Distributor

<h2 id="design">Design</h2>

<p>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 <a href="/facts/Ignition_coil/S67YvhGb">ignition coil</a> via <a href="/facts/Brush_(electric)/NhPpqvFD">brushes</a> at the centre of the rotor. As the rotor spins, its tip passes close to (but does not touch) the output contacts for each <a href="/facts/Cylinder_(engine)/XlMRcfFl">cylinder</a>. As the electrified tip passes each output contact, the high-voltage electricity is able to 'jump' across the small gap.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> This burst of electricity then travels to the <a href="/facts/Spark_plug/Y9lG10hg">spark plug</a> (via <a href="/facts/High_tension_leads/383jQ4wY">high tension leads</a>), where it ignites the air-fuel mixture in the combustion chamber.
</p><p>On most <a href="/facts/Overhead_valve_engine/zd4v8vWf">overhead valve engines</a>, the distributor shaft is driven by a gear on the <a href="/facts/Camshaft/qS8BWXVr">camshaft</a>, often shared with the <a href="/facts/Oil_pump_(internal_combustion_engine)/30IVkeKe">oil pump</a>; on most <a href="/facts/Overhead_camshaft_engine/z2D9nIL5">overhead camshaft engines</a>, the distributor shaft is attached directly to a camshaft.
</p><p>Older distributor designs used a <a href="/facts/Cam_(mechanism)/bxISyXo2">cam</a> on the distributor shaft that operates the <a href="/facts/Contact_breaker/1JSTaoRw">contact breaker</a> (also called <i>points</i>). Opening the points causes a high <a href="/facts/Electromagnetic_induction/T36JjtgY">induction</a> voltage in the ignition coil.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> This design was superseded by an electronically controlled ignition coil with a sensor (usually <a href="/facts/Hall_effect_sensor/bITzh0dk">Hall effect</a> or optical) to control the timing of the ignition coil charging.
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<h3>Ignition advance</h3>
<p>In older distributors, adjusting the <a href="/facts/Ignition_timing/hqpb5yaG">ignition timing</a> is usually achieved through both <i>mechanical advance</i> and <i>vacuum advance</i>. <a href="/facts/Ignition_timing/hqpb5yaG">Mechanical advance</a> 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. <a href="/facts/Ignition_timing/hqpb5yaG">Vacuum advance</a> typically uses <a href="/facts/Manifold_vacuum/pWQSD40u">manifold vacuum</a> to adjust the ignition timing, for example to improve fuel economy and driveability when minimal power is required from the engine.
</p><p>Most distributors used on <a href="/facts/Electronic_fuel_injection/ckF7ERXq">electronic fuel injection</a> 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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<h2 id="direct-ignition">Direct ignition</h2>
<p>Since the early 2000s, many cars have used a 'coil-on-plug' direct ignition system, whereby a small ignition coil is located directly above the spark plug for each cylinder. This design means that high-voltage electricity is only present in the small distance between each coil and the spark plug. See <a href="/facts/Saab_Direct_Ignition/2NhUnj7r">Saab Direct Ignition</a>.
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<h2 id="gallery">Gallery</h2>

<h2 id="history">History</h2>
<p>The first mass-produced electric ignition was the <a href="/facts/Delco_ignition_system/882lsR1K">Delco ignition system</a>, which was introduced in the 1910 <a href="/facts/Cadillac_Model_30/WJwRAru1">Cadillac Model 30</a>. In 1921, <a href="/facts/A._Atwater_Kent/uNuLxL6J">Arthur Atwater Kent Sr</a> invented the competing <i>Unisparker</i> ignition system.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
</p><p>By the 1980s and 1990s, distributors had been largely replaced by <a href="/facts/Electronic_ignition/7Rqqltpr">electronic ignition</a> systems.
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<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/List_of_auto_parts/6cX2e2qH">List of auto parts</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>"How the ignition system works". How a Car Works. Retrieved 2016-02-12. <a href="http://www.howacarworks.com/basics/how-the-ignition-system-works" target="_blank">http://www.howacarworks.com/basics/how-the-ignition-system-works</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>"How the ignition system works". How a Car Works. Retrieved 2016-02-12. <a href="http://www.howacarworks.com/basics/how-the-ignition-system-works" target="_blank">http://www.howacarworks.com/basics/how-the-ignition-system-works</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>"Cadillac History | Kanter Car Tales". kanter-car-tales.com. Archived from the original on 2016-03-05. Retrieved 2016-02-12. <a href="https://web.archive.org/web/20160305094321/http://kanter-car-tales.com/category/cadillac-history/" target="_blank">https://web.archive.org/web/20160305094321/http://kanter-car-tales.com/category/cadillac-history/</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
</ol>

Distributor open-in-new

Distributor