Worm wheel and electric power steering apparatus
AssigneeNsk Ltd.
InventorsHaruhiko Kiyota, Takeshi Yamamoto, Fumiaki Mitsuhashi
Life of this patent
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Abstract
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.
Claims7
A worm wheel comprising:
- a disk-shaped core made of metal;
- and
- an 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 extending in an axial direction, a first axial end surface formed with a first annular recess, and a second axial end surface formed with a second 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 a first 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 a second axial end surface of the outer circumferential portion of the core,
- wherein the rim portion comprises a first inner circumferential portion extending from a first 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, and a second inner circumferential portion extending from a second 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,
- wherein the rim portion is injection-molded in a state in which the core is arranged in a mold such that the second annular recess faces a gate and such that the axial direction of a sprue and the axial direction of the core are aligned with each other,
- wherein 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, and
- wherein a depth of the second annular recess is at least 0.1 mm but not deeper than half of an axial distance between the second axial end surface of the core and the second axial end surface of the rim portion.
Dependencies are inferred from the claim text.