汽車專業(yè)英語讀譯教程 第3版 課件 10-U6TA Starting,Charging and Ignition Systems

UNIT6

ENGINEELECTRICALSYSTEMS

TEXTA

Starting,ChargingandIgnitionSystems

PROFESSIONALENGLISH

UNIT5

ENGINEELECTRICALSYSTEMS

TEXTA

Starting,ChargingandIgnitionSystems

ChargingSystem

StarterSystem

IgnitionSystem

本次課學(xué)習(xí)內(nèi)容NEWWORDSelectromagnetic[ilektrou'm?gnetik]a.電磁的trio['tri:ou]n.三件一套，三個一組，三重唱forward-biased['f?:w?d'bai?st]正向偏壓的reverse-biased[ri'v?:s'bai?st]反向偏壓[偏置]的capacitor[k?'p?sit?]n.電容器thermistor[

?:'mist?]n.熱敏電阻rope[roup]n.繩,索,繩索；v.圍起armature['ɑ:m?tju?]n.電樞collaps[k?'l?ps]v.&n.倒塌，塌陷，消失，減弱high-tension['hai'ten∫?n]a.高（電）壓的reluctor[ri'l?kt?]n.磁阻輪centrifugal[sen'trifjug?l]n.離心的advent['?dv?nt]n.出現(xiàn)，到來，來臨

PHRASESANDEXPRESSIONS

chargingsystem充電系統(tǒng)keepupwith跟上，不落后于magneticfield磁場fieldstrength磁場強度contactpoints觸點powertransistor功率晶體管integratedcircuit集成電路solidstate固態(tài)diodetrio二極管三件組合startingmotor起動機transmissionhousing變速器殼responsiblefor（應(yīng)）對…負(fù)責(zé)，是造成…的（主要）原因，決定著，導(dǎo)致

PHRASESANDEXPRESSIONS

withtheadventof隨著…的出現(xiàn)（到來）intimewith與…合拍（同期）in（constant）contactwith（始終）與…保持接觸pickupcoil傳感線圈electriceye電眼，光電池shutterwheel遮光輪initialtiming初始點火正時vacuumadvance真空式點火提前角調(diào)節(jié)裝置distributorlessignitionsystem無分電器點火系統(tǒng)ChargingSystemThechargingsystemusestherotationoftheenginetocreateelectricity.Theelectricityrechargesthebatteryandprovidespowertooperatethevariousvehicleelectricalsystems.Themodernchargingsystemconsistsofthealternatorandregulator.AlternatorThealternatorisabelt-driven,electromagneticdevice.Aftertheengineisstarted,thealternatorproduceselectricitytomeettheneedsofthevehicleandtokeepthebatterycharged.Themodernvehiclecontainsmanycircuitsthatplaceaheavyloadontheelectricalsystem.

Starting,ChargingandIgnitionSystems

Starting,ChargingandIgnitionSystems

Sincemanyvehiclesareusedinstop-and-gocitydriving,thismakesitdifficulttomaintainthebatteryinafullychargedstate.Therefore,thealternatormustbeextremelyefficientatallspeeds.Atidle,whentherotoristurningrelativelyslowly,thealternatorcankeepupwiththedemandsofthevehicleelectricalsystem.Atnormalvehiclespeeds,thealternatorcanproducemuchmorevoltageandcurrentthanneeded.Toprotectthealternatorandtherestoftheelectricalsystemfromdamage,ameansofreducingtheoutputmustbefound.VoltageRegulatorToreducealternatoroutput,avoltageregulatorisused.Thevoltageregulatorcontrolsthealternatoroutputbyadjustingtheamountofcurrentreachingtherotor.Thiscontrolsthestrengthofthemagneticfieldpassingthroughthestatorwindings.Theregulatorcontrolsthefieldstrengthbyreadingvoltageoutputfromthealternator.Ifoutputvoltagebecomestoohigh,theregulatorreducesfieldstrength.Iftheoutputvoltagedrops,theregulatorincreasesfieldstrength.ElectromechanicalVoltageRegulatorOldervoltageregulatorsusecontactpointsthatareoperatedbyelectromagneticcoils.Thesewerecalled

electromechanicalvoltageregulators.

Starting,ChargingandIgnitionSystems

Starting,ChargingandIgnitionSystems

ElectronicVoltageRegulator(EVR)Allvehiclesmadewithinthelast15yearsuseanelectronicvoltageregulator.Theelectronicvoltageregulatorusespowertransistors,integratedcircuits,diodes,andothersolidstatepartstocontrolalternatoroutput.Theelectronicvoltageregulatoreliminatescontactpointsandmovingpartsthatcanstick,oxidize,orwear.Someelectronicregulatorsareremotelymounted.However,electronicvoltageregulatorsarereliable,durable,andsmallenoughtobeincorporatedintothealternatoritself.

Starting,ChargingandIgnitionSystems

Built-inElectronicRegulatorOperationAcommonchargingsystemcircuitwithabuilt-inregulatorisillustratedinFig.6-1.Asmallamountofcurrentpassesfromthestatorthroughthediodetriototheregulator.Thisequalizesthevoltageoneithersideoftheindicatorlight,puttingitout,andtriestogroundthroughresistorR3.Whenthestatorvoltagereachesacertainlevel,voltagegoingtogroundthroughresistorR3willincreasetothepointthatitwillcauseZenerdiodeD1toconduct.Forward-biased(voltageappliedindirectioncausingcurrentflow)transistorTR2conductsandtransistorTR3isreverse-biasedoff.ThisturnstransistorTR1off.ThefieldcurrentandsystemvoltageimmediatelydecreasewithTR1off.Fig.6-1Achargingsystemcircuitwithabuilt-inregulator

Starting,ChargingandIgnitionSystems

Starting,ChargingandIgnitionSystems

Whensystemvoltagedecreases,voltagethroughR3decreasesandD1stopsconducting.ThiscausestransistorTR2tobecomereverse-biasedoffandtransistorsTR1andTR3forward-biasedon.Outputvoltageandfieldcurrentwillincrease.Thiscycleisrepeatedthousandsoftimespersecond,holdingalternatorvoltageoutputtoapresetlevel.SuddenvoltagechangeacrossR3ispreventedbycapacitorC1,andexcessivebackcurrentthroughTR1athightemperatureispreventedbyR4.TR1isprotectedbyD2thatpreventsahighinducedvoltageinthefieldwindingwhenTR1isoff.Voltagecontroltemperaturecorrectionisprovidedbyathermistor(resistancedecreasesastemperatureincreases).

Computer-ControlledVoltageRegulation

Mostvehiclestodayhaveseveralelectroniccontrolunits(ECUs)orpowertraincontrolmodules(PCM)thatcontroltheengineandothersystems.ECUcanalsobeusedtocontrolvoltagetothefieldwinding,whicheliminatestheneedforaseparateregulator.ThedisadvantageofthissystemisiftheportionoftheECUthatcontrolsvoltageregulationbecomesdefective,theentireECUmustbereplaced[1].

Starting,ChargingandIgnitionSystems

Starting,ChargingandIgnitionSystems

StarterSystemTostartaninternalcombustionengine,itmustbecranked(rotatedbyanoutsidesource).Smalltwo-strokeenginesareoftencrankedbypullingaropewhichcausestheinternalenginepartstorevolve.Thefirstautomobilesusedahandcrankrodforstarting.However,thismethodwasdangerousandimpractical.Amethodwassoondevelopedtostarttheenginebyusinganelectricstartingmotor,orstarter.Thestarterismountedonthetransmissionhousingandoperatesasmallgearthatcanbemeshedwithalargeringgearattachedtotheflywheel.

Starting,ChargingandIgnitionSystems

Toenergizethestarter,thedriverturnstheignitionswitchtostart,whichcompletesanelectricalcircuittothestarter[2].Whenthestartermotorarmaturebeginstoturn,thestartergearmovesoutandengagestheringgear,whichspinsthecrankshaft.Whentheenginestarts,thedriverbreaksthestarterelectricalcircuitbyreleasingtheignitionkeyswitch.Thiscausesthestartergeartomoveoutofmeshwiththeringgear[3].IgnitionSystemThepurposeoftheignitionsystemistocreateasparkthatwillignitethefuel-airmixtureinthecylinderofanengine.

Itmustdothisatexactlytherightinstantanddoitattherateofuptoseveralthousandtimesperminuteforeachcylinderintheengine.

Ifthetimingofthatsparkisoffbyasmallfractionofasecond,theenginewillrunpoorlyornotrunatall.

Theignitionsystemsendsanextremelyhighvoltagetothesparkplugineachcylinderwhenthepistonisatthetopofitscompressionstroke.

Thetipofeachsparkplugcontainsagapthatthevoltagemustjumpacrossinordertoreachground.Thatiswherethesparkoccurs.

Starting,ChargingandIgnitionSystems

Starting,ChargingandIgnitionSystems

Thevoltagethatisavailabletothesparkplugissomewherebetween20,000voltsand50,000voltsorbetter.Thejoboftheignitionsystemistoproducethathighvoltagefroma12voltsourceandgetittoeachcylinderinaspecificorder,atexactlytherighttime.

Theignitionsystemhastwotaskstoperform.First,itmustcreateavoltagehighenough(20,000+)toarcacrossthegapofasparkplug,thuscreatingasparkstrongenoughtoignitetheair/fuelmixtureforcombustion.Second,itmustcontrolthetimingofthatthesparksoitoccursattheexactrighttimeandsendittothecorrectcylinder.

Starting,ChargingandIgnitionSystems

Theignitionsystemisdividedintotwosections,theprimarycircuitandthesecondarycircuit.Thelowvoltageprimarycircuitoperatesatbatteryvoltage(12to14.5volts)andisresponsibleforgeneratingthesignaltofirethesparkplugattheexactrighttimeandsendingthatsignaltotheignitioncoil.Theignitioncoilisthecomponentthatconvertsthe12voltsignalintothehigh20,000+voltcharge.Oncethevoltageissteppedup,itgoestothesecondarycircuitwhichthendirectsthechargetothecorrectsparkplugattherighttime.Thebasicprincipleoftheelectricalsparkignitionsystemhasnotchangedforover75years.Whathaschangedisthemethodbywhichthesparkiscreatedandhowitisdistributed.

Starting,ChargingandIgnitionSystems

ThreeTypesofIgnitionSystemsCurrently,therearethreedistincttypesofignitionsystems.Themechanical（conventional）ignitionsystemwasusedpriorto1975.Itwasmechanicalandelectricalandusednoelectronics.Byunderstandingtheseearlysystems,itwillbeeasiertounderstandthenewelectronicandcomputercontrolledignitionsystems,sodon'tskipoverit.Theelectronicignitionsystemstartedfindingitswaytoproductionvehiclesduringtheearly'70sandbecamepopularwhenbettercontrolandimprovedreliabilitybecameimportantwiththeadventofemissioncontrols.

Starting,ChargingandIgnitionSystems

Finally,thedistributorlessignitionsystembecameavailableinthemid'80s.Thissystemwasalwayscomputercontrolledandcontainednomovingparts,soreliabilitywasgreatlyimproved.Mostofthesesystemsrequirednomaintenanceexceptreplacingthesparkplugsatintervalsfrom60,000toover100,000miles.TheMechanicalIgnitionSystemThedistributoristhenervecenterofthemechanicalignitionsystemandhastwotaskstoperform.First,itisresponsiblefortriggeringtheignitioncoiltogenerateasparkatthepreciseinstant.Second,thedistributorisresponsiblefordirectingthatsparktothepropercylinder.

Starting,ChargingandIgnitionSystems

Thecircuitthatpowerstheignitionsystemissimpleandstraightforward(Fig.6-2).WhenyouinsertthekeyintheignitionswitchandturnthekeytotheRunposition,youaresendingcurrentfromthebatterythroughawiredirectlytothepositive(+)sideoftheignitioncoil.

Insidethecoilisaseriesofcopperwindingsthatlooparoundthecoiloverahundredtimesbeforeexitingoutthenegative(-)sideofthecoil.

Fromthere,awiretakesthiscurrentovertothedistributorandisconnectedtoaspecialon/offswitch,calledthepoints.Whenthepointsareclosed,thiscurrentgoesdirectlytoground.Whencurrentflowsfromtheignitionswitch,throughthewindingsinthecoil,thentoground,itbuildsastrongmagneticfieldinsidethecoil.Fig.6-2Aconventionalignitionsystem

Starting,ChargingandIgnitionSystems

Starting,ChargingandIgnitionSystems

Thepointsaremadeupofafixedcontactpointthatisfastenedtoaplateinsidethedistributor,andamovablecontactpointmountedontheendofaspringloadedarm.Themovablepointridesona4-,6-,or8-lobecam(dependingonthenumberofcylindersintheengine)thatismountedonarotatingshaftinsidethedistributor.

Thisdistributorcamrotatesintimewiththeengine,makingonecompleterevolutionforeverytworevolutionsoftheengine.Asitrotates,thecampushesthepointsopenandclosed.Everytimethepointsopen,theflowofcurrentisinterruptedthroughthecoil,therebycollapsingthemagneticfieldandreleasingahighvoltagesurgethroughthesecondarycoilwindings.Thisvoltagesurgegoesoutthetopofthecoilandthroughthehigh-tensioncoilwire.

Starting,ChargingandIgnitionSystems

Now,wehavethevoltagenecessarytofirethesparkplug,butwestillhavetogetittothecorrectcylinder.Thecoilwiregoesfromthecoildirectlytothecenterofthedistributorcap.Underthecapisarotorthatismountedontopoftherotatingshaft.Therotorhasametalstriponthetopthatisinconstantcontactwiththecenterterminalofthedistributorcap.Itreceivesthehighvoltagesurgefromthecoilwireandsendsittotheotherendoftherotorwhichrotatespasteachsparkplugterminalinsidethecap[4].Astherotorturnsontheshaft,itsendsthevoltagetothecorrectsparkplugwire,whichinturnsendsittothesparkplug.Thevoltageentersthesparkplugattheterminalatthetopandtravelsdownthecoreuntilitreachesthetip.

Itthenjumpsacrossthegapatthetipofthesparkplug,creatingasparksuitabletoignitethefuel-airmixtureinsidethatcylinder.

Starting,ChargingandIgnitionSystems

TheElectronicIgnitionSystemIntheelectronicignition（EI）system,thepointsandcondenserwerereplacedbyelectronics.Onthesesystems,therewereseveralmethodsusedtoreplacethepointsandcondenserinordertotriggerthecoiltofire.Onemethodusedametalwheelwithteeth,usuallyoneforeachcylinder.Thisiscalledanarmatureorreluctor.Amagneticpickupcoilsenseswhenatoothpassesandsendsasignaltothecontrolmoduletofirethecoil.Othersystemsusedanelectriceyewithashutterwheeltosendasignaltotheelectronicsthatitwastimetotriggerthecoiltofire.Thesesystemsstillneedtohavetheinitialtimingadjustedbyrotatingthedistributorhousing.

Starting,ChargingandIgnitionSystems

Theadvantageofthissystem,asidefromthefactthatitismaintenancefree,isthatthecontrolmodulecanhandlemuchhigherprimaryvoltagethanthemechanicalpoints.Voltagecanevenbesteppedupbeforesendingittothecoil,sothecoilcancreateamuchhotterspark,ontheorderof50,000voltsinsteadof20,000voltsthatiscommonwiththemechanicalsystems.Thesesystemsonlyhaveasinglewirefromtheignitionswitchtothecoilsinceaprimaryresistorisnolongerneeded.Onsomevehicles,thiscontrolmodulewasmountedinsidethedistributorwherethepointsusedtobemounted.Onotherdesigns,thecontrolmodulewasmountedoutsidethedistributorwithexternalwiringtoconnectittothepickupcoil.OnmanyGeneralMotorsengines,thecontrolmodulewasinsidethedistributorandthecoilwasmountedontopofthedistributorforaonepieceunitizedignitionsystem.

GMcalleditHighEnergyIgnitionorHEIforshort.

Starting,ChargingandIgnitionSystems

Thehighervoltagethatthesesystemsprovidedallowstheuseofamuchwidergaponthesparkplugsforalonger,fatterspark.Thislargersparkalsoallowsaleanermixtureforbetterfueleconomyandstillinsuresasmoothrunningengine.Theearlyelectronicsystemshadlimitedornocomputingpower,sotimingstillhadtobesetmanuallyandtherewasstillacentrifugalandvacuumadvancebuiltintothedistributor.Onsomeofthelatersystems,theinsideofthedistributorisemptyandalltriggeringisperformedbyasensorthatwatchesanotchedwheelconnectedtoeitherthecrankshaftorthe