Ignition System

Purpose • Distribute high voltage

pulses to spark plugs in correct sequence.

Basic operation

• Ignition switch on

–Switching device closed

• Piston moves close to TDC

–Ignition trigger device opens

–Ignition coil charges

Basic operation

• Current stops going to ignition coil

• Lack of current causes a high voltage surge, ignition coil discharges

Basic operation

• Surge flows across spark plug gap, creating an arc

• Arc ignites air/fuel mixture

Basic operation• Ignition trigger device

closes, recharging coil

–Electricity flows to the coil

–High voltage surge stops

Parts • Battery

• Ignition switch

• Bypass circuit

• Resistance circuit

• Primary circuit

Parts

• Secondary circuit

• Ignition coil

• Spark plugs

• Ignition system wires

Battery-Supply voltage

• Battery supplies voltage at start up

• Battery and alternator supply voltage during operation

Ignition switch

• Hot Switch, one side is connected to the battery and the other side is connected to the ignition system

Primary circuit • Low voltage

• Does not exceed 12.5 volts

• Conventional wires

Secondary circuit • High Voltage

• 4000 – 30 000 volts

• Heavy wire that prevents electrical leakage

Bypass circuit • Makes sure there is enough

voltage for start up• Starts engine using a lot of

voltage

Resistance circuit

• A resistor or resistor wire that makes sure the system can not exceed 9.5 10.5 Volts

Resistance circuit• Newer computer control cars

have computer controlled voltage regulators

• Resistor circuit not needed today

Distributor

• Sends voltage to appropriate spark plugs

• Tells magnetic field inside of coil when to collapse

Spark plug wires

• Cary high voltage from distributor to spark plugs

• 1000 -4000 ohms resistance per foot

Spark plugs

• Provide a spark for ignition

• Is a ground for primary circuit

• Insulated to stop electrical leakage

Ignition coil

• A transformer

• Creates short bursts of high voltage

Ignition coil • Older vehicles

–Small spark plug gaps –Less voltage 4000 – 8000 volts

Ignition coil• Newer vehicles

–Leaner fuel mixture

–Larger spark plug gap

–Voltage ranges from 4000 – 30 000 volts

–Average of 15 000 volts

Ignition coil parts

• 2 sets of windings

• 2 Primary terminals (low voltage)

• Iron core inside of windings • 1 High voltage out put

connection

Primary Windings

• Several hundred turns of heavy gage wire

Secondary windings

• Several thousand turns of light gauge wire

Ignition coil operation

• Current from the battery flows through the secondary windings, creating a magnetic field.

Ignition coil operation

• When current flow is interrupted the magnetic field collapses And sends its current through the secondary windings.

Ignition coil operation

• Because of the high number of secondary windings voltage is increased and current is decreased