Stranded wire coil spring

Abstract

To enhance a degree of freedom for design.SOLUTION: A stranded wire coil spring 10 is formed by winding a spring wire material 11 in a coil manner. The spring wire material 11 is formed by stranding a plurality of single wires 12 each having elasticity.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a stranded coil spring. [Background technology]

[0002] 2. Description of the Related Art As one type of spring, a coil spring is known in which a spring wire made of a single elastic wire is wound into a coil shape (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-199916 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the general coil springs formed by forming a single wire as described above, there are few factors that determine the spring characteristics, such as the wire diameter of the spring wire, the effective number of turns, the center diameter of the coil, etc. Therefore, there is room for improvement in terms of increasing the degree of freedom in designing the coil springs. [Means for solving the problem]

[0005] An embodiment of a stranded coil spring for solving the above problems will be described. [Embodiment 1] A coil spring formed by winding spring wire into a coil, the spring wire being a stranded coil spring formed by twisting together multiple elastic single wires.

[0006] According to the above configuration, the characteristics of a stranded coil spring formed by using a plurality of single wires twisted together as the spring wire material are affected by factors related to the overall shape of the stranded coil spring, such as the effective number of turns, center diameter, etc. In addition, the characteristics of a stranded coil spring are also affected by factors related to the plurality of single wires, such as the wire diameter of each single wire, the number of single wires constituting the spring wire material, the twist angle, etc. Therefore, the number of factors to be designed increases by the amount of factors related to the plurality of single wires. Effect of the Invention

[0007] According to the present invention, the degree of freedom in design can be increased. [Brief description of the drawings]

[0008] [Figure 1] 1 is a photograph of a portion of a stranded coil spring in one embodiment taken from a direction perpendicular to an axis line. [Diagram 2] FIG. 2 is an enlarged view of a portion X in FIG. [Diagram 3] 1 is a photograph of the stranded coil spring in the above embodiment taken from one side in a direction along the axis. [Figure 4] FIG. 2 is a cross-sectional view of the spring wire in the embodiment. [Diagram 5] FIG. 2 is a schematic diagram showing a twisted coil spring according to the embodiment with a portion thereof omitted. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings in which the present invention is embodied in a compression stranded coil spring (hereinafter simply referred to as a "stranded coil spring") that receives a compressive load and stores elastic energy.

[0010] As shown in Figures 1 and 5, the twisted coil spring 10 of this embodiment is formed, like a typical coil spring, by winding a spring wire 11, which is a linear material, in a coil shape (spiral shape) around an axis L1 at a certain distance from the coaxial line L1.

[0011] <Spring wire rod 11> As shown in FIG. 4, spring wire 11 includes a plurality of (three in FIG. 4) metallic solid wires (also called element wires) 12 each having elasticity.

[0012] As the solid wire 12, hard steel wire (SW), piano wire (SWP), oil tempered wire, stainless steel wire, etc. can be used. There are three types of hard steel wire, SW-A, SW-B, and SW-C, which have different carbon contents. Piano wire has higher strength than hard steel wire. There are three types of piano wire, SWP-A, SWP-B, and SWP-V. SWP-B has higher material strength than SWP-A. Oil tempered wire has a tensile strength equal to or greater than piano wire, and is excellent in fatigue resistance and heat resistance.

[0013] In this embodiment, each of the single wires 12 has a circular cross-sectional shape. The total number of turns, wire diameter d, length, etc. of the single wire 12 are selected and set according to the requirements of the user of the stranded coil spring 10.

[0014] 2 and 3, the spring wire 11 is formed by twisting together a plurality of metal solid wires 12 having the same length. In the spring wire 11, adjacent solid wires 12 are held in close contact with each other.

[0015] The number of single wires 12 constituting the spring wire 11 is appropriately selected depending on the spring constant, elastic force, dimensions, etc. required for the twisted coil spring 10. The minimum number is two. When three or more single wires 12 are twisted together, it is preferable that the single wires 12 are twisted together so that the cross section of the spring wire 11 is gathered in a close-packed state (like a stack of rice bales) as shown in FIG. 4. This is because the close-packed state is the most compact among spring wires 11 with the same cross-sectional area. When there are three single wires 12, each single wire 12 is twisted together while being in contact with the other two single wires 12.

[0016] As shown in Fig. 2, an imaginary line passing through the center of each single wire 12 and extending in the length direction of the single wire 12 is referred to as the "axis L2" of the single wire 12. Also, an imaginary line passing through the center of the spring wire 11 and extending in the length direction of the spring wire 11 is referred to as the "central axis CL" of the spring wire 11. As shown in Fig. 4, the central axis CL is located in the center of the space surrounded by the three single wires 12. Also, as shown in Fig. 2, when the spring wire 11 is viewed from a direction perpendicular to the central axis CL, the angle that the axis L2 of each single wire 12 makes (intersects) with the central axis CL is referred to as the "lay angle θ."

[0017] As the twist angle θ increases, the strength of the spring wire 11 increases. However, as the twist angle θ increases, friction between adjacent single wires 12 also increases. Therefore, if the twist angle θ is excessively large, repeated expansion and contraction of the twisted coil spring 10 may cause damage to the single wires 12 due to the friction, resulting in reduced durability. Therefore, it is desirable to set the twist angle θ so that both strength and durability are good.

[0018] By twisting the single wires 12, the length of the spring wire 11 becomes shorter than the length of each single wire 12 before being twisted. <Specifications of the stranded coil spring 10> As shown in Fig. 5, the twisted coil spring 10 has a pair of end turns 14 at both ends in the direction along the axis L1. Each end turn 14 has a seat 14a at both ends in the direction along the axis L1. In this embodiment, each seat 14a is not ground. Note that in Fig. 5, the spring wire 11 is represented by a single wire, and the multiple single wires 12 are not represented. Also, in Fig. 5, the spring wire 11 is represented thicker than in the other drawings in order to explain the dimensions of each part.

[0019] The winding direction, outer diameter De, inner diameter Di, center diameter D, effective number of turns, total number of turns, free length L0, load, etc. of the stranded coil spring 10 are selected and set according to the requirements of a user of the stranded coil spring 10. In particular, it is desirable to set the free length L0 according to the location, purpose, etc. of the use of the stranded coil spring 10.

[0020] <About the production of the stranded coil spring 10> The stranded coil spring 10 is manufactured through the following steps. [Molding process] In the forming process, the spring wire 11 is formed into a coil shape using a coiling machine or the like. Methods for forming the stranded coil spring 10 can be broadly classified into a method in which the spring wire 11 is pressed against a coiling pin to give it a curvature, and a method in which the spring wire 11 is wound around a core bar to form the spring wire 11.

[0021] [Heat treatment process] In the heat treatment process, low-temperature annealing (tempering) is performed. Low-temperature annealing is performed to improve the characteristics of the stranded coil spring 10 and to enhance sag resistance, fatigue strength, etc. Low-temperature annealing is also performed to remove harmful residual stresses that occur during the formation of the stranded coil spring 10 and stabilize the dimensions. The residual stress is a force that occurs inside the spring wire 11 as the spring wire 11 attempts to return to its original shape after the stranded coil spring 10 is formed.

[0022] The low-temperature annealing is performed by heating the stranded coil spring 10 at a temperature of, for example, 250° C. to 450° C. in a spring heat treatment machine such as an electric furnace or a vacuum furnace. The type of equipment (spring heat treatment machine) used for the heat treatment, the temperature, the heating time, and the like are selected and set according to the requirements of the user of the stranded coil spring 10.

[0023] [Shot peening process, setting process] A shot peening process and a setting process are performed after the forming process and the heat treatment process in order to reduce "sag" by improving the strength and durability of the stranded coil spring 10. "Sag" is a phenomenon in which the strength of the stranded coil spring 10 weakens and its elasticity decreases.

[0024] In the shot peening process, small spheres called shot are continuously collided with the stranded coil spring 10 at high speed in order to improve the fatigue resistance of the stranded coil spring 10. These collisions work-harden the surface layer of the stranded coil spring 10. Compressive residual stress remains in the surface layer, which acts to offset repeated loads and increase fatigue strength. The shots and processing time in the shot peening process are selected and set according to the requirements of the user of the stranded coil spring 10.

[0025] In the setting process, a load equal to or greater than the maximum working load is applied to the stranded coil spring 10 in order to reduce settling during use of the stranded coil spring 10. By performing the setting process, the stranded coil spring 10 is plastically deformed, and beneficial residual stress is imparted to the entire surface, improving fatigue strength.

[0026] Next, the operation of the present embodiment configured as above will be described. When a force is applied to the stranded wire coil spring 10 from one side to the other in a direction along the axis L1, the stranded wire coil spring 10 undergoes compressive deformation, and a reaction force of a magnitude corresponding to the amount of compressive deformation is generated. This reaction force acts on whatever is applying the force to the stranded wire coil spring 10. When the force is no longer being applied to the stranded wire coil spring 10, the stranded wire coil spring 10 expands due to its own restoring force.

[0027] Incidentally, the characteristics of a typical coil spring formed from a single spring wire are affected by factors related to the overall shape of the coil spring, such as the number of effective turns, center diameter, etc. The characteristics of the coil spring are also affected by factors related to the spring wire, such as the wire diameter of the spring wire.

[0028] In contrast, the characteristics of the twisted coil spring 10 of this embodiment, in which a plurality of single wires 12 twisted together is used as the spring wire material 11, are affected by factors related to the overall shape of the twisted coil spring 10, such as the effective number of turns and the center diameter D. In addition, the characteristics of the twisted coil spring 10 of this embodiment are also affected by factors related to the plurality of single wires 12, such as the wire diameter d of the single wires 12, the number of single wires 12 constituting the spring wire material 11, the twist angle θ, and the like. Therefore, the number of design targets increases by the amount of factors related to the plurality of single wires 12, and the degree of freedom in designing the twisted coil spring 10 increases. As a result, it becomes possible to design and manufacture a twisted coil spring 10 having spring characteristics that meet various requests from users of the twisted coil spring 10.

[0029] Next, the effects of this embodiment will be described. (1) In this embodiment, the spring wire 11 is formed by twisting together a plurality of elastic metallic solid wires 12. This allows for greater freedom in design compared to a typical coil spring in which the spring wire is made of a single solid wire.

[0030] The total number of turns, wire diameter d, number of wires, twist angle θ, length, etc. of the single wire 12 can be set according to the requirements of the user of the stranded coil spring 10. In addition, the stranded coil spring 10 can be formed so that the winding direction, outer diameter De, inner diameter Di, effective number of turns, total number of turns, free length L0, load, etc. of the stranded coil spring 10 meet the requirements of the user of the stranded coil spring 10.

[0031] (2) Since the spring wire 11 is made of a plurality of elastic metallic single wires 12 twisted together, it is possible to reduce wear, settling, changes in precision, dimensions, etc., compared to a case in which the spring wire 11 is made of a single wire.

[0032] (3) The spring wire 11 can be formed by a simple process of twisting together a plurality of single wires 12. (4) Since each of the pair of end winding portions 14 is not ground, the twisted single wires 12 at the end winding portions 14 are less likely to fray.

[0033] (5) The stranded coil spring 10 continues to function even if some of the multiple single wires 12 that make up the spring wire material 11 breaks. EXAMPLES

[0034] Next, the above embodiment will be described more specifically with reference to a first example and a second example. (I) As a first example, a single wire 12 having the following specifications was used to create a spring wire 11 having the following specifications.

[0035] Material of single wire 12: piano wire (SWP-B) Single wire 12 wire diameter d: 0.55mm Number of single-wire 12s: 3 Length of single wire 12: 140mm Length of spring wire 11: 120mm ·Twisting direction of the single wire 12 in the spring wire 11: left -Twist angle θ of spring wire 11: 20° (II) Next, the spring wire 11 was used to form (coil) a stranded coil spring 10 having end turn portions 14 on both ends in the direction along the axis L1 and having the following specifications:

[0036] Inner diameter Di: 8.2mm Total number of volumes: 36 (effective number of volumes: 34) Load: 7.5N Winding direction: Right (III) The stranded coil spring 10 formed in the above forming step was heat-treated in a heat treatment step at 350° C. for 3 minutes in an electric furnace.

[0037] (IV) After the heat treatment step, a shot peening process was performed on the entire stranded coil spring 10 using white alumina (WA-100) as an abrasive (shot).

[0038] (V) The stranded coil spring 10 obtained through the above-mentioned shot peening process was subjected to setting in a setting process. (VI) In the same manner as in (I) to (V) above, a stranded coil spring 10 of the second embodiment was obtained. In (I) to (V) above, the second embodiment differs from the first embodiment only in the following points.

[0039] Length of single wire 12: 130mm Length of spring wire 11: 110mm Total number of turns of the twisted coil spring 10: 32 turns (effective number of turns: 30 turns) (VII) Then, the stranded coil springs 10 of the first and second examples were repeatedly subjected to stress, stretching them 50,000 times. After that, the occurrence of scratches on the outer peripheral surface 10a and the inner peripheral surface 10b of the stranded coil springs 10 was visually checked. As a result, it was confirmed that no noticeable scratches were generated on the outer peripheral surface 10a and the inner peripheral surface 10b of the stranded coil springs 10 of the first and second examples.

[0040] The above embodiment can also be implemented as modified examples as follows: The above embodiment and the following modified examples can be implemented in combination with each other within a range that does not cause technical contradiction.

[0041] <About Spring Wire Rod 11> Some of the single wires 12 among the plurality of single wires 12 constituting the spring wire 11 may have a different wire diameter d from the other single wires 12, or may be made of a different material.

[0042] The wire 12 may have a cross-sectional shape other than a circle, such as an ellipse or a polygon. Polygons include squares, rectangles, diamonds, etc. Polygons also include shapes with sharp corners as well as shapes that are polygonal as a whole but have rounded corners.

[0043] The solid wire 12 may be one that has been subjected to a surface treatment, for example, one that is covered with a coating. In this case, the solid wire 12 is composed of a core portion made of metal and a coating that covers the core portion. In this way, it is possible to prevent the multiple solid wires 12 that constitute the spring wire material 11 from rubbing against each other and wearing out.

[0044] The multiple single wires 12 twisted together may be joined to each other at both ends, a middle portion, or the like in the direction along the central axis CL of the spring wire 11. <About the stranded coil spring 10> The spring wire 11 in the stranded coil spring 10 may be wound with an uneven pitch or with an even pitch.

[0045] The spring wire 11 in the stranded coil spring 10 may be wound in a cylindrical shape or in other shapes, such as a cone shape, a barrel shape, or a drum shape. The end turn portion 14 of the twisted coil spring 10 may be processed, for example, by modifying the seat surface 14a.

[0046] The twisted wire coil spring 10 of the present invention can also be used as a tension twisted wire coil spring that receives a tensile load, a torsion twisted wire coil spring that receives a torsional moment (torque) about the axis L1, etc. [Explanation of symbols]

[0047] 10...Stranded coil spring 11...Spring wire 12…Single line

Claims

[Claim 1] A coil spring formed by winding a spring wire into a coil shape, The spring wire is a stranded coil spring formed by twisting together a plurality of elastic single wires.

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