Audi A8 2019 Service Training page 69

Rear lap belt tensioner
Introduction
If the Audi A8 is equipped with electrically adjustable
individual rear seats, as opposed to the standard rear bench
seat, lap belt tensioners are installed in the rear outer
seats. They have the following designations:
› Driver Side Rear Seat Belt Tensioner Igniter 2 N749.
› Passenger Side Rear Seat Belt Tensioner Igniter 2 N750.
In an accident, if the occupants are wearing their seat belts,
the lap belt tensioners have the following effect:
› Reduced chest compression.
› Reduced upper thigh load.
› Reduced forward displacement of the pelvis.
› Improved interfacing between the pelvis and seat.
› Reduced submarining.
Accident response sequence
In the event of an accident which meets the criteria for
deployment, the Airbag Control Module J234 deploys the
belt tensioners and the lap belt tensioners. The seat belt is
tensioned by the belt tensioner on the automatic belt
retractor. For safety reasons, the belt force is limited by the
active belt force limiter. The lap belt tensioner tensions the
part of the seat belt in the region of the occupant's pelvis.
Submarining
Submarining occurs if an occupant slides down underneath
the lap belt towards the footwell during a head-on colli-
sion. This can potentially cause serious injury. The adjusta-
bility of the rear seats allows submarining to be reduced
depending on seat setting.
Position of occupant before accident
Installation position
Seat belt travel
The lap belt tensioners counteract submarining by tension-
ing the lap belts and holding the vehicle occupants in a set
position in the seat.
Occupant begins to slide downward
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662_028
Occupant slides down underneath the seat belt
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