JPH0127290B2 - - Google Patents

Description

[Detailed Description of the Invention] Purpose of the Invention Industrial Application Field 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 when in use, 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 used as an accordion spring as the control arm swings due to the relative vertical movement of the vehicle body and wheels. The center line of the coil expands and contracts while curving, as shown in Figure 3. In this case, 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 center line of the coil is kept straight while expanding and contracting, it is necessary to increase the diameter of the strands, resulting in an increase in weight, which is contrary to the aim 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 spring in which the center line of the coil deforms to a curvature different from that in the free state when in use, thereby making it possible to reduce the weight. The purpose is to

Embodiment An embodiment in which the present invention is applied to a compression coil spring will be described based on FIGS. 1 to 5. The compression coil springs of this embodiment face each other as shown enlarged in FIG. As shown in FIGS. 2 and 4, a spring wire 1 with an oval cross section in which a narrow arc portion A and a wide arc portion B are smoothly connected by curves C and C is connected to a straight center line. The coil is wound around X-X at equal pitches with the narrow arc portion A facing the inner circumference, and the planar shape of the coil is as shown in Figure 3. It forms an oval shape in which a circular arc portion a with a small curvature and a circular arc portion b with a large curvature, which face each other, are smoothly connected by curves c and c.

As shown in Fig. 5, this compression coil spring is
When compressed and used so that the center line XX of the coil is curved, the circular arc portion a of the coil with a small curvature is arranged on the side with a small amount of deflection in the direction of the center line XX, that is, on the outside of the curvature. As a result, the shear stress generated in the spring wire 1 in the circumferential direction of the coil is made uniform. The reason is shown in Figures 4 and 5.
This will be explained based on the diagram.

As shown in FIG. 5, when the center line XX of the coil is curved and compressed, the spring wire 1 is on the inside of the curve, that is, on the side where the amount of compression is maximum.
Let the upper position be B ₁ , B ₂ , B ₃ , B ₄ , outside the curve,
In other words, the position on the spring wire 1 on the side where the amount of compression is minimum on the spring wire 1 is A ₁ , A ₂ ,
Assuming A ₃ and A ₄ , this compression coil spring is wound at equal pitches, so in the free state shown in Fig. 4, ∠A ₁ B ₂ A ₂ = ∠A ₂ B ₃ A ₃ = ∠ A ₃ B ₄ A ₄ = ∠B ₁ A ₁ B ₂ = ∠B ₂ A ₂ B ₃ = ∠B ₃ A ₃ B ₄ = α, but in the compressed state shown in Fig. 5, ∠A ₁ B ₂ A ₂ = ∠A ₂ B ₃ A ₃ = ∠A ₃ B ₄ A ₄ = β ∠B ₁ A ₁ B ₂ = ∠B ₂ A ₂ B ₃ = ∠B ₃ A ₃ B ₄ = γ, then α ＞β＞γ, and the positions A ₁ , A 2 , A ₂ on the spring wire 1,
The torsion angle α-γ at A ₃ , A ₄ is at position B ₁ , B ₂ ,
It is larger than the torsion angle α-β at B ₃ and B ₄ ,
The average shear stress caused by this torsional deformation is
The positions A ₁ , A ₂ , A ₃ , and A ₄ are larger than the positions B ₁ , B ₂ , B ₃ , and B ₄ . 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. Moreover, this tendency becomes more pronounced as the spring index, that is, the ratio D/d of the coil diameter D and 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 modification coefficient x and the spring index D/d is as shown in the graph of Figure 8. The maximum shear stress generated inside is approximately 1.1 of the average shear stress of the cross section.
However, when the spring index D/d is 4.0, it is approximately 1.4 times.

However, the compression coil spring of this embodiment has a second
As shown in the figure, a curve c represents a circular arc portion a with a small curvature and a circular arc portion b with a large curvature, which face each other.
Assuming that the spring wire 1 has a circular cross section, if the center line XX of the coil is kept straight and the coil is expanded and contracted, the circular arc portion a with a small curvature will form. Then the spring index D/d
becomes larger, the stress modification coefficient x becomes smaller, D/d becomes smaller and x becomes larger in arc portion b with large curvature. Therefore, the maximum shear stress generated on the inner circumference of the coil is Part a is smaller than arc part b, which has a larger curvature.

Therefore, as explained earlier, when the compression coil spring of this embodiment is compressed so that its center line is curved, the position A ₁ on the outside of the curve where the amount of deflection in the center line XX direction is small is , A ₂ , A ₃ , A ₄ is larger than the average shear stress occurring at positions B ₁ , B ₂ , B ₃ , B ₄ inside the curve where the amount of deflection is large. Assuming that the spring wire 1 has a circular cross section, the arc portion a with a small curvature that reduces the stress correction coefficient x when expanding and contracting while keeping the center line XX of the coil straight is
Positions A ₁ , A ₂ , A ₃ , A ₄ on the outside of the curve where the amount of deflection in the center line XX direction is small, where the average shear stress that occurs when the center line is compressed to curve is large.
On the other hand, if _the circular arc _portion b with _a large curvature where the stress modification _coefficient The maximum shear stress occurring in each cross section of the spring wire 1 in this direction is made uniform.

On the other hand, in each cross section of the spring wire 1, as mentioned above, 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. There is a problem,
In 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, it is described in Japanese Patent Publication No. 3261/1983. As shown in the figure, the shear stress on the inner and outer circumferential sides is equalized by moving the center of the torsional deformation toward the outer circumference. 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 of each cross section of spring wire 1 is also equalized, so that the shear stress on the entire circumference of the coil is equalized. This allows the maximum stress to be kept low.

Next, an embodiment in which the present invention is applied to a tension coil spring will be described based on FIGS. As shown in Figure 3, an arc part a with a small curvature and an arc part b with a large curvature facing each other are smoothly connected by curves c and c to form an oval shape, with the narrow arc part a on the inner circumferential side. The center line of the coil is
X is straight, and this tension coil spring is
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 set to the side where the amount of deflection in the direction of the center line XX is small, that is, If placed inside the curve, the 6th
In Fig. 7 and Fig. 7, α'<β'<γ', and the torsional deformation is maximum at the position inside the curve, and the average shear stress generated in the spring wire 1 is also maximum, but at this position The coil has a circular arc portion a with a small curvature, and the spring index D/d is large, so the stress modification coefficient Although the stress is also minimum, the spring index D/d is small and the stress modification coefficient x is large, so that the maximum shear stress occurring in each cross section of the spring wire 1 in the circumferential direction of the coil is equalized, and further, Since the narrow arc portion of the spring wire 1 with an oval cross section faces toward the inner circumference, the shear stress on the inner and outer circumferential sides of the spring wire 1 is equalized, and the inner circumference of the spring wire 1 is The maximum value of the shear stress generated on the sides is kept extremely low.

In addition, as shown in FIG. 9, the cross-sectional shape of the spring wire 1 is a trapezoid, with a narrow straight part A and a wide straight part B facing each other connected by hypotenuses C and C.
Even when the narrow straight portion A 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 equalized and reaches its maximum value. can be kept low.

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 a free state, is compressed or stretched 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 where the stress modification coefficient x is small 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 when in use, and has a spring wire having a cross-sectional shape whose width gradually decreases from one side to the other. , with the narrow side of the cross section facing the inner circumference, and are wound in a shape that smoothly connects the circular arc part with a small curvature and the circular arc part with a large curvature facing each other, with the circular arc part with a small curvature facing towards the center line. The purpose is to place the circular arc part with a small curvature, where the stress modification coefficient is small, on the side where the amount of deflection is small, where the average shear stress is large, and use it. This makes it possible to equalize the maximum shear stress occurring on the inner periphery of the spring wire in each section in the circumferential direction of the coil, and 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 value of shear stress occurring in the spring wire can be significantly reduced. This has the effect of reducing the diameter of the spring wire and reducing the amount of material and weight.

[Brief explanation of drawings]

Fig. 1 is an enlarged cross-sectional view of a spring wire according to an embodiment of the present invention 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 longitudinal 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: Spring wire, a: Arc part with small curvature (of the coil), b: Arc part with large curvature, A: Narrow part (of the cross-sectional shape of the spring wire), B: Wide part.

Claims (1)

[Claims] 1 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 in width from one side to the other, is It is wound in a shape in which a circular arc part with a small curvature and a circular arc part with a large curvature that face each other are smoothly connected with the narrow side facing the inner circumference, and the circular arc part with a small curvature is the side with a small amount of deflection in the center line direction. A coil spring characterized by being used by being placed in.