1. IGNITION SYSTEM
The purpose of the ignitionsystemistogenerate averyhighvoltage fromthe car's 12 volt battery,and
to sendthisto eachsparkpluginturn,ignitingthe fuel-airmixture inthe engine'scombustionchambers.
The coil is the componentthatproducesthishighvoltage.Itisan electromagneticdevice thatconverts
the low-tension(LT) currentfromthebatteryto high-tension(HT) currenteachtime the distributor
contact-breakerpointsopen.The distributorunitconsistsof ametal bowl containingacentral shaft,
whichisusuallydrivendirectlybythe camshaftor,sometimes,bythe crankshaft. The bowl housesthe
contact-breakerpoints, rotorarm, anda device foralteringthe ignitiontiming. Italsocarriesthe
distributorcap.
Coil ignitionsystem:
An ignitioncoil isreallytwoseparate coilsof wire.
1) Primarycoil.
2) Secondarycoil.
Primary coil: The primarycoil ismade up of several hundredwindingsof relativelythickwire(withthin
insulation). The copperwire isthick because itcarriesmanyamps of electrical current. The insulation
isverythinbecause the voltage isquite low. The primaryignitioncoil carriestenampsormore of
current. Anytime electrical currentflowsthroughawire itsurroundsthat wire witha magnetic
field. Ascurrent flowsthroughthe primarycoil windings,the magnetismaroundeachloopof the coil is
focusedorconcentrated. By tightlycoilingthe primarywire,andrunningmanyampsthroughthose
windings,we create averystrongmagneticfield. Thismagneticfieldsurroundsthe secondarycoil
windings.
Secondary coil: The secondary coil consists of several thousand windings of a very thin
wire. Very thin wire cannot flow very many amps of current and by creating several thousand
loops we are forcing this coil to generate a high voltage. Remember, the purpose of the
ignition coil is to take the relatively low electrical pressure or voltage of the primary windings
and create very high electrical pressure or voltage into the secondary windings. It takes time
for the primary.
Distributor Cap:
A distributor is a device in the ignition system of an internal
combustion engine that routes high voltage from the ignition coil to
the spark plugs in the correct firing order.
2. Distributing the current
The distributorcapis made of nonconductive plastic,andthe currentisfedtoits central electrode by
the HT leadfromthe centerof the coil.Inside the capthere are more electrodesoftencalledsegments
to whichthe sparkplugleadsare connected,one percylinder.
The rotor arm isfittedontopof the central shaft,and connectsto the central electrode bymeansof a
metal springor spring-loadedbrushinthe topof the distributorcap.
On a four-cylinderengine there are fourcams. Witheach full rotationof the shaftthe points
openfourtimes.Six-cylinderengineshave six camsandsix electrodesinthe cap.The positionof the
pointsandthe distributor'sbodyinrelationtothe central shaftcanbe adjustedmanually.Thisaltersthe
timingof the spark to obtainanexact setting(see how engine timingworks).Furtherchangesoccur
automaticallyasthe engine speedvariesaccordingtothe throttle opening.Insome modernignition
systems,micro-electronicsensure the optimumignitiontimingforall enginespeedsandengine load
conditions(see how enginetimingworks).
Completing the circuit:
The sparkplugsare screwedintothe combustionchambersinthe cylinderhead.
HT currentpassesfromeach segmentonthe distributorcapdownthe plugleadstothe plugcaps. It
thenpassesdownthe central electrode,whichisinsulatedalongitslength,tothe nose of the plug.A
side electrode connectedtothe plugbodyprotrudesjustbelow the central one,with the gapbetween
the two usuallysetfrom0.025 in.(0.6 mm) to 0.035 in.(0.9 mm).The currentsparksacross thisgap,
flowsalongthe side electrode,throughthe plugbodyandthe engine,thenbacktothe coil,completing
the circuit.
