JPH11165644A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To convert the rotation of a motor for steering assist into the lengthwise movement of a steering shaft completely by using a simple structure which can eliminate processing of the steering shaft and can facilitate adjusting work for assembly. SOLUTION: A rotating cylindrical body 6 which is rotated coaxially to a rack shaft 1 by transmission from a motor 5 for steering assist is fitted inside a rack housing 2 for storing a rack shaft 1 as a steering shaft. A plurality of feed rollers 7, 7... are fitted to one end surface of the rotating cylindrical body 6 so as to rotate around respective pivoted shafts inclined by an even angle to its axial center in the peripheral direction, and are brought into rolling contact with the outer-periphery surface of the rack shaft 1 through a wedge ring 8 wound respective outer surfaces.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus using an electric motor as a source of a steering assist force, and more particularly, to the rotation of a steering assist motor in the axial direction of a steering shaft. To a mechanism for converting to

[0002]

2. Description of the Related Art An electric power steering apparatus configured to drive an electric motor for assisting steering in response to a steering operation and to transmit a rotational force of the motor to a steering mechanism to perform assisting of steering is used to increase or decrease vehicle speed. Although it has the advantage of being able to flexibly respond to changes in the assisting force characteristics according to driving conditions, such as the magnitude of the steering angle, a transmission system that transmits the rotation of the steering assist motor to the steering mechanism is indispensable. There is a problem that it is difficult to obtain a small motor capable of obtaining a sufficient steering assist force.

A motor for assisting steering is connected to a steering wheel, and both ends of the motor are connected to the middle of a steering column that rotates with the operation of the steering wheel, or to steered wheels (generally, left and right front wheels). The steering shaft for moving in the axial direction to perform steering (for example,
It is arranged in the middle of the rack and pinion type steering mechanism. The former only has to transmit the rotation of the steering assist motor to the steering column, which is a rotating member, and has the advantage that the transmission system can be constituted by a general gear reducer or the like, but has the advantage of distributing the motor including this transmission system. It is difficult to secure the installation position around the steering column, and there is a disadvantage that the applicable range is limited.

On the other hand, in the latter, it is necessary to convert the rotation of the steering assist motor into movement in the direction of the length of the steering shaft. There is an advantage that it is relatively easy to secure the arrangement position of the motor around the steering shaft that is bridged, and it can be used in a wide range of vehicle types. However, also in this configuration, it is an important issue to reduce the space for disposing the motor including the transmission system to the steering shaft, and conventionally, for example, disclosed in JP-A-61-191468. As described above, an electric power steering apparatus has been proposed in which an installation space is reduced by using a ball screw mechanism for the transmission system.

In this electric power steering apparatus, a part of a steering shaft is formed as a male screw part having a ball screw rail formed on its outer periphery, and a nut member screwed to the outside of the male screw part via a number of balls. Is arranged in a housing that supports the steering shaft while restraining the axial movement thereof, and transmits the torque of a steering assist motor to the nut member to rotate the nut member. The steering shaft is moved in the axial direction by utilizing the transmission mechanism capable of obtaining a large reduction ratio inside the housing.The transmission mechanism can be made compact, and the miniaturized motor is mounted on the housing of the steering shaft. By being mounted close to each other, it is possible to meet the above-described demand for reducing the installation space.

[0006]

However, in the transmission system using the above-described ball screw mechanism, high precision is required for the formation of the screw rail on the outer periphery of the steering shaft and the inner periphery of the nut member. There is a problem that processing man-hours are required, and it takes a great deal of time to adjust the screwing state between the steering shaft and the nut member via a large number of balls,
There was a problem that the number of assembling steps increased.

Further, a sound is easily generated along with the rolling of the ball along the screw rail on the outer periphery of the steering shaft and the inner periphery of the nut member, and this sound is generated during a low-speed operation where the engine sound is quiet. There was a problem that the driver heard the sound as an unpleasant noise.

The present invention has been made in view of such circumstances, and a rotation of a steering assist motor can be reliably moved in the axial direction of a steering shaft by a transmission system having a simple configuration instead of a ball screw mechanism. An electric power steering device that can be converted, eliminates the need for machining of the steering shaft, simplifies the adjustment work involved in assembly, and can meet the demand for reducing the installation space of the steering assist motor including this transmission system The purpose is to provide.

[0009]

An electric power steering apparatus according to the present invention transmits a rotational force of a motor driven in response to a steering operation to a steering shaft, and moves the steering shaft in the axial direction to perform steering. In the electric power steering apparatus having a configuration to assist, a rotating cylinder that rotates coaxially with the steering shaft by transmission from the motor, and a part of the rotating cylinder is circumferentially oriented in the same circumferential direction with respect to its axis. A plurality of feed rollers that are rotatably supported around respective pivots inclined at the same angle and that have tapered portions on the outer surface thereof that reduce the diameter in the direction of movement of the steering shaft; A wedge ring is provided separately between the outer peripheral surface of the steering shaft and a wedge ring which comes into pressure contact with the steering shaft as the steering shaft moves.

According to the present invention, the rotary cylinder rotates coaxially with the steering shaft by transmission from the steering assist motor. The rotary cylinder includes a plurality of feed rollers that rotate around respective pivots that are inclined at the same angle in the circumferential direction with respect to the axis, and when the rotary cylinder rotates, each of the feed rollers is steered. Rolling on the outer peripheral surface of the shaft along a trajectory orthogonal to each of the other pivots, the steering shaft is pushed by the axial component of frictional force generated along the trajectory and moves in the axial direction. At this time, the wedge ring enters a tapered portion formed on the outer surface of the feed roller to form a wedge, and is strongly pressed against the tapered portion and the outer peripheral surface of the steering shaft.
The steering shaft can be reliably moved by the above-described rolling of the feed roller. In addition, since the movement of the steering shaft for steering occurs in both directions in the axial length direction according to the steering direction, each of the plurality of feed rollers having the tapered portions in opposite directions corresponding to the respective directions is required. is necessary.

Further, the feed roller is characterized in that it is constituted by a tapered roller bearing having a tapered roller whose diameter is reduced in the same direction as the tapered portion on the outer surface.

In the present invention, a plurality of tapered rollers provided in a tapered roller bearing used as a feed roller act between the outer ring and the inner ring by a pressing force acting via a wedge ring on the outer ring having the tapered portion. , And a wedge action is performed to press the two wheels together, and the feed roller rolls on the outer peripheral surface of the steering shaft to move the steering shaft reliably by a synergistic action with the wedge ring.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 1 is a partially broken front view showing a configuration of an electric power steering device according to the present invention,
FIG. 2 is an enlarged sectional view of the main part.

These figures show an example of application to a rack and pinion type steering device. A rack shaft 1 serving as a steering shaft has a cylindrical shape extending in the left-right direction of a vehicle body (not shown). The rack housing 2 is slidably supported in the axial direction inside the rack housing 2. Both ends of a rack shaft 1 protruding from both sides of the rack housing 2 are connected to left and right steering wheels (not shown) via separate tie rods 10, 10 (only one side is shown). The sliding of the rack shaft 1 is transmitted to the left and right steered wheels via the tie rods 10, 10, so that these are steered.

A pinion housing 3 is provided in the middle of the rack housing 2 so as to intersect the rack housing 2 with the axis thereof. A pinion shaft 4 is supported inside the pinion housing 3 so as to be rotatable around its axis. In FIG. 1, the pinion shaft 4 has only a protruding end protruding upward from the pinion housing 3, and is connected to a steering wheel (not shown) via the protruding end, and rotates around the shaft in accordance with an operation of the steering wheel for steering. It is designed to rotate.

A pinion (not shown) is integrally formed below the pinion shaft 4 extending inside the pinion housing 3. Further, rack teeth (not shown) are formed on the rack shaft 1 supported in the rack housing 2 over an appropriate length including a crossing position with the pinion housing 3, and mesh with the pinion below the pinion shaft 4. The rotation of the pinion shaft 4 caused by the operation of the steering wheel causes the rack shaft 1 to rotate due to the meshing of the pinion and the rack teeth.
And a left-right steering wheel connected to both ends of the rack shaft 1 is steered to form a rack and pinion type steering mechanism.

The rack housing 2 is located at a position separated from the continuous portion of the pinion housing 3 by an appropriate length in the axial direction.
A motor seat 50 protrudes outward at one location in the circumferential direction. The steering assist motor 5 has its axial center substantially parallel to the rack housing 2 and the rack shaft 1 inside the rack housing 2. And is fixed to the motor seat 50 by a flange.

As shown in FIGS. 1 and 2, the interior of the motor seat 50 is a cavity communicating with the interior of the rack housing 2, and the output end of the motor 5 protruding into the cavity is provided with a drive. The pinion 51 is fixed, and the drive pinion 51 is fixed.
Is a spur gear 52 rotatably supported inside the motor seat 50.
Has been engaged.

The steering assist motor 5 is driven based on a result of detection of a steering torque applied to a steering wheel for steering. The steering torque is measured by a torque sensor 9 (FIG. 1) provided inside the pinion housing 3.
). Inside the pinion housing 3, the pinion shaft 4 is divided into an upper shaft including an upwardly projecting end connected to a steering wheel and a lower shaft including the pinion, and is coaxially connected by a torsion bar (not shown). The torque sensor 9 detects a steering torque applied to a steering wheel for steering using a relative angular displacement generated between the upper shaft and the lower shaft with the torsion of the torsion bar as a medium. Sensor. FIG. 1 only shows a terminal box for supplying power to the torque sensor 9 and extracting output.

The rotating cylinder 6 is accommodated in the rack housing 2 so as to correspond to the portion where the motor seat 50 is connected. The rotary cylinder 6 has an inner ring integrally formed on one side thereof.
By the point contact ball bearing 60, the inside of the rack housing 2 is
This is a cylindrical body supported so as to allow only coaxial rotation, and a middle part of the rack shaft 1 is inserted inside the rotary cylinder 6.

A spur gear 61 is integrally formed on the outer periphery of the rotatable cylinder 6 thus supported at a position corresponding to the continuous portion of the motor seat 50 in the axial direction, and is located at the same position from the motor seat 50 side. , And meshes with the spur gear 52 that enters the gear. As a result, the rotation of the motor 5 driven as described above is transmitted to the rotary cylinder 6 via the pinion 51, the spur gear 52, and the spur gear 61, and the rotary cylinder 6 has a four-point contact ball bearing. The rotation position is maintained coaxial with the rack shaft 1 inside the rack housing 2 while maintaining the restrained position by 60.

Four feed rollers 7, 7,... Are mounted on the other end face of the rotary cylinder 6, that is, on the end face opposite to the position supported by the four-point contact ball bearing 60, and these feed rollers are mounted on the respective outer circumferences. As will be described later, the rack shaft 1 is in rolling contact with the outer peripheral surface of the rack shaft 1 projecting to the same side via a wound wedge ring 8.

FIG. 3 is a cross-sectional view taken along the line III-III of FIG. As shown in this figure, four feed rollers 7, 7,.
Are located at positions substantially equidistant in the circumferential direction on the same circumference on the other end surface of the rotary cylinder 6, and each other pivot is inclined in the circumferential direction at the same angle with respect to the axis of the rotary cylinder 6. It is rotatably supported around.

FIGS. 4 and 5 are enlarged cross-sectional views showing the manner in which the feed roller 7 is attached. The feed roller 7 includes an inner ring 7a.
And a plurality of tapered roller bearings 7c in the circumferential direction between the outer ring 7b and the outer ring 7b. A pivot bolt 70 inserted through the inner ring 7a is formed on a screw formed on the end face of the rotary cylinder 6. The inner ring is screwed into the hole 6a and formed by a head of the pivot bolt 70 and a stopper ring 71 fitted externally to the base of the pivot bolt 70.
7a is clamped from both sides, and is rotatably mounted with a pivot bolt 70 as a pivot.

The feed roller 7 shown in FIG.
The reduced diameter side of 7c is attached facing the end face of the rotary cylinder 6,
On the contrary, the feed roller 7 shown in FIG. 5 is mounted with the tapered roller 7c with the diameter-increase side facing the end surface of the rotary cylinder 6. These two types of attachment are made as a set of two feed rollers 7, 7... Arranged on the circumference of the rotary cylinder 6 at positions diametrically opposed to each other. That is, the two feed rollers 7, 7 located at diametrically opposed positions are mounted in the direction shown in FIG. 4, and the remaining two feed rollers 7, 7 are
It is installed in the direction shown.

In FIG. 3, the axes of the feed rollers 7, 7,... And the axes of the heads of the respective pivot bolts 70, 70,. , 7.. And the inclination of the pivot bolts 70, 70... Serving as pivots are evident from the deviation of these axes.

The outer ring 7b of each of the feed rollers 7 attached as described above is formed with a tapered portion 72 tapered in the same direction as the diameter of the tapered roller 7c rolling inward. The tapered portion 72 is wound with a wedge ring 8 having an outer surface slightly larger in diameter than the outer ring 7b and a tapered inner surface aligned with the tapered portion 72. As shown in the figure, the rack shaft 1 is brought into rolling contact with the outer peripheral surface of the rack shaft 1 via the wedge ring 8.

The wedge ring 8 shown in FIGS. 4 and 5 can be formed as a notch ring having a notch 80 at one position in the circumferential direction as shown in a perspective view of FIG. The outer ring 7b is externally fitted to the outer ring 7b in a state where the inner diameter is increased by the widening of the notch portion 80, and is wound as shown in FIGS. 4 and 5 by releasing the widening. On the reduced diameter side of the tapered portion 72, a flange portion 73 is provided in a manner in which the peripheral edge of the outer ring 7b projects outward, and by the action of the flange portion 73,
The configuration is such that the wedge ring 8 is prevented from coming out to the diameter reducing side of the tapered portion 72.

FIG. 7 is an enlarged sectional view showing another embodiment of the wedge ring wound around the feed roller 7. The wedge ring 8a shown in this figure has an inner diameter larger than the outer diameter of the outer ring 7b even on the reduced diameter side, and is configured as a continuous ring that is continuous in the circumferential direction, and a gap is formed outside the outer ring 7b of the feed roller 7. As shown in the figure, a portion of the rack shaft 1 in the circumferential direction facing the outer peripheral surface is sandwiched between the tapered portion 72 and the rack shaft 1 to increase the diameter of the tapered portion 72. The movement in the axial direction is restrained between the side of the rack shaft and the flange portion 73 so that the rack shaft 1 is kept in rolling contact with the outer peripheral surface.

With the above construction, when the rotary cylinder 6 is rotated by the transmission from the motor 5, the feed rollers 7, 7,... Attached to the rotary cylinder 6 are arranged on the outer peripheral surface of the rack shaft 1 by the wedge. Rolling through the ring 8 or 8a, the rack shaft 1
Slides in the axial direction according to the rolling. FIG. 8 is an explanatory diagram of the operation of the feed rollers 7, 7,.

The feed roller 7 has a pivot that is inclined with respect to the axis of the rotary cylinder 6 as described above. Rolling on the outer peripheral surface of the rack shaft 1 is indicated by a two-dot chain line in the figure. As described above, when the rotating cylinder 6 rotates in the direction indicated by the white arrow, the friction force F is generated on the rack shaft 1 along the rolling trajectory of the feed roller 7 when the rotating cylinder 6 rotates in the direction indicated by the white arrow. Works. The rotation of the rack shaft 1 around the shaft is restricted by meshing with the pinion shaft 4 and other appropriate means. When the frictional force F acts on the peripheral surface of the rack shaft 1, the rack shaft 1 extends in the axial direction. is pressed by the force component F _1, slides in the direction of the component force F _1.

As described above, in the electric power steering apparatus according to the present invention, the rotation cylinder 6 rotates inside the rack housing 2 by the rotation of the steering assist motor 5, and the rotation cylinder 6 is rotated by the rotation. When the attached feed rollers 7, 7... Roll on the outer peripheral surface of the rack shaft 1, the rack shaft 1 moves in the axial direction, and the steering performed as described above is assisted in accordance with this movement. This behavior is
The outer peripheral surface of the rack shaft 1, which is the rolling surface of the feed rollers 7, 7,..., Can be realized without any processing, so that the number of processing steps can be reduced and the strength of the rack shaft 1 may be reduced. Not even.

In order to reliably convert the rolling of the feed rollers 7, 7 to the movement of the rack shaft 1 in the axial direction, it is important to reduce the slippage by strengthening the contact between the rolling contact portions of the two. This is realized by the action of the wedge ring 8 wound around each feed roller 7. 4 and 5, the wedge ring 8 is interposed between the tapered portion 72 provided around the outer ring 7b of the feed roller 7 and the outer peripheral surface of the rack shaft 1, and comes into contact with the outer peripheral surface of the rack shaft 1. When the rack shaft 1 moves in the axial direction in this state, a friction force f in a direction opposite to the moving direction is applied to the outer surface of the wedge ring 8 which contacts the outer peripheral surface of the rack shaft 1. Works.

The wedge ring 8 mounted as shown in FIG.
When the movement of the rack shaft 1 occurs in the direction indicated by the white arrow in the drawing, that is, when the rack shaft 1 moves toward the reduced diameter side of the inner diameter of the rack shaft 1, the movement of the rack shaft 1 is performed by the action of the frictional force f generated in the opposite direction. Tapered part
It enters between 72 and the rack shaft 1 (to the right in FIG. 4). Thus, frictional force f ₁ is generated along it between the tapered portion 72, the wedge ring 8, these resultant force f ₂
As a result, the contact between the feed roller 7 and the rack shaft 1 is strengthened by the action of the wedge ring 8 as described above. Similarly, when the movement of the rack shaft 1 occurs in the direction shown by the white arrow in the figure, that is, when the wedge ring 8 shown in FIG. It functions to strengthen the contact with the rack shaft 1.

The operation of the wedge ring 8 is performed at a portion where the tapered portion 72 of the feed roller 7 and the outer peripheral surface of the rack shaft 1 are opposed to each other, and as shown in FIG. It goes without saying that the same effect can be obtained even when the wedge ring 8a having a larger inner diameter is used.

In FIGS. 4 and 5, as described above, the mounting direction of the feed rollers 7, 7 and the directions of the wedge rings 8, 8 wound around these outer rings 7b, 7b are opposite, and The wedge action is generated separately according to the direction of movement of the rack shaft 1. Therefore, the contact of the feed rollers 7, 7 attached as shown in FIGS. 4 and 5 with the rack shaft 1 is strengthened in accordance with the direction of movement of the rack shaft 1, respectively.
The feed roller 7 shown in FIG. 4 operates to move the rack shaft 1 to the left in the figure, and the feed roller 7 shown in FIG.
Performs an operation of moving the rack shaft 1 to the right similarly.

That is, the rack shaft 1 is moved to one side by the action of the two feed rollers 7, 7 which are diametrically opposed among the four feed rollers 7, 7 attached to the end face of the rotary cylinder 6. 4 and 5, the rack shaft 1 is moved to the other side by the action of the other two feed rollers 7, 7, and the rack shaft 1 is provided by preparing the attached feed rollers 7, 7 as shown in FIGS. It can be moved in both directions.

Feed rollers 7, 7 to the outer peripheral surface of rack shaft 1
Are secured by the above-described action of the wedge rings 8, 8 wound around them, so that each feed roller 7 is lightly attached to the outer peripheral surface of the rack shaft 1 by the feed roller 7 in the assembling stage. Only the positioning accuracy required for the contact is required, and the number of assembling steps including adjustment after assembling can be greatly reduced.

Further, since the feed roller 7 is formed by using the tapered roller bearing as described above, when the tapered portion 72 is pressed by the above-described action of the wedge ring 8, this pressing force is provided with a margin. Can bear. The tapered roller bearing used as the feed roller 7 is shown in FIGS.
As shown in the figure, the outer ring 7b is provided with a tapered roller 7c whose diameter is reduced in the same direction as the tapered portion 72. Since a wedge action for strengthening the pressure contact with the 7a side is performed, the feed roller 7 can be reliably rolled on the outer peripheral surface of the rack shaft 1 by a synergistic action with the wedge ring 8 wound around the outer ring 7b. The feed roller 7 rolls on the outer peripheral surface of the rack shaft 1, and the movement of the rack shaft 1 can be reliably performed.

As the feed rollers 7, 7,..., Other types of bearings such as ball bearings may be used, and the present invention is not limited to the bearings, and is rotatably fitted to a pivot bolt 70 as a pivot. It is also possible to use a ring.

As a measure to reduce the slip between the feed rollers 7, 7,... And the rack shaft 1, it is effective to apply traction grease to the rolling contact surfaces of the two. Traction grease is a synthetic lubricating oil containing polycyclic condensed saturated hydrocarbon as a main component. It has the property of generating an oil film (glassy solid film) with large shear resistance under the action of pressure. Is used to increase the frictional resistance of the contact surface to improve the transmission efficiency and to reduce the wear due to direct contact.

The application of the traction grease may be performed on the outer peripheral surface of the rack shaft 1 over the entire area where the traction grease may come into contact with the feed rollers 7, 7,. By the action of grease,
The occurrence of the slip can be more effectively reduced.

In the above-described embodiment, an example in which the rack and pinion type steering mechanism is applied to the rack shaft 1 has been described. However, in the present invention, the steering is performed according to the movement in the axial direction. It can be applied to all types of steering shafts. For example, in some electric power steering devices, a sliding shaft dedicated to steering assistance is provided separately from a rack shaft, and the sliding shaft and the rack shaft are connected in a part thereof, and a steering assist motor is provided. Is transmitted to the rack shaft via the sliding shaft, but such a sliding shaft is also included in the steering shaft in the present invention. Further, the present invention is not limited to the rack and pinion type steering mechanism, and can be applied to a steering shaft that performs the same operation in another type of steering mechanism.

[0044]

As described in detail above, in the electric power steering apparatus according to the present invention, the rotating cylinder arranged coaxially with the steering shaft rotates by the transmission from the steering assist motor, and is attached to the rotating cylinder. The plurality of feed rollers roll on the outer peripheral surface of the steering shaft, and a moving force in the axial direction is applied to the steering shaft. At this time, a wedge ring interposed between the tapered portion formed on the outer surface of the feed roller and the outer peripheral surface of the steering shaft forms a wedge action between the tapered portion and the steering shaft, and strongly presses against both. Therefore, the movement of the steering shaft according to the rolling of the feed roller can be surely performed.
The outer peripheral surface of the steering shaft only needs to be a surface on which the feed roller can roll, and does not require any processing, and when assembled, realizes a rolling contact state that does not require high precision of each feed roller. Only processing and assembly are easy.

Further, since a tapered roller bearing having a tapered roller whose diameter is reduced in the same direction as the tapered portion on the outer surface is used as the feed roller, the tapered roller is moved between the outer ring and the inner ring by a pressing force acting via a wedge ring. I entered between and pressed against both wheels,
The present invention has excellent effects such that the feed roller rolls on the outer peripheral surface of the steering shaft due to the synergistic action with the wedge ring, and can reliably move the steering shaft.

[Brief description of the drawings]

FIG. 1 is a partially cutaway front view of an electric power steering device according to the present invention.

FIG. 2 is an enlarged sectional view of a main part of FIG.

FIG. 3 is a transverse sectional view taken along line III-III of FIG. 2;

FIG. 4 is an enlarged cross-sectional view showing a mounting mode of a feed roller.

FIG. 5 is an enlarged cross-sectional view showing a mounting mode of a feed roller.

FIG. 6 is a perspective view of a wedge ring.

FIG. 7 is an enlarged sectional view showing another embodiment of a wedge ring wound around a feed roller.

FIG. 8 is a diagram illustrating the operation of a feed roller.

[Explanation of symbols]

 Reference Signs List 1 rack shaft 2 housing 5 motor 6 rotating cylinder 7 feed roller 7a inner ring 7b outer ring 7c tapered roller 8,8a wedge ring 70 pivot bolt 72 taper portion

Claims (2)

[Claims] 1. An electric power steering apparatus configured to transmit a rotational force of a motor driven in accordance with a steering operation to a steering shaft and move the steering shaft in an axial direction to assist steering. A rotating cylinder that rotates coaxially with the steering shaft by the transmission of the steering shaft, and a part of the rotating cylinder is rotatable around each pivot axis inclined at the same angle in the same circumferential direction with respect to the axis of the rotating cylinder. A plurality of feed rollers that are pivotally supported and have tapered portions on the outer surface thereof that reduce the diameter in the direction of movement of the steering shaft, and are separately interposed between the tapered portion of each feed roller and the outer peripheral surface of the steering shaft. An electric power steering device, comprising: a wedge ring which presses the steering shaft together with the movement of the steering shaft. 2. The electric power steering apparatus according to claim 1, wherein the feed roller is constituted by a tapered roller bearing having a tapered roller whose diameter is reduced in the same direction as the tapered portion on the outer surface.