Seat Belt Systems: Description and Operation

Each front seat belt has an electrically fired pyrotechnic operated pre-tensioning retractor unit installed at the base of the 'B' post. In the event of severe frontal impact, these provide additional occupant protection by removing any excess slack from the seat belts.






Seat belt pre-tensioning activates when a frontal impact of sufficient force occurs within 30 degrees of vehicle center line. Under such an impact, an impact sensing/control module installed on the transmission tunnel generates a 12 V firing signal to each pre-tensioner assembly. Receipt of this signal by each pretensioner directly triggers a pyrotechnic igniter unit. The resulting detonation propels a train of steel balls through a tube to a ball trap where they are directed onto an impeller mounted on the reel spindle. Rapid rotation of the impeller simultaneously rotates the seat belt reel, preventing forward movement of the occupant. When a pre-tensioner unit has been activated, the seat belt will lock and cannot be retracted or pulled from the reel.

The pre-tensioners are non-serviceable units and dismantling must not be attempted, as unactivated pre-tensioning components contain a solid, flammable material. If a pre-tensioning unit is inadvertently damaged and ingestion or inhalation of the propellant occurs, first aid must be applied and medical advice sought.

The pre-tensioner reel assemblies provide standard emergency locking retraction (ELR) under rapid vehicle deceleration, and incorporate automatic locking retraction (ALR), enabling child seats to be fully restrained by the seat belt.