Cogging torque

Cogging torque ( cogging torque engl. ) refers to a phenomenon of electric motors, the permanent magnets in the stator and a grooved anchor of electrical sheets or vice versa have a grooved stator and an armature with permanent magnets. In engines that are grooved in both the stator and the armature, when operational also on cogging torques. By changing the air gap, when moving from the anchor tooth on armature slots with respect to the permanent magnet, the magnetic resistance, and thus the force on the armature varies. The effect is undesirable in most electrical machines, but is deliberately exploited in reluctance motors. Cogging torques lead to fluctuating torques ( not running smoothly especially at low speeds). The rotor stops only in certain positions after switching off the machine. Motors with ironless armature exhibit no cogging.