HELICAL SPRING

Abstract

According to one embodiment, a helical spring includes a wire rod (2) having one end and the other end. The wire rod (2) of the helical spring includes, with respect to a section of the wire rod (2), a round-section portion (30) of an effective spring portion (13), a square-section portion (31) in which the section is substantially square, and a tapered portion (32). The square-section portion (31) includes an end-turn portion (11)(12). A length on each side of the section of the square-section portion (31) is less than or equal to the square root of 1 / 2 multiplied by a diameter of the wire rod (2) of the round-section portion (30). In the tapered portion (32), from the round-section portion (30) to the square-section portion (31), the section changes from a round shape to a substantially square shape, and the cross-sectional area is reduced.

Description

HELICAL SPRING RRCQnn / cznz / e / Y TECHNICAL FIELD OF THE INVENTION The present invention relates to a helical spring used, for example, for the suspension of a vehicle. BACKGROUND OF THE INVENTION An example of a coil spring used for vehicle suspension consists of a wire rod wound helically. Generally, the cross-section of the wire rod in the coil spring (in other words, a section perpendicular to the longitudinal direction of the wire rod) is round. The coil spring comprises a first end section that is in contact with the first spring seat of the suspension, a second end section that is in contact with a second spring seat, and an effective spring section between the first and second end sections. The effective spring portion comprises a plurality of helical coil portions. In a state where the helical spring is compressed to a predetermined length by a load, a gap is defined between the helical portions of the effective spring portion. Each extreme coil portion is always in contact with the spring seat, regardless of the magnitude of the load. A portion of the effective spring portion makes contact with the spring seat or moves away from the spring seat according to the magnitude of the load. The helical spring extends and retracts through a predetermined range of motion between a minimum and a maximum load. Depending on the vehicle, a helical spring with nonlinear characteristics may be desirable. In a helical spring with nonlinear characteristics, the spring's behavior changes continuously according to the magnitude of the load. For example, when the load is small, the helical spring deflects according to a first spring constant. When the load is large, the helical spring deflects according to a second spring constant. The second spring constant is greater than the first spring constant. A conical helical spring is also known in which the wire diameter decreases towards one end from an intermediate portion of the effective spring. In a conical helical spring, the stiffness of the conical portion is lower. Therefore, in an area where the load is small, the conical portion is primarily deflected. When the load is increased, the conical portion comes into close contact, and thus the effective spring portion deflects, giving it non-conductive characteristics. RAConn / eznz / B / Y linear. In the conical helical spring described in JP S57 11743 A (Patent Document 1), the wire diameter decreases from an intermediate portion of an effective spring part to the extreme loop portion. In the conical helical spring described in JP S56-141431 A (Patent Document 2), the wire rod section of a conical portion and an extreme loop portion has the shape of a rounded octagon similar to a circle. List of appointments Patent documents Patent Document 1: JP S57-11743 A Patent Document 2: JP S56-141431 A Patent Document 3: JP 2000-337415 A Patent Document 4: JP S54-52257 A Summary of the invention Technical problem It is not easy to process a part where the wire diameter is extremely small in a helical spring formed from wire rod with a substantially circular cross-section. For example, a special reducing roller is needed to make the wire diameter sufficiently smaller through plastic working. The wire diameter can be reduced by planing or stamping. RAConn / eznz / B / Y However, the processing cost is high and the processing time is long. Therefore, they are impractical. For these reasons, it was difficult to make the wire diameter of a portion of the wire rod extremely small. Even if there is a limit to the reduction in wire diameter of the tapered and narrow sections of a helical spring with nonlinear characteristics, the spring constant in an area of ​​low load can be reduced by increasing the number of turns in the tapered and narrow sections. However, the tapered and narrow sections of the helical spring with nonlinear characteristics come into close contact when the load is high. These sections become dead-loop sections that no longer function as springs. A helical spring with a high number of turns in the dead-loop section increases the weight of a vehicle. The helical springs described in JP 2000-337415 A (Patent Document 3) and JP S54-52257 A (Patent Document 4) are formed by rolling a portion of a wire rod in the longitudinal direction (i.e., rolling a portion that includes an end portion) into a flat, rectangular cross-section. The flat portion with a rectangular cross-section can be formed with RRCQnn / cznz / e / Y relative ease using a common reduction roller. However, in a flat portion, the polar moment of inertia of the area is very large compared to a wire with a round cross-section. Therefore, in a helical spring with nonlinear characteristics comprising a flat portion, it is difficult to reduce the weight of the helical spring even though the spring with the desired nonlinear characteristics can be obtained. The present invention aims to provide a lightweight helical spring having nonlinear characteristics. Solution to the problem One embodiment of the present invention is a helical spring comprising a wire rod having one end and one end. The helical spring comprises a first end-loop portion including one end of the wire rod, a second end-loop portion including the other end of the wire rod, and an effective spring portion. The effective spring portion comprises a plurality of spiral portions formed between the first end-loop portion and the second end-loop portion, and has a space between adjacent spiral portions. The effective spring portion comprises a round-section portion in which a first section is perpendicular to a longitudinal direction. RRConn / eznz / B / Y of the wire is round. Furthermore, the helical spring of the present embodiment comprises a square-section portion formed from the end of the wire over a length of the first extreme turn, and a conical portion formed between the round-section portion and the square-section portion, having 1.0 turn or more. In the square-section portion, a second section perpendicular to the longitudinal direction is substantially square, and the length of each side of the second section is less than or equal to the square root of 1 / 2 multiplied by the wire diameter of the round-section portion, and the second section is constant in the longitudinal direction. In a section of the conical portion (in other words, a third section perpendicular to the longitudinal direction of the wire), a round shape changes to a substantially square shape, and the cross-sectional area decreases from the round-section portion to the square-section portion. The square-section portion may comprise a first outer surface and a second inner surface along a central axis of the helical spring, and a third upper surface and a fourth lower surface perpendicular to the first and second surfaces and parallel to each other. In the helical spring of the present RRCQnn / cznz / e / Y modality, the square section portion comprises at least a first helical portion and a second helical portion, and may comprise a contact portion in which the third surface of the first helical portion is in contact with the fourth surface of the second helical portion in a state in which the helical spring is compressed. A spiral radius of the second spiral portion of the square section portion may be less than a spiral radius of the first spiral portion. The conical portion may comprise a first flat portion continuous with the first surface of the square 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. RRConn / eznz / B / Y Advantageous effects of the invention The square section portion can be formed relatively easily using a reducing roller, etc. Furthermore, it is not very difficult to make the cross-sectional area of ​​the square section portion sufficiently smaller than that of the round section portion. RACQnn / cznz / e / Y BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a helical spring according to a first modality. Figure 2 is a perspective view in which part of the helical spring shown in Figure 1 is shown by a section in a state in which the helical spring is compressed. Figure 3 is a side view showing a portion of the helical spring wire rod before the wire is wound. Figure 4 is a cross-sectional view that schematically shows an example of the square cross-section portion of the wire rod. Figure 5 is a diagram showing the polar moment of inertia of the area of ​​each of the three types of wire rod that have different cross-sections. Figure 6 is a diagram that schematically shows the elastic characteristics of the helical spring shown in Figure 1 (the relationship between deflection and a load). Figure 7 is a diagram showing the turns from the lower end of the helical spring and a tension (inner side of the spiral). Figure 8 is a perspective view schematically showing a roller device. Figure 9 is a plan view of a part of a winding machine. Figure 10 is a perspective view of a helical spring according to a second modality. Figure 11 is a perspective view showing a section of the helical spring shown in Figure 10. RACQnn / CZnZ / B / Y METHOD FOR CARRYING OUT THE INVENTION Hereafter, this specification describes a helical spring in accordance with an embodiment of the present invention with reference to Figure 1 to Figure 9. Figure 1 shows a helical spring 1 used for the suspension device of a vehicle such as an automobile. The helical spring 1 comprises a helically wound wire rod 2. The wire rod 2 is made, for example, of spring steel. The helical spring 1 comprises a first end loop 11 including one end 2a of the wire rod 2, a second end loop 12 including the other end 2b of the wire rod 2, and an effective spring portion 13. The effective spring portion 13 is formed between the first end loop 11 and the second end loop 12 and comprises a plurality of portions of the coil 13a. When the helical spring 1 is incorporated into the suspension device of a vehicle, the first end loop 11 is located on the upper side, and the second end loop 12 is located on the lower side. In this case, the central axis C1 of helical spring 1 extends in a vertical direction. An example of the effective spring part 13 has a cylindrical shape in which the pitch P1 (shown in Figure 1) is constant and the spiral radius R1 is substantially constant. Here, the expression "substantially constant" indicates that the variation in the tolerance range of the helical spring manufactured by a coiler and the variation in the acceptable range due to spring recovery are practically negligible. The helical spring may have a non-cylindrical shape in which the pitch P1 and the spiral radius R1 change in one direction along the central axis C1. The first extreme return portion 11 is supported by a spring seat 20 (shown in Figure 2) provided at the top of the suspension device. As shown in Figure 1, the second extreme return portion 12 is supported by a spring seat 21 arranged at the bottom of the suspension device. The coil spring 1 is compressed between the upper spring seat 20 and the lower spring seat 21. In a state in the RRConn / eznz / B / Y that the helical spring 1 is compressed in a predetermined loading area (in the load range used as a suspension device), the effective spring part 13 has a space G1 between adjacent spiral portions 13a. The helical spring 1 used for a vehicle's suspension device operates within a load range between a minimum assumed load and a maximum load. The effective spring portion 13 functions as a spring such that adjacent helical portions 13a are not in contact with each other in a fully compressed state, where the helical spring is compressed to a minimum length, or in a fully extended state, where the helical spring is extended to a maximum length. Figure 2 is a perspective view showing a cross-section of a portion of the helical spring 1 (the vicinity of the extreme loop portion 11) in a compressed state. The helical spring 1 of the present embodiment includes a round-section portion 30 included in the effective spring portion 13, a square-section portion 31 forming the first extreme loop portion 11 and a portion of the effective spring portion 13, and a conical portion 32 formed between the round-section portion 30 and the square-section portion 31. The first extreme loop portion 11 comprises the square-section portion RACQnn / cznz / e / Y square 31, and is helically formed. The second extreme turn part 12 comprises a portion of the round section portion 30 and is helically shaped. The effective spring part 13 includes the round section portion 30 and comprises the portions of the spiral 13a that are helically formed. Figure 3 shows a portion of wire rod 2 before winding. The axis XI, passing through the center of wire rod 2, extends in the longitudinal direction of wire rod 2. The wire rod 2 shown in Figure 3 comprises the round section portion 30 of length Ll, the square section portion 31 of length L2, and the tapered portion 32 of length L3. The round section portion 30 has the length Ll required for the spiral portions 13a of the effective spring portion 13. The square section portion 31 is formed by one end 2a of wire rod 2 over length L2. The tapered portion 32 is formed between the round section portion 30 and the square section portion 31 over length L3. As shown in Figure 2, the cross-section of the round portion 30 (in other words, the first SI section perpendicular to the XI axis of wire rod 2) is round. The first SI section is substantially constant in the longitudinal direction of wire rod 2 (in other words, along the XI axis). Since the second part of RRCQnn / CZnZ / B / Y The extreme turn 12 comprises a portion of the round section portion 30, its section being round. The wire diameter of the second portion of the extreme turn 12 is equal to that of the round section portion 30 of the effective spring portion 13. The square section portion 31 comprises a first outer surface 31a and a second inner surface 31b along the central axis C1 (shown in Figure 1 and Figure 2) of the helical spring 1, and a third upper surface 31c and a fourth lower surface 31d perpendicular to the first surface 31a. The third surface 31c and the fourth surface 31d are planes substantially perpendicular to the central axis C1 of the helical spring 1. The square section portion 31 comprises a first portion of coil 41 and a second portion of coil 42. The coil radius r2 of the second portion of coil 42 is smaller than the coil radius rl of the first portion of coil 41. Figure 2 shows a state in which the helical spring 1 is compressed by a load along the central axis 01. When the helical spring 1 is compressed, the upper surface 31c of the first helical portion 41 of the square-section portion 31 overlaps the lower surface 31d of the second helical portion 42 in a direction along the central axis 1C of the helical spring 1. In this way, a contact portion 43 is formed. RRConn / eznz / B / Y Therefore, the second portion of spiral 42 is allowed to avoid entering (sliding) into the interior of the first portion of spiral 41. The section of the square portion 31 (i.e., a second section S2 perpendicular to axis XI) is substantially square. In this specification, the term "substantially square" does not strictly refer to a square in geometry. Similar to the second section S2 represented schematically in Figure 4, the lengths TI, T2, T3, and T4 of the four sides A1, A2, A3, and A4 of the section must be equal to each other within the tolerance range in terms of machining. Each of the lengths TI, T2, T3, and T4 of sides A1, A2, A3, and A4 is less than or equal to the square root of 1 / 2 (1 / 82) multiplied by the diameter DI of the round portion 30. The inside angles Θ1, Θ2, Θ3, and Θ4 between sides A1, A2, A3, and A4 are substantially 90° within the tolerance range in terms of machining. At the intersections of sides A1, A2, A3 and A4, rounded corner parts B1, B2, B3 and B4 can be formed.The second section S2 is substantially constant in the longitudinal direction of wire rod 2 (in other words, a direction along axis XI). In the section of the conical portion 32 (in other words, a third section S3 perpendicular to the XI axis), from the round section portion 30 to the section portion RRCQnn / CZnZ / B / Y square 31, a round shape gradually changes to a substantially square shape, and furthermore, the cross-sectional area is reduced. The conical portion 32 is formed to have 1.0 turn or more between the round cross-sectional portion 30 and the square cross-sectional portion 31. As shown in Figure 2, the section of the conical portion 32 (the third section S3) comprises 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 section portion 31. The first flat portion 32a lies along the central axis C1 of the helical spring 1. The second flat portion 32b is continuous with the second surface 31b of the square section portion 31. The second flat portion 32b lies along the central axis C1 of the helical spring 1. The third flat portion 32c is continuous with the third surface 31c of the square section portion 31. The third flat portion 32c is perpendicular to the first flat portion 32a.The fourth plane portion 32d is continuous with the fourth surface 31d of the square section portion 31. The fourth plane portion 32d is perpendicular to the first plane portion 32a. The first portion of arc 32e comprises a RRCQnn / CZnZ / B / Y curved surface formed between the first flat portion 32a and the third flat portion 32c and having an arc shape. The second arc portion 32f comprises a curved surface formed between the first flat portion 32a and the fourth flat portion 32d and having an arc shape. The third arc portion 32g comprises a curved surface formed between the second flat portion 32b and the third flat portion 32c and having an arc shape. The fourth arc portion 32h comprises a curved surface formed between the second flat portion 32b and the fourth flat portion 32d and having an arc shape. These arc portions 32e, 32f, 32g, and 32h are continuous with the corner portions B1, B2, B3, and B4 of the square section portion 31 (shown in Figure 4), respectively. Figure 5 shows the relationship between the positions of the three types of wire, which have different cross-sections in the longitudinal direction and a polar moment of inertia of area (torsional stiffness). In Figure 5, the solid line MI indicates the polar moment of inertia of area of ​​wire 2 of the present embodiment (shown in Figure 3). The wire diameter of the round cross-section portion 30 of the present embodiment is 15.4 mm, and the length of each side of the square cross-section portion 31 is 6 mm. In Figure 5, the length L3a from zero (0) on the horizontal axis is the polar moment of inertia of area of ​​the conical portion 32, and the length L2a is the polar moment of inertia of area of ​​the conical portion. RACQnn / cznz / e / Y square section 31. The polar moment of inertia of the area of ​​the square section portion 31 is sufficiently less than that of the round section portion 30. In Figure 5, the dashed line M2 indicates the polar moment of inertia of the area of ​​the wire rod of Conventional Example 1 comprising a flat conical portion. The wire rod of Conventional Example 1 comprises a flat conical portion of length L4, extending from the end of a round section portion in which the wire diameter is 15.4 mm to the distal end of the wire rod. The cross-section of the flat conical portion is flat and rectangular. An end surface of the flat conical portion has a width of 15.4 mm and a thickness of 5.5 mm. The polar moment of inertia of the area of ​​Conventional Example 1 comprising the flat conical portion (shown by the dashed line M2) is much greater than that of the present embodiment (shown by the solid line MI). To decrease the first spring constant of Conventional Example 1 comprising the flat conical portion, it is necessary to increase the number of turns of the flat conical portion.Therefore, in a state where the conventional helical spring (Conventional Example 1) is compressed into a second area of ​​the spring constant, the number of turns of a dead turn portion is increased, thus increasing the weight. In Figure 5, the dashed line M3 indicates the RRCQnn / CZnZ / B / Y polar moment of inertia of the area of ​​the wire rod of Conventional Example 2 comprising a round conical portion. The wire rod of Conventional Example 2 comprises a round conical portion having a length L3a from the end of a round section portion, and a small section portion having a length L2a (with a wire diameter of 11.4 mm). The wire diameter of the round section portion is 15.4 mm. The polar moment of inertia of the area of ​​Conventional Example 2 (shown by the dashed line M3) is greater than that of the present embodiment (shown by the solid line MI). To decrease the first spring constant of Conventional Example 2 comprising the round conical portion, it is necessary to increase the number of turns of the round conical portion.Therefore, in a state where the conventional helical spring (Conventional Example 2) is compressed into a second area of ​​the elastic constant, the number of turns of a dead turn portion is increased, thus increasing the weight. When the polar moment of inertia of a square cross-section is equal to that of a round cross-section, the length of each side of the square section is approximately 0.87 to 0.89 times the diameter of the round section. Therefore, the difference between them is small. There is not much difference in torsional stiffness between a round section and a square section of substantially equal size. RAConn / eznz / B / Y among themselves. It is not easy to form a round conical portion with an extremely small diameter by processing a wire rod that has a round cross-section. However, the square cross-section portion 31 can be formed relatively easily using at least a pair of reducing rollers. Plastic working can also be applied in practice to form the square cross-section portion so that the length of each side of the section is less than or equal to the square root of 1 / 2 multiplied by the diameter of the wire of the round cross-section portion. Figure 6 schematically shows the spring characteristics of the helical spring 1 of the present embodiment (the relationship between load and deflection). In Figure 6, the horizontal axis shows deflection and the vertical axis shows a load. The helical spring 1 is compressed between the lower spring seat 21 (shown in Figure 1) and the upper spring seat 20 (shown in Figure 2). When the load is between zero and Wl, the square-section portion 31 is primarily deflected. Therefore, as shown by line K1 in Figure 6, a first area of ​​spring constant El is applied, in which the spring constant is comparatively lower. When the load exceeds Wl, the square-section portion 31 comes into close contact, and the round-section portion 30 of the effective spring portion 13 is deflected. Therefore, as shown RRcann / eznz / B / Y shows by the K2 line of Figure 6, the elastic constant becomes large (a second area E2 of elastic constant). Figure 7 shows the relationship between a tension generated on the inner side of the wire rod when the helical spring 1 is compressed and the turns from the lower end of the wire rod 2. A peak un of the tension is generated for each portion of the spiral 13a of the effective spring part 13. These peaks rmax are less than the accepted stress in the suspension device. A small peak τA is generated in the vicinity of the extreme turn portion 11. After the inventors of the present application engaged in research, it was discovered that the stress in the conical portion 32 exceeds the peak imax of the stress in the effective spring portion 13 when the number of turns in the conical portion 32 is less than 1.0, as shown by t2 in Figure 7. It is preferable that the stress in the conical portion 32 does not exceed that of the effective spring portion 13. For this reason, in the present embodiment, the number of turns in the conical portion 32 is made greater than or equal to 1.0. Figure 8 schematically shows a roller device 50 forming the square section portion 31 and the conical portion 32 on the wire rod 2, which has a round section. The wire rod 2 moves in the direction shown by arrow 1. The roller device 50 comprises a pair of rollers 51 and 52. The space between rollers 51 and 52 RAConn / eznz / B / Y can be controlled. When wire 2 passes through rollers 51 and 52, wire 2 is rolled by rollers 51 and 52. After that, wire 2 rotates around axis XI at 90° and wire 2 is rolled again by rollers 51 and 52. Figure 9 shows a portion of a coiling machine 60 that manufactures the helical spring by hot forming (e.g., greater than or equal to the transformation point A3 and less than or equal to 1150°C). The coiling machine 60 includes a column mandrel 61, a mandrel 62, and a guide portion 63. The guide portion 63 includes a pair of first guide rollers 65 and 66. The wire rod 2, formed from spring steel, is prepared in advance by cutting a wire rod to the length of a helical spring. The wire rod 2 is heated to an austenitizing temperature (greater than or equal to the transformation point A3 and less than or equal to 1150°C), and is fed into the mandrel 61 by means of a feeding mechanism. Mandrel 62 secures the distal end of wire rod 2 to mandrel 61. Guide portion 63 controls the position of wire rod 2 wound around mandrel 61 by guiding it. One end portion 61a of mandrel 61 is supported by a drive head 70 along with mandrel 62. Mandrel 61 is rotated about axis X2 by the drive head 70. The other end 61b of mandrel 61 is rotatably supported by a mandrel holder 71. Guide portion 63 moves in one direction along axis X2. RAConn / eznz / B / Y of the mandrel 61, and guide the wire rod 2 according to the pitch angle of the helical spring to be formed. Wire rod 2 has a length corresponding to the length of a helical spring. Before being fed to mandrel 61, wire rod 2 is heated in an oven. The distal end of the heated wire rod 2 is secured to mandrel 61 by mandrel 62. Mandrel 61 rotates. In synchronization with the rotation of mandrel 61, guide portion 63 moves in one direction along the X2 axis of mandrel 61. In this way, wire rod 2 is wound around mandrel 61 with a predetermined pitch. Each of the comparative examples 1, 2, 3, and 4 described below is a helical spring comprising a round section portion of an effective spring part and a small round section portion including an end loop, and having nonlinear characteristics. Each of the practical examples 1, 2, 3, and 4 is a helical spring comprising the round section portion 30, the square section portion 31, and the conical portion 32, and having nonlinear characteristics, similar to that of the helical spring 1 shown in Figure 1. RACQnn / cznz / e / Y Comparative Example 1 In the helical spring of Comparative Example 1, the diameter of the wire in the round section of the effective spring portion is 18 mm. The diameter of the wire in the small section portion is 13 mm. The total number of turns is 8.5. The weight is 7.0 kg. Practical example 1 In the helical spring of Practical Example 1, the wire diameter of the round section portion 30 of the effective spring part is 18 mm. The length of each side of the square section portion 31 is 7 mm. The total number of turns is 8.5. The length of each side of the square section portion 31 is 40% of the wire diameter of the round section portion 30. The spring characteristics (the relationship between load and deflection) of Practical Example 1 are equivalent to those of Comparative Example 1. The weight of the helical spring in Practical Example 1 is 5.2 kg, which is approximately 24% less than that of the helical spring in Comparative Example 1. Comparative Example 2 In the helical spring of Comparative Example 2, the wire diameter of the round section portion of the effective spring part is 15 mm. The wire diameter of the small section portion is 11 mm. The total number of turns is 8.5. The weight is 7.0 kg. RRConn / eznz / B / Y Practical example 2 In the helical spring of Practical Example 2, the wire diameter of the round section portion 30 of the effective spring part is 15 mm. The length of each side of the square section portion 31 is 7 mm. The total number of turns is 9.0. The length of each side of the square section portion 31 is 47% of the wire diameter of the round section portion 30. The characteristics of the spring in Practical Example 2 are equivalent to those in Comparative Example 2. The weight of the helical spring in Practical Example 2 is 4.0 kg, which is approximately 23% less than that of the helical spring in Comparative Example 2. RRCQnn / cznz / e / Y Comparative Example 3 In the helical spring of Comparative Example 3, the diameter of the wire in the round section of the effective spring portion is 22 mm. The diameter of the wire in the small section portion is 17 mm. The total number of turns is 8.0. The weight is 8.5 kg. Practical example 3 In the helical spring of Practical Example 3, the wire diameter of the round section portion 30 of the effective spring part is 22 mm. The length of each side of the square section portion 31 is 7 mm. The total number of turns is 8.0. The length of each side of the square section portion 31 is 32% of the wire diameter of the round section portion 30. The characteristics of the spring in Practical Example 3 are equivalent to those in Comparative Example 3. The weight of the helical spring in Practical Example 3 is 6.5 kg, which is approximately 22% less than that of the helical spring in Comparative Example 3. Comparative Example 4 In the helical spring of Comparative Example 4, the wire diameter of the round section portion of the effective spring part is 16 mm. The wire diameter of the small section portion is 12 mm. The total number of turns is 10.0. The weight is 6.0 kg. Practical example 4 In the helical spring of Practical Example 4, the wire diameter of the round section portion 30 of the effective spring part is 15 mm. The length of each side of the square section portion 31 is 7 mm. The total number of turns is 9.0. The length of each side of the square section portion 31 is 47% of the wire diameter of the round section portion 30. The characteristics of the spring in Practical Example 4 are equivalent to those in Comparative Example 4. The weight of the helical spring in Practical Example 4 is 5.0 kg, and is less than that of the helical spring in Comparative Example 4 by approximately 18%. The length of each side of the square section portion 31 of each of the helical springs in Practical Examples 1 to 4 is less than or equal to 50% of the wire diameter of the round section portion 30. When using the square section portion 31, the side lengths may differ slightly. However, since the length of each side of the square section portion is made less than or equal to the square root of 1 / 2 multiplied by the wire diameter of the round section portion, the weight can be reduced by approximately 20% compared to conventional helical springs. Figure 10 shows a helical spring 1A according to a second embodiment. Figure 11 is a perspective view showing a portion of the helical spring 1A (the vicinity of an extreme turn portion 11) in cross-section. The helical spring 1A comprises a square-section portion 31 having 2 or more turns, and a conical portion 32 having 1.0 turn or more. The wire rod section of a second extreme turn portion 12 is RRCQnn / cznz / e / Y round. The wire diameter of the second part of the extreme turn 12 is equal to that of a portion of round section 30. The second part of the extreme turn 12 comprises a portion of the spiral of smaller diameter 90 in which the diameter of the spiral decreases towards the other end 2b of the wire rod 2. The wire diameter of the second part of the extreme turn 12 may be less than that of the portion of round section 30. The square section portion 31 that includes the first extreme turn portion 11 of the helical spring 1A comprises at least a first portion of coil 41 and a second portion of coil 42. The diameter of the outer coil r4 of the second portion of coil 42 is smaller than the diameter of an inner coil r3 of the first portion of coil 41. When the helical spring 1A is compressed, as shown by the dotted lines Z1 in Figure 11, the second portion of coil 42 is allowed to enter inside the first portion of coil 41. The other structures and effects are common to helical spring 1A of the second mode and helical spring 1 of the first mode. Therefore, common reference numbers are added for both, and explanations are omitted. Industrial applicability The helical spring of the present invention is RACQnn / CZnZ / B / Y can be used for a helical spring that is installed in various types of appliances such as the suspension of a vehicle. List of reference signs 1, 1A· · · helical spring, 2· · · wire, 11· · · first part of extreme turn, 12··· second part of extreme turn, 13··· effective spring part, 13a··· spiral portion, 30 ··· round section portion, 31··· square section portion, 31a··· first surface, 31b··· second surface, 31c··· third surface, 31d·· fourth surface, S1 · · · first section, S2 · · · second section, S3··· third section, 32··· conical 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 ··· central axis, 41· ·· first spiral portion, 42··· second spiral portion, 43··· contact portion

Claims

1. A helical spring comprising a wire (2) having one end and the other end, the helical spring comprising: a first end-turn portion (11) including the end of the wire (2); a second end-turn portion (12) including the other end of the wire (2); and an effective spring portion (13) comprising a plurality of helical portions (13a) formed between the first end-turn portion (11) and the second end-turn portion (12), having a space (Gl) between adjacent helical portions (13a), the wire (2) comprising: a round-section portion (30) in which a first section (SI) perpendicular to a longitudinal direction of the wire (2) is round;a square section portion (31) formed from the end of the wire rod (2) along the first extreme turn portion (11), and comprising a second section (S2) that is perpendicular to the longitudinal direction and substantially square, the length of each side of the second section (S2) being less than or equal to a square root of 1 / 2 multiplied by a diameter of the wire rod (2) of the round section portion (30), the second section (S2) being RRConn / eznz / B / Y constant in the longitudinal direction; and a tapered portion (32) formed to have 1.0 turn or more between the round section portion (30) and the square section portion (31), and comprising a third section (S3) perpendicular to the longitudinal direction, the third section (S3) changing from a round shape to a substantially square shape and the section area of ​​the third section (S3) decreasing from the round section portion (30) to the square section portion (31).

2. The helical spring according to claim 1, wherein the square section portion (31) comprises a first outer surface (31a) and a second inner surface (31b) along a central axis (Cl) of the helical spring, and a third surface (31c) and a fourth surface (31d) perpendicular to the first surface (31a) and the second surface (31b) and parallel to each other.

3. The helical spring according to claim 2, wherein the square section portion (31) comprises at least a first spiral portion (41) and a second spiral portion (42), and comprises a contact portion (43) in which the third surface (31c) of the first spiral portion (41) makes contact with the fourth surface (31d) of the second spiral portion (42) in a state in which the helical spring is compressed.

4. The helical spring according to claim 2, wherein the conical portion (32) comprises a first flat portion (32a) continuous with the first surface (31a) of the square section portion (31), a second flat portion (32b) continuous with the second surface (31b), a third flat portion (31c) continuous with the third surface (32c), a fourth flat portion (32d) continuous with the fourth surface (31d), a first arc portion (32e) between the first flat portion (32a) and the third flat portion (32c), a second arc portion (32f) between the first flat portion (32a) and the fourth flat portion (32d), a third arc portion (32g) between the second flat portion (32b) and the third flat portion (32c), and a fourth arc portion (32h) between the second flat portion (32b) and the fourth flat portion (32d).

5. The helical spring according to claim 1, wherein a section of the wire rod (2) of the second extreme turn part (12) is round, and the diameter of the wire rod (2) of the second extreme turn part (12) is equal to the diameter of the wire rod (2) of the round section portion (30).

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