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A throttle is the mechanism by which fluid flow 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), but usually decreased. The term ''throttle'' has come to refer, informally and incorrectly, to any mechanism by which the power or speed of an engine is regulated. What is often termed a ''throttle'' (in an aviation context) is more correctly called a thrust lever , particularly for jet engine powered aircraft. For a steam engine, the steam valve that sets the engine speed/power is often known as a regulator. == Internal combustion engines == In a gasoline internal combustion engine, the throttle is a valve that directly regulates the amount of air entering the engine, indirectly controlling the charge (fuel + air) burned on each cycle due to the 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 throttle pedal, as it controls the throttle opening, although "accelerator pedal" is more accurate, since not all vehicles have throttles. A diesel engine does not have a throttle; its power level is controlled by regulating the fuel flow into the engine, thus "throttle" and "gas pedal" are both inaccurate terms when applied to a diesel engine. The throttle is typically a butterfly valve. In a fuel-injected engine, the throttle valve is placed on the entrance of the intake manifold, or housed in the throttle body. In a carbureted engine, it is found in the carburetor. When a throttle is wide open, the intake 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 controlled with a throttle pedal or lever via a direct mechanical linkage. In vehicles with electronic throttle control, the manual throttle control sends a signal to the Engine Control Unit (ECU), which then directly controls the position of the throttle valve. This means that the operator does not have direct control over the throttle valve; the ECU can finely control the valve in order to reduce emissions or maximize performance. In a reciprocating-engine aircraft, the throttle control is usually a hand-operated lever or knob. It controls the engine power ouput, which may or may not reflect in a change of RPM, depending on the propeller installation (fixed-pitch or constant speed). The power output of a diesel engine is controlled by regulating the quantity of fuel that is injected into the cylinder. Because the engines do not need to control air volumes, they lack a butterfly valve in the intake tract. An exception to this generalization is newer diesel engines meeting stricter emissions standards, where a throttle is used to generate intake manifold vacuum, thereby allowing the introduction of exhaust gas (see EGR) to lower combustion temperatures and thereby minimize NOx production. Some modern internal combustion engines (such as some BMW engines) do not use a traditional throttle, instead relying on their variable intake valve timing system to regulate the airflow into the cylinders, although the end result is the same, albeit with less pumping losses. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Throttle」の詳細全文を読む スポンサード リンク
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