Coil spring for an elastic unit

Abstract

A single continuously coiled spring, generally represented in 400, is formed as two distinct spring portions 400A and 400B having a substantially constant pitch, separated by a transition portion 450 along approximately half of the spring 400. The transition portion 450 includes at least one turn, which in this example has a reduced pitch, but which may have a zero pitch or even a negative pitch. The spring is encapsulated in a continuous pocket P. In this case, the transition portion 450 comprises substantially flat turns. The spring portions 400A and 400B comprise a common portion of spring material, which in this case is a spring wire, and the coils are substantially continuous throughout the spring 400.

Description

Technical Field

[0001] The present invention relates to a coil spring for use in a resilient unit and particularly, but not exclusively, to a coil spring for use in a pocketed resilient unit such as may form the core of an upholstered article. Background Art

[0002] Elastic units, such as those used in the core of mattresses, typically comprise an array of helical compression springs. The springs are helically coiled and can have various shapes, including: a simple cylindrical spring, in which the coils all have substantially the same diameter; or a barrel spring, in which the diameter of at least one coil towards the axial middle portion is greater than the diameter of the coil at the axial end; a conical spring, in which the diameter of the coil increases from one axial end to the other; and even an hourglass shape, in which one or more coils towards the axial middle portion of the spring have a reduced diameter compared to the coils at the axial ends. What they have in common is that at the axial ends of the spring, the pitch of the coils, i.e. the distance between the centers of adjacent coils or turns, must decrease. In other words, one or more coils / turns of the spring at the extreme axial ends are flat or even turned back towards the body of the spring. This prevents the wire at the ends of the spring from protruding beyond the ends and thereby causing discomfort to the person using the elastic unit. For pocket spring units, in which the springs are enclosed in separate packs or bags of material, this turning also has the benefit of avoiding unnecessary wear and tear on the pocket material.

[0003] In addition to the shape and elasticity of the springs, the absolute number of springs will have an impact on the comfort of the spring unit. Therefore, manufacturers try to find ways to maximize the number of springs in a mattress. One way to do this is to stack the springs axially one on top of the other. An example of a spring unit with pocket springs stacked axially can be found in our published PCT patent application number WO 2000000065, the entire contents of which are hereby incorporated by reference.

[0004] The very end turns of the spring have a reduced or zero or even negative pitch (turned back into the body of the spring), contributing little or nothing to the spring's resilience. Thus, when the springs are stacked, there is considerable waste of spring material, typically steel wire, where the springs abut. Summary of the invention

[0005] Embodiments of the present invention aim to provide a spring design in which the above-mentioned problems are at least partially solved.

[0006] The present invention is defined in the appended independent claims, to which reference will now be made. Further preferred features can be found in the appended dependent claims.

[0007] According to one aspect of the present invention, there is provided a helical spring for use in an elastic unit, the spring comprising a plurality of coils extending around a spring axis from a first axial end to a second axial end, and having a first spring portion and a second spring portion that are at least substantially coaxial and a transition portion between the first spring portion and the second spring portion, wherein a pitch of the transition portion is smaller than a pitch of the first spring portion and the second spring portion.

[0008] The spring is preferably substantially helically coiled.

[0009] The first spring portion and the second spring portion may comprise a common length of spring material, more preferably a common length of spring wire.The first spring portion and the second spring portion and the transition portion may comprise a substantially continuous wire.

[0010] The first spring portion may include a first number of coils, and the second spring portion may include a second number of coils (turns), and the transition portion may include a third number of coils. In a preferred arrangement, the average pitch of the coils of the transition portion is less than the average pitch of the coils of the first spring portion and / or the second spring portion.

[0011] The first spring portion and the second spring portion may comprise substantially the same shape, which may be any of (but not limited to) the following: for example, cylindrical, barrel-shaped, conical or hourglass-shaped. Alternatively, the first spring portion and the second spring portion may have different shapes.

[0012] The spring can have a substantially constant shape along its length. In a preferred arrangement, the diameter of the first spring portion and the diameter of the second spring portion and more preferably the diameter of the transition portion are substantially the same. The diameter of the coil can be substantially the same along the entire length of the spring. The transition portion can include at least one substantially flat coil portion. This substantially flat coil portion or each substantially flat coil portion can include a substantially flat portion of the coil or a substantially flat coil.

[0013] The coils are preferably spaced apart from each other. This may allow substantially all of the coils to function independently and preferably contribute to the compression characteristics of the spring.

[0014] The end of the spring may include at least one substantially flat coil.

[0015] The spring may be enclosed in a bag.

[0016] The present invention comprises a resilient unit comprising an array of springs according to any statement herein, the resilient unit preferably being suitable for use as or as part of an upholstered article such as a mattress, seat, cushion or panel.

[0017] The invention also comprises an upholstered article, such as a mattress, seat, cushion or panel, comprising one or more springs according to any statement herein, or comprising an elastic unit according to any statement herein.

[0018] According to a second aspect of the present invention, there is provided a method of manufacturing a coil spring, the method comprising producing a coil of a first pitch, then reducing the pitch, and subsequently increasing the pitch.

[0019] The method preferably comprises producing a first spring portion, then producing a transition portion, then producing a second spring portion.The first and second spring portions and the transition portion may comprise a common wire and preferably have a substantially continuous coil.

[0020] The method may include providing a region of significantly reduced pitch at a transition portion between a first spring portion and a second spring portion of the spring. Preferably, the method includes producing a substantially flat coil or turn at a transition portion midway along the axial length of the spring, the transition portion not being at an axial end of the spring.

[0021] The present invention may include any combination of features or limitations mentioned herein, except such combinations of features that are mutually exclusive or mutually inconsistent. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0023] Figure 1 A simple helical coil spring according to the prior art is shown;

[0024] Figure 2 A helical coil spring with the end coils turned inward is shown;

[0025] Figure 3 Two pocket springs stacked upward are shown; and

[0026] Figure 4 A spring according to an embodiment of the invention is shown. DETAILED DESCRIPTION

[0027] Go to Figure 1, which shows a previously considered helical coil spring generally indicated at 100. The spring 100 comprises a plurality of turns or coils 110 about a spring axis A. The turns or coils have a constant pitch - ie the distance D between the turns or coils is substantially constant.

[0028] The manufacture of a helically coiled wire spring currently involves a number of steps. First, the wire is taken from a supply, typically a reel, using a feed roller and, if necessary, straightened to remove any kinks or twists. The wire is then formed into a helical coil by bending the wire in a first direction using a first deflection tool and then bending the wire in a second direction using a second deflection tool arranged substantially perpendicular to the first deflection tool. This forces the wire out of the plane and forms a spiral. An axe controls the separation of adjacent turns or coils as required, and when the coil has a predetermined length, a cutter severs the spring from the rest of the wire, or separation of the spring is achieved in another manner, such as by separating the wire at a previously formed irregularity.

[0029] Figure 2 A previously contemplated helical coil spring, generally designated 200, is shown, which includes turns or coils 210. This spring is suitable for use in a cushioning article (not shown) because there are inwardly turned coils 210a and 210b at each axial end - that is, the pitch of the endmost turns is zero or negative. This is done to provide comfort to the user of the cushioning article incorporating the spring, as it ensures that the spring has no sharp points. This also helps to avoid excessive or premature wear of any bagging material when the spring is enclosed in a bag (not shown).

[0030] Figure 3 A previously considered pocket spring, generally designated 300, is schematically shown. In this case, there are two springs 300A and 300B stacked one on top of the other. Each spring is located in a pocket P. The pockets can be formed in a variety of ways, such as by ultrasonically welding two cloths of pocketing material along the edges and between the springs to form a weld W. For example, the pocketing material can include spunbond polyester. Note that each of the two springs 300A and 300B has a plurality of coils 310 and an inwardly turned coil 310a and 310b at each end, for a total of four inwardly turned coils. Since the inwardly turned coils have zero pitch or negative pitch, their contribution to the elastic properties of the spring is negligible and they are essentially waste material.

[0031] Figure 4An embodiment of the invention is shown in which a single continuously coiled spring, generally indicated at 400, is formed into two distinct spring portions 400A and 400B having a substantially constant pitch, separated by a transition portion 450 approximately halfway along the spring 400. The transition portion 450 comprises at least one turn which in this example has a reduced pitch, but which may have a zero pitch or even a negative pitch. The spring is encapsulated in a continuous pocket P. In this case, the transition portion 450 comprises substantially flat turns. The spring portions 400A and 400B comprise a common portion of spring material, in this case spring wire, and the coil is substantially continuous throughout the spring 400.

[0032] The two spring portions 400A and 400B provide a reference Figure 3 The comfort and resilience of the two separate springs of the prior art example described. However, although there are two different spring portions 400A and 400B, they share a common transition portion 450 and therefore do not require Figure 3 There are only two such coils 410a and 410b at opposite axial ends of the spring 400, unlike the separate inwardly turned ends found in the arrangement of FIG.

[0033] This saves material. Specifically, for each pair of spring portions 400A and 400B, only two inwardly turned ends and one common transition portion are required, rather than four inwardly turned ends of the prior art arrangement, which saves 25% of scrap steel.

[0034] Furthermore, if more integrated spring parts are used, such as three spring parts sharing two transition parts, steel is also saved (33%), and so on for other combinations. The example shown is a spring with exactly two spring parts, with a transition part between the two spring parts. The spring may include three or more spring parts, with a transition part between each pair of adjacent spring parts.

[0035] exist Figure 4 In the example shown, the first spring portion and the second spring portion and the transition portion have substantially the same diameter. In addition, the coils are all spaced apart from each other so that the coils can all act independently of each other and so that substantially all of the coils in the coil can contribute to the compression characteristics of the spring.

[0036] The transition portion may include a single flat turn, or a single turn having a smaller pitch than the turns in the main spring portion, or the transition portion may include multiple turns, one, all or some of the multiple turns having a reduced, zero or negative pitch, or a reduced average pitch.

[0037] The spring parts need not have the same length. For example, the transition portion or one of the transition portions (if there is more than one transition portion) may be closer to one end of the entire spring.

[0038] The spring portions may have substantially the same shape or may have different shapes, which may include, but are not limited to, any one or any combination of the following: for example, flat / cylindrical, barrel-shaped, conical, or hourglass-shaped.

[0039] A transition portion midway along the spring simulates in one or more of its pitch, geometry, and dimensional characteristics an inward rotation region typically found at the axial ends of a spring.

[0040] While in the foregoing description attention has been paid to those features of the present invention regarded as particularly important, it should be understood that the applicants claim protection for any patentable feature or combination of features mentioned herein and / or shown in the accompanying drawings, whether or not specifically emphasized.

Claims

1. A helical spring for use in an elastic unit, the spring comprising a plurality of coils extending around a spring axis from a first axial end to a second axial end and having at least substantially coaxial first and second spring portions and a transition portion between the first and second spring portions, wherein: The pitch of the transition portion is smaller than the pitch of the first spring portion and the second spring portion.

2. The spring according to claim 1, wherein: The first spring portion and the second spring portion comprise a common length of spring material, more preferably a common length of spring wire.

3. The spring according to claim 1 or 2, wherein: The first and second spring portions and the transition portion comprise a substantially continuous wire.

4. A spring according to any one of the preceding claims, wherein The first spring portion includes a first number of coils, and the second spring portion includes a second number of coils (turns), and the transition portion includes a third number of coils.

5. A spring according to any one of the preceding claims, wherein The average pitch of the coils of the transition portion is smaller than the average pitch of the coils of the first spring portion and / or the second spring portion.

6. A spring according to any one of the preceding claims, wherein The first spring portion and the second spring portion include substantially the same shape, which is (but not limited to) one of the following: cylindrical, barrel-shaped, conical, or hourglass-shaped.

7. The spring portion according to any one of claims 1 to 5, wherein: The diameter of the first spring portion and the diameter of the second spring portion and the diameter of the transition portion are substantially the same.

8. The spring portion according to any one of claims 1 to 5, wherein The first spring portion and the second spring portion have different shapes.

9. A spring according to any one of the preceding claims, wherein The transition portion includes at least one substantially flat coil portion.

10. The spring portion according to claim 9, wherein: The or each substantially flat coil portion comprises a substantially flat portion of the coil or a substantially flat coil.

11. A spring according to any one of the preceding claims, wherein The spring is enclosed in a bag.

12. A spring according to any one of the preceding claims, wherein All of the coils are spaced apart from each other.

13. A resilient unit comprising an array of springs according to any one of claims 1 to 12 in or as part of an upholstered article such as a mattress, seat, cushion or panel.

14. An upholstered article, such as a mattress, seat, cushion or panel, comprising one or more springs according to any one of claims 1 to 12, or comprising an elastic unit according to claim 13.

15. A method of making a coil spring, the method comprising producing a coil of a first pitch, then reducing the pitch, and subsequently increasing the pitch.

16. The method of claim 15, comprising producing a first spring portion, then a transition portion, then a second spring portion.

17. The method according to claim 15 or 16, wherein: The method includes providing a region of substantially reduced pitch at a transition portion between the first spring portion and the second spring portion of the spring.

18. A method according to any one of claims 15 to 17, comprising producing substantially flat coils or turns at a transition portion midway along the axial length of the spring, the transition portion not being at an axial end of the spring.

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