The lap pre-tensioner automatically pulls in the seat belt upon a frontal collision to
reduce the forward travel distance of occupants. Upon a collision, when the front impact sensor, attached to the front of the vehicle body,
detects an impact that exceeds the permissible limit, the lap pre-tensioner ignites the gas
generator with the signal from SRS-ECU, and the alternator emits the gas. By the gas pressure, the wire linked to the piston travels in the direction of movement,
then the seat belt is pulled in. Subsequently, when a tension is applied to the seat belt by
the forward travel of an occupant, balls are jammed between the piston and tube because of the
wedge action, and the drawing position is maintained due to the locking.
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