JP2002079350A - Hollow rack shaft, and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive and high-performance hollow rack shaft, particularly a hollow rack shaft for a steering device and a method of manufacturing the same.
Use high-grade materials for the rack, make the hollow rack shaft strong enough, use inexpensive materials for the tube, reduce the thickness of the plate, and obtain a lightweight and low-cost hollow rack shaft. It is an object of the present invention to obtain a hollow rack shaft having an appropriate quality and strength balance without waste. SOLUTION: A plate-shaped rack shaft material 3 is composed of a rack tooth material portion 1 where a rack tooth portion is to be formed and a tube portion material portion 2 where a tube portion is to be formed, and these different materials are welded. A hollow rack shaft 10 is formed by forming one joined rack shaft material 3 and molding the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hollow rack shaft,
More particularly, the present invention relates to a hollow rack shaft used for a steering device of an automobile.

[0002]

2. Description of the Related Art Conventionally, as a method of forming a hollow rack shaft, Japanese Patent Application Laid-Open Nos.
No. 278287 discloses a method.
In any of these methods, the rack teeth are formed in a state of being bent into a plate material or a U-shape having a semicircular cross section, and then the remaining plate portion (leg portion) is further bent to form a cylindrical shape. If there is no problem, it is used as it is, and if more strength is required, the butted portion for forming the above-mentioned cylindrical shape is joined by welding.

[0003]

A pinion connected to a steering shaft is connected to the rack teeth of the hollow rack shaft, and a steering force is transmitted from the pinion. Therefore, a bending stress acts on the tooth roots of the rack teeth. A high contact surface pressure acts on the contact portion of the rack tooth surface. In order to withstand a high contact surface pressure, the rack teeth are generally subjected to a hardening treatment to a hardness of about Hrc60 by carburizing or induction hardening or the like.

On the other hand, since such a large surface pressure does not act on the tube portion where the rack teeth are not formed and only a relatively small bending stress acts, it is not necessary to harden the tube portion.

As described above, conventionally, when a hollow rack shaft is manufactured by molding, a rack shaft material having the same material and the same plate thickness (that is, cut out from one original large material) is used throughout. Therefore, the material and plate thickness were selected and used according to the demanding rack teeth.

That is, in this method, a high-grade material having good hardenability is selected as a rack shaft material in accordance with the rack tooth portion, and the plate thickness is also large according to the rack tooth portion. Since a low-grade, thin-walled material is sufficient for the tube portion, the hollow rack shaft as a product is considered to be of excessive quality from this point and is expensive.

Further, automobiles are required to be reduced in weight in gram units from the viewpoint of improving fuel efficiency.
Having an extra thick part like this is
This would increase the weight of the vehicle, which is undesirable from this point of view.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to obtain a hollow rack shaft that is inexpensive and has high performance, particularly a hollow rack shaft for a steering device, and to easily manufacture the same. is there. In addition, use a high-grade material for the rack part, make the hollow rack shaft have sufficient strength, use an inexpensive material for the tube part, reduce the thickness, and obtain a lightweight and low-cost hollow rack shaft. Further, it is an object of the present invention to obtain a hollow rack shaft having proper quality and strength balance without waste as a whole.

[0009]

The above object is achieved by the following means. That is, the first means for solving the present invention is a hollow rack shaft obtained by forming and processing a rack tooth portion and a tube portion using a plate-like rack shaft material. The rack tooth part material part where the rack tooth part is to be molded and the tube part material part where the tube part is to be molded are different materials,
These are one piece of the rack shaft material welded and joined.

According to a second aspect of the present invention, in the hollow rack shaft according to the first aspect, the plate thickness of the rack tooth portion is greater than the plate thickness of the tube portion. .

According to a third aspect of the present invention, in the hollow rack shaft according to the first or second aspect, the material of the rack tooth material is harder than the material of the tube material. Is a good material.

A fourth solution of the present invention is a hollow rack shaft manufacturing method for manufacturing a hollow rack shaft by forming and processing a rack tooth portion and a tube portion using a plate-shaped rack shaft material. Then, as the rack shaft material,
The rack tooth material part in which the rack tooth part is to be formed and the tube part material part in which the tube part is to be formed are made of different materials, and a single rack shaft material to which these are welded and joined is used. This is a rack shaft manufacturing method.

A fifth aspect of the present invention is a method of manufacturing a hollow rack shaft according to a fourth aspect of the present invention, wherein the thickness of the rack tooth material is greater than the thickness of the tube material. It is.

According to a sixth aspect of the present invention, there is provided the hollow rack shaft manufacturing method according to the fourth or fifth aspect, wherein the material of the rack tooth material is made to be more baked than the material of the tube material. It is made of a material with good insertability.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a plate-like rack shaft material used in an embodiment of the present invention. FIG. 1 (a) is a plan view of the rack shaft material, and FIG. 1 (b) is a side view of FIG. .

As shown in FIG. 1 (a), a rack shaft material 3 serving as a material for a hollow rack shaft has a substantially strip-shaped plate-shaped rack tooth portion material portion 1 and a strip-shaped plate-shaped tube portion material portion. 2 is manufactured. This rack tooth part material part 1
The tube material portion 2 is cut out from a coil-shaped material by means such as press punching or laser cutting.

The material of the rack tooth portion material portion 1 is preferably SCr or SCM which can be carburized and hardened, or carbon steel or the like suitable for induction hardening. In addition, the width of the rack tooth portion material portion 1 is narrow at arrow portions X and X in FIG. The narrow portion 1a is a region (range) in which rack teeth are formed, and as described later,
The width of the plate is narrowed in accordance with the tooth width of the rack of the completed rack shaft and in order to keep the balance in consideration of the volume so that the butted portion P is exactly fitted.

On the other hand, the material of the tube material 2 is low carbon steel or the like, and does not require special hardenability. As shown in FIG. 1, the rack tooth portion material portion 1 and the tube portion material portion 2 are closely adhered at a butt portion R, and the adhered portion is completely welded and joined by laser or the like without interruption over the entire thickness of the plate. The rack shaft material 3 is used.

Since the welded portion tends to harden due to the influence of heat, which is considered to hinder the forming in the subsequent process, it is preferable to soften the hardened portion by performing an annealing process after welding. Is desirable.

In FIG. 1, the rack tooth material portion 1
Is thicker than the tube material part 2.
This is made thicker to increase the strength in consideration of the strength of the rack teeth. In the present embodiment, both the material and the plate thickness are changed between the rack tooth portion material portion 1 and the tube portion material portion 2, but either one may be changed.

FIGS. 2A and 2B show a state in which a first step of forming a U-shape and a U-shape on the rack shaft blank 3 has been completed, wherein FIG. 2A is a front sectional view, and FIGS. (c) and (d) are a BB sectional view, a CC sectional view, and a DD sectional view of (a), respectively.

The forming in the first step is performed by bending the rack shaft blank 3 shown in FIG. 1 by pressing.
As can be seen from FIG. 2, the portions 1b and 1f where the rack teeth are not formed later have a U-shaped cross section as shown in FIGS. 2 (b) and 2 (d), and the upper half is formed in a semicircular shape. . On the other hand, the portion 1c where the rack teeth are formed is shown in FIG.
As shown in the figure, the U-shape is formed into a shape having a flat portion on the upper surface.

In the first step, the bending process itself is not substantially different from the conventional one, except that the rack shaft material 3 is composed of the rack tooth portion material portion 1 and the tube portion material portion 2 having different materials and plate thicknesses. It differs in that it is a welded plate. In this step, since the sheet thickness and the material are different, a mold designed in consideration of the sheet thickness difference is used at the time of bending, and molding is performed by giving a processing condition in consideration of the material difference such as spring back. .

FIG. 3 shows a state of the rack shaft blank 3 on which rack teeth have been formed through the following second step.
Is a cross-sectional plan view after the rack teeth are formed, and FIG.
It is B sectional drawing.

The case of the second step is the same as the conventional one,
In the second step, the rack teeth 1d are formed by using an upper mold having teeth corresponding to the rack teeth and a lower mold having irregularities corresponding to the irregularities of the upper mold (the rack shaft). It is performed by inserting the material 3) between the upper and lower molds, bringing the upper and lower molds close to each other, performing press molding, and transferring the irregularities of the mold to the work. In other words, as shown in FIG. 3A, the cross-sectional shape of the rack teeth is formed to be uneven by the lower die so that even the back surface follows the shape of the front tooth surface.

FIGS. 4A and 4B are views showing a state of the rack shaft blank 3 having passed through the third step, wherein FIG.
(B), (c) and (d) are respectively the B-
It is B sectional drawing, CC sectional drawing, and DD sectional drawing.

In the third step, the openings (legs 1e) of the U-shaped and U-shaped cross sections of the rack shaft blank 3 are bent and formed into a cylindrical shape (the rack formed into a cylindrical shape). Since the shaft blank 3 is almost a hollow rack shaft, it is indicated by reference numeral 10.) As a result of being bent into a cylindrical shape, the plate width of the material is adjusted in advance so that the butted portions P and Q are tightly attached as described above.

Thereafter, the hollow rack shaft 10 thus obtained is subjected to post-processing, after joining the butted portions P and Q by welding or the like, if necessary, and then cutting other than the rack portion as necessary. After imparting the required strength as a rack shaft (teeth) by carburizing and quenching or induction hardening of the rack teeth and other parts, the tubes at both ends forming the shaft are finished by grinding. It should be noted that it is not precluded that a re-bend correction is performed as needed in an intermediate step.

The joint R welded at the plate-like stage
After being subjected to annealing, it is plastically deformed through the forming of the first to third steps, so that the influence of distortion due to welding almost disappears and does not adversely affect the product.

In the present invention, the rack shaft material 3 is constructed by combining two kinds of materials, which are divided into a rack tooth portion and a tube portion. It is also possible to change and set the number of divisions and the like as appropriate. For example, it is also possible to use only high-grade steel with good hardenability in the vicinity of the rack teeth and to set the thickness to be thick.

FIG. 5 shows an example of such a rack shaft blank 3 different from FIG. FIGS. 5A and 5B are a plan view (a) and a side view (b) showing an example in which the rack shaft blank 3 is composed of a tube blank 2 'and a rack tooth blank 1' therein. The thickness and the material are the same as those described above, and the portion serving as the rack teeth is fitted into the other portion serving as the rack tooth material portion 1 and welded. Even when such a rack shaft material is used, there is no particular difference from those already described, and a duplicate description will be omitted.

In the hollow rack shaft 10 shown in the present embodiment, the rack tooth portion material portion 1 is made of high-grade steel that can satisfy both the hardenability and the thickness that can withstand the strength as the rack tooth, and the tube portion. Since the rack shaft raw material 3 using an inexpensive material is used for the raw material portion 2, it is possible to obtain a hollow rack shaft that is not excessive in quality, inexpensive, and lightweight.

[0034]

As described above, according to the present invention, an inexpensive and high-performance hollow rack shaft, in particular, a hollow rack shaft for a steering device can be obtained and can be easily manufactured.

Further, since a high-grade material can be used for the rack portion, a hollow rack shaft having sufficient strength can be obtained, and an inexpensive material can be used for the tube portion. There is an effect that a rack shaft can be obtained. Further, this has the effect that a hollow rack shaft having appropriate quality and strength balance without waste as a whole can be obtained.

[Brief description of the drawings]

FIG. 1 shows a plate-like rack shaft material used in an example of an embodiment of the present invention, wherein (a) is a plan view of the rack shaft material,
(B) is a side view of (a).

FIGS. 2A and 2B show a state in which a first step of forming a U-shape and a U-shape on the rack shaft material 3 has been completed, wherein FIG. 2A is a front sectional view, and FIGS. (D) respectively
It is BB sectional drawing, CC sectional drawing, and DD sectional drawing of (a).

3A and 3B show a state of a rack shaft blank 3 on which rack teeth are formed through a second step, wherein FIG. 3A is a cross-sectional plan view after forming rack teeth, and FIG. 3B is a BB view of FIG. It is sectional drawing.

FIG. 4 is a view showing a state of the rack shaft blank 3 after a third step, wherein (a) is a front sectional view, (b) and (c).
And (d) are BB sectional views of (a) and C-
It is C sectional drawing and DD sectional drawing.

FIG. 5 is a plan view showing an example of another rack shaft material different from FIG. 1 in which the rack shaft material 3 is composed of a tube portion material portion 2 'and a rack tooth portion material portion 1' therein. And a side view (b).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rack tooth material part 2 Tube part material part 3 Rack shaft material 10 Hollow rack shaft R Joining part P, Q Butting part

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) F16H 55/26 F16H 55/26 (72) Inventor Yasushi Watanabe 1-8-1, Soja-cho, Maebashi City, Gunma Prefecture F-term in Japan Seiko Co., Ltd. (reference) 3J030 AC03 BA08 BC05 4E063 AA01 CA02 CA03 MA18 4E087 HA06

Claims (6)

[Claims] 1. A hollow rack shaft obtained by forming and processing a rack tooth portion and a tube portion using a plate-shaped rack shaft material, wherein the rack shaft material has the rack tooth portion formed therein. A hollow rack shaft, wherein a rack tooth portion material portion to be formed and a tube portion material portion to be formed with the tube portion are made of different materials, and these are a single rack shaft material welded and joined. 2. The hollow rack shaft according to claim 1, wherein a plate thickness of said rack tooth material portion is larger than a plate thickness of said tube material material portion. 3. The hollow rack shaft according to claim 1, wherein the material of the rack tooth portion material is:
A hollow rack shaft made of a material having better hardenability than the material of the tube material portion. 4. A hollow rack shaft manufacturing method for manufacturing a hollow rack shaft by forming and processing a rack tooth portion and a tube portion using a plate-shaped rack shaft material, wherein the rack shaft material is The rack tooth portion material portion where the rack tooth portion is to be formed and the tube portion material portion where the tube portion is to be formed are made of different materials, and a single rack shaft material to which these are welded is used. A method for producing a hollow rack shaft. 5. The hollow rack shaft manufacturing method according to claim 4, wherein a plate thickness of said rack tooth portion material portion is larger than a plate thickness of said tube portion material portion. Method. 6. The method of manufacturing a hollow rack shaft according to claim 4, wherein the material of the rack tooth portion material is a material having better hardenability than the material of the tube portion material. A method of manufacturing a hollow rack shaft.