US Patent 8235166 Superimposition device for vehicle steering system

A rotational speed superimposition device for a vehicle steering system is proposed, having an output shaft (2) which is aligned towards the input shaft (1) in its axial direction (22), having a first carrier arrangement (6) which rotatably positions the output shaft (2) and the input shaft (1) at least partly supported, having an auxiliary drive (5, 10) with a rotor (5) which is connected in an operative, torque-proof manner to a first gear element (4) of a superimposition gear unit (7), and having a second carrier arrangement (11) which is arranged in a fixed manner on the chassis and which holds the auxiliary drive (5, 10) and supports the rotor (5) so that it can rotate, wherein the rotor (5) of the auxiliary drive (5, 10) coaxially surrounds the output shaft (2) and/or the input shaft (1), and wherein the superimposition gear unit (7) transmits the rotational speed of the rotor (5) to the rotational speed of the output shaft (2) at a rotational speed ratio that is less than 1. Improved noise damping is achieved because an intermediate piece (3) is arranged between the rotor (5) and the first gear element (4) in such a way that the rotor (5) is connected in an operative manner to the first gear element (4) in the rotational direction only by interconnecting the intermediate piece (3).