U.S. patent application number 12/850694 was filed with the patent office on 2011-03-03 for frequency adapter and return means suitable for being arranged in such a frequency adapter.
This patent application is currently assigned to EUROCOPTER. Invention is credited to Vincent Girard, Charles Louis.
Application Number | 20110052395 12/850694 |
Document ID | / |
Family ID | 41727401 |
Filed Date | 2011-03-03 |
United States Patent
Application |
20110052395 |
Kind Code |
A1 |
Louis; Charles ; et
al. |
March 3, 2011 |
FREQUENCY ADAPTER AND RETURN MEANS SUITABLE FOR BEING ARRANGED IN
SUCH A FREQUENCY ADAPTER
Abstract
A frequency adapter (1) having at least first and second
cylinders (11, 12) having respective elongate first and second side
walls (13, 14), the second cylinder (12) being surrounded at least
in part by the first cylinder (11), resilient return means (20)
being in contact with the first and second side walls (13, 14).
Said return means (20) comprise resilient first and second extreme
layers (21, 22) each in contact with the first and second side
walls (13, 14), said adapter (1) being provided with a fluid (30)
arranged in a single chamber (100) between said first and second
extreme layers (21, 22).
Inventors: |
Louis; Charles; (Aix En
Provence, FR) ; Girard; Vincent; (Venelles,
FR) |
Assignee: |
EUROCOPTER
Marignane Cedex
FR
|
Family ID: |
41727401 |
Appl. No.: |
12/850694 |
Filed: |
August 5, 2010 |
Current U.S.
Class: |
416/106 |
Current CPC
Class: |
F16F 1/38 20130101; F16F
2230/24 20130101; B64C 27/51 20130101 |
Class at
Publication: |
416/106 |
International
Class: |
B64C 27/51 20060101
B64C027/51 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 25, 2009 |
FR |
09 04038 |
Claims
1. A frequency adapter comprising: at least first and second
cylinders having respective elongate first and second side walls,
the second cylinder being surrounded at least in part by the first
cylinder, and with resilient return means in contact with the first
and second side walls so as to be capable of being stressed by the
first cylinder and the second cylinder, wherein said return means
comprise first and second resilient extreme layers each in contact
with the first and second side walls, said adapter being provided
with a fluid arranged in a single chamber between said first and
second extreme layers so as to be suitable for escaping from the
adapter in the event of at least one extreme layer presenting a
crack that requires said adapter to be replaced.
2. A frequency adapter according to claim 1, wherein said fluid is
a liquid or a gas.
3. A frequency adapter according to claim 1, including a pressure
sensor for sensing the pressure of said fluid.
4. A frequency adapter according to claim 1, wherein said first
cylinder is blind having a first side wall extending longitudinally
from a first base that is open to an external medium (EXT) to a
second base that is closed by a plug, said first extreme layer of
the return means facing said external medium (EXT) and said second
extreme layer of the return means facing said plug, a first
longitudinal dimension (DIM1) of said first extreme layer being
shorter than a second longitudinal dimension (DIM2) of said second
extreme layer.
5. A frequency adapter according to claim 1, wherein said return
means include an intermediate layer between said first and second
extreme layers, said intermediate layer including a cavity
constituting said single chamber in which said fluid is
located.
6. A frequency adapter according to claim 5, wherein said
intermediate layer has a resilient first ring secured to the first
and second extreme layers and in contact with the first cylinder,
said intermediate layer also having a resilient second ring secured
to the first and second extreme layers and in contact with the
second cylinder, said cavity having the shape of a central ring and
extending between the first and second extreme layers and between
said first and second rings.
7. A frequency adapter according to claim 1, wherein the return
means is arranged between the first and second cylinders the return
means having a single block of material provided with first and
second extreme layers spaced apart by an intermediate layer, said
intermediate layer including a cavity filled with a fluid.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of FR 09 04038 dated
Aug. 25, 2009, the disclosure of which is incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a frequency adapter and
also to return means suitable for being arranged in such a
frequency adapter.
[0003] The invention lies in the technical field of damping
lead-and-lag or "drag" movements of a blade, and more particularly
in the field of frequency adapters for a rotorcraft rotor.
BACKGROUND OF THE INVENTION
[0004] Conventionally, a rotorcraft rotor comprises a hub driven in
rotation about an axis of rotation by a drive shaft or an outlet
shaft from a main gearbox, together with at least three blades that
are fastened to the hub via appropriate hinges, in particular via
respective laminated spherical thrust bearings dedicated to each of
the blades.
[0005] If each blade were to be fastened to a hub without being
hinged, then the resulting rotor is a rigid rotor. With a rigid
rotor, in hovering flight, the distribution of aerodynamic forces
along a blade gives rise to a bending moment of very large
magnitude at the root of the blade. In horizontal flight, the
so-called "advancing" blade generates more lift than the so-called
"retreating" blade because of the difference in air speeds, as
explained in greater detail below.
[0006] Consequently, the resultant of the aerodynamic forces acting
on a blade does not have the same value in all azimuth positions,
nor does it have the same point of application: the bending moment
at the root of the blade is thus large and varying, thereby
generating alternating mechanical stresses, giving rise to a
fatigue phenomenon that is harmful to materials. Furthermore, the
resultant of the aerodynamic forces from all of the blades is no
longer disposed along the drive axis of the rotor, thereby
generating a roll moment, said roll moment increasing with
increasing forward speed of the rotorcraft, which can make it
difficult to keep the rotorcraft in equilibrium in horizontal
flight.
[0007] In order to remedy those drawbacks, it is known to hinge
each blade on the hub about a respective axis that is perpendicular
to the drive shaft and referred to as the vertical flapping axis,
which corresponds to a vertical flapping hinge that is capable of
transferring lift but that can under no circumstances transfer a
bending moment. Consequently, if a blade has a flapping hinge
connection with the hub, then the flapping bending moment is zero
at the point of attachment constituted by said flapping hinge. For
the blade to be in equilibrium, centrifugal forces keep the blade
extending outwards after it has risen a little so that the
resultant of the lift and the centrifugal forces intersects said
flapping axis, and allowing conicity a.sub.0 to appear.
[0008] Under such conditions, there is no longer a large roll
moment in horizontal flight and the blades no longer rotate in a
plane, but rather their outer ends describe a very flat cone. In
practice, the flapping axis is then no longer on the axis of
rotation but is rather offset therefrom by a distance a, referred
to as eccentricity.
[0009] It should also be recalled that in order to provide a
helicopter with lift in its various configurations, it is necessary
to be able to control the lift provided by the rotor and to vary
it. That is why a pitch hinge is also provided, about an axis that
is substantially parallel to the span of the corresponding blade.
This new degree of freedom enables the lift of the blade to be
controlled by acting on the general pitch control, and also makes
it possible to vary pitch cyclically, thereby enabling the plane of
rotation of the blade to be controlled, which blades then describe
a cone of an axis that no longer coincides with the drive axis: the
resultant of the forces applied to the hub changes direction when
the plane of the rotor changes. As a result, moments are applied
about the center of gravity of the helicopter, thereby making it
possible for it to be piloted.
[0010] As mentioned above, the plane of rotation of the blades may
be other than a plane perpendicular to the drive shaft. Under such
conditions, it is necessary for each blade to be hinged in drag
since the end of each blade is at a distance from the rotor shaft
that varies. Otherwise, inertial forces would generate alternating
bending moments in the plane of each blade, thereby generating
undesirable mechanical stresses. Such a drag hinge is provided by
hinging a blade about a drag axis that is substantially parallel to
the rotor axis, and consequently substantially perpendicular to
drag forces. To enable such a blade to be driven by the drive
shaft, it is naturally necessary for the drag hinge to be far
enough away from the rotor axis to ensure that the moment due to
centrifugal forces balances the moment due to drag and inertial
forces, thus requiring the drag axis to be offset so as to present
eccentricity e, and with it being necessary for the so-called
"drag" angle .delta. not to be too large.
[0011] Consequently, the blades of a hinged rotor of a rotary wing
aircraft, in particular of a helicopter, can move in the following
four ways:
[0012] I) rotation about the rotor axis;
[0013] II) pivoting about a vertical flapping axis, made possible
by the vertical flapping hinge;
[0014] III) pivoting about the drag axis, also referred to as the
horizontal flapping axis, made possible by the horizontal flapping
hinge or drag hinge; and
[0015] IV) pivoting about the axis of the blade made possible by
the pitch hinge (with this not being specific to hinged
rotors).
[0016] By way of example, as described in patent FR 2 497 073, the
above pivoting movements II, III, and IV may be made possible by a
single member such as a laminated spherical thrust-bearing.
[0017] Nevertheless, the oscillations of each blade about its drag
axis may become coupled in unstable manner with the movements or
the elastic deformation modes of the airframe, in particular the
oscillations of a helicopter standing on the ground via its landing
gear: this gives rise to a phenomenon known as "ground resonance"
that can be dangerous for the aircraft when the resonant frequency
of the oscillations of the blades about their drag axes is close to
one of the resonant frequencies of oscillations of the aircraft on
its landing gear.
[0018] Remedies to that phenomenon consist in introducing damping
on the drag axes by means of a damper type device.
[0019] Such dampers include resilient return means of determined
stiffness and damping qualities for combating resonance phenomena,
in particular ground resonance, and also drive train resonance that
can also appear, in particular in helicopters.
[0020] When rotor blades are excited in drag, the blades depart
from their equilibrium positions and may become distributed
unevenly in the circumferential direction, thereby creating an
unbalance by moving the center of gravity of the rotor away from
its axis of rotation. Furthermore, the blades that have moved away
from their equilibrium positions oscillate about those positions at
a frequency .omega..sub..delta. which is the resonant frequency of
the blades in drag, and more exactly of the first mode of vibration
in drag, referred to more simply as drag mode.
[0021] If .OMEGA. is the frequency of rotation of the rotor, it is
known that the fuselage of the helicopter is thus excited at the
frequencies |.OMEGA..+-..omega..sub..delta.|.
[0022] When standing on the ground via its landing gear, the
fuselage of the helicopter constitutes a system comprising a mass
suspended above the ground by a spring and a damper constituted by
the landing gear. The fuselage supported by its landing gear thus
has its own resonant modes of vibration in roll and in pitching.
There is a risk of instability on the ground when the resonant
frequency of the fuselage on its landing gear, in roll or in
pitching, is close to an excitation frequency, and in particular to
the frequency |.OMEGA.-.omega..sub..delta.|, which corresponds to
the ground resonance phenomenon. To avoid this instability, it is
known firstly to seek to avoid these frequencies crossing before
the rotor reaches its nominal speed of rotation, and if they cannot
be prevented from crossing, then it is necessary to damp the
movements of the fuselage on its landing gear sufficiently and also
to damp the blades of the main rotor in their drag movements.
[0023] Consequently, the stiffness of the drag dampers of the
blades of a main rotor must be selected so that the resulting
resonant frequency of the blades in drag makes it possible to avoid
a potential ground resonance zone, while simultaneously having
sufficient damping. When the speed of rotation of the rotor passes
through the critical speed, assuming said speed is lower than the
nominal speed of rotation of the rotor, and regardless of whether
the speed of rotation of the rotor is speeding up or slowing down,
then the movements of the blades must be damped sufficiently to
avoid entry into resonance.
[0024] That is why drag dampers with resilient return means of
determined stiffness are also referred to as frequency
adapters.
[0025] Document FR 2 672 947 describes a frequency adapter provided
with a first cylinder that is elongate and blind, i.e. an elongate
external strength member extending from a closed end to an open end
that opens to the outside of the external strength member. A second
elongate cylinder of the strength member type is then inserted
through said open end into the inside of the first cylinder.
[0026] The frequency adapter then has resilient return means
arranged between the first and second cylinders, specifically an
elastomer ring that is bonded to the first and second
cylinders.
[0027] Similarly, document FR 2 818 717 provides first, second, and
third cylinders that are interleaved in one another, with two
adjacent coaxial cylinders being bonded together by an elastomer
ring.
[0028] More precisely, an elastomer ring connects the inside face
of a side wall of the first cylinder to the outside face of the
side wall of the second cylinder. Likewise, an elastomer ring
connects the inside face of a side wall of the second cylinder to
the outside face of the side wall of the third cylinder.
[0029] Documents EP 0 500 012 and WO 94/15113 also describe
resilient return means arranged between two cylinders.
[0030] Consequently, the state of the art provides frequency
adapters that are provided at least with first and second cylinders
having respective elongate first and second side walls, the second
cylinder being surrounded at least in part by the first cylinder,
with resilient return means being bonded to the first and second
side walls.
[0031] Such frequency adapters are very effective. Nevertheless,
their resilient return means deteriorate over time. This
deterioration is manifested by the appearance of cracks, fissures
in the elastomers, thereby reducing the effectiveness of the
adapter. Depending on the severity of the deterioration, it becomes
necessary to replace the adapter.
[0032] The manufacturers of frequency adapters are consequently
required to establish replacement criteria based on the dimensions
of the cracks that can be seen from the outside in order to
determine whether it has become necessary to replace a frequency
adapter.
[0033] In order to monitor the physical integrity of such return
means, an operator makes use of a small ruler. That method is made
difficult to implement when accessibility to the return means is
poor as a result of the large number of components in their
vicinity, thereby considerably lengthening the time required for
measurement and maintenance.
[0034] Document FR 2 860 582 relating to elastomer members provides
for placing graduations on the visible surface of an elastomer. It
would appear that this teaching applicable to elastomer members is
incomplete in the context of a frequency adapter since the depth of
the crack is not known.
[0035] The thickness of the return means of an adapter is
considerable compared with its visible area, so transposing the
teaching of document FR 2 860 582 to a frequency adapter would
appear to be difficult.
[0036] Document U.S. Pat. No. 5,534,289 provides for placing two
layers of colored microcapsules on a structure. Like document FR 2
860 582, the information provided by the method used remains
fragmented, with it being difficult to evaluate the length and the
depth of a crack.
[0037] Thus, the results of devices implemented in accordance with
documents FR 2 860 582 and U.S. Pat. No. 5,534,289 may be difficult
to interpret without some additional operation.
[0038] Document U.S. Pat. No. 5,493,899 provides for plunging an
elastomer element in a solvent and observing whether the solvent
penetrates into the inside of the element.
[0039] Finally, document U.S. Pat. No. 4,531,403 provides a method
of detecting cracks in a solid material by measuring
permeability.
[0040] The methods of documents U.S. Pat. No. 5,493,899 and U.S.
Pat. No. 4,531,403 appear clearly to be ill-adapted to a frequency
adapter arranged on a rotorcraft lift rotor.
[0041] The provisions set out in technical fields that are remote
from the invention, i.e. remote from frequency adapters, do not, a
priori, provide solutions that are completely satisfactory.
[0042] It should be observed that documents U.S. Pat. No. 5,205,710
and GB 1 568 455 relate to a blade and as a result they are remote
from the technical field of the invention.
[0043] Furthermore, document DE 1 942 853 presents return means
provided with two lateral grooves.
SUMMARY OF THE INVENTION
[0044] An object of the present invention is thus to propose a
frequency adapter that enables an operator to determine easily and
without ambiguity whether the frequency adapter needs to be
replaced, in particular without it being necessary to dismantle the
frequency adapter or to use tools that are bulky and not very
accurate.
[0045] According to one aspect of the invention, a frequency
adapter is provided in particular both with at least first and
second cylinders having respective elongate first and second side
walls, the second cylinder being surrounded at least in part by the
first cylinder, and with resilient return means in contact with the
first and second side walls so as to be capable of being stressed
by the first cylinder and the second cylinder. The return means may
optionally: [0046] adhere to the first and second side walls;
[0047] be compressed between the first and second side walls; or
[0048] be arranged between two shoulders of the first wall and two
shoulders of the second wall.
[0049] This frequency adapter is remarkable in that the return
means comprise first and second resilient extreme layers each in
contact with the first and second side walls, the adapter being
provided with a fluid arranged in a single chamber between the
first and second extreme layers so as to be suitable for escaping
from the adapter in the event of at least one extreme layer
presenting a crack requiring it to be replaced.
[0050] Thus, a fluid is located between the first and second
cylinders and between the first and second extreme layers.
[0051] In the event of a crack appearing having a predetermined
dimension in the first or second extreme layer, the fluid will
escape via said crack. An operator observing this fluid then
understands that the crack has reached a critical size, which means
that the deteriorated frequency adapter needs to be replaced.
[0052] The frequency adapter may also include one or more of the
following additional characteristics.
[0053] Under such circumstances, the fluid is advantageously a
colored liquid, thereby making it easily identified by an operator
in the event of a crack appearing that passes through the first
extreme layer or the second extreme layer. As a variant, the fluid
may be a gas under pressure.
[0054] When the fluid is a liquid, the liquid escapes by
capillarity.
[0055] When the fluid is a gas, it has a pressure that is
sufficiently different from atmospheric pressure.
[0056] Optionally, the frequency adapter may include a sensor for
sensing the pressure of said fluid. A drop in the fluid pressure is
then indicative of a leak, and thus of the presence of a large
crack.
[0057] Furthermore, the first cylinder is blind having a first side
wall extending longitudinally from a first base that is open to an
external medium to a second base that is closed by a plug, the
first extreme layer of the return means facing the external medium
and the second extreme layer of the return means facing the plug, a
first longitudinal dimension of the first extreme layer being
shorter than a second longitudinal dimension of the second extreme
layer.
[0058] Between its first and second cylinders, and starting from
the external medium and moving along an axis parallel to the
longitudinal axis of the first and second cylinders, the frequency
adapter comprises in succession: the first extreme layer; said
fluid; and the second extreme layer.
[0059] Since the first dimension is shorter than the second
dimension, a first crack passing longitudinally through the first
layer will occur before a second crack passing longitudinally
through the second layer, since the first distance to be traveled
by the first crack is thus shorter than the second distance to be
traveled by the second crack for this purpose.
[0060] Since the first extreme layer opens to the external medium
so as to be apparent, i.e. visible to an operator, an operator can
thus easily see when fluid has leaked from the frequency
adapter.
[0061] In a first embodiment, the first and second extreme layers
are distinct, these first and second extreme layers comprising two
distinct blocks of material that are separated by a fluid.
[0062] Conversely, in a second embodiment, the return means include
an intermediate layer between said first and second extreme layers,
the intermediate layer including a cavity constituting the single
chamber in which said fluid is located.
[0063] The first and second extreme layers and the intermediate
layer thus form a single block of elastic material within which a
fluid is held, the first and second extreme layers representing the
extreme bases of the block of elastic material.
[0064] In the first embodiment, the two distinct blocks of elastic
material are separated by a fluid, whereas in the second
embodiment, a fluid is contained within an intermediate portion of
a single block of elastic material.
[0065] Advantageously, the intermediate layer has a first resilient
ring secured to the first and second extreme layers and in contact
with the first cylinder, the intermediate layer also having a
resilient second ring secured to the first and second extreme
layers and in contact with the second cylinder, the cavity having
the shape of a central ring and extending between the first and
second extreme layers and between the first and second rings.
[0066] In addition to the above-described frequency adapter, the
concept of the invention is implemented in return means suitable
for being arranged between first and second cylinders of a
frequency adapter. These return means are remarkable in that they
comprise a single block of material provided with first and second
extreme layers interconnected by an intermediate layer, the
intermediate layer including a cavity filled with a fluid, and said
cavity thus forming a single chamber containing said fluid.
[0067] In addition, the return means include a hollow central
portion. Thus, it is possible to arrange it in a first cylinder of
a frequency adapter and to arrange a second cylinder of said
frequency adapter in the hollow central portion.
BRIEF DESCRIPTION OF THE DRAWING
[0068] The invention and its advantages appear in greater detail in
the context of the following description of embodiments given by
way of example with reference to the accompanying figures, in
which:
[0069] FIG. 1 shows a frequency adapter in a preferred first
embodiment;
[0070] FIG. 2 shows a frequency adapter in a second embodiment;
and
[0071] FIG. 3 shows return means of the invention.
[0072] Elements that are present in more than one of the figures
are given the same references in each of them.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0073] The figures also show three directions X, Y, and Z.
[0074] The directions X and Y are referred to as first and second
transverse directions.
[0075] Conversely, the direction Z is referred to as a longitudinal
direction insofar as the elements shown stretch in this
longitudinal direction. Furthermore, the term "thickness" relates
to dimensions in this longitudinal direction Z.
[0076] FIGS. 1 and 2 show a frequency adapter 1 of the
invention.
[0077] The frequency adapter 1 comprises a first cylinder 11 having
a first side wall 13 extending longitudinally from a first base 15
towards a second base 16. The first cylinder 11 shown in FIGS. 1
and 2 is a hollow cylinder defined by its first side wall 13, the
longitudinal axis AX along which the first cylinder extends
representing the axis of symmetry of the first side wall 13. It
should be observed that the longitudinal axis AX extends along the
longitudinal direction Z.
[0078] Furthermore, the first base 15 of the first cylinder 11
opens to an external medium EXT, while the second base 16 is closed
by a conical plug 17. The plug 17 and the first side wall 13 form a
single part in the configuration shown. Under such circumstances,
the first cylinder 11 is blind, the first cylinder opening to the
external medium solely via its first base.
[0079] Finally, it should be observed that the plug 17 includes
first fastener means 201 for fastening to a blade of a rotorcraft
lift rotor, for example.
[0080] In addition, the frequency adapter 1 has a second cylinder
12 with a second side wall 14 extending longitudinally. The second
cylinder 12 shown in FIGS. 1 and 2 is a solid cylinder defined by
its second side wall 14, the longitudinal axis AX along which the
first cylinder extends also representing the axis of symmetry of
the second side wall 14.
[0081] The second cylinder 12 is arranged at least in part inside
the first cylinder 11. More particularly, the second cylinder 12 is
arranged completely inside the first cylinder 11 in the
configuration shown, with the first and second cylinders having a
longitudinal axis AX of symmetry in common.
[0082] Furthermore, level with the first base 15 of the first
cylinder 11, the second cylinder is provided with second fastener
means 202 suitable for fastening to a blade or to the hub of a
rotorcraft lift rotor, for example.
[0083] Furthermore, the frequency adapter 1 possesses resilient
return means 20 in contact firstly with the first side wall 13 of
the first cylinder 11 and secondly with the second side wall 14 of
the second cylinder 12.
[0084] For example, the resilient return means 20 adhere both to
the first side wall 13 of the first cylinder 11 and to the second
side wall 14 of the second cylinder 12.
[0085] By moving the first cylinder 11 relative to the second
cylinder 12 along the longitudinal axis AX, and vice versa, the
resilient return means 20 are stressed in shear, thereby acting as
a damper.
[0086] Independently of the embodiment, the return means comprise
first and second extreme layers 21 and 22 of a material
constituting an elastomer, e.g. selected for its elastic and/or
damping properties.
[0087] Consequently, the first extreme layer 21 adheres close to
the first base 15 to the first and second cylinders 11 and 12, and
more specifically to the first and second side walls 13 and 14. At
the opposite end, the second extreme layer 22 adheres close to the
second base 16 to the first and second cylinders 11 and 12, and
more specifically to the first and second side walls 13 and 14.
[0088] The first and second extreme layers 21 and 22 are in the
form of rings both having the second cylinder 12 passing
therethrough, and both being surrounded by the first side wall 13
of the first cylinder 11.
[0089] Advantageously, a fluid 30 is then located in a single
chamber 100 between the first and second extreme layers 21 and 22
and between the first and second side walls 13 and 14.
[0090] Thus, a first external face 21' of the first extreme layer
21 faces the first base 15 and thus the external medium EXT, while
a first internal face 21'' of the first extreme layer 21 faces at
least the fluid 30. Similarly, a second external face 22' of the
second extreme layer 22 faces the second base 16 and thus the plug
17, while a second internal face 22'' of the second extreme layer
22 faces at least the fluid 30.
[0091] The fluid 30 may be a colored liquid or indeed a gas, for
example.
[0092] If a crack passes longitudinally through one of the extreme
layers 21 or 22 in its thickness direction, going from the external
face 21', 22' to the internal face 21'', 22'' of said extreme layer
21, 22, and thus reaching said single chamber 100, then the fluid
30 can escape from its housing via the through crack.
[0093] In a variant, the fluid is a colored liquid, so the
appearance of this colored liquid informs an operator that an
extreme layer 21, 22 of the return means 20 has a crack passing
through it. The operator then immediately replaces the faulty
frequency adapter 1.
[0094] Thus, if the crack is a first crack 101 appearing in the
first extreme layer 21, it will be understood that the colored
liquid will reach the first external face 21' of said first extreme
layer 21. This first external face 21' of the first extreme layer
21 faces the external medium EXT, so the operator can observe the
presence of said colored liquid visually and without effort.
[0095] However, if the crack is a second crack 102 appearing in the
second extreme layer 22, the colored liquid will reach the second
external face 22' of said second extreme layer 22. This second
external face 22' of the second extreme layer 22 faces the plug 17
so, a priori, the operator will not observe the presence of said
colored liquid visually. Thus, the plug 17 is advantageously
provided with inspection orifices enabling the operator to observer
the second external face 22' of the second extreme layer 22.
[0096] In order to avoid using such a plug 17 provided with
inspection orifices, for the first extreme layer 21 having a first
longitudinal dimension DIM1 and thus a first thickness from its
first external face 21' to its first internal face 21'', and for
the second extreme layer 22 having a second longitudinal dimension
DIM2 and thus a second thickness from its second external face 22'
to its second internal face 22'', the first dimension DIM1 is made
to be shorter than the second dimension DIM2.
[0097] Thus, the first extreme layer 21 facing a medium EXT that is
external to the frequency adapter 1, and that is thus easily
visible to an operator, has a first longitudinal dimension DIM1
that is shorter than the second longitudinal dimension DIM2 of the
second extreme layer 22.
[0098] Under such circumstances, a first crack 101 will pass
through the first extreme layer 21 before a second crack 102 passes
through the second extreme layer 22.
[0099] The invention thus enables an operator to know when it is
necessary to replace a frequency adapter without it being necessary
to use any instrument, not even a ruler for measuring purposes.
[0100] In another variant, the fluid 30 is a liquid or a gas under
pressure.
[0101] The escape of the fluid can then be observed visually, the
liquid or gas possibly being colored, or it may be detectable by
touch. Under such circumstances, by placing a hand on a crack, an
operator can feel the presence of the liquid or the pressure of the
gas of the fluid 30.
[0102] In order to inspect an extreme layer that is not directly
visible from the external medium EXT, it is possible to use a plug
that is pierced or indeed a first extreme layer 11 for which the
first longitudinal dimension DIM1 is shorter than the second
longitudinal dimension DIM2 of the second extreme layer 12.
[0103] Like the configuration shown in FIG. 1, the frequency
adapter 1 may be provided with a pressure sensor 31 that is
connected to a display screen 32 in order to display the pressure
of the fluid 30.
[0104] Under such circumstances, a drop in this pressure means that
the first and/or second extreme layer 21, 22 possesses a through
crack, i.e. a crack interconnecting the external face of an extreme
layer with its internal face.
[0105] In the first embodiment shown in FIG. 1, the first and
second extreme layers 21 and 22 constitute two distinct blocks of
material. The first internal face 21'' of the first extreme layer
21 is not connected to the second internal face 22'' of the second
extreme layer 22 by a layer of elastic material.
[0106] The first and second extreme layers 21 and 22 form two
distinct entities that can be handled separately, naturally before
they are positioned against, and even fastened, to the first and
second side walls 13 and 14.
[0107] In order to fill the space 30 situated in the sole chamber
100 between the first and second extreme layers 21, 22 and between
the first and second side walls 13, 14 with fluid, a filler orifice
is provided that is closed by conventional means 40.
[0108] With reference to FIGS. 2 and 3, in a second embodiment, the
return means 20 of the frequency adapter comprise a single block 28
of material of the invention provided with a fluid 30 between first
and second extreme layers 21, 22.
[0109] More precisely, with reference to FIG. 3, the single block
28 comprises in succession along a longitudinal axis AX: a first
extreme layer 21; an intermediate layer 23; and a second extreme
layer 22. The first and second extreme layers 21 and 22 and the
intermediate layer 23 are thus inseparable, unlike the first
embodiment. Furthermore, in order to be able to surround a cylinder
of a frequency adapter, the single block 28 has a longitudinal bore
29 passing along the longitudinal axis AX in succession through the
first extreme layer 21, the intermediate layer 23, and the second
extreme layer 22.
[0110] Furthermore, the first extreme layer 21 extends
longitudinally from a first external face 21' facing externally
relative to said single block 28 to a first internal face 21''
facing the intermediate layer. A first dimension DIM1 then extends
between the first external face 21' and the first internal face
21''.
[0111] Similarly, the second extreme layer 22 extends
longitudinally from a second external face 22' facing externally
relative to said single block 28 to a second internal face 22''
facing the intermediate layer. A second dimension DIM2 then extends
between the second external face 21' and the second internal face
21''.
[0112] The first dimension DIM1 is then advantageously shorter than
the second dimension DIM2.
[0113] Furthermore, the intermediate layer 23 has a cavity 26
forming a single chamber 100 in which a fluid 30 is arranged, e.g.
a liquid or gas that is colored and/or at a predetermined pressure.
For this purpose, it is possible to envisage making a local opening
27 and to reclose this local opening once the cavity 26 has been
filled.
[0114] The intermediate layer 23 comprises a resilient first ring
24 secured to the first and second extreme layers 21 and 22 and
suitable for being pressed against or bonded to a first cylinder 11
surrounding the single block 28, the intermediate layer 23 having a
resilient second ring 25 secured to the first and second extreme
layers 21 and 22 and suitable for being pressed against or bonded
to a second cylinder 12 surrounded by the sole block 28, and the
cavity 26 is in the form of a central ring extending between the
first and second extreme layers 21 and 22 and between said first
and second rings 24 and 25.
[0115] It should also be observed that it is possible to insert a
pressure sensor 31 inside the cavity 26, the pressure sensor being
provided with a connection cable 33 leading to a display screen 32.
Care should then be taken to ensure the connection cable 33
projects out from the single block 28.
[0116] With reference to FIG. 2, the single block 28 is placed
between the first and second cylinders 11, 12 of a frequency
adapter of the above-described type.
[0117] Thus, the second cylinder 12 is placed inside the
longitudinal bore 29 in the single block 28, and the peripheral
wall 30 of the single block 28 is bonded to the first cylinder 11
and to the second cylinder 12, by adhesive or by compressing the
single block 28 between the first and second cylinders, for
example.
[0118] Care is then taken to place the first external face 21' of
the first extreme layer 21 level with the first base 15 and thus
facing the external medium EXT. Consequently, the second external
face 22' of the second extreme layer 22 faces the second base 16,
and thus the plug 17.
[0119] Naturally, the present invention may be subjected to
numerous variations as to its implementation. Although several
embodiments are described above, it will be readily be understood
that it is not conceivable to identify exhaustively all possible
embodiments. It is naturally possible to envisage replacing any of
the means described by equivalent means without going beyond the
ambit of the present invention.
[0120] For example, it should be observed that the cylinders need
not be right-circular cylinders and/or that each cylinder may have
a plurality of members without going beyond the invention. Under
such circumstances, the first cylinder may optionally be provided
with at least one external sheath and with an external strength
member extended by a plug. Similarly, the second cylinder may
optionally be provided with at least one internal sheath and with
an internal strength member.
[0121] The resilient means are then secured to the internal and
external sheaths, e.g. by vulcanization, and then the return means
are inserted between the internal and external strength
members.
[0122] More precisely, in the first embodiment, the first extreme
layer is bonded to the first internal sheath and the first external
sheath while the second extreme layer is bonded to the first
internal sheath and to the first external sheath.
[0123] In the second embodiment, a single internal sheath and a
single external sheath are sufficient. Thus, the first and second
extreme layers are bonded to these single internal and external
sheaths. Similarly, the intermediate layer is bonded to these
single internal and external sheaths respectively via its first and
second rings.
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