Determining a force acting on a steering gear power

It should be a way for determining a via a steering rod to a steering gear of a steering device in a vehicle from the outside acting force (Fz) by means of an estimator (21) provided, wherein the steering device is assigned a motor for generating a steering torque. This is achieved in that the externally acting force (Fz) in response to an effective motor torque (tor_RAeff) is estimated, wherein the effective motor torque (tor_RAeff) is determined in dependence on an engine torque and an efficiency and the efficiency as a function of the estimated force (Fz) is determined.