U.S. patent number 3,618,777 [Application Number 04/885,215] was granted by the patent office on 1971-11-09 for low-flow contaminated fuel transfer system for a fuel control.
This patent grant is currently assigned to Chandler Evans Inc.. Invention is credited to Gene A. Meyer.
United States Patent |
3,618,777 |
Meyer |
November 9, 1971 |
LOW-FLOW CONTAMINATED FUEL TRANSFER SYSTEM FOR A FUEL CONTROL
Abstract
A fuel control system, adapted to handle contaminated fuel, has
a primary fuel supply line incorporating a pump and a wash flow
filter downstream of the pump. A bypass line containing a bypass
valve communicates with the primary line at respective positions
upstream of the pump and downstream of the filter. A secondary fuel
supply line communicates with the filter to receive a flow of
filtered fuel. A main fuel supply line includes a window-type
metering valve which receives fuel from either the primary or
secondary line via a transfer valve. At low flows the metering
valve receives fuel from the secondary line so that it will not
become clogged by contaminants in the fuel and at high flows
contaminated fuel is delivered to the metering valve through the
primary line.
Inventors: |
Meyer; Gene A. (Simsbury,
CT) |
Assignee: |
Chandler Evans Inc. (West
Hartford, CT)
|
Family
ID: |
25386414 |
Appl.
No.: |
04/885,215 |
Filed: |
December 15, 1969 |
Current U.S.
Class: |
210/130; 210/90;
210/137; 210/416.4 |
Current CPC
Class: |
B67D
7/08 (20130101) |
Current International
Class: |
B67D
5/08 (20060101); B01d 029/36 () |
Field of
Search: |
;210/87,88,90,130,137,416 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Adee; John
Claims
I claim:
1. In a fuel control system for an engine, the combination
comprising:
a primary fuel supply line for receiving a flow of fuel;
a pump mounted in said primary line for pumping fuel
therethrough;
a main fuel supply line adapted to receive a flow of fuel from said
primary line;
secondary fuel supply line means to communicate with said primary
line for carrying a flow of filtered fuel to said main line
upstream of said metering valve;
a wash flow filter positioned in said primary line to fluidly
interconnect said primary line and said secondary line means;
a fuel bypass line fluidly connected to said primary line
downstream of said filter and upstream of said pump for bypassing
fuel to the inlet side of said pump;
a bypass valve located in said bypass line to control the flow in
said bypass line;
a metering valve for defining a metering opening located in said
main line for metering a flow of fuel therethrough;
a control valve positioned between said primary line and said main
line to prevent the flow of fuel from said primary line to said
metering valve when said metering opening does not exceed a
predetermined area; and
means responsive to the position of said metering valve to position
said control valve when the metering opening exceeds said
predetermined area so as to permit the flow of fuel from said
primary line to said metering valve.
2. The combination of claim 1, wherein said position-responsive
means comprises:
a valve operator operatively connected to the control valve for
imposing a differential pressure thereacross, said differential
pressure serving to position said valve; and
a metering valve position indicator operatively connected to said
operator to transmit a signal thereto.
3. The combination of claim 1, wherein said position-responsive
means comprises:
means to bias said control valve to a position in which flow from
said primary line to said main line is prevented, said control
valve being positionable by a sufficient differential pressure
between said primary line and said main line to permit a flow of
fuel from said primary line to said main line; and
a restriction in said secondary line means to produce said
sufficient differential pressure.
4. In a fuel control system for an engine, the combination
comprising:
a primary fuel supply line for receiving a flow of fuel;
a pump mounted in said primary line for pumping fuel
therethrough;
a main fuel supply line adapted to receive a flow from said primary
line;
secondary fuel supply line means to communicate with said primary
line for carrying a flow of filtered fuel to said main line
upstream of said metering valve;
a wash flow filter positioned in said primary line to fluidly
interconnect said primary line and said secondary line means;
a fuel bypass line fluidly connected to said primary line
downstream of said filter and upstream of said pump for bypassing
fuel to the inlet side of said pump;
a bypass valve located in said bypass line to control the flow in
said bypass line;
a metering valve for defining a metering opening located in said
main line for metering a flow of fuel therethrough; and
means responsive to the position of said metering valve to prevent
the flow of fuel from said primary line to said metering valve when
said metering opening does not exceed a predetermined area and to
permit the flow of fuel from said primary line to said metering
valve when said metering opening exceeds the predetermined area.
Description
BACKGROUND OF THE INVENTION
This invention relates to fuel control systems which embody a
metering valve.
Metering valves of the window type are quite common in prior art
fuel control systems. A requirement frequently imposed upon these
systems is that they be able to accommodate a flow of contaminated
fuel. At low flow settings the outlet opening of the metering valve
is rather small and therefore is likely to become obstructed by
contaminants in the fuel.
In order to overcome the problem alluded to above, metering valves
in the prior art are frequently contoured to provide a minimum
opening which is larger than the largest of the anticipated
contaminants. A prominent drawback to this approach is that large
metering heads are not feasible because of minimum flow
requirements. It is highly desirable to impress a large metering
head across the metering valve to minimize the effects of metering
head regulator friction and flow forces and thereby enhance the
accuracy of the fuel control.
SUMMARY OF THE INVENTION
The invention utilizes a standard wash flow filter positioned in a
primary fuel supply line downstream of a pump. A secondary fuel
supply line communicates with the filter. A main fuel metering
valve is positioned in a main fuel supply line to receive either a
filtered or contaminated flow of fuel, depending on the position of
a control valve, which functions to fluidly interconnect the
primary, secondary and main fuel supply lines. The position of the
control valve is dependent on the position of the main metering
valve such that filtered flows and contaminated flows are delivered
to the main metering valve when it occupies respective low-flow and
normal-flow positions.
The invention is unique in that it allows the minimum metering
valve opening to be reduced to the extent necessary to meter
filtered fuel and thus provides a means to precisely control low
fuel flows.
Accordingly, it is a primary object of the invention to provide a
fuel control system for contaminated fuel having a metering valve,
in which the system is adapted to direct either a filtered or
unfiltered flow through the valve.
Another object is to provide a fuel control system for contaminated
fuel in which the valve is capable of metering low fuel flows.
Yet another object is to provide a wash flow filter arrangement in
a fuel control system for contaminated fuels, in which the filtered
fuel not only serves as servo fluid and wash fluid, but also is
directed to a main fuel supply line which incorporates a metering
valve.
Other objects and advantageous features of the invention will
become apparent from the following description and the accompanying
drawing, wherein for purposes of illustration only, a specific form
of the invention is set forth in detail.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a portion of a fuel control system
incorporating an embodiment of the invention.
FIG. 2 is a schematic view of a portion of a fuel control system
incorporating another embodiment of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
Referring in detail to FIG. 1, wherein there is shown only a
portion of a fuel control system adapted to control the flow of a
contaminated fuel to an engine (not shown), a primary fuel supply
line 10 receives a flow of fuel from an inlet conduit (not shown)
which may incorporate a boost pump such as a centrifugal impeller
pump. An engine-driven gear pump 12 mounted within primary fuel
supply line 10 delivers fuel through the primary line. Pump 12 is
drivingly connected to the engine by means of pump drive 14.
A conventional cylindrical wash flow filter 16 is secured within an
annular recess 18 in primary line 10 in such a manner that the
filter's inner surface is flush with the inner surface of the
primary line. Recess 18 fluidly communicates with a secondary fuel
supply line 20 which carries a filtered flow of fuel emerging from
the outer surface of filter 18. Secondary line 20 fluidly
interconnects with a branch conduit 22 which directs filtered fuel
to the remainder of the fuel system for use as servo fluid in the
various components thereof and for use as wash fluid in the
system's valving (including the main metering valve) to prevent
contaminants in the fuel from hindering movement of movable
elements in the system.
A window-type main fuel metering valve, generally indicated at 24,
is positioned in main fuel supply line 26, the main line embodying
a conventional pressurizing valve (not shown) and a metered fuel
outlet (not shown). The structure of the main metering valve, which
is generally conventional, includes a spool 28 having two spaced
lands 30 and 32 thereon. Spool 28 functions to meter the fuel flow
in main line 26 through a metering orifice or opening defined by
window 34 and land 32. A pressure balance conduit 36 interconnects
the outboard portions of the spool 28 to axially balance the spool.
The valve spool is positioned by a positioning mechanism 29.
A transfer valve, generally designated at 37, fluidly interconnects
the primary line 10 and secondary line 20 with the main line 26.
Valve 37 comprises a spool 38 having lands 42 and 44. Spool 38 is
axially positionable between an upper limit of travel (illustrated
in the drawing), in which land 44 prevents a flow from primary line
10 to metering valve 24, while permitting a flow from the secondary
line 20 to the main line 26, and a lower limit of travel, in which
land 42 blocks flow from secondary line 20 to main line 26, while
allowing a flow from primary line 10 to main line 26.
Transfer valve 37 is operable in a "bang-bang" manner by means of a
differential pressure imposed upon the outboard faces of lands 42
and 44. Pressure conduits 46 and 48 respectively communicate with
these faces to transmit pressure thereto from a suitable valve
operator 50, which is connected to sources of high and low
pressure. The valve operator 50 causes pressure conduits 46 and 48
to either respectively communicate with the low- and high-pressure
sources or the high- and low-pressure sources, in accordance with
signals conveyed thereto by metering valve position indicator 51.
At small openings of window 34, the transfer valve 38 occupies the
illustrated position in which the pressure conduits 46 and 48
respectively communicate with the low- and high-pressure sources,
thereby allowing only filtered fuel to pass therethrough.
Conversely, at a predetermined larger opening, the order of
communication between the pressure conduits and sources is reversed
such that spool 38 is impelled to its lower limit of axial travel,
whereby only unfiltered fuel traverses the transfer valve.
It will be apprehended that the invention is not limited to
mutually exclusive flows of filtered and unfiltered fuel, but that
a transfer valve may be fashioned to provide an intermixture of
filtered and unfiltered fuel in the main fuel supply line, should
design considerations sanction such operation.
A bypass line 60 fluidly communicates with portions of primary line
10 at respective locations upstream and downstream of pump 12. A
conventional bypass valve 62 is positioned within bypass line 60 to
control the flow of bypassed fuel to the inlet side of pump 12. The
bypass valve serves to regulate the pressure differential (metering
head) across the main metering valve 24. Lower member 63 of bypass
valve 62 is fixedly and sealingly secured to a diaphragm 64 which
is sealed to the walls of a chamber 66 so as to divide the chamber
into an upper chamber and a lower chamber. The upper and lower
chambers defined by diaphragm 64 each communicates with respective
upstream and downstream locations in main line 26, as referenced to
metering valve 24, by means of interconnecting conduits 68 and 70.
Bypass valve 62 is resiliently urged to a seated position in the
bypass line by spring 72.
In operation, contaminated fuel enters primary line 10 and is
accelerated by gear pump 12. Transfer valve 37 remains in its
illustrated position until the opening in window 34 is enlarged to
a predetermined extent. Fuel pressure rises rapidly within primary
line 10 after rotation of the pump 12 is initiated, thus causing
bypass valve 62 to unseat and permit a flow in bypass line 60 back
to the inlet side of pump 12. As a result of this bypass flow, a
recirculation of contaminants in the fuel develops. Contaminants,
which would otherwise adhere to filter 15, are washed from the
inner surface thereof and progressively accumulated in the
recirculating flow as long as land 44 blocks primary line 10.
Fuel within the primary line 10 also passes radially through the
filter 16 to emerge at the outer surface thereof, from where it
enters secondary line 20 as a filtered flow. A portion of this
filtered flow in secondary line 20 enters branch conduit 22 and
thence is distributed to the fuel system to wash the valves and
function as servo fluid. Filtered flow emerges from secondary line
20 to pass through transfer valve 38 and enter main line 26.
Fuel flowing in main line 26 is metered through window 34 by land
32 of metering valve 24. Since the metering head across the valve
is maintained at a constant value by the bypass valve, the rate of
flow through the opening 34 is substantially a function of the
metering valve's area. Because of the fact that the metering
orifice, defined by opening 34 and land 32, for low flows, may be
smaller than that which would ordinarily be required to accommodate
contaminated fuel at low flows, the bypass valve may be designed to
maintain a metering head larger than that which would ordinarily be
permissible. This is a significant advantage as it is highly
desirable to maintain a metering head of a large magnitude in order
to mitigate the effects of bypass valve friction and thereby
enhance the accuracy of the fuel control system.
When main metering valve positioning mechanism 29 repositions the
metering valve to a higher flow position, in which contaminants
passing through the metering orifice are not likely to cause a
clogging thereof, main metering valve position indicator 51
transmits a signal to valve operator 50. Valve operator 50, which
is in constant communication with the sources of high and low
pressure, functions to communicate pressure conduits 46 and 48
respectively with the sources of high and low pressure. The
pressure differential occasioned across the spool 38 results in
downward axial movement of the spool until it reaches its lower
limit of downward axial travel. In this position, the secondary
line 20 is blocked by land 42 and the primary line 10 freely
communicates with the main line 26.
Referring now to FIG. 2, wherein like numerals designate elements
similar to those of FIG. 1, another embodiment of the invention is
shown which operates in a manner similar to that of the previous
embodiment, but differs slightly therefrom in construction. Instead
of the transfer valve 37 of FIG. 1, a pressure-responsive
spring-loaded shut-off valve 80 is positioned between primary line
10 and main line 26 to prevent contaminated flow from entering main
line 26 until the metering orifice is sufficiently enlarged. Bypass
valve 82 (metering head regulator) is of the well-known "hour
glass" variety. This type of bypass valve provides flow force
compensation which enables it to regulate the metering head more
accurately than the bypass valve 62 of FIG. 1. Spool 84 of bypass
valve 82 is biased by a spring preload exerted by an adjustable
spring 86. The spring preload determines the nominal value of the
metering head and consequently may be varied to compensate for
changes in fuel density and maintain the proper fuel flow
schedules. Secondary line 20 incorporates a check valve 88 to
permit only a one-way flow of filtered fuel therein from the filter
16 to the main line 26. Secondary line 20 also incorporates a
variable resistance (orifice) 89, which may be employed to adjust
the pressure drop (P.sub.2 -P.sub.3).
Since P.sub.3 -P.sub.4 is held constant by valve 82, the pressure
drop (P.sub.2 -P.sub.3) increases as flow increases through
secondary line 20. Consequently, the differential pressure (P.sub.2
-P.sub.3), produced by the filter element 16 and orifice 89, can be
used as a parameter of metered flow and hence the area of the
metering orifice, as the metered flow is essentially a function of
this area. Therefore, the spring preload acting on valve 80 is
selected so that the valve 80 cracks open when P.sub.2 -P.sub.3
attains a value which is indicative of a metering orifice area
large enough to permit contaminants to pass freely therethrough.
The valve 80 is thus responsive to the position of the metering
valve.
If it is necessary to connect a branch conduit to the line 20 of
FIG. 2, in order to draw filtered flow therefrom for operation of
servos associated with the fuel control or for other purposes,
differential pressure (P.sub.2 -P.sub.3) may no longer be
representative of the metered flow unless orifice 89 is adjusted to
effect a pressure drop thereacross, which is large in comparison to
the pressure drop across the filter. If orifice 89 is so adjusted,
the pressure drop P.sub.2 -P.sub.3 is representative of the metered
flow, but may be of a magnitude which is unacceptable for the fuel
control. If the pressure drop is impractical, two solutions are
available:
A. install a second wash flow filter for servo flow only; or
B. replace valve 80 with either an appropriate spool or poppet
valve and provide suitable pressure conduits on respective sides of
the orifice to communicate pressures to the selected replacement
valve. In solution B, as the communicated pressure differential
will be indicative of the area of the metering orifice, the
replacement valve should be openable to permit a flow from primary
line 10 to main line 26 after the pressure differential attains a
sufficient value.
It will be observed that the embodiments of FIGS. 1 and 2 operate
in two basic modes, namely, a filtered flow and a contaminated flow
mode. It will be appreciated that during periods of operation in
the former mode, the entire filtered output flow (through secondary
line 20) equals the contaminated inlet flow, while the stored
contaminants recirculate in the flow path defined by primary line
10 and bypass line 60.
It will be understood that the invention is not limited to the
construction specifically illustrated. For example, the metering
valve need not be of the window type but may embody other varieties
of valves such as a poppet valve. Also, the spool-type transfer
valve illustrated could readily be replaced with a rotary transfer
valve. Further, the disclosed bypass valves could be replaced with
other available varieties and need not function as metering head
regulators, inasmuch as a separate and distinct valve would be
suitable for that purpose.
While I have shown a particular embodiment of my invention it will
be understood, of course, that I do not wish to be limited thereto,
since many modifications may be made, as fall within the scope and
spirit of my invention.
* * * * *