JP3826655B2 - Hollow rack shaft, rack tooth molding method thereof and mold therefor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hollow rack shaft used for a steering apparatus for automobiles, a rack tooth forming method for a hollow rack shaft, and a mold for the method.
[0002]
[Prior art]
A rack and pinion system is frequently used for a steering apparatus of an automobile. 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 the rack meshing with the pinion, and converted into a lateral movement (the length direction of the rack). Since the rack is coupled to the steering rod, the direction of the front wheels is changed by the lateral movement of the rack. Since such a steering mechanism is well known, further explanation is omitted.
[0003]
Conventionally, the above-mentioned rack has been obtained by cutting a bar-shaped material, but recently, in order to eliminate cutting as much as possible in the manufacture of the rack, plastic processing technology has been incorporated as much as possible. The rack is becoming hollow. JP-A-9-246379, JP-B-4-28582, and JP-A-11-180318 disclose examples of rack manufacturing methods incorporating such plastic working techniques.
[0004]
In the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 9-246379, a first mold split mold is inserted into a tube material, primary molding is performed by a press mold, and then teeth corresponding to rack teeth are formed on a part of the inner surface. A primary molding material is inserted into a secondary molding split mold, a semicircular mandrel is press-fitted from one end, and rack teeth are molded.
[0005]
In addition, a manufacturing method disclosed in Japanese Patent Publication No. 4-28582 is a mold having teeth corresponding to rack teeth in a state in which a mandrel is inserted into a tube material and the periphery of the tube is surrounded by a fixed mold. Is pressed into the outer shape of the tube to form rack teeth.
[0006]
In addition, the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 11-180318 is made by Okubo, one of the inventors of the present invention, and the rack teeth are formed in a substantially central portion of a substantially strip-shaped plate material. Formed by processing (press forming) or bent into a U-shape or U-shape having a semicircular cross section along the longitudinal center of a substantially strip-shaped plate material, and then plastic working near the center of the semicircular portion The rack teeth are formed by the above process, and the remaining plate is bent into a tube shape to form a rack shaft.
[0007]
In the first two publications, tube material is used as a raw material, but this technology uses not plate material but plate material, which is not only advantageous in terms of material cost, transportation cost, and storage cost. In order to secure the thickness of the bottom of the tooth, there is an advantage that a sufficient light weight effect can be obtained without needing to add other parts to other portions.
[0008]
FIG. 4 is an external view of the completed hollow rack shaft according to the prior art and the present invention.
[0009]
FIGS. 5A and 5B are diagrams showing a conventional rack shaft that has been formed by the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 11-180318, and FIG. 5A is a cross-sectional view including the shaft, and FIG. It is II sectional drawing (sectional drawing cut | disconnected in the tooth bottom of a rack) of a).
[0010]
FIG. 6 is a cross-sectional view of a workpiece and its mold in a state in the middle of being formed on the hollow rack shaft and immediately before the tooth profile of the rack is formed in the prior art. Here, (a) is a front sectional view, and (b) is a II-II sectional view of (a) (a sectional view cut at the tooth crest portion of the rack).
[0011]
FIG. 7 is a cross-sectional view of the workpiece immediately after the tooth profile of the rack is formed and its mold in the prior art. Here, (a) is a front cross-sectional view, and (b) is a III-III cross-sectional view of (a) (a cross-sectional view cut at the tooth crest portion of the rack).
[0012]
FIG. 8 is an explanatory diagram for explaining how the material in various parts of the U-shaped plate material, which is a workpiece, flows according to the tooth forming shape.
[0013]
The rack teeth of the work 3 are formed in a prior process between an upper mold 1 having a shape complementary to the rack tooth profile on the lower side and a lower mold 2 having the shape of the back surface of the rack tooth on the upper side. The workpiece formed in a U-shape is placed (state shown in FIG. 6), and the upper mold 1 is lowered to form the workpiece. At this time, on the side surfaces of the upper die 1 and the lower die 2, a pressing die for holding the workpiece 3 from the side surface is provided.
[0014]
As shown in FIG. 5 (b), the dimension B of the location corresponding to the tooth bottom part on the inside of the rack tooth (the hollow part side of the back surface of the rack tooth) is the inner diameter dimension R of the hollow part, the tooth bottom position x, and Geometrically determined by the thickness t of the tooth base. Conventionally, the width of the portion for forming the tooth crest portion of the lower mold 2 has been designed to be the same as this dimension B.
[0015]
For this reason, the material of the part of the workpiece shown by the box D in FIG. 6 flows to the other part of the rack tooth (in the central part of the tooth width, the material of the plate flows to the tooth profile surface and the crest surface. On the other hand, the material of the enclosure D part flows in addition to the tooth profile and the crest part, and also on the end of the tooth trace.) As a result of thinning, as shown by the enclosure E in FIG. There was a phenomenon in which both ends of the top of the tooth sag (if it is expressed differently, it shoulders). This means that the effective tooth width C of the rack (FIG. 7, the tooth width at the pitch surface of the rack) is actually narrower than intended.
[0016]
FIG. 8 is a diagram for explaining this from a different viewpoint. In FIG. 8, after the tooth profile is formed on the top, the bottom shows a U-shaped state before the tooth profile is formed. In this figure, when the meat (material) that was in place i, b, c, d, e, h, is formed into a tooth profile, it is stretched and moved to the place. It can be seen that each original meat must share a larger area after molding. For this reason, the substantial thickness reduction occurs, and the mold surface of the upper mold 1 is not filled with the meat (material). Therefore, the molding is completed without completely transferring the tooth profile of the upper mold 1. . In addition to this, the tooth thickness at the end of the tooth is also reduced for the same reason. As a result, the sagging phenomenon and the shouldering phenomenon occur as described above, and the effective tooth width C decreases.
[0017]
And although it is designed on the assumption that the load is received with a sufficient tooth width as shown by the solid line in FIG. 8, the rack teeth are actually narrow as shown by the dotted line in FIG. Since only the effective tooth width C is provided, it means that the stress increases accordingly. For this reason, there has been a problem that rack teeth are damaged or the life of the rack shaft is shortened during use, for example, during steering.
[0018]
Increasing the pressure applied to the upper and lower molds 1 and 2 and causing the meat near the center of the tooth width to flow to the end of the tooth will put an excessive load on the teeth of the mold, The means cannot be adopted, and even if this is done, there is a problem that the mold life is shortened.
[0019]
In addition, the fact that such sagging or shouldering is recognized in the product has no practical problem in terms of the accuracy of the tooth surface of this product and the gear transmission mechanism, and the above-mentioned damage and life problems occur. There was also a problem that even if it was not possible, the user was questioned about the accuracy of the product.
[0020]
[Problems to be solved by the invention]
The present invention relates to a method for forming a rack tooth of a hollow rack shaft that prevents damage to the hollow rack shaft as described above or shortens the life of the rack shaft, increases durability, and raises no doubt about accuracy. It is another object of the present invention to provide a mold for that purpose.
[0021]
[Means for Solving the Problems]
The above-described problems are solved by the invention having the following solution means. That is,
The hollow rack shaft of the first invention is a plastically processed hollow rack shaft used for an automobile steering device or the like, wherein the width of the tooth crest portion hollow inner surface side of the rack tooth in the cross section perpendicular to the axis of the hollow rack shaft is By forming the protrusions on the back surface of the rack teeth and forming the two protrusions higher than the vicinity of the center of the tooth width by the molds formed at both ends, the inner diameter of the hollow rack shaft, the rack tooth bottom position, and It is made wider than the width geometrically determined by each dimension of the rack tooth bottom plate thickness.
[0022]
[0023]
According to a second aspect of the present invention, there is provided a rack tooth forming method for press forming a rack tooth of a hollow rack shaft used for an automobile steering device or the like from a plate material. width in the width direction, the width by Rukoto two protrusions higher than near face width center are formed at both end portions, than the width of the portion corresponding to the tooth bottom portion of the inner shape of the workpiece co shaping It is press-formed by a wide mold.
[0024]
According to a third aspect of the present invention, there is provided a mold for forming a rack tooth for press forming a rack tooth of a hollow rack shaft used for an automobile steering apparatus or the like from a plate material. In the tooth crest tooth width direction, the central portion is concave, and both end portions are provided with protrusions, so that both end portions of the rack teeth are formed stronger than the central portion.
[0025]
With these configurations, since the rack teeth have a narrower effective tooth width than intended by the sagging as in the prior art, the stress on the rack teeth is increased by that amount, and the rack teeth are damaged. The durability problem that the life of the rack shaft is shortened can be alleviated or eliminated.
[0026]
Also, in order to allow the meat near the center of the tooth width to flow to the tooth end, the protrusions on both ends without taking excessive measures to shorten the mold life on the tooth of the mold. This effectively prevents the occurrence of sagging.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a cross-sectional view of a workpiece and its mold in the middle of being formed on a hollow rack shaft and immediately before the rack tooth profile is formed in the manufacturing method of the present invention. Here, (a) is a front sectional view, and (b) is a IV-IV sectional view of (a) (a sectional view cut at the tooth crest portion of the rack).
[0028]
FIG. 2 is a cross-sectional view of a workpiece immediately after a rack tooth profile is formed and its mold in the manufacturing method of the present invention. Here, (a) is a front cross-sectional view, and (b) is a VV cross-sectional view of (a) (a cross-sectional view cut at the tooth crest portion of the rack).
[0029]
3A and 3B are views showing a rack shaft according to the present invention that has been formed by the manufacturing method of the present invention and the tube forming process in the subsequent step, wherein FIG. 3A is a sectional view including the shaft, and FIG. It is VI-VI sectional drawing (sectional drawing cut | disconnected in the tooth top part of the rack).
[0030]
The rack teeth of the work 3 are formed in a prior process between an upper mold 1 having a shape complementary to the rack tooth profile on the lower side and a lower mold 2 having the shape of the back surface of the rack tooth on the upper side. A workpiece formed in a U-shape is placed (state shown in FIG. 1), and the upper mold 1 is lowered to form the workpiece. At this time, on the side surfaces of the upper die 1 and the lower die 2, a pressing die for holding the workpiece 3 from the side surface is provided. These points are not different from the conventional ones.
[0031]
On the upper surface of the lower mold 2, as shown in FIG. 1 (b) and FIG. 2 (b), two protrusions 21 that are higher than the vicinity of the center of the tooth width are formed. . Then, the length A ′ of the two protrusions 21 is geometrically determined by the inner diameter dimension R, the root position x, and the root plate thickness t of the hollow portion, as shown in FIG. 5B. The size is determined to be larger than the size B of the portion corresponding to the tooth bottom portion on the inner side of the rack tooth (the hollow portion side of the back surface of the rack tooth).
[0032]
The point that the lower mold 2 is provided with the protruding portion 21 as described above is a characteristic point of the present invention that is basically different from the conventional lower mold 2.
[0033]
In the present invention, the protrusion 21 pushes up the meat (material) of the workpiece from below, so that the meat (material) of the workpiece 3 corresponding to this protrudes actively toward the other portion, and the upper mold 1 In this way, the tooth profile surface is filled, and this tooth profile shape is imparted to the workpiece. In other words, since the both end portions of the rack teeth are formed stronger than the center portion of the tooth width by the protruding portion 21 of the lower mold 2 as described above, there is no sagging and no shouldering as in the conventional example, and the rack The rack teeth can be formed so that the effective tooth width C is as originally designed.
[0034]
In this way, the workpiece 3 in which the tooth profile is formed up to the end of the tooth width is a U-shaped foot portion or U-shaped foot portion (FIG. Part) is formed so as to be abutted with each other, the butted portion 23 is joined by laser welding or the like, and further subjected to finishing to complete the product hollow rack shaft as shown in FIG.
[0035]
FIG. 3B shows a cross section of the rack portion of the hollow rack shaft, which is a product, and a recess 22 is formed inside the hollow portion, that is, on the back side of the top of the rack tooth by the protruding portion 21 of the lower mold 1. You can see that it is made.
[0036]
【The invention's effect】
As described above, since the rack tooth has only a narrower effective tooth width than intended by the sagging as seen in the prior art, the stress applied to the rack tooth increases accordingly, and the rack tooth In the present invention, there is an effect that the problem of breakage or the durability problem that the life of the rack shaft is shortened can be reduced or eliminated.
[0037]
Also, in order to allow the meat near the center of the tooth width to flow to the tooth end, the protrusions on both ends without taking excessive measures to shorten the mold life on the tooth of the mold. As a result, the occurrence of sagging is effectively prevented.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a workpiece and its mold in the middle of being formed on a hollow rack shaft and immediately before a rack tooth profile is formed in the manufacturing method of the present invention.
FIG. 2 is a cross-sectional view of a workpiece immediately after a rack tooth profile is formed and its mold in the manufacturing method of the present invention.
FIGS. 3A and 3B are diagrams showing a rack shaft according to the present invention that has been formed by the manufacturing method of the present invention and a tube forming process in a later step, in which FIG. It is VI-VI sectional drawing (sectional drawing cut | disconnected in the tooth top part of the rack).
FIG. 4 is an external view of a completed hollow rack shaft according to the prior art and the present invention.
FIGS. 5A and 5B are diagrams showing a conventional rack shaft that has been processed, in which FIG. 5A is a sectional view including the shaft, and FIG. 5B is a sectional view taken along the line II in FIG. Sectional view).
FIG. 6 is a cross-sectional view of a workpiece and its mold in a state of being formed on a hollow rack shaft and immediately before a rack tooth profile is formed in the prior art. Here, (a) is a front cross-sectional view, and (b) is a II-II cross-sectional view of (a) (a cross-sectional view cut at the tooth crest portion of the rack).
FIG. 7 is a cross-sectional view of a work immediately after a rack tooth profile is formed and its mold in the prior art. Here, (a) is a front cross-sectional view, and (b) is a III-III cross-sectional view of (a) (a cross-sectional view cut at the tooth crest portion of the rack).
FIG. 8 is an explanatory diagram for explaining how the material in various parts of the U-shaped plate material, which is a workpiece, flows according to the tooth forming shape.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Upper mold | type 2 Lower mold | type 3 Work piece 21 Protrusion part 22 Concave part 23 Butt part

Claims (3)

In plastically processed hollow rack shafts used for automobile steering devices, etc.
Two protrusions are formed at both ends of the hollow rack shaft so that the width on the hollow inner surface side of the tooth top of the rack tooth has the shape of the back surface of the rack tooth and is higher than the vicinity of the center of the tooth width. A hollow rack characterized in that it is made wider than the geometrically determined width by the dimensions of the inner diameter of the hollow rack shaft, the position of the rack tooth bottom, and the thickness of the rack tooth base plate axis. In a rack tooth molding method for press forming a rack tooth of a hollow rack shaft used for a steering apparatus for an automobile from a plate material,
Tooth top width of the tooth width direction of the rack teeth of the mold for forming the back surface of the rack teeth by Rukoto two protrusions higher than near face width center are formed at both end portions, U-shape to be molded rack teeth forming method of a hollow rack shaft, characterized in that the press forming by the mold, which is a width wider than the width of the portion corresponding to the tooth bottom portion of the inner shaped for work. A mold for rack tooth molding for press forming a rack tooth of a hollow rack shaft used for a steering apparatus for an automobile from a plate material,
In the crest tooth width direction of the rack tooth of the mold for molding the back surface of the rack tooth, the central part is concave and both ends are provided with protrusions, so that both ends of the rack tooth A mold for forming a rack tooth of a hollow rack shaft, characterized in that is formed stronger than the central portion.

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