A core has an annular inner core portion, a rib-shaped core portion
extending radially from the annular inner core portion and an outer
peripheral core portion. Magnetic pole tooth portions are formed in an
annular shape on the outer periphery of the rib-shaped core portion, and
the core is composed of a plurality of core blocks having the same shapes
as blocks formed by dividing the core in circumferential direction. Each
of the plurality of core blocks has a concave/convex engage portion at an
inner peripheral portion corresponding to the inner periphery of the
annular inner core portion, and the plurality of core blocks gathered so
as to form the core are fastened each other by a cylindrical housing
having an outer surface formed in concave/convex shape, inserted in the
inner peripheral portion so as to engage with each other at the
concave/convex engage portions, and changed in diameter relative to the
core blocks due to thermal shrinkage or expansion of the cylindrical
housing, so that the core blocks are tightly fitted to each other without
any gap between adjacent core blocks.
