JP2016168879A - Steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steering device which enables extension of a life of a disc spring elastically supporting a nut of a ball screw mechanism.SOLUTION: A steering device includes: a ball screw mechanism 8 which applies an axial force to a rack shaft of a vehicle on the basis of rotation of a nut 80; and a bearing 20 which supports the nut 80 so that the nut 80 may rotate relative to the housing 10. The steering device includes: a plate 31 which is disposed spaced away from the bearing 20 in an axial direction ZA and has an axial extension part 31b for restraining movement of the disc spring 32 in a radial direction ZB of the rack shaft; a disc spring 32 disposed between the bearing 20 and the plate 31. The axial extension part 31b is formed so that a length D2 measured in the axial direction ZA of the rack shaft is set so as to be larger than a plate thickness D1 of the disc spring 32.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a steering device.

  As one of the steering devices, there is an electric power steering device including a ball screw mechanism attached to the outer periphery of a rack shaft and a motor connected to the ball screw mechanism through a speed reduction mechanism. In this electric power steering apparatus, when the rotation of the output shaft of the motor is transmitted to the ball screw mechanism via the speed reduction mechanism, the ball screw mechanism applies an axial force to the rack shaft. The axial force applied to the rack shaft becomes an assist force to assist the driver's steering operation. Conventionally, there is a structure described in Patent Document 1 as a support structure of a ball screw mechanism in this type of electric power steering apparatus.

  As shown in FIG. 7, in the electric power steering device described in Patent Document 1, a nut 121 of a ball screw mechanism 120 is rotatably supported via a bearing 130 with respect to a housing 110 that covers the periphery of the rack shaft 100. Yes. An annular elastic member 140 and a plate 141 are installed in the gap between the bearing 130 and the housing 110 in the axial direction ZA of the rack shaft 100. The plate 141 prevents the elastic member 140 from coming into contact with the housing 110. The bearing 130 is sandwiched between the elastic members 140 and 140 in the axial direction ZA. Accordingly, the nut 121 is elastically supported in the axial direction ZA by the elastic members 140 and 140 via the bearing 130.

  According to such a configuration, when an axial force ZA is applied to the rack shaft 100 by the steering operation of the driver, the nut 121 and the bearing 130 are integrated with the rack shaft 100 as an initial operation from the elastic member 140. After moving in the axial direction ZA against the elastic force, the nut 121 rotates relative to the rack shaft 100. Therefore, the rack shaft 100 is easy to move in the axial direction when a force in the axial direction ZA starts to act on the rack shaft 100, so that a feeling of resistance at the initial stage of the steering operation is reduced. Therefore, a smooth steering feeling can be obtained.

International Publication No. 2011/147824

  By the way, as the elastic member 140, for example, a disc spring 142 as shown in FIG. 8A can be used. However, when such a disc spring 142 is used as the elastic member 140, when the bearing 130 moves in the axial direction ZA, there is a possibility that the disc spring 142 is used up to the contact state shown in FIG. . The close contact state indicates a state in which the axial length of the disc spring 142 is equal to or close to the plate thickness. When the disc spring 142 is used up to the close contact state, excessive stress acts on the disc spring 142. This is a factor that shortens the life of the disc spring 142.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a steering device capable of extending the life of a disc spring that elastically supports a nut of a ball screw mechanism.

  A steering device that solves the above-described problem has a cylindrical nut that is screwed into a thread groove formed on an outer peripheral surface of a steering shaft of a vehicle via a plurality of balls, and is steered based on rotation of the nut. A ball screw mechanism for applying an axial force to the shaft is provided. The steering device also includes a motor that applies torque to the nut, a housing that covers the periphery of the steered shaft, a bearing that rotatably supports the nut with respect to the housing, and an axis of the steered shaft with respect to the housing. A disc spring that elastically supports the nut in the axial direction of the steered shaft when relatively moving in the direction, and a plate having an axially extending portion that restricts the movement of the disc spring in the radial direction of the steered shaft. In the axially extending portion, the axial length of the steered shaft is set larger than the plate thickness of the disc spring.

  According to the said structure, the bending of a disc spring is stopped in the range larger than the plate | board thickness of a disc spring by an axial direction extension part becoming support. As a result, it is avoided that the disc spring is shrunk by the axially extending portion in which the axial length of the steered shaft is set larger than the plate thickness of the disc spring, and the disc spring is used until it is in close contact. It becomes difficult. Therefore, since the stress acting on the disc spring can be relaxed, the life of the disc spring can be extended.

In the above steering device, it is preferable that the axially extending portion regulates the deflection of the disc spring by contacting the side surface of the inner ring or the outer ring of the bearing.
According to the above configuration, for example, the deflection of the disc spring can be regulated by a surface having a certain degree of strength such as the side surface of the inner ring or the outer ring rather than the seal portion of the bearing. Thereby, the bending of a disc spring can be controlled more suitably.

However, in order to fulfill the function as a disc spring, it is necessary to bend the disc spring by the design stroke amount of the disc spring.
Therefore, the plate further includes a radially extending portion that restricts the movement of the disc spring in the axial direction of the steered shaft, and the axial length of the steered shaft of the axially extending portion is in a state where the disc spring is not bent. It is preferable that the gap between the radially extending portion and the bearing is set to a size that can secure the design stroke amount of the disc spring.

  According to the above configuration, the axial length of the steered shaft of the axially extending portion is determined from the plate thickness of the disc spring so that the disc spring does not shrink between the radially extending portion and the bearing. Even if it is made larger, a gap (space) in which the disc spring can be bent can be secured. Thereby, the lifetime of a disk spring can be extended, maintaining the function as a disk spring.

  In the above steering apparatus, the motor has an output shaft arranged in parallel to the axis of the steered shaft, and the torque of the motor is applied from the output shaft to the nut via the speed reduction mechanism, and the speed reduction mechanism is applied to the output shaft. It is preferable to include a drive pulley that is integrally attached, a driven pulley that is integrally attached to the nut, and a belt that is stretched between the drive pulley and the driven pulley.

  According to the above configuration, since the life of the disc spring can be extended, the life of the function of elastically supporting the nut in the axial direction of the steered shaft can also be extended. In the so-called rack parallel type in which the motor output shaft is arranged parallel to the axis of the steered shaft, the nut can be frequently moved in the axial direction of the steered shaft. Therefore, it can be said that the effect is particularly great. As a result, it is possible to provide a stable assist for a vehicle driver with a long life by mounting a steering device realized in a rack parallel type having characteristics relating to the axially extending portion on the vehicle. it can.

  ADVANTAGE OF THE INVENTION According to this invention, the lifetime of the disc spring which elastically supports the nut of a ball screw mechanism can be extended.

Sectional drawing which shows the schematic structure about an electric power steering apparatus. Sectional drawing which shows the cross-section of the assist mechanism about an electric power steering apparatus. Sectional drawing which shows the cross-section of the ball screw mechanism about an electric power steering apparatus. The perspective view which shows the disassembled perspective structure about a bearing support part. Sectional drawing which shows the operation example about a bearing support part. Sectional drawing which shows the cross-section of the ball screw mechanism about the modification of an electric power steering device. Sectional drawing which shows the cross-section of the bearing support part of the ball screw mechanism about the conventional electric power steering apparatus. (A), (b) is sectional drawing which shows an example of the cross-section of the bearing support part about the conventional electric power steering apparatus.

  Hereinafter, an embodiment of a steering device will be described. The steering device of the present embodiment is a rack parallel type electric power steering device that applies an assist force to a steering mechanism by a motor.

  As shown in FIG. 1, the electric power steering apparatus 1 includes a steering mechanism 4 for turning the steered wheels 3 based on an operation of the driver's steering wheel 2 and an assist mechanism 5 for assisting the driver's steering operation.

  The steering mechanism 4 includes a steering shaft 40 that serves as a rotating shaft of the steering wheel 2, and a rack shaft 42 that is coupled to a lower end portion of the steering shaft 40 via a rack and pinion mechanism 41. In the present embodiment, the rack shaft 42 corresponds to the steered shaft. In the steering mechanism 4, when the steering shaft 40 rotates in accordance with the driver's operation of the steering wheel 2, the rotational motion is converted into the reciprocating linear motion in the axial direction ZA of the rack shaft 42 via the rack and pinion mechanism 41. When the reciprocating linear motion of the rack shaft 42 in the axial direction ZA is transmitted to the tie rods 43 connected to both ends thereof, the turning angle of the steered wheels 3 is changed, and the traveling direction of the vehicle is changed.

  The assist mechanism 5 is provided on the rack shaft 42. The assist mechanism 5 includes a motor 6 and a power transmission mechanism 7. The power transmission mechanism 7 and the rack shaft 42 are covered with the housing 10. The housing 10 includes a first housing 11 and a second housing 12 that are divided in the axial direction of the rack shaft 42 in the vicinity of the power transmission mechanism 7, and is configured by connecting them together. The motor 6 is assembled to the outer wall of the housing 10 with bolts 13 so that the output shaft 60 thereof is parallel to the axis (center axis) of the rack shaft 42. Further, the output shaft 60 of the motor 6 extends to the inside of the housing 10 through a through hole 14 formed in the housing 10. The power transmission mechanism 7 includes a ball screw mechanism 8 attached to the outer periphery of the rack shaft 42 and a speed reduction mechanism 9 that transmits the rotation of the output shaft 60 of the motor 6 to the ball screw mechanism 8 at a reduced speed.

Next, the structures of the ball screw mechanism 8 and the speed reduction mechanism 9 will be described.
As shown in FIG. 2, a thread groove 44 is formed on the outer peripheral surface of the rack shaft 42. The ball screw mechanism 8 includes a nut 80 that is screwed into the thread groove 44 of the rack shaft 42 via a plurality of balls 82. A spiral thread groove 81 facing the thread groove 44 of the rack shaft 42 is formed on the inner peripheral surface of the nut 80. That is, a rolling path R in which the ball 82 rolls is formed by a spiral space surrounded by the thread groove 44 of the rack shaft 42 and the thread groove 81 of the nut 80. Further, in the nut 80, a not-shown annular flow path that short-circuits between two locations of the rolling path R is formed. Therefore, the ball 82 can circulate infinitely on the rolling path R through the annular flow path in the nut 80.

  An annular flange portion 83 is formed at one end portion of the nut 80 in the axial direction. Further, the inner ring 21 of the bearing 20 is fitted to the outer peripheral surface of the nut 80 so as to be engaged with the flange 83 in the axial direction, and the driven pulley 91 is fitted adjacent to the inner ring 21 of the bearing 20. Is done. The bearing 20 is a double-row angular ball bearing (a general and versatile bearing). A male screw portion 84 is formed on the outer peripheral surface of the end portion of the nut 80 opposite to the flange portion 83. The driven pulley 91 is fixed to the nut 80 by screwing the driven pulley 91 into the male screw portion 84. Further, the inner ring 21 of the bearing 20 is sandwiched between the driven pulley 91 and the flange portion 83, whereby the inner ring 21 of the bearing 20 is fixed to the nut 80. The outer peripheral surface of the outer ring 22 of the bearing 20 is in contact with the housing 10 so as to be slidable in the axial direction ZA of the rack shaft. By this bearing 20, the nut 80 is rotatably supported with respect to the housing 10.

The speed reduction mechanism 9 includes a drive pulley 90, a driven pulley 91, and an endless belt 92 wound around the pulleys 90 and 91, which are integrally attached to the output shaft 60 of the motor 6.
In the assist mechanism 5 including the ball screw mechanism 8 and the speed reduction mechanism 9, when the output shaft 60 of the motor 6 is rotated based on energization of the motor 6, the drive pulley 90 is integrated with the output shaft 60 of the motor 6. Rotate. As a result, the drive pulley 90 rotates the driven pulley 91 and the nut 80 together via the belt 92. At this time, the ball screw mechanism 8 is driven based on the torque applied to the nut 80. That is, in the ball screw mechanism 8, when the nut 80 rotates relative to the rack shaft 42, the ball 82 receives a load (friction) from the nut 80 and the rack shaft 42 and circulates in the rolling path R infinitely. Through the infinite circulation of the balls 82, the torque applied to the nut 80 is transmitted to the rack shaft 42, and the rack shaft 42 moves relative to the nut 80 in the axial direction ZA. That is, a force in the axial direction ZA is applied to the rack shaft 42. The axial force ZA applied to the rack shaft 42 serves as an assist force to assist the driver's steering operation.

  On the other hand, a first support portion 30 </ b> A is provided between one side surface 23 of the outer ring 22 of the bearing 20 and the first housing 11. The second housing 12 is formed with an extending portion 12 a extending toward the other side 24 of the outer ring 22 of the bearing 20. The extending portion 12 a of the second housing 12 and the other side of the outer ring 22 of the bearing 20 are formed. The second support portion 30 </ b> B is provided between The first support portion 30A and the second support portion 30B indirectly elastically support the nut 80 in the axial direction ZA by elastically supporting the outer ring 22 of the bearing 20 in the axial direction ZA. Next, the structure of the first support portion 30A and the second support portion 30B will be described in detail. Since the first support portion 30A and the second support portion 30B have the same structure, only the structure of the first support portion 30A will be described below for convenience.

As shown in FIG. 3, the first support portion 30 </ b> A includes a plate 31 and a disc spring 32.
As shown in FIGS. 3 and 4, the disc spring 32 is made of a ring-shaped metal member that forms a truncated cone. Specifically, the disc spring 32 has a shape in which an inner edge portion 32a protrudes toward one end in the axial direction and an outer edge portion 32b protrudes toward the other end in the axial direction.

  The plate 31 is made of a ring-shaped metal member whose cross-sectional shape perpendicular to the axial direction ZA is L-shaped. That is, in the axial direction ZA, in the axial direction ZA, the radially extending portion 31a having a rectangular cross-sectional shape and the axially extending portion 31b having a square shape that is closer to a square than the radially extending portion 31a are integrally formed. Formed. The radially extending portion 31a is formed to extend in the radial direction of the plate 31 so as to restrict the movement of the disc spring 32 in the axial direction ZA. The axially extending portion 31 b is fitted to the inside of the radial direction ZB (inner edge portion 32 a) with respect to the disc spring 32. That is, the axially extending portion 31b positions the disc spring 32 in the radial direction ZB (regulates the positional deviation of the disc spring 32). Further, the axially extending portion 31b is formed so as to extend (protrude) from the inner peripheral end of the radially extending portion 31a in the axial direction of the plate 31 so as to restrict the deflection of the disc spring 32 in the axial direction ZA. .

  As shown in FIG. 3, the plate 31 is disposed with a gap in the axial direction ZA from the outer ring 22 of the bearing 20. The other side surface 31d opposite to the one side surface 31c facing the disc spring 32 in the radially extending portion 31a is in contact with the housing 10 in the axial direction ZA. An extending surface 31e corresponding to the axially extending portion 31b extending from the one side surface 31c toward the bearing 20 is disposed so as to face the one side surface 23 of the outer ring of the bearing 20. The inner peripheral portion of the disc spring 32 is fitted on the outer periphery of the axially extending portion 31b. The disc spring 32 is disposed such that its inner edge portion 32 a contacts the radially extending portion 31 a and the axially extending portion 31 b of the plate 31, and its outer edge portion 32 b contacts the outer ring 22 of the bearing 20.

  That is, the disc spring 32 is disposed between the radially extending portion 31 a (plate 31) and the outer ring 22 of the bearing 20. The disc spring 32 of the first support portion 30 </ b> A applies an elastic force F <b> 1 to the outer ring 22 of the bearing 20. Similarly, the disc spring 32 of the second support portion 30 </ b> B applies an elastic force F <b> 2 to the outer ring 22 of the bearing 20. The outer ring 22 of the bearing 20 is elastically supported in the axial direction ZA by the respective elastic forces F1, F2 of the first support portion 30A and the second support portion 30B. With such a structure, the nut 80 is elastically supported in the axial direction ZA by the first support portion 30A and the second support portion 30B via the bearing 20.

Here, the configuration of the axially extending portion 31b of the plate 31 will be described in more detail.
As shown in the enlarged view of FIG. 3, the disc spring 32 is disposed between the radially extending portion 31 a (plate 31) and the outer ring 22 of the bearing 20, while the axially extending portion 31 b and the rack shaft 42. Arranged coaxially with the axis (center axis). That is, in the axial direction ZA, the axially extending portion 31 b is disposed between the radially extending portion 31 a and the outer ring 22 of the bearing 20. Moreover, the axial direction extension part 31b makes the support part arrange | positioned inside the radial direction ZB of the disk spring 32 so that the disk spring 32 may be supported to radial direction ZB.

  The length D2 of the axially extending portion 31b in the axial direction ZA is set larger than the plate thickness D1 of the disc spring 32 when the plate thickness of the disc spring 32 is set to the plate thickness D1. The length D2 of the axially extending portion 31b is a clearance between the one side surface 31c of the radially extending portion 31a and the one side surface 23 of the outer ring 22 of the bearing 20 when the disc spring 32 is not bent. When it is set as D3, it sets so that the stroke amount (contraction amount) D4 of the design disc spring 32 can be ensured in this clearance gap D3. The design stroke amount is determined to be an amount empirically derived as being sufficient to elastically support the nut 80 in the axial direction ZA in the electric power steering apparatus 1 such as the power transmission mechanism 7 and the ball screw mechanism 8.

  In other words, the electric power steering apparatus 1 has (plate thickness D1) <(length D2) = ((gap D3) − (stroke amount D4) between the plate thickness D1, the length D2, the gap D3, and the stroke amount D4. )) Is designed to have the relationship. However, if the relationship of (length D2) ≦ ((gap D3) − (stroke amount D4)) is satisfied, in the gap D3 between the one side surface 31c of the radially extending portion 31a and the one side surface 23 of the bearing 20, The designed stroke amount D4 of the disc spring 32 can be secured. For this reason, how much the length D2 in the axial direction ZA of the axially extending portion 31b is made larger than the plate thickness D1 of the disc spring 32 ((length D2) − (plate thickness D1)) is (length D2). It can be adjusted in a range satisfying <((gap D3) − (stroke amount D4)).

According to the electric power steering apparatus 1 described above, the following operations and effects (1) to (5) can be obtained.
(1) When a driver's steering operation causes a force in the axial direction ZA to act on the rack shaft 42, the nut 80 and the bearing 20 of the ball screw mechanism 8 are integrally displaced toward the first support portion 30A. The outer edge portion 32b of the disc spring 32 of the support portion 30A is pressed toward the plate 31 and the disc spring 32 is bent. When the disc spring 32 bends in this way, as shown in FIG. 5, when one side surface 23 of the bearing 20 contacts the extending surface 31e (axial extending portion 31b) of the plate 31, the axial extending portion 31b becomes a support. Thus, the approach between the radially extending portion 31a and the bearing 20 is restricted.

  In this case, a gap having a length D2 in the axial direction ZA of the axially extending portion 31b is larger between the radial extending portion 31a and the bearing 20 than the plate thickness D1 of the disc spring 32 by the axially extending portion 31b. It is formed. In particular, regarding the gap D5 between the radially extending portion 31a and the disc spring 32, a gap substantially equal to ((length D2) − (plate thickness D1)) is formed.

  Thereby, it is avoided by the axial direction extension part 31b that the disk spring 32 shrinks, and it becomes difficult to use the disk spring 32 to a contact | adherence state. Therefore, since the stress acting on the disc spring 32 can be relaxed, the life of the disc spring 32 can be extended.

  (2) The axially extending portion 31 b can regulate the deflection of the disc spring 32 by a surface having a certain degree of strength such as the one side surface 23 of the outer ring 22 of the bearing 20. Thereby, the bending of the disc spring 32 can be controlled more appropriately.

(3) However, in order to fulfill the function as a disc spring, it is necessary to bend the disc spring only by the stroke amount in the design of the disc spring.
In that respect, the axially extending portion 31b ensures a design stroke amount D4 of the disc spring 32 in the gap D3 between the radial extending portion 31a and the bearing 20 when the disc spring 32 is not bent. The size is set as possible. Accordingly, the length D2 of the axially extending portion 31b in the axial direction ZA is set to the plate thickness D1 of the disc spring 32 so that the disc spring 32 is not contracted between the radially extending portion 31a and the bearing 20. Even if it is made larger than this, a gap (space) in which the disc spring 32 can be bent can be secured. Therefore, the life of the disc spring 32 can be extended while maintaining the function as the disc spring 32.

  (4) Operation and Effect As described in (1), the life of the disc spring 32 can be extended, so that the life of the function of elastically supporting the nut 80 in the axial direction ZA can also be extended. In the so-called rack parallel type in which the output shaft 60 of the motor 6 is arranged in parallel to the axis of the rack shaft 42, the nut 80 is frequently moved in the axial direction ZA of the rack shaft 42. It can be said that the effect is particularly great. Thus, by mounting the electric power steering device 1 realized in the rack parallel type having the characteristics related to the axially extending portion 31b on the vehicle, a stable assist is provided for the vehicle driver with a long life. can do.

  (5) The axially extending portion 31b also has a function as a support portion that supports the disc spring 32 in the radial direction ZB. Thereby, since the position shift of the disk spring 32 in radial direction ZB can be suppressed, generation | occurrence | production of the damage | wound etc. of the disk spring 32 by the position shift which is not intended at the manufacturing stage can be suppressed. Therefore, the life of the disc spring 32 can be extended more suitably.

In addition, the said embodiment can also be implemented with the following forms.
As shown in FIG. 6, the axially extending portion 31 b may be formed so as to contact the outside of the disk spring 32 in the radial direction ZB, that is, the inside of the housing 10 in the radial direction ZB. In this case, in the plate 31, the axially extending portion 31 b is fitted to the outer side (outer edge portion 32 b) in the radial direction ZB with respect to the disc spring 32. The axially extending portion 31b is formed so as to extend (project) from the outer peripheral end of the radially extending portion 31a in the axial direction of the plate 31. In this case, the outer peripheral portion of the disc spring 32 is fitted into the inner periphery of the axially extending portion 31b. In other words, the disc spring 32 is disposed such that the outer edge portion 32 b contacts the radially extending portion 31 a and the axially extending portion 31 b of the plate 31, and the inner edge portion 32 a contacts the outer ring 22 of the bearing 20. . Even in such a configuration, the occurrence of unintended misalignment of the disc spring 32 can be suppressed as in the above embodiment, which contributes to a longer life of the disc spring 32.

  As described in the above embodiment, the length D2 of the axially extending portion 31b in the axial direction ZA is (plate thickness D1) <(length D2) ≦ ((gap D3) − (stroke amount D4)). You may change suitably in the range with which a relationship is satisfy | filled.

The length D2 in the axial direction ZA of the axially extending portion 31b only needs to satisfy at least (plate thickness D1) <(length D2), and can be changed as appropriate.
-Although the bearing 20 of the said embodiment was a double row angular contact ball bearing, the bearing 20 is not restricted to this, You may use another bearing.

  The plate 31 and the disc spring 32 may be disposed between the side surface of the inner ring 21 of the bearing 20 and the nut 80. In this case, when the side surface of the inner ring of the bearing 20 comes into contact with the extending surface 31e (axially extending portion 31b) of the plate 31, the axially extending portion 31b serves as a support to bring the radial extending portion 31a and the bearing 20 closer. It will be regulated.

  In the above embodiment, the electric power steering device 1 is embodied by the rack parallel type assist mechanism 5, but any type of assist mechanism that requires the ball screw mechanism 8 is applicable.

-The structure of the said embodiment is applicable not only to an electric power steering apparatus but a steer-by-wire type steering apparatus etc., for example.
Next, a technical idea that can be grasped from the above-described embodiment and another example (modification) will be additionally described below.

  (A) In the steering apparatus, the plate includes a support portion that supports the disc spring in a radial direction of the steered shaft. According to this structure, the position shift of the disc spring in the radial direction of the steered shaft can be suppressed.

  D1 ... Plate spring thickness, D2 ... Axial length of axially extending portion, D3 ... Clearance between radially extending portion and bearing, D4 ... Stroke amount of disc spring, ZA ... Axial direction of rack shaft , ZB ... radial direction of rack shaft, 1 ... electric power steering device (steering device), 6 ... motor, 8 ... ball screw mechanism, 9 ... speed reduction mechanism, 10 ... housing, 20 ... bearing, 31 ... plate, 31a ... diameter Direction extending portion, 31b ... Axial extending portion, 32 ... Belleville spring, 42 ... Rack shaft (steering shaft), 44 ... Thread groove, 60 ... Output shaft, 80 ... Nut, 82 ... Ball, 90 ... Drive pulley, 91 ... driven pulley, 92 ... belt.

Claims (4)

It has a cylindrical nut screwed through a plurality of balls in a thread groove formed on the outer peripheral surface of the turning shaft of the vehicle, and applies axial force to the turning shaft based on the rotation of the nut. A ball screw mechanism to
A motor for applying torque to the nut;
A housing covering the periphery of the steered shaft;
A bearing that rotatably supports the nut with respect to the housing;
A disc spring that elastically supports the nut in the axial direction of the steered shaft when the nut moves relative to the housing in the axial direction of the steered shaft;
A plate having an axially extending portion that restricts movement of the disc spring in the radial direction of the steered shaft,
The axially extending portion is a steering device in which the axial length of the steered shaft is set larger than the plate thickness of the disc spring.   The steering device according to claim 1, wherein the axially extending portion regulates the deflection of the disc spring by contacting a side surface of an inner ring or an outer ring of the bearing. The plate further includes a radially extending portion that restricts movement of the disc spring in the axial direction of the steered shaft,
The axial length of the axially extending portion of the steered shaft is determined by the design of the disc spring in the gap between the radially extending portion and the bearing when the disc spring is not bent. The steering device according to claim 1 or 2, wherein the steering device is set to a size capable of securing an upper stroke amount. The motor is arranged such that its output shaft is parallel to the axis of the steered shaft,
The torque of the motor is applied from the output shaft to the nut via a speed reduction mechanism,
The deceleration mechanism is
A drive pulley integrally attached to the output shaft;
A driven pulley integrally attached to the nut;
The steering device according to any one of claims 1 to 3, comprising a belt that is stretched between the drive pulley and the driven pulley.