Superimposed steering system comprising a mechanical return level

Rotational speed superposition device for a motor vehicle steering system comprising:

• an output drive shaft (1) oriented with respect to an input drive shaft (2) in an axial direction of the output drive shaft, a fixed carrier arrangement (4) which rotatably supports the output drive shaft (1) and the input drive shaft (2) so that the output drive shaft and the input drive shaft are at least partially bearing supported, an auxiliary drive (5, 6, 7) with a rotor (7), connected torsion-tight with a first gearing element (19, 25, 27) and an adjustable locking device (10) for a selectable torsion-tight coupling between the output drive shaft (1) and the input drive shaft (2), wherein the carrier arrangement (4) is stationary with respect to a body of the motor vehicle, the rotor of the auxiliary drive (5, 6, 7) being coaxial to at least one of the output drive shaft (1) and the input drive shaft (2), the first gearing element (19, 25, 27) having a rotational speed transmission ratio of less than 1 and transmitting a rotational speed of the rotor (7) onto rotational speed of the output drive shaft (1), and the rotor (7) being connected torsion-tight with a ferromagnetic or permanent magnetic first contact element (8) concentrically encompassing the axial direction of the output drive shaft (1) and input drive shaft (2), wherein the selectable torsion-tight coupling between output drive shaft (1) and input drive shaft (2) is attained through a frictional locking of the first contact element (8) with a second contact element (9) connected torsion-tight with the carrier arrangement (4) and a press-on force required for the friction force is generated through a magnetic force and wherein at least one of the two contact elements (8, 9) is displaceable in the axial direction, the locking device (10) being a separate compact unit arranged in a separate housing part (17) and being separate from the first gear element (19, 25, 27) and the auxiliary actuator drive (5, 6, 7), the auxiliary drive (5, 6, 7) being between the first gear element (19, 25, 27) and the locking device (10) with respect to the input drive shaft (2), and a coupling element (15) between the rotor (7) and the first contact element (8) for non-rotatable coupling between the rotor (7) and the first contact element (8).