Motor structure having a permanent magnet motor with grooves to reduce torque ripples

Claim 1

A motor structure, comprising: a stator core including a number M salient poles, a rotor including a rotor magnet having a permanent magnet with a number P of poles of said rotor magnet, an air gap between each salient pole and the rotor magnet, whereby P and M are integers, and P is larger than M, said rotor magnet having a main magnet part including N poles and S poles, a frequency generator magnet part positioned at an outer periphery of the rotor magnet, and said rotor magnet having a substantially circular cylindrical surface facing a side of said stator core; a plurality of grooves, each formed in the vicinity of a magnetically neutral part between each and every said N pole and said S pole pair, all around said rotor magnet; wherein a width of the grooves, as observed from a center of the rotor, has a value approximately equal to 360°/X, where X is the least common multiple of P and M, which width of the grooves is 1/3 of the width of the magnetizing pole of said permanent magnet, and wherein a deepest depth of said grooves is substantially equal to the length of the air gap.