Worm wheel, electric power steering device, and method for manufacturing worm wheel

Abstract

To provide a worm wheel capable of reducing difference in an amount of a sink mark in each portion, an electric power steering device and a manufacturing method for a worm wheel.SOLUTION: On axial side surfaces 60A, 60B of an annular convex part 60, a plurality of small-diameter recess parts 61 (first small-diameter recess part 62, second small-diameter recess part 63) extending radially inward from an outer peripheral surface 61C of the annular convex part 60 are provided at predetermined intervals in a circumferential direction. The annular convex part 60 is fixed to a core metal part 50 by insert molding so as to embed a plurality of overhanging parts 53 of the core metal part 50. The tooth part 70 is fixed to the annular convex part 60 by injection molding so as to embed the outer peripheral surface 61C of the annular convex part 60.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a worm wheel, an electric power steering device, and a method for manufacturing a worm wheel. [Background technology]

[0002] 2. Description of the Related Art In an electric power steering device that steers steered wheels by transmitting the rotational force of a motor to a steering mechanism, a worm reduction gear using, for example, a worm wheel is used to transmit the rotational force of the motor to the steering mechanism.

[0003] The outer peripheral surface of the sleeve (core metal portion) of the worm wheel is usually flat in the axial direction. In this case, when the teeth are injection molded, the resin filled in the mold solidifies in order from the part that touches the mold, and the central part of the part that will become the teeth solidifies later. Therefore, in the shrinkage process when the part that will become the teeth solidifies, the axial center part of the outer peripheral surface of the part is pulled toward the sleeve compared to both axial ends, and the amount of concave deformation (amount of sink mark) is larger. As a result, the axial center part of the outer peripheral surface of the teeth of the worm wheel is concave compared to both axial ends, and the flatness precision is reduced.

[0004] In addition, the tooth portion of the worm wheel has a pair of thick portions covering both axial sides of the sleeve (core metal portion), but the axial thickness of the pair of thick portions is usually the same. In this case, if a gate is disposed on one axial side of the sleeve and the tooth portion is injection molded, the thick portion on one axial side of the pair of thick portions becomes large in volume due to the gate and runner, and the amount of sink marks increases. As a result, a difference occurs between the amount of sink marks of one thick portion and the amount of sink marks of the other thick portion. For example, the side of the tooth portion of the worm wheel where the gate is disposed (one axial side) is recessed compared to the opposite side (the other axial side), and the accuracy of flatness of the outer circumferential surface of the tooth portion in the axial direction is reduced. Such a problem is not limited to those used in electric power steering devices, but may occur in any worm wheel in which the tooth portion is injection molded on the sleeve.

[0005] The worm wheel described in Patent Document 1 has an annular sleeve and a tooth portion covering the sleeve. The tooth portion is formed by injection molding so as to cover a part of the sleeve, and has a tooth forming portion provided on the outer peripheral surface of the sleeve, a first thick portion provided on a first side surface which is a surface of the sleeve closer to the injection molding gate in the axial direction, and a second thick portion provided on a second side surface which is a surface of the sleeve opposite to the first side surface in the axial direction. The outer peripheral surface of the sleeve has a central portion in the axial direction which protrudes radially compared to both ends in the axial direction, and the first thick portion has a smaller axial thickness compared to the second thick portion.

[0006] In Patent Document 1, the above-mentioned configuration is intended to prevent the axial central portion of the outer peripheral surface of the tooth portion from being recessed compared to both axial ends, and to prevent the portion of the outer peripheral surface of the tooth portion on the first thick portion side from being recessed compared to the portion of the second thick portion side. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2018-9656 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the worm wheel of Patent Document 1, an engagement hole having a depth in the axial direction is provided on both axial side surfaces of the sleeve. Therefore, during injection molding, the resin is separated into one that flows toward the engagement hole and another that flows toward other portions, which may cause molding defects such as weld lines.

[0009] The present invention has been made in consideration of the above circumstances, and has an object to provide a worm wheel, an electric power steering device, and a method for manufacturing a worm wheel that are capable of reducing the difference in the amount of sink marks between different portions. [Means for solving the problem]

[0010] The above object of the present invention can be achieved by the following configuration. (1) a core metal portion that is fitted onto the outer periphery of an output shaft; an annular protrusion provided on an outer periphery of the core metal portion; a tooth portion fixed to an outer periphery of the annular protrusion; A worm wheel having A plurality of recesses are provided on both axial surfaces of the annular protrusion at predetermined intervals in the circumferential direction, the recesses extending radially inward from the outer circumferential surface of the annular protrusion, The tooth portion is fixed to the annular protrusion by injection molding so as to embed the outer circumferential surface of the annular protrusion. A worm wheel comprising: (2) A plurality of protruding portions extending radially outward are provided at a predetermined interval in the circumferential direction in the axial center of the outer circumferential surface of the core metal portion, The annular convex portion is fixed to the core metal portion by insert molding so as to embed the multiple protruding portions of the core metal portion. The worm wheel according to (1). (3) A protrusion is provided on one axial side surface of the protruding portion, the protruding portion extending radially outward from an outer circumferential surface of the protruding portion, A groove portion is provided on the other axial side surface of the protruding portion, the groove portion extending radially inward from an outer circumferential surface of the protruding portion. (2) A worm wheel as described in (1). (4) The plurality of recesses include a first recess provided on one axial side surface of the annular protrusion and a second recess provided on the other axial side surface of the annular protrusion, The axial width of the first recess is equal to or less than the axial width of the second recess. The worm wheel according to any one of (1) to (3). (5) The first recess has a radially inner side surface connected to one axial side surface of the annular protrusion and extending to the other axial side, and one axial side surface extending radially outward to connect the radially inner side surface of the first recess and an outer circumferential surface of the annular protrusion, the second recess has a radially inner side surface connected to the other axial side surface of the annular protrusion and extending to one axial side, and the other axial side surface extending radially outward so as to connect the radially inner side surface of the second recess and an outer circumferential surface of the annular protrusion, the one axial side surface of the first recessed portion is an inclined surface inclined toward the other axial side as it extends radially outward, The other axial side surface of the second recess is a plane extending in a radial direction so as to be perpendicular to the axial direction. (4) A worm wheel as described in (4). (6) The radially inner side surface of the first recessed portion is an inclined surface that is inclined radially outward as it approaches the other axial side, The radially inner surface of the second recessed portion is an inclined surface that inclines radially outward as it approaches one axial side. (5) A worm wheel as described in (5). (7) The first recess has two circumferential surfaces connecting both circumferential ends of the radially inner surface and an outer circumferential surface of the annular protrusion, The second recess has two circumferential surfaces connecting both circumferential ends of the radially inner surface and an outer circumferential surface of the annular protrusion, Each of the first recessed portion has two circumferential surfaces that are inclined radially outward from a circumferential center of the first recessed portion toward the circumferential outer side, Each of the circumferential surfaces of the second recessed portion is an inclined surface that is inclined radially outward from a circumferential center portion of the second recessed portion toward the circumferential outer side. (5) A worm wheel as described in (5). (8) The tooth portion is fixed to the annular protrusion by injecting resin from a gate provided on one side in the axial direction. The worm wheel according to any one of (4) to (7). (9) The strength of the thermosetting resin material of the annular convex portion is higher than the strength of the thermoplastic resin material of the teeth portion. The worm wheel according to any one of (1) to (8). (10) A worm wheel of a worm reducer of an electric power steering device. The worm wheel according to any one of (1) to (9). (11) An electric power steering device having the worm wheel according to any one of (1) to (10). (12) A core metal portion that is fitted onto the outer periphery of the output shaft; an annular protrusion provided on an outer periphery of the core metal portion; a tooth portion made of a thermoplastic resin material fixed to an outer periphery of the annular protrusion; A method for manufacturing a worm wheel having the following features: A plurality of recesses are provided on both axial surfaces of the annular protrusion at predetermined intervals in the circumferential direction, the recesses extending radially inward from the outer circumferential surface of the annular protrusion, a step of fixing the teeth portion to the annular protrusion by injection molding so as to embed the outer circumferential surface of the annular protrusion; A method for manufacturing a worm wheel, comprising: Effect of the Invention

[0011] According to the present invention, it is possible to provide a worm wheel, an electric power steering device, and a method for manufacturing a worm wheel that are capable of reducing the difference in the amount of sink marks between different portions. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of an electric power steering device including a worm wheel according to a first embodiment. [Diagram 2] FIG. 2 is a perspective view showing a worm wheel according to the first embodiment in a partially cut away state. [Diagram 3] FIG. 2 is a cross-sectional view taken along line II-II of FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. [Diagram 5] FIG. 4 is a view of the annular protrusion as viewed from the radial outside. [Figure 6] FIG. 6 is an enlarged view of a portion VI in FIG. 5. [Figure 7] FIG. 4 is an enlarged view of a main part in FIG. [Figure 8] FIG. 11 is a view of a core portion according to a first modified example, as viewed from the axial direction. [Figure 9] 9 is a cross-sectional view taken along line IX-IX of FIG. 8. [Figure 10] 13 is a view showing a core portion according to a second modified example as viewed from the axial direction. FIG. [Figure 11] 11 is a cross-sectional view taken along the line XI-XI of FIG. [Figure 12] FIG. 11 is a perspective view showing a worm wheel 40 according to a second embodiment in a partially cut away state. [Figure 13] FIG. 11 is a perspective view showing a worm wheel 40 according to a second embodiment in a partially cut away state. [Figure 14] 4 is a view of the worm wheel as seen from the other axial side. FIG. [Figure 15] 15 is a cross-sectional view taken along line XV-XV of FIG. 14. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A worm wheel, an electric power steering device, and a method for manufacturing a worm wheel according to embodiments of the present invention will be described below with reference to the drawings.

[0014] [First embodiment]

[0015] Fig. 1 shows the configuration of an electric power steering device 1 equipped with a worm wheel according to a first embodiment of the present invention. The electric power steering device 1 shown in Fig. 1 is a so-called column type, but the worm wheel of the present invention is also applicable to electric power steering devices of other types (for example, pinion type, dual pinion type, rack type, etc.).

[0016] As shown in FIG. 1, the electric power steering device 1 includes a steering shaft 12 to which a steering wheel 11 can be attached on the rear side of the vehicle body (right side in FIG. 1), a steering column 13 through which the steering shaft 12 is inserted, an assist device (steering assist unit) 20 for applying an assist torque to the steering shaft 12, and a steering gear 30 connected to the front side of the vehicle body of the steering shaft 12 (left side in FIG. 1) via a rack / pinion mechanism (not shown).

[0017] In the steering shaft 12, the female steering shaft 12A and the male steering shaft 12B are spline-fitted to be capable of transmitting rotational torque and to be movable relative to each other in the axial direction. Therefore, in the event of a collision, the female steering shaft 12A and the male steering shaft 12B can move relative to each other at the spline-fitted portion, thereby shortening their overall lengths.

[0018] In addition, the cylindrical steering column 13, through which the steering shaft 12 is inserted, combines an outer column 13A and an inner column 13B to be capable of telescopic movement, and has a so-called collapsible structure in which, when an axial impact is applied during a collision, the energy of the impact is absorbed and the overall length is shortened.

[0019] The vehicle body front end of the inner column 13B is press-fitted and fixed into the vehicle body rear end of the gear housing 21. In addition, the vehicle body front end of the male steering shaft 12B is passed through the inside of the gear housing 21 and connected to the vehicle body rear end of the input shaft (not shown) of the assist device 20.

[0020] The steering column 13 has its middle portion supported by a support bracket 14 on a part of the vehicle body 18, such as the underside of the dashboard. In addition, a locking portion (not shown) is provided between the support bracket 14 and the vehicle body 18. This allows the support bracket 14 to come off the locking portion and move towards the front of the vehicle when an impact is applied to the support bracket 14 in a direction towards the front of the vehicle.

[0021] In addition, an upper end portion of the gear housing 21 is also supported by a part of the vehicle body 18. In addition, the electric power steering device 1 is provided with a tilt mechanism and a telescopic mechanism, so that the position of the steering wheel 11 in the fore-and-aft direction of the vehicle body and the height position can be freely adjusted.

[0022] The output shaft 23 protruding from the vehicle body front end face of the gear housing 21 is connected to the rear end of the intermediate shaft 16 via a cross joint 15. Furthermore, an input shaft 31 of a steering gear 30 is connected to the front end of the intermediate shaft 16 via another cross joint 15. The intermediate shaft 16 has a male shaft 16A and a female shaft 16B. The vehicle body rear side of the female shaft 16B is fitted onto the vehicle body front side of the male shaft 16A. The male shaft 16A and the female shaft 16B are capable of transmitting rotational torque and are capable of relative movement in the axial direction.

[0023] A pinion (not shown) is coupled to the input shaft 31. A rack (not shown) is meshed with this pinion, and rotation of the steering wheel moves the tie rod 32 to steer the wheels (not shown).

[0024] An electric motor 26 is fixed to the gear housing 21 of the assist device 20, and a worm is coupled to a rotating shaft (not shown) of the electric motor 26. A worm wheel 40 (see Figs. 2 to 4) is attached to the output shaft 23, and a worm of the rotating shaft of the electric motor 26 meshes with this worm wheel 40. In this manner, the worm wheel 40 of this embodiment constitutes a worm wheel of a worm reducer of an electric power steering device, but can also be applied as a worm wheel used in any other device.

[0025] Fig. 2 is a perspective view showing a worm wheel 40 according to a first embodiment of the present invention in a partially cut away state. Fig. 3 is a cross-sectional view taken along line II-II in Fig. 2. Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 3. Fig. 5 is a view of the annular protrusion 60 as viewed from the radially outer side. Fig. 6 is an enlarged view of part VI in Fig. 5. Fig. 7 is an enlarged view of a main part in Fig. 3.

[0026] The worm wheel 40 has a core metal portion 50 that is fitted onto the outer periphery of the output shaft 23 of the electric power steering device 1, an annular convex portion 60 provided on the outer periphery of the core metal portion 50, and a teeth portion 70 that is fixed to the outer periphery of the annular convex portion 60. In this embodiment, the core metal portion 50 and the annular convex portion 60 are separate bodies, and the annular convex portion 60 is described as a member that is fixed to the outer periphery of the core metal portion 50. However, the annular convex portion 60 and the core metal portion 50 may be integrally formed from the same member.

[0027] 2 to 4, the core metal portion 50 has an annular portion 51 that is fitted onto the output shaft 23, and a plurality of protruding portions 53 that extend radially outwardly at predetermined intervals in the circumferential direction from an axial center portion of an outer circumferential surface 51B of the annular portion 51 (the outer circumferential surface of the core metal portion 50).

[0028] In FIG. 3, the output shaft 23 is not shown, but the rotation axis O of the output shaft 23 is shown. The direction in which this rotation axis O extends is called the "axial direction." "One axial side" is the right side in FIG. 3, and is indicated by the symbol X1. "The other axial side" is the left side in FIG. 3, and is indicated by the symbol X2. "Radial direction" is a direction perpendicular to the axial direction, and is the up and down direction in FIG. 3. "Radial outer side" is a direction away from the rotation axis O. "Radial inner side" is a direction approaching the rotation axis O. "Circumferential direction" is a direction rotating around the rotation axis O.

[0029] The annular portion 51 is annular in shape and has a central hole 51A through which the output shaft 23 is inserted. The annular portion 51 protrudes further than the annular protrusion 60 and the teeth portion 70 to one axial side X1 and the other axial side X2.

[0030] The multiple protruding portions 53 are formed integrally with the annular portion 51. A space is provided between adjacent protruding portions 53 in the circumferential direction. Therefore, a circumferential uneven structure is formed by the multiple protruding portions 53 and the outer circumferential surface 51B of the annular portion 51. The annular protrusion 60 fixed to the outer periphery of the core metal portion 50 is prevented from rotating by the circumferential uneven structure.

[0031] Further, the protruding portion 53 has a main body portion 53A extending radially outward from the outer circumferential surface 51B of the annular portion 51, a protrusion 53B provided on the main body portion 53A, and a groove portion 53C provided on the main body portion 53A.

[0032] As shown in Fig. 3, the axial width of the main body portion 53A is shorter than the axial width of the annular protrusion portion 60 and the tooth portion 70. As shown in Fig. 4, the main body portion 53A is generally fan-shaped when viewed from the axial direction, and its circumferential width increases radially outward.

[0033] The protrusion 53B is provided in the circumferential center of one axial side surface of the main body 53A and extends radially outward from the outer circumferential surface of the main body 53A. The protrusion 53B has a shape that is approximately similar to that of the main body 53A. That is, the protrusion 53B is approximately fan-shaped when viewed from the axial direction, and its circumferential width increases radially outward.

[0034] Groove portion 53C is provided in the circumferential center of the other axial side surface of main body portion 53A and extends radially inward from the outer circumferential surface of main body portion 53A. Groove portion 53C has a shape similar to that of main body portion 53A and is a shape obtained by rotating protrusion 53B by 180 degrees. That is, groove portion 53C is substantially fan-shaped when viewed from the axial direction, and its circumferential width increases toward the radially inward direction.

[0035] In this manner, an axial uneven structure is provided by the protrusions 53B and the grooves 53C in each of the overhanging portions 53. Therefore, in addition to the circumferential uneven structure, the axial uneven structure further prevents relative rotation between the core metal portion 50 and the annular protrusion 60.

[0036] Furthermore, by providing the axially uneven structure in the overhanging portion 53, high torsional strength can be ensured even if thermal expansion, swelling due to moisture absorption, or shrinkage deformation occurs. Therefore, compared to when the overhanging portion 53 is composed of only the main body portion 53A, when the overhanging portion 53 is composed of the main body portion 53A, the volume of the overhanging portion 53 required to ensure the same strength can be reduced, and weight can be reduced.

[0037] Furthermore, since the shapes of the main body portion 53A, the protrusion portion 53B, and the groove portion 53C when viewed from the axial direction are approximately fan-shaped, the engagement force between the protrusion portion 53 (core metal portion 50) and the annular convex portion 60 is increased compared to when they are simply rectangular in shape.

[0038] The axial width of the protrusion 53B and the axial width of the groove 53C may be set arbitrarily, but for example, the configurations shown in Figs. 8 to 9 may be adopted. Fig. 8 is a view of the core metal part 50 according to the first modified example as viewed from the axial direction. Fig. 9 is a cross-sectional view taken along line IX-IX in Fig. 8. In the example of Figs. 8 to 9, the axial width of the protrusion 53B is h / 3, the axial width of the groove 53C is h / 3, and the axial width between the protrusion 53B and the groove 53C is h / 3, relative to the axial width h of the protrusion 53. With this configuration, the engagement force between the protrusion 53 and the annular convex part 60 is increased, and high torsional strength can be ensured even in normal situations or in situations where expansion or contraction occurs.

[0039] Moreover, configurations as shown in Figs. 10 and 11 may be adopted. Fig. 10 is a view of the core metal portion 50 according to the second modified example as viewed from the axial direction. Fig. 11 is a cross-sectional view taken along the line XI-XI in Fig. 10. In the example of Figs. 10 and 11, the axial width of the protrusion 53B is h / 2 and the axial width of the groove 53C is h / 2, with respect to the axial width of the protrusion 53. With this configuration, even if the environment changes drastically during use and expansion or contraction occurs, the protrusion 53 and the annular convex portion 60 can be reliably engaged with each other with a simple configuration, so that high torsional strength can be ensured.

[0040] The annular protrusion 60 is formed of a thermosetting resin material and fixed to the outer periphery of the core metal portion 50. The annular protrusion 60 is formed on the outer periphery 51B of the annular portion 51 of the core metal portion 50 by insert molding such that the entirety of the multiple protrusions 53 are embedded in the resin of the annular protrusion 60. Therefore, the axial width and radial width of the annular protrusion 60 are larger than the axial width and radial width of the protrusions 53, and the annular protrusion 60 covers the entirety of the protrusions 53.

[0041] As the thermosetting resin material of the annular protrusion 60, one that has high strength and generates little gas during molding is selected, and examples thereof include phenolic resin, melamine resin, cross-linked polyester amide, epoxy resin, etc. Furthermore, these resins may be fiber-reinforced (e.g., reinforced with aramid, carbon, glass, etc.).

[0042] A plurality of small diameter recesses 61 and large diameter recesses 65 extending radially inward from the outer circumferential surface 60C of the annular protrusion 60 are provided at a predetermined interval in the circumferential direction on both axial surfaces (one axial side surface 60A and the other axial side surface 60B) of the annular protrusion 60. The small diameter recesses 61 and the large diameter recesses 65 are alternately arranged in the circumferential direction. In this manner, the small diameter recesses 61 and the large diameter recesses 65 form an uneven structure in the circumferential direction and an uneven structure in the axial direction, thereby preventing relative rotation between the annular protrusion 60 and the teeth portion 70. In addition, since the axial center portion of the outer circumferential surface 60C of the annular protrusion 60 is flat, the teeth portion 70 can be injection molded with high precision.

[0043] 2 and 3, the radial width (groove depth) of the small diameter recess 61 is smaller than the radial width (groove depth) of the large diameter recess 65. More specifically, the radial inner side surfaces 62A, 63A which are the bottom surfaces of the small diameter recess 61 are located radially outward from the radial center portion of the annular protrusion 60 and radially outward from the protrusion 53. In contrast, the radial inner side surface 65A which is the bottom surface of the large diameter recess 65 is located radially inward from the radial center portion of the annular protrusion 60 and overlaps with the protrusion 53 in the radial direction.

[0044] Of the multiple large diameter recesses 65, the one provided on one axial side surface 60A of the annular protrusion 60 is referred to as a first large diameter recess 66, and the one provided on the other axial side surface 60B is referred to as a second large diameter recess 67. The first large diameter recess 66 and the second large diameter recess 67 face each other in the axial direction.

[0045] The first large diameter recess 66 and the second large diameter recess 67 have the same shape. The first large diameter recess 66 and the second large diameter recess 67 are generally fan-shaped when viewed in the axial direction, with the circumferential width increasing toward the radially outer side (see FIG. 2), and are generally rectangular when viewed in the circumferential direction (see FIG. 3).

[0046] In this embodiment, the small diameter recesses 61 and the large diameter recesses 65 are arranged alternately in the circumferential direction, but the large diameter recesses 65 do not have to be provided. When the large diameter recesses 65 are not provided, the small diameter recesses 61 are arranged at a predetermined interval in the circumferential direction. In this case, the flow of resin can be made uniform during injection molding of the teeth portion 70. On the other hand, when the large diameter recesses 65 are provided as in this embodiment, the weight of the annular convex portion 60 can be reduced. Whether or not to provide the large diameter recesses 65 can be appropriately selected depending on the purpose.

[0047] Of the multiple small diameter recesses 61, the one provided on one axial side surface 60A of the annular protrusion 60 is referred to as a first small diameter recess (first recess) 62, and the one provided on the other axial side surface 60B is referred to as a second small diameter recess (second recess) 63. The first small diameter recess 62 and the second small diameter recess 63 face each other in the axial direction.

[0048] The first small diameter recess 62 and the second small diameter recess 63 have different shapes, and the respective shapes will be described below. As described later, the one axial side X1 on which the first small diameter recess 62 is arranged is the side on which a gate is arranged when the tooth portion 70 is injection molded, and the other axial side X2 on which the second small diameter recess 63 is arranged is the opposite side to the side on which the gate is arranged.

[0049] As shown in Figures 5 to 7, the first small diameter recess 62 has a radial inner surface 62A that is connected to one axial side surface 60A of the annular convex portion 60 and extends to the other axial side X2, an axial side surface 62B that extends radially outward to connect the radial inner surface 62A and the outer peripheral surface 60C of the annular convex portion 60, and both circumferential surfaces 62C, 62C that connect both circumferential ends of the radial inner surface 62A to the outer peripheral surface 60C of the annular convex portion 60.

[0050] The radially inner side surface 62A is an inclined surface that inclines radially outward as it approaches the other axial side X2. The axial side surface 62B is an inclined surface that inclines radially outward as it approaches the other axial side X2. Each of the circumferential surfaces 62C, 62C is an inclined surface that inclines radially outward as it approaches from the circumferential center of the first small diameter recess 62 toward the circumferential outside.

[0051] The second small diameter recess 63 has a radial inner surface 63A that is connected to the other axial side surface 60B of the annular protrusion 60 and extends to one axial side X1, an axial side surface 63B that extends radially outward to connect the radial inner surface 63A and the outer peripheral surface 60C of the annular protrusion 60, and both circumferential surfaces 63C, 63C that connect both circumferential ends of the radial inner surface 63A to the outer peripheral surface 60C of the annular protrusion 60.

[0052] The radially inner surface 63A is an inclined surface that inclines radially outward as it approaches one axial side X1. The axial side surface 63B is a flat surface that extends radially so as to be perpendicular to the axial direction. Each of the circumferential surfaces 63C, 63C is an inclined surface that inclines radially outward as it approaches the circumferentially outer side from the circumferential center of the second small diameter recess 63.

[0053] Since each of the first small diameter recess 62 and the second small diameter recess 63 has an inclined surface, the flow of resin during injection molding of the teeth portion 70 is made smooth.

[0054] Moreover, while the axial side surface 62B of the first small diameter recess 62 is an inclined surface, the axial side surface 63B of the second small diameter recess 63 is a flat surface, so that the axial width L1 of the first small diameter recess 62 is equal to or smaller than the axial width L2 of the second small diameter recess 63 (L1≦L2). As a result, as will be described later, the axial width M1 of the first side portion 72 of the tooth portion 70 is equal to or smaller than the axial width M2 of the second side portion 73 of the tooth portion 70 (M1≦M2).

[0055] The teeth portion 70 fixed to the outer periphery of the annular protrusion 60 is formed of a thermoplastic resin material that has good machinability. That is, the thermosetting resin of the annular protrusion 60 is stronger than the thermoplastic resin of the teeth portion 70. Therefore, the annular protrusion 60 fully functions as a core metal structure of the worm wheel 40. In addition, since the annular protrusion 60 has excellent heat resistance, there is no problem such as the influence of heat when the thermoplastic resin of the teeth portion 70 is injection molded.

[0056] The tooth portion 70 has an annular base portion 71, a first side portion 72 extending radially inward from one axial side X1 of the base portion 71, and a second side portion 73 extending radially inward from the other axial side X2 of the base portion 71.

[0057] The axial width of the base 71 is larger than the axial width of the annular protrusion 60 and smaller than the axial width of the core metal portion 50. The first side portion 72 extends slightly radially inward from the first small diameter recess 62 of the annular protrusion 60. The second side portion 73 extends slightly radially inward from the second small diameter recess 63 of the annular protrusion 60. Therefore, the base 71 and the first side portion 72 and second side portion 73 extending from the base 71 cover the outer periphery of the annular protrusion 60. That is, the tooth portion 70 covers the outer periphery of the one axial side surface 60A of the annular protrusion 60, the outer periphery of the other axial side surface 60B, the entire outer periphery surface 60C, all of the first small diameter recesses 62, all of the second small diameter recesses 63, the outer periphery of the first large diameter recesses 66, and the outer periphery of the second large diameter recesses 67.

[0058] The shapes of the first and second side portions 72, 73 of the teeth portion 70, which are formed in the first and second small diameter recesses 62, 63 of the annular projection 60 by injection molding, reflect the shapes of these first and second small diameter recesses 62, 63. As shown in Fig. 7, the axial width L1 of the first small diameter recess 62 is equal to or less than the axial width L2 of the second small diameter recess 63 (L1 ≦ L2), and the axial distances D1, D2 from both axial side surfaces 60A, 60B of the annular projection 60 to the inner surface of a mold (not shown) are equal to each other. Therefore, the axial width M1 (M1 = L1 + D1) of the first side portion 72 of the teeth portion 70 is equal to or less than the axial width M2 (M2 = L2 + D2) of the second side portion 73 of the teeth portion 70 (M1 ≦ M2).

[0059] When the teeth portion 70 is injection molded, the gate and the runner connected to the gate are disposed on one axial side X1. Therefore, normally, the portion that becomes the first lateral portion 72 on one axial side X1 is pulled by the gate and the runner and becomes larger in volume, resulting in a large amount of sink.

[0060] However, in this embodiment, since the axial width M1 of the first side portion 72 is equal to or smaller than the axial width M2 of the second side portion 73 of the teeth portion 70 (M1≦M2), the volume of the first side portion 72 is smaller than the volume of the second side portion 73, and the amount of sink mark is reduced in the first side portion 72. Therefore, the difference in the amount of sink mark between the first and second side portions 72, 73 can be reduced.

[0061] In addition, the outer peripheral surface 60C of the annular protrusion 60 is flat in the axial direction, but in this case, when the teeth portion 70 is injection molded, the resin filled in the mold solidifies in order from the part that touches the mold, and the central part of the part that will become the teeth portion 70 solidifies later. Therefore, in the shrinkage process when the part that will become the teeth portion 70 solidifies, the axial center part of the outer peripheral surface of the part is pulled radially inward compared to both axial ends, and the amount of sink is large. As a result, the axial center part of the outer peripheral surface of the teeth portion 70 is recessed compared to both axial ends, and the flatness precision is reduced.

[0062] However, in this embodiment, the radial width N1 at the axial center of the teeth portion 70 is smaller than the radial width N2 at the portion on one axial side X1 of the teeth portion 70 and the radial width N3 at the portion on the other axial side X2 of the teeth portion 70, so the amount of sink marks at the axial center of the outer peripheral surface of the teeth portion 70 is reduced. Therefore, the difference in the amount of sink marks between the axial center and both axial ends on the outer peripheral surface of the teeth portion 70 can be reduced.

[0063] After the core metal portion 50, the annular projection 60 and the teeth portion 70 are integrated as described above, a gear tooth surface 74 required for the worm wheel 40 is formed on the outer periphery of the teeth portion 70 by cutting.

[0064] In this way, the worm wheel 40 can be made lighter by using the metal core portion 50 only for the portion that fits with the output shaft 23 and using synthetic resin for the other portions. Furthermore, the annular protrusion 60 fixed to the outer periphery of the core portion 50 is made of a thermosetting resin material that is strong and generates little gas during molding, so that the generation of unnecessary excess material can be suppressed. Furthermore, the teeth portion 70 is made of a thermoplastic resin material, so that good processability can be obtained. Furthermore, since only the teeth portion 70 is made of thermoplastic resin, the volume of the thermoplastic resin in the worm wheel 40 can be reduced and the generation of voids in the gear portion can be suppressed.

[0065] As described above, according to the worm wheel 40 of this embodiment, a plurality of small diameter recesses 61 (first small diameter recesses 62, second small diameter recesses 63) extending radially inward from the outer circumferential surface 61C of the annular convex portion 60 are provided at predetermined intervals in the circumferential direction on both axial side surfaces 60A, 60B of the annular convex portion 60, and the teeth portion 70 is fixed to the annular convex portion 60 by injection molding so as to embed the outer circumferential surface 61C of the annular convex portion 60. Therefore, the difference in the amount of sink marks between the axial center portion and both axial ends on the outer circumferential surface of the teeth portion 70 can be reduced.

[0066] A plurality of protruding portions 53 extending radially outward are provided at a predetermined interval in the axial center of the outer circumferential surface of the core metal portion 50, and the annular convex portion 60 is fixed to the core metal portion 50 by insert molding so as to embed the plurality of protruding portions 53 of the core metal portion 50. Therefore, the annular convex portion 60, which is separate from the core metal portion 50, is firmly fixed to the core metal portion 50.

[0067] A protrusion 53B extending radially outward from the outer circumferential surface of the protrusion 53 is provided on one axial side surface of the protrusion 53, and a groove 53C extending radially inward from the outer circumferential surface of the protrusion 53 is provided on the other axial side surface of the protrusion 53. Thus, each protrusion 53 has an axial uneven structure due to the protrusion 53B and the groove 53C. This further prevents relative rotation between the core metal portion 50 and the annular protrusion 60, and ensures high torsional strength.

[0068] The small diameter recesses 61 include a first small diameter recess 62 provided on one axial side surface 60A of the annular projection 60 and a second small diameter recess 63 provided on the other axial side surface 61B of the annular projection 60, and the axial width L1 of the first small diameter recess 62 is equal to or smaller than the axial width L2 of the second small diameter recess 63 (L1≦L2). Therefore, the axial width M1 of the first side portion 72 of the teeth portion 70 formed in the first small diameter recess 62 is equal to or smaller than the axial width M2 of the second side portion 73 of the teeth portion 70 formed in the second small diameter recess 63 (M1≦M2), so that the amount of sink mark of the first side portion 72 is reduced. Therefore, the difference in the amount of sink mark between the first and second side portions 72, 73 can be reduced.

[0069] In particular, since the teeth portion 70 is fixed to the annular convex portion 60 by injecting resin from a gate provided on one axial side X1, the amount of sink mark of the first side portion 72 on one axial side X1 is greater than that of the second side portion 73. However, as described above, since the axial width M1 of the first side portion 72 is equal to or smaller than the axial width M2 of the second side portion 73 of the teeth portion 70 formed in the second small diameter recessed portion 63 (M1≦M2), the amount of sink mark of the first side portion 72 is smaller, and the difference in the amount of sink mark between the first and second side portions 72, 73 can be reduced.

[0070] The axial side surface 62B of the first small diameter recess 62 is an inclined surface that inclines toward the other axial side X2 as it approaches the radial outside, and the axial side surface 63B of the second small diameter recess 63 is a flat surface that extends in the radial direction so as to be perpendicular to the axial direction. Therefore, as described above, the axial width L1 of the first small diameter recess 62 can be set to be equal to or smaller than the axial width L2 of the second small diameter recess 63 (L1≦L2), and the axial width M1 of the first side portion 72 of the tooth portion 70 can be set to be equal to or smaller than the axial width M2 of the second side portion 73 of the tooth portion 70 (M1≦M2).

[0071] The radially inner side surface 62A of the first small diameter recess 62 is an inclined surface that inclines radially outward toward the other axial side X2, and the radially inner side surface 63A of the second small diameter recess 63 is an inclined surface that inclines radially outward toward the one axial side X1. Therefore, these inclined surfaces facilitate the flow of resin during injection molding of the teeth portion 70.

[0072] Both circumferential surfaces 62C of the first small diameter recess 62 are inclined surfaces that incline radially outward from the circumferential center of the first small diameter recess 62 toward the circumferential outside, and both circumferential surfaces 63C of the second small diameter recess 63 are inclined surfaces that incline radially outward from the circumferential center of the second small diameter recess 63 toward the circumferential outside. Therefore, these inclined surfaces facilitate the flow of resin during injection molding of the teeth portion 70.

[0073] The strength of the thermosetting resin agent of the annular protrusion 60 is higher than the strength of the thermoplastic resin agent of the teeth portion 70. Therefore, the annular protrusion 60 fully functions as a core metal structure of the worm wheel 40. In addition, since the annular protrusion 60 also has excellent heat resistance, there are no problems such as heat influences when the thermoplastic resin of the teeth portion 70 is injection molded.

[0074] Although the worm wheel 40 has been described as being used in the worm reduction gear of the electric power steering device 1, it may also be used in other devices.

[0075] [Second embodiment] Fig. 12 and Fig. 13 are perspective views showing a worm wheel 40 according to a second embodiment in a partially cut away state. Fig. 14 is a view of the worm wheel 40 as seen from the other axial side X2. Fig. 15 is a cross-sectional view taken along line XV-XV in Fig. 14.

[0076] In the first embodiment of the worm wheel 40, the first side portion 72 of the tooth portion 70 arranged on one axial side X1 (gate side) extends slightly radially inwardly further than the first small diameter recess 62 of the annular convex portion 60, and the second side portion 73 of the tooth portion 70 arranged on the other axial side X2 (anti-gate side) extends slightly radially inwardly further than the second small diameter recess 63 of the annular convex portion 60.

[0077] In the worm wheel 40 of this embodiment, the first side portion 72 of the teeth portion 70 arranged on one axial side X1 (gate side) extends slightly radially inward from the first small diameter recessed portion 62 of the annular convex portion 60, similar to the first embodiment. On the other hand, the second side portion 73 of the teeth portion 70 arranged on the other axial side X2 (opposite gate side) extends radially inward from the second small diameter recessed portion 63 of the annular convex portion 60, and reaches the bottom surface (radial inner surface 65A) of the second large diameter recessed portion 67. Therefore, the second side portion 73 of the teeth portion 70 covers the entirety of the multiple second large diameter recessed portions 67.

[0078] Therefore, the first side portion 72 of the teeth portion 70 covers an outer periphery of one axial side X1 of the annular convex portion 60, whereas the second side portion 73 of the teeth portion 70 covers most of the other axial side X2 of the annular convex portion 60. In other words, the teeth portion 70 covers the outer periphery of one axial side surface 60A of the annular convex portion 60, a portion excluding the inner periphery of the other axial side surface 60B, all of the outer periphery surface 60C, all of the multiple first small diameter recesses 62, all of the multiple second small diameter recesses 63, the outer peripheries of the multiple first large diameter recesses 66, and all of the multiple second large diameter recesses 67.

[0079] With this configuration, the relative rotation between the annular projection 60 and the teeth portion 70 is further suppressed.

[0080] The present invention is not limited to the respective embodiments, and can be carried out within the scope of the gist of the present invention, and various modifications are possible. [Explanation of symbols]

[0081] 1 electric power steering device, 11 steering wheel, 12 steering shaft, 12A female steering shaft, 12B male steering shaft, 13 steering column, 13A outer column, 13B inner column, 14 support bracket, 15 cross joint, 16 intermediate shaft, 16A male shaft, 16B female shaft, 18 vehicle body, 20 assist device, 21 gear housing, 23 output shaft, 26 electric motor, 31 input shaft, 32 tie rod, 40 worm wheel, 50 core metal portion, 51 annular portion, 51A center hole, 51B outer peripheral surface, 53 protruding portion, 53A main body portion, 53B protrusion, 53C groove portion, 60 annular convex portion, 60A axial one side surface, 60B axial other side surface, 60C outer peripheral surface, 61 small diameter recess (recess), 62 first small diameter recess (first recess), 62A Radial inner surface, 62B axial side surface, 62C circumferential both surfaces, 63 second small diameter recess (second recess), 63A radial inner surface, 63B axial side surface, 63C circumferential both surfaces, 65 large diameter recess, 65A radial inner surface, 66 first large diameter recess, 67 second large diameter recess, 70 tooth portion, 71 base portion, 72 first side portion, 73 second side portion, 74 gear tooth surface

Claims

1. a core metal portion that is fitted onto an outer periphery of an output shaft; an annular protrusion provided on an outer periphery of the core metal portion; a tooth portion fixed to an outer periphery of the annular protrusion; A worm wheel having A plurality of recesses are provided on both axial surfaces of the annular protrusion at predetermined intervals in the circumferential direction, the recesses extending radially inward from the outer circumferential surface of the annular protrusion, The teeth are fixed to the annular protrusion by injection molding so as to embed an outer circumferential surface of the annular protrusion, the plurality of recesses include a first recess provided on one axial side surface of the annular protrusion and a second recess provided on the other axial side surface of the annular protrusion, the first recess and the second recess have different shapes; The volume of the first recess is smaller than the volume of the second recess. A worm wheel comprising:

2. A core metal portion fitted onto the outer periphery of an output shaft; an annular protrusion provided on an outer periphery of the core metal portion; a tooth portion fixed to an outer periphery of the annular protrusion; A worm wheel having A plurality of recesses are provided on both axial surfaces of the annular protrusion at predetermined intervals in the circumferential direction, the recesses extending radially inward from the outer circumferential surface of the annular protrusion, The teeth are fixed to the annular protrusion by injection molding so as to embed an outer circumferential surface of the annular protrusion, A plurality of protruding portions are provided at a central portion in an axial direction of an outer circumferential surface of the core metal portion, the protruding portions extending radially outwardly at predetermined intervals in a circumferential direction, the annular convex portion is fixed to the core metal portion by insert molding so as to embed the plurality of protruding portions of the core metal portion; A protrusion is provided on one axial side surface of the protruding portion, the protruding portion extending radially outward from an outer circumferential surface of the protruding portion, A groove portion is provided on the other axial side surface of the protruding portion, the groove portion extending radially inward from an outer circumferential surface of the protruding portion. A worm wheel comprising:

3. A core metal portion fitted to the outer periphery of an output shaft; an annular protrusion provided on an outer periphery of the core metal portion; a tooth portion fixed to an outer periphery of the annular protrusion; A worm wheel having A plurality of recesses are provided on both axial surfaces of the annular protrusion at predetermined intervals in the circumferential direction, the recesses extending radially inward from the outer circumferential surface of the annular protrusion, The teeth are fixed to the annular protrusion by injection molding so as to embed an outer circumferential surface of the annular protrusion, the plurality of recesses include a first recess provided on one axial side surface of the annular protrusion and a second recess provided on the other axial side surface of the annular protrusion, The axial width of the first recess is equal to or less than the axial width of the second recess. A worm wheel comprising:

4. the first recess has a radially inner side surface connected to one axial side surface of the annular protrusion and extending to the other axial side, and one axial side surface extending radially outward so as to connect the radially inner side surface of the first recess and an outer circumferential surface of the annular protrusion, the second recess has a radially inner side surface connected to the other axial side surface of the annular protrusion and extending to one axial side, and the other axial side surface extending radially outward so as to connect the radially inner side surface of the second recess and an outer circumferential surface of the annular protrusion, the one axial side surface of the first recessed portion is an inclined surface inclined toward the other axial side as it extends radially outward, The other axial side surface of the second recess is a plane extending in a radial direction so as to be perpendicular to the axial direction. The worm wheel according to claim 1 or 3.

5. The radially inner surface of the first recessed portion is an inclined surface that inclines radially outward toward the other axial side, The radially inner surface of the second recessed portion is an inclined surface that inclines radially outward as it approaches one axial side.

5. The worm wheel according to claim 4.

6. The first recess has two circumferential surfaces connecting both circumferential ends of the radially inner surface and an outer circumferential surface of the annular protrusion, The second recess has two circumferential surfaces connecting both circumferential ends of the radially inner surface and an outer circumferential surface of the annular protrusion, Each of the first recessed portion has two circumferential surfaces that are inclined radially outward from a circumferential center of the first recessed portion toward the circumferential outer side, Each of the circumferential surfaces of the second recessed portion is an inclined surface that is inclined radially outward from a circumferential center portion of the second recessed portion toward the circumferential outer side.

5. The worm wheel according to claim 4.

7. The strength of the thermosetting resin material of the annular convex portion is higher than the strength of the thermoplastic resin material of the teeth portion. The worm wheel according to any one of claims 1 to 6.

8. A worm wheel of a worm reducer of an electric power steering device. The worm wheel according to any one of claims 1 to 7.

9. An electric power steering device comprising the worm wheel according to any one of claims 1 to 8.

10. a core metal portion that is fitted onto an outer periphery of an output shaft; an annular protrusion provided on an outer periphery of the core metal portion; a tooth portion made of a thermoplastic resin material fixed to an outer periphery of the annular protrusion; A method for manufacturing a worm wheel having the following features: A plurality of recesses are provided on both axial surfaces of the annular protrusion at predetermined intervals in the circumferential direction, the recesses extending radially inward from the outer circumferential surface of the annular protrusion, a step of fixing the teeth portion to the annular protrusion by injection molding so as to embed the outer circumferential surface of the annular protrusion; Including, the plurality of recesses include a first recess provided on one axial side surface of the annular protrusion and a second recess provided on the other axial side surface of the annular protrusion, an axial width of the first recess is equal to or less than an axial width of the second recess; The tooth portion is fixed to the annular protrusion by injecting resin from a gate provided on one axial side. A method for manufacturing a worm wheel comprising the steps of:

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