JP2013237400A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device silent and capable of inhibiting a difference in steering feeling with a steering direction.SOLUTION: An electric power steering device includes a worm 18 connected swingably to a rotating shaft of an electric motor via a joint. A first end and a second end of the worm 18 are supported by a first bearing and a second bearing 26. A biasing member held by a housing 17a biases the second end 18b to a worm wheel 19 side via the second bearing 26. When steering at a large steering angle (when a large load), a centering mechanism 60 brings tapered drive faces 471, 472 provided on the housing 17a into face contact with tapered driven faces 431, 432 provided on an outer periphery of an outer ring 43 of the second bearing 26 to position the worm 18 at a centering position.

Description

  The present invention relates to an electric power steering apparatus.

In the electric power steering apparatus, the steering operation is torque-assisted by decelerating the output of the electric motor via the worm and the worm wheel and transmitting it to the steering mechanism.
The backlash is necessary for the engagement between the worm and the worm wheel, but there is a possibility that a rattling sound (rattle sound) due to the backlash may occur during traveling.

  Therefore, conventionally, among the pair of bearings that support both ends of the worm, the bearing far from the electric motor is elastically biased toward the worm wheel (in the direction of reducing the center-to-center distance between the worm and the worm wheel). There has been proposed an electric power steering device that elastically biases a bearing near the electric motor in the axial direction (see, for example, Patent Document 1).

JP 2006-290148 A

By the way, in order to make it possible to move the bearing far from the electric motor in a direction to increase or decrease the distance between the centers, a predetermined gap is provided between the bearing far from the electric motor and the bearing holding portion that holds the bearing. An amount of gap is provided.
For this reason, when a large torque is transmitted, the driving reaction force received by the worm from the worm wheel causes the bearing on the side far from the electric motor to swing in the direction perpendicular to the axis within the gap amount.

  On the other hand, because the worm has a leading angle, the direction of the driving reaction force (perpendicular to the axis) seen from the axial direction of the worm differs between left steering and right steering. For this reason, the tooth contact of the worm and the worm wheel is different between the left and right steering. For this reason, in the left and right steering, the meshing rate changes and the transmission torque (assist torque) is different. As a result, the steering feeling is different and the driver may feel uncomfortable.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an electric power steering apparatus that is quiet and can suppress a difference in steering feeling depending on a steering direction.

  In order to achieve the above object, the first aspect of the invention of claim 1 is a first end portion connected to a rotating shaft (20) of an electric motor (16) through a joint (21) so as to be able to swing and transmit torque. 18a) and a worm (18) having a second end (18b) opposite the first end, a worm wheel (19) meshing with the worm, and a housing (17a) housing the worm and the worm wheel ), A first bearing (25) held in the housing and supporting the first end of the worm so as to be rotatable and movable in the axial direction (X1), and the second end of the worm being rotatable And a second bearing (26) that is axially movable together with the second end of the worm, and elastically biases the second end of the worm toward the worm wheel via the second bearing. Biasing member 54) and a centering mechanism (60) for centering the worm with respect to the housing, and the centering mechanism is provided on the housing and has a tapered drive surface (471, inclined with respect to the axial direction). 472) and a tapered driven surface (431, 432) provided on the outer periphery of the second bearing and inclined in the opposite direction with respect to the driving surface. .

In addition, although the alphanumeric character in a parenthesis represents the corresponding component etc. in embodiment mentioned later, this does not mean that this invention should be limited to those embodiment as a matter of course. The same applies hereinafter.
Further, as in claim 2, a pair of elastic members (27A, 27B) disposed on both sides of the first bearing and elastically urging the worm to an axial neutral position via the first bearing. In the state where the worm is in the neutral position, gaps (S1, S2) may be formed between the driving surface and the driven surface.

According to a third aspect of the present invention, the centering mechanism moves the second bearing in the axial direction by bringing the driving surface and the driven surface into surface contact with each other along with the axial movement of the second bearing. The worm may be centered via the second bearing by converting to radial movement.
According to a fourth aspect of the present invention, the drive surface includes a first drive surface (471) and a second drive surface (472) that are inclined in directions opposite to each other with respect to the axial direction of the worm. The surface may include a first driven surface (431) facing the first driving surface and a second driven surface (432) facing the second driving surface.

According to the first aspect of the present invention, the second end portion of the worm is elastically urged toward the worm wheel via the second bearing by the urging member at the time of straight traveling or minute steering, so that the worm and the worm wheel Therefore, the generation of noise due to backlash is suppressed and the operation is quiet.
Further, when steering at a large steering angle (at a large load), the worm that receives the axial component of the driving reaction force is displaced in the axial direction, and the tapered driving surface and the driven surface of the centering mechanism come into contact with each other. Thereby, the axial movement of the second bearing (worm) is converted into the radial movement, and the worm is centered. Therefore, the same assist characteristic can be obtained without changing the meshing rate between the left steering and the right steering, so that a good steering feeling can be achieved.

  According to the invention of claim 2, the worm is in a neutral position and a gap is formed between the driving surface and the driven surface when substantially no load is received during straight traveling or the like. Therefore, the backlash removal by the biasing member is substantially possible. Further, since the movement of the second bearing in the radial direction and the axial direction is ensured when the load increases, centering by the centering mechanism is substantially possible.

According to the invention of claim 3, since the driving surface and the driven surface of the centering mechanism are in surface contact, the axial movement of the second bearing is reliably converted into the radial movement, so that the worm is reliably centered. can do.
According to the fourth aspect of the present invention, since the corresponding driving surface and the driven surface are brought into surface contact according to the rotation direction of the electric motor, the worm can be centered satisfactorily regardless of the steering direction.

1 is a schematic diagram of an electric power steering apparatus according to an embodiment of the present invention, and shows a schematic configuration of the electric power steering apparatus. It is sectional drawing of the principal part of an electric power steering device. It is an expanded sectional view of the principal part of an electric power steering device, and shows the circumference of the 1st end part of a worm. It is an expanded sectional view of the important section of an electric power steering device, and shows the circumference of the 2nd end of a worm. FIG. 5 is a cross-sectional view taken along line VV in FIG. 2 and shows the periphery of a backlash removal mechanism. It is an expanded sectional view of the important section of an electric power steering device, and shows the centering mechanism at the time of large steering angle steering (at the time of heavy load) to the 1st steering direction. It is an expanded sectional view of the important section of an electric power steering device, and shows the centering mechanism at the time of large steering angle steering (at the time of heavy load) to the 2nd steering direction.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. Referring to FIG. 1, an electric power steering device 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, an intermediate shaft 5 connected to the steering shaft 3 via a universal joint 4, A rack as a steered shaft extending in the left-right direction of an automobile, having a pinion shaft 7 connected to the shaft 5 via a universal joint 6 and a rack 8a meshing with the pinion 7a provided in the vicinity of the end of the pinion shaft 7 Bar 8. The pinion shaft 7 and the rack bar 8 constitute a turning mechanism A composed of a rack and pinion mechanism.

The rack bar 8 is supported in a housing 9 fixed to the vehicle body so as to be capable of linear reciprocation through a plurality of bearings (not shown). Both end portions of the rack bar 8 protrude to both sides of the housing 9, and tie rods 10 are coupled to the respective end portions. Each tie rod 10 is connected to a corresponding steered wheel 11 via a corresponding knuckle arm (not shown).
When the steering member 2 is operated and the steering shaft 3 is rotated, this rotation is converted into a linear motion of the rack bar 8 along the left-right direction of the automobile by the pinion 7a and the rack 8a. Thereby, the turning of the steered wheel 11 is achieved.

The steering shaft 3 includes an input-side first steering shaft 3a having a steering member 2 connected to one end thereof, an output-side second steering shaft 3b connected to the pinion shaft 7, a first steering shaft 3a, and a second steering shaft 3b. And a torsion bar 3c connected to be rotatable relative to each other on the same axis.
A torque sensor 13 is provided for detecting a steering torque based on a relative rotational displacement amount between the first steering shaft 3a and the second steering shaft 3b via the torsion bar 12. The torque detection result of the torque sensor 13 is given to an ECU (Electronic Control Unit) 14. The ECU 14 drives and controls the steering assisting electric motor 16 via the drive circuit 15 based on a torque detection result or a vehicle speed detection result given from a vehicle speed sensor (not shown).

  The output rotation of the electric motor 16 is decelerated via a speed reducer 17 as a transmission device and transmitted to the pinion shaft 7 and converted into a linear motion of the rack bar 8 to assist steering. The speed reducer 17 includes a worm 18 as a drive gear that is rotationally driven by the electric motor 16, and a worm wheel as a driven gear that meshes with the worm 18 and is connected to the second steering shaft 3 b of the steering shaft 3 so as to be integrally rotatable. 19.

As shown in FIG. 2, the worm 18 is disposed coaxially with the rotating shaft 20 of the electric motor 16. The worm 18 has a first end 18a and a second end 18b that are separated in the axial direction X1, and a tooth portion 18c at an intermediate portion between the first end 18a and the second end 18b.
The worm wheel 19 is coupled to an intermediate portion in the axial direction of the second steering shaft 3b of the steering shaft 3 so as to be integrally rotatable and immovable in the axial direction. The worm wheel 19 includes an annular cored bar 19a coupled to the second steering shaft 3b so as to be integrally rotatable, and a synthetic resin member 19b surrounding the cored bar 19a and having teeth 19c formed on the outer periphery. The core metal 19a is inserted into the mold when the synthetic resin member 19b is molded with resin, for example.

  The first end portion 18a of the worm 18 and the end portion of the rotary shaft 20 (output shaft) of the electric motor 16 opposed to the first end portion 18a are connected via a joint 21 so as to be able to transmit torque and to swing with each other. Specifically, the joint 21 can rotate integrally with the first engagement member 22 connected to the rotating shaft 20 of the electric motor 16 so as to be integrally rotatable and not movable in the axial direction, and the first end 18 a of the worm 18. And the second engagement member 23 that is connected so as not to move in the axial direction, and is interposed between the first engagement member 22 and the second engagement member 23, and transmits torque between the engagement members 22, 23. The elastic member 24 is provided.

  The first engaging member 22 and the second engaging member 23 have the engaging protrusions 221 and 231 arranged alternately in the circumferential direction. Although not shown, the elastic member 24 has a plurality of engaging arms extending radially from the annular main body. A corresponding engagement arm of the elastic member 24 is sandwiched between engagement protrusions 221 and 231 adjacent to each other in the circumferential direction of both engagement members 22 and 23. The elastic member 24 of the joint 21 is elastically deformed, so that the worm 18 is allowed to swing with respect to the rotating shaft 20.

As shown in FIG. 3 in which a part of FIG. 2 is enlarged, the second engagement member 23 includes a boss 23a fitted to the first end 18a of the worm 18 so as to be integrally rotatable and non-movable in the axial direction, And an annular flange 23b extending radially outward from the boss 23a. The engagement protrusion extends in the axial direction from the annular flange 23b.
Referring again to FIG. 2, the housing 17 a of the reduction gear 17 has an opening 17 b that faces the second end 18 b of the worm 18. The opening 17b is closed by a lid member 17c that is screwed into the inner periphery of the opening 17b and forms a part of the housing 17a.

  The first end 18 a of the worm 18 is rotatably supported by the housing 17 a of the speed reducer 17 via the first bearing 25. The second end 18 b of the worm 18 is rotatably supported by the housing 17 a of the speed reducer 17 via the second bearing 26. The first bearing 25 and the second bearing 26 are constituted by, for example, ball bearings. A pair of elastic members 27A and 27B for urging the worm 18 to the neutral position in the axial direction X1 are disposed at the first end 18a of the worm 18.

The first bearing 25 is held via a bush 30 in an inner ring 28 fitted to the first end 18 a of the worm 18 so as to be integrally rotatable, and a bearing holding hole 29 provided in the housing 17 a of the speed reducer 17. And an outer ring 31.
As shown in FIG. 3, the outer ring 31 and the annular flange 30 a at the end of the bush 30 are screwed into the positioning step 32 provided at the end of the bearing holding hole 29 and the inlet of the bearing holding hole 29. The holding member 33 is held in the axial direction. Thereby, the axial movement of the outer ring 31 is restricted.

  The inner ring 28 of the first bearing 25 is fitted to the outer periphery of the first end 18a of the worm 18 so as to be integrally rotatable. The pair of elastic members 27A and 27B are disposed on both sides of the inner ring 28 in the axial direction, and urge the worm 18 to the neutral position in the axial direction X1. The elastic members 27A and 27B are bushes formed of an elastic material such as rubber or thermoplastic elastomer, for example.

  One elastic member 27 </ b> A is interposed between an annular receiving plate 35 that contacts the positioning step 34 on the outer periphery of the worm 18 and an annular receiving plate 36 that contacts one end surface of the inner ring 28. . The other elastic member 27B is interposed between the annular receiving plate 37 that contacts the other end surface of the inner ring 28 and the receiving plate 38 that contacts the annular flange 23b of the second engaging member 23 of the joint 21. ing. Each receiving plate 35, 36, 37, 38 is made of metal, for example.

On the outer periphery of the first end 18a, a first annular recess 39 fitted with the receiving plate 35 and one elastic member 27A, a second annular recess 40 fitted with the inner ring 28, and a second engagement member And a third annular recess 41 fitted with 23 bosses 23a. In the order of the first annular recess 39, the second annular recess 40, and the third annular recess 41, the outer diameter is gradually reduced.
Referring to FIG. 2 again, the second bearing 26 includes an inner ring 42 and an outer ring 43. The inner ring 42 of the second bearing 26 is fitted in a fourth annular recess 44 provided on the outer periphery of the second end 18b of the worm 18 so as to be integrally rotatable. The inner ring 42 is sandwiched between a nut 45 screwed into a threaded portion provided at the tip of the second end portion 18b of the worm 18 and a positioning step portion 46 provided on the outer periphery of the second end portion 18b. Yes. Thereby, the axial movement of the inner ring 42 relative to the worm 18 is restricted.

A housing hole 47 for housing the second bearing 26 is provided in the housing 17a. The accommodation hole 47 is formed by expanding a part of the accommodation hole for the worm 18 in the housing 17a.
The housing hole 47 causes the second bearing 26 to move in the directions Y1, Y2 in which the distance D1 between the centers of the worm 18 and the worm wheel 19 (corresponding to the distance between the rotation center C1 of the worm 18 and the rotation center C2 of the worm wheel) increases or decreases ( It is formed in a biasing hole (see FIG. 5) that can be held so as to be deflectable in the increasing direction Y1 and the decreasing direction Y2).

The electric power steering apparatus 1 includes a backlash removing mechanism 50 that removes backlash between the worm 18 and the worm wheel 19, and a centering mechanism 60 that centers the worm 18 with respect to the housing 17a.
As shown in FIG. 4, which is an enlarged view of the periphery of the second bearing 26 in FIGS. 2 and 2, the backlash removal mechanism 50 includes a support hole 51 provided in the housing 17 a so as to communicate with the accommodation hole 47, and a support A pressing member 52 supported so as to be reciprocally movable in the depth direction of the hole 51 and in contact with the outer periphery of the outer ring 43 of the second bearing 26; a sealing member 53 for sealing the inlet of the supporting hole 51; It is interposed between the pressing member 52 and elastically attaches the second end 18b of the worm 18 to the worm wheel 19 side (direction Y2 in which the center distance D1 decreases) via the pressing member 52 and the second bearing 26. And an urging member 54 made of, for example, a compression coil spring.

The support hole 51 extends from the accommodation hole 47 in the direction opposite to the worm wheel 19. The male screw portion 53 a provided on the outer periphery of the sealing member 53 is screwed into the female screw portion 51 a provided on the inner periphery of the inlet of the support hole 51, so that the sealing member 53 is fixed to the support hole 51. .
The pressing member 52 includes a pressing portion 52b having a flat pressing surface 52a on the front surface, and a shaft portion 52c extending from the center of the rear surface of the pressing portion 52b to the sealing member 53 side. The outer periphery of one end of the biasing member 54 made of a compression coil spring is fitted to the inner periphery of the annular recess 53b provided on the front surface of the sealing member 53, and the inner periphery of the other end of the biasing member 54 is the shaft portion. The outer periphery of 52c is fitted. Thereby, the fall of the biasing member 54 is suppressed.

Referring to FIG. 5 which is a cross-sectional view taken along line V-V in FIGS. 4 and 2, the inner periphery of the accommodation hole 47 provided in the housing 17 a includes a cylindrical surface 47 a (see FIG. 5) and a cylindrical surface 47 a. A tapered first drive surface 471 and a second drive surface 472 (see FIG. 4) are provided on both sides sandwiched in the axial direction X1 and are inclined in opposite directions with respect to the axial direction X1.
On the other hand, the outer circumference of the outer ring 43 of the second bearing 26 is disposed on both sides of the cylindrical surface 43a (see FIG. 5) facing the cylindrical surface 47a of the accommodation hole 47 and the cylindrical surface 43a sandwiched in the axial direction X1. A tapered first driven surface 431 and a second driven surface 432 (see FIG. 4) that are inclined in opposite directions with respect to X1 are provided.

  The first driving surface 471 and the first driven surface 431 face each other, and the second driving surface 472 and the second driven surface 432 face each other. Further, the first end surface 433 of the outer ring 43 faces the annular first inner wall surface 473 of the accommodation hole 47 in the axial direction X1, and the second end surface 434 of the outer ring 43 constitutes the annular second inner wall surface 474 of the accommodation hole 47. Is opposed to the axial direction X1. The inner wall surfaces 473 and 474 regulate the maximum movement amount of the outer ring 43 of the second bearing 26 in the axial direction X1.

  That is, the centering mechanism 60 is provided on the outer periphery of the outer ring 43 of the second bearing 26 and the tapered first drive surface 471 and the second drive surface 472 that are provided in the housing 17a and are inclined in opposite directions with respect to the axial direction X1. A tapered first driven surface 431 and a second driven surface 432 are provided at both ends in the axial direction X1 and are inclined in opposite directions with respect to the first driving surface 471 and the second driving surface 472, respectively. . The second drive surface 472 and the second inner wall surface 474 are provided on a lid member 17b that forms part of the housing 17a.

  As shown in FIG. 4, when the worm 18 is substantially in the neutral position in the axial direction X <b> 1 during the straight traveling or the small steering angle steering, it is between the first driving surface 471 and the first driven surface 431. In addition, a gap S <b> 1 is formed, and a gap S <b> 2 is formed between the second driving surface 472 and the second driven surface 432. In a state where the worm 18 is in the neutral position in the axial direction X1, the amounts of the gaps S1 and S2 (gap amounts) are made equal.

  The function of the centering mechanism 60 is as follows. That is, the second bearing 26 together with the worm 18 that has received the axial component F1 of the driving reaction force during the large steering angle steering in the first steering direction (at the time of a large load), as shown in FIG. The first driving surface 471 and the first driven surface 431 are in surface contact with each other. Thereby, the centering mechanism 70 functions to convert the axial movement of the second bearing 26 into the radial movement and center the worm 18 via the second bearing 26. As shown in FIG. 6, when the centering is completed, the first end surface 433 comes into contact with the first inner wall surface 473, so that the worm 18 is positioned at the centering position.

  On the other hand, at the time of steering at a large steering angle in the second steering direction (at the time of a large load), the second bearing 26 together with the worm 18 that has received the axial component F2 of the driving reaction force in the axial direction X1 as shown in FIG. The second drive surface 472 and the second driven surface 432 are in surface contact with each other. Thereby, the centering mechanism 70 functions to convert the axial movement of the second bearing 26 into the radial movement and center the worm 18 via the second bearing 26. As shown in FIG. 7, when the centering is completed, the second end surface 434 contacts the second inner wall surface 474, so that the worm 18 is positioned at the centering position.

  As shown in FIGS. 6 and 7, the backlash removal mechanism 50 does not operate when the worm 18 is positioned at the centering position during large steering angle steering (at a large load), but there is no problem. This is because abnormal noise caused by backlash is a problem when driving straight ahead or when the load is low during the initial turning of the steering wheel. Originally, when steering at a large steering angle, a large torque can be used without relying on the backlash removal mechanism 50. This is because the worm 18 and the worm wheel 19 are engaged with each other for transmission and the backlash is zero.

According to the present embodiment, the second end 18b of the worm 18 is elastically urged toward the worm wheel 19 via the second bearing 26 by the urging member 54 during straight traveling or minute steering. Since the backlash between the worm wheel 19 and the worm wheel 19 is removed, the generation of noise due to backlash is suppressed and the operation is quiet.
Further, at the time of steering at a large steering angle (at the time of a large load), the worm 18 that has received the axial component F1 or F2 of the driving reaction force is displaced in the direction corresponding to the axial direction X1, and the centering mechanism 60 is driven in a tapered manner. The surface 471 (or 472) contacts the driven surface 431 (or 432). Thereby, the axial movement of the worm 18 is converted into the radial movement, and the worm 18 is centered. Therefore, the same assist characteristic can be obtained without changing the meshing rate between the left steering and the right steering, so that a good steering feeling can be achieved.

  Further, when the worm 18 is not substantially loaded during straight traveling or at a small steering angle steering, the driven surface 431 corresponding to the driving surfaces 471 and 472 with the worm 18 in the neutral position in the axial direction X1. Since the gaps S <b> 1 and S <b> 2 are respectively formed between the 432 and 432, the backlash removal by the urging member 54 is substantially possible. Further, since the movement of the second bearing 26 in the radial direction and the axial direction X1 is ensured when the load increases, centering by the centering mechanism 60 is substantially possible.

Further, since the driving surfaces 471 and 472 of the centering mechanism 60 and the driven surfaces 431 and 432 are in surface contact, the axial movement of the second bearing 26 is reliably converted into the radial movement, so that the worm 18 is reliably centered. can do.
Further, since the corresponding driving surface 471 (or 472) and the driven surface 431 (or 432) are in surface contact according to the rotation direction of the electric motor 16, the worm 18 can be centered well regardless of the steering direction. Can do.

  The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the claims of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 2 ... Steering member, 3 ... Steering shaft, 7 ... Pinion shaft, 8 ... Rack bar, 16 ... Electric motor, 17 ... Reduction gear, 17a ... Housing, 17b ... Opening, 17c ... Cover member, DESCRIPTION OF SYMBOLS 18 ... Worm, 18a ... 1st end part, 18b ... 2nd end part, 19 ... Worm wheel, 20 ... Rotary shaft, 21 ... Joint, 25 ... 1st bearing, 26 ... 2nd bearing, 27A, 27B ... Elastic member 28 ... inner ring (of the first bearing), 42 ... inner ring of the (second bearing), 43 ... outer ring of the (second bearing), 431 ... first driven surface, 432 ... second driven surface, 433 ... first. 1 end face, 434 ... 2nd end face, 47 ... receiving hole, 471 ... 1st drive surface, 472 ... 2nd drive surface, 473 ... 1st inner wall surface, 474 ... 2nd inner wall surface, 50 ... backlash removal mechanism, 51 ... Support hole 52 ... Pressing member 53 ... Sealing 54, biasing member, 60 ... centering mechanism, A ... steering mechanism, C1 ... center of rotation (worm), C2 ... center of rotation (worm wheel), D1 ... center distance, S1, S2 ... gap, X1 ... Axial direction

Claims (4)

A worm having a first end coupled to a rotating shaft of an electric motor via a joint so as to be able to swing and capable of transmitting torque, and a second end opposite to the first end;
A worm wheel meshing with the worm;
A housing containing the worm and the worm wheel;
A first bearing held in the housing and supporting the first end of the worm so as to be rotatable and movable in the axial direction;
A second bearing that rotatably supports the second end of the worm and is axially movable together with the second end of the worm;
A spring that elastically biases the second end portion of the worm toward the worm wheel via the second bearing;
A centering mechanism for centering the worm with respect to the housing;
The centering mechanism includes a tapered driving surface provided on the housing and inclined with respect to the axial direction; and a tapered driving surface provided on an outer periphery of the second bearing and inclined in a reverse direction with respect to the driving surface. An electric power steering device including a drive surface. In Claim 1, provided with a pair of elastic members which are arranged on both sides of the first bearing and elastically urge the worm to an axial neutral position via the first bearing,
An electric power steering apparatus in which a gap is formed between the driving surface and the driven surface in a state where the worm is in the neutral position.   3. The centering mechanism according to claim 1, wherein the centering mechanism causes the driving surface and the driven surface to come into surface contact with the axial movement of the second bearing so that the axial movement of the second bearing is radial. An electric power steering device for centering the worm via the second bearing by converting to movement. 4. The drive surface according to claim 1, wherein the drive surface includes a first drive surface and a second drive surface that are inclined in opposite directions with respect to an axial direction of the worm,
The electric driven power steering apparatus, wherein the driven surface includes a first driven surface facing the first driving surface and a second driven surface facing the second driving surface.

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