US Patent 7185576 Hydraulic servo-steering valve with steering moment superimposition

A servo-steering valve for a hydraulic servo-steering arrangement has an input shaft, an output shaft, a torsion rod which biases the input shaft and the output shaft relative to each other into a central position, and a valve which consists of a valve sleeve and a valve shaft which with a rotation of the input shaft relative to the output shaft are rotated relative to each other. An adjustment drive is provided, which can rotate one component of the servo-steering valve with respect to another, so that a superimposition value is superimposed on an input value which is given through the actuation of the input shaft.