Coil spring

Abstract

A coil spring according to one embodiment is composed of a wire (2) having a first end (2a) and a second end (2b). The wire (2) includes a circular cross-section portion (30) having a first cross-section (S1) having a circular cross-section perpendicular to the longitudinal direction of the wire (2), a quadrilateral cross-section portion (31) having a second cross-section (S2) having a quadrilateral cross-section perpendicular to the longitudinal direction of the wire (2), and a cross-section changing portion (32) formed between the circular cross-section portion (30) and the quadrilateral cross-section portion (31). The cross-section changing section (32) changes from a circular shape to a quadrilateral shape in the direction of the circular cross-section section (30) toward the quadrilateral cross-section section (31). An end turn portion (11) of a coil spring includes a quadrilateral cross-sectional portion (31). The width (T1) and the thickness (T2) of the second cross-section (S2) are both smaller than the diameter (D) of the first cross-section (S1). The area of the second cross-section (S2) is smaller than the area of a square (Y2) inscribed with the circle of the diameter (D) of the first cross-section (S1).

Description

Technical Field

[0001] The invention relates to a coil spring used in scenarios such as vehicle suspension. Background Art

[0002] An example of a coil spring used in a vehicle suspension system is made of a helically wound wire. Typically, the wire cross section (a cross section perpendicular to the length direction of the wire) of the coil spring is circular. The coil spring has a first end turn portion contacting a first spring seat of the suspension device, a second end turn portion contacting a second spring seat, and an effective portion between the first end turn portion and the second end turn portion. The effective portion has a plurality of winding portions.

[0003] When the coil spring is compressed to a predetermined length by a load, there is a gap between the winding parts of the effective part. Regardless of the load, the end turn part always contacts the spring seat. Depending on the load, a part of the effective part contacts the spring seat or moves away from the spring seat.

[0004] The coil spring expands and contracts with a predetermined stroke between an assumed minimum load and a maximum load. Depending on the vehicle, a coil spring having nonlinear characteristics may be required. The spring constant of a coil spring having nonlinear characteristics changes according to the magnitude of the load. For example, when the load is small, the coil spring deflects with a first spring constant, and when the load becomes larger, the coil spring deflects with a second spring constant. The second spring constant is greater than the first spring constant.

[0005] It is also known that there is a conical coil spring having a conical portion in which the wire diameter decreases from the middle of the effective portion toward the end of the wire. In the conical coil spring, since the rigidity of the conical portion is low, the conical portion is mainly bent in a small load range. When the load increases, the conical portion is in close contact and the effective portion is mainly flexed, resulting in nonlinear characteristics.

[0006] [Reference technical literature]

[0007] [Patent Document]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 57-11743

[0009] [Patent Document 2] U.S. Patent No. 4,111,407

[0010] [Patent Document 3] Japanese Patent Application Laid-Open No. 56-141431

[0011] [Patent Document 4] Japanese Patent Application Laid-Open No. 2000-337415

[0012] [Patent document 5] Japanese Patent Application Publication No. 54-52257. Summary of the invention

[0013] Problems to be solved by the present invention

[0014] The wire diameter of the conical coil spring described in Japanese Patent Laid-Open No. 57-11743 (Patent Document 1) and U.S. Patent No. 4,770,139 gradually decreases. In the conical coil spring described in Japanese Patent Laid-Open No. 56-141431 (Patent Document 3), the cross-section of the wire of the tapered portion and the end turn portion is a rounded octagonal shape close to a circle. In such a coil spring made of a wire having a substantially circular cross-section, it is not easy to shape a portion of the wire having an extremely small diameter.

[0015] For example, in order to sufficiently reduce the diameter of the wire by plastic working, special rolling rollers are required. Although the wire diameter can be reduced by cutting or die forging, the processing cost is high and the processing time is long, which is not suitable for practical use. Due to these circumstances, it is difficult to significantly reduce the diameter of the corresponding part of the wire.

[0016] In a coil spring with nonlinear characteristics, although there is a limit to reducing the wire diameter of the tapered portion and the small cross-section portion (small diameter portion), increasing the number of turns of the tapered portion and the small cross-section portion can still reduce the spring constant in a small load range. The tapered portion and the small cross-section portion of a coil spring with nonlinear characteristics come into close contact as the load increases. Therefore, the tapered portion and the small cross-section portion that are in close contact become dead coils that do not function as springs. A coil spring with many dead coils will increase the weight of the vehicle.

[0017] The coil spring described in Japanese Patent Application Laid-Open No. 2000-337415 (Patent Document 4) and Japanese Patent Application Laid-Open No. 54-52257 (Patent Document 5) includes a portion of the wire in the length direction (including the end turn portion) rolled into a flat portion with a flat cross section, which can be formed using a general rolling roller. However, the flat portion has a much larger area secondary moment than a wire with a circular cross section. Therefore, even if the desired nonlinear characteristics can be obtained, it is difficult to reduce the weight of the coil spring.

[0018] An object of the present invention is to provide a lightweight coil spring having nonlinear characteristics.

[0019] Means of solving the problem

[0020] One embodiment of the present invention is a coil spring made of a wire having a first end and a second end, having a first end turn portion including the first end of the wire, a second end turn portion including the second end of the wire, and an effective portion. The effective portion has a plurality of winding portions formed between the first end turn portion and the second end turn portion, and there is a gap between the winding portions adjacent to each other.

[0021] The wire rod of the present embodiment has a circular cross-section portion, a quadrilateral cross-section portion and a cross-section variation portion, wherein the circular cross-section portion has a first cross-section perpendicular to the length direction of the wire rod and is circular, and the quadrilateral cross-section portion has a second cross-section perpendicular to the length direction and is quadrilateral. The quadrilateral cross-section has at least a first winding portion and a second winding portion, and the width and thickness of the second cross-section are both smaller than the diameter of the first cross-section. In addition, the area of ​​the second cross-section is smaller than the area of ​​a square inscribed in a circle having the diameter of the first cross-section. The cross-section variation portion is formed between the circular cross-section and the quadrilateral cross-section of the wire rod, and the cross-sectional shape perpendicular to the length direction gradually changes from a circle to a quadrilateral from the circular cross-section to the quadrilateral cross-section, and the cross-sectional area decreases.

[0022] A quadrilateral cross section can be processed relatively easily using a rolling roll, etc. Processing to reduce the cross-sectional area of ​​a quadrilateral cross section is easier than processing to reduce the cross-sectional area of ​​a circular cross section.

[0023] The quadrilateral 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 and second winding portions contact each other in a compressed state.

[0024] The cross-sectional variation portion includes a first surface continuous with the first plane, a second surface continuous with the second plane, a third surface continuous with the third plane, and a fourth surface continuous with the fourth plane. The cross-sectional variation portion also includes 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.

[0025] 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. In addition, the width and thickness of the second cross section may also be substantially the same. The width and thickness of the second cross section may both be less than the length of one side of a square inscribed in a circle having the diameter of the first cross section. The width and thickness of the second cross section may each be equal to or less than one-half the square root of the diameter of the first cross section. The number of turns of the quadrilateral cross section may have at least 2.0 turns or more, and starting from the first end, the quadrilateral cross section portion may have a length exceeding the first end turn portion. The cross-sectional variation portion may then have at least 1.0 turns or more.

[0026] Effects of the Invention

[0027] The quadrilateral cross section can be processed relatively easily using a rolling roller etc. The processing to reduce the cross-sectional area of ​​the quadrilateral cross section is easier than the processing to reduce the cross-sectional area of ​​the circular cross section. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1is a perspective view of a coil spring according to a first embodiment.

[0029] Figure 2 Yes means Figure 1 A perspective view showing a section of a portion of a coil spring when the coil spring is shown in a compressed state.

[0030] Figure 3 This is a side view showing a portion of the wire rod of the coil spring before winding.

[0031] Figure 4 is a schematic cross-sectional view of an example of a quadrilateral cross-section of a wire.

[0032] Figure 5 It is a graph showing the secondary axial moment of three wires having different cross sections.

[0033] Figure 6 It is schematically indicated Figure 1 Graph of the spring characteristic (deflection versus load) of a coil spring shown.

[0034] Figure 7 This is a diagram showing the relationship between the winding position from the lower end of the coil spring and the stress.

[0035] Figure 8 It is a perspective view schematically showing a roller device.

[0036] Fig. 9 It is a plan view of a part of a winding machine.

[0037] Fig.10 is a perspective view of a coil spring according to a second embodiment. DETAILED DESCRIPTION

[0038] The coil spring according to the first embodiment of the present invention will be described below with reference to Figures 1 to 9 Provide explanation.

[0039] Figure 1 A coil spring 1 for use in a suspension system of a vehicle such as an automobile is shown. The coil spring 1 has a helically wound wire 2. 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 11 including the first end 2a of the wire 2, a second end turn 12 including the second end 2b, and an effective portion 13.

[0040] The effective portion 13 is formed between the first end turn portion 11 and the second end turn portion 12, and has a plurality of winding portions 13a. When the coil spring 1 is assembled into a suspension system of a vehicle, 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 (given by Figure 2 The double-headed arrow C2 in FIG. 1 is in the radial direction of the coil spring 1 .

[0041] An example of the effective portion 13 is a portion having a constant pitch P1 (eg Figure 1 Here, "substantially constant" means that the variation of the tolerance range of the helical spring manufactured by the winding machine and the variation of the tolerance range due to springback are practically negligible. In addition, non-cylindrical helical springs in which the pitch P1 and the coil diameter R1 vary in the direction along the central axis C1 may also be used.

[0042] The first end turn 11 is formed by a spring seat 20 (such as Figure 2 The second end turn 12 is supported by a spring seat 21 (as shown) on the lower side of the suspension. Figure 1 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 (a load range used as a suspension device), the effective portion 13 has a gap G1 between adjacent winding portions 13a.

[0043] The coil spring 1 for a vehicle suspension system is used within a load range between an expected minimum load and a maximum load. The effective portion 13 effectively acts as a spring in both a maximum compression full impact state and a maximum extension full rebound state, and adjacent winding portions 13a do not contact each other.

[0044] Figure 2 1 is a perspective view showing a portion (near the end turn 11) of the coil spring 1 in cross section, wherein the coil spring 1 is in a compressed state. The coil spring 1 of the present embodiment includes a circular cross-sectional portion 30, a quadrilateral cross-sectional portion 31, and a cross-sectional change portion 32. The cross-sectional change portion 32 is formed between the circular cross-sectional portion 30 and the quadrilateral cross-sectional portion 31. The first end turn 11 includes the quadrilateral cross-sectional portion 31 and is formed in a spiral shape. The second end turn 12 includes a portion of the circular cross-sectional portion 30 and is formed in a spiral shape. The effective portion 13 has a circular cross-sectional portion 30 and has a plurality of spirally formed winding portions 13a.

[0045] Figure 3 A portion of the wire 2 before winding is shown. A central axis X1 passing through the wire 2 extends along the length direction of the wire 2. Figure 3The wire 2 shown has a circular cross-sectional portion 30 with a length L1, a quadrilateral cross-sectional portion 31 with a length L2, and a cross-sectional change portion 32 with a length L3. The circular cross-sectional portion 30 has a length L1 required for the plurality of winding portions 13a of the effective portion 13.

[0046] The quadrilateral cross-sectional portion 31 is formed at a length L2 from the first end 2a of the wire 2. The length L2 corresponds to a length corresponding to two or more turns of the coil spring 1. The cross-sectional change portion 32 is formed at a length L3 between the circular cross-sectional portion 30 and the quadrilateral cross-sectional portion 31. The quadrilateral cross-sectional portion 31 has a length L2 that exceeds the first end turn portion 11 from the first end 2a, and includes at least a first winding portion 41 and a second winding portion 42.

[0047] like Figure 2 As shown, the circular cross-section 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 length direction of the wire 2 (in the direction of the axis X1). Since the second end turn 12 is a part of the circular cross-section portion 30, the cross-section of the wire 2 here is circular. The wire diameter of the second end turn 12 (the cross-sectional diameter of the wire 2) is the same as the wire diameter of the effective portion 13.

[0048] The quadrilateral cross-section portion 31 has a second cross-section S2 which is a quadrilateral cross-section perpendicular to the axis X1 of the wire 2. The quadrilateral cross-section portion 31 has an upper first plane 31a, a lower second plane 31b, an outer third plane 31c, and an inner fourth plane 31d. The first plane 31a and the second plane 31b are both along the radial direction of the coil spring 1 (by Figure 2 The third plane 31c and the fourth plane 31d are both arranged along the central axis C1 of the coil spring 1.

[0049] Figure 2 The state in which the coil spring 1 is compressed by a load along the center axis C1 is shown. The quadrilateral 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 the coil diameter r1 of the first winding portion 41, or is the same as the coil diameter r1 of the first winding portion 41. When the coil spring 1 is compressed, the first plane 31a of the first winding portion 41 and the second plane 31b of the second winding portion 42 overlap in the direction along the center axis 1C of the coil spring 1. As a result, a contact portion 43 is formed in which the first winding portion 41 and the second winding portion 42 contact each other in the thickness direction. Therefore, it is possible to prevent the second winding portion 42 from entering (slipping) into the interior of the first winding portion 41.

[0050] Figure 4 2 is a cross-sectional view schematically showing an example of a quadrilateral cross-sectional portion 31. The second cross-sectional portion S2 is a quadrilateral including a square or a rectangle. Figure 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 quadrilateral cross-sectional portion 31 is substantially constant in the length direction of the wire 2 (in the direction along the axis X1).

[0051] like Figure 4 As shown, the width T1 and thickness T2 of the second cross section S2 are both smaller than the diameter D of the first cross section S1. The area of ​​the second cross section S2 is represented by the product of T1 and T2, that is, (T1·T2). Figure 4 The one-dot chain line in represents a circle Y1 having a diameter D. The circle Y1 corresponds to the contour of the outer peripheral surface of the wire material 2 . Figure 4 The double-dashed line in represents the square Y2 inscribed in the circle Y1. The cross-sectional area of ​​the quadrilateral cross-sectional portion 31, that is, the area of ​​the second cross-sectional area S2, is smaller than the area of ​​the inscribed square Y2 of the circle Y1. That is, T1 <D、T2<D、T1·T2<D2 / 2。

[0052] The cross-sectional width T1 of the quadrilateral cross-sectional portion 31 may be greater than the thickness T2. In this case, the contact area of ​​the contact portion 43 can be increased compared to the square cross-sectional portion. If the width T1 is greater than the thickness T2, the radial direction of the coil (by the diameter of the coil 43) can be increased compared to the end turn portion made of a wire having a circular cross-sectional area. Figure 2 The double-headed arrow C2 in the figure indicates the rigidity on the surface of the first cross section. However, the width T1 and the thickness T2 may be the same. Preferably, the width T1 and the thickness T2 are both equal to or less than 1 / 2 times the square root of the diameter D of the first cross section.

[0053] The angle between the first plane 31a and the third plane 31c is, for example, 90°. The angle between the first plane 31a and the fourth plane 31d is, for example, 90°. The angle between the second plane 31b and the third plane 31c is, for example, 90°. The angle between the second plane 31b and the fourth plane 31d is, for example, 90°.

[0054] The first rounded corner portion 31e may be formed between the first plane 31a and the third plane 31c. The second rounded corner portion 31f may be formed between the second plane 31b and the third plane 31c. The third rounded corner portion 31g may be formed between the first plane 31a and the fourth plane 31d. The fourth rounded corner portion 31h may be formed between the second plane 31b and the fourth plane 31d.

[0055] The cross section of the cross-sectional changing portion 32 (third cross section S3 perpendicular to the axis X1) gradually changes from a circle to a quadrilateral from the circular cross-sectional portion 30 to the quadrilateral cross-sectional portion 31, and the cross-sectional area decreases. The cross-sectional changing portion 32 forms more than 1.0 turn between the circular cross-sectional portion 30 and the quadrilateral cross-sectional portion 31.

[0056] like Figure 2 As shown, the cross section (third cross section S3) of the cross section change portion 32 has a first surface 32a, a second surface 32b, a third surface 32c and a fourth surface 32d. A first arc portion 32e is formed between the first surface 32a and the third surface 32c. A second arc portion 32f is formed between the second surface 32b and the third surface 32c. A third arc portion 32g is formed between the first surface 32a and the fourth surface 32d. A fourth arc portion 32h is formed between the second surface 32b and the fourth surface 32d.

[0057] The first surface 32a is continuous with the first plane 31a of the quadrilateral cross-section 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 both along the radial direction (by Figure 2 The third surface 32c and the fourth surface 32d are both arranged along the central axis C1 of the coil spring 1.

[0058] The first arc portion 32e is aligned with the first corner portion 31e (eg, Figure 4 The second arc portion 32f is continuous with the second corner portion 31f of the quadrilateral cross-sectional portion 31. The third arc portion 32g is continuous with the third corner portion 31g of the quadrilateral cross-sectional portion 31. The fourth arc portion 32h is continuous with the fourth corner portion 31h of the quadrilateral cross-sectional portion 31.

[0059] Figure 5 The graph shows the relationship between the lengthwise position and the secondary moment (torsional stiffness) of three wires with different cross sections. Figure 5 The solid line M1 in φ represents the secondary moment of the wire 2 having the quadrilateral 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 quadrilateral cross-sectional portion 31 are each approximately 6 mm.

[0060] exist Figure 5 , the length L3a from zero (0) on the horizontal axis is the secondary moment of the cross-sectional changing portion 32, and the length L2a is the secondary moment of the quadrilateral cross-sectional portion 31. The secondary moment of the quadrilateral cross-sectional portion 31 is smaller than the secondary moment of the circular cross-sectional portion 30.

[0061] Figure 5The double-dotted line M2 in represents the secondary moment of the wire of Comparative Example A having a flat tapered portion. The wire diameter of the circular cross-section portion of the wire of Comparative Example A is 15.4 mm. A flat tapered portion is provided over a length L4 from the end of the circular cross-section portion to the end of the wire. The cross section of the flat tapered portion (a cross section perpendicular to the length direction of the wire) is a flat quadrilateral. The width of the end face of the flat tapered portion is greater than 15.4 mm, and the thickness is 5.5 mm.

[0062] The secondary moment of the comparative example A (two-dot chain line M2) having a flat tapered portion is much greater than the secondary moment of the wire 2 (solid line M1) having a quadrilateral cross-sectional portion 31. In the case of the coil spring made of a wire of the comparative example A, in order to reduce the first spring constant when flexing in a small load range, it is necessary to increase the number of turns of the flat tapered portion. Therefore, when the coil spring of the comparative example A is flexed with the second spring constant (large load range), the number of turns of the dead coil portion that does not act as a spring increases, and the weight increases accordingly.

[0063] Figure 5 The dotted line M3 in the figure represents the secondary moment of the wire of comparative example B having a conical portion. The wire of comparative example B has a conical portion with a length of L3a from the end of the circular cross-section portion and a small cross-section portion with a length of L2a (wire diameter 11.4 mm). The diameter of the wire of the circular cross-section is 15.4 mm. The secondary moment of the cross section of comparative example B (dotted line M3) is larger than the secondary moment of the cross section of the wire 2 having a quadrilateral cross-section portion 31 (solid line M1).

[0064] In the case of the coil spring made of wire of Comparative Example B, in order to reduce the first spring constant when flexing in a small load range, it is necessary to increase the number of turns of the conical portion. Therefore, when the spring is flexed with the second spring constant (large load range), the number of turns of the dead coil portion that does not act as a spring increases, and the weight increases accordingly. In addition, it is not easy to form the conical portion by processing a wire of a circular cross-section. On the other hand, the use of at least one pair of rollers enables relatively easy processing of the quadrilateral cross-section portion 31.

[0065] Figure 6 The spring characteristic (the relationship between load and deflection) of the coil spring 1 having the quadrilateral cross-sectional portion 31 is schematically shown. Figure 6 The horizontal axis represents deflection, and the vertical axis represents load. The coil spring 1 is compressed on the lower spring seat 21 (such as Figure 1 As shown) and the upper spring seat 20 (as Figure 2 When the load is between zero and W1, bending mainly occurs in the quadrilateral cross-sectional portion 31.

[0066] Therefore, if Figure 6As shown by line K1 in FIG. 1 , the first spring constant region E1 has a relatively small spring constant. When the load exceeds W1, the quadrilateral cross-sectional portion 31 is in close contact, and mainly the circular cross-sectional portion 30 is bent. Therefore, as shown in FIG. Figure 6 As shown by the line K2 in FIG. 1 , the spring constant becomes larger (second spring constant region E2 ).

[0067] Figure 7 The relationship between the stress generated inside the wire when the coil spring 1 is compressed and the position from the lower end of the wire 2 is shown. Stress peaks τmax are generated in each winding portion 13a of the effective portion 13. These peaks τmax are smaller than the allowable stress in the suspension system. A small peak τ1 appears near the end turn portion 1.

[0068] The inventors have conducted extensive research and found that when the number of turns of the cross-sectional changing portion 32 is less than 1.0, the stress in the cross-sectional changing portion 32 reaches the peak value of the stress in the effective portion 13, as shown below: Figure 7 It is known from τ2 in that it exceeds τmax. It is not preferable that the stress in the cross-sectional change portion 32 exceeds the stress in the effective portion 13. Therefore, in this embodiment, the number of turns of the cross-sectional change portion 32 is set to 1.0 or more.

[0069] Figure 8 An example of a rolling device 50 for forming a quadrilateral cross-sectional portion 31 and a cross-sectional variation portion 32 is schematically shown. The wire rod 2 having a circular cross-sectional area moves in the direction indicated by the arrow F1. The rolling device 50 has rollers 51 and 52. The distance between the rollers 51 and 52 can be adjusted. The wire rod 2 is rolled by the rollers 51 and 52. Thereafter, the wire rod 2 is rotated 90 degrees around the axis X1, and the wire rod 2 is rolled by the rolling rollers 51 and 52 again.

[0070] Fig. 9 A portion of a coiling machine 60 for hot forming a coil spring (eg, above the A3 phase transition point and below 1150° C.) is shown. The coiling machine 60 includes a cylindrical mandrel 61 , a chuck 62 and a guide 63. The guide 63 includes a pair of first guide rollers 65,66.

[0071] The wire 2 made of spring steel is cut into the length of one coil spring in advance. The wire 2 is heated to the austenitizing temperature (above the A3 transformation point and below 1150°C) and supplied to the mandrel 61 by the supply mechanism. The chuck 62 fixes the front end of the wire 2 to the mandrel 61. The guide 63 controls the position of the wire 2 wound on the mandrel 61 by guiding the wire 2.

[0072] One end 61a of the mandrel 61 is held on the drive head 70 by the chuck 62. The mandrel 61 is rotated around the axis X2 of the mandrel 61 by the drive head 70. The other end 61b of the mandrel 61 is rotatably supported on the mandrel holder 71. The guide portion 63 moves in the direction along the axis X2 of the mandrel 61, and guides the wire 2 according to the pitch angle of the coil spring to be formed.

[0073] The length of the wire 2 is equivalent to a coil spring. Before the wire 2 is supplied to the mandrel 61, the wire 2 is heated in a heating furnace. The front end of the heating wire 2 is fixed to the mandrel 61 by a chuck 62. When the mandrel 61 rotates, the guide 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 on the mandrel 61 at a predetermined pitch.

[0074] Comparative Examples 1, 2, 3, and 4 described below are coil springs having nonlinear characteristics, each of which has an effective portion having a circular cross section, a circular tapered portion, and a small cross section portion. Figure 1 The coil spring 1 shown is similar, and embodiments 1, 2, 3 and 4 all have nonlinear characteristics, having a circular cross-sectional portion 30, a quadrilateral cross-sectional portion 31 and a cross-sectional variation portion 32. It is a coil spring.

[0075] [Comparative Example 1]

[0076] The coil spring of Comparative Example 1 has a wire diameter of 18 mm in the circular cross section, a wire diameter of 13 mm in the small cross section, a total number of turns of 8.5, and a weight of 7.0 kg.

[0077] [Example 1]

[0078] In the coil spring of Example 1, the wire diameter of the circular cross-section portion 30 is 18 mm, the width and thickness of the cross section (second cross section) of the quadrilateral cross-section portion 31 are each about 7 mm, and the total number of turns is 8.5. The spring characteristics (the relationship between load and deflection) of Example 1 are the same as those of Comparative Example 1. The weight of the coil spring of Example 1 is 5.2 kg, which is about 24% lighter than the coil spring of Comparative Example 1.

[0079] [Comparative Example 2]

[0080] The coil spring of Comparative Example 2 has a wire diameter of 15 mm in the circular cross section, a wire diameter of 11 mm in the small cross section, a total number of turns of 8.5 turns, and a weight of 7.0 kg.

[0081] [Example 2]

[0082] In the coil spring of Example 2, the wire diameter of the circular cross-section portion 30 is 15 mm, the width and thickness of the cross section (second cross section) of the quadrilateral cross-section portion 31 are each about 7 mm, and the total number of turns is 9.0. The spring characteristics of Example 2 are the same as those of Comparative Example 2. The weight of the coil spring of Example 2 is 4.0 kg, which is about 23% lighter than the coil spring of Comparative Example 2.

[0083] [Comparative Example 3]

[0084] The coil spring of Comparative Example 3 has a wire diameter of 22 mm in the circular cross section, a wire diameter of 17 mm in the small cross section, a total number of turns of 8.0 turns, and a weight of 8.5 kg.

[0085] [Example 3]

[0086] In the coil spring of Example 3, the wire diameter of the circular cross-section portion 30 is 22 mm, the width and thickness of the cross section (second cross section) of the quadrilateral cross-section portion 31 are each about 7 mm, and the total number of turns is 8.0. The spring characteristics of Example 3 are the same as those of Comparative Example 3. The weight of the coil spring of Example 3 is 6.5 kg, which is about 22% lighter than the coil spring of Comparative Example 3.

[0087] [Comparative Example 4]

[0088] The coil spring of Comparative Example 4 has a wire diameter of 16 mm in the circular cross section, a wire diameter of 12 mm in the small cross section, a total number of turns of 10.0 turns, and a weight of 6.0 kg.

[0089] [Example 4]

[0090] In the coil spring of Example 4, the wire diameter of the circular cross-section portion 30 is 15 mm, the width and thickness of the cross section (second cross section) of the quadrilateral cross-section portion 31 are each about 7 mm, and the total number of turns is 9.0. The spring characteristics of Example 4 are the same as those of Comparative Example 4. The weight of the coil spring of Example 4 is 5.0 kg, which is about 18% lighter than the coil spring of Comparative Example 4.

[0091] The quadrilateral cross-sectional portion 31 can be formed using a rolling roller. However, the width and thickness of the second section S2 may vary due to shape errors caused during molding. The width and thickness of the second section S2 are both smaller than the wire diameter (the diameter of the first section S1), and the area of ​​the second section S2 is made into a circle with the diameter of the first section S1 as a circle. By making the area of ​​the first section S1 smaller than the inscribed square, the weight can be reduced compared to the conventional coil spring. In particular, when the width T1 and thickness T2 of the quadrilateral cross-sectional portion 31 are both equal to or less than the square root 1 / 2 of the diameter D of the first section S1, the weight can be greatly reduced.

[0092] Fig.10A coil spring 1A according to a second embodiment is shown. The coil spring 1A has a quadrilateral cross-sectional portion 31 of more than 2 turns and a cross-sectional change portion 32 of more than 1.0 turns. The wire cross section of the second end turn 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 turn 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 turn portion 12 may be smaller than the wire diameter of the circular cross-sectional portion 30. Since the coil spring 1A of the second embodiment and the coil spring 1 of the first embodiment have the same structure and operation except for the above, the same reference numerals are given to both of them, and their description will be omitted.

[0093] [Possibility of industrial application]

[0094] The present invention can be applied to suspension coil springs for vehicles such as automobiles, and can also be applied to coil springs for other than vehicles.

[0095] [Explanation of symbols]

[0096] 1, 1A, coil spring; 2, wire; 2a, first end; 2b, second end; 11, first end turn; 12, second end turn; 13, effective portion; 13a, winding portion; G1, gap; S1, d first section; 30, circular section; D, diameter; Y1, circle; Y2, square; S2, second section; T1, width; T2, thickness; 31, quadrilateral section; 31a, first plane; 31b, second plane; 31c, third plane; 31d, fourth plane; 32, section change 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. A coil spring, comprising a wire (2) having a first end (2a) and a second end (2b), comprising a first end turn portion (11) having the first end (2a) of the wire (2); a second end turn portion (12) having the second end (2b) of the wire (2); a plurality of winding portions (13a) formed between the first end turn portion (11) and the second end turn portion (12); and an effective portion (13) having a gap between adjacent winding portions (13a); It is characterized in that The wire (2) comprises a circular cross-section portion (30) having a first cross-section (S1) perpendicular to the length direction of the wire (2) and a circular cross-section; a quadrilateral cross-section portion (31) having a second cross-section (S2) perpendicular to the length direction of the wire (2) and a quadrilateral cross-section; 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 respectively smaller than the diameter (D) of the first cross-section (S1) and the area of ​​the second cross-section (S2) is smaller than the area of ​​a square (Y2) inscribed in a circle with the diameter (D) of the first cross-section (S1); and a cross-section changing portion (32), wherein the cross-section changing portion (32) is formed perpendicular to the length direction of the wire between the circular cross-section (30) and the quadrilateral cross-section (31) of the wire (2), and the cross-section changes from a circle to a quadrilateral in a direction from the circular cross-section portion (30) toward the quadrilateral cross-section portion (31) and the cross-section area decreases.

2. In the coil spring according to claim 1, The quadrilateral cross section (31) has a first plane (31a) and a second plane (31b) along the radial direction of the coil spring and a third plane (31c) and a fourth plane (31d) along the central axis (C1) of the coil spring.

3. In the coil spring according to claim 2, The coil spring has a contact portion (43), and when the coil spring is compressed, the first winding portion (41) and the second winding portion (42) contact each other at the contact portion (43).

4. In the coil spring according to claim 2, The cross-sectional variation portion (32) includes 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), and a fourth surface (32d) continuous with the fourth plane (31d); and also includes a first arc portion (32e) located between the first surface (32a) and the third surface (32c), a second arc portion (32f) located between the second surface (32b) and the third surface (32c), a third arc portion (32g) located 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. In the coil spring according to claim 1, A coil spring, characterized in that: The width (T1) and thickness (T2) of the second cross section (S2) are different from each other.

6. In the coil spring according to claim 5, A coil spring, characterized in that: The width (T1) of the second cross section (S2) is greater than the thickness (T2).

7. In the coil spring according to claim 1, A coil spring, characterized in that: The width (T1) and thickness (T2) of the second cross section (S2) are substantially equal.

8. In the coil spring according to claim 1, The width (T1) and thickness (T2) of the second cross section (S2) are both smaller than the length of one side of an inscribed square (Y2) of the first cross section (S1) and a circular cross section of the diameter (D).

9. In the coil spring according to claim 1, The width (T1) and thickness (T2) of the second section (S2) are both less than or equal to one-half of the square root of the diameter (D) of the circular section in the first section (S1).

10. In the coil spring according to claim 1, The quadrilateral cross section (31) has at least 2.0 turns, and the distance between the quadrilateral cross section (31) and the first end (2a) exceeds the length of the first end turn portion (11), and the cross-sectional change portion (32) has at least 1.0 turn or more.

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