JP2018204632A - Worm reduction gear - Google Patents

Abstract

To achieve a structure capable of restraining backlash while preventing increase in a size of a housing.SOLUTION: A pressed part 27 is placed in a distal end side of a worm shaft 17 compared to a worm tooth part 26 and at a position shifted in an axial direction from a second support shaft part 25 of an outer peripheral surface of the worm shaft 17. An energizing member body 44 is pressed to the axial direction by a pressing member 45 constituting an energizing member 23, and thereby, a plate spring 46 fixed to the energizing member body 44 is pressed onto the pressed part 27, and the other side in the axial direction of the worm shaft 17 is energized in a direction to come close to a worm wheel.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a worm reduction gear incorporated in an electric power steering device or the like.

  The power steering device is widely used because it can reduce the force required for the driver to operate the steering wheel. There are two types of power steering devices: an electric power steering device that uses an electric motor as an auxiliary power source, and a hydraulic power steering device that uses hydraulic pressure as an auxiliary power source. Of these, the electric power steering device is smaller and lighter than the hydraulic power steering device, and has the advantages of easy control of the magnitude of auxiliary power and low engine power loss. Is increasing.

  In the electric power steering apparatus, auxiliary power of the electric motor is applied to the steering rotation shaft that rotates based on the operation of the steering wheel via the reduction gear. As a speed reducer, a worm speed reducer is widely used because a large reduction ratio can be obtained.

  However, since there is an inevitable backlash at the meshing portion between the worm wheel and the worm shaft constituting the worm reducer, it is easy to generate rattling noise when the rotation direction of the worm wheel changes. There's a problem.

  In Japanese Patent Laid-Open No. 2016-23760, among a pair of bearings for rotatably supporting the worm shaft with respect to the housing, a spring is provided between the bearing disposed on the tip side of the worm shaft and the housing. There is disclosed a structure in which an urging member configured to be arranged is arranged to urge the tip of the worm shaft toward the worm wheel. According to such a structure, backlash of the meshing portion can be suppressed, and generation of rattling noise can be suppressed.

JP 2016-23760 A

  In the structure described in Japanese Patent Application Laid-Open No. 2016-23760, the outer peripheral surface of a bearing disposed on the tip side of the worm shaft is configured to be pressed by a biasing member. Accordingly, there is a possibility that the amount of protrusion of the portion of the housing that accommodates the biasing member to the outside in the radial direction increases, and the housing and thus the worm speed reducer increase in size.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to realize a structure capable of suppressing backlash while preventing an increase in the size of a housing.

The present invention includes a housing, a worm shaft, a worm wheel, a first bearing, a second bearing, a biasing member, and a pair of bearing guide surfaces.
The worm shaft has a worm tooth portion on an outer peripheral surface, is disposed on the inner side of the housing, and has an end portion on one side in the axial direction coupled to a motor output shaft of the electric motor so as to be swingable.
The worm wheel has a worm wheel tooth portion that meshes with the worm tooth portion on an outer peripheral surface.
The first bearing supports one side of the worm shaft in the axial direction so as to be rotatable with respect to the housing.
The second bearing rotatably supports the other axial side of the worm shaft.
The biasing member biases the other axial side portion of the worm shaft in a direction approaching the worm wheel.
The pair of bearing guide surfaces are disposed on both outer sides of the second bearing with respect to the axial direction of the worm wheel, and guide the distance movement of the second bearing with respect to the worm wheel.
The worm shaft has a pressed portion in a portion of the outer peripheral surface that is present on the other side in the axial direction than the worm tooth portion and is axially disengaged from the portion where the second bearing is supported.
The biasing member includes a biasing member main body, a pressing member, and a leaf spring.
The urging member main body is arranged such that a central axis is disposed at a position twisted with respect to the central axis of the worm shaft, and is movable in the axial direction inside the housing.
The pressing member presses the urging member main body in the axial direction of the urging member main body.
The leaf spring is supported by the biasing member main body in a state in which the leaf spring is inclined in a direction approaching the worm shaft toward the rear side with respect to the pressing direction by the pressing member with respect to the central axis of the biasing member main body. Is in contact with the pressed portion.

  In the present invention, a part of the leaf spring can be brought into contact with a portion of the outer peripheral surface of the worm shaft between the worm tooth portion and the portion where the second bearing is supported.

  In the present invention, a pair of the urging members are provided, the pressing direction by the first pressing member constituting the first urging member that is one of the pair of urging members, and the second that is the other. The pressing direction by the second pressing member constituting the urging member can be symmetric with respect to a virtual plane that passes through the central axis of the worm shaft and is orthogonal to the axial direction of the worm wheel.

  According to the present invention, it is possible to suppress backlash while preventing an increase in the size of the housing.

FIG. 1 is a partially cutaway side view of a steering apparatus including a worm reduction gear according to a first example of an embodiment. FIG. 2 is a cross-sectional view taken along line AA of FIG. 1 showing a first example of the embodiment. 3 is a cross-sectional view taken along the line BB of FIG. 1 showing a first example of the embodiment. FIG. 4 is a cross-sectional view taken along the line CC of FIG. 2 showing a first example of the embodiment. FIG. 5 is a cross-sectional view taken along the line DD of FIG. 2 showing a first example of the embodiment. FIG. 6 is a diagram corresponding to FIG. 2 and showing a second example of the embodiment. FIG. 7 is a diagram corresponding to FIG. 2 and showing a third example of the embodiment. 8A is a cross-sectional view taken along line EE in FIG. 7 with the housing omitted, and FIG. 8B is a cross-sectional view taken along line FF in FIG. 7 with the housing omitted. FIG. 9 is a diagram corresponding to FIG. 2 and showing a fourth example of the embodiment. FIG. 10 is a diagram corresponding to FIG. 2 and illustrating a fifth example of the embodiment.

[First example of embodiment]
A first example of the embodiment will be described with reference to FIGS.

<Overall structure of electric power steering device>
The electric power steering apparatus is a column assist type electric power steering apparatus, and includes a steering wheel 1, a steering shaft 2, a steering column 3, a pair of universal joints 4a and 4b, an intermediate shaft 5, and a steering gear unit. 6, a pair of tie rods 7, and an electric assist device 8.

  The steering wheel 1 is attached to a rear end portion of a steering shaft 2 that is rotatably supported inside the steering column 3. A front end portion of the steering shaft 2 is disposed inside a housing 9 fixed to the front end portion of the steering column 3, and is connected to the output shaft 11 via a torsion bar 10.

  The output shaft 11 is rotatably supported inside the housing 9 via a pair of rolling bearings 12a and 12b. The rotation of the output shaft 11 is transmitted to the pinion shaft 13 of the steering gear unit 6 through the pair of universal joints 4a and 4b and the intermediate shaft 5. Then, by converting the rotation of the pinion shaft 13 into a linear motion of a rack (not shown), the pair of tie rods 7 are pushed and pulled to give a steering angle to the steered wheels.

  The electric assist device 8 reduces the force required for the driver to operate the steering wheel 1, and includes a torque sensor 14, an ECU (not shown), an electric motor 15, and a worm reducer 16. .

  The torque sensor 14 is disposed around the output shaft 11 and detects the twist direction and the twist amount of the output shaft 11. The ECU determines the auxiliary torque based on information on the steering torque calculated based on the twist direction and the amount of twist of the output shaft 11 detected by the torque sensor 14, information on the vehicle speed measured by a vehicle speed sensor (not shown), and the like. To do. The electric motor 15 is supported and fixed to the housing 9, and the energization direction and the energization amount are controlled by the ECU. The worm reducer 16 decelerates the rotational force of the electric motor 15 and transmits it to the output shaft 11. As a result, since an auxiliary torque is applied to the output shaft 11, the pair of tie rods 7 can be pushed and pulled with a force larger than the force applied to the steering wheel 1.

<Structure of worm reducer>
The worm speed reducer 16 includes a housing 9, a worm shaft 17, a worm wheel 18, a first bearing 19, a second bearing 20, a bearing guide member 21, a worm shaft guide member 22, and an urging member 23. It has.

  The worm shaft 17 has a first support shaft portion 24 on one axial side (right side in FIG. 2) and a second support shaft 25 on the other axial side (left side in FIG. 2). In addition, a worm tooth portion 26 is provided between the first support shaft portion 24 and the second support shaft portion 25. Furthermore, the worm shaft 17 has a pressed portion 27 on the outer peripheral surface of the tip portion that is the end portion on the other axial side of the second support shaft portion 25. Such a worm shaft 17 is arranged inside a bottomed cylindrical worm shaft housing portion 28 constituting the housing 9. The base end, which is one end of the worm shaft 17 in the axial direction, can transmit a rotational force to the motor output shaft 15a of the electric motor 15 by spline engagement or the like and can be slightly oscillated. It is connected. The end portion on one side in the axial direction of the worm shaft 17 can be connected to the motor output shaft 15a via a torque transmission joint provided with an elastic body so as to be able to swing and displace.

  The worm wheel 18 has a worm wheel tooth portion 29 that meshes with the worm tooth portion 26 on the outer peripheral surface, and is fixed to the output shaft 11. Such a worm wheel 18 is arranged inside a cylindrical worm wheel accommodating portion 30 constituting the housing 9. Since the electric power steering device of this example is a column assist type, the worm wheel 18 is fixed to the output shaft 11. However, in the pinion assist type electric power steering device, the worm wheel is fixed to the pinion shaft. .

  The inner peripheral surface of the worm shaft accommodating portion 28 is formed in a concave cylindrical surface shape, and a part in the circumferential direction of the axially intermediate portion opens into the worm wheel accommodating portion 30. Therefore, the internal space of the worm shaft housing portion 28 and the internal space of the worm wheel housing portion 30 are connected to each other. In addition, a small-diameter portion 31 having a smaller inner diameter than a portion adjacent to one side in the axial direction is provided on the inner end surface of the worm shaft housing portion 28 at the back end, which is the end on the other side in the axial direction. .

  The first bearing 19 is a ball bearing such as a single row deep groove type or a four-point contact type, and includes an annular inner ring 32 and an outer ring 33, and a plurality of balls 34. Among these, the inner ring 32 is fitted and fixed to the first support shaft portion 24 of the worm shaft 17, while the outer ring 33 is fixed to the opening portion of the worm shaft housing portion 28. Further, the first bearing 19 has a radial gap between the inner ring 32 and the outer ring 33 and the ball 34. In this example, a first bearing 19 that connects the base end portion of the worm shaft 17 to the motor output shaft 15a so as to be capable of swinging displacement and rotatably supports the first support shaft portion 24 of the worm shaft 17 is provided. Therefore, the worm shaft 17 can swing with respect to the worm shaft housing portion 28 with the center of the first bearing 19 as a fulcrum.

  The second bearing 20 is a single-row deep groove type ball bearing, and includes an annular inner ring 35 and an outer ring 36, and a plurality of balls 37. Among these, the inner ring 35 is externally fitted and fixed to the second support shaft portion 25 of the worm shaft 17, whereas the outer ring 36 is a bearing guide member that is supported and fixed near the inner portion of the worm shaft housing portion 28. 21 is disposed inside.

  The bearing guide member 21 is made of, for example, a synthetic resin and includes a pair of bearing guide elements 38 having an arcuate cross section. Each of the outer peripheral surfaces of the pair of bearing guide elements 38 has a curved surface portion 39 whose radius of curvature is ½ of the inner diameter of the inner peripheral surface of the worm shaft housing portion 28 and a flat surface bearing guide. And a surface 40. Such a pair of bearing guide elements 38 has the curved surface portions 39 of the worm shaft housing portion 28 at two positions on the opposite side in the axial direction of the worm wheel 18 in the back portion of the worm shaft housing portion 28. It is supported and fixed in a state where it abuts against the inner peripheral surface of the back part. In this state, the bearing guide surfaces 40 of the pair of bearing guide elements 38 face each other and are parallel to each other. Specifically, each of the bearing guide surfaces 40 is located on both outer sides of the second bearing 20 with respect to the axial direction of the worm wheel 18, and is orthogonal to the axial direction of the motor output shaft 15 a and the axial direction of the worm wheel 18. It arrange | positions in parallel with the direction (up-down direction of FIG. 4). The distance between the bearing guide surfaces 40 of the pair of bearing guide elements 38 is slightly larger than the outer diameter of the second bearing 20. For this reason, the bearing guide surfaces 40 of the pair of bearing guide elements 38 guide the movement of the second bearing 20 in the X direction, which is a perspective movement with respect to the worm wheel 18.

  The worm shaft guide member 22 is made of a material having a small coefficient of friction with respect to the metal material constituting the worm shaft 17 such as synthetic resin, and is generally formed in a U shape, and is press-fitted into the small diameter portion 31 of the worm shaft housing portion 28. The inner fitting is fixed. The worm shaft guide member 22 includes a partially cylindrical bottom plate portion 41 and a pair of side plate portions 42 that extend from both ends of the bottom plate portion 41 in the X direction. The outer peripheral surface of such a worm shaft guide member 22 is formed in a convex cylindrical surface shape.

  The mutually opposing surfaces of the pair of side plate portions 42 are each a flat surface and are a pair of worm shaft guide surfaces 43 that are parallel to each other. The pair of worm shaft guide surfaces 43 are disposed on both outer sides of the pressed portion 27 with respect to the axial direction of the worm wheel 18 and in parallel with the X direction. The distance between the pair of worm shaft guide surfaces 43 is slightly larger than the outer diameter of the pressed portion 27. For this reason, the pair of worm shaft guide surfaces 43 guide the movement in the X direction, which is a perspective movement of the tip portion of the worm shaft 17 with respect to the worm wheel 18. However, since the movement of the worm shaft 17 in the X direction on the other side in the axial direction is also guided by the pair of bearing guide surfaces 40, the worm shaft guide member 22 can be omitted.

  The urging member 23 urges the pressed portion 27 of the worm shaft 17 in a direction approaching the worm wheel 18 (downward in FIGS. 2 and 5). The urging member main body 44, the pressing member 45, And a leaf spring 46. Such an urging member 23 is disposed inside the urging member accommodating portion 47 constituting the housing 9.

The urging member accommodating portion 47 is provided on the opposite side of the worm wheel accommodating portion 30 (upper side in FIGS. 2 and 5) across the worm shaft accommodating portion 28 and at a position twisted with respect to the worm shaft accommodating portion 28. It has been. A central axis O ₄₇ of the urging member accommodating portion 47 is disposed substantially parallel to the central axis O ₁₈ of the worm wheel 18. The inner peripheral surface of the urging member accommodating portion 47 is formed in a concave cylindrical surface shape, and a part in the circumferential direction of the axially intermediate portion opens into the worm shaft accommodating portion 28. Therefore, the internal space of the urging member housing portion 47 and the internal space of the worm shaft housing portion 28 are connected to each other. The urging member accommodating portion 47 is open only at one end (right side in FIG. 5) in the axial direction. A bottomed cylindrical lid member 48 is internally fitted or screwed to the opening of the urging member accommodating portion 47.

The urging member main body 44 has a substantially rod shape as a whole, and the inner side of the urging member accommodating portion 47 with its own central axis O ₄₄ aligned with the central axis O ₄₇ of the urging member accommodating portion 47. It is arranged to be able to move in the axial direction. Thus, the center axis O ₄₄ of the biasing member body 44 is substantially arranged in parallel to the center axis O ₁₈ of the worm wheel 18. That is, the center axis O ₄₄ of the biasing member body 44 is not limited to a perfectly parallel to the center axis O ₁₈ of the worm wheel 18, as will be described later, based on the pressing force of the pressing member 45, the biasing member body As long as the leaf spring 46 fixed to 44 is pressed against the pressed portion 27 and the pressed portion 27 can be urged in a direction approaching the worm wheel 18, it can be inclined. Specifically, the inclination angle of the central axis O ₄₄ of the biasing member main body 44 with respect to the central axis O ₁₈ of the worm wheel 18 is set to about 0 ° ± 10 °. The urging member main body 44 has an outer surface facing away from the worm shaft 17 in the X direction as a convex cylindrical surface 49 having a radius of curvature substantially equal to the radius of curvature of the inner peripheral surface of the urging member accommodating portion 47. .

  However, the sliding portion between the inner peripheral surface of the urging member accommodating portion 47 and the outer peripheral surface of the urging member main body 44 and the outer surface facing the side opposite to the worm shaft 17 in the X direction is not attached. As long as the urging member main body 44 can be displaced in the axial direction inside the urging member housing portion 47, the sliding member is not limited to the sliding portion between the cylindrical surfaces, and may be a sliding portion between flat surfaces, for example.

  The urging member main body 44 has a cylindrical portion 50 on one side in the axial direction close to the lid member 48, and a semicircular half-section in the axial intermediate portion adjacent to the other axial side of the cylindrical portion 50. A cylindrical portion 51 is provided, and a mounting portion 52 is provided on the other axial side adjacent to the other axial side of the semi-cylindrical portion 51. The surface of the mounting portion 52 facing the worm shaft 17 side in the X direction is a flat surface, and is a mounting surface 53 that is inclined in a direction approaching the worm shaft 17 toward the one side in the axial direction.

  The pressing member 45 is composed of, for example, a spring member such as a compression coil spring, and is arranged in an elastically compressed state between the bottom surface of the cylindrical portion 50 of the biasing member main body 44 and the bottom surface of the lid member 48. ing. Thereby, the biasing member main body 44 is elastically pressed toward the other side in the axial direction. Therefore, the pressing direction by the pressing member 45 coincides with the axial direction of the urging member main body 44, the front side with respect to the pressing direction corresponds to the other axial direction of the urging member main body 44, and the rear side with respect to the pressing direction. This corresponds to one side in the axial direction of the urging member main body 44. Further, most of the pressing member 45 is disposed inside the lid member 48 and the cylindrical portion 50.

The end of one side of the leaf spring 46 in the longitudinal direction (left side in FIG. 5) is fixed to the mounting surface 53 by mounting pins 54. For this reason, the leaf spring 46 is disposed along the mounting surface 53 in a free state, and is one side in the axial direction of the urging member main body 44 with respect to the central axis O ₄₄ of the urging member main body 44 (FIG. 5). It is inclined in a direction approaching the worm wheel 18 side toward the right side. In other words, the leaf spring 46 is inclined with respect to the central axis O ₄₄ of the urging member main body 44 in a direction approaching the worm wheel 18 side toward the rear side in the pressing direction by the pressing member 45. Specifically, the inclination angle of the mounting surface 53 with respect to the central axis O ₄₄ of the urging member main body 44 is set to about 1 to 20 degrees. The total length of the leaf spring 46 is regulated such that the end portion on the other side in the longitudinal direction (the right side in FIG. 5) can abut on the end portion on the other side in the axial direction of the cylindrical portion 50. Further, in a state where the end portion on the other side in the longitudinal direction of the leaf spring 46 is brought into contact with the end portion on the other side in the axial direction of the cylindrical portion 50, there is a cross section between the back surface of the leaf spring 46 and the semi-cylindrical portion 51. A trapezoidal gap 55 exists. The leaf spring 46 can be bent and deformed so that the intermediate portion in the longitudinal direction enters the gap 55.

  The biasing member 23 of this example is a leaf spring 46 fixed to the biasing member main body 44 by pressing the biasing member main body 44 toward the other side in the axial direction (left side in FIG. 5) by the pressing member 45. Is pressed against the pressed portion 27 of the worm shaft 17. Then, the pressed portion 27 of the worm shaft 17 is biased in a direction approaching the worm wheel 18, and the worm shaft 17 is swung with respect to the worm shaft housing portion 28 with the center of the first bearing 19 as a fulcrum. Thereby, the worm tooth portion 26 is elastically pressed against the worm wheel tooth portion 29. As a result, it is possible to effectively prevent the occurrence of rattling noise at the meshing portion between the worm tooth portion 26 and the worm wheel tooth portion 29. Note that the pressing force of the pressing member 45 is appropriately adjusted so that the meshing resistance of the meshing portion between the worm tooth portion 26 and the worm wheel tooth portion 29 is not excessively increased.

Further, when wear occurs at the meshing portion between the worm tooth portion 26 and the worm wheel tooth portion 29, the position of the urging member main body 44 is moved to the other side in the axial direction based on the pressing force by the pressing member 45. The leaf spring 46 is inclined with respect to the central axis O ₄₄ of the urging member main body 44 in a direction approaching the worm shaft 17 toward the rear side in the pressing direction by the pressing member 45, so that the urging member main body 44 is pivoted. By moving to the other side in the direction, the contact position between the leaf spring 46 and the pressed portion 27 can be moved to the side closer to the worm wheel 18 (lower side in FIG. 5). Thus, the swing angle of the worm shaft 17 can be automatically increased according to the amount of wear generated at the meshing portion. Therefore, even when wear occurs in the meshing portion, generation of rattling noise can be suppressed.

  Further, in this example, when the worm wheel 18 is engaged with the worm shaft 17 and a reaction force is applied, and the worm shaft 17 moves away from the worm wheel 18, the leaf spring 46 is bent and deformed by the worm shaft 17. Therefore, it is possible to prevent the surface pressure of the meshing portion from becoming excessive. Further, the worm shaft 17 moves away from the worm wheel 18 due to the tolerance of the coaxiality between the central axis of the worm shaft 17 and the central axis of the worm tooth portion 26 and the influence of thermal expansion occurring in peripheral members such as the worm wheel 18. In this case, it is possible to prevent the surface pressure of the meshing portion from becoming excessive because the leaf spring 46 is bent and deformed.

  The elastic force of the leaf spring 46 is such that the biasing member main body 44 is pressed by the pressing member before the leaf spring 46 is elastically deformed when an excessive meshing reaction force is applied from the worm wheel 18 to the worm shaft 17. The pressure member 45 is appropriately adjusted so as not to be displaced backward in the pressing direction of the pressing member 45 against the pressing force of 45.

  In addition, in this example, the urging member 23 is used to press the pressed portion 27 that is out of the outer peripheral surface of the worm shaft 17 on the other side in the axial direction from the second support shaft portion 25 on which the second bearing 20 is externally supported. It is comprised so that it may press. For this reason, in the housing 9, the protruding amount of the urging member accommodating portion 47 that accommodates the urging member 23 outward in the radial direction is, for example, the second disposed on the tip side of the worm shaft by the urging member. This can be suppressed as compared with the case where the outer peripheral surface of the bearing is pressed. As a result, the housing 9 and thus the worm speed reducer 16 can be prevented from being enlarged.

[Second Example of Embodiment]
A second example of the embodiment will be described with reference to FIG. In the worm speed reducer 16a of this example, a pressed portion 27a is provided on the outer peripheral surface of the worm shaft 17a between the second support shaft portion 25 and the worm tooth portion 26 in the axial direction of the worm shaft 17a. . Then, the pressed portion 27 a is biased in a direction approaching the worm wheel 18 by the biasing member 23 a. In this example, the urging member main body 44a constituting the urging member 23a has an outer surface facing away from the worm shaft 17 in the X direction perpendicular to the axial direction of the worm shaft 17 and the axial direction of the worm wheel 18. The main body side sliding surface 56 is a flat surface. In accordance with this, the portion of the inner peripheral surface of the urging member accommodating portion 47a constituting the housing 9a that slides with the main body side sliding surface 56 of the urging member main body 44a is slid toward the flat surface of the housing 9a. The surface 57 is used. Further, in this example, unlike the first example of the embodiment, no worm shaft guide member is provided around the pressed portion 27a.

  In the present example as described above, it is easy to reduce the size of the worm reduction gear 16a by suppressing the axial dimensions of the worm shaft 17a and the worm shaft accommodating portion 28a as compared with the first example of the embodiment. Other configurations and operational effects are the same as in the first example of the embodiment.

[Third example of embodiment]
A third example of the embodiment will be described with reference to FIGS. In the worm reduction gear 16b of this example, the tip of the worm shaft 17b is pressed by a pair of urging members 23b and 23c. That is, the worm shaft 17b has a first pressed portion 27b in a portion of the outer peripheral surface that is located on the other axial side of the second support shaft portion 25 with respect to the axial direction. A second pressed portion 27c is provided in a portion existing on the other side in the axial direction from 27b. The first pressed member 27b is one of the pair of biasing members 23b and 23c, and the second pressed member 23c is the second pressed member. The part 27c is pressed in a direction approaching the worm wheel 18 respectively.

In this example, the pressing direction of the first urging member main body 44a by the first pressing member 45a constituting the first urging member 23b and the second pressing member 45b constituting the second urging member 23c. The pressing direction of the second urging member main body 44b is symmetrical with respect to a virtual plane α that passes through the central axis O _17b of the worm shaft 17b and is orthogonal to the central axis O ₁₈ of the worm wheel 18. Further, with respect to the center axis O ₁₈ of the worm wheel 18, the central axis and opposite to each other the inclination direction of the central axis of the second biasing member body 44b of the first biasing member body 44a, and the inclination angles It is the same. Specifically, with respect to the center axis O ₁₈ of the worm wheel 18, the inclination angle of the central axis of the central axis and the second biasing member body 44b of the first biasing member body 44a, 1 ° or more, 20 degrees or less It is said.

  In the present example as described above, the force in the axial direction of the worm wheel 18 acting on the worm shaft 17b from the pair of urging members 23b and 23c can be canceled in the worm shaft 17b. About another structure and an effect, it is the same as the 1st example and 2nd example of embodiment.

[Fourth Example of Embodiment]
A fourth example of the embodiment will be described with reference to FIG. In the worm speed reducer 16c of this example, a portion of the outer peripheral surface of the worm shaft 17c existing on one side of the second support shaft portion 25 in the axial direction by the pair of urging members 23b and 23c is used as the worm wheel. 18 is pushed in the direction approaching 18. That is, of the outer peripheral surface of the worm shaft 17c, the first pressed portion 27d is provided on one side portion in the axial direction between the second support shaft portion 25 and the worm tooth portion 26 with respect to the axial direction, and the other side portion in the axial direction. The second pressed parts 27e are provided respectively. The first pressed member 27b is one of the pair of biasing members 23b and 23c, and the second pressed member 23c is the second pressed member. The parts 27e are pressed in the direction approaching the worm wheel 18, respectively. About another structure and an effect, it is the same as the 1st example-3rd example of embodiment.

[Fifth Example of Embodiment]
A fifth example of the embodiment will be described with reference to FIG. In the worm speed reducer 16d of this example, portions of the outer peripheral surface of the worm shaft 17d existing on both sides of the second support shaft portion 25 in the axial direction are formed on the worm wheel 18 by the pair of urging members 23b and 23c. Press in the approaching direction. That is, of the outer peripheral surface of the worm shaft 17d, the first pressed portion 27f is disposed at a portion between the second support shaft portion 25 and the worm tooth portion 26 in the axial direction, and the second support shaft portion 25 in the axial direction. A second pressed portion 27g is provided at the tip end on the other side in the axial direction. The first pressed member 27b is one of the pair of biasing members 23b and 23c, and the second pressed member 23c is the second pressed member. The parts 27g are pressed in the direction approaching the worm wheel 18, respectively. About another structure and an effect, it is the same as the 1st example-3rd example of embodiment.

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3 Steering column 4a, 4b Universal joint 5 Intermediate shaft 6 Steering gear unit 7 Tie rod 8 Electric assist device 9, 9a Housing 10 Torsion bar 11 Output shaft 12a, 12b Rolling bearing 13 Pinion shaft 14 Torque sensor 15 Electric Motor 16, 16a, 16b, 16c, 16d Worm reducer 17, 17a, 17b, 17c, 17d Worm shaft 18 Worm wheel 19 First bearing 20 Second bearing 21 Bearing guide member 22 Worm shaft guide member 23, 23a, 23b, 23c, 23d Biasing member 24 First support shaft portion 25 Second support shaft portion 26 Worm tooth portion 27, 27a, 27b, 27c, 27d, 27e, 27f Pressed portion 28, 28a War Shaft housing portion 29 worm wheel tooth portion 30 worm wheel housing portion 31 small diameter portion 32 inner ring 33 outer ring 34 ball 35 inner ring 36 outer ring 37 ball 38 bearing guide element 39 curved surface portion 40 bearing guide surface 41 bottom plate portion 42 side plate portion 43 worm shaft guide Surface 44, 44a, 44b Energizing member main body 45, 45a, 45b Pressing member 46 Leaf spring 47, 47a Energizing member accommodating portion 48 Lid member 49 Convex cylindrical surface 50 Cylindrical portion 51 Semi-cylindrical portion 52 Mounting portion 53 Mounting surface 54 Mounting Pin 55 Clearance 56 Body side sliding surface 57 Housing side sliding surface

Claims (3)

A housing;
A worm shaft having a worm tooth portion on an outer peripheral surface, disposed on the inner side of the housing, and having an end portion on one side in the axial direction coupled to an electric motor so as to be swingable;
A worm wheel having a worm wheel tooth portion meshing with the worm tooth portion on an outer peripheral surface;
A first bearing that rotatably supports one side of the worm shaft in the axial direction with respect to the housing;
A second bearing that rotatably supports the other axial side of the worm shaft;
An urging member for urging the other axial side of the worm shaft in a direction approaching the worm wheel;
A pair of bearing guide surfaces that are disposed on both outer sides of the second bearing with respect to the axial direction of the worm wheel and guide the movement of the second bearing relative to the worm wheel;
The worm shaft has a pressed portion at a portion of the outer peripheral surface that is on the other side in the axial direction than the worm tooth portion and that is axially removed from a portion where the second bearing is supported. And
The biasing member includes a biasing member main body, a pressing member, and a leaf spring,
The biasing member main body is arranged such that a central axis is disposed at a twisted position with respect to the central axis of the worm shaft, and is movable in the axial direction inside the housing,
The pressing member presses the biasing member main body in the axial direction of the biasing member main body,
The leaf spring is supported by the biasing member main body in a state in which the leaf spring is inclined in a direction approaching the worm shaft toward the rear side with respect to the pressing direction by the pressing member with respect to the central axis of the biasing member main body. Is in contact with the pressed part.
Worm reducer.   2. The worm according to claim 1, wherein a part of the leaf spring is brought into contact with a portion of the outer peripheral surface of the worm shaft between the worm tooth portion and a portion where the second bearing is supported. Decelerator. A pair of biasing members are provided;
The pressing direction by the first pressing member that constitutes the first urging member that is one of the pair of urging members, and the pressing by the second pressing member that constitutes the second urging member that is the other The worm speed reducer according to claim 1, wherein the direction is symmetric with respect to a virtual plane that passes through the central axis of the worm shaft and is orthogonal to the axial direction of the worm wheel.

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