Ac electric heating apparatus and manufacturing method of coil spring

Abstract

To enable a good control of a heating temperature distribution of an element wiring of a coil spring.SOLUTION: An AC electric heating apparatus according to an embodiment comprises: a power supply that can supply an AC current; a first terminal that is attached to a first attachment position of a spiral-shaped element wiring of a coil spring; a second terminal that is attached to a second attachment position of the element wiring that is separated from the first attachment position in a winding direction of the element wiring; and a conductor that is arranged so as to be opposite to a heating object part positioned between the first and second attachment positions of the element wiring. In addition, by flowing an AC current to the element wiring via the first and second terminals, the heating object part is heated.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to an alternating current heating device and a method for manufacturing a coil spring.

Background Art

[0002] For example, coil springs are used in various devices such as vehicle suspension devices. In this type of coil spring, local heating of the wire may be required.

[0003] For example, Patent Documents 1, 2, and 3 disclose techniques for softening a part of the inside or surface of a wire (spring steel) for the purpose of improving the sag resistance and corrosion fatigue resistance of a coil spring. In order to soften a part of the coil spring in this way, it is necessary to locally heat the part.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] As one method of heating a coil spring, there is alternating current heating in which an alternating current is passed through a wire to generate heat. When locally changing characteristics such as the hardness of a wire using alternating current heating, it is necessary to control the heating temperature distribution (current density distribution) during energization of the wire. However, it has been difficult to accurately control such a heating temperature distribution with conventional techniques.

[0006] The present invention has been made based on such circumstances, and one of its objects is to provide an alternating current energization heating device capable of favorably controlling the heating temperature distribution of the wire of a coil spring and a method for manufacturing a coil spring.

Means for Solving the Problems

[0007] The alternating current energization heating device according to the embodiment includes a power source capable of supplying an alternating current, a first terminal attached to a first attachment position of the spiral wire of the coil spring, and a second terminal attached to a second attachment position of the wire separated from the first attachment position in the winding direction of the wire, and a conductor arranged to face a heating target portion located between the first attachment position and the second attachment position of the wire. Further, the alternating current energization heating device heats the heating target portion by flowing the alternating current through the wire via the first terminal and the second terminal.

[0008] The method for manufacturing a coil spring according to the embodiment includes forming a wire into a spiral shape around a coil axis, attaching a first terminal to a first attachment position of the wire, attaching a second terminal to a second attachment position of the wire separated from the first attachment position in the winding direction of the wire, arranging a conductor to face a heating target portion located between the first attachment position and the second attachment position of the wire, and heating the heating target portion by flowing an alternating current through the wire via the first terminal and the second terminal.

Advantages of the Invention

[0009] According to the present disclosure, for example, an alternating current energization heating device capable of favorably controlling the heating temperature distribution of the wire of a coil spring and a method for manufacturing a coil spring can be provided.

Brief Description of the Drawings

[0010]

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DETAILED DESCRIPTION OF THE INVENTION

[0011] Some embodiments will be described with reference to the drawings. In each embodiment, taking a MacPherson strut type suspension device and a coil spring used in the suspension device as an example, a manufacturing method of the coil spring and an AC energization heating device that can be used in the manufacturing method are illustrated. However, the AC energization heating device and the manufacturing method disclosed in each embodiment can also be applied to other types of coil springs.

[0012] [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 (wire) wound in a spiral shape. The wire 2 is formed of a metal material such as spring steel, for example.

[0013] 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.

[0014] The shock absorber 3 includes a cylinder 30 that houses a fluid such as oil, 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 expand and contract parallel to the axis X0 of the shock absorber 3 with respect to the cylinder 30. The damping force generating mechanism applies resistance to the movement of the rod 31.

[0015] The upper end of the shock absorber 3 is attached to the vehicle body 7 via a mount insulator 6. The mount insulator 6 includes a vibration-damping rubber 60 and a support member 61 fixed to the vehicle body 7. The lower end 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.

[0016] The coil spring 1 is attached 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 range of a predetermined amount of deflection (between full rebound and full bump) according to the magnitude of the load.

[0017] 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.

[0018] As shown in FIG. 2, the coil spring 1 has an effective portion 10, a first seat winding portion 11, and a second seat winding portion 12. The first seat winding portion 11 is a portion that can contact the first spring seat 4. The second seat winding portion 12 is a portion that can contact the second spring seat 5. The effective portion 10 is a portion located between the first seat winding portion 11 and the second seat winding portion 12.

[0019] In the present embodiment, the first seat winding portion 11 is not only a portion that always contacts the first spring seat 4, but also separates from the first spring seat 4 when the compressive load applied to the coil spring 1 is less than a predetermined value, and may include a portion that contacts the first spring seat 4 when the compressive load applied to the coil spring 1 exceeds the predetermined value.

[0020] Similarly, the second seat winding portion 12 is not only a portion that always contacts the second spring seat 5, but also separates from the second spring seat 5 when the compressive load applied to the coil spring 1 is less than a predetermined value, and may include a portion that contacts the second spring seat 5 when the compressive load applied to the coil spring 1 exceeds the predetermined value.

[0021] As an example, the first seat winding portion 11 is in the range of 1.2 turns from the lower terminal 2a of the wire 2. Also, the second seat winding portion 12 is in the range of 1.2 turns from the upper terminal 2b of the wire 2.

[0022] In the effective portion 10, the wire 2 is wound a plurality of 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 shown in FIG. 1 and the axis X0 of the shock absorber 3. 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. The first seat winding portion 11 and the second seat winding portion 12 are each aligned with the effective portion 10 in the axial direction DX.

[0023] As shown in FIG. 3, the surface 20 of the wire 2 may be entirely covered by a coating film 21. As an example, the diameter R of the wire 2 is 8 to 18 mm, and the thickness of the coating film 21 is 40 μm or more.

[0024] In this embodiment, the surface 20 of the strand 2 has a first region A1 and a second region A2 (the portion marked with a dot pattern in FIG. 2) 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 helical winding portion 11. Among the surface 20, the portion excluding the second region A2 is the first region A1.

[0025] That is, in at least a part of the surface 20 of the first helical winding portion 11, the hardness distribution in the circumferential direction Dθ centered on the axis X2 of the strand 2 shown in FIG. 4 is not uniform. On the other hand, in the surface 20 of the second helical winding portion 12 and the effective portion 10, the hardness distribution is substantially uniform over the entire circumference in the circumferential direction Dθ.

[0026] As shown in FIG. 3, the 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 helical winding portion 12 is also entirely formed by the first layer L1.

[0027] As shown in FIG. 4, the first helical winding portion 11 includes, in addition to the first layer L1, 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 ratio of the first layer L1 in the cross-sectional area of the strand 2 is larger than the ratio of the second layer L2 in the cross-sectional area of the strand 2. The axis X2 of the strand 2 passes through the first layer L1.

[0028] As shown in FIG. 4, a first position P1, a second position P2, a third position P3, and a fourth position P4 are defined on the surface 20 of the strand 2. The first position P1 is the position on the surface 20 that is farthest from the effective portion 10 in the axial direction DX. The second position P2 is the position on the surface 20 that is closest to the coil axis X1 in the radial direction DR. The third position P3 is the position on the surface 20 that is closest to the effective portion 10 in the axial direction DX (the position on the opposite side of the first position P1 across the axis X2). The fourth position P4 is the position on the surface 20 that is farthest from the coil axis X1 in the radial direction DR (the position on the opposite side of the second position P2 across the axis X2). The first position P1, the second position P2, the third position P3, and the fourth position P4 are arranged in order at 90-degree intervals in the circumferential direction Dθ.

[0029] From another perspective, the first position P1 is a position in contact with the seat surface SF that supports the coil spring 1. The seat surface SF is, for example, a part of the first spring seat 4 shown in FIG. 1. The second position P2 is one of a pair of intersection points where a second center line CL2 that is orthogonal to the first center line CL1 (a line orthogonal to the seat surface SF) at the first position P1 and passes through the axis X2 intersects the surface 20, and is on the inner diameter side (the side closer to the coil axis X1) of the coil spring 1. The third position P3 is one of a pair of intersection points where the first center line CL1 intersects the surface 20, and is on the side opposite to the first position P1 (the side closer to the effective part 10) across the axis X2. The fourth position P4 is one of a pair of intersection points where the second center line CL2 intersects the surface 20, and is on the outer diameter side (the side farther from the coil axis X1) of the coil spring 1. In the example of FIG. 4, the first center line CL1 is parallel to the coil axis X1, but this is not limited to this example.

[0030] In the first seat winding part 11, the first region A1 and the second region A2 are arranged side by side in the circumferential direction Dθ. In the present embodiment, the second region A2 is formed closer to the inner diameter and lower of the wire 2. The boundary B1 between the first region A1 and the second region A2 is between the fourth position P4 and the first position P1 in the circumferential direction Dθ. Also, the other boundary B2 between the first region A1 and the second region A2 is between the second position P2 and the third position P3 in the circumferential direction Dθ. Furthermore, the center C of the second region A2 in the circumferential direction Dθ is between the first position P1 and the second position P2 in the circumferential direction Dθ.

[0031] The second region A2 is formed in the range from the boundary B1 to the boundary B2 in the circumferential direction Dθ and includes the first position P1 and the second position P2. The first region A1 is formed in the range from the boundary B2 to the boundary B1 in the circumferential direction Dθ and includes the third position P3 and the fourth position P4.

[0032] In the example of FIG. 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. That is, in the circumferential direction Dθ, the second region A2 is formed in a narrower range than the first region A1. Not limited to this example, the second region A2 may be formed in a wider range than the first region A1 in the circumferential direction Dθ.

[0033] Note that the first position P1 and the region in its vicinity are always or when the coil spring 1 is compressed in contact with the first spring seat 4 (seat surface SF) shown in FIG. 1. That is, the second region A2 extends at least partially over a portion of the first seat winding portion 11 that can come into contact with the seat surface SF.

[0034] The second region A2 is preferably formed at least partially in the range from the terminal 2a to 1.2 turns in the winding direction DW shown in FIG. 2. The winding direction DW is the direction in which the wire 2 extends spirally around the coil axis X1 (the direction along the axis X2). In the example of FIG. 2, the second region A2 is continuously formed from the terminal 2a over the entire range. As another example, the second region A2 may not be provided in a portion at a certain distance from the terminal 2a, for example, a portion that is always in contact with the first spring seat 4 regardless of the compressed state of the coil spring 1.

[0035] In the example of FIG. 2, the second region A2 is not provided in the effective portion 10 and the second seat winding portion 12. As another example, the second region A2 may be provided in at least a part of the effective portion 10. This second region A2 may be continuous with the second region A2 of the first seat winding portion 11 shown in FIG. 2. Also, the second region A2 may be provided in at least a part of the second seat winding portion 12. In this case, the second region A2 of the second seat winding portion 12 may be located at a portion of the surface 20 that comes into contact with the second spring seat 5.

[0036] In the example of FIG. 4, the thickness t of the second layer L2 is the largest at the center C. The thickness t gradually decreases from the center C toward the boundaries B1, B2. The maximum value of the thickness t is, for example, 0.6 mm or more, preferably 1.0 mm or more. In terms of the relationship with 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.

[0037] Note that the cross-sectional structure shown in FIG. 4 can be applied not only to the portion along the line IV-IV in FIG. 2 but also to other portions of the first coil part 11. In one example, the cross-sections of the portions where the second region A2 is formed in the strand 2 all have the structure shown in FIG. 4.

[0038] FIG. 5 is a graph showing an example of the hardness distribution of the first coil part 11 in the depth direction (the direction from the surface 20 toward the axis X2). This hardness distribution corresponds to that along the line segment passing through the center C and the axis X2. In this graph, the horizontal axis represents the distance [mm] from the surface 20 (center C) of the strand 2, and the vertical axis represents the Rockwell hardness [HRC].

[0039] In the example of FIG. 5, the hardness of the first layer L1 is substantially constant. In the second layer L2, the hardness at the surface 20 (center C) is the smallest, and as it moves away from the surface 20, the hardness gradually increases and reaches the hardness of the first layer L1 at the position of the thickness t.

[0040] Thus, the second layer L2 is generally softer than the first layer L1. Furthermore, the hardness of the second layer L2 has a gradient corresponding to the distance from the surface 20.

[0041] FIG. 6 is a graph showing an example of the hardness distribution of the surface 20 of the first coil part 11 in the circumferential direction Dθ. In this graph, the horizontal axis represents the position [mm] in the circumferential direction Dθ on the surface 20, and the vertical axis represents the Vickers hardness [HV].

[0042] In the example of FIG. 6, the hardness of the first region A1 is substantially constant. In the second region A2, the hardness near the center C is the smallest. Between the center C and the boundary B1, and between the center C and the boundary B2, the hardness gradually increases as it moves away from the center C and reaches the hardness of the first region A1 at the boundaries B1 and B2.

[0043] Thus, the second region A2 is generally softer than the first region A1. Furthermore, the hardness of the second region A2 has a gradient with the center C as the minimum value.

[0044] Next, a method for manufacturing the coil spring 1 will be described. FIG. 7 is a flowchart showing an example of a method for manufacturing the coil spring 1 according to the present embodiment. First, the raw wire 2 is formed (coiled) in a spiral shape by a coiling machine, and the portion formed in the spiral shape is cut by a cutter (step S1). At this point, the surface 20 of the raw wire 2 has the same hardness throughout.

[0045] Subsequently, annealing is performed on the raw wire 2 (step S2). In this annealing, for example, the raw wire 2 is heated in a temperature range of 400 to 500°C for 1 minute or less by applying direct current to the raw wire 2.

[0046] After annealing, a local softening treatment for forming the second region A2 on the surface 20 is performed (step S3). Details of the local softening treatment will be described later with reference to FIG. 8.

[0047] After the local softening treatment, shot peening is performed on the raw wire 2 (step S4). In this shot peening, compressive residual stress is applied to the raw wire 2. After shot peening, a coating film 21 is formed on the entire surface 20 of the raw wire 2 (step S5). Note that the local softening treatment may be performed before annealing.

[0048] FIGS. 8 and 9 are schematic perspective views of an alternating current energization heating device 201 (hereinafter referred to as the heating device 201) used in the local softening treatment. In these figures, a part of the first layer winding portion 11 of the raw wire 2 heated by the heating device 201 is shown, and the remaining part of the raw wire 2 is omitted.

[0049] The heating device 201 includes a first terminal T1 and a second terminal T2. The first terminal T1 is attached to the first attachment position AP1 of the stranded wire 2. The second terminal T2 is attached to the second attachment position AP2 of the stranded wire 2. The first attachment position AP1 and the second attachment position AP2 are respectively located at both ends of the range where the second region A2 is to be formed on the stranded wire 2. That is, the portion of the stranded wire 2 between the first attachment position AP1 and the second attachment position AP2 corresponds to the portion to be heated by the heating device 201.

[0050] In the present embodiment, the second region A2 is formed at least in the first spiral portion 11. Therefore, at least one of the first attachment position AP1 and the second attachment position AP2 is included in the first spiral portion 11. As an example, in FIGS. 8 and 9, the first terminal T1 is attached near the 1.2th turn from the terminal 2a, and the second terminal T2 is attached near the terminal 2a. That is, the second attachment position AP2 is included in the first spiral portion 11 and is located between the terminal 2a of the first spiral portion 11 and the first attachment position AP1 in the winding direction DW of the stranded wire 2.

[0051] For example, the first terminal T1 and the second terminal T2 have recesses on the upper surface with a shape that fits the stranded wire 2. The first terminal T1 and the second terminal T2 are respectively attached to the stranded wire 2 by fitting the first attachment position AP1 and the second attachment position AP2 into these recesses. Note that the method of attaching the first terminal T1 and the second terminal T2 to the first attachment position AP1 and the second attachment position AP2 respectively is not limited to this example. For example, the first terminal T1 may have a pair of portions that sandwich the first attachment position AP1. Similarly, the second terminal T2 may have a pair of portions that sandwich the second attachment position AP2.

[0052] The heating device 201 further includes a conductor 210, a first base 221, a second base 222, a control device 230, and a third terminal T3. The control device 230 includes a power supply 231 that supplies an alternating current. The first base 221 is connected to the power supply 231 via a wiring. Similarly, the second base 222 is connected to the power supply 231 via a wiring. The frequency of the alternating current supplied by the power supply 231 is not particularly limited, but for example, a high frequency of 1 kHz or more can be used.

[0053] The first base 221 and the second base 222 are, for example, plate-shaped conductors. In the example of FIG. 8, the first base 221 and the second base 222 are stacked one above the other with an insulating material 223 therebetween.

[0054] The conductor 210 is arranged to face the heating target portion of the strand 2 with a gap therebetween. The conductor 210 can be formed of a metal material having excellent conductivity such as copper or aluminum. Further, the conductor 210 may have a laminated structure including a conductive layer formed of a metal material and an insulating layer formed of a resin or the like.

[0055] In the examples of FIGS. 8 and 9, the conductor 210 has a bottom portion 211 located below the strand 2 and a side portion 212 located on the side of the strand 2. These bottom portion 211 and side portion 212 are integrally formed, for example. As another example, the bottom portion 211 and the side portion 212 may be divided from each other. Further, at least one of the bottom portion 211 and the side portion 212 may include a plurality of divided portions.

[0056] The conductor 210 is generally in the same spiral shape as the heating target portion of the strand 2. The conductor 210 has end portions E1 and E2 in the winding direction DW. The end portion E1 is located above the end portion E2 in the axial direction DX.

[0057] In the present embodiment, the first terminal T1 is connected to the end portion E1 of the conductor 210. Further, the second terminal T2 is connected to the second base 222. Furthermore, the third terminal T3 is connected to the first base 221 and the end portion E2 of the conductor 210.

[0058] In such a configuration, the first attachment position AP1 of the wire 2 and the conductor 210 are electrically connected via the first terminal T1. Also, the second attachment position AP2 of the wire 2 and the power supply 231 are electrically connected via the second terminal T2 and the second base 222 without passing through the conductor 210. Further, the conductor 210 and the power supply 231 are electrically connected via the third terminal T3 and the first base 221.

[0059] In FIG. 9, the flow of current during heating by the heating device 201 is indicated by thick arrows. The current of the power supply 231 flows in order through the first base 221, the third terminal T3, the conductor 210, the first terminal T1, the wire 2, the second terminal T2, and the second base 222. This flow switches according to the frequency of the power supply 231. When current flows through such a path, the direction of current flow becomes opposite between the wire 2 and the conductor 210.

[0060] FIG. 10 is a schematic cross-sectional view of the conductor 210 and the wire 2 along the line X-X in FIG. 8. FIG. 11 is a schematic cross-sectional view of the conductor 210 and the wire 2 along the line XI-XI in FIG. 8.

[0061] As described above, the conductor 210 has the same spiral shape as the wire 2. Specifically, the bottom 211 of the conductor 210 is inclined so that the distance D1 from the wire 2 in the axial direction DX is constant at each position of the wire 2, for example. A cut portion 210a is formed at the center of the bottom 211. The side portion 212 is curved so that the distance D2 from the wire 2 in the radial direction DR is constant at each position of the wire 2, for example.

[0062] In the examples of FIGS. 8 and 9, the first attachment position AP1 and the second attachment position AP2 are separated by one or more turns in the winding direction DW. Further, the conductor 210 is arranged to face each part of the wire 2 with one or more turns in this way. As a result, as shown in FIG. 11, a part 210b of the conductor 210 overlaps with another part 210c of the conductor 210 in the axial direction DX. From another viewpoint, a part 210c of the conductor 210 is located between the 0th turn and the 1st turn of the wire 2.

[0063] When performing heat treatment by the heating device 201, the first terminal T1 and the second terminal T2 are respectively attached to the first attachment position AP1 and the second attachment position AP2 of the wire 2 formed in a spiral shape. Thereby, at least the heating target portion (the first spiral portion 11 in the present embodiment) between the first attachment position AP1 and the second attachment position AP2 of the wire 2 faces the conductor 210. When the first terminal T1 and the second terminal T2 are attached to the wire 2, a circuit in which the wire 2, the conductor 210, and the power supply 231 are connected in series is formed.

[0064] The control device 230 starts energization of the wire 2 in response to an operation of a switch by an operator or reception of a control signal from the outside. At this time, the direction of the current flowing through the wire 2 periodically changes according to the frequency of the power supply 231.

[0065] Due to such energization, the temperature of the heating target portion of the wire 2 rises. When the timing to stop heating arrives, the control device 230 stops the current supply from the power supply 231.

[0066] Thereafter, the wire 2 is cooled. This cooling may be natural cooling, or may be performed by blowing a fluid such as water or air onto the wire 2 when rapid cooling is required.

[0067] When an alternating current flows through the wire 2, due to the skin effect, the current density near the surface 20 increases. Further, in the wire 2 formed in a spiral shape, since the current path passing through the inner diameter side region of the surface 20 is short, the current density near the inner diameter side region is likely to increase.

[0068] Here, the role of the conductor 210 will be described. When a current flows through a workpiece such as the wire 2, if a conductor is arranged in the vicinity thereof, a so-called proximity effect occurs, and the current flowing through the workpiece is biased toward the conductor side. In the heating device 201 shown in FIGS. 8 to 11, the proximity effect is utilized to control the current density distribution (heating temperature distribution) of the wire 2. That is, the conductor 210 is arranged at a position where the proximity effect occurs in the wire 2.

[0069] Figure 12 is a schematic diagram for explaining the proximity effect, showing a bar-shaped workpiece Ws and a conductor 210s arranged in its vicinity. When a current I from a power source flows through the workpiece Ws A a magnetic field H IA is generated (Ampere's law).

[0070] In the conductor 210s, an eddy current I IA is generated due to this magnetic field H E1 (Lenz's law). Furthermore, a magnetic field H E1 is generated around the conductor 210s due to the eddy current I IE . When this magnetic field H IE acts on the workpiece Ws, an eddy current I E2 is generated in the workpiece Ws.

[0071] The directions in which the current I A , the eddy current I E1 and the eddy current I E2 flow are as indicated by the arrows in the figure. That is, in the workpiece Ws, near the side surface far from the conductor 210s, the direction in which the current I A flows and the direction in which the eddy current I E2 flows are opposite. On the other hand, near the side surface close to the conductor 210s, the direction in which the current I A flows and the direction in which the eddy current I E2 flows coincide. As a result, the current density of the workpiece Ws becomes high near the side surface close to the conductor 210s.

[0072] Furthermore, assume a case where a current I A flows in the direction opposite to the current I B in the conductor 210s. At this time, a magnetic field H IB is generated around the conductor 210s. In the workpiece Ws, an eddy current I IB is generated due to this magnetic field H E3 . The direction in which the eddy current I E3 flows is as indicated by the arrow in the figure. That is, in the workpiece Ws, near the side surface far from the conductor 210s, the direction in which the current I A flows and the direction in which the eddy current I E3flows in the opposite direction. On the other hand, in the vicinity of the side surface closer to the conductor 210s, the current I A flows in the same direction as the direction in which the eddy current I E3 flows. As a result, the current density of the work Ws becomes even higher in the vicinity of the side surface closer to the conductor 210s.

[0073] By utilizing such a proximity effect, it is possible to control the current density distribution and the heating temperature distribution of the work Ws.

[0074] FIG. 13 is a schematic cross-sectional view of the first layer winding portion 11 heated by AC energization without using the conductor 210. As described above, when an alternating current flows through the helical strand 2, the current density at the surface 20 of the strand 2 increases due to the skin effect. Further, in the helical strand 2, the current mainly flows on the inner diameter side. Therefore, among the surface 20 of the strand 2, the portion mainly on the inner diameter side preferentially heats up.

[0075] In one example, when an alternating current flows, the portion on the inner diameter side of the strand 2 is heated to a temperature range below the austenitization start temperature. As a result, a heat affected zone (HAZ) 2H is formed in the strand 2. In the example of FIG. 13, the heat affected zone 2H is formed in the portion on the inner diameter side centered on the second position P2.

[0076] FIG. 14 is a schematic cross-sectional view of the first layer winding portion 11 heated by AC energization using the conductor 210 as shown in FIGS. 8 to 11. The conductor 210 is arranged such that the bottom 211 faces the vicinity of the first position P1 and the side portion 212 faces the vicinity of the fourth position P4. The vicinity of the second position P2 and the vicinity of the third position P3 do not face the conductor 210.

[0077] In this case, due to the proximity effect described above, the current flowing through the strand 2 is attracted toward the conductor 210 side. As a result, the position of the heat affected portion 2H also moves closer to the conductor 210 compared to the example of FIG. 13. In the example of FIG. 14, the heat affected portion 2H is formed in a range including the first position P1 and the second position P2. When this heat affected portion 2H is cooled, a second layer L2 with a reduced hardness compared to the original strand 2 is generated.

[0078] Note that if the temperature of the strand 2 during heating is too high, a part of the strand 2 may be quenched and hardened, and the hardness may increase compared to before heating. Also, when the frequency of the alternating current is too low or the energization time is long, the entire surface 20 may be softened, or the second layer L2 may reach near the axis X2 of the strand 2. Furthermore, when the frequency of the alternating current is too low, the proximity effect described above may not be obtained sufficiently.

[0079] Taking these into consideration, the frequency of the alternating current is preferably a high frequency of 1 kHz or more, and more preferably 100 kHz or more. The frequency of the alternating current may be defined in a higher range of 200 kHz or more. Also, the energization time of the alternating current is preferably 5 seconds or less, and in one example, it is 0.5 seconds.

[0080] The range of the heat affected portion 2H (second layer L2) in the cross section of the strand 2 can be controlled by the shape and position of the conductor 210. In the example of FIG. 14, the side portion 212 is bent in an arc shape toward the bottom portion 211. Thereby, a sudden change in the distance between the conductor 210 and the strand 2 is suppressed, and it becomes easier to guide the heat affected portion 2H to a desired position.

[0081] In the example of FIG. 14, the distance D1 between the bottom portion 211 and the strand 2 (first position P1) is larger than the distance D2 between the side portion 212 and the strand 2 (fourth position P4). This is not limited to this example, and the distance D1 may be the same as the distance D2, or the distance D1 may be smaller than the distance D2.

[0082] In the above-described embodiment, in the first coiled portion 11 of the coil spring 1, the surface 20 of the wire 2 has a second region A2 that is soft. Thus, even when a corrosion pit occurs in the second region A2, it is difficult for this corrosion pit to develop into a crack in the wire 2. Further, even if a crack occurs, its progression can be delayed. That is, by providing the second region A2 in the first coiled portion 11, the corrosion fatigue resistance of the first coiled portion 11 is improved.

[0083] If the second region A2 (second layer L2) is formed entirely on the wire 2, the sag resistance of the coil spring 1 may decrease. In contrast, in this embodiment, the second region A2 is not formed in the effective portion 10. Therefore, the sag resistance can be kept good in the effective portion 10. Since the first coiled portion 11 is a portion where the working stress is lower than that of the effective portion 10, even when the second region A2 is provided in the first coiled portion 11, it is difficult for the sag resistance of the entire coil spring 1 to be affected.

[0084] The first coiled portion 11 is a portion that contacts the first spring seat 4 (seat surface SF) disposed below it. Therefore, when foreign matter such as sand enters between the first coiled 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 coiled portion 11. In contrast, in this embodiment, the second region A2 is provided in a range including the first position P1 that contacts the seat surface SF in the first coiled portion 11. Therefore, even when foreign matter enters between the first coiled portion 11 and the first spring seat 4 and corrosion pits occur, cracks caused by these corrosion pits can be suppressed.

[0085] Further, foreign matter as described above is likely to enter below a portion of the first coiled portion 11 that comes into contact with and separates from the first spring seat 4. Therefore, if the second region A2 is formed so as to include such a portion, it is possible to effectively improve the corrosion fatigue resistance. As described above with reference to FIG. 2, if the second region A2 is formed in a range from at least the terminal 2a to 1.2 turns, good corrosion fatigue resistance can be obtained while maintaining the sag resistance.

[0086] In addition, among the surfaces 20 of the wire strands 2, stress is likely to be applied to the portion on the coil axis X1 side (inner diameter side of the coil spring 1), and corrosion fatigue is also likely to occur. Therefore, as described above with reference to FIG. 4, it is preferable to form the second region A2 below the wire strand 2 and closer to the inner diameter.

[0087] In the manufacturing method using the heating device 201 according to the present embodiment, the second region A2 (second layer L2) is formed by energization heating using a high-frequency alternating current. If energization heating using a direct current or energization heating using a low-frequency alternating current of about 50 Hz or 60 Hz is used, a heat-affected zone may occur up to near the axis X2 of the wire strand 2. Therefore, the second layer L2 is formed in a wide range inside the wire strand 2, and the sag resistance of the first helical winding portion 11 may decrease. On the other hand, in energization heating using a high-frequency alternating current, due to the skin effect described above, the range where the heat-affected zone occurs remains near the surface 20. As a result, as shown in FIG. 4, the vicinity of the axis X2 is maintained as the hard first layer L1, and the sag resistance of the first helical winding portion 11 is enhanced.

[0088] In the heating device 201 according to the present embodiment, as shown in FIG. 9, currents flow in opposite directions in the wire strand 2 and the conductor 210. As a result, as described with reference to the model of FIG. 12, the current density of the wire strand 2 (workpiece) is strongly attracted to the conductor 210. As a result, it is possible to better control the current density distribution and the heating temperature distribution in the wire strand 2.

[0089] [Second Embodiment] FIGS. 15 and 16 are schematic perspective views of an alternating-current energization heating device 202 (hereinafter referred to as the heating device 202) according to the second embodiment. In these figures, a part of the first helical winding portion 11 of the wire strand 2 heated by the heating device 202 is shown, and the remaining part of the wire strand 2 is omitted.

[0090] The heating device 202 includes a first terminal T1, a second terminal T2, a third terminal T3, a conductor 210, a first base 221, a second base 222, and a control device 230, similar to the heating device 201 in the first embodiment. The shape of the conductor 210 is the same as that in the first embodiment. Also, the relationship between the first mounting position AP1 and the second mounting position AP2 is the same as that in the first embodiment.

[0091] In this embodiment, the first terminal T1 attached to the first mounting position AP1 is connected to the first base 221. Also, the second terminal T2 attached to the second mounting position AP2 is connected to the end E2 of the conductor 210. Further, the third terminal T3 is connected to the second base 222 and the end E1 of the conductor 210. As shown in FIG. 16, the end E1 of the conductor 210 is spaced apart from the first terminal T1.

[0092] In such a configuration, the first mounting position AP1 of the strand 2 and the power source 231 are electrically connected via the first terminal T1 and the first base 221 without passing through the conductor 210. Also, the second mounting position AP2 of the strand 2 and the conductor 210 are electrically connected via the second terminal T2. Further, the conductor 210 and the power source 231 are electrically connected via the third terminal T3 and the second base 222.

[0093] FIG. 16 shows the flow of current during heating by the heating device 202 with thick solid arrows. The current of the power source 231 flows in sequence through the first base 221, the first terminal T1, the strand 2, the second terminal T2 (see FIG. 15), the conductor 210, the third terminal T3, and the second base 222. This flow switches according to the frequency of the power source 231. When current flows through such a path, as in the first embodiment, the directions of current flow in the strand 2 and the conductor 210 are opposite.

[0094] Also with the heating device 202 according to this embodiment, it is possible to control the current density distribution and the heating temperature distribution of the strand 2 due to the same proximity effect as the heating device 201 according to the first embodiment.

[0095] [Third Embodiment] Figures 17 and 18 are schematic perspective views of the alternating current energization heating device 203 (hereinafter referred to as the heating device 203) according to the third embodiment. In these figures, a part of the first coiling portion 11 of the element wire 2 heated by the heating device 203 is shown, and the remaining portion of the element wire 2 is omitted.

[0096] Similar to the heating devices 201 and 202 in the first and second embodiments, the heating device 203 includes a first terminal T1, a second terminal T2, a conductor 210, a first base 221, a second base 222, and a control device 230. However, the heating device 203 does not include a third terminal T3. The shape of the conductor 210 is the same as that in the first and second embodiments. Also, the relationship between the first mounting position AP1 and the second mounting position AP2 is the same as that in the first and second embodiments.

[0097] In the present embodiment, the first terminal T1 attached to the first mounting position AP1 is connected to the first base 221. Also, the second terminal T2 attached to the second mounting position AP2 is connected to the second base 222. That is, both the first terminal T1 and the second terminal T2 are electrically connected to the power supply 231 without passing through the conductor 210.

[0098] In the present embodiment, the conductor 210 is in an electrically floating state and is insulated from the first terminal T1 and the second terminal T2. Also, the conductor 210 is insulated from the element wire 2 in a state where the first terminal T1 and the second terminal T2 are attached. As shown in FIG. 18, the end E1 of the conductor 210 is separated from the first terminal T1. Also, the end E2 of the conductor 210 is separated from the second terminal T2. The conductor 210 is supported by, for example, an insulating member (not shown).

[0099] In such a configuration, the first mounting position AP1 of the element wire 2 and the power supply 231 are electrically connected via the first terminal T1 and the first base 221 without passing through the conductor 210. Also, the second mounting position AP2 of the element wire 2 and the power supply 231 are electrically connected via the second terminal T2 and the second base 222 without passing through the conductor 210.

[0100] FIG. 18 shows the flow of current during heating by the heating device 203 with thick arrows. The current from the power source 231 flows through the first base 221, the first terminal T1, the element wire 2, the second terminal T2, and the second base 222 in this order. This flow switches according to the frequency of the power source 231.

[0101] In the configuration of the heating device 203 according to this embodiment, when current flows through the heating target portion of the element wire 2, the conductor 210 is in an electrically floating state. Therefore, the current corresponding to the eddy current I shown in FIG. 12 does not flow through the element wire 2. Even in this case, since the current corresponding to the eddy current I flows through the element wire 2, a proximity effect occurs between the element wire 2 and the conductor 210. As a result, the current flowing through the element wire 2 is attracted toward the conductor 210 side. Therefore, it is possible to control the current density distribution and the heating temperature distribution in the element wire 2 by the conductor 210. E3 The current corresponding to I does not flow through the element wire 2. Even in this case, since the current corresponding to the eddy current I flows through the element wire 2, a proximity effect occurs between the element wire 2 and the conductor 210. E2 As a result, the current flowing through the element wire 2 is attracted toward the conductor 210 side. Therefore, it is possible to control the current density distribution and the heating temperature distribution in the element wire 2 by the conductor 210.

[0102] FIG. 19 is a graph showing the relationship between the heating time and the active power when heating the element wire 2 by the heating devices 201, 202, and 203 according to the first to third embodiments. FIG. 20 is a graph showing the relationship between the heating time and the apparent power when heating the element wire 2 by these heating devices 201, 202, and 203.

[0103] As shown in FIG. 19, there is almost no difference in the active power of the heating devices 201, 202, and 203. On the other hand, as shown in FIG. 20, a difference was found in the apparent power among the heating devices 201, 202, and 203. Specifically, the apparent power of the heating device 201 is the lowest. The apparent power of the heating device 202 is slightly higher than that of the heating device 201, but it is not inferior to the heating device 201. From these facts, it can be seen that the heating devices 201 and 202 are superior to the heating device 203 from the viewpoint of the power capacity of the device.

[0104] Also, in a configuration where the strand 2 and the conductor 210 are insulated as in the heating device 203, disturbances can occur in the current density vector near the center of the conductor 210 (near the coil axis X1) and near the end of the heating target portion. As a result, the heating temperature distribution may be disturbed at the end of the heating target portion. On the other hand, in a configuration where the strand 2 and the conductor 210 are electrically connected as in the heating devices 201 and 202, the current flowing through the conductor 210 can be well controlled. As a result, disturbances in the current density vector are less likely to occur, and the controllability of the heating temperature distribution at the end of the heating target portion is improved. In particular, in the heating device 201, it is possible to well control the heating temperature distribution near the first mounting position AP1.

[0105] Also, in the heating devices 201 and 202 that also pass the current from the power supply 231 through the conductor 210, a higher proximity effect can be obtained compared to the heating device 203 that does not pass the current from the power supply 231 through the conductor 210. Therefore, when realizing a current density distribution similar to that of the heating device 203, in the heating devices 201 and 202, the gap between the strand 2 and the conductor 210 (for example, the distances D1 and D2 described above) can be made wider than that of the heating device 203. As a result, the change in the magnetic field due to the displacement between the strand 2 and the conductor 210 is reduced, and the robustness is improved.

[0106] Note that in the heating device 203, it is not necessary to connect the conductor 210 to the strand 2 and the power supply 231. Therefore, the heating device 203 has the advantage of having a simpler structure than the heating devices 201 and 202.

[0107] The first to third embodiments 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. Some modification examples are shown below.

[0108] Figs. 21 to 26 are schematic cross-sectional views showing the first to sixth modified examples of the configuration applicable to the conductor 210 of the heating device 201. In the first modified example shown in Fig. 21, the bottom portion 211 and the side portion 212 of the conductor 210 are vertically connected. In the second modified example shown in Fig. 22, the conductor 210 does not have a portion corresponding to the side portion 212. Further, in the third modified example shown in Fig. 23, the conductor 210 does not have a portion corresponding to the bottom portion 211.

[0109] In the fourth modified example shown in Fig. 24, the conductor 210 further has an upper portion 213 in addition to the bottom portion 211 and the side portion 212. One end of the upper portion 213 is connected to the upper end of the side portion 212. The upper portion 213 faces the third position P3 of the generatrix 2 in the axial direction DX.

[0110] Also in the fifth modified example shown in Fig. 25, the conductor 210 has a bottom portion 211, a side portion 212, and an upper portion 213. However, the side portion 212 has an arcuate cross section facing the generatrix 2 with a certain interval.

[0111] In the sixth modified example shown in Fig. 26, the conductor 210 has an arcuate cross section as a whole. The conductor 210 surrounds, for example, a range of 180° or more around the generatrix 2.

[0112] In addition to the first to sixth modified examples, various shapes can be applied to the conductor 210. The specific shape of the conductor 210 may be appropriately determined according to the range in which the second region A2 (second layer L2) is to be formed.

[0113] The heating devices 201, 202, 203 may further include a ferromagnetic material formed of ferrite or the like. When such a ferromagnetic material is disposed in the vicinity of the generatrix 2, the magnetic flux generated when current is applied to the generatrix 2 is induced in a direction away from the ferromagnetic material. Therefore, it is also possible to control the region where the temperature rises in the generatrix 2 by the ferromagnetic material.

[0114] In the above embodiment, the case where the strand 2 has the first layer L1 and the second layer L2 was exemplified. However, the strand 2 may have a multilayer structure further including other layers having different hardnesses from the first layer L1 and the second layer L2. For example, when the other layer extends to the surface 20 of the strand 2, other regions having different hardnesses from the first region A1 and the second region A2 may be additionally formed on the surface 20.

[0115] In the above embodiment, the coil spring 1 in which the strand 2 is wound in a cylindrical shape was disclosed. However, the coil spring 1 may have other shapes such as a barrel shape in which the diameter becomes smaller toward the first seat winding portion 11 and the second seat winding portion 12.

[0116] The heating devices 201, 202, 203 can also be used for heat treatment other than local softening treatment. The shape of the conductor 210 can be appropriately deformed according to the shape, position, and range of the portion to be heated in the heat treatment.

Explanation of Reference Numerals

[0117] 1... Coil spring, 2... Strand, 3... Shock absorber, 4... First spring seat, 5... Second spring seat, 10... Effective portion, 11... First seat winding portion, 12... Second seat winding portion, 20... Surface of the strand, 100... Suspension device, A1... First region, A2... Second region, L1... First layer, L2... Second layer, 201, 202, 203... Heating device, 210... Conductor, 221... First base, 222... Second base, 230... Control device, 231... Power supply, T1... First terminal, T2... Second terminal, T3... Third terminal.

Claims

1. A power supply capable of supplying an alternating current, a first terminal attached to a first attachment position of a helical wire of a coil spring, a second terminal attached to a second attachment position of the wire that is separated from the first attachment position in the winding direction of the wire, a conductor arranged to face a heating target portion located between the first attachment position and the second attachment position of the wire, comprising: An alternating current energization heating device that heats the heating target portion by passing the alternating current through the wire via the first terminal and the second terminal.

2. When a current flows through the heating target portion, a current in the opposite direction to the current flows through the conductor. The alternating current energization heating device according to Claim 1.

3. The second attachment position is included in the coiled portion of the wire and is located between the terminal of the coiled portion and the first attachment position in the winding direction. The alternating current energization heating device according to Claim 2.

4. Further comprising a third terminal that electrically connects the power supply and the conductor, the first terminal electrically connects the conductor and the wire, the second terminal electrically connects the wire and the power supply, and the conductor does not intervene between the wire and the power supply connected by the second terminal. The alternating current energization heating device according to Claim 3.

5. Further comprising a third terminal that electrically connects the power supply and the conductor, the second terminal electrically connects the conductor and the wire, the first terminal electrically connects the wire and the power supply, and the conductor does not intervene between the wire and the power supply connected by the first terminal. The alternating current energization heating device according to Claim 3.

6. The first terminal and the second terminal are electrically connected to the power supply without passing through the conductor, when a current flows through the heating target portion, the conductor is in an electrically floating state. The alternating current energization heating device according to Claim 1.

7. The first attachment position and the second attachment position are separated by one or more turns in the winding direction, a part of the conductor overlaps with another part of the conductor and the coil axis of the wire in the axial direction parallel to the coil axis. The alternating current energization heating device according to any one of Claims 1 to 6.

8. The wire is formed in a spiral shape around a coil axis, a first terminal is attached to the first attachment position of the wire, a second terminal is attached to the second attachment position of the wire that is separated from the first attachment position in the winding direction of the wire, A conductor is arranged so as to face a heating target portion located between the first attachment position and the second attachment position among the strand wires. The heating target portion is heated by passing an alternating current through the strand wires via the first terminal and the second terminal. A method for manufacturing a coil spring including this.

9. When a current flows through the heating target portion, a current in the opposite direction to the current flows through the conductor. The method for manufacturing a coil spring according to claim 8.

10. The second attachment position is included in the helically coiled portion of the strand wire and is located between the terminal of the helically coiled portion and the first attachment position in the winding direction. The method for manufacturing a coil spring according to claim 9.

11. The power source of the alternating current and the conductor are electrically connected by a third terminal. The first terminal electrically connects the conductor and the strand wire. The second terminal electrically connects the strand wire and the power source, and the conductor does not intervene between the strand wire and the power source connected by the second terminal. The method for manufacturing a coil spring according to claim 10.

12. The power source of the alternating current and the conductor are electrically connected by a third terminal. The second terminal electrically connects the conductor and the strand wire. The first terminal electrically connects the strand wire and the power source, and the conductor does not intervene between the strand wire and the power source connected by the first terminal. The method for manufacturing a coil spring according to claim 10.

13. The first terminal and the second terminal are electrically connected to the power source of the alternating current without passing through the conductor. When a current flows through the heating target portion, the conductor is in an electrically floating state. The method for manufacturing a coil spring according to claim 8.

14. The first attachment position and the second attachment position are separated by one or more turns in the winding direction. A part of the conductor overlaps with another part of the conductor and the coil axis of the strand wire in the axial direction parallel to the coil axis. The method for manufacturing a coil spring according to any one of claims 8 to 13.

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