Ignition coil
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Ignition_coil".

Bosch ignition coil.

Dual ignition coils (top of picture) on a Saab 92.

An ignition coil (also called a spark coil) is an induction coil in an automobile's ignition system which transforms the battery's 12 volts (6 volts in some older vehicles) 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.

Use in cars

In older vehicles a single (large) coil would serve all the spark plugs via the ignition distributor. A notable exception is the Saab 92 that has one ignition coil per cylinder.

Modern ignition systems

In modern systems, the distributor is omitted and ignition is instead electronically controlled. Much smaller coils are used with one coil for each spark plug or one coil serving two spark plugs (so two coils in a four-cylinder engine). These coils may be remote-mounted or they may be placed on top of the spark plug (coil-on-plug or Direct Ignition). Where one coil serves two spark plugs (in two cylinders), it is through the "wasted spark" system. In this arrangement the coil generates two sparks per cycle to both the cylinders. 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 wasted spark system is more reliable than a single coil system with a distributor and cheaper than coil-on-plug.

Where the coils are remote mounted they may all be contained in a single moulded block with multiple high-tension terminals. This is commonly called a coil-pack.

Tesla coil

The disruptive discharge Tesla coil is an early predecessor of the "ignition coil" in the ignition system. Tesla also gained U.S. Patent 609,250 , "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.
• Low tension coil

Patents

• U.S. Patent 1,391,256  - Induction coil structure - Arthur Atwater Kent - 1921
• U.S. Patent 1,474,152  - Induction coil - Arthur Atwater Kent - 1923
• U.S. Patent 1,474,597  - Induction coil - Arthur Atwater Kent - 1923
• U.S. Patent 1,569,756  - Ignition coil - Arthur Atwater Kent - 1926
• U.S. Patent 1,723,908  - Ignition system - Ernst Alexanderson - 1929

External links

• Interactive tutorial on Ignition Coils National High Magnetic Field Laboratory
• Ignition Coil Driver circuit