Editing Distributor (section)

== Design ==
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A distributor consists of a rotating arm ('rotor') that is attached to the top of a rotating 'distributor shaft'. The rotor constantly receives high-voltage electricity from an [[ignition coil]] via [[brush (electric)|brushes]] at the centre of the rotor. As the rotor spins, its tip passes close to (but does not touch) the output contacts for each [[cylinder (engine)|cylinder]]. As the electrified tip passes each output contact, the high-voltage electricity is able to 'jump' across the small gap.<ref name=":0">{{Cite web|title = How the ignition system works|url = http://www.howacarworks.com/basics/how-the-ignition-system-works|website = How a Car Works|access-date = 2016-02-12}}</ref> This burst of electricity then travels to the [[spark plug]] (via [[high tension leads]]), where it ignites the air-fuel mixture in the combustion chamber.

On most [[overhead valve engine]]s, the distributor shaft is driven by a gear on the [[camshaft]], often shared with the [[Oil pump (internal combustion engine)|oil pump]]; on most [[overhead camshaft engine]]s, the distributor shaft is attached directly to a camshaft.

Older distributor designs used a [[Cam (mechanism)|cam]] on the distributor shaft that operates the [[contact breaker]] (also called ''points''). Opening the points causes a high [[electromagnetic induction|induction]] voltage in the ignition coil.<ref name=":0" /> This design was superseded by an electronically controlled ignition coil with a sensor (usually [[Hall effect sensor|Hall effect]] or optical) to control the timing of the ignition coil charging.

=== Ignition advance ===
In older distributors, adjusting the [[ignition timing]] is usually achieved through both ''mechanical advance'' and ''vacuum advance''. [[Ignition timing#Mechanical timing advance|Mechanical advance]] adjusts the timing based on the engine speed (rpm), using a set of hinged weights attached to the distributor shaft. These weights cause the breaker points mounting plate to slightly rotate, thereby advancing the ignition timing. [[Ignition timing#Vacuum timing advance|Vacuum advance]] typically uses [[manifold vacuum]] to adjust the ignition timing, for example to improve fuel economy and driveability when minimal power is required from the engine.

Most distributors used on [[electronic fuel injection]] engines use electronics to adjust the ignition timing, instead of vacuum and centrifugal systems. This allows the ignition timing to be optimised based on factors other than engine speed and manifold vacuum.
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