US Patent 7612480 Interior permanent magnet motor

A rotor portion of a motor includes a rotor core and a plurality of field magnets arranged in a circumferential direction at the rotor core. The rotor core includes at a flux barrier portion thereof arranged between a pair of field magnets of opposite magnetic polarities arranged next to one another a flux barrier hole. The flux barrier hole is independent of a magnet retaining hole in which the field magnet is retained. The magnet retaining hole includes a concave portion extending from a side thereof nearest to the flux barrier hole toward the corresponding flux barrier hole.