AUTOMOTIVEBASICS车辆工程专业英语

PAGE/NUMPAGESPAGE/NUMPAGES更多汽车资料请访问中国汽车技术论坛：HYPERLINK"http://www.qichejishu.com"www.qichejishu.comCHAPTER1AUTOMOTIVEBASICS1.1 PrincipalComponentsToday'saveragecarcontainsmorethan15,000separate,individualpartsthatmustworktogether.Thesepartscangroupedintofourmajorcategories:engine,body,chassisandelectricalequipment.1.2 EngineTheengineactsasthepowerunit.Theinternalcombustionengineismostcommon:thisobtainsitspowerbyburningaliquidfuelinsidetheenginecylinder.Therearetwotypesofengine:gasoline(alsocalledaspark-ignitionengine)anddiesel(alsocalledacompression-ignitionengine).Bothenginesarecalledheatengines;theburningfuelgeneratesheatwhichcausesthegasinsidethecylindertoincreaseitspressureandsupplypowertorotateashaftconnectedtothetransmission.1.3 BodyAnautomobilebodyisasheetmetalshellwithwindows,doors,ahood,andatrunkdeckbuiltintoit.Itprovidesaprotectivecoveringfortheengine,passengers,andcargo.Thebodyisdesignedtokeeppassengerssafeandcomfortable.Thebodystylingprovidesanattractive,colorful,modernappearanceforthevehicle.1.4 ChassisThechassisisanassemblyofthosesystemsthatarethemajoroperatingpartofavehicle.Thechassisincludesthetransmission,suspension,steering,andbrakesystems.Transmissionsystems―conveysthedrivetothewheels.Themaincomponentsareclutch,gearbox,driveshaft,finaldrive,anddifferential.Suspension―absorbstheroadshocks.Steering―controlsthedirectionofthemovement.Brake―slowsdownthevehicle.1.5 Electrical EquipmentTheelectricalsystemsupplieselectricityfortheignition,horn,lights,heater,andstarter.Theelectricitylevelismaintainedbyachargingcircuit.Thiscircuitconsistsofthebattery,alternator(orgenerator).Thebatterystoreselectricity.Thealternatorchangestheengine'smechanicalenergyintoelectricalenergyandrechargesthebattery.NewWordsPrincipalcomponent 主要部件category 种类，类型body 车身chassis 底盘layout 布置powerunit 动力装置internalcombustionengine 内燃机cylinder 汽缸gasoline 汽油spark 火花ignition 点燃，点火diesel 柴油机compression 压缩shaft 轴transmission 传动系sheetmetal 金属板shell 外壳hood （发动机）罩trunkdeck 行李舱盖cargo 货物styling 样式assembly 总成，装配suspension 悬挂，悬置shock 冲击steering 转向，操纵brake 刹车，制动器clutch 离合器gearbox 变速器driveshaft 传动轴finaldrive 主减速器，后桥differential 差速器slowdown （使）慢下来，减速horn 喇叭starter 起动机charge 充电alternator 交流发电机ReviewQuestionsListthemainpartsofanautomobile?Whatarethecommontypesofavehicleaccordingtobodystyling?Whichsystemsdoesachassisincludeandwhatarethemainfunctionsofthechassis?Whyaresuspensionsystemsusedonvehicles?CHAPTER2INTERNALCOMBUSTIONENGINE2.1principleofoperation2.1.1EngineandpowerEngineisusedtoproducepower.Thechemicalenergyinfuelisconvertedtoheatbytheburningofthefuelatacontrolledrate.Thisprocessiscalledcombustion.Ifenginecombustionoccurswiththepowerchamber.,theengineiscalledinternalcombustionengine.Ifcombustiontakesplaceoutsidethecylinder,theengineiscalledanexternalcombustionengine.Engineusedinautomobilesareinternalcombustionheatengines.Heatenergyreleasedinthecombustionchamberraisesthetemperatureofthecombustiongaseswiththechamber.Theincreaseingastemperaturecausesthepressureofthegasestoincrease.Thepressuredevelopedwithinthecombustionchamberisappliedtotheheadofapistontoproduceausablemechanicalforce,whichisthenconvertedintousefulmechanicalpower.2.1.2EngineTermsLinkingthepistonbyaconnectingrodtoacrankshaftcausesthegastorotatetheshaftthroughhalfaturn.Thepowerstroke“usesup”thegas,someansmustbeprovidedtoexpeltheburntgasandrechargethecylinderwithafreshpetrol-airmixture:thiscontrolofgasmovementisthedutyofthevalves;aninletvalveallowsthenewmixturetoenterattherighttimeandanexhaustvalveletsouttheburntgasafterthegashasdoneitsjob.Enginetermsare:TDC(TopDeadCenter):thepositionofthecrankandpistonwhenthepistonisfartherawayfromthecrankshaft.BDC(BottomDeadCenter):thepositionofthecrankandpistonwhenthepistonisnearesttothecrankshaft.Stroke:thedistancebetweenBDCandTDC;strokeiscontrolledbythecrankshaft.Bore:theinternaldiameterofthecylinder.Sweptvolume:thevolumebetweenTDCandBDC.Enginecapacity:thisisthesweptvolumeofallthecylindere.g.afour-strokehavingacapacityoftwoliters(2000cm)hasacylindersweptvolumeof50cm.Clearancevolume:thevolumeofthespaceabovethepistonwhenitisatTDC.Compressionratio=(sweptvol+clearancevol)\(clearancevol)Two-stroke:apowerstrokeeveryrevolutionofthecrank.Four-stroke:apowerstrokeeveryotherrevolutionofthecrank..2.1.3TheFour-strokeSpark-ignitionEngineCycleThespark-ignitionengineisaninternal-combustionenginewithexternallysuppliedinignition,whichconvertstheenergycontainedinthefueltokineticenergy.Thecycleofoperationsisspreadoverfourpistonstrokes.Tocompletethefullcycleittakestworevolutionsofthecrankshaft.Theoperatingstrokesare:Thisstrokeintroducesamixtureofatomizedgasolineandairintothecylinder.Thestrokestartswhenthepistonmovesdownwardfromapositionnearthetopofthecylinder.Asthepistonmovesdownward,avacuum,orlow-pressurearea,iscreated.Duringtheintakestroke,oneoftheportsisopenedbymovingtheinletvalve.Theexhaustvalveremainstightlyclosed.CompressionstrokeAsthepistonmovesupwardtocompressthefuelmixturetrappedinthecylinder,thevalvesareclosedtightly.Thiscompressionactionheatstheair/fuelmixtureslightlyandconfinesitwithinasmallareacalledthecombustionchamber.PowerstrokeJustbeforethepistonreachesthetopofitscompressionstroke,anelectricalsparkisintroducedfromasparkplugscrewedintothecylinderhead.Thesparkignitesthecompressed,heatedmixtureoffuelandairinthecombustionchambertocauserapidburning.Theburningfuelproducesintenseheatthatcausesrapidexpansionofthegasescompressedwithinthecylinder.Thispressureforcesthepistondownward.Thedownwardstroketurnsthecrankshaftwithgreatforce.ExhauststrokeJustbeforethebottomofthepowerstroke,theexhaustvalveopens.Thisallowsthepiston,asitmovesupward,topushthehot,burnedgasesoutthroughtheopenexhaustvalve.Then,justbeforethepistonreachesitshighestpoint,theexhaustvalveclosesandtheinletvalveopens.Asthepistonreachesthehighestpointinthecylinder,knownasTDC,itstartsbackdownagain.Thus,onecycleendsandanotherbeginsimmediately.2.1.4EngineOverallMechanicsTheenginehashundredsofotherparts.Themajorpartsofengineareengineblock,engineheads,pistons,connectingrods,crankshaftandvalves.Theotherpartsarejoinedtomakesystems.Thesesystemsarethefuelsystem,intakesystem,ignitionsystem,coolingsystem,lubricationsystemandexhaustsystem.Eachofthesesystemshasadefinitefunction.Thesesystemswilldiscussedindetaillater.NEWWORDPiston活塞Connectingrod连杆Crankshaft曲轴Powerstoke活塞行程Expel排出Valve气阀inlet(intake)valve进气阀exhaustvalve排气阀term术语TDC上止点BDC下止点Bore缸径sweptvolume有效容积enginecapacity发动机排量clearancevolume余隙容积,燃烧室容积compressionratio压缩比revolution旋转,转数everyother每隔一个cycle循环spreadover分布,遍及intakestroke进气行程compressionstroke压缩行程knock敲缸,敲打exhauststroke排气行程engineblock发动机缸体lubrication润滑2.2EngineBlockandCylinderHead2.2.1 EngineBlockTheengineblockisthebasicframeoftheengine.Allotherenginepartseitherfitinsideitorfastentoit.Itholdsthecylinders,waterjackets,andoilgalleries.Theengineblockalsoholdsthecrankshaft,whichfastenstothebottomoftheblock.Thecamshaftalsofitsinsidetheblock,exceptonoverhead-camengines(OHC).Inmostcars,thisblockismadeofgrayiron,oranalloy(mixture)ofgrayironandothermetals,suchasnickelorchromium.Engineblocksarecastings.Someengineblocks,especiallythoseinsmallercars,aremadeofcastaluminum.Thismetalismuchlighterthaniron.However,ironwearsbetterthanaluminum.Therefore,thecylindersinmostaluminumenginesarelinedwithironorsteelsleeves.Thesesleevesarecalledcylindersleeves.Someengineblocksaremadeentirelyofaluminum.2.2.2 CylinderHeadThecylinderheadfastenstothetopoftheblock,justasarooffitsoverahouse.Theundersideformsthecombustionchamberwiththetopofthepiston.Themostcommoncylinderheadtypesarethehemi,wedge,andsemi-hemi.Allthreeofthesetermsrefertotheshapeoftheengine'scombustionchamber.Thecylinderheadcarriesthevalves,valvespringsandtherockersontherockershaft,thispartofthevalvegearbeingworkedbythepush-rods.Sometimesthecamshaftisfitteddirectlyintothecylinderheadandoperatesonthevalveswithoutrockers.Thisiscalledanoverheadcamshaftarrangement.Likethecylinderblock,theheadismadefromeithercastironoraluminumalloy.2.2.3 GasketThecylinderheadisattachedtotheblockwithhigh-tensilesteelstuds.Thejointbetweentheblockandtheheadmustbegas-tightsothatnoneoftheburningmixturecanescape.Thisisachievedbyusingcylinderheadgasket.Thisisasandwichgasket,i.e.asheetofasbestosbetweentwosheetsofcopper,boththesematerialsbeingabletowithstandthehightemperatureandpressureswithintheengine.2.2.4 OilPanorSumpTheoilpanisusuallyformedofpressedsteel.Theoilpanandthelowerpartofthecylinderblocktogetherarecalledthecrankcase;theyenclose,orencase,thecrankshaft.Theoilpumpinthelubricatingsystemdrawsoilfromtheoilpanandsendsittoallworkingpartsintheengine.Theoildrainsoffandrunsdownintothepan.Thus,thereisconstantcirculationofoilbetweenthepanandtheworkingpartsoftheengine.NewWordsengineblock 缸体cylinderhead 气缸盖fasten 使固定waterjacket 水套oilgallery 油道camshaft 凸轮轴overhead-cam(OHC) 顶置凸轮grayiron 灰铸铁alloy 合金nickel 镍chromium 铬casting 铸件headcover 汽缸盖罩intakemanifold 进气总管distributor 分电器oilpan 油底壳aluminum 铝belinedwith 镶有cylindersleeve 气缸套hemi 半球形wedge 楔型，楔入semi-hemi 准半球形rocker 摇臂push-rod 推杆gasket 衬垫high-tensile 高强度的stud 螺栓gas-tight 密封的asbestos 石棉crankcase 曲轴箱，曲柄箱encase 封闭，把…包起来drainoff 排出，流出ReviewQuestionWhatdoTDC,BDC,stroke,compressionratioandenginecapacitystandfor?Howdoyoucalculatesweptvolumeandcompressionratio?Whatcontrolsthelengthofthestroke?Listthemainpartsoftheengineoverallmechanics?Whatarethemainfunctionoftheengineblock?2.3PistonConnectingRodandCrankshaft2.3.1PistonAssemblyThepistonisanimportantpartofafour-strokecycleengine.Mostpistonsaremadefromcastaluminum.Thepiston,throughtheconnectingrod,transferstothecrankshafttheforcecreatebytheburningfuelmixture.Thisforceturnsthecrankshaft.Thin,circular,steelbandsfitintogroovesaroundthepistontosealthebottomofthecombustionchamber.Thesebandsarecalledpistonrings.Thegroovesintowhichtheyfitarecalledringgrooves.Apistonpinfitsintoaroundholeinthepiston.Thepistonpinjoinsthepistontotheconnectingrod.Thethickpartofthepistonthatholdsthepistonisthepinboss.Thepistonitself,itsringsandthepistonpinaretogethercalledthepistonassembly.2.3.2.PistonTowithstandtheheatofthecombustionchamber,thepistonmustbestrong.Italsomustbelight,sinceittravelsathighspeedsasitmovesupanddowninsidethecylinder.Thepistonishollow.Itisthickatthetopwhereittakethebruntoftheheatandtheexpansionforce.Itisthinatthebottom,wherethereislessheat.Thetoppartofthepistonisthehead,orcrown.ThethinpartistheskirtThesectionsbetweentheringgroovesarecalledringlands.Thepistoncrownmaybeflat,concave,domeorrecessed.Indieselengine,thecombustionchambermaybeformedtotallyorinpartinthepistoncrown,dependingonthemethodofinjection.Sotheyusepistonswithdifferentshapes.2.3.3PistonRingsAsFig.2-9shows,pistonringsfitintoringgroovesneartheofthepiston.Insimplestterms,pistonringsarethin,circularpiecesofmetalthatfitintogroovesinthetopsofthepistons.Inmodernengines,eachpistonhasthreerings.(Pistoninolderenginessometimeshadfourrings,orevenfive.)Thering’soutsidesurfacepressesagainstthecylinderwalls.Ringsprovidetheneededsealbetweenthepistonandthecylinderwalls.Thatis,onlytheringscontactthecylinderwalls.Thetoptworingsaretokeepthegasesinthecylinderandarecalledcompressionrings.Theloweronepreventstheoilsplashedontothecylinderborefromenteringthecombustionchamber,andiscalledanoilring.Chrome-facecast-ironcompressionringsarecommonlyusedinautomobileengines.Thechromefaceprovideaverysmooth,wear-resistantsurface.Duringthepowerstoke,combustionpressureonthecombustionringsisveryhigh.Itcausesthemtountwist.Someofthehigh-pressuregasgetsinbackoftherings.Thisforcetheringfaceintofullcontactwiththecylinderwall.Thecombustionpressurealsoholdsthebottomoftheringtightlyagainstthebottomoftheringgroove.Therefore,highcombustionpressurecausesatightersealbetweentheringfaceandthecylinderwall.2.3.4PistonPinThepistonpinholdstogetherthepistonandtheconnectingrod.Thispinfitsintothepistonpinholesandintoaholeinthetopendoftheconnectingrod.Thetopendofismuchsmallerthantheendthatfitsonthecrankshaft.Thissmallendfitsinsidethebottomofthepiston.Thepistonpinfitsthroughonesideofthepiston,throughthesmallendoftherod,andthenthroughtheothersideofthepiston.Itholdstherodfirmlyinplaceinthecenterofthepiston.Pinsaremadeofhigh-strenghsteelandhaveahollowcenter.Manypinsarechrome-platedtohelpthemwearbetter.2.3.3ConnectingrodTheconnectingrodismadeofforgedhigh-strengthsteel.Ittransmitsandmotionfromthepistontothecrankpinonthecrankshaft.Theconnectingrodlittleendisconnectedtothepistonpin.Abushmadefromasoftmetal,suchasbronze,isusedforthisjoint.Thelowerendoftheconnectingrodfitsthecrankshaftjournal.Thisiscalledthebigend.Forthisbig-endbearing,steel-backedleadortinshellbearingareused.Thesearethesameasthoseusedforthemainbearings.Thesplitofthebigendissometimesatanangle,sothatitissmallenoughtobewithdrawnthroughthecylinderbore.Theconnectingrodismadefromforgedalloysteel.2.3.5CrankshaftThecrankshaft,inconjunctionwiththeconnectingrod,covertsthereciprocatingmotionofthepistontotherotarymotionneededtodrivethevehicle.Itisusuallymadefromcarbonsteelwhichisalloyedwithasmallproportionofnickel.Themainbearingjournalsfitintothecylinderblockandthebigendjournalsalignwiththeconnectingrods.Attherearendofthecrankshaftisattachedtheflywheel,andatthefrontendarethedrivingwhellsforthetiminggears,fan,coolingwaterandalternator.Thethrowofthecrankshaft,thedistancebetweenthemainjournalandthebigendcenters,controlsthelengthofthestroke.Thestrokeisdoublethethrow,andthestroke-lengthisthedistancethatthepistontravelsfromTDCtoBDCandviceversa.2.3.6FlywheelTheflywheelisthemadefromcarbonsteel.Itfitsontotherearofthecrankshaft.Aswellaskeepingtheenginerotatingbetweenpowerstrokesitalsocarriestheclutch,whichtransmitsthedrivetothetransmission,andhasthestarterringgeararounditscircumference.Thereisonlyoneworkingstrokeinfoursoaflywheelisneededtodrivethecrankshaftduringthetimethattheengineisperformingthenon-powerstrokes.NewWordsComprise由。。。。。。。组成，包含Inter惯性，惯量Radius半径，范围Circular圆形的Steelband钢圈Fitinto放入，放进Groove凹槽Pistonpin活塞销Pinboss活塞销凸台Withstand抵抗Hollow空的Brunt冲力Crown活塞顶Skirt裙部Ringland环带Concave凹的，凹入的Dome圆顶Recessed隐蔽的Cylinderwall气缸壁Cylinderbore缸筒Splash飞溅chrome-face表面镀银的Untwist朝相反方向的Inplace在适当位置Chrome-plated镀铬的Forge伪造，仿造Crankpin曲轴销Bush轴瓦，套筒Bronze青铜Crankshaftjournal曲轴轴颈Steel-backed钢背的Lead铅Tin锡Splint切口，中断，分配，分离Inconjunctionwith连同Reciprocatingmotion往复运动Rotary旋转的Carbonsteel碳钢Journal轴颈Alignwith匹配Overlap重叠Timinggear正时齿轮Throw摆幅Viceverse反之亦然Impulse脉冲Spaceout隔开，分隔Throughout遍及Diagram图表Firingorder点火顺序Companion成对Circumference圆周2.4ValveSystemThevalvesystemismadeupofthosepartsneededtoopenandclosethevalvesatjusttherighttime.2.4.1ValveOperationTocoordinatethefour-strokecycle,agrouppartscalledthevalvetrainopensandclosesthevalves(movesthemdownandup,respectively).Thesevalvemovementsmusttakeplaceatexactlytherightmoments.Theopeningofeachvalveiscontrolledbyacamshaft.1.Camshaft(OHC)ValveTrainOverheadThecamisanegg-shapedpieceofmetalonashaftthatrotatesincoordinationwiththecrankshaft.Themetalshaft,calledthecamshaft,typicallyhasindividualcamsforeachvalveintheengine.Asthecamshaftrotates,thelobe,orhighspotofthecam,pushesagainstpartsconnectedtothestemofthevalve.Thisactionforcesthevalvetomovedownward.Thisactioncouldopenaninletvalve,oropenanexhaustvalveforanexhauststroke.Asthecamshaftcontinuestorotate,thehighspotmovesawayfromthevalvemechanism.Asthisoccurs,valvespringpullthevalvetightlyclosedagainstitsopening,calledthevalveseat.Valveinmoderncarenginesarelocatedinthecylinderheadatthetoptheengine.Thisisknownasanoverheadvalve(OHC)configuration.Inaddition,whenthecamshaftislocatedoverthecylinderhead,thearrangementisknownasoverheadcamshaft(OHC)design.Somehigh-performanceenginehavetwoseparatecamshafts,oneforeachsetofinletandexhaustvalves.Theseenginesareknownasoverhead-camshaft(DHOC)engine.2.Push-rodValveTrainThecamshaftalsocanbelocatedinthelowerpartoftheengine,withintheengineblock.Totransferthemotionofthecamupwardtothevalve,additionalpartsareneeds.Inthisarrangement,thecamlobspushagainstroundmetalcylinderscalledfollowerupward(awayfromthecamshaft).Thecamfollowerridesagainstapushrod,whichpushesagainstarockerarm.Therockerarmpivotsonashaftthroughitscenter.Asonesideoftherockerarmmovesup,theothersidemovesdown,justlikeaseesaw.Thedownward-movingsideoftherockerarmpushesonthevalvestemtoopenthevalve.Becauseapush-rodvalvetrainhasadditionalparts,itismoredifficulttorunathighspeeds.Push-rodenginestypicallyrunatslowerspeedsand,consequently,producelesshorsepowerthanoverhead-camshaftdesignsofequalsize.(Remember,poweristherateatwhichworkisdone.)2.4.2ValveClearanceWhentheenginerunsincompressionstrokeandpowerstroke,thevalvesmustclosetightlyontheirseatstoproduceagas-tightsealandthuspreventthegasesescapingfromthecombustionchamber.Ifthevalvesdonotclosefullytheenginewillnotdevelopfillpower.Alsothevalveheadswillbeliabletobebruntbythepassinghotgases,andthereisthelikelihoodofcrowntouchinganopenvalve,whichcanseriouslydamagetheengine.Sothatthevalvescanclosefullysomeclearanceisneededintheoperatingmechanism.Thismeansthattheoperatingmechanismmustbeabletomovesufficientlyfarenoughawayfromthevalvetallowthevalvestobefullyclosedagainstitsseatbythevalvespring.However,iftheclearanceissettoogreatthiswillcausealightmetallictapingnoise.2.4.3ValveTimingThetimeatwhichvalvesopenandclose(valvetiming)andthedurationofthevalveopeninginstatedindegreesofcrankshaftrotation.Forexample,theintakevalvenormallybeginstoopenjustbeforethepistonhasreachedthetopdeadcenter.ThevalveremainsopenasthepistontravelsdowntoBDCandevenpastBDC.Thisisintakevalveduration.Anexampleofthiscouldbestatedasfollows:IOat17BTDC,ICat51ABDC(or,intakeopens17beforetopdeadcenter,intakecloses51afterbottomdeadcenter).Intakevalvedurationinthiscaseis248ofcrankshaftrotation.Thisleaves129durationforthecompressionstrokesincecompressionendswhenthepistonreachesTDC.Atthispointthepowerstrokebegins.Thepowerstrokeendswhentheexhaustvalvebeginstoopenapproximatelyat51beforebottomdeadcenter.Thedurationofthepowerstrokeinthiscaseisalso129.Sincetheexhaustvalveisopeningat51BBDC,thisbeginstheexhauststroke.TheexhauststrokecontinuesasthepistonpassesBDCandmovesupwardtopastTDC.Withtheexhaustvalveclosingat17TTDC,thedurationoftheexhauststrokeis248.Itisapparentfromthisdescriptionthattheexhaustvalvestaysopenforashortperiodoftimeduringwhichtheintakevalveisalsoopen.Inotherwords,theendoftheexhauststrokeandthebeginningoftheintakestrokeoverlapforashortperiodoftime.Thisiscalledvalveoverlap.Valvetimingandvalveoverlapvaryondifferentengines.OpeningtheintakevalvebeforeTDCandclosingitafterBDCincreasethefillofair-fuelmixtureinthecylinder.Openingtheintakevalveearlyhelpsovercomethestaticinertiaoftheair-fuelmixtureatthebeginningoftheintakestroke,whileleavingtheintakevalveopenafterBDCtakesadvantageofthekentiaofthemovingair-fuelmixture.Thisincreasevolumetricefficiency.Asthepistonmovesdownonthepowerstrokepastthe90ATDCposition,pressureinthecylinderhasdropped,andtheleveragetothecrankshafthasdecreasedduetoconnectingrodangleandcrankshaftposition.Thisendstheeffectivelengthofthepowerstroke,andtheexhaustvalvecannowbeopenedtobeginexpellingtheburnedgases.TheexhaustvalveremainsopenuntilthepistonhasmoveduppasttheTDCposition.Thishelpstoremoveasmuchoftheburnedgasesasispossibleandincreasevolumetricefficiency.2.4.4CamDesignandControlDynamicsThefunctionofthecamistoopenandclosethevalvesasfaraspossible,asfastaspossibleandassmoothlyaspossible.Theclosingforceforthevalvesisappliedbythevalvespringwhichalsomaintaincontactbetweenthecamandthevalves.Dynamicforceimposelimitsoncamandvalvelift.Theentirevalve-trainassemblycanbeviewasaspring\masssysteminwhichtheconversionfromstoredtofreeenergycausesforcevibration.Valve-trainassemblieswithoverheadcamshaftscanberepresentedwithsufficientaccuracybya1-masssystem(consistingofthemovingmass,thevalve-trainassemblystiffnessandcorrespondingdamping).Forsystemwithvalvebottom-mountedcamshaftandpushrods,a2-masssystemisbeingincreasinglyused.Themaximumpermissiblecontactstress,usuallyregardedastheparameterwhichlimitscam-loberadiusandtherateofopeningontheflank,currentlyliesbetween600-700Mpadependinguponthematerialparingsused.2.4.5CamshaftDriveMechanismEachcammustrevolveonceduringthefour-strokecycletoopenavalve.Acycle,remember,correspondswithtworevolutionsofthecranksha