Throttle
4707019
219605323
2008-06-16T01:28:01Z
AndersBot
6986250
robot Adding: [[zh:節流閥]]
{{otheruses1|the control of engine power}}
A '''throttle''' is the mechanism by which the flow of a fluid is managed by constriction or obstruction. An [[engine]]'s power can be increased or decreased by the restriction of inlet gases (''i.e.,'' by the use of a throttle). The term ''throttle'' has come to refer, informally and incorrectly, to any mechanism by which the power or speed of an engine is regulated.
== Internal combustion engines ==
[[Image:USPatent6518683.png|right|150px]]
In a [[petrol]] [[internal combustion engine]], the throttle is a valve that directly regulates the amount of air entering the engine, indirectly controlling the fuel burned on each cycle due to the [[fuel injection|fuel-injector]] or [[carburetor]] maintaining a relatively constant fuel/air ratio. In a motor vehicle the control used by the driver to regulate power is sometimes called the [[Automobile pedal|throttle pedal]] or accelerator.
The throttle is typically a [[butterfly valve]]. In a [[fuel injection|fuel-injected]] engine, the throttle valve is housed in the [[throttle body]]. In a carbureted engine, it is found in the carburetor.
When a throttle is [[wide open throttle|wide open]], the intake [[Manifold (automotive engineering)|manifold]] is usually at ambient atmospheric pressure. When the throttle is partially closed, a [[manifold vacuum]] develops as the intake drops below ambient pressure.
Usually the throttle valve is mechanically linked with the throttle pedal or lever. In vehicles with [[electronic throttle control]], the throttle valve is electronically controlled, which allows the [[Engine Control Unit|ECU]] greater possibilities in reducing air emissions.
Because [[Diesel engine]]s use compression ignition, they do not need to control air volumes or mixture (indeed this would be undesirable). Thus they lack a butterfly valve in the intake tract, and do not have a throttle. They instead regulate engine power by directly controlling the quantity of fuel injected into the cylinder at top [[dead centre]] (TDC) of the compression stroke.
==Environmental aspects==
Regulation of the throttle is also a mechanism for controlling engine exhaust emissions. In many modern internal combustion engines an electronic throttle is used, eliminating the older accelerator cable.<ref>Victor Albert Walter Hillier and Peter Coombes, ‘'Hillier's Fundamentals of Motor Vehicle Technology'‘, 2004, 544 pages ISBN 0748703179</ref>
Throttle application via the accelerator pedal also results in increased sound emission from the engine. At lower operating speeds this component of [[roadway noise|vehicle noise]] is prominent, contrasted with higher operating speeds, for which [[aerodynamic]] and [[tire]] noise are more significant.<ref>[http://www.springerlink.com/content/x1707075n815g604/ C..Michael Hogan, '' Analysis of Highway Noise'', Journal of Water, Air, & Soil Pollution, Vol. 2, No. 3, Biomedical and Life Sciences and Earth and Environmental Science Issue, pages 387-392, Sept., 1973, Springer Verlag, Netherlands ISSN 0049-6979]</ref>
== Other engines ==
Most [[engine]]s have some kind of throttle control, though the particular way that power is regulated is often different.
[[Liquid rocket]]s are throttled by controlling the pumps which send liquid fuel and oxidizer to the combustion chamber. [[Solid rocket]]s are more difficult to throttle, but some may have mechanisms for this.
In a [[jet engine]], engine output is also directly controlled by changing the amount of fuel flowing into the combustion chamber, usually with an [[autothrottle]].
==References==
{{reflist}}
{{wiktionary|throttle}}
{{CarDesign nav}}
[[Category:Engine technology]]
[[Category:Auto parts]]
[[ar:دواسة البنزين]]
[[de:Gaspedal]]
[[nl:Gaspedaal]]
[[ja:スロットル]]
[[zh:節流閥]]