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Seatbelt Pretensioners

The idea of a pretensioner is to tighten up any slack in the belt webbing in the event of a crash.
To make sure a seatbelt restrains an occupant as early as possible in a crash, thereby reduce the load on the occupant in a violent crash, Autoliv has developed pretensioners. These tighten the belt during the very first fractions of a second in a crash. Pretensioners also reduce the risk of "submarining" (the car occupant sliding under a loosely tightened seatbelt). Autoliv´s pretensioners use pyrotechnic devices that are typically controlled by the same sensor system as the airbags. Pretensioners normally work together with conventional seatbelt locking mechanisms, not in place of them.
Pretensioner devices can be added to any of the belt anchorage points and there are typically three different types of seatbelt pretensioners:
1. Retractor pretensioner
2. Buckle pretensioner
3. Lap pretensioner (normally used in combination with retractor or buckle pretensioners).
 Buckle and retractors pretensions




The most common retractor pretensioner is the ball-in-tube version as seen in the image below. A electrical pulse from the Crash electronics (ECU) ignites a pyrotechnical squib. The burning generant generates a great deal of outward pressure. The pressure pushes the ball in the tube forward over a cogwheel. The cogwheel is connected to the spindle in the retractor and when turning it will extract webbing, up to 120mm.







How does it work!

​See for yourself.