WO2022131374A1

WO2022131374A1 - Torsion bar and production method therefor

Info

Publication number: WO2022131374A1
Application number: PCT/JP2021/046819
Authority: WO
Inventors: 誠也吉田; 勝義桑田; 聡一巻田; 暢宏牛尾; 悦則藤田
Original assignee: デルタ工業株式会社
Priority date: 2020-12-19
Filing date: 2021-12-17
Publication date: 2022-06-23
Also published as: JP2022097327A

Abstract

The present invention is designed to improve fatigue strength and suppress the occurrence of surface cracks due to repeated use.　This torsion bar 10 is subjected to heat treatment so that the hardness distribution, in the cross sectional direction, is lower in the surface than in the center thereof. More specifically, the quench depth extends to the center, thus increasing the yield point and improving the fatigue strength. Meanwhile, the toughness of the surface is relatively higher than the center, and this makes it less likely for cracks to occur due to repeated use. Furthermore, the hardness of the surface is relatively lower than the center, and this makes it easier to apply detent processing.

Description

Torsion bar and its manufacturing method

The present invention relates to a torsion bar and a method for manufacturing the torsion bar.

Patent Documents

1 and 2 disclose a seat suspension in which an upper frame provided so as to be vertically movable with respect to the lower frame is elastically supported by a magnetic spring and a torsion bar. The torsion bar is inserted and hung in the pipe-shaped front frame and the rear frame arranged along the width direction of the upper frame on the upper end side of each of the pair of left and right front links and the pair of left and right rear links. Has been done. Then, one end is connected to the upper frame side, the other end is connected to each upper end side of the front link or the rear link, and the rotation of the front link and the rear link twists the torsion bar to determine. Demonstrate the elastic force of. Torsional stress is repeatedly applied to the torsion bar used in this way by a person sitting on the seat supported by the seat suspension, vibration input during traveling, and the like. Further, in particular, the seat suspension used in automobiles is required to be lightweight, and there is a tendency to select a torsion bar having a smaller diameter as the torsion bar adopted therein. Therefore, it is required to improve the fatigue strength.
As a technique for improving the fatigue strength of a torsion bar, for example, a technique for performing heat treatment as disclosed in Patent Document 3 is disclosed.

Japanese Unexamined Patent Publication No. 2010-179719 Japanese Unexamined Patent Publication No. 2010-179720 Japanese Unexamined Patent Publication No. 2006-349080

The technique disclosed in Patent Document 3 performs quenching in a relatively shallow range from the surface, and as shown in FIG. 4 of Patent Document 3, the hardness toward the center in the cross-sectional direction is low, and the hardness is closer to the surface. It has a high hardness distribution. Therefore, repeated use may cause cracks on the surface. Further, if the surface hardness is high, it is difficult to perform detent processing on the member to be connected.

The present invention has been made in view of the above, and it is possible to further improve the fatigue strength, suppress the occurrence of surface cracks due to repeated use, and further achieve both the ease of processing of the anti-rotation process. An object of the present invention is to provide a torsion bar and a method for manufacturing the torsion bar.

In order to solve the above problems, the present invention provides a torsion bar that has been heat-treated and is characterized in that the hardness distribution in the cross-sectional direction is lower on the surface than on the center.
It is preferable that the stress concentration portion adjacent to the portion to which the detent member is fixed is processed to apply residual stress.

Further, in the present invention, a method for processing a torsion bar is characterized in that quenching is performed so that the quenching depth reaches at least the center in the cross-sectional direction, and heat treatment is performed to reduce the hardness of the surface side from the center by tempering. offer.
It is preferable to apply a residual stress to the stress concentration portion adjacent to the portion to which the detent member is fixed.
Further, when the anti-rotation member is fixed to the torsion bar, a part of the anti-rotation member is melted by laser processing, and the molten metal is penetrated into the gap between the anti-rotation member and the torsion bar to be cured. It is preferable to have a step of integrating the detent member with the torsion bar.
Further, the portion of the torsion bar to which the detent member is fixed is processed into a shape having at least one flat surface, and the metal melted by the laser processing is filled in the gap between the detent member and the flat surface. It is preferable to cure the metal.

The torsion bar of the present invention has a distribution in which the hardness in the cross-sectional direction is lower on the surface than in the center due to heat treatment. That is, the quenching depth extends to the center, which raises the yield point and improves the fatigue strength. On the other hand, since the toughness of the surface is relatively higher than that of the center, cracks and the like due to repeated use are unlikely to occur. Moreover, since the hardness of the surface is relatively lower than that of the center, it is easy to perform anti-rotation processing.

1 (a) is a side view showing a torsion bar according to an embodiment of the present invention, and FIG. 1 (b) is an end view. 2 (a) is a side view of a structure in which a detent member is integrated with the torsion bar of FIG. 1, and FIG. 2 (b) is an end view thereof. FIG. 3 (a) is a diagram showing the position where the hardness in the cross-sectional direction was measured in the torsion bar, and FIG. 3 (b) is a diagram showing the measurement of the hardness in the cross-sectional direction in the range near the end of the substantially square cross-section. It is a figure which showed the direction, FIG. 3C is a figure which showed the measurement direction of the hardness in the cross-sectional direction in the range of a circular cross-section, and FIG. 3D is the figure which showed the hardness distribution in the cross-sectional direction. It is a graph. FIG. 4 is a diagram showing the measurement results of hardness in the cross-sectional direction. 5 (a) is a side view of the cherry-shaped torsion bar of Comparative Example 2, FIG. 5 (b) is a cross-sectional view taken along the line BB of FIG. 5 (a), and FIG. 5 (c) is a sectional view taken along the line BB. , FIG. 5 (a) is a sectional view taken along the line CC. 6 (a) to 6 (c) are diagrams for explaining an example of a fixing method when the detent member is fixed to the torsion bar, and FIG. 6 (a) is a state in which the detent member is fixed to the torsion bar. Is a side view, (b) is an end view, and (c) is a sectional view taken along line AA of (b). 7 (a) to 7 (c) are views for demonstrating another example of the fixing method when the detent member is fixed to a torsion bar, and FIG. 7A is a diagram in which the detent member is fixed to the torsion bar. A side view of the state, (b) is an end view, and (c) is a sectional view taken along line BB of (b). FIG. 8 is a diagram for explaining a test method of a three-point bending test. FIG. 9 is a diagram showing the results of a three-point bending test. FIG. 10 is a diagram showing the measurement results of the torsional torque in the test example. FIG. 11 is a diagram showing a reference example of the SN curve.

Hereinafter, the present invention will be described in more detail based on the embodiments shown in the drawings. As shown in FIGS. 1 and 2, in the torsion bar 10 of the present embodiment, the detent member 20 is fixed to the vicinity of each end portion in the longitudinal direction. Among the torsion bars 10, for example, in the case of the seat suspension shown in

Patent Documents

1 and 2, the seat suspension is connected to the upper frame, the lower frame, or the member to be connected such as each link via the detent member 20. To.

The torsion bar 10 of the present embodiment has a round cross section. The cross-sectional shape is not limited to this, but a round shape is preferable in terms of efficiency against twisting. The range (range) 11 of the length a1 near the center in the longitudinal direction from each end surface of the torsion bar 10 is processed into a substantially quadrangular cross section, and the portion thereof is a detent made of a metal tubular member. The member 20 is press-fitted. The detent member 20 is formed in a substantially square cross section, and the minimum distance b1 (distance along a line connecting the center point to the center in the width direction of each face) from the center point of the cross section to the outer surface is the torsion bar 10. It is formed at a distance exceeding the radius b2 of.

The detent member 20 is press-fitted into the range 11 near the ends on both sides of the torsion bar 10 (note that only one detent member 20 is shown in FIG. 2). After press-fitting, it is integrated into the end-side range 11 by welding, preferably laser welding. In the present embodiment, as shown in FIG. 2, a portion having a predetermined width closest to the outer end of the end-approaching range 11 is a portion (fixing portion) 12 to which the detent member 20 is fixed. ..

Here, as the torsion bar 10, a heat-treated one is used. Specifically, it is quenched by a heat treatment apparatus until the quenching depth reaches at least the center P0 of the cross section orthogonal to the longitudinal direction, and then tempering is performed so that the hardness on the surface P1 side is lower than the hardness of the center P0. The one that has been subjected to the above heat treatment is used (see FIGS. 3 (b) and 3 (c)). That is, the torsion bar 10 having such a hardness distribution is obtained by adjusting conditions such as quenching temperature, quenching time, tempering temperature, and tempering time.

FIG. 3D is a graph showing the hardness distribution in the cross-sectional direction orthogonal to the longitudinal direction of the torsion bar 10 of the present embodiment. The graph of FIG. 3 (d) shows the data measured along the cross section (reference numeral C) of the central portion in the longitudinal direction of the torsion bar 10 (length 334 mm, diameter 8.15 mm) shown in FIG. 3 (a), and the data at both ends. The data measured along the cross section (reference numerals B and D) of the boundary with the end side range 11 and the data measured along each cross section (reference numerals A and E) of the end side range 11 are shown. The heat treatment of the torsion bar 10 can be performed by, for example, induction heating.
Further, the portions of the circular cross sections of the cross sections B, C, and D are measured in the diameter direction indicated by the arrows in FIG. 3 (c). As shown in FIG. 3B, the portion of the substantially quadrangular cross section of the cross sections A and E is measured along the direction of the arrow indicated by the “plane” from one facing plane toward the other. At the same time, the measurement is performed in the direction of the arrow indicated by the "corner" from one of the opposite corners toward the other corner.

In FIG. 3D, for comparison, a base material for a torsion bar having the same dimensions and shape as the torsion bar 10 (that is, an untreated product that has not been heat-treated) (Comparative Example 1), and irregularities on the peripheral surface are shown. The hardness distribution of the cross section of the cherry-shaped torsion bar (Comparative Example 2) having the above is also shown. As shown in FIGS. 5 (a) to 5 (c), the cherry-shaped torsion bar 100 has a plurality of irregularities formed on the peripheral surface, and has a hardness on the surface side as in the present embodiment. The tempering process is not performed under the conditions that reduce the temperature.

As shown in FIG. 3D, Comparative Example 1 has a hardness in the range of about 260 to 290 Hv in any direction in the radial direction and is almost constant. Comparative Example 2 has a higher hardness than Comparative Example 1, but is in the range of about 560 to 610 Hv, and it can be said that the hardness in the cross-sectional direction is basically constant. On the other hand, in the case of the torsion bar 10 of the present embodiment, first, in the cross sections B, C, and D, which are in the range of the circular cross section, the "distance from the surface: 1 to 1 to" which is closer to the center P0 from the inside 1 mm from the surface P1. In the range of "7 mm", the hardness is distributed in the range of about 620 to 710 Hv. On the other hand, on the surface P1 (distance from the surface: 0 mm or 8.15 mm), the hardness is about 350 to 520 Hv, which is significantly lower than the hardness of the central PO.

Further, in the cross sections A and E having a substantially quadrangular cross section, the hardness is distributed in the range of about 400 to 460 Hv in the range of "distance from the surface: 1 to 7 mm", and the cross section B in the range of the circular cross section. , C, D are lower than the hardness. Further, the hardness is lower in the cross sections A and E near the surface P1 than in the range of "distance from the surface: 1 to 7 mm". Further, when measured in the direction connecting the opposing angles of the cross sections A and E, the hardness near P1 is as low as about 280 to 320 Hv.

FIG. 4 shows the distribution of cross-sectional hardness at three points of cross-sections A, B, and C. From FIG. 4, it can be seen that the hardness of the surface P1 is lower than that of the center P0 on the entire surface of each cross section. Further, in the cross sections B and C, since the cross section is circular, the hardness distribution is almost the same in the circumferential direction, but in the cross section A having a corner portion, the portion corresponding to the corner portion is on the surface. It tends to have a lower hardness than the corresponding part.

Further, in the present embodiment, residual stress (compressive residual stress) is in a range adjacent to the fixing portion 12 with the detent member 20, that is, in a predetermined range closer to the central portion in the longitudinal direction than the fixing portions 12 on both sides. Has been processed to give. Shot peening is preferably used as the processing for applying this residual stress. The residual stress applying portion 13 processed to apply the residual stress is adjacent to the inside of each fixing portion 12 to which the detent member 20 is fixed (range shown by a2 in FIG. 1), and the torsion bar 10 Stress concentration is likely to occur due to twisting. Therefore, increasing the residual stress at this site can contribute to improving the fatigue strength against torsional stress.

The detent member 20 is integrated into the end-side range 11 as described above, but as is clear from the hardness distributions of the cross sections A and E in FIGS. 3 (d) and 4, the end-side-side range 11 The hardness of the surface P1 is lower than the range of the circular cross section. Further, the hardness of the surface P1 near the corner portion is close to that of Comparative Example 1, and it is easy to integrate the surface P1 by laser processing after press-fitting the detent member 20.

First, the torsion bar 10 of the present embodiment is subjected to heat treatment having the hardness distribution as described above by adjusting conditions such as quenching temperature, quenching time, tempering temperature, and tempering time. Next, shot peening is applied to a predetermined range adjacent to the fixing portion 12 to which the detent member 20 is fixed to form the residual stress applying portion 13. After that, the detent member 20 is press-fitted into the range 11 near the end, and is fixed and integrated by laser welding. In the present embodiment, the hardness of the surface P1 in the range 11 near the end where laser welding is performed is relatively low, and it can be easily processed.

The torsion bar 10 is fitted with a detent member 20 to a member to be connected, for example, in the case of a seat suspension, to a predetermined portion of a frame or a link. Then, due to the relative rotation of the frame or the link, one end side does not rotate but the other end side rotates to be twisted, and a predetermined elastic force is exhibited. As described above, the detent member 20 used in the present embodiment has a distance such that the minimum distance b1 from the center P0 along the cross section to the surface P1 exceeds the radius b2 of the torsion bar 10. Therefore, the torsional stress generated by the relative rotation of the members to be connected is mainly borne by the detent member 20 integrated in the end-side range 11, and the reaction force from the torsion bar 10 is reduced to prevent detent effect. Will increase.

Here, the method of fixing the detent member 20 to the torsion bar 10 will be described in detail with reference to FIGS. 6 and 7. The outer surfaces of the detent members 20 in FIGS. 6 (a) to 6 (c) and 7 (a) to 7 (c) are circular, but this is for convenience only, and the members to be connected are actually used. When mounting, serrations are applied to the outer surface, members for preventing rotation are further connected, or a square outer surface is used as shown in FIGS. 1 and 2. Here, attention will be paid to the adhesion between the torsion bar 10 and the inner surface of the detent member 20.

First, FIGS. 6 (a) to 6 (c) show the torsion bar 10 in which the end-side range 11 is formed into a substantially quadrangular cross section in the same manner as shown in FIGS. 1 and 2. As a result, four planes 11a are formed in the end-side range 11. On the other hand, the detent member 20 has a circular inner surface. When integrating the two, first, the detent member 20 is press-fitted into the range 11 near the end of the torsion bar 10. Since the inner surface of the detent member 20 has a circular cross section, a gap 25 is formed between the torsion bar 10 and the flat surface 11a in the range 11 near the end surface. Then, the laser is applied to the detent member 20 forming the gap 25. As a result, a part of the metal of the detent member 20 is melted, and the gap 25 is filled with the melted metal 20a. When the molten metal 20a is cured, it serves as a detenting key between the torsion bar 10 and the detent member 20, and the detent member 20 is firmly fixed to the end-side range 11 of the torsion bar 10. As a result, the detent member 20 is firmly integrated with the torsion bar 10. If the flat surface 11a formed in the end-side range 11 has at least one surface, it is possible to form a gap 25 in which the molten metal 20a of the rotating member 20 is filled, but it is preferably two surfaces, more preferably. , It is preferable to form four surfaces as in the present embodiment in terms of fixing strength.

Next, FIGS. 7 (a) to 7 (c) show an embodiment in which the end-side range 11 of the torsion bar 10 is left as a circular cross section, and the detent member 20 having a circular inner surface is integrated with the portion. There is. In this case, the laser is irradiated from the inner surface of the detent member 20 at predetermined intervals in the circumferential direction, for example, at six locations as shown in FIG. 7 (b). The metal at the location irradiated with the laser melts, and the melted metal 20a penetrates into the slight gap 25 between the two and hardens. As a result, as in the case of FIG. 6, the hardened metal 20a serves as a detenting key, and the detenting member 20 is integrated into the end-side range 11 of the torsion bar 10.

(Test example)
A three-point bending test was performed on the torsion bar 10 of the above embodiment, the base material for the torsion bar of Comparative Example 1, and the Sakura-shaped torsion bar of Comparative Example 2. As shown in FIG. 8, the three-point bending test was performed by pushing the center of the sample of the torsion bar cut into a length of 200 mm with the distance between the fulcrums set to 100 mm. The pushing speed was 5 mm / min. The results are shown in FIG. It can be seen that the bending strength of the torsion bar 10 of the above embodiment is higher than that of Comparative Example 1 as well as Comparative Example 2.

Next, one end was fixed, the other end was twisted up to 52 degrees, and the torsion torque was measured. As the torsion bar 10 of the above embodiment, four samples (1) to (4) were prepared and compared with the Sakura type torsion bar of Comparative Example 2. As shown in FIG. 10, the torsion bars 10 of the embodiments of the samples (1) to (4) are round, but show a torsion torque equal to or higher than that of the Sakura type torsion bar of Comparative Example 2.

FIG. 11 is a reference example of the SN curve of the heat-treated steel material (pipe heat-treated material, flat plate heat-treated material) and the non-heat-treated steel material (pipe raw material, flat plate raw material). It can be seen that the fatigue strength is increased by performing the heat treatment. Regarding this point, referring to FIG. 9, the displacement amount of the torsion bar 10 of the present embodiment is about 22 mm when the maximum load value is about 9700 N, whereas the Sakura type torsion bar of Comparative Example 2 has the maximum load value of about 22 mm. The displacement amount is about 14 mm when the maximum load value is 9500 N, and in Comparative Example 1 of the untreated product, the displacement amount is about 14 mm when the maximum load value is about 3500 N. While the torsion bar 10 of the present embodiment has the characteristics of high hardness shown in FIGS. 3 and 4 and lower hardness on the surface side than the center side by heat treatment, it is compared with any of Comparative Examples 1 and 2. It also has good characteristics, and these characteristics together contribute to the improvement of fatigue strength.

10 Torsion bar 11 Range closer to the end 12 Fixed part 13 Residual stress applying part 20 Anti-rotation member

Claims

A heat-treated torsion bar
A torsion bar characterized in that the hardness distribution in the cross-sectional direction orthogonal to the longitudinal direction is lower on the surface than in the center.
The torsion bar according to claim 1, wherein the stress concentration portion adjacent to the portion to which the detent member is fixed is processed to apply residual stress.
A torsion bar processing method characterized by quenching so that the quenching depth reaches at least the center in the cross-sectional direction, and then performing heat treatment to lower the hardness of the surface side from the center by tempering.
The method for processing a torsion bar according to claim 3, wherein the stress concentration portion adjacent to the portion to which the detent member is fixed is subjected to processing to apply residual stress.
When the anti-rotation member is fixed to the torsion bar, a part of the anti-rotation member is melted by laser processing, and the molten metal is infiltrated into the gap between the anti-rotation member and the torsion bar to be cured. The method for processing a torsion bar according to claim 4, further comprising a step of integrating the anti-rotation member with the torsion bar.
The portion of the torsion bar to which the detent member is fixed is processed into a shape having at least one flat surface, and the metal melted by the laser processing is filled in the gap between the detent member and the flat surface and cured. The method for processing a torsion bar according to claim 5.