Glossary: Accelerator

The accelerator is a control, usually a foot-operated pedal, used to control the flow of fuel into the engine. In petrol engines, it is done either by linking it to the throttle body (fuel injected engines) or carburetor (carbureted engines). The throttle body can either be mechanically or electronically controlled.

The mechanically controlled version employs a butterfly valve which is housed in the throttle body. The butterfly valve is connected directly to the accelerator pedal by means of a cable. Thus the valve regulates the amount of air entering the engine with respect to the position of the accelerator pedal which is controlled by the driver. There are no electronic components involved.

The electronically controlled version employs a sensor that is connected to the accelerator pedal. Once the gas pedal is depressed, it converts this mechanical movement into an electronic signal and sends it to the vehicle’s computer, which in turn controls the throttle using an electronic actuator. This setup ensures optimized engine performance as the fuel metering is more precise and also results in lower emission levels. The idle control and cruise control systems are controlled by the vehicle’s computer using the same electronic throttle actuator.

In the case of diesel engines, there are no throttle plates involved. Instead, the accelerator pedal is linked to a fuel injection pump which delivers fuel into the engine by means of a fuel injector.