Coil spring

Abstract

To provide a light-weight coil spring having nonlinear characteristics.SOLUTION: A coil spring according to one embodiment is made of a strand (2) having one end and the other end. The strand (2) of the coil spring has, regarding a cross section of the strand (2), an effective portion (13) composed of a circular cross section portion (30), a square cross section portion (31) having a substantially square cross section and including end coil portions (11), (12), and a tapered portion (32). A coil diameter (r1) of the square cross section portion (31) is smaller than a coil diameter (R1) of the circular cross section portion (30). The tapered portion (32) has a cross-sectional area that changes from circular to approximately square and decreases, from the circular cross section portion (30) toward the square cross section portion (31).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a coil spring used in, for example, a vehicle suspension system. [Background technology]

[0002] An example of a coil spring used in a vehicle suspension system is made of a wire rod wound in a spiral shape. Generally, the cross section of the wire of a coil spring (a cross section perpendicular to the length of the wire) is circular. The coil spring has a first end turn portion that contacts a first spring seat of the suspension system, a second end turn portion that contacts a second spring seat, and an active portion between the first end turn portion and the second end turn portion.

[0003] The active portion has a plurality of coil portions. When this coil spring is compressed to a predetermined length by a load, there are gaps between the coil portions of the active portion. The end coil portion always contacts the spring seat regardless of the magnitude of the load. A portion of the active portion contacts or separates from the spring seat depending on the magnitude of the load.

[0004] The coil spring expands and contracts with a predetermined stroke between an assumed minimum load and a assumed maximum load. Depending on the vehicle, a coil spring with nonlinear characteristics may be desired. A coil spring with nonlinear characteristics has a spring constant that changes depending on the magnitude of the load. For example, when the load is small, the coil spring bends with a first spring constant, and when the load increases, it bends with a second spring constant. The second spring constant is greater than the first spring constant.

[0005] Tapered coil springs are also known, which have a tapered section where the wire diameter decreases from the middle of the active section toward the end of the wire. Tapered coil springs have low rigidity at the tapered section, so the tapered section is the main deflection in the low load range. When the load increases, the tapered section comes into contact with the active section, causing deflection of the active section, resulting in nonlinear characteristics.

[0006] In the tapered coil spring described in JP 57-11743 A (Patent Document 1), the wire diameter decreases from the middle of the active section toward the end turn section.In the tapered coil spring described in JP 56-141431 A (Patent Document 2), the cross section of the wire in the tapered section and the end turn section is an octagon with rounded edges that are close to a circle. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 57-11743 [Patent Document 2] Japanese Patent Application Publication No. 56-141431 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-337415 [Patent Document 4] Japanese Patent Application Publication No. 54-52257 Summary of the Invention [Problem to be solved by the invention]

[0008] In a coil spring made of a wire with a substantially circular cross section, it is not easy to process a portion of the wire into an extremely small diameter. For example, to sufficiently reduce the wire diameter by plastic processing, it is necessary to use special rolling rolls. While it is possible to reduce the wire diameter by cutting or swaging, these methods are not practical because of the high processing costs and long processing times. For these reasons, it has been difficult to reduce the wire diameter of a portion of the wire to an extremely small diameter.

[0009] In coil springs with non-linear characteristics, even if there is a limit to how small the wire diameter can be made in the tapered and small cross-section sections (small diameter sections), it is possible to lower the spring constant in the light load range by increasing the number of turns in the tapered and small cross-section sections. However, the tapered and small cross-section sections of a coil spring with non-linear characteristics come into close contact with each other when the load increases. When the tapered and small cross-section sections come into close contact with each other, they become dead coil sections that do not function as springs. A coil spring with a large number of turns in the dead coil section causes the weight of the vehicle to increase.

[0010] In the coil springs described in JP 2000-337415 A (Patent Document 3) and JP 54-52257 A (Patent Document 4), a flat portion with a flat rectangular cross section is formed by rolling a portion of the wire in the longitudinal direction (a portion including the end turn portion). A flat portion with a rectangular cross section can be formed relatively easily using a general rolling mill roll. However, the flat portion has a significantly larger polar moment of inertia of area compared to a wire with a circular cross section. For this reason, it has been difficult to reduce the weight of a coil spring with nonlinear characteristics that has a flat portion, even if the desired nonlinear characteristics are obtained.

[0011] An object of the present invention is to provide a lightweight coil spring having nonlinear characteristics. [Means for solving the problem]

[0012] One embodiment of the present invention is a coil spring made of a wire having one end and the other end, the coil spring having a first end turn part including the one end of the wire, a second end turn part including the other end of the wire, and an effective spring part. The effective part has a plurality of coil portions formed between the first end turn part and the second end turn part, with gaps between adjacent coil portions. The effective part includes a circular cross-sectional portion having a first circular cross-section perpendicular to the longitudinal direction of the wire.

[0013] Furthermore, the coil spring of this embodiment has a square cross-sectional portion having a length extending from the one end of the wire beyond the first end turn portion, and a tapered portion having 1.0 turn or more formed between the circular cross-sectional portion and the square cross-sectional portion. The square cross-sectional portion has a second cross section perpendicular to the length direction that is substantially square and has a coil diameter smaller than the coil diameter of the circular cross-sectional portion. The square cross-section portion has a first winding portion and a second winding portion in a direction along the central axis of the coil spring, and has an abutment portion where the first winding portion and the second winding portion overlap in a direction along the central axis when compressed by a load along the central axis.The cross section of the tapered portion (a third cross section perpendicular to the longitudinal direction of the wire) changes from circular to approximately square and the cross-sectional area decreases from the circular cross-sectional portion to the square cross-sectional portion. The cross-sectional area of ​​the second cross section may be smaller than the cross-sectional area of ​​the first cross section. The polar moment of area of ​​the second cross section may be smaller than the polar moment of area of ​​the first cross section.

[0014] The square cross-sectional portion may have an outer first surface and an inner second surface along the central axis of the coil spring, and an upper third surface and a lower fourth surface that are perpendicular to the first and second surfaces and parallel to each other. In the coil spring of this embodiment, the square cross-sectional portion may have at least a first coil portion and a second coil portion, and may have an abutment portion where the third surface of the first coil portion and the fourth surface of the second coil portion come into contact with each other when the coil spring is in a compressed state. The coil diameter of the second coil portion of the square cross-sectional portion may be smaller than the coil diameter of the second coil portion.

[0015] The tapered portion may have a first flat portion continuous with the first surface of the square cross-section portion, a second flat portion continuous with the second surface, a third flat portion continuous with the third surface, a fourth flat portion continuous with the fourth surface, a first arc portion between the first flat portion and the third flat portion, a second arc portion between the first flat portion and the fourth flat portion, a third arc portion between the second flat portion and the third flat portion, and a fourth arc portion between the second flat portion and the fourth flat portion. [Effects of the Invention]

[0016] The square cross-sectional portion can be processed relatively easily using a rolling mill roll, etc. It is not particularly difficult to make the cross-sectional area of ​​the square cross-sectional portion sufficiently smaller than the cross-sectional area of ​​the circular cross-sectional portion. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a perspective view of a coil spring according to a first embodiment. [Figure 2] 2 is a perspective view showing a cross section of a portion of the coil spring shown in FIG. 1 in a compressed state. FIG. [Figure 3] FIG. 3 is a side view showing a portion of the wire of the coil spring before being coiled. [Figure 4] FIG. 3 is a cross-sectional view schematically showing an example of a square cross-section of the wire. [Figure 5] A diagram showing the polar moment of inertia of area for three types of wires with different cross sections. [Figure 6] 2 is a diagram showing the spring characteristics (relationship between deflection and load) of the coil spring shown in FIG. 1. [Figure 7] FIG. 10 is a diagram showing the relationship between the position from the lower end of the coil spring (turns from the lower end) and stress (inner side of the coil). [Figure 8] FIG. 2 is a perspective view schematically showing a rolling device. [Figure 9] FIG. 1 is a plan view of a portion of a coiling machine. [Figure 10] FIG. 10 is a perspective view of a coil spring according to a second embodiment. [Figure 11] FIG. 11 is a perspective view showing a cross section of a part of the coil spring shown in FIG. 10 . DETAILED DESCRIPTION OF THE INVENTION

[0018] A coil spring according to one embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a coil spring 1 used in a suspension system for a vehicle such as an automobile. The coil spring 1 has a wire rod 2 wound in a spiral shape. The wire rod 2 is made of, for example, spring steel. The coil spring 1 has a first end turn portion 11 including one end 2a of the wire rod 2, a second end turn portion 12 including the other end 2b of the wire rod 2, and an active portion 13. The active portion 13 is formed between the first end turn portion 11 and the second end turn portion 12 and has multiple winding portions 13a. When the coil spring 1 is installed in a suspension system for a vehicle, the first end turn portion 11 is located on the upper side and the second end turn portion 12 is located on the lower side. In this case, the central axis C1 of the coil spring 1 extends in the vertical direction.

[0019] An example of the effective portion 13 is a cylindrical spring having a constant pitch P1 (shown in FIG. 1) and a substantially constant coil diameter R1. Here, "substantially constant" means that variations in the tolerance range of a coil spring manufactured by a coiling machine and variations in the allowable range due to springback are negligible in practical use. Note that the effective portion 13 may also be a non-cylindrical coil spring in which the pitch P1 and coil diameter R1 vary in the direction along the central axis C1.

[0020] The first end winding portion 11 is supported by an upper spring seat 20 (shown in FIG. 2) of the suspension. As shown in FIG. 1, the second end winding portion 12 is supported by a lower spring seat 21 of the suspension. The coil spring 1 is compressed between the upper spring seat 20 and the lower spring seat 21. When the coil spring 1 is compressed within a predetermined load range (the range of load used in a suspension), the active portion 13 has a gap G1 between adjacent winding portions 13a.

[0021] The coil spring 1 used in a vehicle suspension system is used in a load range between the minimum and maximum expected loads. The effective portion 13 functions effectively as a spring, with adjacent windings 13a not coming into contact with each other, both in a fully compressed full bump state and a fully extended full rebound state.

[0022] FIG. 2 is a perspective view showing a cross section of a portion of the coil spring 1 (near the end winding portion 11) when the coil spring 1 is compressed. The coil spring 1 of this embodiment includes a circular cross-sectional portion 30 of the effective portion 13, a square cross-sectional portion 31 of the first end winding portion 11, and a tapered portion 32 formed between the circular cross-sectional portion 30 and the square cross-sectional portion 31. The first end winding portion 11 has the square cross-sectional portion 31 and is formed in a spiral shape. The second end winding portion 12 has a portion of the circular cross-sectional portion 30 and is formed in a spiral shape. The effective portion 13 is made of the circular cross-sectional portion 30 and has a plurality of winding portions 13a formed in a spiral shape.

[0023] FIG. 3 shows a portion of the wire 2 before it is coiled. An axis X1 passing through the center of the wire 2 extends in the longitudinal direction of the wire 2. The wire 2 shown in FIG. 3 has a circular cross-sectional portion 30 having a length L1, a square cross-sectional portion 31 having a length L2, and a tapered portion 32 having a length L3. The circular cross-sectional portion 30 has a length L1 required for the multiple windings 13a of the effective portion 13. The square cross-sectional portion 31 is formed over a length L2 from one end 2a of the wire 2. The tapered portion 32 is formed over a length L3 between the circular cross-sectional portion 30 and the square cross-sectional portion 31.

[0024] As shown in Figure 2, the cross section of the circular cross-section portion 30 (first cross section S1 perpendicular to the axis X1 of the wire 2) is circular. Moreover, the first cross section S1 is substantially constant in the longitudinal direction of the wire 2 (direction along the axis X1). The second end winding portion 12 is made up of a part of the circular cross-section portion 30, and therefore has a circular cross section. The wire diameter of the second end winding portion 12 is the same as the wire diameter of the circular cross-section portion 30 of the effective portion 13.

[0025] The square cross-section portion 31 has an outer first surface 31a and an inner second surface 31b that are aligned along the central axis C1 (shown in FIGS. 1 and 2) of the coil spring 1, an upper third surface 31c that is perpendicular to the first surface 31a, and a lower fourth surface 31d that is perpendicular to the first surface 31a. The third surface 31c and the fourth surface 31d form planes that are substantially perpendicular to the central axis C1 of the coil spring 1. The square cross-section portion 31 has a first winding portion 41 and a second winding portion 42. The coil diameter r2 of the second winding portion 42 is smaller than the coil diameter r1 of the first winding portion 41.

[0026] 2 shows the coil spring 1 in a state where it is compressed by a load along the central axis C1. When the coil spring 1 is compressed, the upper surface 31c of the first winding portion 41 of the square cross-section portion 31 and the lower surface 31d of the second winding portion 42 overlap in a direction along the central axis 1C of the coil spring 1. This forms a contact portion 43. This prevents the second winding portion 42 from entering (sliding) inside the first winding portion 41.

[0027] The cross section of the square cross section portion 31 (second cross section S2 perpendicular to the axis X1) is substantially square (approximately square). In this specification, "substantially square (approximately square)" does not mean square in the strict geometric sense. As in the second cross section S2 schematically shown in FIG. 4, it is sufficient that the lengths T1, T2, T3, and T4 of the four sides A1, A2, A3, and A4 of the cross section are equal to each other within the range of processing tolerances. The lengths T1, T2, T3, and T4 of each side A1, A2, A3, and A4 are each equal to or less than the root (√) / 2 of the diameter D1 of the circular cross section portion 30.

[0028] The interior angles θ1, θ2, θ3, and θ4 formed by the respective sides A1, A2, A3, and A4 are approximately 90° within the range of processing tolerances. Rounded corners B1, B2, B3, and B4 may be formed at the points where the respective sides A1, A2, A3, and A4 intersect. The second cross section S2 is substantially constant in the longitudinal direction of the wire 2 (the direction along the axis X1).

[0029] The cross section of the tapered portion 32 (third cross section S3 perpendicular to the axis X1) gradually changes from circular to approximately square as it moves from the circular cross section portion 30 to the square cross section portion 31, and the cross section area decreases. The tapered portion 32 is formed with 1.0 turns or more between the circular cross section portion 30 and the square cross section portion 31.

[0030] 2, the cross section (third cross section S3) of the tapered portion 32 has a first flat portion 32a, a second flat portion 32b, a third flat portion 32c, a fourth flat portion 32d, a first arc portion 32e, a second arc portion 32f, a third arc portion 32g, and a fourth arc portion 32h. The first flat portion 32a is continuous with the first surface 31a of the square cross-section portion 31. The first flat portion 32a is aligned along the central axis C1 of the coil spring 1.

[0031] The second flat surface 32b is continuous with the second surface 31b of the square cross-section portion 31. The second flat surface 32b is aligned along the central axis C1 of the coil spring 1. The third flat surface 32c is continuous with the third surface 31c of the square cross-section portion 31. The third flat surface 32c is perpendicular to the first flat surface 32a. The fourth flat surface 32d is continuous with the fourth surface 31d of the square cross-section portion 31. The fourth flat surface 32d is perpendicular to the first flat surface 32a.

[0032] The first arc portion 32e is an arc-shaped curved surface formed between the first flat portion 32a and the third flat portion 32c. The second arc portion 32f is an arc-shaped curved surface formed between the first flat portion 32a and the fourth flat portion 32d. The third arc portion 32g is an arc-shaped curved surface formed between the second flat portion 32b and the third flat portion 32c. The fourth arc portion 32h is an arc-shaped curved surface formed between the second flat portion 32b and the fourth flat portion 32d. These arc portions 32e, 32f, 32g, and 32h are connected to corner portions B1, B2, B3, and B4 (shown in FIG. 4) of the square cross-section portion 31, respectively.

[0033] FIG. 5 is a diagram showing the relationship between the longitudinal position and the polar moment of inertia (torsional rigidity) for three types of wires having different cross sections. The solid line M1 in FIG. 5 indicates the polar moment of inertia of the wire 2 (shown in FIG. 3) according to this embodiment. The wire diameter of the circular cross-section portion 30 in this embodiment is 15.4 mm, and the length of one side of the square cross-section portion 31 is 6 mm. In FIG. 5, the length L3a from zero (0) on the horizontal axis indicates the polar moment of inertia of the tapered portion 32, and the length L2a indicates the polar moment of inertia of the square cross-section portion 31. The polar moment of inertia of the square cross-section portion 31 is sufficiently smaller than the polar moment of inertia of the circular cross-section portion 30.

[0034] The two-dot chain line M2 in Figure 5 indicates the polar moment of inertia of the wire of Conventional Example 1, which has a flat taper portion. The wire of Conventional Example 1 has a flat taper portion over a length L4 from the end of the circular cross-section, which has a wire diameter of 15.4 mm, to the tip of the wire. The cross section of the flat taper portion is a flat rectangle. The width of the end face of the flat taper portion is 15.4 mm, and the thickness is 5.5 mm.

[0035] The polar moment of inertia of Conventional Example 1 having a flat tapered portion (two-dot chain line M2) is significantly larger than the polar moment of inertia of this embodiment (solid line M1). To reduce the first spring constant of the coil spring of Conventional Example 1 having a flat tapered portion, it is necessary to increase the number of turns in the flat tapered portion. As a result, in the second spring constant range, the number of turns in the dead coil portion increases, resulting in an increase in weight.

[0036] The dashed line M3 in Figure 5 indicates the polar moment of inertia of the wire of Conventional Example 2, which has a round taper portion. The wire of Conventional Example 2 has a round taper portion with a length L3a from the end of the circular cross-section, and a small cross-section portion (wire diameter 11.4 mm) with a length L2a. The wire diameter of the circular cross-section is 15.4 mm.

[0037] The polar moment of inertia of Conventional Example 2 (broken line M3) is larger than the polar moment of inertia of this embodiment (solid line M1). To reduce the first spring constant of the coil spring of Conventional Example 2 having a round tapered portion, it is necessary to increase the number of turns in the round tapered portion. As a result, in the second spring constant range, the number of turns in the dead coil portion increases, resulting in an increase in weight.

[0038] When the polar moment of inertia of a square cross section and that of a circular cross section are the same, the length of one side of the square cross section is approximately 0.87-0.89 times the diameter of the circular cross section, and the difference between the two is small. Equivalently sized circular and square cross sections have similar torsional rigidity. It is not easy to process a wire with a circular cross section to form a round taper with an extremely small diameter. In contrast, the square cross section portion 31 can be processed relatively easily using at least one pair of rolling rolls. It is practically possible to plastically process the square cross section portion so that the length of one side of the cross section is less than half the root of the diameter of the wire in the circular cross section.

[0039] FIG. 6 schematically shows the spring characteristics (relationship between load and deflection) of the coil spring 1 of this embodiment. In FIG. 6, the horizontal axis represents deflection, and the vertical axis represents load. The coil spring 1 is compressed between the lower spring seat 21 (shown in FIG. 1) and the upper spring seat 20 (shown in FIG. 2). When the load is between zero and W1, the square cross-section portion 31 is primarily deflected.

[0040] As a result, a first spring constant region E1 with a relatively small spring constant is established, as shown by line K1 in Figure 6. When the load exceeds W1, the square cross-section portion 31 comes into close contact, and it is mainly the circular cross-section portion 30 that bends. As a result, the spring constant becomes larger (second spring constant region E2), as shown by line K2 in Figure 6.

[0041] FIG. 7 shows the relationship between the stress generated inside the wire 2 when the coil spring 1 is compressed and the position (turns from the lower end) of the wire 2. Stress peaks τmax occur at each winding 13a of the active portion 13. These peaks τmax are smaller than the stress allowable in the suspension system. A small peak τ1 occurs near the end turn 11.

[0042] As a result of intensive research, the inventors have found that if the number of turns of the tapered portion 32 is less than 1.0, the stress of the tapered portion 32 exceeds the peak stress τmax of the effective portion 13, as shown by τ2 in Fig. 7. It is not preferable for the stress of the tapered portion 32 to exceed the stress of the effective portion 13. Therefore, in this embodiment, the number of turns of the tapered portion 32 is set to 1.0 or more.

[0043] FIG. 8 schematically shows a rolling mill 50 that forms a square cross-section portion 31 and a tapered portion 32 on a wire 2 having a circular cross-section. The wire 2 moves in the direction indicated by the arrow F1. The rolling mill 50 has rolls 51 and 52. The distance between the rolls 51 and 52 can be adjusted. The wire 2 is rolled as it passes through the rolls 51 and 52. Thereafter, the wire 2 is rotated 90° about the axis X1, and the wire 2 is rolled again by the rolls 51 and 52.

[0044] 9 shows a part of a coiling machine 60 that forms a coil spring in a hot state (for example, above the A3 transformation point and below 1150°C). The coiling machine 60 includes a cylindrical mandrel 61, a chuck 62, and a guide unit 63. The guide unit 63 includes a pair of first guide rolls 65, 66.

[0045] The wire 2 made of spring steel is cut in advance to the length of one coil spring. The wire 2 is heated to the austenitizing temperature (above the A3 transformation point and below 1150°C) and fed to the mandrel 61 by a feeding mechanism. A chuck 62 fixes the tip of the wire 2 to the mandrel 61. A guide part 63 guides the wire 2 to control the position of the wire 2 wound around the mandrel 61.

[0046] One end 61a of the mandrel 61 is held by a drive head 70 with a chuck 62. The mandrel 61 is rotated around an axis X2 by the drive head 70. The other end 61b of the mandrel 61 is rotatably supported by a mandrel holder 71. The guide portion 63 moves in a direction along the axis X2 of the mandrel 61, and guides the wire 2 in accordance with the pitch angle of the coil spring to be formed.

[0047] The wire 2 has a length equivalent to that of one coil spring. Before the wire 2 is supplied to the mandrel 61, the wire 2 is heated in a heating furnace. The tip of the heated wire 2 is fixed to the mandrel 61 by a chuck 62. As the mandrel 61 rotates, the guide portion 63 moves in a direction along the axis X2 of the mandrel 61 in synchronization with the rotation of the mandrel 61. As a result, the wire 2 is wound around the mandrel 61 at a predetermined pitch.

[0048] Comparative Examples 1, 2, 3, and 4 described below are each coil springs with nonlinear characteristics that have an effective portion including a circular cross-sectional portion, a round tapered portion, and a small cross-sectional portion. In contrast, Examples 1, 2, 3, and 4 are each coil springs with nonlinear characteristics that have a circular cross-sectional portion 30, a square cross-sectional portion 31, and a tapered portion 32, similar to coil spring 1 shown in FIG. 1.

[0049] [Comparative Example 1] The coil spring of Comparative Example 1 has a wire diameter of 18 mm in the circular cross section portion, a wire diameter of 13 mm in the small cross section portion, a total number of turns of 8.5, and a weight of 7.0 kg.

[0050] [Example 1] The coil spring of Example 1 had a wire diameter of 18 mm in circular cross-sectional portion 30, a side length of 7 mm in square cross-sectional portion 31, and a total number of turns of 8.5. The side length of square cross-sectional portion 31 was 40% of the wire diameter of circular cross-sectional portion 30. The spring characteristics (relationship between load and deflection) of Example 1 were equivalent to those of Comparative Example 1. The weight of the coil spring of Example 1 was 5.2 kg, which was approximately 24% lighter than the coil spring of Comparative Example 1.

[0051] Comparative Example 2 The coil spring of Comparative Example 2 has a wire diameter of 15 mm in the circular cross section portion, a wire diameter of 11 mm in the small cross section portion, a total number of turns of 8.5, and a weight of 7.0 kg.

[0052] [Example 2] The coil spring of Example 2 had a wire diameter of 15 mm in circular cross-sectional portion 30, a side length of 7 mm in square cross-sectional portion 31, and a total number of turns of 9.0. The side length of square cross-sectional portion 31 was 47% of the wire diameter of circular cross-sectional portion 30. The spring characteristics of Example 2 were equivalent to those of Comparative Example 2. The weight of the coil spring of Example 2 was 4.0 kg, which was approximately 23% lighter than the coil spring of Comparative Example 2.

[0053] Comparative Example 3 The coil spring of Comparative Example 3 has a wire diameter of 22 mm in the circular cross section portion, a wire diameter of 17 mm in the small cross section portion, a total number of turns of 8.0, and a weight of 8.5 kg.

[0054] [Example 3] The coil spring of Example 3 had a wire diameter of 22 mm in circular cross-sectional portion 30, a side length of 7 mm in square cross-sectional portion 31, and a total number of turns of 8.0. The side length of square cross-sectional portion 31 was 32% of the wire diameter of circular cross-sectional portion 30. The spring characteristics of Example 3 were equivalent to those of Comparative Example 3. The weight of the coil spring of Example 3 was 6.5 kg, which was approximately 22% lighter than the coil spring of Comparative Example 3.

[0055] Comparative Example 4 The coil spring of Comparative Example 4 had a wire diameter of 16 mm in the circular cross section portion, a wire diameter of 12 mm in the small cross section portion, a total number of turns of 10.0, and a weight of 6.0 kg.

[0056] [Example 4] The coil spring of Example 4 had a wire diameter of 15 mm in circular cross-sectional portion 30, a side length of 7 mm in square cross-sectional portion 31, and a total number of turns of 9.0. The side length of square cross-sectional portion 31 was 47% of the wire diameter of circular cross-sectional portion 30. The spring characteristics of Example 4 were equivalent to those of Comparative Example 4. The weight of the coil spring of Example 4 was 5.0 kg, which was approximately 18% lighter than the coil spring of Comparative Example 4.

[0057] The length of one side of the cross section of square cross section portion 31 of the coil springs in Examples 1-4 is 50% or less of the wire diameter of circular cross section portion 30. When forming square cross section portion 31, the length of one side of the cross section may vary to some extent, but by making the length of one side of the cross section of the square cross section portion equal to or less than the root of half the wire diameter of the circular cross section portion, it is possible to reduce the weight by nearly 20% compared to conventional coil springs.

[0058] FIG. 10 shows a coil spring 1A according to a second embodiment. FIG. 11 is a perspective view showing a cross section of a portion of the coil spring 1A (near the end winding portion 11). The coil spring 1A has a square cross-section portion 31 with 2 or more turns and a tapered portion 32 with 1.0 or more turns. The cross section of the wire of the second end winding portion 12 is circular. The wire diameter of the second end winding portion 12 is the same as the wire diameter of the circular cross-section portion 30. The second end winding portion 12 has a small diameter winding portion 90 in which the coil diameter decreases toward the other end 2b of the wire 2. The wire diameter of the second end winding portion 12 may be smaller than the wire diameter of the circular cross-section portion 30.

[0059] The square cross-section portion 31 including the first end winding portion 11 of the coil spring 1A has at least a first winding portion 41 and a second winding portion 42. The outer coil diameter r4 of the second winding portion 42 is smaller than the inner coil diameter r3 of the first winding portion 41. When the coil spring 1A is compressed, the second winding portion 42 can move into the inside of the first winding portion 41, as shown by the two-dot chain line Z1 in FIG.

[0060] Other than the above, the coil spring 1A of the second embodiment has the same configuration and function as the coil spring 1 of the first embodiment, so the same reference numerals are used for both and the description will be omitted. [Industrial Applicability]

[0061] The coil spring of the present invention can be applied to coil springs used in various types of equipment, including vehicle suspension systems. [Explanation of symbols]

[0062] 1, 1A... coil spring, 2... wire, 11... first end winding portion, 12... second end winding portion, 13... effective portion, 13a... winding portion, 30... circular cross-sectional portion, 31... square cross-sectional portion, 31a... first surface, 31b... second surface, 31c... third surface, 31d... fourth surface, S1... first cross section, S2... second cross section, S3... third cross section, 32... tapered portion, 32a... first flat portion, 32b... second flat portion, 32c... third flat portion, 32d... fourth flat portion, 32e... first arc portion, 32f... second arc portion, 32g... third arc portion, 32h... fourth arc portion, C1... center axis, 41... first winding portion, 42... second winding portion, 43... abutting portion.

Claims

1. It consists of a wire (2) having one end and the other end, a first end turn portion (11) including the one end of the wire (2); a second end turn portion (12) including the other end of the wire (2); an effective portion (13) having a plurality of winding portions (13a) formed between the first end winding portion (11) and the second end winding portion (12), with a gap (G1) existing between adjacent winding portions (13a); A coil spring having The wire (2) a circular cross-sectional portion (30) having a first cross section (S1) perpendicular to the longitudinal direction of the wire (2); a square cross-sectional portion (31) having a length extending from the one end of the wire (2) beyond the first end winding portion (11), a second cross-section (S2) perpendicular to the length direction being substantially square and having a coil diameter (r1) smaller than the coil diameter (R1) of the circular cross-sectional portion (30), having a first winding portion (41) and a second winding portion (42) in a direction along a central axis (C1) of the coil spring, and having an abutment portion (43) where the first winding portion (41) and the second winding portion (42) overlap in a direction along the central axis (C1) when compressed by a load along the central axis (C1); a tapered portion (32) formed between the circular cross-sectional portion (30) and the square cross-sectional portion (31) by 1.0 turns or more, in which a third cross-section (S3) perpendicular to the longitudinal direction changes from a circular shape to a substantially square shape and a cross-sectional area decreases from the circular cross-sectional portion (30) to the square cross-sectional portion (31); A coil spring equipped with

2. 2. The coil spring according to claim 1, A coil spring in which the cross-sectional area of ​​the second cross section (S2) is smaller than the cross-sectional area of ​​the first cross section (S1).

3. 2. The coil spring according to claim 1, A coil spring in which the polar moment of inertia of the second cross section (S2) is smaller than the polar moment of inertia of the first cross section (S1).

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