The seat occupancy detection facility is required in order to inform the airbag system whether the front driver's seat is not occupied, whether it is occupied by a person or whether there is a child's seat mounted on the seat. Based on this information, the airbag control (MRS) unit can trigger the passenger airbag or not corresponding to requirements in the event of an accident.
The seat occupancy detection system II uses two different methods of detecting occupancy of the front passenger's seat.
The SBE control unit II evaluates the measurement results of both subsystems and thus determines seat occupancy. This status is signalled via a data line to the airbag control unit.
The subsystem OC consists of a sensor mat in the seat face and the corresponding electronic circuitry.
The sensor mat detects the weight load and distribution over the sensor points. The connected electronic stage thus determines the nature of the load on the seat. This detected status is signalled via a data line to the SEB II control unit.
The subsystem FDS consists of 4 antennas which are integrated in the seat face and backrest. The antennas are connected to the SBE II control unit.
The antennas consist of two, electrically insulated metal braided mats.
The antennas measure the electrical field of the seat. Objects or persons vary this field. Based on the changes in this field it is possible to determine whether the seat is occupied by an object (child's seat) or a person.
The SBE II control unit is an independent control unit with diagnostic capabilities connected to the diagnostic bus (TxD link). Faults in the antenna and seat mat systems are recognised automatically and stored in the fault code memory. The occupancy status can be read out via the diagnosis queries.
A fault in the SBE II control unit is signalled via a data line to the airbag control unit and results in the airbag indicator lamp being activated.