JP2018194147A - Worm gear speed reducer - Google Patents

Abstract

To attain a structure capable of making an energization direction of an energization member always consistent with an engagement direction between a worm wheel and a worm shaft.SOLUTION: A worm gear speed reducer is configured to cause a pressing member 41 constituting an energization member 20 to press an energization member body 40 in an axis direction, to press against an outer peripheral surface of a second bearing 20 a pressing surface 48 directly provided on the energization member body 40, to energize a one-side lateral part in the axis direction of a worm shaft 17 in a direction of approaching a worm wheel. The pressing surface 48 is arranged in parallel with a second virtual plane P2 containing a central axis Oof a worm wheel 18, of a virtual plane orthogonal to a first virtual plane P1 passing through each of an engagement part M between a worm gear 25 and a worm wheel gear part 27 and the central axis Oof the worm wheel 18.SELECTED DRAWING: Figure 4

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 to 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. Among these, the electric power steering device can be configured to be smaller and lighter than the hydraulic power steering device, and it has advantages such as easy control of the size of auxiliary power and less power loss of the engine. It has become.

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

  However, because there is an inevitable backlash at the meshing part of the worm wheel and 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.

  Japanese Patent Application Laid-Open No. 2009-287647 discloses a spring between a bearing disposed on the tip side of a worm shaft and a housing among a pair of bearings for rotatably supporting the worm shaft with respect to 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 2009-287647 A

  By the way, in the structure in which the tip of the worm shaft is urged toward the worm wheel by the spring constituting the urging member, the pressing direction by the spring and the meshing direction of the worm shaft and the worm wheel are determined by elastic deformation of the spring. Regardless, it is difficult to always place them on the same straight line. For this reason, the bearing arranged on the tip side of the worm shaft is pressed against the inner surface of the housing or the like by the pressing force of the spring constituting the biasing member. As a result, the worm shaft may not be sufficiently biased toward the worm wheel.

  The present invention has been made in view of the circumstances as described above, and the urging direction by the urging member and the meshing direction of the worm shaft and the worm wheel can always be arranged on the same straight line. The purpose is to realize the structure of the worm reducer.

The worm speed reducer of the present invention includes a housing, a worm shaft, a worm wheel, a first bearing, a second bearing, and an urging member.
The worm shaft is disposed inside the housing, and has one axial end connected to the motor output shaft of the electric motor so that the worm shaft can swing.
The worm wheel is disposed inside the housing and meshes with the worm shaft.
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 via the second bearing, and the meshing portion of the worm shaft and the worm wheel; Of the virtual planes orthogonal to the first virtual plane that respectively pass through the central axis of the worm wheel, the second virtual plane including the central axis of the worm wheel has a central axis that is inclined, and inside the housing An urging member main body arranged to be movable in the direction of the central axis inclined with respect to the second imaginary plane, a pressing member that presses the urging member main body in the axial direction, and an outer peripheral surface of the second bearing. A pressing surface parallel to the second virtual plane to be pressed;

In the present invention, the pressing surface can be provided directly on the biasing member main body.
Alternatively, in the present invention, the urging member may have a structure further including a leaf spring fixed to the urging member body, and the pressing surface may be provided on the leaf spring.

  According to the present invention, the urging direction by the urging member and the meshing direction of the worm shaft and the worm wheel can always be arranged on the same straight line.

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 diagram corresponding to FIG. 4 and showing a second 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 guide member 21, and an urging member 22.

  The worm shaft 17 has a first support shaft portion 23 on one side in the axial direction and a second support shaft portion 24 on the other side in the axial direction. A worm tooth portion 25 is provided at an intermediate portion in the axial direction between the support shaft portion 24 and the support shaft portion 24. Such a worm shaft 17 is arranged inside a bottomed cylindrical worm shaft housing portion 26 constituting the housing 9. The base end, which is one end in the axial direction of the worm shaft 17, can transmit a rotational force to the motor output shaft 15 a of the electric motor 15 by spline engagement or the like. Oscillating displacement is connected. Note that the end of the worm shaft 17 on one side in the axial direction is connected to the motor output shaft 15a via a connecting member that enables transmission of other rotational force such as a torque transmission joint provided with an elastic body. It is also possible to connect the shafts so as to be able to swing.

  The worm wheel 18 has a worm wheel tooth portion 27 that meshes with the worm tooth portion 25 on the outer peripheral surface, and is fixed to the output shaft 11. Such a worm wheel 18 is disposed inside a cylindrical worm wheel housing portion 28 that constitutes 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 housing portion 26 is formed in a concave cylindrical surface shape, and a part in the circumferential direction of the axial intermediate portion opens into the worm wheel housing portion 28. Therefore, the internal space of the worm shaft housing portion 26 and the internal space of the worm wheel housing portion 28 are connected to each other.

  The first bearing 19 is a single-row deep groove type or a four-point contact type ball bearing, and includes an annular inner ring 29 and an outer ring 30, and a plurality of balls 31. Among these, the inner ring 29 is fitted and fixed to the first support shaft portion 23 of the worm shaft 17, while the outer ring 30 is fixed to the opening portion of the worm shaft housing portion 26. Further, the first bearing 19 has a radial gap between the inner ring 29 and the outer ring 30 and the ball 31. In this example, the 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 23 of the worm shaft 17. Therefore, the worm shaft 17 is supported so as to be swingable with respect to the worm shaft housing portion 26 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 32 and an outer ring 33, and a plurality of balls 34. Of these, the inner ring 32 is fitted and fixed to the second support shaft portion 24 of the worm shaft 17, while the outer ring 33 is a guide member that is fitted and fixed to the inner portion of the worm shaft accommodating portion 26. 21 is disposed inside.

  The guide member 21 is made of, for example, a synthetic resin and has a substantially U shape as a whole. The guide member 21 is fitted and fixed inside the worm shaft housing portion 26 by press fitting. The guide member 21 has a partially cylindrical bottom plate portion 35 and an X direction (vertical direction in FIG. 4) that coincides with the meshing direction of the worm tooth portion 25 and the worm wheel tooth portion 27 from both ends of the bottom plate portion 35. It has a pair of extended side plate portions 36a, 36b. The outer peripheral surface of such a guide member 21 is formed in a convex cylindrical surface shape. The X direction is a direction orthogonal to the axial direction of the worm shaft 17 and the axial direction of the worm wheel 18.

  The opposing surfaces of the pair of side plate portions 36a and 36b are each a flat surface and are a pair of guide surfaces 37a and 37b parallel to each other. The pair of guide surfaces 37 a and 37 b are arranged on both outer sides of the second bearing 20 with respect to the axial direction of the worm wheel 18 and in parallel with the X direction. The distance between the pair of guide surfaces 37 a and 37 b is slightly larger than the outer diameter of the second bearing 20. For this reason, the pair of guide surfaces 37 a and 37 b guide the movement in the X direction, which is the perspective movement of the second bearing 20 with respect to the worm wheel 18.

  The biasing member 22 biases the other axial side of the worm shaft 17 in the direction approaching the worm wheel 18 (downward in FIGS. 2 and 4) via the second bearing 20. It has a main body 40 and a pressing member 41. Such an urging member 22 is disposed inside the urging member accommodating portion 43 constituting the housing 9.

The urging member accommodating portion 43 is provided on the opposite side of the worm wheel accommodating portion 28 with respect to the worm shaft accommodating portion 26 (the upper side in FIGS. 2 and 4) and at a twisted position with respect to the worm shaft accommodating portion 26. It has been. The central axis O ₄₃ of the biasing member housing portion 43 is a first virtual plane P1 that passes through the meshing portion M of the worm tooth portion 25 and the worm wheel tooth portion 27 and the central axis O ₁₈ of the worm wheel 18 (see FIG. 2). of the virtual plane perpendicular to the, relative to the second imaginary plane including the center axis O ₁₈ of the worm wheel 18 P2 (see FIG. 2), is inclined by a predetermined angle α to the center axis O ₁₇ around the worm shaft 17 . The inner peripheral surface of the urging member accommodating portion 43 is configured as a concave cylindrical surface, and a part in the circumferential direction of the axial intermediate portion opens into the worm shaft accommodating portion 26. Therefore, the internal space of the biasing member housing portion 43 and the internal space of the worm shaft housing portion 26 are connected to each other. The urging member accommodating portion 43 is open only at one end (right side in FIG. 4) in the axial direction. A bottomed cylindrical lid member 44 is internally fitted or screwed to the opening of the biasing member accommodating portion 43.

The urging member main body 40 is generally formed in a rod shape, and the inner side of the urging member accommodating portion 43 is in a state where its own central axis O ₄₀ is aligned with the central axis O ₄₃ of the urging member accommodating portion 43. It is arranged to be able to move in the axial direction. Thus, the center axis O ₄₀ of the biasing member body 40, relative to the second imaginary plane P2 (see FIG. 2), is inclined by a predetermined angle α to the center axis O ₁₇ around the worm shaft 17. The inclination angle α is based on the meshing reaction force applied from the worm wheel 18 to the worm shaft 17, regardless of the pressing force acting on the urging member main body 40 from the second bearing 20. It can be set from 1 degree to 20 degrees, which is a size that does not move backward in the pressing direction of the pressing member 41 against the pressing force of 41, and is 8 degrees in the illustrated example. The biasing member main body 40 has an outer surface facing away from the worm shaft 17 in the X direction as a convex cylindrical surface 45 having a radius of curvature substantially equal to the radius of curvature of the inner peripheral surface of the biasing member accommodating portion 43. .

The urging member main body 40 has a cylindrical portion 46 on one side in the axial direction close to the lid member 44, and has a wedge portion 47 having a wedge-shaped cross section on the other axial side of the cylindrical portion 46. . A surface of the wedge portion 47 facing the worm shaft 17 side with respect to the X direction is a flat surface and is a pressing surface 48 parallel to the second virtual plane P2. Accordingly, the pressing surface 48 is inclined with respect to the central axis O ₄₀ of the urging member main body 40 in a direction approaching the worm shaft 17 toward the one side in the axial direction (the right side in FIG. 4). In this example, the pressing surface 48 and the pair of guide surfaces 37a and 37b are orthogonal to each other.

  The pressing member 41 is formed of a spring member such as a compression coil spring, for example, and is elastically compressed between the bottom surface of the cylindrical portion 46 of the biasing member main body 40 and the bottom surface of the bottomed cylindrical lid member 44. Are arranged. Thereby, the biasing member main body 40 is elastically pressed toward the other side in the axial direction. Therefore, the pressing direction by the pressing member 41 coincides with the axial direction of the urging member main body 40, the front side with respect to the pressing direction corresponds to the other axial direction of the urging member main body 40, and the rear side with respect to the pressing direction. This corresponds to one side of the urging member main body 40 in the axial direction. Further, most of the pressing member 41 is disposed inside the lid member 44 and the cylindrical portion 46.

  The biasing member 22 of the present example is a pressing surface provided directly on the biasing member main body 40 by pressing the biasing member main body 40 toward the other side in the axial direction (left side in FIG. 4) by the pressing member 41. 48 is pressed against the outer peripheral surface of the outer ring 33 constituting the second bearing 20. Then, the second support shaft portion 24 of the worm shaft 17 is urged through the second bearing 20 in a direction approaching the worm wheel 18, and the worm shaft 17 is supported by using the center of the first bearing 19 as a fulcrum. It is swung with respect to the accommodating portion 26. Accordingly, the worm tooth portion 25 is elastically pressed against the worm wheel tooth portion 27. As a result, it is possible to effectively prevent the occurrence of rattling noise at the meshing portion between the worm tooth portion 25 and the worm wheel tooth portion 27. Note that the pressing force of the pressing member 41 is appropriately adjusted so that the meshing resistance of the meshing portion between the worm tooth portion 25 and the worm wheel tooth portion 27 does not become excessively large.

Further, when wear occurs at the meshing portion between the worm tooth portion 25 and the worm wheel tooth portion 27, the position of the biasing member main body 40 is moved to the other side in the axial direction based on the pressing force by the pressing member 41. Here, the central axis O ₄₀ of the urging member main body 40 is inclined with respect to the second virtual plane P2 in a direction approaching the worm shaft 17 from the one side to the other side with respect to the axial direction of the urging member main body 40. Therefore, when the biasing member main body 40 moves to the other side in the axial direction, the contact position between the pressing surface 48 and the second bearing 20 moves to the side closer to the worm wheel 18 (lower side in FIG. 4). Can be made. 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.

  Furthermore, in this example, the pressing surface 48 is parallel to the second virtual plane P2. For this reason, the pressing surface 48 is orthogonal to the X direction, which is the meshing direction of the worm tooth portion 25 and the worm wheel tooth portion 27. Therefore, in this example, the outer peripheral surface of the second bearing 20 can be pressed in the X direction by the pressing surface 48. Further, since the pressing surface 48 is translated in the X direction when the urging member main body 40 is displaced in the axial direction, the outer peripheral surface of the second bearing 20 is moved along the X direction regardless of the elastic deformation of the pressing member 41. Can be pressed in the direction. That is, in this example, the urging direction by the urging member 22 and the meshing direction between the worm wheel 18 and the worm shaft 17, in other words, the direction of the meshing reaction force applied to the worm shaft 17 from the meshing portion are always the same. Can be placed on the line. Therefore, it is possible to prevent the second bearing 20 from being pressed toward the guide surfaces 37a and 37b by the urging by the urging member 22. As a result, the worm shaft 17 can be sufficiently biased toward the worm wheel 18, and the meshing state between the worm tooth portion 25 and the worm wheel tooth portion 27 can be improved.

  Further, in this example, when the meshing reaction force is applied from the worm wheel 18 to the worm shaft 17 and the worm shaft 17 moves away from the worm wheel 18, the second bearing 20 has a pair of guide surfaces. It is guided by 37a, 37b and moves in the X direction. In this example, such movement of the second bearing 20 can be supported by the pressing surface 48 arranged at right angles to the X direction.

[Second Example of Embodiment]
A second example of the embodiment will be described with reference to FIG. In this example, the urging member 22a is composed of an urging member main body 40a, a pressing member 41, and a leaf spring 49, and the pressing surface 48a that presses the outer peripheral surface of the second bearing 20 is used as the urging member. It is provided not on the main body 40a but on the leaf spring 49 fixed to the biasing member main body 40a.

The biasing member main body 40a of the present example is generally formed in a rod shape, and its central axis O _40a is the center of the worm wheel 18 in the virtual plane orthogonal to the first virtual plane P1 (see FIG. 2). for the second imaginary plane including the axis O ₁₈ P2 (see FIG. 2), is inclined by a predetermined angle α to the center axis O ₁₇ around the worm shaft 17.

  The urging member main body 40a has a cylindrical portion 46 on one side in the axial direction, and a semi-cylindrical portion 50 having a semicircular cross section in an axial intermediate portion adjacent to the other axial side of the cylindrical portion 46. And the mounting portion 51 is provided on the other axial side adjacent to the other axial side of the semi-cylindrical portion 50. Of the mounting portion 51, the surface facing the worm shaft 17 side in the X direction that coincides with the meshing direction of the worm tooth portion 25 (see FIG. 2) and the worm wheel tooth portion 27 (see FIG. 2) is flat. The mounting surface 52 is parallel to the second virtual plane P2.

The plate spring 49 is made of metal and is formed in a rectangular plate shape as a whole, and the plate thickness is constant over the entire length. Further, the base end portion of the leaf spring 49 on one side in the longitudinal direction (left side in FIG. 5) is fixed to the mounting surface 52 by mounting pins 53. For this reason, the leaf spring 49 is disposed along the mounting surface 52 in a free state. Therefore, the pressing surface 48a which is a surface of the leaf spring 49 facing the worm shaft 17 side with respect to the X direction is also parallel to the second virtual plane P2. Also in this embodiment, the pressing surface 48a approaches the biasing member body 40a with respect to the central axis O _{40 a} of the biasing member body 40a one axial side of the worm shaft 17 increases toward the (right side in FIG. 5) It is inclined in the direction by a predetermined angle α. The total length of the leaf spring 49 is restricted to such a length that the distal 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 axial side of the cylindrical portion 46. In addition, a cross section between the back surface of the leaf spring 49 and the semi-cylindrical portion 50 in a state where the end portion on the other side in the longitudinal direction of the leaf spring 49 is in contact with the end portion on the other side in the axial direction of the cylindrical portion 46. A trapezoidal gap 54 exists. The leaf spring 49 can be bent and deformed so that the intermediate portion in the longitudinal direction enters the gap 54.

  The biasing member 22a of this example is a leaf spring 49 fixed to the biasing member main body 40a by pressing the biasing member main body 40a toward the other side in the axial direction (left side in FIG. 5) by the pressing member 41. The pressing surface 48 a is pressed against the outer peripheral surface of the outer ring 33 constituting the second bearing 20. Also in this example, the pressing surface 48a is orthogonal to the X direction, which is the meshing direction of the worm tooth portion 25 and the worm wheel tooth portion 27. Therefore, the outer peripheral surface of the second bearing 20 can be pressed in the X direction by the pressing surface 48a. Further, when the urging member main body 40a is displaced in the axial direction, the pressing surface 48a moves in parallel in the X direction, so that the outer peripheral surface of the second bearing 20 is not affected by the elastic deformation of the pressing member 41. Can be pressed in the direction. That is, also in this example, the urging direction by the urging member 22a and the meshing direction of the worm wheel 18 and the worm shaft 17 can always be arranged on the same straight line. Therefore, it is possible to prevent the second bearing 20 from being pressed toward the guide surfaces 37a and 37b by urging by the urging member 22a. As a result, the worm shaft 17 can be sufficiently biased toward the worm wheel 18, and the meshing state between the worm tooth portion 25 and the worm wheel tooth portion 27 can be improved.

  Further, in this example, when the meshing reaction force is applied from the worm wheel 18 to the worm shaft 17, and the worm shaft 17 moves away from the worm wheel 18, the leaf spring 49 is bent and deformed by the second bearing 20. 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 25 and the influence of thermal expansion occurring in peripheral members such as the worm wheel 18. In this case, the leaf spring 49 can be bent and deformed to prevent the surface pressure of the meshing portion from becoming excessive. About another structure and an effect, it is the same as the 1st 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 Housing 10 Torsion bar 11 Output shaft 12a, 12b Rolling bearing 13 Pinion shaft 14 Torque sensor 15 Electric motor 16 Worm reducer 17 Worm shaft 18 Worm wheel 19 First bearing 20 Second bearing 21 Guide member 22, 22a Energizing member 23 First support shaft portion 24 Second support shaft portion 25 Warm tooth portion 26 Warm shaft housing portion 27 Warm wheel Tooth part 28 Worm wheel accommodating part 29 Inner ring 30 Outer ring 31 Ball 32 Inner ring 33 Outer ring 34 Ball 35 Bottom plate part 36a, 36b Side plate part 37a, 37b Guide surface 40, 40a Energizing member Body 41 pressing member 43 biasing member accommodating portion 44 lid member 45 protruding cylindrical surface 46 cylindrical portion 47 wedge 48,48a pressing surface 49 the leaf spring 50 semi-cylindrical portion 51 attachment portion 52 mounting surface 53 mounting pin 54 clearance

Claims (3)

A worm speed reducer comprising a housing, a worm shaft, a worm wheel, a first bearing, a second bearing, and an urging member,
The worm shaft is disposed inside the housing, and is connected to the motor output shaft of the electric motor at one end in the axial direction so that the worm shaft can swing.
The worm wheel is disposed inside the housing and meshes with the worm shaft;
The first bearing supports an axial one side portion of the worm shaft so as to be rotatable with respect to the housing,
The second bearing is rotatably supported on 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 via the second bearing, and the meshing portion of the worm shaft and the worm wheel; Of the virtual planes orthogonal to the first virtual plane that respectively pass through the central axis of the worm wheel, the second virtual plane including the central axis of the worm wheel has a central axis that is inclined, and inside the housing An urging member main body arranged to be movable in the direction of the central axis inclined with respect to the second imaginary plane, a pressing member that presses the urging member main body in the axial direction, and an outer peripheral surface of the second bearing. A worm speed reducer having a pressing surface parallel to the second virtual plane to be pressed.   The worm reduction gear according to claim 1, wherein the pressing surface is provided directly on the biasing member main body.   The worm speed reducer according to claim 1, wherein the biasing member further includes a leaf spring fixed to the biasing member main body, and the pressing surface is provided on the leaf spring.

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