Patent Application
20200318368
The disclosure is related generally to a turnbuckle-style support strut with tunable stiffness.
There is a need for struts or springs that limit load transfer caused by enforced displacements from one structural member to another. For example, a strut may be required in a design where loads for a structure exceed requirements, because the structure is too stiff.
There are a number of existing solutions available, such as coil spring struts, machined spring struts and leaf springs. However, it is difficult to achieve a desired stiffness and travel with a coiled spring strut; it is difficult to achieve the desired stiffness and travel with a machined spring strut while maintaining a positive margin of safety on stress; and leaf springs on mating brackets require that a support strut become shorter to the point where a desired connection may not be feasible.
What is needed, then, is an improved support strut.
To overcome the limitations described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present disclosure describes a turnbuckle-style support strut with tunable stiffness, wherein the turnbuckle-style support strut uses opposing stacks comprised of one or more Belleville spring washers to provide an axial travel range and stiffness to support a given application.
Referring now to the drawings in which like reference numbers represent corresponding parts throughout:
In the following description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration a specific example in which the disclosure may be practiced. It is to be understood that other examples may be utilized and structural changes may be made without departing from the scope of the present disclosure.
Overview
The present invention discloses a turnbuckle-style support strut with tunable stiffness, wherein the turnbuckle-style support strut uses opposing stacks comprised of one or more Belleville spring washers to provide a required axial travel range and stiffness to support a given application. The turnbuckle-style support strut is typically used for coupling one or more structures.
A strut is a structural member of a structural framework of some kind, which carries loads in either tension or compression to help keep the structure as a whole in proper alignment. Struts generally work by resisting longitudinal tension or compression.
A turnbuckle is a device for adjusting the tension, compression, axial loading or length when coupling two structures. A turnbuckle normally is comprised of two threaded structural elements, one screwed into each end of a body, wherein one of the structural elements has a left-hand thread and the other of the structural elements has a right-hand thread. The tension can be adjusted by rotating the body, which causes both structural elements to be screwed in or out simultaneously, without twisting the structural elements, which changes the axial length.
A Belleville spring washer is a coned-disc spring that can be loaded along its axis either statically or dynamically. Belleville spring washers can be used as a single spring or as a stack. In a stack, Belleville spring washers can have the same or an alternating direction to modify the spring constant, the spring rate or the amount of deflection. Stacking in the same direction adds the spring constant in parallel, creating a stiffer structure with the same deflection. Stacking in an alternating direction is similar to adding common springs in series, resulting in a lower spring constant and greater deflection. Mixing and matching directions allow a specific spring constant and deflection capacity to be designed. In addition, different thicknesses of Belleville spring washers can tune the spring rate. However, weight and limited travel length can be issues.
In the present invention, the Belleville spring washers are preloaded to support an axial travel range, while ensuring the washers remain under load to prevent chatter. The support strut contains threaded interfaces at each end (one end has right-hand thread, the opposing end has left-hand thread) to allow for turnbuckle-style motion, in which the end fittings can be drawn in or extended out to facilitate installation, assembly and part variance.
The support strut can be attached to another structure by any number of methods. Typically, support struts are attached using clevis or pin connections with spherical bearings.
The support strut of the present invention limits load transfer caused by enforced displacements and structural shock events from one structural member to another via the spring system of the Belleville spring washers. It does this while maintaining the turnbuckle-style behavior without the need for external springs, such as coil springs, machined springs or leaf springs. The short stroke length and compact nature of Belleville spring washers allows the unit to be much shorter than a conventional spring system.
The threaded plunger 12 and the threaded housing 18 have opposite internal threads along an axis of the support strut 10, i.e., one has a right-hand thread and the other has a left-hand thread. Alternatively, the threaded plunger 12 and the threaded housing 18 could have opposite external threads.
Together, the threaded plunger 12 and the threaded housing 18 allow for turnbuckle-style connections to the end fittings 20. The end fittings 20 have the appropriate right-hand or left-hand threading to match the threading on the plunger 12 and housing 18.
This view also shows the Belleville spring washers 22 assembled within the rotation locking cap 14 and threaded housing 18 along a longitudinal axis of the threaded plunger 12. A flange 24 extending radially from the threaded plunger 12 separates two stacks 26a, 26b of the Belleville spring washers 22, such that the stacks of the Belleville spring washers 22 are on each side of the flange 24.
Other embodiments may include a greater or lesser number of the Belleville spring washers 22 in each stack 26a, 26b, as well as in total. Moreover, other embodiments may have more or less than half of the Belleville spring washers 22 in the stacks 26a, 26b on each side of the flange 24, including embodiments with different numbers of the Belleville spring washers 22 in the stacks 26a, 26b on each side of the flange 24. Further, other embodiments may have different orientations of the Belleville spring washers 22 in the stacks 26a, 26b than those shown herein.
The stacks 26a, 26b of Belleville spring washers 22 determine the stiffness of the support strut 10. In one embodiment, a spring resistance force along the x-axis 28 is provided by the movement of the flange 24 and the resulting compression or de-compression of the stacks 26a, 26b of the Belleville spring washers 22 by the flange 24. The compression of the washers 22 on either side of the flange 24 provides loading to the flange 24 and therefore the plunger 12 is moved relative to the housing 18.
The threaded plunger 12 has a hexagonal interface with the rotation locking cap 14 to react to any torsional load, so that the ends of the support strut 10, namely, the threaded plunger 12 and the threaded housing 18, cannot rotate relative to the other. Torsional loading will depend on how the support strut 10 is connected to another structure. Spherical bearings are typically used in the end fittings 20 to eliminate any torsional loading. If an application of the support strut 10 results in torsional loading, the load would be reacted through the hexagonal interface of the threaded plunger 12 with the rotation locking cap 14, and through the rest of the support strut 10.
In the tension case of
In the compression case of
The Belleville spring washers 22 are tunable, based on a stiffness target, depending on a stiffness and configuration of the Belleville spring washers 22. Both spring stiffness and travel are tailorable, based on a length of the support strut 10 and its components, the number and configuration of the Belleville spring washers 22, and the dimensions and material composition of the Belleville spring washers 22. The support strut 10 and its components can be lengthened or shortened to accommodate more or fewer Belleville spring washers 22. In addition, the diameter of the support strut 10 and its components can be increased or decreased to accommodate larger or smaller diameter Belleville spring washers 22. The spring constant for the washers 22 depends on the washer 22 stiffness, which changes based upon the composition of the washer, the dimensions of the washer 22, the shape of the washer 22, and the configuration of washers 22, including their numbers and orientations, in both serial and parallel stacks 26a, 26b.
The support strut of the present invention provides a number of benefits and advantages. As noted above, spring stiffness and travel are both tailorable. The Belleville spring washers 22 can be arranged to provide an almost unlimited number of combinations of stiffness and travel. In another example, the spring element combined with turnbuckle-type end interfaces allows for simple installation. In yet another example, the support strut 10 provides a compact design with a failure tolerance, such that if one Belleville spring washer 22 were to fail in a manner that significantly alters the stiffness of the washer 22, such as crack or fracture, the strut 10 would maintain a significant percentage of its original stiffness.
Aerospace Applications
Embodiments of the disclosure may be described in the context of aerospace applications, including manufacturing and service methods, as shown in
As shown in
Each of the processes of method 34 may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be any type of company, entity, organization, and so on.
As shown in
Apparatus and methods embodied herein may be employed during any one or more of the stages of the production and service method 34. For example, components or subassemblies corresponding to production processes 40 and 42 may be fabricated or manufactured in a manner similar to components or subassemblies produced while the vehicle or structure 50 is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages 40 and 42, for example, by substantially expediting assembly of or reducing the cost of the vehicle or structure 50. Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the vehicle or structure 50 is in service, for example and without limitation, to maintenance and service 48.
This invention was made with Government support under Contract Number NNM07AB03C awarded by NASA. The government has certain rights in this invention.
