Worm wheel and electric power steering apparatus

A worm wheel comprising:

• a disk-shaped core made of metal;
• and
• a substantially annular rim portion made of synthetic resin and covering an outer circumferential portion of the core;
• wherein a gear is formed on an outer circumferential portion of the rim portion,
• wherein the rim portion is integrally formed with the core by synthetic resin injection molding,
• wherein the core comprises a center hole into which a shaft is fitted, a first axial end surface provided at a radially outermost portion of the core, and a second axial end surface provided opposite the first axial end surface, the first axial end surface being formed with a first annular recess defined by an inner circumferential wall and an outer circumferential wall, the second axial end surface being formed with a second annular recess, and a third annular recess being formed in the outer circumferential wall of the first annular recess so as to be disposed within the first annular recess,
• wherein the first annular recess is formed at a radially inner side with respect to the outer circumferential portion of the core and is recessed toward an axially inner side with respect to the axial end surface of the outer circumferential portion of the core, and the second annular recess is formed at a radially inner side with respect to the outer circumferential portion of the core and is recessed toward an axially inner side with respect to the other axial end surface of the outer circumferential portion of the core, and
• wherein the rim portion comprises a first inner circumferential portion extending from an axial end surface of the rim portion to the radially outer region of the first annular recess and fixed to the radially outer region of the first annular recess, a second inner circumferential portion extending from another axial end surface of the rim portion to a radially outer region of the second annular recess and fixed to the radially outer region of the second annular recess, and a protrusion engaged with the third annular recess.