Coil spring, suspension system, and method for manufacturing a coil spring

Abstract

To provide a coil spring with excellent fatigue resistance and corrosion fatigue resistance.SOLUTION: A coil spring according to one embodiment is formed from a wire wound in a spiral manner, and has a seat turn part and an effective part. The surface of the wire in the seat turn part has a first region, and a second region that is softer than the first region. The first region is formed on an outer diameter side of the wire, and the second region is formed on an inner diameter side of the wire.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a coil spring, a suspension device, and a method for manufacturing a coil spring.

Background Art

[0002] For example, in a suspension device of a vehicle such as an automobile, a coil spring is used. This type of coil spring is required to have good sag resistance and corrosion fatigue resistance.

[0003] If the hardness of the wire forming the coil spring is increased overall, an improvement in sag resistance can be expected. However, in this case, for example, if a part of the coating film applied to the wire peels off and corrosion pits occur on the surface of the wire, cracks may occur in the wire starting from these corrosion pits. If the hardness of the wire is high, the progress of the cracks is also fast, and there is a possibility of premature breakage of the coil spring. On the other hand, if the hardness of the wire is low overall, the sag resistance decreases.

[0004] As examples of studies on the sag resistance and corrosion fatigue resistance of coil springs, Patent Documents 1, 2, and 3 are known. In these documents, attempts are made to improve the sag resistance and corrosion fatigue resistance by softening a part of the inside or surface of the wire (spring steel).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] Even considering Patent Documents 1, 2, and 3, there is still room for improvement regarding the sag resistance and corrosion fatigue resistance of coil springs. Therefore, the purpose of this disclosure is to provide a coil spring with excellent sag resistance and corrosion fatigue resistance, a suspension system equipped with the coil spring, and a method for manufacturing the coil spring. [Means for solving the problem]

[0007] A coil spring according to one embodiment is formed from spirally wound wires and has a seated portion and an effective portion. The surface of the wires in the seated portion has a first region and a second region that is softer than the first region.

[0008] For example, the first region is formed on the outer diameter side of the wire, and the second region is formed on the inner diameter side of the wire.

[0009] In one embodiment, the surface of the wire in the effective portion is Throughout the entire circumference It is harder than the second region mentioned above.

[0010] The wire comprises a first layer including the first region and a second layer including the second region and being softer than the first layer. Preferably, the axis of the wire passes through the first layer in the winding portion.

[0011] For example, the second region is formed in at least a portion of the area from the end of the wire to 1.2 turns in the winding portion. Preferably, the second region has a thickness of 0.6 mm or more.

[0012] For example, the surface of the wire in the effective portion has the first region around its entire circumference.

[0013] A suspension device according to one embodiment comprises a first spring seat, a second spring seat, and the coil spring disposed between the first spring seat and the second spring seat.

[0014] In the method for manufacturing a coil spring according to an embodiment, a coil spring having a seat winding portion and an effective portion is formed by winding a wire in a spiral shape, a pair of electrodes are connected to the spirally wound wire, and an alternating current is passed between the pair of electrodes to heat a part of the seat winding portion, thereby forming a first region on the surface of the wire in the seat winding portion and forming a second region softer than the first region on the surface on the inner diameter side of the wire in the seat winding portion.

Advantages of the Invention

[0015] According to the present disclosure, it is possible to provide a coil spring excellent in sag resistance and corrosion fatigue resistance, a suspension device including the coil spring, and a method for manufacturing the coil spring.

Brief Description of the Drawings

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

Embodiments for Carrying Out the Invention

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

[0018] [First Embodiment] FIG. 1 is a schematic cross-sectional view of a suspension device 100 according to the first embodiment. This suspension device 100 includes a coil spring 1 for vehicle suspension. The coil spring 1 includes a wire 2 wound in a spiral shape. The wire 2 is formed 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] The shock absorber 3 includes a cylinder 30 in which a fluid such as oil is accommodated, a rod 31 inserted into the cylinder 30, a damping force generating mechanism provided inside the cylinder 30, and a cover member 32 that covers the sliding portion of the rod 31. The rod 31 can extend and contract parallel to the axis X0 of the shock absorber 3 with respect to the cylinder 30. The damping force generating mechanism provides resistance to the movement of the rod 31.

[0021] The upper end portion of the shock absorber 3 is attached to the vehicle body 7 via a mount insulator 6. The mount insulator 6 includes a vibration isolator rubber 60 and a support member 61 fixed to the vehicle body 7. The lower end portion of the shock absorber 3 is attached to a knuckle member 8 that supports an axle via a bracket 9. In the example of FIG. 1, the 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 supporting the load applied from above, and expanding and contracting within a predetermined range of deflection (between full rebound and full bump) depending on the magnitude of the load.

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

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

[0025] In this embodiment, the first spring seat portion 11 includes not only a portion that is always in contact with the first spring seat 4, but also a portion that separates from the first spring seat 4 when the compressive load applied to the coil spring 1 is less than a predetermined value, and contacts the first spring seat 4 when the compressive load applied to the coil spring 1 exceeds the predetermined value. Similarly, the second spring seat portion 12 includes not only a portion that is always in contact with the second spring seat 5, but also a portion that separates from the second spring seat 5 when the compressive load applied to the coil spring 1 is less than a predetermined value, and contacts the second spring seat 5 when the compressive load applied to the coil spring 1 exceeds the predetermined value. As an example, the first spring seat portion 11 is in the range of 1.2 turns from the lower end 2a of the wire strand 2, and the second spring seat portion 12 is in the range of 1.2 turns from the upper end 2b of the wire strand 2.

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

[0027] As shown in Figure 3, the entire surface 20 of the wire strand 2 is covered with a coating 21. For example, the diameter R of the wire strand 2 is 8 to 18 mm, and the thickness of the coating 21 is 40 μm or more.

[0028] In this embodiment, the surface 20 of the wire strand 2 has a first region A1 and a second region A2 (the dotted portion in Figure 2) which is softer than the first region A1. In the example in Figure 2, the second region A2 is provided on a part of the first winding portion 11. The portion of the surface 20 excluding the second region A2 is the first region A1.

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

[0030] As shown in Figure 3, the strands 2 in the effective portion 10 are 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.

[0031] As shown in Figure 4, the first winding portion 11 includes a first layer L1 and a second layer L2 which is softer than the first layer L1. The second region A2 corresponds to the surface of the second layer L2. In the example in Figure 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 Figure 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 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 (on the opposite side of the axis X2 from the first base point P1). The fourth base point P4 is the position closest to the coil axis X1 in the radial direction DR (on the opposite side of the axis X2 from the second base point P2). The first base point P1, the second base point P2, the third base point P3, and the fourth base point P4 are arranged sequentially at 90-degree intervals in the circumferential direction Dθ.

[0033] From another perspective, the first base point P1 is the intersection on the effective portion 10 side of a pair of intersections where the first center line CL1, which passes through axis X2 and is parallel to the coil axis X1, intersects the surface 20. The second base point P2 is the intersection on the side furthest from the coil axis X1 of a pair of intersections where the second center line CL2, which passes through axis X2 and is parallel to the radial direction DR, intersects the surface 20. The third base point P3 is the intersection on the opposite side of the first base point P1 of a pair of intersections where the first center line CL1 intersects the surface 20. The fourth base point P4 is the intersection on the opposite side of the second base point P2 of a pair of intersections where the second center line CL2 intersects the surface 20.

[0034] In the first winding section 11, the first region A1 and the second region A2 are aligned in the circumferential direction Dθ. In this embodiment, the first region A1 is formed on the outer diameter side of the wire 2, and the second region A2 is formed on the inner diameter side of the wire 2. 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 between the first base point P1 and the second base point P2.

[0035] The first region A1 is formed in the circumferential direction Dθ from boundary B2 to boundary B1 and includes the second base point P2. The second region A2 is formed in the circumferential direction Dθ from boundary B1 to boundary B2 and includes the first base point P1, the third base point P3, and the fourth base point P4.

[0036] Thus, in the cross-section shown in Figure 4, the length of the second region A2 in the circumferential direction Dθ is longer than the length of the first region A1 in the circumferential direction Dθ. In other words, the second region A2 is formed over a wider area in the circumferential direction Dθ than the first region A1.

[0037] Furthermore, the third base point P3 and the region near it correspond to the seating surface SF that contacts the first spring seat 4 and the coil spring 1 under normal conditions or when the coil spring 1 is compressed, as shown in Figure 1. In other words, the second region A2 extends to at least a part of the seating surface SF of the first seat winding portion 11.

[0038] More specifically, if we consider the first base point P1 as 0 o'clock, the second base point P2 as 3 o'clock, the third base point P3 as 6 o'clock, and the fourth base point P4 as 9 o'clock, then the second region A2 is formed in a range of 240° clockwise from 5 o'clock to 1 o'clock. The first region A1 is formed in a range of 120° clockwise from 1 o'clock to 5 o'clock.

[0039] The range in which the second region A2 is formed is not limited to the range from 5 o'clock to 1 o'clock clockwise. For example, the second region A2 may be formed such that its center in the circumferential direction Dθ is located in the range from the third base point P3 to the first base point P1. In the example in Figure 4, this center coincides with the fourth base point P4. In one example, the second region A2 may be formed such that boundary B1 is located in the range from 5 o'clock to 6 o'clock clockwise, and boundary B2 is located in the range from 12 o'clock to 1 o'clock clockwise.

[0040] The second region A2 is preferably formed in at least a portion of the range from the terminal 2a to 1.2 turns in the direction in which the wire 2 extends spirally (along the axis X2). In the example in Figure 2, the second region A2 is formed continuously from the terminal 2a over the entire range. As another example, the second region A2 does not have to be provided in a portion at a certain distance from the terminal 2a, for example, in a portion that is always in contact with the first spring seat 4 regardless of the compression state of the coil spring 1.

[0041] In the example shown in Figure 4, the thickness t of the second layer L2 is greatest at the center (second centerline CL2) in the circumferential direction Dθ. The thickness t gradually decreases from this center toward the boundaries B1 and B2. The maximum value of the thickness t 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 maximum value of the thickness t is, for example, 2% or more and 8% or less of the diameter R.

[0042] Figure 5 is a graph showing an example of the hardness distribution of the wire strand 2 along the second centerline CL2 in Figure 4. In this graph, the horizontal axis represents the distance [mm] from the surface 20 of the wire strand 2, and the vertical axis represents the Rockwell hardness [HRC].

[0043] In the example shown in Figure 5, the hardness of the first layer L1 is almost constant. In the second layer L2, the hardness is lowest at the surface 20 (second region A2), and the hardness gradually increases as you move away from the surface 20, reaching the same hardness as the first layer L1 at 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 depending on the distance from the surface 20.

[0044] Figure 6 is a graph showing an example of the hardness distribution of surface 20 in the circumferential direction Dθ. In this graph, the horizontal axis represents the position [mm] in the circumferential direction Dθ on surface 20, and the vertical axis represents the Vickers hardness [HV].

[0045] In the example in Figure 6, the hardness of the first region A1 is almost constant. In the second region A2, the hardness is smallest near the second centerline CL2 in the circumferential direction Dθ. Between the second centerline CL2 and boundary B1, and between the second centerline CL2 and boundary B2, the hardness gradually increases as you move away from the second centerline CL2, reaching the hardness of the first region A1 at 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 second centerline CL2 being the minimum value.

[0046] Figure 7 is a flowchart showing an example of a method for manufacturing a coil spring 1. First, the wire strands 2 are wound spirally by a coiling machine, and this wound portion is cut by a cutter (step S1). At this point, the surface 20 of the wire strands 2 has the same hardness throughout. Next, a local softening treatment is performed on the surface 20 to form a second region A2 (step S2). Details of the local softening treatment will be described later with reference to Figure 8.

[0047] After local softening treatment, the wire strand 2 is subjected to electro-annealing (step S3). In this electro-annealing, the wire strand 2 is heated for less than 1 minute at a temperature range of, for example, 400-500°C. After electro-annealing, while the wire strand 2 is still heated, it is subjected to hot setting by applying an overload (step S4).

[0048] Next, the wire strands 2 are subjected to shot peening (step S5), and then pre-setting (step S6). After that, a coating film 21 is formed on the entire surface 20 of the wire strands 2 (step S7). Note that the local softening treatment may be performed before shot peening, or after electrical annealing or hot setting.

[0049] Figure 8 shows an example of localized softening treatment. In this embodiment, an energizing device 200 for high-frequency current heating is used for localized softening treatment.

[0050] The energizing device 200 comprises a power supply PS, a first electrode E1, and a second electrode E2. The power supply PS generates a high-frequency alternating current. The first electrode E1 and the second electrode E2 are connected to the power supply PS by wiring.

[0051] For electrical heating, the first electrode E1 and the second electrode E2 are connected to the coiled wire 2. In the example in Figure 8, the first electrode E1 is connected near terminal 2a. The second electrode E2 is connected at any position within the range from terminal 2a to 1.2 turns.

[0052] Subsequently, the energizing device 200 starts supplying power. At this time, the alternating current from the power supply PS flows through the circuit including the first electrode E1, the wire 2, and the second electrode E2.

[0053] When alternating current flows through the wire 2, the skin effect increases the current density on the surface 20 of the wire 2. Furthermore, after coiling, the current mainly flows towards the inner diameter of the wire 2. Therefore, the inner diameter portion of the surface 20 of the wire 2 is preferentially heated.

[0054] In one example, when an alternating current flows, the inner diameter portion of the wire 2 is heated to a temperature range below the austenitization start temperature. Near the fourth base point P4 shown in Figure 4, it is preferable that the portion from the surface 20 to a depth of at least 0.6 mm (or the portion from the surface 20 to a depth of 2% or more and 8% or less of the diameter R) is heated to the above temperature range.

[0055] This heating process creates a heat-affected zone (HAZ) in the wire 2. The HAZ is formed in an area including, for example, the first base point P1, the third base point P3, and the fourth base point P4 shown in Figure 4, and, like the second layer L2, has the greatest thickness near the fourth base point P4. When the HAZ is air-cooled, a second layer L2 is formed that is less hard than the original wire 2.

[0056] Furthermore, if the temperature of the wire 2 is too high during heating, a portion of the wire 2 may harden due to quenching, increasing its hardness compared to before electrical heating. Also, if the frequency of the alternating current is too low or the energizing time is too long, the entire surface 20 may soften, or the second layer L2 may extend to the vicinity of the axis X2 of the wire 2.

[0057] Considering these factors, the frequency of the alternating current is preferably a high frequency of 1 kHz or higher, and even more preferably 100 kHz or higher. The frequency of the alternating current may be set in an even higher range of 200 kHz or higher. Furthermore, the energizing time of the alternating current is preferably 5 seconds or less, and in one example it is 0.5 seconds.

[0058] The manufacturing methods described using Figures 7 and 8 are merely illustrative examples. The coil spring 1 can be manufactured by various other methods.

[0059] In this embodiment described above, the surface 20 of the wire strands 2 in the first seat winding portion 11 of the coil spring 1 has a first region A1 and a second region A2. Since the second region A2 is softer than the first region A1, even if a corrosion pit occurs in the second region A2, this corrosion pit is less likely to develop into a crack in the wire strands 2. Furthermore, even if a crack does occur, its progression can be slowed down. In other words, by providing the second region A2 in the first seat winding portion 11, the corrosion fatigue resistance of the first seat winding portion 11 is improved.

[0060] If a second region A2 (second layer L2) is formed on the entire strand 2, the sag resistance of the coil spring 1 may decrease. In contrast, in this embodiment, the second region A2 is not formed on the effective portion 10. Therefore, good sag resistance can be maintained in the effective portion 10. Since the first seat winding portion 11 is a part with lower applied stress compared to the effective portion 10, even if a second region A2 is provided on the first seat winding portion 11, it will not significantly affect the overall sag resistance of the coil spring 1.

[0061] The first spring seat portion 11 is the part that contacts the first spring seat 4 located below it. Therefore, if foreign matter such as sand gets between the first spring seat portion 11 and the first spring seat 4, the coating 21 will be damaged during use of the suspension device 100, and corrosion pits are likely to form on the first spring seat portion 11. In contrast, in this embodiment, a second region A2 is provided in the area including the seat surface SF of the first spring seat portion 11. Therefore, even if foreign matter gets between the first spring seat portion 11 and the first spring seat 4 and corrosion pits form, cracks caused by these corrosion pits can be suppressed.

[0062] Furthermore, foreign matter like that described above tends to get trapped below the portion of the first spring seat 11 that comes into contact with or separates from the first spring seat 4. Therefore, by forming the second region A2 to include such a portion, it is possible to effectively improve corrosion fatigue resistance. As described above with reference to Figure 2, by forming the second region A2 in the range from at least terminal 2a to 1.2 turns, good corrosion fatigue resistance can be obtained while maintaining sag resistance.

[0063] Furthermore, stress is easily applied to the portion of the wire 2 surface 20 on the coil shaft X1 side (the inner diameter side of the coil spring 1), and corrosion fatigue is also likely to occur there. For this reason, as described above with reference to Figure 4, it is preferable to form the second region A2 on the inner diameter side of the coil spring 1.

[0064] Corrosion pits can occur not only on the seating surface SF (near the third base point P3) but also near the first base point P1. If the second region A2 is formed in a narrower area than the first region A1 in the circumferential direction Dθ, then both the first base point P1 and the third base point P3 cannot be covered by the second region A2. In contrast, in this embodiment, as shown in Figure 4, the second region A2 is formed in a wider area than the first region A1 in the circumferential direction Dθ. This makes it possible to further improve the corrosion fatigue resistance of the first seating portion 11 by, for example, forming the second region A2 to include both the first base point P1 and the third base point P3.

[0065] In the manufacturing method according to this embodiment, the second region A2 (second layer L2) is formed by energizing with a high-frequency alternating current. If energizing with a direct current or a low-frequency alternating current of about 50 Hz or 60 Hz were used, a heat-affected zone could be generated up to the vicinity of the axis X2 of the wire 2. As a result, the second layer L2 would be formed over a wide area inside the wire 2, potentially reducing the fatigue resistance of the first winding portion 11. In contrast, with energizing with a high-frequency alternating current, the skin effect described above limits the range in which the heat-affected zone occurs to the vicinity of the surface 20. As a result, as shown in Figure 4, the vicinity of the axis X2 remains as the hard first layer L1, and the fatigue resistance of the first winding portion 11 is increased.

[0066] Furthermore, in this embodiment, as shown in Figure 8, the wire strands 2 after coiling are subjected to electric heating. If electric heating were performed on the wire strands 2 before coiling, it would be extremely difficult to control the formation range of the second region A2 in the circumferential direction Dθ. In contrast, when electric heating is performed on the wire strands 2 after coiling, the inner diameter side of the wire strands 2 is mainly heated. Therefore, the second layer L2 and the second region A2 can be formed accurately on the inner diameter side. The range in which the second region A2 is formed in the direction in which the wire strands 2 extend spirally can also be easily controlled by the positions where the first electrode E1 and the second electrode E2 are applied.

[0067] Thus, by using electric heating as a method for forming the second region A2 (second layer L2) on the wire 2, various desirable effects can be obtained. However, this does not necessarily prevent the application of other methods such as laser heating or induction heating to the manufacturing of the coil spring 1 with the configuration described using Figures 2 to 6.

[0068] [Second Embodiment] In the second embodiment, other configurations applicable to the coil spring 1 are illustrated. The configuration of the coil spring 1 and the suspension system 100, unless otherwise specified, are the same as in the first embodiment.

[0069] Figure 9 is a schematic perspective view of the coil spring 1 according to the second embodiment. As shown in Figure 9, in this embodiment, a second region A2 (hereinafter referred to as the second region A2a) is also formed in the second seat winding portion 12.

[0070] The second region A2a is preferably formed in at least a portion of the range from the terminal 2b to 1.2 turns in the direction in which the wire 2 extends spirally. In the example in Figure 9, the second region A2a is formed continuously from the terminal 2b over the entire range. As another example, the second region A2a does not have to be provided in a portion at a certain distance from the terminal 2b, for example, in a portion that is always in contact with the second spring seat 5 regardless of the compression state of the coil spring 1.

[0071] The cross-sectional structure of the wire 2 including the second region A2a is the same as the cross-sectional structure shown in Figure 4. That is, the second region A2a is formed on the inner diameter side of the wire 2. Furthermore, in the second winding portion 12, the second region A2a is formed over a wider area in the circumferential direction Dθ than the first region A1.

[0072] The second region A2a can be formed by electrical heating in the local softening treatment (step S2) shown in Figure 7. The procedure for performing this electrical heating is the same as that described using Figure 8.

[0073] By forming the second region A2a as in this embodiment, corrosion fatigue resistance is improved in the second seat winding portion 12 as well. In addition, the same effects as in the first embodiment can be obtained from this embodiment.

[0074] The first and second embodiments described above do not limit the scope of the present invention to the configurations disclosed in these embodiments. The present invention can be implemented by modifying the configurations disclosed in each embodiment in various ways.

[0075] For example, a second region A2 may be formed over the entire circumference in the circumferential direction Dθ in at least a portion of the first and second winding portions 11 and 12. Furthermore, the second region A2 may extend to a portion of the effective portion 10.

[0076] The wire strand 2 may have a multilayer structure that further includes other layers having different hardness from the first layer L1 and the second layer L2. For example, if the other layers extend to the surface 20 of the wire strand 2, additional regions having different hardness from the first region A1 and the second region A2 may be formed on the surface 20.

[0077] In each embodiment, a coil spring 1 in which strands 2 are wound in a cylindrical shape is disclosed. However, the coil spring 1 may have other shapes, such as a barrel shape, in which the diameter decreases towards the first seat winding portion 11 and the second seat winding portion 12. [Explanation of Symbols]

[0078] 1... Coil spring, 2... Straight wire, 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 the straight wire, 100... Suspension device, A1... First region, A2... Second region, L1... First layer, L2... Second layer, 200... Current supply device.

Claims

1. A coil spring formed from spirally wound wires, having a seated coil portion and an effective portion, The surface of the wire in the aforementioned winding portion has a first region and a second region that is softer than the first region. The first region is formed on the outer diameter side of the wire, The second region is formed on the inner diameter side of the wire, The surface of the wire in the effective portion is harder than the second region over its entire circumference. Coil spring.

2. The aforementioned wire is A first layer including the first region, A second layer, which includes the second region and is softer than the first layer, Equipped with, The axis of the aforementioned wire passes through the first layer in the winding portion. The coil spring according to claim 1.

3. The second region is formed in at least a portion of the area from the end of the wire to 1.2 turns in the winding portion. The coil spring according to claim 1.

4. The second region has a thickness of 0.6 mm or more. The coil spring according to claim 1.

5. The surface of the wire in the effective portion has the first region around its entire circumference. The coil spring according to claim 1.

6. Having a first seat winding portion and a second seat winding portion located on the opposite side of the first seat winding portion, The first winding portion has a first region formed on the outer diameter side of the wire and a second region formed on the inner diameter side of the wire. The surface of the wire in the second winding portion is harder than the second region over its entire circumference. The coil spring according to claim 1.

7. Having a first seat winding portion and a second seat winding portion located on the opposite side of the first seat winding portion, Each of the first and second winding portions has a first region formed on the outer diameter side of the wire and a second region formed on the inner diameter side of the wire. The coil spring according to claim 1.

8. The first spring constellation and The second spring constellation and A coil spring according to any one of claims 1 to 7, disposed between the first spring seat and the second spring seat, A suspension system equipped with [a specific feature].

9. A coil spring having a base winding portion and an effective portion is formed by winding the wires in a spiral shape. A pair of electrodes are connected to the spirally wound strand, By passing an alternating current between the pair of electrodes, a portion of the winding portion is heated to form a first region on the outer diameter side surface of the wire in the winding portion, and a second region that is softer than the first region is formed on the inner diameter side surface of the wire in the winding portion. A method for manufacturing coil springs.

10. In the circumferential direction centered on the axis of the aforementioned wire, the second region is formed over a wider area than the first region. A method for manufacturing a coil spring according to claim 9.

Images