Patent ID: 7321177

Claim:
A synchronous electric motor comprising: a rotor having a rotation axis; and a stator surrounding said rotor through a gap; wherein said rotor includes a rotor core having an outer circumferential surface extending about said rotation axis and a plurality of permanent magnets attached to said rotor core to form plural poles along said outer circumferential surface of said rotor core; wherein said outer circumferential surface of said rotor core is provided, at each of said plural poles, with a contour deviating from a circular arc and bulging out in a radial outward direction, as seen in a cross-section perpendicular to said rotation axis; wherein said plurality of permanent magnets include a plurality of magnet sets individually assigned to said plural poles, each set including two or more permanent magnets; and wherein said gap between said rotor and said stator changes in dimension thereof along a circumferential direction of said outer circumferential surface of said rotor core; and wherein a maximum dimension of said gap G max , a minimum dimension of said gap G min and a thickness H of each of said plurality of permanent magnets have a relationship meeting a formula of G max /(G max +H)≧√2×G min /(G+H).