Hybrid gas generator with a perforating stem

The gas generator for a vehicle air bag comprises an upper (51) and lower (50) tube which are connected to each other, one of the tubes having a partition (26) fixed to the end which is connected. The lower tube contains a detonator and gas generating pyrotechnic device (4) and a gas outlet (25), while the upper acts as a gas reservoir. The partition has a central, S-shaped orifice (27) with a lid (28) over it. A support component (30) positioned between the gas generator and partition, without contacting it or the gas outlet. This contains a piston (31) with an S-shaped column (32) whose cross-section is less than that of the orifice. The base (41)of the column is also S-shaped, but has a cross-section greater than that of the orifice. It has peripheral grooves (45) which prevent the base from contacting the central orifice.