Today is my car’s 45th birthday. In honor of this day, I thought it appropriate to discuss one of the most important technological advancements of the automobile since the 1960s.
Today’s new car is advertised with features like bluetooth, mp3 stereo, or GPS navigation. In the early 1970s, salesmen used features “electronic ignition” or “self-adjusting brakes” to sell cars. Few people know (I would venture very few) what electronic ignition is, and how it changed the automobile. Here is my short summary.
An automobile’s ignition system is responsible for igniting the fuel within the cylinder. Gasoline engines use a spark plug to accomplish this task. Spark plugs require tens of thousands of volts to produce a spark, and a car battery is only twelve volts. Thus, a relatively simple electric circuit, called an “ignition system” is employed to create the necessary voltage using a coil and some form of a “switch”.
The coil is actually two coils of wire nested together, a primary and a secondary coil. When a voltage is applied across the primary coil, it produces a magnetic field. If the current across the primary coil is interrupted (using that “switch”), the magnetic field dissipates by inducing an electrical current in the secondary soil. An automobile’s coil is designed to step up the voltage in the secondary coil; thus the twelve volts is converted to tens of thousands of volts.
One of the most crucial factors determining the economy, power, and smoothness of a gasoline engine is the time at which the spark plug fires in relation to the position of the piston. This is accomplished with the “switch”. Every time the “switch” interrupts the current to the primary coil, a current is induced in the secondary coil and a spark plug fires. For most cars, this task is handled by a component called a “distributor”. Before electronic ignition, there was a mechanical “switch” inside the distributor called a points set, or simply “points”. The points had a lever that rode on a cam on the distributor shaft. The distributor shaft was mechanically connected to the rotation of engine crankshaft through gearing. As the distributor shaft turned, the cam inside the distributor would open and close the points, creating a rhythmic interruption of current in the ignition circuit.
Point type ignition systems have a few disadvantages. The points wear, necessitating adjustment every 6 months for optimum performance. This procedure was commonly referred to as a “tune up”. Points also lose accuracy as engine RPM increases. Points are also limited in how much voltage they can carry, and thus the amount of voltage available to the spark plug is limited. These problems were all remedied by electronic ignition systems.
In an electronic ignition system, there are no points. Instead the switching action is created using components that don’t touch or wear. Typically, a permanent magnet is attached to the distributor shaft. As the shaft rotates, it passes a sensor that senses the changing magnetic field. The output from the sensor is processed using electronic circuitry that creates the interruption in current to the primary coil. The most modern cars do not even use distributors. Instead, ignition is entirely computer controlled.