Worm wheel for electric power steering device

Abstract

According to the present invention, a worm wheel for an electric power steering device comprises: a ring-shaped gear unit having multiple gear teeth formed on the outer circumferential surface thereof and spaced apart from each other in the circumferential direction; a boss unit disposed at the center in the gear unit; and a hub unit disposed between the gear unit and the boss and coupled to the gear unit and the boss unit. The worm wheel is advantageous in that a coupling ring is formed on the inner circumferential surface of the gear unit and is embedded by the hub unit, thereby enhancing the bonding strength between the gear unit and the hub unit.

Description

Worm wheel of electric power steering device

[0001] The present invention relates to a worm wheel for an electric power steering apparatus, and more particularly, to a worm wheel for an electric power steering apparatus in which a gear portion and a hub portion are injection-molded from different plastic materials.

[0002]

[0003] In general, a power steering device that generates the steering force of a vehicle is a device with an added function that makes the steering force of the steering wheel light and smooth while also enabling quick steering.

[0004] Such a power steering device has the advantages of being able to steer with less force, being able to select the steering gear ratio regardless of the operating force, and being able to absorb shock from road surface irregularities and prevent them from being transmitted to the steering wheel.

[0005] In addition, recently, there is a trend to use an electric power steering device that provides optimal steering conditions to the driver by driving a motor in the electronic control unit (ECU) according to the vehicle's driving conditions detected by the vehicle speed sensor and steering torque sensor, thereby providing a light and comfortable steering feel when driving at low speeds, a heavy steering feel and good directional stability when driving at high speeds, and allowing rapid steering in emergency situations.

[0006] Electric power steering devices are usually EHPS (Electri-Hydraulic Power Steering) or MDPS (Motor Driven Power Steering). MDPS is a structure that assists steering power with the rotational force of a motor. The worm gear of a worm shaft connected to the rotational axis of the motor that generates the driving force meshes with the gear teeth of a worm wheel connected to the steering shaft, so that the steering shaft is rotated by the driving force of the motor to assist the steering force.

[0007] Typically, the worm wheel is composed of a gear portion that meshes with the worm gear, a boss portion that is positioned at the center of the gear portion, and a hub portion that is positioned between the gear portion and the boss portion.

[0008] Since the above worm wheel is a structure that rotates by meshing with the above worm gear, the weight and strength of the worm wheel have a significant influence on the driving torque, noise, and vibration. Therefore, recently, the hub part is formed of reinforced engineering plastic and the gear part is formed of non-reinforced plastic, thereby reducing the driving torque, noise, and vibration.

[0009] However, when the MDPS is driven, a circumferential force, an axial force, and a radial force are applied to the worm wheel. When the gear portion and the hub portion are formed of different materials and the hub portion and the boss portion are formed of different materials, it is important to design the worm wheel so that strength reduction due to the circumferential force, axial force, and radial force applied to the joint portion of the gear portion and the hub portion and the joint portion of the hub portion and the boss portion does not occur.

[0010] Korean Patent Publication No. 10-1798906 (November 17, 2017) (hereinafter referred to as “prior art”) discloses “a worm wheel of an electric power steering device and a method for manufacturing the same,” in which the hub portion and the gear portion are formed of different plastic materials.

[0011] The worm wheel of the above-described prior art is configured to include a gear portion having a plurality of gears formed along the outer circumferential direction, a boss portion installed on the inner side of the gear portion, and a hub portion interposed between the gear portion and the boss portion, wherein the hub portion includes a hub portion main body, a circular band-shaped embedded band formed on the outer side of the hub portion main body, a web formed between the hub portion main body and the embedded band and having first embedded grooves provided on both sides, and a coupling head having a plurality of embedded grooves formed at a predetermined interval along the outer circumference of the embedded band and having second embedded grooves provided on surfaces facing each other, and wherein the gear portion is formed by being embedded in the first embedded groove and the second embedded groove.

[0012] However, the above-mentioned conventional technology has a problem in that, since the outer surface of the joining head is formed only as a rectangular plane, the area where the outer surface of the joining head comes into contact with the gear portion is not sufficiently secured, and thus the joining strength of the hub portion and the gear portion is not sufficiently secured.

[0013] In addition, since the above-mentioned conventional technology manufactured the worm wheel by injection-molding the hub portion on the outside of the boss portion and then injection-molding the gear portion on the outside of the hub portion, there was also a problem that the precision was reduced due to the shrinkage of the multiple gear teeth formed on the outer surface of the gear portion during the process of injection-molding and cooling the gear portion.

[0014]

[0015] The technical problem of the present invention is to provide a worm wheel of an electric power steering device in which the joint strength of a gear portion and a hub portion is improved.

[0016] Another technical object of the present invention is to provide a worm wheel of an electric power steering device in which the gear tooth precision of the gear part is improved.

[0017] The technical problems of the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0018]

[0019] In order to achieve the above object, a worm wheel of an electric power steering device according to the present invention comprises a gear portion, a boss portion, and a hub portion. The gear portion is formed in a ring shape. A plurality of gear teeth are formed on the outer surface of the gear portion and spaced apart from each other in the circumferential direction. The boss portion is disposed at the center of the gear portion. The hub portion is disposed between the gear portion and the boss portion and is coupled to the gear portion and the boss portion. A coupling ring is formed on the inner surface of the gear portion and is embedded by the hub portion.

[0020] A plurality of coupling grooves may be formed on both axial sides of the above coupling ring to which the hub portion is coupled. The plurality of coupling grooves may be formed along the circumferential direction.

[0021] The above gear portion and the above hub portion may be formed of a plastic material. The above boss portion may be formed of a metal material.

[0022] The above gear portion and the above hub portion may be formed of different plastic materials.

[0023] When the boss portion is placed at the center of the first injection-molded gear portion and the gear portion is secondarily injection-molded, the hub portion can be injection-molded together with the gear portion and combined with the gear portion and the boss portion.

[0024] The above coupling ring may be composed of a first coupling ring portion and a second coupling ring portion. The first coupling ring portion may be formed to protrude radially from the center of the inner circumferential surface of the gear portion. An axial width of the first coupling ring portion may be formed to be smaller than an axial width of the plurality of gear teeth. The second coupling ring portion may be formed to protrude radially from the center of the inner circumferential surface of the first coupling ring portion. An axial width of the second coupling ring portion may be formed to be smaller than an axial width of the first coupling ring portion. The plurality of coupling grooves may be composed of a plurality of first coupling grooves and a plurality of second coupling grooves. The plurality of first coupling grooves may be formed along a circumferential direction on both axial sides of the first coupling ring portion. The plurality of second coupling grooves may be formed along a circumferential direction on both axial sides of the second coupling ring portion.

[0025] The plurality of first coupling grooves may be formed with radially inner openings. The plurality of second coupling grooves may be formed with radially outer openings. Each of the plurality of second coupling grooves may extend radially inward from the respective axial inner ends of the plurality of first coupling grooves.

[0026] The plurality of first coupling grooves may be formed as an involute surface having an open radially inner side. The plurality of second coupling grooves may be formed as a triangle having an open radially outer side.

[0027] On both axial sides of the second coupling ring portion, a plurality of coupling protrusions may be formed along the circumferential direction radially inside the plurality of second coupling grooves.

[0028] Each of the plurality of connecting protrusions may be formed in a shape corresponding to each of the plurality of second connecting grooves.

[0029] Specific details of other embodiments are included in the detailed description and drawings.

[0030]

[0031] The worm wheel of the electric power steering device according to the present invention has a coupling ring formed on the inner surface of the gear portion, which is embedded in the hub portion, and a plurality of coupling grooves formed along the circumferential direction on both axial sides of the coupling ring, so that when the hub portion is injection-molded, the hub portion is coupled to the plurality of coupling grooves, thereby improving the bonding strength of the gear portion and the hub portion.

[0032] In addition, the worm wheel of the electric power steering device according to the present invention is manufactured in such a way that the hub portion is injection-molded together with the gear portion when the gear portion is secondarily injection-molded after the boss portion is placed at the center of the first injection-molded gear portion, and the worm wheel is manufactured by combining the gear portion and the boss portion by injection-molding the gear portion twice, so that shrinkage of a plurality of gear teeth of the gear portion can be prevented compared to a method of injection-molding the gear portion only once, and thus the precision of the plurality of gear teeth of the gear portion is also improved.

[0033] The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

[0034]

[0035] Figure 1 is a perspective view showing a worm wheel of an electric power steering device according to an embodiment of the present invention;

[0036] Figure 2 is an exploded perspective view of Figure 1;

[0037] Figure 3 is a side cross-sectional view of Figure 1;

[0038] Figure 4 is an enlarged view of part A of Figure 1 (a), and figure (b) is a plan view of figure (a).

[0039] Fig. 5 is a perspective view of the other side of the gear part shown in Fig. 2;

[0040] Figure 6 is an enlarged view of part B of Figure 5, (a) is an enlarged view of part B of Figure 5, (b) is a plan view of Figure (a),

[0041] Fig. 7 is a side cross-sectional view of a portion of the gear part illustrated in Fig. 2 where the engaging groove and engaging projection are not formed, and an enlarged view of a portion thereof.

[0042] Fig. 8 is a side cross-sectional view of a portion of the gear section shown in Fig. 2 where a coupling groove and a coupling projection are formed, and an enlarged view of a portion thereof.

[0043] Figure 9 is an enlarged view of section C of Figure 2;

[0044] Fig. 10 is a perspective view of the other side of the hub portion shown in Fig. 2 and an enlarged view of a portion thereof.

[0045] Figure 11 is an enlarged view of part D of Figure 2.

[0046]

[0047] <Explanation of symbols>

[0048] 1: Worm wheel of electric power steering device 100: Gear part

[0049] 110: Gear teeth 120: Coupling ring

[0050] 121: First coupling ring part 122: Second coupling ring part

[0051] 123, 124: Joining groove 123A, 124A: First joining groove

[0052] 123B, 124B: Second connecting groove 125, 126: Connecting projection

[0053] 200: Boss Department 300: Hub Department

[0054]

[0055] Hereinafter, a worm wheel of an electric power steering device according to embodiments of the present invention will be described with reference to drawings.

[0056] When assigning reference numerals to components in each drawing, it should be noted that identical components are assigned the same numerals whenever possible, even if they appear on different drawings. Furthermore, when describing embodiments of the present invention, if a detailed description of a related known configuration or function is deemed to hinder understanding of the embodiments of the present invention, the detailed description will be omitted.

[0057] When describing components of embodiments of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are only intended to distinguish the components from other components, and the nature, order, or sequence of the components are not limited by these terms. Furthermore, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning they have in the context of the relevant technology, and shall not be interpreted in an idealized or overly formal sense unless explicitly defined in this application.

[0058] In all configurations described below, the terms top, bottom, upper part, lower part, upper surface, and lower surface, which are related to direction, refer to the directions disclosed in the drawings. Accordingly, "bottom" may be synonymous with "one side," "top" may be synonymous with "the other side," "bottom" may be synonymous with "one side," and "upper surface" may be synonymous with "the other side."

[0059] FIG. 1 is a perspective view showing a worm wheel of an electric power steering device according to an embodiment of the present invention, and FIG. 2 is an exploded perspective view of FIG. 1.

[0060] Referring to FIGS. 1 and 2, the worm wheel (1) of the electric power steering device according to the embodiment of the present invention can be formed in a circular gear shape in which a plurality of gear teeth (110) are formed spaced apart from each other in the circumferential direction on the outer surface.

[0061] The above electric power steering device is a device that assists the steering force of a vehicle's steering device. By utilizing the assisting force of the electric power steering device, the driver can reduce the force he or she uses when steering the vehicle's steering device.

[0062] The steering device for the vehicle may include a steering wheel configured to be held and rotated by a driver with a handle, a steering shaft coupled to the upper end of the steering wheel and rotated together with the steering wheel in the rotational direction of the steering wheel, a pinion shaft coupled to the lower end of the steering shaft, a steering gear having a rack bar that moves linearly to the left or right according to the rotational direction of the steering wheel by a pinion gear installed on the outer periphery of the pinion shaft, and left and right tie rods respectively connected to the left and right ends of the rack bar.

[0063] When the driver turns the steering wheel to the left, the steering shaft and the pinion shaft are simultaneously turned to the left along with the steering wheel, and accordingly, the rack bar is moved linearly to the left, thereby causing the left and right tie rods to be moved linearly to the left, so that the front portions of the left and right wheel wheels can face the left.

[0064] When the driver turns the steering wheel to the right, the steering shaft and the pinion shaft are simultaneously turned to the right along with the steering wheel, and accordingly, the rack bar is moved straight to the right, thereby moving the left and right tie rods straight to the right, so that the front portions of the left and right wheel wheels can face the right.

[0065] The above electric power steering device can assist the steering force of a vehicle steering device by assisting the rotational force of the steering shaft.

[0066] The above electric power steering device may include a drive motor, a worm shaft coupled to a rotational shaft of the drive motor, and a worm wheel (1) having a plurality of gear teeth (110) formed on an outer surface thereof spaced apart from each other in the circumferential direction and meshed with a worm gear of the worm shaft.

[0067] A worm wheel (1) may be installed on the steering shaft. A through hole (210) through which the steering shaft passes may be formed in the worm wheel (1). The worm wheel (1) may be installed on the outer circumferential surface of the steering shaft, with the steering shaft passing through the through hole (210).

[0068] The above electric power steering device may further include a torque sensor that detects the rotational torque of the steering shaft, and a control unit (ECU) that controls the driving motor using the detection value of the torque sensor, and the control unit controls the driving motor using the detection value of the torque sensor, thereby rotating a worm wheel (1) installed on the outer surface of the steering shaft to assist the rotational force of the steering shaft, thereby assisting the steering force of the steering device for the vehicle.

[0069] The worm wheel (1) of the electric power steering device according to an embodiment of the present invention may include a gear portion (100), a boss portion (200), and a hub portion (300).

[0070] The gear portion (100) may be formed in a ring shape. A plurality of gear teeth (110) may be formed on the outer surface of the gear portion (100). The plurality of gear teeth (110) may be spaced apart from each other in the circumferential direction.

[0071] The boss portion (200) may be formed in a ring shape. The boss portion (200) may be positioned at the center within the gear portion (100). The center of the boss portion (200) may be the rotation center of the worm wheel (1). A through hole (210) extending axially may be formed in the boss portion (200). The steering shaft may be installed by passing through the through hole (210) of the boss portion (200).

[0072] The hub portion (300) may be formed in a ring shape. The hub portion (300) may be positioned between the gear portion (100) and the boss portion (200). The hub portion (300) may be coupled with the gear portion (100) and the boss portion (200). When the hub portion (300) is injection molded, the radially outer portion of the hub portion (300) may be coupled with the radially inner portion of the gear portion (100), and the radially inner portion of the hub portion (300) may be coupled with the radially outer portion of the boss portion (200). The hub portion (300) may connect the gear portion (100) and the boss portion (200). The hub portion (300) may couple the gear portion (100) and the boss portion (200). The outer surface of the hub portion (300) can be combined with the inner surface of the gear portion (100), and the inner surface of the hub portion (300) can be combined with the outer surface of the boss portion (200).

[0073] The gear portion (100) and the hub portion (300) may be formed of a plastic material, and the boss portion (200) may be formed of a metal material. The gear portion (100) and the hub portion (300) may be formed of different plastic materials. Specifically, the hub portion (300) may be formed of a reinforced engineering plastic, and the gear portion (100) may be formed of a non-reinforced plastic.

[0074] The gear part (100) can be first injection molded in a first injection mold (not shown) and second injection molded in a second injection mold (not shown).

[0075] When the boss portion (200) is placed at the center of the first injection-molded gear portion (100) and the gear portion (100) is secondarily injection-molded, the hub portion (300) can be injection-molded together with the gear portion (100) and combined with the gear portion (100) and the boss portion (200).

[0076] Specifically, after the gear part (100) is first injection-molded in the first injection mold and cooled, the gear part (100) can be taken out from the first injection mold, and then the boss part (200) and the gear part (100) taken out from the first injection mold are placed in the second injection mold, and then the gear part (100) is secondarily injection-molded in the second injection mold and the hub part (300) is injection-molded, thereby manufacturing a worm wheel (1) in which the gear part (100), the boss part (200), and the hub part (300) are combined. After that, the worm wheel (1) can be cooled and then taken out from the second injection mold.

[0077] In this way, since the gear part (100) is manufactured by first injection molding in the first injection mold and then second injection molding in the second injection mold, shrinkage of the plurality of gear teeth (110) formed on the outer surface of the gear part (100) can be minimized, thereby improving the precision of the plurality of gear teeth (110).

[0078] Since the gear part (100) and the hub part (300) are formed of plastic material, the weight of the worm wheel (1) can be reduced, and driving torque, noise, and vibration can be reduced.

[0079] In particular, since the gear portion (100) and the hub portion (300) are formed of different plastic materials, it is important to design them so that the strength of the joint portion between the gear portion (100) and the hub portion (300) does not decrease when the worm wheel (1) rotates. In addition, since the boss portion (200) and the hub portion (300) are formed of different materials, it is important to design them so that the strength of the joint portion between the boss portion (200) and the hub portion (300) does not decrease when the worm wheel (1) rotates. Below, a structure for improving the strength of the joint portion between the gear portion (100) and the hub portion (300) and the strength of the joint portion between the boss portion (200) and the hub portion (300) will be described with reference to FIGS. 3 to 11.

[0080]

[0081] First, the structure for improving the strength of the joint portion of the gear portion (100) and the hub portion (300) is described below.

[0082] Figure 3 is a side cross-sectional view of Figure 1.

[0083] Referring to Fig. 3, a coupling ring (120) embedded in a hub part (300) may be formed protrudingly on the inner surface of the gear part (100). The coupling ring (120) may be formed protrudingly at the axial center of the inner surface of the gear part (100). When the hub part (300) is injection-molded together with the gear part (100), the radially outer portion of the hub part (300) may be embedded in the coupling ring (120) and coupled to the gear part (100).

[0084] On both axial sides of the coupling ring (120), coupling grooves (123, 124) may be formed along the circumferential direction. When the hub portion (300) is injection-molded into the gear portion (100), the hub portion (300) may be inserted into the coupling grooves (123, 124) and coupled with the gear portion (100).

[0085] FIG. 4 is a side perspective view of the gear part shown in FIG. 2, (a) is an enlarged view of part A of FIG. 1, (b) is a plan view of (a), FIG. 5 is a perspective view of the other side of the gear part shown in FIG. 2, FIG. 6 is an enlarged view of part B of FIG. 5, (b) is a plan view of (a), FIG. 7 is a side cross-sectional view of a part of the gear part shown in FIG. 2 where a coupling groove and a coupling protrusion are not formed, and a partial enlarged view thereof, and FIG. 8 is a side cross-sectional view of a part of the gear part shown in FIG. 2 where a coupling groove and a coupling protrusion are formed, and a partial enlarged view thereof.

[0086] Referring to FIGS. 4 to 8, the coupling ring (120) may include a first coupling ring portion (121, see FIG. 7) and a second coupling ring portion (122, see FIG. 7). The first coupling ring portion (121) may be formed to protrude radially from the center of the inner circumference of the gear portion (100). The second coupling ring portion (122) may be formed to protrude radially from the center of the inner circumference of the first coupling ring portion (121).

[0087] The axial width of the first coupling ring portion (121) may be formed to be smaller than the axial width of the plurality of gear teeth (110, see FIG. 2) formed on the outer surface of the gear portion (100). The axial width of the first coupling ring portion (121) may be formed to be larger than the axial width of the second coupling ring portion (122). The axial width of the second coupling ring portion (122) may be formed to be smaller than the axial width of the first coupling ring portion (121).

[0088] The plurality of coupling grooves (123, 124) may include a plurality of first coupling grooves (123A, 124A) and a plurality of second coupling grooves (123B, 124B). The plurality of first coupling grooves (123A, 124A) may be formed along the circumferential direction on both axial sides of the first coupling ring portion (121). The plurality of second coupling grooves (123B, 124B) may be formed along the circumferential direction on both axial sides of the second coupling ring portion (122).

[0089] The plurality of first coupling grooves (123A, 124A) may include a plurality of first-first coupling grooves (123A) formed along the circumferential direction on one axial side of the first coupling ring portion (121), and a plurality of first-second coupling grooves (124A) formed along the circumferential direction on the other axial side of the first coupling ring portion (121).

[0090] The plurality of second coupling grooves (123B, 124B) may include a plurality of second-first coupling grooves (123B) formed along the circumferential direction on one axial side of the second coupling ring portion (122), and a plurality of second-second coupling grooves (124B) formed along the circumferential direction on the other axial side of the second coupling ring portion (122).

[0091] The plurality of coupling grooves (123, 124) may include a plurality of coupling grooves (123) formed along a circumferential direction on one axial side of the coupling ring (120) and a plurality of coupling grooves (124) formed along a circumferential direction on the other axial side of the coupling ring (120). The plurality of coupling grooves (123) may include a plurality of first-first coupling grooves (123A) and a plurality of second-first coupling grooves (123B), and the plurality of coupling grooves (124) may include a plurality of first-second coupling grooves (124A) and a plurality of second-second coupling grooves (124B).

[0092] The plurality of first coupling grooves (123A, 124A) and the plurality of second coupling grooves (123B, 124B) may have open faces facing each other. That is, the plurality of first-first coupling grooves (123A) and the plurality of second-first coupling grooves (123B) may have open faces facing each other, and the plurality of first-second coupling grooves (124A) and the plurality of second-second coupling grooves (124B) may have open faces facing each other.

[0093] Specifically, a plurality of first coupling grooves (123A, 124A) may be formed with their radially inner sides open. That is, a plurality of first-first coupling grooves (123A) may be formed with their radially inner sides open, and a plurality of first-second coupling grooves (124A) may also be formed with their radially inner sides open.

[0094] In addition, a plurality of second coupling grooves (123B, 124B) may be formed with their radially outer sides open. That is, a plurality of second-first coupling grooves (123B) may be formed with their radially outer sides open, and a plurality of second-second coupling grooves (124B) may also be formed with their radially outer sides open.

[0095] Since the axial width of the second coupling ring portion (122) is formed to be shorter than the axial width of the first coupling ring portion (121), the plurality of second coupling grooves (123B, 124B) can be formed to have a shorter axial length than the plurality of first coupling grooves (123A, 124A).

[0096] Each of the plurality of second coupling grooves (123B, 124B) may extend radially inward from the axial inner end of each of the plurality of first coupling grooves (123A, 124A). That is, each of the plurality of second-first coupling grooves (123B) may extend radially inward from the axial inner end of each of the plurality of first-first coupling grooves (123A), and each of the plurality of second-second coupling grooves (124B) may extend radially inward from the axial inner end of each of the plurality of first-second coupling grooves (124A).

[0097] The plurality of first coupling grooves (123A, 124A) may be formed as an involute surface with an open radially inner side. That is, the plurality of first-first coupling grooves (123A) may be formed as an involute surface with an open radially inner side, and the plurality of first-second coupling grooves (124A) may be formed as an involute surface with an open radially inner side.

[0098] The plurality of second coupling grooves (123B, 124B) may be formed as triangles with their radially outer sides open. That is, the plurality of second-first coupling grooves (123B) may be formed as triangles with their radially outer sides open, and the plurality of second-second coupling grooves (124B) may be formed as triangles with their radially outer sides open.

[0099] On both axial sides of the second coupling ring portion (122), a plurality of coupling protrusions (125, 126) may be formed along the circumferential direction radially inward from a plurality of second coupling grooves (123B, 124B). When the hub portion (300) is injection-molded into the gear portion (100), the plurality of coupling protrusions (125, 126) may be embedded in the hub portion (300) and coupled to the hub portion (300).

[0100] The plurality of coupling protrusions (125, 126) may include a plurality of first coupling protrusions (125) formed along a circumferential direction on one axial side of the second coupling ring portion (122), and a plurality of second coupling protrusions (126) formed along a circumferential direction on the other axial side of the second coupling ring portion (122). The plurality of first coupling protrusions (125) may be formed radially inward of the plurality of second-first coupling grooves (123B), and the plurality of second coupling protrusions (126) may be formed radially inward of the plurality of second-second coupling grooves (124B).

[0101] Each of the plurality of engaging protrusions (125, 126) may be formed in a shape corresponding to each of the plurality of second engaging grooves (123B, 124B). In the present embodiment, each of the plurality of second engaging grooves (123B, 124B) is formed in a triangle shape, and therefore each of the plurality of engaging protrusions (125, 126) is formed in a triangle shape corresponding to each of the plurality of second engaging grooves (123B, 124B).

[0102] Fig. 9 is an enlarged view of part C of Fig. 2, and Fig. 10 is a perspective view of the other side of the hub part shown in Fig. 2 and an enlarged view of a portion thereof.

[0103] Referring to FIGS. 2 to 10, as described above, since the engaging grooves (123, 124) are formed on both axial sides of the engaging ring (120) of the gear portion (100), and engaging projections (125, 126) are formed on both sides, when the hub portion (300) and the gear portion (100) are injection-molded, a plurality of engaging projections (323, 324) can be formed on the hub portion (300) by the plurality of engaging grooves (123, 124) of the gear portion (100), and a plurality of engaging grooves (325, 326) can be formed on the plurality of engaging projections (125, 126) of the gear portion (100). When the hub part (300) and the gear part (100) are injection-molded, the plurality of engaging protrusions (323, 324) of the hub part (300) can be inserted into the plurality of engaging grooves (123, 124) of the gear part (100), and the plurality of engaging protrusions (125, 126) of the gear part (100) can be inserted into the plurality of engaging grooves (325, 326) of the hub part (300).

[0104] A ring-shaped groove (320) may be formed on the outer surface of the hub portion (300) by the coupling ring (120) of the gear portion (100). The plurality of coupling protrusions (323, 324) of the hub portion (300) may include a plurality of third coupling protrusions (323) formed along the circumferential direction on one axial inner surface of the ring-shaped groove (320), and a plurality of fourth coupling protrusions (324) formed along the circumferential direction on the other axial inner surface of the ring-shaped groove (320). In addition, the plurality of coupling grooves (325, 326) of the hub portion (300) may include a plurality of third coupling grooves (325) formed along the circumferential direction on one axial inner surface of the ring-shaped groove (320), and a plurality of fourth coupling grooves (326) formed along the circumferential direction on the other axial inner surface of the ring-shaped groove (320).

[0105] When the injection molding of the hub part (300) into the gear part (100) is completed, the plurality of third engaging protrusions (323) of the hub part (300) can be inserted into the plurality of engaging grooves (123) of the gear part (100), respectively, and the plurality of fourth engaging protrusions (324) of the hub part (300) can be inserted into the plurality of engaging grooves (124) of the gear part (100), respectively.

[0106] In addition, when the hub part (300) is injection-molded into the gear part (100), a plurality of first coupling protrusions (125) of the gear part (100) can be inserted into each of the plurality of third coupling grooves (325) of the hub part (300), and a plurality of second coupling protrusions (125) of the gear part (100) can be inserted into each of the plurality of fourth coupling grooves (326) of the hub part (300).

[0107]

[0108] Next, the structure for improving the strength of the joint between the boss portion (200) and the hub portion (300) is described as follows.

[0109] Figure 11 is an enlarged view of part D of Figure 2.

[0110] Referring to FIGS. 2 and 3 and FIG. 11, a coupling ring (220) embedded in the hub part (300) may be formed protruding on the outer surface of the boss part (200). The coupling ring (220) may be formed protruding in the axial center of the outer surface of the boss part (200). When the hub part (300) is injection-molded into the boss part (200), the radially inner part of the hub part (300) may be embedded in the coupling ring (220) to be coupled to the boss part (200).

[0111] When the injection molding of the hub part (300) into the boss part (200) is completed, a ring-shaped groove (330, see FIG. 10) can be formed on the inner surface of the hub part (300) by the coupling ring (220) of the boss part (200). That is, when the injection molding of the hub part (300) into the boss part (200) is completed, the coupling ring (220) of the boss part (200) can be inserted into and coupled to the ring-shaped groove (330).

[0112] The coupling ring (220) of the boss portion (200) may be arranged axially to one side compared to the coupling ring (120) of the gear portion (100).

[0113] A coupling groove (221, 222) to which a hub portion (300) is coupled can be formed on both axial sides of the coupling ring (220).

[0114] When the gear part (100) and the hub part (300) are injection-molded and joined to each other, the hub part (300) can be joined to the boss part (200). When the injection-molding of the hub part (300) to the boss part (200) is completed, the hub part (300) can be inserted into the joining groove (221, 222) and joined to the boss part (200).

[0115] The coupling grooves (221, 222) may include a fifth coupling groove (221) formed on one axial side of the coupling ring (220) and a sixth coupling groove (222) formed on the other axial side of the coupling ring (220). The fifth coupling groove (221) may be formed singly on one axial side of the coupling ring (220) and may be formed in a ring shape. The sixth coupling groove (222) may be formed singly on the other axial side of the coupling ring (220) and may be formed in a ring shape.

[0116] A plurality of coupling protrusions (223, 224, 225) may be formed on the outer surface of the coupling ring (220). The plurality of coupling protrusions (223, 224, 225) may be formed in a square pyramid shape, and the ends may be formed in a flat shape.

[0117] The plurality of coupling protrusions (223, 224, 225) may include a pair of fifth coupling protrusions (223, 224) and a single sixth coupling protrusion (225). On the outer surface of the coupling ring (220), a plurality of configurations in which half of a single sixth coupling protrusion (225) is inserted between a pair of fifth coupling protrusions (223, 224) may be arranged along the circumferential direction.

[0118] When the hub part (300) is injection-molded into the boss part (200), the inner surface of the hub part (300) can be inserted into a groove formed between a pair of fifth coupling protrusions (223, 224) and a groove formed on both axial sides of a single sixth coupling protrusion (225) to be coupled with the boss part (200).

[0119]

[0120] As described above, in the worm wheel (1) of the electric power steering device according to the embodiment of the present invention, a coupling ring (120) embedded in the hub part (300) is formed on the inner surface of the gear part (100), and a plurality of coupling grooves (123, 124) are formed along the circumferential direction on both axial sides of the coupling ring (120). Therefore, when the hub part (300) is injection-molded, the hub part (300) is coupled to the plurality of coupling grooves (123, 124), so that the joint strength of the gear part (100) and the hub part (300) can be improved.

[0121] In addition, the worm wheel (1) of the electric power steering device according to the embodiment of the present invention is manufactured in such a way that, when the gear part (100) is secondarily injection-molded after the boss part (200) is placed at the center of the first injection-molded gear part (100), the hub part (300) is injection-molded together with the gear part (100) and combined with the gear part (100) and the boss part (200), thereby manufacturing the worm wheel (1), and thus, since the gear part (100) is injection-molded twice, shrinkage of the plurality of gear teeth (110) of the gear part (100) can be prevented compared to a method of injection-molding the gear part (100) only once, and thus the precision of the plurality of gear teeth (110) of the gear part (100) can be improved.

[0122]

[0123] Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical concept or essential characteristics thereof. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims that follow rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

[0124]

[0125] The present invention provides a worm wheel of an electric power steering device in which the joint strength of a gear portion and a hub portion is improved.

Claims

1. A ring-shaped gear portion having multiple gear teeth spaced apart from each other in the circumferential direction on the outer surface; A boss portion positioned at the center of the above gear portion; and A hub portion is disposed between the gear portion and the boss portion and is coupled to the gear portion and the boss portion; A worm wheel of an electric power steering device in which a coupling ring is formed on the inner surface of the above gear part and is embedded by the above hub part.

2. In claim 1, A worm wheel of an electric power steering device having a plurality of coupling grooves formed along the circumference on both axial sides of the above coupling ring to which the hub portion is coupled.

3. In claim 1, The above gear portion and the above hub portion are formed of a plastic material, The above boss part is a worm wheel of an electric power steering device formed of a metal material.

4. In claim 3, A worm wheel of an electric power steering device in which the gear portion and the hub portion are formed of different plastic materials.

5. In claim 3, A worm wheel of an electric power steering device in which the boss portion is placed at the center of the first injection-molded gear portion and the gear portion is secondarily injection-molded, and the hub portion is injection-molded together with the gear portion and is combined with the gear portion and the boss portion.

6. In claim 2, The above coupling ring is, A first coupling ring portion formed by protruding radially from the center of the inner surface of the gear portion and having an axial width smaller than the axial width of the plurality of gear teeth; It includes a second coupling ring portion that is formed to protrude radially from the center of the inner surface of the first coupling ring portion and has an axial width smaller than the axial width of the first coupling ring portion. The above multiple joining grooves are, A plurality of first coupling grooves formed along the circumferential direction on both axial sides of the first coupling ring portion, A worm wheel of an electric power steering device including a plurality of second coupling grooves formed along a circumferential direction on both axial sides of the second coupling ring portion.

7. In claim 6, The above plurality of first coupling grooves are formed with an opening on the radial inner side, The above plurality of second coupling grooves are formed with an open radial outer side, A worm wheel of an electric power steering device in which each of the plurality of second coupling grooves extends radially inward from each axial inner end of the plurality of first coupling grooves.

8. In claim 7, The above plurality of first coupling grooves are formed as an involute surface with an open radial inner surface, A worm wheel of an electric power steering device in which the plurality of second coupling grooves are formed in a triangle shape with an open radial outer side.

9. In claim 6, A worm wheel of an electric power steering device, wherein a plurality of coupling protrusions are formed along a circumferential direction radially inside the plurality of second coupling grooves on both axial sides of the second coupling ring portion.

10. In claim 9, A worm wheel of an electric power steering device, wherein each of the plurality of coupling protrusions is formed in a shape corresponding to each of the plurality of second coupling grooves.

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