车辆工程专业英语PPT课件-UNIT-2--ENGINE-MECHANICAL-TEXT-B

No.10039UNIT2ENGINEMECHANICALTEXTBValveSystemsPROFESSIONALENGLISHNo.10039UNIT2ENGINEMECHANICALTEXTBValveSystemsOperationofValveSystemVVT—Toyota'sContinuouslyVariableValveTimingVTEC—HondaVariableValveTimingandLiftElectronicControlMIVEC—MitsubishiInnovativeValvetimingElectronicControlElectronicValveControlSystemSmartValves本次课学习内容No.10039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essence['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nominal['nɔminəl]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camlobe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PHRASESANDEXPRESSIONSValveSystemsOperationofValveSystemYouhaveseenthattheintakevalvemustbeopenedfortheintakestroke,bothvalvesmustremainclosedduringthecompressionandpowerstrokes,andtheexhaustvalveopensduringtheexhauststroke.Thedesignermustdesignadevicetoopenandclosethevalvesatthepropertimes.Theshaftwillhaveanegg-shapedbumpcalledacamlobe.Thecamlobeismachinedasanintegralpartoftheshaft.Thisshaftiscalledacamshaft.Thedistancethevalvewillberaised,howlongitwillstayopen,andhowfastitopensandclosescanallbecontrolledbytheheightandshapeofthelobe[1].Asyouwillseelater,itisimpracticaltohavethecamlobecontacttheendofthevalvestemitself.Youhaveplacedthecamshaftsomedistanceabovetheendofthevalvestem.Whenthecamshaftisturn,thelobeswillnoteventouchthevalvestem.Thelifterisinstalledbetweenthecamlobeandthevalvestem.Theupperendridesonthelobeandthelowerendalmosttouchesthevalvestem.Thelifterslidesupanddowninaholeboredintheheadmetalthatseparatesthevalvestemfromthecamshaft[2].Youhavedevelopedamethodofopeningandclosingthevalves.Thenextproblemishowandatwhatspeedtoturnthecamshafts.Eachvalvemustbeopenforonestroke.Theintakevalveisopenduringtheintakestrokeandremainsclosedduringthecompression,power,andexhauststrokes.Thiswouldindicatethatthecamlobemustturnfastenoughtoraisethevalveeveryfourthstroke.Youcanseethatittakesonecompleterevolutionofthecamlobeforeveryfourstrokesofthepiston.Rememberthatfourstrokesofthepistonrequiretworevolutionsofthecrankshaft.Youcansaythatforeverytworevolutionsofthecrankshaft,thecamshaftmustturnonce.Ifyouarespeakingofthespeedofthecamshaft,youcansaythatthecamshaftmustturnatone-halfcrankshaftspeed.Ifthecrankshaftisturningandthecamshaftmustturnatone-halfcrankshaftspeed,itseemslogicaltousethespinningcrankshafttoturnthecamshaft.Oneverysimplewaytodrivethecamshaftwouldbebymeansofgearsandabelt.Onegearisfastenedontheendofthecrankshaft,andtheotherisfastenedontheendofthecamshaft.Thelargecamshaftgeardrivesthesmallercrankshaftgearthroughthebelt.If,forinstance,thesmallgearonthecrankshafthas10teethandthelargegearonthecamshafthas20teeth,thecrankshaftwillturnthecamshaftatexactlyone-halfcrankshaftspeed.VVT-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.Theheartofthesystemistheintakecampulley,whichconsistsofaninnerandoutersection.Theinnerportionisfixedtothecamshaftandnestsinsidethebelt-drivenouterpulleyviahelicalsplinegears.Anelectronicallycontrolledhydraulicpistonmovesthepulleyhalvesrelativetooneanother,causingthecamportiontorotatewithintheouterpulley.Thisrotationadvancesorretardsintakevalvetiming.AspoolvalvereactingtosignalsfromtheECUcontrolshydraulicpressure.VTEC-HondaVariableValveTimingandLiftElectronicControlBydesigningahighervalvelift,widervalve-timing,andlargervalvediameter,itispossibletoobtainahighervolumetricefficiencytocopewithhigheroutput