The invention relates to a belt retractor.
A belt retractor is known, for example, from European Laid-Open Publication EP 1 219 510 A2. This belt retractor serves for winding up and unwinding a safety belt and has as a force transmission element a connecting pin in the form of a shear pin which is held by a first part of the belt retractor and which is connected to a second part of the belt retractor. In accident-free normal operation, the shear pin connects the locking base and the belt spindle to one another, so that these cannot execute any movement or rotation in relation to one another. The shear pin is held in a recess of the belt spindle and projects into the locking flange, so that it connects the belt spindle and locking flange to one another. In the event of an accident at high speed, a very high shear force acts upon the shear pin, to be precise when the vehicle occupant dives into the safety belt, so that the shear pin shears off and the connection between the locking base and the belt spindle is broken. The shearing off may subsequently result in a relative rotation between the belt spindle and the locking base, so that belt force limitation, for example by means of a torsion bar, becomes possible. As long as the shear pin is not sheared off, the function of any torsion bar present continues to be ineffective.
Furthermore, German Laid-Open Publication DE 197 47 461 A1 discloses a belt retractor in which two torsion bars are used for belt force limitation.
German Patent Specification DE 196 09 524 C2 describes a belt retractor with a torsion bar, the function of which is activated by means of a pawl mechanism as a function of the operating state of a tautener drive. In the initial state, the torsion bar is cut out, to be precise since a force limiter pawl is positioned into a first toothed ring and the belt spindle is connected to a toothing of a shaft tube via the force limiter pawl and the first toothed ring. The torsion bar is cut in only when, after a cut-in of the tautener drive, a tautener pawl engages into an internal toothing of a second toothed ring and a relative movement subsequently occurs between the second toothed ring and a slotted ring. As a result of the relative movement of the slotted ring, the force limiter pawl is pivoted away, so that the latter comes out of engagement with the first toothed ring and the belt spindle can subsequently rotate freely under the torsion of the torsion bar.