发动机状态监测及故障诊断专家系统翻译.docx
《发动机状态监测及故障诊断专家系统翻译.docx》由会员分享,可在线阅读,更多相关《发动机状态监测及故障诊断专家系统翻译.docx(10页珍藏版)》请在冰豆网上搜索。
发动机状态监测及故障诊断专家系统翻译
dieselEngines
Internalcombustiongasolineenginesrunonamixtureofgasolineandair.Theidealmixtureis14.7partsairtoonepartofgasoline(byweight.)Sincegasweightsmuchmorethanair,wearetalkingaboutawholelotofairandtinybitofoil.Onepartofoilthatiscompletelyvaporizedinto14.7partsofaircanproducetremendouspowerwhenignitedinsideanengine.Let'sseehowthemodernengineusesthatenergytomakethewheelsturn.Airenterstheenginethroughtheaircleanerandproceedstothethrottleplate.Youcontroltheamountofairthatpassesthroughthethrottleplateandintotheenginewiththegaspedal.Itisthendistributedthroughaseriesofpassagescalledtheintakemanifold,toeachcylinder.Atsomepointaftertheaircleaner,dependingontheengine,fuelisaddedtotheair-streambyeitherafuelinjectionsystemor,inoldervehicles,bythecarburetor.
1.Enginetype
Theenginescanbeclassifiedinthefollowingseveralways:
operatingcycle;pistonaction;pistonconnection;cylinderarrangement;methodoffuelinjection,andspeed.
(1)operatingcycle
Dieselandgas-burningenginescanbedividedintotwogroupsbasedonthenumberofpistonstrokespercycle,eitherfourortwo.Anenginewhichneedsfourstrokestcompleteonecycleisfour-strokecycleengineor,forshort,afour-cycleengine.Ifitneedsonlytwostrokestocompleteacycle,itiscalledatwo-strokecycleengineor,forshort,atwo-cycleengine.Thus,atwo-cycleenginefirestwiceasoftenasafour-cycleengine.
(2)pistonaction
Anengine’spistonactionmaybeclassifiedassingle-action,double-action,oropposed-piston.
Single-actingenginesuseonlyoneandendofthecylinderandonefaceofthepistontodeveloppower.Thisworkingspaceisattheendawayfromthecrankshaft,thatis,attheupperendofaverticalengine.Double-actingengineusebothendsofthecylinderandbothfacesofthepistontodeveloppowerontheupstrokeaswellasonthedownstroke.Theconstructioniscomplicated;therefore,double-actingenginesarebuiltonlyinlargeandcomparativelylow-speedunits,generallytopowermotorships.Anopposed-pistonenginehascylindersineachofwhichtwopistonstravelinoppositedirections.Thecombustionspaceisinthemiddleofthecylinderbetweenthepistons.Therearetwocrankshafts;theupperpistonsdriveone,thelowerpistonstheother.Notethateachpistonissingle-acting;thatis,itdevelopspowerwithonlyonefaceofthepiston.
(3)pistonconnection
Thepistonmaybeconnectedtotheupperendoftheconnectingrodeitherdirectly(trunkpistontype),orindirectly(crossheadtype).Intrunk-pistonengines,ahorizontalpinwithinthepistonisencircledbytheupperendoftheconnectingrod.Thisbyfarthemostcommonconstruction.Incrosshead-typeengines,thepistonfastenstoaverticalpistonrodwhoselowerendisattachedtoaslidingmembercalledacrosshead,whichslidesupanddowninguides.Thecrossheadcarriesacrossheadpinwhichisencircledbytheupperendoftheconnectingrod.Thismorecomplicatedconstructionisrequiredindouble-actingengines.Itisalsousedinsomelarge,slow-speed,single-actingengines.
(4)cylinderarrangement
Thefourbasiccylinderarrangementsofadieselorgas-burningengineare:
cylinder-in-line;V-arrangement;Flat,andradial.Acylinder-in-linearrangement.Thisisthesimplestandmostcommonarrangement,withallcylindersarrangedverticallyinline.Thisconstructionisusedforengineshavingupto12cylinders.Enginesarealsobuiltwithhorizontalcylinders,usuallyoneortwo,inafewcaseswiththreecylinders.Ifanenginehasmorethaneightcylinders,itbecomesdifficulttomakeasufficientlyrigidframeandcrankshaftwithanin-linearrangement.Also,theenginebecomesquitelongandtakesupconsiderablespace.TheV-arrangement,withtwoconnectingrodsattachedtoeachcrankpin,permitsreducingtheenginelengthbyalmostone-half,thusmakingitmuchmorerigid,withastiffcrankshaft.Italsocostslesstomanufactureandinstall.Thisisacommonarrangementforengineswitheight,twelve,andsixteencylinders.Cylinderslyinginonelinearecalleda“bank”,andtheanglebetweenthebanksmayvary,inmanufacturingpractice,from30゜to120゜,themostcommonanglesbeingbetween40゜and75゜.(Acompletecircleis360゜)AflatengineisaV-enginewiththeanglebetweenthebanksincreasedto180゜.Thisarrangementisusedwherethereislittleheadroom,asintrucks,buses,andrailcars.Flatenginesarealsocalled“opposed-cylinder”engines.Inaradialengineallthecylindersaresetinacircleandallpointtowardthecenterofthecircle.Theconnectingrodsofallthepistonsworkonasinglecrankpin,whichrotatesaroundthecenterofthecircle.Sucharadialengineoccupieslittlefloorspace.Byattachingtheconnectingrodstoamasterdisksurroundingthecrankpin,asmanyastwelvecylindershavebeenmadetoworkonasinglecrankpin.
(5)methodoffuelinjection
Dieselenginesaredividedintoair-injectionenginesandsolidormechanicalinjectionengines.Air-injectionenginesuseablastofhighlycompressedairtoblowthefuelintothecylinder.Airinjectionwascommonlyuseonearlydieselenginesbutwiththedevelopmentofsolid-injectionsystemstheair-injectionengineisrapidlydisappearing.
(6)speed
Alldieselandgas-burningenginesmaybedividedintothreeclassesaccordingtospeed;low-speed,medium-speed,andhigh-speedengines.Automotivedieselenginesoftenrunfasterthan1200rpm,butthegreatmajorityofotherenginesrunbetween350and1200rpmandaretermedmedium-speedengines.
2.HowanEngineWorks
Sincethesameprocessoccursineachcylinder,wewilltakealookatonecylindertoseehowthefourstrokeprocessworks.Thefourstrokesareintake,compression,powerandexhaust.Thepistontravelsdownontheintakestroke,uponthecompressionstroke,downonthepowerstrokeandupontheexhauststroke.
(1)intake
Asthepistonstartsdownontheintakestroke,theintakevalveopensandthefuel-airmixtureisdrawnintothecylinder(similartodrawingbacktheplungeronahypodermicneedletoallowfluidtobedrawnintothechamber).Whenthepistonreachesthebottomoftheintakestroke,theintakevalvecloses,trappingtheair-fuelmixtureinthecylinder.
(2)compression
Thepistonmovesupandcompressesthetrappedairfuelmixturethatwasbroughtinbytheintakestroke.Theamountthatthemixtureiscompressedisdeterminedbythecompressionratiooftheengine.Thecompressionrationontheaverageengineisintherangeof8:
1to10:
1.Thismeansthatwhenthepistonreachesthetopofthecylinder,theair-fuelmixtureissqueezedtoaboutonetenthofitsoriginalvolume.
(3)power
Thesparkplugfires,ignitingthecompressedair-fuelmixturewhichproducesapowerfulexpansionofthevapor.Thecombustionprocesspushesthepistondownthecylinderwithgreatforceturningthecrankshafttoprovidethepowertopropelthevehicle.Eachpistonfiresatadifferenttime,determinedbytheenginefiringorder.Bythetimethecrankshaftcompletestworevolutions,eachcylinderintheenginewillhavegonethroughonepowerstroke.
(4)exhaust
Withthepistonatthebottomofthecylinder,theexhaustvalveopenstoallowtheburnedexhaustgastobeexpelledtotheexhaustsystem.Sincethecylindercontainssomuchpressure,whenthevalveopens,thegasisexpelledwithaviolentforce(thatiswhyavehiclewithoutamufflersoundssoloud.)Thepistontravelsuptothetopofthecylinderpushingalltheexhaustoutbeforeclosingtheexhaustvalveinpreparationforstartingthefourstrokeprocessoveragain.
(5)oilingsystem
Oilisthelife-bloodoftheengine.Anenginerunningwithoutoilwilllastaboutaslongasahumanwithoutblood.Oilpumpismountedatthebottomoftheengineintheoilpanandisconnectedbyageartoeitherthecrankshaftorthecamshaft.Thisway,whentheengineisturning,theoilpumpispumping.Thereisanoilpressuresensorneartheoilpumpthatmonitorspressureandsendsthisinformationtoawarninglightoragaugeonthedashboard.Whenyouturntheignitionkeyon,butbeforeyoustartthecar,theoillightshouldlight,indicatingthatthereisnooilpressureyet,butalsolettingyouknowthatthewarningsystemisworking.Assoonasyoustartcrankingtheenginetostartit,thelightshouldgooutindicatingthatthereisoilpressure.
(6)enginecooling
Internalcombustionenginesmustmaintainastableoperatingtemperature,nottoohotandnottoocold.Withthemassiveamountsofheatthatisgeneratedfromthecombustionprocess,iftheenginedidnothaveamethodforcoolingitself,itwouldquicklyself-destruct.Majorengine
partscanwarpcausingoilandwaterleaksandtheoilwillboilandbecomeuseless.Whilesomeenginesareair-cooled,thevastmajorityofenginesareliquidcooled.Thewaterpumpcirculatescoolantthroughouttheengine,hittingthehotareasaroundthecylindersandheadsandthensendsthehotcoolanttotheradiatortobecooledoff.
3.EngineComponents
Wehaveseenhowthemixtureofairandfuelisdeliveredbythefuelsystemtotheenginecylinder,whereitiscompressed,ignited,andburned.Wehavenotedthatthiscombustionproducesahighpressurethatpushesthepistondownsothatthecrankshaftisrotated.Nowletusexaminethevariouspartsoftheengineindetail.
(1)enginecylinderblock
Thecylinderblockofliquid-cooledenginesformsthebasicframeworkoftheengine.Otherpartsareattachedtothecylinderblockorareassembledinit.Theblockiscastinonepiecefromgra