Electronically commutated motor and stationary assembly therefor with teeth faces having notches and having a skew between the slots and the permanent magnet field to reduce cogging

摘要

An electronically commutated motor has substan­tially constant air gap energy to reduce cogging. A rotat­able assembly has a plurality of permanent magnet elements which rotate about an axis of rotation as the rotatable assembly rotates. The elements are oriented with respect to said axis of rotation to provide a magnetic field with lines of flux along a plane forming a skew angle of s₁ mechanical degrees with respect to the axis of rotation, wherein s is not equal to zero. The elements may be provided with an unmagnetized portion referred to as a phantom skew. A sta­tionary assembly is in magnetic coupling relation with the permanent magnet elements of the rotatable assembly and has t spaced teeth with adjacent teeth defining a slot therebe­tween, wherein t is positive integer. Each tooth has a surface adjacent the rotatable assembly having one or more notches forming a skew angle of s₂ mechanical degrees with the axis of rotation. Each tooth has winding stages adapted for commutation in at least one preselected sequence. The skewed magnetic field, skewed notches and phantom magnetic skews reduce cogging between the rotatable assembly and the stationary assembly as the rotatable assembly rotates while maintaining a back EMF waveform having a maximized flat top width.