Function

Function Schematic:

Seat occupied recognition
If a person is sitting in the passenger seat, the pressure increases on the seat surface. This changes the resistance of the foil pressure sensor in the sensor mat. When the pressure on the seat surface exceeds a defined value (12 kg on a circular area with diameter of 120 mm), the electronic evaluation circuitry recognizes that a person is seating in the passenger seat and sends an occupied signal to the airbag control module (N2/2 or N2/7) via the data bus.

The seat occupied status is checked every 2.5 s (models 215, 220: every 0.72 s). The occupied signal is maintained for 2 min after the load is removed from the passenger seat.

Maintaining the signal protects against the safety devices being switched off immediately when the load on the passenger seat is relieved only momentarily.

Child seat recognition
The child seat recognition feature is ensured only with a child seat which is approved by Mercedes Benz and coded for the control module. The child seat must be equipped with two transponders (resonators) located in the bottom on the left and right sides. When the child seat is positioned, the signals transmitted by the electronic evaluation circuitry into the sensor mat via the transmitter antennas are changed by the resonators in the chi d seat. The phase of the sine wave signals is changed. The signals are received by the corresponding receiving antennas in the sensor mat and transferred to the electronic evaluation circuitry. The electronic evaluation circuitry evaluates the signals and informs the emergency tensioning retractor control module with airbag (N2/2 or N2/7) of the momentary status via the data line. Child seat present/not present; child seat incorrectly positioned; etc. Evaluation of both signals also allows clear identification of the position of the child seat (pointing towards front or rear of vehicle).

Function Schematic:

Front passenger seat occupied recognition
The foil pressure sensor for seat occupied recognition converts the pressure signals resulting from applied force to the seat into resistance signals.

Precise tuning between the weighted surface and the force prevents an occupied signal from being sent by shopping bags, boxes or suitcases. The foil pressure sensor is designed so that a force of 12 kg over a surface with a diameter of 120 mm is required to actuate the occupied signal.

The resistance signals from the pressure sensors are first detected and evaluated by the electronic evaluation circuitry. If an occupied signal is present it is immediately transmitted to the ETR control module with airbag in the form of a digital report for activation of the supplemental restraint equipment on the passenger side.

The seat occupancy is checked every 2.5 s. When the load on the passenger seat is relieved, the occupied signal remains for 2 min. Maintenance of this signal protects against immediate switch-off of the supplemental restraint equipment when the load on the passenger seat is not present for only a short time.

Automatic child seat recognition
The function of the automatic child seat recognition is ensured only with a special type of child seat offered as an MB accessory. The child seat must have a transponder for communication with the inductive child seat recognition in the passenger seat. The MB child seats are equipped with two transponders each, which are installed in the base on the left and right side.

For recognition of the child seat the electronic evaluation circuitry inductively excites the transponders by means of a transmitter antenna in the switching mat. The transponders change the transmitted signal and transfer it back to the two receiver antennas in the switching mat. The electronic evaluation circuitry decodes the transponder signals and signals to the ETR control module with airbag that a child seat is installed using a digital signal.

Different coding of the two transponders allows the electronic evaluation circuitry to also recognize the installation position of the child seat. This information has no significance at present, because the passenger airbag is always inhibited when a child seat is installed regardless of the installation position.