Seatbelt Pretensioner

Published August 9, 2011
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In the event of a crash the seat belt tightens and holds the passenger in the seat to prevent the passenger from jerking forward. This is done by a seatbelt pretensioner. Read on to know more

Mercedes Benz first introduced the seatbelt pretensioner in their 1981 S-Class. Modern seat belts use a three point anchoring system which was invented by Volvo in 1959. Two points of the belt are in the belt housing and one in the clamp that locks the belt in place. The three point seat belt spreads the energy of a moving body in a crash over the shoulder, pelvis and chest. This distribution of force prevents too much force acting over one part of the body which can hurt the occupant.

Pretensioners can be mechanical or electric. Mechanical pretensioners use an inertia wheel with a pendulum device that moves under rapid deceleration and locks the belt in place. A simple tug of the belt when it’s on will demonstrate that the belt refuses to move forward, thereby, reducing occupant travel in the event of a crash. An electrical pretensioner has a sensor which locks the belt in place in the event of a crash.