The present invention pertains to fiber-composite springs.
Composite materials, which have fibers embedded in a supporting matrix material, are used for fabricating strong, lightweight parts. These composites have an attractive combination of properties, and provide significant manufacturing, performance, and economic advantages.
One technology area that has benefitted comparatively little from the use of advanced-composites is spring design. Springs, which find many applications, come in a variety of forms, such as coil springs, Belleville springs, leaf springs, gas/air springs, wave springs, and others.
Coil springs are quite common; they are easy to manufacture and find uses in almost any application where springs are needed. However, coil springs are usually made of metal, which makes them relatively heavy. Also, due to their construction, coil springs store/release energy torsionally, twisting as they compress. Consequently, not all force is axially aligned, and undesirable loads may be transferred to surrounding hardware.
Applying composites technology to coil springs is problematic; a composite coil spring requires very complex fiber orientations to resist not only bending, but also torsion. In addition to being complicated to design, the helical shape of a coil spring is particularly difficult to demold. Accordingly, the usual manufacturing and economic advantages accruing from the use of composites are not realized when applied to composite coil springs.
The present invention provides a fiber-composite spring that addresses some of the shortcomings of the prior art.
Some embodiments of the invention provide a wave spring made from fiber-composite material. A wave spring provides the same functionality as a coil spring. However, while coil springs rely on torsion, a wave spring stores and releases energy by bending. Specifically, as a load is applied, portions of the wave spring flatten, providing an upward force, enabling full axial-load transmission.
As compared to its metal counterpart, a fiber-composite wave spring in accordance with the present teachings is characterized by lighter weight and higher specific strength. In fact, a fiber-composite wave spring in accordance with embodiments of the invention is typically in the range of 40-80% lighter than a metal wave spring having similar spring characteristics.
Embodiments of a wave spring include: (i) those having one or more annular wave-springs elements and (ii) those having one or more curvilinear wave-spring elements.
Annular (but not necessarily circular) wave-spring elements vary in height around the annulus, the variation in height creating one or more “waves” in the element. In some embodiments, attributes of the annular wave-spring element may vary within the wave-spring element itself: for example, the thickness and/or shape, etc. of the cross section may vary along the annulus.
The annular wave-spring elements are stackable into a “vertical” array (although such a stack may be positioned horizontally), and embodiments of a wave spring may include a stack of one or more such annular wave-spring elements. In some embodiments of such embodiments, the design of the individual annular wave-spring-elements within the stack may vary from one another. This enables, for example, a progressive spring rate through the stroke of the spring. As an example, consider a spring that becomes stiffer as it is increasingly compressed. This characteristic can prevent a spring assembly from bottoming out, and transferring undesirably high impulse loads to any surrounding structure.
Similar benefits in spring rate and performance tuning can be achieved with a wave spring comprising a stack of annular wave-spring elements, wherein the individual annular wave-spring elements have different thicknesses in specific locations in the wave spring. Other aspects of each annular wave-spring element can be altered to change the performance of a wave spring incorporating such elements. For example, the thickness, cross-sectional profile, and/or materials composition (fiber type, resin type, fiber-volume-fraction) can be individually selected for any given annular wave-spring-element in a stack of such elements.
In accordance with the present teachings, within a stack of annular wave-spring elements, individual annular wave-spring elements are not rigidly coupled to one another. However, since the alignment of individual annular wave-spring elements within a stack affects spring characteristics, a desired alignment must be maintained. In various embodiments, such alignment is maintained through any one of a variety of structural “keying” arrangements.
In some further embodiments, inserts are placed between individual annular wave-spring elements. For example, in some of such embodiments, the inserts are positioned so that they prevent two annular wave-spring elements from displacing relative to one another once a certain amount of displacement is achieved. This increases the spring rate of the pair of elements, and again provides a progressive spring rate. In some embodiments, inserts are varied in thickness such that different annular wave-spring-element pairs reach the maximum displacement relative to one another at different points in their stroke, further providing tunability for the wave spring.
In some embodiments, external rings are used as spacers to limit the permissible displacement of an annular wave-spring element or a group of such elements before load is transferred to the external rings. When used in a nested arrangement consisting of, for example, three nested annular wave-spring elements that are stacked on top of two nested annular wave-spring elements, that are stacked on a single annular wave-spring element, these rings could prevent the single element from deflecting too far before the two- and three element groups begin to deflect and provide resistance.
In some embodiments, the invention provides a fiber-composite wave spring comprising a plurality of annular wave-spring elements arranged in an array, wherein each of the annular wave-spring elements consist essentially of aligned fibers in a thermoplastic resin matrix, and wherein: (a) the annular wave-spring elements are not rigidly coupled to one another; (b) the annular wave-spring elements are stacked one above another; and an alignment feature that aligns the wave-spring elements to one another.
In some other embodiments, the invention provides a fiber-composite wave spring comprising a plurality of curvilinear wave-spring elements arranged in an array, wherein each wave-spring elements consists essentially of aligned fibers in a thermoplastic resin matrix, and wherein: a first end of each curvilinear wave-spring element is attached to a first member and a second end of each curvilinear wave-spring element is attached to a second member, the plurality of curvilinear wave-spring elements being disposed between the two members; and the plurality of curvilinear wave-spring elements in the array are positioned side by side, the array extending laterally along a length of the first member and second member.
Additional embodiments in accordance with the present invention are provided in the drawings and the accompanying detailed description.
Definitions. The following terms are defined for use in this description and the appended claims:
It is to be understood that any numerical range recited herein is intended to include all sub-ranges encompassed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of about 1 and the recited maximum value of about 10, that is, having a minimum value equal to or greater than about 1 and a maximum value of equal to or less than about 10. As a non-limiting example, a recited range of “1 to 10 µm” includes “5 to 8 µm”, “1 to 4 µm”, “2 to 9 µm”, etc.
Some embodiments in accordance with the present teachings provide a fiber-composite wave spring comprising plural wave-spring elements.
In accordance with the present teachings, the wave-spring elements described herein are formed via a compression-molding process using fiber-composite feed constituents. In the illustrative embodiment, the feed constituents are a plurality of preforms. As part of the molding process, the preforms are arranged into an assemblage; either a preform charge or a lay-up. With the assemblage appropriately registered to the mold cavity, the preforms are positioned so that the preforms will be aligned with the anticipated in-use stress vectors that are expected to arise in the wave-spring elements when the wave spring is in use and under load. During compression molding, the assemblage of preforms are consolidated to form a final part; in this context, a wave-spring element.
Feed Constituents. As previously noted, a wave-spring element is formed from an assemblage of preforms. Preforms are typically formed from towpreg, but may also be sourced from the output of a resin impregnation line. To form a preform from towpreg or the output of a resin impregnation line, the towpreg is cut into segments of a desired size and often shaped (e.g., bent, etc.) as well. Each preform include thousands of co-aligned, resin-infused fibers, typically in multiples of one thousand (e.g., 1k, 10k, 24k, etc.). A preform may have any suitable cross-sectional shape (e.g., circular, oval, trilobal, polygonal, etc.), but is most typically substantially circular/oval.
As noted above, the preforms are organized into an assemblage. The assemblage has a geometry and shape that is close to that of the final structure, which in this case is a wave-spring element. In some embodiments, the preforms are placed one-by-one into the mold (i.e., a lay-up). In some other embodiments, the preforms are first organized into a “preform charge.”
A preform charge includes a plurality of preforms that are “tacked” together. The term “tacking” references heating to the point of softening (but not melting) to effectively join tile preforms to create a single structure. In some cases, minimal compression is applied for tacking. The preform charge, which is often created in a special fixture, conforms to the shape of the mold (and hence the part), or portions of it. Because the resin in the preforms is not heated to liquefication (the preforms are typically heated to a temperature that is above the heat deflection temperature of the resin, but below the melting point), and the applied pressure is typically low (less than 100 psig and in some cases nothing more than tile force of “gravity” acting on the preforms), the preform charge is not fully consolidated and thus could not function as a finished part. Importantly, the preforms within the preform charge substantially maintain their individually and form, and hence their fiber alignment. But once joined in this fashion, the preforms will not move. Thus, the preform charge is a (very nascent) version of the part, and exhibits the fiber alignment (based on the specific alignment/orientation of the preforms therein) desired in the final part. See, e.g., Publ. Pat. Apps. US2020/0114596 and US2020/0361122.
As used herein, the term “assemblage of preforms” refers to either a lay-up of preforms, as formed by placing preforms one-by-one into a mold cavity, or to a preform charge.
As previously noted, a preform, as that term is used herein, is a bundle of resin-infused fibers. The individual fibers can have any diameter, which is typically, but not necessarily, in a range of 1 to 100 microns. The individual fibers can have any length, which is application specific, wherein the length results from the cutting operation that creates the associated preform. Individual fibers can include an exterior coating such as, without limitation, sizing, to facilitate processing, adhesion of binder, minimize self-adhesion of fibers, or impart certain characteristics (e.g., electrical conductivity, etc.).
Each individual fiber can be formed of a single material or multiple materials (such as from the materials listed below), or can itself be a composite. For example, an individual fiber can comprise a core (of a first material) that is coated with a second material, such as an electrically conductive material, an electrically insulating material, a thermally conductive material, or a thermally insulating material.
In terms of composition, each individual fiber can be, for example and without limitation, carbon, carbon nanotubes, glass, natural fibers, aramid, boron, metal, ceramic, polymer, synthetic fibers, and others. Non-limiting examples of metal fibers include steel, titanium, tungsten, aluminum, gold, silver, alloys of any of the foregoing, and shape-memory alloys. “Ceramic” refers to all inorganic and non-metallic materials. Non-limiting examples of ceramic fiber include glass (e.g., S-glass, E-glass, AR-glass, etc.), quartz, metal oxide (e.g., alumina), alumina silicate, calcium silicate, rock wool, boron nitride, silicon carbide, and combinations of any of the foregoing. Non-limiting examples of suitable synthetic fibers include nylon (polyamides), polyester, polypropylene, meta-aramid, para-aramid, polyphenylene sulfide, and rayon (regenerated cellulose).
Any resin -thermoplastic or thermoset- that bonds to itself under heat and/or pressure can be used in conjunction with embodiments of the invention.
Exemplary thermoplastic resins useful in conjunction with embodiments of the invention include, without limitation, acrylonitrile butadiene styrene (ABS), ethylene tetrafluoroethylene (ETFE), fluorinated ethylene propylene (FEP), liquid crystal polymers (LCPs), polyamides (Nylon), polyaryletherketones (PAEK), polybenzimidazole (PBI), polybutylene terephthalate (PBT), polycarbonates (PC), and polycarbonate-ABS (PC-ABS), polyethylene (PE), polyetheretherketone (PEEK), polyetherimide (PEI), polyether sulfones (PES), polyethylene terephthalate (PET), perfluoroalkoxy copolymer (PFA), polyimide (PI), polymethylmethacrylate (PMMA), polyoxymethylene (polyacetals) (POM), polypropylene (PP), polyphosphoric acid (PPA), polyphenylene ether (PPE), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyphenylsulfone (PPSU), Polystyrene (PS), polysulfone (PSU), polytetrafluoroethylene (PTFE), polyurethane (PU), polyvinyl chloride (PVC), styrene acrylonitrile (SAN), and styrene butadiene styrene (SBS). A thermoplastic can be a thermoplastic elastomer such as polyurethane elastomer, polyether ester block copolymer, styrenic block copolymer, polyolefin elastomer, polyether block amide, thermoplastic olefins, elastomeric alloys (TPE and TPV), thermoplastic polyurethanes, thermoplastic copolyesters, thermoplastic polyamides, and thermoplastic silicone vulcanizate.
Non-limiting examples of suitable thermosets include araldite, bakelites, epoxies, melamines, phenol/formaldehydes, polyesters, polyhexahydrotriazines, polyimides, polyisocyanates, polyureas, silicones, urea/formaldehydes, vinyl esters, phenolics, and polycarbonates. Suitable thermosets can be prepared as a partially cured B-stage,
Wave Springs Having Annular Wave-Spring Elements.
Annular wave-spring element 100 has a continuous circular design with an undulating height profile. Many attributes/characteristics of an annular wave-spring element can be customized to generate a desired stiffness behavior, such as, without limitation: vertical height Hw (i.e., wave height), vertical thickness T (constant or varied), radius R (constant or varied), annular width Aw (constant or varied), period of undulation (i.e., wave frequency), shape of inner perimeter Pinner and outer perimeter Pouter (individually selected from: circular, polygonal, symmetric, asymmetric, or otherwise customized), material selection (including both resin and reinforcing fiber), and fiber volume fraction.
A “wave spring” in accordance with the present teachings includes at least one, and typically more than one, wave-spring element, which (in the case of a wave spring having annular wave-spring elements) are positioned one “above” the next in a vertical array or stack. That is, the wave-spring elements are arranged so that they are coextensive. The stack need not be vertically oriented in use.
As depicted in greater detail in later figures, in accordance with the present teachings, the individual annular wave-spring elements in a wave spring are not rigidly coupled to one another. Among other benefits, this facilitates fabrication of a wave spring in which the properties of individual wave-spring elements may vary, such as in any one or more of the attributes disclosed above, thereby providing the ability to create a wave spring with a response characteristic that is highly tuned to the intended use case.
For instance, consider a wave spring in accordance with the present teachings that includes ten of annular wave-spring elements 100 depicted in
As this particular wave spring is compressed, the relatively less-stiff upper annular wave-spring elements will initially compress to a greater degree than the relatively stiffer lower annular wave-spring elements. The force profile of the wave spring will therefore be determined to a relatively larger degree by the upper annular wave-spring elements. As the stroke proceeds, the spring compresses, wherein the relatively thicker bottom annular wave-spring elements will provide greater resistance per unit of stroke length than is experienced at the beginning of the stroke. The wave spring thus provides a progressive spring rate, which is desirable in a variety of applications.
In other embodiments, the stiffness through the “layers” of the wave spring is customized by varying fiber volume fraction (FVF) from wave-spring element to wave-spring element. For example, in the illustrative ten-element wave spring referenced above, consider an embodiment in which the FVF of the uppermost annular wave-spring element is 0.3 and the FVF of the lowermost annular wave-spring element is 0.6. This also results in a progressive spring stiffness throughout the wave spring’s stroke. The variation in FVF (between the uppermost and lowermost annular wave-spring elements) can be linear or non-linear.
Progressive spring rates can be useful, for example, in protecting machinery or other objects from crashes or other unanticipated impact loads. Impulsive accelerations imparted on an object during an event such as a crash can be tens or hundreds of times greater than acceleration due to gravity. If a spring rate is too low, particularly in a high-acceleration event such as a crash, the spring can bottom out and the sprung object can be exposed to impulse loads that can cause severe damage to an object or even destroy it. A progressive spring rate will enable the spring to mitigate higher loads without letting the spring bottom out and become impulsive.
Wave springs can also be made to have a regressive spring rate such that they provide less resistance as they are compressed. For instance, this can be useful for taking up “slop” in machinery or when dealing with higher-than-normal impact loads in vehicle suspensions. For machinery, the regressive spring rate provides enough force to keep components within tolerance, but not impart so much force as to disturb alignment or interfere with the operation of the equipment.
As an example, in farm-equipment suspensions, a certain amount of stiffness might be desirable to ensure that an operator’s ride is smooth and equipment does not bounce too much. However, fields are often much more uneven and varied than roads, and bigger-than-average bumps such as large rocks might impart too much force on a tractor or other piece of equipment and potentially cause damage, or upset a towed piece of machinery. A regressive spring will exhibit a certain amount of stiffness until a threshold level of displacement occurs, and will then decrease in stiffness as the displacement increases beyond the threshold. For a tractor or other piece of farm equipment, this will cause the spring to deform, rather than displacing the equipment that it is supporting, preventing the equipment from being rocked or excessively jolted by larger-than-average obstacles.
Traditional metal wave springs are often manufactured as a single piece, such that their spring elements remain properly aligned. For the decoupled annular wave-spring elements described herein, such alignment must be imposed lest the individual annular wave-spring elements rotate relative to one another and “nest.” Nest(ing) refers to when a major surface of an annular wave-spring element is fully in contact with that of another annular wave-spring element. Several approaches for defining and maintaining a proper alignment of the wave-spring elements are described below.
In some embodiments, alignment is maintained in conjunction with a support structure that extends for the length of the stack of annular wave-spring elements. In some of such embodiments, the support structure is disposed within the central opening of each annular wave-spring element. In some of these embodiments, a groove running the length of the support structure receives a projection that extends radially inward from the inner perimeter of each annular wave-spring element. In some other these embodiments, the support structure can include the projections and each annular wave-spring element can include a cooperating channel to receive a projection.
In some other embodiments, the support structure is positioned beyond the outer diameter of each annular wave-spring element. In some of such embodiments, the support structure completely encircles the stack of annular wave-spring elements. In some other of such embodiments, one or more relatively narrower support structures are positioned beyond the outer diameter of the stack of annular wave-spring elements. Each of such support structures couples with each wave element in the manner described above (cooperating grooves and projections).
In some further embodiments, each annular wave-spring element includes at least two holes that receives two support structures that extend the length of the stack of such elements. Still further arrangements, some of which are described later in this specification, and other arrangements that will occur to those skilled in the art in light of the present disclosure, may suitably be used to define and maintain a desired alignment of the annular wave-spring elements. As desired, one or more annular wave-spring elements are decoupled from the cooperating alignment feature, enabling those annular wave-spring elements to “nest,” as may be desired.
Wave springs in accordance with the invention can include plural stacks of annular wave-spring elements.
Although the nesting of annular wave-spring elements can be undesirable in many instances, there are embodiments in which the annular wave-spring elements are intentionally nested. For example, nesting can be used to create a wave spring with a progressive characteristic without requiring the individual annular wave-spring elements to differ from one another.
In some embodiments, the nesting of identical annular wave-spring elements will provide a stack in which stiffness increases in proportion to the number of nested elements. For example, three nested annular wave-spring elements will be thrice as stiff as an identically configured single annular wave-spring element. In addition to simplifying the manufacturing process (since the wave-spring elements can be identical to one another), nesting enables tuning to be accomplished on an ad-hoc basis. That is, a desired number of annular wave-spring elements can be readily nested as desired.
In one embodiment, three nested annular wave-spring elements are positioned above two nested annular wave-spring elements, which are, in turn, positioned above a single annular wave-spring element. The bottommost single annular wave-spring element will deform nominally, the middle group of two nested elements will require twice the force as the single element for the same amount of deformation, and the topmost group of three nested elements will require thrice the force as the single wave-spring element for the same amount of deformation.
Additional methods of creating progressive spring behavior include placing inserts between annular wave-spring elements. In some embodiments, the inserts are placed so that they prevent two annular wave-spring elements from displacing relative to one another once they attain a certain level of displacement. This would increase the spring rate of the pair of the elements and again provide a progressive spring rate. In some embodiments, the inserts are varied in thickness wherein different pairs of annular wave-spring elements attain the maximum allowed displacement relative to one another at different points in the stroke, further providing tunability.
In some embodiments, in addition to the spacers, external rings are used to limit the extent to which single annular wave-spring element or group of elements displace before the load is transferred to the external rings. When used in a nested arrangement described above, the external rings can prevent the single annular wave-spring element from deflecting too much before the two- and three-element groupings begin to deflect and provide resistance.
The preforms from which wave-spring elements (annular or curvilinear) are fabricated can be chosen such that the resin and fibers are transparent to certain electromagnetic (EM) waves such as radio frequency (RF) waves. This would enable the fabrication of wave springs that provide impact absorption for components such as antennae, transmitters, or other signal processing equipment without reducing signal quality.
In some other embodiments, the preforms may comprise resin/fibers that are electrically and/or thermally insulating, which can benefit applications where a sprung mass needs to be electrically or thermally separated from another part or surface. Examples include a wave spring to provide damping to electronics or batteries in a vehicle such as a car, boat, or aircraft.
Wave-spring element Fabrication. An assemblage of preforms is created from which the wave-spring element is fabricated. If prepared outside of the mold cavity, the assemblage is positioned within a mold cavity. The assemblage is arranged so that, at any given position in the mold cavity, the preforms within the assemblage align with the expected principal stress vectors that the wave-spring element will experience under design loads.
Annular Wave-Spring Element with Protrusions and Depressions.
Protrusions 616 and depressions 612 are formed in the same position along each annular wave-spring element. That is, the protrusions are directly below the depressions on each annular wave-spring element, and the location of the protrusions/depressions is consistent from annular wave-spring element is across plural elements. This enables the protrusions from an overlying annular wave-spring element to cooperate with a depression from an underlying annular wave-spring element, thus registering such adjacent annular wave-spring elements to one another. An advantage of this embodiment is that no additional pieces are required to couple the annular wave-spring elements to one another.
Annular Wave-Spring Element with Holes.
Annular Wave-Spring Element with Radially Extending Protrusions.
Annular Wave-Spring Element with integrated Keyway.
Annular Wave-Spring Element with radially varying inner perimeter.
To register a stack of plural annular wave-spring elements 1000 (such as define a wave spring) to one another, a support structure is suitably used.
Annular Wave-Spring Element with Progressive spring rate.
Wave Spring with Curvilinear Wave-Spring Elements.
Unlike a wave spring formed from a stack of annular wave-spring elements, a wave spring comprising more than one curvilinear wave-spring element is implemented as a lateral array of such elements. It will be appreciated that for a use case involving a vertically acting force, a wave spring comprising laterally arrayed curvilinear wave-spring elements provides a lower profile than a stack of annular wave-spring elements.
A wave spring comprising one or more curvilinear wave-spring elements can be configured in a variety of ways: (i) all curvilinear wave-spring elements 1200 oriented “curve up” (
In a lateral array of such curvilinear wave-spring elements 1200, if they are all facing the same direction (i.e., all “curve up” or all “curve down”), then the elements are oriented in parallel. In such a wave spring, each element in the array has the same deflection, and the spring rate/force of such a wave spring is equal to the number of curvilinear wave-spring elements times the spring force of an individual element (assuming that all elements have the same characteristics). If all curvilinear wave-spring elements alternate (such as depicted in
In some further embodiments, an array of curvilinear wave-spring elements includes some that are oriented “curve up” and others that are “curve down,” yet not alternating with one another. This provides an ability to tune the spring rate and achieve non-linearity in spring rates.
A wave spring such as wave spring 1300 can be molded in a single open/shut two-piece compression-molding tool. Specifically, molding constituents -an assemblage of fiber-bundle preforms- can be situated in a mold cavity that matches the “curve up” and “curve down” architecture, and uses a matching “plunger” to compress the assemblage.
It is to be understood that the disclosure describes a few embodiments and that many variations of the invention can easily be devised by those skilled in the art after reading this disclosure and that the scope of the present invention is to be determined by the following claims.
This case claim priority of US 63/334,325 filed Apr. 25, 2022, and incorporated by reference herein.
Number | Date | Country | |
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63334325 | Apr 2022 | US |