With the aid of the actuator of the throttle valve, the throttle valve can be activated independent of the accelerator pedal position.
The electric throttle valve fulfils following tasks:
- Implementing the driver's load choice
- Idle speed control (separate idle speed actuator dispensed with)
- Vehicle speed control
- ABS / ASC / MSR / DSC intervention
- Emergency operation
- Load cut-in (e.g. seat heating, air conditioning, lights)
- Limitation of top speed v_max
The electric throttle valve (EDK) is adjusted with a DC motor and a gear unit. The position of the throttle valve is detected by means of a double potentiometer that is mounted on the throttle valve shaft and which rotates in the opposite direction.
Corresponding to the position of the throttle valve, the voltage signals for potentiometer 1 are between 0.5 V and 4.5 V and opposingly for potentiometer 2 between 4.5 V and 0.5 V.
The throttle valve actuator is operated by the DME control unit with a pulse-width modulated signal with a basic frequency of 2000 Hz.
The following monitoring functions are realized for the electric throttle potentiometers:
- Monitoring of both potentiometers for electrical faults
- Potentiometer 1 is a control potentiometer
- Potentiometer 2 is a reference for potentiometer 1
- Plausibility monitoring of both potentiometer signals with respect to each other
- Monitoring of throttle valve with regard to stiff movement and snagging
- Check of return spring every time the “ignition is switched on” by brief activation of the EDK
- Adaptation of the electric throttle valve actuator after a waiting time of approx. 30 seconds at “ignition ON”
If a fault occurs during operation a corresponding fault code will be stored in the fault code memory of the DME control unit. Emergency operation is assumed depending on the severity of the fault:
- Indicated permanently in the check control
- Changeover to potentiometer 2 in the event of a fault in potentiometer 1
- Selection of the correct potentiometer in the case of plausibility errors by means of a model based on the measured mass air flow.
- Cut-out of an output stage of throttle valve and safety fuel cut-out in the event of the throttle valve sticking or if allocation of the throttle potentiometer signals is undefined.
If an electric throttle valve is replaced on a vehicle, the limit stops of the throttle valve must be re-learned. For this purpose, the electric throttle valve is activated for approx. 30 seconds after “ignition ON”.
The maximum opening of the throttle valve while learning the positions is 25 %.