CH27 ignition systems STUDENT VERSION rev

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Chapter 27

Ignition Systems

Primary Circuit Components

• Battery

• Ignition switch

• Ballast resistor (older systems)

• Ignition coil primary winding

• Triggering device

• Switching device or control module

Primary Circuit Operation

• Ignition switch on

• Current flows into primary coil winding

• A primary switching device stops current flow through the coil

• This causes the magnetic field to collapse

Secondary Circuit Components

• Ignition coil secondary winding

• Distributor cap and rotor (DI systems)

• Spark plug cables (some systems)

• Spark plugs

Secondary Circuit Operation

• Collapse of the magnetic field in the

primary induces high voltage into the coil secondary

• This voltage is used to establish a complete circuit so current can flow

• The excess energy is used to maintain the current flow across the spark plug gap

Ignition Coils

• Coils are pulse transformers

• Output dependant upon the

number of windings and current flow

• CEMF increases time to become fully saturated

• Dwell is the period of current flow

Secondary Voltage

• Typical voltage requirement to jump the

plug gap is 10,000 volts

• Most coils have at least 25,000 volts

available – called secondary reserve voltage

• Reserve necessary to compensate for high cylinder pressures

Spark Plugs

• Provides the air gap

• Resistor reduces RFI

• Standard plug electrodes

are copper

• Platinum and iridium

electrodes extend plug

life

Ignition Cables

• Carry high voltage to spark plugs

• Carbon fiber core acts as a resistor

• Reduces RFI and increases firing voltage

• Reduces plug wear by reducing current

Triggering and Switching Devices

• A triggering device monitors crankshaft

position

• A switching device controls current flow

through the coil primary winding

• Electronic switching components are part of

an ignition control module or the PCM

Engine Position Sensors

• Magnetic Pulse Generator

– Consists of a reluctor and pickup coil

• Metal Detection Sensor

– The electromagnet is in the pickup coil

• Hall-effect Sensor

– Produces a square wave signal

– Is most commonly used

• Photoelectric Sensor

– Uses an LED and moving slotted disc

Timing Retard and Advance

• Timing controlled by

ignition module

• Older systems used

mechanical and vacuum

systems

• May contain pick up assembly, ignition module, and coil

• Shaft driven by camshaft

• Rotor sits on top of distributor shaft and spins inside of distributor cap

• A typical distributor

Electronic Ignition Systems

• No moving parts

• Cylinders individually controlled

• Flexible mounting locations

• Less radio frequency interference

• No timing adjustments

• More time for coil saturation

Double-Ended Coil or Waste Spark Systems

• One coil fires two

Coil-Per-Cylinder Ignition

• Coil-on-plug and coil-near-plug

• Allows for more time between firings and increased saturation time

• A single coil failure affects only one

cylinder

• COP require adaptors or plug wires to

connect an ignition scope

Hall-Effect Sensors

Magnetic Pulse Generators

Misfire Detection

• The CKP identifies which cylinder

• Detected by variation in crank speed

• PCM uses wheel speed data to determine if crank speed variation is from rough road

conditions or misfire

Basic Timing

• The PCM controls timing and is not

adjustable

• Timing is fixed during cranking

• Once a certain engine speed is reached, the PCM adjusts timing

• Timing inputs include RPM, load, throttle position, and coolant temperature

Coil Cross-Section

• Platinum tipped spark plug

Vacuum advance