JP2003340542A - Thread rolling material for worm - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thread rolling material for a worm which enables a worm having a high-accuracy screw part to be manufactured only by thread rolling and can reduce a production cost of the worm. <P>SOLUTION: This thread rolling material 20 for a worm is used for forming a screw part of a two-line screw by thread rolling using a die 31. The thread rolling material 20 has a screw forming part T at which a screw part is formed. A notch part 26 for equalizing push-in resistance of the material 20 to the die 31 in forming threads in the circumferential direction of the screw forming part T is formed in a taper part 22, which is the end of the screw forming part T including a large-diameter part 21 and a pair of taper parts 22. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a worm having a threaded portion formed by rolling, and more particularly, to a rolling material used to form the threaded portion of the worm only by rolling.

[0002]

2. Description of the Related Art Conventionally, as a technique for forming a thread portion of a worm by rolling, there is one disclosed in Japanese Patent Laid-Open No. 112230/1995. In this technique, the shaft-shaped material used for manufacturing the worm shaft has a shaft portion and a cylindrical base portion on which a worm portion (corresponding to a screw portion) is formed. After the material is held in the guide cylinder by its shaft portion, a pair of rolling dies are pressed against the base portion protruding from the guide cylinder while rotating,
A worm portion (corresponding to a screw portion) is formed on the base portion.

[0003]

By the way, the screw part of the worm is composed of a complete screw thread forming a complete screw part and an incomplete screw thread forming an incomplete screw part.

In this specification, the complete thread has the same shape as the thread which meshes with the worm wheel and the thread (that is, the tooth profile) of the thread which constitutes the thread. It is composed of a thread having a thread portion, and an incomplete thread is a thread thread other than the complete thread among the thread threads that make up the thread portion, and the thread from the end of the thread of the thread portion to the end of the complete thread. It consists of all the threads.

Here, the "cross section" means a cross section in a plane including the central axis of the worm, and the "mountain portion" means a screw thread in the cross section. Also, "cross-sectional area of screw thread"
Means that in the cross section of the screw part, as shown in FIG.
A straight line n that connects the roots m1 of the complete thread m and connects the roots m1 with one crest r1 and r2 (where crest r1 is the crest of the complete thread and r2 is an incomplete thread). Areas s1 and s2 enclosed by and. Furthermore, the total cross-sectional area is the sum of the cross-sectional areas of the screw threads in one cross section of the threaded portion.

Therefore, the shape of the ridge and the cross-sectional area of the screw thread differ between the complete screw thread and the incomplete screw thread. For example,
The diameter of the addendum circle of the incomplete screw thread is equal to or smaller than the diameter of the addendum circle of the complete screw thread, and the sectional area of the incomplete screw thread is smaller than the sectional area of the complete screw portion. The cross-sectional area of the incomplete thread differs depending on the circumferential position of the worm, while the cross-sectional area of the complete screw portion remains the same regardless of the circumferential position.

This will be described with reference to FIGS. 8A and 8B for an example of a worm having a double thread screw thread. The circumferential position w1 on the thread b of the worm a
The number of thread crests in the cross section at 4 is 4
The number of thread crests in the cross section at the circumferential position w2 different from w1 is five. Then, the mountain portion at the circumferential position w1 (hereinafter,
It is called "4 mountain parts". ) Is composed of four ridges of the complete thread, and the ridge at the circumferential position w2 (hereinafter referred to as “5 ridges”) is composed of five ridges of the complete thread.

When the threaded portion b of the worm a is formed by rolling, as shown in FIG. 9 (A1),
At the circumferential position w1, the total cross-sectional area of the screw thread is smaller than at the circumferential position w2. Therefore, the amount of meat of the material f pushed by the die e during rolling at the circumferential position w1 is The die e during rolling at the circumferential position w2 shown in FIG. 9 (B1)
Since the amount of the meat of the material f pushed in by the die becomes larger, and the amount of swelling of the formed screw thread increases, the escape area of the meat of the material f disappears. The resistance that e receives from the material f increases.

For this reason, the predesigned tooth profile thread c
When the rolling load when molding the threaded portion b consisting of is set to the value when molding the five crests, the tooth profile of the five crests is the design tooth profile g (see FIGS. 9 (A2) and (B2)). ) On the other hand, when forming the four crests, the pushing resistance of the material f becomes larger than that at the five crests, so that the frame supporting the die e of the rolling machine has five crests. As shown in FIG. 9 (A2), the amount of rolling is insufficient because the material is bent in a direction away from the material f as compared with the case of molding the portion, and the thread having a tooth profile h having a tooth thickness larger than the designed tooth profile g as shown in FIG. 9 (A2). c is molded, and a large error occurs in the tooth trace.

On the contrary, when the rolling load is set to a value for forming the four crests, the tooth profile of the four crests is molded to the design tooth profile g, while the material of the five crests is formed when the five crests are molded. f
The indentation resistance of is smaller than that in the case of the four crests, and the bending of the frame is smaller than that in the case of molding the four crests. Therefore, the amount of rolling is excessive, and as shown in FIG. 9 (B2). As described above, the screw thread c having the tooth profile k having a tooth thickness smaller than the designed tooth profile g is formed, and in this case also, a large error occurs in the tooth trace.

In the above, the circumferential position including only the complete mountain portion
I explained the difference in the pushing resistance between w1 and w2.
Although there is a difference in the difference in the indentation resistance, the same phenomenon is caused by the circumferential position including the complete screw thread and the incomplete screw thread (for example, position w3 in FIG. 8B) and the circumferential position including only the complete screw thread. It also occurs between the directional position (for example, the position w2 in the figure) and between the circumferential positions including the complete thread and the incomplete thread (for example, the position w3 and the position w4 in the figure). And, as is clear from the above, the difference in the pushing resistance is the largest in the circumferential position including only the complete screw thread, and the screw thread in the circumferential position in which a different number of thread portions exist It is during molding.

[0012] Therefore, conventionally, it is difficult to obtain a worm having a highly accurate threaded portion with a small error of tooth traces only by rolling, so that the threaded portion is finished. However, it is necessary to further grind the threaded portion formed by rolling, which raises a problem that the manufacturing cost of the worm increases.

The present invention has been made in view of the above circumstances, and it is possible to manufacture a worm having a highly accurate screw portion only by rolling, and the worm manufacturing cost can be reduced. The purpose is to provide a material for rolling.

[0014]

[Means for Solving the Problems and Effects of the Invention] The invention according to claim 1 is a rolling method used for forming a threaded portion of a worm, which is composed of a multiple thread, by rolling using a die. A material for use in manufacturing, wherein the screw portion has a screw forming portion, and an adjusting portion for equalizing the pushing resistance of the material with respect to the die in the circumferential direction of the screw forming portion is It is a material for rolling a worm formed on an end portion of the screw forming portion in the central axis direction.

As described above, in the rolling material, the indentation resistance of the material with respect to the die is equalized at different circumferential positions in the screw forming portion by the adjusting portion formed at the end of the screw forming portion. When forming a screw thread at any circumferential position of the screw part, it is rolled with substantially the same amount of rolling, and the tooth profile of the screw thread is formed in the entire screw part to the extent that finishing processing is unnecessary. .

As a result, according to the invention of claim 1,
The following effects are exhibited. That is, in a worm having a threaded portion composed of multiple threads, a notch for equalizing the pushing resistance of the thread forming portion of the rolling material to the die in the circumferential direction is provided with an end of the threaded portion in the central axis direction. By being formed on the threaded portion, the pushing resistance is equalized at different circumferential positions in the thread forming portion, and the threads at any circumferential position of the threaded portion are rolled with substantially the same rolling amount. The tooth profile of the mountain, and thus the threaded portion, is molded with high accuracy and with a small amount of tooth trace error so that finishing processing is unnecessary. Therefore, unlike the prior art, the grinding process for finishing the threaded portion is not necessary, and the manufacturing cost of the worm formed by rolling can be reduced.

According to a second aspect of the present invention, in the worm rolling material according to the first aspect, the worm rolling material includes a notch portion formed in the end portion in the circumferential direction.

As described above, since the adjusting portion is formed by the notch portion, the amount of meat is reduced at the end portion of the screw forming portion, so that the pushing resistance is reduced and the rolling load can be reduced. The bending of the supporting member of the die caused by the reaction force due to the pushing resistance from the material is also reduced.

As a result, according to the invention of claim 2,
In addition to the effects of the invention according to claim 1, the following effects are exhibited. That is, since the adjusting portion is formed by the notch portion, the rolling load can be reduced, and the bending of the supporting member of the die caused by the reaction force from the material is reduced, so that the accuracy of the screw portion can be further improved. You can

In this specification, the equalization of the indentation resistance with respect to the die means the indentation resistance of the material with respect to the die at the time of forming the screw portion in the screw forming portion, and This means that adjustment is performed so that a finished state that does not require another machining for

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. Referring to FIG. 1, which is a partial plan cross-sectional view of an electric power steering apparatus in which a worm having a thread portion processed by rolling is used, which is an embodiment of the present invention, In the gear box 2 of the power steering device 1, a reduction mechanism using a worm gear 4 that reduces the rotation of the electric motor 3 is housed. Worm which is one gear of the worm gear 4.
Reference numeral 10 is a worm wheel 5 that is coupled to the rotating shaft 3a of the electric motor 3 attached to the gear box 2 and is the other gear.
Is coupled to the output shaft 6 having a pinion formed at one end so as to rotate integrally therewith. In the gear box 2, the other end of the output shaft 6 opposite to the one end where the pinion is formed is connected to an input shaft (not shown) via a torsion bar 7, and the pinion is a rack shaft. (Not shown)
Mesh with the rack formed on the.

The steering force applied to the steering wheel is input to the input shaft connected to the steering wheel, and further the torsion bar 7 and the output shaft 6 are connected.
And transmitted to the steered wheels via the rack shaft and the like. At the same time, the electric motor 3 driven and controlled according to the output of the steering torque sensor that detects the amount of twist of the torsion bar 7 based on the steering force acting on the input shaft and the resistance force of the road surface acting on the output shaft 6, the worm 10 To rotate. This allows
The steering assist force generated by the electric motor 3 is transmitted to the steered wheels via the speed reduction mechanism, the output shaft 6 and the rack shaft,
The steering force by the driver is reduced.

Referring also to FIG. 2A, the worm
10 is a thread 12 ₁ , 12 ₂ consisting of two threads in the center
And a pair of shaft portions 13 adjacent to both ends of the screw portion 11 in the direction A1 of the rotation axis (which is also the center axis L of the worm 10) (hereinafter, referred to as “center axis direction A1”). When,
The worm (10) has a base end (14) and a tip end (15) which are both ends. At the base end portion 14, from one shaft portion 13 toward the end portion, a mounting portion 14a to which a cushioning collar 16 is mounted, and a ball bearing 1
A supported portion 14b, which is a portion where the worm 10 is mounted and the worm 10 is rotatably supported by the gear box 2, and a coupling portion 14c which is spline-coupled to the rotation shaft 3a are provided. Also,
A mounting portion 15a to which a cushioning collar 16 is mounted and a ball bearing 17 are mounted to the tip portion 15 from the other shaft portion 13 toward the end portion, and the worm 10 is rotatably supported by the gear box 2. And a supported portion 15b which is a portion to be provided.

Further referring to FIG. 2 (B) together,
The threaded portion 11 is the full threaded portion 11 at the center in the central axis direction A1.
It consists of a and a pair of incomplete threaded portions 11b at both ends. Each screw
Mountain 12 ₁， 12_TwoIs the complete thread 1 that makes up the complete thread 11a.
2₁a, 12_Twoa and the incomplete screw that constitutes the incomplete screw portion 11b
Mountain 12₁b, 12_Twowith b and.

In this embodiment, the end portions 12 ₁ b1 and 12 ₂ b1 of the respective threads 12 ₁ and 12 ₂ are approximately 180 at two locations near the base end 14 and two locations near the tip 15. They are formed at circumferential positions P1 and P2 that form an angle of ° apart from each other in the circumferential direction. The end portion of the complete thread _{12 1 a, 12 2 a 12} 1 a1,12
₂ a1 are at two positions near the base end portion 14, at circumferential positions P3 and P4 that form an angle α from the circumferential positions P1 and P2, respectively, and at two positions near the tip end portion 15, circumferential positions P2, It is formed at circumferential positions P5 and P6 forming an angle α from P1, respectively, in the circumferential direction away from the end portions 12 ₁ b1 and 12 ₂ b1 respectively.
The circumferential positions P3, P4 and the circumferential positions P5, P6 are circumferentially separated from each other at positions forming an angle of approximately 180 °.

It should be noted, "complete thread portion 11a", "incomplete thread portion 11b", "complete thread 12 _{1 a,} 12 ₂ a", "incomplete thread 12 _{1 b,} 12 ₂ b", "cross" , "Mountain portion", "cross-sectional area of screw thread" and "total cross-sectional area" are as defined above.

The number of peaks in the cross section of the threaded portion 11 at different positions in the circumferential direction of the worm 10 is as follows. For example, the end 12 of each thread 12 ₁ , 12 _2.
1 b1 and 12 ₂ b1 are n (n is a natural number) in the cross section at the circumferential positions P1 and P2, which are cross sections passing through, and in this embodiment, four crests are formed (hereinafter , The part where these four crests are formed is referred to as "four crests".), The ends 12 ₁ a1, 12 ₂ a1 of the complete threads 12 ₁ a, 12 ₂ a
In the cross section at the circumferential positions P3 to P6 which is the cross section passing through,
n + 1, in this embodiment, five crests are formed (hereinafter, the part where these five crests are formed is referred to as "five crests").

[0028] Then, 4-crest portions at each circumferential position P1, P2 is composed of four ridges of the complete thread _{12 1 a, 12 2 a,} 5 mountain portions at each circumferential position P3~P6 is , Complete thread 12 ₁ a, 1
It consists of four ridges of 2 ₂ a and _one ridge of incomplete thread 12 ₁ b, 12 ₂ b. At this time, as described above, the shapes of the thread portions of the complete threads 12 ₁ a and 12 ₂ a are all the same, and the cross-sectional areas of the incomplete threads 12 ₁ b and 12 ₂ b are the complete thread 12
Since ₁ a, smaller than the cross-sectional area of 12 _{2 a,} the total cross-sectional area of 5 mountain portions is larger than the total cross-sectional area of 4 mountain portions.

The worm 10 is shown in FIGS. 3 (A), (B),
The material 20 as the first material for rolling shown in (C)
It is formed by rolling using a rolling machine 30 (see FIG. 4) provided with a pair of dies 31. The material 20 molded into a cylindrical bar material with a different diameter cross section by cutting is a material
20 central axis L (also the central axis L of the worm 10)
A large diameter portion 21 in the central portion in the central axis direction A1 which is the direction of
A pair of tapered portions 22 connected to both ends of the large-diameter portion 21 in the central axis direction A1 and a pair of small-diameter portions 23 connected to each tapered portion 22 on the side opposite to the large-diameter portion 21 in the central axis direction A1. When,
It has first and second end portions 24 and 25 in the central axis direction A1.

Each tapered portion 22 has the same diameter as the large diameter portion 21 at the end near the large diameter portion 21, and a small diameter portion 23 smaller than the large diameter portion 21.
The end nearer has the same diameter as the small diameter portion 23. The large-diameter portion 21 and the taper portion 22 form a screw forming portion T, and the thread forming portion T is formed with the thread portion 11 as shown in FIG.

At this time, the two taper portions 22 are formed in the screw forming portion T
It is a portion corresponding to the incomplete threaded portion 11b because it constitutes both ends in the central axis direction A1 and is a portion where the incompletely threaded portion 11b of the threaded portion 11 is formed. Also,
The diameter of the small-diameter portion 23 is set to be smaller than the diameter of the root circle of the threaded portion 11 in a finished state described later after completion of rolling.

A notch 26 is partially formed in each taper portion 22 over a predetermined range in the circumferential direction of the material 20 by machining means such as machining. This notch 26, which is an adjusting portion for adjusting the amount of meat of the thread forming portion T at the circumferential position during rolling, is formed in the thread forming portion T when the thread is rolled by the die 31 of the rolling machine 30. ,
This is for equalizing the pushing resistance of the material 20 to the dies 31 at different circumferential positions.

The shape of the notch 26 is determined as follows, for example. That is, when the notch 26 is not provided in the screw forming portion T, that is, when it is assumed that the screw forming portion T is a standard screw forming portion composed of a rotating body (at this time, in this embodiment, the taper portion 22 is formed). The entire outer peripheral surface of the die is constituted by a conical surface.), And the excess meat that is a factor that increases the pushing resistance by simulating the manner of the die 31 biting into the standard screw forming part. Calculate the position where the fish is and the amount of meat. Then, based on this, the shape of the cutout portion 26 including the range formed in the tapered portion 22 and the depth from the outer peripheral surface thereof is determined with the standard thread forming portion as a reference.

With reference to FIGS. 2 and 3 together, in this embodiment, the notch portion 26 has a circumferential position P in the tapered portion 22.
On the tangent plane at the circumferential positions P1 and P2 in the root circle of the screw threads 12 ₁ and 12 _{2 in} the finished state described later, which is partially formed around the material 1 and P2 in the circumferential direction. And a radial side surface 26a formed by being cut off on a plane extending substantially in the central axis direction A1 and a plane extending in the radial direction orthogonal to the central axis L at the end of the tapered portion 22 near the large diameter portion 21. It is formed by the side face 26b in the direction of the central axis formed by being scraped off.

Therefore, in the notch portion 26, assuming that the standard screw forming portion is used, the circumferential position which is the position showing the largest pushing resistance when the worm 10 is rolled at the circumferential position. The most meat is scraped off at P1 and P2, and from the circumferential positions P1 and P2, the circumferential position P1 and P2
The amount of meat that has been shaved off gradually decreases toward the circumferential positions P3 to P6 that exhibit smaller pushing resistance than P2.

As a result, in the threaded portion 11 of the worm 10, the difference in the pushing resistance at different circumferential positions due to the difference in the total cross-sectional area of the threads 12 ₁ and 12 _{2 in} the cross-section at the circumferential position. As a result, the pushing resistance at the different circumferential positions of the screw portion 11 is equalized. For example, threads
Indentation resistance of the material 20 against the die 31 when forming the parts corresponding to the end parts 12 ₁ b1, 12 ₂ b1 of 12 ₁ , 12 ₂ , that is, the four ridge parts corresponding to the circumferential positions P1, P2, and the complete screw The indentation resistance of the material 20 to the die 31 when forming the portions corresponding to the end portions 12 ₁ a1, 12 ₂ a1 of the ridges 12 ₁ a, 12 ₂ a, that is, the 5 ridge portions corresponding to the circumferential positions P3 to P6, The difference is reduced and equalized.

On the other hand, referring to FIG. 4, the rolling machine 30 in which the rolling load and the number of rotations of the die 31 described later are controlled by the control device is rotatably supported by a frame (not shown) as a supporting member. A pair of supported circular dies 31 and a pair of pushers disposed adjacent to each of the dies 31 in the rotation axis direction A2 of the dies 31 and rotatably supported by the frame. The backing collar 32 and a center stand (not shown) that rotatably supports the material 20 and is movable in the central axis direction A1 are provided. Both dies 31 are rotationally driven by a drive device such as a servomotor so as to rotate in the forward and reverse directions and at the same rotational speed in the same rotational direction. Further, each die 31 has a width in the rotational axis direction A2 that is equal to or larger than the width of the screw forming portion T in the central axis direction A1, and is larger than the width of the screw forming portion T in this embodiment.

The material 20 is rotatably supported around the center axis L on the center stand in a state where the thread forming portion T is positioned in the center axis direction A1 so that the thread forming portion T fits within the width range of the dies 31. To be done. At this time, the central axis direction A1 is parallel to the rotational axis direction A2. After that, as shown in FIGS. 4 (A1) and (A2), both dies 31 that have been normally rotated in the non-rolling position reach the rolling position where they come into contact with the large diameter portion 21 and the taper portion 22 of the material 20. At the same time, the pressing collar 32 is the first and second
The materials are moved in the radial direction of the material 20 by actuators (not shown) to the positions where they come into contact with the ends 24 and 25, respectively.

The dies 31 press the material 20 from the radial direction with a rolling load set so that the predesigned tooth profile threads 12 ₁ and 12 ₂ are formed. At this time, the material 20 is rotated in the opposite direction to both dies 31, and at the same time, the second end 25 is moved away from the dies 31 within the range of the width of both dies 31 (downward in FIG. 4). (2) Move along with the center stand in the central axis direction A1 by a predetermined distance.
Here, the shape of the working tooth tips of both dies 31 is such that the shape of the working tooth in the cross section at right angles is an arc, and in this embodiment is a complex arc having a plurality of curvatures, and moreover, with respect to the center line in the cross section of the working tooth. It is designed to have a symmetrical shape.

When the material 20 is moved by the predetermined distance,
A signal from a position sensor (not shown) for detecting the position in the central axis direction A1 of the is input to the control device, the rotation of both dies 31 is stopped, and after a predetermined stop time elapses, the figure 4 (B1) and (B2), the rotating directions of both dies 31 are reversed. By this reverse rotation,
Material 20 rotates in the opposite direction to both dies 31 while
The end 25 is moved by the predetermined distance in the central axis direction A1 so as to approach the dies 31 (upward in FIG. 4). Then, as in the case of normal rotation, at the time of moving by the predetermined distance, the signal from the position sensor is input to the control device, and the rotation of both dies 31 is stopped. Then, after a lapse of a predetermined stop time, as shown in FIGS. 4 (C1) and (C2), the control means controls both dies 31 to rotate forward again. Therefore, during rolling, the screw forming portion T is always located within the range of the die 31 in the central axis direction A1.

After switching the rotational directions of the dies 31 a plurality of times, for example, 3 to 6 times, the dies 31 and the pressing collar 32 are moved radially outward by the control of the controller. After leaving the material 20 and occupying the non-rolled position, the rotation of both dies 31 is stopped, and the rolling is completed.
In this way, the second material having the threaded portion 11 formed by rolling is obtained.

In this series of rolling operations, as shown in FIG.
As shown in (B), the material 20 has a notch 26 (see FIG. 5).
In (A), a part thereof is shown by a chain double-dashed line. ) Is formed, for example, 4 is formed in the screw forming portion T.
Since the pushing resistance of the material 20 to the die 31 when forming the crest portion and the pushing resistance of the material 20 to the die 31 when forming the five crest portion are equalized, the second material has four crests. The tooth profile in the portion and the five ridges, and by extension, the threaded portion 11 is in a finished state, that is, the threaded portion 11 after completion of rolling does not require another machining such as cutting for finishing. There is.

Thereafter, the second material is subjected to post-processing, for example, mechanical processing such as cutting and grinding, if necessary, so that the small-diameter portion 23 to the shaft portion 13 become the first and second portions. The worm 10 is manufactured by molding the mounting portions 14a and 15a, the supported portions 14b and 15b, and the coupling portion 14c from the ends 24 and 25, respectively.

Next, the effect of the embodiment configured as described above will be described. In a worm 10 having a threaded portion 11 composed of _two threads 12 ₁ and 12 ₂ , a material 20 for rolling
A notch 26 for equalizing the pushing resistance of the screw forming portion T to the die 31 in the circumferential direction of the screw forming portion T is formed in the taper portion 22 which is the end portion of the screw forming portion T in the central axis direction A1. By doing so, the pushing resistance of the material 20 with respect to the die 31 is equalized at different circumferential positions in the screw forming portion T, and the screw threads 12 ₁ , 12 _{2 at} any circumferential position of the screw portion 11 are substantially the same. since the rolling by rolling amount, tooth profile of the thread 12 _1, 12 _2, thus the screw 11, to the extent unnecessary finishing error in tooth less, it is formed with high accuracy. Therefore, unlike the prior art, the screw part
Machining such as grinding for finishing 11 is not required, and the manufacturing cost of the worm 10 formed by rolling can be reduced.

The notch 26 formed in the taper portion 22 in the circumferential direction reduces the amount of meat pushed by the die 31 in the taper portion 22, so that the rolling load can be reduced and the material 20 Since the flexure of the frame caused by the reaction force based on the pushing resistance of is reduced, the accuracy of the screw portion 11 can be further improved.

In the following, an example in which a part of the configuration of the above-mentioned example is modified will be described.
In the above embodiment, the number n of peaks in the direction of the central axis at the first circumferential position is 4 in the above embodiment, but may be 2 or 3 or 5 or more. Also, the screw part 11
The multi-thread screw having three or more threads may be used instead of the two-thread screw.

In the above embodiment, the thread forming portion T is the large diameter portion 21.
However, the thread forming portion T may include only the large diameter portion 21.

The shape of the notch is not limited to the shape in the above-mentioned embodiment, but can be various shapes depending on the form of the screw thread 11. For example, as shown in FIG. 6 (A), the diameter of the tooth bottom of the screw portion 11 (see FIG. 2) is the shaft portion 13
And when it comes to the same diameter, as notch 26 _first radial side _{261 a} is in contact with the small diameter portion 23 may be scraped off deep from the outer peripheral surface of said standard thread forming portion in a radial direction. In addition, FIG.
As shown (B), the radial side 26 _{2 a} is, notch 26 has cross section in the plane perpendicular to the center axis L presents an arcuate
_It may be ₂ . Further, as shown in FIGS. 6 (C1) and 6 (C2), 1 in the direction A1 of the central axis of the thread forming portion T is obtained.
The positions of the notches 26 ₃ and 26 _{4 in} the pair of taper portions 22a and 22b are
They may be offset from each other in the circumferential direction. In addition, the shape of the cutout portion may be an appropriate shape for equalizing the pushing resistance in the circumferential direction in the thread forming portion T as much as possible.

In the above-described embodiment, the adjusting portion is composed of the notch which is the portion where the meat is cut off from the standard screw forming portion, but the protruding portion which is the portion where the meat is added to the standard screw forming portion. By configuring the adjusting part from, the pushing resistance of the material 20 to the dice 31 at different circumferential positions may be equalized.

The rolling machine may be any rolling machine using a plurality of round dies other than the pair of round dies capable of normal rotation and reverse rotation, and further a rolling machine using a pair of flat dies. It may be a machine board.

[Brief description of drawings]

FIG. 1 is a partial plan cross-sectional view of an electric power steering device in which an embodiment of the present invention is used and a worm machined by rolling using the material according to the present invention is used.

2 (A) is a front view of the worm of FIG.
(B) is an enlarged sectional view taken along the line BB of (A).

FIG. 3 shows a rolling material for manufacturing the worm of FIG. 2, (A) is a front view of the material, (B) is a view on arrow B of (A), and (C) is , (A) is an enlarged sectional view taken along the line CC.

FIG. 4 is a view for explaining a rolling process of the material of FIG. 3 by a rolling machine, (A1) shows an outline state when rolling is started by a forward rotating die, and (B1). Shows an outline state when the rolling is continued by the reverse rotating die, (C1) shows an outline state when the rolling is continued by the forward rotating die again, (A2),
(B2) and (C2) are (A1) and (B
The rotation directions of the die and the material in (1) and (C1) are shown.

5A and 5B are schematic views for explaining a state during rolling of the material of FIG. 3, and FIG. 5A is a conceptual partial cross-sectional view of a die and a material when rolling four mountain portions. Yes, (B) is a conceptual partial cross-sectional view of the die and the material when rolling the five ridges.

FIG. 6 shows a modified example of the notch portion formed in the material of FIG. 3, (A) shows a first modified example, and is a cross-sectional view corresponding to FIG. 3 (C); 3C is a cross-sectional view showing a second modified example and corresponding to FIG. 3C, and FIG. 3C1 is a cross-sectional view of a main part corresponding to FIG.
(C2) is a cross-sectional view taken along line C2-C2 of (C).

FIG. 7 is a diagram illustrating a cross-sectional area of a thread ridge portion.

FIG. 8 shows a conventional technique, (A) is a front view of a main part of a worm, and (B) is an enlarged cross-sectional view taken along line BB of (A).

FIG. 9 is a diagram illustrating a state during rolling of a worm rolling material according to a conventional technique, and (A1) is a portion between a die and a material when rolling four ridges. It is sectional drawing, (A2) shows the tooth profile and design tooth profile of the rolled screw part, and (B1) is a partial sectional view of the die and the material when rolling five crests. Yes, (B2) shows the tooth profile and the design tooth profile of the rolled screw part.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Gear box, 3 ... Electric motor, 4 ... Worm gear, 5 ... Worm wheel, 6 ... Output shaft, 7 ... Torsion bar, 10 ... Worm, 11 ... Screw part, 12 ₁ , 12 ₂ … Thread, 13… Shaft, 14…
Base end, 15 ... Tip, 16 ... Buffer collar, 17 ... Ball bearing,
20 ... Material, 21 ... Large-diameter part, 22 ... Tapered part, 23 ... Small-diameter part, 2
4, 25 ... Edge, 26, 26 ₁ , 26 ₂ , 26 ₃ , 26 ₄ ... Notch, 3
0 ... Rolling machine, 31 ... Die, 32 ... Pressing collar, L ... Central axis, A1 ... Central axis direction, T ... Screw forming part, A2 ... Rotation axis direction, P1 to P6 ... Circumferential position.

Continued front page    (72) Inventor Nao Tezuka             1-14, Fujiwara-cho, Gyoda-shi, Saitama 1 Stock             Company Showa Saitama Head Office Factory (72) Inventor Shuichi Amano             2022 Toriizawa Tomihamacho, Otsuki City, Yamanashi Prefecture Stock Association             In company Nissey

Claims (2)

[Claims] 1. A rolling material used for forming a threaded portion of a worm, which is composed of a multi-threaded screw, by rolling using a die, wherein the threaded portion is formed. An adjusting portion for equalizing the pushing resistance of the material with respect to the die in the circumferential direction of the screw forming portion is formed at the end of the screw forming portion in the central axis direction of the material. A material for rolling worms that is characterized by 2. The adjusting portion comprises a cutout portion formed in the end portion in the circumferential direction.
Material for rolling the worm described.