CA1151626A

CA1151626A - Vibration isolator

Info

Publication number: CA1151626A
Application number: CA000371132A
Authority: CA
Inventors: Leon L. Hulett
Original assignee: Barry Wright Corp
Current assignee: Hutchinson Aerospace and Industry Inc
Priority date: 1980-04-11
Filing date: 1981-02-18
Publication date: 1983-08-09
Also published as: GB2074289A; GB2074289B; DE3111015A1; JPS56156535A; FR2480374A1; IT1142335B; JPS6112134B2; IT8147893A0; DE3111015C2; FR2480374B1

Abstract

ABSTRACT OF THE DISCLOSURE

A shock and vibration isolator which provides isolation between components coupled therethrough in a selected plane yet permits free relative motion be-tween the components in directions normal to the selected plane is in the form of an eyebolt, the eye portion of which is provided with an annular resilient shock and vibration absorbing insert having a tubular core with a smooth cylindrical inner surface. The isolator is especially suitable for use in connecting jet engine mountings to aircraft pylon structures.

Description

This invention relates to shock and vibration iso-lators used to connect components together, and more particularly to such devices which offer restraint, with isolation, between the components coupled toyether therethrough from relative motion in a selected plane yet permit free relative motion normal to the plane.
Shock and vibration isolators are well known and widely used, In principle, such isolators resiliently couple a pair of components together, forming in effect a mechanical oscil]ator tuned to oscillate at a frequency lower than that of the vibration to be attenuated by an amount depending on the desired attenuation. The tuning of the mechanical oscillator is accompl~shed by varying the stiffness of the iso-lator; the stiffer the isolator, the higher the tuned frequency. The stiffness of an isolator depends, in turn, not only on the resiliency of the material of construction of the isolator, but also on the dimen-sions (and, in the case of an isolator having damping, on the amount of deflection) of the isolator. The dimensions and disposition of the resilient material may be varied, thereby altering the amount of stiff-ness, and hence the degree of attenuation, in each direction, and isolators incorporating such features are well known.
A particular problem arises when an isolator is required to offer restraint`in all but a selected one direction while allowing free relative motion of the coupled components in this preferred direction. Such an isolator is required, for instance when a component which is subject to thermal expansion is to be mounted ~S~i2~

ancl fully restrained by more than a single isola-tor.
While one or more of the isolators used in such an application could be so dimensioned that their natural resiliency accommodates the thermal expansion, such an approach results in isolators which may not offer adequate restraint in other directions and further may have less than optimum damping, particularly with regard to vibrational excursions parallel to the line(s) joining isolators. Such isolators also gen-erally have undesired assymetric attenuation properties.
An alternative approach, which has found wide application in the mounting of aircraft turbines, secures the components together by a pair of iso-lators, one of which provides restraint in all direc-tions, and the other of which provides restraint in all directions except parallel to the direction of the first. To accomplish this, the second isolator is fabricated in the form of a pair of concentric cylin-ders free to rotate with r~spect to one another yet constrained both axially and radially by resilient pads. This isolator is securely attached by one of the two cylinders to one of the two components to be coupled through it in such a way that the axes of the concentric cylinders lie in a plane which is substan-tially normal to the direction of the anticipated thermal growth (i.e. in a plane normal to the direc-tion to the first isolator). The free cylinder of the isolator is now eccentricalLy attached by an appro-priate universal coupling to the remaining component.
Differential expansion between the components is communicated to the isolator as differential rotation of one cylinder with respect to the other.

6~

Although widely used, this type of vibration isolator is not without its disadvantages. Clearly the amount of free relative linear motion is limited, particularly if close angular alignment of components is to be maintained. Further, the required eccentric mounting of one component, in order to provide the couple to convert linear motion into rotational motion, provides a lever arm through which the loads seen by the isolator are amplified. Then again, in those applications which require the isolator to be so mounted that the axes of the concentric cylinders are vertical, this eccentric mounting insures unequal loading of the resilient components of the isolator through cantilever action. This assymetric loading of the isolator must be compensated for by assymetrically stiffening the resilient elements, with a consequent assymetric change in attenuation and damping properties.
Finally, it should be noted that such isolators are relatively complex, requiring the fabrication and assembly of a number of parts.
Accordingly it is an object of the present inven-tion to provide an isolator which offers restraint, with isolation between a pair of components coupled together therethrough, from relative motion in a selected plane, yet permits free relative motion normal to that plane. Further, it is an object of the present invention to provide such isolators in which the accommodation of the free relative motion in a preferential direction is not accompanied by delete-rious effects of the performance of the isolator.

More specifically, it is an object of the present ~3.5~6Z6 inventlon to provide such an isolator wherein the accommodation of the free relative motion in a pre-ferred direction is accomplished without an adjustment to the stiffness, and hence attenuation properties, of the isolator in any other direction. Further, it is an object of the present invention to provide an isolator in which the free relative motion in a pre-ferred direction may be relatively unlimited in its extent and may be accomplished without a change in the orientation of the two components. Yet a further object of the present invention is to provide such an isolator which is less complex, has few parts, and is easily fabricated and assembled~

These and other objects are provided in the present invention of a shock absorbing fastener which preferably is in the form of a threaded eyebolt, with the eye portion of the fastener bein~ provided with an annular resilient shock- and vibration-absorbing insert having a tubular core with a smooth cylindrical interior surface. This fastener may be rigidly attach-ed to one of the pair of components to be joined together by the bolt portion, with the eye portion so disposed that the tubular core is aligned parallel to the desired direction of free relative motion. The fastener is joined to the other of the pair of com-ponents by a cylindrical rod, dimensioned to smoothly and slidably fit within the tubular core, rigidly affixed to the other component in such disposition as to be coaxial with the core.

~S~ 6 It will be appl^eciated that the freedom of the cylindrical rod and the core to move relative to one another in an axial direction permits free relative motion between the pair of components coupled together therethrough. ~t the same time, relative motion between the pair of components in any other direction will radially compress the annular shock-absorbing insert separating the core from the eye portion of the eyebolt. Consequently, the fastener provides restraint from relative motion, together with shock and vibration isolation, in the plane of the annular insert, while permitting free relative motion normal to this plane.
Further, since the free relative motion is axial while the restraining forces of the annular insert are radial, there is no couple between the free motion and the attenuated motion, and consequently, allowance for the free motion places no restraints on the attenuating properties of the isolator. It should also be noted that the present isolator accommodates the linear motion centrally, and not eccentrically, and therefore the angular relationship between components can be maintained despite the excursion in the unrestrained direction. This configuration also insures that ampli-fied and cantilever loads are not intrinsically applied to the resilient element. Additionally, it will be understood that the extent of the free relative motion is limited only by the extent of the cylindrical rod passing through the isolator.
The invention is illustrated by way of example in the accompanying drawings wherein:

~S~6Z6 Fig. 1 is a view of a preferred form of isolator made in accordance with the principles of the present invention;
Fig. 2 is a cross-sectional view of the isolator of Fig. 1 taken along the llne 2-2; and Fig. 3 is a view, partially in section, from the same direction as Fig. 2, showin~ the isolator joining a pair of components.
In all of the views, like numbers refer to like components.

Referring to Figs. 1 and 2, there may be seen a vibration isolator made in accordance with the prin-ciples of the present invention, which in a preferred embodiment comprises a cone-shaped eye bolt 20, an annular resilient element 30, and a tubular core 32.
In a preferred embodiment intended for use in connect-ing a jet aircraft pylon structure to an engine mount-ing, all components are of metal, such as steel, eye bolt 20 and core 32 being of hardened steel and resil-ient element 30 being of compressed stainless mesh.
It will be understood, however, that the invention has other applications and, therefore, other materials could be employed in vibration isolators made in accordance with the principles of this invention, provided the materials possess the requisite mechan-ical properties (i.e., strength and rigidity in the case of eye bolt 20 and core 32 and resiliency in the case of resilient element 30) for the intended appli-cation. Thus, for example, eye bolt 20 and core 32 could be of aluminum, bronze, or even of such polymers ~151~2~

as polycarbonate, polyphenylene sulfide, and the like, while resilient element 30 could be of a natural or synthetic elastomer or of felt or cork.
Eye bolt 20 is comprised of eye portion 22, shank portion 24, and a bolt portion 26~ In a preferred embodiment, the eye portion 22 is in the general shape of a hollow right circular cylinder having an axial extent somewhat smaller or equal to its outside dia-meter, although it will be understood other dimension-al ratios are possible. Shank portion 24 extends radially from a midpoint on the outer surface of eye portion 22 by a distance chosen primarily on the basis of the desired separation between the components to be joined together by the isolator. In a preferred embodiment, shank portion 24 is substantially in the form of a frustum of a right circular cone, the larger base of which has a diameter on the order of the axial extent of eye portion 22. Coaxial with shank por-tion 24 and extending from the end thereof distal from eye portion 22 is bolt portion 26. In a preferred embodiment, the bolt portion 26 is threaded and has a diameter substantially the same as that of the smaller diameter base of conical shank portion 24. Preferably, eye, shank, and bolt portions 22, 24 and 26 are fabri-cated as a single piece, although it will be understood they may be fabricated separately and then assembled.
~he dimensions of these various portions of eye bolt 20 are established by means well known in the mechanical arts, by consideration of inter alia the magnitude of the load to be supported and the strength of the material of construction.

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The hollow in eye portion 22 is in the form of a substantially concentric cylindrical bore therethrough, the major portion of which is delimlted by cylindrical surface 27, as may be seen by reference to Fig. 2.
For a short axial distance at either end of the bore, the diameter of the inner surface of eye portion 22 is somewhat smaller than the diameter of cylindrical surface 27, thereby forming internal radial flanges 28.
The dimensions of cylindrical surface 27 and flanges 28 are established primarily from considerations of the operation of the isolator, as will be described here-inafter.
Tightly fitting within the bore of eye portion 22 defined by cylindrical surface 27, and held captive from motion parallel to the axis of the cylindrical surface by internal radial flanges 28, is annular resilient element 30. To this end, annular resilient element 30 is dimensioned to have the same axial extent as the separation between internal radial flanges 28 of eye portion 22, and the same outside diameter as the diameter of cylindrical surface 27.
The radial thickness of annular resilient element 30 is established, among other things, by the desired attenuating properties of the isolator, as will be understood by those skilled in the art. In designing the isolator, it should be noted that the maximum radial deflection of a segment of resilient element 30 is less than the radial thickness of the resilient element by at least the sum of the radial dimensions of flange 28 (on eye portion 22) and flange 34 (on core 32, to be described hereinbelow). As mentioned hereinbefore, annular res.ilient element 30 preferably consists of compressed metal mesh (compressed metal mesh members are old in the art of vibration and shock isolators, and are discussed, for example, in U.S.
Patent 3,073,557), although other materials may be useful in certain applications. Annular resilient element 30 may be fabricated either as a single piece or, as shown in Eig. 1, as an assembly of a number of individual resilient annular sectors 31. While the illustrated multisector annular resilient element is made up of six equal sized resilient annular sec-tors 31, the number of individual sectors used to form the complete annulus, and the angular extent of each sector, ma~ obviously be varied if so desired.
Further, it will be understood that the resilient annular sectors need not be so dimensioned angularly as to assembly into a complete annulus, but may be so designed as to leave circumferential gaps as desired.
Such modifications permit isolators to be designed so as to have varying isolation properties in differing radial directions or so as to support a large load in a preferred radial direction while exhibiting substan-tially uniform isolation properties in all radial directions.
Concentrically located within annular resilient elemen~ 30 is core 32. Core 32 is substantially in the form of a right circular cylindrical tube dimen-sioned to tightly fit within, and extend through, annular resilient element 30. Core 32 in axial extent matches eye portion 22. Each of the extremities of core 32 is provided with an external radial flange 34 _ g _.

~s~i so dispo~ed as to be substantially opposite corres ponding internal radial flanges 28 in a fully assem-bled eye bolt 20. A preferred embodiment of core 32 is provided with sleeve 36, in the form of a right circular cylindrical tube the diameter of which matches the inside diameter of core 32 and the axial lenyth of which matches that of the core. Sleeve 36 is disposed concentrically within core 32. Sleeve 36, which is optional, is intended as a bearing surface. Therefore, if used, sleeve 36 is fabricated of an appropriate low-friction material.
With regard to the assembly of the isolator, it will be appreciated that the method of assembly of annular resilient element 30 and core 32 into eye portion 22 depends on the nature of annular resilient element 30. Thus, if annular resilient element 30 is a unitary body, it may be pre-assembled to core 32 by stretching or forming it about the core, and then this subassembly may be forced, by compression of the resilient element, into the bore of eye portion 22.
On the other hand, and particularly for the case where annular resilient element 30 consists of a plurality of resilient sectors 31, assembly may most easily be accomplished by first assembling the annular resilient element in the bore of eye portion 22 and then fitting it with core 32. It will also be recognized that an elastomeric annular resilient element may be cast in place.
While flanges 23 and 34 serve to secure annular resilient element 30 within eye portion 22, and core 32 within the annular resilient element, the flanges may 3~S~2~i also serve to hold annular resilient element 30 in axial compression. This may be desireable in certain types of isolators and for certain methods of fabrica-tion. For instance, resilient element 30 may be formed by the axial compression of a tubular sock of metal mesh having an initial axial extent greater than that of eye portion 22 and subsequently further com-pressed and held in compression by one or another (or both) sets of flanges.
Turning now to Fig. 3, there may be seen an isolator made in accordance with the present invention joining together a pair of components 38 and 40. By way of example, component 38 may be a jet engine mounting ring and component 40 may be the pylon struc-ture of a jet engine aircraft. Component 38 has posts 42 which have aligned holes to accommodate a threaded bolt 44. Posts 42 support bolt 44 parallel to the desired direction of free relative motion between the components. Bolt 44 is sized to slidably fit through sleeve 36, and is secured by nut 46. It will be appreciated that a given isolator may be adapted to mate with bolts 44 of different diameters by appropriately changing sleeve 36. Posts 42 are dimensioned to support bolt 44 so as to provide clear-ance between eye portion 22 and component 38 when eye bolt 20 is secured to the component by posts 42 and bolt 44. The posts are spaced apart a greater dis-tance than the amount of the desired relative motion between components 38 and 40 by more than the axial extent of eye portion 22. Opposite the location of bolt 44, component 40 is provided with an aperture 47 configured to conform -to shank portion 24 and bolt portion 26 of the eye bolt. Aperture 47 has an axis substantially normal to the desired direction of free relative motion and is so dimensioned that, when eye bolt 20 is securely seated in the aperture, clearance is maintained between components 38 and 40 throughout the full excursion of relative motion between the -components. If the a~Io~ed free relative motion between components 38 and 40 is a preferential motion from an initial relationship between the components, the disposition of posts 42 and aperture 47 would be such that, in the initial condition, eye portion 22 of eye bolt 20 would be displaced along bolt 44 toward the post 42 opposite the preferential motion by an appropriate amount. Otherwise, the disposition of posts and aperture would normally be such as to center the eye portion. Eye bolt 20 is secured to compon-ent 40 by nut 48 on bolt portion 26.
In operation, the sliding fit between sleeve 36 and bolt 44 allows free relative motion between components 38 and 40 axially along bolt 44 betw~en the points of contact of eye portion 22 and posts 42.
Relative linear motions between the components normal to the allowed motion are seen as radial compressive displacements by annular resilient element 30. Of the rotational degrees of freedom between the com-ponents, only those about axes orthogonal to the axis of bolt 44 would place loads on the isolator, inasmuch as bolt 44 and eye bolt 20 are free to rotate relative to each other about this latter axis. In normal installations, an additional isolator, situated re-motely from eye bolt 20, would restrict relative rotational motion of components 3~ and 40 abou-t axes normal to the axis of bolt 44. Thus, it may be seen that in normal installations the isolator sees no moments which would tend either to amplify the load experienced by the isolator or cause uneven loading.
It will be appreciated that various modifications may be made to the preferred embodiment of the iso-lator without significantly departing from the inven-tion. ~hus, for instance, while the conical form of shank portion 24 facilitates the accurate and stable location of the isolator relative to component 40, the shank might be fabricated as a cylinder or as some other shape, e.g. so that its cross-section is square, rectangular or triangular; further, it might also be keyed to facilitate the orientation of annular resil-ient element 30. It might also be noted that for some applications the axes of shank portion 24 and bolt portion 26 might more desirably be set at an an~le other than substantially normal to the axis of annular resilient element 30. Furthermore it is contemplated that bolt portion 26 and shank portion 24 may have the same cross-sectional shape and/or maximum size. Still another possible modification is to have the bolt portion 26 unthreaded but connected to component 40 in some other manner, e.g., by welding or an adhesive or by C-shaped locked rings. Other variations and modifi-cations of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents as fall within the true spirit and scope of this invention.

Claims

The embodiments of the invention to which an exclusive property or privilege is claimed are defined as follows:

1. A load supporting vibration and shock ab-sorbing fastener comprising in combination, an eyebolt comprising an eye portion character-ized by a bore therethrough, an elongate shank portion extending from said eye portion, and a bolt portion affixed to said shank portion distal from said eye portion for enabling attachment of said eye bolt to a supporting structure;
an annular vibration and shock-absorbing body mounted within said bore; and means for securing said body within said bore.

2. A fastener in accordance with claim 1 wherein said shank portion is substantially in the form of a truncated right circular cone having a maximum diame-ter substantially equal to the maximum dimension of said eye portion and a minimum diameter substantially the same as that of said bolt portion.

3. A fastener in accordance with claim 2 wherein said eye portion has an axial extent and an external diameter which are substantially equal to one another.

4. A fastener in accordance with claim 1 further including a tubular core concentric with and inside of said vibration and shock-absorbing body.

5. A fastener in accordance with claim 4 wherein said core is secured within said body by a pair of external radial flanges attached to said core and situated at opposite ends thereof.

6. A fastener in accordance with claim 1 wherein said means for securing said body within said bore comprises a pair of internal radial flanges attached to said eye portion and situated at opposite ends of said bore.

7. A fastener in accordance with claim 1 wherein said annular vibration and shock absorbing body is composed of compressed metal mesh.

8. A fastener in accordance with claim 1 wherein said annular body is composed of a plurality of resil-ient annular sectors.

9. A vibration and shock absorbing fastener for interconnecting a mounting ring on an aircraft turbine with an engine pylon structure on an aircraft, said fastener comprising in combination:
an eye bolt comprising an eye portion character-ized by a bore therethrough, an elongate shank portion extending radially from said eye portion and a thread-ed bolt portion, said shank being substantially in the form of a truncated right circular cone tapering from said eye toward said threaded bolt portion, said threaded bolt portion being affixed in axial alignment to said shank distal from said eye for enabling attach-ment of said eye bolt to said pylon structure;

an annular vibration and shock-absorbing body composed of a compressed metal mesh inserted within said bore; and a tubular core concentric with and inside of said vibration and shock-absorbing body, said core being further provided with a substantially smooth finished interior surface;
said core being adapted to accommodate a mounting bolt for slidably attaching said fastener to said mounting ring so as to allow free relative motion between said mounting ring and said pylon structure in a direction parallel with the axis of said mounting bolt, yet offer resilient restraint to relative mo-tions between said mounting ring and said pylon struc-ture in all other directions.

10. A fastener in accordance with claim 7 where-in said compressed metal mesh is formed under axial compression of a tubular metal mesh member and is retained by a pair of flanges carried by said eye bolt.