IGNITION SYSTEM

IGNITION SYSTEMS

Conventional and Modern Electronic Ignition

Ignition System

•Provides a method of turning a spark ignition engine on & off.

•Operates on various supply voltages (Battery & Alternator)

•Produces high voltage arcs at the spark plug electrode.

•Distributes spark to each plug in correct sequence.

•Times the spark so that it occurs as the piston nears the TDC on the compression stroke.

•Varies the ignition timing as engine speed, load and other conditions change.

Parts of Ignition System

BATTERY provides power for system.

IGNITION SWITCH allows driver to turn ignition on and off.

IGNITION COIL changes battery voltage to 30,000V during normal operation and has a potential to produce up to 60,000V.

SWITCHING DEVICE mechanical or electronic switch that operates Ignition coil

SPARK PLUG uses high voltage from ignition coil to produce an arc in the combustion chamber.

IGNITION SYSTEM WIRES connect components.

IGNITION COILS

The heart of any ignition system is the ignition coil.

The coil creates a high-voltage spark by electromagnetic induction.

Many ignition coils contain two separate but electrically connected windings of copper wire.

FIGURE 8-1 Internal construction of an oil-cooled ignition coil. Notice that the primary winding is electrically connected to the secondary winding. The polarity (positive or negative) of a coil is determined by the direction in which the coil is wound.

Distributor

A mechanical timing device

Drives off engine camshaft

Can controls both primary and secondary circuits

May contain advance units

CAP AND ROTOR:

DISTRIBUTES THE SECONDARY VOLTAGE TO THE SPARK PLUGS THROUGH THE HIGH TENSION LEADS.

BIGGEST PROBLEM IS CARBON TRACKING.

HIGH TENSION LEADS:

HIGH VOLTAGE MIN. 10,000 VOLTS RESPONSIBLE FOR GETTING THE ELECTRICITY

FROM THE COIL TO THE CAP & PLUGS. CARBON IMPREGNATED CARBON CORD. RESISTANCE APPROX 3-7 K OHMS PER FOOT. COATINGS

1. SILICONE RUBBER2. HYPALON3. NEOPRENE

SPARK PLUGS

Spark plugs are manufactured from ceramic insulators inside a steel shell.

The threads of the shell are rolled and a seat is formed to create a gastight seal with the cylinder head.

FIGURE 8-32 Parts of a typical spark plug.

BASIC IGNITION SYSTEM

Battery supplies power to entire system

Ignition Switch turns engine on or off

Coil transforms volts

Switching device triggers ignition coil

Spark Plug and wires distribute spark

Coil Ignition System(Primary Circuit)

Primary coil connected to battery, through ignition switch, and to the contact breaker, which is grounded.

Current flows through the primary circuit.

Distributor shaft operated by engine cam ,drives the contact breaker.

Current changes set up magnetic field in the primary circuit and the secondary circuit.

Change in magnetic field induces current in secondary coil.

Coil Ignition System(Secondary Circuit)

Secondary coil connected to spark plug through distributor cap.

Induced current in secondary coil provides the required voltage for producing spark.

For every contact break spark is produced.

Complete Circuit Diagram For Conventional Ignition System

Magneto ignition system

Magneto is a special type of ignition system with its own electric generator to provide the necessary energy for the system.

Magneto can be either rotating armature type or rotating magnet type.

Magneto ignition system

Battery ignition system v/s Magneto ignition system

Battery ignition system Battery is necessary. Current for primary circuit is

obtained from the battery.

A good spark is available at the spark plug even at low speed.

Efficiency of the system decreases with the reduction in spark intensity as engine speed rises.

Magneto ignition system No battery is needed. Required electric current is

generated by the magneto. During starting, quality of

spark is poor due to low speed.

Efficiency of the system improves as the engine speed rises due to high intensity spark.

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Battery ignition system Occupies more space. Commonly used in cars and

light commercial vehicles.

Magneto ignition system Occupies less space. Mainly used in racing cars .

Problems With Conventional Ignition System

Contact Breaker

LIMITATIONS OF CONVENTIONAL IGNITION

1. SLOW COIL SATURATION. 2. SLOW RISE TIME. 3. SIDE THRUST ON DISTRIBUTER SHAFT. 4. CONTACT POINT PROBLEMS. A. LIMITED CURRENT B. BURNING & PITTING 5. GRADUAL LOSS OF TUNE-UP FEELING.

Improvements in Conventional Ignition Systems

Replacement of the mechanical points with a "solid state“ semiconductor switch called a transistor.

ELECTRONIC IGNITION SYSTEM The ability of transistor to interrupt a

circuit carrying a relatively high current makes it an ideal replacement for breaker points and condenser of conventional ignition system.

ELECTRONIC IGNITION SYSTEM

Uses electronic control circuit to operate the ignition coil

More dependable than contact system

Higher secondary Ignition voltages

IGNITION MODULE

PURPOSE: THE IGNITION MODULE USES TRANSISTORS TO TURN THE

CURRENT FLOW FOR THE COIL PRIMARY WINDINGS ON AND OFF

IT GETS IT SIGNAL TO DO THIS FROM THE IGNITION PICK UP COIL

MOST LATE MODEL CARS HAVE A ENGINE CONTROL MODULE (ECM) WHICH COMUNICATES WITH THE IGNITION MODULE THEREFORE CONTROLLING IGN. COIL.

PICK UP COIL

PURPOSE: SIGNALS THE TRANSISTORS IN THE IGNITION MODULE TO

OPERATE. USES A PERMANENT MAGNET AND A COIL OF WIRE AS THE RELUCTOR ( TOOTHED WHEEL MOUNTED TO THE DISTRIBUTOR

SHAFT) PASSES THE PICK UP COIL, A SMALL AMOUNT OF CURRENT IS GENERATED WHICH SENDS A SIGNAL TO THE MODULE

THERE ARE NO WEARING PARTS. AIR GAP IS A CRITICAL ADJUSTMENT AND MUST BE MADE WITH A BRASS

FEELER GUAGE (NON MAGNETIC)

Hall-Effect Sensors

Most popular electronic ignition triggering device Hall Effect Sensors are used in many ignition system distributors

to trigger the primary circuit (fire the coil) and to monitor engine rpm.

Produce a constant voltage signal that can change abruptly from maximum voltage to nearly zero and back again regardless of engine speed.

Produces a square wave output signal that can be easily used by the onboard computer for timing purposes.

MODERN IGNITION SYSTEMS

In modern automobiles the following two types of electronic ignition systems are being used. They are-

1. Transistorised Coil Ignition System (TCI System)

2. Capactive Discharge Ignition System (CDI System)

Transistor Controlled Ignition

Advantages of TCI

The timing of TCI is more precise with the use of the Transistors.

Quicker current build up, high ignition voltages, long duration of spark.

Increased reliability, reduced wear of contact points. Extended spark plug life. Improved ignition of lean mixtures.

Capacitive Discharge Ignition

Advantages of CDI Condenser of CDI system can store much larger energy than

TCI system. This allows high output voltages even at high spark rates.

Faster voltage rise as internal resistance is less. Current drawn from battery is small art lower speeds and

increases with increases with engine speed which is reverse of conventional ignition system which draws high current at low speeds.

Easier cold starting. Output voltage is independent of engine speed. This reduces the

chances of misfiring.

THANK YOU.