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SUPPLEMENTARY RESTRAINT SYSTEM (SRS)
20
Front Seat (Co-Driver) Belt buckle
Front Seat (Driver) Belt buckle
1.7.2.4. RPLL BELTS
RETRACTOR PRETENSIONER LOAD LIMITOR:
Seatbelt pre-tensioner is a device installed in
vehicles to reduce slack that may exist in a
seatbelt system at the moment of a frontal
collision. Having the seatbelt system snug allows
the supplemental restraint airbag system to work
most effectively. A loose seatbelt system does not
keep the occupant in the proper position during
the forces of a crash. In order for airbags to
reduce or eliminate injury, the occupant must be
seated, belted and in the correct position in the
vehicle.
Pretensioner device is mounted in the retractor
unit. The Pretensioner unit essentially consists of
a ball cage comprising of a tube of steel balls
surrounding a toothed wheel. The wheel is
mounted on the belt-webbing spool.
When the ECU senses a crash, depending on the
crash severity, it sends a "fire" signal to the squib
in the belt Pretensioner. The firing of the squib
causes displacement of the balls in the tube. The
movement of the balls causes rotation of the
toothed wheel, which in turn rotates the webbing
spool and removes the slack from the belt.
LOAD LIMITOR
In high speed frontal crashes, passenger moves
forward due to inertia at a very high speed. If the
seat belt gets locked during such crashes it may
cause injuries to the passenger as he is forcibly
held by the seatbelt against the inertia force.
Load limiters are provided to limit the seat belt
loads to a pre-defined value. Load limiters are to
be used only in airbag equipped vehicles. The
load limiter fitted inside the retractor unit is
basically a torsion bar. Whenever the belt load
increases beyond the pre-defined limit, some
length of the belt is released due to twisting of the
torsion bar. The activation of the load limiter does
not depend on signal from the ECU.