Interior permanent magnet electric motor including a rotor having circumferential surface portions with defined curve profiles

An interior permanent magnet motor, having a stator and a rotor, the rotor having main magnetic poles and auxiliary magnetic poles which alternate in a circumferential direction when viewed in cross section perpendicular to the axial direction of the rotor, each of the main magnetic poles having a magnet insert hole for receiving a permanent magnet, the magnet insert hole extending in the axial direction of the rotor, the rotor having a rotary shaft insert hole for receiving a rotary shaft, a semi-tubular rivet insert hole for receiving a semi-tubular rivet and a passage hole, said holes extending in the axial direction of the rotor, the rotary shaft having an outside diameter larger than a bore diameter of the rotary shaft insert hole, wherein:

• an outer circumferential surface of the rotor is formed of first outer circumferential surface portions and second outer circumferential surface portions which are alternately directly connected in the circumferential direction, wherein each of the first outer circumferential surface portions has a first curve profile which bulges radially outward and intersects with a d-axis of the assigned main magnetic pole, and each of the second outer circumferential surface portions has a second curve profile which bulges radially outward and intersects with a q-axis of the assigned auxiliary magnetic pole, as viewed in cross section perpendicular to the axial direction of the rotor, wherein the first curve profile has a circular arc shape having its center of curvature on a center of the rotor on the d-axis and having a radius of Rd, and the second curve profile has a circular arc shape having its center of curvature on a point on the q-axis displaced from the center of the rotor away from the assigned second outer circumferential surface portion, and having a radius Rq larger than the radius Rd, such that the maximum width of a gap between the second outer circumferential surface portion and the inside surface of the stator is larger than the maximum width of a gap between the first outer circumferential surface portion and the inside surface of the stator,
• the semi-tubular rivet insert hole is disposed in each of the main magnetic poles of the rotor and located radially outward of the magnet insert hole in the rotor,
• the passage hole is formed in each of the auxiliary magnetic poles,
• the permanent magnet is inserted into the magnet insert hole such that a gap is formed between the magnet insert hole and the permanent magnet,
• the semi-tubular rivet is inserted into the semi-tubular rivet insert hole such that a gap is formed between the semi-tubular rivet insert hole and the semi-tubular rivet, and
• the rotor has an outer surface contour which is not significantly changed at boundaries between the first and second outer circumferential surface portions, such that flow of magnetic flux is prevented from abrupt chancre when the boundaries between the first and second outer circumferential surface portions pass by teeth of the stator.