Worm reducer and assembly method thereof

Abstract

A pad (20) comprises: a pad base part (55) that is disposed between two guide parts (49) of a holder (19); two pad engagement parts (53) that are provided on side surfaces, on both sides relating to a third direction, of the pad base part (55), and that contact two holder engagement parts (41); a pad recessed part (76) that is provided along a first direction on a side surface on the other side in a second direction of the pad base part (55); and a pad elastic pressing part (77) that applies a preload to the contact portion between the holder engagement parts (41) and the pad engagement parts (53) by elastically pressing a portion of the holder (19) toward the other side in the second direction.

Description

[Technical Field]

[0001] The present disclosure relates to a worm reducer incorporated in, for example, an electric power steering device, and a method for assembling the same. [Background technology]

[0002] 2. Description of the Related Art Electric power steering devices that use an electric motor as an auxiliary power source are widely used as devices for reducing the force required to operate the steering wheel when applying a steering angle to the steered wheels of an automobile.

[0003] Electric power steering devices are broadly classified by the structure of the electric motor, and various structures have been proposed, including a column assist type that applies auxiliary power to a steering shaft rotatably supported inside the steering column, a pinion assist type that applies auxiliary power to a pinion shaft that is the input shaft of a steering gear unit, and a dual pinion type that provides auxiliary power to a pinion shaft separate from the pinion shaft that is the input shaft of the steering gear unit.

[0004] In either structure, auxiliary power from an electric motor is applied via a reducer to a shaft member that rotates or moves linearly when the steering wheel is operated. A worm reducer is widely used as such a reducer. A worm reducer that constitutes an electric power steering device includes a worm that is rotationally driven by an electric motor and a worm wheel that meshes with the worm.

[0005] 25 shows an example of a conventional structure of a worm reducer described in Japanese Patent No. 4381024 as Patent Document 1. The worm reducer 100 includes a housing 101, a worm wheel 102, and a worm 103.

[0006] The housing 101 has a wheel accommodating section 104 and a worm accommodating section 105 whose central axis is at a twisted position relative to the central axis of the wheel accommodating section 104 and whose axially intermediate portion opens into the wheel accommodating section 104.

[0007] The worm wheel 102 has wheel teeth 106 on its outer circumferential surface, and is supported and fixed coaxially around a rotation shaft 107 that is rotatably supported inside the wheel accommodating portion 104 .

[0008] The worm 103 has worm teeth 108 on the outer peripheral surface of an axially intermediate portion thereof that mesh with the wheel teeth 106. The worm 103 is rotatably supported inside the worm accommodating portion 105 by two ball bearings 109a and 109b at two axial positions on either side of the worm teeth 108. Of the two ball bearings 109a and 109b, the outer ring of the ball bearing 109a on the tip side of the worm 103 (the right side in FIG. 25) is press-fitted into a holder 110 that is fixedly fitted inside the deepest end portion of the worm accommodating portion 105. The inner ring of the ball bearing 109a is clearance-fitted onto a large-diameter portion 111 provided on the worm 103 at a portion located closer to the tip side than the worm teeth 108, via a synthetic resin bushing 112. That is, the inner ring of ball bearing 109a is fitted securely onto bushing 112, which is loosely fitted onto large diameter portion 111 of worm 103. The outer ring of ball bearing 109b on the base end side of worm 103 (left side in FIG. 25) is loosely fitted into the opening of worm accommodating portion 105, and the inner ring of ball bearing 109b is fitted onto the base end of worm 103. An output shaft of electric motor 113 is connected to the base end of worm 103 so as to transmit torque. That is, worm 103 can be rotated by electric motor 113.

[0009] In the worm reducer 100, unavoidable backlash exists at the meshing portion between the wheel teeth 106 and the worm teeth 108 due to dimensional errors and assembly errors of the components that make up the worm reducer 100. Due to the presence of this backlash, an unpleasant rattle noise may occur at the meshing portion when the direction of rotation of the steering wheel is changed. In the illustrated example, the tip of the worm 103 is elastically biased toward the worm wheel 102 to suppress the occurrence of such rattle noise.

[0010] That is, the base end of the worm 103 is supported relative to the worm housing portion 105 by a ball bearing 109b having a radial gap so as to be able to oscillate slightly. An annular gap exists around the entire circumference between the outer circumferential surface of the large diameter portion 111 of the worm 103 and the inner circumferential surface of the bushing 112. A pad 114 is fitted onto the tip end of the worm 103, and a torsion coil spring 115 is installed between the pad 114 and the holder 110. The torsion coil spring 115 elastically presses the pad 114 toward the worm wheel 102 in a first direction (the up-down direction in FIG. 25 ) in which the worm 103 moves toward or away from the worm wheel 102, thereby elastically urging the tip end of the worm 103 toward the worm wheel 102 in the first direction (the up-down direction in FIG. 25 ). This reduces backlash between the wheel teeth 106 and the worm teeth 108, thereby reducing the occurrence of rattle noise. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent No. 4381024 Summary of the Invention [Problem to be solved by the invention]

[0012] In the structure described in Japanese Patent No. 4381024, an annular gap exists over the entire circumference between the outer circumferential surface of the large-diameter portion 111 of the worm 103 and the inner circumferential surface of the bushing 112 so that the tip of the worm 103 can be pressed toward the worm wheel 102. In addition, an annular gap also exists over the entire circumference between the tip of the worm 103 and the through hole of the pad 114, although this gap is smaller than the annular gap existing between the outer circumferential surface of the large-diameter portion 111 of the worm 103 and the inner circumferential surface of the bushing 112. Therefore, when changing the rotation direction of the steering wheel, i.e., when changing the rotation direction of the worm 103, the direction of the component of the reaction force applied from the wheel teeth 106 to the worm teeth 108 in a third direction (the front-to-back direction in FIG. 25 ) perpendicular to both the first direction and the second direction (the left-to-right direction in FIG. 25 ), which is the axial direction of the worm housing portion 105, may change, causing the tip of the worm 103 to be forcefully displaced in the third direction. Therefore, there is room for improvement in terms of suppressing the generation of abnormal noise such as gear rattle.

[0013] The present disclosure aims to provide a worm reducer that can make it difficult for the tip of the worm to displace in a third direction perpendicular to both the first direction, which is the biasing direction of the tip, and the second direction, which is the axial direction of the worm accommodating section, when the rotation direction of the worm changes, and that can improve the workability of assembly work. [Means for solving the problem]

[0014] A worm reducer according to one aspect of the present disclosure includes a housing, a worm wheel, a worm, a holder, a pad, and an elastic member.

[0015] The housing has a wheel accommodating portion and a worm accommodating portion that is disposed at a twisted position relative to the wheel accommodating portion and has an axially intermediate portion that opens to the wheel accommodating portion.

[0016] The worm wheel has wheel teeth on its outer circumferential surface and is rotatably supported inside the wheel accommodating portion.

[0017] The worm has worm teeth on its outer circumferential surface that mesh with the wheel teeth, and is rotatably supported inside the worm accommodating portion.

[0018] The holder is disposed between the tip end of the worm and the worm accommodating portion.

[0019] The pad is fitted onto the tip of the worm.

[0020] The elastic member is attached to the holder and elastically biases the tip end of the worm toward the worm wheel via the pad.

[0021] The holder has a held portion that is fitted and held inside the worm accommodating portion in a state where rotation is prevented, two guide portions that protrude toward one side of the second direction, which is the axial direction of the worm accommodating portion, from two positions spaced apart in a third direction that is perpendicular to both the first direction, which is the biasing direction of the elastic member, and the second direction, on a side of the held portion on one side of the second direction, which is the axial direction of the worm accommodating portion, and two holder engaging portions provided on opposing inner surfaces of the two guide portions.

[0022] The pad has a pad base disposed between the two guide portions, two pad engagement portions provided on both side surfaces of the pad base in the third direction and contacting the two holder engagement portions, a pad recess formed on the other side surface of the pad base in the second direction so as to extend in the first direction, and a pad elastic pressing portion that elastically presses a part of the holder toward the other side in the second direction, thereby applying a preload to the contact portion between the holder engagement portion and the pad engagement portion.

[0023] In one embodiment of the worm reducer of the present disclosure, the two holder engagement portions can be configured with two holder inclined surfaces that incline toward each other as they move toward one side of the second direction, and the two pad engagement portions can be configured with two pad inclined surfaces that make surface contact with the two holder inclined surfaces.

[0024] In the worm reducer according to one aspect of the present disclosure, the holder can have a connection portion that connects the ends of the two guide portions that are closer to the worm wheel in the first direction.

[0025] In one embodiment of the worm reducer of the present disclosure, the pad elastic pressing portion can be configured by two pad elastic pressing plates located on one side of the two pad engagement portions in the second direction and each extending from the center of the pad in the third direction toward sides away from each other in the third direction, and the portion of the holder that is elastically pressed toward the other side in the second direction by the two pad elastic pressing plates can be configured by a holder pressed surface provided on the end face on one side in the second direction of each of the two guide portions. In this case, each of the two pad elastic pressure plates may have a slit, which penetrates in the second direction and extends in the first direction, at an end portion on the central side of the pad in the third direction.

[0026] A method for assembling a worm reducer according to one embodiment of the present disclosure is a method for assembling a worm reducer according to one embodiment of the present disclosure, and includes the steps of: positioning the holder relative to a guide jig having a guide protrusion extending in a predetermined direction so that the first direction coincides with the extension direction of the guide protrusion, and so that the central position in the third direction between the two guide portions coincides with the central position in the width direction of the guide protrusion; and, with the guide protrusion inserted inside the pad recess, moving the pad along the guide protrusion to position the pad base between the two guide portions.

[0027] In the method for assembling a worm reducer according to one aspect of the present disclosure, the guide jig may have a width dimension of the guide protrusion that increases toward the front in the direction of movement of the pad.

[0028] In the method for assembling a worm reducer according to one aspect of the present disclosure, in the step, the guide jig and the holder can be positioned in the third direction by engaging a jig-side positioning engaging portion provided on the guide jig with a holder-side positioning engaging portion provided on the holder. That is, by engaging the jig-side positioning engaging portion with the holder-side positioning engaging portion, the guide jig can be disposed in a state in which the extension direction of the guide protrusions coincides with the first direction and the center position of the guide protrusions in the width direction coincides with the center position between the two guide portions in the second direction. [Effects of the Invention]

[0029] According to one embodiment of the worm reducer of the present disclosure, when the rotation direction of the worm changes, the tip of the worm is less likely to displace in a third direction perpendicular to both the first direction, which is the biasing direction of the tip, and the second direction, which is the axial direction of the worm accommodating section, and the workability of the assembly work can be improved. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 is a diagram illustrating an electric power steering device incorporating a worm reduction gear according to a first example of an embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram illustrating a portion of an electric power steering device incorporating a worm reduction gear according to a first example of an embodiment of the present disclosure. [Figure 3] FIG. 3 is a cross-sectional view taken along line AA in FIG. [Figure 4] FIG. 4 is an enlarged view of the upper right portion of FIG. 3, with the housing omitted. [Figure 5] FIG. 5 is a perspective view showing the tip of the worm and the members arranged around it. [Figure 6] FIG. 6 is an exploded perspective view showing the tip of the worm and the members arranged around it. [Figure 7] FIG. 7 is a view from the right side of FIG. [Figure 8]FIG. 8 is a view from the left side of FIG. [Figure 9] FIG. 9 is a view of FIG. 7 as seen from above. [Figure 10] FIG. 10 is a cross-sectional view taken along the line BB in FIG. [Figure 11] FIG. 11 is a partially enlarged view of FIG. [Figure 12] FIG. 12(a) is a perspective view showing the holder removed, and FIG. 12(b) is a perspective view seen from a different direction from FIG. 12(a). [Figure 13] Figure 13(a) is a view of the holder removed and viewed from the right side of Figure 4, Figure 13(b) is a view of the holder viewed from the left side of Figure 13(a), Figure 13(c) is a view of the holder viewed from above Figure 13(a), and Figure 13(d) is a view of the holder viewed from the back side of Figure 13(a) (left side of Figure 4). [Figure 14] FIG. 14(a) is a perspective view showing the pad taken out, and FIG. 14(b) is a perspective view seen from a different direction from FIG. 14(a). [Figure 15] 15(a) is a view of the pad taken out and viewed from the right side of FIG. 4, FIG. 15(b) is a view of the pad viewed from the left side of FIG. 15(a), FIG. 15(c) is a view of the pad viewed from above of FIG. 15(a), and FIG. 15(d) is a view of the pad viewed from the back side of FIG. 15(a) (the left side of FIG. 4). [Figure 16] FIG. 16 is a view of the elastic member taken out and viewed from the right side of FIG. [Figure 17] 17(a) and 17(b) are diagrams for explaining a method for positioning the guide jig relative to the holder. [Figure 18] 18(a) to 18(c) are diagrams sequentially showing the steps of assembling the pad to the holder. [Figure 19] 19(a) and 19(b) are views similar to FIGS. 14(a) and 14(b), showing a pad of a comparative example in comparison with the first example. [Figure 20] FIG. 20 is a diagram similar to FIG. 18(b) and shows a comparative example for the first example. [Figure 21]Figures 21(a) to (d) are views showing the elastic member of a second example of an embodiment of the present disclosure, where (a) is a view from one side of the third direction, (b) is a view from the second direction, (c) is a view from the other side of the third direction, and (d) is a view from the first direction. [Figure 22] Figures 22(a) to (c) are diagrams showing the state in which the elastic members are stacked, where (a) is an oblique view, (b) is a view from the first direction, and (c) is a view from one side in the third direction. [Figure 23] 23(a) to 23(d) are diagrams similar to FIGS. 21(a) to 21(d) and show comparative examples for the second example. [Figure 24] 24(a) to 24(c) are diagrams similar to FIGS. 22(a) to 22(c) and show a comparative example for the second example. [Figure 25] FIG. 25 is a cross-sectional view showing an example of a conventional structure of a worm reducer. DETAILED DESCRIPTION OF THE INVENTION

[0031] [Example 1] A first example of an embodiment of the present disclosure will be described with reference to Figures 1 to 18(c). In this example, a case will be described in which a worm reducer according to one aspect of the present disclosure is applied to a pinion-assist electric power steering device. However, any worm reducer according to one aspect of the present disclosure can be widely applied to column-assist and dual-pinion electric power steering devices, as well as worm reducers incorporated in various mechanical devices other than electric power steering devices.

[0032] 1 shows a pinion-assist electric power steering device 1 incorporating a worm reduction gear 14 of this example. The electric power steering device 1 includes a steering wheel 2, a steering shaft 3, a steering column 4, a pair of universal joints 5a, 5b, an intermediate shaft 6, a steering gear unit 7, and an electric assist device 8.

[0033] The steering wheel 2 is fixedly supported at the rear end of a steering shaft 3. The steering shaft 3 is rotatably supported inside a steering column 4, which is supported on the vehicle body. The front end of the steering shaft 3 is connected to a pinion shaft 9 of a steering gear unit 7 via a rear universal joint 5a, an intermediate shaft 6, and a front universal joint 5b. Therefore, when the driver turns the steering wheel 2, the rotation of the steering wheel 2 is transmitted to the pinion shaft 9 via the steering shaft 3, the pair of universal joints 5a and 5b, and the intermediate shaft 6. The rotation of the pinion shaft 9 is converted into linear motion of a rack shaft 10 of the steering gear unit 7, which is meshed with the pinion shaft 9. As a result, a steering angle corresponding to the amount of rotation of the steering wheel 2 is applied to the pair of steered wheels. An electric assist device 8 applies auxiliary power generated by an electric motor 15 as a power source to the pinion shaft 9. As a result, the force required by the driver to rotate the steering wheel 2 is reduced.

[0034] The steering gear unit 7 includes a housing 11 supported and fixed to the vehicle body, a rack shaft 10, and a pinion shaft 9. The housing 11 has a rack housing 12 extending in the vehicle width direction, and a pinion housing 13 connected to one axial side of the rack housing 12 (the right side in FIG. 1). The central axis of the pinion housing 13 is skewed with respect to the central axis of the rack housing 12. The internal space of the pinion housing 13 communicates with the internal space of the rack housing 12. The rack shaft 10 is supported inside the rack housing 12 so as to be movable only in the axial direction (the vehicle width direction). The pinion shaft 9 is supported inside the pinion housing 13 so as to be capable of rotation only. The pinion shaft 9 has pinion teeth on the outer peripheral surface of its tip half (lower half in FIG. 2), not shown, located inside the pinion housing 13. A base end (upper end in FIG. 2) of the pinion shaft 9 protrudes outside the housing 11 and is connected to the front universal joint 5b. The rack shaft 10 has rack teeth that mesh with the pinion teeth of the pinion shaft 9 on a part of the circumferential direction of the outer circumferential surface of one axial side (not shown) (the right side in FIG. 1) that is arranged inside the rack accommodating portion 12.

[0035] The electric assist device 8 includes a worm reducer 14 and an electric motor 15. The electric assist device 8 is configured so that the rotation of the electric motor 15 is reduced in speed by the worm reducer 14 and transmitted to the pinion shaft 9.

[0036] The worm reducer 14 includes a housing 16, a worm wheel 17, a worm 18, a holder 19, a pad 20, and an elastic member 21.

[0037] The housing (16) has a wheel accommodating portion (22) and a worm accommodating portion (23) that is disposed at a skewed position relative to the wheel accommodating portion (22) and has an axially intermediate portion that opens into the wheel accommodating portion (22).

[0038] That is, the central axis of the wheel accommodating portion 22 and the central axis of the worm accommodating portion 23 are disposed at positions that are twisted relative to each other. Also, an axially intermediate portion of the worm accommodating portion 23 is integrally connected to one circumferential location of the radially outer end portion of the wheel accommodating portion 22, and the internal space of the worm accommodating portion 23 communicates with the internal space of the wheel accommodating portion 22 through this connected portion. In this example, the worm accommodating portion 23 is configured in a cylindrical shape with a bottom, and specifically, its axial tip (right end in FIG. 3) is closed and its axial base end (left end in FIG. 3) is open.

[0039] In this example, the wheel accommodating portion 22 is coaxially and integrally connected to the axially intermediate portion of the pinion accommodating portion 13 that constitutes the housing 11 of the steering gear unit 7. The internal space of the wheel accommodating portion 22 communicates with the internal space of the pinion accommodating portion 13.

[0040] The worm wheel 17 has wheel teeth 24 on its outer circumferential surface, and is rotatably supported inside the wheel accommodating portion 22. In this example, the worm wheel 17 is fitted and fixed to the outside of the pinion shaft 9 at an axially intermediate portion thereof.

[0041] The worm 18 has worm teeth 25 that mesh with the wheel teeth 24 at the axially intermediate portion of its outer circumferential surface, and is rotatably supported inside the worm accommodating portion 23 .

[0042] In this example, the base end (left end in Figure 3) of the worm 18 is supported in the worm accommodating portion 23 so as to be able to move slightly, and is connected to the output shaft 27 of the electric motor 15 so as to be able to transmit torque.

[0043] For this reason, in this example, the worm 18 has a female spline portion 26 on the inner peripheral surface of its base end. The electric motor 15 is coupled and fixed to the axial base end of the worm housing portion 23 by screws, with its output shaft 27 arranged coaxially with the worm housing portion 23. The female spline portion 26 of the worm 18 and a male spline portion 28 provided on the outer peripheral surface of the output shaft 27 of the electric motor 15 are spline-engaged. This connects the base end of the worm 18 and the output shaft 27 of the electric motor 15 so as to enable torque transmission and allow slight oscillating displacement of the worm 18. The base end of the worm 18 is supported by a ball bearing 29 with a radial gap in the worm housing portion 23, allowing slight oscillating displacement.

[0044] In this example, the outer peripheral surface of the tip of the worm 18 is configured as a stepped cylindrical surface. That is, the outer peripheral surface of the tip of the worm 18 has a small-diameter cylindrical surface portion 30 that forms the tip side portion, and a large-diameter cylindrical surface portion 31 that forms the base side portion and has a larger diameter than the small-diameter cylindrical surface portion 30.

[0045] In this example, a support bearing 32 is disposed between the large-diameter cylindrical surface portion 31 of the worm 18 and the inner peripheral surface of the worm accommodating portion 23. In the illustrated example, the support bearing 32 is configured as a ball bearing. That is, the support bearing 32 has an inner ring 33 having an inner ring raceway on its outer peripheral surface, an outer ring 34 having an outer ring raceway on its inner peripheral surface, and a plurality of balls 35, each of which is a rolling element, disposed between the inner ring raceway and the outer ring raceway. However, the support bearing 32 may also be a rolling bearing such as a cylindrical roller bearing in which the rolling elements are cylindrical rollers or a tapered roller bearing in which the rolling elements are tapered rollers, or a plain bearing.

[0046] In this example, the inner ring 33 is fitted onto the large-diameter cylindrical surface portion 31 of the worm 18 with a radial gap therebetween. A cylindrical bushing 36 is disposed between the inner peripheral surface of the inner ring 33 and the large-diameter cylindrical surface portion 31. Specifically, the inner ring 33 is fitted onto the outer peripheral surface of the bushing 36 with an interference fit, and the bushing 36 is fitted onto the large-diameter cylindrical surface portion 31 of the worm 18 with a clearance fit. The bushing 36 is a member that ensures sliding and / or cushioning properties with respect to the outer peripheral surface of the tip end of the worm 18. The bushing 36 is preferably made of a material with a low coefficient of friction with the metal material constituting the worm 18, such as a synthetic resin or a light alloy such as an aluminum alloy. However, the bushing 36 may be omitted, or a bushing fitted onto the outer ring 34 with an interference fit may be fitted into the worm accommodating portion 23 with a radial gap therebetween.

[0047] In this example, the outer ring 34 is clearance-fitted into the inside of the worm accommodating portion 23. This prevents the preload of the support bearing 32 from changing even if the housing 16 thermally expands during use. However, if thermal expansion of the housing does not pose a particular problem, the outer ring can also be press-fitted into the housing.

[0048] As will be described later, the outer ring 34 is sandwiched in the axial direction between a holder 19 disposed inside the worm accommodating portion 23 and a retainer 37 fitted and fixed inside the worm accommodating portion 23. The retainer 37 has a fitting tubular portion 38 fitted and fixed inside the worm accommodating portion 23 by an interference fit, and an inward flange portion 39 bent radially inward from an end portion on one axial side (the right side in FIGS. 3 and 4 ) of the fitting tubular portion 38 over the entire circumference. In this example, the end face on one axial side of the outer ring 34 abuts against a radially outer portion of a side surface on the other axial side (the left side in FIGS. 3 and 4 ) of the annular portion 42 of the holder 19, and the side surface on the other axial side abuts against a side surface on one axial side of the inward flange portion 39 via a wave washer 40. This prevents axial displacement of the support bearing 32. However, the wave washer 40 may be omitted, or a wave washer may be disposed between the outer ring 34 and the holder 19.

[0049] In this example, the tip of the worm 18 is capable of displacement in a first direction (the up and down direction in Figures 3 and 4), which is the direction of movement toward and away from the worm wheel 17 and is the biasing direction of the elastic member 21, based on the radial gap that exists between the inner surface of the inner ring 33 and the outer surface of the tip of the worm 18, specifically, the annular gap that exists between the inner surface of the bushing 36 and the large diameter cylindrical surface portion 31.

[0050] In this example, the support bearing 32 is sandwiched in the axial direction between the holder 19 and the retainer 37, but when implementing a worm reducer according to one embodiment of the present disclosure, the arrangement of the support bearing is not particularly limited as long as it allows the tip of the worm to rotate relative to the worm housing and move toward and away from the worm wheel. For example, a holder can be fitted and fixed inside the worm housing, and the support bearing can be fitted and held inside the holder.

[0051] In the worm reducer 14 of this example, when viewed from the first direction, the central axis O of the worm wheel 17 is 17 and the central axis of the worm 18 (the central axis of the output shaft 27 of the electric motor 15) O 18However, in the present disclosure, when viewed from the first direction, the central axis O of the worm wheel 17 is perpendicular to the 17 and the central axis of the worm 18 (the central axis of the output shaft 27 of the electric motor 15) O 18 The present invention can also be applied to an oblique type worm reducer in which the and form an acute angle.

[0052] In the worm reducer 14 of this example, as shown in FIGS. 3 to 10 , a holder 19, a pad 20, and an elastic member 21 are disposed between the small-diameter cylindrical surface portion 30 of the worm 18 and the inner circumferential surface of the tip end of the worm accommodating portion 23. The holder 19 is disposed between the tip end of the worm 18 and the worm accommodating portion 23. In this example, the holder 19 is disposed around the tip end of the worm 18 inside the worm accommodating portion 23 in a state where rotation is prevented. The pad 20 is fitted onto the tip end of the worm 18. In this example, the pad 20 is fitted onto the tip end of the worm 18 without any play in the radial direction. The elastic member 21 is assembled to the holder 19 and elastically biases the tip end of the worm 18 toward the worm wheel 17 (the lower side in FIGS. 3 and 4 ) via the pad 20. This reduces backlash at the meshing portion between the wheel teeth 24 and the worm teeth 25.

[0053] The holder 19 has a held portion 74 fitted and held inside the worm accommodating portion 23 in a state where rotation is prevented, and two guide portions 49 protruding from two positions spaced apart in a third direction (the front-to-back direction in FIGS. 3 and 4) perpendicular to both the first and second directions on a side surface (the right side in FIGS. 3 and 4) of the held portion 74 in the second direction (the left-to-right direction in FIGS. 3 and 4), which is the axial direction of the worm accommodating portion 23, toward one side in the second direction. Furthermore, the holder 19 has two holder inclined surfaces 41, which are two holder engaging portions, on inner surfaces of the two guide portions 49 facing each other. The two holder inclined surfaces 41 each extend in the first direction and are inclined in directions approaching each other as they approach one side in the second direction. It is preferable that the holder 19 be made of a material having sufficient strength and rigidity, such as a metal material or a high-performance resin material such as polyphenylene sulfide (PPS) mixed with glass fiber.

[0054] 12(a) to 13(d), the holder 19 includes an annular portion 42, a substantially circular ring-shaped side plate portion 43 that extends radially inward from one end of the annular portion 42 in the second direction, and a protrusion 44 that extends radially inward from the radially inner end of the side plate portion 43 and has a substantially U-shaped end face when viewed from one side in the second direction. In this example, the held portion 74 is made up of the annular portion 42 and the side plate portion 43.

[0055] The annular portion 42 has a partially circular end face shape consisting of one straight portion and one arc portion when viewed from one side in the second direction. That is, the annular portion 42 has a flat portion 45 at the end of its outer circumferential surface that is closer to the worm wheel 17 in the first direction. In this example, the annular portion 42 is non-circularly fitted into the inside of the worm accommodating portion 23, thereby holding the holder 19 inside the worm accommodating portion 23 in a state where rotation is prevented.

[0056] The annular portion 42 also has a holder-side positioning engagement portion 75 at the end of its outer circumferential surface that is farther from the worm wheel 17 in the first direction. The holder-side positioning engagement portion 75 is provided on the outer circumferential surface of the annular portion 42 in the second direction. In this example, the holder-side positioning engagement portion 75 has a substantially triangular cross-sectional shape. However, when implementing a worm reducer according to one aspect of the present disclosure, the cross-sectional shape of the pad-side positioning engagement portion can be any shape, such as a substantially rectangular or substantially semicircular shape.

[0057] In this example, as shown in Fig. 13(d), the inner peripheral surface 46 of the side plate portion 43 has recesses 47 on both sides in the third direction. The bottom surfaces of the recesses 47 are formed by flat surfaces perpendicular to the third direction. The portions of the inner peripheral surface 46 of the side plate portion 43 that are not included in the two recesses 47, i.e., the both side portions in the first direction, are formed by cylindrical surfaces that are centered on the central axis of the holder 19.

[0058] In this example, the side surface on one side in the second direction of the radially outer end of the side plate portion 43 is abutted against a step portion 48 (see Figure 3) facing the other side in the second direction and provided on the inner surface of the worm accommodating portion 23, thereby preventing displacement of the holder 19 to one side in the second direction.

[0059] In this example, the protrusion 44 protrudes toward one side in the second direction from a radially inner end of the side plate portion 43, excluding the end farther from the worm wheel 17 in the first direction. That is, the end of the protrusion 44 farther from the worm wheel 17 in the first direction is open. The protrusion 44 includes two guide portions 49 and a connecting portion 50. The two guide portions 49 constitute both end portions of the protrusion 44 in the third direction. That is, as shown in FIGS. 6 , 12(a), 13(a), and 13(d), the two guide portions 49 extend toward one side in the second direction from two locations spaced apart in the third direction at the radially inner end of the side plate portion 43, specifically, from the same circumferential locations as the two recesses 47. The two guide portions 49 have a shape that extends in the first direction. The connecting portion 50 constitutes the end portion of the protrusion 44 closer to the worm wheel 17 in the first direction. That is, the connecting portion 50 extends from the radially inner end of the side plate portion 43, which is closer to the worm wheel 17 in the first direction, toward one side in the second direction, and connects the ends of the two guide portions 49, which are closer to the worm wheel 17 in the first direction. The connecting portion 50 has a partially cylindrical shape centered on the central axis of the holder 19. Note that if the holder has enough strength to prevent deformation of the two guide portions, the connecting portion may be omitted.

[0060] The two holder inclined surfaces 41 constituting the holder 19 are provided on inner side surfaces 51 of the two guide portions 49, which are side surfaces facing each other in the third direction. In this example, as shown in FIG. 13(c), when viewed from the first direction, each of the inner side surfaces 51 of the two guide portions 49 has a crank shape with a stepped surface (holder inclined surface 41) in the middle portion in the second direction. That is, the two holder inclined surfaces 41 are provided on the inner side surfaces 51 of the two guide portions 49 in the middle portion in the second direction, more specifically, on one side portion in the second direction of the middle portion. The two holder inclined surfaces 41 are inclined in directions approaching each other as they approach one side in the second direction. Of the inner side surfaces 51 of the two guide portions 49, a portion located on one side in the second direction of the two holder inclined surfaces 41 and a portion located on the other side in the second direction of the two holder inclined surfaces 41 are each formed by a plane perpendicular to the third direction. Therefore, the distance between the inner surfaces 51 of the two guide portions 49 is narrower in the portion located on one side of the two holder inclined surfaces 41 in the second direction than in the portion located on the other side of the two holder inclined surfaces 41 in the second direction.

[0061] When implementing a worm reducer according to one embodiment of the present disclosure, the inclination angle φ of the holder inclined surface 41 with respect to the second direction can be set to any value within the range of 0°<φ<90°, but is preferably 20° to 80°, and more preferably 30° to 70°. In this example, the inclination angle φ is set to 30°.

[0062] Moreover, the holder 19 has two holder pressed surfaces 52 on the tip surfaces, which are end surfaces on one side in the second direction of the two guide parts 49. Each of the two holder pressed surfaces 52 is configured as a flat surface perpendicular to the second direction. In this example, the two holder pressed surfaces 52 and the tip surface, which is the end surface on one side in the second direction of the connection part 50, are continuous with each other and exist in the same imaginary plane perpendicular to the second direction.

[0063] As shown in Figures 6, 10, 11, and 14(a) to 15(d), the pad 20 comprises a pad base 55 arranged between two guide portions 49, two pad inclined surfaces 53 which are provided on both side surfaces of the pad base 55 in the third direction and which are two pad engagement portions that contact the two holder inclined surfaces 41, a pad recess 76 formed on the other side surface of the pad base 55 in the second direction so as to extend in the first direction, and a pad elastic pressing portion 77 which elastically presses a part of the holder 19 toward the other side in the second direction, thereby applying a preload to the contact portions between the two holder inclined surfaces 41 and the two pad inclined surfaces 53.

[0064] In this example, the two pad inclined surfaces 53 are in surface contact with the two holder inclined surfaces 41, and specifically, are inclined in the same direction and at the same angle as the two holder inclined surfaces 41 (see FIGS. 13(a) to 13(d)). In this example, the parts of the holder 19 that are elastically pressed by the pad elastic pressing portion 77 toward the other side in the second direction are the two holder pressed surfaces 52.

[0065] However, when implementing the present disclosure, such a portion of the holder can be selected arbitrarily. For example, an end face on one side in the second direction of a side plate portion constituting the holder can be used as a portion of the holder (holder pressed surface), and the portion of the holder can be elastically pressed toward the other side in the second direction by a pad elastic pressing portion provided at the base of the pad. Note that the pad 20 is preferably made of a material that has a small coefficient of friction with the metal material constituting the worm 18, such as synthetic resin or a light alloy such as an aluminum alloy.

[0066] In this example, the pad elastic pressing portion 77 is located on one side of the two pad inclined surfaces 53 in the second direction and is composed of two pad elastic pressing plates 54 each extending from the center of the pad 20 in the third direction toward sides away from each other in the third direction.

[0067] More specifically, in this example, the pad 20 has a pad base 55 arranged between two guide portions 49, and a through hole 56 that penetrates the pad base 55 in the second direction and through which the tip of the worm 18 is inserted, and has two pad inclined surfaces 53 on both sides of the pad base 55 in the third direction, and a flat plate portion 57 including two pad elastic pressure plates 54 is connected to the part of the pad base 55 that protrudes to one side in the second direction from between the two guide portions 49.

[0068] The pad base 55 includes a base body 58 and two base extensions 59 .

[0069] The base body 58 extends in the first direction and has a generally rectangular end face shape. The through hole 56 penetrates in the second direction through a half of the base body 58 that is closer to the worm wheel 17 in the first direction. In this example, the through hole 56 is configured as a stepped hole having an oval hole portion 60 on one side in the second direction and a circular hole portion 61 on the other side in the second direction. Of these, the circular hole portion 61 has an inner diameter slightly larger than the outer diameter of the small-diameter cylindrical surface portion 30 of the worm 18.

[0070] The base body 58 also has two pressed portions 62 at both ends in the third direction of the other side portion in the second direction at the end farther from the worm wheel 17 in the first direction. Each of the two pressed portions 62 is formed by a partial cylindrical surface centered on the central axis of the through hole 56. The base body 58 has a pedestal surface portion 63 formed by a flat surface perpendicular to the first direction at the end farther from the worm wheel 17 in the first direction and between the two pressed portions 62 in the third direction.

[0071] The two base protrusions 59 protrude from the other half of the base body 58 in the second direction, closer to the worm wheel 17 in the first direction, toward sides that are farther apart from each other in the third direction. Each of the two base protrusions 59 extends in the first direction.

[0072] The two pad inclined surfaces 53 are provided on one side surface of the two base protrusions 59 in the second direction. The two pad inclined surfaces 53 are inclined in directions approaching each other as they approach one side in the second direction. The inclination angle φ of the pad inclined surfaces 53 with respect to the second direction is the same as the inclination angle φ of the holder inclined surfaces 41 with respect to the second direction.

[0073] The pad recess 76 is formed across the first direction on the side surface of the base main body 58 on the other side in the second direction. That is, the pad recess 76 opens to both end surfaces of the base main body 58 in the first direction. The bottom surface of the pad recess 76 (the surface facing the other side in the second direction) is located on one side in the second direction of the end surfaces of the two base protrusions 59 on the other side in the second direction. In this example, the pad recess 76 has a rectangular cross-sectional shape.

[0074] However, when implementing a worm reducer according to one aspect of the present disclosure, the cross-sectional shape of the pad recess is not limited to a rectangle and can be any shape as long as it can prevent the pad from shifting in the third direction by engaging a guide protrusion provided on a guide jig with the pad recess when assembling the pad to the holder, as will be described later. Also, the pad recess can be formed only in a portion of the side surface of the base body on the other side of the second direction in the first direction, or can be formed in multiple locations in the first direction.

[0075] The flat plate portion 57 is integrally connected to one end of the base body 58 in the second direction and has a circular outer peripheral shape when viewed from one side in the second direction. The through hole 56 penetrates a radial center portion of the flat plate portion 57 in the second direction. Therefore, the flat plate portion 57 is configured in a circular flat plate shape centered on the central axis of the through hole 56. The outer diameter dimension of the flat plate portion 57 is larger than the width dimension of the base body 58 in the third direction. Both end portions of the flat plate portion 57 in the third direction protrude further on both sides in the third direction than the base body 58. The end portion of the flat plate portion 57 closer to the worm wheel 17 in the first direction protrudes further from the worm wheel 17 than the base body 58 in the first direction. The end portion of the base body 58 farther from the worm wheel 17 in the first direction protrudes further from the worm wheel 17 than the flat plate portion 57 in the first direction.

[0076] In this example, the two pad elastic pressure plates 54 constituting the pad 20 are connected to portions of the pad base 55 that protrude from between the two guide portions 49 to one side in the second direction. Specifically, the two pad elastic pressure plates 54 are formed by the end portions on both sides of the flat plate portion 57 in the third direction.

[0077] In this example, as shown in Figures 10, 11, 14(b), and 15(b) to 15(d), each of the two pad elastic pressure plates 54 has ridges 64a, 64b extending in the first direction on the other side in the second direction. In this example, each of the two pad elastic pressure plates 54 has two ridges 64a, 64b. In a free state before the two pad elastic pressure plates 54 are elastically deformed, in other words, in a free state before the pad 20 is assembled to the protrusion 44 of the holder 19, the height in the second direction of at least one ridge 64a, 64b increases continuously or in stages as it moves away from the worm 18 in the third direction.

[0078] In this example, at least one ridge 64a, 64b is composed of two ridges 64a, 64b spaced apart in the third direction. As shown in FIG. 17(a), in the free state, the height in the second direction of the ridge 64a, 64b that is farther from the worm 18 in the third direction is greater than the height in the second direction of the ridge 64b that is closer to the worm 18 in the third direction. In this example, in the free state, the cross-sectional shape of the tip of each of the two ridges 64a, 64b is linear and perpendicular to the second direction. More specifically, in the free state, the tip of each of the two ridges 64a, 64b is composed of a flat surface that is perpendicular to the second direction.

[0079] In this example, each of the two pad elastic pressure plates 54 has a slit 65 that penetrates in the second direction and extends in the first direction at its base end, which is the end toward the center of the pad 20 in the third direction. In this example, the bending rigidity in the second direction of the portions of the base end of the pad elastic pressure plate 54 that are adjacent to both sides of the slit 65 in the length direction is adjusted by appropriately regulating the width and length of the slit 65 and the plate thickness of the pad elastic pressure plate 54. However, when implementing a worm reducer according to one embodiment of the present disclosure, the slits may be omitted.

[0080] As shown in FIGS. 3 to 5 and 7 to 10, the pad 20 is attached to the protruding portion 44 of the holder 19 and fitted onto the tip end portion of the worm 18. As shown in FIGS.

[0081] Specifically, with the portion of the pad base 55 of the pad 20 closer to the worm wheel 17 in the first direction disposed between the two guide portions 49 constituting the protrusion 44 of the holder 19, the two pad inclined surfaces 53 are in surface contact with the two holder inclined surfaces 41. In addition, the tip ends of the protrusions 64a, 64b of the two pad elastic pressing plates 54 elastically press the two holder pressed surfaces 52 toward the other side in the second direction. As a result, a preload is applied to the contact portions between the two holder inclined surfaces 41 and the two pad inclined surfaces 53.

[0082] Furthermore, the small diameter cylindrical surface portion 30 at the tip end of the worm 18 is fitted into the circular hole portion 61 of the through hole 56 of the pad 20 without any radial rattle and in a relatively rotatable manner.

[0083] In this state, a gap exists in the first direction between the side surface of the pad base 55 of the pad 20 that is closer to the worm wheel 17 in the first direction and the side surface of the connection portion 50 that constitutes the protrusion 44 of the holder 19 that is farther from the worm wheel 17 in the first direction. In this example, the pad 20 is able to be displaced in the first direction relative to the holder 19 based on this gap in the first direction.

[0084] 10 and 11, gaps in the third direction exist between the pad base 55 of the pad 20 and portions of the inner surfaces 51 of the two guide parts 49 that are located on one side of the two holder inclined surfaces 41 in the second direction and portions that are located on the other side of the two holder inclined surfaces 41 in the second direction, respectively. In this example, the pad 20 is able to be displaced in the third direction relative to the holder 19 based on these gaps in the third direction.

[0085] In this example, the elastic member 21 is made of a leaf spring. More specifically, in this example, the elastic member 21 is made of a notched cylindrical leaf spring having a discontinuous portion 66 at one location in the circumferential direction, as shown in Figures 6 and 16. Specifically, the elastic member 21 has a base portion 67 located on the side farther from the worm 18 in the first direction, and two arm portions 68 extending in the circumferential direction from both circumferential end portions of the base portion 67.

[0086] In this example, the base 67 is made of a flat plate that is perpendicular to the first direction.

[0087] Each of the two arm portions 68 is configured in a partially cylindrical shape. Each of the two arm portions 68 has a bent portion 69 that is bent radially outward from the tip end portion.

[0088] However, when implementing the worm reducer according to one aspect of the present disclosure, the elastic member may have any configuration as long as it can elastically bias the pad toward the worm wheel 17 in the first direction. For example, when the elastic member is made of a leaf spring, it may have a shape other than a partially cut cylindrical shape. The elastic member may also be made of a torsion coil spring.

[0089] The elastic member 21 is assembled to the holder 19 so as to fit onto the pad base 55 and the two guide portions 49 of the pad 20. In this example, with the pad base 55 of the pad 20 and the protruding portion 44 of the holder 19 inserted radially inside the elastic member 21, the base portion 67 of the elastic member 21 abuts against the seat surface portion 63 of the pad 20, and the inner circumferential surfaces of the base end portions of the two arm portions 68 are elastically pressed against the two pressed portions 62, and the inner circumferential surfaces of the tip end portions of the two arm portions 68 are elastically pressed against the side surface of the connecting portion 50 constituting the protruding portion 44 of the holder 19 that is closer to the worm wheel 17 in the first direction. This elastically biases the tip end portion of the worm 18 via the pad 20 toward the worm wheel 17, i.e., the side closer to the worm wheel 17 in the first direction. This reduces backlash at the meshing portion between the wheel teeth 24 and the worm teeth 25.

[0090] In the worm reducer 14 of this example, the two pad inclined surfaces 53 that constitute the pad 20 are in surface contact with the two holder inclined surfaces 41 that constitute the holder 19. In addition, the tip ends of the protrusions 64a, 64b of the two pad elastic pressing plates 54 that constitute the pad 20 elastically press the two holder pressed surfaces 52 that constitute the holder 19 toward the other side in the second direction. As a result, a preload is applied to the contact portions between the two holder inclined surfaces 41 and the two pad inclined surfaces 53. Therefore, based on the contact between the two holder inclined surfaces 41 and the two pad inclined surfaces 53, displacement of the pad 20 in the third direction relative to the holder 19 is restricted, and it is possible to prevent the pad 20 from rattling without resistance in the third direction relative to the holder 19.

[0091] 10 and 11, in this example, the tip ends of the respective protrusions 64a, 64b of the pad elastic pressing plate 54 elastically press the holder pressed surface 52 toward the other side in the second direction, and as a result, an elastic force (preload force) Fp directed toward one side in the second direction acts from the pad inclined surface 53 on the holder inclined surface 41. Then, this elastic force Fp is converted into an elastic force (preload force) Fx directed outward in the third direction, which acts from the pad inclined surface 53 on the holder inclined surface 41. In the structure of this example, this elastic force Fx can prevent the pad 20 from rattling without resistance relative to the holder 19 in the third direction.

[0092] Therefore, even when the direction of the component related to the third direction of the reaction force applied from the wheel teeth 24 to the worm teeth 25 changes due to a change in the rotation direction of the worm 18, the tip of the worm 18 is less likely to be displaced in the third direction. As a result, it is possible to prevent abnormal noises such as teeth rattles from occurring at the meshing portion between the wheel teeth 24 and the worm teeth 25, and abnormal noises such as collision sounds from occurring between the pad 20 and the holder 19.

[0093] When implementing the worm reducer according to one embodiment of the present disclosure, the bending rigidity in the second direction of the portions of the base end of the pad elastic pressing plate 54 adjacent to both sides of the slit 65 in the length direction can be changed by changing the width and length of the slit 65, the plate thickness of the pad elastic pressing plate 54, the height of the ridges 64a, 64b in the second direction, etc. This makes it possible to change the magnitude of the force with which the tip ends of the ridges 64a, 64b of the pad elastic pressing plate 54 elastically press the holder pressed surface 52 toward the other side in the second direction. Accordingly, the magnitude of the elastic force Fp can be changed as desired.

[0094] The pad elastic pressing plate 54 locally presses the holder pressed surface 52 with the tip ends of the ridges 64a, 64b. Therefore, the pressing force can be stabilized compared to when the pad elastic pressing plate presses the holder pressed surface over a wide area.

[0095] The relational expression "Fx = Fp / tan φ" holds between the elastic force Fx and the elastic force Fp. In this example, since the inclination angle φ is 30°, Fx = Fp / tan 30° = 1.7Fp. In other words, the elastic force Fx is greater than the elastic force Fp. When implementing a worm reducer according to one aspect of the present disclosure, the magnitude of the elastic force Fx can be arbitrarily changed by changing not only the magnitude of Fp but also the magnitude of the inclination angle φ. For example, if φ = 45°, Fx = Fp, and if 45° < φ < 90°, Fx <Fpとすることができ、0゜<φ<45゜とすれば、Fx> The magnitude of the elastic force Fx can be adjusted to Fp. Furthermore, the magnitude of the elastic force Fx can be adjusted by changing the inclination angle φ without changing the material (elastic force based on the material) of the pad 20. Therefore, the magnitude of the elastic force Fx can be easily adjusted at the design stage.

[0096] When implementing a worm reducer according to one embodiment of the present disclosure, the inclination angle of the holder inclined surface 41 with respect to the second direction and the inclination angle of the pad inclined surface 53 with respect to the second direction do not need to be strictly the same, and may differ within the range of manufacturing tolerances. The inclination angle of the holder inclined surface 41 with respect to the second direction may also be slightly (for example, about 0.5°) smaller than the inclination angle of the pad inclined surface 53 with respect to the second direction. In this way, at the contact portion between the holder inclined surface 41 and the pad inclined surface 53, the tip end of the pad inclined surface 53 (the end on the right side in the third direction in FIG. 11 and the end on the other side in the second direction in FIG. 11 ) comes into particularly strong surface contact with the holder inclined surface 41. As a result, the posture of the pad 20 relative to the holder 19 is stabilized.

[0097] Consider a case in which, from a neutral state in which the central axis of the holder 19 and the central axis of the pad 20 are aligned as viewed from the first direction, the pad 20 is displaced to one side in the third direction relative to the holder 19, for example, to the right in FIGS. 10 and 11 . In this case, as the right pad inclined surface 53 slides and displaces along the right holder inclined surface 41, the pad base 55 of the pad 20 is displaced toward the other side in the second direction, and at the same time, the right pad elastic pressing plate 54 is elastically deformed so as to tilt toward one side in the second direction. Then, the elastic pressing force acting from the right pad elastic pressing plate 54 on the right holder pressed surface 52 increases by an amount corresponding to this elastic deformation, and the elastic forces Fp and Fx increase accordingly. As a result, the pad 20 becomes less likely to be displaced toward the right. The same applies to the case where the pad 20 is displaced from the neutral state to the left side in FIGS. 10 and 11 relative to the holder 19.

[0098] The inner peripheral surface of the circumferential center of the elastic member 21 is elastically pressed against two pressed portions 62 provided at both ends in the third direction of the base body 58 constituting the pad 20. As a result, a force is applied to the two pressed portions 62 not only in a direction toward the worm wheel 17 in the first direction, but also in opposite directions in the third direction. This also makes it possible to prevent the tip of the worm 18 from being displaced in the third direction when the rotation direction of the worm 18 changes.

[0099] Furthermore, the worm reducer 14 of this embodiment can improve the workability of assembling the worm reducer 14. Specifically, the workability of assembling the pad 20 to the holder 19 can be improved.

[0100] When the pad 20 is attached to the holder 19, the pad base 55 is inserted between the two guide portions 49 from the end of the protrusion 44 that is farther from the worm 18 in the first direction.

[0101] In this example, the pad base 55 has a pad recess 76 provided on the other side in the second direction across the first direction.

[0102] Therefore, in this example, the holder 19 is positioned with respect to a guide jig 79 having a guide protrusion 78 extending in a predetermined direction so that the first direction coincides with the extension direction of the guide protrusion 78 and the central position in the third direction between the two guide portions 49 coincides with the central position in the width direction of the guide protrusion 78, and by moving the pad 20 along the guide protrusion 78 with the guide protrusion 78 inserted inside the pad recess 76, the pad base 55 can be positioned between the two guide portions 49.

[0103] More specifically, when assembling the pad 20 to the holder 19, first, as shown in Figure 18(a), the holder 19 is placed on a holding jig 80 with one side in the second direction facing upward, and a restraining jig 81 is placed on the upper surface of the holding jig 80 so as to surround the periphery of the annular portion 42 of the holder 19 except for the portion farthest from the worm 18 in the first direction.

[0104] Next, a guide jig 79 is placed on the upper surface of the holding jig 80. The guide jig 79 has a generally rectangular columnar shape. Specifically, the guide jig 79 has a generally rectangular columnar base 82 and a tongue-shaped portion 83 extending from an upper portion of the tip of the base 82. The guide protrusion 78 is provided to span the upper surface of the base 82 and the upper surface of the tongue-shaped portion 83. In this example, the width of the guide protrusion 78 increases from the base end (lower right of FIG. 18(a)) to the tip end (upper left of FIG. 18(a)). The base 82 also has, at the lower portion of the tip, a butting surface 84 that is a concave curved surface having a radius of curvature that is the same as or slightly larger than the radius of curvature of the outer circumferential surface of the annular portion 42 of the holder 19, and a jig-side positioning engagement portion 85 that engages with the holder-side positioning engagement portion 75, at the center of the butting surface 84.

[0105] The base 82 of the guide jig 79 is placed inside a recess 86 provided on the upper surface of the holding jig 80, and the tongue-shaped portion 83 is inserted inside the protrusion 44. Then, as shown in FIGS. 17(a) and 17(b), the abutting surface 84 of the guide jig 79 is abutted against the end of the outer circumferential surface of the annular portion 42 of the holder 19 that is farther from the worm 18 in the first direction, and the jig-side positioning engaging portion 85 is engaged with the holder-side positioning engaging portion 75. This positions the guide jig 79 relative to the holder 19. In particular, based on the engagement between the jig-side positioning engaging portion 85 and the holder-side positioning engaging portion 75, the guide jig 79 and the holder 19 are positioned in the third direction, and the center position between the two guide portions 49 in the third direction is aligned with the center position of the guide protrusion 78 in the width direction.

[0106] 18(a) to 18(c), the pad 20 is placed on the base 82 of the guide jig 79 with the other side in the second direction facing downward, and the guide protrusions 78 are arranged (inserted) inside the pad recesses 76. Furthermore, an insertion jig 87 having a substantially elongated cylindrical shape is inserted into the through-holes 56 of the pad 20 from above. Then, as shown in FIGS. 18(b) to 18(c), the insertion jig 87 is moved in a direction approaching the holder 19 in relation to the extension direction of the guide protrusions 78. As a result, the pad 20 is moved (guided) along the guide protrusions 78 toward the holder 19, and the pad base 55 is positioned between the two guide portions 49.

[0107] As described above, according to the assembly method of this example, when assembling the pad 20 to the holder 19, the guide protrusion 78 is inserted into the pad recess 76, thereby guiding the insertion of the pad base 55 between the two guide portions 49. In other words, when moving the pad 20 toward the holder 19, the pad 20 is prevented from shifting in the third direction. This improves the workability of assembling the pad 20 to the holder 19. This also makes it easier to automate the work of assembling the pad 20 to the holder 19. In particular, even in a structure such as the worm reducer 14 of this example, in which there is no gap between the holder 19 and the pad 20 in the third direction, the workability of assembling the pad 20 to the holder 19 can be improved, making it easier to automate the work.

[0108] In particular, in this example, the width dimension of the guide protrusion 78 increases from the base end toward the tip end, and therefore, the position of the pad 20 in the third direction can be regulated as the pad 20 is moved in a direction approaching the holder 19. In other words, there is no need to increase the positional accuracy excessively when placing the pad 20 on the upper surface of the guide jig 79. This also improves the workability of the work of assembling the pad 20 to the holder 19, and makes it easier to automate the work of assembling the pad 20 to the holder 19.

[0109] 19(a) to 20 , if the pad 20z does not have a pad recess on the side surface of the pad base 55z on the other side in the second direction, and the guide jig 79z does not have a guide protrusion, the pad 20z may shift in the third direction when the pad 20z is attached to the holder 19, causing interference between the end face of the pad base 55z in the first direction and the end of one of the guide parts 49 that is farther from the worm 18 in the first direction. This reduces the efficiency of the task of attaching the pad 20z to the holder 19, making it difficult to automate the task.

[0110] Furthermore, in this example, in a free state before the two pad elastic pressure plates 54 are elastically deformed, the height in the second direction of at least one ridge 64a, 64b provided on each of the two pad elastic pressure plates 54 increases continuously or in stages as the ridge 64a increases away from the worm 18 in the third direction. Specifically, of the two ridges 64a, 64b, the height in the second direction of the ridge 64a that is farther from the worm 18 in the third direction is greater than the height in the second direction of the ridge 64b that is closer to the worm 18 in the third direction. This reliably prevents the tip of the worm 18 from being displaced in the third direction when the rotation direction of the worm 18 changes.

[0111] When the pad 20 is assembled to the protrusion 44 of the holder 19, the tip ends of the protrusions 64a, 64b of the two pad elastic pressing plates 54 are elastically abutted against the two holder pressed surfaces 52 of the holder 19, and the two pad elastic pressing plates 54 are elastically deformed so that they lean in a direction toward one side of the second direction as they move away from the worm 18 in the third direction, centered on their respective base ends.

[0112] If the heights of the two protrusions on each of the two pad elastic pressing plates in the second direction were the same, when the pad was attached to the protrusion of the holder, only the tip of the protrusion closest to the worm in the third direction would abut the pressed surface of the holder, while the tip of the protrusion farthest from the worm in the third direction would not abut the pressed surface of the holder. This could result in an instability in the elastic deformation of the pad elastic pressing plate, or in excessive surface pressure at the contact point between the tip of the protrusion closest to the worm in the third direction and the pressed surface of the holder, resulting in wear at that contact point. As a result, it could be impossible to stabilize the elastic forces Fx and Fp generated when the tip of the protrusion elastically presses the pressed surface of the holder toward the other side in the second direction.

[0113] In contrast, in this example, the height in the second direction of the protrusion 64a on the side farther from the worm 18 in the third direction is made greater than the height in the second direction of the protrusion 64b on the side closer to the worm 18 in the third direction. Therefore, when the pad 20 is assembled to the protrusion 44 of the holder 19, the tip ends of the two protrusions 64a, 64b can be reliably abutted against the holder pressed surface 52. This stabilizes the manner in which the pad elastic pressing plate 54 elastically deforms, and prevents excessive surface pressure at the contact portions between the tip ends of the protrusions 64a, 64b and the holder pressed surface 52, thereby preventing wear at the contact portions. As a result, the elastic forces Fx and Fp generated by the tip portions of the protrusions 64a and 64b elastically pressing the holder pressed surface 52 toward the other side of the second direction can be stabilized, and displacement of the tip portion of the worm 18 in the third direction when the rotation direction of the worm 18 changes can be stably prevented.

[0114] Furthermore, according to the worm reducer 14 of this example, grease can be held between the two protrusions 64a, 64b provided on each of the two pad elastic pressing plates 54 to lubricate the contact portions between the tip ends of the protrusions 64a, 64b and the holder pressed surface 52. This makes it possible to maintain a good lubrication state for a long period of time at the contact portions between the tip ends of the protrusions 64a, 64b and the holder pressed surface 52. This also makes it possible to prevent wear at the contact portions between the tip ends of the protrusions 64a, 64b and the holder pressed surface 52.

[0115] In this example, each of the two pad elastic pressure plates 54 has two protrusions 64a, 64b. However, when implementing a worm reducer according to one embodiment of the present disclosure, each of the two pad elastic pressure plates may have three or more protrusions, or may have only one. When each of the two pad elastic pressure plates has only one protrusion, the tip of the protrusion is configured with an inclined surface that slopes more in the direction toward the other side of the second direction as it moves away from the worm in the third direction. This increases the contact area between the tip of the protrusion and the pressed surface of the holder, preventing unstable elastic deformation of the pad elastic pressure plate and wear of the tip of the protrusion.

[0116] [Example 2] A second example of an embodiment of the present disclosure will be described with reference to Figures 21(a) to 22(c). The worm reducer of this example differs from the worm reducer 14 of the first example in the configuration of the elastic member 21a. The configurations and effects of other parts are the same as those of the worm reducer 14 of the first example, so a description thereof will be omitted.

[0117] 21(a) to 21(d), the elastic member 21a is configured by a notched cylindrical (substantially C-shaped) leaf spring having a discontinuous portion 66 at one location in the circumferential direction. In this example, the elastic member 21a has a base portion 67a located on the side farther from the worm 18 in the first direction, and two arm portions 68a extending in the circumferential direction from both circumferential end portions of the base portion 67a.

[0118] In this example, the base 67a is made of a flat plate perpendicular to the first direction. The base 67a has a constricted portion 70 in the middle in the third direction, which has a smaller width in the second direction than both side portions in the third direction. However, the constricted portion 70 may be omitted.

[0119] Each of the two arms 68a is configured in a partially cylindrical shape. In this example, each of the two arms 68a has, in order from the side closest to the base 67a in the circumferential direction, a base-side wide portion 71, a narrow portion 72, and a tip-side wide portion 73. In this example, the width dimension W71 in the second direction of the base-side wide portion 71 and the width dimension W73 in the second direction of the tip-side wide portion 73 are the same, and the width dimension W72 in the second direction of the narrow portion 72 is smaller than the width dimension W71 in the second direction of the base-side wide portion 71 and the width dimension W73 in the second direction of the tip-side wide portion 73 (W72 <W71=W73)。

[0120] In this example, each of the two arm portions 68a has a bent portion 69 that is bent radially outward from the tip of the tip-side wide portion 73. The width dimension of the bent portion 69 in the second direction is the same as the width dimension W73 of the tip-side wide portion 73 in the second direction. However, the bent portion 69 may be omitted.

[0121] The elastic force of the elastic member 21a can be adjusted by adjusting the width dimension W72 in the second direction of the narrow portion 72 of each of the two arm portions 68a. That is, in the worm reducer of this example, by adjusting the width dimension W72 in the second direction of the narrow portion 72, the force with which the elastic member 21a elastically urges the tip end of the worm 18 toward the worm wheel 17 via the pad 20 can be appropriately adjusted. As a result, backlash is suppressed at the meshing portion between the wheel teeth 24 and the worm teeth 25, and abnormal noise is suppressed, while unnecessary increases in friction at the meshing portion can be suppressed.

[0122] Furthermore, according to this embodiment, the elastic member 21a can be easily handled. The reason for this will be explained with reference to Figures 23(a) to 24(c) in addition to Figures 21(a) to 22(c).

[0123] 23(a) to 24(c) show a comparative example of the second example. In the comparative example, each of the two arms 68z constituting the elastic member 21z has, in order from the side closest to the base 67a in the circumferential direction, only a base-side wide portion 71 and a narrow portion 72z, and does not have a tip-side wide portion 73. The elastic force of the elastic member 21z of the comparative example can also be adjusted by adjusting the width dimension of the narrow portion 72z in the second direction.

[0124] In the elastic member 21z of the comparative example, the width dimension in the second direction of the narrow width portion 72z is smaller than the width dimension in the second direction of the base-side wide width portion 71. Therefore, when multiple elastic members 21z are stacked in the axial direction, they tend to tilt toward the discontinuous portion 66, as shown in Figures 24(a) to 24(c), making handling difficult.

[0125] In contrast, in this example, each of the two arms 68a constituting the elastic member 21a has a base-side wide portion 71 and a tip-side wide portion 73 adjacent to both circumferential sides of the narrow portion 72, with the same width dimensions W71 and W73 in the second direction. Therefore, as shown in FIGS. 22(a) to 22(c), even when multiple elastic members 21a are stacked in the axial direction, tilting can be prevented, ensuring easy handling of the elastic members 21a. This facilitates, for example, the wrapping of multiple elastic members 21a in an axially stacked state, known as "roll wrapping," and / or the easy placement of the multiple elastic members 21a in an axially stacked state in a fixed positioning device.

[0126] In this example, the elastic member 21a has a base 67a formed of a flat plate, and the base 67a has a constricted portion 70 in the middle in the third direction. This makes it easy to align the phase of the elastic member 21a in the circumferential direction with the protrusion 44 of the holder 19. However, aligning the phase of the elastic member with the holder can be performed by any method, such as by displaying a mark. In this case, the base can be formed in a partially cylindrical shape and / or the constricted portion can be omitted.

[0127] Although various embodiments have been described above, it goes without saying that the present disclosure is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure. Furthermore, the components of the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0128] This application is based on a Japanese patent application (Patent Application No. 2022-209401) filed on December 27, 2022, the contents of which are incorporated by reference into this application. [Explanation of symbols]

[0129] 1 Electric power steering device 2 steering wheels 3 Steering shaft 4 Steering column 5a, 5b universal joint 6 Intermediate shaft 7 Steering gear unit 8 Electric assist device 9 Pinion shaft 10 rack axis 11. Housing 12 Rack storage area 13 Pinion housing 14 Worm reducer 15 Electric motor 16 Housing 17 Worm Wheel 18 Warm 19 Holder 20, 20z pad 21, 21a, 21z Elastic member 22 Wheel housing 23 Worm housing 24 wheel teeth 25 worm teeth 26 Female spline part 27 Output shaft 28 Male spline part 29 Ball bearings 30 Small diameter cylindrical surface section 31 Large diameter cylindrical surface 32 Support bearing 33 Inner Circle 34 outer ring 35 balls 36 Bush 37 Retainer 38 Fitting cylinder 39 Inward flange 40 Wave washer 41 holder inclined surface (holder engagement portion) 42 Annular section 43 Side plate part 44 Protrusion 45 Flat area 46 Inner surface 47 Recess 48 Step 49 Guide part 50 Connection 51 Inner surface 52 Holder pressed surface 53 Pad inclined surface (pad engagement portion) 54 Pad elastic pressure plate 55 Pad base 56 Through hole 57 Flat plate part 58 Base body 59 Base overhang 60 oval hole 61 Circular hole 62 Pressurized part 63 Base surface 64a, 64b protrusions 65 Slit 66 Discontinuities 67, 67a base 68, 68a, 68z arm 69 Bending part 70 Neck 71 Wide base part 72, 72z narrow part 73 Wide tip part 74 Holding part 75 Holder side positioning engagement part 76 Pad recess 77 Pad elastic pressing part 78 Guide protrusion 79 Guide Jig 80 Holding jig 81 Restraint Jig 82 Base 83 tongue 84 Abutment surface 85 Jig side positioning engagement part 86 Recess 87 Insertion Jig 100 worm reducer 101 Housing 102 Worm Wheel 103 Warm 104 Wheel housing 105 Worm housing 106 Wheel Teeth 107 Rotational Axis 108 worm teeth 109a, 109b ball bearing 110 Holder 111 Large diameter section 112 Bush 113 Electric Motor 114 Pad 115 Torsion coil spring

Claims

1. a housing having a wheel accommodating portion and a worm accommodating portion disposed at a twisted position relative to the wheel accommodating portion and having an axially intermediate portion that opens to the wheel accommodating portion; a worm wheel having wheel teeth on an outer peripheral surface thereof and rotatably supported inside the wheel accommodating portion; a worm having worm teeth on an outer peripheral surface thereof that mesh with the wheel teeth and that is rotatably supported inside the worm accommodating portion; a holder disposed between the tip end of the worm and the worm accommodating portion; a pad fitted onto the tip of the worm; an elastic member that is assembled to the holder and elastically biases the tip end of the worm toward the worm wheel via the pad; Equipped with The holder has a held portion that is fitted and held inside the worm accommodating portion in a state where rotation is prevented, two guide portions that protrude toward one side of the second direction, which is the axial direction of the worm accommodating portion, from two positions spaced apart in a third direction that is orthogonal to both the first direction, which is the biasing direction of the elastic member, and the second direction, on a side surface of the held portion on one side of the second direction, which is the axial direction of the worm accommodating portion, and two holder engaging portions that are provided on inner surfaces of the two guide portions that face each other, The pad has a pad base disposed between the two guide portions, two pad engaging portions provided on both side surfaces of the pad base in the third direction and contacting the two holder engaging portions, a pad recess formed on the other side surface of the pad base in the second direction so as to extend in the first direction, and a pad elastic pressing portion that elastically presses a part of the holder toward the other side in the second direction, thereby applying a preload to the contact portion between the holder engaging portion and the pad engaging portion. Worm reducer.

2. the two holder engaging portions are configured by two holder inclined surfaces that are inclined in directions that approach each other as they move toward one side of the second direction, 2. The worm reducer according to claim 1, wherein the two pad engagement portions are configured by two pad inclined surfaces that come into surface contact with the two holder inclined surfaces.

3. The worm reducer according to claim 1 , wherein the holder has a connection portion that connects the ends of the two guide portions that are closer to the worm wheel in the first direction.

4. the pad elastic pressing portion is located on one side of the two pad engaging portions in the second direction, and is composed of two pad elastic pressing plates each extending from a center of the pad in the third direction toward sides away from each other in the third direction, a part of the holder that is elastically pressed toward the other side in the second direction by the two pad elastic pressing plates is configured by a holder pressed surface that is provided on an end surface on one side in the second direction of each of the two guide portions; The worm reducer according to claim 1.

5. each of the two pad elastic pressure plates has a slit penetrating in the second direction and extending in the first direction at an end portion on a central side of the pad in the third direction; 5. The worm reducer according to claim 4.

6. The elastic member is formed of a leaf spring. The worm reducer according to claim 1.

7. A method for assembling the worm reducer according to any one of claims 1 to 6, comprising: the holder is disposed relative to a guide jig having guide protrusions extending in a predetermined direction so that the first direction coincides with the extension direction of the guide protrusions and the central position between the two guide portions in the third direction coincides with the central position in the width direction of the guide protrusions; and the pad is moved along the guide protrusions with the guide protrusions inserted into the pad recesses, thereby disposing the pad base between the two guide portions. How to assemble a worm reducer.

8. The guide jig has a width dimension of the guide protrusion that increases toward the front side in the moving direction of the pad. A method for assembling the worm reducer according to claim 7.

9. In the step, a jig-side positioning engaging portion provided on the guide jig and a holder-side positioning engaging portion provided on the holder are engaged with each other to position the guide jig and the holder in the third direction. A method for assembling the worm reducer according to claim 7.

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