Method and device for reducing cogging in an electric motor

The method reduces the reluctance moment of an electric motor known as cogging. The motor has a stator provided with groove openings and a permanent magnetic rotor. The latter has a magnetic flux density distribution, seen in the circumferential direction, with a region of essentially constant magnetic flux density in the middle of a pole. At least one additional reluctance moment is generated in the motor. This additional moment is superimposed on the first mentioned reluctance moment to reduce and/or eliminate the cogging effect. In the electronic commutator motor each pole boundary between adjacent rotor poles is divided into a number of parallel sections. The space between these sections is selected such that the rotor part with sections of a first type cooperates with the stator causing a first reluctance motor in counter-phase to a second moment.