Belt retractor

1. A belt retractor ( 10 ) for a seat belt comprising:

a belt reel ( 20 ) for winding up and unwinding the seat belt, and

a torsion bar ( 30 ) which is arranged outside the belt reel ( 20 ) and is connected at one bar end ( 32 ) to a switchable fixing device ( 50 ), the switchable fixing device ( 50 ), in one state, keeping the bar end ( 32 ) rotationally fixed and, in another state, permitting rotation of the bar end ( 32 ), wherein

the switchable fixing device ( 50 ) has a housing ( 60 ) and a displaceable piston ( 80 ) which, with a piston portion, in a locking position, can secure the bar end ( 32 ) against rotation and, in a release position displaced in relation to the locking position, releases the bar end ( 32 ),

in an outer piston portion located outside the housing ( 60 ) the piston ( 80 ) has a slot-like depression or a slot-like hole ( 82 ) in which—in the locking position of the piston ( 80 )—a locking pin ( 91 ) engages, the locking pin blocking or at least limiting an axial displacement of the piston ( 80 ) in the direction of the release position, and

the locking pin ( 91 ) is of a size that when the gas generator ( 70 ) is activated, the locking pin is sheared off by the piston ( 80 ).

2. The belt retractor ( 10 ) as claimed in claim 1 , wherein

the fixing device ( 50 ) has a gas generator ( 70 ) which, when activated, generates gas and, by means of the gas pressure, moves the piston ( 80 ) in an axial manner from the locking position into the release position.

3. The belt retractor ( 10 ) as claimed in claim 1 , wherein

the switchable fixing device ( 50 ) housing ( 60 ) has an internal gas duct which connects two housing openings ( 62 , 63 ) in the housing ( 60 ) to each other and is rectilinear in portions,

the entire piston ( 80 ) or at least an inner piston portion of the piston ( 80 ) is guided axially in the rectilinear portion of the gas duct, and

after the gas generator ( 70 ) is activated, the gas of the gas generator ( 70 ) is conducted in the direction of the piston ( 80 ) and the piston ( 80 ) is moved exclusively in an axial manner in the rectilinear portion of the gas duct.

4. The belt retractor ( 10 ) as claimed in claim 1 , wherein

the locking pin ( 91 ) is integrally formed in a positioning element ( 90 ) which resiliently fixes the position of the axis of rotation of the torsion bar ( 30 ) in the region of the bar end ( 32 ).

5. The belt retractor ( 10 ) as claimed in claim 1 , wherein

a seal ( 100 ) which seals the piston ( 80 ) in relation to the housing ( 60 ) is fitted on that piston side of the piston ( 80 ) which faces the gas generator ( 70 ).

6. The belt retractor ( 10 ) as claimed in claim 1 , wherein

the bar end ( 32 ) has an interlocking connection portion ( 86 ) in which a complementary interlocking connection portion ( 81 ) of the piston ( 80 ) engages in the locking position and from which the complementary interlocking connection portion of the piston ( 80 ) is separated in the release position.

7. The belt retractor ( 10 ) as claimed in claim 1 , wherein

the piston ( 80 ) is in at least two parts and has at least two parts connected to each other forming one piston basic body ( 500 ) and at least one insert part ( 600 ).

8. The belt retractor ( 10 ) as claimed in claim 7 , wherein

the piston basic body ( 500 ) is composed of plastic and the insert part ( 600 ) of metal.

9. The belt retractor ( 10 ) as claimed in claim 7 , wherein

a seal ( 510 ), in particular a plastics or rubber seal, is integrally formed in one piece by injection mold on that piston end of the piston basic body ( 500 ) which faces the gas generator ( 70 ).

10. A belt retractor ( 10 ) for a seat belt comprising:

a belt reel ( 20 ) for winding up and unwinding the seat belt, and

a torsion bar ( 30 ) which is arranged outside the belt reel ( 20 ) and is connected at one bar end ( 32 ) to a switchable fixing device ( 50 ), the switchable fixing device ( 50 ), in one state, keeping the bar end ( 32 ) rotationally fixed and, in another state, permitting rotation of the bar end ( 32 ), wherein

the switchable fixing device ( 50 ) has a displaceable piston ( 80 ) which, with a piston portion, in a locking position, can secure the bar end ( 32 ) against rotation and, in a release position displaced in relation to the locking position, releases the bar end ( 32 ), and

the piston ( 80 ) has, between the side facing the gas generator ( 70 ) and the side facing away from the gas generator ( 70 ), in the region of the inner piston portion of the piston ( 80 ), a depression ( 86 ) in which, after the release position of the piston ( 80 ) is reached, a spring element ( 61 ) engages such that the return movement of the piston ( 80 ) from the release position into the locking position is prevented.

11. The belt retractor ( 10 ) as claimed in claim 10 , wherein

the depression ( 86 ) is ramp-shaped and has a steep and a gentle flank ( 86 a , 86 b ),

the gentle flank ( 86 a ) lying closer to the gas generator ( 70 ) than the steep flank ( 86 b ).

12. A belt retractor ( 10 ) for a seat belt comprising:

a belt reel ( 20 ) for winding up and unwinding the seat belt, and

a torsion bar ( 30 ) which is arranged outside the belt reel ( 20 ) and is connected at one bar end ( 32 ) to a switchable fixing device ( 50 ), the switchable fixing device ( 50 ), in one state, keeping the bar end ( 32 ) rotationally fixed and, in another state, permitting rotation of the bar end ( 32 ), wherein

the switchable fixing device ( 50 ) has a displaceable piston ( 80 ) which, with a piston portion, in a locking position, can secure the bar end ( 32 ) against rotation and, in a release position displaced in relation to the locking position, releases the bar end ( 32 ), and

a spring element ( 61 ) is attached or is integrally formed in one piece to or on or in the housing ( 60 ), said spring element blocking or at least impeding a displacement of the piston ( 80 ) in the axial direction from the locking position into the release position before the gas generator ( 70 ) is activated.

13. A belt retractor ( 10 ) for a seat belt comprising

a belt reel ( 20 ) for winding up and unwinding the seat belt, and

a torsion bar ( 30 ) which is arranged outside the belt reel ( 20 ) and is connected at one bar end ( 32 ) to a switchable fixing device ( 50 ), the switchable fixing device ( 50 ), in one state, keeping the bar end ( 32 ) rotationally fixed and, in another state, permitting rotation of the bar end ( 32 ), wherein

the switchable fixing device ( 50 ) has a housing ( 60 ) and a displaceable piston ( 80 ) which, with a piston portion, in a locking position, can secure the bar end ( 32 ) against rotation and, in a release position displaced in relation to the locking position, releases the bar end ( 32 ),

the housing ( 60 ) has a housing opening ( 62 ) through which, when the gas generator ( 70 ) is activated, the piston ( 80 ) or at least the inner piston portion is at least partially pushed axially out of the housing ( 60 ), and

a deformable edge portion of the housing ( 60 ) is arranged in the region of the housing opening ( 62 ), said edge portion projecting into the housing opening, operating as a spring element ( 61 ) and blocking or impeding a displacement of the piston ( 80 ) in the axial direction from the locking position into the release position before the gas generator ( 70 ) is activated and, after movement of the piston ( 80 ), preventing a return movement.

14. A belt retractor ( 10 ) for a seat belt comprising:

a belt reel ( 20 ) for winding up and unwinding the seat belt, and

a torsion bar ( 30 ) which is arranged outside the belt reel ( 20 ) and is connected at one bar end ( 32 ) to a switchable fixing device ( 50 ), the switchable fixing device ( 50 ), in one state, keeping the bar end ( 32 ) rotationally fixed and, in another state, permitting rotation of the bar end ( 32 ), wherein

the switchable fixing device ( 50 ) has a displaceable piston ( 80 ) which, with a piston portion, in a locking position, can secure the bar end ( 32 ) against rotation and, in a release position displaced in relation to the locking position, releases the bar end ( 32 ),

the piston ( 80 ) has a snap hook ( 400 ) which, in the position of the piston ( 80 ) blocking the torsion bar ( 30 ) such that before the gas generator ( 70 ) is triggered, is latched in a housing hole ( 410 ) in the housing ( 60 ) and,

after the gas generator ( 70 ) is triggered, prevents the piston ( 80 ) from moving back from the position of the piston ( 80 ) releasing the torsion bar ( 30 ) into the blocking position.