Pyrotechnical jacks

Claim 1

A pyrotechnical jack for stretching the webbing of a safety belt or harness in a motor vehicle with one end of the jack being adapted to be anchored to an element of a motor vehicle, said jack comprising: a cylinder, a piston slidably fitted in said cylinder, a hollow head connected to one end of said cylinder, a traction rod rigidly connected to said piston, an explosive charge, an explosion chamber, means defining a peripheral groove in said piston, means for locking the piston at the end of its operative stroke, said locking means comprising: an expansible split ring in said groove, and a shoulder formed by the end of said cylinder projecting from the inner wall of said hollow head, said shoulder being adapted to retain the piston at the end of its operative stroke by the expansion of the then expanded split ring thereover, means defining a part-spherical socket in the inner surface of the end of said hollow head most remote from said cylinder, a ball joint positioned in said socket for the swivel mounting of the jack, said ball joint comprising a shock absorbing element adapted to co-act with the inoperative face of the piston at the end of the operative stroke thereof, and an element rigidly connected to said ball joint for anchoring the jack to an element of a motor vehicle.