JP2023043069A - Worm wheel, manufacturing method of worm wheel, worm reduction gear and manufacturing method of annular core grid - Google Patents

Abstract

To provide a worm wheel which is further suppressed in the occurrence of a molding failure when manufacturing the worm wheel by injection-molding a resin gear on the radially outer end of a core grid, a manufacturing method of the worm wheel, a worm reduction gear, and a manufacturing method of the annular core grid.SOLUTION: A worm wheel comprises a first annular part, a second annular part located outside the first annular part in a radial direction, an annular core grid located radially outside the second annular part, and a resin gear attached to a third annular part. An annular first plane face part is arranged at the first annular part, a second plane face part is arranged at the second annular part, and an annular third plane face part located at the other side rather than the first plane face part in an axial direction is arranged at the third annular part. The second plane face part can abut on an abutment region of a metal mold, and extends along the radial direction orthogonal to a center axis.SELECTED DRAWING: Figure 5

Description

TECHNICAL FIELD The present disclosure relates to a worm wheel, a method for manufacturing a worm wheel, a method for manufacturing a worm speed reducer, and an annular core bar.

The worm wheel of Patent Document 1 has a metal core and a resin gear, and the teeth of the resin gear mesh with the teeth of the worm shaft. When the worm shaft rotates, the worm wheel rotates through the resin gear.

The worm wheel of Patent Document 1 is manufactured by injection-molding (insert-molding) a resin gear onto a radially outer end portion of a metal core. Specifically, when the mold is opened to accommodate the cored bar, and when the mold is closed, part of the mold is brought into contact with the side surface of the cored bar so that the outer edge of the cored bar in the radial direction is form a cavity in the After that, by filling the cavity with resin and curing the resin, a resin gear is injection-molded on the radially outer end portion of the core bar.

WO2017-135140

During injection molding, if there is a gap between a part of the mold and the side surface of the core bar, resin may leak from the gap, resulting in molding defects.

The present disclosure has been made in view of the above-described problems, and includes a worm wheel, a method for manufacturing a worm wheel, a worm gear, and a worm wheel, in which molding defects are reduced when a resin gear is injection-molded on the radially outer end of a core bar. An object of the present invention is to provide a method of manufacturing a speed reducer and an annular core bar.

In order to achieve the above object, a worm wheel according to one aspect includes a first annular portion extending in a circumferential direction around a central axis and having a shaft insertion hole penetrating the inner periphery thereof; A second annular portion located radially outside the annular portion and extending in the circumferential direction; and a third annular portion located radially outside the second annular portion and extending in the circumferential direction. and a resin gear attached to the third annular portion and extending along the circumferential direction. A ring-shaped second flat portion with which the contact portion can abut is provided, and the second flat portion extends along a radial direction perpendicular to the central axis.

Of the parts of the mold, the contact part that contacts the second flat part usually has a plane perpendicular to the central axis. In the present disclosure, the second planar portion extends along the radial direction perpendicular to the central axis. Therefore, when the cored bar is installed in the metal mold, the contact portion of the metal mold is in close contact with the second flat portion of the cored bar. Therefore, when the mold is filled with resin, the resin is less likely to leak from the abutment portion between the abutment portion of the mold and the second flat portion of the core bar, thereby further suppressing molding defects.

Preferably, the second planar portion is a machined planar surface, so that it is smoother than a non-machined planar surface. Therefore, a gap is less likely to occur between the mold and the second flat portion, and molding defects can be further suppressed.

As a desirable mode, when the cored bar is rotated once around the central axis, the axial position of the second flat portion on one side in the axial direction and the axial position on the other side in the axial direction are the same. The first variation distance, which is the distance along the axial direction, is the axial position of the third flat portion on one side in the axial direction when the cored bar is rotated once around the central axis. It is smaller than the second variation distance, which is the distance along the axial direction from the axial position on the other side in the axial direction.

When the portion of the mold that contacts the second flat portion is flat, the smaller the variation distance, the smaller the gap between the mold and the second flat portion. Therefore, it becomes more difficult for the resin to leak from between the mold and the second flat portion, and molding defects can be further suppressed.

As a desirable aspect, an annular fourth flat portion is provided on the other axial side of the second annular portion, and an annular fifth planar portion is provided on the other axial side of the third annular portion. The axial separation distance between the first plane portion and the fourth plane portion is the third distance, and the axial separation distance between the first plane portion and the fifth plane portion is the third distance. A fourth distance that is less than the three distances.

Thus, the fifth plane portion is located on one side in the axial direction relative to the fourth plane portion. Further, the third flat portion on the opposite side of the fifth flat portion is located on one side in the axial direction of the second flat portion on the opposite side of the fourth flat portion. Therefore, the thickness of the third annular portion in the axial direction is smaller than when the fifth flat portion is located on the other side in the axial direction of the fourth flat portion, so the weight of the entire worm wheel is reduced.

As a desirable mode, the surface of the second plane portion is provided with a plurality of unevenness extending in the circumferential direction around the central axis. The unevenness is, for example, traces of machining such as cutting, grinding, and polishing. Machining makes the second flat portion smoother, making it more difficult for the resin to leak from between the mold and the second flat portion, so that molding defects can be further suppressed.

As a desirable aspect, the second flat portion is a surface-treated flat surface. Physical treatments such as shot bolus and shot peening, and plating treatments can be applied to the surface treatment. The hardness of the second plane portion can be increased by shot bolust, shot peening, or the like, and the rust prevention performance is improved by plating.

A method for manufacturing an annular cored bar according to one aspect includes: a first annular portion extending in a circumferential direction around a central axis and having a shaft insertion hole penetrating the inner circumference thereof; An annular portion having a second annular portion located radially outwardly and extending in the circumferential direction, and a third annular portion located radially outwardly of the second annular portion and extending in the circumferential direction. A method for manufacturing a mandrel, comprising: a preparation step of preparing a forging material; after the preparation step, a forging step of forging the forging material to manufacture a work; and a machining step of machining one side of the second annular portion in the axial direction while rotating the second annular portion in a direction around the axis. According to this, the second flat portion can be formed on the second annular portion of the cored bar by a relatively simple operation.

A method for manufacturing a worm wheel according to one aspect includes: a first annular portion extending in a circumferential direction around a central axis and having a shaft insertion hole penetrating the inner periphery thereof; and a radial direction of the first annular portion. An annular core bar having a second annular portion located outside and extending in the circumferential direction, and a third annular portion located radially outside of the second annular portion and extending in the circumferential direction. and a resin gear attached to the third annular portion and extending along the circumferential direction, the worm wheel manufacturing method comprising: a preparation step of preparing a forging material; After the preparation step, a forging step of forging the forging material to produce a work; A processing step of machining one side to produce a metal core, and after the processing step, placing the metal core inside an injection mold, and and a filling step of filling the inside of the injection mold with a resin after the abutting step. According to this, the resin gear can be easily formed on the core bar having the smooth second plane portion. Also, when molding the resin gear, the resin is less likely to leak from between the part of the injection molding die and the second flat portion of the second annular portion, so that molding defects can be further suppressed.

A worm reduction gear according to one aspect includes: an annular core bar extending in a circumferential direction around a central axis; a resin gear attached to a radially outer portion of the core bar and extending along the circumferential direction; and a housing for housing the worm wheel, wherein the core bar extends in the circumferential direction and has a first annular portion provided with a shaft insertion hole penetrating the inner periphery thereof; a second annular portion located radially outside the first annular portion and extending in the circumferential direction; and a third annular portion located radially outside the second annular portion and extending in the circumferential direction. , wherein the resin gear is attached to the third annular portion, an annular second planar portion is provided on one side of the second annular portion in the axial direction, and the housing includes the third annular portion. It has a protruding portion extending toward the second flat portion and having a distal end facing the second flat portion in the axial direction.

Thus, the housing has a projection, and the tip of the projection axially opposes the second flat portion. Here, since the second flat portion is located on the other side in the axial direction relative to the third flat portion, the tip of the projecting portion can be arranged closer to the second flat portion. If the degree of smoothness of the second plane portion is higher, the tip of the projecting portion can be brought closer to the second plane portion.

According to the present disclosure, when a worm wheel is manufactured by injection-molding a resin gear on the radially outer end portion of a core metal, a worm wheel, a method for manufacturing a worm wheel, and a worm reduction gear that cause less molding defects. and a method for manufacturing an annular cored bar.

FIG. 1 is a schematic diagram of an electric power steering device according to the first embodiment. FIG. 2 is a cross-sectional view showing an enlarged part of FIG. FIG. 3 is a perspective view showing the worm wheel according to the first embodiment. 4 is a front view of FIG. 3. FIG. 5 is a cross-sectional view taken along line VV of FIG. 4. FIG. FIG. 6 is a perspective view of the metal core of the worm wheel. 7 is a front view of FIG. 6. FIG. FIG. 8 is a cross-sectional view taken along line VIII-VIII of FIG. FIG. 9 is a conceptual diagram showing the first variable distance and the second variable distance when the cored bar is rotated once around the central axis. FIG. 10 is a flow chart showing a method for manufacturing an annular cored bar. FIG. 11 is a flow chart showing a method of manufacturing a worm wheel. FIG. 12 is a cross-sectional view showing a state in which a metal mold is used to inject resin into a metal core. FIG. 13 is a cross-sectional view showing a state in which the worm wheel according to the second embodiment is manufactured by injection molding.

A form (embodiment) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the contents described in the following embodiments. In addition, the components described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the components described below can be combined as appropriate. Furthermore, the same reference numerals are given to parts having the same structure, and the description thereof is omitted. In the drawings, the upper side (one side in the axial direction) is indicated by D1, and the lower side (the other side in the axial direction) is indicated by D2. Also, in the description of the embodiments, the upper side (one side in the axial direction) may be referred to as the D1 side, and the lower side (the other side in the axial direction) may be referred to as the D2 side.

[First embodiment]
FIG. 1 is a schematic diagram of an electric power steering device according to the first embodiment.

As shown in FIG. 1, the electric power steering device 80 includes a steering wheel 81, a first steering shaft 82, a second steering shaft 83, a pinion shaft 1, a worm reduction gear 400, a rack shaft 2, and tie rods. 84 , an ECU 89 and a power supply device 90 .

The first steering shaft 82 is connected with the steering wheel 81 . The first steering shaft 82 is rotatably supported. The first steering shaft 82 is rotated by the torque that steers the steering wheel 81 . Specifically, when the driver grips and rotates the steering wheel 81, the rotational torque (steering torque) is transmitted to the first steering shaft 82, and the first steering shaft 82 rotates.

The second steering shaft 83 is connected to the first steering shaft 82 via a first universal joint 85 . The second steering shaft 83 is rotatably supported. Rotational torque of the first steering shaft 82 is transmitted to the second steering shaft 83 via the first universal joint 85, and the second steering shaft 83 rotates.

Here, the housing 87 has a first housing 871 , a second housing 872 and a third housing 873 .

The second housing 872 is positioned below the first housing 871 (D2 side, the other side in the axial direction), and the third housing 873 is positioned below the second housing 872 (D2 side). That is, the first housing 871 is positioned at the upper portion of the housing 87 , the second housing 872 is positioned at the middle portion of the housing 87 , and the third housing 873 is positioned at the lower portion of the housing 87 . Located in

As shown in FIG. 1 , the pinion shaft 1 is connected to a second steering shaft 83 via a second universal joint 86 . Rotational torque of the second steering shaft 83 is transmitted to the pinion shaft 1 via the second universal joint 86, and the pinion shaft 1 rotates. Pinion shaft 1 extends in the axial direction of central axis AX. The pinion shaft 1 rotates around the central axis AX. The pinion shaft 1 is provided with pinion teeth 120 . Pinion shaft 1 is rotatably supported by housing 87 via second bearing 91 and first bearing 92 . The second bearing 91 supports the upper portion of the pinion shaft 1 . The first bearing 92 supports the lower portion of the pinion shaft 1 . Specifically, the second bearing 91 is provided on the cylindrical surface 128 on the upper side (D1 side, one side in the axial direction) of the pinion tooth 120 .

The rack shaft 2 is accommodated inside the second housing 872 . The rack shaft 2 extends in the vehicle width direction (horizontal direction) of the vehicle. Rack teeth 21 are provided on the side of the rack shaft 2 . Rack teeth 21 mesh with pinion teeth 120 of pinion shaft 1 . A pair of tie rods 84 are provided on both left and right sides of the rack teeth 21 . Tie rods 84 are connected to wheels 88 . Therefore, when the pinion shaft 1 rotates, a force in the vehicle width direction is transmitted to the rack teeth 21 meshing with the pinion teeth 120, and the rack shaft 2 moves left and right. As a result, the tie rod 84 moves in the left-right direction, the wheels 88 tilt, and the traveling direction of the vehicle changes.

The worm reduction gear 400 includes a worm shaft 71 , a worm wheel 3 and a third housing 873 . That is, the worm shaft 71 and the worm wheel 3 are housed inside the third housing 873 . The worm shaft 71 is provided on the output shaft of the electric motor 72 . The worm shaft 71 meshes with the worm wheel 3 . A worm wheel 3 is fixed to the lower end of the pinion shaft 1 . Therefore, when the electric motor 72 is operated, the worm shaft 71 rotates, and the worm wheel 3 meshing with the worm shaft 71 rotates together with the pinion shaft 1 . This reduces the force required to steer the steering wheel 81 . The worm speed reducer 400 will be described later in detail.

The ECU 89 is connected to a power supply device 90 (for example, a vehicle-mounted battery), and power is supplied from the power supply device 90 to the ECU 89 . The ECU 89 controls the operation of the electric motor 72 . The ECU 89 acquires signals from a torque sensor and a vehicle speed sensor (not shown). The ECU 89 calculates an assist steering command value based on the steering torque and vehicle speed. The ECU 89 adjusts the power value supplied to the electric motor 72 based on the assist steering command value. The ECU 89 acquires information on the induced voltage from the electric motor 72 or information output from a resolver or the like provided in the electric motor 72 . By controlling the operation of the electric motor 72 by the ECU 89, the force required to steer the steering wheel 81 is reduced as described above.

FIG. 2 is a cross-sectional view showing an enlarged part of FIG. The pinion shaft 1 has an input shaft 11 , an output shaft 12 and a torsion bar 13 . The input shaft 11 is positioned above the output shaft 12 (on the D1 side). The input shaft 11 and the output shaft 12 are connected via a torsion bar 13 . In FIG. 2, a concave portion 12a is provided in the upper end portion of the output shaft 12, and the lower end portion of the torsion bar 13 is fitted in the concave portion 12a. The second bearing 91 is, for example, a needle bearing having a plurality of needles 91a, but may be a normal deep groove ball bearing. The output shaft 12 is accommodated inside the second housing 872 , and the output shaft 12 is rotatably supported with respect to the second housing 872 via the second bearing 91 .

As shown in FIG. 2, a through hole 872a is formed in the second housing 872, and the rack shaft 2, the pressing member 22, the spring 23, and the sealing member 24 are accommodated in the through hole 872a. be. A pressing member 22 is arranged radially outside the rack shaft 2 , a sealing member 24 is arranged radially outside the pressing member 22 , and a gap between the pressing member 22 and the sealing member 24 is A spring 23 is provided. As a result, the rack shaft 2 is pressed against the pinion teeth 120 of the output shaft 12 by the elastic force of the spring 23 .

Rack teeth 21 are provided on the side surface of the rack shaft 2 on the output shaft 12 side. A plurality of rack teeth 21 are provided along the front-rear direction of the paper surface of FIG. Pinion teeth 120 are provided on the outer periphery of the output shaft 12 . The pinion teeth 120 spirally extend in the axial direction of the central axis AX. Pinion teeth 120 mesh with rack teeth 21 . That is, when the pinion shaft 1 and the pinion teeth 120 rotate around the central axis AX, the rack teeth 21 and the rack shaft 2 meshing with the pinion teeth 120 move in the vehicle width direction.

As shown in FIG. 2, a cylindrical surface 126 is provided on the lower side (D2 side) of the pinion tooth 120 among the portions of the pinion shaft 1, and a cylindrical surface 127 is provided on the lower side (D2 side) of the cylindrical surface 126. is provided. A first bearing 92 is attached to the cylindrical surface 126 . A bearing accommodating portion 873a is provided inside the third housing 873, and the first bearing 92 is accommodated in the bearing accommodating portion 873a. Further, the lower side (D2 side) of the third housing 873 has a projecting portion 873b that projects toward the D2 side. A support member 93 is fastened to the inner periphery of the projecting portion 873b. Specifically, a female thread is cut on the inner periphery of the protruding portion 873b, a male thread is cut on the outer periphery of the support member 93, and a male thread on the outer periphery of the support member 93 is meshed with the female thread on the inner periphery of the protruding portion 873b. there is As a result, the first bearing 92 is axially sandwiched between the bearing accommodating portion 873 a and the support member 93 .

A worm wheel 3 is attached to the cylindrical surface 127 . The worm wheel 3 will be described in detail below. FIG. 3 is a perspective view showing the worm wheel according to the first embodiment. 4 is a front view of FIG. 3. FIG. 5 is a cross-sectional view taken along line VV of FIG. 4. FIG. FIG. 6 is a perspective view of the metal core of the worm wheel. 7 is a front view of FIG. 6. FIG. FIG. 8 is a cross-sectional view taken along line VIII-VIII of FIG. FIG. 9 is a conceptual diagram showing the first variable distance and the second variable distance when the cored bar is rotated once around the central axis.

As shown in FIGS. 3 to 8, the worm wheel 3 includes a metal core 4 and a resin gear 5. As shown in FIGS.

The cored bar 4 extends in a circumferential direction around the central axis Ax. The cored bar 4 is, for example, metal. The cored bar 4 includes a first annular portion 41 , a second annular portion 42 , a third annular portion 43 and a flange 44 .

As shown in FIG. 8, the first annular portion 41 has a cylindrical portion 411 extending in the axial direction of the central axis Ax. An annular first plane portion 412 is provided at the end portion on the D1 side (one side in the axial direction) of the cylindrical portion 411 . The first plane portion 412 is orthogonal to the central axis Ax. That is, the intersection angle between the first plane portion 412 and the central axis Ax is approximately 90 degrees. An annular sixth plane portion 416 is provided at the end portion on the D2 side (one side in the axial direction) of the cylindrical portion 411 . A shaft insertion hole 415 is provided on the inner peripheral side of the inner peripheral surface 414 of the cylindrical portion 411 . The cylindrical surface 127 of the pinion shaft 1 shown in FIG. 2 is inserted into the shaft insertion hole 415 . The cylindrical surface 127 is subjected to serration processing (processing to form saw blade-like grooves on the circumferential surface), and the cylindrical surface 127 is press-fitted into the shaft insertion hole 415 (so-called serration press-fitting), so that the core metal 4 and the pinion shaft are connected. 1 may be fixed.

As shown in FIG. 8, the second annular portion 42 is located radially outside the first annular portion 41 and extends in the circumferential direction. An annular second plane portion 421 is provided at the end portion of the second annular portion 42 on the D1 side (one side in the axial direction). The second plane portion 421 is, for example, a machined plane. Machining can be applied, for example, cutting. Moreover, lathe processing, milling processing, etc. are preferable as cutting processing. In lathe processing, for example, the cored bar 4 as a material is rotated, and the second annular portion 42 is machined by pressing a cutting tool against the D1 side of the second annular portion 42 . In milling, for example, a rotating cutting tool is pressed against the D1 side of the second annular portion 42 of the fixed cored bar 4 to machine the second annular portion 42 .

In addition to cutting, various machining such as grinding and polishing can be applied. In lathe processing, for example, the core metal 4 as a material is rotated, and a grindstone is pressed against the D1 side of the second annular portion 42 to process the second annular portion 42 . The second annular portion 42 of the cored bar 4 may be scraped off little by little by a whetstone that rotates at high speed. In the polishing process, a grinder or a barrel processing machine can be used to cut more finely than in the grinding process.

As shown in FIG. 8, the second plane portion 421 extends along the radial direction perpendicular to the central axis Ax. That is, the second flat portion 421 extends from the radially inner end 421a to the radially outer end 421b along the radial direction. In other words, the intersection angle between the second plane portion 421 and the central axis Ax is approximately 90 degrees. Preferably, the second plane portion 421 is orthogonal to the central axis Ax, and the intersection angle between the second plane portion 421 and the central axis Ax is 90 degrees. The second plane portion 421 is located on the D2 side of the first plane portion 412 .

An annular surface portion 413 is provided radially inward of the radially inner end 421a. The annular surface portion 413 extends in the axial direction of the central axis Ax. In other words, the annular surface portion 413 is perpendicular to the second plane portion 421 . An annular surface portion 433 is provided on the radially outer side of the radially outer end 421b. The annular surface portion 433 connects the second plane portion 421 and the third plane portion 431 . The annular surface portion 433 extends in the axial direction of the central axis Ax. In other words, the annular surface portion 433 is perpendicular to the second plane portion 421 . An annular fourth plane portion 422 is provided on the radially outer portion on the D2 side of the second annular portion 42 . That is, the fourth plane portion 422 is located on the opposite side of the second plane portion 421 . A plurality of unevennesses (not shown) extending in the circumferential direction around the central axis Ax may be provided on the D1 side surface of the second flat portion 421 . The unevenness is a trace of machining as described above. Furthermore, the second plane portion 421 may be a surface-treated plane. Surface treatments include physical treatments such as shot bolus and shot peening, and plating treatments for rust suppression.

Note that the annular surface portion 413 and the annular surface portion 433 may be inclined portions that obliquely cross the central axis Ax. That is, for example, the annular surface portion 413 may be inclined toward the D1 side as it goes radially inward. The annular surface portion 433 may be inclined toward the D1 side as it goes radially outward.

As shown in FIG. 8, the third annular portion 43 is located radially outside the second annular portion 42 and extends in the circumferential direction. An annular third planar portion 431 is provided at the end of the third annular portion 43 on the D1 side (one side in the axial direction). The third plane portion 431 extends radially from a radially inner end 431a to a radially outer end 431b. An annular fifth plane portion 432 is provided at a radially outer portion on the D2 side of the third annular portion 43 . That is, the fifth plane portion 432 is located on the opposite side of the third plane portion 431 .

As shown in FIG. 8 , the flange 44 is provided radially outward of the third annular portion 43 . An annular flat portion 441 is provided at the end of the flange 44 on the D1 side (one side in the axial direction). The plane portion 441 is located on the D1 side (one side in the axial direction) of the third plane portion 431 . An outer peripheral surface 443 of the flange 44 is a cylindrical surface extending in the circumferential direction. However, as shown in FIG. 6, the inner peripheral surface 442 of the flange 44 has a groove. The flange 44 is provided with a cylindrical surface portion 444 at the corner on the D2 side. The cylindrical surface portion 444 is orthogonal to the central axis Ax.

Here, as shown in FIG. 8, the axial separation distance between the first plane portion 412 and the second plane portion 421 is the first distance L1. The axial separation distance between the first plane portion 412 and the third plane portion 431 is the second distance L2. The second distance L2 is smaller than the first distance L1.

Furthermore, as shown in FIG. 8, the axial separation distance between the first plane portion 412 and the fourth plane portion 422 is a third distance L3. The axial separation distance between the first plane portion 412 and the fifth plane portion 432 is the fourth distance L4. The fourth distance L4 is smaller than the third distance L3.

As described above with reference to FIG. 2, the lower side (D2 side) of the third housing 873 has a projecting portion 873b that projects toward the D2 side. The projecting portion 873b extends toward the second flat portion 421 . A tip 874 of the projecting portion 873b faces the second flat portion 421 in the axial direction. The tip 874 is close to the second flat portion 421 .

As shown in FIG. 9, the first variation distance L10 and the second variation distance L20 when the cored bar 4 is rotated once about the central axis Ax will be described. The first variation distance L10 is the axial position P1 closest to the D1 side (one side in the axial direction) of the second flat portion 421 when the core bar 4 is rotated once (360 degrees) around the central axis Ax. and the axial position P11 closest to D2 (the other side in the axial direction) along the axial direction. The second variation distance L20 is the axial position P2 closest to the D1 side (one side in the axial direction) of the third plane portion 431 when the core bar 4 is rotated once (360 degrees) around the central axis Ax. and the axial position P21 closest to D2 (the other side in the axial direction) along the axial direction.

As shown in FIG. 9, displacement sensors 200 and 210, for example, can be applied to measure the first variation distance L10 and the second variation distance L20. The displacement sensor 200 can measure the axial displacement of the central axis Ax of the second flat portion 421 . The displacement sensor 210 can measure the axial displacement of the central axis Ax of the third plane portion 431 . In the graph shown in the boxed portion in FIG. 9, the vertical axis indicates the sensor displacement (fluctuation distance in the axial direction), and the horizontal axis indicates the rotation angle θ of the cored bar 4 . The first variation distance L10 is the difference between the axial position P1 and the axial position P11, as shown in the lower squared graph in FIG. The second variation distance L20 is the difference between the axial position P2 and the axial position P21, as shown in the upper squared graph in FIG. The first variation distance L10 is smaller than the second variation distance L20.

Further, as shown in FIG. 5, the resin gear 5 is provided on the third annular portion 43 and the flange 44 of the cored bar 4 . Specifically, for example, the resin gear 5 can be formed by injection-molding resin onto the outside of the third annular portion 43 and the flange 44 of the core bar 4 . As shown in FIGS. 3 and 4 , a plurality of teeth 51 are provided on the outer periphery of the resin gear 5 . The toothed portion 51 of the resin gear 5 meshes with the worm shaft 71 . The worm shaft 71 is rotationally driven by an electric motor 72 as described with reference to FIG.

Next, a method for manufacturing an annular core bar and a method for manufacturing a worm wheel will be described. FIG. 10 is a flow chart showing a method for manufacturing an annular cored bar. FIG. 11 is a flow chart showing a method of manufacturing a worm wheel. FIG. 12 is a cross-sectional view showing a state in which a metal mold is used to inject resin into a metal core.

As shown in FIG. 10, the method for manufacturing the annular cored bar 4 includes a preparation step S1, a forging step S2, and a processing step S3.

In the preparation step S1, a metal forging material to be used for forging is prepared. In the forging step S2, the forging material is forged after the preparation step S1. Forging is performed, for example, by hot forging in which a heated forging material is deformed by applying pressure with a forging die, or cold forging in which a forging material at approximately room temperature is applied with pressure by a forging die and deformed. . In the forging step S2, the forging material is forged to manufacture a workpiece. In the processing step S3, after the forging step S2, the work is machined as described above. Machining is cutting work such as lathe processing and milling. For example, the D1 side (one side in the axial direction) of the second annular portion 42 is machined while rotating the work around the central axis Ax. Thereby, the second plane portion 421 is formed.

Next, a method for manufacturing the worm wheel 3 will be described. The method for manufacturing the worm wheel 3 includes, as shown in FIG. 11, a preparation step S11, a forging step S12, a processing step S13, a contact step S14, and a filling step S15.

The preparation step S11, the forging step S12 and the processing step S13 are the same as the preparation step S1, the forging step S2 and the processing step S3 in the manufacturing method of the annular cored bar 4, so the description thereof will be omitted. It should be noted that the ring-shaped cored bar 4 having the second plane portion 421 is formed by the processing step S13.

Next, a contact step S14 and a filling step S15 are performed. First, the structure of the mold 6, which is an injection mold, will be briefly described.

As shown in FIG. 12 , the mold 6 includes a first mold 61 , a second mold 62 , a third mold 63 and a fourth mold 64 . The first die 61 is arranged on the X2 side of the die 6 . The first mold 61 is a fixed mold, and the second mold 62, third mold 63 and fourth mold 64 are movable molds. The fourth die 64 has an annular shape and is provided with a tooth profile on an inner peripheral surface 64a. The tooth portion 51 of the resin gear 5 is formed by the tooth profile of the inner peripheral surface 64a. The second die 62, the third die 63 and the fourth die 64 are coaxially and integrally assembled. The second mold 62, the third mold 63 and the fourth mold 64 are slidable in the X direction in an integrated state. Therefore, when the mold 6 closes, the second mold 62, the third mold 63, and the fourth mold 64 are integrated and slide to the X2 side, and when the mold 6 opens, the second mold 62, the third mold 63 and the fourth die 64 are integrated and slide to the X1 side.

A front surface 61a of the first die 61 is located on the X2 side of the cored bar 4 . As a result, a gap is created between the front surface 61 a of the first die 61 and the core bar 4 . An inflow path 61 b for the resin 100 is formed in the first mold 61 . The resin 100 can flow into the inflow path 61b from the tip 61c of the inflow path 61b.

The second mold 62 includes a small diameter portion 62a, a medium diameter portion 62b, and a large diameter portion 62c. The medium diameter portion 62b is arranged on the X1 side of the small diameter portion 62a, and the large diameter portion 62c is arranged on the X1 side of the medium diameter portion 62b. A contact portion 62 d on the X2 side of the second die 62 contacts the second flat portion 421 of the second annular portion 42 . A through hole 62e is provided in the second die 62 along the X direction. The small diameter portion 62a has a cylindrical outer peripheral surface 62f, and the medium diameter portion 62b has a planar side surface 62g and a cylindrical outer peripheral surface 62h.

The third die 63 is assembled along the inside of the through hole 62e of the second die 62 . The third die 63 includes a small diameter portion 63a and a large diameter portion 63b. The outer peripheral surface 63 c of the small diameter portion 63 a is inserted into the inner peripheral side of the inner peripheral surface 414 of the cylindrical portion 411 . An inner peripheral surface 64 a of the fourth die 64 is arranged radially outside the flange 44 .

A procedure for injection molding a thermoplastic resin onto the metal core 4 using the mold 6 having the above configuration will be briefly described. The procedure for injection-molding the thermoplastic resin onto the cored bar 4 includes the contact step S14 and the filling step S15, as described above.

First, as shown in FIG. 12 , in the abutment step S14, the mold 6 is opened and the cored bar 4 is arranged inside the mold 6 . Specifically, as described above, the second die 62, the third die 63, and the fourth die 64 are slid to open the die 6, and after the cored bar 4 is housed inside the die 6, the second die 62, the third die 63, and the fourth die 64 are opened. The mold 62, the third mold 63 and the fourth mold 64 are slid to close the mold 6. Then, the contact portion 62 d on the X2 side of the second die 62 contacts the second flat portion 421 of the second annular portion 42 . The contact portion 62d is part of an injection mold.

Next, in the filling step S15, the inside of the mold 6 is filled with the resin 100 after the contacting step S14. That is, as indicated by an arrow 110 in FIG. 12, the resin 100 is injected from the tip 61c into the inflow path 61b. The resin 100 is, for example, a thermoplastic resin, and softens or melts at a high temperature. After moving the inside of the inflow passage 61b toward the X1 side, the resin 100 hits the side surface 63d on the X2 side of the small diameter portion 63a of the third die 63, and then moves radially outward along the core metal 4. do. Then, the resin 100 flows from the radially outer side of the flange 44 to the inner peripheral surface 442 of the flange 44, and the flow of the resin is stopped. Since the inner peripheral surface 442 of the flange 44 has grooves, the resin 100 enters the grooves.

Then, after the resin 100 has hardened, the mold 6 is opened, the molded product is taken out, and the worm wheel 3 is completed by scraping away the excess resin axially inward from the gate cut portion 52 (see FIG. 5).

As described above, the worm wheel 3 according to the present embodiment includes the first annular portion 41 extending in the circumferential direction around the central axis Ax and having the shaft insertion hole 415 penetrating the inner periphery thereof; A second annular portion 42 located radially outside the first annular portion 41 and extending in the circumferential direction, and a third annular portion 43 located radially outside the second annular portion 42 and extending in the circumferential direction. and a resin gear 5 attached to the third annular portion 43 and extending in the circumferential direction. An annular first plane portion 412 is provided on the D1 side (one side in the axial direction) of the first annular portion 41 , and the first plane portion 412 is provided on the D1 side (one side in the axial direction) of the second annular portion 42 . An annular second flat portion 421 is provided on the D2 side (the other side in the axial direction) of the portion 412 , and the first flat portion 412 is provided on the D1 side (one side in the axial direction) of the third annular portion 43 . An annular third plane portion 431 located on the D2 side (the other side in the axial direction) is provided. The second plane portion 421 extends along the radial direction perpendicular to the central axis Ax.

Of the parts of the mold, the contact part that contacts the second plane portion 421 usually has a plane orthogonal to the central axis Ax. In this embodiment, the second plane portion 421 extends along the radial direction orthogonal to the central axis Ax. Therefore, when the metal core 4 is installed in the metal mold, the contact portion of the metal mold 6 is in close contact with the second plane portion of the metal core. Therefore, when the mold is filled with resin, the resin is less likely to leak from the abutment portion between the abutment portion of the mold and the second flat portion of the core bar, thereby further suppressing molding defects.

As shown in FIG. 5, when a force F is applied to the resin gear 5 toward the D1 side or the D2 side of the worm wheel 3 as indicated by the arrows, the resin gear 5 is easily separated from the flange 44 . Here, as described above, the cored bar 4 is provided with the annular surface portion 433 and the cylindrical surface portion 444 . Since the annular surface portion 433 and the cylindrical surface portion 444 extend in the radial direction (vertical direction in FIG. 5), they are perpendicular to the third plane portion 431 and the fifth plane portion 432 . Therefore, even if the force F is applied to the resin gear 5 , the annular surface portion 433 and the cylindrical surface portion 444 are caught by the resin gear 5 , thereby preventing the resin gear 5 from coming off the flange 44 .

Since the second planar portion 421 is a machined plane, it is smoother than a non-machined plane. Therefore, a gap is less likely to occur between the contact portion 62d and the second flat portion 421, and molding defects can be further suppressed.

When the core bar 4 is rotated once around the central axis Ax, the axial position of the second flat portion 421 closest to the D1 side (one side in the axial direction) and the axial position closest to the D2 side (the other side in the axial direction) The first variation distance L10, which is the distance along the axial direction from the axial position, is the most D1 side of the third plane portion 431 (axial is smaller than the second variation distance L20, which is the distance along the axial direction between the axial position on the side of the D2 side (one side of the shaft) and the axial position closest to the D2 side (the other side in the axial direction).

If the portion of the mold 6 that contacts the second flat portion 421 is flat, the smaller the variation distance, the smaller the gap between the mold 6 and the second flat portion 421 . Therefore, it becomes more difficult for the resin 100 to leak from between the mold 6 and the second flat portion 421, and molding defects can be further suppressed.

An annular fourth plane portion 422 is provided on the D2 side (the other side in the axial direction) of the second annular portion 42 , and an annular fourth plane portion 422 is provided on the D2 side (the other side in the axial direction) of the third annular portion 43 . Five flats 432 are provided. The axial separation distance between the first plane portion 412 and the fourth plane portion 422 is the third distance L3, and the axial separation distance between the first plane portion 412 and the fifth plane portion 432 is the third distance. A fourth distance L4 that is smaller than L3.

In this manner, the fifth plane portion 432 is located on the D1 side (one side in the axial direction) of the fourth plane portion 422 . In addition, the third plane portion 431 opposite to the fifth plane portion 432 is located on the D1 side (one side in the axial direction) of the second plane portion 421 opposite to the fourth plane portion 422 .

Therefore, the thickness of the third annular portion 43 in the axial direction is smaller than when the fifth flat portion 432 is located on the D2 side (the other side in the axial direction) of the fourth flat portion 422. 3 Overall weight is reduced.

The surface of the second flat portion 421 is provided with a plurality of unevenness extending in the circumferential direction around the central axis Ax. The unevenness is, for example, traces of machining such as cutting, grinding, and polishing. Machining makes the second flat portion 421 smoother, making it more difficult for the resin 100 to leak from between the mold 6 and the second flat portion 421, thereby further suppressing molding defects.

The second plane portion 421 is a surface-treated plane. Physical treatments such as shot bolus and shot peening, and plating treatments can be applied to the surface treatment. The hardness of the second plane portion 421 can be increased by shot bolus, shot peening, or the like, and the rust prevention performance is improved by plating.

The method for manufacturing the annular core bar 4 according to the present embodiment includes machining the D1 side (one side in the axial direction) of the second annular portion 42 while rotating the workpiece in the direction around the central axis Ax. including step S3. According to this, the second flat portion 421 can be formed on the second annular portion 42 of the cored bar 4 by relatively simple work.

In the method of manufacturing the worm wheel according to the present embodiment, after the processing step S13, the contact portion 62d (part of the injection mold) on the X2 side of the mold 6 is attached to the second flat portion 421 of the second annular portion 42. It includes an abutment step S14 of abutting and a filling step S15 of filling the inside of the mold 6 (injection mold) with the resin 100 . According to this, the resin gear 5 can be easily formed on the core bar 4 having the smooth second plane portion 421 . Further, when molding the resin gear 5, the resin 100 is less likely to leak from between the contact portion 62d (part of the injection molding die) and the second flat surface portion 421 of the second annular portion 42, thereby further reducing molding defects. can be suppressed.

The worm reduction gear 400 includes an annular core 4 extending in the circumferential direction around the central axis Ax, and a resin gear 5 attached to the radially outer portion of the core 4 and extending in the circumferential direction. and a housing 87 that houses the worm wheel 3. The core bar 4 includes a first annular portion 41 extending in the circumferential direction and having a shaft insertion hole 415 penetrating the inner periphery thereof, and a first annular portion 41 located radially outside the first annular portion 41 and extending in the circumferential direction. It has an extending second annular portion 42 and a third annular portion 43 located radially outside the second annular portion 42 and extending in the circumferential direction. The resin gear 5 is attached to the third annular portion 43 , and an annular second planar portion 421 is provided on the D1 side (one side in the axial direction) of the second annular portion 42 . The housing 87 has a protruding portion 873b that extends toward the second flat portion 421 and whose tip is axially opposed to the second flat portion 421 .

In this manner, the housing 87 has a protruding portion 873b, and the tip of the protruding portion 873b faces the second flat portion 421 in the axial direction. Here, since the second flat portion 421 is located on the D2 side (the other side in the axial direction) of the third flat portion 431, the tip of the projecting portion 873b can be arranged closer to the second flat portion 421. . It should be noted that when the degree of smoothness of the second plane portion 421 is higher, the tip of the projecting portion 873b can be brought closer to the second plane portion 421 .

[Second embodiment]
Next, a second embodiment will be described. FIG. 13 is a cross-sectional view showing a state in which the worm wheel according to the second embodiment is manufactured by injection molding.

A metal core 4A according to the second embodiment differs from the metal core 4 according to the first embodiment in the shape of a flange 44A. The shape of the cored bar 4A will be briefly described below.

As shown in FIG. 13, the flange 44A has a thick portion 442A and a thin portion 444A. The outer peripheral surface of the flange 44A is a cylindrical surface extending along the circumferential direction of the central axis AX. The radial distance of the flat portion 441A in the thick portion 442A is greater than the radial distance of the flat portion 441 in the flange 44 of the core bar 4 of the first embodiment. In addition, the inner peripheral surfaces of the thick portion 442A and the thin portion 444A have concave grooves in the same manner as the inner peripheral surface of the flange 44 of the cored bar 4 . The inner peripheral surface of the thin portion 444A is an inclined surface extending radially outward toward the X2 side. Therefore, between the inner peripheral surface of the thin portion 444A and the third flat portion 431, a gap 445A having a triangular cross-section is formed, protruding radially outward.

Next, the structure of the mold 6A will be briefly described.

The mold 6A includes a first mold 61A, a second mold 62A, a third mold 63A, and a fourth mold 64A. The first mold 61A is arranged on the X2 side of the mold 6A. The first mold 61A is a fixed mold, and the second mold 62A, third mold 63A and fourth mold 64A are movable molds. Since the second mold 62A, the third mold 63A and the fourth mold 64A are integrally assembled, they are also integral when sliding. The fourth mold 64A has an annular shape and has a tooth profile on the inner peripheral surface 64Aa. The teeth of the resin gear are formed by the tooth profile of the inner peripheral surface 64Aa.

The front surface 61Aa of the first die 61A is positioned closer to the X2 side than the metal core 4A. The second mold 62A includes a small diameter portion 62Aa and a large diameter portion 62Ab. A contact surface 62Ad on the X2 side of the second die 62A contacts the second flat portion 421 of the second annular portion 42 .

The third die 63A is slidable along the X direction inside the through hole 62Ae of the second die 62A. The third mold 63A includes a small diameter portion 63Aa and a large diameter portion 63Ab. An inner peripheral surface 64Aa of the fourth die 64 is arranged radially outside the flange 44 .

A procedure for injection-molding the thermoplastic resin onto the metal core 4A using the mold 6A having the above configuration will be briefly described. The injection molding procedure includes a placement step and a filling step.

First, in the arrangement step, the mold 6A is opened, the metal core 4A is arranged inside the mold 6A, and then the mold 6 is closed.

Next, in the filling step, as indicated by arrow 110, resin 100 is injected from tip 61c into inflow path 61b. The resin 100 moves inside the inflow passage 61b toward the X1 side, hits the X2 side surface 63Ac of the small diameter portion 63Aa of the third die 63A, and then moves along the X2 side surface of the core metal 4A. Move radially outward. Then, the resin 100 flows from the outer peripheral surface 443A of the flange 44A along the flat portion 441A and then reaches the inner peripheral surface of the thick portion 442A. Here, as described above, since the inner peripheral surfaces of the thick portion 442A and the thin portion 444A have grooves, the resin 100 enters and fills the grooves. After that, the resin 100 flows and fills up to the gap 445A. After the resin 100 has hardened, the mold 6A is opened to take out the molded product, and the worm wheel 3A is completed by scraping away excess resin axially inward from the gate cut portion 52 (see FIG. 5).

As described above, in the present embodiment, the flange 44A has the thick portion 442A and the thin portion 444A, and between the inner peripheral surface of the thin portion 444A and the third plane portion 431, there is a radially outwardly protruding portion. A gap 445A having a triangular cross section is formed.

As shown in FIG. 13, in the worm wheel 3A, when a force F indicated by an arrow is applied to the resin gear on the X1 side or the X2 side, the resin gear is easily separated from the flange 44A. Here, since the resin 100 is also filled in the gap 445A by injection molding, even if the force F is applied to the resin gear, the resin 100 entering the gap 445A separates the resin gear from the flange 44A. is suppressed.

The present embodiment may be applied to a so-called column-assist type electric power steering in which the worm wheels 3 and 3A are attached to the first steering shaft 82 to generate assist torque in the first steering shaft 82 . In this case as well, the housing that stores the worm wheels 3, 3A extends toward the second flat portion provided on the worm wheels 3, 3A, and has a tip that axially opposes the second flat portion. You may be comprised so that a part may be provided.

This embodiment may be applied to a steer-by-wire steering system in which a steering wheel and tires are mechanically separated. A steer-by-wire steering system includes a reaction force device that applies a reaction force to a steering wheel, and a steering device that applies a force to steer tires. The worm speed reducer shown in this embodiment can be used as both a reaction force device and a steering device.

When used as a reaction force device, the worm wheels 3 and 3A are attached to the column shaft that supports the steering wheel, and the reaction torque is applied to the column shaft. When used in a steering device, the worm wheels 3 and 3A are attached to the pinions of a rack and pinion mechanism that generates a steering force on the tires, and the steering force is applied to the tires via the rack and pinion mechanism.

1 Pinion shaft 2 Rack shafts 3, 3A Worm wheels 4, 4A Core metal 5 Resin gears 6, 6A Mold 11 Input shaft 12 Output shaft 12a Recess 13 Torsion bar 21 Rack teeth 22 Pressing member 23 Spring 24 Sealing member 41 First Annular portion 42 Second annular portion 43 Third annular portion 44, 44A Flange 51 Tooth portion 52 Gate cut portions 61, 61A First dies 61a, 61Aa Front surface 61b Inflow passages 62, 62A Second dies 62a, 62Aa Small diameter portion 62Ab Large diameter Part 62Ad Contact surface 62Ae Through hole 62b Middle diameter part 62c Large diameter part 62d Contact part 62e Through hole 62f Outer peripheral surface 62g Side surface 62h Outer peripheral surface 63, 63A Third mold 63a Small diameter part 63b Large diameter part 63c Outer peripheral surface 63Aa Small diameter part 63Ab large diameter portions 64, 64A fourth die 64a inner peripheral surface 64Aa inner peripheral surface 71 worm shaft 72 electric motor 80 electric power steering device 81 steering wheel 82 first steering shaft 83 second steering shaft 84 tie rod 85 first universal joint 87 Housing 88 Wheel 89 ECU
90 Power supply device 91 Second bearing 91a Needle 92 First bearing 93 Support member 100 Resin 120 Pinion teeth 126, 127 Cylindrical surfaces 200, 210 Displacement sensor 400 Worm reducer 411 Cylindrical portion 412 First flat portion 413 Annular surface portion 414 Inner peripheral surface 415 shaft insertion hole 416 sixth flat portion 421 second flat portion 421a radial inner end 421b radial outer end 422 fourth flat portion 431 third flat portion 431a radial inner end 432 fifth flat portion 433 annular surface portions 441, 441A Plane portion 442 Inner peripheral surface 442A Thick portion 443 Outer peripheral surface 444 Cylindrical surface portion 444A Thin portion 445A Gap 871 First housing 872 Second housing 872a Through hole 873 Third housing 873a Bearing accommodating portion 873b Protruding portion 874 Tip Ax Central axis F Force L1 First distance L2 Second distance L3 Third distance L4 Fourth distance L10 First variable distance L20 Second variable distance S1 Preparation step S2 Forging step S3 Processing step S11 Preparation step S12 Forging step S13 Processing step S14 Contact step S15 Filling step

Claims (9)

a first annular portion extending in the circumferential direction around the central axis and provided with a shaft insertion hole penetrating the inner periphery; an annular core bar having a second annular portion extending and a third annular portion located radially outside the second annular portion and extending in the circumferential direction;
a resin gear attached to the third annular portion and extending along the circumferential direction;
An annular second planar portion is provided on one side of the second annular portion in the axial direction,
The second flat portion extends along a radial direction orthogonal to the central axis,
worm wheel. wherein the second planar portion is a machined planar surface;
A worm wheel according to claim 1. An annular first plane portion is provided on one side of the first annular portion in the axial direction,
An annular third plane portion located on the other side in the axial direction of the first plane portion is provided on one side of the third annular portion in the axial direction,
When the cored bar is rotated once around the central axis, in the axial direction between the axial position on one side of the second plane portion and the axial position on the other side of the second flat portion. The first variation distance, which is the distance along
When the cored bar is rotated once around the central axis, the axial position of the third flat portion on one side in the axial direction and the axial position on the other side in the axial direction. less than the second variation distance, which is the distance along
A worm wheel according to claim 1 or 2. An annular fourth plane portion is provided on the other side of the second annular portion in the axial direction,
An annular fifth plane portion is provided on the other side of the third annular portion in the axial direction,
an axial separation distance between the first plane portion and the fourth plane portion is a third distance;
An axial separation distance between the first plane portion and the fifth plane portion is a fourth distance that is smaller than the third distance,
A worm wheel according to claim 3. The surface of the second plane portion is provided with a plurality of unevenness extending in the circumferential direction around the central axis,
A worm wheel according to claim 2. The second planar portion is a surface-treated planar surface,
A worm wheel according to claim 2 or 5. a first annular portion extending in the circumferential direction around the central axis and provided with a shaft insertion hole penetrating the inner periphery; A method for manufacturing an annular core bar having a second annular portion extending and a third annular portion located radially outside the second annular portion and extending in the circumferential direction, the method comprising:
a preparation step to prepare the forging material;
a forging step of forging the forging material to manufacture a workpiece after the preparing step;
After the forging step, machining one side of the second annular portion in the axial direction while rotating the work in a direction around the central axis.
A method for manufacturing an annular core bar. a first annular portion extending in the circumferential direction around the central axis and provided with a shaft insertion hole penetrating the inner periphery; an annular core bar having a second annular portion extending and a third annular portion located radially outside the second annular portion and extending in the circumferential direction;
A worm wheel manufacturing method for manufacturing a worm wheel including a resin gear attached to the third annular portion and extending along the circumferential direction,
a preparation step to prepare the forging material;
a forging step of forging the forging material to manufacture a workpiece after the preparing step;
After the forging step, a processing step of machining one side of the second annular portion in the axial direction while rotating the work in a direction around the central axis to produce a cored bar;
a contacting step, after the processing step, of placing the cored bar inside the injection molding die and bringing a part of the injection molding die into contact with one side of the second annular portion of the cored bar in the axial direction;
a filling step of filling the inside of the injection mold with a resin after the contacting step;
including,
Worm wheel manufacturing method. a worm wheel having an annular core bar extending in a circumferential direction around a central axis; and a resin gear attached to a radially outer portion of the core bar and extending along the circumferential direction;
a housing that houses the worm wheel,
The core bar is
A first annular portion extending in the circumferential direction and provided with a shaft insertion hole penetrating the inner periphery thereof, and a second annular portion positioned radially outwardly of the first annular portion and extending in the circumferential direction. and a third annular portion located radially outside the second annular portion and extending in the circumferential direction, the resin gear being attached to the third annular portion, and the second An annular second plane portion is provided on one side of the annular portion in the axial direction,
The housing has a protruding portion extending toward the second flat portion and having a tip end axially opposed to the second flat portion,
Worm reducer.

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