accelerator

The accelerator is a foot-operated pedal that regulates the flow of fuel or air into an engine, controlling the power output and vehicle speed. In modern vehicles, it is almost always the rightmost of the three pedals and operates on a cable, hydraulic line, or electronic sensor system connected to the engine's throttle valve. Pressing it increases engine RPM; releasing it reduces power and allows the vehicle to slow.

In internal combustion engines, the accelerator does not directly control fuel injection or ignition timing. Instead, it opens the throttle butterfly valve in the intake manifold, allowing more air into the cylinders. On carburetted engines, this increased airflow draws more fuel from the carburetor, enriching the mixture. On fuel-injected engines, throttle position is one input among many (alongside air mass flow, coolant temperature, and load sensors) that the engine control unit uses to calculate injection duration and timing. Heavy vehicles and older designs may use a mechanical cable system; modern cars typically use drive-by-wire, where the pedal position is read by a potentiometer and transmitted electronically to the throttle actuator.

Variants and anomalies

Electric vehicles replace the mechanical throttle with a motor controller that modulates power to the traction motor based on pedal position. Hybrid vehicles switch between engine and electric motor control depending on driving mode. Some trucks and plant equipment use a rotary knob or lever instead of a pedal. Automatic transmissions may incorporate kick-down switches that trigger downshift when the accelerator is pressed fully, improving acceleration from rolling starts.

Common failure modes include sticky or spongy pedal feel (often caused by cable corrosion or sensor drift), loss of response due to sensor malfunction or electrical fault, and unintended acceleration caused by floor mat entrapment or control unit failure. Wear in the throttle linkage can also cause lag or inconsistent response.

The term derives from the Latin accelerare, meaning to hasten. In transport vocabulary, it is sometimes called the gas pedal (colloquially, though 'gas' is technically inaccurate for diesel engines) or the throttle, though throttle more properly refers to the valve itself rather than the control. In industrial machinery and stationary engines, a governor or fuel rack lever often serves the same function but is operated manually or automatically rather than by foot.