JP2013184502A - Electric power steering apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering apparatus capable of reducing sliding resistance between a member biasing a worm to a worm wheel and the worm moving in an axial direction, in a structure comprising a worm speed reducer having a worm shaft movable in the axial direction.SOLUTION: An electric power steering apparatus 1 includes: a worm speed reducer 19 including a worm 20 and a worm wheel 21; a first bearing 30 and a second bearing 31 supporting the worm 20; a housing 29 for receiving the worm speed reducer 19, the first bearing 30, and the second bearing 31; elastic rings 42, 43 elastically supporting the worm 20 in a manner movable in an axial direction X; and a biasing member 60. The biasing member 60 includes a base part 61 disposed on an inner circumferential surface 29A of the housing 29 and a biasing part 62 protruding in a convex shape from the base part 61 toward the second bearing 31. The worm 20 is biased toward the worm wheel 21 by the biasing member 62.

Description

  The present invention relates to an electric power steering apparatus.

  Patent Document 1 discloses an electric power steering apparatus in which a worm reduction gear is incorporated. The worm speed reducer includes a worm wheel fixed to the steering shaft and a worm shaft meshing with the worm wheel. Since the base end portion of the worm shaft is coupled to the rotating shaft of the electric motor, the rotation of the steering shaft can be assisted by transmitting the driving force of the electric motor from the worm shaft to the worm wheel.

The worm shaft is accommodated in the gear housing. In the gear housing, ball bearings are fitted on both ends of the worm shaft (the base end portion and the tip portion described above), and the worm shaft is rotatably supported by the ball bearings on both ends. .
Further, the ball bearing fitted on the tip of the worm shaft is movable so as to be close to and away from the worm wheel in the gear housing. A leaf spring whose surface is covered with an elastic body such as an elastomer is provided on the outer ring of the ball bearing on the side opposite to the worm wheel. The leaf spring biases the tip of the worm shaft toward the worm wheel via the ball bearing. As a result, the worm shaft is inclined with respect to the rotating shaft of the electric motor and the distance between the worm shaft and the worm wheel is reduced, so that the tooth surfaces of the worm shaft and the worm wheel are pressed against each other ( Preload is applied). Thereby, since the clearance gap between the tooth surfaces of a worm axis | shaft and a worm wheel becomes small, the rattling noise of a worm axis | shaft and a worm wheel can be suppressed.

JP 2007-270943 A

In the worm speed reducer of Patent Document 1, the worm shaft is spline-coupled to the rotating shaft of the electric motor at the base end portion, and is movable in the axial direction.
Here, since the leaf | plate spring which urges | biases the ball bearing externally fitted by the front-end | tip part of the worm shaft has thickness in the axial direction of a ball bearing, it is in surface contact with the said ball bearing. Therefore, the sliding resistance between the ball bearing (in other words, the worm shaft supported by the ball bearing) and the leaf spring is relatively large with the surface contact, so the worm shaft moves smoothly in the axial direction. Difficult to do.

  The present invention has been made under such background, and in a configuration including a worm reduction gear having a worm shaft movable in the axial direction, a member for urging the worm to the worm wheel, a worm moving in the axial direction, and An object of the present invention is to provide an electric power steering device capable of reducing the sliding resistance between the two.

  According to the first aspect of the present invention, there is provided a motor (18) for generating a driving force for steering the steering member (2), and a worm (movably connected to the motor via a joint (26)). 20) and a worm wheel (21) coupled to the steering member and meshing with the worm, a worm reduction gear (19) for decelerating the driving force generated by the motor and transmitting it to the steering member, and the worm Bearings (30, 31) that rotatably support, a housing (29) that houses the worm reducer and the bearing, and a first elastic body that elastically supports the worm so that it can move in the axial direction (X). (42, 43), a base portion (61) disposed on the inner peripheral surface (29A) of the housing, and a biasing portion (62) projecting convexly from the base portion toward the bearing or the worm. Hints, characterized in that it comprises a second elastic member for urging the worm to the worm wheel (60) by said biasing unit is an electric power steering device (1).

The invention according to claim 2 is characterized in that a friction reducing member for reducing friction between the bearing and the worm is provided on the surface of the urging portion. It is a steering device.
The invention according to claim 3 is characterized in that the second elastic body further includes a damper portion (63) that extends from the base portion toward the bearing or the worm and damps vibration of the worm. The electric power steering apparatus according to claim 1 or 2.

The invention according to claim 4 is characterized in that the urging portion is arranged at a position where it does not come off from the worm in the axial direction even if the worm moves in the axial direction. The electric power steering device according to any one of the above.
According to a fifth aspect of the present invention, the base portion is curved along the circumferential direction of the inner peripheral surface of the housing, and the urging portion is convex from the base portion toward the bearing or the worm. 5. The electric power steering according to claim 1, comprising a plurality of leaf springs bent so as to bulge out, wherein a plurality of circumferentially spaced intervals are provided in the base portion. 6. Device.

  In addition, in the above, the numbers in parentheses represent reference numerals of corresponding components in the embodiments described later, but the scope of the claims is not limited by these reference numerals.

  According to the first aspect of the present invention, in the second elastic body that urges the worm that can move in the axial direction toward the worm wheel, the urging portion that protrudes convexly toward the worm urges the worm. Yes. In this case, the tip of the convex urging portion contacts the worm (including a bearing supporting the worm) in a state close to a point contact or a line contact. Therefore, since the contact area between the tip of the convex urging portion and the worm (or bearing) is small, the member (second elastic body) for urging the worm to the worm wheel and the worm moving in the axial direction The sliding resistance can be reduced.

According to the second aspect of the present invention, the sliding resistance between the second elastic body and the worm can be further reduced by the friction reducing member provided on the surface of the urging portion.
According to the third aspect of the present invention, not only the sliding resistance between the second elastic body and the worm can be reduced but also the vibration of the worm can be attenuated by the second elastic body.
According to the invention of claim 4, even if the worm moves in the axial direction, the second elastic body can always urge the worm toward the worm wheel at the urging portion.

  According to the fifth aspect of the present invention, the urging portion can be simply configured by the leaf spring, and the worm is reliably directed toward the worm wheel by the plurality of urging portions provided at intervals in the circumferential direction. Can be energized.

FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus 1 according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing the configuration of the worm speed reducer 19 provided in the electric power steering apparatus 1 of FIG. 1 and the vicinity thereof. 3A is a perspective view of the urging member 60, and FIG. 3B is a view of the urging member 60 as viewed from the front. 4 is a cross-sectional view taken along the line AA in FIG. FIG. 5 shows how the worm 20 moves in the axial direction in FIG. FIG. 6 is a perspective view of a biasing member 60 according to a modification. FIG. 7 is a cross-sectional view of a main part of the urging member 60 shown in FIG. FIG. 8 is a diagram in which a modification is applied to FIG.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus 1 according to an embodiment of the present invention. Referring to FIG. 1, an electric power steering apparatus 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, a pinion shaft 5 connected to the steering shaft 3 via an intermediate shaft 4, and a pinion shaft. And a rack bar 8 extending in the left-right direction of the automobile. The pinion shaft 5 and the rack bar 8 constitute a rack and pinion mechanism A as a steering mechanism. Note that not only the members described above, but also members newly described below are all part of the electric power steering apparatus 1.

The steering shaft 3 is divided into an input shaft 9 connected to the steering member 2 and an output shaft 10 connected to the intermediate shaft 4. The input shaft 9 and the output shaft 10 are connected via a torsion bar 11 so as to be relatively rotatable on the same axis.
The rack bar 8 is supported by the rack housing 12 so as to be linearly reciprocable via a plurality of bearings (not shown). Both ends of the rack bar 8 protrude to both sides of the rack housing 12, and steered wheels 14 are connected to the ends via tie rods 13 and knuckle arms (not shown).

By operating the steering member 2, the steering shaft 3 rotates. The rotation of the steering shaft 3 is converted into a linear reciprocating motion of the rack bar 8 in the left-right direction of the vehicle body via the pinion 6 and the rack 7. Thereby, the turning of the steered wheel 14 is achieved.
The steering torque applied to the steering member 2 is detected by a torque sensor 15 provided in the vicinity of the steering shaft 3 based on the relative rotational displacement amount between the input shaft 9 and the output shaft 10. The torque value detected by the torque sensor 15 is given to an ECU (Electronic Control Unit) 16. The ECU 16 drives and controls the steering assist motor 18 via the drive circuit 17 based on a torque value, a vehicle speed given from a vehicle speed sensor (not shown), or the like.

  The driving force generated by the motor 18 under the control of the ECU 16 is decelerated by the worm reducer 19 and transmitted to the output shaft 10 (in other words, the steering member 2) of the steering shaft 3. The force transmitted to the output shaft 10 is transmitted to the rack bar 8 via the pinion shaft 5. This assists steering. Thus, the motor 18 generates a driving force for steering the steering member 2.

  FIG. 2 is a cross-sectional view showing the configuration of the worm speed reducer 19 provided in the electric power steering apparatus 1 of FIG. 1 and the vicinity thereof. Referring to FIG. 2, the worm reduction gear 19 includes a worm 20 that is rotationally driven by a motor 18 and a worm wheel 21 that meshes with the worm 20. A meshing region M between the worm 20 and the worm wheel 21 is filled with a lubricant such as grease.

The worm 20 is a shaft-like body, and integrally includes a first end 22, a second end 23, and a worm main body 24 between the first end 22 and the second end 23. ing. The first end 22 and the second end 23 are reduced in diameter by one step with respect to the worm body 24. On the outer peripheral surface of the worm body 24, spiral teeth 24A centering on the axial center of the worm 20 are formed.
The first end 22 is located closer to the motor 18 than the second end 23, and is connected substantially coaxially to the rotating shaft 25 of the motor 18 via a joint 26. As a result, the output of the motor 18 is transmitted to the worm 20.

  The joint 26 includes a first member 26A coupled to the rotary shaft 25 of the motor 18 so as to be integrally rotatable, a second member 26B coupled to the first end 22 of the worm 20 so as to be integrally rotatable, and a first member 26A. And an elastic member 26C for connecting the second member 26B so as to transmit torque. By bending the elastic member 26 </ b> C, the worm 20 can be inclined to some extent while maintaining a connected state with respect to the rotating shaft 25. That is, the worm 20 is connected to the rotating shaft 25 of the motor 18 through the joint 26 so as to be swingable.

  The worm wheel 21 has a disk shape. The worm wheel 21 includes an annular synthetic resin member 27 coupled to the output shaft 10 so as to be integrally rotatable, and an annular metal member 28 surrounding the synthetic resin member 27. On the outer periphery of the metal member 28, teeth 28A are formed. For example, the metal member 28 is inserted into a mold when the synthetic resin member 27 is molded. The worm wheel 21 is connected to the output shaft 10 (in other words, the steering member 2) in the synthetic resin member 27 so as to be integrally rotatable and not movable in the axial direction.

The teeth 24A of the worm body 24 of the worm 20 and the teeth 28A on the outer periphery of the metal member 28 of the worm wheel 21 mesh with each other. In this state, the worm 20 extends along the tangential direction of the worm wheel 21. The meshed worm 20 and worm wheel 21 are accommodated in a housing 29.
The housing 29 is formed with a first housing space 51 for housing the worm 20 and a second housing space 52 for housing the worm wheel 21. The first accommodation space 51 is a cylindrical space extending along the worm 20 that is slightly larger than the worm 20. Therefore, a cylindrical inner peripheral surface 29 </ b> A that defines the first accommodation space 51 is formed in the housing 29. The second accommodating space 52 is a disk-shaped space that is slightly larger than the worm wheel 21. The second storage space 52 communicates with a middle portion 51A in the axial direction of the first storage space 51 (same as the axial direction X of the worm 20). In the worm 20 housed in the first housing space 51, the worm body 24 is disposed in the middle portion 51 </ b> A of the first housing space 51. The first end 22 of the worm 20 is disposed on the side closer to the rotating shaft 25 of the motor 18 than the midway part 51A in the first accommodating space 51 (the right side in FIG. 2). In the first accommodating space 51, the second end 23 is disposed on the side farther from the rotation shaft 25 of the motor 18 than the midway portion 51 </ b> A (left side in FIG. 2).

  A first bearing 30 is attached to the first end 22 of the worm 20. A second bearing 31 is attached to the second end 23 of the worm 20. For example, rolling bearings are used as the first bearing 30 and the second bearing 31. The first bearing 30 and the second bearing 31 support the worm 20 rotatably at the first end 22 and the second end 23. The first bearing 30 and the second bearing 31 are accommodated in the first accommodation space 51 of the housing 29 in a state of being coaxial with the worm 20.

  The inner ring 32 of the first bearing 30 is externally fitted to the outer peripheral surface 22A of the first end 22 so as to be integrally rotatable. The outer ring 33 of the first bearing 30 is supported by the inner peripheral surface 29 </ b> A that defines the first accommodation space 51 in the housing 29. Here, convex portions 53 are provided on both sides of the outer ring 33 in the axial direction X on the inner peripheral surface 29A. The first bearing 30 is fixed to the inner peripheral surface 29 </ b> A so as not to move in the axial direction X by the outer ring 33 being sandwiched between the convex portions 53 on both sides in the axial direction X.

  On the outer peripheral surface 22A of the first end portion 22, a fitting groove 40 is formed at a position sandwiched between the first bearing 30 and the joint 26. The fitting groove 40 has a positioning rib from the outside in the radial direction. 41 is fitted and integrated with the first end 22. The positioning rib 41 protrudes from the fitting groove 40. An elastic ring 42 (first elastic body) is interposed between the first bearing 30 and the worm main body 24 in the axial direction X, and between the first bearing 30 and the positioning rib 41 in the axial direction X. The elastic ring 43 (first elastic body) is interposed. The elastic rings 42 and 43 are both annular bodies formed of an elastic body such as rubber, and are externally fitted to the first end portion 22. The elastic rings 42 and 43 may be loosely fitted to the first end portion 22 and may be slightly moved in the radial direction.

  The outer peripheral surface 22 </ b> A of the first end 22 of the worm 20 can slide along the axial direction X with respect to the inner peripheral surface of the inner ring 32 of the first bearing 30. As a result, the entire worm 20 can move in the axial direction X. The movement range of the worm 20 is a range in which the elastic rings 42 and 43 can be compressed and deformed. Specifically, when the worm 20 moves to the rotating shaft 25 side (the right side in FIG. 2) of the motor 18, the elastic ring 42 is compressed by the worm body 24 and the first bearing 30, so that the elastic ring 42 is maximized. The worm 20 can move toward the rotating shaft 25 until it can be compressed. On the other hand, when the worm 20 moves to the side away from the rotating shaft 25 of the motor 18 (left side in FIG. 2), the elastic ring 43 is compressed by the positioning rib 41 and the first bearing 30, so that the elastic ring 43 is maximized. The worm 20 can move away from the rotary shaft 25 until it can be compressed. The position of the worm 20 (in the axial direction X) before moving is the “home position”. When the worm 20 moves from the home position, the elastic rings 42 and 43 compressed at that time are urged to return to the home position by attempting to restore the original size. Thus, the elastic rings 42 and 43 elastically support the worm 20 so that it can move in the axial direction X.

  The inner ring 38 of the second bearing 31 is externally fitted to the outer peripheral surface 23A of the second end 23 so as to be integrally rotatable. Here, in the inner peripheral surface 29 </ b> A that divides the first accommodation space 51 in the housing 29, a groove 54 is formed over the entire circumference in a portion facing the outer ring 39 of the second bearing 31 from the radially outer side. Yes. Therefore, in a state where the worm 20 and the worm wheel 21 are engaged with each other, the second bearing 31 is in the same position as the groove 54 in the axial direction X and is separated from the inner peripheral surface 29A (in the groove 54) of the housing 29. (Floating). The second bearing 31 can move in the axial direction X along with the worm 20.

Here, in the groove 54, an urging member 60 (second elastic body) is provided in a region (upper region in FIG. 2) Y on the side opposite to the worm wheel 21 side (the side opposite to the worm wheel 21). Has been placed.
3A is a perspective view of the urging member 60, and FIG. 3B is a view of the urging member 60 as viewed from the front. 4 is a cross-sectional view taken along the line AA in FIG. FIG. 5 shows how the worm 20 moves in the axial direction in FIG.

With reference to FIG. 3, the urging member 60 integrally includes a base portion 61 and a plurality of urging portions 62. The entire urging member 60 is configured by bending a leaf spring (which may be made of metal such as spring steel or resin). Therefore, the urging member 60 can be simply configured by a leaf spring.
The base portion 61 is configured by bending an elongated strip-shaped leaf spring into an arc shape. In this embodiment, the circumferential length of the base portion 61 is a half circumference of a circle (see FIG. 3B), but the length can be arbitrarily changed.

  Each urging portion 62 is configured by bending an elongated strip-shaped leaf spring into an arc shape. The plurality of (here, five) urging portions 62 are connected to one end edge 61 </ b> A in the width direction of the base portion 61, and are arranged at intervals in the circumferential direction of the base portion 61. Of the multiple (here, five) urging portions 62, one urging portion 62 is arranged as a reference urging portion 62A at the center position in the circumferential direction of the base portion 61, and the remaining urging portions 62B are Further, the reference urging portions 62A are equally arranged at equal intervals on both sides (right and left sides in FIG. 3B). The total number of urging units 62 can be set arbitrarily. However, the number of urging parts 62B on both sides of the reference urging part 62A is preferably the same (in the case of FIG. 3, two on each side of the reference urging part 62A), and the total number of urging parts 62 is It becomes an odd number of 3 or more. On each of both sides of the reference urging portion 62A, the urging portion 62B is arranged in a region of 30 ° to 60 ° in the circumferential direction of the base portion 61 from the reference urging portion 62A.

Each urging portion 62 extends from the one end edge 61A of the base portion 61 to the inside in the radial direction of the base portion 61 while extending outward in the axial direction of the base portion 61. It extends to. Therefore, when viewed from the circumferential direction of the base portion 61, the urging portion 62 has a substantially J-shaped claw shape that hangs radially inward from one end edge 61 </ b> A of the base portion 61.
Such an urging member 60 is disposed in the region Y on the opposite side of the worm wheel 21 in the groove 54 described above. As shown in FIG. 4, in the biasing member 60, the base portion 61 is coaxial with the inner peripheral surface 29 </ b> A of the housing 29 in the groove 54, the second bearing 31, and the worm 20. The inner circumferential surface 29A (the bottom 54A of the groove 54) is in surface contact from the radially inner side. In addition, in FIG. 4, the rolling element 80 of the 2nd bearing 31 is illustrated.

  As described above, the base portion 61 is disposed on the inner peripheral surface 29A of the groove 54 and is curved along the circumferential direction of the inner peripheral surface 29A. Each urging portion 62 protrudes (bulges) from the base portion 61 toward the second bearing 31, and at the tip 62C (the portion farthest from the base portion 61 to the second bearing 31), The outer peripheral surface of the outer ring 39 of the second bearing 31 is in contact with the outer side in the radial direction. In particular, in the urging portion 62, the above-described reference urging portion 62A is disposed on a reference line Z (see FIG. 1) passing through the axial center (core) of the worm 20 and the axial center (core) of the worm wheel 21. ing. The reference line Z extends along the center-to-core direction between the worm 20 and the worm wheel 21.

  In this state, referring to FIG. 2, the urging member 60 is compressed between the outer ring 39 of the second bearing 31 and the bottom 54 </ b> A of the groove 54, and each urging portion 62 is compressed at the bottom of the groove 54. It is bent to the 54A side (direction away from the worm wheel 21). That is, a preload is applied to the urging member 60 between the second bearing 31 and the housing 29. At this time, the edge 62D (edge farthest from the base portion 61) of each urging portion 62 is spaced radially inward from the bottom 54A (inner peripheral surface 29A) of the groove 54. Therefore, each urging part 62 can bend freely even in a state where preload is applied.

  Each urging portion 62 that is bent presses the outer ring 39 of the second bearing 31 from the outside in the radial direction by trying to return to the original shape. The force with which each urging portion 62 presses the outer ring 39 of the second bearing 31 is directed toward the center of curvature of the base portion 61 (corresponding to the center of the axis of the second bearing 31 or the worm 20) (FIG. 3A). (See the dashed arrow in) When the force that each urging portion 62 presses the outer ring 39 of the second bearing 31 is combined, the resultant force becomes a force toward the worm wheel 21 as shown by a thick arrow in FIG. The 20 second end 23 is urged toward the worm wheel 21 side. As a result, the worm 20 is slightly inclined with the first end 22 as a fulcrum so that the second end 23 approaches the worm wheel 21 side. As a result, the worm body 24 of the worm 20 is urged toward the metal member 28 of the worm wheel 21, so that the backlash between the teeth 24 </ b> A of the worm 20 and the teeth 28 </ b> A of the worm wheel 21 is reduced. Therefore, the rattling noise between the worm 20 and the worm wheel 21 on the teeth 24A and the teeth 28A can be suppressed.

Thus, the urging member 60 urges the worm 20 toward the worm wheel 21 by the convex urging portions 62. In particular, the worm 20 can be reliably urged toward the worm wheel 21 by a plurality of urging portions 62 (see FIG. 3) provided at intervals in the circumferential direction.
However, in a state where the worm 20 is urged to the worm wheel 21 (a state where a preload is applied to the worm 20), although the rattling noise between the teeth 24A and the teeth 28A can be suppressed, the friction between the teeth 24A and the teeth 28A Therefore, the rotation of the worm wheel 21 becomes dull and the steering feeling of the steering member 2 may be reduced accordingly.

  Thus, the entire worm 20 (including the second bearing 31) can move in the axial direction X as shown in FIG. As a result, the worm 20 in a state of being urged to the worm wheel 21 moves appropriately in the axial direction X, thereby suppressing an increase in friction between the teeth 24A and the teeth 28A, and the teeth between the teeth 24A and the teeth 28A. The hitting sound can be suppressed. In FIG. 5, a part of the outline of the second end portion 23 and the second bearing 31 when the worm 20 moves in the direction farthest away from the rotating shaft 25 of the motor 18 (left side in FIG. 5) is indicated by a broken line. A part of the contour of the second bearing 31 when the worm 20 moves in the direction closest to the rotating shaft 25 (the right side in FIG. 5) is indicated by a one-dot chain line.

When the worm 20 is moving in the axial direction X, the outer peripheral surface of the outer ring 39 of the second bearing 31 moves relative to the tip 62C of each urging portion 62 of the urging member 60 in the axial direction X. The outer peripheral surface of 39 and the tip 62C of each urging portion 62 slide on each other.
Here, even if the worm 20 moves in the movement range in the axial direction X, the tip 62C of each urging portion 62 of the urging member 60 is always against the outer peripheral surface of the outer ring 39 of the second bearing 31. So that they come into contact from the outside in the radial direction. In other words, each urging portion 62 is disposed at a position that does not come off from the second bearing 31 (in other words, the worm 20 supported by the second bearing 31) in the axial direction X even if the worm 20 moves in the axial direction X. Has been. Specifically, when the worm 20 is in the home position described above, the tip 62 </ b> C of each urging portion 62 is in contact with the approximate center in the axial direction X of the outer peripheral surface of the outer ring 39 of the second bearing 31. Therefore, even if the worm 20 moves in any of the axial directions X, each urging portion 62 is in contact (pressing) with the second bearing 31, so that the worm body portion 24 of the worm 20 is a metal member of the worm wheel 21. The state of being biased to 28 is maintained (see the bold arrow in FIG. 5). That is, even when the worm 20 moves in the axial direction X, the urging member 60 can always contact the second bearing 31 at the urging portion 62 and urge the worm 20 toward the worm wheel 21. it can.

  As described above, in the urging member 60 that urges the worm 20 that can move in the axial direction X toward the worm wheel 21, the urging portion 62 that protrudes in a convex shape toward the worm 20 urges the worm 20. ing. In this case, the tip 62C of the convex urging portion 62 contacts the outer ring 39 of the second bearing 31 in a state close to point contact or line contact (point contact when viewed in the axial direction X). Therefore, since the contact area between the tip 62C of the convex urging portion 62 and the second bearing 31 is small, the member that urges the worm 20 toward the worm wheel 21 (the urging member 60) moves in the axial direction X. The sliding resistance with the second bearing 31 (in other words, the worm 20 supported by the second bearing 31) can be reduced.

  Here, the friction reducing member 70 that reduces the friction with the second bearing 21 (worm 20) is provided on the surface of the urging portion 62 (particularly, the surface facing the outer peripheral surface of the outer ring 39 of the second bearing 31). Is provided. Examples of the friction reducing member 70 include a coating layer of fluorine or DLC (diamond-like carbon) and grease. The friction reducing member 70 covers the surface of the urging portion 62. Therefore, the sliding resistance between the urging member 60 and the second bearing 31 can be further reduced by the surface treatment of the urging portion 62 using the friction reducing member 70.

As described above, the worm 20 is urged toward the worm wheel 21 by the urging member 60 having a simple configuration in which the leaf spring is bent, and the worm 20 is moved in the axial direction X while suppressing the aforementioned rattling noise. It can also be supported so as to be able to reduce the friction between the teeth 24A and the teeth 28A due to the above-described decrease in steering feeling.
Further, the urging member 60 always contacts the outer peripheral surface of the outer ring 39 of the second bearing 31 only at a predetermined number of contact positions (that is, the tip 62C of each urging portion 62) (see FIG. 4). Thereby, wear of the urging portion 62 can be suppressed, and the load by which the urging member 60 urges the worm 20 toward the worm wheel 21 can be stabilized.

Therefore, the suppression of the rattling noise and the improvement of the steering feeling can be realized at low cost by the biasing member 60 having a simple configuration.
The present invention is not limited to the embodiment described above, and various modifications can be made within the scope of the claims.
For example, the biasing member 60 can be modified as follows.

FIG. 6 is a perspective view of a biasing member 60 according to a modification. FIG. 7 is a cross-sectional view of a main part of the urging member 60 shown in FIG. FIG. 8 is a diagram in which a modification is applied to FIG.
The urging member 60 may further include a damper part 63 as shown in FIG. 6 in addition to the base part 61 and the urging part 62 described above. A plurality of damper portions 63 are provided so as to be symmetric with respect to the above-described reference urging portion 62A. That is, the same number of damper portions 63 (one in FIG. 6) are equally arranged on both sides of the reference urging portion 62A. Further, in the circumferential direction of the base portion 61, the damper portions 63 and the urging portions 62 may be alternately arranged at equal intervals.

Each damper part 63 is a block comprised by elastic bodies, such as rubber | gum. As shown in FIG. 7, the cross section of the damper portion 63 when viewed from the circumferential direction of the base portion 61 has a semicircular shape that bulges toward the radially inner side of the base portion 61 (lower side in FIG. 7). ing. The damper part 63 is fixed to the inner peripheral surface 61B of the base part 61 by vulcanization adhesion or the like.
As shown in FIG. 8, in a state where the urging member 60 is disposed in the region Y on the opposite side of the worm wheel 21 in the groove 54, each damper portion 63 is moved from the base portion 61 of the urging member 60. The two bearings 31 extend toward the outer ring 39 and are compressed between the base portion 61 and the outer ring 39 to be preloaded. For example, the worm 20 may vibrate due to a sudden external force. In this case, the vibration of the worm 20 is attenuated by compressing or expanding each damper portion 63 to which the preload is applied. That is, the urging member 60 can not only reduce the sliding resistance between the urging member 60 and the second bearing 31, but can also attenuate the vibration of the worm 20.

  In the embodiment described above, the urging member 60 urges the worm 20 toward the worm wheel 21 via the second bearing 31 by the urging portion 62 coming into contact with the second bearing 31 that supports the worm 20. However, the urging portion 62 may be in direct contact with the worm 20. In that case, the urging member 60 urges the worm 20 toward the worm wheel 21 at the urging portion 62 without using the second bearing 31. At this time, each urging portion 62 protrudes (bulges) toward the worm 20 (particularly the second end portion 23), and each damper portion 63 also extends toward the worm 20.

However, when the urging portion 62 is in contact with the second bearing 31 instead of the worm 20, smooth rotation of the worm 20 can be prevented from being hindered by friction between the urging portion 62 and the worm 20.
Moreover, although the base part 61 of the urging member 60 has an arc shape, it may have an annular shape that is not interrupted. In the case where the base portion 61 is annular, the urging portion 62 may be disposed in a region of the base portion 61 that is biased away from the worm wheel 21.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 2 ... Steering member, 18 ... Motor, 19 ... Worm speed reducer, 20 ... Worm, 21 ... Worm wheel, 26 ... Joint, 29 ... Housing, 29A ... Inner peripheral surface, 30 ... 1st bearing , 31 ... second bearing, 42 ... elastic ring, 43 ... elastic ring, 60 ... biasing member, 61 ... base part, 62 ... biasing part, 63 ... damper part, 70 ... wear reducing member, X ... axial direction

Claims (5)

A motor for generating a driving force for steering the steering member;
A worm coupled to the motor via a joint so as to be swingable, and a worm wheel coupled to the steering member and meshing with the worm, and the driving force generated by the motor is decelerated and transmitted to the steering member A worm speed reducer,
A bearing that rotatably supports the worm;
A housing for housing the worm reducer and the bearing;
A first elastic body that elastically supports the worm so as to be movable in the axial direction;
A base portion disposed on an inner peripheral surface of the housing; and a biasing portion projecting convexly from the base portion toward the bearing or the worm, and the worm is moved to the worm wheel by the biasing portion. An electric power steering device comprising: a second elastic body biased toward the second power body.   The electric power steering apparatus according to claim 1, wherein a friction reducing member that reduces friction between the bearing and the worm is provided on a surface of the urging portion.   3. The electric power according to claim 1, wherein the second elastic body further includes a damper portion that extends from the base portion toward the bearing or the worm and damps vibration of the worm. 4. Steering device.   The electric power according to any one of claims 1 to 3, wherein the urging portion is disposed at a position where the worm does not come off the worm in the axial direction even if the worm moves in the axial direction. Steering device. The base portion is curved along the circumferential direction of the inner peripheral surface of the housing,
The urging portion includes a leaf spring bent so as to bulge out from the base portion toward the bearing or the worm, and a plurality of the urging portions are provided at intervals in the circumferential direction in the base portion. The electric power steering device according to any one of claims 1 to 4, wherein

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