Permanent magnet rotor assembly for electro-mechanical transducer

A rotor assembly for an electro-mechanical transducer, comprising:

• a rotor pinion unit including a pinion and a shaft concentric with said pinion, said shaft having a large diameter portion integral with and adjacent said pinion and a small diameter portion integral with said large diameter portion, said small diameter portion extending from said large diameter portion in a direction away from said pinion and including a tapered portion;
• said tapered portion of said shaft comprising successively, in a direction from a free end of said small diameter portion of said shaft toward said pinion, a first portion of increasing diameter and a second portion of decreasing diameter;
• an annular body of a permanent magnet formed of frangible material and having opposite end faces;
• and
• a protecting support member composed of a high molecular material and formed as a unitary structure with said annular body by injection molding, said protecting support member having an axially extending ring portion on which said annular body is integrally mounted and which fits on said large diameter portion of said shaft, end face portions radially extending from both ends of said ring portion and engaging both end faces of said annular body, and an annular axial projection extending axially from one end of said ring portion in a direction away from said pinion, said axial projection receiving said small diameter portion of said shaft and including a tapered inner wall portion directly engaging said tapered portion of said rotor pinion shaft at a position beyond said one end of said ring portion and remote from said annular body to secure said support member and said annular body together whereby said ring portion is unexpanded by said shaft.