Front emergency tensioning retractor, function - GF91.40-P-4000-03E

Model 170, 208 as of 6/98 

Model 210.0 as of 8/98, 210.2 as of 6/98 

Emergency tensioning 

In the event of a collision, the electrical signal for actuation of the emergency tensioning retractor is output by the airbag control module (N2/2  or N2/7)  after reaching a certain deceleration/ acceleration value.

The emergency tensioning retractor is equipped with a force limitation feature which reduces the tension exerted on the body by the seat belt when the seat belt is tensioned during a crash without reducing the protective effect of the seat belt.

In a second crash the normal protective function of the seat belt is still available. The belt reel is arrested by the locking system without tensioning or force limitation so that it absorbs the entire load.

Emergency tensioning retractor function sequence 

(Manufacturer: TRW) 

Three firing stages 

1. Electric ignition of squib (a) by airbag control module.
2. The propellant gas resulting from ignition creates a high gas pressure causing the piston (b) to rotate and tensioning the seat belt.
3. The gas pressure transports the cap 1 (c) in the direction of the ignition cartridge 1 (d).
4. The ignition cartridge is triggered mechanically by the cap.
5. The gas pressure moves the piston (b) on tensioning the seat belt further.
6. The gas pressure transports cap 2 (e) in the direction of ignition cartridge 2 (f).
7. Ignition cartridge 2 is fired.
8. The gas pressure moves the piston (b) to the end position. The red pin becomes visible.
   Fig 1: Identifying Emergency Tensioning Retractor Function Sequence

   Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Compact emergency tensioning retractor (Manufacturer: TRW) 

Recognition of actuation 

Actuation of the ignition stages is indicated by a red pin  extending out of the emergency tensioning retractor housing when all three ignition stages have been actuated

If the red pin is visible  after actuation of the emergency tensioning retractor/compact emergency tensioning retractor, it is necessary to dispose of the emergency tensioning retractor/compact emergency tensioning retractor at a certified disposal company.

Actuation of the three emergency tensioning retractor ignition stages (TRW only) 

In the event of a collision an electrical signal for actuation of the first emergency tensioning retractor ignition stage is output by the airbag control module (N2/2  or N2/7)  after reaching a certain deceleration/ acceleration value. The second and, where applicable, the third ignition stage are actuated if required to completely tension the seat belts. Actuation of the ignition stages is indicated by a red pin  extending out of the emergency tensioning retractor housing. However, this pin only is visible when all three  ignition stages have been actuated.

The emergency tensioning retractor is equipped with a force limitation  feature which reduces the force exerted by the belt on the passenger's body following tensioning of the belt during a collision, without negatively affecting the protective effect of the belt.

In the event of a second collision, the normal protective function of the belt is still present. In this case, the retractor shaft is locked up by the locking system without emergency tensioning or force limitation and takes up the entire load.

Compact emergency tensioning retractor (Manufacturer: Autoliv) 

Function 

The combustion gas resulting from firing the ignition capsule produces a high pressure in the tube of the emergency tensioning retractor, forcing the balls to accelerate. The balls make contact with the pinion gear as they travel through the tube thereby transferring a portion of the energy of motion to the gear. The rotation shaft of the emergency tensioning retractor connected to the pinion gear turns tensioning the seat belt. The balls land in a catch container after passing the pinion gear.