JP3633253B2 - Hollow rack shaft and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
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]
[Prior art]
Conventionally, a method according to Japanese Patent Laid-Open No. 6-246379 is known as a method using plastic working to form rack teeth of a hollow rack shaft. In this method, a tube material is inserted into the first molding part mold, primary molding is performed by a press mold, and then the primary molding material is inserted into a secondary molding part mold having teeth corresponding to rack teeth on a part of the inner surface. However, it has been proposed to mold a rack tooth by press-fitting a semicircular mandrel from one end.
[0003]
Further, as shown in Japanese Patent Publication No. 4-28582, a mold having a tooth corresponding to a rack tooth in a state in which a mandrel is inserted inside the tube material and the periphery of the tube is surrounded by a fixed mold as seen in Japanese Patent Publication No. 4-28582 There has also been proposed a method in which a rack tooth is formed by pushing the tube into the outer shape of the tube.
[0004]
[Problems to be solved by the invention]
However, 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 press-fitted into the inner surface of a narrow tube. For this reason, since the mandrel becomes weak in strength, it is unavoidable to reduce the molding load, so it is not possible to increase the amount of pressing once, and molding is performed little by little in several times, and the processing time is long. Therefore, there is a disadvantage that the number of steps is increased.
[0005]
In the method disclosed in Japanese Patent Publication No. 4-28582, when a die having teeth corresponding to rack teeth is pushed into the outer shape of the tube and forged, the workpiece is moved in the axial direction by the flow of meat during molding. Since the extending force works, the force acts as a tensile force on the mold corresponding to the rack teeth, and there is a drawback that the mold is easily damaged. Further, in order to avoid this, even if a method of reducing the molding load by heating the workpiece, there is a disadvantage that the molding accuracy deteriorates due to the influence of heat.
[0006]
And in these two methods, since the thickness of a tooth bottom part becomes thin, there exists a fault that this part becomes weak. If it is going to secure the thickness of a tooth base, it will add a thin part to the other part, and the fault that sufficient light weight effect cannot be acquired arises.
[0007]
In addition, the conventional technology uses a tube material, and there is a disadvantage that the material cost increases.
[0008]
The present invention solves the above-mentioned drawbacks in the prior art, allows teeth to be molded accurately in a short time without difficulty, and can secure the thickness of the root without any meat, and can reduce the material cost. An object of the present invention is to provide a rack shaft and a manufacturing method thereof.
[0009]
[Means for Solving the Problems]
According to the first aspect of the present invention, the rack teeth are formed by plastic working so that the teeth are aligned in the longitudinal direction on the substantially central flat portion in the short direction of the substantially strip-shaped plate material, and then the remaining plate portion in the short direction is bent. A method for manufacturing a hollow rack shaft is provided.
In the invention of claim 2, after bending the U-shape having a semicircular cross section along the longitudinal center of the substantially strip-shaped plate material, the rack teeth are elongated by plastic working near the central top of the semicircular cross section. Provided is a method for manufacturing a hollow rack shaft, which is formed so that teeth are aligned in the direction, and then the remaining plate portion in the short direction is bent to form a tube shape.
In the hollow rack manufacturing method of Claim 1 or 2, it is preferable to shape | mold the said rack tooth by pinching with an up-and-down metal mold | die.
[0010]
The invention according to claim 4 is a tubular hollow rack shaft having a flat portion manufactured by the method according to any one of claims 1 to 3, wherein the rack tooth portion extends over the inner surface of the flat portion. Provided is a hollow rack shaft in which irregularities are formed side by side in the longitudinal direction.
[0011]
According to the present invention, (1) there is no need to use an expensive tube material,
(2) The rack tooth bottom does not become a book and an ideal thickness balance can be secured.
▲ 3 ▼ We can make a lightweight product without waste,
(4) It can be molded in a short time,
(5) There is an advantage that it is possible to form without difficulty so that the mold is not damaged.
[0012]
In the present invention, it is preferable that the upper and lower molds have teeth corresponding to the rack teeth.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of the present invention will be described below with reference to FIGS.
[0014]
1A and 1B show a material used in an embodiment of the present invention, where FIG. 1A is a front view of the material, and FIG.
[0015]
As shown in FIG. 1A, a hollow rack shaft is manufactured using a substantially strip-shaped plate-like material 1. The substantially strip-shaped plate material is cut out from a coil-shaped material or the like by press punching or laser cutting. The material may be carburized and hardened SCr, SCM, etc., or carbon steel suitable for induction hardening may be used. The plate material 1 has a narrow plate width at the arrow portions X and X in FIG. The narrow plate portion 1a is a range where rack teeth are formed, and the plate width is narrowed in order to maintain balance in consideration of the volume after completion.
[0016]
FIG. 2 shows a state in which the material is molded in the first step, (a) is a front sectional view, (b) is a sectional view taken along II-II in (a), and (c) is a sectional view taken along III in (a). -III represents a cross-sectional view. The molding in the second step is performed by bending the plate 1 shown in FIG. 1 with a press or the like. As can be seen from FIG. 2, the portion 1b where the rack teeth are not formed later has a U-shaped cross section as shown in (c), and the upper half is formed in a semicircular shape, whereas it corresponds to the rack teeth. The portion 1c has a U shape as shown in FIG. 5B, and has a flat portion on the upper surface. The molding in FIG. 2 can be performed uniformly by ordinary press bending molding, or may be performed in a divided manner for convenience of equipment. Bending can be done with ordinary processing techniques.
[0017]
FIG. 3 shows the rack forming step of the second step, where (a) is a front sectional view after rack forming, and (b) is a IV-IV sectional view of (a). 5 shows a rack portion, and FIG. 6 shows an enlarged view of FIG.
[0018]
In the case of the present embodiment, in this second step, the rack teeth 1d are molded 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 workpiece processed in the process is sandwiched between the upper and lower molds, the upper and lower molds are brought close to each other, push molding is performed, and the unevenness of the mold is transferred to the workpiece.
[0019]
Therefore, as shown in FIG. 5, the rack shape according to the present embodiment is formed in a concavo-convex shape along the tooth shape up to the back surface on the tube inner surface side.
[0020]
This is because the work shape is U-shaped and the lower part of FIG. 3 is open, so the back mold of the rack can be pushed perpendicularly to the tooth surface of the work, so that such molding is possible. It becomes.
[0021]
Furthermore, the front and back molding dies can be given sufficient strength because there is no space restriction in the vertical direction. Further, 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 accuracy of the workpiece can be kept good.
[0022]
In rack molding, it is necessary to engrave the shape corresponding to the rack teeth in the mold itself. However, in this embodiment, since the lower part of the work is open, a sufficient space can be taken. The mold structure can be freely crafted to extend the mold life. For example, the teeth corresponding to the rack teeth can be divided into molds in order to prevent cracking. Concerning the back mold, irregularities can be arbitrarily set so that the rack shape of the product can be easily obtained.
[0023]
Furthermore, rack molding can be performed by simultaneous molding of all teeth by a total mold. As another method, it is also possible to partially form rack teeth sequentially. For example, it is possible to form by rolling rolls with unevenness corresponding to rack teeth on the top and bottom (rolling molding), or by molding while swinging the top and bottom dies (oscillating forging). It is. As described above, various methods can be adopted for forming the rack teeth in the second step, and the method is not limited to a specific method.
[0024]
This method is also applicable to a VGR (variable gear ratio) rack shaft. 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, in the conventional method, when molding with a different tooth volume, excess meat is generated as burrs in the small volume part, and thinning occurs in the large volume part. However, according to the present invention, since the volume can be adjusted with the mold on the back surface, even the VGR tooth profile can be formed without any problem.
[0025]
4A and 4B are views showing the third step, where FIG. 4A is a front sectional view, FIG. 4B is a sectional view taken along line V-V in FIG. 4A, and FIG. 4C is a sectional view taken along line VI-VI in FIG.
[0026]
In the third step, the U-shaped and U-shaped cross-sectional openings are bent to form a tube. It is desirable to adjust the width of the material in advance so that the butted portions A and B bent into a tube shape are closely attached.
[0027]
As a method of making a tube by bending an opening, a method of bending a whole region uniformly by a conventional press bending method may be used, or a method of making a tube by bending little by little. The processing method for bending into a tube shape does not require any special advanced technology.
[0028]
In the present embodiment, the method of forming rack teeth in the second step after bending the U-shape and the U-shape in the first step has been described. A method of forming the rack teeth suddenly from the state and then bending them into a U shape and a U shape may be employed, and the rearrangement of the steps can be arbitrarily selected.
[0029]
The butted portions A and B of the tubes may be joined by welding or the like as necessary.
[0030]
As a modification of the present embodiment, a mold having a flat back surface shape may be used in the rack tooth forming in the second step, and the rack shaft shape obtained in this case is the shape obtained by the conventional method. Be the same. Even in that case, the effectiveness of the present invention of making a hollow rack shaft from a plate material is not denied.
[0031]
The hollow rack shaft 10 thus obtained is joined to the butted portions A and B by welding or the like, if necessary, and then subjected to cutting processing other than the rack portion. After giving the required strength by carburizing or induction hardening, the shaft is finished by grinding to produce a product. In addition, you may correct | amend the axis | shaft re-bent as needed in the middle process.
[0032]
【The invention's effect】
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 steering device hollow rack shaft.
[0033]
(1) Since the plate material is used, the manufacturing cost can be reduced.
[0034]
{Circle around (2)} The tooth profile can be formed to be uneven on both the front and back sides, the tooth bottom is not thinned, and the plate thickness of the tooth can be set freely.
[0035]
(3) The mold can provide sufficient strength on both sides.
[0036]
(4) In addition to simultaneous molding of the entire teeth, various molding methods such as rolling and swing forging can be selected.
[0037]
(5) After making into a tube shape, it is possible to straighten the shaft by correcting the bending of the shaft.
[0038]
(6) Welding can be arbitrarily set at the butting portion of the tube, and only necessary portions can be welded.
[0039]
(7) Since the front and back molds are used, the rack tooth shape can be freely selected, and the mold shape corresponding to the desired tooth shape can be freely selected, so that it is possible to cope with a tooth shape such as VGR.
[Brief description of the drawings]
1A and 1B are diagrams illustrating a material according to an embodiment of the present invention, in which FIG. 1A is a front view and FIG. 1B is a cross-sectional view taken along line II of FIG.
FIGS. 2A and 2B are diagrams showing a state in which the material is molded in the first step in the embodiment of the invention, wherein FIG. 2A is a front sectional view, and FIG. 2B is a sectional view taken along II-II in FIG. (C) shows the III-III cross section of (a).
FIGS. 3A and 3B are diagrams showing a state in which rack teeth are formed in the second step in the embodiment of the present invention, where FIG. 3A is a front sectional view and FIG. 3B is a sectional view taken along line IV-IV in FIG. Indicates.
FIGS. 4A and 4B are views showing a state in which the material is formed into a tube shape in the third step in the embodiment of the present invention, where FIG. 4A is a front cross-sectional view, and FIG. 4B is a VV of FIG. Sectional drawing, (c) shows a VI-VI sectional view of (a).
FIG. 5 shows an enlarged view of the tooth portion of FIG.
6 shows an enlarged view of FIG. 3 (b).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Board | plate material 1a Narrow part 1b The part 1c which does not form a rack tooth 1c The part 1d corresponding to a rack tooth Rack tooth 10 Rack shaft

Claims (4)

Forming the rack teeth by plastic working so that the teeth are aligned in the longitudinal direction on the flat part of the substantially strip-shaped plate in the short direction , and then bending the remaining plate in the short direction to form a tube shape A method of manufacturing a hollow rack shaft characterized by the above. After bending into a U-shape having a semicircular cross section along the longitudinal center of a substantially strip-shaped plate material, rack teeth are formed in the vicinity of the central top of the semicircular cross section so that the teeth are aligned in the longitudinal direction. Then, the hollow rack shaft manufacturing method is characterized in that the remaining plate portion in the short direction is bent to form a tube shape. 3. The method of manufacturing a hollow rack shaft according to claim 1, wherein the rack teeth are formed by being sandwiched between upper and lower molds. A tubular hollow rack shaft having a flat portion manufactured by the method according to any one of claims 1 to 3, wherein the rack tooth portion is unevenly formed along the longitudinal direction over the outer surface of the flat portion. A hollow rack shaft characterized by that.

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