Lotus Service Notes Section WD
Page 15
WD.12 - SEAT BELT PRE-TENSIONERS
WARNING:
• Failure to comply with the instructions, safety standards and operating procedures as described
in this section, may cause vehicle damage and/or personal injury.
• Both driver and passenger seat belt assemblies must be replaced after SRS deployment. Do not
attempt to repair or reuse.
Device Operation
The seat belt pre-tensioners are triggered together with the airbags, and use a pyrotechnic device on each
seat belt reel assembly, to operate a rack and pinion mechanism which applies a tightening force to the belt
reel to remove any slack from the belt. Under normal operation, the rack is fully raised and disengaged from
the pinion, allowing normal spooling of the reel for belt withdrawal and retraction.
When airbag/pre-tensioner triggering conditions apply, the SDM signals ignition of the gas generator, the
pressure from which forces the piston and toothed rack downwards, causing rotation of the pinion gear and a
re-winding of the seat belt webbing. The force sustained by the belt and its user is then controlled by a torsion
bar within the belt reel to limit the deceleration force to which the occupant is subjected during the crash event.
The belt pre-tensioning mechanism is designed to operate only once, such that both belt assemblies
should be renewed after airbag/seat belt pre-tensioner deployment. Activation of the pyrotechnic mechanism
is indicated by the belt reel being locked, and allowing neither extraction nor retraction of the belt.
WARNING: Following an impact in which the pre-tensioning element is activated, the seat belt assem-
bly is rendered inoperable. The car should not be driven until the belt assembly has been renewed.
Electrical connector
Gas generator
Belt reel
Piston
w62
Pinion Rack
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