Abstract: A rotary tightening device for a safety belt has a belt retractor including a housing and a belt take-up shaft rotatably supported in the housing. The belt-take-up shaft has one end of the safety belt connected thereto. Upon triggering of the rotary tightening device, the belt take-up shaft is rotated in a belt take-up direction of the safety belt. A drive wheel is connected to the shaft. The housing has a channel extending in a plane parallel to a radial plane of the drive wheel and extending at least partially about a circumference of the drive wheel. Mass bodies are positioned loosely adjacent to one another in the channel. The mass bodies, when accelerated, act on the drive wheel for driving it. The drive wheel has at the circumference a gearing in which the mass bodies are received for driving the drive wheel. A spacing of the gearing is substantially identical to a spacing between the mass bodies.

Abstract: A rotational tensioning device for a safety belt of a motor vehicle has a reeling device with reeling shaft and a drive wheel connected to the reeling shaft. The drive wheel has a circumference with semi-spherical recesses. A channel, having a first and a second end, is positioned in a plane parallel to the drive wheel. It extends at least over a portion of the circumference of the drive wheel. Spherical mass bodies are contained in the channel. A gas generator is connected to the first end of the channel, wherein, upon activation of the gas generator, a gas is released into the channel for accelerating the spherical mass bodies in the channel and driving the spherical mass bodies through the channel into the semi-spherical recesses to thereby drive the drive wheel and the reeling shaft in a direction of winding of the safety belt. A drive piston, for driving the spherical mass bodies, consists of two of the spherical mass bodies fixedly connected to one another to form a twin ball.