Ignition systems have changed over the past four or five decades.
- The ignition system provides the spark to ignite the air/fuel mixture, which facilitates combustion.
- The spark must occur at the correct moment to ensure complete combustion and smooth, economical running.
- It is the job of the ignition system is to provide a consistent spark precisely when needed.
Conventional ignition
- The conventional system (sometimes called the points ignition system) consists of battery, ignition switch, ignition coil, distributor, high tension leads, spark plugs.
- The spark plugs require a voltage of approximately 20,000 volts to ignite the air/fuel mixture and as the conventional vehicle electrical system uses a 6 or 12 volt battery this creates a problem. The ignition coil overcomes this problem by acting as a transformer.
- The battery supplies current to the ignition switch (12 volts usually).
- When the ignition switch is turned on, it supplies current to the positive or switch side of the coil.
- The coil has two circuits, the low tension or primary circuit and the high tension or secondary circuit.
- The current runs from the ignition switch through the coil primary windings to earth when the ignition contact points in the distributor are closed.
- This sets up a magnetic field in the coil.
- When the contact points open the current in the primary circuit stops flowing and the magnetic field collapses.
- This induces a high voltage in the secondary windings, which flows through the rotor and distributor cap, through the spark plug leads and into the spark plugs.
- The high voltage jumps the electrode gap in the spark plugs and creates the spark to ignite the air/fuel mixture.
Electronic ignition
- The distributor was the first thing to change with the advent of electronic ignition.
- A number of different devices now replace the points and condenser.
- They all do the same job as the points - they switch the current on and off at the coil - but they do this electronically.
- This arrangement is better than the old system because there are no contact points to wear out.
- The spark quality is better, which results in a more efficient and environmentally friendly engine.
Computer controlled ignition
- The ignition system has been further developed to take advantage of the latest computer technology.
- Most cars now do not have a distributor.
- The control unit or computer uses transistors to switch the current at the coil.
- Some vehicles do not have high-tension leads; they have a small coil sitting on the top of each spark plug, which is controlled by the computer.
- The big advantage of this system is that it allows for a more accurate control over spark timing and there are fewer moving parts, which means less wear and more reliability.