Pretensionnor of belt

The pre-tensioner (term retained by the French language: Official journal of October 23rd, 1999), is an automobile safety device passive associated with the Safety belt.

Utility

In the event of frontal shock, the body of the occupants is projected forwards. The safety belt retains the body, but it has a certain play: the motorist is never completely plated against the file of the seat, the roller has a light race before being blocked, and the belt will become deformed by elasticity. In the event of shock violate, the head of the occupants before (driver and passenger) can thus strike the wheel, the instrument panel or the central rear view mirror. Moreover, if the car lays out of a inflatable Coussin of safety (airbag) , the head can strike the cushion in full inflation, adding the speed of the fabric to that of the body.

The pre-tensioner of belt is a device which starts in the event of shock and which draws the belt backwards, adjusting for wear in few thousandth seconds and plating the body against the file of the seat. It ensures a better coupling between the occupant and the seat.

In France, the presence of a pre-tensioner is obligatory if there is a inflatable cushion, but there exist some models having a pre-tensioner alone (primarily for the models of the medium of the Années 1990, before the generalization of the airbags ).

Operation

The device of release (Accelerometer, detector of shock) is similar to that of the inflatable cushion.

Traction backwards can be done either by a Ressort, or by a gas cartridge under pressure, or by a pyrotechnic device. This device can be located side of the point of interior anchoring (where the belt is engaged), on the side of the point of external anchoring, or on the level of the roller. The belt can combine several devices of prevoltage in order to optimize its effectiveness.

In general, a device with deformation causes a relaxation of the pressure of the belt after release, reducing the risk of “whiplash” (lesion of the cervical vertebrae by projection of the head forwards compared to the trunk). It can be a question of a metal tear, similar to the system of opening of the metal quills of drink, or of a plastic Déformation in torsion of the axis of the roller.

Risks

The pre-tensioner causes a movement of the body backwards, which goes against the movement forwards. It results an increased risk from it from traumatism of belt (burns of the thorax, fractures coasts and clavicle) and of risk of cervical traumatism. These risks are in general regarded as negligible with respect to the traumatisms incurred in the event of the shock of the head.

If the device did not start, it is likely to start during the operations of Désincarcération; the mobilization of the victim which it causes would worsen its wounds. For this reason, the belt is cut at the beginning of the intervention if the vehicle is on its wheels. In addition, the operations of cutting are likely to damage the device of traction and to release the gas under pressure (explosion) or the spring (which would constitute a wounding projectile).

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