FREQUENCY-DEPENDENT DAMPER AND ROTARY WING SYSTEM
This application claims the benefit of U.S. Provisional Application No. 611419,794,
filed on December 3,2010, which is herein incorporated by reference.
BACKGROUND
Dampers are used on most helicopters with soft in-plane rotors to provide damping to
the lead-lag motion of the rotor blades. The lead-lag motion of a rotor blade is the back and
forth motion of the blade in a horizontal plane. Significant lead-lag motion of a rotor blade
10 occurs at a lead-lag resonant frequency that is typically less than the rotor operating
frequency. The function of the damper is to control this resonance so that the helicopter does
not become unstable. The lead-lag damper provides the damping required at the lead-lag
resonant frequency while imposing unnecessarily high loads on the hub of the rotor and
heating up of the damper at the rotor operating frequency. Thus, a damper that provides the
15 required damping forces at the lead-lag resonant frequency and reduced damping forces at the
rotor operating frequency would be an improvement in the technology.
SUMMARY
In an embodiment, a frequency-dependent damper is provided. The frequencydependent
damper comprises an outer damper body, an inner damper body and a piston. The
20 outer damper body has an internal cavity. A working chamber is defined inside the internal
cavity. The piston has an internal chamber defined therein, wherein the piston is movably
positioned within the internal cavity. The piston separates the working chamber into a first
working chamber and a second working chamber. There is at least one orifice defined on the
piston and disposed between an outer piston wall and an inner piston wall. The orifice
25 provides fluid communication between the internal chamber and the first and second working
chambers. There is an inner piston plate disposed within the internal chamber of the piston.
There is at least one spring element. The spring element is positioned between the inner
piston wall and the inner piston plate. An inner damper body is disposed within the outer
damper body and coupled to the inner piston plate, wherein the inner damper body is capable
30 of receiving a variable-frequency disturbance communicated to the internal cavity.
In an embodiment, a frequency-dependent damper is provided. The frequencydependent
damper comprises at least one input plate, at least a first damped elastomer and a
support member. The first damped elastomer is secured to the input plate. The first damped
elastomer has a damping coefficient. The support member is secured to the first damped
elastomer such that mechanical energy of a damping force is communicated therebetween,
wherein the first damped elastomer is configured to shear in response to relative motion
between the input plate and the support member.
In an embodiment of the invention, a frequency-dependent damper for creating a
5 damping force in response to a variable-frequency disturbance comprises an outer damper
body having an internal cavity, an inner damper body for receiving the variable-frequency
disturbance extending into the internal cavity, a first fluid chamber and a second fluid
chamber defined inside the internal cavity, a piston separating the first and second fluid
chambers, a selected orifice for transferring fluid between the first and second fluid
10 chambers, and a selected spring element arranged serially between the piston and the inner
damper body such that the piston can move relative to the inner damper body through
deformation of the selected spring element.
In an embodiment of the invention, a frequency-dependent damper for creating a
damping force in response to a variable-frequency disturbance comprises an input member
15 for receiving the variable-frequency disturbance, a support member, a damping structure
comprising a first elastomer having a first damping coefficient and a second elastomer having
a second damping coefficient, the first and second elastomers being configured to shear in
response to relative motion between the input member and the support member, the damping
coefficient of the first elastomer being different from the damping coefficient of the second
20 elastomer.
In an embodiment of the invention, a rotary wing system with at least one rotating
blade rotating about a rotation axis, the rotary wing system having a variable-frequency
disturbance when rotating about the rotation axis, comprises a frequency-dependent damper
for controlling the variable-frequency disturbance, the frequency-dependent damper
25 comprising an outer damper body having an internal cavity, an inner damper body for
receiving the variable-frequency disturbance extending into the internal cavity, a first fluid
chamber and a second fluid chamber defined within the internal cavity, a piston separating
the first and second fluid chambers, an orifice for transfer of fluid between the first and
second fluid chambers, and a spring element serially arranged between the piston and the
30 inner damper body such that the piston can move relative to the inner damper body through
deformation of the spring element.
In an embodiment of the invention, a rotary wing system with at least one rotating
blade rotating about a rotation axis, the rotary wing system having a variable-frequency
disturbance when rotating about the rotation axis, comprises a frequency-dependent damper
for controlling the variable-frequency disturbance, the frequency-dependent damper
comprising an input member for receiving the variable-frequency disturbance, a support
member, a damping structure comprising a first elastomer and a second elastomer configured
to shear in response to relative motion between the input member and the support member,
5 the first elastomer having a first damping coefficient, the second elastomer having a second
damping coefficient, the first damping coefficient being different from the second damping
coefficient.
In an embodiment of the invention, a method of making a rotary wing damper
includes providing an outer damper body having an internal cavity, providing an inner
10 damper body, selecting a piston for providing a first fluid chamber and a second fluid
chamber, selecting a spring element, serially arranging the spring element between the piston
and the inner damper body such that the piston is movable relative to the inner damper body
through a deformation of the selected spring element, and receiving the inner damper body in
the outer damper body internal cavity to provide the first fluid chamber and the second fluid
15 chamber defined inside the outer damper body internal cavity, with the piston separating the
first and second fluid chambers, with a selected fluid transferring damping orifice between
the first and second working chambers, wherein with a relative motion of the inner damper
body relative to the outer damper body at a relatively high second frequency (fhigh) above a
selected frequency threshold (fthresholtdh)e selected spring element is substantially deformed
20 and at a relatively low first frequency (flow) below the selected frequency threshold (fthreshold)
the selected spring element is substantially undeformed.
A method of making a rotary wing damper including providing an input member,
providing a support member, providing a damping structure comprising a first elastomer and
a second elastomer, the first elastomer having a first damping coefficient, the second
25 elastomer having a second damping coefficient, the first damping coefficient being different
from the second damping coefficient, and coupling the damping structure to the input
member and support member to allow shearing of the first elastomer and second elastomer in
response to relative motion between the input member and the support member.
BRIEF DESCRIPTION OF DRAWINGS
3 0 FIG. 1 is a cross-sectional view of a frequency-dependent damper of the fluid-elastic
type.
FIG. 2 is another view of the frequency-dependent damper of FIG. 1.
FIG. 3 is another view of the frequency-dependent damper of FIG. 1.
FIG. 4 is a mechanical model of the frequency-dependent damper of FIG. 1.
FIG. 5 is a graph comparing damping stiffness versus frequency curves for a baseline
damper and a frequency-dependent damper.
FIG. 6A is a cross-sectional view of a frequency-dependent damper of the fluidelastic
type.
5 FIG. 6B is a partial cross-sectional view of a frequency-dependent damper of the
fluid-elastic type.
FIG. 7 is a partial cross-sectional view of a frequency-dependent damper of the fluidelastic
type.
FIG. 8 is a partial cross-sectional view of a frequency-dependent damper of the fluid-
10 elastic type.
FIG. 9 is a cross-sectional view of a frequency-dependent damper of the fluid-elastic
type.
FIG. 10 is a cross-sectional view of a frequency-dependent damper of the elastic type.
FIG. 11 is a perspective view of an aircraft including a rotary wing system.
15 FIG. 12 is a perspective view of the rotary wing system of FIG. 1 1.
DETAILED DESCRIPTION
FIG. 1 shows a frequency-dependent damper 10 for creating a damping force in
response to a variable-frequency disturbance. The frequency-dependent damper 10 of FIG.
1 is of the fluid-elastic type. In an embodiment, the frequency-dependent damper 10 has an
20 outer damper body 12 and an inner damper body 14. The outer damper body 12 has an
outer damper body internal cavity 16. Damping spaces in the outer damper body internal
cavity 16 not occupied by solid structures are filled with a damping fluid, an example of
which is silicone damping fluid. The inner damper body 14 is having a portion disposed
within the outer damper body internal cavity 16. The length of the inner damper body 14 is
25 preferably longer than the length of the outer damper body internal cavity 16 so that a
portion of the inner damper body 14 extends outside of the outer damper body internal
cavity 16. An outer damper body coupling 18 is mounted at an outer damper body end 20,
and an inner damper body coupling 22 is mounted at an inner damper body end 23. The
outer and inner damper body couplings 18, 22 can be used to couple the frequency-
3 0 dependent damper 10 to a system prone to variable-frequency disturbances, such as a
rotary wing system of an aircraft, as will be further described below.
Guide bushings 24, 26 are disposed in the outer damper body internal cavity 16,
between the outer damper body 12 and the inner damper body 14. In an embodiment, the
guide bushings 24, 26 are attached to the outer damper body 12. In an embodiment, the
guide bushings 24, 26 are annular. The inner damper body 14 extends through the annuli
of the guide bushings 24,26, and the guide bushings 24,26 support the inner damper body
14 and guide motion of the inner damper body 14 relative to the outer damper body 12. A
working chamber 28 is defined within the outer damper body internal cavity 16 by the
5 guide bushings 24, 26, the outer damper body 12, and the inner damper body 14. Piston 44
is movably positioned in internal cavity 16 of outer damper body 12, thereby being
arranged in the working chamber 28. In an embodiment, the working chamber 28 and the
piston 44 are annular and concentric. The piston 44 is movable within the working
chamber 28 and separates the working chamber 28 into two smaller working chambers 46,
10 48, each having a variable volume depending on the axial position of the piston 44 within
the working chamber 28. Working chambers 46, 48 are also referred to as first working
chamber 46 and second working chamber 48. The working chambers 46, 48 are filled
with a damping fluid.
In an embodiment, in FIG. 2, the piston 44 has orifice 37 defined thereon and
15 positioned adjacent to the working chamber 48. Piston 44 also has orifice 39 defined
thereon and positioned adjacent to the working chamber 46. The piston 44 has a piston
internal chamber 56 defined therein, which is connected to the orifices 37, 39. Thus, the
orifices 37, 39 and piston internal chamber 56 define a flow path in the piston 44 for
pumping of damping fluid between the working chambers 46, 48. Orifices 37, 39 are
20 disposed between outer piston wall 72 and inner piston wall 70. Orifices 37, 39 provide
fluid communication between internal chamber 56 and first working chamber 46 and
second working chamber 48. Fluid is pumped between the working chambers 46, 48 in
response to the piston 44 traversing the working chamber 28. Damping is related to the
amount of fluid pumped through the piston 44. Piston 44 is located between the outer
25 damper body 12 and the inner damper body 14. The piston 44 can move relative to the
outer damper body 12. The piston 44 is coupled to the inner damper body 14 and can
selectively move relative to the inner damper body 14, as will be further described below.
Seals 49 are provided between opposing faces of the piston 44 and the inner damper body
14. Seals 49 may be replaced by slider bearings. A small clearance 51 may be provided
3 0 between opposing faces of the piston 44 and the outer damper body 12 to provide an
alternate flow path between the working chambers 46, 48. The main flow path between the
working chambers 46, 48 is preferably through the piston 44, as defined by the orifices 37,
39 and piston internal chamber 56.
In an embodiment, in FIG. 1 or FIG. 2, the frequency-dependent damper 10
includes at least a first elastomeric ring, such as elastomeric rings 30, 32 arranged at or
near distal ends of the internal cavity 16 of outer damper body 12. The elastomeric rings
30, 32 engage the outer damper body 12 and the inner damper body 14 and thereby
5 provide seals between the outer damper body 12 and inner damper body 14, preferably
non-sliding seals between the outer damper body 12 and inner damper body 14. In an
embodiment, the elastomeric rings 30, 32 are attached, bonded, or otherwise fixed, to the
outer damper body 12 and the inner damper body 14. Preferably the at least first
elastomeric ring is bonded between the outer damper body 12 and the inner damper body
10 14. Elastomeric ring 30 is adjacent to, but spaced from, the guide bushing 24. By this
arrangement, an auxiliary chamber 34 is defined between the elastomeric ring 30, the outer
damper body 12, the inner damper body 14, and the guide bushing 24. Also, the
elastomeric ring 32 is adjacent to, but spaced from, the guide bushing 26. Also, by this
arrangement, an auxiliary chamber 36 is defined between the elastomeric ring 32, the outer
15 damper body 12, the inner damper body 14, and the guide busing 26. In an embodiment,
the auxiliary chambers 34, 36 are annular, and the volume of the auxiliary chambers 34, 36
can change when the elastomeric rings 30, 32 are sheared as a result of the inner damper
body 14 moving relative to the outer damper body 12. The auxiliary chambers 34, 36 are
filled with a damping fluid. Backfill ports(s) and valve(s), not identified separately, may
20 permit fluid flow from the auxiliary chambers 34, 36 to the working chamber 28. In an
embodiment, the backfill port(s) and valve(s) do not permit dynamic fluid flow in the
direction from the working chamber 28 to the auxiliary chambers 34, 36, thereby allowing
the elastomeric rings 30, 32 to be isolated from dynamic pressures in the working chamber
28.
25 In an embodiment, in FIG. 3, the inner damper body 14 has an inner chamber 17
internally positioned, and inside of which is mounted a volume compensator 38. In an
embodiment, the volume compensator 38 includes a gas chamber 69, a fluid chamber 40
and a movable barrier 43 between the chambers 69, 40. The gas chamber 69 can be
charged with a suitable gas, such as nitrogen, through a port 42 and charging valve 45. The
3 0 fluid chamber 40 is connected to the auxiliary chambers 34, 36 and the outer damper body
internal cavity 16 via fluid channels 53. Through a port 41 at an end of the volume
compensator 38, the fluid chamber 40 and working chambers within the outer damper
body internal cavity 16 can be filled with damping fluid. The volume compensator 38
allows for a steady pressure to be applied to the damping fluid within the frequencydependent
damper 10, which prevents cavitation of the fluid. As the frequency-dependent
damper 10 heats up and cools down, the damping fluid within the damper will expand and
contract. The gas in the gas chamber 69 of the volume compensator 38 is compressible to
allow for the expansion and contraction of fluid within the damper.
5 In an embodiment, in FIG. 1, the frequency-dependent damper 10 includes at least
a first spring element 54, arranged serially between the inner damper body 14 and the
piston 44. The term "arranged serially" preferably means that the piston 44 can move
relative to the inner damper body 14 through deformation of the at least a first spring
element 54. The spring element 54 has a spring stiffness and a damping coefficient. When
10 the disturbance applied to the inner damper body 14 is at relatively low first frequencies
(flow),t he following conditions occur within the damper: (i) the spring element 54 force is
substantially higher than the damping force resulting from the working fluid, (ii) the piston
44 is nearly stationary relative to the inner damper body 14, and (iii) the amount of fluid
pumped through the piston 44 and resulting damping force are relatively high. As the
15 frequency of the disturbance applied to the inner damper body 14 increases, the damping
force of the working fluid increases. Eventually, there will be a point [frequency threshold
(fthreshold] )w hen the frequency of the disturbance will be high enough that the relative
motion between the piston 44 and the outer damper body 12 becomes much less than the
motion of the inner damper body 14. Upon crossing the frequency threshold (fthresholadn) d
20 entering the relatively high second frequencies (fhigh),t he following conditions will occur
within the damper: (i) the piston 44 will move substantially relative to the inner damper
body 14, and (ii) the amount of fluid pumped through the piston 44 and the resulting
damping force will be relatively low (with fhighth e amount of fluid pumped with the piston
44 is less than with flow,w ith fhighp iston 44 motion relative to the inner damper body 14 is
25 greater than with flow).
In an embodiment, the piston 44 is made of two piston plates 50, 52 held together,
for example, by means of bolts 55. The orifices (37, 39 in FIG. 2) through which fluid can
be pumped between the working chambers 46, 48 are located in the piston plates 50, 52.
The size of orifice 37, 39 is selected to reduce damping based upon the anticipated variable
3 0 frequencies, and the type of fluid having a known density and viscosity. The two unfixed
output piston plates 50, 52 define the piston internal chamber 56 of the piston 44 that is
connected to the piston orifices (37, 39 in FIG. 2). An inner piston plate 58 is coupled to
the inner damper body 14. extending into the piston internal chamber 56. In an
embodiment, the spring element 54 is in the form of a metal spring and is disposed in the
piston internal chamber 56. The spring element 54 is sandwiched between and makes
contact with the unfixed output piston plates 50, 52 and the inner piston plate 58. In
combination, the size of orifices 36, 37 and the spring stiffness of spring element 54 are
selected to reduce a damping force when a frequency of the variable-frequency disturbance
5 exceeds a selected frequency threshold. In other embodiments, the spring element 54 may
take on other forms. For example, elastomer, foam material, or shape memory alloy may
be used as the spring element 54.
FIG. 4 shows a mechanical model of the frequency-dependent damper 10 of FIG.
1. Ks represents the spring stiffness of the spring element 54, Cs represents damping due
10 to the spring element 54, Mp represents the mass of the piston 44. Cf represents damping
due to the working fluid, Kr represents stiffness of the elastomeric rings 30, 32, Cr
represents damping due to elastomer rings 30, 32, and x(t) represents displacement or
disturbance. In an embodiment, the ratio KsICf is set to a selected frequency threshold. In
an embodiment, the frequency-dependent damper 10 provides damping to the lead-lag
15 motion of rotor blades in a rotary wing system, and the selected frequency threshold is
between the rotor in-plane natural frequency and the rotor operating frequency. In an
embodiment, the selected frequency threshold is greater than 4 Hz. Although, it should be
noted that a different frequency threshold may be selected depending on the application.
FIG. 5 is a graph showing damping stiffness (lbslin) versus frequency (Hz) for a
20 baseline damper and a frequency-dependent damper. The baseline damper does not have a
spring element as described for frequency-dependent damper 10 above (or, in other words,
the spring element is considered infinitely stiffl. The frequency-dependent damper has the
characteristics of the frequency-dependent damper 10 described above. The data for the
graph was generated with an input displacement (disturbance) of k0.080 inches (see x(t) in
25 FIG. 4). Curve 59 represents the baseline fluid damper without the spring element. Curve
60 represents the frequency-dependent fluid damper with the spring element. In FIG. 5,
curve 59 shows that damping stiffness increases monotonically over the studied range of
frequencies for the baseline fluid damper. On the other hand, curve 60 shows that the
spring element incorporates second-order dynamics into the frequency-dependent fluid
3 0 damper such that sufficient damping is created at relatively low first frequencies (flow),a nd
damping does not significantly increase at the relatively high second frequencies (fhigh)I. n
FIG. 5, line 62 represents a rotor in-plane natural frequency with the selected frequency
threshold (fthresholcdo) inciding with the line 62 rotor in-plane natural frequency, and with
the line 64 representing an in-flight rotary wing system rotor operating frequency, with the
selected frequency threshold (fthresholtda)il ored to be below the line 64 rotor operating
frequency, with the line 64 rotor operating frequency in the relatively high second
frequencies (fhigh)C. ompared to the baseline damper, frequency-dependent damper 10,
operating in the manner represented by curve 60, has reduced heat generation, lower
5 operating temperature, reduced loads, and increased component reliability.
FIG. 6A shows a frequency-dependent damper 110 for creating a damping force
in response to a variable-frequency disturbance. The frequency-dependent damper 110 is
of the fluid-elastic type. The frequency-dependent damper 110 and the frequencydependent
damper 10 of FIG. 1 are similar, except for the differences described here.
10 Piston 144 has a internal chamber 156 defined by piston plates 150, 152. The inner piston
plate 158, which is fixed to the inner damper body 14, which extends into the piston
internal chamber 156. The spring element 154 is made of an elastomer and is arranged
within the piston internal chamber 156. The elastomeric spring element 154 has an annular
shape and circumscribes the inner piston plate 158, which is also annular in shape. The
15 elastomeric spring element 154 is sandwiched between the inner piston plate 158 and the
unfixed output piston plates 150, 152 in a radial direction. Disturbance on the inner piston
plate 158 is thus transferred to the unfixed output piston plates 150, 152 via the
elastomeric spring element 154. The disturbance on the inner piston plate 158 will come
from the inner damper body 14 when the inner damper body 14 is coupled to a system
20 subject to the disturbance. As in the case of spring element 54 of FIG. 1, the spring
element 154 is arranged serially between the inner damper body 14 and the piston 144 and
functions to incorporate second-order dynamics into the damping of the frequency
dependent damper 110. Preferably the elastomeric spring element 154 is a shearing
elastomeric spring element, with a first surface bonded to a surface of the inner piston
25 plate 158 and a second radially distal surface bonded to a surface of the unfixed output
piston plates 150, 152.
FIG. 6B shows a frequency-dependent damper 11 10 for creating a damping force
in response to a variable-frequency disturbance. The frequency dependent damper 11 10 is
of the fluid-elastic type. The frequency-dependent damper 11 10 and the frequency-
3 0 dependent damper 110 of FIG. 6A are similar, except for the differences described here.
Piston 1144 has an internal chamber 1156 defined by unfixed output piston plates 1150,
1152. The inner piston plate 1158, which is fixed to the inner damper 14, extends into the
piston internal chamber 1156. Two spring elements 1154A, 1154B, each made of an
elastomer, are arranged within the piston internal chamber 1156, on opposite sides of the
inner piston plate 1158. The elastomeric spring elements 1154A, 1154B are annular in
shape and circumscribe the inner damper body 14. The elastomeric spring elements
1154A, 1154B are sandwiched between the inner piston plate 1158 and the unfixed output
piston plates 1150, 1152. As a result, disturbance on the inner piston plate 1158 can be
5 transferred to the unfixed output piston plates 1150, 1152 via the elastomeric spring
elements 1154A, 1154B. As in the case of the spring element 154 of FIG. 6A, the spring
elements 1154A, 1154B are arranged serially between the inner damper body 14 and the
piston 1144 and function to incorporate second-order dynamics into the damping of the
frequency-dependent damper 11 10.
10 FIG. 7 shows a frequency-dependent damper 210 for creating a damping force in
response to a variable-frequency disturbance. The frequency-dependent damper 210 is of
the fluid-elastic type. The frequency-dependent damper 210 and the frequency-dependent
damper 10 of FIG. 1 are similar, except for the differences described here. In piston 244,
elastomeric snubbers or pads 270,272 are arranged inside the piston internal chamber 256,
15 adjacent to the unfixed output piston plates 250, 252 and distal ends of the spring element
54. The elastomer snubbers or pads 270, 272 limit the axial motion of the spring element
54, which can cause permanent deformation of the spring element 54.
FIG. 8 shows a frequency-dependent damper 310 for creating a damping force in
response to a variable-frequency disturbance. The frequency-dependent damper 310 is of
20 the fluid-elastic type. The frequency-dependent damper 3 10 and the frequency-dependent
damper 10 of FIG. 1 are similar, except for the differences described here. Compared to
the piston 44 of FIG. 1, the piston 344 of FIG. 8 has an additional flow path for pumping
of fluid between the working chambers 46, 48 when there is relative motion between the
piston 344 and the inner piston plate 358. The additional flow path, when open under the
25 conditions described above, further reduce the amount of damping generated by the
damper.
In the piston 344, an auxiliary orifice 374a is formed in the unfixed output piston
plate 350, and an auxiliary orifice 376a is formed in the unfixed output piston plate 352.
The auxiliary orifices 374a, 376a are fluidly connected to the piston internal chamber 356.
3 0 The auxiliary orifices 374a, 376a are in addition to and separate from the orifices normally
used for pumping fluid between the working chambers 46, 48. The orifices normally used
for pumping fluid are not visible in FIG. 8 because of the particular view of the drawing
shown, but they are visible in FIG. 2 as orifices 37, 39. A valve 378a is arranged in the
fluid path defined by the auxiliary orifices 374a, 376a and the piston internal chamber 356.
The valve 378a has two opposing valve heads 380a, 382a on interlocking stems 384a,
386a, respectively. The valve head 380a is adjacent to the piston plate 350 and orifice
374a, and the valve head 382a is adjacent to the piston plate 352 and orifice 376a.
When the piston 344 is stationary relative to the inner piston plate 358, the valve
5 head 380a abuts the piston plate 350 from the inside of the piston 344 and closes off the
orifice 374a. At the same time, the valve head 382a engages the piston plate 352 from the
outside of the piston 344 and closes off the orifice 376a. This means that fluid cannot flow
between the working chambers 46, 48 through the additional flow path including the
orifices 374a, 376a and the piston internal chamber 56. In this position, the spring element
10 354a bears down on the valve head 380a and thereby keeps the valve heads 380a, 382a in
abutting relationship with the piston plates 350, 352, respectively.
When the piston 344 begins to move towards the working chamber 48, the valve
head 382a will move with the piston 344, which will result in the valve 378a also moving
with the piston 344. Eventually, a shoulder 388a on the valve stem 386a carrying the valve
15 head 382a will contact a shoulder 389a on the inner piston plate 358, resulting in the valve
head 382a becoming decoupled from the piston 344. After this, additional motion of the
piston 344 towards the working chamber 46 will not move the valve 378a and the orifices
374a, 376a will open up for pumping of fluid between the working chambers 46,48.
In another portion of the piston 344, an orifice 374b is formed in the piston plate
20 352, and an orifice 376b is formed in the piston plate 350. A valve 378b is arranged to
selectively block the orifices 374b, 376b, as explained above for orifices 374a, 376a and
valve 378a. The orifices 374b, 376b are fluidly connected to the piston internal chamber
356, thereby creating an additional flow path for pumping of fluid between the working
chambers 46, 48. The mechanism for opening the additional flow path including orifices
25 374b, 376b is similar to that described for opening the additional flow path including
orifices 374a, 376a, with the exception that the additional flow path including orifices
374b, 376b is opened as the piston 344 moves towards the working chamber 46. Thus,
with the piston 344, an additional flow path is opened regardless of the travel direction of
the piston 344 when the stiffness of the working fluid is greater than the stiffness of the
3 0 spring element 354a, 354b. The position of the valves 378a, 378b relative to the spring
elements 354a, 354b, respectively, also has the effect of limiting the travel of the spring
elements 354a, 354b, respectively, and reducing the elastic stiffness of the damper.
In an embodiment, in FIG. 9, a frequency-dependent fluid damper 410 of the
fluid-elastic type is shown. The frequency-dependent fluid damper 410 has an outer
damper body 412 and an inner damper body 414. The outer damper body 412 has an outer
damper body internal cavity 416 inside of which is received the inner damper body 414.
The length of the inner damper body 414 is longer than that of the outer damper body
internal cavity 416 so that a portion of the inner damper body 414 extends outside of the
5 outer damper body internal cavity 416. An outer damper body coupling 418 is provided at
an outer damper body end 420. An inner damper body coupling 422 is provided at an inner
damper body end 423. The outer damper body coupling 418 and inner damper coupling
422 can be used to couple the fluid damper 410 to a system prone to variable-frequency
disturbances, such as an aircraft rotary wing system. Guide bushings 424, 426 are disposed
10 in the outer damper body internal cavity 416, i.e., in the annular space between the outer
damper body 412 and the inner damper body 414. In an embodiment, the guide bushings
424, 426 are attached to the outer damper body 412 and provide support to the inner
damper body 414.
The fluid damper 410 includes a working chamber 428 inside the outer damper
15 body internal cavity 416. The working chamber 428 is located between the guide bushings
424, 426, the outer damper body 412, and the inner damper body 414. A piston 444 is
arranged in the working chamber 428. The piston 444 divides the working chamber 428
into smaller working chambers 446 and 448, which are filled with a damping fluid. The
piston 444 has or defines one or more orifices for fluid flow between the smaller working
20 chambers 446, 448 as the piston 444 traverses the working chamber 428. In an
embodiment, the orifice is an annular orifice 429 formed between the outer diameter of the
piston and the inner diameter of the outer damper body 412. In an embodiment, the piston
444 is located between the outer damper body 412 and the inner damper body 414 and can
move relative to the outer damper body 412 and inner damper body 414. The piston 444
25 can move relative to the inner damper body 414 depending on factors that will be further
explained below.
Spring elements 454a, 454b are arranged serially between the inner damper body
414 and the piston 444 so that a variable-frequency disturbance on the inner damper body
414 can be transferred to the piston 444 via the spring elements 454a, 454b. In one
3 0 embodiment, fixed input plates 492 and 494 are fixed to the outer circumference of the
inner damper body 414. The input plates 492, 494 are parallel to each other along an axial
direction of the inner damper body 414. Spring element 454a is arranged in a gap between
the input plate 492 and a side of the piston 444. Spring element 454b is arranged in a gap
between the input plate 494 and a side of the piston 444. Spring elements 454a, 454b make
contact with the fixed input plates 492, 494, respectively, and the unfixed output piston
444. As in the frequency-dependent dampers described above, spring elements 454a, 454b
are arranged serially between the inner damper body 414 and the piston 444 and act to
transfer variable-frequency disturbances on the inner damper body 414 to the unfixed
5 output piston 444. The spring elements 454a, 454b each have a stiffness. The ratio of the
combined stiffness of the spring elements 454a, 454b to the damping coefficient associated
with the working fluid is set to a selected frequency threshold (fthresholdA).t relatively low
first frequencies (flow)s ubstantially below the selected frequency threshold (fthreshomth),e
piston 444 is approximately stationary relative to the inner damper body 414. At the
10 relatively high second frequencies (fhigh) well above the selected frequency threshold
(fthresholdt)h, e piston 444 moves relative to the inner damper body 414. Thus, spring
elements 454a, 454b work similar to the spring element 54 of FIG. 1 to incorporate
second-order dynamics into the frequency-dependent damper 410.
Elastomer rings 430, 432 are provided at the ends of the outer damper body
15 internal cavity 416, in spaced relation to the guide bushings 424, 426. Each of the
elastomer rings 430, 432 are preferably a bonded elastomer ring including an annular nonelastomeric
shim element 430b (432b), an outer elastomer ring element 430a
(432a)bonded to an outer surface of the annular non-elastomeric shim element, and an
inner elastomer ring element 430c (432c) bonded to the inner surface of the annular shim
20 element. Auxiliary chamber 434 is defined between the elastomer ring 430 and guide
bushing 424, and auxiliary chamber 436 is defined between the elastomer ring 432 and
guide bushing 426. The frequency-dependent damper 410 may include back flow port(s)
and valve(s) (not shown separately) for fluid communication between the auxiliary
chambers 434, 436 and in a direction from the auxiliary chambers into the working
25 chambers 446, 448. A volume compensator 438 is provided inside the inner damper body
414. The volume compensator 438 has chambers 439, 440, and a movable barrier 443
between the chambers 439, 440. A spring 496 is arranged in chamber 439. A fluid conduit
498 connects the chamber 440 to the auxiliary chamber 436. The spring 496 extends or
contracts in response to temperature driven changes of the fluid volume of the frequency-
3 0 dependent damper 410, which results in motion of the movable barrier 443, either to push
fluid from the chamber 440 into the fluid conduit 498 or to allow fluid from the fluid
conduit 498 into the chamber 440. This preferably provides the appropriate pressure to be
applied to the fluid in the damper in order to prevent cavitation of the fluid.
FIG. 10 shows a frequency-dependent damper 500 for creating a damping force,
also referred to as a force, in response to a variable-frequency disturbance. The frequencydependent
damper 500 is of the non-fluid elastomeric type. The frequency-dependent
damper 500 has parallel and spaced-apart input plates 502, 504. Input plates 502 and 504
5 are also referred to as input members 502 and 504. A support member 506 is disposed
between the input plates 502, 504. A frequency-dependent damping structure 508a is
arranged in a gap between the input plate 502 and support 506, and a frequency-dependent
damping structure 508b is arranged in a gap between the support 506 and input plate 504.
The damping structure 508a is a laminate of a low-damped elastomer 510a having a
10 stiffness and a damping coefficient, a non-elastomeric shim 512a, and a high-damped
elastomer 514a having a stiffness and a damping coefficient. The low-damped elastomer
510a is attached to the input plate 502, and the high-damped elastomer 514a is attached to
the support member 506. Similarly, the damping structure 508b is a laminate of a lowdamped
elastomer 510b having a stiffness and a damping coefficient, a non-elastomeric
15 shim 512b, and a high-damped elastomer 514b having a stiffness and a damping
coefficient. The low-damped elastomer 510b is attached to the input plate 504, and the
high-damped elastomer 514b is attached to the support member 506.
The damping coefficient of the low-damped elastomer 510a is lower than the
damping coefficient of the high-damped elastomer 514a, and the damping coefficient of
20 the low-damped elastomer 510b is lower than the damping coefficient of the high-damped
elastomer 514b. The damping coefficients of the low-damped elastomers 510a, 510b may
be the same or different, and the damping coefficients of the high-damped elastomers
5 14a, 5 14b may be the same or different.
In one embodiment, elastomer 510a is referred to as first damped elastomer 510a,
25 elastomer 514a is referred to as second damped elastomer 514a, elastomer 514b is referred
to as third damped elastomer 514b, and elastomer 512b is referred to as fourth damped
elastomer 5 12b. Similarly, shim 5 12a is referred to as first shim 5 12a and shim 5 12b is
referred to as second shim 512b. Although FIG. 10 illustrates a laminated structure, it is
understood that support member 506 and input member 502 and first damped elastomer
3 0 510a can form a single structure damping the variable-frequency disturbance. Another
configuration uses a single input plate member 502 as a tube about first damped elastomer
510a, first shim 512a, second damped elastomer 514a and support member 506, where
support member 506 is positioned internally and input member plate 502 is externally
positioned.
The mechanical energy of the force from the variable-frequency disturbance is
communicated between the support member, the second damped elastomer, the shim and
the first damped elastomer.
In one embodiment the damping coefficient associated with the first damped
5 elastomer 510a is substantially similar to the damping coefficient associated with the
fourth damped elastomer 510b, and the damping coefficient associated with the second
damped elastomer 5 14a is substantially similar to the damping coefficient associated with
the third damped elastomer 5 14b. In one embodiment, the damping coefficients associated
with the first and fourth damped elastomers 510a, 510b are less than the damping
10 coefficients associated with second and third damped elastomers 514a, 514b. The
damping coefficients are selected such that the force of the variable-frequency disturbance
is reduced when a frequency of a variable-frequency disturbance exceeds the selected
frequency threshold.
The damping coefficients of the elastomers 5 10a, 5 lob, 5 14a, 5 14b are selected
15 such that the damping force created by the frequency-dependent damper 510 is reduced
when the frequency of the disturbance applied to the input plates 502, 504 exceeds a
selected frequency threshold (fthresholdT)h. e selected frequency threshold (fthresholmd)a y be
between the rotor in-plane natural frequency (line 62 in FIG. 5) and the rotor operating
frequency (line 64 in FIG. 5) for a rotary wing system application. In a preferred
20 embodiment, the selected frequency threshold (fthresholids) less than the rotor operating
frequency (line 64 in FIG. 5) . In preferred embodiments the selected frequency threshold
(fthresholids )p roximate the rotor in-plane natural frequency (line 62 in FIG. 5), preferably
with the selected frequency threshold (fthresholcdo) inciding with rotor in-plane natural
frequency (line 62 in FIG. 5). In preferred embodiments the selected frequency threshold
25 (fthresholids )p roximate the rotor in-plane natural frequency (line 62 in FIG. 5) and below
the rotor operating frequency (line 64 in FIG. 5), preferably with the damper having a
damping stiffness that reaches a peak value at a frequency below the in-flight rotor
operating frequency (line 64 in FIG. 5).
The elastomeric frequency-dependent damper 500 works similar to the fluid-
3 0 elastic frequency-dependent dampers described in FIGS. 1-3 and 6A-9. The low-damped
elastomers 510a, 510b of the elastomeric frequency-dependent damper 500 function
similarly to the spring elements of the fluid-elastic frequency-dependent dampers, and the
high-damped elastomers 514a, 514b function similarly to the working fluid of the fluidelastic
frequency-dependent dampers. In the elastomeric frequency-dependent damper 500,
shearing of elastomers 5 10a, 5 lob, 5 14a, 5 14b in response to relative motion between the
input plates 502, 504 and support 506, not pumping of fluid, is used to create damping.
Preferably the more damping the elastomer has, the less linear its stiffness properties.
Therefore, the stiffness of each of the low-damped elastomers 510a, 510b is preferably
5 more linear than that of the corresponding high-damped elastomer 514b, 514b. The
selection of the elastomers 5 10a, 5 lob, 5 14a, 5 14b will depend on the application. Each of
the high-damped elastomer 514a, 514b will be selected to ensure the proper level of
damping for the application. Based on the selection of the high-damped elastomers 514a,
514b, each of the low-damped elastomers 510a, 510b will be selected to establish the
10 selected frequency threshold.
In use, the input plates 502, 504 are fixed to a system subject to disturbances.
Relative motion of the support 506 to the input plates 502, 504 in response to a disturbance
applied to the input plates 502, 504 will cause shearing of the elastomers in the damping
structures 508a, 508b to provide the damping action. Below a selected frequency threshold
15 (fthresholtdh)e, stiffness of the low-damped elastomer 510a is higher than the stiffness of the
high-damped elastomer 514a and the stiffness of the low-damped elastomer 510b is higher
than the stiffness of the high-damped elastomer 514b, causing the high-damped elastomers
514a, 514b to be sheared, and resulting in high levels of damping. At and above the
selected frequency threshold (fthresholdth)e, stiffness of the high-damped elastomer 514a is
20 higher than the stiffness of the low-damped elastomer 510a and the stiffness of the highdamped
elastomer 514b is higher than the stiffness of the low-damped elastomer 510b,
causing the low-damped elastomers 510a, 510b to be sheared and little to no shearing of
the high-damped elastomers 5 14a, 5 14b. This has the effect of greatly reducing the amount
of damping (with fhighth e amount of shearing of the high-damped elastomers 5 14a, 5 14b is
25 less than with flow).
FIG. 11 shows an aircraft 600 having a rotary wing system 602 including at least
one rotating blade 604 rotating about a rotation axis 606. The rotary wing system 602 is
subject to disturbances when rotating about the rotation axis 606 at least at a rotation
operation frequency. FIG. 12 shows a rotary wing system 602 including dampers 608 for
3 0 controlling the disturbances. The dampers 608 are preferably the frequency-dependent
dampers described above. The rotary wing system 602 has a hub 610. Linkages 612 couple
blades 604 to the hub 610. One of the ends of each damper 608 is coupled to the hub 610,
and the other of the ends of each damper 608 is coupled to the one of the linkages 612. As
a result, disturbances during rotation of the blades 604 is transferred to the dampers 608,
and the dampers 608 work as described above to damp the disturbances based on the
frequency of the disturbances.
While the invention has been described with respect to a limited number of
embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that
5 other embodiments can be devised which do not depart from the scope of the invention as
disclosed herein. Accordingly, the scope of the invention should be limited only by the
attached claims.
We claim:
1. A frequency-dependent damper comprising:
an outer damper body having an internal cavity;
a working chamber defined inside the internal cavity;
5 a piston movably positioned within the internal cavity, the piston separating the
working chamber into a first working chamber and a second working chamber;
at least one orifice providing fluid communication between the first and second
working chambers;
at least one spring element, the spring element positioned between the inner piston
10 wall and the inner piston plate; and
an inner damper body disposed within the outer damper body, wherein the inner
damper body is capable of receiving a variable-frequency disturbance communicated to the
internal cavity, the inner damper body being coupled to the inner piston plate.
2. The frequency-dependent damper of claim 1, wherein a size of the orifice and a spring
15 stiffness of the spring element are selected to reduce a damping force when a frequency of the
variable-frequency disturbance exceeds a selected frequency threshold.
3. The frequency-dependent damper of claim 2, wherein the selected frequency
threshold is less than a rotary wing system rotor operating frequency.
4. The frequency-dependent damper of claim 2, wherein the frequency-dependent
20 damper has a damping stiffness having a peak value at a frequency below a rotary wing
system rotor operating frequency.
5. The frequency-dependent damper of claim 2, wherein the first chamber and the
second chamber contain a damping fluid having a damping coefficient, the spring stiffness,
and a ratio of the spring stiffness to the damping coefficient of the damping fluid is set to the
25 selected frequency threshold.
6. The frequency-dependent damper of claim 1, wherein the spring element is a metal
spring.
7. The frequency-dependent damper of claim 1, wherein the spring element is an
elastomer spring.
30 8. The frequency-dependent damper of claim 1, further comprising at least one
elastomer disposed between the outer damper body and the inner damper body for sealing the
internal cavity from at least one end.
9. The frequency-dependent damper of claim 1, wherein the piston is coupled to the
inner damper body.
10. The frequency-dependent damper of claim 1, further comprising an inner cavity
internally positioned within inner damper body and a volume compensator arranged within
5 the inner cavity.
11. The frequency-dependent damper of claim 10, further comprising a fluid chamber
defined within the inner cavity, the fluid chamber being in fluid communication with the
volume compensator and in fluid communication with the first and second working
chambers.
10 12. The frequency-dependent damper of claim 1, further comprising a first coupling
attached to one end of the outer damper body and a second coupling attached to one end of
the inner damper body, wherein the first and second couplings provide mechanical input from
a system applying the variable-frequency disturbance to the frequency-dependent damper.
13. A frequency-dependent damper comprising:
15 at least one input plate;
at least a first damped elastomer secured to the input plate, the first damped elastomer
having a damping coefficient;
a support member secured to the first damped elastomer such that mechanical energy
of an input force is communicated therebetween, wherein the first damped elastomer is
20 configured to shear in response to relative motion between the input plate and the support
member.
14. The frequency-dependent damper of claim 13, further comprising:
at least one shim secured to the first damped elastomer;
at least a second damped elastomer secured to the shim, the second damped elastomer
25 having a damping coefficient and is configured to shear in response to relative motion
between the input plate and the support member; and
wherein the support member is secured to the second damped elastomer such that
mechanical energy of the input force is communicated between the support member, the
second damped elastomer, the shim and the first damped elastomer.
30 15. The frequency-dependent damper of claim 14, wherein the damping coefficient of the
first damped elastomer is lower than the damping coefficient of the second damped.
16. The frequency-dependent damper of claim 14, further comprising:
at least a second input plate;
at least a third damped elastomer having a damping coefficient;
at least a fourth damped elastomer having a damping coefficient;
at least a second shim;
5 wherein the frequency-dependent damper is laminated, the laminated frequencydependent
damper including:
one input plate having the first damped elastomer secured thereto;
the first damped elastomer secured to the input plate;
one shim secured to the first damped elastomer;
the second damped elastomer secured to the shim;
the support member secured to the second damped elastomer;
the third damped elastomer secured to the support member;
the second shim secured to the third damped elastomer;
the fourth damped elastomer secured to the second shim;
the second input plate secured to the fourth damped elastomer;
wherein the damping coefficient associated with the first damped is substantially
similar to the damping coefficient associated with the fourth damped elastomer, and the
damping coefficient associated with the second damped elastomer is substantially similar to
the the damping coefficient associated with the third damped elastomer;
20 wherein the damping coefficients associated with the first and fourth damped
elastomers are less than the damping coefficients associated with second and third damped
elastomers; and
wherein the damping coefficients are selected such that the input force is reduced
when a frequency of a variable-frequency disturbance exceeds a selected frequency threshold.
25 17. The frequency-dependent damper of claim 13, wherein the damping coefficient is
selected such that the input force is reduced when a frequency of a variable-frequency
disturbance exceeds a selected frequency threshold.
18. The frequency-dependent damper of claim 13, wherein the frequency-dependent
damper is a laminated structure.
30 19. The frequency-dependent damper of claim 18, further comprising a second damped
elastomer and at least one shim, wherein the shim is interposed between the first and second
damped elastomers.
20. The frequency-dependent damper of claim 19, wherein the laminated structure is
circular with the support member being centrally positioned.
21. A rotary wing system with at least one rotating blade rotating about a rotation axis,
the rotary wing system having a variable-frequency disturbance when rotating about the
5 rotation axis, the rotary wing system comprising:
a frequency-dependent damper for controlling the variable-frequency disturbance, the
frequency-dependent damper including:
an outer damper body having an internal cavity;
an inner damper body for receiving the variable-frequency disturbance
10 extending into the internal cavity;
a first fluid chamber and a second fluid chamber defined within the internal
cavity;
a piston separating the first and second fluid chambers;
an orifice for transfer of fluid between the first and second fluid chambers; and
15 a spring element serially arranged between the piston and the inner damper
body such that the piston can move relative to the inner damper body through deformation of
the spring element.
22. A rotary wing system with at least one rotating blade rotating about a rotation axis,
the rotary wing system having a variable-frequency disturbance when rotating about the
20 rotation axis, the rotary wing system comprising:
a frequency-dependent damper for controlling the variable-frequency disturbance, the
frequency-dependent damper including:
an input member for receiving the variable-frequency disturbance;
a support member; and
25 a damping structure having a first elastomer and a second elastomer
configured to shear in response to relative motion between the input member and the support
member, the first elastomer having a first damping coefficient, the second elastomer having a
second damping coefficient, the first damping coefficient being different from the second
damping coefficient.
30 23. A method of making a rotary wing damper, said method including the steps of:
providing an outer damper body having an internal cavity;
providing an inner damper body;
selecting a piston for providing a first fluid chamber and a second fluid chamber;
selecting a spring element;
serially arranging said spring element between the piston and the inner damper body
such that the piston is movable relative to the inner damper body through a deformation of
the selected spring element, and
5 receiving said inner damper body in said outer damper body internal cavity to provide
the first fluid chamber and the second fluid chamber defined inside the outer damper body
internal cavity, with the piston separating the first and second fluid chambers, with a selected
fluid transferring damping orifice between the first and second fluid chambers, wherein with
a relative motion of said inner damper body relative to said outer damper body at a relatively
10 high second frequency (fhigh) above a selected frequency threshold (fthresholds)a id selected
spring element is substantially deformed and at a relatively low first frequency (flow) below
said selected frequency threshold (fthresholds)a id selected spring element is substantially
undeformed.
24. The method of claim 23 including tailoring a first orifice characteristic of the orifice
15 and tailoring a first spring characteristic of the selected spring element wherein that a
damping force is reduced when the relatively high second frequency (fhigh) exceeds said
selected frequency threshold (fthreshold).
25. The method of claim 24, wherein the first chamber and the second chamber contain a
damping fluid having a damping coefficient, and the first spring characteristic is a spring
20 stiffness, and the ratio of the spring stiffness to the damping coefficient of the damping fluid
is set to the selected frequency threshold (fthreshold).
26. A method of making a rotary wing damper, said method including the steps of:
providing an input member;
providing a support member; and
25 providing a damping structure having a first elastomer and a second elastomer, the
first elastomer having a first damping coefficient, the second elastomer having a second
damping coefficient, the first damping coefficient being different from the second damping
coefficient, and coupling the damping structure to the input member and support member to
allow shearing of the first elastomer and second elastomer in response to relative motion
30 between the input member and the support member.