Parts of Seat Belt
Modern three-point seat belts are a vital component of a vehicle’s safety system. In the event of an accident, the seat belt will hold you in place and gradually slow you down, reducing the risk of injury. Having trouble with one of your seat belts? Check to see if there’s a simple solution that might work for you.
A seat belt is made up of polyester fabric, a retractor, a pretensioner, a tongue and a buckle. The webbing is the part that goes across the passenger’s chest, and the retractor holds the excess webbing. The tongue clips into the buckle and holds the occupant in place.
1. Belt Retractor
The seat belt retractor contains a coil spring that pulls the webbing back into the retractor when the seat belt is released.
If the seat belt comes loose during an accident, the seat belt is useless. Inside the retractor are two mechanisms that allow the webbing to lock and hold the occupant in place.
One mechanism uses a metal ball to detect the high G-forces from an accident. When the vehicle decelerates at the start of an impact, the gravity ball rolls out of position and pushes against the pawl, locking the retractor gear in place.
The other mechanism is speed sensing. When you pull hard on the seat belt, it clicks into place. This occurs when the centrifugal force of rewinding the pretensioner moves two cams outward, locking them into the pretensioner gear. This mechanism acts as a safety device for the metal ball.
2. Belt tensioner
Seatbelt pretensioners are cylinders that contain a small amount of propellant, similar to airbags. The pretensioner piston forces the retractor to tension the belt, which keeps the occupant as far away from the steering wheel as possible, thus maximizing the occupant’s deceleration in the event of a collision.
