Throttle Position Sensor (PWG)
The throttle position sensor uses an inductive coil "oscillator" principle for accelerator position recognition input. The PWG consists of:
- Three separate inductive coils.
- One soft iron core eccentric, attached to the accelerator pedal through the PWG shaft.
- One 4° switch, for the external safety path function.
Each coil is supplied with an AC voltage signal, at a specific frequency, from the EML IIIs control module. As the pedal is moved, the eccentric shape of the iron core moves closer to the PWG coils.
This causes the inductance of the coils to increase due to the concentration of the magnetic field. The increasing inductance in the coil causes the amplitude of the AC frequency to be reduced.
The amplitude is decreased as the pedal is pressed down.
The EML control module monitors and processes the changing amplitude as the input request for throttle opening/closing.
The changing amplitude value is a measure of accelerator pedal movement. The EML control module is programmed to recognize pedal movement from 0° (idle) to 99° (WOT) based on the changing voltage signal.
The three inductive coils are used for redundancy purposes. All three signals from the PWG are input and evaluated by both processors of the EML IIIs control module.
If one signal were to fail, the operation of the EML system, from the driver's perspective, would not be affected. The EML IIIs control module would continue to function from the remaining two signals. The fault will be recognized and stored in the fault memory and a failure warning message would be posted in the display matrix. If a second signal were to fail, the system would go into the failsafe operation and the EML IIIs control module would stop responding to the throttle input. The engine will start but not run above idle. This second fault would also be stored in the fault memory.