Core piece, reactor, converter, and power conversion device

A core piece constituted by a molded body of a composite material in which a soft magnetic powder is dispersed in a resin, the core piece comprising:

• a middle core portion configured to be arranged inside a coil;
• and
• an end core portion configured to face an end face of the coil,
• wherein the middle core portion includes a hole portion or a groove portion extending in an axial direction of the coil,
• the hole portion or the groove portion extends continuously from an end face of the middle core portion to an intermediate position in the end core portion, or extends continuously from an outward face of the end core portion to an intermediate position in the middle core portion,
• in a lateral cross-section of the middle core portion, a radius of a first inscribed circle is less than or equal to 0.6 times a radius of a reference inscribed circle, and
• in a horizontal cross-section of the core piece, a radius of a third inscribed circle is less than or equal to 0.6 times the radius of the reference inscribed circle,
• the lateral cross-section being a cross-section of the middle core portion passing through the hole portion or the groove portion along a plane orthogonal to the axial direction of the coil,
• the horizontal cross-section being a cross-section of the core piece passing through the hole portion or the groove portion along a plane orthogonal to a plan view direction of the core piece,
• the first inscribed circle being a largest inscribed circle between an outline of the hole portion or the groove portion in the lateral cross-section and a peripheral outline of the middle core portion in the lateral cross-section,
• the reference inscribed circle being a largest inscribed circle in a first virtual outline,
• the first virtual outline being a smallest quadrilateral circumscribing the lateral cross-section, and
• the third inscribed circle being a largest inscribed circle in contact with the end face of the middle core portion and either a bottom portion of the hole portion or an end portion of the groove portion in the horizontal cross-section, or a largest inscribed circle in contact with the outward face of the end core portion and either the bottom portion of the hole portion or the end portion of the groove portion in the horizontal cross-section.