Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
BACKGROUND OF THE INVENTION
Many ternperature sensors require levers or actuating
rods, bearings, adjustment links and/or pivots and seals all
of which are expensive and subject to wear or malfunction.
A sensor that could produce a pressure signal proportional
to temperature that would be simple, reliabla and light in
weight and avoid the complications of such mechanical elements
as links, pivots and the like is a desirable device that
could serve as a pressure transducer, for example, in a-fuel
control system.
The pr~sent invention is in some respect~ an
improvement on the invention taught in U. S. Patent 4,271,859,
J. W. Lawsing, issued June 9, 1981.
SUMMARY OF THE INVENTION
_
In accordance with a particular embodiment of the
invention a pressure transducer includes a casing having a
hydraulic fluid inlet and outlet and a gas pressure inlet.
A movable valve pl~te in the casing between the fluid inlet
and outlet has a nozzle therein, and a valve element in the
casing is in a position to be engaged by the plate to more
or less close the nozzle. A plurality of bellows are connected
to and support the plate for movement toward and away from
the valve element. Means are provided for exposing one side
of the bellows to gas from the gas pressure inlet and for
exposing one side of each of two bellows to the hydraulic
fluid pressure on opposite sides of the nozzle plate, the
bellows exposed to the gas being larger than and surrounding
one of the bellows exposed to the hydraulic fluid pressure
and the space between these bellows being evacuated.
In accordance with a further embodiment, a
pressure sensing transducer includes a casing having a fluid
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inlet and fluid outlet ~or a control fuid and a gas inlet
for the controlling gas pressure. A valve in the casing
is disposed between the fluid inLet and outlet and consists
of a valve element having a passage therein for the fluid
entering the casing and having a flat inner end and a movable-
valve plate having a passage therein in alignment with the
flat inner end of the valve element. Opposed bellows are
disposed on opposite sides of the plate and support the
plate in the casing, the insides of the bellows being
exposed to the fluid pressure on opposite sides of the plate.
m e spaces surrounding these bellows are evacuated and other
bellows also between the plate and the casing have their
outsides exposed to gas from the inlet.
One feature of the invention is a bellows assembly
directly connected to and actuating a floating nozzle plate
making the device free of levers, links and/or friction
causing elements. Another feature is a simplified form of
adjustment of the device for different hydraulic pressures
and also for a simplified rate adjustment. Another feature
is a bellows arrangement to minimize the influence of the
varying temperatures of the control liquid and also to
minimize signal errors resulting from any changes. The
device also positions the gas pressure sensing bellows in
surrounding relation to one of the other bellows, thereby
providing for a more compact device.
According to the invention a change in temperature
causes a change in gas pressure in the probe or transducer
and this pressure is sensed by bellows acting on a nozzle
valve plate that is supported and guided by the bellows
- 2a -
'.~
18~;
and is movable toward and away from a valve stop by
pressure changes in order to control the flow rate through
the nozzle and thus control the pressure of a hydraulic
fluid at the nozzle, The bel'lows are arranged so that
the outsides of the bellows' are evacuated so that ambient
temperatures or the tempera*ure of the transducer casing
will have a minimum effect on the accuracy of the device.
The gas sensing bellows is also positioned around one of
the hydraulic pressure sensing bellows so that a more compact
lQ device will result, and these two bellows are insulated
by an evacuated cham~er therebetween.
.. . .. . . .. . .
'BRIEF'DES'CR'IP'TION 'OF THE 'DRAWING
. . . _ . _
Pig. 1 is a sectional view through the device.
DESCRIPTIO~ OF THE PREFERRED EMBODI~ENT
The transducer has a T-shaped casing 2 having an
inlet 4 for metered hydraulic fluid at one end and an outlet
6 for drain at the opposite end. The stem of the T has
a gas pressure inlet 8 which is connected to a pressure
source or a temperature sensor 10 consisting of a gas
filled probe or tube 10 by a cond'uit 12. The change in
temperature at 10 causes a change in gas pressure in the
prohe,and this pressure is transmitted through the conduit
12 to the transducer.
Within the casing 2 is a spool shaped flapper valve
plate 14 having a nozzle 16 therein in a position to
engage the end of an adjustable screw forming a valve
stop 18 positioned in the hydraulic fluid inlet 4. This
screw is ~ollow from the inlet end to a cross passage 19
3--
and presents a solid inner end that more or less closes
the nozzle dependent upon the spacing of the nozzle.
The screw is threaded within the inlec and is adjustable
by insertion of a key into khe inlet to engage a hexagonal
recess 20 at the inlet end of the screw.
The nozzle is supported within the casing by a
plurality of bellows~ The bellows 22 adjacent the hydraulic
fluid outlet is filled with the hydraulic fluid and the
outsid~ of the bellows is evacuated. The inner end
of the bellows is secured to the upper annular flange 24
of the nozzle plate 16. selow the flange 24 is a ring 26
secured to the casing in spaced relation to the flange and
a bellows 28 extends between this ring 26 and the lower
annular flange 30 of the nozzle plate. The outside of
this bellows is exposed to gas pressure from the temperature
probe and the inside is evacuated.
Below the lower annular flange 30 is a bellows 32
extending between said flange and a surface 34 on the
casing surrounding the inlet 4. The space within the
bellows is filled with metered hydraulic fluid upstream of
the nozzle and the space outside the bellows is evacuated.
This bellows 32 and the bellows 22 above described are
similar in diameter.
Surrounding the bellows 26 is a larger diameter
bellows 3~, extending between the lower flange 30 and an
annular surface 40 on the casing below the gas pressure
inlet. Thus the space outside this bellows is filled
with gas from the gas inlet as is the space around the
bellows 28. ~ith this arrangement the force transmitted
to the nozzle plate by the gas is equal to the gas
pressure times the difference in the mean effective
--4--
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areas of bellows 28 and 38, this force acting to move the
nozzle toward or away from the valve stop. This ~orce is
opposed by the force exerted on the plate from the
difference in metered hydraulic fluid pressure and drain
pressure times the effective area of the bellows 22
since both bellows 22 and 32 are filled with this fluid.
With this arrangement a chanye in gas pressure caused
by a temperature change at the probe will cause a force
change on the nozzle plate with the result that it will
lQ move toward or away from the adjusting screw resulting
in a change in metered hydraulic pressure proportional to
the change in the gas pressure entering the transducer.
When the device is used in connection with a fuel control
in a gas turbine engine, an increase in the engine inlet
temperature as sensed by the probe located at the inlet,
will result in an increased metered hydraulic fluid
pressure signal proportional to the temperature change
and this metered hydraulic pressure signal will reach the
appropriate servo operated linkage in the fuel control.
When the device is used in this way the hydraulic fluid
in the transducer will usually be fuel.
The device may be connected as shown in the drawin~.
Thus, the sensing line 12, in which the pressure is
- proportional to the temperature sensed by the probe enters
the space around the bellows 28 and the bellows 38. The
hydraulic fluid inlet 4 is connected to duct 42 from
pressure fluid conduit 44. One end of this conduit
44 is connected to the mechanism to be controlled such as,
for example, the fuel valve 46 for the engine for which
the probe is sensing a particular temperature. The fluid
inlet end of conduit is connected to a source of fluid
--5--
under pressure, not shown, which may be the fuel supply
to the engine. This inlet has an oriEice 48 upstream of
the duct 42 so that movement of the nozzle plate 14 will
maintain a metered fluid pressure in duct 42 and in
conduit 44 downstream of the orifice ~8 that is proportional
to the sensed temperature. As above stated, the pressure
in duct 12 is proportional to the sensed temperature and
this provides proportional pressure changes in duct 42
and at the ~uel valve 46.
lQ This device thus proviaes a hydraulic pressure signal
proportional to temperature with a valve operated directly
by the sensing bellows. Rate adjustment may be obtained
by adjusting the charged gas pressure in the probe and
position adjustment is accomplished by adjust~ent of the
valve screw element 18 within the metered pressure inlet.
The operation is simplified by making the fluid passages
~ithin the screw. The design of the valve permits
maximum tolerance for misalignment of parts as will be
apparent.
The arrangement of the bellows places evacuated
chambers between the hydraulic fluid bellows and the gas
bellows to reduce the heat conductive path between the
flui~,s to minimize the influence of hydraulic fluid
temperature changes. The gas volume in the gas sensing
bellows is minimized to reduce signal errors due to
ambient or hydraulic fuel temperature changes. When
the device is used in fuel controls the arrangement and
sizing of the bellows is such that the metered hydraulic
fluid signal will be sufficient to cause t~emain control
linkage of the control to achieve a fail-safe scheduled
--6--
position in the event of failure o~ the probe.
The hydraulic fluid supply to the -transducer is
mete~red so that by changing the' flow throu~h the nozzle
16, there will be a change in the metered fuel pressure at
the inlet 4. The device is arranged so that an increase
of the signal pressure will move the valve plate 14 to
reduce the flow through the nozzIe 16 thereby inc,reasing
the metered fuel pressure in an amount proportional to
the signal pressure, As the device is arranged, changes
lQ in the hydraulic fluid temperature have a minimum of
effect on the accuracy of the device since the bellows
subject to the h~draulic fluid are insulated from the
casing and from the signal pressure bellows. Although not
previously stated it will be understood that the ends of
the bellows are all secured to the surface with which
they engage. The arrangement is particularly advantageous
in that the flapper valve plate is freely movable toward
and away from the valve stop without frictional contact
at any point. The bellows are the sole support for this
movable plate. It may be noted that this device also
requires no mechanical spring -to bias the movable plate.
The pressures acting on the bellows provide the necessary
pressures on the plate.
Although the device has been described primarilv as
a temperature sensor in which the gas pressure entering
the transducer is a function oftemperature, it will be
obvious that the device would equally be applicable for
the measurement of gas pressures directly as by connecting
a pressure sensing probe located, for example, in the
3Q compressor clischarge of the gas turbine engine with the
gas pressure inlet of the device.
--7--
Although the invention has been shown and described
With respect to a preferred embodiment thereof, it should
be understood by those skilled in the art that other
various changes and omissions in the form and detail
thereof may be made therein without departing from the
: spirit and the scope o~ the invention.
