In order to regulate the power produced from the gasoline internal combustion engine (ICE), a restriction is used to control the airflow into the engine. This restriction is known as the throttle blade. The throttle blade will change the throttle effective area, which will regulate the air volume that is moving from the atmosphere into the cylinder.
Traditionally this restriction is controlled directly from the accelerator pedal through a mechanical linkage system that the driver will actuate. This relation between the accelerator pedal and the throttle valve is therefore fixed at one rate of opening and closing. Thus the driver will directly determine the power output of the engine. If more power is required, the driver will simply push the accelerator pedal closer to the floor which in turn changes the throttle effective area.
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This will directly allow more atmospheric air volume to flow into the cylinder, which increases the fuel delivery. This additional fuel will release its chemical potential which will heat the nitrogen (working fluid) creating an expanding gas phase that will push the piston down thus creating greater power at the crankshaft. The throttle blade directly controls the power output of the engine.
With the need for higher control of the power output, better fuel economy and lower tail pipe emissions this age old system of accelerator pedal, linkage and throttle blade has been modified. This modified system is referred to as Electronic Throttle Control (ETC). ETC was first used on vehicles in 1986. These early ETC systems were limited by cost, so only high performance vehicles with traction control were equipped with this system. Some 14 years later ETC systems became common place on the modern vehicle. ETC replaces the mechanical linkage between the accelerator pedal and the throttle valve. Additionally ETC eliminates the idle speed control and the cruise control by directly using the throttle blade for the control of these systems.
ETC systems are used to control the power output from the engine more precisely. ETC is used for emission controls such as catalytic converter lite off compensation, torque output control for traction control, engine speed governor, vehicle speed governor, altitude compensation, launch control compensation and driver selectable performance. ETC accomplishes this not by having to react to the driver input as would occur with a direct linkage to the throttle blade, but by determining through the data input what the best throttle blade angle would be for the current condition and then controlling the throttle blade to allow for the best solution.
ETC was modeled after flight-by-wire. Flight-by-wire is a safety critical system in which redundant operations provide for a higher level of security. In order to eliminate the throttle linkage, several things must occur. The first and most important is to accurately determine diver intent. This is accomplished by using a sensor on the accelerator pedal as seen in Figure 1. This sensor is referred to as the Accelerator Pedal Position Sensor (APPS). This sensor will convert the mechanical input from the driver to an electric output from the sensor.