JP2018047473A - Rack bar manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rack bar manufacturing method enabled to improve the precision of a rack tooth by reducing the compressibility of the rack tooth side.SOLUTION: A rack bar 10 is formed by die-forging a material having a substantially circular transverse section, and is caused to transmit a steering operation to a steering wheel by transforming the rotational motion of a pinion shaft for rotating in association with a steering wheel, into an axial motion. The rack bar is provided with a bulge 15 on the opposite side of a rack tooth 14 and at a position axially symmetric to said rack tooth 14, so that the compressibility of the side of the rack tooth 14 can be lowered to keep the precision of the tooth surface of said rack tooth 14.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method of manufacturing a rack bar that is applied to, for example, a rack and pinion type steering device of a vehicle and serves to transmit a steering force to steered wheels.

  As a rack bar applied to a conventional rack and pinion type steering device, for example, one described in Patent Document 1 below is known.

  That is, this rack bar sandwiches a solid round bar-shaped material between the upper mold and the lower mold, causes the material of the material to plastically flow, and allows the surplus material to escape to the side as a pair of burrs. Rack teeth are formed in a predetermined circumferential range.

JP 2000-2111536 A

  However, in the manufacturing process of the conventional rack bar, the plastic flow is the largest in the vicinity of the rack tooth formation region, the compression ratio is the highest, and the heat generation is the largest. There is a possibility that the side contracts and a bending deformation that warps to the rack tooth side is caused.

  The present invention has been devised in view of such technical problems, and provides a method of manufacturing a rack bar that can reduce the compression rate on the rack tooth side and improve the accuracy of the rack tooth.

  The present invention includes a pair of forming dies each having a first forming die and a second forming die arranged opposite to each other, and forging a die by sandwiching a metal rod-shaped material having a substantially circular cross section from the outer peripheral side. Thus, the rack bar manufacturing method for manufacturing the rack bar for converting the rotational motion of the pinion shaft linked to the steering wheel into the axial motion to be used for steering, wherein the first mold is the pinion teeth of the pinion shaft A rack tooth forming portion for forming a rack tooth that meshes with the rack tooth, and the second mold is substantially opposite to the rack tooth with respect to an axis passing through the center of the material, and substantially in the radial direction of the axis. A convex portion forming portion is provided for forming a convex portion protruding outward from the circular cross-sectional outer shape, and the first molding die and the second molding die are formed by a pair of gaps provided between the respective molding dies. Composed 1 A forging step in which the rack teeth are formed by die forging the material with the first mold and the second mold, and the burr that has flowed out as a burr into the pair of burr outflow parts. And a burr removing step for removing a part of the material.

  According to the present invention, by providing a convex portion at an axially symmetric position of the rack tooth that has relatively little influence on the accuracy of the rack tooth, the compression rate on the rack tooth side is reduced and the accuracy of the rack tooth is maintained. Can do.

1 is a schematic view of a steering apparatus to which a rack bar manufactured according to the present invention is applied. It is a top view of the rack bar shown in FIG. It is a side view of the rack bar shown in FIG. It is sectional drawing which follows the AA line of FIG. FIG. 3 is a cross-sectional view taken along line B-B in FIG. 1 showing a rack bar support mode in the steering apparatus shown in FIG. 1. The manufacturing method (manufacturing process) of the rack bar which concerns on this invention is shown, (a) is the state which set the raw material to the metal mold | die, (b) is a forging process, (c) is the state which released the forged product, (d ) Is a diagram corresponding to FIG. FIG. 7B is a view corresponding to FIG. 6B displaying a state of plastic flow of the material at the time of forging the rack bar. FIG. 7A is a view corresponding to FIG. 7 showing the state of plastic flow of the material during die forging of a conventional rack bar, and FIG. 3B is a view corresponding to FIG. 3 showing the state of warping deformation after die forging of the conventional rack bar. It is.

  Hereinafter, an embodiment of a method of manufacturing a rack bar according to the present invention will be described in detail with reference to the drawings. In the following embodiments, a rack bar manufacturing method applied to a steering apparatus for an automobile is shown as in the prior art.

  First, a steering device to which a rack bar manufactured by the manufacturing method according to the present invention is applied will be described. As shown in FIG. 1, this steering device is linked so that one end in the axial direction can rotate integrally with the steering wheel SW. The input shaft 1 and one end in the axial direction are connected to the other end of the input shaft 1 via a torsion bar (not shown) so as to be relatively rotatable, and are connected to the steered wheels WL and WR via a so-called rack and pinion mechanism RP. Input from the driver based on the detection results of the output shaft 2 to be linked and the torque sensor TS for detecting the steering torque based on the relative rotational displacement amount of the input shaft 1 and the output shaft 2 or a vehicle speed sensor (not shown). A motor unit MU that generates a steering assist torque corresponding to the steering torque, and provided on the other end side of the output shaft 2, transmits the output of the motor unit MU to the output shaft 2 while decelerating the output. A transmission mechanism RG that is mainly comprised.

  The rack and pinion mechanism RP is formed in a predetermined axial range of a pinion tooth 2a formed at an intermediate portion of the output shaft 2 and a rod-shaped rack bar 10 disposed substantially orthogonal to the output shaft 2. The rack bar 10 is configured to mesh with the rack teeth 14, and the rack bar 10 moves in the axial direction according to the rotation direction of the output shaft 2. That is, both ends of the rack bar 10 are linked to the steered wheels WR and WL via a tie rod 3 and a knuckle arm (not shown), respectively, and the rack bar 10 is connected to the illustration via the tie rod 3 as the rack bar 10 moves in the axial direction. By pulling the outer knuckle arm, the directions of the steered wheels WR and WL are changed.

  As shown in FIG. 2 in particular, the rack bar 10 is provided on the one end side in the axial direction, the first member 11 having the rack teeth 14 formed on the outer peripheral side almost in the entire axial direction, and the other end side in the axial direction. And a second member 12 made of a substantially hollow cylindrical pipe member, and is arranged so as to be movable along the inner axial direction of the housing 4.

  As shown in FIGS. 2 to 4, the first member 11 includes a rack body 13 formed of a rod-shaped metal material having a substantially circular cross section, and a substantially circular cross section of the rack body 13 (hereinafter, A rack tooth 14 formed by die forging, which will be described later, around the axis Z passing through the center of the “circular cross section”), and a convex portion 15 protruding from the axis Z on the opposite side of the rack tooth 14. And a pair of left and right burr removing portions 16 formed by removing a part of a burr 19 (see FIG. 6D), which will be described later, formed in accordance with the die forging.

  As shown in FIGS. 3 and 4, the convex portion 15 is formed by plastic flow of the material of the material along with the formation of the rack teeth 14 by pressure deformation during die forging described later. It is provided so as to protrude outward from the outer shape S of the circular cross section (see the phantom line in FIG. 4), that is, to protrude outward in the radial direction of the axis Z with respect to the outer shape S of the circular cross section. Yes.

  In addition, this convex part 15 is not removed after the die forging mentioned later, but as shown in FIG. 5, the said convex part 15 is supported by the support surface 20a of the rack retainer 20 which supports the back side (convex part 15 side) of the rack bar 10. By providing the concave portion 20b that receives the portion 15, the rack bar 10 can be used without removing the convex portion 15.

  The convex portion 15 is formed in a tapered shape such that the width dimension W corresponding to the dimension in the width direction of the rack teeth 14 gradually decreases from the proximal end side toward the distal end side. In the corner portion (corner portion), a proximal end side round portion 17 having a substantially concave arc shape in cross section is formed, and in the distal end side corner portion (corner portion), a distal end side radius portion having a substantially convex arc shape in cross section is formed. A portion 18 is formed. And about both said round parts 17 and 18, the curvature radius r1 of the front end side round part 17 is set so that it may become larger than the curvature radius r2 of the base end side round part 18. FIG.

  Each burr removing portion 16 is made of a material of each burr outflow portion 23 of a first molding die D1 and a second molding die D2 to be described later that is used for the die forging as the rack teeth 14 are formed. Is formed by removing the front end side of the pair of burrs 19 that are formed to protrude by flowing in.

  As shown in FIG. 1, the motor unit MU includes an electric motor 31 that generates steering assist torque, and an electric motor that is attached to the electric motor 31 and is based on predetermined parameters such as a driver's steering torque and vehicle speed. And an electronic controller 32 that drives and controls the motor 31.

  The transmission mechanism RG is fixed to the distal end portion of the output shaft 31a of the electric motor 31 via a shaft coupling (not shown), and the worm shaft 33 that rotates integrally with the output shaft 31a and the outer periphery of the output shaft 2 on the other end side. A worm wheel 34 that is fixed and meshes with the worm shaft 33 to transmit the rotation of the worm shaft 33 to the output shaft 2 while decelerating the rotation of the worm shaft 33.

  Hereinafter, the manufacturing method of the rack bar 10 according to the present embodiment will be specifically described with reference to FIGS. 6 (a) to 6 (d).

  First, before describing the manufacturing method of the rack bar 10, the molding die used in the manufacturing method will be described. As shown in FIG. 6A, the molding die is an axis of the rack body 13 (material). A first molding die D1, which is a movable mold that is arranged on one side around Z and serves to form the rack teeth 14, and is opposed to the opposite side of the first molding die D1, and cooperates with the first molding die D1. The second forming die D2, which is a fixed die used for die forging described later.

  The first mold D1 is continuously formed in an uneven shape in the longitudinal direction of the cavity recessed in the surface facing the second mold D2, and the rack tooth forming portion 21 for forming the rack teeth 14; And a pair of burr outflow portions 22 that are formed on split surfaces with the second mold D2 on both sides of the rack tooth forming portion 21 and serve to form the burrs 19, and have a cavity of the first mold D1. The portion excluding the rack tooth forming portion 21 and the pair of burr outflow portions 22 has a shape along the outer shape S corresponding to the outer shape S (see FIG. 4) of the circular section of the material M1 (substantially in cross section). (Semi-circular shape).

  The second mold D2 is formed in a cavity that is recessed in the surface facing the first mold D1, and is along the outer shape S corresponding to the outer shape S (see FIG. 4) of the circular cross section of the material M1. Formed in a shape (substantially semicircular cross-sectional shape), a material support portion 23 used to support the material M1 and a convex portion provided in the inner bottom portion of the material support portion 23 and used to form the convex portion 15 A part forming part 24 and a pair of burr outflow parts 25 which are formed on the dividing surfaces of the first mold D1 on both sides of the material support part 23 and serve to form the burrs 19 are provided.

  In other words, the second molding die D2 also has a circular cross section of the material M1 except for the convex portion forming portion 24 and the pair of burr outflow portions 25, as in the first molding die D1. Are formed in a shape along the outer shape S (a substantially semicircular cross section).

  Further, the convex portion forming portion 24 is recessed so as to overlap the axis Z and to be symmetrical with respect to the axis Z in the direction along the dividing surface with the first mold D1. In addition, the bottom side is closed.

  In addition, a corner rounded portion 27 for forming the base end side rounded portion 17 is provided on the opening side of the convex portion forming portion 24, and the tip side is provided on the bottom side of the convex portion forming portion 24. A corner radius portion 28 is provided for forming the radius portion 18, and the radius of curvature R 1 of the corner radius portion 27 is set larger than the radius of curvature R 2 of the corner radius portion 28.

  To manufacture the rack bar 10 using the first mold D1 and the second mold D2 as described above, first, as shown in FIG. 6A, the first mold D1 is raised. The material M1 is set on the material support portion 23 of the second mold D2 that has been opened.

  Subsequently, as shown in FIG. 6 (b), the first molding die D1 is lowered, and the material M1 is pressed and deformed in such a manner that the material M1 is sandwiched between the molding dies D1 and D2. 21 and the convex part formation part 24 are transcribe | transferred and die forging is performed (forging process of this invention).

  That is, by pressing the material M1 with the rack tooth forming portion 21 of the first mold D1, the upper end portion of the material M1 is crushed, and the crushed material becomes the convex portion forming portion 24 and both burrs. By forming a plastic flow between the outflow portions 22 and 25 (the gap V between the first and second molding dies D1 and D2 formed by the burr outflow portions 22 and 25), the rack tooth forming portion 21 and the convex portion are formed. The portion 25 is transferred to form the rack teeth 14 and the convex portion 15, and a pair of burrs 19 are formed by the burr outflow portions 22 and 25 (gap V).

  Then, as shown in FIG.6 (c), a 1st shaping | molding die D1 is raised, mold opening is performed, and the said forged product M2 forged-processed is taken out. Finally, as shown in FIG. 6 (d), the pair of burrs 19 formed by the forging process are cut off to form a pair of burrs removing portions 16 (of the present invention). Deburring step) and the production of the rack bar 10 is completed.

  Here, conventionally, as shown in FIG. 8A, when the rack bar 100 is forged, all of the material crushed with the formation of the rack teeth 101 is between the burr outflow portions 22 and 25. Therefore, the compression rate on the rack tooth 101 side is relatively higher and the heat generation is larger than that on the back surface 102 side.

  That is, as a result of an increase in the amount of heat generation between the rack tooth 101 side and the tooth surface 102 side, a difference occurs in the amount of cooling shrinkage between the rack tooth 101 side and the tooth surface 102 side due to the difference in heat generation amount. There is a possibility that the rack bar 100 is warped and deformed as shown in FIG.

  On the other hand, in the manufacturing method of the rack bar according to the present embodiment, the convex portion 15 is provided at the axially symmetrical position of the rack tooth 14 on the opposite side of the rack tooth 14, as shown in FIG. A part of the material crushed with the formation of the rack teeth 14 plastically flows toward the convex portion 15 (see arrow X in FIG. 7), and thus between the burr outflow portions 22 and 25. It is possible to reduce the amount of plastic flow (see arrow Y in FIG. 7).

  That is, by reducing the plastic flow amount, the compression rate on the rack tooth 14 side is reduced and heat generation due to the compression is reduced. On the other hand, by increasing the plastic flow amount on the convex portion 15 side, the convex portion 15 side is reduced. This increases the compression ratio and increases the heat generated by the compression. As a result, the difference in the amount of heat generated between the rack tooth 14 side and the convex portion 15 side is reduced, whereby the warp deformation of the rack bar 10 after die forging as described above can be suppressed.

  As described above, according to the method of manufacturing a rack bar according to the present embodiment, the convex portion 15 is provided at the axially symmetric position of the rack tooth 14 which has a relatively small influence on the accuracy of the rack tooth 14. The compression rate on the teeth 14 side can be reduced, and the accuracy of the tooth surfaces of the rack teeth 14 can be maintained.

  In addition, at this time, the cavity of the second mold D2 is formed along the outer shape of the material M1 except for the convex portion forming portion 24 and the pair of burr outflow portions 25, 25. For this reason, it becomes possible to suppress the increase in the compression rate on the second mold D2 side as much as possible, and the warp deformation of the rack bar 10 accompanying the increase in the compression rate can be suppressed.

  Here, with respect to the first mold D1, it is possible to reduce the compression rate by enlarging the tooth width of the rack tooth 14, but in that case, the accuracy of the tooth surface of the rack tooth 14 is lowered. There is a risk of it. On the other hand, in the present embodiment, the cavity of the first mold D1 is formed along the outer shape of the material M1 except for the rack tooth forming portion 21 and the pair of burr outflow portions 22 and 22, and the rack By maintaining the shape of the material M <b> 1 without increasing the tooth width of the teeth 14, the accuracy of the tooth surfaces of the rack teeth 14 is maintained.

  Moreover, in this embodiment, the convex part formation part 24 of the said 2nd shaping | molding die D2 is obstruct | occluded. In other words, when forging with burrs, the compression ratio of the material M1 may change depending on the amount of the burrs. By forming 15, the accuracy of the tooth surfaces of the rack teeth 14 can be stably maintained.

  Further, the convex portion forming portion 24 of the second mold D2 is formed so as to overlap the axis Z in the direction along the dividing surface of both the molds D1, D2. As a result, the protruding direction of the convex portion 15 is configured along the moving direction of the first mold D1, and the fluidity of the material to the convex portion 15 is improved. As a result, the compression rate on the rack tooth 14 side is effectively reduced. Can be reduced.

  In addition, with this configuration, the convex portion forming portion 24 is formed at a position far from the rack tooth forming portion 21, and therefore the influence on the tooth surface accuracy of the rack teeth 14 due to the provision of the convex portion 15. Less.

  In addition, the convex portion forming portion 24 of the second mold D2 is formed so as to be symmetric with respect to the axis Z in the direction along the dividing surface of the both molds D1, D2. For this reason, it is possible to make the compression rate uniform in the direction of the tooth trace on the rack tooth 14 side, and this is used to improve the balance of the tooth surface accuracy of the rack tooth 14 in the tooth trace direction.

  Further, the convex forming portion 24 of the second mold D2 includes a corner rounded portion 27 on the opening side and a corner rounded portion 28 on the bottom side. In this way, by forming the corners and corners of the convex portion 15 into a so-called round shape having a substantially arc-shaped cross section, it is possible to suppress stress concentration occurring at the corners and corners.

  Moreover, in this configuration, in this embodiment, the radius of curvature R1 of the corner rounded portion 27 is larger than the radius of curvature R2 of the corner rounded portion 28. Thereby, it is possible to suppress the occurrence of the loss of the convex portion 15 due to the insufficient compression rate of the corner rounded portion 27.

  In the present embodiment, the rack bar 10 manufactured through the forging process and the burr removing process is used without removing the protrusions 15. That is, in the present embodiment, the concave portion 20b that receives the convex portion 15 is provided on the support surface 20a on the rack retainer 20 side, and the rack bar 10 is used without removing the convex portion 15 (see FIG. 5). ). Thereby, the man-hour for removing the convex portion 15 can be reduced, and the productivity of the rack bar 10 is improved.

  The present invention is not limited to the configuration of the above-described embodiment, and can be freely changed according to the specification and cost of the application target as long as the above-described effects of the present invention can be achieved.

  Further, the rack bar manufactured according to the present invention can be applied to various steering devices having the rack and pinion mechanism RP, even if the steering device is other than the one disclosed in the above embodiment.

  As a manufacturing method of the rack bar based on the embodiment described above, for example, the following modes can be considered.

  That is, in one aspect of the manufacturing method of the rack bar, a metal bar shape having a substantially circular cross section with a pair of forming dies formed of a first forming die and a second forming die arranged to face each other. A rack bar manufacturing method for manufacturing a rack bar for turning and converting a rotational motion of a pinion shaft linked to a steering wheel into an axial motion by sandwiching the material from the outer peripheral side and die forging, The first mold includes a rack tooth forming portion that forms rack teeth that mesh with the pinion teeth of the pinion shaft, and the second mold is on an opposite side of the rack teeth with respect to an axis passing through the center of the material. A convex portion forming portion that forms a convex portion protruding outward from the substantially circular cross-sectional outer shape of the material in the radial direction of the axis, and the first molding die and the second molding die are the respective molding dies. A forging process comprising a pair of burr outflow portions constituted by a pair of gaps provided on the rack, and forming the rack teeth by die forging the material with the first mold and the second mold. And a burr removing step of removing a part of the material that has flowed out as burrs in the pair of burr outflow portions.

  In a preferred aspect of the method for manufacturing the rack bar, the cavity of the second mold is formed along the outer shape of the material except for the pair of burr outflow portions and the convex portion forming portion.

  In another preferred embodiment, in any one of the manufacturing methods of the rack bar, the cavity of the first molding die follows the outer shape of the material except for the pair of burr outflow portions and the rack tooth forming portions. It is formed as follows.

  In still another preferred aspect, in any one of the aspects of the method for manufacturing the rack bar, the convex portion forming portion is closed.

  In still another preferred aspect, in any one of the aspects of the method for manufacturing the rack bar, the convex portion forming portion is arranged in a direction along a dividing surface of the first molding die and the second molding die, and the axis line. It is formed to overlap.

  In still another preferred aspect, in any one of the aspects of the method for manufacturing the rack bar, the convex portion forming portion is arranged on the axis line in a direction along a dividing surface of the first molding die and the second molding die. It is formed so as to be symmetrical.

  In still another preferred aspect, in any one of the aspects of the method for manufacturing the rack bar, the convex portion forming portion includes a corner round portion provided on the opening side of the convex portion forming portion, and the convex portion forming portion. A corner round portion provided on the bottom side.

  In still another preferred aspect, in any one of the aspects of the rack bar manufacturing method, the convex portion forming portion has a radius of curvature of the corner radius portion that is larger than a radius of curvature of the corner radius portion. Is formed.

  In still another preferred embodiment, in any one of the embodiments of the rack bar manufacturing method, the protrusion formed by the protrusion forming portion is removed from the rack bar manufactured by the forging step and the burr removing step. do not do.

SW ... Steering wheel 2 ... Output shaft (pinion shaft)
DESCRIPTION OF SYMBOLS 10 ... Rack bar 14 ... Rack tooth 15 ... Convex part 16 ... Burr removal part 19 ... Burr 21 ... Rack tooth formation part 24 ... Convex part formation part 22, 25 ... Burr outflow part D1 ... 1st shaping | molding die D2 ... 2nd shaping | molding Mold M1 ... Material S ... Outline Z ... Axis

Claims (9)

A steering wheel is obtained by forging a die by sandwiching a metal rod-shaped material having a substantially circular cross section from the outer peripheral side with a pair of molding dies that are arranged to face each other and having a first molding die and a second molding die. A rack bar manufacturing method for manufacturing a rack bar for converting the rotational motion of the pinion shaft linked to the shaft motion into an axial motion and for use in steering,
The first mold includes a rack tooth forming portion that forms rack teeth that mesh with the pinion teeth of the pinion shaft,
The second mold has a convex portion that protrudes outward from the substantially circular cross-sectional outer shape of the material in the radial direction of the axial line on the opposite side of the rack teeth with respect to an axis passing through the center of the material. A part forming part,
The first mold and the second mold include a pair of burr outflow portions configured by a pair of gaps provided between the molds,
A forging step of forming the rack teeth by die forging the material with the first mold and the second mold;
A burr removing step of removing a part of the material that has flowed out as burr into the pair of burr outflow portions;
The manufacturing method of the rack bar characterized by having.   2. The rack bar according to claim 1, wherein the cavity of the second mold is formed so as to follow the outer shape of the material except for the pair of burr outflow portions and the convex portion forming portion. Manufacturing method.   2. The rack bar according to claim 1, wherein the cavity of the first mold is formed along the outer shape of the material except for the pair of burr outflow portions and the rack tooth forming portion. Manufacturing method.   The rack bar manufacturing method according to claim 1, wherein the convex portion forming portion is closed.   2. The rack according to claim 1, wherein the convex portion forming portion is formed so as to overlap the axis in a direction along a dividing surface of the first molding die and the second molding die. Bar manufacturing method.   The said convex part formation part is formed so that it may become symmetrical with respect to the said axis line in the direction along the division surface of the said 1st shaping | molding die and the said 2nd shaping | molding die. Rack bar manufacturing method.   The convex portion forming portion includes a corner round portion provided on an opening side of the convex portion forming portion, and a corner round portion provided on a bottom surface side of the convex portion forming portion. 2. A method for producing a rack bar according to 1.   The rack bar according to claim 7, wherein the convex portion forming portion is formed such that a radius of curvature of the corner radius portion is larger than a radius of curvature of the corner radius portion.   The rack bar manufacturing method according to claim 1, wherein the convex portion formed by the convex portion forming portion is not removed from the rack bar manufactured by the forging step and the burr removing step.

Images