Seat Belt Tensioner: Description and Operation

Models 170, 208, 210.6,
Models 210.0 up to 8/98, 210.2 up to 6/98
Models 140 and 202as of 6/97

In the event of a crash (Head-on or rear end collision) the emergency tensioning retractor eliminates slack in the seat belt and prevents the seat belt film winding effect.
The tight seat belt allows the passenger to start decelerating with the body sooner.

The emergency tensioning retractors are equipped with a force limitation device which reduces the force of the belt on the passenger's body, however, without affecting the protective function of the seat belt.

Seat Belt Tensioning:

In the event of a collision the ETR control module with airbag (N2/2) puts Out an electrical signal for triggering the emergency tensioning retractor after a certain delay.

The squib in the gas generator is triggered and the resulting combustion gas moves the piston (2) in the gas generator cylinder (3) up at high speed. The pull cable(4) connected to the piston is tensioned causing the cable pulley (5) to turn. Inertia and centrifugal force cause the pawls (7) in the cable pulley to engage in the teeth in the toothed ring (6).

A positive connection is then present between the gas generator piston and the seat belt retractor shaft via the pull cable, the cable pulley and toothed plate pulling and thereby tensioning the seat belt (1).

Force Limitation:

After tensioning the seat belt the gas pressure in the gas generator cylinder (3) decreases. The pull cable (4) is relieved and the force on the cable pulley (5) reduced.

The force exerted by the passenger on the seat belt then changes the direction of pull and the seat belt (1) attempts to unwind. This is prevented by the outer locking pawls (8) in the toothed ring (6). The change in the direction of pull simultaneously causes a change in the direction of rotation of the retractor shaft. Inertia and centrifugal force cause the outer locking pawls (8) on the toothed ring (6) to engage in the inner teeth on the locking ring (10).

As soon as a locking pawl is in contact with the teeth on the locking ring1the latter turns until it locks up.

The arrested locking ring causes the torsion rod (9) to arrest on one side. The torsion rod forms the heart of the retractor shaft and therefore takes up the tension forces acting on the seat belt.

As soon as the force on the seat belt exceeds 4 kN, the torsion rod deforms plastically counteracting a further increase in the load and limiting the force.





As soon as the force on the seat belt decreases, the locking pawls in the toothed ring and the pawls on the cable pulley return to their initial position as the seat belt is retracted. The locking and retracting functions of the inertia reel are effective again.

Triggering of the emergency tensioning retractors is indicated by the open viewing window (arrow) on the tensioning system housing.

In the event of another collision the normal protective function of the seat belt is still available. The retractor shaft is locked up by the locking system without tensioning and force limitation so that the entire force is taken up.

Actuation Sequences for Emergency Tensioning Retractors During Rear End Collision (Applies to Model 210 only):





Actuation of the emergency tensioning retractors during a severe rear end collision depends on the version of the control module for emergency tensioning retractor

Control module manufacturer:
Bosch as of start of production
Temic without sidebag as of 9/95
Temic with sidebag as of breakpoint for sidebags