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Патент USA US3091113

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May 28, 1963
A. J. H. GOODWIN
3,091,103
VIBRATION ISOLATING SHAFT COUPLING
Filed May 5, 1959
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May 28, 1963
A. J. H. GOODWIN
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VIBRATION ISOLATING SHAFT COUPLING
Filed May 5, 1959
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May 28, 1963
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VIBRATION ISOLATING SHAFT COUPLING
Filed May 5, 1959
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May 28, 1963
A. J. H. GOODWIN
3,091,103
VIBRATION ISOLATING SHAFT COUPLING
Filed May 5, 1959
5 Sheets-Sheet 4
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36
May 28, 1963
A. J. H. GOODWIN
VIBRATION ISOLATING SHAFT COUPLING
Filed May 5, 1959
3,091,103
'
5 Sheets-Sheet 5
ATTORNEYS
limited States Patent
3,091,103
ce
Patented May 23, 1963
2
1
the ?rst and second vessel andduct systems respectively
.
referred to the variable-volume container.
73,091,103
VIBRATION ‘ISOLATING SHAFT coUPLrNG
Fo-—Amplitude of the applied periodic-force.
Aubrey John Hutchinson Goodwin, Shandon, Scotland,
assignor to Yarrow and Company Limited, Glasgow,
'Fs-Amplitude of the periodic force transmitted to the
the ?rst body.
K0—Static sti?ness of a complete vibration mounting.
K1 and K2—'Static stiifnesses ‘of the ?rst and second ves
sel and duct systems respectively referred to the variable
volume container.
KA, KB and KR—Static stiifnesses of the component con
Scotland
Filed May 5, 1959, Ser. No. 811,17 8
10 Claims. (Cl. 64-26)
This invention relates to vibration isolators, that is to
say, devices for isolating from a ?rst body a periodic
‘ _
force applied to a second body while at the same time 10s ventional type vibration ‘isolators.
L1 and L2—Lengths of the ducts to the ?rst and second
transmitting to the ?rst body a constant force applied to
?uid-containing vessels respectively.
the second body.
Throughout the speci?cation, the term “periodic force”
M——Mounted mass per mounting.
is used to mean a force that varies periodically with
MB-=Intermediate mass per mounting.
respect to time or a component of a force, which com 15 V1 and V2—Capacities of the ?rst and second ?uid-con
ponent varies periodically with respect to time, the term
taining‘ vessels respectively.
“constant force” is used to mean either a force that re
X—-Maximum value of the ratio
mains substantially constant over a single period of the
periodic force or a component of a force, which compo
nent remains substantially constant over a single period 20
of the periodic force, and the term “isolating” is used to in
Y-—|Factor by which the best attenuation of a ?uid vibra
clude both not transmitting at all and transmitting with
tion isolator exceeds the attenuation, atra given fre~
attenuation.
quency, of an equivalent conventional isolator.
The second body may be, for example, a machine and
g--Gravitation'al acceleration.
the ?rst body may be a supoprt for the machine. The 25
vibration isolator would then serve to isolate from the
m1 and ‘m2—Virtual masses of the fluids in the ducts of
support periodic forces arising from the operation of the
the ?rst, and second vessel and duct systems respec
machine while at the same time supporting or partially
tively referred to the variable-volume container.
supporting the machine by transmittting the Weight, or
p-Pfessure of the ?uid in the variable-volume container.
30
a part of the weight, of the machine to the support.
qz—sti?‘ness ratio
An important application of vibration isolators is for
mounting the engines of vehicles and vessels. In this
52
case, in addition to a periodic force arising from the op
K1
eration of the engine and the constant force arising from
qB—Sti??ness
ratio
the Weight of the engine, forces arise from the move 35
ment of the vehicle or vessel, but such forces usually do
5%
not vary signi?cantly over a single period of the periodic
K1
force and therefore they form part of the constant force
(JR-Stiffness
ratio
that the vibration isolator must be able to transmit.
Another use of vibration isolators arises when it is 40
?r
desired to transmit motion from one body to another.
K1
Thus, for example, when it is desired to transmit rotary
r—The
proportion
of
the
?uid
in the variable-volume con
motion from a driving shaft to a driven shaft and either
tainer
working,
at
any
particular
frequency, in associa
the driving torque applied to the driving shaft or the
tion with the ?rst ?uid-containing vessel of a ?uid
load on the driven shaft varies periodically about a value
vibration having two such vessels.
that remains substantially constant over a single period
S—-Stiffness
ratio
of the varying component of the torque, a rotary coupling
KB
Kn
incorporating one or more vibration isolators may be in
terposed between the driving and driven shafts to transmit
the constant component of the torque while at the same 50
time isolating the periodic component.
t-Time.
I
,
x1-—‘Disp1aceme'nt of the mounted mass from the equilib
The effectiveness of a vibration isolator is measured
rium position.
’
_
by its transmissibil-ity, Which is de?ned as the ratio of the
x2—Displacement of the intermediate mass from the
force transmitted by the vibration isolator to the force
equilibrium position.
applied to the body. When the applied force is constant, 55
y-Displacement from the equilibrium position of the
the transmissibility is unity and the displacement of the
junction between a ?uid vibration isolator and the
body is inversely proportional to the static stiffness, which
convention vibration isolator.
it is desirable should be as large as possible. The trans
sin wt—Periodic function of the applied periodic force.
missibility of the vibration isolator for the periodic force
should, however, be as small as possible.
60 [AD-Static de?ection of the mounted mass under gravity.
'y—-Forcing frequency ratio for a conventional two-mass
The following is a list of symbols which are used in
vibration isolator
the speci?cation and claims together with the meanings
assigned to them:
M M + ME]
A0—Effective cross-sectional area of the variable-volume
=
container.
A1 and A2—-Cross-sectional areas of the ducts to the ?rst
and second vessels respectively.
B; and B2—Bulk moduli of the ?uids in the ?rst and
second vessel respectively.
C1 and C2--Damping effects of the ?uids in the ducts of
65
\/“’ [KS KB ‘
2
__
..
wr-[Forcing frequency ratio for the ?rst ?uid-containing
vessel and associated duct of a ?uid vibration isolator
incorporating two such vessels
2%
3,091,103
., ,
4
3
72~Forcing frequency ratio for the second ?uid-con
taining vessel and associated duct of a ?uid vibration
isolator incorporating two such vessels
FIG. 7 is a diagrammatic axial section of the rotary
coupling shown in FIG. 6.
Throughout the description of the three known forms
of anti-vibration mounting, the effects of damping are
neglected. In practice, some damping will always be
present and this eliminates the sudden phase changes and
ry0—-4Forcing frequency ratio for a complete vibration
in?nite amplitude that occurs at resonances according to
the simpli?ed theory given below, and also reduces the
optimum attenuation given by the mounting. The pres
10 ence of a small degree of damping does not, however,
materially alter the behaviour of the mounting when the
mounting is not in resonance with the applied periodic
A1-—Mass ratio
force.
.
The simplest form of anti-vibration mounting is a
15 system having resilience and negligible mass, and such a
kr-Mass ratio
vibration isolator will hereinafter be referred to as a
simple conventional vibration isolator.
The transmis
sibility of such isolators, of which springs and rubber
Ala-Mass ratio
blocks are examples, is a function of the dynamic stiff
20 ness (which is assumed for the sake of simplicity to be
equal to the static stiffness) of the vibration isolator, the
inertia of the body to which the periodic force is applied,
and the frequency of the applied force.
ing vessels respectively.
Referring to FIG. 1A of the drawings, a periodic force
111 and v2—-Kinematic viscosities of the ?uids in the ducts 25 applied to the body 1 is isolated from the support 2 by
associated with the ?rst and second ?uid-containing ves
a simple conventional vibration isolator, which is shown
sels respectively.
,u.1 and pig-Coefficients of viscosity of the ?uids in the
ducts associated with the ?rst and second ?uid-contain
p1 and ‘Dr-‘Densities of the ?uids in the ducts associated
with the ?rst and second fluid-containing vessels respec
tively.
>
w-JFrequency of the applied periodic force measured in
radians per unit time.
nix-Frequency of the applied periodic force at which
as a spring 3. The force applied to the body 1 causes the
body 1 to be displaced from the position that it would
occupy if no force were applied to it and the spring 3 were
consequently not under load (except for the constant
force). This displacement of the body 1 gives rise to two
forces: the inertia force of the body 1 (which is propor
tional to the square of the frequency of the periodic move
maximum ‘ampli?cation occurs measured in radians
ment of the body 1 and to the displacement of the body
per unit time.
35 1), and the force arising .from the static stiffness of the
wyéF-requency of the applied periodic force at which
spring 3 which is exerted equally and oppositely on the
body 1 and the support 2. The inertia force, however,
acts only upon the body 1. Accordingly, the transmis
of a gas used in a ?uid-vibration isolator.
sibility of the vibration isolator depends upon the relative
In addition to being used to refer to the ?rst vessel and
magnitudes and phases of these two forces in relation to
the applied force.
duct system of a ?uid vibration isolator having two ?uid
containing vessels, the symbols having the su?’ix 1 are
At low frequencies, the inertia force is negligible and
also used to refer to the vessel system of a ?uid vibration
therefore the stiffness of the spring 3 has to oppose the
isolator having only one such vessel.
whole of the applied force. The transmissibility of the
In order to explain the nature of the problem with 45 vibration isolator under these conditions is effectively
which the invention is concerned and to assist in the
unity. In other words, it transmits a constant force with
best attenuation occurs measured.
n-—Exponent of polytropic expansion and compression
understanding of the invention, the operation of three
forms of anti-vibration mounting that have previously
out attenuation.
' As the frequency rises, the inertia force of the body is
been proposed will now be described in some detail with
initially less than the force exerted by the spring 3, and
reference to FIGS. 1A, 1B, 1C and 2 of the accompany 50 this implies that the displacement of the body 1 (and con
ing drawings in which:
'
sequently the inertia force of the body 1) shall be in
FIG. 1A shows schematically a simple conventional
phase with the applied force. Under these conditions,
vibration isolator;
the sti?ness of the spring 3 has to balance both the ap
FIG. 1B shows schematically a conventional two-mass
plied force and the inertia force of the body 1. Accord
vibration isolator;
ingly, the force exerted by the spring 3 has to be larger
FIG. 10 shows schematically a dynamic vibration ab
than in the static case and the transmissibility of the
sorber; and
‘FIG. 2 is a graph comparing the attenuation given
isolator is greater than unity. As the frequency increases
further, the transmissibility continues to increase until
by the conventional two-mass vibration’ isolator shown in
the inertia force of the body 1 becomes equal in magni
FIG. 1B with that given by the simple conventional vibra 60 tude to the force exerted by the spring 3. At the fre
tion isolator shown in FIG. 1A over a range of frequen
cies for di?erent values of the mass ratio of the two
mass vibration isolator.
FIG. 3 shows schematically a vibration isolator con
quency at which this occurs, the system is said to be in
resonance and the displacement of the body 1(and con
,
sequently the transmissibility of the isolator) becomes
inde?nitely ‘large. Under these conditions, the applied
structed ‘according to this invention;
65 force is not opposed at all because the inertia force of the
FIG. 4 is a graphical representation of the attenuation
body 1 and the stilfness of the spring 3 exactly balance
produced by the vibration isolator shown in FIG. 3 over
each other.
.
a range of frequencies in comparison ,with the attenua
Above the resonant frequency, the inertia force of the
tion produced by ‘a simple conventionalvibration isolator
‘body 1 becomes larger than the force exertedrby the
having the same static sti?ness;
70 spring 3, which implies that the displacement of the body
FIG. 15 is an axial section of a plunge and band assem
1 (and consequently the inertia force of the body 1)
bly suitable for use as a variable-volume container of a
shall be in antiphase with the applied force. The force
?uid vibration isolator;
exerted by the spring 3 is then in phase with the applied
FIG. 6 is a diagrammatic transverse section of a rotary
force and, consequently, the inertia force of the body 1
coupling; and
75 has to balance both the applied force and the force
3,091,103
5
6
exerted by the spring 3. For frequencies only slightly
At frequencies higher than the second resonance fre
quency, the movement of the body 1 is in 'antiphase
with the applied periodic force and, as in the case or ‘the
above the resonant frequency, this implies that the
maximum displacement oftthe body 1 (and therefore the
transmissibility of the isolator) is large. As the fre
quency increases further, however, the inertia force of
simple conventional vibration isolator, at very high fre
quenc'ies only a small amplitude of movement of the body
the‘bo'dy 1(which, as stated above, is proportional to the
1 is required for its inertia force to balance both the
square of the frequency) increases rapidly so that the
applied periodic force and the force exerted on 'it by the
inertia force becomes able to balance the applied ‘force
spring 3a. Therefore the spring 3a exerts only small
and the ‘force exerted by the spring 3 for smaller and
force on the [body 4, the inertia force of which balances
smaller maximum displacements of the body 1. This in 10 both this force and the force exerted by the spring-3b
turn reduces the magnitude of the force exerted by the
with only a very small amplitude of movement of the
spring 3, so that the transmissibility of the vibration
body 4.
isolator decreases rapidly.
Thus the transmissibility of the conventional two
The vfrequency at which resonance occurs is a function
mass vibration isolator is very low indeed at high fre
of the mass of the body 1 and the static stiffness of the 15 qencies. In fact, at very high frequencies, the trans
spring 3, the resonant frequency increasing with increas
missibility of a conventional two-mass vibration isolator
ing stiffness of the spring 3. Accordingly, the simple con
is smaller than that of a simple conventional vibration
ventional vibration isolator suffers from two disadvan
isolator having the same static stiifness by a factor which
tages. First, except for frequencies considerably above
is ‘approximately proportional to the square of the fre
the resonant frequency of the system, it is not possible 20 quency of the applied periodic force. This is shown in
to achieve both a low transmissibility and a high static
FIG. 2 of the drawings, which is 1a graph in which the
stiffness. Secondly, in order to reach a state in which the
vertical axis represents the attenuation or ampli?cation
vibration isolator is efficient (i.e. the state in which the
measured in decibels and the horizontal axis represents
frequency of the applied force is considerably above the
"/0, which, as will be seen below, is a quantity linearly
resonant frequency), it is necessary to pass through a
proportional to the frequency of the applied periodic
region (i.e. the region of resonance) in which the trans
force. The full curves represent the attenuation given
missibility is very large. It is possible to reduce the
by conventional two-mass vibration isolators having the
transmissibility of the vibration isolator at resonance by
same static stiffness, but diiferent values of R3 (the ratio
introducing damping, but this increases the transmissibility
of the mass M of the body 1, to the mass MB of the
of the vibration isolator at higher frequencies.
30 body 4). The broken curve represents the attenuation
Another form of vibration isolator that has been pro
given by a simple conventional vibration isolator hav
posed is a system having resilience and mass, the centre
ing :the same static stiffness. The curve 5 represents the
of gravity of the mass being free to move relatively to attenuation when AB=1, that is to say, when the mass
each of the two bodies to which the vibration isolator is
applied. Such a vibration isolator will hereinafter be 35 MB of the body 4 is equal to the mass M of the body
1. The curves 6, 7, 8 and 9 represent the attenuation
referred to as a conventional two-mass vibration isolator,
when the value of i3 is 4-, 10, 20 and 50 respectively.
the term “two-mass” arising from the fact that the
It will be seen that the performance of the conven
isolator utilises both the inertia force of the body to which
tional two-mass vibration isolator improves as the value
the periodic force is applied and the inertia force of the
of AB ‘decreases. As the value of AB increases (i.e. as
vibration isolator itself.
the mass MB of the body 4 decreases), the value of the
Referring to FIG. 1B of the drawings, a periodic force
minimum frequency for which the attenuation provided
applied to the body 1 is isolated from the support 2, by
by the conventional two-mass vibration isolator is bet
ter than the attenuation provided by a simple conven
a conventional two-mas vibration isolator, which consists
of springs 3a and 31), between which there is interposed
a massive body 4-.
The characteristics of the conventional two-mass vi
45 tional vibration isolator having the same static sti?ness,
increases. Thus, as A3 increases, it is necessary to op
erate at higher and higher frequencies in order to ob
bration isolator di?er from those of the simple conven
tional vibration isolator in that it has two resonant fre
t'ain satisfactory attenuation.
The conventional two-mass vibration isolator suffers
than the higher of the two resonant frequencies, a trans 50 from the same disadvantages as the simple conventional
vibration isolator, but gives improved attenuation at high
missibility much lower than that of a simple conven
frequencies at the expense of being more massive.
tional vibration isolator having the same static stiffness
A further form of anti-(vibration mounting that has
can be obtained.
been proposed is the so-called dynamic vibration ab
The ?rst resonance occurs when the inertia force of
the body 1 exactly balances the force exerted by the 55 sorber. Referring to FIGURE 1C of the drawings, a
quencies and ‘that, at frequencies considerably higher
body 1, to which the periodic force is to be applied, is
spring 3a. At frequencies close to this resonant fre
separated ‘from the support 2 by a spring 3 as in the
quency, it requires a very large ‘amplitude of movement
simple conventional vibration isolator. On the side of
of the body 1 in order that the applied periodic force
the body 1 remote from the support 2 (i.e. above the
may be balanced by the difference between the inertia
force of the body 1 and the force exerted by the spring 60 body 1 in the form of vibration absorber shown in FIG
URE 1C) a body 10 is secured to the body 1 through
3a. This results in a large force being exerted ‘by the
a spring 11.
spring 3a on the body 4, which therefore has ‘a large
‘ The dynamic, vibration absorber operates in the fol
amplitude of movement so that large forces are trans
mitted by the spring 312 to the support 2.
lowing way. The periodic force applied to the body 1
the body 4 exactly balances the resultant of the forces
exerted by the springs 3a and 3b. At frequencies close
to this resonance frequency, the :body 4 has to have'a
very large amplitude of movement in order that the dif
ference between the inertia force of the body 4 and the 70
body 10 to vibrate. At some particular frequency (the
resonance frequency of the system consisting of the body
10 and spring 11), the inertia force of the \body 10
exactly opposes the said periodic force. At this fre
quency, the body 1 is held motionless.
The dynamic vibration absorber gives very good at
The second resonance occurs when the inertia force of 65 causes the body 1 to vibrate and this in turn causes the
resultant of the forces exerted by the springs 3a and ‘3b
shall balance any additional force exerted by the spring
3a resulting from movement of the body 1. Therefore
large forces ‘are transmitted by the spring 3b to the
support 2.
tenuation at one particular frequency, but it has two
resonances at which the transmissibility is very large
and it is only suitable for isolating a periodic force of
75 which the frequency remains accurately constant. There
3,091,103
7
fore it is not satisfactory as ‘a mounting for variable
speed machines such as, for example, internal combus
tion engines used as power units for vehicles or vessels.
Thus none of the anti-‘vibration mountings described
8
(1) In the simple conventional vibration isolator oper
ating at frequencies well above the resonance ‘frequency,
the applied ‘force and the force resulting from the stitf
ness of the vibration isolator are in phase and their re
above gives the desired combination of a high static stiff
ness and a low transmissibility, except at high frequencies
or at one particular frequency only.
This invention provides a vibration isolator for iso
sultant is balanced by the inertia force of the second body.
(2) The principle of operation of the conventional two
mass vibration isolator is similar to that of the simple
vibration isolator comprises a variable-volume ?uid-?lled
container for interposition between the said two bodies,
‘frequency of best attenuation, the inertia force of the ad
ditional mass exactly balances the applied force. Thus
tween the two said bodies in the said one sense causes
vibration isolator, and the inertia force of the second body
of the applied periodic force increases, however, the said
diaphragm and ?lled, on one side of the diaphragm, with
conventional vibration isolator, but the mass of the vibra
tion isolator itself gives rise to an inertia force that pro—
lating from a ?rst body a periodic force applied to a sec
ond body while at the same time transmitting to the ?rst 10 vides additional attenuation.
(3) In the dynamic vibration absorber operating at the
body a constant force applied to the second body, which
the second body remains stationary and has no inertia
a vessel containing a ?uid which provides substantially
the whole of the static stiffness of the vibration isolator, 15 force. The static stiffness of the vibration absorber does
not give rise to any periodic force because the body that
conduit means of which the effective cross-sectional area
it supports remains stationary.
is less than the effective cross-sectional area of the said
(4) In the vibration isolator of the invention operating
container, which contains a body of ?uid and which com
at the frequency of best attenuation, the inertia force of
municates with both the interior of the said container and
the interior of the said vessel and provides the sole means 20 the body of ?uid in the conduit means exactly balances
the periodic force arising from the static stiffness of the
of such communication, wherein relative movement be
exactly balances the applied force.
?uid to ?ow in the conduit means towards the vessel
Although the transmissibili-ty of the vibration isolator
against the pressure of the fluid in the vessel and relative
movement ‘between the said bodies in the opposite sense 25 of the invention at resonance is (neglecting damping)
zero, it is necessary to provide a support vfor the resilient
causes ?uid to flow in the conduit means toward the vari
means and a residual periodic force is transmitted to that
able-volume container under the action of the pressure
support through the resilient means. This residual pe
of the ?uid in the vessel.
riodic force may, however, be reduced or eliminated as
‘Because the apparent bulk modulus of the ?uid in the
will be described below.
vessel opposes displacement of the body of ?uid in the
In all forms of the vibration isolator of the invention,
conduit means towards the vessel and relative movement
it is essential that the vibration isolator should be suitably
between the bodies under the action of the constant force
damped in accordance with the purpose to which it is to
necessarily produces such a displacement, the force arising
from the apparent bulk modulus of the ?uid in the vessel 35 be applied, and this is discussed in greater detail below.
The variable-volume ?uid~?lled container may com
opposes relative movement between the two bodies under
prise a cylinder ?tted with a piston slidable therein and
the action of the constant force. When the frequency of
?lled, on one side of the piston, with a liquid, but such
the applied periodic force is very low, the inertia forces
sliding parts almost inevitably result in some leakage and
of the second body and of the body of fluid in the con
preferably, the container is, with the exception of an
duit means are negligibile and the applied periodic force
outlet to the conduit means, completely sealed. Thus the
is balanced entirely by the force arising from the apparent
container may comprise a chamber ?tted with a ?exible
bulk modulus of the ?uid in the vessel. As the frequency
a liquid, or the container may comprise a ?exible bellows
at which they exactly balance the force arising from the 45 ?lled with a liquid.
The effective cross-sectional area of the variable
apparent bulk modulus of the ?uid in the vessel. At this
inertia forces also increase until a frequency is reached
volume ?uid-?lled container is ‘advantageously greater
frequency, the applied periodic ‘force is unopposed and
then the effective cross-sectional area of the conduit
the amplitude of the movement of the second body be
means so that the magnitude of the displacement of the
comes large, which results in \a high transmissibility. As
the vfrequency increases further, the inertia forces become 50 centre ‘of mass of the ?uid in the conduit means caused
by a given relative movement between the said bodies
larger than the ‘force arising from the apparent bulk
is greater than the magnitude of the relative movement.
modulus of the ?uid in the vessel and partially balance
This results in two advantages. First, the inertia of the
the applied periodic force until a frequency is reached at
vibration isolator exceeds the mass of the ?uid in the
which the inertia force of the mass of the vibration iso
lator exactly balances the force exerted on the mass by the 55 conduit means by a factor equal to the square of the
ratio of the two effective cross~sectional areas. Second
resilient means, so that the stiffness of the vibration iso
ly, because the resilient means act directly on the mass,
lator at this frequency is (neglecting damping) zero, and
the magnitude of the force which the resilient means has
the second body responds freely to that force. The am
to exert in order to prevent relative movement between
plitude of vibration of the second body then reaches a
value at which the inertia force of the second body exactly 60 the two bodies under the action of a given constant force
is less than the magnitude of that constant force. There
balances the applied periodic force, which is therefore not
fore the residual periodic force referred to above is re
directly transmitted to the ?rst body.
duced. Thirdly, the relatively large amplitude of move
It will be seen that, while the vibration isolator of the
ment of the ?uid in the conduit means gives rise to a
invention resembles the conventional two-mass vibration
isolator and the dynamic vibration absorber in that it has 65 degree of ‘damping that can readily be controlled (by
selection of a ?uid having an appropriate coe?icient
a signi?cant mass (that of the body of ?uid in the con
of viscosity and a conduit means having an appropriate
duit means) which gives rise to an inertia force, it is
distinguished structurally from them by the fact that, in
cross-sectional area) and which is large by comparison
with any damping provided by the remainder of the
the vibration isolator of the invention, the mass of the
vibration isolator is not resiliently connected to the bodies 70 vibration isolator. Further, the introduction of a sub
stantial degree of damping can be achieved with the
between which it acts. Further, the three anti-vibration
application ‘of only relatively small forces. The effec
mountings described above and the vibration isolator of
tive cross-sectional area .of the container may exceed the
the invention operate in fundamentally different ways.
effective cross-sectional area of the conduit means by a
The principles of operation of the devices may be sum~
75 factor within the range of from 10 to 100. For some
marised as follows:
3,091,103
i0
59
=applications, fthis:tactoradvantageously exceeds 100 and,
vibration isolators having ‘diiferent characteristic fre
quencies results in ampli?cation occurring ‘at two differ
ent frequencies and thus the degree of damping of the
vibration‘isolater of the invention has to be su?iciently
large to provide a useful degree of attenuationat both
these frequencies. A ?uid vibration isolator is especially
suitable for this purpose and the value of
v'ffo'r some-applications, it preferably ‘exceeds 1,000.
l'llhel?uidlinfthe-said ve‘ssel‘may‘be a liquid and there
aimayirb'eliprovided in‘thefvessel,
order to reduce the
static stiffness of the resilient-imeans, a resilient body of
“which the ‘bulk'modulus'lisless than the ‘apparent bulk
modulus of the liquid in the vessel. Theresilient body
1‘may be a body fof Jgas 'iwhichiimay be icontained in a
{sealed hag. Instead, in order to provide additional re
silience when the 'i?uid in the ‘vessel is a liquid, the vessel . 10
C12
mlKl
may be providedwith alresilient-diaphragm or a resilient
(as hereinafter de?ned) is advantageously 'within the
ly loaded.piston or diaphragm.
range of from 0.05 to 0.5.
. As has'been stated above, ‘it is important that the vi
The invention further provides a rotary coupling for
'bration isolator should be ‘suitably damped for the pur
isolating from a ?rst body a periodic torque applied to
pose to *which ‘it 1is ‘to be applied and there may be 15 a second body While at the same time transmitting to the
provided an adjustable throttle '-valve vfor varying the
?rst body a ‘constant torque applied to the second body,
magnitude of the viscous ‘damping of the ?uid in the
which. coupling comprises a ?rst abutment member for
conduit means (which usually amounts to substantially
connection to the ?rst body, a second abutment member,
all the damping of the vibration isolator, the other sources
a rotary coupling for isolating from a ?rst body a periodic
of damping within the vibration isolator being negligible 20 torqueapplied to a second body while ati'the same time
by comparison).
The nonedime'nsionahquantity
transmitting to the ?rst body a constant torque applied
to the second body, which coupling comprises a ?rst
C12
mrKr
abutment member for connection to the ?rst body, a sec
0.5 and for other applications it may be not greater than
containing a ?uid, conduit means of which the e?ective
ond abutment member for connection to-the second body
25 and mounted for rotation relative to the ?rst abutment
2 may be within thes'range'of froms0‘i5' to 2.5. For some
member, a variable-volume ?uid-?lled container inter
applications it may be within the range of from 0.05 to
posed between the said two abutment members, a vessel
0.0001. This quantity is»-a function of the damping of
the vibration isolator and gives a measure of the selec
tivity of the vibration isolator with respect to the fre
quency of the applied periodic'force. Small values of
the quantity correspond to a ‘high selectivity, that is to
say, a vibration isolator for which the quantity is small
has a very low transmissibility at some particular fre
quency, but the transmis‘sibility irises sharply on either
side of that frequency. A vibration isolator for which
the value of the quantity is large, ‘onwthe other hand,
, gives a less good performanceitie. ~a.=higher transmissi
bility) at its optimum frequency of operation, but the
transmissibility rises less sharply on either side of the
optimum ‘frequency.
Fluid vibration :isolators for which the value of
is very small (i.e. less than 0.0001) are suitable for use
>when the frequencyof ‘the ‘periodic .force remains ap
proximately constant for inthis case it is desirable to
produce the greatest possible degree of attenuation at
the frequency fof‘theappliedforce. Vibration isolators
for which the value iof ‘the said quantity is larger (say
cross-sectional area is less than the effective cross-sec
30 tional area of the said container, which contains a body
of ?uid and which communicates with both the interior
'of'the said container and the interior of the said vessel,
athird abutment member'?xed with respect to the ?rst
abutment member, the arrangementbeing such that rela
35 tive rotation between the ?rst and second abutment mem
bers in one sense causes the ?rst and second abutment
members to approach one another and relative rotation
between-the ?rst and second abutment members in the
reverse sense causes the second and third abutment mem
bers to approach one another, a second variable-volume
?uid-?lled container interposed between the second and
third abutmentmembers, a second vessel containing a
?uid, and a second conduit means of which the effective
45 cross-sectional area is less than the elfcctive cross-sec
tional area of the second container, which contains a
body of ?uid and which communicates with both the in
terior of the'second container and the interior of the sec
‘ond'vessel, the mass of the said bodies of ?uid contained
50 inthe said ?rst and second conduit means, the dimen
"sions of the ?rst-and second conduit means, the apparent
bulkmodulus of the ?uidsin the ?rst and second vessels
and the degree ‘of damping applied to thebodies of ?uid
contained in the ?rst and second conduit'means being
0.2 and preferably‘less than 0.5) are suitable for reduc
ing the ‘amplitude of vibration vatrresonance of a mecha
nism having a natural frequency, for example, a body 55 such that, at the said particular frequency of the periodic
torque, the inertia reactions or" the masses of the said
mounted on a conventional vibration isolator. The re
'bodiesof ?uid contained in the ?rst and second conduit
‘ sulting system‘has two resonance frequencies, one at a
means substantially balance the forces exerted on those
lower and the other at a higher frequency than the natural
‘bodies of'?uid ‘by the ?uid in the ?rst and second vessels.
frequency of the mechanism by-itself'an'd it is necessary
The invention also provides a rotary coupling for iso
that the ?uid vibration isolator should provide good at
lating
from a ?rst body a periodic torque applied to a
tenuation over a frequency range which includes both
second body while at the same time transmitting to the
. the resonanceffrequencies of the‘ system.
‘?rst ‘body a constant torque applied to the second body,
i The invention {also ' provides a vibration ' isolating de
which‘coupling comprises a‘?rst member for connection
vice comprisinga'vibrationisolator of the invention con
neoted in series with a simple conventional vibration 65 to'one of the said'bodies, a second member for connec
tion to the other of the said bodies and rotatably mounted
isolator (as hereinbefore de?ned), the part of the simple
‘coaxially vwithin the ?rst member, a plurality of abut
conventional'vibrationisolator that is connected to the
ments extending inwards from the ?rst member, a cor
?rst-mentioned vibration isolator constituting the said
responding nnrnber of abutments extending outwards
second body. Usually,»inasuch_ardevicerthe simple con
ventionalivibration isolator provides the desired very 70 from‘the second member, the said inwardly and outwardly
‘extending abutments being arranged alternately around
good attenuation over a range of high frequencies and
thefcircumference of the inner member, a plurality of
the purpose of the vibration isolator of the invention is to
“variable-volume ?nid~?lled containers interposed one be
provide attenuation at what would, in the absence of the
tween'each pair of'adjacent abutments with their direc
vibration isolator ‘of ‘thief-‘invention, be the resonance
frequency of the system. In‘fact, the presence of two .75, tions of-expansion and contraction extending substan
3,091,103
12
11
-tially circumferentially with respect to the common axis
‘frequencies of the applied periodic force and shows the
of the ?rst and second members, two vessels, each con
taining a ?uid, a plurality of conduit means, one for each
container, the effective cross-sectional area of each of
which is less than the effective cross-sectional area of the
same resonance peak at which the transmissibility is large;
Above the resonance frequency, however, the ?uid vibra
said containers, each of which contains a body of ?uid
and each of which communicates with both the interior
lion isolator gives, over a small range of frequencies, a
greatly reduced transmissibility.
The mathematical analysis of this ?uid vibration isola
tor is as follows:
of one of the said containers and the interior of one of
Equating the forces at the top of the bellows 12 gives:
the said vessels, the conduit means communicating with
every alternate variable-volume container communicating 10
Equating the forces
MilzFo
in thesinduct
Nf—'Aop
14 gives:
with one of the said two vessels and the remaining con
duit means communicating with the other of the said two
vessels, the masses of the said bodies of ?uid contained
A LL1°=A 17' -A°‘”1B
A —81r#1 L142
V1 11
A1
PlllAl
(2)I
in the conduit means, the dimensions of the conduit
Converting Equation 2 to equivalent forces in the
means, the apparent bulk modulus of the ?uid in each of 15
bellows 12 by multiplying by
the two vessels and the degree of damping applied to the
body of ?uid contained in each of the said conduit means
A0
being such that, at a particular frequency of the periodic
torque, the inertia reactions of the said bodies of ?uid
substantially balance the forces exerted on those bodies 20
71
gives:
P1A1L1<%)2i'1=Aop~%glzl—s1tmLi<?-g)zii
of ?uid by the ?uid in the vessels with which the conduit
means containing those bodies of ?uid communicate.
. Advantageously, the said two vessels are each formed by
(3)
cavities in the second member, which cavities have axes
that substantially coincide with the axes of the ?rst and 25
second members, and each conduit means is formed, at
least in part, by a bore which is formed in the second
member and which communicates with the associated
variable-Volume container at a point adjacent to the out
wardly extending abutment that engages that variable 30
volume container. Preferably, there are also provided
(4)
two additional conduit means of which one provides com
munication between the interiors of only the variable
volume containers that are in communication with one
of the said vessels and of which t .e other additional con
duit means provides communication between the interiors
of only the variable-volume containers that are in com
munication with the other of the said vessels.
As will be explained in greater detail below, if the ro
tary coupling is to be used in a transmission system 40
coupling a screw of a vessel to a driving power unit, then
the ?uid in the or each ?uid-containing vessel is advan
tageously a gas.
Referring to FIGURE 3 of the drawings, a periodic’
force applied to a second body- 1 is isolated from a ?rst 45
body in the form of a support 2 by a ?uid vibration
isolator. The ?uid vibration isolator comprises a ?exible
bellows 12 of which the upper end supports the body 1
and the lower end rests on the support 2. The hollow
50
interior of the bellows 12 is placed in communication
with the interior of a vessel "13 by a conduit in the form
of a straight duct 14. The bellows 12, vessel 13
and duct 14 together constitute a closed ?uid-?lled sys
tem. The bellows 12 may ‘be made of rubber, reinforced 55
rubber or thin metal and the vessel 13 and the duct 14
are made of metal of su?icient strength and rigidity to
withstand the imposed stresses.
The ?uid vibration isolator operates in the following
way. Periodic relative movement between the body 1 60
and the support 2 causes the bellows to expand and con
tract periodically and this in turn causes the ?uid in the
duct 14 to ?ow to and fro against the resilient action
of the ?uid in the vessel 13. At the resonance frequency
of the vibration isolator, the inertia force of the ?uid in 65
the duct 14 exactly balances the resilient force applied
.by the ?uid in the vessel 13 so that the bellows 12 have
no stiffness and the body 1 vibrates freely.
The attenuation provided by a vibration isolator of
a this type is represented by the full curve in FIGURE 4,
70
the broken curve representing the attenuation provided
by a simple conventional vibration isolator having the
same static stiffness.
It will be seen that the transmis
sibility of the ?uid vibration isolator closely follows that
of the simple conventional vibration isolator for low 75
and
A
2
final/(Z2) =01
Adding equations 1 ‘and 4 gives:
Mi1+m1i1=Fo sin wt-—K1x1—C1X1
Assuming that the motion is simple harmonic and con
sidering amplitudes of the forces gives:
3,091,103
3113
1114
F5
attenuation at the optimum frequency shall be-very good),
X :must be correspondingly large t(i.e; the maximum ampli
The value of
¢?cation :given. by .the <vibration isolator must 'be corre
F0
spondingly large). Thus, inldesigning a 'sing-le-vesse'ls?uid
tends to a minimum (i.e. the vibration isolator gives best
attenuation) when
vibration isolator for any particular application, a'com
rpromiseihas to :be made. between having ‘very good opti
:mum attenuation, which gives large 'maximumnmpli?ca
:tion ,at-some otherzffrequency, and having low :maximum
'
1—'y12=0 0r 712:1
-It should be noted that this gives:
ampli?cation, which gives poor optimum attenuation.
The procedure in designing a single-vessel ?uid vibra
K1=m1w2
Thus, .as explained qualitatively above, the vibration iso
10 tion isolator for some particular application may be sum
)marised as follows —-M, ‘An and no will be known, and
lator gives best attenuation when the ‘inertia force of the
?uid in the duct 14 exactly balances the force resulting
from the static ‘stiffness of the vibration isolator.
Putting 712:1 in Equation 12 gives:
..
—5 (min) =
F0
we have:
15
012
————————mlK1
2
)\ 2+ 01
1
(13)
miKi
20 In order to ?nd V1, the ?uid ‘to be used in the system
‘The attenuation at this frequency given by a simple con
ventional vibration isolator of the same static stiifness
‘If a gas isused then B1¥=?p
where p is the absolute pressure. Initially,'_n maybe as
sumed to be unity. Subsequently, ‘its exact value should
be determined experimentally. Therefore,
a gas
:,must ~ ?rst be‘ selected.
can be- shown to be approximately
1
25 ?lled system, we have:
M
__Ao2P
.when M is' large. 'Ihus,'if the ?uid vibration isolator
V1- K1
is to give at this frequency an attenuation Y times greater
Now
than the simple conventional vibration isolator, the fol
lowing relationship must hold:
.
1
m1=P1A1L1(-Zg)
A
O12
'm K
and therefore
(14)
A1 + m1 K1
'2
n
m
A1 A02!!!
35
Therefore
Also
012 _
A12
Ni
MKFYZxg-r‘YB
(15)
.m _&
1_wy2
40
The value of
(where my is the frequency at which best attenuation is
.F3
required). .Thus, byl-assuming a value of A1, it is possible
to ?nd L1. Substituting for C1, m1 and K1 in Equation
15 gives:
E
tends .to a maximum (i.e. the vibration isolator gives
45
maximum ampli?cation) when
g~('81r1'1)2
Y2— tog/2A1?
i.e. when
or
7i2=-———-.1
1+)“
50
~Aif2l
Y_
471
(where fy is the frequency in cycles per second 'at'which
Dividing Equation 12 by 712, putting
best attenuation is required). v'From this relation it is
712:
and substituting for
possible to see whether or not the assumed value of A1
55 in fact gives the required degree‘of attenuation. The
1
1+)“
value of A1 may be derived from the relation
_
C12
mlKl
i=2!
m1
from Equation 15 gives:
I
60 and then the value of X maybe found from the relation
M2
is (Max_
- FD
—
+
hie/T1
~ x12
1+)“ Y2A2—1_
x12
Thus it is possible to see 'whether or not the assumed
*
YNF-l
whence
.2 i 2_
XzzY A, , 1+1
Now A; is large and therefor X'~—J.Y V; Thus, if Y is 5
to be greater than 1 (i.e. if the single-vessel ?uid vibra
tionisolator is to. show any advantage over a simple
conventional vibration isolator having the ‘same static
stiffness) then X‘ must be greater than -\/M. 7 Further, if
it is required that Y shall be very large (i.e. that the
65
value of A1 is satisfactory from. the point of view of
the maximumpermissible ampl?cation.
If it does notprove to be possible toachieve the de
sired optimum attenuationwithout exceeding the .rnaxi
mum permissible ampli?catiomthen it- is necessary to
usea ‘more complicated system such as, for example, a
two-vessel ?uid. vibration isolator.
The following example illustrates the application of a
single-vessel ?uid vibration isolator to the mounting of
a 6 cylinder 4-stroke diesel engine. The isolator is to
support a Weight'of 1,000 lbsaandis'to give: best ‘attenua
tion at a frequency of‘SO cycles-pertsecond, which is the
3,091,103
16
15
The frequency of the applied periodic force is related to
70 by the following general formula:
Frequency of the applied periodic force
?ring frequency when the engine is running at a speed
of 1,000 rpm. Further, the de?ection of the vibration
isolator under the static load of 1,000 lbs. is to be 0.75
inch when the pres-sure in the bellows is 50 pounds per
square inch gauge.
in] cycles per second.
1/ A0 inches
In the following calculation, the numbers are given
to a greater number of signi?cant ?gures than would be
justi?ed in practice, in order to indicate clearly the
method of calculation.
In the vibration isolator shown in FIGURE 3 of the
drawings, the bellows 12 may be replaced by the plunger
and-barrel assembly shown in FIGURE 5 of the drawings.
10
Then
The assembly comprises a hollow rigid plunger indi
cated generally by the reference numeral 33 and a flexible
M =1000 lbs.
barrel, indicated generally by the reference numeral 34.
The upper and lower parts, 35 and 36 respectively, of
the plunger side wall are each cylindrical in shape and the
15 middle part 37 is of frusto-conical form tapering up
A0=%=20 square inches
and
wardly so that the diameter of the upper cylindrical part
35 is less than that of the lower part 36. At its lower
Therefore
edge, the lower cylindrical part 36 is welded to the upper
surface of a circular base plate 38, which can be secured
20 to the support 2 by, for example, bolts 39. At the upper
end of the upper part 35 of the plunger side wall, there is
If air is used in the duct -'14 and vessel 13, and liquid is
an inwardly extending annular ?ange 40' of which the
‘used in the bellows 12, then
inner part is of increased thickness and forms an annular
boss 41, which is internally screwethreaded to receive a
V
=19A cubic inches
25 plug 42. Extending outwardly from the upper end of the
plug 42 is an annular ?ange 43 of which the outer diam
For air at ‘a pressure of 50 pounds per square inch gauge
eter is greater than the outer diameter of the boss 41.
and a temperature of 80° F.
The side and bottom walls of the barrel 34 are formed
p1=0.0001782 pound per cubic inch
by a single member, which is of generally tubular form
30 and is made of rubber or ‘other suitable ?exible material.
1q==0h00553 square inch per second
The lower end portion 44 of this ?exible member, which
Now
is of increased thickness and has embedded in it a metal
Ad=0.75 inch
_&__1333>< 32.2>< 12_
reinforcing ring 45, is clamped between the annular ?ange
m1-wY2-————(
21X 50 )2 —5.217 pounds
35
Therefore
~
L1
m1
E = m=
= 69.67 reciprocal inches
Selecting A1=0.1 square inch makes L1=6.967 inches.
Then
247.1 db
~
40 at the top of the plunger 33 and the annular ‘?ange on
the plug 42.
From its lower end, the ?exible member extends out
wards over the upper surface of the annular ?ange 40 and
turns downwards over the rounded edge formed where
the upper part 35 of the plunger side wall meets the ?ange
40
40. The outer surface of the ?exible member here makes
a close ‘?t round the upper cylindrical part 35 of the
plunger side wall before the member turns outwardly
and then upwardly to form the barrel side wall 46. At
the upper end of the barrel side wall 46, the ?exible
That is, the attenuation at a frequency of 50 cycles per
second is 47.1 db beyond that achieved by a simple con 45 member turns inwards and terminates in a thickened end
portion 47 which contains a metal reinforcing ring 48.
ventional vibration isolator of equal static stiffness. With
Surrounding the side wall 46 of the barrel 34 is a re
this value of A1:
inforcing metal band 49, which serves to prevent any sub
M 1000
stantial changes in the e?ective horizontal cross-sectional
50 area of the barrel 34. The band 49 is located axially with
respect to the side wall 46 by means of a ridge '50, which
Therefore
_
is formed in the outer surface of the side wall 46 and en
X=Y\/>\1:226X\/19l.7
gages an annular recess formed by a circumferentially ex
Hence
tending bulge in the band 49.
X=3129=69.91 db
55
The top end wall of the barrel 34 is formed by a circu
lar metal disc 51, having a central circular aperture. At
fy
its periphery, the disc 51 has a flange '52 which extends
fx-i/rrr.
50
_1/ 1 + 191.7
=3.6 cycles per second
downwardly to provide 1a generally cylindrical seating for
the upper end portion v47 of the ?exible barrel member
60 and terminates in an outwardly extending portion. A
circular plate 53 is secured on top of the disc 51 by means
of a nut 54 and a bolt 55‘. The bolt 55 passes through
the circular aperture in the disc 51 and through aeregister
That is, with this value of A1, the system will experience
ing aperture in the plate Y53, and has an axial bore passing
a maximum ampli?cation of about 69.91 db when the fre 65 through it to provide communication between the interior
quency of the applied force is 3.6 cycles per second (i.e.
of the barrel 34 and a tube 14, which is secured to the
when the engine speed is 72 r.p.m.).
bolt 55 by a union nut 56. Apart from the end portion,
Referring to FIGURE 4 of the drawings, the full curve
the tube 14 is straight and extends horizontally.
represents the attenuation provided by the vibration
The body 1 to which the periodic force is to be applied
70
isolator in the above example. The curve also represents,
[is secured to the plate 53 by a number of nuts 57 ‘and
however, the attenuation provided by a ?uid vibration iso
bolts 58, which are arranged at intervals around the
later [that incorporates a single vessel only and for which
raised peripheral portion of the plate 53, and is spaced
§_._ 74065 and 0,2 : 0.00002
from the plate ‘53 by a number of sleeves 59, one on each
nil-A0 inches
mlKl
75 bolt 58.
3,091,103
17
18
-
In operation, an increase in the downward force ap
plied to the assembly by the body 1 causes the ?exible
member of the barrel 34 to roll down over the upper cy
between the members 60 and 61 in one sense causes the
lindrical pant 35 of plunger 33 thereby decreasing the
bellows 12 to be compressed and allows the bellows 12a
internal volume of the barrel 34. When the force
creases, the ?exible member unrolls from the par-t
under the action of the pressure of the ?uid within
assembly and the internal volume of the barrel 34
de
35
the
in
to expand while relative rotation in the other sense causes
case of a liquid-?lled vessel additional resilience may be
through a conduit formed by a circular groove 71 at one
bellows of the set 12 are arranged alternately with the
bellows of the set 12a and therefore relative rotation
the bellows 12a to be compressed and allows the bellows
12 to expand.
Formed in the inner member 60 are two vessels in the
creases. The metal reinforcing band 49 bears a con
form of similar cylindrical cavities 13 and 13a, which are
siderable part of the stress resulting from the pressure of 10 each coaxial with the member 60. Three ducts 14, formed
the ?uid Within the barrel 34 and it is possible to arrange
in part by bores in the member 60, provide communication
that the ?exible member has very little stiffness so that
between the interiors of the bellows 12 and the interior of
as is desired, substantially all the static stiffness of the
the cavity 13, and three similar ducts 14a provide com
assembly against axial compression derives from the pres
munication between the interiors of the bellows 12a and
sure of the ?uid within the barrel.
15 the interior of the cavity 13a. Each of the ducts 14 and
14a enters the bellows 12 or 1241 at a point adjacent to
In the ?uid vibration isolator described above, the re
silience of the system is derived substantially entirely from
the associated outwardly extending rib 69 so that relative
the bulk elasticity of the ?uid in the vessel or vessels
rotation between the members 60 and 61 does not alter the
(assuming that the elasticity of the vessel is negligible by
dimensions or con?gurations of any of the ducts 14
comparison with that of the ?uid it contains). If desired, 20 and 14a.
however, additional resilience may be provided by in
In addition to being in communication with one another
corporating in the vessel a resilient member such as, for
through the ducts 14 and the cavity 13, the interiors of the
example, a spring-loaded piston or diaphragm. In the
bellows 12 are also in communication with one another
provided by having a small quantity of gas in the vessel. 25 end of the outer member 61 and three ducts 72, which
The gas may be either free or contained in a ?exible and
are formed in part by bores in the outer member 61 and
sealed bag.
lead from the bellows 12 to the circular groove 71. Simi
In order to enable the degree of damping of the ?uid
larly, the interiors of the bellows 12a are also in communi
vibration isolator shown in FIGURE 3 to be readily ad
cation with one another through a conduit formed by a
justed, an adjustable throttle valve 76 may be situated in 30 circular groove 71a at the other end of the outer member
the duct 14 adjacent to the vessel 13 to which the duct
61 and three ducts 72a, which are formed in part by
bores in the outer member 61 and lead from the bellows
leads. In the case of the vibration isolator shown in
FIGURE 3, an adjustable throttle valve 76 may be pro
12a to the circular groove 71a. The ducts 72 and 72a
enter the bellows 12 or 12a respectively at points adjacent
vided for each or only one of the ducts 14 and 14a. The
degree of damping may then be increased or decreased 35 to the associated inwardly extending ribs 70 so that rela
by increasing or decreasing respectively the degree of
tive rotation between the members 60 and 61 does not
throttling produced by the valve.
cause any change in the dimensions or con?guration of
the ducts 7.2 and 72a.
The rotary coupling shown in FIGURES 6 and 7 of
the drawings comprises an inner, generally cylindrical,
The bellows 12 and 12a, grooves 71 and 71a, and the
member 69 mounted coaxially within a hollow cylindrical 40 ducts 72 and 72a are ?lled with a liquid, but the cavities
member 61. The inner member 60 is secured at one end
13 and 13a and the ducts 14 and 14a are each ?lled with a
to an enlarged end portion 62 of a shaft 63. The outer
gas. Thus each system consisting of a bellows 12, cavity
13 and duct 14 and each system consisting of a bellows
member 61 is secured, at the end remote from the shaft
12a, cavity 13a and duct 14a constitutes a ?uid vibration
63, to an annular ?ange 64 which extends from an en
larged end portion 65 of a shaft 66 coaxial with the shaft 45 isolator similar to that shown in FIGURE 3, the only im
portant difference being that the cavities 13 and 13a each
63. At the other end, the outer member 61 is secured to
serve as the vessel of three vibration isolators and that
an annular member 67 within which the enlarged end por
the interior of the bellows of each vibration isolator is in
tion 62 of the shaft 63 is rotatably journalled. Secured to
communication with the interior of the bellows of two
the inner member 60 at the end towards the shaft 66 is a
circular keeper plate 68, which is rotatably journalled 50 other vibration isolators.
within the annular ?ange 64.
All the bellows 12 and 12a have the same dimensions
and the same thing applies to the ducts 14 and 14a and
The inner member 60 is formed with three ribs 69,
the cavities 13 and 13a so that each of the vibration iso
which extend radially outwards and which are equally
lators has the same static stiffness and provides the same
spaced around the circumference of the member 60. The
sides of the ribs 69 lie in radial planes of the members 60 55 attenuation at a given frequency and load. The applicaand 61 and the outer surfaces of the ribs 69 lie in an
tion of a torque to one of the shafts 63 and 66 causes a
imaginary cylindrical surface that is coaxial with the
corresponding force to be applied to one or other (which,
members 60 and 61. The outer member 61 is formed with
one depends upon the sense of the torque) of the two
three ribs 70, which extend radially inwards and are
sets of vibration isolators. Thus the coupling serves to
equally spaced around the inner circumference of the 60 transmit a constant torque from the shaft 63 (or the shaft
outer member 61. The sides of the ribs 70 lie in radial
66) to the other, while at the same time isolating from the
planes of the members 60 and 61 and the inner surfaces of
shaft 66 (or the shaft 63) a periodic torque applied to the
the ribs 70 lie in an imaginary cylindrical surface that is
shaft 63‘ (or the shaft 66).
coaxial with the members 60 and 61. When the coupling
From Equation 12 in the analysis of the ?uid vibration
is not under load, each rib 70 is situated exactly midway
isolator, it can be seen that
between each adjacent pair of ribs 69.
Mounted in the annular region between the inner mem
F5
F0
ber 60 and the outer member 61 are two sets of ?exible
bellows 12 and 12a, each of which sets consists of three
bellows.
The six bellows 12 and 12a are mounted one 70 is a function of a number of quantities of which all except
71 are independent of 002. Now, if a gas is used in the
between each adjacent pair of ribs 69 and 70 and with
their axes extending circumferentially with respect to
the axis of the coupling so that one end of each bellows
bears against a side face of a rib 69 and the other end
bears against the opposing side face of a rib 70.
The 75
vessel 13, then
3,091,103
19
20
and so, if pdwz, then 71, would be independent of (.0.
extending outwards from the second member, the said
Under these circumstances,
inwardly and outwardly extending abutments being
arranged alternately around the circumference of the in
ner member, a plurality of variable-volume ?uid-?lled
would be independent of to, that is to say, the attenuation
provided by the vibration isolator would be independent
of the frequency of the applied force.
containers interposed one between each pair of adjacent
abutments with their directions of expansion and contrac
tion extending substantially circumferentially with respect
to the common axis of the ?rst and second members, two
In the rotary coupling, the pressure in the bellows 12
vessels, each containing a ?uid, a plurality of conduit
and ‘12a is proportional to the torque transmitted by the 10 means, one for each container, the effective cross-sectional
coupling. Thus, if the transmitted torque were to be
area of each of which is less than the eifective cross
proportional to the square of the frequency of the varying
sectional area of each of the said containers, each of which
component of the torque, then the attenuation provided
contains a body of ?uid and each of which communicates
would be independent of that frequency. Now the torque
with both the interior of one of the said containers and
required to drive the screw of a vessel is proportional to 15 the interior of one of the said vessels, the conduit’means
the square of the rate of rotation of the screw so that, if
communicating with every alternate variable-volume con
the rotary coupling is used in the transmission system
tainer communicating with one of the said two vessels
coupling a screw to the power unit of the vessel, it can
and the remaining conduit means communicating with
be arranged to give, over the whole range of rotational
the other of the said two vessels, the masses of the said
speeds, optimum attenuation of a periodic component of 20 bodies of ?uid contained in the conduit means, the dimen
the torque of which component the frequency is directly
sions of the conduit means, the apparent bulk modulus
proportional to the rotational frequency of the screw.
of the ?uid in each of the two vessels and the degree of
Thus, the shaft 66 may be coupled (if desired, through
damping applied to the body of ?uid contained in each
gearing) to a prime mover, for example, a diesel engine,
of the said conduit means being such that, at a particular
and the shaft 63 may be the propeller shaft for driving a 25 frequency of the periodic torque, the inertia reaction of
screw. The coupling transmits a constant torque from
the said bodies of ?uid substantially balance the forces
the prime mover to the screw, but greatly attenuates a
exerted on those bodies of ?uid by the ?uid in the vessels
particular periodic component ‘of the torque of which
with which the conduit means containing those bodies of
component the frequency is directly proportional to the
?uid communicate.
rotational frequency of the screw. Such a periodic com 30
6. A rotary coupling as claimed in claim 5, wherein
ponent of the torque may result either from a periodic
the said two vessels are each formed by cavities in the
variation in the torque required to drive the screw arising,
second member, which cavities have axes that substan
for example, from the blades of the screw passing the
tially coincide with the axes of the ?rst and second mem:
hull of the vessel, or from periodic variations in the
bers, and each conduit means is formed, at least in part,
35 by a bore which is formed in the second member and
torque output of the prime mover.
I claim:
which communicates with the associated variable-volume
1. A vibration isolator for isolating from a ?rst body
container at a point adacent to the outwardly extending
a periodic force applied to a second body while at the
abutment that engages that variable-volume container.
same time transmitting to the ?rst body a constant force
7. A rotary coupling as claimed in claim 5, wherein
applied to the second body, which vibration isolator com 40 the said two vessels are each formed by cavities in the
prises a variable-volume ?uid-?lled container for inter
second member, which cavities have axes that substan
position between the said two bodies, a vessel containing
tially coincide with the axes of the ?rst and second mem
a ?uid which provides substantially the whole of the static
bers, each conduit means is formed, at least in part, by a
sti?ness of the vibration isolator, conduit means of which
bore which is formed in the second member and which
the effective cross-sectional area is less than the effective 45 communicates with the associated variable-volume con
cross-sectional area of the said container, which contains
tainer at a point adjacent to the outwardly extending abut
a body of ?uid and which communicates with both the
ment that engages that variable-volume container, and
interior of the said container and the interior of the said
there are provided two additional conduit means of which
vessel and provides the sole means of such communica
one provides communication between the interiors of only
tion, wherein relative movement between the two said 50 the variable-volume containers that are in communication.
bodies in the said one sense causes ?uid to ?ow in the
with one of the said vessels and of which the other addi
conduit means toward the vessel against the pressure of
tional conduit means provides communication between
the ?uid in the vessel and relative movement between the
the interiors of only the variable-volume containers that
said bodies in the opposite sense causes ?uid to ?ow in
are in communication with the other of the said vessels.
said conduit means towards the variable-volume con 55
8. A rotary coupling as claimed in claim 5, wherein
tainer under the action of the pressure of the ?uid in the
the ?uid contained in each of the said two vessels is a gas.
9. A rotary coupling for isolating from a ?rst body a
vessel.
2. A vibration isolator as claimed in claim 1, wherein
periodic torque applied to a second body while at the
the variable-volume container comprises a ?exible bellows.
same time transmitting to the ?rst body a constant torque
3. A vibration isolator as claimed in claim 1, wherein 60 applied to the second body, which coupling comprises a
the effective cross-sectional area of the variable-volume
?rst abutment member for connection to the ?rst body, a
?uidJ?lled container exceeds the effective cross-sectional
second abutment member for connection to the second
area of the conduit means by a factor of at least 10.
body and mounted for rotation relative to the ?rst abut
4. A vibration isolator as claimed in claim 1, wherein
ment member, a third abutment member rigidly connected
the ?uid in the said vessel is a liquid and there is pro 65 to the ?rst abutment member, the arrangement being such
vided in the vessel a body of gas.
that relative rotation between the ?rst and second abut
5. A rotary coupling for isolating from a ?rst body a
ment ‘members in one sense causes the ?rst and second
periodic torque applied to a second body while at the
abutment members to approach one another and relative
same time transmitting to the ?rst body a constant torque
rotation between the ?rst and second abutment members?
applied to the second body, which coupling comprises a 70 in the reverse sense causes the ?rst and second members
?rst member for connection to one of the said bodies, a
to approach one another, two variable-volume ?uid-?lled
second member for connection to the other of the said
containers interposed one between the ?rst and second
bodies and rotatably mounted coaxially within the ?rst
abutment members and the other between the second and
member, a plurality of abutments extending inwards from
third
abutment members, two vessels each containing a
75
the ?rst member, a corresponding number of abutments
3,091,103
22
21
members to approach one another, a second variable
volume ?uid-?lled container interposed between the sec
ond and third abutment members, a second vessel con
of each of the said containers, which each contain a body
taining a ?uid, and a second conduit means of which the
of ?uid and which each communicate with the interior
effective cross-sectional area is less than the e?ective
of one of the said vessels and the interior of one of the
cross-sectional area of the second container, which con
said containers, the masses of the said bodies of ?uid, the
tains a body of ?uid and which communicates with both
dimensions of each of the said conduit means, the appar
the interior of the second container and the interior of
ent bulk modulus of the gas in each of the said vessels
the second vessel, the mass of said bodies of ?uid con
and the degree of damping applied to the said bodies of
?uid being such that, at a particular frequency of the 10 tained in the said ?rst and second conduit means, the
dimensions of the ?rst and second conduit means, the
periodic torque, the inertia reaction of the masses of the
apparent bulk modulus of the ?uids in the ?rst and sec
said bodies of ?uid substantially balance the force ex
ond vessels and the degree of damping applied to the
erted on those bodies of ?uid by the gas in the vessel with
bodies of ?uid contained in the ?rst and second conduit
which the conduit means that contains those bodies of
gas, two conduit means of each of which the cross
sectional area is less than the effective cross-sectional area
15 means being such that, at the said particular frequency
?uid communicates.
of the periodic torque, the inertia reactions of the masses
10. A rotary coupling for isolating from a ?rst body
of the said bodies of ?uid contained in the ?rst and
a periodic torque ‘applied to a second body while at the
second conduit means substantially balance the forces ex
same time transmitting to the ?rst body a constant torque
erted on those bodies of ?uid by the ?uid in the ?rst and
applied to the second body, which coupling comprises
a ?rst abutment member for connection to the first body, 20 second vessels.
a second abutment member for connection to the second
References Cited in the ?le of this patent
body and mounted for rotation relative to the ?rst abut
ment member, a variable-volume ?uid-?lled container
UNITED STATES PATENTS
interposed between the said two abutment members, a
Re.
20,887
Mercier ____________ __..._ Oct. 18,
25
vessel containing a ?uid, conduit means of which the
527,632
Verity _______________ __ Oct. 16,
effective cross-sectional area is less than the eifective
989,958
Frahm ______________ __ Apr. 18,
cross-sectional area of the said container, which contains
1,734,043
Nelson _______________ __ Nov. 5,
a body of ?uid and which communicates with both the
1,917,094
Carlson ______________ __ July 4,
interior of the said container ‘and the interior of the said
Schieferstein _________ __ Sept. 11,
vessel, a third abutment member fixed with respect to 30 1,973,510
2,002,517
Balduf ______________ __ May 28,
the ?rst abutment member, the arrangement being such
that relative rotation between the ?rst and second abut
2,524,405
Storrs _______________ __ Oct. 31,
ment members in one sense causes the ?rst and second
2,683,570
1938
1894
1911
1929
1933
1934
1935
1950
Miller _______________ __ July 12, 1954
abutment members to approach one another and relative
rotation between the ?rst and second abutment members
in the reverse sense causes the second and third abutment
782,933
Great Britain _________ __ Sept. 18, 1957
FOREIGN PATENTS
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