Patent ID: 7737596

Claim:
An anti-cogging apparatus for installation on a permanent magnet electrical machine having a rotor, a stator and a cogging torque, the anti-cogging apparatus for reducing said cogging torque, said anti-cogging apparatus comprising: a first component mechanically coupled to one of said rotor and said stator and having a first set of elements of magnetic material disposed along a first circle; and a second component mechanically coupled to the other one of said rotor and said stator and having a second set of a plurality of elements of magnetic material disposed along a second circle coaxial with said first circle, the elements of said first set being uniformly arranged on the first circle with a first angular period and the elements of said second set being uniformly arranged on the second circle with a second angular period, and with the first and second sets facing each other, with an air gap there between, for passive magnetic interaction; and wherein: at least one of said first and second sets has permanent magnets for generating an anti-cogging torque as a result of the passive magnetic interaction between said first and second sets, said anti-cogging torque having a magnitude substantially matching a magnitude of said cogging torque and a direction opposite to the direction of said cogging torque, thereby substantially canceling out said cogging torque, and said cogging torque has a main angular period component as a function of a mechanical angle between the rotor and the stator, and said main angular period component is equal to a greatest common divisor of said first angular period and said second angular period.