Automobile electronics, Electronics, Motors

Automobile ignition system

In this post I will talk about electronic ignition system to automobiles. I will about each component in the system and your operation as a whole.

This is the complete system which turn on the spark ignitions in the right moment and speed to maximize the efficiency.

Ignition coil

The ignition coil is a step up autotransformer, converts battery voltage in high voltage. The figure below shows the windings on the left and on the right shows this component in cut.

The transformers only work with alternate current and the battery provides continuous current. How the ignition coil will work? An ignition electronic module is used to open and close constantly the current to operate the coil.

Ignition module

The terminals of ignition module:

  1. Positive output of distributer;
  2. Negative output of distributer;
  3. Linked with the tachometer (speed meter, I will talk in another post);
  4. Linked with the ignition key, the primary positive of autotransformer and to a resistive wire;
  5. Ground;
  6. Linked to the coil`s negative primary.

This module replace the platinum and the condenser (capacitor), eliminating the weariness and vibration of contacts, making easier the ignition point adjust and increasing the efficiency due to distributer`s electronic control. The ignition coil is controlled with a power transistor which depends of the distributer`s output signal. The pulses emitter can be inductive or Hall effect. I will explain with more details about the ignition and electronic injection module in other post.


The distributer`s function is distribute the high voltage signals to the ignition sparks in the right order and speed. The inductive distributer has a stator with permanent magnets and induction winding. The rotor spins by a valve command tree, the magnetic flux and the voltage in the stator`s terminals change.

When the stator`s tooth and rotor`s tooth find each other, the voltage U in the terminals increase and decrease when they stay away following this curve.

With the ignition module, the U pulses become rectangular pulses in the same direction. This is an example of inductive distributer.

The Hall distributer uses a Hall effect sensor (3) in front of a permanent magnet (1), the integrated circuit with a Hall sensor also model and amplify the signals, stabilize the voltage and have a temperature compensator. The rotor (7) has magnetic shielding segments (5). The (8) is a vacuum advance unit controlled by the accelerator`s throttle.

When a shielding stays between the sensor and the magnet, the voltage stays close to zero. Here we have a simplified schema of Hall distributer.

Starter motor

The starter motor spin the combustion engine`s crankshaft until start the explosions and then the engine works by itself. This is the crankshaft which also turn on the distributer`s axis by a set of gears in some engines.

The starter motor has a solenoid controlled by ignition key which allow contact between the battery and the motor.

Ignition spark

The spark conducts the high voltage generated by the autotransformer and provided by the distributer to the combustion chamber, where is produced a spark inflaming the moisture of air and fuel. I will explain with more details in another post.

About Pedro Ney Stroski

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