Coil spring

Abstract

A coil spring according to one embodiment comprises an element wire (2) having a first end (2a) and second end (2b). The element wire (2) has a circular cross-section part (30) that has a circular first cross-section (S1) which is at a right angle to the length direction of the element wire (2), a quadrangular cross-section part (31) that has a quadrangular second cross-section (S2) which is at a right angle to the length direction, and a cross-section transition part (32) that is formed between the circular cross-section part (30) and the quadrangular cross-section part (31). The cross-section of the cross-section transition part (32) changes from circular to quadrangular, from the circular cross-section part (30) toward the quadrangular cross-section part (31). An end turn part (11) of the coil spring includes the quadrangular cross-section part (31). The width (T1) and the thickness (T2) of the second cross-section (S2) are each less than the diameter (D) of the first cross-section (S1). The area of the second cross-section (S2) is less than the area of a square (Y2) inscribed in a circle of the diameter (D) of the first cross-section (S1).

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 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. The active portion has multiple turns.

[0003] When this coil spring is compressed to a predetermined length by a load, there is a gap between the windings of the effective portion. The end winding portion is always in contact with the spring seat regardless of the magnitude of the load. A part of the effective portion either contacts the spring seat or moves away 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 effective section to the end of the wire. In tapered coil springs, the tapered section has low rigidity, so in the small load range, the tapered section mainly deflects. When the load increases, the tapered section mainly becomes tightly fitted, and the effective section mainly deflects, resulting in nonlinear characteristics. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 57-11743 [Patent Document 2] U.S. Patent No. 4,111,407 [Patent Document 3] Japanese Patent Application Publication No. 56-141431 [Patent Document 4] Japanese Patent Application Laid-Open No. 2000-337415 [Patent Document 5] Japanese Patent Application Publication No. 54-52257 Summary of the Invention [Problem to be solved by the invention]

[0007] In the tapered coil springs described in Japanese Patent Laid-Open No. 57-11743 (Patent Document 1) and U.S. Pat. No. 4,111,407 (Patent Document 2), the wire diameter decreases from the middle of the active section toward the end turn section. In the tapered coil spring described in Japanese Patent Laid-Open No. 56-141431 (Patent Document 3), the wire cross sections of the tapered section and end turn section are octagonal with rounded edges that are close to circular. In a coil spring made of wires with such a nearly circular cross section, it is not easy to form a portion where the wire diameter is extremely small.

[0008] For example, to sufficiently reduce the wire diameter by plastic processing, it is necessary to use special rolling rolls. Wire diameter can also be reduced by cutting or swaging, but these methods are not suitable for practical use because of the high cost and long processing time required. For these reasons, it has been difficult to reduce the wire diameter of a portion of a wire extremely.

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

[0010] The coil springs described in Japanese Patent Laid-Open No. 2000-337415 (Patent Document 4) and Japanese Patent Laid-Open No. 54-52257 (Patent Document 5) form a flat section with a flat cross section by rolling a portion of the wire in the longitudinal direction (a portion including the end turn portion). The flat section can be formed using a general rolling mill roll. However, the flat section has a significantly larger polar moment of inertia than a wire with a circular cross section. For this reason, it has been difficult to reduce the weight of coil springs with nonlinear characteristics that have flat sections, 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 a first end and a second end, the coil spring having a first end portion including the first end of the wire, a second end portion including the second end of the wire, and an active portion. The active portion has a plurality of windings formed between the first end portion and the second end portion, with gaps between adjacent windings.

[0013] The wire of this embodiment has a circular cross-sectional portion having a first circular cross-section perpendicular to the longitudinal direction of the wire, a quadrangular cross-sectional portion having a second quadrangular cross-section perpendicular to the longitudinal direction, and a cross-sectional variation portion. The quadrangular cross-sectional portion has at least a first winding portion and a second winding portion, and the width and thickness of the second cross-section are each smaller than the diameter of the first cross-section. and the width and thickness of the second cross section are different from each other. Furthermore, the area of ​​the second cross section is smaller than the area of ​​a square inscribed in a circle of the diameter of the first cross section. The cross-section changing portion is formed between the circular cross-section portion and the rectangular cross-section portion of the wire, and the cross-section perpendicular to the length direction changes from circular to rectangular and the cross-sectional area decreases from the circular cross-section portion to the rectangular cross-section portion.

[0014] The rectangular cross-sectional portion can be processed relatively easily using a rolling roll, etc. Processing to reduce the cross-sectional area of ​​the rectangular cross-sectional portion is easier than processing to reduce the cross-sectional area of ​​a circular cross-sectional portion.

[0015] The rectangular cross-sectional portion may have first and second planes along the radial direction of the coil spring, and third and fourth planes along the central axis of the coil spring. The coil spring of this embodiment may have a contact portion where the first winding portion and the second winding portion contact each other in a compressed state.

[0016] The cross-sectional changing portion may have a first surface connected to the first plane, a second surface connected to the second plane, a third surface connected to the third plane, a fourth surface connected to the fourth plane, a first arc portion between the first surface and the third surface, a second arc portion between the second surface and the third surface, a third arc portion between the first surface and the fourth surface, and a fourth arc portion between the second surface and the fourth surface.

[0017] The width and thickness of the second cross section may be different from each other. The width of the second cross section may be greater than the thickness. Alternatively, the width and thickness of the second cross section may be substantially the same. The width and thickness of the first cross section may each be smaller than the length of one side of a square inscribed in a circle of the diameter of the first cross section. The width and thickness of the second cross section may each be equal to or smaller than the root (√) / 2 of the diameter of the first cross section. The rectangular cross section portion may have at least 2.0 turns or more, and the rectangular cross section portion may have a length from the first end that exceeds the first end turn portion. The cross-sectional transition portion may have at least 1.0 turn or more. [Effects of the Invention]

[0018] The rectangular cross-sectional portion can be processed relatively easily using a rolling roll, etc. Processing to reduce the cross-sectional area of ​​the rectangular cross-sectional portion is easier than processing to reduce the cross-sectional area of ​​a circular cross-sectional portion. [Brief explanation of the drawings]

[0019] [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 part of the coil spring shown in FIG. 1 in a compressed state. FIG. [Figure 3] FIG. 2 is a side view showing a part 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 rectangular cross-section of the wire. [Figure 5] FIG. 10 is a diagram showing the polar moments of inertia of three types of wires having different cross sections. [Figure 6] 2 is a diagram schematically showing the spring characteristics (relationship between deflection and load) of the coil spring shown in FIG. 1. FIG. [Figure 7] 10 is a diagram showing the relationship between the position from the bottom end of the coil spring and the stress. FIG. [Figure 8] FIG. 2 is a perspective view schematically showing a rolling mill. [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. DETAILED DESCRIPTION OF THE INVENTION

[0020] A coil spring according to a first 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 2 wound in a spiral shape. The wire 2 is made of, for example, spring steel and has a first end 2a and a second end 2b. The coil spring 1 has a first end turn portion 11 including the first end 2a of the wire 2, a second end turn portion 12 including the second end 2b, and an active portion 13.

[0021] The active portion 13 is formed between the first end turn portion 11 and the second end turn portion 12, and has a plurality of turns 13a. When the coil spring 1 is installed in a vehicle suspension system, the first end turn portion 11, including the first end 2a, is located on the upper side, and the second end turn portion 12, including the second end 2b, is located on the lower side. In this case, the central axis C1 of the coil spring 1 extends in the vertical direction. The direction perpendicular to the central axis C1 (indicated by the double-headed arrow C2 in Figure 2) is the radial direction of the coil spring 1.

[0022] 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.

[0023] The first end winding portion 11 is supported by an upper spring seat 20 (shown in FIG. 2) of the suspension. The second end winding portion 12 is supported by a lower spring seat 21 (shown in FIG. 1) 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 as a suspension), the active portion 13 has a gap G1 between adjacent winding portions 13a.

[0024] 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.

[0025] 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, a rectangular cross-sectional portion 31, and a cross-sectional variation portion 32. The cross-sectional variation portion 32 is formed between the circular cross-sectional portion 30 and the rectangular cross-sectional portion 31. The first end winding portion 11 includes the rectangular cross-sectional portion 31 and is formed in a spiral shape. The second end winding portion 12 includes a portion of the circular cross-sectional portion 30 and is formed in a spiral shape. The active portion 13 is made of the circular cross-sectional portion 30 and has a plurality of winding portions 13a formed in a spiral shape.

[0026] Figure 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 Figure 3 has a circular cross-sectional portion 30 with a length L1, a rectangular cross-sectional portion 31 with a length L2, and a cross-sectionally varying portion 32 with a length L3. The circular cross-sectional portion 30 has a length L1 required for the multiple windings 13a of the effective portion 13.

[0027] The rectangular cross-sectional portion 31 is formed over a length L2 from the first end 2a of the wire 2. The length L2 corresponds to at least two turns of the spirally formed coil spring 1. The cross-sectionally varying portion 32 is formed over a length L3 between the circular cross-sectional portion 30 and the rectangular cross-sectional portion 31. The rectangular cross-sectional portion 31 has a length L2 from the first end 2a that exceeds the first end winding portion 11, and has at least a first winding portion 41 and a second winding portion 42.

[0028] As shown in FIG. 2 , the circular cross-sectional portion 30 has a first cross-section S1 perpendicular to the axis X1 of the wire 2. The first cross-section S1 is circular. The first cross-section S1 is substantially constant in the longitudinal direction of the wire 2 (the direction along the axis X1). Since the second end winding portion 12 is made up of a part of the circular cross-sectional portion 30, the cross-section of the wire 2 is circular. The wire diameter of the second end winding portion 12 (the diameter of the cross section of the wire 2) is the same as the wire diameter of the effective portion 13.

[0029] The rectangular cross-sectional portion 31 has a second cross section S2, the cross section of which is rectangular and perpendicular to the axis X1 of the wire 2. The rectangular cross-sectional portion 31 has an upper first flat surface 31a, a lower second flat surface 31b, an outer third flat surface 31c, and an inner fourth flat surface 31d. The first flat surface 31a and the second flat surface 31b are each aligned along the radial direction of the coil spring 1 (indicated by a double-headed arrow C2 in FIG. 2). The third flat surface 31c and the fourth flat surface 31d are each aligned along the central axis C1 of the coil spring 1.

[0030] FIG. 2 shows the coil spring 1 in a state compressed by a load along the central axis C1. The rectangular cross-sectional 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 or equal to the coil diameter r1 of the first winding portion 41. When the coil spring 1 is compressed, the first flat surface 31a of the first winding portion 41 and the second flat surface 31b of the second winding portion 42 overlap in a direction along the central axis 1C of the coil spring 1. This forms an abutment portion 43 where the first winding portion 41 and the second winding portion 42 come into contact with each other in the thickness direction. This prevents the second winding portion 42 from slipping inside the first winding portion 41.

[0031] FIG. 4 is a cross-sectional view schematically showing an example of the quadrangular cross-section portion 31. The second cross-section S2 is a quadrangle including a square or a rectangle. In FIG. 4, the width of each of the first plane 31a and the second plane 31b is represented by T1. The thickness of each of the third plane 31c and the fourth plane 31d is represented by T2. The cross-section (second cross-section S2) of the quadrangular cross-section portion 31 is substantially constant in the longitudinal direction of the wire 2 (the direction along the axis X1).

[0032] As shown in FIG. 4, the width T1 and thickness T2 of the second cross section S2 are each smaller than the diameter D of the first cross section S1. The area of ​​the second cross section S2 is expressed as the product of T1 and T2, i.e., (T1·T2). The dashed dotted line in FIG. 4 represents a circle Y1 of diameter D. The circle Y1 corresponds to the outline of the outer circumferential surface of the wire 2. The dashed two-dotted line in FIG. 4 represents a square Y2 inscribed in the circle Y1. The cross-sectional area of ​​the quadrangular cross-sectional portion 31, i.e., the area of ​​the second cross section S2, is smaller than the area of ​​the square Y2 inscribed in the circle Y1. In other words, T1 <D、T2<D、かつT1·T2<D 2 The relationship is / 2.

[0033] The width T1 of the cross section of the rectangular cross section portion 31 may be larger than the thickness T2. In this case, the contact area of ​​the abutting portion 43 can be made larger compared to a square cross section. If the width T1 is larger than the thickness T2, the rigidity in the coil radial direction (indicated by the double-headed arrow C2 in FIG. 2) can be made larger compared to an end winding portion made of a wire with a circular cross section. However, the width T1 and the thickness T2 may be the same. It is preferable that the width T1 and the thickness T2 are each equal to or smaller than the root (√) / 2 of the diameter D of the first cross section.

[0034] The angle formed between the first plane 31a and the third plane 31c is, for example, 90°. The angle formed between the first plane 31a and the fourth plane 31d is, for example, 90°. The angle formed between the second plane 31b and the third plane 31c is, for example, 90°. The angle formed between the second plane 31b and the fourth plane 31d is, for example, 90°.

[0035] A rounded first corner 31e may be formed between the first plane 31a and the third plane 31c. A rounded second corner 31f may be formed between the second plane 31b and the third plane 31c. A rounded third corner 31g may be formed between the first plane 31a and the fourth plane 31d. A rounded fourth corner 31h may be formed between the second plane 31b and the fourth plane 31d.

[0036] The cross section of the cross-section changing portion 32 (third cross section S3 perpendicular to the axis X1) gradually changes from circular to rectangular as it moves from the circular cross-section portion 30 to the rectangular cross-section portion 31, and the cross-sectional area decreases. The cross-section changing portion 32 is formed between the circular cross-section portion 30 and the rectangular cross-section portion 31 by 1.0 turns or more.

[0037] As shown in FIG. 2, the cross section (third cross section S3) of the cross-section varying portion 32 has a first surface 32a, a second surface 32b, a third surface 32c, and a fourth surface 32d. A first arc-shaped portion 32e is formed between the first surface 32a and the third surface 32c. A second arc-shaped portion 32f is formed between the second surface 32b and the third surface 32c. A third arc-shaped portion 32g is formed between the first surface 32a and the fourth surface 32d. A fourth arc-shaped portion 32h is formed between the second surface 32b and the fourth surface 32d.

[0038] The first surface 32a is continuous with the first plane 31a of the rectangular cross-sectional portion 31. The second surface 32b is continuous with the second plane 31b. The third surface 32c is continuous with the third plane 31c. The fourth surface 32d is continuous with the fourth plane 31d. The first surface 32a and the second surface 32b are each aligned along the radial direction of the coil spring 1 (indicated by the double-headed arrow C2 in FIG. 2). The third surface 32c and the fourth surface 32d are each aligned along the central axis C1 of the coil spring 1.

[0039] The first arcuate portion 32e is connected to a first corner portion 31e (shown in FIG. 4) of the rectangular cross-sectional portion 31. The second arcuate portion 32f is connected to a second corner portion 31f of the rectangular cross-sectional portion 31. The third arcuate portion 32g is connected to a third corner portion 31g of the rectangular cross-sectional portion 31. The fourth arcuate portion 32h is connected to a fourth corner portion 31h of the rectangular cross-sectional portion 31.

[0040] Figure 5 shows the relationship between the longitudinal position and the polar moment of inertia (torsional rigidity) for three types of wires with different cross sections. The solid line M1 in Figure 5 indicates the polar moment of inertia of the wire 2 having a rectangular cross-sectional portion 31. The wire diameter of the circular cross-sectional portion 30 is 15.4 mm, and the width T1 and thickness T2 of the rectangular cross-sectional portion 31 are approximately 6 mm.

[0041] 5, the length L3a from zero (0) on the horizontal axis is the polar moment of area of ​​the cross-sectional changing portion 32, and the length L2a is the polar moment of area of ​​the quadrangular cross-sectional portion 31. The polar moment of area of ​​the quadrangular cross-sectional portion 31 is sufficiently smaller than the polar moment of area of ​​the circular cross-sectional portion 30.

[0042] The two-dot chain line M2 in Figure 5 indicates the polar moment of inertia of the wire of Comparative Example A, which has a flat tapered portion. The wire of Comparative Example A has a wire diameter of 15.4 mm at the circular cross section. It has a flat tapered portion over a length L4 from the edge of this circular cross section to the tip of the wire. The cross section of the flat tapered portion (a cross section perpendicular to the length of the wire) is a flat rectangle. The width of the end face of the flat tapered portion is 15.4 mm or more, and the thickness is 5.5 mm.

[0043] The polar moment of inertia (two-dot chain line M2) of Comparative Example A, which has a flat tapered portion, is significantly larger than the polar moment of inertia (solid line M1) of wire 2 having a rectangular cross-sectional portion 31. In the case of a coil spring made from the wire of Comparative Example A, in order to reduce the first spring constant when deflecting in the small load range, it is necessary to increase the number of turns in the flat tapered portion. Therefore, when the coil spring of Comparative Example A deflects with the second spring constant (large load range), the number of turns in the dead winding portion, which does not function as a spring, increases, and the weight increases accordingly.

[0044] The dashed line M3 in Figure 5 indicates the polar moment of inertia of the wire of Comparative Example B, which has a round tapered portion. The wire of Comparative Example B has a round tapered 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. The polar moment of inertia of Comparative Example B (dashed line M3) is greater than the polar moment of inertia of the wire 2 having a rectangular cross-section 31 (solid line M1).

[0045] In the case of a coil spring made of the wire of Comparative Example B, in order to reduce the first spring constant when bending in the low load range, it is necessary to increase the number of turns in the round tapered portion. As a result, when bending with the second spring constant (high load range), the number of turns in the dead coil portion that does not function as a spring increases, resulting in a corresponding increase in weight. Moreover, it is not easy to form a round tapered portion by processing a wire with a circular cross section. In contrast, the rectangular cross section portion 31 can be processed relatively easily using at least one pair of rolling rolls.

[0046] FIG. 6 schematically shows the spring characteristics (relationship between load and deflection) of a coil spring 1 having a rectangular cross-sectional portion 31. 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 rectangular cross-sectional portion 31 is primarily deflected.

[0047] This results in a first spring constant region E1 with a relatively small spring constant, as shown by line K1 in Figure 6. When the load exceeds W1, the rectangular cross-sectional portion 31 comes into close contact, and mainly the circular cross-sectional portion 30 bends. This results in a larger spring constant (second spring constant region E2), as shown by line K2 in Figure 6.

[0048] FIG. 7 shows the relationship between the stress generated inside the wire 2 when the coil spring 1 is compressed and the position from the bottom end of the wire 2. A stress peak τmax occurs 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.

[0049] As a result of intensive research, the inventors have found that if the number of turns in cross-section changing portion 32 is less than 1.0, the stress in cross-section changing portion 32 exceeds the peak stress τmax in effective portion 13, as shown by τ2 in Fig. 7. It is not preferable for the stress in cross-section changing portion 32 to exceed the stress in effective portion 13. Therefore, in this embodiment, the number of turns in cross-section changing portion 32 is set to 1.0 or more.

[0050] FIG. 8 shows a schematic diagram of an example of a rolling device 50 for forming the rectangular cross-sectional portion 31 and the cross-sectional varying portion 32. A wire 2 having a circular cross-section moves in the direction indicated by the arrow F1. The rolling device 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° around the axis X1, and the wire 2 is rolled again by the rolls 51 and 52.

[0051] 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.

[0052] 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.

[0053] 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 of the mandrel 61 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.

[0054] 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.

[0055] 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 rectangular cross-sectional portion 31, and a cross-sectionally varying portion 32, similar to coil spring 1 shown in FIG. 1.

[0056] [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.

[0057] [Example 1] The coil spring of Example 1 has a wire diameter of 18 mm in circular cross-sectional portion 30, a width and thickness of the cross-section (second cross-section) of square cross-sectional portion 31 each of approximately 7 mm, and a total number of turns of 8.5. The spring characteristics (relationship between load and deflection) of Example 1 are equivalent to those of Comparative Example 1. The weight of the coil spring of Example 1 is 5.2 kg, which is approximately 24% lighter than the coil spring of Comparative Example 1.

[0058] 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.

[0059] [Example 2] The coil spring of Example 2 has a wire diameter of 15 mm in circular cross-sectional portion 30, a width and thickness of the cross-section (second cross-section) of square cross-sectional portion 31 each of approximately 7 mm, and a total number of turns of 9.0. The spring characteristics of Example 2 are equivalent to those of Comparative Example 2. The weight of the coil spring of Example 2 is 4.0 kg, which is approximately 23% lighter than the coil spring of Comparative Example 2.

[0060] 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.

[0061] [Example 3] The coil spring of Example 3 has a wire diameter of 22 mm in circular cross-sectional portion 30, a width and thickness of the cross-section (second cross-section) of square cross-sectional portion 31 each of approximately 7 mm, and a total number of turns of 8.0. The spring characteristics of Example 3 are equivalent to those of Comparative Example 3. The weight of the coil spring of Example 3 is 6.5 kg, which is approximately 22% lighter than the coil spring of Comparative Example 3.

[0062] 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.

[0063] [Example 4] The coil spring of Example 4 has a wire diameter of 15 mm in circular cross-sectional portion 30, a width and thickness of the cross-section (second cross-section) of square cross-sectional portion 31 each of approximately 7 mm, and a total number of turns of 9.0. The spring characteristics of Example 4 are equivalent to those of Comparative Example 4. The weight of the coil spring of Example 4 is 5.0 kg, which is approximately 18% lighter than the coil spring of Comparative Example 4.

[0064] The rectangular cross-sectional portion 31 can be formed using a rolling mill. However, due to shape errors and the like that occur during forming, the width and thickness of the second cross-section 31 may vary. By making the width and thickness of the second cross-section 31 smaller than the wire diameter (the diameter of the first cross-section 30), and by making the area of ​​the second cross-section 31 smaller than the area of ​​a square inscribed in a circle with the diameter of the first cross-section S1, it is possible to reduce the weight compared to conventional coil springs. In particular, the weight reduction rate was large when the width T1 and thickness T2 of the rectangular cross-sectional portion 31 were each equal to or smaller than half the root (√) of the diameter D of the first cross-section S1.

[0065] FIG. 10 shows a coil spring 1A according to a second embodiment. The coil spring 1A has a rectangular cross-sectional portion 31 with 2 or more turns and a cross-sectionally varying portion 32 with 1.0 or more turns. The cross section of the wire of the second end winding portion 12 is circular, and the wire diameter is the same as the wire diameter of the circular cross-sectional portion 30. The second end winding portion 12 has a small-diameter winding portion 90 in which the coil diameter decreases toward the second 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-sectional portion 30. Other than the above, the coil spring 1A of the second embodiment has the same configuration and operation as the coil spring 1 of the first embodiment, so common reference numerals are used for both and description thereof will be omitted. [Industrial Applicability]

[0066] The present invention can be suitably used for suspension coil springs for vehicles such as automobiles, but can also be applied to coil springs for purposes other than vehicles. [Explanation of symbols]

[0067] 1, 1A...coil spring, 2...wire, 2a...first end, 2b...second end, 11...first end turn portion, 12...second end turn portion, 13...effective portion, 13a...winding portion, G1...gap, S1...first cross section, 30...circular cross section portion, D...diameter, Y1...circle, Y2...square, S2...second cross section, T1...width, T2...thickness, 31...rectangular cross section portion, 31a...first plane, 31b...second plane, 31c...third plane, 31d...fourth plane, 32...cross-sectional changing portion, 32a...first surface, 32b...second surface, 32c...third surface, 32d...fourth surface, 32e...first arc portion, 32f...second arc portion, 32g...third arc portion, 32h...fourth arc portion, 41...first winding portion, 42...second winding portion, 43...contact portion.

Claims

1. It comprises a wire (2) having a first end (2a) and a second end (2b), a first end turn portion (11) including the first end (2a) of the wire (2); a second end turn portion (12) including the second end (2b) 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) between adjacent winding portions (13a), The wire (2) a circular cross-sectional portion (30) having a first cross-section (S1) perpendicular to the longitudinal direction of the wire (2), the first cross-section being circular; a quadrangular cross-sectional portion (31) having a second cross-section (S2) whose cross-section perpendicular to the longitudinal direction is quadrangular, and having at least a first winding portion (41) and a second winding portion (42), wherein the width (T1) and the thickness (T2) of the second cross-section (S2) are each smaller than the diameter (D) of the first cross-section (S1), the width (T1) and the thickness (T2) of the second cross-section (S2) are different from each other, and the area of ​​the second cross-section (S2) is smaller than the area of ​​a square (Y2) inscribed in a circle of the diameter (D) of the first cross-section (S1); a cross-sectional change portion (32) formed between the circular cross-sectional portion (30) and the quadrangular cross-sectional portion (31) of the wire (2), in which a cross section perpendicular to the longitudinal direction changes from a circular shape to a quadrangular shape and a cross-sectional area decreases from the circular cross-sectional portion (30) to the quadrangular cross-sectional portion (31); A coil spring equipped with

2. 2. The coil spring according to claim 1, A coil spring, wherein the rectangular cross-sectional portion (31) has a first plane (31a) and a second plane (31b) extending along the radial direction of the coil spring, and a third plane (31c) and a fourth plane (31d) extending along a central axis (C1) of the coil spring.

3. The coil spring according to claim 2, The coil spring has an abutment portion (43) where the first winding portion (41) and the second winding portion (42) come into contact with each other when the coil spring is in a compressed state.

4. The coil spring according to claim 2, a coil spring in which the cross-sectional changing portion (32) has a first surface (32a) continuous with the first plane (31a), a second surface (32b) continuous with the second plane (31b), a third surface (32c) continuous with the third plane (31c), a fourth surface (32d) continuous with the fourth plane (31d), a first arc portion (32e) between the first surface (32a) and the third surface (32c), a second arc portion (32f) between the second surface (32b) and the third surface (32c), a third arc portion (32g) between the first surface (32a) and the fourth surface (32d), and a fourth arc portion (32h) between the second surface (32b) and the fourth surface (32d).

5. 2. The coil spring according to claim 1, A coil spring in which the width (T1) of the second cross section (S2) is greater than the thickness (T2).

6. 2. The coil spring according to claim 1, A coil spring in which the width (T1) and the thickness (T2) of the second cross section (S2) are each smaller than the length of one side of the square (Y2) inscribed in a circle (Y1) of diameter (D) of the first cross section (S1).

7. 2. The coil spring according to claim 1, A coil spring in which the width (T1) and the thickness (T2) of the second cross section (S2) are each equal to or less than half the root (√) of the diameter (D) of the first cross section (S1).

8. 2. The coil spring according to claim 1, The coil spring has a rectangular cross-sectional portion (31) of at least 2.0 turns or more, a length of the rectangular cross-sectional portion (31) extending from the first end (2a) beyond the length of the first end turn portion (11), and a cross-sectional variation portion (32) of at least 1.0 turn or more.

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