This invention relates to a core in which a strip-shaped core members having a plurality of core pieces connected to each other by connecting portions are stacked so that adjoining edges in the stacking direction of the core pieces overlap each other, and which is formed into a ring by rotation of the connecting portions. In particular, it relates to the shape of the end surfaces of the core pieces.
This type of conventional core is constructed as disclosed in Japanese Published Unexamined Patent Application No. 2000-201458, for example, and as described below.
FIG. 9 is a plan view showing the structure of a conventional core, FIG. 10 is a plan view showing a portion of the core of FIG. 9 deformed into a linear shape, and FIG. 11 is a detailed view for explaining a problem when installing the windings of a conventional core.
In the figures, 1 is a plate-shaped core piece of a magnetic material. A magnetic pole tooth 1a projects from one side, and a recess 1b and a projection 1c are formed on the rear and front surfaces of one end as a connecting means. A first end surface 1d is formed into the shape of a circular arc centered on the center of the recess and the projection 1b and 1c. At the other end is formed a second end surface 1e which can mate with the first end surface 1d of and adjoining core piece 1. 2 is a first core member in which a plurality of core pieces 1 are arranged through the end surfaces 1d and 1e. 
3 is a second core member in which each core piece 1 is arranged oppositely in the lengthwise direction from the first core member 2. It is alternatingly stacked with the first core member 2, and the recesses and projections 1b and 1c of adjoining core pieces 1 in the stacking direction mate with each other whereby they are connected so as to be able to freely rotate. 4 is a core which is formed in the shape of a ring by rotating the recesses and projections 1b and 1c of each core piece 1 of both core members 2 and 3 which are stacked atop each other. The end portions of opposing core pieces 1 overlap each other through the recesses and projections 1b and 1c. 
A conventional core is constituted as described above. As shown in FIG. 10, it is intended to simplify winding operation by deforming both core members 2 and 3 into a straight line and then carrying out winding (not shown) on the magnetic pole tooth 1a. However, even if both core members 2 and 3 are put into a straight line, it is difficult to obtain sufficient space for winding, and rewinding can be performed only with a nozzle.
When rewinding is carried out with a nozzle, as shown in FIG. 11, the bending radius of the inner diameter corner portion (shown by A in the figure) of the discharge opening of the nozzle 5 is small, and depending upon the position of movement of the nozzle, when a magnetic wire 6 is in the positions shown by the solid lines and the dashed lines in the figure, the frictional resistance between the magnet wire 6 and the corner portion varies, and the tension applied to the magnet wire 6 varies, so it is difficult to maintain alignment during rewinding. In addition, when the magnet wire 6 has a large diameter, there are problems such as that strains develop.
This invention was made in order to solve such problems. Its object is to provide a core with which it is possible to perform rewinding operation using a flyer and which can increase the alignment of windings.
The present invention resides in a magnetic core in which a plurality of core pieces have their ends connected to each other to form the shape of a ring. The core pieces have magnetic pole teeth projecting nearly perpendicular to the direction of connecting, a connecting portion is formed on one of the ends, a first end surface of the one of the ends is formed in the shape of a circular arc centered on the connecting portion, and the other end is formed with a second end surface which can mate with the first end surface of an adjoining core piece. A first core member having the cores arranged in the shape of a strip through the end surfaces and a second core member having the cores arranged in the shape of a strip in the opposite direction from the direction of connection of the first core member are stacked such that the ends of adjoining core pieces in the stacking direction overlap each other and the connecting portions are connected so as to be able to freely pivot such that it can be formed into the ring shape with the magnetic pole teeth on the interior. A cutout is formed in the corner on the outer side of the core in the second end surface of each core piece.
Therefore, a core can be provided which makes it possible to perform rewinding with a flyer and which can achieve improved alignment of windings.
A cutout may be formed in each corner on the outer side of the core in the first and second end surface of each core piece.
Portions of the core pieces corresponding in the stacking direction to portions in which the cutouts are formed may be cut out in the same projected cross-sectional shape as the cutouts.
A second cutout may be connected between the cut out portions and forms the shape of the bottom of a boat together with the cut out portions.
Cutouts which are disposed at joints of the ring may have a surface which is formed in the same surface as the second cutouts.
A hole may be formed in the stacking direction in a prescribed location in each core piece.