Note: Descriptions are shown in the official language in which they were submitted.
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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
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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.
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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
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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.
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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:
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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
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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
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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
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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
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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.
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