Worm speed reducer

Abstract

According to the present invention, in the side surface on the other side in a second direction that is an axial direction of a worm housing 23 in each of two pad elastic pressure plates 54, portions in a third direction that is orthogonal to both a first direction that is a biasing direction of an elastic member 21 and the second direction are brought into contact with two respective holder-pressed surfaces 52 of a holder 19 so as to elastically press the two holder-pressed surfaces 52 toward the other side in the second direction, thereby providing a preload to a contact portion between a holder-engaging portion 41 of the holder 19 and a pad-engaging portion 53 of a pad 20. Portions of the two pad elastic pressure plates 54 in the third direction are in surface contact with the two respective holder-pressed surfaces 52, or are in line contact with the two respective holder-pressed surfaces 52 at two or more positions in the third direction.

Description

Technical Field

[0001] The present disclosure relates to a worm reducer incorporated, for example, in an electric power steering apparatus.

Background Art

[0002] When applying a steering angle to a steering wheel of an automobile, an electric power steering apparatus that uses an electric motor as an auxiliary power source is widely used as a device for reducing the force required for operating the steering wheel.

[0003] The structure of the electric power steering apparatus is roughly classified according to the mounting position of the electric motor. Specifically, a column assist type in which auxiliary power is applied to a steering shaft rotatably supported inside a steering column, a pinion assist type in which auxiliary power is applied to a pinion shaft that is an input shaft of a steering gear unit, and a dual pinion type in which the steering gear unit is provided with a pinion shaft different from the pinion shaft that is the input shaft and auxiliary power is applied to the pinion shaft, and various structures have been proposed.

[0004] In any structure, the auxiliary power of the electric motor is applied to a shaft member that rotates or linearly moves by operating the steering wheel via a speed reducer. As such a speed reducer, a worm reducer is widely used. The worm reducer that constitutes the electric power steering apparatus includes a worm that is rotationally driven by an electric motor and a worm wheel that meshes with the worm.

[0005] FIG. 28 shows an example of a conventional structure of a worm reducer described in Japanese Patent No. 4381024. The worm reducer 100 includes a housing 101, a worm wheel 102, and a worm 103.

[0006] The housing 101 has a wheel accommodating portion 104 and a worm accommodating portion 105 whose central axis exists in a twisted position with respect to the central axis of the wheel accommodating portion 104 and whose axial intermediate portion opens into the wheel accommodating portion 104.

[0007] The worm wheel 102 has wheel teeth 106 on its outer peripheral surface and is supported coaxially and fixedly around a rotating shaft 107 rotatably supported inside the wheel accommodating portion 104.

[0008] The worm 103 has worm teeth 108 meshing with the wheel teeth 106 on the outer peripheral surface of its axial intermediate portion. The worm 103 is rotatably supported inside the worm accommodating portion 105 at two axial positions sandwiching the worm teeth 108 by two ball bearings 109a and 109b. Among the two ball bearings 109a and 109b, the outer ring of the ball bearing 109a on the tip side (the right side in Fig. 28) of the worm 103 is press-fitted into a holder 110 internally fitted and fixed to the inner side of the inner end portion of the worm accommodating portion 105. The inner ring of the ball bearing 109a is externally fitted with a clearance fit via a bush 112 made of synthetic resin to a large-diameter portion 111 provided in a portion of the worm 103 located on the tip side of the worm teeth 108. That is, the inner ring of the ball bearing 109a is externally fitted to the bush 112 externally fitted to the large-diameter portion 111 of the worm 103 without play. The outer ring of the ball bearing 109b on the base end side (the left side in Fig. 28) of the worm 103 is internally fitted with a clearance fit to the opening of the worm accommodating portion 105, and the inner ring of the ball bearing 109b is externally fitted to the base end portion of the worm 103. The output shaft of the electric motor 113 is connected to the base end portion of the worm 103 so as to enable torque transmission. That is, the worm 103 can be rotationally driven by the electric motor 113.

[0009] In the worm reducer 100, there is an inevitable backlash at the meshing portion between the wheel teeth 106 and the worm teeth 108 due to dimensional errors and assembly errors of the respective components constituting the worm reducer 100. Based on the existence of this backlash, when changing the rotation direction of the steering wheel, a noisy tooth engagement sound may occur at the meshing portion. In the illustrated example, in order to suppress the generation of such a tooth engagement sound, the tip of the worm 103 is elastically biased toward the side of the worm wheel 102.

[0010] That is, the base end portion of the worm 103 is supported by a ball bearing 109b having a radial clearance with respect to the worm housing portion 105 so as to allow a slight rocking displacement. An annular gap exists over the entire circumference between the outer peripheral surface of the large diameter portion 111 of the worm 103 and the inner peripheral surface of the bush 112. A pad 114 is externally fitted to the tip of the worm 103, and a torsion coil spring 115 is installed between the pad 114 and the holder 110. By the torsion coil spring 115, the pad 114 is elastically pressed toward the side of the worm wheel 102 in the first direction (the vertical direction in FIG. 28), which is the direction in which the worm 103 moves closer to and farther from the worm wheel 102, thereby elastically biasing the tip of the worm 103 toward the side of the worm wheel 102 (the upper side in FIG. 28) in the first direction. Thereby, the backlash between the wheel teeth 106 and the worm teeth 108 is suppressed, and the generation of the tooth engagement sound is suppressed.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] In the structure described in Japanese Patent No. 4381024, since the tip of the worm 103 can be pressed in the direction approaching the worm wheel 102, an annular gap exists over the entire circumference between the outer peripheral surface of the large-diameter portion 111 of the worm 103 and the inner peripheral surface of the bush 112. Also, although smaller than the annular gap existing between the outer peripheral surface of the large-diameter portion 111 of the worm 103 and the inner peripheral surface of the bush 112, an annular gap also exists over the entire circumference between the tip of the worm 103 and the through-hole of the pad 114. Therefore, when changing the rotation direction of the steering wheel, that is, when changing the rotation direction of the worm 103, among the reaction forces applied from the wheel teeth 106 to the worm teeth 108, the direction of the component regarding the third direction (front-back direction in FIG. 28) that is orthogonal to both the first direction which is the biasing direction of the tip portion and the second direction (left-right direction in FIG. 28) which is the axial direction of the worm housing portion 105 changes, and there is a possibility that the tip of the worm 103 is displaced vigorously in the third direction. Therefore, there is room for improvement in terms of suppressing the generation of abnormal noises such as meshing noises.

[0013] An object of the present disclosure is to provide a worm speed reducer that can stably prevent the tip of a worm from being displaced in a third direction that is orthogonal to both a first direction which is the biasing direction of the tip portion and a second direction which is the axial direction of a worm housing portion when the rotation direction of the worm changes. **Means for Solving the Problem**

[0014] A worm speed reducer according to an 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 housing portion and a worm housing portion that is disposed at a twisted position with respect to the wheel housing portion and has an axial intermediate portion opening into the wheel housing portion.

[0016] The worm wheel has wheel teeth on an outer peripheral surface and is rotatably supported inside the wheel housing portion.

[0017] The worm has worm teeth that mesh with the wheel teeth on its outer peripheral surface and is rotatably supported inside the worm housing.

[0018] The holder is disposed between the tip of the worm and the worm housing.

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

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

[0021] The holder has two holder engaging portions provided at positions that sandwich the pad from both sides with respect to a third direction that is orthogonal to both a first direction that is the biasing direction by the elastic member and a second direction that is the axial direction of the worm housing, and two holder pressed surfaces facing one side in the second direction.

[0022] The pad has two pad engaging portions provided on both sides with respect to the third direction and contacting the two holder engaging portions, and two pad elastic pressing plates that are located on one side in the second direction relative to the two pad engaging portions and each extend from the central portion of the pad in the third direction toward the side away from each other in the third direction.

[0023] In the worm reducer according to one aspect of the present disclosure, a part in the third direction of each of the other side surfaces of the two pad elastic pressing plates in the second direction contacts each of the two holder pressed surfaces, and elastically presses each of the two holder pressed surfaces toward the other side in the second direction, thereby applying a preload having components opposite to each other in the third direction to the contact portion between the holder engaging portion and the pad engaging portion. A part in the third direction is in surface contact with each of the two holder pressed surfaces, or is in line contact at at least two locations in the third direction.

[0024] In the worm reducer according to one aspect of the present disclosure, each of the two pad elastic pressing plates is provided with at least one ridge extending in the first direction on the other side surface in the second direction, and a part in the third direction is constituted by the tip of the at least one ridge. The height of the at least one ridge in the second direction becomes continuously or stepwise higher as it is farther from the worm in the third direction.

[0025] The at least one ridge can be constituted by a plurality of ridges spaced apart from each other in the third direction. In this case, the height of the plurality of ridges in the second direction becomes higher as they are located farther from the worm in the third direction.

[0026] In this case, the cross-sectional shape of the tip of each of the plurality of ridges with respect to the virtual plane orthogonal to the first direction can be linear.

[0027] Alternatively or additionally, the tip of the at least one ridge can be constituted by an inclined surface inclined in the direction toward the other side in the second direction as it is farther from the worm in the third direction.

[0028] Each of the two pad elastic pressing plates can have a slit penetrating in the second direction and extending in the first direction at the central side end of the pad in the third direction.

[0029] In this case, the height of the at least one ridge in the second direction can be made lower from the central part toward both sides in the first direction. More specifically, the cross-sectional shape of the tip of the ridge with respect to the virtual plane orthogonal to the second direction can be arc-shaped.

[0030] In the worm reducer according to one aspect of the present disclosure, one of the two holder pressed surfaces and the portion of the two pad elastic pressing plates that presses the two holder pressed surfaces is inclined away from the worm in the third direction, and is closer to the other of the two holder pressed surfaces and the portion of the two pad elastic pressing plates that presses the two holder pressed surfaces in the second direction. It is composed of an inclined surface inclined in the approaching direction.

[0031] The two holder pressed surfaces can be constituted by inclined surfaces inclined in a direction away from the worm in the third direction and toward one side in the second direction. In this case, each of the two pad elastic pressing plates can be provided with at least one protrusion extending in the first direction, which is the portion of the two pad elastic pressing plates that presses the two holder pressed surfaces, on the side surface on the other side in the second direction.

[0032] In the worm reducer according to one aspect of the present disclosure, the two holder engaging portions can be constituted by two holder inclined surfaces that each extend in the first direction and are inclined in a direction approaching each other as they go toward one side in the second direction, and the two pad engaging portions can be constituted by two pad inclined surfaces that are in surface contact with the two holder inclined surfaces.

[0033] In the worm reducer according to one aspect of the present disclosure, the elastic member can be constituted by a leaf spring.

[0034] In this case, the elastic member can be configured as an elliptical cylindrical shape having a discontinuous portion at one circumferential location when viewed from the second direction, and the elastic member can have a base portion located on the side farther from the worm wheel with respect to the first direction, and two arm portions extending circumferentially from both ends in the circumferential direction of the base portion. Each of the two arm portions has, in order from the side closer to the base portion in the circumferential direction, a wide portion on the base side, a narrow portion, and a wide portion on the tip side. The width dimension of the wide portion on the base side in the second direction is the same as the width dimension of the wide portion on the tip side in the second direction. The width dimension of the narrow portion in the second direction is smaller than the width dimension of the wide portion on the base side in the second direction and the width dimension of the wide portion on the tip side in the second direction.

[0035] The worm reducer according to one aspect of the present disclosure can be implemented by appropriately combining the above-described configurations within a range that does not cause contradictions.

Advantages of the Invention

[0036] According to the worm reducer of one aspect of the present disclosure, when the rotation direction of the worm changes, it is possible to stably prevent the tip portion of the worm from being displaced in a third direction that is orthogonal to both the first direction, which is the biasing direction of the tip portion, and the second direction, which is the axial direction of the worm housing portion.

Brief Description of the Drawings

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MODE FOR CARRYING OUT THE INVENTION

[0038] [First Example] A first example of an embodiment of the present disclosure will be described with reference to FIGS. 1 to 17(b). In this example, the case where a worm reducer is applied to a pinion assist type electric power steering device will be described. However, any worm reducer according to an aspect of the present disclosure can be widely applied to a column assist type or dual pinion type electric power steering device, or a worm reducer incorporated in various mechanical devices other than the electric power steering device.

[0039] FIG. 1 shows a pinion assist type electric power steering device 1 incorporating the worm reducer 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.

[0040] The steering wheel 2 is supported and fixed to the rear end portion of the steering shaft 3. The steering shaft 3 is rotatably supported inside the steering column 4 supported by the vehicle body. The front end portion of the steering shaft 3 is connected to the pinion shaft 9 of the steering gear unit 7 via the rear universal joint 5a, the intermediate shaft 6, and the front universal joint 5b. Therefore, when the driver rotates 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, 5b, and the intermediate shaft 6. The rotation of the pinion shaft 9 is converted into a linear motion of the rack shaft 10 of the steering gear unit 7 that meshes with the pinion shaft 9. As a result, a steering angle corresponding to the rotation operation amount of the steering wheel 2 is imparted to the pair of steered wheels. The electric assist device 8 imparts auxiliary power generated using the electric motor 15 as a power source to the pinion shaft 9. As a result, the force required for the driver to rotate the steering wheel 2 is reduced.

[0041] 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 portion 12 extending in the vehicle width direction and a pinion housing portion 13 connected to one axial side portion (the right side portion in FIG. 1) of the rack housing portion 12. The central axis of the pinion housing portion 13 is in a twisted position with respect to the central axis of the rack housing portion 12. The internal space of the pinion housing portion 13 communicates with the internal space of the rack housing portion 12. The rack shaft 10 is supported inside the rack housing portion 12 so as to be movable only in the axial direction (vehicle width direction). The pinion shaft 9 is supported inside the pinion housing portion 13 so as to be rotatable only. The pinion shaft 9 has pinion teeth on the outer peripheral surface of a front half portion (the lower half portion in FIG. 2) disposed inside the pinion housing portion 13. The base end portion (the upper end portion 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 circumferential part of the outer peripheral surface of one axial side portion (the right side portion in FIG. 1) disposed inside the rack housing portion 12.

[0042] The electric assist device 8 includes a worm reducer 14 and an electric motor 15. The electric assist device 8 is configured to decelerate the rotation of the electric motor 15 by the worm reducer 14 and transmit it to the pinion shaft 9.

[0043] 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.

[0044] The housing 16 has a wheel housing portion 22 and a worm housing portion 23 that is disposed in a twisted position with respect to the wheel housing portion 22 and has an axial intermediate portion opening into the wheel housing portion 22.

[0045] That is, the central axis of the wheel housing portion 22 and the central axis of the worm housing portion 23 are arranged in a twisted position relative to each other. Also, the axial middle portion of the worm housing portion 23 is integrally connected to one circumferential position of the radially outer end portion of the wheel housing portion 22, and through this connected portion, the internal space of the worm housing portion 23 communicates with the internal space of the wheel housing portion 22. In this example, the worm housing portion 23 is configured in a bottomed cylindrical shape. Specifically, the tip in the axial direction (the right end in FIG. 3) is blocked, and the base end in the axial direction (the left end in FIG. 3) is open.

[0046] In this example, the wheel housing portion 22 is coaxially and integrally connected to the axial middle portion of the pinion housing portion 13 that constitutes the housing 11 of the steering gear unit 7. The internal space of the wheel housing portion 22 communicates with the internal space of the pinion housing portion 13.

[0047] The worm wheel 17 has wheel teeth 24 on its outer peripheral surface and is rotatably supported inside the wheel housing portion 22. In this example, the worm wheel 17 is externally fitted and fixed to the axial middle portion of the pinion shaft 9.

[0048] The worm 18 has worm teeth 25 that mesh with the wheel teeth 24 on the axially middle portion of its outer peripheral surface and is rotatably supported inside the worm housing portion 23.

[0049] In this example, the base end portion (the left end portion in FIG. 3) of the worm 18 is supported by the worm housing portion 23 so as to allow a slight rocking displacement and is connected to the output shaft 27 of the electric motor 15 so as to enable torque transmission.

[0050] For this purpose, in this example, the worm 18 has a female spline portion 26 on the inner peripheral surface of the base end portion. The electric motor 15 is screwed and fixed to the axial base end portion of the worm housing portion 23 with the output shaft 27 arranged coaxially with the worm housing portion 23. The female spline portion 26 of the worm 18 and the male spline portion 28 provided on the outer peripheral surface of the output shaft 27 of the electric motor 15 are spline-engaged. Thereby, the base end portion of the worm 18 and the output shaft 27 of the electric motor 15 are connected in such a manner as to enable torque transmission and to allow for some rocking displacement of the worm 18. Further, the base end portion of the worm 18 is supported by a ball bearing 29 having a radial clearance with respect to the worm housing portion 23 so as to allow for some rocking displacement.

[0051] In this example, the outer peripheral surface of the tip portion of the worm 18 is constituted by a stepped cylindrical surface. That is, the outer peripheral surface of the tip portion of the worm 18 has a small-diameter cylindrical surface portion 30 constituting the tip side portion and a large-diameter cylindrical surface portion 31 having a larger diameter than the small-diameter cylindrical surface portion 30 and constituting the base end side portion.

[0052] In this example, a support bearing 32 is arranged between the large-diameter cylindrical surface portion 31 of the worm 18 and the inner peripheral surface of the worm housing portion 23. In the illustrated example, the support bearing 32 is constituted by a ball bearing. That is, the support bearing 32 has an inner ring 33 having an inner ring raceway on the outer peripheral surface, an outer ring 34 having an outer ring raceway on the inner peripheral surface, and a plurality of balls 35 each being a rolling element and arranged between these inner ring raceway and outer ring raceway. However, as the support bearing 32, 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 sliding bearing can also be used.

[0053] In this example, the inner ring 33 is externally fitted onto the large-diameter cylindrical surface portion 31 of the worm 18 with a radial gap therebetween. Also, in this example, a cylindrical bush 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 externally fitted onto the outer peripheral surface of the bush 36 by interference fit, and the bush 36 is externally fitted onto the large-diameter cylindrical surface portion 31 of the worm 18 with a clearance fit. Note that the bush 36 is a member for ensuring slidability and / or cushioning property with respect to the outer peripheral surface of the tip portion of the worm 18. Such a bush 36 is preferably made of a synthetic resin, a light alloy such as an aluminum alloy, which is a material having a small coefficient of friction with respect to the metal material constituting the worm 18. However, it is also possible to omit the bush 36 or to internally fit a bush externally fitted to the outer ring 34 by interference fit with a radial gap therebetween inside the worm housing portion 23.

[0054] In this example, the outer ring 34 is internally fitted into the inside of the worm housing portion 23 with a clearance fit. Thereby, even when the housing 16 thermally expands during use, it is possible to prevent the preload of the support bearing 32 from changing. However, when the thermal expansion of the housing is not particularly problematic, the outer ring can also be press-fitted into the housing.

[0055] Further, as will be described later, the outer ring 34 is axially clamped between a holder 19 disposed inside the worm housing portion 23 and a retainer 37 fitted and fixed inside the worm housing portion 23. The retainer 37 has a fitting cylinder portion 38 fitted and fixed to the inner peripheral surface of the worm housing portion 23 by interference fit, and an inward flange portion 39 bent radially inward over the entire circumference from one axial end (the right side in FIGS. 3 and 4) of the fitting cylinder portion 38. In this example, one axial end face of the outer ring 34 abuts against the radially outer portion of the side face 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 face on the other axial side abuts against the side face 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 can be omitted, or a wave washer can be disposed between the outer ring 34 and the holder 19.

[0056] In this example, the tip of the worm 18 is displaceable in the first direction (the vertical direction in FIGS. 3 and 4), which is the direction of approaching and moving away from the worm wheel 17 and the direction of biasing by the elastic member 21, based on the radial gap existing between the inner peripheral surface of the inner ring 33 and the outer peripheral surface of the tip of the worm 18, specifically, the annular gap existing between the inner peripheral surface of the bush 36 and the large-diameter cylindrical surface portion 31.

[0057] In this example, the support bearing 32 is axially clamped between the holder 19 and the retainer 37. However, when implementing the worm reducer according to an aspect of the present disclosure, the arrangement mode of the support bearing is not particularly limited as long as the tip of the worm can rotate with respect to the worm housing portion and move closer to and away from the worm wheel. For example, a holder can be fitted and fixed inside the worm housing portion, and a support bearing can be fitted and held inside the holder.

[0058] In the worm reducer 14 of this example, when viewed from the first direction, the central axis O17 of the worm wheel 17 and the central axis O18 of the worm 18 (the central axis of the output shaft 27 of the electric motor 15) are orthogonal to each other. However, the present disclosure can also be applied to a skew-type worm reducer in which the central axis O17 of the worm wheel 17 and the central axis O18 of the worm 18 (the central axis of the output shaft 27 of the electric motor 15) are skew to each other, that is, form an acute angle, when viewed from the first direction.

[0059] 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 peripheral surface of the tip portion of the worm housing portion 23. The holder 19 is disposed between the tip portion of the worm 18 and the worm housing portion 23. In this example, the holder 19 is disposed in a state of being prevented from rotating inside the worm housing portion 23 around the tip portion of the worm 18. The pad 20 is externally fitted to the tip portion of the worm 18. In this example, the pad 20 is externally fitted to the tip portion of the worm 18 without play in the radial direction. The elastic member 21 is assembled to the holder 19 and elastically biases the tip portion of the worm 18 toward the side of the worm wheel 17 (the lower side in FIGS. 3 and 4) via the pad 20. Thereby, the backlash at the meshing portion between the wheel teeth 24 and the worm teeth 25 is suppressed.

[0060] The holder 19 has two holder engaging portions, two holder inclined surfaces 41, at positions sandwiching the pad 20 from both sides with respect to the third direction (the front-back direction in FIGS. 3 and 4) that is orthogonal to both the first direction and the second direction (the left-right direction in FIGS. 3 and 4) which is the axial direction of the worm housing portion 23. The two holder inclined surfaces 41 each extend in the first direction and are inclined in a direction approaching each other as they go toward one side in the second direction (the right side in FIGS. 3 and 4 in this example). Note that the holder 19 is preferably made of a material having sufficient strength and rigidity, such as a metal material or a high-functional resin material such as polyphenylene sulfide (PPS) mixed with glass fiber.

[0061] Further, the holder 19 has two holder pressed surfaces 52 facing one side in the second direction. Each of the two holder pressed surfaces 52 is constituted by a flat surface orthogonal to the second direction.

[0062] More specifically, in this example, as shown in FIGS. 12(a) to 13(d), the holder 19 includes an annular portion 42, a substantially circular ring-shaped side plate portion 43 extending radially inward from one end of the annular portion 42 in the second direction, and a protruding portion 44 extending from the radially inner end portion of the side plate portion 43 toward one side in the second direction and having a substantially U-shaped end face shape when viewed from one side in the second direction.

[0063] The annular portion 42 has an end face shape of an incomplete circle composed 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 one circumferential position of the outer peripheral surface (in this example, the end portion closer to the worm wheel 17 in the first direction). In this example, by non-circularly fitting the annular portion 42 inside the worm housing portion 23, the holder 19 is held inside the worm housing portion 23 in a state where rotation is prevented.

[0064] In this example, as shown in FIG. 13(d), the inner peripheral surface 46 of the side plate portion 43 has recesses 47 recessed toward both sides in the third direction at both side portions in the third direction. The bottom surface of the recess 47 is constituted by a plane orthogonal to the third direction. Among the inner peripheral surface 46 of the side plate portion 43, the portions excluding the two recesses 47, that is, the both side portions in the first direction, are constituted by a cylindrical surface centered on the central axis of the holder 19.

[0065] In this example, by abutting the side surface on one side in the second direction of the radially outer end portion of the side plate portion 43 against a step portion 48 (see FIG. 3) provided on the inner peripheral surface of the worm housing portion 23 and facing the other side in the second direction, the displacement of the holder 19 in one side in the second direction is prevented.

[0066] In this example, the protruding portion 44 protrudes toward one side in the second direction from a portion of the radially inner end of the side plate portion 43 excluding the end far from the worm wheel 17 in the first direction. The protruding portion 44 includes two guide portions 49 and a connecting portion 50. The two guide portions 49 constitute both ends of the protruding portion 44 on both sides 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 positions spaced apart in the third direction among the radially inner ends of the side plate portion 43, specifically, from the same circumferential positions as the two recesses 47. The two guide portions 49 have a shape extending in the first direction. The connecting portion 50 constitutes the end of the protruding portion 44 close to the worm wheel 17 in the first direction. That is, the connecting portion 50 extends toward one side in the second direction from the end of the radially inner end of the side plate portion 43 close to the worm wheel 17 in the first direction, and connects the ends of the two guide portions 49 close to the worm wheel 17 in the first direction. The connecting portion 50 has a partial cylindrical shape centered on the central axis of the holder 19. If the holder has sufficient strength to sufficiently prevent deformation of the two guide portions, the connecting portion can be omitted.

[0067] The two holder inclined surfaces 41 that constitute the holder 19 are provided on the inner surfaces 51 which are the side surfaces facing each other with respect to the third direction among the two guide portions 49. In this example, each of the inner surfaces 51 of the two guide portions 49 has a crank shape having a stepped surface (holder inclined surface 41) at an intermediate portion with respect to the second direction as shown in FIG. 13(c) when viewed from the first direction. That is, the two holder inclined surfaces 41 are provided at an intermediate portion with respect to the second direction among the inner surfaces 51 of the two guide portions 49, more specifically, at one-side portion in the second direction in the intermediate portion. The two holder inclined surfaces 41 are inclined in a direction approaching each other as they go toward one side in the second direction. Among the inner surfaces 51 of the two guide portions 49, each of the portion located on one side in the second direction from the two holder inclined surfaces 41 and the portion located on the other side in the second direction from the two holder inclined surfaces 41 are constituted by a plane orthogonal to the third direction. For this reason, the distance between the inner surfaces 51 of the two guide portions 49 is narrower at the portion located on one side in the second direction from the two holder inclined surfaces 41 than at the portion located on the other side in the second direction from the two holder inclined surfaces 41.

[0068] When implementing the worm reducer according to an aspect 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 magnitude within the range of 0° < φ < 90°, but it is preferably 20° or more and 80° or less, and more preferably 30° or more and 70° or less. In this example, the inclination angle φ is 30°.

[0069] Also, the two holder pressed surfaces 52 that constitute the holder 19 are provided on the front end surfaces which are the end surfaces on one side in the second direction of the two guide portions 49. In this example, the two holder pressed surfaces 52 and the front end surface which is the end surface on one side in the second direction of the connecting portion 50 are continuous with each other and exist in the same virtual plane orthogonal to the second direction.

[0070] As shown in FIGS. 6, 10, 11, and FIGS. 14(a) to 15(d), the pad 20 has two pad inclined surfaces 53 which are two pad engaging portions that contact two holder inclined surfaces 41 on both sides in the third direction, and are located on one side in the second direction with respect to the two pad inclined surfaces 53, and each has two pad elastic pressing plates 54 that extend from the central portion of the pad 20 in the third direction toward the sides away from each other in the third direction.

[0071] In this example, the two pad inclined surfaces 53 are in surface contact with the two holder inclined surfaces 41, specifically, they are inclined at the same angle in the same direction as the two holder inclined surfaces 41 (see FIG. 11).

[0072] The pad 20 is preferably made of a material with a small coefficient of friction against the metal material constituting the worm 18, such as a synthetic resin or a light alloy such as an aluminum alloy.

[0073] A part in the third direction of the respective other side surfaces in the second direction of the two pad elastic pressing plates 54 of the pad 20 contacts each of the two holder pressed surfaces 52. As a result, each of the two holder pressed surfaces is elastically pressed toward the other side in the second direction, and a preload having components opposite to each other in the third direction is applied to the contact portion between the two holder inclined surfaces 41 which are holder engaging portions and the two pad inclined surfaces 53 which are pad engaging portions. A part of each of the two pad elastic pressing plates 54 in the third direction is in surface contact with each of the two holder pressed surfaces 52 or is in line contact with each of the two holder pressed surfaces 52 at least at two locations in the third direction.

[0074] In this example, a part of each of the two pad elastic pressing plates 54 in the third direction is in line contact with each of the two holder pressed surfaces 52 at least at two locations in the third direction.

[0075] In particular, in this example, each of the two pad elastic pressing plates 54 is provided with at least one ridge 64 extending in the first direction on the side surface on the other side with respect to the second direction, and by elastically pressing each of the two holder pressed surfaces 52 toward the other side in the second direction by the tip of the at least one ridge 64, a preload is applied to the contact portion between the two holder inclined surfaces 41 that are the holder engaging portions and the two pad inclined surfaces 53 that are the pad engaging portions. That is, in this example, a part of each of the two pad elastic pressing plates 54 with respect to the third direction is constituted by the tip of the at least one ridge 64. The height of the at least one ridge 64 with respect to the second direction becomes continuously or stepwise higher as it moves away from the worm 18 with respect to the third direction.

[0076] Although not limited to the following, the structure of the pad 20 in this example will be described more specifically. In this example, the pad 20 includes a base portion 55 disposed between the two guide portions 49, a through hole 56 that penetrates the base portion 55 in the second direction and through which the tip of the worm 18 is inserted, and on both side portions of the base portion 55 with respect to the third direction, it has two pad inclined surfaces 53, and a flat plate portion 57 including two pad elastic pressing plates 54 is connected to a portion of the base portion 55 that protrudes from between the two guide portions 49 to one side in the second direction.

[0077] The base portion 55 includes a base body 58 and two base overhanging portions 59.

[0078] The base body 58 extends in the first direction and has a substantially rectangular end face shape. The through hole 56 penetrates the half portion of the base body 58 closer to the worm wheel 17 with respect to the first direction in the second direction. In this example, the through hole 56 is constituted by a stepped hole having an oval hole portion 60 on one side with respect to the second direction and a circular hole portion 61 on the other side with respect to the second direction. Among 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.

[0079] Further, the base body 58 has two pressed portions 62 at the ends on the side far from the worm wheel 17 in the first direction, at both ends in the third direction of the other side portion in the second 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 on the side far from the worm wheel 17 in the first direction and at the portion between the two pressed portions 62 in the third direction.

[0080] The two base overhang portions 59 project from the portion of the base body 58 closer to the worm wheel 17 in the first direction in the other half on the other side in the second direction, toward the sides away from each other in the third direction. Each of the two base overhang portions 59 extends in the first direction.

[0081] In this example, the two pad inclined surfaces 53 constituting the pad engaging portion of the pad 20 are provided on the side surface of one side in the second direction of the two base overhang portions 59. The two pad inclined surfaces 53 are inclined in a direction approaching each other as they go toward one side in the second direction. The inclination angle φ of the pad inclined surface 53 with respect to the second direction is the same as the inclination angle φ of the holder inclined surface 41 with respect to the second direction.

[0082] The flat plate portion 57 is integrally connected to one end of the base body 58 on one side 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 the central portion in the radial direction of the flat plate portion 57 in the second direction. Therefore, the flat plate portion 57 is configured in an annular 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 ends of the flat plate portion 57 in the third direction protrude to both sides in the third direction from the base body 58. The end portion of the flat plate portion 57 closer to the worm wheel 17 in the first direction protrudes closer to 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 farther from the worm wheel 17 than the flat plate portion 57 in the first direction.

[0083] In this example, the two pad elastic pressing plates 54 constituting the pad 20 are connected to a portion protruding to one side in the second direction from between the two guide portions 49 in the base portion 55 that constitutes the central portion of the pad 20. Specifically, the two pad elastic pressing plates 54 are constituted by both ends of the flat plate portion 57 in the third direction.

[0084] In this example, each of the two pad elastic pressing plates 54 is provided with at least one ridge 64 extending in the first direction on the other side surface in the second direction, as shown in FIGS. 10, 11, 14(b), and FIGS. 15(b) to 15(d). The height of at least one ridge 64 in the second direction becomes continuously or stepwise higher as it is farther from the worm 18 in the third direction. The height of at least one ridge 64 in the second direction is in the free state before the two pad elastic pressing plates 54 elastically deform, that is, in the free state before assembling the pad 20 to the protrusion 44 of the holder 19. Therefore, in the state where the two pad elastic pressing plates 54 elastically deform after assembling the pad 20 to the protrusion 44 of the holder 19, even if the heights of at least one ridge 64 in the second direction of the two pad elastic pressing plates 54 including at least one ridge 64 are the same, in the state after removing the pad 20, if the height of at least one ridge 64 in the second direction is continuously or stepwise higher as it is farther from the worm 18 in the third direction, it is included in the scope of the present disclosure.

[0085] The number of at least one ridge 64 is arbitrary and is preferably 2 or more, and preferably 2 to 4. In this example, at least one ridge 64 is composed of two ridges 64a and 64b arranged at intervals in the third direction. As shown in FIG. 17(a), among the two ridges 64a and 64b, the height ha of the ridge 64a on the side farther from the worm 18 in the third direction in the second direction is higher than the height hb of the ridge 64b on the side closer to the worm 18 in the third direction in the second direction.

[0086] In this example, the cross-sectional shape of the tip of each of the two ridges 64a and 64b is linear and orthogonal to the second direction. More specifically, the tip of each of the two ridges 64a and 64b is composed of a flat surface orthogonal to the second direction. For this reason, in a state where the pad 20 is assembled to the protruding portion 44 of the holder 19, at least one tip of the ridges 64, which corresponds to a part in the third direction of each of the other side surfaces of the two pad elastic pressing plates 54, that is, in this example, the tip of each of the ridges 64a and 64b, is in line contact with each of the holder pressed surfaces 52. Regarding the cross-sectional shape of the tip of at least one ridge 64, it is also in the free state before the two pad elastic pressing plates 54 elastically deform, that is, in the free state before the pad 20 is assembled to the protruding portion 44 of the holder 19. Therefore, in a state where the two pad elastic pressing plates 54 are elastically deformed after the pad 20 is assembled to the protruding portion 44 of the holder 19, even if the cross-sectional shape of the tip of at least one ridge 64 is deformed due to the elastic deformation of the two pad elastic pressing plates 54 including at least one ridge 64, in a state after the pad 20 is removed, if the shape of the tip of at least one ridge 64 is the shape defined in the present disclosure, it is included in the scope of the present disclosure.

[0087] Note that the degree (ha - hb) of making the height ha in the second direction of the ridge 64a on the side farther from the worm 18 with respect to the third direction higher than the height hb in the second direction of the ridge 64b on the side closer to the worm 18 with respect to the third direction is not particularly limited as long as the tips of the ridges 64a and 64b can both be brought into contact with the holder pressed surface 52 in a state where the pad 20 is assembled to the protruding portion 44 of the holder 19. However, in the worm reducer 14 incorporated in the electric power steering device 1, for example, it can be set to be 0.05 mm or more and 0.30 mm or less, preferably 0.10 mm or more and 0.15 mm or less.

[0088] In this example, each of the two pad elastic pressing plates 54 has a slit 65 that penetrates in the second direction and extends in the first direction at the base end portion, which is the central side end portion of the pad 20 with respect to the third direction. In this example, based on appropriately regulating the width and length of such a slit 65, as well as the plate thickness of the pad elastic pressing plate 54, etc., the bending rigidity in the second direction of the portions adjacent to both sides in the length direction of the slit 65 among the base end portions of the pad elastic pressing plate 54 is adjusted. However, when implementing the worm reducer according to an aspect of the present disclosure, the slit can also be omitted.

[0089] As shown in FIGS. 3 to 5 and FIGS. 7 to 10, the pad 20 is assembled to the protruding portion 44 of the holder 19 and is externally fitted to the tip portion of the worm 18.

[0090] Specifically, among the base portion 55 of the pad 20, the portion closer to the worm wheel 17 in the first direction is disposed between the two guide portions 49 that constitute the protruding portion 44 of the holder 19, and the two pad inclined surfaces 53 are in surface contact with the two holder inclined surfaces 41. Also, the tip portions of the ridges 64a and 64b of each of the two pad elastic pressing plates 54 elastically press the two holder pressed surfaces 52 toward the other side in the second direction. Thereby, a preload is applied to the contact portion between the two holder inclined surfaces 41 and the two pad inclined surfaces 53.

[0091] The inclination angle α of each of the two pad elastic pressing plates 54 with respect to the virtual plane orthogonal to the second direction in the state where the pad 20 is assembled to the protruding portion of the holder 19 is not particularly limited, but can be, for example, 0° or more and 15° or less.

[0092] Further, the small-diameter cylindrical surface portion 30 at the tip of the worm 18 is internally fitted into the circular hole portion 61 of the through-hole 56 of the pad 20 without radial play and rotatably relative to each other.

[0093] In this state, between the side surface of the base portion 55 of the pad 20 that is closer to the worm wheel 17 in the first direction and the side surface of the connecting portion 50 that constitutes the protruding portion 44 of the holder 19 that is farther from the worm wheel 17 in the first direction, there is a gap in the first direction. In this example, based on this gap in the first direction, the pad 20 can be displaced in the first direction with respect to the holder 19.

[0094] Also, in this state, as shown in FIGS. 10 and 11, between each of the portions of the inner side surfaces 51 of the two guide portions 49 that are located on one side in the second direction from the two holder inclined surfaces 41 and each of the portions of the inner side surfaces 51 of the two guide portions 49 that are located on the other side in the second direction from the two holder inclined surfaces 41, and the base portion 55 of the pad 20, there is a gap in the third direction. In this example, based on this gap in the third direction, the pad 20 can be displaced in the third direction with respect to the holder 19.

[0095] In this example, the elastic member 21 is constituted by a leaf spring. More specifically, in this example, as shown in FIGS. 6 and 16, the elastic member 21 is constituted by an incomplete cylindrical leaf spring having a discontinuity 66 at one location in the circumferential direction. 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 ends in the circumferential direction of the base portion 67.

[0096] In this example, the base portion 67 is constituted by a flat plate orthogonal to the first direction.

[0097] Each of the two arm portions 68 is configured in a partial cylindrical shape. Each of the two arm portions 68 has a bent portion 69 bent radially outward from the tip end portion.

[0098] However, when implementing the worm reducer according to an aspect of the present disclosure, the elastic member can be of any configuration as long as it can elastically bias the pad toward the side of the worm wheel 17 with respect to the first direction. For example, when the elastic member is configured by a leaf spring, it can have a shape other than an oval cylindrical shape. Also, the elastic member can be configured by a torsion coil spring.

[0099] The elastic member 21 is assembled to the holder 19 so as to fit over the base portions 55 of the pad 20 and the two guide portions 49. In this example, with the base portions 55 of the pad 20 and the protruding portions 44 of the holder 19 inserted through the radially inner side of the elastic member 21, the base portion 67 of the elastic member 21 is brought into contact with the pedestal surface portion 63 of the pad 20, and the inner peripheral surfaces of the proximal end side portions of the two arm portions 68 are elastically pressed against the two pressed portions 62, and the inner peripheral surfaces of the distal end side portions of the two arm portions 68 are elastically pressed against the side surface of the connection portion 50 that constitutes the protruding portion 44 of the holder 19 and is closer to the worm wheel 17 with respect to the first direction. Thereby, the tip portion of the worm 18 is elastically biased toward the side of the worm wheel 17, that is, the side closer to the worm wheel 17 with respect to the first direction via the pad 20. Thereby, the backlash at the meshing portion between the wheel teeth 24 and the worm teeth 25 is suppressed.

[0100] According to the worm reducer 14 of this example, the following operational effects can be achieved.

[0101] The two pad inclined surfaces 53 that make up the pad 20 are in surface contact with the two holder inclined surfaces 41 that make up the holder 19. Also, the tip portions of the ridges 64a and 64b of the two pad elastic pressing plates 54 that make up the pad 20 elastically press the two holder pressed surfaces 52 that make up the holder 19 toward the other side in the second direction. Thereby, a preload is applied to the contact portion between the two holder inclined surfaces 41 and the two pad inclined surfaces 53. For this reason, based on the contact between the two holder inclined surfaces 41 and the two pad inclined surfaces 53, the displacement of the pad 20 in the third direction with respect to the holder 19 is restricted, and it is possible to prevent the pad 20 from rattling without resistance in the third direction with respect to the holder 19.

[0102] Specifically, in this example, as shown in FIGS. 10 and 11, based on the tip portions of the ridges 64a and 64b of the pad elastic pressing plate 54 elastically pressing the holder pressed surface 52 toward the other side in the second direction, an elastic force (preloading force) Fp that faces one side with respect to 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 (preloading force) Fx that faces outward with respect to the third direction and acts from the pad inclined surface 53 on the holder inclined surface 41. In the structure of this example, based on this elastic force Fx, it is possible to prevent the pad 20 from rattling without resistance in the third direction with respect to the holder 19.

[0103] Therefore, even when the direction of the component of the reaction force applied from the wheel tooth 24 to the worm tooth 25 in the third direction changes due to a change in the rotation direction of the worm 18, the tip portion of the worm 18 becomes less likely to be displaced in the third direction. As a result, it is possible to prevent abnormal noises such as tooth striking sounds from occurring at the meshing portion between the wheel tooth 24 and the worm tooth 25, and abnormal noises such as collision sounds from occurring between the pad 20 and the holder 19.

[0104] When implementing the worm reducer according to one aspect of the present disclosure, based on changing the width and length of the slit 65, the thickness of the pad elastic pressing plate 54, the second-direction height of at least one rib 64 (ribs 64a, 64b), etc., the bending rigidity in the second direction of the portions adjacent to both sides in the length direction of the slit 65 among the base end portions of the pad elastic pressing plate 54 can be changed. Thereby, the magnitude of the force with which the tip of each at least one rib 64 (ribs 64a, 64b) of the pad elastic pressing plate 54 elastically presses the holder pressed surface 52 toward the other side in the second direction can be changed. And accordingly, the magnitude of the elastic force Fp can be arbitrarily changed.

[0105] The pad elastic pressing plate 54 locally presses the holder pressed surface 52 by the tips of at least one rib 64 (ribs 64a, 64b). For this reason, the pressing force can be stabilized as compared with the case where the pad elastic pressing plate presses the holder pressed surface in a wide range for surface pressing.

[0106] Between the elastic force Fx and the elastic force Fp, the relational expression "Fx = Fp / tanφ" holds. In this example, since the inclination angle φ = 30°, Fx = Fp / tan30° = 1.7Fp. That is, the elastic force Fx becomes larger than the elastic force Fp. When implementing the worm reducer according to one aspect of the present disclosure, by changing not only the magnitude of Fp but also the magnitude of the inclination angle φ, the magnitude of the elastic force Fx can be arbitrarily changed. For example, if φ = 45°, Fx = Fp can be set; if 45° < φ < 90°, Fx < Fp can be set; if 0° < φ < 45°, Fx > Fp can be set. Also, without changing the material of the pad 20 (elastic force based on the material), by changing the inclination angle φ, the magnitude of the elastic force Fx can be adjusted. For this reason, the magnitude of the elastic force Fx can be easily adjusted at the design stage.

[0107] In addition, when implementing the worm reducer according to an aspect 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 necessarily have to be exactly the same, and may be different within the range of manufacturing errors. Further, the inclination angle of the holder inclined surface 41 with respect to the second direction can be made 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 portion of the pad inclined surface 53 (the right end portion in the third direction in FIG. 11, the other end portion in the second direction in FIG. 11) comes into surface contact with the holder inclined surface 41 particularly strongly. As a result, the posture of the pad 20 with respect to the holder 19 becomes stable.

[0108] Incidentally, as shown in FIGS. 10 and 11 when viewed from the first direction, consider the case where the pad 20 is displaced to either one side with respect to the holder 19 in the third direction, for example, the right side in FIGS. 10 and 11, from the neutral state where the central axis of the holder 19 and the central axis of the pad 20 coincide with each other. In this case, as the right pad inclined surface 53 slides and displaces along the right holder inclined surface 41, the base portion 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 elastically deforms so as to fall to one side in the second direction. Then, as the elastic pressing force acting from the right pad elastic pressing plate 54 to the right holder pressed surface 52 increases by an amount corresponding to the amount of this elastic deformation, the elastic forces Fp and Fx increase. As a result, it becomes more difficult for the pad 20 to be displaced toward the right side. The same applies to the case where the pad 20 is displaced to the left side in FIGS. 10 and 11 with respect to the holder 19 from the neutral state.

[0109] The inner peripheral surface of the central portion in the circumferential direction 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. For this reason, not only a component in the direction approaching the worm wheel 17 with respect to the first direction but also a force having components in opposite directions with respect to the third direction is applied to the two pressed portions 62. Also from this aspect, when the rotation direction of the worm 18 changes, the tip of the worm 18 can be prevented from being displaced in the third direction.

[0110] In particular, in this example, the height in the second direction of at least one ridge 64 provided on each of the two pad elastic pressing plates 54 becomes continuously or stepwise higher as it moves away from the worm 18 in the third direction. Specifically, among the two ridges 64a and 64b, the height ha in the second direction of the ridge 64a on the side farther from the worm 18 in the third direction is higher than the height hb in the second direction of the ridge 64b on the side closer to the worm 18 in the third direction. For this reason, when the rotation direction of the worm 18 changes, the displacement of the tip of the worm 18 in the third direction can be stably prevented. The reason for this will be described with reference to FIGS. 17(a) and 17(b).

[0111] By assembling the pad 20 to the protruding portion 44 of the holder 19, when the tip portions of the respective ridges 64a and 64b of the two pad elastic pressing plates 54 are elastically abutted against the two holder pressed surfaces 52 of the holder 19, the two pad elastic pressing plates 54 are elastically deformed so as to fall in the direction toward one side in the second direction as they move away from the worm 18 in the third direction with respect to their respective base end portions as the centers.

[0112] Figures 18(a) and 18(b) show reference examples for the first example. In the reference examples, the heights hz in the second direction of the two ridges 64z1 and 64z2 provided on each of the two pad elastic pressing plates 54z are the same as each other. When the pad 20z according to such a reference example is assembled to the protruding portion 44 of the holder 19, only the tip of the ridge 64z1 closer to the worm 18 in the third direction abuts against the holder pressed surface 52, and the tip of the ridge 64z2 farther from the worm 18 in the third direction may not abut against the holder pressed surface 52. For this reason, it may become impossible to stabilize the elastic deformation manner of the pad elastic pressing plate 54z, or the surface pressure of the contact portion between the tip of the ridge 64z1 closer to the worm 18 in the third direction and the holder pressed surface 52 may become excessive, and wear may occur at the corresponding contact portion. As a result, there is a possibility that the elastic forces Fx and Fp based on the elastic pressing of the tips of the ridges 64z1 and 64z2 against the holder pressed surface 52 toward the other side in the second direction cannot be stabilized.

[0113] On the other hand, in this example, the height ha in the second direction of the ridge 64a farther from the worm 18 in the third direction is made higher than the height hb in the second direction of the ridge 64b closer to the worm 18 in the third direction. Therefore, in a state where the pad 20 is assembled to the protruding portion 44 of the holder 19, as shown in Fig. 17(b), the tips of the two ridges 64a and 64b can be surely brought into contact with the holder pressed surface 52. For this reason, the elastic deformation manner of the pad elastic pressing plate 54 can be stabilized, and it is possible to prevent the surface pressure of the contact portion between the tips of the ridges 64a and 64b and the holder pressed surface 52 from becoming excessive, and to prevent wear from occurring at the corresponding contact portion. As a result, the elastic forces Fx and Fp based on the elastic pressing of the tips of the ridges 64a and 64b against the holder pressed surface 52 toward the other side in the second direction can be stabilized, and the displacement of the tip of the worm 18 in the third direction when the rotation direction of the worm 18 changes can be stably prevented.

[0114] Further, according to the worm reducer 14 of this example, grease for lubricating the contact portions between the tips of the two ridges 64a and 64b provided on each of the two pad elastic pressing plates 54 and the holder pressed surface 52 can be held between the two ridges 64a and 64b. Therefore, the lubrication state of the contact portion between the tips of the ridges 64a and 64b and the holder pressed surface 52 can be maintained well for a long time. Also from this aspect, it is possible to prevent the occurrence of wear at the contact portion between the tips of the ridges 64a and 64b and the holder pressed surface 52.

[0115] In this example, the number of the ridges 64a and 64b provided on each of the two pad elastic pressing plates 54 is two. However, when implementing the worm reducer according to an aspect of the present disclosure, the number of the ridges provided on each of the two pad elastic pressing plates can be three or more, or can be one. When the number of the ridges provided on each of the two pad elastic pressing plates is one, the tip of the ridge is formed by an inclined surface inclined in a direction toward the other side in the second direction as it is farther from the worm in the third direction. Thereby, the contact area between the tip of the ridge and the holder pressed surface can be increased, and it is possible to prevent the elastic deformation manner of the pad elastic pressing plate from becoming unstable or the tip of the ridge from being worn.

[0116] [Second Example] A second example of the embodiment of the present disclosure will be described with reference to FIGS. 19(a) and 19(b).

[0117] In this example, at least one tip of the ridge 64 corresponding to a part in the third direction of the other side surface of each of the two pad elastic pressing plates 54 is in surface contact with each of the two holder pressed surfaces 52 at at least one location in the third direction. That is, in a state where the pad 20 is assembled to the protruding portion 44 of the holder 19, the contact state between each tip of the ridges 64a and 64b of the two pad elastic pressing plates 54 and each of the holder pressed surfaces 52 becomes surface contact.

[0118] More specifically, in this example, the tip portions of the two ridges 64c and 64d provided on each of the two pad elastic pressing plates 54 are each constituted by an inclined surface that inclines in a direction toward the other side in the second direction as it moves away from the worm 18 with respect to the third direction. In this example, the cross-sectional shape of the tip portion of each of the two ridges 64c and 64d is linear and extends in a direction toward the other side in the second direction as it moves away from the worm 18 with respect to the third direction.

[0119] According to the worm reducer of this example, it is possible to more effectively prevent the elastic deformation manner of the pad elastic pressing plate 54 from becoming unstable and the tip portions of the ridges 64c and 64d from wearing.

[0120] That is, in the first example, the tip portions of the two ridges 64a and 64b provided on each of the two pad elastic pressing plates 54 are each constituted by a flat surface orthogonal to the second direction. Therefore, in a state where the pad 20 is assembled to the protruding portion 44 of the holder 19, as shown in FIG. 17(b), only the end portions of the tip portions of the ridges 64a and 64b that are closer to the worm 18 with respect to the third direction contact the holder pressed surface 52. That is, the contact state between the tip portions of the ridges 64a and 64b and the holder pressed surface 52 becomes a line contact.

[0121] On the other hand, in this example, the tip portions of the two ridges 64c and 64d are each constituted by an inclined surface that inclines in a direction toward the other side in the second direction as it moves away from the worm 18 with respect to the third direction in a free state. Therefore, in a state where the pad 20 is assembled to the protruding portion 44 of the holder 19, as shown in FIG. 19(b), the tip portions of the ridges 64c and 64d can be brought into surface contact with the holder pressed surface 52. As a result, the contact area between the tip portions of the ridges 64c and 64d and the holder pressed surface 52 can be made larger than in the case of the first example, and it is possible to more effectively prevent the elastic deformation manner of the pad elastic pressing plate 54 from becoming unstable and the tip portions of the ridges 64c and 64d from wearing.

[0122] Note that the inclination angle θp of the tip of each of the two ridges 64c and 64d with respect to the virtual plane orthogonal to the second direction is not particularly limited as long as the tip of each of the ridges 64c and 64d can be brought into contact with the holder pressed surface 52 in a state where the pad 20 is assembled to the protruding portion 44 of the holder 19. For example, it can be 3° or more and 10° or less, preferably 5° or more and 8° or less. Also, the inclination angles θp of the tips of the two ridges 64c and 64d can be the same as each other or different from each other.

[0123] The configuration, operation, and effects of other parts of the second example are the same as those of the first example.

[0124] [Third Example] The third example of the embodiment of the present disclosure will be described with reference to FIGS. 20(a) and 20(b).

[0125] In this example, the cross-sectional shape of the tip of each of the two ridges 64c and 64d is an arc shape that extends in a direction toward the other side in the second direction as it moves away from the worm 18 in the third direction.

[0126] The configuration, operation, and effects of other parts of the third example are the same as those of the first and second examples.

[0127] [Fourth Example] The fourth example of the embodiment of the present disclosure will be described with reference to FIGS. 21 to 22(b).

[0128] In this example, the height of at least one ridge 64 provided on each of the two pad elastic pressing plates 54 with respect to the second direction decreases from the central portion toward both sides with respect to the first direction. That is, the cross-sectional shape of the tip of at least one ridge 64 with respect to the virtual plane orthogonal to the second direction is configured as an arc shape.

[0129] More specifically, in this example, the height of each of the two ridges 64e provided on each of the two pad elastic pressing plates 54 in the second direction decreases from the central portion in the first direction toward both sides. That is, the tip of each ridge 64e is formed by an arcuate curved surface that curves convexly on the other side in the second direction as viewed from the third direction. Note that the height of at least one ridge 64 (each of the two ridges 64e) in the second direction is also in the free state before the two pad elastic pressing plates 54 elastically deform, that is, in the free state before the pad 20 is assembled to the protruding portion 44 of the holder 19. Therefore, in the state where the two pad elastic pressing plates 54 elastically deform after the pad 20 is assembled to the protruding portion 44 of the holder 19, even if the height of at least one ridge 64 (the two ridges 64e) in the second direction fluctuates (being substantially the same height in the first direction), when the height of at least one ridge 64 in the second direction becomes lower from the central portion in the first direction toward both sides in the state after the pad 20 is removed, it is included in the scope of the present disclosure.

[0130] According to the worm reducer of this example, it is possible to effectively prevent the elastic deformation manner of the pad elastic pressing plate 54 from becoming unstable or the tip of each ridge 64e from wearing.

[0131] That is, in the structure of this example, since the pad elastic pressing plate 54 has a slit 65 in the intermediate portion in the first direction at the base end portion, the rigidity of the end portions on both sides in the first direction is higher than the rigidity of the intermediate portion in the first direction. For this reason, when the height of the ridge in the second direction is constant over the first direction, in the state where the pad is assembled to the holder, the surface pressure of the contact portion between the tip of the ridge and the holder pressed surface tends to be large at the end portions on both sides in the first direction.

[0132] In contrast, in this example, the height of each of the protrusions 64e in the second direction is made lower from the central portion in the first direction toward both sides in the free state. For this reason, in a state where the pad 20 is assembled to the protruding portion 44 of the holder 19, as shown in FIG. 22(b), each of the two pad elastic pressing plates 54 is curved in an arc shape such that one side in the second direction is convex. Thereby, while preventing the surface pressure at the contact portion between the tip of each of the protrusions 64e and the holder pressed surface 52 from becoming excessive at both end portions in the first direction, the tip of each of the protrusions 64e can be stably brought into contact with the holder pressed surface 52 in the first direction. Therefore, it is possible to effectively prevent the elastic deformation manner of the pad elastic pressing plate 54 from becoming unstable and the tip of each of the protrusions 64e from being worn.

[0133] The configurations and operational effects of other parts of the fourth example are the same as those of the first example.

[0134] [Fifth Example] A fifth example of the embodiment of the present disclosure will be described with reference to FIGS. 23(a) to 24(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. Since the configurations and operational effects of other parts are the same as those of the worm reducer 14 of the first example, the description thereof will be omitted.

[0135] As shown in FIGS. 23(a) to 23(d), the elastic member 21a is constituted by an elliptical cylindrical (substantially C-shaped) leaf spring having a discontinuity 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 end portions in the circumferential direction of the base portion 67a.

[0136] In this example, the base portion 67a is constituted by a flat plate orthogonal to the first direction. The base portion 67a has a constricted portion 70 in the middle portion in the third direction, the width dimension in the second direction of which is smaller than those of both side portions in the third direction. However, the constricted portion 70 can also be omitted.

[0137] Each of the two arm portions 68a is configured to be partially cylindrical. In this example, each of the two arm portions 68a has, in order from the side closer to the base portion 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 of the base-side wide portion 71 in the second direction is the same as the width dimension W73 of the tip-side wide portion 73 in the second direction, and the width dimension W72 of the narrow portion 72 in the second direction is smaller than the width dimension W71 of the base-side wide portion 71 and the width dimension W73 of the tip-side wide portion 73 in the second direction (W72 < W71 = W73).

[0138] In addition, in this example, each of the two arm portions 68a has a bent portion 69 that bends radially outward from the tip portion 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 can also be omitted.

[0139] The elastic member 21a can adjust the elastic force by adjusting the width dimension W72 of the narrow portion 72 of the two arm portions 68a in the second direction. That is, in the worm reducer of this example, by adjusting the width dimension W72 of the narrow portion 72 in the second direction, the elastic member 21a can appropriately adjust the force that elastically biases the tip portion of the worm 18 toward the worm wheel 17 side via the pad 20. As a result, the occurrence of backlash at the meshing portion between the wheel teeth 24 and the worm teeth 25 can be suppressed, the generation of abnormal noise can be suppressed, and an excessive increase in friction at the meshing portion can be suppressed.

[0140] Further, according to this example, the handleability of the elastic member 21a can be improved. The reason for this will be described with reference to FIGS. 25(a) to 26(c) in addition to FIGS. 23(a) to 24(c).

[0141] Figures 25(a) to 26(c) show reference examples for the fifth example. In the reference examples, each of the two arm portions 68z constituting the elastic member 21z has only a base-side wide portion 71 and a narrow portion 72z in order from the side closer to the base 67a in the circumferential direction, and does not have a tip-side wide portion 73. The elastic member 21z of the reference example can also adjust the elastic force by adjusting the width dimension of the narrow portion 72z in the second direction.

[0142] In the elastic member 21z of the reference example, the width dimension of the narrow portion 72z in the second direction is smaller than the width dimension of the base-side wide portion 71 in the second direction. Therefore, when a plurality of elastic members 21z are stacked in the axial direction, as shown in FIGS. 26(a) to 26(c), they will tilt toward the discontinuous portion 66, which makes handling troublesome.

[0143] On the other hand, in this example, each of the two arm portions 68a constituting the elastic member 21a has a base-side wide portion 71 and a tip-side wide portion 73 whose width dimensions W71 and W73 in the second direction are the same as each other at portions adjacent to both circumferential sides of the narrow portion 72. Therefore, as shown in FIGS. 24(a) to 24(c), even when a plurality of elastic members 21a are overlapped in the axial direction, tilting can be prevented, so that good handling of the elastic member 21a can be ensured. For this reason, for example, so-called rod winding packaging in which the periphery is packaged in a state where a plurality of elastic members 21a are overlapped in the axial direction is easy to perform. And / or it is easy to set in the dispensing device in a state of being overlapped in the axial direction.

[0144] The elastic member 21a of this example is configured such that the base 67a is formed of a flat plate, and the base 67a has a constricted portion 70 at an intermediate portion in the third direction. For this reason, it is easy to perform circumferential phase alignment of the elastic member 21a with respect to the protruding portion 44 of the holder 19. However, the phase alignment of the elastic member with respect to the holder can be performed by any method such as displaying a mark. In this case, the base can be configured to be partially cylindrical and / or the constricted portion can be omitted.

[0145] The configurations, functions, and effects of the other parts of the fifth example are the same as those of the first example.

[0146] [Sixth Example] The sixth example of the embodiments of the present disclosure will be described with reference to FIGS. 27(a) and 27(b). This example is an example in which a worm reducer is applied to a pinion assist type electric power steering device. The worm reducer of this example is different from the worm reducer 14 of the first example in the structure of the part that elastically presses the two holder pressed surfaces 52a that make up the holder 19 toward the other side in the second direction by the two pad elastic pressing plates 54 that make up the pad 20. Since the configurations, functions, and effects of the other parts are the same as those of the worm reducer 14 of the first example, the description thereof will be omitted.

[0147] In this example, one of the two holder pressed surfaces 52, 52a that make up the holder 19 and the part that presses the two holder pressed surfaces 52, 52a among the two pad elastic pressing plates 54 is inclined in a direction closer to the other of the two holder pressed surfaces 52, 52a and the part that presses the two holder pressed surfaces 52, 52a among the two pad elastic pressing plates 54 in the second direction as it moves away from the worm 18 in the third direction. It is composed of an inclined surface.

[0148] In this example, the two holder pressed surfaces 52a are composed of inclined surfaces that are inclined in a direction toward one side in the second direction as they move away from the worm 18 in the third direction, and each of the two pad elastic pressing plates 54 has at least one ridge 64 extending in the first direction, which is the part that presses the two holder pressed surfaces 52a among the two pad elastic pressing plates 54, on the side surface on the other side in the second direction.

[0149] More specifically, in this example, the heights of the two ridges 64f corresponding to the at least one ridge 64 provided on each of the two pad elastic pressing plates 54 in the second direction are the same as each other. Also, the tip of each of the two ridges 64f is composed of a flat surface orthogonal to the second direction. However, when implementing the worm reducer of one aspect of the present disclosure, the ridges can also be omitted.

[0150] In this example, each of the two holder pressed surfaces 52a that constitute the holder 19 is an inclined surface inclined in a direction toward one side in the second direction so as to be away from the worm 18 with respect to the third direction. Specifically, each of the two holder pressed surfaces 52a is constituted by a flat surface inclined in a direction toward one side in the second direction so as to be away from the worm 18 with respect to the third direction.

[0151] That is, in this example, in a state where the two pad elastic pressing plates 54 are elastically deformed after the pad 20 is assembled to the protruding portion 44 of the holder 19, the tip portions of the two protrusions 64f corresponding to a part of the other side surface of each of the pad elastic pressing plates 54 with respect to the third direction are in surface contact with each of the two holder pressed surfaces at at least one location (in this example, two locations at the tip portions of the two protrusions 64f) with respect to the third direction. Therefore, according to the worm speed reducer of this example, in a state where the pad 20 is assembled to the protruding portion 44 of the holder 19, the tip portion of each of the two protrusions 64f can be surely brought into contact with the holder pressed surface 52a. For this reason, the manner of elastic deformation of the pad elastic pressing plate 54 can be stabilized, and it is possible to prevent the surface pressure of the contact portion between the tip portion of the protrusion 64f and the holder pressed surface 52a from becoming excessive, and it is possible to prevent wear from occurring at the corresponding contact portion.

[0152] The inclination angle θh of the holder pressed surface 52a with respect to the virtual plane orthogonal to the second direction is not particularly limited as long as the tip portion of each of the two protrusions 64f can be brought into contact with the holder pressed surface 52a in a state where the pad 20 is assembled to the protruding portion 44 of the holder 19, but for example, it can be 3° or more and 10° or less, preferably 5° or more and 8° or less.

[0153] In this example, each of the two holder pressed surfaces 52a is composed of a flat surface inclined in a direction toward one side in the second direction as it moves away from the worm 18 with respect to the third direction. However, each of the holder pressed surfaces can also be composed of a curved surface that is arcuate and inclined in a direction toward one side in the second direction as it moves away from the worm with respect to the third direction, where the cross-section of the curved surface with respect to a virtual plane orthogonal to the third direction is considered.

[0154] In this example, each of the two holder pressed surfaces 52a that constitute the holder 19 is an inclined surface inclined in a direction toward one side in the second direction as it moves away from the worm 18 with respect to the third direction. However, when implementing the worm reducer according to one aspect of the present disclosure, the holder pressed surface can be a flat surface orthogonal to the second direction, and the other side surface of the pad elastic pressing plate can be composed of a flat surface inclined in a direction toward the other side in the second direction as it moves away from the worm with respect to the third direction in a free state.

[0155] The configurations and operational effects of the other parts of the sixth example are the same as those of the first example.

[0156] In the above-described first to sixth examples, a structure is adopted in which the two holder engaging portions are constituted by two holder inclined surfaces, and the two pad engaging portions are constituted by two pad inclined surfaces that are in surface contact with the two holder inclined surfaces. However, when implementing the worm reducer according to one aspect of the present disclosure, as long as the displacement of the pad in the third direction with respect to the holder can be restricted (suppressed or prevented) based on the contact between the two holder engaging portions and the two pad engaging portions, the holder engaging portions and the pad engaging portions are not limited to the holder inclined surfaces and the pad inclined surfaces, and any shape can be adopted. Further, when adopting the holder inclined surfaces and the pad inclined surfaces, these inclined surfaces are not limited to inclined planes, and inclined curved surfaces can also be adopted.

[0157] The above-described first to sixth examples can be implemented in appropriate combinations as long as no contradictions occur.

[0158] The disclosure of this specification includes the following worm reducer.

[0159] [Item 1] A housing having a wheel accommodating portion and a worm accommodating portion that is disposed at a twisted position with respect to the wheel accommodating portion and has an axial intermediate portion opening into the wheel accommodating portion, A worm wheel having wheel teeth on an outer peripheral surface and rotatably supported inside the wheel accommodating portion, A worm having worm teeth meshing with the wheel teeth on an outer peripheral surface and rotatably supported inside the worm accommodating portion, A holder disposed between a tip portion of the worm and the worm accommodating portion, A pad externally fitted to the tip portion of the worm, An elastic member that is assembled to the holder and elastically biases the tip portion of the worm toward the worm wheel side via the pad, The holder includes two holder engaging portions provided at positions sandwiching the pad from both sides with respect to a third direction that is orthogonal to both a first direction that is the biasing direction by the elastic member and a second direction that is the axial direction of the worm accommodating portion, and two holder pressed surfaces facing one side in the second direction, The pad includes two pad engaging portions provided at both side portions with respect to the third direction and contacting the two holder engaging portions, and two pad elastic pressing plates that are located on one side in the second direction with respect to the two pad engaging portions and each extend from a central portion of the pad in the third direction toward sides away from each other in the third direction, A part of each of the other side surfaces of the two pad elastic pressing plates in the second direction contacts each of the two holder pressed surfaces, and elastically presses each of the two holder pressed surfaces toward the other side in the second direction, thereby applying a preload having components opposite to each other in the third direction to a contact portion between the holder engaging portion and the pad engaging portion, and a part in the third direction is in surface contact with each of the two holder pressed surfaces or is in line contact at least at two locations in the third direction. Worm reducer

[0160] [Item 2] Each of the two pad elastic pressing plates is provided with at least one protrusion extending in the first direction on the other side surface in the second direction, and a part in the third direction is constituted by the tip of the at least one protrusion, The worm reducer according to item 1, wherein the height of the at least one protrusion in the second direction becomes continuously or stepwise higher as it moves away from the worm in the third direction.

[0161] [Item 3] The at least one protrusion is composed of a plurality of protrusions spaced apart from each other in the third direction, The worm reducer according to item 2, wherein the height of each of the plurality of protrusions in the second direction is higher as it is located farther from the worm in the third direction.

[0162] [Item 4] The worm reducer according to item 3, wherein the cross-sectional shape of the tip of each of the plurality of protrusions with respect to a virtual plane orthogonal to the first direction is linear and orthogonal to the second direction.

[0163] [Item 5] The worm reducer according to item 2 or 3, wherein the tip of the at least one protrusion is constituted by an inclined surface inclined in the direction toward the other side in the second direction as it moves away from the worm in the third direction.

[0164] [Item 6] The worm reducer according to any one of items 2 to 5, wherein each of the two pad elastic pressing plates has a slit penetrating in the second direction and extending in the first direction at the end on the central side of the pad in the third direction.

[0165] [Item 7] The worm reducer according to item 6, wherein the height of the at least one protrusion in the second direction becomes lower from the central part toward both sides in the first direction.

[0166] [Item 8] The worm reducer according to item 1, wherein one of the two holder pressed surfaces and the portion of the two pad elastic pressing plates that presses the two holder pressed surfaces is constituted by an inclined surface inclined in the direction approaching the other of the two holder pressed surfaces and the portion of the two pad elastic pressing plates that presses the two holder pressed surfaces in the second direction as it moves away from the worm in the third direction.

[0167] [Item 9] The two holder pressed surfaces are constituted by inclined surfaces inclined in the direction toward one side in the second direction as they move away from the worm in the third direction, The worm reducer according to item 8, wherein each of the two pad elastic pressing plates is provided with at least one protrusion extending in the first direction, which is a portion pressing the two holder pressed surfaces among the two pad elastic pressing plates, on the side surface on the other side in the second direction.

[0168] [Item 10] The two holder engaging portions are each composed of two holder inclined surfaces that extend in the first direction and are inclined in a direction approaching each other as they go toward one side in the second direction. The worm reducer according to any one of items 1 to 9, wherein the two pad engaging portions are each composed of two pad inclined surfaces that are in surface contact with the two holder inclined surfaces.

[0169] [Item 11] The worm reducer according to any one of items 1 to 10, wherein the elastic member is composed of a leaf spring.

[0170] [Item 12] The elastic member is configured in an arcuate cylindrical shape having a discontinuity at one circumferential position when viewed from the second direction. The elastic member has a base portion located on the side farther from the worm wheel in the first direction, and two arm portions extending circumferentially from both ends in the circumferential direction of the base portion. Each of the two arm portions has, in order from the side closer to the base portion in the circumferential direction, a base-side wide portion, a narrow portion, and a tip-side wide portion. The width dimension in the second direction of the base-side wide portion is the same as the width dimension in the second direction of the tip-side wide portion. The worm reducer according to item 11, wherein the width dimension in the second direction of the narrow portion is smaller than the width dimension in the second direction of the base-side wide portion and the width dimension in the second direction of the tip-side wide portion.

Description of Symbols

[0171] 1 Electric power steering device 2 Steering wheel 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 shaft 11 Housing 12 Rack housing 13 Pinion housing 14 Worm reducer 15 Electric motor 16 Housing 17 Worm wheel 18 Worm 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 bearing 30 small-diameter cylindrical surface part 31 large-diameter cylindrical surface part 32 support bearing 33 inner ring 34 outer ring 35 ball 36 bush 37 retainer 38 fitting cylinder part 39 inward flange part 40 wave washer 41 holder inclined surface 42 annular part 43 side plate part 44 protruding part 45 flat part 46 inner peripheral surface 47 concave part 48 step part 49 guide part 50 connection part 51 inner side surface 52, 52a holder pressed surface 53, 53a pad inclined surface 54, 54z pad elastic pressing plate 55 base 56 through hole 57 flat plate part 58 base body 59 base overhanging part 60 oval hole part 61 circular hole part 62 pressed part 63 pedestal surface 64, 64a, 64b, 64c, 64d, 64e, 64f, 64z1, 64z2 rib 65 slit 66 discontinuous part 67, 67a base 68, 68a, 68z arm part 69 bent part 70 constricted part 71 base side wide part 72, 72z width constriction 73 tip-side widened part 100 worm reducer 101 housing 102 worm wheel 103 worm 104 wheel housing part 105 worm housing part 106 wheel teeth 107 rotating shaft 108 worm teeth 109a, 109b ball bearings 110 holder 111 large diameter part 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 which is disposed at a twisted position with respect to the wheel accommodating portion and has an axial intermediate portion opening into the wheel accommodating portion; A worm wheel having wheel teeth on an outer peripheral surface and rotatably supported inside the wheel accommodating portion; A worm having worm teeth meshing with the wheel teeth on an outer peripheral surface and rotatably supported inside the worm accommodating portion; A holder disposed between a tip portion of the worm and the worm accommodating portion; A pad externally fitted to the tip portion of the worm; An elastic member which is assembled to the holder and elastically biases the tip portion of the worm toward the worm wheel side via the pad; and The holder has two holder engaging portions provided at positions sandwiching the pad from both sides with respect to a third direction orthogonal to both a first direction which is a biasing direction by the elastic member and a second direction which is an axial direction of the worm accommodating portion, and two holder pressed surfaces facing one side in the second direction; The pad has two pad engaging portions provided at both side portions with respect to the third direction and contacting the two holder engaging portions, and two pad elastic pressing plates which are located on one side in the second direction with respect to the two pad engaging portions and each extend from a central portion of the pad with respect to the third direction toward sides away from each other with respect to the third direction; A part of each of the second-direction other-side surfaces of the two pad elastic pressing plates in the third direction contacts each of the two holder pressed surfaces, and elastically presses each of the two holder pressed surfaces toward the other side in the second direction, thereby applying a preload having components opposite to each other in the third direction to a contact portion between the holder engaging portion and the pad engaging portion, and a part in the third direction is in surface contact with each of the two holder pressed surfaces or is in line contact at at least two locations in the third direction; A worm reducer.

2. Each of the two pad elastic pressing plates is provided with at least one protrusion extending in the first direction on a second-direction other-side surface, and a part in the third direction is constituted by a tip portion of the at least one protrusion; The worm reducer according to claim 1, wherein the height of the at least one rib in the second direction increases continuously or stepwise away from the worm in the third direction.

3. The at least one rib is composed of a plurality of ribs spaced apart from each other in the third direction, The worm reducer according to claim 2, wherein the height of each of the plurality of ribs in the second direction is higher as it is located farther from the worm in the third direction.

4. The worm reducer according to claim 3, wherein the cross-sectional shape of the tip of each of the plurality of ribs with respect to a virtual plane orthogonal to the first direction is linear in a direction orthogonal to the second direction.

5. The worm reducer according to claim 2, wherein the tip of the at least one rib is composed of an inclined surface inclined in a direction toward the other side in the second direction as it is farther from the worm in the third direction.

6. The worm reducer according to claim 2, wherein each of the two pad elastic pressing plates has a slit penetrating in the second direction and extending in the first direction at an end on the central side of the pad in the third direction.

7. The worm reducer according to claim 6, wherein the height of the at least one rib in the second direction decreases from the central part toward both sides in the first direction.

8. The worm reducer according to claim 1, wherein one of the two holder pressed surfaces and the portion of the two pad elastic pressing plates that presses the two holder pressed surfaces is composed of an inclined surface inclined in a direction approaching the other of the two holder pressed surfaces and the portion of the two pad elastic pressing plates that presses the two holder pressed surfaces in the second direction as it is farther from the worm in the third direction.

9. The two holder pressed surfaces are composed of inclined surfaces inclined in a direction toward one side in the second direction as they are farther from the worm in the third direction, The worm reducer according to claim 8, wherein each of the two pad elastic pressing plates is provided with at least one rib extending in the first direction, which is the portion of the two pad elastic pressing plates that presses the two holder pressed surfaces, on the side surface on the other side in the second direction.

10. The two holder engaging portions are each composed of two holder inclined surfaces that extend in the first direction and are inclined in a direction approaching each other as they go toward one side in the second direction. The two pad engaging portions are each composed of two pad inclined surfaces that are in surface contact with the two holder inclined surfaces. The worm reducer according to claim 1. **Claim 11** The worm reducer according to any one of claims 1 to 10, wherein the elastic member is composed of a leaf spring. **Claim 12** The elastic member is configured in an arcuate cylindrical shape having a discontinuity at one location in the circumferential direction when viewed from the second direction. The elastic member has a base portion located on the side farther from the worm wheel in the first direction, and two arm portions extending circumferentially from both ends of the base portion in the circumferential direction. Each of the two arm portions has, in order from the side closer to the base portion in the circumferential direction, a base-side wide portion, a narrow portion, and a tip-side wide portion. The width dimension of the base-side wide portion in the second direction is the same as the width dimension of the tip-side wide portion in the second direction. The width dimension of the narrow portion in the second direction is smaller than the width dimension of the base-side wide portion in the second direction and the width dimension of the tip-side wide portion in the second direction. The worm reducer according to claim 11.