Automotive Ignition Coil


The ignition coil generates a high voltage that is sufficient for arcing sparks between the electrodes of a spark plug. The primary and secondary coils are wound around the core. The secondary coil is wound approximately 10times more than the primary coil. One end of the primary coil is connected to the igniter, and one end of the secondary coil is connected to the spark plug. The other end of each coil is connected to the battery.

Operation of Ignition Coil

1. Current flowing to the primary coil When the engine is running, the current from the battery flows via the igniter to the primary coil, in accordance with the ignition timing signal (IGT) that is output by the engine ECU. As a result, lines of magnetic force are generated around the coil, which contains a core in the center.

2. Current stopped to the primary coil

As the engine continues to run, the igniter rapidly stops the current to the primary coil, in accordance with the IGT signals that are output by the engine ECU. As a result, the magnetic flux of the primary coil starts to decrease. Thus, an EMF (Electromotive Force) is generated in a direction that impedes the loss of the existing magnetic flux through the self-induction of the primary coil and the mutual induction of the secondary coil. The self-induction effect generates approximately 50V of EMF in the primary coil, and the accompanying mutual induction effect of the secondary coil generates a high EMF voltage of approximately 3kV. This induces the spark plug to produce a spark. The more abruptly the primary current stops and the greater the primary current, the higher the corresponding secondary voltage will be.

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