Bosch ignition coil

An ignition coil (also called a spark coil) is an induction coil in a automobile's ignition system which transforms a storage battery's 12 volts to the thousands of volts needed to spark the spark plugs.

This specific form of the autotransformer, together with the contact breaker, converts low voltage from a battery into the high voltage required by spark plugs in an internal combustion engine.

In modern ignition systems, the ignition distributor is omitted and ignition is instead electronically controlled. Firing voltage is achieved either by using individual coils placed on top of the spark plug (coil-on-plug or Direct Ignition), or through a "waste spark" system, in which two spark plugs share the same coil, causing both to fire simultaneously - the fuel in the cylinder that is nearing the end of its compression stroke is ignited, whereas the spark in its companion that is nearing the end of its exhaust stroke has no effect. The waste spark system is more reliable than a single coil system with a distributor, and cheaper than coil-on-plug.

The disruptive discharge Tesla coil is an early predecessor of the "ignition coil" in the ignition system. Tesla also gained U.S. Patent 609250, "Electrical Igniter for Gas Engines", on August 16, 1898. It used the principles of the ignition coil used today in automobiles. A. Atwater Kent, in 1921, patented the modern form of the ignition coil.

Related coils

• An Oudin coil is a disruptive discharge coil.

Patents

• U.S. Patent 1391256 - Induction coil structure - Arthur Atwater Kent - 1921
• U.S. Patent 1474152 - Induction coil - Arthur Atwater Kent - 1923
• U.S. Patent 1474597 - Induction coil - Arthur Atwater Kent - 1923
• U.S. Patent 1569756 - Ignition coil - Arthur Atwater Kent - 1926
• U.S. Patent 1723908 - Ignition system - Ernst Alexanderson - 1929