Working principle of traditional ignition system

The working principle of the traditional ignition system is as follows

Turn on the ignition switch and the engine will start running. When the engine is running, the cam of the circuit breaker keeps turning, so that the contacts of the circuit breaker keep opening and closing.

When the contacts of the circuit breaker are closed, the current of the battery starts from the positive pole of the battery, passes through the ignition switch, the primary winding of the ignition coil, the movable contact arm of the circuit breaker, the contacts and the distributor housing, and then flows back to the negative pole of the battery.

When the contact of the circuit breaker is pushed away by the cam, the primary circuit is cut off, the current in the primary winding of the ignition coil quickly drops to zero, and the magnetic field around the coil and in the iron core also rapidly decays or even disappears, so an induced voltage is generated in the secondary winding of the ignition coil, which is called secondary voltage, in which the current flowing through it is called secondary current, and the loop through which the secondary current flows is called secondary circuit.

After the contact is disconnected, the higher the primary current drop rate, the greater the flux change rate in the iron core, and the higher the induced voltage in the secondary winding, the easier it is to break through the spark plug gap.

When the magnetic flux in the ignition coil core changes, not only high voltage (mutual inductance voltage) is generated in the secondary winding, but also self-inductance voltage and current are generated in the primary winding. At the moment when the contacts are separated and the primary current drops, the direction of the self-induced current is the same as that of the original primary current, and its voltage is as high as 300V V, which will break through the gap between the contacts and produce a strong electric spark between the contacts, which will not only make the contacts quickly oxidized and ablated, but also affect the normal work of the circuit breaker. At the same time, the change rate of primary current, secondary winding induced voltage and spark in spark plug gap is reduced, which makes the mixture difficult to ignite.

In order to eliminate the adverse effects of self-induced voltage and current, a capacitor C 1 is connected in parallel between the contacts of the disconnector. When the contacts are separated, the self-induced current charges the capacitor, which can reduce the spark between the contacts, accelerate the attenuation of primary current and magnetic flux, and improve the secondary voltage.