JP2010254194A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device which can prevents the generation of noise by a simple structure over a long period of time, and is excellent in durability. <P>SOLUTION: The electric power steering device includes: a worm shaft 23 which is swingingly supported around its first end 27 by a first bearing 33 for rotatably supporting the first end 27; an elastic biasing member 25 for swinging the worm shaft 23 around the first end 27 by elastically biasing a second bearing 34 for supporting a second end 28 in a direction that shortens the center-to-center distance D1 between the worm shaft 23 and a worm wheel 24; and a joint 26 for connecting the first end 27 and the rotary shaft 32 of an electric motor 20 in a manner of transferring torque. The joint 26 includes: a regulation mechanism 54 for regulating the swing of the worm shaft 23 by acting on the first bearing 33 when the electric motor 20 is activated; and a deregulation mechanism 51 for removing the regulation of the regulation mechanism 54 when the electric motor 20 stops. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus.

Various electric power steering devices are known as vehicle steering devices (see, for example, Patent Documents 1 and 2).
In the electric power steering apparatus of Patent Document 1, a worm cylinder that is movable in the axial direction is externally fitted to a rotating shaft that is coupled to a drive shaft of an electric motor. In addition, a pair of elastic members that elastically urge the worm cylinder from both sides are fitted on the rotating shaft. Further, a torque cam mechanism is provided on both sides of the pair of elastic members to sandwich the worm cylinder from both sides via the elastic member in accordance with the increase in the rotational torque of the rotary shaft and to rotate the worm cylinder integrally with the rotary shaft. It has been.

In Patent Document 1, an appropriate backlash is secured by integrating the worm cylinder and the rotating shaft when the electric motor rotates, and the backlash is eliminated by the pressing force in the axial direction of the elastic member when the electric motor is stopped. I have to.
On the other hand, the electric power steering device of Patent Document 2 is provided with a biased portion in which a part of the teeth of the worm wheel is biased in the direction of reducing the backlash, and the backlash amount in the region near the steering neutral position is set to be larger than that in the remaining region. It is set small.

JP 2002-337703 A JP 2004-182013 A

In the above-mentioned Patent Document 1, the worm shaft is composed of two parts, a rotating shaft and a worm cylinder, and further provided with a pair of elastic members and a pair of torque cam mechanisms, so the structure is complicated. Moreover, in said patent document 2, there exists a possibility that a rattling sound (rattle sound) may generate | occur | produce when a biasing part wears and a backlash becomes large.
By the way, there is an electric power steering device that supports a worm shaft so that it can swing around one end thereof, and removes backlash by urging the worm shaft through an elastic member via the other end of the worm shaft.

As described above, in the system in which the worm shaft is swung to remove backlash, a high surface pressure is locally generated when torque is transmitted between the worm shaft and the worm wheel while the worm shaft is swung. This may cause uneven wear and reduce durability. Moreover, there is a risk that rattling noise (rattle noise) may be generated regardless of the oscillating bias due to the promotion of uneven wear.
SUMMARY OF THE INVENTION An object of the present invention is an electric power steering apparatus that removes backlash by swinging a worm shaft, and can prevent generation of noise over a long period of time with a simple structure and has excellent durability. Is to provide a device.

  To achieve the above object, the present invention has a first bearing (33) having first and second ends (27, 28) and rotatably supporting the first end. The distance between the center of the worm shaft and the worm wheel (24) is the worm shaft (23) supported so as to be swingable about the end portion and the second bearing (34) supporting the second end portion of the worm shaft. An elastic biasing member (25) that swings the worm shaft around the first end by elastically biasing (D1) in the direction of shortening, and the first end of the worm shaft And a rotary shaft (32) of the electric motor (20), and a joint (26, 226) that connects the torque shaft so that torque can be transmitted. The joint acts on the first bearing when the electric motor is driven to act on the worm shaft. The regulation mechanism (54, 254) that regulates the swing of the motor and Restriction release mechanism for releasing the restriction by the restricting mechanism (51) is an electric power steering apparatus characterized by comprising (1) (claim 1).

  According to the present invention, when the electric motor is stopped, the regulation of the worm shaft is released by the regulation release mechanism provided in the joint, so that a pressing force due to torque transmission is applied between the worm shaft and the worm wheel. The backlash between the worm shaft and the worm wheel can be removed by swinging the worm shaft with an elastic biasing force in a state where it does not act. Thereby, generation | occurrence | production of the rattle sound at the time of a straight drive can be prevented, for example.

In addition, since the worm shaft swing is restricted by a restriction mechanism provided in the joint when the electric motor is driven, the surface pressure between the worm shaft and the worm wheel during torque transmission does not increase locally. As a result, durability can be improved through prevention of uneven wear. Moreover, generation of rattle noise due to uneven wear can be prevented over a long period of time.
Furthermore, since the restriction mechanism and the restriction release mechanism are provided in the joint, the structure can be simplified.

  The first bearing includes an outer ring (38) that cannot move in the axial direction (X1), an inner ring (37) that can move in the axial direction (X1), and a rolling element (39). The first bearing has an internal gap (G1) for allowing the worm shaft to swing, and when the inner ring moves in the axial direction relative to the outer ring until the internal gap is removed, the worm shaft There is a case where the swing of the shaft is restricted (claim 2). In this case, by moving the worm shaft in the axial direction, the outer ring and the inner ring can be relatively moved in the axial direction, and the internal clearance of the first bearing can be removed. Thereby, the swing of the worm shaft can be restricted.

  The joint includes a first member (43, 243) coupled to the worm shaft so as to be capable of rotating together with a worm shaft, and a second member (44, 244) coupled to be capable of rotating together with the rotary shaft of the electric motor. A drive mechanism (54, 254) as the restricting mechanism for moving the worm shaft in the axial direction in accordance with a phase shift in the rotation direction of the first and second members may be included (claim 3). In this case, when the electric motor is driven, the phases of the rotation directions of the first and second members are shifted. The drive mechanism moves the worm shaft in the axial direction in accordance with the phase shift in the rotational direction of the first and second members. Thereby, the internal clearance of the first bearing is removed, and the swing of the worm shaft is restricted. The drive mechanism preferably includes a cam mechanism (54, 254).

  The deregulation mechanism includes an elastic member (51) that connects the first and second members, and the elastic member includes the first and second members so as to eliminate a phase shift between the first and second members. In some cases, an urging force is applied to the member. In this case, when the electric motor is stopped, torque from the electric motor acting on the first and second members disappears, so that the phases of the first and second members are matched by the biasing force of the elastic member. Thereby, the force from the drive mechanism is removed. Therefore, the internal clearance is secured again in the first bearing, and the restriction by the restriction mechanism is released.

  In the above description, the alphanumeric characters 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.

It is a mimetic diagram of a schematic structure of an electric power steering device concerning one embodiment of the present invention. It is an illustration figure of the speed reduction mechanism at the time of a stop of an electric motor, and the structure relevant to this. It is an illustration appearance figure of a joint at the time of a stop of an electric motor, and the composition relevant to this. It is an illustration fragmentary sectional view of a joint at the time of a stop of an electric motor, and the composition relevant to this. It is an illustration side view of the joint at the time of a stop of an electric motor, and the composition relevant to this. It is an illustration side view of the joint at the time of the drive of an electric motor, and the composition relevant to this. It is an illustration sectional view of the 1st bearing at the time of a stop of an electric motor. It is an illustration sectional view of the 1st bearing at the time of the drive of an electric motor. It is an illustration figure of the principal part of a deceleration mechanism. The state at the time of a stop of an electric motor is shown with the schematic side view of the coupling concerning a 2nd embodiment of the present invention, and the composition relevant to this. The state at the time of the drive of an electric motor is shown with the schematic side view of the coupling which concerns on 2nd Embodiment of this invention, and the structure relevant to this. The state at the time of a stop of an electric motor is shown with the schematic fragmentary sectional view of the joint concerning a 2nd embodiment of the present invention, and the composition relevant to this.

FIG. 1 is a schematic diagram of a schematic configuration of an electric power steering apparatus 1 according to an embodiment of the present invention. Below, with reference to FIG. 1, schematic structure of the electric power steering apparatus 1 is demonstrated.
The electric power steering device 1 is, for example, a so-called column assist type steering device. The electric power steering apparatus 1 includes a steering wheel 2 as a steering member, a steering shaft 3 coupled to the steering wheel 2, a rack and pinion mechanism 4 as a steering mechanism, and a steering assist mechanism that assists the driver's steering. And 5.

  The steering shaft 3 includes an input shaft 7 and an output shaft 8 that are connected to each other via a torsion bar 6 so as to be relatively rotatable. One end of the input shaft 7 is connected to the steering wheel 2, and one end of the output shaft 8 is connected to one end of the intermediate shaft 10 via the first universal joint 9. The other end of the intermediate shaft 10 is connected to the rack and pinion mechanism 4 through the second universal joint 11. The steering wheel 2 is connected to the rack and pinion mechanism 4 via the steering shaft 3, the intermediate shaft 10, and the like.

  When a steering torque is input to the steering wheel 2, the input shaft 7 and the output shaft 8 rotate in the same direction while relatively rotating. The steering torque input to the steering wheel 2 is detected by a torque sensor 12 disposed in the vicinity of the steering shaft 3. The torque sensor 12 detects a steering torque based on the relative rotational displacement amount of the input shaft 7 and the output shaft 8. The torque detection result of the torque sensor 12 is input to an ECU 13 (Electronic Control Unit).

  The rack and pinion mechanism 4 includes a pinion shaft 14 and a rack shaft 15. The steering wheel 2 is connected to the pinion shaft 14 via the steering shaft 3, the intermediate shaft 10, and the like. A steered wheel 17 is connected to each end of the rack shaft 15 via a tie rod 16 and a knuckle arm (not shown). The rotation of the steering wheel 2 is transmitted to the pinion shaft 14, and the rotation of the pinion shaft 14 is converted into an axial movement of the rack shaft 15 by the pinion 18 and the rack 19. The two steered wheels 17 are steered in conjunction with the movement of the rack shaft 15 in the axial direction.

  The steering assist mechanism 5 includes an electric motor 20, a speed reduction mechanism 21, and a gear housing 22 that houses the speed reduction mechanism 21. The speed reduction mechanism 21 includes a worm shaft 23 as a drive gear and a worm wheel 24 as a driven gear that meshes with the worm shaft 23. The worm shaft 23 is connected to the electric motor 20, and the worm wheel 24 is connected to the middle portion of the output shaft 8 so as to be able to rotate together. The rotation of the electric motor 20 is transmitted to the output shaft 8 via the worm shaft 23 and the worm wheel 24. Thereby, the rotation of the electric motor 20 is transmitted to the rack and pinion mechanism 4 to assist the driver's steering. The electric motor 20 is controlled by the ECU 13 based on a torque detection result of the torque sensor 12, a vehicle speed detection result of a vehicle speed sensor (not shown), and the like.

FIG. 2 is an illustrative view of the speed reduction mechanism 21 and the related configuration when the electric motor 20 is stopped. Hereinafter, the steering assist mechanism 5 will be described more specifically with reference to FIG.
The steering assist mechanism 5 includes the worm shaft 23 and the worm wheel 24, an elastic urging member 25 that elastically urges the worm shaft 23, and a joint 26 that connects the worm shaft 23 and the electric motor 20 so that torque can be transmitted. And. The worm shaft 23 includes a first end portion 27 and a second end portion 28, and a worm 29 disposed between the first end portion 27 and the second end portion 28. The worm shaft 23 is made of, for example, a material containing iron. The worm wheel 24 includes an annular core 30 connected to the output shaft 8 (see FIG. 1) so as to be able to rotate together, and a synthetic resin member 31 that surrounds the periphery of the core 30 and has teeth formed on the outer periphery thereof. Including. The core metal 30 is connected to the synthetic resin member 31 by insert molding, for example.

  The first end portion 27 of the worm shaft 23 is connected to the rotating shaft 32 of the electric motor 20 by a joint 26 so that torque can be transmitted. The first end portion 27 is rotatably supported by the first bearing 33. Further, the second end portion 28 of the worm shaft 23 is rotatably supported by the second bearing 34. The first bearing 33 and the second bearing 34 are respectively held by a first holding part 35 and a second holding part 36 provided in the gear housing 22. Therefore, the worm shaft 23 is rotatably supported by the gear housing 22 via the first bearing 33 and the second bearing 34.

  The first bearing 33 and the second bearing 34 are, for example, radial rolling ball bearings. The first bearing 33 includes a first inner ring 37, a first outer ring 38, and a first rolling element 39. The second bearing 34 includes a second inner ring 40, a second outer ring 41, and a second rolling element 42. The shapes and sizes of the first inner ring 37, the first outer ring 38, and the first rolling element 39 are set so that an internal gap is generated in the first bearing 33. The shapes and sizes of the second inner ring 40, the second outer ring 41, and the second rolling element 42 are set so that an internal gap is generated in the second bearing 34. As will be described later, when the electric motor 20 is stopped, an internal gap is secured in the first bearing 33 and the second bearing 34 (see FIG. 7).

The first inner ring 37 is connected to the first end portion 27 so as to be able to move along the axial direction X1 of the worm shaft 23. The first outer ring 38 is supported by the gear housing 22 so as not to move with respect to the axial direction X1 and the radial direction of the first outer ring 38.
On the other hand, the second inner ring 40 is connected to the second end portion 28 so as to be able to move along the axial direction X1 of the worm shaft 23. Further, the second outer ring 41 is supported so as to be movable in the second holding portion 36 in a predetermined direction A1 (up and down direction of the paper surface in FIG. 2). Therefore, the second outer ring 41 and the second end portion 28 of the worm shaft 23 can move in the second holding portion 36 in the predetermined direction A1. In a state where an internal clearance is secured between the first bearing 33 and the second bearing 34, the worm shaft 23 is supported so as to be swingable about the first end portion 27 with respect to the gear housing 22.

  The elastic biasing member 25 elastically biases the second bearing 34 in the predetermined direction A1 (see the arrow in FIG. 2). Examples of the elastic biasing member 25 include an elastic body made of synthetic rubber or synthetic resin, a spring such as a curved leaf spring, and a compression coil spring. The second end portion 28 of the worm shaft 23 is elastically urged by the elastic urging member 25 via the second bearing 34. When the electric motor 20 is stopped, the worm shaft 23 is oscillated and displaced about the first end portion 27 by the urging force of the elastic urging member 25. As a result, the center distance D1 between the worm shaft 23 and the worm wheel 24 is shortened, and the backlash of the meshing portion between the worm shaft 23 and the worm wheel 24 is temporarily removed under the condition that the electric motor 20 is stopped. .

FIG. 3 is an illustrative external view of the joint 26 and the related configuration when the electric motor 20 is stopped. FIG. 4 is a schematic partial cross-sectional view of the joint 26 and the configuration related thereto when the electric motor 20 is stopped. Hereinafter, the joint 26 will be described with reference to FIGS. 3 and 4.
The joint 26 includes a first member 43 that is connected to the first end portion 27 of the worm shaft 23 so as to be able to rotate together with the first member 27, and a second member 44 that is connected to the rotary shaft 32 of the electric motor 20 so as to be able to rotate together. including. The first member 43 includes a cylindrical first peripheral wall 45 and a disk-shaped first end wall 46 connected to one end of the first peripheral wall 45. The second member 44 includes a cylindrical second peripheral wall 47 and a disk-shaped second end wall 48 connected to one end of the second peripheral wall 47. The first member 43 is connected to the worm shaft 23 so as to be able to move along the axial direction X1 of the worm shaft 23.

  As shown in FIG. 3, a plurality of first chevron teeth 49 and a plurality of second chevron teeth 50 are formed at the other end portion of the first peripheral wall 45 and the other end portion of the second peripheral wall 47, respectively. Has been. The plurality of first chevron teeth 49 and the plurality of second chevron teeth 50 mesh with each other. As shown in FIG. 4, the first end wall 46 and the second end wall 48 are connected to each other so as to be relatively rotatable by an elastic member 51 as a restriction release mechanism. The elastic member 51 is made of, for example, a material containing synthetic rubber or synthetic resin.

The plurality of first chevron teeth 49 are arranged in the circumferential direction of the first peripheral wall 45. Each first chevron 49 protrudes in the axial direction of the first peripheral wall 45. Each first chevron 49 includes a pair of first inclined surfaces 52 inclined in opposite directions.
The plurality of second chevron teeth 50 are arranged in the circumferential direction of the second peripheral wall 47. Each second chevron tooth 50 projects in the axial direction of the second peripheral wall 47. Each second chevron tooth 50 includes a pair of second inclined surfaces 53 inclined in opposite directions. Each second inclined surface 53 is engaged with the corresponding first inclined surface 52. The torque transmitted from the electric motor 20 to the second member 44 is transmitted to the first member 43 via the engaging portions of the first inclined surface 52 and the second inclined surface 53.

  The first member 43 and the second member 44 are each made of a low friction material having a smaller friction coefficient than iron. Further, the first member 43 and the second member 44 each contain reinforcing fibers. Examples of the low friction material include nylon materials such as PA6, PA66, PA46, PA12, PA11, PA610, and PA612, aromatic nylons such as PPA, PA6, PA6T, and PA9T, PPS, POM, PET, PBT, PI, Examples include materials containing PAI and PEEK. Examples of the reinforcing fiber include CF (carbon fiber), GF (glass fiber), and AF (aramid fiber).

  FIG. 5 is a schematic side view of the joint 26 and the configuration related thereto when the electric motor 20 is stopped. FIG. 6 is a schematic side view of the joint 26 and the related configuration when the electric motor 20 is driven. Hereinafter, the operation of the joint 26 when the electric motor 20 is driven and when the electric motor 20 is stopped will be described with reference to FIGS. 5 and 6.

  When the electric motor 20 is driven, torque is transmitted to the second member 44. At this time, as shown in FIG. 6, the meshing of the first chevron teeth 49 and the second chevron teeth 50 is shifted in the rotational direction, and the phase in the rotational direction of the first member 43 and the second member 44 is shifted. . In this embodiment, since the first member 43 and the second member 44 are each formed of a low friction material, the phase in the rotational direction of the first member 43 and the second member 44 can be easily shifted. it can.

  Further, when the meshing of the first chevron 49 and the second chevron 50 is shifted in the rotational direction, the first member 43 is closer to the worm shaft 23 than the second member 44 as shown in FIG. Move in the axial direction X1. Further, as the first member 43 moves in the axial direction with respect to the second member 44, the elastic member 51 elastically extends in the axial direction X1. Furthermore, the elastic member 51 is elastically twisted around the central axis along with the phase shift in the rotational direction of the first member 43 and the second member 44. In this embodiment, the plurality of first chevron teeth 49 and the plurality of second chevron teeth 50 constitute a cam mechanism 54 as a restriction mechanism and a drive mechanism.

  On the other hand, when the drive of the electric motor 20 is stopped, the elastic member 51 causes the first member 43 and the second member 44 to eliminate the phase shift in the rotation direction of the first member 43 and the second member 44. Giving power to. More specifically, the first member 43 and the second member 44 rotate relative to each other by the restoring force generated by the elastic torsional deformation of the elastic member 51, and the rotation direction of the first member 43 and the second member 44. Are in phase. Further, the first member 43 is pulled toward the second member 44 by the restoring force generated by the elastic extension of the elastic member 51, so that the first member 43 approaches the second member 44. Move in direction X1. Thereby, the relative positional relationship between the first member 43 and the second member 44 is restored to the state before the electric motor 20 is driven.

FIG. 7 is a schematic cross-sectional view of the first bearing 33 when the electric motor 20 is stopped. FIG. 8 is a schematic sectional view of the first bearing 33 when the electric motor 20 is driven. Hereinafter, the operation of the first inner ring 37 when the electric motor 20 is driven and stopped will be described with reference to FIGS. 2, 7, and 8.
When the electric motor 20 is driven, the first member 43 moves in the axial direction X1 toward the worm shaft 23 with respect to the second member 44 as described above. Therefore, the worm shaft 23 connected to the first member 43 so as to be able to move along the axial direction X1 of the worm shaft 23 moves in the axial direction X1 of the worm shaft 23. Further, the first inner ring 37 connected to the first end portion 27 so as to be able to move along with the axial direction X1 of the worm shaft 23 moves in the axial direction X1 of the worm shaft 23. Therefore, when the electric motor 20 is driven, the first inner ring 37 and the first outer ring 38 are moved relative to each other in the axial direction X1 of the worm shaft 23 as shown in FIG. The internal gap G1 (see FIG. 7) that has been made is removed. Although not shown, when the worm shaft 23 moves in the axial direction X1, the second inner ring 40 connected to the second end portion 28 so as to be able to move along with the axial direction X1 of the worm shaft 23 is the axis of the worm shaft 23. Move in direction X1. Therefore, the second inner ring 40 and the second outer ring 41 move relative to each other in the axial direction X1 of the worm shaft 23, and the internal clearance secured in the second bearing 34 is removed.

FIG. 9 is an illustrative view of a main part of the speed reduction mechanism 21. Below, with reference to FIG. 2 and FIG. 9, the state of the worm shaft 23 at the time of the drive of the electric motor 20, a stop, and the transition from a drive state to a stop state is demonstrated.
When the electric motor 20 is stopped, an internal gap is secured in the first bearing 33 and the second bearing 34 as described above. Further, when the electric motor 20 is stopped, the worm shaft 23 is supported so as to be swingable with respect to the gear housing 22 around the first end 27. Further, the second end portion 28 of the worm shaft 23 is elastically urged by the elastic urging member 25 via the second bearing 34. Therefore, when the electric motor 20 is stopped, the worm shaft 23 swings around the first end portion 27 by the urging force of the elastic urging member 25 as shown in FIG. Yes. Thereby, the backlash of the meshing part of the worm shaft 23 and the worm wheel 24 is temporarily removed.

  On the other hand, when the electric motor 20 is driven, the cam mechanism 54 moves the worm shaft 23 in the axial direction X1. More specifically, the cam mechanism 54 moves the worm shaft 23 in the axial direction X1 in accordance with the phase shift in the rotational direction of the first member 43 and the second member 44. As a result, the first inner ring 37 moves in the axial direction X1 with respect to the first outer ring 38, and the internal clearance of the first bearing 33 is removed. Further, the second inner ring 40 moves in the axial direction X1 with respect to the second outer ring 41, and the internal clearance of the second bearing 34 is removed.

  By removing the internal gap between the first bearing 33 and the second bearing 34, a force in the direction opposite to the biasing force by the elastic biasing member 25 acts on the worm shaft 23 (FIG. 9A). (See arrow at). Therefore, when the electric motor 20 is driven, the worm shaft 23 returns to the swing origin position as shown in FIG. 9B. Thereby, an appropriate backlash is ensured in the meshing portion of the worm shaft 23 and the worm wheel 24. Further, since the internal gap between the first bearing 33 and the second bearing 34 is removed, the swing of the worm shaft 23 around the first end 27 is restricted. Therefore, in a state where the electric motor 20 is driven, a state where an appropriate backlash is secured in the meshing portion of the worm shaft 23 and the worm wheel 24 is maintained.

  On the other hand, when the driving of the electric motor 20 is stopped, the elastic member 51 causes the first member 43 and the second member 44 to eliminate the phase shift in the rotation direction of the first member 43 and the second member 44. Giving power to. Thereby, the relative positional relationship between the first member 43 and the second member 44 is restored to the state before the electric motor 20 is driven. Therefore, the worm shaft 23 moves in the axial direction X1 of the worm shaft 23, and an internal gap is secured in the first bearing 33 and the second bearing 34. Therefore, the restriction on the swing of the worm shaft 23 by the cam mechanism 54 is released. As a result, the worm shaft 23 again swings around the first end portion 27 by the urging force of the elastic urging member 25, and the backlash of the meshing portion of the worm shaft 23 and the worm wheel 24 is removed.

  As described above, in this embodiment, the worm shaft 23 can be swung when the electric motor 20 is stopped. Therefore, when the electric motor 20 is stopped, the worm shaft 23 can be swung by the urging force of the elastic urging member 25 to press the worm shaft 23 against the worm wheel 24. That is, the backlash of the meshing part of the worm shaft 23 and the worm wheel 24 can be temporarily removed. Thereby, for example, when the vehicle travels straight on a rough road, it is possible to prevent rattle noise from being generated.

  Further, the swing of the worm shaft 23 can be restricted when the electric motor 20 is driven. Therefore, when the electric motor 20 is driven, an appropriate backlash can be secured at the meshing portion between the worm shaft 23 and the worm wheel 24, and the meshing between the worm shaft 23 and the worm wheel 24 can be made normal. Thereby, it is possible to prevent the surface pressure at the meshing portion of the worm shaft 23 and the worm wheel 24 from being increased and promoting the wear of the worm shaft 23 and the worm wheel 24. Therefore, shortening of the lifetime of the worm shaft 23 and the worm wheel 24 can be prevented. Furthermore, since the cam mechanism 54 as the restriction mechanism and the drive mechanism and the elastic member 51 as the restriction release mechanism are provided inside the joint 26, the structure of the steering assist mechanism 5 can be simplified and miniaturized.

  FIG. 10 is a schematic side view of the joint 226 according to the second embodiment of the present invention and the configuration related thereto, and shows a state when the electric motor 20 is stopped. FIG. 11 is a schematic side view of the joint 226 according to the second embodiment of the present invention and the configuration related thereto, and shows a state when the electric motor 20 is driven. FIG. 12 is a diagrammatic partial cross-sectional view of the joint 226 according to the second embodiment of the present invention and the configuration related thereto, and shows a state when the electric motor 20 is stopped. 10 to 12, the same components as those shown in FIGS. 1 to 9 are given the same reference numerals as those in FIG. 1 and the description thereof is omitted. Below, with reference to FIGS. 10-12, the coupling 226 which concerns on 2nd Embodiment of this invention is demonstrated.

  The joint 226 includes a first member 243 that is connected to the first end portion 27 of the worm shaft 23 so as to be able to rotate together with the first end portion 27, and a second member 244 that is connected so as to be able to rotate together with the rotary shaft 32 of the electric motor 20. And a pair of balls 55 held between the first member 243 and the second member 244. The first member 243 includes a cylindrical first peripheral wall 245 and a disk-shaped first end wall 46 connected to one end of the first peripheral wall 245. The second member 244 includes a cylindrical second peripheral wall 247 and a disk-shaped second end wall 48 connected to one end of the second peripheral wall 247.

  The first peripheral wall 245 and the second peripheral wall 247 include a first facing surface 56 and a second facing surface 57 that face each other in the axial direction X1 of the worm shaft 23, respectively. The first facing surface 56 includes a pair of first cam surfaces 58. Similarly, the second facing surface 57 includes a pair of second cam surfaces 59. 10 and 11, only one first cam surface 58 and one second cam surface 59 are illustrated. Each first cam surface 58 is inclined with respect to the circumferential direction of the first peripheral wall 245. Each of the second cam surfaces 59 is inclined in the direction opposite to the corresponding first cam surface 58 with respect to the circumferential direction of the second peripheral wall 247 and faces the corresponding first cam surface 58. is doing.

  Further, a first raceway groove 60 and a second raceway groove 61 are formed on the first cam surface 58 and the second cam surface 59, respectively. The first raceway groove 60 and the second raceway groove 61 are inclined along the first cam surface 58 and the second cam surface 59, respectively. Each ball 55 is rotatably held between the corresponding first raceway groove 60 and second raceway groove 61.

  When the electric motor 20 is driven, torque is transmitted to the second member 244. At this time, as shown in FIG. 11, the corresponding first cam surface 58 and second cam surface 59 are displaced in the rotational direction with the rolling of the ball 55 between them, and the first member 243 and the first cam surface 59 The phase of the rotation direction of the second member 244 is shifted. Therefore, as shown in FIG. 11, the first member 243 moves in the axial direction X1 toward the worm shaft 23 with respect to the second member 244. Thereby, the swing of the worm shaft 23 is restricted. In this embodiment, the ball 55, the first cam surface 58, and the second cam surface 59 constitute a cam mechanism 254 as a restriction mechanism and a drive mechanism.

  On the other hand, when the driving of the electric motor 20 is stopped, the elastic member 51 causes the first member 243 and the second member 244 to eliminate the phase shift in the rotation direction of the first member 243 and the second member 244. Giving power to. More specifically, the first member 243 and the second member 244 are relatively rotated by the restoring force generated by the elastic torsional deformation of the elastic member 51, and the first member 243 and the second member 244 are rotated. The phase in the rotational direction is matched. Further, the first member 243 is pulled toward the second member 244 by the restoring force generated by the elastic extension of the elastic member 51 so that the first member 243 approaches the second member 244. Move in the axial direction X1. Thereby, the relative positional relationship between the first member 243 and the second member 244 is restored to the state before the electric motor 20 is driven. Therefore, the swing regulation of the worm shaft 23 is released.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the contents of the above-described embodiments, and various modifications can be made within the scope of the claims.

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 20 ... Electric motor, 23 ... Worm shaft, 24 ... Worm wheel, 25 ... Elastic biasing member, 26, 226 ... Joint, 27 ... -1st end part, 28 ... 2nd end part, 32 ... Rotating shaft, 33 ... 1st bearing, 34 ... 2nd bearing, 38 ... 1st outer ring | wheel ( Outer ring), 37 ... first inner ring (inner ring), 39 ... first rolling element (rolling element), 43, 243 ... first member, 44, 244 ... second member , 51 ... elastic member (regulation release mechanism), 54, 254 ... cam mechanism (regulation mechanism, drive mechanism), D1 ... distance between centers, G1 ... internal gap, X1 ... (worm) Axial direction

Claims (5)

A worm shaft having first and second ends and supported so as to be swingable about the first end by a first bearing rotatably supporting the first end;
The second bearing supporting the second end of the worm shaft is elastically biased in a direction in which the distance between the centers of the worm shaft and the worm wheel is shortened, so that the worm shaft is centered on the first end. An elastic urging member that swings,
A joint for connecting the first end of the worm shaft and the rotating shaft of the electric motor so as to transmit torque;
The joint includes a restriction mechanism that acts on the first bearing to restrict the swing of the worm shaft when the electric motor is driven, and a restriction release mechanism that releases the restriction by the restriction mechanism when the electric motor is stopped. An electric power steering device. In Claim 1, the first bearing includes an outer ring that is not movable in the axial direction, a worm shaft, an inner ring that is movable in the axial direction, and a rolling element.
The first bearing has an internal gap for allowing the worm shaft to swing,
An electric power steering device characterized in that the swing of the worm shaft is restricted when the inner ring moves in the axial direction with respect to the outer ring until the internal clearance is removed.   The joint according to claim 2, wherein the joint includes a first member coupled to be rotatable along with the worm shaft, a second member coupled to rotate along with the rotating shaft of the electric motor, and the first and second members. An electric power steering apparatus comprising: a drive mechanism as the restriction mechanism that moves the worm shaft in the axial direction in accordance with a phase shift in the rotation direction of the member.   4. The electric power steering apparatus according to claim 3, wherein the drive mechanism includes a cam mechanism.   5. The restriction release mechanism according to claim 3, wherein the restriction release mechanism includes an elastic member that couples the first and second members, and the elastic member eliminates a phase shift between the first and second members. An electric power steering device characterized in that a biasing force is applied to the second member.

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