Fig. 8.52. Seat belt pretensioner
Pretensioner operation
In the event of a frontal impact at a certain angle, in the event of a vehicle collision, the electrical circuit controlling the gas generator in the SRS electronic control unit is closed, which ignites the electric igniter of the gas generator.
The gas produced by the gas generator causes the piston in the intake manifold housing of the pretensioner (cylinder) to move, which acts on the ratchet (rack gear).
The ratchet drives the piston gear, and the drive gear drives the planetary gears (planet gears).
Finally, the seat belt webbing is retracted (tensioned) by the rotation of the inertia reel. In this way, the seat belt pretensioner helps reduce the risk of injury to the driver (or front passenger) by tightening his or her seat belt. As a result, the driver (or front passenger) is prevented from moving forward and hitting the steering wheel or dashboard in a vehicle collision.