IGNITION SYSTEM

Towards the end of the compression stroke of an engine, an electric spark is required to ignite
the petrol-air mixture. The spark has to have sufficient energy to start the charge burning and it
must be timed to occur at the correct instant.
The high voltage spark can be generated by a magnet or coil ignition system.

Types of Ignition Systems

1. Conventional ignition system
2. Electronic ignition system
3. Capacitor discharge ignition system (CDI)
4. Programmable ignition system
5. Distributor-less ignition system
6. Magnetic ignition system

Conventional Ignition System Components

i. Battery - which stores current
ii. Ignition coil - multiplies voltage
iii. Contact breaker point - interrupts flow of current and helps in timing
iv. Ballast resistor - It resists flow of current
v. Distributor - Which distributes high tension current to the correct spark plug
for each cylinder.
vi. H.T.C. (High tension cables) - transmits high voltage to spark plugs
vii. L.T.C (Low Tension Cable) - which transmits low current to the
components.
viii. Spark plugs - which transmits spark plugs to the engine cylinders
ix. Condensor (capacitor) - Its function is to improve the quality of sparks
produced. It also stores charges and prevents excessive arcing of contact
points.

COIL IGNITION SYSTEM

This system uses electrical energy produced by a battery or alternator to supply the law-tension
ignition current.
The ignition coil transforms the voltage to that required to produce a high voltage spark
compared with a magneto, the coil ignition system makes engine starting easier. Also it is simple
to control the maximum voltage to suit the conditions.

COIL IGNITION SYSTEM

KETTERING TYPE
The conventional battery-inductive ignition system was introduced by Kettering in 1908
 OPERATION
When the driver switches the ignition to the on position, the current flows from the battery
through the switch and then to the ignition coil. The ignition coil battery voltage i.e. 12 volts is
multiplied to high voltage (more than 12,000 volts). The negative terminal of the ignition coil is
connected to the contact breaker point where the primary ignition current is interrupted just
before the compression stroke reaches the TDC. The interruption of this current produces a
collapse on the magnetic field which induces a high voltage current in the secondary circuit. The
contact breaker is set such that the contact breaks the primary circuit every time a cylinder is in
position to receive a spark. The high-tension cable from the ignition coil is connected to the
distributor. Ignition current is transmitted to the distributor chamber through high tension
cables and carbon electrodes. Carbon rod is used to transmit high voltage to the distributor
rotor. The distributor rotor is used to spread high voltage to specific engine cylinder according to
the engine firing order. Then the current flows from the distributor to the engine cylinder
through the spark plug.
A condenser is connected in a parallel connection with the for the purpose of:
a. Preventing excess arcing
b. Improving the quality of sparks produced
A ballast resistor is connected in series connection with the ignition coil to limit excess flow of
current to the ignition coil.

Advantages
1) Simple to maintain
2) Cheap
3) Easy to design and construct

Disadvantages
1) It does not abide with international automobile regulations (because the
engine produces more emissions)
2) Engine produces more emissions
3) Engine produces less power output
4) It requires regular maintenance
5) The system's limit to flow of current is about 4 amps

Conventional Ignition System Components

Contact breaker
Consists of two contact points.
A cam normally driven by the engine camshaft, operates the movable contact against the
reaction of a strip type spring.
The spark at the plug occurs at the instant the contact separate. So the assembly is set (timed)
in relation to the crankshaft to give a spark at the correct time.

Capacitor/ condenser
It stores charge while contacts are open, so as to release it when they are closed in order to
speed up current build up and magnetism.
Distributor
The high-tension switch used to select the appropriate plug is called the distributor.
It consists of a hard plastic distributor cap, inside which is a rotor arm. The high-tension lead
from the coil fits in the centre of the cap and a carbon brush rubs on the rotor to transmit the
electrical charges.
At the instant the spark occurs the rotor arm is set to point to the correct brass(segment) in the
cap that is connected to the plug that requires the charge.
The distributor cap, rotor, contact breaker assembly and automatic advance system are all
incorporated in one unit called distributor unit.
Operation of the ignition coil
Operation When the driver switches on the
ignition switch, the current flows through the
primary winding. This creates a magnetic field
in the iron core. As the circuit is interrupted by
the contact breaker the primary current
collapses. This also collapses the magnetic
field in the core. This sudden breakage of the
magnetic field induces a very high voltage
across the secondary winding. This high
voltage is then transferred to the spark plug
through the distributor to produce sparks for
the ignition.
Symptoms of ignition coil failure
 Backfiring
 Starting problems
 Less fuel economy
 Engine misfiring
 Engine shaking
MAGNETO IGNITION SYSTEM

ADVANTAGES
 With the use of cobalt steel and nickel aluminum magnet metals, very light and
compact units can be made which require very little room.
 More reliable as there is no battery or connecting cables
 More suitable for medium and very high-speed engines.

Disadvantages
I. At low speeds and during cranking the voltage is very low.

OPERATION

The system produces its own current and distributes it to engine cylinders. Magneto is a self
contained device which generates current, steps it up to high voltage and distributes it.
It consists of a rotating magnet and a fixed coil. The current produced by the magnet is made to
flow to the induction coils. When the magnets rotate the direction of magnetic flux through the
armature of the coil reverses direction. As a result of which a voltage is induced in the primary
and secondary coils. The contact breaker points and the condenser produce an increae in the
rate of change of magnetic flux. When the contact breaker points are opened by the cam on the
rotor shaft, the condenser get charged by current from the primary coil. The highly charged
condenser discharges itself into the primary winding and this produces a rapid change in
magnetic flux. Due to the rapid change a very high voltage induced in the secondary winding is
distributed to the correct spak plug and causes spark.

TRANSISTORIZED IGNITION IGNITION SYSTEM ( TRANSISTOR ASSISTED IGNITION SYSTEM)

The main disadvantages of the conventional ignition system (contact breaker system) is that the
output voltage of the coil is reduced as the speed of the engine is increased. (this is because the
time taken for the current built up in primary coil is induced (reduced dwell angle)).
Another disadvantage is the erosion of the contact breaker points, and of the sparking plugs
electrodes occures fairly rapidly and affects the efficiency of the system.
These disadvantages maybe overcome or reduced by yhe use of transistor.

TRANSISTOR- ASSISTED IGNITION

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In this system the contact breaker is used only to interrupt the flow of a very small current
through the emitter and base circuit of a resistor. The emitter and collector of the transistor are
connected into the primary circuit so the normal action of the transistor results in the
interuption of the heavier primary current without this heavier passing through the contacts.
The contacts therefore have a much longer service lifein these system as much more rapid
establishment and collapse of the primary magnetic field is obtained by the use of a low-
inductance primary winding. This results in the production of much higher secondary voltage
which are not reduced by an increase in engine speed, and a long life for the sparking plugs as
their normal erosion has less effect upon the higher voltage sparks.
In another transistorised system, the contact breaker is replaced by a rotating magnetic device,
the magnet producing electrical impulses which triggers the amplifier which inturn actuates a
spark generator connected to a distributor to supply the high voltages to the sparking plugs in
the correct timing sequences.
DISADVANTAGES
I. The transistor can be permanently damaged by exccessive heat.
II. The transistors will be destroyed if the battery connectors are accidentally reversed.
III. Where contacts are retained oil or dirt can prevent the passage between them.
IV. The system requires specialised skills to repair it.

OPERATION
When the ignition switch is on and the contact breaker points are clossed, current flows from
the battery through resistor 2 through the CB points and to the earth. Therefore driver
transistor is not switched on due to lack of base current. At the same time current flows from
the battery through resistor 1 to the base of power transistor switching it on and allowing
current to flow through primary windings of the coil through the balast resistor to the collector
or power transistor to its emmitter and back to the battery negative. During this time magnetic
flux is building up in the primary windings which also cuts across the secondary windings.
When the CB points are open, current flows from battery through the resistor 2 and 3 and to
the base of driver transistor, this causes current to flow from collector to emitter and to the
battery negative thus denying the power transistor, its base current this switches off the power
transistor, since no current now flows in the primary winding, magnetic flux dies inducing EMF
in secondary winding wich is conveyed to the distributor by the high tension lead distributed to
the correct spark plug.

ELECTRONIC IGNITION (BREAKERLESS SYSTEM)

ADVANTAGES
I. Accurate spark timing achieved throughout the speed range.
II. No contacts to erode and wear.
III. Build up time for the ignition coil can be varied by altering the dwell period to suit the
conditions.
IV. No bouncing of contacts at high speed to rob the coil off its primary current.
V. Rapid collapse of magnetism since current is cut off at once, hence leading to a strongr
spark.
VI. Requires less maintenance since it has no moving parts
VII. Engine produces high power output
VIII. Engine produces less emissions
IX. It abides with the international automobile regulations.
X. It allows flow of current exceeding 4 amps

DISADVANTAGES
1. It requires more skilled personnel for repair and maintenance
2. It is expensive
3. It is not easy to design and construct

The contact breaker is replaced by an electronic switch called a pulse generator. This device
generates an electrical pulse to signal when the spark is required.
The signal is then sent to the control module. The duty of the solenoid-state control module is
to make and breake electronically primary current for the ignition coil.
To do this it must amplify and process the signal received from the pulse generetor.
In addition to the switching duty, the control module senses the engine speed from the pulse
frequency and use this information to vary the dwell to suit the engine speed.
LAYOUT OF ELECTRONIC

Types of Pulse generators (trigger systems)

I. Inductive pulse generators
II. Optical pulse generators
III. Hall - IC pulse generators

INDUCTIVE PULSE GENERATOR

OPERATION
The permanent magnet and inductive winding are fixed to the baze plate and an iron trigger
wheel is driven by the distributor shaft. The number of teeth formed on the trigger wheel or
reluctor matches the number of engine cylinders.
When a tooth is positioned close to the soft iron startor core, the magnetic path is completed
and this gives a flux flow. When the trigger wheel is moved away from the position shown, the
air gap between the stator core and the trigger tooth is increased, this larger gap increases the
magnetic resista]nce, so the flux in the magnetic circuit is decreased.

Generation of EMF in the inductive winding fitted around the iron stator core occures as a result
of the change in the magnetic flux, so maximum voltage is induced when the rate of change of
flux is greater. This occures just before and after the point which the trigger tooth is closest to
stator core.

The build up of flux gives a positive peak, and the delay of flux gives a negative peak. In the
trigger position of greatest flux, no emf is induced into the winding.
It is this mid point of change between the positive and negative pulse that is used to signal that
the spark is required.
(Operation
When the rotor rotates, the tooth of the rotor passes close to the permanent magnet and
interrupts the magnetic field. This causes the coil windings to generate voltage hence producing
a signal, the signal is sent to the ECU.)
Optical Pulse Generator
Comprises of rotor, shutter, light emitting diode (LED), phototransistor
(semiconductor sensitive to light).

Operation
When the distributor rotates the shutter passes between LED and the phototransistor and
projected beam of light is interrupted. The off and on signal voltage that is produced by this
action is passed to the control module and used to determine the engine speed and position.
Hall - IC Pulse Generator
Operation

When the shaft rotates the vane also rotates. When the vane passes between magnet of hall IC
the vane diverts the magnetic flux from the magnet away from the hall IC, the change in
magnetic flux causes the hall IC to switch the sensor on and off. A signal voltage is passed to the
control module. The control module is therefore able to detect the engine speed and position
from the hall IC generated signal. The signal for the spark occurs the instant the vane leaves the
air gap.

TRANSISTOR IGNITION SYSTEM CIRCUIT

It has four important semi-conductor stages which perform the duties of pulse shaping, dwell
period control, voltage stabilization and primary switching.

PULSE SHAPPING
The output voltage from an inductive-type generator is an alternating current signal (ac). This
signal is fed into the shaping circuit to produce a direct current (dc) rectangular form of signal.

Dwell Period and Voltage Stabilization

The dwell period is the time the current flows in the primary windings of the coil. This stage
normally varies the dwell period by altering the start of the dwell period. Secondary output is
reduced when the dwell period is decreased, so by means of this control feature, the period of
time that current flows through the primary winding of the coil is altered to suit the engine
speed.
The voltage supplied to the resistor-capacitor network must not vary, even though the supply
voltage to the control module alters due to change in changing output and consumer loads, this
control duty is performed by a voltage stabilization section of the control module.

DARLINGTON OUTPUT STAGE (PRIMARY SWITCHING)

Switch control of the primary circuit current is normally performed by a Darlington Amplifier.
Pulse signals received from the dwell period control stage are passed to the driver transistor
(T1) which acts as a control current amplifier. When T1 is switched on current flows to the base
of T2 switching it on, this causes current to flow through the primary windings.
When there is no signal from the dwell stage, transistor T1 is switched off hence the power
transistor T2 is also off and there is current flowing in the primary circuit. This action collapses
the magnetic field which had been created in the primary and secondary windings, inducing a
voltage in the secondary windings. The high-tension voltage is then distributed to various spark
plug by the distributor via high tension leads.

CAPACITOR DISCHARGE
Capacitor discharge system operate in a slightly different way to conventional ignition system,
although an ignition coil is still used, the coil does not store energy as in the case with most
systems, the ignition coil on a CD system functions as a pulse transformer, in effect a short and
relatively high voltage pulse (typically of 400 volts) is passed through the primary winding of
the coil, thus causes a very rapid buildup of a magnetic flux (magnetic field) in the primary
winding. Because the secondary winding is exposed to the rapidly created magnetic field, a very
high voltage (typically around 400kv) is then induced into the secondary winding. To create the
short 400-volt pulse, a capacitor in the module is charged effectively during a dwell period.
However, when a trigger signal is provided the capacitor discharges its stored energy through
the primary winding.
The trigger signal from the pulse generator is passed to the pulse shaper, the processed signal
from the pulse shaper is then passed to the trigger stage, and the signal from the trigger stage
will cause the capacitor to discharge.
CD systems provide a short but very high voltage coil output, which is typically around 0.1ms in
duration, this short duration spark is not effective in maintaining the combustion process with
weaker air/fuel mixtures. However, the high intensity 40kv coil output is consistent across most
engine speeds and is very effective at igniting relatively rich mixtures.
One advantage of CD systems is that the high voltage at the spark burns off carbon fouling and
oil on spark plugs.
DISTRIBUTORLESS ELECTRONIC IGNITION SYSTEM
One distributorless system uses one high tension ignition coil for every two cylinders, so a four-
cylinder engine has two coils. This system has its secondary winding connected to the spark
plugs one at each end of the winding.

ADVANTAGES
 Less electromagnetic radio interference particularly at higher frequencies, which was
caused on earlier systems by the unscreened 2kv spark at the rotor gap.
 Less nose because sparking is eliminated.
 No moving parts to wear.
 Fewer cables.
COIL ON PLUG DIRECT IGNITION SYSTEM (the modern system)
High tension leads have caused problems over the years such as:
 Short circuiting of HT current, either to earth or to leads connected to cylinders with
lower gas pressure.
 Mutual induction to other HT leads and delicate sensor circuit.
 Leakage due to damp operating conductions.
 Radio and TV interferences
 Suppression difficulties

Nearly all manufacturers have eliminated HT tension leads on their engines by making the
sparking plugs and ignition coil an integral unit.
Each coil plugs unit needs only two LT connections, one to supply battery voltage and the other
to provide the ECU trigger signal.
The only disadvantage is the size of the unit and the extra cost
 Programmable Ignition System
Operation When the engine is cranked the ECU collects the information from the camshaft
position sensor, the ECU uses this information together with information from the other
sensors, i.e. engine knock sensor crankshaft speed and position sensor, to determine time of
ignition coil to produce sparks.

Advantages
1. It is accurate