Front emergency belt tensioner - function - GF91.40-P-4000-03S
As of 01.09.02 the standard catalog designation has changed from the control module for airbags (N2/7) to the restraint systems control module (N2/7).
Belt tensioner
If a crash occurs the electrical signal to trigger the emergency tensioning retractor is released by the airbag control module (N2/7) from a particular deceleration/acceleration.
Emergency tensioning retractor functional sequence
The emergency tensioning retractor unit is equipped with a force limiter, which, after the retractor is tensioned in the event of a crash, reduces the belt load on the occupant's body without compromising the protective effectiveness of the seat belt.
In a further crash, the normal protective function of the belt is retained. Without tensioning and force limiting, the inertia reel shaft is then blocked by the locking system and absorbs the complete load.
Ignition in three stages
- Electrical ignition of ignition squib (a) by airbag control module.
- The combustion gas produced by ignition, generates a high pressure and thus causes the piston (b) to rotate and the belt is tensioned.
- The gas pressure transports the 1st ignition cap (c) in the direction of the 1st ignition cartridge (d).
- The ignition cartridge is mechanically ignited by the ignition pylon.
- The gas pressure moves the piston (b) further and causes the belt to be tensioned further.
- The gas pressure transports the 2nd ignition cap (e) in the direction of the 2nd ignition cartridge (f).
- The 2nd ignition cartridge is ignited.
- The gas pressure moves the piston (b) into the end state. The red pin is visible.
Triggering the three ignition stages of the emergency tensioning retractor unit
If a crash event occurs, the electrical signal for deploying the first ignition stage of the emergency tensioning retractor is transmitted by the airbag control module (N2/7) from a particular deceleration/ acceleration. After this, depending on when complete belt tensioning occurs, the second and, if necessary, the third ignition stage are activated. Activation of the ignition stages is signaled by a red pin which projects out of the housing of the emergency tensioning retractor unit. This pin is only visible, however, once all three ignition stages have been activated.
The emergency tensioning retractor unit is equipped with a force limiter which, after belt emergency tensioning in the event of a crash, reduces the load of the belt on the body of the occupant without affecting the protection offered by the belt.
In a further crash, the normal protective function of the belt is retained. Without tensioning and force limiting, the inertia reel shaft is then blocked by the locking system and absorbs the complete load.
Recognition of deployment
The triggering of the ignition stages is signaled by a red pin which is moved out of the emergency tensioning unit housing when all three ignition stages have been triggered.
If all three ignition stages were not triggered in an accident, ignition stages which have not triggered must be emptied via the disposal detonation.