JP2001219854A - Hollow rack shaft and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-strength hollow rack shaft having a small-sized tube portion and a rack portion having a wide tooth width, and having irregularities along the rack on the back surface of the rack portion. It is another object of the present invention to provide a hollow rack shaft having high strength and to provide a manufacturing method for manufacturing such a hollow rack shaft. SOLUTION: A hollow rack shaft 10 has a rack tooth at a center portion and a cylindrical portion near both ends, and a tooth width D of the rack tooth is defined by a surface including a tooth bottom and a circle of the cylindrical portion. By setting the length greater than the length C of the chord formed by the above, the tooth width is increased to increase the strength. This rack shaft 10
Is formed from the plate material 1 by plastic working.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hollow rack shaft, and more particularly to a hollow rack shaft for a steering device used in an automobile.

[0002]

2. Description of the Related Art Rack and pinion systems are frequently used in automobile steering systems. In this method, the rotation of the steering wheel operated by the driver is transmitted to the pinion. The rotation of the pinion is transmitted to a rack that meshes with the pinion, and is converted into a movement in a lateral direction (length direction of the rack). Since the rack is connected to the steering rod, the lateral movement changes the orientation of the front wheels. Since such a steering mechanism is well known, further description is omitted.

[0003] The above rack has been obtained by cutting a bar-shaped material, but in recent years, in order to eliminate cutting work as much as possible in the manufacture of the rack, plastic working techniques have been introduced as much as possible. Racks are becoming hollow. JP-A-9-24637
No. 9, JP-B-4-28582 and JP-A-11-180318 disclose examples of a rack manufacturing method incorporating such a plastic working technique.

[0004] In the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 9-246379, a tube material is inserted into a first split mold,
The primary molding is performed by a press mold, then the primary molding material is inserted into a secondary molding split mold having teeth corresponding to the rack teeth on a part of the inner surface, and a semicircular mandrel is press-fitted from one end to remove the rack teeth. It is to be molded.

[0005] Further, in the manufacturing method disclosed in Japanese Patent Publication No. 4-28582, a mandrel is inserted into a tube material,
In a state where the circumference of the tube is surrounded by a fixed die, a die having teeth corresponding to the rack teeth is pushed into the outer shape of the tube to form the rack teeth.

The manufacturing method disclosed in Japanese Patent Application Laid-Open No. H11-180318 is performed by Okubo, one of the inventors of the present invention, and a rack is provided substantially at the center of a substantially strip-shaped plate. After the teeth are formed by plastic working, or bent into a U-shape having a semicircular cross section along the longitudinal center of a substantially strip-shaped plate, rack teeth are formed by plastic working near the center of the semicircular part. Then, the remaining plate is bent to form a tube to form a rack shaft. In the first two publications, tube material is used as a raw material, but this technology uses a plate material without using a tube material, which is advantageous only in terms of material cost, transportation cost, and storage cost. In addition, there is no need to add waste to other parts in order to secure the thickness of the tooth bottom, and there is an advantage that a sufficient lightweight effect can be obtained.

[0007]

In recent years, a rack (rack shaft) for an automobile steering has been required to be reduced in weight and size in order to improve fuel efficiency. The rack shaft is required to be compact and have a larger load capacity. This requirement does not change the size of the rack shaft,
This can be achieved by making only the tooth width of the rack as large as possible. In other words, by increasing only the tooth width, the load capacity applied to the rack can be increased, but the overall size should not be increased.

However, in the conventional method, since a tube material is used, it is practically impossible to fabricate such that the tooth width exceeds the size of a chord crossing the outer periphery of the tube material (material) in principle. It was possible.

In the method disclosed in JP-A-6-246379, when a material is pushed into a mold corresponding to a rack tooth by the action of a mandrel, a thin mandrel is pressed into the inner surface of a narrow tube. As a result, the size of the mandrel is limited, and a rack having a large tooth width cannot be formed.

In the method disclosed in Japanese Patent Publication No. 4-28582, when a mold having teeth corresponding to the rack teeth is pressed into the outer shape of the tube and forged, the work is set up in the center axis direction. Therefore, it is almost impossible to increase the tooth width.

[0011] In these methods, since the back surface of the rack tooth is flat, the bottom of the tooth is inevitably thinned and this part is weakened. If the thickness of the bottom of the tooth is to be ensured, the remaining portion is left unfinished, and there is a disadvantage that a sufficient light weight effect cannot be obtained.

The present invention is a further development of the technique disclosed in Japanese Patent Application Laid-Open No. H11-180318, which solves the above-mentioned drawbacks, has a small tube portion, and has a small tooth width. It is an object to provide a hollow rack shaft having a high strength and a wide rack portion.

Still another object of the present invention is to provide a hollow rack shaft having high strength, which has irregularities along the rack on the back surface of the rack portion.

Another object of the present invention is to provide a manufacturing method for manufacturing such a hollow rack shaft.

[0015]

The above object can be attained by the following means.

A hollow rack shaft according to a first aspect of the present invention is a hollow rack shaft for a steering device having a rack tooth at a center portion, a cylindrical portion near both ends, and a hollow hole extending in a longitudinal direction therein. This hollow rack shaft is a step of bending a substantially strip-shaped plate material in which the width of a portion where rack teeth are formed later is formed wide along the length direction, and forming both side walls. The connecting bottom portion is formed in a U-shape having a semicircular portion near both ends in the longitudinal direction, and in the meantime, a U-shape is formed therebetween, and the width of the U-shaped portion is changed to a U-shape. A first step of forming a portion larger than the diameter of the semicircle of the portion formed in the first step; Forming the rack teeth by plastically flowing the portion And a third step of forming a tube having a hollow inner surface by bending both side walls thereof and abutting the edges thereof in this order. It is a thing.

Further, the hollow rack shaft of the second invention is
The tooth width of the rack teeth is set to be larger than the length of a chord formed by intersecting the plane including the tooth bottom and the semicircle.

Further, a hollow rack shaft according to a third aspect of the present invention includes:
On the inner surface of the hollow hole that forms the back surface of the rack teeth, irregularities are formed substantially in accordance with the shape of the rack teeth.

Further, the hollow rack shaft according to the fourth invention comprises:
The edges butted by the third step are welded together, partially or entirely.

With the above configuration, these hollow rack shafts have the following excellent points.

Since the size of the tooth width can be made larger than the length of the chord traversing the outer circumference of the tube, the load on the teeth can be increased. The tooth profile can be formed into irregularities on both sides, the bottom of the tooth does not become thin, and the thickness of the tooth portion can be set relatively freely. Since a plate is used, manufacturing costs can be reduced. Welding can be arbitrarily set at the butt portion of the tube, and welding can be performed only on necessary portions. Since the front and back dies are used, the shape of the rack teeth can be freely selected,
Since you can freely select a mold that matches the desired tooth shape,
It is possible to cope with a tooth profile such as VGR. The mold can be designed so as to provide sufficient strength on both sides. For the tooth portion, various molding methods such as rolling and swing forging can be selected in addition to simultaneous molding on the entire surface. After the tube is formed, it is possible to straighten the shaft by straightening it.

The fifth and sixth aspects of the present invention relate to a method of manufacturing a hollow rack shaft. Each of the fifth and sixth aspects has a rack tooth at a central portion, a cylindrical portion near both ends, and a long portion inside the cylindrical portion. A hollow rack shaft manufacturing method for manufacturing a hollow rack shaft for a steering device having a hollow hole along the width direction, wherein the width of a portion where rack teeth are formed later is formed in a substantially rectangular shape. In the step of bending the plate material along its length direction, a bottom portion connecting both side walls is formed in a U-shape having a semicircular portion near both ends in the longitudinal direction,
In the meantime, during this time, it is formed in a U shape,
The first step of forming the width of the U-shaped portion larger than the diameter of the semicircle of the U-shaped portion, and the above-described first step, A second step of forming rack teeth by plastically flowing a material at the bottom of the V-shaped bottom part and a part of the material of the side walls thereof, and bending the edges after the second step by bending both side walls thereof And a third step of forming a tube having a hollow inner surface in this order by abutting the parts, and further,
The fourth step of welding the edges of the both side walls butted in the third step to each other partially or entirely is performed.

These production methods have the above-mentioned excellent effects not only in the production of hollow rack shafts, but also on the hollow rack shafts produced thereby.

[0024]

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

FIGS. 1A and 1B show a raw material used in an embodiment of the present invention, wherein FIG. 1A is a front view of the raw material, and FIG. 1B is a sectional view taken along line II of FIG.

As shown in FIG. 1A, the hollow rack shaft is manufactured by using a substantially strip-shaped plate material (plate material) 1. This substantially strip-shaped plate material is cut out from a coil-shaped material or the like by press punching, laser cutting, or the like. The material used is SCr, SCM or the like that can be carburized and hardened, or carbon steel or the like suitable for induction hardening. In addition, this plate material has a large plate width at arrow portions X and X in FIG. The wide portion 1a is a region (range) in which rack teeth are formed. As will be described later, the rack tooth width of the completed rack shaft can be widened so that the balance is taken into account in consideration of the volume. The width of the board is widened to keep it.

FIG. 2 shows a state in which the raw material 1 is formed in the following first step, wherein (a) is a front sectional view,
(B) is a II-II sectional view of (a), (c) is a III-III sectional view of (a), and (d) is a bottom view (view from below) of (a).

The forming in the first step is performed by bending the plate material 1 shown in FIG. 1 with a press or the like. FIG.
As can be seen from FIG.
Has a U-shaped cross section as shown in FIG. 2 (c), and the upper half is formed in a semicircular shape, whereas the portion 1c corresponding to the rack teeth is formed as shown in FIG. 2 (b). And has a flat portion on the upper surface.

Further, as shown in FIG. 2 (d), the width between the side walls 1e corresponding to the rack teeth is such that the width A at the arrow Y in FIG. 2 (d) does not form the rack teeth later. It is wider than the width B of the portion. The portion having a large bending width is set to be large (A> B) in order to increase the tooth width of the rack teeth.

The first step can be carried out uniformly by ordinary press bending, or can be carried out by dividing it according to the convenience of equipment. Bending can be handled by ordinary processing techniques without using special processing techniques.

FIGS. 3A and 3B show a state in which the rack teeth are formed through the following second step. FIG. 3A is a front sectional view after the rack teeth are formed, and FIG. FIG.

The second step is similar to that of JP-A-11-180318, but differs in the following points. For the upper die and the lower die used for molding the rack teeth in this step, a die having a tooth width that is as wide as the tooth width of the finished product is used. Further, the side wall 1e forming the wide portion in FIG. 2A is deformed in the process of forming the rack teeth 1d in FIG. 3 to have a width equal to the diameter of the semicircle of the portion 1b where the rack teeth are not formed. This is because at the time of molding, a part of the material forming the side wall 1e flows to the part of the rack teeth 1d to supplement the material.

That is, in the second step, the rack teeth are formed in the first step by using an upper die having a wide tooth width corresponding to the rack teeth and a lower die having a wide unevenness corresponding to the unevenness of the upper die. The processed work is sandwiched between an upper die and a lower die, and they are brought close to each other to perform the press molding. At this time, a part of the material of the original side wall 1e moves to the part 1d of the rack teeth. Thereby, the unevenness of each mold is transferred to the work (the plate material having undergone the first step). In this step, it is possible to gradually change the combination of the dies to be used and to include multiple steps so as to finally obtain the shape shown in FIG.

As shown in FIG. 3 (a), the cross section 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 side tooth surface. Further, as shown in FIG. 3 (b), the tooth width D of the rack teeth is made larger than the length C of the chord that crosses the outer shape of the tubular portion near both ends of the rack shaft formed in a later step. (See FIG. 5). That is, the teeth of the rack teeth are smaller than the chords formed by intersecting the outer circle of the cylindrical portion (formed in the third step) near both ends of the rack axis with the plane including the bottoms of the rack teeth. The width has been increased.

The reason why this is possible is as follows.
The shape of the work having undergone the steps of (1) and (2) is U-shaped, and the lower part is opened as shown in FIG. 3. This is because it can be pushed perpendicularly to the tooth surface.

Furthermore, since there is no restriction on the space in the vertical direction as when a tube material is used as a material, there is an advantage that sufficient strength can be given to the front and back molding dies (upper die and lower die). is there. In addition, since the degree of restraint can be reduced and the shape is simple except for the tooth forming portion, the mold structure can be simplified and the holding precision of the work can be kept good.

In order to form the rack teeth, it is necessary to engrave a shape corresponding to the rack teeth in the mold itself. However, in the present embodiment, a sufficient space is required because the shape is such that the lower part of the work is open. Since the mold can be designed, the structure of the mold can be designed relatively freely, so that the mold life can be extended.

For example, teeth corresponding to rack teeth can be divided into separate dies in order to prevent cracks. There is also an advantage that the mold on the back side can arbitrarily set irregularities so that the rack shape of the product can be easily obtained.

Further, rack molding can be performed by simultaneous molding of all teeth using a total mold. Alternatively, it is also possible to partially form the rack teeth sequentially. For example, a method in which rolls with irregularities corresponding to the rack teeth are arranged on the top and bottom and formed while rolling (rolling molding) is also possible, or a method in which the upper and lower dies are rocked (rocking forging) is also possible It is. As described above, various methods can be adopted for the shaping of the rack teeth in the second step. In the present invention, the shaping of the rack teeth is not limited to a specific method as described above, and an appropriate processing method can be employed. Can be adopted.

Further, the present invention is applicable to the manufacture of a rack shaft having a VGR (variable speed ratio). In the case of VGR, the shape of the rack teeth changes in the axial direction, and the volume of the tooth portion also changes in the axial direction. Therefore, according to the conventional method, when molding a tooth having a different volume, a phenomenon occurs in which excess is generated in a portion having a small volume and an underfill is generated in a portion having a large volume, and molding is difficult. But,
According to the present invention, since the volume can be adjusted by the mold on the back surface, the VGR tooth shape can be formed without any problem.

FIGS. 4A and 4B are views showing a state after the third step, wherein FIG. 4A is a front sectional view, and FIG.
FIG. 5C is a sectional view taken along line VI-VI of FIG.

In the third step, the openings of the U-shaped and U-shaped cross sections are bent to form a tube. At this time, the rear portion of the portion having the rack teeth is bent in an arc shape, and the size of the arc is bent to be the same as the size of the arc (tube radius) of the tube portion having no rack teeth. The width of the material is adjusted in advance so that the abutting portions E and F bent into a tube shape are tightly adhered.
If the butt portions E and F of the tubes are partially or wholly joined along the butt using a joining method such as laser welding, the strength of the completed hollow rack shaft 10 (FIG. 6) can be greatly enhanced. .

The thus obtained hollow rack shaft 10
As described above, after welding the butted portions E and F as necessary, cutting other than the rack portion is performed. In post-processing, after imparting the required strength by carburizing or induction hardening of the rack and other parts,
The shaft is finished by grinding to produce a product. In addition, it does not prevent performing the re-bending correction as needed in an intermediate step.

FIG. 6 shows the hollow rack shaft 10 manufactured as described above.

[0045]

Since the present invention is manufactured as described above, it has the following effects, and can easily manufacture an inexpensive and high-performance hollow rack shaft, particularly a hollow rack shaft for a steering device. be able to.

(1) Since the size of the tooth width can be made larger than the length of the chord traversing the outer periphery of the tube, the load capacity of the tooth portion increases.

(2) The tooth profile can be formed unevenly on both sides, the bottom of the tooth does not become thin, and the thickness of the tooth can be set relatively freely.

(3) Since a plate is used, manufacturing costs can be reduced.

(4) Welding can be arbitrarily set at the butted portion of the tube, and welding can be performed only on necessary portions.

(5) Since the front and back dies are used, the shape of the rack teeth can be freely selected, and the dies corresponding to the desired tooth shape can be freely selected, so that the tooth shape such as VGR can be handled.

(6) The mold can provide sufficient strength on both sides.

(7) In addition to simultaneous molding of the entire surface, various molding methods such as rolling and rocking forging can be selected.

(8) After the tube is formed, straightness can be obtained by correcting the bending of the shaft.

[Brief description of the drawings]

FIG. 1 is a view for explaining an example of a material 1 used in the present invention, wherein (a) is a front view of the material,
(B) is an II sectional view of (a).

FIGS. 2A and 2B show a state in which the material 1 is formed in a first step, wherein FIG. 2A is a front sectional view, and FIG.
II-II sectional view of (a), III-III of (a)
Sectional drawing, (d) is a bottom view of (a).

3A and 3B show a material shape after a second step, wherein FIG. 3A is a front sectional view after rack molding, and FIG.
FIG. 4 is a sectional view taken along line IV-IV of FIG.

4A and 4B are diagrams showing a material shape after a third step, wherein FIG. 4A is a front sectional view, FIG. 4B is a sectional view taken along line V-V of FIG. It is VI sectional drawing.

FIG. 5 is an enlarged view of FIG. 4 (b).

FIG. 6 is a perspective view of a manufactured hollow rack shaft.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 plate-shaped material 1a wide portion of plate-shaped material 1 1b portion not forming rack teeth of plate-shaped material 1 1c portion corresponding to rack teeth of plate-shaped material 1 1d rack teeth 1e side wall 10 hollow rack shaft

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasushi Watanabe 1-8-1, Soja-cho, Maebashi-shi, Gunma F-term (reference) in Japan Seiko Co., Ltd. 3J030 AC02 AC03 BA08 BB06 BB18 BC05 BC10 BD06 CA10 4E028 EA03 EA04

Claims (6)

[Claims] 1. A hollow rack shaft for a steering device having a rack tooth at a center portion, a cylindrical portion near both ends, and a hollow hole extending in a longitudinal direction inside thereof. The shaft is a process of bending along a longitudinal direction a substantially strip-shaped plate material in which a width of a portion where a rack tooth is formed later is formed wide, and a bottom portion connecting both side walls is formed near both ends in the longitudinal direction. In a U-shape having a semi-circular portion, and in the meantime, while being formed in a U-shape, the width of the U-shaped portion is changed to the width of the semi-circle of the U-shaped portion. A first step of forming a diameter larger than the diameter, and a rack tooth formed by plastically flowing a material of a bottom portion of the U-shaped bottom portion and a part of a material of a side wall thereof after the first step. A second step of forming And a third step of forming a tube having a hollow inner surface by bending both side walls and abutting the edges thereof in this order. 2. The hollow rack shaft according to claim 1, wherein a tooth width of the rack tooth is larger than a length of a chord formed by intersecting a plane including a root of the tooth and the semicircle. And hollow rack shaft. 3. The hollow rack shaft according to claim 1, wherein a portion of the inner surface of the hollow hole that forms a back surface of the rack tooth is formed with irregularities substantially along the shape of the rack tooth. A hollow rack shaft. 4. The hollow rack shaft according to claim 1, wherein the edges abutted in the third step are welded to each other partially or entirely. Characterized by a hollow rack shaft. 5. A hollow rack for manufacturing a hollow rack shaft for a steering device having a rack tooth at a center portion, a cylindrical portion near both ends, and a hollow hole extending in a longitudinal direction therein. This hollow rack shaft manufacturing method is a step of bending a substantially strip-shaped plate material in which the width of a portion where rack teeth are formed later is formed to be wide, along the length direction thereof. The bottom portion connecting the both side walls is formed in a U-shape having a semicircular portion near both ends in the longitudinal direction, and in the meantime, the width of the U-shaped portion is formed between the U-shaped portions. A first step of forming a larger than the diameter of the semicircle of the U-shaped portion; and a material and a side wall of the bottom of the U-shaped bottom portion after the first step. Rack teeth by plastically flowing some of the material A second step of forming, and a third step of forming a tube having a hollow inner surface by bending both side walls and abutting edges thereof after the second step. A method for manufacturing a hollow rack shaft, wherein 6. The hollow rack shaft manufacturing method according to claim 5, wherein the hollow rack shaft manufacturing method further comprises: partially or entirely removing the edges of the both side walls butted in the third step. And performing a fourth step of welding to each other over the hollow rack shaft.