Patent ID: 6998813

Claim:
A device to generate an rpm-dependent signal for a three-phase electric motor having a plurality of magnet elements ( 64 , 66 ) of alternating polarity which are arranged and distributed around the circumference of a shaft ( 16 ), and a plurality of coils ( 40 ), parallel to the axis, which are arranged on a supporting member ( 38 ) at an axial distance to the magnet elements ( 64 , 66 ), whereby the magnet elements ( 64 , 66 ) and the coils ( 40 ) are arranged relative to each other spatially and can be rotated in relation to each other with the rotation of the shaft ( 16 ) in order to induce an rpm-dependent signal in the coils ( 40 ), and with a circuit arrangement ( 70 , 72 ) which receives the signals induced in the coils ( 40 ) and superimposes a DC voltage on the signals in order to generate voltage-displaced signals, an analysis and control device ( 78 ) to analyze the amplitude of the voltage-displaced, rpm-dependent signals, and a rotational position sensor ( 62 ) which registers the rotational position of the shaft ( 16 ), whereby the analysis and control device ( 78 ), depending on the output signals of the rotational position sensor, decides which half-wave of the rpm-dependent signal of which coil ( 40 ) is to be analyzed to determine the speed, whereby the rotational position sensor includes four Hall sensors (HA, HB, HC, HD), whereby two (HD, HC) of the Hall sensors are arranged phase-shifted by 90° electric in order to generate a determining signal in respect of the half-wave to be analyzed, and three (HA, HB, HC) of the Hall sensors are arranged phase-shifted by 120° electric in order to determine the rotational position of the shaft ( 16 ).