EP-4737762-A1 - POWER TRANSMISSION RESIN GEAR AND METHOD OF PRODUCING POWER TRANSMISSION RESIN GEAR

EP4737762A1EP 4737762 A1EP4737762 A1EP 4737762A1EP-4737762-A1

Abstract

A power transmission resin gear 1 includes an annular resin part 3 having, on an outer peripheral surface thereof, teeth 10 of a gear. The annular resin part 3 includes an annular inner resin member 4 that covers an outer periphery of a core metal 2 and an annular outer resin member 5 that covers an outer periphery of the annular inner resin member 4. The annular inner resin member 4 has a plurality of axially downgauged portions 6 arranged at intervals in a circumferential direction. The annular outer resin member 5 has filling portions 8 respectively filling the axially downgauged portions 6 and an axial surface covering portion 9 that is located radially inward RI of a tooth side 10C of the teeth 10 and covers the filling portions 8. According to the power transmission resin gear 1, deformation of a molded product due to forcible removal can be reduced without preparing a special tooth shape.

Inventors

UEDA, HIROFUMI
KIKUCHI, ARATA
YAMAMOTO, TAICHI
NAKAMURA, MASAYOSHI
NAKA, YUKIMASA

Assignees

JTEKT Corporation
Nakanishi Metal Works Co., Ltd.

Dates

Publication Date: 20260506
Application Date: 20251027

Claims (4)

A power transmission resin gear comprising: an annular resin part having, on an outer peripheral surface thereof, teeth of a gear, wherein the annular resin part includes an annular inner resin member that covers an outer periphery of a core metal and an annular outer resin member that covers an outer periphery of the annular inner resin member, the annular inner resin member has a plurality of axially downgauged portions arranged at intervals in a circumferential direction, and the annular outer resin member has filling portions respectively filling the axially downgauged portions and an axial surface covering portion that is located radially inward of a tooth side of the teeth and covers the filling portions.
The power transmission resin gear according to claim 1, wherein each of the teeth has a tooth bottom with an arc shape that fits an outer peripheral shape of a worm, and a tooth surface that is a curved surface with an arc shape, and the power transmission resin gear serves as a worm wheel to be used as a worm gear reducer in combination with the worm.
The power transmission resin gear according to claim 1 or 2, further comprising: a plurality of axial protrusions arranged at intervals in the circumferential direction on an outer peripheral surface of the annular inner resin member, the outer peripheral surface being located radially inward of the teeth on an outer peripheral surface of the annular outer resin member, wherein the axially downgauged portions are located radially inward of the axial protrusions.
A method of producing a power transmission resin gear that includes an annular resin part having, on an outer peripheral surface thereof, teeth of a gear, the annular resin part including an annular inner resin member that covers an outer periphery of a core metal and an annular outer resin member that covers an outer periphery of the annular inner resin member, the annular inner resin member having a plurality of axially downgauged portions arranged at intervals in a circumferential direction, and the annular outer resin member having filling portions respectively filling the axially downgauged portions and an axial surface covering portion that is located radially inward of a tooth side of the teeth and covers the filling portions, the method comprising: a primary molding step; and a secondary molding step, wherein in the primary molding step, molten resin for the primary molding step is injected in a cavity of a primary-molding mold in a state where the core metal is set in the primary-molding mold opening and closing in an axial direction, so as to mold the annular inner resin member through injection molding, thereby producing a primary-molded product including the core metal and the annular inner resin member, in the secondary molding step, molten resin for the secondary molding step is injected in a cavity of a secondary-molding mold in a state where the primary-molded product is set in the secondary-molding mold opening and closing in the axial direction, so as to mold through the injection molding the annular outer resin member provided with the teeth, and the filing portions and the axial surface covering portion in the annular outer resin member are located on a side of the secondary-molding mold, in which a mold sprit surface of the secondary-molding mold is located.

Description

Field The present invention relates to a power transmission resin gear that includes a core metal and an annular resin part. Background For the power transmission resin gear that includes the core metal and the annular resin part covering an outer periphery of the core metal, there has been a worm wheel, for example, to be used in combination with a worm in a worm gear reducer (see Patent Literatures (PTLs) 1 to 3, for example), in order to meet the needs for weight reduction and quietness. In the case where teeth of the worm wheel are formed on an outer peripheral surface of the annular resin part through injection molding, each of the teeth has an undercut shape with respect to a mold that molds the teeth. Due to the undercut shape, the worm wheel that is a molded product will be forcibly removed from the mold when taken out of the mold. This causes the teeth of the worm wheel that has been taken out of the mold to be deformed. In PTL 1, a number of slide cores for molding tooth grooves are arranged radially around a core, and the slide cores are supported to be retractable in a radial direction. Such a mold structure avoids forcible removal. In PTL 2, a special tooth shape is molded in a mold that opens and closes in an axial direction. A tooth bottom of a half of the width of the tooth on a side far from a mold split surface of the mold is made in parallel to the axial direction. This configuration avoids the forcible removal. In PTL 3, a special tooth shape is molded in a mold that opens and closes in the axial direction. A shape of the tooth on a side far from a mold split surface of the mold has a smaller undercut amount. This configuration enables forcible removal. Citation List Patent Literature PTL 1: Japanese Unexamined Patent Application Publication No. 2002-254478PTL 2: Japanese Unexamined Utility Model Application Publication No. Hei. 4-49254PTL 3: Japanese Unexamined Patent Application Publication No. 2009-41595 Summary Technical Problem If the mold structure including the slide cores as in PTL 1 is used, difficulty in production of molds increases. Specifically, a mold becomes large, cost of the mold increases, and productivity is lowered. In addition, burrs occurring on a split surface of the slide cores may degrade the quality of a molded product. If the aforementioned special tooth shape as in PTL 2 is used, it is necessary to change design specifications for a tooth shape of the worm wheel. In addition, a tooth thickness of the worm wheel is reduced and a surface in contact with a worm that engages the worm wheel is reduced, causing strength of the worm wheel to be lowered. If the aforementioned special tooth shape as in PTL 3 is used, it is necessary to change design specifications of a tooth shape of the worm wheel. In addition, a molded product will be forcibly removed from a mold, so that deformation of the molded product cannot be controlled. An object of the present invention is to provide a power transmission resin gear that can prevent deformation of a molded product due to forcible removal, without preparing a special tooth shape. Solution to Problem A power transmission resin gear according to the first aspect of the present invention includes an annular resin part having, on an outer peripheral surface thereof, teeth of a gear. The annular resin part includes an annular inner resin member that covers an outer periphery of a core metal and an annular outer resin member that covers an outer periphery of the annular inner resin member. The annular inner resin member has a plurality of axially downgauged portions arranged at intervals in a circumferential direction. The annular outer resin member has filling portions respectively fill the axially downgauged portions and an axial surface covering portion that is located radially inward of a tooth side of the teeth and covers the filling portions. According to a power transmission resin gear of the second aspect of the present invention in the power transmission resin gear of the first aspect, each of the teeth has a tooth bottom with an arc shape that fits an outer peripheral shape of a worm, and a tooth surface that is a curved surface with an arc shape, and the power transmission resin gear serves as a worm wheel to be used as a worm gear reducer in combination with the worm. A power transmission resin gear of the third aspect of the present invention in the power transmission resin gear of the first aspect or the second aspect further includes a plurality of axial protrusions arranged at intervals in the circumferential direction on an outer peripheral surface of the annular inner resin member, the outer peripheral surface being located radially inward of the teeth on an outer peripheral surface of the annular outer resin member. The axially downgauged portions are located radially inward of the axial protrusions. A method of producing a power transmission resin gear according to the fourth aspect of the present invention is a m