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Title:
TENSION-COMPRESSION COIL SPRING SYSTEM
Document Type and Number:
WIPO Patent Application WO/2019/099516
Kind Code:
A1
Abstract:
A coil spring system is disclosed that includes collinear first and second coil springs of opposite sense. First ends of the springs are captured in a first plate; second ends of the springs are captured in a second plate. Under compression and left unconstrained, the springs can bend, rotate, and increase in diameter in compensation to the applied force. According to the embodiments of the disclosure, hooks formed at the ends of the coil springs are captured in orifices in plates and the points of capture in the plates are selected so that the bending force of the first spring counteracts the bending force of the second spring and the plates are constrained from rotating. Thus, the springs compensate to the applied force by increase in diameter.

Inventors:
YATES, David (509 N. 7th St, Ann Arbor, MI, 48103, US)
HOFBAUER, Peter (3280 Pine Lake Knoll Dr, W. Bloomfield, MI, 48324, US)
HUANG, YueXin (41651 Steinbeck Glen, Novi, MI, 48377, US)
KAZA, Sai, Ronit (4515 Swiss Stone Court, Apt. 1AYpsilanti, MI, 48197, US)
Application Number:
US2018/061049
Publication Date:
May 23, 2019
Filing Date:
November 14, 2018
Export Citation:
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Assignee:
THERMOLIFT, NC. (209 Advanced Energy Center, 1000 Innovation RoadStony Brook, NY, 11794-6044, US)
International Classes:
F16F3/04; F16F1/12
Domestic Patent References:
WO2018200588A12018-11-01
Foreign References:
US20140225318A12014-08-14
JP2001124055A2001-05-08
JP2013245708A2013-12-09
JP2008039113A2008-02-21
CN206145041U2017-05-03
Attorney, Agent or Firm:
BREHOB, Diana (21526 Garrison St, Suite BDearborn, MI, 48124, US)
Download PDF:
Claims:
We claim:

1.A spring system, comprising:

a first coil spring having a central axis, the first coil spring being formed into a helix and the first coil spring wound clockwise;

a first hook formed in a first end of the first coil spring;

a second hook formed in a second end of the first coil spring;

a second coil spring having a central axis coincident with the central axis of the first spring, the second coil spring being formed into a helix and the second coil spring wound counter clockwise;

a third hook formed in a first end of the second coil spring;

a fourth hook formed in a second end of the second coil spring;

a first member having first and second orifices defined therein with the first hook engaged in the first orifice and the third hook engaged in the second orifice; and a second member having third and fourth orifices defined therein with the second hook engaged in the third orifice and the fourth hook engaged in the fourth orifice wherein:

the first, second, third, and fourth hooks are bent outwardly from their associated coil spring so that end portions of the hooks are substantially parallel to the central axis of the coil spring.

2. The spring system of claim 1 wherein the first, second, third, and fourth hooks are affixed to their respective members via one of: a weld, a braze, a friction weld, a swage, an epoxy, an adhesive.

3. The spring system of claim 1 wherein the first, second, third, and fourth orifices are chamfered.

4. The spring system of claim 1 wherein the first member is coupled to a stationary member that thereby prevents the first member from rotating about an axis parallel to the central axis of the first coil spring.

5. The spring system of claim 1 wherein the first and second members are prevented from rotating about an axis parallel to the central axis of the first coil spring.

6. The spring system of claim 1 wherein the outer of the first and second coil springs is sufficiently larger in diameter than the inner of the first and second coil springs such that the springs do not touch when compressed and do not touch when extended.

7. The spring system of claim 1, wherein:

a bending direction of the first coil spring, when a force along the central axis is exerted on the first coil spring, is estimated;

a bending direction of the second coil spring, when the force is exerted on the second coil spring, is estimated; and

the location of the first, second, third, and fourth orifices are selected so that the bending direction of the first coil spring is opposite the bending direction of the second coil spring with respect to the central axis.

8. The spring system of claim 1 wherein:

a magnitude of bending of the first spring is determined as a function of force exerted on the first spring along the central axis;

a magnitude of bending of the second spring is determined as a function of force exerted on the second spring along the central axis; and

the first and second springs are fabricated so that their magnitudes of their responses to force exerted along the central axis is substantially similar.

9. The spring system of claim 1 wherein:

the first and second ends of the first and second springs are hooked; and the springs and their hooked ends when viewed axially, appear as an annulus.

10. The spring system of claim 4 wherein the first coil spring is made of a wire having a first cross-sectional shape and a first cross-sectional area; and the second coil spring is made of a wire having a second cross-sectional shape and a second cross-sectional area.

Description:
Tension-Compression Coil Spring System

Field of Invention

[0001] The present disclosure relates to tension-compression coil springs.

Background and Summary

[0002] Mechanical springs are well known in the art. Springs adapted to move between a compression mode and a tension mode are not as commonly employed as compression springs, tension springs, or torsion springs. One example of a tension- compression spring 500 is disclosed in commonly-assigned PCT/US16/51821, which is shown as Figure 1. Helical grooves 502 and 504 are machined into a hollow cylinder to make spring 500. A first half of the grooves 502 have one rotational direction and a second half of the grooves 504 are formed in an opposite sense as first half of the grooves 502. The drawing in Figure 1 shows mounting holes 506 in a top end of spring 500 to affix spring 500 to a component. Mounting holes, which allow affixing spring 500 to a second component, in a bottom end of spring 500 are not visible in Figure 1.

Because spring 500 is symmetrical, twisting of spring 500 due to grooves 502 is substantially the same as the twisting caused by grooves 504 thereby causing the midsection 508 to twist back and forth when the spring goes between tension and compression. Tension-compression spring 500 is much more expensive and heavier than coil springs. Thus, an alternative to spring 500 is desired, particularly for mass production purposes.

[0003] Coil springs can be used in tension and compression, however, only if the ends of the spring are constrained in the direction parallel to the centerline of the coil. Some prior art attempts for constraining the coil spring ends are not robust. For example, one method is to weld the end of the windings to a plate. It has been found that such a configuration has very high forces in the location of the weld and the spring cannot withstand much tension before the spring breaks. The propensity to break in the location that the coil is affixed has led to the adoption of the type of spring shown in Figure 1 for applications in which a tension-compression spring is desired.

[0004] Coil springs react to compression or tension by: coiling up more or less, bending, increasing or decreasing in diameter, or a combination of modes. If the coil spring is allowed to coil or uncoil, at least one of the attachment ends rotate with respect to the other end. Depending on the application, one or more of the modes of compensation cannot be accommodated. For example, in some applications, a bend in the coil leads to binding in the system and cannot be tolerated. In other applications, allowing one of the spring ends to rotate cannot be tolerated. A coil spring system that is robust and that avoids undesirable compensation modes (e.g., rotation due to coiling up or bending) is of interest.

Summary

[0005] To overcome at least one problem in the prior art, a spring system is disclosed that has a first coil spring having a central axis, the first coil spring being formed into a helix. The first coil spring is wound clockwise. A first hook is formed in a first end of the first coil spring and a second hook is formed in a second end of the first coil spring. The spring system includes a second coil spring having a central axis coincident with the central axis of the first spring. The second coil spring is formed into a helix and the second coil spring is wound counter clockwise. A third hook is formed in a first end of the second coil spring. A fourth hook is formed in a second end of the second coil spring. A first member has first and second orifices defined therein with the first hook engaged in the first orifice and the third hook engaged in the second orifice. A second member has third and fourth orifices defined therein with the second hook engaged in the third orifice and the fourth hook engaged in the fourth orifice. The first, second, third, and fourth hooks are bent outwardly from their associated coil spring so that end portions of the hooks are substantially parallel to the central axis of the coil spring.

[0006] The first, second, third, and fourth hooks are affixed to their respective members via one of: a weld, a braze, a friction weld, a swage, an epoxy, an adhesive.

[0007] The first, second, third, and fourth orifices are chamfered.

[0008] The first member is coupled to a stationary member that thereby prevents the first member from rotating about an axis parallel to the central axis of the first coil spring.

[0009] The first and second members are prevented from rotating about an axis parallel to the central axis of the first coil spring. [0010] The outer of the first and second coil springs is sufficiently larger in diameter than the inner of the first and second coil springs such that the springs do not touch when compressed and do not touch when extended.

[0011] A bending direction of the first coil spring, when a force along the central axis is exerted on the first coil spring, is estimated. A bending direction of the second coil spring, when the force is exerted on the second coil spring, is estimated. The location of the first, second, third, and fourth orifices are selected so that the bending direction of the first coil spring is opposite the bending direction of the second coil spring with respect to the central axis.

[0012] A magnitude of bending of the first spring is determined as a function of force exerted on the first spring along the central axis. A magnitude of bending of the second spring is determined as a function of force exerted on the second spring along the central axis. The first and second springs are fabricated so that their magnitudes of their responses to force exerted along the central axis is substantially similar.

[0013] The first and second ends of the first and second springs are hooked. The springs and their hooked ends when viewed axially, appear as an annulus.

[0014] The first coil spring is made of a wire having a first cross-sectional shape and a first cross-sectional area. The second coil spring is made of a wire having a second cross-sectional shape and a second cross-sectional area.

[0015] Also disclosed is a spring system that has a first coil spring having a central axis, the first coil spring being wound with a particular rotational sense and a second coil spring having a central axis coincident with the central axis of the first coil spring. The second coil spring is wound with a rotational sense opposite to that of the particular rotational sense of the first coil spring. A first hook is formed in a first end of the first coil spring. A second hook formed in a second end of the first coil spring. A first hook is formed in a first end of the second coil spring. A second hook is formed in a second end of the second coil spring. A first plate has first and second orifices defined therein. The first hook of the first coil spring is inserted into the first orifice of the first plate. The first hook of the second coil spring is inserted into the second orifice of the first plate. A second plate has first and second orifices defined therein. The second hook of the first coil spring is inserted into the first orifice of the second plate. The second hook of the second coil spring is inserted into the second orifice of the second plate. [0016] The first and second hooks are bent outwardly from their respective coil spring so that end portions of the first and second hooks are substantially parallel to the central axis of their respective coil spring. The first hooks of the first and second coil springs are affixed to the first member. The second hooks of the first and second coil springs are affixed to the second member.

[0017] The first and second plates each have an inner side adjacent to the coil springs and an outer side facing away from the coils springs. The orifices are chamfered proximate the inner side of their respective plate.

[0018] The first and second hooks are affixed such that they are opposite each other with respect to the central axis.

[0019] The first and second hooks of the first and second coil springs are inserted into their respective orifices in the plates when the temperature of the first and second coil springs is significantly lower than the temperature of the first and second plates.

[0020] A bending direction of the first coils spring, when a force is exerted on the first coil spring along the central axis, is estimated. A bending direction of the second coil spring, when the force is exerted on the second coil spring along the central axis, is estimated. Locations of the first and second orifices in the first plate. Locations of the first and second orifices in the second plate are selected so that the bending direction of the first spring is diametrically opposed to the bending direction of the second spring with respect to the central axis.

[0021] A first coil spring having a central axis. A second coil spring having a rotational sense opposite to that of the first coil spring. A central axis of the second coil spring is substantially collinear with the central axis of the first coil spring. A first end of the first coil spring is captured in a first plate. A second end of the first coil spring is captured in a second plate. A first end of the second coil spring is captured in the first plate. A second end of the second coil spring is captured in the second plate. A bending direction of the first spring, when a force is exerted on the first spring along the central axis, is estimated. A bending direction of the second coil spring, when the force is exerted on the second coil spring along the central axis, is estimated. Points of capture of the ends of the first and second springs are selected so that the bending direction of the first spring is diametrically opposed to the bending direction of the second spring with respect to the central axis. [0022] A magnitude of the bending of the first spring is determined as a function of force exerted on the first spring along the central axis. A magnitude of the bending of the second spring is determined as a function of force exerted on the second spring along the central axis. The first and second springs are fabricated so that the magnitude of their responses to force exerted along the central axis is substantially similar.

[0023] The first and second plates each have first and second orifices defined therein. Axes of the first and second orifices are parallel to the central axis. The first and second ends of the first and second springs are hooked in a manner such that the ends are parallel to the central axis. The hooks of the first ends of the first and second springs are affixed into orifices in the first plate. The hooks of the second ends of the first and second springs are affixed into orifices in the second plate.

[0024] The first and second ends of the first and second springs are hooked. The springs and their hooked ends when viewed axially, appear as an annulus.

[0025] Advantages of disclosed embodiments include at least that the spring system is low cost, light weight, and doesn’t bend and/ or rotate when the amount of tension/compression on the spring is changed.

Brief Description of Drawings

[0026] Figure 1 illustrates a tension-compression spring with first and second sets of helical grooves formed therein;

[0027] Figure 2 illustrates a coil spring system having an inner and an outer coil spring each with hooks on the ends;

[0028] Figure 3 illustrates a spring pair coupled to plates;

[0029] Figure 4 illustrates the coil spring pair of Figure 3 bending due to compression;

[0030] Figure 5 illustrates a top view of one of the plates of Figure 3;

[0031] Figure 6 illustrates a plan view of a coil spring pair;

[0032] Figures 7 and 8 show a cross section of a portion of a plate with an orifice defined therein to accommodate a hook of a spring; and

[0033] Figure 9 illustrates an embodiment of a heat pump having pairs of coil springs acting on displacers. Detailed Description

[0034] As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The

combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated.

[0035] In Figure 2, a pair of coil springs 200 and 210 is shown with outer coil spring 200 wound with an opposite sense to inner coil spring 210. Coil spring 200 is provided with hooks 202 and 204 that are diametrically opposed and the ends of which are substantially parallel to a central axis of coil spring 200. Similarly, coils spring 210 is provided with hooks 212 and 214 that are diametrically opposed. The ends of hooks 212 and 214 are substantially parallel to a central axis of coil spring 210. In other embodiments, hooks 202, 204, 212, and 214 are slightly canted with respect to their respective central axis.

[0036] In Figure 3, a spring system is shown that has an outer spring 240 and an inner spring 250 that have centerlines on axis 260. Figure 3 is similar to coil springs 200 and 210 shown in Figure 2, although the hooks in Figure 3 are captured in plates. Outer spring 240 is wound with an opposite sense as that of inner spring 250. A hook 242 of outer spring 240 and a hook 252 of inner spring 250 are mounted in a plate 248. A hook 244 of outer spring 240 and a hook 254 of inner spring 250 are mounted in a plate 246. Hooks 242 and 252 are 180 degrees displaced with respect to centerline 260. As described above, a coil spring that is constrained from rotating when being compressed, will bend. It was theorized that by arranging hooks 252 and 254 diametrically opposed to hooks 242 and 244, respectively, would cause the bending force of coil spring 240 to largely cancel the bending force of coil spring 250. However, it has been found that by arranging hooks 242, 244, 252 and 254 as shown in Figure 2, the two bending forces partially reinforce each other, as shown in Figure 4, to cause enough bending to cause operational problems. The degree of bending shown in Figure 4 is exaggerated for illustrative purposes. In one simulated example, the spring system bends about 0.5 degrees. That is an unacceptable amount of side-to-side displacement for an element that is displaced far from the pivot point of the bend of the spring system.

[0037] A top view of the plate 248 is shown in Figure 5. Plate 248 has an opening 256 defined therein that might accommodate a shaft for a displacer or other member. Ends of hook 242 of spring 240 and hook 252 of spring 250 are visible through the orifices in plate 248 that provided to accommodate the hooks. Hooks 242 and 252 are diametrically opposed to each other with respect to the centerline of the spring system.

[0038] As discussed above, it was theorized that by arranging the hooks of the springs in the plate diametrically opposed, as shown in Figures 3-5, that the bending of the inner and outer springs would largely cancel. However, through simulation, it was found that a different angle leads to the forces acting each other. In one example configuration, it was found that a 30 degree offset, as shown in Figure 6, leads to that desired outcome. From an end view of a spring system 218 that has an outer spring 220 and an inner spring 230, having hooks 222, and 232, respectively, a 30 degree offset is appropriate. A gap 224 between the spring is provided to ensure that the springs do not interfere or bind under compression or tension due to changing diameters of the spring in reaction to the compression or tension.

[0039] It is not believed that a 30 degree offset is appropriate for all coil spring combinations. Instead, it depends on the spring material, wire diameter and shape (e.g., oval or square, as two non-limiting examples) used to form the coil spring, the number of turns, and heat treating or other processes that affect material properties. Although proper selection of the mounting locations for the hooks leads to the forces acting against each other, it does not ensure that the magnitudes are equal. Thus, unless balanced, there would be some bending. The magnitudes are matched by careful selection of the material properties and number of winds of the coil springs. The present disclosure is not limited to two concentric springs, but is extendible to adding pairs of concentric springs or even odd numbers of concentric springs, although greater than a one spring.

[0040] In some embodiments, the orifices provided in the plates for

accommodating the hooks are cylindrical. In other embodiments, a chamfer is provided, as shown in Figure 7 in which a portion of a plate 300 has an orifice 302 that has a chamfer 304 at one end. In Figure 8 a portion of spring 312 has a hook 310 inserted into orifice 302. Chamfer 304 prevents stress risers from forming in hook 310.

[0041] A heat pump 10 in which a coil spring system can be applied is shown in Figure 9. Heat pump 10 has a hot end 12 and a cold end 14. In hot end 12, a hot displacer 20 is disposed with a hot cylinder 22. In operation displacer 20 reciprocates within cylinder 22. The position of displacer 20 controls the amount of volume inside a hot chamber 25 and the volume inside a hot-warm chamber 26. Displacer 20, as shown in Figure 9 is in mid-stroke, thus each of chambers 25 and 26 have a considerable volume of gas therein.

[0042] Cold end 14 of heat pump 10 has a cold displacer 120 that is disposed within a cold cylinder 122. The position of displacer 120 shown in Figure 9 is near one end of travel such that most of the volume is in cold-warm chamber 27 and very little in cold chamber 28.

[0043] In Figure 9, hot cylinder 22 and cold cylinder 122 are collinear (along central axis 50) and have the same diameter. In alternative embodiments, the cylinders are of different diameters and offset from each other.

[0044] Hot displacer 20 has a linear actuation system that includes electrical coils 23 and 33, an armature 30, and a spring system. The armature 30 that is coupled to a shaft 24 of displacer 20. Armature 30 is acted upon by coils 32 and 33 that are surrounded by back irons 34. Movement of armature 30 is delimited by end plates 36 and 38. End plates extend across cylinder 22 and also serve as back irons. Either of electrical coils 32 or 33 can be provided a current which then exerts a force on armature 30 that causes armature 30 to move thereby moving displacer 20. The amount of current required to cause displacer 20 to move when displacer 20 is far from ends of travel is very high. Even more demanding is when displacer 20 is at one end of travel, e.g., at an upward position, meaning that armature 30 is at an upward position farthest away from coil 33, making it very challenging for coil 33 to provide attractive force to draw armature 30 downward. To help with movement, a tension-compression spring system is provided. The spring system includes an outer spring 42 that has a first wind direction (sense); and an inner spring 44 that has a second wind direction. A diameter of outer spring 42 is selected to be large enough so that inner spring 44 can be disposed within outer spring 42 and to avoid interference due to changes in the spring dimensions during reciprocation of displacer 20. Sense of outer spring 42 is opposite that of spring 44. Springs 42 and 44 are in compression when displacer 20 is close to end plate 38 and in tension when displacer 20 is far away from end plate 38, i.e., near end plate 36. To constrain the springs from rotating and pulling away, two orifices are provided in each plate 40 and end plate 38. Hooks 50 and 54 that are formed at the ends of outer spring 42 are held in place in orifices formed in plate 40 of displacer 20 and in end plate 38, respectively. Hooks 50 and 54 are affixed in the orifices so that when spring 42 is in tension hooks 50 and 54 remain in place. Hooks 50 and 54 are welded in their respective orifices in one embodiment. However, any other suitable way to affix the hooks into the orifices may be used including brazing, friction welding, using an adhesive, swaging, and by heating the element, end plate in this case, prior to inserting the hooks and/or cooling the hooks prior to insertion. Hooks 52 and 56 of inner spring 44 are coupled to plate 40 and end plate 38, analogously.

[0045] A linear actuation system is provided for cold displacer 120 that is analogous to that described for hot displacer 20. Cold displacer 120 has a shaft 124 that is coupled to an armature 130 that is acted upon by electrical coils 130 and 132, back iron 134, and end plates 136 and 138. The spring system that exerts force on displacer 120 to facilitate much of the travel from end to end includes an inner spring 144 and an outer spring 142. Hooks 150, 152, 154, and 156 of springs 142 and 144 are mounted on one end into orifices in a plate 140 coupled to displacer 120 and at the other end into orifices in an end plate 138.

[0046] The heat pump in Figure 9 is one application for the coil-spring system disclosed herein. Such a spring system may be used in a Stirling engine, a conventional internal combustion engine valve train, and other mechanical systems employing springs.

[0047] While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and

implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.