JPH10226339A - Rack shaft of steering device for vehicle and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent production of an acute angle in the inner angular part so as to heighten the strength of a rack shaft by connecting the inner angular parts where the flat part and a circular-arc part intersect each other inside a steel pipe by a taper surface or a recessed curved surface in the rack shaft where rack teeth is formed on the outside surface of the flat part of the hollow steel pipe having a substantially D-shaped section. SOLUTION: A rack shaft has rack teeth 12 meshed with a pinion on the axial midway part of a steel pipe 11 having a substantially circular section. The part where the rack teeth 12 are formed is deformed to be flat by plastic working, and its cross- sectional form is substantially hollow D-shape having a flat part 13 and a circular-arc part 14. In this case, the outside angular part 15 where the outside of the flat part 13 and the outside of the circular-arc part 14 intersect each other is plastic-deformed to be tapered in such a manner as to be inside a virtual circle C including the circular- arc part 14. The inside angular part 16 where the inside of the flat part 13 and the inside of the circular-arc part 14 intersect each other is connected to the taper of the outer angular part 15 by a substantially parallel taper surface, whereby the generation of creased in the inside angular part 16 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rack shaft for a vehicle steering system and a method of manufacturing the same, and more particularly, to a hollow rack shaft having a steel pipe having rack teeth formed in a part thereof and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as a steering device for a vehicle, a pinion is meshed with a rack tooth formed on a rack shaft, and the rack shaft is moved in an axial direction with rotation of the pinion by steering. 2. Description of the Related Art A rack and pinion type steering device for steering a vehicle has been provided. As shown in FIGS. 6 and 7, the rack shaft used in the rack-and-pinion type steering device is formed of a steel pipe P to reduce the weight, and a rack meshing with the pinion is provided at an intermediate portion in the axial direction. Teeth 90 are formed. The rack teeth 90 are formed by forming a flat portion 92 by plastic working with a press while leaving the arc portion 91 of the steel pipe P, and performing gear cutting on the outer surface thereof. Rack teeth 9
The portion 0 is hardened to a predetermined hardness by induction hardening.

[0003]

However, when the conventional rack shaft is plastically deformed at an intermediate portion thereof flatly,
The inner corner portion 93 where the flat portion 92 and the arc portion 91 inside the steel pipe intersect is deformed at an acute angle, and due to the sudden change in shape, wrinkles extending in the axial direction are easily generated in the inner corner portion 93, and the wrinkles are substantially reduced. In the case of induction hardening, a crack occurs at the wrinkled portion during induction hardening, and the strength of the rack shaft is reduced. The present invention has been made in view of the above problems, and when a part of a steel pipe is plastically deformed flatly, wrinkles are hardly generated at inner corners thereof, and a reduction in strength of a rack shaft is prevented. It is an object of the present invention to provide a rack shaft of a steering device for a vehicle and a manufacturing method thereof.

[0004]

In order to achieve the above object, a rack shaft of a vehicle steering system according to the present invention has a substantially D-shaped cross section formed by flatly plastically deforming an axially middle portion of a steel pipe having a substantially circular cross section. In a rack shaft of a vehicle steering device having a hollow shape and having a rack tooth meshing with a pinion on an outer surface of the flat portion, a flat portion and an arc portion of the steel pipe outside of the portion where the rack tooth is formed intersect. The outer corners are plastically deformed inside the virtual circle including the arc part, and the inner corners where the flat part inside the steel pipe of the part where the rack teeth are formed intersects with the arc part are tapered surfaces or It is characterized by being continuous with a concave curved surface.

[0005] According to the rack shaft of the vehicle steering system having the above-described structure, the inner corner portion is continuously formed by a tapered surface or a concave curved surface. It is possible to suppress wrinkles from occurring in the part. Moreover, since the outer corners are plastically deformed inward from the imaginary circle including the arc portion of the steel pipe, the surplus generated by this plastic deformation is wrapped around the inner corners, and the inner corners are moved inward. It can be bulged, which can effectively prevent an acute angle from being formed at the inner corner.

It is preferable that the outer corners are plastically deformed into a tapered shape. In this case, the rate of change in cross section is made larger than when the outer corners are plastically deformed into a convex curved shape. Since the inner corners can be more effectively bulged inward, it is possible to more reliably prevent wrinkles from being generated at the inner corners.

Further, a method of manufacturing a rack shaft according to the present invention
An axially intermediate portion of a steel pipe having a substantially circular cross section is flatly plastically deformed into a substantially D-shaped hollow shape, and a rack of a vehicle steering device is formed with rack teeth meshing with a pinion on an outer surface of the flat portion. In the shaft manufacturing method, the portion corresponding to the outer corner where the flat portion and the arc portion of the steel pipe outside of the portion forming the rack teeth intersect with each other, the plastic deformation of the flat portion and the virtual circle including the arc portion at the same time. It is characterized by being plastically deformed inward so that an inner corner portion where a flat portion and an arc portion on the inner side of the steel pipe intersect is continuous with a tapered surface or a concave curved surface.

According to the method of manufacturing the rack shaft, when a part of the steel pipe is plastically deformed flat, the part corresponding to the outer corner is plastically deformed inward from an imaginary circle including an arc part of the steel pipe. The extra thickness generated by the plastic deformation can be wrapped around the inner corner to bulge the inner corner inward, so that the inner corner is tapered or concave without forming an acute angle. It is possible to suppress the occurrence of wrinkles at the inner corners by continuing the curved surface.

In the method of manufacturing the rack shaft, it is preferable that a portion corresponding to the outer corner is plastically deformed into a tapered shape. In this case, the outer corner is plastically deformed into a convex curved shape. Since the rate of change in cross section can be increased, the inner corners can be more effectively bulged inward, and wrinkles can be more reliably prevented from being generated at the inner corners. .

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 2 is a sectional view showing a rack and pinion type steering device equipped with the rack shaft S of the present invention. The steering device includes an input shaft 1 connected to a steering handle (not shown), a pinion 2 that rotates with the rotation of the input shaft 1, the rack shaft S that meshes with the pinion 2, and the rack shaft S. And a housing 3 for covering. The rack shaft S is slidably held by the housing 3 via a rack bush 4.
Both ends of the rack shaft S protrude from both end openings 3a and 3b of the housing 3, and ball joints 5 and 6 are integrated with the protruding ends. Tie rods 7, 8 are attached to the respective ball joints 5, 6, and both ends of the rack shaft S are connected to the steered wheels via the tie rods 7, 8. Therefore, by rotating the handle, the pinion 2 is rotated via the input shaft 1 to move the rack shaft S in the axial direction (vehicle width direction).
The vehicle can be steered. A hydraulic cylinder 9 for assisting the steering force is provided inside the housing 3.
In the oil chambers 9a and 9b, hydraulic oil for steering force is selectively supplied from a hydraulic control valve 10 provided on the outer periphery of the input shaft 1 according to the steering direction and the steering resistance. It can be supplied.

Referring to FIG. 1, the rack shaft S is formed of a steel pipe 11 having a substantially circular cross section, and a rack tooth 1 meshing with the pinion 2 is provided at an intermediate portion in the axial direction.
2 are formed. The rack teeth 1 of the rack shaft S
The portion where 2 is formed is deformed flat by plastic working, and its cross-sectional shape is a substantially D-shaped hollow shape having a flat portion 13 and an arc portion 14. The outer peripheral shape of the arc portion 14 is substantially the same as the outer peripheral shape of the steel pipe 11 before the flat portion 13 is formed.

In the above cross-sectional shape, the outer corner 15 where the outside of the flat portion 13 and the outside of the arc portion 14 intersect is formed into a tapered shape so as to be inside the virtual circle C including the arc portion 14. It has been transformed. The inner corner 16 where the inside of the flat portion 13 intersects with the inside of the circular arc portion 14 is continued without an acute angle by a tapered surface substantially parallel to the taper of the outer corner 15. The cross-sectional shape of the rack shaft S other than the portion where the rack teeth 12 are formed is:
It has a substantially circular shape, which is the original cross-sectional shape of the steel pipe 11.

In manufacturing the rack shaft S, first,
As shown in FIGS. 3A and 3B, a steel pipe 11 having a substantially circular cross section is used as a work, and a core metal 21 is inserted therein. The cross-sectional shape of the core metal 21 is a substantially D-shaped shape having an arc portion 21a that matches a substantially lower half portion of the inner periphery of the steel pipe 11 and a flat surface 21b for forming the flat portion 13. At both corners where the arc portion 21a and the flat surface 21b intersect, a tapered surface 21c that matches the inner corner 16 of the rack shaft S is formed.

Next, a part of the peripheral surface of the steel pipe 11 at an intermediate portion in the axial direction is plastically deformed by, for example, press working to form a flat portion 13 (see FIGS. 3C and 3D). Simultaneously with the formation of the flat portion 13, the portion corresponding to the outer corner portion 15 is plastically deformed inward from the virtual circle C including the arc portion 14, and the outer corner portion 15 is formed into a tapered shape. The extra thickness of the steel pipe 11 generated by the above is wrapped around the inner corner 16 and the inner corner 16 is bulged inward. As a result, the inner corner portion 16 can be made continuous with a tapered surface that matches the tapered surface 21c of the cored bar 21, and an acute angle can be prevented from being generated at the inner corner portion 16. Thereafter, the flat portion 13 is subjected to gear cutting to form rack teeth 12 (see FIGS. 3E and 3F), and the rack teeth 12 are hardened to a predetermined hardness by induction hardening.

The rack shaft S manufactured as described above can prevent an acute angle from being formed in the inner corner portion 16, so that when the flat portion 13 is formed, wrinkles are not generated in the inner corner portion 16. Can be prevented. For this reason, in the induction hardening step, it is possible to prevent the occurrence of quenching cracks in the inner corner portions 16, and to solve the conventional disadvantage that the strength of the rack shaft S is reduced due to quenching cracks. it can. In particular, in the above embodiment, since the outer corner 15 of the rack shaft S is plastically deformed into a tapered shape, the cross-sectional change rate is larger than when the outer corner 15 is plastically deformed into a convex curved shape. can do. For this reason, the inner corner portion 16 can be more effectively bulged inward, and can be reliably aligned with the core metal 21.
Therefore, it is possible to more reliably prevent wrinkles from being generated in the inner corner portions 16.

The cross-sectional shape of the outer corner 15 is as follows.
In addition to the tapered shape, as shown in FIG. 4, a convex curved surface shape may be used. The inner corners 16 may also be continuous on a concave curved surface as shown in FIG.

Further, instead of the method of manufacturing the rack shaft S shown in FIGS. 3A and 3B, the rack shaft S may be manufactured by a method shown in FIG. That is, the core metal 21 is provided inside the steel pipe 11.
Instead of inserting the outer corners 15 of the steel pipe 11
The portion below the portion corresponding to the vicinity of the lower end of the taper is restrained by an integral or split type clamp mold 22, and the upper portion of the remaining steel pipe is plastically deformed using a punch 23 or a roll for forming the flat portion 13. Then, the flat part 13
In this case, the lower part of the steel pipe 11 is constrained by a clamp die 22, and the inner peripheral side of the steel pipe 11 is substantially the same as the punch 23 or roll pressing type. Since the shape is similar, the inner corner portion 16 having no acute angle can be formed.

[0018]

As described above, according to the rack shaft of the vehicle steering system according to the first aspect, since the inner corner portion is continuous with the tapered surface or the concave curved surface, a part of the steel pipe is plastically flattened. When deforming, it is possible to suppress the occurrence of wrinkles at the inside corners. For this reason, it is possible to prevent the occurrence of inconvenience that burn cracking occurs due to the wrinkles and the strength of the rack shaft decreases. In addition, since the outer corners are plastically deformed inward from the imaginary circle including the arc portion of the steel pipe, the extra thickness generated by the plastic deformation is wrapped around the inner corners, and the inner corners are moved inward. , Which can more effectively prevent an acute angle from being formed at the inner corner.

According to the rack shaft of the vehicle steering system according to the second aspect, since the outer corner is plastically deformed into a tapered shape, the outer corner is plastically deformed into a convex curved shape. The rate of change can be increased. For this reason, the inside corners can be effectively bulged inward, so that wrinkles can be more reliably prevented from being generated at the inside corners.

According to the method of manufacturing a rack shaft according to the third aspect, when a part of the steel pipe is plastically deformed flat, the part corresponding to the outer corner portion is made smaller than the virtual circle including the arc part of the steel pipe. It is plastically deformed inward, and the excess thickness caused by the plastic deformation is wrapped around the inside corner, and the inside corner can be bulged inward, so that the inside corner is tapered without generating an acute angle. It can be continuous with a surface or a concave surface. For this reason, it is possible to suppress the occurrence of wrinkles at the inner corners, and it is possible to prevent the occurrence of inconvenience such as the occurrence of burning cracks due to the wrinkles and a decrease in the strength of the rack shaft.

According to the method of manufacturing a rack shaft according to the fourth aspect, the portion corresponding to the outer corner is plastically deformed into a tapered shape, so that the outer corner is plastically deformed into a convex curved shape. Thus, the rate of change in cross section can be increased, and the inner corners can be effectively bulged inward, so that wrinkles can be more reliably prevented from being generated at the inner corners.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of a rack shaft according to the present invention, wherein FIG. 1 (a) is a front view of a main part, and FIG.
It is an I-line enlarged sectional view.

FIG. 2 is a sectional view of a vehicle steering system equipped with a rack shaft according to the present invention.

FIG. 3 is a process chart showing a method of manufacturing a rack shaft according to the present invention.

FIG. 4 is a cross-sectional view showing another embodiment.

FIG. 5 is a cross-sectional view showing still another embodiment.

FIG. 6 is a front view of a main part showing a conventional example.

FIG. 7 is an enlarged sectional view taken along line VII-VII of FIG. 6;

[Explanation of symbols]

 Reference Signs List 1 rack shaft 11 steel pipe 12 rack tooth 13 flat part 14 arc part 15 outer corner part 16 inner corner part 2 pinion C virtual circle

Claims (4)

[Claims] 1. A vehicle in which a steel pipe having a substantially circular section is axially plastically deformed flatly into a substantially D-shaped hollow section, and a rack tooth meshing with a pinion is formed on an outer surface of the flat portion. In the rack shaft of the steering device, the outer corner portion where the flat portion and the arc portion of the steel pipe outside of the portion where the rack teeth are formed intersects plastically inwardly with respect to the virtual circle including the arc portion, A rack shaft for a vehicle steering system, wherein an inner corner portion where a flat portion inside the steel pipe and an arc portion of a portion where the rack teeth are formed intersects with each other by a tapered surface or a concave curved surface. 2. A rack shaft for a vehicle steering system according to claim 1, wherein said outer corner portion is plastically deformed into a tapered shape. 3. A vehicle in which an axially middle portion of a steel pipe having a substantially circular cross section is plastically deformed flatly into a substantially D-shaped hollow cross section, and a rack tooth meshing with a pinion is formed on an outer surface of the flat portion. In the method of manufacturing a rack shaft for a steering device, a portion corresponding to an outer corner where a flat portion outside the steel pipe and an arc portion of a portion forming the rack teeth intersect with each other is formed into an arc portion simultaneously with the plastic deformation of the flat portion. Manufacturing of a rack shaft of a vehicle steering system, characterized in that plastic deformation is performed inside a virtual circle including the inside, and an inner corner portion where a flat portion and a circular arc portion inside a steel pipe intersect is continuous with a tapered surface or a concave curved surface. Method. 4. The method according to claim 3, wherein the portion corresponding to the outer corner is plastically deformed into a tapered shape.