Seat Belt Pretensioner

The task of the pyrotechnical seat belt tensioner is to minimize the seat belt slack in the pelvis and shoulder areas in the event of a crash, thereby improving the restraining action.

The seat belt catch pretensioners are located on the driver's and front passenger seats. The seat belt catch tensioners are triggered in the event of a head-on or rear-end crash and on vehicles with rollover sensor in the event of a rollover.

In the event of a crash of sufficient severity, the squibs in the seat belt catch tensioner are triggered by the crash safety module. The seat belt buckle is connected by means of a steel cable to the piston in the tensioning tube. If the squib is triggered, gas pressure is created, which moves the piston in the tensioning tube. At this, the seat belt buckle is pulled down by the cable and the seat belt is tensioned.

Fig 1: Identifying Seat Belt Pretensioner

Courtesy of BMW OF NORTH AMERICA, INC.