US Patent 7176598 Brushless DC motor

A bridge (8) in conformity with a tooth opening angle of the stator (1) is provided between a permanent magnet (5) and a permanent magnet (5) in a rotor (4), so that a magnetic flux for a reluctance torque is made to pass an inner side of the permanent magnet (5). An opening angle of each of ribs (7) on both sides of the permanent magnet (5) is set to be equal to or smaller than the teeth interval opening angle and equal to or larger than a half thereof. Thereby, reluctance of the rib (7) against a magnetic flux in a circumferential direction is increased and leakage of the magnetic flux of the permanent magnet (5) is prevented.