Ignition Systems


Automobile Ignition Systems

The evolution of the automobile ignition system:

  • Magneto Ignition System
  • Battery Ignition System
  • Electronic Ignition System
  • Engine Management System

Magneto Ignition System

A magneto is a perfect example of applied science. In 1831 Michael Faraday, an Englishman, stated and demonstrated by experiment his theory of electromagnetic induction (Joseph Henry, an American, also reached the same conclusion independently in 1832). Farday’s experiment consisted of two windings or coils of wire (a primary and a secondary) insulated from each other, but both wrapped around a steel bar. When a current was applied to the primary coil, a transient current was induced in the secondary coil; and when the current was removed from the primary coil, a transient current again appeared in the secondary coil. Faraday observed that the current in the secondary coil was induced by a change in magnetic flux (magnetic field) of the primary coil.

Referring to the diagram – top right: This magneto schematic shows a rotating permanent magnet to create a low voltage AC current pulse in the primary coil by rising and collapsing (changing) magnetic fields. When the breaker contact is “open” the primary circuit is open and no current flows; however, the electrical capacitor (condenser) maintains a voltage potential across it. When the “Breaker Contact” is “closed”, the primary winding circuit is complete and current flows to ground. At the instant of current flow, in the primary coil, there is a change in magnetic flux and a current is induced in the secondary coil/circuit. The primary and secondary windings also function as a voltage transformer. Automobile magnetos transform the low primary voltage to high voltages of 10,000-20,000 volts in the secondary winding. This extremely high but transient voltage potential appears at the spark plug terminal. A spark is created when the current “jumps” the spark plug air gap to reach the spark plug electrode which is grounded. Automobile magnetos were designed using a horseshoe shaped stationary permanent magnet and having primary and secondary coils attached to a shaft rotating inside the magnet.

In automobile applications where multiple spark plugs are used, a “distributor” devise synchronized to the engine pistons, switches the secondary winding electrical current to the specific spark plug at the proper time for ignition of the fuel/air mixture in the combustion chamber.

Automobile induction magnetos using permanent magnets did not perform uniformly at all engine speeds. At lower engine rpm they did not perform as well. The permanent magnets also had to be re-magnetized periodically. The magneto devise was also very heavy.

Battery Ignition Systems

The Battery Ignition System uses the same science as the magneto (Faraday’s Law of induction). The only difference is in equipment – the battery replaces the permanent magnets to supply the current and voltage. The battery supplies a steady DC current replacing the variable AC current pulses of the permanent magnets. In a battery ignition system the primary/secondary windings/transformer are referred to simply as the “coil.” The battery ignition system is more reliable than the magneto ignition system because it supplied a steady dc current (from the battery) at all engine speeds, versus the engine rpm dependent AC current pulses produced by the magnets in the magneto. Also, there were no magnets to recharge.

A reliable battery ignition system built by Charles Kettering’s Dayton Engineering Laboratories Company (DELCO) in Dayton Ohio was installed on the 1910 Cadillac. Interestingly, the first automotive self-starter motor was installed on the 1911 Cadillac at the request of Henry M Leland, founder of Cadillac. The first battery ignition system appeared on a Buick automobile in 1918 when Walter Marr, Chief Engineer at Buick, approved its use on Buick Automobiles.

Electronic Ignition Systems

The Battery Ignition System uses the same science as the magneto (Faraday’s Law of induction). The only difference is in equipment – the battery replaces the permanent magnets to supply the current and voltage. The battery supplies a steady DC current replacing the variable AC current pulses of the permanent magnets. In a battery ignition system the primary/secondary windings/transformer are referred to simply as the “coil.” The battery ignition system is more reliable than the magneto ignition system because it supplied a steady dc current (from the battery) at all engine speeds, versus the engine rpm dependent AC current pulses produced by the magnets in the magneto. Also, there were no magnets to recharge.

A reliable battery ignition system built by Charles Kettering’s Dayton Engineering Laboratories Company (DELCO) in Dayton Ohio was installed on the 1910 Cadillac. Interestingly, the first automotive self-starter motor was installed on the 1911 Cadillac at the request of Henry M Leland, founder of Cadillac. The first battery ignition system appeared on a Buick automobile in 1918 when Walter Marr, Chief Engineer at Buick, approved its use on Buick Automobiles.

Engine Management Systems

Today automobile ignition systems consists of computers and various sensors and are called – “Engine Management Systems”.

The following is from Wikipedia:

In an Engine Management System (EMS), electronics control fuel delivery and ignition timing. Primary sensors on the system are crankshaft angle (crankshaft or Top Dead Center (TDC) position), airflow into the engine and throttle position. The circuitry determines which cylinder needs fuel and how much, opens the requisite injector to deliver it, then causes a spark at the right moment to burn it. Early EMS systems used an analogue computer to accomplish this, but as embedded systems dropped in price and became fast enough to keep up with the changing inputs at high revolutions, digital systems started to appear.

Some designs using an EMS retain the original ignition coil, distributor and high-tension leads found on cars throughout history. Other systems dispense with the distributor altogether and have individual coils mounted directly atop each spark plug. This removes the need for both distributor and high-tension leads, which reduces maintenance and increases long-term reliability.

Modern EMSs read in data from various sensors about the crankshaft position, intake manifold temperature, intake manifold pressure (or intake air volume), throttle position, fuel mixture via the oxygen sensor, detonation via a knock sensor, and exhaust gas temperature sensors. The EMS then uses the collected data to precisely determine how much fuel to deliver and when and how far to advance the ignition timing. With electronic ignition systems, individual cylinders can have their own individual timing so that timing can be as aggressive as possible per cylinder without fuel detonation. As a result, sophisticated electronic ignition systems can be both more fuel efficient, and produce better performance over their counterparts.

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