JP2013148134A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device, which can suppress deformation of a screw groove of a nut.SOLUTION: A ball screw nut 61 is supported by a ball bearing 87 through a mounting member 70 in a manner freely rotating. The mounting member 70 has a lower rigidity compared to the rigidity of the ball screw nut 61 and the rigidity of the ball bearing 87. When the ball screw nut 61 is mounted to the ball bearing 87 through the mounting member 70, the right side face 66A of the body 66 is set as a top and the ball screw nut 61 is pressed into a small diameter part 71 from the side of a large diameter part 72 of the mounting member 70, and from the side of the small diameter 71 of the mounting member 70, an inner wheel 87A of the ball bearing 87 is pressed into the large diameter part 72.

Description

  The present invention relates to an electric power steering apparatus having an electric motor having an output shaft, a nut that converts a rotational motion of the electric motor into a linear motion and transmits the linear motion to a steered shaft, and a bearing that rotatably supports the nut.

  The electric power steering apparatus of Patent Document 1 houses a rack shaft coupled to a steering shaft, a ball screw mechanism that converts the rotational motion of the electric motor into a linear motion and transmits the linear motion to the rack shaft, and the rack shaft and the ball screw mechanism. And a bearing that supports the ball screw mechanism in a state in which the ball screw mechanism can rotate with respect to the housing.

  The ball screw mechanism includes a nut that is coaxial with the rack shaft, and a plurality of balls that spirally and endlessly circulate between the screw groove of the nut and the screw groove of the rack shaft. The nut is press-fitted into the bearing.

JP 2002-145080 A

In the ball screw mechanism, there is a possibility that the thread groove of the nut is deformed when the load when the nut is press-fitted into the inner ring of the bearing exceeds the allowable stress of the nut.
In order to solve the above-described problems, an object of the present invention is to provide an electric power steering device capable of suppressing deformation of a thread groove of a nut.

  (1) The first means is the invention according to claim 1, that is, an electric motor having an output shaft, a nut that converts a rotational motion of the electric motor into a linear motion and transmits the linear motion to the steered shaft, and the nut An electric power steering apparatus having a bearing for supporting the nut includes a nut and a low-rigidity member having rigidity lower than that of the bearing, and the nut is supported by the bearing via the low-rigidity member. And

  The low rigidity member is less rigid than the nut and the bearing. For this reason, the deformation amount of the nut when the low-rigidity member is fitted into the nut is smaller than the deformation amount when the bearing is fitted into the nut. For this reason, deformation of the thread groove of the nut can be suppressed.

  (2) The second means is the invention according to claim 2, that is, in claim 1, the low-rigidity member has a small-diameter portion fixed to the nut, an inner diameter and an outer diameter larger than the small-diameter portion. A large-diameter portion that is fixed to the bearing and a connecting portion that connects the small-diameter portion and the large-diameter portion to each other, and the small-diameter portion and the large-diameter portion are mutually connected in the axial direction of the nut. The gist is that they are located in different places.

  The connecting portion of the low-rigidity member is deformed by the force that the small diameter portion receives from the nut and the force that the large diameter portion receives from the bearing. For this reason, the force which acts when the large diameter portion is fitted into the bearing is not easily transmitted to the nut. For this reason, deformation of the thread groove of the nut is suppressed.

  (3) The third means is the invention according to claim 3, that is, an electric motor having an output shaft, a nut for converting a rotational motion of the electric motor into a linear motion and transmitting it to a steered shaft, and the nut The nut includes a first peripheral wall portion and a second peripheral wall portion that is lower in rigidity than the bearing, and the bearing supports the second peripheral wall portion. The gist is to do.

  The second peripheral wall portion is less rigid than the first peripheral wall portion of the nut and the bearing. For this reason, the deformation amount of the second peripheral wall portion when the second peripheral wall portion is fitted into the bearing is larger than the deformation amount of the first peripheral wall portion when it is assumed that the first peripheral wall portion is fitted into the bearing. For this reason, compared with a nut that does not have a low-rigidity portion, that is, a nut having a configuration in which the entire peripheral wall portion has the same rigidity as the first peripheral wall portion, the peripheral wall portion when the nut is fitted into the inner ring of the bearing Deformation is not easily transmitted to the thread groove. For this reason, deformation of the thread groove of the nut can be suppressed.

(4) The fourth means is the invention according to the fourth aspect, that is, the third aspect, wherein the second peripheral wall portion has a space formed therein.
The space formed inside the second peripheral wall portion can be easily formed by changing the design of the nut. For this reason, compared with the case where the member for suppressing the deformation | transformation of the thread groove of a nut is provided separately, the manufacturing cost of an electric power steering device is suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the deformation | transformation of a nut can be suppressed in the electric power steering apparatus provided with the ball screw mechanism.

The sectional view showing the section structure about the electric power steering device of a 1st embodiment of the present invention. Sectional drawing which shows the cross-section of the ball screw mechanism in the plane in alignment with the rotation center axis | shaft of an electric motor, and its peripheral components about the electric power steering apparatus of 1st Embodiment. FIG. 1A is a perspective view showing an external appearance of an attachment member attached to a ball screw mechanism, and FIG. Sectional drawing which shows the cross-section of the ball screw mechanism in the plane in alignment with the rotation center axis | shaft of an electric motor, and its peripheral components about the electric power steering apparatus of 2nd Embodiment of this invention. About the electric power steering device of 2nd Embodiment, (a) is a perspective view which shows the external appearance of a ball screw nut, (b) is a top view which shows the external appearance of a ball screw nut.

(First embodiment)
The overall configuration of the electric power steering apparatus 1 will be described with reference to FIG.
The electric power steering apparatus 1 houses a steering mechanism 10 that transmits the rotation of a steering wheel (not shown) to a wheel (not shown), an assist mechanism 20 that assists steering of the steering wheel, and the steering mechanism 10 and the assist mechanism 20. Housing 30.

  The housing 30 includes a first divided housing 31, a second divided housing 32, and a third divided housing 33. The second divided housing 32 is attached to the first divided housing 31 via an O-ring 81. The third divided housing 33 is attached to the first divided housing 31 via an O-ring 82.

  The first divided housing 31 has a right end 31A and a left end 31B, and an opening 31C. The opening 31C is provided in the vicinity of the left end 31B that does not hinder the mounting of the first divided housing 31 and the second divided housing 32. The second divided housing 32 includes an end portion 32A, a female screw portion 32B, an opening portion 32C, and a step portion 32D. The female thread portion 32B is formed on the inner surface portion of the end portion 32A that does not hinder the attachment of a double-row bearing 86 described later. A center nut 85 is attached to the female thread portion 32B. The step portion 32D is formed on the inner surface between the end portion 32A and the opening portion 32C. The third divided housing 33 has an end portion 33A.

  The steering mechanism 10 includes a pinion shaft 11 connected to a steering shaft (not shown), a steered shaft 12 whose both ends are connected to wheels via tie rods (not shown), and a rack guide 13. The pinion 11 </ b> A of the pinion shaft 11 meshes with the rack 12 </ b> A of the steered shaft 12. The pinion shaft 11 is accommodated in the second divided housing 32. The steered shaft 12 is accommodated in the housing 30. The rack guide 13 is attached to the opening 32C.

  Here, a direction parallel to the axial direction of the steered shaft 12 is defined as “axial direction X”. Further, the direction from the second divided housing 32 toward the third divided housing 33 in the axial direction X is “right XA”, and the direction from the third divided housing 33 toward the second divided housing 32 is “left XB”. .

  The assist mechanism 20 includes an electric motor 40, a rotation sensor 50 that detects the rotation of the electric motor 40, and a ball screw mechanism 60 that transmits the driving force of the electric motor 40 to the steered shaft 12.

  The electric motor 40 includes a motor shaft 41 and a stator 42 that surrounds the outer periphery of the motor shaft 41. The electric motor 40 is connected to an external power source (not shown) via a power supply connector 43 located in the vicinity of the right end 31A of the first divided housing 31. The motor shaft 41 corresponds to an “output shaft”.

  The motor shaft 41 includes a right end portion 41A and a left end portion 41B, a fitting portion 41C and a female screw portion 41D formed on the inner peripheral surface of the right end portion 41A, and a male screw portion 41E formed on the outer peripheral surface of the left end portion 41B. And a step portion 41F. 41 C of fitting parts are located in the opening vicinity of 41 A of right end parts. The female thread portion 41D is located on the left side XB of the fitting portion 41C and is adjacent to the fitting portion 41C. The male screw portion 41E is located in the vicinity of the opening of the left end portion 41B. The step portion 41F is located on the right side XA of the male screw portion 41E, and has a predetermined gap with the male screw portion 41E.

  A magnet 46 is fixed to the outer peripheral surface of the motor shaft 41. The magnet 46 is located between the female thread portion 41D and the step portion 41F in the axial direction X. A nut 84 is attached to the male screw portion 41E. The motor shaft 41 and the steered shaft 12 are disposed on the same axis m. The left end portion 41 </ b> B of the motor shaft 41 is rotatably supported by a double row bearing 86.

  The inner ring 86 </ b> A of the double row bearing 86 is sandwiched between the stepped portion 41 </ b> F and the nut 84. The inner ring 86 </ b> A is fixed to the motor shaft 41 according to the tightening amount of the nut 84. The outer ring 86 </ b> B of the double row bearing 86 is sandwiched between the stepped portion 32 </ b> D and the center nut 85. The outer ring 86 </ b> B is fixed to the housing 30 according to the tightening amount of the center nut 85. That is, the position of the double row bearing 86 in the axial direction X is fixed according to the tightening amount of the nut 84 and the center nut 85.

  The stator 42 has a coil 47 that can be energized. When power is supplied from an external power source via the power supply connector 43, the coil 47 is energized. The stator 42 is fixed to the inner surface of the first divided housing 31 facing the magnet 46.

  The rotation sensor 50 includes a sensing unit 51 and a connector unit 52. The rotation sensor 50 is attached to the first divided housing 31 in a state of being positioned between the electric motor 40 and the center nut 85. The sensing unit 51 is disposed so as to face the motor shaft 41. The connector part 52 is arranged in a state protruding from the outer surface of the first divided housing 31. The sensing unit 51 and the connector unit 52 are connected via the opening 31 </ b> C of the first divided housing 31.

The operation of the electric power steering apparatus 1 will be described with reference to FIG.
The driver inputs the steering torque to the steering wheel when changing the turning angle of the wheel. The pinion shaft 11 rotates in conjunction with steering of the steering wheel. The steered shaft 12 moves in the axial direction X according to the rotation of the pinion shaft 11. The rack guide 13 supports the steered shaft 12 so as to be movable in the axial direction X.

  The assist mechanism 20 supplies the electric motor 40 with a current corresponding to the magnitude of the steering torque input to the steering wheel. The electric motor 40 rotates the motor shaft 41 about the axis m by applying an electromagnetic force corresponding to the electric power supplied to the coil 47 to the magnet 46. The rotation of the motor shaft 41 is transmitted to the ball screw mechanism 60.

  The ball screw mechanism 60 converts the rotational motion of the motor shaft 41 into a linear motion in the axial direction X and transmits it to the steered shaft 12. The rotation sensor 50 detects the rotation angle of the motor shaft 41 through the sensing unit 51, supplies power via the connector unit 52, and outputs an electrical signal corresponding to the rotation angle detected by the sensing unit 51.

  The electric signal output from the connector unit 52 is input to a control device (not shown) that controls the electric power steering device 1. The control device controls power supply to the electric motor 40 based on the rotation angle of the motor shaft 41 detected through the rotation sensor 50. Thereby, the drive of the electric motor 40 is controlled. The steered shaft 12 translates in the axial direction X with the operation of the pinion shaft 11 and the operation of the ball screw mechanism 60. The steering angle of the wheels changes according to the translation of the steered shaft 12 in the axial direction X.

A detailed configuration of the ball screw mechanism 60 will be described with reference to FIGS. 2 and 3.
As shown in FIG. 2, the ball screw mechanism 60 includes a ball screw nut 61 and a plurality of balls 62. The ball screw nut 61 is disposed on the same axis m as the steered shaft 12. The ball 62 is disposed across the spiral groove 68 formed on the inner peripheral surface of the ball screw nut 61 and the screw shaft 12 </ b> B formed on the outer peripheral surface of the steered shaft 12. The ball screw nut 61 corresponds to a “nut”.

  The ball screw nut 61 has a main body portion 66 and an engaging portion 67. The main body 66 includes a right end surface 66A and a left end surface 66B, an annular flow channel 66C, and a spiral groove 68. The annular flow channel 66 </ b> C is formed inside the main body 66 in a state where two portions of the spiral groove 68 are short-circuited.

  The engaging portion 67 has a male screw portion 67A and a fitting portion 67B formed on the outer peripheral surface, and a spiral groove 68. The fitting portion 67 </ b> B is located in the vicinity of the left end surface 66 </ b> B of the main body portion 66. The male screw portion 67A is located on the left side XB of the fitting portion 67B and is adjacent to the fitting portion 67B.

  The ball screw nut 61 is fixed to the right end 41 </ b> A of the motor shaft 41 and is rotatably supported by the ball bearing 87 via the mounting member 70. The attachment member 70 integrally includes a small diameter portion 71, a large diameter portion 72, and a connecting portion 73 that connects the small diameter portion 71 and the large diameter portion 72 to each other. The attachment member 70 corresponds to a “low-rigidity member”. Further, the ball bearing 87 corresponds to a “bearing”.

  In the axial direction X, the position of the small diameter portion 71 and the position of the large diameter portion 72 are different from each other. The small diameter portion 71 and the large diameter portion 72 have a cylindrical shape (see FIG. 3A). The large diameter part 72 has an outer diameter R3 larger than the outer diameter R1 of the small diameter part 71 and an inner diameter R4 larger than the inner diameter R2 of the small diameter part 71 (see FIG. 3B). The connecting portion 73 has a truncated cone shape (see FIG. 3A). The small-diameter portion 71, the large-diameter portion 72, and the connecting portion 73 are formed by drawing a cylindrical metal member having a thin plate thickness.

  The small diameter portion 71 is fixed to the ball screw nut 61. The large diameter portion 72 is fixed to the inner ring 87 </ b> A of the ball bearing 87. The connecting portion 73 is deformed by the force received by the small diameter portion 71 from the ball screw nut 61 and the force received by the large diameter portion 72 from the inner ring 87 </ b> A of the ball bearing 87. For this reason, the mounting member 70 has lower rigidity than the rigidity of the ball screw nut 61 and the rigidity of the ball bearing 87. The outer ring 87 </ b> B of the ball bearing 87 to which the large diameter portion 72 is fixed is assembled to the inner surface of the first divided housing 31 via the O-ring 83.

The operation of the ball screw mechanism 60 will be described with reference to FIG.
When the electric motor 40 (FIG. 1) is driven, the ball screw nut 61 rotates together with the motor shaft 41. The ball 62 spirally moves while rolling between the spiral groove 68 and the screw shaft 12B, and moves in an endless circulation by moving through the annular flow channel 66C.

  In the ball screw mechanism 60, the rotational force of the motor shaft 41 is converted into a force that moves the steered shaft 12 in the axial direction X, that is, an assist force that assists the operation of the steering wheel. The ball screw mechanism 60 applies assist force based on the rotational force of the electric motor 40 to the steered shaft 12. As a result, when the driver steers the steering wheel, the assist mechanism 20 assists the movement of the steered shaft 12 in the axial direction X.

With reference to FIG. 2, an example of a method for assembling the ball screw nut 61 and the ball bearing 87 via the mounting member 70 will be described.
First, the ball screw nut 61 is press-fitted into the small-diameter portion 71 from the large-diameter portion 72 side of the mounting member 70 with the right end surface 66A of the main body portion 66 as the head. When the end of the small diameter portion 71 on the side not connected to the connection portion 73 and the right end surface 66A coincide with each other, the press-fitting of the ball screw nut 61 into the small diameter portion 71 is completed.

  Subsequently, the ball screw nut 61 to which the mounting member 70 is fixed is connected to the right end portion of the motor shaft 41 by screwing the male screw portion 67A and the female screw portion 41D and fitting the fitting portion 67B and the fitting portion 41C. Fix to 41A. Finally, the inner ring 87 </ b> A of the ball bearing 87 is press-fitted into the large diameter portion 72 from the small diameter portion 71 side of the mounting member 70. When the outer ring 87B of the ball bearing 87 is fixed by the pressing force of the O-ring 83, the press-fitting of the ball bearing 87 into the large diameter portion 72 is completed.

The electric power steering apparatus 1 of the present embodiment has the following effects.
(1) The ball screw nut 61 is rotatably supported by the ball bearing 87 via the mounting member 70. The attachment member 70 has a lower rigidity than the rigidity of the ball screw nut 61 and the rigidity of the ball bearing 87.

  The mounting member 70 is less rigid than the ball screw nut 61 and the ball bearing 87. For this reason, the deformation amount of the main body portion 66 of the ball screw nut 61 when the attachment member 70 is fitted into the ball screw nut 61 is smaller than the deformation amount when the ball bearing 87 is fitted into the ball screw nut 61. For this reason, deformation of the spiral groove 68 of the ball screw nut 61 can be suppressed.

  (2) The mounting member 70 has a small diameter portion 71 fixed to the main body portion 66 of the ball screw nut 61, an inner diameter and an outer diameter larger than the small diameter portion 71, and a large diameter fixed to the inner ring 87 </ b> A of the ball bearing 87. Part 72 and a connecting part 73 that connects the small diameter part 71 and the large diameter part 72 to each other. The small diameter portion 71 and the large diameter portion 72 are located at different locations in the axial direction X of the ball screw nut 61.

  The connecting portion 73 of the mounting member 70 is deformed by the force that the small diameter portion 71 receives from the main body portion 66 of the ball screw nut 61 and the force that the large diameter portion 72 receives from the inner ring 87 </ b> A of the ball bearing 87. For this reason, the force acting when the large-diameter portion 72 is fitted into the inner ring 87 </ b> A is not easily transmitted to the main body portion 66 of the ball screw nut 61. For this reason, deformation of the spiral groove 68 of the ball screw nut 61 is suppressed.

(Second Embodiment)
The electric power steering apparatus 1 of this embodiment shown in FIG. 4 has the following differences as main differences from the electric power steering apparatus 1 of the first embodiment shown in FIG. That is, the ball screw mechanism 60 of the first embodiment is indirectly supported by the ball bearing 87 via the mounting member 70. On the other hand, the ball screw mechanism 60 of this embodiment is directly supported by the ball bearing 87. Below, the detail of a different point from the electric power steering apparatus 1 of 1st Embodiment is demonstrated, about the structure which is common in 1st Embodiment, the same code | symbol is attached | subjected and the part or all of the description is abbreviate | omitted.

  As shown in FIGS. 4 and 5, the ball screw nut 61 further has a groove 66 </ b> D formed inside the main body 66. The main body portion 66 has an outer edge portion 66G between the outer peripheral surface and the groove portion 66D. The groove 66D is formed in a predetermined range from the right end surface 66A of the main body 66 to the left XB in the axial direction X, and in a predetermined range that does not communicate with the annular flow channel 66C in the rotation direction of the main body 66 (FIG. 5B). ))). The outer peripheral surface of the groove portion 66 </ b> D is located in a portion close to the outer peripheral surface of the main body portion 66. The groove 66D corresponds to a “space”.

  The main body 66 has a first peripheral wall 66E that does not have the groove 66D in the cross-sectional structure of the ball screw nut 61 in the plane along the axis m, and a second peripheral wall 66F that has the groove 66D in the cross-sectional structure in the same plane. For this reason, the 2nd surrounding wall part 66F has low rigidity compared with the rigidity of the 1st surrounding wall part 66E. The first peripheral wall portion 66E corresponds to a “first peripheral wall portion”. The second peripheral wall portion 66F corresponds to a “second peripheral wall portion”.

  The ball screw nut 61 is rotatably supported by the ball bearing 87. At this time, the main body 66 is fixed to the inner ring 87A of the ball bearing 87 at the second peripheral wall 66F. The ball screw mechanism 60 of this embodiment performs the same operation as the ball screw mechanism 60 of the first embodiment.

With reference to FIG. 4, an example of a method for assembling the ball screw nut 61 and the ball bearing 87 of the present embodiment will be described.
In the present embodiment, the ball screw nut 61 is fixed to the right end portion 41A of the motor shaft 41 by screwing the male screw portion 67A and the female screw portion 41D and fitting the fitting portion 67B and the fitting portion 41C. Then, the inner ring 87A of the ball bearing 87 is press-fitted into the ball screw nut 61 from the right end surface 66A side of the main body 66. When the outer ring 87B of the ball bearing 87 is fixed by the tight force of the O-ring 83, the press-fitting of the ball bearing 87 into the ball screw nut 61 is completed.

The electric power steering apparatus 1 of the present embodiment has the following effects.
(1) The ball screw nut 61 includes a first peripheral wall portion 66E and a second peripheral wall portion 66F having rigidity lower than that of the ball bearing 87. The ball bearing 87 supports the second peripheral wall portion 66F.

  The second peripheral wall portion 66F has lower rigidity than the first peripheral wall portion 66E of the ball screw nut 61 and the ball bearing 87. For this reason, the deformation amount of the second peripheral wall portion 66F when the second peripheral wall portion 66F is fitted into the ball bearing 87 is the first peripheral wall portion 66E when the first peripheral wall portion 66E is assumed to be fitted into the ball bearing 87. Greater than the amount of deformation. For this reason, the ball screw nut 61 has no inner ring of the ball bearing 87 as compared with the ball screw nut 61 having no low rigidity portion, that is, a nut having a configuration in which the entire peripheral wall portion has the same rigidity as the first peripheral wall portion 66E. The deformation of the peripheral wall portion when fitted into 87 </ b> A is not easily transmitted to the spiral groove 68. For this reason, deformation of the spiral groove 68 of the ball screw nut 61 can be suppressed.

(2) The main body 66 of the second peripheral wall 66F has a groove 66D formed therein.
The groove portion 66D formed inside the second peripheral wall portion 66F can be easily formed by changing the design of the ball screw nut 61. For this reason, compared with the case where the member for suppressing the deformation | transformation of the spiral groove 68 of the ball screw nut 61 is provided separately, the manufacturing cost of the electric power steering apparatus 1 is suppressed.

(Other embodiments)
The present invention includes embodiments other than the first and second embodiments. Hereinafter, the modification of the said embodiment as other embodiment of this invention is shown. The following modifications can be combined with each other.

  The attachment member 70 (FIG. 3) of the first embodiment is formed by drawing a cylindrical metal member having a thin plate thickness. On the other hand, the mounting member 70 of the modified example is formed by injection molding a resin having lower rigidity than the rigidity of the ball screw nut 61 and the rigidity of the ball bearing 87.

  The attachment member 70 (FIG. 3) of the first embodiment is formed by drawing a cylindrical metal member having a thin plate thickness. On the other hand, the mounting member 70 of the modified example is formed by joining a plurality of metal members having lower rigidity than the rigidity of the ball screw nut 61 and the ball bearing 87 by welding or the like.

  -In the attachment member 70 (FIG. 3) of 1st Embodiment, the small diameter part 71 and the large diameter part 72 have a cylindrical shape, and the connection part 73 has a truncated cone shape. On the other hand, the attachment member 70 of the modified example has one or more slits formed in a predetermined range in the axial direction X in addition to the shape of the first embodiment. The slit may be formed only in one of the small diameter part 71 and the large diameter part 72, or may be formed in two or more of the small diameter part 71, the large diameter part 72, and the connecting part 73.

  The main body 66 (FIG. 5) of the second embodiment is formed in a predetermined range from the right end surface 66A of the main body 66 to the left XB in the axial direction X, and the annular channel 66C in the rotation direction of the main body 66. A groove 66D is formed in a predetermined range (see FIG. 5B) that does not communicate with each other. On the other hand, the groove portion 66D of the modification is formed on the entire circumference of the main body portion 66 in the rotation direction. Part or all of the groove 66D is formed in the outer diameter portion of the main body 66 that does not communicate with the annular flow channel 66C.

-The main-body part 66 (FIG. 5) of 2nd Embodiment has the groove part 66D which the right end surface 66A side opens. On the other hand, the main body portion 66 of the modified example has an internal space in which the right end surface 66A side is closed.
-The main-body part 66 (FIG. 5) of 2nd Embodiment has the groove part 66D formed in the axial direction X and a rotation direction without a break. On the other hand, the main body portion 66 of the modified example has a groove portion 66D formed intermittently in at least one of the axial direction X and the rotational direction.

  -The main-body part 66 (FIG. 5) of 2nd Embodiment has the groove part 66D formed in the axial direction X and a rotation direction. On the other hand, the main body 66 of the modified example has one or more slits formed in a predetermined range in the axial direction X in addition to the shape of the second embodiment. The slit has a shape that allows communication between the outer peripheral surface of the second main body portion and the groove 66D.

(Additional notes based on the descriptions of the first and second embodiments)
Items obtained by superposing the items described in the above embodiment will be described below.
(Additional remark 1) In Claim 2, the said low-rigidity member has one or more slits formed in the predetermined range of the said axial direction.

  (Additional remark 2) In Claim 4, the said space is a groove part formed from the one end surface side of the said nut.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 10 ... Steering mechanism, 11 ... Pinion shaft, 11A ... Pinion, 12 ... Steering shaft, 12A ... Rack, 12B ... Screw shaft, 13 ... Rack guide, 20 ... Assist mechanism, 30 ... Housing, 31 ... First divided housing, 31A ... Right end, 31B ... Left end, 31C ... Opening, 32 ... Second divided housing, 32A ... End, 32B ... Female thread, 32C ... Opening, 32D ... Stepped portion, 33 ... Third divided housing, 33A ... End, 40 ... Electric motor, 41 ... Motor shaft, 41A ... Right end, 41B ... Left end, 41C ... Fitting part, 41D ... Female thread part, 41E ... Male thread part, 41F ... Step part 42 ... Stator 43 ... Power feeding connector 46 ... Magnet 47 ... Coil 50 ... Rotation sensor 51 ... Sensing part 52 Connector part, 60 ... ball screw mechanism, 61 ... ball screw nut, 62 ... ball, 66 ... main body part, 66A ... right end face, 66B ... left end face, 66C ... annular flow path, 66D ... groove part, 66E ... first peripheral wall part, 66F ... second peripheral wall portion, 66G ... outer edge portion, 67 ... engagement portion, 67A ... male screw portion, 67B ... fitting portion, 68 ... spiral groove, 70 ... mounting member, 71 ... small diameter portion, 72 ... large diameter portion 73 ... Connecting part, 81 ... O-ring, 82 ... O-ring, 83 ... O-ring, 84 ... Nut, 85 ... Center nut, 86 ... Double row bearing, 86A ... Inner ring, 86B ... Outer ring, 87 ... Ball bearing, 87A ... inner ring, 87B ... outer ring, m ... axis, X ... axial direction, R1 ... outer diameter, R2 ... inner diameter, R3 ... outer diameter, R4 ... inner diameter, XA ... right side, XB ... left side.

Claims (4)

In an electric power steering apparatus having an electric motor having an output shaft, a nut that converts the rotational motion of the electric motor into a linear motion and transmits the linear motion to a steered shaft, and a bearing that supports the nut,
A low-rigidity member having lower rigidity than the nut and the bearing;
The nut is supported by the bearing via the low-rigidity member. In claim 1,
The low-rigidity member includes a small-diameter portion that is fixed to the nut, a large-diameter portion that has an inner diameter and an outer diameter that are larger than the small-diameter portion, and is fixed to the bearing, and the small-diameter portion and the large-diameter portion. A connecting portion that connects to each other,
The electric power steering device, wherein the small-diameter portion and the large-diameter portion are located at different locations in the axial direction of the nut. In an electric power steering apparatus having an electric motor having an output shaft, a nut that converts the rotational motion of the electric motor into a linear motion and transmits the linear motion to a steered shaft, and a bearing that supports the nut,
The nut has a first peripheral wall portion and a second peripheral wall portion having lower rigidity than the bearing,
The bearing is an electric power steering device that supports the second peripheral wall portion. In claim 3,
An electric power steering device in which a space is formed inside the second peripheral wall portion.