Mechnical front seat belt pre-tensioner

MECHNICAL FRONT SEAT BELT PRE-TENSIONER

Pre-tensioners are safety devices which have the task of improving the efficiency of conventional seat belts.

In effect, they act on the seat belt webbing, in the case of an impact, further tensioning the belt, ensuring that the passenger stays firmly put in their seat.

This device, together with AIR-BAGS, considerably reduces the danger of injury to passengers in the case of serious head-on collisions.

The operation of the device is based on a suitably calibrated mechanical deceleration sensor which detects the impact condition; the sensor is made up of a mass which moves in the direction in which the vehicle is travelling, releasing a pre-tensioned spring, connected to a bowden cable which tensions the seat belt webbing.

Composition

The seat belt pre-tensioning system is an assembly which is fitted underneath the seat and is made up of the following elements:

• a sensor (1) which is capable of detecting the degree of deceleration of the vehicle;
• a power unit (2) which houses the pre-loaded spring;
• a bowden cable which has the task of transmitting the movement and the force from the power unit to the webbing locking system;
• a locking system (4) which allows the locking of the webbing (5) once the spring has been activated, preventing the webbing from being released on account of the counter-thrust of the actual spring;
• the webbing (5) which is capable of retracting up to a maximum of 8 cm once the system has been activated.

1. Deceleration sensor
2. Power unit
3. Bowden cable
4. Locking system
5. Seat belt webbing
6. Safety clip