Abstract: Three magnetically cooperating parts are movable relative to one another, one part being provided for connection to a drive shaft, one part being provided for connection to an output shaft, and one part being provided as a stationary part. A first part surrounds a second part, these parts having permanent magnets which alternately exhibit north poles and south poles along the circumference. The third part comprises a yoke surrounding the first part, which yoke serves as a magnetic return element, and which has magnetically conductive teeth at the inner side of the yoke.