Electric throttle valve positioner (EDK)

The S62 and S54 engines have individual throttle valves. On the S62, they are mounted on a common shaft for each row of cylinders. The two throtlle valve shafts are mechanically linked. On the S54 a single throttle valve shaft is used. The individual throttle valves are operated by an electric positioning motor without a direct mechanical link to the accelerator pedal.

Tasks of electric throttle valve (EDK)

The electric throttle valve fulfils following tasks:

- Implementing the driver's load choice

- Vehicle speed control

- Intervention by the vehicle handling control systems

- Emergency operation

- Load cut-in (e.g. seat heating, air conditioning, lights)

- Maximum speed limitation

Design and function of electric throttle valve

The electric throttle valve (EDK) is operated by DC motor via a gearing system. The position of the throttle valves is detected by two potentiometers which are positioned on the throttle valve shaft of each row of cylinders (see also Throttle Valve Potentiometer).

The voltage signals from the two potentiometers are opposite to each other and are within the following ranges:

The throttle valve actuator is operated by the DME control unit with a pulse-width modulated signal with a basic frequency of 2000 Hz.

Monitoring functions

The following monitoring functions for the EDK have been implemented:

• Monitoring of both potentiometers for electrical faults
  
• Potentiometer 1 is the control potentiometer
  
• Potentiometer 2 is the reference for potentiometer 1
  
• Plausibility of the two potentiometer signals in relation to each other
  
• Monitoring of throttle valve for stiffness and jamming
  
• Checking spring when the ignition is switched on by brief activation of the EDK
  

Emergency operation function

If a fault occurs during operation, a corresponding fault code is stored in the fault memory of the DME control unit. Emergency operation is assumed depending on the severity of the fault:

• Always indicated on the Check Control
  
• Changeover to potentiometer 2 in the event of a fault on potentiometer 1
  
• Selection of the correct potentiometer in the case of plausibility errors by means of a model based on the measured air mass flow.
  
• Deactivation of the throttle valve output stage and safety fuel shut-off if the throttle valve is sticking.
  
• Deactivation of throttle valve output stage if throttle-valve potentiometer signals cannot be unambiguously identified
  
• Safety fuel shut-off if throttle-valve potentiometer signals cannot be unambiguously identified
  

Replacement of electric throttle valve

If the EDK is replaced on a vehicle, the throttle valve stops must be reset. The precise procedure is explained in the repair manual. On completion of the mechanical adjustments, idling speed synchronisation must be carried out. To do so, go to ”3 Service functions” in the diagnosis program and select the option ”5 Idling speed synchronisation”