Nsk Corporation

Fumiaki Mitsuhashi

Takeshi Yamamoto

Haruhiko Kiyota

Kentaro Ogi

Worm wheel construction that is able to sufficiently increase the strength of the connecting portion between a huband a gear portion, and to maintain sufficient durability even when applied to an electric power steering apparatus that applies a large auxiliary torque, is achieved. A synthetic resin gear portionis molded and formed in the end portion on the outer-diameter side of a metal hub. A first annular concave portionis provided on one surface side in the axial direction of the hub, and a second annular concave portionis provided on the other surface side in the axial direction thereof. Part of the synthetic resin of the gear portionis fed into the portions near the outer diameter of the first annular concave portionand the second annular concave portionto form a first restraining portionand a second restraining portion. These restraining portionstightly hold the end portion on the outer-diameter side of the hub, and improve the strength and rigidity of the connecting portion between the huband the gear portion

Worm wheel and electric power steering apparatus

A core of a worm wheel has an axial end surface formed with a first annular recess, another axial end surface formed with a second annular recess, and a third annular recess formed in a radially outer region of the first annular recess. A rim portion has a first inner circumferential portion fixed to the first annular recess, a second inner circumferential portion fixed to the second annular recess, and a protrusion engaged with the third annular recess.

A core of a worm wheel has an axial end surface formed with a first annular recess nad and another axial end surface formed with a second annular recess. An outer circumferential wall surface of a radially outer region of the second annular recess has a tapered surface extending from a bottom surface of the second annular recess to form an obtuse angle relative to the bottom surface, and a third annular recess formed radially outside the tapered surface. A cross-section of the third annular recess is a right-angled triangle having, as two sides, a surface parallel to the bottom surface of the second annular recess and a surface perpendicular to the bottom surface of the second annular recess. A rim portion has a first inner circumferential portion fixed to the first annular recess and a second inner circumferential portion fixed to the second annular recess.

A core of a worm wheel has an axial end surface formed with a first annular recess and another axial end surface formed with a second annular recess. A rim portion has a first inner circumferential portion fixed to the first annular recess and a second inner circumferential portion fixed to the second annular recess. An outer circumferential wall surface of the second annular recess extends from a bottom surface of the second annular recess so as to be perpendicular to the bottom surface. A depth of the second annular recess is at least 0.1 mm but not deeper than half of a gate thickness.

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Maebashi, Japan

Fumiaki Mitsuhashi