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A gas generator comprises a tubular housing of a pressure-resistant material and a propellant strand incorporated in the housing. The propellant strand is provided with an envelope surrounding the propellant strand. The envelope is dimensionally stable and substantially rests against the entire oute

A gas generator comprises a tubular housing of a pressure-resistant material and a propellant strand incorporated in the housing. The propellant strand is provided with an envelope surrounding the propellant strand. The envelope is dimensionally stable and substantially rests against the entire outer surface of the propellant strand. The envelope is formed such that in the case of an increase in pressure it expands and rests against the inner surface of the housing.

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1. A gas generator comprising a tubular housing of a pressure-resistant material and defining a chamber, a propellant strand in said housing chamber, said propellant strand having an envelope surrounding said propellant strand, wherein said envelope is dimensionally stable and rests substantially ag

1. A gas generator comprising a tubular housing of a pressure-resistant material and defining a chamber, a propellant strand in said housing chamber, said propellant strand having an envelope surrounding said propellant strand, wherein said envelope is dimensionally stable and rests substantially against the entire outer surface of said propellant strand and has at least a portion spaced from an inner surface of said chamber, and said envelope being formed such that in the case of an increase in pressure said envelope expands and rests against the inner surface of said chamber.2. The gas generator as claimed in claim 1, wherein said tubular housing comprises a plurality of layers.3. The gas generator as claimed in claim 1, wherein said propellant strand is cylindrical.4. The gas generator as claimed in claim 1, wherein on at least part of the outer surface of said propellant strand, said propellant strand is provided with a coating of an ignition mixture.5. The gas generator as claimed in claim 1, wherein said envelope is formed of a metal film.6. The gas generator as claimed in claim 1, wherein said envelope is formed of a plastic film.7. The gas generator as claimed in claim 6, wherein said plastic film is metal-coated.8. The gas generator as claimed in claim 1, wherein the periphery of the envelope extends a first distance from the longitudinal axis of said envelope under ambient conditions, the periphery of said envelope extending a second distance from the longitudinal axis of said envelope upon said envelope expanding, said second distance being greater than said first distance.9. The gas generator as claimed in claim 1, wherein said gas generator is designed to be used in a vehicle occupant restraint system.10. A gas generator comprising a tubular housing of a pressure-resistant material and defining a chamber, a propellant strand in said housing chamber, said propellant strand having an envelope surrounding said propellant strand, wherein said envelope is dimensionally stable and rests substantially against the entire outer surface of said propellant strand, and said envelope being formed such that in the case of an increase in pressure said envelope expands and rests against an inner surface of said chamber, wherein said housing has an inner layer as well as an outer layer of plastic material as well as a middle layer of aluminum connected with said inner and outer layers.11. A gas generator comprising a tubular housing of a pressure-resistant material and defining a chamber, a propellant strand in said housing chamber, said propellant strand having an envelope surrounding said propellant strand, wherein said envelope is dimensionally stable and rests substantially against the entire outer surface of said propellant strand, said envelope being formed such that in the case of an increase in pressure said envelope expands and rests against an inner surface of said chamber, wherein on at least part of the outer surface of said propellant strand, said propellant strand is provided with a coating of an ignition mixture, and wherein said ignition mixture is a mixture of boron and potassium nitrate or aluminum and potassium perchlorate.12. The gas generator as claimed in claim 11, wherein said envelope has a flattened portion, which is at least one time laid around the total circumference of said propellant strand.13. The gas generator as claimed in claim 12, wherein said flattened portion has a single layer to form a double layer envelope around said propellant strand.14. The gas generator as claimed in claim 12, wherein said flattened portion has two layers to form a triple layer envelope around said propellant strand.15. A gas generator comprising a tubular housing of a pressure-resistant material and defining a chamber, a propellant strand in said housing chamber, said propellant strand having an envelope surrounding said propellant strand, wherein said envelope is dimensionally stable and rests substantially against the entire outer surface of said propellant strand, and said envelope being formed such that in the case of an increase in pressure said envelope expands and rests against an inner surface of said chamber, wherein on a longitudinal side of said envelope, said envelope has at least one laterally protruding flattened portion.16. The gas generator as claimed in claim 15, wherein there are provided two substantially opposite and laterally protruding flattened portions.17. The gas generator as claimed in claim 16, wherein said flattened portion is supported on an inner surface of said housing.18. The gas generator as claimed in claim 15, wherein said flattened portions extend substantially over the entire length of said envelope.19. A gas generator comprising a tubular housing of a pressure-resistant material and defining a chamber, a propellant strand in said housing chamber, said propellant strand having an envelope surrounding said propellant strand, wherein said envelope is dimensionally stable and rests substantially against the entire outer surface of said propellant strand, and said envelope being formed such that in the case of an increase in pressure said envelope expands and rests against an inner surface of said chamber, wherein said envelope surrounding said propellant strand is welded and at least partly evacuated.