Electronically commutated motor having skewed magnetics

An electronically commutated motor having substantially constant air gap energy to reduce cogging comprising:

• a rotatable assembly having a plurality of permanent magnet elements which rotate about an axis of rotation as the rotatable assembly rotates;
• and
• a stationary assembly in magnetic coupling relation with the permanent magnet elements of said rotatable assembly and having t spaced teeth with adjacent teeth defining a slot therebetween, each said tooth having a surface adjacent said rotatable assembly with n elongate notches therein of length L, transverse width W and radial depth D, each said notch being along a helical path which traverses a skew angle of substantially 360/2(n+1)t mechanical degrees with respect to the axis of rotation, said stationary assembly having a winding stage on each tooth adapted for commutation in at least one preselected sequence, wherein n is a positive even integer, and t is a positive integer and the skew angle is not equal to zero;
• and
• means for sensing the back electromotive force (back EMF) induced in each of the winding stages by the permanent magnet elements and for commutating the winding stages in response thereto to rotate the rotatable assembly.

An electronically commutated motor having substantially constant air gap energy to reduce cogging comprising:

• a rotatable assembly having a plurality of permanent magnet elements which rotate about an axis of rotation as the rotatable assembly rotates, said elements being oriented with respect to said axis of rotation to provide said magnetic field with lines of flux along a plane forming a skew angle of substantially s.sub.1 mechanical degrees with the axis of rotation;
• and
• a stationary assembly in magnetic coupling relation with the permanent magnet elements of said rotatable assembly and having t spaced teeth with adjacent teeth defining a slot therebetween, each said tooth having a surface adjacent said rotatable assembly with n elongate notches therein along the axis of length L, transverse width W and radial depth D forming a skew angle of S.sub.2 mechanical degrees, said stationary assembly having a winding stage on each tooth adapted for commutation in at least one preselected sequence, wherein n is a positive even integer, t is a positive integer, and a total skew angle s.sub.t w is equal to s.sub.1 plus s.sub.2 substantially equals 360/4(n+1)t;
• and
• means for sensing the back electromotive force (back EMF) induced in each of the winding stages by the permanent magnet elements and for commutating the winding stages in response thereto to rotate the rotatable assembly whereby the notches and the skewed magnetic field reduce cogging of the electronically commutated motor.

A stationary assembly for reducing cogging in an electronically commutated motor having a rotatable assembly having a plurality of permanent magnet elements adapted to rotate about an axis of rotation and having a magnetic field in magnetic coupling relation with said stationary assembly, said motor further having means for sensing the back electromotive force (back EMF) induced in the stationary assembly by the permanent magnet elements and for commutating the stationary assembly in response thereto to rotate the rotatable assembly;

• said stationary assembly comprising:
• a stator core having t spaced teeth with adjacent teeth defining a slot therebetween, each tooth having a surface adjacent said rotatable assembly with n elongate notches therein of length L, transverse width W and radial depth D, each said notch being along a helical path which traverses a skew angle of s mechanical degrees with respect to the axis of rotation, where n and t are positive integers and s is not equal to zero;
• and
• a plurality of distributed winding stages on the teeth adapted for commutation in at least one preselected sequence whereby the notches reduce cogging between the rotatable assembly and the stationary assembly as the rotatable assembly rotates.

A rotatable assembly for reducing cogging in an electronically commutated motor having a stationary assembly having t spaced teeth with adjacent teeth defining a slot therebetween, each tooth having a surface adjacent said rotatable assembly, and having winding stages on the teeth adapted for commutation in at least one preselected sequence, where n and t are positive integers, the motor also having means for sensing the back electromotive force (back EMF) induced in each of the winding stages by the rotatable assembly and for commutating the winding stages in response thereto to rotate the rotatable assembly;

• said rotatable assembly comprising:
• an armature having a plurality of permanent magnet elements adapted to rotate about an axis of rotation so that said elements are adjacent the surface of each tooth and a magnetic field of said elements is in magnetic coupling relation with said stationary assembly, said elements being oriented to provide said magnetic field with lines of flux along a plane forming an angle of s mechanical degrees with the axis of rotation, each said permanent magnet element being radially polarized and including an axially elongate, substantially unmagnetized portion forming a skew angle of s.sub.1 mechanical degrees with respect to the axis of rotation, wherein s is not equal to zero whereby the notches and the skewed magnetic field reduce cogging of an electronically commutated motor including said rotatable assembly.

An electronically commutated motor having substantially constant air gap energy to reduce cogging comprising:

• a rotatable assembly having a plurality of permanent magnet elements which rotate about an axis of rotation as the rotatable assembly rotates;
• and
• a stationary assembly in magnetic coupling relation with the permanent magnet elements of said rotatable assembly and having t spaced teeth with adjacent teeth defining a slot therebetween, each said tooth having a surface adjacent said rotatable assembly with n elongate notches therein along the axis, said stationary assembly having winding stages on the teeth adapted for commutation in at least one preselected sequence, wherein n and t are positive integers;
• a tip laterally transversely extending from at least one of said teeth and forming part of the surface adjacent said rotatable assembly;
• wherein a portion of one of the notches in said one tooth is in the tip and forms an angle with the remaining portion of the notch in said one tooth;
• and
• wherein the tip has a second radially inwardly tapering surface opposite the surface of said tip adjacent said rotatable assembly with the portion of the one notch having a surface substantially parallel to the second surface, and the remaining portion of the one notch has a surface substantially parallel to the surface of said one tooth adjacent said rotatable assembly whereby the notches reduce cogging between the rotatable assembly and the stationary assembly as the rotatable assembly rotates.