汽车实用英语

P82UnitEighttextEngineIgnitionSystemAllgasolineenginesrequiresomeformofignitionsystem．Thepurposeofthissystemisto。supplytothesparkplugs，withintheenginecombustionchambers，high．voltagesurges．Furthermore，theignitionsystemmustprovidethesesurgesorsparkstothecorrectcylinder0ftheengineatthepropertimeinitsoperatingcycleformostefficientcombustion．Theresultofthesesparks，ofcourse，isignitionoftheair—fuelmixturewithineach0fthecombustionchambers.Modernignitionsystemsoperatefromabattery．Conventionalsystemsconsistofthebattery,ignitioncoil，distributor,condenser,ignitionswitch，sparkplugs，resistorandnecessarylowandhightensionwiring．Thebatteryistheheatofthetotalelectricalsystem．Inregardtotheprimarycircuit,itsfunctionistosupplyvoltageandcurrentflowtotheprimarywindingsoftheignitioncoil．inordertoproduceanelectromagnet．Theprimarysideoftheignitioncoilconnectsinseriesbetweentheresistorandthebreakerpoints·Thefunctionofthiscoilwhencurrentpassesthroughitistocreateaverystrongp83electromagneticfield.Inotherwords,thecoilbecomesanelectromagnetwithNandSpoles.Themagneticfieldfromthiscoil,inturn,inducesavoltageinthesecondarywindingsthatisnecessarytocauseanarcatthesparkpluggap.Thesecondaryignitioncircuitnotonlytransformsthe6or12voltsofthebatterytoavoltagehighenoughtocauseanarcatthesparkplugbutalsodeliversthishigh-voltagesurgetothesparkplugs.Theautomotivebatterysupplieseither6or12voltstotheprimarycoilwindings.Butthevoltagenecessarytojumpacrossthesparkplugairgapandignitetheair-fuelmixturecanrangefrom5000to25000voltsormore,dependingupontheengine'soperatingconditionatanygiventime.Theignitiondistributorhasseveralfunctions.Itopensandclosestheprimaryignitioncircuit.Itdistributesthehightensioncurrenttotherespectivecylindersoftheengine.Italsohasamechanismthatcontrolsthepointatwhichthebreakerpointsopen,therebyadvancingorretardingthesparkinaccordancewithenginerequirements.Thedistributorcapandrotorreceivethehigh-voltagesurgefromthesecondarycoilwindingsthroughahigh-tensionwire.Thissurgeentersthedistributorcapthroughitscenterterminal,knownasthecoiltowertosparkplugelectrodesformedintotherimofthecap.Therotoritselfmountsontheupperdistributorshaftandrotateswithit.Asaresult,therotorelectrodemovesfromonecapsparkplugelectrodetoanother,followingthespecificfiringorderoftheengine.Thepurposeoftheignitioncondenseristoreducearcingatthebreakerpoints,andprolongtheirlife.Mostautomotivecondensersareformedfromtwothinfoilstrips,separatedbyseverallayersofinsulation.Theinsulatingmaterialisknownasadielectricandisusuallypaperoranysimilarnonconductivematerial.Thesparkplugprovidesthegapinthecombustionchamberacrosswhichthehigh-tensionelectricalsparkjumpstoignitethecombustioncharge.Thepurposeoftheignitionswitchistoconnectanddisconnecttheignitionsystemfromthebattery,sotheenginecanbestartedandstoppedasdesired.WiththeignitionswitchON,andignitiondistributorcontactsclosed;currentwillflowfromthebattery,throughtheprimarywindingoftheignitioncoil,tothedistributorcontact(breaker)points,tothegroundconnectionandbacktothebattery.Thecurrentflowingthroughtheprimarywindingoftheignitioncoilproducesamagneticfieldinthecoil,Whenthedistributorcontactpointsopen(break),themagneticfieldcollapseandthemovementofthemagneticfieldinducescurrentinthesecondarywinding.Sincetherearemanymoreturnsofwireinthesecondarywindingthanthereareintheprimarywinding,thevoltageisincreasedupto20000V.Thedistributorthendirectsthishighvoltagetothepropersparkplug,whereitjumpstothegap.Theheatofthesparkignitestheair-fuelmixtureinthecombustionchamber.Theburningfuelexpandsandforcesthepistondown.Downwardmotionofthepiston,inturn,rotatesthecrankshaft.Theignitioncoilisapulsetransfomerdesignedtostepupprimaryvoltage(receivedfromP84electromagneticfield.Inotherwords,thecoilbecomesanelectromagnetwithNandSpoles.Themagneticfieldfromthiscoil,inturn,inducesavoltageinthesecondarywindingsthatisnecessarytocauseanarcatthesparkpluggap.Thesecondaryignitioncircuitnotonlytransformsthe6or12voltsofthebatterytoavoltagehighenoughtocauseanarcatthesparkplugbutalsodeliversthishigh-voltagesurgetothesparkplugs.Theautomotivebatterysupplieseither6or12voltstotheprimarycoilwindings.Butthevoltagenecessarytojumpacrossthesparkplugairgapandignitetheair-fuelmixturecanrangefrom5000to25000voltsormore,dependingupontheengine'soperatingconditionatanygiventime.Theignitiondistributorhasseveralfunctions.Itopensandclosestheprimaryignitioncircuit.Itdistributesthehightensioncurrenttotherespectivecylindersoftheengine.Italsohasamechanismthatcontrolsthepointatwhichthebreakerpointsopen,therebyadvancingorretardingthesparkinaccordancewithenginerequirements.Thedistributorcapandrotorreceivethehigh-voltagesurgefromthesecondarycoilwindingsthroughahigh-tensionwire.Thissurgeentersthedistributorcapthroughitscenterterminal,knownasthecoiltowertosparkplugelectrodesformedintotherimofthecap.Therotoritselfmountsontheupperdistributorshaftandrotateswithit.Asaresult,therotorelectrodemovesfromonecapsparkplugelectrodetoanother,followingthespecificfiringorderoftheengine.Thepurposeoftheignitioncondenseristoreducear