HowCarEnginesWorkHerewelldiscussthebasicideabehindanengine,andthengointodetailabouthowallthepiecesfittogetherandhowtoincreaseperformance!InternalCombustionAlmostallcarscurrentlyusewhatiscalledafour-strokecombustioncycletoconvertgasolineintomotion.Thefour-strokeapproachisalsoknownastheOttocycle,inhonorofNicholasOtto,whoinventeditin1867.Theyare:IntakestrokeorsuckstrokeCompressionstrokeorsqueezestrokeCombustionstrokeorbangstrokeExhauststrokeorblowstrokeThepistonisconnectedtothecrankshaftbyaconnectingrod.Hereswhathappensastheenginegoesthroughitscycle:1.Thepistonstartsatthetop,theintakevalveopens,andthepistonmovesdowntolettheenginetakeinacylinder-fullofairandgasoline.Thisistheintakestroke.Onlythetiniestdropofgasolineneedstobemixedintotheairforthistowork.2.Thenthepistonmovesbackuptocompressthisfuel/airmixture.Compressionmakestheexplosionmorepowerful.3.Whenthepistonreachesthetopofitsstroke,thesparkplugemitsasparktoignitethegasoline.Thegasolinechargeinthecylinderexplodes,drivingthepistondown.4.Oncethepistonhitsthebottomofitsstroke,theexhaustvalveopensandtheexhaustleavesthecylindertogooutthetailpipe.Nowtheengineisreadyforthenextcycle,soitintakesanotherchargeofairandgas.Noticethatthemotionthatcomesoutofaninternalcombustionengineisrotational.Inanenginethelinearmotionisconvertedintorotationalmotionbythecrankshaft.Therotationalmotionisnicebecauseweplantoturn(rotate)thecarswheelswithitanyway.Almostallcarstodayuseareciprocatinginternalcombustionenginebecausethisengineis:Relativelyefficient(comparedtoanexternalcombustionengine)Relativelyinexpensive(comparedtoagasturbine)Relativelyeasytorefuel(comparedtoanelectriccar)Theseadvantagesbeatanyotherexistingtechnologyformovingacararound.Nowletslookatallthepartsthatworktogethertomakethishappen.PartsofanEngineHeresaquickdescriptionofeachone,alongwithalotofvocabularythatwillhelpyouunderstandwhatallthecaradsaretalkingabout.CylinderThecoreoftheengineisthecylinder.Thepistonmovesupanddowninsidethecylinder.Theenginedescribedherehasonecylinder.Thatistypicalofmostlawnmowers,butmostcarshavemorethanonecylinder(four,sixandeightcylindersarecommon).Inamulti-cylinderenginethecylindersusuallyarearrangedinoneofthreeways:inline,Vorflat(alsoknownashorizontallyopposedorboxer),asshowninthefollowingfigures.Figure1.Inline-Thecylindersarearrangedinalineinasinglebank.Figure2.V-Thecylindersarearrangedintwobankssetatanangletooneanother.Figure3.Flat-Thecylindersarearrangedintwobanksonoppositesidesoftheengine.Differentconfigurationshavedifferentsmoothness,manufacturing-costandshapecharacteristicsthatmakethemmoresuitableinsomevehicles.SparkplugThesparkplugsuppliesthesparkthatignitestheair/fuelmixturesothatcombustioncanoccur.Thesparkmusthappenatjusttherightmomentforthingstoworkproperly.ValvesTheintakeandexhaustvalvesopenatthepropertimetoletinairandfuelandtoletoutexhaust.Notethatbothvalvesareclosedduringcompressionandcombustionsothatthecombustionchamberissealed.PistonApistonisacylindricalpieceofmetalthatmovesupanddowninsidethecylinder.PistonringsPistonringsprovideaslidingsealbetweentheouteredgeofthepistonandtheinneredgeofthecylinder.Theringsservetwopurposes:Theypreventthefuel/airmixtureandexhaustinthecombustionchamberfromleakingintothesumpduringcompressionandcombustion.Theykeepoilinthesumpfromleakingintothecombustionarea,whereitwouldbeburnedandlost.Mostcarsthatburnoilandhavetohaveaquartaddedevery1,000milesareburningitbecausetheengineisoldandtheringsnolongersealthingsproperly.CombustionchamberThecombustionchamberistheareawherecompressionandcombustiontakeplace.Asthepistonmovesupanddown,youcanseethatthesizeofthecombustionchamberchanges.Ithassomemaximumvolumeaswellasaminimumvolume.ThedifferencebetweenthemaximumandminimumiscalledthedisplacementandismeasuredinlitersorCCs(CubicCentimeters,where1,000cubiccentimetersequalsaliter).Soifyouhavea4-cylinderengineandeachcylinderdisplaceshalfaliter,thentheentireengineisa2.0literengine.IfeachcylinderdisplaceshalfaliterandtherearesixcylindersarrangedinaVconfiguration,youhavea3.0literV-6.Generally,thedisplacementtellsyousomethingabouthowmuchpoweranenginehas.Acylinderthatdisplaceshalfalitercanholdtwiceasmuchfuel/airmixtureasacylinderthatdisplacesaquarterofaliter,andthereforeyouwouldexpectabouttwiceasmuchpowerfromthelargercylinder(ifeverythingelseisequal).Soa2.0literengineisroughlyhalfaspowerfulasa4.0literengine.Youcangetmoredisplacementeitherbyincreasingthenumberofcylindersorbymakingthecombustionchambersofallthecylindersbigger(orboth).ConnectingrodTheconnectingrodconnectsthepistontothecrankshaft.Itcanrotateatbothendssothatitsanglecanchangeasthepistonmovesandthecrankshaftrotates.CrankshaftThecrankshaftturnsthepistonsupanddownmotionintocircularmotionjustlikeacrankonajack-in-the-boxdoes.SumpThesumpsurroundsthecrankshaft.Itcontainssomeamountofoil,whichcollectsinthebottomofthesump(theoilpan).EngineSubsystemsAnenginehasanumberofsystemsthathelpitdoitsjobofconvertingfuelintomotion.Mostofthesesubsystemscanbeimplementedusingdifferenttechnologies,andbettertechnologiescanimprovetheperformanceoftheengine.Heresalookatallofthedifferentsubsystemsusedinmodernengines:ValvetrainThevalvetrainconsistsofthevalvesandamechanismthatopensandclosesthem.Theopeningandclosingsystemiscalledacamshaft.Thecamshafthaslobesonitthatmovethevalvesupanddown,asshowninFigure4.Mostmodernengineshavewhatarecalledoverheadcams.Thismeansthatthecamshaftislocatedabovethevalves,asyouseeinFigure5.Thecamsontheshaftactivatethevalvesdirectlyorthroughaveryshortlinkage.Olderenginesusedacamshaftlocatedinthesumpnearthecrankshaft.Rodslinkedthecambelowtovalveliftersabovethevalves.Thisapproachhasmoremovingpartsandalsocausesmorelagbetweenthecamsactivationofthevalveandthevalvessubsequentmotion.Atimingbeltortimingchainlinksthecrankshafttothecamshaftsothatthevalvesareinsyncwiththepistons.Thecamshaftisgearedtoturnatone-halftherateofthecrankshaft.Manyhigh-performanceengineshavefourvalvespercylinder(twoforintake,twoforexhaust),andthisarrangementrequirestwocamshaftsperbankofcylinders,hencethephrasedualoverheadcams.StartingsystemThestartingsystemconsistsofanelectricstartermotorandastartersolenoid.Whenyouturntheignitionkey,thestartermotorspinstheengineafewrevolutionssothatthecombustionprocesscanstart.Ittakesapowerfulmotortospinacoldengine.Thestartermotormustovercome:AlloftheinternalfrictioncausedbythepistonringsThecompressionpressureofanycylinder(s)thathappenstobeinthecompressionstrokeTheenergyneededtoopenandclosevalveswiththecamshaftAlloftheotherthingsdirectlyattachedtotheengine,likethewaterpump,oilpump,alternator,etc.Becausesomuchenergyisneededandbecauseacarusesa12-voltelectricalsystem,hundredsofampsofelectricitymustflowintothestartermotor.Thestartersolenoidisessentiallyalargeelectronicswitchthatcanhandlethatmuchcurrent.Whenyouturntheignitionkey,itactivatesthesolenoidtopowerthemotor.Above,wearediscussingabasicphilosophyofengine,andadetailedunderstandingofhowtointegrateallthecomponentstogether,andhowtoimprovetheperformanceofthat!Thus,theworkoftheengineforvehicleisveryimportant.汽車發(fā)動(dòng)機(jī)如何工作在這里，我們將討論的