High performance tightener

Self-blocking seat belt comprises a housing (10), a blocking device (23) for the seat belt shaft (12), and a tightening device acting on the shaft and consisting of a drive wheel (13) placed in a rotating position by a drive device (51). The drive wheel can be connected to the seat belt shaft via the blocking device. Preferred Features: The drive wheel can be directly connected to the seat belt shaft via the blocking device. The blocking device has a blade arranged on the blocking device and activated by the drive wheel to couple the wheel with the blocking device. The drive wheel is fixed on the housing in its resting position.