Permanant magnet field type rotor structure for an electric machine

A permanent magnet field type rotor structure for an electric machine comprising:

• a shaft;
• a pair of axially spaced end plates which are secured to the shaft and have respective facing inner walls, each of said inner walls having a recess;
• a plurality of permanent magnets each extending radially outward from the shaft and extending axially from end plate to end plate;
• and
• a plurality of yokes arranged between adjacent magnets and extending axially between the end plates for supporting the magnets, the yokes at each end thereof being received by the recess in the inner wall of the respective end plate and wherein the outer surfaces of the yokes define an intermittent cylindrical outer surface, which is tapered so as to have a smaller diameter at each end than in the middle, and the recess of each of the inner walls of the end plate is cylindrically shaped such that the yokes are press-fit into the end plates, the outer surfaces of the yokes tapering at each end therefore to be fit essentially flush with said magnets, and said yokes overlapping a part of the exposed surfaces of said permanent magnets between said end plates.