TIE ROD END AND METHOD OF PRODUCING THE SAME

Abstract

A tie rod end of a vehicle steering apparatus, wherein a first end of the tie rod end is coupled to an axial member disposed so as to extend in a vehicle width direction and configured to move in the width direction in accordance with a steering operation, and a second end of the tie rod end is coupled to a steering knuckle holding a wheel, wherein the tie rod end includes a curved portion which is curved between the first end and the second end, the curved portion including a first-end-side portion located near to the first end, a second-end-side portion located near to the second end, and an intermediate portion located between the first-end-side portion and the second-end-side portion, and wherein a width of the curved portion in a curve direction is larger at the intermediate portion than at the first-end-side portion and the second-end-side portion.

Claims

1. A tie rod end of a steering apparatus for a vehicle, wherein a first end of the tie rod end is coupled to an axial member which is disposed so as to extend in a width direction of the vehicle and which is configured to move in the width direction in accordance with a steering operation, and a second end of the tie rod end is coupled to a steering knuckle holding a wheel of the vehicle, wherein the tie rod end includes a curved portion which is curved between the first end and the second end, the curved portion including a first-end-side portion located near to the first end, a second-end-side portion located near to the second end, and an intermediate portion located between the first-end-side portion and the second-end-side portion, and wherein a width of the curved portion in a curve direction is larger at the intermediate portion than at the first-end-side portion and the second-end-side portion.

2. The tie rod end according to claim 1, wherein one of an outer portion of the curved portion located on an outer side in a curvature of the curved portion and an inner portion located on an inner side in the curvature of the curved portion has a thickness smaller than the other of the outer portion and the inner portion at least at the intermediate portion, so as to be formed as a thin portion.

3. The tie rod end according to claim 2, wherein the outer portion of the curved portion located on the outer side in the curvature of the curved portion is the thin portion.

4. The tie rod end according to claim 3, wherein at least the intermediate portion is shaped such that the outer portion of the curved portion located on the outer side in the curvature of the curved portion is a web and the inner portion of the curved portion located on the inner side in the curvature of the curved portion is a flange.

5. The tie rod end according to claim 1, wherein the width of the curved portion in the curve direction gradually decreases toward the first end and the second end.

6. The tie rod end according to claim 1, wherein, in a state in which the tie rod end is installed on the vehicle, the curved portion is curved so as to be convex toward a front side or a rear side of the vehicle.

7. The tie rod end according to claim 1, wherein, where a straight line connecting a center of the first end and a center of the second end is defined as an axis of the tie rod end, a section of the curved portion in its longitudinal direction that is shifted from the axis by the largest amount does not overlap the axis.

8. A method of producing the tie rod end defined in claim 1, wherein, where a straight line connecting a center of the first end and a center of the second end is defined as an axis of the tie rod end and a direction of extension of the axis is defined as an axial direction, the method comprising a plurality of forging steps which are successively performed and in each of which two dies are closed in a direction perpendicular to both of the axial direction and the curve direction, and wherein the plurality of forging steps are performed such that an amount by which the curved portion shifts from the axis increases with an increase in the number of times of the plurality of forging steps performed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The objects, features, advantages, and technical and industrial significance of the present disclosure will be better understood by reading the following detailed description of an embodiment, when considered in connection with the accompanying drawings, in which:

[0036] FIG. 1 is a perspective view showing a state in which a tie rod end according to one embodiment is disposed in a steering apparatus of a vehicle;

[0037] FIG. 2 is a plan view of the tie rod end of the embodiment and includes cross-sectional views of the tie rod end; and

[0038] FIGS. 3A, 3B and 3C are schematic views for explaining forging steps performed in a method of producing the tie rod end of the embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENT

[0039] Referring to the drawings, there will be explained below in detail a tie rod end according to one embodiment of the claimable invention and a method of producing the tie rod end. It is to be understood that the claimable invention is not limited to the details of the following embodiment but may be embodied based on the forms described in Forms of the Invention and may be changed and modified based on the knowledge of those skilled in the art.

[A] Vehicle Steering Apparatus including Tie Rod End

[0040] A tie rod end according to the present embodiment is employed as a constituent component in a vehicle steering apparatus that is partly illustrated in FIG. 1. The steering apparatus is configured to steer (turn) a wheel supported by a strut type suspension apparatus. While the wheel is not illustrated, the wheel is rotatably supported by a steering knuckle 12 supported by a suspension lower arm 10. The steering knuckle 12 is supported by the lower arm 10 via a ball joint 14 so as to be pivotable about a king pin axis. In FIG. 1, a principal part of a suspension apparatus for a front right wheel of the vehicle and a part of the steering apparatus are illustrated.

[0041] The steering apparatus is of a rack and pinion type and includes therein a gear box in which is disposed a rack bar 15 on which a rack is formed. In FIG. 1, the gear box is not illustrated, and the rack bar 15 is indicated by the long dashed double-short dashed line. FIG. 1 further illustrates a boot 18 disposed at an end portion of the gear box and a rack end 16 which is coupled to the rack bar 15 via a ball joint and which extends from the gear box. The rack bar 15 and the rack end 16 function as an axial member which is disposed so as to extend in a width direction of the vehicle and which moves in the width direction of the vehicle in accordance with a steering operation. It is noted that only the rack bar 15 may be regarded as the axial member or only the rack end 16 coupled to an end portion of the rack bar 15 may be regarded as the axial member.

[0042] A tie rod end 20 of the present embodiment is disposed so as to connect the rack end 16 and the steering knuckle 12. Specifically, an end portion of the rack end 16 is externally threaded. A first end of the tie rod end 20 (one of opposite ends of the tie rod end 20 nearer to a center of the body of the vehicle in the vehicle width direction) is coupled to and threadedly engaged with the externally threaded end portion of the rack end 16. The steering knuckle 12 includes a knuckle arm 22 extending from a main body thereof. A second end of the tie rod end 20 (the other of the opposite ends of the tie rod end 20 nearer to an outer portion of the body of the vehicle in the vehicle width direction) is coupled to a distal end portion of the knuckle arm 22 via a ball joint 24.

[0043] The gear box, namely, the rack bar 15, is disposed so as to shift toward a rear side of the vehicle with respect to a straight line connecting centers of rotation of the right and left wheels, namely, with respect to a wheel axis. Similarly, the rack end 16 and the tie rod end 20 are disposed so as to shift toward the rear side of the vehicle.

[B] Structure of Tie Rod End

[0044] FIG. 2 is a plan view of the tie rod end 20 according to the present embodiment. FIG. 2 also shows cross sections of the tie rod end 20 at five locations in the plan view which are spaced apart from each other in a longitudinal direction of the tie rod end 20. As shown in FIG. 2, the present tie rod end 20 has, at its first end (i.e., at a left end of the tie rod end 20 in FIG. 2), an internally threaded bore with which the externally threaded end portion of the rack end 16 is engaged. Thus, the tie rod end 20 is fixed at the first end thereof to the rack end 16 by a lock nut 26. Further, the tie rod end 20 has, at its second end (i.e., at a right end of the tie rod end 20 in FIG. 2), a through-hole 28 in which a stud of the ball joint 24 is fitted. The second end of the tie rod end 20 is formed as an attachment portion 30. Here, a straight line connecting a center of the first end and a center of the second end, specifically, a straight line connecting respective cross-sectional centers of the first end and the second end (a center of the through-hole 28 for the second end) is defined as an axis L of the tie rod end 20. The tie rod end 20 includes a curved portion C which is curved with respect to the axis L between the first end and the second end.

[0045] When the wheel 32 is largely steered as indicated in the long dashed double-short dashed line in FIG. 2, specifically, when the right wheel 32 is largely steered rightward, a part of the wheel 32 (e.g., a rim of the wheel) may interfere with the tie rod end 20. The curved portion C is curved so as to be convex toward the front side of the vehicle, namely, the curved portion C is curved such that a curve direction is a forward direction. Thus, the curved portion C is effective for obviating the interference. In the present tie rod end 20, the curved portion C is curved such that a section thereof in the longitudinal direction that is shifted from the axis L by the largest amount does not overlap the axis L. In other words, at the section of the curved portion C that is shifted from the axis L by the largest amount, the axis L is spaced apart form the tie rod end 20.

[0046] It is noted that, in the case where the tie rod end is disposed so as to be shifted toward the front side of the vehicle with respect to the wheel axis, the tie rod end is configured such that the curve direction of its curved portion is a rearward direction, namely, the tie rod end is configured to have the curved portion that is curved convex toward the rear side of the vehicle, so that the interference with the wheel can be obviated. It is noted that the curved portion is effective for obviating interference with not only the wheel but also constituent components of a suspension apparatus.

[0047] The curved portion C is effective for lowering the stiffness of the tie rod end 20. In a steering operation, the tie rod end 20 receives a load in a direction of extension of the axis L (hereinafter referred to as axial direction where appropriate). The presence of the curved portion C provides a cushioning function with respect to the load. That is, the stiffness of the curved portion C is appropriately lowered, thereby improving the steering feeling.

[0048] On the other hand, the presence of the curved portion C leads to a decrease in the strength of the tie rod end 20 with respect to the load in the axial direction. Thus, in the tie rod end 20, a width w of the curved portion C in the curve direction is made larger. Here, a portion of the curved portion C located near to the first end is referred to as a first-end-side portion C.sub.L, a portion of the curved portion C located near to the second end is referred to as a second-end-side portion C.sub.R, and a portion intermediate between these two portions C.sub.L, C.sub.R is referred to as an intermediate portion C.sub.c. In the present tie rod 20, a width w.sub.e of the intermediate portion C.sub.C is larger than a width w.sub.L of the first-end-side portion C.sub.L and a width w.sub.R of the second-end-side portion C.sub.R. Further, the width w is the largest at a central portion of the intermediate portion C.sub.C in the axial direction, and the width w gradually decreases toward the first end and the second end of the tie rod end 20. In this configuration, the width w continuously and gradually changes, so that no steps exist in the longitudinal direction of the tie rod end 20. Thus, the strength of the tie rod end 20 is effectively enhanced.

[0049] The increase in the strength of the tie rod end 20 by increasing the width of the curved portion leads to an increase in the weight of the tie rod end 20. In the present tie rod end 20, therefore, a thickness d.sub.O of an outer portion of the curved portion C located on an outer side in a curvature of the curved portion C (i.e., outer portion in the curvature of the curved portion C) is made smaller than a thickness d.sub.I of an inner portion of the curvature of the curved portion C located on an inner side in the curvature of the curved portion C (i.e., inner portion in the curvature of the curved portion C) over an entire length of the curved portion C, as shown in the cross-sectional views in FIG. 2. That is, a hatched portion in the plan view in FIG. 2 is formed as a thin portion T. Thus, the tie rod end 20 has, at least at the intermediate portion C.sub.C, a T-like cross sectional shape taken along a plane perpendicular to the axial direction. In other words, the tie rod end 20 is configured such that, at least at the intermediate portion C.sub.C, the outer portion in the curvature of the curved portion C functions as a web and the inner portion in the curvature of the curved portion C functions as a flange. It is noted that the curved portion C has a vertically symmetric cross-sectional shape. Thus, the bending strength and the stiffness of the tie rod end 20 in the up-down direction are uniform. In other words, the bending strength and the stiffness of the tie rod end 20 are the same in the upward direction and the downward direction.

[0050] Like the width w of the curved portion C, a width of the thin portion T in the curve direction is the largest at a central portion thereof in the axial direction of the intermediate portion C.sub.C, and the width of the thin portion T gradually decreases toward the first end and the second end of the tie rod end 20. In short, it may be considered that the width of the curved portion C changes generally in accordance with a change in the width of the thin portion T. As later explained, the tie rod end 20 of the present embodiment is formed by forging, and a cross-sectional area of the curved portion C is substantially the same over the entire length of the curved portion C.

[C] Method of Producing Tie Rod End

[0051] As shown in FIG. 3, the tie rod end 20 according to the present embodiment is formed by performing a thermal forging step a plurality of times. FIG. 3 schematically shows a case in which the tie rod end 20 is formed by performing the thermal forging step two times. FIG. 3A shows a blank. The blank is a round bar formed of steel and having a circular shape in cross section. FIG. 3B includes a perspective view of an article after a first forging step has been performed and a cross-sectional view of a portion of the article corresponding to the intermediate portion of the curved portion. FIG. 3C includes a perspective view of an article after a second forging step has been performed and a cross-sectional view of a portion of the article corresponding to the intermediate portion of the curved portion. In the cross-sectional views of FIGS. 3B and FIG. 3C, die sets 40, 42 used in the respective first and second forging steps are also shown in a state in which two dies of each die set are closed. While, in the present producing method, two articles are formed from one blank in each forging step, the method may be modified otherwise.

[0052] The die set 40 is constituted by an upper die 40a and a lower die 40b, and the die set 42 is constituted by an upper die 42a and a lower die 42b. A cavity is formed when the upper die 40a, 42a and the lower die 40b, 42b are closed. In each forging step, the blank is forged into a shape corresponding to the cavity while the material plastically flows. In each of the plurality of forging steps of the present method, a direction of closing the dies of the die set 40, 42, namely, in a die closing direction, coincides with the up-down direction. In other words, in all of the forging steps of the present method, the dies are closed in the same direction, namely, a direction perpendicular to both of the axial direction and the curve direction. Thus, the posture, i.e., the orientation, of the article is not changed between any of the successively performed forging steps, namely, throughout the successively performed forging steps, so that the forging steps can be easily performed.

[0053] As apparent from FIG. 3, every time the forging step is performed, the portion of the article corresponding to the curved portion moves in the curve direction while the material plastically flows. In other words, the plurality of forging steps are performed such that an amount by which the curved portion shifts from the axis L increases with an increase in the number of times of the forging steps performed. As explained above, the tie rod end 20 of the present embodiment has the thin portion T at the outer portion in the curvature of the curved portion C. Accordingly, an amount of the plastic flow of the material is smaller in the present tie rod end 20 having the thus formed thin portion T, as compared with a tie rod end having the thin portion at the inner portion in the curvature of the curved portion C. This contributes to facilitation of the forging steps and reduction in the number of the forging steps.

[0054] After the plurality of forging steps have been performed, forging burrs are removed by cutting. Further, the first end is processed to form the internally threaded bore, and the attachment portion 30 at the second end is processed to bore the through-hole 28. Thus, the tie rod end 20 is obtained.