Mechanical Seat Belt TENSIONERS

The mechanical seat belt tensioner is a simple method of countering the effects of the occupant moving forward (seat belt stretch) during the sharp deceleration of a collision.

Fig 1: Identifying Mechanical Seat Belt Tensioners

Courtesy of BMW OF NORTH AMERICA, INC.

The seat belt tensioner consists of a cable operated seat belt latch, a tension spring and an inertia mechanism.

When the inertia mechanism is triggered during a collision, The linkage releases the tension spring and the seat belt latch is pulled downward to tighten the belt across the occupant's body. This action counters the effects of inertia and the "spooling" of the seat belt itself.

Fig 2: Identifying Inertia Mechanism

Courtesy of BMW OF NORTH AMERICA, INC.