вход по аккаунту


Патент USA US3100385

код для вставки
uav 1.
Original Filed June 4, 1957
United States Patent 0 ’
Patented Aug. 13, 1963
where K equals the ?uid speci?c heat at constant pressure
divided by the ?uid speci?c heat at constant volume,
will provide the critical pressure ratio for any compres
Thomas P. Farkas, Bloom?eld, Conm, assignor to United
Aircraft Corporation, East Hartford, Comm, a corpora
sible gas as explained on pages 281 and 299 of Fluid
Mechanics, by R. C. Binder, Third Edition. The signi?
; cance of having ori?ce 1'6 choked is that ?ow therethrough
is unaffected by pressure variations downstream thereof.
Continuation of application Ser. No. 663,491, June 4,
Servo piston 18, located within cylinder 20, is attached
H57. This application Nov. 16, 1960, Ser. No. 70,1113
to variable area valve 22 through rod 24. Spring 26 per
2 Claims. (Cl. 60-97)
10 forms the function of biasing servo piston 18 in a direction
such that variable area valve 22 is normally in its full
This is a continuation application of US. application
open position. Multi-cavity diaphragm chamber 28 is
Serial No. 663,491 and the invention relates to pneumatic
provided and is illustrated, for purposes of description
pressure ratio sensing devices and more particularly to
simpli?cation, as comprising chambers 30 and 32 sepa
servo actuated pneumatic pressure ratio sensing devices
which give a mechanical output indicative of the sensed 15 rated by ?exible diaphragm 34. Line 36 places chamber
30 into communication with duct 12 between restrictions
pneumatic pressure ratio.
tion of Delaware
It is an object of this invention to teach a pressure ratio
sensing device for a pneumatic system which is servo
14 and 16. Pneumatic pressure P2, which may be con
stant or subject to variation, is directed into chamber 32
through line 38. A third pneumatic pressure or pressure
'It is a further object of this invention to teach a pres 20 source, the supply pressure PH, passes through line 40,
through ?xed ori?ce 42 and then to servo chamber 44
sure ratio sensing device comprising two ori?ces in series
where it provides a force tending to close variable area
in a pneumatic ?ow system, one being a ?xed area and
valve 22 and ‘area all in opposition to spring 26. Bleed
one being a variable area and the latter being servo
line 46 stems from servo pressure line 40 and terminates
actuated and wherein the downstream ori?ce is choked
25 adjacent diaphragm 34 to form servo valve 48 therewith.
and the upstream ori?ce may or may not be choked.
The area of servo valve 48 and the ?ow therethrough
It is a further object of this invention to teach a servo ‘
is governed by the position of diaphragm 34 and since
actuated pressure ratio sensing device for a pneumatic
servo valve 48 bleeds air from servo pressure line 41?,
system and which is capable of sensing the pressure ratio
the‘diaphragm position and servo valve ?ow determine
between gases of two different systems and which is also
capable of utilizing parameter outputs from different con 30 the pressure in servo chamber 44 and hence the variable
area restriction or valve closing force.
trol units ‘and integrating the outputs in a de?nite propor
tion, and of providing a minimum proportion limiter.
Other objects'aud advantages will be‘ apparent from the
following speci?cation and claims, and from the accom
panying drawings which illustrate an embodiment of the
In the drawings:
‘FIG. 1 is a simple showing of my servo actuated pneu
matic pressure sensing device.
FIG. 2 represents a practical embodiment of this de—
vice in which servo units produce linear parameter out
puts which are combined through a divider unit to actuate
the variable area restriction in my pneumatic pressure
ratio sensor.
The principle involved in the system shown in FIG. 1
includes sensing the desired pressure ratio and establish
ing a mechanical output signal representative thereof,
including directing one of the pneumatic pressures to be
sensed, P2, to one side of a diaphragm 34 and passing the
other pneumatic pressure to be sensed, P1, through a line
having two restrictions, the area of which is variable,
preferably including a ?xed and a variable area restriction
with the downstream ori?ce choked, so as to ‘establish a
reference pressure, PX,‘ between these restrictions which
will be directed to the opposite side of the diaphragm 34
from P2. A servo unit such as 18 is provided to actuate
variable area restriction or valve 22 and area a1 independ
FIGURE 3 is a graphic representation of the parameter 45 ent of any attachment to ?exible diaphragm 34, thereby
avoiding the problems of ?ow and movement hindrances
proportion generated by the embodiment illustrated in
encountered in any ?ow system and further avoiding the
FIG. 2 plotted against a sensed pneumatic pressure ratio
problem ‘ involved in attempting to have the valve
and illustrating the minimum proportion.
diaphragm actuated after diaphragm ?exibility weakens
‘ My invention will be described as a pneumatic system
throughout and it will be clear to those skilled in the art 50 at high temperatures. Because pressures PX and P2 are
on opposite sides of diaphragm 34, they will be substantial
that this describes any gas which is capable of operating
ly equal and the size and ?ow through bleed line 46 is
at a critical pressure ratio across a restriction to ‘attain
chosen to be such that it vw'll have little or no effect upon
sonic ?ow therethrough and hence a choked condition
‘pressure P2.
therein could be used.
FIG. 1 illustrates the basic principle of my servo 55 My invention teaches a pneumatic servo construction
in which ori?ce 16 is choked and the ‘area all of ori?ce
actuated pneumatic pressure ratio sensor while FIG. 2
14 varies as a function of the pressure ratio P1/P2 in such
illustrates a practical and particular embodiment thereof.
a manner that for each pressure ratio Pl/Pz, there will be
First referring to FIG. 1, the pneumatic pressure ratio
a unique value of a1. This is true whether ori?ce 14 is
to be sensed is ‘Pl/P2. Pneumatic pressure P1, which
may be constant or subject to variation, enters line 12 of 60 choked or unchoked but the relationship between all and
P1/P2 is di?ierent for the choked and unchoked conditions.
servo actuated pneumatic ‘pressure ratio sensor unit 11}
For example, when :ori?ce 14 is choked, we may write
and passes through variable area restriction 14, which
the following weight ?ow equation of the gas passing
may be choked or unchoked, and then through ?xed
area choked restriction 16. Air flow through a sharp
edged ori?ce under conditions to create a minimum pres 65
sure ratio of 1.89 thereacross will cause sonic ?ow and
hence a choked condition while the formula
For ori?ce 14: W1=K1a1P1
For ori?ce 16: W2=.K2a2P2
As the weight ?ow through both ori?ces will be the same,
70 from Equations 1 and 2 we arrive at the equation:
Solving for a1 We obtain:
7 So for ori?ce 14 to be choked 4115053122, and for ori?ce
a?“ K1P1
As 11;, is also a constant we may express K2a2/K1 as C1,
which leads to:
The constant K1 ‘and K2 are proportional to the discharge
coe?icients of the respective ori?ces.
Two ori?ces of
similar geometery will have equal coe?iicients. ‘If ‘this is
‘the case, then Equation 3 may be written as: ,
“1P1 =azP2
which 'is the equation given in line 16, page~3 of the re -'
erenced application. It is accordingly 'seen that when
14 to be unchoked a1;0.53a2. Flow duct 12, shown in
FIGURE 1 of referenced application and ?ow duct 12',
shown in FIGURE 2 of referenced application, both lead
to drain. In order for ori?ce ,16 to be choked, as is neces
sary in the operation of this servo device, the pressure
ratio Pz/Pdmm must be at least that as de?ned by Equation
14. For air this would be P2/Pdmm= 1.89, 'However,
if ori?ce 16 is of venturi shape as shown in both FIGURE
1 and FIGURE 2 of this application, then the critical pres
sure ratio of Equation 14 must exist between P2 and the
pressure at the throat of the venturi, and the pressure ratio
Pz/Pdmm may be as low as 1.2 for air. This increases the
i effective range of the device. Further, since a1 is deter
15 mined by the position‘ of piston 18, we may calibrate a
scale so that the position of piston 18 indicates area a1
and hence the pressure ratio P2/P1. This is accomplished
both ori?ces 14 and 16 are choked,‘ area al'varies as a
by varying servo actuating pressure PS in chamber 44
Considering the case
where ori?ce 14 is not choked, thefweight ?ow through
through the bleed action of servo valve 48‘ as a function
‘function of pressure ' ratio 'P1/P2.
a1 may be given as:
_ :
‘Equation 8 is a slight approximation, however, the conclu
sions drawn using this equation are the same as those fol
lowing use of a rigorous expression for-‘W1. Squaring
Equation 8 and Equation 2 and equating the resulting
By transposing we arrive at the equation:
P22 -
Kzaz -'
change.> As the pressure P5 is a function of
(9) 30 when PX¢P2 and will cause servo piston 18 to change
‘position. The valve of a1 is determined by the position
of servo piston 18 and the’ ratioPl/Px is determined by
l: KI'JP1/PZ-1
considered to be in equilibrium, at its null position, when
Px=P2. When PxeePz the position (opening) of servo
?xed'ori?ce 42 and servo valve opening 48, PS will change
1 _(K1")2 (131132-1322)
‘6712- Kzzllzz
ent on the controlling interaction of servo valve 48 and
‘ servo piston_1‘8. Diaphragm 34 in chamber 28 maybe
valve 48
W12 and W22, we obtain: ~
of the movement of diaphragm 34, which i-s'responsive
to changes in the P2/P1 ratio. More particularly, as
'shown in FIG. 1 there are three input pressures P1, P2,
and PH. Two additional pressures PK and P5 are depend
Substituting C2 for Kf/Kz a,, we obtain:
a1, hence the control action will continue until PX=P2.
For a given‘ P2, hence a given PX, the position of a1 will
be dependent on the value of P1, and this dependence is
such that position a1 is unique for every value of the pres
sure ratio P1/P2 as previously demonstrated.
In addition to sensing pressure ratio, a unit of the type
shown in FIG. -1 may be used to control a pressure ratio
(12 )
40 “by utilizing the movement of servo piston 18 to operate
choked. In a pneumatic system the minimum pressure
P1/P2 referred, to in FIG. ‘1.
It will be notedthat if phantom link 24-’ were provided
in ‘FIG. 2 ‘and pivotally attached to pivotable bar 50, we
a device which ‘performs the function of controlling the
‘pressure'ratio to‘ a degree proportionate to the’ movement
a1=_f(P1/l’z)_ ‘
of servopiston 18. For example, the movementof servo
Hence, whenrori?ce 14 is unchoked and ori?ce
is' ' 'piston {118 may be utilized in a system to vary the pressure
choked, area a1 varies as a function of pressure ratio 45 P1 possibly by controlling the position of the exhaust
nozzle of a jet engine. '
Pl/Pz. It will therefore be ‘seen from Equations 6 and 1,3 ,
‘FIG. 2 represents a preferred and ‘practical embodiment
_ that there is a unique area a1, and therefore a unique
of-my invention and may be used to govern two control
position of piston 18 for each’pressure' ratio Pi/Pa when
means in response to "a pneumatic pressure ratio, such as
ori?ce 16 is choked, whether ori?ce 14_is choked or un
ratio across anori?ce for the ori?ce .to be choked is: ,
CV7 ?uid specific heat at; constant volume
:Fnom’Equation 7, it can be seen that 'for ‘the condition
' o6)
Therefore, for the ‘choked condition:
, t
,1 (17,)
a‘; ( Pi/Pocmn.
For example, if the gas is air:
(P1P2)oritical= 1.89M
and providing pneumatic pressure P2’ to chamber 30'
which is on the opposite side of diaphragm 34' ‘from cham~
ber F32’. Pneumatic supply pressure PH enters line 40'
and enters chamber 44’ of servo piston '18’ to move the
Ipiston upwardly in opposition to spring 26’. Pressure
PS in chamber Q6’ is ‘governed by the‘ amount of bleed
_ ?ow discharged'into chamber 82’ through servo valve 48’.
By using the same equations discussed in connection with
FIG. 1, it will be obvious that the position of variable
area valve 22’ and the movement of piston '18-’ will be.
proportional to the pressure ratio P1/P2.
The embodiment shown in FIG. 2 is intended to dem
onstrate a more extensive use of my invention and there
and for the unchoked condition:
matic pressure P1 entering duct 12’ and passing through
variable ori?ce area :14’ and then through ?xed ori?ce 16
_C‘,, ?uid speci?c heat at constant pressure
where ori?ce 14 is choked:
would have the unit shown in FIG. -1 with pneumatic pres
sure P2 entering chamber 32’ through line'38' and pneu
vfore, phantom line 24' is not attached to pivotable lever 50
but servo piston 18 is used to produce dimension A4
which ‘will be united through divider unit 52 with the
dimension As such that variable area valve 22’ will be
positioned as a function of dimensions A, and A3. The
75 movement of shafts 66 (A4) and 60 (A3) will preferably
be fed to controls which change any parameter, such as
temperature, pressure or area in accordance with the
movements of these shafts.
As shown, the equation to be followed by this FIG.
arrangement may be stated as
As already described, dimension A4 is produced by
In many instances, it may be desirable to vary the dimen
sion A4/A3 in the fashion shown in the graph in FIG. 3
such that it does not reduce below a preselected minimum
value. This is accomplished by providing servo stop 122
which consists of a linkage bar ‘124, one end of which is
positioned to contact plate i126 of valve 22’, while the
other end positions valve :128. When the parameter
A4/A3 reaches the predetermined minimum, as shown in
FIG. 3, plate 126 contacts lever ‘arm 124- causing the lever
servo piston 1-8’ and is provided to divider 52 to be joined 10 arm to rotate in a counterclockwise direction and reduce
the area of valve 128 to increase the pressure PS to prevent
with dimension A3 to vary the position of divider fulcrum
:further lowering of the dimension A4/A3. Obviously, a
point 54 and thereby position movable valve 22’ as a
maximum ratio control could also be used.
function of A4/A3. It is well known that constants such
While not necessarily so limited, the embodiments
as K can be introduced into the system by any means,
such as by varying linkage lengths or by varying the vari 15 shown in FIG. 2 could represent control actuators to posi
tion the convergent section of a convergent-divergent
ous pivot ‘adjustments such as 56, 57 and 58.
nozzle of the type used in modern aircraft turbojet en
It will be noted by reference to FIG. 2 that a down
gines as a function of dimension A3 and to vary the di
ward movement of servo piston 18' constitutes an increase
vergent section as a ?unotion of the dimension A4 accord
of signal of dimension A4 while a rightward movement of
lever 60 produces an increase of dimension A3. Further, 20 ing to a pressure ratio curve such as shown in FIG. 3.
While particular embodiments of this invention have
the rightward movement of lever 61) would cause fulcrum
been shown for purposes of illustration, it should be borne
point 54- to move to the right such that linkage bars 62
in mind that other arrangements, consistent with the teach
would be permitted to rotate clockwise in response to the
urging of spring 64, thereby increasing area al’ to increase
ing herein, will be obvious to those skilled in the art.
pressure PX and therefore pressure PS, while a downward 25
I claim:
1. A control system comprising a ?rst means including
movement of lever 66, attached to servo piston 18', would
produce the opposite e?ect.
Considering the portion of the control which provides
a duct de?ning a gas passage, ‘a ?xed area restriction in
said gas passage, is. variable area restriction in said gas
the A3 dimension, it will be noted that a movable cam- 68
passage and located upstream of said ?xed area restriction,
actuates one end of pivotable bar 79’ and that dimension 30 means to pass gas through said duct thereby establishing
d1 of cam 68 is less than dimension d2 of cam- 68 such
a ?rst pressure upstream of said restrictions and a refer
that a clockwise movement of cam 68 moves linkage 70
ence pressure Which is a function of said ?rst pressure
to the left while a counter-clockwise movement of cam 68
between said restrictions and to establish choked flow
moves linkage 70 to the right. Linkage 70' positions pilot
through said ?xed area restriction, a double chamber
valve '72 which comprises three lands 74, 76 and 78, the 35 diaphragm unit comprising a ?rst chamber communicat
latter of which is provided with grooves 80 which permit
ing with said reference pressure, a second pneumatic pres
relatively low pressure P3 to pass from chamber 82 through
line 84- and thence into chambers 86 and 83. In the pilot
valve position shown in FIG. 2, the valve is shown to be
diaphragm unit which second chamber is independent of
said duct and coacting with said reference pressure to posi
centered or in a neutral position so that pressure P3 can
not proceed beyond land 76. A counter-clockwise move
ment of cam 68 would move both land 78 and land 76
to the right thereby permitting servo chamber 99 to drain
to the pressure P3 through line 92. Pressure P3 is selected
to be of such a value that it will be overcome by spring
sure in communication with a second chamber of said
tion said diaphragm as a function of the pressure ratio
between said ?rst Kand second pressures, and servo means
responsive to diaphragm movement to produce a ?rst
ilinear parameter output proportional to said pressure
ratio, second means including a spring biased servo piston,
a pilot valve to selectively provide actuating pressures to
96 and servo piston 94 will move to the left thereby mov 45 said servo piston, means to actuate said pilot valve so that
ing linkage 98 to the left and linkage bar 60‘ to the right
said servo piston is moved to produce a second linear
in view of pivot point 109 to increase dimension A3.
parameter outputand means including a divider to com—
The movement of cam 68 clockwise will move lever 70
bine said ?rst ‘and second outputs proportionately and
and pilot valve 7-2 to the left thereby introducing a rela
50 position said ?rst means variable area restriction to main
tively higher pressure P4 through line 1% to chamber it)
through chamber 104- and line 92. Pressure P4 is selected
to be of such a value that it will overcome spring 96 and
move lever ‘98 to the right thereby decreasing dimension
A3. It will be noted that the movement of servo piston 94
tain 1a selected proportion between said ?rst vand second
outputs proportional to said pressure ratio, and means to
maintain said proportion above a preselected ilimit.
2. A control system comprising a ?rst means including
a duct de?ning a gas passage, a ?xed ‘area restriction in
in response to pressures P3 and P4 serves to return pilot 55 said gas passage, a variable ‘area restriction in said gas
valve 72 to its neutral position as shown in FIG. 2. In
passage and located upstream of said ?xed area restric
this fashion, bar 60 serves to vary dimension A3 and also _ tion, means to pass gas through said duct thereby estab
to move divider 52 and pivot point 54 in a plane along
lishing a first pressure upstream of said restrictions and
the axis of shaft 60.
a reference pressure which is a function of said ?rst pres
An overriding unit :106 may be used to bleed chamber
sure between said restrictions and to establish choked flow
99 in response to a temperature, pressure or other read
said ?xed area restriction, la double-chamber dia#
ing. For instance, if there is a particular temperature
phragm unit comprising a ?rst chamber communicating
limit which should not be exceeded, this temperature may
with said reference pressure, a second pneumatic pressure
be sensed by probe 108 and fed to proportioning solenoid
11,10 to act upon pivotable lever 112. which pivots about 65 in communication ‘with a second chamber of said dia
phragm unit which second chamber is independent of said
pivot point 114 to move plunger 116 away from bleed jet
118 thereby premitting or increasing flow tln‘ough line
120 to reduce the pressure in chamber 90 thereby increas
ing the dimension A3.
Divider 52 which is based upon the similar triangle
principle, combines the movement ‘of servo piston 18',
which represents dimension A4, and the movement of servo
piston 94 which represents dimension A3 to produce a
motion to variable ‘area valve 22' which represents the
proportion Ag/Ag.
duct and coacting with said referencepressure to posi
tion said diaphragm as a function of the pressure ratio
between said ?rst and second pressures, and servo means
responsive to diaphragm movement to produce a ?rst
linear parameter output proportional to said pressure
ratio, a second servo actuated means to produce a second
linear parameter output, and means including a divider
to combine said ?rst and second outputs proportionately
75 and position said ?rst means variable ‘area restriction to
_maintain ‘a selected proportion between said ?rst and
‘second outputs proportional to said pressure ratio, and
means to maintain said proportion above a preselécted
' limit.
References Cited in the ?le of this patent
.Simb ________ __'___'_____ Feb. 28, 1950
Lombard ______________ _._ Dec. 2, 1952
Clark _____________ __'__ Aug. 12, 1958
Lombard ___'_ ________ __ Feb. 17, 1959
' Longfellow ______ __'_____ Dec. 15, 1959
Biehl _____________ __'_’___ Feb. 2, 1960
Reed _______ __ _______ __ Apr. 25, 1961
-Great Britain _________ _._ Aug. 31, ‘1955
Без категории
Размер файла
712 Кб
Пожаловаться на содержимое документа