GF91.60-P-0002GI Supplemental Restraint System (SRS) - Function

GF91.60-P-0002GI Supplemental Restraint System (SRS) - Function
- as of 1.12.99

The supplemental restraint system (SRS) serves to protect vehicle occupants in the event of various types of accidents.

For this purpose, the vehicle has the following airbag and belt tensioning units:
- Up to: 31.08.00Driver airbag, single-stage with driver airbag initiator (R12/3)
- as of 1.09.00Driver airbag 2-stage, with driver airbag initiator 1 (R12/13) and driver airbag initiator 2 (R12/14)
- up to: 31.08.00Passenger airbag, single-stage with passenger airbag initiator 1 (R12/4)
- as of 1.09.00: Front passenger airbag 2-stage with initiator 1 front passenger airbag (R12/4) and initiator 2 front passenger airbag (R12/5)
- Left front side airbag with left front side airbag initiator (R12/20)
- Right front side airbag with right front side airbag initiator (R12/10)
- for code 293: Left rear side airbag with right rear side airbag initiator (R12/11)
- In code 293-equipped vehicles: Right rear side airbag with right rear side airbag detonator (R12/12)
- Driver emergency tensioning retractor unit with driver ETR initiator (R12/1)
- Passenger emergency tensioning retractor unit with passenger ETR detonator (R12/2)
- Left rear emergency tensioning retractor unit with left rear ETR initiator (R12/6)
- Right rear emergency tensioning retractor unit with right rear ETR detonator (R12/7)

Innovations as of 1.09.01:
- Left rear window airbag with left rear window airbag initiator (R12/22) and
- Side airbag and window airbag sensor, left (A53/1)
- Right rear window airbag with right rear window airbag initiator (R12/23) and
- Side airbag and window airbag sensor, right (A54/1)

Function overview
Principal item of the supplemental restraint system (SRS) is the restraint systems control module (N2/7).
The restraint systems control module (N2/7) contains all acceleration sensors required for detecting a head-on collision, rear end collision or side collision. All crash-related vehicle data is stored in the memory of the restraint systems control module (N2/7).

The current measured data of the integrated acceleration sensors are continuously analyzed and
compared with the values stored in the memory. The electronic circuit in the restraint systems control module (N2/7) in the event of crash detects the
- Crash severity (discrete levels),
- Direction of collision,
- Status of the individual belt buckles and the
- Front passenger seat occupation (child seat or person)

Innovation as of 1.09.01:
The left side airbag and window airbag sensor (A53/1) and the right side airbag and window airbag sensor (A54/1) are read in for analysis during a side collision.

Occupation of the front passenger seat by a child's seat or a person is detected by the passenger seat occupied and automatic child seat recognition sensor (B48) and sent to the restraint systems control module (N2/7). The sensor can identify whether or not a person is sitting in the front passenger seat or whether it is occupied by a child restraint seat. If a child seat with child seat transponder is mounted to the front passenger seat, the AIRBAG OFF malfunction indicator lamp (A1e56) illuminates and indicates that the front passenger airbag has been deactivated.

In the event of a crash the restraint systems control module (N2/7) deploys the vehicle's supplemental restraint system (driver/front passenger airbags, side airbags and as of 1.09.01 window airbags and emergency tensioning retractors for the driver, front passenger and the rear left and right seats) as required to ensure maximum occupant protection. For details on the module's deployment logic, see the pages cross-referenced below.

The restraint systems control module (N2/7) records the switching states of the following belt buckles:
- Left front seat belt buckle switch (S68/7)
- Right front seat belt buckle switch (S68/8)
- Left rear seat belt buckle switch (S68/11)
- Right rear seat belt buckle switch (S68/12)

Each respective emergency tensioning retractor is only triggered if the attendant belt buckles have been connected.

Faulty belt buckles are deemed to be not connected.

Features
The restraint systems control module (N2/7) is made up of a:
- Fault memory
- Diagnostic interface
- Non-volatile post-crash memory (for up to 3 crash events),
- An energy reserve in the event of an interruption to the supply voltage for a period of 150 ms.

One second after disconnecting the supply voltage the restraint systems control module (N2/7) should not trigger any more initiators.

Communication
In the event of a crash the restraint systems control module (N2/7) sends an analog crash signal upon activation of a supplementary restraint system to the All-activity module (AAM) (N10) and each respective engine control unit. This causes the All Activity Module (AAM) (N10) to unlock all the vehicle's doors and switch on both the interior lights and the hazard flashers. The engine control unit then switches off the engine.

Safety mechanisms
The restraint systems control module (N2/7) reads out two separated acceleration sensors and the additional safety sensor, which is integrated into the restraint systems control module (N2/7). The safety sensor operates mechanically and serves to protect reliably against any erroneous activation, which could, for example be caused by electromagnetic interference. The front airbag and emergency tensioning retractor are triggered only if the mechanical safety sensor detects a crash instance.
(With one exception: A rear end collision will activate the ETRs without reference to the mechanical safing sensor.)

Deployment characteristic










During a crash event, the vehicle undergoes increasing changes in velocity. These changes in velocity serve as a criterion for triggering the individual detonators. The ETRs and the driver/ front passenger airbags are only deployed when there is a very abrupt change in the vehicle's longitudinal velocity.
In contrast, the side airbags (as of 1.09.01 with window airbags) are only deployed when the vehicle's longitudinal speed experiences an abrupt change.
The sensors of the restraint systems control module (N2/7) only record abrupt changes in speed for the longitudinal and transverse directions, in the event of an collision from any given direction. Depending upon these measured values the airbags for the driver/front passenger, ETRs or side airbags (as of 1.09.01 with window airbags) are accordingly activated.

Malfunctions in the SRS system, as well as the passenger seat occupied and automatic child seat recognition sensor (B48) are displayed by the airbag indicator and warning lamp (A1e15) in the instrument cluster (A1).
If the passenger seat occupancy and child seat sensor (B48) does not properly recognize child restraint seats, the system will automatically assume that such a seat is present.
The working condition of the AIRBAG OFF malfunction indicator lamp (A1e56) is not automatically checked by the restraint systems control module (N2/ 7).
The seat belt warning light (A1e9) illuminates after engine start up for approx. 6 seconds.