JPS60241542A - Coil spring - Google Patents

Abstract

PURPOSE:To obtain a lightweight coil spring by making uniform the shear stress generated on a strand in the peripheral direction of a coil. CONSTITUTION:A spring strand 1 is formed by smoothly connecting a circular- arc part (a) having a smaller curvature and a circular-arc part (b) having a larger curvature by curves (c) and (c) and has a circular section. When said strand 1 is extended and contracted, keeping straight the center line X-X of a coil, the spring constant of the circular-arc part (a) having a smaller curvature increases and the stress correction coefficient reduces, and the spring constant of the circular-arc part (b) having a large curvature reduces, and the stress correction coefficient increases. Therefore, the max. shear stress generated on the inner periphery of the coil reduces on the circular-arc part (a) in comparison with the circular-arc part (b).

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention Industrial Field of Application The present invention relates to a coil spring in which the center line of the coil deforms to a curvature different from that in the free state in the used state, and is applicable to both compression coil springs and tension coil springs. It is possible.

Problems to be Solved by the Invention For example, a coil spring used as a chassis spring in an independent vehicle suspension system is an accordion spring that is used as a chassis spring when a control arm swings due to the relative vertical movement of the vehicle body and axle. The center line of the coil expands and contracts while curving, as shown in Figure 2. In such cases, the shear stress generated in the strands in the circumferential direction of the coil becomes uneven, resulting in excessive stress in some parts. Compared to the case where the coil expands and contracts while keeping the center line of the coil straight, it is necessary to increase the diameter of the strands, resulting in an increase in weight, which is contrary to the goal of reducing the weight of the vehicle.

As described above, the present invention makes it possible to equalize the shear stress generated in the strands in the circumferential direction of the coil in a coil whose center line deforms to a curvature different from that in the free state in the use state, thereby making it possible to reduce the weight. The purpose is to

Embodiment An embodiment in which the present invention is applied to compression coil springs will be explained based on FIGS. The narrow arc part A and the wide arc part opening are curved C,
As shown in Figs. 2 and 4, the spring wire l with an egg-shaped cross section connected smoothly with C is placed around the straight center line The planar shape of the coil is as shown in Fig. 3, where an arc portion a with a small curvature and an arc portion with a large curvature face each other. Jtlc
, c form a smoothly connected oval shape.

When this compression coil spring is compressed and used so that the center line XX of the coil is curved, as shown in FIG. By arranging it on the side where the amount of deflection is small, that is, on the outside of the curve, the shear stress generated in the spring wire 1 in the circumferential direction of the coil is made uniform. The reason for this will be explained based on FIGS. 4 and 5.

As shown in FIG. 5, when the center line XX of the coil is curved and compressed, the positions on the spring wire 1 on the inside of the curve, that is, on the side where the amount of compression is maximum, are B1 and B2.
, B3, old and outside of the curve.

That is, the position on the spring element gA1 on the side where the amount of compression is the smallest is A1, Az, A3, A
4, this compression coil spring is wound at the same pitch, so in the free state shown in Fig. 4, /A+ Bz Az = lAz B3 A3 = lA3
Bq A+=/B+ AIBz=/BλAzBs =l
B3A3 B+=α, but in the compressed state shown in FIG. 5, /A+BzAλ=/AλB3 A3 = /
Ax B+ A÷=β/BIAIBz=/BzAzB3
If =/B5A3B+=y, then α>β>γ, and the position A1 on the spring wire 1. Az, A
3. The torsion angle α-γ at A+ is at positions B+, BZ, B
3. It is larger than the torsion angle α-β at B+.

The average shear stress caused by this torsional deformation is at position A,
, A,, A3, A4 are better MB+, Bz, B
J, larger than B+. By the way, when a coil spring made by winding a spring wire with a circular cross section in a circle is expanded or contracted while keeping the center line of the coil straight, the spring wire will be twisted by a certain angle per unit length. However, since the arc on the inner circumference of the coil is shorter than the arc on the outer circumference, the shear strain is greater on the inner circumference of the coil than on the outer circumference, and the resulting shear stress is also greater on the inner circumference of the coil than on the outer circumference. It is,
Moreover, this tendency becomes more pronounced as the spring index, that is, the ratio D/d of the coil diameter to the wire diameter d, decreases, and the maximum shear stress generated on the inner circumference of the spring wire becomes smaller. The ratio of the cross-section to the average shear stress.

That is, the relationship between the stress correction coefficient and the spring index D/d is as shown in the graph of FIG.
When /d is 12.0, the maximum shear stress generated inside the coil is approximately 1.1 times the average shear stress of its cross section, whereas when the spring index D/d is 4.0, it is approximately 1. .4 times.

However, as shown in FIG. 2, the compression coil spring of this embodiment has a planar shape in which a circular arc portion a with a small curvature and a circular arc portion with a large curvature facing each other are smoothly connected by a curve C1C. Assuming that the strand 1 has a circular cross section, if the coil is expanded and contracted while keeping the center line In the arc portion b''Q, where the curvature is small and the curvature is large, D/d is small and the ni is large. Therefore, the maximum shear stress generated on the inner circumference of the coil is greater than the arc portion a where the curvature is small. is smaller than the arc portion with large curvature.

Therefore, as explained earlier, when the compression coil spring of this embodiment is compressed so that its center line is curved, the positions A1, Ax, outside the curve where the amount of deflection in the direction of the center line XX is small, A3. Positions Bl, BZ, B3 .
Considering that the stress is larger than the average shear stress generated in B+, assuming that the spring wire I has a circular cross section, the stress correction factor when expanding and contracting while keeping the center line X-X of the coil straight is 1iA+, Aλ, A3 , Place it on the A+ side, and conversely, place the circular arc part with a large curvature where the stress correction coefficient becomes large, on the side where the average shear stress is small.
By arranging them at B+, Bz, and B3.84m, the maximum shear stress generated in each cross section of the spring wire l in the circumferential direction of the coil is made uniform.

On the other hand, in each cross section of the spring wire 1, as already mentioned,
However, there is a problem in that the shear stress generated on the inner circumferential side of the coil is higher than on the outer circumferential side, and when a high load is applied, cracks occur from the inner circumferential side of the coil and breakage occurs.

A coil spring in which a spring wire 1 having an oval cross section is wound with the narrow circular arc portion A of the cross section facing the inner circumferential side as in this embodiment is described in Japanese Patent Publication No. Sho 27-3261. As shown in FIG. In addition to equalizing the maximum shear stress that occurs in each cross section of spring wire 1, the shear stress on the inner and outer circumferential sides in each cross section of spring wire 1 is also equalized, so that the shear around the entire circumference of the coil is equalized. This allows the maximum stress to be kept low.

Next, a sixth example in which the present invention is applied to a tension coil spring will be described.
9 and 7, the coil spring of this embodiment also has a spring element @i with an oval cross section, as in the above embodiment, as shown in FIG. It is an egg shape in which the circular arc part A with a large curvature is smoothly connected by curves C and C, and one narrow circular arc part A is wound toward the inner circumference at 9 equal pitches, and in a free state. As shown in Fig. 6, this is a tension coil spring in which the center line XX of the coil is straight.

As shown in FIG. 7, when the coil is tensioned so that the center line XX is curved, the circular arc portion a of the coil with a small curvature is the center @ the side with a small amount of deflection in the XX direction, that is,
If it is placed inside the curve, β'<β'<γ' as shown in FIGS. However, since the arc portion a of the coil with a small curvature is arranged at this position and the spring index D/d is large, the stress modification coefficient χ becomes small, whereas the position outside the curvature , the torsional deformation is the highest /IX and the average shear stress is the highest, but the spring index D / d is small and the stress modification coefficient is large, and each cross section of the spring wire l in the circumferential direction of the coil Furthermore, since the narrow arc portion of the spring element vAl with an oval cross section faces the inner circumference side, the shear stress on the inner circumference side and the outer circumference side of the spring element wire 1 is reduced. Also, the maximum value of the shear stress generated on the inner peripheral side of the spring wire 1 can be suppressed to a significantly low value.

As shown in Fig. 9, the cross-sectional shape of the spring wire 1 is a trapezoid with the narrow straight part A and the wide straight part facing each other connected by hypotenuses C and C. Even when the wire is wound toward the inner circumference, the center of torsional deformation moves toward the outer circumference as in the above embodiment, and the shear stress on the inner and outer circumferences is made uniform and its maximum value is kept low.

Furthermore, the present invention can also be applied to the case where a coil spring, which is formed so that the center line of the coil is curved in the free state, is compressed or tensioned so that the curvature of the center line changes. Therefore, even in such a case, the average shear stress on the side where the amount of deflection in the center line direction is small is the maximum, and by placing an arc portion with a small curvature that reduces the stress correction coefficient at this position, it is possible to It is possible to create stress.

Structure and Effects of the Invention As specifically explained in the above embodiments, the coil spring of the present invention is a coil spring in which the center line of the coil deforms to a curvature different from that in the free state in the use state, A spring element wire with a cross-sectional shape that gradually decreases in width toward the side, with the narrow side of the cross-section facing the inner circumference, smoothly connects the circular arc part with a small curvature and the circular arc part with a large curvature that face each other. It is designed to be wound into a shape with a small curvature and placed on the side with a small deflection in the direction of the splitting centerline of the arcuate part, and has a small deflection claw where the average shear stress is small. Since the circular arc portion with a small curvature where the stress modification coefficient is small is placed on the side, the maximum shear stress generated on the inner periphery of the spring wire can be made uniform in each cross section in the circumferential direction of the coil. Furthermore, since the narrow side of the cross-sectional shape of the spring wire is wound toward the inner circumference, the stress on the inner and outer circumferences of the wire can be equalized, and the maximum shear stress generated in the spring wire can be The value can be kept extremely low, and the diameter of the spring wire can be reduced to achieve the effect of saving materials and reducing weight.

[Brief explanation of the drawing]

Fig. 1 is an enlarged cross-sectional view of an example spring wire in which the present invention is applied to a compression coil spring, Fig. 2 is a partial perspective view thereof, Fig. 3 is a plan view thereof, and Fig. 4 is a vertical cross-section of the spring wire in its free state. Figure 5 is a vertical sectional view in a used state, Figure 6 is a partial longitudinal sectional view in a free state of an embodiment in which the present invention is applied to a tension coil spring, and Figure 7 is a partial vertical sectional view in a used state. FIG. 8 is a graph showing the relationship between the spring index and the stress modification coefficient, and FIG. 9 is an enlarged sectional view showing a modification of the cross-sectional shape of the spring wire. 1: Arc part with small curvature (of the spring element fiat (coil)) b: Arc part with large curvature A: Narrow part (of the cross-sectional shape of the spring wire) ii) Wide part Applicant: Agent for Chuo Spring Co., Ltd. Person Patent Attorney Hiroki Noguchi Figure 2 Part 1

Claims (1)

[Claims] A coil spring in which the center line of the coil deforms to a curvature different from that in the free state when in use, and whose cross-sectional shape gradually decreases from the negative side to the other side, is called a coil spring whose cross-sectional width is narrow. With the side facing the inner circumference, the circular arc portion with a small curvature and the circular arc portion with a large curvature that face each other are wound in a shape that smoothly connects them. A coil spring characterized by being used by placing it on the smaller side.