Front seat belt pre-tensioning devices

1. Prise and remove the left-hand trim.

1. Disconnect the electrical connection of the passenger side Air Bag module.
   2. Slacken the fastening screws and remove the passenger side Air Bag module.

FRONT SEAT BELT PRE-TENSIONING DEVICES

DESCRIPTION

The seat belt pre-tensioners are devices which are integrated in the rewinding mechanisms and which, during an impact, take up the slack caused by the weight of the wearer so that he or she is pressed firmly against the back of the seat. A second device makes it possible to activate the pretensioner only when the seat belt is fastened. Knocks (other than those caused by irregularities in the road surface of bumping over kerb stones etc.), vibration or heat applied to the pre-tensioners may cause their activation.

Seat belt pre-tensioners are pyrotechnical devices which are commanded mechanically to intervene during impact, to take up the slack in the seat belt caused by the pressure of the wearer's body.

The seat belts must adhere as closely as possible to the wearer in roder to gradually absorb the kinetic energy to which he is subject during impact. The main reasons for which the seat belts may not always press the wearer towards the seat back during an impact are mainly due to:

• a delay in the intervention of the inertial locking device;
• stretching of the fibers in the seat belt;
• spooling effect;
• clothes of a certain thickness which create an excessive space between the belt and the thorax.

Combining all these causes it can easily be seen that the seat belt may only become effective as a restraining device after the wearer has moved some distance forwards.

PRINCIPLES OF OPERATION

The operation of these devices is based on the inertia force which arises during deceleration on the vehicle in relation to the mass of the cylinder-piston assembly. Lever A is hinged onto the piston-cylinder assembly on pin F. When in the rest position this lever is subject to the tension exercised by spring I and locked by tooth G. When, following impact, the force of inertial acting on the mass of the assembly A overcomes force I, the assembly rotates slightly and frees the lever E from tooth G.