Ignition system with mechanical contact breaker — general description (Opel Ascona C)

In order for the engine to operate properly, it is necessary for the spark plug to ignite the working mixture in the combustion chamber at the right time in relation to the engine speed and its load. Low voltage from the battery is supplied to the ignition coil, where it is converted into high voltage, the value of which is sufficient to cause a spark to jump between the spark plug electrodes at high pressure developed in the cylinders.

The ignition system is divided into 2 circuits: high and low voltage.

Low voltage circuit (sometimes also called primary) consists of a battery, a wire leading to the ignition switch, a wire leading from the ignition switch to the primary winding of the coil, and a wire leading from the primary winding of the coil to the contacts of the breaker and the capacitor in the distributor.

The high voltage circuit consists of the secondary winding of the coil, the spark plug wire leading from the center of the coil to the center of the distributor cap, the rotor, the spark plug wires leading to the spark plugs, and the spark plugs themselves.

The ignition system works as follows. Low voltage is converted into high voltage in the ignition coil by opening and closing the contacts of the breaker in the low voltage circuit. High voltage is supplied through the "carbon" in the center of the distributor cap to the rotor on the cap, and whenever the rotor is brought into contact with one of the four electrodes on the distributor cap that are connected to the spark plug wires, the opening and closing of the breaker contacts causes a build-up of high voltage, causing a spark to jump between the rotor and the corresponding electrode. The voltage is transmitted via the ignition wire to the spark plug, between the electrodes of which a spark jumps, causing the mixture to ignite, after which the current goes to ground.



To ensure that the mixture is ignited at the right time in relation to the engine speed and load, the ignition timing is automatically adjusted.

The ignition timing angle is controlled by mechanical and vacuum regulators. Mechanical (centrifugal) the regulator consists of two weights, which, due to centrifugal force, diverge when the speed of rotation of the distributor shaft increases and turn the cam relative to the distributor shaft, thereby accelerating the spark jump. The weights are held by two springs, and the correct mechanical adjustment of the ignition timing angle depends on the tension of the springs.

The vacuum regulator consists of a membrane, one side of which is connected by a thin tube to the carburetor, and the other to the contact breaker plate. The vacuum in the intake manifold and carburetor, which varies depending on engine speed and throttle opening, causes the diaphragm to move, which moves the contact breaker plate accordingly, accelerating or retarding the spark jump (see photo).



A resistor in the low voltage wire to the coil holds the coil voltage at 6 volts during normal operation. This resistor is bypassed when the starter is engaged to compensate for the resulting drop in battery voltage.