CARS Automotive Training Series

Module 6 Disc 1

Ignition Systems
Menu Sub Menu Summary
Principles of Ignition When the air/fuel mixture in the cylinders is richer or leaner than the ideal ratio of 14.7 to 1, a higher level of electrical energy is required to ignite it.
The plug firing voltage needed to establish the spark is higher than the spark voltage needed to sustain the spark.
Contact Breaker System Contact breaker ignition systems provide a simple means of establishing and interrupting the current flowing in the primary ignition circuit.
The secondary winding, with about 100 times as many turns as the primary winding, can have an induced voltage about 100 times greater than the primary induced voltage. However, the actual firing voltage depends on many factors, including whether the engine is idling, or operating under load.
A ballast resistor coil is designed to operate at approximately 7.5 volts and still provide the step-up transformer action needed, for secondary circuit operation.
The dwell angle in contact breaker systems is designed to allow sufficient time for current to flow through the primary winding and establish the necessary magnetic field.
The ignition timing point can be advanced by a centrifugal type mechanism according to engine speed and by a vacuum operated mechanism, according to load
Contact Breaker System Components Battery Used to supply a voltage to the system components.
Ballast Resistor Used to reduce the voltage to the ignition coil during normal running conditions.
Ignition Coil A standard ignition coil has a secondary winding with 15000 to 30000 turns of very thin enameled copper wire, wound around a laminated iron core. The primary winding with a few hundred turns of heavier copper wire is wound on the outside of the secondary.
Contact Breaker The contact breaker is a mechanically operated electrical switch in the primary ignition circuit. The contacts open and close automatically with engine rotation.
Capacitor Used to assist in the rapid collapse of the magnetic field in the ignition coil.
Distributor The distributor in a contact breaker system distributes the high tension voltage surges to the spark plugs in the correct sequence and at the correct instant in time in the engine cycle.
HT Leads Used to transmit the high voltage required by the spark plugs to ignite the fuel air/mixture in the cylinders.
Spark Plugs Spark plugs are identified by thread size or diameter, the reach or length of the thread and by the heat range.
Advance and Retard Mechanisms Ignition timing can be varied by a centrifugal advance mechanism, according to engine speed and by a vacuum advance unit according to engine load.
Electronic Systems and Components Induction In electronic ignition systems the contact breaker is eliminated and the switching or triggering of the primary circuit is carried out electronically.
Inductive type pulse generators use the principles of electro-magnetic induction to produce an AC voltage. This can be used to signal an ignition module to turn the primary circuit ‘on’ and ‘off’.
Low inductive ignition coils have a low number of primary turns and a low primary resistance. The ignition module limits maximum primary current to a safe value.
Hall A hall effect sensor provides voltage pulses, that are generated by alternately shielding the sensor from a magnetic field, then exposing it.
Voltage pulses from a Hall generator can be used by an ignition module to control the operation of the primary circuit.
Optical Optical type sensors inside the distributor can be used to sense crank angle position. This information can be used by an engine management electronic control unit, to control ignition system operation.
Distributorless Systems In a waste spark system, each spark plug is fired by a high voltage impulse from an ignition coil shared with a companion cylinder.
Identification of each pair of cylinders is provided by a dual crank sensor attached to the engine timing cover.

BACK