Patent ID: 6181035
Filing Date: 2001-01-30
Classification: H02K

Abstract:
An improved permanent magnet motor having reduced cogging torque, the improved permanent magnet motor comprising:a rotor rotatable about a central motor axis and having a plurality of permanent magnet elements disposed at equally spaced intervals, the magnet elements providing an angular distribution of the magnetic polarity about the rotor;motor windings; anda stator disposed coaxially with the rotor and separated from the rotor by a circumferential air gap and having a number of slots formed therein for housing the motor windings, the slots facing the air gap, wherein:the permanent magnet elements are shaped and arranged such that the distribution of the density of magnetic energy that is stored in the air gap in the absence of stator slots, as a function of a linear coordinate taken along a circumference disposed within the air gap and coaxial to the motor axis, exhibits an increasing transition in magnitude in a first angular position near a first end of a magnetic polarity and a decreasing transition in magnitude in a second angular position near a second end of the magnetic polarity, the transitions being asymmetrical with respect to each other and the density of magnet energy being substantially constant between consecutive transitions; andthe slots of the stator are disposed in positions such that during operation, if a first slot is in a first angular position corresponding to the first angular position of the increasing transition in magnitude of the distribution of magnetic energy density, a second slot is in a second angular position that corresponds to the second angular position of the decreasing transition in magnitude of the distribution of magnetic energy density, each slot functioning to modify the distribution of the density of magnetic energy in the air gap according to a modulation function which has a local development symmetrical to a radial plane passing through the center of the slot.