1-Phase self-starting disk-type brushless motor with cogging-producing element

Claim 1

A 1-phase energized brushless motor, comprising: a magnet rotor mounted for rotation and having 2P north and south poles, P being an integer equal to or greater than 1; at least one coreless armature coil disposed at a stationary same-phase position in an opposing relationship to said magnet rotor with an air gap left therebetween; a stator yoke for mounting said armature coil thereon; a single position-detecting element for determining in which direction electric current flows through said armature coil; and an electric circuit for detecting a pole of said magnet rotor to selectively energize said armature coil; said stator yoke having formed therein at least one cutaway portion defined by an arc of the stator yoke and two ends, each of which extends in a radial direction of the stator yoke or a direction oblique to the radial direction, and between said ends, having an angular width θ determined substantially by the following expression: T≦m·T≦θ<2n·T where T is the angular width of each pole of said magnet rotor, m is an integer ranging from 1 to 2n; and n is an integer of at least 1 with 2n being equal to or smaller than the total number 2P of the poles of said magnet rotor; said stator yoke being located such that at least one of said ends of said cutaway portion thereof is positioned within a range from a position at which a maximum starting torque can be obtained or any other same-phase position to a position spaced backwardly therefrom by a distance equal to about one half of the angular width of each pole of said magnet rotor in the direction of rotation of said magnet rotor.