JP2010036643A - Electric power steering apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve steering feeling by suppressing a drum-shaped deformation of a nut in a ball screw mechanism in an electric power steering apparatus provided with a ball screw mechanism.
In an electric power steering apparatus, an output from a rotating shaft 11 of an electric motor 10 is transmitted to a steering shaft 30 via a ball screw mechanism 20. A stepped inner hole 11a that opens on the large-diameter inner hole portion 11a1 side is provided on the inner periphery of one end of the rotating shaft 11, and a nut 21 is accommodated in the large-diameter inner hole portion 11a1 so as to be detachable in the axial direction. The nut 21 is tightened and fixed to the opening end of the stepped inner hole 11a toward the stepped portion 11a3 of the stepped inner hole 11a, and the nut 21 is coupled to the rotary shaft 11 so as to be integrally rotatable. Is assembled so as to be removable in the axial direction. Tapered washers 25 and 26 are provided between one end of the annular fixture 24 and the nut 21 and between the step portion 11 a 3 of the stepped inner hole and the other end of the nut 21.
[Selection] Figure 1

Description

  The present invention relates to an electric power steering apparatus provided in a vehicle.

As one of the electric power steering devices, a nut of a ball screw mechanism is coaxially and integrally rotatable with respect to a rotating shaft of an electric motor that is rotatable relative to a housing and immovable in an axial direction. In some cases, the screw shaft of the ball screw mechanism is integrally formed with the steering shaft, and the output from the rotating shaft is transmitted to the steering shaft via the ball screw mechanism. Has been.
JP 2000-168589 A

  In the electric power steering apparatus described in Patent Document 1 described above, a circlip is used around one end of the rotating shaft so as to be immovable in the axial direction, and the nut is removed in the axial direction inside. A cylindrical holder that can be accommodated, and an annular fixture that is detachably assembled to the inner periphery of one end of the holder and fastens and fixes the nut accommodated in the holder toward the one end of the rotating shaft. The structure which couple | bonds the said nut with respect to the one end part of the said rotating shaft so that torque transmission is possible is described.

  In the electric power steering apparatus described in Patent Document 1 described above, the nut can be detached from the rotating shaft and the holder in the axial direction, and the nut can be attached to and detached from the rotating shaft and the holder ( Although the maintainability of the electric power steering apparatus can be improved, a circlip is used on the outer periphery of one end of the rotating shaft to couple the nut to the one end of the rotating shaft so that torque can be transmitted. A cylindrical holder that is fixed so as to be immovable in the axial direction and an annular fixture that is detachably assembled to the inner periphery of one end of the holder are necessary, and an increase in cost due to the holder is inevitable.

  Such a problem is that a portion corresponding to the holder is formed integrally with the rotating shaft, that is, as illustrated in FIG. 5, the large-diameter inner hole portion 1 a 1 is opened on the inner periphery of one end portion of the rotating shaft 1. A stepped inner hole 1a is provided, and a nut 2 is accommodated in the large-diameter inner hole portion 1a1 of the stepped inner hole 1a so as to be detachable in the axial direction. It can be eliminated by tightening and fixing toward the stepped portion 1a3 of the stepped inner hole 1a with the annular fixture 3 assembled to the (female screw portion).

  However, in this case, the axial load applied to the inner peripheral portion of the nut 2 and the axial load applied to the outer peripheral portion of the nut 2 are substantially the same, or the axial load applied to the outer peripheral portion of the nut 2 is the nut. 2 (see the arrow in FIG. 5), the nut 2 is slightly deformed into a drum shape by tightening and fixing the annular fixture 3 as shown exaggeratedly in FIG. As a result, the ball groove 2a formed in the nut 2 may be distorted, and this may inhibit the rolling of the ball in the ball groove 2a, thereby deteriorating the steering feeling.

  The present invention has been made to cope with the above-mentioned problem (deterioration of steering feeling), and is a ball screw with respect to a rotating shaft of an electric motor that is assembled with a housing so as to be rotatable and axially immovable. A nut of the mechanism is arranged coaxially and integrally rotatable, a screw shaft of the ball screw mechanism is integrally formed with the steering shaft, and an output from the rotating shaft is transmitted to the steering shaft through the ball screw mechanism. The stepped inner hole that opens on the large diameter inner hole side is provided on the inner periphery of the one end portion of the rotating shaft, and the stepped inner hole has a large diameter inner hole portion. The nut is accommodated so as to be detachable in the axial direction, and the nut is fastened and fixed to the opening end portion of the stepped inner hole toward the step portion of the stepped inner hole. An annular fixture that can be connected to and rotated together is removed in the axial direction. And at least one of the annular fixture and one end of the nut and between the step portion of the stepped inner hole and the other end of the nut by tightening and fixing the annular fixture. The load setting part which makes the axial load applied to the outer peripheral part of the nut smaller than the axial load applied to the inner peripheral part of the nut is provided.

  In this case, the load setting portion is an annular washer interposed between at least one of the annular fixture and the nut and between the step of the stepped inner hole and the other end of the nut, The washer can be tapered or stepped so that the axial thickness decreases from the inner diameter portion toward the outer diameter portion. The load setting portion is an annular protrusion formed on at least one of an end portion of the annular fixture facing one end of the nut and a step portion of the stepped inner hole facing the other end of the nut. The protrusion may be tapered or stepped so that the amount of protrusion in the axial direction decreases from the inner diameter portion toward the outer diameter portion. The load setting portion is an annular protrusion formed on at least one of the one end of the nut facing the annular fixture and the other end of the nut facing the step of the stepped inner hole. In addition, this protrusion may be tapered or stepped so that the amount of protrusion in the axial direction is reduced from the inner diameter portion toward the outer diameter portion.

  In the electric power steering apparatus according to the present invention, the nut can be detached from the rotating shaft in the axial direction by removing the annular fixture from the opening end of the stepped inner hole in the rotating shaft. The nut can be attached to and detached from the rotating shaft in the axial direction with the shaft assembled to the housing, and the nut can be attached to and detached from the rotating shaft (maintenance of the electric power steering device) is good. can do.

  In the electric power steering apparatus according to the present invention, the nut can be attached to and detached from the rotating shaft in the axial direction with the rotating shaft of the electric motor assembled to the housing. Since there is no need to disassemble and reassemble the rotating shaft with respect to the housing at the time of attaching / detaching to the shaft, the assembling accuracy of the rotating shaft with respect to the housing will not be deteriorated. The performance of the electric motor can be guaranteed (maintained).

  Further, in the electric power steering apparatus according to the present invention, a stepped inner hole opened on the large diameter inner hole side is provided on one end inner periphery of the rotating shaft, and the large diameter inner hole of the stepped inner hole is provided. The nut is removably accommodated in the axial direction, and the nut is tightened and fixed at the opening end of the stepped inner hole toward the stepped portion of the stepped inner hole. An annular fixture is assembled that is coupled to the shaft for integral rotation. For this reason, compared with the electric power steering apparatus described in Patent Document 1 described above, it is possible to reduce the cost by simplifying the housing structure of the nut in the ball screw mechanism of the electric power steering apparatus. It is.

  Further, in the electric power steering apparatus according to the present invention, at least one of the annular fixing tool and one end of the nut and at least one of the stepped inner hole and the other end of the nut is provided with the annular fixing tool. A load setting portion is provided that reduces the axial load applied to the outer peripheral portion of the nut as compared with the axial load applied to the inner peripheral portion of the nut by tightening and fixing. For this reason, it is possible to suppress the nut from being deformed into a drum shape by tightening and fixing the annular fixture, and it is possible to suppress distortion of the ball groove formed in the nut. As a result, smooth rolling of the ball in the ball groove of the nut is ensured, and the steering feeling can be improved.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of the present invention. In the electric power steering apparatus according to the first embodiment, the rotation of the rotating shaft 11 in the electric motor 10 is converted into the axial movement of the steering shaft 30. A nut 21 of a known ball screw mechanism 20 for transmission is arranged coaxially and integrally rotatable with the rotary shaft 11, and a screw shaft 22 of the ball screw mechanism 20 is integrated with the steering shaft 30 to rotate. The output from the shaft 11 is transmitted to the steering shaft 30 via the ball screw mechanism 20. A number of balls (steel balls) 23 are interposed between the nut 21 and the screw shaft 22 of the ball screw mechanism 20.

  The rotating shaft 11 of the electric motor 10 is assembled to the housing 40 via a bearing at its right end (not shown) so as to be rotatable and axially immovable, and at its left end to the housing 40 via a bearing 50. It is assembled so that it can rotate but cannot move in the axial direction. Further, the steering shaft 30 is provided so as to extend in the left-right direction of the vehicle, and is assembled with the housing 40 so as not to rotate and to move in the axial direction. (Not shown) is steered.

  By the way, in this 1st Embodiment, the stepped inner hole 11a opened in the large diameter inner hole part 11a1 side is provided in the left end part inner periphery of the rotating shaft 11, and the large diameter inner hole part of this stepped inner hole 11a is provided. A nut 21 is accommodated in 11a1 so as to be detachable in the axial direction. Further, the nut 21 is tightened and fixed to the female threaded portion 11a2 formed at the opening end of the stepped inner hole 11a toward the stepped portion 11a3 of the stepped inner hole 11a, and the nut 21 is rotated integrally with the rotary shaft 11. An annular fixture 24 that can be coupled is screwed so as to be detachable in the axial direction. The annular fixture 24 is a fixing screw having an external thread portion that engages with the internal thread portion 11a2 of the rotating shaft 11 on the outer periphery, and can be rotated by a dedicated tool (not shown) that can be attached to a recess provided in the inner peripheral portion. It is.

  In the first embodiment, an annular washer 25 is interposed between the annular fixture 24 and the left end of the nut 21, and an annular washer is provided between the step portion 11 a 3 of the stepped inner hole 11 a and the right end of the nut 21. A washer 26 is interposed. Each washer 25, 26 is a load that sequentially reduces the axial load applied to the outer peripheral portion of the nut 21 as compared to the axial load (stress) applied to the inner peripheral portion of the nut 21 by tightening and fixing the annular fixture 24. As shown in an exaggerated manner in FIGS. 1 and 2, the setting portion (stress distribution setting portion) has an axial thickness that decreases from the inner diameter portion toward the outer diameter portion. It is tapered so that

  The taper formed in each of the washers 25 and 26 is a small taper having an angle of about 0.5 to 3 deg. In a state where the annular fixture 24 is screwed to the female thread portion 11a2 of the rotary shaft 11 sufficiently and sufficiently. The end faces of the washers 25 and 26 facing the nut 21 (end faces where the taper is formed) abut on the end face of the nut 21 substantially as a whole. For this reason, an axial load is applied to substantially the entire end face of the nut 21 as shown by the arrow in FIG.

  In the electric power steering apparatus according to the first embodiment configured as described above, by removing the annular fixture 24 from the opening end of the stepped inner hole 11a in the rotating shaft 11, a nut is attached to the rotating shaft 11. 21 can be attached / detached in the axial direction, so that the nut 21 can be attached / detached in the axial direction with respect to the rotary shaft 11 in a state where the rotary shaft 11 is assembled to the housing 40. 11 can be improved in the attachment / detachment exchangeability (maintenance of the electric power steering apparatus).

  In the electric power steering apparatus according to the first embodiment, the nut 21 can be attached to and detached from the rotary shaft 11 in the axial direction in a state where the rotary shaft 11 of the electric motor 10 is assembled to the housing 40. Thus, when the nut 21 is attached to or detached from the rotating shaft 11, it is not necessary to disassemble and reassemble the rotating shaft 11 with respect to the housing 40, so that the assembling accuracy of the rotating shaft 11 with respect to the housing 40 is deteriorated. No, the performance of the electric motor 10 can be guaranteed (maintained) even after the nut 21 is removed and replaced (after maintenance).

  In the electric power steering apparatus according to the first embodiment, a stepped inner hole 11a that opens on the large-diameter inner hole portion 11a1 side is provided on the inner periphery of one end of the rotary shaft 11, and this stepped inner hole is provided. A nut 21 is accommodated in the large-diameter inner hole portion 11a1 of 11a so as to be detachable in the axial direction, and the nut 21 is directed toward the step portion 11a3 of the stepped inner hole 11a at the opening end portion of the stepped inner hole 11a. An annular fixture 24 is attached that fastens and fixes the nut 21 so as to be integrally rotatable with the rotary shaft 11. For this reason, compared with the electric power steering apparatus described in Patent Document 1 described above, the nut 21 in the ball screw mechanism 20 of the electric power steering apparatus can be simplified to reduce costs. Is possible.

  In the electric power steering apparatus according to the first embodiment, the annular fixture 24 is provided between the annular fixture 24 and the left end of the nut 21 and between the step portion 11a3 of the stepped inner hole 11a and the right end of the nut 21. Washers 25 and 26 are provided as load setting portions that reduce the axial load applied to the outer peripheral portion of the nut 21 as compared with the axial load applied to the inner peripheral portion of the nut 21 by tightening and fixing. For this reason, it is possible to suppress the nut 21 from being deformed into a drum shape as shown by exaggerating the phantom line in FIG. 2 by tightening and fixing the annular fixture 24, and the distortion of the ball groove 21a formed in the nut 21 can be reduced. It is possible to suppress. Thereby, the smooth rolling of the ball 23 in the ball groove 21a of the nut 21 is ensured, and the steering feeling can be improved.

  In the first embodiment described above, washers 25 and 26 having tapered end faces on the nut side between the annular fixture 24 and the left end of the nut 21 and between the stepped portion 11a3 of the stepped inner hole 11a and the right end of the nut 21. However, either one of the washers 25 or 26 is omitted, or a normal washer whose both end faces are flat is adopted as either one of the washers 25 or 26. It is also possible to implement.

  Further, in the above-described first embodiment, the washer 25, 26 is adopted as the load setting unit, but the configuration of the second embodiment shown in FIG. 3 or the configuration shown in FIG. 4 is used as the load setting unit. It is also possible to adopt the configuration of the third embodiment. Note that, in the second embodiment shown in FIG. 3 and the third embodiment shown in FIG. 4 as well, it is possible to obtain the same effects as those of the first embodiment described above.

  In the second embodiment shown in FIG. 3, the load setting portion is formed in the right end portion of the annular fixture 124 facing the left end of the nut 121 and the step portion 111 a 3 of the stepped inner hole 111 a facing the right end of the nut 121. The annular protrusions 124a and 111a4 thus formed are employed. The protrusions 124a and 111a4 are tapered so that the amount of protrusion in the axial direction decreases from the inner diameter portion toward the outer diameter portion.

  The taper of each protrusion 124a, 111a4 is a small one having an angle of about 0.5 to 3 deg. When the annular fixture 124 is screwed to the female thread 111a2 of the rotating shaft 111 sufficiently and sufficiently, each protrusion 124a, 111a4 is tapered. The end faces (end faces where the taper is formed) of the portions 124a and 111a4 facing the nut 121 are substantially in contact with the end face of the nut 121. For this reason, the axial load similar to the above-described first embodiment is applied to substantially the entire end surface of the nut 121.

  The other configurations of the second embodiment shown in FIG. 3 are the same as the configurations of the first embodiment described above, and therefore the same reference numerals in the 100s are attached and description thereof is omitted. Moreover, when implementing this 2nd Embodiment, it is also possible to abbreviate | omit either one of protrusion 124a, 111a4.

  On the other hand, in the third embodiment shown in FIG. 4, as the load setting portion, the left end portion of the nut 221 that faces the annular fixture 224 and the right end portion of the nut 221 that faces the step portion 211a3 of the stepped inner hole 211a. The formed annular protrusions 221a and 221b are employed. The protrusions 221a and 221b are tapered so that the amount of protrusion in the axial direction decreases from the inner diameter portion toward the outer diameter portion.

  The taper of each protrusion 221a, 221b is a small one having an angle of about 0.5 to 3 deg. When the annular fixture 224 is screwed to the female thread 211a2 of the rotating shaft 211 sufficiently and sufficiently, it is annularly fixed. Steps 221a, 221b facing the right end surface of the tool 224 and the stepped portion 211a3 of the stepped inner hole 211a are substantially entirely stepped with the right end surface of the annular fixture 224. It abuts on the step portion 211a3 of the inner hole 211a. For this reason, the axial load similar to the above-described first embodiment is applied to substantially the entire end surface of the nut 221.

  The other configuration of the third embodiment shown in FIG. 4 is the same as the configuration of the first embodiment described above, and therefore, the same reference numerals in the 200s are attached and description thereof is omitted. Moreover, when implementing this 3rd Embodiment, it is also possible to abbreviate | omit either one of protrusion 221a, 221b.

  In each of the embodiments described above, tapered washer 25 and 26, tapered protrusions 124a and 111a4, and tapered protrusions 221a and 221b are employed as the load setting part. It is also possible to employ a stepped washer (25, 26), a stepped protrusion (124a, 111a4), and a stepped protrusion (221a, 221b). In addition, the level | step difference of a step part is as small as about 0.1-0.5 mm, and the number of step parts can be set suitably.

It is a principal part longitudinal section front view showing a 1st embodiment of an electric power steering device by the present invention. It is explanatory drawing of the state which fastened the nut with the annular fixture in the electric power steering device shown in FIG. It is a principal part vertical front view which shows 2nd Embodiment of the electrically driven power steering device by this invention. It is a principal part vertical front view which shows 3rd Embodiment of the electrically driven power steering device by this invention. It is explanatory drawing of the state which tightened the nut with the annular fixture in embodiment which removed both washers from the electric power steering device shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electric motor, 11 ... Rotating shaft, 11a ... Stepped inner hole, 11a1 ... Large diameter inner hole part, 11a2 ... Female thread part, 11a3 ... Step part, 20 ... Ball screw mechanism, 21 ... Nut, 22 ... Screw shaft, 23 ... ball, 24 ... annular fixture, 25,26 ... washer, 30 ... steering shaft, 40 ... housing

Claims (4)

A nut of a ball screw mechanism is disposed coaxially and integrally with a rotating shaft of an electric motor that is assembled with a housing and is not movable in the axial direction. The screw shaft of the ball screw mechanism is a steering shaft. And an electric power steering apparatus in which an output from the rotating shaft is transmitted to the steering shaft via the ball screw mechanism,
A stepped inner hole that opens on the large diameter inner hole side is provided on the inner periphery of one end of the rotating shaft, and the nut can be attached and detached in the large diameter inner hole of the stepped inner hole in the axial direction. An annular fixture that is housed and is fastened and fixed to the opening end portion of the stepped inner hole toward the step portion of the stepped inner hole so that the nut is integrally rotatable with the rotation shaft. Is attached so as to be detachable in the axial direction, and the annular fixture is provided between at least one of the annular fixture and one end of the nut and between the step portion of the stepped inner hole and the other end of the nut. And a load setting portion for reducing an axial load applied to the outer peripheral portion of the nut as compared to an axial load applied to the inner peripheral portion of the nut by tightening and fixing. Steering device.   2. The electric power steering apparatus according to claim 1, wherein the load setting portion is provided between at least one of the annular fixture and one end of the nut and between a step portion of the stepped inner hole and the other end of the nut. An electric washer is an annular washer that is provided with a taper or a step so that the thickness in the axial direction decreases from the inner diameter portion toward the outer diameter portion. apparatus.   2. The electric power steering apparatus according to claim 1, wherein the load setting unit includes an end of the annular fixture facing one end of the nut and a step of the stepped inner hole facing the other end of the nut. It is an annular protrusion formed on at least one of the parts, and the protrusion is tapered or stepped so that the amount of protrusion in the axial direction decreases from the inner diameter part toward the outer diameter part. Electric power steering device.   2. The electric power steering apparatus according to claim 1, wherein the load setting portion includes one end of the nut facing the annular fixture and the other end of the nut facing the step of the stepped inner hole. An annular protrusion formed on at least one of the protrusions, wherein the protrusion is tapered or stepped so as to reduce the amount of protrusion in the axial direction from the inner diameter portion toward the outer diameter portion. Electric power steering device.

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