Device for tightening a seatbelt

A device for tightening a seatbelt comprising:

• a piston-like drive member arranged in a guide tube,
• a drive means for producing a propellant gas which drives the drive member by expanding in pressure chambers adjoin the drive member, and a movement transmitting system connecting the drive member and the seatbelt to be tightened, the drive member is a step piston which is provided with a first pressure chamber and a second pressure chamber, in that a propellant gas discharge system for supplying the propellant gas into the pressure chambers in the starting position of the step piston adjoins the latter in such a way that the first and second pressure chambers are separated from one another with a discharge orifice positioned between the first and second pressure chambers, and the propellant gas initially flows into the first pressure chamber, said propellant gas discharge system comprises a tubular discharge portion that extends in an axial longitudinal direction into a recess, forming the first pressure chamber, in the step piston and is sealed at its periphery against an internal face of the recess, said recess comprises an internal region with a cross section which is constant over the axial length of the first path of movement and an adjoining outer region with an enlarged cross section, the enlarged cross section forming the discharge orifice from the first to the second pressure chamber;
• and
• the step piston which is set into motion by the propellant gas acting in the first pressure chamber clears the discharge orifice into the second pressure chamber after covering a first distance so that the propellant gas flowing into the second pressure chamber and acting therein to additionally drive the step piston.

A device for tightening a seatbelt comprising:

• a piston-like drive member arranged in a guide tube,
• a drive means for producing a propellant gas which drives the drive member by expanding in pressure chambers adjoining the drive member, and a movement transmitting system connecting the drive member and the seatbelt to be tightened,
• the drive member is a step piston which is provided with a first pressure chamber and a second pressure chamber, in that a propellant gas discharge system for supplying the propellant gas into the pressure chambers in the starting position of the step piston adjoins the latter in such a way that the first and second pressure chambers are separated from one another with a discharge orifice positioned between the first and second pressure chambers and the propellant gas initially flows into the first pressure chamber, said propellant gas discharge system comprises a tubular discharge portion which extends in an axial longitudinal direction into a recess, forming the first pressure chamber in the step piston and is sealed at its periphery against an internal face of the recess, and the second pressure chamber is defined by a piston end face;
• and
• the step piston which is set into motion by the propellant gas acting in the first pressure chamber clears the discharge orifice into the second pressure chamber after covering a first distance so that the propellant gas flowing into the second pressure chamber and acting therein to additionally drive the step piston.