Abstract: A seatbelt tensioner for a seat belt retractor, having a pipe (1) with a tensioner drive wheel, a gas generator (10), a piston (3), and at least one mass body (4). The mass body (4) is drivable by gas from the gas generator (10) acting on the piston (3) between the gas generator (10) and a mass body (4). The mass body drives the tensioner drive wheel. The pipe (1) has a receiving section (5) with a first inner diameter (2), in which the piston (3) in its initial state is arranged with an initial-state outer diameter (8). The pipe (1) has a guide section (6) which adjoins the receiving section (5) and which has a second inner diameter (7). The second inner diameter (7) is smaller than the first inner diameter (2) and smaller than the initial-state outer diameter (8) of the piston (3).

Abstract: A seatbelt tensioner for a seat belt retractor, having a pipe (1) with a tensioner drive wheel. A pyrotechnical gas generator (10), a piston (3), and at least one mass body (4) in the pipe (1), wherein the at least one mass body (4) is drivable by the pressure generable by the gas generator (10) and acting on the piston (3) between the gas generator (10) and a mass body (4), and which can be made to mesh in a force-transmitting manner with the tensioner drive wheel, thus driving a belt shaft of the seat belt retractor in a belt tensioning direction. The pipe (1) has a receiving section (5) with a first inner diameter (2), in which the piston (3) in its initial state is arranged with an initial-state outer diameter (8) prior to the ignition of the gas generator (10). The pipe (1) has a guide section (6) which adjoins the receiving section (5) and which has a second inner diameter (7).