Patent ID: 6837824

Claim:
A final control element for superimposed steering engagement in a vehicle steering system, comprising, a superposition gear ( 12 ) having first and second input shafts ( 13 , 14 ) and an output shaft ( 15 ) coaxial with the first input shaft ( 13 ), an electric motor ( 20 ) coupled to the second input shaft ( 14 ) for varying the superposition ratio between a change in the rotational angle at the first input shaft ( 13 ) and the change in the rotational angle at the output shaft as a function of predetermined parameters, the superposition gear ( 12 ) having a two-stage, modified planetary gear ( 25 ), with a planet carrier ( 30 ), at least one stepped planet ( 31 ), the at least one stepped planet comprising two axially aligned planet wheels ( 311 , 312 ) connected to one another in a manner fixed against relative rotation and held rotatably on the planet carrier ( 30 ), and two sun wheels ( 32 , 33 ); one planet wheel ( 311 ) of the at least one stepped planet ( 31 ) meshing with one sun wheel ( 32 ), and the other planet wheel ( 312 ) of the stepped planet ( 31 ) meshing with the other sun wheel ( 33 ); the first input shaft ( 13 ) being connected to one sun wheel ( 32 ), and the output shaft ( 15 ) being connected to the other sun wheel ( 33 ), in each case in a manner fixed against relative rotation; the planet carrier ( 30 ) being drivable via the second input shaft ( 14 ), a self-locking worm gear ( 26 ) disposed between the second input shaft ( 14 ) and the planet carrier ( 30 ), the worm gear ( 26 ) including a worm ( 27 ) connected to the second input shaft ( 14 ) in a manner fixed against relative rotation and a worm wheel ( 28 ) connected to the planet carrier ( 30 ) in a manner fixed against relative rotation; and a coaxial, smaller worm wheel ( 42 ) coupled to the worm wheel ( 28 ) via an annular spring ( 43 ), in such a way that the tooth flanks of the two worm wheels ( 28 , 42 ) rest on both sides of the tooth flanks of the worm ( 27 ).