The system is installed in both front seats. A sudden deceleration of the vehicle in a frontal or near-frontal collision is detected by a mass sensor. If the deceleration is large enough, the sensor moves forward and activates the seat belt pretensioner. This occurs before the occupant restrained by the seat belt is thrown forward by the collision. As a result, the seat belt is tensioned by approximately 120 mm, which is distributed between the shoulder and lap branches.
Fig. 21. Seat belt tensioning mechanism: 1 - seat belt buckle, 2 - ratchet
After the seat belt tensioner mechanism has been activated, the seat belt buckle 1 (Fig. 21) under the influence of the ratchet mechanism 2 cannot return to its original position on its own, it bounces down, below the edge of the seat cushion. The seat belt pretensioner system is activated in a collision at a speed of over 12 km/h.
