Abstract: A worm wheel includes: a sleeve; and a toothed portion provided by injection molding so as to cover a part of the sleeve, the toothed portion including a first thick portion provided on a first side face, which is a surface of the sleeve on a side closer to an injection-mold gate in an axial direction, and a second thick portion provided on a second side face, which is a surface on an opposite side to the first side face. 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. The first thick portion of the toothed portion has a smaller thickness in the axial direction than the second thick portion.

Abstract: A worm wheel includes: a sleeve; and a toothed portion provided by injection molding so as to cover a part of the sleeve, the toothed portion including a first thick portion provided on a first side face, which is a surface of the sleeve on a side closer to an injection-mold gate in an axial direction, and a second thick portion provided on a second side face, which is a surface on an opposite side to the first side face. 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. The first thick portion of the toothed portion has a smaller thickness in the axial direction than the second thick portion.

Abstract: A speed reducer for an electric power steering system includes a worm, a worm wheel, and a housing. Only a meshing section where the worm and the worm wheel mesh with each other and a space between the worm wheel and the housing are filled with grease. The grease in the space is in contact with both tooth surfaces of the worm wheel and an inner peripheral face of the housing, the inner peripheral face facing the worm wheel.

Abstract: A speed reducer for an electric power steering system includes a worm, a worm wheel, and a housing. Only a meshing section where the worm and the worm wheel mesh with each other and a space between the worm wheel and the housing are filled with grease. The grease in the space is in contact with both tooth surfaces of the worm wheel and an inner peripheral face of the housing, the inner peripheral face facing the worm wheel.

Abstract: A gear (27; 27A; 27B; 27C) includes: an annular metal core (28; 28A; 28B) having a recess (37; 67: 37B) provided in a first side face (34) thereof; and an annular resin member (29) molded on the metal core (28; 28A; 28B) as covering an outer peripheral surface (32) of the metal core (28; 28A; 28B) and the first side face (34) of the metal core (28; 28A; 28B) and having teeth (46) provided on an outer peripheral surface thereof by injecting a resin material toward the recess (37; 67; 37B).