Worm wheel, electric power steering system, and manufacturing method for worm wheel

A manufacturing method for a worm wheel obtained such that a toothed portion is injection-molded so as to cover a part of a sleeve having an annular shape, the toothed portion including a tooth forming portion on an outer peripheral surface, which is a surface of the sleeve in a radial direction, a first thick portion on a first side face, which is one surface of the sleeve in an axial direction, and a second thick portion on a second side face, which is a surface of the sleeve on an opposite side to the first side face in the axial direction, the manufacturing method comprising:

• placing the sleeve in a die so that a gate from which resin is injected is positioned on a side closer to the first side face of the sleeve, wherein a central part, in the axial direction, of the outer peripheral surface of the sleeve projects in the radial direction relative to both ends in the axial direction, and an axial interval between the first side face of the sleeve and an inner surface of the die, the inner surface being opposed to the first side face is smaller than an axial interval between the second side face of the sleeve on an opposite side to the first side face and an inner surface of the die, the inner surface being opposed to the second side face;
• and
• supplying the resin into the die in a state where the sleeve is placed inside the die.