Patent ID: 8405270

Claim:
A permanent magnet buried type electric motor comprising: a stator having a winding wound on a stator core having a plurality of teeth at the inner circumferential side of a yoke; a rotor rotatably held opposite to the teeth; and a rotor core, as part of the rotor, having a plurality of magnet burying holes in which permanent magnets are buried for forming magnetic poles, and having an outer circumference composed of a plurality of arcs different in radius, wherein, supposing a straight line joining a rotation center of the rotor and a magnetic pole middle, that is, a middle of the permanent magnets to be a d-axis, and a straight line joining the rotation center and an intermediate point of mutually adjacent permanent magnets to be a q-axis, the mutually adjacent arcs are composed such that the radius of the arc at the d-axis side is larger than the radius of the arc at the q-axis side, and that, at an intersection point of the mutual arcs, angle a of a tangent of the arc at the q-axis side with respect to a tangent of the arc at the d-axis side is set by −3 degrees ≦α≦2 degrees; and further wherein the magnet burying holes include a rectangular hole, a protrusion, and a recess adjacent to the rectangular hole and protrusion, wherein the recess reduces deviation of the buried permanent magnets in a longitudinal direction within the rectangular hole.