JP6361386B2 - Rack shaft and steering device - Google Patents

Description

  The present invention relates to a rack shaft having a rack tooth row and a steering device including the rack shaft.

  For example, as shown in Patent Document 1, a rack shaft having a rack tooth row is applied to a power steering device that assists steering of a vehicle wheel. And, for example, as shown in Patent Document 2, on the rack shaft, a portion where the rack tooth row is formed (rack tooth forming portion), a portion where the rack tooth row is not formed (non-rack tooth portion), A portion (connecting portion) for connecting the portion where the rack tooth row is formed and the portion where the rack tooth row is not formed is formed.

JP2013-6517A JP 2014-79769 A

  In general, invalid rack teeth, that is, discarded teeth are inevitably formed at the axial ends of the rack tooth rows on the rack shaft. The conventional rack shaft has a limit to shortening the axial length of the rack shaft because the rack tooth forming portion in which the rack tooth row including the discarded teeth is formed and the non-rack tooth portion are connected by the connecting portion. is there.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a rack shaft capable of reducing the axial length and a power steering device including the rack shaft.

(Rack shaft)
(Claim 1) A rack shaft according to the present invention includes a rack tooth forming portion in which an outer peripheral surface of a shaft member is plastically deformed into a concave shape to form an effective rack tooth row, a non-rack tooth portion having no rack teeth, A connecting portion that is positioned at an axial end of the recessed region and is plastically deformed in accordance with plastic deformation of the rack tooth forming portion, and connects the rack tooth forming portion and the non-rack tooth portion; In the rack shaft, an invalid rack tooth adjacent to the effective rack tooth row is formed in the connecting portion.

  Accordingly, since the invalid rack teeth are formed at the connecting portion, the rack shaft can be shortened by an amount corresponding to the invalid rack teeth as compared with the conventional rack shaft. Therefore, the steering device to which the rack shaft is applied can be downsized.

(Claim 2) The connecting portion may be provided on both axial sides of the rack tooth forming portion.
Thereby, the rack shaft can further shorten the shaft length.
(Claim 3) The shaft member may be a solid member.
A solid shaft member can secure a large amount of material for the shaft member that escapes during plastic deformation, so that it is possible to suppress the elongation of the shaft member and to increase the rack teeth at the end of the effective rack tooth row in the rack tooth forming portion. It can be formed with high accuracy.

(Claim 4) The connecting portion includes the invalid rack tooth, an inclined portion that connects the rack tooth forming portion and the non-rack tooth portion, and the axis of the shaft member and the teeth of the effective rack tooth row The shape of the inclined portion viewed from a direction perpendicular to the stripe is a shape that tapers from the non-rack tooth portion toward the rack tooth forming portion, and passes through the center of the tooth line of the effective rack tooth row. And it is good to form symmetrically with respect to the straight line parallel to the axis line of the said shaft member.
Thereby, the operator can easily grasp the flow of the material of the shaft member when the shaft member is warm-forged, and thus can design a mold capable of forging the effective rack tooth row with high accuracy.

(Claim 5) When the invalid rack tooth is viewed from a direction perpendicular to the axis of the shaft member and the tooth of the effective rack tooth row, it passes through the center of the tooth of the effective rack tooth row and the It may be formed on both sides with respect to a straight line parallel to the axis of the shaft member.
As a result, the area where the invalid rack teeth are formed becomes a material escape area, so that the accuracy of the effective rack teeth can be ensured.

(Claim 6) The connecting portion includes the invalid rack tooth, and an inclined portion that connects the rack tooth forming portion and the non-rack tooth portion, and the axis of the shaft member and the teeth of the effective rack tooth row The shape of the inclined portion viewed from a direction perpendicular to the stripe is a shape that tapers from the non-rack tooth portion toward the rack tooth forming portion, and passes through the center of the tooth line of the effective rack tooth row. And it is good to form in the asymmetrical shape with respect to the straight line parallel to the axis line of the said shaft member, and the shape shifted | deviated to the one end side of the said tooth trace.
As a result, the rack tooth that cannot be meshed with the teeth of the pinion shaft in the symmetrically inclined portion is changed to a rack tooth that can mesh with the teeth of the pinion shaft by making the inclined portion an asymmetrical shape. In some cases, the length of the rack shaft can be further shortened.

(Steering device)
(Seventh aspect) A steering device according to the present invention includes a housing, the rack shaft according to any one of the first to sixth aspects, which is supported by the housing so as to be movable in the axial direction, and is connected to the wheels of the vehicle. A pinion supported by the housing so as to be rotatable about an axis, meshed with the effective rack tooth row of the rack shaft, and connected to the steering of the vehicle.

  (8) The steering device is attached to the housing, and is provided at a position different in the axial direction with respect to the effective rack tooth row, and assists the axial movement of the rack shaft. It is good to have.

(Claim 9) The assist device includes a motor attached to the housing, a speed reduction mechanism that reduces the rotation of the motor, and a ball nut that is rotatably supported by the housing, and the rack shaft includes: A ball screw portion formed on the non-rack tooth portion and threadably engageable with the ball nut. The rotation decelerated by the speed reduction mechanism is converted into an axial movement of the rack shaft via the ball nut and the ball screw portion. Then, it is preferable to assist the movement of the rack shaft in the axial direction.
The steering device of the present invention can be miniaturized by applying the rack shaft described above.

FIG. 1 is a diagram showing an entire power steering device in a cross section of a ball screw portion of a rack shaft viewed from a direction perpendicular to an axis. It is the sectional view on the AA line of FIG. 1, and is the figure which looked at the rack tooth formation part of the rack axis | shaft from the orthogonal | vertical direction with respect to the axis line. It is the figure which looked at the rack tooth formation part of the rack axis | shaft, the ball screw part, and the connection part from the direction orthogonal to the axis and the tooth trace of an effective rack tooth row. It is the AA line sectional view of Drawing 3A, and is a figure which made the slope part into a section along an axis. FIG. 3B is a cross-sectional view taken along line B-B in FIG. 3A, in which the inclined portion is taken along a straight line parallel to the axis. It is the figure which looked at the rack tooth formation part of the rack shaft of another form, the ball screw part, and the connection part from the direction orthogonal to the axis and the tooth trace of an effective rack tooth row.

(Structure of steering device)
The steering device of this embodiment will be described with reference to FIGS. 1 and 2.
As shown in FIG. 1, the steering device 10 includes a rack and pinion mechanism 11 that converts rotation of a steering wheel (not shown) into axial movement of the rack shaft 13, and an electric motor that applies axial assist force to the rack shaft 13. This is an electric power steering device including an assist unit 20 and the like.

  As shown in FIGS. 1 and 2, the rack and pinion mechanism 11 includes a pinion shaft 12 to which the rotation of the steering wheel is transmitted via a column (not shown), a gear housing 14 that rotatably supports the pinion shaft 12, A rack shaft 13 that meshes with the pinion shaft 12 to convert the rotation of the pinion shaft 12 into an axial movement of the rack shaft 13, and a rack guide that presses the rack shaft 13 from behind the rack shaft 13 in a direction to mesh with the pinion shaft 12. A mechanism 60 and the like.

  The gear housing 14 is fixed to a vehicle body not shown. Both ends of the rack shaft 13 protrude outward from the gear housing 14, an electric housing 24 and a reduction housing 25 described later, respectively. A universal joint 81 is screwed to the joint coupling portions 13D at both ends of the rack shaft 13. The wheels are connected to each other via unillustrated tie rods and knuckle arms via the universal joints 18. As will be described in detail later, the rack shaft 13 includes a rack tooth forming portion 13A in which an effective rack tooth row 131 is formed, and a ball screw portion 13B in which a male screw 132 is formed (corresponding to the “non-rack tooth portion” of the present invention). The connecting portion 13C for connecting the rack tooth forming portion 13A and the ball screw portion 13B, the joint connecting portion 13D (corresponding to the “non-rack tooth portion” of the present invention) forming the female screw 133, the rack tooth forming portion 13A and the joint It has the connection part 13E which connects 13D of coupling parts.

  The pinion shaft 12 has a torsion bar (not shown) in the middle in the axial direction, and when a rotational torque acts on the input side of the pinion shaft 12, the input side of the pinion shaft 12 and the output side of the pinion shaft 12 rotate relative to each other. A torque sensor 80 for detecting the relative rotation between the input side and the output side is provided in the gear housing 14.

  The rack guide mechanism 60 is screwed into a guide hole 61 formed in the gear housing 14, a yoke 62 slidably fitted in the guide hole 61, and a screw hole formed at one end of the guide hole 61. A filling plug 63, a pressing spring 64 inserted between the yoke 62 and the filling plug 63, and a resin sheet 65 attached to the yoke 62 and in sliding contact with the rack shaft 13 are provided. The rack shaft 13 is pressed in a direction to mesh with the pinion shaft 12 by the pressing force of the pressing spring 64.

  A stopper portion 15 with which the universal joint 81 abuts is formed at one end of the gear housing 14. An annular mounting groove 16 is formed coaxially with the rack shaft 13 in the stopper portion 15, and a ring-shaped buffer member 75 is fitted into the mounting groove 16. The stopper portion 15 has a function of restricting the movement of the rack shaft 13 in the axial direction, and the buffer member 75 absorbs the energy of the movement of the rack shaft 13 in the axial direction and reduces the interference sound when hitting the stopper portion 15. It has a function. The buffer member 75 is made of urethane material by injection molding or the like. An electric housing 24 is attached to the other end of the gear housing 14, and an electric motor 21 is attached to the electric housing 24, and a speed reduction housing 25 is connected via a bolt 26.

  The electric assist unit 20 includes an electric motor 21, a speed reduction mechanism 30 that decelerates the rotation of the rotating shaft 22 of the electric motor 21, and a ball screw mechanism 40 that converts the decelerated rotation into an axial movement of the rack shaft 13. Prepare. The electric motor 21 is controlled by an unillustrated ECU (Electronic Control Unit) based on signals from the torque sensor 80 and an unillustrated vehicle speed sensor.

  As shown in FIG. 1, the speed reduction mechanism 30 includes an input shaft 34 disposed coaxially with the rotating shaft 22 of the electric motor 21, a drive gear 31 formed integrally with the input shaft 34, and a ball nut 41 described later. A reduction gear 33 fitted and fixed to the outer periphery of the end, an intermediate shaft 35 disposed in parallel between the rack shaft 13 and the input shaft 34, and an intermediate shaft 35 are formed integrally with the drive gear 31 and the reduction gear 33. Intermediate gear 32 and the like meshing with each other. The reduction gear 33 has a larger number of teeth than the drive gear 31 and reduces the rotation of the drive gear 31 and transmits it to a ball nut 41 described later. A resin coupling 23 is inserted between the rotary shaft 22 and the input shaft 34, and the rotation of the rotary shaft 22 is transmitted to the input shaft 34 via the coupling 23. The coupling 23 has a role of absorbing an axial shift or inclination between the rotary shaft 22 and the input shaft 34.

  The ball screw mechanism 40 includes a ball screw portion 13B formed integrally with a part of the rack shaft 13, a ball nut 41 arranged coaxially so as to surround the periphery of the ball screw portion 13B, and the ball screw portion 13B and the ball nut 41 between them. A plurality of intervening balls 43 and the like. A circulator (not shown) for circulating the ball 43 moved to one end side of the ball nut 41 back to the other end side of the ball nut 41 is attached to the ball nut 41 on the inner diameter side of a double-row angular ball bearing 54 described later. It is done.

  The speed reduction mechanism 30 and the ball screw mechanism 40 are accommodated in the electric housing 24 and the speed reduction housing 25. The input shaft 34 is rotatably supported by a pair of ball bearings 50 and 51 held by the electric housing 24 and the speed reduction housing 25. The intermediate shaft 35 is rotatably supported by a pair of ball bearings 52 and 53 held by the electric housing 24 and the speed reduction housing 25. The ball nut 41 is rotatably supported by a double row angular ball bearing 54 held by the electric housing 24.

  The outer ring of the double row angular ball bearing 54 is sandwiched between the stepped portion of the electric housing 24 and the lock nut 44, and the lock nut 44 is screwed into the screw hole of the electric housing 24. The inner ring of the double row angular ball bearing 54 is sandwiched between the stepped portion of the ball nut 41 and the lock nut 44, and the lock nut 44 is screwed into a threaded portion on the outer periphery of one end of the ball nut 41.

  The reduction gear 33 and the ball nut 41 are cantilevered only by the double-row angular ball bearing 54. When the reduction gear 33 is cantilevered, the alignment error of the reduction gear 33 may increase. Therefore, it is preferable to provide crowning in the tooth line direction on the tooth surface of the reduction gear 33. Thereby, an increase in gear noise can be suppressed regardless of an increase in alignment error.

(Rack shaft)
As described above, the rack shaft 13 includes the rack tooth forming portion 13A, the ball screw portion 13B, the connecting portion 13C, the joint coupling portion 13D, and the connecting portion 13E. The connecting portion 13C that connects the rack tooth forming portion 13A and the ball screw portion 13B has the same structure as the connecting portion 13E that connects the rack tooth forming portion 13A and the joint coupling portion 13D. Hereinafter, the description will be made focusing on the rack tooth forming portion 13A, the ball screw portion 13B, and the connecting portion 13C, which are the main portions of the rack shaft 13.

  As shown in FIG. 3A, the rack shaft 13 includes a rack tooth forming portion 13A in which the outer peripheral surface on one end side of the shaft member W is plastically deformed into a concave shape by warm forging to form an effective rack tooth row 131, and the shaft member W. The ball screw portion 13B, in which the outer peripheral surface of the other end side is cut to form the male screw 132, and the axial end portion of the concave region on the ball screw portion 13B side, are used for plastic deformation of the rack tooth forming portion 13A. It has a connecting portion 13C formed by plastic deformation.

  The rack tooth forming portion 13A is formed by heating a solid shaft member W made of steel to 750 ° C. to 790 ° C. and pressing it with a mold. The reason for using the solid shaft member W is that the solid shaft member W can secure a large amount of the material of the shaft member W that escapes during plastic deformation. The rack teeth at the end of the effective rack tooth row 131 in the forming portion 13A can be formed with high accuracy. In addition, the solid shaft member W is more rigid than the hollow shaft member with respect to bending due to an impact when the vehicle wheel rides on a step or the like. In addition, the solid shaft member W can suppress an increase in material cost, processing cost, and the like as compared with a hollow shaft member.

  The connecting portion 13 </ b> C includes invalid rack teeth 134 and inclined portions 135. That is, as shown in FIGS. 3A, 3B and 3C, the ball screw portion 13B of the effective rack tooth row 131 is formed with invalid rack teeth 134 adjacent to the effective rack tooth row 131. And the ball screw portion 13B are gently connected by an inclined portion 135. Therefore, since the invalid rack tooth 134 is formed so as to overlap the inclined portion 135, the axial length of the rack shaft 13 can be shortened. The axial length of the rack shaft 13, that is, the axial length of the connecting portion 13 </ b> C can be adjusted by changing the inclination angle of the inclined portion 135.

  The invalid rack teeth 134 are rack teeth that interfere with the inclined portion 135, that is, rack teeth that cannot mesh with the teeth of the pinion shaft 12. The invalid rack tooth 134 passes through the center of the tooth trace G of the effective rack tooth row 131 and the shaft member W when viewed from a direction perpendicular to the axis L of the shaft member W and the tooth stripe G of the effective rack tooth row 131. Are formed on both sides with respect to a straight line parallel to the axis L.

  The reason why the invalid rack teeth 134 are formed is that, as described above, the outer peripheral surface of the solid shaft member W is plastically deformed into a concave shape by warm forging to form the effective rack tooth row 131. Part of the material may escape in the axial direction of the shaft member W and affect the accuracy of the effective rack tooth row 131. Therefore, the formation area of the invalid rack teeth 134 is used as the material escape region of the effective rack tooth row 131. This is to ensure accuracy. The remaining material of the concave portion escapes in the radial direction of the shaft member W and becomes a burr, so that the burr is removed by post-processing.

  The shape of the inclined portion 135, that is, the shape viewed from the direction perpendicular to the axis L of the shaft member W and the tooth trace G of the effective rack tooth row 131 (hereinafter referred to as a planar shape) is from the ball screw portion 13B to the rack tooth forming portion 13A. The taper is tapered toward the center of the effective rack tooth row 131 and is formed symmetrically with respect to a straight line passing through the center of the tooth trace G of the effective rack tooth row 131 and parallel to the axis L of the shaft member W. More specifically, as shown in FIG. 3A, the planar shape of the inclined portion 135 is formed in a substantially isosceles triangle shape, and as shown in FIGS. 3B and 3C, the side surface shape of the inclined portion 135, that is, the shaft member. The shape seen from the direction perpendicular to the axis L of W and the planar shape is formed in a substantially right triangle shape.

  In other words, the three-dimensional shape of the inclined portion 135 is a shape obtained by cutting a substantially conical shape in half in the axial direction (substantially semiconical shape), that is, a semicircular bottom surface is positioned on the ball screw portion 13B side, and the rack tooth forming portion 13A. It is formed in a substantially semi-conical shape with the apex P located on the side. Thereby, since the operator can grasp | ascertain easily the flow of the material of the shaft member W at the time of warm forging the shaft member W, the metal mold | die which can forge the effective rack tooth row | line | column 131 with high precision can be designed. .

The connecting portion 13C is a range from a boundary line F1 between the connecting portion 13C and the rack tooth forming portion 13A to a boundary line F2 between the connecting portion 13C and the ball screw portion 13B. Here, as shown in FIG. 3A, the boundary line F1 between the connecting portion 13C and the rack tooth forming portion 13A is a straight line that is parallel to the rotation axis G of the pinion shaft 12 and passes through the apex P of the inclined portion 135. The boundary line between the connecting portion 13C and the ball screw portion 13B is a straight line that passes through the boundary between the portion subjected to the concave plastic deformation by the warm forging and the portion not subjected to the plastic deformation. The range sandwiched between these straight lines is the connecting portion 13 </ b> C, and rack teeth that are in this range and cannot mesh with the teeth of the pinion shaft 12 become invalid rack teeth 134.
The reason for forming the connecting portion 13E that connects the rack tooth forming portion 13A and the joint coupling portion 13D is to ensure the strength of the rack shaft 13 by separating the female thread 133 of the joint coupling portion 13D from the effective rack tooth row 131. It is to do.

  The shape of the inclined portion 135 is not limited to the above-described symmetrical shape, and is viewed from a direction perpendicular to the axis L of the shaft member W and the tooth trace G of the effective rack tooth row 131 as shown in FIG. The shape is tapered toward the rack tooth forming portion 13A from the ball screw portion 13B, and is asymmetric with respect to a straight line passing through the center of the tooth trace G of the effective rack tooth row 131 and parallel to the axis L of the shaft member W. You may form in the shape and the shape shifted | deviated to the one end side (lower side of a figure) of the tooth trace G. FIG. Thereby, in the inclined part 135 of the above-mentioned symmetrical shape, the rack tooth 134 (see FIG. 3A) that cannot be meshed with the teeth of the pinion shaft 12 is formed into the asymmetrical inclined part 135, whereby the pinion In some cases, the rack teeth 134a (see FIG. 4) can be engaged with the teeth of the shaft 12. Therefore, the axial length of the rack shaft 13 can be further shortened.

  The steering device 10 of the present embodiment can be miniaturized by applying the rack shaft 13. The rack shaft 13 of the above-described embodiment has been described by taking the ball screw portion 13B and the joint coupling portion 13D as examples of the non-rack tooth portion. However, for example, the same effect can be obtained even if the rack shaft 13 is a simple cylindrical shaft portion. Moreover, although the case where the rack shaft 13 of the above-mentioned embodiment is applied to an electric power steering apparatus has been described, it can be similarly applied to a hydraulic power steering apparatus or a steering apparatus without assist.

10: Steering device, 11: Rack and pinion mechanism, 12: Pinion shaft, 13: Rack shaft, 13A: Rack tooth forming portion, 13B: Ball screw portion (non-rack tooth portion), 13C: Connecting portion, 13D: Joint coupling portion ( Non-rack tooth portion), 13E: connecting portion, 131: effective rack tooth row, 134: invalid rack tooth, 135: inclined portion, 20: electric assist portion, 21: motor, 30: speed reduction mechanism, 40: ball screw mechanism, W : Shaft member

Claims (9)

A rack tooth forming portion that plastically deforms the outer peripheral surface of the shaft member into a concave shape to form an effective rack tooth row; and
A non-rack tooth portion having no rack teeth;
A connecting portion that is positioned at an axial end of the recessed region and is plastically deformed with plastic deformation of the rack tooth forming portion, and connects the rack tooth forming portion and the non-rack tooth portion;
A rack shaft having
A rack shaft in which invalid rack teeth adjacent to the effective rack tooth row are formed in the connecting portion.   The rack shaft according to claim 1, wherein the connecting portion is provided on both axial sides of the rack tooth forming portion.   The rack shaft according to claim 1 or 2, wherein the shaft member is a solid member. The connecting portion includes the invalid rack tooth, and an inclined portion that connects the rack tooth forming portion and the non-rack tooth portion,
The shape of the inclined portion viewed from a direction perpendicular to the axis of the shaft member and the tooth trace of the effective rack tooth row is a shape that tapers from the non-rack tooth portion toward the rack tooth forming portion. The rack shaft according to any one of claims 1 to 3, wherein the rack shaft is formed symmetrically with respect to a straight line that passes through a center of a tooth line of the effective rack tooth row and is parallel to an axis of the shaft member.   The invalid rack teeth pass through the center of the effective rack tooth row and the axis of the shaft member when viewed from a direction perpendicular to the axis line of the shaft member and the tooth line of the effective rack tooth row. The rack shaft according to claim 4, wherein the rack shaft is formed on both sides of a parallel straight line. The connecting portion includes the invalid rack tooth, and an inclined portion that connects the rack tooth forming portion and the non-rack tooth portion,
The shape of the inclined portion viewed from a direction perpendicular to the axis of the shaft member and the tooth trace of the effective rack tooth row is a shape that tapers from the non-rack tooth portion toward the rack tooth forming portion. The asymmetrical shape is formed with respect to a straight line that passes through the center of the tooth line of the effective rack tooth row and is parallel to the axis line of the shaft member, and is formed in a shape shifted to one end side of the tooth line. The rack shaft of any one item. A housing;
The rack shaft according to any one of claims 1 to 6, which is supported by the housing so as to be movable in an axial direction, and is connected to a wheel of a vehicle.
A pinion supported by the housing so as to be rotatable about an axis, meshed with the effective rack tooth row of the rack shaft, and connected to the steering of the vehicle;
A steering apparatus comprising: The steering device is
The steering device according to claim 7, further comprising: an assist device that is attached to the housing and is provided at a position different in an axial direction with respect to the effective rack tooth row, and assists an axial movement of the rack shaft. The assist device is
A motor attached to the housing;
A speed reduction mechanism for reducing the rotation of the motor;
A ball nut rotatably supported by the housing;
With
The rack shaft has a ball screw portion formed on the non-rack tooth portion and screwable with the ball nut,
9. The steering apparatus according to claim 8, wherein the rotation decelerated by the speed reduction mechanism is converted into an axial movement of the rack shaft via the ball nut and the ball screw part to assist the axial movement of the rack shaft.

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