Electric throttle actuator
The corresponding position of the throttle valve is calculated in the engine control unit from the position of the accelerator pedal and other variables. The throttle valve is opened and closed electrically by the engine control unit.
Two potentiometers register the current position of the throttle valve. The engine management controls the position by means of the electric drive until the current valve opening corresponds to the set position. Two potentiometers are used for safety reasons. The characteristic curves of the two potentiometers are contra-rotating. The engine control unit powers both potentiometers with an exact voltage of 5 V. This voltage source is also used to supply sensor 1 of the pedal position sensor or accelerator pedal module.
Throttle-valve potentiometer characteristics
|DKG1||Signal path of throttle-valve potentiometer 1|
|DKG2||Signal path of throttle-valve potentiometer 2|
Monitoring the signal voltages
The engine control unit permanently monitors the two voltages of the potentiometers. The monitoring function checks whether the two signal voltages are within the permissible range and are plausuble in relation to one another. It also monitors whether there is a short circuit. The engine control unit can determine which of the two signal voltages is faultless based on the air mass signal.
If the engine control unit detects that the signal voltage of a potentiometer is defective, the maximum possible valve opening is limited to 20 degrees.
If the signal voltages of both potentiometers are detected as implausible, the activation of the throttle valve is switched off. Under these circumstances, it is no longer possible to determine the current position of the throttle valve and, consequently, the return spring closes the throttle valve.
Monitoring the throttle valve position
The engine control unit continuously checks whether the actual position corresponds to the set position of the throttle valve. thus making it possible to determine when a valve is sticking. In the case of fault, for safety reasons, the maximum possible engine speed is limited to 1300 rpm.
A stiff throttle valve that therefore moves only slowly is switched off and closed by the return spring. In this case, the maximum possible engine speed is limited to 1300 rpm by cutting out the fuel injection.