Belt Tensioners

Seat belts must be worn tightly so they can restrain occupants quickly in the event of an accident. But because of clothing and the soft inertia reel mechanism, this is not always the case and the result is termed belt slack. Pyrotechnic belt tensioners compensate for belt slack by tightening the belt on impact. They are triggered by a gas generator via the airbag control unit. The belt tensioner has a lower trigger threshold than the front airbag, meaning it may trigger in response to a collision which is not serious enough to activate the airbag. When triggered, the tensioners pre-tension the belt strap. As the belt is then tighter to the body, the occupants slow down at an earlier stage, and the loading on the body is distributed evenly across the full restraint process, reducing the risk of injury.