Patent ID: 6166470
Filing Date: 2000-12-26
Classification: H02K

Abstract:
A brushless DC motor comprising:a rotor having a rotor yoke and a rotor magnet forming a plurality of magnetic poles in a circumferential direction disposed on the rotor yoke,a stator having a stator yoke with a plurality of magnetic poles alternately disposed at regular intervals in the circumferential direction on the stator yoke having a constant air gap next to the rotor magnet,a coil unit disposed on the stator yoke and having a magnetic field coil for exciting the magnetic poles of the stator,a magnetic pole sensing element set at a position shifted in the circumferential direction from an intermediate position of one magnetic pole of the rotor magnet for detecting a pole of the rotor magnet,wherein an open angle of the magnetic poles of the stator is set at no less than 75% but less than 100% of an open angle per magnetic pole of the rotor so that a static stable point position where the rotor stops by a cogging torque in a magnetic circuit consisting of the rotor and stator is in vicinity of a maximum point of torque generated by an electric current passed to the magnetic field coil.