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

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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