Electronic ignitions explained

Q. Cars now have electronic ignitions. What is the difference between an electronic ignition and the old kind?

A. The old kind used a set of switch contacts in series with the primary of the ignition coil. The contacts, called “points,” were opened and closed by a cam linked to the distributor shaft. When the points closed, current flowed through the primary of the ignition coil, building up a magnetic field in its core.

Then the contacts were opened so that the magnetic field began to collapse quickly. This induced a high voltage in the secondary of the ignition coil, producing the spark to fire each cylinder at the right time. A capacitor, which mechanics usually call a “condenser,” was connected in parallel with the points. Its purpose was to resonate with the inductance of the primary of the ignition coil when the points opened. This made the spark voltage an oscillating Waveform of decreasing amplitude. Instead of being one brief pulse, the spark voltage continued for a short time, helping to ignite the fuel / air mixture more effectively.

In an electronic ignition, the points are replaced by a transistor that is operated as a switch. It still sends on/ off pulses to the ignition coil’s primary in the same way as the points had. In some cars, there is a separate spark coil and transistor for each pair of cylinders. 

Various methods are used to control the timing of the transistor`s pulses, most of them being either magnetic or optical devices operated by a mechanism connected to the crankshaft. The points in the old kind of ignition would gradually burn up as they operated, so that they had to be replaced periodically. The mechanism which operated them would also wear a bit, so that periodic adjustments were necessary. This was the purpose of the “tune-up” The capacitor was usually replaced in a tune-up, too.

Since the electronic ignition has a transistor instead of points, the problem of burned points has been eliminated. The transistor can also deliver a more energetic spark, making ignition more efficient. For these reasons, modern automobiles do not require this kind of a tune-up. Usually, all that needs to be done in a tune-up now is to make minor adjustments to the ignition timing, and sometimes replacement of the spark plugs.

Leave your comment