamhas3differentprofileslocatedattheintakeandexhaustofeachcylinder.Thecentercamisusedexclusivelyforhighspeedandthe2outsidecamsforlowspeed.ValveSystemsTherockerarmassemblyiscomposedofamidrockerarmwithprimaryandsecondaryrockerarmsoneachside.Insidetherockerarmsare2hydraulicpistons,astopperpin,andareturnspring,whichmakeupthechangeovermechanism.Themidrockerarmhasalostmotionspringsothatthevalveoperatessmoothlyathighspeedsandalsostopsthearmatlowspeeds.ThewholesystemisoperatedbyahydraulicactuatorwhichiscontrolledbytheEngine-ControlUnit(ECU).ValveSystems1Camshaft2CamLobeforLowSpeedRange3CamLobeforHighSpeedRange4PrimaryRockerArm5MidRockerArm6SecondaryRockerArm7HydraulicPistonA8HydraulicPistonB9StopperPin10Lost-motionSpring11ExhaustValve12IntakeValveFig.2-3VTECSystemConstructionValveSystemsVTECOperationFig.2-4showstheVTECmechanismwhileoperatingatlowenginespeeds.Inthelow-speedmodethe3rockerarmsareseparatedandusecamsA&Bonly.Atthistimethemidrockerarmisincontactwiththehighspeedcamduetothespringforceinthelostmotionmechanism.Itisseparatedfromtheprimaryandsecondaryrockerarmandthusisnotactuatingthevalves.Fig.2-5showstheVTECmechanismwhileoperatinginthehighspeedmode.Duringhighspeedengineoperationthe3rockerarmsareconnectedandmovetogetherduetothe2hydraulicpistonswhichhavemovedoverduetoincreasedhydraulicpressure.Fig.2-4RockerArmOperation(LowSpeedRange)ValveSystemsValveSystemsFig.2-7operationofcamshaftadjustmentValveSystemsBMWVariablecamshaftcontrol(VANOS)Thesystemconsistsofhydraulicadjuster,mechanicaladjusterandsolenoidvalveforhydraulicactuation(Fig.2-6).ThissystemissimilartoToyota’sVVTdescribedaboveindesignandoperation.Withthissystemtheinletcamshaftisrotatedintheoppositedirectiontothecamshaftgear.Dependingonthepositionofthesolenoidvalve,thehydraulicpistonisdisplacedtotheleftorright.Theaxialmovementofthehydraulicpistoncausescamshaftadjust(turn)inthe"Advance"or"Retard"directioninthemechanicaladjusterbymeansofthehelicalteeth(Fig.2-7).Adjustmentcanbeperformedsteplessly.ValveSystemsFig.2-6DesignofcamshaftadjustmentValveSystemsFig.2-7operationofcamshaftadjustmentValveSystemsVaneCam—avane-typeadjuster

Additionaladjustmentoftheexhaustcamshaftbringsaboutanincreaseintorqueinthelowertomiddlespeedrangeaswellasinthemiddletoupperspeedrange.Avane-typeadjuster(VaneCam)isshowninFig.2-8.Theouterrotorispermanentlyconnectedtothesprocketandtheinnerrotortothecamshaftrespectively.Theouterrotorandinnerrotorcanberotatedinopposingdirections.Theoilpressureintherespectiveoilchamberisvariablycontrolledbythehydraulicvalves.Thecamshaftsareadjustedinthisway.Themaximumturningangleoftheinnerrotortotheouterrotoris,forexample,52°CAfortheinletcamshaftand22°CAfortheexhaustcamshaft.Fig.2-8Avane-typeadjusterValveSystemsValveSystemsElectronicValveControlSystemAnelectronicvalvecontrol(EVC)systemreplacesthemechanicalcamshaft,controllingeachvalvewithactuatorsforindependentvalvetiming.TheEVCsystemcontrolstheopeningandclosingtimeandliftamountofeachintakeandexhaustvalvewithindependentactuatorsoneachvalve.Changingfromamechanicalcamshaftdrivenvalveintoindependentlycontrolledactuatorvalvesprovidesahugeamountofflexibilityinenginecontrolstrategy.VehiclesutilizingEVCcanrealizeseveralbenefitsincluding:1)increasesenginepowerandfueleconomy.ValveSystems2)allowscentralizedanddistributedEVCsystemstoperformattheirfullpotential.3)adaptstoenginesofvariedcylindercounts.

Withalloftheimprovedefficienciesandconsumerbenefits,automanufacturersareeagertogettheirfirstEVCsystemsontheroad.TheEVCsystemistargetedtooperateintemperaturesupto125℃,whiletheactuatoristargetedtorunupto6000r/min.Theactuatorcanbecontrolledinacentralizedsystemwithahigh-speedmultiplexbus(upto10Mbps)orinadistributedsystemwithanominalspeedbusValveSystemsEVCsystemsmustbecompactinsize,specificallytheactuatorsthatmustbesmallenoughtofitintheenginespace.Avehiclethatusesa42VsystemisidealforEVCbecauseitrequireshighvoltagetocontrolthevalveactuators,andEVCistargetedforV8andV12engines.SmartValvesValeoisactivelydevelopingtechnologyforreducingfuelconsumptionandemissions