JP4501068B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus that generates a steering assist force by an electric motor.

A reduction gear is used in an electric power steering system (EPS) for automobiles. For example, in the column type EPS, the rotation of the output shaft of the electric motor is decelerated through the worm shaft and the worm wheel, so that the output of the electric motor is amplified and transmitted to the steering mechanism, and the steering operation is torque-assisted. Yes.
A moderate backlash is necessary for the meshing of the worm shaft and the worm wheel, but for example, when driving on a rough road, a rattling sound due to the backlash is generated due to reverse input from the road surface. There is.

  In order to prevent the occurrence of rattling noise, it is necessary to strictly adjust the amount of backlash generated between the worm shaft and the worm wheel within the range of machining accuracy of each component. Conventionally, when assembling the worm shaft and the worm wheel, each part is selected according to the degree of variation in dimensional accuracy, and the components with the appropriate combination accuracy are combined (so-called matching assembly). The work was very laborious and the manufacturing cost was high.

Even if the backlash is initially set to an appropriate range by matching assembly, the backlash may increase due to wear of the tooth portion due to a change over time, and noise may be generated.
Therefore, one end of the worm shaft is supported so as to be able to advance and retreat to the radial worm wheel side, and one end of the worm shaft is urged to the radial worm wheel side by the biasing means, so that the worm shaft and the rotation center of the worm wheel are It has been proposed to automatically adjust the distance (so-called center distance) to eliminate backlash (see, for example, Patent Document 1).
JP 2000-43739 A

From the specifications of the teeth of the worm shaft and worm wheel, the direction of the driving reaction force that the worm shaft receives from the worm wheel when the drive is actually transmitted by the worm shaft and worm wheel is determined by the application of the biasing means. It is different from the trend direction. Therefore, an appropriate preload cannot be applied to the meshing portion of the worm shaft and the worm wheel.
Further, when the worm shaft rotates forward and backward, the direction of the driving reaction force that the worm shaft receives from the worm wheel differs between when rotating in the forward direction and when rotating in the reverse direction. On the other hand, conventionally, it is only urged in a single urging direction. From this point as well, an appropriate preload cannot be applied to the meshing portion.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an electric power steering device that can apply an appropriate preload to the meshing portion and suppress the generation of noise.

In order to solve the above problems, the present invention provides a worm shaft connected to an output shaft of an electric motor for assisting steering and capable of rotating in a first rotational direction and a second rotational direction opposite to the first rotational direction , And a worm wheel meshing with the worm shaft, and a transmission device for transmitting power to the steering mechanism, and an urging means for urging the worm shaft in a direction to shorten the distance between the center of the worm shaft and the worm wheel. the biasing means, seen including a leaf spring providing a biasing force to a plurality of locations spaced apart in the circumferential direction of the bearing for supporting the worm shaft, said plate spring, first and second respectively impart a biasing force to the bearing The urging force of the first urging portion includes a radial component of a driving reaction force that the worm shaft receives from the worm wheel when the worm shaft rotates in the first rotation direction. Up in the opposite direction The urging force of the second urging portion urges the bearing, and the urging force of the second urging portion is opposite to the radial component of the driving reaction force that the worm shaft receives from the worm wheel when the worm shaft rotates in the second rotation direction. The bearing is biased, and the biasing forces of the first and second biasing portions are different from each other .

In the present invention, an urging force is applied to a plurality of locations separated in the circumferential direction of the bearing. Therefore, when the worm shaft rotates forward and backward, an urging force having a magnitude corresponding to the rotational direction is applied in the direction corresponding to the rotational direction. It becomes possible to grant. As a result, an appropriate preload can always be applied to the meshing portion, and noise generation can be suppressed.
The upper Symbol plate springs each comprise first and second biasing portions of imparting a biasing force to the bearing, since the biasing force of the first and second biasing portions are different from each other, each of the leaf springs The urging portion can urge the worm shaft via the bearing with an urging force having an appropriate magnitude according to the rotation direction in an appropriate direction according to the rotation direction.

  In the present invention, the leaf spring includes a base and a pair of elastic pieces extending in an inclined manner from one end and the other end of the base and intersecting in an X shape, and the first and second portions are formed by a pair of elastic pieces. May be configured. In this case, the pair of elastic pieces intersecting in an X shape come into contact with the bearing in a slanting manner and elastically bias it so that the bearing is displaced in a direction other than the direction in which the distance between the centers is shortened. Can be effectively suppressed.

Hereinafter, 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, 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 rack teeth 8a meshing with pinion teeth 7a provided in the vicinity of the end of the pinion shaft 7 Rack bar 8. The pinion shaft 7 and the rack bar 8 constitute a steering mechanism A including 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 steering 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 teeth 7a and the rack teeth 8a. Thereby, steering of the wheel 11 is achieved.

The steering shaft 3 is divided into an input-side upper shaft 3 a that is continuous with the steering member 2 and an output-side lower shaft 3 b that is continuous with the pinion shaft 7. These upper and lower shafts 3 a and 3 b are connected via a torsion bar 12. Are connected to each other so as to be relatively rotatable on the same axis.
A torque sensor 13 is provided for detecting a steering torque based on the amount of relative rotational displacement between the upper and lower shafts 3a, 3b via the torsion bar 12, and the torque detection result of the torque sensor 13 is obtained from an ECU (Electronic Control Unit: 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 the speed reducer 17 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 shaft 18 that is rotationally driven by the electric motor 16 and a worm wheel 19 that meshes with the worm shaft 18 and is coupled to the lower shaft 3b of the steering shaft 3 so as to be integrally rotatable.
Referring to FIG. 2, worm shaft 18 is arranged coaxially with output shaft 20 of electric motor 16. The worm shaft 18 has first and second end portions 18a and 18b that are separated from each other in the axial length direction, and has a tooth portion 18c at an intermediate portion between the first and second end portions 18a and 18b.

  The worm wheel 19 is connected to an intermediate portion in the axial direction of the lower 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 lower shaft 3b so as to be integrally rotatable, and a synthetic resin member 19b that surrounds the cored bar 19a and has 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 18 a of the worm shaft 18 and the opposite end portion of the output shaft 20 of the electric motor 16 are connected to each other via a power transmission joint 21 so as to be able to transmit power.
The first and second end portions 18a and 18b of the worm shaft 18 are rotatably supported by the housing 17a of the speed reducer 17 via corresponding first and second bearings 22 and 23, respectively. The first and second bearings 22 and 23 are ball bearings, for example.

  Inner rings 24, 25 of the first and second bearings 22, 23 are fitted to the first and second end portions 18a, 18b of the worm shaft 18 so as to be integrally rotatable. The inner rings 24 and 25 are in contact with the corresponding positioning step portions 18d and 18e of the worm shaft 18 which are opposite to each other. The outer rings 26 and 27 of the first and second bearings 22 and 23 are held in corresponding bearing holding holes 28 and 29 of the housing 17a of the speed reducer 17.

  The end surface of the outer ring 27 of the second bearing 23 is positioned in the axial direction by contacting the end wall 17b of the housing 17a. On the other hand, the outer ring 26 of the first bearing 22 is pressed against the positioning step 17c of the housing 17a by the preload adjusting and backlash adjusting screw members 36 screwed into the screw holes 35 connected to the corresponding bearing holding holes 28. And is positioned in the axial direction.

The bearing holding hole 29 for the second bearing 23 has a longer and shorter center distance D1 between the worm shaft 18 and the worm wheel 19 (corresponding to the distance between the rotation center C1 of the worm shaft 18 and the rotation center C2 of the worm wheel). It is formed in a hole that can be held so as to be deflectable in the directions X1 and X2.
Specifically, as shown in FIG. 3, the bearing holding hole 29 is configured as a circular hole having an inner diameter that is a predetermined amount larger than the outer diameter of the outer ring 27 of the second bearing 23. Therefore, the second bearing 23 can be displaced in an arbitrary radial direction only by the relationship between the bearing holding hole 29 and the second bearing 23. However, the displaceable direction is restricted to the above-described directions X1 and X2 by the annular elastic member 30 that is fitted to the outer peripheral surface of the outer ring 27 and serves as a restraining means, and is thereby orthogonal to the above-described directions X1 and X2. The displacement of the second bearing 23 in the direction V is suppressed.

  That is, the elastic member 30 is made of, for example, a synthetic resin. The elastic member 30 includes an annular main body 31 and ribs 32 and 33 formed on the outer peripheral surface of the main body 31. The ribs 32 and 33 protrude from the outer peripheral surface of the main body 31 in a direction V perpendicular to the direction X1 and X2 in which the center-to-center distance D1 increases and decreases, and elastically contact the inner peripheral surface of the bearing holding hole 29. Yes. One or more ribs 32 and 33 are provided. For example, when the second bearing 23 is concentric with the bearing holding hole 29, it is between the remaining portion of the main body portion 31 where the ribs 32 and 33 are not provided and the inner peripheral surface of the bearing holding hole 29. Is provided with a gap.

Thus, the second bearing 23 and the elastic member 30 are held by the bearing holding hole 29 so as to be capable of being deflected along the directions X1 and X2 in which the center distance D1 is increased or decreased. Further, the ribs 32 and 33 suppress the displacement of the second bearing 23 in the orthogonal direction V as the direction intersecting the directions X1 and X2.
The second bearing 23 is elastically urged by the urging member 60 via the elastic member 30 in the direction X2 in which the center distance D1 is shortened.

Specifically, the housing 17 a has a screw hole 70 that opens in a direction perpendicular to the axis of the bearing holding hole 29, and a screw member 71 is screwed into the screw hole 70. The screw member 71 has a holding portion 72 that is a concave portion that holds the biasing member 60.
With reference to FIGS. 3 and 4, the urging member 60 includes a leaf spring interposed between the bottom 72 a of the holding portion 72 and the elastic member 30 covering the outer ring 27 of the second bearing 23. The leaf spring includes a base 61 made of a flat plate received by the bottom 72a of the holding portion 72, and first and second urging portions 62 and 63 that apply urging forces F1 and F2 to the second bearing 23, respectively. Including.

Referring to FIG. 3, holding portion 72 has inner walls 72 b and 72 c that receive one end 611 and the other end 612 of base 61, respectively. Thereby, the holding portion 72 restricts the base 61 from being displaced in the circumferential direction of the second bearing 23.
Referring to FIGS. 3 and 4, the first and second urging portions 62 and 63 are a pair of long lengths extending in an inclined shape from one end 611 and the other end 612 of the base 61 and intersecting in an X shape. It consists of an elastic piece. The first and second urging portions 62 and 63 are cantilevered by the base 61. The first and second urging portions 62 and 63 made of elastic pieces respectively apply urging forces F1 and F2 to the plurality of locations separated in the circumferential direction of the second bearing 23 via the elastic member 30.

  In addition, as shown in FIG. 4, there are two elastic pieces constituting the first urging portion 62, and one elastic piece constituting the second urging portion 63 is provided. The elastic piece of the urging portion 63 is inserted between the two elastic pieces of the first urging portion 62 so that the elastic pieces of the first and second urging portions 62 and 63 are X-shaped with each other. Crossed. The first and second urging portions 62 and 63 make the urging forces F1 and F2 different from each other by making the number of elastic pieces different from each other. By making the lengths and widths of the elastic pieces different from each other, the urging forces F1 and F2 can be made different.

As shown in FIG. 3, the urging force F1 of the first urging portion 62 is the diameter of the driving reaction force that the worm shaft 18 receives from the worm wheel 19 when the worm shaft 18 rotates in the first rotation direction R1. The second bearing 23 is urged as a force against the radial component G1 in the direction opposite to the directional component G1.
Similarly, the urging force F2 of the second urging portion 63 is the radial component G2 of the driving reaction force that the worm shaft 18 receives from the worm wheel 19 when the worm shaft 18 rotates in the second rotation direction R2. The second bearing 23 is urged as a force against the radial component G2 in the opposite direction.

The circumferential position of the elastic member 30 with which the elastic pieces constituting the urging portions 62 and 63 come into contact can be appropriately adjusted by changing the shape of the elastic pieces.
Next, the power transmission joint 21 will be described in detail with reference to FIG. 5 which is a cross-sectional view taken along the line VV in FIG. 2 and FIG. 2 and FIG. 6 which is an exploded perspective view. First, referring to FIG. 2, the power transmission joint 21 includes a first engagement member 41 coupled to the output shaft 20 of the electric motor 16 so as to be integrally rotatable, and a worm shaft 18 as an input shaft of the speed reducer 17. Between the first and second engaging members 41 and 42, and a second engaging member 42 connected to the first end 18a of the first end 18a so as to be integrally rotatable. And an elastic member 43 for transmitting torque. The first and second engaging members 41 and 42 are made of, for example, metal. The elastic member 43 is made of, for example, synthetic rubber or synthetic resin such as polyurethane.

Next, referring to FIGS. 5 and 6, the elastic member 43 includes an annular main body 44 and a plurality of engagement arms 45 extending in the radial direction from the main body 44. The plurality of engagement arms 45 are arranged at equal intervals in the circumferential direction Z of the main body 44. Each engagement arm 45 has a pair of power transmission surfaces 46 that face each other in the circumferential direction Z.
Referring to FIG. 6, the first and second engaging members 41, 42 are annular main portions 51, which form fitting holes 49, 50 for fitting the output shaft 20 and the worm shaft 18, respectively. 52 and a plurality of first and second engaging protrusions 55 and 56 formed to project from the opposing surfaces 53 and 54 of the main body portions 51 and 52, respectively.

The first and second engagement protrusions 55 and 56 of the first and second engagement members 41 and 42 are arranged at equal intervals in the circumferential direction of the corresponding main body portions 51 and 52, respectively.
In the assembled state of the power transmission joint 21, as shown in FIG. 5, the first and second engagement protrusions 55 and 56 of the first and second engagement members 41 and 42 are alternately arranged in the circumferential direction, A corresponding engagement arm 45 of the elastic member 43 is sandwiched between the first and second engagement protrusions 55 and 56 adjacent to each other in the circumferential direction. In other words, the first and second engaging protrusions 55 and 56 adjacent in the circumferential direction are engaged with each other with the corresponding engaging arm 45 of the elastic member 43 sandwiched in the circumferential direction.

As shown in FIGS. 5 and 6, the first and second engagement protrusions 55 and 56 include power transmission surfaces 57 and 58 of the corresponding engagement arm 45 of the elastic member 43, respectively.
According to the present embodiment, an urging force is applied by the urging member 60 made of a leaf spring to a plurality of locations spaced apart in the circumferential direction of the second bearing 23. Therefore, when the worm shaft 18 rotates forward and backward, its rotation It is possible to apply urging forces F1 and F2 having magnitudes corresponding to the rotation directions R1 and R2 in the direction corresponding to the directions R1 and R2. As a result, an appropriate preload can always be applied to the meshing portion, and noise generation can be suppressed.

  Further, the first and second urging portions 62 and 63 are provided on the leaf spring constituting the urging member 60, and the urging forces of these urging portions 62 and 63 are different from each other. The parts 62 and 63 attach the worm shaft 18 to the appropriate direction according to the rotation directions R1 and R2 via the second bearing 23 with the urging forces F1 and F2 having the appropriate magnitude according to the rotation direction. It will be possible to

Moreover, the first and second urging portions 62 and 63 are constituted by a pair of elastic pieces that intersect in an X shape. Therefore, a direction X1 in which the second bearing 23 increases or decreases the center distance D1 by the pair of elastic pieces intersecting in an X shape coming into contact with the second bearing 23 and urging it elastically. , X2 can be effectively suppressed from being displaced in directions other than X2.
Further, directions other than the directions X1 and X2 in which the second bearing 23 increases or decreases the center distance D1 by the elastic member 30 with the ribs 32 and 33 interposed between the second bearing 23 and the bearing holding hole 29. By suppressing the displacement, the meshing preload between the worm shaft 18 and the worm wheel 19 can be made more appropriate.

In addition, the elastic member 30 can prevent the generation of hitting sound between the second bearing 23 and the bearing holding hole 29. In particular, the occurrence of hitting sound can be reliably prevented by the ribs 32 and 33 of the elastic member 30.
FIG. 7 shows another embodiment of the present invention. Referring to FIG. 7, this embodiment is different from the embodiment of FIG. 3 in that the first and second urging portions 62A and 63A of the urging member 60A are each constituted by one elastic piece. The point is that an arcuate portion 64 is formed along the outer ring 27 of the second bearing 23 at the tip of each elastic piece.

Further, the elastic member 30 is abolished, and a pair of flat portions 291 and 292 are formed on the inner peripheral surface of the bearing holding hole 29 formed of a circular hole so as to form a two-surface width therebetween. The second bearing 23 is prevented from being displaced in the direction V perpendicular to the directions X1 and X2 in which the center distance D1 is longer or shorter.
Also in the present embodiment, the same operational effects as those of the embodiment of FIG. 3 can be obtained, an appropriate preload can be applied to the meshing portion, and the generation of noise can be suppressed.

  9A shows yet another embodiment of the present invention. With reference to FIGS. 9A and 9B, in the present embodiment, a holding recess 18f made of, for example, a conical tapered surface is provided on the end face of second end portion 18b of worm shaft 18, and steel is provided in this holding recess 18f. A made ball 80 is held. On the other hand, a synthetic resin lid member 81 is fixed to the opening 17d formed in the end wall 17b of the housing 17a by, for example, press fitting.

The lid member 81 is formed with guide grooves 82 extending along the directions X1 and X2 in which the center distance D1 increases and decreases, and the guide groove 82 causes the ball 80 to extend in the directions X1 and X2 in which the center distance D1 increases and decreases. It is guided to be displaced along. As a result, the deflection direction of the second end portion 18b of the worm shaft 18 is restricted to the directions X1 and X2 in which the center distance D1 increases or decreases.
In the present embodiment, the deflection direction of the worm shaft 18 can be regulated using a simple structure, and an appropriate meshing preload can always be applied. In particular, by using the ball 80, the worm shaft 18 can be smoothly deflected. In addition, since the lid member 81 that is in sliding contact with the ball 80 is made of synthetic resin, the noise reduction effect can be enhanced.

  Next, FIG. 10 shows still another embodiment of the present invention. Referring to FIG. 10, in the present embodiment, as a power transmission joint 21A for connecting the output shaft 20 of the electric motor 16 and the worm shaft 18, for example, press fitting or spline fitting to the first end 18a of the worm shaft 18 is performed. A cylindrical joint body 85 coupled so as to be integrally rotatable, and an elastic member 86 such as a compression coil spring that is wound around the joint body 85 and the output shaft 20 so as to straddle the joint body 85 and the output shaft 20. Prepare. One end 86a of the elastic member 86 is fixed to the joint body 85 by welding, for example, and the other end 86b of the elastic member 86 is fixed to the outer periphery of the output shaft 20 by welding, for example.

The power transmission joint 21 </ b> A transmits power between the output shaft 20 and the worm shaft 18 by the elastic member 86. The elastic member 86 elastically biases the worm shaft 18 toward the second bearing 23 (left side in FIG. 10). Further, the elastic member 86 allows the axis of the worm shaft 18 to tilt (tilt) with respect to the axis of the output shaft 20.
On the other hand, between the outer ring 27 of the second bearing 23 and the bearing holding hole 29, for example, a rubber cylindrical elastic member 87 is interposed. The elastic member 87 has an annular side wall 88 at one end, and the annular side wall 88 is sandwiched between the end surface of the outer ring 27 of the second bearing 23 and the end wall 17b of the housing 17a. Further, crowning for allowing the worm shaft 18 to swing is applied to at least one of the inner peripheral surface of the inner ring 25 of the second bearing 23 and the second end portion 18b of the worm shaft 18 fitted thereto. And a predetermined curvature is given. On the other hand, the first bearing 22 is provided with a bearing gap corresponding to the swing of the worm shaft 18.

  In the present embodiment, the worm shaft 18 and the worm wheel 19 are assembled with a negative gap, and the center distance D1 between the worm shaft 18 and the worm wheel 19 is automatically adjusted using the elastic member 86.

It is a mimetic diagram showing a schematic structure of an electric power steering device of one embodiment of the present invention. It is sectional drawing of the principal part of an electric power steering device. It is sectional drawing which follows the III-III line of FIG. It is a perspective view of a biasing member. It is sectional drawing which follows the VV line of FIG. It is a disassembled perspective view of a power transmission coupling. It is sectional drawing of the principal part of the electric power steering apparatus of another embodiment of this invention. It is a perspective view of the urging member of the embodiment of FIG. 9A is a cross-sectional view of a main part of an electric power steering apparatus according to another embodiment of the present invention, and FIG. 9B is a cross-sectional view taken along line 9B-9B of FIG. 9A. It is sectional drawing of the principal part of the electric power steering apparatus of another embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 2 Steering member 3 Steering shaft 5 Intermediate shaft 7 Pinion shaft 8 Rack bar 10 Tie rod 11 Wheel A Steering mechanism 16 Electric motor 17 Reduction gear 17a Housing 18 Worm shaft 19 Worm wheel 20 Output shafts 21 and 21A of the electric motor Power transmission joint 29 Bearing holding hole 30 Elastic member (means for suppressing the displacement of the bearing in the direction intersecting the direction of shortening the center-to-center distance)
31 Main part 32, 33 Rib 60, 60A Energizing member 61 Base 611 One end 612 Other end 62, 62A First energizing part (elastic piece)
63, 63A Second urging portion (elastic piece)
64 Arc-shaped portion 71 Screw member 72 Holding portion 80 Ball 81 Lid member 82 Guide groove 85 Joint body 86 Elastic member 87 Elastic member 88 Annular side wall X1 Direction to increase the center-to-center distance X2 Direction to decrease the center-to-center distance V Direction to be orthogonal (Intersection direction)
R1 First rotational direction R2 Second rotational direction F1, F2 Energizing force G1, G2 Radial component of driving reaction force

Claims (2)

A steering wheel includes a worm shaft connected to an output shaft of an electric motor for assisting steering and capable of rotating in a first rotational direction and a second rotational direction opposite to the first rotational direction , and a worm wheel meshing with the worm shaft. A transmission device for transmitting power to the mechanism;
Urging means for urging the worm shaft in a direction that shortens the distance between the center of the worm shaft and the worm wheel;
It said biasing means, seen including a leaf spring providing a biasing force to a plurality of locations spaced apart in the circumferential direction of the bearing for supporting the worm shaft,
The leaf spring includes first and second urging portions that respectively apply an urging force to the bearing, and the urging force of the first urging portion is obtained by rotating the worm shaft in the first rotation direction. Sometimes the worm shaft urges the bearing in a direction opposite to the radial component of the driving reaction force received from the worm wheel,
The urging force of the second urging portion urges the bearing in a direction opposite to the radial component of the driving reaction force received by the worm shaft from the worm wheel when the worm shaft rotates in the second rotation direction. And
An electric power steering device in which the urging forces of the first and second urging portions are different from each other . 2. The leaf spring according to claim 1, wherein the leaf spring includes a base and a pair of elastic pieces extending in an inclined manner from one end and the other end of the base and intersecting in an X shape, and the first and second elastic pieces are formed by a pair of elastic pieces. An electric power steering device including an urging unit.

Images