Motor Driven Throttle Valve
The MDK control function has been integrated into the PCM. The purpose is for precision throttle operation, OBD II compliant for fault monitoring, ASC/MSR control, and cruise control. This integration reduces extra control modules, wiring, and sensors. The MDK control function is integrated into the Siemens PCM. The PCM carries this function out by regulating the engine throttle valve. The engine throttle valve performs precision intake air control.
The new engine throttle valve (MDK) differs from the familiar EML in that the accelerator pedal potentiometer (PWG) is now integrated in the MDK housing and a throttle cable is used to actuate the throttle potentiometers and also serves as a back-up to open the throttle plate (full control) if the MDK system is in failsafe. The throttle cable (foot pedal controlled) is connected to a pulley on the side of the MDK. The pulley is linked by springs to one end of the throttle shaft, the MDK electric motor is attached to the other end of the throttle shaft. See Fig 1.
With the pulley linked by springs to the throttle shaft, this allows ASC intervention to override the driver's set throttle position. As the pulley and shaft are rotated, the twin potentiometers (integral in the MDK housing) are sensing the requested load. A twin potentiometer is used for back up redundancy (failsafe). The PCM will actuate the MDK motor pulse width modulated in both directions (at a basic frequency of 600 Hz) which positions the throttle plate. The second twin potentiometers feedback the actual throttle plate position, allowing the PCM to verify correct throttle position. Again, twin potentiometers are used for back up redundancy (failsafe).