Manufacturing method of coil springs

Abstract

To provide a method for producing a coil spring which is excellent in fatigue resistance and corrosion fatigue resistance.SOLUTION: A method for producing a coil spring according to one embodiment includes: molding a coil spring, having end coil parts and an effective part, by winding an element wire spirally; radiating a laser beam to a surface of the element wire in at least a part of the coil end part locally to soften a part of the element wire and form an area, which is softer than the surface of the element wire in the effective part, on the surface of the element wire in the coil end part. Further, when the laser beam is radiated, the element wire is fixed and a laser device which radiates the laser beam is moved.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a coil spring. [Background technology]

[0002] For example, coil springs are used in suspension systems for vehicles such as automobiles, etc. This type of coil spring is required to have good resistance to sag and corrosion fatigue.

[0003] Increasing the overall hardness of the wire that forms the coil spring is expected to improve sag resistance. However, in this case, if corrosion pits occur on the surface of the wire, for example due to part of the coating applied to the wire peeling off, cracks may occur in the wire starting from the corrosion pits. If the hardness of the wire is high, the cracks will progress quickly, which may lead to early breakage of the coil spring. On the other hand, if the hardness of the wire is low overall, sag resistance will decrease.

[0004] Patent Documents 1, 2, and 3 are known as examples of studies on the sag resistance and corrosion fatigue resistance of coil springs. Patent Documents 1 and 2 disclose a wire (spring steel wire) that includes a first layer on the surface, a second layer located more inward than the first layer, and a third layer located more inward than the second layer and reaching the center, with the second layer having a lower hardness than the first and third layers. According to Patent Documents 1 and 2, the second layer improves fatigue properties, and the first and third layers improve sag resistance.

[0005] Patent Document 3 discloses a wire (spring steel) whose hardness decreases from the inside to the outside. According to Patent Document 3, such a wire configuration can slow down the spread of cracks on the wire surface. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6587993 [Patent Document 2] JP 2019-7081 A [Patent Document 3] JP 2010-133558 A Summary of the Invention [Problem to be solved by the invention]

[0007] Even when Patent Documents 1, 2, and 3 are taken into consideration, there is still room for improvement in the sag resistance and corrosion fatigue resistance of coil springs. For example, in Patent Documents 1, 2, and 3, the same layer structure is formed over the entire length of the wire. However, the properties required for a coil spring, such as sag resistance and corrosion fatigue resistance, may differ depending on the portion of the coil spring, such as the end turn portion and the effective portion.

[0008] In addition, in Patent Documents 1, 2, and 3, a wire having a layer structure with partially different hardness is obtained by heating the wire by high-frequency induction heating. In such a manufacturing method, it is difficult to control the temperature distribution in the cross section of the wire during heating, and as a result, there is a possibility that a wire having the intended layer structure cannot be obtained.

[0009] An object of the present disclosure is to provide a manufacturing method for a coil spring having excellent resistance to sag and corrosion fatigue. [Means for solving the problem]

[0010] A method for manufacturing a coil spring according to one embodiment includes forming a coil spring having an end turn portion and an effective portion by winding a wire in a spiral shape, softening a part of the wire by locally irradiating a surface of the wire in at least a part of the end turn portion with a laser beam, thereby forming a region on the surface of the wire in the end turn portion that is softer than the surface of the wire in the effective portion. Furthermore, when irradiating the laser beam, a laser device that fixes the wire and irradiates the laser beam is moved.

[0011] For example, the laser light is irradiated so that the surface of the wire in the end turn portion has a first region and a second region that is softer than the first region and is aligned with the first region in a circumferential direction centered on the axis of the wire, and so that the surface of the wire in the effective portion has the first region over the entire circumference in the circumferential direction.

[0012] The wire comprises a first layer including the first region and a second layer including the second region and softer than the first layer, and preferably the laser light is irradiated so that the axis of the wire passes through the first layer in the end turn portion.

[0013] The laser light may be irradiated so that the second region is formed in at least a part of the seat surface of the end turn portion. Preferably, the laser light is irradiated so that the second region is formed in a range of at least 0.4 turns and not more than 0.9 turns from the end of the wire in the end turn portion. Also, preferably, the laser light is irradiated so that the second region has a thickness of 0.6 mm or more.

[0014] In a cross section of the wire including the first region and the second region, the surface of the wire has a first base point which is an intersection point on the effective portion side among a pair of intersection points where a first center line passing through the axis of the wire and parallel to the coil axis intersects with the surface of the wire, a second base point which is an intersection point on the side farther from the coil axis among a pair of intersection points where a second center line passing through the axis of the wire and parallel to a radial direction centered on the coil axis intersects with the surface of the wire, a third base point which is an intersection point on the opposite side to the first base point among a pair of intersection points where the first center line intersects with the surface of the wire, and a fourth base point which is an intersection point on the opposite side to the second base point among a pair of intersection points where the second center line intersects with the surface of the wire. In one example, the laser light is irradiated so that the center of the second region is located between the third base point and the fourth base point in the circumferential direction which passes through the first base point, the second base point, the third base point, and the fourth base point in this order. Preferably, the laser light is irradiated so that a center of the second region is located between the third base point and the fourth base point in the circumferential direction. Effect of the Invention

[0015] According to the present disclosure, it is possible to provide a manufacturing method for a coil spring having excellent resistance to sag and corrosion fatigue. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic cross-sectional view of a suspension device according to the first embodiment. [Diagram 2] FIG. 2 is a schematic perspective view of the coil spring according to the first embodiment. [Diagram 3] FIG. 3 is a schematic cross-sectional view of the coil spring taken along line III-III in FIG. [Figure 4] FIG. 4 is a schematic cross-sectional view of the coil spring taken along line IV-IV in FIG. [Diagram 5] FIG. 5 is a graph showing an example of hardness distribution inside a wire of a coil spring. [Figure 6] FIG. 6 is a graph showing an example of hardness distribution on the surface of a wire. [Figure 7] FIG. 7 is a flowchart showing an example of a method for manufacturing a coil spring. [Figure 8] FIG. 8 is a diagram showing an example of a local softening treatment performed on a wire during the manufacture of a coil spring. [Figure 9] FIG. 9 is a schematic perspective view of a coil spring according to the second embodiment. [Figure 10] FIG. 10 is a schematic cross-sectional view of a coil spring according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Several embodiments will be described with reference to the drawings. In each embodiment, a McPherson strut type suspension device, a coil spring used in the suspension device, and a manufacturing method of the coil spring are illustrated. The coil spring disclosed in each embodiment can be used in other types of suspension devices, and can also be used for purposes other than suspension devices.

[0018] [First embodiment] 1 is a schematic cross-sectional view of a suspension system 100 according to a first embodiment. This suspension system 100 includes a coil spring 1 for suspending a vehicle. The coil spring 1 includes a wire 2 wound in a spiral shape. The wire 2 is made of, for example, spring steel.

[0019] The suspension device 100 further includes a shock absorber 3, a first spring seat 4, and a second spring seat 5. The second spring seat 5 is located above the first spring seat 4 in the vertical direction Z. The coil spring 1 is attached to the suspension device 100 in a compressed state between the first spring seat 4 and the second spring seat 5.

[0020] Shock absorber 3 includes a cylinder 30 containing a fluid such as oil, a rod 31 inserted into cylinder 30, a damping force generating mechanism provided inside cylinder 30, and a cover member 32 covering a sliding portion of rod 31. Rod 31 can extend and retract parallel to axis X0 of shock absorber 3 relative to cylinder 30. The damping force generating mechanism provides resistance to the movement of rod 31.

[0021] An upper end of the shock absorber 3 is attached to a vehicle body 7 via a mount insulator 6. The mount insulator 6 includes an anti-vibration rubber 60 and a support member 61 fixed to the vehicle body 7. A lower end of the shock absorber 3 is attached to a knuckle member 8 that supports the axle via a bracket 9. In the example of FIG. 1, an axis X0 of the shock absorber 15 is inclined at an acute angle θ0 with respect to the vertical direction Z.

[0022] The coil spring 1 is mounted in a compressed state between the first spring seat 4 and the second spring seat 5, elastically supports the load applied from above, and expands and contracts within a predetermined range of deflection (between full rebound and full bump) depending on the magnitude of the load.

[0023] Fig. 2 is a schematic perspective view of the coil spring 1 according to the present embodiment. Fig. 3 is a schematic cross-sectional view of the coil spring 1 taken along line III-III in Fig. 2. Fig. 4 is a schematic cross-sectional view of the coil spring 1 taken along line IV-IV in Fig. 2.

[0024] As shown in Fig. 2, the coil spring 1 has an effective portion 10, a first winding seat portion 11, and a second winding seat portion 12. The first winding seat portion 11 is a portion that contacts the first spring seat 4. The second winding seat portion 12 is a portion that contacts the second spring seat 5. The effective portion 10 is a portion located between the first winding seat portion 11 and the second winding seat portion 12.

[0025] In this embodiment, the first winding seat portion 11 includes not only a portion that always contacts the first spring seat 4, but also a portion that moves away from the first spring seat 4 when the compressive load applied to the coil spring 1 is less than a predetermined value and moves into contact with the first spring seat 4 when the compressive load applied to the coil spring 1 exceeds the predetermined value. Similarly, the second winding seat portion 12 includes not only a portion that always contacts the second spring seat 5, but also a portion that moves away from the second spring seat 5 when the compressive load applied to the coil spring 1 is less than a predetermined value and moves into contact with the second spring seat 5 when the compressive load applied to the coil spring 1 exceeds the predetermined value. As an example, the first winding seat portion 11 is in a range of one turn from the lower terminal 2a of the wire 2, and the second winding seat portion 12 is in a range of one turn from the upper terminal 2b of the wire 2.

[0026] In the effective portion 10, the wire 2 is wound multiple times around the coil axis X1. For example, the coil axis X1 is inclined so as to form an acute angle with respect to the vertical direction Z and the axis X0 of the shock absorber 3 shown in Fig. 1. Hereinafter, as shown in Fig. 2, an axial direction DX parallel to the coil axis X1 and a radial direction DR centered on the coil axis X1 are defined.

[0027] 3, surface 20 of wire 2 is entirely covered with coating 21. As an example, diameter R of wire 2 is 10 to 15 mm, and thickness of coating 21 is 40 μm or more.

[0028] In this embodiment, the surface 20 of the wire 2 has a first region A1 and a second region A2 that is softer than the first region A1. In the example of Fig. 2, the second region A2 is provided in a part of the first end winding portion 11. The portion of the surface 20 excluding the second region A2 is the first region A1.

[0029] That is, in at least a portion of the surface 20 of the first end winding portion 11, the distribution of hardness is not uniform in the circumferential direction Dθ centered on the axis X2 of the wire 2 shown in Fig. 4. On the other hand, in the surfaces 20 of the second end winding portion 12 and the effective portion 10, the distribution of hardness is uniform over the entire circumference in the circumferential direction Dθ.

[0030] 3, the wire 2 in the effective portion 10 is entirely formed of the first layer L1. The first region A1 corresponds to the surface of the first layer L1. The second end winding portion 12 is also entirely formed of the first layer L1.

[0031] As shown in Fig. 4, the first end winding portion 11 includes a first layer L1 and a second layer L2 that is softer than the first layer L1. The second region A2 corresponds to the surface of the second layer L2. In the example of Fig. 4, the proportion of the cross-sectional area of ​​the wire 2 that is occupied by the first layer L1 is greater than the proportion of the cross-sectional area of ​​the wire 2 that is occupied by the second layer L2. The axis X2 of the wire 2 passes through the first layer L1.

[0032] As shown in FIG. 4, a first base point P1, a second base point P2, a third base point P3, and a fourth base point P4 are defined on the surface 20 of the wire 2. The first base point P1 is the position on the surface 20 that is closest to the effective portion 10 located above the axial direction DX. The second base point P2 is the position on the surface 20 that is farthest from the coil axis X1 in the radial direction DR. The third base point P3 is the position farthest from the effective portion 10 in the axial direction DX (the position opposite the first base point P1 across the axis X2). The fourth base point P4 is the position closest to the coil axis X1 in the radial direction DR (the position opposite the second base point P2 across the axis X2). The first base point P1, the second base point P2, the third base point P3, and the fourth base point P4 are arranged in order at intervals of 90 degrees in the circumferential direction Dθ. From another point of view, the first base point P1 is the intersection point on the effective portion 10 side of a pair of intersection points where the first center line CL1, which passes through the axis X2 and is parallel to the coil axis X1, intersects with the surface 20. The second base point P2 is the intersection point farther from the coil axis X1 of a pair of intersection points where the second center line CL2, which passes through the axis X2 and is parallel to the radial direction DR, intersects with the surface 20. The third base point P3 is the intersection point opposite the first base point P1 of the pair of intersection points where the first center line CL1 intersects with the surface 20. The fourth base point P4 is the intersection point opposite the second base point P2 of the pair of intersection points where the second center line CL2 intersects with the surface 20.

[0033] In the first end winding portion 11, the first region A1 and the second region A2 are arranged side by side in the circumferential direction Dθ. In this embodiment, a boundary B1 between the first region A1 and the second region A2 is located between the second base point P2 and the third base point P3. Another boundary B2 between the first region A1 and the second region A2 is located at the fourth base point P4. The first region A1 is formed in a range from the fourth base point P4 (boundary B2) to the boundary B1 in the circumferential direction Dθ, and includes the first base point P1 and the second base point P2. The second region A2 is formed in a range from the boundary B1 to the fourth base point P4 (boundary B2) in the circumferential direction Dθ, and includes the third base point P3.

[0034] 4, the length of the second region A2 in the circumferential direction Dθ is shorter than the length of the first region A1 in the circumferential direction Dθ. The second region A2 is formed on the surface 20 of the wire 2, below in the axial direction DX and toward the inside of the coil spring 1. The third base point P3 and its neighboring region correspond to the seating surface SF that is in contact with the first spring seat 4 shown in FIG. 1 at all times or when the coil spring 1 is compressed. In other words, the second region A2 is formed in at least a part of the seating surface SF of the first end winding portion 11.

[0035] More specifically, if the first base point P1 is 0 o'clock, the second base point P2 is 3 o'clock, the third base point P3 is 6 o'clock, and the fourth base point P4 is 9 o'clock, the second area A2 is formed in the range from 4 o'clock to 9 o'clock.

[0036] The range in which the second region A2 is formed is not limited to the range from 4 o'clock to 9 o'clock. For example, the second region A2 may be formed so that its center C is located in the range from the second base point P2 to the fourth base point P4 in the circumferential direction Dθ. The center C is equidistant from the boundaries B1 and B2 in the circumferential direction Dθ. Preferably, the center C is located in the range from the third base point P3 to the fourth base point P4 in the circumferential direction Dθ.

[0037] The first end winding portion 11 does not need to have the cross-sectional structure shown in Fig. 4 at all positions. In the example of Fig. 2, the second region A2 is not provided in a portion 11a that is a certain distance from the terminal 2a. The portion 11a is a portion that always contacts the first spring seat 4 regardless of the compression state of the coil spring 1 when the coil spring 1 is assembled in the suspension device 100, for example. From another point of view, in the example of Fig. 2, the second region A2 is provided in a portion that comes into contact with or separates from the first spring seat 4 depending on the load applied to the coil spring 1.

[0038] Preferably, the second region A2 is formed in a range of at least 0.4 turns and no more than 0.9 turns from the terminal 2a. However, the second region A2 may be formed beyond this range or smaller than this range. Also, the second region A2 may be formed continuously within a certain range from the terminal 2a.

[0039] In the example of Fig. 4, the thickness t of the second layer L2 is greatest at the center C. The thickness t gradually decreases from the center C toward the boundaries B1, B2. The thickness t at the center C is, for example, 0.6 mm or more, and preferably 1.0 mm or more. In relation to the diameter R of the wire 2, the thickness t at the center C is, for example, 2% or more and 8% or less of the diameter R.

[0040] Fig. 5 is a graph showing an example of hardness distribution of the wire 2 along the center C in Fig. 4. In the graph, the horizontal axis represents the distance [mm] from the surface 20 of the wire 2, and the vertical axis represents Rockwell hardness [HRC].

[0041] In the example of Fig. 5, the hardness of the first layer L1 is almost constant. In the second layer L2, the hardness is smallest at the surface 20 (second region A2), and the hardness gradually increases with increasing distance from the surface 20, reaching the hardness of the first layer L1 at the thickness t. Thus, the second layer L2 is generally softer than the first layer L1. The hardness of the second layer L2 has a gradient according to the distance from the surface 20.

[0042] 6 is a graph showing an example of the hardness distribution in the circumferential direction Dθ on the surface 20. In the graph, the horizontal axis represents the position [mm] in the circumferential direction Dθ on the surface 20, and the vertical axis represents Vickers hardness [HV].

[0043] In the example of FIG. 6, the hardness of the first region A1 is almost constant. In the second region A2, the hardness is lowest near the center C. Between the center C and the boundary B1, and between the center C and the boundary B2, the hardness gradually increases with increasing distance from the center C, reaching the hardness of the first region A1 at the boundaries B1 and B2. Thus, the second region A2 is generally softer than the first region A1. The hardness of the second region A2 has a gradient with the center C being the minimum value.

[0044] Fig. 7 is a flow chart showing an example of a method for manufacturing the coil spring 1. First, the wire 2 is wound in a spiral shape by a coiling machine, and this wound portion is cut by a cutter (step S1). At this point, the surface 20 of the wire 2 has the same hardness as a whole. Next, a local softening treatment is performed to form a second region A2 on the surface 20 (step S2). Details of the local softening treatment will be described later with reference to Fig. 8.

[0045] After the local softening treatment, the wire 2 is subjected to electric annealing (step S3). In this electric annealing, the wire 2 is heated, for example, at a temperature range of 400 to 500°C for one minute or less. After the electric annealing, the wire 2 is subjected to hot setting in which an overload is applied to the wire 2 in a heated state (step S4).

[0046] Next, the wire 2 is subjected to shot peening (step S5), and further to presetting (step S6). After that, a coating film 21 is formed over the entire surface 20 of the wire 2 (step S7). Note that the local softening treatment may be performed before shot peening, or may be performed after electric annealing or hot setting.

[0047] 8 is a diagram showing an example of the local softening process. In this embodiment, the local softening process uses a laser device 200. For example, the laser device 200 is a semiconductor laser, but is not limited to this example.

[0048] Laser device 200 irradiates laser light LZ onto an area in first end winding portion 11 where second region A2 is to be formed. When forming second region A2 in the area from 4 o'clock to 9 o'clock as shown in Fig. 4, irradiation axis XL of laser light LZ is tilted with respect to axial direction DX. The position where irradiation axis XL intersects with surface 20 corresponds to center C shown in Fig. 4.

[0049] When irradiating the laser light LZ, for example, the position of the laser device 200 may be fixed and the wire 2 may be rotated around the coil axis X1. In this case, the wire 2 may be moved in the axial direction DX as the wire 2 rotates so that the distance between the part of the wire 2 irradiated with the laser light LZ and the laser device 200 remains constant. This makes it possible to suppress deviation of the focus of the laser light LZ. As another example, the wire 2 may be fixed and the laser device 200 may be moved.

[0050] The wire 2 is heated by being irradiated with the laser beam LZ. This heating forms a heat affected zone (HAZ) in the wire 2. When the heat affected zone is air-cooled, a second layer L2 having a reduced hardness compared to the original wire 2 is generated.

[0051] In one example, the portion of the wire 2 irradiated with the laser beam LZ is heated to a temperature range below the austenitization start temperature. At the position corresponding to the irradiation axis XL, it is preferable that a portion from the surface 20 to a depth of at least 0.6 mm (or a portion from the surface 20 to a depth of 2% to 8% of the diameter R) is heated to the above temperature range.

[0052] If the temperature of the wire 2 during heating is too high, a part of the wire 2 may be quench-hardened, and the hardness may increase compared to before irradiation with the laser beam LZ. The output [kW] and irradiation time [sec] of the laser beam LZ need to be adjusted so that such quench-hardening does not occur.

[0053] 7 and 8 are merely examples, and the coil spring 1 can be manufactured by various other methods.

[0054] In the above embodiment, in the first seat turn portion 11 of the coil spring 1, the surface 20 of the wire 2 has the first region A1 and the second region A2. Because the second region A2 is softer than the first region A1, even if a corrosion pit occurs in the second region A2, the corrosion pit is less likely to develop into a crack in the wire 2. Even if a crack does occur, its progression can be slowed. In other words, by providing the second region A2 in the first seat turn portion 11, the corrosion fatigue resistance of the first seat turn portion 11 is improved.

[0055] If the second region A2 (second layer L2) were formed over the entire wire 2, the sag resistance of the coil spring 1 could decrease. In contrast, in this embodiment, the second region A2 is not formed in the effective portion 10. Therefore, the effective portion 10 can maintain good sag resistance. Since the first seat winding portion 11 is a portion that is subjected to a lower acting stress than the effective portion 10, even if the second region A2 is provided in the first seat winding portion 11, the sag resistance of the entire coil spring 1 is unlikely to be affected.

[0056] The first winding end portion 11 is a portion that comes into contact with the first spring seat 4 that is disposed therebelow. Therefore, if foreign matter such as sand gets between the first winding end portion 11 and the first spring seat 4, the coating film 21 is damaged as the suspension device 100 is used, and corrosion pits are likely to occur in the first winding end portion 11. In contrast, in this embodiment, the second region A2 is provided in an area that includes the seat surface SF of the first winding end portion 11. Therefore, even if foreign matter gets between the first winding end portion 11 and the first spring seat 4 and causes corrosion pits, cracks caused by these corrosion pits can be suppressed.

[0057] Moreover, such foreign matter is likely to enter under the portion of the first end turn portion 11 that comes into contact with and separates from the first spring seat 4. Therefore, by forming the second region A2 locally in such a portion, it is possible to effectively improve the corrosion fatigue resistance of the coil spring 1 while maintaining the sag resistance. In this regard, the range of 0.4 turns or more and 0.9 turns or less from the terminal 2a is a region where corrosion pits due to foreign matter are likely to occur. Moreover, this range is more likely to be subjected to stress when the coil spring 1 is compressed than the range from the terminal 2a to 0.4 turns. Therefore, as described above with reference to FIG. 2, it is preferable to form the second region A2 at least in the range of 0.4 turns or more and 0.9 turns or less from the terminal 2a.

[0058] Furthermore, the portion of the surface 20 of the wire 2 on the coil axis X1 side (the inner side of the coil spring 1) is likely to be subjected to stress and is likely to suffer from corrosion fatigue. Therefore, as described above with reference to FIG. 4, it is preferable to form the second region A2 closer to the inner side of the coil spring 1.

[0059] In this embodiment, the case where laser light is used for the local softening treatment is exemplified. However, the local softening treatment can also be performed by other methods such as high-frequency heating. However, as exemplified with reference to FIG. 8, when laser light is used for the local softening treatment, the second region A2 can be formed in a shorter time than when the wire 2 is heated by other methods. Furthermore, if the wire 2 is heated by other methods such as high-frequency heating, it may be difficult to locally increase the temperature of the wire 2. In this regard, when laser light is used, it is possible to heat a specific portion of the wire 2 with high precision. In addition to the above, various other advantageous effects can be obtained from this embodiment.

[0060] [Second embodiment] The second embodiment illustrates another configuration that can be applied to the coil spring 1. The configuration of the coil spring 1 and the configuration of the suspension device 100 that are not specifically mentioned are similar to those of the first embodiment.

[0061] Fig. 9 is a schematic perspective view of a coil spring 1 according to the second embodiment. As shown in Fig. 9, in this embodiment, a second region A2 (hereinafter referred to as second region A2a) is also formed in an area of ​​surface 20 of wire 2 in effective portion 10 that may come into contact with second end winding portion 12 during compression.

[0062] In the example of Fig. 9, the second region A2a is not formed in a portion 12a that is a certain distance from the terminal 2b. Specifically, in the example of Fig. 9, the second region A2a is formed in a range of one turn or more and two turns or less from the terminal 2b. As another example, the second region A2a may extend to the second end winding portion 12. Furthermore, the second region A2a may extend to the terminal 2b.

[0063] The cross-sectional structure of the portion including the second region A2a is the same as the cross-sectional structure shown in FIG. 4 turned upside down. However, the range in which the second region A2a is formed in the circumferential direction Dθ can be changed as appropriate. In the example of FIG. 9, the second region A2a is formed in a portion of the surface 20 of the effective portion 10 that faces the second end turn portion 12. This portion is a location that may come into contact with the second end turn portion 12 when the coil spring 1 is compressed. Even if a corrosion pit occurs in the wire 2 due to this contact, the second region A2a prevents the pit from developing into a crack.

[0064] [Third embodiment] The third embodiment illustrates still another configuration that can be applied to the coil spring 1. The configurations of the coil spring 1 and the suspension device 100 that are not specifically mentioned are similar to those of the first embodiment.

[0065] 10 is a schematic cross-sectional view of a coil spring 1 according to a third embodiment. This cross-section corresponds to, for example, a part of the first winding end portion 11, but a similar structure can also be applied to the second winding end portion 12.

[0066] In the example of Fig. 10, the second layer L2 covers the first layer L1 over the entire circumference in the circumferential direction Dθ. That is, the surface 20 of the wire 2 is formed by the second region A2 over the entire circumference. In the example of Fig. 10, the thickness of the second layer L2 is constant in the circumferential direction Dθ. However, the thickness of the second layer L2 may vary locally.

[0067] The second region A2 is formed in a range of at least 0.4 turns and no more than 0.9 turns from the terminal 2a, as in the first embodiment. There may be a portion between the second region A2 and the terminal 2a where the second region A2 is not formed. The second region A2 may be formed continuously in a certain range from the terminal 2a.

[0068] The effective portion 10 is entirely formed of the first layer L1, similarly to the example of Fig. 3. That is, the surface 20 of the effective portion 10 is entirely the first region A1.

[0069] Even with the configuration of this embodiment, it is possible to improve the corrosion fatigue resistance of the first end winding portion 11 and the second end winding portion 12. Moreover, by forming the effective portion 10 entirely from the first layer L1, it is possible to impart good sag resistance to the coil spring 1.

[0070] The scope of the present invention is not limited to the configurations disclosed in the first to third embodiments described above. The present invention can be implemented by modifying the configurations disclosed in each embodiment in various ways.

[0071] For example, in the first and second embodiments, the second region A2 may be formed in a portion of the surface 20 of the first seat winding portion 11 that faces the effective portion 10. Also, the second region A2 may be formed in a portion of the second seat winding portion 12 that comes into contact with or separates from the second spring seat 5 depending on the load applied to the coil spring 1. Furthermore, when the second region A2 is formed in the second seat winding portion 12, the second region A2 does not necessarily have to be formed in the first seat winding portion 11. The second region A2 may extend to a part of the effective portion 10.

[0072] The wire 2 may have a multi-layer structure including another layer having a hardness different from that of the first layer L1 and the second layer L2. For example, when the other layer extends to the surface 20 of the wire 2, another region having a hardness different from that of the first region A1 and the second region A2 may be additionally formed on the surface 20.

[0073] In each embodiment, the coil spring 1 is disclosed in which the wire 2 is wound in a cylindrical shape. However, the coil spring 1 may have another shape, such as a barrel shape whose diameter decreases toward the first end winding portion 11 and the second end winding portion 12. The claims as originally filed in this application are set forth below. [1] A coil spring formed of a wire wound in a spiral shape and having an end turn portion and an effective portion, a surface of the wire in the end winding portion has a region that is softer than a surface of the wire in the effective portion; Coil spring. [2] The surface of the wire in the end turn portion is A first region; A second region that is softer than the first region and is aligned with the first region in a circumferential direction around the axis of the wire; having The surface of the wire in the effective portion has the first region over the entire circumference in the circumferential direction. The coil spring according to [1] above. [3] The wire is a first layer including the first region; a second layer including the second region and softer than the first layer; Equipped with The axis of the wire passes through the first layer in the end turn portion. The coil spring according to [2] above. [4] The second region is formed on at least a part of the seat surface of the end turn portion. The coil spring according to [2] or [3] above. [5] The second region is formed in a range of at least 0.4 turns and not more than 0.9 turns from an end of the wire in the end turn portion. The coil spring according to any one of [2] to [4] above. [6] The second region has a thickness of 0.6 mm or more. The coil spring according to any one of [2] to [5] above. [7] In a cross section of the wire including the first region and the second region, the surface of the wire is a first base point which is an intersection point on the effective portion side of a pair of intersection points where a first center line which passes through the axis of the wire and is parallel to the coil axis intersects with a surface of the wire; a second base point being one of a pair of intersections at which a second center line, which passes through the axis of the wire and is parallel to a radial direction centered on the coil axis, intersects with a surface of the wire, the second base point being the intersection farther from the coil axis; a third base point, which is an intersection point opposite to the first base point, of a pair of intersection points where the first center line intersects with a surface of the wire; a fourth base point, which is an intersection point opposite to the second base point, of a pair of intersection points where the second center line intersects with a surface of the wire; having The center of the second region is located between the second base point and the fourth base point in the circumferential direction passing through the first base point, the second base point, the third base point, and the fourth base point in this order. The coil spring according to any one of [2] to [6] above. [8] The center of the second region is located between the third base point and the fourth base point in the circumferential direction. The coil spring according to [7] above. [9] A first spring seat; A second spring seat disposed vertically above the first spring seat; The coil spring according to any one of [1] to [8], which is disposed between the first spring seat and the second spring seat; and A suspension device comprising:

[10] A coil spring having an end turn portion and an active portion is formed by winding a wire in a spiral shape; a laser beam is locally irradiated onto a surface of the wire in at least a part of the end winding portion to soften a part of the wire, thereby forming a region on the surface of the wire in the end winding portion that is softer than the surface of the wire in the effective portion; A method for manufacturing coil springs. [Explanation of symbols]

[0074] 1...coil spring, 2...wire, 3...shock absorber, 4...first spring seat, 5...second spring seat, 10...active part, 11...first turn-around portion, 12...second turn-around portion, 20...surface of wire, 100...suspension device, A1...first region, A2...second region, L1...first layer, L2...second layer.

Claims

1. A coil spring having an end turn portion and an active portion is formed by winding a wire in a spiral shape; a laser beam is locally irradiated onto a surface of the wire in at least a part of the end winding portion to soften a part of the wire, thereby forming a first layer and a second layer softer than the first layer in the wire in the end winding portion; Including, When irradiating the laser light, the wire is fixed and a laser device is moved, and the laser light is irradiated from the laser device so that the second layer having a thickness of 0.6 mm or more is formed, and a first region which is a surface of the first layer and a second region which is a surface of the second layer and is aligned with the first region in a circumferential direction centered on the axis of the wire are formed on a surface of the wire in the end turn portion. A method for manufacturing coil springs.

2. the laser light is irradiated so that a surface of the wire in the end winding portion has the first region and the second region, and a surface of the wire in the effective portion has the first region over an entire circumference in the circumferential direction. The method for manufacturing the coil spring according to claim 1.

3. The laser light is applied so that the axis of the wire passes through the first layer in the end turn portion. The method for manufacturing a coil spring according to claim 2.

4. The laser light is irradiated so that the second region is formed on at least a part of the seat surface of the end turn portion. The method for manufacturing a coil spring according to claim 2 or 3.

5. the laser light is irradiated so that the second region is formed in a range of at least 0.4 turns and not more than 0.9 turns from an end of the wire in the end turn portion; A method for manufacturing a coil spring according to any one of claims 2 to 4.

6. In a cross section of the wire including the first region and the second region, the surface of the wire is a first base point which is an intersection point on the effective portion side of a pair of intersection points where a first center line which passes through the axis of the wire and is parallel to a coil axis intersects with a surface of the wire; a second base point being one of a pair of intersections at which a second center line, which passes through the axis of the wire and is parallel to a radial direction centered on the coil axis, intersects with a surface of the wire, the second base point being the intersection point farther from the coil axis; a third base point, which is an intersection point opposite to the first base point, among a pair of intersection points where the first center line intersects with a surface of the wire; a fourth base point, which is an intersection point opposite to the second base point, of a pair of intersection points where the second center line intersects with a surface of the wire; having The laser light is irradiated so that a center of the second region is located between the second base point and the fourth base point in the circumferential direction passing through the first base point, the second base point, the third base point, and the fourth base point in this order. A method for manufacturing a coil spring according to any one of claims 2 to 5.

7. The laser light is irradiated so that a center of the second region is located between the third base point and the fourth base point in the circumferential direction. The method for manufacturing a coil spring according to claim 6.

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