Throttle

Throttle refers to a mechanism that regulates the flow of a fluid, most commonly air, into a system such as an internal combustion engine. In automotive and aviation contexts, the throttle determines the amount of air entering the engine, thereby controlling power and speed. The term also applies to devices in hydraulic, pneumatic, and industrial systems that restrict flow to regulate pressure and rate of flow.

Common forms include mechanical throttles, in which an accelerator pedal or other actuator directly moves a throttle plate in a throttle body; and electronic throttles, or drive-by-wire systems, in which sensors report pedal position to an engine control unit that commands an electric motor to set the valve opening. In many engines the air-control element is a butterfly valve.

Operation involves adjusting the throttle opening to change the engine’s air intake, which affects fuel metering and combustion. At idle, the throttle is nearly closed and idle air is metered by an idle control system. Modern engines coordinate throttle position with mass air flow or manifold pressure sensors and rely on the engine control unit to regulate fuel delivery.

Throttling extends beyond vehicles to industrial and process-control applications, where a throttling valve or orifice restricts flow to manage pressure, flow rate, or energy use. Safety features in electronic throttles include redundancy, fault monitoring, and fail-safe or limp-home modes to prevent unintended acceleration.

See also: throttle body, butterfly valve, throttle position sensor, drive-by-wire, flow-control valve.