JP2002048220A - Hollow rack shaft and its assembling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hollow rack shaft capable of reducing the weight of a tube part at a hollow shaft to a required, absolute minimum, without requiring special additional processes and also to provide the hollow rack shaft of low price and fall performance level due to no need for addition of processes. SOLUTION: The hollow rack shaft 10, which is equipped with a rack tooth 1d formed of a plate material 1, has a rack tooth, a rack tooth formed on the opposite side of the rack tooth made of a semi-cylindrical part and the tube part cylindrically formed at both sides of the rack tooth in the direction of the rack shaft, and at least one-side diameter Dt of both tube parts is smaller than the diameter of a rack tooth Dr.

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]

FIG. 5 shows an example of such a conventional hollow rack shaft (final processing state).
Is a front view, and (b) and (c) are B of the rack tooth portion of (a).
It is sectional drawing in CC of -B and a tube part. A pinion connected to the steering shaft is meshed with the rack teeth of the hollow rack shaft, and a steering force is transmitted from the pinion. Therefore, a bending stress acts on the root of the rack teeth, and a contact portion of the tooth surface of the rack teeth is formed. High contact pressure acts. 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. .

However, as can be seen in the above-mentioned literature and FIG. 5, conventionally, the rack tooth portion and the tube portion of the hollow rack shaft have substantially the same diameter, that is, as shown in FIG. The diameter Dr of the rack tooth portion (b) and the diameter Dt of the tube portion (c) were designed to be equal. However, as described above, it is understood that the function as a product is not impaired even if the diameter of the tube portion is set smaller than that of the rack tooth portion on which the rack teeth are formed.

[0006] Now, automobiles are required to be reduced in weight in gram units from the viewpoint of improving fuel efficiency, and this is being competed, but as described above, the diameter of the tube portion must be larger than necessary. This has led to an increase in the weight of the hollow rack shaft and, consequently, the vehicle weight, which has hindered the reduction of the vehicle weight.

In order to reduce the diameter of the tube portion, it is possible to perform drawing in a later step, but the weight is not reduced. It is also conceivable to cut the outer diameter of the tube portion to reduce the diameter, but the cutting process itself becomes difficult because there is only a small shaving allowance. Further, adding an extra post-process increases the cost and is not a good idea.

An object of the present invention is to provide a hollow rack shaft capable of reducing the weight of a tube portion in a hollow rack shaft to a necessary minimum without requiring any special additional steps, and a method of manufacturing the same. Another object of the present invention is to provide an inexpensive hollow rack shaft having sufficient performance and a method for manufacturing the same, since no additional process is required.

[0009]

The above object is achieved by the following means. That is, a first means for solving the present invention is a hollow rack shaft having rack teeth formed from a plate-like material, and the hollow rack shaft has:
It has a rack tooth portion composed of a rack tooth and a semi-cylindrical portion formed on the opposite side of the rack tooth, and a tube portion formed in a cylindrical shape on both sides of the rack tooth portion in the rack axial direction. At least one of the tubes has a diameter different from the diameter of the rack teeth.

According to a second aspect of the present invention, in the hollow rack shaft of the first aspect, at least one of the diameters of the tube portion is smaller than the diameter of the rack tooth portion.

A third aspect of the present invention is a manufacturing method for forming a hollow rack shaft having rack teeth from a plate-like material, wherein the hollow rack shaft includes a rack tooth and the rack tooth. A hollow rack shaft having a rack tooth portion formed of a semi-cylindrical portion formed on the opposite side of the rack member and tube portions formed in a cylindrical shape on both sides of the rack tooth portion in the rack axis direction, A portion having a plate width for forming a rack tooth portion, and a plate width having a plate width for forming the tube portion and a width smaller than the plate width for forming the rack tooth portion. The rack tooth portion and the tube portion are formed by plastically deforming a plate-shaped material using a material having the above-mentioned portions.

According to the above-mentioned solution, the diameter of the tube portion can be made smaller (smaller) than that of the rack tooth portion without increasing the number of special steps, and the weight of the hollow rack shaft can be reduced. In addition, the wall thickness of the tube part can be maintained equal to the wall thickness of the rack tooth part, and the required strength can be maintained. Overall, it has a balanced and proper shape without waste. Thus, a hollow rack shaft can be obtained. Further, it is possible to easily manufacture an inexpensive and high-performance hollow rack shaft, particularly a hollow rack shaft for a steering device.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to FIGS. 1A and 1B show a raw material used in an embodiment of the present invention, wherein FIG. 1A is a plan view of the raw material, and FIG. 1B is a side view of FIG.

As shown in FIG. 1A, the hollow rack shaft of the present invention is manufactured using a substantially strip-shaped plate material (plate material 1). As the substantially strip-shaped plate-shaped material 1, a material cut out from a coil-shaped material or the like by press punching, laser cutting, or the like is used.

The material of the substantially strip-shaped plate-like material 1 is preferably SCr or SCM which can be carburized and burned, or carbon steel suitable for induction hardening may be used. In addition, the plate-shaped material 1 has a narrow plate width 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 butt portion A is adjusted to the rack tooth width of the completed rack shaft.
(See FIG. 4, (c)), the width of the plate is narrowed in order to keep the balance in consideration of the volume so that they abut exactly.

The width of the plate-shaped material 1 is narrow at an arrow Y in FIG. 1 (a). This portion 1g is a range in which a small-diameter tube is formed. Since the tube becomes a small-diameter tube after completion, the plate width is smaller than that of a portion 1h which is a semi-cylindrical portion near the rack teeth.

As described above, in the present embodiment, the plate-shaped material 1 has a portion having a plate width for forming a rack tooth portion, and a plate having a plate width for forming a tube portion and a rack tooth portion. A material having a portion having a smaller board width than the board width to be formed is used.

FIGS. 2A and 2B show a state in which the plate material 1 is formed in the first step. FIG. 2A is a front sectional view, FIG. 2B is a sectional view taken along line BB of FIG. 6A is a cross-sectional view taken along the line CC in FIG. 5A, and FIG. 5D is a cross-sectional view taken along the line DD in FIG.

In the first step, the plate material 1 shown in FIG.
Is bent by a press or the like.
As can be seen from FIG. 2, portions where the rack teeth are not formed later (the large diameter portion 1b and the small diameter portion 1f have a U-shaped cross section as shown in FIGS. 2 (b) and 2 (d), and the upper half is semicircular. While the portion 1c corresponding to the rack teeth is shown in FIG.
As shown in (c), it has a U-shaped cross-sectional shape and has a flat upper surface. This step is described in JP-A-11-18.
This is substantially the same as the content disclosed in Japanese Patent Publication No. 0318, but is different in that the small diameter portion 1f is continuously provided on the right side of the plate-shaped material 1 (the right side in FIG. 2A). The connection between the large-diameter portion 1b and the small-diameter portion 1f is provided with a step via the tapered portion 1k, and consideration is given to facilitate processing during the bending process in the first step.

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

In the case of this step, too, refer to JP-A-11-180318.
As described in the publication, 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. Then, the work processed in the first step (the plate material 1 being processed) is sandwiched between the upper and lower molds, the upper and lower molds are brought close to each other, and the molding is performed, and the unevenness of the mold is transferred to the work. It is performed by

As shown in FIG. 3 (a), the lower surface of the plate-shaped material 1 is formed into a concave-convex shape so that the cross-sectional shape of the rack teeth follows the shape of the tooth surface on the front side.

FIGS. 4A and 4B are views showing a state after the third step, wherein FIG. 4A is a front sectional view, and FIG.
FIG. 3C is a cross-sectional view of (B), (c) is a cross-sectional view of C-C of (a), and (d) is a cross-sectional view of DD of (a).

In the third step, the openings of the U-shaped and U-shaped cross sections, that is, the legs 1e are bent to form cylindrical and semi-cylindrical shapes, respectively. This step is described in JP-A-11-1803.
This is the same as the content disclosed in Japanese Patent Application Publication No. 18-180, except that the small diameter portion 1f is continuously provided on the right side of the plate-shaped material 1 (the right side in FIG. 4A). The connection between the large-diameter portion 1b and the small-diameter portion 1f is provided with a step via a tapered portion 1k so as to facilitate processing at the time of bending in the third step.

By this bending, a hollow rack shaft having a tube portion having a smaller diameter (smaller diameter) than the rack tooth portion is obtained as shown in FIG. It is desirable to adjust the plate width of the material in advance so that the butted portions A and B bent into a cylindrical shape and a semi-cylindrical shape can be exactly butted. Also, the butted portions A and B can be joined together by welding or the like as necessary, thereby increasing the strength.

As described above, the hollow rack shaft 10 is provided with the rack teeth formed from the plate-shaped material 1, and has the rack teeth and the rack teeth formed of the semi-cylindrical portions formed on the opposite sides of the rack teeth. A cylindrical tube portion is formed on both sides of the rack tooth portion in the rack axial direction, and at least one of the tube portions on both sides has a diameter different from the diameter of the rack tooth portion, and more preferably a small diameter. Have been. FIG. 4 shows the diameter Dr of the large diameter portion 1b, that is, the rack tooth portion (and the equivalent portion), and the diameter Dt of the tube portion.

The hollow rack shaft 10 thus obtained is
After the butted portions A and B are joined by welding or the like as described above, cutting other than the rack portion is performed as necessary, and carburizing and quenching of the rack portion and other portions in the post-processing, or After imparting the necessary strength by induction baking, the shaft (both ends of the rack shaft) is finished by grinding to produce a product. It should be noted that this does not exclude the necessity of performing a straightening correction as needed in a halfway process in order to remove a bending generated during the processing.

In the above embodiment, the rack tooth portion and the tube portion have a large diameter of the rack tooth portion and a small diameter of the tube portion. However, the present invention is not limited to this. For example, both sides of the rack tooth portion may have a small diameter, or depending on the application, may be set so that a large-diameter tube comes to an extension of the small-diameter tube. On the contrary, it is also possible to apply the present invention to increase the diameter of the small-diameter portion by design.

[0029]

As described above, the hollow rack shaft and the method of manufacturing the same according to the present invention can make the tube portion smaller (smaller) than the rack tooth portion without any additional process. There is an effect that the weight of the rack shaft can be reduced.

Further, the thickness of the tube portion can be maintained equal to the thickness of the rack tooth portion, and the necessary strength can be maintained. There is an effect that a hollow rack shaft having a shape can be obtained. Furthermore, there is an effect that an inexpensive and high-performance hollow rack shaft, in particular, a hollow rack shaft for a steering device can be easily manufactured.

[Brief description of the drawings]

FIG. 1 shows a material used in an embodiment of the present invention, wherein (a) is a plan view of the material and (b) is a side view of (a).

FIGS. 2A and 2B show a state in which a plate material 1 is formed in a first step, wherein FIG. 2A is a front sectional view, and FIG.
FIG. 3C is a cross-sectional view taken along line CC of FIG. 3A, and FIG. 4D is a cross-sectional view taken along line DD of FIG.

3A and 3B show a state where rack teeth are formed through a second step, and FIG. 3A is a front sectional view after rack teeth are formed;
(B) is BB sectional drawing of (a).

FIGS. 4A and 4B are views showing states after a third step, wherein FIG. 4A is a front sectional view, FIG. 4B is a sectional view taken along line BB of FIG.
(C) is a cross-sectional view taken along the line CC of (a), and (d) is a line D- of (a).
It is D sectional drawing.

5A and 5B show examples of a conventional hollow rack shaft (final processing state), wherein FIG. 5A is a front view, and FIGS. 5B and 5C are BB of a rack tooth portion and C of a tube portion of FIG. It is sectional drawing in -C.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plate-shaped material 10 Hollow rack shaft 1a, 1g, 1h, 1c part 1b Large diameter part 1d Rack tooth 1e Leg part 1f Small diameter part 1k Taper part Dr, Dt diameter

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasushi Watanabe 1-8-1, Sojacho, Maebashi-shi, Gunma F-term in Japan Seiko Co., Ltd. (reference) 3J030 AC02 AC03 BA08 BB16 BC02 BC05

Claims (3)

[Claims] 1. A hollow rack shaft provided with rack teeth formed from a plate-like material, wherein the hollow rack shaft is formed from the rack teeth and a semi-cylindrical portion formed on the opposite side of the rack teeth. And a tube portion formed in a cylindrical shape on both sides of the rack tooth portion in the rack axis direction. At least one of the tube portions on both sides has a diameter different from the diameter of the rack tooth portion. A hollow rack shaft having: 2. The hollow rack shaft according to claim 1, wherein a diameter of at least one of the tube portions is smaller than a diameter of the rack tooth portion. 3. A manufacturing method for forming a hollow rack shaft provided with rack teeth from a plate-like material, wherein the hollow rack shaft has the rack teeth and a half cylinder formed on the opposite side of the rack teeth. A hollow rack shaft having a rack tooth portion formed of a cylindrical portion and cylindrical tube portions formed on both sides in the rack axis direction of the rack tooth portion, wherein the plate tooth material is formed with the rack tooth portion. And a portion having a plate width for forming the tube portion, and a portion having a plate width smaller than the plate width for forming the rack teeth portion. A method of manufacturing a hollow rack shaft, comprising forming the rack teeth and the tube by plastically deforming the plate-shaped material.