Patent ID: 7122930

Claim:
An electric motor comprising a stator with a plurality of coils wound around a ring-shaped iron core; and a rotor rotatably disposed inside the stator, the rotor comprising a rotor shaft, a yoke integrally mounted on the rotor shaft, a plurality of magnet holes formed at equal pitches near a periphery of the yoke, and a plurality of plate-like permanent magnets disposed in respective ones of the magnet holes, wherein the yoke has a plurality of air holes, equal in number to the number of permanent magnets and provided between the rotor shaft and the permanent magnets, for accelerating heat release of the rotor; and wherein with a center of the rotor shaft as C, one of each two adjacent permanent magnets as M 1 , a point of intersection of a perpendicular line-drawn from the center C to the permanent magnet M 1 and the periphery of the yoke as P 1 , a permanent magnet adjacent to the permanent magnet M 1 as M 2 , a point of intersection of a perpendicular line drawn from the center C to the permanent magnet M 2 and the periphery of the yoke as P 2 , and a point of intersection where a radial line passing through the center C and a midpoint between the adjacent permanent magnets M 1 , M 2 intersects with the periphery of the yoke as Q, when a circle of a radius r passing through the intersection point P 1 and the intersection point P 2 is drawn around the intersection point Q, the air holes lie outside of the circle in symmetric relation relative to respective ones of the perpendicular lines.