Permanent magnet type electric motor

Claim 1

A permanent magnet type electric motor, comprising: a cylindrical yoke (11), a plurality of arcuate field magnet poles (13) arranged on an inner peripheral surface of said cylindrical yoke such that a plurality of open spaces (12) individually remain between adjacent circumferential ends of said poles, a plurality of stop members (17; 21) extending radially inwardly from the inner peripheral surface of the yoke and directly engaging opposite axial ends of each field magnet pole to axially position and restrain said poles, and armature core (19) rotatably disposed in a region surrounded by said field magnet poles, each field magnet pole comprising a permanent magnet (14) adhesively bonded to the inner peripheral surface of the yoke, and an auxiliary magnetic pole (15) of high permeability material arranged in parallel with said permanent magnet and welded to said inner peripheral surface of said cylindrical yoke, at least two bolts (18) disposed in and extending through two of said open spaces remaining between adjacent field pole ends, wherein said stop members engage substantially less than full axial end surfaces of said field magnet poles, and wherein said stop members comprise a pair of resilient rings disposed in pressure contact with said inner peripheral surface of said cylindrical yoke, each ring defining at least two radially inwardly bent portions (23) disposed in axial alignment with said two of said open spaces to provide clearance for the passage of said bolts.