Lesson 8 Ignition System.ppt

lesson8ignitionsystem,thepurposeoftheignitionsystemistocreateasparkthatwillignitethefuel-airmixtureinthecylinderofanengine.itmustdothisatexactlytherightinstantanddoitattherateofuptoseveralthousandtimesperminuteforeachcylinderintheengine.theignitionsystemsendsanextremelyhighvoltagetothesparkplugineachcylinderwhenthepistonisatthetopofitscompressionstroke.,thetipofeachsparkplugcontainsagapthatthevoltagemustjumpacrossinordertoreachground.thevoltagethatisavailabletothesparkplugissomewherebetween20,000voltsand50,000voltsorbetter.thejoboftheignitionsystemistoproducethathighvoltagefroma12voltsourceandgetittoeachcylinderinaspecificorder,atexactlytherighttime.,theignitionsystemhastwotaskstoperform.first,itmustcreateavoltagehighenough(20,000+)toarcacrossthegapofasparkplug,thuscreatingasparkstrongenoughtoignitetheair/fuelmixtureforcombustion.second,itmustcontrolthetimingofthatthesparksoitoccursattheexactrighttimeandsendittothecorrectcylinder.,theignitionsystemisdividedintotwosections,theprimarycircuitandthesecondarycircuit.thelowvoltageprimarycircuitoperatesatbatteryvoltage(12to14.5volts)andisresponsibleforgeneratingthesignaltofirethesparkplugattheexactrighttimeandsendingthatsignaltotheignitioncoil.,theignitioncoilisthecomponentthatconvertsthe12voltsignalintothehigh20,000+voltcharge.oncethevoltageissteppedup,itgoestothesecondarycircuitwhichthendirectsthechargetothecorrectsparkplugattherighttime.,currently,therearethreedistincttypesofignitionsystems.themechanicalignitionsystemwasusedpriorto1975.itwasmechanicalandelectricalandusednoelectronics.byunderstandingtheseearlysystems,itwillbeeasiertounderstandthenewelectronicandcomputercontrolledignitionsystems,sodontskipoverit.,theelectronicignitionsystemstartedfindingitswaytoproductionvehiclesduringtheearly70sandbecamepopularwhenbettercontrolandimprovedreliabilitybecameimportantwiththeadventofemissioncontrols.finally,thedistributorlessignitionsystembecameavailableinthemid80s.thissystemwasalwayscomputercontrolledandcontainednomovingparts,soreliabilitywasgreatlyimproved.,1themechanicalignitionsystem,thedistributoristhenervecenterofthemechanicalignitionsystemandhastwotaskstoperform.first,itisresponsiblefortriggeringtheignitioncoiltogenerateasparkatthepreciseinstantthatitisrequired(whichvariesdependinghowfasttheengineisturningandhowmuchloaditisunder).second,thedistributorisresponsiblefordirectingthatsparktothepropercylinder(whichiswhyitiscalledadistributor).,thecircuitthatpowerstheignitionsystemissimpleandstraightforward.whenyouinsertthekeyintheignitionswitchandturnthekeytotherunposition,youaresendingcurrentfromthebatterythroughawiredirectlytothepositive(+)sideoftheignitioncoil.whencurrentflowsfromtheignitionswitch,throughthewindingsinthecoil,thentoground,itbuildsastrongmagneticfieldinsidethecoil.,thepointsaremadeupofafixedcontactpointthatisfastenedtoaplateinsidethedistributor,andamovablecontactpointmountedontheendofaspringloadedarm.themovablepointridesona4,6,or8lobecam(dependingonthenumberofcylindersintheengine)thatismountedonarotatingshaftinsidethedistributor.thisdistributorcamrotatesintimewiththeengine,makingonecompleterevolutionforeverytworevolutionsoftheengine.,asitrotates,thecampushesthepointsopenandclosed.everytimethepointsopen,theflowofcurrentisinterruptedthroughthecoil,therebycollapsingthemagneticfieldandreleasingahighvoltagesurgethroughthesecondarycoilwindings.thisvoltagesurgegoesoutthetopofthecoilandthroughthehigh-tensioncoilwire.,thecoilwiregoesfromthecoildirectlytothecenterofthedistributorcap.underthecapisarotorthatismountedontopoftherotatingshaft.therotorhasametalstriponthetopthatisinconstantcontactwiththecenterterminalofthedistributorcap.itreceivesthehighvoltagesurgefromthecoilwireandsendsittotheotherendoftherotorwhichrotatespasteachsparkplugterminalinsidethecap.,astherotorturnsontheshaft,itsendsthevoltagetothecorrectsparkplugwire,whichinturnsendsittothesparkplug.thevoltageentersthesparkplugattheterminalatthetopandtravelsdownthecoreuntilitreachesthetip.itthenjumpsacrossthegapatthetipofthesparkplug,creatingasparksuitabletoignitethefuel-airmixtureinsidethatcylinder.,1.1theignitionswitchtherearetwoseparatecircuitsthatgofromtheignitionswitchtothecoil.onecircuitrunsthrougharesistorinordertostepdownthevoltageabout15%inordertoprotectthepointsfromprematurewear.theothercircuitsendsfullbatteryvoltagetothecoil.theonlytimethiscircuitisusedisduringcranking.,1.2thedistributorwhenyouremovethedistributorcapfromthetopofthedistributor,youwillseethepointsandcondenser.thecondenserisasimplecapacitorthatcanstoreasmallamountofcurrent.thepointsrequireperiodicadjustmentsinordertokeeptheenginerunningatpeekefficiency.,1.3ignitioncoil,theignitioncoilisnothingmorethatanelectricaltransformer.itcontainsbothprimaryandsecondarywindingcircuits.thecoilprimarywindingcontains100to150turnsofheavycopperwire.thiswiremustbeinsulatedsothatthevoltagedoesnotjumpfromlooptoloop,shortingitout.,thecoilsecondarywindingcircuitcontains15,000to30,000turnsoffinecopperwire,whichalsomustbeinsulatedfromeachother.thesecondarywindingssitinsidetheloopsoftheprimarywindings.tofurtherincreasethecoilsmagneticfieldthewindingsarewrappedaroundasoftironcore.therearetwomechanismsthatallowthetimingtochange:centrifugaladvanceandvacuumadvance.,centrifugaladvancechangesthetiminginrelationtothespeed(rpm)oftheengine.itusesapairofweightsthatareconnectedtothespinningdistributorshaft.theseweightsarehingedononesidetothelowerpartoftheshaftandconnectedbyalinkagetotheuppershaftwherethedistributorcamis6.theweightsareheldclosetotheshaftbeapairofsprings.,vacuumadvanceworksbychangingthepositionofthepointsinrelationshiptothedistributorbody.anengineproducesvacuumwhileitisrunningwiththethrottleclosed.vacuumadvanceusesavacuumdiaphragmconnectedtoalinkthatcanmovetheplatethatthepointsaremountedon.,bothvacuumandcentrifugaladvancesystemsworkedtogethertoextractthemaximumefficiencyfromtheengine.oncecomputercontrolswereabletodirectlycontroltheenginestiming,vacuumandcentrifugaladvancemechanismswerenolongernecessaryandwereeliminated.,1.4ignitionwires,thejobofthesparkplugwiresistogetthatenormouspowertothesparkplugwithoutleakingout.sparkplugwiresareroutedaroundtheengineverycarefully.forinstance,apopularv8enginefiringorderis1,8,4,3,6,5,7,2.thecylindersarenumberedfromthefronttotherearwithcylinder#1onthefront-leftoftheengine.sothecylindersontheleftsideoftheenginearenumbered1,3,5,7whiletherightsidearenumbered2,4,6,8.,1.5sparkplugs,theignitionsystemssolereasonforbeingistoservicethesparkplug.itmustprovidesufficientvoltagetojumpthegapatthetipofthesparkpluganddoitattheexactrighttime,reliablyontheorderofthousandsoftimesperminuteforeachsparkpl