汽车构造(发动机)中英文课件1-4课件

STRUCTUREOFAUTOMOBILEENGINE汽车发动机构造汽车运用教研组黄银娣开发Chapter1:TheInternalCombustionEngine§1-1General

●Definition:TheInternalCombustionengineVSTheExternalCombustionEngine------Thecombustion(orburning)fueltakesplaceinsidetheengine.

●Fuel:1.Mostautomobileengineproducepowerbyburningamixtureofairandgasoline;2.somekindsofenginebydieselfuel;3.somebyalternativefuelssuchasCNG（天然气）,LNG（液化石油气）,Methanol(甲醇）,ethanol(乙醇）andetc.汽车运用教研组黄银娣开发2003年8月Mainobjection:

Tostudytheinternalcombustionengine汽车运用教研组黄银娣开发2003年8月§1-2Gasolineasafuelknowaboutfollowingpoints:●NO.1Howtheburningofgasolineproducesmechanicalpower?(1)Gasolineinliquidformisnoncombustible(non-burning)(2)however,gasolineVapordoesburn,combinedwithair(oxygeninair),gasolinevaporburnsinsidetheenginetoproducepower.汽车运用教研组黄银娣开发●NO.2Howdoestheliquidgasolineinthegastankbecomegasolinevapor?Evaporation:Gasolinebecomesavaporbyevaporation,whichistheprocessofturningaliquidintoavapor.Gasolinebeginstoevaporateatamuchlowertemperaturethanwater:

Tevaporationofgasoline﹤Tevaporationofwateritmeans:Gasolineismoreeasytovaporizethanwater.汽车运用教研组黄银娣开发Evaporate

Evaporationtakesplaceabovethesurfaceofaliquidwhenitisexposedtotheair.-----thus,gasolinevaporwillfillthespaceabovethesurfaceofgasoline.letshaveanexperiment:seeFig.1-1★Remember:thereisalwaysvaporabovethesurfaceofgasoline.Whiletheliquidmaynotburn,thevaporwill.汽车运用教研组黄银娣开发AtomizedparticlesAtomizer1-1:thevapormadebyasprayevaporatesquickly.汽车运用教研组黄银娣开发SprayingthegasolineintotheairThebestwaytoevaporategasolineistoexposetotheairasmuchofitssurfaceaspossible------tomakeliquidgasolineintothetinydroplets.e.gFig.1—2Thevapormadebyasprayevaporatesquickly.汽车运用教研组黄银娣开发fuseFuel-airmixturestopper1-2:Inthisexperiment,gasolinevaporburninginacanhasenoughpowertohavethestopperout.汽车运用教研组黄银娣开发2003年8月No.3Whathappenswhengasolineevaporates?Theevaporatinggasolinemixedwithair.Theevaporatinggasolineexpandstofillmorespacethanitdidasaliquid.Ifaflameistouchedtothismixture,thegasolinevaporandairburnrapidlyproducingintenseheat.Whenveryhot,themixturequicklyexpandsevenmore.汽车运用教研组黄银娣开发No.4Whathappenstothemixturewhenitisburnedinsideaclosedcontainer?Fig.1---3Suppose:①attheopenendofatincan------putacork(塞子）；②throughtheclosedend------ranafuse(引线，导火线）③closedspace

filledwithfuel-airmixtureinside汽车运用教研组黄银娣开发2003年8月SparkplugExhaustvalveIntakevalveCombustionchamberpistoncylinder1-3:Inthisengine.Atight-fittingpistonmovesupanddowninthecylinder.Theintakevalvetakesinvapor.Theexhaustvalvereleasestheburnedmixture.汽车运用教研组黄银娣开发2003年8月Makeanexperiment:

First:sprayedinamixtureofvaporizedgasolineandairwithatomizer.Second:litthefuseThen:thefusewillignitethegasolinevapor.Thelast:theburningvaporwouldexpandwithsuchforcethatitwouldblowthestopper

off---that’s“explosion”★conclusion:Internalcombustionengineburnsgasolinevaporandairtoproducepower.汽车运用教研组黄银娣开发§1-3AOne-cylinderInternalCombustionengineThetincan------LikethecylinderofengineThestopperinthetincan------LikeapistonThefuseinthetincan------LikeasparkplugSpacebetweenthetopofthepistonandthetopofthecylinder.------Thecombustionchamber汽车运用教研组黄银娣开发Intakevalve------themixtureisletinandignitedExhaustvalve------exhaustgaswasreleasedfromthecylinderthroughtheexhaustvalveCrankshaft(曲轴）-----lookslikeastraightbarwithanoffset(n.偏置）sectioninthecenterofit(crankshaft)function:tochangepiston’supanddownmotiontotherotationofthecrankshaft●Aconnectingrod------joinsthepistonandthecrankshaft

PistonConnectingrodcrankshaft1-4:thecrankshaftisstraight,withanoffsetsectioninthemiddleofit.Itisjoinedtothepistonmovesthecrankshaft.Thisconvertstheverticalmotionofthepistonintotherotarymotionofthecrankshaft.汽车运用教研组黄银娣开发§1-5Boreandstroke汽车运用教研组黄银娣开发2003年8月汽车运用教研组黄银娣开发2003年8月汽车运用教研组黄银娣开发2003年8月§1-6pistonstrokesIntakestroke(进气行程)Compressionstroke(压缩行程)Powerstroke(做功行程)Exhauststroke(排气行程)汽车运用教研组黄银娣开发第二节四冲程发动机工作原理四冲程柴油机工作过程汽车运用教研组黄银娣开发2003年8月汽车运用教研组黄银娣开发2003年8月汽车运用教研组黄银娣开发2003年8月汽车运用教研组黄银娣开发2003年8月汽车运用教研组黄银娣开发2003年8月汽车运用教研组黄银娣开发汽车运用教研组黄银娣开发汽车运用教研组黄银娣开发汽车运用教研组黄银娣开发§1-7enginedisplacement

汽车运用教研组黄银娣开发2003年8月汽车运用教研组黄银娣开发CompressionratioCompressionratioisacomparisonbetweenthevolumeinthecylinderwhenthepistonstandsatBDCagainstthevolumeatTDC.ε=Va/Vccar(gasoline)ε:8:1-11:1;someracingcar:13:1-14:1汽车运用教研组黄银娣开发汽车运用教研组黄银娣开发Reviewquestion1.Whymustgasolinebevaporizedinanengine?2.Whereistheair-fuelmixtureignited?3.WhatdoestheabbreviationTDCstandfor?4.whatisthefinalstrokesinanenginecycle?5.listthefourenginestrokes.6.howisdisplacementmeasured?7.howdoyoucalculatecompressionratio?汽车运用教研组黄银娣开发CH2:Enginefundamentals§2－1Enginesystems§2－2Engineconfiguration

thein-lineengineThewaytoarrangecylindersinagroupistolinethemupinastraightrow.Usuallyhaveevennumber(four,six,eightlinecylinders,it’sbalanced.Butsometimehave3or5cylinders.2－1：Anexampleofanin-lineenginethathasfourcylindersinaline.TheV-typeengineTheV-8enginewasdesignedtoproducethepowerofthein-lineeightinasmallerengine.Hastwofour-cylinderin-lineenginesplacedbesideeachotherintheshapeofaVHasonlyonecrankshaft,withalleightcylindersconnected.IntheUnitedStates,itwasforyearsthemoatpopularengine.Today,thereareV-4enginejusttwocylinderlong;V-6type;V-8,evensomeexpensiveforeigncarshaveV-12engines,whichhavetwobankofsixcylinderseach.2-2:

AutomanufacturesmakeV-typeenginesoffour,six,andeightcylinders.AV-6configurationisshownhere.2-3:

thehorizontally-opposedenginehastwobanksofcylinderspointinginoppositedirections.Becausethebankshavea180anglebetweenthem,thisengineiscalledaflatengine.Theflatengine

SeeFig.2-3Ithastwobanksofcylindersoppositeoneanother.JustliketheV-typebecomeaflathorizontalline.Eg.Air-cooledVolkswagens(大众）usetheflat-fourengine.ManyPorschesusetheflat-six.§2－3Engineplacement发动机驱动：Frontengine,rearwheeldrive(truck,jeepetc.)Rearengine,rearwheeldrive(Passengercars)Frontengine,frontwheeldrive(mostcar)发动机位置：In-linepowertrain（纵向发动机）:theengineiscenteredandtheshaftsrunthelengthofthecar.（与车轴垂直）Transverseengine(横向发动机）:theengineiscrosswiseinthecar.Inthiscase,theengineisrightoverthefrontaxle.Whichitdrives.Acarwithsuchadesignhasatransverseengine.（与车轴平行)ABEngineEngineDriveshaftDrivingaxleDrivingaxle2-4:(A)Manycarshaveanin-lineenginearrangementwiththeengineanddriveshaftrunningfront-to-rear.(B)Intransverseenginearrangementtheenginerunsfromsidetoside.§2－4Theenginesystem

thefuelsystemAsshowinFig.2-5Function:thefuelsystemstoresfuelanddeliversittotheengineasneeded.Composition:fourbasicpartsmakeupthefuelsystem.Theyarethefueltank,fuellines,fuelpumpsandthefuelfilter.FueltankFuellineFuelpumpFuelfilter2-5:Thefuelsystemstoresthefuelanddeliversittotheengineasneeded.§2－5TheintakesystemSeeFig.2-6Function:takesfuelfromthefuelsystem,mixesitwithjusttherightamountofair,andthendeliversittothecombustionchamber.Composition:theaircleaner,theairfilter,thecarburetor,theintakemanifold,theintakepartsetc.AircleanerAirfiltercarburetorIntakemanifoldblock2-6:themainpartsoftheintakesystem.§2－6Theignitionsystem

Seefig.2-7Function:theignitionsystemignites(orfires)theair-fuelmixtureinthecombustionchamberatjusttherightinstant.thisinstantisattheendofthecompressionstrokeandthebeginningofthepowerstroke.Unlessthefuelisignitedatthecorrectmoment,theenginewillnotrunproperly.Composition:battery,sparkplugs,thecoil,andthedistributoretc.CoilwirebatteryCoilSparkplugwiresdistributorSparkplugs2-7:theignitionsystemtakeselectricityfromthebatteryanddeliversittothesparkplugstoignitethefuel-airmixture.§2－7thecoolingsystem

Seefig.2-8,2-9Function:tocarryawaytheheatproducedbythecombustionengineinsidethechamber.Types:a.theair-cooledengine（风冷发动机）(mostmotorcycle)b.andthewatercooledengine（水冷发动机）(mostcars)Thewatercooled:alsocalledliquid-cooled.amixtureofwaterandachemical，theliquidpreventsfreezinginthewinterandboilinginthesummer.thechemical:isantifreeze(防冻剂）(it’sscientificnameisethyleneglycol)airairfanCoolingfins2-8:Anair-cooledengineusestheoutsideairpassingovertheenginetocarryawaytheheatproducedbytheburningmixture.WaterjacketWaterpumpcoolantradiator2-9:Awater-cooledengineusesaliquidtocooltheengine.Thenitusesairtocooltheliquid.§2－8ThelubricationsystemSeeFig.2-10,11Partsofthelubricationsystem:1.Theoilpan(油底壳）:istheholder,orsump,forthe3-6qts.(about3-5L)ofoil.2.anoilpump（油泵）:drawstheoilfromthepanandpushesitthroughtheoilfilter.3.theoilfilter（滤清器）:removesdirtfromtheoil.4.oilgalleries(油道）：passagestheoilthroughintheenginepartsthatneedlubrication.Pushingforce

forceoffriction

2-10:frictionistheforcethatresistsmotionbetweentwosurfacesincontact.Oilgalleries

Oilpan

OilpickupOilpumpOilfilter2-11:thelubricationsystemprovidesoiltoallinternalengineparts,toreduceheatinsidetheengine.

§2－9Theexhaustsystem(排气系统）

Function:takestheburnedgasesfromthecylinder,carriesthemawayfromtheengine,anddischargesthemintotheair.Seefig.2-12Partsoftheexhaustsystem:exhaustmanifold（排气歧管）,exhaustpipe（排气管）,intermediatepipe（中间排气管）,muffle（消声器）,andtailpipe（排气尾管）.TailpipemufflerIntermediatepipeExhaustpipeExhaustmanifold2-12:theexhaustsystemCarriestheburnedgasesawayfromtheengineandoutintotheair.Italsolessenstheloudnoiseproducedbytheengine.Reviewquestions1.Whatisengineconfiguration?2.whatisahorizontally-opposedengine(水平对置，平置发动机）?3.listthesixenginesystems.4.Whatisatransverseengine(横置发动机）?5.whatdoesthedistributordo?6.whyisliquidcoolingneededinmodernengines?7.whyisoilneededinanengine?Chapter3:engineblocksandcylinderheads（发动机机体和汽缸盖）Seefig.3-1IntakemanifolddistributorPistonandrodcrankshaftblockOilpanWaterpumpCylinderheadHeadcover3-2:theblockisthemainsupportpiecefortheengine.Allotherenginepartsfitinsidetheblockorfastentoit.Theengineblock

Engineblockisthebasicframeoftheengine.Allotherenginepartseitherfitsinsideitorfastentoit.

Itholdsthecylinders（汽缸),waterjackets(水套）,andoilgalleries(油道）；Italsoholdsthecrankshaft,whichfastenstothebottomoftheblock.Thecamshaftalsofitsinsidetheblock,exceptonoverhead-camengine(OHC)(顶置式凸轮轴）。Inthemostcars,theblockismadeofgrayiron(灰铁）,oranalloy（合金）(mixture)ofgrayironandothermetals,suchasnickel（镍）orchromium（铬）.Engineblocksarecastings（铸造).Acastingisproducedbyheatingmetaluntilitbecomesaliquidandthenpouringitintoamold(模子),whereithardensintothecorrectshape.Someengineblocksinthesmallcars,aremadeofcast

aluminum(铸铝），thismetalislighterthantheiron.however,ironwearsbetterthanaluminum.therefore,thecylindersinmostaluminumenginearelinedwithironorsteelsleeves(衬套）。Thissleevesarecalledcylinderlinersorcylindersleeves.(缸套）Someblocksaremadeentirelyofaluminum.Castironblockaluminumblocksleeves3-3:theengineblockismadeofcastironorcastaluminum.Inmostaluminumengines,thecylindersarelinedwithironorsteel.Thecylinderhead

Seefig.3-2,thecylinderheadfastenstothetopoftheblock,justasarooffitsoverahouse.Theheadisthewidthandlengthoftheblock.Mostcylinderheadsaremadeofcastiron,thoughsomeareofcastaluminum.,insomeengines,theblockandthecylinderheadaremadeofdifferentmaterials.Seefig.3-4,v-8enginehastwocylinder

heads,eachbankhavefourcylinders.HeadHeadblockblockblockV-8In-linefourFlatfour3-4:thenumberofcylinderheadsonanenginedependsonthenumberofbanksofcylindersithas,Eachbankrequiresonehead.CombustionchamberOilandwaterpassagesValvesetsExhaustportsPushrodguideholesValveguidesSparkplugHolesIntakeports3-5:theundersideoftheheadhaspocketsforthetopofthecombustionchamber.Thetopoftheheadcontainsvalveseatsandrockerstands.Rockershaft

Headbolthole

ValvespringRockerarm

portPushrodguideholevalve3-6:Afullyassembledcylinderheadhasmanyparts.finsHeadsurfaceHeadsurfaceBlockdeckBlockdeckgasketNogasket3-8:pressedbetweentwosurfaces,agasketfillsintheirregularitiesandprovidesatightseal.3-7:anair-cooledheadhasfinsbutnowaterjacketpassages.BoltholesOilpassageholesWaterpassageholesCylinderholesboltholes3-9:theheadgaskethasholescutintofittheholesinthedeckandheadsurfaces.Onceaheadgasketisremoved,youshouldreplaceitwithanewone.ValvecoverExhaustmanifoldheadcarburetorIntakemanifold3-10:thevalvecover,exhaustmanifold,andintakemanifoldarefastenedtothecylinderhead.carburetorIntakemanifoldheadheadExhaustmanifoldLittervalleyExhaustmanifoldTimingcoverOilpanblockOilpan3-11:AsingleintakemanifoldfitsintothecentralpartofaV-8engine,coveringtheliftervalley.Anexhaustmanifoldboltstotheoutsideofeachhead.3-12:theoilpanandthetimingcover.hemiwedgeSemi-HemihemiwedgeSemi-Hemi3-13:thethreemostcommontypesofautomobileengineheadarethehemi,wedge,andsemi-hemi.frontFrontofcarfrontfrontflywheelflywheelflywheelflywheelrearrearFrontofengineBackofengineSteeringwheelleftright3-14:3-15:3-16:3-17:Reviewquestion1.Whatisacasting?2.Whyisacylinderheadneeded?3.Wherearetheintakeandexhaustportslocated?4.Howisthecylinderheadsealedtotheblock?5.Whatarethethreemostcommoncylinderheadshapes?6.listthemajorpartsthatarefastenedtotheblock?Chapter4:

Connectingrods,bearings,

andcrankshafts连杆,轴瓦.曲轴Connectingrodslinkthepistontothecrankshaft.theserodsconvertthereciprocating(up-and-down)motionofthepistonintotherotarymotionofthecrankshaft.fig.4-1.Theconnectingrodsareprotectedbybearings.4-1:

theconnectingrodlinksthepistontothecrankshaft.Thischangesreciprocatingmotiontorotarymotion.4-2:ConnectingrodsSeefig.4-2Composition:mainpartofrod(连杆),rodcap(连杆盖),,rodboltsandnut(连杆螺栓与螺母)Connectingrod’srequirements:hepassengercar:theyaremadeofforgedorcaststeel;Engineforracingcar:theyaremadeofaluminumorotheralloys.＊Eachrodcapmustmatchedwith

rodbystampingwithanumber.Seefig.4-3CylindernumberAlignmentnotch4-3:Anumberstampedonthebigendofeachrodmatchesanumberontherodcapthatgoeswithit.Connecting-rodjournals(连杆轴径)Seefig.4-4,5Connecting–rodjournal,rodjournal,orcrankpin(连杆轴径)Thissmooth,shapedpieceisoffset(偏置)fromthecenterlineofthecrankshaft.Theamountofoffsetequalshalfoftheenginestroke(偏置量等于发动机行程的一半).seefig.4-5Rodjournal(crankpin)Crankshaftcenterline4-4:

theconnectingrodfastenstotheconnecting-rodjournalofthecrankshaft.borestrokeCrankshaftoffsetCrankshaftoffsetFig4-5theoffsetofthecrankshaftequalshalfthestrokeoftheengine.Attopdeadcenter,theoffsetpointsstraightup.Atbottomdeadcenter,itpointsstraightdown.Rodbearings(连杆轴承)Function:arodbearingisusedtolessenfrictionbetweenthecrankshaftandtheconnectingrod.Seefig.4-6,7therodbearingisathinsheetofsoft,smoothmetalthatfitsaroundtherodjournal.Thereisasmallamountofclearance(间隙),whichisoil-filled.thesebearingsseparateintotwohalvesforsimpleinstallation.Rodbearingarecalledinsertbearingbecausetheyareinsertedbetweentherodandtherodjournal.BearinginsertrodRodcapFig4-6theconnecting-rodbearingfitsbetweenthebigendoftherodandtheconnecting-rodjournalofthecrankshaft.bearingrodRodjournalFig4-7therodbearingisalsocalledaninsertbearing,becauseitisinsertedbetweenthecrankpinandtherod.Rodbearingconstruction

Seefig.4-8therodbearingfitsbetweentherodandtherodjournal.Thebearingdoesnotturnwiththecrankshaft.Instead,alocating,orlockingtab,holdsthebearingintheplacesintherod.thislocatingtab(定位键或锁止键)fitsintoaslot(槽)

intherodcap(连杆盖).bearingTab(定位键)slotRodcapFig4-8whentherodfastentothecrankshaft,alockingtabonthebearinglinesupwithaslotintherodcap.Bearingcrush(轴承抱紧,挤压,压碎)Seefig.4-9Everybearingmusthavetheproperbearingcrush.WHY?Toensuretheproperbearingcrush,eachhalfofthebearingisslightlylargerthantherodhalves.Thus,whentherodcapfastensontotherod,theendsofthebearinghalvesmeetbeforetherodcapcontactstherod.whentherodcapjoinstherod,theforcetotightentheboltswillslightlycrushthebearinghalves.Thispressureforcesthebearingtightlyintoplace.bearingFig4-9Bearinghalvesaremadelongerthantheinnersurfacesoftherod’sbigend.Thebearinghalvesarecrushedintoplacewhentherodcapistightenedagainsttherod.Crushheight4-10.Theamountofcrushisknownasthecrushheight.BearingmaterialsThebearingusedintoday’senginesmustbe:Strongenoughtowithstandthepressuresofthemotionofthepistonandconnectingrod;Long-wearingenoughtolastfortensofthousandsofmiles;Softenoughtoshapethemselvestothejournalwithoutdamagingthejournal.Thefoundationofamodernbearingisahalf-circlesteelshell(半圈钢片)calledthebackingshell(基片)orbearingshell(轴承片).Asecondmetalismeltedontotheinsideofthisshelltofromtheinnersurfaceofthebearing.Thissecondmentalisaluminum(铝),tin(锡),acopper-leadalloy(铜铅合金),orbabbitt(巴比合金,一种铜,锑,锡合金,(机)巴比合金轴承衬)(asoftalloyoftin,copper,andantimony(锑)).Somebearinghavelayersofdifferentmaterials.Seefig.4-11,bearingmadeofthreemetalsarecalledtri-mentalbearings.Therealsoarebabbittbearings,aluminum-coated(镀,涂层)bearing,andcopper-leadbearings(铜铅轴承).BearingmetalSteelbackingshellFig4-11Bearingshaveasteelshell.Alayerofoneormoresoftmetalsgivesthebearingasmoothinnersurface.ThefunctionofbearingsLoad-carryingcapacity(承载能力)Highcompressionratio----ashighasseveralthousandpoundspersquareinch(1000psi=6895Kpa)Fatigueresistance(抗疲劳性)

themetalmakinguptheinnersurfaceofthebearingmustbesoftenoughtowithstandfatigue.Embeddability(吸收小颗粒能力)istheabilityofbearingtoabsorbsmallpiecesofdirt.Conformability(与轴径尺寸的变形一致)Thebearingmustbesoftenoughtoconformtotheshapeofthejournal.Corrosionresistance(抗腐蚀性)

tocombatcorrosionproducedbyacidsthatcombustioncreates.Wearability(磨损性)

mustbehardenoughtowearwell.MainbearingsSeeFig4-12CrankshafthasanothersetofjournalscalledMainjournalsormain-bearingjournals(主轴径)#seeFig4-13Inthebodyofengine,thebearingsthatfitaroundthemainjournalsarecalledmainbearingsor(主轴承)mains.#seeFig4-14,15Onemainbearingdiffersfromtheothers.Thisiscalledthrustbearing(推力轴承),

ithaslips,orflanges.Theseflangesrubagainstapolishedsurfaceontheedgeofthemainjournal.Thefront-to-backcrankshaftmovementiscalledcrankshaftthrust.Thethrustbearingstopsexcessivecrankshaftthrust(曲轴推力)andendplay.(曲轴轴向间隙).MainbearingcapsSeeFig4-16Semicircularcapscalledmain-bearingcapsbolttothebottomoftheengineblock.Inmostpassengercarengineusemaincapswithtwobolts(带有两个螺栓的主轴承盖).seeFig4-16Manyhigh-dutyandhigh–performanceengineshavefourmaincapboltstofastenthecapstotheblock.seeFig4-17MainbearingcapboltsMainjournalEngineblockMaincap

Fig4-16mainbearingcapsbolttothebottomoftheengineblock.Thesecapsfitaroundthemainbearingsandhelpsupportthecrankshaft.Fig.4-17inacross-bolted,twoboltsgothroughthesideoftheengineblock.Theothertwoboltsgoinfromthebottom.counterweightsCounterweightshelpbalancetheweightoftherodjournal,rodsandpistons.Theypreventvibrationasthecrankshaftturns.Withoutcounterweights,vibrationwouldoccur.Thiswoulddamagetheengine.Fig4-18thethreemajorpartsofthecrankshaftarethemainjournals,rodjournals,andcounterweights.MainjournalsRodjournalscounterweightsNumberingthecrankshaftmainjournalsandtherodjournalsFrontofengineBackofenginepistoncylindersConnectingrod

RodjournalsMainjournalsFig4-19themainjournalsonacrankshaftarenumberedinorderfromfronttoback.ThiscrankshafthasfivemainjournalsFig4-20InaV-8,thecylindersinonebankareslightlyforwardofthecylindersintheotherbank.thus,theconnectingrodsofoppositecylinderscanattachtothesamerodjournalofthecrankshaft.CylinderfiringorderRodjournalarrangementandfiringorderTDCTDCTDCcrankpinBDCBDCFig4-21whenthecrankthrowpointsstraightuptowardthecylinder,thepistonstandsatTDC.Fig4-22whenthecrankthrowpointsstraightdown,awayfromthecylinder,thepistonstandsatBDC.Fig4-23whenthecrankthrowpointsawayfromthecylinderata90°angle,thepistonishalfwayupthecylinder.Intervalbetweencrankshaftthrows

(1)forfour-cylinderengine=180°

(2)forin-linesix-cylinderengine=120°

(3)inav-8,thecrankshaftthrowsareat90°intervals.seefig4-24

90°Fig4-24theVangleinav-8equals90.This90keepstheproperfiringintervalsandanglesbetweentherodjournals.Cylinderfiringorderinv-8engine

Eachfour-strokecycleofthepistonhasonepowerstroke.Onthisstrokethesparkplugignitestheair-fuelmixture,causingittoexpandandforcethepistondownward.Thereforethepowerstrokeisalsocalledthefiringstroke.forv-8,eachcylinderfiresata90°intervalfromthecylindersfiringbeforeandafterit.Cylinderfiringorderinfour–cylinderandsix-cylinderengineFourcylinder=720°/4=180°Sixcylinder=72