Patent ID: 7990010
Filing Date: 2011-08-02
Classification: H02K

Abstract:
1. A small motor having a polygonal external shape in which a field magnet having four or more poles is attached to an inner circumferential surface of a motor casing made of metal, the motor comprising: the motor casing having a side wall formed into a polygonal shape such that flat side portions equal in number to the poles and arcuate corner portions equal in number to the side portions and located at respective corners between the side portions are continuously joined together; and the field magnet which has an outer circumferential shape approximately coinciding with the inner circumferential shape of the motor casing, having magnet side portions and magnet corner portions corresponding to the side portions and corner portions, respectively, of the motor casing, and having a rib provided on outer circumferential surfaces of the magnet side portions, wherein the magnet is disposed, through press-fitting, within the motor casing such that the rib comes into contact with the inner circumferential surface of the motor casing, the magnet side portions, excluding the rib, being formed such that small clearances are formed between the magnet side portions and the side portions of the motor casing, or at least such that no pressing force acts on the magnet side portions, excluding the rib.