Ignition coil

The ignition coil is a component of the ignition system of a gasoline engine or a gas combustion system. The structure corresponds to a transformer, in particular an autotransformer.

Basics

Ignition coils work like a spark coil. With the ignition on the primary winding of the ignition coil of current flowing through it, creating a magnetic field forms around the coil. This magnetic field is transmitted by the common iron core of both windings on the secondary winding. The opening of the breaker in the primary circuit of the ignition coil is induced in the secondary circuit a high voltage pulse, since the magnetic field to collapse rapidly. The high voltage passes through the ignition cable to the spark gap of a spark plug, for instance, to ignite the fuel / air mixture in the cylinder of a gasoline engine at the right time.

It is used in gasoline engines to together with the breaker to create ( today usually electronically) to the interrupter and the parallel capacitor of the on-board voltage of 12V, a high voltage of about 15,000 to 30,000 volts.

The capacitor in parallel to the contact to reduce the one hand the arcing of the circuit breaker contacts (increased burn-out) and on the other hand form complexes with the primary coil of a resonant circuit having the same resonance frequency as the secondary coil. In this way energy transfer is enhanced by the primary to the secondary circuit. In conventional ignition coils often the optimum is 0.22 uF.

Ignition coil in gasoline engines

Automotive ignition coils have three terminals: The primary circuit receives voltage from the ignition switch to terminal 15 (DIN 72572 ) of the ignition coil, passes through the primary winding and connected to terminal 1 Breaker ( Ignition ) to ground. The removed high voltage terminal 4 of the secondary circuit is passed through the distributor to the spark plugs, the restore the connection to ground via the radio link. Chance find ignition coils with 4 ports use: In addition to terminal 1 and 15 for the primary winding of the mass of the secondary winding to terminal 4 is connected separately. To prevent unwanted misfire by switching on the magnetic field ( single spark coil) is installed on the secondary side, a series circuit of diode cascade. Together they reach a blocking voltage of about 2000 - 5000 volts. However, this circuit makes a resistance check on the secondary side with commercially available instruments impossible ( measurement result: open line ).

In ignition coils for systems with Wasted Spark the two ends of the secondary winding are performed for each spark plug to the outside, so they are not auto-transformers, but each have a separate primary and secondary windings.

For retrofitting of older vehicles can be bought commercially and ignition coils with a higher secondary voltage. These usually have to be operated with a series resistor in order to avoid thermal overloading. You can bypass the series resistor with the starter relay to compensate for the voltage drop of the electrical system during the starting phase.

In training as a car mechanic was up in the 1970s nor the elaborate taught ( up ) winding of the ignition coils - a procedure that due to the current practice, such items easy to replace, has become obsolete, but in the restoration of classic cars is certainly still practiced.

In newer vehicles, the Full Electronic Ignition ( VEZ ) is mostly associated with their "resting ignition distribution " is used: above each spark plug sits an ignition module with its own ignition coil this way, the reliability is increased because when an error occurs, only one cylinder fails the elaborate distributor with his. . mechanics is omitted as well as the vulnerable high-voltage cable. since a flashover occurs only in the spark plug, the radio interference is kept to a minimum.