Spiral spring, suspension device and spiral spring manufacturing method

Abstract

A coil spring according to one embodiment is formed of a steel wire wound in a coil shape, and has a seating portion and an effective portion, a surface of the steel wire in the seating portion having a region softer than a surface of the steel wire in the effective portion.

Description

Technical Field

[0001] This invention relates to a helical spring, a suspension device, and a method for manufacturing a helical spring. Background Technology

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

[0003] If the overall hardness of the steel strand forming the helical spring is increased, its dent resistance is expected to improve. However, in this case, corrosion pits may appear on the surface of the steel strand due to factors such as partial coating peeling, and cracks may start to develop from these pits. If the steel strand is too hard, the cracks will develop rapidly and may cause the helical spring to break prematurely. On the other hand, if the overall hardness of the steel strand is too low, its dent resistance will be reduced.

[0004] As is well known, prior art documents 1, 2, and 3 are examples of studies on the dent resistance and corrosion fatigue resistance of helical springs. Prior art documents 1 and 2 disclose a steel strand (spring strand) having a first layer on its surface, a second layer in the middle starting from the first layer, and a third layer in the middle from the second layer to the center, wherein the hardness of the second layer is lower than that of the first and third layers. According to prior art documents 1 and 2, the second layer improves fatigue performance, while the first and third layers improve dent resistance.

[0005] Prior art document 3 also discloses a steel strand (spring steel) whose hardness decreases from the inside out. According to prior art document 3, this structure of the steel strand can delay the propagation of cracks on the surface of the steel strand.

[0006] Preliminary technical documents

[0007] Comparison documents

[0008] [Comparative Document 1] Patent No. 6587993 Publication

[0009] [Comparative Document 2] Published in Japan on January 2019-7081

[0010] [Comparative Document 3] JP 2010-133558 Summary of the Invention

[0011] The problem this invention aims to solve:

[0012] Even considering prior art documents 1, 2, and 3, there is still room for improvement in the dent resistance and corrosion fatigue resistance of helical springs. For example, in prior art documents 1, 2, and 3, a similar layered structure is formed along the entire length of the steel strand. However, the required properties of helical springs, such as dent resistance and corrosion resistance, may vary in different parts of the helical spring, such as the seat winding and the active part.

[0013] In comparative documents 1, 2, and 3, all steel strands were heated using high-frequency induction heating to obtain layered steel strands with varying hardness. In this manufacturing method, it is difficult to control the temperature distribution within the cross-section of the steel strand during heating, thus potentially preventing the production of steel strands with the desired layered structure.

[0014] The purpose of this disclosure is to provide a helical spring with excellent resistance to dents and corrosion fatigue, a suspension device equipped with the helical spring, and a method for manufacturing the helical spring.

[0015] Solution to the problem:

[0016] According to one embodiment, a helical spring is formed of steel strand wound in a helical shape and has a seat portion and an effective portion, wherein the surface of the steel strand in the seat portion has a region that is softer than the surface of the steel strand in the effective portion.

[0017] For example, the surface of the steel strand in the winding portion has a first region and a second region that is softer than the first region, the second region being aligned with the first region in a circumferential direction centered on the axis of the steel strand. The surface of the steel strand in the effective portion has the first region over the entire circumference in the circumferential direction.

[0018] The steel strand has a first layer including the first region and a second layer including the second region and being softer than the first layer. Preferably, in the winding portion, the axis of the steel strand passes through the first layer.

[0019] The second region may be at least partially formed on the seat surface of the winding portion. Preferably, the second region forms at least 0.4 windings, but no more than 0.9 windings, starting from the end of the steel strand in the winding portion. Additionally, preferably, the thickness of the second region is at least 0.6 mm.

[0020] On the cross-section of the steel strand including the first region and the second region, the surface of the steel strand has a first base point, which is the effective portion of the intersection point of a pair of intersection points between the surface of the steel strand and a first center line passing through the axis of the steel strand and parallel to the axis of the coil; a second base point, which is the intersection point on the side away from the axis of the coil of a pair of intersection points between the surface of the steel strand and a second center line passing through the axis of the steel strand and parallel to the radial direction around the axis of the coil; a third base point, which is the intersection point on the opposite side of the first base point in a pair of intersection points between the first center line and the surface of the steel strand; and a fourth base point, which is the intersection point on the opposite side of the second base point in a pair of intersection points between the second center line and the surface of the steel strand. In one example, in the circumferential direction passing sequentially through the first base point, the second base point, the third base point, and the fourth base point, the center of the second region is located between the third base point and the fourth base point. Preferably, the center of the second region is located between the third base point and the fourth base point in the circumferential direction.

[0021] According to one embodiment, the suspension device includes a first spring seat, a second spring seat arranged vertically above the first spring seat, and a helical spring according to any one of claims 1 to 7 arranged between the first spring seat and the second spring seat.

[0022] In a method of manufacturing a helical spring according to one embodiment, a helical spring having a seat portion and an effective portion is formed by winding steel strands into a helical shape. A portion of the steel strands is softened by irradiating a laser beam locally onto the surface of at least a portion of the seat portion of the steel strands, so that a region softer than the surface of the effective portion of the steel strands is formed on the surface of the seat portion of the steel strands.

[0023] Effects of the invention:

[0024] The present invention provides a helical spring with excellent dent resistance and corrosion fatigue resistance, a suspension device equipped with the helical spring, and a method for manufacturing the helical spring. Attached Figure Description

[0025] Figure 1 A cross-sectional schematic diagram of the suspension device according to the first embodiment is shown.

[0026] Figure 2 A side view of a helical spring according to the first embodiment is shown.

[0027] Figure 3 It shows along Figure 2 A cross-sectional schematic diagram of the helical spring on line III-III.

[0028] Figure 4 It shows along Figure 2 A cross-sectional schematic diagram of the helical spring along line IV-IV.

[0029] Figure 5 An example of the internal stiffness distribution of the steel strand of a helical spring is shown.

[0030] Figure 6 An example of the hardness distribution on the surface of a steel strand is shown.

[0031] Figure 7 A flowchart illustrating an example of a method for manufacturing a helical spring is shown.

[0032] Figure 8 An example of localized softening treatment of the stranded wire during the manufacturing process of a helical spring is shown.

[0033] Figure 9 This is a side view of the helical spring according to the second embodiment.

[0034] Figure 10 This is a cross-sectional schematic diagram of the helical spring according to the third embodiment.

[0035] Symbol Explanation

[0036] 1. Helical spring, 2. Steel strand, 3. Shock absorber, 4. First spring seat, 5. Second spring seat, 10. Effective part, 11. First seat winding part, 12. Second seat winding part, 20. Surface of steel strand, 100. Suspension device, A1. First area, A2. Second area, L1. First layer, L2. Second layer. Detailed Implementation

[0037] Some embodiments will now be described with reference to the accompanying drawings. In each embodiment, a MacPherson strut suspension, a coil spring for said suspension, and a method of manufacturing said coil spring are illustrated. The coil springs disclosed in each embodiment can be used in other types of suspension or in applications other than suspension.

[0038] [First Embodiment]

[0039] Figure 1 This is a schematic cross-sectional view of the suspension device 100 according to the first embodiment. The suspension device 100 has a coil spring 1 for vehicle suspension. The coil spring 1 has a steel strand 2 (metal wire) wound in a spiral shape. The steel strand 2 is made of, for example, spring steel.

[0040] The suspension device 100 also 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. A coil spring 1 is installed in a compressed state between the first spring seat 4 and the second spring seat 5 of the suspension device 100.

[0041] The shock absorber 3 has a cylinder 30 containing a fluid such as oil, a rod 31 inserted into the cylinder 30, a damping force generating mechanism located inside the cylinder 30, and a cover plate component 32 covering the sliding portion of the rod 31. The rod 31 can extend and retract relative to the cylinder 30 parallel to the axis X0 of the shock absorber 3. The damping force generating mechanism provides resistance to the movement of the rod 31.

[0042] The upper end of the shock absorber 3 is connected to the vehicle body 7 via a mounting insulator 6. The mounting insulator 6 has a vibration-damping rubber 60 and a support component 61 fixed to the vehicle body 7. The lower end of the shock absorber 3 is connected to the steering knuckle component 8 that supports the axle via a bracket 9. Figure 1 In the example, the axis X0 of the shock absorber 15 forms an acute angle θ0 with the vertical direction Z.

[0043] The helical spring 1 is installed in a compressed state between the first spring seat 4 and the second spring seat 5, elastically supporting the load applied from above, and extending or contracting within a predetermined deformation range (between full rebound and full bulge) according to the load size.

[0044] Figure 2 This is a schematic diagram of the helical spring 1 according to this embodiment. Figure 3 It is along Figure 2 A cross-sectional schematic diagram of the helical spring 1 on line III-III. Figure 4 It is along Figure 2 A cross-sectional schematic diagram of the helical spring 1 on line IV-IV.

[0045] like Figure 2 As shown, the helical spring 1 has an effective portion 10, a first winding portion 11, and a second winding portion 12. The first winding portion 11 is the portion that contacts the first spring seat 4. The second winding portion 12 is the portion that contacts the second spring seat 5. The effective portion 10 is the portion located between the first winding portion and the second winding portions 11 and 12.

[0046] In this embodiment, the first winding portion 11 includes not only a portion that is always in contact with 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 helical spring 1 is below a predetermined value, and a portion that contacts the first spring seat 4 when the compressive load applied to the helical spring 1 exceeds the predetermined value. Similarly, the second winding portion 12 includes not only a portion that is always in contact with 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 helical spring 1 is below the predetermined value, and a portion that contacts the second spring seat 5 when the compressive load applied to the helical spring 1 exceeds the predetermined value. For example, the first winding portion 11 is located in a winding at a distance of 2a from the lower end of the steel strand 2, and the second winding portion 12 is located in a winding at a distance of 2b from the upper end of the steel strand 2.

[0047] In the effective portion 10, the steel strand 2 is wound several times around the coil axis X1. For example, the coil axis X1 is... Figure 1 The vertical direction Z shown forms an acute angle with the axis X0 of the shock absorber 3. For example... Figure 2 As shown, the direction parallel to the coil axis X1 is defined as the axial direction DX, and the direction centered on the coil axis X1 is defined as the radial direction DR.

[0048] like Figure 3 As shown, the surface 20 of the steel strand 2 is completely covered by the coating 21. As an example, the diameter R of the steel strand 2 is 10-15 mm, and the thickness of the coating 21 is 40 μm or more.

[0049] In this embodiment, the surface 20 of the steel strand 2 has a first region A1 and a second region A2, wherein the second region A2 is softer than the first region A1. Figure 2 In the example, region A2 is part of the first surrounding portion 11. The portion of surface 20 excluding region A2 is region A1.

[0050] In other words, in Figure 4 In at least a portion of the surface 20 of the first winding portion 11 shown, the hardness distribution in the circumferential direction Dθ around the axis X2 of the steel strand 2 is not uniform. However, in the surface 20 of the second winding portion 12 and the effective portion 10, the hardness is uniformly distributed in the entire circumferential direction Dθ.

[0051] like Figure 3 As shown, the steel strand 2 in the effective portion 10 is entirely formed by the first layer L1. The first region A1 corresponds to the surface of the first layer L1. The second winding portion 12 is also entirely formed by the first layer L1.

[0052] like Figure 4As shown, in addition to the first layer L1, the first winding portion 11 also has 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. Figure 4 In the example shown, the proportion of the first layer L1 in the cross-section of the steel strand 2 is greater than that of the second layer L2. The axis X2 of the steel strand 2 passes through the first layer L1.

[0053] like Figure 4 As shown, four base points are defined on the surface 20 of the steel strand 2: the first base point P1, the second base point P2, the third base point P3, and the fourth base point P4. The first base point P1 is the position on the surface 20 closest to the effective portion 10, located above the axial direction DX. The second base point P2 is the position on the surface 20 furthest from the coil axis X1 in the radial direction DR. The third base point P3 is the position furthest from the effective portion 10 in the axial direction DX (opposite to the first base point P1, sandwiching the axis X2). The fourth base point P4 is the position on the radial direction DR closest to the coil axis X1 (opposite to the second base point P2, sandwiching the axis X2). The first base points P1, P2, P3, and P4 are spaced 90° apart in the circumferential direction Dθ.

[0054] In other words, the first base point P1 is the effective portion 10 side of a pair of intersections between the first center line CL1, which passes through axis X2 and is parallel to coil axis X1, and surface 20. The second base point P2 is the intersection point on the side furthest from coil axis X1 among a pair of intersections between the second center line CL2, which passes through axis X2, is parallel to the radial direction DR, and surface 20. The third base point P3 is the intersection point opposite to the first base point P1 among a pair of intersections between the first center line CL1 and surface 20. The fourth base point P4 is the intersection point opposite to the second base point P2 among a pair of intersections between the second center line CL2 and surface 20.

[0055] In the first surrounding portion 11, the first region A1 and the second region A2 are aligned in the circumferential direction Dθ. In this embodiment, the 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 the circumferential direction Dθ from the fourth base point P4 (boundary B2) to the boundary B1, including the first base point P1 and the second base point P2. The second region A2 is formed in the circumferential direction Dθ from the boundary B1 to the fourth base point P4 (boundary B2), including the third base point P3.

[0056] Therefore, in Figure 4In the cross-section, the length of region A2 in the circumferential direction Dθ is shorter than the length of region A1 in the circumferential direction Dθ. Region A2 is formed on the surface 20 of the steel strand 2, and is located lower in the axial direction DX, closer to the inner side of the helical spring 1. The third base point P3 and its adjacent region correspond to the seat surface SF, which is always or when the helical spring 1 is compressed. Figure 1 The first spring seat 4 is in contact as shown. In other words, the second region A2 is at least partially formed on the seat surface SF of the first seat winding portion 11.

[0057] More specifically, if we consider the first base point P1 as the 0 o'clock direction, the second base point P2 as the 3 o'clock direction, the third base point P3 as the 6 o'clock direction, and the fourth base point P4 as the 9 o'clock direction, then the second region A2 is formed within the range of 4 o'clock to 9 o'clock.

[0058] The area forming the second region A2 is not limited to the range from point 4 to point 9. For example, the second region A2 can be formed such that its center C lies within 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 lies within the range from the third base point P3 to the fourth base point P4 in the circumferential direction Dθ.

[0059] The first winding section 11 does not necessarily have it in all positions. Figure 4 The cross-sectional structure shown. In Figure 2 In the example, the second region A2 is not provided in the portion 11a that maintains a certain distance from end 2a. For example, when the coil spring 1 is installed in the suspension device 100, regardless of the compression state of the coil spring 1, the portion 11a is always the part where the coil spring 1 contacts the first spring seat 4. From another perspective, in Figure 2 In the example, the second region A2 is located in the part that is in contact with or away from the first spring seat 4, depending on the load applied to the helical spring 1.

[0060] Preferably, the second region A2 is formed at a distance of at least 0.4 windings and no more than 0.9 windings from the end 2a. However, the second region A2 may also be larger or smaller than this range. The second region A2 may also be formed continuously within a certain range starting from the end 2a.

[0061] exist Figure 4 In the example, the thickness t of the second layer L2 is greatest at the center C. The thickness t gradually decreases from the center C towards the boundaries B1 and B2. For example, the thickness t at the center C is 0.6 mm or greater, preferably 1.0 mm or greater. Relative to the diameter R of the steel strand 2, the thickness t at the center C is, for example, greater than 2% and less than 8% of the diameter R.

[0062] Figure 5 It is steel strand 2 along Figure 4 Example diagram of the hardness distribution at center C. In this diagram, the horizontal axis represents the distance from the surface 20 of the steel strand 2 [mm], and the vertical axis represents the Rockwell hardness [HRC].

[0063] exist Figure 5 In the example, the hardness of the first layer L1 remains almost constant. In the second layer L2, the hardness is lowest at surface 20 (region A2), gradually increasing with distance from surface 20, reaching the hardness of the first layer L1 at thickness t. Therefore, the second layer L2 is generally softer than the first layer L1. The hardness of the second layer L2 varies in a gradient with distance from surface 20.

[0064] Figure 6 This is an example diagram of the hardness distribution of surface 20 along the circumferential direction Dθ. In this diagram, the horizontal axis represents the position of surface 20 along the circumferential direction Dθ [mm], and the vertical axis represents the Vickers hardness [HV].

[0065] exist Figure 6 In the example, the hardness of region A1 remains almost constant. In region A2, the hardness is lowest near the center C. Between center C and boundary B1, and between center C and boundary B2, the hardness gradually increases with distance from center C, reaching the hardness of region A1 at boundaries B1 and B2. Therefore, region A2 is generally softer than region A1. The hardness of region A2 exhibits a gradient change with a minimum value at center C.

[0066] Figure 7 A flowchart example of a method for manufacturing a helical spring 1 is shown. First, steel strand 2 is wound into a helical shape using a winding machine, and then the wound portion is cut using a cutting machine (step S1). At this point, the surface 20 of the steel strand 2 has a uniform hardness throughout. Then, the surface 20 is locally softened to form a second region A2 (step S2). The following will refer to... Figure 8 A detailed introduction to the local softening process.

[0067] After local softening treatment, the steel strand 2 is subjected to electrical annealing (step S3). In this electrical annealing, the steel strand 2 is heated to a temperature range of 400-500°C for one minute or less. After electrical annealing, the steel strand 2 is heat-set, and during the heat-setting process, an overload is applied to the steel strand 2 while it is being heated (step S4).

[0068] Then, the steel strand 2 is shot-peened (step S5) and further pretreated (step S6). Afterward, an integral coating 21 is formed on the surface 20 of the steel strand 2 (step S7). Local softening treatment can be performed before shot peening or after electrical annealing or heat setting.

[0069] Figure 8 An example of localized softening is shown. In this embodiment, a laser device 200 is used for localized softening. For example, the laser device 200 is a semiconductor laser, but is not limited to this example.

[0070] The laser device 200 irradiates the region where the second region A2 should be formed in the first winding portion 11 with a laser beam LZ. For example... Figure 4 As shown, when the second region A2 is formed within the range of 4 to 9 o'clock, the irradiation axis XL of the laser beam LZ is tilted relative to the axial direction DX. The position where the irradiation axis XL intersects with surface 20 corresponds to... Figure 4 The center C is shown in the diagram.

[0071] For example, when irradiating the laser beam LZ, the position of the laser device 200 can be fixed, while the steel strand 2 can rotate around the coil axis X1. In this case, as the steel strand 2 rotates, it can move in the axial direction DX, thus keeping the distance between the portion of the steel strand 2 irradiated by the laser beam LZ and the laser device 200 constant. This can suppress the shift of the laser beam LZ focus. Another example is that the steel strand 2 can be fixed, while the laser device 200 can be moved.

[0072] The laser beam LZ heats the steel strand 2. This heating creates a heat-affected zone (HAZ) in the steel strand 2. When the HAZ cools, a second layer L2 with a lower hardness than the original steel strand 2 is formed.

[0073] In one example, the portion of the steel strand 2 irradiated by the laser beam LZ is heated to a temperature range below the austenitization initiation temperature. Preferably, the portion from the surface 20 to a depth of at least 0.6 mm (or from the surface 20 to a depth of 2% to 8% of the diameter R) is heated to the aforementioned temperature range at the location corresponding to the irradiation axis XL.

[0074] If the temperature of the steel strand 2 becomes too high during the heating process, a portion of the steel strand 2 will be hardened by quenching, resulting in a higher hardness than before laser beam LZ irradiation. To avoid this hardening, the output power [kW] and irradiation time [seconds] of the laser beam LZ must be adjusted.

[0075] Figure 7 and Figure 8 The manufacturing method described is just one example. The helical spring 1 can be manufactured by various other methods.

[0076] In the above embodiment, in the first winding portion 11 of the helical spring 1, the surface 20 of the steel strand 2 has a first region A1 and a second region A2. The second region A2 is softer than the first region A1, so even if corrosion pits appear in the second region A2, these pits are unlikely to form cracks on the steel strand 2. Even if cracks do appear, their development can be delayed. In other words, by providing the second region A2 in the first winding portion 11, the corrosion fatigue resistance of the first winding portion 11 can be improved.

[0077] If the second region A2 (second layer L2) is formed entirely relative to the steel strand 2, the anti-dent performance of the helical spring 1 will be reduced. Conversely, in this embodiment, the second region A2 is not formed in the effective portion 10. Therefore, the anti-dent performance can be well maintained in the effective portion 10. Since the first winding portion 11 is the portion where the applied stress is lower than that of the effective portion 10, the overall anti-dent performance of the helical spring 1 is not affected even if the second region A2 is provided in the first winding portion 11.

[0078] The first winding portion 11 is the portion that contacts the first spring seat 4 located below the first winding portion 11. Therefore, if foreign objects such as sand enter between the first winding portion 11 and the first spring seat 4, the suspension device 100 may be damaged during use, and corrosion pits may appear on the first winding portion 11. In contrast, in this embodiment, the second region A2 is provided in the region including the seat surface SF of the first winding portion 11. Therefore, even if foreign objects enter between the first winding portion 11 and the first spring seat 4 and cause corrosion pits, cracks caused by such corrosion pits can be suppressed.

[0079] Furthermore, the aforementioned foreign matter often enters the area below the portion of the first winding portion 11 that contacts or is away from the first spring seat 4. Therefore, if a second region A2 is formed locally in this portion, it is possible to effectively improve the corrosion fatigue resistance of the helical spring 1 while maintaining its anti-dent performance. In this regard, the area from the end 2a to 0.4 windings and less than 0.9 windings is a region where corrosion pits caused by foreign matter are prone to occur. Moreover, compared to the area from the end 2a to 0.4 windings, this area is more susceptible to stress when compressing the helical spring 1. Therefore, as mentioned above... Figure 2 The second region A2 is preferably formed within a range of at least 0.4 windings and less than 0.9 windings from the end 2a.

[0080] On the surface 20 of the steel strand 2, the portion located on the side of the coil axis X1 (inside the helical spring 1) is susceptible to stress and corrosion fatigue. Therefore, as mentioned above... Figure 4 As stated, the second region A2 is preferably close to the inner side of the helical spring 1.

[0081] This embodiment illustrates the use of a laser beam for localized softening. However, localized softening can also be performed using other methods, such as high-frequency heating. However, as... Figure 8 As shown, when using a laser beam for localized softening, the formation time of region A2 is shorter than that of heating the steel strand 2 using other methods. If other methods (such as high-frequency heating) are used to heat the steel strand 2, it may be difficult to locally increase its temperature. In this respect, when using a laser beam, it is possible to precisely heat specific portions of the steel strand 2.

[0082] In addition to the above, this embodiment can also achieve various other suitable effects.

[0083] [Second Embodiment]

[0084] In the second embodiment, other structures applicable to the helical spring 1 are described. The configuration of the helical spring 1 and the suspension device 100, unless otherwise specifically mentioned, is the same as in the first embodiment.

[0085] Figure 9 A side view of the helical spring 1 according to the second embodiment is shown. Figure 9 As shown, in this embodiment, a second region A2 (hereinafter referred to as the second region A2a) is also formed within the surface 20 of the steel strand 2 in the effective portion 10, which can contact the second winding portion 12 during compression.

[0086] exist Figure 9 In the example, the second region A2a is not formed in the portion 12a at a certain distance from the end 2b. Specifically, in Figure 9 In the example, the second region A2a is formed within a range of one winding or more but less than two windings from the end 2b. As another example, the second region A2a may extend to the second winding portion 12. Furthermore, the second region A2a may extend to the end 2b.

[0087] The cross-sectional structure of part of region A2a and Figure 4 The cross-sectional structures shown are similar, vertically inverted. However, the extent of the second region A2a formed in the circumferential direction Dθ can be varied depending on the circumstances. Figure 9 In the example, the second region A2a is formed on the surface 20 opposite to the second winding portion 12 of the effective portion 10. This region is the part of the helical spring 1 that comes into contact with the second winding portion 12 during compression. Even if corrosion pits appear on the steel strand 2 due to this contact, the second region A2a prevents them from developing into cracks.

[0088] [Third Embodiment]

[0089] In the third embodiment, a further configuration that the helical spring 1 can adopt is described. The configurations of the helical spring 1 and the suspension device 100, unless otherwise specifically mentioned, are the same as in the first embodiment.

[0090] Figure 10 A cross-sectional view of the helical spring 1 according to the third embodiment is shown. For example, this cross-section corresponds to a portion of the first winding portion 11, but the same structure can also be applied to the second winding portion 12.

[0091] exist Figure 10 In the example, the second layer L2 covers the first layer L1 along the entire circumferential direction Dθ. In other words, the surface 20 of the steel strand 2 is formed by the second region A2 along the entire circumferential direction. Figure 10 In the example, the thickness of the second layer L2 remains constant in the circumferential direction Dθ. However, the thickness of the second layer L2 can vary locally.

[0092] Such a second region A2, for example as in the first embodiment, is formed within a range of at least 0.4 windings and no more than 0.9 windings from the end 2a. There may be a portion between the second region A2 and the end 2a where the second region A2 is not formed. Furthermore, the second region A2 can be formed continuously within a certain range starting from the end 2a.

[0093] and Figure 3 As in the example, the effective portion 10 is entirely formed by the first layer L1. In other words, the surface 20 in the effective portion 10 is entirely located in the first region A1.

[0094] Even with the structure of this embodiment, the corrosion fatigue resistance of the first winding portion 11 and the second winding portion 12 can be improved. Furthermore, by forming the effective portion 10 entirely from the first layer L1, the helical spring 1 can possess excellent anti-dentation properties.

[0095] The first to third embodiments described above do not limit the scope of the invention to the configurations disclosed in these embodiments. The invention can be implemented by modifying the configurations disclosed in the embodiments into various forms.

[0096] For example, in the first and second embodiments, a second region A2 may be formed on the surface 20 of the first winding portion 11 opposite to the effective portion 10. In the second winding portion 12, the second region A2 may be formed at the portion of the second winding portion 12 that contacts or separates from the second spring seat 5, depending on the load applied to the helical spring 1. Furthermore, when the second region A2 is formed in the second winding portion 12, the second region A2 may not be formed in the first winding portion 11. The second region A2 may extend into a portion of the effective portion 10.

[0097] The steel strand 2 may have a multi-layer structure, including other layers with different hardness than the first layer L1 and the second layer L2. For example, if the other layers extend to the surface 20 of the strand 2, additional regions with different hardness than the first region A1 and the second region A2 may be formed on the surface 20.

[0098] In each embodiment, a helical spring 1 with steel strand 2 wound in a cylindrical shape is disclosed. However, the helical spring 1 may also have other shapes, such as a barrel shape with a diameter decreasing toward the first and second winding portions 11 and 12.

Claims

1. A helical spring formed from steel strand wound in a spiral shape, having a seat portion and an effective portion, wherein the surface of the steel strand in the seat portion has: Area 1, and The second region is softer than the first region and is aligned with the first region in a circumferential direction centered on the axis of the steel strand. The surface of the steel strand in the effective portion has the first region along the entire circumferential direction.

2. The helical spring according to claim 1, wherein the steel strand comprises The first layer, which includes the first region, and The second layer, which includes the second region, is softer than the first layer. The axis of the steel strand passes through the first layer in the winding section.

3. The helical spring according to claim 1, wherein the second region is at least partially formed on the seat surface of the seat winding portion.

4. The helical spring according to claim 1, wherein the second region is formed at a position at least 0.4 windings and no more than 0.9 windings from the end of the steel strand of the seat winding portion.

5. The helical spring according to claim 1, wherein the thickness of the second region is at least 0.6 mm.

6. The helical spring according to claim 1, wherein, on the cross-section of the steel strand including the first region and the second region, the surface of the steel strand has, The first base point is the intersection point on one side of the effective portion of a pair of intersection points where a first center line passing through the axis of the steel strand and parallel to the coil axis intersects with the surface of the steel strand. The second base point is the intersection point on the side furthest from the coil axis among a pair of intersection points where a second center line passing through the axis of the steel strand and parallel to the radial direction centered on the coil axis intersects the surface of the steel strand. The third base point is the intersection point opposite to the first base point among a pair of intersection points where the first center line intersects the surface of the steel strand. The fourth base point is the intersection point opposite to the second base point among a pair of intersection points where the second center line intersects the surface of the steel strand. The center of the second region is located between the second and fourth base points in the circumferential direction that passes through the first, second, third, and fourth base points in sequence.

7. The helical spring according to claim 6, wherein the center of the second region is located in the circumferential direction between the third base point and the fourth base point.

8. A suspension device, comprising First spring seat, The second spring seat is vertically disposed above the first spring seat. A helical spring, which is a helical spring according to any one of claims 1 to 7, is located between the first spring seat and the second spring seat.

9. A method for manufacturing a helical spring, comprising winding steel strands into a helical shape to form a helical spring having a seat portion and an effective portion. A laser beam is used to locally irradiate at least a portion of the surface of the steel strand in the winding portion, softening a portion of the steel strand and thereby forming a first region and a second region on the surface of the steel strand in the winding portion. The second region is softer than the first region and is aligned with the first region in a circumferential direction centered on the axis of the steel strand. The surface of the steel strand in the effective portion has the first region along the entire circumferential direction.

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