Automotive Ignition Systems

Powerful Essays
Ignition Systems:

New and Old

Ignitions systems in motor vehicles have evolved in the past thirty years. Points was a simple concept but was not reliable and needed adjustment and replacement of components seemed constant. Today a magnetic sensor relays a signal to the computer which in turn sends the voltage to the selected cylinder to ignite the fuel/air mixture. There are not mechanical parts to fail or become corroded and brittle. There are many different parts to an ignition system. These parts differ between modern and old ignition systems. There is a coil. Sometimes one coil provides the increased voltage to the distributor or there is no distributor at all and each cylinder has its own coil to provide voltage for the spark plug.

The coil is a compact, electrical transformer that boosts the battery's 12 volts to as high as 20,000 volts. The incoming 12 volts of electricity pass through a primary winding of about 200 turns of copper wire that raises the power to about 250 volts. Inside the distributor, this low-voltage circuit is continuously broken by the opening and closing of the points, each interruption causing a breakdown in the coil's electromagnetic field. Each time the field collapses, a surge of electricity passes to a secondary winding made up of more than a mile of hair-like wire twisted into 25,000 turns. At this point, the current is boosted to the high voltage needed for ignition and is then relayed to the rotor.

The distributor is separated into three sections: the upper, middle, and lower. In the middle section, the corners of the spinning breaker cam strike the breaker arm and separate the points some 160 miles an hour. High-voltage surges generated by the action of the coil travel to the rotor that whirls inside a circle of high-tension terminals in the distributor cap, at each terminal, current is transferred to wires that lead to the spark plugs. Two other devices - the vacuum advance and the centrifugal advance - precisely coordinate the functions of the points and the rotor assembly as the requirements of the engine vary.

An ignition circuit consists of two sub-circuits: the primary, which carries low voltage; and the secondary, which carries high voltage. The primary circuit, controlled by the ignition key, releases 12 volts of electricity from the battery or alternator through the coil to a set of breaker points ...

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...r fires every other revolution so the distributor shaft must revolve at one half crankshaft speed. After the high tension surge is produced in the ignition coil by the opening of the breaker points, the current passes from the coil to the center terminal of the distributor cap. From there, it passes down to the rotor mounted on the distributor shaft and revolves with it. The current passes along the rotor, and jumps the tiny gap to the cap electrode under which the rotor is positioned at that instant. This cap electrode is connected by high tension wiring to the spark plug. As the rotor continues to rotate, it distributes current to each of the cap terminals in turn. connected by high tension wiring to the spark plug. As the rotor continues to rotate, it distributes current to each of the cap terminals in turn.






5) Engine Management: Optimizing Modern Fuel and Ignition Systems, Dave Walker. © Sept. 2001, MBI Distribution Services
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