Note: Descriptions are shown in the official language in which they were submitted.
1152~7~
BACKGROUND OF THE INVENTION
Field of the Invention - This invention relates to
-
systems for providing a fluid of a select temperature by
mixing of two fluids of differing temperatures or by dis-
position of such fluids in mutual heat transfer relation-
ship and more particularly to such a system for use in
supplying bleed air of a particular temperature from a gas
turbine engine.
Description of the Prior Art - It is well known to
air-condition aircraft cabins and power various aircraft
subsystems with air bled from the aircraft's propulsion
system. In air-conditioning the cabin of a gas turbine
engine powered aircraft, it has been the practice to sup-
ply the cabin with air bled from the compressor section of
the engine, such air being cooled to the desired tempera-
ture by mixture or mutual heat transfer with cooler air
supplied by the engine's fan. Inasmuch as differing
engine operating conditions cause variations in the tem-
perature of the compressor bleed air, systems which moni-
tor the temperature of the bleed air and cool the bleed air
with a controlled flow of cooler fan air are necessitated.
Such systems have in the past been of two general types.
The first type as exemplified by the systems disclosed in
U. S. Patents Nos. 3,441,213 and 3,537,644 each assigned
to the assignee of the present invention, generally com-
prises a pneumatic temperature sensor controlling a pneu-
matic fan air modulating or control valve. While such
pneumatic temperature sensors exhibit fairly accurate
steady state response, it has been found that the transient
performance of such sensors could be improved upon. While
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certain fast-acting pneumatic or mechanical temperature
sensing transducers have been proposed, the accuracy of
such sensing devices has been found inadequate for air-
craft cabin air-conditioning systems.
Other proposed fluid temperature control systems
such as that shown in U. S. Patent No. 2,919,859 to
Krueger employ electrical temperature sensors, and con-
trols, and, while such systems may exhibit both adequate
steady state accuracy and rapid transient response, they
require the disposition of rather delicate electrical
sensors and connectors in the hostile environmer.t of the
gas turbine engine and therefore are subject to damage
from heat and/or vibration resulting in poor system
reliability.
It is therefore an object of the present invention
to provide a fluid temperature control system which over-
comes the deficiencies of the prior art.
It is another object of the present invention to pro-
vide such a fluid temperature control system of enhanced
steady state accuracy.
It i9 another object of the present invention to pro-
vide a fluid temperature control system which responds
rapidly to sudden changes in inlet fluid temperature.
It is another object of the present invention to
provide a fluid temperature control system which employs
no electrical components.
It is another object of the present invention to
provide such a fluid temperature control system of en-
hanced reliability.
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SUMMARY OF TEIE INVENTION
These and other objects which will become more
readily apparent from the following detailed description
taken in connection with the accompanying drawings, are
achieved by the fluid temperature control system of the
present invention in which a first fluid is either warmed
or cooled by a controlled flow of a second fluid to achieve
an outlet fluid flow at a preselected temperature. The flow
rate of the second fluid is controlled by a modulation or
control valve set by an actuator responsive to the pressure
of a supply or servo fluid. The temperature of the outlet
fluid supplied by the system of the present invention is
continuously monitored by a temperature sensing means oper-
atively connected to means which continually adjusts the
servo fluid pressure in response to the output of the temper-
ature sensing means. The servo fluid pressure is adjusted
such that the change of pressure from that of the prior steady
stat~ condition is initially great, diminishing with time to a
~maller Qteady state value. This initial servo fluid pr~ssure
change in xesponse to the temperature change detected by the
temperature senqing means causes the modulation valve actuator
to respond quickly to any transient fluid temperature
fluctuations.
In accordance with a particular embodiment of the
invention there is provided a system for controlling the fluid
supply temperature of a first fluid flowing through a first
duct by disposition of the first fluid in heat transfer
relationship with a second fluid flowing through a second
duct at a temperature different from that of the first fluid.
The system comprises a valve disposed in the second duct for
regulating the flow of fluid therethrough and an actuator
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- operatively connected to the valve for the modulation thereof.
The actuator communicates with and is responsive to the
pressure of a supply of servo fluid. The system further com-
prises means for adjusting the pressure of the servo fluid
in response to the supply temperature of the first fluid
thereby effecting the operation of the actuator and the
modulation of the valve. The means adjusts the servo fluid
pressure such that the change of the servo fluid pressure
from steady state diminishes with time from the initiation
of the servo fluid pressure adjustment from an initial
greater value to a subsequent lesser steady state value
thereby enhancing the transient response of the control
system.
In accordance with a further embodiment of the
invention there is provided a system for controlling the fluid
supply temperature of a first fluid flowing through a first
duct by disposition of the first fluid in heat transfer
xelationship with a second fluid flowing through a second
duct. ~he system comprises a valve disposed in the second
duct for regulating the flow of fluid therethrough and an
actuator for modulating the valve in response to the pressure
of a primary supply of servo fluid with which the actuator
communicates. Means are provided for controlling fluid
pressure in the primary servo fluid supply in response to the
temperature of the first fluid thereby selectively activating
the actuator. A secondary servo fluid supply communicates
with the primary servo fluid supply through a flow restrictor
whereby initial adjustments in fluid pressure in the primary
servo fluid supply from a steady state condition are damped
by delayed servo fluid pressure equalization between the
primary and secondary supplies.
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BRIEF DESCRIPTION OF THE DRAWINGS
. _
Figure 1 is a schematic illustration of the fluid
temperature control system of the present invention.
Figure 2 is a plot of the time change in servo
system fluid pressure for a sudden change in supply fluid
temperature.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, the fluid temperature
control system of the present invention is shown generally
at 10. The system controls the temperature of a first
fluid flowing through a first duct 15 by either mixing
that fluid with a second fluid at a different temperature
flowing through a second duct 20 or by the disposition of
the two fluids in mutual heat transfer relation to achieve
the desired temperature in the resulting supply fluid flow-
ing through a third duct 25. The system of the present
invention is particularly useful for Rupplying air at a
predetermined temperature for cabin air-conditioning and
thermal anti-icing of a gas turbine engine powered air-
craft. When so employed, the first fluid in first conduit
15 may comprise air, bled from the compressor section of
the gas turbine engine, while second fluid flowing throùgh
second conduit 20 may comprise cooler fan a~r, the two
fluids channeled through a precooler or heat exchanger 27
at the intersection of ducts 15 and 20 wherein heat from
the compressor bleed air is given up to the cooler fan air.
The resulting controlled temperature fluid exit~ the ap-
paratu8 to the aircraft air supply sy~tems through duct 25.
However, it will be appreciated that the temperature con-
trol system of the present invention is useful wherever it
is desired to control the temperature of a first fluid by
either mixing that fluid with a second fluid at a differ-
ent temperature or disposing the two fluids in heat trans-
fer relationship to one another.
Broadly, the present invention comprises a modulating
1~5i247J.
or throttle valve 30 operated by valve actuator 35 respon-
sive to the pressure of a supply of servo fluid 40 which
communicates with the actuator. For economy of construc-
tion, the servo fluid may be obtained from a tap of one
of ducts 15 or 20 by third duct 45. However, it will be
appreciated that a separate source of servo fluid may be
employed if so desired. The servo fluid pressure is ad-
justed by means 50 responding to the output of tempera-
ture responsive means 55 which continually senses the
temperature of the bleed supply air. In the preferred
embodiment, the temperature responsive means comprises a
bimetallic element which changes length in response to
exposure to varying temperatures. However, it will be
understood that any of various other temperature sensors
may be employed without departing from this invention. A
change in the temperature of the bleed air i8 therefore
sensed by means 55 which actuates means S0 to adjust the
~ervo fluid pressure. The adjusted servo fluid pressure,
i5 ~en~ed by actuator 35 responding to this adjusted
pres~ure by actuation of valve 30 which adjusts the flow
rate of fan air to mixing chamber or heat exchanger 27
thereby elevating or depressing the temperature of the
compressor bleed air to the desired value.
Valve 30 may be of any known varieties of flow con-
trol valves depending of course on the nature of the fluid
controlled thereby. In the preferred embodiment, where
for example the valve is employed to control the flow
rate of fan air, valve 30 is preferably of the butterfly
variety, the plate or valve element being connected to
actuator 35 by means of any suitable linkage 60.
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Likewise, actuator 35 may be of any of a number of
known varieties depending on the nature of the actuated
valve and the type of ser~o fluid employed therewith.
As shown, the actuator comprises a housing 65 enclosing
a diaphragm piston 70 biased toward the upper end of
servo fluid chamber 75 by spring 80. A connecting rod
85 connects the piston to linkage 60 and valve 30. In
operation, the spring urges the diaphragm piston in a
valve opening direction, the piston being urged in an
opposite direction to close valve 30 in response to servo
fluid pressure in chamber 75.
Means 50 for adjusting the servo fluid pressure in
response to an input from temperature sensing means 55
comprises a fixed orifice 91 in duct 45 and an orifice
or port 90 in the end of branch line 95 in communication
with conduit 45. The effective area of port 90 is adjusted
between totally open and totally closed conditions in
response to the temperature of engine bleed air in conduit
15 by means of a closure member or flapper 100 fixed to
or integrally comprising a lever 105 pivotally connected
to a stationary mount at 110. The end of lever 105 op-
posite that which adjoins flapper 100 is connected to a
counterbalance spring 115 fîxedly mounted to a stationary
surface 120 at 125. Thus, it will be seen that the spring
115 . disposed between lever 105 and fixed mount 125 i8
compressed, maintaining the equilibrium of the lever and
flapper in conjunction with spring 116 when the flapper
is exposed to positive servo fluid pressure through port
90. Spring 116 transmits a driving force to the lever,
from bimetallic element 55 connected to the spring by way
115Z471
of bellcrank 130 pivotally connected to tempexature xe-
sponsive means 55 at one end thereof and at the other end
thereof to shaft 135 which is in turn connected to spring
11~ at an end thereof opposite that connected to lever 105.
It will be seen then, that the fluid temperature con-
trol system of the present invention describes a single
feedback loop control circuit wherein bimetallic element
55 when actuated by an error in air temperature within
duct 25 changes length transmitting a signal to lever 105
via bellcrank 130, shaft 135 and spring 116. This signal
results in a force change on the lever thereby causing
the flapper to ad~ust the effective area of port 90 until
a balancing pressure force change on the lever is produced.
This adjustment in servo fluid pressure within duct 45 and
actuator chamber 75 activates actuator 35 which reposi-
tions valve 30. This repositioning, adjus~ the flow rate
of fluid through duct 20 to correct the sen~ed temperature
error within duct 15.
It will be appreciated that the ~ignal provided by a
mechanical temperature ~ensor such as bimetallic element
55 or an equivalent pneumatic temperature actuator lags
in time the temperature variation which causes the sensor
to initiate such a ~ignal. ~o compen~ate for such a time
lag, the temperature control system of the present inven-
tion is provided with a chamber or secondary servo fluid
supply 140 in fluid communication with branch 95 of servo
fluid duct 45 through a flow restrictor or orifice 145.
One wall of chamber 140 comprises a diaphragm 150 which
is connected to lever 105 by link 155. In steady state,
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the fluid communication of chamber 140 with duct 45 ef-
fects an equalization of servo fluid pressure within
those members. However, the restrictive properties of
orifice 145 and the compressibility imparted to chamber
140 by diaphragm 150 cause equalization of servo fluid
pressures in duct 45 and chamber 140 to lag an adjustment
of servo fluid pressure in actuator chamber 75 when spring
116 is compressed by a change in sensed temperature.
Referring to Figs. 1 and 2 it will be seen that a
change in force applied to lever 105 by spring 116 at time
tl, in response to a step error in compressor bleed air
temperature initially causes the flapper to open thereby
causing an immediate drop in servo fluid pressure in duct
45 and actuator chamber 75 from Pl to P2. As the servo
fluid pressure in chamber 75 decreases, a pressure dif-
ferential is formed across orifice 145, causing servo
fluid flow from chamber 140, through orifice 145 thereby
decreasing the pressure in chamber 140. This causes the
control lever to gradually reclose the flapper 100 thereby
increasing the pressure in chamber 75 and duct 40 to P3.
Th~s~ it will be appreciated that upon a step change in
spring force 116 the initial signal presRure change in
duct 45 (a Pa) is proportional to the product of the change
in loading on lever 105 from actuation of the bimetallic
element and the inverse of the surface area of that por-
tion of the flapper in registry with port 90. However in
a steady state conditi,on, the change in servo fluid pres-
sure ( ~Pb) from the previous steady state condition is
significantly less, being proportional to the product of
the force change on the lever and the inverse of the sum
of the flapper and diaphragm areas. The system of the
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present invention operates similarly, i.e., yielding a
large initial servo pressure change followed by a gradually
decreasing pressure change when the flapper is operated to
close off port 90 for closing control valve 30.
Therefore, though valve actuator 35 requires a par-
ticular steady state servo fluid pressure drop to (~ Pb)
to adjust the valve 30 to effect a particular steady state
temperature change in duct 15, the initial pressure (~ Pa)
drop seen by valve actuator 35 is much higher than that
steady state drop. Therefore, the actuator piston will
be moved initially beyond that point effecting a steady
state adjustment of valve 30 and will then approach the
steady state point as the pressures within branch 95 and
chamber 140 equalize. Thus it will be appreciated that
this rapid and extensive actuation of valve 30 compen-
sates to a degree for the inherent delay in the actuation
of valve 30 in response to a temperature change detected
by bimetallic member 55. This "lead" compensating char-
acteristic of the system of the present invention, is par-
ticularly beneficial when the system is called upon to
adju8t the fan airflow in response to compressor bleed
air temperature variations of short duration. Such "slugs"
of compressor bleed air would, in prior art mechanical
or pneumatic systems, be dealt with by a gradual position-
ing of the fan air control valve in response to a gradual
increase in pressure change within the servo fluid duct.
Thus, such a slug could completely traverse duct 15 be-
tween cooler 25 and the aircraft supply system before the
system responds to the temperature change. However, with
the present invention, such a short term discontinuity is
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met by a rapid and extensive adjustment of valve 30
thereby effectively altering the flow of fan bleed air
to compensate for the varying temperature slug of
compressor bleed air.
While in the preferred embodiment, a chamber 140 is
provided to effect a continuous decrease in the change
in pressure of the servo fluid, it will be understood
that various other means of effecting such decrease in
servo pressure change with time may be employed. By way
of example, a separate supply of servo fluid adapted to
bleed into duct 45 upon actuation of flapper 100 may be
employed. It will be understood by those skilled in the
art that various other modifications may be made to the
embodiment shown in the drawings without departing
from the invention and it is intended by the appended
claims to cover such modifications as fall within the
true spirit and scope of this invention.
