Power window position recognition, function - GF72.29-P-4000T

model 211.0/2/6 

Direction recognition 

Fig 1: Hall Sensor Square Wave Pulse

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Function 

Two Hall sensors (b1, b2) are located on each of the power window motor shafts. They react on the motion of the magnets and transmit a square-wave pulse for each rotation of the motor shaft. The corresponding door control module senses these pulses and evaluates them for rotation direction and position recognition.

Direction recognition 

From the time difference between pulses from Hall sensor (b1) and pulses from Hall sensor (b2) the corresponding control module recognizes the rotation direction of the power window motor.

Position recognition 

The door control module counts the pulses of the 2nd Hall sensor taking account of the rotation direction of the motor. The value in the position counter is reduced when the window closes. When the window opens, the value in the position counter is increased. The zero position is defined as the upper mechanical limit stop, i.e. when the window is fully closed the counter should be at zero.

The zero position is set through normalization. If the zero position is exceeded in the closing direction, the count becomes negative and thus invalid. In this case, the control module performs a renormalization.