Electromechanical power steering system, method for determining an absolute angle of rotation, and method for calibrating a measuring device for measuring an absolute angle of rotation

A method for calibrating a measurement device for measuring a second absolute angle of rotation Xt of a rotational position of a rotatably supported steering shaft, wherein rotation of a rotor of an electric motor with a gearing with a gearing transmission factor K for power assistance is coupled into rotation of the rotatably supported steering shaft, the method comprising:

• powering the electric motor to shift the rotational position of the rotatably supported steering shaft in a first direction;
• continuously measuring a rotor angle Yt of a rotational position of the rotor with a rotor position sensor with a detection interval;
• continuously measuring an angle of rotation Xt1 of an absolute rotational position of the rotatably supported steering shaft with a steering angle sensor unit, wherein the angle of rotation Xt1 is detected with a gearing with a transmission factor UF at the detection interval;
• saving a measurement value pair from a rotor angle Xtlia, Yia if the angle of rotation Xt1 changes relative to a value measured at a directly-preceding detection point;
• powering the electric motor to shift the rotational position of the rotatably supported steering shaft in a second direction;
• continuously measuring the rotor angle Yt of the rotational position of the rotor by way of the rotor position sensor at the detection interval;
• continuously measuring the angle of rotation Xt1 of the absolute rotational position of the rotatably supported steering shaft with the steering angle sensor unit, wherein the angle of rotation Xt1 is detected with the gearing with the transmission factor UF;
• saving a measurement value pair from the rotor angle Xtlib, Yib if the angle of rotation Xt1 changes relative to a value measured at a directly-preceding detection point;
• forming a measurement tuple comprising an absolute angle of rotation of the rotatably supported steering shaft Xk0 as an average of both measured angles of rotation Xt1a and Xt1b, and a rotor angle Yk0 as an average of both measured rotor angles Ya and Yb;
• and
• saving the measurement tuple Xk0, Yk0 on a storage means and saving a value of zero as a current revolution number value N into a memory unit.