JPH11207431A - Method of manufacturing energy absorbing shaft - Google Patents

Abstract

(57) [Problem] To provide an energy-absorbing shaft that has high rigidity and hardly twists up to a certain limit with respect to an increase in input torque, and easily twists when the torque exceeds the limit at a low cost. The present invention provides a manufacturing method that can be manufactured. SOLUTION: A wire rod formed by drawing steel having a circular cross section is used, and at least a shaft portion g1 is formed into a predetermined diameter only by cold forging of the wire rod, and a predetermined thickness is formed around the shaft portion g1. High hardness layer g with higher hardness than inside
An energy absorbing shaft g on which 1 'is formed is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an energy absorbing shaft used for, for example, a retractor of an automobile seat belt, and belongs to the technical field of manufacturing automobile parts and the like.

[0002]

2. Description of the Related Art A seat belt retractor in an automobile is connected to one end of a seat belt to urge the belt in a winding direction, and a sudden tensile load acts on the seat belt in a collision or the like. Sometimes
An energy absorbing shaft which is twisted by a torque based on the tensile load to absorb impact energy may be used.

As shown in FIG. 18, the shaft A is
Polygonal engagement portions A1 and A2 provided at both ends to engage the torque input member and the fixed member, respectively, and a shaft portion A3 at an intermediate portion thereof are integrally formed. The material and the diameter or the torsional rigidity of the shaft portion A3 are set such that the shaft portion A3 is appropriately twisted when a large torque acts between the engaging portions A1 and A2 at both ends via the seat belt at the time of a collision of the vehicle. Will be done.

[0004]

By the way, the energy absorbing shaft for the seat belt retractor exerts a large rigidity against a torque acting in the event of a collision of the vehicle, so that the occupant can pass through the seat belt. It is required that the seat belt be sufficiently twisted to loosen the seat belt in order to reliably support the vehicle and immediately after the operation of the air bag, in order to release the occupant to the air bag.

In other words, as shown by a solid line curve in FIG. 19, it is required to exhibit high rigidity to a certain limit with respect to an increase in input torque and hardly twist, and to easily twist if the torque exceeds the limit. It is done.

However, a conventional shaft in which a middle portion is formed into a shaft portion having a predetermined diameter by cutting (hereinafter referred to as a conventional product).
In the case of FIG. 19, as shown by the broken line curve shown as a conventional example in FIG. There is a possibility that it may not be able to sufficiently withstand a large tensile load acting on the steel.

On the other hand, in order to impart the above-mentioned characteristics to the conventional product, it is conceivable to perform other processing such as quenching. However, in this case, the manufacturing cost is high. Become.

Therefore, it is an object of the present invention to provide a method of manufacturing an energy absorbing shaft having such characteristics that it exhibits high rigidity and hardly twists up to a certain limit with respect to an increase in input torque, and easily twists if the torque exceeds the limit. Make it an issue.

[0009]

Means for Solving the Problems In order to solve the above problems, the present invention is characterized in that it is configured as follows.

First, the invention according to claim 1 of the present application (hereinafter, referred to as the invention)
The first aspect of the present invention is an energy absorbing shaft having an engagement portion at each end with which a torque input member and a fixed member are respectively engaged, and an intermediate portion serving as a shaft portion twisted by an input torque from the input member. The method according to claim 1, wherein a wire having a circular cross section is drawn as a material, and at least a shaft portion is formed into a predetermined diameter only by cold forging the wire.

The invention according to claim 2 (hereinafter referred to as the second invention) relates to the manufacturing method of the first invention, wherein the cold forging is constituted by a die and a punch facing each other. Using a multi-stage cold forging machine having a plurality of stations, while forming the shaft portion and the engaging portion at one end of the shaft portion by a plurality of stations on the upper stage side,
An engaging portion at the other end of the shaft is formed by a downstream station provided with a split die.

According to the above configuration, the following operation can be obtained.

First, in the method of the first invention, a wire drawn by drawing a metal having a circular cross section is used as a material, and the wire has a hardened surface at the time of drawing. Then, using this wire, at least the shaft portion is formed into a predetermined diameter only by cold forging, so that the hardened surface of the wire is not cut or broken, and the hardened surface is cooled. By the forging, the thickness increases toward the inside, and a high hardness layer having a higher hardness than the inside having a predetermined thickness is formed around the shaft portion.

Therefore, according to the first aspect of the present invention, up to a certain limit with respect to an increase in the input torque, the high-hardness layer exhibits high rigidity due to endurance of this torque and is hardly twisted. If it exceeds, the high-hardness layer is destroyed, so that an energy absorbing shaft that is easily twisted as a whole is manufactured.

According to the method of the second aspect of the present invention, a shaft and an engaging portion of one end thereof are formed by a plurality of stations on an upper stage by using a multistage cold forging machine, and a split die is formed. Since the engaging portion at the other end of the shaft portion is formed by the station provided at the subsequent stage, the engaging portion is provided at both ends, and the hardness around the shaft portion is smaller than that of the inside having a predetermined thickness. The energy absorbing shaft on which the large high hardness layer is formed is continuously and efficiently manufactured.

The material of the wire is preferably steel, but stainless steel or another metal may be used.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing an energy absorbing shaft according to an embodiment of the present invention will be described below.

The wire used in this embodiment is made of steel (J
IS display SWCH8R) is drawn by drawing several times from a large diameter to a small diameter in the cold state, and the intermediate φ9.4 ~ 1
After the cloth drawing of No. 1, the wire diameter is 9.2 mm.
Further, this wire has a circular cross section and its surface is hardened by drawing.

First, as shown in FIG. 1, the wire is cut into a predetermined length to obtain a rod-like diameter D1.
Forms a material a of 9.2 mm.

Next, in the first cold forging step, as shown in FIG. 2, an intermediate material b having a reference shaft portion b1 corresponding to the material a and a small-diameter shaft portion b2 provided at one end thereof. Is formed.

Next, in the second cold forging step, as shown in FIG.
An intermediate material c having a small-diameter shaft portion c2 at one end thereof and a large-diameter portion c3 provided at the other end of the reference shaft portion c1 is formed.

Next, as shown in FIG. 4, a hexahedron having a reference shaft portion d1 and a small-diameter shaft portion d2 and a large-diameter portion c3 of the intermediate material c formed by a third cold forging step. An intermediate material d having a portion d3 and a flange d4 adjacent to the portion d3 is formed.

Next, in a fourth cold forging step, as shown in FIG. 5, a hexagonal body part d3 and a flange part d4 of the intermediate material d having a reference shaft part e1 and a small diameter shaft part e2 are formed. The intermediate material e having the engaging portion e3 thus formed is formed.

Further, in the fifth cold forging step, FIG.
As shown in the figure, the reference shaft portion f1, a small-diameter shaft portion f2 at one end thereof, and an engaging portion f3 at the other end thereof, and a large-diameter shaft is provided between the reference shaft portion f1 and the small-diameter shaft portion f2. The intermediate product f provided with the portion f4 is formed.

By performing post-processing as necessary, as shown in FIG. 7, the intermediate shaft g1 and the engaging portions g2 and g3 formed on the hexahedrons at both ends thereof are connected to one of the engaging portions g2 and g3. An energy absorbing shaft g as a final product having a small-diameter shaft portion g4 extending from the joint portion g3 and having a parallel two-faced portion g5 provided at the tip of the small-diameter shaft portion g4 is formed.

Incidentally, this post-processing may be performed by any processing such as forging, cutting, pressing and the like.

As described above, in this embodiment, the wire rod a of 9.2 mm is subjected to cold forging five times to gradually increase the thickness of the reference shaft portion, and the shaft of the energy absorbing shaft g as the final product is obtained. Although the diameter D2 of the portion g1 is formed to 9.5 mm, the wire obtained by hardening the surface is repeatedly subjected to cold forging, as shown in FIG. As the thickness increases, a high-hardness layer g1 'is formed around the shaft portion g1.

FIG. 9 shows the hardness distribution in the cross section of the shaft portion g1 of the energy absorbing shaft g (in FIG. 9, referred to as a forged product), and a shaft formed of the same material and the same shape as the shaft g by cutting (hereinafter, referred to as a forged product). This is compared with a hardness distribution in a cross section of a shaft portion of a cut product.

As shown in FIG. 9, in the case of a cut product, the surface of the shaft portion only has a large hardness, whereas in the case of the energy absorption shaft g by forging, the shaft portion g1
Thus, a high hardness layer g1 'having a high hardness is formed over a range of 0.5 mm or more from the surface.

Thus, the energy absorbing shaft g
A high-hardness layer g1 'having a predetermined thickness and a higher hardness than the inside thereof is formed on the surface of the shaft portion g1, so that the high-hardness layer g1' is formed between the engaging portions g2 and g3 at both ends of the shaft portion g1. When a large torque acts on the shaft, as shown in FIG. 10, in the case of a cut product, the shaft portion starts to be twisted at an early stage of a torque value of 3.5 kgf · mm, but the shaft g (in FIG. 10, called a forged product). In the case of, the shaft g until the torque value is 5.8 kgf
1 is hardly twisted.

That is, in the case of the shaft g, the hardened layer exhibits high rigidity due to endurance of this torque and hardly twists until the input torque increases to a certain limit. When the high hardness layer is broken, the whole is easily twisted.

Therefore, the energy absorbing shaft g
When used in the seat belt retractor for automobiles,
Exhibits great rigidity against the torque that is applied in the event of a car collision, and reliably supports the occupant via the seat belt. It acts to loosen the seat belt.

As a material of the wire, steel (JI
Although S display SWCH8R) is used, stainless steel or another metal may be used as the material.

Next, for example, one manufacturing apparatus used for manufacturing the energy absorbing shaft according to this embodiment will be described.

As shown in FIG.
A cold multi-stage forging device for forming an intermediate product of an energy absorbing shaft at a stage cold forging station X1 to X5, comprising a machine base 1, a cutter device (not shown), and die units 11 to 15 A plurality of punch units 21 to 25 are attached to a ram 2 which is reciprocatingly moved so as to approach and separate from the machine base 1 so as to face the die units 11 to 15 respectively.

First, as shown in FIG. 1, when a rod-shaped material a cut to a predetermined length from a wire is supplied to a first cold forging station X1 by a supply device, as shown in FIG. As the ram 2 advances, the punch unit 21 advances until it comes into contact with the die unit 11, and the material a is formed in the forming hole 32 of the die 32 held by the die holder 31.
a and the punch-side die 34 held by the punch holder 33
Is held in the molding hole 34a. After that,
As the ram 2 advances, the presser plate 35
The intermediate material b (shown in FIG. 2) is formed by abutting the punch 37 into the forming hole 34a of the punch-side die 34 while compressing the pressing member 36.

Then, the punch unit 21 retreats due to the retreat of the ram 2, and thereafter, the knockout pin 38 penetrating from the rear end face to the front end face of the die 32 protrudes toward the ram 2, thereby discharging the intermediate material b. It is supplied to the second cold forging station X2.

Next, when the intermediate material b is supplied to the second cold forging station X2 by the supply device, the punch unit 22 advances by the advance of the ram 2 until the punch unit 22 contacts the die unit 12, as shown in FIG. Then, the intermediate material b is held in the forming hole 42a of the die 42 held by the die holder 41 and the forming hole 44a of the punch-side die 44 held by the punch holder 43. Thereafter, the pressing plate 45 is further moved by the advance of the ram 2 so that the spring 4
While pressing the punches 47 while compressing 6, 46,
By punching the punch 47 into the forming hole 44a of the punch-side die 44, an intermediate material c (shown in FIG. 3) is formed.

Then, the punch unit 22 retreats due to the retraction of the ram 2, and thereafter, the knockout pin 48 penetrating from the rear end face to the front end face of the die 42 projects toward the ram 2, thereby discharging the intermediate material c. It is supplied to the third cold forging station X3.

Next, when the intermediate material c is supplied to the third cold forging station X3 by the supply device, the punch unit 23 moves forward by the advance of the ram 2 as shown in FIG. Punch side die 5 held
The surface of the second forming hole 52a is in contact with the front end surface of the intermediate material c, and the intermediate material c is held by the die holders 53, 54 by the advancement of the punch-side die 52. The intermediate material d (shown in FIG. 4) is formed by being driven into 56a.

Then, the punch unit 23 retreats due to the retraction of the ram 2, and thereafter, the knockout pin 57 penetrating from the rear end face to the front end face of the die 56 projects toward the ram 2, thereby discharging the intermediate material d. It is supplied to the fourth cold forging station X4.

Next, when the intermediate material d is supplied to the fourth cold forging station X4 by the supply device, the punch unit 24 is advanced by the advance of the ram 2 shown in FIG. Forming hole 62a of punch 62
Surface comes into contact with the front end face of the intermediate material d, and the advance of the punch 62 causes the intermediate material d to move into the die holder 63,
Forming holes 6 of dies 65 and 66 held at
5a, 66a into the intermediate material e
(Shown in FIG. 5) is formed.

Then, the punch unit 24 retreats due to the retreat of the ram 2, and thereafter, the knockout pin 67 penetrating from the rear end face to the front end face of the die 66 protrudes toward the ram 2, thereby discharging the intermediate material e. It is supplied to the fifth cold forging station X5.

Next, when the intermediate material e is supplied to the fifth cold forging station X5 by the supply device, the punch unit 25 is advanced by the advance of the ram 2 shown in FIG. Forming hole 72a of punch 72
Surface comes into contact with the front end surface of the intermediate material e, and the material e is driven into the die.

In the process of pushing the intermediate material e into the front die 73 as the punch 72 moves forward,
The punches 72 come into contact with the plurality of divided die members 74.
The die members 74... 74 are pushed into the mounting holes 1 a of the machine base 1 together with the front die holder 76 while compressing 5. At this time, the above-mentioned die members 74... 74 have a first tapered surface 74 a.
b is the first tapered surface 7 of the inner peripheral surface of the front die holder 76
6a and the second taper surface 76b, the springs 77 ... 77 for urging the dice members 74 ... 74 to expand the diameter are compressed to reduce the diameter as a whole.

The reduced-diameter die members 74...
The intermediate material e is gripped by the forming hole 73a constituted by 74, and in this state, the intermediate material e is driven into the forming hole 79a of the rear die 79 held by the rear die holder 78 by the advance of the punch 72. Intermediate product f
(Shown in FIG. 6) is formed.

Then, as shown in FIG. 17, the punch unit 25 retreats due to the retraction of the ram 2, and then the front die holder 76 grips the intermediate product f by the urging force of the compressed springs 75. 74 together with the held die members 74... 74 until they come into contact with the stopper plate 76. After that, a knockout pin 81 penetrating from the rear end face to the front end face of the rear die 79 protrudes toward the ram 2 so that the die member 7 is formed via the intermediate product f.
4. While 74 moves back in the front die holder 76,
These die members 74... 74 are expanded in diameter by the urging force of the compressed springs 77. And then,
The intermediate product f is discharged by the knockout pin 81 protruding toward the ram 2.

Then, by performing post-processing as required, an energy absorbing shaft g (shown in FIG. 7) as a final product is formed.

According to such a manufacturing method, by providing a station having split dies which can be expanded and contracted in a multi-stage forging machine, even if the energy absorbing shaft has engagement portions at both ends of the shaft portion, the die can be easily formed. Exhausted from inside.

[0050]

As described above, first, in the method of the first invention, a wire obtained by drawing a metal having a circular cross section is used as a material, and this wire has a hardened surface at the time of drawing. Then, using this wire, at least the shaft portion is formed into a predetermined diameter only by cold forging,
The hardened surface of the wire is thickened toward the inside by cold forging without being scraped or broken, and the hardness around the shaft is larger than that of the predetermined thickness. A hard layer will be formed.

Therefore, according to the first aspect of the present invention, up to a certain limit with respect to an increase in the input torque, the high-hardness layer exhibits high rigidity due to withstanding this torque and is hardly twisted. If it exceeds, the high-hardness layer is destroyed, so that the energy-absorbing shaft that is easily twisted as a whole can be easily manufactured at low cost without requiring other processing such as quenching.

According to the method of the second aspect of the present invention, a shaft and an engaging portion of one end thereof are formed by a plurality of upper stations using a multistage cold forging machine, and a split die is formed. Since the engaging portion at the other end of the shaft portion is formed by the station provided at the subsequent stage, the engaging portion is provided at both ends, and the hardness around the shaft portion is smaller than that of the inside having a predetermined thickness. It becomes possible to continuously and efficiently manufacture an energy absorbing shaft on which a large high hardness layer is formed.

[Brief description of the drawings]

FIG. 1 is a view showing a shape of a material before being processed by a manufacturing apparatus using a manufacturing method according to the present invention.

FIG. 2 is a view showing a shape of an intermediate material obtained by a first cold forging step of the manufacturing apparatus.

FIG. 3 is a view showing a shape of an intermediate material obtained by a second cold forging process of the manufacturing apparatus.

FIG. 4 is a view showing a shape of an intermediate material obtained by a third cold forging step of the manufacturing apparatus.

FIG. 5 is a view showing a shape of an intermediate material obtained by a fourth cold forging step of the manufacturing apparatus.

FIG. 6 is a view showing a shape of an intermediate product obtained by a fifth cold forging step of the manufacturing apparatus.

FIG. 7 is a view showing the shape of a final product obtained by post-processing.

FIG. 8 is an enlarged sectional view of a shaft portion of a final product.

FIG. 9 is a diagram showing the hardness from the surface to the center of the shaft portion of the forged product and the cut product.

FIG. 10 is a diagram illustrating a relationship between input torque and torsional rotation speed at a shaft portion of a forged product and a cut product.

FIG. 11 is a schematic front view of a manufacturing apparatus using the manufacturing method according to the present invention.

FIG. 12 is a longitudinal sectional view of a first cold forging station of the manufacturing apparatus.

FIG. 13 is a longitudinal sectional view of a second cold forging station of the manufacturing apparatus.

FIG. 14 is a longitudinal sectional view of a third cold forging station of the manufacturing apparatus.

FIG. 15 is a longitudinal sectional view of a fourth cold forging station of the manufacturing apparatus.

FIG. 16 is a longitudinal sectional view showing a state where a die member of a fifth cold forging station of the manufacturing apparatus is reduced in diameter.

FIG. 17 is a longitudinal sectional view showing a state where a die member of a fifth cold forging station of the manufacturing apparatus is expanded in diameter.

FIG. 18 is a view showing a shape of a conventional energy absorbing shaft.

FIG. 19 is a diagram showing required characteristics and conventional characteristics of an energy absorbing shaft.

[Explanation of symbols]

 g Energy absorption shaft g1 Shaft g2, g3 Engagement

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kiyoshi Ogawa 12 Kirihara-cho, Fujisawa-shi, Kanagawa Nippon Seiko Co., Ltd. (72) Masatoshi Shimizu 2-1-1 Edagawa, Koto-ku, Tokyo Nissan Sales Inside the company

Claims (2)

[Claims] 1. Production of an energy absorbing shaft having an engaging portion at each end with which a torque input member and a fixing member are respectively engaged, and an intermediate portion serving as a shaft portion twisted by an input torque from the input member. A method for producing an energy absorbing shaft, comprising: using a wire drawn from a metal having a circular cross section as a material, and forming at least a shaft portion to a predetermined diameter by only cold forging the wire. 2. The cold forging uses a multi-stage cold forging machine having a plurality of stations constituted by dies and punches facing each other, and a plurality of upper-stage stations form a shaft and one of the shafts. 2. The energy engaging part according to claim 1, wherein the engaging part at the other end of the shaft is formed by a post-stage station provided with a split die. Manufacturing method of absorption shaft.