| 摘要 |
PURPOSE:To prevent magnetic flux convergene in a field core portion by giving a taper-like form to an axially extended supporter portion for retaining the field coil of the field core so that the root of said portion will be thicker than its tip end. CONSTITUTION:The inner periphery of a field coil supporter portion 3'b of a field core 3' becomes thicker from its tip end to its root in the shape of a taper. Portions 3'a, 3'c of the field core 3' have an inner diameter equal to that of the root of the field coil supporter portion 3'b. The rotor shaft 2'a opposed to the field core 3' has a gap ga', which is uniform overall between the inner periphery of the field core 3' and said shaft. This structure is so constituted that the diameter of the shaft 2'a of the rotor core 2' will become smaller so far as tapering of the field coil supporter portion 3'b of the field core 3' reduces the inner diameter of said field core.
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