汽車構(gòu)造(發(fā)動(dòng)機(jī))中英文課件1-4課件

STRUCTUREOFAUTOMOBILEENGINE汽車發(fā)動(dòng)機(jī)構(gòu)造汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)Chapter1:TheInternalCombustionEngine§1-1General

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

●Fuel:1.Mostautomobileengineproducepowerbyburningamixtureofairandgasoline;2.somekindsofenginebydieselfuel;3.somebyalternativefuelssuchasCNG（天然氣）,LNG（液化石油氣）,Methanol(甲醇）,ethanol(乙醇）andetc.汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)2003年8月Mainobjection:

Tostudytheinternalcombustionengine汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)2003年8月§1-2Gasolineasafuelknowaboutfollowingpoints:●NO.1Howtheburningofgasolineproducesmechanicalpower?(1)Gasolineinliquidformisnoncombustible(non-burning)(2)however,gasolineVapordoesburn,combinedwithair(oxygeninair),gasolinevaporburnsinsidetheenginetoproducepower.汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)●NO.2Howdoestheliquidgasolineinthegastankbecomegasolinevapor?Evaporation:Gasolinebecomesavaporbyevaporation,whichistheprocessofturningaliquidintoavapor.Gasolinebeginstoevaporateatamuchlowertemperaturethanwater:

Tevaporationofgasoline﹤Tevaporationofwateritmeans:Gasolineismoreeasytovaporizethanwater.汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)Evaporate

Evaporationtakesplaceabovethesurfaceofaliquidwhenitisexposedtotheair.-----thus,gasolinevaporwillfillthespaceabovethesurfaceofgasoline.letshaveanexperiment:seeFig.1-1★Remember:thereisalwaysvaporabovethesurfaceofgasoline.Whiletheliquidmaynotburn,thevaporwill.汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)AtomizedparticlesAtomizer1-1:thevapormadebyasprayevaporatesquickly.汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)SprayingthegasolineintotheairThebestwaytoevaporategasolineistoexposetotheairasmuchofitssurfaceaspossible------tomakeliquidgasolineintothetinydroplets.e.gFig.1—2Thevapormadebyasprayevaporatesquickly.汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)fuseFuel-airmixturestopper1-2:Inthisexperiment,gasolinevaporburninginacanhasenoughpowertohavethestopperout.汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)2003年8月No.3Whathappenswhengasolineevaporates?Theevaporatinggasolinemixedwithair.Theevaporatinggasolineexpandstofillmorespacethanitdidasaliquid.Ifaflameistouchedtothismixture,thegasolinevaporandairburnrapidlyproducingintenseheat.Whenveryhot,themixturequicklyexpandsevenmore.汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)No.4Whathappenstothemixturewhenitisburnedinsideaclosedcontainer?Fig.1---3Suppose:①attheopenendofatincan------putacork(塞子）；②throughtheclosedend------ranafuse(引線，導(dǎo)火線）③closedspace

filledwithfuel-airmixtureinside汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)2003年8月SparkplugExhaustvalveIntakevalveCombustionchamberpistoncylinder1-3:Inthisengine.Atight-fittingpistonmovesupanddowninthecylinder.Theintakevalvetakesinvapor.Theexhaustvalvereleasestheburnedmixture.汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)2003年8月Makeanexperiment:

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

off---that’s“explosion”★conclusion:Internalcombustionengineburnsgasolinevaporandairtoproducepower.汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)§1-3AOne-cylinderInternalCombustionengineThetincan------LikethecylinderofengineThestopperinthetincan------LikeapistonThefuseinthetincan------LikeasparkplugSpacebetweenthetopofthepistonandthetopofthecylinder.------Thecombustionchamber汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)Intakevalve------themixtureisletinandignitedExhaustvalve------exhaustgaswasreleasedfromthecylinderthroughtheexhaustvalveCrankshaft(曲軸）-----lookslikeastraightbarwithanoffset(n.偏置）sectioninthecenterofit(crankshaft)function:tochangepiston’supanddownmotiontotherotationofthecrankshaft●Aconnectingrod------joinsthepistonandthecrankshaft

PistonConnectingrodcrankshaft1-4:thecrankshaftisstraight,withanoffsetsectioninthemiddleofit.Itisjoinedtothepistonmovesthecrankshaft.Thisconvertstheverticalmotionofthepistonintotherotarymotionofthecrankshaft.汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)§1-5Boreandstroke汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)2003年8月汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)2003年8月汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)2003年8月§1-6pistonstrokesIntakestroke(進(jìn)氣行程)Compressionstroke(壓縮行程)Powerstroke(做功行程)Exhauststroke(排氣行程)汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)第二節(jié)四沖程發(fā)動(dòng)機(jī)工作原理四沖程柴油機(jī)工作過(guò)程汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)2003年8月汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)2003年8月汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)2003年8月汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)2003年8月汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)2003年8月汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)§1-7enginedisplacement

汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)2003年8月汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)CompressionratioCompressionratioisacomparisonbetweenthevolumeinthecylinderwhenthepistonstandsatBDCagainstthevolumeatTDC.ε=Va/Vccar(gasoline)ε:8:1-11:1;someracingcar:13:1-14:1汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)Reviewquestion1.Whymustgasolinebevaporizedinanengine?2.Whereistheair-fuelmixtureignited?3.WhatdoestheabbreviationTDCstandfor?4.whatisthefinalstrokesinanenginecycle?5.listthefourenginestrokes.6.howisdisplacementmeasured?7.howdoyoucalculatecompressionratio?汽車運(yùn)用教研組黃銀娣開(kāi)發(fā)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(大眾）usetheflat-fourengine.ManyPorschesusetheflat-six.§2－3Engineplacement發(fā)動(dòng)機(jī)驅(qū)動(dòng)：Frontengine,rearwheeldrive(truck,jeepetc.)Rearengine,rearwheeldrive(Passengercars)Frontengine,frontwheeldrive(mostcar)發(fā)動(dòng)機(jī)位置：In-linepowertrain（縱向發(fā)動(dòng)機(jī)）:theengineiscenteredandtheshaftsrunthelengthofthecar.（與車軸垂直）Transverseengine(橫向發(fā)動(dòng)機(jī)）:theengineiscrosswiseinthecar.Inthiscase,theengineisrightoverthefrontaxle.Whichitdrives.Acarwithsuchadesignhasatransverseengine.（與車軸平行)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（風(fēng)冷發(fā)動(dòng)機(jī)）(mostmotorcycle)b.andthewatercooledengine（水冷發(fā)動(dòng)機(jī)）(mostcars)Thewatercooled:alsocalledliquid-cooled.amixtureofwaterandachemical，theliquidpreventsfreezinginthewinterandboilinginthesummer.thechemical:isantifreeze(防凍劑）(it’sscientificnameisethyleneglycol)airairfanCoolingfins2-8:Anair-cooledengineusestheoutsideairpassingovertheenginetocarryawaytheheatproducedbytheburningmixture.WaterjacketWaterpumpcoolantradiator2-9:Awater-cooledengineusesaliquidtocooltheengine.Thenitusesairtocooltheliquid.§2－8ThelubricationsystemSeeFig.2-10,11Partsofthelubricationsystem:1.Theoilpan(油底殼）:istheholder,orsump,forthe3-6qts.(about3-5L)ofoil.2.anoilpump（油泵）:drawstheoilfromthepanandpushesitthroughtheoilfilter.3.theoilfilter（濾清器）:removesdirtfromtheoil.4.oilgalleries(油道）：passagestheoilthroughintheenginepartsthatneedlubrication.Pushingforce

forceoffriction

2-10:frictionistheforcethatresistsmotionbetweentwosurfacesincontact.Oilgalleries

Oilpan

OilpickupOilpumpOilfilter2-11:thelubricationsystemprovidesoiltoallinternalengineparts,toreduceheatinsidetheengine.

§2－9Theexhaustsystem(排氣系統(tǒng)）

Function:takestheburnedgasesfromthecylinder,carriesthemawayfromtheengine,anddischargesthemintotheair.Seefig.2-12Partsoftheexhaustsystem:exhaustmanifold（排氣歧管）,exhaustpipe（排氣管）,intermediatepipe（中間排氣管）,muffle（消聲器）,andtailpipe（排氣尾管）.TailpipemufflerIntermediatepipeExhaustpipeExhaustmanifold2-12:theexhaustsystemCarriestheburnedgasesawayfromtheengineandoutintotheair.Italsolessenstheloudnoiseproducedbytheengine.Reviewquestions1.Whatisengineconfiguration?2.whatisahorizontally-opposedengine(水平對(duì)置，平置發(fā)動(dòng)機(jī)）?3.listthesixenginesystems.4.Whatisatransverseengine(橫置發(fā)動(dòng)機(jī)）?5.whatdoesthedistributordo?6.whyisliquidcoolingneededinmodernengines?7.whyisoilneededinanengine?Chapter3:engineblocksandcylinderheads（發(fā)動(dòng)機(jī)機(jī)體和汽缸蓋）Seefig.3-1IntakemanifolddistributorPistonandrodcrankshaftblockOilpanWaterpumpCylinderheadHeadcover3-2:theblockisthemainsupportpiecefortheengine.Allotherenginepartsfitinsidetheblockorfastentoit.Theengineblock

Engineblockisthebasicframeoftheengine.Allotherenginepartseitherfitsinsideitorfastentoit.

Itholdsthecylinders（汽缸),waterjackets(水套）,andoilgalleries(油道）；Italsoholdsthecrankshaft,whichfastenstothebottomoftheblock.Thecamshaftalsofitsinsidetheblock,exceptonoverhead-camengine(OHC)(頂置式凸輪軸）。Inthemostcars,theblockismadeofgrayiron(灰鐵）,oranalloy（合金）(mixture)ofgrayironandothermetals,suchasnickel（鎳）orchromium（鉻）.Engineblocksarecastings（鑄造).Acastingisproducedbyheatingmetaluntilitbecomesaliquidandthenpouringitintoamold(模子),whereithardensintothecorrectshape.Someengineblocksinthesmallcars,aremadeofcast

aluminum(鑄鋁），thismetalislighterthantheiron.however,ironwearsbetterthanaluminum.therefore,thecylindersinmostaluminumenginearelinedwithironorsteelsleeves(襯套）。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連桿,軸瓦.曲軸Connectingrodslinkthepistontothecrankshaft.theserodsconvertthereciprocating(up-and-down)motionofthepistonintotherotarymotionofthecrankshaft.fig.4-1.Theconnectingrodsareprotectedbybearings.4-1:

theconnectingrodlinksthepistontothecrankshaft.Thischangesreciprocatingmotiontorotarymotion.4-2:ConnectingrodsSeefig.4-2Composition:mainpartofrod(連桿),rodcap(連桿蓋),,rodboltsandnut(連桿螺栓與螺母)Connectingrod’srequirements:hepassengercar:theyaremadeofforgedorcaststeel;Engineforracingcar:theyaremadeofaluminumorotheralloys.＊Eachrodcapmustmatchedwith

rodbystampingwithanumber.Seefig.4-3CylindernumberAlignmentnotch4-3:Anumberstampedonthebigendofeachrodmatchesanumberontherodcapthatgoeswithit.Connecting-rodjournals(連桿軸徑)Seefig.4-4,5Connecting–rodjournal,rodjournal,orcrankpin(連桿軸徑)Thissmooth,shapedpieceisoffset(偏置)fromthecenterlineofthecrankshaft.Theamountofoffsetequalshalfoftheenginestroke(偏置量等于發(fā)動(dòng)機(jī)行程的一半).seefig.4-5Rodjournal(crankpin)Crankshaftcenterline4-4:

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

Seefig.4-8therodbearingfitsbetweentherodandtherodjournal.Thebearingdoesnotturnwiththecrankshaft.Instead,alocating,orlockingtab,holdsthebearingintheplacesintherod.thislocatingtab(定位鍵或鎖止鍵)fitsintoaslot(槽)

intherodcap(連桿蓋).bearingTab(定位鍵)slotRodcapFig4-8whentherodfastentothecrankshaft,alockingtabonthebearinglinesupwithaslotintherodcap.Bearingcrush(軸承抱緊,擠壓,壓碎)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(半圈鋼片)calledthebackingshell(基片)orbearingshell(軸承片).Asecondmetalismeltedontotheinsideofthisshelltofromtheinnersurfaceofthebearing.Thissecondmentalisaluminum(鋁),tin(錫),acopper-leadalloy(銅鉛合金),orbabbitt(巴比合金,一種銅,銻,錫合金,(機(jī))巴比合金軸承襯)(asoftalloyoftin,copper,andantimony(銻)).Somebearinghavelayersofdifferentmaterials.Seefig.4-11,bearingmadeofthreemetalsarecalledtri-mentalbearings.Therealsoarebabbittbearings,aluminum-coated(鍍,涂層)bearing,andcopper-leadbearings(銅鉛軸承).BearingmetalSteelbackingshellFig4-11Bearingshaveasteelshell.Alayerofoneormoresoftmetalsgivesthebearingasmoothinnersurface.ThefunctionofbearingsLoad-carryingcapacity(承載能力)Highcompressionratio----ashighasseveralthousandpoundspersquareinch(1000psi=6895Kpa)Fatigueresistance(抗疲勞性)

themetalmakinguptheinnersurfaceofthebearingmustbesoftenoughtowithstandfatigue.Embeddability(吸收小顆粒能力)istheabilityofbearingtoabsorbsmallpiecesofdirt.Conformability(與軸徑尺寸的變形一致)Thebearingmustbesoftenoughtoconformtotheshapeofthejournal.Corrosionresistance(抗腐蝕性)

tocombatcorrosionproducedbyacidsthatcombustioncreates.Wearability(磨損性)

mustbehardenoughtowearwell.MainbearingsSeeFig4-12CrankshafthasanothersetofjournalscalledMainjournalsormain-bearingjournals(主軸徑)#seeFig4-13Inthebodyofengine,thebearingsthatfitaroundthemainjournalsarecalledmainbearingsor(主軸承)mains.#seeFig4-14,15Onemainbearingdiffersfromtheothers.Thisiscalledthrustbearing(推力軸承),

ithaslips,orflanges.Theseflangesrubagainstapolishedsurfaceontheedgeofthemainjournal.Thefront-to-backcrankshaftmovementiscalledcrankshaftthrust.Thethrustbearingstopsexcessivecrankshaftthrust(曲軸推力)andendplay.(曲軸軸向間隙).MainbearingcapsSeeFig4-16Semicircularcapscalledmain-bearingcapsbolttothebottomoftheengineblock.Inmostpassengercarengineusemaincapswithtwobolts(帶有兩個(gè)螺栓的主軸承蓋).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